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Preparation and reactivity of heterosubstituted 1,3-Dienes Stone, Charles 1988

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P R E P A R A T I O N A N D R E A C T I V I T Y O F H E T E R O S U B S T T T U T E D 1 , 3 - D I E N E S By Charles Stone B . Sc., The University of Strathclyde, 1982 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF DOCTOR OF PHILOSOPHY in T H E F A C U L T Y OF G R A D U A T E STUDIES (DEPARTMENT OF CHEMISTRY) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August 1988 © Charles Stone 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date ^ 1 S K ? DE-6 (2/88) ii Abstract The chemoselective hydrozirconation reaction of a series of l-ene-3-yne molecules 51a-d, using the commercially available hydride reagent, Cp2ZrCl(H) 1, provides an efficient route to the syntheses of 1,3-dienes 55a-d, substituted at the 1-position by the Cp2ZrCl moiety. Similar chemoselectivity was observed in the hydrozirconation reaction of a.pVunsaturated nitriles, to generate the corresponding 1-azadienyl complexes 68-71. The complexes 55a-d were found to be useful general precursors in the preparation of other heterosubstituted 1,3-dienes. Thus, corresponding tin-, phosphorus-, boron-, selenium-and sulfur-heterosubstituted 1,3-dienes 77a-d, 79a-d, 87a-d, 88a-d and 89a-d were readily prepared in good to excellent yields by a stereoselective transfer reaction from zirconium. The 1-azadienyl complexes also served as useful starting materials in the preparation of selenium-and phosphorus-substituted 1-azadienes. The selenium-substituted 1,3-dienes 88a-d underwent a facile isomerization reaction when exposed to fluorescent light, and when thermolysed in the dark at 80°C in unsealed reactors. Mechanistic studies of this isomerization process suggested that an intermolecular pathway involving free radical intermediates was operable. A comparable photochemical isomerization reaction of the sulfur-substituted 1,3-dienes was also observed. When the cycloaddition reactions of 88a-b and 88d with maleic anhydride were performed in the absence of light at reson able temperatures, good yields of the expected endo-cycloadducts were obtained. However, when the same reactions were repeated in room light or at temperatures in excess of those required for formation of the endo-cycloadducts an, interesting, apparent [l,3]-shift of the phenylselenenyl moiety resulted. The results of a crossover experiment indicated that this rearrangment was intermolecular in nature. The preparation of the trialkylstannyl and phenylselenenyl 2-substituted 1,3-dienes (128 and 129) was achieved via a transmetalation reaction of the Grignard reagent 24. iii The Diels-Alder reactivity of 1,3-dienes 128 and 129, with a series of electron-deficient dienophiles, was successfully investigated. 51a-d 55a-d M 77a-d Sn 79a-d P 87a-d B 88a-d Se 89a-d S ZrCp 2Cl R 3 68-71 24 128 129 a Bu b Me iv Table of Contents Page Abstract ii Table of Contents iv List of Tables viii List of Figures ix List of Abbreviations xii Acknowledgments xv Chapter 1: Introduction. 1.1 General. 1 1.2 Hydrozirconation. 2 1.2.1 Reactions of Alkyl- and Alkenylzirconium Complexes. 9 1.3 Transmetalation and Transfer Reactions. 12 1.4 Synthetic Routes to Heterosubstituted 1,3-Dienes. 17 1.4.1 Use of Molecules Already Containing a 1,3-Diene Fragment 17 1.4.2 Pericyclic Reactions. 20 1.4.3 Trapping Enolates of a,pVUnsaturated Ketones. 22 Chapter 2: Insertion Reactions of l-Ene-3-ynes, Nitriles and a,(3-Unsaturated Nitriles: Reaction of 1,3-Dienyl-zirconium Complexes with Carbon Monoxide. 2.1 Hydrozirconation of l-Ene-3-ynes. 25 2.1.1 Deuterium-labelling S tudies.. 3 3 2.2 Hydrozirconation of Nitriles and cc,P-Unsaturated Nitriles. 37 V 2.3 Carbonylation and Attempted Diels-Alder Reactions of 1,3-Dienylzirconium Complexes. 43 Chapter 3: Preparation of Heterosubstituted 1,3-Dienes, Imines and 1-Azadienes by a Transfer Reaction from Zirconium. 3.1 Preparation of a 1,3-Dienylnickel Complex. 51 3.2 Transfer of 1,3-Dienyl Moieties from Zirconium to Tin. 55 3.3 Transfer of 1,3-Dienyl Moieties from Zirconium to Phosphorus. 60 3.4 Transfer of 1,3-Dienyl Moieties from Zirconium to Boron.. 72 3.5 Transfer of 1,3-Dienyl Moieties from Zirconium to Selenium and Sulfur. 75 3.6 Preparation of Heterosubstituted Imines and 1-Azadienes. Transfer from Zirconium to Selenium and Phosphorus. 81 3.6.1 Transfer of Imine and 1-Azadienyl Moieties from Zirconium to Selenium. 83 3.6.2 Transfer of Inline and 1-Azadienyl Moieties from Zirconium to Phosphorus. 90 Chapter 4: Reaction of l-(Phenylseleno)-l,3-dienes under Photochemical and Thermal Conditions. Diels-Alder Reactivity with Maleic Anhydride. 4.1 Photochemical Isomerization. 95 4.2 Mechanistic Studies on the Isomerization Process. 103 vi 4.3 Photochemical Isomerization of 1 -(Phenylthio)-1,3-dienes. 120 4.4 Thermal Isomerization. 124 4.5 Diels-Alder Reaction of 1 -(Phenylseleno)-1,3-dienes with Maleic Anhydride. 126 Chapter 5: Preparation and Diels-Alder Reactivity of 2-(TrialkyIstannyl)-l,3-butadienes and 2-(PhenylseIeno)-l,3-butadiene. 5.1 Synthesis and Cycloaddition Reactions of 2-(Phenylseleno)-1,3-butadiene and 2-(Trialkylstannyl)-1,3-butadienes. 144 5.1.1 Diene Synthesis and Diels-Alder Reactivity. 145 5.1.2 Transmetalation from Tin to Selenium.. 153 5.2 Attempted Syntheses of Type B 1,3-Dienes where MLn is Cp2ZrCl. 155 Conclusion 162 Chapter 6: Experimental. 6.1 General. 164 6.2 Solvents and Reagents. 166 6.2.1 Reagents Prepared by Literature Procedures. 167 6.3 Insertion Reactions of l-Ene-3-ynes, Nitriles and a,P-Unsaturated Nitriles. Reaction of 1,3-Dienylzirconium Reagents with Carbon Monoxide 168 6.3.1 Reaction of 1 -Ene-3-ynes with Cp2ZrCl(H) 1 and Cp2ZrCi(D) 2. 168 6.3.2 Reaction of Nitriles and a,p^Unsaturated Nitriles with Cp 2ZrCl(H) 1. 172 vii 6.3.3 Carbonylation Reactions of 1,3-Dienylzirconium Complexes. 175 6.4 Preparation of Heterosubstituted 1,3-Dienes, Imine and 1 -Azadienes. 181 6.4.1 Preparation of a 1,3-Dienylnickel Complex. 181 6.4.2 Preparation of 1,3-Dienylstannanes. 182 6.4.3 Preparation of 1,3-Dienylphosphines. 185 6.4.4 Preparation of 1,3-Dienylboranes. 193 6.4.5 Preparation of l-(Phenylseleno)- and l-(Phenylthio)-1,3-dienes. 197 6.4.6 Preparation of Heterosubstituted Imines and 1 - Azadienes: Transfer of Zirconium to Selenium and Phosphorus. 203 6.5 Photochemical Isomerization of l-(Phenylseleno)- and l-(Phenylthio)-1,3-dienes. Thermal Isomerization of (Phenylseleno)-1,3-dienes and Diels-Alder Reactivity with Maleic Anhydride. 211 6.5.1 Photolysis of 1 -(Phenylseleno)-1,3-dienes. 211 6.5.2 Mechanistic Studies on the Isomerization of l-(Phenylseleno)-1,3-dienes 214 6.5.3 Photochemical Isomerization of 1 -(Phenylthio)-1,3-dienes. 227 6.5.4 Thermal Isomerizations. 228 6.5.5 Diels-Alder Reactivity of l-(Phenylseleno-l,3-dienes with Maleic Anhydride. 230 6.6 Preparation and Diels-Alder Reactivity of 2-(Trialkylstannyl)-1,3-butadienes and 2- (Phenylseleno)-1,3-butadiene. 237 6.6.1 Synthesis and cycloaddition Reactions of 2-(Phenylseleno)-1,3-diene and 2-(Trialkylstannyl)-1,3-butadienes. 237 6.6.2 Attempted Synthesis of Type B 1,3-Dienes where MLn is Cp2ZrCl. 246 References 250 viii List of Tables Page Table I. Preparation of 13-dienylzirconium complexes 55a-b. 27 Table II. Preparation of 1-azadienylzirconium complexes 68-71. 39 Table HI. Carbonylation reactions of 55a-d with CO; IR and 1 3 C NMR data. 44 Table IV. 1 3 C - 1 3 C and ^C^K coupling for complexes 70a-d-di. 49 Table V. Reaction of 55a-d with Bu3SnCl; 3 / A B and VfiSn for 77a-d. 58 Table VI. 1 H - 3 1 P coupling constants and 3 1 P NMR chemical shift data for 79a-d. 62 Table VII. 1 H - 3 1 P coupling constants and 3 1 P NMR chemical shift data for 80a-d. 62 Table VIII. 1 H - 7 7 S e coupling constants and 7 7 Se NMR chemical shift data for 88a-d. 77 Table DC. Reaction of 2-(Trialkylstannyl)-1,3-butadienes 128a-b. 148 Table X. Reaction of 2-(Phenylseleno)-1,3-butadiene 129. 150 ix List of Figures: Page Figure 1. General structures for heterosubstituted 1,3-dienes of types A and B. 23 Figure 2. Proposed synthetic route to 1,3-dienylzirconium complexes of type A. 25 Figure 3. 400 MHz * H NMR spectrum of 55b in C6D6- 29 Figure 4. 400 MHz * H NMR spectrum of 55c in CDCI3. 30 Figure 5. 400 MHz * H NMR and NOEDIFF spectra of 55d in C6D 6- 31 Figure 6. Conformation of 55a-c, as related to 1,3-butadiene. 32 Figure 7. 400 MHz * H N M R spectra of 55a and 55a-di. 34 Figure 8. Heteroallene-type structure for 62. 38 Figure 9. 400 MHz * H NMR spectrum of 69 in C ^ . 40 Figure 10. Molecular structure and selected bond lengths and angles for 69. 42 Figure 11. Proposed solid state conformation for the complexes 68-71. 41 Figure 12. 400 MHz NMR and NOEDIFF spectra of 70d in CDCI3. 46 Figure 13. 400 MHz * H N M R spectra of 70d, 70d-di, 70d- 1 3 C in CDCI3. 47 Figure 14. Portion of the 1 3 C - ! H heterocorrelation 75-300 MHz spectrum for 70b- 1 3 C in CDCI3. 48 Figure 15. 400 M H z * H NMR spectrum of 73 in C6D6. 53 Figure 16. 400 M H z lK NMR spectrum of 77b in C6D6. 59 Figure 17. 400 MHz lH and lH{3*P} N M R spectra of 79b in C ^ . 63 Figure 18. 400 M H z ] H NMR spectrum of 80c in Q>D6. 66 Figure 19. 400 MHz * H NMR spectrum of 81b in Q D 6 . 68 Figure 20. 400 M H z lH N M R spectra of 81b as a single rotamer and as a 2:1 mixture of rotamers in C6D6. 70 Figure 21. Rationale for the formation of rotamers for 81b and 81d. 69 X Figure 22. 400 MHz * H NMR spectrum of 87a in CDCI3. 74 Figure 23. 400 M H z ! H NMR spectrum of 88d in C7D8. 76 Figure 24. 400 MHz *H NMR spectrum of 89b in CDCI3. 79 Figure 25. Rotation of heteroallene complexes via changes in hybridization. 82 Figure 26. 400 M H z ! H NMR spectrum of 92 in C ^ - 85 Figure 27. 400 MHz *H NMR spectrum of 93 in CgD^ 87 Figure 28. 400 MHz * H NMR and NOEDIFF spectra of 94 hi Q D ^ 88 Figure 29. 400 MHz * H NMR and NOEDIFF sprectra of 99 in C6D6. 91 Figure 30. 400 MHz *H NMR spectrum of 100 in CDCI3. 93 Figure 31. 400 MHz *H NMR spectrum of a 2:1 mixture of E/Z isomers of 88a in C^D^. 97 Figure 32. 400 MHz *H NMR spectrum of all four stereoisomers of 88b in CD 2 C1 2 . 99 Figure 33. 400 MHz lH NMR spectrum of the expanded region from 5-7 ppm for the stereoisomers of 88b in CD2CI2. 100 Figure 34. 76.3 MHz 7 7 Se NMR spectrum of the four stereoisomers o f 8 8 b i n C D C l 3 . 101 Figure 35. General design for crossover experiments using labelled (*) versions of 88a-d. 103 Figure 36. Molecular ion fragmentation patterns for the control and crossover experiments using 88b-di and 88b-d5. 108 Figure 37. Molecular ion fragmentation patterns for the control and crossover experiments using 108d and SSd-d\. I l l Figure 38. 400 MHz * H NMR spectra of the mixture 108d and 88d-di before and after photolysis in C^Ds. 112 Figure 39. Molecular ion fragmentation patterns for the control and crossover experiments for the mixture of Ph 2Se 2 and Ph2Se2-rfio. 115 Figure 40. Molecular ion fragmentation patterns for the control and crossover experiments for the mixture of 88b and Ph2Se2-rfio. 116 Figure 41. Proposed mechanism for the photochemical isomerization of88a-d. 119 xi Figure 42. 400 MHz *H NMR spectrum of the four stereoisomers of 89b in CDC1 3 . 122 Figure 43. 400 MHz l H NMR spectrum of the expanded region from 5-7 ppm for the stereoisomers of 89b in CDCI3. 123 Figure 44. 400 M H z * H N M R and NOEDIFF spectra for 114 in C ^ . 127 Figure 45. 400 MHz J H N M R spectra of 114 and 115 in CDCI3 and C6D6, respectively. 129 Figure 46. Proposed structures for the epimers of 115. 130 Figure 47. 400 M H z * H N M R spectrum of lU-de in CDCI3. 132 Figure 48. Molecular ion fragmentation patterns for the control and photochemical crossover experiments using mixtures of 114 and 114-<i6- 133 Figure 49. Proposed rationale for the formation of 116 and 114. 134 Figure 50. 400 MHz *H N M R and NOEDIFF spectra for 121 in C 7 D 8 . 136 Figure 51. Possible structures for the apparent [l,3]-shift cycloadducts 122 and 123. 138 Figure 52. 400 MHz lH NMR spectrum of 124 in C6D 6 . 139 Figure 53. 400 MHz lH NMR and NOEDIFF spectra of 124 in Q5D6. 141 Figure 54. 400 MHz *H NMR spectrum of 125 in C6D 6- 142 Figure 55. Proposed structures for the epimers 126 and 127. 140 Figure 56. 400 MHz ! H NMR spectrum of 129 in CgD^ I 4 7 Figure 57. 400 MHz * H N M R spectrum of 131 and 133 in C 6 D 6 and CDCI3, respectively 149 Figure 58. 400 MHz lH NMR spectrum of 137 in QsD^ 152 Figure 59. 400 MHz lH NMR spectrum of 147 in C6D 6- 158 Figure 60. 400 MHz *H N M R and NOEDIFF spectra of 147 in C6D 6 . 159 Figure 61. 400 MHz *H NMR spectrum of 148 in Q5D6. 160 Figure 62. Molecular Structure and selected bond lengths and angles for 148. 161 xii List of Abbreviations arm Ac acac AIBN b BHT Bu i-Bu r-Bu C 13C{!H} cat. COD Cp CP* d d 5 2D dd ddd dddd DLBAL e equiv atmosphere(s) acyl acetylacetonate azoisobisbutyronitrile broad 2,6-di-rm-butyl-4-methylphenol butyl group, - (CH 2)2CH 3 wo-butyl group, -CH 2 CH(CH 3)2 tertiary-butyl group, -C(CH3)2CH3 Celsius carbon-13 observe, broadband proton decoupling catalyst cyclooctadiene, C8H12 T|5-cyclopentadienyl ligand, C5H5-Ti5-pentamethylcyclopentadienyl ligand, 05(013)5-doublet deuterated chemical shift two-dimensional doublet of doublets doublet of doublet of doublets doublet of doublet of doublet of doublets diisobutylaluminum hydride extinction coefficient equivalent(s) xiii Et ethyl group, -CH2CH3 Fp T\5-cyclopentadienyldicarbonyliron, [Cp(CO)2Fe] G L C gas-liquid chromatography GCMS gas chromatography-mass spectrometry h hour *H{3lp} proton observe, phosphorus broadband decoupling Hz hertz, seconds"1 IR infrared / coupling constant Kcal Kilocalories L ligand X wavelength m multiplet M + molecular ion max maximum Me methyl group, -CH3 MHz megahertz rnin minute mL millilitre mmol millimole mol mole MM2 molecular mechanics MS mass spectrometry NBS /Y-bromosuccinimide NCS N-cMorosuccinimide N-C1PSP 7V-(4-cMorophenyl)phmajirnide N-PSP ^(phenylseleno)phmalimide xiv iV-PTP N-(phenyltMo)phmalimide NMR nuclear magnetic resonance NOEDIFF nuclear Overhauser effect difference ORTEP Oakridge Thermal Ellipsoid Plotting Program 3!p{lH} phosphorus-31 observe, proton broadband decoupling Ph phenyl group, -C6H5 ppm parts per million i-Pr isopropyl group, -CHCCFTjte PVP poly(4-vinylpyridine) q quartet R. T. room temperature s singlet 7 7 Se {^} selenium-77 observe, proton broadband decoupling t triplet TEMPONE 4-oxo-2,2,6,6-tetramethylpiperidinyloxy radical tert tertiary T H F tetrahydrofuran U V ultraviolet UV-vis ultraviolet-visible XV Acknowledgements I would like to thank both my supervisors Dr. Michael Fryzuk and Dr. Gordon Bates for their encouragement and patience during the course of this work. I am also very grateful to Dr. R. Chadha for X-ray crystallographic analysis, and to Dr. Tom Keller for performing molecular mechanics calculations. I am also grateful for the assistance and services provided to me by the departmental technical staff. Thanks are also due to Dr. Edward Piers and Dr. John Scheffer for many helpful and enlightening conversations. I also gratefully acknowledge the guidance and friendship of Dr. Patricia MacNeil. In addition, special thanks are extended to Mr. Terry Jarvis, Dr. Graham White and several others for their invaluable assistance during the production of this thesis. Finally, I would like to acknowlegde the very special friendship and understanding shown towards me by Brad Chiasson during the last few years of my graduate work. xvi For my sister, Sandra and my father. 1 C H A P T E R 1 Introduction 1.1 General. The role of organometallic chemistry in the development of new synthetic methods, directed towards organic synthesis, has increased significantly over the past 20 years.1 The use of organometallic reagents, both in catalytic and stoichiometric reactions, has undoubtedly enhanced the means by which simple and complex molecules are constructed. In this regard, two major classes of reactions which have found general use are hydrometalation and transmetalation. Both of these reactions are known to take place with a high degree of regio-and stereoselectivity. It is, perhaps, this feature which makes these reactions so attractive to the organic chemist. The hydrometalation reaction, which encompasses such processes as hydroboration2 (although boron is not classically regarded as a metal, it tends to be placed in this category), hydroalumination3 and hydrostannation,4 has found wide use in organic synthesis. A supplementary reaction to these latter processes came about with the synthesis of chlorobis(T]5-cyclopentacuenyl)hydridozirconium(IV) [Cp2ZrCl(H)]x l . 5 M 1 — R + M 2 — X « » M 2 — R + M 1 — X (1) M 1 = metal M 2 = metal or non-metal R = organic fragment X = organic fragment or halogen 2 The transmetalation reaction provides a method by which organic fragments can be exchanged from one metal to another in a stereochemically-controlled manner (equation 1). This process can be expanded to the more general case in which an organic moiety a-bonded to a metal, is transferred to either another metal or a non-metal. This latter, more general process, may then be simply termed a transfer reaction. The transfer may be considered to involve the exchange of either two similar fragments (i.e where X and R are both organic moieties) or else two different fragments, such as the exchange of a o-bound organic moiety for a halogen. The Diels-Alder reaction has been shown to be one of the most useful carbon-carbon bond forming reactions available to the synthetic organic chemist, especially in the construction of six-membered ring systems. Greater understanding of the mechanism of this reaction has led to the preparation of heterosubstituted 1,3-dienes, since the presence of these heteroatoms has enhanced both the reactivity of the 1,3-dienes, as well as the regio- and stereoselectivity of the reaction. Also, the presence of the heteroatoms provides means for further transformations by exploiting their known chemistry. Thus, through the use of the hydrozirconation reaction and the transfer procedure, we hoped to generate a general synthetic method for the construction of a variety of stereochemically defined heterosubstituted 1,3-dienes. For ease of presentation, the majority of the 1,3-dienes in this thesis are drawn in the s-cis conformation. 1.2 Hydrozirconation. The hydrozirconation reaction6 involves the insertion of unsaturated organic substrates into the metal-hydrogen bond of [Cp2ZrCl(H)]x 1. For simplicity, henceforth in this thesis, hydride 1 shall be represented as Cp2ZrCl(H). The synthesis of Cp2ZrCl(H) was first reported in 1969 by Wailes and co-workers.7 In the same communication they reported the preparation of bis(T|5-cyclopentadienyl)deuteriozirconium(IV) Cp2ZrCl(D) 2 by a similar method. The infrared spectrum of these compounds strongly indicated the presence of 3 bridging hydrides (deuterides) in the polymeric structure. Preliminary investigation by these workers 5 ' 8 provided evidence for the insertion reaction of alkenes and alkynes with 1; however, the products were poorly characterized. Subsequent reports by Schwartz and co-workers brought to light the true potential of the hydrozirconation reaction.9 The structure of this commercially available hydride has not been clearly determined. However, due to its characteristic insolubility, it is presumed to be polymeric. The binuclear zirconocene hydride [(T|5-C5H4CH3)2ZrH(pi-H)]2 has been structurally characterized by single-crystal X-ray diffraction methods.10 This study provided the first structural evidence of bridging hydrides for binuclear hydride complexes of zirconium. During their investigations with the pentamethylcyclopentadienyl ligand (Cp*), Bercaw and co-workers11 synthesized the monomeric Cp*2ZrCl(H), along with its dihydride analogue Cp*2ZrH2. Both of these complexes are known to react with alkenes and alkynes via insertion into the Zr-H bonds. To understand why Cp2ZrCl(H) has become such a useful transition metal hydride reagent for the functionalization of unactivated alkenes and alkynes, one must examine the insertion process (Scheme 1). To achieve insertion of an alkene or alkyne into a metal-3 H 5 M - H + H 4 6 Scheme 1 4 hydrogen bond, the equilibria in Scheme 1 must lie far to the right. Thus, formation of the o-alkyl-metal complex 5 over the hydride alkene complex 3 (or the o-alkenyl-metal complex 6 over the hydride alkyne complex 4) must be strongly favored. For hydride complexes of transition metals in low formal oxidation states, the equilibria in Scheme 1 lie far to the left. This is presumably because alkene (rc-acceptor) complexes of electron-rich metals are more stable than the corresponding alkyl (a-donor) complexes. This rationale therefore suggests that electron-poor transition metals in high formal oxidation states should favor the formation of a-alkyl or a-alkenyl complexes.12 To date, hydrozirconation is probably the most extensively studied reaction of this type and has been used to produce stable, isolable (mostly crystalline) zirconium alkyl and alkenyl complexes. Reaction of hydride 1 with terminal alkynes has been shown to proceed stereoselectively; placing the zirconium and hydride cis to one another, with the zirconium occupying the terminal position as outlined in equation 2 8 R — E E = — H + Cp 2ZrCl(H) 1 R = Et, Ph Schwartz and co-workers13 found that addition of 1 to disubstituted alkynes also proceeded with cis stereochemistry to give a mixture of zirconium alkenyl complexes, the ratio of which was dependent on the relative steric bulk of the methyl versus an alkyl group (equation 3). Interestingly, these workers also noted that the presence of excess Cp2ZrCl(H) induced isomerization to an equilibrium mixture of zirconium alkenyls 7 and 8 at room temperature. To explain this observation, the intermediacy of a 1,2-dimetalated alkenyl (2) >98% terminal >98% cis addition 5 derivative 9 was proposed,1 3 the formation of which could be accounted for by a second hydrozirconation reaction8 of the mixture 7/8. The retention of stereochemistry in the alkenyl zirconium complex, during the isomerization process, can be understood on the basis that both metal-hydride addition and elimination are known to take place with cis stereochemistry. Hydride 1 was found to react under mild conditions with a series of terminal, internal and cyclic alkenes (Scheme 2).9 It is evident from Scheme 2 that hydrozirconation of internal alkenes gives rise to the same product as the corresponding terminal alkene. This rearrangement is brought about by a series of |J-elimination-insertion reactions which continue until the Cp2ZrCl fragment is at the least hindered position in the alkyl chain.9 The facile nature of this rearrangement is in contrast to the corresponding organoboron1 4 or organoaluminum 1 5 compounds, which only undergo similar processes at elevated temperatures. From the series of reactions shown in Scheme 2, it was possible to determine relative rates of hydrozirconation. The order of reactivity was as follows: terminal alkenes > cis internal alkenes * trans internal alkenes > exocyclic alkenes > cyclic alkenes > disubstituted alkenes > trisubstituted alkenes. Tetrasubstituted alkenes and trisubstituted cyclic alkenes did not react with 1 after several hours at room temperature.9 Scheme 2 Hydrozirconation has been shown to take place with high stereo- and regioselectivity in the insertion reactions with alkynes. In addition, reaction of 1 with 1,3-dienes generally proceeds with high chemoselectivity to generate zirconium substituted y,5-unsaturated alkenes by insertion of the least hindered alkene, with the zirconium positioned at the least substituted carbon. 1 6 The regiochemistry was as observed previously, with zirconium occupying a position at the least substituted carbon (Scheme 3). The use of 3-methyl-l,3-pentadiene led to 7 , * Cp 2ZrCl(H) ^ ^ ~ ^ ^ 1 ^ 1 ZrCp 2 Cl Cp 2ZrCl(H) \ •ZrCp 2Cl ft Y Cp 2ZrCl(H) ^ / •ZrCp 2Cl Scheme 3 a breakdown in the high degree of regioselectivity resulting in the formation of a 10:1 mixture of regioisomers about the least substituted double bond-Over the years, the hydxozirconation reaction has been extended to encompass insertion CpjZrCKH) ClCpjZr— PhCEN •Ph H PhCH 2NSC: Cp2ZrCl(H) \, ClCr^ Zr N CH2Ph > CP2ZrCl(H) \ / O - C l C p 2 Z r — ° ~ \ H .R R R v CP2ZrCl(H) H R \=S CICpjZr—S R 1 " ° CpjZrCKH) / \ *~ ClCp^ — O— CH 2 — CH3 Scheme 4 8 reactions with nitriles, 1 7 isonitriles1 8 (note the unusual mode of insertion), ketones, 1 9 thioketones20 and epoxides17 (Scheme 4). A series of hydrozirconation reactions which extended the previously observed chemoselectivity of the process has appeared in a recent communication.21 In an effort to develop a general synthetic sequence to a series of uridine nucleosides 11, a variety of alkenylzirconium complexes 10 was prepared. The terminal alkynes used in this procedure contained a various potentially reactive functionalities; for example, nitrile, alkyne, alkene, ester and halogen. Although the alkenyl zirconium complexes 10 were not isolated, no evidence of insertion of the secondary functionalities was observed in the final isolated products (Scheme 5). ZrCpiCl R' H + CpjZrCKH) 1 R" = -(CH2)3C1 -<CH2)3CN R' 10 -(CH 2 ) 2 C=CH -(CH2)8C02Me -C(CH 3 )=CH 2 t 30-89% dR 11 dR = deoxyribosc Scheme 5 9 1.2.1 Reactions of Alkyl- and Alkenylzirconium Complexes. A major reason for the synthetic utility of the hydrozirconation reaction lies in the many versatile and stereochemically defined cleavage reactions available to both alkyl and alkenylzirconium complexes. 2 2 A wide variety of electrophilic halogenation reagents (e.g., BT2, I2, N-bromosuccinimide (NBS), /V-chlorosuccinimide (NCS) or iodobenzene dichloride (PMCI2)) react smoothly with alkylzirconium complexes to give good to excellent yields of the corresponding alkyl halides (Scheme 6).9 In a similar fashion, unsaturated Cp 2 ZrCl R R = alkyl, alkenyl r < Br, PhlCl, NBS NCS RBr RI RC1 RBr RC1 Scheme 6 alkylzirconium complexes have been shown to react with NBS to generate the corresponding bromo-compounds (Scheme 7). 1 6 In general, the use of NBS rather than B r 2 in the cleavage reaction of these zirconium complexes gave higher yields. A possible mechanism for the electrophilic cleavage of alkylzirconium complexes has been proposed, 2 3 based on the observation that cleavage of dideuterated-3,3-10 Scheme 7 dimethylbutylzirconium 12 with B r 2 proceeded with retention of configuration at carbon (equation 4). The retention of stereochemistry at carbon was accounted for by an initial (4) r-Bu r-Bu 12 coordination of B r 2 to zirconium, through donation of a pair of electrons to its low lying orbital, thus allowing frontside attack on the C-Zr bond (equation 5). 2 3 C P . . . Q / C . N d > D I t-Bu M> Br - -Br H C > D \ r-Bu Br * D (5) r-Bu + Cr^ZrCKBr) 11 The stereochemistry observed on cleavage of alkenylzirconium complexes with NBS, can be rationalized in a similar manner to that described above for the reaction of alkylzirconium complexes with B r 2 (equation 6). 1 3 ZrCp 2 Cl C H 3 Br NBS 95% H ^ ^ C H 3 (6) Alcohols can be prepared from alkylzirconium complexes by a variety of procedures.24 Oxidation of these compounds with basic hydrogen peroxide gives good yields of the desired alcohol (equation 7). This is analogous to the preparation of alcohols using the hydroboration/oxidation procedure.25 C l C p 2 Z r ( C H 2 ) 7 C H 3 H 2 02 /H 2 0 NaOH H O ( C H 2 ) 7 C H 3 (7) Insertion of carbon monoxide into the Zr -C bond of a l k y l 2 6 , a lkenyl 2 6 or y,5-unsaturated alkylzirconium complexes18 proceeds smoothly at room temperature under C p 2 Z r C l QQ Cp2ZrCl R = alkyl, alkenyl and y,8-unsaturated alkyl H , 0 + H 2 0 2 N B S Br-, C H 3 O H R C H O R C 0 2 H R C O B r R C 0 2 M e Scheme 8 12 1.5 arm of CO. The acyl complexes thus produced, serve as starting materials for a host of other compounds (Scheme 8). The use of alkenylzirconium complexes has been further extended by employing them as coupling partners, with a variety of other substrates, in a series of nickel(0)-catalyzed carbon-carbon bond forming reactions. These reactions, as well as a collection of other methods for the further synthetic elaboration of organozirconium species, are discussed in the following section. 1.3 Transmetalation and Transfer Reactions. The transmetalation reaction is, as the name suggests, one in which one metal center is exchanged for another. This reaction, and the more general transfer reaction, provide an extremely useful method for the stereochemically-controlled transfer of organic moieties from one heteroatom to another. A classical example of such a process is seen in equation 8, where a transmetalation (transfer) takes place between tin and lithium.2 7 It is important to note that in many cases the transmetalation reaction is a reversible process. R 3 S n R ' + R " L i « * R ' L i + R 3 S n R " (8) It has been proposed that replacement of zirconium in organozirconium complexes by other metals should be favorable when the other metal is more electronegative than zirconium. 2 8 However, further argument suggests that since this proposal is based on a thermodynamic argument, its generality may be constrained by reactions that have high kinetic barriers 2 9 The mechanism by which transmetalation reactions occur is not clear. Negishi and Takahashi29 have proposed that a four-centered process, requiring the availability of an empty orbital on each metal, may represent the most likely pathway (equation 9). 13 0 0 Q±£&0 0 0 LM— X + Y - M ' L n ^ = S : LM M'L :==: L n M — Y + X-M'L n 0 0 0 0 (9) Schwartz and co-workers30 have investigated a series of stoichiometric transmetalation reactions with Lewis acidic metal halides (Scheme 9). Reaction of alkyl or alkenylzirconium Cp 2ZrCl R R = alkyl Cp 2ZrCl R R = alkenyl A1C1, ZnCl, HgCl 2 CuCl PdCl, Scheme 9 RA1C12 RZnCl RHgCl RCu RPdCl complexes with aluminum trichloride at 0*C in dichloromethane proceeds quantitatively (by * H N M R spectroscopy) in less than 10 minutes. Competitive studies using mixtures of alkyl and alkenylzirconium complexes, with a deficiency of AICI3, showed that transmetalation of the alkenyl substituent is faster. Due to the thermal instability of the aluminum complexes 13 and 14, they were immediately reacted with acid halides to generate the corresponding ketones 15 and 16 (Scheme 10). 2 8 Attempts to directly acylate the alkenylzirconium complexes were unsuccessful. 14 (i)Cp 2ZrCl(H) / , \ _ ^ C _ I H X ( i i ) A i a 3 \ 1 / n O I ^ ^ ^ R ( -Cp 2 ZrCl 2 ) 1 3 II 1 5 c i ^ o (i) CftZrCKH) f , \ . 3 0 . C . II ( -Cp 2 ZrCl 2 ) 14 n Jl 16 c i ^ Scheme 10 By a procedure analogous to that used for the stereochemical investigation of the cleavage of alkylzirconium complexes with Br 2 (see equation 5, p 10), it was shown that transmetalation of Zr to A l proceeds with retention of stereochemistry at carbon.2 8 The same stereochemical result was observed for the transmetalation of alkenylzirconium complexes. In an attempt to synthesize more robust alkenylaluminum species, the transmetalation of 17 using dialkylaluminum chlorides 18 was successfully investigated (equation 10) 2 8 Z r C ^ C l 17 C H 3 + R2A1C1 C H ^ C l 2 ^ C H 3 (10) 18 pentane R = Me, i-Bu (- C p ^ Z r C y The transmetalation of an alkenylzirconium complex to copper using copper(T) chloride gave 1,3-diene 20, formed by slow decomposition of the intermediate alkenylcopper compound 19 . 3 0 b Product analysis indicated that the 1,3-diene exhibited the regio- and stereochemistry inherent in the starting alkenyl complex (equation 11). Identical organic 15 20 products were obtained from the transmetalation of alkenylzirconium species with palladium(H) chloride. 3 0 b A l l of the above transformations are representative examples of stoichiometric transmetalation reactions. However, transmetalation of zirconium to other transition metals has been proposed as an important step in many catalytic carbon-carbon bond forming processes 2 9 The literature abounds with examples of such processes; namely, the transition metal catalyzed reaction of organic halides using alkenylstannanes,31 alkenyl Grignard reagents,3 2 alkenylboranes,33 alkenylzinc, 3 4 and others l d as coupling partners. Due to a tolerance of other functional groups, stereospecificity, high yields and experimental simplicity, transition metal catalyzed coupling reactions represent one of the most important new techniques for the formation of carbon-carbon bonds. A novel nickel(0)-catalyzed cross-coupling reaction between alkenylzirconium complexes and aryl halides has been developed (equation 12). 3 5 a This reaction has been R R" = alkyl 16 extended, using a palladium(0) complex as the catalyst, to include vinyl halides 3 5 b and alkynyl halides 3 5 c as coupling partners. In these examples, the stereochemistry of the product was >98% E, indicating retention of configuration at carbon during the coupling reaction. Reaction of the (£)-l-heptenylzirconium derivative 21 with one equivalent of 1-naphthylnickel complex 22 gave 23 at a rate that was comparable to that observed with use of 10 mol % Ni(PPh3)4 in the corresponding catalytic reaction (equation 13). 3 5 a Thus, it was proposed that a likely 21 22 23 catalytic cycle should involve the oxidative addition of the aryl halide to the nickel complex, followed by transmetalation from zirconium to nickel, and finally reductive elirnination to yield the coupling product. A later study proposed that oxidative addition of aryl halides to reduced nickel species probably proceeds by an electron transfer mechanism.36 Addition of alkenylzirconium complexes to cc,|3-unsaturated ketones, via nickel(O) catalysis, has been shown to be an important extension of organozirconium chemistry (equation 14).37 R" = alkyl 17 The application of the transmetalation (transfer) reaction, along with several other approaches towards the synthesis of heterosubstituted 1,3-dienes, is discussed in the following section. 1.4 Synthetic Routes to Heterosubstituted 1,3-Dienes 3 8 The synthetic utility of the Diels-Alder reaction has encouraged many research groups to develop new general approaches to the preparation of functionalized 1,3-dienes. These endeavors have been made in the hope that new dienes possessing enhanced reactivity and flexibility towards further elaboration can be prepared. The following section outlines some of the general procedures that have been developed for the preparation of heterosubstitued 1,3-dienes. These procedures fall into three categories (i) use of starting materials already containing a 1,3-diene fragment, (ii) combined use of various pericyclic reactions, and (iii) trapping enolates of a,(^unsaturated ketones. 1.4.1 Use of Molecules Already Containing a 1,3-Diene Fragment. The synthesis of 2-(l,3-butadienyl)magnesium chloride 24 by Aufdermarsh, 3 9 24 M = Bu3Sn, Ph2P, ClHg modified later by Sultanov et a l . , 4 0 led the way to a general method for the preparation of 2-substituted- 1,3-dienes via transfer of the 1,3-diene fragment from magnesium to tin, phosphorus and mercury (equation 15). 18 More recently, Reich et a l . 4 1 have shown that 2,3-bis(trimethylstannyl)-l,3-butadiene 25, via transmetalation to lithium, is a versatile reagent for the preparation of mono- and ^substituted 1,3-dienes (Scheme 11). MeaSn SnMe3 (i) MeLi, THF,-78'C (ii) Electrophile, RX 25 Me3Sn R = Me 3Si, PhS (i) MeLi, THF, -78°C (2-3 equiv) (ii) Se powder (iii) PhCH 2Cl R = Me 3Si (i) MeLi, THF, -78°C (ii) Ph 2S 2 PhCH2Se SeCH 2Ph PhS. SiMe, Scheme 11 The preparation of 1,3-dienes containing a-bonded transition metals is rare. 4 2 However, a potentially general route to dienyliron complexes has been developed. The procedure involved reaction of Na[Cp(CO)2Fe] (NaFp) 26 with dienoyl chlorides 27 to afford the transition metal acyl complexes 28. These complexes were then photochemically decarbonylated to yield the desired dienes 29 (equation 16) 4 3 Other workers have also used NaFp to prepare dienyliron complexes; however the reaction procedures were rather elaborate and poor yielding. 4 4 Another example of the preparation of o-bound transition metal dienes represents a high yielding, quite general procedure. In this reaction a hexane solution of l,5-cyclooctadienebis(triethylphosphine)nickel(0) [Ni(PEt3)2(l,5-CgHi2)] 30 was added to a 19 -78'—>R.T. R' T H F F P Na[Cp(CO)2Fe] 26 hu (350 nm) -5-C (16) a R = H, R' = C H 3 b R = C H 3 , R' = H 29 solution of 2-chloro-l,3-butadiene 31 to yield, after crystallization, the desired 1,3-dienylnickel complex 32 (equation 17).45 a Ni(PEt 3 ) 2 ( l ,5 -C 8 H 1 2 ) 2 + 30 C K P E t ^ N i hexane R.T. (17) 31 32 20 1.4.2 Pericyclic Reactions. The retro-Diels-Alder reaction in combination with electrocyclic ring opening has proved extremely useful in providing general synthetic routes to heterosubstituted 1,3-dienes.46 As shown in Scheme 12, deprotonation of sulfone 33 followed with trapping with an appropriate electrophile gives 34. Thermolysis of the substituted sulfone 34 generates the desired 1,3-dienes 35 and sulfur dioxide. Thermolysis a R = Me3Si (89%, 96% E) b R = Me3Sn (25%, 85% E) Scheme 12 A similar procedure was used in the synthesis of 2-(phenylthio)-l,3-butadiene 36 4 7 a and 2-(phenylseleno)-l,3-butadiene 37 (equation 18). 4 7 b The latter compound was not isolated, and was used as the sulfone for further transformations. 21 X R Thermolysis , X R S 0 9 + / (18) 36 X = S, 37 X = Se A general procedure for the preparation of 1,4-disubstituted- 1,3-dienes was developed by Trost and co-workers.48 This synthesis involved the retro-Diels-Alder reaction of 38 to give cyclobutene 39, which on ring opening gave the 1,3-diene 40 (equation 19). X *"Y (19) 39 40 Y a X = OAc, Y > SPh b X = Y = OAc A further example of the use of electrocyclic ring opening reactions to generate heterosubstituted 1,3-dienes, involves the preparation of dienes 42 and 43. Silylation of 41 OSiMea 42 BO* BO*'' •H 41 M i NEt3, M^SiCI BO ^OSiMej H»*" BO*'" H \ BO"*** Scheme 13 OSiMe3 BO SiMej BO 43 22 followed by thermolysis, gave a 3:2 mixture of the 1,3-dienes 42 and 43 (respectively) in good overall yield (Scheme 13).49 A similar procedure was used to prepare tetrasubstituted 1,3-dienes.49 1.4.3 Trapping Enolates of ot,(3-Unsaturated Ketones. A simple and general method for the preparation of heterosubstituted 1,3-dienes has been exploited by several research groups. Silylation of the enone 44 gave the 1,3-diene 45 directly in good yield . 5 0 3 Further substitution of 45 with phenylselenenyl chloride (PhSeCl), followed by resilylation, gave the 1,3-diene 46 (Scheme 14). 5 0 b In a similar fashion, the 44 OMe 45 OMe PhSeCl SePh SePh 46 OMe OMe Scheme 14 1,3-diene 4 8 5 0 c was prepared from the enone 47, while silylation of the enone 49 gave the 1,3-diene 50 (Scheme 15). 5 0 d 23 49 50 Scheme IS An outline of the hydrozirconation and transmetalation (transfer) reactions and, in the latter section, a brief overview of the methods currently available for the synthesis of heterosubstituted 1,3-dienes has been presented in the Introduction. Based on the studies presented in this Introduction, we were interested in generating general synthetic routes for the preparation of heterosubstituted 1,3-dienes. Such investigations would involve: (i) the hydrozirconation reaction of l-ene-3-yne molecules in the hope of generating a series of a-bonded dienylzirconium complexes of type A (where MLn would be Cp2ZrCl), (ii) the transmetalation reactions of the dienyl Grignard reagent 24 (Figure 1). It was further hoped that the dienylzirconium reagents could be exploited as R " Type A Type B Figure 1. General structures for heterosubstituted 1,3-dienes of types A and B. 24 general percursors in the preparation of other heterosubstituted 1,3-dienes of type A (where M L n would represents some substituted heteroatom), whereas compounds such as 24 could serve as useful starting material for the synthesis of heterosubstituted 1,3-dienes of type B. If these procedures proved successful, the effects of the heteroatom substituents on the reactivity of these dienes could then be investigated. The following Chapters outline the progress that has been made in this regard. 25 C H A P T E R 2 Insertion Reactions of l-Ene-3-ynes, Nitriles and a,(3-Unsaturated Nitriles: Reaction of 1,3-Dienylzirconium Complexes with Carbon Monoxide. 2.1 Hydrozirconation of l-Ene-3-ynes. A general synthetic procedure for the preparation of heterosubstituted 1,3-dienes of type A could be envisaged to proceed through the chemoselective hydrozirconation of l-ene-3-ynes (Figure 2). Preferential insertion of the alkyne functionality of l-ene-3-ynes into the metal-hydrogen bond of the hydride Cp2ZrCl(H) 1, coupled with the well documented stereo- and regiochemical outcome of such a process, would afford the desired 1,3-dienes of the type A (where MLn is Cp2ZrCl). Figure 2. Proposed synthetic route to 1,3-dienylzirconium complexes of type A . Such chemoselectivity in the insertion of l-ene-3-ynes molecules has been observed previously for other hydrometalation reactions. Hydroboration of l-ene-3-yne 51d has been shown to proceed chemoselectively to give the diene 52, after workup with acid (equation 20).51 Other workers52 have observed similar selectivity in the hydroalumination of 26 O - (i) R 2 B H (ii) C H 3 C 0 2 D \ _ y \> D 51d 52 53 with dusobutylaluminohydride (/-BU2AIH) to give the diene 54; however, hydrostannation of the same substrate gave a mixture of products (Scheme 16). * ^ E t 3 S n > ^ ^ ^ S n E t 3 53 J-BU 2 A1H 54 Al(/-Bu)2 Scheme 16 It was found that the room temperature reaction of hydride 1 with a series of l-ene-3-yne molecules 51a-d generated the desired 1,3-dienylzirconium complexes 55a-d in good yields (81-90%).53 Thus, the syntheses of 1,3-dienes of the type A where MLn is Z r C p 2 C l can be readily achieved (Table I). Although other examples of chemoselective hydrometalation of l-ene-3-ynes are known, 5 4 hydrozirconation of the unsubstituted l-buten-3-yne 51a, to our knowledge is the most selective and highest yielding. Dienes 55a-d exhibited strong absorptions in the JR from 1600-1621 cm - 1 , which are characteristic of molecules containing a 1,3-dienyl moiety. The l-ene-3-ynes 51a and 51c were commercially available, whereas 51b and 51d were synthesized by literature procedures.5 5 The hydride Cp 2 ZrCl(H) 1, although commercially available, was prepared in our laboratory by the reaction of lithium tri-rerr-27 Table I: Preparation of 1,3-dienylzirconium complexes 55a-d. Entry l-ene-3-ynea 1,3-dienylzirconium yieldb complex (%) 51a OMe 4:1 E:Z 51b OMe 51c 51d ZrCp 2 Cl 55a 81 ZrCp 2 Cl 85 83 55 d 90 B 51a and 51c were purchased from Pfaltz and Bauer and the Aldrich Chemical Co., respectively. b Yields of isolated, crystalline products. 28 butoxyalummohydride [LiAl(f-BuO)3H] and dicMorobis(ri5-cyclopentadienyl)zirconium(rV) (Cp2ZrCl2) (equation 21). LiAKf-BuO^H + Cp2ZrCl 2 — » - Cp 2ZrCl(H) (21) dark T H F 1 As shown in Table I, the l-ene-3-yne 51b was isolated as an inseparable mixture of geometric isomers. The ratio of these isomers was determined to be approximately 4:1 E/Z by ! H N M R spectroscopy and G L C . However, reaction of this isomeric mixture, using a sufficient excess of 51b to allow for 1 equivalent of the E isomer, gave the desired 1,3-dienylzirconium complex 55b. The LK NMR spectrum of 55b indicated that the required E,E isomer had been obtained (Figure 3). The most diagnostic data, obtained from the LH NMR spectrum, confirming the stereochemistry of 55b, were the / A B and JQD coupling constants which were measured as 18 Hz and 13 Hz, respectively.56 In the initial crystallized batches of 55b, the presence of 3-5% of the E,Z isomer (55c), could be readily detected by ! H N M R spectroscopy. This isomeric impurity was easily removed by further recrystallizations. The hydrozirconation of 51c proceeded more slowly than that of the isomeric mixture 51b, when an excess of the latter is used to provide one equivalent of the E isomer. This empirical observation was made by measuring the time required for the formation of a homogeneous solution (i.e., complete reaction of the insoluble hydride 1) in separate reactions of 51b and 51c. Both reactions were carried out under identical conditions. This observed difference in rate of reaction may account for the almost exclusive formation of 55b from an E/Z mixture of the l-ene-3-yne 51b. The * H NMR spectrum of 55c, readily interpreted as that of the E,Z isomer, showed coupling constants for JAB and / C D of 18 Hz and 6 Hz, respectively (Figure 4). 5 6 There was 29 30 31 no evidence of any double bond isomerization during the hydrozirconation of 51c, as indicated by the absence of any of the isomeric complex 55b. The assignment of protons H A and H B for the complex 55d derived from NOEDIFF (nuclear Overhauser effect difference) spectroscopy. Irradiation of He gave clean enhancement of H B and of the neighboring allylic protons (Figure 5). Further evidence for this assignment Cp H A H B _JUJl He Irradiated here ZrCp 2 Cl 64d Normal Spectrum NOEDIFF Spectrum ppm Figure 5. 400 MHz LH NMR and NOEDIFF spectra of 55d in C6D 6 . was obtained from deuterium labelling studies (vide infra). Interestingly, for the complex 55d, decoupling experiments indicated a five-bond coupling of H A to He of 0.75 H z . 5 6 Comparison of the V B C coupling constants of the dienes 55a and 55b, with those of 1,3-butadiene,5 7 suggest that these dienes adopt the s-trans conformation in solution (Figure 6). The V B C coupling constants for 55a and 55b were both measured as 10.0 Hz; this correlates well with the hterature value for s-trans 1,3-butadiene of 10.7 H z . 5 7 The lower value of 8.5 Hz for the 3/BC coupling constant of the complex 55c may represent a deviation 32 ZrCpsCl ZrCp 2 Cl MeO H D H E (OMe) 55a-b 55c 3 7 R r = 10.0 Hz 3 7 R r = 10.7 Hz ^JTIC = 8.5 Hz Figure 6. Conformation of 55a-c, as related to 1,3-butadiene. from planarity in the 1,3-butadiene fragment. This could be due to steric repulsion between the OMe group and H B . The conformation of the diene 55d cannot be determined by this method. However, the results of the NOEDIFF experiment (vide supra) suggest that it is likely s-trans or slightly skewed from that planar conformation. If the conformation was s-cis or close to that orientation, some enhancement of H A would be expected. 33 2.1.1 Deuterium-Labelling Studies. In an attempt to obtain some mechanistic information regarding the chemoselective hydrozirconation of l-ene-3-ynes, the insertion reactions of the deuterated analogue of 1, Cp2ZrCl(D) 2 were investigated. When the reactions of 51a-d with 2 were carried out, analysis of the products (55a-d-^i) by * H NMR spectroscopy showed that no scrambling of the deuteron label had occurred (Scheme 17). This fact can be readily seen by comparison of the lH NMR spectra of \ 51a Cp2ZrCl(D) ZrCp 2 Cl 55a-cf! 4:1 EZ 51b OMe OMe 51c — O Cp2ZrCl(D) Cp2ZrCl(D) Cp2ZrCl(D) ZrCp 2 Cl 51d SSb-d SSc-d^ 5 5 d - ^ Scheme 17 Figure 7. 400 MHz * H NMR spectra of 55a and 55a-rfi. 35 the dienes 55a and 55a-Ji (Figure 7). In the * H NMR spectrum of the latter complex, the resonance attributable to H B is now absent and the resonance for H A has collapsed to a pseudo-1:1:1 triplet. The latter resonance shows a 2.5 Hz coupling to deuterium, which correlates well with the expected value of approximately 3 Hz. Finally, the resonance for He has reduced to a doublet of doublets, showing some broadening due to fine coupling to deuterium. Similar observations were made from the * H NMR spectra of the complexes 55b-d-^i. Analysis of the * H NMR spectra of these deuterated complexes indicated that, as for 55a-di, the deuteron label was incorporated exclusively at the ^-carbon, cis to the ZrCp2Cl moiety. The above results are consistent with a mechanism which involves direct, irreversible insertion of the alkyne functionality of 51a-d into the Zr-D bond of hydride 2, thereby placing the deuteron label exclusively at the ^-carbon. Such a process would therefore imply a kinetic preference for insertion of the alkyne functionality over the alkene group. Another possible mechanism which could account for the observed chemoselectivity of this insertion reaction is shown in Scheme 18 (next page). Insertion of the alkene functionality of l-ene-3-ynes 51a-d would give the complex 56. If this complex then underwent P-elimination (to regenerate starting materials) more rapidly than bond rotation to give 56', followed by irreversible insertion of the alkyne functionality to form 55a-d-</i, no scrambling of the deuteron label would be observed. However, if the reverse argument was true (i.e., bond rotation being faster than ^-elimination) one would expect to observe double bond isomerization, as well as scrambling of the deuteron label (56"). In the hydrozirconation of 51c no double bond isomerization was observed, thus suggesting that for 56 f3-elimination is faster than bond rotation. This mechanism would suggest a thermodynamic preference for the alkyne functionality. Therefore, based on the results of the deuterium-labelling experiments it was not possible to determine whether the chemoselectivity was due to a kinetic- or thermodynamically-controlled process. 36 ! ZrCp 2 Cl + Cp2ZrCl(D) R 2 2 insertion pVelimination 51a-d ZrCp 2 Cl R 3 S S a - d - ^ ZrCp 2 Cl R^ 5 6 " z bond rotation D ; " ' Z r C p 2 C l 56 ' a R 1 =R 2 =R 3 =H b R ^ R ^ H , R 3 =OMe c R !=R 3=H, R 2 =OMe d R 1 R 3 = - C C H 2 ) 4 - R 2 =H Cp 2ZrCl(R 1) 1 double bond isomerization Scheme 18 37 2.2 Hydrozirconation of Nitriles and oc,|3-Unsaturated Nitriles. Other workers have investigated the hydrometalation of oc,p-unsaturated nitriles. Reaction of acrylonitrile 57 with triphenylgermane 58 gave the addition product 59, thus exhibiting exclusive reaction with the alkene functionality (equation 22).5 8 An extensive study H v y C E N |T + Ph 3 GeH ^ P h 3 G e ( C H 2 ) 2 C = N (22) 57 58 59 of the hydrostannation of acrylonitrile,59 also revealed exclusive reaction with the alkene functionality of 57, to give a mixture of a- and [J-isomers 60 and 61, respectively. The ratio of the isomers was determined by the reaction conditions and the type of stannane used (equation 23). 5 9 > C E N T 57 C H 3 + R 3 S n H » R 3 S n — C H — C = N (23) a-isomer 60 + R 3 Sn(CH 2 ) 2 C s N fi-isomer 61 Previous workers 1 7 have shown that insertion of the nitrile functionality into the metal-hydride bond of Cp2ZrCl(H) 1 is a facile process. In analogy to the insertion of alkynes with 1, these workers assumed that the process occurred with overall cis stereochemistry, with the zirconium bonded to the nitrogen, the least stoically demanding position. The syntheses of the known imine zirconium complex 62, and the hitherto unknown analogue 63 were performed (Scheme 19). Erker and co-workers60 have shown, by X-ray analysis, that the 38 ZrCp 2 Cl Ph N + Cp 2ZrCl(H) 1 62 ZrCp 2 Cl C H 3 C==N + Cp 2ZrCl(H) 1 H 3 C 63 Scheme 19 complex 62 has a heteroallene-type structure, with a near linear Zr-N=C fragment (Figure 8). Such a structure is believed to arise from donation of the nitrogen lone-pair of electrons into the empty d-orbital of the zirconium, thus giving formally an 18-electron complex.60 Figure 8. Heteroallene-type structure for 62. In line with the observed chemoselectivity in the hydrozirconation of l-ene-3-ynes, the analogous reactions with a,P-unsaturated nitriles were investigated. It was discovered that reactions of a series of commercially available a,|i-unsaturated nitriles 64-67 with the hydride 1, at room temperature, gave the desired 1-azadienylzirconium complexes 68-71 in good yields (77-85%), as shown in Table II. As hoped, a chemoselective insertion of the nitrile functionality in the presence of the alkene group was observed. Cp Cp 39 Table II: Preparation of 1-azadienylzirconium complexes 68-71. Entry a,P-unsaturated 1-azadienylzirconium yieldb nitrilea complex (%) ZrCp 2 Cl 64 ZrCp 2 Cl 2 3 4 9 78 0 81 1 77 a b Nitriles 64-67 were purchased from Aldrich Chemical Co., and were purified by distillation prior to use. Yields of isolated, crystalline products. 41 The exact nature of the structure in the Zr-N=C fragment of the 1-azadienylzirconium complexes 68-71 could not be clearly determined by lH NMR spectroscopy. The ! H NMR spectrum for complex 69 is shown in Figure 9. To provide an answer to this structural question, crystals of the complex 69 were obtained from toluene/hexanes solution and a single crystal was subjected to X-ray analysis. The analysis was performed by Dr. R. Chadha of the University of Manitoba; the details of the data collection and refinement will be reported elsewhere. An ORTEP diagram of the molecular structure of 69, as well as selected bond lengths and angles can be seen in Figure 10 (next page). The most striking feature of the molecular structure of 69 is the almost linear Zr-N=C(l) fragment. The bond angle of the latter fragment was determined to be 167(2)°; this compares favorably with Erker's structure of the complex 62, where the corresponding bond angle was measured as 170 .5 (5 )° . 6 0 The Z r - N bond distance for the complex 69 was found to be 2.03(2) A, as compared with a distance of 2.013(2) A for 62. Based on the X-ray data obtained for the complex 69, the products from the chemoselective hydrozirconation of a,p-unsaturated nitriles 64-67 cannot be, formally, regarded as 1-azadienyl complexes. Instead, it would be more correct to consider them as having the heteroallene-type structure shown in Figure 11. Figure 11. Proposed solid state <x>riformation for the complexes 68-71. That these compounds 68-71 can be regarded as being 18-electron species may account for their enhanced stability in air as compared to the very air sensitive, formally 16-electron, 1,3-dienylzirconium complexes 55a-d. 42 Selected bond lengths (A) and angles (°) for 69 Z r — C I 2.505(7) C(l) — C(2) 1.44(3) Z r — N 2.03(2) C(2) —C(3) 1.34(3) N—C<1) 1.28(3) C(3) — C(31) 1.48(3) C l - Z r - N 102.2(6) C(2)-C(3)-C(31) 119(2) Zr -N-C( l ) 167(2) C(3)-C(31)-C(32) 119(2) N-C(l)-C(2) 126(2) C(3)-C(31)-C(36) 119(2) C(l>-C(2)-C(3) 119(2) Figure 10. Molecular structure and selected bond lengths and angles for 69. 43 2 .3 C a r b o n y l a t i o n and A t t e m p t e d D i e l s - A l d e r Reac t ions of 1,3-Dienylzirconium Complexes. Initial investigations of the reactivity of complexes 55a-d began with the complex 55b as a potentially reactive diene in the Diels-Alder reaction. Reaction of 55b with a variety of dienophiles (methyl acrylate, methacrylonitrile, maleic anhydride and dimethyl acetylenedicarboxylate) at room temperature or at elevated temperatures, gave either no reaction or led to decomposition of the diene (equation 24). However, room temperature reaction of c NO REACTION OR (24) c DECOMPOSITION R DIENOPHILE 55a-d either 55b or 55c with tetracyanoethene gave low yields (20-30%) of orange solids. The lH N M R spectra of these solids were extremely simple but structurally uninformative. Attempts to characterize these complexes further by IR, MS and microanalysis were unsuccessful. Therefore, due to the poor isolated yields and the inability to grow single crystals for X-ray analysis, further work on these complexes was abandoned. The lack of reactivity of the 1,3-dienylzirconium complexes 55a-d in the Diels-Alder reaction is, with hindsight, perhaps understandable if one considers that the bulky, electron-poor ZrCp2Cl substituent is unlikely to greatly activate the diene towards reaction with electron-deficient dienophiles. The carbonylation reaction of alkenylzirconium complexes has been shown to be an important step in the stereocontrolled preparation of various cc,|3-unsaturated acyl derivatives.2 6 As such, the reactivity of the complexes 55a-d with carbon monoxide was 44 Table DI: Carbonylation reactions of 55a-d with CO and 1 3 C O ; IR and 1 3 C NMR data. Reaction Reaction8 IR (cm1)1* 1 3 C N M R ( p p m ) c Yieldd with C O with 1 3 CO rj2-acyl Tl2-acyl (%) ZrCr^Cl 70a 70a- 1 3 C 1499 (1439) 301 73 (66) ZrCp 2 Cl 70b OMe 1468(1426) 293 OMe 83 (72) ZrCr^Cl 1492 (1447) 296 68 (61) ZrCp 2 Cl 70d 70d- 1 3 C 1498 (1444) 298 82 (80) a The symbol * denotes the position of the C label. b The T|2-acyl absorptions for the 13C-labelled complexes are shown in parenthesis. c These resonances are for the 13C-labelled complexes. Yields are not optimized; yields for the C-labelled complexes are shown in parenthesis. 45 investigated. Exposure of a toluene solution of these dienes to one atmosphere of CO produced an immediate color change, followed within 2-3 minutes by precipitation of a yellow-orange solid, the structures of which were detennined by NMR and IR spectroscopy. Initial analysis of these CO "insertion" products 70a-d by IR spectroscopy indicated strong absorptions characteristic of the T|2-acyl moiety (Table HI). That these IR absorptions are characteristic of the T|2-acyl moiety is evident from other literature examples.61 Further evidence for the assignment of these particular IR bands as the rj 2-acyl absorptions was obtained by the preparation and characterization of the corresponding 1 3C-labelled complexes 70a-d- 1 3C (the 1 3 C O used was 90 atom % 1 3 C ) . The IR stretching frequency of these T|2-acyl complexes is shown in parenthesis in the appropriate column of Table DI. The observed shifts obtained by using 1 3 C O are in good agreement with the calculated values. Additional evidence for the T|2-acyl functionality present in the complexes 70a-d- 1 3C was obtained from 1 3 C NMR spectroscopy. As observed by previous workers,61 Tj 2-acyl complexes exhibit a resonance for the acyl carbon at remarkably low field. Resonances for the complexes 70a-d- 1 3C were observed in the region 293-301 ppm, in good agreement with the values observed for other rj2-acyl complexes of zirconium.61 The * H NMR assignments for the complex 70d were based on the results from both NOEDIFF spectroscopy and deuterium-labelling experiments. Irradiation of proton He resulted in a clean enhancement of proton H B and the corresponding allylic protons (Figure 12, next page). It was possible to differentiate between protons H A and H B by comparison of the *H NMR spectra of the complex 70d and its deuterium-labelled analogue 70d-^i (synthesized by reaction of the complex SSd-d\ with CO). The lVL N M R spectra of the complexes 70d and 70d-di, along with that of the 1 3C-labelled complex 70d- 1 3 C are shown in Figure 13 (p 47). From the J H NMR spectrum of 70- 1 3 C is was possible to obtain values for the ^C-lH coupling constants for protons H A and H B - These values were measured as 2 Hz and 7.5 Hz, respectively. The magnitude of these coupling constants lends further credence to the assignments made for protons H A and H B . 5 6 3 46 Figure 12. 400 MHz * H NMR and NOEDIFF spectra of 70d in CDCI3. The assignments of the 1 3 C NMR spectra of complexes 70a-d- 1 3C were determined by use of two-dimensional (2D) NMR experiments. As the dienyl-proton resonances of these complexes had already been assigned, it was possible to identify the corresponding 1 3 C resonances by analyses of the 2D l 3 C - l H heteronuclear NMR correlation maps. Having identified particular proton resonances, these connectivity maps allow the 1 3 C nucleus directly bound to each proton to be assigned. The 2D 1 3 C - * H heteronuclear N M R correlation map, along with partial 1 3 C and * H NMR spectra for 70b- 1 3 C are shown in Figure 14 (p 48). The 1 3 C - 1 3 C and the ^C-lH coupling constants for 70a-d- 1 3 C are given in Table IV (p 49). In general, for these complexes, it was observed that the two-bond 1 3 C - 1 3 C coupling constants were slightly larger than the three-bond 1 3 C - 1 3 C couplings constants. This observation was in 47 Cp * denotes 1 3 C Cp 70b- 1 3 C OMe *H NMR Spectrum He 1 3 C NMR Spectrum C5 C3 H, D = ^ L ko C2 t CDCI3 OMe I I I I T I I M I I I I I I I I I I I I I I I I I I I I I [ I I M I I I I I I I I I 1 I I I 140 120 100 BO 60 PPM I 1 1 1 1 1 1 1 1 1 1 1 1— 1 7 0 1 6 0 1 5 0 1 4 0 1 3 0 1 2 0 1 1 0 1 0 0 9 0 8 0 7 0 b O SO F2 (PPM) OO Figure 14. Portion of the " C ^ H heterocorrelation 75-300 MHz spectrum for 70b- 1 3 C in CDCI3. 49 Table IV: 1 J C - C and C - H coupling constants for complexes 70a-d-d Complex* l r ij ll Jj • /cic2 • /cic3 • /cic4 JcmA C1HB (Hz) (Hz) (Hz) (Hz) (Hz) 0 70a- 1 3 C 34.5 9.8 8.8 8.0 O 70b- 1 3 C 36.7 11.6 8.2 2.5 7.0 OMe MeO-70c- 1 3 C 35.8 10.6 8.7 2.5 7.5 35.4 10.4 9.5 2.0 7.5 a The symbol * denotes the position of the C label. b No coupling was observed. 50 contrast to the 1 3 C - 1 3 C coupling constants measured for a series of 1 3C-labelled aromatic compounds, in which the opposite order was noted.6 2 Attempts to prepare the corresponding methyl dienyl ester of 70d by reaction with TY-bromosuccinimide (NBS), followed by addition of ~10 equivalents of methanol, resulted in the isolation of a mixture of products in which the desired ester 71 was present in less than 10% (by lH NMR spectroscopy) (equation 25). The other products were not identified. As ZrCp 2 Cl NBS MeOH PVP + UNIDENTIFIED PRODUCTS (25) 70d 71 (<10%) PVP - poly(4-vinylpyridine) various changes in the reaction conditions produced no improvement in the overall yield of 71 this reaction was abandoned. Having successfully prepared a series of 1,3-dienylzirconium complexes 55a-d, their ability to serve as general precursors in the preparation of other heterosubstituted 1,3-dienes remained to be investigated. The results of this investigation are outlined in Chapter 3. 51 C H A P T E R 3 Preparation of Heterosubstituted 1,3-Dienes, Imines and 1-Azadienes by a Transfer Reaction from Zirconium. 3.1 Preparation of a 1,3-Dienylnickel Complex. As mentioned previously in Chapter 1, the synthesis of a 2-substituted 1,3-butadienylnickel complex 32 has already been achieved.45 Complex 32 was synthesized by oxidative addition of 2-chloro-1,3-butadiene 31 to a nickel(O) complex 30 (equation 17). It was envisaged that by combining the chemoselective hydrozirconation reaction with the oxidative addition to nickel(O) complexes, a method for the preparation of 1-substituted 1,3-dienylnickel complexes could be developed. Previous workers1 3 have shown that reaction of alkenylzirconium complexes with N-bromosuccimmide (NBS) proceeds readily to generate the corresponding alkenyl bromide with retention of stereochemistry about the double bond (see equation 6, p 11). When complex 55d was reacted with NBS at room temperature, the desired bromodiene 72 was obtained in 89% isolated yield. Oxidative addition of 72 to Ni(PEt3)2(l,5-CgHi2) 30 proceeded rapidly at + (17) 30 31 32 52 room temperature to give, on workup, orange crystals of the l,3-dienylnickel(n) complex 73 (equation 26). The * H NMR spectrum of complex 73 is shown in Figure 15. The resonances for protons H A and H B appear as a tightly coupled ABX2 spin system, with the A B quartet for H A and H B , being further coupled to two equivalent phosphines. Thus, it was not possible to directly assign the stereochemistry of complex 73 from its * H NMR spectrum. However, there are sufficient literature examples of oxidative addition reactions of vinyl halides to nickel(O) complexes to conclude that, in general, such processes occur with retention of stereochemistry.3515'63 The assigned stereochemistry for bromodiene 72 is based on the 3 / A B coupling constant of 14 H z . 5 6 The trans orientation of the phosphines in the complex 73 is based on much literature precedent.64 In accordance with these data we therefore propose the structure for the complex 73 is as shown in equation 26. Attempts to unravel the complex coupling pattern of protons H A and H B for 73 by using different deuterated solvents, gave either no change in the spectrum or led to decomposition of the complex. In effect, the procedure outlined in equation 26 represents a two-step process for the stereoselective transfer of a 1,3-dienyl moiety from zirconium to nickel. Much effort was expended in an attempt to develop a method for the direct transfer of the 1,3-dienyl fragments from zirconium to other transition metals. It was hoped that this could be achieved by the reaction of the 1,3-dienylzirconium complexes 55a-d with a series of mononuclear transition metal halide complexes of the general formula M L n X m (e.g., (COD)PdCl2, CpNi(PPh3)Cl, 53 54 (PEt3)2PtCl2, (PEt3)2NiCl2). When the reactions were carried out at room temperature, no evidence for the transfer of the 1,3-dienyl fragments from zirconium was obtained. On performing the reactions at elevated temperatures, either no reaction or decomposition of the starting materials resulted (equation 27). A recent report has been published which presents NO REACTION + M I A ^ OR (27) *R 2 DECOMPOSITION M = Ni, Pd, Pt L = ancillary ligand(s) 55a-d X = halogen(s) evidence for the intramolecular transfer of a methyl group from zirconium to platinum.65 Due to the electron-rich nature of the nickel(II) center in complexes 32 and 73 (relative to the zirconium(rV) center of 55a-d), reaction with a variety of dienophiles was attempted. When either 32 or 73 was reacted with a series dienophiles (methyl acrylate, methacrylonitrile, maleic anhydride, dimethyl acetylenedicarboxylate and tetracyanoethene) at room temperature or at elevated temperatures no reaction or decomposition of the complex was observed. This lack of reactivity may be due in part to the bulk of the triethylphosphine (PEt3) ligands. Also, the assumption that the relatively electron-rich nickel center can activate the 1,3-dienyl fragment towards reaction with electron deficient dienophiles may be unfounded. At present, the transfer of the 1,3-dienyl fragments from zirconium to other transition metals in a stoichiometric, high yielding process seems most attractive via the indirect cleavage-oxidative-addition method outlined in equation 26. However, this procedure would be limited to those metals which can undergo oxidative addition with vinyl halides. Attempts to transfer the 1,3-dienyl fragment of the complexes 55a-d from zirconium to silicon, using trimethylsilyl chloride, failed even when the reaction was performed at elevated temperatures. The use of different silicon transfer reagents, such a l-(trimethylsilyl)imidazole or trimethylsilyl 55 trifluromethanesulfonate also failed to generate the desired 1,3-dienylsilanes. Other workers have observed similar difficulties in obtaining transfer of organic fragments from zirconium to silicon, even with the use of silicon tetrachloride.66 However, the direct transfer of organic moieties from zirconium to other elements such as tin, phosphorus, boron, selenium and sulfur was more successful. This procedure is discussed in detail in the following sections. 3.2 Transfer of 1,3-Dienyl Moieties from Zirconium to T i n . Several research groups have attempted the preparation of tin-substituted 1,3-dienes by the hydrostannation of l-ene-3-yne molecules. In general, this method appears to be very substrate dependent. The hydrostannation of l-buten-3-yne 51a led to 1,4-addition to generate R 3 Sn — C H = C = C H C H 3 74 51a R 3 S n H 1,4-addition ^8) R = C 3 H 7 , C6H5 R 3 Sn — C H = C H — C H = C H 2 75 1 ^ -addition the allenic derivative 74, rather than 1,2-addition to give the desired 1,3-diene 75 (equation 28). 5 4 b The reaction of l-ethoxy-l-buten-3-yne with one equivalent of tributyltin Bu 3 SnH H C = C — C H = C H — O E t Bu 3Sn — C H = C H — C H = C H , — OEt (29) AD3N 2 76 56 hydride and a catalytic amount of azobisisobutyronitrile (AIBN), gave the diene 76 as a mixture of geometric isomers (equation 29).6 7 The ratio of isomers was not reported. An extensive study of the hydrostannation of alkyl substituted l-ene-3-ynes, indicated that a wide variety of products were formed. 6 8 These products were shown to result from extensive isomerization, induced by trialkylstannyl radicals during and prior to addition to the l-ene-3-ynes. The latter observations are consistent with those reported previously for the hydrostannation of 2-methyl-l-buten-3-yne.52 The preparation of the tributylstannyl 1,3-diene 77a was later achieved by a rather elaborate synthetic sequence (Scheme 20). 6 9 The TBSC1 R 3 S n H O H \ OTBS R,Sn ^ 1 OTBS R 4 N + F P h 3 P = C H 2 " O 77a " B a M n O / R,Sn O H R = Bu TBS = f-Bu(Me)2Si Scheme 20 stereoselective hydrostannation of the l-ene-3-yne 51d has been reported to give the diene 77d (equation 30). 7 0 With the exception of the latter reaction, the hydrostannation of Bu 3 Sn — O Bu 3 SnH AIBN (30) 51d 77d 57 l-ene-3-yne molecules does not appear to be an efficient method for the syntheses of stereochemically defined tin-substituted 1,3-dienes. Preliminary results from another research group, indicated that the transfer of organic moieties from zirconium to tin, using tin tetrachloride, was a facile process.28 However, due to the sensitive nature of these trichlorotin species, it was decided to investigate the reaction of the complexes 55a-d with a trialkyltin chloride. Reaction of these complexes with tributyltin chloride in toluene, proceeded at room temperature or at elevated temperatures to afford the desired tin-substituted 1,3-dienes 77a-d in moderate to good yields (Table V , next page).53 These compounds were readily separated from the Cp2ZrCl2 by-product by extraction with hexanes and filtration. The IR spectra of the dienes 77a-d contained a band at 1620-1519 c m - 1 , which is indicative of compounds containing a 1,3-dienyl moiety. 5 6 a Analysis of the products by ! H N M R spectroscopy, indicated that the transfer of the 1,3-dienyl moiety from zirconium to tin had proceeded in a stereoselective manner. For example, the assignment of the diene 77b as the E,E isomer was based on the magnitude of the 3 / A B and V C D coupling constants of 18.5 Hz and 12.5 Hz, respectively (see Figure 16, p 59). Further evidence for the stereoselective nature of the transfer reaction, results from the VfiSn coupling constant of 62 Hz. This value is consistent with previously reported cis 3/HSn coupling constants.71 The corresponding 3 / A B and 3/BSn coupling constants for the dienes 77a, 77c and 77d can be seen in Table V . Dienes 77a and 77c were prone to isomerization when stored as neat liquids at room temperature. This isomerization was inhibited by storing these compounds in the dark at -30°C. No such isomerization was observed for the dienes 77b and 77d, which were found to be stable for months at room temperature in the dark. Overall, the combination of the hydrozirconation of l-ene-3-yne molecules and the subsequent transfer reaction to tin, provides an expedient syntheses of tin-substituted 1,3-dienes. 58 Table V : Reaction of 55a-d with Bu 3SnCl; and V B S n for 77a-d. 1,3-dienylzirconium 1,3-dienylstannane reagent product (Hz) •^ BSn (Hz) Yield8 (%) ZrCp 2 Cl SnBuq 18.5 60 68 55a ZrCp 2 Cl 77a SnBu 3 18.5 62 75 OMe 55b ZrCp 2 Cl OMe 77b SnBuq 18.5 19.5 62 67 71 79 55d 77d a Yields of isolated products. t denotes 1 1 7 S n / 1 1 9 S n satellites OMe Figure 16. 400 MHz lH NMR spectrum of 77b in 60 3.3 Transfer of 1,3-Dienyl Moieties from Zirconium to Phosphorus. The development of a general synthetic route for the preparation of 1,3-dienylphosphines is attractive from many viewpoints. As tertiary phosphines, their coordination to transition metals and subsequent reactivity would be of potential interest Also, as heterosubstituted dienes their reactivity with dienophiles, either as independent molecules or when bound to a transition metal, could generate interesting results. Although there are numerous literature procedures for the syntheses of stereochemically defined 1,3-dienylphosphoryl compounds,38*72 only one general method for the preparation of 1,3-dienylphosphines 78 has been reported (Scheme 21).7 3 Ph2P — CH 2—CH= CH II S BuLi Ph2P—CH—CH—CH II S Li ; + THF -70*C S reflux S (72-92%) (54-65%) Cp2Ni 60*C 78 (40-65%) Cp I a R1 = Ph, R2 = b R1 = R2 = Ph c R1 = R2 = Me (55-70%) H Scheme 21 61 It was hoped, that a more direct and higher yielding syntheses of such compounds could be developed by the stereoselective transfer of the 1,3-dienyl moiety, of the complexes 55a-d, from zirconium to phosphorus. Reaction of these complexes with one equivalent of cUorodiphenylphosphine (Ph2PCl) in toluene at room temperature, proceeded rapidly to afford the corresponding stereochemically pure 1,3-dienylphosphines 79a-d (equation 31). 7 4 Isolated yields of 79-88% were readily obtained by extraction with hexanes and filtration. + Cp 2 ZrCl 2 (31) 55a-d 79a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H, R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = — (CH 2 ) 4 — , R 2 = H The IR spectra of 79a-d contained a band at 1620-1516 cnr 1 , which is indicative of compounds containing a 1,3-dienyl moiety.5 6* The assignment of the stereochemistry for these compounds was made by analysis of their lH NMR spectra. In all cases a large 3 / A B coupling constant of ~17 Hz, which is indicative of a trans coupling, provided evidence for the stereoselective nature of the transfer reaction. The resonances for protons H A and H B were complicated by an additional coupling to the phosphorus-31 nucleus. The values for the 1 H - 3 1 P coupling constants, and the 3 1 P chemical shifts for the phosphines 79a-d are shown in Table VI. The coupling constants were determined from homonuclear or heteronuclear decoupling experiments. The * H N M R spectrum resulting from an experiment in which the 3 1 P chemical shift range for 79b was broadband decoupled while observing the lH chemical 62 Table VI: H - P coupling constants and 3 1 P NMR chemical shift data for 79a-d. 2 3 1,3-dienylphosphine JAP •'BP 8 3 1 P N M R (Hz) (Hz) (ppm) 79a 10.0 11.5 -12.4 79b 3.5 14.0 -11.7 79c 4.0 14.5 -11.3 79d 5.5 15.0 -11.7 Table VII: 1 H - 3 1 P coupling constants and 3 1 P NMR chemical shift data for 80a-d. 2 3 1,3-dienylphosphine Y AP -^BP 5 3 1 P N M R (Hz) (Hz) (ppm) 80a 12.0 10.5 -50.8 80b 8.0 10.0 -50.4 80 c 11.0 12.0 -50.2 80d 9.0 15.0 -50.7 63 'Hf 3 1 ?} spectrum OMe 7 6 _ J i L P P m 5 4 3 2 T Figure 17. 400 MHz *H and lH{ 3 1P} NMR spectra of 79b in C6D 6 . 64 shift range (i.e , ^ f 3 1 ? } ) is shown in Figure 17 . To highlight the changes made by 3 1 P broadband decoupling, the normal * H NMR spectrum of 79b is also shown in Figure 17. Comparison of these two spectra shows that the resonances for protons H A and H B have collapsed to a doublet and doublet of doublets, respectively. These changes provided a clear means of detennining the 1 H - 3 1 P coupling constants. The reported values were fairly consistent throughout for these phosphines, with the exception of the 2 / A P for 79a (see Table VI). The only other 2 / A P coupling constant reported for a 1,3-dienylphosphine, was for (E,E)-(4-phenyl-l,3-butadienyl)cuphenylphosphine.73 The value of 14 Hz given here, was in reasonable agreement with the 10 Hz coupling measured for phosphine 79a, but in poor agreement with the corresponding coupling constants for phosphines 79b-d. An analogous series of 1,3-dienylphosphines was prepared in a similar way by reaction of 55a-d with chlorodimethylphosphine (Me2PCl). As with Ph2PCl, the reaction with Me2PCl was almost instantaneous at room temperature to give, after workup, the 1,3-dienylphosphines 80a-d (equation 32). These compounds were isolated in good yields (77-82%). + Cp 2 ZrCl 2 (32) 55a-d 80a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H, R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = — ( C H 2 ) 4 — , R 2 = H 65 The main features of the * H NMR spectra of phosphines 80a-d were as observed for the diphenylphosphino 1,3-dienes 79a-d. The * H NMR spectrum of the phosphine 80c is shown in Figure 18 (next page). Measurement of the 3 / A B coupling constants (~16 Hz) indicated that the transfer reaction had taken place with retention of stereochemistry. Interestingly, the same trend in the 1 H - 3 1 P coupling constants for 79a-d, was observed for the dimethylphosphino 1,3-dienes. The values of these coupling constants, as well as the 3 1 P chemical shifts, for phosphines 80a-d are shown in Table VII (see p 62). Analysis of the 1 H -3 1 P coupling constants given in Tables VI and VII, highlights the anomalously large 2 / A P coupling constant for phosphine 79a. Also, in general, the 2 / A P coupling constants are larger for the dimethylphosphino-substituted 1,3-dienes than for the diphenylphosphino-substituted 1,3-dienes. However, the 3 / B P coupling constants are quite consistent throughout This latter observation could, with further examples, lead to a general method for the assignment of stereochemistry for alkenyl- and 1,3-dienylphosphines. In the lH N M R spectra of phosphines 80a-d, small traces (~3-5%) of another compound were observed. In all cases, it was apparent from the similarity in the resonances that the impurity was isostructural with the 1,3-dienylphosphine. Measurement of the appropriate i H ^ H coupling constants, indicated that these impurities were not geometric isomers. Therefore, they did not arise from some isomerization process, or by a deviation from complete stereoselectivity in the transfer from zirconium to phosphorus. Interestingly, when the reaction conditions were changed, namely, if instead of using neat Me2PCl it was added as a solution in toluene, analysis of the products by *H NMR spectroscopy showed no sign of the previously observed impurities. When complexes 55a-d were reacted with chlorodiisopropylphosphine (I-PT2PC1) at room temperature for 24 hours, less than 50% conversion to the corresponding 1,3-dienylphosphines was observed. The reaction proceeded more smoothly at 80°C, to give excellent isolated yields (83 and 92%) of the 1,3-dienylphosphines 81b and 81 d (Scheme 22, p 67). 66 67 Cp 2 ZrCl 2 Cp 2 ZrCl 2 55d 81d Scheme 22 Analysis of these compounds by lH NMR spectroscopy, in each case, indicated the presence of a 2:1 mixture of isostructural compounds. These observations were similar to those made for the trace impurities seen in the preparation of phosphines 80a-d, when neat Me2PCl was used. The * H NMR spectrum of the two component mixture for 81b is shown in Figure 19. Comparison of the relevant coupling constants ( 3 /AB and 3 / C D ) for the two species, indicated that they were not geometric isomers. Although the " ^ H - 1 ! ! coupling constants were identical within a given pair of isomers, the 2 / A P as well as the 3 / A P coupling constants were different. Also, the difference in chemical shift between the same protons for each component was greatest for proton H A , and thereafter decreased as the distance from the phosphorus center increased. From the 3 1 P { 1 H } NMR spectrum of 81b, the difference in chemical shift of the two components was 16 ppm. These observations suggest that the structural difference between the two components, exists at or close to the phosphorus center. The ratio of the two components of the mixture did not change on further heating for 4 days at 80*C. Also, no change in the lH NMR spectrum of the mixture was observed on 68 69 increasing the probe temperature to 80°C. However, when the reaction was carried out using approximately one-third the overall concentration of the previous reactions, the * H N M R spectrum of the products 81b and 81d showed only one set of resonances. These resonances corresponded, in each case, to the major component of the previously observed mixture. For comparison, the * H NMR spectra of the 2:1 mixture and that of the single component, for the phosphine 81b, are shown in Figure 20 (next page). Based on the data outlined above, it is suggested that the two components formed in the more concentrated reaction are actually rotamers, having restricted rotation about the phosphorus-carbon bond of the 1,3-diene fragment. These rotamers may arise due to different orientations of the bulky isopropyl groups in the transition states leading to product formation (Figure 21). If the two postulated intermediates 82 and 83 are in equilibrium, the formation of 82 R = 1,3-dienyl moiety 83 (-Cp2ZrCl2) (-CpjZrCla) 84 85 Figure 21. Rationale for the formation of rotamers for 81b and 81d. 70 Figure 20. 400 MHz *H NMR spectra of 81b as a single rotamer and as a 2:1 mixture of rotamers in C6D6. 71 only one rotamer due to dilution of the reaction mixture, may result from a longer induction period prior to formation of the product. Rotamers 84 and 85 would have a different orientation of the phosphorus lone-pair. For conformationally rigid systems, it has been shown that the 1 H - 3 1 P coupling constants can depend on the orientation of the phosphorus lone pair. 7 5 This may account for the differences observed between the two sets of 2//j> as well as the V B P coupling constants, for each of the two rotamers of phosphines 81b and 81d. The formation of rotamers for tertiary phosphines has been observed previously for the compound clhsopropylphenylphosphine (/-Pr2PhP)76 72 3.4 Transfer of 1,3-DienyI Moieties from Zirconium to Boron. Formation of 1,3-dienylboranes by direct hydroboration of l-ene-3-yne molecules is well documented.51'77 A recent communication outlined a general route to the preparation of a variety of 1,3-dienylboronates 86 (Scheme 23).7 8 In concert with this method, we discovered alcohol or diol B Y , Jt 86 Scheme 23 that complexes 55a-d reacted cleanly with bromodiphenylboron (Ph2BBr) at room temperature to give the desired 1,3-dienylboranes 87a-d (equation 33).7 4 These compounds were isolated in good yields (80-88%) as white solids or colorless oils. While this two step method may not be as convenient as the hydroboration of l-ene-3-ynes, there is the advantage that less hindered boranes can be used as the regiochemistry is defined in the hydrozirconation step. Also, to our knowledge, the direct hydroboration of the unsubstituted l-buten-3-yne 51a to generate 1,3-dienyls of type 87a has not been achieved. * J B(OBu) 2 73 ZrCp 2Cl BPh 2 + Ph2BBr toluene + Cp2ZrCl(Br) (33) R.T. dark R 3 R 3 55a-d 87a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H, R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = — ( C H 2 ) 4 — , R 2 = H I I The IR spectra of 87a-d contained a band at 1602-1621 cm - 1 , which is indicative of compounds containing a 1,3-dienyl moiety. 5 6 a The stereochemistry of these dienes was deduced directly from their *H NMR spectra. The 1 H NMR spectrum of the 1,3-dienylborane 87a is shown in Figure 22 (next page). The large 3 / A B coupling constant of 17 Hz indicates a trans stereochemistry, confirming the stereoselective nature of the transfer reaction from zirconium to boron. Compounds 87a-d were found to be light sensitive, as such the best yields of pure products were obtained by performing the transfer reaction in the dark. The photochemical lability of 1,3-dienylboranes has been previously observed and investigated.79 74 PL 75 3.5 Transfer of 1,3-Dienyl Moieties from Zirconium to Selenium and Sulfur. While many synthetic procedures for the preparation of sulfur-functionalized 1,3-dienes are available, 3 8 we are aware of only two reports of stereochemically defined 1,3-dienylselenides. A methoxyselenation-elimination sequence applied to 1,3-butadiene and isoprene has been reported; however, the assignment of stereochemistry was superficial and ambiguous. 8 0 The other report described the preparation, stereochemical analysis and reactivity of l-(phenylseleno)-2-(trimethylsiloxy)-4-methoxy-1,3-butadiene 46 (see Scheme 14, p 22).5°a,81 It was found that reaction of complexes 55a-d with iV-(phenylseleno)phthalimide (N-PSP) at -20°C in the dark, gave excellent yields of the desired selenium-functionalized 1,3-dienes 88a-d (equation 34).8 2 a R1 = R2 = R3 = H C T ^ " ^ b R1 = R2 = H, R3 = OMe c R1 = R3 = H, R2 = OMe d R1 R3 = —(CH 2 ) 4 — , R2 = H The IR spectra of 88a-d contained a band at 1619-1635 cnr 1 , which is indicative of compounds containing a 1,3-dienyl moiety. 5 6 a The stereoselective nature of the transfer reaction from zirconium to selenium, was determined by analysis of the products using J H N M R spectroscopy. The lH NMR spectrum of the diene 88d is shown in Figure 23. The ZrCp2Cl SePh Figure 23. 400 MHz *H NMR spectrum of 88d in C7D8. 77 large 3 / A B coupling constant of 15.5 Hz is indicative of a trans stereochemistry. The 2 /ASe and 3 /BSe coupling constants, as well as the 7 7 Se NMR chemical shifts, for compounds 88a-d are shown in Table VIII. The general observed trend is that 2 /ASe coupling constants are larger than the corresponding 3/BSe values. A similar trend was reported previously for a series of phenylselenenyl-functionalized alkenes.83 The same report gave the 7 7 Se NMR chemical shifts for the phenylselenium-functionalized alkenes. These values were in good agreement with those given in Table V m for 88a-d. Table VTJI: ^ - ^ S e coupling constants and 7 7 Se NMR chemical shift data for 88a-d. 1,3-dienylselenide j^ ASe ^BSC 8 7 7 S e N M R 3 (Hz) (Hz) (ppm) 88a 88b 88c 88d 15.5 14.5 15.5 15.5 11.0 10.0 10.0 379 367 374 369 a Not observed When the transfer reaction of 1,3-dienyl moieties from zirconium to selenium was performed at room temperature under fluorescent light, mixtures of products were observed for 88a-c. This is in contrast to the stereoselective formation of single products when the reactions were carried out at -20°C in the dark. Thus suggesting that the selenium-substituted 1,3-dienes may be photochemically and/or thermally labile. To investigate this phenomenon, a 78 detailed study of the photochemical and thermal reactivity of these compounds was undertaken, the results of which will be discussed later in Chapter 4. With regard to the above study, it was decide to prepare the corresponding sulfur-substituted 1,3-dienes by a similar transfer reaction from zirconium. Reaction of the complexes 55a-d with 7Y-(phenylthio)phthalimide ( N - P T P ) at room temperature in the dark, gave no reaction after 24 hours. However, when the reaction was performed at 80°C in the dark, the sulfur-substituted 1,3-dienes 89a-d were isolated in low yields (equation 35). Since ZrCpiCl I 55a-d a R1 = R2 = R3 = H b R1 = R2 = H, R3 = ( c R1 = R3 = H, R2 = ( d R1 R3 = -(CH 2 ) 4 SPh dark ;oluen< 80'C N-PTP ^ . X H A + Cp2ZrCl(phth) (35) o R3 89a-d P h t h = N J l (25-39%) o it was not our main desire to develop a synthetically useful procedure for the preparation of these 1,3-dienes, no attempt was made to optimize these low yields. It is interesting to note the difference in reactivity of the complexes 55a-d with N-PTP as compared to TV-PSP. The reasons for this dramatic difference in reactivity are unclear. The IR spectra of 89a-d contained a band at 1621-1634 cm*1, which is diagnostic of 1,3-dienyl compounds.5 6 3 The stereochemical purity of these compounds was determined by * H N M R spectroscopy. The * H N M R spectrum of 89b is shown in Figure 24. The large 3 / A B coupling constant of 15 Hz indicates a trans stereochemistry, confirming the stereoselective nature of the transfer reaction from zirconium to sulfur. 79 80 The transfer of the 1,3-dienyl fragment from zirconium has been shown to proceed in a stereoselective manner, to generate a series of type A 1,3-dienes where the heteroatom (M) can be tin, phosphorus, boron, selenium or sulfur (equation 36). In general, these reactions proceed rapidly at low or moderate temperatures to give good yields of a range of heterosubstituted 1,3-dienes. ZrCp 2 Cl ML, M L n X (36) R (- ZrCp 2Cl(X)) R 55a-d A M = Sn, P, B, Se, S 81 3.6 Preparation of Heterosubstituted Imines and 1-Azadienes. Transfer from Zirconium to Selenium and Phosphorus. The heteroallene-type complexes 62,63 and 68-71, prepared by the hydrozirconation of nitriles and a,p-unsaturated nitriles, did not initially appear to be likely candidates as irnine and 1-azadiene transfer reagents. The solid state structure of these complexes indicated H , C ZrCp 2 Cl C H , ^ ^ 62 63 68 significant delocalization of the nitrogen lone-pair into an empty d-orbital of zirconium. Thus, as formally 18-electron complexes they lacked the empty orbital presumed necessary for the transfer of an organic moiety from one species to another, via a four-centered transition state. However, as solution state structure does not always parallel solid state structure, attempts were made to obtain imine and 1-azadiene transfer from zirconium to selenium and phosphorus. 82 In a very recent publication describing the synthesis and X-ray crystal structure analysis of the heteroallene-type metallocene Cp2Zr(N=CPh2)2 (90), the authors expressed surprise at the poor correlation between solution and solid state data for this complex.84 From the X-ray structure, it was expected that the lK NMR spectrum of 90 would show two sets of phenyl resonances. However, even at low temperature these workers only observed one type of aromatic resonance. They accounted for this observation by proposing a pathway in which a change in hybridization at the "azomethine" nitrogen occurred (Figure 25). This process initially involves a "decoupling" of the Zr=N multiple bond (rc-interaction), followed by a rapid rotation about the Z r - N bond (a-rotation) and finally, reformation of the Zr=N multiple bond. Such a process could account for the observed facile transfer reaction of imine and 1-azadiene moieties from zirconium to selenium and phosphorus. ^-interaction X R R' 0-rotation Figure 25. Rotation of heteroallene complexes via changes in hybidization. 83 3.6.1 Transfer of Imine and 1-AzadienyI Moieties from Zirconium to Selenium. Although many examples of sulfinirriines possessing both the imine function and a sulfur-nitrogen bond exist,85 few examples of the corresponding selenoimines are known. 8 6 There are also examples of sulfur-substituted 1-azadienes in the literature,850 but we are unaware of any reported examples of selenium-substituted 1-azadienes. Therefore, it was our desire to investigate the preparation of imine and 1-azadiene species, substituted at nitrogen by selenium. We hoped to access such compounds by the transfer of the inline and 1-azadiene moieties from zirconium to selenium. Reaction of 62 with phenylselenenyl chloride (PhSeCl) at room temperature in the dark, caused an immediate discharge of the deep red color of the PhSeCl. Analysis of the bright yellow oil, obtained after workup, by * H NMR spectroscopy indicated the presence of only one isomer of the desired selenoimine 91 (equation 37). Further analysis of the ZrCp^Cl SePh + Cp 2 ZrCl 2 (37) 62 91 73% * H NMR spectrum revealed a 3 /ASe coupling constant of 28 Hz, the magnitude of which is probably indicative of the stereochemistry of the product. Based on this and the results of an 1 H NOEDIFF experiment on a related compound (94), it was assumed that 91 was the E isomer (vide infra). Previous workers have used lH NOEDIFF spectroscopy to differentiate E and Z isomers of methyl enol ethers87 and trimethylsilyl enol ethers.88 In these experiments, the 84 vinyl proton was irradiated and an enhancement of the methyl of the enol ether, or the methyls of the silyl enol ether were observed only for the E isomer. Attempts to prove the stereochemistry of the selenoimine 91 by this method were unsuccessful. This was due, in part, to the poor stability of this compound. It was observed to decompose readily at room temperature, to give diphenyl diselenide (Ph2Se2) and some unidentified organic products. The propensity of compounds containing selenium-nitrogen bonds to decompose, generating diselenides has been previously reported.86 The selenoimine 92 was prepared by reaction of 63 with PhSeCl (equation 38). ZrCpjCl SePh + Cp 2 ZrCl 2 (38) 63 92 75% Again, only one isomer was observed by J H N M R spectroscopy. Attempts to prove the stereochemistry of this product by * H NOEDIFF spectroscopy were unsuccessful. It was assumed that selenoimine 92 has the same stereochemistry as 91, due to the similarity of the 3^ASe coupling constants of 29.5 and 28 Hz, respectively. The * H NMR spectrum of 92 is shown in Figure 26. Although the latter compound was more stable than 91, significant decomposition to Ph2Se2 was observed after 24 hours at room temperature. Reaction of the complex 68 with PhSeCl at room temperature gave, after workup, the desired selenium-substituted 1-azadiene 93 (equation 39, p 86). Product analysis, by *H N M R spectroscopy, indicated that only one isomer was present. No direct evidence for the stereochemistry of the product could be obtained; however, the 3 /ASe coupling constant of 29 Hz suggests that it has the same stereochemistry as the selenoimines 91 and 92. This selenium-substituted 1-azadiene was found to be quite unstable at room temperature, and 86 ZrCpzCl SePh 1 H 1 f * N toluene A > * N I + PhSeCl - I + Cp 2 ZrCl 2 (39) 68 93 72% decomposed readily to Ph2Se2- The presence of Ph2Se2 can be clearly seen in the lH NMR spectrum of 93, shown in Figure 27 (next page). The 1-azadienes 94 and 95 were prepared by similar procedures from complexes 69 and 70, using N-PSP as the selenium transfer reagent (Scheme 24). For these compounds, ZrCp 2Cl SePh 1 H 1 H -N toluene A > V * N A > ^ N ^ S e P h + AT-PSP T + T R.T. -(Cp2ZrCl2) Ph Ph Ph 5:1 69 94 81% ZrCp 2Cl SePh I H 1 H - N toluene A > ^ N A v ^ N \ + N-PSP » I + ' i e ™ R.T. -(Cp2ZrCl2) OEt OEt OEt -1.2:1 70 95 69% Scheme 24 ! H N M R spectroscopy indicated that a mixture of geometric isomers had been obtained. The 1-azadiene 94 was obtained as a 5:1 mixture of geometric isomers. Assignment of the stereochemistry for the major component as the E isomer was obtained by "'H NOEDIFF SePh PPm 7 6 5 4 3 Figure 27. 400 MHz *H NMR spectrum of 93 in C6D6-88 Irradiated here Normal Spectrum NOEDIFF Spectrum ppm 8 Figure 28. 400 MHz LH NMR and NOEDIFF spectra of 94 in C6D 6-spectroscopy (Figure 28). Irradiation of the imine proton, for the major component, gave enhancement of the orf/io-phenyl protons of the PhSe group, and of proton He. The enhancement of proton He suggests that the 1-azadiene 121 adopts the s-trans conformation in solution. The ^ASe coupling constant for the major isomer was measured as 28 Hz, due to the relative intensity of H A for the minor isomer the magnitude of its coupling to selenium could 89 not be clearly determined. The 3 /ASe coupling constant for the major isomer of 94 lends further credence to the assignment of E stereochemistry for the compounds 91-93. For the 1-azadiene 95, the isomers were formed in an approximately 1.2:1 ratio. Use of 1 H NOEDIFF spectroscopy, to directly assign the stereochemistry of the major isomer was not possible due to the small chemical shift difference between the imine protons of the two isomers. However, the 3/ASe coupling constants for the major isomer was measured as 28.5 Hz; therefore by analogy to compound 94, it was assumed that the major component was the E isomer. It should be noted that the use of N-PSP for the preparation of 1-azadienes 94 and 95 gave higher isolated yields than PhSeCl, but did not effect the ratio of isomers. Also, it appears that the isomeric ratio is determined during the transfer process from zirconium to selenium, as neither irradiation with fluorescent light, nor thermolysis at 80°C brought about a change in the ratio of isomers. Attempts to prepare the 1-azadiene 96, by reaction of the complex 71 with either N-PSP or PhSeCl proved unsuccessful (equation 40). The isolation of PhSeCl or ; i * | (40) /V-PSP diphenyl diselenide, in near quantitative amounts, suggests that the transfer reaction may indeed proceed; however, under the reaction conditions employed 96 is extremely unstable and readily decomposes. 90 3.6.2 Transfer of Imine and 1-Azadienyl Moieties from Zirconium to Phosphorus. The preparation of heterosubstituted imines, containing a phosphorus-nitrogen bond has been described in the general syntheses of diphenylphosphmylimines 97 (equation 41).8 9 O Ph 2 PCl || R 1 R 2 C = N O H • R 1 R 2 C = NOPPh 2 • R 1 R 2 C = N P P h 2 (41) -40°C 97 However, to our knowledge, there are no examples of phosphinoimines or phosphorus-substituted 1-azadienes, where phosphorus is directly bonded to nitrogen. Therefore, as a means of extending the generality of the imine and 1-azadiene transfer reaction from zirconium, and to provide a general route to phosphinoimines and phosphorus-substituted 1-azadienes, it was decided to investigate the reaction of complexes 62, 63 and 68-71 with PI12PCI. + Ph2PCl toluene R.T. + Cp2ZrCl2 62 98 83% 63 Scheme 25 99 86% 91 Reaction of the complexes 62 and 63 with Ph2PCl at 80°C gave, after workup, the desired phosphinoimines 98 and 99 (Scheme 25). In each case, product analysis by ! H N M R spectroscopy indicated that only one isomer had been formed. The stereochemistry of compound 99 was determined by ' H NOEDIFF spectroscopy (Figure 29). Irradiation of H A J L JL. 99 Normal Spectrum Irradiated here ^ > U ^ NOEDIFF Spectrum Ppm 8 7 6 s i % Figure 29. 400 MHz ] H NMR and NOEDIFF spectra of 99 in C6D 6 . the orffo-phenyl protons of the PI12P group, gave enhancement of the imine proton and of the mete-phenyl protons of the Ph2P group. The stereochemistry of the latter compound was therefore assigned as the E isomer. The 3 / B P coupling constant for this compound was measured as 22 Hz. It was assumed that the magnitude of this coupling constant would be indicative of the stereochemistry of structurally similar molecules. As such, the phosphmoimine 98 was assigned as the E isomer, due to an observed 3 / B P coupling constant of 21 Hz. 92 The phosphorus-substituted 1-azadienes 100-102, were prepared in a similar manner, by reaction at room temperature of complexes 69-71 with Ph2PCl (Scheme 26). In each 2jrCp2Cl N + Ph 2PCl toluene R.T. toluene Ph 2PCl + Cp 2 ZrCl 2 R.T. 1 + Ph 2PCl • + Cp 2 ZrCl 2 R.T. Scheme 26 case, only one isomer was formed, the stereochemistry of which was assigned based on the magnitude of the V B P coupling constant. The 3 / B P coupling constants for the compounds 100-102 were measured as 22, 23 and 25 Hz, respectively. It was therefore assumed that they all possessed the E configuration about the imine functionality of the 1-azadiene fragment. The * H N M R spectrum of 100 is shown in Figure 30. 93 94 Unfortunately, reaction of complex 68 with PI12PCI, under a variety of conditions, gave extremely poor yields (~5% or less) of the desired 1-azadiene 103 (equation 42). At (42) ZrCpoCl PPh, I I r^-N toluene r ^ N + Ph2PCl • C H 3 ^ R T - C H 3 - ^ 68 103 -5% temperatures below 40°C negligible product formation was observed, whereas above this temperature the product appeared to decompose as it was formed. Through the procedures outlined above, a series of general methods has been developed for the transfer of 1,3-dienyl, imine and 1-azadienyl moieties from zirconium to various heteroatoms. In the case of the transfer of 1,3-dienyl moieties from zirconium, the reaction was observed to occur with complete stereoselectivity. From this array of heterosubstituted organic molecules, the reactivity of the 1-(phenylseleno)-1,3-dienes 88a-d under photochemical and thermal conditions was investigated in detail. A preliminary investigation into their Diels-Alder reactivity was also made. The results of these experiments are discussed in Chapter 4. 95 C H A P T E R 4 Reaction of l-(Phenylseleno)-l,3-dienes under Photochemical and Thermal Conditions. Diels-Alder Reactivity with Maleic Anhydride. 4.1 Photochemical Isomerization. As described in Chapter 3, the stereoselective syntheses of the selenium-substituted 1,3-dienes 88a-d were achieved by reaction of the complexes 55a-d with iV-PSP at -20°C in the dark (equation 34). These conditions were necessary to avoid the formation of mixtures of 55a-d 88a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H , R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = — ( C H 2 ) 4 - , R 2 = H I I products when the reactions were performed at room temperature in the presence of fluorescent light; in addition, there was no beneficial effect by using other selenium transfer reagents, i.e., PhSeCl or Ph2Se2, under the same conditions. Analysis of these mixtures by * H N M R spectroscopy indicated that they were comprised of geometric isomers. Thus, 96 reaction of 55a with 7Y-PSP at room temperature under fluorescent light resulted in the formation of an E/Z mixture of geometric isomers of 88a. Analysis of the 1 H NMR spectra of the products obtained by reaction of the complexes 55b or 55c under identical conditions, indicated the presence of four compounds as evidenced by four singlets in the methoxy region (3.5-3.7 ppm) of each spectrum. In each case, the mixture of compounds appeared to be identical by J H NMR spectroscopy. In contrast, the diene 88d could be prepared isomerically pure, by the room temperature reaction of 55d with N-PSP under fluorescent light. As the dienes could be synthesized isomerically pure by control of the reaction conditions, experiments were designed to determine whether the isomerization process was thermally and/or photochemically initiated. An isomerically pure sample of 88a (~0.20-0.25 M in C7D8) was placed in the probe of a 400 MHz * H NMR spectrometer held at -20°C. Great care was taken to exclude light. The probe temperature was then increased to 30°C in 10°C increments. After each temperature increase, data for a * H N M R spectrum were acquired. In all instances, no sign of isomerization was observed. The probe temperature was then increased to 90°C for 1 h. Again, no isomerization resulted. Finally, the sample was removed from the probe and taped to a fluorescent tube for approximately 1.5 h. After this exposure, the subsequent *H NMR spectrum of the sample revealed the presence of a 2:1 mixture of E/Z geometric isomers of 88a (equation 43). 7 4 The * H NMR spectrum of this 2:1 mixture of geometric isomers is SePh SePh 88a shown in Figure 31 (next page). Further irradiation of the sample with fluorescent light, for up to 48 h, gave no change in the observed 2:1 mixture of isomers. That this 2:1 mixture of P P m 7 6 5 4 Figure 31. 400 MHz ! H NMR spectrum of a 2:1 mixture of E/Z isomers of 88a in C6D6-98 geometric isomers for 88a represents an equilibrium mixture was evident upon perturbing the equilibrium by addition of the isomerically pure E isomer of 88a . Further photolysis of this new mixture of E/Z isomers resulted in the formation of the original 2:1 mixture. When similar variable temperature lH NMR experiments were performed using 88b and 88c, no isomerization was observed. However, when the samples were irradiated with fluorescent light for 1.5 h, an identical mixture of all four possible stereoisomers was obtained in each case (Scheme 27). The *H NMR spectrum for the mixture of stereoisomers for 88b is SePh E,Z Z ,Z Scheme 27 presented in Figure 32 (p 99). Through a series of * H N M R decoupling and NOEDIFF experiments, it was possible to assign all of the vinyl resonances in the region from 5-7 ppm. The spectrum of this expanded region, along with the appropriate assignments is shown in Figure 33 (p 100). Further evidence for the presence of four independent selenium-containing compounds, from the photolysis of 88b can be seen in the 7 7 S e N M R spectrum of the mixture (Figure 34, p 101). The ratio of the four geometric isomers was obtained from SePh SePh four stereoisomers of 88b ppm 7 6 5 Figure 32. 400 MHz *H NMR spectrum of all four stereoisomers of 88b in CD2CI2. OMe OMe H D H D E,E Z,E E,Z Z,Z four stereoisomers of 88b Figure 33. 400 MHz lR NMR spectrum of the expanded region from 5-7 ppm for the stereoisomers of 88b in CD2CI2. 101 102 the *H NMR spectrum. Over a series of different experiments, the ratio was observed to vary only very slighdy, and was determined as 41(±2) :13(±1) :36(±2) :10(±1) Z,E/Z,Z/E,E/E,Z. These values correlate well with those determined from the 7 7 S e N M R spectrum of the mixture. Previous workers have observed that direct irradiation of methyl (£,£)-2,4-hexadienoate resulted in the formation of all four possible stereoisomers.90 In this case, U V irradiation at 254 nm, close to the X m a x of the ester, was used. The irradiation source used in the experiments outlined here was a fluorescent lamp, which emits wavelengths from 380-800 nm. However, the possibility exists that some stray U V emission may result due to the nature of operation of a fluorescent lamp. The UV-vis spectrum of 88b showed a broad ill-defined A m a x from 250-268 nm (e 13800-14000), with 88c exhibiting a relatively sharp Xmax at 270 nm (e 15,900). The dienes 88a and 88d showed maximum absorptions at similar wavelengths. However, the dienes 88a-d showed only low intensity absorptions (e< 100) trailing into the visible region. 103 4.2 Mechanistic Studies on the Isomerization Process. To determine whether the isomerization process was occurring via an intra- or intermolecular process, a crossover experiment was performed. It was assumed that if an intermolecular process was operable, cleavage would most likely occur at the selenium-carbon bond of the 1,3-diene unit Therefore, it was required that the dienes 88a-d be labelled in one case at the PhSe group to give 104, and in the other case at the diene unit to give 105 (Figure 35). The crossover experiment would involve irradiation of a mixture of 104 and * + 104 105 + R R 3 106 * R 3 107 J 104 105 V crossover products Figure 35. General design for crossover experiments using labelled (*) versions of 88a-d. 104 (45) 55a-d 88a-d-d5 a R1 = R2 = R3 = H b R1 = R2 = H, R3 = OMe c R1 = R3 = H, R2 = OMe d R1 R3 = —(CH 2) 4— , R2 = H I I 105 105. From analysis of the products, it could be determined whether or not the predominant pathway during the photochemical isomerization of 88a-d was intra- or intermolecular. In the former case, one would not expect to see any of the crossover products 106 and 107, whereas for an intermolecular process one would expect significant formation of these compounds. As the deuterium-labelled complexes 55a-d-di had already been prepared by reaction of Cp2ZrCl(D) 2 with l-ene-3-ynes 51a-d, these could be used to label the diene unit of 88a-d with a deuteron at the 2-position. Thus, the labelled dienes 88a-d-^i were prepared according to equation 44. Analysis of these compounds by both * H NMR spectroscopy and a R 1 = R 2 = R 3 = H b R 1 = R 2 = H, R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = —(CH 2 ) 4 — , R 2 = H mass spectrometry, indicated that the deuterium incorporation was >98%. The labelling of the phenyl group of the PhSe fragment was performed in two ways. To make the change in structure as subtle as possible, so as to avoid any possible change in the mechanism of the isomerization reaction, N-(phenylseleno)phthalimide-ds (N-PSP-ds) was first synthesized (Scheme 28). Reaction of N-PSP-ds with the complexes 55a-d, as outlined in equation 45, gave the dienes 88a-d-ds having the phenyl group of the PhSe fragment fully deuterated. Analysis of these compounds by lH NMR spectroscopy and mass spectrometry, indicated that 106 the deuterium incorporation was >98%. A different label for the PhSe fragment was developed by the synthesis of N-(4-chlorophenylseleno)phthalimide (/V-C1PSP) as outlined in Scheme 29. Reaction of N-C1PSP with 55a-d at -20°C in the dark proceeded cleanly to give a a CI 7V-C1PSP Scheme 29 the dienes 108a-d, having the phenyl group of the PhSe fragment labelled with a para-chloro substituent (equation 46). Although the para-chloro substituent may affect the isomerization 55a-d 108a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H, R 3 = OMe c R 1 = R 3 = H, R 2 = OMe d R 1 R 3 = — ( C H 2 ) 4 - , R 2 = H I I 107 process by changing the electronic nature of the selenium dienes, it was hoped that it would provide a sufficient structural difference to allow the detection of crossover products by * H NMR spectroscopy. Whereas, the combination of 88a-d-di and 88a-d-^5 would yield crossover products that would be indistinguishable by *H NMR spectroscopy. Using these labelled compounds, two sets of crossover experiments were designed. In the first set of experiments, approximately equal concentrations of 88a-d-rfi and 88a-d-^5 were mixed together and the mixture was irradiated for ~1.5 h with fluorescent light. The products were then analyzed by lH NMR spectroscopy and mass spectrometry. Analysis of the photolyzed mixture by *H N M R spectroscopy was performed to establish that isomerization had taken place to yield the equilibrium mixture of isomers. It was envisaged that the use of mass spectrometry for this determination could prove difficult, as the masses of the products would only differ by one and five units. Also, each molecular ion fragment would be extremely complex due to the six isotopes of selenium. Five of these isotopes occur in reasonable natural abundance, namely, 7 6 S e (9.0%), 7 7 S e (7.6%), 7 8 S e (23.5%), 8 0 S e (49.8%), 8 2 Se (9.2%), with 7 4 S e being present in only 0.9% natural abundance. Therefore, to avoid any ambiguity in the determination of crossover products by mass spectrometry, a control experiment was designed in which approximately equal concentrations of 88b-<2i and 88b-^5 were irradiated independently, and then mixed prior to analysis by mass spectrometry. The molecular ion fragmentation pattern for this experiment was then compared with the one resulting from the crossover experiment in which 88b-di and 88b-ds were mixed and then irradiated with fluorescent light. The results of these experiments are shown in Figure 36. Using 8 0 Se as the major isotope, molecular weights for 88b-di and 88b-d5 were calculated to be 241 and 245, respectively. The two compounds resulting from crossover would therefore have the unit masses of 240 (88b) and 246 (SSb-d^). The molecular ion fragmentation patterns for the control and crossover experiments are distincdy different, indicating that some degree of crossover has indeed taken place, and that the photochemical isomerization reaction does involve an intermolecular process. SePh 88b-rfi SePh SePh-oV CONTROL EXPERIMENT T T 241 SePh-rfc 2 4 0 241 hi) CROSSOVER EXPERIMENT T I I I I I I | I 260 i248 I I I I I I I I 2 4 0 2 6 0 Figure 36. Molecular ion fragmentation patterns for the control and crossover experiments using 880-0*1 and 880-0*5. 109 Similar experiments were performed for the mixtures 88a-tfV88a-d5 and 88c-tf*i /88c-^5; in each case crossover products were evident by mass spectrometry. When the crossover experiment was performed with the mixture of 88d-tf*i and 88d-d5, analysis by mass spectrometry indicated that significant crossover had taken place. Assuming that the isomerization reaction and the presence of crossover products are directly linked, this result was somewhat surprising as 88d had shown no sign of isomerization by 1 H N M R spectroscopy. It was therefore concluded that since the isomerization process yields equilibrium mixtures of geometric isomers, perhaps the E isomer of 88d was by far the predominant one in equilibrium, with only a small concentration of the Z-isomer. If this was the case, such small quantities of the Z isomer may not have been detectable by lH NMR spectroscopy. To investigate this postulate, a sample of the Z isomer of 88d was prepared and irradiated with fluorescent light to determine if isomerization to a mixture of geometric isomers greatly dominated by the E isomer would be obtained. Previous workers have reported the isomerization of alkenylzirconium complexes upon irradiation with UV-l ight . 1 8 It was thought that 55d would undergo a similar isomerization, thereby allowing for the preparation of a mixture of geometric isomers of 88d via a transfer reaction with 7Y-PSP. Irradiation of 55d with fluorescent light for 19 h resulted in the formation of a 65:35 E/Z mixture of stereoisomers. This mixture was then reacted with Af-PSP to give a 65:35 mixture of E/Z geometric isomers of 88d. This result thus represents the first example of stereo specific transfer of an organic moiety from zirconium. When the 65:35 E/Z mixture of 88d was irradiated with fluorescent light, isomerization was observed to take place by lK N M R spectroscopy to give, after 18 h, a 95:5 E/Z mixture of 88d (Scheme 30, next page). Thus, under conditions where equilibration between the E and Z isomers of 88d can occur, the former species was found to compose 95% of the mixture. It is believed that this result accounts for the apparent absence of isomerization, and the observation of crossover on irradiation of 88d. 110 SePh SePh 95:5 E/Z mixture 65:35 E/Z mixture Scheme 30 The second set of crossover experiments involved the use of the dienes 108a-d, which contain the /?ara-chloro substituent on the PhSe fragment. A similar series of crossover experiments, as described previously, were performed using mixtures of 108a-d and 88a-d-di. In all cases, the differences between the molecular ion fragmentation patterns for the control experiments versus the crossover experiments were sufficiently great to conclude that crossover had taken place. These results are exemplified for the mixture 108b and 88b-di which, after irradiation with fluorescent light, resulted in the molecular ion fragmentation patterns shown in Figure 37 (next page). As predicted, the presence of the para-chloro substituent provided a sufficiendy different environment for the nearby protons that the presence of crossover products could be readily identified by * H NMR spectroscopy. This observable difference by * H NMR spectroscopy is most easily seen in the lH NMR spectrum of the photolyzed mixture of 108d and SSd-di. The l¥L NMR spectra of the 108d and 88d-di mixture before and after photolysis are shown in Figure 38 (p 112). Analysis of I l l SePh Se—f v A—CI + I I I 2 4 1 U B 2 4 1 1 h\> 2 7 4 2 8 0 2 7 3 I I I I I I I I I I I I I | I I I I I 2 4 0 2 6 0 2 8 0 Figure 37. Molecular «*n fragmentation patterns for the control and crossover experiments using 108band 88b-di. 112 88d-J 108d 108d V 88d Hp-Hp" \J V v crossover products + 88d-</j + 108d H A' H A " II AFTER PHOTOLYSIS • H / J JUL j J U J h J n . Jl A Hp/ H, H A' BEFORE PHOTOLYSIS 7 6 -3 ppm S 4 3 2 Figure 38. 400 MHz * H NMR spectra of the mixture 108(1 and 88d-di before and after photolysis in C 6 D 6 -113 these crossover experiments by * H NMR spectroscopy made it possible to obtain qualitative information on the degree of crossover. In general, crossover was observed to give an approximately equal mixture of all possible products. This can be seen by examination of the * H N M R spectrum of the 108d and SSd-di mixture after photolysis (Figure 38). By observing that there was a strong correlation between the degree of crossover and the time of exposure of the mixtures to fluorescent light, it is proposed that the extent of isomerization is indeed directly linked to the amount of crossover. The results outlined above suggest that the photochemical isomerization of the dienes 88a-d occurs by an intermolecular process, which likely involves cleavage of the selenium-carbon bond of the 1,3-diene fragment. The reaction was investigated further to determine if the process leading to diene isomerization involved an ionic or free radical pathway. The empirical observation that both the rate of isomerization and the degree of crossover were unaffected by changing the solvent from either C$>6 or C7D8 to CD2CI2 or CDCI3, tends to rule against an ionic process. To probe the mechanism further, the effects of 2,6-ferr-butyl-4-methylphenol (BHT), 4-oxo-2,2,6,6-tetramethylpiperidinyloxy radical (TEMPONE) and 1,4-cyclohexadiene on the isomerization process were examined. These reagents were chosen for their ability to intercept and, in general, effect in some way a change in reactions which involve free radicals. The presence of up to two equivalents of BHT was necessary to cause a significant rate change in the isomerization of 88b, as observed by * H NMR spectroscopy. As T E M P O N E is itself a free radical, amounts greater than approximately 5 mol % concentrations of this reagent caused significant deterioration of the spectral resolution, such that its effect on the isomerization process could not be clearly demonstrated by *H NMR spectroscopy. The most extensive studies were performed using 1,4-cyclohexadiene as a free radical trapping agent. Photolysis of a 0.20-0.25 M solution of 88a in 1,4-cyclohexadiene showed significant retardation of the isomerization process. A 9:1 E/Z mixture of products resulted after a 2 h irradiation with fluorescent light. This ratio differs considerably from the 2:1 E/Z mixture obtained when photolysis was performed in the absence of 1,4-cyclohexadiene. When similar 114 experiments were performed for 88b and 88c the isomerization process was also retarded, but to a lesser extent to that observed for 88a. When the crossover experiment for the mixture 88d-di and 88d-<i5 was performed in neat 1,4-cyclohexadiene, there was no evidence of any crossover products as determined by * H NMR spectroscopy and mass spectrometry. These results provide evidence for the involvement of free radicals in the photochemical isomerization of 88a-d. Further to the proposal of free radicals as intermediates in the photochemical isomerization process, was the presence of small amounts (<5%) of Ph2Se2 detected by lH NMR spectroscopy after irradiation of 88a-d. The ability of Ph2Se2 to form PhSe' free radicals by cleavage of the selenium-selenium bond under the photochemical conditions necessary for isomerization was therefore investigated. In this regard, a 1:1 mixture of Ph2Se2 (mle 314) and Ph2Se2-dio (mle 324) was irradiated with fluorescent light for 2 h and analyzed by mass spectrometry for the presence of Ph2Se2-^5 (mle 319). A control experiment was also performed to exclude the possibility of formation of the crossover product Ph2Se2-<i5, in the mass spectrometer during analysis. In the latter experiment a 1:1 mixture of Ph2Se2 and Ph2Se2-dio was analyzed by mass spectrometry immediately after mixing. Comparison of the results obtained from these experiments showed significant differences in the molecular ion fragmentation patterns of the control versus the crossover reaction (Figure 39, next page). It is proposed that these differences are due to the presence of Ph2Se2-d5 (m/e 319), thus indicating the formation of PhSe' radicals during photolysis . When a 1:1 mixture of Ph2Se2-dio and 88b was irradiated with fluorescent light for 2 h, mass spectrometry indicated the presence of significant amounts of 88b-^5 (mle 245) and Ph2Se2-^5 (Figure 40, p 116). This result provides evidence for the exchange of PhSe' radicals produced from the cleavage of Ph2Se2-^io with the PhSe group of 88b. A similar control experiment to that described above was performed to ensure that formation of the crossover products 88b-ds and Ph2Se2-^5 did not occur to any great extent in the mass spectrometer (Figure 40). When these experiments were repeated for a mixture of Ph2Se2-dio 115 314 Ph 2 Se 2 + P h 2 S e 2 - d 1 0 CONTROL EXPERIMENT 324 3 2 0 319 P h 2 S e 2 + Ph2Se2-<*io to) CROSSOVER EXPERIMENT 3 2 0 Figure 39. Molecular ion fragmentation patterns for the control and crossover experiments for the mixture of Ph2Se2 and Ph2Se2-^ io-116 2 4 0 SePh + P h 2 S e 2 - d 1 0 CONTROL EXPERIMENT OMe 88b 2 4 0 2 4 0 SePh + Ph 2Se 2-dj( to) CROSSOVER EXPERIMENT OMe 88b 2 4 0 Figure 40. Molecular ion fragmentation patterns for the control and crossover experiments for the mixture of 88b and Ph2Se2-dio-117 and 88a, similar results were obtained, namely, the formation of large amounts of 88a-a"5 and Ph2Se2-d5. Although the reactions with Ph2Se2-a"io provide further evidence for the involvement of free radicals in the isomerization process, they also present an added complexity. As Ph2Se2 is seen by lH NMR spectroscopy in small amounts by the photolysis of 88a-d, there exists the possibility that it may play some part in the mechanism leading to diene isomerization. This postulate is not unreasonable since catalytic amounts of diphenyl disulfide have been employed in the cis to trans isomerization of poly butadiene.91 To determine if this photochemical isomerization process is a general reaction for molecules having the PhSe group attached to unsaturated organic fragments, it was decided to investigate the photochemical stability of a vinylselenide. The E isomer of 109 was synthesized by the hydrozirconation of isopropylacetylene to give 110, followed by reaction with /V-PSP to generate the desired product (equation 47). Photolysis of a deuteriobenzene ZrCp 2 Cl SePh < Cp 2ZrCl(H) I N-PSP : - ^ - ^ (47) 1 X dark -20°C 110 109 solution of 109 under identical conditions to those used for 88a-d, produced no isomerization as determined by *H NMR spectroscopy. However, after 24 h irradiation with fluorescent light a 92:8 E/Z mixture of geometric isomers resulted. The UV-vis spectrum of 109 has a A.m ax at 258 nm (e 9500), with only background level absorptions in the visible region. After 19 h of irradiation with U V light an 86:14 E/Z mixture was obtained. Following irradiation of 109 with U V light (330-380 nm), the presence of small amounts of Ph2Se2 was detected by * H N M R spectroscopy. As Ph2Se2 has been shown to produce PhSe' radicals on irradiation with fluorescent light, a solution of 109 was photolyzed in the presence of a catalytic amount of Ph2Se2- After 24 h irradiation with fluorescent light, this 118 mixture produced an 87:13 ratio of E/Z geometric isomers, similar to that obtained by U V irradiation. If, as proposed, the isomerization of 88a involves the free radical PhSe', then photolysis of a mixture of 88a and 109 should result in isomerization of the latter species. Thus, a mixture of 88a (70 mol %) and 109 was irradiated with fluorescent light for 24 h. As expected, this resulted in isomerization of 88a to a 2:1 mixture of E/Z isomers. In turn, the vinylselenide had isomerized to give an 86:14 E/Z mixture; the same ratio observed by both U V irradiation, and fluorescent light irradiation in the presence of Ph2Se2- In conclusion, the photochemical isomerization of 109 occurs under a variety of conditions, with the extent of isomerization being enhanced by the presence of Ph2Se2 and 88a. The effect of the PhSe' radical on the photochemical isomerization of a stereochemically stable 1,3-diene was then investigated. Irradiation of the phosphorus-substituted 1,3-diene 79b for up to 48 h with fluorescent light showed no signs of PPh 2 OMe 79b isomerization by * H NMR spectroscopy. However, after only 1.5 h irradiation of this diene with fluorescent light in the presence of a catalytic amount of Ph2Se2, isomerization was observed to yield a 69:17 mixture of E,E/E,Z isomers with the remainder being an unidentified isomer. When the experiment was repeated using 88a (70 mol %) instead of Ph2Se2, no isomerization of 79b occurred until 88a began to isomerize, implying that the presence of 79b was somehow inhibiting the isomerization of 88a. After 18 h of irradiation with fluorescent light 88a began to isomerize, resulting in the concomitant isomerization of 79b. After a total of 65 h irradiation a 64:16 mixture of E,E/E,Z isomers resulted, the remainder being composed of a mixture of unidentified stereoisomers. The presence of any Ph2Se2 119 could not be determined due to the complexity of the lH NMR spectrum. Once again, Ph2Se2 and 88a have induced photochemical isomerization of an molecule which in the absence of these selenium-containing compound is photochemically stable. The following mechanism is proposed for the photochemical isomerization of the dienes 88a-d (Figure 41). This mechanism embodies the main experimental results, SePh SePh PhSe* 111 SePh SePh (- PhSe") bond rotation SePh SePh 112 bond rotation SePh (- PhSe) SePh SePh 3 Figure 41. Proposed mechanism for the photochemical isomerization of 88a-d. 120 indicating an intermolecular process which involves the PhSe' radical operating in a series of addition-elimination reactions resulting in the observed isomerization. Thus, the propagation step is proposed to involve addition of the PhSe" radical to the diene resulting in the formation of the ally lie radical 111. Isomerization of the "upper" double bond can then occur, by elimination of the PhSe' radical. The isomerization about the "lower" double bond could occur by a similar process (pathway a). Alternatively, bond rotation of 112, followed by loss of PhSe' radical to generate 113 would also result in the observed isomerization (pathway b). 4.3 Photochemical Isomerization of l-(Pheny!thio)-l,3-dienes To explore the generality of the photochemical isomerization reaction described above for the selenium-substituted dienes 88a-d, the closely related sulfur-functionalized dienes 89a-d were synthesized (equation 35). The UV-vis spectra of these dienes were very similar (35) 55a-d 89a-d a R 1 = R 2 = R 3 = H b R 1 = R 2 = H , R 3 = OMe c R 1 = R 3 = H , R 2 = OMe d R 1 R 3 = _ ( C H 2 ) 4 - , R 2 = H I I 121 to 88a-d, with the replacement of the PhS group with the PhSe group resulting in a bathochromic shift of the "kma*. by approximately 10 nm. Irradiation of 89a with fluorescent light for 5 h resulted in isomerization to afford a 2:1 E/Z mixture of geometric isomers. This result is in direct analogy to the previously reported data for the photolysis of 88a. Similar photochemical reactions of 89b and 89c resulted in isomerization to give identical mixtures of all four possible stereoisomers. The ratio of the isomers was determined from the lH NMR spectra of several different experiments, and was found to vary only slightly to give a 39(±2) :13(±1) :35(±2)13(±1) mixture of Z,E/Z,Z/E,E/E,Z geometric isomers. In a fashion similar to that described previously for 88b, the vinyl resonances of these isomers were identified. The lH N M R spectrum and the expanded region from 5-7 ppm indicating the relevant assignments for the stereoisomeric mixture of 89b are shown in Figures 42 and 43 (pp 122 and 123). Irradiation of a solution of 89d for up to 24 h with fluorescent light gave no isomerization. This apparent absence of isomerization for 89d was assumed to result from an equilibrium mixture of geometric isomers which greatly favored the E isomer, as shown previously for 88d. In all cases, small quantities of diphenyl disulfide were observed in the * H N M R spectra of the photolyzed dienes 89a-d. Although detailed experiments were not performed to probe the mechanism of the isomerization of 89a-d, it is assumed that they isomerize by a similar process to that outlined above for 88a-d. SPh SPh PPm 7 6 5 4 Figure 42. 400 MHz ! H NMR spectrum of the four stereoisomers of 89b in CDCI3. Hi HR SPh 1 H A ^ H A 1 [^^SPh OMe OMe EJE SPh H B ^ V - J ^ H H C ^ Y H D A OMe ZJE E,Z four stereoisomers of 89b H C ^ y SPh OMe HR Z,Z HDofZ£ H„ofE,Z HDofE,E HBofZZ 1/ H„ofE,E H A of E,E HcofEZ P P m 6 7 5 «-50 ^ 2 5 IFo ZlS S lo" Figure 43. 400 MHz lH NMR spectrum of the expanded region from 5-7 ppm for the stereoisomers of 89b in CDCI3. 124 4.4 Thermal Isomerization. Under thermal conditions, the dienes 88a-c were observed to isomerize to ratios of stereoisomers identical to those already outlined for the photochemical process. However, in contrast to the photochemical reaction, the thermal isomerization was rather sluggish and less reproducible. Initial experiments involved thermolysis of the dienes 88a-d in capped NMR tubes at 80oC in the dark for 24-48 h. Using these conditions, 88a gave a 2:1 mixture of E/Z geometric isomers, while both dienes 88b and 88c gave the previously observed mixtures of all four possible stereoisomers. The presence of trace amounts of Ph2Se2 was again observed by * H NMR spectroscopy. As with the photochemical reaction, thermolysis of 88d under the conditions described above did not result in any detectable isomerization. As proposed previously for the photochemical reaction, the apparent lack of isomerization for 88d by thermolysis, is due to the relative stability of the Z isomer under these equilibrating conditions. Crossover experiments, identical to those described previously for the photochemical isomerization of 88a-d, were performed for the thermal isomerization reactions. The results of these experiments indicated that once again a predominantly intermolecular process was operable. Isomerization rate inhibition experiments, using B H T and 1,4-cyclohexadiene, provided evidence for the presence of free radicals during the thermally-induced isomerizations of 88a-d. When solutions of 88a-c were heated at 80°C in the dark for up to 48 h in NMR tubes sealed under pre-purified nitrogen, no isomerization was observed for 88a, and isomerizations of 88b-c were strongly inhibited. When the crossover experiments were performed under identical conditions, the degree of crossover correlated well with the changes in the isomerization in that the presence of crossover products was greatly reduced. From these results it appears that the thermal isomerization of 88a-d may be initiated by some contaminant which can permeate the capped NMR tubes but not the sealed tubes. Various experiments were performed to determine the source of this contamination. 125 Thermolysis of 88a was performed in a sealed NMR tube under an atmosphere of pre-dried air to determine the effect of oxygen on the isomerization reaction. After 48 h at 80° C in the dark, no isomerization was observed by * H NMR spectroscopy. The same observation was made when 88a was thermolyzed in an HC1-washed NMR tube sealed under pre-purified nitrogen. Thus, it does not appear that the thermal isomerization of 88a-d is promoted by oxygen or by traces of mineral acids. However, when the thermolysis of 88a was carried out in a sealed NMR tube under nitrogen, containing a catalytic amount of the free-radical initiator AIBN, isomerization of 88a to a 2:1 E/Z mixture of geometric isomers was observed after only 3 h at 80°C in the dark. This provides strong evidence for the involvement of free radicals in the thermal isomerization process. In general, it is believed that the mechanism involved in the thermal process is similar to that described for the photochemical isomerization reaction. Thus, although 88a-d are photochemically labile, they exhibit stereochemical rigidity under thermolysis in sealed reactors at 80°C in the dark for several hours. We hoped to take advantage of this selective thermal stability to investigated the Diels-Alder reactivity of dienes 88a-d. The reactivity of the latter compounds with maleic anhydride is discussed in the following section. 126 4.5 Diels -Alder Reaction of l-(Phenylseleno)-l ,3-dienes with Maleic Anhydride. The reactivity of the selenium-substituted 1,3-dienes 88a-d with maleic anhydride in the Diels-Alder reaction was investigated. As functionalities such as methyl ether functionalities are known to activate 1,3-dienes towards reaction with electron-deficient dienophiles, it was thought that 88b would be the most reactive member of this series of dienes. In addition, the E,E stereochemistry should enable 88b to more easily adopt the necessary s-cis conformation, required for the Diels-Alder reaction, than 88c which has the E,Z geometry. Interestingly, the reaction of an equilibrium mixture of all four geometric isomers of 88a with maleic anhydride in the dark at 80°C, resulted in the formation of a single stereoisomeric product in 78% isolated yield (equation 48). 7 4 The stereochemistry of this 88b 114 isomeric mixture Diels-Alder cycloadduct (114) was confirmed by * H N M R decoupling and NOEDIFF experiments. Proton He was identified both from its chemical shift, 5 6* and from an NOEDIFF experiment in which irradiation of the methyl protons of the OMe group gave strong enhancement of this proton. In turn, irradiation of He gave enhancement of H A and H E , which permitted differentiation between the two vinyl and the two ring-junction resonances (Figure 44). Also, irradiation of proton H B resulted in enhancements of H A and HD - These latter results provide evidence for the cis stereochemistry for the ring junction of the 6/5-bicyclic system and confirm that 114 is the endo-cycloadduct, resulting from 127 OMe 1 JUL H F JL H E J L He H r H t H> JliLJL. Normal Spectrum J l NOEDIFF Spectrum Irradiated here PhSe Hr , . / H B . 0 1 OMe MeO 114 A JLjl UIL_JL_ Normal Spectrum NOEDIFF Spectrum Irradiated here p p m ' O 3 4 Figure 44. 400 M H z ] H NMR and NOEDIFF spectra for 114 in C6D 6 . exclusive reaction of the E,E isomer of 88b with maleic anhydride. As the isolated yield of 114 is far in excess of the amount of E,E isomer (of 88b) present in the equilibrium mixture, it appears that the latter compound has been kinetically depleted from the equilibrium mixture of stereoisomers. Not surprisingly, this cycloadduct was also prepared in good yield by reaction of an isomerically pure sample of 88b at 80°C in the dark with maleic anhydride. As the presence 128 of all four geometric isomers of 88b had not affected the ultimate formation of 114, it was decided to attempt the reaction of isomerically pure 88b with maleic anhydride at 80° C while exposing the reaction to room light. Workup of the crude yellow oil obtained from this reaction, afforded a 70% yield of what appeared to be a stereoisomer of 114, along with a 10% yield of cycloadduct 114; the remaining material was identified as Ph2Se2- The ! H NMR spectra of 114 and its stereoisomer 115 are shown in Figure 45 (next page). Comparison of these two spectra shows that the resonances of the latter cycloadduct are more strongly coupled than the former, suggesting that some change in geometry of the 6/5-bicyclic system has taken place. Based on a series of lH NMR decoupling and NOEDIFF experiments similar to those outlined above for 114, the structure of the cycloadduct has been tentatively assigned as 115 (equation 49). Although, it was clear that the PhSe group MeO MeO 88b H 5 had undergone an apparent [l,3]-shift, the relative stereochemistry of the latter group with respect to the methoxy group was uncertain. It was expected that there would be a significant energy difference between the cycloadduct 115 and its epimer 115', where the PhSe and OMe groups are oriented cis to one another (Figure 46, p 130). Based on this assumption, molecular mechanics calculations were performed for the two epimers to determine which one possessed the lower energy. For these calculations the parameters of the 1985 MM2 force field were used92, with the exception of the bond lengths CSp3-Se and C s p ^ e and the bond angle Csp3-Se-Csp2, which were obtained from another literature source.93 The results of such calculations for the epimers 115' and 115 indicated that the latter compound was 129 PPm 7 6 5 4 3 Figure 45. 400 MHz lH NMR spectra of 114 and 115 in CDCI3 and C6D6. respectively. 130 OMe O OMe O PhSe H O O H PhSe O O H H 3.6 kcal/mol Okcal/mol 115 115 Figure 46. Proposed structures for the epimers of 115. approximately 3.6 kcal/mol more stable than the former. This difference in energy corresponds to an equilibrium mixture of >99:1 in favor of 115 over 115' at 80°C. Therefore, based on the results of these calculations and on the assignments made for a previously investigated system94 (vide infra), cycloadduct 115 was assigned the structure in which the OMe and PhSe groups are trans to one another. Allylselenides have been previously observed to undergo [l,3]-shifts induced by mild thermolysis.9 5 However, in our case it is obvious that the rearrangement is promoted by light. Thermolysis of 114 at 80°C in the dark for up to 24 h showed no signs of the apparent [l,3]-shifted compound 115, by * H N M R spectroscopy. However, irradiation of a deuteriochloroform solution of 114 with fluorescent light for 18 h resulted in an 80% conversion to 115. Further irradiation of this mixture gave an almost quantitative yield of Ph2Se2 along with other unidentified organic materials. The formation of the Ph2Se2 again suggested the possible involvement of free radicals in the rearrangement process. To determine if the apparent [1,3]-shift was proceeding by an intra- or intermolecular process, a crossover experiment was performed. This experiment required the synthesis of the cycloadduct 114-de, which was readily prepared by reaction of maleic anhydride with 88b-<i6 (equation 50). The latter compound was prepared by a transfer reaction of the complex 55b-rfi with N-FSP-ds. The * H NMR spectrum of 114-^6 is shown in Figure 47 (p 132). 131 8 8 b d 6 114-4, To facilitate the assignment of crossover products by mass spectrometry, a control experiment was designed in which 114 and 114-a*6 were independently irradiated with fluorescent light and then mixed prior to analysis. The crossover experiment involved the photolysis of a 1:1 mixture of 114 (m/e 338) and 114-06 ( m / « 344) for 15 h and subsequent analysis by mass spectrometry. The molecular ion fragmentation patterns for the control and crossover experiments are shown in Figure 48 (p 133). There is a clear difference in the pattern shown for the control as compared to the crossover experiment, thus strongly suggesting that crossover has taken place. This result indicates that a significant intermolecular process is involved in the apparent [l,3]-allylic rearrangement. Other workers have observed a similar apparent [l,3]-shift of an allylsulfide for the cycloadduct 116.9 4 These workers reported that exposure of a deuteriochloroform solution of 116 to room light for 1.5-2 days resulted in quantitative rearrangement to the isomer 117 (equation 51). The X-ray crystal structure analysis of 117 showed that the phenylthio group was attached to the opposite face of the cycloadduct, indicating that it had 132 133 PhSe H . O MeO 114 3 3 8 I T 3 4 0 CONTROL EXPERIMENT 3 3 8 T T ft 3 4 0 + h\) </5-PhSe MeO U4-d6 3 4 4 T T T T T T 3 4 0 CROSSOVER j EXPERIMENT 3 4 4 TV T T 3 4 0 Figure 48. Molecular ion fragmentation patterns for the control and photochemical crossover experiments using mixtures of 114 and 114-^ 6. 134 moved from one face of the six-membered ring to the other during the rearrangement process. They concluded that this observation was consistent with a free radical chain mechanism, whereby the incoming phenylthio radical approaches opposite to the bulky resident phenylthio group (Figure 49.). A similar argument can be used to account for the stereochemistry observed for the apparent [l,3]-shifted cycloadduct 115. Figure 49. Proposed rationale for the formation of 116 and 114. To understand why the rearrangement of 114 to 115 should be such a facile process, it is necessary to consider the angle strain inherent in a cis-fused 6/5-bicyclic system. To account for the formation of a single product (119) in the thermodynamic deprotonation and subsequent silylation of 118, earlier workers proposed that the presence of a double bond opposite to the ring junction of a cis-fused 6/5-bicyclic system (compound 120) enhanced the angle strain at that junction (equation 51).96 This strain can be relieved somewhat by removal 135 of the double bond or by changing its position in the structure. These workers performed force field calculations which showed an energy difference of 1.9 kcal/mol at 25 ° C between compounds 119 and 120, the former compound possessing the lower energy. It is therefore proposed that the apparent [1,3]-rearrangement from 114 to 115 is promoted by the relief of angle strain inherent in having a double bond opposite the ring junction of a cis-fused 6/5-bicyclic system. To gain further evidence for this proposal, attempts were made to prepare the Diels-Alder cycloadducts of 88b with either dimethyl fumarate or dimethyl maleate. As these cycloadducts would no longer possess the bicyclic structure of 114, their photochemical stability would lend credence to the proposed argument for the driving force inherent in the rearrangement process. Unfortunately, attempts to prepare these cycloadducts were unsuccessful. Reaction of 88b with either dimethyl fumarate or dimethyl maleate at temperatures up to 140°C failed to yield anything more than trace amounts of the desired cycloadducts, suggesting that these dienophile are insufficiently reactive to undergo Diels-Alder reaction with 88b. The reaction of 88a with maleic anhydride proceeded smoothly at 110°C in the dark to give the desired cycloadduct 121 after 22 h (equation 53). One product was formed which 88a 121 was identified as the endo-adduct by * H NOEDIFF spectroscopy, since irradiation of H B resulted in enhancement of protons H A and H D (Figure 50, next page). The proton assignments for this cycloadduct resulted from experiments similar to those described previously for 114. Attempts to induce a similar rearrangement of the PhSe group of 121 by 136 PhSe - i 1 1 1 —— » r 7 6 5 4 3 2 Figure 50. 400 MHz lU NMR and NOEDIFF spectra for 121 in C7D8. repeating the reaction in the presence of room light or by photolysis of the preformed cycloadduct, resulted in decomposition to Ph2Se2 and other unidentified organic products. However, when the Diels-Alder reaction was performed at 140°C in the dark, a 1:1 mixture of stereoisomeric products 122 and 123 was formed after 24 h. The formation of this mixture was accompanied by some decomposition to Ph2Se2 (-5%) and other unidentified materials. After further thermolysis up to 63 h, a 2:1 mixture of stereoisomers was present by *H NMR spectroscopy. Continued thermolysis resulted in significant decomposition to Ph2Se2. A similar mixture was obtained by thermolysis, in the dark, of the preformed cycloadduct 121 at 140°C for 48 h. Analysis of the complex * H NMR spectrum of this mixture indicated that both products had arisen from an apparent [l,3]-allylic rearrangement of the PhSe group. Through a series of * H N M R decoupling and NOEDIFF experiments, it was possible to 137 assign the protons for each isomer. The two stereoisomers were tentatively assigned the structures shown in equation 54. Unfortunately, it was not possible to clearly determine by 123 * H N M R spectroscopy which was the major isomer . However, by use of the molecular mechanics program (MM2) it was possible to determine that cycloadduct 122 possessed the lower energy structure. For cycloadduct 123 two possible conformations were calculated, both of which were of higher energy than 122 (Figure 51, next page). Using this calculated energy difference an equilibrium ratio of 2:1 at 140°C was determined for 122:123. This ratio is in excellent agreement with the ratio of stereoisomers determined by * H N M R spectroscopy. Also, the assignment of 122 as the major isomer is consistent with the argument that the apparent [l,3]-shift occurs by attack of the PhSe' radical on the face of the six-membered ring opposite to the bulky resident PhSe group. Presumably, the minor isomer is formed as a result of free radical epimerization at the carbon bearing the PhSe group. 138 PhSe H H 1.2kcal/mol O O o PhSe 0 kcal/mol 122 Figure 51. Possible structures for the apparent [l,3]-shift cycloadducts 122 and 123. The reaction of 88d with maleic anhydride occurred at 60°C in the dark to yield the expected cycloadduct 124 (Scheme 31). At higher temperatures this reaction led to the PhSe 88d 60'C dark toluene 110'C dark toluene PhSe Scheme 31 formation of significant amounts of the apparent [l,3]-shifted cycloadduct 125. The l¥L N M R spectrum of 124 is shown in Figure 52. The structural assignment of this 139 140 cycloadduct resulted from *H NMR decoupling and NOEDIFF experiments. The proposed stereochemistry was arrived at from the latter experiments which showed enhancement of the protons H A and H D by irradiation of H B , and enhancement of protons H A from irradiation of He (Figure 53, next page). Attempts to prepare 125 directly via the reaction at 60°C in room light or by photolysis of preformed 124, resulted in decomposition to Ph2Se2 and other unidentified products. However, reaction of 88d with maleic anhydride at 110°C for 18 h in the dark, gave the cycloadduct 125 in 78% yield. That this product resulted from an apparent [1,3]-rearrangement of the PhSe group was immediately apparent from the presence of two vinyl resonances in the * H NMR spectrum. The NMR spectrum of the cycloadduct 125 is shown in Figure 54 (p 142). Although many of the protons were readily assigned by * H NMR decoupling and NOEDIFF experiments, it was not possible to determine the relative stereochemistry of the PhSe group. The molecular mechanics program MM2 was used once more to determine which of the two epimers 126 or 127 represented the lower energy conformation (Figure 55). Calculations indicated that there was an approximate 4 kcal/mol 4.0 kcal/mol 0 kcal/mol Figure 55. Proposed structures for the epimers 126 and 127. energy difference between the lowest energy conformations of these two epimers, with the cycloadduct 127 possessing the lower energy. This implies that in an equilibrium mixture of these two epimers at 80°C, 127 would compose >99% of the mixture. The stereochemistry of this compound is in contrast to the other apparent [l,3]-shifted products described here, in 141 PhSe Normal Spectrum NOEDIFF Spectrum Irradiated here mJ[ 8 7 6 5 4 3 2 PP™ Figure 53. 400 MHz * H and NOEDIFF spectra of 124 in C6D6-142 143 that it could not have been formed direcdy by attack of the PhSe' radical on the face opposite the resident PhSe group. It may have formed indirectly by this latter mechanism, followed by free radical epimerization to the more stable stereoisomer. The Diels-Alder reactivity of the dienes 88a-b and 88d with maleic anhydride has presented some interesting results. By varying the reaction conditions, the preparation of two distinct sets of compounds can be achieved using the same starting materials. 144 C H A P T E R 5 Preparation and Diels-Alder Reactivity of 2-(TrialkylstannyI)-l,3-butadienes and 2-(Phenylseleno)-l,3-butadiene. 5.1 Synthesis and Cycloaddition Reactions of 2-(Phenylseleno)-l,3-butadiene and 2-(Trialkylstannyl)-l,3-butadienes. Further to the major theme of this thesis, the preparation and Diels-Alder reactivity of type B 1,3-dienes (MLn = metalloid or transition metal complex) were examined. A rational approach to the syntheses of these compounds was to use the readily available, inexpensive, starting material chloroprene 31, and examine its conversion to type B 1,3-dienes via the Grignard reagent 24. It had been reported that attempts to prepare 24 from chloroprene gave polymers; however, the preparation of this Grignard reagent was achieved from the less accessible 4-chloro-l ^ -butadiene.39 More recently, a modification was published that allowed 24 to be prepared directly from 31 by first activating the magnesium with zinc chloride and 1,2-dibromoethane.40 As noted previously, Grignard reagent 24 has been shown to be a X M - C 1 ^ - J + M g C l 2 (15) L f c M ^ ^ . 2 4 M = Bu 3Sn, Ph2P, ClHg TypeB useful starting material for the syntheses of other 2-substituted-l,3-butadienes, via a transfer reaction from magnesium (equation 15).39 It was decided to use this procedure to prepare 145 a R = Bu b R = Me 2-trialkylstannyl-l,3-butadienes 128 and 2-phenylseleno-1,3-butadiene 129. Previous workers have reported on alternative syntheses and Diels-Alder reactivity of 128a-b; a "tin-cupration" of 2-butyne-l,4-diol followed by "silyl-cupration" generated 128a in reasonable yield, 9 7 while an equally elaborate Wurtz-type coupling yielded 128b.9 8 No report on the preparation of 129 was found, although the synthesis of the SC«2-masked derivative 130 has been recently described along with a study of its Diels-Alder reactivity.99 5.1.1 Diene Synthesis and Diels-Alder Reactivity. Chloroprene 31 was readily converted into the corresponding Grignard reagent 24 by activating the magnesium with 1-3 mol % anhydrous ZnCl2 and small amounts of 1,2-dibromoethane. In this fashion, 0.25-0.60 M solutions of 24 in T H F were prepared. Subsequent reaction with tributyltin chloride, trimethyltin chloride and phenylselenenyl chloride allowed for the convenient, one-pot preparation of the dienes 128a-b and 129 on a multi-gram scale (Scheme 32, next page). Diene 129, previously uncharacterized due to its ready polymerization, 1 0 5 was isolated and found to be stable for months at -20°C under nitrogen in the dark. The lH N M R spectrum of this compound is shown in Figure 56 (p 147). 146 129 Scheme 32 The 2-tributylstannyl- 1,3-butadiene 128a underwent facile reaction with electron-deficient dienophiles, as is evidenced by the reactions summarized in Table IX (p 148). The corresponding reaction of 128a with the electron-rich dienophile diphenylacetylene failed to yield any cycloaddition product, even after extended periods (several days) at reflux in toluene. In general, the reactions with electron-deficient dienophiles proceeded smoothly at elevated temperatures to give good yields of the Diels-Alder cycloadducts (131-135). However, reaction of 128a with maleic anhydride for extended periods of time at room temperature gave the best yields of cycloadduct 131. In the workup of 133, by column chromatography on silica, enolization took place producing small quantities of the corresponding hydroquinone 136. The * H NMR spectra of 133 and 136 are shown in OH OH 136 147 C 6D 5H H D PhSe H A 129 H , He Hp 1 H , § denotes 7 7 Se satellites V H, D u ppm 7 Figure 56. 400 MHz J H NMR spectrum of 129 in C 6D 6. Figure 57 (p 149). Hydroquinone production was also observed when reaction times in excess of 12 h were used. Similar results were noted in the preparation and workup of 139 (see Table X, p 150), albeit to a lesser extent. The results of the cycloaddition reactions of the phenylseleno diene 129 with a variety of activated dienophiles is outlined in Table X. The reaction of 129 at room temperature with maleic anhydride and at elevated temperature with less activated dienophiles yielded cycloadducts 137-141. Thermolysis of 129 with diphenylacetylene for several days at reflux in toluene resulted in the quantitative recovery of starting materials, suggesting that as with the 148 Table IX. Reaction of 2-(Trialkylstannyl)-l,3-butadienes 128a-b. Entry Dienophile Conditions Products Yields 135a 135b * No reaction with diphenylacetylene 150 Table X. Reaction of 2-(Phenylseleno)-1,3-butadiene 129. Entry Dienophile Conditions Products Yields 141a 141b * No reaction with diphenylacetylene 151 stannyl functionality the selenenyl moiety does not activate the 1,3-diene towards reaction with electron-rich dienophiles. The structural assignments for these cycloadducts followed from analysis of their * H NMR and IR spectra. The * H N M R spectrum of 137 is shown in Figure 58 (next page). In an attempt to determine the directing effect of the stannyl moiety, the reaction of 128b with methyl acrylate at reflux in toluene was examined. In analogy to results previously observed in cycloaddition reactions of silylbutadienes,100 the stannyl moiety was found to exhibit only a weak directing effect, resulting in a 2:1 mixture of paraimeta regioisomers 135a/135b, as determined by G L C and * H NMR spectroscopy. Other workers have shown that use of 15 mol % Et2AlCl in die reaction of 128a with ethyl acrylate gave a 10:1 ratio of paraimeta regioisomers.973 This latter observation suggests that the poor regioselectivity seen in the uncatalyzed reaction of 128b with methyl acrylate should be significantly improved by the use of a Lewis acid catalyst The assignment of 135a as the major regioisomer was based on literature precedent 1 0 5 ' 1 0 8 Attempts to separate mixtures of 135a/135b using column chromatography proved difficult; however, an enriched 7:1 (135a/135b) mixture was obtained. It was hoped that by use of lH NOEDIFF spectroscopy on this enriched mixture, more physical evidence for the assignment of the major regioisomer could be achieved. Unfortunately, the results of such experiments at 400 MHz were equivocal. Regiochemical investigation of the Diels-Alder reactivity of 129 involved reaction with methyl acrylate at reflux in toluene. An excellent yield of 141a/141b (90%) was obtained; the ratio of regioisomers being 4:1 (paraimeta) as determined by G L C and lH NMR spectroscopy. This result was in agreement with published data on the products obtained by reaction of 129 with ethyl acrylate.99 The results of this study show that, in reaction with methyl acrylate, the selenenyl moiety has a greater directing effect than the stannyl substituent. 152 153 5.1.2 Transmetalation from T i n to Selenium. Addition of PhSeCl to a solution of the 1,3-dienylzirconium complexes 55a-d resulted in smooth transfer of the dienyl unit from zirconium to selenium with immediate discharge of the deep red color of PhSeCl. In an attempt to gain further comparative information on the reaction of dienylstannane 128b and dienylselenide 129 with methyl acrylate, a solution of PhSeCl was added to a 2:1 mixture of 135a/135b. Stirring the mixture overnight at room temperature caused discharge of the deep red color of the PhSeCl, which on workup yielded a 2:1 (para'jneta) mixture of 141a/141b as deterniined by * H NMR spectroscopy (equation 55). Me 3Sn - i - C 0 2 M e + PhSeCl 135a/135b 2:1 para:meta R.T. toluene (- Me^nCl) PhSe - T - C O , M e (55) 141a/141b 2:1 paraimeta This result indicates that the major regioisomer formed in the reaction of 128b with methyl acrylate has the same regiochemistry (i.e., the para isomer) as that observed from the corresponding reaction of 129 with methyl acrylate. The reaction appears to be quite general for vinylstannanes as evidenced in the reaction of 128b with PhSeCl to give 129 (equation 56). The latter reaction is also highly chemoselective as no products of the addition of PhSeCl to the isolated double bond are observed. Me 3Sn R T . PhSeCl toluene (- MegSnCl) PhSe (56) 128b 129 154 Transmetalation of tin in vinylstannanes has precedent in reactions at low temperature with alkyllithium reagents,27 and in coupling reactions catalyzed by palladium(O) complexes.31 Stereoselective transmetalation from mercury to selenium by reaction of vinyl mercuric compounds with PhSeCl has also been observed.1 0 2 However, the above observations are, to the best of our knowledge, the first reported examples of transmetalation from tin to selenium. The reaction of vinylstannanes with PhSeCl may be analogous to a previously reported reaction in which iodine is used to cleave the tin-carbon bond producing a vinyl iodide. 1 0 3 Much work has already been done on the mechanism of areneselenenyl chloride addition to alkenes. Schmid and Garratt1 0 4 proposed three possible mechanisms, which differ only in the relative amount of carbon-selenium bond making and selenium-chlorine bond breaking leading up to the formation of a seleniranium ion. For the system described here, collapse of the analogous seleniranium ion 142 to give 129 could proceed via attack of the chloride at the least-substituted carbon or at the tin, followed by loss of MesSnCl. 142 155 5.2 Attempted Syntheses of Type B 1,3-Dienes where M L n is Cp2ZrCI . The Grignard reagent 24 has proved to be a useful starting material for the syntheses of type B 1,3-dienes. However, the method appears to lack the generality of the transfer reaction of organic fragments from zirconium (equation 36), as regards the ease with which other 55a-d Type A M = Sn, P, B, Se, S functionalities can be introduced. To address this deficiency, preliminary investigations into the syntheses of type B 1,3-dienes, having the Cp2ZrCl fragment at the 2-position, were performed. R " Type B The initial plan centered around the fact that in the hydrozirconation reaction of disubstituted acetylenes, the Cp2ZrCl fragment always occupied the least sterically crowded position.1 3 With this in rnind, the trimethylstannyl-substituted l-ene-3-yne 143 was prepared by reaction of the lithium salt of 51d with trimethyltin chloride. The presence of the trialkylstannyl group was also attractive as it introduced another functionality which could prove useful for further synthetic elaboration. Subsequent reaction of 143 with a slight excess 156 of Cp2ZrCl(H) 1, resulted in a 95:5 mixture of stereoisomers in which compound 144 was identified (by * H NOEDIFF experiments) as the major isomer (Scheme 33). The 51d 143 144 Scheme 33 regiochemical outcome of this reaction was initially somewhat surprising, as it had been anticipated that the Me3Sn group would prove more sterically demanding than the cyclohexenyl group. However, it is likely that the effective steric bulk of the Me3Sn group is somewhat lessened by the length of the tin-carbon bond (~2.1 A). Another possible route to type B 1,3-dienes involves the preparation of zirconium T|2-alkyne complexes 146, by reaction of 145 with an excess of Me3P (equation 57). 1 0 5 The ZrCp 2Me ^ Me 3 P ^ T " R \ C p 2 Z r r ] (57) i ( - C H 4 ) | ^ PMe 3 145 146 T|2-alkyne functionality of these complexes is very reactive, and undergoes a series of cleavage and insertion reactions.100 Based on these precedents, the preparation of 147 was carried out using the procedure outlined in Scheme 34 (next page). The * H N M R spectrum of 147 is 157 ZrCp 2 Cl MeLi, T H F -78'C ZrCp2Me ( - C H 4 ) PMe 3 C p 2 Z r ^ | PMe 3 A 55d 147 Scheme 34 shown in Figure 59 (next page). The assigned structure is consistent with the results of a * H NOEDIFF experiment in which irradiation of the methyls of the Me3P group gave enhancement of proton H A and the cyclopentadienyl ligands (Figure 60, p 159). In the anticipation that cleavage of the Tj2-alkyne would occur to place the Cp2ZrCl group at the 2 position, leaving the Me3Sn group at the 1-position, 147 was reacted with trimethyltin chloride. This reaction proceeded smoothly at room temperature to give a single crystalline product 148, tentatively assigned the structure shown in equation 58. The * H NMR spectrum of 148 is shown in Figure 61 (p 160). Analysis of the spectrum shows a 43 Hz 1 H 1 1 7 / 1 1 9 S n coupling for proton H A . The magnitude of this coupling strongly suggested that the Me3Sn group and proton H A are geminal.71 The results of * H NOEDIFF experiments confirmed this assignment; however, the determination of the relative stereochemistry of the (58) 147 148 H A J L _ H B Normal spectrum Cp 159 Cp 2Zr: PMe3 H a 161 PMej iu NOEDIFF spectrum Irradiated here I ppm 7 Figure 60. 400 MHz *H NMR and NOEDIFF spectra of 147 in Q ; D 6 . Cp2ZrCl and Me3Sn groups remained uncertain. To remove this ambiguity a single crystal (prepared by Dr. Randy Alex) was subjected to X-ray structure analysis. The solid state structure for 148 is shown in Figure 62 (p 161), along with selected bond lengths and angles. It is clear from this structure determination that the Cp2ZrCl and Me3Sn groups are oriented trans to one another. Utilization of the literature procedure, 1 0 5 followed by cleavage of the rj2-alkyne functionality provides a path to the desired 1,3-dienes of type B, substituted at the 1-position with a Me3Sn group. 1 0 6 The removal of the latter functionality could be achieved by selective "lithiation", followed by an aqueous workup. Also, further work in this area suggests that cleavage of the T|2-alkyne functionality of 147 with gaseous HC1 may provide a direct route to type B 1,3-dienes.107 5 Ppm 4 3" 2 T Figure 61. 400 MHz lH NMR spectrum of 148 in Q D ^ . 161 Selected bond lengths (A) and angles (") for 148 Z r — C I 2.52(2) C(14) —C(15) 1.34(8) Z r — C(15) 2.24(7) C(15) — C(16) 1.48(9) Sn — C(14) 2.14(6) C(16) —C(17) 1.32(9) Cl-Zr-C(15) 115(2) Zr-C(15)-C(16) 140(4) Sn-C(14)-C(15) 128(5) C(15)-C(16)-C(17) 121(7) Zr-C(15)-C(14) 95(5) C(15>-C(16)-C(21) 118(6) C(14)-C(15)-C(16) 125(6) C(17)-C(16)-C(21) 122(6) Figure 62. Molecular structure and selected bond lengths and angles for 148. 162 Conclusion The reaction of the hydride reagent Cp2ZrCl(H) 1 with bifunctional molecules such as l-ene-3-ynes and a,P-unsaturated nitriles has been shown to proceed in a chemoselective manner to provide general synthetic methods for the preparation of 1-substituted 1,3-dienyl-and 1-azadienylzirconium complexes in good to excellent yields. The reactions of l-ene-3-ynes with the deuterium-labelled reagent Cp2ZrCl(D) 2, failed to provide clear evidence as to the nature of the observed chemoselectivity. The 1,3-dienylzirconium reagents underwent a facile reaction with carbon monoxide to generate a series of well-characterized rj2-acyl- 1,3-dienyl complexes. The 1,3-dienylzirconium reagents (55a-d) were successfully employed as general precursors for the preparation of other heterosubstituted 1,3-dienes. In this reaction the 1,3-dienyl fragment was stereoselectively transferred from zirconium to tin, phosphorus, boron, selenium and sulfur. Although this transfer reaction was a clean and efficient procedure for the syntheses of these 1,3-dienes, attempts to transfer of the 1,3-dienyl moiety from zirconium to silicon or to various transition metals (e.g., Ni, Pd and Pt) were unsucessful. An X-ray crystal structure of the 1-azadienylzirconium complex 69, indicated that significant double-bond character was present in the zirconium-nitrogen linkage; suggesting that these complexes were formally 18-electron species and as such were unlikely to undergo transfer reactions. However, for the most part, reaction of these 1-azadienyl complexes with selenium and phosphorus transfer reagents proceeded smoothly to afford in reasonable yields a quite novel series of heterosubstituted 1-azadienes. During investigations into the transfer of the 1,3-dienyl moiety from zirconium to selenium, the formation of isomeric mixtures of products was observed. This could be avoided through careful control of the reaction conditions, namely by performing the reaction at -20°C in the dark. Separate studies indicated that the formation of isomeric mixtures for these compounds could be induced by photolysis with fluorescent light or by thermolysis in the dark 163 at 80°C. Mechanistic studies of this isomerization reaction involved the use of crossover experiments and free radical traps and initiators. These studies indicated that an intermolecular process involving free radicals was likely responsible for the observed isomerization. Similar isomerization of the sulfur-substituted 1,3-dienes was noted after several hours of irradiation with fluorescent light. The Diels-Alder reactivity of the selenium-substituted 1,3-dienes (88a-b, 88c) with maleic anhydride uncovered an interesting photochemically and thermally induced apparent [l,3]-shift of the PhSe group in the pre-formed cycloadducts. The Grignard reagent 2-chloromagnesium-1,3-butadiene (24) proved to be a useful starting material for the prepartion of the corresponding tin- and selenium-substituted 1,3-dienes (128 and 129). These 1,3-dienes reacted efficiently with a variety of electron-deficient dienophiles to afford a series of cyclohexenes containing the vinylstannane or the vinylselenide functionality. Reaction of trimethylstannyl-1,3-butadiene (128b) with PhSeCl yielded exclusively the corresponding selenium-substituted 1,3-diene (129) via a novel transmetalation reaction from tin to selenium. Attempts to provide a more general route to 2-substituted 1,3-dienes involved the preparation of a dimetalated 1,3-diene (148), containing the Cp2ZrCl substituent at the 2-position and the Me3Sn group at the 1-position. It was envisaged that such a molecule would undergo similar transfer reactions of the 1,3-dienyl fragment, as outlined for 55a-d (Chapter 3), to generate the corresponding series of 2-heterosubstituted 1,3-dienes. Opportunities for further research regarding the material presented in this thesis could involve: (i) investigation of the directing influence of the various heterosubstituted 1,3-dienes in cycloaddition reactions with unsymmetrical dienophiles, (ii) use of the 1,3-dienylzirconium complexes in natural product synthesis for the stereocontrolled introduction of a 1,3-dienyl unit, and (iii) further effort directed towards the synthesis of 1,3-dienes substituted at the 2-position by the Cp2ZrCl moiety. 164 C H A P T E R 6 Experimental 6.1 General . A l l manipulations were performed under prepurified nitrogen 1 0 8 in a Vacuum Atmospheres HE-553-2 glovebox equipped with a MO-40-2H purifier, or in standard Schlenk-type glassware under argon (as supplied) or prepurified nitrogen. The term "reactor bomb" refers to a cylindrical, thick-walled Pyrex® vessel (50-75 mL in volume) equipped with a 5 mm Kontes® needle valve and a ground glass joint for attachment to a vacuum line. Larger reactor bombs (250-500 mL in volume) are equipped with 10 mm Kontes® valves. Infrared spectra (IR) were recorded on a Nicolet 5D-X spectrophotometer (internal calibration) as KBr pellets, or on NaCl plates as Nujol mulls or liquid films, or as solutions in dichloromethane (CH2CI2), and are reported in cm - 1 . UV-vis spectra were performed on a Hewlett-Packard 8452A Diode Array spectrophotometer using spectroscopic-grade hexane and a 1 cm quartz cell; Xmax values are reported in nm. Proton nuclear magnetic resonance (lH NMR) spectra were obtained on a Bruker WH-400 spectrometer (at 400 MHz) as solutions in chloroform-di (CDCI3), dichloromethane-d2 (CD2CI2), benzene-rf6 (C^De) o r toluene-ds (C7D8). Signal positions are given on the delta (8) scale in ppm with reference to CHCI3 at 7.25 ppm, CHDC1 2 at 5.32 ppm, C6D5H at 7.15 ppm, or C6D5CHD2 at 2.09 p p m . 5 6 a ^ C p H } N M R measurements were performed at 75.4 MHz on a Varian XL-300 spectrometer, signal positions were measured in 8 relative to CDCI3 at 77.0 p p m . 5 6 a 3 1P{ 1H} N M R spectra were recorded on a Bruker WP-80 (32.4 MHz), Bruker WH-^00 (162.2 MHz) or on a Varian XL-300 (121.5 MHz); signal positions are given on the 8 scale with reference to 165 external rrimethylphosphite at 141 p p m . 5 6 a 7 7Se{ 1H} NMR data were obtained on a Bruker WH-400 (76.3 MHz); signal positions are given relative to an external sample of diphenylselenide (Ph2Se, 60% v/v in CDCI3) at 416 p p m . 1 0 9 Where reported, hydrogen-tin coupling constants (JuSn) are quoted as an average of the 1 1 7 S n and 1 1 9 S n values. Low and high resolution mass spectra were recorded on a Kratos/AEI MS-50 mass spectrometer. For compounds containing the ri5-cyclopentadienyl ligand (Cp), the integral for this resonance was consistently less than the expected value. This phenomenom has be previously observed and is believed to result from a long spin-lattice relaxation time for the Cp ligand. 1 1 0 Gas chromatography-mass spectroscopy (GCMS) analyses were performed using a Varian Vista 6000 (DB1-100% Dimethyl-polysiloxane 5 |im film thickness x 30 m) coupled to a Delsi-Nermag R10-10C mass spectrometer. Gas-liquid chromatography (GLC) was performed on a Hewlett-Packard 5880a gas chromatograph using a 12 m x 0.2 mm column (Carbowax 10M). Column chromatography was carried out using Merck Kieselgel 60 (230-400 mesh A S T M ) . For thin-layer chromatography silica gel 13181 (Eastman chromagram®) sheets were used. Microanalyses were performed by Mr. P. Borda of this department. X-ray crystal structure determination were performed by Dr. R. Chadha at the University of Manitoba. Mr. Tom Keller is acknowledged for the performance of the reported MM2 calculations. For reactions carried out at -20°C, the reagents were cooled to this temperature in a refrigerator contained in the glovebox. Removal of bis(Tj5-cyclopentadienyl)zirconium(TV) dichloride (CP2Z1CI2), produced as a by-product in most of the zirconium transfer reactions, was performed (unless stated otherwise) by filtration through basic alumina, Brockman Activity 1 (80-200 mesh). For reactions carried out in the dark, the appropriate vessel was simply covered with aluminum foil. All photolysis reactions were carried out in capped (or sealed) 5 mm 507PP NMR tubes under prepurified nitrogen (unless stated otherwise) using a Sylvania (GTE) 34 W Cool White fluorescent light The irradiation source emitted white light covering the spectrum of wavelengths from 380 to 800 nm. Samples for photolysis were 166 simply taped to the fluorescent light, the solution being -3-4 cm from the source. Measurements indicated that the temperature of the sample did not exceed 29°C. 6.2 Solvents and Reagents NMR solvents CDCI3, CD2CI2, C6D6 and C7D8 were purchased from MSD Isotopes, and were dried over 3A molecular sieves, with the exception of CDCI3 which was distilled from calcium hydride (CaH2)- AH solvents were dried under argon. Hexanes and diethyl ether (Et20) were dried over sodium-benzophenone ketyl. Toluene and tetrahydrofuran (THF) were predried over sodium wire and CaH2, respectively, and then distilled from sodium-benzophenone ketyl. Dichloromethane and petroleum ether (30-60°C) were dried by refluxing over CaH2. Methyllithium in Et20, bis(Tj5-cyclopentadienyl)zirconium(rV) dichloride (Cp2ZrCl2), trimethyltin chloride, tributyltin chloride, phenylselenenyl chloride (PhSeCl), diphenyl diselenide (Ph2Se2), cyclooctadiene (COD), 2,6-di-rerf-butyl-4-methylphenol (BHT), 1,4-cyclohexadiene, /V-bromosuccinimide, azobisisobutyronitrile (AIBN), chlorodiphenylphosphine (Ph2PCl), methyl acrylate, methacrylonitrile, benzonitrile, o-tolunitrile, maleic anhydride, N-phenylmaleimide p - b e n z o q u i n o n e , dimethyl acetylenedicarboxylate, cinnamonitrile, ( £ ) - 3 - e t h o x y a c r y l o n i t r i l e , (1^-3-dimethylammoacrylorritr^^ chloride and (Z)-l-methoxy-l-buten-3-yne were all purchased from the Aldrich Chemical Co., Inc.. Al l of the above reagents were purified by standard means prior to use. The reagents 2-chloro-1,3-butadiene and l-buten-3-yne were purchased from Pfaltz and Bauer Chemicals, Inc.; both were obtained as solutions in xylene. The former was dried over 4A molecular sieves and vacuum transferred several times to remove any xylene, the latter compound was simply vacuum transferred twice prior to use. CMorodimethylphosphine (Me2PCl), trimethylphosphine (PMe3) and triethylphosphine (PEt3) 167 were purchased from Strem Chemical Co., and were used without further purification. Bromodiphenylboron was purchased from Alfa Chemical Co., isopropylacetylene was purchased from Farchan Chemical Co., and 1 3 C O (90 atom %) was purchased from MSD Isotopes; these reagents were used as supplied. Carbon monoxide was obtained from Matheson Gas Products and was used without further purification. Gratitude is expressed to Mr. J. B. Ng (UBC) for providing a sample of cWorocinsopropylphosphine (i-Pr2PCl), Dr. G. Herring for a loan of 4-oxo-2,2,6,6-tetramethylpiperidinyloxy radical (TEMPONE) and to Dr. M . Pinto (Simon Fraser University) for his kind gift of bis(4-chlorophenyl)diselenide. 6.2.1 Reagents Prepared by Literature Procedures The following reagents were prepared by literature procedures: l-methoxy-l-buten-3-yne (-4:1 E /Z) , 5 5 1-ethynylcyclohexene,55 lithium tri-rerr-butoxyaluminohydride,111 lithium tri-ferr-butoxyaluminodeuteride,111 chlorobis(T| 5-cyclopentadienyl)hydridozirconium(IV) [Cp2ZrCl(H)],7 chlorobis(rj5-cyclopentadienyl)deuteriozirconium(IV) [Cp2ZrCl(D)]7 N-(phenylseleno)phthalimide ( /V-PSP) , 1 1 2 iV-(phenylthio)phthalimide ( N - P T P ) , 1 1 2 2-chloromagnesium- 1,3-butadiene,40 bis(l,5-cyclooctadiene)nickel(0) [Ni(COD)2], 1 1 3 and (benzenememanimmato)cMcrobis(Ti5-cycto 1 7 168 6.3 Insertion Reactions of l-Ene-3-ynes, Nitriles and a , f i - U n s a t u r a t e d Nitriles. Reaction of 1,3-DienyIzirconium complexes with Carbon Monoxide. General Procedure 1: Preparation of ZrCp 2Cl(CH=CH-CR=CR'R"), ZrCp 2Cl(N=CH-R)  and ZrCp 2Cl(N=CH-CR=CR'R") The hydride Cp 2ZrCl(H) 1 was added in three portions, at room temperature in the dark, to a stirred solution in toluene of the appropriate l-ene-3-yne or nitrile or a,|i-unsaturated nitrile (1 equiv, respectively). The resulting white slurry was stirred in the dark (reaction vessel was simply covered with aluminum foil), until a homogeneous solution was obtained. The solvent was evaporated to approximately one-third of its original volume, at which point hexanes was added and the solution was allowed to crystallize at -30° C. 6.3.1 Reaction of l-Ene-3-ynes with Cp 2 ZrCI(H) 1 and C p 2 Z r C l ( D ) 2, ( £ ) - ! , 3-ButadienylcMorobis(Tis-cyclopenmdienyl)zirconium(rV) 55a and  (£)-1,3-butodienylchlorobis(ri5-cyclopentadienyl)zirconium(rV)-2-^ 55z-d\ 169 The preparation of 55a deviated slightly from general procedure 1 due to the low boiling point of l-buten-3-yne (2'C). To a stirred slurry of Cp2ZrCl(H) 1 (3.00 g, 11.63 mmol) in 60 mL of toluene, contained in a large reactor bomb, was vacuum transferred l-buten-3-yne (1.82 g, 34.90 mmol). The mixture was stirred in the dark at room temperature until a red homogeneous solution resulted. Workup as described in general procedure 1 gave 55a as yellow-orange crystals (2.92 g, 81%); PR (KBr): 3095, 2890, 1600, 1532, 1441, 1020, 1000, 908 and 629 cm-1; 8 (QD6, 400 MHz, ^H NMR) 4.99 (1H, ddd, H E , JEC = 10 Hz, 7 E D = 1.75 Hz, / E B = 0.75 Hz), 5.12 (1H, ddd, H D , Jryc = 17 Hz, 7 D E = 1.75 Hz, / D B = 0.75 Hz), 5.80 (10H, s, Cp), 6.27 (1H, dddd, He, JCD = 17 Hz, 7 C B = / C E = 10 Hz, JCA = 0.75 Hz), 6.59 (1H, dddd, H B , JBA = 19 Hz, JBC = 10 Hz, / B D = -^BE = 0.75 Hz), 7.12 (1H, dd, H A , JAB = 19 Hz, JAc = 0.75 Hz). Anal, calcd. for C i 4 H i 5 C l Z r : C 54.24, H 4.84, CI 11.46; found: C 53.85, H 4.72, CI 11.65. Reaction of Cp2ZrCl(D) 2 (1.00 g, 3.86 mmol) and l-buten-3-yne (0.60 g, 11.59 mmol) afforded yellow crystals of 55a-di (0.99 g, 82%); 8 ( C 6 D 6 , 400 MHz, * H NMR): 5.02 (1H, dd, H E , / E C = 10 Hz, / E D = 1.75 Hz), 5.14 (1H, dd, H D , JJX: = 17 Hz, / D E = 1.75 Hz), 5.78 (10H, s, Cp), 6.28 (1H, b dd, H c , JCD = 17 Hz, JQE = 10 Hz), 7.11 (1H, b t, H A , JAd = 2.5 Hz). (£,£)-Chlorobis(Ti5-cyclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(iV) 55b and  (£'^E)-chlorobis(T|5-cyclopentadienyl)(4-methoxy-1,3-butadienyl)zirconium(rV) -2-d 55b-fl"i 170 To a stirred solution of l-methoxy-l-buten-3-yne (-4:1 E/Z) (1.19 g, 13.96 mmol) in 60 mL of toluene was added Cp2ZrCl(H) 1 (3.00 g, 11.63 mmol), in three portions. Upon formation of an orange-red homogeneous solution workup of the reaction mixture, as described in general procedure 1, was performed to yield yellow crystals of 55b (3.36 g, 85%); IR (Nujol): 3104, 3048, 1617, 1543, 1294, 1214, 1144, 1018, 984, 913 and 802 cm-ijS (C6D 6 , 400 MHz, * H NMR): 3.19 (3H, s, OMe). 5.47 (1H, ddd, He, JCD = 13 Hz, JQB = 10 Hz, / C A = 0.75 Hz), 5.86 (10H, s, Cp), 6.51 (1H, ddd, H B , / B A = 18 Hz, / B C = 10 Hz, / B D = 0.75 Hz), 6.58 (1H, dd, H D , J D C = 13 Hz, / D B = 0.75 Hz), 7.17 (1H, dd, H A , JAB = 18 Hz, 7 A C = 0.75 Hz). Anal, calcd. for C i 5 H i 7 C 1 0 Z r : C 52.98, H 5.00, CI 10.45; found: C 52.81, H 5.07, CI 10.66. Reaction of Cp2ZrCl(D) 2 (1.00 g, 3.86 mmol) and l-methoxy-l-buten-3-yne (-4:1 E/Z) (0.40 g, 4.83 mmol) afforded yellow crystals of 55b-rfi (1.14 g, 87%); 8 (C6D 6, 400 MHz, l H NMR): 3.19 (3H, s, OMe). 5.47 (1H, b d, He, JCD = 12.5 Hz), 5.86 (10H, s, Cp), 6.58 (1H, d, H D , / D C = 12.5 Hz), 7.15 (1H, b s, H A ) . (£^-CMorobis(Ti5-cyclopentadienyl)(4-memoxy-l,3-butadienyl)zirconium(rV) 55c and  (E,Z)-chlorobis(T^5-cyclopentadienyl)(4- -2-d55c-di To a stirred solution of (Z>l-methoxy-l-buten-3-yne (0.95 g, 11.63 mmol) in 60 mL of toluene was added Cp2ZrCl(H) 1 (3.00 g, 11.63 mmol) in three portions. The resulting orange-red homogeneous solution was worked up as described in general procedure 1, to yield H A O M e H A O M e 171 yellow crystals of 55c (3.28 g, 83%); IR (Nujol): 3097, 1617, 1517, 1260, 1113, 1070, 990 and 805 cm" 1 ; 8 ( C 6 D 6 , 400 MHz, l H NMR): 3.15 (3H, s, OMe). 5.04 (1H, ddd, He, JQB = 8.5 Hz, 7 C D = 6 Hz, / C A = 0.75 Hz), 5.60 (1H, ddd, H D , / D C = 6 Hz, / D A = ^ D B = 0.75 Hz), 5.83 (10H, s, Cp), 7.20 (1H, ddd, H B , JBA = 18 Hz, / B C = 8.5 Hz, / B D = 0.75 Hz), 7.27 (1H, ddd, H A , JAB = 18 Hz, / A C = ^ A D = 0.75 Hz). Anal, calcd. for C i 5 H i 7 C 1 0 Z r : C 52.98, H 5.00, CI 10.45; found: C 52.69, H 4.83, CI 10.52. Reaction of Cp2ZrCl(D) 2 (1.00 g, 3.86 mmol) and (Z)-l-methoxy-l-buten-3-yne (0.32 g, 3.86 mmol) afforded yellow crystals of 55c-di (1.08 g, 82%); 8 (C6T>6, 400 MHz, l H NMR): 3.15 (3H, s, OMe). 5.07 (1H, b d, He, JCD = 6 Hz), 5.60 (1H, dd, H D , / D C = 6 Hz, / D A = 0.5 Hz), 5.83 (10H, s, Cp), 7.25 (1H, b t, H A , J M = 2.75 Hz). (£Q-CMoro[2-(l-cyclohexen-l-yl)eftenyl]bis(^ 55d and (£)-chloro[2-(l-cyclohexen-l-yl)ethenyl]bis(ri5-cyclopentadienyl)zirconium(rV)-2-rf 55d-<ii To a stirred solution of 1-ethynylcyclohexene (1.23 g, 11.63 mmol) in 60 mL of toluene was added Cp2ZrCl(H) 1 (3.00 g, 11.63 mmol) in three portions. Workup of the resulting red solution, as described in general procedure 1, afforded pale yellow crystals of 55d (3.81 g, 90%); IR (KBr): 3102, 2926, 2853, 1621, 1522, 1439, 1316, 1018, 988 and 804 cm- 1 ; 8 (QD6, 400 MHz, l H NMR): 1.54 (2H, m), 1.61 (2H, m), 2.08 (2H, m), 2.15 (2H, m), 5.74 (1H, m, H c ) , 5.87 (10H, s, Cp), 6.66 (1H, d, H B , JBA = 18.5 Hz), 7.14 (1H, 172 dd, H A , JAB = 18.5 Hz, / A C = 0.75 Hz). Anal, calcd. for C2oH 2 iClZr: C 59.37, H 5.77, CI 9.76; found: C 59.17, H 5.67, CI 10.00. Reaction of Cp2ZrCl(D) 2 (1.00 g, 3.86 mmol) and 1-ethynylcyclohexene (0.39 g, 3.86 mmol) afforded pale yellow crystals of 55d-di (1.25 g, 89%); 8 (C6D6, 400 MHz, l H NMR): 1.54 (2H, m), 1.61 (2H, m ), 2.08 (2H, m), 2.15 (2H, m), 5.74 (1H, m, H c ) , 5.87 (10H, s, Cp), 7.13 (1H, b t, H A , JM = 2.5 Hz). 6.3.2 Reaction of Nitriles and a,p-Unsaturated Nitriles with C p 2 Z r C l ( H ) 1. Chlorobis(Ti5-cyclopentadienyl)(2-memylbenzenem^ 63 To a stirred solution of o-tolunitrile (0.45 g, 3.88 mmol) in 50 mL of toluene was added Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in three portions. Workup of the resulting orange-red homogeneous solution, as described in general procedure 1, afforded bright yellow microcrystals of 63 (1.15 g, 79%); IR (Nujol): 1650, 1595, 1204, 1027, 826, 803, 756 and 660 cm-1; 8 (C6D6, 400 MHz, * H NMR): 2.37 (3H, s, CH3), 5.92 (10H, s, Cp), 6.97 (1H, b d, H E / = 7.5 Hz), 7.11 (1H, td, H D , / = 7.5 Hz, / B D = 1-50 Hz), 7.21 (1H, b t, H C , / = 7.5 Hz), 7.81 (1H, b d, H B , / = 7.5 Hz), 9.38 (1H, s, H A ) . Anal, calcd. for C i 8 H i 8 C l N Z r : C 57.65, H 4.84, N 3.73; found: C 57.36, H 4.85, N 3.62. H 3 C 173 ClCp 2Zr N He To a stirred solution of methacrylonitrile (0.26 g, 3.88 mmol) in 50 mL of toluene was added Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in three portions. Workup of the resulting red homogeneous solution, as described in general procedure 1, afforded yellow microcrystals of 68 (1.07 g, 85%); IR (Nujol): 3104, 2802, 1656, 1016, 928, 803 and 677 enr*; 8 (QD6, 400 MHz, * H NMR): 1.77 (3H, s, CH3), 5.11 (1H, m, H B ) , 5.33 (1H, m, He), 5.79 (10H, s, Cp), 8.60 (1H, s, H A ) . Anal, calcd. for Ci4Hi 6 ClNZr : C 51.74, H 4.98, N 4.31; found: C 51.96, H 4.77, N 4.08. (£)-CMorobis(Ti5-cyclopentadienyl)[2-(2-phenylemenyl)memanimmato]zr^ 69 To a stirred solution of cinnamonitrile (0.50 g, 3.88 mmol) in 50 mL of toluene was added Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in three portions. Workup of the resulting red homogeneous solution, as described in general procedure 1, afforded orange crystals of 69 (1.17 g, 78%); IR (Nujol): 1641, 1611, 1015, 987, 975, 800, 742, 688 and 646 cm" 1; 174 8 (C6D 6 , 400 MHz, ^H NMR): 5.88 (10H, s, Cp), 6.39 (1H, dd, H B > / B C = 16 Hz, / B A = 8 Hz), 6.63 (1H, d, H C , / C B = 16 Hz), 7.02-7.10 (3H, m), 7.20 (2H, m), 8.75 (1H, d, H A , / A B = 8 Hz). Anal, calcd. for C i 9 H i 8 C l N Z r : C 58.96, H 4.69, N 3.62; found: C 58.97, H 4.77, N 3.45. (E)-Chlorobis(Tis-cyclopentedie^^ 70 To a stirred solution of (E)-3-ethoxyacrylonitrile (0.38 g, 3.88 mmol) in 50 mL of toluene was added Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in three portions. Workup of the resulting deep-red homogeneous solution, as described in general procedure 1, afforded orange-brown crystals of 70 (1.12 g, 81%); IR (Nujol): 3097, 1649, 1613, 1318, 1201, 1021, 801, 728 and 662 cm- 1 ; 8 (CoD 6 , 400 MHz, LK NMR): 0.88 (3H, t, CH3, / = 8 Hz), 3.24 (2H, q, CH2,7 = 8 Hz), 5.25 (1H, dd, H B > / B C = 13 Hz, / B A = 8.5 Hz), 5.91 (10H, s, Cp), , 6.55 (1H, d, H C , / C B = 13 Hz), 8.45 (1H, d, H A , JAB = 8.5 Hz). Anal, calcd. for C i 5 H i 8 C l N O Z r : C 50.75, H 5.11, N 3.95; found: C 51.00, H 5.09, N 4.03. 175 (JQ-Chlorobis(Ti5-cyclopCT To a stirred solution of (£)-3-dimemylaminoacrylonitrile (0.37 g, 3.88 mmol) in 70 mL of toluene was added Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in three portions. Workup of the resulting deep-red homogeneous solution, as described in general procedure 1, afforded orange crystals of 71 (1.06 g, 77%); IR (Nujol): 3104, 2795, 1635, 1590, 1438, 1286, 1108, 970, 798 and 645 cm- 1 ; 8 (CDC1 3, 400 MHz, !H NMR): 2.90 (6H, s, N M e A 4.55 (1H, dd, H B , JBC = 13 Hz, JBA = 9 Hz), 6.11 (10H, s, Cp), 6.60 (1H, d, H C , / C B = 13 Hz), 8.38 (1H, d, H A , JAB = 9 Hz). Anal, calcd. for C i 5 H i 9 C l N 2 Z r : C 50.89, H 5.41, N 7.91; found: C 50.95, H 5.38, N 7.91. 6.3.3 Carbonylation Reactions of 1,3-Dienylzirconium Complexes. General Procedure 2: Preparation of ClCp2Zr(CO-CH=CH-CR=CR'R") and  ClCp 2 Zr(CO-CH=CH-CR=CR'R")- 1- 1 3 C Carbonylation reactions were carried out in reactor bombs with 250 mg of the appropriate (£)-l-chlorobis(Ti5-cyclopentadienylzirconium(TV) 1,3-dienes 55a-d dissolved in 2 mL of toluene. After several freeze-pump-thaw cycles, to remove nitrogen from the bomb and the solution, the reactor bomb was left under vacuum (~10*2 Torr). The stirred solution 71 176 was then placed under 1 atmosphere of carbon monoxide (CO or 1 3 C O ) at room temperature. On addition of CO, there was an immediate color change (yellow to orange/red), followed by precipitation of the product from solution. The slurry was diluted with hexanes and the product collected by filtration. Analytical samples were obtained by recrystallization from dichloromethane/hexanes at low temperature (-30°C). The position of dienyl protons H A , H B , He, etc., for complexes 70a-d, 70a-d- 1 3 C are as shown for the corresponding complexes 55a-d. (£) - l-Ti2-Acyl-2,4-butam^nylchlorobis(ri5-cyclopentadienyl)zirconium(rV) 70a and  (E)-l-T|2-acyl-2,4-butadienylchlorobis(Ti5-cyclopentodienyl)zirconium(iV)-l-13C 70a- 1 3C Carbonylation of 55a (250 mg, 0.81 mmol) was carried out according to general procedure 2. On addition of CO, the orange solution darkened to orange-red. After ~3 min stirring at room temperature, an orange-red slurry resulted. Recrystallization gave orange crystals of 70a (246 mg, 73%); IR (KBr): 3106, 3081, 2926, 2853, 1627, 1582, 1512, 1499 (ri2-acyl), 1194, 1015 and 809 cm" 1; 8 (CDC1 3, 400 MHz, * H NMR): 5.87 (1H, d, H E , JEC = 10 Hz), 5.94 (10H, s, Cp), 6.02 (1H, d, H D , JCD = 17 Hz), 6.83 (1H, ddd, He, JCD = 17 Hz, JQE = 10 Hz, JCB = 10.5 Hz), 6.85 (1H, d, H A , JAB = 15.5 Hz), 7.63 (1H, dd, H B , / B A = 15.5 Hz, JBC = 10.5 Hz). Anal, calcd. for C i 5 H i 5 C 1 0 Z r : C 53.31, H 4.47; found: C 53.50, H 4.55. 70a 70a- 1 3 C 177 In the case where, 55a (150 mg, 0.48 mmol) was carbonylated with 1 3 C O ; recrystallization yielded orange crystals of 70a- 1 3C (109 mg, 66%); IR (Nujol): 3090, 1623, 1439 (Tl2-acyl), 1182, 1014 and 804 cm-1; 8 (CDC1 3 , 400 MHz, ! H NMR): 5.87 (1H, d, H E , JEC = 10 Hz), 5.94 (10H, s, Cp), 6.02 (1H, d, H D , / C D = 17 Hz), 6.83 (1H, ddd, He, JQD = 17 Hz, JCB = 10.5 Hz, JCE = 10 Hz), 6.85 (1H, b d, H A , JAB = 15.5 Hz), 7.61 (1H, ddd, H B , JBA = 15.5 Hz, JBc = 10.5 Hz, / B i 3 C = 8 Hz); 8 (CDCI3, 75.4 MHz, ^ C ^ H } NMR): 109.40 (s, Cp), 129.71 (d, C2, / C 2 C l = 34.5 Hz), 129.84 (s, C5), 135.2 (d, C4, / C4Cl = 8.8 Hz), 159.14 (d, C3, / C3Cl = 9.8 Hz), 301.44 (s, CI). (£,£)-1 -rt2-Acyl-chlorobis(T| s-cyclopentadienyl)(4-methoxy-2,4-butadienyl) zirconium(TV) 70b  and (7f^-l-Ti2-acyl-cMorobis(Ti5<yclopentadienyl)(4-memoxy-2,4-butamenyl)zircom 1- 1 3 C 70b- 1 3 C Carbonylation of 55 b (250 mg, 0.74 mmol) was carried out according to general procedure 2. On addition of CO, the yellow solution darkened to yellow-orange. After ~3 min stirring at room temperature, a yellow-orange slurry resulted. Recrystallization gave yellow crystals of 70b (225 mg, 83%); IR (KBr): 3077, 2933, 1617, 1589, 1468 (r|2-acyl), 1200, 1009, 807 and 654 cm" 1; 8 (CDCI3, 400 MHz, NMR): 3.86 (3H, s, OMe). 5.92 (10H, s, Cp), 6.03 (1H, dd, He, / C D = / C B = 12 Hz), 6.82 (1H, d, H A , JAB = 15 Hz), 7.34 (1H, d, H D , / D C = 12 Hz), 7.64 (1H, dd, H B , / B A = 15 Hz, / B c = 12 Hz). Anal, calcd. for Ci6Hi 7 C10Zr: C 52.22, H 4.66; found: C 52.32, H 4.80. 178 In the case where, 55b (150 mg, 0.44 mmol) was carbonylated with 1 3 C O ; recrystallization yielded yellow crystals of 70b- 1 3 C (117 mg, 72%); IR (Nujol): 3076,1617, 1590, 1426 012-acyl), 1184, 1010, 808 and 654 cnr 1 ; 8 (CDC1 3, 400 MHz, l H NMR): 3.86 (3H, s, O M e l , 5.90 (10H, s, Cp), 6.03 (1H, dd, He, JCD = JQB = 12 Hz), 6.81 (1H, dd, H A , JAB = 15 Hz, / A i 3 c = 2.5 Hz), 7.34 (1H, d, H D , JDC = 12 Hz), 7.67 (1H, ddd, H B , JBA = 15 Hz, JBC = 12 Hz, / B i 3 C = 7 Hz); 8 (CDCI3, 75.4 MHz, ™C{LH} NMR): 58.14 (s, OCH3), 106.32 (d, C4, / C 4 C l = 9.6 Hz), 109.19 (s, Cp), 125.02 (d, C2, / C 2 C l = 36.7 Hz), 159.28 (d, C3, / C3C1 = H-2 Hz), 162.59 (s, C5), 293.22 (s, CI). (E,Z)-l-Ti2-Acyl-cMorobis(Tl5-cyclopenta^ 70c  and (£,Z)-1 -Tl2-acyl-cMorobis(T^5-cyclopentadienyl)(4-meu^^  1 - 1 3 C 70c-rfi ZrCp 2 Cl ZrCp 2 Cl Carbonylation of 55c (250 mg, 0.74 mmol) was carried out according to general procedure 2. On addition of CO, the yellow solution darkened to deep red. In this case, precipitation of the product occurred only after cooling the solution to -30°C. Recrystallization gave orange-red crystals of 70c (183 mg, 68%); IR (Nujol): 3111, 1614, 1587, 1492 (rj2-acyl), 1275, 1191, 1085, 800 and 724 cm- 1; 8 (CDCI3,400 MHz, LH NMR): 3.96 (3H, s, O M e l , 5.59 (1H, dd, He, JCB = 11.5 Hz, 7 C D = 6 Hz), 5.93 (10H, s, Cp), 6.57 (1H, d, 179 H D , / D C = 6 Hz), 6.75 (1H, d, H A , JAB = 15 Hz), 8.04 (1H, dd, H B , / B A = 15 Hz, 7 B C = 11.5Hz). Anal, calcd. C i 6 H i 7 C 1 0 Z r : C 52.22, H 4.66; found: C 52.35, H 4.74. In the case where, 55c (150 mg, 0.44 mmol) was carbonylated with 1 3 C O ; recrystallization yielded orange-red crystals of 70c- 1 3 C (98 mg, 61%); IR (Nujol): 3097, 1620, 1587, 1447 (rj2-acyl), 1275, 1185, 1081, 800 and 723 cm-1; 8 (CDC1 3, 400 MHz, * H NMR): 3.96 (3H, s, OMe). 5.59 (1H, dd, H e , JCB = H-5 Hz, / C D = 6 Hz), 5.93 (10H, s, Cp), 6.57 (1H, dd, H D , / D C = 6 Hz, / D B = 0.75 Hz), 6.75 (1H, dd, H A , / A B = 15 Hz, / A 1 3 C = 2-5 Hz), 8.04 (1H, dddd, H B , JBA = 15 Hz, / B C = 11.5 Hz, / B i 3 c = 7.5 Hz, / B D = 0.75 Hz); 8 (CDCI3, 75.4 MHz, ^C{LH) NMR): 61.87 (s, OCH3), 105.89 (d, C4, / C 4 C l = 8.7 Hz), 109.19 (s, Cp), 125.57 (d, C2, / C 2 C l = 35.8 Hz), 153.65 (d, C3, / C 3 C l = 10.6 Hz), 157.68 (s, C5), 296.25 (s, CI). (£>l-Ti2-AcylcMoro[2-(l-cyclohexen-l-yl)efteny^ 70d,  (£)-1 -,r|2-acylchloro[2-( 1 -cyclohexen-1 -yl)emenyl]bis(Ti5-cyclopentedienyl)zirconium(iV)-1- 1 3 C 70d- 1 3 C and (£)-l-Ti2-acylchloro[2-(l-cyclohexen-l-yl)ethenyl]bis(ris- cyclopentadienyl)zirconium(rV)-2-rf 70d-tfi Carbonylation of 55d (250 mg, 0.69 mmol) was carried out according to general procedure 2. On addition of CO, the yellow solution darkened to orange. After ~3 min stirring at room temperature an orange slurry resulted. Recrystallization gave yellow-orange crystals of 180 70d (221 mg, 82%); IR (Nujol): 1620, 1588, 1498 (rj2-acyl), 1190, 985, 829, 800 and 726 cm-1; 8 (CDC1 3, 400 MHz, * H NMR): 1.73 (2H, m), 1.80 (2H, m), 2.33 (2H, m), 2.39 (2H, m), 5.93 (10H, s, Cp), 6.64 (1H, m, H c ) , 6.78 (1H, dd, H A , / A B = 15.5 Hz, JAC = 0.75 Hz), 7.64 (1H, d, H B , / B A = 15.5 Hz). Anal, calcd.for C 2 i H 2 i C 1 0 Z r : C 57.99, H 5.76; found: C 57.93, H 5.70. In the case where, 55d (150 mg, 0.41 mmol) was carbonylated with 1 3 C O ; recrystallization yielded orange crystals of 70d- 1 3 C (129 mg, 80%); IR (Nujol): 1620,1588, 1444 Cn2-acyl), 1167, 984, 828, 799 and 725 cm-*; 8 (CDCI3, 400 MHz, ^H NMR): 1.73 (2H, m), 1.80 (2H, m), 2.33 (2H, m), 2.39 (2H, m), 5.93 (10H, s, Cp), 6.64 (1H, m, He), 6.78 (1H, dd, H A , / A B = 15.5 Hz, / A i 3 c = 2 Hz), 7.64 (1H, dd, H B , JEA = 15.5 Hz, / B i 3 c = 7.5 Hz); 8 (CDCI3, 75.4 MHz, ^C{lH} N M R ) : 21.94 (s), 21.98 (s), 24.41 (s), 27.30 (s), 109.26 (s, Cp), 123.15 (d, C2, / C 2 C l = 35.4 Hz), 136.64 (d, C4, / C 4 C 1 = 9.5 Hz), 144.85 (s, C5), 164.14 (d, C3, / C 3 C 1 = 10.4 Hz), 297.91 (s, CI). Carbonylation of 55d-di (75 mg, 0.21 mmol) was carried out according to general procedure 2. On addition of CO, the yellow solution darkened to orange. After ~3 min stirring at room temperature an orange slurry formed, from which was obtained, after filtration, an orange powder 70d-di (68 mg, 84%); 8 (CDCI3, 400 MHz, lH NMR): 1.73 (2H, m), 1.80 (2H, m), 2.33 (2H, m), 2.39 (2H, m), 5.93 (10H, s, Cp), 6.64 (1H, m, He), 6.80 (1H, b s, H A ) . 181 6.4 Preparation of Heterosubstituted 1,3-Dienes, Imines and 1-Azadienes. 6.4.1 Preparation of a 1,3-Dienylnickel Complex. (E)-1 -Bromo[2-( 1 -cyclohexen-1 -yl)ethene] 72 To a stirred solution of 55d (500 mg, 1.37 mmol) in 3 mL of T H F was added N-bromosuccinimide (271 mg, 1.52 mmol). The white slurry was stirred at room temperature for 3 h. The mixture was diluted with 10 mL of hexanes and filtered through basic alumina to remove Cp2ZrQ(Br). After careful evaporation of the solvent, a colorless liquid resulted 72 (225 mg, 89%); IR (film): 3083,1678, 1586, 1434,1202,942,760 and 745 cm-l; 5 (CDCI3, 400 MHz, LH NMR): 1.59 (2H, m), 1.67 (2H, m), 2.08 (4H, m), 5.76 (1H, m, H c ) , 6.12 (1H, dd, H A , JAB = 14 Hz, JAc = 0.5 Hz), 6.68 (1H, d, / B A = 14 Hz). Anal, calcd. for CgHnBr: C 51.36, H 5.93, Br 42.71; found: C 51.27, H 6.07, Br 42.50. (£)-Bromo[2-( 1 -cyclohexen-1 -yl)ethenyl] bis(triethylphosphine)nickel(II) 73 H A H C 182 A solution of Ni(PEt3)2<COD) was prepared by stirring Ni(COD)2 (300 mg, 1.09 mmol) and PEt3 (256 mg, 2.18 mmol) in 2 mL of hexane. The yellow-brown solution was then slowly added to (E)-l-bromo[2-(l-cyclohexen-l-yl)ethene] 72 (206 mg, 1.11 mmol) in 3 mL of hexane at room temperature. After the addition was complete, the orange-brown solution was cooled to -30°C to allow for crystallization. This yielded orange crystals of 73 (403 mg, 77%); IR (Nujol): 1627, 1542, 1410, 1258, 1038, 1000, 959, 761, 723 and 629 cm-l; 5 (Q6D6, 400 MHz, * H NMR): 1.07 (18H, m, PCH2CH3), 1.58 (12H, m, PCH2CH3), 1.60 (2H, m), 1.65 (2H, m), 2.09 (2H, m), 2.19 (2H, m), 5.47 (1H, m), 6.13 (1H, m), 6.20 (1H, m); 8 (C6D6, 121.5 MHz, 31p{lH} NMR): 10.4 (s). Anal, calcd.for C 2 oH4iBrP 2 Ni: C 49.82, H 8.57, Br 16.57; found: C 50.03, H 8.66, Br 16.30. 6.4.2 Preparation of 1,3-DienyIstannanes. ( £ ) - ! , 3-Butadienyl-l-tributylstannane 77a Tributyltin chloride (368 mg, 1.13 mmol) was added to a stirred solution of 55a (350 mg, 1.13 mmol) dissolved in 1.5 mL of toluene. Upon addition, the solution changed from orange to yellow. The mixture was then stirred at room temperature in the dark for 2-3 days. After this time, a pale yellow slurry was observed. The reaction mixture was diluted with hexanes and filtered through basic alumina. Evaporation of the solvent yielded a pale 183 yellow oil 77a (264 mg, 68%); IR (film): 2958, 2934, 2856, 1635, 1565, 1460, 1375, 1071, 984, 748 and 667 cm-l; 5 (C6D 6 , 400 MHz, l H NMR): 0.92 (9H, t, / = 7.5 Hz), 0.96 (6H, t, / = 7.5 Hz), 1.35 (6H, dt, / = 7.5 Hz), 1.56 (6H, m), 4.98 (1H, ddd, H E , JEC = 10 Hz, / E D = 1.75 Hz, 7 E B = 0.75 Hz), 5.11 (1H, ddd, H D > / D C = 17 Hz, / D E = 1.75 Hz, / D B = 0.75 Hz), 6.34 (1H, dd, H A , JAB = 18.5 Hz, JAc = 1 Hz), 6.36 (1H, dddd, H c , JQD = 17 Hz, 7cE = 10 Hz, JQB = 10 Hz, JQA = 1 Hz), 6.63 (1H, dddd, H B , JBA = 18.5 Hz, JBC = 10 Hz, 7 B D = / B E = 0.75 Hz, 7BSn = 60 Hz). Anal, calcd. for C i 6 H 3 2 S n : C 56.01, H 9.40; found: C, 55.76, H 9.40. ( £ , £ ) - (4-Methoxy-1,3-butadienyl)-1 -tributylstannane 77b The preparation of 77b was identical to that described above for 77a. In this case, tributyltin chloride (335 mg, 1.03 mmol) and 55b (350 mg, 1.03 mmol) were reacted to give, after distillation under vacuum (10 - 2 Torr), 77b (288 mg, 75%) as a colorless oil; IR (film): 2958, 2928, 2872, 2852, 1631, 1462, 1217, 1143, 958 and 664 cm-l; 5 (QD6, 400 MHz, l H NMR): 0.94 (9H, t, J = 7.5 Hz), 0.99 (6H, t, / = 7.5 Hz), 1.39 (6H, dt, / = 7.5 Hz), 1.65 (6H, m), 3.10 (3H, s, OMe). 5.63 (1H, dd, He, JCD = 12.5 Hz, / CB = 10 Hz), 6.09 (1H, d, H A , JAB = 18.5 Hz, / A S n = 73 Hz), 6.51 (1H, d, H D , J D C = 12.5 Hz), 6.57 (1H, dd, H B , / B A = 18.5 Hz, / B C = 10 Hz, / B S n = 62 Hz). Anal, calcd. for C i 7 H 3 4 O S n : C 54.72, H 9.18; found: C, 54.54, H 9.15. 184 (£,Z)-(4-Methoxy-1,3-butadienyl)- 1-tributylstannane 77c Bu 3 Sn H A O M e The preparation of 77c was identical to that described above for 77a. In this case, tributyltin chloride (335 mg, 1.03 mmol) and 55c (350 mg, 1.03 mmol) were reacted to give, after distillation under vacuum (10"2 Torr), 77c (274 mg, 71%) as a colorless oil; IR (film): 2956, 2921, 2851, 1639, 1462, 1263,1123, 994, 806 and 664 cm-l; 5 (Q5D6, 400 MHz, ! H NMR): 0.89 (9H, t, / = 7.5 Hz), 0.95 (6H, t, / = 7.5 Hz), 1.35 (6H, dt, / = 7.5 Hz), 1.59 (6H, m), 3.06 (3H, s, OMe). 5.22 (1H, ddd, H C , JCB = 10.5 Hz, / C D = 6 Hz, JQA = 0.75 Hz), 5.50 (1H, ddd, H D , 7 D C = 6 Hz, / D A = JDB = 0.75 Hz), 6.28 (1H, ddd, H A , JAB = 18.5 Hz, JAC = JAD = 0.75 Hz, 7 A S n = 75 Hz), 7.37 (1H, ddd, H B , JBA = 18.5 Hz, / B C = 10.5 Hz, / B D = 0.75 Hz, / B S n = 62 Hz). Anal, calcd. for C n H ^ O S n : C 54.72, H 9.18; found: C, 54.45, H 9.20. (£ ) - [2-(l-Cyclohexen-l-yl)ethenyl]- 1-tributylstannane 77d H A H C 185 A solution of tributyltin chloride (313 mg, 0.96 mmol) and 55d (350 mg, 0.96 mmol) in 1.5 mL of toluene were heated in a reactor bomb, in the dark, at 80°C for 16 h. The workup as described above gave, after distillation under vacuum (IO - 2 Torr), a colorless oil 77d (313 mg, 79%); IR (film): 2967, 2925, 2872, 2854, 1620, 1558, 1464, 1377, 1010, 903 and 663 cm- 1 ; 8 (C6D 6, 400 MHz, lU NMR): 0.94 (9H, t, / = 7.5 Hz), 1.00 (6H, t, / = 7.5 Hz), 1.36 (6H, dt, / = 7.5 Hz), 1.58 (6H, m), 1.42 (2H, m), 1 51 (1H, m), 2.00 (2H, m), 2.17 (2H, m), 5.63 (1H, m, He), 6.24 (1H, dd, H A , / A B = 19.5 Hz, / A C = 0.75 Hz, / A S n = 74 Hz), 6.80 (1H, d, / B A = 19.5 Hz, / B S n = 67 Hz). Anal, calcd. for C 2 o H 3 8 S n : C 60.48, H 9.64; found: C, 60.44, H 9.55. 6.4.3 Preparation of 1,3-Dienylphosphines. General Procedure 3: Preparation of Dimethyl and Diphenylphosphino 1,3-Dienes 79a-d and  80a-d To a stirred solution of the appropriate ( £ ) - l - c h l o r o b i s ( T i 5 -cyclopentamenylzirconium(TV) 1,3-dienes 55a-d in 1 mL of toluene at room temperature, was added a solution of Ph 2 PCl or Me 2 PCl (1 equiv in ~1 mL of toluene). On addition of the phosphine, there was an immediate color change from yellow (or orange in the case of 55a) to colorless. The reaction was complete within 5 min, and the solution was then diluted with hexanes to produce a white slurry. The slurry was filtered through basic alumina and evaporated to give the product as a white solid or colorless liquid. 186 (£)-1,3-Butadienyl- 1-diphenylphosphine 79a Ph 2 P According to general procedure 3,55a (150 mg, 0.48 mmol) was reacted with PI12PCI (107 mg, 0.48 mmol) to give, after workup, a white solid 79a (96 mg, 83%); IR (Nujol): 1620, 1584, 1479, 1005, 911, 741 and 697 cm-1; 5 (C6D6, 400 MHz, * H NMR): 4.91 (1H, d, H E , JEC = 10 Hz), 4.95 (1H, d, H D , J D C = 17 Hz), 6.27 (1H, ddd, He, / C D = 17 Hz, / C B = 10.5 Hz, / C E = 10 Hz), 6.33 (1H, dd, H A , / A B = 17 Hz, Z A P = 10 Hz), 6.59 (1H, ddd, H B , JBA = 17 Hz, 7 B P = H-5 Hz, / B G = 10.5 Hz), 7.06 (6H, m), 7.44 (4H, m); 5 ( C 6 D 6 , 32.4 MHz, 31p{lH} NMR): -12.4 (s). Anal, calcd. for C i 6 H 1 5 P : C 80.66, H 6.35; found: C 80.39, H 6.36. (E,E)-(4-Methoxy-l,3-butadienyl)- 1-diphenylphosphine 79b According to general procedure 3,55b (150 mg, 0.44 mmol) was reacted with Ph2PCl (97 mg, 0.44 mmol) to give, after workup, a white solid 79b (99 mg, 85%); IR (Nujol): 1631,1444, 1227,1146,981,739 and 696 cm" 1; X m a x (hexane): 256 nm (e 17,500), 250 nm (e 16,700) and 260 nm (e 16,500); 5 (C6D 6, 400 MHz, lH NMR): 3.03 (3H, s, OMe). 5.52 187 (1H, dd, He, JCD = 12.5 Hz, JCB = 11 Hz), 6.14 (1H, dd, H A , JAB = 16.5 Hz, / A P = 3.5 Hz), 6.32 (1H, d, H D , 7 D C = 12.5 Hz), 6.64 (1H, ddd, H B , JBA = 16.5 Hz, / BP = 14 Hz, / B C = 11 Hz), 7.11 (6H, m), 7.60 (4H, m); 8 (C6D6, 32.4 MHz, 31p{lH} NMR): -11.7 (s). Anal, calcd. for C17H17OP: C 76.11, H 6.39; found: C 76.10, H 6.50. (E,Z)-(4-Methoxy-1,3-butadienyl)- 1-diphenylphoshine 79c According to general procedure 3, 55c (150 mg, 0.44 mmol) was reacted with Ph2PCl (97 mg, 0.44 mmol) to give, after workup, a colorless oil 79c (92 mg, 79%); IR (film): 1636, 1480, 1433, 1389, 1265, 1126, 1086, 825, 741 and 696 cm" 1 ; 8 (CDCI3, 400 MHz, :H NMR): 3.67 (3H, s, OMe). 5.23 (1H, ddd, He, JCB = 11 Hz, / C D = 6 Hz, / C A = 0.75 Hz), 5.98 (1H, ddd, H D , JDC = 6 Hz, / D B = 1 Hz, 7 D A = 0.75 Hz), 6.23 (1H, dddd, H A , / A B = 16.5 Hz, JAP = 4 Hz, / A C = JAD = 0.75 Hz), 7.07 (1H, dddd, H B , / B A = 16.5 Hz, / B P = 14.5 Hz, 7 B C = 11 Hz, / B D = 1 Hz), 7.32 (6H, m), 7.42 (4H, m); 8 ( C 6 D 6 , 162.2 MHz, 31p{lH} NMR): -11.4 (s); m/e (relative intensity): 107 (23.2), 108 (22.1), 109 (25.1), 115 (27.5), 133 (18.9), 159 (27.7), 183 (28.7), 237 (100), 238 (30.3) and 268 (M+,30.0). Exact Mass calcd. for C17H17OP: 268.1019; found: 268.1012. 188 (£)-[2-(l-Cyclohexen-l-yl)ethenyl]-l-diphenylphosphine 79d Ph 2 P H A H C According to general procedure 3,55d (150 mg, 0.41 mmol) was reacted with Ph2PCl (91 mg, 0.41 mmol) to give, after workup, a white solid 79d (107 mg, 88%); IR (Nujol): 1631, 1578, 1432, 974, 823, 741 and 695 cm-l; 5 ( C 6 D 6 , 400 MHz, l H NMR): 1.39 (4H, m), 1.92 (4H, m), 5.59 (1H, m, H C ) , 6.31 (1H, dd, H A , / A B = 16.5 Hz, / A P = 5.5 Hz), 6.82 (1H, dd, H B , / B A = 16.5 Hz, / B P = 15 Hz), 7.09 (6H, m), 7.52 (4H, m); 8 (C6D6, 162.2 MHz, 31p{lH} NMR): -11.7 (s). Anal, calcd. for C20H21P: C 82.17, H 7.24; found: C 82.37, H 7.30. (£)-1,3-Butadienyl-1 -dimethylphosphine 80a According to general procedure 3,55a (150 mg, 0.48 mmol) was reacted with Me 2 PCl (47 mg, 0.48 mmol) to give, after workup, a colorless oil 80a (74 mg, 81%); IR (CH 2C1 2): 1620, 1578, 1430,1294,1007, 943 and 904 cm" 1; 8 (C6D 6,400 MHz, l H NMR): 0.87 (6H, d, PMeo. / H P = 3 Hz), 4.93 (1H, ddd, H E , / E C = 10 Hz, / E D = 1.5 Hz, / E B = 1 Hz), 5.04 (1H, ddd, H D , / D C = 17 Hz, / D E = 1.5 Hz, / D B = 1 Hz), 5.93 (1H, ddd, H A , / A B = 16.5 189 Hz, Z A P = 12 Hz, / A C = 1 Hz), 6.27 (1H, dddd, He, JCD = 17 Hz, / C B = 10 Hz, JQE = 10 Hz, JCA = 1 Hz), 6.41 (1H, ddddd, H B , / B A = 16.5 Hz, / B P = 10.5 Hz, 7 B C = 10 Hz, / B D = / B E = 1 Hz); 8 (C6D6,162.2 MHz, 31p{lH} NMR): -50.8 (s); mle (relative intensity): 43 (30.3), 44 (49.5), 53 (19.1), 57 (76.5), 59 (22.4), 69 (40.9), 97 (67.8), 99 (100), 113 (79.0) and 114 (M+,95.5). Exact Mass calcd. for CoHiiP: 114.0598; found: 114.0597. (E,£)-(4-Methoxy-1,3-butadienyl)-1 -dimethylphosphine 80b According to general procedure 3,55b (150 mg, 0.44 mmol) was reacted with Me2PCl (43 mg, 0.44 mmol) to give, after workup, a colorless oil 80b (65 mg, 77%); IR (CH2CI2): 1635, 1265, 1228, 1146, 979, 940 and 907 cm-1; 8 (QDg, 400 MHz, lH NMR): 0.97 (6H, d, PMS2, / H P = 3.5 Hz), 3.13 (3H, s, OMe). 5.48 (1H, dd, He, / C D = 12.5 Hz, / C B =10.5 Hz), 5.72 (1H, dd, H A , / A B = 16 Hz, Z A P = 8 Hz), 6.37 (1H, d, H D , / D C = 12.5 Hz), 6.54 (1H, ddd, H B , JBA = 16 Hz, 7 B P = 13 Hz, / B C = 10.5 Hz); 8 (C6D6, 121.5 MHz, 31p{lH} NMR): -50.4 (s); mle (relative intensity): 97 (27.6), 99 (25.0), 113 (100), 114 (25.4), 129 (16.3) and 144 (M+, 62.3). Exact Mass calcd. for C7H13OP: 144.0704; found: 144.0702. 190 (E,Z)-(4-Methoxy-1,3-butadienyl)-1 -dimemylphosphine 80c According to general procedure 3,55c (150 mg, 0.44 mmol) was reacted with Me2PCl (43 mg, 0.44 mmol) to give, after workup, a colorless oil 80c (67 mg, 79%); IR (CH2CI2): 1640, 1497, 1390,1279, 1264, 1086,977, 940 and 903 cm- 1; 8 ( C ^ , 400 MHz, J H NMR): 0.93 (6H, d, P M £ 2 , / H P = 2.5 Hz), 3.04 (3H, s, OMe), 5.11 (1H, ddd, He, JCB = 10.5 Hz, JQD = 6 Hz, 7 C A = 0.75 Hz), 5.51 (1H, ddd, H D , / D C = 6 Hz, 7 D B = 1 Hz, / D A = 0.75 Hz), 5.92 (1H, dddd, H A , / A B = 16.5 Hz, / A p = 11 Hz, / A C = JAD = 0.75 Hz), 7.18 (1H, dddd, H B , / B A = 16.5 Hz, / B P = 12 Hz, / B C = 10.5 Hz, / B D = 1 Hz); 8 (Cf3D6, 162.2 MHz, 31p{lH} NMR): -50.2 (s); mle (relative intensity): 41 (19.8), 57 (15.4), 97 (14.6), 113 (100) and 144 (M+,12.4). Exact Mass calcd. for C 7 H 1 3 O P : 144.0704; found: 144.0705. (E)-[2-(l -Cyclohexen-1 -yl)ethenyl]-1 -dimethylphosphine 80d According to general procedure 3,55d (150 mg, 0.41 mmol) was reacted with Me2PCl (40 mg, 0.41 mmol) to give, after workup, a colorless oil 80d (95 mg, 82%); IR (film): 1635, 1429, 971, 962, 939 and 905 cm" 1 ; 8 (C6D 6 , 400 MHz, ! H NMR): 0.98 (6H, d, 191 PM£2, / H P = 3 Hz), 1.45 (4H, m), 1.92 (4H, m), 5.65 (1H, m, He), 5.90 (1H, dd, H A , / A B = 17 Hz, Z A P = 9 Hz), 6.61 (1H, dd, H B , / B A = 17 Hz, / B p = 13 Hz); 8 (QD6, 32.4 MHz, 31p{lH} NMR): -50.7 (s); m/e (relative intensity): 79 (41.7), 105 (18.4), 125 (21.7), 139 (86.4), 140 (58.0), 153 (25.2), 167 (100) and 168 (M+, 99.0). Exact Mass calcd. for C10H17P: 168.1075; found: 168.1068. (£,£)-(4-Methoxy-1,3-butadienyl)-1 -diisopropylphosphine 81b To a stirred solution of 55b (200 mg, 0.58 mmol) in 5 mL of toluene was added i-PT2PC1 (90 mg, 0.58 mmol). The solution was then transferred to a reactor bomb and heated at 80°C, in the dark, for 18 h. On cooling the mixture to room temperature, a white crystalline material deposited (Cp2ZrCl2) from the pale yellow (initially bright yellow) solution. The mixture was then diluted with hexanes and filtered through basic alumina to give a colorless oil 89b (98 mg, 83%); IR (film): 1636, 1462, 1226, 1147, 982 and 802 cm-l; 5 (C6D 6 , 400 MHz, l H NMR): 1.08 (12H, m, PCHMS2), 1-70 (2H, m, P C H M e 2 ) , 3.05 (3H, s, OMe). 5.56 (1H, dd, He, / C D = 12.5 Hz, / C B = 10 Hz), 5.74 (1H, dd, H A , / A B = 16.5 Hz, Z A P = 4.5 Hz), 6.38 (1H, d, H D , Z D c = 12.5 Hz), 6.73 (1H, ddd, H B , Z B A = 16.5 Hz, Z B P = 13.5 Hz, Z B C = 10 Hz); 8 (C^D6, 121.5 MHz, 31p{ lH} NMR): 5.3 (s); m/e (relative intensity): 41 (45.2), 83 (28.2), 85 (75.8), 99 (19.0), 115 (59.1), 169 (100) and 200 (M+, 38.1). Exact Mass calcd. for C n H 2 i O P : 200.1330; found; 200.1323. 192 When the above reaction was performed in a more concentrated solution of 55b (250 mg, 0.74 mmol) and 1 equiv 1-PT2PCI dissolved in 2 mL of toluene, a 2:1 mixture of rotamers was formed. In this mixture, the major component has the * H and 3 1P{ *H} NMR data described above. The lH and 3 1P{ !H} NMR data for the minor component, taken from spectra of the 2:1 mixture, were as follows; 8 (C6D6, 400 MHz, * H NMR): 1.11 (12H, m, PCHMe2), 1.70 (2H, m, PCHMe 2 ) , 3.07 (3H, s, OMe). 5.54 (1H, dd, He, JCD = 12.5 Hz, JQB = 10 Hz), 5.90 (1H, dd, H A , JAB = 16.5 Hz, 7AP = 3 Hz), 6.34 (1H, d, H D , 7 D C = 12.5 Hz), 6.70 (1H, ddd, H B , / B A = 16.5 Hz, / B P = 12.5 Hz, / B C = 10 Hz); 8 (CeD6, 121.5 MHz, 31p{lH} NMR): -9.00 (s) (£ ) - [2- (1 -Cyclohexen-1 -yl)ethenyl] -1 -diisopropylphosphine 81d The preparation of 81d was identical to that described above for 81b. In this case, 55d (300 mg, 0.82 mmol) and 1 equiv j'-Pr2PCl were dissolved in 5 mL of toluene and heated at 80°C for 18 h. After workup, a colorless oil 81d (170 mg, 92%) was isolated; IR (film): 2828, 2864, 1635, 1577, 1460, 1381, 1362, 926 and 785 cm" 1 ; 8 ( C 7 D 8 , 400 MHz, lH NMR): 1.06 (12H, m, PCHMfi2), L41 (2H, m), 1.50 (2H, m), 1.70 (2H, m, P C H M e 2 ) , 1.93 (2H, m), 2.07 (2H, m), 5.65 (1H, m, H C ) , 5.82 (1H, ddd, H A , / A B = 16.5 Hz, / A P = 3.5 Hz, / A C = 0.75 Hz), 6.86 (1H, dd, H B , / B A = 16.5 Hz, / B P = 14.5 Hz); 8 ( C 7 D 8 , 121.5 MHz, 31p{lH} NMR): 4.8 (s); mle (relative intensity): 43 (41.4), 79 (30.8), 111 (21.1), 139 H A He 193 (100), 181 (75.7), 182 (67.6) and 224 (M+, 58.8). Exact Mass calcd. for C 1 4 H 2 5 P : 224.1694; found; 224.1698. As observed for 81b, when the reaction was performed in a more concentrated solution of 55d (250 mg 0.69 mmol) and 1 equiv /-Pr 2PCl in 2 mL of toluene a 2:1 mixture of rotamers was observed by J H and 3 1 P{ 1 H} NMR. The *H and 3lp{lH} N M R data (taken from the spectra of the 2:1 mixture) for the minor isomer were; 8 (C^Dg, 400 MHz, * H NMR): 1.12 (12H, m, PCHMe?). 1.40 (2H, m), 1.48 (2H, m), 1.71 (2H, m, PCHMe 2 ) , 1.91 (2H, m), 2.07 (2H, m), 5.62 (1H, m, He), 6.08 (1H, ddd, H A , / A B = 16.5 Hz, / A p = 3.5 Hz, / A C = 0.75 Hz), 6.84 (1H, dd, H B , / B A = 16.5 Hz, / B p = 13 Hz); 8 (C6D 6 , 121.5 MHz, 31p{lH}NMR): -9.66 (s). 6.4.4 Preparation of 1,3-Dienylboranes. General Procedure 4: Preparation of Diphenylboron 1,3-dienes 87a-d To a stirred solution, in the dark, of the appropriate (Zi)-l-chlorobis(rj 5 -cyclopentadienylzirconium(TV) 1,3-diene 55a-d in 1 mL of toluene, at room temperature, was added Ph 2 BBr (1 equiv). An immediate color change from yellow (or orange in the case of 55a) to colorless was observed on addition of the neat Ph 2BBr; this was closely followed by formation of a white slurry (precipitation of Cp2ZrCl(Br)). The reaction was diluted with hexanes, filtered through basic alumina, and evaporated to give the product as a white solid or colorless oil. 194 (E)-1,3-Butadienyl-1 -diphenylborane 87a As outlined in general procedure 4, 55a (150 mg, 0.48 mmol) was reacted with Ph2BBr (119 mg, 0.48 mmol) at room temperature, in the dark. Workup provided, as a colorless oil, 87a (84 mg, 82%); IR (film): 1620, 1593, 1570, 1433, 1273, 1198, 1018, 919, 750 and 695 cm-l; 5 (CDCI3, 400 MHz, *H NMR): 5.46 (1H, dd, H E , JEC = 10 Hz, / E D = 1.75 Hz), 5.52 (1H, dd, H D , JDC = 17 Hz, / D E = 1.75 Hz), 6.70 (1H, ddd, He, JCD = 17 Hz, JQB = 10 Hz, JQE = 10 Hz), 6.98 (1H, dd, H B , JBA = 17 Hz, 7 B C = 10 Hz), 7.08 (1H, d, H A , JAB = 17 Hz), 7.47 (2H, m), 7.56 (4H, m), 7.75 (4H, m); m/e (relative intensity): 54 (21.8), 84 (31.2), 87 (24.7), 89 (32.3), 103 (20.1), 113 (49.3), 114 (40.1), 126 (36.1), 127 (29.9), 128 (52.6), 139 (57.0), 140 (100), 163 (21.6) and 218 (M+, 37.3). Exact Mass calcd. for C i e H i s ^ B : 218.1267; found: 218.1269. (E,E)-(4-Methoxy-1,3-butadienyl)-1 -diphenylborane 87b As oudined in general procedure 4, 55 b (150 mg, 0.44 mmol) was reacted with Ph2BBr (108 mg, 0.44 mmol) at room temperature, in the dark. Workup provided, as a 195 colorless oil, 87b (92 mg, 84 %); IR (film): 1602, 1438, 1328, 1301, 1025, 970, 748 and 697 cm-1; 5 (CDC1 3, 400 MHz, * H NMR): 3.71 (3H, s, OMe). 5.93 (1H, dd, H c , JCD = 13 Hz, / C B =10 Hz), 6.88 (1H, d, H A , JAB = 17 Hz), 6.89 (1H, d, H D , / D C = 13 Hz), 7.04 (1H, dd, H B , JBA = 17 Hz, JBC = 10 Hz), 7.41-7.53 ( 6 H , m), 7.70 ( 4 H , m); mle (relative intensity): 39 (100), 41 (83.6), 51 (42.3), 69 (75.8), 84 (93.5), 105 (27.5), 115 (47.8), 117 (36.0), 119 (51.0), 128 (48.7), 129 (70.4), 154 (32.3), 160 (41.1), 182 (24.3), 233 (12.2) and 248 (M+, 1.6). Exact Mass calcd. for C 1 7 H 1 7 I I B O : 248.1373; found: 248.1379. (E,Z)-(4-Methoxy-1,3-butadienyl)- 1-diphenylborane 87c As outlined in general procedure 4, 55c (150 mg, 0.44 mmol) was reacted with Ph2BBr (108 mg, 0.44 mmol) at room temperature, in the dark. Workup provided, as a colorless oil, 87c (88 mg, 80 %); IR (film): 1602, 1440, 1349, 1274, 1093, 1027, 970, 749 and 701 cm-1; 5 ( C ^ , 400 MHz, l H NMR): 2.90 (3H, s, OMe). 5.44 (1H, ddd, H e , / C B = 11 Hz, / C D = 6 Hz, JCA = 0.75 Hz), 5.64 (1H, ddd, H D , / D C = 6 Hz, / D B = 1 Hz, / D A = 0.75 Hz), 7.14 (1H, ddd, H A , JAB = 17 Hz, / A C = JAD = 0.75 Hz), 7.91 (1H, ddd, H B , JBA = 17 Hz, 7 B C = 11 HZ, / B D = 1 Hz), 7.30 (6H, m), 7.82 (4H, m); mle (relative intensity): 39 (100), 41 (83.4), 51 (36.5), 69 (83.1), 84 (82.9), 115 (43.0), 117 (29.7), 119 (41.4), 128 (42.8), 129 (59.1), 160 (31.4), 233 (10.0) and 248 (M+,1.0). Exact Mass calcd. for C17H17HBO: 248.1373; found: 248.1382. H A O M e 196 (£)-[2-( 1-Cyclohexen-1 -yl)ethenyl]-1 -diphenylborane 87d As outlined in general procedure 4, 55 d (150 mg, 0.41 mmol) was reacted with Ph2BBr (101 mg, 0.41 mmol) at room temperature, in the dark. Workup provided, as a white solid, 87d (99 mg, 88 %); IR (Nujol): 1621, 1593, 1573, 1458, 1376, 1234, 1007, 892, 755 and 697 cm-1; 5 (C6D 6 , 400 MHz, l H NMR): 1.39 (2H, m), 1.49 (2H, m), 1.87 (2H, m), 2.22 (2H, m), 5.67 (1H, m, He), 7.05 (1H, d, H A , JAB = 18 Hz), 7.19 (1H, d, H B , / B A = 18 Hz), 7.30 (6H, m), 7.83 (4H, m); mle (relative intensity): 77 (43.0), 78 (47.9), 79 (75.9), 89 (33.3), 93 (51.3), 103 (33.8), 108 (28.6), 113 (47.7), 115 (31.4), 126 (33.2), 137 (24.9), 141 (21.8), 153 (21.9), 154 (21.6), 163 (63.0), 165 (100), 182 (63.0), 191 (32.1), 192 (27.7), 194 (43.7), 204 (23.1) and 272 (M+, 55.3). Exact Mass calcd. for C 2 o H 2 i u B : 272.1739; found: 272.1738. 197 6.4.5 Preparation of l-(Phenylseleno)- and l-(Phenylthio)-l,3-Dienes. To a stirred solution of the appropriate ( £ ) - l - c h l o r o b i s ( r | 5 -cyclopentadienylzirconium(TV) 1,3-diene 55a-d in 1 mL of toluene, in the dark at -20°C, was added 1 equiv of ArSeX. ArSeX = phenylselenenyl chloride (PhSeCl, added as a solution in 0.5 mL of toluene), diphenyldiselenide (Ph2Se2, added as a solution in 0.5 mL of toluene), 7V-(phenylseleno)phthatimide (7V-PSP, added as a solid), 7Y-(phenylseleno)phthalimide-d5 (TV-PSP-as) orN-(4-cMorophenylseleno)phthalimide (7V-C1PSP). All reactions were complete within 5 min at -20°C. The initial yellow (or orange in the case of 55a) color of the zirconium 1,3 diene changed to colorless or pale yellow on addition of ArSeX. Workup of the reaction involved dilution with hexanes, resulting in precipitation of the zirconium by-product, and filtration through basic alumina. Solvent evaporation yielded the desired products as colorless to pale yellow oils. Identical products were obtained with use of either PhSeCl, Ph2Se2 or /V-PSP. However, when TV-PS P was employed, the yield and ease of separation of the required products was facilitated. (£)-1 -(Phenylseleno)-1,3-butadiene 88a General Procedure 5: Preparation of 1-Arylseleno 1,3-Dienes 198 As outlined in general procedure 5, 55a (75 mg, 0.24 mmol) was reacted with /V-PSP (73 mg, 0.24 mmol) to yield a pale yellow oil 88a (45 mg, 90%); IR (film): 3074, 3059, 3022, 2997, 1619, 1579, 1476, 1215, 996, 735 and 690 cm-l; A m a x (hexane): 278 nm (e 16,900); 8 ( C 6 D 6 , 400 MHz, l H NMR): 4.83 (1H, dd, H E , JEC = 10 Hz, / E D = 1-75 Hz), 4.87 (1H, dd, H D , / D C = 17 Hz, / D E = 1.75 Hz), 6.10 (1H, ddd, H c , / C D = 17 Hz, JCB = ^ C E = 10 Hz), 6.39 (1H, dd, H B , / B A = 15.5 Hz, / B C = 10 Hz), 6.48 (1H, d, H A , 7 A B = 15.5 Hz, / A Se = 15.5 Hz), 6.95 (3H, m), 7.38 (2H, m); 8 (CDC1 3, 76.3 MHz, 7?Se NMR): 379 (s). Anal, calcd. for CioHioSe: C 57.43, H 4.82; found: C 57.10, H 4.86. (E,E)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene 88b As outlined in general procedure 5,55b (75 mg, 0.22 mmol) was reacted with /V-PSP (67 mg, 0.22 mmol) to yield a pale yellow oil 88b (49 mg, 92%); IR (film): 3054, 3020, 2935, 2837, 1633, 1578, 1474, 1438, 1220, 1144, 966, 735, 689 and 626 cm-l; xm a x (hexane): 250 nm (e 14,000), 264 nm (e 13,800) and 268 nm (e 13,900); 8 (CD 2 C1 2 , 400 MHz, l H NMR): 3.60 (3H, s, OMe). 5.64 (1H, dd, H e , / C D = 12.5 Hz, / C B = 10.5 Hz), 6.39 (1H, d, H A , / A B = 15 Hz, / A S e = 14.5 Hz), 6.55 (1H, ddd, H B , / B A = 15 Hz, / B C = 10.5 Hz, / B D = 0.75 Hz, / B S e = 11 Hz), 6.65 (1H, d, H D , / D C = 12.5 Hz), 7.23-7.27 (3H, m), 7.43 (2H, m); 8 (CDCI3,76.3 MHz, ??Se NMR): 367 (s). Anal, calcd. for C n H i 2 O S e : C 55.24, H 5.06; found: C 55.44, H 5.04. 199 (E,Z)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene 88c PhSe H, D As outlined in general procedure 5, 55c (75 mg, 0.22 mmol) was reacted with N-PSP (67 mg, 0.22 mmol) to yield a pale yellow oil 88c (47 mg, 90%); IR (film): 3054, 2928, 2837, 1635, 1573, 1475, 1433, 1219, 1107,926, 732 and 690 cm-1; XMAX (hexane): 270 nm (e 15,900); 8 ( C D 2 C 1 2 , 400 MHz, ! H NMR): 3.66 (3H, s, OMe). 5.11 (1H, ddd, H c , JQB = 10.5 Hz, JCD = 6 HZ, / C A = 0.5 Hz), 5.96 (1H, ddd, H D , JDC = 6 Hz, / D B = 1 Hz, / D A = 0.5 Hz), 6.52 (1H, ddd, H A , / A B = 15.5 Hz, / A C = / A D = 0.5 Hz, / A S e = 15.5 Hz), 6.89 (1H, ddd, / B A = 15.5 Hz, / B c = 10.5 Hz, / B D = 1 Hz, / B S e = 10 Hz), 7.27 (3H, m), 7.46 (2H, m); 8 (CDC1 3 , 76.3 MHz, 7?Se NMR): 374 (s). Anal, calcd. for C n H i 2 O S e : C 55.24, H 5.06; found: C 55.28, H 5.00. (£)-1 -Phenylseleno- [2- (1 -cyclohexen-1 -yl)ethene] 88d As outlined in general procedure 5,55d (75 mg, 0.21 mmol) was reacted with N-PSP (64 mg, 0.21 mmol) to yield a pale yellow oil 88d (55 mg, 95%); IR (film): 3034, 2928, 2854, 2830, 1630, 1577, 1476, 1437, 949, 740, 690 and 668 cm" 1; A m a x (hexane): 280 nm H A H C 200 (e 15,500), 270 nm (e 14,900) and 284 nm (e 15,000); 8 (CD 2 Cl2, 400 MHz, * H NMR): 1.39 (4H, m), 1.88 (4H, m), 5.48 (1H, m, H e ) , 6.48 (1H, dd, H A , JAB = 15.5 Hz, JAC = 0.75 Hz, / A s e = 15.5 Hz), 6.65 (1H, d, H B , JBA = 15.5 Hz, / B s e = 10 Hz), 6.95-7.01 (3H, m), 7.48 (2H, m); 8 (CDCI3, 76.3 MHz, 7 7 S e NMR): 369 (s). Anal, calcd. for C i 4 H 1 6 S e : C 63.88, H 6.13; found: C 64.13, H 6.17. General Procedure 7: Preparation of l-(phenylthio)-1,3-dienes 89a-d To a stirred solution, in the dark, of the appropriate (E) - l -chlorobis(r i 5 -cyclopentadienylzirconium(IV) 1,3-diene 55a-d in 2 mL of toluene, was added 1 equiv of 7Y-(phenylthio)phthalimide (7V-PTP, added as a solid). The mixture was then heated in a reactor bomb at 80°C for 2 h. The initial yellow (or orange in the case of 55a) color of the zirconium 1,3-diene changed to an orange-brown slurry. Partial evaporation of the toluene, dilution with hexanes, and filtration through basic alumina yielded the desired products as colorless to pale yellow oils. (£)-1 -(Phenylthio)-1,3-butadiene 89a 201 As outlined in general procedure 7,55a (250 mg, 0.81 mmol) was reacted with 7V-PTP (206 mg, 0.81 mmol) to yield a colorless oil 89a (39 mg, 30%); IR (film): 3062,3020,1621, 1583, 1478, 996, 743 and 691 cm-l; xmax (hexane): 288 nm (e 7,000), 282 nm (e 6,200), 294 nm (e 6,300); 8 (C6D 6 , 400 MHz, l H NMR): 4.81 (1H, dd, H E , / E D = 10 Hz, JED = 1-75 Hz), 4.90 (1H, dd, H D , / D C = 16.5 Hz, / D E = 1-75 Hz), 6.13 (1H, ddd, H c , JQD = 16.5 Hz, / C B = 10.5 Hz, / C E = 10 Hz), 6.19 (1H, d, H A , JAB = 15 Hz), 6.29 (1H, dd, H B , JBA = 15 Hz, JBC = 10.5 Hz), 6.95 (3H, m), 7.24 (2H, m); m/e (relative intensity): 51 (15.6), 85 (100), 128 (24.2), 129 (58.2) and 162 (M+, 59.0). Exact Mass calcd. for C I O H I Q S : 162.0503; found: 162.0501. (E,E)-l-(Phenylthio)-4-methoxy-l,3-butadiene 89b OMe As outlined in general procedure 7, 55b (250 mg, 0.74 mmol) was reacted with /V-PTP (188 mg, 0.74 mmol) to yield a pale yellow oil 88b (42 mg, 30%); IR (film): 3113, 2935, 2828, 1634, 1578, 1479, 1229, 1157, 1118, 966, 740 and 690 cm-l; ^ m a x (hexane): 290 nm (e 13,000); 8 (CDC1 3, 400 MHz, l H NMR): 3.66 (3H, s, OMe). 5.74 (1H, dd, He, JCD = 12.5 Hz, JCB = 10.5 Hz), 6.21 (1H, d, H A , JAB = 14.5 Hz), 6.50 (1H, ddd, H B , JBA = 14.5 Hz, JBC = 10.5 Hz), 6.74 (1H, d, H D , JDC = 12.5 Hz), 7.27 (1H, m), 7.35-7.42 (4H, m); m/e (relative intensity): 39 (19.1), 115 (46.5), 116 (31.9), 147 (33.8), 161 (32.7) and 192 (M+, 100). Exact Mass calcd. for C11H12OS: 192.0609; found: 192.0603. 202 (EZ)-1 -(Phenylthio)-4-methoxy-1,3-butadiene 89c PhS H A OMe As outlined in general procedure 7,55c (250 mg, 0.74 mmol) was reacted with 7Y-PTP (188 mg, 0.74 mmol) to yield a colorless oil 89c (55 mg, 39%); IR (film): 2928,2830, 1631, 1579,1476, 1228, 1115,964,739 and 692 cm-1; X m a x (hexane): 298 nm (e 15,400), 296 nm (e 15,300), 306 nm (e 14,300); 8 (CDC1 3, 400 MHz, * H NMR): 3.72 ( 3 H , s, OMe). 5.23 (1H, ddd, H C , JCE = 11 Hz, JQD = 6 Hz, / C A = 0.75 Hz), 6.01 (1H, ddd, H D , / D C = 6 Hz, / D B = 1 Hz, / D A = 0.75 Hz), 6.32 (1H, ddd, H A , / A B = 15 Hz, J A C = / A D = 0.75 Hz), 6.87 (1H, ddd, H B , / B A = 15 Hz, / B c = H Hz, / B D = 1 Hz), 7.24 (1H, m), 7.35 ( 4 H , m); mle (relative intensity): 39 (19.6), 109 (31.6), 115 (51.8), 116 (32.7), 147 (34.8), 161 (33.7) and 192 (M+, 100). Exact Mass calcd. for C 1 1 H 1 2 O S : 192.0609; found: 192.0608. (£)-1 -Phenylthio-[2-( 1 -cyclohexen-1 -yl)ethene] 89d H A H c As oudined in general procedure 7, 55d (250 mg, 0.69 mmol) was reacted with N-PTP (175 mg, 0.69 mmol) to yield a pale yellow oil 89d (38 mg, 25%); IR (film): 3027, 2928, 2858, 1632, 1582, 1532, 1478, 949, 739 and 689 cm- 1 ; Xmax (hexane): 290 nm 203 (e-12,000), 294 nm (e 11,500) and 284 nm (e 11,400); 8 (CDCI3,400 MHz, * H NMR): 1.61 (2H, m), 1.71 (2H, m), 2.18 (4H, m), 5.77 (1H, m, He), 6.24 (1H, dd, H A , JAB = 15.5 Hz, J A C = 0.75 Hz), 6.46 (1H, d, H B , / B A = 15.5 Hz), 7.21 (1H, m), 7.33 (4H, m). Anal, calcd. for C i 4 H i 6 S : C 77.73, H 7.45; found: C 77.50, H 7.40. 6.4.6 Preparation of Heterosubstituted Imines and 1-Azadienes: Transfer of Zirconium to Selenium and Phosphorus (E)-1 - (Phenylseleno)tenzenemethanimine 91 To a stirred solution of (benzenemethaniminato)chlorobis(rj 5-cyclopentadienyl)zirconium(IV) 62 (150 mg, 0.42 mmol) in 1 mL of toluene, at room temperature, was added a solution (in 2 mL of toluene) of phenylselenenyl chloride (PhSeCl) (80 mg, 0.42 mmol). On addition, the deep red color of the PhSeCl was immediately discharged and the initially bright yellow solution changed to pale yellow. Shortly after the addition was complete, a pale yellow slurry formed. Dilution with hexanes, followed by filtration through Celite®, gave a pale yellow oil 91 (80 mg, 73%); 8 ( C 6 D 6 , 400 MHz, *H NMR): 7.00 (1H, m), 7.00-7.05 (3H, m), 7.10 (2H, m), 7.46 (2H, m), 7.64 (2H, m), 8.34 (1H, s, H A , /ASe = 28 Hz); 8 (CDCI3, 76.3 MHz, 7?Se NMR): 897 (s); mle (relative 204 intensity): 39 (32.5), 50 (59.5), 51 (72.4), 77 (100), 83 (48.0), 85 (32.2), 103 (41.4) and 261 (M+ 15.8). Exact Mass calcd. for C n H n N S O S e : 261.0057; found: 261.0056. Preparation of 92 was identical to that described above for 91. Chlorobis(Tj5-cyclopentadienyl)(2-methylbenzenememanmiinato)zirconium(IV) 63 (150 mg, 0.40 mmol) was reacted with PhSeCl (77 mg, 0.40 mmol) to produce, after workup, a pale yellow oil 92 (82 mg, 75%); 8 ( C 6 D 6 , 400 MHz, * H NMR): 2.07 (3H, s, CH3), 6.83 (1H, m), 6.98 (2H, m), 7.01 (1H, m), 7.09 (2H, m), 7.65 (2H, m), 7.82 (1H, m), 8.74 (1H, s, / A Se = 29.5 Hz); 8 (CDCI3, 76.3 MHz, 77se NMR): 903 (s); m/e (relative intensity): 39 (56.7), 50 (86.2), 51 (46.1) , 63 (31.3), 65 (48.5), 76 (100), 77 (50.4), 91 (68.9), 103 (43.2), 104 (60.4), 117 (47.2) , 118 (58.8), 119 (30.2), 147 (47.4) and 275 (M+, 1.5). Exact Mass calcd. for C i 4 H i 3 N 8 0 S e : 275.0213; found: 275.0210. (E)-1 -(Phenylseleno)-3-methyl-1,3-azadiene 93 H 3 C (£)-1 -(phenylseleno)-2-methylbenzenemethanimine 92 PhSe Preparation of 93 was identical to that described above for 91. Chlorobis(rj5-cyclopentadienyl)[2-(2-propen-l-yl)methanimmato]zirconium(rV) 68 (150 mg, 0.46 mmol) 205 was reacted with PhSeCl (88 mg, 0.46 mmol) to yield, after workup, a yellow oil 93 (75 mg, 72%); 8 (C6D6, 400 MHz, lH NMR): 1.87 (3H, s, CH3), 4.77 (1H, m, H B ) , 5.10 (1H, m, H C ) , 6.69 (1H, m), 7.06 (2H, m), 7.59 (2H, m), 8.08 (1H, s, H A , JASe = 29 Hz); 8 (CDCI3, 76.3 MHz, 7 7 S e NMR): 882 (s); mle (relative intensity): 39 (100), 41 (72.5), 55 (46.0), 68 (75.0), 122 (81.3), 144 (18.8), 157 (25.0) and 225 (M+, 13.4). Exact Mass calcd. for CioHnNSOSe: 225.0056; found: 225.0055. (£ ,£) -1 -(Phenylseleno)-4-phenyl-1,3-azadiene 94 Preparation of 94 was as described above for 9 1 , except that, 7V-(phenylseleno)phthalimide (N-PSP) was used as the selenium transfer reagent. (E)-CUOTobis(Tj5-cyclopentamenyl)[2-(2-phe 69 (150 mg, 0.39 mmol) and N-PSP (117 mg, 0.39 mmol) were reacted at room temperature in the dark, to yield a pale yellow oil 94 (91 mg, 81%) on workup. It was evident from the J H and 7 7 S e N M R spectra that 94 was actually a mixture of two isomers; namely, a 5:1 mixture of geometric isomers about the C=N bond (as shown in the structures above). Evidence that the major isomer was the (E,E)-isomer was obtained from J H nuclear Overhauser effect difference (NOEDIFF) spectroscopy; irradiation of H A of the major isomer, produced enhancement of the orf/jo-phenyl protons of the PhSe group and of proton He- Al l data presented were obtained by analysis of the mixture. Major isomer ; 8 (C6D6,400 MHz, *H NMR): 6.28 (1H, d, He, 7 CB = 16 Hz), 6.90 (1H, dd, H B , / B c = 16 Hz, / B A = 9 Hz), 6.96-7.13 (8H, m), 7.67 (2H, 206 m), 8.17 (1H, d, / A B = 9 HZ, /ASe = 28 Hz); 8 (C6D 6 , 76.3 MHz, 7 7 S e NMR): 859 (s); Minor isomer ; 8 ( C 6 D 6 , 400 MHz, ! H NMR): 6.37 (1H, d, H c , Jew = 1 6 ^ 6.79 (1H, dd, H B - , / B - c = 16 Hz, / B ' A ' = 9 Hz), 6.96-7.13 (8H, m), 7.82 (2H, m), 8.34 (1H, d, H A s JA'B' = 9 Hz); 8 (C6T>6, 76.3 MHz, 7 7 S e NMR): 801 (s). Mass spectra data for the mixture were; mle (relative intensity): 50 (58.7), 51 (46.0), 74 (32.5), 75 (27.4), 76 (68.5), 77 (68.8), 78 (57.3), 103 (55.4), 130 (100), 147 (33.4), 157 (29.1) and 287 (M+, 10.4). Exact Maw calcd. for CisHisNSOSe: 287.0213; found: 287.0211. (E,E)-l-(Phenylseleno)-4-ethoxy-l,3-azadiene 95 Preparation of 95 was as described above for 94. (E)-chlorobis(r| 5 -cyclopentamenyl)[2-(2-emoxyemenyl)memaniminato]zirconium(rV) 70 (150 mg, 0.42 mmol) was reacted with N-PSP (80 mg, 0.42 mmol) to yield, on workup, a yellow oil (74 mg, 69%). * H and 7 7 S e N M R spectra indicated that 95 was actually a rnixture of two isomers (—1.2:1). In this case, the use of * H NOEDIFF spectroscopy to determine the stereochemistry of the major component was not successful. However, the chemical shift of the 7 7 S e N M R resonance, and /ASe value for the major isomer indicate that it is likely the (E,E)-isomer. All data were determined by analysis of the mixture. Major isomer ; 8 (C6D6, 400 MHz, lH NMR): 0.91 (3H, t, / = 7 Hz), 3.28 (2H, q, / = 7 Hz), 5.83 (1H, dd, H B , / B C = 12.5 Hz, / B A = 9 Hz), 6.38 (1H, d, He, / C B = 12.5 Hz), 7.05 (1H, m), 7.21 (2H, m), 7.78 (2H, m), 8.07 (1H, d, H A , JAB = 9 Hz, /ASe = 28.5 Hz); 8 (CDC1 3, 76.3 MHz, 7 7 S e NMR): 893 (s); 207 Minor isomer ; 5 (QDo, 400 MHz, l H NMR): 0.91 (3H, t, / = 7 Hz), 3.22 (2H, q, / = 7 Hz), 5.64 (1H, dd, H B , JBC = 12.5 Hz, / B A = 9 Hz), 6.38 (1H, d, He, JCB = 12.5 Hz), 7.05 (1H, m), 7.17 (2H, m), 7.92 (2H, m), 8.12 (1H, d, H A , JAB = 9 Hz); 8 (CDC1 3, 76.3 MHz, 7 7 S e NMR): 819 (s). Mass spectra data for the mixture were; m/e (relative intensity): 56 (26.8), 82 (10.2), 84 (100), 147 (5.3) and 255 (M+, 4.4). Exact Mass calcd. for CnHi 3 NO80Se: 255.0162; found: 255.0155. (£) - l-(Diphenylphosphino)benzenemethanimine 98 To a stirred solution of 62 (150 mg, 0.42 mmol) in 1.5 mL of toluene was added PI12PCI (93 mg, 0.42 mmol). The yellow solution was then transferred to a reactor bomb and heated, in the dark, at 80°C for 1 h. On cooling to room temperature, a white crystalline material (Cp2ZrCl2) precipitated from a pale yellow solution. The mixture was diluted with hexanes and filtered through basic alumina to give, after evaporation of the solvent, a white solid 98 (100 mg, 83%); IR (Nujol): 3063, 3046, 1625, 1611, 1576, 1433, 1311, 1215, 1092, 1024, 844, 776, 743 and 696 cm-l; 5 ( C 6 D 6 , 400 MHz, l H NMR): 7.00-7.20 ( 9 H , m), 7.54-7.68 ( 6 H , m), 8.26 ( 1 H , d, H A , / A P = 21 Hz); 8 (C6D6, 121.5 MHz, 31p NMR): 49.9 (s). Ana/, calcd. for C19H16NP: C 78.88, H 5.57, N 4.84; found: C 79.12, H 5.70, N 4 . 8 1 . 208 (E)-1 -(Diphenylphosphmo)(2-mem^ 99 Preparation of 99 was identical to that described above for 98. Ph2PCl (88 mg, 0.40 mmol) and 63 (150 mg, 0.40 mmol) afforded, after workup, a pale yellow oil 99 (104 mg, 86%); IR (film): 3070, 3052, 3020, 1614, 1593, 1568, 1480, 1434, 1282, 1221, 1093, 1025, 807, 741 and 696 cm-l; 5 ( Q D ^ 400 MHz, l H NMR): 2.11 (3H, s, CH3), 6.83 (1H, m), 7.01 (1H, m), 7.03-7.15 (7H, m), 7.63 (4H, m), 8.03 (1H, m), 8.63 (1H, d, H A , JAP = 22 Hz); 8 (C6D 6, 121.5 MHz, 31p NMR): 51.9 (s); m/e (relative intensity): 91 (36.2), 107 (20.5), 108 (44.9), 117 (27.0), 118 (100), 183 (34.1), 288 (19.5) and 303 (M+, 10.0). Exact Mass calcd. for C20H18NP: 303.1177; found: 303.1183. (EyE)-1 -(Diphenylphosphino)-4-phenyl-1,3-azadiene 100 H A A P h 2 p — N ' y— Ph To a stirred solution of 69 (150 mg, 0.39 mmol) in 2 mL of toluene, at room temperature, was added Ph2PCl (86 mg, 0.39 mmol). There was an immediate color change from orange to pale yellow, closely followed by precipitation of a white solid (Cp2ZrCl2). After stirring at room temperature for a further 30 min, the reaction was diluted with hexanes 209 and filtered through basic alumina. Evaporation of the solvent gave a pale yellow solid 100 (102 mg, 83%); IR (Nujol): 3052, 3035, 1601, 1585, 1434, 1146, 1102, 980, 747 and 695 cm- 1 ; 5 (CDC1 3, 400 MHz, ! H NMR): 6.90 (1H, dd, He, JCB = 16 Hz, / C H = 1-25 Hz), 7.05 (1H, dd, H B , JBC = 16 Hz, JBA = 8.5 Hz), 7.32-7.46 (9H, m), 7.48 (2H, m), 7.51 (4H, m), 8.07 (1H, dd, H A , JAP = 22 Hz, / A B = 8.5 Hz); 8 (C6D 6, 121.5 MHz, 3 1 P NMR): 49.9 (s); mle (relative intensity): 108 (39.9), 109 (30.6), 130 (33.5), 183 (60.1), 185 (25.5), 238 (32.2) and 315 (M+, 100). Exact Mass calcd. for C 2 i H i 8 N P : 315.1177; found: 315.1181 (E,E)-1 -(Diphenylphosphino)-4-ethoxy-1,3-azadiene 101 The preparation of 101 was identical to that described above for 100. PI12PCI (93 mg, 0.42 mmol) and 70 (150 mg, 0.42 mmol) were reacted to yield, after workup, a yellow oil 101 (93 mg, 78%); IR (film): 3055, 2977, 1638, 1619, 1479, 1435, 1321, 1207, 1093, 743 and 696 cm-1; 8 (C6D6, 400 MHz, l H NMR): 0.79 (3H, t, / = 7 Hz), 3.19 (2H, q, / = 7 Hz), 6.90 (1H, dd, H B , JBC = 13 Hz, / B A = 9 Hz), 7.30 (1H, d, He, JCB = 13 Hz), 8.07 (2H, m), 8.15 (4H, m), 8.74 (4H, m), 9.01 (1H, dd, H A , JAP = 23 Hz, / A B = 9 Hz); 8 ( Q D e , 121.5 MHz, 3 1 P NMR): 51.2 (s); mle (relative intensity): 39 (29.8), 77 (9.2), 105 (5.54), 125 (4.1), 183 (9.3), 210 (30.0), 238 (31.4), 254 (100) and 283 (M+ 2.5). Exact Mass calcd. for CnHigNOP: 283.1126; found: 283.1128. 210 ( £ , £ ) - l-(Diphenylphosphmo)-4-(d^emylamino)-1,3-azadiene 102 H A H B Ph2P N N M e , H ; The preparation of 102 was carried out as described above for 100. Ph2PCl (93 mg, 0.42 mmol) was added to a slurry of 71 (150 mg, 0.42 mmol) in 2 mL of toluene. After 5 min at room temperature the slurry had become homogeneous. Workup of the reaction mixture yielded a yellow oil 102 (87 mg, 73%); IR (film): 3055, 2907, 1629, 1588, 1564, 1388, 1109, 943, 792 and 696 cm-l; 5 ( C 6 D 6 , 400 MHz, l H NMR): 1.97 (6H, s, NMe?). 5.45 (1H, b dd, H B , / B C = 13 Hz, / B A = 9 Hz), 5.96 (1H, b d, He, / C B = 13 Hz), 7.07 (2H, m), 7.18 (4H, m), 7.88 (4H, m), 8.28 (1H, dd, H A , / A P = 9 Hz, / A B = 9 Hz); 8 (C6D6, 121.5 MHz, 31P NMR): 51.8 (b s); m/e (relative intensity): 42 (26.4), 56 (22.2), 97 (88.0), 108 (41.2), 109 (53.5), 154 (35.8), 162 (26.0), 183 (65.5), 185 (27.6), 201 (53.7), 205 (41.2), 222 (30.5), 238 (20.5) and 282 (M+, 100). Exact Mass calcd. for C17H19N2P: 282.1286; found: 282.1282. 211 6.5 Photochemical Isomerization of l-(Phenylseleno)- and l-(Phenylthio)-1,3-dienes. T h e r m a l Isomerization of l-(Phenylse!eno)-l,3-dienes and Diels-Alder Reactivity with Maleic Anhydride. 6.5.1 Photolysis of l-(Phenylseleno)-l,3-dienes. Photolysis of (£)-!-(phenylseleno)-1,3-butadiene 88a A solution of (E)-l-(phenylseleno)- 1,3-butadiene 88a (30 mg, 0.14 mmol) in 0.5 mL of CoT>6 was placed in a capped NMR tube under nitrogen. The pale yellow solution was then irradiated with fluorescent light for 2 h. * H and 7 7 Se NMR of the solution, after photolysis, indicated that isomerization of 88a had taken place to give a 2:1 mixture of E/Z isomers. Addition of (E)-l-(phenylseleno)-1,3-butadiene to the 2:1 E/Z mixture resulted in a change in this ratio, which was reestablished after a further 2 h irradiation with fluorescent light. Continued irradiation up to 24 h gave no change in the E/Z ratio. * H and 7 7 S e NMR data, taken from the spectrum of the mixture, of (Z)-l-(phenylseleno)-1,3-butadiene were; 5 (C^D^ 400 MHz, l H NMR): 5.04 (1H, dd, H E , / E C = 10 Hz, / E D = 1.75 Hz), 5.11 (1H, dd, H D , 7 D C = 17 Hz, / D E = 1.75 Hz), 6.35 (1H, dd, H B , JBA = 9 HZ, J B C = 10 Hz), 6.40 (1H, d, H A , JAB = 9 Hz), 6.71 (1H, ddd, He, JCD = 17 Hz, JCB = JCE = 10 Hz), 6.93 (2H, m), 7.33 (2H, m); 5 (CDC1 3, 76.3 MHz, 77se NMR): 341 (s). 212 Photolysis of (£,£)-l-(phenylseleno)-4-methoxy-l,3-butodiene 88b A solution of (£ ,£ ) - l - (phenylseleno) -4 -methoxy- 1,3-butadiene 88b (32 mg, 0.13 mmol) in 0.5 mL of CD2CI2 was photolyzed with fluorescent light for 1.5 h. * H and 7 7 Se NMR of the solution, after photolysis, indicated that isomerization of 88b had taken place to give a 41(±2) :13(±1) :36(±2) :10(±1) mixture of Z,E/Z,Z/E,E/E,Z isomers. These ratios were determined, from the *H NMR, by integration of the OMe resonances. That these were representative of the equilibrium composition of these isomers was determined by continuing the photolysis for a further 24 h, during which time the ratios did not change beyond those values stated above. When the equilibrium was disturbed by addition of (£,£)-l-(phenylseleno)-4-methoxy- 1,3-butadiene, further photolysis (~1.5 h) reestablished the equilibrium values. * H and 7 7 S e N M R data, taken from the spectrum of the mixture, were: (Z,£)-l-(phenylseleno)-4-methoxy- 1,3-butadiene; 8 (CD2CI2, 400 MHz, * H NMR): 3.62 (3H, s, OMe). 5.63 (1H, ddd, He, JCD = 12.5 Hz, / C B = 10.5 Hz, JCA = 0.75 Hz), 6.22 (1H, ddd, H A , / A B = 9 HZ, / A C = JAD = 0.75 Hz), 6.52 (1H, ddd, H B , / B C = 10.5 Hz, / B A = 9 HZ, / b d = 0.5 Hz), 6.78 (1H, d, H D , /px; = 12.5 Hz), 7.20-7.32 (3H, m), 7.42-7.51 (2H, m); 8 (CDCI3,76.3 MHz, 7 7 Se NMR): 310 (s); (Z^)-l-(phenylseleno)-4-methoxy-1,3-butadiene; 8 (CD 2 C1 2 , 400 MHz, l H NMR): 3.69 (3H, s, OMe), 5.31 (1H, ddd, H C , / C B = 11 Hz, JCD = 6.5 Hz, / C A = 1 Hz), 6.11 (1H, ddd, H D , / D C = 6.5 Hz, / D A = 1.5 Hz, / D B = 1 Hz), 6.34 (1H, ddd, H A , / A B = 9 Hz, / A D = 1.5 Hz, / A c = 1 Hz), 6.92 (1H, ddd, H B , / B C = 11 Hz, / B A = 9 Hz, / B D = 1 Hz), 7.20-7.32 (3H, m), 7.42-7.51 (2H, m); 8 (CDCI3, 76.3 MHz, 7 7 S e NMR): 323 (s). 213 Photolysis of (E,Z)-l-(phenylseleno)-4-methoxy-1,3-butadiene 88c A solution of (£ ,Z)- l - (phenylseleno)-4-methoxy-l ,3 -butadiene 88c (31 mg, 0.13 mmol) in 0.5 mL of CD2CI2 was photolyzed with fluorescent light for 1.5 h. By lH and 7 7 Se NMR, an isomeric mixture identical to that described above for the photolysis of 88b was observed. Preparation and photolysis of a 65:35 E/Z mixture of l-phenylseleno-[2-(l-cyclohexen-l- yl)ethene] 88d A solution of ( E ) - c h l o r o [ 2 - ( 1 - c y c l o h e x e n - 1 - y l - e t h e n y l ] b i s ( r j 5 -cyclopentadienyl)zirconium(rV) 55d (80 mg, 0.22 mmol) in 0.5 mL of C6E>6 was photolyzed with fluorescent light in a sealed (under nitrogen) 5 mm NMR tube for 19 h. The lH NMR indicated the formation of a 65:35 E/Z mixture of cMoro[2-(l-cyclohexen-l-yl-ethenyl]bis(T|5-cyclopentadienyl)zirconium(IV). The orange solution (initially yellow) was then reacted with /V-PSP (66 mg, 0.22 mmol) according to general procedure 5. Workup yielded a yellow oil (48 mg, 83%) which by lH N M R spectroscopy was identified as a 65:35 E/Z mixture of l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene] 88d. Photolysis of this mixture with fluorescent light, for up to 18 h, gave a 95:5 E/Z mixture of 88d. (£)-l-Phenylseleno-[2-(l-cyclohexen-l-yl)ethene] did not isomerize under the same photochemical conditions. (Z)-Chloro[2-(l-cyclohexen-l-yl-ethenyl]bis(ri5-cyclopentadienyl)zirconium(rV); 8 (C0D6, 65:35 E/Z 214 400 MHz, l H NMR): 1.54-1.71 (4H, m), 2.00 (2H, m), 2.16 (2H, m), 5.47 (1H, m, He), 5.98 (10H, s, Cp), 6.13 (1H, d, H A , JAB = 13 Hz), 7.24 (1H, d, H B , JBA = 13 Hz); (Z)-l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene]; 8 (CDC13, 400 MHz, lH NMR): 1.55-1.75 (4H, m), 2.14 (2H, m), 2.32 (2H, m), 5.80 (1H, m, He), 6.39 (2H, A B q , H A / H B ) , 7.25 -7.35 (3H, m), 7.56 (2H, m). 6.5.2 Mechanistic Studies on the Isomerization of l-(Pheny!seIeno)-l,3-dienes. Crossover Experiments, a Mechanistic Probe: Intramolecular vs. Intermolecular Process  N-(Phenylseleno)phthalimide-^s (TV-PSP-^s) N-(phenylseleno)phthalimide-£f5 was prepared according to literature procedure104-starting from benzene-d6 to yield white crystals (3.23 g, 64% over 4 steps). The following data were recorded for this compound; IR (Nujol): 2274,1774,1720,1343, 1280, 1066, 710 and 676 cm" 1; 8 (CDCI3,400 MHz, lH NMR): 7.73 (2H, m), 7.90 (2H, m). Anal, calcd. for C i 4 H 4 D 5 N S e : C 54.73, H 2.95, N 4.56; found: C 55.00, H 3.00, N 4.49. O O 215 A,-(4-Cmorophenylseleno)phmalimide (/V-C1PSP) O a o N-(4-chlorophenylseleno)phthalimide was prepared according to literature procedures 1 0 4 * 1 1 2 using bis(4-chlorophenyl)diselenide (2.5 g, 6.60 mmol) to a yield pale yellow microcrystalline material (2.87 g, 75%); IR (Nujol): 1775, 1725, 1344, 1277, 1064, 1011, 731 and 711 cm" 1; 8 (CDC13, 400 MHz, NMR): 7.31 (2H, m), 7.76 (2H, m), 7.81 (2H, m), 7.91 (2H, m). Anal, calcd. for C i 4 H 8 C l N S e : C 49.95, H 2.40, N 4.16; found: C 50.12, H 2.44, N 4.14. (£ ) - l-(phenylseleno)-1,3-butadiene-2-a' 88a-<ii As outlined in general procedure 5, ( £ ) - l , 3 - b u t a d i e n y l c h l o r o b i s ( r j 5 -cyclopentadienyl)zirconium(IV)-2-a'55a-di (75 mg, 0.24 mmol) was reacted with 7V-PSP (73 mg, 0.24 mmol) to yield a pale yellow oil 88a-di (43 mg, 85%); IR (film): 3075, 2985, 1617, 1578, 1475, 1215, 996, 737 and 690 cm" 1; 8 (CDCI3, 400 MHz, lR NMR): 5.06 (1H, dd, H E , JEC = 10 Hz, JED = 1.75 Hz), 5.13 (1H, dd, H D , JDC = 17 Hz, 7 DE = 1-75 Hz), 6.34 (1H, b dd, H A , JCD = 17 Hz, JQE = 10 Hz), 6.70 (1H, b t, H A , JAd = 2.5 Hz), 7.30 216 (3H, m), 7.51 (2H, m); mle (relative intensity): 51 (25.2), 77 (25.3), 78 (24.7), 129 (41.1), 130 (100), 131 (28.3), 134 (29.7) and 211 (M+, 25.4). Exact Mass calcd. for CioH92H80se: 211.0011; found: 211.0007. (E^)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene-2-d 88 W i As outlined in general procedure 5, (£,£)<Morobis(Ti5K;yclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(IV)-2-d 55b-rfi (75 mg, 0.22 mmol) was reacted with 7Y-PSP (67 mg, 0.22 mmol) to yield a pale yellow oil 88twzi (48 mg, 91%); IR (film): 3060, 2932, 2832, 1632, 1577, 1478, 1219, 1145, 968, 734 and 691 cm- 1 ; 8 (CDC1 3 , 400 MHz, lH NMR): 3.64 (3H, s, OMe). 5.64 (1H, b d, He, JCD = 12.5 Hz), 6.41 (1H, b t, H A , Jhd = 2.5 Hz), 6.66 (1H, d, H D , / D C = 12.5 Hz), 7.27 (3H, m), 7.48 (2H, m); mle (relative intensity): 51 (30.0), 77 (44.6), 78 (24.5), 116 (52.8), 117 (38.3), 145 (36.6), 146 (21.9), 157 (41.0), 160 (87.9), 161 (100) and 241 (M+, 71.7). Exact Mass calcd. for CnHi^HOSOSe: 241.0116; found: 241.0117. 217 (£,Z)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene-2-tf 8Sc-di PhSe H A O M e As outlined in general procedure 5, (£^)-chlorobis(rj5-cyclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(IV)-2-d55c-di (75 mg, 0.22 mmol) was reacted with iV-PSP (67 mg, 0.22 mmol) to yield a pale yellow oil 88c-di (44 mg, 83%); IR (film): 2935, 2830, 1628, 1577, 1476, 1437, 1213, 1109, 929, 736 and 688 cm-1; 8 (CDC1 3 , 400 MHz, l H NMR): 3.61 (3H, s, OMe). 5.06 (1H, b d, He, JQD = 6 Hz), 5.87 (1H, dd, H D , / DC = 6 Hz, 7 DA = 0.5 Hz), 6.46 (1H, b t, H A , JAd = 2.5 Hz), 7.22 (3H, m), 7.42 (2H, m); mle (relative intensity): 51 (21.0), 77 (38.1), 78 (32.3), 116 (42.6), 117 (25.5), 118 (24.2), 129 (38.1), 130 (34.6), 145 (28.6), 146 (16.3), 155 (19.1), 160 (74.8), 161 (100) and 241 ( M + , 54.9). Exact Mass calcd. for C i i H i i 2 H O 8 0 S e : 241.0116; found: 241.0119. (£)-l-Phenylseleno-[2-(l-cyclohexen-l-yl)ethene]-2-<i88d-<ii As outlined in general procedure 5, (E)-chloro[2-(l-cyclohexen-l-yl-ethenyl]bis(rj5-cyclopentadienyl)zirconium(IV)-2-rf 55d-rfi (75 mg, 0.21 mmol) was reacted with iV-PSP (64 mg, 0.21 mmol) to yield a pale yellow oil 88d-di (52 mg, 93%); IR (film): 1628, 1578, H A He 218 1477, 1438, 829, 733, 690 and 669 cm-l; 5 (CDCI3, 400 MHz, l H NMR): 1.62 (2H, m), 1.70 (2H, m), 2.17 (4H, m), 5.79 (1H, m, He), 6.51 (1H, b s), 7.25-7.34 (3H, m), 7.50 (2H, m); m/e (relative intensity): 51 (58.1), 65 (22.0), 77 (75.2), 78 (94.2), 80 (99.6), 106 (50.0), 141 (21.4), 142 (100), 143 (30.1), 156 (25.8), 184 (67.8), 186 (34.3), 188 (61.0) and 265 (M+, 54.4). Exact Mass calcd. for C u H ^ H S O S e : 265.0480; found: 265.0481. (£ ) - l-(Phenylseleno)-1,3-butadiene-o*5 888-0*5 As outlined in general procedure 5, (E ) - l , 3 -butadienylchlorobis (T| 5 -cyclopentadienyl)zirconium(rV) 55a (75 mg, 0.24 mmol) was reacted with 7V-PSP-o*5 (74 mg, 0.24 mmol) to yield a pale yellow oil 88a-o*5 (42 mg, 82%); IR (film): 2288, 2274, 1620, 1568, 1545, 1341, 1215, 993, 936, 900, 806 and 641 cm-l; 1 H N M R was identical to 88a with the absence of the aromatic resonances; m/e (relative intensity): 54 (41.9), 82 (37.3), 83 (38.0), 131 (28.0), 132 (37.1), 133 (100) and 215 (M+, 20.2). Exact Mass calcd. for CioHi 52H 580Se: 215.0261; found: 215.0264. 219 (£,E)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene- ds SSb-ds rf5-PhSe—^ H A H D OMe As outlined in general procedure 5, (E^)-chlorobis(r]5-cyclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(TV) 55b (75 mg, 0.22 mmol) was reacted with TV-PSP-ds (68 mg, 0.22 mmol) to yield a pale yellow oil 88b-rf5 (45 mg, 84%); IR (film): 2290, 2276, 1630, 1578, 1542, 1222, 1145, 965, 827 and 628 cm"l; l H N M R was identical to 88b with the absence of the aromatic resonances; m/e (relative intensity): 54 (25.4), 82 (38.9), 119 (29.9), 120 (32.4), 121 (23.8), 132 (24.8), 133 (22.5), 134 (35.1), 149 (25.2), 160 (25.8), 162 (50.5), 163 (54.8), 164 (34.8), 165 (100) and 245 (M+, 87.7). Exact Mass calcd. for C i i H 7 2 H 5 O 8 0 S e : 245.0367; found: 245.0362. (E,Z)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene-rfs 88c-a5 As outlined in general procedure 5, (E,Z)-cMorobis(Ti5-cyclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(TV) 55c (75 mg, 0.22 mmol) was reacted with /V-PSP-os (68 mg, 0.22 mmol) to yield a pale yellow oil 88c-05 (46 mg, 86%); IR (film): 2274, 1633, 1575, 1546,1227, 1146,962, 828 and 630 cm" 1; lH N M R was identical to 88c with the absence of H A OMe 220 the aromatic resonances; mle (relative intensity): 54 (23.7), 82 (36.7), 119 (28.3), 120 (32.5), 121 (38.3), 149 (22.4), 160 (24.9), 162 (50.4), 163 (55.1), 165 (100) and 245 (M+, 74.3). Exact Mass calcd. for C i i H ^ H s O S O S e : 245.0367; found: 245.0364. (£)-1 -Phenylseleno-[2-(l-cyclohexen-1 -yl)ethene]-d$ 88d-^5 As outlined in general procedure 5, (£)-chloro[2-(l-cyclohexen-l-yl-ethenyl]bis(ri 5-cyclopentamenyl)zirconium(rV) 55d (75 mg, 0.21 mmol) was reacted with iV-PSP-^5 (65 mg, 0.21 mmol) to yield a pale yellow oil 88d-rfs (51 mg, 91%); IR (film): 3027, 2991, 2928, 2274, 1630, 1578, 1544, 1435, 1339, 1022, 952, 764 and 639 cm" 1; lB. N M R was identical to 88d with the absence of the aromatic resonances; mle (relative intensity): 54 (30.5), 78 (44.8), 79 (100), 80 (21.7), 82 (36.9), 83 (40.9), 105 (41.3), 107 (25.7), 145 (36.9), 146 (65.6), 159 (19.5), 160 (19.9), 185 (27.4), 187 (54.8), 188 (45.2) and 269 (M+, 42.7). Exact Mass calcd. for Ci 4 Hn2H 5 8 0Se : 269.0731; found: 269.0736. H A H C 221 General Procedure 6: Crossover Experiments for Photochemical and Thermal Isomerization  Process. A known ratio (approximately 1:1) of l-(phenylseleno)-l,3-diene-^5 [or l-(4-chlorophenylseleno)-1,3-diene] and l-(phenylseleno)-l,3-diene-2-rf were dissolved in 0.5 mL of CDCI3 (C6D6 or C7D8 for thermolysis reactions) and placed in a capped (or sealed) 5 mm N M R tube. The mixture was then photolyzed (1.5 h with fluorescent light) or heated at 80°C in the dark (48 h). Analyses for crossover products were performed by * H N M R and low resolution mass spectrometry. See pp 107-112 and 124-125 for a discussion of these results. Effect of 1,4-cyclohexadiene on crossover When crossover experiments (thermal and photochemical) were carried out according to general procedure 6, using 1,4-cyclohexadiene as the solvent instead of deuterated solvents, a reduction in the amount of crossover was observed by lH NMR and low resolution mass spectrometry. Effect of 2,6-ferf-butyl-4-methylphenol (BHT) Photolysis of a solution of (£,£)-l-(phenylseleno)-4-methoxy- 1,3-butadiene 88b (29 mg, 0.12 mmol) in 0.5 mL of C7D8, containing B H T (2 equiv), showed a significant decrease in the rate of isomerization. It was necessary to photolyze the solution for 20 h before the Z,E/Z,Z/E,E/E,Z ratio approached the equilibrium value (see above). 222 A solution of (£ ,£ ) - l - (phenylseleno)-4-methoxy-l ,3 -butadiene 88b (27 mg, 0.11 mmol) in 0.5 mL of C7D8, containing B H T (2 equiv), gave an isomeric mixture of 15:4:69:12 Z,E/Z,Z/E,E/E,Z after 48 h thermolysis at 80°C in the dark. This ratio shows a concentration of the E,E-isomer far in excess of the equilibrium value. Subsequent photolysis of this solution, for 20 h with fluorescent light, gave the equilibrium ratios for the Z,E/Z,Z/E,E/E,Z isomeric mixture. Effect of 4-oxo-2,2,6,6-tetramethylpiperidinyloxy radical (TEMPONE) Photolysis of a solution of (£,£)-l-(phenylseleno)-4-methoxy- 1,3-butadiene 88b (28 mg, 0.12 mmol) in 0.5 mL of C7D8, containing TEMPONE (1 mg, 5 mol %) showed little effect on the rate of isomerization. Equilibrium values of Z,E/Z,Z/E,E/E,Z were reached within 2 h of photolysis with fluorescent light. A solution of (£ ,£ ) - l - (phenylseleno) -4-methoxy- 1,3-butadiene 88b (27 mg, 0.11 mmol) in 0.5 mL of C7D8, containing T E M P O N E (1 mg, 5 mol %), had little effect on the thermal isomerization process, with equilibrium values for Z,E/Z,Z/E,E/E,Z attained after 48 h at 80°C in the dark. Effect of 1,4-cyclohexadiene A solution of (£)-l-(phenylseleno)-1,3-butadiene 88a (28 mg, 0.13 mmol) in 0.5 mL of 1,4-cyclohexadiene was photolyzed, in a capped 5 mm NMR tube, for 2 h with fluorescent 223 light. A 9:1 E/Z mixture was observed by lH NMR, indicating significant retardation of the isomerization process. A solution of (E)-l-(phenylseleno)-1,3-butadiene 88a (28 mg, 0.13 mmol) in 0.5 mL of 1,4-cyclohexadiene was heated at 80°C in capped NMR tube for 48 h. A 20:1 E/Z mixture was observed by * H NMR, indicating significant retardation of the isomerization process. A solution of (E,E)-l-(phenylseleno)-4-methoxy-l,3-butadiene 88b (28 mg, 0.13 mmol) in 0.5 mL of 1,4-cyclohexadiene was photolyzed, in capped NMR tube, for 1.5 h with fluorescent light An isomeric ratio of 29:13:34:15 Z,E/Z,Z/E,E/E,Z was obtained, indicating a slight retardation of the isomerization process. A solution of (£,£)-l-(phenylseleno)-4-methoxy- 1,3-butadiene 88b (30 mg, 0.13 mmol) in 0.5 mL of 1,4-cyclohexadiene was heated at 80°C in capped NMR tube for 48 h. An equilibrium ratio was obtained after 48 h, but a significant retardation in the initial stages was observed with 92% of the E,E isomer remaining in solution after 24 h. Effect of diphenyldiselenide-a'io (Ph2Se2-a'io)114 It was shown, by mass spectroscopy, that when 1:1 mixtures of Ph2Se2-<2io and Ph2Se2 were photolyzed with fluorescent light in C6D6 significant quantities of Ph2Se2-a5 were produced. A similar result was seen on thermolysis (80°C in the dark for 24 h) of such a mixture. A solution of (E)-l-(phenylseleno)-l,3-butadiene 88a (26 mg, 0.12 mmol) in 0.5 mL of C6D6 [or (£ ,£ ) - l - (phenylseleno) -4 -methoxy- 1,3-butadiene 88b (30 mg, 0.13 mmol) in CDCI3] containing Ph2Se2-rfio (1 equiv) was photolyzed, in a capped 5 mm 224 N M R tube, for 2 h with fluorescent light. Mass spectroscopy indicated the presence of significant amounts of l-(phenylseleno)-l,3-butadiene-d5 [or l-(phenylseleno)-4-methoxy-l,3-butadiene-d5] and Ph2Se2-ds. A similar result was observed on thermolysis (at 80°C), in the dark, of these mixtures. (£)-CMorobis(ri5K;yclopentadlenyl)(3-memylbuten-l-yl)zircomum(iV) 110 and  1 - (phenylseleno)- 3-methylbut-1 -ene 109 Isopropyacetylene (0.53 g, 7.76 mmol) was vacuum transferred to a stirred slurry of Cp2ZrCl(H) 1 (1.00 g, 3.88 mmol) in 25 mL of toluene, contained in reactor bomb. The mixture was stirred in the dark at room temperature until a pale yellow homogeneous solution resulted. The amount of solvent was reduced to ~10 mL and, after addition of hexanes, the solution was left to crystallize at -30°C. The desired product was isolated as white crystals 110 (1.05 g, 83%); IR (Nujol): 3111, 3093, 1653, 1570, 1309, 1018, 990, 810 and 734 cm* 1 ; 8 ( C 6 D 6 , 400 MHz, ! H NMR): 0.92 (6H, d, CHMe?. / = 7 Hz), 2.06 (1H, m, C E M e 2 , J = 7 Hz, JQB = 6 Hz, / CA = 1 Hz), 5.73 (1H, dd, H B , JBA = 18 Hz, / B c = 6 Hz), 6.25 (10H, s, Cp), 6.72 (1H, dd, JAB = 18 Hz, JAC = 1 Hz). Anal, calcd. for CisHioClZr: C 55.27, H 5.78; found: C 55.42, H 5.78. To a stirred solution of 110 (75 mg, 0.23 mmol) in 1 mL of toluene at -20°C, in the dark, was added N-PSP (70 mg, 0.23 mmol). Workup according to general 225 procedure 5yielded a colorless oil 109 (43 mg, 83%); A . m a x (hexane): 258 nm (e 9,500); 8 (CDC1 3 , 400 MHz, l H NMR): 0.81 (6H, d, CHMe?. 7 = 7 Hz), 2.09 (1H, m, C H M e 2 , / = 7 Hz, JQB = 7 Hz, JQA = 1 Hz), 6.00 (1H, dd, H B , JBA. = 15 Hz, / B C = 7 Hz, / B S e = 10.5 Hz), 6.30 (1H, dd, JAB = 15 Hz, JAc = 1 Hz), 6.94-7.02 (3H, m), 7.40 (3H, m). Photolysis of l-(phenylseleno)-3-methylbut-l-ene 109 A solution of l-(phenylseleno)-3-methylbut-l-ene 109 (43 mg, 0.19 mmol) in 0.5 mL of C6D6, in a capped 5 mm N M R tube, was photolyzed with fluorescent light for 24 h. * H NMR spectroscopy indicated that isomerization had taken place to give a 92:8 E/Z isomeric mixture. Effect of diphenyldiselenide (Ph2Se2) on the photolysis of (£Jg)-l,3-butadienyl-4-methoxy-l- diphenylphosphine 79b and l-(phenylseleno)-3-methylbut-l-ene 88a To a solution of (E,E)-l,3-butadienyl-4-methoxy- 1-diphenylphosphine 79b (35 mg, 0.13 mmol) in 0.5 mL of C6D6 was added Ph 2 Se 2 (3 mg, 7 mol %). The mixture was then photolyzed with fluorescent light. * H N M R spectroscopy indicated that isomerization had taken place to give a 69:17 of E,E/E,Z:unknown mixture of stereoisomers after only 1.5 h irradiation. To a solution of l-(phenylseleno)-3-methylbut-l-ene 109 (34 mg, 0.15 mmol) in 0.5 mL of of CoD6 was added Ph 2 Se 2 (3 mg, 6 mol %). The mixture was then photolyzed 226 with fluorescent light. * H NMR spectroscopy indicated that isomerization had taken place to give a 87:13 E/Z mixture of stereoisomers after 24 h irradiation. Effect of (E)-l-(phenylseleno)-1,3-butadiene 88a on the photolysis of (£,£)-1,3-butadienyl-4- methoxy-l-diphenylphosphine 79b and l-(phenylseleno)-3-methylbut-l-ene 109 To a solution of (E,E)-l,3-butadienyl-4-methoxy-l-diphenylphosphine 79b (39 mg, 0.15 mmol) in 0.5 mL of C6D6 was added (£)-l-(phenylseleno)-l,3-butadiene 88a (21 mg, 0.10 mmol, 0.70 mol %). The mixture was then photolyzed with fluorescent light. No isomerization of 79b was observed until 88a began to isomerize. lH NMR spectroscopy indicated that isomerization had taken place to give a 64:16 of E,E/E,Z:unknown mixture of stereoisomers after 65 h irradiation. At this point 88a was present as an 2:1 E/Z isomeric rnixture. To a solution of l-(phenylseleno)-3-methylbut-l-ene 109 (32 mg, 0.14) in 0.5 mL of C6E>6 was added (E)-l-(phenylseleno)-l,3-butadiene 88a (21 mg, 0.10 mmol, 0.70 mol %). The mixture was then photolyzed with fluorescent light. * H NMR spectroscopy indicated that isomerization had taken place to give an 86:14 E/Z mixture of stereoisomers after 24 h irradiation. At this point 88a was present as an 2:1 E/Z isomeric mixture. 227 6.5.3 Photolysis of l-PhenyIthio-l,3-dienes Photolysis of (E)-l-(phenylthio)- 1,3-butadiene 89a A solution of (£)-l-(phenylthio)- 1,3-butadiene 89a (25 mg, 0.15 mmol) in 0.5 mL of C^D6 was placed in a capped NMR tube under nitrogen. The solution was then irradiated with fluorescent light for 5 h. The * H N M R spectrum of the solution, after photolysis, indicated that isomerization of 89a had taken place to give a 2:1 mixture of E/Z isomers. * H NMR data, taken from the spectrum of the mixture, of (Z)-l-(phenylthio)-1,3-butadiene were; 5 (C(£>6, 400 MHz, * H NMR): 5.03 (1H, dddd, H E , JED = 10 Hz, / E D = 1-75 Hz, / E B = 0.75 Hz, JEA = 0.5 Hz), 5.11 (1H, dddd, H D , / D C = 17 Hz, 7 D E = 1.75 Hz, J D A = 1 Hz, / D B = 0.75 Hz), 5.99 (1H, dddd, H A , JAB = 9 Hz, / A D = 1 Hz, / A C = 0.75 Hz, JAE = 0.5 Hz), 6.10 (1H, dddd, H B , / B C = 10 Hz, / B A = 9 Hz, / B D = / B E = 0.75 Hz), 6.13 (1H, dddd, H c , JCD = 17 Hz, / C B = JCE = 10 Hz, JQA = 0.75 Hz), 6.89 (1H, m), 6.95 (2H, m), 7.23 (2H, m). Photolysis of (£,£)-!-phenylthio-4-methoxy- 1,3-butadiene 89b A solution of (£ ,£) - l - (phenylthio)-4-methoxy- 1,3-butadiene 89b [or (E,Z)-1-(phenylthio)-4-methoxy-1,3-butadiene 89c] (27 mg, 0.14 mmol) in 0.5 mL of CDCI3 was photolyzed with fluorescent light for 1.5 h. * H N M R of the solution, after photolysis, indicated that isomerization of 89b had taken place to give a 39(±2) :13(±1) :35(±2)13(±1) mixture of Z,E/Z,Z/E,E/E,Z isomers. These ratios were determined, from the * H NMR, by integration of the OMe resonances. * H NMR data, taken from the spectrum of the mixture, were: (Z^)-l-(phenylthio)-4-methoxy- 1,3-butadiene; 6 (CDCI3,400 MHz, 1HNMR): 3.63 (3H, s, OMe) . 5.98 (1H, ddd, .H A , JAB = 9 Hz, / A C = 0.75 Hz, JAD = 0.5 Hz), 5.99 228 (1H, ddd, He, JCD = 12.5 Hz, / C B = 10.5 Hz, / C A = 0.75 Hz), 6.39 (1H, ddd, H B , / B C = 10.5 Hz, / B A = 9 Hz, / B D = 0.5 Hz), 6.82 (1H, d, H D , JDC = 12.5 Hz), 7.21-7.27 (1H, m), 7.30-7.42 (4H, m); (Z^-l-(phenylthio)-4-methoxy- 1,3-butadiene; 5 (CDCI3, 400 MHz, ! H NMR): 3.69 (3H, s, OMe). 5.19 (1H, ddd, He, JCB = 10.5 Hz, / C D = 6 Hz, / C A = 1 Hz), 6.11 (1H, ddd, H D , 7 D C = 6 Hz, / D A = 1.5 Hz, / D B = 1 Hz), 6.13 (1H, ddd, H A , JAB = 9 Hz, JAD = 1.5 Hz, JAC = 1 Hz), 6.74 (1H, ddd, H B , 7 B C = 10.5 Hz, / B A = 9 Hz, 7 B D = 1 Hz), 7.21-7.27 (1H, m), 7.30-7.42 (4H, m). 6.5.4 Thermal Isomerization of l-(Pheny!seleno)-l,3-dienes in Capped and Sealed 5 mm N M R Tubes A solution of (£)-l-(phenylseleno)-l,3-butadiene 88a (28 mg, 0.13 mmol) in 0.5 mL of was placed in a capped N M R tube under nitrogen. The pale yellow solution was then heated in the dark at 80°C for 48 h. * H N M R spectroscopy of the solution indicated that isomerization had taken place to give an 2:1 E/Z mixture of 1-(phenylseleno)-1,3-butadiene. A solution of (E,E)-l-(phenylseleno)-4-methoxy-l,3-butadiene 88b (30 mg, 0.13 mmol) in 0.5 mL of C7D8 was placed in a capped NMR tube under nitrogen. The pale yellow solution was then heated in the dark at 80°C for 48 h. * H N M R spectrum of the solution indicated that isomerization had taken place to a give a mixture of isomers (Z,E/Z,Z/E,E/E,Z) of the composition described above. A solution of (E,Z)-l-(phenylseleno)-4-methoxy- 1,3-butadiene 88c (29 mg, 0.12 mmol) in 0.5 mL of C7D8 was placed in a capped NMR tube under nitrogen. The pale yellow solution was then heated in the dark at 80°C for 48 h. * H N M R spectrum of the solution indicated that isomerization had taken place to a give a mixture of isomers (Z,E/Z,Z/E,E/E,Z) of the composition described above for the thermolysis of 88b. 229 Thermolysis at 80° C of a solution of (E)-l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene] 88d (34 mg, 0.13 mmol) in 0.5 mL of CgD6in the dark showed no isomerization after 4 days. Thermolysis, at 80°C in the dark, of a solution of l-(phenylseleno)-1,3-butadiene 88a (27 mg, 0.13 mmol) in 0.5 mL of C^De in a sealed tube under nitrogen for 48 h resulted in no isomerization. When the experiment was repeated (same concentration of 88a) with the tube sealed under dry air (air was passed through a 20 x 2 cm column of Drierite®) or under nitrogen in an acid-washed tube (tube was soaked in 12 M HC1 for 3 h, then dried at 120°C for 3 h) the same results were obtained: no isomerization. A solution of 88a (35 mg, 0.17 mmol) in 0.5 mL of C6D6 containing azobisisobutyronitrile (AIBN) (2 mg, ~5 mol %) when heated at 80°C in the dark for 3 h resulted in a 2:1 E/Z mixture of stereoisomers. Thermolysis, at 80°C in the dark, of a solution of l-(phenylseleno)-4-methoxy-1,3-butadiene 88b (29 mg, 0.12 mmol) in 0.5 mL of C7D8 contained in a sealed tube under nitrogen for 48 h resulted in only limited isomerization (less than 30% conversion of the E,E isomer of 88b). When the experiment was repeated (same concentration of 88b) with a tube sealed under dry air or under nitrogen in an acid-washed tube, both reactions gave rise to pre-equilibrium isomeric mixtures (~40% conversion of the E,E isomer of 88b). A solution of 88b (33 mg, 0.14 mmol) in 0.5 mL of C7D8 containing azobisisobutyronitrile (AIBN) (2 mg, ~5 mol) when heated at 80°C in the dark for 3 h resulted in an equilibrium mixture of E,Z/Z,Z/E,E/Z,E stereoisomers. 230 6.5.5 Diels-Alder Reactivity of l-(PhenylseIeno)-l,3-dienes with Maleic Anhydride. Diels-Alder adducts of ( £ ) - ! - (phenylseleno)- 1,3-butadiene 88a and maleic anhydride  121, 122 and 123 To a pale yellow solution of 1-(phenylseleno)-1,3-butadiene 88a (137 mg, 0.66 mmol) in 2 mL of toluene was added maleic anhydride (64 mg, 0.66 mmol). The solution immediately turned bright yellow, and was transferred to a reactor bomb and heated in the dark for 22 h at 110°C. On evaporation of the pale yellow solution a yellow oil was obtained. Crystallization from a toluene/hexanes mixture at -30"C gave a white solid 121 (156 mg, 78%); IR (Nujol): 1855, 1778, 1577, 1241, 1023, 968, 733 and 687 cm" 1; 8 ( C 7 D 8 , 400 MHz, LH NMR): 1.79 (1H, dddd, He, JCE = 17 Hz, / C A = 11 Hz, JQF = 6 Hz, / C G = 1.75 Hz), 2.14 (1H, dddd, H E , JEC = 17 Hz, JEA = 7 HZ, / e f = 2.75 Hz, / E G = 2.25 Hz), 2.42 (1H, ddd, H A , / A C = 11 Hz, JAB = 10.5 Hz, / A c = 7 Hz), 2.84 (1H, dd, H B , JBA = 10.5 Hz, JBD = 5.5 Hz), 3.68 (1H, dd, H D , / D G = 6 HZ, / D B = 5.5 Hz), 5.32 (1H, ddd, H F , / F G = 10 Hz, / F C = 6 Hz, JEE = 2.75 Hz), 5.76 (1H, dddd, H G , JQF = 10 Hz, / G D = 6 Hz, / G E = 2.25 Hz, JQC = 1.75 Hz), 7.00 (3H, m), 7.43 (2H, m). Anal, calcd. for C n H ^ O s S e : C 54.74, H 3.94; found: C 54.47, H 3.91. To a pale yellow solution of l-(phenylseleno)-l,3-butadiene 88a (68 mg, 0.33 mmol) in 0.5 mL of C7D8 was added maleic anhydride (32 mg, 0.33 mmol). The solution 231 immediately turned bright yellow, and was sealed under nitrogen in a 5 mm NMR tube and heated in the dark for 63 h at 140°C. On evaporation of the pale yellow solution a yellow oil was obtained. The oil was washed with hexanes to remove Ph2Se2 formed during the reaction; all attempts at crystallization failed. The pale yellow oil 122/123 (74 mg, 70%) was seen to be a 2:1 mixture of cycloadducts by 1 H NMR. The following data were obtained for the mixture; IR(film): 1870, 1783, 1478, 1435, 1220, 1107, 932, 745 and 694 cm' 1 ; Major isomer 122 8 ( C 7 D 8 , 400 MHz, * H NMR): 1.47 (1H, dddd, He, JQE = 14 Hz, JQA = 9.5 Hz, JCF = 5 Hz, 7 C B = 0.5 Hz), 1.74 (1H, ddd, H E , JEC = 14 Hz, / E A = JEF = 5.5 Hz), 2.59 (1H, dddd, H B , JBA = 10 Hz, 7 B D = 4.5 Hz, / B G = 2.5 Hz, / B C = 0.5 Hz), 2.86 (1H, ddd, H A , JAB = 10 Hz, / A C = 9.5 Hz, / A E = 5.5 Hz), 3.32 (1H, dddd, Hp, / F E = JFG = 5.5 H z ^ F c = 5 Hz, / F D = 1.25 Hz), 5.45 (1H, ddd, H D , / D G = 9.5 Hz, / D B = 4.5 Hz, / D F = 1.25 Hz), 5.72 (1H, ddd, H G , JQD = 9.5 Hz, / G F = 5.5 Hz, / G B = 2.5 Hz), 6.96-7.05 (3H, m), 7.32 (2H, m); Minor isomer 123 8 ( C 7 D 8 , 400 MHz, l H NMR): 1.53 (1H, dddd, He, JQE = 14.5 Hz, J C A = 7.5 Hz, / C F = 5 Hz, 7 C B = 1 Hz), 1.92 (1H, ddd, H E , JEC = 14.5 Hz, JEF = 4.5 Hz, 7 E A = 4.0 Hz), 2.29 (1H, ddd, H A , JAB. = 10 Hz, 7 A C = 7.5 Hz, / A E = 4 Hz), 2.77 (1H, dddd, H B , JBA = 10 Hz, 7 B D = 5.5 Hz, / B G = 2 Hz, / B C = 1 Hz), 3.35 (1H, dddd, Hp, JFG = 5.5 Hz, / F C = 5 Hz, / F E = 4.5 Hz, 7 F D = 1 Hz), 5.49 (1H, ddd, H D , / D G = 9.5 Hz, 7 D B = 5.5 Hz, / D F = 1 Hz), 5.79 (1H, ddd, He, 7 G D = 9.5 Hz, / G F = 5.5 Hz, J C B = 2 Hz), 6.96-7.05 (3H, m), 7.47 (2H, m); mle (relative intensity): 51 (33.9), 77 (100), 78 (57.7), 79 (56.1), 123 (50.3), 129 (20.5), 154 (29.2), 155 (29.1), 157 (39.8), 158 (54.4), 195 (22.6) and 308 (M+, 68.2). Exact Mass calcd. for C i 4 H i 2 O 3 8 0 S e : 307.9951; found: 307.9946. 232 Diels-Alder adducts of (£,£)-l-(phenylseleno)-4-memoxy-1,3-butadiene 88b and maleic anhydride 114 and 115 PhSe O O O PhSe it... O O O OMe 114 115 To a pale yellow solution of l-(phenylseleno)-4-methoxy-l,3-butadiene 88b (117 mg, 0.49 mmol) in 2 mL of toluene was added maleic anhydride (48 mg, 0.49 mmol). The solution immediately turned bright yellow, and was transferred to a reactor bomb and heated in the dark for 20 h at 80° C. On cooling to room temperature a white solid precipitated; the solid was collected by filtration and washed with a 1:1 mixture of toluene and hexanes to yield 114 (142 mg, 86%); IR (Nujol): 1858, 1777, 1220, 1040, 925, 784, 756 and 697 cm- 1 ; 8 (CDC1 3 , 400 MHz, * H NMR): 3.29 (3H, s, OMe). 3.38 (1H, dd, H A , JAB = 11 Hz, / A C = 5 Hz), 3.79 (1H, dd, H B , JBA = 11 Hz, / B D = 8.5 Hz), 3.90 (1H, dd, H D , / D B = 8.5 Hz, / D F = 7.5 Hz), 4.29 (1H, dd, H C , / C E = 5.5 Hz, JQA = 5 Hz), 6.09 (1H, dd, H E , / E F = 9 Hz, / E c = 5.5 Hz), 6.56 (1H, dd, H F , / F E = 9 Hz, / F D = 7.5 Hz), 7.30 (3H, m), 7.71 (2H, m). Anal, calcd. for C i 5 H i 5 0 4 S e : C 53.42, H 4.22; found: C 53.62, H 4.22. To a pale yellow solution of l-(phenylseleno)-4-methoxy-1,3-butadiene 88b (155 mg, 0.65 mmol) in 2 mL of toluene was added maleic anhydride (64 mg, 0.65 mmol). The solution immediately turned bright yellow, and was transferred to a reactor bomb and heated under light from a 275 W sunlamp (positioned 30 cm from the bomb) for 20 h at 80°C. Hexanes was added dropwise to the rapidly stirred bright yellow solution, resulting in precipitation of a white solid (19 mg - shown to be 114 by * H N M R spectroscopy). On evaporation a yellow oil was obtained, which was washed thoroughly with hexanes (to remove 233 Ph 2Se 2), leaving a pale yellow oil 115 (149 mg, 68%); IR (film): 1874, 1785, 1480, 1438, 1226, 936, 740 and 690 cm-l; 5 (C^D6,400 MHz, * H NMR): 2.32 (1H, ddd, H B , / B A = 9.5 Hz, 7 B D = 4 Hz, / B F = 2.5 Hz), 2.52 (3H, s, OMe), 3.27 (1H, dd, H A , / A B = 9.5 Hz, J A C = 4 Hz), 3.49 (1H, ddd, H E , / E F = 5.5 Hz, 7 E C = 3 Hz, / E D = 0.75 Hz), 3.80 (1H, ddd, He, JQA = 4.5 Hz, 7 C E = 3 Hz, 7 C F = 1-25 Hz), 5.54 (1H, dddd, Hp, / F D = 10 Hz, 7pE = 5.5 Hz, / F B = 2.5 Hz, / F C = 1-25 Hz), 5.67 (1H, ddd, H D , / D F = 10 Hz, 7 D B = 4 Hz, / D E = 0.75 Hz), 6.86-6.97 (3H, m), 7.29 (2H, m); m/e (relative intensity): 50 (20.4), 77 (41.7), 148 (31.4), 171 (100) 156 (29.9), 158 (59.9) and 338 (M+, 10.3). Exact Mass calcd. for C i 5 H 1 5 O 4 8 0 S e : 338.0057; found: 338.0060. (EJL)-1 -(Phenylseleno)-4-methoxy-1,3-butadiene-o*5-2-fl* 88-06 As outlined in general procedure 5, (E,£)-chlorobis(h5-cyclopentadienyl)(4-methoxy-l,3-butadienyl)zirconium(iV)-2-d 55-di (75 mg, 0.22 mmol) was reacted with TV-PSP-ds (68 mg, 0.22 mmol) to yield a pale yellow oil 88-0*6 (47 mg, 87%); IR (film): 2274, 1628, 1543, 1458, 1338, 1213, 1110, 928 and 640 cm-l; 1H N M R was identical to 88-0*1 with the absence of the aromatic resonances; m/e (relative intensity): 54 (35.0), 82 (41.4), 83 (20.8), 121 (27.3), 123 (33.6), 133 (25.8), 134 (21.0), 135 (34.4), 149 (21.5), 160 (21.2), 162 (40.2), 164 (66.6), 165 (27.2), 166 (100) and 246 (M+, 73.7). Exact Mass calcd. for CnH62H6O80Se: 246.0430; found: 246.0425. 234 MeO 143-d 6 The preparation of 114-d^ was as described above for 114. To a solution of (E ,£ ) - l -(phenylseleno)-4-methoxy-l,3-butadiene-d5-2-d 88-^6 (160 mg, 0.65 mmol) in 2 mL of toluene was added maleic anhydride (64 mg, 0.65 mmol). Workup provided a white solid lU-d6 (187 mg, 84%); IR (Nujol): 2287, 1859, 1778, 1229, 1087, 938, 841, 768 and 683 cm- 1 ; 5 (CDC1 3, 400 MHz, LH NMR): 3.29 (3H, s, OMe). 3.38 (1H, dd, H A , JAB = H Hz, / A C = 5 Hz, 3.79 (1H, dd, H B , / B A = 11 Hz, 7 B D = 8.5 Hz), 3.90 (1H, d, H D , / D B = 8.5 Hz), 4.29 (1H, dd, H C , JCE = 5.5 Hz, / C A = 5 Hz), 6.09 (1H, d, H E , JEC = 5.5 Hz); mle (relative intensity): 83 (100), 105 (36.7), 110 (14.9), 149 (15.6), 161 (25.2), 162 (18.8), 163 (48.4), 181 (14.7) and 344 (M+, 6.5). Exact Mass calcd. for C i 5 H 8 2 H 6 O 4 8 0 S e : 344.0434; found: 344.0435. Diels-Alder adduct of (£)-l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene] 88d and maleic  anhydride 124 and 125 PhSe O O O 125 124 235 To a colorless solution of (£)-l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene] 88d (81 mg, 0.31 mmol) in 2 mL of toluene was added maleic anhydride (30 mg, 0.31 mmol). The solution immediately turned bright yellow, and was transferred to a reactor bomb and heated in the dark for 55 h at 60°C. Evaporation of the pale yellow solution gave a yellow oil . Crystallization from a toluene/hexanes mixture at -30*C gave a white solid 124 (87 mg, 78%); IR (Nujol): 1860, 1776, 1224, 1011, 933, 902, 793 and 740 cm-l; 5 (C6D 6 , 400 MHz, l H NMR): 0.97 (2H, m), 1.30 (1H, m), 1.42 (1H, m), 1.56 (2H, m), 1.80 (1H, m), 1.91 (1H, m), 2.39 (1H, m), 2.42 (1H, dd, H A , JAD = 10.5 Hz, / A B = 9 Hz), 2.77 (1H, dd, H B 7 B A = 9 Hz, 7 B C = 5.5 Hz), 3.74 (1H, dddd, H c , / C B = JCE = 5.5 Hz, JCD=J= 1.5 Hz), 5.47 (1H, ddd, H E , JEC = 5.5 Hz, / E D = J = 1.5 Hz), 6.99 (3H, m), 7.55 (2H, m). Anal. calcd. for C i 8 H i 7 0 3 S e : C 59.84, H 5.02; found: C 59.90, H 5.00. As described above, (E)-l-phenylseleno-[2-(l-cyclohexen-l-yl)ethene] 88d (208 mg, 0.79 mmol) in 2 mL of toluene containing maleic anhydride (77 mg, 0.79 mmol) were heated in the dark at 110°C for 18 h. Crystallization from toluene/hexanes yielded a white solid 125 (223 mg, 78%); IR (Nujol): 1851, 1778, 1210, 1020, 936, 793, 740 and 693 cm-l; 8 (CDCI3, 400 MHz, l H NMR): 1.32 (2H, m), 1.71 (1H, m), 1.95 (2H, m), 1.97 (1H, m, H D ) , 1.98 (1H, m), 2.17 (2H, m), 3.22 (1H, dd, H B , / B A = 10 Hz, / B D = 7.5 Hz), 3.82 (1H, ddd, H A , 7 A B = 10 Hz, / A c = 6 Hz, J A E = 1-75 Hz), 5.39 (1H, dd, H E , / E C = 9.5 Hz, 7 E A = 1-75 Hz), 5.61 (1H, dd, He, JCE - 9.5 Hz, / C A = 6 Hz), 7.23-7.35 (3H, m), 7.47 (2H, m). Anal, calcd. for C i 8 H i 7 0 3 S e : C 59.84, H 5.02; found: C 59.99, H 5.08. 236 Effect of Ph.2Se2-^ io and AIBN on the 1,3-rearrangement of 114 To a solution of 114 (30 mg, 0.09 mmol) in 0.5 mL of C6D6 was added Ph2Se2-rfio (7 mg, 25 mol %) or AIBN (4 mg, 25 mol %). The mixtures were sealed in 5 mm NMR tubes and heated at 80°C in the dark for 20 h. For Ph2Se2-^ io» 5% conversion of 114 to 115 was observed by lK NMR spectroscopy, while AIBN gave only 15% conversion. Crossover Experiment on the photochemical 1,3-rearrangement of 114 to 115 A known ratio (approximately 1:1) of 114 (25 mg, 0.07 mmol) and 114-^6 (25 mg, 0.07 mmol) dissolved in 0.5 mL of CDCI3 was photolyzed with fluorescent light (at 29°C) in a 5 mm N M R tube. Analysis for crossover products was obtained by low resolution mass spectrometry. See pp 130-133 for a discussion of the results. 237 6.6 Preparation and Diels-Alder Reactivity of 2-(TrialkyIstannyI)-l,3-butadienes and 2-(PhenylseIeno)-l,3-butadiene. 6.6.1 Synthesis and Cycloaddition Reactions of 2-(PhenylseIeno)-l,3-butadiene and 2-(Trialkyl)-l,3-butadienes. Tributyltin chloride (14.64 g, 45 mmol) dissolved in 25 mL of T H F was added dropwise, at room temperature, to a stirred solution of Grignard reagent 24 (75 mL, 45 mmol; 0.6 M solution in THF) under nitrogen. The mixture was stirred at room temperature for a further 6 h, when 10 mL of water was added to decompose any unreacted Grignard reagent. At this stage, most of the THF was evaporated leaving a white slurry which was extracted with 3 x 100 mL portions of diethyl ether (Et20). The Et20 layer was washed with 2 x 100 mL portions of aqueous 2 M potassium fluoride to remove any unreacted Bu3SnCl. Finally the organic layer was washed with 2 x 100 mL of water and dried over anhydrous MgSC>4. Evaporation of the solvent and distillation under vacuum yielded one fraction (40-50°C/10-3 Torr, 1 Torr = 133.3 Pa) of a colorless liquid 128a (10.9 g, 71%). Spectroscopic data for 128a were consistent with those reported in the literature.973 l,3-Butadienyl-2-tributylstannane 128a 238 l,3-Butam^nyl-2-trimethylstannane 128b M e 3 S n ' X Trimethyltin chloride (6.0 g, 30 mmol) dissolved in 25 mL of T H F was added dropwise, at room temperature, to a solution of Grignard reagent 24 (50 mL, 30 mmol; 0.6 M in THF) under nitrogen. The mixture was stirred at room temperature for a further 6 h. The workup was identical to that described for 128a. Distillation, at reduced pressure, yielded 128b (4.35 g, 65%) as a colorless liquid, distilling at 42°C/11 Torr. Spectroscopic data for this compound were identical to those reported in the literature.98 2-(Phenylseleno)-1,3-butadiene 129 Phenylselenenyl chloride (PhSeCl) (4.78 g, 25 mmol) dissolved in 25 mL of T H F was added dropwise, at room temperature, to a stirred solution of Grignard reagent 24 (100 ml, 25 mmol; 0.25 M in THF) under nitrogen. The deep red color of the PhSeCl discharged immediately on addition to 24; the reaction was then stirred at room temperature for a further hour. The workup was identical to that described for 128a, with the omission of the aqueous 239 K F washings. After drying the organic layer over MgSC>4, evaporation of the solvent yielded a yellow oil. Distillation of the latter under vacuum (10'3 Torr) gave a pale yellow oil 129 (3.66 g, 70%); IR (film): 1620, 1572, 1477, 1439, 1214, 914 and 735 cm" 1; 8 (C6D 6 , 400 MHz, * H NMR): 5.00 (1H, d, / = 10.5 Hz), 5.34 (1H, m), 5.53 (1H, m), 5.62 (1H, d, J = 17 Hz), 6.24 (1H, dd, / = 10.5 Hz, 17 Hz), 6.94 (3H, m) and 7.44 (2H, m). Anal, calcd. forCioHinSe: C 57.43, H 4.82; found: C 57.66, H 4.81. Diels-Alder adduct of 128a with maleic anhydride 131 A solution of 128a (500 mg, 1.46 mmol) and maleic anhydride (143 mg, 1.46 mmol) in 2 mL of toluene was stirred at room temperature under nitrogen for 48 h. The solvent was evaporated and the residue was purified directly by column chromatography on silica (eluent: ether/petroleum ether 1:2) yielding 131 (482 mg, 75%) as a white solid. Spectroscopic data for 131 were identical to that reported in the literature.973 Diels-Alder adduct of 128a with N-phenylmaleimide 132 O O o N-Ph O 240 A solution of 128a (500 mg, 1.46 mmol) and N-phenylmaleimide (252 mg, 1.46 mmol) in 3 mL of toluene was refluxed for 8 h. The solvent was evaporated and the residue was subjected to column chromatography on silica (eluent: ether/petroleum ether 1:3) which yielded 132 (675 mg, 90%) as a yellow oil; IR (film): 1779, 1712, 1499, 1456, 1378, 1190, 1171 and 690 cm" 1; 5 (C 6D6,400 MHz, * H NMR): 0.90 (15H, m), 1.29 (6H, m), 1.48 (6H, m), 1.84 (1H, m), 1.99 (1H, m), 2.53 (2H, m), 2.63 (1H, dd, J = 6 Hz, 15 Hz), 2.85 (1H, d, J = 15 Hz), 6.01 (1H, m), 7.00 (1H, m), 7.15 (2H, m) 7.41 (2H, m). Anal. calcd. for C 2 6H3 9 N0 2 Sn: C 60.49, H 7.61, N 2.71; found: C 60.60, H 7.79, N 2.60. Diels-Alder adduct of 128a with rj-benzoquinone 133 A solution of 128a (500 mg, 1.46 mmol) and /?-benzoquinone (158 mg, 1.46 mmol) in 3 mL of toluene was refluxed under nitrogen for 5 h. The solvent was evaporated and the residue was purified by column chromatography on silica (eluent: dichloromethane) to give 133 as a yellow oil (453 mg, 69%); IR (film): 1684, 1602, 1260, 1090 and 850 cm- 1 ; 5 (C6D 6 ) 400 MHz, *H NMR): 0.90 (15H, m), 1.32 (6H, m), 1.32 ( 6H, m), 1.54 (6H, m), 1.84 (1H, m), 2.17 (1H, m), 2.39 (1H, m) 2.57 (1H, m), 2.63 (1H, m), 2.70 (1H, m), 5.72 (1H, m), 6.05 (2H, s). From the chromatography of 136 a white solid (53 mg, 8%) was obtained. Spectroscopic data, as follows, indicated that this solid was the hydroquinone of 133; IR (Nujol): 3286, 1625, 1595, 1311, 1242, 992, 807 and 743 cm" 1 ; 8 ( C 6 D 6 , 400 MHz, * H NMR): 0.93 (9H, t, / = 7 Hz), 0.99 (6H, t, / = 8 Hz), 1.37 (6H, m), 1.58 (6H, O O 241 m), 3.27 (2H, m), 3.63 (2H, m), 3.83 (2H, b s, 8 was concentration dependent and signal disappeared on D 2 0 exchange). 6.06 (1H, m), 6.10 (1H, d, / = 8.5 Hz), 6.22 (1H, d, J = 8.5 Hz); mle (relative intensity): 56 (93.1), 147 (70.0), 161 (100), 281 (13.4), 338 (6.4), 395 (14.3). Exact Mass calcd. for C i 8 H 2 7 O 2 1 2 0 S n (M-n-Bu)+: 395.1033; found: 395.1027. Diels-Alder adduct of 128a with dimethyl acetylenedicarboxylate 134 A solution of 128a (500 mg, 1.46 mmol) and dimethyl acetylenedicarboxylate (207 mg, 1.46 mmol) in 3 mL of toluene was refluxed overnight under nitrogen. The solvent was evaporated and the residue was purified by column chromatography on silica (eluent: ether/petroleum ether 1:7) to give 134 (503 mg, 71%) as a colorless liquid; IR (film): 1736, 1726, 1668, 1618, 1434, 1261 and 1065 cnr*; 8 (C6D 6 , 400 MHz, ! H NMR): 0.91 (15H, m), 1.32 (6H, m), 1.51 (6H, m), 2.93 (2H, m), 3.27 (2H, m), 3.42 (3H, s), 3.45 (3H, m), 5.63 (1H, m). Anal, calcd. for C 2 2 H 3 8 0 4 S n : C 54.46, H 7.89; found: C 54.61, H 7.87. Diels-Alder adduct of 128b with methyl acrylate 135a/135b 242 A solution of 128b (1.73 g, 7.98 mmol) and methyl acrylate (3.43 g, 39.92 mmol) in 10 mL of toluene was refluxed overnight under nitrogen. The solvent and excess methyl acrylate were evaporated and the residue was subjected to column chromatography on silica (eluent: ether/petroleum ether 1:20) yielding 135a/135b (1.74 g, 72%). Capillary G L C and * H N M R indicated that the regioisomers 135a/135b were present in a 2:1 ratio. The following data were obtained for this mixture; IR (film): 1737,1618,1437, 1166 and 767 cm-1; 8 ( C 6 D 6 , 400 MHz, * H NMR): 0.07 (9H, s), 1.67-2.54 (7H, m), 3.36 and 3.37 (3H, 2 singlets; 135a and 135b, respectively), 5.75 (1H, m). Anal, calcd. for CnH2o02Sn: C 43.61, H 6.65; found: C 43.91, H 6.80. Diels-Alder adduct of 129 with maleic anhydride 137 O A solution of 129 (750 mg, 3.59 mmol) and maleic anhydride (351 mg, 3.59 mmol) in 3 mL of toluene was stirred at room temperature for 48 h, under nitrogen. White crystals gradually deposited from solution. Low temperature recrystallization of this material (from ether/petroleum ether) yielded pure 137 (771 mg, 70%); IR (Nujol): 1845,1780,1245,1010 and 942 cm" 1; 8 (Q>D6, 400 MHz, J H NMR): 1.42 (1H, m), 1.76 (1H, m), 2.04 (1H, m), 2.11 (2H, m), 2.37 (1H, m), 5.61 (1H, m), 6.97 (3H, m), 7.33 (2H, m). Anal, calcd. for C i 4 H i 2 0 3 S e : C 54.74, H 3.94; found: C 54.56, H 3.92. 243 Diels-Alder adduct of 129 with A'-phenylmaleimide 138 O PhSe N-Ph O A solution of 129 (1.00 g, 4.78 mmol) and A'-phenylmaleimide (829 mg, 4.78 mmol) in 3 mL of toluene was refluxed for 8 h under nitrogen. The solvent was evaporated and the residue was subjected to chromatography on silica (eluent: ether/petroleum ether 1:3) to give a yellow oil 138 (1.39 g, 76%); IR (film): 1960, 1882, 1782, 1715, 1597, 1575, 1384, 1180 and 745 cm" 1; 8 ( C 6 D 6 , 400 MHz, lH NMR): 1.75 (1H, m), 2.08 (1H, m), 2.40 (2H, m), 2.49 (1H, m), 2.78 (1H, m), 5.92 (1H, m), 6.98-7.50 (10H, m). Anal, calcd. for C 2 o H n N 0 2 S e : C 62.83, H 4.48, N 3.66; found: C 62.91, H 4.63, N 3.80. Diels-Alder adduct of 129 with p-benzoquinone 139 A solution of 129 (657 mg, 3.14 mmol) and p-benzoquinone (340 mg, 3.14 mmol) in 2 mL of toluene was refluxed for 2 h under nitrogen. Upon cooling the reaction to room temperature a white solid deposited. After evaporation of the bulk of the solvent, the residue was dissolved in CH2CI2 and passed through a short column (4 cm x 2 cm) of silica. Removal of the solvent and recrystallization from toluene/petroleum ether yielded white crystals of 139 O o 244 (638 mg, 64%); IR (KBr): 1676, 1598, 1577, 1475, 1435, 1263, 737 cm-l; 5 ( c 6 D 6 , 400 MHz, l H NMR): 1.68 (1H, m), 2.05 (1H, m), 2.17 (1H, m), 2.41 (2H, m), 2,59 (1H, m), 5.87 (1H, m), 5.92 (1H, s), 5.93 (1H, s), 7.00 (3H, m) and 7.47 (2H, m). Anal, calcd. for Ci6Hi4C»2Se: C 60.58, H 4.45; found: C 60.56, H 4.52. Purification of 139 using long columns of silica (>10 cm x 2 cm) led to significant decomposition, as well as formation of small quantities (generally < 3%) of the corresponding hydroquinone. * H NMR data of the latter is as follows; 8 ( 0 ^ , 400 MHz): 3.21 (2H, m), 3.58 (2H, m), 3.77 and 3.90 (2 broad singlets, 8 was concentration dependent; signals disappeared on D 2 0 exchange), 6.08 (1H, d, / = 8.5 Hz), 6.13 (1H, d, / = 8.5 Hz), 6.20 (1H, m), 6.93 (3H, m), 7.46 (2H, m). Diels-Alder adduct of 129 with dimethyl acetylenedicarboxylate 140 A solution of 129 (1.00 g, 4.78 mmol) and dimethyl acetylenedicarboxylate (680 mg, 4.78 mmol) in 3 mL of toluene was refluxed overnight under nitrogen. The solvent was evaporated and the residue directly subjected to column chromatography on silica (eluent: ether/petroleum ether 1:7), which yielded a yellow oil 140 (1.36 g, 81%); IR (film): 1731, 1669, 1640, 1578, 1434, 1263, 1064, 742 and 689 cm-l; 5 (C6D 6 , 400 MHz, ! H NMR): 2.78 (2H, m), 3.16 (2H, m), 3.27 (3H, s), 3.41 (3H, s), 5.80 (1H, m), 6.96 (3H, m), 7.42 (2H,m). Ana/, calcd. for C i 6 H i 6 0 4 S e : C 54.71, H 4.59; found: C 55.00, H 4.67. 245 Diels-Alder adduct of 129 with methyl acrylate 141a/141b A solution of 129 (1.30 g, 6.22 mmol) and methyl acrylate (1.60 g, 18.66 mmol) in 3 mL of toluene was refluxed overnight under nitrogen. The solvent was evaporated and the resulting yellow liquid was distilled, under vacuum (10"3 Torr), to yield a pale yellow liquid (1.65 g, 90%). A l l data reported are for the 4:1 mixture of para:meta regioisomers 141a/141b; the ratio having been determined by 1 H NMR and capillary G L C ; IR (film): 1738, 1578, 1475, 1437, 1169,1020, 738 and 692 cm-*; 5 ( C 6 D 6 , 400 MHz, * H NMR): 1.46-2.71 (7H, m), 3.23 and 3.30 (3H, 2 singlets; 141a and 141b, respectively), 6.00 and 6.03 (1H, 2 multiplets), 6.97 (3H, m), 7.44 and 7.47 (2H, 2 multiplets). Anal, calcd. for C i 4 H i 6 0 2 S e : C 56.96, H 5.46; found: C 56.71, H 5.49. Reaction of 128b with PhSeCl To a solution of 128b (200 mg, 0.92 mmol) in 1 mL of toluene was added, dropwise, a toluene solution of phenylselenenyl chloride (176 mg, 0.92 mmol). On addition, the deep red color of the PhSeCl discharged immediately. The mixture was stirred overnight at room temperature, after which 75 mg of K F and 3 mL of of T H F were added to destroy the Me3SnCl by-product After a further 2 h at room temperature, the resulting slurry was filtered through a short column of basic alumina. Evaporation of the solvent yielded a pale yellow oil 246 (164 mg, 85%); spectroscopic data for which were identical to that reported for the phenylseleno diene 129. Reaction of 135a/135b with PhSeCl To a solution of 135a/135b (2:1 para.meta) (150 mg, 0.50 mmol) in 1 mL of toluene was added a solution of phenylselenenyl chloride (95 mg, 0.05 mmol). The mixture was stirred overnight at room temperature during which time the deep red color of the mixture had changed to a bright yellow. The reaction workup was identical to that described in the above reaction. A yellow oil was isolated whose spectroscopic data were consistent with those for 141a/141b, with the exception that lH NMR and capillary G L C indicated a para:meta ratio of 6.6.2 Attempted Syntheses of Type BJ 1,3-Dienes where M L „ is C p 2 Z r C l . (1 -Cyclohexenylethynyl)trimethylstannane 143 2:1. To a stirred solution of 1-ethynylcyclohexene 51d (5.0 g, 47.2 mmol) in 100 mL of T H F was added, dropwise, methyllithium (37 mL, 51.9 mmol, 1.4 M in THF) at -78°C. After 247 stirring at this temperature for 30 min, the mixture was warmed to -20°C and stirred for 30 min. A solution of trimethyltin chloride (10.35 g, 51.9 mmol) in 25 mL of T H F was added slowly and the reaction was stirred for 30 min at -20°C. The reaction was warmed to room temperature and stirred for 1 h . The solution was extracted with 3 x 100 mL of aqueous potassium fluoride to remove the excess Me3SnCl. Extraction with 3 x 100 mL portions of Et20, followed by washing of the organic layer with 2 x 100 mL of water and subsequent drying over MgS04 gave, after evaporation of the solvent, a yellow oil. Distillation, at reduced pressure (75°C/12 Torr), yielded a colorless liquid 143 (8.0 g, 63%); IR (film): 3027, 2928, 2858, 2127, 1436, 1348, 1154, 1043, 918 and 768 cm' 1 ; 5 (C6D 6 , 400 MHz, * H NMR): 0.15 (9H, s, / H S n = 58 Hz), 1.40 (4H, m), 1.80 (2H, m), 2.33 (2H, m), 6.22 (1H, m). Anal, calcd. for CnHigSn: C 49.12, H 6.75; found: 48.90, H 6.80. ( £ > 1 -Trimethylstannyl-1 -chlorobis(T|5-cyclopentadienyl)- [2-( 1 -Cyclohexen-1 -yl)ethenyl]zirconium(TV) 144 ZrCp 2 Cl To a stirred solution of (l-cyclohexenylethynyl)trimethylstannane (500 mg, 1.86 mmol) in 20 mL of toluene was added, at room temperature in the dark, in three portions Cp2ZrCl(H) 1 (528 mg, 2.05 mmol). After 3 h the resulting orange homogeneous solution was evaporated. Analysis of the crude oil, by * H NMR, showed the presence of two isomers in the ratio 95:5. Crystallization of the oil from toluene/hexanes gave yellow crystals 144 (714 mg, 73%); IR (Nujol): 1556, 1016, 919, 807, 758 and 608 cm" 1; 8 ( C 6 D 6 , 400 MHz, 248 l H NMR): 0.31 (9H, s, / H S n = 49 Hz), 1.40-1.56 (4H, m), 1.99 (4H, m), 5.67 (1H, m, H C ) , 5.86 (10H, s, Cp), 7.42 (1H, b s, H A , / H S n = 230 Hz). Anal, calcd. for C2iH 2oClSnZr: C 47.88, H 5.55, CI 6.73; found: C 48.10, H5.70, CI 6.95. (Trimemylphosphine) [2-( 1 -cyclohexen-1 -yl)-Ti2-ethynyl]bis(T| s-cyclopentodienyl)zirconium(II) 146 To a solution of ( £ ) - c h l o r o [ 2 - ( l - c y c l o h e x e n - l - y l ) e t h e n y l ] b i s ( r t 5 -cyclopentadienyl)zirconium(TV) 55d (1.0 g, 2.75 mmol) in 5 mL of toluene at -1%°C was added methyllithium (1.96 mL, 2.75 mmol, 1.4 M). The reaction was stirred at this temperature for 30 min, after which it was slowly allowed to warm to room temperature. On warrning, the pale yellow homogeneous solution became cloudy and darkened to an orange-red slurry. On reaching room temperature the solvent was evaporated and the product extracted with -10:1 hexanes:toluene and filtered through Celite® to give (E)-[2-(l-cyclohexen-1-yl)emenyl]bis(Tj5-cyclopentam^nyl)(methyl)zirconium(rV) (0.89 g, 94%); IR (Nujol): 1627, 1593, 1418, 1283, 1009, 951, 780, 743 and 666 cm" 1; 5 (QD6, 400 MHz, * H NMR): 0.08 (3H, s, M£) , L52 (2H, m), 1.60 (2H, m), 2.07 (2H, m), 2.14 (4H, m), 5.73 (1H, m, H c ) , 5.80 (10H, s, Cp), 6.47 (1H, d, H B , / B A = 19 Hz), 6.94 (1H, d, H A , / A B = 19 Hz); the thermal instability of this compound did not allow for further analysis. Due to this instability, (0.89 g, 2.60 mmol) was immediately reacted with PMe3 (1.98 g, 26.0 mmol) in 2 mL of toluene for 3 days at room temperature in the dark. Evaporation of the volatiles and 249 crystallization of the orange-red oil from toluene/hexanes gave orange crystals of 148 (687 mg, 66%); IP (Nujol): 1627, 1593, 1418, 1283, 1009, 951, 780, 743 and 666 cm-l; 5 ( C 6 D 6 , 400 MHz, l H NMR): 0.97 (9H, d, / H P = 6 Hz), 1.80 (2H, m), 1.90 (2H, m), 2.53 (2H, m), 2.75 (2H, m), 5.42 (10H, d, Cp, / H p = 1.5 Hz), 6.33 (1H, m, H B ) , 7.51 (1H, d, H A , / A P = 4 Hz); 5 ( C 6 D 6 , 121.5 MHz, 31p{lH} NMR): 1.0 (s). Anal, calcd. for C2iH2aPZr: C 62.49, H 7.24; found: C 62.31, H 7.38. (£)-[2-(l-Cyclohexen-l-yl)emenyl]-l-trimethylstannyl-2-chlorobis(r|5- cyclopentadienyl)zirconium(rV) 148 To a solution of 147 (100 mg, 0.25 mmol) in 1.5 mL of toluene was added Me3SnCl (99 mg, 0.50 mmol). The mixture was stirred at room temperature for 3 h, resulting in a color Change from orange to yellow. Evaporation of the volatiles followed by crystallization from toluene/hexanes gave yellow crystals 148 (97 mg, 74%); IR (Nujol): 1620, 1340, 924, 805, 769 and 727 cm" 1 ; 8 ( C 6 D 6 , 400 MHz, l H NMR): 0.23 (9H, s, / HSn = 53 Hz), 1.55 (2H, m), 1.63 (2H, m), 1.98 (2H, m), 2.11 (2H, m), 5.28 (1H, m, H B ) , 5.78 (10H, s, Cp), 7.22 (1H, s, H A , /ASn = 43 Hz). Anal, calcd. for C 2 iH 2 9ClSnZr: C 47.88, H 5.55; found: C 48.20, H 5.74. ClCp 2 Zr H A • ^ ^ S n M e 3 250 References (1) (a) Hegedus, L . S. / . Organomet. Chem. 1988, 342, 147. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G . Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987; pp 669-937. (c) Parshall, G. W.; Nugent, W. A. ; Chan, D. M . T. ; Tam, W. Pure Appl. Chem. 1985,57,1809. (d) Negishi, E. Organometallics in Organic Synthesis; Wiley: New York, N.Y., 1980. (2) (a) Brown, H . C ; Singaram, V . Pure Appl. Chem. 1987,59, 879. (b) Brown, H . 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