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Condensations of methyl propiolate with olefins and acetylenes mediated by group 6 dinitrosyl cations Vessey, Edward G. 1990

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CONDENSATIONS OF M E T H Y L PROPIOLATE WITH OLEFINS AND ACETYLENES MEDIATED BY GROUP 6 DINITROSYL CATIONS By EDWARD G. VESSEY B.Sc, The University of Prince Edward Island, 1988  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA December 1990 ® Edward George Vessey  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 The University of British Columbia Vancouver, Canada Date  DE-6  (2/88)  ii Abstract  The [Cp'M(NO)2]BF (M = Cr, Mo or W; Cp' = Cp or Cp*; except CpW) cations 4  effect the condensation of methylpropiolate and 2-methyl-2-butene within their coordination spheres. The isolated product ratios of the reaction vary with the formation of the sixmembered ring [Cp'M(NO) -C=C(H)C(Me)(H)C(Me) OC(=OCH )]BF complexes being 2  2  3  4  favoured over the five-membered ring [Cp'M(NO) 2  C=C(H)C(Me)(C(H)(Me)2)OC(=OCH )]BF4 complexes. Furthermore, the isolated product 3  ratios vary from metal to metal with the percentage of six-membered ring product increasing from Cr < Mo < W. The connectivity extant in the molecular structures of the cationic complexes was determined by single crystal X-ray crystallographic analysis of a representative example of this class, [Cp*Cr(NO)2-C=C(H)C(Me)(H)C(Me) OC(=OCH )]BF4. 3  2  These cationic lactone complexes may be demethylated by reacting their THF solutions with Nal to afford the neutral lactone complexes, Cp'M(NO) 2  C=C(H)C(Me)(H)C(Me) OC(=O) and Cp'M(N0) -C=C(H)C(Me)(C(H)(Me) )0C(=0). 2  2  2  2-Methyl-2-pentene and methyl propiolate are condensed in the presence of [Cp*Mo(NO) ]BF to generate the six-memberedringcomplex as the only isolable product. 2  4  The condensation of methylpropiolate and diphenylacetylene or 1-phenyl-1-propyne by [Cp*Mo(NO)2]BF results in an unprecedented formation of the cationic a-pyrone 4  complexes [Cp*Mo(NO) -C=C(H)C(R)=C(Ph)OC(=OCH )]BF (R = CH or Ph). These 2  3  4  3  complexes may be demethylated to produce the neutral a-pyrone complexes, Cp*Mo(NO) 2  C==C(H)C(R)==C(Ph)OC(=0) (R = CH or Ph). Only one regioisomer is formed with the 3  regiochemistry of the 1-phenyl-1-propyne complex being confirmed by a single crystal X-ray crystallographic analysis of the neutral complex, Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0). 3  iii Table of Contents  Abstract  ii  List of Figures  iv  List of Tables  v  List of Abbreviations  • • • vi  Acknowledgements CHAPTER 1  viii  General Introduction  1  References and Notes CHAPTER 2  7  Condensations of Methyl Propiolate with olefins in the Presence of [Cp'M(NO)2]BF (M = Cr, Mo or W; Cp' = Cp or Cp*; except CpW) 4  Complexes  .  9  Introduction  10  Experimental Section  12  Results and Discussion  18  References and Notes  45  CHAPTER 3  Condensations of Methyl Propiolate with Acetylenes in the Presence of [Cp*Mo(NO)2]BF  4  47  Introduction  48  Experimental Section  50  Results and Discussion  53  Epilogue  67  References and Notes  71  Appendix  74  iv List of figures  Figure 2.1  The 200 MHz *H NMR spectrum of the product mixture of the fiveand six-membered ring cationic complexes la and lb in acetone-^  Figure 2.2  The proposed mechanism for the formation of the five- and six-memberedringcationic lactone complexes  Figure 2.3  26  The IR spectrum of the product mixture of the five- and six-membered ring cations 2a and 2b as a Nujol mull  Figure 2.4  25  34  The 200 MHz *H NMR spectrum of the product mixture of the five- and six-memberedringlactone complexes 6a and 6b in acetone-Jg  Figure 2.5  35  Solid-state molecular structure of [Cp*Cr(NO) 2  C=C(H)C(H)(CH )C(CH ) OC(=OCH )]BF 3  Figure 2.6  3  2  3  38  4  (a) Selected dimensions for the lactone ligand of CpMo(NO) 2  C=C(H)C(CH ) C(CH ) OC(=O). (b) Selected bond lengths for the 3  2  3  2  methylated lactone ligand of [Cp*Cr(NO) 2  C=C(H)C(H)(CH )C(CH ) OC(=OCH )]BF 3  Figure 3.1  3 2  3  37  4  The 200 MHz *H NMR spectrum of [Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=OCH )]BF 3  3  55  4  Figure 3.2  The IR spectrum of Cp*Mo(NO) -C=C(H)C(CH )=C(Ph)OC(=O)  Figure 3.3  The 200 MHz H NMR spectrum of Cp*Mo(NO) -  2  3  !  2  C=C(H)C(CH )=C(Ph)OC(=0)  60  3  Figure 3.4  Solid-state molecular structure of Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0)  62  Comparison of a-pyrone structures  65  3  Figure 3.4  59  V  List of Tables  Table 2.1  Percentages of each Product for the Cationic Lactone Salts Formed with 2-Methyl-2-butene  Table 2.2  1  19  H NMR Data for the Six-membered Ring Cationic Lactone Complexes from 2-Methyl-2-butene  Table 2.3  20  *H NMR Data for the Five-membered Ring Cationic Lactone Complexes from 2-Methyl-2-butene  22  Table 2.4  Physical Data for the Cationic Products 1-5  23  Table 2.5  *H NMR Data for the Six-membered Ring Neutral Lactone Complexes from 2-Methyl-2-butene  Table 2.6  28  *H NMR Data for the Five-membered Ring Neutral Lactone Complexes from 2-Methyl-2-butene  30  Table 2.7  Physical Data for the Neutral Products 6-10  32  Table 2.8  Percentages of each Product for the Neutral Lactone Complexes Formed with 2-Methyl-2-butene  Table 2.9  33  Selected Bond Lengths (A) for [Cp*Ci(NO) 2  C=C(H)C(H)(CH3)C(CH3)20C(=OCH )]BF4  39  3  Table 2.10  Selected Bond Angles (in degrees) for [Cp*Cr(NO) 2  C=C(H)C(H)(CH3)C(CH3)20C(=OCH )]BF4  40  Table 2.11  Comparison of Lewis Acidity  43  Table 3.1  Selected Bond Lengths (A) for Cp*Mo(NO) -  3  2  C=C(H)C(CH )=C(Ph)OC(=0)  63  3  Table 3.2  Selected Bond Angles (in degrees) for Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0) 3  64  vi List of Abbreviations  A  -  angstrom  cm"  -  wavenumbers  calcd  -  calculated  CDCI3  -  chloroform-d  CD Cl2  -  dichloromethane-^  Cp  -  if-GfHs  Cp*  -  Cp'  -  Cp or Cp*  5  -  chemical shift in ppm referenced to Me^i at 5 = 0 ppm  d  -  doublet (in the NMR spectrum)  Et  -  CH CH , ethyl  Et 0  -  (CH CH2) 0, diethyl ether  Fp  -  CpFe(CO)  g  -  gram  h  -  hour  hv  -  photolysis  *!!  -  proton  IR  -  infrared  J  -  coupling constant (in the NMR spectrum)  m  -  multiplet (in the NMR spectrum)  M  -  Cr, Mo or W  m/z  -  mass-to-charge ratio in the mass spectrum  Me  -  CH , methyl  mmol  -  millimole  v  -  IR stretching frequency  NMR  -  nuclear magnetic resonance  1  2  2  rf-CsiCH^  2  3  3  2  2  3  parent ion (in the mass spectrum) C H , phenyl 6  5  parts per million quartet (in the NMR spectrum) singlet (in the NMR spectrum) triplet (in the NMR spectrum) C H 0 , teu^ydrofuran 4  8  viii Acknowledgements  I would like to thank Peter Legzdins. His faith in me supplied the energy to work through the hard times and his friendship, patience and guidance have made it possible for the completion of this work. The past and present members of the Legzdins research group have helped me greatly in completing this work. Their support is greatly appreciated and their constant abuse kept me smiling. I have learned a lot from the experience of working with such a diverse group of people. I must also thank, in particular, Nancy for getting me started, Neil for keeping my spirits up during the work, and George for his proofreading and helpful discussion while writing this thesis. I thank the other members of the group who helped proofreading the thesis, Mike, Penny, John, Jeff and Peter. Thanks to Drs. F. W. B. Einstein and R. J. Bachelor for their collaboration on the Xray crystallography work. I would, also, like to thank the technical staff at the department whose prompt service kept everything running as smoothly as possible, especially, Zoltan Germann, Steve Rak, Sean Adams, Peter Borda and staff in the NMR lab. I would like to thank the Natural Sciences and Engineering Research Council for their support of this work through a postgraduate scholarship.  1  CHAPTER 1  General Introduction  2 Over the past number of years there has been increasing interest in the use of organometallic transition-metal reagents for the transformation of organic substrates into new organic molecules. The main reason for this interest is the ability of these reagents to impart unique outcomes to organic reactions that would not be possible when these reagents are not employed. These complexes may be used in organic transformations to activate or deactivate functional groups within organic molecules, to increase the regiospecificity of organic reactions, to induce chirality and to possibly provide catalytic routes to the products of these reactions. Electrophilic organotransition-metal cations are particularly useful reagents for effecting organic transformations. The electron-withdrawing effect of these cations allows 1  these complexes to drastically alter the chemistry of unsaturated organic molecules coordinated to their metal centers. Coordinated olefins or acetylenes will be expected to have reduced electron density in their unsaturated bonds and may undergo nucleophilic attack, a reverse of the reactivity of these unsaturated organic molecules when not coordinated to the cationic metal center.  (1.1)  >  (M = organometallic complex; Y = nucleophile)  Reactivity, like that shown in equation 1.1, has stimulated research into the use of cationic metal centers to mediate organic transformations. Very little was known about cationic organotransition metal complexes until the last two decades and their use in organic 2  synthesis has been limited until very recently. Today there are a number of well developed systems with many more being developed. The most well studied complex of this type is [CpFe(CO)2] , F p , cation. Much of +  +  the organic chemistry carried out by this cation was developed by Rosenblum over the last 3  3 twenty years. This cation forms stable, isolable 1:1 adducts with a wide range of olefins and acetylenes. These complexes may be formed by refluxing a solution of Fp(ij -isobutylene) 2  +  with the desired unsaturated organic ligand, equation 1.2.  4  +  olefin  +  (Fp = CpFe(CO)2)  These complexes may undergo nucleophilic attack on the olefin to give neutral or cationic FpOj -alkyl) complexes when charged or uncharged nucleophiles are used, 1  respectively. The regiospecificity of this reaction depends on the olefin and nucleophile used. However, when the olefin is an alkyl vinyl ether, the reaction is very specific with nucleophilic attack on the carbon containing the alkoxy substituent, e.g. equation 1.3. The 5  alkyl vinyl ether complex may be considered a vinyl cation equivalent of which there are few examples.  +  Fp  OR  + RO  I  Fpl  (1.3)  +  The F p cation has also been used to prepare 0-lactams and other natural products by utilizing +  Fp(T7 -olefin) complexes 2  +  Furthermore, the F p has proven useful as a protecting group when coordinated to an +  unsaturated bond in a molecule containing more than one site of unsaturation. It has been used to protect olefins as shown in equation 1.4 during the electrophilic substitution of Br on the aromatic ring.  6  OH  OH OMe  F  OMe  + P  + Fpl  (1.4)  Organotransition metal cations have also been developed as Diels-Alder catalysts. Hersh and coworkers have synthesized Me P(CO) (NO)W0t-F)SbF and demonstrated its 7  3  3  5  potential as a Diels-Alder catalyst in the reaction shown below in equation 1.5.  (1.5)  Me  The main driving force of these studies is the potential these organotransition metal cations have for developement as chiral catalysts. These chiral catalysts would hopefully offer a route to asymmetric Diels-Alder products that would greatly increase the range of enantiomerically pure organic compounds for the organic chemist. Chiral organotransition metal cations have been developed. One cation in particular, 8  CpRe(NO)(PPh ) has been well characterized by Gladysz and coworkers. This cation has +  3  been obtained in optically pure form by fractional crystallization of the amide complex as in equation 1.6.  9  5  ON  ^ vy*P  Ph,P  I  NH  J  b, c,d  > 95:5  a  BF„  ratio of  ON » ^  diastereomers  PhgP  ,,,  (1.6)  E  CO  (R* =(+)-(^)-a-(l-naphmyl)emylamine (a) recrystallization from benzene/hexane (b) CF C0 H; (c) NaBF ; (d)K C0 3  2  4  2  3  This optically pure compound has shown a diverse reactivity with unsaturated and saturated organic ligands. With aldehydes, chiral esters may be produced, e.g. equation 1.7.  BF„ ON '' ^ Ph P 3  e  -  ON  ?  E  >^  A HOH  10  ,A  H  R H  H  J  (1.7)  °  This chiral cation can also be converted into the neutral alkyl complexes. Deprotonated to the carbene complex with retention of configuration and alkylation of the resulting carbene complex produces a chiral alkyl ligand as shown in equation 1.8.  11  Many of these cations contain strong x-acid ligands, i.e. CO and NO. The electronwithdrawing abilities of these ligands enhances the metal centers' electrophilicity. The bonding in these systems may be represented as a combination of ^-donation and x-back donation as shown in the diagram below for the NO ligand bonding to a metal.  .  f  M<X>N=0  .  a donation  Utr*  x donation  Na  c7"W"\> Mdx  • NOpx  The x bonding makes a larger contribution to the overall metal to nitrosyl or carbonyl bond, thus the overall effect of the bond is a net withdrawal of electron-density from the metal center. The strong x-acidity of these ligands allows them to increase the electrophilicity of the metal and the organometallic cation as a whole. The degree of M d x - » N O p x  electron  donation depends on the electron density of the metal center. This electron density donation into the N O p x * orbital causes a reduction of N O bond order. Changes in the electron donation are therefore related to the N O bond strength which may be quantified by the nitrosyl stretching frequency (»>NO) as observed in the IR spectrum of the complex. These bands are also useful in monitoring the course of a reaction involving complexes with these ligands. This thesis deals with the electrophilic cations, [Cp'M(NO)2] (M = Cr, Mo or W; +  Cp' = C5H5 or C (Me)5). Chapter 2 deals with the condensation of olefins with methyl 5  propiolate within the metals' coordination spheres. The outcome of these reactions along with the spectroscopic properties of the products are discussed. Chapter 3 contains the reactions of these cations with methyl propiolate and acetylenes. The products of these reactions are discussed along with the spectroscopic properties of the new class of compounds synthesized.  7  References and Notes  1  Collman, J. P.; Hegedus, L. S.; Horton, J. R.; Finke, R. G. Principles of Organotransition Metal Chemistry, University Science Books: Mill Valley, California, 1987, Chapters 7, 16 and 17.  2  (a) Sen, A. Acc. Chem. Res. 1988, 21, 421. (b) Beck, W.; Sunkel, K. Chem. Rev. 1988, 88, 1405.  3.  Rosenblum, M.; Bucheister, A.; Chang, T. C. T.; Cohen, M.; Marsi, M.; Samuels, S. B.; Scheck, D.; Sofen, N.; Watkins, J. C. Pure Appl. Chem. 1984, 56, 129.  4.  (a) Cutler, A.; Ehntholt, P.; Lennon, P.; Nicholas, K.; Marten, D. F.; Raghu, S.; Rosan, A.; Rosenblum, M. J. Am. Chem. Soc. 1975, 97, 3149. (b) Cutler, A.; Ehntholt, P.; Giering, W. P.; Lennon, P.; Raghu, S.; Rosan, A.; Rosenblum, M.; Trancede, J.; Wells, D. J. Am. Chem. Soc. 1976, 98, 3495 and references therein.  5.  Chang, T. C. T.; Rosenblum, M.; Samuels, S. B. J. Am. Chem. Soc. 1980,102, 5931.  6.  Collman, J. P.; Hegedus, L. S.; Horton, J. R.; Finke, R. G. Principles of Organotransition Metal Chemistry; University Science Books: Mill Valley, California, 1987, p 847.  7.  Bonnesen, P. V.; Puckett, C. L.; Honeychuck, R. V.; Hersh, W. H. J. Am. Chem. Soc. 1989, Ul, 6070.  8.  (a) The first organotransition metal complex to be resolved was [CpMn(NO)(PPh )] , +  3  Brunner, H. Angew. Chem., Int. Ed. Engl. 1969, 8, 392. See also (b) Brunner, H. Adv. Organomet. Chem. 1980,18, 151. (c) Flood, T. C ; Campbell, K. D.; Downs, H., H.; Nakanishi, S. Organometallics 1983, 2, 1590. (d) Faller, J. W.; Chao, K . H. Organometallics 1984, 3, 927. (e) Consiglio, G.; Morandini, F. Chem. Rev. 1987, 87, 761. (f) Hommelsoft, S. I.; Baird, M. C. Organometallics 1986, 3, 1380. (g) Davies, S. G.; Dordor-Hedgecock, I. M.; Sutton, K. H.; Walker, J. C ; Bourne, C ; Jones, R. H.; Prout, K. J. Chem Soc., Chem. Commun. 1986, 607. (h) .  8 Brookhart, M.; Liu, Y. Organometallics 1989, 8, 1572. 9.  Merrifield, J. H.; Strouse, C. £.; Gladysz, J. A. Organometallics 1982,1, 1204.  10.  Garner, C. M.; Mendez, N. Q.; Kowalczyk, J. J.; Fernandez, J. M.; Emerson, K.; Larsen, R. D.; Gladysz, J. A. J. Am. Chem. Soc. 1990,112, 5146.  11.  Kiel, W. A.; Lin, G. Y.; Constable, A. G.; McCormick, F. B.; Strouse, C. E.; Eisenstein, O.; Gladysz J. Am. Chem. Soc. 1982,104, 4865.  9  CHAPTER 2  Condensations of Methyl Propiolate with Olefins in the Presence of [Cp'M(NO) ]BF4 2  (M = Cr, Mo or W; Cp' = Cp or Cp*; except CpW) Complexes.  10 Introduction  The [Cp M(NO) ]BF (M = Cr, Mo, or W; Cp' =. Cp or Cp*; except CpW) ,  2  4  complexes are formed by abstraction of halide from their chloro precusors using AgBF as 4  shown in equation 2.1.  Cp'M(NO) Cl 2  1,2  +  AgBF  [Cp'M(NO)2]BF  4  4  +  AgCH  (2.1)  (Cp' = Cp or Cp ; M = Cr, Mo or W)  These complexes behave as the formally 16-electron [Cp'M(NO)2] fragments. For +  example, the Mo and W complexes form adducts with Lewis bases such as phosphines and phosphites.  3,4  All the Cp complexes abstract Ph" from the BPh " anion to form the 4  CpM(NO) Ph (M = Cr , Mo or W ) compounds. The only isolable olefin adducts of these 2  2  3  2  complexes are the Mo and W complexes with cyclooctene. To date there are no known 5  3  acetylene adducts of these complexes. Rosenblum and coworkers showed that some olefins and acetylenic esters will condense in the coordination sphere of the [CpFe(CO)2] , F p , cation to produce a variety of +  +  cyclobutene, 1, 3-diene, and Fp(7j -lactone) complexes, equation 2.2, depending on the type 6  1  of olefin used in the reaction.  O  7  F  COOMe Fp  +  p  \  +  COOMe R = H, Me a  \  = C H ^ , RT  b = Nal, THF JIT  ^  oc OC  =  Fp  11 Recently it has been shown in our research group that the [Cp'M(NO)2] cations +  react with 2,3-dimethyl-2-butene and methyl propiolate to form the six-memberedringlactone complexes shown below in equation 2.3.  (R = H or Me; M = Cr, Mo or W)  At the beginning of this work equation 2.3 had only been successfully accomplished with 2,3-dimethyl-2-butene and methyl propiolate. This chapter describes the results of varying the nature of the substitution of the olefin.  12 Experimental Section  All reactions and subsequent manipulations were performed under anaerobic and anhydrous conditions using conventional Schlenk techniques, or using a Vacuum Atmospheres Corp. Dri-Lab Model HE-43-2 drybox, under an atmosphere of dinitrogen, unless otherwise specified. Solvents were obtained from either BDH Chemicals or Aldrich and were purified according to published procedures. Hexanes and acetonitrile were dried over CaH ; diethyl 8  2  ether and tetrahydrofuran were predried on CaH ^ 2  m  e  n  distilled from Na/benzophenone;  CH C1 was distilled from P C«5; and methanol (Omnisolv) was used without further 2  2  2  purification. The solvents were freshly distilled and purged with N for approximately 10 2  minutes before use. All chemicals were of reagent grade or comparable purity, and were purchased from commercial suppliers or prepared by published procedures. Methyl propiolate (99%), 2,3dimethyl-2-butene (98%), 2-methyl-2-butene (99+%), 2-methyl-2-pentene (98%), 2,4,4trimethyl-2-pentene (99%), phenylacetylene (98%) and AgBF (98%) were purchased from the 4  Aldrich Chemical Co. and were used without further purification. Cyclohexene (98%, Kodak), cis,trans-2-butene (technical grade, Matheson Gas Co.) and Nal (Mallinckrodt) were also used without further purification. l-phenyl-3,3,4,4-tetramethylcyclobutene was prepared by the published procedure.  2  The CpM(NO) Cl compounds (M = Cr, Mo, or W) and Cp*W(NO) Cl were 9  3  2  2  prepared by published procedures. Cp Mo(NO) Cl was prepared in a similar manner to the 2  analogous tungsten complex, while the known chromium congener was prepared by a new method presented later in this section. The purity of these starting materials was checked by elemental analyses. Infrared spectra were obtained with a Nicolet Model 5DX FT-IR instrument, internally calibrated with a He/Ne laser, as solutions in AgCl cells or as Nujol mulls between NaCl plates. All *H NMR spectra were obtained on a Bruker AM-200E spectrometer and the chemical shifts are reported in parts per million downfield from Me Si, and referenced to the 4  13 residual proton signal of the solvent employed. Low resolution mass spectra (EI, 70 eV) were recorded on a Kratos MS50 spectrometer using the direct insertion method by Dr. G.K. Eigendorf and Mr. M.A. Lapawa. Analytical gas chromatography was carried out using a Shimadzu GC-14A gas chromatograph and GC-MS samples were run using a Varian Vista 6000 gas chromatograph interfaced with a Nermag R10-10 Quadrupole mass spectrometer. All elemental analyses were performed by Mr. P. Borda of this department. Preparation of C p * C r ( C O ) ( N O ) . To a solution of Cp*Cr(CO) H in THF (250 10  3  2  mL) was added slowly a THF (40 mL) solution of Diazald (20.5 g, 96 mmoles), via an addition funnel over a period of 30 minutes. CAUTION: Large amounts of CO gas are evolved during the addition and care must be taken to avoid the buildup of excess pressure during the initial stages of the reaction and to vent the CO to a fumehood. The reaction mixture was stirred for 3 h, and the solvent was then removed in vacuo. Sublimation of the residue under dynamic vacuum (5 x 10" mm) at 60°C onto a water-cooled 3  probe afforded 16.2 g (59.3 mmol, 62% yield based on Diazald) of Cp*Cr(CO) (NO). 2  Preparation of [Cp'M(NO)2]BF (Cp* = C p or Cp*; M = Cr, Mo, or W; except 4  CpW).  These complexes were all prepared by treatment of CH Cl2 (40 mL) solutions of the 2  Cp M(NO) Cl complexes with stoichiometric amounts of AgBF as described previously/ In 2  4  a typical experiment, the reaction was followed by IR spectroscopy and took 15 to 45 minutes to go to completion. In each case the conversion was clean (by IR) and assumed to be quantitative. The AgCl precipitate was removed by filtration of the final reaction mixture through a plug of Celite (2x3 cm) on a medium-porosity frit, and thefiltrateswere then reacted with the desired organic substrates. Reaction of [CpCr(NO)2]BF with 2,3-Dimethyl-2-butene and Phenylacetylene. 4  To a 3-necked round-bottomed flask containing a green CH C1 (40 mL) solution of 2  2  [CpCr(NO) ]BF (2.0 mmol) was added phenylacetylene (1.10 mL, 1.02 g, 10.0 mmol) and 2  4  2,3-dimethyl-2-butene (1.19 mL, 0.842 g, 10.0 mmol) by syringe. A slight color change to a darker green occurred immediately upon addition. The reaction mixture was stirred overnight,  14 and the resulting green solution was filtered through a short (2x4 cm) column of alumina (Brockman neutral, activity 1) supported on a medium porosity frit. The volatile components were removed in vacuo at room temperature to leave l-phenyl-3,3,4,4-tetramethylcyclobutene (0.63 g, 34% yield) as a slightly yellow oil. J  H NMR (CDC1 ): 6 7.50-7.20 (m 5H, C H ) , 6.30 (s 1H, vinyl H), 1.40 (s 6H, 3  6  C(CH ) -), 1.20 (s 6H, -C(Cff ) -). 3  2  3  5  4  2  Reaction of [CpMCNO^BF^ with 2-Methyl-2-butene and Methyl Propiolate. All reactions were carried out with a 2-3 times excess of organic reagents. (a) M = Cr. Methyl propiolate (0.5 mL) and 2-methyl-2-butene (0.5 mL) were added sequentially by syringe to a 3-necked round-bottomed flask containing a green CH C1 2  2  (40 mL) solution of [CpCr(NO) ]BF (2.0 mmol). A slight color change to a darker green 2  4  occurred immediately upon addition of the organic reagents. The reaction mixture was stirred overnight under reflux. The solution was concentrated to approximately 5 mL and Et 0 (100 2  mL) was added to the concentrate, causing a green oily solid to deposit on the sides of the flask. Trituration of the solid with Et 0 afforded a powder that was washed with Et 0 (2 x 50 2  2  mL) and dried in vacuo to afford 0.63g (75%) of a mixture six- and five-membered ring cationic lactone products, [CpCr(NO) -C=C(H)C(CH )(H)C(CH3) OC(=OCH )]BF4, la, 2  3  2  3  and [CpCr(NO) -C=C(H)C(C(H)(CH ) )OC(=OCH )]BF , lb, respectively, as an olive2  3 2  3  4  green solid. The pentamethylcyclopentadienyl analogue was synthesized in a similar manner, however, the reflux was carried out for only 2 h. The *H NMR data are reported in Tables 2.2 and 2.3, with IR, and elemental analyses data presented in Table 2.4. (b) M = Mo. These reactions were carried out in a similar manner to those of their Cr congeners, but the reaction was completed by stirring the reaction mixture for 1 h at room temperature. (c) M = W. This reaction was performed in a similar manner to that of its chromium congener, but the reaction was initially begun at -70 °C and allowed to warm slowly to room  15 temperature. Reaction of Cationic Lactone Complexes with Nal. All reactions of the cationic lactone complexes with Nal follow the same procedure as outlined for CpCr lactone complex. To a stirred green solution of the CpCr cationic lactones in THF (40 mL) was added Nal (0.16 g, 1.1 mmol). The reaction mixture was stirred for 2 h then filtered through alumina (2 x 3 cm Woelm neutral, activity 1) supported on a medium porosity frit. The alumina column was then washed with THF (20 mL) and the combined filtrates were taken to dryness in vacuo to produce 0.09g (28%) of a mixture of six- and five-membered ring neutral lactone products as an olive-green solid. Physical, analytical, mass spectral, IR and *H NMR data for these complexes are presented in Tables 2.5 - 2.7. Reaction of 2-Methyl-2-pentene and Methyl Propiolate with Cp*Mo(NC»2BF4. . Methylpropiolate (0.5 mL) and 2-methyl-2-pentene (0.5 mL) were added sequentially by syringe to a green CH C1 (40 mL) solution of Cp*Mo(NO) BF (2.0 mmol). The reaction 2  2  2  4  mixture was stirred and the progress of the reaction was monitored by IR spectroscopy. After 2 h there was no more shift of the P^Q JR bands to lower wavenumbers and the reaction was deemed to be complete. The solvent was reduced to approximately 5 mL with the subsequent addition of Et 0 (80 mL) causing the precipitation of a green gummy solid. Upon trituration 2  for several minutes this solid became a light green powder. Removal of solvent via cannulation, followed by washing the product with Et 0 (2 x 40 mL), allowed the isolation of 2  a light green solid. This solid was redissolved in THF (40 mL) and Nal (0.33 g, 2.2 mmoles) was added. The mixture was then stirred for 2 h and the resulting solution filtered through a column of alumina (2 x 3 cm Woelm neutral, activity 1) supported on a medium porosity frit. The column was washed with 30 mL of THF and the combinedfiltrateswere taken to dryness in vacuo. The resulting light green powder was then recrystallized from CH Cl /hexanes to 2  2  yield 0.40 g (48%) of Cp*Mo(NO) -C=C(H)C(CH CH )(H)C(CH ) OC(=0) as analytically 2  pure dark green crystals.  2  3  3 2  16 Anal. Calcd. for C H N 0 M o : C, 51.34; H, 6.36; N, 6.30. Found: C, 51.07; H, 19  28  2  4  6.52; N, 6.03. IR (Nujol Mull) 1709(s), 1676(s), 1634(w), 1603(s) cm- ; ( O ^ C l ^ v 1  1717(s), 1674(s), 1620(s) cm' . K NMR (<*-acetone) 5 6.75 (d 1H, -C=C(fl)-, 7HH = 3.5 1  l  3  6  Hz), 2.11 (dt 1H, -C(fl)(CH CH ), 7HH = 3.5 Hz; 7HH = 11.0 Hz), 1.82 (s 15H, 3  2  3  3  C (CH ) ), 1.61-1.43 (m 2H, -C(H)(CH CH )), 1.27 (s 3H, -C(CH ) -0), 1.14 (s 3H, 5  3  5  2  3  3  2  C(C# ) -0), 0.94 (t 3H, -C(H)(CH Ci/ ), ^JQJ = 7.5 Hz). Low-resolution mass spectrum 3  2  2  3  (probe temperature 120°C) m\z 416 [P -(NO)]. +  This reaction sequence was used for all other olefins used in this study. Decomposition of Neutral Lactone Complexes in Air. When an NMR tube containing a solution of the neutral lactone complex was exposed to air the solution turned yellow within 30 minutes. The *H NMR spectrum of the resulting product showed new signals that were assignable to the Cp'Mo(=0) (»; -lactone) complexes. 1  2  CpMo(=0) -C=C(H)C(H)(CH )C(CH ) OC(=O). *H NMR (rf-acetone) 5 6.80 2  3  3  2  6  (d, 1H, =C(#)-, 7HH = 3-5 Hz), 6.52 (s, 5H, C ff ), 2.56 (dq, 1H, -C(fl)(CH )-, 7 H = 3  3  5  5  H  3  3.5 Hz; 7HH = 7.5 Hz), 1.37 (s, 3H, -C(C# ) O), 1.26 (s, 3H, -C(C# ) -0), 1.04 (d, 3H, 3  3  r  3  2  -C(H)(Ci? )-, JHH = 7.5Hz). 3  3  Cp*Mo(=0) -C=C(H)C(H)(CH )C(CH ) OC(=O). *H NMR (d-acetone) 8 6.74 2  3  3 2  6  (d, 1H, =C(#)-, 7HH = 3.5 Hz), 2.60 (dq, 1H, -C(fl)(CH )-, V H H = 3.5 Hz; 7 H = 7.5 3  3  H  3  Hz), 2.02 (s, 15H, C (Cff ) ), 1.40 (s, 3H, -C(Cff ) -0), 1.29 (s, 3H, -C(C# ) -0), 1.11 5  3  5  3  2  3  2  (d, 3H, -C(H)(Cff )-, 7HH = 7.5 Hz). 3  3  Cp*Mo(=0) -C=C(H)C(H)(CH CH )C(CH ) OC(=0). *H NMR (d-acetone) 5 2  2  3  3  2  6  6.81 (d, 1H, =C(H)-, / H H = 3.5 Hz), 2.35 (dt, 1H, -C(fl)(CH CH )-, 7HH = 3.5 Hz; 3  3  2  3  3  7HH = 10.5 Hz), 2.02 (s, 15H, C (C# ) ), 1.75 - 1.58 (m, 2H, -C(H)(Ctf CH )-) 1.40 (s, 5  3  5  2  3  3H, -C(Cff ) -0), 1.27 (s, 3H, -C(Cff ) -0), 1.03 (t, 3H, -C(H)(CH C# )-, 7HH = 7.5 3  3  2  3  2  2  3  Hz). The chromium analogues changed color from green to brown after being exposed to air for several days, but the *H NMR spectra of the solutions showed only broad unresolved peaks that could not be assigned.  17 NMR Tube Reactions of [Cp'Cr(NO)2]BF (Cp* = Cp or Cp*) Cations with 4  Crotonaldehyde . All reactions were performed in a dry box in the same manner and the reaction of CpCr complex is given as an example. CpCr(NO) Cl (0.075 g, 0.35 mmol) was dissolved in 1 mL of CD C1 in a vial and 2  2  2  AgBF (0.068 g, 0.35 mmol) was added. This solution was stirred for 8 h to ensure 4  completion of the reaction. This solution was filtered through a short plug of Celite (to remove the AgCl precipitate) into an NMR tube containing approximately 2 equivalents of crotonaldehyde. A H NMR spectrum of this mixture showed new signals for H3 of 1  coordinated crotonaldehyde at 7.65 ppm (7.75 ppm for the Cp*Cr cation) while H3 for free crotonaldehyde appeared at 6.89 ppm. X-ray Crystallographic Analysis of [Cp*Cr(NO)2C=C(H)C(CH3)(H)C(CH3)20C(=OCH )]BF4. Suitable crystals for a single crystal X-ray 3  structural analysis were obtained by placing a saturated CH Cl /hexanes solution of 2  2  [Cp*Cr(NO) -C=C(H)C(H)(CH )C(CH3) OC(=OCH )]BF in the refrigerator at 5°C. After 2  3  2  3  4  one week suitable crystals were formed. The X-ray structural analysis was performed by Drs. F. W. B. Einstein and R. J. Bachelor at Simon Fraser University.  18 Results and Discussion  Although the [Cp'M(NO)2] (M = Cr, Mo or W; Cp' = Cp or Cp*; except CpW) +  cations do not form isolable 1:1 adducts with olefins (with the exception of cyclooctene for CpMo or CpW) or acetylenes, they do allow the condensation of olefins and acetylenic esters within the metals' coordination spheres to form cationic lactone salts. For example, when 2methyl-2-butene and methyl propiolate are condensed in the presence of [Cp'M(NO)2]  +  cations, the reaction proceeds as shown in equation 2.4.  The product ratios of this reaction vary depending on which cation is used, but the reaction strongly favors the formation of the six-membered ring. The percentages of each isomer formed in the reaction for each cation are listed in Table 2.1.  12  Separation of the five- and  six-memberedringcomplexes was not carried out, and the identification of the five-membered ring complexes was accomplished by *H NMR spectroscopy of the product mixture.  19 Table 2.1 Percentages of each Product for the Cationic Lactone Salts Formed with 2-  Methyl-2-butene.  a  Metal fragment  six-membered ring .  five-membered ring  CpCr(NO)  82  18  Cp*Cr(NO)  87  13  CpMo(NO)  the five-membered ringcould not be detected  2  2  2  Cp*Mo(NO)  95  Cp*W(NO)  the five-membered ringcould not be detected  2  2  5  The percentages are based on the integration of the OCH signal. 3  These cationic lactone salts may be handled as solids in air with no noticeable decomposition over a period of hours. The spectral, physical, and analytical data on these compounds are presented in Tables 2.2 - 2.4. The H NMR spectra of these complexes are !  illustrated with the spectrum of the cyclopentadienylchromium complex shown in Figure 2.1 (the assignments are as presented in the figure). The coupling of the -C(#)(Me)- with the vinyl proton, along with the downfield shift of the NMR signals due to the C(C// ) protons is 3  2  indicative of the regiochemistry presented for the six-membered ring in reaction 2.4. Chemical shifts for the OMe protons for the five six-membered ring complexes appear in the 4.38 - 4.47 ppm range and are typical for alkoxymethyl cations.  13  This narrow range of  values would indicate that the metal centers do not interact with the OMe group to any appreciable degree. If the metal centers were helping to delocalize the positive charge on the cation, it would be expected that the range of shifts for these signals would be greater than that observed. There may be some electron-density withdrawn from the C=C double bond, however, since the range of values seen for the vinyl proton 7.36 - 7.55 ppm is somewhat greater than that seen for the OMe signals. All the shifts are very similar to those observed for the previously produced lactone complexes of this type when 2,3-dimethyl-2-butene was used as the olefin.  2  20 Table 2.2. H NMR Data for the Six-membered Ring Cationic Lactone Complexes from 2-Methyl-2-butene. 1  Compound  *H NMR data 6  (CD$ = C  2  7.36 (d, 1H, =C(fl)-  / H H = 4.0 Hz)  3  5.88 (s, 5H, C5H5) 4.40 (s, 3H, O C H 3 ) |  OMe  II  C r  ON  3.12 (dq, 1H, -C(fl)(CH )7HH = 4.0 Hz / H H = 7.5 Hz) 1.76 (s, 3H, -C(Ctf ) -0) 1.60 (s, 3H, -C(C# ) -0) 1.24 (d, 3H, -C(H)(CH )7HH = 7.5 Hz) 3  3  BF " 4  3  3  2  3  2  3  3  7.38 (d, 1H, =C(fl)-  7 = 4.0 Hz) 4.44 (s, 3H, OCH ) 3.13 (dq, 1H, -C(fl)(CH )7 = 4.0 Hz 7 = 7.5 Hz) 1.85 (s, 5H, C H ) 1.77 (s, 3H, -C(Ctf ) -0) 1.63 (s, 3H, -C(C# ) -0) 1.26 (d, 3H, -C(H)(C# )7HH = 7-5 Hz) 3  +  ~  O N ^ ' . ON  | C  Fl  ~* OMe r v  H H  3  3  3  H H  3  y  BF "  H H  4  S  ,  S  3  2  3  2  3  3  7.49 (d, 1H, =C(fl)7HH = 4.0 Hz) 3  + OMe  I  1  l l 30  6.30 (s, 5H, C5H5)  4.38 (s, 3H, OCH ) 3.15 (dq, 1H, -C(#)(CH )7 = 4.0 Hz 7HH = 7.5 Hz) 1.76 (s, 3H, -C(C# ) -0) 1.61 (s, 3H, -C(C# ) -0) 1.25 (d, 3H, -C(H)(C# )7HH = 7.5 Hz) 3  3  BF " 4  3  H H  3  3  2  3  2  3  3  0  21 Table 2.2. continued. *H NMR data (CD^C=O  Compound  +  | 4a  "5—]-^T OMe  3  3  1  ON  7.49 (d, 1H, =C(fl)V H H = 4.0 Hz) 4.44 (s, 3H, OCH ) 3.19 (dq, 1H, -C(fl)(CH )/ H H = 4.0 Hz 7HH = 7.5 Hz) 1.99 (s, 15H, C (CH ) ) 1.80 (s, 3H, -C(C# ) -0) 1.66 (s, 3H, -C(CH ) -0) 1.29 (d, 3H, -C(H)(CH )7HH = 7.5 Hz) 3  3  BF " 4  5  3  3  2  3  2  5  3  3  7.55 (d, 1H, =C(fl)7HH = 4.0 Hz) 4.47 (s, 3H, OCH ) 3.24 (dq, 1H, -C(fl)(CH )7 = 4.0 Hz 7HH = 7.0 Hz) 2.09 (s, 15H, C (C# ) ) 1.80 (s, 3H, -C(Ci/ ) -0) 1.67 (s, 3H, -C(C# ) -0) 1.32 (d, 3H, -C(H)(C/7 )7HH = 7.0 Hz) 3  +  1 ON »  , , ,  r^i  OMe  'y \ J l ^ W  3  3  3  H H  3  BF " 4  5  3  5  3  2  3  2  3  3  22 Table 2.3. H NMR Data for the Rve-membered Ring Cationic Lactone Complexes from 2-Methyl-2-butene. 1  a  Compound  % NMR data (CD ) C=0 3  6  2  8.40 (s, 1H, =C(fl)5.93 (s, 5H, C5H5) 4.62 (s, 3H, OCH3)  I  2.34 (septet, 1H, -C(fl)(CH ) 3  OMe  "f\A  3  BF -  M  J H H = 7.0 Hz)  1.74 (s, 3H, -C(Cff )1.12 (d, 3H, -C(H)(Cff ) -0) 7HH = 7.0 Hz) 1.05 (d, 3H, -C(H)(C# ) -0) 7HH = 7.0 Hz)  4  3  |T o  ON*  2  3  2  3  2  3  3  8.38 (s, 1H, =C(fl)4.68 (s, 3H, OC# ) 2.34 (septet, 1H, -C(#)(CH ) 7 = 7.0 Hz) 1.89 (s, 5H, C (CH ) ) 1.76 (s, 3H, -C(C# )1.15 (d, 3H, -C(H)(CH ) -0) 7HH = 7.0 Hz) 1.10 (d, 3H, -C(H)(C# ) -0) 7 = 7.0 Hz) 3  +  1 ~ | O N . , . -  ^  1  I  OMe M  2  b  1  0  2  H H  5  BF " 4  ON  3  3  3  5  3  3  2  3  3  2  3  H H  8.54 (s, 1H, =C(H)4.67 (s, 3H, OCH ) -C(/J)(CH ) - signal not observed C5 (Ctf ) 5 signal obscured by solvent signal 1.78 (s, 3H, -C(Cff )1.12 (d, 3H, -C(H)(Cff ) -0) 7HH = 7.0 Hz) 1.08 (d, 3H, -C(H)(CH ) -0) 3  | 4b |  +  |  3  2  3  OMe  L ^_  BF " 4  3  3  2  3  3  3  2  7HH = 7.0HZ)  * The signals for the CpMo(NO) and the Cp*W(NO) complexes could not be assigned. 2  2  Table 2.4. Physical Data for the Cationic Products 1-5. IR (Nujol)  b  Color  (cm")  C (calcd)  1  fCpCr(NO)2C-C(H)C(HKMe)C(Me)20C(-0Me)]BF4  [Cp*Cf<N0)2C - C(H)C(HKMe)C(Me)20C(- OMe)lBF  75  C-C(H)C(H)(Me)C(Me) OC(-OMe)JBF  2  1759(s), 1659(s), 1510(m)  1680(s), 1559(w),  light green  75  1750(s), 1632(8), 15t8(m)  1678(s), 1570(m),  light brown  78  1715(s), 1620(8), 15I2(m)  1644(s), 1562(m),  1698(8), 1561(w),  1609(8), 1514(w)  ti-C(H)CXHXMe)C(Me)20C(-OMe)IBF  4  tCp*W(N0)2C - C(H)C(H)(Me)C(Me)20it( - OMe)]BF  light green  56  4  • Compound mixtures represented by the six-membered ring form. b  IR bands in the 1900-1500 cm" region.  c  Elemental analysis was not obtained.  1  1684(s), 1508(m)  92  4  [Cp*Mo(NO) -  1800(s), 1559(m),  golden green 4  ICpMo(NO)22  light green  Analytical Data  Yield  Compound"  H (calcd)  N  (calcd)  39.52  4.56  6.60  (40.21)  (4.59)  (6.70)  46.44  6.10  5.71  (46.73)  (6.00)  (5.74)  32.69  4.07  5.85  (36.39)  (4.15)  (6.06)  42.62  5.68  5.12  (42.87)  (5.50)  (5.26)  c  c  c  24  CsH  s  OCH  vinyl H  CH 's 3  3  C(/i)(CH )» 3  uu  i l l  I ' 10.0 1  1  1  1  I• 9.0  i Ii iiiIiiiiIi i ' I '  6.0  7.0  6.0  5.0 PPM  4.0  3.0  2.0  1.0  5  0.0  Figure 2.1. The 200 MHz *H NMR spectrum of the product mixture of the five- and sixmembered ring cationic complexes la and lb in acetone-^ (•). [(•) an impurity in the deuterated solvent].  25 Thefive-memberedring complexes are also indentified in the *H NMR spectra of the products by a pair of doublets at approximately 1 ppm. This pair of doublets is a result of the H in the -C(fl)(CH ) - grouping coupling to the methyl groups. The rest of the peaks that 3  2  may be seen for the other protons are all singlets as expected, except for the -C(fl)(CH ) 3  2  proton which appears as a septet. This proton signal is about 0.8 ppm upfield from the position of the -C(7J)(CH )- in the six-membered ring complexes, indicating that it is no 3  longer on a C atom that is bonded to an sp carbon. The signals for the vinyl H's appear 2  approximately 1 ppm further downfield than the corresponding protons in the six-membered ring complexes. A second Cp' signal is also observed and appears slightly downfield from the signals for the six-membered ring complexes. The elemental analyses for some of these cationic complexes are close to the expected values, but have a lower carbon content than the calculated value. This may be a result of the difficulty of separating the cationic complexes from other inorganic salts in the reaction mixture. The outcome of these reactions may be explained by the mechanism shown in Figure 2.2. The reaction is believed to involve initial coordination of the acetylenic ester to the metal center through the triple bond. This complex then undergoes nucleophilic attack by the alkene to give the intermediate carbocation shown in Figure 2.2. This carbocation may close directly to form the six-membered-ring complex, or may rearrange before closure to give the fivememberedringlactone. The cationic complexes may be converted to the neutral lactone complexes by reaction with a stoichiometric amount of Nal as shown in equation 2.5 for the six-membered ring system.  26  Figure 2.2. The proposed mechanism for the formation of the five- and six-membered ring cationic lactone complexes.  27  *5  BF„  o Nal  ON  (2.5)  ¥  THF  (R = H or Me; M = Cr, Mo or W; except CpW)  The neutral lactone products are air-stable for several hours as solids, but solutions of the compounds decompose when exposed to air for several hours. The Mo complexes decompose to form the corresponding dioxo species as shown in equation 2.6,  14  (2.6)  R'  R'  (R = H or Me; R' = Me or Et)  whereas, the Cr complexes decompose to intractable compounds. The physical, analytical and spectral data for these neutral lactone complexes is presented in Tables 2.5 - 2.7 and a list of the percentages of each isomer is presented in Table 2.8. The IR data for the products show that the v  co  for the products do not vary significantly  for the five six-memberedringcompounds. In the case of the Cp*Cr(NO)2 products, 15  28 Table 2.5. *H NMR Data for the Six-membered Ring Neutral Lactone Complexes from 2-Methyl-2-butene.  *H NMR data ( C D ^ C ^ O 6  Compound  6.49 (d, 1H, =C(fl)-  V H H = 3.5 Hz) 5.65  (s, 5H, C5H5)  2.47 (dq, 1H, -C(fl)(CH )7HH = - Hz 7HH = 7.5 Hz) 1.34 (s, 3H, -C(CH ) -0) 1.23 (s, 3H, -C(C# ) -0) 1.05 (d, 3H, -C(H)(CH )3  3  3  5  3  3  2  3  2  3  3  7a  J H H = 7.5 Hz)  6.32 (d, 1H, =C(H)7 = 4.0 Hz) 2.44 (dq, 1H, -C(fl)(CH )'HH = 4.0 Hz 7HH = 7.5 Hz) 1.78 (s, 5H, C (C# ) ) 1.35 (s, 3H, -C(CH ) -0) 1.23 (s, 3H, -C(Cff ) -0) 1.04 (d, 3H, -C(H)(C/7 )7HR = 7.5 Hz) 3  H H  3  3  5  3  5  3  2  3  2  3  3  6.60 (d, 1H, =C(fl)7HH = 3.5 Hz) 6.05 (s, 5H, C5# ) 2.46 (dq, 1H, -C(fl)(CH )7JJJJ — 3.5 Hz 7HH = 7.5 Hz) 1.32 (s, 3H, -C(CH ) -0) 1.20 (s, 3H, -C(Ctf ) -0) 1.03 (d, 3H, -C(H)(Cff )7 = 7.5 Hz) 3  5  3  3  3  3  2  3  2  3  3  H H  29 Table 2.5. continued.  Compound  J  H NMR data (CD ) C=0 6 3  9a  2  6.55 (d, 1H, =C(fl)V H H = 4.0 Hz) 2.48 (dq, 1H, -C(fl)(CH )V H H = 4.0 Hz ->HH = 7.5 Hz) 1.92 (s, 15H, C (CH ) ) 1.37 (s, 3H, - C(C// ) -0) 1.26 (s, 3H, -iC(Ctf ) -0) 1.07 (d, 3H, •C(H)(Ctf )^HH = 7.5 Hz) 3  ON  3  S  3  5  3  2  3  2  3  3  10a  6.68 (d, 1H, =C(#)7HH = 4.0HZ) 2.50 (dq, 1H, -C(#)(CH )7HH = - ° Hz 7HH = 7.0HZ) 2.01 (s, 15H, C (C# ) ) 1.38 (s, 3H, -C(C# ) -0) 1.27 (s, 3H, -C(C# ) -0) 1.09 (d, 3H, -C(H)(CH )7HH = 7.0 Hz) 3  3  ON  3  4  3  5  3  3  2  3  2  5  3  3  30 Table 2.6. H NMR Data for the Five-membered Ring Neutral Lactone Complexes from 2-Methyl-2-butene. 1  a  Compound  *H NMR data ( C D ) C = 0 6 3  2  7.21 (s, 1H, =C(fl)5.73 (s, 5H, C5H5)  -C(fl)(CH )- signal not observed 1.30 (s, 3H, -C(Cff )-0) 0.90 (s, 3H, -C(H)(C# ) / H H = 7.0 Hz) 0.86 (d, 3H, -C(H)(CH ) / = 7.0 Hz) 3  3  3  2  3  3  2  3  H H  7.08 (s, 1H, =C(fl)1.80 (s, 5H, C (Cff ) ) -C(fl)(CH )- signal not observed 1.31 (s, 3H, (s, 3H, -C(Ctf )-0) 0.96 (s, 3H, -C(H)(C# ) 5  3  5  3  3  3  3  2  7HH = 7.0 Hz)  0.91 (d, 3H, -C(H)(Ctf ) 3  3  2  J H H = 7.0 Hz)  7.30 (s, 1H, =C(fl)6.13 (s, 5H, C5H5)  -C(f/)(CH )- signal not observed 1.29 (s, 3H, -C(C# )-0) 0.88 (s, 3H, -C(H)(Ctf ) 3  3  3  3  2  7HH = 7.0 Hz)  0.82 (d, 3H, -C(H)(CH ) 3  3  J H H = 7.0 Hz)  2  31 Table 2.6. continued.  *H NMR data (CD ) C=0  Compound  3  2  6  7.29 (s, 1H, =C(fl)1.95 (s, 5H, C (CH ) ) -C(fl)(CH )- signal not observed 1.33 (s, 3H, (s, 3H, -C(Cff )-0) 0.99 (s, 3H, -C(H)(Ctf ) V H H = 7.0 Hz) 0.93 (d, 3H, -C(H)(CH ) 7 H = 7.0 Hz) 5  ON  ON'  v  3  5  3  V°  3  3  3  3  H  * The signals for the Cp*W(NO) complex could not be assigned. 2  2  2  Table 2.7. Physical Data for the Neutral Products 6-10. Compound"  CpCr(N0)2-C-C(H)C(HKMe)C(Me)20C(-0)  Cp*Cr(NO)2^»C(H)C(H)(Me)C(Me)20C(-0)  CpMo(NO) ^»C(H)C(H)(Me)C(Me)20C(-0) 2  Cp*Mo(NO)2^-C(H)(^(Me)C(Me)20C(-0)  CpV(N0)2^»C(H)C(H)(Me)C(Mc)20<5(-0)  Color  olivegreen  olivegreen  light green  lightbrown  lightgreen  Yield %  28  Analytical Data C H N (calcd) (calcd) (calcd) 47.90  5.02  8.27  Mass Spectrum m/z  IR (Nujol)  b  i»  57  (5.11)  (8.86)  54.65  6.65  6.85  69  65  19  (6.80)  (7.25)  43.41  4.54  7.61  (43.34)  (4.49)  (7.78)  50.05  6.06  6.39  (50.23)  (6.10)  (6.51)  39.06 (41.71)  4.87 (5.07)  4.79 (5.41)  * Compound mixtures represented by the six-memberedringform. b  IR bands for the six-memberedringcomplex unless otherwise specified.  c  t>co assigned to thefive-memberedringcomplex.  co  cm"  1796 1694  1694  386.IPJ+ 356, [P-NO] 326, fP-2NO]  1759 1653  1676 1715°  1744 1651 1645  1682  1715 1620  1671  402, [P-NOr  518. [P] 488, IP-NO]  1699 1597  1678  +  +  (55.94)  v  31MPJ+ 286, [P-NO] 256, [P-2NO] +  (49.36)  cm*  1  N0  362, [P] 332, IP-NO] +  432, rp]  +  +  '  +  +  1  33 a second VQQ is seen in the IR spectrum of the product mixture, (Figure 2.3) that is probably due to the five-memberedringlactone complex that is also formed. The VQQ for a fivemembered ring lactone is expected to be approximately 35 cm" higher in energy than that seen 1  for a six-membered ring lactone.  16  Table 2.8 Percentages of each Product for the Neutral Lactone Complexes Formed with 2-Methyl-2-butene.  a  Metal fragment  six-membered ring  five-membered ring  CpCr(NO)  95  5  Cp*Cr(NO)  2  92  8  CpMo(NO)  2  97  3  Cp*Mo(NO)  94  6  Cp*W(NO)  the five-memberedringcould not be detected  2  2  2  The percentages are based on the integration of the C(C# ) and C(H)(C# ) signals. 3  2  3  2  The signals in the NMR spectra are easily assigned for the six-membered ring product (Figure 2.4). The values for the chemical shifts of all protons are shifted upfield. The most notable shift is that for the vinyl proton which moves by 0.65 - 0.95 ppm upfield, indicating that a significant amount of deshielding for this proton was taking place in the cation complexes. Also, the signal attributed to the OMe group is not seen in any of the spectra, which is consistent with the successful accomplishment of 0-dealkylation as outlined in 17  equation 2.5. The low resolution mass spectra of the neutral products all show the parent ions as the highest m/z peaks. The use of 2-methyl-2-pentene as the olefin in reactions 2.6 and 2.7 for [Cp*Mo(NO) ] , results in the formation of the six-memberedringlactone Cp*Mo(NO) +  2  2  C=C(H)C(H)(CH CH )C(CH3) OC(=0) as the exclusive isolated product of this reaction. 2  3  2  Examination of the K NMR spectrum of the product of this reaction does not reveal any of L  the five-memberedringlactone to be present in the sample.  34  WAVCNUMBERS <CM-1>  Figure 2.3. The IR spectrum of the product mixture of the five- and six-membered ring cations 2a and 2b as a Nujol mull.  35  CsH  s  CH 's 3  {  vinyl H  C(fl)(CH ) 3  HI  •I •  10.0  1  •  1 1 1 1 1 1 1 1 1 1 1 1 1 1  9.0  8.0  7.0  6.0  JL  JvuU.  J l  ' I ' s.o PPM 1  4.0  -I T—I | I I I I | 1 I I I | 3.0  2.0  1.0  t  0.0  Figure 2.4. The 200 MHz H NMR spectrum of the product mixture of the five- and sixJ  membered ring lactone complexes 6a and 6b in acetone-tf (•). [(•) an impurity in the 6  deuterated solvent].  36 Regrettably, reactions involving other more sterically bulky olefins are less successful. When the reactions are carried out using 2,4,4-trimethyl-2-pentene as the olefin, the product is mostly Cp*Mo(NO) I with presumably a small amount of the lactone product formed. A mass 2  spectrum of the sample contains peaks characteristic of Cp*Mo(NO) I, but also contains an 2  isotope pattern indicative of the expected lactone complex minus an NO group. A similar result is also realized when 3,3,4,4-tetramethyl-l-phenylcyclobutene is used as the olefin. When cyclohexene, a cyclic 1,2-disubstituted alkene, is used as the olefin in this reaction, the only product formed after neutralization with Nal is Cp*Mo(NO) I. This fact 2  along with the observation of the C E C stretching frequency in the IR spectrum of the reaction mixture suggests that cyclohexene may block the coordination site and not allow the coordination of the acetylenic ester which is required for a reaction to occur between the organic substrates. The same result is found when the the monosubstituted olefin propene is used. No organometallic lactone complexes could be isolated from the reaction mixture. Attempts have been made to isolate coordinated olefin complexes of the dinitrosyl cations. Stirring CH Cl2 solutions of CpMo(NO)2 cation with various olefins (cyclohexene, +  2  2,3-dimethyl-2-butene, trans-2-hexene) and acetylenes (diphenylacetylene and 1-phenyl-lpropyne) did not yield the expected olefin adducts. The IR spectra of the reaction mixtures showed that the coordinated unsaturated organic compound may be in equilibrium with the uncoordinated compound. All attempts to isolate products from this reaction have resulted 18  in intractable green oils. The only isolable olefin adduct of the [Cp'M(NO)2] (M = Cr, Mo +  or W; Cp* = Cp or Cp*) cations is that of [CpW(NO) (*r -cyclooctene)]BF . This complex 2  2  3  4  has been shown to be in equilibrium with the uncoordinated cyclooctene and [CpW(NO)2]BF . 4  It is not understood why other olefins or acetylenes cannot be isolated as adducts. This is in contrast with the isoelectronic CpFe(CO)2 , Fp, cation, which readily forms olefin and +  acetylene adducts that may be obtained as solids.  19  In order to confirm the linkage in the cationic lactone complexes, a single crystal Xray crystallographic study was performed on the [Cp*Cr(NO)2C=C(H)C(CH3)(H)C(CH3) OC(=OCH )]BF complex. Single crystals were obtained by 2  3  4  37 recrystallizing the cationic complex from a CH Cl /hexanes solvent mixture that remained at 2  2  5°C for several days. The solid-state molecular structure of this complex is displayed in Figure 2.5, and selected bond lengths and angles are given in Table 2.9 and Table 2.10, respectively. This compound has the expected three-legged piano stool structure, with a N(l)-Cr-N(2) bond angle of 100.4(3)°. This angle is comparable to the bond angle seen in the structurally characterized CpCr(NO) Cl complex that has a N(l)-Cr-N(2) angle of 93.9°. Bond angles of 171.7(5)° 20  2  for 0(1)-N(l)-Cr and 170.5(5)° for 0(2)-N(2)-Cr indicate that the NO ligands are essentially linear and, therefore, are functioning formally as three-electron donors. The structure has no bond lengths in the Cp*Cr(NO) fragment that are significantly 2  different from those of the reported CpCr(NO) Cl complex. However, the methylated lactone 2  fragment differs substantially from the neutral fragment in the structurally characterized CpMo(NO) -C=C(H)C(CH ) C(CH ) OC(=O) lactone complex. Figure 2.6 shows a 9  2  3 2  3 2  comparison between the relevant bond distances in the neutral (Figure 2.6(a)) and cationic (Figure 2.6(b)) lactone ligands for the two structurally characterized compounds.  Figure 2.6. (a) Selected dimensions for the lactone ligand of CpMo(NO) 2  C=C(H)C(CH ) C(CH ) OC(=0). (b) Selected bond lengths for the methylated lactone 3  2  3  2  ligand of [Cp*Cr(NO) -C=C(H)C(CH )(H)C(CH ) OC(=OCH )]BF . 2  3  3 2  3  4  38  Figure 2.5. Solid-state molecular structure of [Cp*CT(NO) 2  C=C(H)C(H)(CH )C(CH3)20C(=OCH3)]BF . 3  4  39 Table 2.9. Selected Bond Lengths (A) for [Cp*Cr(N0) 2  C=C(H)C(H)(CH3)C(CH3) OC(=OCH3)]Br4.  a  2  Bond  Length  Length  Bond  Cr - N(l)  1.694(5)  C(2) - C(12)  1.506(8)  Cr - N(2)  1.698(6)  C(3) - C(4)  1.419(8)  Cr - C(l)  2.186(5)  C(3) - C(13)  1.487(8)  Cr - C(2)  2.213(5)  C(4) - C(5)  1.448(8)  Cr - C(3)  2.257(6)  C(4) - C(14)  1.504(8)  Cr - C(4)  2.221(6)  C(5) - C(15)  1.477(8)  Cr - C(5)  2.206(6)  C(7) - C(6)  1.457(8)  Cr - C(6)  2.073(6)  C(6) - C(10)  1.374(8)  Cr - Cp centroid  1.858  C(10) - C(9)  1.516(8)  0(1) - N(l)  1.179(6)  C(9) - C(19)  1.515(8)  0(2) -N(2)  1.178(7)  C(9) - C(8)  1.530(8)  0(3) - C(7)  1.271(6)  C(8) - C(18)  1.488(9)  0(3) - C(8)  1.516(7)  C(8) - C(28)  1.523(8)  0(4) - C(7)  1.285(7)  0(4) - C(17)  1.466(7)  C(l) - C(2)  1.414(8)  B - F(l)  1.366(8)  C(l) - C(5)  1.406(8)  B - F(2)  1.336(8)  C(l)-C(ll)  1.501(8)  B - F(3)  1.371(8)  C(2) - C(3)  1.417(8)  B - F(4)  1.369(9)  a  E. s. d.'s are in parentheses.  b  a restraint was placed on this bonds.  b  b  Table 2.10. Selected Bond Angles (in degrees) for [Cp*Cr(NO) 2  C=C(H)C(H)(CH3)C(CH )20C(=OCH )]BF4.  a  3  3  N(2) - Cr - N(l)  100.4(3)  C(6) - Cr - N(l)  97.9(2)  C(6) - Cr - N(2)  95.6(3)  0(1)-N(l)-Cr  171.7(5)  0(2) - N(2) - Cr  170.5(5)  C(10) - C(6) - Cr  121.7(6)  C(10) - C(6) - C(7)  114.7(6)  C(9) - C(10) - C(6)  124.5(9)  C(8) - C(9) - C(10)  108.4(8)  C(9) - C(8) - 0(3)  113.8(6)  C(8) - 0(3) - C(7)  119.9(4)  C(6) - C(7) - 0(3)  126.1(5)  C(6) - C(7) - 0(4)  117.5(5)  C(8) - C(9) - C(19)  109.0(6)  C(28)-C(8)-C(9)...  119.0(6)  C(28) - C(8) - 0(3)  101.7(5)  C(17) - 0(4) - C(7)  118.6(5)  a  E. s. d.'s are in parentheses.  41 The significant differences between the two structures suggest that there is considerable delocalization of the positive charge over a large part of the organic ligand in the cation complex. The sirriilarity of the bond lengths for both the C-0 bonds for the carbonyl carbon indicate that the positive charge is shared almost equally over the -O-C-O- region of the ring system and may be represented by the partial structure shown below.  /  C  H  3  O  o  I  Another bond length of significance is the C(Me) -0, C(8)-0(3), bond (1.516A) 2  which is considerably longer than that observed for other six-memberedringlactones, where the average bond length for six lactones of this type is 1.462(13)A, and is also longer than 21  the neutral CpMo lactone complex (C-0 distance of 1.477A). This longer than normal C-0 bond indicates that there is some sharing of the positive charge on this carbon as well. Furthermore the n -C to the carbonyl carbon, C(6)-C(7), distance (1.457(8)A) is l  shorter than that seen in the neutral complex (1.477(3)A) which itself is shorter than that expected for an unconjugated C-C bond of this type (1.497A). This bond in the cation 22  complex is even slightly shorter than the expected bond length in an a,|S-unsaturated system (1.470A).  22  The C=C double bond distance in the chromium cation structure is 1.374(8)A, considerably longer than the same bond in the neutral molybdenum complex, 1.331(3)A, indicating a loss of electron-density between these two carbon atoms. Thus electron density is probably delocalized over this part of the ring system also. Therefore, the positive charge is shared over theringsystem from C(10)—*C(8). The Cr-C(6) bond length at 2.073(6)A is in the same range seen for other Cr-sp C 2  bond lengths. This agrees with the spectroscopic data which indicate that there is little 23  42  delocalization of charge over the Cp'M(NO) fragment. 2  Finally the orientation of the methylated lactone ligand is different from that of the neutral lactone complex. The orientation of the lactone ring in the Cr complex lies parallel to the Cp ligand, while the plane of the lactone ligand in the neutral molybdenum complex bisects the two nitrosyl groups, i.e.,  ON'"' I '"'NO  O  cationic lactone  NO  N  neutral lactone  This change in orientation may be due to steric interactions between the methyl groups of the Cp* ligand and the 0-CH group of the cationic lactone ligand. The orientation of the lactone 3  ligand in the Cr complex is similar to that of the neutral a-pyrone ligand discussed in Chapter 3.  In order to further probe the relative magnitude of the Lewis acidity of the [Cp'M(NO)2]BF cations, an attempt to quantify their electrophilic behavior was undertaken. 4  A method used by Hersh to determine the Lewis acidity of organometallic cations involved H ]  NMR studies of the crotonaldehyde adducts of these cations.  24  Upon coordination through the  carbonyl oxygen, the H3 signal of the crotonaldehyde shifts downfield, with the greater shift indicating a stronger Lewis acid. Solutions of the dinitrosyl cations with crotonaldehyde prepared in CD Cl2 were 2  studied by *H NMR spectroscopy. The [CpCrfNCOJ " and [Cp^rOSfO)^ cations formed -1  +  complexes with crotonaldehyde and the downfield shift of the signal for the H3 could be measured with the results shown in Table 2.11 along with other Lewis acids that have been measured previously. The two chromium dinitrosyl cations appear to be stronger Lewis 24  acids than the isoelectronic carbonyl complexes of [CpMo(CO) ] and [CpFe(CO)2] . Also +  3  +  43 of note is the stronger Lewis acidity of the Cp*Cr analogue over than of the CpCr complex. The more electron-donating permethylated Cp ring would be expected to increase the electrondensity on the metal center and cause a complex to be a weaker Lewis acid. Clearly, molecular orbital calculations needtobe performed on the [Cp'M(NO) ] complexes to help +  2  elucidate distribution of electron density. The same experimental conditions when used for the molybdenum cations did not give the desired crotonaldehyde complex, but a number of unresolved peaks appeared in the region where the signals for H3 were expected.  Table 2.11. Comparison of Lewis Acidity Lewis acid  A5  BBr  1.49  1.00  1.23  0.82  1.17  0.77  0.93  0.62  0.86  0.58  0.76  0.51  0.70  0.47  0.54  0.36  c 3  A1C1  C  3  BF  C 3  Me P(CO) (NO)W 3  3  Cp*(NO) Cr  +e  2  Cp(NO) Cr  +e  2  Cp(CO) Mo  +f  3  Cp(CO) Fe « +  2  a  b  +d  relative power'  a  Downfield shift of H3 signal for coordinated crotonaldehyde. A5(adduct)/A5(BBr3).  c  Data originally published in reference 25.  d  Adduct prepared in situ from the rMe P(CO) (NO)WFSbF ] complex, reference 23. 3  e  Adduct prepared in situ from the BF " cations. 4  f  Isolated as the PF ' salt, reference 24. 6  8  3  Isolated as the BF salt, reference 24. _  4  5  44 While the two [Cp'Cr(NO)2] cations are not as electrophilic as the classic Lewis +  acids, such as AICI3, they are considerably more electrophilic than the [CpFe(CO)2] cation. +  The greater electrophilicity of these cations may very well increase the utility of these reagents to facilitate organic reactions that F p cannot accomplish. Further studies on these +  complexes need to be carried out to determine the range of organic transformations that these complexes will perform.  45 References and Notes  1.  Richter-Addo, G. B. Ph.D. Dissertation, University of British Columbia, 1988.  2.  Legzdins, P.; Richter-Addo, G. B.; Einstein, F. W. B.; Jones, R. H. Organometallics, 1990, P, 431.  3.  Legzdins, P.; Martin, D. T. Organometallics 1983, 2, 1785.  4.  Stewart, R. P.; Moore, G. T. Inorg. Chem. 1975,14, 2699.  5.  The molybdenum analogue of this compound has been briefly described, see: Hames, B. W.; Legzdins, P. Organometallics 1982,1, 116.  6.  (a) Rosenblum, M.; Scheck, D. Organometallics 1982,1, 397. (b) Samuels, S. B.; Berryhill, S. R.; Rosenblum, M. J. Organomet. Chem. 1979,. 166, C9.  7.  The products of these reactions depend strongly on the structure of the olefin reactant. • used. For example, cyclic 1,2-disubstituted olefins yield cyclobutene products, open chain 1,2-disubstituted olefins produce a mixture of cyclobutenes and 1,3-dienes, while 1,1-disubstituted and trisubstituted olefins yield only the lactone products.  8.  Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 2 ed.; Pergamon: Toronto, 1980.  9.  Legzdins, P.; Malito, J. T. lnorg.Chem. 1975, 14, 1875.  10.  Leoni, P.; Landi, A.; Pasquali, M. J. Organomet. Chem. 1987, 328, 365.  11.  Martin, D. T. Ph.D. Dissertation, University of British Columbia, 1984.  12.  These percentages are based on the integration of selected peaks in the *H NMR spectra of the reaction product mixtures.  13.  Ramsey, B. G.; Taft, R. W. J. Am. Chem. Soc. 1966, 88, 3058.  14.  For the formation of the W dioxo complexes from the neutral dinitrosyl lactone complexes see reference 1.  15.  The CpCr(NO) -C=C(H)C(H)(CH )C(CH ) OC=O complex had coincidental J / 2  3  3 2  N O  and PQO bands in CH C1 . The two bands have been observed when solutions of the 2  2  complex in other solvents were used to obtain the spectrum: IR (hexanes) V^Q'S 1802  46 and 1703 cm , v -1  co  1690 cm ; (Et^) y 's 1798 and 1701 cm , »/ 1686 cnT , -1  -1  N0  (THF) "'NO'S 94 and 1698 cm , P 17  16.  -1  L  co  1682 cm . -1  C  O  Pavia, D. L.; Lampman, G. M.; Kriz, G. S. Introduction to Spectroscopy: a Guide for Students of Organic Chemistry; Saunders College: Philadelphia, 1979; p 58.  17.  Further examples of O-dealkylation in organometallic chemistry may be found in the following: (a) Davison, A.; Reger, D. L. 7. Am. Chem. Soc. 1972, 94, 9237. (b) Bodner, G. S.; Smith, D. E.; Hatton, W. G.; Heah, P. C ; Georgiou, S.; Rheingold, A. L.; Geib, S. J.; Hutchinson, J. P.; Gladysz, J. A. 7. Am. Chem. Soc. 1987, 109, 7688.  18.  For the reaction involving [CpMo(NO)2]BF and 1-phenyl-1-propyne the •'NO'S bands 4  appear at 1788(s), 1775(s) and 1688(s, br) cm . The [CpMo(NO)2]BF i> 's appear -1  4  N0  at 1788 and 1698 cm . -1  19.  (a) Cutler, A.; Ehntholt, P.; Lennon, P.; Nicholas, K.; Marten, D. F.; Raghu, S.; Rosan, A.; Rosenblum, M. 7. Am. Chem. Soc. 1975, 97, 3149. (b) Cutler, A.; Ehntholt, P.; Giering, W. P.; Lennon, P.; Raghu, S.; Rosan, A.; Rosenblum, M.; Trancede, J.; Wells, D. 7. Am. Chem. Soc. 1976, 98, 3495 and references therein.  20.  Greenhough, T. J.; Kolthammer, B. W.; Legzdins, P.; Trotter, 7. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1980, B36, 795.  21.  Schweizer, W. B.; Dunitz, J. D. Helv. Chim. Acta 1982, 65, 1547.  22.  Allen, F. H. Acta Crystallogr., Sect. B: Struc. Crystallogr. Cryst. Chem. 1981, B37  890. 23.  Kirtley, S. W. in Comprehensive Organometallic Chemistry, 1982, Vol. 3; Wilkinson  G.; Stone, F. G. A.; Abel, E. W., eds. 24.  Bonnesen, P. V.; Puckett, C. L.; Honeychuck, R. V.; Hersh, W. H. 7. Am. Chem. Soc. 1989, 111, 6070.  25.  Childs, R. F.; Mulholland, D. L.; Nixon, A. Can. 7. Chem. 1982, 60, 801.  CHAPTER 3  Condensations of Methyl Propiolate with Acetylenes in the Presence of [Cp*Mo(NO)2]BF . 4  48 Introduction  As has been shown in the previous chapter, the [Cp'M(NO)2J (M = Cr, Mo, or W; +  Cp' = Cp or Cp*; except CpW) cations are useful reagents for forming organometallic a,Bunsaturated lactone complexes. In order to extend the use of these cations to the formation of other organic products, I decided to use acetylenes instead of olefins in the condensation reaction to form complexes of the type shown in reaction 3.1.  R  R (Cp' = C H 5  5  or C M e ; M = Cr, Mo or W; R and R' = any substituent) 5  5  The product species is a 3-metallated a-pyrone complex. For a description of the 1  numbering scheme for these compounds refer to reference 1. This organic group exists in many naturally occurring compounds. For instance, a-pyrone compounds and their derivatives display a wide range of biological activity such as being selective inhibitors of human leukocyte elastase, potential photochemotherapeutic compounds for the treatment of psoriasis, and probes for platelet antiaggregatory mechanism studies. Certain a-pyrone compounds have antihistamine, antibiotic, and antiulcer activity. Other derivatives of a2  pyrones exhibit a variety of pharmacological properties (e.g. sedative and soporific, potentiation of barbiturate narcosis, protection against chemo- and electroshock, local anesthetic, spasmolytic and smooth muscle relaxant, analgetic, antimycotic, and antiedemic). a-Pyrone derivatives are also known to undergo cycloaddition reactions with acetylenes in the synthesis of highly substituted benzenes and in the preparation of natural substances containing suchringsystems.  4  49  O  R  1  R  Finally, cyclobutadiene ligands in organometallic chemistry are sometimes formed from a-pyrones. This reaction wasfirstcompleted by Rosenblum using a-pyrone itself and it 5  has subsequently been extended to substituted a-pyrones to give substituted cyclobutadiene ligands, e.g.  6  o  50 Experimental Section  All reactions and subsequent manipulations were carried out under anhydrous and anaerobic conditions unless otherwise specified. The general experimental procedures used in this study have been described in the previous chapter. Methyl propiolate (99%), diphenylacetylene (99%), 1-phenyl-1-propyne (99%), and AgBF4 (98%) were purchased from the Aldrich Chemical Co. and Nal, purchased from Mallinckrodt were used without further purification. Cp*Mo(NO) Cl and [Cp*Mo(NO)2] BF were prepared as described in Chapter +  2  4  2. Reaction of [Cp*Mo(NO)2l BF4 with Methyl Propiolate and 1-Phenyl-l-propyne. +  To a dark green CH C1 solution (40 mL) of [Cp*Mo(NO) ]BF (2.0 mmoles) were added 0.5 2  2  2  4  mL (6.5 mmoles) of methyl propiolate and 0.5 mL (4.0 mmoles) of 1-phenyl-1-propyne. The stirred reaction mixture darkened instantly upon addition of the organic reagents. The progress of the reaction was monitored by IR spectroscopy and was deemed complete after two hours when no further change in the veto's was evident in the IR spectrum. In the final spectrum of the reaction mixture the P^Q bands for [Cp*Mo(NO)2] B F were not seen but +  4  new J'NQ'S were evident at 1725 and 1651 cm . Concentration of the CH C1 solution to -1  2  2  approximately 5 mL in vacuo, followed by the addition of Et 0 (120 mL), caused the 2  precipitation of a brown oily solid which upon trituration became a powdery light brown solid. The supernate was removed by cannulation and the product was washed with another 80 mL of Et 0 before being dried in vacuo to obtain 0.78g (67%) of [Cp*Mo(NO) 2  2  C=C(H)C(CH )=C(Ph)OC(=OCH )]BF (1). 3  3  4  Anal. Calcd. for C H N 0 MoBF : C, 47.77; H, 4.72; N, 4.85. Found: C, 23  27  2  4  4  47.49; H, 4.66; N, 4.72. IR (Nujol mull) 1721(s), 1640(s), 1613(sh), 1574(w), 1501(m), 1364(w) cm" . 1  J  H NMR (d-acetone) 5 8.71 (s, 1H, C=C(H)), 8.07-7.95 (m, 2H, ortho H), 6  7.72-7.61 (m, 3H, meta and para H), 4.61 (s, 3H, OCH ), 2.56 (s, 3H, C=C(C# )), 2.00 (s, 3  3  15H, C (C# ) ). 5  3  5  Preparation of Neutral a-Pyrone Complexes. Following the above procedure to  51 produce the cationic a-pyrone complex (vide supra), a second sample of this complex was prepared. After washing the cationic product with ether, the solid was redissolved in THF (30 mL). Solid Nal (0.33 g, 2.2 mmoles) was added and the reaction mixture was stirred for 2 h. The solvent was then removed in vacuo to obtain a brown oil. The oil was redissolved in an 8:1 Et 0/CH Cl2 (40 mL) solvent mixture and filtered through a column of alumina (2x3 2  2  cm, Woelm neutral, activity 1) supported on a medium porosity frit. The alumina was washed with THF (40 mL) and the combined filtrates were taken to dryness to obtain a gummy brown solid. Trituration of this solid with pentane (40 mL) produced a light brown powder that was washed with pentane (1 x 40 mL) and then dried in vacuo to obtain 0.33g (35%) of Cp*Mo(NO) -C=C(H)C(CH )=C(Ph)OC(=O). 2  3  Anal. Calcd. for C H N 0 M o : C,55.46; H , 5.09; N, 5.88. Found: C, 55.20; H , 2 2  2 4  2  4  5.10; N, 6.00. IR (Nujol mull) 1726(s), 1713(s), 1690(s), 1674(s), 1632(sh), 1626(s), 7  1508(w), 1492(w) cm" ; (O^Clj) 1721(s), 1690(m), 1672(s), 1632(s), 1510(m), 1491(m) 1  cm . -1  ]  H NMR (rf -acetone) 5 7.65-7.36 (m 6H, C # a n d C=C(H)), 2.13 (s, 3H, 6  6  5  C=C(C// )), 1.95 (s, 15H, C5(CH ) ). Low-resolution mass spectrum (probe temperature 3  3  5  120°C) m/z 448 [P -NO], +  The neutral a-pyrone complex formed using diphenylacetylene was prepared in the same manner as the 1-phenyl-1-propyne product to obtain 0.65g (64%) of Cp Mo(NO) 2  C=C(H)C(Ph)=C(Ph)OC(=0) as an orange-brown powder. Anal. Calcd. for C H N 0 M o : C, 60.22; H , 4.87; N, 5.20. Found: C, 60.40; H, 2 7  2 6  2  4  4.86; N, 5.31. IR (Nujol mull) 1711(s), 1694(s), 1663(w), 1622(s), 1616(s), 1576(w), 1481(w) cm" ; ( C H j C y 1721(s), 1686(s), 1669(m), 1630(s) cm" . H NMR (^-acetone) 5 1  1  X  7.59-7.20 (m, 11H, C ^ and C=C(fl)), 1.98 (s, 15H, C (C# ) ). Low resolution mass 5  3  5  spectrum (probe temperature 120°C) m/z 510 [P -NO]. +  Reaction of Cp*Mo(NO) -C=C(H)C(CH ) = C(Ph)OC(=0) with Air. When an 2  3  brown-orange Et 0 solution (10 mL) of Cp*Mo(NO) -C=C(H)C(CH )=C(Ph)OC(=O) 2  2  3  (0.07g 0.16 mmol) was exposed to air for several days, a light yellow-brown precipitate formed. The supernatant was removed, and the precipitate was washed successively with  52 hexanes (20 mL) and Et 0 (2 x 10 mL). The supernatant and the washings were combined 2  and the solvent evaporated to give 0.03g (42%) of Cp*Mo(0) 2  C=C(H)C(CH )=C(Ph)OC(=O): IR (Nujol mull) y 3  9 1 6 (m) and 883 (m) cm" ; also 1  M o = 0  1696 (m), 1682 (m), 1613 (w), 1557 (w), 1503 (w) cm" . H NMR (acetone-<*) 5 7.61-7.36 1  J  6  (m, 5H, Cgtf-j), 7.30 (s, 1H C=C(H)), 2.03 (s, 3H, C=C(Ctf )), 1.93 (s, 15H, C (Ctf ) ). 3  5  3  5  Low-resolution mass spectrum (probe temperature 120°C) m/z 450 [P ], 432 [P -H 0]. +  +  2  X-ray Crystallographic Analysis of Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0). Suitable crystals for a single-crystal X-ray structural 3  analysis were obtained by making a saturated Et 0 solution of Cp Mo(NO) 2  2  C=C(H)C(CH )=C(Ph)OC(=O) at approximately 30°C and allowing the solution to stand at 3  room temperature for 2 h. The X-ray structural analysis of the compound was performed by Drs. F. W. B. Einstein and R. J. Bachelor at Simon Fraser University.  53 Results and Discussion  The addition of 1-phenyl-1-propyne and methyl propiolate to a solution of the [Cp*Mo(NO)2] cation generates the organometallic a-pyrone salt as shown in reaction 3.2. +  The condensation of an acetylenic ester with another acetylene has not been reported previously for the synthesis of a-pyrones.  8  This reaction is carried out in a fashion similar to those involving olefins as substrates. An excess of organic reagents is used, with the progress of the reaction being monitored by IR spectroscopy. When no more change in the V^Q bands is observed, the reaction is deemed to be complete and the product isolation commences. The organometallic cation complex has v^o's  m  th reaction mixture at 1723 and 1656 cm" , while the starting e  1  cation, [Cp*Mo(NO)2]BF , bands are approximately 20-30 cm" higher in energy at 1755 and 1  4  1671 cm" . The cationic a-pyrone complex has similar ^NO'S 1  t 0  those of other neutral  Cp*Mo(NO) -containing compounds such as Cp*Mo(NO) Cl which has 2  2  at 1726 and  1642 cm" . These results suggest that a Mo-C sigma bond has been formed and that the 1  cationic charge is more localized on the organic ligand than on the metal center. The IR bands are similar to those observed for the reactions to form the cationic lactone compounds discussed in Chapter 2. Isolation of the cationic a-pyrone product from reaction 3.2 is carried out in a similar manner as that for the a,j8-unsaturated lactone cationic complexes that are discussed in  54 Chapter 2. Precipitation of the compound with Et 0 gives a gummy solid that is triturated to 2  give a light brown powder. The trituration step for this compound is completed within a couple of minutes while those for the lactone products range anywhere from 5-30 minutes. The H NMR spectrum of this complex (Figure 3.1) is rather straightforward with 1  singlets appearing for all but the phenyl protons whose signals appear as multiplets in the region between 7.6 and 8.1 ppm. The Cp* signal appears in the same region as that of the Cp*Mo(NO) cationic lactone complex discussed in Chapter 2 (both occur at 2.00 ppm). The 2  OMe signal is slightly further downfield in the pyrone (4.61 ppm) than in the lactone complex (4.45 ppm). The -C(CH )= signal appears at 2.56 ppm, considerably downfield from the 3  methyl signals of the cationic lactone complexes. This is not unexpected since the methyl group is bonded to an sp C in this case while in the cationic lactone it bonded to an sp C . 2  3  9  The regiochemistry of the pyrone complex could not be assigned by the H NMR data but was J  subsequently determined by single crystal X-ray crystallography (vide infra). The H NMR data shows a singlet integrating for one hydrogen at 5 8.71, which is X  assigned to the C=C(H) proton on the a-pyrone ring. This signal is downfield from the corresponding proton in the cationic lactone products by approximately 1.2 ppm. This downfield shift is believed to be caused by delocalization of the positive charge over the whole ring system. A similar chemical shift is seen for the corresponding proton in methylated apyrone itself as summarized in the next paragraph. a-Pyrone may be methylated using strong methylating agents like trimethyloxonium 10  tetrafluoroborate or methyl fluorosulphonate to give the pyrylium derivative as shown in Equation 3.3.  (3.3)  55  CH  OCH,  C (CH ) 5  3  Al.]U  10.0  i i'  5  Ph  H  • i i i i i  3  i  i i | i i 1 1 [ i i i i | i i 1  B.O  9.0  1  7.0  HJU  Ju  i i | i i i i | i r i i | i 1i i | i i i i 1  6.0  5.0  4.0  3.0  2.0  ii  1.0  i •  i  i ~  h 0.0  PPM  Figure 3.1. The 200 MHz *H NMR spectrum of [Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=OCH )]BF in acetone-d . [(•) an impurity in the deuterated 3  solvent].  3  4  6  56 The *H NMR spectrum of this salt shows that all the proton resonances of the heterocyclic ring move downfield by approximately 1 ppm relative to the signals for a-pyrone, with two multiplets at 5 7.5 and 8.6 when the spectrum is obtained using a C D 3 C N solution of the organic cation. Delocalization of the positive charge over the a-pyrone ring system is 10  believed to be the cause of this downfield shift. The combination of a shift to lower wavenumbers for the v^ds of the dinitrosyl fragment and the downfield resonances for the C=C(H) proton indicate that the positive charge is delocalized over theringsystem with a smaller contribution from the Cp*Mo(NO)2 in stabilizing the positive charge. Since the product has a six-membered pyronering,the mechanism for its formation is probably similar to that invoked for olefins condensing with methyl propiolate in the coordination spheres of the dinitrosyl cations discussed in Chapter 2. If the mechanism is indeed that shown in Equation 3.4, *  +  R R = Me, Ph  (3.4)  R' = Ph  then a 5-memberedringlactone is not possible unless there is a 1,2-migration of the methyl  57 group. This is a rather unlikely scenario, since the cation formed from such a migration would probably be less stable than the originally formed cation that would be stabilized by the phenyl ring.  11  This restriction to the formation of the five-membered ring lactone complex may  account for the formation of only a six-memberedringcomplex in this reaction. It is still not understood why the regiochemistry is directed in the way that it is for the reaction using 1-phenyl- 1-propyne. If the mechanism is that of Equation 3.4, then it could be due to a reversible first step with the more stable intermediate regioisomer (i.e. the isomer that is better able to stabilize a positive charge) having a longer lifetime, thereby allowing cyclization to the pyrone complex before dissociation. If a concerted mechanism is involved as shown in Equation 3.5  +  R = Me,  Ph  R* =  Ph  then a combination of steric and electronic factors may explain the regiochemistry observed. To form the neutral a-pyrone products, THF solutions of the respective cation species are treated with Nal as summarized in Equation 3.6.  58  (3.6)  The neutral product complexes have similar ^NO'  s  to  m  e  cationic reactant, further  indicating that the positive charge of the cation is more localized on the pyrone fragment. Another interesting aspect of the TR spectra of the neutral products (illustrated with the CH Cl2 solution spectrum the 1-phenyl-l-propyne reaction product in Figure 3.2) is that two 2  bands appear for the carbonyl group where only one is expected in their solution IR spectra. For the 1-phenyl-l-propyne a-pyrone complex there are two bands at 1690 and 1672 cm and -1  two bands at 1686 and 1669 cm* for the diphenylacetylene a-pyrone complex. This 1  phenomenon is seen in free a-pyrones and has been suggested to be caused by Fermi resonance, i.e. coupling between a the C=0 streching mode and an overtone or combination band.  12  Spectra of the two neutral a-pyrone complexes as their Nujol mulls show splitting of  the ^ N O ' and ^co' bands. This splitting of bands is also observed for free a-pyrones when s  8  spectra are obtained as KBr pellets, and is believed to be due to solid-state effects. 12b  The H NMR spectra of the neutral complexes (illustrated with the 1-phenyl-l1  propyne reaction product in Figure 3.3) have the exact position of the C=C(H) signal obscured by signals due to the phenyl protons, but these signals are in the same region as the 1  H NMR chemical shifts exhibited by free a-pyrone. For a-pyrone itself, this proton has a 10  chemical shift of 5 7.56, a region in which phenyl proton signals are seen. The mass-spectral data for these complexes have the [P-(NO)] as the highest assignable peak in the spectrum. +  The lack of a parent-ion isotope pattern might be due to the probe temperature (120°C) causing the loss of a NO ligand in these complexes, a condition that is common in metalnitrosyl compounds.  59  a  WAVENUMBERS  <CM-1>  Figure 3.2. The IR spectrum of Cp*Mo(NO) -C=C(H)C(CH ) =C(Ph)OC(=0) as a solution 2  in CH C1 . 2  2  3  60  If  Cs(CH)5 3  i—| i i i i | i 10.0  i i i |i r »i |i  9.0  6.0  7.0  i  i i |i 6.0  i  i i |ii i i |i < i i |i i i i |i 1  6.0  4.0  3.0  PPM  Figure 3.3. The 200 MHz *H NMR spectrum of Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0) in acetone-^ (•). 3  6  2.0  i  i  i | i 1.0  i i i |— J  0.0  61  These diamagnetic complexes may be handled in air for short periods of time with no noticeable decomposition, and they may be stored under a dinitrogen atmosphere at -5°C for at least 3 months. They are soluble in polar organic solvents, but are only sparingly soluble in non-polar solvents such as hexanes and n-pentane. Et 0 solutions of these compounds when 2  exposed to air, also, decompose to the dioxo complexes as do their lactone counterparts as shown in equation 2.6.  Me  Me  The regiochemistry of the a-pyrone ring formed using 1-phenyl-1-propyne as the acetylene was confirmed by a single-crystal X-ray crystallographic analysis. The solid-state molecular structure of this compound is shown in Figure 3.4, and selected bond lengths and angles are given in Table 3.1 and Table 3.2, respectively. This compound has a N(l)-MoN(2) angle of 95.66(9)° which is similar to that exhibited by other complexes of this type that have been structurally characterized. The only other structurally characterized neutral Cp'Mo(NO) R compound is CpMo(NO) -C=CHC(CH )C(CH )OC(=O) (referred to as the 13  2  2  3  3  lactone complex). Its CpMo(NO) fragment is almost indentical to the same fragment in the 2  structurally characterized CpM(NO) Cl (M = Cr or W) compounds. The lactone complex 14  2  has a N(l)-Mo-N(2) bond angle of 92.3(1)° compared to 93.9° and 92.0° found for Cr and W, CpM(NO) Cl, compounds respectively. Bond angles for the a-pyrone complex of 2  168.7(2)° for 0(l)-N(l)-Mo and 171.9(2)° for 0(2)-N(2)-Mo are typical values seen in all the dinitrosyl complexes that are structurally characterized and indicate that the NO ligands are essentially linear, thus acting as three electron donors to the metal center.  62  C(25)  Figure 3.4. Solid-state molecular structure of Cp*Mo(NO)  2  C=C(H)C(CH )=C(Ph)OC(=0). 3  63 Table 3.1. Selected Bond Lengths (A) for the Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0).  a  3  Bond  Length  Bond  Length  Mo - N(l)  1.817(2)  C(2) - C(12)  1.505(4)  Mo - N(2)  1.827(2)  C(3) - C(4)  1.413(4)  Mo - C(l)  2.338(2)  C(3) - C(13)  1.507(4)  Mo - C(2)  2.375(2)  C(4) - C(5)  1.432(4)  Mo-C(3)  2.383(2)  C(4) - C(14)  1.499(4)  Mo - C(4)  2.351(2)  C(5) - C(15)  1.512(4)  Mo - C(5)  2.337(2)  C(7) - C(6)  1.434(3)  Mo - C(6)  2.177(2)  C(6) - C(10)  1.348(3)  Mo - Cp centroid  2.024  C(10) - C(9)  1.439(3)  0(1) - N(l)  1.180(3)  C(9) - C(19)  1.511(3)  0(2) - N(2)  1.178(3)  C(9) - C(8)  1.350(3)  0(3) - C(7)  1.396(3)  C(8) - C(21)  1.477(3)  0(3) - C(8)  1.370(2)  C(21) - C(22)  1.390(3)  0(4)-C(7)  1.211(3)  C(21) - C(26)  1.393(3)  C(l) - C(2)  1.417(3)  C(22) - C(23)  1.386(4)  C(l) - C(5)  1.405(4)  C(23) - C(24)  1.359(4)  Cd)-C(ll)  1.518(4)  C(24) - C(25)  1.364(4)  C(2) - C(3)  1.422(3)  C(25) - C(26)  1.380(4)  a  E. s. d.'s are in parentheses.  64 Table 3.2 Selected Bond Angles (in degrees) for Cp*Mo(NO) 2  C=C(H)C(CH )=C(Ph)OC(=0).  a  3  N(2) - Mo - N(l)  95.66(9)  C(6) - Mo - N(l)  98.90(8)  C(6) - Mo - N(2)  96.69(8)  0(1) - N(l) - Mo  168.7(2)  0(2) - N(2) - Mo-  171.9(2)  C(10) - C(6) - Mo  127.7(2)  C(10) - C(6) - C(7)  116.1(2)  C(9) - C(10) - C(6)  125.1(2)  C(8)-C(9)-C(10)~  117.3(2)  C(9) - C(8) - 0(3)  119.6(2)  C(8) - 0(3) - C(7)  123.6(2)  C(6) - CC7) - 0(3)  118.2(2)  C(6) - C(7) - 0(4)  128.0(2)  C(8)-C(9)-C(19)—  124.3(2)  C(21) - C(8) - C(9)  130.9(2)  C(21) - C(8) - 0(3)  109.5(2)  angle between planes C(21) - C(26) and C(6) - C(10) and 0(3) E. s. d.'s are in parentheses.  23.6  65  There are several bond lengths to note in this compound. The C(Ph)-0 bond length of 1.370(2)A is considerably shorter than the similar bond in the lactone complex where the bond length is 1.477(3)A, and the C(=0)-0 bond length of L396(3)A is 0.042A longer than the corresponding bond in the lactone complex. This shows that the a-pyrone complex has little or no participation from the -C(0")=0 -C resonance form, which is invoked for the +  lactone complex. A comparison may be made between the metallated structure shown here and purely organic a-pyrones in order to understand the effect of the dinitrosyl on the ring system. A search of the Cambridge Crystallographic Database by Johnstone et. al., allowed for the 15  structure of an average a-pyrone complex to be made, for comparison to other a-pyronecontaining compounds. The bond lengths for the averageringsystem and the dinitrosyl apyrone complex are shown in Figure 3.5(a) and 3.5(b), respectively.  1.348  1.359 1.424  1.439  1.328  Figure 3.5(a)  1.350  Figure 3.5(b)  Figure 3.5. Comparison of a-pyrone structures.  The most significant differences in the two rings are the carbonyl bond length and the adjacent C-C bond. The carbonyl bond in the dinitrosyl complex (1.211 A) is considerably shorter and the adjacent C-C bond (1.434A) is longer than those in the averaged structure (1.240A and 1.394A respectively). These differences are probably a result of the electron-  withdrawing effect of the Cp*Mo(NO) fragment that decreases the T-delocalization from the 2  C-C bond into the carbonyl bond. The same result is seen when the electron-withdrawing  66 group C(=0)OCH  i:> 3  is in the in the 3-position on the ring.  The phenylringplane, C(21)-C(26), and the C(6)-C(10) and 0(3) plane of the pyrone ring have an angle of 23.6° between them. The torsion angle results from an interaction between the ortho hydrogen on the phenylringand the 4-methyl substituent.  o  This steric interaction outweighs any resonance stabilization that may be gained from a completely planar structure that would allow delocalization. Structural analysis of related 4pyrone systems shows that the molecule has a torsion angle of 23.8° between the phenyl 16  group and the rest of the molecule in the case of 7,8-benzoflavone. These results correspond to the biphenyl systems which have been analyzed in detail and are quite often non-planar in the solid state.  17  A very noticeable difference between the dinitrosyl a-pyrone complex and the dinitrosyl a,/3-unsaturated lactone complex is the alignment of the ring system with respect to the metal center. In the a./ff-unsaturated lactone the ring system bisects the two nitrosyl groups while in the a-pyrone system the pyrone ring is almost coplanar to the nitrosyl groups, i.e.,  ON  a-pyrone  NO  ON  NO  lactone  67 However, a similiar orientation to the a-pyrone complex is seen for the cationic a,Bunsaturated lactone complex in Chapter 2, which also contains a pentamethylcyclopentadienyl ligand. Thus a steric interaction between the carbonyl oxygen and the methyl groups on the Cp* ligand may be responsible for this orientation.  Epilogue  The *H NMR spectra for both the cation and neutral products formed using 1-phenyll-propyne showed no peaks that could be assigned to any other isomer possible from this reaction. This high degree of regioselectivity is important from a synthetic point of view. The use of an appropriately functionalized acetylene in this reaction may thus allow for the synthesis of an a-pyrone that may be selectively substituted in the 3, 5, and 6 positions on the ring. This will offer the ability to obtain a wide range of substituted a-pyrone compounds from relatively cheap starting materials in a one-pot reaction. Currently there are many ways of forming a-pyrones.  Most of these methods allow  18  selective substitution on certain positions of the ring but no one synthetic method allows substitution on all positions on the ring with generality. The most general methods have been developed using organic substrates but recently transition metals have been used to effect these transformations of organic substrates to produce a-pyrones. A few of the more important and general reactions are presented here. Methyl-3-oxopentanoate and methyl butynoate react in the presence of a catalytic amount of NaOMe to give 6-ethyl-4-methyl-2-oxo-2H-pyran-5-carboxylate in excellent yield (96%). This method has been extended to other acetylenic esters, ROCH C • CC0 Me (R 19  2  2  = THP, MeOCH , Me), but the yields are much lower (0-33%). This reaction involves an 2  initial Michael addition followed by a facile cyclization under the basic conditions of the reaction to produce the a-pyrone. Related to this is the use of ethyl acetoacetate. This reaction forms only a non-cyclic condensation product if acetylacetone is used. Brassard has developed a very useful route to a-pyrones.  20  Chloro-ketene dimethyl  68 acetal and an a,/3-unsaturated ketone are heated to give 3-chloro-3,4-dihydro-2,2dimethoxypyrans that upon treatment with NaOMe produces the desired a-pyrones.  o  This reaction works for a wide range of a,j8-unsaturated ketones, thus giving a range of substituents on the pyrone ring in the 4, 5, and 6 positions. A 3-chloro substituent for one reaction has been produced but the generality of this synthetic methodology is uncertain. This reaction also requires high temperatures (120-150°C) that would make it unsuitable for thermally sensitive starting materials or products. Another novel way of producing a-pyrones is by using the reactive substrate carbon suboxide in conjunction with an equimolar amount of trimethylsilylenolether to give the 21  pyrones in high yields. This reaction is successful for a range of trimethylsilylenolethers, but it does not allow substitution in the 3-position of the pyrone ring.  o=c=c=c=o •  ,1 OSiMe  H  3  O  '  y  "R  1  R R = H, alkyl;  R = H, alkyl, aryl; 1  R and R may be a ringsystem. 1  Various catalytic and stoichiometric reactions of forming a-pyrones using transitionmetal complexes exist. Many of these reactions have been developed only recently and the general applicability of these reactions to produce a-pyrones is not fully known in many cases. Ni(0) catalysts have been used to build a-pyrones from alkynes and C 0 . 2  2 2  69  O  R Ni(0)  II  +  C 0  2  P(alkyl)  R1  3  R'  + cyclotrimers and oligomers of alkynes  R  R «= H R = (CHJ^CHJ; 1  R = H R = OEt; 1  R and R  1  «=Me, Et  In a lot of cases, these reactions produce cyclotrimers or oligomers of the alkynes used in the reaction. Selectivity in these reactions may be controlled by using the appropriate trialkyl phosphine ligand. Recently these catalytic systems have been extended to functionalized alkynes by using ethoxyacetylene. Tsuda has taken diynes and CO2 in the presence of Ni(0) catalysts and formed bicyclo-a-pyrones. This reaction has been successful for both terminal and substituted diynes and has also been recently extended to diynes containing a trimethylsilyl group on the diynes allowing for the formation of 3- or 6-silyl substituted bicyclo-a-pyrones. This reaction has varying selectivity and the ability to extend this reaction to a large range of substitution patterns at the 4 and 5 positions on the pyroneringseem limited. Other catalytic systems have been developed for the formation of a-pyrone from alkynes and C 0 . 2  2 3  4,6-dimethyl-2-pyrone is produced, along with cyclotrimers, when  propyne and C 0 are combined in the presence of mildly oxidized Rh and F^Rl^ carbonyl 2  4  cluster-derived catalysts. Yield of a-pyrone in these reactions, however, are never more than 8 mole% of the total products with the cyclotrimers making up the bulk of the products. Vinyl cyclopropenyl ketones and the cyclopropenyl esters from which they are formed may be converted to a-pyrones using a Rh catalyzed carbonylation at one atmosphere of C O .  24  70  2%[ClRh(CO) ]  2 2  CO (latm)  R  R  3  2  H R  = H, alkyl, silyl  R  2  = alkyl, aryl, haloalkyl  R  3  •= OEt, alkyl, aryl  H  H ^ 0 ^  R  1  R  3  ^ O ^ R  This reaction allows for good to excellent yields with varying degrees of regiospecificity (some reactions only form one product while others have approximately 50:50 mixtures of products). Alkynylalkoxycarbene metal (Cr, W) complexes can be used in conjunction with ethyldiethoxyacrylate to produce similar pyran-2-ylidene complexes.  25  DMSO is used as the  oxidizing agent to remove the pyran-2-ylidene ligand as an a-pyrone.  EtO  C0 Et 2  OEt EtO  (CO) M = 3  DMSO  H (CO) M  5  s  OEt  M  = Cr, W  R = 1  Me,  Et  R - Ph, *Bu 2  The reactions presented here all have limitations on the substitution pattern that can be introduced to the ring system, as do the reactions that have not been presented here. I suggest that the condensation of acetylenic esters and acetylenes mediated by Cp'M(NO) cations +  2  potentially offers a convenient and direct route to the synthesis of 3, 5, and 6 substituted apyrones.  71 References and Notes  These compounds are also called 2-pyrones and 2H-pyran-2-ones and pyran-2-ones. The numbering of the ring atoms is shown for a-pyrone, the parent compound of this class of molecules.  O  5 For a more comprehensive look at the reactivity, structure and synthesis of these compounds see: Brogden, P.J.; Gabbutt, C. D.; Hepworth, J. D. In Comprehensive Heterocyclic Chemistry; Boulton, A. J.; McKillop, A., Eds.; Pergamon: Toronto, 1984; Vol. 3, p 581. 2.  Bonsignore, L.; Cabiddu, S.; Giuseppe, L.; Secci, D. Heterocycles 1989, 29, 913.  3.  Israili, Z. H.; Smissman, E. E. 7. Org. Chem. 1976, 41, 4070.  4.  (a) Salomon, R. G.; Burns, J. R.; Dominic, W. J. 7. Org. Chem. 1976, 41, 2918 and reference 1 therein, (b) Jung, M. E.; Hagenah, J. A. 7. Org. Chem. 1987, 52, 1889. (c) Jung, M. E.; Lowe, J. A.; Lyster, M. A.; Node, M.; Pfluger, R. W.; Brown, R. W. Tetrahedron 1984, 40, 4751. (d) Jung, M. E.; Lowe, J. A. 7. Chem. Soc, Chem. Commun. 1978, 95.  5.  Rosenblum, M.; Gatsonis, C. 7. Am. Chem. Soc 1967, 89, 5074.  6.  Davies, S. G. Organotransition Metal Chemistry: Applications to Organic Synthesis  Pergamon: Toronto, 1982; pp 99-100 and references therein. 7.  Solid state effects cause splitting of the bands in the Nujol mull IR spectrum of the apyrone complexes.  72 8.  A literature search on a-pyrones was conducted and did not reveal any condensations involving acetylenes and acetylenic esters to produce a-pyrones.  9.  Pavia, D. L.; Lampman, G. M.; Kriz, G. S. Introduction to Spectroscopy: a Guide for Students of Organic Chemistry; Saunders College: Philadelphia, 1979; p 94.  10.  Staunton, J. In Comprehensive Organic Chemistry; Sammes, P. G., Ed.; Pergamon: Toronto, 1979; Vol. 4, p 631.  11.  (a) March J. Advanced Organic Chemistry, 3rd ed.; Wiley-Interscience: Toronto, 1985;p 950.  12.  (a) Jones, R. N.; Angell, C. L.; Ito, T.; Smith, R. J. D. Can. 7. Chem. 1959, 37, 2007. (b) Yamada, K. Bull. Chem. Soc. Jpn. 1962, 35, 1323.  13.  Legzdins, P.; Richter-Addo, G. B.; Einstein, F. W. B.; Jones, R. H. Organometallics 1990, 9, 431.  14.  Greenhough, T. J.; Kolthammer, B. W.; Legzdins, P.; Trotter, 7. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1980, B36, 795.  15.  Chadwick, D. J.; Easton, I. W.; Johnstone, A. W. Tetrahedron 1984, 40, 2451.  16.  Rossi, M.; Cantrell, J. S.; Farber, A. J.; Dyott, T.; Carrell, H. L.; Glusker, J. P. Cancer Res. 1980, 40, 2774.  17.  Brock, C. P.; Minton, R. P. 7. Am. Chem. Soc. 1989, Ul, 4586.  18.  For a more comprehensive treatise on the synthesis of a-pyrones see (a) ref. 8 pp 638641. (b) Ref. 1(b) pp 789-809.  19.  Jung, M. E.; Hagenah, J. A. 7. Org. Chem. 1987, 52, 1889.  20.  Brassard, P.; Manger, A. Can. 7. Chem. 1975, 53, 201.  21.  Bonsignore, L.; Cabiddu, S.; Loy, G.; Seed, D. Heterocycles 1989, 5, 913.  22.  (a) Tsuda, T.; Morikawa, S.; Sumiya, R.; Saegusa, T. 7. Org. Chem. 1988, 53, 3145. (b) Tsuda, T.; Morikawa, S.; Hasegawa, N.; Saegusa, T. 7. Org. Chem. 1990, 55, 2978. (c) Inoue, Y.; Itoh, Y.; Hashimoto, H. Chem. Lett. 1978, 633. (d) Tsuda, T.; Kunisada, K.; Nagahama, N.; Morikawa, S.; Saegusa, T. Synth. Commun. 1989,19, 1575.  73 23.  Pillai, S. M.; Ohnishi, R.; Ichikawa, M. J. Chem. Soc., Chem. Commun. 1990, 246.  24.  Liebeskind, L. S.; Cho, S. H. J. Org. Chem. 1987, 52, 2631.  25.  Camps, F.; Moreto, J. M.; Ricart, S.; Viiias, J. M.; Molins, E.; MiravitUes, C. J. Chem. Soc, Chem. Commun. 1989,  1560.  74  Appendix  75 The IR spectrum of [Cp*Mo(NO)2]BF in CH C1 . 4  2  2  o •  245D. O  1S25. O  1625. O 1325. O 1025. O WAVENUMBERS <CM-1>  6 0 0 . OO  76 The IR spectrum of the product mixture of CpCr(NO) -C=C(H)C(H)(CH )C(CH ) OC(=O) 2  and CpCr(NO) -C=C(H)C(CH )(C(H)(CH ) )OC(=0) as a Nujol muU. 2  3  3 2  3  3 2  The IR spectrum of the product mixture of [Cp*Cr(NO) 2  C=C(H)C(H)(CH )C(CH3) OC(=OCH )]BF and [Cp*Cr(NO) 3  2  3  4  2  C=C(^C(CH )(C(^(CH ) )OC(=OCH )]BF4 as a Nujol mull. 3  3  2  3  78  The IR spectrum of the product mixture of C^*Cr(NO) -C=C(H)C(H)(CH )C(CH ) OC(=O) 2  and Cp*Cr(NO) -C=C(H)C(CH )(C(H)(CH ) )OC(=0) as a Nujol mull. 2  3  3 2  3  3 2  The IR spectrum of the product mixture of [Cp*Mo(NO) 2  C=C(H)C(H)(CH3)C(CH3)20C(=OCH )]BF4 and [Cp*Mo(NO) 3  C=C(H)C(CH )(C(^(CH ) )OC(=OCH3)]BF4 as a Nujol mull. 3  3 2  2  80 The ER spectrum of the product rnixture of Cp*Mo(NO) 2  C=C(H)C(H)(CH )C(CH ) OC(=0) and Cp*Mo(NO) 3  3  2  2  C=C(H)C(CH )(C(H)(CH3)2)OC(=0) as a Nujol mull. 3  81 The IR spectrum of [Cp*W(NO) -c"=C(H)C(H)(CH )C(CH ) OC(= OCH )]BF as a Nujol 2  mull.  3  3 2  3  4  82 The IR spectrum of Cp*Mo(NO)2-C=C(H)C(H)(CH CH3)C(CH3)20C(=0) as a Nujol mull. 2  83 The IR spectrum of [Cp*Mo(NO) -C=C(H)C(CH )=C(Ph)OC( =OCH )]BF as a Nujol 2  mull.  3  3  4  84  The IR spectrum of [Cp*Mo(NO) -C=C(H)C(CH )=C(Ph)OC( =OCH )]BF in CH C1 . 2  3  3  4  2  2  85 The IR spectrum of Cp*Mo(NO) -C =C(H)C(Ph)=C(Ph)OC(=0) as a Nujol muU. 2  86 The CH C1 solution IR spectrum of [CpMo(NO) ]BF and 2,3-dimethyl-2-butene after the 2  2  2  4  solution has been stirring for 5 days at room temperature.  87 The CH C1 solution IR spectrum of [CpMo(NO) ]BF after the solution has been stirring for 2  2  3 days at room temperature.  2  4  88 The IR spectrum of Cp*Mo(0) -C=C(H)C(CH ) =C(Ph)OC(=0) as a Nujol mull. 2  3  

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