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Aspects of the organometallic nitrosyl chemistry of Cr, Mo and W Hunter, Allen Dale 1985

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ASPECTS OF THE ORGANOMETALLIC NITROSYL CHEMISTRY OF Cr, Mo and W By ALLEN D. HUNTER B.Sc, UNIVERSITY OF BRITISH COLUMBIA, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA SEPTEMBER 1985 © ALLEN DALE HUNTER, 1985 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 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) i i Abstract The principal organometallic products resulting from the reactions of Na [(Ti 5-C 5H i tR)Cr(CO) 3] (R = H or Me) with a l l y l chlorides in THF are the green, dimeric [ ( T} 5-C 5H 4R)Cr(C0) 3] 2 complexes (51-67% yields). The red organometallic by-products usually formed during these conversions are novel (n 6-6-alkenylfulvene)Cr(C0) 3 complexes (5-8% yields) which have been characterized completely by conventional spectroscopic methods. Dark green [W(N0) 2Cl 2] n may be synthesized in high yields by two preparative methods. The f i r s t method involves treatment of WClg in CH2C12 with an excess of NO, and i t proceeds via the isolable intermediate complexes, dark violet cis-W(N0) 9Cl u and bright green fac_-W(NO)3C13. The second method involves controlled reaction of W(CO)g with two equivalents of C1N0 in CH2C12. It is initiated by traces of oxidant and probably proceeds via a catalytic, radical-chain mechanism that is described. If either reaction is effected in the presence of two equivalents of CH3CN, then yellow-green W(N0)C13(CH3CN)2 is the only nitrosyl-containing product formed. Polymeric [W(N0) 2Cl 2] n may be cleaved by a variety of Lewis bases, L, and (n-Bu) 3Sn(C &H 5) to form W(N0)2C12L2 (L = phosphine, phosphite, CH3CN, etc.) and CpW(N0)2Cl (Cp - n 5-C 5H 5), respectively, in good yields. The synthesis of the electron-rich nitrosyl complexes CpM(NO)L2 (M = Cr, Mo, or W; L ° P(0Me)3, PMePh2, P(n-Bu) 3, SbPh3 or 1/2 (dppe)) is described. They are preparable in moderate to high yields by the reduction i i i of the iodo dimers [CpM(NO)In]2 (M = Cr, n = 1; M = Mo or W, n = 2) with sodium amalgam in THF ln the presence of the appropriate Lewis base, L, and they exhibit metal-dependent trends in v^Q (Cr » Mo > W), 6 3 1P (Cr > Mo » W), and 2J3ip_3ip (Cr < Mo < W). These reduction reactions proceed via a number of transient intermediates, some of which are isolable. A unified mechanism for these reductive syntheses is proposed. The novel complexes, CpMo(NO)(r|i4-trans-diene) (diene = acyclic conjugated diene) and CpMo(NO)(T)'t-cis-2,3-dlmethyl-butadiene)t are preparable in moderate yields by the reduction of [CpMo(NO)I2]2 with sodium amalgam in THF in the presence of the appropriate diene. The reaction between [CpMo(NO)I2]2 a n d C4Hg«Mg»2(THF) results in the formation of a green, isolable oligomeric complex CpMo(NO)I(Ti3-C3HitR) (where R = CH2MgI and the nitrosyl oxygen acts as a Lewis base towards Mg) that can be hydrolyzed to CpMo(NO)I(ri3-CltH7) or converted to CpMo(NO)(T)'+-trans-CuHfi). These diene complexes have been f u l l y characterized by conventional spectroscopic techniques (extensive *H and *3C NMR spectra being particularly informative) and by single-crystal X-ray structural determinations of CpMo(NO)(r|'t-trans-2,5-dimethyl-2,4-hexadiene) and CpMo(N0)(^-cls-2,3-dimethyl-butadlene). A molecular orbital rationale for the structural and spectrocopic properties and relative s t a b i l i t i e s of these c i s - and trans-diene complexes is then presented. i v Table of Contents Abstract i i Table of Contents i v L i s t of Tables v i i L i s t of Figures v i i i L i s t of Schemes i x Abbreviations and S t y l i s t i c Notes x Acknowledgements x i i CHAPTER ONE - GENERAL INTRODUCTION 1 CHAPTER TWO - NOVEL (T|6-6-ALKENYLFULVENE)TRICARB0NYLCrlR0MIUM(0) COMPLEXES RESULTING FROM THE REACTIONS OF Na[( T ^ - C ^ R ' )Cr(C0) 3 ] (R'=H or Me) WITH SOME ALLYL CHLORIDES 13 Introduction 14 Experimental Section 15 Results and Discussion 20 References and Notes 31 CHAPTER THREE - ON THE TRAIL OF DICHLORODINITROSYLTUNGSTEN: A TALE OF TWO REACTIONS 34 Introduction 35 Experimental Section 36 Results and Discussion 47 Reductive N i t r o s y l a t i o n of WCl g 47 Treatment of W(C0) 6 With C1N0 53 Some Ch a r a c t e r i s t i c Chemistry of [W(N0) 2Cl 2] n 61 V Conclusions • 65 References and Notes 66 CHAPTER FOUR - REDUCTIVE SYNTHESIS OF THE COMPLEXES CpMo(NO)L2 (M = Cr, Mo, OR W; L = LEWIS BASE): TRENDS IN THEIR PHYSICAL PROPERTIES AND MECHANISM OF FORMATION 69 Introduction 70 Experimental Section 72 Results and Discussion 84 Synthesis and Physical Properties of the Complexes CpM(N0)L 2 (M = Cr, Mo, or W; L = Lewis Base) 84 Synthesis and Physical Properties of the Complexes CpMo(N0)I 2L and [CpMo(NO)IL 2]I (L = Lewis Base) .... 98 Mechanism of the Reductive Synthesis of the CpM(N0)L 2 Complexes 104 Conclusions • 117 References and Notes 121 CHAPTER FIVE - THE SYNTHESIS AND PHYSICAL PROPERTIES OF THE NOVEL CIS- AND TRANS-DIENE COMPLEXES CpMoCNOX^-diene) 127 Introduction 128 Experimental Section 129 Results and Discussion 137 Synthesis and Physical Properties of the CpMo(NO) (n^-trans-diene) Complexes 137 Synthesis and Physical Properties of Cp Mo(NO) ( n l t-trans-2,5-dimethyl-2,4-hexadiene ) 145 v i Synthesis and Physical Properties of CpMo(NO) (iV+-cis-2, 3-dimethylbutadiene) 147 Reaction of [CpMo(NO)I 2] 2 with C^Hg.Mg.ZCTHF) 150 *H and 1 3 C NMR Spectroscopic Properties of the Diene Products 154 Mechanistic Pathway of the Reductive Synthesis of CpMo(NOXn1*-diene) Complexes 164 Mechanism of the Reaction of Butenediylmagnesium with [CpMo(N0)I 2] 2 171 Conclusions 174 References and Notes 176 CHAPTER SIX - STRUCTURAL AND ELECTRONIC EFFECTS OF "CpMo(NO)" ON CIS- AND TRANS-BUTADIENE COORDINATION 181 Introduction 182 Experimental Section 183 Results and Discussion 184 Conclusions 196 References and Notes 198 Epilogue 200 Appendix 201 v i i List of Tables Table 2.1 LH NMR Data for the Isolated ( r r 6-6-Alkenyl-fulvene)Cr(CO) 3 Complexes i n CDC13 25 Table 2.2 1 3C{ 1H} NMR Data for the Isolated (t) 6-6-Alkenylfulvene)Cr(CO) 3 Complexes i n CDC13 26 Table 4.1 A n a l y t i c a l and Mass Spectral Data for the Complexes .. 88 Table 4.2 IR, 3 1 P and XH NMR Data for the Complexes 90 Table 4.3 *H NMR Parameters for Methyl Resonances of CpM(NO)[P(OMe) 3] 2 (M = Mo, W) 99 Table 4.4 N i t r o s y l - s t r e t c h i n g Frequencies of Complexes Detectable by IR Spectroscopy During Reductions of [CpMo(N0)X 2] 2 by Na/Hg i n THF i n the Presence of 4L .. 105 Table 5.1 A n a l y t i c a l , IR, and Mass Spectral Data for the Diene Complexes •• 139 Table 5.2 Numbering Scheme for the Diene Complexes 140 Table 5.3 XH NMR Chemical S h i f t s of the Diene Complexes 141 Table 5.4 1H NMR Coupling Constants of the Diene Complexes 142 Table 5.5 1 3 C NMR Chemical S h i f t s of some Diene Complexes 143 Table 5.6 1 3 C NMR ^Ji„ \3r Coupling Constants of some Diene Complexes 144 Table 6.1 Selected Bond Distances ( A ) and Angles (deg) of CpMo(NO) ( T) l*-cis-2,3-dimethylbutadiene) and CpMo(NO)( T^-trans-2,5-dimethyl-2,4-hexadiene) 191 Table 6.2 Calculated Mulliken Populations of CpMo(NO) ( T ^ - c i s - C u H j and CpMo(NO ) ( T i 4-trans-C l tH 6) 193 v i i i L i s t of Figures Figure 2.1 The 100.6-MHz 13C{1H} NMR spectrum in the hydrocarbon ligand region of (n 6-C 1 3H 1 8)Cr(C0) 3 in CDC13 27 Figure 4.1 Variation of with the acceptor number (AN) of the solvent • 93 Figure 4.2 XH and 3 1P NMR spectra of CpM(NO)[P(OMe)3]2 in the P(OMe)3 region 95 Figure 4.3 XH NMR spectrum of CpW(NO)[P(OMe)3]2 in the P(0Me)3 region 97 Figure 5.1 Variation of v N Q with the acceptor number (AN) of the solvent 146 Figure 5.2 The AH NMR spectrum of 5 156 Figure 5.3 The 1 3C{ 1H} NMR spectrum of 5 157 Figure 5.4 1H- 1 3C chemical shift correlation plot of 5 160 Figure 6.1 Molecular structure of CpMo(NO)(ntt-trans-2,5-dimethyl-2,4-hexadiene) 189 Figure 6.2 Molecular structure of CpMo(N0)(nu-cis-2,3-dimethylbutadiene) 190 Figure 6.3 Molecular orbital diagram of the upper valence orbitals of CpMo(N0)(n't-cis-C4H6) and CpMo(NO) (n^-trans-C^Hj 192 ix L i s t of Schemes Scheme 2.1 29 Scheme 3.1 54 Scheme 3.2 58 Scheme 4.1 107 Scheme 5.1 165 X Abbreviations and S t y l i s t i c Notes In general the abbreviations used i n t h i s thesis are those reommended i n "Handbook for Authors of Papers i n American Chemical Society Publications". Tables, Figures, Schemes, and Equations are numbered x.y, where x represents the chapter and y resets to 1 at the beginning of each chapter. Bibliographic references and notes are indicated by superscripts and are reported separately for each chapter.. In addition, the following are also employed: \ A angstrom (10 - 1 0 m) cm - 1 wavenumber Cp Cp' H 5-C 5H„Me Cp n5-C5Me5 CP centroid of a Cp ligand dppm bis(diphenylphosphino)methane dppe 1,2-bis(diphenylphosphino)ethane FT Fourier transform HOMO highest occupied MO L two-electron Lewis base (usually PR 3) LUMO lowest unoccupied MO MO molecular o r b i t a l PR3 phosphine or phosphite R a l k y l or a r y l group S solvent molecule SLUMO second lowest unoccupied MO THF tetrahydrofuran X C l , Br or I ligand V^Q i n f r a r e d n i t r o s y l stretching frequency Aooi/o peak width at half height x i i A c k n o w l e d g e m e n t s I wish to thank the fac u l t y and technical s t a f f of the Chemistry Department for t h e i r expert assistance and guidance during the course of thi s study. The h e l p f u l services of Mr. S. Rak, Mr. S. Takacs, Mr. P. Borda, Mrs. M.T. Aus t r i a , Ms. M.A. Heldman, Ms. L.M. Darge, and Dr. S.O. Chan were p a r t i c u l a r l y appreciated. I would also l i k e to acknowledge my many useful discussions with Drs. E.E. Burnell and M.D. Fryzuk of t h i s Department, Drs. F.W.B. E i n s t e i n and A.C. W i l l i s of Simon Fraser University, and Drs. B.E. Bursten and M.G. Gatter of Ohio State Un i v e r s i t y . I am indebted to the members of the 319/325 group, both past and present, for providing a great environment. In p a r t i c u l a r , those with whom I have worked most c l o s e l y (namely: Jimmie, Charlie , Dave, Dunk, Frank, B6, Nathalie, Ev, and Nancy) made my days i n the lab both enjoyable and productive. I also had many useful discussions and inte r a c t i o n s with the "other guys" (namely: J e f f , L u i s , and George) i n 325 with whom I never had the good fortune of sharing a lab. The d i l i g e n t e f f o r t s of my proofreaders ( e s p e c i a l l y Nancy, Nathalie, and Peter) and Bev (who typed t h i s manuscript) were above and beyond "the c a l l of duty", and I am i n th e i r debt. I would also l i k e to thank the people of Canada who supported my graduate career v i a a Natural Sciences and Engineering Research Council of Canada scholarship. F i n a l l y , I wish to express my gratitude to Professor Peter Legzdins whose frie n d s h i p , support, and enthusiasm f i r s t attracted me to Chemistry and then made the completion of t h i s work possible. 1 CHAPTER ONE GENERAL INTRODUCTION 2 Transition-metal organometallic chemistry i s a dynamic and r a p i d l y growing f i e l d . Although a few organometallic compounds such as coenzyme (vitamin) B^^" e x i s t i n nature and the f i r s t such man-made complex, namely Zeise's s a l t (K[(T) 2-C 2H i t)PtCl 3]), was reported i n 1827, there were only sporadic additions to the knowledge of and i n t e r e s t i n organometallic species u n t i l the early 1950's. In a notable example of the synergy of theory and experiment, t h i s changed dramatically when reasonable bonding 3 4 rationales for metal carbonyls and ferrocene were proposed i n 1951 and 1952, r e s p e c t i v e l y . Since that time, there has been rapid growth i n the knowledge of the synthesis, r e a c t i v i t y , physical properties, and bonding of transition-metal organometallic compounds. Indeed, the novel structures and bonding i n such species and t h e i r u t i l i t y i n synthetic organic and i n d u s t r i a l chemistry have kept t h i s d i s c i p l i n e at the forefront of modern chemistry.^ The development of organometallic n i t r o s y l chemistry has lagged somewhat behind that of the more f a m i l i a r carbonyl chemistry.*' H i s t o r -i c a l l y , t r a n s i t i o n metal n i t r o s y l and carbonyl complexes have been 6a considered to possess very s i m i l a r bonding, structures, and r e a c t i v i t y . However, with the renewed i n t e r e s t i n n i t r o s y l complexes over the l a s t two decades ' i t has become clear that they d i f f e r markedly from carbonyl compounds. The n i t r o s y l ligand i s known to p a r t i c i p a t e i n three p r i n c i p a l bonding forms:** a) terminal, l i n e a r M-N-0 ; b) terminal, bent M-lK n ; 3 c) bridging. The terminal, linear bonding mode of nitrosyl ligands is the most common, particularly for organometallic compounds. The NO ligand functions 6e f as a net three-electron donor in the terminal, linear form. ' The idealized MNO angle is 180°, but in reality this angle is usually between 165° and 180°.^e'*> The bonding involves a synergic combination of * o-donation from the nitrosyl ligand to the metal and Mn -*• NOn back-6e bonding. The extent of metal n-donation is dependent on the degree of electron density at the metal center, which in turn is influenced by the ancillary ligands and the charge on the complex. The linear NO ligand is considered to be one of the strongest it-acids known.^'^ In situations where NO and CO have to compete for relatively low electron density at the metal center they appear to have similar n-acceptor a b i l i t i e s . On more 7a electron-rich metal centers, the NO ligand is the stronger it-acid. Four simple valence-bond resonance hybrids can be envisaged for the terminal, linear metal-nitrosyl linkage, i.e. + - - + ~ 2 + + M=N-0: <-> M£=N=d; <-> M=N=d: <-> M«-N=0: • • • Traditionally, however, i t has been considered to be bound formally as N0+, which is isoelectronic with CO.*' In valence-bond terms, both the N and the 0 atoms are sp hybridized. The N0+ formalism breaks down the metal-nitrosyl interactions into three components: a) reduction of the metal by 4 NO to give M~ and N0 +; b) a-donation of the n i t r o s y l lone pair from the nitrogen atom of N0 + to the metal and; c) back-donation from the f i l l e d metal dn o r b i t a l s to the i t antibonding o r b i t a l s of the N0 + fragment. ( i . e . dn pu ). The N0 + formalism spawns from the desire to treat n i t r o s y l and carbonyl chemistry as being e s s e n t i a l l y s i m i l a r . ' However, besides being somewhat cumbersome to use, th i s formalism can lead to some i n t u i t i v e l y and p h y s i c a l l y "unreasonable" i n t e r p r e t a t i o n s . For example, the electron density that i s f i r s t transferred from NO to M to give M~ and * NO"1" i s subsequently involved i n dn -*• pit back-donation ( i . e . giving with one hand and taking away with the other). However, the major area of d i f f i c u l t y associated with t h i s formalism centers on the assignment of formal oxidation states. Namely, consideration of the l i n e a r n i t r o s y l ligands as N0 + leads to the assignment of "unreasonable" formal oxidation state numbers ( i . e . -1, -2, -3 and -4 for Co(CO) 3(NO), Fe(CO) 2(NO) 2, Mn(CO)(NO)3 and (^(NO)^, respectively) to metal centers i n many complexes. For organometallic n i t r o s y l complexes, where the bonding in t e r a c t i o n s are 6c l a r g e l y of a covalent nature, i t i s best to avoid rationales involving the N0 + formalism and formal oxidation states.** 8 The l i n e a r n i t r o s y l ligand i s thus considered to be a neutral three-electron donor. However, the best d e s c r i p t i o n of the bonding obviously must involve molecular 6c, E o r b i t a l treatments. The terminal, bent bonding mode of NO has no analogue i n metal-carbonyl chemistry ' and i s not nearly as common as the terminal, l i n e a r 5 mode i n organometallic compounds. It i s generally found i n n i t r o s y l complexes of l a t e t r a n s i t i o n metals, at the a p i c a l p o s i t i o n of a square-6e base pyramid or di s t o r t e d octahedral coordination sphere. ° The bent n i t r o s y l ligand i s best considered to be a neutral one-electron donor with s p 2 hybridized N and 0 atoms ( i n Valence Bond terms), i . e . + M <- Nv < > M - NN. *bs ^ 0 : It i s thus analogous to an organic nitroso compound. Although the id e a l i z e d s p 2 MNO angle i s 120°, MNO angles are observed to vary between the two extremes of 120° and 180° ( p e r f e c t l y l i n e a r ) , depending on the 6f 8 extent of the i n t e r a c t i o n of the nitrogen lone pair with the metal. ' Although rare, both doubly- and t r i p l y - b r i d g i n g forms of the n i t r o s y l ligand are known. They are considered to be neutral three-electron donors. For instance, the trimer Cp 3Mn 3(NO) 1 + contains three doubly-bridging NO groups around the perimeter of an Mn3 t r i a n g l e with a 9 t r i p l y - b r i d g i n g NO cap. A di s t i n g u i s h i n g t r a i t of the d-block elements i s th e i r a b i l i t y to form complexes with a wide v a r i e t y of ligands. However, as expected from the d i v e r s i t y of complexes known, the structures and bonding i n these species are n o n - t r i v i a l . ^ Some systematization may be obtained by the ap p l i c a t i o n of a set of electron bookkeeping r u l e s . They a r i s e from the la r g e l y empirical observation that organometallic complexes ( e s p e c i a l l y 6 those of the mid-transltion-metals) tend to obey the "18-electron r u l e " . This states that a metal complex i s most stable when the sum of the metal's valence electrons and those donated by the ligands i s eighteen. As noted above, for organometallic n i t r o s y l complexes the assignment of formal oxidation states to ligands and metal centers (except for the net charge on the complex) i s best avoided. Thus, throughout t h i s work, the oxidation state formalism i s not generally used. Instead, ligands are a l l treated as formally neutral ( r e f l e c t i n g the p r i m a r i l y covalent nature of t h e i r bonding inte r a c t i o n s ) and considered to donate the following number of electrons to a metal center: C l , Br, I, H and R ( a l k y l or a r y l ) give one; CO, alkenes and PR3 ( i . e . a l k y l or a r y l , phosphine or phosphite) give two; T ) 3 - a l l y l gives three; •n^-butadiene gives four; n 5-cyclopentadienyl gives f i v e and T) 6-arene gives s i x . Again, such bonding interactions are best described i n Molecular O r b i t a l terms; however, more q u a l i t a t i v e descriptions are often s u f f i c i e n t and these have been described previously."* I would l i k e to emphasize b r i e f l y some relevant d e t a i l s here. The two most common ligands i n organometallic chemistry are the cyclopentadienyl and carbonyl groups. The cyclopentadienyl group (C 5R 5, R=H, a l k y l ) contains a delocalized Tt system, and t h i s i s involved i n bond-7 ing to the metal center. This group can donate either one, three or f i v e electrons to the metal-ligand i n t e r a c t i o n depending on whether one, three, or f i v e carbons are within bonding distance of the metal atom ( i . e . r) 1, r|3 or T I 5 ) , r e s p e c t i v e l y . In the most common mode of attachment, namely T I 5 , the cyclopentadienyl group i s e s s e n t i a l l y planar and i s a net electron donor to the metal center. This electron donation i s enhanced when a l k y l groups replace the hydrogens on the cyclopentadienyl l i g a n d . The carbonyl group i s a formal two electron donor. I t i s involved i n a synergic bonding i n t e r a c t i o n with the metal analogous to that seen for 3 6e the terminal, l i n e a r NO li g a n d . ' Thus, a lone pair of electrons on the carbonyl carbon i s donated to a a-symmetry o r b i t a l on the metal while electrons i n f i l l e d metal dn o r b i t a l s are back-donated to the empty carbonyl TI o r b i t a l s . It i s thus r e a d i l y apparent that an increase i n electron density on the metal would increase back-bonding to the carbonyl it* o r b i t a l s and thus decrease both i t s carbon-oxygen bond order and inf r a r e d (IR) stretching frequency ( v C Q ) « a s i m i l a r argument i s made for NO. Indeed, t h i s s h i f t i n the stretching frequencies Is one of the most sen s i t i v e probes to changes i n the "electron richness" of the metal center i n a complex as i t s a n c i l l a r y ligands are var i e d . Ligands somewhat analogous to CO are the t r i v a l e n t group 1 5 ^ species ER 3 (where E = P, As, Sb and R = a l k y l , a r y l , alkoxy and f l u o r o ) . The f l u o r i n a t e d phosphine, PF 3, exhibits bonding s i m i l a r to that of CO except that the back-bonding i s into empty d o r b i t a l s on the phosphorus and i t i s a somewhat stronger n-acceptor ( i . e . n-acid) than CO.^ In contrast, 8 the a l k y l and a r y l phosphines are strong a-donors with l i t t l e , i f any, T t-acid character.^ The phosphite species, P(OR) 3, are poorer o-donors than the phosphines and may exhibit some degree of back-bonding l i k e t h e i r PF 3 analogues. The e l e c t r o n i c and s t e r i c properties of phosphines and phosphites ( i . e . donor a b i l i t y and cone angle, respectively) are well documented^'^ and may be varied independently by suitable choices of R to perturb the properties of a complex. A c e n t r a l theme i n organometallic n i t r o s y l chemistry has been the comparison of the chemistry of i s o s t r u c t u r a l and i s o e l e c t r o n i c carbonyl and n i t r o s y l complexes. Recent work i n our research group on the chemistry of various group s i x n i t r o s y l complexes has shown that such comparisons almost i n v a r i a b l y lead to the observation of divergent chemical r e a c t i v i t y . For example, i t has been shown that compared to the generally protonic carbonyl hydride complexes the n i t r o s y l hydride CpW(NO)2H i s hydridic i n 12 character. The electrochemical properties of some related carbonyl and n i t r o s y l complexes are also markedly d i f f e r e n t . This comparison has been 13 made for the dimers [CpCr(NO) 2] 2 a n d [CpFe(CO) 2] 2 and the related species 14 CpCr(NO) 2R and CpFe(CO) 2R (R = a l k y l ) . The unusual properties of n i t r o s y l complexes are also well demonstrated by the novel 16-electron J complexes, CpW(NO)R 2,^ which exhibit unprecedented r e a c t i v i t y with 0 2 , ^ 17 18 Sg and various other small molecules. The differences between metal carbonyl and n i t r o s y l chemistry are extensive; however, I f e e l that they r e f l e c t two primary f a c t o r s . The most obvious of these i s that NO i s a better u-acid than CO. A less obvious 9 effect i s that NO i s a formal three-electron donor while CO donates only two electrons. This results i n the molecular structures of cyclopen-tadienyl n i t r o s y l complexes having different "legged" piano stools than related carbonyl complexes of the same metal ( i . e . 3 vs"4 for CpCr(NO)2R and CpCr(CO)3R, respectively). Substitution of NO for CO to obtain isoelectronic and is o s t r u c t u r a l compounds necessitates a s h i f t to the l e f t across the periodic table for the metal center ( i . e . CpFe(CO)2R to CpCr(NO)2R). This causes the metal center of such n i t r o s y l complexes to be r e l a t i v e l y electron poor. These factors combine to give NO complexes 13-15 19 qu a l i t a t i v e l y different bonding than related CO species. * Thus, one can r e l a t i v e l y safely expect t r u l y novel and unexpected chemistry when studying metal n i t r o s y l s and their effects on a n c i l l a r y ligands. The work presented i n this thesis has had three primary objectives: the f i r s t was to synthesize some novel metal-nitrosyl complexes either by adding the NO group(s) to metal centers and/or by further derivatizing other ligands on a n i t r o s y l complex, the second involved developing mechanistic insights into these reactions, and the th i r d involved deter-mining the effects of n i t r o s y l ligands on other species i n the metal's coordination sphere. In other words, the effects of the n i t r o s y l ligand on the structures, properties and r e a c t i v i t i e s of some transition-metal organometallic complexes were investigated. Chapter Two deals not with n i t r o s y l chemistry but with the i s o l a -t i o n and characterization of a highly unusual by-product i n the synthesis of [CpCr(CO) 3] 2 (a starting material for chromium n i t r o s y l chemistry) by the reaction of Na[CpCr(CO) 3] with various a l l y l chlorides. 10 Chapter Three i s concerned with the synthesis of [W(NO) 2Cl 2] n from W(C0) 6 and N0C1 or WC16 and NO gas. Mechanisms for these reactions are proposed and various intermediates are observed and characterized. Some r e a c t i v i t y of [W(NO) 2Cl 2] n i s also reported. Chapter Four deals with the reduction of the metal n i t r o s y l dimers [CpM(N0)I n] 2 (M=Cr; n=l; M=Mo or W, n=2) i n the presence of various group 15 Lewis bases, L, to produce the e l e c t r o n - r i c h n i t r o s y l complexes CpM(N0)L 2. A mechanism for these reactions i s proposed and i s related to the analogous diene reductions i n Chapter Fiv e . Trends i n the physical properties of the resultant complexes are also discussed. Chapter Five describes the synthesis of some novel c i s - and trans-diene complexes of molybdenum [ i . e . CpMo(NO)(diene)]. The IR, *H and 1 3 C NMR properties of these species are described i n d e t a i l . Solution state structures are then proposed. In Chapter Six, the X-ray c r y s t a l structures of CpMo(NO)(cis-2,3-dimethylbutadiene) and CpMo(NO)(trans-2,5-dimethyl-2,4-hexadiene) are reported. These are related to the spectroscopic properties of the complexes and a molecular o r b i t a l r a t i o n a l e for t h e i r unusual structures and s t a b i l i t i e s i s proposed. 11 References and Notes (1) Lenhart, P.G.; Hodgkin, D.C. Nature 1961, 192, 937. (2) Zeise, W.C. Ann. Phys. 182^7, 9_» 9 3 2 ' (3) Pauling, L. "The Nature of the Chemical Bond"; Cornell Univ. Press: Cor n e l l , 1960 and references c i t e d therein. (4) Wilkinson, G.; Rosenblum, M.; Whiting, M.C.; Woodward, R.B. J . Am. Chem. Soc. 1952, 74, 2125. (5) An excellent discussion of the p r i n c i p l e s of transition-metal organometallic chemistry i s provided by Collman, J.P.; Hegedus, L.S. "P r i n c i p l e s and Applications of Organotransition Metal Chemistry"; University Science Books: M i l l V a l l e y , 1980. (6) Organometallic n i t r o s y l chemistry has been extensively reviewed, see for example: (a) Caulton, K.G. Coord. Chem. Rev. 1975, 14, 317. (b) Connelly, N.G. Inorg. Chim. Acta Rev. 1972, 6, 47. (c) Enemark, J.H.; Feltham, R.D. Coord. Chem. Rev. 1974, 13, 339. (d) McCleverty, J.A. Chem. Rev. 1979, 79, 53. (e) Cotton, F.A.; Wilkinson, G. "Advanced Inorganic Chemistry"; 4th Ed.; Wiley Interscience: Toronto, 1980, Chapter 3. ( f ) G r i f f i t h , W.P. Adv.  Organomet. Chem. 1968, _7» 211. (g) Feltham, R.D.; Enemark, J.H. i n "Topics i n Inorganic and Organometallic Steriochemistry", Geoffroy, G., Ed.; Wiley Interscience: Toronto, 1981, Volume 13, 155. (7) (a) Harrocks, J r . , W.D.; Taylor, CR. Inorg. Chem. 1963, 2, 725. (b) Chen, H.W.; J o l l y , W.L. Inorg. Chem. 1979, 18, 2548. (c) Chatt, 12 J.; Kan, C.T.; Leigh, J . ; P i c k e t t , C.J.; Stanley, D.R. J . Chem. S o c , Dalton Trans. 1980, 2032. mm •• i i . • .. . . . . . i. — • /s^rorNTs/ (8) Pierpont, C.G.; Van Derveer, D.G.; Durland, W.; Eisenberg, R. J . Am.  Chem. Soc. 1970, 92, 4760. (9) Elder, R.C. Inorg. Chem. 1974, 13, 1037. — — mi • — • f mm i • MI rs*-S*^*-W» —mm -(10) In accordance with the recommendations of the nomenclature committees of the ACS and IUPAC the old group IVB elements (namely: N, P, As, Sb and B i ) ; are now named as group 15: Chem. Eng. News, 198J5, Feb. 4, 26. (11) Tolman, C A . Chem. Rev. 1977, 77, 313. (12) (a) Legzdins, P.; Martin, J.T.; Oxley, J.C. Organometallics, 1985, 4_, 1263. (b) Legzdins, P.; Martin, D.T. Inorg. Chem. 1979, 18, 1250. (13) Legzdins, P.; Martin, D.T.; Nurse, CR.; Wassink, B. Organometallics 1983, 2, 1238. (14) Legzdins, P.; Wassink, B., unpublished observations. (15) Legzdins, P.; Re t t i g , S.J.; Sanchez, L.; Bursten, B.; Gatter, M.G. J. Am. Chem. Soc. 1985, 107, 1411. (16) Legzdins, P.; Ret t i g , S.J.; Sanchez, L. J . Am. Chem. S o c , i n press. (17) Legzdins, P.; Sdnchez, L. J . Am. Chem. S o c , i n press. (18) Legzdins, P.; Sanchez, L., unpublished observations. (19) Bursten, B.; Gatter, M.G.; Hunter, A.D.; Legzdins, P., unpublished observations• 13 C H A P T E R TWO N O V E L ( T l 6 - 6 - A L K E N Y L F U L V E N E ) T R I C A R B O N Y L C H R O M I U M ( 0 ) C O M P L E X E S R E S U L T I N G F R O M T H E R E A C T I O N S O F N a K i ^ - C ^ R ' K ^ C O ^ J ( R » • H or M e ) W I T H SOME A L L Y L C H L O R I D E S 1 14 Introduction The chromium compound [CpCr(CO) 3] 2 may be used to prepare a v a r i e t y 2 of n i t r o s y l complexes. This dimer may be prepared by methods such as and Cp 2Cr + CO 1 5o?° 17o^ c > [ c P C r ( C O ) 3 ] 2 (2.1)3 THF 4 2 CpCr(CO) 3H r g f l u x > [ C P C r ( C 0 ) 3 ] 2 + H 2 (2.2) but the generally accepted procedure for synthesizing the complex i n bulk quantities involves the treatment of Na[CpCr(CO) 3] with various organic halides such as tropylium bromide, a l l y l bromide, or a l l y l c h l o r i d e , i . e . 2 Na[CpCr(CO) 3] + 2 RX d l g l v m e > [ c PCr(CO) 3] 2 + 2 NaX + R-R ( 2 . 3 ) 5 where R = C yH 7 or C 3H 5; X = Br or C l . 2 Not s u r p r i s i n g l y , therefore, we found during our e a r l i e r work that reaction 2.3 proceeded as described"* with RX = C 3H 5Br even when THF was employed as the solvent i n place of diglyme. We subsequently observed, however, that when a l l y l c hloride i n THF was used, the published work-up procedure afforded markedly i n f e r i o r y i e l d s of [CpCr(CO) 3] 2. Furthermore, 15 inf r a r e d s p e c t r a l monitoring of the progress of the l a t t e r reaction indicated the formation of other carbonyl-containing products i n addition to the desired dimer. Intrigued by these observations, we decided to examine more c l o s e l y the reactions of Na[CpCr(CO) 3] and i t s methylcyclo-pentadienyl analogue i n THF with some a l l y l c h l o r i d e s . In Chapter Two, the re s u l t s of my studies of this reaction are presented. Experimental Section A l l reactions and subsequent manipulations were performed under anaerobic and anhydrous conditions under an atmosphere of p r e p u r i f i e d nitrogen either on the bench using conventional techniques for the manipu-l a t i o n of a i r - s e n s i t i v e compounds** or In a Vacuum Atmospheres Corp. D r i -Lab Model HE-43-2 drybox. A l l chemicals used were of reagent grade or comparable p u r i t y and were e i t h e r purchased from commercial suppliers or prepared according to published procedures. Reagent purity was ascertained by elemental a n a l y s i s , melting point determinations and/or other s u i t a b l e methods. Melting points were taken i n c a p i l l a r i e s (sealed under nitrogen for t r a n s i t i o n metal compounds) by using a Gallenkamp Melting Point appara-tus and are uncorrected. A l l solvents were dried by standard procedures,^ d i s t i l l e d and deaerated with p r e p u r i f i e d nitrogen just p r i o r to use. Unless otherwise s p e c i f i e d , the chemical reactions described below were effected at ambient temperatures. Infrared spectra were recorded on a Perkin-Elmer 598 spectrophoto-meter ( c a l i b r a t e d with the 1601-cm - 1 band of polystyrene film) or on a 16 Nicolet 5DX FT-IR Instrument ( i n t e r n a l l y c a l i b r a t e d with a He/Ne l a s e r ) . Proton magnetic resonance spectra were obtained on a Bruker WP-80, WH-400, Nicolet-Oxford H-270, or Varian XL-300 spectrometer with reference to the deuterium signal of the solvent employed. A l l '*H chemical s h i f t s are reported i n parts per m i l l i o n downfield from Me l tSi. Carbon-13 NMR spectra were recorded on Bruker WP-80, WH-400, or Varian XL-300 spectrometers with reference to the solvent used, but a l l 1 3 C chemical s h i f t s are reported i n ppm downfield from Me^Si. Phosphorus-31 NMR spectra were recorded at 40.5 MHz on a Varian Associates XL-100 spectrometer or at 32.38 MHz on a Bruker WP-80 instrument using deuterium as the i n t e r n a l lock. The observed resonances were referenced to external P(0Me) 3 which was considered to have a chemical s h i f t of + 141 ppm downfield from 85% H 3P0 4. Mrs. M.T. Aus t r i a , Ms. M.A. Heldman, Ms. L.K. Darge, and Dr. S.O. Chan assis t e d i n obtaining the NMR data. Mass spectra were recorded at 70 eV on an Atlas CH4B or a Kratos MS50 spectrometer using the d i r e c t - I n s e r t i o n method by Dr. G.K. Eigendorf, Mr. J.W. Nip, and Mr. M.A. Lapawa. Elemental analyses were performed by Mr. P. Borda of t h i s Department. Reaction of Na[CpCr(C0)3] with 3-Chloropropene. To a s t i r r e d , bright yellow s o l u t i o n of Na[CpCr(C0) 3] 8 (5.00 g, 22.3 mmol) i n THF (150 mL) was added f r e s h l y - d i s t i l l e d 3-chloropropene (5.5 mL, 67 mmol), and the progress of the reaction was monitored by IR spectroscopy. The c h a r a c t e r i s t i c , strong carbonyl absorptions of the anionic reactant at ca. 1895(m), 1790(s) and 1740(a) cm"1 gradually diminished i n i n t e n s i t y , and the reaction mixture developed a green c o l o r . The carbonyl anion was 17 consumed after 3 days, the f i n a l mixture consisting of a brown p r e c i p i t a t e and a dark green so l u t i o n whose IR spectrum displayed absorptions at ca. 2005(m), 1985(m), 1940(e), 1915(s) and 1895(s) cm"1. The p r e c i p i t a t e was removed by f i l t r a t i o n through a medium porosity f r i t , and the f i l t r a t e was taken to dryness i n vacuo. The r e s u l t i n g dark green tar was then extracted with hexanes (4 x 30 mL). The red extracts were concentrated under reduced pressure to a volume of ca. 5 mL, at which point an IR spectrum exhibited bands at 2020(w), 1999(s), 1950(m), 1934(s), 1915(s) and 1890(w) cm - 1. The concentrated extracts were transferred by syringe to the top of a F l o r i s i l column ( 3 x 6 cm) made up i n hexanes. E l u t i o n of the column with hexanes developed a red band which was c o l l e c t e d and taken to dryness i n vacuo. Sublimation of the residue at ambient temperature under high vacuum (<0.005 mm) onto a water-cooled probe afforded 0.32 g (5.1% y i e l d based on Cr) of ( n 6 - C 1 1 H 1 1 + ) C r ( C 0 ) 3 (1) as an a n a l y t i c a l l y pure red s o l i d . Anal, calcd for C 1 1 +H 1 1 +Cr0 3: C, 59.57; H, 5.00; Cr, 18.42. Found: C, 59.45; H, 4.95; Cr, 18.37. IR (hexanes): v C Q 1999(s), 1934(s), 1915(s) cm - 1; Mass spectrum (probe temperature 120°C): most intense parent ion m/z 282; mp ( i n a i r ) 55-56°C. The insoluble green s o l i d remaining a f t e r the extraction with hexanes was then extracted with benzene (4 x 50 mL). Solvent was removed from the extracts under reduced pressure to obtain 3.01 g (67% y i e l d based on Cr) of spectroscopically pure [CpCr(CO) 3] 2 as a green, m i c r o c r y s t a l l i n e s o l i d . A n a l y t i c a l l y pure samples of the compound were obtained by r e c r y s t a l l i z a t i o n from benzene/hexanes. 18 Anal, calcd for C 1 6 H 1 Q C r 2 0 6 : C, 47.78; H, 2.51. Found: C, 47.76; H, 2.38. IR(CH 2C1 2): v c o 2007(m), 1945(s), 1919(s) cm - 1; *H NMR (CDC1 3): 6 6.45 ( A u 1 / 2 = 20 Hz). Q Reaction of Na[Cp ,Cr(C0) 3] with 3-Chloropropene. This reaction was effected i n a manner i d e n t i c a l to that described i n the preceding section. In t h i s case, however, the conversion was complete i n only 2 days. The f i n a l reaction mixture was worked up i n the customary fashion with the exception that the red hexanes extracts were chromatographed t h r i c e rather than once to obtain 0.42 g (6.6% y i e l d based on Cr) of ( r i 6 - C 1 2 H 1 6 ) C r ( C 0 ) 3 (3) as an a n a l y t i c a l l y pure, viscous red l i q u i d . Anal, calcd for C 1 5 H 1 6 C r 0 3 : C, 60.81; H, 5.44. Found: C, 60.69; H, 5.73. IR (hexanes): v 1993(s), 1927(s), 1910(s) cm - 1. Mass spectrum CO (probe temperature 25°C): most intense parent ion m/z_ 296. The usual work-up also resulted In the i s o l a t i o n of 2.5 g (54% y i e l d based on Cr) of [Cp'Cr(CO) 3] 2 as a green s o l i d . The i s o l a t e d material could be further p u r i f i e d by c r y s t a l l i z a t i o n from hexanes to obtain 1.5 g (32%) of dark green c r y s t a l s . Anal, calcd for C 1 8 H 1 1 + C r 2 0 6 : C, 50.24; H, 3.28. Found: C, 50.03; H, 3.40. IR (CH 2C1 2): v C Q 2000(m), 1941(s), 1915(s) cm"1;  lYL NMR (CDC1 3): 6 5.64 (2H, Au) 1 / 2 = 15 Hz), 5.49 (2H, Aw1/2 = 15 Hz), 3.51 (3H, Aw1/2 = 14 Hz); Mass spectrum (probe temperature 60°C): highest m/z_ ion 215; mp 70°C dec. Reactions of Na[CpCr(C0)3] with 3-Chloro-2-methylpropene. (a) In THF at Ambient Temperature. To a s t i r r e d yellow so l u t i o n 19 of Na[CpCr(CO) 3] (3.00 g, 13.4 mmol) In THF (100 mL) was added fr e s h l y d i s t i l l e d 3-chloro-2-methylpropene (6 mL, 61 mmol). The reaction mixture became green very slowly, 7 days being required for the anionic reactant to be consumed completely. Work-up of the f i n a l reaction mixture (a green so l u t i o n and a brown p r e c i p i t a t e ) i n the manner described above afforded 1.42 g (52.7% y i e l d based on Cr) of green [ C p C r ( C 0 ) 3 ] 2 and 0.33 g (7.9% y i e l d based on Cr) of ( n 6 - C 1 3 H 1 8 ) C r ( C 0 ) 3 (2) as a viscous, bright red l i q u i d . Anal, calcd for C 1 6 H 1 8 C r 0 3 : C, 61.93; H, 5.85. Found: C, 61.48; H, 5.77. IR (hexanes): v C Q 1994(s), 1932(s), 1910(s) cm - 1; Mass spectrum (probe temperature 120°C): most intense parent ion m/z_ 310. In a separate experiment, i t was found that the addition of a few mg of 2,2*-azobis(2-methylpropionitrile) to the o r i g i n a l reaction mixture had no e f f e c t on the rate of the reaction or on the i s o l a t e d y i e l d s of the products indicated above. However, the free r a d i c a l i n i t i a t o r did f a c i l i -tate the formation i n trace amounts of other carbonyl-containing products (IR (hexanes): v_„ 20O5(m), 1950(s), 1895(m) cm - 1), but these products were not characterized f u r t h e r . (b) In Refluxing THF. The reaction between Na[CpCr(C0) 3] (0.50 g, 2.2 mmol) and 3-chloro-2-methylpropene (1 mL, 10 mmol) i n r e f l u x -ing THF (40 mL) was complete i n 5 h, as judged by the attendant IR sp e c t r a l changes. IR spectroscopy also indicated that the product ( n 6 - C 1 3 H 1 8 ) C r ( C O ) 3 (2) and [( C p C r ( C 0 ) 3 ] 2 complexes were formed i n y i e l d s 20 comparable to those observed when the conversions were effected at room temperature. R e a c t i o n o f N a [ C p C r ( C 0 ) 3 ] w i t h 3 - C h l o r o - l - b u t e n e . This reaction was performed i n a manner i d e n t i c a l to that described previously for 3-chloropropene. However, i n t h i s instance, 10 days were required for the conversion to go to completion, and extraction with hexanes of the f i n a l reaction residue did not produce any substituted fulvene-containing organometallic complex. The customary work-up afforded a 51% y i e l d (based on Cr) of [ C p C r ( C 0 ) 3 ] 2 . R e a c t i o n o f [ C p C r ( C 0 ) 3 ] 2 w i t h 3 - C h l o r o p r o p e n e . Freshly d i s t i l l e d 3-chloropropene (0.6 mL, 7.4 mmol) was added to a green THF s o l u t i o n (40 mL) of [CpCr(CO) 3] 2 (0.40 g, 1.0 mmol). The r e s u l t i n g s o l u t i o n was s t i r r e d at room temperature for 18 h with no apparent change occurring i n i t s IR spectrum. The so l u t i o n was then refluxed for 22 h, whereupon i t darkened to a mauve c o l o r . An IR spectrum of the f i n a l s o l u t i o n revealed that the only carbonyl-containing complex i n so l u t i o n was ( r| 6-C 1 1H 1 1 +)Cr(C0) 3 (1) which was i s o l a t e d i n 25% y i e l d by using the standard procedures. R e s u l t s a n d D i s c u s s i o n When effected i n THF, the reactions between Na [ (T i 5-C 5H l tR')Cr(C0) 3 ] (R' = H or Me) and a l l y l chlorides exhibit several c h a r a c t e r i s t i c s which are d i f f e r e n t from those observed when diglyme i s employed as the solvent 0 ( c f . eq 2.3). F i r s t l y , the transformations occur at a much slower r a t e . 21 Consequently, greater than equlmolar amounts of the a l l y l chlorides are required to consume completely the anionic reactants within reasonable periods of time. Typically, i n i t i a l 1:3 mixtures of anion:chloride reach completion after 3-7 days at ambient temperatures. The rates of reaction are enhanced by refluxing the reaction mixture, but the f i n a l distribution of products is unaltered by doing so. Secondly, the use of THF as the solvent permits the more convenient separation of the organometallic products formed during these reactions. In particular, previously unknown (T) 6 -6-alkenylfulvene)tricarbonylchromium(0) complexes can be readily isolated from the f i n a l reaction mixtures. The principal organometallic products formed during these conver-sions in THF (just as in diglyme) are the dimeric [(T^-CJH^R')Cr(CO) 3] 2 (R' = H or Me) species, i.e., R R I I H2C=C-CHC1 [(n5-C5H4R')Cr(CO)3r THF > [(^-Cg^R')Cr(CO) 3 ] 2 (2.4) + by-products where R,R' = H or Me. The dimers are most conveniently separated by benzene extraction of the residues remaining after hexanes extraction of the dried f i n a l reaction mixtures. Removal of solvent from the benzene extracts in vacuo affords the dimeric complexes suitable for most purposes 22 i n y i e l d s of 51-67%. A n a l y t i c a l l y pure samples may be obtained by r e c r y s t a l l i z a t i o n of these materials from benzene-hexanes or hot hexanes. The physical properties of [CpCr(CO) 3] 2, including i t s s o l i d - s t a t e molecular structure, have been amply described previously. "''^'^ To the best of our knowledge, however, the properties of [Cp*Cr(CO) 3] 2 have not been r e p o r t e d . ^ The methylcyclopentadienyl dimer i s a dark green, a i r - s e n s i t i v e s o l i d (mp 70°C dec) which i s f r e e l y soluble i n common organic solvents, but less so i n p a r a f f i n hydrocarbons at ambient temperatures. Its IR [(CH 2C1 2): v C Q 2000(m), 1942(s), 1915(s), cm - 1] and *H NMR spectra [(CDC1 3): 6 5.64 (2H, Ao> 1 / 2 * 15 Hz), 5.49 (2H, A u 1 / 2 = 15 Hz), 3.51 (3H, Au>1/2 = 14 Hz)] are consistent with i t being i s o s t r u c t u r a l with i t s C 5H 5 9 analogue and displaying s i m i l a r behavior i n s o l u t i o n . Its 70 eV mass spectrum (probe temperature 60°C) exhibits no signals due to ions containing two chromium atoms. The p r i n c i p a l s pectral features are peaks due to the ions (C 5H 1 +Me)Cr(C0) n + (n = 3,2,1 or 0) which indicate the weak-ness of the Cr-Cr linkage i n the di m e r . ^ 12 The organometallic by-products usually formed during these conversions are novel (r|^-6-alkenylfuIvene)Cr(C0) 3 complexes. They can be separated from the dried f i n a l reaction mixtures by hexanes extraction and are i s o l a b l e i n y i e l d s of 5-8% by subsequent chromatography on F l o r i s i l and sublimation i n vacuo onto a water-cooled probe. They are bright red, low melting s o l i d s or l i q u i d s at room temperature which can be handled i n a i r for short periods of time without the occurrence of noticeable decomposition. They are f r e e l y soluble i n common organic solvents to 23 produce bright red s o l u t i o n s . Their s p e c t r a l properties i n d i c a t e that the complexes possess the molecular structures i n which the chromium atoms a t t a i n the favored 18-electron configuration by hexahapto coordination to J, R' = R = H 2, R' = H; R = Me 3, R' = Me ; R = H the substituted alkenylfulvenes as shown. The monomeric natures of the compounds are suggested by t h e i r mass spectra, a l l of which display prominent peaks due to the parent ions and ions r e s u l t i n g from the succes-sive loss of CO groups from them. IR spectra of solutions of the complexes exhibit three strong carbonyl absorptions, i n d i c a t i v e of a Cr(C0) 3 group-24 ing, i n the region previously reported for other (n 5-fulvene)Cr(CO) 3 13 species. The lH and 1 3 C {1H} NMR data for these complexes (Table 2.1 and Table 2.2) are consistent with t h i s formulation. In p a r t i c u l a r , these spectra of compound 3 i n CDC13 (Table 2.1, Table 2.2 and Figure 2.1) c l e a r l y indicate the presence of the f i v e isomers having R* = Me at any one of the secondary fulvene carbons ( i . e . C l - C4 and C6) i n approximately equal amounts. Regrettably, we have not as yet succeeded i n growing suitable c r y s t a l s of IL (the only s o l i d complex) for X-ray d i f f r a c t i o n studies so that precise intramolecular dimensions can be determined for a 14 representative compound of t h i s type. The substituted fulvene complexes are somewhat thermally unstable, the i s o l a t e d compounds decomposing p a r t i a l l y to green o i l s when stored under an N 2 atmosphere at -6°C for several months. The rate of decomposi-t i o n i s enhanced when the compounds are heated i n vacuo at 60°C, s i g n i f i -cant amounts of the green products being present a f t e r several days. We have i s o l a t e d a small amount of the green complex r e s u l t i n g from the thermal decomposition of 1 by chromatography on F l o r i s i l with hexanes as eluant. I t s low r e s o l u t i o n mass spectrum (probe temperature 100°C) exhibits signals due to the ions L 2 C r 2 ( C O ) n + (where L 2 = C 2 2 H 3 0 and n = 3, 2,1 or 0), and i t s IR spectrum [(hexanes: v 1900(s), 1880(s) cm - 1] i s i n d i c a t i v e of C r (C0) 2 groupings [ c f . v C Q for [Cp'Cr(C0) 2] 2 i n hexanes at 1901(s) and 1883(s) cm - 1].*' 1 It thus appears that thermal decomposition involves a dimerization of the o r i g i n a l complex with concomitant loss of CO. An analogous mode of decomposition has been reported recently for 25 Table 2.1 *H NMR Data for the Isolated (n 6-6-Alkenylfulvene)Cr(CO) 3 Complexes i n CDC13. Assignment— H(l,4) 4.79(m) H(2,3) 5.31(s), 5.35(s) 4.76(s), 4.87(s) 5.29(s), 5.32(a) 4.74(m), 4.81(m) 5.31(m) H(6) H(7) H(8) H(9) H(10) H ( l l ) H(12) H(13) H(14) 4.21(s) 2.03(br) 1.21(d,Jg_7=7Hz) 2.23(m), 2.55(br) 5.88(m) 5 . 1 1 ( d , J n a # 1 0 = 1 0 H Z ) > 5.14(d,J n b. 1 0=16Hz) 4.03(s) 1.20(s) 2.32(s) 4.96(s), 5.03(8) 1.31(e)-1.85(B)-4.14(s), 4.21(s) 2.07(m) 1.24(m) 2.26(m), 2.58(br) 5.84(br) 5.17(t) 1.72(s), 2.08(s), 2.14(s)-— These assignments are i n accord with observed s i g n a l i n t e n s i t i e s and have been confirmed by homonuclear decoupling experiments. Chemical s h i f t s are i n ppm. — For R = CH 3 at C7. — For R = CH 3 at CIO. iL For R' = CH 3 at Cl - C4 or C6. 26 Assignment— 0(1,2,3,4) C(5) C(6) C(7) C(8) C(9) C(10) C ( l l ) C(12) C(13) C(14) CO T a b l e 2 . 2 ^C^H} NMR Data for the Isolated (n 6-6-Alkenylfulvene)Cr(CO) 3 Complexes i n CDC13. 89.78(d) 90.03(d) 92.27(d) 93.54(d) 105.29(s) 109.96(d) 35.81(d) 24.05(q) 41.80(t) 135.40(d) 117.29(t) 90.30(d) 91.34(d) 91.65(d) 93.97(d) 103.97(s) 120.51(d) 39.83(s) 25.00(q) 53.02(t) 142.54(s) 116.00(t) 26.10(q)-30.07(q)-238.71(s) 88.29(d), 89.52(d), 92.44(d), 104.65(s), 105.79(s) 108.49(d), 110.08(d), 35.13(d), 35.39(d), 23.74(q), 41.54(t), 135.22(d), 116.85(t), 89.30(d), 89.77(d), 94.93(d), 89.34(d), 89.81(d), 95.88(d) 104.67(s), 105.49(s), 109.50(d), 109.88(d), 111.20(s) 35.18(d), 35.23(d), 35.44(d) 23.89(q) 41.60(t), 41.65(t) 135.27(d) 116.88(t) 11.37(q), 13.70(q), 237.44(s) 13.99(qF-— The indicated m u l t i p l i c i t i e s were derived from single frequency off-resonance decoupling (SF0RD) of protons at 6 = -2 ppm. Chemical s h i f t s are i n ppm. *L For R = CH 3 at C7 £ For R = CH 3 at C10 £ For R = CH 3 at C1-C4 or C6 — Not observable under the conditions employed for complexes 2 and 3. Figure 2.1 The 100.6-MHz 1 3C {^ H} FT NMR spectrum i n the hydrocarbon ligand region of ( T 1 6 - C 1 3 H 1 8 ) C r ( C 0 ) 3 (3) i n CDC13. JL A MJL 100 5 0 28 ( T i 6-diethylfulvene)Cr(CO) 3. The exact mechanism by which the (T) 6-6-alkenylfulvene)Cr(CO) 3 complexes originates during the reactions summarized by eq 2.4 remains to be ascertained. Nevertheless, the following observations are pertinent. The p r i n c i p a l products of eq 2.4, i . e . the [ ( T ^ - C ^ R ' ) C r ( C O ) 3 ] 2 dimers, do not react with a l l y l chlorides i n THF at ambient temperatures.^ Hence, the alkenylfulvene-containing byproducts must a r i s e from the d i r e c t reactions of the [(•n 5-C 5Hi +R ,)Cr(CO) 3]~ anions with the various H2C=CRCH2C1 (R = H or Me) reactants. Furthermore, the addition of a few milligrams of 2,2'-azobis(2-methylpropionitrile) to the reaction mixtures at room temper-ature has no apparent e f f e c t on the rates of reaction, thereby suggesting that free r a d i c a l s are not involved i n the rate-determining step of the mechanism. One pl a u s i b l e reaction sequence that accounts for the formation of both the [(TI 5-C 5H 1 +R' ) C r ( C O ) 3 ] 2 and (T) 6-6-alkenylfulvene)Cr(CO) 3 products under ambient conditions i s shown i n Scheme 2.1. I n i t i a l e l e c t r o p h i l i c attack on the metal centers i n the anionic reactants would r e s u l t i n the formation of n^-aHyl complexes. These complexes may convert d i r e c t l y to the [(T) 5-C 5H t fR')Cr(CO) 3] 2 dimers (the predominant path (a)) or may transfer the a l l y l groups to the cyclopenta-dienyl rings i n an endo fashion (step ( b ) ) . The l a t t e r complexes would probably have the structures i n d i c a t e d , the chromium atoms a t t a i n i n g 18-electron configurations. These d i e n e - o l e f i n complexes could then undergo condensation reactions with t h e i r respective r ^ - a l l y l precursors, processes which r e s u l t i n the formation of the r e q u i s i t e carbon skeleton. 29 Scheme 2.1 30 The dinuclear condensation products could then rearrange to give the f i n a l , i s o l a b l e (T ) 6 - 6-alk.enylfulvene)Cr(C0) 3 products v i a n o n - t r i v i a l rearrangements that may involve metal-assisted migrations of various substituents. (The (T^-C^H^R*)Cr(C0) 3H products r e s u l t i n g from the l a s t step would slowly convert to [ ( T ) 5 - C 5 H L T R ' ) C r ( C 0 ) 3 ] 2 at ambient temperature.)*** Even though the postulated steps ( b ) 1 ^ and ( c ) * 8 have precedents i n the l i t e r a t u r e of organometallic chemistry, i t i s obvious that t h i s proposed reaction sequence must be subjected to experimental scrutiny. 31 References and Notes (1) Taken i n part from: Hunter, A.D.; Legzdins, P. Organometallics 1983, 2, 525. (2) Kolthammer, B.W.S.; Legzdins, P.; Malito, J.T. Inorg. Chem. 1977, 16, 3173. (3) Fischer, E.O.; Hafner, W. Z. Naturforsch. B. 1955, 102, 140. (4) Keppie, S.A.; Lappert, M.F. J . Chem. Soc. A. 1971, 3216. (5) King, R.B.; Stone, F.G.A. Inorg. Synth. 1963, 7_t 104. (6) Shriver, D.F. "The Manipulation of A i r - S e n s i t i v e Compounds"; McGraw-Hill: New York, 1969. (7) Per r i n , D.D.; Armarego, W.L.F.; Perring, D.R. " P u r i f i c a t i o n of Laboratory Chemicals"; 2nd ed.; Pergamon Press: Oxford, 1980. (8) Hoyano, J.K.; Legzdins, P.; Malito, J.T. Inorg. Synth. 197J3, 18, 126. (9) Adams, R.D.; C o l l i n s , D.E.; Cotton, F.A. J . Am. Chem. Soc. 1974, 96, x r * ,. • i ... . • • — • I . , — - rsjn*#-*ur*j •• •  9 749. (10) King, R.B. J . Am. Chem. Soc. 1966, 88, 2075. (11) [C p ' C r ( C 0 ) 3 ] 2 has been used to prepare [Cp'Cr(C0) 2] 2; see Hackett, P.; O ' N e i l l , P.S.; Manning, A.R. J . Chem. S o c , Dalton Trans. 1974, 1625. (12) The reaction between Na[CpCr(C0) 3] and 3-chloro-l-butene does not produce detectable amounts of a substituted fulvene-containing complex. Also, the (T) 6-C 1 1 +H 2 0)Cr(CO) 3 by-product from the reaction of Na[Cp'Cr(C0) 3] with 3-chloro-2-methylpropene may only be detected 32 spectroscopically [IR (hexanes): v C Q 1990(s), 1928(s), 1907(B) cm - 1] as i t has i n s u f f i c i e n t thermal s t a b i l i t y to permit i t s i s o l a t i o n i n a pure state at ambient temperature. (13) For representative examples see: (a) Cooper, R.L.; Fischer, E.O.; Semmlinger, W. J . Organomet. Chem. 1967, 9, 333. (b) Andrianov, V.G.; Struchkov, Y.T.; Setkia, V.N.; Zdanovich, V.I.; Zhakaeva, A.Z.; Kursanov, D.N. J . Chem. Soc., Chem. Commun. 1975, 117. (c) Edelmann, F.; Behrens, U. J . Organomet. Chem. 1977, 134, 31. (d) Edelmann, F.; WormsbScher, D.; Behrens, U. Chem. Ber. 1978, 111, 817. (e) Koch, 0.; Edelmann, F.; Behrens, U. Chem. Ber. 198j2, 115, 1313. ( f ) Drews, R.; Behrens, U. Chem.  Ber. 1985, 118, 888. (14) The s o l i d state molecular structures of two simpler ( r i 6 - f u l v e n e ) -Cr(C0) 3 complexes, namely (•n 6-C 5H l tCPh 2)Cr(C0) 3 and (T) 6-C 5H £ tCH 2)Cr(CO) 3 1 3 e, have been determined. (15) [CpCr(CO) 3] 2 does react with CH2CHCH2C1 i n re f l u x i n g THF to produce 1 as the only carbonyl-containing product. This may well r e f l e c t the formation i n s i t u of s i g n i f i c a n t amounts of [CpCr(CO) 3]~ under these conditions ( c f . reference 11). I t has previously been reported [Fischer, E.O.; Ulm, K.; Kuzel, P. Z. Anorg. A l l g . Chem. 1963, 319, 253] that the dimer i s converted to (CpCrX 2»THF by CH2CHCH2X (X = Br or I) i n the presence of THF. (16) Fischer, E.O. Inorg. Synth. 1963, T_t 136. 33 (17) Attack on the metal by an e l e c t r o p h i l e followed by endo migration to the cyclopentadienyl r i n g has been invoked for reactions of CpMn(CO)3 and related complexes: Balem, M.P.; Le Plouzennec, M.; LoueT, M. Inorg. Chem. 1982, 21, 2573, and references contained therein. (18) Carbon-carbon bond formation by condensation of CpFe(CO) j ^ ^ - a l l y l ) complexes with CpFe(CO) 2(r) 2-olefin) cations has been demonstrated by Rosenblum and coworkers: Lennon, P.J.; Rosan, A.; Rosenblum, M.; Tancrede, J.; Waterman, P. J . Am. Chem. Soc. 1980, 102, 7033. CHAPTER THREE ON THE TRAIL OF DICHLORODINITROSYLTUNGSTEN: A TALE OF TWO REACTIONS1 35 Introduction 2 During previous investigations i n these l a b o r a t o r i e s , we had occasions to prepare the polymeric complexes [M(NO) 2Cl 2] n (M = Mo or W). These compounds are green, hygroscopic powders, and t h e i r molecular structures are believed to involve kinked chains having bridging chlorine atoms and terminal c i s - n i t r o s y l groups attached to octahedral metal 3 centers. Two p r i n c i p a l methods have been reported for the synthesis of these materials, namely (1) treatment of the respective binary carbonyls with an excess of Of n i t r o s y l c h l o r i d e , i . e . 3 ' ^ M(CO) 6 e Xg ^1 H° »' [M(NO) 2Cl 2] n (3.1) (M = Mo or W), and (2) reductive n i t r o s y l a t i o n of the appropriate metal c h l o r i d e , , 5 i . e . MoCl 5 or WC16 CT°c1 • [M(NO) 2Cl 2] n (3.2) (M = Mo or W). 2 In our hands, reaction 3.1 proceeded e s s e n t i a l l y as described for M = Mo, but appeared to be much more complex when M = W. S p e c i f i c a l l y , we f i r s t observed that traces of 0 2 were necessary to i n i t i a t e a reaction between W(CO)6 and C1N0, and we then found that use of an excess of n i t r o s y l 36 chloride led to a marked decrease i n both the y i e l d and the purity of the desired product. Consequently, we next attempted to employ reaction 3.2 for the synthesis of [W(NO)2CI2] n« We soon discovered that t h i s method was extremely s e n s i t i v e to v a r i a t i o n s i n reaction conditions such as concentra-ti o n and s c a l i n g up of the amounts of the reactants. Indeed, we found that a va r i e t y of c h l o r o n i t r o s y l complexes of tungsten could be i s o l a t e d from the f i n a l reaction mixtures a f t e r treatment of WC16 with NO under s l i g h t l y d i f f e r e n t experimental conditions. Intrigued by the apparent complexities of these two synthetic methods, we set out to determine exactly how [W(NO) 2Cl 2] n could be prepared reproducibly by reactions 3.1 and 3.2. In so doing, we have also acquired some insight into the probable mechanisms of these reactions and have i d e n t i f i e d other complexes which are intermediates or by-products formed during these transformations. The complete r e s u l t s of my investigations involving reactions 3.1 and 3.2 when M = W along with some d e r i v a t i v e chemistry of the [W(NO) 2Cl 2] n product are described i n Chapter Three. For c l a r i t y of presentation, reaction 3.2 i s considered f i r s t . Experimental Section Caution. Phosphines and phosphites are foul-smelling, toxic compounds that should only be handled i n an efficient fume hood. General procedures are the same as those described previously.^ Trimethylphosphite was d i s t i l l e d from sodium and was stored under N 2 at -10°C p r i o r to use.^ N i t r i c oxide (Matheson CP grade, 99.0% minimum) was 37 p u r i f i e d by passing the gas through a column of activated s i l i c a gel maintained at -78°C. A mass spectrum of the ef f l u e n t gas exhibited only a sharp peak at m/z_ 30 assignable to N0 +; i t did not display signals a t t r i b u t a b l e to ions such as N 0 2 + or N20+. Reactions of WC16 with NO. A. To Produce W(N0) 2C1 H. A 500-mL, three-necked f l a s k was equipped with two gas i n l e t valves, one being connected to a Nujol bubbler and the other to a two-way stopcock connected to cylinders containing dry N 2 and NO gases. The f l a s k was charged under N 2 with WC16 (5.00 g, 12.6 mmol) and CH 2C1 2 (250 mL) to obtain a red supernatant s o l u t i o n over a v i o l e t - b l a c k s o l i d . The mixture was s t i r r e d rapidy at room temperature as the N 2 atmosphere was gradually replaced by NO at a flow rate of approximately 20 mL/min at the e x i t bubbler. The i n i t i a l l y rapid uptake of NO resulted a f t e r ca. 17 min i n the formation of a brown s o l i d and a l i g h t green supernatant so l u t i o n whose IR spectrum displayed a v^Q a t 1846 cm - 1 due to dissolved C1N0. The NO was then flushed out of the system, and the reaction mixture was refluxed under a N 2 flow (ca. 20 mL/min) for 3.5 h to remove the C1N0 byproduct. This operation produced a red s o l u t i o n (devoid of n i t r o s y l absorbances i n i t s IR spectrum) over a dark v i o l e t s o l i d . The s o l i d was c o l l e c t e d by f i l t r a t i o n on a medium porosity f r i t , washed with CH 2C1 2 u n t i l the washings were c o l o r l e s s (3 x 30 mL), and dried i n vacuo (5 x 10" 3 mm) at ambient temperature to obtain 2.29 g (47% y i e l d ) of W(N0)2C11+ as a v i o l e t - b l a c k , m i c r o c r y s t a l l i n e s o l i d . Anal. Calcd for WNjO^l^: C, 0.00; H, 0.00; N, 7.25; C l , 36.79. 38 Found: C, 0.00; H, 0.00; N, 7.23; Cl 36.35. IR (Nujol mull) v N Q 1934(m), 1798(s) cm - 1; mp 140° C dec. B. To produce W(N0)3C13. The treatment of WClg with NO was effected i n a manner i d e n t i c a l to that described i n part A. However, i n t h i s instance, NO was passed over the reaction mixture for ca. 30 min u n t i l i t consisted of a bright green s o l i d suspended i n a bright green so l u t i o n whose IR spectrum displayed a v ^ at 1846 cm - 1 c h a r a c t e r i s t i c of dissolved C1N0. The s o l i d was then c o l l e c t e d by f i l t r a t i o n as described i n part A to obtain W(N0) 3C1 3 (2.90 g, 61% y i e l d ) as a bright green, m i c r o c r y s t a l l i n e s o l i d . Anal. Calcd for WN 30 3C1 3: C, 0.00; H, 0.00; N, 11.05; C l , 27.97. Found: C, 0.20; H, 0.00; N, 10.49; C l , 27.70. IR (Nujol mull) v N Q 1927(m), 1800(sh), 1760(s) cm - 1; IR (CH 2C1 2) v N Q 1919(s), 1782(s) cm - 1; mp 128°C dec. Reaction of WClg with NO and CH3CN. A 500-mL, three-necked f l a s k was equipped as described i n part A and was charged with powdered WClg (5.00 g, 12.6 mmol), CH3CN (1.32 mL, 25.2 mmol), and CH 2C1 2 (180 mL). As NO was passed over the r a p i d l y s t i r r e d mixture at ambient temperature, the supernatant red so l u t i o n i n i t i a l l y became more intense i n color as a l l the WClg di s s o l v e d . Continued treatment with NO resulted i n the sol u t i o n paling i n color and i n the formation of a l i g h t green p r e c i p i t a t e a f t e r ca. 1 h. The volume of the f i n a l mixture was reduced to 50 mL i n vacuo, and the mixture was then cooled to 0°C for 15 min. The p r e c i p i t a t e was i s o l a t e d by f i l t r a t i o n and the c o l l e c t e d s o l i d was washed with cold CH 2C1 2 39 (2 x 10 mL at 0°C) and then hexanes (4 x 20 mL) at room temperature. F i n a l drying of the s o l i d under reduced pressure (5 x 10" 3 mm) for 18 h afforded 3.56 g (70% y i e l d ) of yellow-green W(N0)C1 3(CH 3CN) 2 as an a n a l y t i c a l l y pure, powdery s o l i d . Anal. Calcd for WC l tH 6N 3OCl 3: C, 11.94; H, 1.50; N, 10.44. Found: C, 11.96; H, 1.43; N, 10.28. IR (Nujol mull) v Q N 2990(m), 2315(m) cm - 1 v N Q 1682(s) cm - 1; IR (CH 2C1 2) v N Q 1695(s) cm - 1; IR (CH3CN) v N Q 1693(s) cm - 1. Reaction of W(C0) 6 with C1N0. A 500-mL, three-mecked f l a s k was equipped with a gas i n l e t and an addition funnel and was charged with 17.6 g (50.0 mmol) of powdered W(C0) g. The en t i r e system was then thoroughly purged with p r e p u r i f i e d dinitrogen, and CH 2C1 2 (90 mL) was added. The addition funnel was charged with a CH 2C1 2 s o l u t i o n (ca. 30 mL) g of f r e s h l y prepared C1N0 (6 mL, 120 mmol). Approximately 6 mL of t h i s red solution (~24 mmol C1N0) was then added to the r a p i d l y s t i r r e d reaction mixture. No change was evident a f t e r continued s t i r r i n g f o r 0.5 h at room temperature. Introduction of a small aliquot (ca. 0.5 mL) of a i r into the 9 reaction vessel by means of a syringe i n i t i a t e d a vigorous r e a c t i o n . The supernatant so l u t i o n changed i n color from red to black as copious quantities of CO were r a p i d l y evolved. The mixture was s t i r r e d u n t i l CO evolution had ceased (ca. 5 min) whereupon i t consisted of green and white s o l i d s suspended i n a green s o l u t i o n . The addition of the C1N0 so l u t i o n was then continued i n 0.5 mL a l i q u o t s , care being taken to ensure that CO evolution had ceased and that the reaction mixture had returned to a green 40 co l o r a t i o n before a new aliquot of the reagent was introduced (ca. 3-5 min i n t e r v a l s ) . After 2 h, ca. 80 mmol of C1N0 i n t o t a l had been added. The addition of the C1N0 s o l u t i o n was then completed dropwise over a period of 1 h with c a r e f u l IR monitoring of the progress of the conversion. S l i g h t l y more than 2 equiv of C1N0 i n t o t a l were required to cause the carbonyl absorption due to W(C0) 6 at 1977 cm - 1 to just disppear from the IR spectrum of the supernatant so l u t i o n which also displayed bands at ~ 2140(m), ~ 2070(m), ~ 2050(m) ~ 1920(w), ~ 1800(s, br) and ~ 1700(s, br) cm"1. The addition funnel was then replaced by a r e f l u x condenser, and the f i n a l green suspension was refluxed under a stream of N 2 (ca. 60 mL/min) for 1 h. After cooling to room temperature, the green p r e c i p i t a t e was separated from the orange-green supernatant s o l u t i o n by f i l t r a t i o n of the mixture through a medium porosity f r i t . The s o l i d was washed with CH 2C1 2 (6 * 25 mL) and dried i n vacuo (5 x 10~ 3 mm) for 18 h at 20°C to obtain 14.52 g (92% y i e l d ) of [W(N0) 2Cl 2] n as an o l i v e green powder. Anal. Calcd for WN 20 2C1 2: C, 0.00; H, 0.00; N, 8.90; C l , 22.52. Found: C, 0.28; H, 0.00; N, 8.88; C l , 21.97. IR (Nujol mull) v N Q 1794(s, b r ) , 1680(s, br) cm - 1 [ l i t e r a t u r e : 1805, 1680 cm - 1; 3 1797, 1696 cm - 1. 5] mp: 190°C dec. Reaction of W(C0)6 with C1N0 and CH3CN. To a s t i r r e d suspension of W(C0) 6 (2.10 g, 5.97 mmol) i n CH 2C1 2 (30 mL) was added CH3CN (0.79 mL, 12 mmol) and C1N0 (ca. 1 mL, 20 mmol) and the r e s u l t i n g mixture was s t i r r e d at room temperature for 3 days, 2 mL aliquots of a i r being introduced into the system each day. The f i n a l mixture consisted of green and white s o l i d s 41 beneath a red s o l u t i o n . An IR spectrum of this s o l u t i o n revealed that the c h a r a c t e r i s t i c absorption due to C1N0 at 1846 cm - 1 had diminished to ca. 10% of i t s i n i t i a l i n t e n s i t y and that a new, strong n i t r o s y l band had grown i n at 1696 cm - 1. Solvent was removed from the f i n a l mixture i n vacuo, and unreacted W(C0) 6 was separated from the r e s u l t i n g residue by sublimation at 40°C (5 x 10" 3 mm) onto a water-cooled probe. C r y s t a l l i z a t i o n of the remaining s o l i d from CH 2Cl 2/hexanes afforded 0.28 g (0.70 mmol, 12% y i e l d ) of W(N0)C1 3(CH 3CN) 2 which was i d e n t i f i e d by comparison with an authentic sample (vide supra). Reaction of W( 00)^110)01 with C1N0. To a s t i r r e d yellow solution of W(C0) 4(N0)C1 1 0 (0.40 g, 1.1. mmol) i n CH 2C1 2 (45 mL) was added an excess of C1N0 (ca. 7 mmol). While being s t i r r e d at ambient temperature for 19 h, the i n i t i a l l y orange so l u t i o n became dark green and a bright green s o l i d p r e c i p i t a t e d . The s o l i d was c o l l e c t e d by f i l t r a t i o n and washed with CH 2C1 2(2 x 10 mL) to obtain 0.30 g (72% y i e l d ) of W(N0) 3C1 3 which was i d e n t i f i e d by i t s c h a r a c t e r i s t i c physical properties (vide supra). The addition of 1 mL of a i r to an i d e n t i c a l I n i t i a l r eaction mixture did not increase the rate of the conversion. Reactions of [W(N0) 2Cl 2] n with Various Lewis Bases ( L ) . A. L -PMePh2, P(0Me) 3 or PPhj. A l l three of these reactions were performed i n a si m i l a r manner. The experimental procedure, using the case when L = PMePh2 as a representative example, was as follows: A stoichiometric amount of neat methyldiphenylphosphine (5.70 mL, 30.6 mmol) was added to a s t i r r e d suspension of [W(N0) 2Cl 2] n (4.81 g, 15.3 42 mmol of W) i n benzene (50 mL), and the mixture was warmed to 50°C for 2 h. This operation afforded a small quantity of a l i g h t green s o l i d suspended i n a dark green s o l u t i o n . This mixture was f i l t e r e d through a 2 x 6 cm column of alumina (Woelm, neu t r a l , a c t i v i t y 1) supported on a medium-porosity f r i t , and the column was then washed with 100 mL of warm (50°C) benzene. The combined f i l t r a t e s were concentrated i n vacuo at 20°C to ca. 50 mL, and hexanes (25 mL) were added to induce the p r e c i p i t a t i o n of dark green c r y s t a l s . The c r y s t a l s were is o l a t e d by f i l t r a t i o n , washed with 2:1 benzene/hexanes (3 * 20 mL) and dried for 16 h at 5 x 10~ 3 mm and 20°C to obtain 9.33 g (81% y i e l d ) of a n a l y t i c a l l y pure W(N0) 2Cl 2(PMePh 2) 2 ' ^ Z 6 R 6 ' Anal. Calcd f or WC 2 9H 2 9N 20 2C1 2P 2: C, 46.18; H, 3.88; N, 3.71; 0, 4.24. Found: C, 46.14; H, 3.90; N, 3.65; 0, 4.19. IR (CH 2C1 2) v N Q 1764(s), 1656(s) cm - 1; XH NMR (CDC1 3) 6 7.45(m, 23H), 2.29 ( t , 6H, N = 8.60 Hz); XH NMR ((CD.)_C0) 6 7.50 (m, 20H, Ph), 7.30 (s, 3H, C,H,), 2.32 ( t , J L 0—0 6H, Me, N = 8.4 Hz); low-resolution mass spectrum (probe 150°C), m/z_ 715 (unsolvated P + ) ; mp 167°C. The analogous unsolvated trimethylphosphite and triphenylphosphine complexes were i s o l a t e d as l i g h t e r green c r y s t a l l i n e s o l i d s i n y i e l d s of 69% and 81%, r e s p e c t i v e l y . Anal. Calcd for WC 6H 1 8N 20gCl 2P 2: C, 12.80; H, 3.22; N, 4.98; 0, 22.74. Found: C, 12.96; H, 3.22; N, 4.97; 0, 22.44. IR (CH 2C1 2) v N Q 1776(s), 1670(B) cm - 1; lU NMR (CDC1 3) 6 3.84 ( t , N = 11.24 Hz); low-resolution mass spectrum (probe 150°C), m/z 563 ( P + ) ; mp 150°C. 43 Anal. Calcd for WC 3 6H 3 0N 2O 2Cl 2P 2: C, 51.49; "H, 3.58; N, 3.33; C l , 8.46. Found: C, 51.72; H, 3.63; N, 3.10; C l , 8.37. IR (CH 2C1 2) v N Q 1763(a), 1650(s) cm - 1; IR (Nujol mull) v N Q 1749(a), 1640(a) cm"1 [ l i t e r a -t u r e : 5 1748, 1638 cm - 1]; mp 240°C dec [ l i t e r a t u r e : 3 236°C]. If commercial, reagent grade trimethylphosphite was used without p u r i f i c a t i o n 7 i n the above procedure, W(N0) 2Cl 2[0P(Me)(0Me) 2] 2 was also formed i n low y i e l d s during the rea c t i o n . This complex was separated from W(N0) 2C1 2[P(OMe) 3] 2 by chromatography of the concentrated f i n a l reaction mixture on alumina with CH 2C1 2 as eluant and was p u r i f i e d by c r y s t a l l i z a -t i o n from benzene/hexanes. Anal. Calcd f o r WC 6H 1 8N 20 8C1 2P 2: C, 12.80; H, 3.22; N, 4.98. Found: C, 12.59; H, 3.24; N, 4.93. IR (CH 2C1 2) v N Q 1757(s), 1644(s) cm - 1; XH NMR (CDC1 3) 6 3.87 (d, 12H, OMe, J_ = 12 Hz), 1.70 (d, 6H, Me, J = 18 Hz). B. L =» Ph 2PCH 2PPh 2. To a s t i r r e d suspension of powdered [W(N0) 2Cl 2] n (1.97 g, 6.26 mmol of W) i n benzene (200 mL) was added bis(diphenylphosphino)methane (dppm, 4.81 g, 12.5 mmol), and the r e s u l t i n g mixture was warmed to 45°C for 28 h to obtain a l i g h t green supernatant s o l u t i o n and a darker green p r e c i p i t a t e . The f i n a l mixture was f i l t e r e d through a medium porosity f r i t , and the co l l e c t e d s o l i d was washed with benzene u n t i l the washings were c o l o r l e s s ( t y p i c a l l y 4 x 25 mL). The combined f i l t r a t e and washings were then concentrated under reduced pressure to ca. 5 mL to induce the p r e c i p i t a t i o n of a pale yellow-green s o l i d . C o l l e c t i o n of th i s s o l i d by f i l t r a t i o n and i t s r e c r y s t a l l i z a t i o n 44 from benzene/hexanes afforded 0.88 g (13% y i e l d ) of a n a l y t i c a l l y pure W(NO) 2Cl 2(dppm) 2. Anal. Calcd for WC 5 0H M tN 2O 2Cl 2P l t: C, 55.42; H, 4.09; N, 2.59. Found: C, 55.43; H, 4.17; N, 2.70. IR (CH 2C1 2) v N Q 1762(s), 1657(s) cm - 1; LH NMR (CDC1 3) 6 7.7-7.1 (m, 40H, Ph ), 3.68 (m, 4H, CH^; 3 1 P NMR (CDCI3) 6 24.88 ( t , 2P, J 3 i p _ 3 1 p - 19 Hz, J 3 i p _ i 8 3 w = 276 Hz), -15.18 ( t , 2P); mp 155°C dec. The green, benzene-insoluble s o l i d separated previously was then extracted with CH 2C1 2 u n t i l the extracts were c o l o r l e s s (5 x 25 mL). The combined dark green extracts were concentrated i n vacuo to a volume of ca. 5 mL, whereupon a l i g h t green p r e c i p i t a t e formed. An IR spectrum of the supernatant so l u t i o n exhibited two strong absorptions at 1752 and 1641 cm - 1. The p r e c i p i t a t e was c o l l e c t e d by f i l t r a t i o n and was r e c r y s t a l l i z e d from CH 2C1 2 to obtain 0.43 g (10% y i e l d ) of W(N0) 2Cl 2(dppm) -O^C^ as a l i g h t green c r y s t a l l i n e s o l i d . Anal. Calcd for WC 2 6H 2^N 20 2Cl l tP 2: C, 39.83; H, 3.08; N, 3.57. Found: C, 39.94; H, 3.00; N, 3.86. IR (CH 2C1 2) v N Q 1756(s), 1651(s) cm - 1; ! H NMR (CDCJl ) 6 7.8-7.2 (m, 20H, Ph), 5.54 (s, 2H, CH^Cl^), 4.30 (m, 2H, CH^); mp 210°C dec. The o l i v e green, CgHg- and C H 2 C l 2 - i n s o l u b l e s o l i d remaining a f t e r the operations described above was i d e n t i f i e d as unreacted [W(N0) 2Cl 2] n (0.82 g, 42%) by comparison with an authentic sample. 45 Attempts to improve the y i e l d s of the products i s o l a t e d from t h i s conversion by increasing the reaction time and/or temperature led only to decomposition of the desired compounds. C. L - CH3CN, THF or E t 2 0 . Powdered [W(NO) 2Cl 2] n (12.9 g, 41.0 mmol of W) was added to CH3CN (100 mL), and the s t i r r e d mixture was warmed to 50°C to complete the d i s s o l u t i o n of the n i t r o s y l reactant. The f i n a l dark green s o l u t i o n was f i l t e r e d while warm though a short ( 2 x 5 cm) column of C e l i t e supported on a medium porosity f r i t , and the column was then washed with CH3CN (2 x 10 mL) at room temperature. The volume of the combined f i l t r a t e s was reduced to ca. 20 mL i n vacuo, and benzene (20 mL) was then added to complete the c r y s t a l l i z a t i o n of a pale green s o l i d . The s o l i d was c o l l e c t e d on a medium porosity f r i t , washed with 1:2 CH3CN/benzene (2 x 15 m L ) , and dried at 20°C and 5 x 10~ 3 mm for 18 h to obtain 9.54 g (59% y i e l d ) of m i c r o c r y s t a l l i n e W(N0) 2C1 2(CH 3CN) 2-Anal. Calcd for WC^HgN^OjCl^: C, 12.11; H, 1.52; N, 14.12. Found: C, 12.11; H, 1.50; N, 13.85. IR (CH3CN) v N Q 1772(s), 1668(s) cm - 1; IR (CH 2C1 2) v N Q 1776(s), 1674(s) cm - 1; LH NMR (CD 3N0 2) 6 2.57 (s, 3H), 2.50 (s, 3H); mp 155°C dec. The reactions between [W(NO) 2Cl 2] n and THF or E t 2 0 proceeded i n a manner analogous to that described above. However, i n these cases, no attempt was made to i s o l a t e the W(N0) 2C1 2L 2 (L = THF or E t 2 0 ) products. They were generated either i n the appropriate ethereal solvent or by the reaction of [W(NO) 2Cl 2] n with two equivalents of the ether i n CH 2C1 2 and were used i n s i t u . Their spectroscopic properties are presented below. 46 W(N0) 2C1 2 ( T H F ) 2 : IR (THF) v N Q 1761(s), 1660(s) cm - 1; IR (CH 2C1 2) v N Q 1760(s), 1655(s) cm"1. W ( N O ) 2 C l 2 ( E t 2 0 ) 2 : IR (Et 20) v N Q 1767(s), 1661(s) cm - 1; IR (CH 2C1 2) v N Q 1777(s), 1679(B) cm"1. R e a c t i o n s o f W(N0) 2C1 2 L 2 ( L - T H F , E t 20 o r CH3CN) w i t h ( t i - B u ^ S n C C g H g ) . These conversions were effected s i m i l a r l y ; the reaction having L = THF was representative. A s t i r r e d suspension of powdered [W(NO) 2Cl 2] n (2.42 g, 7.68 mmol of W) i n CH 2C1 2 (50 mL) was treated with tetrahydrofuran (THF, 1.25 mL, 15.4 mmol). Within 5 min a deep green sol u t i o n of W(N0) 2C1 2(THF) 2 formed. To th i s s o l u t i o n was added (n_-Bu) 3Sn(C 5H 5) 1 1 (2.41 mL, 7.68 mmol), and the mixture was s t i r r e d at ambient temperature for 2 h. During t h i s time the so l u t i o n darkened i n col o r , and IR monitoring revealed the gradual decrease of the n i t r o s y l bands due to the reactant at 1760 and 1655 cm - 1 and the concomitant growth of two new absorptions at 1733 and 1650 cm - 1. The volume of the f i n a l brown solution was reduced to 10 mL i n vacuo, and the concentrated s o l u t i o n was transferred by syringe onto a 2 x 7 cm column of F l o r i s i l made up i n CH 2C1 2. E l u t i o n of the column with CH 2C1 2 produced an i n i t i a l green band which was c o l l e c t e d and taken to dryness under reduced pressure. R e c r y s t a l l i z a t i o n of the r e s u l t i n g residue from CH 2C1 2/hexanes afforded CpW(N0) 2Cl (1.05 g, 40% y i e l d ) as a bright green c r y s t a l l i n e s o l i d which was i d e n t i f i e d by i t s c h a r a c t e r i s t i c spectroscopic p r o p e r t i e s ^ [IR (CH 2C1 2) v 1732(s), 1650(s) cm'1;  lE NMR (CDCI3) 6 6.15 ( s ) ] . 47 In a s i m i l a r manner, treatment of W(NO) 2Cl 2(0Et2)2 a n Q" W(N0) 2C1 2(CH 3CN) 2 (both generated i n s i t u ) with (n-Bu) 3Sn(C 5H 5) i n CH2C12 for 4 h and 4 days, r e s p e c t i v e l y , resulted i n the i s o l a t i o n of CpW(NO)2Cl i n y i e l d s of 34 and 13%, r e s p e c t i v e l y . n - B u 3 S n ( C 5 H 5 ) i s t o x i c a n d m u s t b e h a n d l e d w i t h c a r e . The attempted use of Na(C 5H 5) or T1(C 5H 5) as cyclopentadienylating agents i n the above conversions resulted i n decomposition and no r e a c t i o n , r e s p e c t i v e l y . R e s u l t s a n d D i s c u s s i o n R e d u c t i v e N i t r o s y l a t i o n o f W C l g . As has been previously noted by 5 12 other i n v e s t i g a t o r s , ' the treatment of WClg with NO can r e s u l t i n the formation of a v a r i e t y of c h l o r o n i t r o s y l complexes of tungsten. As a res u l t of our st u d i e s , we believe that this system i s best viewed as involving the sequential transformations W C 16 -C1N0 ' W<N 0>C 15 - c i N O ' W ( N ° ) 2 C ^ <3'3> 2N0, -CINO -C1N0 < * W(N0)3C13 < > i - [W(N0)2C12] +C1N0, -2N0 +C1N0 i n which the introduction of each two equivalents of NO r e s u l t s i n the incorporation of a n i t r o s y l group into the metal's coordination sphere and 48 the expulsion of one equivalent of n i t r o s y l c h l o r i d e . In addition, both the net progress of the reaction and the nature of the products ultimately recovered from the f i n a l reaction mixture are markedly dependent on the scale of the reaction, the amount of NO employed, and the f i n a l workup procedure. For instance, consistent with the report of Bencze and co-workers,"* we f i n d that treatment of a s o l u t i o n containing l g of WClg i n CH 2C1 2 (50 mL) at room temperature with excess NO u n t i l no further uptake of the gaseous reactant occurs and subsequent r e f l u x i n g of the r e s u l t i n g green mixture under a current of N 2 u n t i l C1N0 evolution ceases does r e s u l t i n the deposition of [W(N0) 2Cl 2] n. This product i s i s o l a b l e by f i l t r a t i o n as a s l i g h t l y impure,"* powdery green s o l i d i n y i e l d s of 70-80%. However, scaling up of the WClg s o l u t i o n by a factor of f i v e while maintaining the same flow of NO slows the rate of reaction 3.3 s u f f i c i e n t l y so that two of the intermediate chloro n i t r o s y l complexes may be i s o l a t e d by c a r e f u l control of the reaction conditions as s p e c i f i e d i n d e t a i l i n the Experimental Section. The f i r s t complex i s o l a b l e i s W(N0) 2C1 1+ which can be obtained as a dark v i o l e t s o l i d i n 47% y i e l d . This s o l i d i s somewhat a i r - s e n s i t i v e but i s stable at room temperature under N 2 i n d e f i n i t e l y . Its Nujol mull IR spectrum exhibits two absorptions at 1934(m) and 1798(s) cm - 1 i n d i c a t i v e of the n i t r o s y l groups being attached i n a c i s - f a s h i o n to an octahedrally coordinated tungsten center, i . e . 49 Cl Cl Cl NO NO Cl 13 These r e l a t i v e l y high v N Q values ( c f . that of NO(g) at 1888 cm - 1) presumably r e f l e c t the lack of electron density a v a i l a b l e at W for TI back-bonding to the NO ligands. Furthermore, these n i t r o s y l absorbances are quite d i f f e r e n t than those displayed by [W(N0)Cl 3] n (1590 cm - 1 as a Nujol 14 i mull) and C1N0 (1846 cm - 1 i n CH 2C1 2) and hence indi c a t e that W(N0) 2C1 4 i s indeed a discre t e compound and not simply a 1:1 adduct such as W(N0)C1 3«C1N0. 5 Since W(N0) 2Cl l t i s v i r t u a l l y insoluble i n non-donor solvents, there i s possibly some association of the monomeric units i n the s o l i d s tate. Nevertheless, any asso c i a t i o n i s not s u f f i c i e n t l y strong to prevent the complex from gradually decomposing to [W(N0) 2Cl 2] n as the only n i t r o s y l - c o n t a i n i n g product when refluxed as a suspension In CH 2C1 2 for 3 days, i . e . W(N0) 2C1 H r e f l u x * [W(N0) 2C1 2] n (3.4) 50 On the other hand, W(N0) 2Cl l t reacts r e a d i l y with donor solvents such as CH3CN or THF according to the stoichiometry WCNO^Cl,, + 2S -> W(N0)C1 3S 2 + CJINO (3.5) S = CH3CN or THF. The product complex having S = CH3CN has been recently prepared by Bencze and Kohan^ as a dark v i o l e t s o l i d by e f f e c t i n g the reductive n i t r o s y l a t i o n of WClgin the presence of a c e t o n i t r i l e , i . e . CH2CI2 WC16 + 4 NO + 2 CH3CN • W(N0)C1 3(CH 3CN) 2 + 3 C1N0 (3.6) In our hands, however, both reactions 3.5 and 3.6 afford comparably good yie l d s of a n a l y t i c a l l y pure W(N0)C1 3(CH 3CN) 2 as a powdery yellow-green s o l i d [IR(CH 2C1 2) v N Q 1695(s) c m - 1 ] . Solutions of th i s extremely a i r -s e n s i t i v e complex i n CH3CN remain green i n d e f i n i t e l y under N 2 at room temperature, but analogous CH 2C1 2 solutions slowly develop a red c o l o r a -t i o n probably due to p a r t i a l loss of the l a b i l e CH3CN ligands, i . e . processes such as CH^Cl^ , 2 W(N0)C1 3(CH 3CN) 2 < f f l f f l ' [W(N0)C1 3(CH 3CN)] 2 + 2 CH3CN (3.7) 51 since the color change can be reversed by the addition of CHgCN. Consis-tent with this inference i s the fact that our W(N0)C1 3(CH 3CN) 2 reacts cleanly with two equivalents of PPh 3 i n CH 2C1 2 t o produce the known complex, W(NO)Cl 3(PPh 3) 2.^ 5 I t thus appears that either the previously described W(N0)C1 3(CH 3CN) 2 [IR(CH 2C1 2) v N Q 1710 c m - 1 ] 1 5 was contaminated to some extent by a highly colored impurity or was another isomeric form. As suggested by equation 3.3, treatment of WCl g i n CH 2C1 2 with ca. 75% more NO than required for the formation of WCNO^Cl^ res u l t s i n the p r e c i p i t a t i o n of the second i s o l a b l e intermediate, W(N0) 3C1 3, as a bright green m i c r o c r y s t a l l i n e s o l i d i n 61% y i e l d . [ A l t e r n a t i v e l y , W(N0) 3C1 3 may also be synthesized independently by the reductive n i t r o s y l a t i o n of a suspension of W(N0) 2Cl l t i n CH 2C1 2 with the r e q u i s i t e amount of NO.] T r i c h l o r o t r i n i t r o s y l t u n g s t e n may be handled i n a i r for short periods of time without the occurrence of noticeable decomposition. It i s thermally stable under N 2 apparently i n d e f i n i t e l y and for at least 18 h under 5 x 1 0 - 3 mm pressure at ambient temperatures. Its IR spectra [(Nujol mull) V^Q 1927(m), 1800(sh), 1760(s) cm - 1; (CH 2C1 2) v N Q 1919(s), 1782(s) cm - 1] are consistent with i t s molecular structure possessing the expected f a c -octahedral stereochemistry, i . e . 52 Cl Cl« 0 N Cl •NO •NO and rule out i t s being a W(NO) 2C1 2»C1N0 adduct. The monomeric nature of this 18-electron compound i s also indicated by i t s s l i g h t s o l u b i l i t y i n CH 2C1 2. However, upon d i s s o l u t i o n i n t h i s solvent, the c l e a r green solution i n i t i a l l y formed r e a d i l y ( t 1 / 2 = c a * ^ min at 20°C) becomes cloudy as reaction 3.8 •. CH 2C1 2 W(N0) 3C1 3 > [W(NO) 2Cl 2] n+ + C1N0 (3.8) 16 occurs. This mode of decomposition of W(N0) 3C1 3 has been previously noted by Feltham and co-workers. 1^ In t e r e s t i n g l y , IR monitoring of the progress of t h i s decomposition indicates the transient formation of an intermediate [IR (CH 2C1 2) v N Q 1760(w), 1660(w) cm - 1] which we believe may be solvated, monomeric W(N0) 2C1 2 which eventually associates to form the i s o l a b l e product. 53 W(N0) 3C1 3 reacts r a p i d l y with donor solvents such as THF or CH3CN with concomitant NO evolution to produce red-brown solutions which contain W(N0) 2C1 2S 2 (S = CH3CN or THF), W(N0)C1 3S 2 and C1N0 i n d i f f e r i n g r a t i o s (as measured by IR spectroscopy). These observations indicate the occurrence of the p a r a l l e l reactions W(N0) 3C1 3 + 2S > W(N0) 2C1 2S 2 + C1N0 (3.9) W(N0) 3C1 3 + 2S W(N0)C1 3S 2 + 2 NO (3.10) where S = CH3CN or THF. IR monitoring also indicates that reaction 3.10 becomes less prevalent as the temperature i s lowered. The product complexes having S = CH3CN have been i s o l a t e d during other portions of our work. W(N0)C1 3(CH 3CN) 2 has been considered above (reactions 3.5 and 3.6), and the properties of W(N0) 2C1 2(CH 3CN) 2 are presented i n d e t a i l l a t e r . The i n t e r r e l a t i o n s h i p s of the c h l o r o n i t r o s y l complexes of tungsten and t h e i r CH3CN derivatives considered i n t h i s section are summarized i n Scheme 3.1. 3 4 Treatment of W(C0) g with C1N0. It has been reported ' that when W(C0) g i s treated with an excess of C1N0 i n deaerated CH 2C1 2 at room temperature ( i . e . eq 3.1), a vigorous reaction ensues a f t e r a b r i e f induction period. As the reaction proceeds, CO i s evolved and a green p r e c i p i t a t e forms. The f i n a l mixture i s s t i r r e d for 2 h, and solvent and unreacted W(C0) 6 are then removed i n vacuo to afford green [W(N0) 2C1 2] i n 54 Scheme 3*1 WCI6 4 N 0 - J 2CINO-*4 WW01.CU -gg^ 2 N 0 > f ^ 2 NO C l N O - ^ - C l N O W(N0)3CI5 --CINO li [w(N0)2CI2J • CNO 2 CH3CN WCI6 + 2 CH3CN L^~4N0 |^*-3CINO W(N0)CI3(CH3CN)2 2 CH3CN W(N0)2CI2(CH3CN)j 55 high y i e l d . However, we and others have been unable to repeat t h i s reaction as described. S p e c i f i c a l l y , our investigations of t h i s system have revealed two important features, namely (1) Under anhydrous and anaerobic conditions no reaction between W(CO)6 and C1N0 i n CH 2C1 2 occurs for at least 18 h at ambient temperatures. However, upon the introduction of c a t a l y t i c amounts of oxidants such as a i r , AgBF1+ or NOBF^ into the system, the vigorous reaction described above i s immediately i n i t i a t e d . [Lewis bases such as H 20, CH3CN or THF t o t a l l y i n h i b i t t h i s reaction (vide Infra).] (2) Use of an excess of C1N0 a f t e r i n i t i a t i o n r e s u l t s i n the formation of a mixture of green, red and black s o l i d s whose elemental analysis does not correspond to the [W(NO) 2Cl 2] n formulation. Furthermore, a Nujol mull IR spectrum of these s o l i d s exhibits numerous absorptions i n the n i t r o s y l - s t r e t c h i n g region (1950-1600 cm - 1) reminiscent of those displayed by W(N0) 3C1 3 and WCNO^Cl^ (vide supra). Dissolution of the s o l i d mixture i n donor solvents, S, such as CH3Cn or THF r e s u l t s i n the vigorous evolution of NO gas and the formation of red solutions whose IR spectra confirm the presence of C1N0, W(N0) 2C1 2S 2 and W(N0)C1 3S 2. I t thus appears, and can be v e r i f i e d independently, that the desired [W(N0) 2Cl 2] n reacts with excess C1N0 to produce a mixture of W(N0) 2C1 1+ and W(N0) 3C1 3 whose behaviour i n donor solvents has been delineated above ( c f . Scheme 3.1). In the l i g h t of these observations, the preferred procedure for the synthesis of [W(N0) 2C1 2] i s as follows. F i r s t , the suspension of W(C0) 6 56 i n CH 2Cl2 i s treated with a small amount of C1N0, and the reaction i s i n i t i a t e d with a trace amount of an oxidant. Once begun, the conversion i s continued by addition of the C1N0 i n a slow, controlled manner u n t i l a l l the W(CO)6 has just been consumed (see Experimental Section). The re s u l t i n g green suspension must then be refluxed under a stream of N 2 for 1 h before the desired pure product can be co l l e c t e d by f i l t r a t i o n i n 92% y i e l d . This method for the synthesis of [W(N0) 2Cl 2] n i s to be preferred over the reductive n i t r o s y l a t i o n of WClg (equation 3.3) since i t more conveniently affords the polymeric product i n better purity and y i e l d . This transformation of W(CO)6 into [W(NO) 2Cl 2] n may be accounted for by invoking the occurrence of the following sequential, elementary reactions: w< c o>6 :^§T> W<C0VN0>C1 ZTW~> W(C0) 2(N0) 2C1 2 _ 2 C Q > I [W(NO) 2Cl 2] n (3.11) the f i r s t two of which involve the displacement of two carbonyl ligands either by one equivalent of C1N0 or by sequential attack of N0 + and C l - . Support for t h i s view comes from the fact that the IR spectrum of the f i n a l supernatant reaction s o l u t i o n p r i o r to re f l u x exhibits r e l a t i v e l y weak carbonyl and n i t r o s y l absorptions at ca. 2140, 2070, 2050 and 1920 cm - 1 which can be at t r i b u t e d to the presence i n low concentrations of W(C0) 1 +(N0)C1 1° and W(C0) 2(N0) 2C1 2. 2 a However, the sequential reactions of 57 eq 3.11 cannot account e i t h e r for the fa c t that an oxidant i s needed to s t a r t the entire process or for the extremely rapid rate of the o v e r a l l reaction once i n i t i a t e d . For instance, while i t i s known that W(C0) 2(N0) 2C1 2 does indeed decarbonylate q u a n t i t a t i v e l y to [W(NO) 2C1 2] q i n 2a CH 2C1 2, the h a l f - l i f e for t h i s process i s ca. 18 h at room temperatures. S i m i l a r l y , we have v e r i f i e d i n a separate experiment that W(C0)^(N0)C1 does indeed react with excess CINO i n CH 2C1 2 i n the absence of a i r as indicated, but again more than 19 h at ambient temperatures are required to consume completely the i n i t i a l reactant. F i n a l l y , i t i s well known that W(CO)6 i s i n e r t to thermal s u b s t i t u t i o n reactions with Lewis bases under ambient 18 conditions. Nevertheless, once i n i t i a t e d , the consumption of W(CO)6 by two equivalents of CINO i s complete i n less than 5 min at 20°C and produces 4 more than 10 moles of [W(N0) 2Cl 2] n for each mole of oxidant added. Obviously, some mechanism other than that represented by eq 3.11 must be operative. We believe that the c a t a l y t i c , r a d i c a l chain mechanism summarized i n Scheme 3.2 best accounts for our experimental observations and i s i n accord with l i t e r a t u r e precedents. The chain i n i t i a t i o n step involves oxidation of a small portion of + the W(C0) 6 reactant to W(C0) 6» by the c a t a l y t i c amount of oxidant added. By analogy to re l a t e d 17-electron r a d i c a l s such as M(C0)g L^*" [M = Cr, Mo, or W; L = CH3CN or p y r i d i n e ] , W(C0) 6* should be s u b s t i t u t i o n a l ^ more 18 19 l a b i l e by many orders of magnitude than i t s 18-electron precursor. ' Hence, i t would r a p i d l y undergo the s u b s t i t u t i o n reaction 58 Scheme 3.2 W(C0) 6 Vn [w (N0) 2 CI 2 ] n | O ^ N O V A g W(CO)«" W(CO) ( W(N0)2CI2t W(C0) 2(N0) 2CI 2t CO W(CO)« W t C O J e ^ / - C I N O W(CO)s(NO)CI(NOCD* W(CO) 6 W(C0) 2(N0) 8CI 8 •WtCOle' W(C0)4(N0)CI 59 W(CO) 6* + C1N0 -»• W(CO) 5(NOCl)* + COt (3.12) 19 probably v i a an associative pathway, the tungsten-containing product converting i n turn to the 17-electron W(C0)1+(N0)C1^, i . e . W(CO)5(NOCl)t -»• W(CO)4(NO)Cl"i' + COt (3.13) Both transformations 3.12 and 3.13 are i r r e v e r s i b l e since the r a p i d l y evolved CO i s l o s t from the system. The bulk of the s u b s t i t u t i o n a l ^ l a b i l e WCCO^CNO^l* generated i n t h i s fashion could then undergo further rapid s u b s t i t u t i o n by C1N0 to form W(CO) 2(N0)2^2* *-n a manner analogous to that shown for W(CO) 6* i n eq 3.12 and 3.13. Again, the primary thermo-dynamic d r i v i n g force for these conversions i s provided by the loss of CO. The f i n a l steps of the cycle would then involve rapid decarbonylation of the 17-electron W(CO) 2(NO) 2C1 2^ and immediate reduction of the W(N0) 2C1 2* thus produced by W(CO)g to give the i s o l a b l e [W(NO) 2Cl 2] nand regenerate w ( c o ) 6 * f ° r resumption of the cycle at reaction 3.12. The net process effected by the c a t a l y t i c cycle i s thus CH 2C1 2 -I W(CO)6 + 2 C1N0 > £ [W(NO) 2Cl 2] n + 6 COt (3.14) 60 as i s observed experimentally. According to t h i s proposed mechanism, the traces of neutral W(C0)1+(N0)C1 and W(C0) 2(N0) 2C1 2 detectable by IR spectroscopy i n the reaction mixture (vide supra) a r i s e from side reactions which involve reduction of the respective 17-electron c a t i o n i c precursors by W(C0) 6 i n s o l u t i o n . Such a rat i o n a l e i s consistent with the fact that W(C0)[+(N0)C1 undergoes an i r r e v e r s i b l e , one-electron oxidation at potentials which are some 0.5 V more p o s i t i v e than those required for the electrochemical 20 oxidation of W(C0) 6 under i d e n t i c a l experimental conditions. In other words, replacement of two CO ligands by an NO and a Cl ligand increases the oxidation p o t e n t i a l of a complex ( i . e . makes the complex more d i f f i c u l t to 19 o x i d i z e ) . Hence, i n accord with established c r i t e r i a , i t i s not + + unreasonable to expect that W(CO) 2(NO) 2Cl 2» and W(N0) 2C1 2» (the precursor to the f i n a l product i n Scheme 3.2) should both be capable of functioning as oxidants towards W(C0) 6 as shown. Int e r e s t i n g l y , i f the reaction between W(C0) 6 and excess CINO i n CH 2C1 2 i s effected i n the presence of traces of a i r and two equivalents of CH3CN, the only n i t r o s y l - c o n t a i n i n g product (formed slowly and i n low y i e l d s ) i s W(N0)C1 3(CH 3CN) 2. It i s thus evident that the c y c l i c mechanism o f Scheme 3.2 i s not followed i n the presence of Lewis bases such as CH3CN. Instead, these experimental observations may be r a t i o n a l i z e d i n terms of the i n i t i a l oxidation of W(C0) 6 occurring i n the following manner 61 W(CO)6 ~ 6 ~ > W(CO)6t > W(CO) 6_ n(CH 3CN) n 2+ + n COf (3.15) 21 a process that has been observed electrochemically. The d l c a t i o n thus formed could then engage l n one of two subsequent reactions, i . e . CH2CI2 21 W(CO), (CH,CN)2+ + (m-n) CH,CN • W(CH,CN) 2 + + (6-n) COf (3.16) b —n 3 n 3 •> m or CH2CI2 W(CO) 6_ n(CH 3CN) 2 + + 3 CINO • W(N0)C1 3(CH 3CN) 2 + 2 N0+ + (6-n) COT + (n-2) CH3CN (3.17) In addition to producing the f i n a l n i t r o s y l - c o n t a i n i n g product, reaction 3.17 also generates N0 + which could function as the oxidant for the resumption of the cycle v i a eq 3.15. Nevertheless, the low conversion of W(CO)6 to W(N0)C1 3(CH 3CN) 2 indicates that i f indeed such a c a t a l y t i c cycle ( i . e . eq 3.15 and 3.17) i s operative under these conditions, i t has a low turnover rate either due to competition from reaction 3.16 as a termination step or due to the i n t r i n s i c s u b s t i t u t i o n a l Inertness of the diamagnetic dications involved. Some Characteristic Chemistry of [W(N0)2Cl2ln» I t i s well known that Lewis bases (L) cleave the chloride bridges i n [W(N0) 2C1 2] and form 62 i n good y i e l d s monomeric W(N0) 2C1 2L 2 complexes which possess c i s - n i t r o s y l 3 ligands, i . e . | [W(NO) 2Cl 2] n + 2L 4 o f g g ? g e > W(N0) 2C1 2L 2 (3.18) 22 In connection with other studies, we have employed reaction 3.18 to prepare the new products having L = PMePh2 or P(OMe) 3 as diamagnetic, green, a i r - s t a b l e s o l i d s . Their IR spectra display two n i t r o s y l absorp-tions i n accord with the documented electron-donating a b i l i t i e s of the 23 Lewis bases ( i . e . PMePh2 > P(OMe) 3). Furthermore, t h e i r *H NMR spectra exhibit 1:2:1 t r i p l e t s due to the methyl groups. This v i r t u a l 2A 23 26 coupling ' establishes unambiguously that the stereochemistry of these octahedral complexes involves the following arrangement of ligands: Cl-L W N 0 L Such an arrangement has been previously demonstrated for the congeneric Mo 63 complexes. When a p o t e n t i a l l y chelating ligand such as Ph 2PCH 2PPh 2 (dppm) i s employed as the Lewis base i n reaction 3.18, the conversion proceeds more slowly than with monodentate bases. Nevertheless, two d i f f e r e n t types of products may be separated by f r a c t i o n a l c r y s t a l l i z a t i o n from the f i n a l reaction mixture. The f i r s t i s W(NO) 2Cl 2(dppm) 2 which i s i s o l a b l e as a pale green s o l i d i n 13% y i e l d . Its spectroscopic properties indicate that i t possesses the same cis-NO, c i s - C l , trans-L arrangement of ligands around the tungsten center as the analogous PMePh2and P(OMe) 3 complexes. That the two trans-dppm ligands are both monodentate i s c l e a r l y evident from the *H and 3 1P{ 1H} NMR spectra of the compound. The former indicates that the PCH2P-W-PCH2P grouping constitutes an AA ,MM ,X 2X 2' spin system, 2^' 2 6 and the l a t t e r v e r i f i e s the existence of two equivalently coordinated and two equivalent uncoordinated phosphorus atoms. The second new product containing dppm which i s i s o l a b l e as a CH 2C1 2 solvate i n 10% y i e l d i s l i g h t green W(N0) 2Cl 2(dppm). This sparingly soluble s o l i d e x h ibits v N Q ' s at 1756 and 1651 cm - 1 i n i t s IR spectrum when dissolved i n CH 2C1 2, thus confirming the presence of c i s - n i t r o s y l ligands. S t e r i c and e l e c t r o n i c considerations require the dppm ligand to be coordinated i n a bidentate manner to c i s positions i n the coordination sphere. The *H NMR spectrum of the compound does not permit the d i f f e r e n t i a t i o n between the remaining isomeric p o s s i b i l i t i e s of c i s - or trans-Cl ligands. Hard Lewis bases such as CH3CN, THF or E t 2 0 also react with [W(N0) 2C1 2] i n the manner depicted i n eq 3.18. The new W(N0) 2C1 2(CH 3CN) 2 64 can thus be i s o l a t e d from neat CH3CN as a pale green', m i c r o c r y s t a l l i n e s o l i d i n 59% y i e l d . Its IR spectra display two n i t r o s y l absorptions, and i t s 1H NMR spectrum In CD 3N0 2 consists of two sharp sin g l e t s of equal i n t e n s i t y . Consequently, i t s molecular structure must be 0 N Cl Cl •NO NCCH, N C CK The analogous W(NO) 2C1 2(THF) 2 and W( N O ) 2 C l 2 ( E t 2 0 ) 2 complexes may be generated appropriately i n s i t u . A l l of these compounds are useful pre-cursors for the synthesis of CpW(NO)2Cl by metathesis with (n-Bu) 3Sn(C 5H 5), i . e . W(N0) 2C1 2L 2 + (n-Bu) 3Sn(C 5H 5) CH2CI2 »• CpW(NO)2Cl + (n-Bu) 3SnCl + 2L (L = THF, E t 2 0 or CH3CN) (3.19) Reaction 3.19 affords the organometallic n i t r o s y l product more d i r e c t l y from W(CO) 6, a l b e i t i n somewhat lower y i e l d , than does the generally 65 accepted preparative method. Conclusions This work has established that [W(NO) 2Cl 2] n may indeed be prepared by employing reactions 3.1 and 3.2, but c a r e f u l attention must be paid to experimental d e t a i l s . Since the reductive n i t r o s y l a t i o n of WClg i n CH 2C1 2 (eq 3.2) proceeds v i a the i s o l a b l e intermediates W(N0) 2C1 H and W(N0) 3C1 3 (Scheme 3.1), the suspension of WClg must f i r s t be exposed to gaseous NO at room temperature u n t i l no further uptake of the gas occurs. Subsequent r e f l u x i n g of the r e s u l t i n g mixture under a current of N 2 to expel a l l of the C1N0 by-product from the system then affords the insoluble d i c h l o r o d i n i t r o s y l t u n g s t e n polymer. On the other hand, to synthesize t h i s complex by the reaction of C1N0 with W(CO)6 i n CH 2C1 2 (eq 3.1), traces of an oxidant are f i r s t required to i n i t i a t e the reaction which probably proceeds v i a a c a t a l y t i c , r a d i c a l chain mechanism (Scheme 3.2). The addi -t i o n of the remaining C1N0 must then be effected i n a controlled manner with concomitant monitoring of the progress of the conversion by IR spectroscopy so that an excess of t h i s reagent i s avoided. Such an excess simply converts some of the desired [W(NO) 2Cl 2] n to W(N0) 3C1 3 and W(NO) 2Cli t contaminants, a conversion that may be reversed (eq 3.3) by r e f l u x i n g the f i n a l r eaction mixture for a short time under a purge of N 2« Of the two preparative methods, reaction 3.1 affords [W(NO) 2Cl 2] n i n the greatest y i e l d and p u r i t y and i s most convenient f o r the synthesis of the polymeric complex on a large s c a l e . 66 R e f e r e n c e s a n d N o t e s (1) Taken i n part from: Hunter, A.D.; Legzdins, P. Inorg. Chem. 19J34, 23, 4198. (2) (a) Kolthammer, B.W.S.; Legzdins, P.; Malito, J.T. Inorg. Chem. 19^ 77, 16, 3173 and (b) Legzdins, P.; Oxley, J.C. Inorg. Chem. 1984, 23, 1053. (3) Cotton, F.A.; Johnson, B.F.G. Inorg. Chem. 1964, 3^, 1609. (4) Johnson, B.F.G.; Al-Obadi, K.H. Inorg. Synth. 1970, 12, 264. (5) Kohan, J . ; Vastag, S.; Bencze, L. Inorg. Chim. Acta 1975, 14, L l and references c i t e d therein. (6) See Chapter Two. (7) P(0Me) 3 isomerizes on heating to 0P(Me)(0Me) 2; c f . Marck, V. Mech. Mol. Migr. 1969, 2, 319. (8) For a de s c r i p t i o n of the handling of CINO solutions see Hoyano, J.K.; Legzdins, P.; Malito, J.T. Inorg. Synth. 1978, 18, 126. (9) I n i t i a t i o n of the reaction could also be accomplished by dipping a spatula into the supernatant s o l u t i o n , exposing i t to a i r for 2 sec, and then returning i t into the s o l u t i o n . (10) Legzdins, P.; Malito, J.T. Inorg. Chem. 1975, 14, 1875. (11) F r i t z , H.P.; K r e i t e r , C.G. J . Organomet. Chem. 1964, 1_, 323. (12) (a) Buslaev, Yu.A.; Ovchinnlkova, N.A.; Ershova, M.M.; Glushkova, M.A. Izv. Akad. Nauk SSSR, Ser. Khim. 1972, 4, 950. (b) Seyferth, K.; Rosenthal, K.; KUhn, G.; Taube, R. Z. Anorg. A l l g . Chem. 1984, 513, 57. 67 (13) Johnson, B.F.G.; McCleverty, J.A. Prog. Inorg. Chem. 1966, 7_, 277. (14) Davis, R.; Johnson, B.F.G.; Al-Obaidi, K.H. J . Chem. S o c , Dalton Trans. 1972, 508. (15) Bencze, L.; Rohan, J . Inorg. Chim. Acta 1982, 65, L17. (16) A bulk conversion of a suspension of 0.5 g of W(N0) 3C1 3 i n CH 2C1 2 (50 ml) to [W( N 0 ) 2 C l 2 ] n requires ca. 2 h at room temperature to go to e f f e c t i v e completion. (17) Feltham, R.D.; Si l v e r t h o r n , W.; McPherson, G. Inorg. Chem. 1969, 8, 344. (18) Darensbourg, D.J. Adv. Organomet. Chem. 1982, 21, 113. (19) Hershberger, J.W.; K l i n g l e r , R.H.; Kochi, J.K. J . Am. Chem. Soc. 1982, 104, 3034; 1983, 105, 61 and references c i t e d therein. (20) Wassink, B., Ph.D. D i s s e r t a t i o n , University of B r i t i s h Columbia, Vancouver, B r i t i s h Columbia, 1985. (21) Christopher, J . ; Pletcher, D. J . Chem. S o c , Dalton Trans. 197J5, 879. (22) Hunter, A.D.; Legzdins, P. unpublished observations. (23) Tolman, C A . Chem. Rev. 1977, 77, 313. (24) Harris, R.K. Can. J . Chem. 1964, 42, 2275. (25) For a more de t a i l e d discussion of v i r t u a l coupling and AA'X^X^' spin systems 2 4 (n =» 3 for PMePh2, n = 9 for P(0Me) 3) see Chapter Four. I t should be noted, however, that at the l i m i t where the mult i p l e t observed due to coupling to A becomes a " v i r t u a l t r i p l e t " , the s p l i t -i i 24 ting of the outer pair of l i n e s ( i . e . N = |J + J ^ , ! ) can be 68 approximated as ( i . e . i n CDC13, 2^-pQE 3 1 P = 8.60 Hz for W(NO) 2Cl 2(PMePh 2) 2 and 3 J p ( 0 C H ^ ) f 3 1 P = 1 1 ' 2 4 ^ F O R W(NO) 2Cl 2[P(OMe) 3] 2). (26) (a) Bertrand, R.D.; O g i l v i e , F.B.; Verkade, J.G. J . Am. Chem. Soc. 197, 92, 1908. (b) O g i l v i e , F.B.; Jenkins, J.M.; Verkade, J.G. JN Am. Chem. Soc. 1970, 92, 1916. (27) (a) Visscher, M.O.; Caulton, K.G. J . Am. Chem. Soc. 1972, 94, 5923. (b) Hughes, W.B.; Zuech, E.A. Inorg. Chem. 1973, 12, 471. s 69 CHAPTER FOUR REDUCTIVE SYNTHESIS OF THE COMPLEXES CpM(NO)L2 ( M = Cr, Mo, OR W; L = LEWIS BASE): TRENDS IN THEIR PHYSICAL PROPERTIES AND MECHANISM OF FORMATION1 70 Introduction 2a Previous work i n these laboratories (by Charles Nurse) established that ambient temperature reduction of [CpMo(NO)I 2] 2 (Cp = r) 5-C 5H 5) with sodium amalgam i n the presence of a c y c l i c conjugated dienes i n THF r e s u l t s i n the formation of novel ^ - t r a n s - d i e n e complexes, i . e . THF [CpMo(N0)I 2] 2 + 4 Na/Hg + 2 diene 2 CpMo(N0)(T} 4-diene) + 4 Nal + Hg (4.1) where diene = 2-methylbutadiene, 2,3-dimethylbutadiene, or 2,5-dimethyl-2,4-hexadiene. The product organometallic complexes are i s o l a b l e i n ~10% o 2 y i e l d as yellow, somewhat a i r - s e n s i t i v e c r y s t a l s . During subsequent 2b studies, I discovered that v a r i a t i o n of the experimental conditions such as the nature of the reducing agent or the solvent led, i n a l l cases, to markedly diminished y i e l d s of the desired Ti^-diene complexes. Furthermore, attempts to extend the synthetic methodology of reaction 4.1 to encompass either other unsaturated organic ligands such as alkenes or alkynes or the congeneric complexes containing chromium or tungsten met with f a i l u r e . We reasoned that these disheartening r e s u l t s r e f l e c t e d e i t h e r the i n t r i n s i -c a l l y unstable nature of an intermediate species such as solvated "CpM(NO)" (M = Cr, Mo, or W) or the r e l a t i v e i n e f f i c i e n c y of the unsaturated organic molecules to function as trapping agents for such an intermediate complex. Consequently, we decided to attempt the reductions analogous to reaction 71 4.1 i n the presence of phosphines or phosphites (L) with a view to e f f e c t i n g the conversions THF [CpMo(NO)I 2] 2 + 4 Na/Hg + 4 L ^§7j> 2 CpMo(NO)L2 + 4 Nal + Hg. (4.2) It was hoped that the use of r e l a t i v e l y strong Lewis bases such as L = PMePh2 or P(OMe) 3 i n reaction 4.2 would permit the spectroscopic detection and perhaps i s o l a t i o n of any intermediate species, thereby providing some insigh t into the probable mechanisms of transformations 4.1 and 4.2. We also deemed i t worthwhile to expand our Investigations of reaction 4.2 to include the related chromium and tungsten systems since the anticipated product complexes, CpM(NO)L2 (M = Cr, Mo, or W) are desirable e l e c t r o n - r i c h n i t r o s y l compounds that are not generally preparable by other synthetic routes. Indeed, the only four such complexes known at the time 3 4 we i n i t i a t e d our work were CpM(NO)(Ph 2PCH 2CH 2PPh 2) (M = Cr, or Mo ) and 4 4 CpM(NO)(PPh 3) 2 (M = Cr, or Mo ). They had been obtained from the reactions CpM(NO)(CO)2 + 2 L A ° r " V> CpM(NO)L2 + 2 COt (4.3) 3 4 where M = Cr or Mo, and 2L = Ph 2PCH 2CH 2PPh 2 or L = PPh 3. ' However, the 72 is o l a t e d y i e l d s of products from these reactions were generally low, and the analogous tungsten complexes could not be synthesized at a l l i n th i s manner. In Chapter Four, the r e s u l t s of my studies involving several series of such CpM(NO)L2 (M = Cr, Mo, or W) compounds are described. Experimental Section A l l reactions and subsequent manipulations were performed under anaerobic and anhydrous conditions i n a well - v e n t i l a t e d fume hood unless s p e c i f i e d otherwise. General procedures are the same as those described p r e v i o u s l y . 5 The h a l o n i t r o s y l reagents, [CpCr(NO)I] 2, 6 [CpMo(NO)I] 2, 7 8 8 9 [CpMo(NO)I 2] 2, [CpMo(NO)Br 2] 2, and [CpW(NO)I 2] 2, were prepared by the published procedures. The Lewis bases containing group 15 elements 1^ were used as purchased from commercial suppliers except for P(OMe) 3 which was d i s t i l l e d from sodium and stored under N 2 p r i o r to u s e . 1 1 Reactions of [CpM(N0)I n] 2 (M • Cr, n • 1; M • Ho or W, n • 2) with Na/Hg in the Presence of Lewis Bases, L. A l l of these reactions involved an excess of sodium amalgam and two equivalents of Lewis base per t r a n s i t i o n metal. The experimental procedures, using the molybdenum complexes as representative examples throughout, were as follows. A. L - P(OMe)3; M - Cr, Mo, W. An excess of s o l i d sodium amalgam (9.00 g, 9.36 mmol Na) was l i q u e f i e d by the addition of mercury 12 (~3 mL), THF (50 mL) was added, and the mixture was s t i r r e d r a p i d l y at 73 room temperature. To t h i s s t i r r e d mixture were added P(OMe) 3 (0.94 mL, 7.96 mmol) and [CpMo(N0)I 2] 2 (1.77 g, 1.99 mmol) to obtain a deep red supernatant so l u t i o n whose IR spectrum exhibited a v N Q at 1678(s) cm - 1. S t i r r i n g was continued for 1 h (to ensure completion of the reaction) whereupon the so l u t i o n had become yellow-brown i n color and i t s n i t r o s y l absorption had s h i f t e d to 1592(s) cm - 1. The f i n a l supernatant so l u t i o n was f i l t e r - c a n n u l a t e d away from the mercury-containing residue. The residue was washed with THF (2 x 10 mL), the washings were combined with the i n i t i a l f i l t r a t e , and solvent was removed from the r e s u l t i n g s o l u t i o n i n vacuo to obtain a brown o i l . This o i l was then extracted with E t 2 0 (4 x 40 mL) u n t i l the extracts were c o l o r l e s s , and the combined extracts were taken to dryness under reduced pressure. The r e s u l t i n g brownish residue was r e c r y s t a l l i z e d from Et 20-hexanes at -20°C to obtain 1.02 g (58% y i e l d ) of CpMo(NO)[P(OMe) 3] 2 as large yellow c r y s t a l s . The analogous chromium and tungsten complexes were i s o l a t e d s i m i l a r l y as orange needles (33% y i e l d ) and yellow c r y s t a l s (46% y i e l d ) , r e s p e c t i v e l y . The a n a l y t i c a l , mass s p e c t r a l , IR, and 1H and 3 1 P NMR data for these and the other new complexes synthesized during this work are c o l l e c t e d i n Tables 4.1 and 4.2. B. L «• PMePh2; M ™ Cr, Mo, W. As i n case A, s o l i d sodium amalgam (10.0 g, 10.4 mmol Na) was l i q u e f i e d with Hg (~3 mL), THF (80 mL) was added, and the s t i r r e d mixture was treated with PMePh2 (1.67 mL, 9.00 mmol) and [CpMo(N0)I 2] 2 (2.00 g, 2.25 mmol). The IR spectrum of the 74 i n i t i a l l y red supernatant s o l u t i o n displayed a n i t r o s y l absorption at 1668(s) cm - 1. However, i n th i s case, as the reaction mixture was s t i r r e d , the solution became green-brown af t e r 5 min, and i t s IR spectrum at th i s point revealed that new bands at 1614(s) and 1559(w) cm - 1 had appeared at the expense of the 1668 cm - 1 feature. After 10 min of reaction, the super-natant s o l u t i o n was orange, and the only v ^ evident i n i t s IR spectrum was a strong band at 1559 cm - 1. The f i n a l orange s o l u t i o n was removed from the mercury-containing residue (vide supra) and was taken to dryness i n vacuo 13 to obtain an orange-brown s o l i d . This s o l i d was extracted with E t 2 0 (150 mL) i n a Soxhlet extractor for 3 days, and the volume of the extracts was then diminished to ~10 mL under reduced pressure. The orange c r y s t a l s which had pr e c i p i t a t e d during these l a t t e r operations were i s o l a t e d by c a n n u l a - f i l t r a t i o n , washed with E t 2 0 (10 mL) and hexanes (2 x 20 mL) and dried under vacuum (5 x 1 0 - 3 mm) at ambient temperature. In th i s manner, 2.37 g (89% y i e l d ) of CpMo(N0)(PMePh 2) 2 as an a n a l y t i c a l l y pure, orange c r y s t a l l i n e s o l i d were obtained. The congeneric chromium and tungsten complexes were obtained analogously as red (84% y i e l d ) and orange (81% y i e l d ) c r y s t a l s , respec-t i v e l y . C. L • P(n-Bu) 3; M • Mo. To a s t i r r e d mixture containing l i q u e -f i e d sodium amalgam [10.0 g of s o l i d Na/Hg (10.4 mmol Na) i n 3 mL of Hg] and THF (80 mL) was added P(n-Bu) 3 (2.25 mL, 9.00 mmol) and then [CpMo(NO)I 2] 2 (2.00 g, 2.25 mmol). The progress of the reaction was moni-tored by IR spectroscopy of the supernatant s o l u t i o n . After 1 min, the 75 solu t i o n was red, and v ^ ' s were evident at 1691(m), 1659(m), and 1611(w) cm - 1. After 3 min, the s o l u t i o n had become brown, the absorption at 1691 cm - 1 had vanished, and the n i t r o s y l bands now appeared at 1654(m), 1611(s), and 1551(w) cm - 1. During the next 15 min, the band at 1654 cm - 1 gradually disappeared while that at 1551 cm - i increased i n i n t e n s i t y at the expense of the 1611 cm - 1 feature. F i n a l l y , a f t e r 1 h, only the absorption at 1551 cm - 1 persisted i n the V^Q region, and the sol u t i o n was orange-red i n c o l o r . This s o l u t i o n was c a n n u l a - f i l t e r e d away from the mercury-containing residue, and solvent was removed from the f i l t r a t e i n vacuo to obtain a red o i l . This o i l was extracted with hexanes (50 mL), the volume of the extracts was diminished to ~10 mL under reduced pressure, and the r e s u l t i n g s o l u t i o n was transferred by syringe to the top of an alumina column (3 x 6 cm, neutral, a c t i v i t y 1) made up i n hexanes. The column was f i r s t washed with hexanes (150 mL) i n an attempt to remove any unreacted P(n_-Bu)3. Subsequent e l u t i o n of the column with E t 2 0 (100 mL) removed a single red band which was c o l l e c t e d . Removal of solvent from the eluate i n vacuo afforded a red l i q u i d which was sequentially exposed to a dynamic vacuum (4 x 10" 3 mm) at ambient temperature for 24 h and then cooled at -20°C for 16 h to induce the formation of s t i c k y red c r y s t a l s of CpMo(NO)[P(n-Bu) 3] 2 (2.03 g, 76% y i e l d ) s l i g h t l y contaminated with PCn-Bu),, (Table 4.1). The preparation of the analogous Cr and W complexes was not attempted. 76 D. L • SbPh 3; M = Mo. To a s t i r r e d mixture containing l i q u e f i e d Na/Hg [6.00 g of s o l i d sodium amalgam (6.24 mmol Na) i n 3 mL of Hg] and THF (40 mL) was added s o l i d SbPh 3 (1.59 g, 4.50 mmol) and [CpMo(N0)I 2] 2 (1.00 g, 1.13 mmol). An IR spectrum of the i n i t i a l red, supernatant solution exhibited a n i t r o s y l band at 1664(s) cm - 1. After the reaction mixture had been s t i r r e d for 10 min at room temperature, the so l u t i o n had become red-brown, and i t s IR spectrum displayed only a weak, absorption at 1587 cm - 1 a t t r i b u t a b l e to v ^ . The f i n a l supernatant s o l u t i o n was f i l t e r -cannulated away from the mercury-containing residue (vide supra), and the combined f i l t r a t e s were taken to dryness i n vacuo to obtain a brown s o l i d . This s o l i d was extracted with E t 2 0 (4 x 50 mL) u n t i l the extracts were c o l o r l e s s , and the combined extracts were again taken to dryness under reduced pressure. Excess SbPh 3 (~0.8 g) was removed from the r e s u l t i n g s o l i d by sublimation (70°C, 5 x 1 0 - 3 mm) onto a water-cooled probe. The residue remaining a f t e r t h i s operation was r e c r y s t a l l i z e d from E t 2 0 at -20°C to obtain 0.31 g (15% y i e l d ) of CpMo(N0)(SbPh 3) 2 as a n a l y t i c a l l y pure, orange c r y s t a l s . No attempt was made to prepare the congeneric chromium and tungsten complexes. E. 2L - Ph 2PCH2CH 2PPh 2; M - Mo. This reaction was effected i n a manner i d e n t i c a l to that described i n the preceding section for SbPh 3, but on twice the s c a l e . The only intermediate n i t r o s y l absorptions detectable by IR spectroscopy occurred at 1684 cm - 1 and 1616 cm - 1, the l a t t e r being a shoulder on the band at 1586 cm - 1 c h a r a c t e r i s t i c of the f i n a l organometal-77 l i e product. This product was i s o l a t e d by the customary f i l t e r - c a n n u l a -t i o n , chromatography on alumina ( 3 x 8 cm, Woelm neutral, a c t i v i t y 1) with CH 2C1 2 as eluant, and c r y s t a l l i z a t i o n from CH 2Cl 2-hexanes at -20°C for 18 h. These operations afforded 1.74 g (66% y i e l d ) of CpMo(NO)(Ph 2PCH 2CH 2PCH 2) as an orange, c r y s t a l l i n e s o l i d . \ Again, no attempt was made to synthesize the analogous chromium and tungsten complexes. F. L • P(t-Bu) 3; M = Mo, W. These reactions were performed i n a manner i d e n t i c a l to that described above i n case C for P(n-Bu) 3. However, both reactions resulted i n f i n a l THF solutions that were brown i n color rather than orange-red. Furthermore, IR spectra of these solutions were devoid of absorptions a t t r i b u t a b l e to n i t r o s y l ligands, and work up of these solutions i n the usual fashion (vide supra) afforded no n i t r o s y l -containing products. G. L - PPh 3; M - Mo. This reaction was effected as for L = SbPh 3 (case D above). In this case, the i n i t i a l l y red supernatant s o l u t i o n ( V ^ Q 1672(s) cm - 1) became green i n ~2 min (V^Q 1618(s) cm - 1). After 1 h, however, an IR spectrum of the f i n a l brown sol u t i o n exhibited no n i t r o s y l absorptions. Again, the customary work-up procedure yielded no n i t r o s y l - c o n t a i n i n g products. H. L • AsPh 3; M • Mo. This reaction was also c a r r i e d out i n a manner i d e n t i c a l to that described above for L = SbPh 3- During 4 min, the i n i t i a l red s o l u t i o n ( vM n 1669(s) cm - 1) gradually became brown (v N f ) ' s 78 1616(w), 1580(m) and 1547(m) cm - 1). After 10 min, however, an IR spectrum of the brown so l u t i o n contained only a very weak n i t r o s y l absorption at 1580 cm - 1. Attempts at i s o l a t i o n of the product at t h i s point i n the usual manner only afforded trace amounts of a pink s o l i d whose IR spectrum i n E t 2 0 exhibited a band at 1582 cm - 1. Reaction of [CpMo(N0)Br2]2 with Na/Hg and PMePh2 i n THF. This reaction was set up as described for the diiodo dimer i n case B above, and i t proceeded s i m i l a r l y . Monitoring the conversion by IR spectroscopy of the supernatant s o l u t i o n revealed the appearance and eventual disappearance of n i t r o s y l bands at 1665 and 1610 cm - 1 u n t i l only the band at 1559 cm - 1 c h a r a c t e r i s t i c of the product p e r s i s t e d . This CpMo(NO)(PMePh2)2 product was i s o l a t e d i n 88% y i e l d by the procedure outlined i n part B. Reaction of [CpMo(N0)I 2]2 with Na/Hg and PMePh2 i n Et 20. Again, t h i s reaction was performed on the scale outlined i n part B above. The purple s o l i d reactant was slowly consumed and replaced by an orange s o l i d during 10 min. Because of the low s o l u b i l i t y of the n i t r o s y l complexes i n E t 2 0 , IR monitoring of the supernatant sol u t i o n was s i n g u l a r l y uninforma-t i v e . C r y s t a l l i z a t i o n of the f i n a l orange s o l i d from E t 2 0 afforded CpMo(N0)(PMePh 2) 2 i n 60% y i e l d . Reaction of [CpMo(N0)I 2]2 with NaC 1 QH 8 and PMePh2 i n THF. A s o l u t i o n of sodium naphthalene was prepared by introducing sodium metal (~0.06 g) into a THF (30 mL) s o l u t i o n of naphthalene (0.29 g, 2.25 mmol) and by s t i r r i n g of the mixture for 1.5 h at ambient temperature to obtain a dark green s o l u t i o n . To t h i s s t i r r e d s o l u t i o n were added stoichiometric 79 amounts of PMePh2 (0.42 mL, 2.25 mmol) and then [CpMo(N0)I 2] 2 (0.50 g, 0.56 mmol). The solu t i o n r a p i d l y (< 1 min) became red, and i t s IR spectrum at thi s point exhibited only the ubiquitous n i t r o s y l band at 1559 cm - 1. The f i n a l mixture was worked up i n a manner s i m i l a r to that used i n case D above (e.g. the naphthalene was removed by sublimation) to obtain 0.52 g (78% y i e l d ) of CpMo(NO)(PMePh 2) 2. R e a c t i o n o f [ C p M o ( N 0 ) I 2 ] 2 w i t h N a [ H 2 A l(0CH 2 C H 20CH 3) 2] a n d P M e P h 2 i n T H F . To a s t i r r e d , f r e s h l y prepared, red solu t i o n (V^Q 1668 cm - 1) of PMePh2 (0.42 mL, 2.25 mmol) and [CpMo(N0)I 2] 2 (0.50 g, 0.56 mmol) i n THF (50 mL) was added dropwise a toluene so l u t i o n of Na[H 2Al(OCH 2CH 2OCH 3) 2] (0.66 mL, 2.25 mmol).^ The solu t i o n gradually became brown i n 5 min, and i t s IR spectrum displayed the f a m i l i a r band at 1559 cm - 1. CpMo(N0)(PMePh 2) 2 was i s o l a t e d i n the customary manner ( c f . part B) from the f i n a l mixture i n 59% y i e l d (0.38 g). R e a c t i o n s o f [ C p M o ( N 0 ) I 2 ] 2 w i t h P M e P h 2 > P(0Me) 3, o r 0PMePh2. These three reactions were performed i n an i d e n t i c a l manner. The procedure involving PMePh2 i s presented i n d e t a i l as a representative example. To a r a p i d l y s t i r r e d , purple suspension of [CpMo(N0)I 2] 2 (6.00 g, 6.75 mmol) i n CH 2C1 2 (50 mL) was added dropwise PMePh2 (2.51 mL, 27.0 mmol). The purple s o l i d was consumed and a f t e r 30 min, and the f i n a l r e -action mixture consisted of a c l e a r , red solu t i o n whose IR spectrum exhib-i t e d a v„ r t at 1668 cm - 1. This s o l u t i o n was f i l t e r e d through a F l o r i s i l NO column ( 2 x 3 cm) supported on a medium-porosity f r i t . Dropwise add i t i o n of hexanes (50 mL) over 1 h induced the p r e c i p i t a t i o n of a brick-red 80 s o l i d . This p r e c i p i t a t e was c o l l e c t e d by f i l t r a t i o n , washed with hexanes (3 x 25 mL) and dried i n vacuo (5 x 10" 3 mm) for 3 h at room temperature to obtain 8.36 g (96% y i e l d ) of CpMo(N0)I 2(PMePh 2) as an a n a l y t i c a l l y pure, red powder. 14 CpMo(N0)I 2[P(0Me) 3] and CpMo(N0)I 2(0PMePh 2) were i s o l a t e d s i m i l a r l y i n 82% y i e l d as brick-red microcrystals and a yellow powder, res p e c t i v e l y . Reaction of CpMo(N0)I2(PMePh2) with PMePh2. To a red solu t i o n of CpMo(N0)I 2(PMePh 2) (1.50 g, 2.33 mmol) i n THF (50 mL) was added PMePh2 (0.43 mL, 2.33 mmol), and the mixture was s t i r r e d at room temperature for 2 h. The so l u t i o n remained red throughout, and i t s IR spectrum (V^Q 1668 cm - 1) did not change. The f i n a l s o l u t i o n was taken to dryness under reduced pressure, and the remaining residue was p u r i f i e d by c r y s t a l l i z a -t i o n from CH 2Cl 2/hexanes to obtain 1.88 g (95% y i e l d ) of [CpMo(NO)I(PMePh 2) 2]I as a yellow powder. Reaction of [CpMo(N0)I2]2 with dppe* A red solu t i o n of [CpMo(N0)I 2] 2 (2.00 g, 2.25 mmol) i n THF (60 mL) was treated with two equivalents of Ph 2PCH 2CH 2PPh 2 (dppe, 1.79 g, 4.50 mmol), and the mixture was s t i r r e d at ambient temperature for 10 min, the solu t i o n remaining red throughout. Removal of v o l a t i l e s i n vacuo and c r y s t a l l i z a t i o n of the residue from CH 2Cl 2/hexanes produced 2.32 g (61% y i e l d ) of [CpMo(N0)I(Ph 2PCH 2CH 2PPh 2)]I as a l i g h t brown powder. Thermal Decomposition of [CpMo(N0)I]2. A red suspension of [CpMo(N0)I] 2 (0.60 g, 0.94 mmol) was s t i r r e d i n r e f l u x i n g toluene (60 mL) 81 for 21 h, whereupon the s o l i d was consumed and a brown so l u t i o n formed. An IR spectrum of th i s s o l u t i o n revealed that the n i t r o s y l band c h a r a c t e r i s t i c of the reactant at 1574 cm - 1 had been replaced by weaker absorptions at 1674 and 1760 cm"1. The brown sol u t i o n was taken to dryness i n vacuo, and the residue was p u r i f i e d by chromatography on F l o r i s i l ( 2 x 6 cm) with CH 2C1 2 as eluant. This operation produced a single green band which was eluted from the column and c o l l e c t e d . The eluate was again taken to dryness under reduced pressure, and the remaining s o l i d was r e c r y s t a l l i z e d from CH 2C1 27hexanes to obtain 0.10 g (30% y i e l d based on NO) of CpMo(N0) 2I as green c r y s t a l s . The product complex was r e a d i l y i d e n t i f i a b l e by i t s c h a r a c t e r i s t i c spectroscopic properties: 1** IR(CH 2C1 2): V NQ 1676, 1765 cm"1.  lE NMR (CDC1 3): 6 6.08(s). Reaction of [CpMo(N0)I]2 with Na/Hg and PMePh2 in THF. To a s t i r r e d , two-phase system con s i s t i n g of s o l i d sodium amalgam (4.00 g, 4.16 mmol Na) that had been l i q u e f i e d with Hg (~2 mL) and THF (40 mL) were added PMePh2 (1.17 mL, 6.29 mmol) and [CpMo(N0)I] 2 (1.00 g, 1.57 mmol). An IR spectrum of the i n i t i a l l y red supernatant, so l u t i o n contained just one n i t r o s y l band at 1617 cm - 1. After s t i r r i n g of the reaction mixture for 0.5 h, the so l u t i o n had become l i g h t e r red i n color, and i t s IR spectrum displayed v N Q ' s at 1580(w), 1559(m), and 1530(w) cm"1. This f i n a l super-natant s o l u t i o n was f i l t e r - c a n n u l a t e d away from the mercury-containing residue. The residue was washed with THF (2 x 30 mL), the washings were combined with the i n i t i a l f i l t r a t e , and solvent was removed from the 82 r e s u l t i n g s o l u t i o n i n vacuo to obtain a red s o l i d . This s o l i d was treated with CH 2C1 2 (20 mL), and the mixture was f i l t e r e d through a column of F l o r i s i l ( 2 x 3 cm) supported on a medium-porosity f r i t to obtain an orange f i l t r a t e . The f i l t r a t e was taken to dryness under reduced pressure, and the remaining orange s o l i d was r e c r y s t a l l i z e d from E t 2 0 to obtain 0.63 g (34% y i e l d ) of CpMo(N0)(PMePh 2) 2. Reaction of [CpMo(N0)I(PMePh2)2]I with Na/Hg i n THF. S o l i d sodium amalgam (5.60 g, 5.80 mmol Na) was l i q u e f i e d by the addition of mercury (~3 mL), THF (40 mL) was added, and the mixture was s t i r r e d r a p i d l y at ambient temperature. The addition of [CpMo(N0)I(PMePh 2) 2]I (1.00 g, 1.18 mmol) to t h i s s t i r r e d mixture resulted i n the immediate formation of a yellow powder suspended i n a green supernatant so l u t i o n (V^Q 1644(w) and 1614(m) cm - 1). Further s t i r r i n g of the reaction mixture for 0.5 h caused the yellow s o l i d to dissolve and the supernatant s o l u t i o n to become orange (v 1559(s) cm - 1). Treatment of th i s solution i n the manner described i n part B above afforded CpMo(NO)(PMePh 2) 2 (0.56 g, 80% y i e l d ) . Reactions of CpMo(N0)I2L [L - PMePh2 or P(0Me) 3] with Excess Na/Hg i n THF. To a s t i r r e d mixture containing l i q u e f i e d Na/Hg [4.50 g of s o l i d sodium amalgam (4.70 mmol Na) i n 3 mL of Hg] and THF (40 mL) was added s o l i d , brick-red CpMo(N0)I 2(PMePh 2) (1.00 g, 1.55 mmol). The i n i t i a l s o l u t i o n was red i n color, and i t s IR spectrum contained a strong n i t r o s y l band at 1668 cm - 1 due to the reactant and weaker bands at 1645 and 1614 cm - 1 a t t r i b u t a b l e to intermediate species. Within a few minutes, the 83 solution became deep green, and only the 1614(s) cm - 1 band persisted i n i t s IR spectrum. F i n a l l y , a f t e r 15 min of reaction, the supernatant solution was red-brown, and i t s IR spectrum exhibited a single n i t r o s y l absorption at 1559(m) cm - 1 c h a r a c t e r i s t i c of CpMo(NO)(PMePh 2) 2« This product was i s o l a t e d i n the usual manner ( c f . part B above) i n 38% y i e l d (0.35 g). The analogous reaction involving CpMo(N0)I 2[P(0Me) 3] proceeded cleanly from a red s o l u t i o n (V^Q 1678 cm - 1) to a green one ( v ^ Q 1 6 2 6 cm - 1). However, beyond t h i s stage, the supernatant so l u t i o n r a p i d l y became brown, and the n i t r o s y l bands i n i t s IR spectrum dramatically decreased i n t o t a l i n t e n s i t y . After 15 min, a weak absorption at 1592 cm - 1 due to CpMo(NO)[P(0Me) 3] 2 p e r s i s t e d , and t h i s product was i s o l a b l e i n the customary manner ( c f . part A above) i n only 5% y i e l d . Reactions of CpMo(N0)I2L [L - PMePh2 or P(OMe)3] with One Equiva-lent of Na/Hg i n THF. S o l i d sodium amalgam (1.18 g, 1.23 mmol Na) was l i q u e f i e d with Hg (5 mL), and then THF (40 mL) was added. To t h i s s t i r r e d mixture was added CpMo(NO)I 2(PMePh 2) (1.00 g, 1.55 mmol) whereupon the f a m i l i a r red supernatant so l u t i o n ( V N Q 1668 cm - 1) was produced. After 5 min of reaction, the so l u t i o n became green, and i t s IR spectrum v e r i f i e d the consumption of the n i t r o s y l reactant, e x h i b i t i n g only a single v N Q at 1614 cm - 1. An ESR spectrum of an aliquot of t h i s s o l u t i o n at room temperature displayed a strong, broad s i g n a l . The reaction mixture was s t i r r e d for an a d d i t i o n a l 20 min, and the green solution was then cannula-f i l t e r e d away from the mercury-containing residue. Slow concentration of the green f i l t r a t e under reduced pressure caused i t to become red and 84 ultimately produced a red-brown o i l . A l l attempts to i s o l a t e the green product [ v N Q 1614 cm"1 (THF) and 1610 cm"1 (CH 2C1 2)] were thwarted by i t s p r o c l i v i t y to decompose thermally. The analogous reaction involving CpMo(N0)I 2[P(0Me) 3] 2 (0.088 g, 0. 16 mmol) also produced a green sol u t i o n ( V ^ Q 1626 cm - 1(THF)) having a s i m i l a r l y strong, broad ESR s i g n a l . This paramagnetic product also could not be i s o l a t e d because of i t s thermal i n s t a b i l i t y . R e s u l t s a n d D i s c u s s i o n S y n t h e s e s a n d P h y s i c a l P r o p e r t i e s o f t h e C p M ( N 0 ) L 2 ( M » C r , M o , W ; L * L e w i s B a s e ) C o m p l e x e s . As we had anticipated, reduction of the i o d o n i t r o s y l dimers, [CpM(N0)I n] 2 (M = Cr, n = 1; M = Mo or W, n = 2), by sodium amalgam i n THF i n the presence of a v a r i e t y of Lewis bases, L, does indeed produce CpM(N0)L 2 complexes i n moderate to high i s o l a t e d y i e l d s , 1. e. The transformations summarized by eq 4.4 are clean, rapid and s t r a i g h t -forward, and an excess of sodium amalgam may be used with no deleterious e f f e c t s . This synthetic methodology encompasses a l l three t r a n s i t i o n metals of the group 6 t r i a d , and i s p a r t i c u l a r l y successful for strong [CpM(N0)I n] 2 + 2n Na/Hg + 4L THF. -> 2 CpM(N0)L2 + 2n Nal + Hg (4.4) Lewis bases. 17 The new complexes that have been prepared i n t h i s fashion 85 are presented i n Tables 4.1 and 4.2. The primary l i m i t a t i o n of reaction 4.4 appears to be the s t e r i c bulk, of the Lewis bases employed. If bulky phosphines such as P(_tj-Bu)3 (M = Mo or W) or PPh 3 (M = Mo) are employed, no n i t r o s y l - c o n t a i n i n g products are formed, and even the somewhat less s t e r i -c a l l y demanding AsPh 3 and SbPh 3 (M = Mo) only afford low y i e l d s of the desired products. Nevertheless, for Lewis bases that are incorporated e f f i c i e n t l y into the metals' coordination spheres by reaction 4.4, a number of variants of the synthetic methodology also produce the CpM(NO)L2 complexes. This feature i s c l e a r l y i l l u s t r a t e d by the various methods by which CpMo(NO)(PMePh2)2 may be generated, as summarized i n eq 4.5-4.8. THF [CpMo(NO)Br 2] 2 + 4 Na/Hg + 4 PMePh2 -=^ -> 2 CpMo(NO)(PMePh 2) 2 + 4 NaBr + Hg (4.5) (88% y i e l d ) E t 2 0 [CpMo(NO)I 2] 2 + 4 Na/Hg + 4 PMePh2 > 2 CpMo(NO)(PMePh 2) 2 + 4 Nal + Hg (4.6) (60% y i e l d ) 86 [CpMo(NO)I 2] 2 + 4 NaC 1 0H g + 4 PMePh2 ——> 2 CpMo(NO)(PMePh 2) 2 + 4 Nal + 4 C 1 0 H 8 (4.7) (78% y i e l d ) [CpMo(NO)I 2] 2 + 4 Na[H 2Al(OCH 2CH 2OCH 3) 2] + 4 PMePh2 > 2 CpMo(NO)(PMePh 2) 2 + Al-containing by-products (4.8) (59% y i e l d ) From a p r a c t i c a l point of view, however, i t should be noted that the changes of solvent or reducing agent introduced i n reactions 4.6, 4.7, and 4.8 lead to s l i g h t l y more cumbersome experimental procedures f or i s o l a t i o n of the desired n i t r o s y l product. In general, reaction 4.4 i s the synthetic method of choice for the preparation of CpM(N0)L 2 complexes since the previously employed synthetic routes that lead to t h i s class of compounds, i . e . CpM(NO)(CO) 2 + L A ° r h V > CpM(NO)(CO)L + C0 T (4.9) CpM(NO)(CO)L + L A ° r h V > CpM(NO)L2 + C0+ (4.10) are, as noted i n the Introduction, of li m i t e d u t i l i t y . For instance, the thermal s u b s t i t u t i o n reaction presented i n eq 4.9 i s a r e l a t i v e l y f a c i l e 87 S N2 p r o c e s s 1 8 of apparently general a p p l i c a b i l i t y ^ ' 1 8 2 0 which proceeds 18 17 most r a p i d l y for M = Mo and more basic phosphines. However, the 4 r e q u i s i t e second step (eq 4.10) f a i l s thermally for most Lewis bases, the notable exception being Ph 2PCH 2CH 2PPh 2 (M = Cr or Mo) which benefits 3 21 thermodynamically from the chelate e f f e c t . ' The s u b s t i t u t i o n reaction 4.9 can also be effected photochemically, being p a r t i c u l a r l y e f f i c i e n t when 22 M = Cr. Again, however, d i f f i c u l t i e s a r i s e i n carrying out the second s u b s t i t u t i o n under these experimental conditions since the desired conver-23 sion (eq 4.10) i s accompanied by competing reactions. Nevertheless, photochemical methods have been used to synthesize CpM(N0)(PPh 3) 2 (M = Cr, A Mo) i n low y i e l d s (amongst a v a r i e t y of other products) and 3 4 CpM(N0)(Ph 2PCH 2CH 2PPh 2) (M = Cr, Mo ) i n good y i e l d s by reactions 4.9 and 4.10. No such tungsten complexes have been previously prepared by either thermal or photochemical means. The various CpM(N0)L 2 compounds i s o l a t e d during our work (Table 4.1) are yellow-to-red, diamagnetic s o l i d s . The P(0Me) 3- and P(n-Bu) 3-containing complexes are very soluble i n common organic solvents such as THF, CH 2C1 2, benzene and E t 2 0 and are somewhat less soluble i n hexanes. The other complexes exhibit less s o l u b i l i t y i n benzene and E t 2 0 and are insoluble In hexanes. The phosphite derivatives are thermally unstable i n the s o l i d state, decomposing i n a matter of weeks at ambient temperatures, but they remain unchanged i n d e f i n i t e l y at -20°C. In contrast, the s o l i d phosphine complexes appear to be thermally stable when maintained at room Table 4.1. Analytical and Mass Spectral Data for the Complexes low resultion mass spectral complex color mp,°C analytical data dataS-C H N P+.m/zl calcd found calcd found calcd found CpCr(NO)[P(OMe)3]2 orange 96--7 33.43 33.33 5.87 5.77 3.55 3.62 395 CpMo(NO)[P(OMe)3]2 yellow 79--80 30.08 30.03 5.28 5.20 3.19 3.10 441 CpW(NO)[P(OMe)3]2- yellow 63--4 25.07 25.21 4.40 4.50 2.66 2.70 527 CpCr(NO)(PMePh2)2 red 161--2 68.00 68.35 5.70 5.69 2.56 2.42 532*-CpMo(NO)(PMePh2)2 orange ~ 65 dec 62.95 62.83 5.28 5.36 2.37 2.30 593 CpW(NO)(PMeFh2)2 orange ~110 dec 54.80 54.55 4.60 4.59 2.06 2.15 679 CpMo(NO)[P(n-Bu)3] 2 - red 52--57 58.47 59.60 9.98 10.44 2.35 2.47 597 CpMo(NO)(SbPh3)2 orange ~100 dec 54.89 54.73 3.93 3.98 1.56 1.63 f_ CpMo(NO)(Ph2 PCH2 CH2PPh2) orange ~160 dec 63.17 62.89 4.96 4.96 2.38 2.35 591 CpMo(NO)I2(PMePh2) red ~130 dec 33.52 33.78 2.81 2.86 2.17 2.20 447& CpMo(N0)I2tP(0Me)3] red 124--5 16.89 16.84 2.48 2.40 2.46 2.47 447& CpMo(NO)I2(0PMePh2) yellow -160 dec 32.70 32.69 2.74 2.60 2.12 2.32 447& [CpMo(NO)I(PMePh2)2]I yellow -150 dec 44.05 44.03 3.70 3.70 1.66 1.69 -[CpMo(NO)I(Ph2 PCH2 CH2 PPh2)]I brown -185 dec 44.15 43.95 3.47 3.49 1.66 1.60 -— Probe temperatures 100-150°C. — Assignments involve the most abundant naturally occurring isotopes in each species (i.e. 5 2Cr, 98Mo, and — Oxygen analysis. Calcd: 21.15. Found: 21.45. 1 Attributable to [P-Me]+. — Sample slightly contaminated with P(n-Bu), which has similar solubility properties and volatility. — No signal due to P detectable; highest m/z observable is 487. S- Attributable to [P-L]+ where L - Lewis base ligand. o o o o 89 temperatures for extended periods of time ( i . e . up to one year). A l l the CpM(NO)L2 species are very a i r - s e n s i t i v e both i n the s o l i d state and i n solutions, the P(n-Bu) 3 complex of molybdenum being p a r t i c u l a r l y notable i n thi s regard. They also decompose i n halogenated solvents, r a p i d l y i n CHC13 and more slowly i n CH 2C1 2. Their formulations as monomeric, 18-electron complexes are supported by t h e i r elemental analyses and low-resolution mass spectral data (Table 4.1). The spectroscopic properties of the CpM(NO)L2 compounds (Table 4.2) are consistent with t h e i r possessing the f a m i l i a r "three-legged piano s t o o l " molecular structures, i . e . L A L N 0 Thus, IR spectra of THF solutions of the complexes exhibit single strong absorptions i n the region 1625-1550 cm - 1 a t t r i b u t a b l e to terminal n i t r o s y l l i g a n d s . 4 ' 2 1 For a given L, the v „ 0 values diminish i n the order Cr » Mo Table 4.2 IR, 3 1P and *H NMR Data for the Complexes IR (THF) 31P{1H} NMR v N 0,cm - 1 (C6D6),6 CpCr(NO)[P(OMe)3]2 1624 229.3 CpMo(NO)[P(OMe)3l2 1592 206.1 CpW(N0)[P(0Me)3]2 1579 171.0 CpCr(N0)(PMePh2)2 1597 75.4 CpMo(N0)(PMePh2)2 1559 52.4 CpW(N0)(PMePh2)2 1548 16.2 CpMo(N0)[P(n-Bu)3]2 1551 CpMo(N0)(Ph2PCH2CH2PPh2) 1568 *H NMR (n5-c5H5) 4.73 (t, 3 J i H . 3 1 p = 2 - 2 8 H z ) 5.21 (t, 3 J i H . 3 1 p " 0 - 7 9 H z ) 5.13 (t, 3 J i H _ 3 1 p - n - 8 1 H z ) 4.51 (t, 3J l H_ 3 1 p-2.15 Hz) 4.93 (t, 3Ji H_3i p=0.93 Hz) 4.93 (t, 3 J i H _ 3 i p - 0 . 9 0 Hz) 5.05 (t, 3 J l H _ 3 1 p = 0 - 6 3 ««) 5.00 (s) 4.92 (t, 3Jl H_31 p=0.5 Hz) 6 D6>» 6 L 3.52 (m, 18^1^11.00 Hz.CHp 3.52 (m,18H,N-11.69 Hz, CH3) 3.54 (m,18H,N-11.74 Hz, CH3) 7.6-6.9 (m^OH.CgH^), 1.39 (m,6H,N-7.04 Hz.CHj) 7.6-6.9 (m,20H, CgHg), 1.50 (m,6H,N»6.92 Hz.ClLj) 7.6- 6.9 (m.lOH.CgHg), 1.61 (m,6H,N-7.67 Hz, CHj) 2.1-1.2 (m,36H,(CH2)3CH3), 1.15-0.85 (m,18H,(CH2)3CH3) 7.7- 7.4 (m,12H,C6H5), 7.25-6.95 (m.lSH.CgHj) 8.3-8.0 (m^H.CgH^), 7.5-6.9 (m.UH.CgHj), 2.7-1.8 (m,4H,CH2) o Table 4.2 IR, 3 1 P and *H NMR Data for the Complexes (continued) CpMo(NO)I2(PMePh2)- 1668 5.71 (d, 3 J l H _ 3 1 p « 2 . 6 3 Hz) 7.7-7.4 (m.lOH.C^), 2.68 (d,3H, 2J l H_ 3 1 p«9.86 Hz.Cl^) CpMo(NO)I 2[P(OMe) 3]^ 1678 6.02 (d, 3 J l a _ 3 1 p - 2 . 5 5 Hz) 3.88 (d,9H, 3J l H_ 3 1 p-11.00 Hz.CHj) CpMo(N0)I2(0PMePh2)^- 1669 6.19 (s) 8.0-7.4 (m.lOH.CgHg), 2.20 (d,3H, 2J l H_ 3 1 p»13.22 Hz.CHj) [CpMo(N0)I(PMePh 2) 2]I- 1668 10.7 5.77 (t, 3 J l a _ 3 1 p - 2 . 1 8 Hz) 7.9-7.4 (m^OH.C^), 2.86 (t,6H,N=9.48 Hz, CH3) [CpMo(NO)I(Ph 2PCH 2CH 2PPh 2]I- 1684 62.7,36.3 5.67 (d, 3J l f l _ 3 1 p o 2.42 Hz) 8.12-8.02 (m^H.CgHg), (d» 2J31 P.31p 7.70-7.25 ( m . ^ . C ^ ) , »41 Hz) 4.78 (br.lH.P-CH^-CH^-P), 3.38 (dm.lH.P-CH^g-CH^Hp-P), 3.07 (ddt.lH.P-CH^Hg-CH^-P), 1.85 (m, IH, P-CH^HJJ-CH^JJ-P ) L The integrations of the resonances due to the cyclopentadienyl protons were often lower than required because of their long relaxtion times.^ — N " lJAX + JAX,I a s d e f l n e d i n F l g " r e 3* — NMR spectra recorded in CDCI3. vO 92 > W, thereby r e f l e c t i n g increased M •*• NO backbonding, a trend that has previously been observed for other organometallic n i t r o s y l complexes 24 containing these t r a n s i t i o n metals. Furthermore, for a given M (e.g. Mo), v N Q decreases as L varies i n the order P(OMe) 3 > PMePh2 > P(n-Bu) 3, a trend consistent with the documented electron-donating and -accepting properties of these phosphorus-containing l i g a n d s . 1 7 F i n a l l y , i t must be noted that the frequency of the n i t r o s y l - s t r e t c h i n g absorptions observed i s strongly dependent on the solvent employed. Indeed, the v ^ Q ' S vary 25 l i n e a r l y with the "acceptor number" of the solvent, as i l l u s t r a t e d i n Figure 4.1 for CpMo(NO)(PMePh 2) 2 and CpMo(NO)[P(OMe) 3] 2. This v a r i a t i o n simply r e f l e c t s the a b i l i t y of the indicated solvents to function as Lewis acids towards the CpMo(NO)L2 complexes v i a the lone pair of electrons on 26 the oxygen atoms of the NO groups. Previous studies i n these labora-t o r i e s have demonstrated that the related CpM(NO)(CO)2 (M = Cr, Mo, W) complexes form analogous i s o n i t r o s y l linkages with strong Lewis acids such 27 as Cp 3Ln (Ln = a lanthanide metal). Hence, i t i s not s u r p r i s i n g that the r e l a t i v e l y e l e c t r o n - r i c h NO ligands i n the CpM(NO)L2 complexes can function as Lewis bases towards weaker Lewis acids such as the organic solvents indicated i n Figure 4.1. The acid-base interactions i n the l a t t e r cases are not s u f f i c i e n t l y strong, however, to permit the i s o l a t i o n of these adducts. The 3 1 P NMR spectra of the CpM(NO)L2 complexes exhibit a number of i n t e r e s t i n g features, the 3 1P{ 1H} data being presented i n Table 4.2. F i r s t l y , for a given L, the s h i e l d i n g of the 3 1 P resonances increases i n 93 Figure 4.1 V a r i a t i o n of vN Q with the acceptor number (AN) of the s o l v e n t s = CpMo(NO)[P(OMe) 3] 2, O = CpMo(NO)(PMePh2) 2) . 201 CH2CI FDMF AN HAcetoi 1<H M HF hEtoO 0 J-Hex/ 1600 1550 V N O > c m •1 94 the order Cr < Mo < W. This trend i s as expected on the basis of the r e l a t i v e electron densities a v a i l a b l e at the metal centers and i s i n accord with the trend i n v ^ values discussed i n the preceding paragraph. However, the magnitude of the chemical s h i f t difference between analogous Mo and W complexes (~35 ppm) i s somewhat larger than might be a n t i c i -28 pated. For instance, for the compounds M(CO)gL and c i s - and trans-M(CO) 1 +L 2 (M = Cr, Mo, or W; L = phosphine), a consecutive s h i f t of the 3 1 P NMR signal to higher f i e l d by only ~20 ppm occurs as M varies from Cr to Mo to W. Secondly, the 31p_183 w coupling constants of the CpW(NO)L2 compounds are much larger than those observed for related carbonyl complexes. Thus, J 3 i p _ i 8 3 w for CpW(NO)[P(OMe) 3] 2 and CpW(NO)(PMePh2)2 i s 689 and 481 Hz, re s p e c t i v e l y , whereas for CpW(CO)2LX (X = SnMe3, PbMe3 or Me) i t i s ~490 Hz when L = P(OMe) 3 and ~305 Hz when L = PMePh2. Indeed, the 31 P_183 W coupling constant of CpW(NO)[P(OMe) 3] 2 appears to be the largest of i t s kind yet reported and resembles most nearly those found f or analogous n i t r o s y l complexes, e.g. 595 Hz for [CpW(NO)H{P(OPh) 3}] 2. 5 b F i n a l l y , as shown i n Figure 4.2, the proton-coupled 3 1 P NMR spectra of the CpM(NO)[P(OMe) 3] 2 species are highly second-order ( i . e . a X 9AA'X 9' spin system). Nevertheless, the signals are c l e a r l y resolved for the tungsten complex but progressively less so for the molybdenum and chromium congeners. The 1H NMR spectra of the CpM(NO)L2 complexes (Table 4.2) also display several informative features. The resonance for the cyclopentadienyl protons of each compound i s a t r i p l e t due to coupling of 95 96 the signal to two equivalent phosphorus n u c l e i . The values of 3 J i j j _ 3 i p of ~0.6-0.9 Hz for the molybdenum and tungsten compounds and ~2.2 Hz for the 4 chromium analogues are normal. More i n t e r e s t i n g are the multiplets due to the protons of the methyl groups i n the P(OMe) 3 and PMePh2 complexes. As shown i n Figure 4.2, these multiplets of the CpM(NO)[P(OMe) 3] 2 compounds are examples of second-order spectra r e f l e c t i n g the existence of v i r t u a l coupling a r i s i n g from the presence of chemically equivalent but magnetically inequivalent methyl protons. While these e n t i t i e s constitute an X 9AA'X 9' spin system, the methyl proton signals exhibited by the tungsten complex approach the l i m i t of an AX 9 spin system, those of the chromium compound approach the l i m i t of an A 2 X l g spin system, while those 29 of the molybdenum complex are somewhere i n between these l i m i t i n g cases. These spectral patterns can be analyzed by the method developed by Harris 30 for such X AA'X ' spin systems, a method that has been previously n n employed to analyze the *H NMR spectra of complexes such as M(C0)^LL' (M = ) 31 b Cr, Mo, W; L, L' = phosphine or phosphite), ' M(Me)(CO) 2L 2L* (M = Fe, Ru; L = PMe3; L' = phosphine), 3 1° and W(N0) 2C1 2L 2 (L = P(0Me) 3, PMePh2 32 e t c ) . Such an analysis affords values of N, S^(l) and S^(2) (see Figure 33 4.3) from which the absolute values of the coupling constants and J ^ , (and the r e l a t i v e signs of J ^ a n d J ^ t ) may he computed (absolute 28 31' signs were assigned by comparison to l i t e r a t u r e values ' for rel a t e d compounds). These l a t t e r values correspond to 2J3ip_3ip» 3«JiH_3ip a n d 5 ^ l j j 31p» r e s p e c t i v e l y , for the P(0Me) 3 complexes and are tabulated for 97 Figure 4.3 XH NMR spectrum of CpW(NO)[P(OMe) 3] 2 i n the P(OMe) 3 region. N S|(2) Sjd) 10 Hz 98 the molybdenum- and tungsten-containing species i n Table 4.3. Regrettably, the r e q u i s i t e signals for the chromium complex are not s u f f i c i e n t l y resolved (see Figure 4.2) to permit the computation of i t s 2 J 3 i p _ 3 i p coupling constant. Nevertheless, i t i s cl e a r that t h i s parameter i s much more negative ( i . e . | 2 ^ 3 i p _ 3 i p | i s larger) than that for the molybdenum congener. A s i m i l a r trend of J 2 J 3 i p _ 3 i p | decreasing as the metal i s varied from Cr to Mo to W i s also evident i n the *H NMR spectra of the 29 CpM(NO)(PMePh 2) 2 compounds. Such a trend has been observed previously i n 28 31 28 other systems, ' and has been r a t i o n a l i z e d for octahedral complexes i n terms of a decrease i n energy of the E bonding molecular o r b i t a l (with respect to the T ^ and A ^ o r b i t a l s ) as a periodic group of t r a n s i t i o n metals i s descended. I t i s tempting to speculate that s i m i l a r changes i n the r e l a t i v e o r b i t a l energetics of the CpM(NO)L2 complexes may be at le a s t p a r t l y responsible for the observed trends i n t h e i r physical properties such as v N Q (Cr » Mo > W), 6 3 1 P (Cr > Mo » W), and 2 J 3 i p _ 3 i p ( C r < Mo < W). However, such an inference must obviously await a detailed t h e o r e t i c a l analysis and a photoelectron spectroscopic study of these compounds. Syntheses and Physical Properties of the Complexes CpMo(NO)I2L and [CpMo(NO)IL2]I (L - Lewis Base). Monitoring of the progress of the reduction reaction 4.4 when M = Mo by IR spectroscopy reveals that several intermediate species are formed on the way to the f i n a l CpMo(NO)L2 products (vide i n f r a ) . Some of these intermediate complexes may be synthesized and i s o l a t e d independently. For instance, the reaction 99 T a b l e 4.3 1H NMR Parameters for Methyl Resonances of CpM(NO)[P(OMe) 3] 2 (M = Mo, W). parameter— Mo W 6 (ppm) 3.52 3.54 N^ 11.69 11.74 S i ( l ) 1.21 3.06 Si(2) 3.49 7.52 l£ 11.91 12.16 2 J p p , -58.0 -22.6^-3 J H P 11-8 11.9 *JW -0.1 0.2 — A l l parameters except 6 are recorded i n Hz with C 6D 6 as solvent. — « - I 3 J H P + 5 J H P I f L- I 3 J H P - 5 J H P I — For t h i s complex, the value can be measured d i r e c t l y from the spectrum (Figure 4.3) and thi s gives a value of | J p p t | = 21.1 Hz (a good agreement). 3 3 100 CH2CI2 [CpMo(NO)I 2] 2 + 2L > 2 CpMo(N0)I 2L (4.11) (where L = PMePh2, P(0Me) 3 or 0PMePh2) proceeds smoothly to afford the indicated products i n high i s o l a t e d y i e l d s . The physical properties of the product complexes (summarized i n Tables 4.1 and 4.2) are s i m i l a r to those 34 reported previously for the analogous compounds having L = PPh 3, PMe2Ph, or P(0Ph) 3 which were prepared i n an i d e n t i c a l manner. S p e c i f i c a l l y , these properties are consistent with the CpMo(N0)I 2L complexes possessing monomeric "four-legged piano s t o o l " molecular structures i n which the two iodo ligands are mutually c i s , i . e . Mo Thus, the resonances due to the cyclopentadienyl protons i n the XH NMR spectra of the phosphine and phosphite complexes are doublets rather than 34b the s i n g l e t expected for the trans isomers. Curiously, t h i s resonance 101 of the 0PMePh2 complex i s deshielded by ~0.5 ppm r e l a t i v e to that of the PMePh2 species even though both complexes exhibit v i r t u a l l y i d e n t i c a l n i t r o s y l - s t r e t c h i n g frequencies i n t h e i r IR spectra (Table 4.2). It should also be noted at this point that the PMePh2 complex i s cleanly oxidized to i t s 0PMePh2 analogue by elemental oxygen, i . e . CDCI3 CpMo(N0)I 2(PMePh 2) + \ 02 > CpMo(N0)I 2(0PMePh 2) (4.12) ( v e r i f i a b l e by *H NMR spectroscopy) whereas uncomplexed PMePh2 i s unaffected by 0 2 under i d e n t i c a l experimental conditions. The second s u b s t i t u t i o n reaction, i . e . THF CpMo(N0)I 2L + L ^-> [CpMo(N0)IL 2]I (4.13) (where L = PMePh2) also proceeds straightforwardly. The i s o l a b l e 34b [CpMo(N0)I(PMePh 2) 2]I s a l t resembles i t s PMe2Ph analogue, and i t s physical properties (Tables 4.1 and 4.2) indicate that the cation possesses the trans, "four-legged piano s t o o l " molecular structure depicted below. 102 Ph2MeP PMePh NO + Hence, the *H NMR spectrum of the s a l t i n CDC13 displays t r i p l e t s for the resonances a t t r i b u t a b l e to the protons of the cyclopentadienyl and methyl groups. The dppe analogue of [CpMo(N0)I(PMePh 2) 2]I Is preparable i n an i d e n t i c a l manner, i . e . 32 THF. [CpMo(N0)I 2] 2 + 2 dppe 2 [CpMo(N0)I(dppe) ]I (4.14) but the spectroscopic properties of the product complex indicate that i n this case the organometallic cation possesses the novel c i s geometry, i . e . 103 + as a consequence of the chelating nature of the diphosphine l i g a n d . This feature i s most c l e a r l y evident i n the 3 1P{ 1H} and 1H NMR spectra of t h i s complex i n CDCI3. The former spectrum consists of two doublets ( 2J3ip_3ip= 41 Hz) centered at 6 62.7 and 36.3 due to two coordinated phosphorus atoms 1 1 i n markedly d i f f e r e n t chemical environments. The more deshielded doublet i s probably due to the phosphorus atom situated trans to the 35 strongly electron-withdrawing n i t r o s y l ligand i n the metal's coordination sphere. In a complementary fashion, the *H NMR spectrum confirms that the sig n a l due to the C 5H 5 protons i s coupled to only one of the phosphorus atoms, presumably the one c i s to the NO group. This inference i s consistent with the observations (vide supra) that i n trans-[CpMo(NO)I(PMePh 2) 2]I the cyclopentadienyl proton signal i s coupled to both 104 phosphorus atoms and i n CpMo(N0)I 2L i t exhibits coupling to 3 1 P only i n the 34 c i s isomer. F i n a l l y , as tabulated i n Table 4.2, each of the methylene protons of the bound dppe ligand gives r i s e to *H NMR signals having quite d i f f e r e n t chemical s h i f t s ( i . e . 6 1.85, 3.07, 3.38 and 4.78). This feature i s simply a manifestation of the d i f f e r i n g s p a t i a l o r i e n t a t i o n of these protons, i . e . c i s or trans with respect to the n i t r o s y l ligand and towards or away from the cyclopentadienyl r i n g . It seems l i k e l y that the two sets of deshielded resonances are due to the methylene protons (designated as H^and H^ i n the above structure and Table 4.2) nearest to the phosphorus atom which i s trans to the NO group. Mechanism of the Reductive Synthesis of the CpM(N0)L2 Complexes. Monitoring of the progress of the reaction [CpMo(N0)X 2] 2 + 4 Na/Hg + 4L 2 CpMo(N0)L 2 + 4 NaX + Hg (4.4) (where X = Br or I) by IR spectroscopy indicates the transient formation of a number of intermediate n i t r o s y l complexes p r i o r to the ultimate formation of the desired CpMo(N0)L 2 products. Complete d e t a i l s of such monitoring of i n d i v i d u a l reactions are presented In the Experimental Section. These conversions are p a r t i c u l a r l y convenient to follow since they proceed at r e l a t i v e l y slow rates and the intermediate species generally a t t a i n detectable concentrations. The various molybdenum-containing intermediates that have been detected during reaction 4.4 are summarized i n Table 4.4. The transient existence of these species i s consistent with the o v e r a l l 105 Table 4.4 N i t r o s y l - s t r e t c h i n g Frequencies of Complexes Detectable by IR Spectroscopy During Reductions of [CpMo(N0)X 2] 2 by Na/Hg i n THF i n the Presence of 4L.— complex v N Q (THF), cm"1 X = I X = I X = I X = Br L=PMePh2 L=P(0Me) 3 L=P(n-Bu) 3 L=PMePh. CpMo(N0)X2(THF) CpMo(N0)X2L [CpMo(N0)XL 2]X CpMo(N0)XL» CpMo(N0)L 2 1691 1668 1668 1614 1559 1691 1678 c_ 1626 1592 1691 1659 1654 1611 1551 1691 1665^ 1665*-1610 1559 — For reference, the v N Q of [CpMo(N0)I] 2 i n THF i s 1617 cm - 1. — Assigned by analogy to the analogous iodo complexes. — This complex i s presently unknown. / 106 reaction 4.4 proceeding v i a the sequential transformations summarized i n Scheme 4.1 for X = I. The proposed mechanistic pathway presented i n t h i s Scheme best accounts for our experimental observations and i s most i n accord with l i t e r a t u r e precedents. The experimental evidence on which these mechanistic proposals are based i s considered i n d e t a i l i n the following paragraphs. The i n i t i a l dimeric reactant, [CpMo(N0)I 2] 2» i s v i r t u a l l y insoluble i n polar, noncoordinating solvents such as CH 2C1 2, but i s extremely soluble i n coordinating solvents such as acetone or dimethylsulfoxide. In these 34 l a t t e r solvents, i t has been shown f i r s t to cleave r a p i d l y to the solvated monomer, i . e . [CpMo(N0)I 2] 2 + 2 S < > 2 CpMo(N0)I 2S (4.15) (where S = solvent) and then to convert more slowly (~30 min i n acetone under ambient conditions) into the s a l t containing the disolvated cati o n , i . e . CpMo(N0)I 2S + s ^ > [CpMo(N0)IS 2]I (4.16) 34 As indicated, both reactions 4.15 and 4.16 are r e v e r s i b l e . Since THF and 25 acetone have s i m i l a r coordinating properties and [CpMo(N0)I 2] 2 i s f r e e l y soluble i n THF, i t seems l i k e l y that the d i i o d i d e species present i n THF solutions (v„„ 1691 cm - 1) of the complex i s a c t u a l l y CpMo(N0)I 2(THF). It 107 Scheme 4.1 CpMo(NO)L 2 108 is u n l i k e l y , however, that [CpMo(NO)I(THF) 2]I i s formed i n any appreciable amounts during the reduction reaction 4.4 since i t s THF-containing precursor reacts very r a p i d l y with the various Lewis bases present. Indeed, the f i r s t species to be observable by IR spectroscopy of the reduction reaction mixtures i s usually not the solvated s t a r t i n g material 36 having i n THF at 1691 cm - 1. Rather, n i t r o s y l - s t r e t c h i n g absorptions i n the region 1650-1680 cm - 1 appear, and these s p e c t r a l features may be attributed (Table 4.4) to the presence of the complexes CpMo(N0)I 2L and/or [CpMo(N0)IL 2]I which are formed v i a steps a and b of Scheme 4.1. As described i n the preceding section, the formation of the CpMo(N0)I 2L complexes from [CpMo(N0)I 2] 2 i s very rapid, even when the transformation i s effected heterogeneously i n CH 2C1 2 ( c f . reaction 4.11). Hence, during the reduction reaction 4.4, these complexes r e s u l t from either of the reactions THF [CpMo(N0)I 2] 2 + 2 L -^-> 2 CpMo(N0)I 2L (4.17) THF CpMo(NO)I 2(THF) + L •==•> CpMo(N0)I 2L + THF (4.18) the l a t t e r probably being the dominant pathway for step a. In contrast, the rate of the next step i n the sequence ( i . e . b i n Scheme 4.1) i s depen-dent on the nature of L. When L = PMePh2, step b i s rapid ( c f . reaction f 109 4.13), and so the predominant unreduced species i n solution must be [CpMo(NO)I 2(PMePh 2) 2]I. Unfortunately, the n i t r o s y l - s t r e t c h i n g absorption of this s a l t i n THF (1668 cm"1) i s i d e n t i c a l to that exhibited by CpMo(N0)l2(PMePh 2) i n the same solvent, a fact v e r i f i a b l e by independent syntheses of the two organometallic complexes (vide supra). When L = P(n-Bu) 3, both CpMo(N0)I 2[P(n-Bu) 3] ( v N Q i n THF of 1659 cm - 1) and then [CpMo(NO)I{P(n-Bu) 3} 2]I ( v N Q i n THF of 1654 cm"1) are observable, thereby i n d i c a t i n g that i n t h i s case step b i s occurring at a somewhat slower rate than step a. F i n a l l y , when L = P(0Me) 3, only CpMo(NO)I 2[P(OMe) 3] ( v N Q i n THF at 1678 cm"1) i s present during the reduction reaction 4.4. Indeed, the cation, [CpMo(NO)I(P(OMe) 3) 2]I i s not available v i a the route used to 37 form Its PMePh2 analogue ( c f . reaction 4.13). The reduction of [CpMo(NO)I 2] 2 to [CpMo(N0)I] 2 (step c of Scheme 7 38 4.1) i s a very f a c i l e process, ' the monoiodide dimer being generally synthesized on a preparative scale by t h i s conversion, e.g.^ 2 CpMo(N0)(C0) 2 [CpMo(NO)I 2] 2 b e n z e n e > 1 0 o » c > [CpMo(N0)I] 2 (84%) (4.19) In the context of step c, we have found that conversion 4.19 may also be effected i n high y i e l d s i n THF at ambient conditions when Na/Hg, Zn/Hg, Mg or just Hg are employed as the reducing agents i n place of CpMo(N0)(C0) 2. However, since [CpMo(N0)I 2] 2 i s r a p i d l y converted to the CpMo(N0)I 2L species i n the presence of Lewis bases, L, i t i s u n l i k e l y that the r e l a -t i v e l y slower step c contributes s i g n i f i c a n t l y to the o v e r a l l reduction 110 reactions leading to the CpMo(N0)L 2 products. Reduction of the CpMo(N0)I 2li complexes with one equivalent of sodium amalgam (step d of Scheme 4.1), i . e . THF CpMo(N0)I 2L + Na/Hg ^-> CpMo(N0)IL- + NaT + Hg (4.20) has been effected independently for the cases when L = PMePh2 or P(0Me) 3. Both reactions 4.20 proceed to completion i n high y i e l d s (> 80% as monitored by IR spectroscopy) i n under f i v e minutes at room temperature. The i n i t i a l l y red solutions become green, and the n i t r o s y l bands s h i f t from 1668 and 1678 cm - 1 to 1614 and 1626 cm - 1 for the PMePh2 and P(0Me) 3 complexes, r e s p e c t i v e l y . During the reduction of the PMePh2 complex, i t i s noteworthy that as long as s t a r t i n g material Is present (V^Q 1668 cm - 1), then i n addition to the medium i n t e n s i t y band at 1614 cm - 1 (assignable to CpMo(NO)I(PMePh2)•) there i s also a weak band at 1645 cm - 1 i n the IR spectrum of the reaction mixture. This weak band disappears, however, as soon as a l l the CpMo(NO)I 2(PMePh 2) i s consumed, and the f i n a l green sol u t i o n exhibits n i t r o s y l bands at only 1614 (s) and 1559 (w) cm - 1, the l a t t e r being diagnostic for CpMo(NO)(PMePh 2) 2. I t seems most reasonable to propose that the weak band at 1645 cm - 1 i s due to the NO ligand of CpMo(NO)I 2(PMePh 2)~, the 19-electron r a d i c a l anion formed by electron transfer to the i n i t i a l organometallic reactant. This r a d i c a l anion must then r a p i d l y and i r r e v e r s i b l y lose I " to form the r e l a t i v e l y more stable, 17-electron CpMo(NO)I(PMePh2)• r a d i c a l . In other words, step d probably I l l involves the sequential conversions CpMo(NO)I 2L + Na/Hg — > CpMo(N0)I 2L~ + Na+ + Hg (4.21) — THF CpMo(NO)I 2L. CpMo(NO)IL. + I" (4.22) the CpMo(NO)I 2L~ intermediate being detectable spectroscopically for L = PMePh2 but not for L = P(OMe) 3. This r e f l e c t s the fact that for L = PMePh 2 > the rate of reaction 4.21 must be greater than that of reaction 4.22 at least u n t i l steady-state conditions are attained. Obviously, confirmation of the occurrence of reactions 4.21 and 4.22 must await the r e s u l t s of d e t a i l e d electrochemical investigations of the redox properties of the various CpMo(NO)I2L complexes. Once formed, the green CpMo(NO)IL« r a d i c a l s are stable i n THF solutions for several hours at ambient temperatures, thus i n d i c a t i n g that step g of Scheme 4.1 must make a n e g l i g i b l e contribution to the o v e r a l l reduction reaction 4.4. They do, however, begin to decompose eventually i n these solutions, the rate of decomposition increasing markedly when solvent i s removed under reduced pressure. This thermal i n s t a b i l i t y has so far thwarted a l l attempts to i s o l a t e these very a i r - s e n s i t i v e , paramagnetic species. The p r i n c i p a l decomposition products appear to be [CpMo(NO)I] 2 and free L ( i . e . step {>), although other as yet u n i d e n t i f i e d compounds are also formed. This observation i s consistent with the f a c t that the reverse of step j» ( i . e . step f ) does not occur under ordinary conditions, i . e . 112 [CpMo(NO)I] 2 + 2L 2 CpMo(NO)IL» (4.23) and at elevated temperatures i t just affords n i t r o s y l - c o n t a i n i n g products r e s u l t i n g from the thermal decomposition of the dimeric reactant, i . e . 39 CpMo(NO) 2I. [In contrast, reaction 4.23 proceeds smoothly and nearly q u a n t i t a t i v e l y for the congeneric chromium complexes.]** Nevertheless, the formulation of the CpMo(NO)IL» r a d i c a l s as such i s supported by the facts that (a) the i r green THF solutions exhibit strong ( a l b e i t broad) ESR signals, (b) the analogous, well-characterized^ CpCr(NO)XL« (X = C l , Br or I) 17-electron species are also green, and (c) the chromium congeners also exhibit v J J Q ' s within 10 cm - 1 of t h e i r precursor dimers ( c f . reaction 40 4.23). No other reasonable formulation for the molybdenum-containing species i s r e a d i l y apparent. The reduction of the monoiodo dimer to the f i n a l product (step I of Scheme 4.1), i . e . THF [CpMo(N0)I] 2 + 2 Na/Hg + 4L — > 2 CpMo(N0)L 2 + 2 Nal + Hg (4.24) has been performed s t o i c h i o m e t r i c a l l y for the case when L = PMePh2. The conversion i s complete at room temperature i n approximately f i v e minutes, and IR monitoring of i t s progress reveals the replacement of the n i t r o s y l band of the reactant at 1617 cm - 1 by the analogous absorption due to the product at 1559 cm - 1. There i s no evidence ( i . e . development of a green c o l o r a t i o n or v„„ at 1614 cm - 1) for the formation of r a d i c a l intermediates NO 113 such as CpMo(NO)I(PMePh2)• during t h i s transformation. Reaction 4.24 i s also not the only process occurring i n t h i s mixture as evidenced by the facts that the desired CpMo(NO)[PMePh 2] 2 product i s i s o l a b l e i n only 34% y i e l d and an IR spectrum of the f i n a l reaction mixture contains bands at 1530 and 1580 cm - 1 due to uncharacterized n i t r o s y l - c o n t a i n i n g by-products. It thus appears that even the r e l a t i v e l y n u c l e o p h i l i c PMePh2 does not e f f i c i e n t l y trap whatever solvated intermediates are generated during t h i s reduction. In any event, we have already concluded that steps c and g of Scheme 4.1 produce l i t t l e , i f any, of [CpMo(N0)I] 2 during the o v e r a l l reduction reactions 4.4. On the basis of our observations concerning reaction 4.24, we can further conclude that step i contributes n e g l i g i b l y to the o v e r a l l y i e l d of the CpMo(N0)L2 products. Hence, only steps ^ and k remain as v i a b l e paths by which these products may be formed. When CpMo(N0)I 2L (L = PMePh2 or P(0Me) 3) i s treated with an excess of sodium amalgam i n THF at room temperature, the f i r s t step (d i n Scheme 4.1, reactions 4.21 and 4.22) to produce CpMo(N0)IL» i n nearly quantitative y i e l d i s complete i n ~1 min (as judged from IR monitoring). The next step £ requires ~ 15 min to reach completion, and no n i t r o s y l - c o n t a i n i n g intermediates or by-products are detectable during t h i s conversion. This l a t t e r step probably involves the sequential reactions CpMo(N0)IL« + Na/Hg THF. -> CpMo(N0)L(THF) + Nal + Hg (4.25) CpMo(NO)L(THF) + L THF. -> CpMo(N0)L2 + THF ( 4 . 2 6 ) 114 where the second L required for reaction 4.26 i s produced by thermal decom-41 p o s i t i o n of CpMo(NO)IL' (vide supra) and CpMo(NO)L(THF) (vide i n f r a ) . When L = PMePh2, the o v e r a l l reaction represented by steps d and ^  (with no free phosphine added) affords the f i n a l CpMo(NO)(PMePh 2) 2 product i n 76% is o l a t e d y i e l d with respect to the bound phosphine i n i t i a l l y present. This observation indicates that the presence of one coordinated PMePh2 ligand s t a b i l i z e s the intermediate CpMo(NO)(PMePh2)(THF) species long enough to permit i t to be trapped by ad d i t i o n a l PMePh2 i n good y i e l d (reaction 4.26). In contrast, when L = P(OMe) 3, the second step ^ produces CpMo(NO)[P(OMe) 3] 2 i n only 10% i s o l a t e d y i e l d with respect to ava i l a b l e P(0Me) 3. It thus appears that P(0Me) 3, being a weaker Lewis base, does not s t a b i l i z e the intermediate complex, CpMo(NO)[P(OMe) 3](THF), nearly as well and hence reaction 4.26 i n this case proceeds to a markedly lesser extent. This rat i o n a l e explains why the o v e r a l l reduction reaction 4.4 produces the f i n a l CpMo(NO)[P(OMe) 3] 2 product i n r e l a t i v e l y lower y i e l d s ( i . e . ~ one-42 half that of th e i r PMePh2 analogues). Similar reasoning also accounts for the observation that less basic organic ligands such as dienes or alkynes are incorporated into the molybdenum's coordination sphere i n even 2 lower ( i . e . 0-10%) o v e r a l l y i e l d s . The f i n a l pathway leading to the CpMo(N0)L 2 products which begins with step e of Scheme 4.1 s h a l l now be considered for the s p e c i f i c case when L = PMePh2. When [CpMo(NO)I(PMePh 2) 2]I i s reduced i n THF with an excess of sodium amalgam, i . e . 115 [CpMo(NO)I(PMePh 2) 2]I + 2 Na/Hg -^^-> CpMo(NO)(PMePh 2) 2 + 2 Nal + Hg (4.27) the f i n a l organometallic product i s obtainable i n 80% i s o l a t e d y i e l d . Monitoring of the progress of reaction 4.27 by IR spectroscopy indicates that two n i t r o s y l - c o n t a i n i n g intermediates are produced during the course of t h i s conversion. Thus, bands at 1644 and 1614 cm - 1 appear together i n the i n i t i a l l y green, supernatant solution over the suspended, yellow s t a r t i n g m aterial. After the [CpMo(NO)I(PMePh 2) 2]I s a l t has a l l been consumed, the band at 1644 cm - 1 In the green so l u t i o n disappears immediately while that at 1614 cm - 1 diminishes i n i n t e n s i t y more slowly and i s eventually replaced by the f i n a l product band at 1559 cm - 1 as the supernatant s o l u t i o n concomitantly becomes orange i n c o l o r . These observations are consistent with the f i r s t intermediate (v.T_ i n THF at 1644 NO cm - 1) being formed by electron transfer from sodium amalgam to the cation of the i n i t i a l reactant (step e of Scheme 4.1), i . e . THF [CpMo(N0)I(PMePh 2) 2]I + Na/Hg - i ^ > CpMo(N0)I(PMePh 2) 2» + Nal + Hg (4.28) The 19-electron r a d i c a l thus produced i s analogous to the r a d i c a l anions 43 invoked e a r l i e r during step d ( i . e . equation 4.21). Once formed, t h i s r a d i c a l can then, i n p r i n c i p l e , undergo the two competing reactions desig-nated as steps h and k i n Scheme 4.1, i . e . 116 THF CpMo(N0)I(PMePh2)2, > CpMo(NO)I(PMePh2)• + PMePh2 (4.29) THF CpMo(NO)I(PMePh 2) 2« + Na/Hg > CpMo(NO)(PMePh 2) 2 + Nal + Hg (4.30) Reaction 4.29 (step h) produces the f a m i l i a r 17-electron CpMo(N0)I(PMePh 2)» r a d i c a l ( V N Q i n THF at 1614 cm - 1) which could then undergo reduction v i a step ^ as described above. Reaction 4.30 (step k), on the other hand, affords the desired CpMo(NO)(PMePh 2) 2 d i r e c t l y . However, as with reactions 4.21 and 4.22, p o s i t i v e i d e n t i f i c a t i o n of these r a d i c a l species as well as a determination of the r e l a t i v e rates of reactions 4.29 and 4.30 must await a detailed electrochemical study of these processes. In summary, then, our experimental observations indicate that the o v e r a l l reduction reaction THF [CpMo(N0)I 2] 2 + 4 Na/Hg + 4L > 2 CpMo(N0)L2 + 4 Nal + Hg (4.4) proceeds v i a steps a, d, and ^ of Scheme 4.1 when L = P(0Me) 3 or weaker Lewis bases. However, when L = PMePh2, i t proceeds v i a a more complex pathway a f t e r step a i s traversed. In this case, steps b + e and d compete, with reduction e probably becoming dominant af t e r ~ 1 min into reaction 4.4 at which point step b should be e s s e n t i a l l y complete. Once the CpMo(N0)I(PMePh 2) 2» r a d i c a l i s formed, i t i s then r a p i d l y converted to the CpMo(NO)I(PMePh 2) 2 product v i a either step k or steps h and ^. 117 Analyses of the IR spectral changes accompanying reaction 4.4 when L = P(n-Bu) 3 and the analogous conversion involving [CpMo(NO)Br 2] 2 and L = PMePh2 (Table 4.4) suggest that these two reductions also follow the more complex pathway. It i s i n t e r e s t i n g to note that during the s i m i l a r reductions of [CpW(NO)I 2] 2 and [CpCr(NO)I] 2, no p a r t l y reduced, intermediate n i t r o s y l complexes are detectable by IR spectroscopy. In the tungsten case, the n i t r o s y l bands of the unreduced reactant (either CpW(NO)I2L or [CpW(NO)IL 2]I) are cleanly replaced by the analogous absorptions of the CpW(NO)L2 products. This observation indicates that i n t h i s case the steps analogous to ^ and k i n Scheme I must be fa s t e r than those analogous to d and e i f a s i m i l a r mechanism i s operative. [Exactly the opposite i s true for the molybdenum complexes.] In the chromium case, the i n i t i a l l y observed n i t r o s y l bands are those of the well-known** CpCr(NO)IL« r a d i c a l s (e.g. v N Q i n THF at 1668 cm - 1 f o r L = PMePh 2). The reduction pathway i n t h i s case thus involves steps analogous to f and £ and not i as occurs for the congeneric molybdenum complexes (for which step f does not occur). Conclusions This work has established that reduction of the i o d o n i t r o s y l dimers, [CpMo(NO)I n] 2 (M = Cr, n = 1; M = Mo or W, n = 2), with sodium amalgam i n THF i n the presence of group 15 Lewis bases, L, conveniently affords the otherwise inaccessible CpM(NO)L2 complexes i n moderate to high i s o l a t e d y i e l d s . The spectroscopic properties of the CpM(NO)L2 products 118 exhibit a number of Interesting, metal-dependent trends. The observed changes i n v N Q (Cr » Mo > W), 6 3 1 P (Cr < Mo « W), and 2 J 3 i p _ 3 i p (Cr < Mo < W) may well be a manifestation of the d i f f e r i n g o r b i t a l energetics of the compounds ( i . e . a diminishing separation i n energy between the highest occupied molecular o r b i t a l s and the next lowest f i l l e d molecular o r b i t a l s ) as the metal varies from Cr to Mo to W. Our experimental observations of various bulk and stoichiometric reduction reactions have led us to propose a u n i f i e d mechanistic pathway for the o v e r a l l reduction reactions of the [CpM(NO)I n] 2 dimers which i s presented i n Scheme I for the case when M = Mo and n = 2. Furthermore, we have been able to draw the following general conclusions concerning t h i s mechanism: (1) when L = a strong Lewis base such as PMePh2 or P(n-Bu) 3, the predominant pathway involves steps a, b and e for the molybdenum complexes; poorer Lewis bases such as P(OMe) 3 r e s u l t i n steps a, d and ^ being followed. (2) L must be a r e l a t i v e l y good Lewis base to s t a b i l i z e species such as CpMo(NO)L(THF) which are probable intermediates during step ^ so that they may be trapped by a second L p r i o r to decomposition. (3) for the tungsten complexes, steps analogous to ^ and k are much fas t e r than for the congeneric molybdenum species; consequently, the presence of good s t a b i l i z i n g donor ligands i s of paramount importance i f CpW(N0)L2 products are to be obtained ( c f . conclusion 2 above). (4) for the chromium complexes, the o v e r a l l reduction reactions proceed v i a steps analogous to f and j,; hence, the L's present must be 119 s u f f i c i e n t l y basic to e f f e c t the cleavage involved i n the f i r s t step. These conclusions account for a number of trends encountered during the bulk reductions of the i o d o n i t r o s y l dimers, namely (a) conclusions 1-4 explain why these reductions r e s u l t i n much higher y i e l d s of the CpM(NO)L2 complexes when L i s a strong Lewis base (e.g. PMePh 2). (b) conclusions 3 and 4 explain why the y i e l d s of the Cr, Mo, and U complexes are s i m i l a r when strong Lewis bases are employed but are markedly les s for Cr i n the presence of weaker Lewis bases. (c) conclusions 1 and 2 explain why very weak Lewis bases such as a c y c l i c , conjugated dienes a f f o r d only low y i e l d s of the CpMo(NO)(n^-diene) complexes; furthermore, conclusions 3 and 4 account for why such diene complexes containing tungsten and chromium cannot be prepared i n an analogous manner. (d) conclusions 1 and 2 also explain why the reactions to form the CpMo(NO)(,nl+-diene) complexes proceed i n diminished y i e l d s when solvents that are poorer or better donors than THF are employed; the poorer donors (e.g. benzene) f a i l to s t a b i l i z e intermediate organometallic n i t r o s y l species, and the better donors (e.g. DME or CH3CN) preclude the incorpora-t i o n of the diene i n the molybdenum's coordination sphere. Despite the considerable i n s i g h t into the o v e r a l l reduction reaction 4.4 that has been gained during t h i s work, some questions remain unanswered. The most i n t r i g u i n g of these i s why the use of bulky phos-phines such as P(t^-Bu) 3 or PPh 3 during these reactions f a i l s to produce any 120 n i t r o s y l - c o n t a i n i n g products, even when such products (e.g. CpM(N0)(PPh 3) (M = Cr, Mo)) are preparable by other synthetic routes. 121 References and Notes (1) Taken i n part from: (a) Hunter, A.D.; Legzdins, P. Organometallics submitted for pu b l i c a t i o n , (b) Hunter, A.D.; Legzdins, P.; Martin, J.T.; Sanchez, L. Organomet. Synth. 3, i n press. (2) (a) Nurse, C.R., Ph.D. Di s s e r t a t i o n , University of B r i t i s h Columbia, Vancouver, B r i t i s h Columbia, 1984. (b) Hunter, A.D.; Legzdins, P.; Nurse, C.R.; E i n s t e i n , F.W.B.; W i l l i s , A.C. J . Am. Chem. Soc. 1985, Mm—.m, . • Mm Ml .. — .- /S^SJVMVN/ 107, 1791. (c) See Chapter F i v e . (3) Sellmann, D.; Kleinschmidt, E. Z. Naturforsch., B: Anorg. Chem.,  Org. Chem. 1977, 32B, 1010. (4) Brunner, H. J . Organomet. Chem. 1969, _1*>., 119. (5) (a) See Chapter Two. (b) Legzdins, P.; Martin, J.T.; Oxley, J.C. Organometallics 198j5, 4_, xxx, i n press. (6) Legzdins, P.; Nurse, CR. Inorg. Chem. 1985, 24, 327. (7) [CpMo(N0)I] 2 was prepared by a modification of the procedure described by James, T.A.; McCleverty, J.A. J . Chem. Soc. A 1971, 1068. (8) McCleverty, J.A.; Seddon, D. J . Chem. S o c , Dalton Trans. 1972, 2526. (9) Legzdins, P.; Martin, D.T.; Nurse, CR. Inorg. Chem. 1980, 19, 1560. (10) The elements N, P, As, Sb and Bi are so designated by the recently recommended notation: Chem. Eng. News 1985, Feb. 4, 26. (11) (a) Hunter, A.D.; Legzdins, P. Inorg. Chem. 1984, 23, 4198. (b) See 122 Chapter Three. (12) A l t e r n a t i v e l y , the r e q u i s i t e sodium amalgam may also be generated d i r e c t l y i n s i t u . (13) R e c r y s t a l l i z a t i o n of t h i s s o l i d from CH2C12/hexanes produced orange c r y s t a l s i n ~ 80% y i e l d of the desired product complex as a d i c h l o r o -methane solvate, i . e . CpMo(NO)(PMePh2)2.y CH 2C1 2. Anal. Calcd f o r C31 5H3]NOP2ClMo: C, 59.68; H, 5.09; N, 2.21. Found: C, 60.00; H. 5.14; N, 2.39. Its 1H NMR spectrum (CfiD6) contained the features presented i n Table 4.2 for the unsolvated material and a si n g l e t of the correct i n t e n s i t y at 6 5.29 a t t r i b u t a b l e to CH 2C1 2. (14) The 0PMePh2 reagent required for the synthesis of t h i s complex was prepared by the oxidation of PMePh2 with an excess of 30% H 20 2 i n acetone.1 5 Subsequent r e c r y s t a l l i z a t i o n of the f i n a l reaction residue from CH2C12/Et20/hexanes produced 0PMePh2 as a waxy, white s o l i d i n 77% y i e l d . lE NMR (CDC13): 6 7.9-7.4 (m, 10H, CgHg), 2.02 (d, 3H, J i H _ 3 l p = 13.2 Hz, CH3). 31P{1H> NMR (CDCI3): 6 27.97. Mp: 107-108°C. (15) This i s a modification of the procedure published by Steube, C ; LeSueur, W.M.: Norman, G.R. J . Am. Chem. Soc. 1955, 77, 3526. (16) Stewart, R.P.; Moore, G.T. Inorg. Chem. 1975, 14, 2699. (17) For a discussion of the Lewis b a s i c i t i e s and s t e r i c requirements of phosphines and phosphites see: Tolman, C.A. Chem. Rev. 1977,, 77, 313. 123 (18) Casey, CP.; Jones, W.D.; Harsy, S.G. J . Organomet. Chem. 1981, 206, C38. (19) Brunner, H.; Schindler, H.D.; Schmidt, E.; Vogel, M. J . Organomet. Chem. 1970, 24, 515. (20) (a) Brunner, H.; Doppelberger, J . B u l l . Soc. Chim. Belg. 1975, 84, 923. (b) Reisner, M.G.; Bernal, I.; Brunner, H.; Doppelberger, J . J . Chem. S o c , Dalton Trans. 1978, 1664. (c) King, R.B.; Gimeno, J . Inorg. Chem. 1978, 17, 2396. (21) Behrens, H.; Schindler, H. Z. Naturforsch., B: Anorg. Chem. Org. Chem. 1968, 23B, 1110. (22) Herberhold, M.; Smith, P.D.; A l t , H.G. J . Organomet. Chem. 1980, 191, 79 and references therein. (23) McPhail, A.T.; Knox, G.R.; Robertson, C.G.; Sim, G.A. J . Chem. S o c A 1971, 205. (24) Cf. Legzdins, P.; Malito, J.T. Inorg. Chem. 1975, 14, 1875. (25) (a) Mayer, U.; Gutmann, V.; Gerger, W. Monatsh. Chem. 1975, 106, 1235. (b) Gutmann, V. Ibid 1977, 108, 429. (26) Interaction of the solvents with other base s i t e s on the CpMo(N0)L2 complexes such as the metal center or the cyclopentadienyl ring would cause V ^ Q to increase i n energy as the Lewis a c i d i t y of the solvent 27 increased, a trend exactly opposite to that observed experimentally (Figure 1). (27) Crease, A.E.; Legzdins, P. J . Chem. S o c , Dalton Trans. 1973, 1501 and references therein. 124 (28) Pregosin, P.S.; Kunz, R.W. In "NMR, Basic P r i n c i p l e s and Progress"; Diehl, P.; Fluck, E.; Kosfeld, R., Eds; Springer-Verlag: New York, 1979; Vol. 16. (29) The  lE NMR spectra of the CpM(NO)(PMePh 2) 2 complexes exhibit s i m i l a r trends. However, the much lower Jij j _ 3 i p coupling constants existent i n these systems r e s u l t i n the i n t e r n a l l i n e s appearing as an envelope rather than as well-resolved s i g n a l s . (30) Harris, R.K. Can. J . Chem. 1964, 42, 2275. (31) See, for example: (a) Bertrand, R.D.; O g i l v i e , F.B.; Verkade, J.G. J . Am. Chem. Soc. 1970, 92, 1908 and 1916. (b) Schenk, W.A.; Buchner, W. Inorg. Chim. Acta 1983, 70, 189. (c) Pankowski, M.; Chodkiewicz, W.; Simonnin, M-P. Inorg. Chem. 1985, 24, 533. (32) The methyl proton signals displayed by these complexes approach the l i m i t of an A.2X^n (where n = 1 for L = PMePh2 and n = 3 for L = P(0Me) 3) spin system 1 1 and thus give r i s e to a v i r t u a l t r i p l e t . 3 ^ (33) If the outer pair of l i n e s i s observable (Figure 4.3), l-J^, | i s measurable d i r e c t l y . (34) (a) King, R.B. Inorg. Chem. 1967, 30. (b) James, T.A.; McCleverty, J.A. J . Chem. Soc. A 1971, 1596. (35) Chen, H.W.; J o l l y , W.L.; Xiang, S.F.; Legzdins, P. Inorg. Chem. 1981, 20, 1779 and references therein. (36) The only exception i s the case when L = P(n-Bu) 3 f o r which, a f t e r one minute of reaction, v M 's at 1691 and 1659 cm - 1 are evident. This 125 observation r e f l e c t s the o v e r a l l slower rate of th i s reduction reaction, presumably because of the slow d i s s o l u t i o n of P(n-Bu) 3 i n THF. It i s c e r t a i n l y not a r e f l e c t i o n of the Lewis b a s i c i t y of th i s phosphine since the analogous reaction with the equally basic PMe3 proceeds very r a p i d l y . " ^ (37) Christensen, N.J.; Hunter, A.D.; Legzdins P.; Sanchez, L. unpublished observations. (38) Hames, B.W.; Legzdins P.; Oxley, J.C. Inorg. Chem. 1980, 19, 1565. (39) Unlike i t s chromium analogue,** [CpMo(N0)I] 2 i s stable i n sol u t i o n at room temperature. At elevated temperatures, however, i t slowly decomposes, CpMo(N0) 2I being the only i s o l a b l e n i t r o s y l - c o n t a i n i n g product. (40) THF solutions of [CpMo(N0)I] 2 display a n i t r o s y l - s t r e t c h i n g absorp-t i o n at 1617 cm - 1. (41) If excess L were present, the CpMo(N0)L 2 products would also be produced v i a steps b and e i n a competitive fashion. (42) Recall that step i i s n e g l i g i b l e and step b does not occur for the P(0Me) 3 complexes. (43) The si m i l a r v N Q ' s i n THF of the 19-electron r a d i c a l s , CpMo(N0)I(PMePh 2) 2» (1644 cm - 1) and CpMo(N0)I 2(PMePh 2)~ (1645 cm - 1) are not p a r t i c u l a r l y s u r p r i s i n g since i t i s known that the i n t e r -change of I - and phosphine ligands such as PMe2Ph does not have a s i g n i f i c a n t e f f e c t on the n i t r o s y l - s t r e t c h i n g frequencies exhibited by related complexes. For instance, the V N 0 ' 8 (KBr) of 126 Et l tN[CpMo(NO)I 3], CpMo(NO)I 2(PMe 2Ph), and [CpMo(NO)I(PMe 2Ph) 2]I are Q 1650, 1650 and 1652 cm - 1, r e s p e c t i v e l y . 127 CHAPTER FIVE THE SYNTHESIS AND PHYSICAL PROPERTIES OF THE NOVEL CIS- AND TRANS-DIENE COMPLEXES CpMoCNOXn^-dlene)1 128 Introduction We recently Investigated the reduction of the i o d o n i t r o s y l dimers, [CpM(NO)I n] 2 (M=Cr, n=l; M=Mo or W, n=2), i n the presence of phosphines or phosphites ( L), i . e . THF [CpM(NO)I n] 2 + 2n Na/Hg + 4L •=-=—> 2 CpM(NO)L2 + 2n Nal + Hg (5.1) This reaction produces the desired e l e c t r o n - r i c h n i t r o s y l complexes, 2 CpM(NO)L2, i n moderate to high y i e l d s . Further, monitoring by IR spectro-scopy of the progress of the reaction (where M=Mo) revealed the transient formation of intermediate n i t r o s y l complexes. This, and the r e s u l t s from various stoichiometric reactions, were used to propose a u n i f i e d mechanism for the reductive syntheses seen i n equation 5.1 which accounts for the dependence of the yi e l d s of CpMo(NO)L2 on the nature of M (Mo > W » Cr), L, and the solvent employed. Indeed, the s t a b i l i z a t i o n of the solvated 2 "CpM(NO)" intermediate was found to be the key step i n th i s process. We recently reported that the related reduction reaction [CpM(NO)I 2] 2 + 4 Na/Hg + 2 diene — > CpMo(NO)(Ti l t-diene) + 4 Nal + Hg (5.2) (where diene=2-methylbutadiene, 2,3-dimethylbutadiene, or 2,5-dimethyl-2,4-hexadiene) when performed at ambient temperature i n THF produced the novel n^-trans-diene complexes, CpMo(NO)(n 4-trans-diene), i n ~10% y i e l d as 129 yellow, somewhat a i r - s e n s i t i v e c r y s t a l s . Based on the predictions a v a i l -able from the study of the mechanism of such reductions, we reasoned that the low o v e r a l l y i e l d s of diene products i s o l a t e d must r e f l e c t the i n a b i l i t y of the unsaturated organic ligand to trap e f f e c t i v e l y the solvated "CpMo(NO)" intermediate under the reaction conditions used. We therefore decided to extend our investigations of reaction 5.2. In so doing, we have extended the range of trans-diene products a v a i l a b l e , dramatically increased the y i e l d of reaction 5.2, and i s o l a t e d the f i r s t example of a new class of c i s - d i e n e n i t r o s y l complexes ( i . e . CpMo(NO)(Ti't-4 cis-2,3-dimethylbutadiene)• In Chapter Five, the complete r e s u l t s of my studies, including, the det a i l e d spectroscopic characterization of a l l i s o l a t e d products are reported. Experimental Section A l l reactions and subsequent manipulation were performed under anaerobic and anhydrous conditions i n a well - v e n t i l a t e d fume hood unless s p e c i f i e d otherwise. General procedures ro u t i n e l y employed have been 2 5 described i n d e t a i l previously. * The h a l o - n i t r o s y l reagents, [CpCr(NO)I] 2 6, [CpMo(NO)I 2] 2 7, [CpMo(NO)I] 2 7, [CpMo(NO)Br 2] 2, 8 [Cp Mo(N0)I 2] 2 ' (where Cp - n5-C5Me5) and [CpW(N0)I 2] 2, were prepared by published procedures. Proton NMR spectra were c o l l e c t e d on a Varian XL-300, Bruker WP-80 or WH-400 spectrometers with reference to the solvent used, but are reported i n ppm downfield from Me^Si. The following were performed on a Varian XL-300 spectrometer. To avoid unnecessary heating of the 130 samples, the low-power Waltz-16 broad band proton decoupling technique ( 1 3C{ 1H}) was used. The use of gated decoupling ({1H} off during data acquisition (~.8s) and on between acquisition (~1.6s)) allowed the collection of proton coupled 1 3C NMR spectra with excellent signal to noise and resolution in reasonable times (1-16 h). Proton nuclear Overhauser effect (NOE) difference experiments were collected using a 90° pulse (48 lis) with gated, low-power homonuclear decoupling (i.e. decoupling off during data acquisition (~2s) and on between acquisition (~4s)) of the Cp resonance, usually one or more diene methyl resonances and the "undecoupled spectrum" (where irradiation occured at one f i e l d width (~1500 Hz) downfield of the edge of the spectrum (i.e. at ~9.5 ppm)). Between 256 and 4864 transients ( i . e . ~l-24 h) of the interleaved spectra were collected and phased and then the appropriate pairs of FIDs were subtracted and Fourier transformed to give the fi n a l difference spectra. The two dimensional heterocorrelation (2D HETCOR) experiments used Varian's 2D HETCOR pulse program. The 90° 1 3C pulse was 11 us, the 90° *H pulse from the decoupler was 80 us, the acquisition time was ~0.1 s, and presaturation was used. The proton and carbon-13 spectral widths were 5 and 132 ppm centered at 2.8 and 70 ppm, respectively. The number of incremental spectra was 128, each containing between 32 and 160 2K transients ( i . e . between 2.4 and 12 h acquisition time). Zero f i l l i n g and a 2D-Fourier transformation resulted in a spectrum with a resolution of 6 Hz and 100 Hz in the proton and carbon dimensions, respectively. Preparation of CpMo(NO)(T)**-trans-dlene). A l l of these reactions 12 involved an excess of solid sodium amalgam liquefied with 2-5 mL of 131 mercury. The diene was also typically present in 5-20 fold excess. Method A* This reaction was performed in a similar manner and at ambient temperature for a l l dienes. The experimental procedure, using the case where diene = 2,5-dimethyl-2,4-hexadiene as a representative example, was as follows: To a flask containing sodium amalgam (10 mmol of Na in 5 mL Hg) and THF (80 mL) was added 2,5-dimethyl-2,4-hexadiene (2.0 mL) and [CpMo(N0)I2]2 (2.00 g, 2.25 mmol). The i n i t i a l red solution rapidly (<5 min) became yellow-brown as an exothermic reaction occurred. After being stirred for 15 min (to ensure completion of the reaction) the supernatant solution was filtered through alumina ( 3 x 5 cm, neutral, activity 1), washed with THF (3 x 25 mL) and the combined f i l t r a t e s were taken to dryness in vacuo. Crystallization of the resulting orange residue from hexanes at -20°C afforded CpMo(NO)(n1<-trans-2,5-dimethyl-2,4-hexadiene) (0.14 g, 10%) as yellow crystals. Other acylic conjugated dienes (except (E,E)-l,4-diphenyl-butadiene, vide infra) afforded the analogous CpMo(NO)(ri^-trans-diene) complexes in ~10% yields. The analytical, mass spectral, IR, and *H and 1 3C NMR data for these and the other new rt^-diene complexes synthesized during this work are collected in Tables 5.1-5.6. Method B. This reaction was performed in a similar manner for a l l dienes and the case where diene = (E,E)-2,4-hexadiene is presented as a representative example. A flask containing sodium amalgam (10 mmol of Na in 5 mL Hg) and THF (40 mL) was cooled to -20°C (using a saturated, aqueous CaCl, bath) and 132 then (E,E)-2,4-hexadiene (1.0 mL) and [CpMo(N0)I2]2 (2.00 g, 2.25 mmol) were added. The dark violet [CpMo(N0)I2]2 slowly dissolved to give a red solution whose IR spectrum i n i t i a l l y exhibited a single V ^ Q at 1691 cm - 1. After about 10 min the solution was dark brown and displayed two strong nitrosyl absorptions at 1691 and 1668 cm - 1 and two weak ones at 1580 and 1548 cm - 1. The low energy absorptions continued to increase in intensity at the expense of the other two. After 15 min the band at 1691 cm-1 had disappeared, that at 1668 cm"1 had broadened, weakened, and grown a shoulder (at 1653(w) cm - 1) and the other two absorptions had become more intense ( v N Q 1580(m) and 1548(s) cm - 1). After a further 5 min only the IR absorptions at 1651(w), 1580(m) and 1548(s) cm - 1 remained. These gradually decreased in intensity to give a yellow-brown solution having a weaker nitrosyl band at 1598(m) cm - 1. The final supernatant solution was f i l t e r -cannulated away from the mercury-containing residue. This residue was washed with THF (2x25 mL), the washings were combined with the i n i t i a l f i l t r a t e , and solvent was removed from this solution in vacuo. The resulting brown solid was extracted with Et 20 (4x30 mL) until the extracts were colorless and the resulting yellow-brown solution was taken to dryness under reduced pressure. Recrystallization of the resulting brown residue from hexanes at -20°C produced CpMo(N0)(n^-trans-(E,E)-2,4-hexadiene) (0.40 g, 33% yield) as yellow crystals. The analogous reactions for diene = (Z,E)-2,4-hexadiene, 2,5-dimethyl-2,4-hexadiene and butadiene proceeded with similar changes in their IR spectra and in 53, 44 and 37% isolated yields, respectively. 133 The reduction of [CpMo(NO)Br2]2 l n the presence of 2,5-dimethy1-2,4-hexadiene (i.e. Method A) produced the desired complex CpMo(CO)(Ti^-trans_-2,5-dimethyl-2,4-hexadiene) in less than 0.5% yield. Similarly, substitution of the related iodonitrosyl dimers (namely [CpMo(N0)I]2, [CpW(N0)I2]2, or [CpCr(N0)I]2) for [CpMo(N0)I2]2 or different organic Lewis bases (such as (E,E)-2,4-diphenyl-butadiene; 2,3-butanedione; 3-butene-2-one; diphenylacetylene; 3-hexyne; ethylene; norbornadiene; 1,3-cyclohexadiene; 1,3-cyclooctadiene; 1,5-cyclooctadiene and cycloheptatriene) for the acyclic conjugated dienes used in these reduction reactions (i.e. Methods A and B) resulted in the total decomposition of the organometallic reagent and the loss of a l l nitrosyl-containing species from solution. it Preparation of Cp Mo(N0)(nH-trans-2>5-dimethyl-2,4-hexadiene) (where Cp* » n 5-C 5Me 5). A flask containing sodium amalgam (~13 mmol of Na in 5 mL Hg) and THF (40 mL) was cooled to -20°C and then 2,5-dimethyl-2,4-hexadiene (5 mL) and [Cp*Mo(N0)I2]2 (1.00 g, 0.97 mmol) were added to obtain a deep red supernatant solution whose IR spectrum exhibited two v 's at 1664(m) and 1620(m) cm"1. After being stirred for NO 10 min the solution became brown (v„rt 1620(s) cm"1) while after 1 h the NO resulting golden colored solution had only one nitrosyl absorption present ( v N Q 1585(s) cm"1). The same work-up procedure as used in method B resulted in the isolation of Cp*Mo(NO)(r^-trans-2,5-dimethyl-2,4-hexadiene) (0.34 g, 47% yield) as yellow crystals. Reaction of [CpMo(NO)I2]2 with Na/Hg i n the Presence of 2,3-dimethylbutadiene at 0*C. A flask containing sodium amalgam (~2.5 134 mmol Na in 5 mL Hg) and THF (50 mL) was cooled to 0°C. Then 2,3-dimethyl-butadiene (5 mL) and [CpMo(N0)I2]2 (5.00 g, 5.60 mmol) were added. The i n i t i a l stirred red solution ( vN Q 1691(s) cm-1) rapidly darkened and after 3 min exhibited a number of nitrosyl absorptions in the IR at 1668(s), 1650(w,sh), 1588(m) and 1548(m) cm - 1. Three minutes later, the strong band at 1668 cm - 1 had disappeared and those at 1644(m), 1588(s) and 1548(s) cm - 1 remained. Over the next 15 minutes, these IR bands disappeared and two new ones at 1608(m) and 1567(s) cm - 1 appeared in the dark red solution. The fi n a l supernatant solution was cannulated away from the mercury-containing residue into a flask which had been cooled to 0°C and then taken to dryness In vacuo. The resulting orange-brown residue was extracted with Et 20 (8x25 mL), hexanes (100 mL) were added to the extracts and the resulting orange solution was concentrated under reduced pressure to ~80 mL. This resulted in the formation of a dark orange solid suspended in a pale orange solution. The orange solid was collected by f i l t r a t i o n , washed with hexanes (2x25 mL) and recrystallized from Et20/hexanes at -20° to give orange crystals of CpMo(N0)(r|l+-ci£-2,3-dimethylbutadiene) (0.39 g, 13% yield). The combined supernatant solution and hexanes wash from the previous operations were then filtered through alumina (2x4 cm, neutral, activity 1, 5x40 mL Et 20 wash) to give a yellow solution which was taken to dryness in vacuo. The resulting yellow residue was recrystallized from hexanes at -20°C to give CpMo (NO) (Ti't-trans-2,3-dimethylbutadiene) (1.13 g, 37% yield) as yellow crystals. Reaction of [CpMo (N0)I 2] 2 with C^H g»Mg»2(THF). A. In E t 2 0 . To a 135 13 rapidly stirred, pale yellow suspension of butenediylmagnesiuin (C^Hg'Mg*(THF)2, 1.00 g, 4.50 mmol) in Et 20 (100 mL) was added [CpMo(NO)I2]2 (2.00 g, 2.25 mmol). The i n i t i a l mixture of pale yellow and dark violet solids was replaced after 16 h by a dark green solid suspended in an extremely pale pink solution. The solid was collected by f i l t r a t i o n , washed with Et 20 (4x25 mL) and dried in vacuo (<0.005 torr, 1 h) to give a green powdery solid (2.58 g, 99%). Removal of solvent from the combined supernatant solution and Et 20 extracts, in vacuo, resulted in the formation of only a trace (<0.05 g) of solid residue. The green solid is best formulated as a solvate of CpMo(N0)I2»CltH6«Mg»x(Et20) where the i n i t i a l product has x = 1/2. Anal. Calcd. for MoC nH 1 6N0 1. 5I 2Mg: C, 23.58; H, 2.88; N, 2.50. Found: C, 23.61; H, 3.05; N, 2.52. IR (Nujol mull) v N Q 1491(s,br), cm - 1; (CH2C12) v N Q 1450(s,br) cm"1. Exposure of this material to vacuum (<0.005 torr, 18 h) for an extended period results in the loss of the solvent of crystallization. Anal. Calcd. for MoC9H11N0I2Mg: C, 20.66; H, 2.12; N, 2.68. Found: C, 20.00; H, 2.86; N, 2.17. B. In THF. Work-up Procedure I. To a stirred red solution of [CpMo(N0)I2]2 (2.00 g, 2.25 mmol) in THF (100 mL) at -78°C ( v N Q 1691(s) cm") was added butenediylmagnesium (1.00 g, 4.50 mmol). After 5 min, the reaction mixture consisted of a dark green solid suspended in a green solution. The mixture was stirred for 1 h at -78°C then allowed to warm to room temperature (~20°C) whereupon the green solid dissolved, the solution became brown and a grey solid precipitated. This suspension was taken to 136 dryness in vacuo, CH2C12 (20 mL) was added, and this produced a brown solution ( v N Q I450(s,br) cm - 1) over a white solid. This mixture was then filtered through alumina (3x3 cm, neutral, activity 1, 3x20 mL CH2C12 wash) to produce a red f i l t r a t e ( v N Q 1599(w) and 1650(s) cm - 1). This f i l t r a t e was taken to dryness in vacuo and the resulting brown o i l was extracted with hexanes (5x40 mL) to give a pale orange solution and a brown residue. The hexanes extract was filtered through alumina (3x4 cm, activity 1, 4x40 mL Et 20 wash), taken to dryness in vacuo, and recrystallized from Et20/hexanes to give yellow crystals of CpMo(N0)(n4-trans_-butadiene) (~0.10 g, 9% yield), vide supra. Recrystallization of the brown hexanes-insoluble residue from CH2C12/hexanes gave orange crystals (1.10 g, 65% yield) of CpMo(NO)I(Ti3-CltH7). Anal. Calcd. for MoC9H12NOI: C, 28.98; H, 3.24; N, 3.75. Found: C, 28.70; H, 3.25; N, 3.65. IR(CH,2C12) v N Q 1650(a) cm-1; low-resolution mass spectrum (probe 75°C), m/z_ 375 (P +). C* In THF. Work-up Procedure 2. This reaction was effected in a manner similar to that just described (Part B, above). However, after being warmed to room temperature, the brown solution ( V N Q 1656(vw), 1612(vw) and 1592(vw) cm - 1) was stirred for five days. The resulting mixture (v T„ 1656(w), 1612(s) and 1592(vw) cm - 1) was then filtered through NO alumina (3x12 cm, neutral, activity 1, 2x50 mL THF wash), taken to dryness in vacuo and crystallized from hexanes to give CpMo(NO)(-n^-trans-butadiene) in 38% yield (0.42 g). 137 Results and Discussion Syntheses and Physical Properties of the CpMo(NO)(n^-trans_-diene) 3 Complexes* As we have previously reported, the ambient temperature reduction of [CpMo(NO)I2]2 with sodium amalgam in THF in the presence of acyclic conjugated dienes results in the formation of novel T^-trans-diene complexes (i . e . reaction 5.2), CpMo(NO)(-n'*-trans-diene). Although these transformations are rapid, straightforward, and an excess of sodium amalgam may be used with no deleterious effects, these room-temperature reactions (Method A) are accompanied by extensive decomposition and result in the formation of the desired CpMo(NO)(nl*-trans_-diene) products in low yields. This d i f f i c u l t y i s exacerbated by the highly exothermic nature of this reduction which results in a significant warming of the reaction mixture. These d i f f i c u l t i e s can be largely overcome i f the reduction is performed at reduced temperatures (i.e. just above the melting point of the sodium amalgam, -20°C) and in the 4 presence of a heat sink, i.e. [CpMo(NO)I2]2 + 4 Na/Hg + 2 diene ^ > CpMo (NO) (T^-trans-diene) • + 4 Nal + Hg (5.3) These modifications to the published procedure (Method B, equation 5.3) result in much cleaner reactions and an increase in the yields of the 3 4 desired trans-diene products from ~10% to 30-60% . For optimum yields, the reaction solution should be separated from the mercury-containing residue and taken to dryness (at <0°C) as quickly as possible after the 138 reaction ( i . e . eq 5.3) has gone to completion since the decomposition of the desired organometallic product appears to be accelerated by some constituent of this mixture. Extraction of the fi n a l brown residue with Et 20 followed by crystallization from hexanes at -20°C of the ether soluble component produces the desired CpMo(NO)(T)'t-trans-diene) products. The various CpMo(NO)(r\*-trans-diene) compounds isolated during this work, are yellow, diamagnetic, crystalline solids. They are very soluble in common organic solvents such as THF, CH2C12, and benzene, somewhat less so in Et 20, and only slightly soluble in hexanes. They are thermally stable as solids but slowly decompose in solution at ambient temperatures (in CgD6 t j ^ 2 ~3 days at 20°C). This decomposition is fastest in polar solvents such as THF and slowest in hexanes and results in the precipitation of a l l proton and nitrosyl containing species from solution as evidenced by *H NMR and IR, respectively. The trans-diene products form yellow somewhat air-sensitive solutions but are less air-sensitive in the solid state and may be safely handled in air for short periods. Their formulations as monomeric, 18-electron complexes are supported by their elemental analyses and low-resolution mass spectral data (Table 5.1). The IR, *H NMR and 1 3C NMR spectroscopic properties of these compounds (Tables 5.2-5.6) and a 3 14 single crystal X-ray diffraction study of 6 ' establish that they possess a "three-legged piano stool" molecular structure with the diene ligand in a trans orientation (Table 5.2). The IR spectra (Table 5.1) of these compounds exhibit single strong absorptions in the region 1599-1584 cm - 1 (in CH2C12) attributable to T a b l e 5.1 Analytical, IR aad Mass Spectral Data for the Diene Complexes, ^ -g,. complex complex number calcd analytical data C H found calcd found calcd N found low resolution mass spectral P+.m/zP-VNC (CH 2C1 2] IR ,,cm-1 i (THF] CpMo ( NO) (n1* -trans-butadiene) 1 44.10 43.81 4.52 4.46 5.71 5.63 247 1599 1612 CpMo(N0)(ri'»-tran8-2-methylbutadiene) 2 46.34 46.41 5.06 5.24 5.41 5.16 261 1593 1610 CpM( NO) ( T)1* -t rans-2,3-dimethylbutadiene ) 3 48.36 48.94 5.53 5.84 5.13 4.54 275 1590 1608 CpM(NO)(T)'4-trans-(E,E)-2,4-hexadiene) 4 48.36 48.48 5.53 5.57 5.13 5.16 275 1582 1602 CpM(N0)(Tiu-tran8-(Z,E)-2,4-hexadiene) 5 48.36 48.70 5.53 5.40 5.13 5.30 275 1587 1604 CpMo(NO)(ri',-trans-2,5-diemthyl-2,4-hexadiene) 6 51.83 51.95 6.36 6.44 4.65 4.66 303 1584 1601 Cp 'Mo(NO) (n'*-trans-2,5-dimethyl-2,4-hexadiene) 7 58.22 57.76 7.87 7.70 3.77 3.70 373 1566 1585 CpMo(NO)(n'»-cia-2,3-dimethylbutadlene) 8 48.36 48.49 5.53 5.30 5.13 5.40 275 1552 1567 — Probe temperatures 70-150°C — Assignments for 9 8Mo. 140 Table 5.2 Numbering Scheme for the Diene Complexes 1-7 and 8 Table 5.3 1H NMR Chemical Shifts of the Diene Complexes. compound 1± 2A> 2B* Cp 5.58(a) 5.49(s) 5.53(8) chemical s h i f t s (C gD 6, 6 in ppm) *11 3.30(m) a 1 2 2.67(m) t v 2 1 2.67(m) ^32 R R M2 3.40(d,d,d) 2.12(d,d,d) 3.57(d,d,d) 3.54(d) 2.76(d) 1.25(s) 3.17(d,d) 2.73(d,d) 3.74(d,d) 3.35(d,d) 2.88(d,d) 2.37(d,d) 1.53(a) 1.94(d,d) 3.45(d) 5.04(s) 3.31(d,d) 3.01(d,d) 0.90(a) 1.70(a) 2.37(d) 5J£ 5B* 6 7 8 4.94(8) 1.49(d) 3.55(m) 2.02(d,d) 3.17(d,d) 2.46(m) 4.90(8) 1.52(d) 3.50(m) 2.75(d,d) 2.92(d,d) 0.89(d) 4.91(8) 3.90(m) 1.79(a) 1.68(d,d) 3.79(d,d) 2.45(m) 4.93(a) 1.68(a) 1.89(a) 2.44(d) 3.41(d) 1.70(a)- 1.68(a) 1.84(a) 2.34(d) 3.59(d) 1.05(8) 1.13(8) 5.13(a) -0.36(d) 3.84(d) 2.22(a) 2.22(a) -0.36(d) 3.48(d,d) 1.93(d,d) 4.37(m) 1.94(d) 2.14(a) 2.03(8) 3.84(d) — Recorded i n CD2C12. — Recorded i n CDC13, isomers 2A and 2B exist i n a 1:3 r a t i o . — Isomers 5A and 5B exist i n a 7:5 r a t i o . A This i s n5-C5Me5. Table 5.4 *H NMR Coupling Constants of the Diene Complexes 142 compound coupling constants (C gDg, i n Hz) J l1-12 J41-42 J l l - 2 1 J32-i*2 J12-21 J32"i+1 J 2 1 _ 3 2 J l l - 4 2 J 2 i - 4 : rkmf 2.25 3.05 6.94 6.2 14.0 13.1 9.8 0.55 1.0 2A* 1.9 3.6 - 6.6 - 14.0 - - 0.8 2.8 3.1 7.0 - 14.4 - - - 0.8 3 2.68 3.65 - - - - - 1.0 -4 6.4 6.0 - - 12.6 11.9 10.5 - -5A 6.3 6.9 - 7.6 12.5 - 11.4 - -5B 6.8 6.1 5.7 - - 11.6 11.4 - -6 - - - - - - 11.8 - -7 - - - - - - 11.5 - -8 5.04 5.04 — — — — — — — — Recorded i n CD 2C1 2. — Recorded i n CDClg. Table 5.5 1 3C NMR Chemical Shifts of some Diene Complexes. compound chemical shifts (CgDg, 6 in ppm)— Cp C 2 C 3 R J J R 1 2 &2l R 3 2 R<»1 R " « 2 1 94.88(d) 51.76(t) 82.98(d) 98.04(d) 55.08(d,d) 3 96.42(d) 54.59(t) 103.05(8)- 109.90(a)- 54.45(t) - 23.87(q) 21.31(q) 4 95.73(d) 68.78(d) 82.68(d) 94.96(d) 71.88(d) 20.35(q) - - -5A 96.82(d) 70.34(d) 86.92(d) 90.12(d) 70.54(d) 20.60(q) - - 16.15(q) 5B 95.08(d) 69.14(d) 77.88(d) 99.12(d) 72.35(d) - 20.95(q) - -6 97.43(d) 86.18(s)- 83.24(d) 92.28(d) 86.77(B)- 31.01(q) 23.32(q) - 23.44(q) 7 105.49(a)- 83.44(3)- 88.87(d) 91.27(d) 88.52(B)- 28.89(q) 24.03(q) - 20.48(q) 8 95.01(d) 52.15(d,d) 117,33(8) 117.33(8) 52.15(d,d) - - 22.57(q) 22.57(q) -20.86(q) 16.20(q) — The letters in brakets denote 1J„_ multiplicities. h — Note, these C 2 vs C 2 or C 1 vs C 4 assignments are tentative. — This is T) 5-CcMe 5, the methyl carbons resonate at 6 10.08(q) ppm. Table 5.6 1 3C NMR ^H-^C Coupling Constants of some Diene Complexes compound coupling constant (C 6D 6, in Hz)— Cp C l C2 C3 C4 R l l R 1 2 R 2 1 R32 Ri»l R 4 2 1 176.2 157.5 155.7 164.1 150.4 - - - - - -161.9 3 175.1 155 - - 155 - - 127.9^ 127.9^ - - -4 175.1 154.8 153.2 156 148 126.2 - - - - 125.8 5A 175.1 153 155.5 163.5 153 126.3 - - - 126.8 -5B 175.1 153 162.5 154.8 152.6 - 127.0 - - - 125.7 6 174.6 - 153.1 160.3 - 126.0 126.5 - - 126.5 126.0 7 d - 152.0 159.8 - 125.3 126.8 - - 126.1 125.5 8 176.2 146.5^ _ _ 146.5^ 127.3- 127.3^ _ _ 162.5 162.5 - Recorded using broad band gated decoupling, see text. - 3 J A =» 3.3 Hz, 3 J f i - 7.7 Hz. - 3 J 4 » 4.4 Hz, 3 J D = 8.3 Hz. d A D - This is Tj5-C5Me5, the methyl carbons have M • 126.8 Hz. - 3 J - 4.4 Hz. - 3 J t « 4.6 Hz, 3 J D - 6.8 Hz. A D 145 linear, terminal nitrosyl ligands. As would be expected, the v N Q values diminish with increasing methyl substitution of the diene ligand. Indeed, the observed nitrosyl stretching frequencies are intermediate between those 15 2 observed for CpMo(NO)(CO)2 and CpMo(NO)[PMePh2]2 ( v N Q 1663 and 1539 cm - 1, respectively, in CH2C12) and are similar to those of CpMo(NO)(P(OMe)3)22 and CpMo(NO)(CO)(PMePh2)16 (at 1574 and 1603 cm - 1, respectively, in CHjClj). Thus, the trans-diene complexes appear to have much more electron-rich metal centers than their dicarbonyl analogues. Furthermore, the trans-diene ligands appear to transfer almost as much net electron density to the metal-nitrosyl interaction as the more familiar Lewis base P(OMe) 3« 1 7 Finally, i t must be noted that the frequency of the nitrosyl-stretching absorptions observed is highly dependent on the solvent medium employed. Indeed, a similar although somewhat less pronounced trend 2a has been reported for their phosphine and phosphite analogues ( i . e . CpMo(N0)L2, L = PMePh2, P(0Me)3, etc.). The v^'s vary as a function of 18 the solvent "acceptor number," as illustrated in Figure 5.1. This variation is due to the formation of weak isonitrosyl linkages between the lone pair of electrons on the oxygen atom of the NO groups and Lewis acid sites on the s o l v e n t . 2 a ' 1 8 * i. S y n t h e s i s a n d P h y s i c a l P r o p e r t i e s o f C p M o ( N O ) ( n H - t r a n s - 2 , 5 -* c d i m e t h y l - 2 , 4 - h e x a d i e n e ) ( C p - n s - C 5 M e 5 ) . The substitution of the penta-methylcyclopentadienyl ligand for i t s perhydro analogue often allows the isolation, in good yields, of compounds that are unstable or available only in low yields for the cyclopentadienyl species.^'^ With this in mind, i t 146 Figure 5.1. V a r i a t i o n of VJJQ with the acceptor number (AN) of the solvent (• =CpMo(N0 ) (Ti l t-trans-2 >3-dimethylbutadlene) >O aCpMo(NO)(T^-cis-2,3-dimethylbutadiene). 147 was decided to attempt the reduction of [Cp Mo(NO)I 2] 2 ' with sodium amalgam in THF and in the presence of the acyclic conjugated diene 2,5-dimethyl-2,4-hexadiene, i.e. * THF * • [Cp Mo(NO)I 2] 2 + 4 Na/Hg + 2 diene z^O^ 2 Cp Mo(NO)(^-trans-diene) + 4 Nal + Hg (5.4) This reaction is much cleaner and produces the desired product, * i Cp Mo(NO)(TT-trans-2,5-dimethyl-2,4-hexadiene) (7), in slightly higher yield (47%) than does reaction 5.3 (44%). 6 9 As expected, ' the physical properties of £ are very similar to those of 6. The Cp complex is a bright yellow, diamagnetic solid that is thermally stable as a solid but decomposes slowly in solution. It is much more soluble in common organic solvent than is 6 producing yellow, somewhat air-sensitive solutions. Its physical properties are very similar to those of i t s Cp analogue and unequivocally show that i t possesses a "three-legged piano stool" molecular structure containing the diene ligand in a trans orientation similar to that found for 6. Finally, the IR spectrum of £ exhibits a nitrosyl absorption at ~20 cm - 1 lower energy than i t s Cp analogue. This simply reflects the fact that methyl substitution on a cyclopentadienyl ligand results in more electron-rich metal centers^ and 9 thus a lower nitrosyl stretching frequency. Synthesis and Physical Properties of CpMo(NO) ( T)**-cis-2,3-dimethylbutadiene) 8. During the synthesis of the trans-diene complex of 148 2,3-dimethylbutadiene, 3, the appearance of an extra nitrosyl band (v^g 3b 1567 cm-1) in the IR spectrum of the reaction mixture was noted. However, this i n i t i a l l y very strong absorption rapidly decreased in inten-sity either upon stirring at ambient temperature or f i l t r a t i o n through 3b alumina such that no products, other than 3 were isolated. Intrigued by this observation, i t was decided to investigate in detail the low temperature reduction of [CpMo(NO)I2]2 in THF in the presence of 2,3-dimethylbutadiene, i.e. [CpMo(N0)I2]2 + 4 Na/Hg + 2 diene ~^£-> CpMo(N0)(n4-cis-diene) + CpMo(NO)(n^-trans-diene) + 4 Nal + Hg (5.5) For the case where diene = 2,3-dimethylbutadiene, reaction 5.5 proceeds rapidly to completion to give a mixture of the previously isolated trans-diene complex, 3, and the novel species CpMo(NO)(T)lt-cis-2,3-4 dimethylbutadiene), 8. Although reaction 5.5 i n i t i a l l y produces 8 in large excess over 3 (~2-4 fold by IR spectroscopy), the desired cisoidal product rapidly decomposes ( t 1 / 2 <5 min at 20°C) when in contact with the fin a l brown reaction mixture, even at reduced (i.e. -20°C) temperatures. Therefore, this mixture must be separated from the mercury-containing residue and taken to dryness in vacuo at reduced temperatures (i.e. <0°C) and as expeditiously as possible. The delay involved in the Et 20 extraction of the resultant brown residue results in lower yields of 8 since this species in also quite thermally unstable in Et 20 at ambient 149 temperatures. Nevertheless, the solubility properties of 8 dictate that the extraction be effected under these conditions. By the time the two products, 3 and 8, have been crystallized from hexanes or Et20/hexanes, 4 respectively, the trans product is isolated in 2 fold excess. No evidence for the formation of other cis-diene complexes, analogous to 8, was observed during the syntheses of compounds 1, 2 and 4-7. The novel complex, CpMo(N0)(t)l*-cis-2,3-dimethylbutadiene), i s a red, diamagnetic solid. It is somewhat less soluble in common organic solvents than i t s trans analogue ( i . e . 3) and thus i t is only moderately soluble in Et 20 and very slightly soluble in hexanes to give orange to red, air-sensitive solutions. The solid is somewhat more air and temperature sensitive than is 3. Thus, 8 should be stored at <—10°C under nitrogen but i t may be handled in air for short periods. As previously noted, solutions of the cisoidal complex rapidly decompose at ambient temperatures ( t 1 / 2 ~^ day in C gD 6 at 20°C) and this problem is exacerbated in even weakly 4 donating solvents such as Et 20. The physical properties of 8 (Tables 5.1-5.6) suggest that i t is a "three-legged piano stool" with the diene ligand in a cisoidal orientation (Table 5.2). Indeed, this structure has been confirmed by a solid state 4 14 X-ray crystal structure determination. ' The IR spectrum of 8 (Table 5.1) exhibits a nitrosyl absorption at ~40 cm - 1 lower energy than i t s trans analogue, 3. This IR band at 1552 cm - 1 (in CH2C12) occurs within 13 cm - 1 of that of CpMo(NO)(PMePh2)2 ( i . e . 1539 cm"1 in C H 2 C l 2 ) 2 a . Thus, 8 appears to contain a much more electron-rich metal center than 3 and this, 150 presumably, r e f l e c t s a greater net transfer of electron density from the 14 cis-diene to the ' CpMo(NO)" group than from the trans-diene. Further, the n i t r o s y l absorption of 8 exhibits a si m i l a r solvent dependence (with the same int e r p r e t a t i o n ) to that of i t s trans analogue, 3 (Figure 5.1). Reaction of [CpMo(N0)I2]2 with ^H 6»Mg»2(THF). Although most diene complexes have t r a d i t i o n a l l y been synthesized by the d i r e c t reaction 19 of low-valent metal complexes with the appropriate 1,3-diene, a number of other routes to these species e x i s t . One of the most i n t e r e s t i n g of these involves the reaction of the useful reagent butenediylmagnesium (C 4H 6«Mg»2(THF)) 1 3 with metal d i h a l i d e s , for example: Cp 2MCl 2 + CuH6.Mg.2(THF) — > Cp^ n'M^Hg) + MgCl 2 (5.6) 19 20 where M=Zr or Hf. ' Since reaction 5.3 i n i t i a l l y f a i l e d to produce the parent trans-diene complex, 1, i n good y i e l d , we decided to tr y to synthesize i t using t h i s reagent. 13 When [CpMo(N0)I 2] 2 I s reacted with butenediylmagnesium the i n i t i a l product i s not the desired trans-diene species, !L, but rather an addition product of the two reagents. When t h i s reaction i s ca r r i e d out i n 13 19 E t 2 0 ( i n which both reagents are only sparingly soluble ' ) the i n i t i a l mixture of pale yellow and dark v i o l e t s o l i d s i s replaced by a dark green s o l i d , i . e . 1 E t 2 ° j [CpMo(N0)I 2] 2 + C l tHg«Mg»2(THF) yg-^> CpMo(NO)I 2.C 1 +H 6.Mg.xEt 20 (5.7) 151 This green adduct, 9, is insoluble in Et 20 and thus may be collected by f i l t r a t i o n in quantitative yield. Its physical and chemical properties indicate that i t possesses the empirical composition shown in equation 5.7 and the -j- Et 20 of crystallization may be removed by exposure to vacuum We believe that compound 9 is a derivative of CpMo(NO)I(r) -CoILR) In which the R group (R = CH2~Mg-I) functions as a Lewis acid towards the oxygen atom of the nitrosyl group, i.e. This proposal is supported by the following observations: c -(1) The IR spectrum of 9 displays only one absorption (at 1491(s,br) or 1450(s) cm - 1 in a Nujol mull or CH2C12, respectively) that may be attributed to a nitrosyl ligand. This band occurs in the region 21 expected for a terminal isonitrosyl linkage, i.e. (18 h). 152 M-N=0: >LA or M ± T N=0V^ LA where LA i s a strong Lewis a c i d . Indeed, the magnesium atom i s the only strong Lewis acid present i n t h i s species. (2) There i s an excellent precedent for such a met a l n i t r o s y l -22 Mg(II) i n t e r a c t i o n i n the product of the c l o s e l y related reaction, i . e . E t 2 0 [CpM(NO)I 2] 2 + 4 RMgCl -> [CpM(NO)R 2] 2MgIX.-j(Et 20) + 3 M g X 2 ( E t 2 0 ) n (X = C1,I) (5.8) (where M = Mo, W, and R = CH 2SiMe 3). A p a r t i a l single c r y s t a l X-ray s t r u c t u r a l determination on t h i s species has indicated i t to possess a very 22 similar i s o n i t r o s y l linkage, i . e . 153 Indeed, i t s n i t r o s y l stretching frequency ( v N Q 1520(e) cm - 1 Nujol mull) occurs i n a s i m i l a r region to that observed for 9 ( v ^ 1491). (3) F i n a l l y , 9 i s r a p i d l y converted into CpMo(NO)I(n 3-C l +H 7), 10, by water, i . e . CpMo(N0)I2'Cl>H6.Mg.xS + H 20 — > CpMo(N0)I(Ti 3-C l tHy) + MgI(0H)S y (5.9) (where S i s the so l v e n t ) . For instance, addition of water to a THF sol u t i o n of 9 causes an instantaneous color change of the s o l u t i o n from green to brown and the appearance of the IR band for 1£, vide i n f r a , at 1656 cm - 1. The reaction of 9 with water (even adsorbed on alumina, equation 5.9) i s a good route to the methallyl complex, 10, which has previously 23 been synthesized by n u c l e o p h i l i c attack of I~ on CpMo(N0)(C0)(Ti 3-C l tH 7) +, i . e . CpMo(N0)(C0)(Ti 3-C l tH 7) + + r > CpMo(N0)I(n 3-C l 4H 7) + CO (5.10) The physical and spectroscopic properties of compound 1£, vide supra, suggest that i t i s a mixture of isomers of the "three-legged piano s t o o l " type. This hypothesis was confirmed by comparison of the 400 MHz *H NMR spectrum of 10 with that reported for authentic CpMo(NO)I(n 3-C t tH 7) whose 24 s o l i d state X-ray c r y s t a l structure has been reported. The desired ^^-trans-butadiene complex, 1, can also be produced 154 from complex 9; however, t h i s transformation involves not hydrolysis but a thermal rearrangement. Thus,, i f a green THF solution of the adduct, 9, i n THF (either i s o l a t e d from E t 2 0 as 9 or produced i n s i t u ) i s allowed to warm to room temperature and i s then s t i r r e d for f i v e days i t i s converted to CpMo(N0)(n 4-trans-butadiene), 1, i . e . THF CpMo(NO)I2.CltH6.Mg.x(THF) S^£> CpMo(NO)( Ti 4-trans-C l tH 6) + MgI 2(THF) n (5.11) The desired product, .1, i s only i s o l a t e d i n 38% y i e l d , however, because of i t s concomitant thermal decomposition, vide supra. 1H and 1 3C NMR Spectroscopic Properties of the Diene Products, 1-9. **** rss Although numerous examples of monomeric transition-metal complexes contain-ing a c y c l i c conjugated dienes, have been reported, 1 7** the vast majority 25 contain the diene ligand bonded i n a planar n^-cis manner. Indeed, the only previous examples to date of n 1*-trans diene coordination to a s i n g l e 26 metal occur i n Cp 2M(r \ *-diene) complexes (where M = Zr, Hf), 11, which 19 exhibit i n t e r e s t i n g s t r u c t u r a l , chemical and spectroscopic properties. Further, i t has been shown that the bent metallocene ( i . e . Cp2M, M = Zr, Hf) and "CpM(NO)" fragments produce dramatically d i f f e r e n t diene-metal 3 4 14 i linkages. ' ' F i n a l l y , a preliminary i n v e s t i g a t i o n of the iH NMR spectra of 2, 3 and 6 showed that they possessed a number of i n t e r e s t i n g and highly 3 4 informative features. * Intrigued by these observation, (and since so few T)*+ -trans-diene complexes are known) i t was decided that the *H and 1 3 C NMR 155 spectroscopic properties of the trans-diene compounds, 1-7, merited an extensive investigation. To obtain the maximum amount of information from the NMR spectra of compounds 1 to 8 i t was necessary to assign both the position on the diene ligand ( i . e . Cj vs C 2, H]^ vs H 1 2) and orientation with respect to the cyclopentadienyl ring of each nucleus responsible for the observed *H and 1 3C resonances (see Table 5.2). This task was accomplished by a combina-tion of one- and two-dimensional NMR (ID and 2D NMR, respectively) experi-27 ments. The *H NMR spectra of the complexes (Tables 5.3 and 5.4) were used to determine proton coupling networks and the orientation of these 28 with respect to the Cp ring were obtained from the NOE difference spectra of each. Finally, the 2D HETCOR experiment was used to produce a two-28 dimensional 1H- 1 3C chemical shift correlation map for each complex. I Q 29 This, along with the i JC NMR spectra for each complex (Tables 5.5 and 5.6), established the *H-13C connectivities and thus completed the spectral assignments. This process of spectral analysis is best illustrated using the n1*-trans complexes of (Z,E)-2,4-hexadiene, !5, as examples. The somewhat complex *H NMR spectrum of 5 (Figure 5.2) displays a number of interesting and informative features. It is clear that, as expected for a diene ligand with no center of inversion, two isomers, 5A and 5B, of this complex exist (in a 7:5 ratio, respectively). Careful integration of the spectrum results in the assignment of a pair of methyl doublets (3H) and four inequivalent vinylic hydrogens (IH each) to each of the isomers (the major and minor isomers are labelled A and B respectively, in Tables 5.2-5.6 and Figures 5.2 and 5.3). 156 Figure 5.2 The  lR NMR spectrum of 5.-A11 A41 B 4 2 B 1 2 A4 2 B11B32 A12 A3 2A2 1 B41 A .Aili ii Alk A 21 J - 1 — r — j — I — I — i — i — | — i — i — i — i — | — i — i — i — i — | — i — t — i — I — | — I — I — I — I — | — I — i — i — I — | — I — I — I — I — | — r — i — I — I — | — i r — l i r—r-5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 PPM — The symbols A_,„ and B v „ denote isomers A and B, res p e c t i v e l y , and xy xy xy denotes the diene substituent ( i . e . R x y, see Table 5.2) Figure 5.3 The 1 3C{ 1H} NMR spectrum of 5.-- A ACp BCp B 3 WW, A 4 *1 B, B. B 4 2 *41 '11 B 12 -1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—r 17.0 16.0 PPM iKrW»|l»<l il 1 «m>»<if J»^ M ' 1 ' " i—1— 1 — 1 — 1 — 1—I— 1 — 1 — 1 — 1—1— 1 — 1 — 1 — 1—I—r— T — 1 — 1—1— 1 — 1 — 1 — 1—r 120 100 80 - 1 r—l 1 1 1 1 1 1 1 1 1 1 1 I I 1 1 1 1 T—| 40 20 PPM 0 l 1 1 1 1 1 r 60 — The symbols A^y (or A z) and B x y (or B z) denote isomers A and B, re s p e c t i v e l y , and xy denotes the diene substituents ( i . e . R^y) while z denotes the diene carbon ( i . e . C z, see Table 5.2). 158 The connectivities for each isomer are then assigned on the basis of the peak multiplicities (Table 5.3) and coupling constants (Table 5.4) and then confirmed by homonuclear decoupling experiments. In this manner, each proton signal is assigned to the correct position on the diene backbone; however, i t is not known which "edge" of the diene points towards the Cp ring (i.e. is the "cis " methyl group pointing towards the Cp in 30 isomer 5A or 5B). This question can be answered by an NOE difference **JTS* /N4-VV experiment. Thus, when the Cp signals of 5A and 5B are simultaneously irradiated only the methyl groups at 6 1.52 ppm (the "trans" methyl of 5A) shows significant NOE enhancement. The structures of 5A and 5B can thus be assigned (Table 5.2), as can their 1H NMR spectra. The assignment of the 1 3C spectra of 5A and 5J5 is somewhat more d i f f i c u l t than for their proton spectra even though each signal is resolved in the 13C{1H} spectrum (Figure 5.3). The chemical shifts (Tables 5.5), intensities (Figure 5.3), and 1Ji„ 13-, multiplicities and magnitudes (Table 11 29 5.6) of the  liC signals allow their assignment to the appropriate isomer and distinguish the Cp, diene and methyl resonances. Further, comparison with the 1 3C spectrum of 4 allows the assignment of the methyl resonances 32 as "trans" (~21 ppm) or "cis" (~16 ppm). However, no further assignment of these signals can be made with any assurance from these data. Indeed, even the assignment of certain signals to isomers 5A or 5B is somewhat tentative. However, a 2D HETCOR experiment can be used to complete the 1 3C assignment of this mixture since assignment of i t s proton spectrum is complete. The cross-correlation available from the contour plot of the 159 iH- i ; 3C chemical s h i f t c o r r e l a t i o n spectrum obtained (Figure 5.4) allows the assignment of the remainder of the 1 3 C NMR spectrum. The -^H and 1 3 C NMR spectra of the other diene complexes were assigned i n a si m i l a r manner. The i n t e r n a l consistency of the NMR data sets (Tables 5.3-5.6) when analogous s t r u c t u r a l segments (Table 5.2) are compared enhances the c o n f i -dence i n these assignments. The conformation of the diene ligands on compounds 1-8 may be r e l i a b l y established from th e i r NMR spectra. For symmetrically substituted dienes complexed to "CpMo(NO)", the two ends of the diene are equivalent for c i s coordination (because of the mirror plane b i s e c t i n g the ligands, 30 Table 5.2) and inequivalent for trans coordination. For example, the four v i n y l hydrogens and two methyl groups of 8 and 3 give r i s e to three and s i x *H NMR si g n a l s , r e s p e c t i v e l y ; while, two and four 1 3C{ 1H} NMR signals are observed for the diene carbons i n 8 and 3, re s p e c t i v e l y . For unsymmetrically substituted dienes only one isomer of the c i s complex but two of i t s trans analogue are expected. Experimentally, two isomers for 2 and 5 are observed thus i n d i c a t i n g t h e i r t r a n s o i d a l natures. These c r i t e r i a demonstrate that 1-7 possess trans-diene ligands while 8 exhibits cis-diene coordinations. This analysis i s confirmed by the c r y s t a l s t r u c -3 14 4 14 i tures of 6 ' and 8 ' . The 1H NMR proton-proton coupling constants and 1 3 C NMR chemical s h i f t s of 4 and 5 (Tables 5.4 and 5.5) also indicate that the E,E an Z,E geometries, r e s p e c t i v e l y , of the diene reagent are main-tained upon coordination to "CpMo(NO)". Indeed, even though Cp 2Zr(Ti l +-trans-(Z,E)-2,4-hexadiene) has been found to r a p i d l y isomerize to i t s (E,E) Figure 5.4 1H- 1 3C chemical s h i f t c o r r e l a t i o n plot of 5 . 'H 161 analogue above 0°C. No such Isomerization is seen for 5, even after extended periods at 30°C (which result in i t s thermal decomposition). The cyclopentadienyl ligands of 1^-8 exhibit the expected *H and 1 3C NMR properties. Their *H NMR resonances are sharp singlets (~4.9-5.6 ppm) which, for compounds !L-6 and 8 integrate for less than five hydrogens when normal pulse delays (i.e. 0-5 s) are used (due to the long relaxation times of the n5-C&H5 protons^). This inconvenience has previously been observed for other "CpM(NO)" (where M = Mo, W) complexes. The i 3C signals of the cyclopentadienyl carbons of 1-8 are doublets with the expected chemical shifts (95-98 ppm) and one bond proton-carbon-13 coupling constants (174-177 Hz). 3 1 The most chemically interesting feature of the NMR spectra of 1-8 involves the signals due to the diene ligands. The inequivalence of the spectroscopic properties of the two halves of even symmetrically substi-tuted trans-diene complexes is remarkable: (1) the chemical shift of C 2 is much less than that of C 3 in the 1 3C NMR. (2) the substituents of are much more widely separated in chemical shifts than those of Cl in the  lE (i.e. R = H) and 1 3C (i.e. R = Me) NMR. (3) the geminal ( 2 J i H _ i H ) and vicinal ( 3 J i H _ i H ) coupling constants are larger and smaller, respectively, for and C 3 than for and C2-The molecular orbital interaction of "CpMo(NO)" with the two ends of the 14 diene ligands is somewhat asymmetric, however, the exact origin of (1) to (3), above, remains unclear. 162 The *H and 1 3 C NMR spectra also provide some information about the bonding i n these diene complexes. The bonding i s cis-diene complexes can be v i s u a l i z e d as having two components where Ia i s referred to as the TC,TC and lb as the a,n,a form. Most c i s -diene complexes of the l a t e t r a n s i t i o n metals ( i . e . Fe(CO) 3(n l +-cis-C l tH 6)) are best described as c l a s s i c a l l y n-bonded diene complexes ( i . e . Ia); while, those of early t r a n s i t i o n metals, e s p e c i a l l y those of type 11, are best described as adopting CT,TC,O" bonding ( i . e . I b ) . 1 7 ^ ' 1 ^ Indeed, for the zirconocene complexes, 11, there appears to be a smooth progression from such diene complexes (lb) to ones i n which the r| 2-metallocyclopentene 19 double bond i s not coordinated at a l l . A s i m i l a r d e s c r i p t i o n for the bonding i n trans-diene complexes i s proposed 163 where again I l a i s referred to as the it,it and l i b as the 0,11,0 form. The differences between forms a and b should be r e a d i l y apparent i n the NMR spectra of the complex because the terminal carbons i n a are sp 2-hybridized rather than sp 3-hybridized as i n b. The terminal diene carbons of 8 exhibit a geminal proton-proton coupling constant ( 2 ^ n _ ] L 2 = 2 ^ 4 i 4 2 = ^ * ^ H z ^ 19 33 much closer to that observed for Fe(CO) 3(n^-cis-C^Hg) (2J=2.4 Hz, it,it) ' 19 than to that for Cp 2Zr(n l t-cis-C l +H 6) (2J=10 Hz, O,IT,O-). Further, the one bond proton-carbon coupling constant for t h i s species (*J=146.5 and 162.5 31 Hz) i s what i s expected for an s p 2 carbon ( i . e . 155-160 Hz) and larger 34 than that for C p 2 Z r ( c i s - C 4 H 6 ) ( i . e . 144 Hz). It thus seems that the metal-diene linkage i n 8 more c l o s e l y resembles that i n the l a t e r t r a n s i -t i o n metals ( i . e . Ia, it,it) rather than that found i n !LL ( i . e . Ib, a,it,a), 14 although contributions from both resonance forms are c l e a r l y evident. In contrast, the trans-diene complexes, l-£, exhibit very small geminal 164 coupling constants (2^n_i2~2^41-42~2-4 t n a t approach those of free butadiene (2J=1.7 Hz)3"* and are smaller than those of 11 (2J~4-6 H z ) . 1 9 Further the v i c i n a l coupling constants of 1-7 (across the C^-C2 and Cg-C^ bonds) are smaller ( i . e . 3 J . ~6-7 Hz and 3 J ~11-15 Hz) than those of c i s trans either 11 ( 3 J , ~7 Hz and 3 J ~16 H z ) 1 9 or free butadiene ( 3 J , =10.1 Hz ~~ c i s trans, ' c i s and 3 J =16.9 H z ) 3 5 (where for 1-7 3 J , = 3J-. ... and 3 J . _ and trans ' v ~ ~ c i s 11-21 32-42 3 J = 3J.._, 1 and 3 J o 9 _ / . i ) « F i n a l l y , the coupling constant across the formal single bond ( i . e . C 2 _ C 3 ) for 1-7^  ( i . e . J2i-32~^ - 1 2 * s s i m : H a r to that of free butadiene (10.3 Hz) but much less than that of 11 (~15-16 Hz). These observations on the NMR of the r^-trans-diene complexes of "CpMo(NO)" suggest that I l a i s a good representation for the bonding i n t h i s species and that resonance form l i b contributes less to the bonding i n 14 1-7 than i t does i n 11. Mechanistic Pathway of the Reductive Synthesis of the CpMo(NO) (n^-diene) Complexes* Monitoring of the progress of the reduction reactions, 5.3, by IR spectroscopy indicates the transient formation of a number of intermediate n i t r o s y l complexes p r i o r to the ultimate formation of the desired CpMo(NO)(T)1+-diene) products. Complete d e t a i l s of such monitoring of i n d i v i d u a l reactions are presented i n the Experimental Section. These conversions are p a r t i c u l a r l y convenient to follow since they proceed at r e l a t i v e l y slow rates and the intermediate species generally a t t a i n detectable concentrations. The transient existence of these species i s consistent with the o v e r a l l reaction 5.3 proceeding v i a the sequential transformations summarized i n Scheme 5.1. The proposed 165 Scheme 5*1 1/2 [ C p M o ( N O ) I 2 ] 2 166 mechanistic pathway best accounts for our experimental observations and i s most in accord with literature precedents, especially that of the related reductions in the presence of phosphines and phosphites (i . e . equation 2 5.1). The experimental evidence on which the mechanistic proposals are based is considered in detail in the following paragraphs. The i n i t i a l dimeric reactant, [CpMo(NO)I2]2» is virtually insoluble in polar, noncoordinating solvents such as CH2C12 but is extremely soluble in coordinating solvents such as THF which rapidly cleave i t to form the 2 36 solvated monomer ' (step a of Scheme 5.1) [CpMo(NO)I2]2 + 2 THF i = ± CpMo(NO)I2(THF) (5.12) in a reversible reaction. This cleavage of the diiodide dimer to produce a red solution ( v N Q 1691 cm - 1) of CpMo(NO)I2(THF) is undoubtedly the f i r s t step in the reduction reactions since they also produce red solutions (V^Q 1691) after the dark violet [CpMo(NO)I2]2 dissolves. In reaction 5.1, the 37 next step is the displacement of the solvated THF molecule by a group 15 2 (i . e . phosphine or phosphite) ligand, i.e. CpMo(N0)I2(THF) + L —> CpMo(NO)I2L (5.13) However, the much weaker organic Lewis bases (i . e . dienes) are unable to displace THF from CpMo(NO)I2(THF) or even cleave the diiodide dimer in CH2C12. Thus, the reaction to produce CpMo(NO)I2(Ti2-diene), i.e., 167 [CpMo(NO)I2] T H F d ^ H 2 C l 2 > CpMo(NO)I2(n2-diene) (5.14) f a i l s to produce isolable or even spectroscopically detectable (IR, *H NMR) quantities of the r)2-diene product. The next step in the reaction must proceed via electron transfer (step b of Scheme 5.1), i.e. CpMo(NO)I2(THF) + Na/Hg — > CpMo(NO)I2(THF)n* + Na + + Hg (5.15) to produce a radical anion intermediate of undetermined solvation (i.e. n=0 or 1). This corresponds to the i n i t i a l l y red solution becoming brown and a strong new IR band appearing at 1668 cm - 1. The position of this band is independent of the diene used and i t is notable that It disappears as soon as a l l of the CpMo(NO)I2(THF) is consumed (t 1 / 2<2 min at -20°C). An analogous intermediate was detected in the reduction of CpMo(NO)I2(PMePh2) ( v N Q 1645 cm"1) and was assigned to CpMo(NO)I2(PMePh)~. Thus, i t seems most reasonable to propose that the transient intermediate (V^Q 1668 cm - 1) is also due to such a radical anion (namely, CpMo(NO)I2(THF)n ). This intermediate could then undergo, in principle, a number of reactions. The f i r s t that may be proposed is the elimination of I~ to form the neutral radical, CpMo(NO)I2(THF)n' —> CpMo(NO)I(THF)^ + I" (5.16) 168 (n=0 or 1) which would then be i n equilibrium with i t s monoiodide dimer.'' However, two pieces of evidence argue against t h i s p o s s i b i l i t y , namely: (1) the IR spectrum of [CpMo(NO)I] 2 i n THF exhibits a strong band at 1617 cm - 1 which i s not observed i n any of these reactions. (2) independent reduction of the monoiodide dimer i n the presence of dienes, i . e . , THF [CpMo(NO)I] 2 + 2 Na/Hg + diene -===-> 2 CpMo(NO)(diene) + 2 Nal + Hg (5.17) f a i l s to produce any i s o l a b l e products and even i n the presence of good 2a Lewis bases (such as PMePh2) proceeds only i n low y i e l d s . It i s thus apparent that t h i s reaction, 5.16, does not make an appreciable contribu-38 t i o n to the o v e r a l l process. However, two other processes probably contribute to reactions 5.3. The f i r s t involves s u b s t i t u t i o n of a diene for I - . This reaction accounts for the appearance of weak n i t r o s y l bands at ~1650 cm - 1 as that at 1668(s) cm - 1 disappears. The p o s i t i o n and i n t e n s i t y of t h i s band i s very dependent on the added ligand ( i . e . 1644, 1651, 1653 and 1659 cm - 1 i n the syntheses of 3, 4, 6, and 5, res p e c t i v e l y ) as i s the analogous band due to CpMo(NO)IL» i n the phosphine reductions 2a (v„ r t 1614 and 1626 cm - 1 for PMePh0 and P(OMe),, r e s p e c t i v e l y ) . It NO * 0 therefore seems that step d of Scheme 5.1 makes a small contribution to the o v e r a l l process, i . e . CpMo(NO)I 2(THF)« + diene + Na + — > CpMo(NO)I(diene)• + Nal (5.18) 169 A second reduction of t h i s r a d i c a l ( i . e . step f of Scheme 5.1). CpMo(NO)I(diene). + Na/Hg — > CpMo(NO)(nlt-diene) + Nal + Hg (5.19) would then produce a portion of the f i n a l diene product and account for the slow ( t 1 / 2 m ^ n a t ~20°C) loss of t h i s band from s o l u t i o n . Since the 2 monoiodide dimer cannot be cleaved by added dienes (or even phosphines ) the back reaction of equation 5.20 may compete with reaction 5.19; however, the absence of the n i t r o s y l band for [CpMo(N0)I] 2, vide supra, suggests that any such contribution ( i . e . equation 5.20) must be n e g l i g i b l e . The bulk of the r a d i c a l anion intermediate (V^Q 1668 cm - 1) i s not converted to the minor intermediate at ~1650 cm - 1. Instead, as the 1668 cm - 1 band i s consumed i t i s replaced by a strong diene-independent band i n the golden-brown so l u t i o n at 1548 cm - 1. Indeed the p o s i t i o n of th i s n i t r o s y l 2a st r e t c h and i t s diene-independence suggest that t h i s product may be [CoMo(N0)I] 2 + 2 diene THF ox 2 CpMo(N0)I(diene) (5.20) CpMo(N0)(THF) 2» i . e . CpMo(N0)I 2(THF). + Na/Hg + Na + THF. -> CpMo(N0)(THF) 2 + 2 Nal + Hg (5.21) It i s c l e a r , however, that reaction 5.21 (step c of Scheme 5.1) i s complex and the exact sequence of the reduction (namely the order and/or co-op e r a t i v l t y of electron transfer and I" loss) remains uncertain. The 170 subsequent steps of conversion 5.3, however, are straightforward. The 39 f i r s t such step would be the formation of the (n 2-diene) intermediate via substitution of one double bond of a diene for a THF, i.e. CpMo(N0)(THF)9 + diene — > CpMo(NO)(THF)(n2-diene) (5.22) This reaction (step e of Scheme 5.1) accounts for the appearance of the strong diene-dependent nitrosyl band at ~1580 cm - 1 (1580 cm - 1 for 4 and 5, 1587 cm-1 for 6 and 1588 cm - 1 for 3) that increases in intensity before the fin a l ri^-diene product is observed and is then consumed at i t s expense. This fi n a l process is the replacement of the fi n a l solvent molecule to give the isolated -n1*-diene products (step g of Scheme 5.1), i.e. THF CpMo(NO)(THF)(Ti2-diene) -—> CpMo(NO)(r^-diene) (5.23) Although the exact nature of some of the intermediates (especially CpMo(NO)I2(THF)n«) and reactions (especially reaction 5.21, step c of Scheme 5.1) presented in Scheme 5.1 are speculative in nature, i t is clear that the mechanistic pathway proposed for the reduction reaction, 5.3, best accounts for our experimental observations. However, a more detailed understanding of the steps of this process and confirmation of i t s exact nature must await a detailed electrochemical investigation of these processes. Nevertheless, this proposed mechanism answers a number of questions about these reductions. Since thermal decomposition of the proposed CpMo(N0)(THF)2 intermediate was found to be rapid at ambient 171 temperatures, i t competes with e and g of Scheme 5.1. Therefore, lowering the reaction temperature resulted i n the diene ligands trapping i t more e f f i c i e n t l y and thus raised the y i e l d . In a similar vein, when solvents that are poorer or better donors than THF were employed, the poorer donors (e.g. benzene) were unable to s t a b i l i z e "CpMo(NO)" while better donors (e.g. DMF or CH3CN) preclude the substitution of the weakly donating diene 2a i n the molybdenum's coordination sphere. F i n a l l y , the use of conjugated dienes speeded step g of Scheme 5.1 v i a the chelate e f f e c t . Mechanism of the Reaction of Butenediylmagnesium with 13 [CpMo (N0)I 2 ]2« T n e reaction of butenediylmagnesium, 12, with a metal 19 42 dihalide occurs via a two-step metathetical process. ' In solution, the 12b magnesium reagent exists as an oligomer of butene-l,4-diylmagnesium, i . e . / ,CH=CH. \ -^CH 2 X C H 2 - M g ^ The f i r s t metathesis produces a substituted T ^ - a l l y l complex, i . e . 172 L | » M X 2 + { c H 2 / C H = C ^ C H 2 - M g } n S > (5.24) X L n r / ,CH=CH. n S C H 2 x CH 2 -MgX where S is the solvent (usually Et 20 or THF) and L QMX 2 is the metal 42 dihalide (e.g. Cp 2ZrCl 2 )• The second metathesis,, however, requires a 19 42 preliminary 1,3-allylic shift of the -MgX subsitutent, i.e. ' L n r / /CH=CH n V C H 2 N CH 2 -MgX X MgX L X / C H\ n X C H 2 CH=CH2 (5.25) Thus, the reaction proceeds not via, 1,4 additon to give a metallocyclo-pentene intermediate ( i . e . equation 5.26) but through 1,2 addition to give 19 a T)2-diene Intermediate ( i . e . equation 5.27). V L n M ' ,CH=CH. L M jL. + MgX 2 S 2 (5.26) n V C H 2 N CH 2 -MgX N n 173 x ygx L X / C H\ N N C H 2 CH=CH 2 •n CH M-II CH-CH-> n 1 .CH M g X 2 S 2 (5.27) The f i n a l diene products r e s u l t from coordination of the free double bond. The reaction of [CpMo(NO)I 2] 2 with 12 i s somewhat more complex than 42 43 those previously reported ( i . e . with L nMX 2=Cp 2ZrCl 2 or CpTaCl^ ). This r e f l e c t s two primary properties of the n i t r o s y l containing s t a r t i n g material; namely, the oxygen atom of the n i t r o s y l ligand i n these species i s a strong Lewis base, vide supra, and so w i l l tend to strongly bind to Lewis acids l i k e the RMgX intermediate and th i s diodide s t a r t i n g material , 24 has a great p r o c l i v i t y to form CpMo(NO)(TT-allyl)X products. These two factors r e s u l t i n the i n i t i a l l y formed T ^ - a l l y l complex 1/2 [CpMo(NO)I2]2 + -(cH 2 / C H = C H ^ C H 2 - M g | n CpMX l ,CH=CH CH 2 v C H 2 - M g X (5.28) ra p i d l y isomerizing to the is o l a t e d (S=Et 20) or observed (S=THF) n 3 - a l l y l Lewis acid-base oligomer, 9 ( i . e . equation 5.29). The formation of the 174 / N CpMo-I ,0 S CpMo-NOX CH 2 -MgX n (5.29) nitrosyl oxygen to magnesium dative bonds and the T i 3 - a l l y l linkage dramatically slow the 1,3 a l l y l i c shift of reaction 5.25. This allows the isolation of this intermediate, from Et 20 (cf. reaction 5.7), which may then either be hydroyzed to CpMo^CKr^-C^Hy)! (reaction 5.9) or slowly isomerized to the desired CpMo(N0)(r)l*-CltH6) (reaction 5.11). Thus the isolation of 9 supports the general mechanism proposed for reactions of 19 42 butenediylmagnesiums with metal dihalides. ' Conclusions This work has established that the reduction of [CpMo(N0)I2]2 with sodium amalgam in THF in the presence of acyclic conjugated dienes ( i . e . equation 5.3) conveniently affords the novel c i s - and trans-diene complexes CpMo(NO)(TI'•-diene) (8 and 1.-7, respectively) in moderate yields. The nitrosyl stretching frequencies of these species exhibit a strong solvent dependency (i.e. reflecting the Lewis basicity of the nitrosyl oxygen) and demonstrate the electron-rich nature of the metal centers. Their NMR 175 properties suggest that t h e i r bonding i s best described as H,TI ( i . e . Ia and Ila ) rather than o,%,<3 ( i . e . Ib and l i b ) . A mechanistic pathway for these reduction reactions was proposed (Scheme 5.1). This accounts for the IR spectral changes observed i n these reactions. It also accounts for the temperature, solvent, and diene dependence of the reduction reactions. A mechanism was also proposed for the reaction of butenediylmagnesium with [CpMo(NO)I 2] 2 ( i . e . equation 5.7) to produce a green i s o l a b l e intermediate, 9, that possesses a novel Lewis acid bridged oligomeric structure. The intermediate, 9, may be converted to either CpMo(NO)(1)3-0^)1 or CpMo(NO)(n^-trans-C^Hg). Despite the considerable i n s i g h t into reactions 5.3 and 5.7 that has been gained i n t h i s work some questions remain unanswered. The most i n t r i g u i n g of these i s whether the f a i l u r e of reaction 5.3 with most common organic ligands or with the molybdenum center replaced by chromium or tungsten r e f l e c t s the I n t r i n s i c i n s t a b i l i t i e s of the desired CpM(N0)L 2 complexes or whether i t r e f l e c t s a f a i l u r e of the synthetic route. Studies are c u r r e n t l y underway to prepare an expanded range of CpM(N0)L2 complexes (where M=Cr, Mo, and W and L 2 = unsaturated organic ligands) by other routes and a d e t a i l e d electrochemical i n v e s t i g a t i o n of these reduction reactions w i l l soon be undertaken. A detailed discussion of the structures and bonding of the c i s - and trans-diene complexes (including the X-ray c r y s t a l structures of 6 and 8 and the interconversion of 3 and 8) i s presented i n the following chapter. 176 References and Notes (1) Taken in part from Hunter, A.D.; Legzdins, P. manuscript in preparation. (2) (a) Hunter, A.D.; Legzdins, P. Organometallics submitted for publication, (b) Hunter, A.D.; Legzdins, P.; Martin, J.T.; Sanchez, L. Organomet. Synth. 3, in press, (c) See Chapter Four. (3) (a) Nurse, C.R., Ph.D. Dissertation, University of British Columbia, Vancouver, British Columbia, 1984. (b) Hunter, A.D.; Legzdins, P.; Nurse, CR.; Einstein, F.W.B.; Wil l i s , A.C. J. Am. Chem. Soc. 1985, 107, 1791. (4) (a) Hunter, A.D.; Legzdins, P.; Einstein, F.W.B.; Wil l i s , A.C; Bursten, B.E.; Gatter, M.G., submitted for publication. (5) (a) See Chapter Two. (b) Legzdins, P.; Martin, J.T.; Oxley, J.C. Organometallics 1985 , 4_, xxx, in press. (6) Legzdins, P.; Nurse, CR. Inorg. Chem. 1985, 24, 327. (7) James, T.A.; McCleverty, J.A. J. Chem. Soc. A. 1971, 1068. (8) McCleverty, J.A.; Seddon, D. J. Chem. Soc. Dalton Trans. 1972, 2526. (9) (a) Malito, J.T.; Shakir, R.; Atwood, J.L. J. Chem. Soc. Dalton Trans. 1980, 1253. (10) Legzdins, P.; Martin, D.T.; Nurse, CR. Inorg. Chem. 1980, 19, 1560. (11) Shaka, A.J.; Keeler, J.; Freeman, R. J. Mag. Res. 1983, 53, 313. (12) Solid sodium amalgam (either 1.00 or 1.04 mmol Na/g) was stored under nitrogen but was weighed out in a i r . 177 (13) (a) Butenediylmagnesium was supplied by Dr. M. Fryzuk and Mr. A. Carter, (b) Yasuda, H.; Kajihara, Y.; Mashima, K.; Lee, K.; Nakamura, A. Chem. Lett. 1981, 519. (c) Fujita, K.; Ohnuma, Y.; Yasuda, H.; Tani, H. J. Organomet. Chem. 1976, 113, 201, and references cited therein. (14) For a more detailed discussion of the X-ray crystal structures of 6 and 8 and of the bonding in compounds 1-8 see: (a) Hunter, A.D.: Legzdins, P.L.; Einstein, F.W.B.; Wil l i s , A.C; Bursten, B.E.; Gatter, M.G. manuscript in preparation, (b) Chapter Six. (15) Hoyano, J.K.; Legzdins, P.; Malito, J.T. Inorg. Synth. 1978, 18, 126. (16) Hunter, A.D.; Legzdins, P. unpublished observation. (17) (a) Tolman, CA. Chem. Rev. 1977, 77_, 313. (b) Collman, J.P.; Hegedus, L.C "Principles and Applications of Organotransition Metal Chemistry"; University Science Books: M i l l Valley, 1980. (18) (a) Mayer, U.; Gutmann, V.; Gerger, W. Monatsh. Chem. 1975, 106, 1235. (b) Gutmann, V. Ibid. 1977, 108, 429. (19) (a) Yasuda, H.; Tatsumi, K.; Nakamura, A. Acc. Chem. Res. 1985, 120. (b) Erker, C ; KrUger, C ; Mailer, G. Adv. Organomet. Chem., in press, and references cited therein. (20) Yasuda, H.; Kajihara, Y.; Mashima, K.; Nagasuna, K.; Lee, K.; Nakamura, A. Organometallics 1982, 1^, 388. (21) (a) Legzdins, P.; Nurse, CR. Inorg. Chem. 1982, 21, 3110. (b) Crease, A.E.; Legzdins, P. J. Chem. Soc, Dalton Trans. 1973, 1501, and references cited therein. 178 (22) Legzdins, P.; Rettig, S.J.; Sanchez, L. submitted for publication. (23) Faller, J.W.; Shvo, Y. - J. Am. Chem. Soc. 1980, 102, 5396, and references cited therein. (24) (a) Faller, J.W.; Chodosh, D.; Katahira, D.A., unpublished observations, (b) Katahira, D.A., Ph.D. Dissertation, Yale University, New Haven, Connecticut, 1979. (25) See, for example (a) Chinn, J.W.; Jr.; Hall, M.B. Organometallics 1984, 3, 284. (b) Reference 19, and references cited therein. (26) Transoidal 1,3-butadiene is known to function as a bridging ligand 19 between two metal centers. See, for example: (a) Ziegler, M.L. Z.  Anorg. A l l g . Chem. 1967, 355, 12. (b) Sasse, H.E.; Ziegler, M.L. Ibid. 1972, 392, 167. (c) Pierpont, C.G. Inorg. Chem. 1978, 17, 1976. (27) For two previous examples of the use of these techniques to assign the *H and 1 3C NMR spectra of organometallic compounds see: (a) Dunach, E.; Halterman, R.L.; Vollhardt, K.P.C. J. Am. Chem. Soc. 1985, 107, 1664. (b) Green, M.L. H.; O'Hare, D. J. Chem. Soc. Chem. Commun. 1985, 332. (28) Very "readable" introductions to the use and interpretation of NOE difference, two dimensional, and other less familiar NMR techniques are provided by the following recent reviews, namely: (a) Levy, G. C.; Craik, D.J. Science 1981, 214, 291. (b) Benn, R.; GUnther, H. Angew. Chem. Int. Ed. Engl. 1983, 22, 350 and (c) Hall, L.D.; Sanders, J.K.M. J. Am. Chem. Soc. 1980, 102, 5703. ' _ — — ^ ^ ^ ^ — — — _ — . — — — — — — _ • _ — _ — — — — — — — — — — . < U t * * J 1 - » J • • — 179 (29) For a useful discussion of the acquisition and interpretation of 1 3C NMR spectra see: (a) Levy, G.C.; Lichter, R.L.; Nelson, G.L. "Carbon-13 Nuclear Magnetic Resonance Spectroscopy", 2nd Ed.; John Wiley and Sons: New York, 1980 and references cited therein. A large compilation of 1 3C NMR data of organometallic compounds and an introduction to it s interpretation has recently been published, see: (b) Mann, B.E.; Taylor, B.F. " 1 3C NMR Data for Organometallic Compounds"; Academic Press: London, England, 1981. (30) It should be pointed out that each trans-diene complex of "CpMo(NO)" must exist as a pair of enantiomers. (31) The magnitude of one bond proton-carbon 13 coupling constants i s diagnostic of the carbon's hybridization, namely: *J 3~125 Hz, ! j 2~155-160 H z 2 9 a and *J„ ~170-180 Hz. 2 9 b sp z Cp (32) The "cis" methyl resonances occur ~5-10 ppm upfield of their "trans" analogues in these complexes. (33) Ruh, S.; Philipsborn, W. von J. Organomet. Chem. 1977, 127, C59, and references cited therein. (34) Erker, G.; Wicher, J.; Engel, K.; Krtlger, C. Chem. Ber. 1982, 115, 3300. (35) Segre, A.L.; Zetta, L.; Di Corato, A. J. Mol. Spectrosc. 1969, 32, 296. (36) (a) King, R.B. Inorg. Chem. 1967^ 6, 30. (b) James, T.A.; McCleverty, J.A. J. Chem. Soc. A 1971, 1596. (37) The elements N, P, As, Sb and Bi are so designated by the recently 180 recommended notation: Chem. Eng. News 1985, Feb. 4, 26. (38) (a) It is somewhat surprising that this 19-electron radical anion does not immediately eliminate I~ (i.e. equation 5.16); however, similar kinetic stabilization (towards halide loss) of other halonitrosyl 19-electron radical anions has been observed. Wassink, B., Ph.D. Dissertation, University of British Columbia, Vancouver, British Columbia, 1985. (b) Indeed, preliminary electrochemical 38c investigations indicate that this reduction is electrochemically reversible, (c) Hunter, A.D.; Legzdins, P.; Richter-Addo, G., unpublished observation. (39) Other such n2-diene complexes of "CpMo(N0)L" (L=C04° or PMePhj41) are known. Indeed, the complex CpMo(NO)(PMePh2) (•n2-2,5-dimethyl-2,4-hexadiene) has a similar nitrosyl stretch (v N Q(THF) 1570 cm-1). (40) Faller, J.W.; Chao, K.H.; Murray, H.H. Organometallics 1984, 3^  1231. (41) Hunter, A.D.; Legzdins, P., unpublished observation. (42) Dorf, U.; Engle, K.; Erker, G. Organometallics 1983, 2_, 463. (43) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.; Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J. Am. Chem. Soc. 1985, 107, 2410. CHAPTER SIX STRUCTURAL AND ELECTRONIC EFFECTS OF "CpMo(NO)" ON CIS-AND TRANS-BUTADIENE COORDINATION1 1 182 Introduction In the vast majority of transition-metal complexes containing conjugated dienes, the diene ligands are attached to the metal center in a planar n^-cis manner. Indeed, the only examples of n^-trans-diene co-3 7 ordination to a single metal occur in CpjMCn^-diene) and CpMo(NO)(T|lt-diene) complexes (M = Zr, Hf; diene = acyclic conjugated diene). For the bent metallocene complexes, the cis and trans isomers are in equilibrium with each other and have comparable thermodynamic 7 9 s t a b i l i t i e s , but the cis conformer is generally favored. ' In contrast, the cis-diene complex isolated for "CpMo(NO)" is much less stable than i t s trans analogue ( i . e . for 2,3-dimethylbutadiene, 8 and 3 respectively) and g is not even spectroscopically detectable for other dienes used. The spectroscopic properties of CpMo(NO)('n'*-trans-diene), 1-6 (Table 5.2), and CpMo(NO)(r)**-cis-2,3-dimethylbutadiene), 8, display a number of interesting features. For instance, the IR nitrosyl stretching frequencies of these complexes indicate substantial backbonding to the NO * 8 u orbitals in these species. Further, the nitrosyl ligand of the cis complex, 8, appears to be much more electron-rich than that of i t s trans analogue, 3. The *H and 1 3C NMR spectra of these complexes establish the gross geometry of the diene ligands (i.e. cis vs. trans coordination) as well as giving an indication of their bonding to the metal center. Indeed, these NMR data were used to predict that the bonding interactions of the metal-diene linkage in these species are of the (rather than a,it,a) 183 type. To explain these chemical and spectroscopic observations, collabor-ative studies of the structures and bonding in these CpMo(NO)(n^-diene) complexes have been undertaken. Dr. F.W.B. Einstein and Dr. A.C. Willis of Simon Fraser University carried out single-crystal X-ray crystallographic analyses of CpMo(NO)(iy-trans-2,5-dimethyl-2,4-hexadiene), 6, and CpMo(NO)(T/*-CJS-2,3-dimethylbutadiene),lb 3. Dr. B.E. Bursten and Dr. M.G. Gatter of Ohio State University then performed molecular orbital (MO) calculations on the model cis and trans complexes, CpMo(NO)(rilt-C1+H6) (12 and 1, respectively). 1 In this chapter, a summary of their crystallo-graphic and MO results and my unified rationale for the unusual properties of these CpMo(NO)(r)lt-diene) complexes is presented. Experimental Section Crystals of CpMo(NO)(Ti4-trans-2,5-dimethyl-2,4-hexadiene) and CpMo(NO)(ri'+-cis_-2,3-dimethylbutadIene) suitable for X-ray crystallographic analysis were grown from hexanes and Et20/hexanes, respectively, at -20° C and were sealed in thin-walled glass capillaries. The structural determin-ations were performed by Dr. A.C. Willis and Dr. F.W.B. Einstein on an Enraf-Nonius CAD4F diffTactometer using Mo radiation and a graphite monochromator (X(K )=0.70930 A). These results 1^*' 1 1 are presented in al Table 6.1 (selected bond lengths and angles) and Figures 6.1 and 6.2 (molecular structures). These results were then used by Dr. B.E. Bursten and Mr. M.G. Gatter to provide the geometrical parameters for the model 184 c i s - and trans-butadiene complexes, CpMoCNOKrp-C^Hg), on which they 12 performed Fenske-Hall MO calculations. The results of these 13 calculations are presented in Table 6.2 (calculated Mulliken populations of the "CpMo(NO)" and diene fragments) and Figure 6.3 (MO diagram). Results and Discussion In Chapter Five, the reductive synthesis of the c i s - and trans-dienenitrosyl complexes CpMo(NO)(r)1*-diene) (diene = acyclic conjugated diene) is described, i.e. THF [CpMo(NO)I2]2 + 4 Na/Hg + 2 diene •==-> CpMo(NO)(T)'t-diene) + 4 Nal + Hg (6.1) This reaction produces the appropriate CpMo(NO)(ri^-trans-diene) complexes in about 10% yield when performed at ambient temperature. When the reaction is performed at reduced temperatures (-20-0°C) the transoidal products are isolated in about 40% yield due to the stabilization of solvated "CpMo(NO)" intermediates (see Chapters Four and Five). Further, the use of 2,3-dimethylbutadiene allows the isolation of the cisoidal complex CpMo(NO)(T^-cis-2,3-dimethylbutadlene), 8, in 13% yield. No analogous cis-diene complexes are detected, even spectroscopically, when other acyclic conjugated dienes (i.e. butadiene, 2-methylbutadiene, (E,E) and (Z,E)-2,4-hexadiene, and 2,5-dimethyl-2,4-hexadiene) are used in place of 2,3-dimethylbutadiene. IR monitoring of the course of reaction 6.1 (where diene = 2,3-185 dimethylbutadiene) indicates that the cisoidal complex, 8, is i n i t i a l l y g formed in a large excess (2-4 fold) over i t s transoidal analogue, 3. However, during the work-up of the this reaction mixture, the nitrosyl stretch of the cis-diene product is observed to decrease rapidly in inten-sity while the IR nitrosyl band due to 3 increases in intensity ( t 1 / 2 < 5 min at 20°C). Thus, the transoidal complex is isolated in a two fold g excess. These results can be explained in terms of the cis complex under-going an isomerization to i t s trans analogue, i.e. CpMo(NO)(n*4-cis-diene) —> CpMo(NO)(n^-trans-diene) (6.2) Indeed, this isomerization can be observed by IR, *H and 1 3C NMR spectro-scopy to proceed rapidly in donor solvents such as THF but more slowly in non-coordinating solvents such as benzene ( t 1 / 2 ~^ ^ a v a t 20°C) with some attendant decomposition. However, this isomerization is not reversible as is observed for Cp2M(n4-diene) (M=Zr,Hf) where the c i s - and trans-diene complexes are in equilibrium at ambient temperatures.^ Indeed, no spectro-scopic evidence for the reverse of reaction 6.2 is found, even when solutions of the various trans-diene complexes, 1-6, are heated until the complex decomposes. This evidence suggests that the cis-diene complex, 8, is the kinetically favored product of reaction 6.1 while the trans-diene complex, 3, is the thermodynamically favored isomer. Indeed, the evidence suggests 186 that for acyclic conjugated ""dienes coordinated to "CpMo(NO)" the transoidal isomer i s the thermodynamically preferred mode of linkage while the c i s o i d a l form, at least for 2,3-dimethylbutadiene, i s the k i n e t i c a l l y favored product of reaction 6.1. This contrasts sharply with the related CpjMCn^-diene) (M = Zr, Hf) complexes where the trans isomer i s the k i n e t i c product but the c i s isomer i s generally thermodynamically favored. 7 For the bent metallocene complexes, this isomerization i s thought to proceed via a 16-electron, T)2-diene intermediate. 7 The fact that the k i n e t i c a l l y favored cis-diene complex i s isolable for 2,3-dimethylbutadiene but not for the other dienes can be rationalized i f a similar ri 2-diene complex i s invoked as an intermediate i n reaction 6.2. For 2,3-disubstituted dienes any such T) 2-diene intermediate (where S = solvent and n = 0 or 1) would experience s t e r i c repulsions between the non-coordinated moiety ( i . e . the CH3 or =CH2 groups on carbon-3) and the metal center that would hinder rotation about 187 the C 2 -C 3 bond and thus cis to trans isomerization. For the other dienes used, the diene ligand has an H atom rather than a CH3 substituent bound to carbon-3 (see Table 5.2), and thus any such rotation about Cj-Cg would not be as hindered. Thus, i f cisoidal complexes (analogous to 8) are the kinetic products of reaction 6.1 for the other dienes used, then they would be expected to rapidly isomerize to the thermodynamically preferred trans form. Indeed, the fact that the ratios of the two isomers observed for the trans-diene complexes of 2-methylbutadiene (2A and 2B) and (Z,E)-2,4-hexadiene (5A and 5B) do not change as a function of temperature or solvent (by 1H NMR) suggest that the requisite cisoidal intermediate (necessary for changing the face of the diene coordinated to "CpMo(NO)") is too energetically unfavorable to be involved at ambient temperatures (even in spectroscopically undetectable quantities) in any cis «f > trans equilibrium. The "CpMo(NO)" and "Cp2M" (M = Zr, Hf) fragments also confer signi-g ficantly different NMR properties onto bound diene ligands. These can be interpreted to show that the diene ligands of the nitrosyl complex have significantly more nt% (and less a,it,a) character than their bent metallo-cene analogues for both the c i s - and especially the trans-diene g complexes. To explain the origin of the strong thermodynamic preference for transoidal coordination and to elucidate the bonding in these species, the crystal structures of representative c i s - and trans-diene complexes (8 and 6, respectively) have been determined and MO calculations were performed on the model butadiene complexes u t i l i z i n g these geometries. The molecular structures of CpMo(NO) (r)t*-trans-2,5-dimethyl-2,4-188 hexadiene) , 6, and CpMo(NO)(Ty-cis-2,3-dimethylbutadiene), 8, deter-mined by single crystal X-ray crystallographic analyses, 1^' 1 1 are shown in Figures 6.1 and 6.2, respectively, and a l i s t of selected bond lengths and angles is shown in Table 6.1. The excellent R factors for these w structures (0.024 and 0.028, respectively) result in the determined bond lengths and angles being quite accurate (to ~.002 - .004 A and 0.2 - 0.3 deg). Both complexes possess types of "three-legged piano stool" geometries with complex 8 having a crystallographically imposed mirror plane through C4, Mo, N, and 0 that bisects the diene ligand. The two g complexes have the anticipated trans- and cis-diene geometries. The results of the calculations on the model c i s - and trans-butadiene complexes of "CpMo(NO)" (1£ and 1^  respectively), performed by 12 13 the Fenske-Hall method, ' are presented in Figure 6.3 (the M0 inter-action diagram) and Table 6.2 (the calculated Mulliken populations of the complexed diene and "CpMo(NO)" fragments). As expected, the transoidal complex exhibits a large stabilization with respect to i t s cisoidal analogue. This contrasts with the results of the calculations on the analogous Cp2Zr(Ti't-diene) complexes which were found to be energetically 9 very similar, with the cis-diene complex being slightly favored. The large stabilization of the trans complex arises from the asymmetry of the trans-diene ligand with respect to the "CpMo(NO)" valence orbitals which results, in turn, in increased overlap between these orbitals and those on the diene fragment. The cyclopentadienyl ligands of 6 and 8 exhibit normal Cp-Mo 189 Figure 6.1. Molecular structure of CpMo(N0)(r) 1 +-trans-2,5-dimethyl-2,4-hexadiene). Views (a) along the axis b i s e c t i n g the Cp-Mo-NO angle and (b) down the C4-C5 bond. Figure 6.2. Molecular structure of CpMo(NO)(rT-cis-2,3-dimethyl-butadiene). Views (a) along the axis b i s e c t i n g the Cp-Mo-NO angle and (b) along the axis passing through Mo and perpendicular to the c r y s t a l l o -g r a p h i c a l l y imposed mirror plane containing C4, Mo, N, and 0. Mo 191 Table 6.1 Selected Bond Distances (A) and Angles (deg) of CpMo(NO)(ritt-cis-2,3-dimethylbutadiene) and CpMo(NO)(T)**-trans-2,5-dimethyl-2,4-hexadiene). c i s — trans Mo-CP- 2.017(2) Mo-CP 2.037(2) Mo-N 1.773(3) Mo-N 1.767(2) N-0 1.218(4) N-0 1.213(3) Mo-N-0 161.0(3) Mo-N-0 172.2(2) C1-C2 1.410(4) C3-C4;C5-C6 1.418(4);1.401(4) C2-C2' 1.414(6) C4-C5 1.408(4) Mo-Cl 2.220(3) Mo-C3;Mo-C6 2.390(3);2.365(3) Mo-C2 2.338(2) Mo-C4;Mo-C5 2.209(3);2.234(3) C2-C3 1.504(5) C(Me)-C(av) 1.510(7) C1-C2-C2' 122.0(2) C3-C4-C5;C4-C5-C6 122.3(3);122.1(3) C1-C2-C3 117.3(3) C(me)-C-C(av) 120(2) C3-C2-C2' 119.8(3) C1-C3-C2;C7-C6-C8 112.7(3);112.6(3) — The crystallographically imposed mirror plane passes through Mo, N, 0, and C4 and bisects the diene ligand. — Where CP is the centroid of the cyclopentadienyl ligand. 192 Figure 6.3. Molecular o r b i t a l diagram of the upper valence o r b i t a l s of CpMo(NO)(ril+-cis_-CltH6) and CpMo(NO)(ii' t-trans-C l tH A). c i s complex trans complex free/T~\\ CpMo(NO) (/f~\[) "CpMo (NO) 11 CpMo (NO) (//\#) free /0V/ 193 T a b l e 6 . 2 Calculated Mulliken Populations of CpMo(NO)(T)lt-cis-CltH6) and CpMo(NO)(n't-trans-C4H6). cis trans 1.87 1.86 n 2 1.63 1.55 u 3 0.68 0.50 Tt4 0.03 0.11 NOTC* 0.765 0.738 x NOTC 0.800 0.773 y d 1.98 1.90 xz d 1.78 1.86 xy d o 1.50 1.60 z z d 0.47 0.50 yz sp 0.18 0.23 y 194 14 linkages with no s t e r i c interactions observed between atoms on the diene and Cp ligands. Indeed, no s i g n i f i c a n t intermolecular contacts are evident. E l e c t r o n i c a l l y , the Cp-Mo linkages of both complexes appear very similar with the cyclopentadienyl ligand being a s i m i l a r net electron donor to both metal centers. The IR n i t r o s y l - s t r e t c h i n g frequency of the c i s complex (8, (CH 2C1 2) 1552 cm - 1) i s much lower than that of either i t s trans analogue (3, v N O ( C H 2 C l 2 ) 1591 cm - 1) or of trans complex 6 ( v N ( ) ( C H 2 C l 2 ) 1584 cm - 1). This indicates that the n i t r o s y l ligand i n the c i s complex accepts more electron density into Its NO it o r b i t a l s than do i t s transoidal 8 15 analogues. ' This i n t e r p r e t a t i o n i s supported by the calculated electron * * populations of the NO it o r b i t a l s of these species. The two it o r b i t a l s of the c i s complex contain more electron density (1.565 electrons) than do those of i t s trans analogue (1.511 electrons) even though both NO groups are s i m i l a r o-donors 1^ to the metal center. The Mo-N and N-0 bond lengths for 6 (1.767(2) A and 1.213(3) A, respectively) and 8 (1.773(3) A and 1.218(4) A, respectively) are s i m i l a r to those previously reported for the 14a 14b-d related CpMo(NO)(CO)L complexes (L = phosphine, alkene ; Mo-N ~ 1.77-1.81A, N-0 ~ 1.20-1.22 A ) . The M-N-0 angle of 6 (172.2(2)°) i s 14 similar to those previously observed (~173-177° ) but i s much larger than that of the related c i s complex, 8 (161.0(3)°). The decreased M-N-0 angle * 15 16 of the c i s complex also r e f l e c t s the increased NO it density ' observed on this ligand. As presented i n Chapter Five, NMR studies suggest that the c i s - and trans-diene ligands of "CpMo(NO)" are i n character with e s s e n t i a l l y 195 sp 2 hybridized terminal diene carbons. This evidence also suggests that the cis complex exhibits more sp 3 character for these carbons (i.e. t r , T c , o " ) than does i t s trans analogue. The carbon-carbon bond lengths for the external ( i . e . C^-Cj and Cg-C^) and internal (i.e. C 2 -C 3) diene bonds are approximately equivalent for both 6 l a and 8 l b (C-C = 1.401-1.418 A, Table 6.1). This is in marked contrast to the zirconocene complexes where the cis species exhibit long-short-long bond length alternation (~1.45 A, ~1.40 A , ~1.45 A ) 7 while their trans analogues exhibits short-long-short bond length alternation (1.40 A, 1.48 A, 1.40 A ) 7 similar to that seen in free butadiene (~1.34 A, ~1.48 A, ~1.34 A ) . 1 7 Further, in the trans complex, 6, the central carbons are slightly closer to the metal center (Mo-C~2.22 A) than are the terminal carbons (Mo-C~2.38 A) while the opposite is true for 8 (i.e. 2.338(2) A and 2.220(3) A, respectively). This trend is also evident for the Cp 2Zr(Ti' t-diene) complexes.7 The observation that Cl and C4 are closer to Mo than are C2 and C3 in the cisoidal complex, 8, is further evidence of some a,Tt,o" contribution to the bonding in this species. 7 Finally, a twist angle of 124.8(4)° is observed about the C4-C5 bond of 6 (see Figure 6.1(b)) similar to that observed for Cp ?Zr ( n l t-trans - ( E , E)-l,4-diphenylbutadiene) ( i . e . 126.1°). These structural results are in accord 1 8 with the expectations ' that both the c i s - and trans-diene ligands of . * CpMo(N0)(TT-diene) exhibit substantial backbonding into the diene TC3 molecular orbitals and that the backbonding into this orbital is greatest (thus giving the largest a,%,a contribution) to the cis complex. The molecular orbital calculations (Table 6.2) show substantial 196 backbonding into the n 3 orbitals of the bound diene ligands. This explains the observed equalization of diene bond lengths in these species. Further, the enhanced ix3 electron population of 1£ over 1^  may explain the more sp 3 character of the terminal diene carbons of the cisoidal complex. Finally, i t can be seen that more net electron density is transferred to both the NO and diene ligands (Table 6.2) of the cis complex than i t s trans analogue and this results in a relatively electron poorer metal atom for 12 than for 1 ( i . e . net charge on Mo is +0.15 and -0.08 electrons, respec-ti v e l y ) . Thus, the spectroscopic and structural differences between the c i s - and trans-diene complexes of "CpMo(NO)" and between these and their "Cp2M" (M = Zr, Hf) analogues may be understood in terms of the differing MO energetics of these species. C o n c l u s i o n s This work has established that the trans-diene complexes of "CpMo(NO)" exhibit unprecedented thermodynamic stability with respect to their cisoidal analogues. However, the cis-diene complexes are the kinetically favored products of reaction 6.1. The spectroscopic and struc-tural properties of these species are very different from their CpjMCn1*-diene) (M = Zr, Hf) analogues. This appears to reflect the decreased o,n,a contribution to the metal-diene linkage in the nitrosyl complexes. The MO structure of the CpMo(N0)(-n't-diene) complexes is used to rationalize these spectroscopic and structural features as well as the enhanced thermodynamic stability of the transoidal complex. 197 It should be noted that these c a l c u l a t i o n s on the CpMo(NO)(rf-diene) complexes as well as those on the related CpjZrCn^-diene) systems allow us to formulate two general c r i t e r i a that must be met i n order to s t a b i l i z e trans-diene coordination, namely: (1) the L^M (L^ = a n c i l l i a r y ligands) fragment should possess a set of valence o r b i t a l s with the HOMO and LUMO being coplanar and of a and TC symmetry, res p e c t i v e l y , towards the centroid of the diene l i g a n d . (2) the trans complex should be most favored where L^M i s r e l a t i v e l y electron d e f i c i e n t since for the c i s complex the HOMO gives up more electron density and the LUMO and SLUMO (second lowest unoccupied MO) receive less electron density than i t s trans conformer. With these thoughts i n mind, the search for other trans-diene complexes should be expedited. 198 References and Notes (1) Taken in part from: (a) Hunter, A.D.; Legzdins, P.; Nurse, CR.; Einstein, F.W.B.; Wil l i s , A.C. J. Am. Chem. Soc. 1985, 107, 1791. (b) Hunter, A.D.; Legzdins, P.; Einstein, F.W.B.; Willis , A.C; Bursten, B.E.; Gatter, M.G. submitted for publication. (2) See, for example: Chinn, J.W., Jr.; Hall, M.B. Organometallics 1984, 3, 284 and references therein. (3) Transoidal, 1,3-butadiene is known to function as a bridging ligand i 4 between two metal centers in [CpMn(C0)2]2 (u^-tV-C^Hg) , [Mn(C0)1+]2 ( u ^ - C ^ H g ) 5 and Os 3(CO) 8 (u^-C^Hg) . 6 (4) Ziegler, Von M. Z. Anorg. Al l g . Chem. 1967, 355, 12. (5) Sasse, H.E.; Ziegler, M.L. Z. Anorg. Allg. Chem. 1972, 392, 167. (6) Pierpont, C.6. Inorg. Chem. 1978, 17, 1976. (7) (a) Yasuda, H.; Tatsumi, K.; Nakamura, A. Acc. Chem. Res. 1985, 18, 120. (b) Erker, C ; KrUger, C ; Mailer, G. Adv. Organomet. Chem., in press, and references cited therein. (8) See reference 1 and Chapter Five. (9) Tatsumi, K.; Yasuda, H.; Nakamura, A. Isr. J. Chem. 1983, 23, 145. (10) The X-ray data for CpMo(NO)(n1*-trans-2,5-dimethyl-2,4-hexadiene) : monoclinic; S.G. P21/(,; a - 12.153(2) A, b = 9.275(1) A, c -12.909(4) A; 6 = 117.31(2)°; V = 1292.9 A 3 ; Z = 4; u = 9.69 cm"1; scan range 0 < 29 < 50°; reflections = 1862 with Io > 3aIo; R = 0.021, R = 0.024. A l l atoms were refined, w (11) The X-ray data for CpMo(NO) (T) 4-cis-2,3-dimethylbutadiene): orthorhombic; S.G. Pnma; a = 17.414(3) A; b - 9.116(4) A; c = 7.280(1) 199 A; V = 1155.67 A 3 ; Z = 4; u = 10.78 cm-1; scan range 0 < 29 < 60°; reflections = 1352 with lo > 3aIo; R = 0.028, R = 0.028. A l l atoms w were refined. (12) Hall, M.B.; Fenske, R.F. Inorg. Chem. 1972, 11, 768. (13) Fenske-Hall calculations were carried out as previously described: Bursten, B.E.: Gatter, M.G. J. Am. Chem. Soc. 1984, 106, 2554. (14) (a) Reisner, M.G.; Bernal, I.; Brunner, H.; Doppelberger, J. J. Chem. Soc, Dalton Trans. 1978, 1664. (b) Faller, S.W.; Chao, K.H.; Murray, H.H. Organometallics 1984, jJ, 1231. (c) Adams, R.D.; Chadosh, D.F.; Faller, J.W.: Rosan, A.M. J. Am. Chem. Soc. 1979, 101, 2570. (d) McCleverty, J.A.; Murray, A.J. Transition Met. Chem. 1979, 4, 273. (15) See Chapter One. (16) Geiger, W.E.; Rieger, P.H.; Tulyathan, B.; Rausch, M.D. J. Am. Chem.  Soc. 1984, 106, 7000. (17) Marais, D.J.; Sheppard, N.; Stoicheff, B.P. Tetrahedron 1962, 17, 163. 200 Epilogue Chapters Two and Three of this work provide an important lesson to the synthetic chemist. Both resulted from attempts to repeat l i t e r a t u r e reports of well known synthetic procedures using r e l a t i v e l y minor experi-mental modifications. In both cases, t h i s led to i n i t i a l l y confusing r e s u l t s ; however, a de t a i l e d r e i n v e s t i g a t i o n of the these reactions resulted i n the i s o l a t i o n of some novel complexes and increased i n s i g h t into the mechanisms of these reactions. The reduction reactions explored In Chapters Four and Five led to the i s o l a t i o n of an i n t e r e s t i n g series of e l e c t r o n - r i c h n i t r o s y l complexes, CpM(N0)L2 (M = Cr, Mo, and W; L = Lewis Base), and the novel c i s - and trans-diene complexes CpMo(MO)(Ti^-diene). Pathways for the syntheses of these compounds were proposed that are i n accord with the observed IR spectral changes and stoichiometric reactions. However, confirmation of these paths must await a detai l e d electrochemical i n v e s t i g a t i o n of these reactions. The spectrocopic and s t r u c t u r a l properties of the diene complexes were r a t i o n a l i z e d i n terms of MO theory i n Chapter Six. These r e s u l t s were used to propose general c r i t e r i a for the formation of stable trans-diene complexes. Obviously these predictions and the r e a c t i v i t y of the c i s - and trans-diene complexes with nucleophiles and e l e c t r o p h i l e s must next be investigated. O v e r a l l , t h i s work has again demonstrated that the s p e c i a l charac-t e r i s t i c s of the n i t r o s y l ligand discussed i n Chapter One give i t s complexes t r u l y i n t e r e s t i n g and unexpected chemistry! 201 Appendix Selected Infrared Spectra of Compounds Described i n t h i s Thesis, 202 [Cp'Cr(CO) 3]2 as a hexanes s o l u t i o n . j FREQUENCY (CM"') 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 (T) 6-C 1 1H l l +)Cr(CO) 3 as a hexanes so l u t i o n . 2 0 3 204 W(N0) 2C1 2(CH 3CN) 2 as a CH3CN so l u t i o n . j FREQUENCY (CM"') 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 c W(N0)C1 3(CH 3CN) 2 as a CH3CN so l u t i o n . 205 I FREQUENCY (CM"') 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 W(NO) 2Cl 2(PMePh 2) 2 as a CH 2C1 2 s o l u t i o n . 2 0 6 | FREQUENCY (CM"') 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 207 2 0 8 [CpMo(NO)I(PMePh 2) 2]I as a Nujol mull. 209 210 CpMo(NO)(V_trans-2,5-dimethyl-2)4-hexadiene) as a hexanes solution. W A V E , ' J U M B e N 3 C C M - - 1 > 211 

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