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The chemistry of group VIB organometallic nitrosyl complexes Hames, Barry Wayne 1981

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THE CHEMISTRY OF GROUP V I B ORGANOMETALLIC NITROSYL COMPLEXES b y BARRY WAYNE HAMES B.Sc . ( H o n o u r s ) , The U n i v e r s i t y o f R e g i n a , 1 9 7 6 A THESIS SUBMITTED I N P A R T I A L FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES ( D e p a r t m e n t o f C h e m i s t r y ) . We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF B R I T I S H COLUMBIA A p r i l , 1 9 8 1 (^ cT) B a r r y Wayne Hames, 1 9 8 1 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Chemistry The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date May 22, 1981 ABSTRACT The reaction of chromocene with nitrogen monoxide in a variety of organic solvents leads to the formation of C pCr(NO) 2 ( n 1 - C5 H5) a s t n e major product, as well as CpCr(NO) 2(N0 2) and [CpCr(NO) 2] 2 a s minor products. Their formation i n these conversions can be r a t i o n a l i z e d i n terms of the reactive intermediate CpCr(NO)^•. The reaction of photochemically generated molybdenocene with nitrogen monoxide to produce CpMo (NO) 2 (n1-C,-H5) i s also described. Sodium dihydridobis(2-methoxyethoxy)aluminate, I, undergoes metathetical reactions in benzene with a v a r i e t y of n i t r o s y l halide complexes. Thus treatment of CpCr(NO) 2X (X = N0 3, N0 2, I, n 1-C 5H 5, or BF^), CpMn(CO) (NO)I, CpCo(NO)I, and [CpMo(NO) T^] 2 with I i n 1:1 stoichiometries affords the respective dimeric compounds [CpCr (NO) 21 2> [CpMn (CO) (NO) ] 2 / [CpCo(NO)] 2/ and [CpMo (NO) I] 2 . These l a t t e r conversions probably proceed v i a thermally unstable hydrido complexes. The chromium dimer also r e s u l t s from the reaction [CpCr(NO) 2(CO)]PF g with the aluminum reagent and reacts further with I to produce i n low y i e l d s a mixture of Cp 2Cr 2(NO) (NH 2), Cp 2Cr 2(NO) 2(NH 2) 2, and Cp 2Cr 2(NO) 2~ (NH2)(OH). In a similar manner, Fe(NO)^Cl i s converted by I to Fe 2 (NO) 4 (NH2) 2 . Reduction of [CpCr(NO) 2] 2 with BH^ and with LiEt^BH produces the same three b i m e t a l l i c products as when I serves as the reducing agent, and i n comparably low y i e l d s . - i i i -However, with LiEt^BH as reductant the complexes CpCr(NO) 2Et and Cp 2Cr 2(NO) 3(EtNBEt 2) are also formed, r e f l e c t i n g unpre-cedented modes of r e a c t i v i t y of the hydridoborate. An x-ray crystallographic analysis of the new Cp 2Cr 2(NO)^(EtNBEt 2) complex has been performed. The most chemically i n t e r e s t i n g feature of the molecular structure i s the novel EtNBEt 2 ligand which i s coordinated v i a N i n a symmetrical fashion to the two Cr atoms. The coordination environment around N i s that of a d i s t o r t e d tetrahedron, but the N-B distance of 1.459(5) & suggests some degree of multiple bonding between these two atoms. Such an inference i s consistent with the s t a b i l i t y of the complex and i t s spectroscopic properties. The preparation and characterization of several organometallic hydridonitrosyl complexes, i . e . CpMo(NO)2H and [Cp 2M 1M 2 (NO) 4H] +X~ (M][ = M2 = Mo, W; 1^ = Mo, M2 = W: X = BF 4 and/or PF g) are described^ The monometallic hydride i s prepared by reduction of CpMo(NO) 2Cl with I, while the homonuclear b i m e t a l l i c cations are formed upon reaction of CpM(NO)2H (M = Mo, W) with 0.5 equivalents of a hydride abstraction agent such as Ph 3C +X or C^H^BF^ i n CH 2C1 2. The heteronuclear cation can be prepared by the reaction of CpMo(NO) 2Cl with AgBF 4 to produce CpMo(NO) 2 +BF 4~, which may then be reacted with CpW(NO)2H to y i e l d the cation. Attempts to deprotonate these cations with a variety of bases r e s u l t i n cleavage of the metal-metal bond to y i e l d the "• hydride and a monometallic cation of the type CpM(NO)2(L) (where L i s the base used). - i v -The f a i l u r e o f t h e attem p t e d d e p r o t o n a t i o n s l e d t o an e x a m i n a t i o n o f t h e Lewis base p r o p e r t i e s o f CpW(NO) 2H and o f t h e Lewis a c i d p r o p e r t i e s o f CpW(N0)2 +. S p e c i f i c a l l y , t h e i n t e r a c t i o n o f CpW(NO) 2H w i t h a v a r i e t y o f s o f t ( i . e . C r ( C O ) 5 , W(CO) 5, (MeCp)Mn(CO) 2, H g C l 2 , and C d C l 2 ) , b o r d e r -l i n e ( i . e . Z n C l 2 ) , and h a r d ( i . e . H +, A l C l ^ , and BEt^) Lewis a c i d s i s o b s e r v e d s p e c t r o s c o p i c a l l y . The o b s e r v e d Lewis base c h a r a c t e r i s t i c s o f CpW(NO) 2H are d i s c u s s e d i n l i g h t o f th e s e r e s u l t s , and when combined w i t h the Lewis a c i d p r o p e r t i e s o f CpW(NO) 2 +, i t i s p o s s i b l e t o r a t i o n a l i z e t h e f a i l u r e t o p r e p a r e t h e dimers [CpM(NO) 2J 2 (M = Mo, W) v i a t h e d e s i r e d r o u t e . - v -ACKNOWLEDGEMENTS I w i s h t o t h a n k t h e f a c u l t y and t e c h n i c a l s t a f f o f t h e c h e m i s t r y d e p a r t m e n t f o r t h e i r e x p e r t a s s i s t a n c e and a d v i c e t h r o u g h o u t t h i s s t u d y . I n p a r t i c u l a r , I w i s h t o t h a n k P r o f e s s o r s F. Aubke and E.E. B u r n e l l who r e a d p o r t i o n s o f t h i s t h e s i s and o f f e r e d s u g g e s t i o n s f o r i t s improvement. The d i l i g e n t p r o o f r e a d i n g o f D.T. M a r t i n i s a l s o g r e a t l y a p p r e c i a t e d . I am e s p e c i a l l y i n d e b t e d t o Dr. B r i a n W.S. Kolthammer and D a v i d T. M a r t i n whose w i t and d e d i c a t i o n t o e x c e l l e n c e p r o v i d e d a p l e a s a n t a t m o s p h e r e f o r work. The many 'committee m e e t i n g s ' a f t e r work were a c o n s t a n t s o u r c e o f s o l a c e and enc o u r a g e m e n t ; I e s p e c i a l l y a c k n o w l e d g e Dr. Howard E. M o r t o n and Randy J . M i k u l a . F i n a n c i a l a s s i s t a n c e f r o m t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada (1976-80) i s g r a t e f u l l y a c k n o w l e d g e d . F i n a l l y , I w i s h t o e x p r e s s my g r a t i t u d e t o Dr. P e t e r L e g z d i n s . f o r h i s g u i d a n c e , s u p p o r t , and c o n s t a n t e n t h u s i a s m , w i t h o u t w h i c h t h e c o m p l e t i o n o f t h i s t h e s i s would n o t have been p o s s i b l e . - v i -T A B L E : OF CONTENTS Page ABSTRACT . • . ... . .. .... . ........ .... ... .: .. . .............. i i ACKNOWLEDGEMENTS . . . ... , ... . . . . v TABLE OF CONTENTS . ... . ... .. • v i LIST OF TABLES • .............. i x L Z S T Of FIGURES" . . . . . . . . . x ABBREVIATIONS AND COMMON NAMES" . x i CHAPTER, I INTRODUCTION 1 I:. The Ba s i s of the Problem . 1 I I . The Reaction of NO wit h T r a n s i t i o n - m e t a l Complexes 4 I I I . The Bonding and R e a c t i v i t y of T r a n s i t i o n -metal Coordinated Nitrogen Monoxide ... 5 CHAPTER IT SOME REACTIONS OF NITROGEN MONOXIDE WITH ELECTRON-DEFICIENT METALLOCENES 11 Experimental 12 Resu l t s and Di s c u s s i o n . . . . . . . v 21 Reactions of Nitrogen Monoxide w i t h Cp 2Cr 21 Reactions of Nitrogen Monoxide wi t h Cp2Mo 28 Reaction of Nitrogen Monoxide w i t h Cp 2V 30 Summary and Conclusions 3 0 CHAPTER I I I REACTIONS OF SODIUM DIHYDRIDOBIS— (2—METHOXYETHOXY) ALUMINATE WITH' SOME CATIONIC AND NEUTRAL NITROSYL COMPLEXES 31 Experimental ............ . . . . ........... 33 Results and D i s c u s s i o n . ... ................ 41 - v i i -P a g e R e a c t i o n s - o f Sodium D i h y d r i d o b i s -C2-methoxy^t'lldxy^aluminate .. . . ............ 41 (a. I. With. Monomeric Chromium N i t r o s y l C o m plexes . . ..... .,....................................... 41 (b) With. Some. Monomeric I o d o n i t r o s y l Complexes- . . . . . . . . . . . . . . . . . ......... . .......... 42 (c) With. [CpMo (NO)X 2] 2 (X = I , CI) Complexes 4 4 (d I Wi.th. {CpCr (NO\ } .... 46 ( e l W i t h F e ( N O ) 3 C l 52 CHAPTER IV REACTIONS' OF B I S [ (.n,5 —CYCLOPENTADIENYL). — DINITROSYLCHROMIUM] WITH LITHIUM TRIETHYL-BOROHYDRIDE AND WITH BORANE 57 E x p e r i m e n t a l ......... 58 R e s u l t s and D i s c u s s i o n 61 The R e a c t i o n o f L i E t ^ B H w i t h [ C p C r ( N O ) 2 ] 2 61 The R e a c t i o n o f BH^ w i t h [ C p C r ( N O ) 2 ] 2 77 CHAPTER V A, STUDY OF THE LEWIS BASE PROPERTIES OF CYCLOPENTADIENYLTUNGSTENDINITROSYL HYDRIDE AND THE LEWIS ACID PROPERTIES OF THE CYCLOPENTADIENYLTUNGSTENDINTTROSYL CATION 7 9 E x p e r i m e n t a l 83 R e s u l t s and D i s c u s s i o n . 109 The P r e p a r a t i o n and C h a r a c t e r i z a t i o n o f CpMo (NO) 2 H . . ... . ..... . . .. . 109 The P r e p a r a t i o n _ a n d C h a r a c t e r i z a t i o n o f [Cp 2W 2 (NO) 4H] X (X = B F 4 , P F 6 ) 111 The P r e p a r a t i o n and C h a r a c t e r i z a t i o n , o f I Cp 2MQ 2 (NO 14H] PF 6 ., .... . . . . . . . ... ... . . ... 124 The P r e p a r a t i o n and C h a r a c t e r i z a t i o n o f [Cp 2MoW(NOI 4 H]BF 4 125 - v i i i -Page Attempted Deprotonations of [Cp 2M 2 (NO) H] (M = Mo, W) 131 Summary of the Properties of [Cp„M,M„-(NO) .H] (M, = M_ = Mo, W; M, = Mo, :,_ M2 = W) . 7 7 . 134 Attempted Synthesis of [Cp 2Cr 2(NO) H] ... 136 The Interaction of CpW(NO)'„H With Lewis Acids 7 138 (a) The Interaction of CpW(NO)?H With M(CO) (M = Cr, W) and With (MeCpjMn(CO)2 7. 142 (b) The Interaction of CpW(NO),H With MCI, (M = Zn, Cd, Hg) 7 148 (c) The Reaction of CpW(NO)2H With H + 152 (d) The Reaction of CpW(NO)2H With AlClg 153 (e) Summary and Conclusions 154 EPILOGUE 158 REFERENCES AND NOTES 15 9 - ix -LIST OF TABLES Table Page I Low-Resolution Mass Spectral Data for CpCr (NO) 2Cn 1-C 5H 5) and CpCr(NO) 2(N0 2) 15 IT Low-Resolution Mass Spectral Data for Cp 2Cr 2 (NO) 2(NH 2)X (X = NH2 or OH) Complexes . 48 III High-Resolution Mass Spectral Data for F e 2 (N0) 4 (NH 2) 2 •• 55 IV Selected Bond Distances and Bond Angles (deg) for Cp 2Cr 2 (NO) 3 (EtNBEt 2) 68 V High-Resolution Mass Spectral Data for Cp 2Cr 2(NO) 3(EtNBEt 2) 72 VI NMR Data for Cp 2Cr 2(NO) 3(EtNBEt 2) i n CDC13 .. 74 VII C h a r a c t e r i s t i c N i t r o s y l Absorptions of CpM(NO)2H (M = Mo, W) Derivatives 123 VIII Low-Resolution Mass Spectral Data for CpCr(NO) 2(0 3SC 6H 4-pCH 3) 139 IX C h a r a c t e r i s t i c N i t r o s y l Absorptions of CpW(.N0)9H Adducts 144 - x -LIST OF FIGURES Figure Page 1 Stereoscopic view of the contents of a unit c e l l of Cp 2Cr 2 (NO) 3 (EtNBEt 2) 65 2 A perspective view of the molecular structure of Cp 2Cr 2(NO) 3(EtNBEt 2) including the atom numbering scheme 66 3 The XH NMR Spectrum of [Cp?W (NO) .H] BF. in CD 3N0 2 Solution ... 116 4 The hydride region of the *H NMR spectrum of a [CpJVI„ (NO) .H] PF mixture (Mo:W r a t i o 1.5:1) in CD 3N0 2 ... 129 - x i -ABBREVIATIONS AND COMMON NAMES R Angstrom A n a l . C a l c d a n a l y s i s c a l c u l a t e d atm atmosphere(s) br broad °C degrees C e l s i u s cm c e n t i m e t r e ( s ) cm wave numbers i n r e c i p r o c a l c e n t i m e t r e s Cp p e n t a h a p t o - c y c l o p e n t a d i e n y l d d o u b l e t dec decomposes deg plane angle DMF N,N-dimethylformamide e e l e c t r o n ( s ) eq equation(s) Et e t h y l eV e l e c t r o n v o l t s f s t r e t c h i n g f o r c e constant g gram(s) h hour(s) Harpoon Base .. 2 , 2 , 6 , 6 , - t e t r a m e t h y l p i p e r i d i n e HMPA hexamethylphosphoramide Hz Hertz, c y c l e s per second hv i r r a d i a t i o n I Nuclear Spin i n u n i t s of h/2-rr I NaAlH 2(OCH 2CH 2OCH 3) 2 "IR i n f r a r e d J homonuclear magnetic resonance c o u p l i n g constant J h e t e r o n u c l e a r magnetic resonance c o u p l i n g constant, where x i s the number of bonds s e p a r a t i n g the spin-coupled n u c l e i and y s p e c i f i e s the coupled n u c l e i m m u l t i p l e t - x i i -M * M mdyn Me min mL mmol mp m/z (MeCp) NMR Ph PPm P r o t o n Sponge . R r e l abund s s h s t t - B u THF T o r r w S - n 1  v a "5 m o l e s p e r l i t r e m e t a s t a b l e i o n (s) , -.-..''i m i l l i d y n e s m e t h y l m i n u t e ( s ) m i l l i l i t r e ( s ) m i l l i m o l e ( s ) m e l t i n g p o i n t m a s s - t o - c h a r g e r a t i o p e n t a h a p t o - m e t h y l c y c l o p e n t a d i e n y l n u c l e a r m a g n e t i c r e s o n a n c e p h e n y l p a r t s p e r m i l l i o n N , N , N ' , N 1 - t e t r a m e t h y l - 1 , 8 - n a p h t h a l e n e -d i a m i n e a l k y l o r a r y l r e l a t i v e abundance s i n g l e t s h o u l d e r s t r o n g t e r t i a r y - b u t y l t e t r a h y d r o f u r a n m i l l i m e t r e s o f m e r c u r y p r e s s u r e weak NMR c h e m i c a l s h i f t i n p a r t s p e r m i l l i o n monohapto i n f r a r e d s t r e t c h i n g f r e q u e n c y a p p r o x i m a t e l y p e r c e n t - x i i i -A series of judgements, revised without ceasing, goes to make the incontestable progress of science. Pierre Emile Duclaux (1840-1904) - 1 -CHAPTER 1 INTRODUCTION I. The Basis of the Problem The anticipated shortage of future o i l supplies has focused international attention on coal as a poten t i a l source of energy and as a raw material for industry. The current emphasis on the u t i l i z a t i o n of coal centres on i t s conversion into o i l , gas, and feedstocks for the petrochem-i c a l i n d u s t r i e s 1 ' 2 . A p r i n c i p a l method of liquefying coal for these purposes i s Fischer-Tropsch synthesis 1, which i s presently employed i n the SASOL plants i n South A f r i c a to produce waxes, o i l s , motor f u e l , and chemicals. The essen-t i a l steps i n t h i s method a r e 2 : (1) combustion of coal i n the presence of oxygen and steam to generate a gas composed mostly of carbon monoxide and hydrogen ( i . e . raw synthesis gas), the p r i n c i p a l exothermic reaction being C + H 20 • CO + H 2 (2) p u r i f i c a t i o n of the gas to remove undesirable impurities (including p o t e n t i a l c a t a l y s t poisons). (3) adjustment of the CO:H2 r a t i o to s u i t the p a r t i c u l a r synthesis required by using the Water Gas S h i f t Reaction: H 20 + CO — • H 2 + C0 2 - 2 -followed by removal of C0 2 for most subsequent reactions. (4) reaction of CO with H 2 using appropriate c a t a l y s t s to promote the formation of the desired products 3. The exhaust gases i n coal combustion (step 1). also contain s i g n i f i c a n t amounts of nitrogen oxides (primarily NO and a lesser amount of N0 2) or i g i n a t i n g from atmospheric nitrogen and/or from the coal i t s e l f . The removal of these oxides from the eff l u e n t gases i s of paramount environmental importance since they are involved i n the formation of both photochemical smog and acid r a i n . In p r i n c i p l e , t h i s removal can be effected either by d i r e c t decomposition of the oxides into nitrogen and oxygen or by reduction of the NO species to N~ with various reducing agents'*' 5. Hence, X Zt previous e f f o r t s to remove nitrogen monoxide e f f i c i e n t l y from both stationary and mobile exhaust stream e f f l u e n t s have included: CI) attempts to decompose NO d i r e c t l y into N 2 and 0 2 Ca thermodynamically favourable but k i n e t i c a l l y unfavourable process) by employing reduced m e t a l l i c c a t a l y s t s or oxide c a t a l y s t s 4 ' - 5 . However, the m e t a l l i c c a t a l y s t s are deactivated r a p i d l y by the 0 2 released from the decomposed NO, and the oxide c a t a l y s t s which are stable i n oxidative reaction conditions display low a c t i v i t i e s for NO decomposition. C2). studies of the homogeneous c a t a l y t i c oxygen-transfer process: - 3 -2N0 + CO • C0 2 + N 20 a reaction which i s catalyzed, a l b e i t slowly, by io n i c rhodium and iridium complexes such as [ R h ( N O ) 2 ( p P n 3 ) 2 ^ + ' [Rh(CO) 2C1 2]~, and [ I r ( N O ) 2 ( P P h 3 ) 2 ] + , as well as some platinum- and palladium-containing compounds6. (3) complete conversion of NO into N 2 and C0 2 by using composite catal y s t s such as Co-La 20 3-Pt supported on active carbon, i r r e s p e c t i v e of the coexistence of 0 2 ?« This process involves a high-temperature, c a t a l y t i c gas-solid reaction at atmospheric pressure which requires no additional gaseous reducing agents but does consume the active carbon. (4) Exxon's Denox process (presently in use),.which effects the,overall'gas-phase reaction NO + NH3 + l/ 4 0 2 * N 2 + 3/2H20 in the combustion zone, apparently v i a a complex f r e e -r a d i c a l chain mechanism8. The above reaction i s i n competition with NH3 + 5/402 • NO + 3/2H20 but within a narrow temperature range these reactions can be balanced to permit e f f i c i e n t net reduction of NO with l i t t l e r esidual NH3 l e f t over i n the f l u e gases. While these and related processes have been success-f u l i n removing nitrogen monoxide from exhaust gases to varying degrees, the emphasis of most of the work has been to accomplish the conversion of NO into less noxious prod-ucts, p r i n c i p a l l y N„. However, the N~ thus produced i s - 4 -quite nonreactive, and nitrogen f i x a t i o n (another area of current intense research e f f o r t 9 ) must be effected i n order to convert i t into important nitrogen-containing chemicals such as f e r t i l i z e r s , explosives, p l a s t i c s , etc. Thus an alternative approach to t h i s problem which merits i n v e s t i -gation i s the d i r e c t transformation of NO into useful compounds. At the outset of t h i s research, one of the; objectives -was to. study the- f e a s i b i l i t y of carrying out these trans-formations by: Cl) trapping the nitrogen monoxide on e l e c t r o n - r i c h t r a n s i -tion-metal centres (such as those present i n organo-m e t a l l i c compounds) to form n i t r o s y l complexes, and (2) examining and exploiting the r e a c t i v i t y of the coordin-ated n i t r o s y l ligand (which can reasonably be expected to be d i f f e r e n t from that displayed by NO i n the gas phase) to a t t a i n the desired objective. I I . The Reaction of NO with Transition-metal Complexes Ample precedents e x i s t i n the chemical l i t e r a t u r e to indicate that the f i r s t step of the proposed study ( i . e . the trapping of NO on transition-metal centres) i s indeed poss-i b l e 1 0 . Although a systematic study of t h i s mode of reaction has not been conducted, i t i s nevertheless well established that nitrogen monoxide can react with appropriate t r a n s i t i o n -metal complexes to e f f e c t : (1) simple adduct formation, e.g. Cr(NR 2) 3 + NO • Cr(NO)(NR 2) 3 - 5 -Co( c h e l a t e l 2 + NO » Co (NO) (chelate) 2 (where chelate = dithiocarbamate, d i t h i o l a t e , dimethylglyoxime or Schiff base). This type of behaviour occurs when the reactant complex possesses either a 15- or 17-electron configuration at the metal centre. The iso l a t e d adducts then s a t i s f y the i n e r t gas configuration. (2) substitution whereby each NO group replaces ligands capable of formally donating 3 electrons to the metal, e.g. Cr(CO) g + 4N0 (hv i n pentane) — • Cr(NO) 4 + 6C0 [CpV(.CO)3 (CN) ]" + 2N0 • CpV (CO) (NO) 2 + 2CO + CN~ [CpCr (CO) 3 ] 2 + 2N0 • 2CpCr (CO) 2 (NO) + 2C0 (a Cr-Cr single bond being cleaved) However, reaction of NO with a coordinatively unsatur-ated complex often r e s u l t s i n a redox reaction with concomitant disproportionation of the nitrogen mon-oxide 1 0. (3) reductive n i t r o s y l a t i o n , e.g. rC p C r C l 2 ] 2 N ° > CpCr(NO) 2Cl MoClg (in CH 2C1 2) N ° » Mo (NO) 2C1 2 The oxidized product i n these transformations i s prob-ably C1N0. III. The Bonding and Reactivity of Transition-metal Coordi- nated Nitrogen Monoxide Once incorporated into the metal's coordination sphere i n t h i s manner, the bound NO group can engage i n one - 6 -of three p r i n c i p a l bonding modes , namely; (1) i t can function as a 3-electron donor ( i . e . formally N0+) to the metal centre when involved i n a terminal, l i n e a r M-NO grouping. Such linkages e x i s t i n the great majority of n i t r o s y l complexes (e.g. Cr(NO) (NR,,)^ and CpCr (NO)2C1 specified previously). (2) i t can function as a 1-electron donor ( i . e . formally N0~) to the metal centre when involved i n a terminal, bent M-N-0 linkage, the bond angle being approximately 12 0 ° / Several of the Co CNO) (chelate) 2 compounds have, been shown to contain bent Co-N-0 groups 1 0. (3) i t can bridge two or more metal atoms, a feature, well exemplified by the s o l i d - s t a t e structure of Cp^Mn^-(NO) 4, i . e . 1 1 -MnCp Molecular o r b i t a l c alculations are customarily required to provide an adequate description of the metal-nitrosyl bonding i n such compounds. (A) Terminal, l i n e a r M-NO bonds While the M-NO bonding descriptions i n cases (1) and (2) above are oversimplifications, they are nevertheless useful guides for predicting the r e a c t i v i t y of a coordinated n i t r o s y l ligand. For instance, a terminal, l i n e a r M-N-0 grouping can be represented by the resonance hybrid - 7 -M-NEG F> M=N=0 Ca} (b) Consequently, i n accord with Pearson's c r i t e r i o n that "hard acids prefer to associate with hard bases, and soft acids prefer to associate with soft bases" 1 2, i t would be expected that terminal, l i n e a r n i t r o s y l ligands would undergo attack by hard acids ( i . e . electrophiles) at the n i t r o s y l 0 atom and attack by hard bases ( i . e . nucleophiles) at the n i t r o s y l N atom. Furthermore, since coordination by N0 + to metals i s d i r e c t l y analogous to metal-carbonyl bonding with i t s synergic coupling _of o and TT bonding components 1 3, i t would also: be anticipated that gradations i n the ligand r e a c t i v i t y would occur as the net electron density on the n i t r o s y l ligand (influenced by both M-HSIO cr bonding and M->NO TT bonding) varied. Indeed, the anticipated r e a c t i v i t y i s known for a number of coordination compounds6, e.g. , 0 [ I r C l 3 (NO) (PPh 3) 2] + OEt — • IrClg C^-OEt 1 C.PPh3 ) 2and i t has been proposed 1 1* that those metal n i t r o s y l compounds having v N Q > 1886 cm Cor, better, f N Q > 13.8 mdyn A - 1) w i l l be susceptible to attack at the N atom by nucleophiles such as;.OH~, 0R~, NH3, N 2H 4, NH2OH, and N3"~. It i s of obvious i n t e r e s t to determine whether a similar c r i t e r i o n can be established for the NO ligand r e a c t i v i t i e s of organometallic n i t r o s y l compounds. It follows that species having p a r t i c u l a r l y - l o w values of v N Q would be l i a b l e to attack by ele c t r o p h i l e s , either at the N or 0 atom. Lewis acids such as EX- CE = B - 8 -or A l , X = a halide or pseudohali.de). would be expected to form i s o n i t r o s y l linkages with appropriate organometallic n i t r o s y l s v i a M-NO + EX 3 • M-N=0-^EX3 interactions. Some precedent for t h i s type of behavior i s known, with a c i d i c Cp 3Ln complexes (Ln = a lanthanide metal), having been shown to p r e f e r e n t i a l l y form i s o n i t r o s y l linkages with CpM(CO)2(NO) (M = Cr, Mo, or W). compounds 1 5. However, the generality and factors influencing such acid-base i n t e r -actions s t i l l remain to be ascertained. Of course, e l e c t r o p h i l i c attack could also occur d i r e c t l y at the n i t r o s y l N atom, i . e . A + M-N=0 • [M-N=0] (where A+- = H +, a carbocation, etc.) i f there i s s u f f i c i e n t electron density on the NO ligand. However, i n t h i s case, the soft t r a n s i t i o n metal and the oxygen atom w i l l probably be competing centres of r e a c t i v i t y . Hence, i n investigations of M-NO reactions with e l e c t r o p h i l e s , p a r t i c u l a r attention should be given to determining the factors which influence the r e g i o s e l e c t i v i t y of these trans-formations. The presently known examples of e l e c t r o p h i l i c 2+ attack at N (e.g. the reaction of [Co(diars) 2(NO)] with HBr) can be r a t i o n a l i z e d i n terms of pr i o r bending of the M-NO bond angle, i . e . 6 [Co (diars) (NO) ] 2 + — • [Co (dia r s ) 2 B r (NO)] + • (18e~, l i n e a r Co-N-O) C20e~, l i n e a r Co-N-O) - 9 --*• [Co Cdiars) 2Br CN0I3 + H + [Co Cdiars) 2 B r CN-H) ] 2+ C18e , bent Co-N-Ol (B) Terminal, bent M-NO bonds and bridging NO linkages In a similar manner, the Lewis structures of terminal, bent M-N-0 linkages and doubly-bridging n i t r o s y l groups, i . e . -N* \ M 0: and •ff-M M suggest that the N atom i n the former should undergo e l e c t r o -p h i l i c attack whereas the N atom i n the l a t t e r should be susceptible to nucleophilic attack. The oxygen atoms i n both cases are again s i t e s of hard Lewis b a s i c i t y and should thus form stable coordinate covalent bonds with hard Lewis acids such as the t r i v a l e n t compounds of the l i g h t e r group 3A elements. 0: 0: 'N^ I M o-I I M M + A + A A N ^ M •N k 0 : + A + B II M ^M M" "M where A = a Lewis acid C e l e c t r o p h i l e l and B = a Lewis base Cnucleophile) Some of these expectations concerning the r e a c t i v i t y of a - 10. -coordinated n i t r o s y l ligand have been r e a l i z e d during prev-ious s t u d i e s 6 . However, t h i s e a r l i e r work was concerned almost e x c l u s i v e l y with coordination compounds in which the NO ligands are attached to t r a n s i t i o n metals i n p o s i t i v e formal oxidation states. An aim of t h i s research was to ascertain the general v a l i d i t y of the expectations outlined above by investigating the r e a c t i v i t y of coordinated NO groups i n a v a r i e t y of organometallic n i t r o s y l compounds. Unfortunately, no organometallic compounds containing a terminal, bent M-NO linkage are presently known, but several complexes containing doubly-bridging n i t r o s y l ligands (e.g. [CpCr CN0).232, [CpCo(N0)] 2, and [CpFeCNOl] 2) are available to te s t the v a l i d i t y of the l a t t e r two reactions. In t h i s context, Chapter II describes the reactions of several neutral organometallic compounds with free NO to produce organometallic n i t r o s y l complexes. Chapter TTI presents reactions of the nucleophilic hydride source. Na[A1H 2(OCH 2CH 2OCH 3) 21 with transition-metal n i t r o s y l com-pounds containing a v a r i e t y of other functional groups (especially halides). In Chapter IV the reactions of [CpCr-(NO) 2] 2 with the extremely nucleophilic hydride LiEt^BH and with the Lewis acid BH^ are compared to i t s reaction with Na [AlH^lOCH^C^OCH^ 2] . In the f i n a l chapter, attempts to prepare the analogous complexes [CpM(NO) 2] 2 (M = Mo, Wl are described. This chapter concludes with a study of the Lewis base properties of CpW(NO)2H and the Lewis acid properties of CpW(N0) 9 +. C H A P T E R r r SOME REACTIONS OF NITROGEN MONOXIDE WITH ELECTRON-DEFICIENT  METALLOCENES There was no general preparative route to t r a n s i t i o n metal n i t r o s y l compounds before 1970. Also, many of the then e x i s t i n g methods produced the desired products i n low y i e l d s and/or with much expenditure of e f f o r t . Recently, more generally useful procedures have been reported involving the treatment of a n i o n i c 1 6 or n e u t r a l 1 7 carbonyl complexes with n i t r o s y l chloride, e.g. (Ph_P) _N[W(CO) _Br] + CINO — • W(C0) . (NO) Br CD 5 Z O 4 Fe (CO) 2 (NO) 2 + CINO • Fe(NO) 3Cl C2) Another p o t e n t i a l l y general method for the synthesis of v these n i t r o s y l complexes i s the reaction of nitrogen mon-oxide with el e c t r o n - d e f i c i e n t or coordinatively unsaturated organometallic compounds. The l a t t e r c l a s s i f i c a t i o n of reactants encompasses those species i n which the metal attains coordinative unsaturation during thermolysis or photolysis. Some reactions of t h i s type have been i n d i v i d -u a l l y reported p r e v i o u s l y 1 0 , e.g. CrlN(SiMe 3) 2 J 3 + NO — • Cr (NO) IN (SiMe 3)^] 3 C3) Cp2Mn + NO f Cp 2Mn 2 (NO)3 (n 1-C 5H 5) C4) Cr(CO) 6 + NO h V » ,CrCN0) 4 C5) - 12 -but a systematic study of these transformations has not been ca r r i e d out. This chapter describes reactions between nitrogen monoxide and a v a r i e t y of cyclopentadienylchromium complexes. The chromium systems were chosen as a convenient sta r t i n g point because several of the cyclopentadienylchromium n i t r o -syls one might l o g i c a l l y expect as products have been char-acterized p r e v i o u s l y 1 6 - 1 8 . Also, i n the context of u t i l i z i n g NO formed during the production of raw synthesis gas (see Chapter I ) , chromocene has the added advantage of being unreactive with either CO or H 2 under ambient conditions. The reactions of NO with Cp 2MoH 2 and Cp 2V are also discussed. Experimental A l l chemicals used were of reagent grade or compar-able p u r i t y and were either purchased from commercial suppliers or prepared according to published procedures. Their p u r i t y was ascertained by elemental analyses and/or melting point determinations. A l l melting points are uncorrected and were taken i n c a p i l l a r i e s under pr e p u r i f i e d nitrogen using a Gallenkamp Melting Point Apparatus. Nitrogen monoxide was further p u r i f i e d by passing i t through o a column of activated s i l i c a gel maintained at -78 C. A mass spectrum of the e f f l u e n t gas exhibited only a sharp peak at m/z =30 assignable to NO+; i t did not exhibit peaks attributable to ions such as N20- or N0 2 . A l l solvents were dried according to standard procedures 1 9, d i s t i l l e d , and thoroughly deaerated p r i o r to use. A l l manipulations, - 13 -unless otherwise stated, were performed on the bench using conventional techniques for the manipulation of a i r -sensitive compounds 2 0 or i n a Vacuum Atmospheres Corporation Dri-Lab model HE-43-2 dry box f i l l e d with pre p u r i f i e d n i t r o -gen. Infrared spectra were recorded on Perkin Elmer 457, 710A, or 598 spectrophotometers and calibr a t e d with the 1601 cm ^ absorption band of a polystyrene f i l m . Proton magnetic resonance spectra were recorded on a Varian Associ-ates T-60 spectrometer using tetramethylsilane as an i n t e r -nal standard or on Bruker WP-80, WH-400 or Varian Associ-ates XL-100 spectrometers with reference to the solvent used. A l l 1H chemical s h i f t s are reported i n ppm downfield from Me^Si. Carbon-13 NMR spectra were recorded on a Varian Associates CFT-20 spectrometer with reference to the solvent used, but the 1 3 C chemical s h i f t s are reported i n ppm down-f i e l d from Me^Si. The X 1 B spectra were recorded on a Bruker WP-80 spectrometer with reference to the solvent used, and the chemical s h i f t s are reported i n ppm downfield from BF 3«OEt 2. Dr. S.O. Chan, Mrs. M.M. Tracey, Mr. J.K. Chow, and Ms. M.A. Heldman assisted i n obtaining the various NMR spectra. The low-resolution mass spectra were obtained at 7 0 eV on an Atlas CH4B spectrometer and the high-resolution mass spectral data were acquired on an Associated E l e c t r i c a l Industries MS902 spectrometer using the d i r e c t - i n s e r t i o n method with the assistance of Mr. J.W. Nip and Mr. G. Gunn. Elemental .analyses were performed by Mr. P. Borda. The ... - 14 -x-ray s t r u c t u r a l determination was carried out by Dr. R.G. B a l l . Reaction of Nitrogen Monoxide with Chromocene. (a) In hexanes. A slow stream of prepurified nitrogen monoxide was passed over a r a p i d l y s t i r r e d , red solution of Cp 2Cr 2 : 1 (0.91 g, 5.0 mmol) in hexanes (150. mL) at Q?Cv Immediately the solution developed a dark brown colouration and a brown pr e c i p i t a t e was formed. The nitrogen monoxide atmosphere was maintained over the reaction mixture for 15 min to ensure complete reaction. The volume of the solvent was reduced to ~15 mL i n vacuo and the reaction mixture was then transferred to the top of a 2 x 15 cm column of alumina (Woelm neutral, a c t i v i t y grade IV). Elution of the column with hexanes developed two bands. The f i r s t band, golden brown in colour, was collected and the solvent was removed from the eluate i n vacuo to obtain CpCr (NO) 2 (TI 1 - C g H 5 ) as a dark brown s o l i d . Anal. Calcd for C 1 ( )H 1 0CrN 2O 2: C, 49.59; H, 4.16; N, 11.56. Found: C, 49.75; H, 4.31; N, 11.20. IR (CH 2C1 2): V N Q 1785, 1686 cm"1. *H NMR (CDCl 3): 6 6.01 (s, 5H), 4.99 (.s, 5H) . ^Cl 1!!} NMR (CDC1 3): 5 113.89 (s) , 101.41 (s) . Mp (in air) 64-5°C. Its mass spectrum i s summarized in Table I. Elution of the second band from the column with hexanes produced a purple solution which contained [CpCr-(.NO)2l2, i d e n t i f i e d by i t s infrared spectrum 2 2. This dimeric product was isolated as a red-violet s o l i d by taking the eluate to dryness in vacuo, and i t s i d e n t i t y was con-- 15 -Ta b l e I . Low-Re s o l u t i o n Mass S p e c t r a l r D a t a f o r CpCr (NO) 0 Cn.1-c5H5) and CpCr (NO) V ( N O 0 1 a CpCr (NO) 0 irt/z R e l abund Assignment 242 13 CC 5H 5). 2Cr ( N O ) 2 + 182 100 C C 5 H 5 l 2 C r + 177 8 ( C 5 H 5 ) C r ( N O ) 2 + 147 7 ( C 5 H 5 ) C r CNO} + 117 36 C C 5 H 5 ) C r + 65 5 C 5 H 5 + 52 31 C r + CpCr CNOJ. 2 ( N 0 2 ) m/z R e l abund Assignment 223 18 (.C 5H 5)Cr (NO) 2 (N0 2) + 193 7 CC 5H 5)Cr (NO) CN0 2) + 177 49 ( C 5 H 5 ) C r (NO) 2 + 163 39 ( C 5 H 5 ) C r (N0 2) + 147 5 ( C 5 H 5 ) C r (NO) + 133 100 ( C 5 H 5 ) C r O + 117 12 ( C 5 H 5 ) C r H r > 105 2 9 C 4 H 5 C r + ' 65 3 C 5 H 5 + 52 27 C r + The assignments i n v o l v e t h e most abundant n a t u r a l l y -o c c u r r i n g i s o t o p e s i n each fragment. - 16 -firmed by; i t s c h a r a c t e r i s t i c mass spectrum A t h i r d band was then eluted from the alumina column with dichloromethane as eluant, thereby producing a green solution which after addition of hexanes and slow removal of solvent i n vacuo, afforded green, m i c r o c r y s t a l l i n e CpCr-(N0) 2 (N02) . Anal. Calcd for C,_H[-CrNo0/, : C, 26.92; H, 2.26; N, DO J 4 18.83. Found: C, 27.21; H, 2.15; N, 18.76. IR (CH 2C1 2 1: v N Q 1825, 1719 cm"1. *H NMR (CDClg) : 6 5.78 (s). Mp (in air) 86-7°C. F i n a l l y , e l u t i o n of the column with tetrahydrofuran produced an orange-brown solution which was taken to dryness under reduced pressure. Proton NMR and mass spectroscopy indicated that the remaining brown s o l i d [ V ^ Q (CH 2C1 2):* 1640-1660 cm ^] was an aggregated species. For instance, i t s mass spectrum at 200°C exhibited the highest m/z peak at 466 which could be assigned to the (Cj-H^) 2 C r 3 (N°) g + i° n-Unfortunately, t h i s s o l i d could not be rendered pure by chromatography, sublimation or r e c r y s t a l l i z a t i o n . (b) In benzene or tetrahydrofuran. These reactions were performed i n a manner similar to that described i n part (a) except that the benzene reaction mixture was maintained at ~6°C and the reaction time was extended to 3 0 min for both conversions. In both cases, the f i n a l reaction mixture consisted of a very dark solution with no p r e c i p i t a t e being present. Separation of the products was effected as i n (a), but [CpCr (NO) „] „ was not detected i n either solvent. - 17 -In a l l three solvents-, the y i e l d s of the n i t r o s y l products were somewhat variable, appearing to depend both on the rate of introduction of NO and on the reaction time. Typical y i e l d s are tabulated below. Yield (%) CpCr(NO) 2-Solvent C n 1 "C 5H 5) [CpCr (NO) 2] 2 CpCr (NO) 2 (N02) hexanes 35 6 4 benzene 25 0 10 tetrahydrofuran 13 0 10 Reaction of Nitrogen Monoxide with CpCr (NO) _ (n 1-CrHi-) . A-—-•—-• 2- 5—5 slow stream of prepurified nitrogen monoxide was passed over a s t i r r e d , brown solution of CpCr(NO) 2(n 1 —C^H^) (0.018 g, 0.10 mmol) i n hexanes (2 5 mL) at ambient temperature for 1 h, during which time a dark brown p r e c i p i t a t e was gradually formed. The solvent was removed from the reaction mixture i n vacuo and the residue was redissolved i n a small amount (~5 mL) of dichloromethane. An infrared spectrum of the dichloromethane solution revealed that ~3 5% of the organo-metallic reactant had been consumed and that the only other nitrosyl-containing complex present was CpCr(NO) 2 (N0 2). Treatment of a hexanes solution of [CpCr(N0) 2] 2 with nitrogen monoxide i n an i d e n t i c a l manner resulted i n the formation of the n i t r i t e species i n low y i e l d s . Reaction of N i t r o s y l Chloride with Chromocene. To a s t i r r e d - 18 solution of Cp 2Cr CO.27 g, 1.5 mmolI i n dichloromethane C50 mL) at 0°C was added an excess of CINO 2 3 dissolved i n dichloromethane. Immediately the solution developed a blue-green colouration, but no p r e c i p i t a t e was formed. The solution was s t i r r e d for 3 0 min while i t was permitted to slowly warm to room temperature. It was then concentrated at reduced pressure to ~15 mL and was transferred by syringe onto a 2 x 7 cm F l o r i s i l column. Elution of the column with dichloromethane developed a green band which was c o l l e c t e d . The olive-green eluate contained only CpCr(NO) 2Cl, 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 infrared and 1H NMR s p e c t r a 1 6 . Photonitrosylation of Cp 2MoH 2. A s t i r r e d yellow solution of Cp 2MoH 2 2 1 (0.43 g, 1.9 mmol) i n hexanes (200 mL) was i r r a d i -ated for 0.5 h i n a photoreactor using a medium-pressure mercury lamp (Hanovia L-4 50W) housed i n a water-cooled Pyrex immersion well, with prepurified nitrogen monoxide bubbled through the solution during the i r r a d i a t i o n . Nitrogen was then passed through the solution to remove any unreacted NO, and the l i g h t brown solution and flo c c u l e n t brown p r e c i p i t a t e were transferred as a s l u r r y to another flask where the v o l a t i l e s were removed from the reaction mixture i n vacuo. An IR spectrum of the r e s u l t i n g brown residue i n CH 2C1 2 solution revealed two strong n i t r o s y l absorptions at 1737 and 1650 cm The solution was transferred to the top of a 3 x 7 cm column of alumina (Wbelm neutral, a c t i v i t y grade IV). Elution of the column with CH 2C1 2 developed a single orange-brown band, which was c o l l e c t e d and the solvent - 19 -removed under reduced pressure. Sublimation of the residue onto a water-cooled probe at 45°C and 0.005 Torr yielded 0.07 g (13% yield) of orange-brown CpMo(NO)2(n1-C,-H,-)2 4 , mp 77-8°C. IR CCH2C12) : v N Q 1737 , 1650 'cm"1; "• l:E." NMR. (CDC 1 ^) : <5 6.18 Cs, 5H) , 5.40 (s, 5H). A mass spectrum of the s o l i d was also i d e n t i c a l to that of an authentic sample of the compound. Unfortunately, s a t i s f a c t o r y a n a l y t i c a l data could not be obtained. Anal. Calcd for C 1 0H 1 QMoN 2O 2: C, 41.98; H, 3.52: N, 9.79. Found: C, 44.35; H, 4.14; N, 9.14. Photolysis of Cp 2WH 2 2 1 under comparable conditions yielded a yellow-brown s o l i d ( v N Q (CH 2C1 2): 1640, 1555 cm - 1) which defied a l l attempts to p u r i f y i t . Reaction of Cp 2MoH 2 with NO. Nitrogen monoxide was passed over a solution containing Cp 2MoH 2 (0.23 g, 1.0 mmol) i n hexanes (4 0 mL) for 3 0 min at room temperature during which, time the solution slowly darkened. The solvent was then removed under reduced pressure and the brown residue d i s -solved i n CH 2C1 2. An IR spectrum revealed two weak, broad n i t r o s y l absorptions at 1820 and 1590 cm Reaction of Cp 2MoCl 2 with Na/Hg i n an NO Atmosphere. A green THF solution .(75 mL) containing 1.63 g (5.5 mmol) of Cp 2MoCl 2 2 5 was transferred to a fla s k containing -2.5 equiv-alents of a 2% Na amalgam, and the vigorously s t i r r e d reaction mixture was immediately placed under an atmosphere of prepurified nitrogen monoxide. A gray s o l i d formed over a period of approximately 10 minutes to produce an opaque - 20. -suspension. After 30 min the fl a s k was purged with N 2, and the supernatant was c a r e f u l l y removed by syringe and taken to dryness i n vacuo. An IR spectrum of a Nujol mull of the gray residue revealed no absorptions attributable to coord-inated NO, so the reaction product was not investigated further. Reaction of C p 2 v with Nitrogen Monoxide. Prepurified nitrogen monoxide was slowly passed over a purple benzene solution (125 mL) containing 0.84 g (0.46 mmol) of Cp 2V 2 1. Reaction was immediate and yielded a black solution and pr e c i p i t a t e . The mixture was s t i r r e d for 1 h to ensure complete reaction and was then f i l t e r e d through a medium porosity f r i t t e . An IR spectrum of the f i l t r a t e revealed n i t r o s y l absorptions at 1675 and 1565 cm . The f i l t r a t e was concentrated under reduced pressure to a volume of approximately 10 mL, and the solution was transferred to the top of a 5 x 9 cm column of F l o r i s i l . With benzene as eluant an orange band developed at the top of the column, but would not elute further. With CH^Cl,, as eluant, the band smeared; THF eluted the band cleanly. Solvent removal from the THF eluate afforded 0.2 g of an orange-brown s o l i d . IR (CH 2C1 2): v N Q 1776 (w), 1673 (st) , 1618 (w), 1566 (st) cm \ *H NMR and mass spectra of the product, as well as elemental analyses, varied from reaction to reaction, although the IR spectrum was quite reproducible. Numerous attempts at chromatography on a vari e t y of supports and r e c r y s t a l l i z a t i o n from a va r i e t y of solvent mixtures - 21 -(invariably giving powders1, as well as attempted sublima-ti o n (the s o l i d i s quite non-volatile) f a i l e d to y i e l d a pure product. Results and Discussion Reactions of Nitrogen Monoxide with Cp^Cr. Despite the fact that chromocene requires an addi-'" t i o n a l two electrons for the central metal to achieve a noble gas configuration, chromocene appears to be a f a i r l y non-reactive complex 2 6. Thus, no reaction i s observed with H 2, C 2 H4' PhC=CPh, or HC=CH under the conditions i n v e s t i -g a t e d 2 6 . With carbon monoxide reaction i s incomplete; a product i s observable but i s unstable at standard tempera-ture and pressure, i . e . Cp 2Cr + CO , Cp 2Cr(CO) (6) Further reaction with CO can occur, but t h i s process requires both high temperatures and high pressures of CO to bring about the displacement of a cyclopentadienyl r i n g 2 7 : C P 2 C r + C 0 ^ i C 0 ' [C P C r ( C O ) 3 ] 2 (7) In sharp contrast, when a hexanes solution of Cp 2Cr at 0°C i s exposed to an atmosphere of prepurified NO, the organometallic reactant i s r a p i d l y consumed i n the reaction. Cp 2Cr + excess NO —hexanes fc C p C r ( N 0 ) (_ni_c H ^ + CpCr(NO) 2(N0 2) + [CpCr(NO) 2] 2 (8) [A p r i n c i p a l product i n t h i s reaction i s a red-brown c l u s t e r - 22 -compound whose exact formulation has yet to be determined.] Indeed, the ease with which nitrogen monoxide reacts with chromocene resembles i t s ready r e a c t i v i t y with manganocene 2 8 and nickelocene 2 9 at room temperature and pressure, i . e . Cp 2Ni + NO • CpNi (NO) (9) Cp2Mn + NO • Cp 2Mn 2(NO) 3 (n 1-C 5H 5) (10) The major i s o l a b l e product of the reaction with chromocene i s CpCr(NO) 2 (n 1 _C^H^) which can be obtained i n ~35% y i e l d . This complex has been prepared previously by the metathetical reactions of CpCr (NO)2C1 with CgH^Tl 3 0 or CpCr(NO) 2Br with Cj-Hj-Na31 i n y i e l d s of 16 and 20% respectively. Even when the gentle a l k y l a t i n g agent (n 1-C^H^)^Al i s employed i n such metatheses, the desired complex can only be obtained i n 17% y i e l d 3 2 . Hence, reaction 8 represents the most convenient and highest-yield preparative route to the bis(cyclopenta— dienyl) species. CpCr(NO) 2 (n 1-C^H^) i s a dark-brown, v o l a t i l e , a i r -sensitive s o l i d that i s known 3 0 to be stereochemically nonrigid i n solution at room temperature. Its formation i n reaction 8 can be viewed as r e s u l t i n g from the sequential addition of NO groups to chromocene, a process i n which, coordination of even the f i r s t n i t r o s y l ligand as a three-electron donor to the e l e c t r o n - d e f i c i e n t chromium atom requires a change i n the bonding mode of one of the c y c l o -pentadienyl rings i f the i n e r t gas formalism i s to be s a t i s f i e d . The CpCr(NO) 2(n 1 _C^H^) so formed can then react 23 -further with excess NO to give the n i t r i t e complex, i . e . CpCr (NO) 2 (n 1-C 5H 5) + excess NO • CpCr (NO) 2 ( N 0 2 ) (.11) but performing t h i s reaction separately reveals that t h i s conversion proceeds rather slowly under the experimental conditions employed. Since CpCr(NO) 2 ( N 0 2 ) has been mentioned only i n passing i n the l i t e r a t u r e 2 8 , i t s physical properties merit delineation. CpCr(NO)^ (N0 2) i s an olive-green, diamagnetic s o l i d (mp 86-7°C) which can be handled i n a i r for short periods of time without noticeable decomposition occurring. It i s f r e e l y soluble i n common organic solvents (except p a r a f f i n hydrocarbons) to give a i r - s e n s i t i v e , green solu-tions, and i t sublimes at 40°C (5 x 10 ^ Torr) with con-comitant decomposition. The 1H NMR spectrum of the complex i n CDClg exhibits a sharp resonance at 6 5.78 c h a r a c t e r i s t i c of a pentahapto cyclopentadienyl r i n g . The infrared spec-trum of CpCr (NO) 2 ( N 0 2 ) i n CH^C^, which shows two strong bands at 1825 and 1719 cm attributable to terminal n i t r o -s y l groups, i s also consistent with the compound having the molecular structure - 24 -Its mass spectrum (summarized i n Table. I) exhibits the parent ion and the expected fragmentation pattern, namely the sequential loss of ligands from the metal centre. Interestingly, the base peak i s due to the (C^H^)CrO+ ion; si m i l a r oxo-ions have been previously detected i n the mass spectra of other organometallic n i t r o s y l compounds 3 3. Based on the slow rate at which CpCr (NO) ^ (n. 1 —C,-H,-). reacts with NO to produce CpCr(NO) 2(N0 2), i t i s apparent that t h i s i s not the major route by which the n i t r i t e com- . plex i s formed. Its formation can, however, be r a t i o n a l i z e d v i a the r a d i c a l intermediate CpCr(NO) 2« and indeed the i s o -l a t i o n of [CpCr (NO) 2] 2 from reaction 8 i s consistent with, the formation of such a transient species. Relevant to t h i s p o s s i b i l i t y i s the observation that when, a hexanes solution of ;CpCr (CO) 2l (NO) i s subjected to u l t r a v i o l e t i r r a d i a t i o n i n the presence of nitrogen monoxide, the organometallic react— ant i s gradually converted to a mixture of [CpCr (NO) 2] 2 and CpCr(NO) 2(N0 2) as the only nitrosyl-containing p r o ducts 3 2, i . e . CpCr(CO) 2(NO) + excess NO - • hexanes [CpCr (NO) 21 2 + CpCr (NO) 2 (N02) (12) Analogously, when the photogenerated species CpCr (CO) (NO)-(THF) i s reacted with NO i n the absence of l i g h t , the same products are again i s o l a t e d 3 2 , i . e . THF CpCr(CO)(NO)(THF) + excess NO — » - 25 -[CpCr CN012] 2 + CpCrCNO)2(N02). (.13) The formation of CpCr (NO) 2 (.N02) as- the p r i n c i p a l product i n reactions 12 and 13 can be r a t i o n a l i z e d i n the manner depic-ted below. CpCr (CO) 2 (NO) + NO ^ _ 2 C 0 eq. 12 eq. 13 CpCr (CO) (NO) (THF) + NO -""""-THF , -CO followed by CpCr (NO) 2 • C14) CpCr(NO) 1/2 [CpCr CNO)2] 2 NO CpCr(NO) 2(N0 2) (15) I n i t i a l l y the incoming nitrogen monoxide could replace two l a b i l e (or dissociated) ligands capable of donating two electrons each to the metal to form the seventeen—electron species, CpCr(NO) 2'• This e n t i t y could then either dimer-ize to [CpCr (NO) 212 o r react further with NO to produce the n i t r i t e . The l a t t e r complex could also r e s u l t , i n part, from the reaction of the dimer with nitrogen monoxide. The following experimental facts are i n accord with t h i s r a -t i o n a l : CD [CpCr (NO) 2] 2 i s indeed converted to CpCr (NO) 2 (N02). by NO, but only slowly at ambient temperature i n solvents such. as tetrahydrofuran or hexanes. The rate of the. reaction i n - 26 -hexanes can be enhanced s i g n i f i c a n t l y by i r r a d i a t i o n of the reaction m i x t u r e 3 2 , an increase that probably r e f l e c t s the ef f e c t of the photodissociation of the dimer, i . e . [CpCr (NO) 2] 2 —i^ L_> 2CpCr(NO) 2- (16) [Since the completion of t h i s work other photochemical reac-tions involving [CpCr (NO) 2] 2 have been reported, i . e . Mn 0(CO) i n + CpCr(N0) oCl hv, CO M n ( C O ) c C l + 2 10 c 2 heptane 5 CpCr (CO) 2 (NO) + [CpCr (NO) 2 J 2 ( 1 7> [ C P C r ( N O ) 2 ] 2 heptane » CpCr (CO) 2 (NO) (18) and the authors also r a t i o n a l i z e t h e i r r e s u l t s as involving the r a d i c a l CpCr(NO) 2• 3 k.] (2) The photonitrosylation of CpCr(CO) 2(NO) i n either CHC13 or CC1 4 r e s u l t s i n complete decarbonylation and formation of a homogeneous yellow-brown solution containing CpCr— (N0) 2C1 3 5. This transformation can also be understood i n terms of the reactive intermediate CpCr(NO) 2* which, once formed, could abstract halogen from the solvent to give the f i n a l product. Such halogen-abstraction reactions are well known for a va r i e t y of organometallic carbonyl r a d i c a l s 3 6 . (3) The i s o l a t i o n of a n i t r i t e - c o n t a i n i n g species from reactions involving transition-metal complexes and nitrogen monoxide has several precedents i n the l i t e r a t u r e 1 0 ' 3 7. Generally, such complexes are believed to arise, from the. oxidation of a coordinated n i t r o s y l ligand by nitrogen monoxide. A sim i l a r mechanism, i . e . - 27 -0 N CpCr CNO) 2- •+•• NO •+ CpCr-N50 0 o N CpCr-N=0 + 2NO NN 0 CpCr (NO) 2 (N0 2 ) + N 2 ° C19) (2 0 ) involving e l e c t r o p h i l i c attack of free NO on the bound NO group may well be operative i n t h i s system. Thus i t i s quite l i k e l y that the formation of both CpCr(NO) 2(N0 2) and [CpCr(NO) 2] 2 i n reaction 8 occurs v i a CpCr(NO)2*• Based on the r e l a t i v e rates of the various reactions under comparable conditions, i t appears that pro-duction of CpCr(NO) 2" can occur without the involvement of CpCr(NO)2 dl1~C^H^) as an intermediate, i . e . Cp 2Cr + NO • CpCr(NO) (n*-C 5H 5) -C 5H 5 {CpCr(NO)} +NO CpCr(NO) 2 -N ° » CpCr (NO) 2 t n . 1 -C 5 H 5 } -fexcess- NO - C 5 H 5 . +exeess NO CpCr(NO) 2(N0 2) +exce.ss NO 1/2[CpCr(NO) 2] 2 The observation that a comparable d i s t r i b u t i o n of products i s obtained when the reaction i s c a r r i e d out at -78°C i n hexanes argues against i n i t i a l formation of some 'activated' form of CpCr(NO)2(n 1 _C^H^) which subsequently either loses Ci-H,.' or loses i t s excess energy v i a c o l l i s i o n s with other molecules. The f a c t that the dimer i s not detected when the same reaction i s performed i n tetrahydrofuran or benzene but - 28 -improved y i e l d s of CpCr (NO) 2 (NO,,) are obtained probably r e f l e c t s a longer l i f e t i m e for CpCr(NO) 2" in these solvents, a longevity that increases the li k e l i h o o d of i t s reaction with NO as depicted in equations 19 and 20. In contrast to i t s behavior towards NO, chromocene reacts only slowly with CINO in CH 2 C l 2 at 0°C to y i e l d CpCr(NO) 2Cl as the only nitrosyl-containing product. Infra-red monitoring of the reaction f a i l s to detect any of the products from reaction 8 as intermediates even though some reactions of CINO can be understood 1 6 in terms of the equi-librium shown below: 2C1NO * 2NO + C l 2 Reactions of Nitrogen Monoxide with Cp2Mo. While chromocene i s stable and re a d i l y prepared, neither molybdenocene nor tungstenocene are s u f f i c i e n t l y stable to allow t h e i r i s o l a t i o n . They can, however, be generated as highly reactive species by a vari e t y of r o u t e s 3 8 . Thus reduction of Cp^MG^ (M = Mo, W) with sodium amalgam produces Cp2M as a transient species, as does the i r r a d i a t i o n of solutions of Cp2MH2. The photochemical generation of Cp2Mo from a hexanes solution Cp 2MoH 2 while bubbling NO through the solution leads to the formation of CpMo (NO) 2 (n 1 -C,-H,-) i n low y i e l d as the sole nitrosyl-containing product, i . e . Cp 2M0H 2 + NO h ^ a n e s » C PMo(NO) 2 (n 1-C 5H 5) + { ( C ^ M o ) ^ (22) - 29 -While an a n a l y t i c a l l y pure product could not be is o l a t e d , the IR, 1H NMR, and mass spectra of the product are i n d i s -tinguishable from those of CpMo (NOJ 2 Ox1-C^H,.) prepared by metathesis of CpMo(NO) 2Cl with either C 5H 5T1 or ( n 1 - C 5 H 5 ) 3 ~ Al2h. The reaction of CP2M0H2 with NO i n the absence of i r r a d i a t i o n i s found to lead slowly to a d i f f e r e n t , uniden-t i f i e d n i t r o s y l species which has thus far defied a l l p u r i f i c a t i o n attempts. CpMo (NO) 2 ( n 1 -C,-H,-) i s an orange-brown, v o l a t i l e s o l i d which dissolves r e a d i l y i n common organic solvents to y i e l d a i r - s e n s i t i v e solutions. Its :H NMR spectrum con-s i s t s of two sharp singlets {6 6.18 (s, 5H) , 5.40 (s, 5H) i n CDCl^} revealing that, l i k e i t s Cr analogue, CpMoCNO)^— (n 1 _C^H^) i s stereochemically nonrigid i n solution at room temperature. The reaction of NO with CP2M0 (generated by the reduction of CP2M0CI2 with sodium amalgam) under an atmo-sphere of nitrogen monoxide f a i l s to y i e l d any organometallic nitrosyl-containing products. Any CpMo (NO) ^  (Tl1 -Cj-H,-) formed in t h i s reaction must subsequently decompose under the con-d i t i o n s of the experiment. The reaction of CP2W, generated by photolysis of CP2WH2, with a nitrogen monoxide atmosphere y i e l d s a n i t r o -syl-containing product ( v N 0 (CH 2C1 2): 1640, 1555 cm - 1) which has- defied a l l attempts- to isolate, i t ; i t i s not, however, CpW(NO) 2 ( n ^ - C ^ ) 2 " Cv N 0 (CH^C^) : 1710, 1628 cm ^) as might have been expected by analogy with the Mo reaction. Reaction of Nitrogen Monoxide with Cp^V. The reaction of NO with a solution of Cp 2V occurs very rapi d l y to y i e l d , a f t e r p a r t i a l p u r i f i c a t i o n , an orange-brown nitrosyl-containing product ( V N 0 (CI^C^) : 1675, 1565 cm ^ ) . It has not, however, been obtained i n s u f f i c i e n t l y pure form to allow i t s i d e n t i f i c a t i o n . Summary and Conclusions Although some success i n preparing n i t r o s y l - c o n t a i n -ing products from the reaction of NO with elec t r o n - d e f i c i e n t metallocenes has been achieved, i t i s rather li m i t e d . The compounds prepared are iso l a t e d only i n r e l a t i v e l y low y i e l d s , and considerable d i f f i c u l t y i n attempting to p u r i f y the n i t r o s y l products formed i s encountered. This appears to be a r e s u l t of the r e a c t i v i t y of the C^ -H,.* released i n the course of the reaction, r e s u l t i n g i n the formation of organic by-product with unfavourable physical properties. Even when the n i t r o s y l complexes formed can be chromato-graphed, pure products are often not obtained. It therefore appears that t h i s method of preparing organometallic n i t r o -s y l complexes i s not as convenient as was anticipated. It i s clear, nevertheless, that selective reaction of organo-meta l l i c complexes with NO i n the presence of CO and i s a r e a l i s t i c objective. C H A P T E R I I I R E A C T I O N S O F S O D I U M D I H Y D R I D O B I S ( 2 - M E T H O X Y E T H O X Y ) A L U M I N A T E  W I T H S O M E C A T I O N I C A N D N E U T R A L N I T R O S Y L C O M P L E X E S R e s e a r c h i n t r a n s i t i o n m e t a l h y d r i d e c h e m i s t r y i s c u r r e n t l y b e i n g c o n d u c t e d a t a v i g o r o u s p a c e . C o v a l e n t m e t a l h y d r i d e c o m p l e x e s h a v e b e e n i m p l i c a t e d a s i n t e r m e d i -a t e s i n h o m o g e n e o u s c a t a l y t i c r e a c t i o n s , i n c l u d i n g h y d r o -g e n a t i o n a n d h y d r o f o r m y l a t i o n r e a c t i o n s o f o l e f i n s 3 9 . I n a d d i t i o n c l u s t e r h y d r i d e c o m p l e x e s h a v e b e e n s y n t h e s i z e d w i t h t h e a i m o f m o d e l l i n g h e t e r o g e n e o u s c a t a l y s t s 4 0 . T h u s t h e s t r u c t u r a l , a n a l y t i c a l , a n d c h e m i c a l c h a r a c t e r i s t i c s o f t h e h y d r i d e l i g a n d h a v e p a r a m o u n t s i g n i f i c a n c e i n o r g a n o -t r a n s i t i o n - m e t a l c h e m i s t r y 3 9 . I n c o n t r a s t t o t h e a t t e n t i o n o r g a n o m e t a l l i c c a r b o n y l h y d r i d e s h a v e r e c e i v e d a n d c o n t i n u e t o r e c e i v e , a n a l o g o u s n i t r o s y l c o m p l e x e s , e v e n t h o u g h c a p a b l e o f e x i s t e n c e i n p r i n c i p l e , r e m a i n v i r t u a l l y u n k n o w n . I n d e e d , t h e o n l y o r g a n o m e t a l l i c n i t r o s y l h y d r i d e t h a t h a d b e e n i s o l a t e d w h e n t h i s w o r k w a s b e g u n w a s C p R e ( C O ) ( N O ) H 4 1 . W h i l e t h e r e a r e m a n y m e t h o d s f o r s y n t h e s i z i n g t r a n s i t i o n - m e t a l h y d r i d e s , f e w a r e g e n e r a l 3 9 . O n e o f t h e m o s t u s e f u l m e t h o d s f o r p r e p a r i n g t r a n s i t i o n - m e t a l h y d r i d o c o m p l e x e s i n v o l v e s t h e r e p l a c e m e n t o f a n a n i o n i c l i g a n d , s u c h a s h a l i d e , b y e m p l o y i n g h y d r i d e r e a g e n t s s u c h a s L i A l H . o r N a B H . 3 9 . A f a c t o r w h i c h p o t e n -- 32 -t i a l l y can complicate the preparation of n i t r o s y l hydrides i s the occurrence of simultaneous chemical attack on a coordinated NO of the reactant, which can proceed by both i n t e r - and intra-molecular mechanisms and leads to compli-cated redox changes at the n i t r o g e n 3 9 . In the context of the o v e r a l l objective of studying the r e a c t i v i t y of coordf-inated NO i n organometallic environments, i t i s of inte r e s t to determine what reagents react with the n i t r o s y l unit i n the presence of other potential s i t e s of r e a c t i v i t y . Instances where the n i t r o s y l ligand reacts concurrently with other ligands could perhaps prove to be an asset rather than a complication. In recent years a great var i e t y of new organoaluminum and organoboron hydrides have been prepared, and t h e i r u t i l i t y as agents for the s e l e c t i v e reduction of organic functional groups i n v e s t i g a t e d 4 2 . In t h i s chapter the r e a c t i v i t y of one such reducing agent, sodium bis(2-methoxy-ethoxy)aluminumdihydride (I), towards a var i e t y of t r a n s i -tion—metal n i t r o s y l complexes i s reported. [In Chapter V the successful preparation of several organometallic n i t r o s y l hydrides i s discussed i n the context of an attempted syn-thesis of [CpM(.NO)2]2 CM = Mo, W).] The extreme s o l u b i l i t y of I i n aromatic hydrocarbons and ethers combined with a reducing strength comparable to lithium aluminum hydride and d i i s o b u t y l aluminum hydride make t h i s a i r - s t a b l e alum-inum hydride both more convenient and safer to handle than the other hydrides mentioned 4 2. - 33 -Experimental A l l experimental procedures described were performed under the general conditions detailed i n Chapter I I . Reaction of CpCr (NO) 2 (NO3) with I. To a s t i r r e d green solu-t i o n of CpCr (NO) 2 C.NO.JJ "* 3 ("0.66 g, 2.8 mmol) i n benzene (30 mL) at room temperature was added dropwise a 0.5 M benzene solution of NaAlH 2 (OCH2CH2OCH3J 2 ( I ) 1 * 4 . The solution grad-u a l l y darkened and became purple i n colour. The progress of the reaction was monitored by IR spectroscopy, and the benzene solution of I was added u n t i l the n i t r o s y l absorp-tions due to the i n i t i a l reactant had disappeared. Exactly one equivalent of I was required for complete reaction. The f i n a l solution was concentrated i n vacuo to ^5 mL and was transferred by syringe onto a 4 x 4 cm column of alumina (Woelm neutral, a c t i v i t y grade 1). Elution of the column with benzene developed a single red band which was c o l l e c t e d and taken to dryness under reduced pressure to obtain red-purple, m i c r o c r y s t a l l i n e [CpCr (NO)2]2 CO.15 g, 31% y i e l d ) , 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 IR, 1H NMR, and mass s p e c t r a 2 2 . Reactions of I with CpCr (NO) 2 C^L1 —C^H^) 3 J , CpCrCNO)^-I 2 8 , and CpCr(NO) 2(N0 2) 2 8 i n benzene, [CpCr(NO)^\ BF^ 4 3 i n CH 2C1 2, and [CpCr (NO) 2 (CO) ] P F g 4 5 i n THF were ca r r i e d out i n a similar manner. In each instance, [CpCr(NO)^\ 2 was the only nitrosyl-containing product formed. Reaction of CpCr (NO) 0 (N0o) with. NaBH^ . To a s t i r r e d green 34 -solution of CpCr (NO) 2 (NOg) (0.66 g, 2.8 mmol); i n 1:1 benzene-tetrahydrofuran at room temperature was added an excess of s o l i d NaBH4 (0.2 0 g, 5.3 mmol). The reaction mixture began to darken aft e r 1 h. IR monitoring indicated that the : reaction was only p a r t i a l l y completed after 24 h, and an additional 0.2 0 g of NaBH^ were added. After an additional 24 h the reaction was adjudged to be complete, and the reac-ti o n mixture was taken to dryness i n vacuo. P u r i f i c a t i o n of the residue by chromatography on alumina with benzene as eluant (vide supra), afforded 0.08 g (16% yield), of [CpCr-(NO) 2] 2, as i d e n t i f i e d by i t s IR and 1H NMR spectra. Reaction of CpMn(CO) (NO)I with I. A s t i r r e d benzene solution (30 mL) containing CpMn(CO)(NO)I h 6 (~2 mmol) was treated dropwise at room temperature with a benzene solution of IV Th.e green-brown reaction mixture slowly became red - v i o l e t , and a s o l i d p r e c ipitated. The reaction was monitored by IR spectroscopy, and the addition of the reducing agent was stopped when a l l the sta r t i n g material had reacted. At t h i s point, the mixture was concentrated under reduced pressure to -10 mL and transferred by syringe to the top of a 2 x 5 cm column of alumina. Elution of the column with benzene produced a r e d - v i o l e t band which was c o l l e c t e d and taken to dryness i n vacuo. The r e s u l t i n g residue was i d e n t i f i e d as [CpMn (CO) (NO) ] 2 , f 7 by i t s IR, JH NMR, and mass spectra. Reaction of CpCo(NO)I with I. To a toluene solution (80 mL) containing 0.43 g (1.5 mmol) of CpCo(NO)!1*8 at -7 8°C was - 35 -added dropwise with, s t i r r i n g a Benzene-toluene solution containing one equivalent of 1.. The o r i g i n a l green solution darkened, and then a tar r y p r e c i p i t a t e deposited as the addition proceeded. The f i n a l reaction mixture consisted of t h i s p r e c i p i t a t e and a v i r t u a l l y colourless supernatant l i q u i d ; i t was permitted to warm slowly to room temperature. The solvent was removed under reduced pressure, the residue was extracted with tetrahydrofuran ( 3 x 2 5 mL), the extracts were f i l t e r e d , and the f i l t r a t e was taken to dryness i n vacuo. The f i n a l residue was dissolved i n 10 mL of CH 2C1 2 and chromatographed on a 2 x 7 cm F l o r i s i l column with C H 2 C I 2 as eluant. A single, dark purple band developed and was co l l e c t e d , and the eluate was concentrated to 50 mL under reduced pressure. Addition of an equal volume of hexanes and slow concentration under reduced pressure induced the c r y s t a l l i z a t i o n of [CpCo(NO)] 2" 8 (0.12 g, 51% yield) whose i d e n t i t y was established by comparison of i t s XR, 1E NMR, and mass spectra with those of an authentic sample of the complex. Reaction of [CpMo (NO) T_2] 2 with I. S o l i d [CpMo (NOI T2] 2 4 9 (1.93 g, 2.17 mmol) was suspended i n benzene C200 mL) at room temperature, disso l v i n g only s l i g h t l y to give a pale v i o l e t solution. A 0.45 M benzene solution of I was added dropwise over a period of 1.5 h, the slow addition being required to permit the [CpMo (NO) I,,] 2 to eq u i l i b r a t e with, the solution. As I was added, a dark p r e c i p i t a t e formed and the solution turned green; with, s t i r r i n g , i t became orange; then as more st a r t i n g material dissolved, the solu-t i o n again became v i o l e t . The addition of I was stopped when the v i o l e t colouration no longer returned; two equiva-lents of I were required to reach t h i s point. The solvent was then removed i n vacuo; the residue was dissolved i n 15 mL of CH2CT2; and the r e s u l t i n g dark solution was syringed onto a 3 x 8 cm alumina ( a c t i v i t y grade I) column. Elution with. C I ^ C ^ developed two bands: a leading pale green band which decomposed part way down the column, and an orange band which required 3 00 mL of CH2CI2 for complete elu t i o n . The eluate was taken to dryness under reduced pressure, and the residue was r e c r y s t a l l i z e d from hot toluene to obtain 0.25 g (18% yield) of a n a l y t i c a l l y pure, orange [CpMo(NO)I]2 Anal. Calcd for C H Mo N O I : C, 18.89; H, 1.59; 10 10 2 2» 2* 2* N, 4.41. Found: C, 19.14; H, 1.68; N, 4.47. IR (CH^Cl^ : v N Q 1648 cm - 1. Mp (in air) 135°C dec. The reaction between [CpMo (NO) C^] 2 a n d I i n benzene was performed and worked up i n an i d e n t i c a l manner. No organometallic products were i s o l a b l e by chromatography. Reaction of [CpCr(NO)„]„ with I'. At room temperature. 0.91 g (2.6 mmol) of [CpCr (NO). ^ \^ 2 2 were dissolved i n benzene, and 2 equivalents of I i n benzene were added dropwise to the s t i r r e d solution. The red-purple solution gradually became orange-brown, and a small amount of a black precipitate, deposited. After a l l the aluminum reagent had been added, the reaction mixture was s t i r r e d for an additional 0.5 h to - 37 -ensure complete reaction. The. mixture was- then concentrated under reduced pressure to *10 mL and was transferred onto a 3 x 8 cm F l o r i s i l column. El u t i o n of the column with benzene developed two bands. The broad, dark green, f i r s t band eluted with ~250 mL of benzene. The solvent was removed from the eluate i n vacuo, and the re s u l t i n g residue was c r y s t a l l i z e d from dichloromethane-hexanes to obtain green c r y s t a l s (0.129 g, 15% yield) of Cp 2Cr 2(NO) 3 (NH 2 1 5 0 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 IR, 1H NMR, and mass s p e c t r a 1 8 . The orange second band was then eluted from the column with dichloromethane. Addition of hexanes to the eluate and slow concentration of the mixture under reduced pressure resulted i n the formation of orange c r y s t a l s (0.02 g, 2% yield) of Cp 2Cr 2 (NO) 2 (NH2) 2 . Anal. Calcd for cj_o Hi4 C r2 N4°2 : C ' 3 6 * 8 2 ; H ' 4- 3 3'" N, 17.17. Found: C, 36.76; H, 4.20; N, 16.93. IR (THF)_ : V N Q 1625 cm - 1.  1 E NMR CCDClg). : 5 5.39 (s, 5H) , 2.08 (br, 2H) . Mp (in air). 130°C dec. F i n a l l y , e l u t i o n of the column with tetrahydrofuran produced a single brown-orange band which was co l l e c t e d and taken to dryness under reduced pressure. C r y s t a l l i z a t i o n of the residue from dichloromethane-hexanes afforded orange c r y s t a l s (0.03 g, 3% yield) of Cp 2Cr 2 (NO) 2 (NH2) (OH).. Anal. Calcd for C 1 Q H 1 3 C r 2 N 3 0 3 : C, 36". 71; E, 4.00; N, 12.84. Found: C, 36.59; H, 3.83; N, 12.53. IR (THF);: v M n 1655, 1625 cm 1 . Mp (in air) 150°C dec. Mass spectrum: •r> 3 8 most intense parent ion m/'z 326. 97 69. Reaction of Cp 2Cr 2 (NO) 3 (NH,,) with I. Two equivalents of I i n benzene were added to a benzene solution (30 mLl contain-ing 0.12 g (.0.35 mmol) of the amide at room temperature. As the mixture was s t i r r e d , the i n i t i a l green colour changed to a dark orange—brown. IR monitoring of the reaction indicated that most of the reactant was consumed afte r 30 min. The f i n a l mixture was concentrated i n vacuo and chroma-tographed on F l o r i s i l (vide supra) to obtain 0.035 g of unreacted Cp 2Cr 2 (NO) 3 (NH2> , 0.010 g of Cp 2Cr 2 (NO) 2 (NH2> 2 and -0.001 g of Cp 2Cr 2(NO) 2(NH 2) (OH). The y i e l d s of the l a t t e r two complexes were 12% and 1% respectively, based on the amount Cp 2Cr 2 (NO) 3 (NH2) consumed. Reaction of CpCr(NO) 2Cl with NaNH2. A THF solution (.20 mL) containing 1.01 g (4.71 mmol) of CpCr (NO) 2C1 2 3 was added to an excess of s o l i d NaNH2 (0.65 g, 17 mmol), and the mixture was s t i r r e d at ambient temperature. Periodic monitoring of the supernatant l i q u i d by IR spectroscopy showed a gradual disappearance of the absorptions due to the organometallic reactant as the solution changed from o l i v e green to orange-brown and a black p r e c i p i t a t e formed. After 1.5 h, the reaction mixture was f i l t e r e d through a short (2 x 4 cm) column of C e l i t e supported on a medium porosity f r i t t e . The solvent was removed from the f i l t r a t e i n vacuo, the residual s o l i d was suspended i n 10 mL of CH 2C1 2, and the mixture was transferred to the top of a 2 x 6 cm F l o r i s i l - 39 -column. El u t i o n of the column with. CH^Cl^ developed a single green band which was c o l l e c t e d and taken to dryness. The golden s o l i d thus obtained O0.02 g) was i d e n t i f i e d as un-reacted CpCr (NO)2CT by i t s TR and 1H NMR s p e c t r a 2 3 . Further elution of the column with THF resulted i n the development of a dark orange-brown band which was c o l l -ected. Removal of solvent from the eluate under reduced pressure followed by r e c r y s t a l l i z a t i o n of the residue from CH 2Cl 2-hexanes afforded 0.06 g (8% yield) of Cp 2Cr 2 (NO) 2~ (NH2)(OH) 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 IR, *H NMR, and.mass spectra,(vide supra). Reaction of Fe(NO)^Cl with I. A stream of prepurified n i t r o -gen monoxide was passed over a vigorously s t i r r e d THF solu-t i o n (100 mL) containing 1.0 g (3.3 mmol) of [Fe(NO) 2C1] 2 1 6 for 2 0 min. The s t i r r e d solution was then placed under a nitrogen atmosphere, and a 0.5 M benzene solution of I was added dropwise. IR monitoring indicated that a s l i g h t excess of I was required to react completely with the Fe(N0)gCl generated i n s i t u , but the reaction mixture remained dark throughout. After the reaction was complete, the solvent was evaporated i n vacuo; the residual s o l i d was suspended i n 10 mL of CH 2C1 2; and the suspension was transferred onto a 3 x 8 cm F l o r i s i l column. A single brown band developed when the column was eluted with a 1:3 mixture of THF:CH2C1 2, and i t was c o l l e c t e d . The eluate was .taken to dryness, and the remaining s o l i d was c r y s t a l l i z e d by slow cooling of a concentrated 10:1 CH9C19:THF solution from room temperature - 40 -t o -2.0°C t o o b t a i n 0.0.4 g C5% y i e l d ) ; o f F e 2 (NQ) 4 ( N H 2 ) 2 , A n a l . C a l c d f o r H 4 F e 2 N & 0 4 : C, 0.00; H, 1.53; N, 31.86. Found: C, 0.16; H, 1.52; N, 31.64. IR ( C H 2 C 1 2 ) : v N Q 1763, 1727 cm" 1. 1 K NMR CCDC1 3): 6 5.15 (br) ; ( X C D 3 ) 2 C 0 ) : 6 6.80 ( b r ) . Mp (under N 2) 176°C dec. Mass spectrum: most i n t e n s e p a r e n t i o n m/z 263.9013. Reaction of Fe(N0) 3Cl with NaBH4. To a s t i r r e d solution (20 mL) containing 3.32 mmol of Fe(NO) 3Cl (prepared i n s i t u as described i n the previous section) at room temperature was added s o l i d NaBH4 (0.25 g, 6.7 mmol). The reaction mixture immediately darkened, heat was given o f f , and gas evolution occurred. The f i n a l reaction mixture was worked up i n a manner i d e n t i c a l to that described i n the preceeding paragraph to obtain 0.03 g (7% yield) of Fe 2 (NO) 4 (NH2) 2 , as i d e n t i f i e d by i t s IR and mass spectra. In a separate experiment, the NaBH4 was added i n small portions, and the IR spectrum of the supernatant l i q u i d was recorded after each addition. The only detect-able n i t r o s y l absorptions were those attributable to either the s t a r t i n g material or the isola t e d product. Reaction of FeCNO) 3Cl with NaNH2. [Fe (NO) 2C1] 2 (0.62 g, 2.0 mmol) was dissolved i n THF (30 mL) and converted to Fe(N0) 3Cl as described above. Solid NaNH2 (0.31 g, 8.0 mmol) was added, and the reaction mixture was s t i r r e d for 24 h at room temperature whereupon i t gradually darkened. F i l t r a t i o n of the mixture, removal of solvent, and chroma— - 41 1 -tography of the residue as before produced Q..0.54 g (10% yield) of Fe 2 (NO) ^ (NH2) 2 which, was i d e n t i f i e d by i t s IR and mass spectra. Results and Discussion Reactions of Sodium Dihydridobis (2-methoxyethoxy)aluminate (a) With Monomeric Chromium N i t r o s y l Complexes. Previous work has established that reduction of CpCr(NO)_2Cl with Na[AlH 2(OCH 2CH 2OCH 3) 21 (I) i n toluene at room temperature produces [CpCr(NO) 2] 2 ^ n 2 2 % y i e l d 5 1 . This reaction i s believed to proceed v i a the thermally unstable hydrido-chromium complex CpCr (NO)2H, which subsequently dimerizes to the observed product with concomitant expulsion of hydrogen 5 2. Further support for the involvement of such a hydrido intermediate i s provided by the present observation that [CpCr (NO)2]2 ^ s formed i n comparable y i e l d s during reactions of I with a va r i e t y of CpCr (NO)2X precursors at ambient temperature, i . e . C ? C r C N 0 ) 2 X benzene or CI^Cl, » [ C p C r ^ O ) ^ (23) X = NO_, N0 o, I, rZ-C.-H.- or BF. Monitoring of the progress of reaction 23 by infrared spec-troscopy indicates that the optimum stoichiometric r a t i o of reactants i s 1:1 and that the dimeric species i s the only nitrosyl-containing product formed. These reactions also demonstrate the a b i l i t y of I to substitute H for both halide and pseudohalide ligands and to transfer H to a coordina-- 42 -t i v e l y unsaturated metal centre such, as that i n I CpCr (NO)^] -BF^. Reaction 23 can also be effected i n tetrahydrofuran with NaBH, being employed i n place of I, but the y i e l d of the dimeric product i s lower. For instance, [CpCr(NO) 2 1 2 i s i s o l a b l e i n only 15% y i e l d from such a reaction when CpCr (NO)2 (NOg) i s used as the s t a r t i n g material. A similar observation has been reported for the reduction of CpCr(NO) 2~ C l by either I or NaBH^ 5 1. The ubiquitous n i t r o s y l dimer also r e s u l t s from the reaction I [CpCr (NO) 2 (CO) ] PF^ • [CpCr(NO) 2] 2 (24) a transformation which p a r a l l e l s the synthesis of [CpMn (CO)-(NO)] 2 " and [CpFe (CO) 2] 2 5 3 bY hydride attack on the i s o -electronic cations [CpMn (CO) 2(NO)] + and [CpFe(CO) 3] +, respectively. Presumably, reaction 24 occurs v i a the un-stable CpCr(NO) 2H since i t i s known that treatment of the analogous cation [CpW(NO) 2(CO)] + with NaBH^ produces the thermally stable complex CpW(NOy^H51. From a synthetic viewpoint, however, reactions 23 and 24 are not p a r t i c u l a r l y useful since [CpCr (NO) 212 i s best prepared by the reaction of CpCr (NO)^Cl with sodium amalgam in benzene 2 2. (b) With gome Monomeric Iodonitrosyl Complexes. Just as with CpCr (NO)2I (eq. 2 3 ) , I also undergoes simple meta-t h e t i c a l reactions with other monomeric io d o n i t r o s y l com-plexes to produce hydridonitrosyl species which may or may not be thermally stable at ambient temperature. Examples - 43 r. of these reactions are summarized i n equations 25—2.7 r CpMn CCO) (NO) I 1 benzene * [ C p M n ( C 0 } C N 0 1 1 2 ( 2 5 } (Mecp)Mn (NO) (.pph3);r b e J e n e » (MeCp) Mn (NO) („PPh3) H 54 (2 6) I CpCo (NO} I • [ CpCo (NO) ] 2 C2 7 ) toluene, -78 C Again, the optimum stoichiometry of the reactants i s 1:1, and the transformations proceed smoothly and i n reasonable y i e l d s . Due to the thermal i n s t a b i l i t y of CpMn (CO). (NOIIh 6 , a precise y i e l d for reaction 25 could not be determined. Nevertheless, an o v e r a l l y i e l d of ~65% could be achieved for the conversion of the manganese dimer to the iodide by the action of ^  followed by reduction with I back to the dimer. The dimeric products formed i n reactions 25 and 27 again probably ari s e from the thermal decomposition of the corresponding monomeric hydridonitrosyl complexes, but no d i r e c t physical evidence for the existence of these species could be obtained. However, consistent with the view that CpMn CCO) (NO) H i s the l a b i l e intermediate i n reaction,. 25 i s the fact that (MeCp)Mn(NO) (PPh3)II was subsequently i s o l a t e d from reaction 265k. Evidently, Introduction of the better electron-donating (MeCp) and PPh 3 groups into the coo r d i -nation sphere of the manganese atom s t a b i l i z e s the l a t t e r hydride, whereas the analogous hydridocarbonyl complex i n reaction 25 i s so unstable that i t cannot be detected by conventional spectroscopic techniques. - 44 -(c) With. [CpMo CNOjXj 2 (X I, CI) Complexes. In view of the r e a c t i v i t y patterns- of I described above, i t was of i n t e r e s t to investigate i t s reactions with complexes con-taining both bridging and terminal halide ligands. It seemed reasonable that sel e c t i v e substitution of the terminal halides could be achieved while leaving the halide bridges i n t a c t . Indeed, just such a transformation does occur when [CpMo(NO)I 2]2 i s treated with two equivalents of I at room temperature, i . e . forming the well-known dimer [CpMo (NO) I] 2 5 5 i n 18% y i e l d . By analogy with, the reactions described i n the preceeding sections, reaction 28 probably proceeds v i a the unstable dihydrido intermediate [CpMo (NO) (I) (H) ] 2 • During the reac-t i o n a green colour, perhaps due to the intermediate, appears after the addition of each aliquot of I; but t h i s colour p e r s i s t s only for several seconds before being replaced by the c h a r a c t e r i s t i c orange colour of the f i n a l product. The species responsible for the green colour i s not present i n s u f f i c i e n t concentration to allow i t s detection by IR spectroscopy. - 45 -5 6. Subsequently, the. preparation of [CpWCNO). I'2] 2 allowed i t s reaction with I to be examined 5 4. In t h i s instance a green hydrido—tungsten species could be i s o -lated, i . e . ' Cp Cp Cp Cp ON WK W NO — r - * ON W ,W NO C29) / x-r/ \ benzene ^. \jj \^ I I H H It was characterized by i t s IR, 1H NMR, and mass s p e c t r a 5 4 , although i t s thermal i n s t a b i l i t y precluded the i s o l a t i o n of an a n a l y t i c a l l y pure sample. It was, however, further characterized chemically by reaction with P(OPh) 3, i . e . 1 [CpW(NO) (I) (H)] 2 + 2P-(0Ph) 3 • — b e n Z e n e > 2CpW(N0) (I) CH) [P(OPh.)3] C30) The r e s u l t i n g tungsten hydride was f u l l y characterized. Curiously, thermal decomposition of [CpW(NO) CI)(H) ] 2 either i n the s o l i d state or i n solution does not r e s u l t i n the formation of the analogous ['CpW (NO). (I) ] 2 (vide supra)., a complex which has yet to be prepared. In view of reaction 28, i t was hoped that the reaction between [CpMo(NO) (C1) 21 2 5 7 and I would afford the s t i l l unknown [CpMo(NO) ( C l ) ] 2 complex i n a similar manner. While the two reagents do react, no organometallic products can be iso l a t e d from the f i n a l reaction mixture. Previously attempted reductions of [CpMo(NO) ( C l ) 2 ] 2 with sodium amalgam, zinc dust, or NaBH^ have also been unsuc-^ 46 r-c e s s f u l 5 8 . These failures-may r e f l e c t the i n a b i l i t y of the CI atoms to bridge the Mo centres i n the desired product. Cd) With [CpCr (NO). 23 2 . The 1:1 stoichiometry of the react-ants i n reactions 23 and 24 i s important for the formation of [CpCr (NO) 2] 2 i n maximum yi e l d s since the dimeric product can react further with the reducing agent. Hence, two equivalents of I are required to consume completely [CpCr-CNO) 2] 2 and produce, a l b e i t i n low y i e l d s , a mixture of Cp 2Cr 2 (N0).3 CNH2) , Cp 2Cr 2 (NO) 2 (.NH2) 2 , and Cp 2Cr 2 (NO) 2 (NH2) (OH) The l a t t e r products appear to be formed by the sequential reactions 31 and 32: [C PCr(.NO) 2] 2 b e n ; e n e » C p 2 C r 2 (NO) 3 (NH 2) (31) Cp 2Cr 2(NO) 3(NH 2) b e n ~ e n e »  C^ 2Cr2(N0)2(NH2>2 + Cp 2Cr 2 (NO) 2 (NH2) (OH) (32). Supporting" t h i s are the observations that a s l i g h t excess-o f . I • i n reactions 23 and 24 produces just a trace of Cp 2Cr2 (NO) 3(NH 2) , and reaction 32 can be performed indepen-dently. The products of reaction 3 2 do not react further with I under ambient conditions. The complex Cp 2Cr 2(NO) 3(NH 2) was f i r s t i s o l a t e d i n 1% y i e l d from the reduction of CpCr(NO) 2Cl with NaBH'4 i n water-benzene 5 0, and a report of i t s i s o l a t i o n as a bypro-. duct of the reactions of carbanions with [CpCr-(NO) 2] 2 5 9 appeared while t h i s work was i n progress. Tt has been com-pl e t e l y characterized and i s known to possess the. molecular - 47 -structure H H NO-ON Cp i n the s o l i d state 6 tt In terms of t h e i r gross stereochemical features, the two new complexes formed i n reaction 3 2 are probably i s o s t r u c t u r a l with the monoamido complex, with the bridging NO group i n the l a t t e r being replaced by either an NH~ or an OH group i n the former species. stable, non-volatile, orange s o l i d which begins to decompose gradually at 13 0°C. I t has limited s o l u b i l i t y i n benzene, dichloromethane, and tetrahydrofuran; but the orange solu-tions formed are a i r - and water-stable. An IR spectrum of a THF solution of the complex exhibits a strong absorption at 1625 cm ^ attributable to the terminal n i t r o s y l ligands. The weak V J J H absorptions at 3380 and 3330 cm can only be observed i n the IR spectrum of the complex i n a concentrated Nujol mull, but they occur i n the same range as those reported for Cp 2Cr 2 (NO) ^  (NH2) 50 . The low-resolution mass spectrum of the complex (taken with a probe temperature of 220°C and summarized i n Table II) i s consistent with i t s formulation as a dimer and displays a fragmentation pattern similar to that observed for [CpCr(NO)Cl] 2 1 7. For example, * peaks due to metastable ions can be detected at M = 23 9 and 125, and they are assignable to the fragmentation processes The diamido complex, Cp 2Cr 2 (NO) 2(NH 2j i s an a i r -T a b l e I I . L o w - R e s o l u t i o n Mass S p e c t r a l D a t a f o r C p 0 C r 0 (NO) 0(NH 0 ) X (X = NH n o r OH) Compl X = NH 2 z x = OH m/z R e l abund A s s i g n m e n t m/z R e l abund A s s i g n m e n t 326 39 ( C 5 H 5 ) 2 C r 2 C N O ) 2 ( N H 2 ) 2 + 327 25 ( C 5 H 5 l 2 C r 2 (NO) 2 (_NH2) (OH) 296 60 ( C 5 H 5 ) 2 C r 2 ( N O ) ( N H 2 ) 2 + 297 81 ( . C 5 H 5 ) 2 C r 2 (NO) (NH 2) (OH) + 266 100 ( C 5 H 5 ) 2 C r 2 ( N H 2 ) 2 + 28 0 11 ( C 5 H 5 ) 2 C r 2 ( N 0 ) 0 + 249 11 ( C 5 H 5 ) 2 C r 2 (NH) + 267 65 ( C 5 H 5 ) 2 C r 2 ( N H 2 ) ( O H ) + 200 17 ( C 5 H 5 ) C r 2 CNH 2) (NH) + 250 100 ( C 5 H 5 ) 2 C r 2 0 + 182 70 ( C 5 H 5 ) 2 C r + 201 11 C C 5 H 5 l C r 2 ( N H 2 ) 0 + 148 5 ( C 5 H 5 ) 2 C r 2 ( N O ) ( N H 2 ) 2 2 + 182 79 ( C 5 H 5 ) 2 C r + 133 36 ( C 5 H 5 ) C r ( N H 2 ) + 133.5 21 ( C 5 H 5 ) 2 C r 2 ( N H 2 ) ( O H ) 2 + 117 21 C 5 H 5 C r + 117 19 C 5 H 5 C r + 52 19 C r + 52 25 C r + The a s s i g n m e n t s i n v o l v e t h e most abundant n a t u r a l l y o c c u r r i n g i s o t o p e s i n e a c h f r a g m e n t . 49 -Cp 2Cr 2 (NO) (JJH2I 2 + Cp 2Cr 2 (NH2 )1 2 + and Cp 2Ci? 2 (NH 21 2 + ^ Cp 2Cr +, respectively. However, peaks: corresponding to bim e t a l l i c ions are r e l a t i v e l y more abundant i n the mass spectrum of the b i s ('amidol species. The 1K NMR spectrum of the compound i n CDCl^ consists of a sharp resonance at 6" 5.39 and a broad resonance at 6 2.08 of r e l a t i v e i n t e n s i t y 5:2 which are attri b u t a b l e to the cyclopentadienyl and amido protons, respectively. Since c i s - t r a n s interconversions of the related [CpCr (NO) (NMe 2)] 2 complex are known to begin only at elevated temperatures 6 1, t h i s spectrum probably indicates that only one isomer (either c i s or trans), of Cp 2Cr 2(NO) 2(NH 2) 2 exists i n solution at ambient temperatures. Isomerization could not be induced to occur by heating a s o l i d sample of the complex at 125 QC for 1.5 h. The physical properties of the other new dichromium complex isol a t e d generally resemble those displayed by the bis (amido) compound. Thus, Cp 2Cr 2 (NO) 2 (NH2) (OH) i s an orange-brown s o l i d which can be handled i n a i r for short periods of time. It i s moderately soluble i n benzene, C H 2 C I 2 / and THF to y i e l d a i r - s e n s i t i v e solutions. Its IR spectra display c h a r a c t e r i s t i c strong (1655 and 1625 cm - 1 i n THF) and weak v r.TTJ absorptions (3490, 3405 I.Nil Or Un.) and 3320 cm 1 i n a Nujol mull). ; and i t s mass spectrum (Table II, probe temperature of 200°C) confirms i t s b i m e t a l l i c nature. [The i d e n t i t y of the hydroxo complex was also con-firmed by high-resolution mass spectrometry. Calcd for C 1 0 H 1 3 N 3 ° 3 5 2 C r : m ^ Z 3 2 6 - 9 7 6 7 - Found: m/z 326.9769.] - 50 -Interestingly, the mass- spectrum also exhibits- a metastable * peak at M = 234 i n d i c a t i v e of the fragmentation process Cp 2Cr 2(NH 2) (0H) + + C p 2 C r 2 0 + . A similar loss of NH^ occurs during the fragmentation of the bis (amido) complex (Table I I ) . However, unlike for Cp 2Cr 2(NO)V (NH 2) 2, the *H NMR spectrum of the hydroxo compound i n CDCl^ consists of three sharp resonances at <5 5.29, 5.48, and 5.55 due to the cyclopenta-dienyl protons i n addition to two weak, broad signals at 6 2.62 and 3.42 a t t r i b u t a b l e to NH2 and/or OH protons. Apparently, the complex exists i n solution as a mixture of isomers, these being presumably the one trans and two c i s geometrical isomers expected i f i t s molecular structure resembles that of Cp 2Cr 2 (NO)^(NH2) (vide supra). These isomers do not r e a d i l y interconvert i n solution at ambient temperature since they can be p a r t i a l l y separated by frac - t t i o n a l c r y s t a l l i z a t i o n from CH 2Cl 2-hexanes, and the lE NMR spectra of the c r y s t a l l i z e d materials i n CDCl^ display d i f f e r i n g i n t e n s i t y r a t i o s of the three Cp resonances. The s o l u b i l i t y differences of the isomers are not s u f f i c i e n t l y large, however, to allow the i s o l a t i o n of any one isomer i n t h i s manner. Nevertheless, satisfactory- elemental analyses can be obtained f or . any • of-the cry s t a l l i n e , species-'produced. The formation of the amido products in reactions 31 and 32 can be viewed as a r i s i n g from the nucleophilic attack, of H on the nitrogen atom of a bridging n i t r o s y l ligand. The monoamido complex could thus r e s u l t from the two-step mechanism on the following page: - 51 -C r — : — - C r / \ / \ O N N N O 0 H ~ Cr Cr O N W N O 0 H H H cp N NC Cp Cr Cr \ x \ N N O O N ' O C A ) The . 0~ released i s ' scavenged - %--the'Le'wis acid present i n the reaction mixture. A similar sequence of reactions involving the monoamido species as the i n i t i a l reactant would then afford the bis(amido) compound. The fact that the complex t-Bu. O H C P X C P Cr Cr ON"'"'' ^ N ^ N O O can be prepared by the reaction of t-BuLi with. [CpCr (HOI 23 2 and subsequent h y d r o l y s i s 5 9 provides supporting evidence for the involvement of an intermediate such as (A) which i t s e l f may be s t a b i l i z e d by a coordinate O+Al bond involving - 52 -the bridging HNO group. However, t h i s rationale i s contrary to the expectation that the N atoms of terminal NO groups should be attacked p r e f e r e n t i a l l y by n u c l e o p h i l e s 1 h ; and so i t i s possible that the iso l a t e d products are simply the most thermodynamically stable species r e s u l t i n g from rear-rangements of precursors formed by the reduction of terminal NO ligands i n the i n i t i a l reactant. In t h i s connection, though, i t can be noted that the terminal n i t r o s y l groups of [CpCr(NO)(NH 2)] 2 undergo no reaction with I under ambient conditions. Nevertheless, the r e a c t i v i t y of these organo-me t a l l i c n i t r o s y l complexes towards H contrasts with that reported for [CpCo (NO). ] 2 and CpNiNO 6 2. Both of the l a t t e r species are converted to n i t r o s y l - f r e e cyclopentadienyl— hydrido c l u s t e r s when treated with. LiAlH^/AlCl^. in THF at 2 0°C and then hydrolyzed. The o r i g i n s of the hydroxo complex, Cp 2Cr 2(NO) 2~ (NH 2)(OH), are somewhat perplexing at the present time since several possible oxygen sources are present i n the reaction mixture. It i s i n t r i g u i n g , nonetheless, that i t i s the only nitrosyl-containing product formed when CpCr (NO) c i i s treated with NaNH2 i n THF at room temperature. (e) With Fe(NO)^Cl. In view of the reactions of I with monomeric iodonitrosyl complexes of f i r s t - r o w t r a n s i t i o n metals described i n section (b), i t was hoped that treatment of Fe(NO) 3Cl with a hydridic reagent would produce the as yet unknown binary n i t r o s y l Fe 2(NO)^ i n an analogous manner. However, when either I or NaBH. i s used as the reductant i n 5 3 -t h e r e a c t i o n r o r N a B H 4 2 F e ( N 0 ) o C l — A • 1 " A > • m ^ • F e „ CNO) . ( N H 0 ) 0 C33) 3 b e n z e n e a n d / o r T H F 2 4 2 2 T h e o n l y n i t r o s y l p r o d u c t i s o l a b l e i n l o w y i e l d s i s F e 2 (NO) ^ (_NH 2). 2 , a s p e c i e s w h i c h c o u l d b e f o r m e d v i a f u r t h e r r e d u c t i o n o f i n i t i a l l y p r o d u c e d F e 2 CNO) g i n m u c h t h e s a m e w a y t h a t C p 2 C r 2 CNO) 2 C N H 2 ) 2 i s f o r m e d f r o m C p 2 C r 2 ( N 0 1 4 ( s e c t i o n ( d ) ) . F e 2 ( N O ) 4 C .NH 2 ) 2 c a n a l s o b e s y n t h e s i z e d b y .. t h e r e a c t i o n N a N H -F e C N O ) 3 C l T £ ^ L • l / 2 [ F e C N O ) 2 C N H 2 ) ] 2 (34 ) . T h i s o b s e r v a t i o n r e v e a l s t h e t h e r m o d y n a m i c s t a b i l i t y o f t h e d i m e r a n d s u g g e s t s t h a t i n r e a c t i o n 3 3 i t c o u l d a l s o r e s u l t f r o m t h e a s s o c i a t i o n o f m o n o m e r i c a m i d o s p e c i e s f o r m e d u p o n i n i t i a l r e d u c t i o n o f F e C N O j ^ C l . F e 2 (NO)I C N H 2 ) _ 2 i s a g o l d e n - b r o w n , a i r - a n d w a t e r -s t a b l e s o l i d w h i c h i s s p a r i n g l y s o l u b l e i n m o s t c o m m o n o r g a n i c s o l v e n t s . I t s m o l e c u l a r s t r u c t u r e i s p r o b a b l y s i m i l a r t o t h a t f o u n d f o r o t h e r [ F e C N O ) 2 X ] 2 (X - I , S E t , o r 6 3 P ( C F 3 ) 2 ) c o m p l e x e s , n a m e l y O N ^ / N \ F e F e O N ^ N N N / / ^ N O H ' N H T h e l o c a l g e o m e t r y a b o u t t h e F e a t o m s i s a p p r o x i m a t e l y t e t r a -h e d r a l . T h u s , t h e I R s p e c t r u m o f t h e c o m p l e x i n C H 2 C 1 2 e x h i b i t s s t r o n g v N Q a b s o r p t i o n s a t 1 7 6 3 a n d 1 7 27 c m 1 a n d 54 T-i t s 1K NMR s p e c t r a d i s p l a y - a broad resonance. 05"" 5,1.5 i n CDC1 3; & 6.8 0 i n (CD 3) 2 C ° ) due t o t h e amido p r o t o n s . I t s -mass spectrum ( r e c o r d e d w i t h a probe t e m p e r a t u r e o f 80°C and summarized i n Ta b l e ITI)_ i n d i c a t e s t h a t t h e t e r m i n a l n i t r o s y l l i g a n d s a r e l o s t p r e f e r e n t i a l l y from t h e dimer d u r i n g t h e f r a g m e n t a t i o n p r o c e s s e s and t h a t an NR"3 group i s l o s t by t h e r e m a i n i n g F e 2 (NR"2) 2 + i o n ( c f . T a b l e I I I ) . The s t r e n g t h o f t h e amide b r i d g e s i n t h e complex i s a l s o i n d i c a t e d by t h e f a c t t h a t F e 2 (NO) 4 CNH2).2 i s not c l e a v e d by n i t r o g e n monoxide under ambient c o n d i t i o n s whereas t h e c o r r e s p o n d i n g h a l o d i m e r s , [ F e ( N O ) 2 X ] 2 , r e a d i l y c o n v e r t t o Fe(NO)_ 3X i n t h e pr e s e n c e o f NO. I t i s l i k e l y t h a t t h e b i s (amido) complex was f i r s t p r e p a r e d i n 1960 by t h e r e a c t i o n 6 1 * F e 2 (CO) (NH 2) 2 + 4NO benzene ^ F (NO) 4 (NH 2 ) 2 (35) + 6CO At t h a t t i m e , however, b o t h t h e s t a r t i n g m a t e r i a l and p r o d -u c t were i n c o r r e c t l y f o r m u l a t e d as F e 2 (CO)^(NH) 2 and F e 2 ( N O ) 4 (NH) 2, r e s p e c t i v e l y . Subsequent x - r a y and mass s p e c t r o m e t r i c s t u d i e s o f t h e c a r b o n y l r e a c t a n t e s t a b l i s h e d i t s t r u e i d e n t i t y and l e d t h e i n v e s t i g a t o r s t o suggest t h a t t h e n i t r o s y l p r o d u c t o f r e a c t i o n 35 i s a l s o p r o b a b l y a b i s ( a m i d o ) s p e c i e s 6 5 . Comparison o f t h e s p e c t r a l p r o p e r t i e s d i s p l a y e d by an a u t h e n t i c sample o f F e 2 ( N O ) 4 ( N H 2 ) 2 w i t h t h o s e r e p o r t e d f o r " F e 2 ( N O ) 4 ( N H ) 2 " s u p p o r t s such a v i e w . For b o t h t h e chromium amido complexes d e s c r i b e d i n - .5.5 -Table I I I . Hig h-Re solut ion Mass" :Spe ;ctrai Data for FeV (NO) 4(NH n I 2 m/z Rel. Measd Calcd "abund Assignment 263 . 901 2 63.899 7 0 Fe 2 (NO) 4 (NH2) 2 + 233.898 233.901 77 Fe 2 (NO)3 (NH 2) 2 + 2 03.903 2 03.903 50 Fe 2 (NO)2 (NH2) 2 + 173.906 173.906. 97 Fe 2(NO)(NH 2) 2 + 143.906 143.907 100 Fe 2 (NH 2 ) 2 + 126.881 12 6.8 81 73 Fe 2 CNH) + 12.5.874 . 125.875 30 Fe 2N + 112.878 112.878 7 Fe 2H + 111.869 111.870 13 Fe +  e2 101.94 9 10.1. 952 8 Fe(NO)(NH 2) + The assignments involve the most abundant n a t u r a l l y occurring isotopes i n each, fragment. - 56. -section C d ) and Fe 2 (NO) 4 (NH,,) 2 , no evidence for the i n t e r -conversion of NO and NH2 ligands between bridging and terminal positions was obtained. However, unlike for Cp 2Cr 2 (N0) 2 (NH2) 2 , the iron dimer 'does react further with. I to produce as yet unidentified nitrosyl-containing products. CHAPTER IV REACTIONS OF BIS [ (n. 1 -CYCLOPENTADIENYL) DINITROSYLCHROMIUM]  WITH LITHIUM TRIETHYLBOROHYDRIDE AND WITH BORANE. To o b t a i n f u r t h e r i n f o r m a t i o n r e l a t i n g t o the mech-anism by which hydride r e d u c t i o n of c o o r d i n a t e d n i t r o g e n monoxide oc c u r s , i t i s of i n t e r e s t t o examine the e f f e c t s t h a t v a r i a t i o n s i n the redu c i n g agent have upon the y i e l d s and d i s t r i b u t i o n s of the products i s o l a t e d . Large v a r i a -t i o n s i n both the redu c i n g power and the r e l a t i v e nucleo-. p h i l i c i t y of the hydride source are p o s s i b l e . L i t h i u m t r i e t h y l b o r o h y d r i d e has a redu c i n g a b i l i t y s i m i l a r t o t h a t of l i t h i u m borohydride. However, i t i s an extremely n u c l e o p h i l i c h y d r i d e , being 10,000 times more n u c l e o p h i l i c than l i t h i u m borohydride and about 40 times more n u c l e o p h i l i c than L i A l H ^ 4 2 . The r e p o r t e d chemistry of LiEt^BH r e v e a l s t h a t i t i s an e x c e p t i o n a l l y c l e a n reagent f o r the f a c i l e r e d u c t i v e dehalogenation of a l k y l h a l i d e s and f o r the r e g i o - and s t e r e o - s p e c i f i c r e d u c t i o n of e p o x i d e s 6 6 . I t a l s o r e a c t s smoothly with v a r i o u s t r a n s i t i o n - m e t a l c a r b o n y l complexes to form, i n the f i r s t i n s t a n c e , formyl d e r i v a t i v e s i n v i r t u a l l y q u a n t i t a t i v e y i e l d s 6 7 . In t h i s chapter i s d e s c r i b e d i t s r e a c t i o n with [CpCr ( N O ) 2 ] 2 , ^ n which LiEt^BH a c t s not o n l y as a source of H but a l s o d i s p l a y s unprecedented r e a c t i o n modes. - 58 -In contrast to both Na[AlH 2 (OCH 2CH 2OCH 3) 2] and LiEt^BH, BH3 can act as a Lew-is acid as well as- a hydride^ transfer agent 6 8. This has. been suggested as a r a t i o n a l i -zation of the great reducing power BH^-THF exhibits for a-oxygenated ligands i n general, and can lead to altered r e a c t i v i t y as i l l u s t r a t e d by the following example 6 8 and as outlined i n Chapter I: r 1 - . (3 6) The reaction of BH^• THF with [CpCr(NO) 2] 2 i s thus also reported, and the r e s u l t s obtained are compared to the anal-ogous reactions involving LiEt^BH and Na[AlH 2 (OCH 2CH 2OCH 3) 21. Experimental A l l experimental procedures described were performed under the general conditions described i n Chapter I I . Reaction of LiEt 3BH with [CpCr (NO) 2] 2 . A s t i r r e d tetrahydro-furan solution C3 0 mL) of [CpCr (NO) 2] 2 2 2 (0. 90 g, 2.5 mmol). at ambient temperature was treated dropwise with a THF solution of L i E t 3 B H 6 9 . : re.actipn. recurred'" i j ^ e d i ; ^ ^ and the o r i g i n a l red-purple solution gradually became dark yellow-brown i n colour. IR monitoring of the progress of - 59 the reaction, indicated that two equivalents of LiEt^BH were, required to consume completely the organometallic reactant. Solvent was removed from the f i n a l solution under reduced pressure to obtain a brown residue which was redissolved i n a minimum of benzene (~5 mL). To e f f e c t a p a r t i a l separa-t i o n of the products, the benzene solution was chromato-graphed on a 3 x 8 cm column of F l o r i s i l . A broad orange-brown band was f i r s t eluted with benzene, and the remaining products were then eluted with THF. The THF eluate was taken to dryness i n vacuo, the r e s u l t i n g residue was dissolved i n CH^C^ (~5 mL), and the solution was transferred by syringe onto a 1 x 4 cm F l o r i s i l column. Elution of the column with CH 2C1 2 and removal of the solvent from the eluate under reduced pressure yielded 0.04 g (5% yield) of orange C p 2 C r 2 (.NO) 2 (NH2) Elution with THF afforded 0.02 g (.2% yield), of orange-brown Cp 2Cr 2 (NO) 2 ~ (NH2) (OH) aft e r solvent removal. Both products were r e a d i l y i d e n t i f i a b l e by t h e i r c h a r a c t e r i s t i c IR, *H NMR, and mass spectra (see Chapter I I I ) . The o r i g i n a l benzene eluate was also taken to dry-ness i n vacuo, and the residue was extracted with hexanes (4 x 15 mL). The hexanes-insoluble matter was dissolved i n CH 2C1 2, an equal volume of hexanes was added, and the solu-t i o n was slowly concentrated under reduced pressure to induce the formation of green c r y s t a l s (0.13 g, 15% yield) of C p 2Cr 2(NO) 3(NH 2) 5 0 which were i d e n t i f i e d by t h e i r char-a c t e r i s t i c IR, JH NMR, and mass spectra. - 60. The dark-red hexanes'extracts were concentrated i n vacuo to ^7 mL and were transferred onto a 1 x 2 0 cm F l o r i s i l column. Elution of the column with, hexanes developed a yellow band which afforded ^0.04 g (5% yield) of a yellow o i l a f t e r complete elut i o n and solvent removal. The o i l was i d e n t i f i e d as CpCr(NO) 2Et 7 0 by i t s c h a r a c t e r i s t i c spectro-scopic properties [TR (CR"2C12) : v N Q 1770, 1645 cm - 1. 1U NMR (C,D^) : 6 4.55 (s, 5H), 1.4 Cm, 5H)]. A low-resolution b b mass spectrum of the o i l was also i d e n t i c a l to that displayed by an authentic sample of CpCr(NO) 2Et. Further elution of the column with benzene (.200 mL) afforded a red-brown eluate from which the solvent was removed under reduced pressure. The r e s u l t i n g residue was redissolved i n CH 2C1 2 (.5 mL) and hexanes (.20 mL) were added. Slow concentration of t h i s solution i n vacuo resulted i n the c r y s t a l l i z a t i o n of a n a l y t i c a l l y pure, purple-red Cp 2Cr 2 (NO)^-(EtNBEt 2) (.0.068 g, 6% y i e l d ) . Anal. Calcd for C 1 6 H 2 5 C r 2 N 4 0 3 B : C, 44.06; H, 5.78; N, 12.84. Found: C, 44.06; H, 5.95; N, 12.81. IR (CH 2C1 2): v N Q 1644, 1495 cm - 1. Mp (in air) 151-3°C dec. 1R NMR: see Table VI, page 74. Reaction of BH., • THF with [CpCr (NO) p ] 2 • To a s t i r r e d THF solution (3 0 mL) containing 0.3 6 g (1.0 mmol) [CpCr(NO) 2] 2 was added 2.0 equivalents of a 1 M solution of BH^ (pur-chased from the A l d r i c h Chemical Co. as a 1 M solution i n THF, s t a b i l i z e d with <0.05 M NaBH^). Over a period of 40 h the solution gradually turned a brown-purple colour and a - 61 -p r e c i p i t a t e formed. The reaction mixture, was- f i l t e r e d through C e l i t e , the volatiles- were removed i n vacuo, and the residue was p u r i f i e d By chromatography on a F l o r i s i l column as described previously on pages 36 to 38. In addition to unreacted [CpCr (NO) 2] 2 C22% y i e l d ) , the complexes Cp 2Cr 2-(NO) 3 (NH2) , Cp 2Cr 2 (NO) 2 (NH2) 2 , and Cp 2Cr 2 (NO) 2 (NH2) (OH) were is o l a t e d i n y i e l d s of 10, 1 and 3% respectively based on unrecovered [CpCr (NO) 2] 2. The products were i d e n t i f i e d by t h e i r c h a r a c t e r i s t i c IR, *H NMR, and mass spectra. Results and Discussion The Reaction of LiEt 3BH with [CpCr(NO)2^2* In the previous chapter i t was noted that treatment of [CpCr (NO) 2] 2 with two equivalents of NaAlH 2 (OCH2CH2OCH3). 2 i n benzene at room temperature affords, in low y i e l d s , a mixture of Cp 2Cr 2 (NO) 3 (NH2) (15%), Cp 2Cr 2 (NO) 2 (NH2 ) 2 ( 2%) , and Cp 2Cr 2(NO) 2(NH 2) (OH) (3%) as the only i s o l a b l e n i t r o s y l -containing complexes. The formation of these amido products can be viewed as a r i s i n g from the nucleophilic attack of H on the nitrogen atoms of the n i t r o s y l ligands i n the organo-m e t a l l i c reactant. With the hopes of preparing these pro-, duct complexes i n higher y i e l d s and of gaining further insight into the mechanism of reduction, of a coordinated NO group, an investigation of the reactions of [CpCr (NO)2]2 with other potent hydride donors was i n i t i a t e d . Of p a r t i -cular i n t e r e s t were those hydride sources which, unlike NaAlH2(OCH2CH2OCH3)2, contain only one transferable H per - 62 -mole and should thus provide Better defined chemistry 6 7, For the reasons c i t e d i n the Introduction/ the. reagent of choice was LiEt^BH. The reaction of ' LiE't 3BH with [CpCr (NO) 2'] 2 at ambient temperature i s quite a complex process, i . e . cP A /n° Cr—-Cr + 2 LiEt3BH ON N Cp 0 THF Et BEt \ / 2 C371 CD N v ,N0 /N1J2 \ / ' N /™ / ' " S T CpCr(NO)2Et + C r — P r + Cp(NO)Cr Cr(NO)Cp ON N Cp V V Y / 0 * (I*) X = NO (ii) X=NH2 (iii) X=OH Again, two equivalents of the hydride donor are required to consume completely the organometallic reactant, and the f i v e n itrosyl-containing products indicated can be is o l a t e d i n y i e l d s ranging from 2 - 15%. Regrettably, the y i e l d s of the l a s t three products Ci - i i i ) are comparable to those . obtained when NaAlH^(OCH^CH^OCH^)2 i s employed as the reduct-ant; but t h e i r formation i n t h i s reaction nevertheless indicates that they probably r e s u l t from the usual reaction mode of Et^BH as a hydride source. Just as f o r the trans-formation involving N'aAlH^ COC^CH^OCH^) 2 i i t c a n b e demon-strated that Cp 2Cr 2 CNO) 3 (NH2) reacts further with LiEt-jBH - 63 -to y i e l d both Cp 2Cr 2 (NO) 2 (NH2) 2 and Cp 2Cr 2 (NO) 2 (NH2). (OH) , and that neither of these l a t t e r complexes undergoes further reaction with excess hydride under the conditions of the experiment. Consequently, i t seems reasonable to conclude that similar mechanisms for formation of the bi m e t a l l i c amido compounds are operative i n both systems. A plausible mechanism for the conversion of an NO ligand to a coordina-ted NH2 group by H _ attack i s outlined i n the previous chapter. The monomeric product of the reaction, CpCr (NO) 2Et, i s also well-known, having been synthesized e a r l i e r by the action of Et^Al on CpCr (NO) 2C1 7 0. However, i t s formation during the present conversion i s somewhat surprising since the transfer of an ethyl group from boron to chromium i s not a common chemical occurrence. In t h i s connection, though, i t i s of in t e r e s t to note that treatment of [CpFe(CO) 2] 2 (isoelectronic and i so s t r u c t u r a l with [CpCr (NO) 2] 2)_ with. LiEt^BH i n THF-HMPA does not r e s u l t i n formation of any of the corresponding a l k y l complex, CpFe(CO) 2Et, but rather i n quantitative conversion of the carbonyl dimer to the anion [CpFe(CO) 2] 7 1 . In contrast, c a r e f u l IR monitoring of reaction 37 provides no evidence for the formation of anionic n i t r o s y l products. The most i n t r i g u i n g product iso l a t e d from the f i n a l reaction mixture i s the novel complex Cp 2Cr 2 (NO)^ (EtNBEt 2), a purple-red s o l i d (mp 151°C dec) which dissolves r e a d i l y i n common organic solvents to y i e l d a i r - s t a b l e , red—brown T- 64 ~ solutions. Its- I R spectrum Cin •. .-CH^ C^ ~^ e x n i & £ t s - strong absorptions at 1644 and 1495 cm 1 a t t r i b u t a b l e to terminal and bridging NO ligands, respectively. I t s mass spectrum (Table V) confirms i t s b i m e t a l l i c - nature, and i t s ambient temperature 1H and 1 3 C NMR spectra (Table VI) indicate the absence of molecular symmetry and are consistent with the presence of a bridging EtNBEt2 group. To ascertain i t s molecular structure, a s i n g l e - c r y s t a l x-ray s t r u c t u r a l analysis of the complex was carried out by Dr. R.G. B a l l 7 2 . The c r y s t a l structure of Cp 2Cr 2(NO) 3(EtNBEt 2) con-s i s t s of a well-separated array of discrete molecular units, the intermolecular distances corresponding to normal van der Waals contacts. The molecular packing within the c r y s t a l i s i l l u s t r a t e d i n Figure 1. Each molecule (Figure 2) adopts a trans configuration of the n i t r o s y l and cyclopentadienyl ligands with respect to the mean plane of the ce n t r a l , c y c l i c C"r2N2 fragment and has an o v e r a l l geometry similar to that displayed by trans-[CpCr(NO)(NMe 2)] 2 7 3, t r a n s - [ C p C r ( N O ) 2 ] 2 7 4 , and trans-Cp 2Cr 2 (NO)3 (NH 2) 6 0. Selected bond distances and interbond angles are given i n Table IV. The i n d i v i d u a l molecular dimensions of Cp 2Cr 2(NO) 3-(EtNBEt 2) are also comparable to those found i n the other cyclopentadienylchromium n i t r o s y l complexes mentioned above. S p e c i f i c a l l y , the bond lengths and angles within each mole-cule are consistent with the views that: (a) The Cp rings function as formal five-electron, donors to the metal centres. [The rings have normal geometries 7 5, Bottom Figure 1. Stereoscopic view of the contents of a unit c e l l of Cp 2Cr 2(NO) 3(EtNBEt 2). The view i s down c, and the hydrogen atoms are omitted for c l a r i t y . - 66 Figure 2. A perspective view of the molecular structure, of Cp 2Cr 2 CNOJ.3 CEtNBEt2). including the atom numbering scheme. Hydrogen atoms are omitted, and the thermal e l l i p s o i d s are drawn at the 50% probab-i l i t y l e v e l . C(I4) C(3) 68 -T a b l e IV. S e l e c t e d Bond D i s t a n c e s - and Bonff A;h:gTes: "(deg). f o r C p 2 C r 2 C N O l y ( E t N B E t 2 ) . Bond D i s t a n c e s C r ( 1 ) - C r ( 2 ) 2. 668 0 C8I Cr (1) C(l). 2. 255 (4) Cr CD - N(l) 1. 892 (.31 Cr ( D C (21 2. 2.3 8 (41 Cr CD - N(2) 1. 67 9 (3) Cr C D CC3) 2. 202 (4) Cr (1) - N(4) 2.068 (3) Cr CD - C(4) 2. 212 (4) C r ( 2 ) - N CD 1.924 (3) Cr ( D — CC5) 2. 226 (41 CrC2). - NC3). 1.680 C.31 Cr (2) - C(6I 2. 194 (51 Cr(.2> - NC4). 2.070 (31 Cr (.2) - C(71 2. 256 C5) N C D - 0(1) 1.196 (41 Cr C2); — C(8} 2. 262 (4) N(2) - 0(2) 1.191 (4) Cr (2) - C(9) 2. 22 5 C4J N(3) - 0(3) 1.199 (41 Cr (2) - C(10) 2. 183 (41 NC4) - B 1.459 (5) CC111 - C(12) 1. 53 6(6) N(4) - C (15) 1.498 C51 CC13) - CC14) 1. 519 (71 B - c a n 1.578 (51 CC15) CC.16). 1. 508 C.7) B - CC131 1.601(6) Bond Angles NCD - Cr (1) - N (4) 94.1 (1)_ C r C D - N(l) - Cr (2 ) 88.7 (1) N ( .D - CrC2) - N (4 1 93.1 CD C r ( D - N(4) - Cr (2) 8 0.3 (1)1 Cr (1) - N(l) - 0(1) 137.6(3} N(4) - B • - c a n 122. 5 (41 CrC2) - NCD - 0(1) 131.5 (3) NC41 - B • - CC131 120.3 (3) Cr (1) - N(2) - 0(2) 170.0(3) c a n - B - CC13} 116.1 (3) Cr (2) - N(3) - 0(3} 168.4 (3) B - c a n - CC12} 109.2 (4) Cr (1) - N(4) - B 12 9.0(2) B - C(13) - CC14) 1.15.7 (4)1 Cr(2). - NC41 - B 91.6 (2) N(4) - C(15) - C(16) 111. 5 (41 B - N(4) - CC151 113.8 (3). - 69 -being e s s e n t i a l l y pla,nar with, mean C-C distances of 1.39(1) R and i n t e r n a l angles of 108 (1) °; and the mean Cr-r-C distance i s 2.22 C41 £,] (b) Both the terminal and bridging n i t r o s y l groups are normal three—electron donor ligands i n th e i r respective bonding environments. [The two terminal NO groups are of the l i n e a r t y p e 7 6 , having Cr-N-0 angles of approximately 170°, a mean Cr-N distance of 1.680(4) R, and a mean N-0 distance of 1.195(6) R. A s l i g h t asymmetry i n the bonding of the bridging NO ligand i s indicated by the difference i n the Cr—N(l) bond lengths of 0. 032 R (or 8a) whereas no other chemically equivalent bonds d i f f e r by more than 3a.] (c) A Cr-Cr single bond exists i n the molecule. [The existence of t h i s linkage i s indicated not only by the Cr-Cr separation of 2.6680(8) R but also by the dihedral angle of 167.3° between N(l)-Cr-N(4) planes and the acute Cr-N-Cr angles of 88.7(1) and 80.3 ( 1 ) 0 . ] 6 5 ' 7 7 Consequently, i n order that each chromium atom i n the complex may a t t a i n the favored 18-electron configuration, the bridging EtNBEt2 group (li k e the bridging NO, NH2, and NMe2 groups i n the related complexes) apparently functions as a formal three-electron donor. The most chemically int e r e s t i n g feature of the structure i s the novel EtNBEt 2 ligand. It i s coordinated v i a N i n a symmetrical fashion to the two Cr atoms, the mean Cr-N bond distance being 2.069(4) R. This distance i s simi l a r to the Cr-N(sp 3) bond lengths of 1.99(2) to 2.04(2) R i n [CpCr (NO) (NMe9) ] 9 7 3. The coordination environment - 7 0- -around the N atom i s distorted from an ideal tetrahedral geometry i n a manner which, can Be viewed as- a r i s i n g from a rotation of the C (.15) -N ('4) -Cr- (2) plane. Such a d i s t o r t i o n i s consistent with: minimizing the non—Bonded repulsions Between the cyclopentadienyl rings and the methylene hydro-gens of the EtNBEt2 ligand. Within the group i t s e l f , the C-C, N—C, and B-C Bond lengths are those expected for normal single Bonds. For instance, the B-C distances of 1.578(5) and 1.601(5) R are within the range of values, 1.577 (5) to 1.619(3) R 7 8 , commonly oBserved for single B-C Bonds. However, the N(4)-B distance of 1.459(5) £ i s intermediate Between the values of 1.4 4 and 1.57 R for B-N douBle 7 9 and single Bonds 8 0, respectively, and suggests some degree of multiple Bonding Between the B and N atoms. Consistent with 2 t h i s view are the oBserved planar (sp ) geometry around the Boron atom and the a i r - s t a b i l i t y of the compound ( r a t i o n a l -izaBle i n terms of N->BpfT interaction) . Hence, within t h i s Bimetallic complex, there appears to Be a competition Between the two Cr atoms and the B atom for the "lone pair" of electrons on N. However., the r e s u l t i n g feature of a four-coordinate nitrogen atom engaging i n concomitant multiple Bonding cannot Be r a t i o n a l i z e d i n terms of l o c a l -ized, two-centre Bonds. The spectroscopic properties of Cp 2Cr 2 (NO) ^  (EtNBEt 2 ) can Be more f u l l y understood i n terms of i t s molecular structure. Its mass spectra contain peaks assignable to the parent ion and ions r e s u l t i n g from the sequential l o s s of - 71 -ligands from both, the parent and monometallic species a r i s -ing from cleavage of the parent; high.—resolution data are presented i n Table V. Similar fragmentation patterns- have been reported for related molecules 8 1. Hence, ions r e s u l t -ing from losses of NO, C^H^ (from either N-Et or B-Et), NBCgH^^, and EtNBEt 2 are observable; and the occurrence of peaks due to metastable ions i n the low-resolution mass spectrum of the complex provides d i r e c t evidence for several of these fragmentation modes. Thus, peaks at m/z of 242, 215, 176, and 153 correspond to the respective fragmentations Cp 2Cr 2 (NO) 3 (EtNBEt 2) + • Cp 2Cr 2 (NO) 3 H + + NBC gH 1 4 CpCr(EtNBEt 2) + • CpCrCNBC4H ) + + C 2H 4 Cp 2Cr 2(NO) 2H + • CpCr + + CpCr(NO) 2H and CpCr(EtNBEt 2) + • CpCr + + EtNBEt 2 Indeed, the whole series of ions Cp 2Cr 2(NO) xH + (x = l-*-3) i s observable. Of p a r t i c u l a r i n t e r e s t i s the occurrence of the nitride-containing ions Cp 2Cr 2(NO) 2(NEt)N +, Cp 2Cr 2(NEt 2)N +, and Cp 2Cr 2 (NEt)N +. In each of these ions NEt or NEt 2 groups remain, thereby suggesting that the N atom has resulted from fragmentation of a n i t r o s y l ligand. The elimination of elect r o n - d e f i c i e n t BEt or BEt 2 fragments from the various-precursor ions may a s s i s t t h i s unusual fragmentation process. In general, oxo ions are more abundant than n i t r i d e ions i n the mass spectra of chromium n i t r o s y l s 8 2 . F i n a l l y , i t can be noted that migration of the cyclopentadienyl group between metal atoms occurs more, r e a d i l y for Cp 2Cr 2 (N0l 3~ - 72 -Table. V. High—Re so l u t i.on Mass S p e c t r a l D a t a f o r C p 2 C r 2 CNO)-> ( E t N B E t 2 1 m/z Measd^ C a l c d R e l Abund 436.081 436.083 28 (C 5H 406.087 406.08 5 5 (C 5H 376.0.88 376.087 2 (C 5H 351.003 351.001 2 (C 5H 324.964 324.961 15 (C 5H 320.040 320.044 3 (C 5H 319.018 319.017 3 CC 5H 2 94.964 2 94.963 3 (C 5H 2 91.000 291.005 17 (C 5H 264.965 264.965 25 CC 5H 258.100 258.100 28 (C 5H 249.973 249.978 23 (C 5H 22 9.109 229.109 100 (C 5H 201.078 201.07 8 75 (C 5H 182.019 182.019 60 (C 5H 176.975 176.976 1 (C 5H 171.031 171.031 18 (C 5H 116.980 116.980 25 (C CH D a Probe t e m p e r a t u r e ~150°C b ±0.001 mass u n i t c The assignments i n v o l v e t h e most Assignment^ 2 C r 2 (N01 3 C.EtNBEt 2J 2 C r 2 ( N O ) 2 ( E t N B E t 2 ) 2 C r 2 ( N O ) CEtNBEt 2) + 2 C r 2 ( N O ) 2 ( N E t ) N 2 C r 2 ( N O ) 3 H + 2 C r 2 ( N E t 2 ) N + 2 C r 2 (NO) (NBC 2H 6) + 2 C r 2 ( N O ) 2 H + 2 C r 2 ( N E t ) N + 2 C r 2 ( N O ) H + Cr (NO) (NBC 6H 1 4) + 2 C r 2 ( N H 2 ) + Cr ( E t N B E t 2 ) + Cr(NBC.H ) + ^ + Cr CNO) 2 C r ( N B C 0 H C ) + ^ + 2 5 ' Cr + + o c c u r r i n g i s o t o p e s , e.g. 5 2 C r , i n each fragment. 73 -(EtNBEt 2) than for Cp 2Cr 2 (NO) ^  1 8 (cf. the. r e l a t i v e abund-ances of the Cp 2Cr + ion); and ions containing two Cr atoms are less abundant i n the mass- spectra of the former compound. The asymmetric molecular structure observed for-Cp 2Cr 2 CN0)3 C.EtNBEt2) i n the s o l i d state apparently p e r s i s t s in solution, as evidenced by i t s a n d 1 3 C NMR spectra (.Table VI).. Hence, i n i t s ambient-temperature *H NMR spectrum, the inequivalence of the cyclopentadienyl rings and the diastereo-topic nature of the a-H atoms i n the N-Et moiety are c l e a r l y evident. Also, the ethyl groups attached to the boron atom are seen to be inequivalent, t h e i r assignments given i n Table VI being based p r i n c i p a l l y on the integration of the spectrum. Similar features are displayed by the 1 3 C NMR spectrum of the complex. However, the methylene carbons of the ethyl groups bonded to boron give r i s e to a broad 1 3 C signal centred at 6 14.0 presumably due to couplings with, the 1 J B (I = 3/2) and 1 °B (I = 3.) nuclei which, are incompletely relaxed by the quadrupole mechanism 8 3. The methyl carbons give r i s e to only one peak, probably due to coincidental overlap. The chemical s h i f t s of the d i f f e r e n t resonances also provide information about the various nuclei i n the novel EtNBEt 2 ligand. That the asymmetric nitrogen atom c a r r i e s at least a p a r t i a l p o s i t i v e charge i s indicated by the down-f i e l d p o s ition of the resonances due to the protons a to the N ( i . e . 6 4.62, 4.94). These signals occur at s l i g h t l y lower f i e l d s than the corresponding resonances displayed by 74 -T a b l e V I . NMR Data; f o r Cp,,Cr 2 (NO) ( E t N B E t D i n . C D C 1 2 H B H Q C H 2 C H 3 y C B ~ CHgCH^ (HC)3C \ / N 1H. D a t a Cp( NO) Cr—— Cr( NO) Cp \ / N 0 a b S_ R e l I n t e n s i t y A s s i g n m e n t 5.34 Is). 5 Cp 5.27 (s) 5 Cp 4.94 (m) J . = 12 Hz 1 N-CH ab a 4.62 (m) 1 N-CH D * 1.51 Ct). J = J . = 7 Hz 3 N - C H „ - C C H ) ciC DC ^ C 0.81 C.br, m) 8 B - E t , B-CH 2 -0.06 Cbr) 2 B-CH '2 1 3 C D a t a a 1 -r - K 6 1 3 C - H A s s i g n m e n t 102.53 C Cp 102.04 J 1 7 7 H Z I Cp .62.86 137 Hz N-CH 2-CH 3 24.33 126 Hz N-CH 2~CH 3 14.0 (br) — B-CH 2-CH 3 9.27 123 Hz B-CH 2-CH 3 a The i n d i c a t e d c h e m i c a l s h i f t s a r e i n ppm d o w n f i e l d f r o m M e . S i . T h e s e a s s i g n m e n t s have been c o n f i r m e d b y a s e r i e s o f h o m o n u c l e a r and h e t e r o n u c l e a r d e c o u p l i n g e x p e r i m e n t s . - 75 -t y p i c a l t e t r a a l k y l ammon ium compounds (5 3.3 — 4.. 8 vs., 6; 3,0. — 3.7 for t e r t i a r y amines'84).. The: ^ CPE) NMR, spectrum reinforces t h i s impression, the signal due to the, a—carbon nucleus being at 6" 62.86 versus 6' ~52 for Et^NX compounds and & ~48 for E t ^ N 8 4 . In addition, the existence of some N-B multiple bonding i s suggested by the 11B NMR spectrum of Cp 2Cr 2(NO) 3(EtNBEt 2) i n CDC13 which consists of a single, broad resonance centred at -4 6.9 ppm from external BF 3-OEt 2 (peak width at half-height = 17.6 ppm). This chemical s h i f t f a l l s i n the range ( i . e . 6 -41.8 to -48.7) previously i reported for a series of R^ -^ -^ BR.^  compounds 8 5. It i s thus not surprising that the complex as a whole appears to be stereochemically r i g i d i n solution at ambient temperature. Indeed, i t s 1H NMR spectrum i n dg-toluene over the range -70 to 90°C s t i l l displays the p r i n c i p a l spectral features l i s t e d i n Table VI. At the upper l i m i t , however, the o r i g i n a l l y broad peak at 6 = -0.06 due to the B-CH2 protons appears as a quartet, thereby confirming i t s assignment. Admittedly, the JH NMR data do not rule out rapid rotation of the Et 2B group about the B-N(4) bond because of the diastereotopic nature of i t s methylene groups, but in.view of the other evidence for some N—B multiple bonding (vide supra), t h i s p o s s i b i l i t y i s considered to be less l i k e l y . Interestingly, NMR i s more sensitive than IR to the molecular asymmetry as evidenced by the fact that only one terminal NO stretch, i s observed for the complex whereas two such, stretches are expected to be IR active. - 76 -The net transformation effected by LrEt^BH during the formation of t h i s product i s thus^ Et BEt2 0 \ / 2 \ / I iFt RH V / £x — Cr L l E f 3 B H w .Cr — C r namely the conversion of a bridging n i t r o s y l ligand to a bridging EtNBEt 2 group. The mechanism of t h i s remarkable reaction remains unknown, but i t can be demonstrated independently that the EtNBEt 2-containing product i s not obtained from the further reaction of LiEt^BH with any of the b i m e t a l l i c amido complexes isolated from the o r i g i n a l reaction mixture (vide supra). It may, however, r e s u l t from the attack of BEt 3 (the by-product formed when Et^BH -functions as a hydride source) on the o r i g i n a l organometallic reactant, [CpCrCNO) 2] 2. Thus, treatment of the n i t r o s y l dimer with, an equimolar amount of BEt^ i n THF-hexanes at room temperature does afford Cp 2Cr 2(NO). 3(EtNBEt 2) i n 4% y i e l d , but the p r i n c i p a l i s o l a b l e product i s CpCr(NO)„2Et (.20% y i e l d ) . It was also shown that CpCr(NO) 2Et does not react further with BEt 3. When free NO i s reacted with BEt 3 at -30°C 8 6 Et 2BN(N0)0Et i s obtained, whereas at 70°C Et 2BON(Et)BEt 2 and Et 2BONEt 2 are is o l a t e d ; no products i n which' cleavage of the N-0 bond has occurred were found except when the reaction mixture was subsequently treated with concentrated E^SO^. In any event, the reaction of - 77 -LiEt^BK with. [ CpCr CNO I ^ ] 2 i s c e r t a i n l y more, complex than. with, analogous carbonyl compounds, the l a t t e r being cleaved to anions with the accompanying formation of the v o l a t i l e by-products H 2 and B E t ^ 6 7 . The fact that the corresponding n i t r o s y l anion, [CpCr(NO) 2] t i s not i s o l a b l e from the pre-sent reaction probably r e f l e c t s upon i t s inherent i n s t a b i l i t y , i t being as yet unknown 1 8. The Reaction of BH., with. [CpCr CNO) J 2 > Very l i t t l e difference i n the o v e r a l l y i e l d s or i n the d i s t r i b u t i o n of the [CpCr CNO) 2] 2 r e d u c t i o n products ( i -i i i ) i s observed when the very potent nucleophile LiHBEt^ i s substituted for NaAlH,, COCH2CH2OCH3) 2 as reductant, despite the i s o l a t i o n of unexpected additional products. S i m i l a r l y , when the e l e c t r o p h i l i c 6 8 reducing agent BH^ i s used, the bim e t a l l i c amido products C i - i i i ) are again obtained i n low y i e l d , although the reaction i s s i g n i f i c a n t l y slower. Thus, markedly modifying the nature of the reductant used f a i l s to produce either d i f f e r e n t reduction products or v a r i a t i o n s i n the y i e l d s of the compounds iso l a t e d , and therefore provides no new evidence as to the mechanism of the n i t r o s y l reduction. Another pote n t i a l means of obtaining mechanistic information r e l a t i n g to the mode of reduction of the chromium n i t r o s y l dimer i s to carry out the reduction on the corresponding thioni.trosyl compound, [CpCr CNO) CNS)] 2 , depicted on. the following page. The better TT—acid ligand, NS 4 5, should p r e f e r e n t i a l l y occupy the bridging position as does the CSN ligand in'the i s o e l e c t r o n i c complex [CpFe CCO) CCSl] 8 7 . - 78 -Cr • •Cr ON^ ^ N ^ ^NjO Examination of any reduction products isolated would then allow one to i n f e r whether the i n i t i a l s i t e of attack i s a bridging or a terminal ligand. Unfortunately, attempts to extend the reduction of [CpCr (CO) (NO) 2\PF g to [CpCr (.NO) 2] 2 (discussed i n Chapter III) to the t h i o n i t r o s y l analogue, [CpCr (CO) (NO) (NS)]PF C 4 5, D u t i l i z i n g either NaAlH 2(OCH 2CH 2OCH 3) 2 o r LiEt 3BH as the hydride source were unsuccessful. A complicating factor i s the i n s t a b i l i t y of [CpCr(CO) (NO) (NS)]PF_ i n the presence of D donor solvents, combined with i t s lack of s o l u b i l i t y i n non-coordinating s o l v e n t s 4 5 . Although nitrosyl-containing products are observed i n the infrared spectra of the reaction mixtures, no n i t r o s y l - or thionitrosyl-containing species could be successfully i s o l a t e d . CHAPTER V A STUDY OF THE LENTS' BASE PROPERTIES OF CYCLOPENTADIENYL—  TUNGSTENDINITROSYL HYDRIDE AND THE LENTS ACID PROPERTIES OF THE CYCLOPENTADTENYLTUNGSTENDINTTROSYL CATION. In l i g h t of the large differences i n the r e a c t i v i t i e s of the i s o s t r u c t u r a l and is o e l e c t r o n i c complexes [CpFe(CO) 2] 2> [CpMn(CO)(NO)]2, and [ C p C r ( N O ) 2 ] 2 1 8 ' " 7 , i t was of obvious intere s t to extend t h i s comparison to the second and t h i r d row transition-metal analogues of these compounds. Unfort-unately, although the Ru 8 8 and O s 8 9 congeners of [CpFe (CO) 2] 2 have been known for some time and [CpRe(CO)(NO)] 2 has 9 0 recently been successfully prepared , the Mo and W n i t r o s y l complexes have not as yet been synthesized. One of the questions to be answered concerned the structures of the n i t r o s y l complexes — would the n i t r o s y l ligands a l l be terminal, or would two bridge the metal-metal bond? In solution, [CpFe(CO) 2] 2 has been shown to ex i s t as a ra p i d l y e q u i l i b r a t i n g mixture of p r i n c i p a l l y c i s and trans isomers with bridging CO groups 9 1, i . e . c p \ A . c p \ „ / c p _ _ i K A A 9 C C C C C C D 0 0 U0 0 0 ° ° Variable temperature NMR studies demonstrated the. intercon-- 80 -version of these isomers with concomitant interchange of the CO groups between bridging and terminal positions. These processes were explained by a concerted opening of the CO bridges to give a non-bridged CpCCO^Fe—FefCO^Cp intermed-ia t e , rotation about the F e — F e bond, and then reclosing of the CO bridges to produce either a c i s or a trans isomer 9 2. [CpMn(CO) (NO)]2 9 3 a n d [CpCr(NO) 2] 2 9 3 have been shown to undergo corresponding intramolecular rearrangement processes. In contrast, [CpRu(CO) 2] 2 was observed to e x i s t as an approximately 50/50 mixture of CO bridged and non-bridged forms i n hydrocarbon solution at room temperature 9 4. Intro-duction of an aluminum a l k y l into the solution drove the equilibrium completely to the bridged form, with A l R 3 coord-inating to a bridging carbonyl l i g a n d 9 5 , i . e . ^ c^ A / c° A1R_ + [CpRu(CO) 1„ RU- -Ru 3 2 2 / \ / \ o c 1  C p A 1 R 3 The osmium carbonyl complex was found to exi s t s o l e l y i n the non-bridged form i n s o l u t i o n 8 9 . The solution structure of [CpRe(CO)(NO)] 2 i s not as yet c l e a r l y understood, but i t appears to e x i s t s o l e l y i n non-bridged forms 9 0. Whether the Mo and W analogues of [CpCr(N0) 2] 2 would display a similar trend i n t h e i r structures and behaviour i n solution was one question to be answered upon t h e i r preparation. Another reason for inter e s t in the synthesis of [CpMo(NO) 2] 2 and [CpW(NO) 2] 2 was the known a f f i n i t y of - 81, -[CpCr ( N O 1 ^ o r halogens.. Previous- work, i n t h i s laboratory f i r s t demonstrated the a b i l i t y of [CpCr(NO) 2] 2 to abstract halogen from some inorganic and organometallic complexes 1 8, and l a t e r showed that i t s e l e c t i v e l y removed halogen from a v a r i e t y of organic h a l i d e s 9 6 . It was hoped that the Mo and W analogues would also have an a f f i n i t y for halides but with, altered s e l e c t i v i t i e s , thus providing a series of reagents useful i n synthetic organic chemistry. A t h i r d reason for i n t e r e s t i n the preparation of these b i m e t a l l i c n i t r o s y l complexes centred on the reactions of [CpCr (NO),,] 2 described in the previous two chapters. Thus, while i t was possible to e f f e c t the conversion of coordinated NO to NH2 and to N(Et.)BEt 2, no mechanistic information r e l a t i n g to these conversions could be obtained. It was therefore hoped that the reduction of [CpMo(NO) 2] 2 or [CpW(NO).2]2 would lead to the detection and perhaps the i s o l a t i o n of the intermediates associated with the reduction of coordinated NO. The basis for optimism that these attempts would be successful whereas those on the chromium complex were not was the known k i n e t i c p r i n c i p l e that the r e a c t i v i t y of i s o s t r u c t u r a l complexes often follows the j -I st ^ „nd ^ _.rd , ... ., . , 3 9 order: 1 row > 2 row > 3 row t r a n s i t i o n metals . The success achieved by Casey 6 8, G l a d y s z 9 7 , Graham 9 8 and t h e i r co-workers i n unravelling the mechanism of the reduc-t i o n of coordinated CO to CH^ i n the model system CpRe (CO) 2~ (NO) + + H*~ — * CpRe (CO) (NO) (CHD was- also a source of encouragement,. - 82 -The preparation of the compounds [CpMo (NO) 2 ^ and [CpWCNO^^ n a <3 thus been a goal i n t h i s laboratory for some time, with considerable e f f o r t having been expended toward t h i s end 9 9. However, the reactions demonstrating the reduc-tion of coordinated NO in [CpCr(NO)2\ 2 rejuvenated i n t e r e s t i n these complexes, and a personal, communication from Professor W.A.G. Graham r e l a t i n g the successful synthesis of [CpRe(CO) (NO)]2 (which had s i m i l a r l y defied repeated e a r l i e r attempts at i t s preparation in his laboratory) v i a the route outlined i n equations 38 and 39, i . e . CH 9C1« 2CpRe(C0) (NO)H + Ph 3C X - • X = BF 4 or PF g [Cp 2Re 2(CO) 2(NO) 2H] +X~ (38) : , '_ ' CH ?C1 ? [Cp 2Re 2 (CO) 2 (NO) H] X + NEt 3 • [CpRe(CO)(NO)] 2 + HNEt 3 +X~ (39) led to hope that the desired compounds could be prepared i n an analogous manner. Successful completion of the f i r s t step for both the Mo and W analogues was followed by numerous attempts to carry out the subsequent deprotonations; these were unsuc-c e s s f u l , as were e f f o r t s along other routes. In conjunction with these reactions, an examination of the Lewis base prop-e r t i e s of CpW(NO)2H and of the Lewis acid properties of CpW(NO) 2 + was carr i e d out. S p e c i f i c a l l y , CpWCNO^H i s observed spectroscopically in the presence of a var i e t y of soft ( i . e . Cr(CO) 5, W(CO)5, (MeCp)Mn(CO) , HgCl 2, and Cd C l 2 ) , borderline ( i . e . ZnCl 0), and hard ( i . e . H +, A1C1,, and BEt ) - 83 -Lewis a c i d s 1 2 . The Lewis base c h a r a c t e r i s t i c s of CpW(NO)2H are discussed i n l i g h t of these r e s u l t s , and when combined with the res u l t s of a study of the Lewis acid properties of CpW(NO)2+, i t i s possible to provide a r a t i o n a l i z a t i o n of the f a i l u r e to prepare the dimers [CpM(NO) 2] 2 (M = Mo, W) vi a the indicated route. Experimental A l l experimental procedures outlined were performed under the general conditions described in Chapter II. Reaction of CpMo(NO)2C1 with NaAlH 2(OCH 2CH 2OCH 3) 2. A solu-t i o n of NaAlH 2(OCH 2CH 2OCH 3)^ h (1.2 mL, 4.2 mmol) i n toluene (2 5 mL) was added dropwise to a s t i r r e d green solution of CpMo(NO) 2C1 2 3 (1.00 g, 3.91 mmol) i n toluene (80 mL) at -78°C, and the reaction was monitored by IR spectroscopy. As the addition proceeded, the solution became a dark o l i v e green and a brown pr e c i p i t a t e formed; addition was terminated when the n i t r o s y l absorptions due to the i n i t i a l reactant had disappeared from the IR spectrum of the supernatant solution. While s t i l l cold, the mixture was quickly f i l t e r e d through a short (.3 x 5 cm) column of alumina (Brockman neutral, a c t i v i t y grade I) supported on a medium porosity f r i t t e . The bright green f i l t r a t e was allowed to warm to room temperature; an IR spectrum of the f i l t r a t e showed two strong, sharp absorptions i n the n i t r o s y l region at 17 32 and 1642 cm \ A l l attempts to remove the solvent from the f i l t r a t e under reduced pressure resulted i n rapid decomposition of the - 84 -green product as the l a s t of the; v o l a t i l e s were: removed, yi e l d i n g a red—brown, intractable s o l i d . Similarly-, s t i r r i n g the green solution i n a nitrogen atmosphere at ambient temperature resulted i n slow deposition of the red—brown s o l i d ( h a l f - l i f e approximately 3 days). Thus, subsequent reactions of the product, CpMo(NO)2H were carried out on freshly prepared solutions of the compound. Reaction of C p M o ( N O ) w i t h CH^N^. A freshly prepared ether solution of approximately 1 M C R ^ ^ 1 0 0 (provided by G.N. Rickards) was dried over KOH and deaerated with argon. Two millimoles of diazomethane: Xaniexcess) ~_was:-rfchen--added~to_ a solution of CpMo(NO)2H i n toluene (95 mL) prepared from 0.50 g (1.96 mmol) of CpMo(NO) 2Cl. Over a period of 15 min-utes the solution gradually turned slate green, and slow gas evolution was observed. After 1.5 h, gas evolution appeared to have ceased, so the v o l a t i l e s were removed i n vacuo. The residue was then transferred as a benzene sl u r r y to the top of a 2 x 7 cm column of alumina (Woelm neutral, a c t i v i t y grade I ) . A yellow band developed with CH 2C1 2 e l u t i o n , and was eluted from the column with THF. The v o l a t i l e s were removed from the eluate under reduced pressure, and the green o i l 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 IR and mass spectra as CpMo(NO) 2Me 7 0 (0.05 g, 10% y i e l d based on CpMo (N0)2C1) . Reaction of CpMo(NO)2H with. MeX. To a toluene, solution (9,5 mL) of CpMo(NO)2H prepared from 0.50 g (1.96 mmol) CpMo-- 85 -(NO) 2 C 1 was added an e x c e s s (1.0. ml*, 11 mmol) o f Me.I, and t h e s o l u t i o n was s t i r r e d a t room t e m p e r a t u r e f o r 4 days-. D u r i n g t h i s t i m e a red—brown p r e c i p i t a t e formed and t h e c o l o u r o f t h e s o l u t i o n f a d e d t o a p a l e y e l l o w . The v o l a t i l e s were removed i n vacuo, and t h e r e s i d u e was t r a n s f e r r e d o n t o a s h o r t (2 x 4 cm) column of F l o r i s i l a s a C H 2 C 1 2 s l u r r y . A y e l l o w band d e v e l o p e d u p o n . e l u t i o n o f t h e column w i t h C H 2C1 2. The band was c o l l e c t e d and t a k e n t o d r y n e s s under reduced p r e s s u r e , y i e l d i n g a s m a l l amount o f g r e e n CpMo ( N O ) 2 1 1 0 1 (0.01 g, 2% y i e l d based on CpMo CNO) 2C1) w h i c h was c h a r a c t e r -i z e d by i t s m e l t i n g p o i n t and i t s IR and mass s p e c t r a . R e a c t i o n o f CpMo CNO), w i t h p-CH-^CgH^SO^ (CH 3 ) NO. t o l u e n e s o l u t i o n C60 mL), o f CpMo (NO) 2 H p r e p a r e d from 0.40 g C.1.57 mmol). o f CpMo (NO) 2 C 1 was t r e a t e d w i t h 0.67 g (.3.14 mmol). o f p — C H 3 C g S O 2 N (CH 3)NO, and t h e s o l u t i o n was s t i r r e d a t ambient t e m p e r a t u r e . The s o l u t i o n g r a d u a l l y darkened and, a f t e r 4 h, became c l o u d y . A f t e r 2 d a y s , t h e s o l u t i o n was a l m o s t c o l o u r l e s s , and a red-brown p r e c i p i t a t e had formed. The s o l u t i o n was c o n c e n t r a t e d under reduced p r e s s -ure.; an IR spectrum o f t h e s u p e r n a t a n t l i q u i d showed o n l y a b s o r p t i o n s a t t r i b u t a b l e t o p-CH 3C 6H 4S0 2N CCH3 ).NO and t o l -uene . R e a c t i o n o f CpW CNO),yH w i t h P h 3 C B F 4 . To a b r i g h t g r e e n , s t i r r e d s o l u t i o n c o n t a i n i n g CpW (NO) 2 H 5 1 C_4 . 53 g, 14. & mmol I i n C H 2 C 1 2 C80 mL) was added an orange C H 2 C 1 2 s o l u t i o n (40 mL) o f P h 3 C B F 4 1 0 2 (2.41 g, 7.3 0 mmol).. As t h e a d d i t i o n - 86 -proceeded, the solution darkened to an. olive-green, colour, and a green p r e c i p i t a t e began to form. Monitoring of the IR spectrum of the supernatant solution showed complete loss of the n i t r o s y l absorptions due to CpW(NO)2H after 0.5 equiv-alents of Ph 3CBF 4 had been added. Concentration of the reaction mixture i n vacuo to a volume of approximately 20 mL yielded further s o l i d and a pale green supernatant solution. The dark green, m i c r o c r y s t a l l i n e s o l i d was i s o l a t e d by f i l t r a t i o n , washed with CH 2C1 2 (3 x 5 mL), and dried i n vacuo (< 0. 005 Torr) to obtain a n a l y t i c a l l y pure [Cp 2W 2(NO) 4-H]BF 4 (.3.70 g, 72% y i e l d ) . Anal. Calcd for c 1 0 H n W 2 N 4 ° 4 B F 4 : C ' 1 7 - 0 2 ' H ' 1-57; N, 7.94. Found: C, 16.91; H, 1.48; N, 7.85. IR (Nujol mull): vNQ 1775, 1748, 1707, 1660 (br); also 1432 (w), 1422 (w) , 1359 (w)., 1290 (w) , 1070 (st, br) , 1000 (st, br), 852 (st, br) cm - 1. IR (CH"3CN) : vNQ 1731, 1716, 1649, 1633 cm"1. 1H NMR (CD 3N0 2): 6 6.48 (s, 10H), -8.33 (s, IH) (see discussion). Mp (under N 2) 95°C dec. Reaction of CpW(NO)2H with Ph 3CPF 6 (in CH^Cl.,). . This reac-t i o n was c a r r i e d out i n a fashion analogous to that described in the preceding section, with 2.50 g (8.06 mmoll CpWXNO)2H in 3 0 mL CH 2C1 2 being reacted with a solution containing 0.79 g (4.03 mmol) Pf^CPFg i n CH 2C1 2 (25 mL) to y i e l d green, m i c r o c r y s t a l l i n e , a n a l y t i c a l l y pure [Cp2W2 (NO) 4H] PF & (2.82 g, 91.6% y i e l d ) . Anal. Calcd for C ] _ 0 H l l W 2 N 4 O 4 P F 6 ' : C ' 1 5- 7 2'' H ' ! - 4 5 ; N, 7.33. Found: C, 15.70; H, 1.38; N, 7.25. IR (Nujol - 87 -mull): v N Q 1752 (br), 1685 (br); also 1427 (m), 1068 (w), 1010 (w), 888 (s t ) , 865 (s t ) , 849 (s t ) , 836 (s t ) , 811 (st), and 740 (w) cm"1. IR (CH 2C1 2): v N Q 1722 (br), 1650, 1632 cm"1. 1H NMR (CD 3N0 2): 6 6.48 (s, 10H), -8.33 (s, IH) (see discussion). Mp (under N^) 122°C,dec. Preparation of [Cp^W^(NO)^D]PF^. To a solution (4 0 mL) containing [CpW(NO) 2(CO)]PF g 1 0 1 (0.19 g, 4.54 mmol) was added an excess of NaBD^ (0.19 g, 4.5 mmol) and the solution was s t i r r e d for 0.5 h. The res u l t i n g mixture was p u r i f i e d by the l i t e r a t u r e method 5 1 to y i e l d CpW(NO)2D. This was then dissolved i n 10 mL CH 2C1 2 and to t h i s solution an excess (by IR monitoring) of Ph^CPF^ was added, producing green, mi c r o c r y s t a l l i n e [Cp 2W 2(NO) 4D]PF g (0.21 g, 17% o v e r a l l y i e l d ) . A *H NMR spectrum (in CD 3N0 2) confirmed that the deuterium l a b e l was i n fact present: 6 6.48 (s, 10H), -8.33 (s, <0.05H). A Nujol mull IR spectrum of the product was indistinguishable from that of [Cp2W2(NO)^H]PFg. Treatment of [Cp2W2 (NO) ^H] PF £ with Ph-^CPFg. To a suspension of [Cp 2W 2(NO) 4H]PF g (0.25 g, 0.33 mmol) i n CH 2C1 2 (20 mL) was added one equivalent of Ph3CPFg (0.127 g), yi e l d i n g an orange supernatant solution. S t i r r i n g the mixture for 4 h produced no changes i n the IR spectrum of the supernatant; r e - i s o l a t i o n of the green s o l i d yielded only [Cp 2W 2(NO) 4H]PF^ as i d e n t i f i e d by i t s IR spectrum and decomposition point. Reaction of CpW(NO)2H with C^H^BF^ To a vigorously s t i r r e d C H 2 C l 2 solution (70 mL) containing 1.30 g (3.87 mmol) of - 88 -CpW (NO) 2 E was added 0. 23 g (1.29 mmol) of white C ^ B F ^ 0 3 . As the reaction proceeded, the sol u t i o n gradually darkened and then a green precipitate, began to form; concurrently, the insoluble white C^H^BF^ was slowly consumed. After 1.5 h no white s o l i d remained. An IR spectrum of the supernat-ant solution at t h i s point revealed that although only 0.33 equivalents of C^H^BF^ had been added to the reaction mix-ture, the n i t r o s y l absorptions attributable to CpW(NO)2H had diminished to approximately 35% of t h e i r i n i t i a l i n t e n s i t y . Isolation of the green p r e c i p i t a t e by f i l t r a t i o n afforded 0.60 g (66% y i e l d based on C 7H 7BF 4) of a n a l y t i c a l l y pure [Cp2W2 (NO)4H] BF 4 (.vide supra). Reaction of CpW(N0)oH with Ph-CPF,, (in CH-CN). An orange z j b J solution of Ph 3CPF 6 (0.29 g, 0.74 mmol) i n CH3CN (.5 mL) was added dropwise to a s t i r r e d solution of CpW(_NO)2H (.0.23 g, 0.74 mmol) i n CH3CN) (18 mL) at -10°C. After complete mixing of the two solutions, an IR spectrum of the res u l t i n g blue-green solution indicated that [CpW(NO) 2(CH 3CN)] + ( i . e . v N Q 1730 and 1649 cm "*") .was the only nitrosyl-containing species p r e s e n t 1 0 1 . IR monitoring during the addition showed only n i t r o s y l absorptions attributable to either [CpW(NO)„(CH-CN)]PFr ( i . e . v.Trt 1730 and 1649 cm - 1) or CpW^ -(NO)2H ( i . e . v 1715 and 1631 cm-1).. Treatment of [CpW (NO) 2 (,CH3CN) ] PF £ with CpW(N0)2H. To a blue-green solution containing 0.74 mmol CO.37 g) [CpWXNO)2— CCH3CN);]PF6 i n 35 mL CH^CN' was added an excess of CpW (NO) 2H - 89 -CO. ..31, g, IvQ- mmol I... An IR spectrum of the. r e s u l t i n g mixture revealed no inte r a c t i o n between the two complexes-. Removal of the excess CH^CN under reduced pressure yielded a brown o i l . Dissolution of the o i l i n CH 2C1 2 (40 mL) produced a clear green solution whose IR spectrum revealed only absorb-ances attributable to CpWCNO) 2H and [CpW(NO) 2 CCHgCN) ] PF g (1.e. V N Q 1716, 1630 and 1729, 1648 cm 1 , res p e c t i v e l y ) . Reaction of CpMo (NO) 2H with Ph 3CPF 6. A solution of CpMo-(NO)2H i n toluene (190 mL) was prepared i n the usual manner from 5.10 g (19.9 mmol) of CpMo(NO)2C1. The solution was then concentrated i n vacuo to a volume of approximately 3 0 mL, with some attendant decomposition occurring as evidenced by the formation of small amounts of the red—brown s o l i d . The solution was then syringed onto a 4 x 9 cm column, of F l o r i s i l prepared i n CR"2C12. Elution of the column with CH 2C1 2 developed a single green band which was co l l e c t e d , and the eluate was concentrated to 105 mL under reduced pressure. To 7 0 mL of t h i s solution was then added s o l i d Ph^C-PFg with IR monitoring. As the t r i t y l hexafluorophosphate was added, a green p r e c i p i t a t e formed; 0.5 equivalents of Ph 3CPF g (0.87 g, 2.24 mmol) were s u f f i c i e n t to bring about complete loss of the n i t r o s y l absorptions attributable, to CpMo (NO)2H. Toluene (10 mL) was then added to the suspension, and solvent was removed i n vacuo to give a f i n a l volume of approximately 50 mL. The green s o l i d was col l e c t e d by f i l -t r a t i o n , washed with toluene (2 x 5 mL), and dried (<0.005 Torr) to obtain 0.75 g (19% y i e l d based on CpMo(NO)~C1; 57% - 90. -based on Ph^CPFgl of a n a l y t i c a l l y pure [ C p 2 M o 2 ( N O ) 4 H ] P F g . A n a l . C a l c d f o r c 1 0 H i i M o 2 N 4 ° 4 P F 6 : C f 2 0 ' 4 2 ; H ' 1-89; N, 9.53. Found: C, 20.24; R, 1.77; N, 9.42. IR CNujol m u l l ) : v N Q 1783 ( b r ) , 1675 ( b r ) ; a l s o 1430 (w). , 1070 Cw) , 1015 (w) , 860 ( s t , b r ) , 820 ( s t ) c m - 1 . IR ( C H 2 C 1 2 ) : v N Q 1795, 1768, 1707, 1695 (sh.) cm" 1. 1H NMR (CD 3N0 2) : 6 6.37 ( s , 10H), -9.78 ( s , I H ) . Mp Cunder N 2) 119°C dec. P r e p a r a t i o n , o f [Cp2MoWCNO) ^ H] BF^. A s l i g h t e x c e s s o f AgBF 4 CO. 2.3 g, 1.18 mmol) was added t o a s t i r r e d C H 2 C 1 2 s o l u t i o n (20 mL). c o n t a i n i n g 0.26 g (1.0 mmol) CpMo(NO) 2Cl. IR m o n i t o r i n g showed t h a t t h e a b s o r p t i o n s a t t r i b u t a b l e t o CpMo (NO) 2C1 d i s a p p e a r e d c o m p l e t e l y w i t h i n 45 m i n u t e s , two new bands a p p e a r i n g a t ~25 cm 1 h i g h e r energy ( i.e. 1783, 1692 cm "*") . F i l t r a t i o n y i e l d e d an u n s t a b l e g r e e n s o l u t i o n , w h i c h began t o become c l o u d y w i t h i n ~1 m i n u t e . A d d i t i o n o f 1 mL c y c l o o c t e n e produced a more s t a b l e b l u e -g r e e n s o l u t i o n h a v i n g v N Q a t 1800 and 1717 cm 1 i n d i c a t i v e o f t h e f o r m a t i o n o f t h e Mo analogue o f t h e known [CpWCNO) 2~ (cyclooctene).] B F 4 J 0 "*. The s o l u t i o n was th e n f i l t e r e d , and 1.0 mmol (.0.31 g) CpW CNO) 2H added t o t h e f i l t r a t e , g i v i n g a green s o l u t i o n w h i c h e x h i b i t e d numerous p o o r l y r e s o l v e d IR a b s o r p t i o n s i n t h e n i t r o s y l r e g i o n C v N Q 1795, 1778, 1757, 1703, 1680, and 1640 cm ^ ) . The s o l u t i o n was s t i r r e d f o r 0.5 h, whereupon 3 0 mL hexanes were added, r e s u l t i n g i n t h e fo r m a t i o n , o f a f l o c c u l e n t g r een p r e c i p i t a t e . The m i x t u r e was c o n c e n t r a t e d i n vacuo t o a volume o f "-10 mL, and t h e c o l o u r l e s s s u p e r n a t a n t l i q u i d was removed by s y r i n g e and - 9.1 -discarded. The residue was then, redissolved in. 50. mL CH^Cl^ f i l t e r e d to remove a trace of insoluble material, and 3 0. mL hexanes were added. The solution, was- concentrated slowly under reduced pressure to induce the c r y s t a l l i z a t i o n of a dark green, mi c r o c r y s t a l l i n e s o l i d . The s o l i d was iso l a t e d by f i l t r a t i o n , washed with hexanes (2 x 10 mL), and dried at <0.005 Torr for 1 h to obtain 0.353 g C57% yield) of a n a l y t i c a l l y pure [Cp2MoW(NO)4H]BF4. Anal. Calcd for C 1 QH 1 1MoWN 40 4BF 4: C, 19.44; H, 1.79; N, 9.07. Found: C, 19.37; H, L.89; N, 8.82. IR (Nujol mull);: v N Q 1790, 1769 (sh) , 1756, 1718, 1660 (br) ; also 1419 (w), 1287 (w) , 1060 (st, br) , 1000 (st, br) , 850 (st, br) cm"1. IR (CH 2C1 2): v N Q 1790, 1765 (sh), 1751, 1706, 1678, 1650 (sh) cm"1. JH NMR (CD3N02) : 6 6.47 (s, 5H) , 6.37 (s, 5H), -8.33 (s, 0.2H), -8.92 (s, 0.6H), -9.78 (s, 0.2H) (see discussion). Mp (under N 2) 115°C dec. Reaction of [Cp 2W 2(NO) 4H]BF 4 with Et^N. To a s t i r r e d sus-pension of [Cp 2W 2(NO) 4H]BF 4 (0.20 g, 0.28 mmol) i n CH 2C1 2 (40 mL) was added a large excess (1 mL) of dry, deaerated Et^N. The s o l i d r a p i d l y dissolved to y i e l d a clear yellow-brown solution whose IR spectrum exhibited two bands i n the n i t r o s y l region (1718 and 1632 cm "*") . Addition of 40 mL Et 2 0 produced a flo c c u l e n t , yellow-brown p r e c i p i t a t e which was i s o l a t e d by f i l t r a t i o n . The f i l t r a t e was taken to dry-ness i n vacuo and redissolved i n a minimum of CH 2C1 2; an IR spectrum of t h i s solution showed two strong absorptions i n the n i t r o s y l region at 1718 and 163 2 cm 1 f a t t r i b u t a b l e to - 92 -CpW(NO) 2II. A Nujol mull of the. .yellow-brown, s o l i d showed broad IR absorption at 1720'. and 1600 cm"1. Reaction of [Cp2W2 (NO) H^] PF g with. PhyP^C^. To a s t i r r e d suspension containing 0.28 g (.0.37 mmol) of [Cp2W2 (NO) 4H] PF g i n 15 mL CR^C^ was added dropwise 1 equivalent of an orange, ether solution of 0.3 M Ph 3P=CH 2 1 0 5. Immediately upon adding Ph3P=CH2, the solution darkened to olive-green, with the o r i g i n a l suspended s o l i d r a p i d l y d i s s o l v i n g . To t h i s solu-t i o n was then added 50 mL of E t 2 0 whereupon a tan p r e c i p i -tate formed, which was iso l a t e d by f i l t r a t i o n . Extraction of the s o l i d with CH 2C1 2 gave an orange-brown solution exhibiting strong IR absorptions at 1728 and 1647 cm 1 . V o l a t i l e s were removed from the f i l t r a t e under . reduced pressure, and the residue was then dissolved i n benzene and chromatographed on a 2 x 5 cm F l o r i s i l column with benzene as eluant to obtain CpWCNO)2H, as 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 IR and *H NMR s p e c t r a 5 1 . Reaction of [Cp^Wp CNO) ^Hj BF ^ with. (Me2N).3PO. To a s t i r r e d CH 2C1 2 suspension C10 mL) containing 0.3 0 g CO.42 mmol) of [Cp2W2 (NO) 4H] BF 4 was added 1 mL of dry (Me2N) 3P0 (provided by H.E. Morton). The s o l i d immediately dissolved giving a dark green solution exhibiting three strong IR absorbances i n the n i t r o s y l region not attributable to CMe2N)3PO Ci.e. v N Q 1735, 1721, 1630 cm"1!.. Numerous attempts to separate the excess (Me^Nl^PO from the. nitrosyi-containing species- by means such as extraction with. H20, c r y s t a l l i z a t i o n from a 93 -variety; of solvent mixtures (invari a b l y y i e l d i n g oils!., and chromatography on F l o r i s i l were unsuccessful.. Reaction of [Cp2W2 (NO) H^] BF^ With KOII/EtOH. A 0.07 M solu-t i o n of KOH i n 95% ethanol was added dropwise to a s t i r r e d suspension of [Cp2W2 CNO)^H]BF^ (0.30 g, 0.43 mmol) in CH2C1. (.2 0 mL) with IR monitoring. Upon addition of the f i r s t few drops, the s o l i d r a p i d l y dissolved to give a l i g h t green solution whose IR spectrum displayed a broad, weak band at -19.00 cm 1 as well as two strong, sharp bands at 1718 and 1632 cm - 1, a l l a t t r i b u t a b l e to CpWCNO)2H. As further KOH/ EtOH was added, to a t o t a l of 1 equivalent of KOH, the only change observed i n the n i t r o s y l region of the IR spectra was a gradual diminution i n i n t e n s i t y of these bands as the solution became more d i l u t e . The v o l a t i l e s were removed from the reaction mixture under reduced pressure, and the residue was transferred as a suspension i n benzene to the top of a 2 x 5 cm F l o r i s i l column. Elution of the column with benzene developed a green band which, when co l l e c t e d , taken to dryness, and redissolved i n CH 2C1 2, exhibited two strong absorptions at 1718 and 1632 cm 1 as well as a weak one at 1900 cm - 1 ( i . e . CpW(.NO)2H). Elution of the column with THF slowly developed a yellow band; with H 20 as eluant the band was c o l l e c t e d , the solvent removed i n vacuo, and an IR spectrum of the residue i n THF was obtained which displayed at 1718 and 1610 cm 1.. Reaction of [Cp ? W? C.N0) . H] PF with. C T n H g CNMe? 1 2 . Upon addi-- 9.4 -tron of 1 equivalent CO, 05 g l of C 1 QH: & CNMe.212 (N, N,N', N' — tetramethyl—1,8—naphthalenediamine., sold by A l d r i c h under the trade name Proton Spongel to a suspension of [Cp2W2 CN0) 4 — H]PF 6 CO.18 g, 0.24 mmoll i n 10 mL of CH 2CT 2, the super-natant solution immediately turned yellow. However, even after being s t i r r e d for 3 0 minutes, the green s o l i d did not appear to be di s s o l v i n g , and the supernatant solution exhib-i t e d only weak IR absorptions at 1718 and 163 2 cm 1 . A .... large excess of Proton Sponge was therefore added (a t o t a l of 10 equivalents), and the reaction was monitored by IR spectroscopy. The bands at 1718 and 1632 cm 1 gradually increased i n i n t e n s i t y as the solution darkened, but afte r 3 h green s o l i d s t i l l remained. After 18 h, the bands were even more intense, and only a brown pr e c i p i t a t e was present. The s o l i d was isola t e d by f i l t r a t i o n and extracted with THF; an IR spectrum of the extracts revealed only weak, broad absorptions at 1720 and 1615 cm 1 . The f i l t r a t e was concen-trated i n vacuo, and i t s IR spectrum showed strong bands at 1718 and 1632 cm 1 and a weak band at 1900 cm 1 Ci.e. CpW(NO)2H) as the only absorptions i n the n i t r o s y l region not att r i b u t a b l e to the C,nH,(NMe„),.. ± U b 2 2 The reaction was repeated i n CD^ NO.^  with 1H NMR monitoring of i t s progress. I n i t i a l l y the cation was..cleaved to y i e l d CpW(NO)2H (5 6.13 (a, 5H);, 2.08 (s, 1HJ.I and another cyclopentadienyl tungsten compound (_& 6.35 Cs-, 5H)_, but the l a t t e r r a p i d l y decomposed to give a brown, insoluble residue.. - 95 -Reaction of [Cp^W^(NO)^H]PF'g with NaBH^ .. A small sample of [Cp2W2 (NO) 4H] PF 6 was- dissolved i n 10 mL of dry- CH 3N0 2 to give a yellow-green solution exhibiting two IR absorptions (1728 (sh) , 1718 cm "*"). i n the portion of the n i t r o s y l region not obscured by the solvent (cut-off -1650 cm 1 ) . To t h i s s t i r r e d solution was added 10 • equivalents of solid. NaBH^;, , a f t e r 48 h only the band at 1718 cm 1 remained. Solvent removal under reduced pressure yielded a s o l i d which was extracted with CH 2C1 2; an IR spectrum of the extracts showed bands at 1900 (w) , 1718, and 1632 cm - 1 a t t r i b u t a b l e to CpWCNO)2H. After chromatography of the extracts on F l o r i s i l with. CH 2C1 2 as eluant, a JH NMR of the residue obtained by removal of the solvent i n vacuo from the eluate confirmed that the product was indeed CpW(NO)2H; only a trace of impur-i t y remained at the top of the column. Reaction of [Cp 2W 2(NO)^H]PF 6 with Cp2MoH2. To a s t i r r e d CH 2C1 2 suspension (20 mL) containing 0.10 g (.0.13 mmol) of [Cp 2W 2(NO) 4H]PF g was added an excess (0.035 g, 0.15 mmol) of Cp 2MoH 2 2 1, yi e l d i n g a yellow supernatant solution. No immediate reaction was observed, but af ter --2 ihbur s^onl-y^r. a:browru-'Solid.-'rem.ained, -aridi'the. sup.eEnatantr.seiutionwwas almost colourless. The brown s o l i d , isolated by f i l t r a t i o n , was insoluble i n common organic solvents. Its mull XR spectrum exhibited only broad peaks at 1710 (wl and 1600 -1 cm Reaction of [Cp 2W 2(NO)^H]PF g with Sodium Naphthallde. A THF - 96 -s o l u t i o n (50 mL) c o n t a i n i n g 5.0 mmol (0.64 g) naphthalene was s t i r r e d f o r 18 h over an excess of N a 1 Q 6 . A f t e r a l l o w -in g the i n t e n s e l y green r e a c t i o n mixture t o s e t t l e f o r 1 h, 3.3 mL of the supernatant s o l u t i o n was sy r i n g e d onto 0.2 5 g (0.33 mmol) of s o l i d [Cp„W„(NO)„H]PF r. R e a c t i o n was immed-Z Z 4 D i a t e and the f i n a l r e a c t i o n mixture c o n s i s t e d of a red-brown s o l i d , which was i n s o l u b l e i n common o r g a n i c s o l v e n t s , below a yellow-green s o l u t i o n . An IR spectrum of the s o l u t i o n showed a b s o r p t i o n s at 1900 (w, sh), 1712, and 1632 cm 1 , a l l a t t r i b u t a b l e to CpW(NO) 2H. A m u l l IR spectrum of the s o l i d showed no a b s o r p t i o n s i n the n i t r o s y l r e g i o n . Reactions of [Cp^Mo^(NO)^H]PF^ wi t h V a r i o u s E l e c t r o n Donors. Ca) With acetone. To a C.D3N02< s o l u t i o n of [Cp 2Mo 2(NO) 4H]PF g were added 8 e q u i v a l e n t s of (CR~ 3) 2C0; no i n t e r a c t i o n was det e c t e d by  X E NMR. (b). With n i t r o g e n - c o n t a i n i n g bases. With the a d d i t i o n of the n i t r o g e n - c o n t a i n i n g bases N E t 3 and C^gHg(NMe 2) 2 (Proton Sponge), CD 3N0 2 s o l u t i o n s of the c a t i o n immediately turned;from green t o brown; i n each i n s t a n c e  1 E NMR s p e c t r a demonstrated the absence of any remaining [Cp 2Mo 2(NO)^H] + and the presence of s e v e r a l d i f f e r e n t resonances i n the c y c l o p e n t a d i e n y l r e g i o n . Repeating the experiment i n (CD 3) 2C0 again y i e l d e d m u l t i p l e resonances i n the r e g i o n 6 6.2->6.7 ppm. (c) With magnesium s i l i c a t e . A suspension of [Cp 2Mo 2(NO) 4~ H]PF_ (0.10 g) i n CH 0C1 0 (10 mL) was t r a n s f e r r e d t o the top b z Z of a 2 x 4 cm F l o r i s i l column. E l u t i o n of the column w i t h - 97 -C H 2 C T 2 developed a, green band; c o l l e c t i o n of t h i s band and concentration, of the eluate under. reduced pressure to a volume of ~3 mL gave a solution of CpMo (NO) 2 H a s indicated by i t s IR spectrum ( i . e . V N Q 1738, 1647; V M O _ R 1805 (w) cm "*").. Removal of the remaining solvent was accompanied by the formation of a brown s o l i d ; extraction of the residue with (CD^^CO gave a green solution of CpMoCNO^H, whose 1H NMR spectrum showed resonances at § 6.43 (s, 5H). and 3.80 (s, IH). . Treatment of [Cp2W2(NO)^H]BF^ with propene. A slow stream of propene (~2 mL/min) was passed over a vigorously s t i r r e d suspension of [Cp 2W 2(NO) 4H]BF 4 (0.10 g, 0.14 mmol) in CH 2C1 2 (20 mL) for 4 h. During t h i s time no changes were detected in the IR spectrum of the supernatant solution except for concentration e f f e c t s a r i s i n g from the evaporation of some of the solvent. A small amount of a brown s o l i d did form during the reaction period. After 4 h, the v o l a t i l e s were removed i n vacuo and the residue dissolved i n CD3N02. A *H NMR spectrum of t h i s solution showed the s t a r t i n g mater-i a l to be l a r g e l y unreacted; there were also several smaller peaks present which were attri b u t a b l e only to decomposition products. There was no evidence for the formation of either CpW (NO). 2 H or [ CpW (NO) 2 (propene) ] BF 4 . Reaction of [CpCr (NO) 2] 2 with HBF4 • OMe2 • To, a s t i r r e d CH 2C1 2 solution (95 mL) of [CpCr (NO)^] 2 2 (0.50 g, 1.41, mmol) was added an excess (1.0 mL) of HBF^OMe^- With-- 98 -s t i r r i n g , the. dark purple CH^C^ phase gradually turned a gold colour, while the acid phase darkened to a brown, colour. After 15 minutes-, an IR spectrum of the CH 2C1 2 solution revealed that a l l of the [CpCr(NO) 2] 2 had been consumed; two new n i t r o s y l absorptions- were present at 1828 and 1721 cm 1 . Water X150 mL) was then added, and the CH^C^ removed i n vacuo to y i e l d a golden solution and a trace of p r e c i p i t a t e . To t h i s suspension were then added two equivalents (1.00 g) of NaBph^, immediately producing a flocculent yellow precip-i t a t e . F i l t r a t i o n of t h i s suspension was followed by thorough washing of the col l e c t e d s o l i d with R^ O (2 x 3 0 mL). Subsequent extraction of the s o l i d with CH^C^ (2 x 30 mL) and addition of benzene (.30 mL) and hexanes (15 mL) followed by slow concentration i n vacuo yielded 0.54 g of green m i c r o c r y s t a l l i n e s o l i d . IR (CR"2C12) : V N 0 1828, 1721 cm"1. XH NMR ((.CD^CO): 6 6.8-7.6 (m, 40H), 6.06 (s, 5H), 5.68 (s, 5H), -5.35 (s, IH); no change was observed with added D 20. Mp 119-20°C. Elemental analysis, found: C, 62.98; H, 4.72; N, 6.86. Reaction of [CpCr (NO) 2] 2 with HPFg (65% solution i n water) gave comparable r e s u l t s ; a l l attempts to c r y s t a l l i z e either the BF. or PF- s a l t s were unsuccessful. 4 6 Small samples of the above s o l i d were dissolved i n CR"2C12 (5 mL) and treated with either excess NEt^ or 0.3 M Ph3P=CH2 (in E t 2 0 ) . In each instance no change was observed i n the IR spectrum. - 99 -Reaction of [CpCr (NO) ] 2 wi'tK p-CiL,C £E 4SO :,H:, To a dark-purple CH 2C1 2 solution (.40 mL) containing 0.5:4 g (1.53 mmol). of [CpCr (NO) 2] 2 was added 1 equivalent (.0.2 65 g) of p-CH 3~ CgH^SO^H with vigorous s t i r r i n g . IR spectral monitoring of the solution revealed the gradual decrease in i n t e n s i t y of the n i t r o s y l absorptions attr i b u t a b l e to [CpCr(NO) 2] 2 (i« e. at 1667, 1505 cm "*") and the appearance of two new absorptions at 1829 and 1722 cm 1 over a period of ~10 minutes. Only one-half of the [CpCr(NO) 2] 2 w a s consumed by the p-toluene-sulfonic acid, so an additional 1 equivalent was added. This led to the complete disappearance of the n i t r o s y l IR absorptions att r i b u t a b l e to the sta r t i n g complex, and a change i n the colour of the solution from purple to dark orange. The addition of an equal volume of hexanes yielded, upon concentration under reduced pressure, a green powder which, was subsequently isolated by f i l t r a t i o n . 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 CH 2C1 2/Et 20 gave CpCr(NO) 2OS0 2C 7H 7 (0.4 8 g, 4 5% yield) as a fine green powder, mp 64-6°C. Anal. Calcd for C 1 2H 1 2CrN 20 5S: C, 41.38; H, 3.47; N, 8.04. Found: C, 40.84; H, 3.68; N, 7.36. IR (CH 2Cl 2). : v N Q 1829, 1722 cm - 1. 1E NMR (CDC1 3): 6 7.72 (d, 2H> J"= . - : '• 8.30 Hzi)i , 7 . 2 1 (d, 2H«, 7 J ; . = . 8 . 0 - . H z ) ; j i ; 5 . 7 5 : p ( s p - 5 H ) ; 2.36 (s, 3H) . Reaction of CpW(NO)2H with Cr(CO) 5(THF). A solution of Cr(CO) 5CTHF) 1 0 7 was generated by i r r a d i a t i n g a THF solution (210 mLl of Cr(CO) 6 (.0.65 g, 2.95 mmol). for 1 h. ( I n a photo-reactor using a medium-pressure mercury lamp [Hanovia L-4 50W] housed i n a water—cooled Pyrex immersion well), while, gently - 10.0. -bubbling N'2 through, the. solution to remove, the. free. CQ produced. The. r e s u l t i n g orange solution was; then, concen-trated to a volume of 2^.5 mL under reduced pressure, and cooled to —78°C. To t h i s s t i r r e d solution was added 0.58 g (1.87 mmol). of CpW(NO) 2H, which dissolved r a p i d l y to give an orange-brown solution. After s t i r r i n g for 2 5 minutes, an IR spectrum of the solution showed four bands i n the n i t r o s y l region ( v N Q 1736, 1718, 1661; and 1629 cm - 1) as well as a poorly resolved envelope of bands i n the carbonyl region ( v C Q 2085 (w). , 1995 (sh) , 1975, and 1920 (br) cm - 1). After 1 h, the solution was allowed to warm to room tempera-ture, with, no change i n the IR spectrum being detected. The v o l a t i l e s were then removed i n vacuo to y i e l d a s o l i d which was only p a r t i a l l y soluble in CH 2C1 2 or THF. IR spectra of the respective orange supernatant solutions were comparable, exhibiting absorptions attributable to both coordinated carbonyl ( v c o (THF).: 2085 (w) , 2003, 1972, and 1928 cm"1), and n i t r o s y l ( v N 0 (THF): 1738 (w), 1718 (w), 1661, and 1634 (w, sh) cm 1). groups. Frac t i o n a l sublimation of the s o l i d at reduced pressure (0.005.Torr) yielded f i r s t . C r ( C 0 ) 6 i a 7 (0.20 g, 31% yield) at 35°C and then CpW (CO \ 2 (NO) 2 3 (0.12 g, 17% y i e l d based on W) at ~55°C. Each, product 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 infrared and mass spectra. A mull IR spectrum of the intractable brown residue which remained exhibited broad absorptions- at 1920 and 1660 -1 cm In a subsequent t r i a l , i t was noted that the decom— - 10.1 -position of the i n i t i a l product and formation, of CpW;(COL2 (NO), occurred during solvent removal: even i f the. solvent was not completely removed the transformation s t i l l occurred. The reaction of CpW (NO) 2H with. Cr (CO) 5 (NMe^) 1 0 8 gave comparable r e s u l t s . The reaction was also carried out in (CDD-^CO with 1H NMR monitoring. Thus, upon addition of less than one equivalent of "Cr (CO) 5 (THF) " (prepared as above, but with v i r t u a l l y a l l of the excess THF removed) at -80°:C, a* s h i f t to lower f i e l d ' offe~the--resonance 1 attribufcable'^to'ithe cyclopenta-dienyl protons was observed. Unfortunately, the hydride resonance was not observed; i t was l i k e l y obscured by the tetrahydrofuran or solvent peaks. Warming of the reaction mixture to 0°C followed by acq u i s i t i o n of a spectrum revealed that clean conversion of a portion of the CpW(NO)2H (6 6.24 (s, 5H), 2.19 (s, IH)) to CpW (CO) 2 (NO). (6 6.49) had occurred. The fate of the hydride ligand could not be determined. Addition of further "Cr(CO) 5(THF)" at t h i s temperature simply resulted i n further formation of CpW(CO)2(NO); no intermediate was observed after the ~2 min required to mix the reactants and obtain a spectrum. Reaction of CpW(NO)2H with W(CO) 5 (THF) . A yellow-orange solution containing W(CO) 5(THF) 1 0 7 (1.51 mmol) i n THF (15 mL) was prepared i n a manner analogous to that used for Cr(CO),- — (THF), and the solution was cooled to -78°C. Addition of a t o t a l of 0.43 g (1.38 mmol) CpW (NO) ~H was made incrementally-- 1.0.2. -with IR monitoring.. Four absorptions- in the nitrosyl. region appeared i n i t i a l l y " , and they maintained comparable, relative, intensities- as further CpW"(NO) 2H was- added. The two stronger absorptions CvNu 1717, 1631 cm 1I-were attributable to free CpW (NO) 2H; the other two peaks CvNQ 1738, 1663 cm were approximately half as intense. A f r a c t i o n of t h i s solution C.5 mL). was then allowed to warm to room temperature, during which time i t turned from green to orange. The v o l a t i l e s were removed i n vacuo to y i e l d a gummy brown residue. Extraction of the residue with 5 mL THF revealed that part of the material was no longer soluble; an IR spectrum of the extract revealed that the r e l a t i v e i n t e n s i t i e s of the two pairs of absorptions i n the n i t r o s y l region were now reversed. Removal of the solvent followed by drying under high vacuum C<0.005 Torr for 1.5 h) resulted in complete decomposition of the residue to produce an intractable brown s o l i d . The remaining 10 mL of the reaction mixture was then allowed to warm to room temperature to determine the thermal s t a b i l i t y of the products. Although no change i n the IR spectrum was observable, a brown s o l i d began to pr e c i p i t a t e a f t e r approximately 1 h.. After 18 h the r e l a t i v e i n t e n s i t i e s of the two pairs of n i t r o s y l absorptions were approximately equal.. One week, l a t e r the supernatant was almost colourless and exhibited only very weak. IR absorptions- in the n i t r o s y l region.. The brown pr e c i p i t a t e was isolated by f i l t r a t i o n and dissolved i n CCE,)_SO; an.IR spectrum of t h i s solution - 1.0.3 -revealed only- absorptions attributable to the solvent. Reaction: of CpW (NO) 2H with (MeCp) Mn (CO).y (THF) . A THF s o l u -t i o n C220 mL) containing (MeCp)Mn (CO) 3 (2.0 mL, 13 mmol) was placed i n a photoreactor and, while gently being purged with. N 2, was i r r a d i a t e d using a medium-pressure mercury lamp (Hanovia L-150W) housed i n a water-cooled immersion well. IR spectral monitoring of the reaction showed optimal conversion to (MeCp)Mn (CO) 2 (THF) 1 0 7 after 1.5 h. of i r r a d i a -t i o n , leaving a cl e a r , dark red solution. The solution was transferred to a round-bottom f l a s k and cooled to -78°C. In a separate f l a s k , 0.20 g (0.64 mmol) of CpW(NO)2H in 10 mL THF were cooled to -78°C, and to t h i s were added 20 mL of the (MeCp)Mn(CO)2 (THF) solution (1.2 mmol of t o t a l Mn).. At -78°C there appeared to be no reaction. After warming to room temperature, the green-red solution turned dark brown over a period of 0.5 h, and some p r e c i p i t a t e appeared. The solution was concentrated i n vacuo to a v o l -ume of approximately 2 mL; an IR spectrum of the supernatant solution showed two new bands i n the n i t r o s y l region (.1725 (sh), 1661 cm ^) but no detectable change i n the carbonyl region of the spectrum. Addition of further (MeCplMn(CO)2~ (THF) solution simply resulted in a uniform decrease i n i n t e n s i t y of a l l 4 bands i n the n i t r o s y l region, but with, s t i r r i n g more pr e c i p i t a t e formed, and a l l bands i n the n i t r o s y l region as well as those attributable to (MeCp)Mn-(CO) 2 CTHF). were observed to decrease i n i n t e n s i t y . The solvent was then removed i n vacuo, and the residue extracted - 104 -with CH 2C1 2 and f i l t e r e d ; the f i l t r a t e exhibited IR absorp-tions not attributable to the solvent at 2020, 1900 (br), and 1658 cm 1 . A l l attempts to puri f y t h i s product were unsuccessful, but i t was clear that i t was no.longer the i n i t i a l l y - f o r m e d adduct at t h i s stage. Reaction of CpW(NO)2H with (MeCp)Mn(CO) 2(H)(SiPh 3) 1 0 9 gave comparable r e s u l t s . Reaction of CpW(N0)2H with ZnCl,,. An excess of ZnCl 2«xH 20 (0.20 g, -1.4 mmol) was added to a THF solution (15 mL) containing 0.20 g (0.65 mmol) of CpW(NO)2H, and the r e s u l t -ing solution was s t i r r e d at room temperature for 48 h. IR monitoring during t h i s period showed the slow growth of poorly resolved shoulders at 1717 and 1631 cm 1 ( i . e . at s l i g h t l y higher energy than the n i t r o s y l absorptions of CpWCNO)2H). The solvent was then removed i n vacuo, with a brown p r e c i p i t a t e forming during solvent removal. Following extraction of the residue with a small amount of CDCl^, a lE NMR spectrum of the extract showed the presence of CpW(NO)2Cl (6 6.17) and CpW(.NO)2H (.6 6.00 (s, 5H) , 2.07 (s, 1H) ) in a r a t i o of 3:2. Due to the p a r t i a l decomposi-tio n of the sample during solvent removal, the degree of conversion to the chloride could not be r e l i a b l y ascertained. The reaction was next carried out i n (CD^). 2CO with :H NMR monitoring at ambient temperature. The i n i t i a l spectrum of the CpW(NO)2H/ZnCl2 mixture showed the reson-ances attributable to both the cyclopentadienyl and hydride - 105 -protons shifted to higher f i e l d by 4.8 and 7..8 Hz respect-i v e l y Cthe uncertainty i n the peak . p o s i t i o n s was- approxi-mately 0.3 Hz), r e l a t i v e to free CpW (NO) 2H. The addition, of D 20 to the solution produced no s h i f t in these peaks, thereby r u l i n g out the p o s s i b i l i t y that the traces of H^ O introduced with the ZnCl 2 contributed to the observed changes. The conversion of the hydride to CpWCNO)2Cl was ~15% complete afte r 11 h at ambient temperature. Treatment of C p W ( N O ) w i t h CdCl 2. To a suspension of white CdCl 2 (.0.23 g, 1.23 mmol) i n THF (90 mL) was added 1 equiv-alent (.0.38 g) of CpW(N0)2H. S t i r r i n g of the mixture for two days at room temperature resulted i n no discolouration of the white s o l i d , and no changes were detected i n the IR spectrum of the supernatant solution. The CpWCNO)2H was recovered qu a n t i t a t i v e l y by f i l t r a t i o n and subsequent solvent removal. Reaction of CpW(NO)2H with HgCl 2. To a s t i r r e d mixture of CpW(NO)2H (0.27 g, 0.87 mmol) and HgCl 2 (0.23 g, 0.87 mmol) were added 3 0 mL THF. Both s o l i d s dissolved r a p i d l y to y i e l d a c l e a r , lime green solution. However, within 1 minute, the solution became cloudy, and a white p r e c i p i t a t e then formed. After 1.5 h, the suspension was f i l t e r e d to obtain a gray s o l i d and an olive-green solution. The f i l t r a t e was taken to dryness i n vacuo, and the residue r e c r y s t a l l i z e d from CH 2C1 2/hexanes to y i e l d 0.2.0. g (0.58 mmol, 67% yield) of CpWCNO) 2Cl 1 6 as 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 I;R, 1K NMR, and mass spectra and by elemental analysis.. 1.06 -r. The: gray- s o l i d was> qualitatiyeiy- i d e n t i f i e d 1 " 1 a' as HgCl CO. 11 g, 53% yield): By- reacting i t with NHjQH to give a very dark gray residue CHg•• Hg(NH2) CI) . The reaction was also carried out at ^8 0°C i n (CD^l^CO with 1H NMR monitoring . I n i t i a l l y , a sharp peak, was observed at 5 6.53 Cs, 5H) (cf. 6" 6.23 for CpW (NO) 2H and 6.40 for CpWXNO)2Cl) along* with a broader peak at 6 4.3 5 (s, IH) , both, attributable to the complex CpW (NO) 2H-HgCl 2. Upon warming to 0°C a reaction occurred, with the resonance attributable to the cyclopentadienyl protons broadening and s h i f t i n g to 5.-6.40. The reaction was then car r i e d out at -78°C i n THF; several attempts to r a p i d l y obtain an IR spectrum of the reaction mixture yielded only spectra displaying n i t r o s y l absorptions indistinguishable, from those of CpW (NO). 2C1 ( j . e. V N Q 164 6, 1728 cm" 1). Reaction of CpW(N0)2H with Pt (PPh-,).. To a s t i r r e d toluene solution (2.0 mL) of CpW'CNO) 2H (0.188 g, 0.609 mmol); were added 0.50 equivalents (10 mL) of a Pt CPPh-3) 3 1 1 1 solution C1.205 g, 1.2.3 mmol i n 4 0 mL of toluene) y i e l d i n g an immed-ia t e , f l o c c u l e n t , yellow—brown p r e c i p i t a t e and, upon s e t t -l i n g , a yellow supernatant solution. An XR spectrum of the solution showed that approximately one-half of the CpWCNO)2H had been consumed, but no new absorptions- appeared in. the n i t r o s y l region. 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 , washed with toluene (2 x 10 mL), and dried i n vacuo. The s o l i d was only sparingly soluble i n THF, but quite CH 9C1 9 107 ^ soluble: TR spectra of the s o l i d in. CH^Cl^ solution, and as a Nujol mull showed only; weak, absorptions i n the n i t r o s y l region.. A mass spectrum of the s o l i d at a probe temperature of approximately 200°C revealed no metal—containing f r a g -ments, but i t should be noted that the s o l i d decomposed at 125°C under N 2; flame p y r o l y s i s yielded a metal residue. Reaction of CpWCNCQ^H with BEt^. To a hexanes suspension (10 mL) of CpW(.N0)2H (.0.20 g, 0.65 mmol) were added with s t i r r i n g 5 mL of 1 M BEt^ i n hexanes. S u f f i c i e n t additional solvent (10 mL) was then added to completely dissolve the CpW(.N0)2H. An IR spectrum of the solution showed only absorptions att r i b u t a b l e to CpW(NO)2H ( v N 0 1730, 1650 cm"1) in the n i t r o s y l region. Within 10 min a brown p r e c i p i t a t e began forming, and within 1 h the solution was a pale green colour. After 16 h no IR absorptions were detectable i n the n i t r o s y l region of the spectrum. Addition of 3 mL THF f a i l e d to dissolve any of the s o l i d . With the addition of only 1 equivalent of BEt^ to a CpW (.NO). 2H solution, decomposition occurred at a slower rate; however, no new n i t r o s y l absorptions could be detected in solution even after 1 h. Reaction of CpW(NO)2H with HBF^ »OMe 2. To a s t i r r e d , green solution of CpW CNO) 2H (0.30 g, 0.97 mmol) in CH 2C1 2 (25 mL). was added dropwise an emulsion containing 0.5 mL C5.6 mmol) HBF 4«OMe 2 i n 5 mL CH 2C1 2, and the progress of the reaction was monitored by IR spectroscopy. As addition proceeded, - 1.08 -the. solution became a dark; green, and the: n£t;ros.yl absorptions attr i b u t a b l e to the star t i n g hydride diminished in. i n t e n s i t y : simultaneously, two new- bands- were observed to grow in at s l i g h t l y higher energy CvN0 1733, 1648 cm'1}.. Upon complete consumption of the CpW(NO)2H (requiring <*1 equivalent of HBF 4 « O M e 2 ) , the addition was terminated and the v o l a t i l e s removed, thereby leaving a dark green o i l . An IR spectrum of the o i l dissolved i n a minimum of THF showed the absorp-tions shifted to 1722 and 1641 cm Addition of 0.5 mL (an excess) of dry Et^N produced no s h i f t in the absorptions, and no colour change was detected. No attempt was made to i s o l a t e the nitrosyl-containing product. The reaction was also carried out at -2 0°C i n C D 3 N O 2 : addition of less than 0.5 equivalents of HBF4'OMe2 resulted i n the clean conversion of CpWXNOj^H to [Cp2W2 (NO). 4 ~ H]BF 4 16 6.47 (s, 10H), -8.33 (s, IH)). Warming of the sample to room temperature resulted i n the destruction of the b i m e t a l l i c cation and the formation of a brown p r e c i p i -tate. In contrast, addition of H 2S0 4 to a CD^ NO,, solution of CpWCNO)2H did not y i e l d [Cp 2W 2(NOJ 4H] +, but rather a new resonance at 5 6.3 5 was observed. No other peaks attribu-s< table to either W—H or free H'+ were detectable. Reaction of CpW (NO) 2H with. A i d , . To a CDC13 solution of CpW(NO)2H were added ~ L 2 equivalents of A l C l ^ as a solution in. CDCl^. After mixing well, the r e s u l t i n g solution, was-monitored by 1H NMR spectroscopy at ambient temperature. - 1,0.9 -Over- a period of ~ 3 0^ min the slow- disappearan.ce: of peaks at 6' 5 . 9 9 (s, 5 H ) . and 2 , 0 . 7 ( > , I H ) (attributable to CpW (NO) 2H) was observed along with, the concomitant growth, of a new peak at 6' 6 . 1 4 due to CpW (NO) 2 C 1 * T R e peak, positions for each, of the compounds- were indistinguishable from those found i n the absence of A l C l ^ , FR monitoring of the 1 : 1 reaction of CpW'(NO) 2H with. A 1 C 1 3 i n CH : 2 C 1 2 solution revealed only a gradual s h i f t of the n i t r o s y l absorptions to higher energy as- the hydride (^Ng 1 7 1 8 , 1 6 3 2 cm ^) was- converted into CpW (NO) 2 C 1 Cv N 0 1 7 3 3 , 1 6 5 0 cm"1).. No evidence of adduct formation was detected. Results and Discussion The Preparation and Chara'cte'rizatlon of CpMo (NO) 2H. In l i g h t of the observed formation of [CpCr(NO) 2J 2 When the complexes CpCr (NO) 2X (X = C I , I, N© 2, N© 3, q ; 1 - ^ ^ , BF.4, or (CO)PF6) are reacted with NaAlH 2 (OCH2CH2OCH3) 2 (described i n Chapter 3 ) , i t was anticipated that the reduc-ti o n of CpM(NO) 2Cl (M - Mo, W) might y i e l d the corresponding dimers, [CpM(NO) 2J 2. A l t e r n a t i v e l y , as the s t a b i l i t y of iso e l e c t r o n i c and i s o s t r u c t u r a l complexes i s known to \ . increase going down a p a r t i c u l a r group of t r a n s i t i o n metals in the periodic t a b l e 3 9 , the hydride compounds might them-selves prove to be. i.solable. Indeed, the reaction of CpMo (NO) 2 C 1 with. NaAlH:2 ( 0 C H : 2 C H 2 0 C H : 3 ) 2 i n toluene at - 7 8°C leads to the formation of a bright green solution containing the unstable complex CpMo (NO)„H, which thus far has defied - 110. -a l l attempts at i s o l a t i o n 5 ' 1 ., Toluene: solutions containing CpMo CNO 1 2 ff slowly deposit a''red—Brown s o l i d when s t i r r e d at ambient temperature i n an atmosphere of prepurified nitrogen, the decomposition being complete after ^3 days. The rate of decomposition of the hydride complex is- markedly enhanced by removal of the solvent i n vacuo, a procedure which, only affords the. red—brown solid.. This- s o l i d does not dissolve :y i n any common organic solvents, and i t s infrared spectrum (as a Nujol mull) i s devoid of any absorptions attributable to coordinated nitrogen-.monoxide . . Nevertheless IR spectral evidence Cv N 0 (toluene): 1732, 1642 cm - 1 vs. 1753, 1663 cm""1 for CpMo(N0) 2Cl) and the chemical properties (vide infra) of the green toluene solutions are completely consist-ent with the presence of CpMo(NO)2H. The reactions used to characterize CpMo (NO)^E chem-i c a l l y are best performed using f r e s h l y prepared toluene solutions of the complex. Thus, treatment of such a solu-t i o n with an ether solution of diazomethane leads to the formation of the known compound CpMo (.NO) 2Me i n low y i e l d as 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 IR and mass spectra, i . e . Et„0/toluene CpMo (NO) 2H + CH 2N 2 • CpMo (NO) 2Me + N 2 (.4 0.) Comparable conversions have previously been shown to occur when various carbonyl hydrides-, eg. CpMo (COI^H: (M Mo, WI 3 1 , are reaeted with diazomethane 1 1 2. Additional evidence supporting this- formulation i s obtained by reacting the ^ 111 " green, toluene, solutions-- witft excess- 'Mel: to. y i e l d , after s t i r r i n g for several days- at ambient temperature, trace, amounts- of CpMo (NO) 2 I a s s i d e n t i f i e d by- its-melting point and i t s XR and mass- spectra," "i.e. CpMo (NO) 2H + Mel • . t o l u e n e , » CpMo (NO) 2 I (41) The. reaction of CpMo (NO) 2H: with. I' to give the iodo deriva-t i v e i n good y i e l d 5 1 lends- further support for the presence of a metal hydride l i n k , as numerous carbonyl hydrides undergo comparable reactions with, halogens. Although some transition-metal carbonyl hydrides are known to react with p-CH-C,H.S0oN(CH_)NO (Diazald) to y i e l d j b 4 I. 5 n i t r o s y l complexes 1 0, reaction of CpMo (NO)2H with Diazald i n toluene r e s u l t s only i n the slow p r e c i p i t a t i o n of red-brown, n i t r o s y l - f r e e decomposition products at a rate comparable to that observed i n the absence of Diazald, i . e . CpMo CNO) 2H + Diazald rr' • CpMo (NO) 3 C.4 2) In retrospect, i t can be noted that CpMo(NO)2H was previously prepared v i a the reaction of CpMoCNO)2Cl with. NaBH^ i n EtOH s o l u t i o n 1 1 k , although s u f f i c i e n t evidence for th i s formulation i s only now available. The Preparation and Characterization of [Cp2W_2 (.NO) H^] X  (X =• BF d, PF 6) . In contrast to CpMo(NO)2H, the tungsten analogue i s is o l a b l e and has been f u l l y characterized, i t s chemical properties suggesting an unexpected hydridic character of ~ 1.12. -the W-H l i n k a g e 5 1 , In. a donor solvent such, as- acetonitrile./ CpW (NO) reacts- with, the well-known hydride abstractor Pfi-C +X~ v i a loss- of H^ 5 1 "iYe... CpW (NO) 2H + Ph 3C +X~ — — — - — — • lCpWtNO):2.(eH3GNI ]'+X (X = BF 4, PP 6) + Ph3CH (.43) The comparable reaction is- also known to occur when the i so s t r u c t u r a l and is o e l e c t r o n i c complex CpRe (CO) (NO)H is-treated with Ph 3C +X~ (X = BF 4, PFg) i n donor solvents (L), producing I CpRe (CO) (NO)](Ll] +X~ 9 : ( r. In CH 2C1 2 solution with 2:1 stoichiometry, however, hydride abstraction brings about the formation of the bi m e t a l l i c cation [Cp 2Re 2(CO) 2CNO) 2H] +, which has been characterized f u l l y 9 0 , ' i . e . CH 7C1 9 2CpRe (CO) (NO)H + Ph 3C X • (3 8) (X = BF 4, PF 6) [Cp2Re2(CO)2(.NO)2H]+x" Similar reaction of CpW(NO)2H with the hydride abstractors Ph 3C +BF 4~, Ph 3C +PF 6~, or C 7H 7 +BF 4~ i n CH^C^ leads to the formation of a sparingly soluble, dark green s o l i d [Cp2W2-(NO) 4H] +X~ (X = BF 4 or PFg): CH2C1,2 2CpW(.NO)2H + Ph 3C X • : — • (X - BF 4, PF 6) [Cp2W2 (NO) 4H] +X~ + Ph3CH (44). 2CpW(NO).2H + C 7II ? BF 4 [Cp2W2 (NO) 4H] BF 4 + C7IIg (45) The products of these reactions p r e c i p i t a t e from solution as mic r o c r y s t a l l i n e , a n a l y t i c a l l y pure s o l i d s i s o l a b l e i n good 1.1.3 -to excellent; yields-.. lCp 2W 2 (NO):4H] BF 4 i s a dark; green, s o l i d (mp 95®'C dec); which can be handled in a i r for short periods- of time with-out the occurrence of noticeable: decomposition, and i t may be stored under for periods- of at least several months. It is- insoluble in p a r a f f i n hydrocarbons or in benzene, and i s only sparingly soluble i n CH2C12.. The cation has good s o l u b i l i t y only in nitromethane and, presumably, other strongly solvating but weakly donating s o l v e n t s 1 1 5 . However, slow decomposition of the cation ix^./2 ~^ ^ l s ^nvar^-a^Y observed i n nitromethane solution, although the mode of decomposition i s unclear. Treatment of the complex with donor solvents such as (CH'O^CO or CH^CN re s u l t s i n the rapid d i s s o c i a t i o n of the bim e t a l l i c cation to give monomeric products, i . e . [Cp 2W 2(NO) 4H] +BF 4" + L • CpW(NO)2H + (X = a 2e~ donor) [CpW(NO) 2 L ] + B F 4 ~ C46) Thus i n CD 3N0 2 solution, 1H NMR monitoring of the addition of the donor solvents mentioned above r e s u l t s i n the loss of the peaks attr i b u t a b l e to [Cp 2W 2(NO) 4H]BF 4 C$ 6.48 Cs, 10H), —8.33 Cs, IH)) and the appearance of new resonances (at 5 6.15 Cs, 5H), and 1.94 (s, IH)) c h a r a c t e r i s t i c of CpW(NO)2H. Resonances due to the donor solvent added also appear, along with, several new peaks at low f i e l d C6> > 6.15). , presumably attri b u t a b l e to [CpW (NO) 2L] + . An IR spectrum of an a c e t o n i t r i l e solution of 10^2^2 ^ F6 displays: nitrosyl. absorptions- at positions? indistinguishable from those of C p W Q K ^ H : &m 171.5, 1.631. cm-1), and [CpW(NO) . (CH-CN) ] PF^. (v 1730, 164 9 cm"1) in the. 2 3 6 ' NO same solvent. Thus- both, the: PR and 1 H~ NMR spectral evidence indicates that the reaction of the bimetallic cation with, donor solvents- yields- CpW(NQ)2H',. with, the IR evidence i n d i -cating that the remaining products are i n a l l l i k e l i h o o d of the type [CpW(NO)2L]+X~ (X.= BF^, PF g). The 1E NMR spectra of the compounds [Cp2W2 (NO). 4H] +X~ (X•= BF 4 or PFg) at ambient temperature i n nitromethane solutions- show a sharp si n g l e t at <5* 6.4 8 a t t r i b u t a b l e to 10 equivalent cyclopentadienyl protons as- well as a high-f i e l d s i n g l e t due to one hydrogen at 5 -8.33, i , e . in the region t y p i c a l of metal—bound protons 1 1 6.. Several workers have suggested that, for derivatives of the same metal, the resonance of a bridging hydrogen i n hydridometal c l u s t e r s appears at higher f i e l d than that of a terminally bonded hydrogen 1 1 6. Examination of some reported s h i f t values for hydridotungsten s p e c i e s 1 1 6 , however, reveals no such c o r r e l a -t i o n for tungsten complexes. Thus the large s h i f t of the hydride resonance to high f i e l d (A6 = 10.27 ppm) upon conver-sion of CpW(NO)2H (<S W_ H (CD3N02). : 1.94) to [Cp2W2 (NO) 4H] + ( 5 W _ H (CD^ NO,,) : —8.33) i s not a r e l i a b l e guide in determin-ing whether the hydride i s bonded i n a bridging or a terminal fashion i n the l a t t e r species-. Further evidence is- obtained, however, by the acqui-s i t i o n of a spectrum with a very large signal—to—noise r a t i o - 1.15 T-( i . e . ~1, 000:1 for the; main hydride resonance) in. which, six s a t e l l i t e peaks are r e a d i l y apparent (see Figure 3 1 . - A detailed analysis of the t h e o r e t i c a l peak patterns for a W 2 H 1 1 7 • • spin system i s available in the l i t e r a t u r e , with, consid-eration given to a l l possible combinations of a terminal S_w system with 0 < 2 J 1 8 3 w _ H < ^ i s s ^ , with 2 J 1 8 3 W _ H unresolved ( i . e . ~0), and with slow or fas t exchange (on the NMR time scale) of the hydride between the two metal centres; also considered i s a symmetrically bridging ^/ system. The p o s s i b i l i t y of a l i n e a r W : — H — W l i n k , considered i n a l a t e r p a p e r 1 1 8 , would y i e l d a spectrum indistinguishable from that expected for the bridged case. The observed 7-peak pattern (Figure 3) i s consistent only with the model in which the hydrogen atom i s terminally bound (with spin-coupling to the remote tungsten being observable), and rapid intramolecular exchange of the hydride ligand between the two metal atoms i s occurring: unfortunately, the t h e o r e t i c a l analyses are i n c o r r e c t 1 1 9 i n t h i s p a r t i c u l a r instance, and the excellent agreement obtained between the predicted peak i n t e n s i t i e s (0.51:12.24:0.51:73.48:0.51:12.24:0.51) and the integrated peak areas obtained experimentally (0.5:11.4: 0.5:74.5:0.5:11.8:0.5) i s only fortuitous. As mentioned, the analyses of the t h e o r e t i c a l s p e c t r a 1 1 7 ' 1 1 8 are incorrect for the case i n question, i . e . where 2 J i s resolved and rapid intramolecular exchange of the proton between the two tungsten nuclei occurs. For VI those molecules in which both metal centres are 1 8 3 W a - 116 -F i g u r e 3. The 2 H NMR S p e c t r u m o f [ C p 2 W 2 ( N O ) 4 H ] B F 4 i n C D 3 N 0 2 S o l u t i o n . (a) The c o m p l e t e s p e c t r u m , (b) The h y d r i d e r e g i o n ( a m p l i t u d e x 8) showing t h e 1 8 3WW s a t e l l i t e s , and (c) The h y d r i d e r e g i o n ( a m p l i t u d e x 128) r e v e a l i n g t h e 1 8 3Wn and 1 5NN, . - . s a t e l l i t e s . i 1 1 l 1 1 1 V.. « . » i . 6 = 6.48; a t t r i b u t a b l e t o the ( n 5 - C 5 H 5 ) r i n g s , i i . 6 = 4.33; a t t r i b u t a b l e t o CHD 2N0 2 p r e s e n t i n the s o l v e n t , i i i . 6 = -8.33; a t t r i b u t a b l e t o a metal-bound hydrogen. i i i . The metal-bound hydrogen, <5 = -8.33 a. The 183WW s a t e l l i t e s ; s e p a r a t i o n e q u a l s 114.2 Hz. b. The 1 8 3W 2 s a t e l l i t e s ; s e p a r a t i o n e q u a l s 228.4 Hz. c. The 1 5 N N 3 s a t e l l i t e s ; s e p a r a t i o n e q u a l s 63.8 Hz. a b F i g u r e 3b 1 I .1 L. I L I I , 1 119 -i n F i g u r e 3c I i - 1,2.0 -doublet, of doublets-, o,f main, separation. J& and small separa-t i o n 2J', was- predicted, each: resonance haying 0,51% of the t o t a l hydride, i n t e n s i t y . Applying the time—averaging of the spin—spin coupling of the proton with the two 1 8 3W nuclei c o r r e c t l y predicts- instead a 1:2:1' t r i p l e t 1 1 9 , with, the two outer peaks- again each, exhibiting 0.51%, of the: t o t a l i n t e n s i t y and a separation of (1 J' + 2J) , as- in the previous analyses. However/ due to the rapid s i t e exchange, peaks of separation i1 j — 2 J ) are not expected to be present ( i . e . with s i t e exchange, the difference between the two s i t e s vanishes and C-j' - 2 J ) goes to 0, tftds\ y i e l d i n g a peak of i n t e n s i t y 1.02% coincident with, the central peak).. As the two unassigned resonances were shown not to be spinning side-bands by acquiring the spectrum at a v a r i e t y of sample spinning speeds, the only source of o r i g i n remain-ing to be considered i s spin-spin coupling with some other-nucleus in the molecule. Coupling with a nucleus of spin 1/2 would produce a doublet, while coupling with a nucleus of spin 1 would y i e l d a 1:1:1 t r i p l e t , with the centre resonance being coincident with the main hydride resonance (1,e. a pseudo—doublet). An examination of a l l p o s s i b i l i t i e s i d e n t i f i e s 1 5N, an isotope with spin 1/2 and a natural abundance of 0.37%, as the only possible source of the obser-ved spin-spin coupling. Thus with 4 equivalent (due to s i t e exchange of the proton) n i t r o s y l ligands each. with. 0.37% of the 1 5N isotopomer present, and only those molecules- i n which, neither tungsten nucleus- is- 1 8 3W contributing to the: in.ten.--0. 121 s i t y of tHe.se. peaks>, t h e i r c^l.cul.a,ted' ' ' a ^ e ' 0...54% each.. Thus, coincident a l l y , the: i n t e n s i t i e s are. expected to be almost i d e n t i c a l to those of the two outermost s a t e l l i t e bands ( i . e . 0.54 vs. 0.51%I, as- was- i n fact observed.. With the aim of obtaining further evidence to support t h i s i n t e r -pretation., attempts were made to observe the 1 5N s a t e l l i t e bands associated with those isotopomers of [Cp 2W 2(NO) 4H] + containing one 183W, which, are of even smaller predicted i n t e n s i t y ( i . e . 0.091%). It was indeed possible to observe the outer resonances a r i s i n g from the combined 183W-H and 1 5N-H spin-spin couplings at the expected positions, although the peaks a r i s i n g from the difference of these couplings could not be located due to t h e i r proximity to the central hydride resonance and the limited s t a b i l i t y of the complex in CD 3N0 2. Unfortunately, t h i s reanalysis of the th e o r e t i c a l hydride spectra leads to the conclusion that i t i s not possible, on the basis of the observed isotope couplings, to dis t i n g u i s h between a terminally bound hydrogen r a p i d l y exchanging between the metal centres and one which, bridges those centres. It i s possible to extract a 1H-183W coupling constant of 114.2 Hz, but i t is- uncertain whether t h i s value r e f l e c t s a d i r e c t coupling a J ' ' of a 8 3w to a bridging hydro-gen, or whether this: value instead reflects- an averaging of the 1 J'i 8 3 TT- TT a n d 2 J i B3T7- TT terms which a r i s e i n the alternate VV—rl W—n interpretation. S i m i l a r l y , Ji 5 v t T T is- observed to be 63.8 Hz, N—n but i t too may be an average: of more than one discrete spin-122. -s p i n coupling-.. No 1 N-M—K -J1 c o u p l i n g :c©n.s,tan,ts- appear to have been r e p o r t e d 1 2 0 , although, one study- of the: 1 5~N' s h i f t s o f n i t r o s y l ligands- i n a v a r i e t y ©f o r g a n o m e t a l l i c complexes has appeared 1 i n the chemical l i t e r a t u r e 1 2 1 . No obvious s t r u c t u r a l i n f o r m a t i o n can be obtained from the magnitude of the c o u p l i n g c o n s t a n t . C a r e f u l a c q u i s i t i o n of the IR s p e c t r a of [Cp 2W 2(NO) 4-H] +X~ (X = BF 4, PF g) i n CH 2C1 2 s o l u t i o n s and as N u j o l m u l l s r e v e a l s the presence of 4 n i t r o s y l a b s o r p t i o n s , a l l i n the r e g i o n c h a r a c t e r i s t i c of t e r m i n a l n i t r o s y l g r o u p s 1 2 2 . S i m i l a r l y , although i n nitromethane the s o l v e n t obscures a p o r t i o n of the n i t r o s y l a b s o r p t i o n r e g i o n / two n i t r o s y l 1 .... bands are d e t e c t e d a t e n e r g i e s comparable t o the higher energy bands observed i n CH 2C1 2 s o l u t i o n C s e e Table VII).. As the r e l a t i v e i n t e n s i t i e s of the bands are comparable i n each i n s t a n c e , i t i s reasonable t o conclude t h a t a l l f o u r bands a r i s e from a s i n g l e s t r u c t u r a l isomer of the c a t i o n . A s t r u c t u r e c o n s i s t e n t with both the IR and  1 E NMR s p e c t r a l data, as w e l l as i t s chemical p r o p e r t i e s (vide i n f r a ) i s as-shown below. s WI fcW. 0 N - | j ^ N O N N: 0 0 In t h i s - v iew an 18e~ u n i t , CpW(NOl2H:, acts- as- a Lewis- base, and p r o v i d e s e l e c t r o n d e n s i t y from a f i l l e d metal o r b i t a l t o a vacant o r b i t a l of the 16e~ CpW (.NO) 2 + u n i t , which, acts- as a 123 T, Table: VII.,' : C h a r a c t e r i s t i c N i t r o s y l Absorptions- qf CpM(NO) ^ II. CM = Mo,' W) Derivatives'-Complex - -VNO'' ^ .. -1 other absorp— " " "tionS5," cm"1 CpMo(NO)2Ha 1732, 1642. CpMo(NO) 2H b 1738, 1647 V M . „ 1805 (w) Mo-H. CpW(NO) 2H b' 5 1 1718, 163 2 VW-H: 1 9 0 0 ( W ) [CpW(NO) 2(CH 3CN)]PF 6° 1730, 164 9 CpMo(NO) 2Cl b' 2 3 1759, 16 65 CpW(NO) 2Cl f a' 23 '  1733, 1650 [Cp2W2 CNO)4H] B F 4 d 1775, 1748, 1707, 1660 [Cp2W2(NO)4H] P F 6 b 1722 Cbr), 1650, 1632 [Cp2W2 CNO)4H] P F g d 1752 (br) , 1685 (br) [Cp 2Mo 2 CNO)4H] P F g d 1783 (br), 167 5 (br) [Cp 2Mo 2(NO) 4H]PF 6 1795, 1695 1768, 1707, (sh) [Cp2MoWCNO)4H] B F 4 b 1790, 1706, 1765 (sh), 1751, 1678, 1650 (sh) [Cp2MoW(NO)4H]BF4 1790 , 1718 , 1769 (sh), 1756, 1660 (br) [Cp2W2 CNO)4H] P F g e 1728, 1718 (sh) [Cp2W2 (NO)4H] P F 6 C 1730, 1712, 1648, 1631 CpW(NO)2HC 1715, 1631 a b in toluene; i n CE 2 C l 2 ; ° in CH3CN; as a Nujol. mull; in CH 3N0 2 - 1,2.4 . i i Lewis- acid.. An. alternate explanation, i s a structure, invoking a 3-centre—2-r-electron. W2H?B6nd; on. the: Basis-of cneni$ca.l. evidence discussed l a t e r , this- structure, i s cons-Merre.d to.-be less l i k e l y . Unfortunately-, although [Cp2W2 (NO)4D] PF g i s r e a d i l y prepared from the known compound CpW(NO) 2D 5 1, comparison, of i t s concentrated mull IR spectra with those of [Cp2W2 (NO). ^ H] + X (X = BF. or PF ) gives no in d i c a t i o n of any absorptions 4 b attributable to a metal-hydrogen unit. 1 H NMR spectra of the deuterated cation show a decrease in i n t e n s i t y of the h i g h — f i e l d resonance to < 5% of i t s o r i g i n a l i n t e n s i t y , confirming the successful incorporation of the D i n the desired position. [Cp 2W 2(NO) 4H]PF g i s a green s o l i d (mp 122 QC) which exhibits a i r s t a b i l i t y and s o l u b i l i t y ^properties similar to those of the BF 4~ s a l t . In CT>3N02 solution i t s *H NMR spectrum i s indistinguishable from that of the BF 4 analogue, thereby r u l i n g out any cation-anion interaction i n solution. S i m i l a r l y , i t s CH 2C1 2 and Nujol mull IR spectra display n i t r o s y l stretching frequencies comparable to those found for [Cp2W2 (NO) 4H] BF 4 (see Table VII). The Preparation and Characterization of [Cp2Mo2(NO)^H]PF^. Pale green [Cp 2Mo 2(NO) 4H]PF g, mp 119 GC dec, i s rea d i l y prepared i n an analogous fashion by reacting Ph^CPFg with CH 2Cl 2/toluene solutions of CpMo (NO) 2H, i,e.. CH C I / 2C PMO(NO) 2H + Ph 3C PF 6" t o l u e n e ' - 125 -• [Cp 2Mo 2 CNO)4H]PFg + Ph3CH (47) Although the o v e r a l l y i e l d of the cation based on CpMo(NO)2C1 i s only 19%, t h i s i s comparable to the top yi e l d s obtained from the reactions used to characterize CpMo(NO)2H. It i s l i k e l y that the low y i e l d i s attributable mainly to losses associated with the preparation and p u r i f i c a t i o n of the CpMo(NO)2H solution. Indeed, making the l o g i c a l assumption that Ph-CPF, reacts in a 1:2 fashion with CpMo(NO)„H as was j b £ v e r i f i e d for the tungsten system, the isolated y i e l d of [Cp2Mo2,.(:NO) .4.H]'PF6;;is::fairly,;good ; i.57.%;.basedcon--~the,Aa^o^nt, ,0f Ph 0CPF, added). 3 6 The IR spectra of [Cp 2Mo 2(NO) 4H]PF^ are comparable to those obtained for the tungsten congener (see Table VII), thereby suggesting that the two bimetallic cations are is o s t r u c t u r a l . A lE NMR spectrum of the complex i n CD 3N0 2 also supports t h i s conclusion. Thus a sharp singlet i s observed at low f i e l d ( 6 6.37, 10H) while the remaining resonance i s located at high f i e l d ( 6 -9.78 (s, IH)). Those Mo isotopes which have nuclear spin magnetic moments ( i . e .  95Mo, 9 7Mo) are quadrupolar nuclei (I = 5/2 in each instance) and no metal-hydrogen spin-spin coupling i s observed because of the rapid quadrupolar relaxation of the quadrupolar nucleus. The Preparation and Characterization of [Cp2MoW(NO)4H]BF4. The mononuclear Mo and W cations having been successfully prepared, i t i s c l e a r l y also of intere s t to - 126 -synthesize, the. heteronuclear analogue, [Cp2MoW (NO) ^Hj for comparative: purposes-.. Since Both. CpMo OSTOI^ H- and CpWXNQX^K react immed lately- with. the t r i t y l cation, i t seemed u n l i k e l y that either hydride would react p r e f e r e n t i a l l y with Ph^C* i f i t were added to a 1:1 mixture of the two compounds. + Nevertheless-, 1H NMR spectra of the compounds [Cp2M-^M2 (CO) ^ H] BF 4~ CM = M2 = Mo, W; = Mo, M 2 = W) show that the various Bimetallic cations do not equiliBrate i n s o l u t i o n 1 1 7 , a f a c t which suggests that an alternate route to the mixed n i t r o s y l cation should Be successful. The aBstraction of halide from the complexes CpFe(CO) 2X (X = C l , Br, I) i n the presence of excess o l e f i n brings ahout the formation of o l e f i n cations of the type [ C p F e ( C O ) 2 ( o l e f i n ) ] + 1 2 3 . S i m i l a r l y , the reaction of CpW(NO)2Cl with AgBF^ i n the presence of cyclooctene produces [CpW(NO) 2(cyclooctene)]BF 4 1 0 4, i n which the o l e f i n i s only very weakly coordinated to the metal centre. Displacement of the o l e f i n by CpMo(NO)2H should therefore y i e l d the desired heteronuclear cation; reversing the roles of the Mo and W complexes should produce i d e n t i c a l r e s u l t s , i . e . [CpM1 (NO) 2 (cyclooctene) ] BF 4 + CpM2 CNO) 2H — »• [Cp 2M 1M 2 (NO). 4H] BF 4 + cyclooctene. (148)1 (M^ - Mo, M2 = W or vice: versa). The use of CpW CNO). 2H as the hydride source i s preferable because i t affords the advantage of carrying out the reaction, with well—defined stoichiometry. S t i r l i n g a CH 2C1 2 solution of CpMo (NO). 2C1. in, the presence of an excess of AgBF^ for 4 5" -minut.es> fQ.llp.wed by f i l t r a t i o n and the addition of cyclooctene to. the f i l t r a t e , y i e l d s a green solution of iCpM©(NO)2(cyclooctenel] BF^ exhibiting n i t r o s y l absorptions- ("VN0 18 00, 1717 cm"1), com-parable to those observed for the W analogue ( v N O 17 69, 1689 cm - 1); 1 0" (see Table VII). After again f i l t e r i n g the solution, 1 equivalent of CpW(N0)2H i s added to the f i l t r a t e . Monitoring of the IR spectrum of the mixture reveals the presence of at least 6 poorly resolved n i t r o s y l absorptions at t h i s point ( v N Q 1795, 1778, 1757, 1703, 1680, and 1640 cm 1) although peaks due to unreacted CpW(N0)2H (.V^ Q 1718, 1632 cm "S appear to be absent. The addition of hexanes pr e c i p i t a t e s a green s o l i d which, upon r e c r y s t a l l i z a t i o n from CH 2Cl 2/hexanes, y i e l d s a n a l y t i c a l l y pure [Cp2MoW(NO)^H] BF 4~ (mp 115°C'dec). Mull and solution IR spectra of t h i s complex exhibit numerous poorly resolved n i t r o s y l stretching absorptions (vide supra) , consistent with the t o t a l of eight absorptions-expected for the two isomers of the heteronuclear cation depicted below: Cp H 0N- -W- -Mo* / Cp •NO N O N O C p O N ' I N: o H; i -Mo I N: o / Cp •NO [Only 4 bands- would be. expected i f the hydride was- i n a, bridging position^]. Surprisingly, a 1H NMR spectrum of 1.2.8 -[Cp2MoW CNO) 4H] BF 4 i n CD 3N0 2 reveals the. presence of both, of the homonuclear cations (\ 6.47, -8.33; \ 6.V37, -9.78) w2 2 in addition, to the hete'ronuclear cation ("5- T T S 6.47, 6.37, • • • • MoW -8.921, suggesting that the: complexes- are i n equilibrium i n solution.. This- can. be confirmed by d i s s o l v i n g a -mixture of [Cp 2Mo 2 (NO) 4H] PF 6 and lCp 2W 2(NO) 4H]PF 6 i n CD 3N© 2 to give a solution whose 1H NMR spectrum i s consistent with, the pre-t sence of a l l three c a t i o n i c complexes i n solution Csee Figure 4), l . e . + + C D 3 N 0 2 [Cp2W2(.NO)4H] + [Cp 2Mo 2 (NO)4H] -2 [Cp2MoW(.NO) 4H] + (.4 9) The observation of only two peaks in the cyclopentadienyl region of the spectrum suggests that changing the i d e n t i t y of the remote metal (from Mo to W or vice versa) does not bring about a resolvable s h i f t i n the resonance att r i b u t a b l e to the cyclopentadienyl protons. Integration shows that the two peaks are of the expected r e l a t i v e i n t e n s i t i e s , lending further credence to t h i s interpretation. The appearance of the hydride resonance of the. heteronuclear cation at a s h i f t position intermediate to those of the ditungsten and dimolybdenum species i s not surprising. The observation of only one new resonance when two s t r u c t u r a l isomers- of [Cp2MoW (NO) 4H] PF^ are possible i s again consistent either with exchange of the H ligand between, the two metal centres- at a rate that i s rapid on the NMR time scale or with a bridging hydride.. That two isomers-- 129 -F i g u r e 4. The h y d r i d e ' r e g i o n .of t h e *H NMR s p e c t r u m o f a [ C p 2 M 2 ( N O ) 4 H ] P F g (Mo:W r a t i o 1.5:1) m i x t u r e i n C D 3 N 0 2 . (A) P e a k s a t t r i b u t a b l e t o [ C p 2 W 2 ( N O ) 4 H ] + (6 = -8.33, = 114.3 Hz) (B) P e a k s a t t r i b u t a b l e t o [ C p 2 M o W ( N O ) 4 H ] + (6 = -8.92, 1 , 2 J = 123.6 Hz) (C) Peak a t t r i b u t a b l e t o [ C p 2 M o 2 ( N O ) 4 H ] + (6 - -9.78) 1 3 0 -- 1.31 T -po,ssessing terminally- bound hydride?- are. in. fact, pre.s.on.t. i s , as- mentioned previously, suggested by the: Nujol mull i:R spectrum of the complex, even though, the interpretation of its- solution spectrum is- complicated by- the: e q u i l i b r a t i o n of the b i m e t a l l i c cations-.. A further i n d i c a t i o n that [Cp2MoW(N0). 4H] PF g has a structure analogous to that of the ditungsten species i s the s i m i l a r i t y i n magnitude of the observed spin-spin coupling with the 1 8 3W n u c l e i . Thus the observed coupling ( 1 , 2 J i 8 3 T 7 „ W— ti or 1J,\ of 123.6 Hz i s of comparable magnitude to the corresponding value for the ditungsten system, i . e . C^IBSTT rr + 2 J i 8 3 T T „)/2 or 1 J r = 114.3 Hz. As the Mo-H and v v — v v — t i -the W—H bond strengths are not l i k e l y to be i d e n t i c a l , the observed coupling 1 , 2 J would not be a true average of the 1 J' and 2 J spin-spin couplings of 1E with 1 8 3W due to the unequal l i f e t i m e s expected for the two isomers. Attempted Deprotonations of [Cp^M^(NO)^H]+ (M = Mo, W). As mentioned previously, [Cp 2Re 2 (CO) 2 (NO) 2H] +X (X = BF^, PFg) i s r e a d i l y deprotonated with NEt^ to produce [CpRe (CO) (NO) ] 2 9 ° ( c c?- 39, p. 82) . • S i m i l a r l y , a-variety of bases are known to deprotonate the ca t i o n i c complexes [Cp 2M 1M 2 (CO) g H ] + (M1 = M 2 = Mo, W; M 1 = Mo, M 2 = W) to give the corresponding neutral metal carbonyls 1 2 4 , 1. e., [Cp 2M 1M 2 (CO) 6H] + + B — — - » lCp 2M 1M 2 CC0)1&] + IIB+ (50) The hydrido c a t i o n !Cp2Pe.2 CCOJ^K]+' also reacts- r e a d i l y with. NEt 3 to y i e l d the related dimer, {CpFe (CO)„2] 2 • I : n sharp 132 -contrast, reaction of a CH^CT^ suspension of [Cp2W2 (.NO) 4 H ] + with. NE.t3 rapidly; r e s u l t s in. the formation'. o,f CpW (NQ). 2H. and, presumably, lCpW~(NO)I.2 (JNEt^ D Stronger bases such, as (Me 2N) 3P0, KOH/EtOH, and Ph3P=CH2 likewise bring about very rapid cleavage of the: metal-metal bond to produce the ubiqui-tous CpWCNOl2H: and the corresponding ca t i o n i c products, i . e . [Cp2W2 (NO) 4H] + + L * CpW(NO)2H + [CpW(NO) 2L] + (.46) (L = a 2e donor) With the highly s t e r i c a l l y hindered base N,N,N',N',-tetra-methyl-1,8-naphthalenediamine (sold by A l d r i c h Chemical Co. under the trade name Proton Sponge) reaction 4 6 requires several hours, but once again no deprotonation occurs and CpW(.NO)2H i s formed. In nitromethane, where both the tungsten cation and Proton Sponge are soluble, [Cp2W2(NO)4H] + i s rapidly cleaved to give CpW(NO)2H as indicated by 1H NMR spectral monitoring. This may involve CD 2N0 2 as the nucleo-p h i l e , however, as nitromethane. i s a r e l a t i v e l y ^acidic solvent, pKa = 1 0 1 2 5 . In several of the reactions mentioned, the formation of a cati o n i c product of the general formula [CpW(NO) 2L] + i s i nferred on the basis of the IR spectra of the reaction mixtures and the successful i s o l a t i o n of CpW(NO)2H as a reaction product. No attempts were made to i s o l a t e these cations as they are known to be quite reactive, and previous attempts to i s o l a t e s o l i d PF^ s a l t s of the cations-[CpW(NO) 2 (CH3CN) J + and [CpW(NO)2( (CH 3) 2CO}] + by other workers ^ 133 -were u n s u c c e s s f u l 1 0 1 , The addition of a, THF solution, of sodium*-naphthal.ene to a s o l i d sample of [Cp 2W 2(NO) 4H]PF g affords a small amount of CpW'CN0l2H: along with- a n i t r o s y l — f r e e red—brown s o l i d . Reaction, of [Cp2W2 (NO) 4H] with NaBH4 i n nitromethane r e s u l t s i n the reduction of the cation to again produce CpW(NO)2H, i . e . CH-NO„ [Cp2W2 (NO)4H] PF 6 + NaBH4 i-* 2CpW(N0) 2H (51) Treatment of the cation with, the Lewis base Cp 2MoH 2 unexpect-edly r e s u l t s i n the decomposition of both species to produce a red-brown, n i t r o s y l - f r e e s o l i d which i s insoluble i n common organic solvents. The in t e r a c t i o n of a CH 2C1 2 suspension of [Cp 2Mo 2-(NO)4H]PFg with a column of F l o r i s i l ( i . e . magneslum f l u o r o -s i l i c a t e ) r e s u l t s in the formation of monomeric products analogous to those formed by the tungsten system. Thus eluti o n of the column with CH 2C1 2 gives a green CH 2C1 2 solu-t i o n of CpMo(NO)2H, as i d e n t i f i e d by i t s n i t r o s y l CV N Q 1732, 1642 cm "*") and metal-hydride (-VM H 1805 cm 1) IR stretching frequencies. This method of preparation of CpMo(NO)2H allows the detection of the weak Mo—H absorbance whereas the pre-viously described route involves the use of toluene as solvent, which obscures this;peak. Removal of the CH 2C1 2 under reduced pressure at low temperature C< 0 GC) r e s u l t s i n some decomposition, of the hydride, but does- allow- a switch, to C C D ^ 12CO as solvent, thereby permitting the acquisition, for - 13 4 -the f i r s t , time of a NMR; spectrum o,f the complex.„ A sharp s i n g l e t attributable, to the cyclopentadienyl protons- is- found at 6' 6.A3 C5H) while the hydride resonance is- found at <$' 3.8 0 C1H)1; as for CpWCNOl^H;51 , the hydride resonance occurs- at unusually low- field,. The addition of acetone to a CD^NC^ solution of [Cp 2Mo 2CNO) 4H]PFg with concomitant monitoring of the 1E NMR spectrum of the mixture reveals no in t e r a c t i o n between the various acid and base species, in contrast with the tungsten complex. However, with the bases NEtej and Proton Sponge rapid cleavage of the bi m e t a l l i c cation to produce CpMo(NO)2H and, presumably, [CpMo (NO) 2L] + , : ' i s observable. Summary of the Properties of [Cp^-^M,, (NO) ^ H] + (M^ = M 2 =  Mo, W; M± - Mo, M 2 = W). To summarize, the solution properties of the [Cp 2M 2(NO)^H] + cations are as follows. 1E NMR spectroscopy i s consistent with these compounds being Lewis acid—Lewis base adducts, with the metal possessing the terminal hydride ligand functioning as a formal Lewis base and providing electron density from a metal-centred o r b i t a l to a vacant o r b i t a l , also metal-centred, of the formally 16e~ CpM(NO)_2+ portion of the molecule. At a rate that i s rapid on the NMR time scale ( i . e . k greater than about 4 00 sec "*") at ambient temperature, the hydride ligand i s exchanged between the two metal centres, thereby reversing t h e i r acid—base, r o l e s i n the complex. Simultaneously, at a rate that i s slow on the. NMR time scale ( i . e . k less than about 300 sec ^). but s u f f i c i e n t l y T. 1,3 5 T. rapid that, equilibrium between, the. dimolybdenum and didlingsten, cations is- established within, the time: required to dissolve the compounds and obtain a spectrum (>5 min), the; acid-base pairs are e q u i l i b r a t i n g with, each other, probably v i a a d i s s o c i a t i v e pathway-, I An associative mode of exchange seems un l i k e l y for s t e r i c reasons,] The concentration of the proposed monomeric species shown in equation 52 must be very low, however, as- the species CpM(NO)2H and/or CpM(NO) 2 + are not detectable i n the solution 1H NMR spectra of the complexes: [Cp2W2 (NO) 4H] + - - CpW(.NO)2H + CpW(.NO)2 + [Cp„Mo 0 (NO) „H] + « ^ CpMo (NO) „H + CpMo (NO) * Z Z 4 Z Z ( 5 2 ) [Cp2MoW (NO) 4H] * 5 CpMo(NO)2H + CpW (NO) 2 [Cp2MoW(NO) 4H] ^ CpW (NO) 2H + CpMo (NO) 2 Even upon addition of weak donors such as o l e f i n s or THF no evidence of i n t e r a c t i o n can be observed. Nevertheless-, a v a r i e t y of C, N, and 0 bases do not deprotonate the bimet-a l l i c species; i n every instance monomeric products r e s u l t . This system i s thus i n marked contrast to the. cations [Cp 2Fe 2 (CO) 4H] +, [Cp 2Re 2(CO) 2(NO) 2H] +, and [ C p ^ ^ (CO). 6H] + (M^ = M 2 = Mo, W; M^ = Mo, M2 = W) i n which, the proton also int e r a c t s d i r e c t l y with the b i m e t a l l i c core, but the combined strength of the metal-metal l i n k and the a c i d i t y of the metal hydride are s u f f i c i e n t to allow deprotonation to the respec-t i v e dimers by a v a r i e t y of bases. Although apparently no attempt has- been made to - 136. T - , deprotonate. {Cp 2Ru 2 (COl^Hj , it. can. also, be. prepared by-pro ton.ation, of the: neutral; *dimer? 2-e» H^rNM^ R, studies of the protonation of the neutral dimer s- [Cp 2M 2 (CO) ^ ] (M = Fe, Ru) y i e l d equilibrium constants- K"2 for the protonation reaction,, equation 53, of 10 -^" ^  L mol 1 for M = Fe and a [Cp 2M 2 CCO);4] + H 2S0 4 , [Cp 2M 2 CCO)4H] + [HS0 4]" (53) { [Cp 2M 2 (CO)4H] + [HS04] "} (M = Fe, Ru) K 2 . { [ C p 2M 2 ( c o). 4]}{H 2S0 4} 2 -1 ' lower l i m i t of ~10 L mol for the Ru compound. Poten-tiometric studies, carried out only for M = Fe, y i e l d a pK^ of 7.5 ± 0.3 for [Cp 2Fe 2 (CO) 4] . It i s thus apparent that the Ru complex i s s i g n i f i c a n t l y more basic than the iron system. In l i g h t of t h i s observation, i t becomes of intere s t to see whether t h i s trend c a r r i e s over to the n i t r o s y l analogues. Attempted Synthesis of [Cp 2Cr 2(NO) 4H] +. In hope of preparing the corresponding chromium cation, [Cp 2Cr 2(NO) 4H] +, dichloromethane solutions of [CpCr(NO) 2] 2 can be treated with aqueous solutions of either HPFg or HBF 4«OMe 2. S t i r r i n g brings about a rapid colour change i n the CH 2C1 2 layer from i t s i n i t i a l dark purple to a golden yellow colour. Solvent removal followed by c r y s t a l -l i z a t i o n attempts unfortunately f a i l to y i e l d a c r y s t a l l i n e s o l i d for either product. Metathesis of the counterion v i a addition of NaBPh4 to aqueous solutions of either compound affords a flocculent yellow s o l i d which, upon c r y s t a l l i z a t i o n , - 1.37 -yields.- C, K, and N analyses-which., when, examined along with, the *H NMR and PR spectral data, f a i l to suggest, any reason-able chemical formulation. The novel complex is- a green s o l i d (mp 119-20QC) which, i& s l i g h t l y soluble i n benzene and has- good s o l u b i l i t y in CH 2C1 2 and in donor solvents- such as (CH^). 2C0 and THF. An. IR spectrum of i t s CH 2C1 2 solution exhibits strong absorp-tions at 1828 and 1721 cm 1 , attributable to terminal n i t r o -s y l groups 1 2 2 ., A 1H NMR spectrum of the complex i n (CD3) 2C0 indicates- the presence of two inequiValent cyclopentadienyl rings: (.6 6. 06 (s, 5H) and 5.68 (>, 5H) ) and a metal-bound hydrogen CS —5,3 5 Cs-, I f f ! I; the presence of small singlets-on the low- f i e l d side of each, of the cyclopentadienyl reson-ances- suggests that there are two isomers- present i n solution. Two tetraphenylborate ions- are present CS 6.8+1..6 (m, 4 0.H'H per pair of cyclopentadienyl rings. The addition of D2<D to the sample produces no change in i t s 1H NMR spectrum, there-by indicating the absence of strongly a c i d i c protons. S i m i l a r l y , IR spectral monitoring of the treatment of C H 2 C l 2 solutions: of the complex with. NEt^ and with Ph3'P=CH.'2 reveals no in t e r a c t i o n between the chromium complex and these bases. Thus far attempts to obtain a pure sample of t h i s compound with a counter ion other than BPh^ have, been unsuc-c e s s f u l , as have attempts- to grow single crystals- of the BPh^ s a l t . No molecular structure consistent with, the: presently available information i s readily- apparent. In light, of the resistance of the complex to deprotonation, the T*1 138 -aH: NMR data, and the elemental;. ratios- found, .it does seem certai n that [Cp 2Cr 2 CNOL4H3 is- not formed by protonation, of [CpCr (NO) 2^2" When [CpCr CNO)!2J 2 i s protonated with, the coordinating acid p-CH^CgH^SO-jH, the dimer i s ra p i d l y cleaved to y i e l d CpCr (NO) 2 C0 3SC 6H 4~pCH 3) , the W analogue of which, has been previously reported 5: 1 . If less than two equivalents of acid are added, only the unreacted dimer and the f i n a l product are observed i n the IR spectra of the solution; no intermedi-ates are detected. CpCr(NO) 2C0 3SCgH 4-pCH 3) can be isolated by p r e c i p i t a t i o n with hexanes to y i e l d an a i r - s t a b l e green s o l i d (mp 64-6°C) whose solution IR spectrum C v N 0 (Cr^C^) • 182 9, 1722 cm "*") i s consistent with the presence of two terminal n i t r o s y l groups. I t s 1H NMR spectrum i s completely consistent with, the presence of a pentahapto cyclopenta-dienyl ring (_$ CCDC13): 5.7 5 Cs, 5H) ) and a p-toluenesul-fonate ligand QS 7.7 2 Cd, 2.H) , 7.21 Cd, 2H) , and 2.3 6 Cs, 3H)) Its low-resolution mass spectrum (.see Table VIII) confirms the monomeric nature of t h i s complex. The Interaction of CpWCNO^H With. Lewis Acids. One pot e n t i a l way to gain an insight into the basis of the differences i n s t a b i l i t y found upon comparing the Mo and W n i t r o s y l hydride cations to the Mo, W, Re., Fe, and Ru hydrido cations discussed previously i s to investigate, the Lewis base properties of CpWCNOj^H and the Lewis- acid prop-erties- of CpW (NO) 2 +1 and then make comparisons with, t h e i r carbonyl counterparts.. - 139 -T a b l e V I I I . L o w - R e s o l u t i o n Mass S p e c t r a l D a t a f o r CpCr (NO) 0 CO, S C 6 H 4 - p C H 3 ) a m/ z R e l abund. A s s i g n m e n t 318 8 ( C c H _ ) C r (NO) (0 oSC_H_) b o 3 11 288 100 ( C 5 H 5 ) C r ( 0 3 S C y H 7 ) + 224 16 ( C 5 H 5 ) C r ( O C 7 H y ) + 206 7 ( C 5 H 5 ) C r ( C 7 H 5 ) + 133 18 ( C 5 H 5 ) C r O + 117 18 ( C 5 H 5 ) C r + The a s s i g n m e n t s i n v o l v e t h e most a b u n d a n t n a t u r a l l y o c c u r r i n g i s o t o p e s i n e a c h f r a g m e n t . A l s o o b s e r v e d a r e m e t a s t a b l e p e a k s M* a t m/z v a l u e s o f 174 and 190, c o r r e s p o n d i n g t o t h e f o l l o w i n g f r a g m e n t a t i o n p r o c e s s e s : (C 5H,-)Cr ( 0 3 S C 7 H 7 ) + • ( C 5 H 5 ) C r ( ° C 7 H 7 ) + + { s 0 2 ^ (,C 5H 5)Cr ( 0 C ? H 7 ) + » ( C 5 H 5 ) C r ( C 7 H 5 ) + + {H 20} 140 -In, examining the, inte'ract.ion. of Lewis- acids with. CpWCN'Ol^HT, i t is- Important t o keep in.-mind the p o s s i b i l i t y of coordination occurring' at any of a v a r i e t y of sites-.. Thus Lewis- acids- are known to interact with t r a n s i t i o n metal complexes- to form adducts- v i a both, the metal centre and the ligands.. The mode of reaction i s dependent upon the r e l a r 1 tive. b a s i c i t i e s of the metal atom and the ligands-, as well as the nature of the acceptor and the solvent. The same t r a n s i t i o n metal complex can intera c t i n d i f f e r e n t ways with d i f f e r e n t Lewis acids; competition between s i t e s r e s u l t i n g rn the simultaneous formation of adducts of d i f f e r e n t types i s also possible. At present, extensive q u a l i t a t i v e data concerning the b a s i c i t y of t r a n s i t i o n metal complexes are a v a i l a b l e 1 2 7 , but there are v i r t u a l l y no quantitative data based on the study of the k i n e t i c s and thermodynamics of t h e i r i n t e r a c t i o n with e l e c t r o p h i l e s . The structure of acid-base adducts i s usually arrived at sol e l y on the basis of spectroscopic data, with the equilibrium position being inferred q u a l i t a t i v e l y from such data. The r e l a t i v e b a s i c i t i e s of complexes- can be established i n accordance with the occurrence or non-occur— rence of an inte r a c t i o n with a standard Lewis acid under i d e n t i c a l conditions. Complexes containing the. CO ligand have been, most widely investigated because, the. CO stretching frequencies are extremely sensitive to changes i n the electron, density at the metal. The inte r a c t i o n of an acceptor molecule with. - 141 T> the central -metal atom, leacls- t© an. increase 0 f the. stretchy ing frequencies- of the CO groups.. This- is- associated with, the decrease of the electron dens-ity at the metal atom which brings- about a weakening of the d^ . (M) -•p,^  (CO) backbonding and an increase of the CO bond order i n the complex. Such, a frequency- s h i f t (generally 100->150 cm "*") i s believed to be. a c h a r a c t e r i s t i c feature of the involvement of the metal atom i n coordination to the Lewis a c i d 1 2 7 . Other types of coordination of an acceptor lead to quite d i f f e r e n t changes i n the IR spectra. In adducts involving coordination at a ligand other than CO, the electron density on the metal centre i s again reduced, but to a smaller extent; consequently the observed hypsochromic s h i f t i s generally smaller. However, coordina-t i o n of the Lewis acid to a hydride ligand i s u n l i k e l y as i t possesses no lone pair of electrons; few metal—H-metal l i n k s i n the absence of metal-metal bonding are known 1 1 6' 1 2 8. Addition to a cyclopentadienyl r i n g , while common when the e l e c t r o p h i l e i s H + or a carbonium ion, i s uncommon for other e l e c t r o p h i l e s . Another type of i n t e r a c t i o n of Lewis acids with t r a n s i t i o n metal complexes involves the formation of adducts v i a a non—bonding pair of electrons on one of the ligand atoms-, eg., the 0 atom of the NO groups i n CpW (NO) 2H. Inter-action of the e l e c t r o p h i l e with, the; n i t r o s y l ligand is-c h a r a c t e r i s t i c of the hardest Lewis acids, t y p i f i e d by 7 boron and aluminum d e r i v a t i v e s 1 2 7 , as well as lanthanide - 142. complexes 1 5.„ Interaction, wifchv/te^^ina/l CQf N'2 f or NQ ligands, leads to a s i g n i f i c a n t decrease: of'tRe stretching -vibration. frequency- of the coordinated group and to an increase of the stretching v i b r a t i o n frequencies- of those ligands- not attached to the e l e c t r o p h i l e . For example \>CQ = 192 9 and 2 011 cm 1 and v N Q = 1660 cm"1 for CpW(CO)2(NO) i n CH 2C1 2 solution, while v„„ = 2010 and 2055 cm 1 and v„T^ - 1450 cm 1 for CO NO CpW (CO) 2CN0^A1C1 3) 1 2 9. However, absorptions attributable to a given ligand are not always independent ( i . e . t h e i r v i b r a -tions are coupled). , and thus adduct formation v i a one n i t r o -s y l (or CO, etc.) may not r e s u l t i n an increase i n the other related v i b r a t i o n frequencies. For example, for CpCr(NO) 2C1 v N Q - 1818 and 1712 cm - 1 while for CpCr (NO) ( C D CNO+ErCp3) v A T •= 1786 and 1688 cm" 1 1 5. NO As CpW(NO)2H interacts with the Lewis acids CpM(NO) 2 + (M = Mo, W) v i a the metal centre,(possibly with concomitant inte r a c t i o n with the hydride ligand to y i e l d a bridged prod-uct) , i t i s l o g i c a l to f i r s t examine i t s i n t e r a c t i o n with soft Lewis acids, which are also expected to coordinate at the metal c e n t r e 1 2 , Ca) The Interaction of CpW (NO) 2H With. M (CO) CM = Cf, W)  and With (MeCp)Mn (CO) 2 . Cr (CO) 6 , W(CO) 6 , and (MeCp)Mn (CO) 3 each, lose one carbonyl ligand upon UV i r r a d i a t i o n i n tetrahydrofuran. solution to y i e l d Cr CCO) 5 (THF)., WCCO) 5 (THF) , and (MeCp)Mn-(CO)2(THF) r e s p e c t i v e l y 1 3 0. In each compound, the THF ligand i s l a b i l e , thus providing a convenient source of a soft Lewis T. 143 T. acid; extensive use; ha^ Been made of these and s i m i l a r e l e c t r o p h i l e s to demonstrate the presence of base s i t e s i n a v a r i e t y of t r a n s i t i o n metal complexes 1 2 7. Due to the l a b i l i t y of the. THF ligand, however, these species cannot be isol a t e d but instead are generated and used i n solutions. As the CO released from one molecule may recombine to give the s t a r t i n g material, the THF adducts are t y p i c a l l y gener-ated by i r r a d i a t i o n with, a flow of an in e r t gas being passed through the solution to help purge i t of free CO. Even so, complete conversion i s not generally achieved; t h i s leads to uncertainty as to the actual concentration of the e l e c t r o -phile i n the solution. The presence of unreacted s t a r t i n g material also i n t e r f e r e s with the IR spectral monitoring of the carbonyl region. Thus i n the reactions with CpW(NO)2H, the n i t r o s y l IR absorptions provide the most accessible evidence of what interactions are occurring i n solution. As i s r e a d i l y apparent from the data displayed i n Table IX, comparable s h i f t s of the n i t r o s y l absorptions aris e from the i n t e r -action of CpW(.NO)2H with each of Cr(CO) 5, WCCO) g , and (MeCp)Mn CCO) 2 . That the new n i t r o s y l bands are at higher energies than those of free CpW(NO)2H immediately rules out i n t e r a c t i o n v i a the n i t r o s y l oxygen. The addition of CpW(NO)2H: to a -78°C solution, of orange Cr(CO) 5(THF)/Cr(CO) g produces an orange solution displaying four PR absorptions i n the n i t r o s y l region, att r i b u t a b l e to free CpW(NO) 0H Cv 1718, 1629 cm""1): as well - 144 -T a b l e IX. C h a r a c t e r i s t i c N i t r o s y l A b s o r p t i o n s o f CpW(NO) A d d u c t s . a -1 R e a c t i o n m i x t u r e ' CpW(NO) 2H C p W ( N O ) „ H + C r ( C O ) c ( T H F ) 2 D CpW(NO) 2H + W(CO) 5(THF) CpW(NO) 2H + (MeCp)Mn (CO) 2 (THF) [Cp 2W 2 ( N O ) 4 H ] P F 6 [ C p W ( N O ) 2 ] B F 4 b ' 1 0 4 CpW(NO) 2H + HBF 4-OMe 2 C p W ( N O ) 2 G l b ' 2 3 [ C p M o ( N O ) 2 ] B F 4 b [ C p M o ( N O ) 2 ( c y c l o o c t e n e ) ] B F 4 b [CpW(NO) 9 ( c y c l o o c t e n e ) ] BF b ' 1 0 "* 2 4 v N Q , cm 1718, 1632 1736, 1718, 1661, 1629 1738, 1717, 1663, 1631 1725 ( s h ) , 1718, 1661, 1634 1715, 1632 1762, 1675 1733, 1648 1733, 1650 1783, 1692 1800, 1717 1769, 1689 i n THF s o l u t i o n u n l e s s o t h e r w i s e s p e c i f i e d i n C H 2 C 1 2 s o l u t i o n ^ 14 5 T-, as to the adduct Cp (NO) - (H.) W*Cr (CO); _ fV.T~ 173 6 , 1,661 cm ) ,. 4- 2. 5 N O . • — No change i n the IF, spectrum is- detectable upon allowing the. solu t i o n to warm to room temperature.. Solvent removal under reduced pressure does- bring about further reaction, however, with much, of the residue obtained being no longer soluble i n THF. Fra c t i o n a l sublimation of the reaction residue at reduced pressure y i e l d s f i r s t Cr (CO)^ (either formed by reaction of Cr CCO)!,. with. CO freed during solvent removal, or present throughout the reaction sequence) and then, at s l i g h t l y higher temperatures, CpW(CO)2(NO). The absence of a, carbonyl absorption i n the region 2005-2050 cm - 1 i n the i n i t i a l reaction mixture r u l e s out the p o s s i b i l i t y that the n i t r o s y l absorption detected at 1661 cm 1 was i n fact a t t r i -butable to CpW (CO) 2 (NO) C v c o 2011, 1929 cm"1; v N Q 1660 cm - 1). Thus the following sequence of reations apparently occurs in the reaction mixture: -8 0 C; monitoring of the 1H NMR spectrum reveals only one cyclopentadienyl resonance, shifted to lower f i e l d , upon addition of less than one equivalent of Cr(CO)(THF) as a THF slurry, . The. observation of only one resonance, a t t r i b u -table to cyclopentadienyl protons requires that the. free, and complexed: CpW (NO) 2H species- are e q u i l i b r a t i n g at a rate that i s f a s t on the NMR time scale, even at —80.GC, i.e.. The reaction may also be carried out i n (CD )_„CO at - 14 6 — CpW(NO)2H. + Cr (CO) 5 (S) Cp (NO). 2 (H) W**Cr CCQ) 5 + S (S == CCD3 l2CO or THF); (55) Also consistent with, this- conclusion, is- the observation that the size, of the s h i f t is- dependent upon the amount of Cr CCOXg. CTHF-)! solution added, although, no s h i f t i s observed when THF i s added.. Unfortunately, the hydride resonance cannot be observed i n the presence of the excess THF. This i n i t s e l f argues against the Cr (CO)^ being coordinated to the hydride, however, since the few examples of metal-H-metal li n k s known a l l exhibit hydride resonances shifted to high f i e l d (eg. (CO )„ ^  Re—H-W (CO) , 6 R -14.4 1 1 6 vs. 6 -5.7 for Re(CO) cH 1 2 8 a) . The addition of CpW(NO)2H to a -78 QC solution con-, taining W(CO) (THF) brings about changes in the n i t r o s y l region of the IR spectrum which are almost i d e n t i c a l to those observed with. Cr (CO) 5 (THF) (see Table IX). Thus two n i t r o s y l absorptions are found at positions attributable to free CpW(NO)2H (V NQ 1717, 1631 cm "*") along with two additional bands at higher energy CV^Q 1738, 1663 cm "*") assignable to Cp (NO) 2 (H) W+W (CO) 5 . As additional CpW(NO)_2H i s added a l l four bands increase i n i n t e n s i t y but t h e i r r e l a t i v e inten-s i t i e s remain constant, again indicating that the free and complexed CpW (NO). 2H e n t i t i e s are in equilibrium. Warming the mixture to room temperature and concentration, of the solution i n vacuo bring about a s h i f t i n the equilibrium i n favour of the complexed hydride, but complete solvent removal brings about decomposition, to produce an. i n f r a c t — - 1.47;. -able brawn, s o l i d . Simply warming the original, solution to room temperature: under a nitrogen ^ atmosphere - a.lsp: i n i t i a t e s p r e c i p i t a t i o n of the brown..decomposition product, but at a much, slower rate ( x r v 2 days)!. The addition of a red THF solut i o n of (MeCp)Mn (CO) 2 ~ (THF) to a green, -7 8°C solution of CpW(NO)2H i n THF pro-duces no apparent i n t e r a c t i o n of the t r a n s i t i o n metal com-plexes as judged by the absence of new n i t r o s y l absorptions in the IR spectrum of the reaction mixture. Upon warming to room temperature, the red-green solution turns brown over a period of approximately 0.5 h and some p r e c i p i t a t e forms C (MeCp)Mn (CO). 2 CTHF) i t s e l f slowly decompses at room temperature 1 3 0). At t h i s point the supernatant solution exhibits four n i t r o s y l IR absorptions, at 1718 and 1635 cm 1 Ci.e. CpWCNO)2H) and at 1725 (sh) and 1661 cm"1 a t t r i b u t a b l e to Cp CNO)2 (.HlW^ -Mn (CO) 2 (MeCp) . Solvent removal under reduced pressure r e s u l t s i n the p a r t i a l decomposition of the mixture to produce an intractable s o l i d ; the soluble f r a c t i o n •/'[ exhibits IR absorbances at 2020, 1900 (br), and 1658 cm - 1 i n CH 2C1 2. Attempts to i s o l a t e this, product (apparently not a simple adduct) were unsuccessful. It has been noted i n the chemical literature, that i n some instances photogenerated species such as (MeCp)Mn(CO)2_ (THF) 1 3 1 (and presumably Cr (CO) 5 CTHF) and W(CO),- (THF) ) may contain, traces of impurities i n the solutions- which, catalyze the decomposition of the complexes prepared from these; solutions. To r u l e out t h i s p o s s i b i l i t y , Cr (CO) ,- QSIMe-, ) 2 0 : 8 - 14 8 -and (MeCp);Mn. (COL 2 CS-iPhJl C r i p 1 0 : 9 can. be. prepared and iso l a t e d , and the; analogous reactions with. CpW (NO) H: c a r r i e d out... The reactions- proceed very much as- do the. reactions- involving the THF species-, but unfortunately- decomposition of the CpW (NO) 2H adducts formed again occurs- upon removal of the solvent i n vacuo.. (b) The Interaction of CpW(NO)2H With MC12 (M = Zn, Cd, Hg). Numerous examples of Group IIB metal ( i . e . Zn, Cd, and Hg) halides interacting with t r a n s i t i o n metal complexes are known. There are no examples of coordination via 1 the lone pairs of ligands such as CO, NO, N 2, CN or halogen by Group IIB derivatives, although coordination of HgX2 to the sulfur atom of the CS ligand i s known 1 2 7. There i s also a pos s i b i l i t y - of the mercuration of iT-coordinated aromatic ligands with the formation of a C-HgX bond, which i s char-a c t e r i s t i c of ferrocene and CpM(.CO)3 (M = Mn or R e ) 1 2 7 . A p a r t i c u l a r l y relevant example of acid-base complex formation i s provided by the inte r a c t i o n of the Group IIB halides with Cp 2MH 2 i n THF to y i e l d the adducts Cp2MH2•EX2•THF (M = Mo, W; E = Zn, Cd, Hg; X = C l , B r ) 1 3 2 . In each instance the adduct forms i n v i r t u a l l y quantitative y i e l d , with the product p r e c i p i t a t i n g from solution. Thus equimolar amounts of Cp 2MH 2 and EX 2 can be weighed out, mixed, and then d i s -solved i n THF; the. adduct r a p i d l y p r e c i p i t a t e s from solution (for CdCl 2, because of i t s low s o l u b i l i t y , the. hali.de; i s dissolved f i r s t and then added to the dihydride)... A c r y s t a l structure of the derivative Cp0MoH0 • ZnBr 9 -DMF confirms- the 1-4 9 -existence. o.f a Mo—Zn bond,. The: same: procedure:, when, applied to CpW (NO). 2H/ y i e l d s d i f f e r e n t results-.. I.h the presence of a two-fold excess- of Z n C l 2 , no PR spectral evidence of coordination to CpW'(NOl.2H: i s detectable:.. Over a period of two days, the .-r slow growth, of poorly resolved shoulders i s observed on the high, energy side of the n i t r o s y l IR absorptions of CpW (NO) H . Removal of the solvent r e s u l t s i n some decomposition occur-ring; extraction of the red-brown residue with CDCl^ provides a solution whose 1H NMR reveals the presence of CpW(.NO)2Cl (6 6.17) in addition to unreacted CpW(NO)2H (6 6. 00 (s, 5H) and 2.07 (s, IH)), i . e . CpW(NO)„H + ZnCl„ ^ CpW (NO) H • ZnCl„ * V (56) CpW(NO)2Cl + 'ZnCl' This, i s consistent with the TR spectral observations, as CpW(NO)2Cl displays n i t r o s y l absorptions at s l i g h t l y higher energy ( v N Q 1728, 1647 cm - 1) than does CpW(NO)2H ( V N 0 1717, 1636 cm "*") . That the chloro complex does not arise as a r e s u l t of the p a r t i a l decomposition which occurs during solvent removal can be confirmed by carrying out the reaction in (CD 3)2 C O a n d monitoring the 1H NMR spectrum. This exper-iment demonstrates the slow formation of CpW(NO)2C1 (>15% conversion i n 11 h. at ambient temperature) in. the absence of any detectable decomposition. It also reveals- a small but s i g n i f i c a n t s h i f t to low f i e l d of. the resonances attributable: to the cyclopentadienyl and- hydrido protons- CA: 4,8 ± 0...3 and 15 0 7,8 ±. Q-,.3 Hz, respect i y e l y l of CpVTCNOL^ H;, a, fea,ture CQn.sist.T-ent with, transient adduct ifo-rmation. A, 'reversible i n t e r -action with, the cyclopentadienyl r i n g is- u n l i k e l y , so t h i s s h i f t presumably- reflects- an interaction of ZnCl^ at the metal centre.. In the presence of CdCl 2, no coordination to CpW (NO) 2H i s detectable by IR spectral monitoring. After two days at ambient temperature, the CpW(NO)2H i s recoverable in v i r t u a l l y quantitative y i e l d ; there i s no evidence of any reaction. The addition of THF to an equimolar mixture of CpWCNO)2H and HgCl 2 gives, b r i e f l y , a clear solution. The solution r a p i d l y becomes cloudy, however, followed by the p r e c i p i t a t i o n of a white s o l i d . After 1.5 h at ambient tem-perature, CpW(NO)2Cl ( i d e n t i f i e d by i t s spectral properties and by elemental analysis) can be isolated i n good y i e l d from the reaction mixture. Qualitative testing i d e n t i f i e s the p r e c i p i t a t e formed as HgCl. A r e p e t i t i o n of the reaction at -78°C with several attempts to obtain an TR spectrum of the i n i t i a l product y i e l d s only spectra indistinguishable from that of CpW(.NO)2Cl. Repetition of the reaction at -8 0°C i n (CD^^CO with. 1H NMR monitoring reveals a large s h i f t to low f i e l d of the cyclopentadienyl and hydrido resonances CO.3 0 and 2.4 0 ppm respectively) . Warming the sample to O^ C results- i n broaden-ing of the peaks (as a r e s u l t of the formation of a p r e c i p i -tate in the sample tube! and a s h i f t i n g of the cyclopenta-dienyl resonance to higher f i e l d while the hydrido resonance. - 15-1 -loses i n t e n s i t y and is- eventually lost, in, the: baseline, noise... I t therefore appears that CpW (NO) 2H interacts- with HgCl 2 to form i n i t i a l l y ^ an adduct (presumably- of the type Cp(NO) 2 (H)W-*HgCl2-S; S = THF or acetone) , which, subsequently reacts- further to produce CpWXNO)2Cl, HgCl, and presumably 1/2H2, i . e . CpW (NO) „H + HgC 1 9 <^r Cp CNO) (H) W—»HgC 1 0 • S -8Q°C ( 5 7 ) (S = THF or acetone) Cp(NO) 0 (H)W—*HgCl9-S — - + CpW(NO)„Cl + HgCl Z 1 C58I + {1/2H2} Unfortunately, reaction 58 occurs too r a p i d l y to allow an IR spectrum of the adduct to be obtained. The f a i l u r e of CpWCNO)2H to form strong adducts with either Z n C l 2 or CdCl 2 r e f l e c t s a limited a b i l i t y on i t s part to act as a Lewis base, as s t e r i c factors are not l i k e l y to be a factor i n l i g h t of the va r i e t y of ele c t r o p h i l e s shown to i n t e r a c t with the metal centre. The conversion of CpW(NO)2H>adduct to CpW(NO)2Cl contrasts sharply with the known s t a b i l i t y of the Cp2MH2• EX 2• THF adducts.. I t i s possible that the rapid p r e c i p i t a t i o n of the Cp 2MH 2 complexes from solution prevents further reaction. In passing, i t may be noted that two additional reactions aimed at the formation of adducts unexpectedly lead only to decomposition products. The treatment of toluene and hexanes solutions of CpW(NO)2H with Pt(PPhO 3 and BEt_ re s p e c t i v e l y y i e l d only n i t r o s y l - f r e e decomposition, products,, (cl; The Reaction of" CpW^NO^H: With: tr*'.. Protonation of t r a n s i t i o n metal complexes- is- known to be quite, a general reaction, with, the possible sites- of attack, being o l e f i n i c or ^ —aromatic ligands, the metal centre, or other ligands- (eg.. ^ CO '+• H + —\> ^COH + 1 3 3 ) . When a metal centre possesses a lone pair of electrons, protonation at the metal i s a common means of demonstrating i t s presence. Some hydrido t r a n s i t i o n metal complexes are re a d i l y protonated to give quite stable derivatives, as i s the case for - Cp^ReHl1 3 a n d Cp2MH2 (M = Mo,,. W) 13 5. Others, require very strongly a c i d i c environments. For instance, C p W ( C O ) i s not protonated in t r i f l u o r o a c e t i c acid, but can be protonated in BF^,H20—CF^COOH to give CpW(CO) 3H 2 + 1 1 7. S t i l l other complexes are believed to undergo protonation at the metal centre, but hydrogen evolution follows so rap i d l y that no spectroscopic evidence for protonation can be obtained (eg. CpMo(CO) 3H + H + —»- CpMo (CO) 3 + + H 2 1 1 7 ) . The factors which, determine whether or not hydrogen evolution w i l l occur upon, protonation are not f u l l y understood, but i t i s clear that, going down a group of is o s t r u c t u r a l complexes, the protonated species gain k i n e t i c s t a b i l i t y against loss of TT 117 H 2 Prot.on.at.ion. of CpWCNO)„2H: with, l e s s than Q.„5 equiva-l e n t s of HBF 4«OMe 2 i n CD 3N0 2 at -2 0®C results- i n the immedi-loss- of E 2 to produce CpW (NO) 2 , as evidenced by- the appear-ance of 1H: NMR resonances att r i b u t a b l e to [Cp9W0 (NOI^H] , - 1 5 3 -l y e . . . CpW'(NO).2H + H + . --i » {CpW (NO) 2 H 2 + ^ T^~ T^ cpw(No 1 2 + •+ { H 2 } (5 9); CpW(.NO)2+ + CpW(NO)2H [Cp2W2 (NO) ^ H] + (€01 Upon warming the sample to room temperature, the bim e t a l l i c cation i s l o s t , however; t h i s presumably arises because of the Me20 present in the reaction mixture. With H^SO^ as the acid, protonation i s again immediate, but the bime t a l l i c 2-cation does not form i n the presence of SO^ . The clean appearance of a single peak i n the 1E NMR at 6 6.35 in CD 3N0 2 solution instead suggests the formation of [CpW-(NO). 2] 2so 4. The protonation of CpW(NO)2"H in CH 2C1 2 solution with HBF4*OMe2 produces a stable green solution exhibiting IR spectral absorptions shifted to higher energy ( v N Q s h i f t from 1718, 1632 cm"1 to 1733, 1648 cm" 1). While the s t a b i l -i t y of the res u l t i n g solution suggests the formation of [CpW(NO) 2(OMe 2)] + (CpW(NO)2+ i s known to be very u n s t a b l e 1 o h ) , the position of the IR absorbances suggests the formation of CpW(.NO)2Cl ( v N 0 1733, 1650 cm" 1 1 6) in the IR c e l l (NaCl windows) as has been noted previously with [CpW (NO) 2 ~ . . . (CH 3CN1] + 1 a i . •(;d): The Reaction of CpW(NO)2H With A i d . , ^ Like. H; , A1.C13 i s a strong, hard Lewis- acid , Thus-, unlike the Group ITB metal chlorides- discus-sed previously-, A1C1 3 might be expected; to form an adduct with, a n i t r o s y l 0 - .153 -atom which, i s : e x p e c t e d t o Be: the; h a r d e s t Base s i t e - in. the. molecule.. Numerous- examples- ©.£.. the; f o r m a t i o n , o f i;s©carB©nyl l i n k a g e s - have. Been documented. 1 2 7. I t i s - t h e r e f o r e somewhat s u r p r i s i n g t h a t no e v i d e n c e o f adduct f o r m a t i o n , i s - o B s e r v ed B y e i t h e r J-R o r 1H: NMR spectroscopy- when CpWCNO^H" i s r e a c t e d with. 1 e q u i v a l e n t o f A l C l ^ . That t h e s e two compounds do r e a c t t o produce CpWCNO) 2 C 1 o v e r a p e r i o d o f a p p r o x i m a t e l y 3 0. m i n u t e s a t amBient t e m p e r a t u r e i s l e s s s u r p r i s i n g i n l i g h t of t h e r e s u l t s d i s c u s s e d e a r l i e r . ( e l Summary and C o n c l u s i o n s On t h e B a s i s o f t h e aBove e x p e r i m e n t s i n v e s t i g a t i n g the. L e w i s Base p r o p e r t i e s o f CpW(N0) 2H as w e l l as t h o s e r e l a t i n g t o t h e Lew i s a c i d i t y o f CpM(NO) 2 + (M = C r , Mo, and W) d e s c r i B e d here and e l s e w h e r e 1 0 1 * ' 1 3 6 , i t i s p o s s i B l e t o c a t e g o r i z e t h e s e s p e c i e s . A m e t a l - c e n t r e d p a i r o f e l e c t r o n s from CpW(NO) 2H has Been shown By s p e c t r o s c o p i c methods t o compete s u c c e s s f u l l y f o r t h e Lew i s a c i d CpW(NO) 2 + a g a i n s t t h e v e r y weak Lewis Bases BF. , PF, and CH„C1„ as w e l l as a g a i n s t more conven-4 b 2. z t i o n a l L e w i s Bases such as propene, c y c l o o c t e n e , and even THF. I n t h e presence o f ~1 e q u i v a l e n t o f t h e above-mentioned L e w i s Bases, no f r e e CpW(NO) 2H c o u l d Be d e t e c t e d By 1 H NMR in. CD3N.Q2 s o l u t i o n s ' c o n t a i n i n g lCp . 2^2_CNQl 4H] .. With, s t r o n g e r L e w i s Bases- (eg, N E t 3 , Proton. Sponge, Harpoon. Base, HMPA, ph 3P=CH 2, KOH/EtOH, o r magnesium f l u o f o s i i i c a t e l the. 'C B i m e t a l l i c c a t i o n i s - c o m p l e t e l y d i s s o c i a t e d , d e m o n s t r a t i n g th e i n a b i l i t y o f CpWCN0)„K t o compete with, t h e s e h a r d L e w i s - 1 5 5 ^ bases:.. The hydride is- found to compete: with. THF for the, soft Lewis acid sites- of (MeCp)Mn (CO) 2 , Cr (CO) 5 , and W(CO) 5 in. THF solution, where: roughly half the acid sites- are occupied by- CpW (NO) 2H i n each instance Cby TR) even though a thousand-fold excess of THF i s present. Also, although CpW(NO)2H competes i n e f f e c t i v e l y with one equivalent of (CH 3L 2CO for the Lewis acid CpW(NO);2+ in CD 3N0 2 solution, i t i s somewhat successful i n competing for Cr(.CO)^ in (CD 3) 2CO solution. In THF solution CpW(NO)2H interacts f a i r l y strongly with the soft Lewis acid HgCl 2 (as adjudged by the magnitude of the s h i f t s of the 1H NMR resonances), yet with the i s o e l e c t r o n i c ZnCl 2 (considered intermediate between hard and soft in i t s Lewis acid p r o p e r t i e s 1 2 ) an inte r a c t i o n i s barely detectable by 1E NMR, and no i n t e r -action with the hard acid A l C l ^ can be detected. These observations are a l l consistent with the conclusion that CpW(NO)2H functions as quite a soft Lewis base. It i s not found to inter a c t with hard Lewis acids (even v i a the n i t r o s y l oxygens) except i n cases where reac-r t i o n occurs (eg. H +, A l C l ^ , and BEt^). . CpW(NO) 2 + on the other hand appears to i n t e r a c t only very weakly with weak bases such as o l e f i n s or CO 1 0-. Derivatives involving better cp-donating ligands such, as PPfi^, SbPh 3, AsPh 3, PCOMe)3, or P CQPhJ 3 1 0 , iC CR, a,lkyi. ©r 4 aryl) 7 a, and x"~ (X = C l , Br, and I ) 1 0 1 are more stable. The f i r s t transition-series- analogue, CpCr CNO) „ +, has-very - 1 5 6 -recently been, reported 1 3 G to form an adduct;. with. PFg , indic a t i n g that i t i s a very hard Lewis aci d . Like CpWrCN.O^ '" (cyclooctene) + 1 Q't, CpCr (N0) 2 (FPFD i s apparently stable. in the presence, of the very weak, base CO; r t i s also unreactive towards: styrene, With, better donors such as CH^CN, CgH^CN, p-CH 3C 6H 4NH 2, C&H1 ; LNC, and (,CH3) 2C0 adduct formation i s observed. Although derivatives of the type CpW(NO)2X, where X i s BF^ or PF^, have as.yet defied i s o l a t i o n , i t seems l i k e l y that, l i k e CpCr (NO) 2 + , CpW(NO)2 + i s a strong, hard Lewis acid. I t thus seems reasonable to r a t i o n a l i z e the observed l a b i l i t y of the [Cp 2M 2(NO)^H] + unit on the basis of the w e l l -documented incompatability of hard Lewis acids with soft Lewis b a s e s 1 2 ' 1 2 7 . Although r e l a t i v e l y stable i n the pre-sence of weakly coordinating solvents and counterions, the. metal-metal bond i s very r a p i d l y cleaved upon the addition of stronger Lewis bases, thus precluding the desired depro-r tonation reaction. It therefore seems u n l i k e l y that the f a i l u r e to obtain the desired dimers, [CpM (NO) 2] 2, by t h i s route r e f l e c t s any inherent i n s t a b i l i t y of these compounds. Although the evidence suggests that the hydride, ligands i n the [Cp2M^M2 (NO)^H] + complexes are terminally bound, t h i s evidence i s not conclusive. However, the con-clusions concerning the Lewis acid and base properties of the constituent fragments of these cations would be unaffec-ted i f the hydride ligand i s i n a bridging position; only the r a t i o n a l i z a t i o n of the i n s t a b i l i t y of the. b i m e t a l l i c 1.57- -cations, toward donor molecules: is- dependent upon. the. l o c a t i o n of the hydride l i g a n d . - 158 -EPILOGUE When t h i s research was begun, a prevalent point of view was that n i t r o s y l ligands are largely u n r e a c t i v e 1 k , although t h i s conclusion was based almost e n t i r e l y on expe iments performed on coordination complexes. The r e s u l t s presented here demonstrate that i n organometallic compound a great variety of coordinated ligands are p r e f e r e n t i a l l y attacked by nucleophiles i n the presence of the n i t r o s y l ligand. However, in the absence of other reactive s i t e s , n i t r o s y l ligands have, themselves been shown to undergo attack by various reagents ( i . e . by NO, NaBH^, LiEt^BH, BH NaAlH 2(OCH 2CH 2OCH 3) , and BEt^) to lead to a v a r i e t y of products. While the objectives i n the introduction have been achieved, much further work w i l l be required to f i n d systems which can be put to use i n d u s t r i a l l y . Although the acid-base properties of organometalli carbonyl complexes have been, and continue to be, studied extensively, few investigations of n i t r o s y l complexes have been car r i e d out. The current study of CpW(NO)2H reveals the hydride ligand to be s u r p r i s i n g l y reactive i n the presence of the n i t r o s y l ligands, and unexpectedly reveals that both hard and soft Lewis acids p r e f e r e n t i a l l y form adducts at the metal centre. 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