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Vol. 85
COMMUNICATIONS T O THE EDITOR Five-Coordinate Hydrido-Carbonyl Complexes of Rhodium and Iridium and their Analogy with C O H ( C O ) ~ Sir: We have synthesized quinquecovalent compounds of rhodium and iridium, [MH(CO)(Ph3P)3],by a peculiar reaction (eq. 1) which testifies t o the unique tendency of certain ds-complexes to five-coordination, The new hydride complexes2 are analogous with the carbonyl hydride of cobalt, CoH(C0)d (see Table I ) , but thermaland air-stable, and thus amenable to detailed investigation of their structures3 and other properties. 2[1rCl(CO)(Ph~P)21 (cryst.) [IrH(CO)(Ph3P)31(cryst.)
+ n '/&Ha + (IrC1(CO)(Ph3P)(XzH~)n-1. ..) ( s o h ) + SzHsCl + '/zNz(1)
mixture (eq. l ) , the yield of [IrH(CO)(Ph,P):{] is nearly quantitative (95% based on Ir), thus representing the recommended procedure for synthesis. On the other hand, treatment of the alcohol-soluble portion (containing excess hydrazine) with Ph3P after the reaction (eq. 1) is complete does not produce additional hydride complex, suggesting t h a t the presence of [IrCl(CO)(PhsP)z] is required during the formation of [IrH(CO)(Phd')31. Infrared and proton resonance spectra of the rhodium and iridium complexes are given in Table I , together TABLE I
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Yellow crystals of the iridium compound are obtained by treating an ethanolic suspension of the trans-square complex, [IrCl(CO)(Ph3P)z],4with an excess of hydrazine (95% aqueous solution). Anal. Calcd. for I T P ~ C ~ ~ HIr, ~ ~19.1; O : P, 9.2; C , 65.5; H , 4.6; 0, 1.6. Found: Ir, 19.3; P, 9 . 3 ; C, 65.5; H , 4.5; 0, 1 , s . The yellow rhodium analog is synthesized from [RhCl(CO)(Ph3P)2I5 by the same procedure. Anal. Calcd. for RhP&H460: Rh, 11.2; P, 10.1; C, 71.9; H. 5.1; 0, 1.7. Found: Rh, 11.1; P, 10.0; C, 71.9; H, 5.3; 0, 1.7. The complexes are diamagnetic, nonconducting in acetone and nitrobenzene, and the iridium compound is monomeric in benzene (mol. wt. 1008, calcd. ; 990, found).6 These properties, together with infrared and proton resonance spectra (Table I ) , have led us to formulate the compounds as molecular hydride complexes of five-coordinate and univalent metals. The method of reduction with hydrazine was first used by Malatesta' to prepare zerovalent complexes of platinum, and later by Chatt and Shaw,8who found that cis- [PtClz(Et3P)z] (but not the trans isomer) reacts with hydrazine to give a complex hydride, [PtHCl(Et3P)z] (90%). Our original objective was to apply the same procedure for synthesis of an (as yet unknown) isoelectronic (d8) hydride complex, [IrH(CO)(Ph3P)2]. The surprising result that five-coordinate complexesg were obtained instead poses interesting mechanistic questions. We have not yet isolated the alcohol-soluble iridium complex (formulated as a monophosphine-hydrazine compound in eq. l ) , but the following evidence indicates the stoichiometry for Ir and Ph,P given in eq. 1 : the yields of the alcohol-insoluble [IrH(CO)(Ph3P)3] from numerous experiments have approached but never exceeded the calculated values (for eq. I), 50yobased on Ir (found, 45-50%), and 75% based on Ph3P (found, 70-7577,). When triphenylphosphine, 2-6 moles per [IrCl(CO)(Ph3P)2],is added initially to the reaction (1) R . S. Xyholm, Proc. Chem. Soc., 273 (1981). (2) [IrH(CO)(Ph3P)s] h a s been synthesized also by L. Malatesta ( b y a different m e t h o d ) , Symposium "Current T r e n d s in Organometallic Chemist r y , " Cincinnati, Ohio, June 12-13, 19G3 ( 3 ) S . J . LaPlaca and J . .4. Ibers, J . A m . Chem. S o c . , 86, 3501 (1963). ( 4 ) L Vaska and J W . IXLuzio, i b i d . , 83, 2784 (1981). ( 5 ) Prepared b y t h e same method a s [ I r C I ( C O ) ( P h a P ) l ] ,see ref. 4 . ( 6 ) [ R h H ( C O ) (Ph8P)s) is highly dissociated i n benzene solution (mol. wt. 919, calcd ; ,407, found) ( 7 ) I,, Malatesta and R . Ugo, J . Chem. Soc., 2080 (1963). a n d references quoted ( 8 ) J . C h a t t a n d B . L . Shaw. i b i d . , 5075 (1962), and references cited therein. (9) T h e fo!lowing discussion is equally applicable t o t h e preparation of [ K h H ( C O )(PhaP)a].
Compound ( P = PhrP)
Infrared spectrum, crn.-1"
x.m.r.,b
wH 6ME r(M-H) CoH( CO)r 2043c 1934d 703d 20.7" R h H (C 0 ) P s 1926 2004 784 19.9 1930 2068 822 21 2 IrH( CO)P1 The spectra of the Rh and Ir compounds were obtained on a Beckman IR-9 high resolution spectrometer. Y C O ( v s ) and Y M A ( s ) were measured in C6Hs solution, ~ M H( m ) in Kujol mull. The spectra of the Rh and Ir hydrides were measured in CHC13 solution on a Varian Associates HR-60 spectrometer. In vapor phase, ref. 10; only the strongest band listed (for comparison). In vapor phase, d a t a from ref. 11. e Kef. 12, measured in liquid and solid phase. yco
*
with those of C O H ( C O ) ~reported previously.10-12 Comparison of metal-hydrogen vibrational spectra of the three compounds indicates an increase in frequencies on descending the group, and this sequence has been observed previously in other vertical triads of group VI11 hydride complexes absorbing in the same spectral regions.13 The resonance of the hydridic proton of the iridium compound shows a quartet structure ( J = 42 c.P.s.)l 4 with intensity ratios 1: 3 : 3 : 1 of the four equally spaced bands, which indicates an interaction with phosphorus-31 nucleii (spin I / * ) and equivalence of the three coordinated phosphines. Accordingly, a trigonal bipyramidal structure is implied, and this has been confirmed by crystal structure analysis for the rhodium c ~ m p l e x . ~Based on their X-ray powder patterns, the Rh and Ir compounds are isostructural. Chemical and spectroscopic investigations on transition metal hydride complexes in this laboratory 'j and elsewhere, 1 3 ' and crystal structure studies on these have strongly implied a covalent metalhydrogen bond and a normal stereochemical position for hydrogen in tertiary phosphine-stabilized complexes. This view has now been substantiated by the first direct determination of a metal-hydrogen distance in a molecular complex, [RhH(CO)(Ph3P)3]..3 Exaniination of the data in Table I suggests essentially the same immediate electronic environment for hydrogen and ( I O ) W. F Edgell, C . hlagee, a n d G Gallup, J . A m . Chem Soc., 78, 4185 (1956). (11) W , F. Edgell and R . S u m m i t t , i b i d . , 83, 1772 (1961). (12) R . A . Friedel, I . Wender, S. L. Shufler, and H. W. Sternberg, i b i d , 77, 3951 (1958). (13) For references, see J . C h a t t , Proc. Chem. Soc., 318 (1962). (14) T h e spectrum of [ R h H ( C O ) ( P h s P ) a ]s h o w s a broad band which could not be resolved. I n this case a f u r t h e r splitting by Rhioa would be expected (cf. r e f . 1 3 ) . (15) L Vaska, J . A m . Chem. S o c , 8S, 7 S f i (1961); I., Vaska and J W DiLuzio, i b i d . , 83, 1262, 2784 (1961); i b i d . , 84, H79. 4988 ( 1 9 6 2 ) ; and u n p u b ished results. (16) L. Malatesta, "Advances in t h e Chemistry of t h e Coordination Compounds," S. Kirschmer, E d . , T h e Macmillan C o m p a n y , S e w Y o r k , X . Y., 1961, p. 4 7 5 . (17) P. H . Owston, J. M . Partridge, and J M . Rowe, Acta C r y s t , 13,240 (1960). (18) P. L. Orioli a n d L . Vaska, Proc. Chem. S o c . , 333 (1962).
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COMMUXICATIONS TO THE EDITOR
Xov. 5 , 1963
A
the same type of 11-H bonding in the three compounds. I t thus appears t h a t some earlier viewsIg on metalhydrogen bond character in unsubstituted carbonyl hydrides may need to be modified. *O (19) ( a ) F A Cotton and G Wilkinson, Chem I n d (London), 1305 (1956); fb) F A Cottrin. J . A m . r h e i n . Sol , 8 0 , 4425 (1958). (c) E. 0. Bishop, J . I,. I h w n , P R E m t a g e , R E Richards, and G . Wilkinson, J . C h e m . S O C . , 248-1 (19.59) [this paper summarizes much of t h e discussion on carbonyl hydrides] (20) A theoretical study proposing a normal covalent distance for Co-H in CoH(CO)r h a s been recently reported. R . M Stevens, C . W . Kerns, and W M I.ipscornb, J Chem. P h y s , 37, 279 ( 1 9 6 2 ) ; see also L. I
