260
ing between the metal and ligand. The (linear) valence bond structures
[
[
(diphos)&I W-=N+=N+
Ph
i
( d i p h o ~ ) ~ W=N+-N CI
H '
. /"I' H '
ii
must be considered as important and, in the absence of a precise W-N bond order-bond length relationship, would be distinguished by the stereochemistry of the nitrogen atom N(2), but difference electron density Ph syntheses do not indicate clearly the hydrogen atom positions. Ph The qetal-phosphorus bond lengths are similar W (*0.03 A) to those which have been established for tertiary phosphine complexes of metal tri- and tetr$Figure 1. [W(NaHt)Cl(diphos)2]+, a perspective view of the cchalides3 while the W-CI bond leagth of 2.421 (1) A ordination around the tungsten atom. Bond lengths are (A) suggests a trans influence (-0.1 A) of the hydrazido W-P(l) 2.517 (4), W-P(2) 2.515(4), W-P(3) 2.540 (4), W-P(4) 2.517 (4), W-C1 2.421 (4), W-N(1) 1.73 (l), and N(l)-N(2) 1.37 ligand which is comparable with that of dimethylphenyl(2); the bond angle W-N(1)-N(2) is 171 (1)'. phosphine. 3 The enhanced multiple bonding between the metal and hydrazido ligand, compared with that in the metal-dinitrogen complex, and the consequent is carried out in the presence of sodium tetraphenylweakening of the nitrogen-nitrogen bond follow simborate or if [W(NzH2)Cl,(diphos)z](I) is treated with ple expectations based on molecular orbital theory since NaBPh?, the 1 : 1 electrolyte [W(N,H,)C1(dipho~)~]- protonation of dinitrogen must considerably stabilize BPh4(11) is obtained. its T* levels. A comparison with the structural data Spectroscopic datal were taken to suggest the monofor the protonated azo complex, [ReCl2(NH3)(NzHhapto diimine arrangement (a) for I but the apparent CsH5)(P(CH3)zC6H5)z]Br,4 indicates that the canonical equivalence of the diimine protons ('H nmr) and the structure (ii) is of relatively little importance in the smaller separation of the v(N-H) bands suggested the rhenium complex ; we imagine that the substituent monohapto hydrazido structure (b) or the dihapto effect of the phenyl gfoup and, more importantly, the diimine configuration (c) for 11. effective Lewis basicity of W@- I)+ compared with Ren+, serve to reduce metal to ligand charge transfer in the rhenium species. YH Recent speculations on the mode of action of the M+N M=?;--NHI -=--NH nitrogenase enzyme complex are based on the assertion5 that monohapto dinitrogen complexes are nonreactive a b C with respect to protonation, thus providing prima facie evidence that the enzyme binds dinitrogen as the diAn X-ray diffraction analysis of [W(N2H2)Cl(di- hapto T complex; this discussion5 curiously overlooks ph~s)~]BPh, has now been completed. Crystals (meththe early synthetic results' which the present report conanol) are monoclinic ,and a = 12.472 (l), b = 19.658 firms in detail. An X-ray analysis of [WClZ(N2Hz)(2), c = 27.056 (3) A, p = 92.53 (l)",z space group ( d i p h o ~ ) ~is] in hand to test the prediction' that, in P21/c, and Z = 4. Independent (5599) reflections with this case, the diimine structure (a) will be adopted, but F a z 3 3u(FO2)(4' 6 28 6 45"; Mo KCY,graphite it is already obvious that the coordination number of monochromator) were observed by the w-28 scan the metal is an important factor in determining the routine using an automatic four-circle diffractometer. geometry of the reduced NzHzspecies.'j The structure was solved by conventional heavy-atom (3) L. Aslanov, R. Mason, A. G. Wheeler, and P. 0. Whimp, Chem. techniques. Refinement of positional parameters of Commun., 30 (1970). all nonhydrogen atoms, of anisotropic temperature (4) R. Mason, I3130 cm-I. of 26445 (5) A should be compared with t t a t of 2.458 Crystals of [ReC1z(NH3)(NNHC6H5)(P(CH3)zC6H5)2]-(6) A in ReC13(PMe2Ph)3and 2.505 (3) A in ReCLBr (ethanol) are monoclicic with a = 9.561 (l), b = (PMe2Ph)z;5thus both the metal-phosphorus and N-N 31.802(3), c = 11.004 (1) A, /3 = 122.47 (l)", and space bond lengths suggest that the net charge distribution is group P2'/n. Independent reflections (2197) (Mo K a , that of a protonated azo complex of rhenium(II1); graphite monochromator, w-28 scan routine, four-circle an aminonitrene-rhenium(1) formulation is excluded (1) G. W. Parshall, J . Amer. Chem. Soc., 89, 1822 (1967); 87, 2133 by the observed planarity of N(2). In all three (1965). rhenium-azo complexes, the Re-N2R group is approxi(2) K. R. Laing, S. D. Robinson, and M. F. Uttley, J . Chem. SOC., mately planar, allowing of some electron delocalizaChem. Commun., 176 (1973). (3) J. Chatt, G. A. Heath, and R. L. Richards, J. Chem. SOC.,Chem. tion, and hence stabilization of the protonated azo
'"J
1/
I
Y-ph
Commun., 1011 (1972). (4) J. Chatt, G . A. Heath, and G. J. Leigh, J. Chem. Soc., Chem. Commun., 444 (1972).
( 5 ) L. Aslanov, R. Mason, A. G. Wheeler, and P. 0. Whimp, Chem. Commun., 30 (1970).
Communications to the Editor
262
ligand relative to the hydrazido(2 -) form where the nitrogen-nitrogen bond length approaches 1.4 A.6 The presently available structural data for azo comp l e x e ~ ~all - ~ indicate linear bonding. The reactivity of the platinum(I1) complex' argues for a nonlinear M-N-N bond which, one might anticipate by analogy with the nitrosyl ligand, would also be stabilized by low oxidation state metals in particular stereochemical configurations. lo
Scheme I
(6) G. A. Heath, R. Mason, and K. M. Thomas, J . Amer. Chem.
Fe
(b) n e a t SO,, -60'
2 hr, - 5 5 %
/I OC'
CH,
C,H,
. I
\
'P(C,H,),
o=s=o
Y
I
CH 2
Soc., 96, 259 (1974).
(7) V. F. Duckworth, P. G. Douglas, R. Mason, and B. L. Shaw, Chem. Commun., 1083 (1970). (8) V. F. Duckworth, G. J. Gainsford, and R. Mason, manuscript in
1
preparation. (9) J. A. Ibers and B. L. Haymore, unpublished results cited in ref 2: A. J. Schultz. J. V. McArdle, R. L. Henry, and R. Eisenberg, Proceedings of the American Crystallographic Association, Summer Meeting 1973, Abstract P.5. (10) D. M. P. Mingos, Inorg. Chem., 12, 1211 (1973), and references therein.
R. Mason,* K. M. Thomas, J . A. Zubieta School of Molecular Sciences, University of Sussex Brighton, England
C,H,
CK
I
(a) HI, CH,CI,.
On, C 5 min, 6 7 - 8 7 %
Yf
CH,
Fe
I 3
Stereochemical changes occurring at CY carbon in reactions of transition metal-alkyl complexes have been the subject of considerable interest. 1-4 By contrast, the stereochemistry at metal of these reactions has not been extensively e ~ p l o r e d . Complementary ~~~ data on changes in configuration at a carbon and at metal are necessary for a complete understanding of mechanisms of transformations at metal-carbon bonds. Herein we report on the stereochemistry at metal of SO2 insertion into and of the electrophilic cleavage by HI, 12,and Hg12 of an iron-carbon u bond (Scheme I). The SO2 insertion is highly stereospecific whereas, for the first time, the cleavage processes are shown to involve a reaction intermediate. The parent methyl complex 1 exists in the form of two diastereomerically related pairs of enantiomers, l a and lb,7 owing to the presence of a chiral metal and an unsymmetrically substituted h5-cyclopentadienyl ring. l a and l b were prepared and isolated in varying degrees of isomeric purity (up to 100%) by the stereo-
specific photochemical decarbonylation of the two diastereomers of the corresponding acetyl,s followed by fractional crystallization from benzene-pentane. The 'H nmr spectrum of 1 showed that both the ring ( T 8.22 and 8.53) and the ligated ( T 9.91 d, 9.82 d ; J = 6.4 Hz) CH3groups are diastereotopic. Reaction between l a or l b and SO2 (50-fold excess, 0.4 M ) in CH2C12yielded 2 (ir (CHCl,) 1958, (KBr) 1161, 1031 cm-l). The nmr spectra of 2 [diastereotoyic CH3 groups at T 8.11 and 8.20 (ring) and T 7.60 and 7.61 (sulfinate)] derived from l a and l b revealed that each conversion occurred with >95 % stereoselectivity at iron. When this same reaction was carried out in liquid SO2, stereoselectivities of 76 and 82% were observed for the transformation of the two diastereomers of 1 into 2. On the basis of a recent kinetic studyYand the observation of inversion of configuration at CY carbon in the reaction of h5-CjH6Fe(CO)2CHDCHDC(CHI), with SOz,' a mechanism has been proposed for the SO2 insertion which involves the intermediacy of a contact ion pair ([M]+SO,R-) and the O-~ulfinate.~ The stereochemical result of this study indicates that such an ion pair must possess high configurational stability. Partial epimerization (-20%) at iron in the reaction conducted in neat SO? likely resulted from a high concentration of the 0-sulfinate which is present in equilibrium with the ion pair.'O We cannot determine whether the high degree of stereospecificity corresponds to retention or inversion at iron;" however, the former appears much more likely on mechanistic grounds. Reaction of 1 with HI, 12, or HgI2 proceeded very rapidly to 3 (ir (CHCI,) 1949 cm-I). Iodine-containing
(1) (a) G. M. Whitesides and D. J. Boschetto, J . Amer. Chem. Soc., 93, 1529 (1971); (b) P. L. Bock, D. J. Boschetto, J. R. Rasmussen, J. P. Demers, and G. M. Whitesides, J . Amer. Chem. Soc., in press. (2) (a) D. Dodd and M. D. Johnson, Chem. Commun., 571 (1971); (b) S. N. Anderson, D. H. Ballard, J. 2. Chrzastowski, D. Dodd, and M. D. Johnson, J . Chem. Soc., Chem. Commun., 685 (1972). (3) R. W. Johnson and R. G. Pearson, Chem. Commun., 986 (1970). (4) F. R. Jensen, V. Madan, and D. H. Buchanan, J . Amer. Chem. Soc., 93,5283 (1971). (5) P. W. Robinson, M. A. Cohen, and A. Wojcicki, Inorg. Chem., 10, 2081 (1971). (6) K. Noack and F. Calderazzo, J. Organometal. Chem., 10, 101 (1967). (7) l a and l b are derived, respectively, by the decarbonylation of the more and less soluble diastereomer of the acetyl. 2a and 3a are the dominant diastereomers obtained from la, and 2b and 3b, from l b .
(8) T.G. Attig, P. Reich-Rohrwig, and A. Wojcicki, J . Organomelal. Chem., 51, C21 (1973). (9) S . E. Jacobson and A. Wojcicki, J . Amer. Chem. Soc., 95, 6962 (1973). (10) (a) S. E. Jacobson, P. Reich-Rohrwig, and A. Wojcicki, Inorg. Chem. 12, 717 (1973); (b) P. Reich-Rohrwig, private communication, 1971. (11) Studies have commenced to resolve this problem by X-ray crystallography. We have recently learned that T. C. Flood and D. L. Miles ( J . Amer. Chem. Soc., 9 5 , 6460 (1973)) studied the stereochemistry at iron of the insertion of SO1 into the Fe-C bond of hS-CsHsFe(CO)[PBy using nmr ( C ~ H ~ ) ~ ] C H ~ C ( O ) O [ClOHl$O C ~ O H I ~= (-)-mentholate]. and circular dichroism spectroscopy, they showed that the insertion in neat Sot occurs with >90% retention of configuration at iron. We thank Professor T.C. Flood for communicating this result to us prior to publication.
P. G . Douglas, A. R. Galbraith, B. L. Shaw
School of Chemistry, University of Leeds Leeds, England Received July 18, 1973
Stereochemistry of Some Electrophilic Reactions at Iron-Carbon u Bonds Sir:
Journal o j t h e American Chemical Society
/ 96:l / January 9, 1974
