Organometallics 1986, 5, 388-390
388
I
~
//,
roo
+-L_. 600
L 500
of the molecules have not been detected.'l The regions of the spectrum between 700 and 400 cm-l of the parent molecule, HMoCp(CO),, contain many of the M-CO stretching and deformation modes, and they are quite sensitive to the isotope of hydrogen. When HMoCp(CO), is photolyzed in D2-containingmatrices, the spectrum gives evidence of slow isotope exchange in the parent molecule as shown in Figure 2. The bands of the deuterium isotopomer that are marked by D are, in two instances, quite well resolved from the correlated bands of HMoCp(CO),, and over periods of several hours of photolysis there is clear evidence of the formation of DMoCp(CO),, especially in the presence of 7 mol % CO. The extra CO increases the probability that H M O C ~ ( C Owill ) ~ react with CO to give back starting material but is not so concentrated that no adduct forms. In the presence of 13 mol % CO no significant quantities of adduct forms and no H-D exchange is noted. This precludes the possibility that the exchange is due to reactions of hydrogen atoms.'J2 Registry No. HMoC~(CO)~, 85150-17-0; HMoCp(CO),, 12176-06-6;DMoCp(CO),, 79359-05-0.
J
cm"
Figure 2. Spectra obtained during the photolysis of HMoCp(CO), in a matrix composed of 20 mol % D2 and 7 mol % CO in argon. Tracing a is of the unphotolyzed matrix. Tracing b was of a spectrum taken after 60 of irridation by a low-pressuremercury lamp. Tracing c was made of a spectrum taken after 75 additional minutes of photolysis, using a medium pressure mercury lamp. The spectrum was recorded with a 2X ordinate expansion. Bands marked by D show the positions of absorptions which are assignable to D M o C ~ ( C O The ) ~ shoulder on the high energy side of the band at 655 cm-' is due to COz. The species to which the band at 630 cm-' belongs is unknown.
carbonyl stretching vibrations of the hydrogen-containing moiety with those of H M O C ~ ( C O )If~ .the hydrogen had oxidatively added, it is reasonable to expect a fairly dramatic blue shift of the carbonyl modes. For example, the oxidative addition of Hz to Fe(CO), results in a 42 cm-l shift in the totally symmetric breathing m0de.l This behavior has been rationalized by presuming hydride ligands are negatively charged and processes which involve the formation of the hydride from hydrogen atoms result in electron density being withdrawn from the metaL8l9 The dependability of this group property is the basis for the reliability of the force constant calculations by Timney.lo The symmetric stretching vibrations of the cis isomer is shifted by 13 cm-' to shorter wavelengths than the similar mode of H M O C ~ ( C O )short ~ : of the shift observed for Fe(CO), and considerably larger than the 3 cm-' shift observed for Cr(CO)5.3 Taken at face value, these comparisons suggest an interaction which comes closer to being described as oxidative addition than what is exhibited by H2CrCO),. A full vibrational characterization of these species has not been possible because the new species are themselves photolyzed by the radiation which is used to create them. Thus, adequate infrared intensity has only been achieved for the carbonyl modes; the largest optical density of any of the adduct modes that has been achieved thus far is 1.3 0.d. With so little adduct formed in these experiments, other modes which are important for the characterization
(11) Unfortunately, both the M-H stretching and deformation modes of HMoCp(CO), are weak. Although the M-H stretching frequency has been observed, there have been no studies which have assigned the M-H deformation mode for this molecule or the analogous HWCP(CO)~. Davison, A.; McCleverty, J. A.; Wilkinson, G. J. Chem. SOC.1963,1133. Davidson, G.; Duce, D. A. J. Organomet. Chem. 1976, 120, 229. (12) The photolysis of HMoCp(CO), gives evidence of the homolytic cleavage of the Mo-H bond in C07and H2-containingmatrices. In solid deuterium, hot hydrogen atoms have been shown to abstract deuterium, although the reaction gives a 40% yield, a t best. The reaction is the function of the excess energy of the hydrogen atom and, in this study, the arobabilitv of the hvdrwen atom collidine with a deuterium molecule befdre it is thermalize& Miyazaki, T.; Tsu;uta, H.; Fueki, K. J . Phys. Chem. 1983,87, 1611.
Pentacoordlnated Slllcon Hydrides: Very Hlgh Afflnlty of the SI-H Bond for the Equatorial Position Claire Brellire, Francis CarrO, Robert J. P. Corriu, Monique Poirier, and GCard Royo Znstitut de Chimie Fine -Hgtgrochimie et aminoacides -UA 1097 Universitg des Sciences et Techniques du Languedoc 34060 Montpellier Cgdex, France Received July 16, 1985
Summary: An X-ray investigation of two pentacoordinated silicon hydrides shows that the Si-H bonds occupy equatorial positions in the trigonal-bipyramidal structures.
It is well-known that nucleophilic substitution at silicon takes place with either retention or inversion of configuration according to the nature of the leaving group.' In a previous paper, we have reported a scale of apicophilicity deduced from the study of pentacoordinate silicon comligand is pounds such as 1 in which the o-Me2NCH2C6H4 intramolecularly bonded to the silicon atom.2
q, X
/ \
(8) Sweany, R. L.; Owens, J. W. J . Organomet. Chem. 1983,255,327.
(9) Photolyses of HWCp(CO), in hydrogen-containing matrices lead to the growth of bands which correlate to those reported herein. In addition, bands grow in which are a t or to higher energy of 2060 cm-'. Work is proceeding to identify the species which are responsible for these bands. Consistent with this line of reasoning would be a claim that these species had resulted from the oxidative addition of hydrogen. (10) Timney, J. A. Inorg. Chem. 1979, 18,2502.
0276-733318612305-0388$01.50/0
p
2
N -\Rt - - CH3 \
CH3
1
(1) Corriu, R. J. P.; Guerin, C.; Moreau, J. J. E. Top. Stereochem. 1984, 15, 43 and references therein.
0 1986 American
Chemical Society
Organometallics, Vol. 5, No. 2,1986 389
Communications
We have observed that the apicophilicity of X is related to the polarizability or, in other words, to the ability of the Si-X bond to be stretched. This order is parallel to the ability of the X group to be displaced with inversion of configuration. pentacoordination ability:
X z H , O R < F . S R C O A c , CI, Br
stereochemistry: retention
-
inversion
In the case of silicon bonded to alkoxy, hydride, and alkyl groups, no diastereotopy could be observed in the NMe2 group by 'H NMR down to -90 0C.2However, %Si NMR brings new evidence for intramolecular pentacoordination. When silicon is bonded to alkyl or alkoxy groups, we do not observe an upfield chemical shift corresponding to pentac~ordination.~The 29SiNMR shows a significant upfield shift in the range of pentacoordinated structures for silicon hydrides. For instance, in the case of o-N Me2CH2C6H4Si(a-CloH7)H2, although we do not observe the diastereotopismof NMe2groups, the %Sichemical shift is displaced 11.6 ppm upfield (at 30 "C) indicating the formation of a Si-N coordinative bond.3 This apparent anomalous behavior can be explained if the two hydrogen atoms occupy equatorial positions, resulting in a plane of symmetry. It is interesting to consider the structure of the adducts formed by N-Si coordination in systems similar to 1 since these are good models for the intermediates involved in nucleophilic substitution at silicon. The Si-H bond is always displaced with retention of configuration, and several pathways have been proposed.' In this paper, we report the structure of two silicon hydrides 2 and 3 in which there is an intramolecular S i N bond. &NMe,
I
-,Me,
I
7
3
N
2
3
The important aspect of the present work is the equatorial position of the Si-H bond, the apical position in both cases being occupied by the phenyl group (Figure 1). These results show the great aptitude of the Si-H bond for pentacoordinated structures and its ability to be in the equatorial p ~ s i t i o n . ~It, ~is now interesting to discuss this (2) Corriu, R. J. P.; Royo, G.; de Saxce, A. J. Chem. Soc., Chem. Commun. 1980, 892. (3) (a) Helmer, B.J.; West, R.; Corriu, R. J. P.; Poirier, M.; Royo, G.; de Saxce, A. J. Organomet. Chem. 1983, 251, 295. (b) In the case of compounds 2, and 3, the 29Sichemical shifts observed are -25.84 and -44.16 ppm upfield than -19.81 ppm measured for 1-C1,,H7(C6H5)Si(Me)H and -35.62 ppm for 1-CloH7(C6H5)SiH2. (4) Crystallographic information: Silane 2: Cd2,NSI; a = 11.857 (3) A, b = 13.078 (4) A, c = 11.087 (3) A; space group P212121;2 = 4; Mo Ka radiation; R = 0.078 for 739 unique observed reflections. T h e space group indicates that the crystal grown for the structure determination was the result of a spontaneous resolution of the compound from the racemic solution. The absolute configuration displayed in Figure 1 was determined via the Hamilton test (Hamilton W. C. Acta Crystallogr. 1966,18, 502), comparing the present structure, with x , y, z coordinates, with a molecule having -x, y , z coordinates. The R, factors were 0.086and 0.087, respectively. In the final refinement only the Si atom had an anisotropic temperature factor. Silane 3 C18y19NSI;a = 12.341 (3)A, b = 8.187 (2) A, c = 15.667 (4) A, @ = 91.43 (1) ,space group P2,/n;2 = 4, Cu Ka radiation; R = 0.056 for 1784 unique reflections. The hydrogen atoms were located by difference Fourier synthesis, and their coordinates were kept fixed during the last least-squares refinement cycles, where all non-hydrogen atoms had adjustable anisotropic temperature factors. Full details of these structures are available as supplementary material. ( 5 ) Cook, D. I.; Fields, R.; Green, M.; Haszeldine, R. N.; Iles, B. R.; Jones, A.; Newlands, M. J. J . Chem. SOC. A 1966, 887.
Figure 1. Perspective views of the silanes 2 and 3. Main features for compound 2 are Si-CI = 1.88 (l),Si-C14 = 1.90 (2), Si-Czl = 1.91 (l), and Si+N = 2.66 (1)A and N-Si-Czl = 166.8 (6), N-Si-C1 = 80.8 (5), and C1-Si-Czl = 104.3 (6)O. Bond lengths (A) and angles (deg) for compound 3: S t C 1 = 1.881 (4), Si-H = 1.44 (2), S i c l l = 1.893 (4), S i k N = 2.584 (3); N-Si-Cll = 178.7 (l), N-Si-C1 = 76.0 (l),C1-Si-Cll = 105.2 (2), mean H-Si-N = 75.3, mean H-Si-Cll = 104.7O. The hydrogen atoms were not determined for silane 2.4
observation in connection with the retention of configuration in nucleophilic substitution at silicon. In the preceding papers devoted to this problem, we have shown that electrophilic assistance is not the driving force for retention of configuration at si1icon.l We proposed an equatorial attack of the nucleophile to explain the frontal displacement.l The results reported here show that equatorial attack certainly is not the most favorable process. The nucleophilic displacement of the Si-H bond with retention of configuration certainly takes place by apical attack of the nucleophile, the Si-H bond being in the equatorial position as suggested recently by the results obtained by Deiters and H01mes.~ Furthermore, these results provide further evidence that electrophilic assistance does not control the process of retention as proposed in SNi-Siprocess:8 even in the ab(6) Ebsworth, E.A. V., private communication. (7) Deiters, J. A.;Holmes, R. P. "Oral Presentation in Organosilicon Symposium", Baton Rouge, LA, April 1985. (8) Sommer, L. H. In "Stereochemistry, Mechanism and Silicon"; McGraw-Hill: New York, 1965; p 177.
Organometallics 1986, 5, 390-391
390
sence of any interaction, we observe frontal attack; the N-Si-H angle measured here for the compound 3 is as small as 75.3", whereas in the case of pentacoordinated silicon chlorides as previously reported, the coordination of the nitrogen atom takes place opposite to the leaving group, in good agreement with the geometry of the inversion of configuration.' These results are a good demonstration of the fact that the attack of nucleophile (frontal or back side) at silicon is mainly controlled by the nature of the leaving group. A further important problem which we have to consider now is to determine whether the hydrogen atom departs directly from the equatorial position or whether a pseudorotation process occurs, resulting in departure of hydrogen atom from an apical position. Finally these results provide a good model for the nucleophilic activation of Si-H bonds in reductions performed by silicon hydrides activated by the fluoride ion.
Acknowledgment. We wish to acknowledge T. Stout for help in preparing the English version of this manuscript. F.C. thanks Pr. J. Lapasset, Groupe de Dynamique des Phases CondensBes, L.A. au CNRS no. 233, Universit6 des Sciences et Techniques du Languedoc, for accurate collecting of a data set with compound 3, on a CAD-3 diffractometer. Registry No. 2, 99642-64-5; 3, 99642-65-6. Supplementary Material Available: Tables I and 11, lists of structure factors amplitudes for compounds 2 and 3, Table 111, sutnmary of crystal data, intensity measurements, and refinement, Table IV, atomic coordinates and thermal parameters for compound 2, Tables V and VI, bond lengths and bond angles for 2, Tables VII-XI, fractional coordinates for the Si, N, and C atoms, anisotropic temperature factors for these atoms, fractional coordinates and isotropic temperature factors for the H atoms, bond lengths, and selected bond angles for compound 3, respectively (24 pages). Ordering information is given on any current masthead page. (9)(a) Corriu, R. J. P.; Perz, R.; RBy6, C. Tetrahedron 1983,39,999 and references therein. (b) Sharma, R. K.; Fry, J. L. J.Org. Chem. 1983, 48,2112.
Decomposition of Iridlum Alkoxide Complexes trans-ROIr(CO)(PPh,), (R = Me, n-Pr, and i-Pr): Evidence for ,f3-Ellminatlon Karen A. Bernard, Wayne M. Rees, and Jim D. Atwood*+ Department of Chemistry University at Buffalo, State University of New York Buffalo, New York 14214 Received May 15, 1985
Summary: Decomposition of trans -ROIr(CO)(PPh,),
in
the presence of PPh, leads to HIr(CO)(PPh,), for R = Me, n-Pr, and i-Pr. For R = H, t-Bu, or Ph, this decomposition is not observed. For R = i-Pr similar quantities of acetone and 2-propanol are observed with total yield of 90% based on starting iridium complex. Propanal is formed for R = n-Pr. The reaction between trans-iPrOIr(CO)(PPh,), and HIr(CO)(PPh,), readily yields 2propanol. Thus a @-hydrogenabstractin to yield organic carbonyl and HIr(CO)(PPh,), is indicated with 2-propanol possibly formed by a binuclear reaction between transi-Pro I r(CO)(PPh,), and H Ir(CO)(PPh,),. 0276-7333/S6/2305-0390$01.50/0
Alkoxide complexes have considerable utility in organic synthesis, especially for reactions catalyzed by The synthesis and structures of a number of alkoxides have been r e p ~ r t e d , ' ~ although ~ ~ ~ - ' ~ several simple reactions of Our alkoxide complexes are only now being high yield syntheses of tr~ns-ROIr(CO)(PPh,)~'allow the study of simple reactions utilizing the coordination site available on iridium. We have previously reported on carbonylation rea~tions;'~J~ we now report on the decomposition which leads to iridium hydride through a mechanism of p-elimination. The decomposition of alkyl complexes by p-elimination is well established for a number of c ~ m p l e x e s . * ~ Al-~~ though such a step may be important in synthetic applications of transition-metal alkoxide complexes,28only one study of the decomposition of transition-metal alkoxide complexes has been reported.' This study of the decomposition of "CuOR" near 100 "C led to Cu(O),alcohol, and ketone or aldehyde for secondary and primary alkoxides, respectively (eq 1). The results indicated competing mechanisms of 6-elimination of aldehyde (ketone) and homolytic scission of the Cu-0 bond producing alkoxy radicals.'
'Alfred P. Sloan Foundation Fellow. (1)Whitesides, G. M.; Sadowski, J. S.; Lilburn, J. J.Am. Chem. SOC. 1974,96,2829. (2)Milstein, D.;Huckaby, J. L. J. Am. Chem. SOC.1982,104, 6150. (3)Wasserman, H. H.; Robinson, R. P.; Carter, C. G. J. Am. Chem. SOC.1983,105,1697. (4)Cornforth, J.; Sierakowski, A. F.; Wallace, T. W. J . Chem. SOC., Perkin Trans I 1982,2299. (5)Huche, M.; Berlan, J.; Pourcelat, G.; Cresson, P. Tetrahedron Lett. 1981,22,1329. (6)Leoni, P.; Pasquali, M. J. Organomet. Chem. 1983,255,C31. (7)Cornforth, J.; Sierakowski, A. F.; Wallace, T. W. J . Chem. SOC., Chem. Commun. 1979,294. (8)Chan, T. H.; Harrod, J. F.; van Gheluwe, P. Tetrahedron Lett. 1974,4409. (9)Bradley, D. C. Prog. Inorg. Chem. 1960,2,303. (10)Bradley, D.C. Adu. Znorg. Chem. Radiochem. 1972,15,259. (11)Mehrota, R. C. Znorg. Chim. Acta Reo. 1967,I , 99. (12)Ku, R. V.; San Filippo, J., Jr. Organometallics 1983, 2, 1360. (13)Bochmann, M.; Wilkinson, G.; Young, G. B.; Hursthouse, M. B.; Malik, K. M. A. J . Chem. SOC.,Dalton Trans. 1980,1863. (14)Pasquali, M.; Fiaschi, P.; Floriani, C.; Gaetani-Manfredotti, A.J. Chem. SOC.,Chem. Commun. 1983,197. (15)Rees, W. M.; Atwood, J. D. Organometallics 1985,4, 402. (16)Rees, W. M.; Fettinger, J. C.; Churchill, M. R.; Atwood, J. D. Organometallics 1985,4,2179. (17)Banditelli, G.; Bonati, F.; Minghetti, G. Synth. Znorg. Met.-Org. Chem. 1973,3,415. (18)Bryndza, H.E.,"The 11th International Conference on Organometallic Chemistry", Callaway Gardens, GA, Oct 1983. (19)Bryndza, H.E. Organometallics 1985,4,406. (20)Chisholm, M.H.; Cotton, F. A. Acc. Chem. Res. 1978,11,356and references therein. (21)Eller, P. G.; Kubas, G. J. J. Am. Chem. Soc. 1977,99, 4346. (22)Tsuda, T.; Watanabe, K.; Miyata, K.; Yamamoto,H.; Saegusa, T. Znorg. Chem. 1981,20,2128. Sanada, S I . ; Ueda, K.; Saegusa, T. Inorg. Chem. 1976, (23)Tsuda, T.; 15,2329. (24)Atwood, J. D. 'Inorganic and Organometallic Reaction Mechanisms"; Brooks/Cole Publishing Company: Monterey, CA, 1985. (25)Whitesides, G. M.; Stedronsky, E. R.; Casey, C. P.; Fillippo, J. S., Jr. J. Am. Chem. SOC.1970,92,1426. (26)Whitesides, G.M.; Gaasch, J. F.; Stedronsky, E. R. J. Am. Chem. SOC.1972,94,5258. (27)Evans, J.; Schwartz, J.; Urquhart, P. W. J. Organomet. Chem. 1974,81,C37. (28)Kaesz, H.D.;Saillant, R. Chem. Reu. 1972,72, 231.
0 1986 American Chemical Society
