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 a n d thermal parameters for compound 2, Tables V a n d VI, bond lengths and bond angles for 2, Tables VII-XI, fractional coordinates for t h e 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 A m e r i c a n Chemical Society
Organometallics 1986,5, 391-393
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391
"RCH~OCU" Cu(0) + RCHzOH + RCH(0) (1) Three pieces of evidence strongly implicate a P-elimination in the decomposition of t r a n ~ - R 0 I r ( C O ) ( P P h ~ ) ~ , The alkoxides were prepared by reactions similar to R = Me, n-Pr, or i-Pr. (1)The decomposition only occurs those previously reported.15J6 The spectroscopic paramfor alkoxides which contain @-hydrogens.(2) The decometers are consistent with the formulation trans-ROIrposition produces an iridium hydride, HIr(C0)(PPh,),, the (CO)(PPh3)2.29 Decomposition reactions of the alkoxides expected complex from a &hydrogen elimination. (3) For are carried out as follows: a solution of 0.10 g of the iridium the n-propoxy and isopropoxy complexes the expected alkoxide complex and 0.08 g of PPh3 (-2-3 equiv) in 20 organic products (propanal and acetone, respectively) are mL of cyclohexane are placed in a pressure tube fitted with observed in high yield. The alcohol product that is also a Teflon stopcock and allowed to stir at 70 "C for several observed may result from a binuclear elimination between hours. To detect the organic products by gas chromathe alkoxide complex and the formed hydride. tography (Varian 2440 FID, 1 2 f t Carbowax, 60 "C), the reaction is carried out in 10 mL of HPLC grade toluene Acknowledgment. We acknowledge the donors of the (Aldrich) which was dried over CaHz and distilled directly Petroleum Research Fund, administered by the American onto the alkoxy complex. Chemical Society, and the Alfred P. Sloan Foundation for The alkoxides which contain P-hydrogens trans-ROIrpartial support of this research. A loan of IrC13.XH20was (CO)(PPh,), (R = Me, i-Pr, and n-Pr) decompose at generously provided by Johnson Matthey Corp. moderate rates at 70 "C; in the presence of PPh, the irdium product is HIr(CO)(PPh,), identified by comparison to independently prepared samples.,O Similar reactions are not observed for R = H, Ph, or t-Bu. For trans-iAn Unusual Solvent Effect In the Reaction of PrOIr(CO)(PPh,), the decompositionleads to acetone and Ethylmagneslum Bromide wlth Triethylborane In Ethyl 2-propanol (eq 2). The acetone and 2-propanol were Ether or Tetrahydrofuran. A Simple Direct Route to tr~ns-i-PrOIr(CO)(PPh~)~ + PPh3 Tetraorganylborate Complexes HIr(CO)(PPh,), + CH3C(0)CH3+ CH3CHOHCH3 (2) formed in comparable amounts (total yield of the two is Herbert C. Brown' and Uday S. Racherla 90% as an average of three decompositions). Similar deRichard 6. Wetherill Laboratory, Purdue University composition of tr~ns-n-PrOIr(CO)(PPh,)~ leads to propWest Lafayette, Indiana 47907 anal (92%). We have been unable to detect formaldehyde Received September IO, 1985 during decompositionof trans-MeOIr(C0)(PPh3)2.31The observation of ketone and alcohol for R = i-Pr indicates Summary: The reaction of organic halides, magnesium that decomposition of these alkoxides may be similar to turnings, and boron trifluoride etherate yields triorganylcopper(1) alkoxides where both products were also obboranes quantitatively in anhydrous ethyl ether (modified served.' As suggested previously the alcohol may arise from fission of the metal-alkoxide bond with hydrogen organometallic method) but leads to quantitative formation abstraction or from a binuclear reaction between the of tetraorganylborate complexes in tetrahydrofuran. A formed hydride and remaining alkoxide. detailed study of the reaction of ethylmagnesium bromide To check the latter possibility, we have examined the with triethylborane revealed that essentially no reaction reaction between HIr(CO)(PPh3), and trans-i-PrOIroccurs in ethyl ether, EtMgBr BEt,, but complete com(co)(PPh3)2. bination occurs in tetrahydrofuran, Et,BMgBr. This detrans-i-PrOIr(CO)(PPhJ2 HIr(C0)(PPh3)3 velopment provides a simple, convenient route for the i-PrOH ? (3) synthesis of tetraorganylborate complexes. Reaction 3 proceeds readily at room temperature to give Recently we described a general quantitative synthesis a good yield of 2-propanoland an unidentified air-sensitive of triorganylboranes via a modified organometallic method' iridium compound. No trace of acetone was observed in (eq 1). this binuclear elimination. This binuclear elimination of alcohol from a metal hydride and a metal alkoxy could 3RX + 3Mg BF3.OEt2 R3B 3MgFX (1) arise from a hydrogen bridging (as a hydride) between the 90-99 % two iridium atoms or a hydrogen bond interaction (as a During this study, we discovered an unusual solvent proton) between the HIr and the oxygen of the alkoxy. effect. llB NMR examination of the reaction mixture Further experiments are in progress to delineate the revealed that the reaction of ethyl bromide, magnesium mechanism of the binuclear elimination. Use of transturnings, and boron trifluoride etherate (taken in 3.5:3.5:1 CD301r(CO)(PPh3)2 or ~~u~~-(CD,),CDOI~(CO)(PP~~)~ in molar ratio) in ethyl ether forms triethylborane (loo%), C6H12 leads to D I I - ( C O ) ( P P ~identified ~)~ by comparison but in tetrahydrofuran, the reaction leads to the exclusive to an independently prepared sample and previous reformation of the bromomagnesium tetraethylborate-THF port.33,34 complex2 (eq 2).
-
+
+
-+
-
+
(29) The carbonyl stretching frequency (CCH12)and NMR spectra (in benzene-&-each spectra has a multiplet at -7 ppm): trans-CH,OIr(CO)(PPh,), 1951 cm-', 3.4 ( 8 ) ppm; trans-n-PrOIr(CO)(PPh,)z, 1951 1951 cm-', 3.65 (t), 1.16 (m), 0.60 (t) ppm; trans-t-BuOIr(CO)(PPh3)2, cm-l, 0.89 (e) ppm; trans-PhOIr(CO)(PPh3)2,1958 cm-'; trans-i-PrOIr(CO)(PPh&, 1945 cm-', 0.72 (d), 4.0 (septet) ppm; trans-HOIr(C0)(PPh3)2,1923 cm-'; HIr(CO)(PPh3)3,2070 (IR-H), 1933 cm-' (C-0). (30) Wilkinson, G.Znorg. Synth. 1972,13, 127. (31) Formaldehyde undergoes reactions with many of the iridium complexes through an apparent initial oxidative addition.32 (32) Bernard, K. A.; Atwood, J. D., manuscript in preparation. (33) Vaska, L. J. Am. Chem. SOC.1966,88, 4100. (34) Based on the absence of the Ir-H stretch at 2070 cm-', we estimate the amount of HIr(CO)(PPh,), at less than 10%.
0276-7333/86/2305-0391$01.50/0
35EtBr
+ 3 5Mg +
+
Et@ t 3MgFBr 100%
BF3.0Etz
1 t 0 5 EtMgBr
EtqBMgBrsnTHF t
2h
87 5% l/sBF3 'THF
t
'1/BMgFBr
(2)
12 5%
(1) Brown, H.C.; Racherla, U. S. J. Org. Chem., in press. (2) Both reactions were performed at 0.25 M concentration. By llB NMR, all of the species formed,namely, triethylborane (6 86.6), BF,.OEt, (6 O), and the ate complex (6 -16.6), could be readily distinguished.
0 1986 American Chemical Society
