1070
Organometallics 1996, 14, 1070-1072
Reactions of Secondary Silanes with [Pt2(I(1=CO)(C0)2(I(1=dppm)2]: Synthesis and Characterization of Silylene-BridgedPlatinum Dimers Kimberly A. Brittingham,la Thomas N. Gallaher,lb and Serge Schreiner*Ja Departments of Chemistry, Randolph-Macon College, Ashland, Virginia 23005, and James Madison University, Harrisonburg, Virginia 22807 Received July 11, 1994@ Summary: The secondary silanes MezSiHz, EtzSiHz, PhzSiHz, and MePhSiHz react with the binuclear complex [Ptz(p-CO)(CO)2(p-dppm)d (1;dppm = Ph2pCH2pPh2) to give zerovalent p-SiRR' complexes of the form [PtdpSiRR7(CO)dp-dppm)d (R = R = Me (2), Et (3), Ph (4); R = Me, R' = Ph (5)). 31P(111)N M R data suggest that these compounds can be formulated as W-frame complexes. I n the reaction of 1 with PhzSiHz leading to 4, low-temperature, multinuclear N M R data show that the reaction proceeds via an intermediate formulated as [Ptz(H)(SiHPh2)(CO)(p-dppm)d (6). The activation of silicon-hydrogen bonds2 is an important step in a number of transition metal catalyzed reactions: dehydrogenative coupling of primary and secondary silanes? olefin hydr~silation,~ and silane alcoholy~is.~ The majority of the studies describing the oxidative addition of silanes to transition metal complexes have focused on their interaction with mononuclear, low-valent metal center^,^^^ which in some cases has led to the formation of binuclear silylene clusters.6-8 More recently, the reactions of bimetallic carbonyl Abstract published in Advance ACS Abstracts, December 1, 1994. (1) (a) Randolph-Macon College. (b) James Madison University. (2)Collman, J. P.; Hegedus, L. 5.;Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987;pp 293,564,761and references therein. (3)(a)Tilley, T. D. In The Chemistry oforganosilicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989;Part 2,Chapter 24,p 1415 and references therein. (b) MacKay, K. M.; Nicholson, B. K. In Comprehensive Organometallics; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, England, 1982;Vol. 6,Chapter 43,p 1043. (c) Aylett, B. J. Adu. Inorg. Chem. Radiochem. 1982,25, 1. (d) Aitken, C.; Barry, J.-P.; Gauvin, F.; Harrod, J. F.; Malek, A.; Rousseau, D. Organometallics 1989,8,1732. (e) Chang, L. S.; Corey, J. Y. Organometallics 1989,8,1885. (0 Campbell, W. H.; Hilty, T. K.; Yurga, L. Organometallics 1989,8,2615. (g) Woo, H.-G.; Walzer, J. F.; Tilley, T. D. Macromolecules 1991,24, 6863. (h) Zhang, 2.-F.; Babonneau, F.; Laine, R. M.; Mu, Y.; Harrod, J. F.; Rahn, J. A. J . Am. Chem. SOC.1991,74,670. (i) Corey, J . Y.; Zhu, X.-H.; Bedard, T. C.; Lange, L. D. Organometallics 1891,10,924. (i) Woo, H.-G.; Tilley, T. D. J . A m . Chem. SOC.1989,111,3757.(k) Woo, H.-G.; Tilley, T. D. J . Am. Chem. Soc. 1989,111,8043. (4)(a) Harrod, J. F.; Chalk, A. J. In Organic Synthesis Via Metal Carbonyls; Wender, I., Pinto, P., Eds.; Wiley: New York, 1977;Vol. 2. (b) Speier, J. L.Adu. Organomet. Chem. 1979,17,407. (c) Ojima, I. In The Chemistry of Organosilicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Vol. 2, Chapter 25, p 1479. (d) Schubert, U. J . Organomet. Chem. 1988, 358, 215. (e) Seitz, F.; Wrighton, M. 5.Angew. Chem., Int. Ed. Engl. 1988,27, 289. (0 Brinkman, K. C.; Blakeney, A. J.; Krone-Schmidt, W.; Gladysz, J . A. Organometallics 1984,3,1325. ( 5 ) (a) Ojima, I.; Kogure, T.; Nihonyanagi, M.; Kono, H.; Inaba, S.; Nagai, Y. Chem. Lett. 1973,501. (b) Corriu, R. J. P.; Moreau, J. J . E. J . Organomet. Chem. 1976,114,135. (c) Blackbum, S.N.; Haszeldine, R. N.; Parish, R. V.; Setchfi, J. H. J. Organomet. Chem. 1980,192, 329. (d) Dwyer, J.; Hilal, H. 5.;Parish, R. V. J . Organomet. Chem. 1982,228,191. (e) Lukevics, E.; Dzintara, M. J . Organomet. Chem. 1986,295,265. (0 Crabtree, R. H.; Luo, X.-L. J . Am. Chem. SOC.1989, 111,2527. (6)Carre, F. C.; Moreau, J. J. E. Inorg. Chem. 1982,21,3099. (b) Brookes, A.; Knox, 5.A. R.; Stone, F. G. A. J . Chem. SOC.A 1971,3469. (7)Michalczyk, M. J.; Recatto, C. A.; Calabrese, J . C.; Fink, M. J . J . A m . Chem. SOC.1992,114,7955. @
0276-733319512314-1070$09.00/0
complexes of rhodiumg and iridiumlO with primary and secondary silanes have been investigated. Our own work on the oxidative-addition reactions of [Ptz@-CO)(C0)2@-dppm)zll1(1) as well as the importance of platinum complexes in the formation of Si-Si oligomerd2 prompted us to investigate the reactivity of this complex with organosilanes. In this note, we wish to report the reactions of 1 with secondary alkyl-, aryl-, and alkylarylsilanes to yield (psily1ene)platinum dimers. Experimental Section General Comments. The complex [Pt&&O)(C0)2&dppm)~]was prepared as previously reported." Biddipheny1phosphino)methane (Strem Chemicals) and all silanes (United Chemical Technologies, Inc.) were used as purchased. All manipulations were performed using standard Schlenk techniques. 'H NMR, 13C{lH} NMR, 31P{1H}NMR, and lg5Pt{lH} NMR were recorded on a Bruker ACE-200 FT-NMR between 24 and -80 "C, and chemical shifts were referenced to TMS, 85%H3P04, and HzPtCh, respectively. When possible, coupling constants and chemical shifts are reported as measured directly from the experimental spectra. In all other cases, the values listed are those determined using spectral simulations. IR spectra were recorded on a Mattson 4020 FTIR spectrometer. Microanalyses were carried out by Atlantic Microlab, Inc., Norcross, GA. Preparation of Compounds. [Pta(u-SiMed(CO)z(udppmhl (2). To 10 mL of CO-purged benzene was added 0.100 g (0.0804 mmol) of 1. The resulting yellow-orange solution was stirred and dimethylsilane was slowly bubbled through the solution for ca. 30 s, producing a bright yellow color. The solution was stirred for 30 min. A yellow solid started t o precipitate. Addition of hexanes (50 mL) caused complete precipitation of the yellow solid. The suspension was vacuum filtered (0.071 g, 75%), washed with CO-purged methanol, and dried in uucuo. Anal. Calc for C S ~ H ~ O O Z P ~ P ~ Z Si: C, 50.90; H, 3.93. Found: C, 49.95; H, 3.89. Mp (dec): 101 "C. IR (Kl3r): 1951, 1940 cm-' (YCO). lH NMR (CDZC12, 24 "C): 6 1.02 (s, CH3), 2.76 (br, CH,Hb), 5.10 (br, CHJ-fb), 6.30-7.66 (m, CsH5). 13C{lH} NMR (CDZC12, 13C0 enriched, 24 "C): 6 187.8 (9, CO), 'Jpt-c = 1780.0 Hz, 'Jpt-c = 141.8 Hz. 31P{1H}NMR (CDZClz, 24 "C): 6 -3.57 (s), 'Jpt-p = 2606.0 Hz, 'Jpt-p = -61.1 Hz, 'Jp-p = 54.0 Hz, 3Jp-p = 175.3 Hz; 3Jp-p (8)Heyn, R. H.; Tilley, T. D. J . A m . Chem. SOC.1992,114,1917. (9)(a) Wang, W.-D.; Eisenberg, R. J . Am. Chem. SOC.1990,112, 1833. (b) Wang, W.-D.; Hommeltoft, 5.I.; Eisenberg, R. Organometallics 1988,7,2417. (10)Cowie, M.; McDonald, R. organometallics 1990,9,2468. (11)Schreiner, S.;Gallaher, T. N. Organometallics 1993,12,4201. (12)(a) Brown-Wensley, K. A. Organometallics 1987,6 , 1590. (b) Onopchenko, A,; Sabourin, E. T. J. Org. Chem. 1987,52, 4118. (c) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J. J . A m . Chem. SOC. 1988,110,4068. (d) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J. J . Chem. Soc., Chem. Commun. 1989,577.
0 1995 American Chemical Society
Notes
Organometallics, Vol.14, No. 2, 1995 1071
+ RRSiH, [Pt,+-SiRR)(CO),+-dppm),I + CO + H,
[Pt,+-CO)(CO),+-dppm),I
R = R' = Me, Et, Ph; R = Me, R Figure 1. Proposed structure of [Ptz@-SiRR)(CO)&dppm)~] (R = R' = Me (2), Et (31, Ph (4); R = Me, R = Ph (6); P = PPhz). = 10.3 Hz, 'Jpt-pt = 1574.4Hz. 196Pt{'H} NMR (CD2C12, 24
"C): 6 -5293 (t).
[Ptz(lr-SiEtz)(CO)n(lr-dppm)aI (3). To 10 mL of CO-purged benzene was added 0.100g (0.0804mmol) of 1. The resulting yellow-orange solution was stirred, and excess diethylsilane (0.5 mL) was added. The solution color changed immediately to bright yellow. After 30 min, hexanes (50mL) was added causing the precipitation of a yellow solid. The suspension was vacuum filtered (0.072g, 69%), washed with CO-purged methanol, and dried in uucuo. Anal. talc for C&&zP4&Si: C, 51.65;H, 4.15. Found: C, 51.71;H, 4.19. Mp (dec): 104 "C. IR (KBr): 1947,1939 cm-' (YCO). 'H NMR (CDzClZ, 24 "c): 6 1.14 (4,CHz, 3 J ~=-7.4 ~ HZ), 1.36 (t, CH3, 'JH-H = 7.4Hz), 2.82(br, CHaHb),4.93(br, cH&,), 6.9-8.1(m, CeH6). 13C{1H}NMR (CD2C12, 13C0enriched, 24 "C): 6 187.6(s, CO), 'Jpt-c = 1768.6Hz, 'Jpt-c = 147.6 Hz. 31P{1H} NMR (CD2Clz, 24 "C): 6 -4.44 (s), 'Jpt-p = 2574.1 Hz, 'Jpt-p = -63.3 Hz, 2Jp-p = 56.7 Hz, 3Jp-p = 180.4Hz, 3Jp-p = 8.23 Hz; 'Jpt-pt = 1703.1 Hz. 1g6P{1H}NMR (CDzC12, 24 "C): 6 -5312 (t). [Pt2(lr-SiPh2)(CO)2(lr-dppm)~] (4). To 10 mL of COpurged benzene was added 0.075 g (0.0603"01) of 1. The resulting yellow-orange solution was stirred, and excess diphenylsilane (0.5 mL) was added. The solution color changed immediately to bright yellow. After 30 min, hexanes (50mL) was added causing precipitation of a yellow solid. The suspension was vacuum filtered (0.080 g, 95%), washed with CO-purged methanol, and dried in uacuo. Anal. Calc for C&6402P4Pt2Si: C, 54.97;H, 3.86. Found: C, 55.49;H, 4.28. Mp (dec): 138 "C. IR (KBr): 1953,1944cm-l (YCO). 'H NMR (CD2C12, 24 "c): 6 3.28(m, CHaHb), 4.34(m, CHab), 6.2-7.9 (m, C&). 13C{lH} NMR (CD2C12, 13C0 enriched, 24 "C): 6 184.2(s, CO), 'Jpt-c = 1730.2Hz, 'e7pt-c = 146.0Hz. 31P{1H} NMR (CD2C12, 24 "C): 6 -5.52 (s), 'Jpt-p = 2593.0Hz, 'Jpt-p = -62.3 Hz, 'Jp-p = 34.5Hz, %Jp-p = 170.9 Hz, V p - p = 3.68 Hz, 'Jpt-pt = 1544.3 Hz. 1g6Pt{'H}NMR (CD2C12, 24 "C): 6 -5290 (t).
[Pta(lr-SiMePh)(CO)a(lr-dppm)21 (5). To 10 mL of COpurged benzene was added 0.100 g (0.0804mmol) of 1. The resulting yellow-orange solution was stirred, and excess methylphenylsilane (0.5 mL) was added. The solution color changed immediately to bright yellow. After 30 min, hexanes (50mL) was added causing a yellow precipitate to form. The suspension was vacuum filtered (0.073g, 68%), washed with CO-purged methanol, and dried in uucuo. Anal. Calc for C59H5202P4Pt~Si:C, 52.99;H, 3.89.Found: C, 52.38;H, 3.99. Mp (dec): 92 "C. IR (KBr): 1968,1947 cm-I (YCO). 'H NMR (CD2C12, 24 "C): 6 1.03 (s, CH3), 2.87 (br, C&,Hb), 3.06 (br, CHfib), 4.72(br, CH,Hd), 4.78(br, CHad), 6.2-8.0(m, CsH5). 13C{'H} NMR (CD2C12, 13C0enriched, 24 "C):6 185.1(s, CO), 'Jpt-c = 1760.8 Hz, 'Jpt-c = 146.4 Hz. 31P{'H} NMR (CD2Clz, -20 "C): 6 2.45(m, PA),Vpt-p = 2582.6Hz, 2Jpt-p = -56.1 Hz, 'Jp-p = -45.8 Hz, 3Jp-p = 179.1Hz, 3Jp-p = -8.43 Hz; 6 -9.73 (m, PB),lJpt-p = 2594.1 Hz, 2Jpt-p = -58.3 Hz, ?Jp-p = -45.8 Hz, V p - p = 159.5Hz, 3Jp-p = -8.43 Hz, 'Jpt-pt = 1542.4 Hz. 195Pt{1H}NMR (CDZClz, 24 "C): 6 -5295 (t). Results and Discussion
Reaction of dialkyl-, diaryl-, and alkylarylsilane with [Pt2Cu-CO)(CO)~@-dppm)21 under ambient conditions results in the formation of the silylene-bridged dimers 2-5 (Figure 1) (eq 1).These dimers are formulated as
(1)
= Ph
zerovalent complexes with a platinum-platinum bond, each metal having an 18 electron valence shell. The IR spectra of these complexes exhibit absorptions attributable to terminally coordinated carbon monoxide but no absorption due to bridging CO. In the solid state and in solution, the complexes are thermally stable and moderately sensitive to air. All compounds are very soluble in aromatic hydrocarbons (benzene, toluene) and chlorinated hydrocarbons (chloroform,dichloromethane) but insoluble in polar solvents. The proton NMR spectra of complexes 2-4 show two different methylene resonances for dppm which can be integrated as two protons each, while the spectrum for 5 displays four different resonances for the four inequivalent methylene protons. The silylene methyl protons of 2 appear as a singlet a t 6 1.02,the protons of the SiEt2 group of 3 appear as triplet and quartet at 6 1.36 and at 6 1.14, respectively, and the methyl protons of the SiMePh group of 5 appear as a singlet a t 6 1.03. The phosphorus NMR spectra of compounds 2-4 are described as AA'AAXX' spin systems, while the spectrum for 6 is best described as an AA'BBXX' system (Figure 2). Spectral simulations for all complexes yield coupling constants whose magnitudes are consistent with those obtained for triply bridged platinum dimers with a platinum-platinum bond.11J3 Two-bond Pt-P coupling constants and two-bond P-P coupling constants for the silylene-bridged complexes are similar in magnitude to those for complexes adopting the so-called cradle structure.11J4 On the basis of this information, it appears that our platinum dimers have the two dppm ligands cis to each other and can be formulated as W-frame complexes. Mechanistic information on the oxidative addition of the secondary silanes to [PtzCu-CO)(C0)2Cu-dppm)21can be obtained by monitoring the reaction of 1 with diphenylsilane at low temperature by NMR. Reaction of equimolar amounts of 1 and diphenylsilane at -80 "C generates an intermediate, which upon warming yields the final product 4. This intermediate, which has been formulated as [Pt~(H)(SiHPh~)(CO)@-dppm)21(6), is the result of a Si-H addition to one Pt atom with concomitant loss of CO (eq 2). The high-field region of [Pt,+-CO)(CO),+-dppm),I
+ Ph,SiH,
-
[Pt,(H)(SiHPh,)(CO)+-dppm),I+ 2CO (2)
the lH NMR spectrum of the reaction mixture displays = 939 Hz; ,JP-H= 16.2 a resonance at 6 -6.78 (lJpt-~ Hz) attributable to 6 which is characteristic of a hydride coordinated to platinum. In addition, a resonance at 6 6.53 is attributed to a proton attached to s i l i c ~ n . The ~J~ 31P{1H} NMR spectrum of the intermediate is characterized by two multiplets centered at 6 10.7 P J p t - p = 3239 Hz) and at 6 -18.4 (4Jpt-p = 2795 Hz), indicating two inequivalent phosphorus environments. The 13C{ lH) NMR spectrum of the reaction mixture displays a (13)Brown, M. P.; Fisher, J. R.; Franklin, S. J.; Puddephatt, R. J.
J. Orgunomet. Chem. 1978, 161,C46.
(14)Hunt, C. T.; Matson, G. B.; Balch, A. L. Inorg. Chem. lOSl,20, 2270.
1072 Organometallics, Vol. 14, No. 2, 1995
Notes
Figure 2. 31P(1H} NMR spectrum (lower trace) and computer simulation (upper trace) of [Pt~01-SiMePh)(CO)z~-dppm)~I at -25 "C. single carbon resonance for 6 at 6 183.5 (lJpt-c = 1572 Hz) characteristic of a terminal carbonyl carbon as well as a carbon resonance at 6 182.3 caused by dissolved CO. When the reaction mixture is slowly warmed to -25 "C, 6 undergoes reductive elimination of HZ (as evidenced by the disappearance of the resonances at -6.78 and at 6.53 ppm in the lH NMR spectrum) and new resonances attributable to 4 and dissolved hydrogen (6 4.52) start to appear (eq 3).
spectrum and a new resonance at 186.1 ppm due to 4 appears. Studies on the reactions of primary silanes with [R2@-CO)(CO)z(p-dppm)z] are currently in progress.
Acknowledgment. This work was supported in part by the Alan Rashkind Endowment administered by Randolph-Macon College and the National Science [Ptz(H)(SiHPh2)(CO)01-dppm)zlCO Foundation (Grants CHE-9000748 and USE-9152585). ~ P t z ~ - S i P h z ~ ~ C O ~ z ~ - dH p,p m (3)~ z l K.A.B. gratefully acknowledges support by the Council on Undergraduate Research. Simultaneously, the carbon resonance due to dis-
+
-
+
solved CO and 6 disappeared in the 13C{lH) NMR
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