MANGANESE CARBONYL BROMIDE-CATALYZED ALCOHOLYSIS OF THE MONOHYDROSILANE HSIME2PH

The dimeric manganese carbonyl bromide [Mn(CO)4Br]2 is an effective ca talyst for the alcoholysis of dimethylphenylsilane in benzene at room temperature. Preparative scale procedures using a 1200:1200:1 mixture of alcohol, HSiMe2Ph, and [Mn(CO)4Br]2 (0.084 mol %) afforded samples of analytically pure alkoxysilanes in good yields. tert-Butyl alcohol, for example, gave (CH3)3CO-SiMe2Ph in 82% yield after a 35-min reacti on time, and allyl and propargyl alcohols quantitatively transformed t o their alkoxysilane derivatives, with no evidence of competing hydros ilation of the carbon-carbon multiple bonds. Competitive reactions inv olving 1:1:1 mixtures of 2-butanol-acetone-HSiMe2Ph and [Mn(CO)4Br]2 a s Catalyst exhibited chemoselective alcoholysis of dimethyl-phenylsila ne. H-1 NMR spectral monitoring of catalyzed reactions between methano l or 2-butanol and HSiMe2Ph was used in screening other manganese carb onyl complexes as potential HSiMe2Ph alcoholysis catalysts. Their reac tion times varied as follows: [Mn(CO)4Br]2 > Mn(CO)5-Br much greater t han Mn(CO)5CH3 almost-equal-to Mn(CO)5C(O)Ph > Mn(PPh3)(CO)4-Br > Mn(P Ph3)(CO)4C(O)CH3 much greater than Mn(CO)5(SiMe2Ph) much greater than Mn2(CO)10 almost-equal-to Rh(PPh3)3CI (no reaction). Solvent-dependent turnover frequencies were determined for the [Mn-(CO)4Br]2-catalyzed dehydrocoupling of 2-butanol and HSiMe2Ph for 0.289 M solutions of 2-b utanol and HSiMe2-Ph with 1.4 mol % precatalyst LMn(CO)4Br]2: Nt = 218 3 (THF), 2728 (C6H6), and 5457 h-1 (CH2Cl2). In a second procedure, a preparative-scale reaction in CH2Cl2 containing only 0.084 mol % preca talyst but 3.12 M for each reactant afforded a much higher turnover fr equency of 11 217 h-1.