A STUDY OF THE SILANOLYSIS OF TRIPHENYLSILANE AND P-METHOXYPHENOL CATALYZED BY (PME3)4RUH2 AND THE STOICHIOMETRIC REACTIONS OF (PME3)4RU(H)(OC6H4-P-X) (X=ME, OME) WITH PH3SIH

The ruthenium dihydride cis-(PMe3)4Ru(H)2 (1) catalytically converts Ph3SiH and HOC6H4-p-OMe to the alcoholysis products Ph3SiOC6H4-p-OMe and H-2. This reaction was studied kinetically and the rate was found to be first-order in [1], first-order in [HOC6H4-P-OMe], and independent of [Ph3SiH]. The stoichiometric reactions of cis-(PMe3)4Ru(H)(OC6H4-p-X) (X = Me, 2; OMe, 3) with Ph3SiH were also studied in the presence of varying amounts of free para-substituted phenol. In the absence of the free phenol, compounds 2 and 3 reacted with Ph3SiH to give Ph3SiOC6H4-p-X and a compound we believe to be (PMe3)3Ru(H)3(SiPh3) (4). In the presence of large amounts of phenol (> 10 equiv.), (PMe3)4Ru(H)2 (1) was formed. However, at intermediate concentrations of free phenol, compounds 2 and 3 exhibited divergent behavior. Complex 2 gave dihydride 1 in a reaction whose rate was found to be first-order in the concentration of the starting aryloxy hydride 2, first-order in phenol and independent of [Ph3SiH]. In contrast, complex 3 reacted with less than 0.5 equiv. of p-methoxyphenol to form 1, but when approximately 1 equiv. of p-methoxyphenol was added to the solution of 3 and Ph3SiH a mixture of trihydride 4 and dihydride 1 were formed. The mechanisms of these complicated transformations, and their potential relationship to the dihydride-catalyzed silanolysis reaction, are discussed.