LINKING OF BENZYNE AND CARBON-MONOXIDE AT A TRIRUTHENIUM CENTER BY MIGRATORY INSERTION

The mu(3)-benzyne complex [Ru-3(CO)(7)(mu-PPh2)(2) (mu(3)-C6H4)] (1a) reacts at room temperature (r.t.) with carbon monoxide (1 atm), trimet hylphosphite, or t-butylisocyanide to give complexes [Ru-3(CO)(6)L-2(m u-PPh2)(2)(mu(3)-C6H4CO)] (2a, L = CO; 2b, L = P(OMe)(3); 2c, L='BuNC) containing an ortho-metallated mu(3)-benzoyl ligand. Studies with (CO )-C-13 confirm that the reaction involves a migratory insertion of CO into a benzyne-CO sigma-bond. The mu(3)-benzoyl products are formed ex clusively when a large excess of the pi-acceptor ligand is used, but a t lower concentrations substitution of CO by the incoming ligand also occurs to give the complexes [Ru-3(CO)(6)L(mu-PPh2)(2)(mu(3)-C6H4)] [1 b, L = P(OMe)(3); 1c, L = 'BuNC]. Although C-13-labeling studies show that the reaction of 1a with CO is irreversible at r.t., it is readily reversed by warming complex 2a in hexane. No reaction occurs at r.t. between complex 1a and triphenylphosphine or tri-isopropylphosphine, b ut on heating in toluene the phosphine-substituted complexes [Ru-3(CO) (6)(PR3)(mu-PPh2)(2)(mu(3)-C6H4)] (1d, R=Ph; 1e, R='Pr) are formed, wh ich upon carbonylation give complexes [Ru-3(CO)(7)(PR3)(mu-PPh2)(2)(mu (3)-C6H4CO)] (2d, R = Ph; 2e, R = 'Pr). The structure of the complexes 2 has been established by an X-ray diffraction study on the tri-isopr opylphosphine-substituted cluster 2e. Benzaldehyde is obtained from co mplex 2a by bubbling hydrogen through a heated solution of the complex . A mechanism for the carbonylation of mu(3)-benzyne is proposed and i mplications for metal surface chemistry discussed. (C) 1998 Elsevier S cience S.A. All rights reserved.