Linking of benzyne and carbon monoxide at a triruthenium centre by migratory insertion

Abstract

The μ 3-benzyne complex [Ru 3(CO) 7( μ-PPh 2) 2( μ 3-C 6H 4)] ( 1a) reacts at room temperature (r.t.) with carbon monoxide (1 atm), trimethylphosphite, or t-butylisocyanide to give complexes [Ru 3(CO) 6L 2( μ-PPh 2) 2( μ 3-C 6H 4CO)] ( 2a, L=CO; 2b, L=P(OMe) 3; 2c, L= t BuNC) containing an ortho-metallated μ 3-benzoyl ligand. Studies with 13CO confirm that the reaction involves a migratory insertion of CO into a benzyne-CO σ-bond. The μ 3-benzoyl products are formed exclusively when a large excess of the π-acceptor ligand is used, but at lower concentrations substitution of CO by the incoming ligand also occurs to give the complexes [Ru 3(CO) 6L( μ-PPh 2) 2( μ 3-C 6H 4)] [ 1b, L=P(OMe) 3; 1c, L= t BuNC]. Although 13C-labelling 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, but on heating in toluene the phosphine-substituted complexes [Ru 3(CO) 6(PR 3)( μ-PPh 2) 2( μ 3-C 6H 4)] ( 1d, R=Ph; 1e, R= i Pr) are formed, which upon carbonylation give complexes [Ru 3(CO) 7(PR 3)( μ-PPh 2) 2( μ 3-C 6H 4CO)] ( 2d, R=Ph; 2e, R= i Pr). The structure of the complexes 2 has been established by an X-ray diffraction study on the tri-isopropylphosphine-substituted cluster 2e. Benzaldehyde is obtained from complex 2a by bubbling hydrogen through a heated solution of the complex. A mechanism for the carbonylation of μ 3-benzyne is proposed and implications for metal surface chemistry discussed.