BENZYNE COMPLEXES OF RUTHENIUM - MODELS FOR DISSOCIATIVE CHEMISORPTION OF BENZENE ON A METAL-SURFACE - CRYSTAL-STRUCTURES OF [RU4(CO)10(MU-CO)(MU-4-PR)(MU-4-ETA-4-C6H4)] (R = PH AND CH2NPH2), [RU5(CO)13(MU-4-PPH)(MU-5-ETA-6-C6H4)] AND [RU6(CO)12(MU-4-PME)2(MU-3-ETA-2-C6H4)2]

Title full: Benzyne complexes of ruthenium: Models for dissociative chemisorption of benzene on a metal surface. Crystal structures of [Ru4(CO)10(μ-CO)(μ4-PR)(μ 4-η4-C6H4)] (R = Ph and CH2NPh2), [Ru5(CO)13(μ4-PPh)(μ5- η6-C6H4)] and [Ru6(CO)12(μ4-PMe)2(μ 3-η2-C6H4)2]. Heating a solution of [Ru3(CO)11(PPh3)] in toluene gives the μ3-, μ4- and μ5-benzyne complexes [Ru3(CO)7(μ-PPh2)2(μ 3-η2-C6H4)] (1a) (33%), [Ru4(CO)10(μ-CO)(μ4-PPh)(μ 4-η4-C6H4)] (2a) (50%) and [Ru5(CO)13(μ4-PPh)(μ5- η6-C6H4)] (3a) (7%), respectively. The structures of 2a and 3a have been established by X-ray diffraction, revealing that the benzyne in each case is bound to a square of ruthenium atoms by CRu σ-bonds to two adjacent rutheniums, and by η2-interactions to the other two atoms of the Ru4 square. In 3a there is also η2-co-ordination to a third ruthenium atom, so that there is η6-co-ordination overall. The five metal atoms of 3a are arranged like a step site on a metal (111) surface and the complex can be viewed as a model for the aftermath of benzene CH activation on such a surface. The thermolysis of [Ru3(CO)11(PPh2CH2NPh2 )] gives the μ4-PCH2NPh2 analogue 2b of 2a, while from [Ru3(CO)11(PPh2Me)] the new cluster [Ru6(CO)12(μ4-PMe)2(μ 3-η2-C6H4)2] (11) is isolated in 11% yield. The structures of 2b and of 11 have been determined by X-ray diffraction; 11 contains two μ3-benzyne ligands bound to triruthenium faces of an Ru6P2 cluster. Thermolysis of the tritolylphosphine complexes [Ru3(CO)11(PAr3)](Ar = C6H4-m-Me or C6H4-p-Me) affords only analogues of 1 and 2, containing in each case the μ-C6H3-4-Me ligand. Heating [Ru3(CO)11(AsPh3)] gives low yields of the arsenic analogues of 2 and 3 in addition to the major product [Ru2(CO)6(μ-AsPh2)2] (65%). The fluxional behaviour of complexes 1 and 2, involving benzyne rotation on Ru3 and Ru4 centres, respectively, is discussed, and pathways for the formation of 1, 2 and 3 are proposed. © 1990.