Benzyne complexes of ruthenium: models for dissociative chemisorption of benzene on a metal surface. Crystal structures of 4-PR)(μ4-η4-C6H4)> (R = Ph and CH2NPh2), 4-PPh)(μ5-η6-C6H4)> and 4-PMe)2(μ3-η2-C6H4)2>

Article abstract of DOI:10.1016/0022-328X(90)87246-A

Heating a solution of in toluene gives the μ_3-, μ_4- and μ_5--benzyne complexes 3-η²-C6H4)> (1a) (33percent), 4-η⁴-C6H4)> (2a) (50percent) and 4-PPh)(μ₅-η⁶-C6H4)> (3a) (7percent), 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 C-Ru ?-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 model for the aftermath of benzene C-H activation on such a surface.The thermolysis of gives the μ₄-PCH2NPh2 analogue 2b of 2a, while from the new cluster 4-PMe)2(μ₃-η²-C6H4)2> (11) is isolated in 11percent 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 (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 gives low yields of the arsenic analogues of 2 and 3 in addition to the major product (65percent).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.