Stepwise and Selective Carborane Substitution in the B(3,6) Positions of a 16e CpCo Half-Sandwich Complex Containing a Chelating ortho-Carborane-1,2-dithiolate Ligand

The reactions of the 16e half-sandwich complex, CpCo(S(2)C(2)B(10)H(10)) (1), with alkynones at ambient temperature lead to complexes CpCo(S(2)C(2)B(10)H(9))(CH=CH-C(O)R) (R = Ph (2), 2-naphthyl (3)). Both 2 and 3 are still 16e half-sandwich complexes containing a B(3)-substituted ortho-carborane-1,2-dithiolate ligand. Treatment of 2 with excess alkynes R(1)C[triple bond]CR(2) (R(1) = H, R(2) = Ph, C(O)Ph, CO(2)Me; R(1) = R(2) = CO(2)Me) affords five complexes, CpCo(S(2)C(2)B(10)H(8))(CH(2)CPh)(CH=CH-C(O)Ph) (4), CpCo(S(2)C(2)B(10)H(8))(CH=CH-C(O)Ph)(2) (5), CpCo(S(2)C(2)B(10)H(8))(CH=CH-CO(2)Me)(CH=CH-C(O)Ph) (6), CpCo(S(2)C(2)B(10)H(9))(MeO(2)C-C=C-CO(2)Me)(CH=CH-C(O)Ph) (7), and CpCo(S(2)C(2)B(10)H(9))(MeO(2)C-C=C-CO(2)Me)(2)(CH=CH-C(O)Ph) (8). Complex 4 is an 18e complex bearing a B-CH(2) unit. Both 5 and 6 retain a 16e half-sandwich structure but contain a B(3,6)-disubstituted ortho-carborane-1,2-dithiolate ligand. However, in 7 and 8 one or two alkynes are inserted into one of the Co-S bonds to generate 18e species, respectively. Heating 7 leads to the 16e complex, CpCo(S(2)C(2)B(10)H(8))(MeO(2)C-C=CH-CO(2)Me)(CH=CH-C(O)Ph) (9), having a B(3,6)-disubstituted ortho-carborane-1,2-dithiolate ligand as in 5 and 6. All complexes were fully characterized by spectroscopic techniques and elemental analysis. The solid-state structures of 2 and 3 and 5-9 were further characterized by X-ray structural analysis.