STERIC AND INDENYL EFFECTS IN THE CHEMISTRY OF ALKYLIDYNE COMPLEXES OF TUNGSTEN AND MOLYBDENUM

Reaction between LiC(5)Me(5) or KC9H7 and [M(=C(6)H(3)Me(2)-2,6)(CO)(2)(NC(5)H(4)Me-4)(2)Br] affords the complexes [M(=CC(6)H(3)Me(2)-2,6)(CO)(2)L] (L = eta-C(5)Me(5), M = W (1a); Mo (1b); L = eta(5)-C9H7, M = MO (1c)). The complexes 1a and 1b react with PMe(3) to give eta(2)-ketenyl compounds [M{eta(2)-C(O)CC(6)H(3)Me(2)-2,6}(CO)(PMe(3))(eta-C(5)Me(5))] (M = W (2a), Mo (2b)) while the reaction of 1c with PMe(3) or P(OMe)3 gives [Mo(=CC(6)H(3)Me(2)-2,6)(CO)L'(eta(5)-C9H7)] (L' = PMe(3) (3a), P(OMe)(3) (3b)). Thermolysis of 2a provides 1a rather than the anticipated complex [W(=CC(6)H(3)Me(2)-2,6)(CO)(PMe(3))(eta-C(5)Me(5))]. Compound 1b has been employed to prepare the range of heterobimetallic compounds [MoFe(mu-CC(6)H(3)Me(2)-2,6)(CO)(5)(eta-C(5)Me(5))] (4), [MoFe(mu-CC(6)H(3)Me(2)-2,6)(CO)(3)(mu-dppm)(eta-C(5)Me(5))]. (5), [MoFe(mu-eta(2)-SeCC(6)H(3)Me(2)-2,6)(CO)(5)(eta-C(5)Me(5))] (6), and [MoCu(mu-CC(6)H(3)Me(2)-2,6)(CO)(mu-CO)(eta-C(5)Me(5))(2)] (8b), with bonds between molybdenum and iron or copper supported by the xylylmethylidyne unit, to assess the effects of steric encumbrance on bridge-assisted cluster asembly.