Formation and Structure of Heptacoordinate Dihalogeno Carbene-C,O Chelate Complexes and Dihalogeno Carbene-C,O Chelate Phosphine Complexes of Molybdenum(II) and Tungsten(II) : A New Class of Fischer Type Carbene Complexes

Abstract

The carbene-C,O chelate carbonyl tungsten(0) complex (1) reacts with phosphines by opening of the chelate ring to form [(CO)4(PR3)WC(OMe)C6H4OMe-o] (R = Me (5), nBu (6), Ph (7), Cy (8)). Treatment of 5 and 6 with SnX4 affords by oxidative decarbonylation, depending on R and X, either one or two isomers of the carbene-C,O chelate dicarbonyl phosphine tungsten(II) complexes (R = Me, X = Cl (9a), Br (9b), I (9c-A/9c-B); R = nBu, X = Cl (10a), Br (10b-A/10b-B), I (10c)). The isomers do not interconvert. In the corresponding reaction of 7 with SnBr4 instead of a carbene-C,O chelate dicarbonyl phosphine tungsten(II) complex the carbene-C,O chelate tricarbonyl tungsten(II) complex (3b) is formed. When 8 is treated with SnBr4, the formation of a carbene-C,O chelate phosphine tungsten(II) complex cannot be detected any more. Like the o-OMe tungsten(0) complexes 5 and 6 the p-OMe tungsten(0) complex [(CO)4(PnBu3)WC(OMe)C6H4OMe-p] (11) and the ring-unsubstituted complex [(CO)4(PnBu3)WC(OMe)Ph] (13) react with SnBr4 by oxidative decarbonylation and formation of W(II) complexes, [Br2(CO)3(PnBu3)WC(OMe)R‘] (R‘ = C6H4OMe-p, Ph) (two isomers each). Dicarbonyl carbene-C,O chelate trimethylphosphine metal(II) complexes (M = Mo, W; X = Cl, Br) are also accessible by substitution of PMe3 for a CO ligand in However, when PMe3 is replaced by the bulkier PPh3 in the reaction with instead of substitution, the opening of the chelate ring is observed.