Molybdenum and tungsten complexes of sulfene (thioformaldehyde S,S-dioxide)

Propionitrile complexes fac-[M(CO)(3)(P-P)(NCEt)] (M = Mo (3), W (4); P-P = Ph(2)PCH(2)PPh(2) (a), Ph(2)PC(2)H(4)PPh(2) (b), Ph(2)PC(3)H(6)PPh(2) (c), (S,S)-Ph(2)PCHMeCHMePPh(2) (d), Fe(C(5)H(4)PPh(2))(2) (e)) were synthesized from [M(CO)(3)(NCEt)(3)] and the corresponding diphosphine. Reactions of 3 and 4 with sulfur dioxide initially gave complexes fac-[M(CO)(3)(P-P)(eta(2)-SO(2))] (M = Mo (5), W (6)), which slowly isomerized to mer-[M(CO)(3)(P-P)(eta(1)-SO(2))] (M = Mo (7), W (8)). The structures of 7b and 8b were determined by X-ray crystallography. Both compounds are isostructural (monoclinic, space group P2(1)/n (No. 14)) with almost identical unit cell dimensions (7b, a = 14.511(5) A, b = 12.797(2) A, c = 16.476(6) A, beta = 115.92(2); 8b, a = 14.478(8) A, b = 12.794(3) A, c = 16.442(9) A, beta = 116.01(2)) and molecular geometries. Treatment of either fac-[M(CO)(3)(P-P)(eta(2)-SO(2))] or mer-[M(CO)(3)(P-P)(eta(1)-SO(2))] with diazomethane yielded the sulfene complexes mer-[M(CO)(3)(P-P)(eta(2)-CH(2)SO(2))] (M = Mo (9), W (10)). The structure of 10a was determined crystallographically: monoclinic, space group P2(1)/n (No. 14), a = 11.719(2) A, b = 17.392(4) A, c = 13.441(3) A, beta = 95.58(2). The tungsten atom resides in the center of a distorted pentagonal bipyramid. The sulfene ligand occupies two adjacent equatorial sites with the bond distances W-C, 2.322(13) A, W-S, 2.353(3) A, and S-C, 1.721(12) A. The latter equals the S-C single bond distance in thiirane S,S-dioxide, indicating a high degree of charge density transfer into the LUMO of the sulfene ligand.