Coupling of cyclooctyne with carbon monoxide on divalent molybdenum and tungsten. Crystal and molecular structure of a bis(hexamethylene)cyclopentadienonetungsten complex, W(S2CNMe2)2(CO){(C8H12)2CO}

Abstract

Cyclooctyne (C8H12) in excess reacts with the dialkyldithiocarbamato complexes M(S2CNR2)2(CO)2 (R = Me, Et; M == Mo, L = PPh3; M = W, L = CO, PPh3) to give a mixture of two complexes, M(S2CNR2)2)(CO){(C8H12)2CO} (1-4) and M(S2CNR2)2(C8H12){(C5H12)2CO} (5-8). These contain tetrahapto-bis-(hexamethylene)cyclopentadienone, (C8H12CO, formed by the condensation of two molecules of cyclooctyne with one molecule of CO. Crystals of W(S2CNMe2)2(CO){(C8H12)2CO} (3) are monoclinic, space group P21/n, with a 15.132(1), b 15.705(2), c 11.346(1) Å, β 93.68(2)°, and Z = 4. The structure was solved by heavy-atom methods and refined by least-squares methods to R = 0.027 (Rw = 0.045) for 5811 unique data [I ≧ 3σ(I)]. The molecule is approximately pentagonal bipyramidal, with terminal CO and one sulphur atom of a bidentate Me2NCS2 ligand in the axial positions. The equatorial sites are occupied by the other sulphur atom of this Me2NCS2 ligand, the second bidentate Me2NCS2 ligand, and the mid-points of the coordinated CC bonds of η4-(C8H12CO. As in other cyclopentadienone complexes, the CC distances in the η4-dienone are almost equal (av. 1.45 Å) and the CO group is bent away from the plane of the ring (dihedral angle 17.6°). Infrared and NMR (1H, 13C) data suggest that complexes 5-8 are similar to 1-4, with cyclooctyne acting as a 2π-electron donor in place of CO. Show more