Mono-cyclooctyne complexes of divalent and tetravalent molybdenum and tungsten

Abstract

Cyclooctyne (C 8H 12) reacts with the dialkyldithiocarbamato complexes Mo(S 2CNR 2) 2(CO) 2(PPh 3) and W(S 2CNR 2) 2(CO) 3 (R = Me, Et) in a 1:1 mol ratio to give the divalent metal alkyne complexes M(S 2CNR 2) 2(CO)(C 8H 12). These are oxidized by bromine or iodine to tetravalent metal alkyne complexes MX 2(S 2CNR 2) 2(C 8H 12) (M = Mo, W; X = Cl, Br; R = Me, Et). Carbon-13 NMR and IR spectroscopic data indicate that in these compounds and in the triethylphosphine complexes MBr 2(CO)C 8H 12)(PEt 3) 2 (M = Mo, W) cyclooctyne behaves as a 4π-electron donor, whereas in the oxomolybdenum(IV) cyclooctyne complexes MoO(S 2CNR 2) 2C 8H 12) (R = Me, Et) it donates approximately π-electrons owing to competing π-donation from the oxo ligand.