The seven-coordinate adducts M(S2CNEt2)2(CO)2L and [M(S2CNEt2)2(CO)2]2-μ-L (M = Mo, W;L below), derived from the 16-electron complexes M(S2CNEt2)2(CO)2, have been investigated by 95Mo and 183W n.m.r. spectroscopy. The molybdenum and tungsten adducts exhibit resonances in the regions from 310 to -430 and from -465.5 to -1500 ppm , respectively. All the resonances are shielded relative to those of the M(S2CNEt2)2(CO)2 precursors. The dependence of the nuclear shielding on L is as follows. For M = Mo: NH2NHSO2C6H4Me < Cl - < OPPh3 < μ- pyrazine < pyridine < NH2NHCOPh < NH2NMe2 < μ-NH2NHMe < μ-NH2NH2 < μ-NH2CH2CH2NH2 < NH3
< N3- < F- < AsPh3 < PPh3 < SbPh3 < PPh2Et < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3 < CO. For M = W: NH2NHCOPh < AsPh3 < Ph2PCH2PPh2 < PPh3 < PPh2Et < Ph2PCH2CH2PPh2 < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3
< CO. The OPPh3, halide and nitrogen-donor ligand adducts participate in a dynamic equilibrium with Mo(S2CNEt2)2(CO)2 on the n.m.r . time scale. The remaining adducts do not exhibit such behaviour. The chemical shifts of both the molybdenum and tungsten adducts are correlated with the π- acceptor ability of the ligand , L, and the stereochemistry of the adducts. A linear relationship between the chemical shifts of analogous molybdenum and tungsten complexes is observed; the equation of the line is δ(183W) = 1.46δ(95Mo)-857.5.
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