An Investigation of Adduct Complexes of M(S₂CNEt₂)₂(Co)₂ (M=Mo,W) by ₉₅Mo and ₁₈₃W N.M.R-Spectroscopy

Abstract

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 < C^{l -} < 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.