Correlation of 95Mo NMR chemical shifts, electronic absorption bands, and solvent donor numbers for some dimeric Mo 2(O 2CR) 4L 2 solvent adducts

Abstract

The 95Mo NMR chemical shifts are reported for two series of solvent adducts of the dimeric molybdenum(II) complexes Mo 2(O 2CR) 4L 2 (R = CF 3, Bu t ; L - solvent). The large deshielding effect (over 450 ppm for the R = CF 3 series as the solvent changes from chloroform to hexamethylphosphoramide) correlates well with the donor number of the solvent. The lowest energy electronic absorption band corresponding to the δ− δ * transition also moves to longer wavelength with the more strongly coordinating solvents, which is consistent with weakening of the MoMo quadruple bond and the dominance of the ΔE parameter in the paramagnetic term which controls the magnitude of δ( 95Mo).