Transition-metal chemical shifts in complexes of molybdenum(0) and tungsten(0)

Abstract

Molybdenum-95 and tungsten-183 n.m.r. spectra have been measured by direct observation and by multiple-resonance methods respectively for 65 related derivatives of [Mo(CO)₆] and [W(CO)₆] with (mainly) phosphorus ligands. The chemical shifts of the two nuclei are remarkably parallel, those for ^l83W being ca. 1.7 times more sensitive to changes in chemical environment than those for ⁹⁵Mo. The chemical shifts are temperature-dependent, and trends in them can be largely accounted for by variations in the mean electronic excitation energy. The metal–phosphorus spin-coupling constants are very predictable. Molybdenum-95 linewidths in many cases are quite small, and can be broadly explained by the use of a point-charge model.