Heteronuclear 1,3-intramolecular metal shifts in pentacarbonyl-chromium, -molybdenum, and -tungsten derivatives of 2-thia-4-selenapentane. A dynamic nuclear magnetic resonance investigation

Abstract

The mononuclear complexes [M(CO)₅(MeSeCH₂SMe)](M = Cr, Mo, or W) have been prepared and are present in solution as isomers with both S → M and Se → M bonding. In addition to the facile pyramidal atomic inversion of the metal-co-ordinated sulphur and selenium atoms, a novel 1,3-metal shift between the two different ligand atoms occurs. From static and dynamic n.m.r. studies the relative populations of sulphur- and selenium-bonded species have been obtained, along with the activation energy for both S → Se and Se → S metal shifts Energy profiles for these 1,3-shifts reveal the distinction in ground-state energies between the sulphur- and selenium-bonded isomers and essentially quantify the difference in bond energy between the S → M and Se → M bonds; such values are not otherwise easily accessible.