Applications of 95Mo N.M.R. Spectroscopy. XVI Structure and Bonding in [Mo(CO)3(η6-arene)] Complexes from 95Mo, 13C and 17O Relaxation Times

Abstract

Spin-lattice relaxation times (T1) have been measured for the 95Mo, 17O and methine and carbonyl 13C nuclei for a series of [Mo(CO)3(η6-C6H6- nMen)] complexes. In addition to the expected decrease in T1 with increasing molecular volume, the 95Mo and methine 13C data are interpreted in terms of variations in arene-molybdenum bonding. The methine 13C T1 values decrease in the order o-xylene > toluene > p-xylene > m-xylene > mesitylene. The methyl substitution pattern determines the distribution of electron-rich sites on the arene ligand, affecting the molybdenum-arene bond strength and the barrier to arene rotation. These observations support an earlier proposal that downfield 95Mo chemical sh..