Oxygen-17 nuclear magnetic resonance spectra of mononuclear manganese and dinuclear Group 6 metal carbonyl complexes

Abstract

Oxygen-17 n.m.r. spectra have been measured for two series of metal carbonyl derivatives, [MnR(CO)5](R = H, CH3, and Br) and [MM′(CO)10]n–(n= 0 for M = M′= Mn; n= 1 for M = Mn, M′= Cr, Mo, and W; n= 2 for M = M′= Cr, Mo, and W), at natural 17O abundance. Oxygen-17 chemical shifts for mononuclear [MnR(CO)5] are explained in terms of substituent electronegativity which would be expected to increase the paramagnetic shielding as the charge density at the oxygen 2p orbitals decreases. For the dinuclear metal carbonyls, the diamagnetic shielding effect due to the metal–metal bond appears to be responsible for a subtle change in 17O resonance frequencies.