Analysis of the 13C chemical shift tensor in CO, Ni(CO)4, and Fe(CO)5 and its relationship to π-back bonding

Abstract

Components of the 13C shielding tensor. σ are presented for CO, Ni(CO)4, and Fe(CO)5. These shift components are separated into diamagnetic and paramagnetic parts using theoretical estimates for the former and spin rotation constants for the latter. The paramagnetic part of the perpendicular component of the chemical shift σp is shown to be mainly responsible for the large isotropic shift between free CO and metal bound CO. This fact is interpreted in terms of π‐back bonding in the metal carbonyls