Molybdenum-95 and carbon-13 nuclear magnetic shielding and bonding relationships in sandwich complexes

Abstract

N.m.r. shifts of ⁹⁵Mo and ¹³C in sandwich complexes with a range of C₅, C₆, and C₇ ring types are interpreted on a ligand-field model, by comparison with orbital ionisation energies. The shielding increases with forward- and back-bonding, also with η⁵, σ-C₅H₄CR₂ bonding of the fulvene ligand. The shielding therefore decreases with increase in ring size and from closed to open π systems, and thus with increase in reactivity (or decrease in stability), as observed in sandwich compounds of other transition metals.