Solid State Carbon-13 NMR of Metal Carbonyls

Abstract

The first carbon-13 NMR spectrum of a metal carbonyl was reported in 1958 for iron pentacarbonyl by Cotton and Waugh.[1] The result, a single resonance in the carbonyl region, has been shown to be correct by several subsequent investigations.[2] In fact the single resonance for Fe(CO)5 persists to −160 °C.[3] The structure of iron pentacarbonyl in solution is trigonal bipyramidal thus the carbon-13 NMR spectrum for this complex should contain 2 signals of relative intensity 2 to 3. Of the possible explanations for the single resonance it is now accepted that the trigonal bipyramidal structure undergoes a reorientation which is fast on the NMR time scale and exchanges equatorial and axial carbonyl groups. The most likely mechanism for the exchange of carbonyls is the well known Berry psuedorotation.[4]