Influence of stereochemistry on the formation and reactivity of phosphorus-bridged dinuclear metal carbonyls. Part II. The structure of (OC)3Ni(PPh2)2Ni(CO)3

Abstract

The structure of (OC)₃NiPPh₂·PPh₂Ni(CO)₃ has been determined by X-ray diffraction.

The co-ordination round the nickel atoms is tetrahedral, and the diphosphine link between the nickel atoms has the catenary form. The molecule consists of two identical halves, related by a centre of symmetry. The bond lengths and angles within each half-molecule are normal, but the phosphorus–phosphorus bond linking the two halves is longer than usual. This is attributed to steric strain resulting from repulsion between the phenyl groups and between phenyl and carbonyl groups.

This steric interaction provides a reason for the difficulty in preparing compounds of the catenary type from tetraaryldiphosphines. The effectiveness of the compound as an initiator for certain free-radical reactions may result from the ease with which the phosphorus–phosphorus link dissociates to form the free radical {(OC)₃Ni(PPh₂)·}.