Influence of stereochemistry on the formation and reactivity of phosphorus-bridged dinuclear metal carbonyls. Part V. Crystal structure of bis-µ-diphenylphosphido-bis(dicarbonylnickel)

Abstract

Bis-µ-diphenylphosphido-bis(dicarbonylnickel), [(OC)₂Ni(PPh₂)₂Ni(CO)₂], forms triclinic crystals (space group P), with a unit cell of dimensions a= 8·894(3), b= 8·740(5), c= 17·486(7)Å, α= 93·27(3), β= 87·34(2), γ= 106·49(2)°, containing two crystallographically different centrosymmetric molecules. A least-squares analysis with anisotropic thermal parameters of 2068 independent structure amplitudes, measured on a four-circle diffractometer, led to a final R of 0·045.

The two molecules are identical within experimental error, except for minor conformational differences. In each, the two nickel atoms are linked by a planar di-µ-phosphido-bridge (Ni–P 2·19 Å) and by a strong metal-metal bond (2·51 Å). The metal-metal bond causes intramolecular crowding which is relieved by a reduction of the Ni–P–Ni bond angles to 70°, but all other bond lengths and bond angles in this nickel(I) complex are similar to those in tetrahedral nickel(O) complexes. The crystallographic evidence for π-bonding in the Ni–C [1·79(1)Å] and Ni–P bonds [2·193(3)Å] is discussed, and it is concluded that π-bonding, if it exists at all in this complex, has negligible effect on bond lengths.