Synthesis, reactions and structure of bromo(η5-diphenylphosphinylcyclopentadienyl)nickel(II) dimer

The reaction of diphenylphosphinylcyclopentadienylthallium (1) with NiBr2·2DME has produced Ni2(η5-C5H4PPh2)2Br2 (2) in quantitative yield. A reaction of 2 with methyl-lithium affords Ni2(η5-C5H4PPh2)2(CH3)2 (3) in high yield. Both 2·0.5CH2Cl2 and 3 have been characterized by means of single crystal X-ray diffraction studies and shown to be homobimetallic, with cyclic dimeric structures. Each ligand bridges two metal centers via P coordination to one and η5-coordination of the cyclopentadienyl moiety to a second Ni2+. Each nickel atom is thus formally five-coordinate with average bonding parameters of Ni–Centroid (Cp), Ni–P, and Ni–X of 1.760(5), 2.154(5), Br: 2.301(8) Å (2) and 1.769(5), 2.113(5), CH3: 1.944(1) Å (3). The P–Ni–X angles are compressed in 3 compared to 2 by an average of 4°.