A Nickel(0) Dimer/Monomer System with Facile and Reversible Carbon Monoxide Uptake: Ni2(CO)x(dppm)2 (x = 3, 4) and Ni(CO)3(η1-dppm)

Article abstract of DOI:10.1021/ja00215a018

Ni(CO)2 decomposes slowly at room temperature to produce the bis(diphenylphosphino)methane (dppm) bridged nickel(0) dimer Ni2(CO)3(dppm)2 (4).Complex 4 crystallizes in the orthorhombic space group Pbcn with a = 14.015 (2) Angstroem, b = 18.784 (5) Angstroem, c = 22.743 (8) Angstroem, V = 5987 (4) Angstroem³, and Z = 4.A total of 3913 reflections were collected using Mo Kα radiation, and the structure was solved and refined by using 1237 independent reflections with F₀² > 3?(F₀)², leading to a final R₁ = 0.062.Ignoring the Ni-Ni bond, the structure of 4 shows approximate tetrahedral geometry about the two nickel atoms with an unusual cis arrangement of the two bridging dppm ligands, one bridging carbonyl ligand, and two terminal carbonyl ligands.The molecule sits on 2-fold axis passing through the bridging carbonyl group, and there are three solvent molecules of benzene per nickel dimer in the cell unit.The Ni-Ni bond distance of 2.603 (4) Angstroem is in the proper range for the expected single bond. 4 readily reacts with 1 equiv of carbon monoxide under ambient conditions to form the 18-electron binuclear complex with terminal CO ligand, Ni2(CO)4(dppm)2 (5), which has been characterized spectroscopically.Although 5 is a saturated 18-electron species, it also readily reacts with CO to fragment, producing Ni(CO)3(η¹-dppm) (6) in which the dppm ligand is only bound by one phosphorus atom.Spectroscopic data on 6 supporting the Ni(CO)3(η¹-dppm) formulation are presented.The CO-based equilibrium 4 <*> 5 <*> 6 is fully reversible in solution.