Tris(tert-butyl isocyanide-κC)carbonylnickel(0)

The title compound, [Ni(C5H9N)3(CO)], was prepared from Ni(CO)4 and a tenfold excess of tert-butyl isocyanide. It crystallizes with two symmetry-independent molecules per asymmetric unit. The central Ni atom of each independent molecule has a nearly perfect tetrahedral coordination environment, comprising one carbon monoxide and three isocyanide ligands. The title compound is the first structurally characterized Ni0 compound with a mixed CO/RNC coordination.

The title compound, [Ni(C 5 H 9 N) 3 (CO)], was prepared from Ni(CO) 4 and a tenfold excess of tert-butyl isocyanide. It crystallizes with two symmetry-independent molecules per asymmetric unit. The central Ni atom of each independent molecule has a nearly perfect tetrahedral coordination environment, comprising one carbon monoxide and three isocyanide ligands. The title compound is the first structurally characterized Ni 0 compound with a mixed CO/RNC coordination.

Experimental
Crystal data [Ni(C 5 Halbauer et al. (2006); M = Mo: ). Due to the enhanced reactivity of Ni(CO) 4 we nevertheless attempted the synthesis of complexes of the type [Ni(CN) 2 ( t BuNC) 4 ] from the reaction of Ni(CO) 4 with an excess of the corresponding isocyanide leading to the formation of the title compound.
The molecular structure of one of the symmetry independent molecules of the title compound is depicted in Fig. 1. As it is expected the central nickel atom is almost perfectly tetrahedrally coordinated by three isocyanide and one carbon monoxide ligand. The metal carbon bond lengths of the isocyanide carbons atom are about 11 pm in average longer compared to the Ni-CO bond reflecting the higher π-acceptor properties of the latter. Both CO and isocyanide ligands are nearly not bent out of linearity. The bond lengths of the two molecules in the asymmetric unit are identical within experimental errors. In contrast to this observation the bond angles show slight deviations which may be caused by the bulkiness of the tert-butyl groups connected with packing effects. As it is expected the shortest intermolecular distances are of the C-H···O type. But whereas O1B is engaged in the three shortest interactions observed (C6A-H6AC···O1B 2.721 (8) Å; C11A-H11B···O1B 2.817 (8) Å; C16A-H16A···O1B 2.876 (8)), O1A shows only one contact below 3 Å (C16B-H16E···O1A 2.949 (9) Å).
All of these contacts are well in the range discussed by Desiraju & Steiner as C-H···O hydrogen bonds (Desiraju & Steiner (1999).

Refinement
Hydrogen atoms were calculated in idealized positions and refined with distances of 0.96 Å. All hydrogen atoms were refined using a riding model with U iso (H) = 1.5 times U iso (C). Fig. 1. Molecular structure of one of the symmetry independent molecules of the title compound showing the labelling scheme. Displacement ellipsoids are drawn at the 40% probability level.