Bis{μ-cis-1,3-bis[(di-tert-butylphosphanyl)oxy]cyclohexane-κ2 P:P′}bis[carbonylnickel(0)] including an unknown solvent molecule

The title compound, [Ni2(C22H46P2O2)2(CO)2], is located about a centre of inversion with the Ni0 atom within a distorted trigonal–planar geometry. The cyclohexyl rings are in the usual chair conformation with the 1,3-cis substituents equatorially oriented. No specific intermolecular interactions are noted in the crystal packing. A region of disordered electron density, most probably a disordered deuterobenzene solvent molecule, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Its formula mass and unit-cell characteristics were not taken into account during refinement.

The title compound, [Ni 2 (C 22 H 46 P 2 O 2 ) 2 (CO) 2 ], is located about a centre of inversion with the Ni 0 atom within a distorted trigonal-planar geometry. The cyclohexyl rings are in the usual chair conformation with the 1,3-cis substituents equatorially oriented. No specific intermolecular interactions are noted in the crystal packing. A region of disordered electron density, most probably a disordered deuterobenzene solvent molecule, was treated using the SQUEEZE routine in PLATON [Spek (2009). Acta Cryst. D65,[148][149][150][151][152][153][154][155]. Its formula mass and unit-cell characteristics were not taken into account during refinement.  Financial support from the Swedish Research Council and the Knut and Alice Wallenberg Foundation is gratefully acknowledged.

Structural commentary
The title compound is formed through a carbon monoxide induced dimerization of a previously synthesized POCOP pincer Ni II hydride complex. The course of the reaction is likely to proceed via a reductive elimination of a C-H bond between the metallated carbon and the hydride ligand. In the absence of carbon monoxide the POCOP pincer Ni II hydride complex is stable towards reductive elimination in solution, even at 80 °C and upon addition of 1 eq. diphenylacetylene.
Tricoordinate nickel(0) species are coordinately unsaturated, and the steric bulk of the tert-butyl substituents on the phosphorus atoms is likely to have a crucial stabilizing impact on the title compound. It decomposes over a period of hours upon exposure to air.
The title compound has a low solubility in C 6 D 6 and attempts to obtain 1 H-and 13 C-NMR spectra has been unsatisfactory. Dissolving the red crystals of the title compound in CDCl 3 results in a yellow/green solution and decomposition to several compounds, as indicated by 31 P-NMR spectroscopy; none was successfully isolated or characterized.

Refinement
The H atoms were positioned geometrically and treated as riding on their parent atoms with C-H distances of 0.96-0.98 Å, and with U iso (H) = 1.2-1.5 U eq . The asymmetric unit contains half a molecule of the title complex and half a molecule of benzene but this could not be modelled successfully. Solvent contributions were therefore removed from the diffraction data with PLATON using the SQUEEZE procedure (Spek, 2009). SQUEEZE estimated the electron count in the void volume of 680 Å 3 to be 140 which is in reasonable agreement with a total number of four benzene molecules in supplementary materials sup-2 Acta Cryst. (2014). E70, m176-m177 the unit cell.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.