Phosphorus as a heteroatom in metallaborane structures: Cyclopentadienylcobalt diphosphaboranes

The icosahedral cobaltadiphosphaborane CpCoP2B9H9 and its indenyl analog were recently synthesized by Welch and coworkers and characterized structurally by X-ray crystallography. The complete series of related cobaltadiphosphaboranes CpCoP2Bn-3H3 (n = 8-12) have now been studied by density functional theory. A significantly larger number of low-energy CpCoP2Bn-3Hn-3 structures relative to the global minima were found than for the carbon analogs CpCoC2Bn-3Hn-1 suggesting more complicated energy surfaces and possible fluxional systems. In all of the lowest energy CpCoP2Bn-3Hn-3 structures the central CoP2Bn-3 polyhedra are found to be the most spherical deltahedra similar to those found in the corresponding BnHn2-- dianions. The lowest energy CpCoP2Bn-3Hn-3 structures typically but not always have the cobalt atom at a degree 5 or 6 vertex and the phosphorus atoms at degree 4 vertices. For the icosahedral CpCoP2B9H9 system the four structures with adjacent phosphorus vertices all lie at higher energies relative to all five structures with non-adjacent phosphorus vertices. (C) 2014 Elsevier Ltd. All rights reserved.