Dispersion Forces, Disproportionation, and Stable High-Valent Late Transition Metal Alkyls.

The transition metal tetra- and trinorbornyl bromide complexes, M(nor) (M=Fe, Co, Ni) and Ni(nor) Br (nor=1-bicyclo[2.2.1]hept-1-yl) and their homolytic fragmentations were studied computationally using hybrid density functional theory (DFT) at the B3PW91 and B3PW91-D3 dispersion-corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M-C bond lengths for the stable complexes, and it was found that Fe(nor) receives a remarkable 45.9 kcal mol stabilization from the dispersion effects whereas the tetragonalized Co(nor) shows stabilization of 38.3 kcal mol . Ni(nor) was calculated to be highly tetragonalized with long Ni-C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor) confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.