Arene C(sp(2))-H Metalation at Ni(II) Modeled with a Reactive PONCPh Ligand

Coordination of the reactive phosphinitopyridylphenyl PONCPh ligand L(H) to NiBr2 initially yields paramagnetic brown NiBr2(L(H)) (1), but addition of triethylamine results in fast and facile cyclometalation at Ni(II), giving NiBr(κ(3)-P,N,C-L) (2) as well-defined species. This is a rare example of direct cyclometalation at Ni(II) from a C-H bond in a ligand structure other than encumbering ligands (e.g., ECE pincers). Diamagnetic yellow complex 2 reacts instantaneously with HBF4 to give purple [NiBr(κ(3)-P,N-L(H))]BF4 (3). A very unusual (an)agostic Ni(CPh-H) interaction in the solid-state structure of 3 was unequivocally demonstrated using single-crystal X-ray crystallography and was interpreted by density functional theory calculations (quantum theory of atoms in molecules and electron localization function analysis). These compounds may be viewed as models for key intermediates in the Ni-catalyzed C-H functionalization of arenes.