Intramolecular Agostic Interactions and Dynamics of a Methyl Group at a Preorganized Dinickel(II) Site.

Alkyl nickel intermediates relevant to catalytic processes often feature agostic stabilization, but relatively little is known about the situation in oligonickel systems. The dinickel(I) complex K[LNi], which is based on a compartmental pyrazolato-bridged ligand L with two β-diketiminato chelate arms, or its masked version, the dihydride complex [KL(Ni-H)] that readily releases H, oxidatively add methyl tosylate to give diamagnetic [LNi(CH)] () with (Ni···Ni) ≈ 3.7 Å. Structural characterization shows that the methyl group in is bound to one Ni and exhibits an intramolecular agostic interaction with the more distant Ni. This is supported spectroscopically (viz., a ν(C-H) stretch at 2658 cm and lowered of 114 Hz) and by DFT calculations, including topological analysis of the computed electron density for . NMR spectroscopy reveals very fast hopping of the CH group between the two Ni ions, which according to DFT has a minute barrier of 4 kcal mol and proceeds via a planar CH moiety in the transition state (Walden-like inversion). The alkylidene group in K[LNi(μ-CHSi(Me))], obtained from the reaction of [KL(Ni-H)] with NCHSiMe, is symmetrically bridging. This work provides new insight into the stabilization and dynamics of alkyl ligands at dinickel sites with a constrained metal···metal distance.