Silent Neighbors? Dissecting Borane–Carbonyl Interactions at Nickel–Oxirane Models

Metalloxiranes are mechanistically relevant intermediates in carbonyl functionalization by metals. Herein, we investigate carbonyl activation using a nickel complex supported by a diphosphine ligand bearing a pendent Lewis-acidic monoborane. Reaction of this ambiphilic system with a series of carbonyl substrates affords nickeloxiranes whose isomeric distributions and relative energies were examined experimentally and computationally through density functional theory. Despite the proximity of borane functionality, the nickeloxiranes derived from benzophenone and acetophenone exhibited no definitive evidence for intra- or intermolecular O→B interactions. In contrast, the benzaldehyde analogue displayed a well-defined noncovalent O→B interaction in both the solution and solid states. These findings provide insights into the factors governing carbonyl activation by ambiphilic nickel systems.