From Dead Ends to Catalyst Reservoirs: Bimetallic Reactivation of Homoleptic Nickel Pincer Complexes

Homoleptic nickel(II) pincer complexes are commonly regarded as thermodynamically stable off-cycle species that terminate catalytic activity. Here we show that such complexes can undergo clean conversion to monohalide LNiBr species through a bimetallic reactivation pathway. Treatment of a homoleptic Ni(II) pincer complex with NiBr2 generates a transient binuclear intermediate formed by association of the external metal salt with the pincer complex. UV–vis monitoring reveals the accumulation and subsequent decay of this intermediate during the transformation. Time-dependent DFT calculations identify characteristic metal–metal charge-transfer (MMCT) transitions that provide an electronic signature for the binuclear species and support the proposed structure. Notably, simple halide salts such as LiBr also promote conversion of the homoleptic complex to the monohalide LNiBr complex. These results provide insight into the reactivity of homoleptic nickel pincer complexes and illustrate how transient bimetallic interactions can mediate their transformation.