Lewis Acid-Promoted Oxidative Addition at a [Ni0(diphosphine)2] Complex: The Critical Role of a Secondary Coordination Sphere

Oxidative addition represents a critical elementary step in myriad catalytic transformations. Here, the importance of thoughtful ligand design cannot be overstated. In this work, we report the intermolecular activation of iodobenzene (PhI) at a coordinatively saturated 18-electron [Ni0(diphosphine)2] complex bearing a Lewis acidic secondary coordination sphere. Whereas alkyl-substituted diphosphine complexes of Group 10 are known to be unreactive in such reactions, we show that [Ni0(P2BCy4)2] (P2BCy4 = 1,2-bis(di(3-dicyclohexylboraneyl)-propylphosphino)ethane) is competent for room-temperature PhI cleavage to give [NiII(P2BCy4)(Ph)(I)]. This difference in oxidative addition reactivity has been scruti-nized computationally – an outcome that is borne out in ring-opening to provide the reactive precursor – for [Ni0(P2BCy4)2], a “boron-trapped” 16-electron κ1-diphosphine Ni(0) complex. Moreover, formation of [NiII(P2BCy4)(Ph)(I)] is inherent to the P2BCy4 secondary co-ordination sphere: treatment of the Lewis adduct, [Ni0(P2BCy4)2(DMAP)8] with PhI provides [NiII(P2BCy4)2(DMAP)8(I)]I via iodine-atom abstraction and not a [NiII(Ph)(I)(diphosphine)] compound – an interesting secondary sphere effect. Last, the reactivity of [Ni0(P2BCy4)2] with 4-iodopyridine was surveyed, which resulted in a pyridyl-borane linked oligomer. The implica-tions of these outcomes are discussed in the context of designing strongly donating, and yet labile diphosphine ligands for use in a critical bond activation step relevant to catalysis.