Lewis Acid‐Promoted Oxidative Addition at a [Ni <sup>0</sup> (diphosphine) <sub>2</sub> ] Complex: The Critical Role of a Secondary Coordination Sphere
Joseph A. Zurakowski, Brady J. H. Austen, Maeve C. Dufour, Denis M. Spasyuk, David J. Nelson, Marcus W. Drover
Abstract
Abstract 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 [Ni 0 (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 [Ni 0 (P 2 B Cy 4 ) 2 ] (P 2 B Cy 4 =1,2‐ bis (di(3‐dicyclohexylboraneyl)‐propylphosphino)ethane) is competent for room‐temperature PhI cleavage to give [Ni II (P 2 B Cy 4 )(Ph)(I)]. This difference in oxidative addition reactivity has been scrutinized computationally – an outcome that is borne out in ring‐opening to provide the reactive precursor – for [Ni 0 (P 2 B Cy 4 ) 2 ], a “boron‐trapped” 16‐electron κ 1 ‐diphosphine Ni(0) complex. Moreover, formation of [Ni II (P 2 B Cy 4 )(Ph)(I)] is inherent to the P 2 B Cy 4 secondary coordination sphere: treatment of the Lewis adduct, [Ni 0 (P 2 B Cy 4 ) 2 (DMAP) 8 ] with PhI provides [Ni II (P 2 B Cy 4 ) 2 (DMAP) 8 (I)]I via iodine‐atom abstraction and not a [Ni II (Ph)(I)(diphosphine)] compound – an unusual secondary sphere effect. Finally, the reactivity of [Ni 0 (P 2 B Cy 4 ) 2 ] with 4‐iodopyridine was surveyed, which resulted in a pyridyl‐borane linked oligomer. The implications 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.