Lewis acid-promoted oxidative addition at a [Ni0(diphosphine)2] complex : the critical role of a secondary coordination sphere

Zurakowski, Joseph A. and Austen, Brady J. H. and Dufour, Maeve C. and Spasyuk, Denis M. and Nelson, David J. and Drover, Marcus W. (2021) Lewis acid-promoted oxidative addition at a [Ni0(diphosphine)2] complex : the critical role of a secondary coordination sphere. Chemistry - A European Journal, 27 (64). pp. 16021-16027. ISSN 0947-6539 (https://doi.org/10.1002/chem.202103121)

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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 2B Cy 4) 2] (P 2B Cy 4=1,2-bis(di(3-dicyclohexylboraneyl)-propylphosphino)ethane) is competent for room-temperature PhI cleavage to give [Ni II(P 2B 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 2B Cy 4) 2], a “boron-trapped” 16-electron κ 1-diphosphine Ni(0) complex. Moreover, formation of [Ni II(P 2B Cy 4)(Ph)(I)] is inherent to the P 2B Cy 4 secondary coordination sphere: treatment of the Lewis adduct, [Ni 0(P 2B Cy 4) 2(DMAP) 8] with PhI provides [Ni II(P 2B 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 2B 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.