Electronic and Structural Variations of a Nickel(0) N-Heterocyclic Phosphenium Complex in Comparison to Group 10 Analogues.

ABSTRACT

The bonding interactions and electronic structure of a diphosphine pincer ligand featuring an N-heterocyclic phosphenium/phosphido (NHP±) central moiety with nickel are explored. Treating Ni(COD)2 with the pincer ligand [PPP]Cl in the presence of a two-electron phosphine donor ligand PMe3 generates chlorophosphine complex (PPClP)Ni(PMe3) (2a). The cationic Ni complex [(PPP)Ni(PMe3)][BPh4] (3a) can be prepared by subsequent halide abstraction from 2a with NaBPh4. The assignment of 3a as a Ni0/NHP+ complex, based on analysis of structural parameters and computational investigations, lies in contrast to its previously reported group 10 MII/NHP- (M = Pd, Pt) analogues. The activation of O-H bonds across the Ni-PNHP bond is demonstrated by the addition of isopropanol to afford the metal hydride species [(PPOiPrP)Ni(PMe3)(H)][BPh4] (4). Notably, the installation of a P-H bond in the NHP unit by treatment of 2a with LiAlH4 yields (PPHP)Ni(PMe3) (6). The ambiphilic nature of the P-H bond was demonstrated through reactivity studies of P-H bond cleavage in comparison to a Pd analogue (PPHP)Pd(PPh3) (8).