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

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 PMe 3 generates chlorophosphine complex (PP Cl P)Ni(PMe 3 ) ( 2a ). The cationic Ni complex [(PPP)Ni(PMe 3 )][BPh 4 ] ( 3a ) can be prepared by subsequent halide abstraction from 2a with NaBPh 4 . The assignment of 3a as a Ni 0 /NHP + complex, based on analysis of structural parameters and computational investigations, lies in contrast to its previously reported group 10 M II /NHP - (M = Pd, Pt) analogues. The activation of O-H bonds across the Ni-P NHP bond is demonstrated by the addition of isopropanol to afford the metal hydride species [(PP O i Pr P)Ni(PMe 3 )(H)][BPh 4 ] ( 4 ). Notably, the installation of a P-H bond in the NHP unit by treatment of 2a with LiAlH 4 yields (PP H P)Ni(PMe 3 ) ( 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 (PP H P)Pd(PPh 3 ) ( 8 ).