Synthesis and characterization of NiAl-hydride heterometallics: perturbing electron density within Al–H–Ni subunits

Abstract

Heterometallic hydride complexes are of growing interest due to their potential to contribute to highly active insertion-based catalysis; however, methods to modulate electron density within this class of molecules are underexplored. Addition of ancillary ligands to heterotrimetallic NiAl₂H₂ species (1) results in the formation of heterobimetallic NiAl-hydride complexes with varying phosphine donors (2-(L)₂). Incorporation of sigma donating ancillary ligands of increasing strength led to contractions of the Ni–Al distances correlated to a strengthening of a back donation interaction to the Al–H sigma antibonding orbital, most prominently present in 2-(PMe₃)₂. Demethylation of the aryl ether from 2-(PMe₃)₂ provides access to a novel anionic nickel–aluminum complex (3) with a maintained bridged hydride moiety between Ni and Al. Increased negative charge in complex 3 results in an elongation of the Ni–Al interaction. Combined crystallographic, spectroscopic, and computational studies support a 3-center interaction within the Al–H–Ni subunits and were used to map the degree of Ni–H character of the series within the Al–H–Ni bonding continuum.