Amine, amido, and imido complexes of tantalum supported by a pyridine-linked bis(phenolate) pincer ligand: Ta-N pi-bonding influences pincer ligand geometry.
A series of tantalum imido and amido complexes supported by a pyridine-linked bis(phenolate) ligand has been synthesized. Characterization of these complexes via X-ray crystallography reveals both C(s) and C(2) binding modes of the bis(phenolate)pyridine ligand, with complexes containing two or fewer strong pi-donor interactions from ancillary ligands giving C(s) symmetry, whereas three strong pi-donor interactions (e.g., three amido ligands or one amido ligand and one imido ligand) give C(2)-symmetric binding of the bis(phenolate)pyridine ligand. DFT calculations and molecular orbital analyses of the complexes have revealed that the preference for C(s)-symmetric ligand binding is a result of tantalum-phenolate pi-bonding, whereas in cases where tantalum-phenolate pi-bonding is overridden by stronger Ta-N pi-bonding, C(2)-symmetric ligand binding is preferred, likely because conformationally this is the lowest-energy arrangement. This electronically driven change in geometry indicates that, unlike analogous metallocene systems, the bis(phenolate)pyridine pincer ligand is not a strong enough pi-donor to exert dominant control over the electronic and geometric properties of the complex.
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, USA.
Ian A
IA
Tonks
Larry M
LM
Henling
Michael W
MW
Day
John E
JE
Bercaw