Until recently only a few monomeric metal imidazolate complexes were known, in contrast to a vast number of metal complexes having isoelectronic cyclopentadienyl ligand. This is mainly due to the tendency of imidazolate ligands to form coordination polymers where both nitrogen atoms bind to a metal center in η1 coordination mode. The alternative coordination of imidazolate ligands, η5, is rare. In this work a series of monomeric metal complexes with sterically hindered tert-butyl imidazolate ligands were synthesized and structurally characterized. The displacement of chloride ion from TiCl4 by 2,4,5-tri-tert-butylimidazole provided monomeric titanium(tBu3-imidazolate) trichloride where the imidazole ligand is coordinated to the metal center in η5 mode. The titanium(tBu3-imidazolate) trichloride was then reacted with methoxide ion to displace one or two chloride ions to yield titanium(tBu3-imidazolate)methoxide dichloride and titanium(tBu3-imidazolate)dimethoxide chloride complexes, respectively. While titanium(tBu3-imidazolate)trimethoxide was not isolated, monomeric complex with more sterically hindered alkoxide ligand, titanium(tBu3-imidazolate)triisopropoxide, was prepared where imidazolate ligand is coordinated to the metal center in η1 mode. Quantum chemical studies suggested that η1 coordination mode was more favorable for trialkoxide imidazolate metal complexes while bridging through methoxide group was also favorable for trimethoxide metal complex. Synthesis, characterization, crystal structures and quantum studies of various metal complexes with sterically hindered imidazolate ligands will be discussed in this presentation.

Coordination modes of sterically hindered imidazolate ligands in metal complexes

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.