The titanium tris-anilide cation [Ti(N[tBu]Ar)3]+ stabilized as its perfluoro-tetra-phenylborate salt: structural characterization and synthesis in connection with redox activity of 4,4′-bipyridine dititanium complexes

Abstract

This work explores the reduction of 4,4′-bipyridine using two equivalents of the titanium(III) complex Ti(N[^tBu]Ar)₃ resulting in formation of a black, crystalline complex, (4,4′-bipy){Ti(N[^tBu]Ar)₃}₂, for which an X-ray structure determination is reported. The neutral, black, 4,4′-bipyridine-bridged bimetallic was found to be redox active, with mono- and di-anions being accessible electrochemically, and with the mono- and di-cations also being accessible chemically, and isolable, at least when using the weakly coordinating anion [B(C₆F₅)₄]⁻ as the counter-ion. It proved possible to crystallize the salt [(4,4′-bipy){Ti(N[^tBu]Ar)₃}₂][B(C₆F₅)₄]₂ for a single-crystal X-ray structure investigation; in this instance it was revealed that the aromaticity of the 4,4′-bipyridine ligand, that had been disrupted upon reduction, had been regained. A rare cationic d⁰ metal tris-amide complex, shown by X-ray crystallography to contain an intriguing pyramidal TiN₃ core geometry, namely {Ti(N[^tBu]Ar)₃}⁺, could also be isolated when using [B(C₆F₅)₄] as the essentially non-interacting counter-ion. This highly reactive cation should be considered as a potential intermediate in the plethora of reactions wherein Ti(N[^tBu]Ar)₃ has been shown to effect the reduction of substrates including halogenated organic molecules, carbonyl compounds, organic nitriles, and metal complexes.