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Homoleptic seven-coordinate Ti(0) and Zr(0) through a new stabilization mode
Ivan Antsiburov1,2, Raphael Bühler1,2,3, Johannes Stephan1,2
1Department of Chemistry, Technical University of Munich, TUM School of Natural Sciences, Chair of Inorganic and Metal-Organic Chemistry Garching Germany.
None:
The stabilization of zero oxidation state group (IV) metal centers in readily accessible compounds on a preparative scale remains a significant challenge. Substituting hydrocarbon ligands in the precursor complexes [Ti(η6-toluene)2] and [Zr(η6-cycloheptatriene)2] with monovalent GaTMP (TMP = 2,2,6,6-tetramethylpiperidinyl) yields the first homoleptic seven-coordinate Ti0 and Zr0 complexes, [Ti(GaTMP)7] (1) and [Zr(GaTMP)7] (2), which are exclusively coordinated by metalloligands. The bonding situation of 1 and 2 was rationalized through DFT calculations, revealing the critical importance of tangential Ga⋯Ga covalent interactions for stabilizing the compounds. Oxidation of 2 leads to the formation of [Zr(GaTMP)8]2+ (5), showcasing a similar bonding situation. These Ga⋯Ga interactions arise from significant π-backbonding from the Ti0 and Zr0 centers into the constructive combinations of the diffuse 4p orbitals of the Ga(i) centers. This unique cooperative feature of the all-Ga metalloligand sphere marks a clear distinction from the bonding properties of formally isolobal carbonyls, phosphines, or N-heterocyclic carbenes.
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