Formally Zerovalent Bis(arene) Germylene Complexes of Zirconium and Hafnium

Tetrachlorides of zirconium and hafnium form adducts (2, 3) with an intramolecular germylene phosphine Lewis pair. Two electron reduction treating the adducts with [^MesNacnacMg]₂ gives the low-valent metal complexes (4, 5) featuring η⁶-Trip coordination at the Zr(II) and Hf(II) metal atom. Reduction of the M(II)-complexes gives the zerovalent metal complexes of zirconium (6) and hafnium (7), which have been structurally characterized. Two arene moieties and the germylene exhibit metal coordination. Puckered coordination of a P-phenyl unit was observed for both derivatives 6 and 7. Four electron reduction of a reaction mixture of metal tetrachloride with the germylene phosphine Lewis pair also gives the zerovalent complexes in good yield. Carbonyl complexes were synthesized treating the reduced metal complexes with carbon monoxide. Dimethylbutadiene shows a reaction with an arene moiety and the coordinated germylene ligand of the zerovalent complexes. A cyclohexadienyl and a triorganogermate ligand are formed. For zirconium this reaction is reversible at room temperature.