Tantalum-Mediated Substitution at Germanium:  A Germolyl-to-Germole Transformation Leading to η⁴-C₄Me₄GeMeCl Complexes

The germole reagent C4Me4GeMeSiMe3 (1), synthesized via reaction of K[C4Me4GeSiMe3] with MeI, reacted with TaCl5 to give [(η4-C4Me4GeMeCl)TaCl3(Et2O)x]2 (2; x = 0.5−1.0) with loss of Me3SiCl. Complex 2 reacted with various two-electron donors to give stable adducts (η4-C4Me4GeMeCl)TaCl3L (3, L = PPh3; 4, L = CNXyl; Xyl = 2,6-dimethylphenyl) and (η4-C4Me4GeMeCl)TaCl3L2 (5, L = CNXyl; 6, L = pyridine). The X-ray structure of (η4-C4Me4GeMeCl)TaCl3(CNXyl)2 (5) confirmed η4-coordination of the germole unit and the exo orientation of the Ge−Cl bond. Complex 2 also reacted with CpTl to give air-stable Cp(η4-C4Me4GeMeCl)TaCl2 (7), which was also characterized by X-ray crystallography. Attempts to generate η5-germolyl tantalum complexes are described.