Coordination Chemistry of a Kinetically Stabilized Germabenzene: Syntheses and Properties of Stable η 6 ‐Germabenzene Complexes Coordinated to Transition Metals

The first stable η 6 ‐germabenzene complexes, that is, [M(CO) 3 (η 6 ‐C 5 H 5 GeTbt)] {M = Cr ( 2 ), Mo ( 3 ), and W ( 4 ); Tbt = 2,4,6‐tris[bis(trimethylsilyl)methyl]phenyl}, have been synthesized by ligand‐exchange reactions between [M(CO) 3 (CH 3 CN) 3 ] (M = Cr, Mo, and W) and the kinetically stabilized germabenzene 1 and characterized by 1 H and 13 C NMR, IR, and UV/Vis spectroscopy. In the 1 H and 13 C NMR spectra of 2 – 4 , all of the signals for the germabenzene rings were shifted upfield relative to their counterparts in the free germabenzene 1 . X‐ray crystallographic analysis of 2 and 4 revealed that the germabenzene ligand was nearly planar and was coordinated to the M(CO) 3 group (M = Cr, W) in an η 6 fashion. The formation of complexes 2 – 4 from germabenzene 1 should be noted as the application of germaaromatics as 6π‐electron ligands toward complexation with Group 6 metals. On the other hand, treatment of 1 with [{RuCp*Cl} 4 ] (Cp* = C 5 Me 5 ) in THF afforded a novel η 5 ‐germacyclohexadienido complex of ruthenium—[RuCp*{η 5 ‐C 5 H 5 GeTbt(Cl)}] ( 9 )—instead of the expected η 6 ‐germabenzene‐ruthenium cationic complex [RuCp*{η 6 ‐C 5 H 5 GeTbt}]Cl ( 10 ). Crystallographic structural analysis of 9 showed that the five carbon atoms of the germacyclohexadienido ligand of 9 were coordinated to the Ru center in an η 5 fashion.