Coordination Chemistry of a Kinetically Stabilized Germabenzene: Syntheses and Properties of Stable η⁶‐Germabenzene Complexes Coordinated to Transition Metals

Abstract

The first stable η⁶‐germabenzene complexes, that is, [M(CO)₃(η⁶‐C₅H₅GeTbt)] {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(CH₃CN)₃] (M = Cr, Mo, and W) and the kinetically stabilized germabenzene 1 and characterized by ¹H and ¹³C NMR, IR, and UV/Vis spectroscopy. In the ¹H and ¹³C 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 η⁶ 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* = C₅Me₅) in THF afforded a novel η⁵‐germacyclohexadienido complex of ruthenium—[RuCp*{η⁵‐C₅H₅GeTbt(Cl)}] (9)—instead of the expected η⁶‐germabenzene‐ruthenium cationic complex [RuCp*{η⁶‐C₅H₅GeTbt}]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 η⁵ fashion.