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

Abstract

The first stable eta6-germabenzene complexes, that is, [M(CO)3(eta6-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 eta6 fashion. The formation of complexes 2-4 from germabenzene 1 should be noted as the application of germaaromatics as 6pi-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 eta5-germacyclohexadienido complex of ruthenium-[RuCp*{eta5-C5H5GeTbt(Cl)}] (9)-instead of the expected eta6-germabenzene-ruthenium cationic complex [RuCp*{eta6-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 eta5 fashion.

Aromaticity of Group 14 Organometallics: Experimental Aspects

“…An unusual reaction of dilithio‐2,3,4,5‐tetraphenyl‐1‐silacyclopentadienediide [ 14 2 ‐ Li + 2 ] with 1,3‐dienes producing spirosilacyclopentadienes and elemental lithium was reported by West and co‐workers 131. Transition‐metal derivatives featuring either η 6 ‐germabenzene (Cr ( 45a ), Mo ( 45b ), W complexes) or η 5 ‐germabenzene (Ru complex) ligands have been prepared by the group of Tokitoh 132. The first ferrocene derivative [(η 5 ‐C 5 Me 5 )Fe{η 5 ‐(CPh)(CH)Si 2 Ge(SiMe t Bu 2 ) 3 }] incorporating three heavy Group 14 elements (two Si and one Ge) in one of the cyclopentadienyl rings was synthesized by Sekiguchi and co‐workers 133…”

Heavy Analogs of Aromatic Compounds

“…218 The η 3 -Si 3 H 3 ligand was even found to be capable of forming sandwich-type complexes with the core atoms represented by the main group elements, such as boron and carbon, which were stabilized by charge transfer from the ligand to the core atom. 222 The reaction of germabenzene 20 65 with the Ru derivative [(η 5 -C 5 Me 5 )RuCl] 4 in THF afforded the novel complex [(η 5 -C 5 Me 5 )Ru {(η 5 -C 5 H 5 )GeTbt(Cl)}] 92a with a reduced hapticity of coordination, in which the germacyclohexadienyl ligand was pentahaptocoordinated to the Ru center (Scheme 6.50). 68,220 -222 The complexation smoothly proceeded upon the ligand exchange reaction of stable silabenzene 16, 61 germabenzene 20 65 All of these complexes featured nearly planar heavy arene rings, which were η 6 -coordinated to transition metals.…”

“…219 The neutral heavy aromatics (Section 6.3.2.1) have recently found an application as π -arene ligands of the type η 6 -C 5 E (E = Si, Ge) and η 6 -C 9 E (E = Sn) for complexes of group 6 (Cr, Mo, W) and 8 (Ru) metals. 222 The formation of this complex was achieved through the initial formation of cationic η 6 -complex 92b, followed by nucleophilic attack of the chloride ion on the Ge atom accompanied by cleavage of the Ge-Ru bond (Scheme 6.50). The spectral data of complexes 90a-c suggest that germabenzene can efficiently serve as the π -arene ligand for transition metal complexes, like the parent benzene.…”

“…68,220 -222 The complexation smoothly proceeded upon the ligand exchange reaction of stable silabenzene 16, 61 germabenzene 20 65 All of these complexes featured nearly planar heavy arene rings, which were η 6 -coordinated to transition metals. 222 One should also mention the interesting sila-and 1,4-disilabenzene complexes of ruthenium recently synthesized by Tilley et al 223 Thus, the first transition metal silabenzene complex [(η 5 -C 5 Me 5 )Ru(η 6 -C 5 H 5 Sit-Bu)] + • [BH(C 6 F 5 ) 3 ] − 93 + • [BH(C 6 F 5 ) 3 ] − was readily prepared by oxidation of the silacyclohexadienyl complex (η 5 -C 5 Me 5 )Ru[(η 5 -C 5 H 5 SiHt-Bu)] with B(C 6 F 5 ) 3 (Scheme 6.51). 222 The reaction of germabenzene 20 65 with the Ru derivative [(η 5 -C 5 Me 5 )RuCl] 4 in THF afforded the novel complex [(η 5 -C 5 Me 5 )Ru {(η 5 -C 5 H 5 )GeTbt(Cl)}] 92a with a reduced hapticity of coordination, in which the germacyclohexadienyl ligand was pentahaptocoordinated to the Ru center (Scheme 6.50).…”

Aromatizität von metallorganischen Verbindungen mit Gruppe‐14‐Elementen: experimentelle Aspekte

“…Übergangsmetallderivate mit η 6 ‐Germabenzol‐ [Cr‐ ( 45 a ), Mo‐ ( 45 b ), W‐Komplexe] oder η 5 ‐Germabenzol‐Liganden (Ru‐Komplex) wurden von Tokitoh et al. synthetisiert 132. Sekiguchi et al.…”