Synthesis of a rhodium(i) germyl complex: a useful tool for C–H and C–F bond activation reactions

Abstract

The dihydrido germyl complex cis,fac-[Rh(GePh₃)(H)₂(PEt₃)₃] (2) was synthesized by an oxidative addition of HGePh₃ at [Rh(H)(PEt₃)₃] (1). Treatment of 2 with neohexene generated the rhodium(I) germyl complex [Rh(GePh₃)(PEt₃)₃] (3). Alternatively, treatment of the methyl complex [Rh(CH₃)(PEt₃)₃] (4) with HGePh₃ furnished at room temperature also 3. Low-temperature NMR measurements revealed an initial formation of the oxidative addition product fac-[Rh(GePh₃)(H)(CH₃)(PEt₃)₃] (5), which transforms into the intermediate complex [Rh(GePh₃)(H)(CH₃)(PEt₃)₂] (6) by dissociation of a triethylphosphine ligand. The reductive elimination of methane and coordination of PEt₃ afforded the germyl complex 3. Treatment of 3 with CO gave the biscarbonyl complex [Rh(GePh₃)(CO)₂(PEt₃)₂] (7). The molecular structures of the complexes 2, 3 and 7 were determined by X-ray crystallography. The germyl complex 3 reacted with 2,3,5,6-tetrafluoropyridine or pentafluorobenzene to furnish the C–H activation products [Rh(4-C₅NF₄)(PEt₃)₃] (8) and [Rh(C₆F₅)(PEt₃)₃] (9), respectively. The reaction of 3 with hexafluorobenzene or perfluorotoluene gave selectively the C–F activation products 9 and [Rh(4-C₆F₄CF₃)(PEt₃)₃] (10). Treatment of 3 with pentafluoropyridine resulted in the formation of the C–F activation products 8 and [Rh(2-C₅NF₄)(PEt₃)₃] (11) in a 1 : 10 ratio. The two isomeric activation compounds [Rh{(E)-CFCF(CF₃)}(PEt₃)₃] (12) and [Rh{(Z)-CFCF(CF₃)}(PEt₃)₃] (13) were obtained in a 3 : 1 ratio by reaction of 3 with hexafluoropropene. On exposure to oxygen the highly air sensitive complex 12 reacts to yield the peroxido-bridged dirhodium complex [Rh{(E)-CFCF(CF₃)}(μ–κ¹:η²-O₂)(PEt₃)₂]₂ (14). The molecular structure of 14 was determined by X-ray crystallography.