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)-CF[double bond, length as m-dash]CF(CF3)}(PEt3)3] (12) and [Rh{(Z)-CF[double bond, length as m-dash]CF(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)-CF[double bond, length as m-dash]CF(CF3)}(μ-κ(1):η(2)-O2)(PEt3)2]2 (14). The molecular structure of 14 was determined by X-ray crystallography.