Reactivity of cationic methyl rhodium(III) complexes cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4] toward ligands of different character: pyridine, carbon monoxide, and triphenylphosphine

Cationic methyl complex of rhodium(III), cis-[Rh(Acac)(PPh3)2(CH3)(Py)][BPh4] (1) as a single isomer with Py in the trans to PPh3 position, is formed upon the reaction of cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] with pyridine in methylene chloride solution.Complex 1 was characterized by elemental analysis and by 31P{1H} and 1H NMR spectra.Cationic pentacoordinate acetyl complexes, trans-[Rh(Acac)(PPh3)2(COCH3)][BPh4] (2) and trans-[Rh(BA)(PPh3)2(COCH3)][BPh4] (3), are prepared by action of carbon monoxide on cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4], respectively, in methylene chloride solutions.Complexes 2 and 3 were characterized by elemental analysis and by IR, 31P{1H}, 13C{1H} and 1H NMR. According to NMR data, 2 and 3 in solution are non-fluxional trigonal bipyramids with β-diketonate and acetyl ligands in the equatorial plane and axial phosphines.In solutions, 2 and 3 gradually isomerize into octahedral methyl carbonyl complexes trans-[Rh(Acac)(PPh3)2(CO)(CH3)][BPh4] (4) and trans-[Rh(BA)(PPh3)2(CO)(CH3)][BPh4] (5), respectively.Complexes 4 and 5 were characterized by IR, 31P{1H}, 13C{1H} and 1H NMR, without isolation.Upon the action of PPh3 on cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] and cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)] [BPh4], reductive elimination of the methyl ligand as a phosphonium salt, [CH3PPh3][BPh4], occurs to give square planar rhodium(I) complexes [Rh(Acac)(PPh3)2] and[Rh(BA)(PPh3)2], respectively. The reaction products were identified in the reaction mixtures by 31P{1H} and 1H NMR.

Graphical abstractCationic methyl complexes of rhodium(III), cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4], react readily with ligands of different nature (pyridine, carbon monoxide, triphenylphosphine).On the action of carbon monoxide, they yield pentacoordinate acetyl complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide