Synthesis, structure, chemical and electrochemical investigation of some dinuclear rhodium conplexes

The electrochemical oxidation of trans-Rh₂(μ-dppm)(CO)₂Cl₂ (dppm - Bis(diphenylphosphino)methane) in the presence of chloride has been investigated. The oxidation affords an unsjrmmetrical dirhodium(II) complex, Rh₂Cl₃(μ-Cl)(CO), 14, which is readily converted to a symmetrical complex, [Rh₂(μ-dppm)₂Cl₂(μ-CO)(μ-Cl)] (PF₆), 4. Complex 4 has been shown to undergo addition reactions with chloride, carbon monoxide and t-butylisocyanide to generate other new dirhodium(II) complexes.

The electrochemical and chemical reactivity of Rh₂(μ-dppp)₂Cl₂(μ-CO), 5, (dppp - diphenylphosphinopyridine) have been examined. Electrochemical oxidation of 5 in CH₂CI₂/TBAH/CI^- affords Rh₂(μ-dppp)₂Cl₃(μ-Cl)CO, 9; while in CH₂Cl₂/TBAN/Cl^-, Rh₂(μ-dppp)₂CI₃(μ-NO₃), 7, is generated. The crystal structure of 7 has been obtained which displays a disorder involving the CO on one rhodium atom, and the staggered Cl on the second rhodium atom. Complex 9 has been shown to undergo addition reactions with carbon monoxide and t-butylisocyanide to afford other dirhodium(II) complexes.

Novel trans-dppm dinuclear Rh(I) A-frame complexes that contain triazolate, pyrazolate and substituted pyrazolate ligands at the bridgehead position have been studied. Electrochemical investigation of these complexes in CH₂Cl₂ reveals two consecutive one-electron oxidation waves. Paramagnetic species are generated via bulk oxidation between the two waves. ESR spectroscopy has been employed to investigate the nature of these paramagnetic complexes, some of which display a thermochromic effect. Electrochemical oxidation of some of the diisocyanide complexes has shown that they undergo oxidative-addition reactions. The electrolysis of [Rh₂(μ- dppm)₂(t-BuNC)₂(μ-Pz)](PF₆) in TBAH/TBAAc/CH₂CI₂ generates [Rh₂(μ-dppm)₂(t-BuNC)₂Cl₂(μ-Pz)](PF₆), 40, whose structure has been determined by x-ray structural analysis. The structure of 40 reveals a unique folding of the methylene groups of the dppm ligands over the open site opposite the bridgehead position. The electrochemical behavior of [Rh₂(μ-dppm)₂(t-BuNC)₂(μ-4MPz)](PF₆) in the presence of a coordinating solvent and a variety of pyridines is also discussed. Reactivity of these A-frame complexes containing terminal t-butylisocyanide ligands with a variety of acids and halogens have been explored.

Electrochemical behavior of novel tetrarhodium(I) complexes of the type, ([Rh₂(μ-dppm)₂L₂]₂Z)(PF₆)₂ (L - CO,t-BuNC; Z - 3,5,3'5'-tetramethylbipyrazolate,4,4'-methylenebis(3,5-dimethylpyrazolate)), has been investigated in CH₂Cl₂.