Triazenide-bridged dirhodium complexes containing redox-active cyanomanganese ligands

Abstract

The complex [Rh₂(CO)₄(µ-RN₃R)₂]1 reacted with the cyanomanganese ligands cis-[Mn(CN)(CO)₂(L–L)][L–L = Ph₂PCH₂PPh₂(dppm), L = P(OEt)₃2 or P(OPh)₃3; L–L = Ph₂PCH₂CH₂PPh₂(dppe), L = PEt₃4] in n-hexane under reflux, or with trans-[Mn(CN)(CO)₂L(L–L)][L–L = dppm, L = P(OEt)₃8 or P(OPh)₃9] or [Mn(CN)(NO)L(cp′)][L = P(OPh)₃12 or PPh₃13, cp′=η-C₅H₄Me], in CH₂Cl₂ in the presence of ONMe₃, giving [Rh₂{(µ-NC)MnL_x}(CO)₃(µ-RN₃R)₂]{L_x=cis-(CO)₂[P(OEt)₃](dppm)5, cis-(CO)₂[P(OPh)₃](dppm)6, cis-(CO)₂(PEt₃)(dppe)7, trans-(CO)₂[P(OEt)₃](dppm)10, trans-(CO)₂[P(OPh)₃](dppm)11, (NO)[P(OPh)₃](cp′)14 or (NO)(PPh₃)(cp′)15}. The tricarbonyls underwent one-electron oxidation at a platinum-disc electrode and reacted with [Fe(cp)₂][PF₆](cp =η-C₅H₅) in CH₂Cl₂ to give the corresponding paramagnetic complexes 5⁺–7⁺, 10⁺, 11⁺, 14⁺ and 15⁺ which contain [Rh₂]³⁺ cores. The addition of compounds 2 or 8 to 5⁺ or 10⁺, or of 3 or 9 to 6⁺ or 11⁺, resulted in further carbonyl substitution to give the dicarbonyl complexes [Rh₂{(µ-NC)MnL_x}₂(CO)₂(µ-RN₃R)₂]⁺16⁺–21⁺ which reacted with [Fe(cp)₂][PF₆] in the presence of chloride ion to give the diamagnetic [Rh₂]⁴⁺-containing cations [Rh₂Cl{(µ-NC)MnL_x}₂(CO)₂(µ-RN₃R)₂]⁺22⁺–24⁺. The ESR spectra of the paramagnetic [Rh₂]³⁺-containing cations, and the effects of varying the cyanomanganese ligand on the order in which the redox-active sites (Rh₂ and Mn) of the tri- and tetra-metallic complexes are oxidised, are discussed.