Syntheses and redox properties of mixed isocyanide, carbonyl, or nitrile complexes of rhenium(I)trans-[Re(CNMe)L(Ph2PCH2CH2PPh2)2]X [L = CNR (R = alkyl or aryl), CO, or NCMe; X = Cl, BF4, or PF6]

Abstract

Complexes trans-[Re(CNMe)L(dppe)₂]X[1;L = CNR (R = Me, Bu^t, Ph, C₆H₄Me-4, C₆H₄Cl-4, or C₆H₂Prⁱ₃-2,4,6,), CO, or NCMe; dppe = Ph₂PCH₂CH₂PPH₂; X = Cl, BF₄, or PF₆] were prepared from the reaction of trans-[ReCl(CNMe)(dppe)₂] with the appropriate substrate (L), either in the presence to TIX (1; X = BF₄ or PF₆), in tetrahydrofuran (thf) or CH₂Cl₂, or in the absence of the thallium salt (1; X = Cl) in refluxing CH₂Cl₂; the latter route was also applied to the syntheses of trans-[Re(CNR)₂(dppe)₂]Cl [R = Me or C₆H₂Prⁱ₃-2,4,6 (2)] directly from the dinitrogen complex trans-[ReCl(N₂)(dppe)₂]. At a platinum electrode, in thf or NCMe–0.2 mol dm^–3[Bu₄N][BF₄], complexes (1) undergo at least one reversible single-electron oxidation by cyclic voltammetry. The observed values of the half-wave oxidation potential are in agreement with those predicted from the application of equations relating the electrochemical ligand parameter P_L′ electron richness E_s′ and polarisability β of the binding metal centre; these parameters were also estimated for the {Re(CNR)(dppe)₂}⁺ sites. An expression is also proposed to estimate the redox potential of mixed-ligand complexes of the type [M′_sL(L′)](M′_s= 14-electron metal site), as the average of the redox potential of [M′_sL₂] and [M′_sL′₂]; the conditions for its application are discussed and it was shown to be valid for complexes (1).