Properties of isocyanide ligands in metal complexes. Characterisation and voltammetric properties of bis(tertiary phosphine)tris(iso-nitrile)cobalt(I) complexes

Abstract

The cobalt complexes [Co(PPh₃)₂(CNR)₃][PF₆](R = Me, Prⁱ, Bu^t, p-MeC₆H₄, or p-ClC₆H₄), [Co(PMePh₂)₂-(CNR)₃][PF₆], [Co(Ph₂PCH₂CH₂PPh₂)(CNR)₃][PF₆](R =p-Me₆CH₄ or p-ClC₆H₄) and [Co(Ph₂PCH₂CH₂PPh₂)(CNBu^t)₄][PF₆]₃, have been prepared and characterised. The half-wave potential for the general reaction [Co(PR′₃)₂(CNR)₃]⁺⇌[Co(PR′₃)₂(CNR)₃]²⁺+ e^– depended on the nature of R and R′. Chemical oxidation of the appropriate cobalt(I) complex afforded [Co(PPh₃)₂(CNBu^t)₃][PF₆]₂. Assuming that the σ-donor characteristics of RNC remain constant, it is shown that as a π-acceptor Bu^tNC is better than MeNC, and that aryl iso-cyanides are better than their alkyl analogues.