Collect. Czech. Chem. Commun. 2001, 66, 291-306

Coupling of Electron Transfer and Bond Dissociation Processes in Dinuclear Complexes with Rhodium and Iridium Reaction Centres Bridged by 2,2'-Bipyrimidine

Wolfgang Kaima,*, Ralf Reinhardta, Stefan Greulicha, Monika Siegera, Axel Kleina and Jan Fiedlerb

a Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
b J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-182 23 Prague, Czech Republic


The complexes [{MCl(η5-C5Me5)}2(μ-bpym)](PF6)2, bpym = 2,2'-bipyrimidine and M = Rh or Ir, were obtained as isomerically pure species (M = Ir) or as mixtures of cis/trans isomers (M = Rh). Even though these compounds undergo partial dissociation into the mononuclear bpym- and solvento-complexes in DMF or acetonitrile, cyclic voltammetry and, in part, spectroscopy (NMR, EPR, UV-VIS) could be used to analyze their reduction with up to five electrons. In acetonitrile at room temperature, the dirhodium compound displays two sequential chloride-dissociative two-electron cathodic steps, leading to the very reactive [{Rh(η5-C5Me5)}2(μ-bpym)]. At -15 °C in DMF, the diiridium compound was found to be sufficiently inert towards dissociation; it is then reversibly reduced to an EPR-detectable radical cation [{IrCl(η5-C5Me5)}2(μ-bpym)]•+ before two separated chloride-dissociative steps occur.

Keywords: 2,2'-Bipyrimidine; EPR spectroscopy; Iridium complexes; Rhodium complexes; Spectroelectrochemistry; Cyclic voltammetry; Electroreductions.

References: 50 live references.