First Examples of Heteroleptic Dipyrrin/η⁵<i>-</i>Pentamethylcyclopentadienyl Rhodium/Iridium(III) Complexes and Their Catalytic Activity

Heteroleptic pentamethylcyclopentadienyl rhodium/iridium(III) complexes imparting dipyrrins as co-ligands with the general formulations [(η5-C5Me5)MCl(L)] [(M = Rh(III) or Ir(III); L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm] have been synthesized. Reactivity of the complexes [(η5-C5Me5)MCl(L)] (M = Rh(III), Ir(III); L = ndpm and cydpm) with various species, viz., sodium azide (NaN3), ammonium thiocyanate (NH4SCN), triphenylphosphine (PPh3), 4,4′-bipyridine (bpy), and bis(diphenylphosphino)hexane (dpph), has been examined. Resulting complexes have been characterized by elemental analyses and spectral and electrochemical studies. Molecular structures of the representative complexes [(η5-C5Me5)RhCl(cydpm)], [(η5-C5Me5)RhCl(ndpm)], [(η5-C5Me5)Rh(PPh3)(cydpm)]SO3CF3, and [(η5-C5Me5)Ir(PPh3)(ndpm)]SO3CF3 have been determined crystallographically. The complexes [(η5-C5Me5)MCl(L)] [(M = Rh(III) or Ir(III) and L = cydpm, ndpm, or bdpm) effectively catalyze reduction of terephthalaldehyde to 4-hydroxymethybenzaldehyde in the presence of HCOOH/CH3COONa in water under aerobic conditions. Among these complexes the rhodium complex [(η5-C5Me5)RhCl(ndpm)] is most effective in this regard.