The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl2(η6-p-cymene){PR2(p-Ph3BC6H4)}] (E = Bu4N+: R = Ph, 1a, iPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP+: R = Ph, 1a′, iPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a–c and 1a′–c′ are proposed to form monomer–dimer equilibria as a result of chloride ligand dissociation. Complexes 1a–c and 1a′–c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η6-p-cymene){PR2(p-Ph3BC6H4)}] (L = pyridine: R = Ph, 2a, iPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, iPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO3 or MeOTf.