Cp*rhodium and iridium complexes with bisoxazolines: synthesis, fluxionality and applications as asymmetric catalysts for Diels–Alder reactions

Reaction of the dimers [MCl2Cp*]2 (M=Rh, Ir) with bis-oxazolines [NN=bis(2-oxazoline) (box), 2,2-bis(2-oxazolinyl)propane (bop), 1,2-bis(2-oxazolinyl)benzene (benbox)] in the presence of NaSbF6 (or KPF6) gives complexes [MCl(NN)Cp*][EF6] (E=P or Sb) which have been fully characterised. Treatment of some of these with AgSbF6 generates dications [Rh(OH2)(NN)Cp*]2+, some of which are fluxional at room temperature. One of these is an enantioselective catalyst for the Diels–Alder reaction of methacrolein and cyclopentadiene. Three complexes, [RhCl(iPr-box)Cp*][SbF6], [RhCl(iPr-bop)Cp*][SbF6] and [RhCl(Et-benbox)Cp*][SbF6] have been characterised by X-ray crystallography.