Unbridged Rh(ii)-Rh(ii) complexes of N-heterocyclic carbenes and reactions with O2 to form dirhodium(μ-η1:η1-O2) complexes

Dimeric rhodium(ii) complexes and rhodium(iii) peroxide complexes supported by N-heterocyclic carbenes were synthesized. The treatment of [Ag-3(L)(2)](PF6)(3) (L = bis(N-pyridylimidazolylidenyl)methane) with [Rh(COD)Cl] afforded [Rh(L)(CH3CN)](2)(PF6)(4) in which two [Rh(L)] moieties are bound together via an unsupported Rh-Rh bond. The substitution of axial acetonitrile by phosphines led to the insertion of O-2 into the Rh-Rh bond and the isolation of [Rh(L)(PPh3)](2)(-(1):(1)-O-2)(PF6)(4) and [Rh(L)(PCy3)](2)(-(1):(1)-O-2) (PF6)(4).