Strain in organometallics II: controlling the properties of tetra-coordinated iridium complexes using diastereomers of a bis(tropp) ligand system

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(troppPh)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(troppPh)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(troppPh)ethane was separated by fractional crystallisation and reacted with [Ir(cod)2]OTf (cod=cylcooctadiene, OTf−=CF3SO3 −) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(troppPh)ethane)(cod)]+, where the bis(troppPh)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(troppPh)ethane)(cod)]+: k