Rhodium(I) macrocyclic and cage-like structures containing diphosphine bridging ligands

Abstract

Three series of rhodium organometallic complexes, mono-(1c, 2c, 5c, 6c), di-(1a-6a) and tetranuclear (1b, 5b, 6b), containing six different diphosphines (1,1'bis(diphenylphosphino)methane or dppm (1), 1,2-bis(diphenylphosphino)ethane or dppe (2), 1,4-bis(diphenylphosphino)butane or dppb (3), bis(diphenylphosphino)acetylene or dppa (4), 1,2-bis(diphenylphosphino)benzene or dppbz (5) and 4,5-bis(diphenylphosphino)-9,9'-dimethylxanthene or xantphos (6) were successfully synthesised. These Rh(I) complexes were characterised by conventional techniques. The influence of the flexibility/rigidity of these P-donor ligands was carefully analysed, including their effect on both synthesis and catalysis. The luminescent properties of the dinuclear and tetranuclear complexes were investigated and only those containing dppa, dppbz and xantphos displayed luminescence. Structures of dinuclear complexes were modelled by using DFT methods in order to elucidate the most possible conformation. The different types of complexes were applied in the catalytic hydrogenation of (E)-4phenylbut-3-en-2-one, showing high activity and similar catalytic behaviour. No cooperative effect could be inferred.