Synthesis of cationic rhodium(I) and iridium(I) carbonyl complexes of tetradentate P(CH2CH2PPh2)3 ligand: An implication of steric inhibition and catalytic hydroformylation reaction

Article abstract of DOI:10.1016/j.molcata.2013.10.016

New cationic carbonyl complexes of the type [M(CO)L]Cl (1) [M = Rh (a) and Ir (b); L = P(CH₂CH₂PPh₂)₃] have been synthesized and characterized by various spectroscopic techniques including the single crystal X-ray diffraction. Both the complexes crystallize in trigonal bipyramidal symmetry with the metal at the centre. Two strong intermolecular hydrogen bonds are observed in 1a. Despite the high trans effect of the CO group, the symmetrical tetradentate phosphine ligand bonded strongly to the metal centre through all sites and thereby expelling the Cl^- ion outside the coordination sphere. The complexes are very stable and inert towards the oxidative addition (OA) of small molecules like CH₃I, C₂H₅I and I₂ at room as well as higher temperature. However, the complexes show catalytic activity towards the hydroformylation of alkene to the corresponding aldehydes under the reaction conditions: pressure 35 ± 2 bar, temperature 80 ± 2°C, 500 rpm and time 5-8 h. The yields of the aldehyde products are in the ranges 55-75%. The complexes exhibited dissociation of weaker MP bond under the above reaction conditions to form a vaccant coordination site for initiation of the catalytic cycle.