LAUSR

Abstract A series of halocarbonyliridium(I) complexes of the type [Ir(CO)(P ~ Se)2X] (1) {where P-Se = 1,2-bis(diphenylphosphinomethaneselenide); X = Cl (1a), Br (1b), I (1c)} have been synthesized by the reaction of [Ir(CO)2X2]− with the ligand Ph2PCH2P(Se)Ph2. The complexes exhibit a single ν (CO) band in the region 1926 cm−1 which is significantly lower in frequency compared to Vaska’s complex, trans-[Ir(CO)Cl(PPh3)2] (1965 cm−1), and substantiate the enhanced electron density at the metal centre. The complexes undergo oxidative addition (OA) reactions with electrophiles like CH3I and C2H5I to form Ir(III) alkyl species like [Ir(CO)R(P ~ Se)2IX]; [R = CH3 (2), C2H5 (3)] which exhibit ν (CO) bands in the region of 2070 cm−1. Kinetic measurements for the CH3I oxidative addition with complex 1a indicate a first order reaction. The complexes have been characterized by elemental analyses, IR and NMR spectroscopy. Density functional calculations reveal that the activation barrier for the OA is the lowest with 1a, which is also in tune with the experimental observations.