Effect of positive-charges in diphosphino-imidazolium salts on the structures of Ir-complexes and catalysis for hydroformylation

The effect of positive charges in the diphosphino-imidazolium salts of L2 was investigated in terms of coordinating character, structures of corresponding Ir-complexes and catalysis for hydroformylation. It was found that the involved positive charges exhibited strong electron-withdrawing effect on the neighbored phosphine fragment, rendering L2 more π -acceptor ability than the corresponding neutral counterpart of L1 . Consequently, the changed coordinating ability of L1 and L2 led to the variety in the structures and components for the Ir-complexes ( Ir-L1a , Ir-L1b , Ir-L2a , and Ir-L2b ). The complexation of L2 with Ir(acac)(CO) 2 led to a novel five-coordinate Ir(II)-complex of Ir-L2a chelated by a PCC (phosphine–carboanion–carbene) pincer in tripodal mode, whereas the complexation of L1 with Ir(acac)(CO) 2 led to a four-coordinate square-planar Ir(I)-complex of Ir-L1a chelated by a PCP (phosphine–carboanion–phosphine) pincer. In addition, the different catalytic performances of these Ir-complexes ligated by L1 and L2 for hydroformylation of olefins were investigated.