ACTIVATION OF HYDROGEN ON IRIDIUM(I) CENTERS IN WATER - SOLVENT EFFECTS, PH EFFECTS, AND IRIDIUM-HYDRIDE EXCHANGE WITH D2O

The water-soluble iridium complexes trans-Ir(CO)L2X (X = Cl, OH; L = P Ph2(m-C6H4-SO3K) (TPPMS), P(m-C6H4SO3Na)(3) (TPPTS)) have been used to extend the range of solvent effect for H-2 activation at an iridium(I ) center and to examine the effect of pH changes on the rate of H-2 ad dition to an organometallic center. Hydrogen adds to the square-planar iridium(I) complexes in H2O and DMSO to give products analogous to th ose for trans-Ir(CO)(Cl)(PPh3)2 in organic solvents. The kinetic deute rium isotope effect, k(H)/k(D) = 1.1 (L = TPPMS) and 1.2 (L = TPPTS), for addition of H-2 to trans-Ir(CO)(Cl)L-2 in water is the same as tha t observed for trans-Ir(CO)(C1)(PPh3)(2) in toluene and indicates a co mmon mechanism. More polar solvents accelerate the rate of H-2 additio n to trans-Ir(CO)(Cl)L-2, indicating polarity in the transition state. Increasing the pH causes a decrease in the rate of H-2 addition for t rans-Ir(CO)(C1)(TPPMS)(2) and trans-Ir(CO)(Cl)(TPPTS)(2) in water. Thi s pH effect, coupled with a shift of v(CO) to higher frequency in wate r, is ascribed to protonation/hydrogen bonding to the iridium center. The hydride ligands undergo H/D exchange with D2O in a process that is quite dependent on the trans ligand.