Karakterisering en oksidatiewe addisiereaksies van dimeriese iridium(I) pirasoolkomplekse met jodometaan

English: The aim of this study was to synthesise and characterise different binuclear iridium(I) pyrazole complexes and to investigate the oxidative addition reactions between this type of complexes and iodomethane (CH3I). The iridium(I) complexes used in this study, (Bu4N)[Ir2(-Dcbp)(cod)2] and (Bu4N)[Ir2(-Dcbp )(C0)2(PCY3)2], were characterised by physical methods such as NMR, IR and element analysis. A product of the reaction between (Bu4N)[Ir2(µ-Dcbp)(CO)2(PCY3)2] and l,2-dichloroethane was isolated and characterised by X-ray crystallography. The crystals of the product, trans-[IrCI(CO)(PCY3)2], are triclinic with space group Pï. The importance of this structure determination centres on the fact that (Bu4N)[Ir2(µ-Dcbp)(COh(PCY3)2] as well as (BU4N)[Ir2(µ-Dcbp )(cod)2] react slowly with different solvents. The oxidative addition of iodomethane to (BU4N)[Ir2(µ-Dcbp )(cod)2] takes place according to the following scheme: (see the scheme 1 on full text) The kinetic results of the oxidative addition of CH3I to (Bu4N)[Ir2(µ-Dcbp)(cod)2] show that the oxidative addition can occur via a direct pathway (K1-equilibrium) or a solvent-assisted pathway (K2, k3). The oxidative addition occurs mainly along the direct pathway, which is a factor 10 - 40 faster than the solvent-assisted pathway. The observed solvent effect can not be attributed to the polarity or donosity of the solvents. The positive ∆H≠ values and fairly negative ∆S≠ values of the oxidative addition step are indicative of an associative process. The fairly negative ∆S≠ values together with the solvent effect indicates a three-center mechanism for oxidative addition. In the case of the (Bu4N)[Ir2(µ-Dcbp )(C0)2(PCY3)2] complex an iridium(III)alkyl complex is formed during oxidative addition (k1/k.1 pathway, Scheme 2) which is followed by the slow formation of the corresponding acyl complex (k2 pathway, Scheme 2). The equilibrium between the starting complex and the alkyl complex is maintained during the formation of the acyl complex. A very fast oxidative addition step (k'1/k'-1)-pathway, Scheme 2) leads only to the formation of an iridium(III)alkyl complex probably because of a trans configuration of the carbonyl and methylligands which inhibits carbonyl insertion or methyl migration. The first reaction, the formation of the alkyl complex, is reversible and dependent on the iodomethane concentration. (see the scheme 2 on full text) The activation parameters, ∆H≠ and ∆S≠,or the alkyl formation indicate associative activation for both the forward (k1) and the reverse (k-1) steps. This is in contrast to the expected associative forward (k1) and dissociative reverse (k1) reactions for oxidative addition. A three-center mechanism, similar to that for the (Bu4N)[Ir2(µ-Dcbp)(cod)2] complex, is proposed.