Iridium complexes oxidative addition

Oxidative addition of XY substrates to [IrL2(/x-pz)]2 [La = (CO)2, cod] and [Ir(CD)(PPh3)(/i,-pz)]2 occurs via a two-center, two-electron route toward the iridium-iridium bond-containing species 131 (960M3785 980M2743). Complex 132, which is prepared by the ligand-substitution reaction from [Ir(CO)2 (/x-pz)]2, adds methyl iodide to give 133. 

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. 

R, e.g. cyclohexyl, p-tolyl) readily undergo oxidative addition with molecules like Cl2 and Mel to give iridium(III) complexes... 

The most interesting work on the isocyanide complexes of the elements in this subgroup has been done with rhodium and iridium. For the most part, the work is involved with the oxidative addition reactions of d square-planar metal complexes. 

One most important observation for the mechanistic discussion is the oxidative addition/insertion/reductive elimination processes of the iridium complex (31) (Scheme 1-10) [62]. The oxidative addition of catecholborane yields an octahedral iridium-boryl complex (32) which allows the anti-Markovnikov insertion of alkyne into the H-Ir bond giving a l-alkenyliridium(III) intermediate (34). The electron-... 

Schemes 6-4 Oxidative addition of water and methanol to cationic iridium phosphine complex 37...

Schemes 6-5 Oxidative addition of water to neutral iridium phosphine complexes...

Schemes 6-10 Oxidative addition of alcohol, phenol, and water to cationic iridium phosphine complex 67...

Merola reported the preparation of hydrido(carboxylato)iridium(lll) complexes, mer-[lrCl(0C(0)R)(H)(PMe3)3] (90) (R = Ph, Me), by oxidative addition of acetic acid or benzoic acid to [Ir(cod)(PMe3)3]Cl (67) [46]. The structure of 90 (R = Ph) in which the carboxylato ligand coordinates as an T -ligand, was confirmed by X-ray analysis. The reaction of 67 with salicylic acid yielded the product 91, which resulted from activation of the O-H bond of the carboxylato but not of the hydroxo group (Scheme 6-13). 

S. J. Pool and K.H. Shaughnessy. Effects of ionic liquids on oxidative addition to square planar iridium and rhodium complexes. Abstracts of Papers, 231st ACS National Meeting, Atlanta, GA, USA, March 26-30,2006 (2006). 

Actually, a similar approach was used in studying the oxidative addition of methane to an iridium complex. Hydrocarbon solvents would have reacted faster than methane with the photochemically produced unsaturated iridium species, therefore J.K. Hoyano et al chose perfluorinated hexane as being an inert solvent. The elevated pressure was necessary in order to increase the concentration of the methane in the solution sufficiently to shift equilibrium (15) to the right /20/. 

Iridium hydride complexes effectively catalyze addition of nitriles or 1,3-dicarbonyl compounds (pronucleophiles) to the C=N triple bonds of nitriles to afford enamines.42S,42Sa Highly chemoselective activation of both the a-C-H bonds and the C=N triple bonds of nitriles has been observed (Equation (72)). To activate simple alkane dinitriles, IrHs(P1Pr3)2 has proved to be more effective (Equation (73)). The reaction likely proceeds through oxidative addition of the a-C-H bonds of pronucleophiles to iridium followed by selective insertion of the CN triple bonds to the Ir-C bond. 

In order to get a catalytic cycle it is necessary that the metal sulfide intermediate can react with hydrogen to form the reduced metal complex (or compound) and H2S. For highly electropositive metals (non-noble metals) this is not possible for thermodynamic reasons. The co-ordination chemistry and the oxidative addition reactions that were reported mainly involved metals such as ruthenium, iridium, platinum, and rhodium. 

---