Iridium complexes partially oxidized

Pincer-ligated iridium complexes have been used as homogeneous catalysts for the dehydrogenation of aliphatic polyalkenes to give partially unsaturated polymers. The catalyst appears to be selective for dehydrogenation in branches as compared with the backbone of the polymer.56 The mechanism shown in Scheme 1 has been suggested for an [IrCl(cod)]2-catalysed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols.57... 

In this compound and several other structurally analogous organic and inorganic compounds, the conductivity is inversely dependent on temperature over a limited temperature region, and other characteristically metal-like properties are observed. Included in this group are polymeric sulfur nitride, (SN)a , and a group of partially oxidized, square planar platinum and iridium complexes that are collectively referred to as KCP in Figure 1 both are discussed elsewhere in this volume. 

In the case of iridium zeolite the acetyl formation was not reported to occur spontaneously though the oxidative addition was a rapid step. The resulting complex was stable and did not rearrange even at 170°C. Only partial decarbonylation occurred.However under carbon monoxide pressure the adduct complex seemed to rearrange into the acetyl or perhaps give rise to yet another surface organic carbonyl species. 

Exchange of formyl hydrogens for tritium is observed to occur in both aryl aldehydes (with concurrent ortho labeling in appropriate cases) and aliphatic aldehydes using [(cod)Ir(PCy3)(py)]PF6. Partial reduction of aldehydes to alcohols may occur in some cases. Labeling by other iridium phosphine catalysts has not been reported but is likely to occur. This type of catalytic activity, which likely involves reversible oxidative addition of the iridium center into the formyl C—H bond, is different in outcome from that of organorhodium complexes, whose insertion into formyl C—H bonds proceeds instead to decarbonylation. 

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