Iridium complexes oxygen ligands

In 1963 Vaska 164) discovered that the iridium complex Ir(PPh3)2C (CO) takes up molecular oxygen reversibly with 1 1 stoichiometry. This complex has since been shown to reversibly sorb (1 1) ethylene (755), carbon dioxide (765), F2C=CF2 and F3C—C=C—CF3 (767), as well as various other ligands (765). Ibers md La Placa (769)... 

An X-ray crystal structure of 55, redrawn as Fig. 10, supported the formulation of the complex as that of a peroxo system. Further, the structure demonstrated that no interactions between the [Of-] ligand and the borate moiety were possible because of the relative arrangement of the [Of-] and borate ligands about the iridium center. Such interactions were implicated in the oxygen-initiated decomposition of the iridium complex of 52, while the lack of reactivity of the iridium complexes of 53 and 54 was attributed to steric factors arising from the alkyl chains connecting the sulfur atoms. 

Iridium complexes having oxygen ligands are not nearly as extensive as those having nitrogen. Examples include acetylacetonates [Ir(P(C(5H5)3)2 (acac)H2] [64625-61-2], aqua complexes Ir(OH2)6]3+ [61003-29-0], nitrato complexes [Ir(0N02)(NH3),J2 [42482 42-8], and peroxides IrCl(P(C6I fy)3)2(02-/-(>/ I I9)2(CO) [81624-11-5]. Unlike rhodium, very few Ir(II) carboxylate-bridged dimers have been claimed and [Ir,2(OOCCI I3)4 has not been reported. Some Ir(T) complexes exhibit reversible oxidative addition of 02 to form Ir(III) complexes. That chemistry has been reviewed (172). 

Ligand effects appear to be important, the yield of acetophenone increasing in the order I < Br < Cl , although the amounts of this product are much reduced if SnCU or HgCl is bonded to the iridium. In the former case, a strong trans effect may promote formation of an iridium-styrene-oxygen intermediate. Ruthenium-oxygen complexes have also been shown to be... 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

---