Iridium complexes monodentate

In the rhodium and iridium complexes, the C-coordination, carbene function, and cyclometallated cases prevail. Benzothiazole-2-thione was studied extensively as a ligand and various situations of the exocyclic S-monodentate coordination as well as N,S-combinations in the di-, tri-, and tetranuclear species were discovered. 

In 2008, Vries group reported asymmetric hydrogenation of quinolines catalyzed by iridium complexes based on monodentate BINOL derived phos phoramidites PipPhos. They used tri ortho tolylphosphine and/or chloride salts as additives, and enantioselectivities were strongly enhanced to 89% ee (Scheme 10.13) [17]. Toluene and DCM were the best solvents, and the reaction was carried out at 60°C for 24h in the pressure of 50 bar H2, and a series of 2 substituted and 2,6 disubstituted quinolines were examined with excellent... 

Partial or complete displacement of the coordinated acetonitrile ligands may be achieved with monodentate ligands (e.g., phosphines ), bidentate ligands (e.g., dienes), or tridentate ligands, providing a convenient entry to a range of (i -pentamethylcyclopentadienyl)rhodium and -iridium complexes. 

M(NO)(OCOCF3)2(PPh3)2. Both these complexes have 5-coordinate geometries with monodentate carboxylates. The rhodium compound has a square pyramidal structure with bent Rh-N-O (122°) but the iridium compound has a tbp structure with straight equatorial Ir-N—O (178°). The position of i/(N—O) reflects this difference (1800 cm-1 (Ir) and 1665 cm-1 (Rh)). 

Iridium chemistry also holds a rare example of a monodentate guanidinate ligand. The monomeric parent amido complex Cp Ir(PMe3)(Ph)(NH2) cleanly undergoes an insertion reaction on treatment with diisopropylcarbodiimide (Scheme 153). Spectroscopic data and an X-ray structural analysis revealed the presence of a nonchelating guanidinate ligand. ... 

The reactivities of several hydrido(carboxylato) complexes of iridium have been studied [58]. Complexes 88 reacted with carbon monoxide to afford carbonyl complexes, [IrCl(H)(OCOR)(CO)(PPh3)2] (98), in which the carboxylato ligands changed to monodentate ligands and exist as a mixture of isomers (Eq. 6.31). 

R. J. Watts, J. S. Harrington, and J. Van Houten, A stable monodentate 2,2-bipyridine complex of iridium (III) A model for reactive intermediates in ligand displacement reactions of tris 2,2-bipyridine metal complexes, J. Am. Chem. Soc. 99, 2179-2187 (1977). 

Iridium 2-pyridinylmethyl imidazolylidene C,N-chelates were obtained by transmetallation of the silver carbene complexes and tested for catalytic activity in the TH of benzophenone and nitroarenes by isopropanol [55]. The neutral monodentate complexes [(L-KC)Ir(COD)Clj [61a,b L = l-methyl-3-(6-mesityl-2-pyridinylmethyl)-2-imidazolylidene, l-mesityl-3-(6-mesityl-2-pyridinylmethyl)-2-... 

Because of the relatively poor coordinating properties displayed by the P-menthyl-substituted monodentate ligands toward some catalytically useful metals like rhodium and iridium, development of the coordination chemistry of chelating phosphetanes was required. Early studies established that the bidentate ligand P(6 ),C (6 )-43 binds well to rhodium centers. It gives the chelating complex 26 with [Rh(COD)2]PF6 and the bimetallic compound 68 when reacted with [Rh(COD)Cl]2 under an atmosphere of CO (COD = cyclooctadiene Scheme 5) <19950M4983>. 

The bonding in the rhodium(I) and iridium(I) complexes [M(cod)(TIME" )]PFg (M = Rh, Ir) [393] is very similar except that the metal centre requires only two monodentate ligands, which results in a monoprotonated bidentate [2+1] type hgand coordination (see Figure 3.142). Use of two metal precursors per ligand results in a [2+1] bridging coordination mode with a cationic and a neutral end (see Figure 3.143). 

The diphenylphosphino group can be substituted by a phenylmercaptyl moiety [154] that would coordinate in chelate fashion to a rhodium centre, but only as a monodentate ligand (with the carbene) in the case of iridium. Interestingly, the rhodium complex, iso-structural to the P functionalised complex, is absolutely inactive in the hydrogenation of itaconate whereas the corresponding phosphino functionalised catalyst was reported to be highly active [154],... 

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