Iridium phosphino

Li, S. Zhu, S.-R Xie,J.-H. Song, S. Zhang, C.-M. Zhou, Q.-L. Enantioselective hydrogenation of a-aryloxy and a-alkoxy a, 3-unsaturated carboxylic acids catalyzed by chiral spiro iridium/phosphino-oxazoline complexes. /. Am. Chem. Soc. 2010,132,1172-1179. 

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

SYNTHESIS AND APPLICATION OF HETEROCYCLIC PHOSPHINO OXAZOLINE(HetPHOX) IRIDIUM COMPLEXES FOR THE ASYMMETRIC HYDROGENATION OF ALKENES... 

When a pyrazole ring is used as a scaffold to two pendant carbene donor groups, dime-tallic complexes can be formed [75] (see Figure 3.22). Similar complexes were also synthesised for nickel, rhodium and iridium [76,77]. Appreciable metal-metal interactions could not be observed in any of these complexes, with the exception of argentophilic [77,78] or aurophilic [79] interactions. As with other functionalised carbenes, these pyrazole bridged ones have precedences, in this case amine [80,81], phosphino [82] and Cp [83] functionalised pyrazole ligands. 

We are in for a few surprises with the chemistry of rhodium and iridium. Let us stay with the phosphino functionalised imidazolium salt PhjPCHjCHJmMes and react it with the precursor complexes [M(cod)OEt]j (M = Rh, Ir) [296]. As expected, the corresponding cationic phosphino functionalised carbene complexes are formed (see Figure 3.96). 

Figure 3.96 Rhodium(l) and iridium(l) complexes of a phosphino functionalised NHC ligand.

The corresponding reactions with iridium(I) precursors again behave differently. When the phosphino functionalised imidazolium salt is reacted with [IrlcodlCl], the phosphane adduct with a pendant imidazolium moiety is formed. A similar reaction with the more reactive [Ir(cod)( Li-H)(p,-Cl)2]2 yields a five coordinate iridium(I) complex that might be described as having square pyramidal geometry with the bromide in apical position and the carbene in abnormal coordination mode [47-49] (see Figure 3.97). 

Figure 3.97 Synthesis of an iridium (I) complex with abnormally coordinated phosphino functionalised NHC ligand.

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],... 

This ring thereby constitutes an unusual yu-ij. ij -vinyl group whereby the phosphino carbon is also metalated. Intramolecular oxidative addition of the ortho C-H bond of the phenyl substituents is a common feature in crowded iridium phosphine complexes [65, 309, 310]. 

Silica-supported homogeneous catalysts, especially phosphino-iridium compounds, appear more promising in the hydrogenation of a,y9-unsaturated aldehydes, provided that their productivity can be improved and catalyst deactivation is avoided so that recycling of these materials could be meaningful [35]. 

The iridium homoscorpionate chemistry continues to be very rich and close to that of rhodium, several papers in the last period reporting analogous [M(Tpx)(L)] (M = Rh or Ir) complexes. Hydride-,433,434 phosphino-,435,436 carbonyl-437,438 and diene-Ir439-442 complexes and their reactivity were widely reported in the first edition also. 

Determined that -20% conversion of cycloalkanes to arenas can be achieved with the iridium arsino pincer catalyst than is obtained with the analogous phosphino catalyst. 

We have found that the higher levels of conversion of cycloalkanes to arenes can be achieved with the iridium arsino pincer complex, IrH2(C5H3-2,6-(CH2AsBu 2)2) than are obtained with the analogous phosphino catalyst. However, inhibition of the arsino pincer catalyst is observed at the -20% dehydrogenation level for methylcyclohexane, decalin, and dicyclohexyl. 

Aminodiphosphane (P,N,P)-ligands form active catalysts with iridium(I) for transfer hydrogenation (249). A novel phosphino-dihydrooxazol, modified with perfluoroalkyl groups proved to be excellent ligand for enantioselective hydrogenation in supercritical carbon dioxide (250). 

Smidt, S. R Pfaltz, A. Martmez-Viviente, E. Pregosin, P. S. Albinati, A. X-ray and NOE studies on trinuclear iridium hydride phosphino oxazoline (PHOX) complexes. Organometallics 2003,22,1000-1009. 

C2 sHft 2CI2C0N3O4P, Chloro(bis-(2-(diethylamino)ethyl)-2-(diphenyl-phosphino)ethylamine)cobalt(II) perchlorate, 38B, 1041 C26Ha6ClIrOP2, Carbonylchloro(1,9-bis(di-t-butylphosphino)nona-l,3-diyne)iridium, 44B, 1066... 

---