Iridium-BINAP

Very air-sensitive iridium diphosphine complexes carrying a peraryldiphosphine ligand, [IrCl(diphosphine)]2 (42a, 42b)(a diphosphine = BPBP b diphosphine = BINAP [47, 48]) can also activate MeOH in addition to HjO at room temperature very easily. Reaction of 42 with excess MeOH in toluene at room temperature gave ah-stable and thermally stable colorless hydrido (me thoxo) complexes, [ IrH(diphos-phine) 2( 4-OMe)2( i-Cl)]Cl (69) quantitatively (Eq. 6.21) [49]. The shucture of 69b,... 

The dinuclear iridium(l) diphosphine complexes 42 can also activate carboxylic acids easily. For example, the reaction of [IrCl(binap)]2 (42b) with an excess of acetic acid or benzoic acid in toluene at room temperature gave the corresponding (hydri-... 

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... 

Asymmetric hydrogenation of nitrones in an iridium catalyst system, prepared from [IrCl(cod)]2, (S)-BINAP, NBu 4 BH4, gives with high enantioselectivity the corresponding A-hydroxylamines which are important biologically active compounds and precursors of amines (480). Further reduction of hydroxylamines to secondary amines or imines can be realized upon treatment with Fe/AcOH (479), or anhydrous titanium trichloride in tetrahydrofuran (THF) at room temperature (481). 

An iridium(I) complex with the l,2-bis(tcrt-butylmethylphosphino)ethane (4) and tetrakis(3,5-bis(trifluoromethyl)phenyl)borate as the counter anion catalyzes the hydrogenation of several acyclic aromatic Ai-arylimines under atmospheric hydrogen pressure at room temperature, giving the desired chiral amines with high-to-excellent enantioselectivities (up to 99%, Fig. 6) [19]. The authors also tested (S )-BINAP (Fig. 1) and (/ )-Ph-PHOX (PHOX = 2-[2-(diphenylphosphino) phenyl]-4,5-dihydrooxazole) hgands with lower enantioselectivities [19]. Both steric and electronic properties of the ligand and the combination with the BArF anion are in the base of the efficacy of this catalytic system. On the other hand, attempted hydrogenations of Ai-(2,2,2-trifluoro-l-phenylethylidene)aniline and M-(l,2,2-trimethyl-propylidene)aniline under the same conditions resulted in... 

The BINAP derivative of the ort/io-cyclometallated iridium catalyst has been characterized by single crystal X-ray diffraction analysis [280]. Remarkably, although the reaction sequence depends upon oxidation of either the reactant alcohol or isopropanol, the enantiomeric purity of the homoallylic alcohol product... 

Insertion of aUcynes into aromatic C-H bonds has been achieved by iridium complexes. Shibata and coworkers found that the cationic complex [Ir(COD)2]BF4 catalyzes the hydroarylation of internal alkynes with aryl ketones in the presence of BINAP (24) [111]. The reaction selectively produces ort/to-substituted alkenated-aryl products. Styrene and norbomene were also found to undergo hydroarylation under similar condition. [Cp IrCl2]2 catalyzes aromatization of benzoic acid with two equivalents of internal alkyne to form naphthalene derivatives via decarboxylation in the presence of Ag2C03 as an oxidant (25) [112]. 

Milestones in the development of the diphosphane family include the establishment of BINAP [10] and DuPHOS [11]. The potential offered by the chiral diphosphane complexes of ruthenium [12] and iridium [13] in hydrogenation was also recognized. In parallel inves-... 

BINAP complexes have been used extensively in asymmetric synthesis, for example in hydrogenations,389,390 olefin isomerizations,390 arylation of olefins,391 and enantioselective allylation of aldehydes.392 Palladium or platinum complexes of (165) find important applications in enantioselective C—C bond formation,393-396 whilst iridium complexes are catalysts for the hydrogenation of nonfunctionalized tri- and tetrasubstituted olefins. 97... 

In 2006, Genet and Mashima developed a new and convenient one pot reaction to prepare mononuclear halide carboxylate iridium(III) complexes and cationic triply halogen bridged dinuclear iridium(III) complexes of BINAP, p TolBINAP, and SynPhos. These iridium(III) complexes were tested as catalyst precursors for asymmetric hydrogenation of 2 phenylquinoline (Scheme 10.8) [10]. Cationic iododi nuclear p TolBINAP (S) L6e and SynPhos (S) L3c complexes had better enantios... 

The only ruthenium and iridium catalysts tried ([Ru2Cl4(S-BINAP)2]NEt3 in methanol and [Ir(COD)py(Pcy3)]PF6 in dichloromethane were completely inactive. 

Another sulfonated derivative of BINAP was mentioned in a patent of Takasago International Corporation [8]. Cationic complexes of ruthenium and or iridium with this ligand - sulfonated on the 5- and 5 -positions of the naphthyl rings - are claimed to affect asymmetric hydrogenation of olefins, ketones, and imines. 

Rhodium and iridium catalysts incorporating bisphosphine ligands such as BINAP and derivatives have also been shown to be effective in the asymmetric Pauson—Khand reaction of 1,6-enynes, and some high ees have been obtained with substrates incorporating heteroatoms. As an example, the allylpropargylamine (8.243) is converted into the bicychc product (8.244) with high ee in the presence of an iridium/ToIBINAP catalyst. It has been shown that, in some cases, aldehydes... 

The first example of direct enantioselective addition of a C—H bond to a ketone was reported by Shibata and co-workers in 2009 using the cationic Ir/ (S)-Hg-BINAP as the catalyst in the synthesis of a chiral 4-acetyl-3-hydroxy-3-methyl-2-oxindole with 72% ee. Recently, Yamamoto and co-workers developed a cationic Ir/(R,R)-Me-BIPAM catalyzed asymmetric intramolecular direct hydroarylation of a-keto amides 178 affording the chiral 3-substi-tuted 3-hydroxy-2-oxindoles 179 in high yields with complete regioselectivity and high enantioselectivity (84-98% ee). In their proposed reaction mechanism, the aryl iridium complex formed via C—H bond activation is coordinated with the two carbonyl groups of the amide (Scheme 5.65). 

More recent work on the asymmetric PKR has focused on reactions catalyzed by rhodium and iridium complexes. Jeong and co-workers reported reactions catalyzed by a combination of [Rh(CO)jCl]2, (S)-BINAP, and AgOTf. Good to excellent ee s were obtained for a small range of substrates (Equation 17.79). After the observation that phosphine ligands improve the yield of the Ir-catalyzed PKR, Shibata reported intramolecular PKRs catalyzed by the combination of Tol-BINAP and [Ir(COD)Cl]2 in excellent yields and enantioselec-tivities (Equation 17.80). ... 

Iridium(I)-diphosphane complexes are known as effective hydrogenation catalysts for a long time. Lately, BINAP, BCPM, and dihydrooxazol derivatives were used as ligands for enantioselective hydrogenation of imines (244). Iridium-(P-Phos) catalysts have been used for the asymmetric hydrogenation of the C=N bond of quinolines (245). 

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