Isopropanolate ligand

The nanostructure formation proceeds via C—C bond formation between ben2yl alcohol and the isopropanolate ligand, and yttrium oxide catalyzed hydride transfer reactions to form benzoic acid and toluene, limiting the growth of the thickness of the lamellae [128]. 

The hydrogen transfer reaction (HTR), a chemical redox process in which a substrate is reduced by an hydrogen donor, is generally catalysed by an organometallic complex [72]. Isopropanol is often used for this purpose since it can also act as the reaction solvent. Moreover the oxidation product, acetone, is easily removed from the reaction media (Scheme 14). The use of chiral ligands in the catalyst complex affords enantioselective ketone reductions [73, 74]. 

Certain other metal ions also exhibit catalysis in aqueous solution. Two important criteria are rate of ligand exchange and the acidity of the metal hydrate. Metal hydrates that are too acidic lead to hydrolysis of the silyl enol ether, whereas slow exchange limits the ability of catalysis to compete with other processes. Indium(III) chloride is a borderline catalysts by these criteria, but nevertheless is effective. The optimum solvent is 95 5 isopropanol-water. Under these conditions, the reaction is syn selective, suggesting a cyclic TS.63... 

The catalysts are best prepared in situ by mixing a half-equivalent of the di-chloro-metal aromatic dimer with an equivalent of the ligand in a suitable solvent such as acetonitrile, dichloromethane or isopropanol. A base is used to remove the hydrochloric acid formed (Fig. 35.3). If 1 equiv. of base is used, the inactive pre-catalyst is prepared, and further addition of base activates the catalyst to the 16-electron species. In the IPA system the base is conveniently aqueous sodium hydroxide or sodium isopropoxide in isopropanol, whereas in the TEAF system, triethylamine activates the catalyst. In practice, since the amount of catalyst is tiny, any residual acid in the solvent can neutralize the added base, so a small excess is often used. To prevent the active 16-electron species sitting around, the catalyst is often activated in the presence of the hydrogen donor. The amount of catalyst required for a transformation depends on the desired reaction rate. Typically, it is desirable to achieve complete conversion of the substrate within several hours, and to this extent the catalyst is often used at 0.1 mol.% (with SCR 1000 1). Some substrate-catalyst combinations are less active, requiring more catalyst (e.g., up to 1 mol.% SCR 100 1), in other reactions catalyst TONs of 10000 (SCR 10000 1) have been realized. 

PfefFer, de Vries and coworkers developed the use of ruthenacycles, based on chiral aromatic amines as enantioselective transfer hydrogenation catalysts. These authors were able to develop an automated protocol to produce these catalysts by reacting ligand and metal precursor in the presence of base, KPFS in CH3CN. After removal of the solvent, isopropanol was added followed by the substrate, acetophenone, and KOtBu. In this way, a library of eight chiral... 

The use of 2 equiv. of MonoPhos (10 a) in the rhodium-catalyzed enantioselective hydrogenation of the key cinnamic acid derivative 15 resulted in the formation of 16 in 50% conversion and 20% ee after 5 h in isopropanol at 60 °C and 25 bar of hydrogen. Other phosphoramidites, such as the sterically demanding ligand 10 c, resulted in slightly better activity and enantioselectivity. In seeking a... 

Chiral methyltitanium reagents.1 The N-sulfonamides (1) formed from norephedrine have been used as chiral ligands for a methyltitanium reagent. Thus addition of 1 to TiCl4 and CH3Li (1 4) and then to isopropanol provides a reagent... 

Reductive cross-dimerization has been established with ketones and 0-meth-oximes upon reduction in isopropanol with a Sn cathode as a convenient route to yS-amino alcohols, diastereoselectivities of up to 85 15 were obtained. A chiral ligand was obtained this way from the coupling of (-) - menthone with O-methyl acetaldoxime. Similarly, ketones could be coupled to hydrazones and nitrones. Also, intramolecular couplings were achieved with good yields and diastereoselectivity (Fig. 56) [308]. 

A series of chiral N,S-chelates was synthesized as ligands for the iridium(l)-catalyzed reduction of ketones using either HCOOH/NEtj or isopropanol as hydrogen sources. The ligands were obtained by sulfoxidation of an (R)-cysteine-based aminosulfide, providing a diastereomeric ligand family containing a chiral sulfur... 

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