Ruthenium complex reductive amination

The three steps 32-34 have been suggested77 to be equilibria, and the overall equilibrium must lie far to the left because no adduct 23 is found in the reaction mixture when the reaction of sulfonyl chloride with olefin is carried out in the absence of a tertiary amine. A second possible mechanism involving oxidative addition of the arenesulfonyl halide to form a ruthenium(IV) complex and subsequent reductive elimination of the ruthenium complex hydrochloride, [HRulvCl], was considered to be much less likely. 

Another useful reduction process is asymmetric transfer hydrogenation (ATH) where the hydrogen is transferred from the solvent, often isopropanol, to the ketone or imine function to produce the enantiopure alcohol or amine. For example, Baratta et alP made ruthenium complexes containing the (/ ,S)-Xyliphos ligand to reduce a simple ketone to (5)-l-(3-trifluoromethylphenyl)ethanol, used in the synthesis of the fungicide (5)-MA20565 (Scheme 3). 

Ruthenium complexes need a strong reductant or oxidant for chemiluminescent reactions of type (b) and (c) above. These reactive compounds are usually radicals derived from simple organic compounds such as amines, amino acids, the reduced form of )S-nicotinamide adenine dinucleotide (NADH), and some antibiotics. Analytical procedures have been developed for some of these compounds on this basis, e.g., for tripropylamine, which gives a detection limit of 2 X 10 moll. ... 

Recently, Ru-JOSIPHOS complexes were found extraordinary effective for the enantioselective transfer hydrogenation of aryl ketones (168). A novel bidentate diphosphine with axial chirality (DM-SEGPHOS) was reported to form active catalyst with ruthenium for asymmetric reductive amination (169). 

Chemical methods for the TH of C=N bonds, and notably the reduction of imines to amines, have been known for many decades, early examples being the use of ruthenium complex Ru3(CO)i2 [20] and [RuCl2(PPh3)] [21]. In both cases, IPA was used as the reducing agent and a base was used to activate the catalyst. Relevant to the latter example, it was later demonstrated that [RuH2(PPh3)] was an active TH catalyst which did not require added base [22, 23]. 

Binuclear complexes with bridging trimethyltriazoldiylidene ligands were also used in TH and p-alkylation reactions. Thus, complexes 124 and 125 were applied for TH of ketones and imines in KOH/i-PrOH (Figure 13.14). The reductions of ketones and N-ben lidene anilines were complete within 1 h. Related 126 and 127 ruthenium complexes were investigated as catalysts in the p-alkylation of secondary alcohols with primary alcohols. Such catalytic systems were very selective and more active than the previously reported catalysts. Cationic Ru" complexes 128 with a picolyl-functionalized NHC catalyzed the N-alkylation of amines under mild conditions. Ru" complexes 129, with benzimidazol-2-ylidene, gave excellent yields of <99% for the alkylation of various amines using benzylic and aliphatic alcohols at 130 C under solvent free conditions. ... 

A number of bis(arylamido)- and bis(diarylamido)ruthenium(IV) porphyrin complexes have been reported. In general, these complexes can be prepared by the reduction of [Ru(0)2(por)] with corresponding aromatic amines or by the oxidative deprotonation of [Ru (por)(ArNH2)2], as shown in Scheme 18. 

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