The Hydration of Chloroacetonitriles Catalyzed by Mono‐ and Dinuclear Ru^II‐ and Os^II‐Arene Complexes

Abstract

The hydration of nitriles to the corresponding amides is an important reaction for both laboratory and industry purposes. The classical synthesis method requires harsh conditions, gives low yields, and is nonselective due to further hydrolysis of the amides into carboxylic acids. To obtain good yields and high selectivity, transition metal complexes have been utilized as catalysts for this transformation. Herein, a series of Ru(II)- and Os(II)-arene complexes--based on pyranone, thiopyranone, and pyridinone ligands--were assayed on the hydration of chloroacetonitriles. The influence of the substitution pattern of the ligand, and of the nuclearity and of the type of substrate on the yield, the selectivity, and the turnover numbers are discussed.

Metal-catalyzed nitrile hydration reactions: The specific contribution of ruthenium

“…H-bonding between the OH group and the incoming water molecule in the secondary coordination sphere of the catalyst was again In addition to all the examples commented above, other hydration processes catalyzed by homogeneous ruthenium catalysts described in the literature include (Scheme 14): (i) The hydration of the benzoxazolylacetonitrile 31 by dimer [{RuCl(µ-Cl)(η 6 -p-cymene)} 2 ], which allowed the synthesis of the benzoxazolylacetamide 32 in high yield [46]. (ii) The hydration of the chloroacetonitriles 33 employing the mononuclear arene-ruthenium(II) complexes 35 containing different pyranone-and pyridinone-based ligands [47]. The corresponding chloroacetamides 34, a particular class of compounds that exhibit biological properties and are widely used as building blocks in preparative organic chemistry [48], could be obtained in modest to high yields employing low ruthenium loadings (0.1-0.2 mol%) and pure water as solvent .…”

Phosphite‐Derivatized Ruthenium‐Carbohydrate Complexes in the Catalytic Hydration of Nitriles. Short Communication

“…The formation of dichloroacetamide was not satisfactory providing poor yields ( Table 2). However, a slightly better result than for a and analogous complexes [28] was observed with doubled yield and similar selectivity factors.…”

“…The result of the reaction was determined by evaporating the solvents under reduced pressure, dissolving the residues in (D 6 )DMSO and quantifying the yields by 1 H-NMR with 1,3,5-trimethoxybenzene as internal standard. The results of the catalytic hydration of trichloroacetonitrile with 1 -3 are given in Table 1 with the Ru-cymene-ethylmaltolato complex a as reference compound [28]. The selectivity of the formation of trichloroacetamide was characterized by 1 H-NMR based on the signal at 8.35 ppm for the amide H-atoms compared to the signal at 7.12 ppm (ammonium) of the side product.…”

Ruthenium-Catalyzed Amide-Bond Formation

“…Secondary coordination sphere activation of water, via hydrogen bonding with the OH group of the ligand, also explains the outstanding performances of the related phosphiniteruthenium(II) complex [RuCl 2 ( 6 -p-cymene){PMe 2 (OH)}] (12), which was also able to hydrate cyanohydrins [50,51]. Although other catalytic systems for the selective hydration of organonitriles in water have been described [52][53][54][55][56][57], none of them presented an activity and scope comparable to those of the bifunctional catalysts 4-12. Additional examples of nitrile hydration reactions catalyzed by homogeneous ruthenium catalysts in organic media are (Scheme 8): (i) The hydration of benzoxazolylacetonitrile by the arene-ruthenium(II) dimer [{RuCl(-Cl)( 6 -p-cymene)} 2 ], which led to benzoxazolylacetamide in high yield [58], and (ii) the asymmetric hydration of -benzyl--methylmalononitrile by the chiral catalysts 13 [59].…”