Organometallic Chemistry in Aqueous Solution. Hydration of Nitriles to Amides Catalyzed by a Water-Soluble Molybdocene, (MeCp)₂Mo(OH)(H₂O)⁺

Abstract

Cp′ 2 Mo(µ-OH) 2 MoCp′ 2 ] 2+ (1) (Cp′ ) η 5 -CH 3 C 5 H 4 ) is a precatalyst for the hydration of nitriles in aqueous solution under mild conditions (∼80 °C). Among the nitriles hydrated were acetonitrile, isobutyronitrile, benzonitrile, 3-hydroxypropionitrile, 3-bromopropioamide, 4-cyanopyridine, succinonitrile, methyl cyanoacetate, 2-methoxyacetonitrile, and acrylonitrile. Except in the case of 2-methoxyacetonitrile, hydrolysis of the resulting amide products did not occur. Hydration of the CdC double bond did not occur in acrylonitrile, but hydrolysis of ester and ether linkages did occur in nitriles containing those functional groups. The apparent rate constants and turnover frequencies of the catalytic reactions were determined using an iterative kinetics-fitting program. The rates and turnover frequencies are comparable to those reported for many homogeneous nitrile hydration catalysts described in the literature. In aqueous solution, 1 is in equilibrium with [Cp′ 2 Mo(OH)(H 2 O)] + (2), and this monomer is proposed to be the active hydration catalyst. The hydration is proposed to occur by an intramolecular attack of a hydroxide ligand on a coordinated nitrile. The hydration reaction is irreversibly inhibited by product and reversibly inhibited by substrate (nitrile).

Selective Ruthenium‐Catalyzed Hydration of Nitriles to Amides in Pure Aqueous Medium Under Neutral Conditions

“…In contrast to these catalytic processes performed in organic solvents, and despite the growing interest to develop environmentally benign and safety processes, metal catalysts able to promote such a transformation in pure aqueous media are much scarcer (water is one of the best choices to replace organic solvents because of its low cost, availability, and nontoxic nature). [12,13] Moreover, the practical application of these homogeneous catalysts, including rhodium, [14] palladium, [15] iridium, [16] molibdenum, [17] nickel, [18] and zinc [19] complexes, [20] shows serious drawbacks mainly due to their low activities and very limited scope of the substrates.…”

Efficient Hydration of Nitriles to Amides in Water, Catalyzed by Ruthenium Hydroxide Supported on Alumina

“…Many efficient methods that use microorganisms for enzymatic hydration of nitriles [5,6] or homogeneous complexes of transition metals such as cobalt, [7] copper, [8] molybdenum, [9] ruthenium, [10] rhodium, [11] palladium, [12,13] and platinum [14,15] have been reported. However, these systems have disadvantages: difficulty in catalyst/product separation and necessity of special handling of microorganisms and metal complexes.…”

Direct Synthesis of Organic Carbonates from CO2and Alcohols Using Heterogeneous Oxide Catalysts

“…The reaction rate of benzonitrile hydration was higher than that of acetonitrile hydration, especially in the case of low CO 2 pressure. The higher activity and selectivity of benzonitrile hydration over acetonitrile hydration have been reported for other catalyst systems, such as [Cp′ 2 Mo(OH)(OH 2 )] + [49], [(dippe)Ni(η 2 -NCR)] [50], and [{Rh(OMe)(cod)} 2 ]PCy 3 [51]. The higher selectivity for benzonitrile hydration was interpreted in terms of the higher stability to alcoholysis of benzamide than acetamide.…”