Selective Hydration of Nitriles to Corresponding Amides in Air with Rh(I)-N-Heterocyclic Complex Catalysts

Abstract

A new synthetic method for obtaining [RhCl(cod)(NHC)] complexes (1–4) (cod = η4-1,5-cyclooctadiene, NHC = N-heterocyclic carbene: IMes, SIMes, IPr, and SIPr, respectively) is reported together with the catalytic properties of 1–4 in nitrile hydration. In addition to the characterization of 1–4 in solution by 13C NMR spectroscopy, the structures of complexes 3, and 4 have been established also in the solid state with single-crystal X-ray diffraction analysis. The Rh(I)-NHC complexes displayed excellent catalytic activity in hydration of aromatic nitriles (up to TOF = 276 h−1) in water/2-propanol (1/1 v/v) mixtures in air.

A Comprehensive Analysis of the Metal–Nitrile Bonding in an Organo-Diiron System

“…On the other hand, the computed Fe–N bond energy (in absolute value) increases in the order ( M2 ) + < ( M3 ) + < ( M4 ) + < ( 2 ) + < ( 6 ) + < ( 3 ) + = ( 7 ) + < ( 4 ) + < ( 5 ) + , pointing out that an appropriate balance of s-donation and p-back donation may be beneficial to the iron–nitrile bond stability. Interestingly, complex ( 5 ) + (R = 4-C 6 H 4 NMe 2 ) combines the lowest CT π tot /CT 0 ratio with the highest BDE of the series: the special strength of the coordination of 4-dimethylaminobenzonitrile in ( 5 ) + agrees with experimental findings on another iron system (see Introduction) [ 16 ].…”

“…Interestingly, one other iron complex with the 4-dimethylaminobenzonitrile ligand was previously crystallographically characterized; i.e., the piano-stool [FeCp(Prophos){NC(4-C 6 H 4 NMe 2 )}] + [ 16 ]. In this case, the Fe II -nitrile and N≡C bond lengths are consistent with the situation in (5Z)CF 3 SO 3 .…”

“…They most commonly behave as monodentate ( end-on ) ligands, and have been widely employed as weakly coordinating agents in complexes of low- to middle-valent transition metals, since their substitution by more strongly coordinating ligands is a convenient strategy to access a multitude of derivatives, catalysts and materials [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Furthermore, nitrile ligands are usually susceptible to nucleophilic attack [ 12 , 13 , 14 ] and may be engaged in a great variety of chemical transformations mediated by the adjacent metal centre, either catalytic [ 15 , 16 , 17 , 18 ] or stoichiometric [ 12 , 19 , 20 , 21 , 22 , 23 ].…”

Redox Isomerization of Allylic Alcohols Catalyzed by New Water-Soluble Rh(I)-N-Heterocyclic Carbene Complexes

“…In the 13 C{ 1 H} NMR spectrum recorded in MeOD, the resonance signal of the carbene carbon atom appears at 212. 43 [45], and with the values obtained for water-insoluble analogues [46]. Unfortunately, despite all our attempts, 1 could not be isolated as a pure solid.…”

Organoselenium ligands for heterogeneous and nanocatalytic systems: development and applications

“…Amides are an important class of compounds that are found in a variety of biologically active compounds, polymers and synthetic intermediates, 132 and a variety of synthetic methods have been developed for their formation. 132 Nitrile hydration provides an atom-efficient synthesis of amides and is carried out on an industrial scale, 133 for example in the production of acrylamide and nicotinamide. The direct nucleophilic addition of water to the C-N bond is kinetically slow, and hence a variety of catalysts have been developed.…”