Bifunctional Water Activation for Catalytic Hydration of Organonitriles

Abstract

Treatment of [Rh(COD)(μ-Cl)] 2 with excess t BuOK and subsequent addition of 2 equiv of PIN•HBr in THF afforded [Rh(COD)(κC 2 -PIN)Br] (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of 1 confirms ligand coordination to "Rh(COD)Br" through the carbene carbon featuring an unbound naphthyridine. Compound 1 is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h −1 was achieved for the acrylonitrile. A similar Rh(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst−water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site via double hydrogen-bonding interactions, providing significant entropic advantage to the hydration process. The calculated transition state (TS) reveals multicomponent cooperativity involving proton movement from the water to the naphthyridine nitrogen and a complementary interaction between the hydroxide and the nitrile carbon. Bifunctional water activation and cooperative proton migration are recognized as the key steps in the catalytic cycle.

The 3rddegree of biomimetism: associating the cavity effect, ZnIIcoordination and internal base assistance for guest binding and activation

“… 46 – 51 Relatively recently however, the so-called bifunctional catalysts have been reported for the hydration of nitriles. 52 – 56 These catalysts either employ a heteroatom in the ligand backbone to direct the water attack to the nitrile carbon atom, or use a hemilabile basic group for water activation. They are based mostly on precious metals such as Ru, Rh or Pt, although a very recent report describes a Ni II catalyst displaying hemilability-driven water activation for the hydration of a coordinated nitrile.…”

Exploring Rhodium(I) Complexes [RhCl(COD)(PR3)] (COD = 1,5-Cyclooctadiene) as Catalysts for Nitrile Hydration Reactions in Water: The Aminophosphines Make the Difference

“…19 Indeed, in our knowledge, such behaviour has not precedents with any homogeneous catalyst. 40 Only heterogeneous systems, such as Au/TiO 2 , CeO 2 or Ni 0.7 Mn 0.3 O, have shown a comparatively higher effectiveness with heteroaromatic nitriles.…”

Supramolecular catalysis. Part 1: non-covalent interactions as a tool for building and modifying homogeneous catalysts

“…Very recently, Bera and co-workers reported the use of a NHC derivative tethered with a 1,8-naphthyridine group as a ligand in the rhodium-catalysed hydration of organonitriles at 25 °C (TOF up to 20,000 h -1 for acrylonitrile). 375 DFT calculations suggest the formation of a hydrogen bond between the 1,8naphthyridine group of the NHC ligand and a water molecule 70 coordinated to the Ru atom (see 129, Fig. 34, b).…”