Film-shear reactors and more water-soluble ligands; new tools for doing inorganic and organometallic chemistry in aqueous solution

Abstract

Four developments from the author’s laboratory related to doing organometallic and inorganic chemistry in aqueous solution are reviewed. First, the development of new water-soluble cyclopentadienyl ligands and bidentate phosphine ligands is discussed. These ligands were developed because many of the standard water-solubilizing ligands contain –SO3− or –OH groups, which can bond to metal centers and thus inhibit catalysis. The new cyclopentadienyl ligands were used to generate water-soluble 19-electron complexes, and the water-soluble (CH3OCH2CH2CH2)2PCH2CH2P(CH2CH2CH2OCH3)2 ligand was used in a pressure-swing process to separate nitrogen from natural gas. Next, the catalytic hydration of nitriles, acetone cyanohydrin in particular, is discussed. The ability to catalytically hydrate acetone cyanohydrin (ACH) in aqueous solution would be particularly useful because ACH hydration is used in the preparation of methyl methacrylate and other methacrylates. The industrial method for hydrating ACH, known as the acetone cyanohydrin process, uses sulfuric acid and produces large amounts of by-product, which requires large amounts of energy to properly dispose of. An aqueous catalytic process could save energy and materials. Next, the use of a film-shear reactor for intimately mixing reactants in an aqueous solvent with reactants in an immiscible organic solvent is described. Finally, the inertness of the η2-H2 ligand in water-soluble Fe-(η2-H2) and Ru-(η2-H2) complexes to substitution by water in aqueous solution is discussed. Surprisingly, the substitution by water is approximately thermochemically neutral so there is little driving force for the reaction. Dihydrogen hydrogen bonding may also contribute somewhat to the inertness.