Homogeneous Catalysis without Metals

Several important chemical reactions are catalyzed simply by H+ or OH ions. Examples include aldol reactions, esterifications and trans-esterifications, and 

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This survey of theoretical methods for a qualitative description of homogeneous catalysis would not be complete without a mention to the Hartree-Fock-Slater, or Xot, method [36]. This approach, which can be formulated as a variation of the LDA DFT, was well known before the formal development of density functional theory, and was used as the more accurate alternative to extended Hiickel in the early days of computational transition metal chemistry. 

Homogeneous Catalysis A catalyst is a substance, usually used in small amounts relative to the reactants, that increases the rate of a reaction without being consumed in the process. Liquid-phase reactions are often conducted in the presence of homogeneous catalysts. Typically, homogeneous catalysts are ions or metal coordination... 

Keeping our target of homogeneous catalysis in mind, we adopted a broad definition of organometallic complexes and included compounds without metal-carbon bonds (e. g., metal-phosphine and metal-nitrosyl complexes) as far as they retain the structural and reactivity features of typical organometallic compounds. Recent developments, e. g., the substitution of phosphine by carbene ligands (cf Section 3.1.1.1), support the validity of this view. 

Transition-metal homogeneous catalysis is first and foremost a synthetic tool (1). Kinetic and mechanistic studies represent only small fraction of the literature, and mass-transfer studies are rather scarce. It appears that mass-transfer considerations are all too often an afterthought when dealing with homogeneously catalyzed reactions. This is unfortunate for the discipline because syntheses do not occur without mass transfer. Indeed, mass-transfer consideration should be an integral part of the experiments. The fact that mass transfer can and often does influence both rate and selectivity is probably not sufficiently appreciated in the homogeneous catalysis community. 

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