Homogeneous Catalysis of Organic Reactions by Transition Metal Complexes

Abstract

Over the current reporting period, a number of reviews on homogeneous catalysis have appeared. Drent has summarized opportunities for homogeneous catalysis and pointed out a number of industrial-scale applications, such as olefin carbonylations, the hydroformylation of formaldehyde and of olefins, the reductive carbonylation of aromatics and olefin dimerisation.⁽¹⁾ An extensive review compiles and critially evaluates thermodynamic data on transition metal—hydrogen and carbon bond strength; such data are of key importance for the evaluation of catalytic reactions.⁽²⁾ A literature survey on homogeneous catalysis covering the year 1989 has appeared.⁽³⁾ Another comprehensive article surveys oligomerizations of α-olefins, including a number of industrial processes.⁽⁴⁾ A fundamental aspect of oligomerization and polymerization chemistry is the insertion of alkenes into M — R bonds, a subject reviewed by Lehmkuhl, with emphasis on ethylene insertions into nickel—carbon bonds, together with some C — H activation reactions catalyzed by ruthenium complexes.⁽⁵⁾ C — H activation of alkenes instead of polymerization is a typical feature of the chemistry of very early transition metals such as scandinum, and Bercaw has summarized some recent results of this very topical aspect.⁽⁶⁾ Further reviews deal with the synthesis of cyclobutane and cyclopentane derivatives via homogeneous catalysts,⁽⁷⁾ the role of metal complex catalysis in electrochemical reactions,⁽⁸⁾ and the coordination chemistry and carbonylation catalysis of complexes with hemilabile oxygen—phosphorus ligands.⁽⁹⁾ Herrmann has discussed the role of rhenium in oxidation catalysis and metathesis⁽¹⁰⁾; the latter aspect is also the topic of an article by Schrock on the living ring-opening metathesis polymerization by well-characterized transition metal alkylidene complexes.⁽¹¹⁾ Palladium continues to play a prominent role on C — C forming reactions, e.g., in the arylation of olefins, especially norbomene,⁽¹²⁾ in hydroarylation and hydrovinylations of C — C multiply bonded substrates,⁽¹³⁾ in 1,2-additions to heteroatom-substituted olefins,⁽¹⁴⁾ and in stereoselective annulations, mainly involving functionalization of cyclohexenes⁽¹⁵⁾ Iridium and ruthenium hydrides have important organic-synthetic applications in the stereoselective isomerization of acetylenic derivatives to conjugated dienes.⁽¹⁶⁾ The mild conditions of many homogeneously catalyzed reactions are frequently exploited in asymmetric synthesis. Ruthenium complexes of chiral chelating binaphthylphosphines are especially valuable,^(17,18) particularly in asymmetric hydrogenations.⁽¹⁹⁾ Finally, Brunner has reviewed a number of enantioselective catalytic reactions, such as the transfer hydrogenation of itaconic acid, styrene cyclopropanation, and the Khand—Pauson reaction.⁽²⁰⁾