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)