摘要:

Mechanistic studies of homogeneous catalysts1have begun to give a fairly clear picture of the mechanism in a number of different systems. In the case of low valent organometallic catalysts, the metal often shuttles between two different oxidation states, and between 16- and 18-electron configurations.2Many catalysts have one or more labile ligands that dissociate to allow access for the substrate(s) involved in the reaction. We have been particularly interested for several years in studying complexes that have multiple labile ligands that can provide many sites for the substrate(s) to bind. This has led us to think in terms of the partitioning of the electron count of the catalytic intermediates between the part derived from the substrate(s) and from the permanently bound ligands. Since we can easily adjust the number of permanently bound ligands and the total electron count must not exceed218, this gives us a way of altering the number of sites available to the substrate(s). Such changes can have a profound effect on the outcome of the catalytic reaction. The purpose of this Comment is to rationalize the results of some transition metal catalyzed reactions on the basis of this partitioning scheme.

ISSN:0260-3594    

DOI:10.1080/02603598508072264

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Homogeneous catalytic systems for CO hydrogenation often include promoters which improve the activity or selectivity for a certain product. A major function of these components is apparently to maintain the organometallic catalyst species in the appropriate oxidation state. This can be accomplished, for example, by coordination to the metal center or by a reductive deprotonation process. Amounts of promoter added are often critical because an excess can result in overreduction or overoxidation of the metal catalyst component.

ISSN:0260-3594    

DOI:10.1080/02603598508072265

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In organometallic clusters with three, four, five, and six metal atoms metal-ligand fragments can be replaced by isolobal units. Fe(CO)3and Co(CO)3are good leaving groups. Organometallic units of the chromium, manganese, iron, cobalt, and nickel subgroups have been incorporated. The yields of the reactions can be remarkably high considering that during the replacement at least three bonds have to be broken and reformed. One-step and two-step reactions can be employed. Mechanistically, three reaction pathways have to be considered: fragmentation-reconstitution, elimination-addition, and addition-elimination. The new clusters obtained open up hitherto inaccessible aspects of cluster chemistry.

ISSN:0260-3594    

DOI:10.1080/02603598508072266

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Molecular scientists now have an opportunity to add an important new dimension to synthesis. Preparation of chemical systems, comprising two or more components, to achieve a function is possible. While rational strategies exist for some simple systems, major advances in fundamental reaction chemistry at the molecular and macromolecular level, especially at interfaces, are required to achieve practically significant synthetic objectives. Synthetic chemical systems inspired by nature and microelectronic devices illustrate some of the aspects of systems synthesis. These example systems include multicomponent catalysts, the photosynthetic apparatus for solar energy conversion, diodes, and transistors.

ISSN:0260-3594    

DOI:10.1080/02603598508072267

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603598508072263

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor