摘要:

AbstractInterfaces and heterojunctions which are incorporated into a crystal in well‐defined geometrical and spatial arrangements can lead to a structuring or engineering of (semiconducting) solids down to atomic dimensions. The electrical and optical properties are then defined locally, and phenomena related to extremely small dimensions (“quantum size effects”) become more important than the actual chemical properties of the materials used. The technique of molecular beam epitaxy allows an atomic layer‐by‐layer deposition in a two‐dimensional growth process, and crystalline materials in alternating layers of arbitrary composition and only a few atomic layers thickness are formed. The synthesis of microscopically structured solids by molecular beam epitaxy affords access to a new class of materials with accurately tailored electrical, optical, magnetic, dielectric, mechanical etc. properties. The semiconductor and metal superlattices described in this article, which are made of alternating thin layers of two different materials, symbolize just the beginning of a new area of materials engineering on a molecular (or atomic) scale. This periodic modulation of the chemical composition normal to the surface imposes an artificial periodicity on the semiconductor or metal crystal, a periodicity of one or two orders of magnitude larger than its natural lattice spacing. The synthesis of other materials combinations, including semiconductor/metal, semiconductor/insulator, metal/insulator, polymers, and magnetic materials, with entirely different properties and for completely different applications will certainly follow. Finally, a large variety of desired combinations of elements can be selected, and even metastable compounds with novel exciting properties can be synthesized by molecular b

ISSN:0570-0833    

DOI:10.1002/anie.198805933

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractIn recent years, the most significant development in the field of synthetic organic chemistry has been the application of biological systems to chemical reactions. Reactions catalyzed by enzymes and enzyme systems display far greater specificities than more conventional organic reactions. Biological and/or enzymatic syntheses and transformations, that is, “microbial transformations,” have great potential. Some of these reactions have already been shown to have useful applications in the fields of synthetic organic chemistry and biotechnology. This article reviews the current status of the rapidly developing field of microbial transformation, the methodology, available technological procedures, and fields of application being described especially in relation to conventional organic synthesis meth

ISSN:0570-0833    

DOI:10.1002/anie.198806221

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractParallel to organic electrocatalysis, the field of organotransition metal electrocatalysis has developed explosively since 1980. The theoretical and experimental foundations established byFeldbergin 1971 (ECE mechanism) have been applied, using fast electrochemical techniques, to various organometallic reactions such as isomerization, ligand exchange, chelation, decomplexation, and CO insertion and extrusion. Most of the work performed to date concerns ligand exchange reactions of N‐donors and P‐donors in mononuclear compounds, initiated by oxidants (or anodes) and of carbonyls and P‐donors in clusters, initiated by reducing agents (or cathodes). The preparative aspects of electrocatalysis have already been impressively developed in cluster chemistry and indicate that the technique is extremely useful. This review first delineates the principles and characteristics of electrocatalysis applied in organotransition metal chemistry, and then, after outlining the choice of efficient initiating reagents, goes on to describe the systems up to August

ISSN:0570-0833    

DOI:10.1002/anie.198806431

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe carbon dioxide molecule has been of limited importance as a synthetic unit in organic chemistry. When it is coordinated to transition metals, however, completely new possibilities arise; CO2can bond to metal complexes in a variety of ways and can enter into insertion and coupling reactions, or become catalytically attached to other substrates. The formation of CC bonds between carbon dioxide and unsaturated hydrocarbons under conditions of homogeneous catalysis makes available new synthetic routes to industrially interesting organic compound

ISSN:0570-0833    

DOI:10.1002/anie.198806611

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractFor the synthesis of organic compounds, reduction is an indispensible reaction type which is also widely used on an industrial scale. In industrial processes hydrogen is usually used as reducing agent, since strong reducing agents like alkali metals and hydrides can only be used to a limited extent for safety and economic reasons. Very economical reducing agents that are convenient to handle and have high potential application are hydrocarbons in presence of carbon. Hydrocarbon/carbon systems can be readily used instead of molecular hydrogen and expensive metal catalysts for the hydrogenation of compounds containing, for example, CC‐, CO‐, or NO‐double bonds. Furthermore, these systems can be used for carrying out reductions which hitherto required strong reducing agents such as zinc, tin, alkali metals and hydrides. Especially suitable as economic sources of hydrogen are refinery products such as vacuum gas oil, fuel oil S or vacuum residue oil. Hydrocarbons are dehydrogenated to unsaturated systems and finally to c

ISSN:0570-0833    

DOI:10.1002/anie.198806791

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198806831

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198806841

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198806851

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198806871

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198806891

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY