摘要:

AbstractTransition‐metal complexes in which two or more metal atoms are bridged by one or more arene ligands led a shadowy existence in comparison to the extensive class of mononuclear arene complexes. Arene bridges can occur in a variety of coordination modes and with almost all of the transition–metal elements of the periodic table. Nowhere else are found so many forms of distorted and bent arene rings. The binuclear compounds can be divided into two classes: adducts which show relatively weak metal–arene bonding and complexes which show strong arene–metal interaction. Most of the adducts are in equilibrium with mononuclear complexes in solution or are only stable in the solid state (often as polymers). In both classessynandanticoordination occurs; their geometries show a wide variation between the extreme cases of η1: η1‐bridge and η6: η6‐triple‐decker structure. Metal surfaces with chemisorbed arenes can be seen as a form of multinuclear arene–metal complexes. On transition‐metal surfaces, benzene can be bonded to one, two, or four surface atoms. Molecular clusters with face‐capping arene ligands that are bonded to three metal atoms have until now mainly been limited to two classes. The arenes bound to {(CO)3M}3(M = Ru, Os) or (CpCo)3clusters as μ3‐η2: η2: η2ligands show only a weak trigonal distortion towards a Kekulé structure. Detailed investigations of the molecular structure and ligand dynamics of [(CpCo)3(μ3‐arene)] complexes considerably help the understanding of the bonding of arenes to met

ISSN:0570-0833    

DOI:10.1002/anie.199202473

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractMicroscopic insights into elementary molecular processes are only feasible through the observation of unique quantum states and the study of their couplings and time‐dependent behavior. In the case of larger chemically relevant molecules, the corresponding transitions lie so close that they mostly overlap and lead to band structures. For example, electronic band spectra of large molecules cannot be resolved into single lines even by high resolution UV‐spectrometers. The reason for this is the Doppler broadening, arising from the random velocity of the molecules in the gas phase. In this article, we want to demonstrate that modern laser spectroscopic methods make it possible to overcome this “Doppler barrier” and to resolve the line structure in band spectra. The selective excitation of unique quantum states yields precise information on the mechanisms responsible for energy redistribution in molecules. Energy redistribution processes represent a crucial first step preceding chemical reactions, which they influence decisively. Very high resolution spectroscopy elucidates the influence of molecular rotation on the energy redistribution. Through Coriolis forces in rotating molecules, vibrations can couple, causing a flow of energy from the selectively excited vibrations to the many other vibrational degrees of freedom. Weak interactions, namely van der Waals interactions and hydrogen bonding, determine the structure of large molecules (biomolecules) and supermolecular systems. Weak intermolecular interactions, given their selectively resolved quantum states, can be analyzed and understood at the microscopic level. “Doppler‐free spectroscopy” with its resulting line spectra furnishes information on the structure, including bond lengths, of van der Waals complexes. With this information, Doppler‐free spectroscopy provides the model parameters indispensable for the quantitative description of

ISSN:0570-0833    

DOI:10.1002/anie.199202631

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCompounds with highly coordinated, polyvalent main‐group elements represent an interesting alternative to the many well‐known transition‐metal complexes. Among the oldest and best known stable examples of such organic molecules are the iodine(III) compounds. Diaryliodonium species, Ar2IX, for example, have been known for over a hundred years and play an important role in lithography. Likewise, acetylenes and olefins are among the oldest, most important, and most valuable compounds in chemistry. Besides simple hydrocarbon alkenes and alkynes, numerous functionalized derivatives are also known and widely employed in organic chemistry. Despite the ubiquity and prominance of both IIIIspecies and olefins and acetylenes, the combination of these two types of functional groups in a single molecular unit, namely compounds with polyvalent iodine and at least one alkyne or olefin residue, was unknown until recently. The successful preparations of simple alkynyl‐ and alkenyl‐(phenyl)iodonium species during the 1980s has resulted in a renaissance in both acetylene and IIIIchemistry. These alkynyliodonium compounds readily undergo nucleophilic substitution on the alkyne moiety (SN‐A reactions) which are difficult with other substrates. The application of a wide variety of nucleophiles in this reaction resulted in diverse functionalized alkynes including previously unknown acetylenic carboxylates, sulfonates, and phosphates. These are excellent substrates for cycloaddition reactions as well as numerous other interesting chemical tran

ISSN:0570-0833    

DOI:10.1002/anie.199202741

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202861

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202881

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202901

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202921

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202931

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199202991

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199203011

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY