Novel Organometallic Chemistry

The reductive elimination to form C-C and C-H bonds [45] is a crucial step in the cross-coupling processes, as well as many other transition metal-catalyzed reactions. Reductive elimination reactions comprise an early chapter in any organometallic text. Many examples of these reactions have been studied, and a great deal is known about the mechanisms of these processes. Similarly, the cleavage of C-H bonds by oxidative addition, including the C-H bond in methane, is now known [46]. Again, questions remain about how these reactions occur, but a variety of mechanistic studies have revealed key features of these reactions. Even some remarkably mild C-C cleavage reactions have now been observed with soluble transition metal complexes [47,48]. 

In contrast, few examples of reductive elimination reactions that form the C-N bond in amines are known. Only in the past several years have complexes been isolated that undergo these reactions [49-54]. These reductive eliminations are the crucial C-N bond-forming step of the aryl halide and triflate amination chemistry discussed in this review. Information on how these reactions occur, and what types of complexes favor this process, has been crucial to the understanding and development of new amination catalysts [50], 

the selectivities, deactivation mechanisms, and potential transformations of alkoxo and amido intermediates in such reactions are not well understood. It is even rare for transition metal amido and alkoxo complexes to be clearly identified as intermediates in catalytic chemistry. The hydrogenation of imines and ketones presumably involves such intermediates [68], but they have not been clearly detected in these reactions [69]. The catalytic reduction of CO on surfaces may involve alkox-ides, but well-characterized homogeneous analogs are unusual [58]. 

The cleavage of allcylamine N-H bonds by late transition metals to form metal amido complexes is also rare [69, 70]. When the transition metal is a low valent, late metal, the resulting amido complexes are highly reactive [71, 72]. It appears that the amination of aryl halides can involve an unusual N-H activation process by a palladium alkoxide to form a highly reactive palladium amide [65, 73]. 

This review covers palladium-catalyzed amination of aryl halides and sulfonates. The nickel-catalyzed process [82-85] requires much higher catalyst loads and has a narrower substrate scope. Thus, it is not reviewed. Sections 4.2 to 4.5 cover the development of different palladium catalysts for the synthesis of arylamines and related structures. This work has 

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Since Chatt and Davidson13 observed the first clear example of simple oxidative addition of a C—H bond of naphthalene to a ruthenium metal center, Ru(dmpe)2 (dmpe = Me2PCH2CH2PMe2), hydrocarbon activation has been the subject of many transition metal studies.11 c Sometimes, the efforts in this field have ended in findings different from the initial objectives, which have been the starting point for the development of novel organometallic chemistry. 

Because of the sheer volume of work published over the last 5 years, only certain specialist topics will be discussed in any depth (Sections III-V). Whereas this survey covers many areas in a cursory fashion, it amply illustrates the rapid growth of knowledge in Os chemistry. It also serves to indicate where future advances are likely to occur, especially in the organometallic chemistry of Os(NH3) Lm]JC+ complexes, which often mimics or surpasses the extensive chemistry normally associated with phosphine ligands. Examples wherein novel organometallic chemistry has occurred are the Tj2-ketone and rj2-arene complexes of penta-ammineosmium. 

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected stnicture types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaboranc elusters, ". Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helpful m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride clu.ster chemistry, metallaboranc and metallacarbaborane chemistry (pp. 189-95). organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

Development of more efficient transition metal catalyst systems including using novel and efficient ligands has been one of the focuses in organometallic chemistry.35 The developments in this area will allow not only to synthesize polymers under mild conditions with higher or desired molecular weights but also to use less expensive, more readily available materials for the polymerizations. 

The following is a comprehensive smwey of the chemistry of macrocycles comprised entirely of phenyl and acetylenic moieties. Although over fom" decades old, this area of research has come into its own just in the last few years. Widespread interest in the field has been spurred by recent discoveries utilizing these compoimds as ligands for organometallic chemistry, hosts for binding guest molecules, models of synthetic carbon allotropes, and precursors to fullerenes and other carbon-rich materials. This review will discuss the preparation of a tremendous variety of novel structm-es and detail the development of versatile synthetic methods for macro cycle construction. 

The outstanding performances of five-membered NHC ligands in organometallic chemistry and catalysis prompted Grubbs and co-workers to develop a novel stable four-membered NHC [64]. Following their interest in developing new ruthenium olefin metathesis catalysts, they synthesised and fully characterised complex 51 to study the impact of the architecturally unique NHC ligand on the activity of the Ru-based catalyst [65] (Fig. 3.20). In the RCM of 1 at 40°C in CH Cl with 51 (5 mol% catalyst), the reaction reached completion within 20 min, whereas less than 10 min are required for standard catalysts 14 and 16. It should be noted that catalysts 14 and 16 are able to complete the RCM of 1 with only 1 mol% catalyst at 30°C. 

Novel anionic gold(I) and gold(III) organocomplexes. Journal of Organometallic Chemistry, 131(3), 471 75. 

Ade, A., Cerrada, F., Contel, M., Laguna, M., Merino, P. and Tejero, T. (2004) Organometallic gold(III) and gold(I) complexes as catalysts for the 1,3-dipolar cycloaddition to nitrones synthesis of novel gold-nitrone derivatives. Journal of Organometallic Chemistry, 689(10), 1788-1795. 

Not included in the present review is the fascinating new chemistry which results from reaction between diazo compounds and low-valent transition-metal complexes bearing easily displaceable two-electron ligands as well as with metal-metal multiple bonds and metal hydrides whereby a variety of novel organometallic molecules could be obtained. This field has been covered, in accord with its rapid development, by successive reviews of Hermann 19 22) and Atbini23). 

J. R Candy, B. Didillon, E. L. Smith, T. M. Shay, and J. M. Basset, Surface organometallic chemistry on metals A novel and effective route to custom-designed bimetallic catalysts, J. Mol. Catal. 86, 179-204 (1994). 

Steps (i) through (v) are crucial prerequisites from coordination or organometallic chemistry for the development of novel radiopharmaceuticals. There are a number of excellent reviews on the coordination chemistry of technetium which have appeared over the past 30 to 50 years. Some... 

Considering that the literature on the development of experimental methods and important fields of application of X/Y correlations in inorganic, organoelement and organometallic chemistry up to 1997 has been covered in earlier reviews,11 we will focus here on recent improvements of experimental techniques and novel applications for compound characterisation. Despite the recently increasing interest in the application of X/Y correlation spectroscopy in solids,12,13 this review will cover only solution NMR techniques. Likewise, a survey of specialised triple-resonance NMR experiments devoted to the characterisation of bio-molecules, and their application, is considered beyond the scope of this article. 

The development of metal atom vapor technology over the last 15 years has made available to the chemist a new and useful synthetic technique. A number of novel transition metal compounds have been isolated by the method, particularly in the field of organometallic chemistry. However, the use of vaporized metal atoms for the synthesis of metal alkoxides and phenoxides by condensation into the neat alcohol has been only briefly mentioned in the literature.27... 

The industrial processes and related reactions described above, combined with the progress of organometallic chemistry, have stimulated further remarkable development in applying transition metal complexes to organic synthesis. Various novel synthetic methods, which are impossible by conventional means, have been discovered, bringing revolution in organic synthesis. 

We were first drawn into studies on alkylidynetricobalt nonacarbonyl complexes because in these one is dealing with a carbon atom in a most unusual environment. We felt that this novel class of complexes would show some rather interesting organic and organometallic chemistry and we... 

Dr. Bill Coleman, for several chemical steps in Syntex s synthesis of the oral contraceptive chlormadinone. With Haldor Christensen, sodium dispersion chemistry led to a superior process for the manufacture of the Eh Lilly herbicide, diphenamid. We devised novel patented chemistry, with the inspiration of Dr. Martin Hultquist, for the manufacture of DDQ. The list could go on and on, but the essence is that in Arapahoe we became chemical process development chemists. We learned that there were no such chemists as steroid chemists, organometallic chemists, heterocyclic chemists, and so on. There are only process development chemists, capable of synthesizing anything. Being scientists in a small company we also learned to accommodate other disciplines and business requirements in creating our chemical processes. 

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