Organometallic reagents overview

The main focus of this overview will be the reactivity of organometallic reagents with oxide supports, mainly silica, alumina, and silica alumina. Before discussing the reactivity, it is necessary to briefly describe these supports. An oxide support, E Oj, can be described as a network consisting of oxygen (O) and heteroelements (E) (Scheme 2), and the surface functionalities are, therefore, E-O-E bridges and hydroxyls groups (HO-E). All these solids are usually submitted to a thermal treated under vacuum, the temperature T and surface atoms are described as E, Qy (r) and E, respectively. 

It is an axiom of modern organometallic chemistry that the pursuit of late transition metal complexes is ultimately driven by the need to formulate ever more efficient catalysts and reagents for chemical synthesis. In this respect, the field of poly(pyrazolyl)borate chemistry is no different from any other, albeit that in the case of the group 10 triad the breadth of study is perhaps more limited than for other metals and/or ligands. This section provides an overview of prominent results in respect of both catalysis and the C—H activation processes that underpin them. 

In this volume of Topics in Organometallic Chemistry, some remarkable recent achievements of organozirconium derivatives are described giving a unique overview of the many possibilities of these organometallic compounds as reagents and catalysts, which is one of the main reasons for their enduring versatility as intermediates over the years. 

The use of organometallic reactions in the synthesis of steroids, whether with main group or transition metal reagents, is too large a topic for this chapter. In fact, there are few modern syntheses that do not take advantage of organometallic strategies, and Refs [74,75] may provide a useful overview. 

This article provides an overview of cataljrtic cyclopropanation. To have a more focused discussion, we concentrate on catalytic reactions that combine two fragments of two- and one-carbon units to give a final three-membered carbocycle. Decomposition of diazo compounds by different metal catalysts, which is the most common source of a one-carbon unit, is discussed first which is followed by the use of organometallic carbenoid reagents and other carbene sources. Asymmetric cyclopropanation and intramolecular propanation are then discussed in detail. Important syntheses other than combining two fragments of two- and one-carbon... 

Anionic initiation has been accomplished in a variety of solvents, both polar and nonpolar. Typically, initiation can proceed by electron transfer reactions from alkali or alkaline earth metals, polycyclic aromatic radical anions, or alkali and magnesium ketyls. The other possibility includes the nucleophilic addition of organometallic compounds to the monomers. Related monofunctional initiators comprise alkyl derivatives of alkali metals or organomagnesium compounds such as Grignard reagents. Difunctional species are alkali derivatives of a-methylstyrene tetramer or the dimer of 1,1-diphenylethylene. An overview of the initiation process in carbanionic polymerization is given in Ref. [159]. 

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