Metallocenes metalation, review

In this chapter we will review the synthesis, structural aspects, and basic chemical properties of formally divalent and trivalent titanium and zirconium metallocene complexes. We have restricted our coverage to the low-valent bis(rj-cyclopentadienyl) and related metallocenes metal halide complexes and organometallic mixed metal systems will not be discussed here. We have not attempted to present an exhaustive coverage of the field. Rather, our aim has been to describe critically and to evaluate the often confusing chemistry that has been reported for the reactive low-valent titanium and zirconium metallocenes. More general reviews (7) and a book (2) on the organometallic chemistry of titanium, zirconium, and hafnium have been published. 

A60. J. P. Candlin, K. A. Taylor, and D. T. Thompson, "Reactions of Transition-Metal Complexes. Elsevier, Amsterdam, 1968. A review of types of reactions of metal complexes (e.g., substitution, combination, redox) reactions with various reagents (e.g., hydrocarbons, halides, carbon monoxide, and isonitrile) and preparation of new stabilised organic systems (e.g., metallocenes, carbenes). Intended for research workers, consequently written at a fairly high level, with emphasis on organometallics. A61. H. J. Keller, NMR-Untersuchungen an Komplexverbindungen. Springer, Berlin, 1970. Expansion of review article 37.1. 

Section 3 will deal with catalytic systems whose stereospecificity is mainly controlled by the chirality of the environment of the transition metal, independently of the possible chirality of the growing chain (chiral site stereocontrol). In particular, in Section 3.1 the chirality and stereospecificity of homogeneous catalytic systems based on metallocenes of different symmetries and in different experimental conditions will be reviewed. In Section 3.2 the chirality of model catalytic sites, which have been supposed for isospecific first-generation TiCl3-based and high-yield MgC -supported catalysts, is described. In Section 3.3 we will present a comparison between model catalytic sites proposed for heterogeneous and homogeneous stereospecific site-controlled catalysts. 

For a review of enantioselec-tive catalysis by metallocenes of group IV transition metals, see ... 

For industrial applications for the polymerization of norbomenes into COCs, zirconium based metallocene catalysts are most popular. However, other metal based catalysts have been described too. Catalysts for olefin polymerization have been reviewed in the literature (10,23,24). 

This review summarizes some earlier qualitative work as well as recent quantitative studies of redistribution equilibria and describes the principles underlying the mathematical treatment of such equilibria as well as the general implications of these equilibria with respect to general chemistry. In line with the general objective of the Advances in Organometallic Chemistry series, this article is limited to carbon-metal-bonded systems, metal hydrides, metal carbonyl compounds, metallocenes, and similar complexes. Excluded therefore are halogen-, sulfur-, nitrogen, and phosphorus-based systems.Various aspects of redistribution reactions were reviewed previously (42, 74, 87, 88,150,186, 285, 286, 288). 

Metallocenes and related compounds for which mass spectral data have been reported are given in Tables I-XII, but in many cases only the molecular ion is reported. Metal carbonyls, nitrosyls and their derivatives, and fluorocarbon complexes are not discussed in this review, but Table XIX summarizes the compounds for which mass spectral data have been reported since Bruce s review (27). 

The exclusion of metal elements from the catalyst structure is not always strictly considered. Catalysts where the metal arguably is not the reaction center ( spectator ) such as in metallocenes are discussed, under certain conditions. For an excellent review of this chemistry see ... 

The chemical reactivity of metallocenes varies widely with the metal and the substituents on the rings a general discussion of such properties is outside the scope of this review. The particular case of air (oxygen) sensitivity, however, can be analyzed with reference to the metal electron... 

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