Organozirconium derivatives

Scheme 1.17. Two types of organic synthesis by organozirconium derivatives.

The kinetic product distribution can be further shifted in excess reagent to get organozirconium derivatives with high regioselectivity. Even subtle steric differences such as in 2-pentyne ensure high selectivity [Eq. (6.77), a]. As Eq. (6.77) demonstrates, hydrozirconation of alkynes is an exclusive syn process. 

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. 

General Preparation of Principal Organotitanium and Organozirconium Derivatives... 

Ethyl levulinate (1) is reported to afiord the lactone (2) when treated with methyltitanium triisopropox-ide (equation 3). In cases like this, in order to prevent lactonization, it may be expedient to use organozirconium derivatives that have a generally milder reactivity. 

J2.1 Chemical Properties and Comparison with Traditional Organometallic Reagents IS 2 2 General Preparation of Principal Organotitanium and Organozirconium Derivatives... 

The use of organozirconium compounds as carbanion equivalents is greatly facilitated by trans metallations to the more reactive aluminum [11,100], copper [104—106], nickel [96—98], and palladium [99] derivatives. Copper-catalyzed carbon—carbon bond-forming reactions of alkyl- and alkenylzirconocene compounds have been particularly well studied, and have found considerable application in organic synthesis [107,108]. 

Although there are many different types of Zr(IV) and Zr(II) compounds, roughly 75—80% of the currently known well-characterized organozirconium compounds are zircono-cene derivatives [2]. They are even more dominant in the application of Zr to organic synthesis (Generalization 3). For this reason, essentially all the Zr compounds discussed in this chapter are ZrCp2 derivatives. 

Review. This review covers preparation and recent synthetically useful reactions of organozirconium compounds (178 references). Many of the recent bondforming reactions involve zirconocene derivatives. 

The great majority of examples of organozirconium(m) and organohafnium(m) complexes are bent metallocene derivatives. Complexes are prepared through either electrochemical or chemical reduction of M(iv) precursors, the mild oxidation of M(ll) precursors, or ligand exchange at M(lll) centers. 

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