Organozinc compounds have been known for more than 150 years. With the exception of zinc enolates (Reformatsky reagents) and iodomethylzinc derivatives (Simmons‐Smith, Furukawa, and Sawada reagents), their synthetic potential has only been recently recognized. This is certainly due to their low reactivity and to the absence of general methods of preparation. Although the carbon‐zinc bond in diethylzinc has a dissociation energy of 34.5 kcal/mol, it has, because of the similar electronegativities of zinc and carbon, a highly covalent character (ca. 85 %), which is comparable to a carbon‐tin bond. The carbon‐zinc bond is therefore inert to moderately polar electrophiles such as aldehydes, ketones, esters, or nitriles. On the other hand, the presence of empty low‐lying p orbitals at the zinc center allows transmetallations with a number of transition metal complexes. This is favored for both kinetic and thermo‐dynamic reasons. The availability of d orbitals at the metal center in these compounds allows for new reaction pathways with electrophilic reagents that were not available for the corresponding zinc reagents. This reactivity has been exploited for the formation of new carbon‐carbon bonds and efficient cross‐coupling reactions between organozinc derivatives and unsaturated organic halides, as Negishi has demonstrated using catalytic amounts of palladium(0) salts. Similar catalytic processes have been reported with copper(I) and titanium(IV) complexes, which can mediate numerous reactions of organozinc reagents with organic electrophiles. The scope and synthetic applications of zinc organometallics were greatly extended when it was found that these species can accommodate a wide range of functional groups. They are ideally suited for the construction of polyfunctional organic molecules without the use of multiple protection and deprotection steps. Although some functionalized organozinc compounds bearing ester groups such had been reported, it was only recently that systematic studies have shown the synthetic potential of these reagents. This chapter describes methods for the preparation of functionalized organozinc halides, diorganozincs, and organozincates and their reactions with electrophilic reagents in the presence of transition metal catalysts, as well as synthetic applications demonstrating their synthetic utility for natural product synthesis. Only the preparation and reactivity of zinc organometallics bearing relatively reactive functional groups are covered. Thus, the chemistry of organozinc compounds bearing an ether, acetal, ketal, trialkylsilyl, or polyfluoroalkyl group is, in general, not covered.

The stoichiometric reaction of B(C6F5)3 and NEt2Ph I, at room temperature, in an aromatic solvent, has been investigated by 1D and 2D NMR spectroscopy (1H, 11B,13C, 15N and 19F). No Et2PhN·B(C6F5)3 adduct was observed. An equilibrium between free B(C6F5)3, NEt2Ph, [HB(C6F5)3]−(HNEt2Ph)+ and two zwitterionic stereoisomers (E)‐ and (Z)‐[EtPhN+=CH‐CH2‐B−(C6F5)3] (30%) in an E/Z ratio of 3:2 was observed. Whatever the protic reagent Z‐OH [Z = H, SiPh3, (c‐C5H9)7O12Si8, or silanol group of silica], all the equilibria involved in solutions of I are quantitatively displaced towards the ionic form [Z‐O‐B(C6F5)3]−(HNEt2Ph)+. In the case of dimethylaniline, besides free B(C6F5)3 and Me2NPh, the 1:1 adduct (C6F5)3B·NMe2Ph and an iminium salt [PhCH3N=CH2]+[HB(C6F5)3]− have been identified. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.