Organometallics organozincs

Knochel, P., Jones, P., Langer, F. Transition metal catalyzed reactions of zinc organometallics. Organozinc Reagents 1999,179-212. 

High ee values have also been obtained with organometallics," including organotitanium compounds (methyl, aryl, allylic) in which an optically active ligand is coordinated to the titanium," allylic boron compounds, and organozinc compounds. 

Addition of Organometallic Reagents other than Organozinc Reagents... 

A large number of all citations to organozinc compounds deal with the use of these compounds as precursors for solid-state materials, particularly for MOCVD applications. The latter area has become so interdisciplinary and grown to such an extent that the editors of this edition considered it prudent to devote an entire volume (Volume 12) to the use of organometallic compounds in materials chemistry. While the syntheses and structures of potential organozinc precursors for such applications will be treated in this chapter, the detailed aspects of the conversion of organozinc compounds to solid-state materials are the topic of Volume 12. 

In this edition, one of the most obvious changes is the separation of the organometallic chemistry of zinc from that of cadmium. This change was made necessary by the ever-increasing number of publications for both elements and the need to keep the amount of material manageable. Even with this focus on only one element the current chapter cannot be an all-inclusive coverage of organozinc chemistry. 

The report by Resa et al. on a hydrocarbon-soluble, molecular compound of monovalent zinc, namely decamethyl-dizincocene, therefore caused considerable excitement among inorganic and organometallic chemists alike.233 Organozinc compounds with direct zinc-transition metal bonds have also been reported recently, and this area of organozinc chemistry with direct metal-metal bonds will undoubtedly witness considerable growth in the near future. 

The report of the first zinc compound with a Zn-Zn core elicited a number of critical comments on the structure and bonding of decamethyldizincocene, and the interpretation of the results.236,237 None of the authors of these commentaries questioned the data or their interpretation. Parkin, however, has pointed out that the formal oxidation state of +1 for zinc in this compound is merely due to the convention that metals are assigned an oxidation state of 0 when they form bonds with like atoms.237 If the conventional definition of valence, namely the capacity of atoms to form bonds to other atoms is used, then the zinc atoms in decamethyldizincocene are not monovalent, but divalent. The synthesis of a paramagnetic organozinc compound in which zinc uses only one of its two 4s electrons will remain an interesting challenge to many synthetic organometallic chemists. 

One of the important new directions in the study of addition reactions of organozinc compounds to aldehydes is the use of ionic liquids. Usually, application of these compounds in reactions with common organometallic reagents has a serious problem ionic solvents are usually reactive toward them, particularly Grignard and organolithium derivatives. It has been recently reported that carbonyl compounds react with allylzinc bromide formed in situ from allyl bromide and zinc in the ionic liquid 3-butyl-l-methylimidazolium tetrafluoroborate, [bmim][BF4].285 Another important finding is that the more reactive ZnEt2 alkylates aldehydes in a number of ionic liquids at room temperature.286 The best yields (up to 96%) were obtained in A-butylpyridinium tetrafluoroborate, [bpy][BF4] (Scheme 107). 

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