Lithium zincates

The reaction of diorganozincs bearing bulky trimethylsilyl-substituted methyl groups and methyl- or phenyllithium in the presence of the 1,3,5-trimethyl-1,3,5-triazacyclohexane (TAGH), Scheme 53, afforded the corresponding lithium zincates as poorly soluble ion pairs.124... 

If the nucleophile R1 is replaced with bis(trimethylsilyl)amide, Scheme 54, a much more soluble lithium zincate 69 is isolated as a contact ion pair. A further increase in the steric bulk of either the organic substituents of the diorganozinc or of the nucleophile gave equilibria from which no organozincates could be isolated. 

Mixtures of hexamethyldisilazane, /z-butyllithium, and dimethylzinc reacted, Scheme 55, with the formation of a lithium zincate 70. In the solid state, Figure 37, 70 consists of four-membered, -symmetric LiN2Zn rings, which form a polymeric structure through bridging methyl groups from zinc to lithium.126... 

In Scheme 1 the metathesis reactions of 5 with lithium amides, phosphanides and arsanides are summarized. The sterically demanding triisopropylsilyl group leads to an alkylzinc-substituted amine and to bis(alkylzinc) substituted phosphanes and arsanes. Smaller substituents at the central atom give solvent-separated lithium zincates with a central Zn2E2 moiety due to oligomerization, as is also common for alkylzinc phosphanides [12,13] and arsanides [14]. 

Formation of Zincate Complexes. Zincate compounds such as K(ZnCH2SiMe3)3 are formed in a transmetalation reaction of bis[(trimethylsilyl)methyl]zinc with elemental potassium, or by reaction with potassium salts. Lithium zincates such as Li[Zn(CH2SiMe3)2R] [R = Me, Ph, N(SiMe3)2] can be prepared by reacting the title compound with the corresponding organo-lithium compounds.Transmetalation with alkaline earth metals such as strontium, barium, and calcium affords zincates of the type illustrated in eq... 

Fig. 10 Equilibrium between lower-order and higher-order lithium zincate...

Fig. 18 Solvent dependence on basicity of lithium zincate reagent...

Fig. 23 Proposed alternative metalation pathways for homoleptic lithium zincates and cadmates...

Abstract Organozincates are the oldest class of organometallic ate compounds in the history of chemistry. Their special molecular structures lead to synergetic operations which contribute to unique chemical properties. Therefore, these compounds have attracted considerable attention from organometallic chemists nowadays and also have been widely employed as an efficient synthetic tool towards various functional molecules. As a representative example, hthium zincates present many advantages such as easy preparation, adjustable reactivity/selectivity as well as diversified applicability. This chapter provides an overview of the research advances on lithium zincate, including observation history, general characterization, preparative methods, synthetic utilities as well as further applications. 

Halogen-Zinc Exchange of Lithium Zincate and Subsequent Trapping Reactions ... 

Applications of Lithium Zincates for Developing New Cross-Coupling Reactions. 193... 

In 2010, Mongin and co-workers expanded this amino Li/Zn mixture model to a new combination alkyl/amino Li/Zn model, LiR/Zn(TMP)2 (1/1) [78]. NMR analysis and calculation indicated formation of the zincate LiZn(TMP)2R in these circumstances. Exceptionally, when (trimethylsilyl)methyllithium was used instead, the calculation showed that formation of a lithium zincate became unlikely and thus the reaction route may then be similar to that of the LiTMP/Zn(TMP)2 combination. Nevertheless, these zincates or base mixtures are also effective for deprotonation of arenes (Eq. 24). 

Wheatley AEH (2004) Recent developments in the synthetic and structural chemistry of lithium zincates. New J Chem 28 435 43. doi 10.1039/6314042c... 

Blair VL, Blakemore DC, Hay D et al (2011) Alkali-metal mediated zincation of N-heterocyclic substrates using the lithium zincate complex, (THF)Li(TMP)Zn( Bu)2 and applications in in situ cross coupling reactions. Tetrahedron Lett 52 4590-4594. doi 10. 1016/j.tetlet.2011.06.090... 

Five research groups with expertise in the field summarize recent fascinating developments, including l,4-dUithio-1,3-butadienes and their transmetallated organo-di-metallic compounds, mixed dimers of lithium amide/alkyllithium, gem-diorganometallic compounds, alkali-metal mixed-metal ate compounds, and lithium zincates. 

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