Herstellung fester polyfunktioneller Alkinylzinkpivalate mit verbesserter Luft- und Feuchtigkeitsstabilität

C versus O Protonation in Zincate Anions: A Simple Gas-Phase Model for the Surprising Kinetic Stability of Organometallics

For better understanding the intrinsic reactivity of organozinc reagents, we have examined the protolysis of the isolated zincate ions Et₃ Zn^- , Et₂ Zn(OH)^- , and Et₂ Zn(OH)₂ Li^- by 2,2,2-trifluoroethanol in the gas phase. The protonation of the hydroxy groups and the release of water proceed much more efficiently than the protonation of the ethyl groups and the liberation of ethane. Quantum-chemical computations and statistical-rate theory calculations fully reproduce the experimental findings and attribute the lower reactivity of the more basic ethyl moiety to higher intrinsic barriers, which override the thermodynamic preference for its protonation. Thus, our minimalistic gas-phase model provides evidence for the intrinsically low reactivity of organozinc reagents toward proton donors and helps to explain their remarkable kinetic stability against moisture and even protic media.

Preparation of Polyfunctional Arylzinc Organometallics in Toluene by Halogen/Zinc Exchange Reactions

A wide range of polyfunctional diaryl- and diheteroarylzinc species were prepared in toluene within 10 min to 5 h through an I/Zn or Br/Zn exchange reaction using bimetallic reagents of the general formula R'₂ Zn⋅2 LiOR (R'=sBu, tBu, pTol). Highly sensitive functional groups, such as a triazine, a ketone, an aldehyde, or a nitro group, were tolerated in these exchange reactions, enabling the synthesis of a plethora of functionalized (hetero)arenes after quenching with various electrophiles. Insight into the constitution and reactivity of these bimetallic mixtures revealed the formation of highly active lithium diorganodialkoxyzincates of type [R'₂ Zn(OR)₂ Li₂ ].

Mechanochemical Activation of Zinc and Application to Negishi Cross-Coupling

A form independent activation of zinc, concomitant generation of organozinc species and engagement in a Negishi cross-coupling reaction via mechanochemical methods is reported. The reported method exhibits a broad substrate scope for both C(sp3 )-C(sp2 ) and C(sp2 )-C(sp2 ) couplings and is tolerant to many important functional groups. The method may offer broad reaching opportunities for the in situ generation organometallic compounds from base metals and their concomitant engagement in synthetic reactions via mechanochemical methods.