Low valent organozinc compounds
Introduction
The predominant oxidation state for Zn and Mg compounds is +II. A few decades ago, theoretical studies as well as matrix isolation experiments already indicated the stability of complexes with the metal in the formal oxidation state +I. However, only recently Carmona et al. were able to report on the synthesis and structural characterization of the first stable molecular organozinc compound with a Zn-Zn bond.[1]
Scheme 1: Synthesis of dizincocene Cp*2Zn2.
The epoch-making synthesis of Cp*2Zn2 has been the starting point of intense research activity. Consequently, new Zn(I) complexes of the general type R2Zn2 with sterically demanding ligands have been synthesized by Wurtz analogous coupling reactions of the corresponding halide-substituted compounds RZnX (X = Cl, Br, I).[2]
Scheme 2: General synthetic pathway for low-valent Zn or Mg compounds through Wurtz analogous coupling reactions.
The experimental studies have always been accompanied by theoretical investigations on the nature of the Zn-Zn bond.[3] At almost the same time Jones et al. were able to report on the synthesis, structural characterization and initial studies on the reactivity of the first low-valent Mg(I) complexes.[4, 5] As opposed to this, there has not been much information on the reactivity of Zn(I) complexes for a long time.