Recently, the synthesis and structural characterization of decamethyldizincocene [Cp* ZnZnCp*](1; Cp*= η5-C5Me5, ZnÀZn 2.305 (3)) was reported by Carmona and co-workers.[1] It was the first stable compound that contained a ZnÀZn bond.[2] This landmark development was confirmed by calculations which showed that the ZnÀZn bond is formed mainly by the overlap of the Zn 4s orbitals while the Zn 4p orbitals interact with the η5-C5Me5 ligand.[1b, 3] A further example of a compound with a ZnÀZn bond,[{HC-(CMeNAr) 2} ZnZn {HC (CMeNAr) 2}](Ar= 2, 6-iPr2C6H3)(2), was reported by Robinson and co-workers,[4] and this species has a ZnÀZn bond length of 2.3586 (7). The zinc atoms are three-coordinate, and the metal–metal bond has 95% s character. The ZnÀZn bond in 2 is about 0.05 longer than that in 1 despite its lower metal coordination number. Clearly, the type of ligand exerts a large influence on the ZnÀZn bond length. It is therefore desirable to have zinc–zinc-bonded species in which the Zn atoms are bound to only one ligand atom to provide the simplest possible bonding arrangement and also to show that ZnÀZn bonds can in fact be stabilized by monodentate ligands. Furthermore, the synthesis of the singly or doubly bridged hydride derivatives of such a species would provide further information on the nature of the ZnÀZn bonding. We now describe the synthesis and characterization of the zinc–zinc-bonded species Ar’ZnZnAr’(4)(Ar’= C6H3-2, 6-(C6H3-2, 6-iPr2) 2), the hydride-bridged dimer Ar’Zn (μ-H) 2ZnAr’(5), which has a Zn··· Zn separation very similar to that in 4, and the unique compound Ar’Zn (μ-H)(μ-Na) ZnAr’(6), in which the Zn atoms are connected by a new type of ZnÀZn interaction. Dinuclear 4 was synthesized by the reduction of Ar’ZnI (3) with Na. The hydride, Ar’Zn (μ-H) 2ZnAr’(5), was prepared by the treatment of 3 with NaH. Rather than forming zinc–zinc-bonded compound 4 (as indicated in the indirect route for 1 whereby KH was used to reduce the [Zn (Cp*) 2] species in situ [1b] or whereby [Cp* ZnZnCp*] was obtained by the unforeseen ligand exchange between [ZnCp* 2] and ZnEt2 [1a](Scheme 1)), further reduction of 5 by NaH provided the unprecedented sodium hydride-bridged species Ar’Zn (μ-H)(μ-Na) ZnAr’(6, Scheme 2).

The crystal structure of 4 (Figure 1)[5] confirms the presence of a ZnÀZn bond. The observed ZnÀZn bond length in 4 (2.3591 (9)) is about 0.05 larger than that in 1 (2.305 (3)) and is essentially the same as that in 2 (2.3586 (7)). The two Ar’ligands are arranged in a nearly orthogonal orientation to each other, which provides effective steric protection of the ZnÀZn moiety. An almost linear arrangement is observed for the {C (ipso)-Zn-Zn-C (ipso)} interior, which is in contrast to the other known metal–metalbonded dimers ArMMAr,(M= Cr,[6a] Ga,[6b] Ge,[6c] As,[6d] or Se [6e]) which for numerous reasons display strongly trans-bent geometries.