Synthesis and Characterization of the Homologous M−M Bonded Series Ar‘MMAr‘ (M = Zn, Cd, or Hg; Ar‘ = C6H3-2,6-(C6H3-2,6-Pri2)2) and Related Arylmetal Halides and Hydride Species

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Abstract
The synthesis and structural characterization of the first homologous, molecular M−M bonded series for the group 12 metals are reported. The compounds Ar‘MMAr‘ (M = Zn, Cd, or Hg; Ar‘ = C6H3-2,6-(C6H3-2,6-Pri2)2) were synthesized by reduction of the corresponding arylmetal halides by alkali metal/graphite (Zn or Hg) or sodium hydride (Cd). These compounds possess almost linear C−M−M−C core structures with two-coordinate metals. The observed M−M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) Å for the zinc, cadmium, and mercury species, respectively. The shorter Hg−Hg bond in comparison to that of Cd−Cd is consistent with DFT calculations which show that the strength of the Hg−Hg bond is greater. The arylmetal halides precursors (Ar‘MI)1 or 2, and the highly reactive hydrides (Ar‘MH)1 or 2, were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar‘HgI, is monomeric. The arylzinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) μ-H-bridged structures. The Ar‘HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar‘HgH by Ar‘H. It was also shown that the decomposition of Ar‘Cd(μ-H)2CdAr‘ at room temperature leads to the M−M bonded Ar‘CdCdAr‘, thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate.

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