Jeffrey J. Ellison

Synthesis and structural characterization of magnesium and cobalt derivatives of the bulky aryl ligand −C6H3-2,6-Mes2

Abstract The synthesis and structural characterization of the new metal-terphenyl derivatives [BrMC6H3-2,6-Mes2(THF)]2 (M  Mg (1), Co (2); Mes  −C6H2-2,4,6-Me3) are described. The magnesium derivative 1 was synthesized by reaction of the previously known iodide IC6H3-2,6-Mes2 with activated magnesium. Subsequent treatment of 1 with CoCl2 affords 2 in moderate yield. Compounds 1 and 2 have very similar dimeric structures, in which two bromides bridge two metals. Each is also coordinated to a −C6H3-2,6-Mes2 group and a THF molecule. The metals are thus four-coordinated. The cobalt species 2 is a very unusual example of a stable Co(II) σ-bonded hydrocarbyl. The CoCo separation of ca. 3.5 A precludes the existence of significant metal-metal bonding. Crystal data at 130 K with Mo Kα ( λ = 0.71073 A ) radiation: 1, a = 9.432(2), b = 21.973(5), c = 12.558(2) A , β = 94.87(2)°, Z = 2 , monoclinic, space, grou P21/c, R = 0.058 for 3006(1 > 2 σ(I)) data, 2, a = 9.394(2), b = 22.033(7), c = 22.033(7), c = 12.390(3) A , β = 94.99(2)°, Z = 2 , monoclinic, space group P21/c, R = 0.077 for 2675(I > 2σ(I)) data.

Metal-Carbon Bonds in Nature

In contrast to most metabolic processes, but similar to some industrial catalysts, vitamin B12 contains a cobalt-active species and is sometimes referred to as “natures organometallic catalyst.” Kovacs et al. provide background and commentary to accompany the research report by Kumar et al. (p. 628) describing a second organometallic intermediate in biology—an active nickel species that serves as a precursor to acetic acid through its reaction with carbon monoxide and acetyl-CoA synthase.