| Abstract
| - The synthesis and characterization of carboxylate-bridged dimetallic complexes are described. By using m-terphenyl-derived carboxylate ligands, a series of dicobalt(II), dicobalt(III), dinickel(II), and dizinc(II) complexes were synthesized.The compounds are [Co2(μ-O2CArTol)2(O2CArTol)2L2] (1), [Co2(μ-OH2)2(μ-O2CArTol)2(O2CArTol)2L2] (2a−c), [Co2(μ-OH)2(μ-O2CArTol)2(O2CArTol)2L2] (3), [Ni2(μ-O2CArTol)4L2] (4), [Ni2(μ-HO···H)2(μ-O2CArTol)2(O2CArTol)2L2] (5), and[Zn2(μ-O2CArTol)2(O2CArTol)2L2] (6), where ArTolCO2H = 2,6-di(p-tolyl)benzoic acid and L = pyridine, THF, or N,N-dibenzylethylenediamine. Structural analysis of these complexes revealed that additional bridging ligands can bereadily accommodated within the {M2(μ-O2CArTol)2}2+ core, allowing a wide distribution of M···M distances from2.5745(6) to 4.0169(9) Å. Unprecedented bridging units {M2(μ-OH2)2(μ-O2CR)2}n+ and {M2(μ-HO···H)2(μ-O2CR)2}n+were identified in 2a−c and 5, respectively, in which strong hydrogen bonding accommodates shifts of protonsfrom bridging water molecules toward the dangling oxygen atoms of terminal monodentate carboxylate groups.Such a proton shift along the O···H···O coordinate attenuates the donor ability of the anionic carboxylate ligand,which can translate into increased Lewis acidity at the metal centers. Such double activation of bridging watermolecules by a Lewis acidic metal center and a metal-bound general base may facilitate the reactivity ofmetallohydrolases such as methionine aminopeptidase (MAP).
- Dinuclear cobalt(II), cobalt(III), nickel(II), and zinc(II) complexes were synthesized by using a sterically hindered carboxylate ligand, ArTolCO2-. Unprecedented {M2(μ-OH2)2(μ-O2CR)2}n+ and {M2(μ-HO···H)2(μ-O2CR)2}n+ bridging units were identified, in which a strong hydrogen-bonding interaction promotes intramolecular proton shifts from bridging water ligands to dangling carboxylate groups. Activation of nucleophiles thus could be achieved by dual action of Lewis acidic metal center and metal-bound general base, a process which may be relevant to the action of metallohydrolases having carboxylate-bridged dimetallic centers.
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