Sterically Hindered Carboxylate Ligands Support Water-Bridged Dimetallic Centers That Model Features of Metallohydrolase Active Sites

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 [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (1), [Co(2)(mu-OH(2))(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (2a-c), [Co(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (3), [Ni(2)(mu-O(2)CAr(Tol))(4)L(2)] (4), [Ni(2)(mu-HO...H)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (5), and [Zn(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (6), where Ar(Tol)CO(2)H = 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 be readily accommodated within the [M(2)(mu-O(2)CAr(Tol))(2)](2+) core, allowing a wide distribution of M...M distances from 2.5745(6) to 4.0169(9) A. Unprecedented bridging units [M(2)(mu-OH(2))(2)(mu-O(2)CR)(2)](n+) and [M(2)(mu-HO...H)(2)(mu-O(2)CR)(2)](n+) were identified in 2a-c and 5, respectively, in which strong hydrogen bonding accommodates shifts of protons from 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 water molecules by a Lewis acidic metal center and a metal-bound general base may facilitate the reactivity of metallohydrolases such as methionine aminopeptidase (MAP).

μ-Aqua-κ2O:O-di-μ-phenylacetato-κ4O:O′-bis[(1,10-phenanthroline-κ2N,N′)(phenylacetato-κO)cobalt(II)]

“…This dimer is arranged around a twofold axis which passes through the bridging water molecule. The Co1-O1W distance of 2.1248 (11) Å and Co1-O1W-Co1 i angle of 113.47 (9) [symmetry code: (i) Àx + 1, y, Àz + 3 2 ] are within the expected ranges for related structures (Turpeinen et al, 1987;Corkery & Hockless, 1997;Lee et al, 2002;Miao et al, 2004). Each Co II atom shows an approximate octahedral geometry, with three carboxylate O atoms from different phenylacetate ligands, two N atoms from 1,10-phenanthroline ligands and one water molecule.…”

Standard molar enthalpies of formation and of sublimation of the terphenyl isomers

“…Some of these terphenyl derivatives have quite relevant biological activities, behaving as immune suppressants, antioxidants, neuroprotectives, cytotoxic, anti-thrombosis and anticoagulants [1]. Terphenyls have been the object of extensive research over the years, enhancing their characteristics and applications such as, the ability to form polyphenylene conducting polymers [2][3][4][5], use in organic light emitting diodes (OLEDs), field-effect transistors (FETs) and nonlinear optical devices [6][7][8][9], usage as ultraviolet organic lasers [10], host organic material for dopants [11][12][13][14][15][16], in catalysis [17,18], enzyme simulation [19], metal-organic frameworks [20] and modelling glass forming systems [3,21,22]. These vast applications require the knowledge of the energetics involving these polyphenyl oligomers as well as its relation with their structures.…”

The first dinuclear cobalt complex bridged by acetylamidate ligands: di-μ-acetylamido-κ2O:N;κ2N:O-di-μ-hydroxido-κ4O:O-bis[bis(pyridine-κN)cobalt(III)] bis(perchlorate) acetonitrile disolvate

“…The CoÁ Á ÁCo distance in the dimer is 2.6847 (4) Å and is longer than the equivalent CoÁ Á ÁCo distance in three other complexes containing the [Co 2 (OH) 2 (O 2 CCR) 2 ] 4+ core obtained from a search of the Cambridge Structural Database (CSD, Version 5.33; Allen, 2002) (Denisova et al, 2003), (ii) 2.669 (2) Å in the analogous benzene solvate (Denisova et al, 2006) and (iii) 2.6802 5 Lee et al, 2002).…”

“…These types of compounds have been studied as model metal centers for different enzymes. Lee et al (2002) stabilized the dimeric core using sterically hindered carbocyclic acid derivatives to study the active site in metallohydrolases. Williams et al (1999) used 1,4,7-triazacyclononane to stabilize a related cobalt dimer in order to study the hydrolyses of phosphate esters in metallophosphatase enzymes.…”