Contribution of Intramolecular NH···O Hydrogen Bonds to Magnesium–Carboxylate Bonds

Abstract

A series of magnesium carboxylate complexes containing intramolecular NH···O hydrogen bonds were synthesized. Their molecular structures were determined by X-ray analysis. A direct NH···O hydrogen bond to the coordinated oxygen atom elongated the Mg-O bond, while a hydrogen bond to the carbonyl group shortened the Mg-O bond. Double NH···O hydrogen bonds significantly lowered the basicity of the carboxylate anion and prevented coordination to the Mg ion in a trans configuration; however, a cis-dicarboxylate complex was successfully obtained. Strong coordination of water to the Mg(2+) ion stabilizes the weak Mg-carboxylate bond at the trans position. In contrast, a weak Mg-carboxylate bond strengthens the Mg-O(water) bond, probably increasing the acidity. Based on the experimental results and theoretical calculations, a new switching mechanism is proposed. In the proposed mechanism, the acidity of the coordinated water on magnesium is controlled during catalytic hydrolysis in endonuclease.

Synthesis and structures of soluble magnesium and zinc carboxylates containing intramolecular NH⋯O hydrogen bonds in nonpolar solvents

“…The metal complexes described in this paper were synthesized by a similar procedure in the literature. 23 To a solution of L1H (56.6 mg, 0.084 mmol) in ethanol (30 mL) was added an aqueous solution of Mg(OAc) 2 •4H 2 O (136 mM, 0.32 mL, 0.044 mmol) at room temperature and the solution was dried in vacuo. The residue was dissolved in ethanol, and the solution was evaporated under reduced pressure.…”

“…The opposite effect was also seen, depending on the mode of the hydrogen bond, which led to the proposal of a new switching mechanism based on controlling the acidity of the coordinated water molecule by regulating the strength of the Mg-OH 2 bond. 23 However, the insolubility of the complexes prevented an investigation of the real solution structures and experimental evaluation of the hydrolytic activity.…”

“…In this article, we present the synthesis of readily soluble carboxylic acids with the Ar 3 CCONH groups, 2,6-(Ar 3 C-CONH) 2 C 6 H 3 COOH (L0H), 2-Ar 3 CCONH-6-n-BuCONHC 6 H 3 -COOH (L1H), and 2-Ar 3 CCONHC 6 H 4 COOH (L2H). The sterically hindered L0H was designed to prevent the second coordination of the ligand to give [Mg(L0)(H 2 O) 5 ] + , with water coordinated trans to the carboxylate ligand, which is analogous 23 However, this trial met with failure. The desired magnesium complexes with L1 or L2 were readily soluble in nonpolar solvents.…”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…Among his honors,h ew as awarded the Madinabeitia-LourenÅo Prize from the Spanish RoyalC hemical Society and the Prizes of the Portuguese Chemical and Electrochemical Societies. [29,43,82,83] These RAHB moieties are ubiquitous in variousf ields, includingo rganic [84][85][86] and inorganic synthesis, [87,88] crystal growth and design, [89][90][91][92] supramolecular chemistry, [93,94] medicinal chemistry, [95][96][97][98] and materials chemistry, [99,100] andh ave been used in the activation of covalent bonds, crystal engineering, dynamic combinatorial chemistry,m olecular recognition, E/Z isomeric resolution, racemization/epimerization of amino acids, solvatochromism, and liquid-crystalline materials, among other applications. [6] According to the electrostatic-covalent hydrogen bond model, the strongest H-bonds must be homonuclear( X ÀH···X) and symmetrical at both sides of the H-bond.O nly in this situation, the two wavefunctions corresponding to XÀH···X and X···HÀXr esonance forms are isoenergetic and can mix to agreater extent.…”

“…The most well‐established cases of RAHB (Scheme ) include intramolecular H‐bonds in β‐diketones ( I ), β‐enaminones ( II ), Schiff bases ( III ), β‐enaminoimines ( IV ), hydrazones ( V and VI ), formazans ( VII ), 1,3,5‐triazapentadienes ( VIII ), ortho ‐substituted aromatic compounds ( IX – XII ), oximes ( XIII – XVI ), mercaptans (or thiols) ( XVII – XIX ), thioketones ( XX – XXII ), selenones or tellurones ( XXIII and XXIV ), and 8‐ or 10‐membered RAHB system containing compounds ( XXV and XXVI ) . These RAHB moieties are ubiquitous in various fields, including organic and inorganic synthesis, crystal growth and design, supramolecular chemistry, medicinal chemistry, and materials chemistry, and have been used in the activation of covalent bonds, crystal engineering, dynamic combinatorial chemistry, molecular recognition, E / Z isomeric resolution, racemization/epimerization of amino acids, solvatochromism, and liquid‐crystalline materials, among other applications. The thermodynamic stability of the RAHB can also be recognized as a reason for its popularity …”