Mononuclear Nitrogen/Sulfur-Ligated Zinc Methoxide and Hydroxide Complexes:  Investigating Ligand Effects on the Hydrolytic Stability of Zinc Alkoxide Species

Abstract

The synthesis and properties of mononuclear zinc methoxide ([(ebnpa)Zn-OCH3]ClO4) (1) and hydroxide ([(ebnpa)Zn-OH]ClO4) (2) complexes of a new mixed nitrogen/sulfur ligand (ebnpa = N-2-(ethylthio)ethyl-N,N-bis(6-neopentylamino-2-pyridylmethyl)amine) are reported. The structures of 1 and 2 were determined by X-ray diffraction. Each possesses a single zinc-coordinated anion (methoxide or hydroxide) and exhibits an overall trigonal bipyramidal geometry. Structural and spectroscopic studies indicate the presence of two hydrogen-bonding interactions involving the oxygen atom of the zinc-bound anion in each complex. Treatment of [(ebnpa)Zn-OH]ClO4 with CH3OH results in the formation of an equilibrium mixture of 1 and 2. 1H NMR spectroscopic methods were used to examine the equilibrium as a function of temperature, yielding KMe (304 K) = 0.30(8), DeltaHMe = -0.9(1) kcal/mol, and DeltaSMe = -5(1) eu. The negative enthalpy indicates that spontaneous zinc alkoxide formation from a hydroxide precursor occurs in this system at low temperature. Using the experimentally determined DeltaHMe value, we found the homolytic Zn-O bond dissociation energy (BDE) in the Zn-OCH3 unit to be approximately -14 kcal/mol relative to the Zn-O BDE in the Zn-OH unit.

Plasticity in the copper–thioether bond: Manifestation in blue Cu proteins and in synthetic analogs

“…An early example of 5-coordinate Zn involves the work of Teixidor et al [50] with long Zn-S contacts of 2.63-2.74 Å, whereas Garner et al [51] later reported a similar case, now with just one Zn-S bond (2.49 Å). With pyrazoles, Bouwman found distances of 2.67-2.68 Å [52], whereas Berreau reported much shorter distances of 2.29-2.43 Å [53].…”

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

“…Traditional syntheses of (L) n M/OH complexes involve self-assembly [25][26][27][28] or substitution [29,30] reactions with excess OH À /H 2 O in protic solvents. Here we describe a new strategy involving aprotic conditions (THF) and a nearly stoichiometric amount of water to give the hydroxide-containing complexes [(Py 2 S) 4 Fe 5 (m-OH) 2 ](BF 4 ) 4 (3) and [(Py 2 S) 2 Fe 2 (m-OH)]BF 4 (4).…”

Bioinorganic Chemistry of Group 12 Complexes Supported by Tetradentate Tripodal Ligands Having Internal Hydrogen‐Bond Donors

“…[19] To examine the influence of hydrogen bonding on the formation and reactivity of nitrogen/sulfurligated zinc-aryloxide and -alkoxide complexes, two new tetradentate tripodal ligand systems containing one or more internal hydrogen-bond donors were employed ( Figure 8). [46,55] Using the bmnpa and benpa ligands, a series of mononuclear N 2 S 2 -ligated zinc-aryloxide complexes were prepared and characterized. [46] In each complex, a hydrogen-bonding interaction is present between the zinc-bound aryloxide oxygen atom and the secondary amine moiety of the supporting chelate ligand.…”

“…1 Particularly interesting results were obtained using the tripodal N 3 S-donor ebnpa {[2-(ethylthio)ethyl]bis[(6-neopentylamino-2-pyridyl)methyl]amine} ligand (Figure 8). [55] The mononuclear zinc-methoxide and -hydroxide complexes, [ …”