Mononuclear nitrogen/sulfur-ligated zinc methoxide and hydroxide complexes: investigating ligand effects on the hydrolytic stability of zinc alkoxide species.
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.
Department of Chemistry and Biochemistry, Utah State University, Logan 84322-0300, USA.
Dewain K
DK
Garner
Sarah B
SB
Fitch
Lenore H
LH
McAlexander
Lisa M
LM
Bezold
Atta M
AM
Arif
Lisa M
LM
Berreau
D000426:Alcohol Dehydrogenase / Q000737:chemistry; D006860:Hydrogen Bonding; D006868:Hydrolysis; D006878:Hydroxides / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D000432:Methanol / Q000031:analogs & derivatives* / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry
D006878:Hydroxides; D008024:Ligands; D017967:Zinc Compounds; D013455:Sulfur; D000426:Alcohol Dehydrogenase; D015032:Zinc; D009584:Nitrogen; C052745:zinc hydroxide; D000432:Methanol