Redox behavior of nickel in sulfur ligation
The compound N,N[prime]-bis(mercaptoethyl)-1,5-diazacyclooctane-nickel(II), (bme-daco)Ni[sup II] or 1, and is derivatives are used to examine the redox chemistry of Ni in sulfur ligation. Investigations include a comparison of the electrochemical effects of various sulfur ligands on the Ni[sup III/II] and Ni[sup II/I] couples and mechanistic studies of the oxygenation of Ni(II)-bound thiolates. Cyclic voltammetry was used to obtain Ni[sup II/I] and Ni[sup II/III] redox potential data for structurally characterized NiN[sub 2]S[sub 2] complexes based on (bme-daco)Ni[sup II]. Crystallography has established that the nickel sites in the complexes are largely square planar with distortions towards tetrahedral from 1[degrees] to 18.3[degrees]. All complexes show reversible reduction waves in CH[sub 3]CN, assigned to the Ni[sup II/I] couple by EPR of chemically reduced solutions. Irreversible oxidations are observed for all complexes with thiolate donors. Changes in the donor character of the sulfur ligands have a consistent and additive effect on the redox potentials. Potential measurements in water demonstrate large hydrogen-bonding effects for complexes with thiolate or sulfinate donors. The metallated derivatives display variable stabilization of the Ni[sup I] state by electron delocalization. A comparison with octahedral N[sub 2]S[sub 2]O[sub 2] donor derivatives reveals axial ligation inhibits the Ni[sup I] state, causing irreversible reductions. Solutions of 1 react slowly with dioxygen, forming sulfur-oxygenated derivatives. The same products are formed by reaction of 1 with H[sub 2]O[sub 2]. The mechanistic pathway for the dioxygen reaction is highly dependent on solvent. In nonprotic solvents two sulfinate products are formed. Isotopic labelling experiments show both result from addition of molecular oxygen. Methanol inhibits the dioxygen reaction, whereas in water a monosulfenate product is formed, presumably by O-atom addition.
- Research Organization:
- Texas A and M Univ., College Station, TX (United States)
- OSTI ID:
- 6970525
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
NICKEL
REDOX REACTIONS
THIOLS
CHEMICAL REACTION KINETICS
DERIVATIZATION
ELECTROCHEMISTRY
LIGANDS
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
KINETICS
METALS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
REACTION KINETICS
TRANSITION ELEMENTS
400400* - Electrochemistry