Exhaustive oxidation of a nickel dithiolate complex: some mechanistic insights en route to sulfate formation

Abstract

A study of the step-wise oxidation of a Ni(II) diaminodithiolate complex through the formation of sulfate, the ultimate sulfur oxygenate, is reported. Controlled oxygenations or peroxidations of a neutral, planar, tetracoordinate, low-spin Ni(II) complex of a N(2)S(2)-donor ligand, (N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-propanediaminato) nickel(ii) (1), led to a series of sulfur oxygenates that have been isolated and characterized by ESI-MS and single-crystal X-ray diffraction. A monosulfenate complex (2) was detected by ESI-MS as a product of oxidation with one equivalent of H(2)O(2). However, this complex proved too unstable to isolate. Reaction of the dithiolate (1) with two equivalents of H(2)O(2) or one O(2) molecule leads to the formation of a monosulfinate complex (3), which was isolated and fully characterized by crystallography. The oxidation product of the monosulfinate (3) produced with either O(2) or H(2)O(2) is an interesting dimeric complex containing both sulfonate and thiolate ligands (4), this complex was fully characterized by crystallography, details of which were reported earlier by us. A disulfonate complex (7) is produced by reaction of 1 in the presence of O(2) or by reaction with exactly six equivalents of H(2)O(2). This complex was isolated and also fully characterized by crystallography. Possible intermediates in the conversion of the monosulfinate complex (3) to the disulfonate complex (7) include complexes with mixed sulfonate/sulfenate (5) or sulfonate/sulfinate (6) ligands. Complex 5, a four-oxygen adduct of 1, was not detected, but the sulfonate/sulfinate complex (6) was isolated and characterized. The oxidation chemistry of 1 is very different from that reported for other planar cis-N(2)S(2) Ni(ii) complexes including N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-ethylenediaminato) nickel(II), (8), and N,N'-bis(mercaptoethyl)-1,5-diazacyclooctane nickel(II). To address the structural aspects of the reactivity differences, the crystal structure of 8 was also determined. A comparison of the structures of planar Ni(II) complexes containing cis-dithiolate ligands, strongly suggests that the differences in reactivity are determined in part by the degree of flexibility that is allowed by the NN' chelate ring.

Quenching of tryptophan fluorescence in various proteins by a series of small nickel complexes

“…Complexes 1 and 9 have been previously synthesized, and crystal structures reported. 95,97,98 All characterization data, including ESI-MS spectra and elemental microanalysis are consistent with the formulations and structures given for each complex (see SI #1). Selected bond lengths and angles for 1, 2, 9, and 10 are given in Table 1.…”

“…Complex 1 97 and 9 98 have been previously studied by X-ray crystallography. Complex 2 (Figure 2) and 10 (Figure 3) are novel.…”

The Bismuth Hydrogen Sulfate [Bi2(SO4)2(dmso)8](HSO4)2

“…The formation of sulfate ions was verified by the observation of a colorless precipitate after addition of an aqueous BaCl 2 solution, and thus, we concluded that Bi 3+ induces the formation of sulfate from thiosalicylic acid. Note that the oxidation of ( N , N ′‐dimethyl‐ N , N ′‐bis(2‐mercaptoethyl)‐1,3‐propanediaminato) nickel(II) gave [Ni(dmf) 5 (H 2 O)]SO 4 45. It is reported that the stepwise oxidation of the cis ‐dithiolate by hydrogen peroxide or oxygen in DMF produces a number of sulfur oxygenate nickel complexes.…”

“…It is reported that the stepwise oxidation of the cis ‐dithiolate by hydrogen peroxide or oxygen in DMF produces a number of sulfur oxygenate nickel complexes. Starting from the cis ‐dithiolate, insertion of oxygen primarily leads to the sulfenate complex, subsequent oxidation gives the sulfinate followed by the sulfonate right up to the sulfate [Ni(dmf) 5 (H 2 O)]SO 4 45. In case of [Bi 2 (SO 4 ) 2 (dmso) 8 ](HSO 4 ) 2 ( 1 ) a similar formation process might be conceivable.…”

Nickel, palladium and platinum

“…The isolation of intermediate dimer 9 demonstrated that peroxidations and oxygenations do not necessarily proceed from the monosulfinate to the disulfinate en route to the disulfonate complexes, and that the ultimate decomposition of the ligand leads to the formation of sulfate. 12 The rate of metal-thiolate oxygenation by hydrogen peroxide was measured for the model complex 10 of nickel-containing superoxide dismutase (NiSOD). Under typical synthetic conditions the reaction proceeds within seconds yielding S-oxygenate products but under physiological conditions half-life times extended to several hours making the S-oxygenation of NiSOD kinetically limited under such conditions.…”