Selective Oxidations of a Dithiolate Complex Produce a Mixed Sulfonate/Thiolate Complex

Oxygenation or peroxidation of a planar, tetracoordinate, low-spin
nickel(II) complex of a N2S2-donor ligand, (N,N‘-dimethyl-N,N‘-bis(2-mecaptoethyl)-1, 3-propanediaminato)nickel(II), proceeds via the
formation of a mixed sulfinate/thiolate complex and leads to the
production of a novel dimeric complex containing both sulfonate
and thiolate ligands. Thus, reaction proceeds via selective oxidation
of the sulfinate sulfur atom, leaving the thiolate reduced. The novel
sulfonate/thiolate complex has been isolated and characterized
by electospray ionization mass spectrometry and single-crystal
X-ray diffraction. Crystals form in the monoclinic space group P21/c
with cell dimensions a = 8.4647(12) Å, b = 12.592(3) Å, and c
= 12.531(2) Å, angles α = γ = 90° and β = 106.645(11)°, and
Z = 2. The structure was refined to R = 5.20% and Rw = 12.86%
[I > 2σ(I)]. The isolation of this mixed sulfonate/thiolate complex
from oxidation of a mixed sulfinate/thiolate complex provides
experimental evidence for the formation of a sulfonate ligand via
a Ni−O−O−SO2R intermediate, as suggested by recent density
functional theory calculations.