Synthesis and Oxygenation of a Nickel(II) and Zinc(II) Dithiolate: An Experimental and Theoretical Comparison

The diamino-dithiolato N2S2 ligand N,N‘-bis-2-methyl-mercaptopropyl-N,N‘-dimethylethylenediamine, H2(bmmp-dmed),
and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated.
Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon
addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields
an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and
decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography,
and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur
p character in the HOMO of each complex. However, 1 also shows significant metal d character that is π-antibonding
with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the
HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.