Correlation of electrochemistry, nucleophilicity and density functional calculations of the cis-dithiolate (bme*-daco)Ni

Upon the sequential stoichiometric addition of methyl iodide to acetonitrile solutions of the square planar nickel (II) complex of N,N'-bis(2-mercapto-2-methylpropyl)-1,5-diazacyclooctane, (bme*-daco)Ni, mono- and bis-methylated thioether compounds were isolated. Both are crystallographically and electrochemically characterized and compared to analogues of N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctane, (bme-daco)Ni. Density functional theory calculations carried out at the B3LYP level using the LANL2DZ basis set with modified exponents compared HOMO/LUMO energies for the dithiolates, the mono-S-methylated and bis-S-methylated complexes. The presence of the methyl groups on the alpha-carbon next to the sulfur creates steric encumbrance about the thiolate sulfurs, but there was found no significant differences in the frontier molecular orbitals. The more positive shifts of the Ni(II/I) reduction potentials are reflected by changes in LUMO energies upon S-methylation. (C) 2000 Elsevier Science S.A. All rights reserved.