The synthesis, characterization, and hemithioacetal isomerization reactivity of a mononuclear Ni(II) deprotonated amide complex, [(bppppa(-))Ni]CIO4 center dot CH3OH (1, bppppa(-) = monoanion of N,N-bis-[(6-phenyl-2-pyridyl) methyl]-N-[(6-pivaloylamido-2-pyridyl) methyl]amine), are reported. Complex 1 was characterized by X-ray crystallography, H-1 NMR, UV-vis, FTIR, and elemental analysis. Treatment of 1 with an equimolar amount of the hemithioacetal PhC(O)CH(OH)SCD3 in dry acetonitrile results in the production of the thioester PhCH(OH)C(O)SCD3 in similar to 60% yield. This reaction is conveniently monitored via H-2 NMR spectroscopy. A protonated analogue of 1, [(bppppa)Ni](ClO4)(2) (2), is unreactive with the hemithioacetal, thus indicating the requirement of the anionic chelate ligand in 1 for hemithioacetal isomerization reactivity. Complex 1 is unreactive with the thioester product, PhCH(OH)C(O)SCD3, which indicates that the pK(a) value for the PhCH(OH)C(O)SCD3 proton of the thioester must be significantly higher than the pK(a) value of the C-H proton of the hemithioacetal (PhC(O)CH(OH)SCD3). Complex 1 is the first well-characterized Ni(II) coordination complex to exhibit reactivity relevant to Ni(II)-containing E. coli glyoxalase I. Treatment of NiBr2 center dot 2H(2)O with PhC(O)CH(OH)SCD3 in the presence of 1-methylpyrrolidine also yields thioester product, albeit the reaction is slower and involves the formation of multiple -SCD3 labeled species, as detected by H-2 NMR spectroscopy. The results of this study provide the first insight into hemithioacetal isomerization promoted by a synthetic Ni(II) coordination complex versus a simple Ni(II) ion.