Nickel(II) complexes of the monoanionic borato ligands [Ph2B(CH2SCH3)(2)] (abbreviated Ph(2)Bt), [Ph2B((CH2SBu)-Bu-t)(2)] (Ph(2)Bt(tBu)), [Ph2B(1-pyrazolyl)(CH2SCH3)], and [Ph2B(1-pyrazolyl)((CH2SBu)-Bu-t)] have been prepared and characterized. While [Ph(2)Bt] formed the square planar homoleptic complex, [Ph(2)Bt](2)Ni, the larger [S-2] ligand with tert-butyl substituents, [Ph(2)Bt(tBu)], yielded an unexpected organometallic derivative, [Ph(2)Bt(tBu)]Ni(eta(2)-CH2SBut), resulting from B-C bond rupture. The analogous thiametallacycle derived from the [S-3] ligand, [PhB((CH2SBU)-B-t)(3)] (PhTt(tBu)), has been structurally authenticated (Schebler, P. J.; Mandimutsira, B. S.; Riordan, C. G.; Liable-Sands, L.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 331). The [SN] borato ligands formed exclusively the cis stereoisomers upon reaction with Ni(II) sources, [Ph2B(1-pyrazolyl)(CH2SR)](2)Ni. Analysis of the Ni(II/I) reduction potentials by cyclic voltammetry revealed a similar to600 mV anodic shift upon replacement of two thioether donors ([Ph(2)Bt](2)Ni) with two pyrazolyl donors ([Ph2B(1-pyrazolyl)(CH2SCH3)](2)Ni) consistent with the all thioether environment stabilizing the lower oxidation state of nickel.