title: Electrophilic alkylation of pseudotetrahedral nickel(II) arylthiolate complexes.
abstract: A kinetic study is reported for reactions of pseudotetrahedral nickel(II) arylthiolate complexes [(Tp(R,Me))Ni-SAr] (Tp(R,Me) = hydrotris{3-R-5-methyl-1-pyrazolyl}borate, R = Me, Ph, and Ar = C6H5, C6H4-4-Cl, C6H4-4-Me, C6H4-4-OMe, 2,4,6-Me3C6H2, 2,4,6-(i)Pr3C6H2) with organic electrophiles R'X (i.e., MeI, EtI, BzBr) in low-polarity organic solvents (toluene, THF, chloroform, dichloromethane, or 1,2-dichloroethane), yielding a pseudotetrahedral halide complex [(Tp(R,Me))Ni-X] (X = Cl, Br, I) and the corresponding organosulfide R'SAr. Competitive reactions with halogenated solvents and adventitious air were also examined. Akin to reactions of analogous and biomimetic zinc complexes, a pertinent mechanistic question is the nature of the reactive nucleophile, either an intact thiolate complex or a free arylthiolate resulting from a dissociative pre-equilibrium. The observed kinetics conformed to a second-order rate law, first order with respect to the complex and electrophile, and no intermediate complexes were observed. In the absence of a mechanistically diagnostic rate law, a variety of mechanistic probes were examined, including kinetic effects of varying the metal, solvent, electrophile, and temperature, as well as the 3-pyrazolyl and arylthiolate substituents. Compared to zinc analogues, the effect of Ni-SAr covalency is also of interest herein. The results are broadly interpreted with respect to the disparate mechanistic pathways.
authors.affiliation: Department of Chemistry and Biochemistry, Ohio University , Athens, Ohio 45701, United States.
authors.forename: Tapash
authors.initials: T
authors.lastname: Deb
authors.forename: Michael P
authors.initials: MP
authors.lastname: Jensen
mesh_terms: D000478:Alkylation; D001881:Borates / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D007700:Kinetics; D009532:Nickel / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*; D012997:Solvents; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001881:Borates; D056831:Coordination Complexes; D011720:Pyrazoles; D012997:Solvents; D013438:Sulfhydryl Compounds; D009532:Nickel