title: Mechanism of Lithium Diisopropylamide-Mediated Ortholithiation of 1,4-Bis(trifluoromethyl)benzene under Nonequilibrium Conditions: Condition-Dependent Rate Limitation and Lithium Chloride-Catalyzed Inhibition.
abstract: Lithiation of 1,4-bis(trifluoromethyl)benzene with lithium diisopropylamide in tetrahydrofuran at -78 °C occurs under conditions at which the rates of aggregate exchanges are comparable to the rates of metalation. Under such nonequilibrium conditions, a substantial number of barriers compete to be rate limiting, making the reaction sensitive to trace impurities (LiCl), reactant concentrations, and isotopic substitution. Rate studies using the perdeuterated arene reveal odd effects of LiCl, including catalyzed rate acceleration at lower temperature and catalyzed rate inhibition at higher temperatures. The catalytic effects are accompanied by corresponding changes in the rate law. A kinetic model is presented that captures the critical features of the LiCl catalysis, focusing on the influence of LiCl-catalyzed re-aggregation of the fleeting monomer that can reside above, at, or below the equilibrium population without catalyst.
authors.affiliation: Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States.
authors.forename: Jun
authors.initials: J
authors.lastname: Liang
authors.affiliation: Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States.
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Hoepker
authors.affiliation: Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States.
authors.forename: Russell F
authors.initials: RF
authors.lastname: Algera
authors.affiliation: Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States.
authors.forename: David B
authors.initials: DB
authors.lastname: Collum
mesh_terms: D002384:Catalysis; D005464:Fluorobenzenes / Q000737:chemistry*; D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D018021:Lithium Chloride / Q000737:chemistry*; D011437:Propylamines / Q000737:chemistry*
chemical_list: D005464:Fluorobenzenes; D011437:Propylamines; C044697:benzotrifluoride; D008094:Lithium; C007442:diisopropylamine; D018021:Lithium Chloride