Cu(II)-promoted methanolysis of N,N-bis(2-picolyl)carbamates: rate-limiting metal ion delivery of coordinated alcoholate nucleophile followed by fast partitioning of a tetrahedral intermediate.

ABSTRACT

Five O-aryl/alkyl N,N-bis(2-picolyl)carbamates were prepared with the O-aryl/alkyl portions being p-nitrophenoxy, m-nitrophenoxy, trifluoroethoxy, methoxy, and isopropoxy (4a,b,c,d,e, respectively) and the kinetics and reaction products of their methanolysis reactions in the presence of Cu(O3SCF3)2 determined. The catalyzed reactions have maximal rates for each substrate at a 11 ratio of [4][Cu²âº] at (s)(s)pH 7.9, where the active forms are Cu(II)4(⁻OCH3). The reactions are fast, that for the complex of 4a having a t(1/2) of 30 s. The products of the reaction with 4a and 4b arise exclusively from C-OAr cleavage those with 4d and 4e arise exclusively from C-N cleavage. With 4c, products from both C-O and C-N cleavage are observed in a 2.171 ratio. The common mechanism involves rate-limiting delivery of a Cu(II)-coordinated methoxide to the C═O unit to form a tetrahedral intermediate followed by fast partitioning to products by two pathways with relative barriers dependent on the (s)(s)pK(a)(HOAr/HOR). The data allow one to predict an effective (s)(s)pK(a) of ∼15.6 for the (s)(s)pK(a)(NH) of Cu(II)bis(2-picolyl)amine.