Synthesis and reaction kinetics of Pd(1,5-cyclooctadiene)Cl2 with N,N′-methylene-bis(2-aminopyridyl): an efficient catalyst for Suzuki-cross-coupling reactions

Abstract

An inexpensive bidentate ligand N,N′-methylene-bis(2-aminopyridyl) (1) has been synthesized. Reaction of 1 with [Pd(COD)Cl2] affords a stable chelate complex, [{NC5H4N(H)(μ-CH2)(H)NC5H4N-κN,κN}PdCl2] (2). The kinetics of the pseudo-unimolecular reaction of N,N′-methylene-bis(2-aminopyridyl) with Pd(1,5-cyclooctadiene)Cl2 has been studied over the range 3.0 less-than-or-equals, slant 103 [1] less-than-or-equals, slant 7.0 mol dm−3, 30 °C less-than-or-equals, slant t less-than-or-equals, slant 40 °C. The rate constants and equilibrium constants were calculated. Entropy and enthalpy of the reaction are found to be −42 ± 1 J K−1 mol−1 and 75 ± 1 kJ mol−1, respectively, which clearly indicates that the substitution reaction follows associative mechanism. The complex 2 was tested for the Suzuki-cross-coupling reaction of a variety of aryl halides with aryl boronic acids in methanol at room temperature or at 60 °C, giving generally high yields for both activated and inactivated aryl bromides. The effect of solvents as well as the effect of base on the Suzuki-coupling reaction is also investigated.