Bulky 2,6-Dibenzhydryl-4-methylaniline Derived Schiff Base Complexes of Pd(II) as Efficient Catalysts for Suzuki Coupling: Effect of Coordinated Anion on the Catalytic Activity

Reaction of bulky 2,6-dibenzhydryl-4-methylaniline with 2-pyridinecaboxyaldehyde yielded [N,N] donor Schiff base, N-(2,6-dibenzhydryl-4-methylphenyl)-1-(pyridin-2-yl)methanimine (L¹). Reaction of L¹ with PdCl₂ in toluene under reflux conditions afforded mononuclear complex, L¹PdCl₂ (1). Complex 1 underwent salt metathesis with AgNO₃ or NaN₃ under ambient conditions to afford complexes, L¹PdX₂ (X=NO₃ (2), N₃ (3)). The new complexes were characterized by spectroscopic (IR, ESI-mass, NMR, UV-Vis), microanalytical (CHN) and thermal (TGA) techniques, in addition to a single crystal X-ray diffraction study for each of these compounds. Complexes 1-3 were employed in Suzuki coupling to evaluate their catalytic activity as well as the influence of coordinated anion on the course of catalysis. All the three complexes were found to be efficient catalysts in the coupling reactions involving aryl bromides with phenyl boronic acid while complex 3 was found to show the best activity. This is attributed to the thermal instability of azides and thus ease of decomposition of the terminal azido moiety under catalytic reaction conditions, facilitating the formation of L−Pd(0) species.