Efficient catalysis of Suzuki-Miyaura C-C coupling reactions with palladium(II) complexes of partially hydrolyzed bisimine ligands: A process important in environment context

Potentially hexadentante [O-,N,E:E,N,O-] chalcogenated bisimine ligands L1-L3 have been synthesized by reaction of 1,1 '-(4,6-dihydroxy-1,3-phenylene)bisethanone with H2N (CH2)(2-) S- Ph, H2N (CH2)(2) Se Ph and H2N (CH2)(2) Te C6H4-4-OMe respectively. The L1-L3 react with Na2PdC14 resulting in their partial hydrolysis, which appears to be metal-promoted. Of the two [ -(CH3)C= N (CH2)(2) EAr] fragments of L1-L3, one is converted to- (CH3)C=O and H2N (CH2)(2)- E -Ar eliminated. The hydrolysis products 1-[C(CH3)=N- (CH2)(2) -SPH]-3-[C(CH3)=O]-4,64-[OH](2)C6H2 (L1'), 1 -[C(CH3)=N- (CH2)(2) -SePh]-3-[C(CH3 =O]-4,6-[OH](2)C6H2 (L2') and 1-[C(CH3)= N- (CH2)(2)- Te- C6H4- 4-OMe]-3 -[C(CH3)=O]-4,6-[OH](2) C-6 H-2 (L3') have formed complexes [PdCI(L'-H)] (1,3 and 5). The other product of hydrolysis H2N (CH2)(2) -E- Ar (L) reacted with Na2PdCl4 yielding the complexes [PdLCl-2] (2, 4 and 6). All the complexes (1-6) were found thermally and air stable. Complexes 1, 3 and 5 have been investigated as catalysts for Suzuki-Miyaura C C coupling reactions. The catalytic activities of 1 and 3 which are palladium complexes of S- and Se-containing Schiff base derivatives respectively, were found good for the Suzuki-Miyaura cross-coupling of aryl bromides with phenylboronic acid under mild reaction conditions. The Pd(II) complex (3) of selenated ligand was found active to catalyze the coupling of 2-chlorobenzaldehyde and 3-chlorotoluene. The activity of Te analog was found to be the lowest one as it failed in catalyzing the coupling of electronically deactivated aryl bromides. (C) 2013 ElseVier B.V. All rights reserved.