Palladacycles of unsymmetrical (N,C⁻,E) (E = S/Se) pincers based on indole: their synthesis, structure and application in the catalysis of Heck coupling and allylation of aldehydes.

Unsymmetrical (N,C,E)-type pincer ligand precursors [ and : E = S/Se] with an indole core were synthesized for the first time by the condensation of 1-(2-phenylsulfanyl/selenylethyl)-1H-indole-3-carbaldehyde with benzyl amine. The synthetic protocols are easy and give good yields (>85%). and on reaction with sodium tetrachloropalladate(ii) in the presence of CH3COONa result in complexes [Pd(/-H)Cl] (/), where they bind in a tridentate (N,C(-),E) mode. and , their aldehyde precursors and Pd(ii)-complexes, and , have been characterized by (1)H, (13)C{(1)H} and (77)Se{(1)H} NMR and HR-MS. Palladium(ii) complexes and and precursor aldehydes of and were verified using single crystal X-ray diffraction. The catalytic activities of complexes and were investigated for Heck coupling and allylation of aldehydes. The two reactions require 0.1-0.3 and 1 mol% loading of complexes as catalysts, respectively.