Multiple Functionalization of Bis(2‐pyridylimino)isoindole (BPI) Ligands: Their Modular Synthesis and Coordination to Palladium(II)

Abstract

Abstract Polyether dendritic wedges have been attached to bis(2‐pyridylimino)isoindole (BPI) ligands, and the corresponding Pd II complexes have been synthesized and studied as hydrogenation catalysts. The fixation of dendrons at the ligand framework was carried out at the stage of the phthalodinitrile precursor of the BPI ligands by nucleophilic substitution of 4‐nitrophthalodinitrile with the in situ generated alcoholates. Reaction of 1,3‐dibenzyloxy‐2‐propanol [G‐1] and the coupling of Fréchet's first and second generation arylether dendrons [(3,5)‐G‐1]‐OH, [ t ‐Bu‐(3,5)‐G‐1]‐OH and [(3,5)‐G‐2]‐OH with 4‐nitrophthalodinitrile gave the corresponding O‐coupled phthalodinitrile derivatives. The synthesis of the BPI ligands was achieved by reaction with two molar equivalents of 2‐amino‐5‐bromopyridine to give the protioligands (11‐Br)‐BPI‐[G‐1] ( 4 ) and (11‐Br)‐BPI‐[R‐(3,5)‐G‐1] (R = H: 5a , tBu: 5b ) whereas the reaction of compound 5a with Me 3 SiCCH, Ph 3 SiCCH and PhCCH, using Sonogashira's [Pd(PPh 3 ) 4 ]/CuI catalyst, gave the corresponding bis(alkynyl)‐derivatives. All the protioligands were cleanly metallated to give the corresponding palladium(II) complexes. In contrast to the unsubstituted complex, its dendrimer functionalized derivatives [(11‐Br)‐BPI‐[R‐(3,5)‐G‐1]‐PdCl] (R = H: 9a , t Bu : 9b ) and [(11‐Br)‐BPI‐[(3,5)‐G‐2]‐PdCl] ( 11 ) hydrogenated styrene and 1‐octene without decomposition (TOF = 5 h −1 at T = 295 K, p(H 2 ) = 1 bar, 2 mol% cat.) and among these, catalyst 11 , carrying the 2 nd generation dendron displayed sufficient stability to be isolated and reused several times.