Benzoato and thiobenzoato ligands in the synthesis of dinuclear palladium(iii) and -(ii) compounds: stability and catalytic applications

Abstract

New palladium(III) compounds of formula Pd2[(C6H4)- PPh2]2[OXC(C6H5)]2Cl2 [3a (X = O);3b (X = S)] were obtained by the oxidation of the analogous palladium(II) ones with PhICl2 and were characterized by 31P,1H, and 13C NMR spectroscopy at 223 K. Compound 3a was also structurally characterized by single-crystal X-ray diffraction methods, which revealed a Pd–Pd distance of 2.5212(10) Å. DFT calculations were conducted to study the stability of all of these new palladium(III) and -(II) compounds with focus on the influence of the O↔S substitution of the donor atom in the ligand. The palladium (II) compounds Pd2[(C6H4)PPh2]2- [OXC(C6H5)]2 [2a (X = O),2b (X = S)] were also tested as pre-catalyst in two reactions: (1) the acetoxylation of 2-phenylpyridine and (2) the room-temperature 2-phenylation of indoles. Compound 2b is a better precatalyst than 2a in the first reaction (4 h; isolated yield, 67.5 vs. 50.4%). In the second catalytic reaction, isolated yields of 97 (10 h, substrate: 1-methylindole) and 99% (24 h, substrate: indole) were obtained with 2a as the precatalyst, whereas 2b gave low or noconversion