Synthesis, structures and catalytic properties of bis(2-pyridylimino)-isoindolatopalladium complexes

Reaction of the bis(2-pyridylimino)isoindole derivatives (10-Me)-BPI (1a), (11-Me)-BPI (1b), (11-Br)-BPI (1c), (4-Me)-BPI (1d) and 4-Me-10-tBuBPI (1e) with [PdCl2(PhCN)(2)] and triethylamine in benzene gave the square-planar palladium(II) complexes [PdCl{(10-Me)-BPI}] (2a), [PdCl{(11-Me)-BPI}] (2b), [PdCl{(11-Br)-BPI}] (2c), [PdCl(4-MeBPI)] (2d) and [PdCl(4-Me-10-tBuBPI)] (2e), respectively. Extraction of the crude product 2b with aqueous sodium carbonate solution led to the formation of the dinuclear carbonato-bridged complex [{(11-Me-BPI)Pd}(2)(mu-CO3)] (3) which was characterized by an X-ray structure analysis. Reaction of 11-Br-BPI (1c) with a large excess (6 equiv.) of the acetylenes Me3SiCCH, Ph3SiCCH and PhCCH under Sonogashira conditions gave the alkynylated derivatives 11-(Me3SiCC)-BPI (4a), 11-(Ph3SiCC)-BPI (4b) and 11-(PhCC)-BPI (4c), which were metallated with bis(benzonitrile)dichloropalladium(II) to yield the Pd-II complexes [PdCl{11-(Me3SiCC)-BPI}] (5a), {PdCl{11-Ph3SiCC)-BPI}] (5b) and [PdCl{11-(PhCC)-BPI}] (5c), respectively. The activity of 2b in the catalytic hydrogenation of C= C double bonds was tested for the reaction with styrene, 1-octene and cyclohexene, The stability of the palladium complex, the reproducibility of the reaction kinetics, the different behaviour towards the three olefins chosen as substrates, as well as the possibility of isolating the non-decomposed catalyst after several catalytic runs, provides circumstantial evidence for molecular catalysis with the BPI-palladium complexes. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.