Cyclometallated compounds of Pd(II) with pyrazole derivatives. Unusual double palladation of diarylbis(N-pyrazolyl)methanes

Article abstract of DOI:10.1016/0022-328X(94)87180-9

Reaction between palladium(II) acetate and bis(arylpyrazolyl)methanes with two aryl groups 3-RC6H4, 2a-c or the 3-RC6H4 and one 5-RC6H4, 3a-c (R=H, 3'-OCH3, or 2'-Br) 3a-c in refluxing acetic acid, affords metallacycles of stoichiometry LPd2, with two different five- and six-membered palladacycles, one containing an aromatic carbon-metal bond and the other a pyrazole carbon-metal bond, respectively.Treatment of acetate-bridged palladacycles 5a-c and 6a-c with Tl(acac) yields monomeric products 7a-c and 8a-c of formula .The products have been characterized by elemental analysis (C, H, N) and NMR spectroscopy.The preferential formation of a six-membered metallacycle in the first step of the reaction is discussed.Keywords: Palladium; Cyclometallation; Bis(cyclometallation); 5-, 6-membered rings; Pyrazole