CYCLOMETALATED COMPOUNDS OF PD(II) WITH PYRAZOLE DERIVATIVES - UNUSUAL DOUBLE PALLADATION OF DIARYLBIS(N-PYRAZOLYL)METHANES

Reaction between palladium(II) acetate and bis(arylpyrazolyl)methanes with two aryl groups 3-RC(6)H(4), 2a-c or the 3-RC(6)H(4) and one 5-RC (6)H(4), 3a-c (R = H, 3'-OCH3, or 2'-Br) 3a-c in refluxing acetic acid , affords metallacycles of stoichiometry LPd(2), with two different fi ve- and six-membered palladacycles, one containing an aromatic carbon- metal bond and the other a pyrazole carbon-metal bond, repectively. Tr eatment of acetate-bridged palladacycles 5a-c and 6a-c with Tl(acac) y ields monomeric products 7a-c and 8a-c of formula [LPd(2)(acac)(2)]. T he products have been characterized by elemental analysis (C, H, N) an d NMR spectroscopy. The preferential formation of a six-membered metal lacycle in the first step of the reaction is discussed.