SYNTHESES AND MECHANISTIC STUDIES IN THE FORMATION OF ENDO-CYCLOMETALATED AND EXO-CYCLOMETALATED PLATINUM COMPOUNDS OF N-BENZYLIDENEBENZYLAMINES

The bifunctional ligands 2-XC6H4CH = NCH2-2'-X'C6H4, and related ligands with more substituents on the aryl rings, react with [Pt2Me4(mu-SMe2)2] to give cyclometalated complexes [PtMe2X-(SMe2)(C6H4CHNCH2-2'-X'C6H4)] (4) by oxidative addition of C-X bonds (X = Cl, Br), or complexes [PtMe(SMe2)(C6H4CHNCH2-2'-X'-C6H4)] 5 by orthometalation with loss of methane. In both types of compound the iminic functionality is endo to the cycle. Complexes 4 with an exocyclic structure are obtained only for X' = Br, or for X' = Cl when the ligand 2,4,6-C6H2(CH3)3CH = NCH2-2'-ClC6H4 is used. Compounds 5 with an exocyclic structure are not formed. The following order of reactivity has been deduced: C-Cl endo almost-equal-to C-Br exo > C-H endo > C-Cl exo >> C-H exo. Complexes 4 and 5 and the coordination compounds [PtMe2(SMe2)(2,4,6-C6H2(CH3)3CH = NCH2-2'-XC6H4)] (3) have been characterized by NMR spectroscopy. Complexes 4 react with PPh3 to give a displacement reaction of SMe2 for PPh3, and the resulting compounds have been characterized by NMR spectroscopy; the compound [PtMe2Cl(PPh3)(C6H3ClCHNCH2C6H5)] (6c) has been characterized crystallographically. Complex 6c crystallizes in the monoclinic space group P2(1)/a, with a = 17.677 (3) angstrom, b = 15.495 (3) angstrom, c = 11.371 (2) angstrom, beta = 104.59 (2)-degrees, and Z = 4. The kinetics of formation of compounds 4 and 5 has been studied. It is suggested that formation of coordination compounds 3 takes place prior to the oxidative addition, which follows first-order kinetics and occurs by a concerted mechanism.