Regiospecific C(naphthyl)-H bond activation: Isolation and characterization of cyclopalladates

摘要

In ethanol medium disodium tetrachloropalladate selectively activates the C8-H bond of naphthyl group present in 1-(2'-hydroxy-5'-methylphenylazo)naphthalene(H2L1) at room temperature and produces cyclometallate [PdL1(PPh3)] in presence of triphenylphosphine. Under similar reaction condition, the C(naphthyl)-H bond activation of 1-(2'-methoxy-5'-methylphenylazo) naphthalene (HL2) occurs at C2 and cyclopalladate [(PdLCl)-Cl-2] has been isolated as product. The labile nature of the Pd <-:O(R) bond of ((PdLCl)-Cl-2] in solution is established from the electronic and NMR spectra. Cyclopalladate [(PdLCl)-Cl-2] reacts with thallium(l) cyclopentadienide and yields [PdL2(Cp)], where both sigma- and pi-palladium(II)-carbon bonds exist. All the cyclopalladates have been isolated in pure form and characterized on the basis of their spectral data. The molecular structure of cyclopalladate [PdL1(PPh3)] has been determined by single crystal X-ray diffraction method. In [PdL'(PPh3)], the metal ion is bonded to C8 (peri-position of 1-azonaphthyl fagment), N1 of diazene function, O1 of phenolic group and P1 of triphenylphosphine. The tetra-coordination around palladium(II) is in a distorted square-planar geometry. (c) 2006 Elsevier B.V. All rights reserved.