Palladium complexes of 8-(di-tert-butylphosphinooxy)quinoline

The preparation of the new ligand 8-(di-tert-butylphosphinooxy)quinoline (1) and the palladium derivatives [PdCl2(1)] (2), [Pd(g3-all)(1)]+ [all = C3H5 (3a), 1-PhC3H4 (3b) and 1,3-Ph2C3H3 (3c)] and [Pd(g2-ol)(1)] [ol = dimethyl fumarate (4a) and fumaronitrile (4b)] is reported. The cationic species 3a–3c have been isolated as BF4 salts. The complex 3a(BF4) is obtained either from the reaction of 1 with [Pd(l-Cl)(g3-C3H5)]2 or from the reaction of ClP(CMe3)2 with [Pd(g3-C3H5)(8-oxyquinoline)], followed in both cases by chloride abstraction with NaBF4. In the complexes, the ligand 1 is P,N chelated to the central metal, as shown by the X-ray structural analysis of 3a(BF4). At 25 C in solution, 3a(BF4) and 3b(BF4) undergo a fast g3g1g3 dynamic process which brings about a syn–anti exchange only for the allylic protons cis to phosphorus, while for 4a and 4b a slow rotation of the olefin around its bond axis to palladium takes place. The complexes 2 and 3a(BF4) are efficient catalyst precursors in the coupling of the phenylboronic acid with aryl bromides and chlorides.