Synthesis and characterization of palladium(ii) complexes with new diphosphonium-diphosphine and diphosphine ligands. Production of low molecular weight alternating polyketonesvia catalytic CO/ethene copolymerisation

Abstract

The bis-cationic diphosphonium-diphosphine 6,7-di(di-2-methoxyphenyl)phosphinyl-2,2,4,4-tetra(di-2-methoxyphenyl)-2λ⁴,4λ⁴-diphosphoniumbicyclo[3.1.1]heptane-bis(PF₆) ((o-MeO-PCP)(PF₆)₂) and the diphosphine rac-2,4-bis((di-2-methoxyphenyl)phosphino)pentane (rac-o-MeO-bdpp) have been synthesized. Both ligands have been employed to coordinate PdCl₂ and Pd(OAc)₂ to give [PdCl₂(o-MeO-PCP)](PF₆)₂ (1a), PdCl₂(rac-o-MeO-bdpp) (1b), [Pd(OAc)₂(o-MeO-PCP)](PF₆)₂ (2a) and Pd(OAc)₂(rac-o-MeO-bdpp) (2b). The ligands and complexes have been fully characterized in solution by multinuclear NMR spectroscopy. In addition, 1a and 1b have been authenticated by single crystal X-ray structure analyses. The Pd^II complexes 1a and 1b have been employed as catalyst precursors for the CO/ethene copolymerisation in water–acetic acid mixtures, while 2a and 2b have been tested in methanol in the presence of p-toluenesulfonic acid. Irrespective of the reaction media, perfectly alternating polyketones were obtained in excellent yields and with number-average molecular weights ranging from 7.1–13.9 kg mol⁻¹ with the diphosphonium-diphosphine catalysts and from 37.2–48.2 kg mol⁻¹ with the diphosphine catalysts.