A novel linkage-isomeric pair of dinuclear Pd(II) complexes, bearing a bis-bidentate tetraphos ligand

The tetraphosphane all trans tetrakis-(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) has been employed to coordinate metal dichlorides (metal = NiII, PdII and PtII), stereoselectively yielding the dinuclear complexes [Ni2Cl4(m-(kP1:kP2:kP3:kP4-o-MeO-dppcb))] (3a6) and [Pt2Cl4(m-(kP1,kP2:kP3,kP4-o-MeO-dppcb))] (2a5), characterized by two six and two five-membered metallacycles, respectively. Conversely, the reaction with PdCl2 led, under comparable synthetic conditions, to the formation of the linkage-isomeric pair [Pd2Cl4(m-(kP1,kP2:kP3,kP4-o-MeO-dppcb))] (1a5) and [Pd2Cl4(m-(kP1:kP2:kP3:kP4-o-MeO-dppcb))] (1a6) in a ca. 4 : 1 ratio. The compounds obtained have been characterized in solution by multinuclear NMR spectroscopy and in the solid state by CP-MAS NMR spectroscopy, XRPD and single crystal X-ray diffraction. Compounds 1a5 and 1a6 have been tested as catalyst precursors for the CO-ethene-propene co-and terpolymerization in water-acetic acid mixtures. Their catalytic performance has been compared to that of [PdCl2(o-MeO-dppe)] (1b) (o-MeO-dppe = 1,2-(bis(di(2-methoxyphenyl)phosphanyl))ethane) and of [PdCl2(o-MeO-dppp)] (1c) (o-MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane). The most striking result that emerged from the CO-ethene copolymerization study was that 1a5 was three times more productive than 1a6, outperforming, under identical catalytic conditions, even 1b and 1c, that are classified amongst the most active catalysts for the CO-ethene copolymerization reaction.