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

2009 
The tetraphosphane all transtetrakis-(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(μ-(κP1:κP2:κP3:κP4-o-MeO-dppcb))] (3a66) and [Pt2Cl4(μ-(κP1,κP2:κP3,κP4-o-MeO-dppcb))] (2a55), 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(μ-(κP1,κP2:κP3,κP4-o-MeO-dppcb))] (1a55) and [Pd2Cl4(μ-(κP1:κP2:κP3:κP4-o-MeO-dppcb))] (1a66) 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 1a55 and 1a66 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 1a55 was three times more productive than 1a66, outperforming, under identical catalytic conditions, even 1b and 1c, that are classified amongst the most active catalysts for the CO–ethene copolymerization reaction.
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