Selective Polymerization Of Conjugated Dienes Based On Non-cyclopentadienyl Rare-earth Metal Catalysts

In this thesis, three kinds of rare-earth metal complexes based on non-cyclopentadienyl(non-Cp) were synthesized:(1) β-diimidosulfonate-ligated rare-earth metal complexes,(2) β-imidophosphonamido-ligated rare-earth metal complexes,(3) ligand-free trialkyl homoleptic rare-earth metal complexes and heteroleptic dialkyl rare-earth metal complexes and their catalytic behaviors towards the traditional and renewable conjugated dienes were thoroughly studied.(1) The rare-earth metal complexes bearing NSN-bidentate β-diimidosulfonate ligands(RNSNdipp)Ln(CH2SiMe3)2(THF)n and NPN-bidentate β-imidophosphonamido(NPN)Lu(CH2SiMe3)2(THF) were synthesized and confirmed by NMR spectrum and X-ray diffraction analysis. Upon activation with [PhMe2NH][B(C6F5)4] and AliBu3, all these complexes exhibited highly 3,4-regioselectivity for the polymerization of isoprene. The electronics of substituted groups on NSN-ligand frame works affects the catalytic performances that the electron withdrawing groups arouse increase of the activity and facilitates the formation of the isotactic sequences. For the precursors bearing the NPN-ligands, based on their 3,4-regio-selectivity, those having more opening coordination centers display excellent isospecific stereoselectivity while those bearing the crowded coordination sphere switch to the syndioselectivity. DFT calculation has revealed that isoprene coordinates to the active spieces in η4-cis-mode followed by 3,4-insertion to give η3-allyl intermediate; the next incoming isoprene molecule and the allyl group form exo-endo arrangement towards the active sites, which ensures the isoselective regularity.(2) A series of rare-earth metal bis(alkyl) complexes(Ln = Sc, Lu, Y, Er, Nd, La) bearing a sterically bulky iminophosphonamide ancillary ligand was synthesized and well defined, which were employed to initiate isoprene polymerization upon activation with aluminum alkyls and organoborate. The catalytic behavior was strongly depending on the size of rare-earth metals and the kinds of aluminum alkyls, of which complexes 1–4 based on the smaller Lu, Sc, Y, Er metals, under the assistance of AliBu3 and [(Ph3C)(B(C6F5)4)] exhibited high 3,4-selectivities, whilst those bearing larger La and Nd metals provided moderate 3,4-slectivities. Strikingly, these large La and Nd complexes activated by [Ph3C][B(C6F5)4] and less steric AlEt3 gives trans-1,4 selectivity up to 96.5% in high activity, realizing for the first time from 3,4- to trans-1,4 selectivity. These results shed a new light on controlling the stereoregularity of polydienes by choosing the metal size and the cocatalyst, which establishes an efficient route to access high performance diene based elastomers with variable microstructures.(3) 13 kinds of rare-earth metal trialkyl complexes were synthesized and used to polymerize 1,3-butadiene. The catalytic behavior was strongly depended on the metal ion radius. When the central metal was Dy, cis-1,4-selectivity was the highest(91.6%). A heteroleptic gadolinium dibenzyl complex was also synthesized and exhibited a good catalytic activity and cis-1,4-selectivity, based on which, the diblock copolymers of DMB and BD comprising the crystalline cis-1,4-PDMB and amorphous cis-1,4-PBD sequences were obtained by sequential addition or concurrent addition of both monomers.(4) Polymerization of renewable myrcene: by means of a cationic lutetium-based coordination complex bearing the β-diimidosulfonate ligand, perfect 3,4-regio- and isospecific stereo-selective(3,4-selectivity > 99%, mmmm > 99%) PMY was achieved for the first time. This unprecedented polymer is a new elastomer having a lower glass transition temperature(-42 oC). Moreover, the isoprene–myrcene diblock copolymers,(iso-3,4-PMY)-b-(iso-3,4-PIP), composed of the amorphous elastic iso-3,4-PMY unit and the iso-3,4-PIP unit, as well as the random copolymers, have been obtained through sequential addition or mixing the two monomers in one pot; by means of a cationic lutetium-based coordination complex bearing the β-imidophosphonamido ligand, moderate 3,4-PMY was obtained(3,4-selectivity > 99%, rr = 66%). Change the ligand substituting group, the stereoselectivity was switching from syndiotactic to isotactic; by the means of a cationic lanthanum-based coordination complex bearing the β-imidophosphonamido ligand, trans-1,4-PMY was achieved for the first time with non-Cp catalysis.(5) Renewable cyclic conjugated diene 3-methylenecyclopentene(MCP) was synthesized via closed-ring metathesis of myrcene. Perfect 1,4 selectivity-PMCP has been achieved for the first time using coordination polymerization, which catalytic activity was as high as 11520 kg of PMCP/mol Lu·h and the subsequent hydrogenation afforded that better thermal properties.