Synthesis and application of the new titanium-based catalysts : Olefin polymerization and pinacol coupling reaction = 올레핀 중합과 피나콜 커플링 반응에 대한 신규 티타늄 촉매에 관한 연구
Olefin polymerization and pinacol coupling reaction
A new set of Cp/non-Cp mixed compound 1~7 containing non-Cp chelate ligands with multi binding sites, Lewis base centers, of N and O atoms was synthesized and structurally characterized.$CpL_2MX$ type complexes(1~5) were synthesized by the routine method and $CpLMX_2$ type dinuclear complexes(6 and 7) was synthesized by the hydrolysis reaction of $CpL_2MX$ type complex distinctively.
The 1 / MAO catalytic system produces PEs with multimodal MWD. The modulation of MWD can be explained in terms of the coupled use of Lewis acid-base interaction and the stepwise dissociation of picolinate ligand. The possible involvement of in situ generated different isomers in modulating MWD has been ruled out.
The first example of heteroleptic bridged titanium dinuclear complex (2) containing oxo bridging system was synthesized and characterized. The complex 2 has a high stability in air, moisture and high temperature. 2 / MAO system showed a high activity and syndiotacticity for styrene homopolymerization, the highest activity in high polymerization temperature of 90℃ and changing modality as a polymerization temperature. The catalytic system exhibited a high activity for ethylene / styrene copolymerization and produced sPS / polyethylene block copolymer.
The dissociation step of titanium-based reductive pinacol coupling reaction of aldehydes or ketones proceeds via hydrolysis reaction of pinacolato-titanium intermediate. Here, for the first time the precise mechanism of the half-titanocene-based dissocation step was proven by a X-ray crystallographic analysis of isolated intermediate and $^1H$ NMR spectrum monitoring. We confirmed the existance of the oxo and pinacolate dibridged dinuclear titanium complex and oxo bridged dinuclear complex without pinacolate ligand as an intermediate of the pinacol dissocation process. Furthermore, oxo bridged multinuclear titanium complex and free pinacol as final products of the reaction of metalla-pinacol complex and $H_2O$ were observed. ...