Raman Sumesh K, Deacy Arron C, Pena Carrodeguas Leticia, Reis Natalia V, Kerr Ryan W F, Phanopoulos Andreas, Morton Sebastian, Davidson Matthew G, Williams Charlotte K
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, U.K.
Centre for Sustainable Chemical Technologies, Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.
Organometallics. 2020 May 11;39(9):1619-1627. doi: 10.1021/acs.organomet.9b00845. Epub 2020 Feb 11.
Titanium(IV) complexes of amino-tris(phenolate) ligands (LTiX, X = chloride, isopropoxide) together with bis(triphenylphosphine)iminium chloride (PPNCl) are active catalyst systems for the ring-opening copolymerization of carbon dioxide and cyclohexene oxide. They show moderate activity, with turnover frequency values of ∼60 h (0.02 mol % of catalyst, 80 °C, 40 bar of CO) and high selectivity (carbonate linkages >90%), but their absolute performances are lower than those of the most active Ti(IV) catalyst systems. The reactions proceed with linear evolution of polycarbonate (PCHC) molar mass with epoxide conversion, consistent with controlled polymerizations, and evolve bimodal molar mass distributions of PCHC (up to = 42 kg mol). The stoichiometric reaction between [LTiO Pr] and tetraphenylphosphonium chloride, PPhCl, allows isolation of the putative catalytic intermediate [LTi(O Pr)Cl], which is characterized using single-crystal X-ray diffraction techniques. The anionic titanium complex [LTi(OR)Cl] is proposed as a model for the propagating alkoxide intermediates in the catalytic cycle.
氨基三（酚盐）配体的钛（IV）配合物（LTiX，X = 氯、异丙氧基）与双（三苯基膦）亚胺氯化物（PPNCl）一起，是二氧化碳和环氧环己烷开环共聚的活性催化剂体系。它们表现出中等活性，周转频率值约为60 h⁻¹（0.02 mol%的催化剂，80 °C，40 bar的CO₂）且选择性高（碳酸酯键>90%），但其绝对性能低于最具活性的Ti（IV）催化剂体系。反应过程中聚碳酸酯（PCHC）摩尔质量随环氧化物转化率呈线性增长，这与可控聚合一致，并且产生双峰摩尔质量分布的PCHC（高达Mw = 42 kg mol⁻¹）。[LTiO-iPr]与四苯基氯化鏻（PPh₄Cl）之间的化学计量反应，使得能够分离出假定的催化中间体[LTi(O-iPr)Cl]，并使用单晶X射线衍射技术对其进行表征。阴离子钛配合物[LTi(OR)Cl]被提议作为催化循环中增长的醇盐中间体的模型。
