Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization

Carbon dioxide copolymerization is a front-runner CO₂ utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO₂ ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h⁻¹ and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.     

Titanium Dioxide as a Mild and Efficient Catalyst for Conversion of Epoxides to Thiiranes

Abstract

Titanium dioxide (TiO₂) efficiently catalyze the reaction of a variety of epoxides with ammonium thiocyanate in refluxing acetonitrile to afford the corresponding thiirane in high to excellent yields.     

Synthesis and Crystal Structure of a Dinuclear Titanium(IV) Complex containing an Allopyranosidato Ligand

The reaction of methyl‐4,6‐O‐benzylidene‐α‐D ‐allopyranoside (α‐MeBAH₂) with trichlorocyclopentadienyltitanium [CpTiCl₃] and triethylamine in dichloromethane led to the dinuclear complex [(CpTiCl₂)₂‐μ‐(α‐MeAG)] ( 1 ). 1 was characterized by elemental analysis, ¹H NMR spectroscopy as well as single crystal X‐ray diffraction.     

Regio- and Chemoselective Formal (4+1) Carbocyclization of Chalcones with Internal Alkynes via Rhodium(III) Catalysis

A rhodium(III)-catalyzed oxidative cyclization of chalcones with internal alkynes is reported, generating biologically important 3,3-disubstituted 1-indanones along with reusable aromatic aldehydes. This transformation features unique (4+1) reaction mode, excellent regioselectivity in alkyne insertion, broad substrate scope, allows for the construction of quaternary carbon centers, and is scalable. Steric hindrance from substrate and ligand probably controls the chemoselectivity of this carbocyclization. Importantly, this discovery enables a practical two-step protocol switching the overall reaction of acetophenones with internal alkynes from a (3+2) to a (4+1) annulation.     

Synthesis of five- to seven-membered polyfunctional terpenic carbocycles via Ti(III)-catalyzed radical cyclizations of epoxypolyprenes

Ring size on Ti(III)-mediated radical cyclization of monoepoxypolyprenoids can be controlled by varying the substitution pattern and/or the electronic distribution of the double bond involved in the ring closure. The feasibility of applying this idea to tandem cyclizations has also been proven. Besides, when a silyloxy function is located in α position to the oxirane ring of the acyclic polyprene, the cyclization leads to carbocyclic terpenoids doubly functionalized in the A ring with acceptable yields. These results widen significantly the scope of this methodology.     

新型手性双核Salen Zn(II)配合物的分子识别研究

采用新型Salen中间体合成了新型Salen Zn(II)配合物. 用紫外-可见光谱滴定法研究了主体双核Salen Zn(II)与咪唑、二胺类等含氮小分子的分子识别行为, 测定了它们的缔合常数. 对咪唑类客体的缔合常数顺序为K^θ(Im)＞K^θ(2-MeIm)＞K^θ(EMeIm); 对二胺类客体缔合常数顺序为K^θ(DAP)＞K^θ(DAE). 主体与咪唑类和二胺类客体的配位数分别是2和1. 主体与这些客体的识别过程为放热、熵减的焓驱动反应. 利用圆二色光谱研究了识别过程的Cotton效应. 用分子力学方法研究了主客体体系的最低能量构型, 通过量化计算对实验事实做了进一步解释.     

Catalysis and inhibition of benzimidazole units on thermal imidization of poly(amic acid) via hydrogen bonding interactions

The effect of benzimidazole units on thermal imidizaiton was studied when they were introduced into the main chain of poly(amic acid)(PAA). The thermal imidization process of PAA-PABZ synthesized by 3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA) and 2-(4-aminophenyl)-5(6)-aminobenzimidazole(PABZ) was studied by TGA, DSC, DMA, FTIR and in situ FTIR. The results of FTIR and in situ FTIR indicate benzimidazole units act as an "in situ" catalyst to accelerate thermal imidization of PAA to polyimide(PI) when the temperature is lower than 170 °C. FTIR and 1H-NMR results demonstrate that in situ catalysis is caused by the hydrogen bonding interactions between C=N of benzimidazole and ―NH― in ―CONH― of PAA and the semi-ionization of the H in imidazole ring of benzimidazole. However, when the imidization temperature is higher than 170 °C, the thermal imidization process is inhibited. DMA and in situ FTIR results illustrate that the decreased mobility of PI-PABZ macromolecular chains and the reduced reactive ability of anhydride formed during the intramolecular breakdown of polymer chains lead to the inhibition of thermal imidization process.     

聚合物键合Cu（Salen）的合成及其催化作用

一些简单的无机配合物已经广泛地用作氧载体和氧化催化剂,其中研究较多的是过渡金属卟啉和席夫碱（Schiff base）－过渡金属配合物。其中,席夫碱－过渡金属配合物的合成简单、易于控制配体的电子与立体因素,因而其催化性能的调变更具有灵活性,其分子氧体系已用于烯烃的环氧化和醇类的氧化,卟啉钴配合物－分子氧体系对硫醇的催化氧化研究已报道,其于席夫碱－金属配合物具有结合分子氧的特性和催经作用,以及高分子配合物催化剂的特点,我们合成了聚合物键合双水扬醛缩乙二胺合铜（Ⅱ）,并将其用于催化分子氧氧化丙硫醇转化成二硫化物。     

新型手性双核Salen锰（III）配合物对咪唑、吡啶类客体的分子识别研究

合成并表征了新型手性双核Salen配体1及其锰（III）配合物2（主体2）。用 紫外-可见光谱滴定法研究了主体2与四种咪唑类、四种吡啶类客体在CHCl_3中的分 子识别行为。实验结果表明：对咪唑客体的缔合常数按K（Im） > K (2 - Melm) > K (N-MeIm) > K (EtMelm)顺序递减；吡啶类顺序为K （PyO） > K (4-PhPyO) > K (DMAP) > K(Py)，配位数n值均为2。测定了识别过程的Δ_rH_m，Δ_rS_m， 发现此类反应为放热、熵减小的过程，反应体系中存在焓熵补偿关系。与单核的 Salen锰（III）配合物3（主体3）进行比较，除EtMeIm与3的配位数为1外，其他唑 类客全的配位数均为2。就与客体的缔合能力而言，主体2比3大。用圆二色光谱（ CD）研究了主-客体的分子识别行为。     

Silsesquioxane Chemistry, 4.: Silsesquioxane Complexes of Titanium(III) and Titanium(IV)

Reaction of the incompletely condensed silsesquioxane derivative Cy₇Si₇O₉(OH)₃ (1) with Ti(OEt)₄ affords the dimeric titanasilsesquioxane [(Cy₇Si₇O₁₂)Ti(μ-OEt)(EtOH)]₂ (13) in 81% yield. The known titanasilsesquioxane [Cy₇Si₇O₁₁(OSiMe₃)]₂Ti (18) has been prepared through a modified procedure starting from titanium tetraalkoxides. Novel oxotitanium silsesquioxane derivatives are obtained from reactions of titanocene dihalides with Cy₇Si₇O₉(OH)₂(OSiMe₃) (14). Cp₂TiCl₂ yields dinuclear (μ-O)[{Cy₇Si₇O₁₁(OSiMe₃)}TiCp]₂ (19), while with Cp^*₂TiCl₂ the trinuclear titanacycle Cp^*₂Ti₃O₃[Cy₇Si₇O₁₁(OSiMe₃)]₂ (20) is obtained. In addition, a new synthetic route to model compounds for titanium catalysts immobilized on silica has been developed. Disilylated Cy₇Si₇O₉(OH)(OSiMe₃)₂ (15) cleanly reacts with the ‘tucked-in’ fulvene complex Cp*Ti(C₅Me₄CH₂) to give the titanium(III) silsesquioxane Cp*₂Ti[Cy₇Si₇O₁₀(OSiMe₃)₂] (21). In a similar manner treatment of Cp*Ti(C₅Me₄CH₂) with Cy₇Si₇O₉(OH)₂(OSiMe₃) (14) affords the mono(pentamethylcyclopentadienyl) complex Cp*Ti[Cy₇Si₇O₁₁(OSiMe₃)][Cy₇Si₇O₁₀-(OH)(OSiMe₃)] (22) which is an advanced model compound for a catalytically active titanium center on a silica surface. The molecular structures of these titanium silsesquioxane derivatives have been determined by X-ray diffraction analyses.     

Merging Copper(I) Photoredox Catalysis and Iodine(III) Chemistry for the Oxy-monofluoromethylation of Alkenes

A simple process for the oxy-monofluoromethylation of alkenes is described. In combination with visible-light copper(I) photoredox catalysis, an easily accessible iodine(III) reagent containing monofluoroacetoxy ligands serves as a powerful source of a monofluoromethyl (CH₂F) radical, enabling the step economical synthesis of γ-fluoro-acetates from a broad range of olefinic substrates under mild conditions. Applications to late-stage diversification of alkenes derived from complex molecules, amino acids and the synthesis of fluoromethylated heterocycles are also demonstrated.     

双核锌(Ⅱ)大杂环配合物的超声催化合成和结构表征

用超声辐射催化方法,合成了C23H19N2SF3O2Zn(1)-Zn(2)C8H5SF3O2双核锌大杂环配合物,经IR, 1H NMR, 13C NMR, MS和元素分析表征.通过波谱分析表明,Zn(1)采取dsp3杂化与1,2-二氮-5,8-二氧-3,4,10,11-双(苯并)环十四-13-三氟甲基-1-噻吩配位,Zn(2)采取sp2杂化与1′-噻吩-3′-三氟甲基-1′,3′-二丙酮配位,形成双核锌(Ⅱ)树状型配合物.     

双核锌(II)大杂环配合物的超声催化合成和结构表征

用超声辐射催化方法 ,合成了C2 3 H19N2 SF3 O2 Zn(1) Zn(2 )C8H5SF3 O2 双核锌大杂环配合物 ,经IR ,1HNMR ,13 CNMR ,MS和元素分析表征 .通过波谱分析表明 ,Zn(1)采取dsp3 杂化与 1,2 二氮 5 ,8 二氧 3 ,4,10 ,11 双 (苯并 )环十四 13 三氟甲基 1 噻吩配位 ,Zn(2 )采取sp2 杂化与 1′ 噻吩 3′ 三氟甲基 1′ ,3′ 二丙酮配位 ,形成双核锌 (II)树状型配合物     

Supramolecular Catalysis of Ester and Amide Cleavage by a Dinuclear Barium(II) Complex

Five components spontaneously self‐assemble to yield the productive complex 1 , where one barium ion delivers an ethoxide to the carbonyl group of an amide substrate anchored by means of a distal carboxylate moiety to the other barium ion. High substrate specificity, fairly high reaction rates with catalytic turnover, and competitive inhibition by inert substrates are observed.     

Synthesis,Structure, and Polymerization Activity of a Titanium Complex with a Chelating [(Hydroxy‐κO)amino‐κN]phenolato(2−)‐κO Ligand

A novel titanium complex with a chelating nitroxide ligand, dichloro‐2‐{[(hydroxy‐κO)phenylamino‐κN)phenylmethyl}phenolato(2?)‐2κO}(tetrahydrofuran)titanium ( 1 ), was synthesized and characterized by NMR spectroscopy, elemental analysis, and single‐crystal X‐ray crystallography. In the presence of methylaluminoxane (MAO), 1 displayed moderate activity for the polymerization of propylene.