Synthesis and characterization of new ring opening polymerization（ROP）catalysts based on aluminium or tungsten complexes

Cyclic esters provide versatile biocompatible and biodegradable polymers possessing good mechanical properties. These polymers are also models for studying the kinetics, thermodynamics, and mechanisms of many elementary reactions in polymerization. Both organoaluminium and tungsten complexes for ring opening polymerization have received increasing attention over the last few years. The aim of this study is to investigate a series of new complexes incorporating aluminium and tungsten metals in combination of various ligands, and assess their ability as catalysts for the ring opening polymerization of ε−caprolactone and rac-lactide.Reaction of Me₃Al (two equivalents) with anisidines formed a family of organoaluminium complexes, viz {[1,2-(OMe),N-C₆H₄(μ-Me₂Al)](μ-e2Al)}₂ (1), [1,3-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]₂ (2) and [1,4-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]₂ (3). Complexes 1 - 3 were found to be highly active for the ring opening polymerization (ROP) of ε-caprolactone either with or without benzyl alcohol present; at various temperatures, the activity order 1 > 2 ≈ 3 was observed. For the ROP of rac-lactide results for 1 – 3 were poor (Chapter 2).By varying the reaction conditions, the reaction of [W(eg)3] (eg = 1,2-ethanediolato) with p-tert-butylcalix[n]areneHn (n = 6 or 8) in refluxing toluene affords different tungstocalixarene complexes. Complexes {[W(eg)]₂(μ-O)p-tert-butylcalix[6]arene} (1), {[W(eg)]₂p-tert-butylcalix[8]arene}·MeCN (3), {1,2-[W(eg)2]2p-tert-butyl calix[8]areneH₄}/{1,3-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4a)/(4b)• 3.5MeCN and {[WO(eg)]₂p-tert- butyltetrahomodioxacalix[6]areneH₂} (5) have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; conversion rates were poor at temperatures below 110 oC. All tungsten complexes have similar conversion rates, yet ROP using complex 3 has outstanding polymerization weight compared with other co-catalysts (Chapter 3)

Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone

Reaction of the pro-ligand α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L¹H₄) with two equivalents of [NbCl₅] in refluxing toluene afforded, after work-up, the complex {[NbCl₃(NCMe)]₂(μ-p-L¹)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl₅] afforded the yellow complex {[TaCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α′,α′tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L²H₄) only the use of [Nb(O)Cl₃(NCMe)₂] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L²H₂)₂]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L²H₂)₂]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L¹H₄ and m-L²H₄·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat)

界面を駆使した複数の配位性官能基を持つ機能性π共役ニッケル錯体ナノシートの構築

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 西原 寛, 東京大学教授 小澤 岳昌, 東京大学教授 塩谷 光彦, 東京大学准教授 岡林 潤, 東京大学特任教授 原野 幸治University of Tokyo(東京大学

BAKing up to Survive a Battle: Functional Dynamics of BAK1 in Plant Programmed Cell Death

In plants, programmed cell death (PCD) has diverse, essential roles in vegetative and reproductive development, and in the responses to abiotic and biotic stresses. Despite the rapid progress in understanding the occurrence and functions of the diverse forms of PCD in plants, the signaling components and molecular mechanisms underlying the core PCD machinery remain a mystery. The roles of BAK1 (BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1), an essential co-receptor of multiple receptor complexes, in the regulation of immunity and development- and defense-related PCD have been well characterized. However, the ways in which BAK1 functions in mediating PCD need to be further explored. In this review, different forms of PCD in both plants and mammals are discussed. Moreover, we mainly summarize recent advances in elucidating the functions and possible mechanisms of BAK1 in controlling diverse forms of PCD. We also highlight the involvement of post-translational modifications (PTMs) of multiple signaling component proteins in BAK1-mediated PCD

Organoaluminium complexes of ortho-, meta-, para-anisidines: synthesis, structural studies and ROP of ε-caprolactone (and rac-lactide)

Reaction of Me₃Al (two equivalents) with ortho-, meta- or para-anisidine, (OMe)(NH₂)C₆H₄, affords the complexes {[1,2-(OMe),NC₆H₄(μ-Me₂Al)](μ-Me₂Al)}₂ (1), [1,3-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]2 (2) or [1,4-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]₂ (3), respectively. The molecular structures of 1–3 have been determined and all three complexes were found to be highly active for the ring opening polymerization (ROP) of ε-caprolactone. 1 was found highly active either with or without benzyl alcohol present; at various temperatures, the activity order 1 > 2 ≈ 3 was observed. For the ROP of rac-lactide results for 1–3 were poor

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: Synthesis, characterization and ROP of ε-caprolactone

By varying the reaction conditions, the reaction of [W(eg)₃] (eg = 1,2-ethanediolato) with p-tert-butylcalix[n]areneHn (n = 6 or 8) in refluxing toluene affords, following work-up, a number of products which have been fully characterized. From the reaction of p-tert-butylcalix[6]areneH₆ with one or two equivalents of [W(eg)₃], only the oxo-bridged complex {[W(eg)]₂(μ-O)p-tert-butylcalix[6]arene} (1) could be isolated, whereas the use of four equivalents of [W(eg)₃], in the presence of molecular sieves, afforded {[W(eg)₂]₂p-tert-butylcalix[6]areneH₂}·2MeCN (2); molecules of 2 pack in bi-layers. Under similar conditions, use of one or two equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ afforded {[W(eg)]₂p-tert-butylcalix[8]arene}·MeCN (3) in which each tungsten centre was bound by four calixarene oxygens. By contrast, the small orange prisms resulting from the use of four equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ were shown by synchrotron radiation to be a mixture of two isomers (4a/4b·3.5MeCN). In the major isomer {1,2-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4a), two tungsten centres bind to neighbouring sets of phenolate oxygens, whereas in the minor isomer {1,3-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4b), there is a protonated phenolic group between the two pairs of phenolate oxygens bound to tungsten; the major:minor ratio is about 83:17. Use of p-tert-butyltetrahomodioxacalix[6]areneH₆ with two equivalents of [W(eg)₃] resulted in the isolation of {[WO(eg)]₂p-tert-butyltetrahomodioxacalix[6]areneH₂} (5·0.83toluene·MeCN), in which each dimethyleneoxa bridge is bound to an oxotungsten(VI) centre. Complexes 1–5, together with the known complex [W(eg)p-tert-butylcalix[4]arene] (6), have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for 1, 2 and 5, 6 conversion rates were good (>88%) at 110 °C over 12 or 24 h, whereas the calix[8]arene complexes 3 and 4 under the same conditions were inactive

Thermochemistry of the Initial Steps of Methylaluminoxane Formation. Aluminoxanes and Cycloaluminoxanes by Methane Elimination from Dimethylaluminum Hydroxide and Its Dimeric Aggregates

Results are presented of ab initio studies at levels MP2(full)/6-31G* and MP2(full)/6-311G* of the hydrolysis of trimethylaluminum (TMA, 1) to dimethylaluminumhydroxide (DMAH, 2) and of the intramolecular 1,2-elimination of CH4 from 2 itself to form methylaluminumoxide 3, from its dimeric aggregate 4 to form hydroxytrimethyldialuminoxane 5 and dimethylcyclodialuminoxane 6, and from its TMA aggregate 7 to form 8 and/or 9, the cyclic and open isomers of tetramethyldialuminoxane, respectively. Each methane elimination creates one new Lewis acid site, and dimethylether is used as a model oxygen-donor molecule to assess the most important effects of product stabilization by Lewis donor coordination. It is found that the irreversible formation of aggregate 4 (ΔG298 = -29.2 kcal/mol) is about three times more exergonic than the reversible formation of aggregate 7 (ΔG298 = -9.9 kcal/mol), that the reaction free enthalpies for the formations of 5 (ΔG298 = -9.0 kcal/mol) and 6 (ΔG298 = -18.8 kcal/mol) both are predicted to be quite clearly exergonic, and that there is a significant thermodynamic preference (ΔG298 = -7.2 kcal/mol) for the formation of 6 over ring-opening of 5 to hydroxytrimethyldialuminoxane 10. The mechanism for oligomerization is discussed based on the bonding properties of dimeric aggregates and involves the homologation of HO-free aluminoxane with DMAH (i.e., 9 to 13), and any initially formed hydroxydialuminoxane 10 is easily capped to trialuminoxane 13. Our studies are consistent with and provide support for Sinn\u27s proposal for the formation of oligoaluminoxanes, and in addition, the results point to the crucial role played by the kinetic stability of 5 and the possibility to form cyclodialuminoxane 6. Dialuminoxanes 9 and 10 are reversed-polarity heterocumulenes, and intramolecular O→Al dative bonding competes successfully with Al complexation by Lewis donors. Intramolecular O→Al dative bonding is impeded in cyclodialuminoxane 6, and the dicoordinate oxygen in 6 is a strong Lewis donor. Ethylene polymerization catalysts contain highly oxophilic transition metals, and our studies suggest that these transition metal catalysts should discriminate strongly in favor of cycloaluminoxane-O donors even if these are present only in small concentrations in the methylaluminoxane (MAO) cocatalyst

Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of epsilon-caprolactone

Reaction of the pro-ligand α,α,α’,α’-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L1H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L1)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L1)}·312 MeCN·0.614toluene (2·312 MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L1)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α’,α’tetra (3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L2H4) only the use of [Nb(O)- Cl3(NCMe)3] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb-(NCMe)Cl(m-L2H2)2]}·312 MeCN (4·312MeCN) or {[Nb(NCMe)Cl(m-z2H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L1H4 and m-L2H4·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat)

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: synthesis, characterization and ROP of epsilon-caprolactone

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: synthesis, characterization and ROP of epsilon-caprolacton