Synthesis of aluminium complexes bearing a piperazine-based ligand system

Johnstone, Nick C.; Aazam, Elham S.; Hitchcock, Peter B.; Fulton, J. Robin

doi:10.1016/j.jorganchem.2009.10.016

Cited by 31 publications

(29 citation statements)

References 24 publications

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“…According to the literature data, which account for the trend of halogen atoms to form bridges between metal atoms such as Mg [25] and Al, [26] we assumed the formation of such complexes and postulated the formation of pentacoordinated aluminum, also in agreement with literature data. [27] For the several possibilities studied, complex 25 resulted the most stable (PM3) and it was used for the above-mentioned conformational study. This study showed the presence of six relevant stationery points, that is, three minima and three maxima (Figure 3).…”

Section: Resultsmentioning

confidence: 99%

Tunable Diastereoselection of Biased Rigid Systems by Lewis Acid Induced Conformational Effects: A Rationalization of the Vinylation of Cyclic Nitrones En Route to Polyhydroxylated Pyrrolidines

Delso

Marca

Mannucci

et al. 2010

Chemistry A European J

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The diastereofacial selection in addition reactions to biased rigid systems can be modulated by the action of Lewis acids. As an example, the stereoselectivity of the nucleophilic addition of vinyl magnesium bromide (VMB) to cyclic nitrones in the presence of diethylaluminum chloride (DEAC) shows a strong dependence on the temperature and the carbon substituent adjacent at the reaction center; it is remarkable that whereas a high selectivity is obtained at higher temperatures, in the presence of DEAC, a trend to invert the stereochemical course of the reaction is observed at lower temperatures, provided the substituent at C3 of the pyrrolidine ring allows delivery of the vinyl moiety. This behavior and difference in selectivity is to be attributed to the high conformational barriers of the intermediate nitrone-DEAC-VMB complex. A clear inversion of the selectivity is observed at -78 degrees C for the reaction of the nitrone protected as an O-methyl derivative. The present study provides a rationalization for the stereocontrolled addition of nucleophiles to rigid systems (cyclic nitrones).

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Section: Resultsmentioning

confidence: 99%

Tunable Diastereoselection of Biased Rigid Systems by Lewis Acid Induced Conformational Effects: A Rationalization of the Vinylation of Cyclic Nitrones En Route to Polyhydroxylated Pyrrolidines

Delso

Marca

Mannucci

et al. 2010

Chemistry A European J

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“…Some examples of previously reported piperazinyl and morpholinyl aminephenolate based complexes (R = alkyl or aryl). 10,27,28,39,40 Recently, we reported the synthesis of piperazinyl-aminephenolate zinc complexes (II), which showed good activity in ROP of rac-lactide and ε-caprolactone. 27 These zinc complexes, however, showed poor activity in the cycloaddition of carbon dioxide and epoxides.…”

Section: Introductionmentioning

confidence: 99%

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

et al. 2012

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Abstract:A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONE R1,R2 ]-) {[ R 1 = t Bu, R 2 = Me, E = NMe (L1); R 1 = R 2 = t Bu, E = NMe (L2); R 1 = R 2 = t Bu, 1 E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1 H, 13 The catalytic activity of complexes 1-3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogs for ROP of rac-lactide. Characteristics of the polymer as well as polymerization kinetics and mechanism were studied. Polymer end-group analyses were achieved using 1 H NMR spectroscopy and MALDI-TOF MS. Eyring analyses were performed and the activation energies for the reactions were determined, which were significantly lower for 1 and 2 compared with 3. This could be for several reasons: (1) the methylamine (NMe) group of 1 and 2, which is a stronger base than the ether (O) group of 3, might activate the incoming monomer via non-covalent interactions, and/or (2) the ether group is able to temporarily coordinate to the metal center and blocks the vacant coordination site towards incoming monomer, whilst the amine cannot do this. Preliminary studies using 4 and 5 towards copolymerization of cyclohexene oxide with carbon dioxide have been performed. 4 was inactive and 5 afforded polyethercarbonate (66.7% epoxide conversion, polymer contains 54.0% carbonate linkages).

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“…Aluminum salen complexes are tolerant to a variety of initiating groups, as discussed previously (48). Fulton demonstrated that changing the nature of the initiating group between methoxide, ethoxide, isopropoxide, tert-butoxide and triflate had relatively little effect on the polymerization.…”

Section: End Group Controlmentioning

confidence: 79%

“…Fulton reported the synthesis of a piperazine bridged salan complex (48) (48). The study focussed on the nature of the metal complex as well as the initiating X group.…”

Section: Catalyst Tuningmentioning

confidence: 99%

Aluminum Salen and Salan Polymerization Catalysts: From Monomer Scope to Macrostructure Control

MacDonald

Shaver

2015

ACS Symposium Series

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Tel +44 (0) 131 650 4726.Aluminum salen and salan complexes have been extensively employed as catalysts for the ring-opening polymerization of cyclic esters. The high tunability of the ligand framework has encouraged the systematic study of substituent effects on optimizing polymer and copolymer synthesis. Building on early work, designed catalysts are able to produce highly isotactic or heterotactic poly(lactic acid). The monomer scope has grown to include β-lactones, δ-valerolactone, lactide, (substituted) ε-caprolactones and macrolactones, with a significant level of control over molecular weight and dispersity (Đ). Polymer macrostructures have also been explored, often resulting in well-defined and predictable products. Macrostructures synthesized include random copolymers, AB diblock and ABA triblock copolymers and polymer stars.Polymer macrostructure control can tune properties not accessible through homopolymerization.

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Synthesis of aluminium complexes bearing a piperazine-based ligand system

Cited by 31 publications

References 24 publications

Tunable Diastereoselection of Biased Rigid Systems by Lewis Acid Induced Conformational Effects: A Rationalization of the Vinylation of Cyclic Nitrones En Route to Polyhydroxylated Pyrrolidines

Tunable Diastereoselection of Biased Rigid Systems by Lewis Acid Induced Conformational Effects: A Rationalization of the Vinylation of Cyclic Nitrones En Route to Polyhydroxylated Pyrrolidines

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

Aluminum Salen and Salan Polymerization Catalysts: From Monomer Scope to Macrostructure Control

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