Aluminium compounds containing bidentate ligands: ligand base strength and remote geometric control over degree of association

McMahon, C. Niamh; Francis, Julie A.; Bott, Simon G.; Barron, Andrew R.

doi:10.1039/a806350h

Cited by 26 publications

(9 citation statements)

References 35 publications

(15 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It should be noted that this structure is one of many possibilities, but a structure with large degrees of rotational freedom is not consistent with the isoselectivity of the Vandenberg-catalyzed epoxide polymerizations. On the basis of foundational work by Atwood − and Barron, − we propose that the structure of the Vandenberg catalyst is likely closer to the more rigid bis-μ-oxo-dialuminum structure shown in Scheme b. A conclusive structure of the initiating and catalytic motifs for the Vandenberg catalyst have never been substantiated to the best of our knowledge.…”

Section: Resultsmentioning

confidence: 88%

Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight

Chwatko

Lynd

2017

Macromolecules

View full text Add to dashboard Cite

Copolymerization provides a modular strategy for compositional control of structure−property relationships in polymeric materials. However, this versatility is typically limited to structurally homologous comonomers. To further expand the scope of copolymerization in heterocyclic systems, we explored the copolymerization of structurally distinct lactones and epoxides utilizing the classical Vandenberg catalyst. Copolymerizations were conducted between monomer pairs selected from among two common lactones (DL-lactide, ε-caprolactone) and four epoxides (epichlorohydrin, butylene oxide, propylene oxide, ethylene oxide). The resultant materials had molecular weights of up to 16 Mg/mol. Reactivity ratios were determined for the copolymerization of DL-lactide and propylene oxide, which were consistent with a gradient copolymer with propylene oxide (PO) being the preferred monomer: r PO = 2.81 ± 0.27 and r LA = 0.36 ± 0.02. The copolymerization between ε-caprolactone and propylene oxide was also monitored by 1 H NMR spectroscopy. A greater preference for propylene oxide was evident, but incomplete consumption of the ε-caprolactone under these reaction conditions complicated determination of reactivity ratios. Meyer−Lowry analysis of the time-dependent compositional data provided estimates of r PO = 2.17 ± 0.04 and r CL = 0.08 ± 0.01. Distinct ester−ether dyad signals were observed in the 1 H NMR spectra of the copolymers, and thermal properties of the copolymers were distinct from those of the respective pure homopolymers. The expected hydrolytic degradability of poly[(DLlactide)-co-(ethylene oxide)] was demonstrated under neutral and basic conditions.

show abstract

Section: Resultsmentioning

confidence: 88%

Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight

Chwatko

Lynd

2017

Macromolecules

View full text Add to dashboard Cite

show abstract

“…As a first step toward combining the advantages of AROP and CROP, we sought to develop an initiator with the simplicity and efficiency of the Vandenberg catalyst, but with a well-defined structure providing control of molecular weight and chain-end functionality. The structure of the Vandenberg catalyst is unknown; however, new insight into compositionally homologous organoaluminum species over the intervening decades has provided new insight. − On the basis of this foundational work, we posited that a bis(μ-alkoxoalkylaluminum) ([R 2 Al(μ-OCH 2 CH 2 OMe)] 2 , R = Me, Et, iBu) motif was likely homologous to the resting-state structure of the Vandenberg catalyst with respect to epoxide polymerizations. While synthesizing a series of bis(μ-alkoxoalkylaluminum)s by tuning the stoichiometry between an N-substituted ethanolamine ligand and triethylaluminum (TEAl) at −78 °C in hexane, in one instance we isolated an asymmetric organoaluminum species that proved to be effective for epoxide polymerizations; the triethylaluminum adduct of (2-dibenzylamino)ethoxydiethylaluminum, or TAxEDA, where x refers to the specific N-substitution (here x = 2-dibenzylamino-).…”

Section: Resultsmentioning

confidence: 99%

Ring-Opening Polymerization of Epoxides: Facile Pathway to Functional Polyethers via a Versatile Organoaluminum Initiator

et al. 2017

View full text Add to dashboard Cite

We report a new class of organoaluminum-based initiator for anionic ring-opening polymerization of epoxides that is simple to synthesize from readily available precursors. The resultant organometallic initiator was the triethylaluminum adduct of (2-dibenzylamino)ethoxydiethylaluminum (TAxEDA) [(AlEt3)·(O(AlEt2)CH2CH2N(Bn)2)], which was isolated by direct crystallization from the reaction medium and then compositionally and structurally characterized by NMR spectroscopy and XRD. We studied the reactivity and versatility of the new initiator through the polymerization of propylene oxide, butylene oxide, epichlorohydrin, and allyl glycidyl ether into homopolymer, statistical copolymer, and block copolymer architectures with heterobifunctional end-groups consisting of dibenzylamine and hydroxyl functionalities. The TAxEDA-initiated polymerizations were consistent with a controlled, living, anionic mechanism that was tolerant of chemical functionality and exhibited no chain transfer to monomer that limits the traditional anionic ring-opening polymerization of substituted epoxides.

show abstract

“…The Al(1)−N(1) bond (1.915(1) Å) is shorter than those of 7 (1.926(3), 1.933(3) Å), but it is longer than the Al−N amide σ bond in the aluminum amide complexes [(2,6-Pr i 2 C 6 H 3 )N(SiMe 3 )AlMe 2 ] 2 (average 1.821 Å) and [(Me 3 Si)N{CH 2 CH 2 (Me 3 Si)N} 2 AlCl] (average 1.807 Å) . The Al(1)−S(1) bond (2.316(5) Å) in 6 is longer than the Al−S σ bond in [(Bu t ) 2 Al(SCH 2 CH 2 NEt 2 )] (2.272(4) Å) . Similar to the case for compounds 3 and 4 , the P−C bonds are shortened and the P−N/P−S bonds are lengthened in 6 compared with those of 1 .…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Characterization of Magnesium and Aluminum Bis(phosphoranyl)methanediide Complexes

et al. 2010

View full text Add to dashboard Cite

The reaction of [CH 2 (PPh 2 dNSiMe 3 )(PPh 2 dE)] (E = S (1), NSiMe 3 (2)) with Mg(Bu n ) 2 in refluxing toluene afforded the magnesium bis(phosphoranyl)methanediide complexes [{(PPh 2 dNSiMe 3 )-(PPh 2 dE)}CMg] 2 (E = S (3), NSiMe 3 (4)), respectively. The X-ray structures and DFT calculations of 3 and 4 show that they are bimetallic methanediide complexes of magnesium containing a strong Mg-C methanediide electrostatic bonding. Treatment of 4 with water in toluene gave 2 and the magnesium hydroxide complex [HC(PPh 2 dNSiMe 3 ) 2 Mg(μ-OH)] 2 (5), confirmed by X-ray crystallography. The reaction of 1 with AlMe 3 in refluxing toluene afforded the aluminum bis(phosphoranyl)methanediide complex [{(PPh 2 dNSiMe 3 )(PPh 2 dS)}CAlMe] 2 (6). The X-ray structure of 6 shows that a methanediide carbon is bonded to one aluminum atom. DFT calculations of 6 demonstrate that Al-C methanediide is highly polar with weak covalent bonding, consistent with the topological analysis of electron densities of 6.

show abstract

Aluminium compounds containing bidentate ligands: ligand base strength and remote geometric control over degree of association

Cited by 26 publications

References 35 publications

Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight

Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight

Ring-Opening Polymerization of Epoxides: Facile Pathway to Functional Polyethers via a Versatile Organoaluminum Initiator

Synthesis and Characterization of Magnesium and Aluminum Bis(phosphoranyl)methanediide Complexes

Contact Info

Product

Resources

About