Five-Coordinate, Solvent-Free Aluminum Cations

Muñoz‐Hernández, Miguel‐Ángel; Sannigrahi, Biswajit; Atwood, David A.

doi:10.1021/ja990376g

Cited by 48 publications

(33 citation statements)

References 12 publications

(11 reference statements)

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“…The steric balance also plays an important role in stabilizing 2−7, as others typically observe a dimerization upon halide abstraction, for example, Atwood's synthesis of aluminum salpen and salophen dications. 26 Herein, the outer-sphere oxygen of the morpholine coordinates to aluminum and the tert-butyl groups are sufficiently bulky, thus preventing dimerization from occurring. In our structures, the bond lengths and angles are similar to each other, as expected, and are in the range typical for Al−phenolate and Al−amino complexes.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

2019

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The first structures exhibiting bidentate (N, O) chelation of a morpholine group to a p-block element (aluminum) have been prepared and characterized by X-ray diffraction methods: Al[L] + [WCA] − , where [L] = 4-(2aminoethyl)morpholinylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate) and [WCA] − is a weakly coordinating anion. These compounds are easily synthesized by reacting Al[L]Cl with an equimolar amount of anhydrous Lewis acid and were characterized by elemental analyses, ESI−MS, MALDI−TOF MS, 1 H, 13 C{ 1 H}, and multinuclear NMR spectroscopy. DFT calculations showed that Al[L] + cations containing bidentate NO coordination of the morpholine group are at least 21.1 kJ/mol more stable when compared to hypothetical monodentate (N bound) structures. When combined with protic co-initiators (EtOH, glycerol carbonate), the cationic complexes, where [WCA] − = [GaCl 4 ] − or [InCl 4 ] − , are living catalyst systems for the polymerization of ε-caprolactone, producing polycaprolactone with narrow dispersity (D̵ = 1.00−1.05). Employing glycidol as a co-initiator furnished polymers with narrow dispersity (D̵ = 1.01−1.07) but experimental molecular weights diverged considerably from the calculated values. Similar reactivity toward ROP was observed for all complexes containing a stable [WCA] − but where [WCA] − = [AlCl 4 ] − , upon combination with alcohols, alcoholysis was observed. Kinetic studies (Eyring analyses) allowed the determination of activation parameters, which were consistent with a coordination−insertion mechanism for the catalysts containing [WCA] − = [GaCl 4 ] − or [InCl 4 ] − . End group analyses using MALDI−TOF mass spectrometry and 1 H NMR spectroscopy showed hydroxyl and ester end groups within the polymer, corroborating the proposed mechanism. Stoichiometric reactions of EtOH, glycidol or tert-butyl alcohol with the complex, where [WCA] − = [GaCl 4 ] − , showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

2019

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“…t Bu)Al} 2 ] 2ϩ [GaCl 4 Ϫ ] 2 , features four t Bu resonances 15. There is only one imine resonance for 1 (δ 8.06) in keeping with the symmetric geometry.…”

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confidence: 96%

Six-coordinate aluminium cations: characterization, catalysis, and theory

Muñoz‐Hernández

McKee

Keizer

et al. 2002

J. Chem. Soc., Dalton Trans.

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“…For ligands containing both oxygen and nitrogen as potential bridging atoms, it is found that compounds having oxygen bridges between aluminium atoms [23,24,39,[47][48][49][50] predominate over those with nitrogen bridges. [37,51] Examples are known with both O and N atoms bridging in hydroxypyridine ligands (in an isolobal disposition to carboxylatebridged ligands) [25] or with an amidate group [52][53][54][55] between two aluminium atoms.…”

Section: Resultsmentioning

confidence: 99%

“…This structural behaviour contrasts with that found in the literature: O-bridging structures are generally observed in polynuclear aluminium derivatives supported by bridging phenoxido-imino and related ligands. [22,25,39,40] …”

Section: Introductionmentioning

confidence: 99%

An Unusual N‐Bridged (Amido)(hydrido)(phenoxido)aluminium Dinuclear Compound – The Role of Nitrogen Substituents in Determining Nuclearity: A Combined Experimental and Theoretical Study

et al. 2010

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The iminophenol 3,5‐tBu2‐2‐(OH)C6H2CH=NR and theaminophenol 3,5‐tBu2‐2‐(OH)C6H2CH2‐NHR (R = tBu, 2,6‐Me2C6H3, C6F5) were prepared in good yields by the appropriate synthetic methods. Reactions of these compounds with AlH3·NEtMe2 in toluene gave the mononuclear [AlH{3,5‐tBu2‐2‐(O)C6H2CH2‐NR}·NEtMe2] [R = 2,6‐Me2C6H3 (3), C6F5 (4)] or dinuclear [AlH{μ‐3,5‐tBu2‐2‐(O)C6H2CH2‐NtBu}]2 (5) phenoxido–amido aluminium derivatives. All synthesized complexes were characterized by NMR spectroscopic and analytical methods. The X‐ray structure of 5 shows a dinuclear molecule in which the aluminium centres are unusually linked by μ2‐N(amido) atoms to form a central planar Al2N2 ring in a clearly preferential disposition over the more common Al2O2 ring. The experimental work has been assisted by the B3LYP functional and the 6‐31G* basis sets as implemented in Gaussian 03 calculations to determine the role played by the nitrogen substituent group in the structural disposition adopted by the prepared (monohydrido)aluminium compounds, in order to evaluate the factors affecting the coordination modes of the phenoxido–amido ligand on aluminium.

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Five-Coordinate, Solvent-Free Aluminum Cations

Cited by 48 publications

References 12 publications

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

Six-coordinate aluminium cations: characterization, catalysis, and theory

An Unusual N‐Bridged (Amido)(hydrido)(phenoxido)aluminium Dinuclear Compound – The Role of Nitrogen Substituents in Determining Nuclearity: A Combined Experimental and Theoretical Study

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