One-pot conversion of tetraiminodiphenols to diiminodiaminodiphenols <i>via</i> methyl transfer at aluminium

Arbaoui, Abdessamad; Redshaw, Carl; Hughes, David L.

doi:10.1080/10610270802438846

Cited by 16 publications

(6 citation statements)

References 45 publications

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“…Treatment with either two or four equivalents of R 3 Al afforded the complexes 13-18 and 19-22, respectively (see Scheme 4) [13]. The structure of the compound 19 is shown in Figure 1, and reveals that, as for 5, intramolecular regioselective methyl transfer to two imine moieties (originating from the same dianiline) of the macrocycle has occurred; such methyl transfers are well established in imine chemistry [26][27][28][29][30]. The bonding in 19 is asymmetrical in that one of the aluminium centres is five-coordinate, whilst the other three are distorted tetrahedral.…”

Section: Organoaluminium Complexesmentioning

confidence: 99%

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Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

Redshaw

2017

Catalysts

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Schiff base macrocycles are emerging as useful scaffolds for binding two or more catalytic metals in close proximity. Such coordination chemistry allows for the evaluation of potentially beneficial catalytic cooperative effects. In the field of ring opening polymerization (ROP) of cyclic esters, only a handful of metal systems bound by Schiff base [2 + 2] type macrocycles have been studied. Nevertheless, results to date have, for certain metals, identified some interesting structure activity relationships, whilst for other systems results have revealed particular combinations of metals and macrocycles to be virtually inactive. This perspective review takes a look at two types of recently-reported Schiff base macrocycles that have been employed as pro-ligands in the metal-catalyzed ROP of cyclic esters, specifically ε-caprolactone and rac-lactide.

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Section: Organoaluminium Complexesmentioning

confidence: 99%

“…Furthermore, the systems 27 and 29 exhibit an induction period that, following a 15%-20% Scheme 7. Zinc complexes (27)(28)(29)(30)(31)(32).…”

Section: Use Of Iihmentioning

confidence: 99%

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

Redshaw

2017

Catalysts

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“…One of them leads directly to V with a barrier of only 12 kcal/mol ( TSIII-V ). The other is the reduction associated with the methyl group transfer, , prevented by the significantly higher barrier of ca. 26 kcal/mol ( TSIII-VI ), and yielding the Al-substituted amine species VI .…”

Section: Resultsmentioning

confidence: 99%

Impact of Organoaluminum Compounds on Phenoxyimine Ligands in Coordinative Olefin Polymerization. A Theoretical Study

2013

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The reduction of the phenoxyimine moiety in three individual speciesnamely free ligand, aluminum complex, and titanium complexwith aluminum alkyls and aluminum hydride has been studied by means of DFT. It was demonstrated that the free phenoxyimine ligand in an equimolar mixture with trimethylaluminum does not undergo reduction. Instead, experimentally observed formation of the six-membered cyclic aluminum−phenoxyimine complex, useful in the ring-opening polymerization of lactones, takes place as the kinetically and thermodynamically favored process. However, it is anticipated that a 2-fold excess of the aluminum compound, especially aluminum hydride, acting on the resulting cyclic complex can convert the imine to the aluminum-subsituted amine functionality easily with an energetic barrier of approximately 10 kcal/mol. Finally, the propensity of the imine moiety in the titanium-based precursor of the coordinative olefin polymerization toward reduction with organoaluminum compounds is revealed and the mechanism of this reaction is also suggested.

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“…0.2 Å is observed. The five-membered chelate rings display some variation in the degree of puckering between structures which is best exemplified by the C(7)-C( [45][46][47][48][49][50][51][52], and indeed computational studies suggest a radical pathway for the transformation [44]. The closest comparators to 1 are [2-{CMe2N(2,6-iPr2C6H3)}-6-(R)C5H3N]AlMe2 (R = i-Pr, t-Bu) which display similar bond parameters [45].…”

Section: Synthetic and Structural Aspectsmentioning

confidence: 99%

“…We have been attracted by the intriguing properties displayed by pyridylimine-containing ligands including their redox activity [43,44] and their capacity to undergo nucleophilic attack on the imine carbon [45][46][47][48][49][50] and the pyridine ring [51]. Indeed, the thermally-induced migration of an Al-alkyl to the imino carbon of a coordinated N,N-pyridylimine represents a powerful tool for transforming a pyridylimine into a pyridyl-alkylamide (and pyridyl-alkylamine on hydrolysis [45,52]).…”

Section: Introductionmentioning

confidence: 99%

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

et al. 2015

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Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a-1c reveal that complexation has resulted in concomitant C-C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp.

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One-pot conversion of tetraiminodiphenols to diiminodiaminodiphenols via methyl transfer at aluminium

Cited by 16 publications

References 45 publications

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

Impact of Organoaluminum Compounds on Phenoxyimine Ligands in Coordinative Olefin Polymerization. A Theoretical Study

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

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