Aluminium Complexes of a Phenoxyimine Ligand with a Pendant Imidazolium Moiety: Synthesis, Characterisation and Evidence for Hydrogen Bonding in Solution

Milione, Stefano; Grisi, Fabia; Centore, Roberto; Tuzi, Angela

doi:10.1002/ejic.200800742

Cited by 4 publications

(6 citation statements)

References 34 publications

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“…The IR spectra contained a relatively strong v (C=N) band at approximately 1628 cm –1 , whilst in the 1 H NMR spectrum, the chemical shift of OH typically appeared at δ = 13.68 ppm. The proligands L 1 H and L 4 H have been previously reported , . Crystals suitable for single‐crystal X‐ray diffraction of L 3 H(dpa), obtained by the use of benzhydrylamine (or diphenylamine, dpa), were grown from a saturated acetonitrile solution at ambient temperature.…”

Section: Resultsmentioning

confidence: 99%

“…Reaction with 1.1 equivalents of Me 3 Al with the parent Schiff bases in toluene heated at reflux afforded, after work‐up, moderate to good yields (55–97 %) of the complexes [R 1 R 2 CHN=CH(3,5‐ t Bu 2 C 6 H 2 ‐ O ‐2)AlR 3 2 ] (R 1 = R 2 = R 3 = Me 1 ; R 1 = R 2 = R 3 = Et 2 ; R 1 = R 3 = Me, R 2 = Ph 3 ; R 1 = Me, R 2 = Ph, R 3 = Et 4 ; R 1 = R 2 = Ph, R 3 = Me 5 ; R 1 = R 2 = Ph, R 3 = Et 6 ), see Scheme . Complex 1 was previously reported by Milione et al and used for halide anion binding through hydrogen‐bonding, whereas the debutylated version of complex 5 has recently been employed by Chiang, Chen and Chen and co‐workers for the ROP of ε‐caprolactone (ε‐CL) and l ‐lactide; however, the structure of debutylated 5 was not reported. [6v] Herein, crystals of 5 suitable for an X‐ray diffraction study were grown from acetonitrile on prolonged standing at ambient temperature.…”

Section: Resultsmentioning

confidence: 99%

“…The precursor 1‐NH 2 ,2‐PPh 2 C 6 H 4 was prepared by the literature method . Proligands L 1 H and L 4 H and complexes 1 and 7 were prepared as described previously , …”

Section: Methodsmentioning

confidence: 99%

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Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

et al. 2017

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Reaction of R 1 R 2 CHN=CH(3,5-tBu 2 C 6 H 2 -OH-2) (R 1 = R 2 = Me L 1 H; R 1 = Me, R 2 = Ph L 2 H; R 1 = R 2 = Ph L 3 H) with slightly greater than one equivalent of R 3 3 Al (R 3 = Me, Et) afforded the complexes [(L 1-3 )AlR 3 2 ] (L 1 , R 3 = Me 1, R 3 = Et 2; L 2 , R 3 = Me 3, R 3 = Et 4; L 3 R 3 = Me 5, R 3 = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph 2 NCH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (7). The known Schiff base complex [2-Ph 2 PC 6 H 4 CH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH 2 ,2-PPh 2 C 6 H 4 with Me 3 Al, namely {Ph 2 PC 6 H 4 N[(Me 2 Al) 2 μ-Me]-(μ-Me 2 Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me 3 Al with diphenylamine (or benzhydrylamine), namely {Ph 2 N[(Me 2 Al) 2 μ-Me]} (10) and [Ph 2 CHNH(μ-Me 2 Al)] 2 ·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph 2 CHNH 2 and 2,2′-Ph 2 C(CO 2 H)(NH 2 ), together with those of complexes 5, 7 and 9-11·MeCN were determined; 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the [a] Scheme 1. Compounds (proligands) employed herein. Scheme 2. Complexes studied herein.1952 tBu 2 C 6 H 2 -O-2)AlR 3 2 ] (R 1 = R 2 = R 3 = Me 1; R 1 = R 2 = R 3 = Et 2; R 1 = R 3 = Me, R 2 = Ph 3; R 1 = Me, R 2 = Ph, R 3 = Et 4; R 1 = R 2 = Ph, R 3 = Me 5; R 1 = R 2 = Ph, R 3 = Et 6) and compare their behaviour against organoaluminium complexes derived from the amine component only (i.e., minus the phenoxy-containing 3,5-di-tert-butylsalicyl motif, see Schemes 1 and 2). We note that Nomura and colleagues have previously investigated the effect of the imino substituent on the ROP of ε-caprolactone (CL) and observed greatly enhanced activity for aryl substituents (C 6 F 5 , 2,6-iPr 2 C 6 H 3 ) versus aliphatic substituents (adamantyl, tert-butyl). [7] Herein, we initially targeted diphenylglycine (dpg) and derivatives thereof given the tendency of related motifs to form highly crystalline products. [9] However, the loss of CO 2 during the formation L 3 H(dpg), see discussion below, led us to explore the family of proligands with both aliphatic and aromatic substituents bound to the N-bound CH group.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

et al. 2017

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“…reacted the same phenoxyimino functionalised imidazolium salt with trialkyl alanes in an attempt to form the corresponding carbene complex of aluminium(III) [ 71 ] (see Figure 4.19 ). reacted the same phenoxyimino functionalised imidazolium salt with trialkyl alanes in an attempt to form the corresponding carbene complex of aluminium(III) [ 71 ] (see Figure 4.19 ).…”

Section: Note : Functionalisation Of a Carbene With A Hydroxy Group Omentioning

confidence: 99%

“…16 VE complex, nothing out of the ordinary. Abstraction of chloride from this complex, with AgPF 6 , results in the cationic, square planar 14 VE rhodium(III) complex shown at the bottom ofFigure 4.71 .Note :The square planar, cationic 14 VE rhodium(III) carbene complex inFigure 4.71 is supported and made possible by the strongly π -donating NHC ligands 71. This agostic interaction is thought to result in a proper C -H activation with loss of molecular hydrogen and formation of a distorted square pyramidal 16 VE complex without Rh -H groups.…”

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N‐Heterocyclic Carbenes with Anionic Functional Groups

Kühl

2010

Functionalised N‐Heterocyclic Carbene Complexes

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We have already seen that many functionalised NHC ligands are modelled on previously known functionalised phosphanes. In the case of an oxygen -containing functional group where the oxygen atom can carry a (formal) negative charge, we can expect functionalised NHC ligands that resemble phosphinophenols [ 1 , 2 ], phosphinoalcohols [ 3 -5 ] or phosphino carboxylic acids [ 6 ]. All these functionalised phosphane groups were employed as ligands in catalytic reactions.The rationale behind the concept of NHC ligands carrying anionic oxygen functional groups goes beyond the application in catalysis. NHC ligands do not bond strongly to the early transition metals [ 7 ] or alkaline earth metals [ 8 ]. However, both these groups of metals bind strongly to alkoxides or aryloxides. It is therefore reasonable to design functionalised NHC ligands with a view to an oxygen (nitrogen) based anchor group in addition to the somewhat loosely binding carbene unit. This results in the formation of a hemilabile chelate ligand [ 9 ].Conversely, NHC bind strongly to the late transition metals (group 9 and group 10), metals that have only a low affi nity to oxygen. Here, the oxygen -containing functional group serves as the hemilabile ligand [ 10 ]. We will therefore see a great versatility in the anionic tether and in the range of (transition) metal employed.Thiel and coworkers reacted imidazole with epoxycyclohexane to form the racemic hydroxycyclohexyl imidazole. Attempts to separate the enantiomers by kinetic resolution with lipase B of Candida antarctica and isopropenyl acetate as acylating agent [ 11 , 12 ] failed, but gave the racemic ester in high yields (see Figure 4.1 ). Alkylation was then Functionalised N-Heterocyclic Carbene ComplexesOlaf Kühl

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