A Calix[4]arene Monoalkyl Ether as a Model of a Tris(phenolate) Ligand with a Hemilabile Anisole Moiety: Syntheses, Molecular Structures and Bonding of Calix[4]arene Ether Supported Titanium Complexes and Their Catalytic Activity in Epoxidation Reactions

Friedrich, Andreas; Radius, Udo

doi:10.1002/ejic.200400430

Cited by 28 publications

(34 citation statements)

References 102 publications

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“…The strongest resonances correspond to 13 C labeled methoxy lower-rim substituents. Resonances between 20-40 ppm arise due to upper-rim tert-butyl substituents, which are not isotopically enriched shorter Ti-OCH 3 bond distances in the di-R-Ti complex relative to mono-R-Ti, consistent with previously reported single-crystal X-ray diffraction data, in which Ti-OCH 3 bond distances were measured for mono-C 1 -Ti and di-C 1 -Ti at 2.4 [22] and 2.1 Å [24], respectively. These distances suggest stronger dative methoxy coordination to the Ti Lewis acid site in di-C 1 -Ti compared to mono-C 1 -Ti and support the observed downfield shift in the grafted sites described above.…”

Section: Physicochemical Characterization Of Titanocalixarene Graftinsupporting

confidence: 80%

“…Enrichment at this position is evidenced by 1 H solution-phase NMR spectroscopy, showing a doublet for O-CH 3 with very strong coupling ( 1 J = 144-145 Hz), due to direct coupling with the 13 C nucleus. In contrast, a singlet is observed at this position for a regular 12 C nucleus due to the absence of coupling [22], [24]. As shown in Fig.…”

Section: Physicochemical Characterization Of Titanocalixarene Graftinmentioning

confidence: 95%

“…The main difference between the synthesized titanocalixarenes was dictated by ligand coordination of mono-R versus di-R ligands (see Scheme 1, where R = alkyl chain). Mono-C 1 -Ti has been previously synthesized, characterized [22], grafted, and studied for alkene epoxidation [15][16][17]; it is stable when grafted, has C s symmetry, displays one weak methoxy oxygen-Ti dative interaction, and is an active epoxidation catalyst. The di-C 1 -Ti complex has been synthesized [23,24], but to our knowledge it has never been grafted on a surface or tested in olefin epoxidation.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

et al. 2016

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The effect of calixarene ligand symmetry, as dictated by lower-rim substitution pattern, on the coordination to a Ti(IV) cation is assessed in solution and when grafted on SiO 2 , and its effect on epoxidation catalysis by Ti(IV)-calixarene grafted on SiO 2 is investigated. C 2v symmetric Ti-tert-butylcalix[4]arene complexes that are 1,3-alkyl disubstituted at the lower rim (di-R-Ti) are compared to previously reported grafted C s symmetric complexes, which are singly substituted at the lower rim (mono-R-Ti). 13 C MAS NMR spectra of complexes isotopically enriched at the lower-rim alkyl position indicate that di-R-Ti predominantly grafts onto silica as the conformation found in solution, exhibiting a deshielded alkyl resonance compared to the grafted mono-R-Ti complexes, which is consistent with stronger alkyl ether?Ti dative interactions that are hypothesized to result in higher electron density at the Ti center. Moreover, 13 C MAS NMR spectroscopy detects an additional contribution from an ''endo'' conformer for grafted di-R-Ti sites, which is not observed in solution. Based on prior molecular modeling studies and on 13 C MAS NMR spectroscopy chemical shifts, this ''endo'' conformer is proposed to have similar Ti-(alkyl ether) distances at the lower-rim and electron density at the Ti center relative to grafted mono-R-Ti complexes. Differences between grafted mono-R-Ti and di-R-Ti sites can be observed by ligand-to-metal charge transfer edge-energies, calculated from diffuse-reflectance UV-visible spectroscopy at 2.24 ± 0.02 and 2.16 ± 0.02 eV, respectively. However, rates of tert-butyl hydroperoxide consumption in the epoxidation of 1-octene are found to be largely unchanged when compared to those of the grafted mono-R-Ti complexes, with average rate constants of *1.5 M -2 s -1 and initial TOF of *4 ks -1 at 323 K. This suggests that an ''endo'' conformation of grafted di-R-Ti may prevail during catalysis. Despite this, grafted di-C 1 -Ti complexes can be more selective than mono-C 1 -Ti complexes (45 vs. 34 % at a 50 % conversion at 338 and 353 K), illustrating the importance of the Ti coordination environment on epoxidation catalysis.

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Section: Physicochemical Characterization Of Titanocalixarene Graftinsupporting

confidence: 80%

Section: Physicochemical Characterization Of Titanocalixarene Graftinmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

et al. 2016

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“…Of particular interest in this study, another amido reagent, the thermally highly stable lithium diphenylamide (LiNPh 2 ), has shown promise in a range of synthetic transformations. As well as regioselective deprotonation reactions, [6][7][8][9][10] it has also been used in catalytic aldol reactions involving silyl enol ethers and aldehydes; [11,12] in elimination applications; [13,14] in metathetical reactions; [15][16][17][18][19][20][21][22][23][24][25][26][27] during the preparation of amino-containing carbenes, [28] and as an initiator in the polymerisation of methyl methacrylate. [29] utilised as the metallating agent.…”

Section: Introductionmentioning

confidence: 99%

Structural Elucidation of tmeda‐Solvated Alkali Metal Diphenylamide Complexes

et al. 2009

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Lithium, sodium and potassium salts of diphenylamine have been prepared by using a deprotonative route and characterised in both, solid state (by X‐ray crystallography) and solution (by NMR spectroscopic studies). In each case the metal atom's coordination sphere is completed by coordination to the synthetically important co‐ligand N,N,N′,N′‐tetramethylethylenediamine (tmeda). Complexes 1 and 2 [{(tmeda)M(NPh2)}2] (M = Li for 1, Na for 2) can be prepared by treating 1 mol.‐equiv. of the parent amine with an equimolar quantity of nBuM and tmeda in hexane solution. In the solid state, 1 and 2 are essentially isostructural, being dimeric with a four‐atom M–N–M–N framework. The coordination sphere of each M atom is completed by a bidentate tmeda molecule. Complex 3 [{(tmeda)3/2K(NPh2)}2] has been prepared in a similar way to 1 and 2 except that benzylpotassium has been utilised as the metallating agent. In addition, 4 mol‐equiv. of tmeda is required to fully solubilise the heavy alkali metal amide mixture. In the solid state, 3 exists as a polymeric array of dinuclear K–N–K–N rings. Akin to 1 and 2, the K atom is coordinated to a bidentate tmeda molecule; however, each K atom is also bound to another tmeda molecule that acts as a monodentate bridge, thus producing the coordination polymer. Crystalline 1 and 2 are soluble in C6D6; hence, NMR spectroscopic studies could be performed. These show that the solid‐state structure appears to stay intact in arene solution. On the other hand, 3 is not soluble in C6D6; so solution studies have been performed in [D8]thf. These studies reveal that 3 readily looses tmeda during in‐vacuo isolation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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“…[9] Bis(phenolate) compounds with para-substituted phenolate ligands have been isolated in good to excellent yields from reaction of the imidotitanium complex [Ti(NtBu)(Me 2 Calix)] and two equivalents of the corresponding phenol to afford complexes in which the calix [4]arene is coordinated in an elliptically distorted cone conformation. These complexes undergo elimination and/or rearrangement reactions in non- In titanium complexes of the type [TiX(MeCalix)] (X = Cl, OR, SR, NR 2 ) [10] the calix [4]arene ligand adopts an elliptically distorted cone conformation in which the Ti-O distances to the anisole oxygen atoms vary in the solid-state structures in a range between 234.2 and 243.8 pm.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Molecular Structure and Reactivity of a Calix[4]arene Monomethyl Ether Supported Nitridomolybdenum Complex

et al. 2005

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The calix[4]arene monomethyl ether supported nitridomolybdenum complex [MoN(MeCalix)] (1) was obtained in high yield from the reaction of [MoN(OtBu)3] and calix[4]arene methyl ether (H3MeCalix). Contrary to the calix[4]arene dimethyl ether supported dioxomolybdenum complex [MoO2(paco‐Me2Calix)] published earlier, the calix[4]arene ligand in 1 adopts a cone conformation. Complex 1 reacts smoothly with GaCl3 and GaEt3 to yield the compounds [Mo(NGaCl3)(MeCalix)] (2) and [Mo(NGaEt3)(MeCalix)] (3), respectively. Complex 2 is the first structurally characterized example of a nitrido‐bridged dinuclear compound of a group 6 metal and a group 13 halide (EX3). The [Mo≡N–GaCl3] unit, in which both metal atoms are unsymmetrically bridged with a short Mo≡N and a long Ga–N contact, shows significant bending at the nitrido bridge. This deviation from a linear alignment is attributed to packing forces. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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A Calix[4]arene Monoalkyl Ether as a Model of a Tris(phenolate) Ligand with a Hemilabile Anisole Moiety: Syntheses, Molecular Structures and Bonding of Calix[4]arene Ether Supported Titanium Complexes and Their Catalytic Activity in Epoxidation Reactions

Cited by 28 publications

References 102 publications

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

Structural Elucidation of tmeda‐Solvated Alkali Metal Diphenylamide Complexes

Synthesis, Molecular Structure and Reactivity of a Calix[4]arene Monomethyl Ether Supported Nitridomolybdenum Complex

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