Noncovalently Functionalized Dendrimers as Recyclable Catalysts

Groot, Debby de; Waal, Bas F. M. de; Reek, Joost N. H.; Schenning, Albertus P. H. J.; Kramer, Patrick; Meijer, E. W.; Leeuwen, Piet W. N. M. van

doi:10.1021/ja005774u

Cited by 133 publications

(61 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Therefore it was characterized by an X-ray analysis (Figure 1 and ref. [62] ) and by solid-state NMR; 13 C CP/MAS NMR (TPPM decoupled, [19] 100. 6 The signals of the ipso-C nuclei have only low intensity.…”

Section: Synthesis Of the Nickel Complexes 10 ± 19mentioning

confidence: 99%

“…[3] Alternative recent strategies for improved removal of the catalysts from the reaction mixtures make use of biphasic fluorous systems, [4] microencapsulation of catalysts, [5] or non-covalently functionalized dendrimers. [6] The key feature of all these different approaches is to improve catalyst recovery and recycling. For some time our group, like others, [7,8] has pursued this idea by immobilizing homogeneous catalysts on oxidic inorganic supports.…”

Section: Introductionmentioning

confidence: 99%

“…, crystal system monoclinic, space group P2 1 /c, Z 4, a 8.6869(4) , b 24.5197 (11) , c 12.6866 (6) , a 908, b 109.101(1)8, g 908, V 2553.5(2) 3 , r1.452 g/cm 3 , T 200(2) K, 2V max 27.488, radiation Mo-Ka, l 0.71073 , 0.38 w-scans with CCD area detector, covering a whole sphere in reciprocal space, 26130 reflections measured, 5855 unique (R(int) 0.0331), 4821 observed (I > 2s(I)), intensities were corrected for Lorentz and polarization effects, an empirical absorption correction was applied using SA-DABS [66] based on the Laue symmetry of the reciprocal space, m 1.11 mm…”

mentioning

confidence: 99%

See 2 more Smart Citations

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

Reinhard¹,

Šoba²,

Röminger³

et al. 2003

Adv Synth Catal

View full text Add to dashboard Cite

New dicarbonylnickel catalysts with a variety of mono-and bidentate phosphine ligands, such as Ph 2 P(CH 2 ) x PPh(CH 2 ) y Si(OEt) 3 (x 2, 3; y 2, 3), have been synthesized and fully characterized, three of them by X-ray analyses. All the catalysts have been immobilized on silica by reaction of the ethoxysilane or hydroxy groups of the phosphine linkers with the surface silanol groups. The clean immobilization was proved by 31 P solid-state NMR. It has been demonstrated that the C À O À Si bridge, in contrast to the strong Si À O À Si bond, is easily cleaved by organic solvents and water. With respect to the cyclotrimerization of phenylacetylene the optimal reaction conditions for all molecular and immobilized catalysts have been determined. Cyclooctane was the best solvent, and the optimal reaction temperature was 100 8C for reactions in homogeneous phase, and 155 8C for surface-bound catalysts. The bite angles and spacer lengths of the chelating ligands did not play a major role for the performance of the homogeneous or immobilized catalysts. The latter could be recycled for 12 times, with final substrate conversions still typically between 30 and 40%, and turnover numbers (TON) around 1500. With an excess of substrate in one run a TON of 4810 was obtained for an immobilized carbonylnickel complex with a dppp-type chelate phosphine (x 3, y 2). Reduction of the surface coverage generally resulted in catalysts with longer lifetimes, for example, reduction to one fourth gave a record TON of 7616 for this catalyst. The selectivities of the catalysts all followed one trend. The main products were the cyclotrimers 1,2,4-and 1,3,5-triphenylbenzene, besides dimers, linear trimers and tetramers as side-products. The fraction of the latter decreased at higher temperatures with homogeneous catalysts, and vanished entirely after a few cycles with the immobilized catalysts. On recycling, the initial ratio of unsymmetrical to symmetrical cyclotrimers of typically 5 : 1 gradually changed to about 1 : 1 for all catalysts.

show abstract

Section: Synthesis Of the Nickel Complexes 10 ± 19mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

Reinhard¹,

Šoba²,

Röminger³

et al. 2003

Adv Synth Catal

View full text Add to dashboard Cite

show abstract

“…There are high aspirations 3,4 of chemists and physicists regarding applications of such novel polymers as advanced materials for medicinal 5 uses, superior catalysts 6,7 , and drug delivery vehicles 8 , to mention just a few. Importantly for such applications, dendrimers are quite flexible molecules, which have a well accessible interior part as well as a large exterior surface.…”

Section: Introductionmentioning

confidence: 99%

Conformations of dendrimers in dilute solution

Timoshenko

Kuznetsov

Connolly

2002

The Journal of Chemical Physics

View full text Add to dashboard Cite

Conformations of isolated homo-dendrimers of G = 1 − 7 generations with D = 1 − 6 spacers have been studied in the good and poor solvents, as well as across the coil-to-globule transition, by means of a version of the Gaussian self-consistent (GSC) method and Monte Carlo (MC) simulation in continuous space based on the same coarse-grained model. The latter includes harmonic springs between connected monomers and the pair-wise Lennard-Jones potential with a hard core repulsion. The scaling law for the dendrimer size, the degrees of bond stretching and steric congestion, as well as the radial density, static structure factor, and asphericity have been analysed. It is also confirmed that while smaller dendrimers have a dense core, larger ones develop a hollow domain at some separation from the centre.PACS numbers: 36.20.Ey, 61.25.Hq

show abstract

“…Therefore, molecular-weight enlargement of the respective transition metal complexes with an appropriate soluble carrier is needed. A wide variety of soluble supports, e.g., linear or dendrimeric polymers, [26] has been introduced to transition metal complexes through different strategies, e.g., covalent or non-covalent bonding, cluster, or colloid formation [27][28][29] ; in some cases their perfomance was even demonstrated and analyzed in continuously operated membrane reactors. [30][31][32][33][34][35][36][37][38][39] Among the different classes of supports, star-shaped polymers are remarkable candidates.…”

Section: Introductionmentioning

confidence: 99%

Continuous Application of Polyglycerol‐Supported Salen in a Membrane Reactor: Asymmetric Epoxidation of 6‐Cyano‐2,2‐dimethylchromene

Beigi¹,

Haag²,

Liese³

2008

Adv Synth Catal

View full text Add to dashboard Cite

In the current work, suitability of hyperbranched polyglycerol as a high loading catalyst support is demonstrated. A polyglycerol-supported manganese-salen complex (chemzyme) is applied as a homogeneous catalyst in the epoxidation of 6-cyano-2,2-dimethylchromene. The recyclability of the corresponding catalyst was investigated in repetitive batch experiments as well as a continuous operation of the reaction in an ultrafiltration membrane reactor. An enhanced stability of the catalyst in repetitive batches was observed as a result of immobilization whereby the total turnover number increased from 23 in a single batch to 80 in four repetitive batches. To enable continuous operation, a continuously operated, stirred tanked reactor (CSTR) was equipped with an ultrafiltration membrane (MPF-50) and a retention of 98% was determined. The continuous chemzyme membrane reactor was operated over the course of 20 residence times. After approximately 12 residence times, the steady state was reached yielding 70% conversion as well as an enantiomeric excess up to 92%. A space-time yield (sty) of 458 g L À1 d À1 and a turnover frequency (TOF reaction ) of up to 18 h À1 was reached in the steady state. It was determined that the total turnover number (TTN) was enhanced by a factor of 10 from 24 (batch) up to 240 for 20 residence times in CSTR operation.

show abstract

Noncovalently Functionalized Dendrimers as Recyclable Catalysts

Cited by 133 publications

References 23 publications

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

Conformations of dendrimers in dilute solution

Continuous Application of Polyglycerol‐Supported Salen in a Membrane Reactor: Asymmetric Epoxidation of 6‐Cyano‐2,2‐dimethylchromene

Contact Info

Product

Resources

About