Improved Rhodium Hydrogenation Catalysts Immobilized on Oxidic Supports

Merckle, C.; Blümel, Janet

doi:10.1002/adsc.200202197

Cited by 61 publications

(22 citation statements)

References 17 publications

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“…[15] Detachment of the metal fragment from the phosphine moieties [11,12] can be prevented by chelat-ing phosphines with ethoxysilane groups. [10,12,14] As we have demonstrated recently, catalyst deactivation by dimerization can also be inhibited by diluting the metal centers on the surface. [12,14] The surface-modified supports are amorphous materials, and thus cannot be characterized with conventional analytical methods other than IR.…”

Section: Introductionmentioning

confidence: 86%

“…[10,12,14] As we have demonstrated recently, catalyst deactivation by dimerization can also be inhibited by diluting the metal centers on the surface. [12,14] The surface-modified supports are amorphous materials, and thus cannot be characterized with conventional analytical methods other than IR. Nowadays, the method of choice to study the immobilized species is classical solid-state NMR, which we have optimized especially for the measurement of immobilized phosphines and molecular catalysts.…”

Section: Introductionmentioning

confidence: 86%

“…In this way, deactivation by dimerization [73] has, for example, successfully been curbed back in the case of Wilkinsontype Rh hydrogenation catalysts. [14] Although in the case of carbonylnickel catalysts the main decomposition mechanism is the loss of the metal fragment from the phosphine linker, the surface dilution also seems to play a role. [12] For example, if 18i is diluted to one fourth (about 4 metal centers per 100 nm 2 ) of the maximal surface density (16), a record TON of 7616 in one cycle with an excess of 22 can be obtained.…”

Section: Recycling Of the Immobilized Catalystsmentioning

confidence: 99%

“…This has been proved recently with Rh catalysts by using supports with different pore sizes. [14] However, this drawback is made up for by the easy separation of the catalyst from the reaction mixture by simply decanting the supernatant solution after the asc.wiley-vch.de catalytic run. Furthermore, the supernatant solution does not have to be filtered prior to its application to the GC column, as it has to be done for runs with homogeneous catalysts.…”

Section: Comparison Of Catalysts With Different Types Of Ligandsmentioning

confidence: 99%

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New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

Reinhard¹,

Šoba²,

Röminger³

et al. 2003

Adv Synth Catal

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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.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 86%

Section: Recycling Of the Immobilized Catalystsmentioning

confidence: 99%

Section: Comparison Of Catalysts With Different Types Of Ligandsmentioning

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

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“…Heterogeneous catalysis also helps to minimize wastes derived from reaction workup, contributing to the development of green chemical processes [23,24]. Supported rhodium catalysts have successfully been used for hydrogenation [25,26], hydroformylation [27][28][29], hydrosilylation [30,31], polymerization of aromatic acetylenes [32] and hydrothiolation of acetylenes [33]. Developments on the mesoporous material MCM-41 provided a new possible candidate for a solid support for immobilization of homogeneous catalysts [34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Diphosphino-Functionalized MCM-41-Immobilized Rhodium Complex: A Highly Efficient and Recyclable Catalyst for the Hydrophosphinylation of Terminal Alkynes

et al. 2012

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Diphosphino-functionalized MCM-41-immobilized rhodium complex (MCM-41-2P-RhCl 3 ) was conveniently synthesized from commercially available and cheap c-aminopropyltriethoxysilane via immobilization on mesoporous MCM-41, followed by reacting with diphenylphosphinomethanol and rhodium chloride. It was found that this heterogeneous rhodium complex is a highly efficient catalyst for the hydrophosphinylation of terminal alkynes with diphenylphosphine oxide and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 10 consecutive trials without any decreases in activity.

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Immobilization Techniques

Tth¹,

Geem²

2006

The Handbook of Homogeneous Hydrogenation

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Improved Rhodium Hydrogenation Catalysts Immobilized on Oxidic Supports

Cited by 61 publications

References 17 publications

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

New Silica‐Immobilized Nickel Catalysts for Cyclotrimerizations of Acetylenes

Diphosphino-Functionalized MCM-41-Immobilized Rhodium Complex: A Highly Efficient and Recyclable Catalyst for the Hydrophosphinylation of Terminal Alkynes

Immobilization Techniques

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