Immobilized nickel catalysts for cyclotrimerizations of acetylenes: enhancement of activities, stabilities, and lifetimes

Reinhard, S.; Behringer, Klaus D.; Blümel, Janet

doi:10.1039/b300677h

Cited by 29 publications

(49 citation statements)

References 15 publications

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“…[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: 89%

“…[12] But even within this group there are marked differences. While, for example, catalyst 10 gives quantitative conversion of the substrate after 3 h at 100 8C in cyclooctane, under otherwise the same reaction conditions in decane even after 3 days the conversion is lower than 10%.…”

Section: Improvement Of Catalysis Conditions In Homogeneous and Hetermentioning

confidence: 96%

“…[17] Importantly, in the case of the nickel compound, no uncomplexed phosphine can be detected on the surface. [12] Recently the formation of EtOH layers on silica surfaces in cyclohexane has been investigated. [69] The reaction of alcohols with silica has already been described by Iler [70] and one of us.…”

Section: Crystal Structures Of the Nickel Complexesmentioning

confidence: 99%

“…[16,18] As soon as there is one covalent Si-O-Si bond established, the linker is irreversibly bound. [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.…”

Section: Introductionmentioning

confidence: 99%

“…[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: 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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