Immobilization of Carbonylnickel Complexes:  A Solid-State NMR Study

Behringer, Klaus D.; Blümel, Janet

doi:10.1021/ic950756c

Cited by 37 publications

(26 citation statements)

References 30 publications

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“…The ligands 1 to 3 have been synthesized in high yields as described previously, [9,17] as well as the phosphines 4 ± 9 in yields of 89 ± 93%. [10] They have been fully characterized by the usual analytical methods, and the NMR signal assignments are based upon former results, [9,10,13,17] and 13 …”

Section: Synthesis Of the Phosphine Ligandsmentioning

confidence: 99%

“…Only the complexes 10, [9] 12, [9] and 16 [10] have been described previously. Data for the new systems are given in the Experimental Section.…”

Section: Synthesis Of the Nickel Catalystsmentioning

confidence: 99%

“…[19,59] A more detailed overview of diamagnetic versus paramagnetic Ni(II) diphosphine complexes has been given by Booth. [60] All the other diamagnetic nickel complexes have been fully characterized by the usual analytical methods, and the NMR signal assignments are based upon former results, [9,10,13,17] comparisons with values from the literature [61] and 13 …”

Section: Nmr Properties Of the Nickel Complexesmentioning

confidence: 99%

“…The compounds 1 ± 3, [9,17] and 4, 5 [10] have been synthesized and characterized as described previously.…”

Section: Experimental Section General Remarksmentioning

confidence: 99%

“…[9±14] Since the tethering is achieved by bifunctional linkers such as Ph 2 P(CH 2 ) 3 Si(OEt) 3 (1), [9] the homogeneous character of the catalysts should be retained, while the solid support allows the easy separation of the catalyst by decanting the supernatant reaction mixture. Thus, ideally, the advantages of homogeneous and heterogeneous catalysts should be combined.…”

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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Section: Synthesis Of the Phosphine Ligandsmentioning

confidence: 99%

“…Only the complexes 10, [9] 12, [9] and 16 [10] have been described previously. Data for the new systems are given in the Experimental Section.…”

Section: Synthesis Of the Nickel Catalystsmentioning

confidence: 99%

Section: Nmr Properties Of the Nickel Complexesmentioning

confidence: 99%

“…The compounds 1 ± 3, [9,17] and 4, 5 [10] have been synthesized and characterized as described previously.…”

Section: Experimental Section General Remarksmentioning

confidence: 99%

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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Immobilization – Homogeneous

Tóth

Geem

2002

Encyclopedia of Catalysis

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Supported or immobilized homogeneous catalysts combine the merit of easy separation of a heterogeneous catalyst with the uniform active sites and high performance of the homogeneous analogue. In ideal cases, these hybrid catalysts can provide higher selectivity/activity than that of the homogeneous counterparts because of synergetic effects with the support material or reluctance of the supported metal complexes to undergo undesirable dimerization or cluster formation. The immobilization of homogeneous catalyst to a chosen inorganic or polymer support can be achieved with various methods, which are reviewed and evaluated in this article. Thus, entries are made for physically attached catalysts, which are obtained by adsorbing metal complexes or their solutions (supported liquid‐phase) to solids, and by encapsulating or by entangling homogeneous catalysts to microporous solids or in polymers, respectively. Chemically attached catalysts are classified by the nature of binding to the support, ie, covalent or ionic binding of metal centers and/or ligands to supports. Furthermore, support materials and site isolation are also addressed in the article. Although the type of reaction with immobilized catalysts was not the basis for the overview, numerous examples are given for specific applications.

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