A Robust, Environmentally Benign Catalyst for Highly Selective Hydroformylation

Sandee, Albertus J.; Veen, Lars A. van der; Reek, Joost N. H.; Kamer, Paul C. J.; Lutz, Martin; Spek, Anthony L.; Leeuwen, Piet W. N. M. van

doi:10.1002/(sici)1521-3773(19991102)38:21<3231::aid-anie3231>3.3.co;2-2

Cited by 45 publications

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“…As part of a broader effort to study the immobilization of transition metal catalysts,14–17 we were curious whether catalyst immobilization could be studied by fluorescence imaging. For this purpose we envisioned the class of xanthene‐based phosphorus ligands, also known as Xantphos, suitable for various reasons.…”

Section: Methodsmentioning

confidence: 99%

“…Metal complexes of these ligands have outstanding catalytic properties in various catalytic reactions (e.g., Rh‐catalyzed hydroformylation, Pd‐catalyzed cross‐coupling), and the ligands show facile coordination to various metals and are highly stable and easy to modify 18. 19 In addition, some members of the xantphos family, such as nixantphos ( 1 , see Scheme ) display strong fluorescence upon excitation and have previously been used for ligand immobilization 14–17. This led us to study the photophysical properties of 1 and particularly the possibility to use the immobilized ligand as a two‐photon excitation probe to study the immobilization process.…”

Section: Methodsmentioning

confidence: 99%

“…We anticipated that cluster formation was not occurring on the solid support (glass or silica) but is the result of a condensation reaction of the trialkoxysilane groups in solution, a process that also takes place during sol–gel synthesis 17. 18 To investigate this we performed immobilization experiments in which ligand 2 was covalently anchored on silica (particle size 200–400 μm; pore size 60 Å) by methods A and B22 and sampled the reaction solution over time.…”

Section: Methodsmentioning

confidence: 99%

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Phosphorus Ligand Imaging with Two‐Photon Fluorescence Spectroscopy: Towards Rational Catalyst Immobilization

et al. 2010

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Catalyst recovery is an important topic in homogeneous catalysis, since product/catalyst separation is one of the main obstacles towards application of this type of catalysis. So far, several strategies for catalyst recycling have been explored, but a general strategy remains elusive. [1][2][3] A widely studied approach to facilitate catalyst/product separation is attachment of homogeneous catalysts to soluble or insoluble supports, which can consist of organic polymers [4][5][6][7] or dendrimers, [8,9] inorganic materials, [10,11] or hybrids thereof. Inorganic materials have proved to be particularly suited as solid supports for homogeneous catalysts because of their physical strength and chemical inertness, and many such immobilized catalyst systems have been reported. Common drawbacks, however, are the generally lower activity and selectivity compared to the homogeneous counterpart. Surprisingly, however, an in-depth investigation of the effect of the immobilization process on the performance of the catalyst appears to be lacking. To gain more insight into immobilization of transition metal catalysts we set out to design a method for the detection of bis-phosphine ligands on surfaces. The ligand studied acts as a fluorescence probe, and detection is achieved by two-photon excitation fluorescence microscopy. In principle, this allows the immobilization product to be imaged with high spatial resolution (down to single molecules). Here we report the findings of the first study on the immobilization process employing an intrinsically fluorescent ligand imaged on a submicrometer level, which indicated that precondensation of ligands takes place prior to immobilization under the standard immobilization conditions, a conclusion supported by analysis of the liquid phase. These results directly translate to simple procedures that do not have these precondensation problems. The resulting immobilized catalysts show superior performance in hydroformylation catalysis, and open the way toward rational catalyst immobilization.Two-photon excitation (TPE) fluorescence microscopy has shown astonishing potential, but application has been mainly restricted to imaging biological samples.[12] Twophoton absorption (TPA) is a process in which two photons are absorbed simultaneously. Such a process only occurs at a very high flux of photons by focusing a pulsed near-infrared laser, thus restricting the excitation to a very small focal volume, with no appreciable off-focal fluorescence. Generally, the two-photon selection rule yields low background fluorescence, and hence high contrast in the images can be produced. [12,13] As part of a broader effort to study the immobilization of transition metal catalysts, [14][15][16][17] we were curious whether catalyst immobilization could be studied by fluorescence imaging. For this purpose we envisioned the class of xanthene-based phosphorus ligands, also known as Xantphos, suitable for various reasons. Metal complexes of these ligands have outstanding catalytic properties in various catalytic ...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Phosphorus Ligand Imaging with Two‐Photon Fluorescence Spectroscopy: Towards Rational Catalyst Immobilization

et al. 2010

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“…Another severe problem of coordinatively anchored catalysts is their limited stability towards metal leaching. However, the exceptional stability of a rhodium catalyst that had been immobilized on a silica support by a trans ‐chelating bidentate phosphane tether has recently been reported 4…”

Section: Methodsmentioning

confidence: 99%

Heterogeneous Dinuclear Rhodium(II) Hydroformylation Catalysts—Performance Evaluation and Silsesquioxane-Based Chemical Modeling

Nowotny

Maschmeyer

Johnson³

et al. 2001

Angew. Chem. Int. Ed.

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Supported, air stable, and reusable hydroformylation catalysts have been prepared by immobilizing dinuclear rhodium(II) complexes bearing ortho‐metalated arylphosphane ligands on amorphous silica and mesoporous MCM‐41 supports by phosphane tethers. The oligosilsesquioxane model complex of the catalytic site 1 has been prepared analogously and characterized by single‐crystal X‐ray diffraction analysis.

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“…This can cause significant metal leaching and has restricted their industrial application. Hence, we designed and synthesized the aza‐based ligand SiCH 11 NHP(O)(2‐py) 2 , with bidentate bis‐pyridyl functionality (py‐P‐py 105.5°),10 which could exhibit a large py‐M‐py bite angle when coordinated to metal centers and has the potential for greater catalyst stability and regioselectivity 1b, 11. As anticipated, homogeneous Pd II complexes were covalently immobilized by the ligating bis‐pyridyl groups to afford the soluble, polysiloxane‐supported Pd II complex 4 (Scheme ) with small specific surface areas (≈25 m 2 g −1 (BET(N 2 )).…”

Section: Methodsmentioning

confidence: 99%

Immobilization of Homogeneous Palladium(II) Complex Catalysts on Novel Polysiloxanes with Controllable Solubility: Important Implications for the Study of Heterogeneous Catalysis on Silica Surfaces

2001

Angew. Chem.

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Immobilization of homogeneous transition metal complex catalysts by tethering them to silica supports has been intensively studied during the past few decades. [1] These supported homogeneous transition metal complex catalysts should in principle combine the advantages of both heterogeneous and homogeneous systems. However, the problems of significant metal leaching [2] and low catalyst selectivity [1h, 3] are major drawbacks that prevent their potential use. Due to the insoluble nature of these supported catalysts, it has been difficult to obtain detailed information about the exact chemical structures of the catalyst systems and to estimate any loss of activity resulting from heterogenization. Therefore, a major development in this field would be the development of a method that would allow silica-supported homogeneous transition metal complexes and their reactions to be investigated by NMR spectroscopy with the resolution typically attained for soluble systems. [4] Here we describe the preparation and characterization of homogeneous Pd II complex catalysts tethered to a range of polysiloxanes. These materials were designed to mimic the surface of silica gel but with properties that are more readily controlled than those of silica gel. The molecular weight and degree of cross-linking can be systematically varied to provide catalyst systems ranging from soluble, homogeneous model compounds to heterogeneous three-dimensional networks. The structures and reaction chemistry of the soluble system were studied by NMR spectroscopy in solution, while the reactivity and regioselectivity were investigated in the catalytic [222] cyclotrimerization of alkynes.The incomplete acid-catalyzed hydrolysis [5] of (MeO) 3 -Si(CH 2 ) 11 N 3 (1) in THF generated silica fragments small enough to be soluble in conventional organic solvents. Subsequent silylation with trimethylsilyl chloride (TMSCl) was performed to end-cap the remaining Si-bound hydroxy groups to prevent further self-condensation of polysiloxanes (Scheme 1). The resulting polysiloxane 2 can then be readily derivatized with P(2-py) 3 (2-py 2-pyridyl) in situ or after isolation to afford polysiloxane 3 with NHP(O)(2-py) 2 functionality. [6] Polysiloxanes 2 and 3 with molecular weights around 5500 and polydispersity indexes of about 1.5 were thus obtained. [7] As expected, these polymers exhibited excellent

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A Robust, Environmentally Benign Catalyst for Highly Selective Hydroformylation

Cited by 45 publications

References 0 publications

Phosphorus Ligand Imaging with Two‐Photon Fluorescence Spectroscopy: Towards Rational Catalyst Immobilization

Phosphorus Ligand Imaging with Two‐Photon Fluorescence Spectroscopy: Towards Rational Catalyst Immobilization

Heterogeneous Dinuclear Rhodium(II) Hydroformylation Catalysts—Performance Evaluation and Silsesquioxane-Based Chemical Modeling

Immobilization of Homogeneous Palladium(II) Complex Catalysts on Novel Polysiloxanes with Controllable Solubility: Important Implications for the Study of Heterogeneous Catalysis on Silica Surfaces

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