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Paul C. J. Kamer - One of the best experts on this subject based on the ideXlab platform.
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P-stereogenic wide Bite Angle diphosphine ligands
Tetrahedron, 2019Co-Authors: Christine Fee Czauderna, Alexandra M. Z. Slawin, David B. Cordes, Jarl Ivar Van Der Vlugt, Paul C. J. KamerAbstract:Abstract Two modular synthetic approaches for the preparation of novel wide Bite Angle diphosphine ligands containing stereogenic P-atoms have been developed, leading to compounds (S,S)-2,2′-bis(methylphenylphosphino)diphenyl ether (L1) and (S,S)-2,2′-bis(ferrocenylphenylphosphino)diphenyl ether (L2) in very good diastereomeric ratios. Both protocols involve diphenyl ether as backbone and (2RP,4SC,5RC)-(+)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine borane (RP)-5 as initial auxiliary to induce chirality at phosphorus. The absolute configuration of intermediates (S,S)-9-(BH3)2 and (R,R)-10-(BH3)2 as well as the ligands (S,S)-L1-BH3 and (S,S)-L2 was determined by X-ray crystallographic analysis.
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electronic and Bite Angle effects in catalytic c o bond cleavage of a lignin model compound using ruthenium xantphos complexes
Catalysis Science & Technology, 2017Co-Authors: Luke Shaw, D. M. Upulani K. Somisara, Rebecca C. How, Nicholas J. Westwood, Pieter C. A. Bruijnincx, Bert M. Weckhuysen, Paul C. J. KamerAbstract:Bite Angle and electronic effects on the ruthenium–diphosphine catalysed ether bond cleavage of the lignin β-O-4 model compound 2-phenoxy-1-phenylethanol were tested. Enhanced conversion of the substrate was observed with increasing σ-donor capacity of the ligands. Kinetic and thermodynamic data suggest oxidative addition of the dehydrogenated model compound to the diphosphine Ru(0) complex to be rate-limiting.
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Electronic and Bite Angle effects in catalytic C–O bond cleavage of a lignin model compound using ruthenium Xantphos complexes
Catalysis Science & Technology, 2017Co-Authors: Luke Shaw, D. M. Upulani K. Somisara, Rebecca C. How, Nicholas J. Westwood, Pieter C. A. Bruijnincx, Bert M. Weckhuysen, Paul C. J. KamerAbstract:Bite Angle and electronic effects on the ruthenium–diphosphine catalysed ether bond cleavage of the lignin β-O-4 model compound 2-phenoxy-1-phenylethanol were tested. Enhanced conversion of the substrate was observed with increasing σ-donor capacity of the ligands. Kinetic and thermodynamic data suggest oxidative addition of the dehydrogenated model compound to the diphosphine Ru(0) complex to be rate-limiting.
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synthesis and reactivity of chiral wide Bite Angle hybrid diphosphorus ligands
European Journal of Inorganic Chemistry, 2014Co-Authors: Christine Fee Czauderna, Alexandra M. Z. Slawin, David B. Cordes, Christian Müller, Dieter Vogt, Jarl Ivar Van Der Vlugt, Paul C. J. KamerAbstract:Effective and modular synthetic approaches toward phosphine-phosphite ligands and phosphine-phosphonite ligands featuring a diphenyl ether backbone have been developed. The phosphine-phosphite ligands are obtained by a two-step protocol from 2-bromo-2-methoxydiphenyl ether. The phosphine-phosphonite ligands are prepared in a four-step synthetic protocol that involves a novel, unsymmetrical diphenyl ether derived phosphine-phosphorusdiamide as key building block. Structural studies on Pt-II complexes with either phosphine-phosphite or phosphine-phosphonite ligands indicate strict cis coordination for these ligand systems. High-pressure NMR spectroscopy studies of Rh complexes under syngas indicate the presence of two ea isomers for Rh(H)(CO)(2)(PP). The existence of this mixture is further supported by high-pressure IR spectroscopy studies. In order to benchmark the activity and selectivity of these novel, wide-Bite-Angle, mixed-donor ligands, they were screened in Pd-catalyzed asymmetric allylic alkylation as well as Rh-catalyzed hydrogenation and hydroformylation reactions. The ligands give 100% conversion and low-to-moderate enantioselectivity in the allylic alkylation of 1,3-diphenyl-2-propenyl acetate and cyclohexyl-2-enyl acetate with dimethyl malonate. In the hydroformylation of styrene, good conversion and regioselectivities are achieved but only moderate enantioselectivity. The ligands give good conversions in asymmetric hydrogenation of typical substrates, with good-to-excellent enantioselectivities of up to 97% depending on the substrate.
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Synthesis and Reactivity of Chiral, Wide‐Bite‐Angle, Hybrid Diphosphorus Ligands
European Journal of Inorganic Chemistry, 2013Co-Authors: Christine Fee Czauderna, Alexandra M. Z. Slawin, David B. Cordes, Jarl Ivar Van Der Vlugt, Christian Müller, Dieter Vogt, Paul C. J. KamerAbstract:Effective and modular synthetic approaches toward phosphine-phosphite ligands and phosphine-phosphonite ligands featuring a diphenyl ether backbone have been developed. The phosphine-phosphite ligands are obtained by a two-step protocol from 2-bromo-2-methoxydiphenyl ether. The phosphine-phosphonite ligands are prepared in a four-step synthetic protocol that involves a novel, unsymmetrical diphenyl ether derived phosphine-phosphorusdiamide as key building block. Structural studies on Pt-II complexes with either phosphine-phosphite or phosphine-phosphonite ligands indicate strict cis coordination for these ligand systems. High-pressure NMR spectroscopy studies of Rh complexes under syngas indicate the presence of two ea isomers for Rh(H)(CO)(2)(PP). The existence of this mixture is further supported by high-pressure IR spectroscopy studies. In order to benchmark the activity and selectivity of these novel, wide-Bite-Angle, mixed-donor ligands, they were screened in Pd-catalyzed asymmetric allylic alkylation as well as Rh-catalyzed hydrogenation and hydroformylation reactions. The ligands give 100% conversion and low-to-moderate enantioselectivity in the allylic alkylation of 1,3-diphenyl-2-propenyl acetate and cyclohexyl-2-enyl acetate with dimethyl malonate. In the hydroformylation of styrene, good conversion and regioselectivities are achieved but only moderate enantioselectivity. The ligands give good conversions in asymmetric hydrogenation of typical substrates, with good-to-excellent enantioselectivities of up to 97% depending on the substrate.
Piet W. N. M. Van Leeuwen - One of the best experts on this subject based on the ideXlab platform.
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Bite Angle effects in hydroformylation catalysis.
Chinese Journal of Chemistry, 2010Co-Authors: Piet W. N. M. Van Leeuwen, Paul C. J. Kamer, Lars A. Van Der Veen, Joost N. H. ReekAbstract:Recent advances in rhodium catalyzed hydroformylation using xanthene-based ligands will be reviewed. The calculated natural Bite Angles of the ligands discussed are in the range 100–123°. While the general trend is clear—higher 1: b ratios at wider Angles, small changes in the Bite Angle do not exhibit a regular effect on the selectivity of the reaction. The same is true for the rate of CO dissociation; the larger the rate of the CO dissociation, the larger the rate of hydroformylation, but for small changes the effects do not comply with this rule.
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Bite Angle effects of diphosphines in C-C and C-X bond forming cross coupling reactions.
Chemical Society reviews, 2009Co-Authors: Mandy‐nicole Birkholz, Zoraida Freixa, Piet W. N. M. Van LeeuwenAbstract:Catalytic reactions of C–C and C–X bond formation are discussed in this critical review with particular emphasis on cross coupling reactions catalyzed by palladium and wide Bite Angle bidentate diphosphine ligands. Especially those studies have been collected that allow comparison of the ligand Bite Angles for the selected ligands: dppp, BINAP, dppf, DPEphos and Xantphos. Similarities with hydrocyanation and CO/ethene/MeOH reactions have been highlighted, while rhodium hydroformylation has been mentioned as a contrasting example, in which predictability is high and steric and electronic effects follow smooth trends. In palladium catalysis wide Bite Angles and bulkiness of the ligands facilitate generally the reductive elimination thus giving more efficient cross coupling catalysis (174 references).
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Bite Angle effects in diphosphine metal catalysts: steric or electronic?
Dalton Trans., 2003Co-Authors: Zoraida Freixa, Piet W. N. M. Van LeeuwenAbstract:The effects of wide Bite Angles of bidentate phosphine ligands on three catalytic reactions are reviewed: rhodium catalysed hydroformylation, nickel catalysed hydrocyanation, and palladium catalysed reactions of ethene, carbon monoxide and methanol leading to polyketone or methyl propanoate. The P–M–P Bite Angle plays a crucial role in determining the selectivity and rate in all three reactions. In this review an attempt is made to separate the mode of action into a steric and an electronic one. The regioselectivity of hydroformylation seems to be governed by steric factors, while the rate of reaction is determined by the electronic influence of the Bite Angle. The rates in hydrocyanation and polyketone formation were previously thought to be determined by orbital effects, but that should be questioned. Selectivity in the palladium carbonylation reaction is mainly due to steric factors.
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Synthesis and characterisation of Bite Angle-dependent (η1-allyl)Rh and (η3-allyl)Rh complexes bearing diphosphine ligands. Implications for nucleophilic substitution reactions
Comptes Rendus Chimie, 2002Co-Authors: Richard J. Van Haaren, Paul C. J. Kamer, Piet W. N. M. Van Leeuwen, Kees Goubitz, Jan Fraanje, Erik Zuidema, Gino P. F. Van StrijdonckAbstract:Abstract Several novel rhodium allyl complexes have been prepared and their structures have been studied using NMR spectroscopy and X-ray crystallography. Depending on the Bite Angle of the ligand and the substitution pattern of the allyl group, two different coordination modes (η1 and η3) have been observed for the allyl moiety. The activities of these Rh allyl complexes in the allylic alkylation reaction have been tested. We have shown that both coordination modes give active complexes in this reaction, but that the regioselectivity is dependent on the coordination mode of the allyl group.
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On the influence of the Bite Angle on the allylic alkylation of (E) and (Z) substrates: loss and retention of double bond stereochemistry.
European Journal of Inorganic Chemistry, 2001Co-Authors: Richard J. Van Haaren, Henk Oevering, Joost N. H. Reek, Paul C. J. Kamer, Gino P. F. Van Strijdonck, Piet W. N. M. Van LeeuwenAbstract:The Bite Angle of bidentate phosphane ligands has a pronounced influence on the degree of retention of the double bond geometry of the allylic substrate in the allylic alkylation reaction. To study the effect of the ligand on the regioselectivity, (Z)- and (E)-pent-2-enyl acetate were used as substrates. The alkylation of substrates with an (E) conformation of the double bond results in the preferential formation of the linear (E) product. A larger Bite Angle of the ligand results in an increase of the regioselectivity to >98% for the Sixantphos ligand. Analogously, the alkylation of (Z) substrates results in the formation of the linear (Z) product. Remarkably, for (Z) substrates, a larger Bite Angle of the ligand leads to an increased regioselectivity for the formation of the branched product instead of the linear product, up to 47.5% for Sixantphos. The observed regioselectivities are rationalized in terms of: a) a competition between syn-anti isomerization and alkylation, and b) a combination of steric and electronic effects in the transition state of the reaction. For all ligands tested, the reaction is faster for the (E) than for the (Z) substrate. However, competition experiments using the Sixantphos ligand show a relatively fast reaction rate for the (Z) substrate, which indicates that the coordination of the substrate to palladium is the discriminating, but not the rate-determining, step when both substrates are present.
Andrew S Weller - One of the best experts on this subject based on the ideXlab platform.
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fluoroarene complexes with small Bite Angle bisphosphines routes to amine borane and aminoborylene complexes
European Journal of Inorganic Chemistry, 2017Co-Authors: Annie L Colebatch, Alasdair I Mckay, Nicholas A Beattie, Stuart Macgregor, Andrew S WellerAbstract:Fluoroarene complexes of the small Bite Angle bisphosphine Cy2PCH2PCy2 (dcpm) have been prepared: [Rh(dcpm)(η6-1,2−F2C6H4)][Al{OC(CF3)3}4] and [Rh(dcpm)(η6-1,2,3− F3C6H3)][Al{OC(CF3)3}4]. These complexes act as precursors to a previously inaccessible σ−amine−borane complex [Rh(dcpm)(η2-H3B·NMe3)][Al{OC(CF3)3}4] of a small Bite-Angle phosphine. This complex is a poor catalyst for the dehydrocoupling of H3B·NMe2H. Instead, formation of the bridging borylene complex [{RhH(µ−dcpm)}2(µ−H)(µ−BNMe2)][Al{OC(CF3)3}4] occurs, which has been studied by NMR, mass spectrometry, crystallographic and DFT techniques. This represents a new route to bridging borylene complexes.
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Fluoroarene Complexes with Small Bite Angle Bisphosphines: Routes to Amine–Borane and Aminoborylene Complexes
European Journal of Inorganic Chemistry, 2017Co-Authors: Annie L Colebatch, Alasdair I Mckay, Nicholas A Beattie, Stuart Macgregor, Andrew S WellerAbstract:Fluoroarene complexes of the small Bite Angle bisphosphine Cy2PCH2PCy2 (dcpm) have been prepared: [Rh(dcpm)(η6-1,2−F2C6H4)][Al{OC(CF3)3}4] and [Rh(dcpm)(η6-1,2,3− F3C6H3)][Al{OC(CF3)3}4]. These complexes act as precursors to a previously inaccessible σ−amine−borane complex [Rh(dcpm)(η2-H3B·NMe3)][Al{OC(CF3)3}4] of a small Bite-Angle phosphine. This complex is a poor catalyst for the dehydrocoupling of H3B·NMe2H. Instead, formation of the bridging borylene complex [{RhH(µ−dcpm)}2(µ−H)(µ−BNMe2)][Al{OC(CF3)3}4] occurs, which has been studied by NMR, mass spectrometry, crystallographic and DFT techniques. This represents a new route to bridging borylene complexes.
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Variable coordination modes and catalytic dehydrogenation of B-phenyl amine–boranes
Dalton transactions (Cambridge England : 2003), 2016Co-Authors: Amit Kumar, Isobel K. Priest, Thomas N. Hooper, Andrew S WellerAbstract:The chemistry of N-substituted amine–boranes and their reactivity towards transition metal centres is well established but the chemistry of B-substituted amine–boranes is not. Here we present the coordination chemistry of H2PhB·NMe3 towards a range of Rh(I) fragments with different P–Rh–P ligand Bite Angles, {Rh(PiPr3)2}+, {Rh(PiBu3)2}+, {Rh(iPr2P(CH2)3PiPr2)}+, {Rh(Ph2P(CH2)nPPh2)}+ (n = 3, 5), as characterised by NMR spectroscopy and single-crystal X-ray diffraction. This reveals a difference in the coordination mode of the amine–borane, with large Bite Angle fragments favouring η2-coordination through a sigma-interaction with BH2, whereas fragments with small Bite Angles favour η6-coordination through the aryl group of the amine–borane. The catalytic dehydrocoupling of H2PhB·NMe2H is also explored, with the aminoborane HPhBNMe2 found to be the sole dehydrogenation product. Stoichiometric reactivity with H2PhB·NMe2H again showed small Bite Angle fragments to prefer η6-aryl coordination, while the larger Bite Angle {Rh(PiPr3)2}+ gave rapid dehydrogenation to form a mixture of the Rh(III) dihydride [Rh(PiPr3)2(H)2(η2-H2PhB·NMe2H)][BArF4] and the low coordinate aminoboryl complex [Rh(PiPr3)2(H)(BPhNMe2)][BArF4]. These results suggest that precatalysts which η6-bind arenes strongly should be avoided for the dehydrocoupling of amine–boranes bearing aryl substituents.
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Rhodium Cyclopentyl Phosphine Complexes of Wide-Bite-Angle Ligands DPEphos and Xantphos
Organometallics, 2012Co-Authors: Romaeo Dallanegra, Adrian B. Chaplin, Andrew S WellerAbstract:Rh(I) and Rh(III) complexes of tricyclopentylphosphine (PCyp3), or its dehydrogenated variant PCyp2(η2-C5H7), partnered with wide-Bite-Angle chelating diphosphine ligands DPEphos and Xantphos have been prepared and characterized in solution and the solid state with the aim of studying their potential for reversible dehydrogenation of the PCyp3 ligand. The complexes fac-[Rh(κ3-P,O,P-L){PCyp2(η2-C5H7)}][BArF4] (L = DPEphos, Xantphos) show pseudo-trigonal-bipyramidal structures in which the dehydrogenated phosphine alkene ligand acts in a chelating manner. Addition of H2 to fac-[Rh(κ3-P,O,P-DPEphos){PCyp2(η2-C5H7)}][BArF4] resulted in an equilibrium mixture of hydride and hydride-dihydrogen complexes, fac-[Rh(κ3-P,O,P-DPEphos)(H)2(PCyp3)][BArF4] and [Rh(κ2-P,P-DPEphos)(η2-H2)(H)2(PCyp3)][BArF4], in which the DPEphos acts as a hemilabile ligand. For the more rigid Xantphos ligand two dihydride isomers, fac-[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF4] and mer-[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF4], are formed,...
Christian Müller - One of the best experts on this subject based on the ideXlab platform.
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synthesis and reactivity of chiral wide Bite Angle hybrid diphosphorus ligands
European Journal of Inorganic Chemistry, 2014Co-Authors: Christine Fee Czauderna, Alexandra M. Z. Slawin, David B. Cordes, Christian Müller, Dieter Vogt, Jarl Ivar Van Der Vlugt, Paul C. J. KamerAbstract:Effective and modular synthetic approaches toward phosphine-phosphite ligands and phosphine-phosphonite ligands featuring a diphenyl ether backbone have been developed. The phosphine-phosphite ligands are obtained by a two-step protocol from 2-bromo-2-methoxydiphenyl ether. The phosphine-phosphonite ligands are prepared in a four-step synthetic protocol that involves a novel, unsymmetrical diphenyl ether derived phosphine-phosphorusdiamide as key building block. Structural studies on Pt-II complexes with either phosphine-phosphite or phosphine-phosphonite ligands indicate strict cis coordination for these ligand systems. High-pressure NMR spectroscopy studies of Rh complexes under syngas indicate the presence of two ea isomers for Rh(H)(CO)(2)(PP). The existence of this mixture is further supported by high-pressure IR spectroscopy studies. In order to benchmark the activity and selectivity of these novel, wide-Bite-Angle, mixed-donor ligands, they were screened in Pd-catalyzed asymmetric allylic alkylation as well as Rh-catalyzed hydrogenation and hydroformylation reactions. The ligands give 100% conversion and low-to-moderate enantioselectivity in the allylic alkylation of 1,3-diphenyl-2-propenyl acetate and cyclohexyl-2-enyl acetate with dimethyl malonate. In the hydroformylation of styrene, good conversion and regioselectivities are achieved but only moderate enantioselectivity. The ligands give good conversions in asymmetric hydrogenation of typical substrates, with good-to-excellent enantioselectivities of up to 97% depending on the substrate.
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Synthesis and Reactivity of Chiral, Wide‐Bite‐Angle, Hybrid Diphosphorus Ligands
European Journal of Inorganic Chemistry, 2013Co-Authors: Christine Fee Czauderna, Alexandra M. Z. Slawin, David B. Cordes, Jarl Ivar Van Der Vlugt, Christian Müller, Dieter Vogt, Paul C. J. KamerAbstract:Effective and modular synthetic approaches toward phosphine-phosphite ligands and phosphine-phosphonite ligands featuring a diphenyl ether backbone have been developed. The phosphine-phosphite ligands are obtained by a two-step protocol from 2-bromo-2-methoxydiphenyl ether. The phosphine-phosphonite ligands are prepared in a four-step synthetic protocol that involves a novel, unsymmetrical diphenyl ether derived phosphine-phosphorusdiamide as key building block. Structural studies on Pt-II complexes with either phosphine-phosphite or phosphine-phosphonite ligands indicate strict cis coordination for these ligand systems. High-pressure NMR spectroscopy studies of Rh complexes under syngas indicate the presence of two ea isomers for Rh(H)(CO)(2)(PP). The existence of this mixture is further supported by high-pressure IR spectroscopy studies. In order to benchmark the activity and selectivity of these novel, wide-Bite-Angle, mixed-donor ligands, they were screened in Pd-catalyzed asymmetric allylic alkylation as well as Rh-catalyzed hydrogenation and hydroformylation reactions. The ligands give 100% conversion and low-to-moderate enantioselectivity in the allylic alkylation of 1,3-diphenyl-2-propenyl acetate and cyclohexyl-2-enyl acetate with dimethyl malonate. In the hydroformylation of styrene, good conversion and regioselectivities are achieved but only moderate enantioselectivity. The ligands give good conversions in asymmetric hydrogenation of typical substrates, with good-to-excellent enantioselectivities of up to 97% depending on the substrate.
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Wide-Bite-Angle diphosphinines: design, synthesis, and coordination properties
Organometallics, 2008Co-Authors: Christian Müller, Zoraida Freixa, Martin Lutz, Anthony L. Spek, Dieter Vogt, Van Pwnm Piet LeeuwenAbstract:A wide-Bite-Angle diphosphinine ligand has been designed and synthesized, which exhibits structural features for a preferred formation of trans complexes. Due to the linear orientation of the lone-pair electrons of the phosphorus donors in combination with an appropriate P−P distance, trans coordination toward a Rh center was observed and the corresponding LRh(CO)I complex could be characterized crystallographically. Although typical reactivities usually observed for trans complexes were found, reaction of the diphosphinine with the cis-enforcing precursor [Rh(nbd)2]BF4 did result in the formation of several species at low temperature, to which cis-structures were attributed.
P W N M Van Leeuwen - One of the best experts on this subject based on the ideXlab platform.
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Bite Angle effects of diphosphines in carbonylation reactions
Modern carbonylation methods, 2008Co-Authors: P W N M Van Leeuwen, Zoraida FreixaAbstract:This chapter contains sections titled: * Introduction * Rhodium-Catalyzed Hydroformylation o Introduction o Steric Bite Angle Effect and Regioselectivity o Electronic Bite Angle Effect and Activity o Isotope Effects [24] * Platinum-Catalyzed Alkene Hydroformylation * Palladium-Catalyzed CO/Ethene Copolymerization o Polyketone Formation o Chain Transfer Mechanisms (Initiation-Termination) o Methyl Propanoate Formation o Theoretical Support * Rhodium-Catalyzed Methanol Carbonylation: the Ligand-Modified Monsanto Process * References
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Ruthenium dihydrogen complexes with wide Bite Angle diphosphines.
Inorganic chemistry, 2003Co-Authors: K.a. Lenero, P W N M Van Leeuwen, P.c.j. Kamer, Mirko Kranenburg, Yannick Guari, Sylviane Sabo-etienne, Bruno ChaudretAbstract:The wide Bite Angle diphosphines homoxantphos (10,11-dihydro-4,5,-bis(diphenylphosphino)dibenzo[b,f]oxepine), sixantphos (4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin), and thixantphos (2,8-dimethyl-4,6-bis(diphenylphosphino)phenoxathiin) were used to prepare cis[MH2(diphosphine)2] complexes (1a−f) by reaction of [Ru(cod)(cot)] (cod = cyclo-octa-1,5-diene, cot = cyclo-octa-1,3,5-triene) with 2 equiv of the diphosphine under dihydrogen pressure. The electronic properties of the thixantphos ligand were varied. Complexes 1a−f can be protonated with HBF4 or CF3COOH to yield hydrido(dihydrogen) complexes cis[MH(H2)(diphosphine)2]+ (2a−f), which were characterized by VT (variable temperature) NMR and T1 measurements. These complexes show fast hydrogen atom exchange between the η2-H2 and the terminal hydride at all temperatures studied. They are thermally unstable toward dihydrogen loss yielding the cationic monohydride complexes cis[MH(diphosphine)2]+ (3a−f). Coordination of the η2-H2 is dominated by σ...
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Unraveling the Bite Angle Effect: New Ligands for Selective Hydroformylation of Internal Alkenes.
CATTECH, 2002Co-Authors: L.a. Van Der Veen, P.c.j. Kamer, P W N M Van LeeuwenAbstract:Rhodium catalyzed hydroformylation is one of the most important applications of homogeneous catalysis in industry[1]. The addition of CO and H2 to alkenes is a mild and clean method for the functionalization of hydrocarbons. The atom economy of the reaction can be 100% and the selectivity for the desired aldehyde can be very high. Most of the six million tons of aldehydes produced annually by this process is converted into plasticizers for polymers and detergent alcohols. Since the linear aldehydes are the desired products for these applications, a key issue in industrial hydroformylation is the control of regioselectivity. The generally accepted hydroformylation mechanism is shown in Scheme 1. The active catalyst is the five-coordinated complex A, which usually contains two phosphorus ligands. This catalyst consists of two isomeric structures in which the phosphine ligands coordinate in a diequatorial (e-e) and in an equatorial-apical (e-a) fashion. Bidentate ligands can give rise to either of these two complexes depending on their natural Bite Angle.
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An X-ray study of the effect of the Bite Angle of chelating ligands on the geometry of palladium(allyl) complexes: implications for the regioselectivity in the allylic alkylation.
Inorganic chemistry, 2001Co-Authors: R.j. Van Haaren, Henk Oevering, B. Coussens, J.n.h. Reek, P.c.j. Kamer, Kees Goubitz, Jan Fraanje, G.p.f. Van Strijdonck, P W N M Van LeeuwenAbstract:X-ray crystal structures of a series of cationic (P-P)palladium(1,1-(CH3)2C3H3) complexes (P-P = dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1‘-bis(diphenylphosphino)ferrocene), and DPEphos (2,2‘-bis(diphenylphosphino)diphenyl ether)) and the (Xantphos)Pd(C3H5)BF4 (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) complex have been determined. In the solid state structure, the phenyl rings of the ligand are oriented in the direction of the nonsymmetrically bound [1,1-(CH3)2C3H3] moiety. An increase of the Bite Angle of the chelating ligand results in an increase of the cone Angle. In complexes containing ligands having a large cone Angle, the distances between the phenyl rings and the allyl moiety become small, resulting in a distortion of the symmetry of the palladium−allyl bond. In solution, two types of dynamic exchange have been observed, the π−σ rearrangement and the apparent rotation of the allyl moiety. At the same time, the folded structure of the ligand changes from an endo to an e...
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Origin of the Bite Angle Effect in Rhodium Diphosphine Catalyzed Hydroformylation.
Organometallics, 2000Co-Authors: L.a. Van Der Veen, P W N M Van Leeuwen, H. Keeven, G.c. Schoemaker, J.n.h. Reek, P.c.j. Kamer, Martin Lutz, A.l. SpekAbstract:The Bite Angle effect on the rhodium diphosphine catalyzed hydroformylation was investigated in detail. A series of xantphos-type ligands with natural Bite Angles ranging from 102° to 121° was synthesized, and the effect of the natural Bite Angle on coordination chemistry and catalytic performance was studied. X-ray crystal structure determinations of the complexes (nixantphos)Rh(CO)H(PPh3) and (benzoxantphos)Rh(CO)H(PPh3) were obtained. In contrast to the natural Bite Angle calculations, approximately the same diphosphine Bite Angles were observed in both crystal structures. The solution structures of the (diphosphine)Rh(CO)H(PPh3) and (diphosphine)Rh(CO)2H complexes were studied by IR and NMR spectroscopy. The spectroscopic studies showed that all (diphosphine)Rh(CO)2H complexes exhibit dynamic equilibria between diequatorial (ee) and equatorial−apical (ea) isomers. The equilibrium compositions could not be correlated with the calculated natural Bite Angles. In the hydroformylation of 1-octene an increa...