Mechanism of asymmetric epoxidation. 2. Catalyst structure

Finn, M. G.; Sharpless, K. Barry

doi:10.1021/ja00001a019

Cited by 331 publications

(213 citation statements)

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“…The uptake of cyclohexene by the Ti-modified silica is pseudo-first-order, as shown by the fit to the exponential curve in Figure 2. Furthermore, the measured pseudo-first-order rate constants are linearly dependent on the amount of Ti present in the reactor, Figure 3, consistent with the rate law shown in eq 7: -d[C 6 H 12 ]/dt = 2k[C 6 H 12 ]n Ti (7) where the factor of 2 arises from the conversion of two equiv. of cyclohexene on each Ti site (see above).…”

Section: Kinetics Of Epoxidationsupporting

confidence: 80%

“…Their propensity for association to multinuclear species is also well-established (6). The active form of a homogeneous, enantioselective titanium-tartrate catalyst was demonstrated to be dinuclear in titanium (7). In contrast, heterogeneous catalysts consisting of titanium embedded in an aluminosilicate framework contain mostly isolated titanium sites (8), although the assertion that such sites are uniquely responsible for catalyst activity is based on indirect (and disputed) spectroscopic evidence (9).…”

Section: Introductionmentioning

confidence: 99%

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Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

Bouh¹,

Hassan²,

Scott³

2002

Catalysis of Organic Reactions

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Section: Kinetics Of Epoxidationsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

Bouh¹,

Hassan²,

Scott³

2002

Catalysis of Organic Reactions

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“…were two distinct ester OCH heptets with a corresponding pair of OCH peaks and two C=O peaks, but both of these lay near the position of the C=O signal from free H,dipt. This contrasted with the widely separated ester signals produced by Ti2(tartrate),(OtBu), (5,12), ~i , d i p t , (~'~r ) , , and Ti,dipt-(OIPr), (2) that were attributed to the presence of one Tibound side chain with downfield-shifted signals, and one that remained free with relatively stationary signals. Clearly, the dipt unit in the new product was asymmetrically and rigidly bound but neither of its ester carbonyls was coordinating, as in the Zr complex.…”

Section: -Hydroxyquinolinementioning

confidence: 78%

“…Firstly, Scheme 1 requires that ~i , d i~t , ( O '~r ) , have the 10-membered macrocyclic form depicted, a structure that has been the subject of some controversy (5); it would be very difficult to account for the products otherwise. In particular, the condensed, D-like form preferred by the Sharpless group (1,6,12) would be expected to give products with only D-derived architectures.…”

Section: Discussionmentioning

confidence: 99%

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An NMR study of mixed, tartrate-containing Ti^IV complexes

Potvin¹,

Fieldhouse²

1995

Can. J. Chem.

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chelating diolate units and to decide if the side-chain groups are coordinated (3).The Katsuki-Sharpless catalysts (1) are fluxional because the side-chain ester groups are reversibly and weakly bound, complicating the study of their structures and their interactions with substrates. We recently undertook to examine certain mixed complexes for two reasons: Firstly, the loosely bound ester groups could be supplanted by more stably bound groups from companion ligands, permitting an easier characterization. Two existing X-ray structures (6) were to serve as controls. Secondly, acting as "proxies" for the catalytic substrates, companion ligands could provide mixed species that model the catalytic intermediates.A rich chemistry has emerged, which this paper assembles and discusses. As well as presenting more complete details of the mixed ligand species already communicated (4, 5), many new examples and an entirely new and unique tartrate binding mode are reported for the first time. Overall, the products were formed with surprising selectivity, providing three new tartrate binding modes and evidence of transient O'Pr bridges. Further insights have also been gained into reactivity, the Katsuki-Sharpless catalyst structure, and new catalyst designs. Experimental sectionGeneral Diisopropyl R,R-or S,S-tartrate, diethyl R,R-tartrate, and titanium tetraisopropoxide were freshly distilled. CDCl, was dried over Mg(ClO,),. Unless otherwise stated, NMR spectra were obtained at 19-20°C on a Bruker AM-300 instrument operating at 300 MHz for 'H or 75.1 MHz for 13c, using pulse sequences from the Bruker library. Integration was performed digitally, at times after digital enhancement of the resolution, which was achieved by zeroing the last half of a 16-kbyte-long FID and zero-filling an additional 48 kbytes before Fourier transformation. Baseline correction was at times used to integrate AB quartets. Spectra were also obtained with simultaneous irradiation of the CH, region to simplify the OCH region and to establish the numbers and positions of OCH heptets. Single-frequency homo-decoupling ('H-'H) and heterodecoupling ('H-',c) and 2-dimensional shift correlation experiments were used to establish connectivities. 'H-',c couplings were measured by gated decoupling. Chemical shifts are reported in ppm from TMS and coupling constants are in hertz (Hz). For AB quartets, the JAB and calculated A6 values are reported. Abbreviations include v for very, b for broad, h for heptet, and m for multiplet. J, , denotes apparent couplings. Mass spectrometry was pedormed by Dr. B. Khouw on a VG instrument (York) or on a ZAB-80 instrument at the McMaster Regional Centre for Mass Spectroscopy. EI experiments were conducted at 70 eV. CI experiments with NH, and FAB in various matrices were less informative.Unless specifically indicated in the results section, reaction mixtures were obtained in one or more ways, depending on which reagent, if any, needed to be added last or whether the proportion of a reagent was to be varied. Solutions 37-42 mM in...

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Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components

Duda

Erker²,

Fröhlich

et al. 1998

Eur. J. Inorg. Chem.

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6‐Amino‐6‐methylfulvene (4) is cleanly N‐acylated by treatment with pivaloylchloride/triethylamine to give the fulvene (C5H4)=C(CH3)NHCOCMe3 (5c). Treatment of 4 with trimethylchlorosilane similarly yields the mono‐N‐silylated fulvene (C5H4)=C(CH3)NHSiMe3 (7). Both 5c and 7 are cleanly doubly deprotonated e.g. by treatment with LDA to give ligand systems [(C5H4)C(=CH2)NR]Li2 [8a (R = COCMe3) and 8b (R = SiMe3), respectively]. Their treatment with MCl4 · 2 THF (M = Ti, Zr) yield the spiro‐metallocenes [(C5H4)C(=CH2)NR]2M (9, 10). Complex 10a (M = Zr, R = COCMe3) was characterized by X‐ray diffraction. The reaction of 8a with (Et2N)2ZrCl2 in THF gives rise to the formation of [(C5H4)C(=CH2)NCOCMe3]Zr(NEt2)2 (11) (70 % isolated), and the reaction of 8b with (Et2N)2ZrCl2 yields [(C5H4)C(=CH2)NSiMe3]Zr(NEt2)2 (12) (76 % isolated). Treatment of complex 12 with an excess of methylalumoxane (MAO) in toluene solution results in the generation of an active homogeneous Ziegler catalyst for the polymerization of ethene. A comparison with the usually employed [(Me5C4)SiMe2NCMe3]ZrCl2/MAO “constrained‐geometry” Ziegler catalyst system reveals a similar catalyst activity and performance of this novel type of a C1‐bridged “constrained‐geometry” catalyst as it is exemplified by the [(C5H4)C(=CH2)NSiMe3]ZrX2 (12)/MAO combination.

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Mechanism of asymmetric epoxidation. 2. Catalyst structure

Cited by 331 publications

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Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

An NMR study of mixed, tartrate-containing Ti^IV complexes

Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components

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Mechanism of asymmetric epoxidation. 2. Catalyst structure

Cited by 331 publications

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Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

Stoichiometry and Kinetics of Gas Phase Cyclohexene Epoxidation by a Silica-Supported tert-Butylperoxidititanium Complex

An NMR study of mixed, tartrate-containing TiIV complexes

Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components

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An NMR study of mixed, tartrate-containing Ti^IV complexes