Mechanism of asymmetric epoxidation. 1. Kinetics

Woodard, Scott S.; Finn, M. G.; Sharpless, K. Barry

doi:10.1021/ja00001a018

Cited by 205 publications

(76 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…We demonstrated, via the mass balance, that the reaction on Aerosil-200 silica pretreated at 200°C results exclusively in the formation of dinuclear oxo-bridged complexes regardless of Ti loading (13) The dinuclear Ti complex assembles spontaneously on the silica surface via a non-hydrolytic alkoxide condensation reaction which generates the Ti-O-Ti bridge as well as C 3 H 6 (16). Confirmation of this condensation process was obtained via the exposure to Ti(O'Pr) 4 of a silica fully loaded (i.e., with no unreacted hydroxyl groups) with a mononuclear titanium alkoxide complex. The latter was prepared by grafting of Ti(NEt 2 ) 4 followed by ligand metathesis with 'PrOH, eq 2.…”

Section: Composition Of the Titanium Sites In The Grafted Catalystmentioning

confidence: 94%

“…The catalyst was prepared by the reaction of Ti(O'Pr) 4 (99.999%, Aldrich) with a non-porous, pyrogenic silica, as described previously (13). Degussa Aerosil™-200 (surface area 183 m 2 /g) was rehydrated then partially dehydroxylated in vacua at 200°C, after which treatment the hydroxyl content is reproducible at 2.6 OH/nm 2 (14).…”

Section: Experimental Preparation Of Silica-supported Titanium Catalystmentioning

confidence: 99%

“…We previously reported the preparation and quantitative characterization of welldefined, uniform titanium alkoxide complexes on a silica surface, via the grafting of Ti(O'Pr) 4 . We demonstrated, via the mass balance, that the reaction on Aerosil-200 silica pretreated at 200°C results exclusively in the formation of dinuclear oxo-bridged complexes regardless of Ti loading (13) The dinuclear Ti complex assembles spontaneously on the silica surface via a non-hydrolytic alkoxide condensation reaction which generates the Ti-O-Ti bridge as well as C 3 H 6 (16).…”

Section: Composition Of the Titanium Sites In The Grafted Catalystmentioning

confidence: 99%

“…The preparation of solid catalysts by reaction of Ti(O' Pr) 4 with silica has been reported by several groups (10,11). This material appears to have several desirable properties compared to other heterogeneous Ti/silicate materials, viz., lower moisture-sensitivity and an absence of steric constraint on substrate size (12).…”

Section: Introductionmentioning

confidence: 99%

“…Both solid and soluble versions containing high valent, d° transition metal ions activate peroxides heterolytically, thereby facilitating oxygen atom transfer to electron-rich substrates (1). However, mechanistic studies have been undertaken largely with the more readily characterized soluble catalysts (2)(3)(4). For heterogeneous catalysts, the fraction of metal sites which participate in selective oxidation is generally unknown.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

Bouh¹,

Hassan²,

Scott³

2002

Catalysis of Organic Reactions

View full text Add to dashboard Cite

Section: Composition Of the Titanium Sites In The Grafted Catalystmentioning

confidence: 94%

Section: Experimental Preparation Of Silica-supported Titanium Catalystmentioning

confidence: 99%

Section: Composition Of the Titanium Sites In The Grafted Catalystmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Bouh¹,

Hassan²,

Scott³

2002

Catalysis of Organic Reactions

View full text Add to dashboard Cite

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.

View full text Add to dashboard Cite

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.

show abstract