Mechanistic insights into the hydrosilylation of allyl compounds – Evidence for different coexisting reaction pathways
摘要:
The hydrosilylation of allyl compounds is often accompanied by the formation of high amounts of byproducts. The formation processes have not been fully understood so far. In this work, the allyl hydrosilylation mechanism is investigated in detail and experimental and theoretical evidence for multiple, coexisting reaction pathways is provided. Based on earlier reports and the observations during an extensive catalytic study, different pathways, leading to the observed byproducts, were identified and proven by labeling experiments and DFT calculations. Oxidative addition of the silane and the insertion of the allyl compound into the Pt-H bond turned out to be the crucial, selectivity-determining steps within the catalytic cycle. Based on these findings, it should be possible to systematically influence these steps and pave the way to a rational and straightforward design of more selective catalysts. (C) 2012 Published by Elsevier Inc.
Investigations on the question of multiple mechanisms in the cope rearrangement
作者:D.C. Wigfield、S. Feiner、G. Malbacho、K. Taymaz
DOI:10.1016/s0040-4020(01)97471-x
日期:1974.1
occurrence of the ionic Coperearrangement, and other non-concerted mechanisms is discussed. The synthesis of 2 - (1 - ethyl - 1 - propenyl) -2- (3 - p - methoxyphenylallyl)malononitrile (1b) and its clean thermal 1,3 rearrangement to (1 - ethyl - 5 - p - methoxyphenyl - 2 - methyl - 4 - pentenylidene)malononitrile (4) are reported. This result contrasts with the rearrangement of 2 - (1,1 - dideuterioallyl)
The preparation of HCF2CdX and HCF2ZnX via direct insertion into the carbon halogen bond of CF2HY (Y=Br, I)
作者:Donald J. Burton、Greg A. Hartgraves
DOI:10.1016/j.jfluchem.2007.05.015
日期:2007.10
The difluoromethylcadmium and zinc reagents have been prepared in DMF via direct insertion of Cd-0 into the carbon halogen bond of CF2HY (Y = Br, I). These reagents are stable at 65-75 degrees C and exhibit prolonged stability and activity at room temperature. Metathesis of the difluoromethylcadmium reagents with Cu(I)X (X = Br, Cl) at -55 degrees C rapidly produces difluoromethylcopper. The copper reagent is significantly less stable than the cadmium or zinc reagent and rapidly decomposes at room temperature. The difluoromethylcadmium and copper reagents exhibit good reactivity with allylic halides, propargylic derivatives and 1-iodoalkynes to provide good yields of the corresponding difluoromethylalkenes, difluoromethylallenes and difluoromethyl-2-alkynes. Alkylation is successful only with reactive alkyl halides. Generally, the difluoromethylcopper reagent is more reactive than the difluoromethylcadmium reagent and generally exhibits higher regioselectivity in reactions that can occur by either alpha- or -gamma-attack. (C) 2007 Elsevier B.V. All rights reserved.
Mechanistic insights into the iridium-catalyzed hydrosilylation of allyl compounds
作者:Korbinian Riener、Teresa K. Meister、Peter Gigler、Wolfgang A. Herrmann、Fritz E. Kühn
DOI:10.1016/j.jcat.2015.09.003
日期:2015.11
The hydrosilylation of allyl compounds is very important for the industrial production of gamma-substituted propylsilanes; however, it is also a process known to suffer from either substantial selectivity issues or short catalyst lifetimes. While there are reports on the platinum-catalyzed variant, this study is the first comprehensive work on the more recently employed iridium-catalyzed process. A combination of stoichiometric and catalytic experiments as well as reactions with isotope-labeled compounds is used to elucidate the critical parameters influencing the catalytic performance and to identify the main deactivation pathways. This report is intended to pave the way toward the optimization of current iridium-catalyzed processes and the design and synthesis of improved catalyst structures. (C) 2015 Elsevier Inc. All rights reserved.
Palladium-catalyzed polyhetero-Claisen rearrangement of 2-(allylthio)pyrimidin-4(3H)-ones
作者:Masato Mizutani、Yuzuru Sanemitsu、Yoshinao Tamaru、Zenichi Yoshida
DOI:10.1021/jo00206a007
日期:1985.3
Unimolecular reactions of ionized methyl allyl ether
作者:Richard D. Bowen、Andrew D. Wright、Peter J. Derrick
DOI:10.1002/oms.1210270812
日期:1992.8
AbstractThe fragmentation of CH2CHCH2OCH3+· cation‐radicals has been investigated by means of 2H‐ and 13C‐labelling experiments and by analysis of collision‐induced dissociation spectra. Metastable C4H8O+· species decompose via one of three main channels which involve loss of (a) a hydrogen atom, (b) a methyl radical or (c) a formaldehyde molecule. Extensive, but not complete, exchange of the hydrogen and deuterium atoms in specifically labelled C4H8‐nDnO+· analogues precedes each of the three fragmentation pathways. The role of distonic ions in the rearrangement steps which bring about hydrogen exchange is discussed. The influence of isotope effects on the relative rates of the major reactions and the associated kinetic energy releases is examined. Only loss of a hydrogen atom is subject to a substantial isotope effect. Elimination of a methyl radical releases a large amount of kinetic energy, as is shown by the broad and dish‐topped appearance of the corresponding metastable peak (T1/2 ≈ 42 kJ mol−1). The carbon atom of the original methoxy group is specifically expelled in this process. Both the large T1/2 value and the unusual site selectivity are atypical of methyl and other alkyl radical losses from ionized alkenyl methyl ethers. The carbon atom of the methoxy group also participates specifically in formaldehyde elimination, but the two hydrogen atoms are not always selected from the three contained in the initial methoxy group. The implications of these labelling results for the synchronicity of concert of formaldehyde loss, which can be formu lated as a pericyclic process, is analysed.