- Generation and Trapping of Bis(dialkylamino)silylenes: Experimental Evidence for Bridged Structure of Diaminosilylene Dimers
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Reduction of dichlorobis(diisopropylamino)silane and dichlorobis(cis-2,6-dimethylpiperidino) silane by alkali metals gave the corresponding bis(diisopropylamino)silylene and bis(cis-2,6-dimethylpiperidino)silylene, respectively. These were successfully trapped by toluene and benzene as well as by hydrosilane, olefin, and acetylene. As the first evidence for the existence of the bridged-dimer of the diaminosilylenes, we have found scrambling of the amino-substituents on a silicon atom during the simultaneous generation of two different bis(dialkylamino)silylenes in benzene. Diaminosilyenes generated thermally from the other new precursors designed here gave no evidence for the bridged dimer, due to the high temperature required for the generation.
- Sakamoto, Kenkichi,Tsutsui, Shinobu,Sakurai, Hideki,Kira, Mitsuo
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p. 253 - 260
(2007/10/03)
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- Unimolecular Reactions of Isolated Organic Ions: Reactions of the Immonium Ions CH2=N+(CH3)CH(CH3)2, CH2=N+(CH3)CH2CH2CH3 and CH2=N+(CH2CH2CH3)2
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The reactions of metastable CH2=N+(CH3)C3H7 immonium ions have been investigated by means of 2H-labelling experiments and kinetic energy release measurements.Loss of C3H6, with specific β-H transfer, is the sole channel for dissociation of CH2=N+(CH3)CH(CH3)2.This process gives rise to a Gaussian metastable peak.The isomeric ion, CH2=N+(CH3)CH2CH2CH3, also expels C3H6; however, both α-H and γ-H as well as β-H transfer occurs in this case, and the reaction proceeds with an increased kinetic energy release.The role of ion-neutral complexes in C3H6 loss from CH2=N+(CH3)C3H7 ions is discussed.In addition, CH2=N+(CH3)CH2CH2CH3 eliminates C2H4.This fragmentation yields a broad dish-topped metastable peak, corresponding to a very large kinetic energy release (T1/2 ca. 73 kJ mol-1), and it involves specific and unidirectional γ-H transfer.A potential energy profile summarising the reactions of CH2=N+(CH3)CH2CH2CH3 and CH2=N+(CH3)CH(CH3)2 is constructed.The mechanisms by which immonium ions of this general class eliminate C3H6 and C2H4 have been further probed by studying the behaviour of the higher homologue, CH2=N+(CH2CH2CH3)2.The mechanistic conclusions derived from this work are found to be in excellent qualitative agreement with those of previous studies.
- Bowen, Richard D.,Colburn, Alex W.,Derrick, Peter J.
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p. 2363 - 2372
(2007/10/02)
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- Unimolecular Reactions of Ionised 4-Methoxyheptane
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The dissociation of metastable ionised 4-methoxyheptane has been examined by means of extensive 2H-labelling experiments.Only two significant fragmentations are observed, corresponding to loss of ether methanol or propane.Each of these processes involves a hydrogen transfer step in which a pronounced site-selectivity is observed.However, the site-selectivities found for the two fragmentations are distinctly different.Expulsion of methanol, which is characterised by a rather small kinetic energy release, takes place after a unidirectional 1,4-hydrogen transfer to oxygen has occurred; this step is subject to a very large isotope effect.In contrast, loss of propane involves ejection of an intact propyl group, together with an α-hydrogen atom from the second propyl group, via a formal 1,2-elimination.Primary and secondary isotope effects of comparable magnitudes intervene in propane loss from ionised methoxyheptanes in which either or both propyl groups carry 2H-labels on the α-carbon atom.The possibility that ion-neutral complexes are important in the reactions of those C8H18-nDnO+. species is discussed.
- Bowen, Richard D.,Derrick, Peter J.
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p. 1041 - 1047
(2007/10/02)
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