- Organic and organometallic derivatives of pentaphenylbenzene, C 6Ph5X: Correlation of peripheral phenyl ring orientations with the steric bulk of "x"
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A series of C6Ph5X compounds, including X = H, Br, CO2H, CO2R, CCPh, cis-BrC=C(Br)Ph, 2-bornenyl, and ferrocenyl, have been characterized by use of X-ray crystallography. Also, the first organometallic complexes of pentaphenylbenzene have been prepared by reaction with chromium hexacarbonyl to yield (η6-C 6Ph5H)Cr(CO)3 complexes in which the metal tripod is attached either to an ortho peripheral ring or to the central ring. Crystalline pentaphenylbenzoic acid exists as a hydrogen-bonded dimer; however, the steric bulk of the substituents does not allow the carboxylic acid moieties to be linked directly but instead via two bridging methanol molecules. In the solid state, the orientation of the peripheral rings in bulky C 6Ph5X systems is very sensitive to the size of the "X" substituents, such that the twist angle of the para ring responds inversely with increasing bulk of "X", which drives the ortho rings farther out of the plane of the central ring. The relevance of these observations to correlated motion in molecular propellers, and ultimately to molecular machines, is discussed.
- Brydges, Stacey,Gildea, Brendan,Grealis, John P.,Mueller-Bunz, Helge,Stradiotto, Mark,Casey, Michael,McGlinchey, Michael J.
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p. 1098 - 1111
(2013/11/06)
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- Switching from dimerization to cyclotrimerization selectivity by FeCl 3 in the Y[N(TMS)2]3-catalyzed transformation of terminal alkynes: A new strategy for controlling the selectivity of organolanthanide-based catalysis
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Y[N(TMS)2]3/FeCl3 has been found to be an efficient bimetallic catalyst system for the cyclotrimerization of terminal alkynes, which cannot be achieved by either trivalent iron or trivalent lanthanide catalysts. Furthermore, this reaction also occurs efficiently in the presence of Fe[N(TMS)2]3 and YCl3. Both aromatic and aliphatic alkynes are compatible with this catalytic system. It is postulated that the catalytic cyclotrimerization proceeds through a tandem intermolecular diinsertion of alkynes into the yttrium-alkynyl bond and intramolecular electrophilic addition of a π-coordinated alkyne moiety, and the π-coordination of Fe3+ to alkyne may play an important role in controlling the insertion degree of advancement and selectivity. The observed catalytic reaction is sharply in contrast with the cyclotrimerization of alkynes, known to proceed through a typical metallacyclopentadiene intermediate.
- Bu, Xiuli,Zhang, Zhengxing,Zhou, Xigeng
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scheme or table
p. 3530 - 3534
(2010/10/03)
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- OBSERVATIONS AND COMMENTS ON THE THERMAL BEHAVIOR OF 7-SILANORBORNADIENES
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Evidence for a radical mechanism in the termal decomposition of a 7-silanorbornadiene is presented.It is demonstrated that 2-carboxy-7-silanorbornadienes undergo a formal 1,5-migration of silicon to form O-silyl enol ethers.An earlier suggested rearrangement of a 7-silanorbornadiene to a silepin or silanorcardiene is excluded.A recent report of thermal and photochemical epimerization of 7-silanorbornadienes is shown to be incorrect.
- Barton, Thomas J.,Goure, William F.,Witiak, Joanne L.,Wulff, William D.
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