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Sakaki S Takayama T Sumimoto M Sugimoto M 《Journal of the American Chemical Society》2004,126(10):3332-3348
The Cp(2)Zr-catalyzed hydrosilylation of ethylene was theoretically investigated with DFT and MP2-MP4(SDQ) methods, to clarify the reaction mechanism and the characteristic features of this reaction. Although ethylene insertion into the Zr-SiH(3) bond of Cp(2)Zr(H)(SiH(3)) needs a very large activation barrier of 41.0 (42.3) kcal/mol, ethylene is easily inserted into the Zr-H bond with a very small activation barrier of 2.1 (2.8) kcal/mol, where the activation barrier and the energy of reaction calculated with the DFT(B3LYP) method are given and in parentheses are those values which have been corrected for the zero-point energy, hereafter. Not only this ethylene insertion reaction but also the coupling reaction between Cp(2)Zr(C(2)H(4)) and SiH(4) easily takes place to afford Cp(2)Zr(H)(CH(2)CH(2)SiH(3)) and Cp(2)Zr(CH(2)CH(3))(SiH(3)) with activation barriers of 0.3 (0.7) and 5.0 (5.4) kcal/mol, respectively. This coupling reaction involves a new type of Si-H sigma-bond activation which is similar to metathesis. The important interaction in the coupling reaction is the bonding overlap between the d(pi)-pi bonding orbital of Cp(2)Zr(C(2)H(4)) and the Si-H sigma orbital. The final step is neither direct C-H nor Si-C reductive elimination, because both reductive eliminations occur with a very large activation barrier and significantly large endothermicity. This is because the d orbital of Cp(2)Zr is at a high energy. On the other hand, ethylene-assisted C-H reductive elimination easily occurs with a small activation barrier, 5.0 (7.5) kcal/mol, and considerably large exothermicity, -10.6 (-7.1) kcal/mol. Also, ethylene-assisted Si-C reductive elimination and metatheses of Cp(2)Zr(H)(CH(2)CH(2)SiH(3)) and Cp(2)Zr(CH(2)CH(3))(SiH(3)) with SiH(4) take place with moderate activation barriers, 26.5 (30.7), 18.4 (20.5), and 28.3 (31.5) kcal/mol, respectively. From these results, it is clearly concluded that the most favorable catalytic cycle of the Cp(2)Zr-catalyzed hydrosilylation of ethylene consists of the coupling reaction of Cp(2)Zr(C(2)H(4)) with SiH(4) followed by the ethylene-assisted C-H reductive elimination. 相似文献
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Mukai C Inagaki F Yoshida T Yoshitani K Hara Y Kitagaki S 《The Journal of organic chemistry》2005,70(18):7159-7171
[reaction: see text] Rhodium(I)-catalyzed PKR of allenynes was found to be applicable for constructing azabicyclo[5.3.0]decadienone as well as oxabicyclo[5.3.0]decadienone frameworks. In addition, a reliable procedure for constructing a 10-monosubstituted bicyclo[5.3.0]deca-1,7-dien-9-one ring system by the rhodium(I)-catalyzed PKR of allenynes was developed under the condition of 10 atm of CO. Investigation of the rhodium(I)-catalyzed cycloisomerization of 4-phenylsulfonylnona-2,3-dien-8-ynes under nitrogen atmosphere gave the corresponding cyclohexene derivatives, whereas the C1-homologated allenynes produced cycloheptene derivatives and/or bicyclo[5.2.0]nonene skeletons depending on the substitution pattern at the allenic terminus. Thus, proper choice of the starting allenynes and reaction conditions led to the selective formation of 2-phenylsulfonylbicyclo[5.3.0]deca-1,7-dien-9-ones (Pauson-Khand-type product), 3-alkylidene-1-phenylsulfonyl-2-vinylcycloheptene derivatives, and bicyclo[5.2.0]nonene frameworks. 相似文献
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Tatsunori Iwamura Takashi Ichikawa Hiroshi Shimizu Tadashi Kataoka 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):471-472
Abstract Reactions of thiazolo[3,2-b]-1,2,4-triazolium N-methylides with electron-deficient acetylenes gave the thiazole ring-opened products as a mixture of the E-and Z-isomers. In contrast, the N-phenacylides reacted with dimethyl acetylenedicarboxylate to give the thiobenzoates together with the thiazole ring-opened products. The mechanism for formation of these compounds is described. 相似文献
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Akiko Watanabe Naotoshi Kiyota Tetsuo Yamasaki Kazuhiro Tanda Tatsunori Miyagoe Masanori Sakamoto Masami Otsuka 《Journal of heterocyclic chemistry》2011,48(5):1132-1139
Four isomers of the monomer of peptide nucleic acid (PNA) were derived from (2S,4R)‐4‐hydroxyproline; they had different stereochemistries at the C2 and C4 positions in the pyrrolidine ring. These different backbone conformations corresponding to four different stereochemistries were realized through a combination of inversions at the C2 and the C4 positions in pyrrolidine ring. The obtained backbone frameworks were reacted with N‐benzoyl thymine to give the corresponding PNA monomers. Spectroscopic comparison of the resultant monomers confirmed their stereochemistries. J. Heterocyclic Chem., (2011). 相似文献
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Tatsunori Sakano Hiroki Fukuoka Yoshihiro Yata Toshiharu Saiki Minoru Obara 《Applied Physics A: Materials Science & Processing》2008,93(3):697-703
We employed epi-GaN substrates for ZnO film growth, and studied the deposition and post-annealing effects. ZnO films were
grown by pulsed laser deposition (PLD) method. The as-grown films were annealed for one hour under atmospheric pressure air.
ZnO morphologies after annealing were investigated and the post-annealed ZnO films grown at T
g
=700oC have very smooth surfaces and the rms with roughness is about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted
between ZnO epilayer and GaN/sapphire substrates. It is confirmed by AFM that growth temperature of 700oC helps the films grow in step-flow growth mode. It is observed by cathode luminescence spectrum that the ZnO film grown at
700oC has very low visible luminescence, indicating the decrease of the deep level defects. It is also revealed by Hall measurements
that carrier concentration is decreased by increasing the growth temperatures. It is suggested that low temperature buffer
layer growth and post-annealing technique can be used to fabricate ZnO hetero-epitaxy. 相似文献