Mechanistic Investigation of Cycloreversion/Cycloaddition Reactions between Zirconocene Metallacycle Complexes and Unsaturated Organic Substrates.
Mechanistic Investigation of Cycloreversion/Cycloaddition Reactions between Zirconocene Metallacycle Complexes and Unsaturated Organic Substrates.
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锆茂金属环配合物与不饱和有机底物之间环化/环加成反应的机理研究。
DOI：
10.1021/om010091o
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发表时间：
2001
期刊：
影响因子：
2.8
通讯作者：
Bergman,RobertG
中科院分区：
文献类型：
--
作者：
Zuckerman,RebeccaL;Bergman,RobertG
Treatment of the diazametallacycle Cp2Zr(N(t-Bu)CN(SiMe3)N(SiMe3)) (4a) with diphenylacetylene resulted in the formation of the azametallacyclobutene Cp2Zr(N(t-Bu)C(Ph)C(Ph)) (6a) and Me3SiNCNSiMe3in high yield. A kinetic study using UV−vis spectroscopy was carried out on the transformation. Saturation kinetic behavior was observed for the system, which is supportive of a mechanism that involves a reversible formal [2 + 2] retrocycloaddition of4ato generate the transient imido species Cp2ZrN-t-Bu (7a) and Me3SiNCNSiMe3. Trapping7awith diphenylacetylene in an overall [2 + 2] cycloaddition reaction affords zirconacycle6a. The study of cycloreversion/cycloaddition reactions between diazametallacycle complexes and diphenylacetylene was extended to other zirconocene systems. Detailed kinetic studies were performed for the exchange reactions between the diazametallacycle complexes Cp2Zr(N(2,6-Me2Ph)CN(SiMe3)N(SiMe3)) (8a) and Cp2Zr(N(2,6-Me2Ph)CN(t-Bu)N(t-Bu)) (8b) with diphenylacetylene (5a) to give the corresponding azametallacyclobutene complex Cp2Zr(N(2,6-Me2Ph)C(Ph)C(Ph)) (6c) and extruded carbodiimides (Me3SiNCNSiMe3for8aand (t-Bu)NCN(t-Bu) for8b). For both systems, the reactions were found to be first order in metallacycle and zero order in alkyne. Treatment of the diazametallacycle complexes Cp2Zr(N(2,6-i-Pr2Ph)CN(Cyc)N(Cyc)) (9a) and Cp2Zr(N(2,6-i-Pr2Ph)CN(i-Pr2)N(i-Pr2)) (9b) with alkyne5aresulted in the formation of the six-membered zirconacycles10a,b, respectively, upon heating at 75 °C. The products10a,bare generated from the overall insertion of alkyne5ainto the nitrogen−carbon bond of the zirconium-containing diazacyclobutane. Complex10ahas been characterized by an X-ray crystallographic study. When the azacyclobutene Cp2Zr(N(2,6-i-Pr2Ph)C(Ph)C(Ph)) (6e) was treated with CycNCNCyc or (i-Pr)NCN(i-Pr), the same six-membered zirconacycle complexes10a,bwere obtained. Kinetic analysis of the reaction of6eand (i-Pr)NCN(i-Pr) to yield10bsupports an associative process wherein alkyne5adirectly inserts into the zirconium−carbon bond of6e. The diazametallacycle complex4aunderwent a stoichiometric metathetical exchange with symmetrical carbodiimides RNCNR (R =p-Tol,m-Tol,i-Pr, Cyc) to generate new cyclic zirconocene complexes and Me3SiNCNSiMe3. Kinetic studies were carried out on the exchange reaction between4aand (m-Tol)NCN(m-Tol) to form4eand Me3SiNCNSiMe3. The experimental rate data obtained are consistent with a dissociative mechanism. Additionally, the saturation rate constant derived for this system from the data is the same (within experimental error) as the saturation rate constant obtained from the kinetic study of4aand diphenylacetylene to form6aand Me3SiNCNSiMe3. These findings provide additional support for a dissociative mechanistic pathway in the exchange reactions, since the rate constant in the formal [2 + 2] retrocycloaddition reaction to generate imidozirconocene species Cp2ZrN-t-Bu (7a) and Me3SiNCNSiMe3should be the same for both reactions.
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影响因子：
2.2
作者：
GRISHAM, MB;ENGERSON, TD;JONES, HP
通讯作者：
JONES, HP
膜糖蛋白复合物 CDw18 (LFA) 的单克隆抗体可抑制体内 PMN 积累和血浆渗漏
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
K. Arfors;C. Lundberg;L. Lindbom;K. Lundberg;M. Harlan
通讯作者：
M. Harlan
影响因子：
--
作者：
GRISHAM, MB;HERNANDEZ, LA;GRANGER, DN
通讯作者：
GRANGER, DN
趋化因子诱导的细胞粘附性对粒细胞功能的调节影响。
DOI：
10.1172/jci109466
发表时间：
1979
期刊：
The Journal of clinical investigation
影响因子：
--
作者：
J. Fehr;C. Dahinden
通讯作者：
C. Dahinden
白细胞在急性实验性胰腺炎中产生氧自由基的作用。
影响因子：
3.8
作者：
Sarr,MG;Bulkley,GB;Cameron,JL
通讯作者：
Cameron,JL