Electron Redistribution of Aromatic Ligands in (Arene)Cr(CO)<sub>3</sub> Complexes. Structural (Bond-Length) Changes as Quantitative Measures
作者:P. Le Maguères、S. V. Lindeman、J. K. Kochi
DOI:10.1021/om000658l
日期:2001.1.1
Arene ligands experience significant ring expansion upon coordination with chromiumtricarbonyl, as established by precise X-ray crystallographic analyses of various (η6-arene)Cr(CO)3 complexes. Such changes in ligand structures result from the charge (electron) redistribution, Ar+−Cr-, upon arene coordination, since they are closely related to those found in the intermolecular 1:1 complexes of the
Novel Synthesis and Structures of Tris-Annelated Benzene Donors for the Electron-Density Elucidation of the Classical Mills−Nixon Effect
作者:R. Rathore、S. V. Lindeman、A. S. Kumar、J. K. Kochi
DOI:10.1021/ja980805v
日期:1998.6.1
alternation relevant to the Mills−Nixoneffect. Most importantly, the efficient synthesis of 1s crystals of extraordinary quality allows us (for the first time) to make precise electron-density measurements of the “banana-type” distortion and the ellipticity (π-character) of the various aromatic C−C bondssufficient to identify the electronic origin of the classical Mills−Nixoneffect. The unique electron-donor
Synthesis, structure, and reduction of the cyclooctatetraene tetra-annelated with bicyclo[2.2.2]octene frameworks
作者:Koichi Komatsu、Tohru Nishinaga、Shuji Aonuma、Chitaru Hirosawa、Ken'ichi Takeuchi、Hans J. Lindner、Jens Richter
DOI:10.1016/s0040-4039(00)93598-6
日期:1991.11
The COT derivative 3 having rigid σ-frameworks has been newly synthesized and its X-ray structure determined; 3 is readily reduced to the dianion 32- in spite of severe steric hindrance.
Palladium-catalysed cyclotrimerisation reactions of polycyclic alkenes under the Stille and Grigg coupling conditions
作者:Antonio Paulon、Sergio Cossu、Ottorino De Lucchi、Cristiano Zonta
DOI:10.1039/b006698m
日期:——
Preformed or in situ generated polycyclic
bromostannylalkenes react under palladium catalysis under Stille or Grigg
reaction conditions to afford cyclotrimerised adducts via a
three-fold carbon–carbon coupling reaction.
Reaction of 2,3-dibromobicyclo[2.2.2]oct-2-ene (10) with n-butyllithium in THF at -78-degrees-C affords a series of oligomeric dibromides 11 (n = 2-5), which are composed of linearly bonded bicyclo[2.2.2]oct-2-ene units. A trapping experiment indicated that the reaction proceeds via formation of a highly strained acetylene, bicyclo[2.2.2]octyne (18), as a reactive intermediate. Upon treatment with sodium naphthalenide, the trimer 11 (n = 3) reductively cyclizes to tris(bicyclo[2.2.2]octeno)benzene (12) in high yield. The benzene 12 exhibits a reversible oxidation wave at +1.25 V vs Ag/AgNO3 on cyclic voltammetry and gives a stable cation radical 12.+ electrolytically or by oxidation with H2SO4 in air. In FSO3H, 12 is 100% protonated to give the arenium ion 22. The results of variable-temperature C-13 NMR study indicate that the activation energy for the intermolecular proton transfer of 22 is lower than that for the hexamethylbenzenium ion (23). The rate of intramolecular hydrogen migration is also much faster in 22. These results are in agreement with the relative instability of 22 (pK(AH+) -10.2) as compared with 23 (pK(AH+) -9.01).