Seven cyclopentadienyl-NHC piano-stool ironcomplexes were prepared and studied in the catalytichydrosilylation of aldehydes and ketones under visible light irradiation. A significant acceleration of the rate was observed when the reactions were carried out under solvent-free conditions. Single-crystal X-ray structural analyses were performed for complexes 5 and 7.
制备了七种环戊二烯基-NHC钢琴-凳铁配合物,并研究了可见光照射下醛和酮的催化氢化硅烷化反应。当反应在无溶剂条件下进行时,观察到速率显着加快。对配合物 5 和 7 进行了单晶 X 射线结构分析。
Piano-Stool Iron(II) Complexes as Probes for the Bonding of <i>N</i>-Heterocyclic Carbenes: Indications for π-Acceptor Ability
作者:Laszlo Mercs、Gaël Labat、Antonia Neels、Andreas Ehlers、Martin Albrecht
DOI:10.1021/om060637c
日期:2006.11.1
A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest pi acceptor, while the behavior of pyridine and carbene is nearly identical. This suggests that in these complexes comprising an electron-rich iron(cp)( carbene) fragment, N-heterocyclic carbenes are not pure sigma donors but also moderate pi acceptors. Theoretical calculations support this bonding model and indicate charge saturation at the metal as key for pi back-bonding to N-heterocyclic carbenes. On the basis of voltammetric measurements, the Lever electrochemical parameter of these carbenes has been determined: E-L = + 0.29. Systematic substitution of the wingtip groups of the carbene revealed only subtle changes in the electronic properties of the iron center, thus providing a suitable methodology for ligand-induced fine-tuning of the coordinated metal.