J. Hesschenbrouck et al., Chromium-(II) and -(III) over a planar oxo surface modelled by calix[4]arene anions: redox chemistry and formation of Cr-C functionalities, J CHEM S DA, (2), 2000, pp. 191-198
Citations number
50
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
The metallation of [p-Bu(t)calix[4](ONa)(2)(OMe)(2)] 1 was performed using
[CrCl3(THF)(3)] and the resulting complex [Cr{p-Bu(t)calix[4](O)(2)(OMe)(2)
}(Cl)(THF)] 2 allowed entry into low valent and organometallic chemistry of
chromium. In the presence of strong bases or nucleophiles the ligand under
went demethylation exemplified by the reaction of 2 with pyridine, which le
d to [C5H4NMe][Cr{p-Bu(t)calix[4](O)(3)(OMe)}Cr(py)(Cl)] 3. The alkylation
of 2 was successful only when the concurrent reduction to Cr-II was irrelev
ant, in which case the two well characterized organometallic derivatives [C
r{p-Bu(t)calix[4](O)(2)(OMe)(2)}(Mes)] 4 [Mes=2,4,6-Me3C6H2] and [Cr{p-Bu(t
)calix[4](O)(2)(OMe)(2)}(eta(5)-C5H5)] 5 were obtained. None of them showed
, even under photochemical or thermal forced conditions, any sign of reacti
vity, due to the kinetic inertness of the d(3) configuration. Complex 2 was
easily reduced to the chromium(II) derivative [Cr{p-Bu(t)calix[4](O)(2)(OM
e)(2)}(THF)] 6, which underwent facile oxidative functionalization. The rea
ction with O-2 led to an unprecedented di-mu-oxo chromium(IV) derivative, [
Cr-2{p-Bu(t)calix[4](O)(2)(OMe)(2)}(2)(mu-O-2)] 7, which displays a ferroma
gnetic coupling between the two d(2) centres. The proposed structures are s
upported by X-ray analyses of complexes 2-4, 6 and 7.