Vanadium calixarene complexes as molecular models for supported vanadia

Abstract

Reaction of dimethylated tert-butyl calix[4]arene, H 2 A Me2 , with O VCl 2(thf) 2 unexpectedly led to the isolation of Cl V IV A Me , 2, whose crystal structure was determined. Hence, one of the MeO–C bonds present in H 2 A Me2 has been cleaved and one equivalent of HCl eliminated leaving three phenolate and one phenolether function to coordinate at the V centre. 2 smoothly reacts with O 2 to give O V V A Me , B, i.e. the chloride ligand has been replaced by a terminal oxo ligand with concomitant oxidation of the vanadium atom to the oxidation state +5. B crystallises isostructurally with 2; crystallisation of a mixture of 2 and B even leads to crystals that contain both compounds beside each other. However, when B was co-crystallised together with H 2 A Me2 , from acetonitrile a different structure with a partial cone conformation was obtained. The mechanism by which B is formed from 2 is discussed. To obtain information concerning the fate of the chloride ligand in 2, a derivative, Ph 3SiO–V IV A Me , 3, has been synthesised and investigated with respect to its behaviour in the presence of O 2: it reacts the same way as 2.