THE CHEMISTRY OF VANADIUM-CARBON BOND FUNCTIONALITIES OVER AN OXO-SURFACE DEFINED BY THE CALIX[4]ARENE SKELETON - THE REDOX RELATIONSHIP BETWEEN VANADIUM(III) AND VANADIUM(IV) ASSISTED BY CARBON-OXYGEN BOND-CLEAVAGE

This report deals with the chemistry of V-C functionalities anchored t o a quasi-planar O-4 matrix represented here by the [p-Bu-t-calix[4]-( OMe)(2)(O)(2)](2-) macrocycle. The starting material [p-Bu-t-calix[4]- (OMe)(2)(O)(2)V-Cl], 2, has been converted into the corresponding alky l and aryl derivatives [p-Bu-t-calix[4]-(OMe)(2)(O)(2)V-R] (R = Me, 3; R = CH2Ph, 4; R = p-MeC6H4, 5) by conventional procedures. The struct ure of 5 reveals the self-assembling of the monomeric unit into a colu mnar arrangement with the p-tolyl substituent functioning as a guest m oiety in a neighboring unit. Complexes 3-5 undergo migratory insertion reactions with CO and (BuNC)-N-t to the corresponding eta(2)-acyls [p -Bu-t-calix[4]-(OMe)(2)(O)(2)V(eta(2)-COR)] (R = Me, 6; R = CH2Ph, 7) and eta(2)-iminoacyls [p-Bu-t-calix[4]-(OMe)(2)(O)(2)V{eta(2)-C(NBut)R }] (R = Me, 8; R = CH2Ph, 9; R = p-MeC6H4, 10), the reaction with CO b eing strongly dependent on the R substituent. The structural model for the hexacoordinate intermediate leading to the inserted product is ex emplified by the d(2) high-spin [p-Bu-t-calix[4]-(OMe)(2)(O)(2)V(Cl)(C NBut], 11, and proves the presence of four available orbitals at the m etal for driving the reactivity in the [p-Bu-t-calix[4]-(OMe)(2)(O)(2) V] fragment. The bonding mode of the organic functionalities at the me tal and the conversion of the alkyl substituent into the eta(2)-acyl h ave been inspected by extended Huckel calculations. The oxidative deme thylation of 3 and 5 by a controlled amount of iodine opened an intere sting synthetic route to the corresponding vanadium(IV) organometallic derivatives [p-Bu-t-calix[4]-(OMe)(O)(3)V-X] (X = Cl, 12; X = p-MeC6H 4, 13). A structural report on 2, 5, and 9 is included.