Binuclear alkoxide complexes of niobium and tantalum in lower oxidation states

Abstract

Our knowledge of Nb and Ta complexes with RO/sup -/ and ROH ligands is almost exclusively limited to those in the highest oxidation state of the metals. Thus while extensive and multifaceted studies have been carried out for the M(V) species, there have been only a few reports dealing with such compounds involving tetravalent metals and none in lower oxidation states. In view of the very rich chemistry of Mo and W alkoxides and recent developments in the chemistry of low-valent Nb and Ta complexes, where interesting novel complexes and remarkable reactivity patterns have been found, there seems to be a considerable potential in the compounds of these two elements in oxidation states lower than +5 with alcohol-related ligands. Accordingly the authors have explored the reaction of the confacial bioactahedral Nb/sub 2/Cl/sub 6/(THT)/sub 3/ (1), THT = tetrahydrothiophene, with alcohols, ROH, for R = Me, Et and i-Pr. Three different types of compounds have been characterized by X-ray crystallography. A purple solution of 1 in toluene changes to brown within several hours upon addition of excess alcohol. For R = Et and i-Pr the removal of solvent under vacuum affords a compound of the formula Nb/sub 2/Cl/sub 5/-(OR)ROH)/sub 4/ (2)more » in the form of an orange or yellow-brown powder or a brown crystalline solid. 19 references, 3 figures.« less