Metal telluride clusters composed of niobocene carbonyl, telluride, and cobalt carbonyl units: syntheses, structures, and reactivity

Abstract: The reaction of Cp#2NbTe2H] (1#; Cp# = Cp* (C5Me5) or Cp(x) (C5Me4Et)) with two equivalents of Co2(CO)8] gives a series of cobalt carbonyl telluride clusters that contain different types of niobocene carbonyl fragments. At 0 degrees C, Cp#2NbTe2CO3(CO)7] (2#) and Co4Te2(CO)10] (3) are formed which disappear at higher temperatures: in boiling toluene a mixture of cat2]Co9Te6(CO)8] (5#) (cat= Cp#2Nb(CO)2]+) and cat2]Co11Te7(CO)10] (6#) is formed along with cat]Co(CO)4] (4#). Complexes 6# transform into cat]Co11Te7(CO)10] (7#) upon interaction with HPF6 or wet SiO2. The molecular structures of 2(Cp(x)), 4(Cp(x)), 5(Cp*), 6(Cp*) and 7(Cp*) have been determined by X-ray crystallography. The structure of the neutral 2(Cp(x)) consists of a Co3(CO)6Te2] bipyramid which is connected to a (C5Me4Et)2Nb(CO)] fragment through a mu4-Te bridge. The ionic structures of 4(Cp(x)), 5(Cp*), 6(Cp*) and 7(Cp*) each contain one (4, 7) or two (5, 6) Cp#2Nb(CO)2]+ cations. Apart from 4, the anionic counterparts each contain an interstitial Co atom and are hexacapped cubic cluster anions Co9Te6(CO)8]2- (5) or heptacapped pentagonal prismatic cluster anions Co11Te7(CO)10]n- (n=2: 6]2- , n=1: 7]-), respectively. Electrochemical studies established a reversible electron transfer between the anionic clusters Co11,Te7(CO)10]- and Co11Te7(CO)10]2in 6# and 7# and provided evidence for the existence of species containing Co11Te7(CO),0] and Co11Te7(CO)0]3-. The electronic structures of the new clusters and their relative stabilities are examined by means of DFT calculations.