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

The reaction of [(Cp2NbTe2H)-Nb-#] (1(#); Cp-# = Cp* (C5Me5) or Cp-x (C5Me4 Et)) with two equivalents of [Co-2(CO)(8)] gives a series of cobalt carbony l telluride clusters that contain different types of niobocene carbonyl fra gments. At 0 degrees C, [(Cp2NbTe2Co3)-Nb-#(CO)(7)] (2(#)) and [Co4Te2(CO)( 10)] (3) are formed which disappear at higher temperatures: in boiling tolu ene a mixture of [cat(2)][Co9Te6(CO)(8)] (5(#)) (cat = [(Cp2Nb)-Nb-#(CO)(2) ](+)) and [cat(2)][Co11Te7(CO)(10)] (6(#)) is formed along with [cat][Co(CO )(4)] (4(#)). Complexes 6(#) transform into [cat][Co11Te7(CO)(10)] (7(#)) u pon 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 crystallo graphy. The structure of the neutral 2(Cp-x) consists of a [Co-3(CO)(6)Te-2 ] bipyramid which is connected to a [(C5Me4Et)(2)Nb(CO)] fragment through a mu(4)-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) [(Cp2Nb)-Nb-#(CO)(2)](+) cations. A part from 4, the anionic counterparts each contain an interstitial Co atom and are hexacapped cubic cluster anions [Co9Te6(CO)(8)](2-) (5) or heptacap ped pentagonal prismatic cluster anions [Co11Te7(CO)(10)](n-) (n = 2: [6](2 -), n = 1: [7](-)), respectively. Electrochemical studies established a rev ersible electron transfer between the anionic clusters [Co11Te7(CO)(10)](-) and [Co11Te7(CO)(10)](2-) in 6# and 7# and provided evidence for the exist ence of species containing [Co11Te7(CO)(10)] and [Co11Te7(CO)(10)](3-). The electronic structures of the new clusters and their relative stabilities a re examined by means of DFT calculations.