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.

[{(tBuC5H4)2Nb(CO)}3Co9(CO)8Te6⋅3 Cr(CO)5]: Unusual Stabilization of a Cubic Body-Centered Metal Telluride Cluster by Peripheral Complex Fragments

“…The first cobalt-containing representative of the [M 9 L 8 (m 4 -E) 6 ] class of compounds is the cluster salt [(C 5 Me 5 ) 2 Nb(CO) 2 ] 2 [Co 9 (CO) 8 Te 6 ] ([(C 5 Me 5 ) 2 Nb(CO) 2 ] 2 (1)), which was only obtained in very low yields, so that it is impossible to further investigate its chemical properties. [6] We now report on a rational synthesis of a cluster, that is closely related to the anion [1] 2À , but whose metal telluride sphere is expanded by peripheral transition metal complex fragments.The reaction of [Cp' 2 Nb(Te 2 )H] (Cp' tBuC 5 H 4 ) [7] with two equivalents of [Co 2 (CO) 8 ] in boiling toluene gave the dark red neutral compound [{Cp' 2 Nb(CO)} 3 Co 9 (CO) 8 Te 6 ] (2) in good yield after chromatographic work-up on silica gel. As mass spectra of 2 could not be obtained, its composition was derived from an X-ray diffraction analysis of the Cr(CO) 5 -adduct 3 (see below) and confirmed by C, H analyses.…”

“…[1] Clusters of the type [M 9 L 8 (m 4 -E) 6 ] (M Ni, Pd; L PPh 3 , CO, Cl; E GeEt, [2] As, [3] Sb, [4] Te [5] ) are characterized by an additional metal atom in the center of the cluster. The first cobalt-containing representative of the [M 9 L 8 (m 4 -E) 6 ] class of compounds is the cluster salt [(C 5 Me 5 ) 2 Nb(CO) 2 ] 2 [Co 9 (CO) 8 Te 6 ] ([(C 5 Me 5 ) 2 Nb(CO) 2 ] 2 (1)), which was only obtained in very low yields, so that it is impossible to further investigate its chemical properties. [6] We now report on a rational synthesis of a cluster, that is closely related to the anion [1] 2À , but whose metal telluride sphere is expanded by peripheral transition metal complex fragments.…”

“…These have been carried out on the structure model of the Co 9 (CO) 8 Te 6 cluster core bearing two-and threefold negative charge, for example [1] 2À [6] and [1] 3À . The MO scheme of [1] 3À is built up as following: Its HOMO, which is already known from [1] 2À to contain a high Co1-d z 2 orbital portion as well as significant s/p contributions of the axial Te atoms in a 1g symmetry, incorporates the additional valence electron of the Co 9 Te 6 core.…”

“…At 0 8C [Co 4 (CO) 10 Te 2 ] [13] and low quantities of [{Cp' 2 Nb(CO)}Co 3 (CO) 6 Te 2 ] are formed. The latter contains, like its peralkylated analogue, [6] a trigonalbipyramidal Co 3 (CO) 6 Te 2 cluster to which a Cp' 2 Nb(CO) fragment is connected through an apical Te ligand. At higher temperature the neutral cluster 2 is formed.…”

“…At higher temperature the neutral cluster 2 is formed. This is in strong contrast to the system [(C 5 Me 5 ) 2 Nb(Te 2 H)]/[Co 2 (CO) 8 ], which gives rise to the formation of salts that are built up from pentagonal-prismatic [Co 11 (CO) 10 Te 7 ] nÀ ions (n 1, 2) [6] and [(C 5 Me 5 ) 2 Nb(CO) 2 ] ions. The formation of such different cluster skeletons may be a consequence of the different structures of the employed niobocene tellurides.…”