Synthesis and molecular structure of [Cp′2V(μ-S)2VCp′]2(μ-O)

Kekia, Omar M.; Rheingold, Arnold L.

doi:10.1016/s0022-328x(97)00353-7

“…A similar structure has been found in [CpЈ 6 V 4 S 4 O]. [17] The diamagnetic nature of the molecule is deduced from its 1 H NMR spectrum (see below) and it may be explained by the presence of direct NbϪNb interactions: Whereas the TeϪTe distances (4.236 Å ) approximately correspond to the sum of the van der Waals radii [18] the NbϪNb distances (3.43 Å ) are only slightly longer than those in [(C 5 H 5 ) 2 Nb(µ-S)] 2 [d(NbϪNb) 3.2340(8) Å ] [19] or in [C 5 H 5 (C 5 H 4 )NbH] 2 (3.105 Å ), [20] for which NbϪNb bonds have been postulated. The possibility of through-space NbϪNb coupling in complexes containing Nb 2 Te 2 rings has been investigated for compounds 5, [6]I, and [7]I 2 (see below).…”

Section: Preparation and Characterization Of Complexes 1؊4supporting

confidence: 81%

Bis(η-tert-butylcyclopentadienyl)hydridoniobium Ditelluride, a Convenient Reagent for the Synthesis of Polynuclear Metal Telluride Complexes

Brunner¹,

Cattey²,

Evrard³

et al. 2002

Eur. J. Inorg. Chem.

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Reaction of [Cp′2NbH3] (Cp′ = tBuC5H4) with Te powder in THF gives [Cp′2Nb(Te2)H] (1) and [Cp′6Nb4Te4O] (2). The yield of 1 varies between 10 and 81% depending on the degree of oxygen contamination of the reagents. Complexes 1 and 2 react with [Cr(CO)5THF] to give [Cp′2Nb(Te2)H·Cr(CO)5] (3) and [Cp′6Nb4Te4O·2Cr(CO)5] (4), respectively. The crystal structures of 2−4 have been determined. In 3 a Te2 unit and an H ligand are coordinated to a bent niobocene moiety; the Cr(CO)5 group is attached to the lateral Te atom. The molecular cores of 2 and 4 are practically identical in that they contain two planar Nb2Te2 rings connected by a nearly linear oxygen bridge. Each of the “outer” Nb atoms bears two Cp′ ligands, whereas the “inner” Nb atom only has one such ligand. An additional structural feature in 4 is two Cr(CO)5 groups, attached to one Te bridge of each Nb2Te2 ring. Thermolysis of 3 leads to the formation of diamagnetic [Cp′4Nb2Te2] (5), which also contains a planar Nb2Te2 core. The relatively long transannular Nb−Nb distance (3.647 Å) is consistent, according to DFT calculations, with a through‐space Nb−Nb coupling. Complex 5 reacts with CH3I with successive methylation of both Te bridges to give [Cp′4Nb2Te(CH3Te)]I ([6]I) and [Cp′4Nb2(CH3Te)2]I2 ([7]I2). The crystal structure of [7]I2 may be derived from that of 5, the incoming CH3 groups being fixed at the Te bridges in a trans position. 1H NMR spectroscopic investigations reveal a restricted rotation around the Cp′−Nb bonds in 2 and 5 at −90 °C and in 4 and [7]I2 at ambient temperature. Electrochemical studies have been carried out on 5, [6]I, and [7]I2, showing that all compounds undergo two reversible one‐electron reduction steps. The reduction potential decreases by ca. 1.6 V when going from 5 to [7]I2. There is also a clear linear correlation between the reduction potentials measured for 5 to [7]I2 and the energies of the corresponding LUMO’s calculated at the DFT/B3LYP level. These LUMO’s bear some 70% contribution from both Nb atoms and, consequently, the reduction processes mainly operate at both metallic centers. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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“…A similar structure has been found in [CpЈ 6 V 4 S 4 O]. [17] The diamagnetic nature of the molecule is deduced from its 1 H NMR spectrum (see below) and it may be explained by the presence of direct NbϪNb interactions: Whereas the TeϪTe distances (4.236 Å ) approximately correspond to the sum of the van der Waals radii [18] the NbϪNb distances (3.43 Å ) are only slightly longer than those in [(C 5 H 5 ) 2 Nb(µ-S)] 2 [d(NbϪNb) 3.2340(8) Å ] [19] or in [C 5 H 5 (C 5 H 4 )NbH] 2 (3.105 Å ), [20] for which NbϪNb bonds have been postulated. The possibility of through-space NbϪNb coupling in complexes containing Nb 2 Te 2 rings has been investigated for compounds 5, [6]I, and [7]I 2 (see below).…”