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Bis(η‐ tert ‐butylcyclopentadienyl)hydridoniobium Ditelluride, a Convenient Reagent for the Synthesis of Polynuclear Metal Telluride Complexes
Author(s) -
Brunner Henri,
Cattey Helene,
Evrard David,
Kubicki Marek M.,
Mugnier Yves,
Vigier Estelle,
Wachter Joachim,
Wanninger Robert,
Zabel Manfred
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200206)2002:6<1315::aid-ejic1315>3.0.co;2-0
Subject(s) - chemistry , ligand (biochemistry) , crystallography , telluride , reagent , moiety , crystal structure , metal , yield (engineering) , ring (chemistry) , stereochemistry , organic chemistry , biochemistry , materials science , receptor , metallurgy
Reaction of [Cp′ 2 NbH 3 ] (Cp′ = t BuC 5 H 4 ) with Te powder in THF gives [Cp′ 2 Nb(Te 2 )H] ( 1 ) and [Cp′ 6 Nb 4 Te 4 O] ( 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) 5 THF] to give [Cp′ 2 Nb(Te 2 )H·Cr(CO) 5 ] ( 3 ) and [Cp′ 6 Nb 4 Te 4 O·2Cr(CO) 5 ] ( 4 ), respectively. The crystal structures of 2−4 have been determined. In 3 a Te 2 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 Nb 2 Te 2 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 Nb 2 Te 2 ring. Thermolysis of 3 leads to the formation of diamagnetic [Cp′ 4 Nb 2 Te 2 ] ( 5 ), which also contains a planar Nb 2 Te 2 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 CH 3 I with successive methylation of both Te bridges to give [Cp′ 4 Nb 2 Te(CH 3 Te)]I ([ 6 ] I ) and [Cp′ 4 Nb 2 (CH 3 Te) 2 ]I 2 ([ 7 ] I 2 ). The crystal structure of [ 7 ] I 2 may be derived from that of 5 , the incoming CH 3 groups being fixed at the Te bridges in a trans position. 1 H NMR spectroscopic investigations reveal a restricted rotation around the Cp′−Nb bonds in 2 and 5 at −90 °C and in 4 and [ 7 ] I 2 at ambient temperature. Electrochemical studies have been carried out on 5 , [ 6 ] I , and [ 7 ] I 2 , 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 ] I 2 . There is also a clear linear correlation between the reduction potentials measured for 5 to [ 7 ] I 2 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)