245656-79-5Relevant academic research and scientific papers
Reactions of (Butadiene)tantalocene Cation with Alkyl Isocyanides
Strauch, Hans Christian,Wibbeling, Birgit,Fr?hlich, Roland,Erker, Gerhard,Jacobsen, Heiko,Berke, Heinz
, p. 3802 - 3812 (1999)
Treatment of (η4-s-trans-butadiene)tantalocene cation (3, with methyltris(pentafluorophenyl)borane anion) with tert-butyl isocyanide (4 h, at 45°C in bromobenzene) yields the [(η2-butadiene)(C≡NCMe3)TaCp2 +] complex 4a (70% isolated, v?(C≡NR) 2164 cm-1). Likewise treatment with n-butyl or cyclohexyl isocyanide gives the analogous products 4b and 4c, respectively. The cyclohexyl isocyanide adduct 4c was characterized by X-ray diffraction. It shows the η2-butadiene ligand oriented at the front of the Cp2Ta+ bent metallocene wedge with the noncoordinated butadiene vinyl group located in the vinyl-inside position. The Ta-C≡N-R unit is almost linear (angles Ta-C-N = 177.2(5)°, C≡N-R = 174.0(8)°; d(C≡N) = 1.152(6) A?). Photolysis of [(butadiene)TaCp2+] (3) with excess cyclohexyl isocyanide followed by thermal treatment gave rise to the formation of [bis(κC-cyclohexyl isocyanide)-TaCp2+] (8, with [CH3B(C6F5)3-] counteranion; >50% isolated, v?(C≡NR) 2134 and 2088 cm-1). Complex 8 was characterized by an X-ray crystal structure analysis. It shows a pseudotetrahedral [Cp2Ta(C≡NR)2+] cation (R = C6H11). The Ta-C≡N-R units are both slightly bent at nitrogen (angles C≡N-R = 169.0(13) and 163.7(8)°; the corresponding Ta-C-N angles are 179.4(9) and 177.4(7)°). The bonding situations of complexes 4 and 8 were analyzed by DFT calculations. The computational study shows that metal to isonitrile back-bonding does not contribute significantly to the CP2Ta+-C≡NR bonding interaction in these complexes. The bonding between Cp2Ta+ and the C≡NR ligands is dominated by electrostatic effects.
