Basuli Falguni, Bailey Brad C, Brown Douglas, Tomaszewski John, Huffman John C, Baik Mu-Hyun, Mindiola Daniel J
Department of Chemistry, School of Informatics and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, USA.
J Am Chem Soc. 2004 Sep 1;126(34):10506-7. doi: 10.1021/ja0472376.
Four-coordinate vanadium complexes containing a terminal neopentylidyne functionality have been prepared by two consecutive alpha-hydrogen abstraction reactions both of which were induced by one-electron oxidations. Among these vanadium-alkylidyne complexes are the neutral and the cation (Nacnac)VCtBu(OTf) and [(Nacnac)VCtBu(THF)]+, respectively (Nacnac- = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3). The vanadium-alkylidynes have been characterized by 1H, 13C, 51V NMR spectroscopy and single-crystal X-ray diffraction and are consistent with a short VC bond. These alkylidynes were found to transform to azametalacyclohexatriene systems via an intramolecular cross-metathesis reaction. Kinetic studies of the transformation of (Nacnac)VCtBu(OTf) in C7D8 reveal the formation of the azametalacyclohexatriene to be independent of solvent (toluene vs THF) and the reaction to be first order in vanadium (k = 3.30(5) x 10-5 s-1 at 80 degrees C, with activation parameters DeltaH= 25.4(3) kcal/mol, DeltaS = -6(3) cal/molK). High-level DFT calculations on the full model suggest an intramolecular mechanism invoking only one transition state. The overall thermodynamic driving force for the reaction (DeltaG) in solution phase was estimated to be -21.3 kcal/mol.
通过两个连续的α-氢提取反应制备了含有末端新戊炔基官能团的四配位钒配合物，这两个反应均由单电子氧化引发。在这些钒-亚烷基配合物中，分别有中性的和阳离子型的(Nacnac)VCtBu(OTf)和[(Nacnac)VCtBu(THF)]⁺（Nacnac⁻ = [Ar]NC(CH₃)CHC(CH₃)N[Ar]，Ar = 2,6-(CHMe₂)₂C₆H₃）。这些钒-亚烷基配合物已通过¹H、¹³C、⁵¹V核磁共振光谱和单晶X射线衍射进行了表征，并且与短的V-C键一致。发现这些亚烷基通过分子内交叉复分解反应转化为氮杂金属环己三烯体系。对(Nacnac)VCtBu(OTf)在C₇D₈中的转化进行的动力学研究表明，氮杂金属环己三烯的形成与溶剂（甲苯与四氢呋喃）无关，并且该反应对钒为一级反应（在80℃时k = 3.30(5)×10⁻⁵ s⁻¹，活化参数ΔH = 25.4(3) kcal/mol，ΔS = -6(3) cal/mol·K）。对完整模型进行的高水平密度泛函理论计算表明，分子内机制仅涉及一个过渡态。溶液相中该反应的整体热力学驱动力（ΔG）估计为-21.3 kcal/mol。
