Terminal Vanadium−Neopentylidyne Complexes and Intramolecular Cross-Metathesis Reactions to Generate Azametalacyclohexatrienes

• Published in: Journal of the American Chemical Society Vol. 126; no. 34; pp. 10506 - 10507
• Main Authors: Basuli, Falguni, Bailey, Brad C, Brown, Douglas, Tomaszewski, John, Huffman, John C, Baik, Mu-Hyun, Mindiola, Daniel J
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.09.2004; Amer Chemical Soc
• Subjects: Chemical reactivity; Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; Organic chemistry; Physical Sciences; Reactivity and mechanisms; Science & Technology; ACETYLENES; HYDROGEN; ALKYLIDYNE; METAL-CARBON BONDS; Intramolecular reaction; Vanadium Organic compounds; Organic ligand; Theoretical study; Density functional method; Transition metal Complexes; Experimental study; Chemical reactivity; Ylidyne complex
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0472376

Four-coordinate vanadium complexes containing a terminal neopentylidyne functionality have been prepared by two consecutive α-hydrogen abstraction reactions both of which were induced by one-electron oxidations. Among these vanadium−alkylidyne complexes are the neutral and the cation (Nacnac)V⋮CtBu(OTf) and [(Nacnac)V⋮CtBu(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 V⋮C bond. These alkylidynes were found to transform to azametalacyclohexatriene systems via an intramolecular cross-metathesis reaction. Kinetic studies of the transformation of (Nacnac)V⋮CtBu(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) × 10-5 s-1 at 80 °C, with activation parameters ΔH ⧧= 25.4(3) kcal/mol, ΔS ⧧ = −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 (ΔG) in solution phase was estimated to be −21.3 kcal/mol.