TY - DATA T1 - Synthesis, Structure, and Dynamics of Molybdenum Imido Alkyne Complexes PY - 2004/08/16 AU - Elon A. Ison AU - Thomas M. Cameron AU - Khalil A. Abboud AU - James M. Boncella UR - https://acs.figshare.com/articles/dataset/Synthesis_Structure_and_Dynamics_of_Molybdenum_Imido_Alkyne_Complexes/3328690 DO - 10.1021/om049942t.s001 L4 - https://ndownloader.figshare.com/files/5167900 KW - 3 SiN KW - 2 C 6 H 4 KW - bond KW - Molybdenum Imido Alkyne Complexes KW - transition state KW - VT NMR spectroscopy KW - imido π donation KW - 3LYP KW - ONIOM KW - NBO KW - alkyne fragment KW - alkyne rotation KW - complex KW - cis imido ligand N2 - The monomeric alkyne complexes (η2-alkyne)Mo(NPh)(o-(Me3SiN)2C6H4) (3) have been synthesized by the displacement of isobutylene from (η2-isobutylene)Mo(NPh)(o-(Me3SiN)2C6H4) (2). The alkyne fragment in these complexes is oriented perpendicular to the MoN bond of the cis imido ligand, as confirmed by an X-ray structural analysis of 3e. The deshielded nature of the chemical shifts of the α-carbons and terminal protons of the alkyne fragments in these complexes strongly suggests the participation of the alkyne π⊥ electrons in the Mo−alkyne interaction. The alkyne fragment in 3 rotates freely about the Mo−alkyne bond, resulting in the fluxional behavior of these complexes at room temperature. An activation barrier of 13.2 kcal/mol for the alkyne rotation was measured using VT NMR spectroscopy. Computational studies using a two-layer ONIOM model, and the B3LYP hybrid functional, provided insight into the Mo−alkyne bonding. The transition state for alkyne rotation has been calculated and is characterized by a parallel orientation of the alkyne fragment to the cis imido ligand. A natural bond orbital (NBO) population analysis reveals that alkyne π⊥ donation to Mo is more extensive in the transition state than in the ground state. Weaker Mo−N(imido) bonds are also observed in the transition state, because π donation from the alkyne ligand competes with imido π donation. ER -