%0 Generic %A Ison, Elon A. %A Cameron, Thomas M. %A Abboud, Khalil A. %A Boncella, James M. %D 2004 %T Synthesis, Structure, and Dynamics of Molybdenum Imido Alkyne Complexes %U https://acs.figshare.com/articles/dataset/Synthesis_Structure_and_Dynamics_of_Molybdenum_Imido_Alkyne_Complexes/3328690 %R 10.1021/om049942t.s001 %2 https://acs.figshare.com/ndownloader/files/5167900 %K 3 SiN %K 2 C 6 H 4 %K bond %K Molybdenum Imido Alkyne Complexes %K transition state %K VT NMR spectroscopy %K imido π donation %K 3LYP %K ONIOM %K NBO %K alkyne fragment %K alkyne rotation %K complex %K cis imido ligand %X 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. %I ACS Publications