Electrophilic vs. nucleophilic reactivity in complexes containing multiply-bonded (alkylidene, imido or oxo) ligands. A conceptual model

Terminal Imido Complexes of the Groups 9–11: Electronic Structure and Developments in the Last Decade

“…However, the energies of the valence d ‐orbitals decrease when moving to the late transition metals (Figure 2B); the same is true when moving from the 3 d to the 4 d or 5 d elements of the late transition metals [17] or for high‐valent complexes of the group 8 and 9 metals. This renders the bonds with the ligands increasingly covalent and reduces the formal bond order due to the population of anti ‐bonding molecular orbitals.…”

Catalytic Oxo/Imido Heterometathesis by a Well‐Defined Silica‐Supported Titanium Imido Complex

“…Our initial attempts focused on Mo and V,– and more recently Ta . However, the reactivity of the imido complexes increases drastically when going left across the d‐block of the periodic table, the most exciting examples being found for Ti– and Zr– by Mountford, Bergman, and others. At the same time, terminal oxo derivatives of these metals show a pronounced tendency to oligomerize with the formation of bridging μ‐oxo ligands, which restricts their application in catalysis.…”

“…In particular, V and Mo catalysts, which are very efficient in imidation of aldehydes, display poor activities already in the case of benzophenone, and only Ta is competent under these reaction conditions, albeit with much lower activity than Ti/SiO 2 . These observations are fully consistent with the periodic trends identified in the studies of stoichiometric reactivity of molecular imido complexes and indicate that Ti is indeed the metal of chose for these reactions –…”

Bis(organoimido)-complexes of tungsten(IV): the crystal and molecular structures of tetrachlorobis(t-butylamine)bis(t-butylimido)bis(µ-p-tolylimido)-ditungsten(VI) and tetrachlorobis(µ-phenylimido)-bis(t-butylamine) bis(t-butylimido)ditungsten(VI)

“…-1 781( 15) N( 3 12) Cl( 13) Cl( 14) C( 2) Cl( 21) Cl( 22) Cl( 23) Cl( 24) Cl( 25) Cl( 26 ( 14) imido ligand is preferred. In general the a-carbon resonance position for these complexes does not distinguish between bridging or terminal imido ligands.…”