Lewis Base Behavior of Bridging Nitrido Ligands of Titanium Polynuclear Complexes

The Lewis base behavior of μ₃‐nitrido ligands of the polynuclear titanium complexes {Ti(η⁵‐C₅Me₅)(μ‐NH)}₃(μ₃‐N)] ( 1 ) and {Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)₄] ( 2 ) to MX Lewis acids has been observed for the first time. Complex 1 entraps one equivalent of copper(I ) halide or copper(I ) trifluoromethanesulfonate through the basal NH imido groups to give cube‐type adducts XCu{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₃‐N)}] (X=Cl ( 3 ), Br ( 4 ), I ( 5 ), OSO₂CF₃ ( 6 )). However, the treatment of 1 with an excess (≥2 equiv) of copper reagents afforded complexes XCu{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₄‐N)(CuX)}] (X=Cl ( 7 ), Br ( 8 ), I ( 9 ), OSO₂CF₃ ( 10 )) by incorporation of an additional CuX fragment at the μ₃‐N nitrido apical group. Similarly, the tetranuclear cube‐type nitrido derivative 2 is capable of incorporating one, two, or up to three CuX units at the μ₃‐N ligands to give complexes {Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)_4?n{(μ₄‐N)CuX}_n] (X=Br ( 11 ), n=1; X=Cl ( 12 ), n=2; X=OSO₂CF₃ ( 13 ), n=3). Compound 2 also reacts with silver(I ) trifluoromethanesulfonate (≥1 equiv) to give the adduct {Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)₃{(μ₄‐N)AgOSO₂CF₃}] ( 14 ). X‐ray crystal structure determinations have been performed for complexes 8 – 13 . Density functional theory calculations have been carried out to understand the nature and strength of the interactions of {Ti(η⁵‐C₅H₅)(μ‐NH)}₃(μ₃‐N)] ( 1′ ) and {Ti(η⁵‐C₅H₅)}₄(μ₃‐N)₄] ( 2′ ) model complexes with copper and silver MX fragments. Although coordination through the three basal NH imido groups is thermodynamically preferred in the case of 1′ , in both complexes the μ₃‐nitrido groups act as two‐electron donor Lewis bases to the appropriate Lewis acids.