Lewis Base Behavior of Bridging Nitrido Ligands of Titanium Polynuclear Complexes

Abstract

The Lewis base behavior of mu(3)-nitrido ligands of the polynuclear titanium complexes [{Ti(eta(5)-C(5)Me(5))(mu-NH)}(3)(mu(3)-N)] (1) and [{Ti(eta(5)-C(5)Me(5))}(4)-(mu(3)-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) trifluorornethanesulfonate through the basal NH imido groups to give cube-type adducts [XCu{(mu(3)-NH)(3)Ti(3)(eta(5)-C(5)Me(5))(3)(mu(3)-N)}] (X=Cl (3), Br (4), I (5), OSO(2)CF(3) (6)). However, the treatment of 1 with an excess (>= 2 equiv) of copper reagents afforded complexes [XCu{(mu(3)-NH)(3)Ti(3)(eta(5)-C(5)Me(5))(3)(mu(4)-N)(CuX)}] (X=Cl (7), Br (8), I (9) OSO(2)CF(3) (10)) by incorporation of an additional CuX fragment Lit the mu(3)-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 mu(3)-N ligands to give complexes [{Ti(eta(5)-C(5)Me(5))}(4)(mu(3)-N)(4-n)-{(mu(4)-N)CuX}(n)] (X=Br (11), n=1; X=Cl (12) n=2; X=OSO(2)CF(3) (13), n=3). Compound 2 also reacts with silver(I) trifluoromethanesulfortate (>= 1 equiv) to give the adduct [{Ti(eta(5)-C(5)Me(5))}(4)(mu(3)-N)(3){(mu(4)-N)AgOSO(2)CF(3)}] (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(eta(5)-C(5)H(5))(mu-NH)}(3)(mu(3)-N)] (1') and [{Ti(eta(5)-C(5)H(5))}(4)-(mu(3)-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 V, in both complexes the mu(3)-nitrido groups act as two-electron donor Lewis bases to the appropriate Lewis acids.