Synthesis, structure, and LLCT transitions in terminal hydrazido(2-) bipyridine complexes of titanium

Addition of 2,2'-bipyridine and its derivatives to Ti(NMe2)2(dpma), where dpma is N,N-di(pyrrolyl-alpha-methyl)-N-methylamine, followed by various hydrazine derivatives was used to generate a series of terminal hydrazido(2-) complexes. Among the new complexes is Ti=NN(H)Ph](But-bpy)(dpma), which was structurally characterized, where But-bpy is 4,4'-tert-butyl-2,2'-bipyridine. Other new complexes reported are Ti(NNMe2)(Me-bpy)(dpma), Ti(NNMe2)(bpy)(dpma), Ti(NNMe2)(Ph-bpy)(dpma), TiNN(Me)Ph](But-bpy)(dpma), TiNN(Me)p-tolyl](But-bpy)(dpma), and TiNN(Me)4-FC6H4](But-bpy)(dpma). Titanium hydrazido(2-) complexes bearing bpy substituents possess a low-energy transition, leading them to have blue or green colors, which is somewhat unusual for titanium(IV) species. Through absorption studies on the derivatives, it was determined that the low-energy transition is the result of an unusual ligand-to-ligand charge transfer where electron density residing on the hydrazido(2-) is transferred to the bpy pi* orbitals.