Early transition metal-catalyzed nitrene transfer reactions

Abstract

There are a myriad of uses for nitrogen-containing compounds in pharmaceuticals, natural products, dyes, materials, and ancillary ligands. Along these lines, formulating new sustainable methodologies for the rational and economical synthesis of C-N bonds is of the utmost importance. With respect to sustainability, Ti is a highly abundant resource that has received a relative lack of attention outside of α-olefin polymerization, in spite of its abundance and non-toxic properties. This is in part due to the propensity of Ti to remain in its highest oxidation state, a property that is shared among most early transition metals. The difficulty of reversibly accessing low-valent states is problematic in the development of new redox-catalytic transformations with Ti. Herein we discuss Ti- catalyzed nitrene transfer reactions for the synthesis of carbodiimides and α,β- unsaturated imines, as well as the synthesis and reactivity of an unusual 2-electron reduced carbodiimide complex of Ti, namely Cp2Ti-(κ2-tBuNCNtBu), which bears a free carbene. In addition, the development of two V-based systems for the [2+2+1] synthesis of pyrroles from alkynes and diazenes is discussed.