Aza-Michael Addition of Dinitrogen to α,β-Unsaturated Carbonyl Compounds in a Dititanium Framework

The direct use of dinitrogen (N2) as a building
block
for the synthesis of NN-containing organic compounds is of fundamental
interest and practical importance but has remained a formidable challenge
to date. Here, we report an unprecedented 1,4-conjugate (aza-Michael)
addition of N2 to α,β-unsaturated carbonyl
compounds in a dititanium framework. The resulting hydrazinopropenolate
products could be easily converted to diverse NN-containing organic
compounds such as β-hydrazine-functionalized esters and amides,
pyrazolidinones, and pyrazolines depending on the types of Michael
acceptors through protonation with MeOH. Further transformations of
a hydrazinopropenolate titanium complex through C–C and N–C
bond formations with electrophiles such as CO2 and benzaldehyde
have also been achieved. The mechanistic details of the N2 addition reaction have been elucidated by computational studies,
revealing the importance of redox-active metal centers in this event.
This work showcases the potential of using N2 as a building
block for the synthesis of NN-containing organic compounds through
activation and functionalization in a molecular metal framework.