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

Abstract

The direct use of dinitrogen (N 2 ) 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 N 2 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-hydrazinefunctionalized 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 CO 2 and benzaldehyde have also been achieved. The mechanistic details of the N 2 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 N 2 as a building block for the synthesis of NN-containing organic compounds through activation and functionalization in a molecular metal framework.

Iron(I) Complex Bearing an Open-Shell Diazenido Ligand

“…have received great research interests on their formation, structure, and reactivity . As early as the 1970s, Chatt had reported the intermediacy of (phosphine) 4 M­(NNH)­X (M = Mo, W; X = halides) in the protonation reactions of (phosphine) 4 M­(N 2 ) 2 . − Ever since then, an array of early transition-metal diazenido complexes, including those of Ti, Zr, Hf, Cr, , Mo, , and W, − have been prepared from the reactions of their dinitrogen complexes with electrophiles. Late transition-metal diazenido complexes derived from N 2 -functionalization reactions had remained unknown until this century.…”

Enantioselective Access to β-Amino Carbonyls via Ni-Catalyzed Formal Olefin Hydroamidation

“…The increasing interest in the synthesis of β-amino acid derivatives is driven by their presence in numerous biologically active compounds with significant biorelevant properties in drugs and natural products. − In addition, versatile utilities of (a)­cyclic oligo-β-peptides as a stable peptidomimetic motif demonstrate the importance of β-amino acids (Scheme a). , In pursuit of accessing this structural unit, present methodological refinement embraces classic approaches, such as the Mannich reaction of imines, , Arndt–Eistert homologation of α-amino carboxylic acids, and the acclaimed Noyori–Knowles-type hydrogenation of β-aminoacrylates . Recent innovations, including photocatalyst- or transition metal-enabled alkene carboamination, have also been explored. − In this progress, considering the broad availability of α,β-unsaturated esters, aza-Michael addition would be one of the most straightforward routes to the β-amino acid unit in an asymmetric manner. − Seidel et al recently accomplished a highly enantioselective conjugate addition of cyclic amines to α,β-unsaturated esters, facilitated by a selenourea-thiourea organocatalyst . However, the intrinsic low nucleophilicity of alkyl­(aryl) amide nucleophiles poses a significant challenge in realizing the targeted direct amidation of Michael acceptors.…”

Hydroamination of alkenes with dinitrogen in a trititanium polyhydride framework

“…Extensive studies on transition metal-mediated direct conversion of N 2 into nitrogen-containing organic compounds have been carried out 2,3,4,9,10,11,12,13,14, 15,16 . Typically, N 2 needs to be initially reduced to activated nitrogen species, which then enable to react with reactive carbon sources 17,18,19,20,21,22,23,24,25,26,27,28,29,30 . The carbon sources in such reaction processes are largely limited to carbon electrophiles.…”