Trinuclear (aminonitrone)Zn^II complexes as key intermediates in zinc(ii)-mediated generation of 1,2,4-oxadiazoles from amidoximes and nitriles

Abstract

Amidoximes react with zinc salts in undried EtOAc furnishing the trinuclear species, where amidoximes are stabilized in the aminonitrone form.

A Dimetallic Aminonitrone Nickel(II) Complex: Further Insights into Metal‐Mediated Nucleophilic Activation of Amidoximes

“…In the aminonitrone ligand, the O(1)‐N(1) bond is shorter than a normal single O‐N sp2 bond, whereas the N(1)‐C(1) and N(2)‐C(1) distances [1.295(4)‐1.297(2) and 1.318(4)‐1.324(3) Å, respectively] are intermediate between single and double bonds, which has been previously observed for aminonitrone ligands ,. The aminonitrone and amidoxime ligands are in a ( Z )‐configuration ,…”

“…In our previous work, we succeeded in the selective generation of trimetallic zinc(II) aminonitrone complexes (4 examples) featuring bridging aminonitrone ligands (type C ) and confirmed the availability of the aminonitrone form of the ligands in solutions. Our further investigations of aminonitrone complexes generated from amidoximes are described below.…”

“…The infrared (IR) spectrum of [ 1 ]Cl 4 •6H 2 O in KBr displays the characteristic features of two bands related to ν(C=N). The narrow band at 1670 cm −1 is characteristic of ν(C=N) in the aminonitrone ligands,, whereas the broad band at 1636 cm −1 is typical for two overlapped ν(C=N) bands of the O ‐iminoacyl amidoxime ligands ,,…”

“…In the chelating O ‐iminobenzoyl acetamidoxime ligand, the N(3)‐C(3) bond [1.258(4)‐1.268)4 Å] is a double bond, and the O(2)‐C(3) [1.345(3)‐1.354(2) Å] and O(2)‐N(4) [1.453(2)‐1.461(2) Å] distances correspond to single bonds, whereas the N(4)‐C(4) [1.296(4)‐1.304(3) Å] and N(5)‐C(4) distances [1.321(4)‐1.334(3) Å] intermediate between single and double bonds; all these distances are typical for chelating O ‐iminoacyl amidoximes ,,. In the aminonitrone ligand, the O(1)‐N(1) bond is shorter than a normal single O‐N sp2 bond, whereas the N(1)‐C(1) and N(2)‐C(1) distances [1.295(4)‐1.297(2) and 1.318(4)‐1.324(3) Å, respectively] are intermediate between single and double bonds, which has been previously observed for aminonitrone ligands ,. The aminonitrone and amidoxime ligands are in a ( Z )‐configuration ,…”

“…Coordination to a metal centre can stabilize amidoxime species in their tautomeric aminonitrone form, which consists of two coordination modes of amidoximes ( B and C ) among their three known types of coordination ( A ‐ C , for neutral amidoxime species) . In our recent report, we demonstrated that O ‐coordinated amidoximes in the C form were activated to participate in amidoxime‐nitrile coupling reactions. Due to this observation and the wide utilization of amidoxime O ‐functionalization reactions, from the one hand, and our interest to metal‐mediated reactions of NCR species with HO‐nucleophiles, such as amidoximes and oximes, from the other hand, further study of the metal‐mediated nucleophilic activation of these species and, especially, the development of factors providing this activation are worthy investigations.…”