Highly Reactive Ni^II‐Bound Nitrile–Oxime Coupling Intermediates Stabilized by Substituting Conventional Nitriles with a Dialkylcyanamide

Abstract

Nickel(II)‐mediated coupling between the cyanamide Me2NCN and the ketoximes Me(R)C=NOH (R = Me, Ph) gives chelates of the general formula [NiClx(H2O)y{HN=C(NMe2)(ON=C(R)Me)}2]n+ ([1]+: R = Me; x = 1, y = 0; salts with both Cl– and [NiCl4]2– were isolated; [2]2+: R = Me; x = 0, y = 2; salt with Cl– was isolated; [3]+: R = Ph; x = 1, y = 1; salt with Cl– was isolated) and the iminium salts [H2N=C(NMe2)ON=C(R)Me]+ ([4]+: R = Me; salt with [NiCl4]2– was isolated; [5]+: R = Ph; salt with Cl– was isolated). This reaction demonstrates the difference in the reactivity between conventional nitriles and dialkylcyanamides: whereas nitriles RCN (R = Alk, Ar) react with NiII/ketoxime systems to afford (1,3,5‐triazapentadiene)NiII species, formed by postulated nitrile–oxime coupling intermediates, cyanamides under the same conditions give either stable cyanamide–oxime coupling products or the Busch‐type complex [Ni{HN=C(Me)CH2C(Me2)NH2}2]Cl2 ([6]Cl2). The reason for the different stability of the coupling products was interpreted theoretically on the basis of quantum chemical calculations (M06‐L/6‐31G* level of theory). The NMe2 moiety in the chelate ligands leads to an increase in electron‐density delocalization and also stabilizes the systems in terms of electrostatic factors.

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

“…Secondly, we demonstrated that nickel(II) promotes conventional nitrile‐amidoxime coupling, resulting in the formation of O ‐iminobenzoyl acetamidoxime ligands. On one hand, Ni II electrophilically activated PhCN towards the addition of the HO ‐nucleophile, which is in agreement with our and other groups results of Ni II ‐mediated reactions of RCN ,. On the other hand, binding to Ni II centre through the O atom stabilized the amidoxime in the aminonitrone form, which was highly reactive in nucleophilic addition to the ‐C≡N bond .…”

“…The complex was precipitated from the reaction mixture as the hexahydrate [ 1 ]Cl 4 •6H 2 O in 47% average isolated yield (the synthesis was repeatedly reproduced in ±3% yield deviations). The reaction is likely specific for amidoximes, as no generation of similar complexes featuring ketonitrone ligands were previously detected when ketoximes MeC(R’)=NOH (R’=Me, Ph) were employed in this reaction . A similar reaction of acetamidoxime with aliphatic nitriles, viz.…”

“…The high‐resolution electrospray ionisation mass spectrometry (HRESI + ‐MS) data are typical for the fragmentation ions of this type of complex (see characterization) ,,,. Due to kinetic lability of nickel(II) complexes, we paid special attention to studying the structure of the complex in solution.…”

Structure, Spectroscopy, and Electrochemistry of Manganese(I) and Rhenium(I) Quinoline Oximes

“…Metal-assisted deoximation of oxime ligands to a variety of products, including primary imines, has been reported previously. ,,− While definitive mechanisms have not been established, it has been suggested that the electrophilicity of the oxime moiety is a key factor in deoximation. ,, Our results favor this proposal, as the electron withdrawing CF 3 moiety (as well as nitrogen coordination to the metal center) in the quinoline oxime Re4im would increase the electrophilicity of the oxime carbon atom. The lack of an electron-withdrawing substituent in the aldoxime analogue Re-6 appears to disfavor deoximation.…”

Preparation of Diethylcyanamide and Cyanoguanidine Complexes of Iridium

“…The coordination chemistry and reactivity af amino‐functionalised nitriles such as cyanamides N≡CNH 2 and N≡CNR 2 (R = alkyl or aryl) and its dimeric form cyanoguanidine N≡CN(H)C(NH 2 )=NH have been well developed in the last years and a number of studies have been reported in the literature Interesting appear not only the preparation of new complexes, but also the nucleophilic attack on the cyanamide carbon atoms affording new derivatives ,,,,. However, the papers reported on dialkylcyanamide and cyanoguanidine complexes of transition metals are still relatively few‐ as compared to nitrile RCN derivatives .…”