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Issue 17, 2020
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Nickel(ii)-mediated cyanamide–pyrazole coupling highlights distinct reactivity of NCNR2 and NCR nitrile ligands

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Abstract

The reaction between pyrazole (PzH), the N,N-disubstituted cyanamides NCNR2 (R2 = Me2, Et2, C4H8, C5H10, C5H10O), and the nickel salts NiX2·nH2O (X = NO3, OTf, ClO4, Cl, OTs, n = 6; Br, n = 3) affords complexes featuring ligands derived from the NiII-mediated cyanamide–pyrazole coupling. The composition of the products and their yields are strongly affected by the choice of NiX2·nH2O and a molar ratio between the reactants. The [Ni(PzH)2{NH[double bond, length as m-dash]C(NR2)Pz}2](X)2 ([1–5](X)2; R2 = Me21, Et22, C4H83, C5H104, C5H10O 5; X = NO3, OTf – in all combinations, and R2 = Me21 for X = Cl, Br) complexes (named here as bis-chelate complexes), featuring two chelated ligands derived from the cyanamide–pyrazole coupling, were obtained selectively from NiX2·nH2O when the molar ratio between the reactants NiX2 : PzH : NCNR2 was 1 : 4 : (2.3). By using NiX2·6H2O (X = ClO4, OTs) and with the molar ratio NiX2 : PzH : NCNR2 1 : 3 : (3.5), the pure tris-chelate species [Ni{NH[double bond, length as m-dash]C(NR2)Pz}3]X2 ([6–7](ClO4)2, R2 = C4H86, C5H107; [8](OTs)2, R2 = Me2) were isolated. Structurally similar complexes are not formed under the coupling conditions when conventional nitriles NCR (R = Alk; for instance, NCMe) were applied as the nitrile component of the reaction. Quantum-chemical calculations demonstrate that generation of the tris-chelate [Ni{NH[double bond, length as m-dash]C(NR2)Pz}3]2+ species is thermodynamically driven with the energetic difference 4.6 kcal mol−1 between appropriate bis- and tris-chelate products, while for conventional nitrile derivatives the bis-chelate products are thermodynamically more preferable. The structures of eight complexes, viz. [1](Cl)2, [1–2](NO3)2, [4](NO3)2, [1–2](OTf)2, [3](OTf)2·Me2CO, and [9](OTf)2 were established by single crystal X-ray diffraction.

Graphical abstract: Nickel(ii)-mediated cyanamide–pyrazole coupling highlights distinct reactivity of NCNR2 and NCR nitrile ligands

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Supplementary files

Article information


Submitted
10 Feb 2020
Accepted
06 Apr 2020
First published
06 Apr 2020

New J. Chem., 2020,44, 6979-6991
Article type
Paper

Nickel(II)-mediated cyanamide–pyrazole coupling highlights distinct reactivity of NCNR2 and NCR nitrile ligands

L. E. Zelenkov, M. L. Kuznetsov, E. V. Andrusenko, M. S. Avdontceva, G. L. Starova, N. A. Bokach and V. Yu. Kukushkin, New J. Chem., 2020, 44, 6979
DOI: 10.1039/D0NJ00704H

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