Nickel(ii)-mediated cyanamide-pyrazole coupling highlights distinct reactivity of NCNR2and NCR nitrile ligands

Lev E. Zelenkov, Maxim L. Kuznetsov, Elena V. Andrusenko, Margarita S. Avdontceva, Galina L. Starova, Nadezhda A. Bokach, Vadim Yu Kukushkin

Результат исследований: Научные публикации в периодических изданияхстатья

Аннотация

The reaction between pyrazole (PzH), theN,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=C(NR2)Pz}2](X)2([1-5](X)2; R2= Me21, Et22, C4H83, C5H104, C5H10O5; X = NO3, OTf - in all combinations, and R2= Me21for 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:NCNR2was 1:4:(2.3). By using NiX2·6H2O (X = ClO4, OTs) and with the molar ratio NiX2:PzH:NCNR21:3:(3.5), the pure tris-chelate species [Ni{NH=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=C(NR2)Pz}3]2+species is thermodynamically driven with the energetic difference 4.6 kcal mol−1between 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)2were established by single crystal X-ray diffraction.

Язык оригиналаанглийский
Страницы (с-по)6979-6991
Число страниц13
ЖурналNew Journal of Chemistry
Том44
Номер выпуска17
DOI
СостояниеОпубликовано - 7 мая 2020

Предметные области Scopus

  • Катализ
  • Химия (все)
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