TY - JOUR

T1 - Nickel(ii)-mediated cyanamide-pyrazole coupling highlights distinct reactivity of NCNR2and NCR nitrile ligands

AU - Zelenkov, Lev E.

AU - Kuznetsov, Maxim L.

AU - Andrusenko, Elena V.

AU - Avdontceva, Margarita S.

AU - Starova, Galina L.

AU - Bokach, Nadezhda A.

AU - Kukushkin, Vadim Yu

N1 - Funding Information: This work has been supported by the Russian Science Foundation (19-13-00013, synthetic experimental work) and Fundação para a Ciência e a Tecnologia (FCT), Portugal, project UIDB/00100/ 2020 of Centro de Qúımica Estrutural (theoretical studies). Physicochemical measurements were performed at Center for XRD Studies and Center for Chemical Analysis and Material Research (all belonging to Saint Petersburg State University). The authors deeply thank Prof. A.G. Starikov (Southern Federal University, Russia) for his kind help with a part of the theoretical calculations.

PY - 2020/5/7

Y1 - 2020/5/7

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85084412689&partnerID=8YFLogxK

U2 - 10.1039/d0nj00704h

DO - 10.1039/d0nj00704h

M3 - Article

AN - SCOPUS:85084412689

VL - 44

SP - 6979

EP - 6991

JO - New Journal of Chemistry

JF - New Journal of Chemistry

SN - 1144-0546

IS - 17

ER -