title: Reactivity of nickel(II) and copper(II) complexes of a β-aminohydrazone ligand with pyridine-2-aldehyde: macrocyclization vs unprecedented pyrazole ring synthesis via C-C bond-forming reaction.
abstract: The synthesis and characterization of a mononuclear nickel(II) complex [Ni(L(2))](ClO(4))(2) (1) and an analogous mononuclear copper(II) complex [Cu(L(2))](ClO(4))(2) (2) of a 15-membered azamacrocycle (L(2) = 3-(2-pyridyl)-6,8,8,13,13,15-hexamethyl-1,2,4,5,9,12-hexaazacyclopentadeca-5,15-diene) are reported. The macrocyclic ligand is formed during the reaction of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone (L(1)) with pyridine-2-aldehyde (PyCHO) templated by metal ions. The X-ray crystal structure of 1 exhibits a distorted square-pyramidal coordination geometry, where the metal ion sits in the macrocyclic cavity and the pendant pyridine group of L(2) occupies the axial position. While 1 is stable in the presence of an excess of PyCHO, 2 reacts further with copper(II) salt and PyCHO to form a mononuclear copper(I) complex, [Cu(H(2)L(3))](ClO(4))(3) (3). The structure of the complex cation of 3 reveals a distorted tetrahedral coordination geometry at the copper center with a pseudo 2-fold screw axis. A two-dimensional (2D) polymeric copper(II) complex, {[Cu(2)(L(4))(2)](ClO(4))(2)}(n) (4) is obtained by reacting complex 2 (or [Ni(L(1))](ClO(4))(2)) with copper(II) perchlorate and pyridine-2-aldehyde in a methanol-water solvent mixture. Complex 4 is also obtained by treating 3 with copper(II) perchlorate and pyridine-2-aldehyde in the presence of a base. The X-ray structural analysis of 4 confirms the formation of a pyrazolate bridged dimeric copper(II) complex. The extended structure in the solid state of 4 revealed the formation of a 2D coordination polymer with the dimeric core as the repeating unit. The ligand (HL(4)) in 4 is a 3,4,5-trisubstituted pyrazole ring formed in situ via C-C bond formation and represents an unprecedented transformation reaction.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
authors.forename: Oindrila
authors.initials: O
authors.lastname: Das
authors.forename: Ennio
authors.initials: E
authors.lastname: Zangrando
authors.forename: Tapan Kanti
authors.initials: TK
authors.lastname: Paine
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D006835:Hydrazones / Q000737:chemistry*; D008024:Ligands; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D006835:Hydrazones; D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D011720:Pyrazoles; D003300:Copper; D009532:Nickel