Versatility of the bis(iminopyrrolylmethyl)amine ligand: tautomerism, protonation, helical chirality, and the secondary coordination sphere with halogen bonds in the formation of copper() and nickel() complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-10, Vol.49 (39), p.1384-13853
• Main Authors: Kumar, Rajnish, Guchhait, Tapas, Subramaniyan, Vasudevan, Schulzke, Carola, Mani, Ganesan
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Chirality; Chloroform; Coordination compounds; Copper compounds; Copper converters; Crystal lattices; Crystallography; Enantiomers; Geometry; Ligands; Molecular structure; Nickel chloride; NMR; Nuclear magnetic resonance; Protonation
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt02964e

The reaction of N , N -di(2,6-bis(isopropyl)phenylimino-pyrrolyl-α-methyl)- N -methylamine H 2 L1 with copper( i ) sources such as CuX (X = Cl ( 1 ), Br ( 2 ), and I ( 3 )) afforded bis(chelated) ionic copper( ii ) complexes of the type [Cu L1 H]X. A similar type of mononuclear structure was obtained with Cu(NO 3 ) 2 ·(H 2 O) 3 . Conversely, binuclear copper( ii ) complexes [Cu 2 (μ- L1 )(μ-OOCCH 3 )(μ-OH)]( 4 ) and [Cu 2 (μ- L1 H)(μ-OOCPh)(μ-O)] ( 5 ) were obtained from the reaction of Cu(O 2 CR) 2 ·H 2 O with H 2 L1 . Notably, these reactions in the presence of a base yielded the neutral copper( ii ) complex [Cu L1 ] ( 6 ). This product was also obtained from the reaction of complex 2 or 4 with NaOH in methanol. All structures feature a dianionic imino-pyrrole motif and a protonated central amine function except 4 . The reaction of H 2 L1 with NiCl 2 ·DME gave the mononuclear complex [NiCl 2 ( L1 H 2 )], 7 . In contrast to this, the reaction of the newly synthesized sterically less encumbered ligand N , N -di(phenylimino-pyrrolyl-α-methyl)- N -methylamine H 2 L2 with NiCl 2 ·DME gave the binuclear complex [NiCl( L2 H 2 )(HOMe)] 2 [Cl] 2 ( 8 ). Both 7 and 8 show the amine-azafulvene ligand form and coordination of the central amine. The reaction of complex 7 with NaHBEt 3 yielded a neutral complex [Ni L1 ] ( 8 ) containing the imino-pyrrole form. In the molecular structures, interesting secondary coordination spheres incorporating guest molecules such as CHCl 3 and MeOH in the crystal lattices and the presence of helical enantiomers were observed and analysed. In one case, CHCl 3 was found inside an unusual cage-like structure supported by halogen bonds. Preliminary DFT calculations on the geometry of the nickel complex with H 2 L1 showed that the pentacoordinated tbp geometry is more stable than the square planar geometry. Showcasing the versatility of bis(iminopyrrolylmethyl)amine ligands: central amine coordination, protonation, tautomerism, chirality, and halogen bonds in the second coordination sphere.