Versatility Of The Bis(Iminopyrrolylmethyl)Amine Ligand: Tautomerism, Protonation, Helical Chirality, And The Secondary Coordination Sphere With Halogen Bonds In The Formation Of Copper(Ii) And Nickel(Ii) Complexes

The reaction of N,N-di(2,6-bis(isopropyl)phenylimino-pyrrolyl-alpha-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 (CuL1H)X. A similar type of mononuclear structure was obtained with Cu(NO3)(2).(H2O)(3). Conversely, binuclear copper(o) complexes [Cu-2(mu-L1)(mu-OOCCH3)(mu-OH)1(4) and (Cu-2(mu-L1H)(mu-OOCPh)(mu-O)] (5) were obtained from the reaction of Cu(O2CR)(2).H2O with H(2)L1. Notably, these reactions in the presence of a base yielded the neutral copper(o) complex (CuL1) (6). This product was also obtained from the reaction of complex 2 or 4 with NaOH in methanol. All structures feature a dianionic iminopyrrole motif and a protonated central amine function except 4. The reaction of H(2)L1 with NiCl2.DME gave the mononuclear complex (NiCl2(L1H(2))), 7. In contrast to this, the reaction of the newly synthesized sterically less encumbered ligand N,N-di(phenylimino-pyrrolyl-alpha-methyl)-N-methylamine H(2)L2 with NiCl2.DME gave the binuclear complex (NiCl(L2H(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 NaHBEt3 yielded a neutral complex [NiL1] (8) containing the imino-pyrrole form. In the molecular structures, interesting secondary coordination spheres incorporating guest molecules such as CHCl3 and MeOH in the crystal lattices and the presence of helical enantiomers were observed and analysed. In one case, CHCl3 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.