Metal complexes of new scorpionate ligands: 2,2′-Bis(pyrazolyl)ethylamine and its derivatives

The new bis(pyrazolyl)amine ligand NH2CH2CH(pz)2 (1) was prepared from the reaction of N-[2,2-bis(pyrazolyl)ethyl]-1,8-naphthalimide with hydrazine monohydrate. A substituted derivative, C6H5CH2NHCH2CH(pz)2 (2), was prepared by the reaction of 1 with benzaldehyde followed by reduction with NaBH4. Ligand 1 was also converted by two methods to the new bitopic, para-linked bis(pyrazolyl)amine ligand p-C6H4(CH2NHCH2CH(pz)2)2, (3). The reactions of the ligands 1–3 with [Cu(PPh3)2]NO3 yields {(PPh3)Cu[(pz)2CHCH2NH2]}NO3, {(PPh3)Cu[(pz)2CHCH2NHCH2C6H5]}NO3 and {[(PPh3)Cu]2[p-((pz)2CHCH2NHCH2)2C6H4]}(NO3)2·solvate, respectively. Complex {(N3)2Cu[(pz)2CHCH2NHCH2C6H5]} was obtained from a methanol solution of 2, copper(II) acetate monohydrate and sodium azide. The complex {Cd[(pz)2CHCH2NHCH2C6H5]2}(PF6)2·3C3H6O was synthesized by reaction of the protonated form of ligand 2, [(pz)2CHCH2NH2CH2C6H5]PF6, with Cd(acac)2. In all of the structures the ligands are tridentate, bonding to the metal through the lone pair on the amine group as well as through the pyrazolyl rings – they act as true scorpionates. The solid state structures all have extensive non-covalent interactions, with the N–H functional groups of the amines participating in both N–H⋯π and N–H⋯O or N–H⋯N hydrogen bonding interactions.

The new amine substituted dihydrobis(pyrazolyl)methane ligands NH2CH2CH(pz)2, C6H5CH2NHCH2CH(pz)2 and bitopic p-C6H4(CH2NHCH2CH(pz)2)2 have been prepared and their complexes with a variety of metal systems developed. In all of the new complexes the ligands act as scorpionates, binding through both of the pyrazolyl rings and the nitrogen atom from the amine group.Figure optionsDownload as PowerPoint slide