Compounds of Nickel(II) With trans-6,13-Dinitro- and trans-6,13-diamino-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane, with Structural Studies of Five (trans-6,13-Diamino-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II) Compounds

Abstract

Compounds of Ni^II with the macrocyclic ligand trans-6,13-dimethyl-6,13-dinitro-1,4,8,11-tetraazacyclotetradecane ( dino ), which is formed by condensation of bis (ethane-1,2-diamine)nickel(II) salts, nitroethane and formaldehyde, are described, together with homologues formed by substituting propane-1,2-diamine and/or 1-nitropropane. The nitro functions of [Ni( dino )]²⁺ were reduced by catalytic hydrogenation to form (trans-6,13-diamino-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II), [Ni( diam )]²⁺, isolated as approximately equal amounts of two isomeric forms; designated α (with the R,S,R,S configuration of the chiral nitrogen centres, overall configuration 1α,4α,6β,8α,11α,13α), and β (with the R,R,S,S, 1α,4β,6α,8β,11α,13β configuration). The α-isomer is metastable, and in solution isomerizes to the β-isomer, with rate constant of 5.0(5)×10^-5 s^-1 in 2 mol l.^-1. NaCl solution at 50°C, the rate of this reaction increasing in both acid and base. Protonation constants (pK at 25°C in 0.1 mol l.^-1 NaClO₄) for diam are 11.2(1), 9.7(1), 6.2(1), 5.3(1), and for the isomeric nickel(II) cations are α 4.94(2), 2.4(5); and β 4.5(1), 4.0(1). Compounds of diam with the β-configuration were prepared with triplet ground state Ni^II with diam in hexadentate coordination (e.g. β-[Ni(diam-N₄)] Cln ) and in tetradentate coordination with the neutral (e.g. trans-β-[Ni(diam-N₄)(NCS)₂]) or diprotonated ligand (e.g. trans-β-[Ni(diamH₂-N₄)(NCS)₂](CNS)₂). Compounds prepared with the α-configuration with triplet ground-state Ni^II had pentadentate diam with the neutral (e.g. trans-α-[Ni(diam-N₅)(H₂O)]Cl₂) or monoprotonated ligand (e.g. trans-α-[Ni(diamH-N₅) Cl ] (ClO₄)₂). Singlet ground-state Ni^II compounds with the square planar diprotonated ligand were prepared for both configurations. Structures are reported for β-[Ni(diam-N₆)](ClO₄)₂(H₂O), R 0.062 for 5708 reflections; β-[Ni(diam-N₆)] [ZnCl₄].1.5H₂O, R 0.064 for 4332 reflections; β-[Ni(diam-N₆)]Cl₂.6H₂O, R 0.044 for 2001 reflections; trans-β-[Ni(diam-N₄)(NCS)₂] R 0.056 for 1521 reflections; and trans-α-[Ni(diamH-N₅) Cl ](ClO₄)₂(H₂O), R 0.047 for 2667 reflections.