Synthesis of New Binucleating Cylindrical Macrotricyclic Ligands Where Two Cyclam Rings Are in a Face-to-Face Conformation. Characterization of Their Dicopper(II) and Dinickel(II) Complexes

Synthesis of new symmetrical cylindrical macrotricyclic ligands 1a,b, where two cyclam subunits are linked through nitrogen atoms by two aromatic chains of various lengths (meta-xylylenyl, para-xylylenyl) has been achieved. These compounds have been prepared according a five step procedure. The readily available trisheteroprotected cyclam 4 has been reacted with the appropriate bis(bromomethyl)benzene to give the bimacrocycle intermediates 5a,b. The selective deprotection of the tert-butyloxycarbonyl group leads to the diamine bimacrocycles 6a,b. Condensation of these diamines with the appropriate diacid dichloride under high-dilution conditions yields the diamide macrotricycles 7a,b in a significant yield. After reduction of the amide moieties and deprotection of the tosyl groups, new cylindrical macrotricycles 1a,b were obtained. Macrotricyclic ligands 1a,b coordinate Cu²⁺ and Ni²⁺ to form binuclear species. The crystal structure of the [Ni₂(1a)](ClO₄)₄·2CH₃CN complex has been determined by single-crystal X-ray analysis. C₁₈H₃₀N₄Ni(ClO₄)₂·CH₃CN crystallizes in the triclinic space group P1̄ with unit cell dimensions of a = 10.716 (3) Å, b = 12.805(4) Å, c = 9.292(3) Å, α = 95.82(2)°, β = 103.06(2)°, γ = 94.94(2)°, and V = 1227.8 ų, Z = 2, 2396 observations, and R(F) = 0.036. The cationic part of the complex is a dimer lying on a crystallographic inversion center. Each metal ion is coordinated to four nitrogen atoms of a cyclam unit giving an approximatively square planar coordination geometry, with an intermetallic distance of 6.830(1) Å. The ESR spectra of the binuclear Cu²⁺ complexes clearly show metal−metal cooperative interactions.