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
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Abstract
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 Å3, 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.
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