Synthesis and structure of [6,6'-bi(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecane)]dinickel(II) triflate and its catalytic activity for photochemical CO2 reduction

A new bimacrocyclic NI(II) complex, [6,6'-bi(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecane)]dinickel(II) triflate, was synthesized and its structure was determined by X-ray crystallography (C28H54N8Ni2F12S4O12, monoclinic space group P2(1)/a, a = 15.282(2) Angstrom, b = 16.967(2) Angstrom, c = 9.172(1) Angstrom, beta = 94.01(1)degrees, Z = 2). Two dimethylcyclam units in the trans III form are linked equatorially with respect to the chair-form six-membered chelate ring, and the chirality due to a pair of asymmetric carbons in both macrocycles is C*-meso (5R(S), 7S(R)). The most remarkable feature, different from the case of corresponding monocyclic complex, is the configuration of methyl groups which occupy the axial positions of the six-membered chelate rings. Such a dimeric structure reduces the capability for accepting axially coordinating water molecules. On the other hand, the catalytic activity of the bimacrocyclic complex significantly exceeds that of the monocyclic Ni(II) complexes for photochemical CO2 reduction.