Embracing ligands. A synthetic strategy towards new nitrogen-thioether multidentate ligands and characterization of the cobalt(III) complexes

The synthesis of the hexadentate ligand 2,2,9,9-tetra(methyleneamine)-4,7-dithiadecane (EtN4S2amp) is reported. The ligand is of a type in which bifurcations of the chain occur at atoms other than donor atoms. The cobalt(III) complex [Co(EtN4S2amp)]3+(1) was isolated and characterized. The synthetic methodology also results in a number of by-products, notably 2,9,9-tris(methyleneamine)-9methylenehydroxy-4,7-dithiadecane (Et(HO)N3S2amp) and an eleven-membered pendant arm macrocyclic ligand 6,10-dimethyl-6,10-bis (methyleneamine)-1,4-dithia-8-azaacycloundec-7-ene (dmatue). The complexes [Co(Et(HO)N3S2amp)]3+(2), in which the alcohol is coordinated to the metal ion, and [Co(dmatue)Cl]2+(4) were isolated and characterized. Et(HO)N3S2amp also undergoes complexation with cobalt(III) to produce two isomers endo-[Co(Et(HO)N3S2amp)Cl]2+(endo-3) and exo-[Co(Et(HO)N3S2amp)Cl]2+(exo-3), both with an uncoordinated alcohol group. endo-3 has the alcohol positioned cis, and exo-3trans, to the sixth metal coordination site. Reaction of 1 with isobutyraldehyde, paraformaldehyde and base in dimethylformamide results in the encapsulated complex [Co(1,5,5,9,13,13hexamethyl-18,21-dithia-3,7,11,15-tetraazabicyclo[7.7.6]docosa-3,14-diene)](ClO4)3·2H2O ([Co(Me6docosadieneN4S2)]3+(5). All complexes have been characterized by single crystal X-ray study. The low-temperature (11 K) absorption spectrum of 1 has been measured in Nafion films with spin-allowed 1A1g(right arrow)1T1g and 1A1g(right arrow)1T2g and spin forbidden 1A1g(right arrow)3T1g and 1A1g(right arrow)3T2g bands observed. The octahedral ligand-field parameters were determined (10Dq= 22570 cm^-1, B= 551 cm^-1; C= 3500 cm^-1). For 5 10Dq and B were determined (20580 cm^-1; 516 cm^-1, respectively) and compared with those for similar expanded cavity complexes [Co(Me8tricosatrieneN6)]3+ and [Co(Me5tricosatrieneN6)]3+.