Quinquedentate Co-ordination of Amino-substitiuted Tetraazacycloalkanes to Co(III). Part 3. Synthesis of an Unsymmetric Ligand and Crystal Structure of its cis-Chlorocobalt(III) Complex

Article abstract of DOI:10.1039/DT9920001649

The unsymmetric pendant-arm macrocycle 9-methyl-9-nitro-1,4,7,11-tetraazacyclotetradecane (L¹) was prepared by a copper(II)-directed condensation of 3,6-diaazanonan-1,9-diamine with nitroethane and formaldehyde.Reduction of the copper(II) complex of (L¹) with zinc in aqueous acid produced the new potentially quinquedentate polyamine 9-methyl-1,4,7,11-tetraazacyclotetradecan-9-amine (L²).Reaction of L² in water with cobalt(II) ion and air, followed by aqueous hydrochloric acid and equilibration with activated charcoal, yielded exclusively cis-2(Cl)>2 which crystallized in the monoclinic space group P2₁/c, with a = 12.745(5), b = 11.438(5), c = 14.414(8) Angstroem and β = 104.80(3) deg.The pendant primary amine and two adjacent secondary amines necessarily occupy an octahedral face, with the chloro ligand cis to the primary amine, and secondary amines adopt RRSS stereochemistries.The average Co-N distance is 1.96(0) Angstroem, and the Co-Cl distance is 2.252(1) Angstroem.Stereoretentive base hydrolysis (k(OH) 9100 dm³ mol^-1 s^-1) and other structural and physical properties are compared with those of the symmetric analogue 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine.

Full text of DOI:10.1039/DT9920001649

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