Quinquedentate co-ordination of amino-substituted tetraazacycloalkanes to cobalt(III). Part 3. Synthesis of an unsymmetric ligand and crystal structure of its cis-chlorocobalt(III) complex
- 1 January 1992
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 10,p. 1649-1652
- https://doi.org/10.1039/dt9920001649
Abstract
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-diazanonane-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-[CoL2(Cl)][ClO4]2, which crystallized in the monoclinic space group P21/c, with a= 12.745(5), b= 11.438(5), c= 14.414(8) and β= 104.80(3)°. 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 1.960Å, and the Co–Cl distance is 2.252(1)Å. Stereoretentive base hydrolysis (kOH 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.Keywords
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