Three step vs one pot synthesis and X-ray crystallographic investigation of heptadentate triamide cyclen (1,4,7,10-tetraazacyclododecane) based ligands and some of their lanthanide ion complexes

The synthesis of several lanthanide complexes from the tris alkylated cyclen (1,4,7,10-tetraazacyclododecane) ligands 1 and 2 is described. The syntheses of 1 and 2 were investigated by means of two different synthetic routes (Method 1 and Method 2). The first of these involves the mono protection of cyclen using 4-methoxyphenylsulfonyl chloride, followed by alkylation of the remaining three secondary amines of cyclen, and deprotection using solvated Na(s). Using this approach only 1 was successfully formed. The X-ray crystal structure of the intermediate, 9 and the corresponding La(III) complex, 9.La is presented. The second method involved the direct synthesis of the two ligands in a single step. The X-ray crystallography of the Eu(III) complex of one of these ligands is presented. Whereas, Method 1 yielded the product 1 in high purity, but in low overall yield, Method 2 gave higher yields for both ligands (similar to50% for both). (C) 2003 Elsevier Ltd. All rights reserved.