CHEMICAL MODIFICATION OF METAL-COMPLEXES - AN EFFICIENT PROCEDURE FORO-ACYLATION OF AN ANIONIC METAL-COMPLEX HAVING A NONCOORDINATED HYDROXYL GROUP

The noncoordinated hydroxyl group of [Co(dhpta)](-) (where dhpta = ,3- diamino-2-hydroxypropane-N,N,N',N'-tetraacetate ion) was O-acylated by reaction with a series of acid anhydrides (acetic anhydride, n-valeri c anhydride, benzoic anhydride, phthalic anhydride, succinic anhydride , octanoic anhydride, and dodecanoic anhydride) in the presence of 4-( dimethylamino)pyridine, after the potassium salt of the complex was di ssolved in acetonitrile by using cryptand 222. Fairly high yields unde r remarkably mild conditions were achieved without altering the coordi nation sphere. The esterified complexes were characterized by elementa l analysis, electronic absorption and NMR spectroscopies, and X-ray cr ystallography. X-ray crystal structure determinations of (DMAP-H)[Co-( Ben-dhpta)] (10) and (STC-H)[Co(Val-dhpta)].6H(2)O (11) are reported, where DMAP-H, Ben-dhpta, STC-H, and Val-dhpta represent 4-(dimethylami no)pyridinium cation, O-benzoylated dhpta, strychnine cation, and O-va lerylated dhpta, respectively. Crystal data for 10: formula C25H29N4O1 0Co, space group P2(1)2(1)2(1) (orthorhombic); a = 12.5709 (9) Angstro m, b = 25.338 (3) Angstrom, c = 8.0707 (6) Angstrom, Z = 4, R = 0.1034 . Crystal data for 11: formula C37H57N4O18Co, space group P2(1) (monoc linic); a = 19.498 (10) Angstrom, b = 11.625 (5) Angstrom, c = 9.038 ( 2) Angstrom, beta = 95.33 (3)degrees, Z = 2, R = 0.072. In both comple xes, the cobalt is octahedrally coordinated with a hexadentate dhpta u nit. The oxygen atom of the noncoordinated hydroxyl group of dhpta bin ds to the carboxylic carbon atom of each acid residue to form an ester bond. Measurements of cobalt-59 NMR for the aqueous solutions of the cobalt(III) complexes having a long alkyl (octyl and dodecanoyl) chain ligand indicated the formation of ion-aggregates above cmc (critical micelle concentration), which was determined from the surface tension.