We report the difunctional modification of anionic cobalta bis(dicarbollide)(1-) cluster with a B(8,8)-oxygen bridging unit that provides structural rigidity and an organic alkylazide substituent(s) on the carbon atoms of the...

Cross-bridged cyclam derivatives bearing two phosphonate (H 4 L 1 ), bis(phosphinate) (H 4 L 2 ), or phosphinate (H 2 L 3 ) pendant arms were synthesized and studied with respect to their application as copper radioisotope carriers in nuclear medicine. The ligands show high macrocycle basicity (pK 1 > 14) and high Cu(II) complex stability (log K = 20−24). The complexation and dissociation kinetics of the Cu(II) complexes were studied by ultraviolet−visible spectroscopy. Phosphonate Cu(II)-H 4 L 1 and bis(phosphinate) Cu(II)-H 4 L 2 complexes form very quickly, reaching quantitative formation within 1 s at pH ∼6 and millimolar concentrations. Conversely, the formation of the phosphinate complex Cu(II)-H 2 L 3 is much slower (9 min at pH ∼6) due to the low stability of the out-of-cage reaction intermediate. All studied complexes are highly kinetically inert, showing half-lives of 120, 11, and 111 h for Cu(II)-H 4 L 1 , Cu(II)-H 4 L 2 , and Cu(II)-H 2 L 3 complexes, respectively, in 1 M HClO 4 at 90 °C. The high thermodynamic stability, fast formation, and extreme kinetic inertness of Cu(II) complexes indicate that phosphonate and bis(phosphinate) derivatives are promising ligands for nuclear medicine.

Ligands combining a bis(phosphonate) group with a macrocycle function as metal isotope carriers for radionuclide-based imaging and for treating bone metastases associated with several cancers. However, bis(phosphonate) pendant arms often...

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A bicyclic ligand, 1,4,7-triazacyclononane 1,4-bridged with methylene-bis(phosphinate) and bearing benzyl substituent on the remaining amino group, was synthesized from N-benzyltacn and CH 2 (PO 2 H 2 ) 2 by two sequential Mannich-type reactions in a high yield. Basicity of the macrocycle is high (pK 1 = 12.25). Complexes with Cu II and Ni II ions show dimeric structures in the solid state. The structures exhibit distorted octahedral environment with two ring amino groups from one molecule and two oxygen atoms of chelating bis(phosphinate) anion from the other molecule in the equatorial plane, and with the apical positions occupied by the remaining macrocycle amino group and by one of the phosphinate oxygen atoms. The metal ions in the dimers are additionally bridged by one phosphinate group. Stability of the Cu II complex is more than ten orders of magnitude lower than that of the [Cu(nota)] À complex due to a different number and different nature of the pendant arms, and inappropriate arrangement of donor atoms in the ligand bicyclic structure. Rigidity of the short PÀ CÀ P chain of the geminal methylene-bis(phosphinate) does not allow simultaneous coordination of both phosphinate groups and the ring amines to the same metal ion. The low solubility of Ni II and Zn II complexes disabled determination of their stability constants.