Synthesis and Characterization of Novel^99gTc(V) and Re(V) Complexes with Water-Soluble Tetraaza Diamido Dipyridino Ligands:  Single-Crystal X-ray Structural Investigations of Mono- and Dinuclear Complexes

Abstract

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N(4)) water-soluble ligands (2-C(5)H(4)NCH(2)NHCO)(2)CH(2), 1 (L(1)H2), (2-C(5)H(4)NNHNHCO)(2)CH(2), 2, and [2-C(5)H(4)N(+)(O)(-)CH(2)NHCO](2)CH(2), 3, were synthesized. Reaction of L(1)H2 with ReOCl(3)(PPh(3))(2) resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(L(1))(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex mu-oxo [ReO(L(1))](2)O. Reaction of 1 with [n-Bu(4)N][ReOCl(4)] resulted in the neutral complex 6, trans-[ReO(L(1))]Cl. Similarly, when ligand 1 was reacted with [n-Bu(4)N][(99g)TcOCl(4)], the neutral trans-[(99)TcO(L(1))]Cl complex 7 was formed, which upon dissolution transformed into a cationic complex 8, trans-[(99)TcO(L(1))(OH(2))](+)Cl(-). The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear mu-oxo [TcO(L(1))](2)O, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.

[Tc(OH2)(CO)3(PPh3)2]+: A Synthon for Tc(I) Complexes and Its Reactions with Neutral Ligands

“…11 B NMR (CD 2 Cl 2 , ppm): −0.8 (s). 31 P NMR (CD 2 Cl 2 , ppm): 25.1 (s, ν 1/2 = 24 Hz), 17.5 (s, ν 1/2 = 290 Hz). 99 Tc NMR (CD 2 Cl 2 , ppm): −1077 (t, ν 1/2 = 248 Hz, 1 J Tc−P = 549 Hz).…”

“…The isolated cubes were suitable for X-ray diffraction. Yield: 40 mg (0.05 mmol, 98% 31 P NMR (CD 2 Cl 2 , ppm): 50 (unresolved dec., ν 1/2 = 4962 Hz, 1 J P−Tc = ca. 500 Hz).…”

“…11 B NMR (CD 2 Cl 2 , ppm): −2.3 (s). 31 P NMR (CD 2 Cl 2 , ppm): 50 (unresolved dec., ν 1/2 = 5120 Hz, 1 J P−Tc = ca. 510 Hz).…”

“…11 B NMR (CD 2 Cl 2 , ppm): −3.1 (s). 31 P NMR (CD 2 Cl 2 , ppm): 41 (s, ν 1/2 = 5302 Hz). 99 Tc NMR (CD 2 Cl 2 , ppm): −1503 (s, ν 1/2 = 2728 Hz).…”

Single amino acid chelates (SAAC): a strategy for the design of technetium and rhenium radiopharmaceuticals

“…8) with different pharmacokinetic properties, other donor types, N 4 , N x P y and S x P y have also been developed. 60,[80][81][82][83][84] An alternative strategy exploits a mixed ligand set of a tridentate ligand, generally a dithiolate of the type (S-X-S) 2À where X = O, S or NR, and a monodentate thiolate, referred to as 3 + 1 mixed ligand complexes. [86][87][88] However, such complexes tend to undergo further substitution reactions in vivo to achieve a closed shell and the monodentate ligand is labile in the presence of competing ligating groups.…”