Organometallic complex of fac-[Re(CO) 3 ] + moiety with a modified tetraamine macroheterocyclic molecule dodecahydropyrimido[2',1':3,4]pyrazino[1,2-a]pyrimidine chelate: Synthesis and X-ray crystallography characterization

The demand for the design of novel anticancer drugs for chemotherapy and radiotherapy purposes is pressing due to cancer spreading worldwide, which is affecting a great number of people across the world. Among other existing compounds in the cancer chemotherapy, rhenium and technetium complexes are particularly emerging in the pipeline, and they are being investigated because of their promising biological applications and minimal in vivo toxicity. The coordination behaviour of various macromolecules around the fac -[Re(CO) ₃ ] ⁺ moiety has significantly contributed to the preparation of various radiopharmaceuticals and other compounds with a variety of specific applications. Herein, we report the synthesis and characterization of an unusual non-radioactive rhenium complex fac -[Re(CO) ₃ (H ₂ dpp)Cl] ( 1 ) that was isolated from the reaction of Re(CO) ₅ Cl with a crown macrocyclic tetraamine compound, (8 E ,10 E )-1,4,8,11-tetraazacyclotetradeca-8,10-diene (H ₂ tazd) in toluene. This compound fac -[Re(CO) ₃ (H ₂ dpp)Cl] ( 1 ) was then crystallographically analysed using single X-ray diffraction techniques. The produced compound is a monomeric rhenium complex with H ₂ dpp coordinating neutrally as a bidentate N , N′ -donor chelate. The unusual behavior observed in the crystal structure of ( 1 ) is dominated by the ring rearrangement of the used H ₂ tazd ligand into the coordinated macromolecule chelate; dodecahydropyrimido[2',1':3,4]pyrazino[1,2-a]pyrimidine (H ₂ dpp) molecule. The coordinated amine ligand, H ₂ dpp is also a result of the intramolecular conversion process via the reduction of imine bonds in H ₂ tazd, leadingd to a chelate with three fused rings in the structure of compound 1 . These findings revealed that both H ₂ tazd and H ₂ dpp macromolecules could be a source of macrocyclic chelating agents suitable for the preparation of a wide range of rhenium(I)-based complexes with the fac -[Re(CO) ₃ ] ⁺ moiety. The refinement of compound 1 predicts the ring formation in the macrocyclic ligand, and this phenomenon is rare in the coordination chemistry of rhenium and was probably catalysed by rhenium(I) in the complex.