New approach for the synthesis of water soluble -[M(CO)] bis(diarylphosphino)alkylamine complexes (M = Tc, Re).

A novel proof-of-concept is reported to modify the water solubility and potential biological effects of a bis(diphenylphosphino)alkylamine (PNP) ligand and the corresponding metal complex, by introducing an amine group on the outer periphery of the pendant ligand arm. Thus, a tertiary butoxycarbonyl protected '-Boc-ethylenediamine-,-bis(diphenylphosphino) ('-Boc-PNP) ligand (1) was synthesized by reacting the protected ethylenediamine and chlorodiphenylphosphine in a 1 : 2 molar ratio. The corresponding -[Re(CO)('-Boc-PNP)Br] (1A) complex was then obtained by reacting '-Boc-PNP (1) with (EtN)-[Re(CO)Br] in equimolar amounts in DCM at 50 °C. De-protection of the '-Boc pendant amine group in 1A with TFA leads to -[Re(NH-PNP)(CO)Br]·CFCOO (1B) which is soluble in DO (>0.05 M). Treating 1B with saturated aqueous NaHCO yields -[Re(NH-PNP)(CO)Br]·MeOH (1C) in near quantitative yield. Although both 1A and 1C are not soluble in DO, addition of TFA easily generates 1B (P NMR), confirming the formation of the protonated amine. Isolation of -[Tc(CO)(-Boc-PNP)(Cl)] (1D) confirmed that the rhenium and technetium (Tc) can be easily interchanged in this process. Reported are hence the unique rhenium series of compounds 1A, 1B and 1C and the corresponding technetium complex 1D, unequivocally characterized by single crystal XRD, as well as IR and H NMR spectroscopy. Preliminary antimicrobial evaluation indicates that ligand 1 and its respective rhenium complexes (1A-1C) were not active against selected fungi () and bacteria (, , , and ). These types of ligands and complexes therefore present themselves as excellent radio models for further evaluation using Re, Re and Tc to potentially study the toxicity of appropriately designed complexes.