Synthesis and Characterization of Novel [2+1] Tricarbonyl Rhenium Complexes with the Hydrophilic Phosphine Ligands PTA and CAP

In the pursuit of hydrophilic model fac-[Re(CO)(3)](+) complexes for (radio) pharmaceutical applications, six novel [2 + 1] mixed-ligand complexes of the general type fac-[Re(CO)(3)(bid)P] were synthesized and characterized, where bid is a bidentate ligand bearing either (N, O) or (S, S ') donor atom sets and P is the hydrophilic phosphine 1,3,5-triaza-7-phosphoadamantane (PTA) or its macrocyclic homologue 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP). The (N, O) ligands used in this study were picolinic and quinaldic acid, while the (S, S ') ligand was diethyldithiocarbamate. The complexes were synthesized in generally high yields and purity and the characterization was performed by spectroscopic methods, IR, NMR, and elemental analysis. Detailed X-ray crystallographic study of molecular packing by using Hirshfeld analysis tools revealed a plethora of intermolecular interactions such as hydrogen bond, pi MIDLINE HORIZONTAL ELLIPSIS pi, C-HMIDLINE HORIZONTAL ELLIPSIS pi, and carbonyl-carbonyl interactions. To our knowledge, the CAP complexes reported herein are the first example of [2 + 1] mixed-ligand fac-[Re(CO)(3)](+) complexes with CAP. The new complexes might have the potential to serve as platforms for the design of target-specific complexes with favorable pharmacokinetics.