Water-soluble carbonyl complexes of 99Tc(I) and Re(I) with adamantane-cage aminophosphines PTA and CAP

Abstract

Pentacarbonyl complexes of 99Tc and Re [M(CAP)(CO)5]X and [M(PTA)(CO)5]X (M = 99Tc or Re and X = ClO4− or OTf–) with aminophosphine ligands 1,4,7-triaza-9-phosphatricyclo[5.3.214,9]tridecane (CAP) and 1,3,5-triaza-7-phosphaadamantane (PTA) were prepared for the first time by the reaction of [MX(CO)5] (M = 99Tc or Re, X = ClO4− or OTf–) with CAP and PTA in CH2Cl2 at room temperature. The reaction of [TcCl(CO)5] with CAP in refluxing CH2Cl2 yields the tricarbonyl complex [99TcCl(CAP)2(CO)3]. Treatment of [Re(H2O)3(CO)3]Cl with CAP in aqueous solution at 40–50 °C gives the rhenium analog [ReCl(CAP)2(CO)3]. Both penta- and tricarbonyl phosphine complexes were characterized by spectroscopic methods (IR, NMR, MS) and single crystal X-ray diffraction. The [M(PTA)(CO)5]X complexes are soluble in aqueous solutions, whereas their CAP analogs are not. The CAP complexes become water-soluble after acidification with dilute acids. As the pH of their aqueous solutions increases, they start to slowly degrade at pH 8 and completely decompose at pH 14. In acidic media, the pentacarbonyl complexes undergo stepwise protonation and are stable indefinitely.