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[5.3.2^14,9]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.