Reaction of the dimer [(η<SUP>5</SUP>-C<SUB>5</SUB>Me<SUB>5</SUB>)RhCl(μ<SUB>2</SUB>-Cl)]<SUB>2</SUB> with 2 or 4 equiv of the water-soluble phosphine 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (pta) affords [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>Me<SUB>5</SUB>)(pta)Cl<SUB>2</SUB>] and [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>Me<SUB>5</SUB>)(pta)<SUB>2</SUB>Cl]Cl, respectively. Both complexes have been characterized in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction, the latter as the chloride and BPh<SUB>4</SUB><SUP>-</SUP> salts. In addition, the rhodium(I) complexes [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>Me<SUB>5</SUB>)(CO)(pta)] and [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>H<SUB>5</SUB>)(pta)<SUB>2</SUB>] have been prepared from [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>Me<SUB>5</SUB>)(CO)<SUB>2</SUB>] and [Rh(η<SUP>5</SUP>-C<SUB>5</SUB>H<SUB>5</SUB>)(PPh<SUB>3</SUB>)<SUB>2</SUB>], respectively, by reaction with pta. An in vitro evaluation of these compounds, together with [Os(η<SUP>6</SUP>-C<SUB>10</SUB>H<SUB>14</SUB>)(pta)Cl<SUB>2</SUB>] and the well-characterized antimetastasis drug [Ru(η<SUP>6</SUP>-C<SUB>10</SUB>H<SUB>14</SUB>)(pta)Cl<SUB>2</SUB>], RAPTA-C, was undertaken using HT29 colon carcinoma, A549 lung carcinoma, and T47D breast carcinoma cells. In the HT29 cell line, the two nearest congeners