In this work, the reaction of the 16-electron species [Rh(η3-C8H13)-(η5-C 2B9H9Me2)] with PPh3 was investigated and the product, [exo-nido-Rh-(PPh3)2(η5-C2B 9H10Me2)], which is in an equilibrium with the closo analogue was characterized by 31p{1H}, 1H, 13C and 11B NMR spectroscopy. A mechanism for the complex formation is suggested which is related to the previously reported reactions between the 16-electron complex and PR3 (R = Me and Et) ligands.