A series of SY/11- and aSY/11- phobane ligands of the type PhobPZ (Z = F, OR, NRR' and CR)) have been synthesised. These P(III) compounds have been coordinated to [RhCl(CO)zh and the Veo has been measured to probe the a-donation and n-acceptor properties of the compounds, and to give insight into their use as ligands in the Co- and Rh-catalysed hydrofonnylation of l-alkenes. The Tolman electronic parameter has been calculated for PhobPZ ligands in [Ni(COhL], where Z = F, OR, NRR' and CR), and these results illustrate the agreement between the experimental data obtained from the synthesis of[RhCl(CO)(PhobPZ)z] complexes and computational data.