The replacement of phenylethanethiolate (SC2Ph) ligands on 1.1 nm (core diameter) Au-38(SC2Ph)(24) monolayer-protected clusters (MPCs) with varied amounts of triphenylphosphine (PPh3) is investigated in methylene chloride. U-V-vis spectra suggest that changes in the MPC An core size occur when large amounts (> 10 equiv moles per cluster) of PPh3 are reacted with Au-38(SC2Ph)(24), H-1 and P-31 NMR spectra following the addition of smaller amounts (< 5 equiv moles) of PPh3 indicate that the reaction liberates a Au(1)SC2Ph complex, as opposed to a SC2Ph thiol, disulfide, or anion. A H-1 NMR kinetic study shows that the exchange is surprisingly rapid, even faster than exchanges of thiolates with other thiolates, at room temperature and in air. The reaction is slowed when cooled or conducted under Ar. The difference in potentials of the initial one-electron voltammetric reduction and oxidation of Au-38(SC2Ph)(24) decreases slightly upon reaction with small amounts of PPh3.