The aminophosphine ligand (2-aminoethyl)diphenylphosphine (edpp) has been coordinated to the W-3(mu-S)(mu-S)(3) cluster unit to afford trimetallic complex [W3S4Br3(edpp)(3)](+) (1+) in a one-step synthesis process with high yields. Related [W3S4X3(edpp)(3)](+) clusters (X = F, Cl, NCS; 2(+)-4(+)) have been isolated by treating 1(+) with the corresponding halide or pseudohalide salt. The structure of complexes 1(+) to 4(+) contains an incomplete W3S4 cubane-type cluster unit, and only one of the possible isomers is formed: the one with the phosphorus atoms trans to the capping sulfur and the amino groups trans to the bridging sulphurs. The remaining coordination position on each metal is occupied by X. Detailed studies using stopped-flow, P-31{H-1} NMR, and ESI-MS have been carried out in order to understand the solution behavior and the kinetics of interconversion among species 1(+), 2(+), 3(+), and 4(+) in solution. Density functional theory (DFT) calculations have been also carried out on the reactions of cluster 1(+) with the different anions. The whole set of experimental and theoretical data indicate that the actual mechanism of substitutions in these clusters is strongly dependent on the nature of the leaving and entering anions. The interaction between an entering F and the amino group coordinated to the adjacent metal have also been found to be especially relevant to the kinetics of these reactions.