Sterically demanding secondary potassium phosphides (4) were synthesized and investigated. Reaction with halophosphanes (5) yields diphosphanes (6), whereas reaction with CS2 yields phosphanyl dithioformates (10). These can be further converted to the corresponding phosphanyl esters of dithioformic acid R2P-C(S)S-PR2 (8). One of these thioesters (8) was found to undergo a migration reaction, resulting in the formation of a phosphanylthioketone with an additional phosphanylthiolate group (9), which was used as a chiral ligand in gold coordination chemistry. The phosphanyl migration reaction was investigated by spectroscopic and theoretical methods, revealing a first-order reaction via a cyclic transition state. All species mentioned were fully characterized.