Phosphabenzamidine [mes-NH-C(Ph)= P-mes) (1) and phosphaformamidine (mes-NH-CH = P-mes) (4) ligands have been synthesized and characterized. The conjugate bases of 1 and 4 coordinate by each bridging three Cu(I) ions, forming hexa- and tetranuclear clusters Cu-6[mes-N = C(Ph)-P-mes](3)Cl4Li(THF)(2) (3) and Cu-4[mes-N = CH-P-mes](4) (5), respectively. Both clusters have been fully characterized using H-1 NMR, P-31 NMR, and X-ray crystallography. Complexes 3 and 5 exhibit a previously unknown coordination mode of phosphaamidinates, which are far less studied than their well-known amidinate counterparts.