The title complex (1) reacted with [Mn-2(CO)(10)] under visible-UV irradiation (toluene solution and quartz glassware) to give a mixture of the phosphinidene complex [MnMoCp(mu-kappa(1):kappa(1),eta(6)-PMes*)(CO)(4)], the cluster [Mn2Mo2Cp2(mu-kappa(1):kappa(1),eta(6)-PMes*)(mu(3)-S)(CO)(8)], and the thiophosphinidene complex [MnMoCp(mu-kappa(2):kappa(1),eta(4)-SPMes*)(CO)(5)], in yields of ca. 60, 20, and 10% respectively (Mes* = 2,4,6-(C6H2Bu3)-Bu-t). The major product follows from formal replacement of the SMoCp(CO)(2) fragment in 1 with a Mn(CO)(4) fragment, and displayed multiple bonding to phosphorus (Mn-P = 2.1414(8) angstrom); the tetranuclear cluster results from formal insertion of a Mn-2(CO)(6) fragment in 1, with cleavage of P-S and P-Mo bonds, to render a mu(3)-S bridged Mn2Mo core bearing an exocyclic phosphinidene ligand involved in multiple bonding to one of the Mn atoms (Mn-P = 2.140(2) angstrom); the thiophosphinidene complex (Mn-P = 2.294(1) angstrom) formally results from addition of sulfur and carbon monoxide to the major MnMo product, a transformation which actually could be performed stepwise, via the MnMo thiophosphinidene complex [MnMoCp(mu-kappa(2):kappa(1),eta(6)-SPMes*)(CO)(4)]. When the photolysis of 1 and [Mn-2(CO)(10)] was performed in tetrahydrofuran solution and using conventional glassware, then the V-shaped cluster [Mn2MoCp{mu-kappa(1):kappa(1):kappa(1),eta(5)-P((C6H3Bu3)-Bu-t)}(CO)(8)] was obtained selectively (Mo-Mn = 3.2910(5) angstrom, Mn-Mn = 2.9223(5) angstrom), which unexpectedly displays a cyclohexadienylidene-phosphinidene ligand resulting from H atom abstraction at the aryl ring of the precursor. Density functional theory calculations on the complexes [LnM(mu-kappa(1):kappa(1),eta(6)-PMes*)MoCp] (MLn = MoCp(CO)(2), Mn(CO)(4), Co(CO)(3)) revealed that the degree of delocalization of the metal-phosphorus pi-bonding interaction over the Mo-P-M chain is significantly conditioned by the heterometal fragment MLn, it being increased in the order Mn <= Mo < Co.