The rare-earth-metal organic cyclo-P4 complex (LY·DMAP)2[1,2-R2- cyclo-P4] (2, L = N, N'-2,6-diisopropylphenyl-1,4-diazabutadiene, DMAP = 4- N, N'-dimethylpyridine, R = CH2C6H4NMe2-2) was synthesized by direct functionalization of P4 using the rare-earth-metal alkyl complex LYR(THF) (1) for the first time. Further investigations indicated that three selective conversions of the cyclo-P4 species have been realized by alkyl migration. Complex 2 was slowly transformed into a R2P-substituted cyclo-P3 cluster (LY·DMAP)2[ cyclo-P3PR2] (3) under heating conditions. The reaction of 2 with 1 equiv of KR gave the unsubstituted cyclo-P3 complex (LY·THF)2[ cyclo-P3]K (4) in quantitative yield, accompanied by the elimination of the organophosphorus compound PR3 (5). Treatment of 2 with HMPA afforded the structurally characterized Zintl-type P7 complex (LY·HMPA)3P7 (6). The formation of complexes 3, 4, and 6 revealed that unusual alkyl migrations in the polyphosphorus complexes occurred in these reactions, and the transformations from cyclo-P4 into cyclo-P3 also provided a new insight into the stepwise degradation of P4 using metal complexes.