We report the synthesis of germanium-containing polyphosphorus ligands in transition metal complexes through the insertion of an Ar′GeCl unit into a P–P bond of polyphosphorus ligands (Ar′ = 2,6-(2,6-iPr2C6H3)2-C6H3). Germatetraphosphido complexes [(L)Co(η4-P4GeAr′)] (1a: L = PHDI; 1b: L = Ar*BIAN; PHDI = bis(2,6-diisopropylphenyl)phenanthrene-9,10-diimine, Ar*BIAN = 1,2-bis(arylimino)acenaphthene, aryl = 2,6-dibenzhydryl-4-isopropylphenyl) were obtained by treatment of the anionic cyclo-P4 complexes [K(18c-6)][(L)Co(η4-P4)] with [Ar′GeCl]2 . Similar reactions of the cyclo-P3 complexes [cat][(L)Co(CN)(η3-P3)] ([cat]+ = [nBu4N]+ or [K(18c-6)]+) afforded [cat][(L)Co(η3-P3GeAr′Cl)(CN)] (2a: L = PHDI, [cat]+ = [nBu4N]+; 2b: L = Ar*BIAN, [cat]+ = [K(18c-6)]+). The reactivity of 2a was studied toward group 14 electrophiles, yielding neutral germatriphosphido analogues [(PHDI)Co(η3-P3GeAr′Cl)(CNER3)] (3-ER3, ER3 = CPh3, Si(iPr)3). Furthermore, treatment of 2a with the group 13 Lewis acid GaCl3 gave [nBu4N][(PHDI)Co(η3-P3GeAr′Cl)(CNGaCl3)] (4-Ga) and [(PHDI)Co(η3-P2Ge(PAr′))(CNGaCl3)] (5-Ga), which features a remarkable P3GeAr′ ligand. Compounds 1–5 were isolated as crystalline materials and characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy supported by DFT calculations.