The anionic half-sandwich complex Na+ [CpCo[P(O)(OEt)2]3]- (NaL; Cp = h5-cyclopentadienyl) crystallizes as the trimeric aggregate (NaL)3.2H2O. The complex anion L- reacts as an O tripod ligand with M(CO)6 to form [LM(CO)3]- [I; M = Mo (II), M = W]. II reacts with allyl iodide to give [LMo(CO)2(h3-C3H5)]. The hydride complexes [LM(CO)3H] (III), obtained by protonating I, undergo insertion reactions with isoprene to give the allyl complexes [LM(CO)2(h3-C5H9)]. III [M = W (IV)] is halogenated to give [LW(CO)3X] (X = Cl, Br, iodo). Air oxidn. of IV yields the oxo complex L2W2O6. The ML2 complexes [VOL2], [VL2]PF6, [CrL2]PF6, [TiL2]PF6 and [TiL2](PF6)2 are prepd. by treating NaL in H2O or THF with oxovanadium(IV), V(III), Cr(III) and Ti(III) salts. The mixed-ligand complexes [LSnCl3], [LZrCl3], [LMo(O)Cl2], Ph4P[LRhCl3] and [LRhCl2]2 are prepd. analogously.