Book excerpt: Ligand hybrid design is becoming an increasingly important area of the synthetic activity in organometallic chemistry. The coordination chemistry of diallylphosphines and phosphine-stabilized germylenes has been studied in this thesis. In particular, phosphine-stabilized germylenes have not only been studied by its potential use as ligands for transition metals, but also as possible synthetic tools in organic chemistry. Diallylphosphine behave as bidentate ligands to stabilize cationic rhodium species of type [Rh(COD){?3(P,C,C)RP(CH2CH=CH2)2}][BF4] [R= iPr2N, tBu and Ph]. Hemilabile properties of diallylphosphine ligands have been demonstrated by ligand exchange reactions. In solution, a dynamic equilibrium of exchange between the two allylic double bonds was detected by low temperature NMR analysis. In the same way, the reversible displacement of coordinated allylic double bond by acetonitrile could be observed. Theoretical calculations have been performed to explain the experimental results for the order of reactivity on removing the acetonitrile under vacuum. Germylenes stabilized by coordination of a phosphine ligand have been synthesized and fully characterized. Reactivity studies showed that phosphine-stabilized germylenes are unreactive toward unsaturated compounds, such as: alkyne, alkene and carbonyl derivatives, but reactive toward 2,3-dimethylbutadiene. The reactivity of phosphine-stabilized germylenes toward transition metal complexes have been studied by reaction with the dimer complex [Rh2(μ-Cl2)(COD)2], demonstrating that phosphine-stabilized germylenes are useful ligands with high potential in organometallic chemistry. The first isolable germanium analogue of alkynes, known as germyne, stabilized by coordination of a phosphine ligand has been synthesized and fully characterized. Synthesized germynes rearrange at RT affording a phosphaalkene and a new stable N-heterocyclic germylene. Keywords: Hybrid ligands, hemilabile properties, coordination chemistry, diallylphosphines, phosphine-stabilized germylene, germyne.