The aim of this work is to investigate the suitability of homoleptic indium complexes [In(R)3(solv)n] as precursors for cationic complexes. The main interest is focused on removing the trimethylsilylmethyl as well as the allyl or 2-methallyl ligand with either Lewis- or Brønsted-acidic reagents to achieve the cationic complexes.Chapter 2 describes the synthesis of the cationic [In(CH2SiMe3)2(THF)2][B(C6F5)4] complex from the homoleptic precursor [In(CH2SiMe3)3] and crystallographic investigations of the product.Chapter 3 deals with the synthesis of a series of different bis(phenolate)indium complexes [In(OSSO)R], their structural characterization and their use as active catalyst for the ringopening polymerization of lactide. The [In(OSSO)]-cations were also obtained but could neither be structurally investigated nor used as catalysts.Chapter 4 describes the investigations of a full series of homoleptic and heteroleptic indium allyl and 2-methallyl complexes. The dynamic behavior of the allyl and 2-methallyl ligands in solution has been intensively studied. A new type of bridging 2-methallyl ligand was found in a crystal structure. Unfortunately their utilization as active initiators for the 1,3butadiene polymerization failed with regards to their enormous temperature sensitivity.Chapter 5 deals with the synthesis of homoleptic aluminum allyl and 2-methallyl complexes and their cations. Insertion reactions of ketones and aldehyds have been briefly studied.Chapter 6 describes the synthesis of a bis(allyl) magnesium complex and the investigation of its crystal structure formed as a polymeric chain with bridging 1,4-dioxane molecules.