Novel synthesis of tripodal borate ligands
Sanchez Perucha, Alejandro
Perucha, Alejandro Sanchez
Poly(azolyl)borate ligands have proven to be extremely popular ligands since their introduction by Trofimenko in the late 60´s. The basic skeleton of these ligands involves usually three heterocycle units linked to a central boron apex via the azole nitrogen atoms. These ligands have been applied in diverse research areas such as homogeneous catalysis, materials science and bio-inorganic chemistry. More than 2000 papers, including books and reviews regarding the properties of these compounds, have been published. However, only a few synthetic methods for the preparation of such ligands have been reported and only a few examples of chiral borate-centred ligands are known. This thesis deals with the development of a novel synthetic route to tripodal borate ligands using B(NMe2)3 as the boron source. The mechanism of the reaction of this borane with azole heterocycles has been established by exploring the reactivity of a range of azoles. One of the major features of this new synthetic protocol is that it allows the formation of chiral tripodal ligands where the chiral groups are located either at the forth position at the boron atom or at the azole heterocycles. Coordination studies of the ligands have been undertaken and the metal complexes have been studied by a combination of spectroscopic and X- ray diffraction techniques. Preliminary application of the most representative ligands in the Asymmetric Transfer Hydrogenation (ATH) of prochiral ketones has been undertaken in collaboration with Prof. Dieter Vogt at the Technical University of Eindhoven.