Sousa Pedrares
Research themes
Coordination Chemistry of Carborane Ligands
Research
FORMER CIQUS RESEARCH GROUP, 2011-2015
Ortho-closo-carboranes are clusters with ten boron atoms and two adjacent carbon atoms in an icosahedral arrangement. This icosahedral structure, known as the “cage” of the carborane, is responsible for the unusual properties of this molecule and its derivatives. Its great thermal, photolytic and chemical stability is due to the close shell structure of the carborane cage.
One of the most interesting properties of o-carborane is its irregular electron density distribution, which is responsible for the electronic properties and the reactivity of the carborane molecule. The carbon atoms of the carborane cage are the ones with less electron density, which means that a group attached to these positions will experience an electron-withdrawing effect.
The electron density on the boron atoms depends on their position; the ones furthest from the carbon atoms are the ones with more electron density, which means that a group attached to these positions will experience an electron-donating effect.
Carborane chemistry: functionalization of o-carborane fragments with potential donor atoms
Our interest is focused on using the final compounds as ligands for the synthesis of coordination compounds. In particular, we are interested in ligands with two different donor atoms (heterobidentate ligands). Despite the potential applications in homogeneous catalysis, these heterobidentate carborane ligands have hardly been explored, possibly due to the greater difficulty of their synthesis.
One of the objectives of this research is to evaluate the reduction of the coordination ability of donor atoms adjacent to the carborane cage. We have design a series of heterobidentate ligands with nitrogen donor groups (imine, iminophosphorane, etc) and additional donor atoms (X). The auxiliary donor atoms X will be soft atoms with great thermodynamic tendency to bind the metal atoms (palladium and platinum):
N= imine, iminophosphorane, etc.; X= S, Se, P, etc.; M= Pd, Pt
The objective is to find ligands with hemilabile behavior. These ligands are very important in homogeneous catalysis because they can dissociate the low coordinating donor atom, generating the vacant site needed to coordinate the substrate:
Study of supramolecular interactions that determine the crystal packing of the compounds.
Carborane derivatives tend to establish weak interactions involving the carborane cage. In fact, these compounds usually display “dihydrogen” interactions, CH...HB, which are weak interactions typical of these compounds that may be of interest in the field of self-assembly and supramolecular chemistry.
FORMER CIQUS RESEARCH GROUP, 2011-2015