Sterically Protected Trifunctional Silanes as Rigid Ligand Systems

Stable silanols have attracted considerable interest, because they are valuable precursors for silsesquioxanes and metallasiloxanes and are moreover well defined model compounds for silica surfaces. The research activity on this field continues to have substantial impact on the fertile area between homogeneous and heterogeneous catalysis. In our own previous work we introduced sterically hindered terphenyl substituents to stabilize reactive silicon intermediates. The aim of the current project is to extend the knowledge obtained for silanetriols towards heterosilanetriols, in which the OH groups on a trifunctional silicon center are replaced with functionalities such as SH, SeH, NH 2 and PH 2 by taking advantage of the steric protection exerted by bulky terphenyl substituents. So far only few examples for such compounds with other substituents have been described in the literature. We intend to synthesize such stable heterosilanetriols protected by terphenyl substituents and to use them as ligands towards transition metals. The influence of the bulky terphenyl substituent is expected to reduce the degree of association observed for related metallasiloxanes and therefore to make the coordinated metal centre available for further reactions. The hemilabile character of the terphenyl substituent should therefore be beneficial for the catalytic activity of metal centers coordinated in this fashion. Moreover, such heterosilanetriols should be ideal building blocks for the controlled build up of polyhedral cluster architectures involving heavier main group elements. The synthetic realization of terphenyl substituted heterosilanetriols will provide a novel multifunctional ligand system, for which a fertile coordination chemistry can be expected. Due to the presence of three donor sites within a fixed arrangement, a multitude of coordination modes for mono or oligo nuclear transition metal complexes is feasible, thus offering a structural flexibility which is essential for catalytically active systems. From the structural and spectroscopic information for these ligands and their complexes a deeper understanding of the principles governing the stability of functional silicon compounds can be expected. Furthermore, the investigation of such trifunctional ligand systems with donor sites varying from hard to soft, will provide important insight into the metal-ligand bonding situation for rigid chelating ligand systems.

Stable silanols have attracted considerable interest, because they are valuable precursors for silsesquioxanes and metallasiloxanes and are moreover well defined model compounds for silica surfaces. The research activity on this field continues to have substantial impact on the fertile area between homogeneous and heterogeneous catalysis. In our own previous work we introduced sterically hindered terphenyl substituents to stabilize reactive silicon intermediates. The aim of the current project is to extend the knowledge obtained for silanetriols towards heterosilanetriols, in which the OH groups on a trifunctional silicon center are replaced with functionalities such as SH, SeH, NH 2 and PH 2 by taking advantage of the steric protection exerted by bulky terphenyl substituents. So far only few examples for such compounds with other substituents have been described in the literature. We intend to synthesize such stable heterosilanetriols protected by terphenyl substituents and to use them as ligands towards transition metals. The influence of the bulky terphenyl substituent is expected to reduce the degree of association observed for related metallasiloxanes and therefore to make the coordinated metal centre available for further reactions. The hemilabile character of the terphenyl substituent should therefore be beneficial for the catalytic activity of metal centers coordinated in this fashion. Moreover, such heterosilanetriols should be ideal building blocks for the controlled build up of polyhedral cluster architectures involving heavier main group elements. The synthetic realization of terphenyl substituted heterosilanetriols will provide a novel multifunctional ligand system, for which a fertile coordination chemistry can be expected. Due to the presence of three donor sites within a fixed arrangement, a multitude of coordination modes for mono or oligo nuclear transition metal complexes is feasible, thus offering a structural flexibility which is essential for catalytically active systems. From the structural and spectroscopic information for these ligands and their complexes a deeper understanding of the principles governing the stability of functional silicon compounds can be expected. Furthermore, the investigation of such trifunctional ligand systems with donor sites varying from hard to soft, will provide important insight into the metal-ligand bonding situation for rigid chelating ligand systems.