Octaalkynylsilsesquioxanes, Nano Sea Urchin Molecular Building Blocks for 3-D-Nanostructures

The design and construction of 3-D molecular scaffolds is currently an area of extreme interest for a variety of reasons including hydrogen storage, gas separation and molecular sieving. Octahedral silsesquioxanes, [RSiO1.5](8), represent a class of unusually robust, nanometer size molecules with cubic symmetry that places each functional group in a different octant in Cartesian space. This 3-D array of functional groups offers the potential to design nanobuilding blocks to construct multifunctional, nanocomposite materials including molecular scaffolds. We describe here detailed studies on the synthesis of octaalkyne silsesquioxanes using Sonogashira coupling of octaiodophenylsilsesquioxane, [p-IC6H4SiO1.5](8) (I8OPS) and a related bromine derivative with terminal alkynes. We describe versatile and reliable methods for synthesizing octaalkyne silsesquioxanes in moderate to high yields with 100% conversion of the I8OPS to the octaalkynes. The inorganic core provides 3-D rigidity and the heat capacity of crystalline SiO2 making them quite robust in many environments. The alkyne "spines" provide excellent solubility in organic solvents and the ability to polymerize on heating, to form robust 3-D polyalkyne networks with air stabilities to >500 degrees C suggesting potential utility as matrix materials for high temperature composites. With appropriate functionality on the external point of the spine, all of these molecules should also serve as 3-D connection points for the construction of molecular scaffolds.