Single-site organolanthanum complexes supported on mesoporous silica nanoparticles, La{C(SiHMe2)(3)}(n)@MSNs, catalyze the ring-opening hydroboration reaction of aliphatic and styrenic epoxides with pinacolborane (HBpin). The surface-bound complexes, synthesized by reaction of the homoleptic tris(alkyl)-lanthanum La{C(SiHMe2)(3)}(3) and SBA-type MSN treated at 700 degrees C (MSN700), are mostly monopodal SiO-La{C(SiHMe2)(3)}(2) and contain an average of one bridging La <- H-Si per alkyl ligand. This structure was established through a combination of solid-state NMR (SSNMR) experiments, including J-resolved SiH coupling and quantitative Si-29 measurements, diffuse reflectance IR, and elemental analysis. These rigorous analyses also established that grafting reactions in pentane provide a preponderance of SiO-La{C(SiHMe2)(3)}(2) sites and are superior to those in benzene and THF, and that grafting onto MSN treated at 550 degrees C (MSN550) results in a mixture of surface species. The single-site supported catalysts are more selective and in most cases more active than the homogeneous analogue, allow easy purification of products from the catalyst, are strongly resistant to leaching into solution phase, and may be recycled for reuse at least five times. After reaction of La{C(SiHMe2)(3)}(n)@MSN and HBpin, species including SiO-La{C(SiHMe2)(3)}(H(2)Bpin) and SiO-La{C(SiHMe2)(3)}{kappa(2)-pinB-O(CMe2)(2)OBH3} are identified by detailed 1D and 2D B-11 SSNMR experiments.