Ytterbium triisopropoxide

Both samarium iodide and ytterbium triisopropoxide catalyse the ring opening45 of epoxides by TMS-azide in the latter case, due to an acidic work-up, the products are isolated as vicinal azido alcohols. 

Yamamoto has reported that ytterbium triisopropoxide, prepared in situ from Yb(OTf)3 and LiOPr in THF, can be used in a very mild, highly efficient, and widely applicable procedure for the azidolysis of epoxides. In every case except styrene oxide, products are derived from the attack of azide at the less hindered carbon atom. The method appears to be quite tolerant of functionality, leaving preexisting tosyl, acyl, and siloxy groups intact (e.g.,... 

Ytterbium triisopropoxide (10-20 mol%) catalyzes the ring-opening of epoxides with trimethylsilyl azide at ambient temperature to yield vicinal azide alcohols (eq. (25)) [191]. Complexation/chelation interactivity of functionalized substrates affects the regioselectivity in the product. 

---