Chelate tris-silanol ligands synergize exceedingly well with molybdenum alkylidynes and hence lead to some of the very best catalysts for alkyne metathesis known to date. In certain cases, however, the reported routes to these compounds were low yielding because of competing condensation with formation of siloxanes. This issue has been revisited and resolved by revealing the Si−OH groups in the last step, only after the tripodal framework has been forged. Key to success was the chemoselective threefold oxidation of stable tris-silane precursors in the presence of the tertiary amine that serves ligand scaffolding purposes. This demanding transformation was accomplished under essentially neutral conditions with the aid of (CO) 5 MnBr as catalyst and water as the oxygen source, thus furnishing the desired ligands in good yield and excellent purity, such that they could be directly used in the subsequent complexation reaction. The new method is applicable to known catalysts as well as to a previously inaccessible variant that exhibits promising activity in the metathesis of otherwise quite challenging substrates. • high performance catalysts for alkyne metathesis • chemoselective catalytic silane oxidation • tripodal silanol ligands • ring closing alkyne metathesis reactions of encumbered substrates
Breustedt et al. (Fri,) studied this question.