Siloxide Podand Ligand as a Scaffold for Molybdenum-Catalyzed Alkyne Metathesis and Isolation of a Dynamic Metallatetrahedrane Intermediate

Triphenylsiloxide is one of the most successful ancillary ligands for Mo­(VI)-alkyne metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of Mo≡C and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of Mo≡C. It also allowed for the isolation of a rare metallatetrahedrane of Mo­(VI) which was found to be dynamic in solution.