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.