Ancillary X‐Type Ligand Effects in Alkyne and Diyne Metathesis with Fluoroalkoxy Molybdenum Alkylidynes

Seven hexa‐ and nonafluoroalkoxy‐substituted 2,4,6‐trimethylbenzylidyne molybdenum(VI) complexes [MesC≡Mo{OC(CF 3 ) n (CH 3 ) 3–n } 2 (X)] ( MoFn‐X , n = 6, 9; X = imidazolin‐2‐imide, phosphoraneimide, or siloxide) have been synthesized via salt metathesis from fluoroalkoxy precursors [MesC≡Mo{OC(CF 3 ) 2 CH 3 } 3 )] ( MoF6 ) and [MesC≡Mo{OC(CF 3 ) 3 } 3 )] ( MoF9 ). Structural characterization by X‐ray diffraction and NMR spectroscopy confirm the successful incorporation of the ancillary X‐type ligands. In two cases, the reaction with 3‐hexyne leads to the formation of molybdenacyclobutadiene (MoCBD) complexes of the type [(C 3 Et 3 )Mo{OC(CF 3 ) 3 } 2 X] (X = NIm t Bu, OSi(O t Bu) 2 Ph), characterized by single‐crystal X‐ray diffraction, revealing distorted square‐pyramidal geometries with coplanar orientations of the ancillary ligands relative to the metallacyclic MoC 3 unit. The incorporation of N‐donor ligands is found to be detrimental for catalytic alkyne and diyne metathesis, whereas the siloxy‐functionalized MoF9‐OSi(O t Bu) 2 Ph complex exhibits high activity in alkyne metathesis and excellent selectivity in converting sterically demanding pentadiynes (RC≡CC≡CMe, R = i Pr 3 Si, Ph 3 Si, 2,4,6‐Me 3 C 6 H 2 , 2‐ i PrC 6 H 4 ) into symmetrical triynes (RC≡CC≡CC≡CR) and 2‐butyne (MeC≡CMe). These findings provide insights into the critical electronic and steric factors governing diyne metathesis and underscore the critical role of siloxide ligands in promoting efficient diyne disproportionation catalysis.