Molybdenum(III) chloride–tetrahydrothiophene (tht) complexes in the catalytic polymerization and cyclotrimerization of alkynes: structures and reactivities of the possible intermediates [MoCl3(tht)2(PhCCR)](R = Me or Et)

Abstract

The binuclear complexes [Mo₂Cl₆(tht)₃](both the C_2v and C_s isomers, tht = tetrahydrothiophene) have been found to be active catalysts for the selective polymerization and cyclotrimerization of a variety of alkynes. The mononuclear complex [MoCl₃(tht)₃] shows similar behaviour, leading to the postulate that the active species in all cases is mononuclear. Two unique molybdenum(III) alkyne complexes, [MoCl₃(tht)₂L](L = PhCCMe or PhCCEt) have been isolated and structurally characterized. The structural parameters for these complexes suggest that the alkynes behave as four-electron donors. These complexes are also catalytically active, and the alkyne L is incorporated into the product cyclotrimers and polymers suggesting they are the first intermediates in the formation of active catalysts from the original thioether complexes.