Carboxylate-Based Molybdenum Alkylidene Catalysts: Synthesis, Characterization, and Use as Initiators for 1,6-Heptadiyne Cyclopolymerizations

The carboxylate species Mo(NR)(CHCMe2R′)(O2CCPh3)2 (R = various aryl groups or 1-adamantyl; R′ = Ph or Me) have been synthesized by salt metathesis between Mo(NR)(CHCMe2R′)(OTf)2(DME) (OTf = trifluoromethanesulfonate; DME = 1,2-dimethoxyethane) and sodium triphenylacetate. Other carboxylate compounds that have been prepared by this route include Mo(NAr)(CHCMe2Ph)(O2CR′′)2 (Ar = 2,6-i-Pr2C6H3; R′′ = CPh2Me, Si(SiMe3)3) and Na[Mo(NAd)(CHCMe2Ph)(O2CAr′)3] (Ar′ = 2,6-Me2C6H3). Terphenylcarboxylate species Mo(NR)(CHCMe2Ph)(O2CTer)2 (Ter = 2,6-diphenyl-4-methylphenyl or 2,6-diphenyl-4-methoxyphenyl) were prepared through protonolysis of Mo(NR)(CHCMe2R′)(Me2Pyr)2 with TerCO2H, and one of them was characterized through X-ray crystallography. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated, and the X-ray crystal structure of Mo(NAr′′)(CH-t-Bu)(O2CCPh3)2(PMe3) (Ar′′ = 2-t-BuC6H4) was obtained. Several of the triphenylacetate complexes are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM).