Tungsten and molybdenum alkylidyne complexes containing bulky thiolate ligands

Article abstract of DOI:10.1021/om00092a030

Complexes of the type Mo(C-t-Bu)(TMT)₃ and Mo(C-t-Bu)(TIPT)₃ (TMT = 2,4,6-trimethylbenzenethiolate; TIPT = 2,4,6-triisopropylbenzenethiolate) can be prepared by adding 3 equiv of LiSAr (SAr = TMT or TIPT) to Mo(C-t-Bu)Cl₃(dme). The TMT derivative is believed to be dimeric on the basis of NMR spectra. Reactions between M(C-t-Bu)Cl₃(dme) (M = Mo or W), ArSH, and NEt₃ yield complexes of the type [Et₃NH][M(C-t-Bu)(SAr)₃Cl]. W(C-t-Bu)(SAr)₃ complexes can be prepared by removing chloride ion from the [Et₃NH][W(C-t-Bu)(SAr)₃Cl] species with zinc chloride. M(C-t-Bu)(SAr)₃ complexes do not react with 3-hexyne, 2-butyne, or phenylacetylene, and only minute traces of 3-heptyne metathesis products are observed after 3 days at 25°C. The reaction between W(C₃Me₃)Cl₃ and LiTIPT yields W(C₃Me₃)(TIPT)₃ (in situ), the reaction between W(C₃Me₃)Cl₃, TIPTH, and NEt₃ (or that between W(C₃Me₃)(TIPT)₃ and Et₃NHCl) gives [Et₃NH][W(CMe)(TIPT)₃Cl], and the reaction between the η³-cyclopropenyl complex W(C₃-t-BuMe₂)Cl₃(py)₂ and LiTMT yields a mixture of W(CMe)(TMT)₃(py) and W(C-t-Bu)(TMT)₃(py). Both Mo(CPr)(TIPT)₃ and W(CMe)(TIPT)₃ are stable and isolable. We conclude from these studies that M(CR)(SAr)₃ complexes react too slowly with ordinary acetylenes to be active catalysts, either because coordination of sulfur (in a dimer) competes effectively with coordination of the acetylene or because the metal is simply not electrophilic enough, or both.