High-oxidation-state
group 6 metal alkylidenes have been dominated
by imido and oxo ligands. Here, the first neutral tungsten sulfido
alkylidene and cationic tungsten sulfido alkylidene N-heterocyclic carbene (NHC) complexes are presented. A synthesis
route that entails the reaction of the corresponding tungsten alkylidyne
precursors with H2S in tetrahydrofuran is outlined. Schrock-type
complexes bearing chlorides as well as pentafluorophenoxide ligands
were synthesized, while variations in the NHC (1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene (IMes), 1,3-dimesityl-4,5-dichloro-1,3-dihydro-2H-imidazol-2-ylidene (IMesCl2), and 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IDipp)) as well as in the anionic
ligand (chloride, pentafluorophenoxide, and 2,6-diphenylphenoxide)
were carried out for the cationic tungsten sulfido alkylidene NHC
complexes. All complexes were tested in benchmark olefin metathesis
reactions in which the cationic tungsten sulfido alkylidene NHC complexes
showed high productivities. Atomic charges were calculated for several
cationic tungsten sulfido alkylidene NHC complexes and compared to
those of the analogous tungsten oxo and imido complexes. These calculations
revealed charge distribution between the NHC and the metal, yet lower
charges at the metal and less polarization of the metal alkylidene
bond compared to their tungsten oxo and imido analogs.