Fluorine shifts from sulfur in dimethylaminodifluorosulfane complexes of cyclopentadienyl metal carbonyls of chromium, molybdenum, and tungsten

Previous theoretical studies predict metal SF₃ complexes to be disfavored relative to shift of a fluorine atom from the SF₃ ligand to the metal atom to give complexes with separate SF₂ and fluorine ligands. We now explore metal complexes of the Me₂NSF₂ ligand hoping that substituting one of the electron-withdrawing fluorine atoms with an electron releasing dimethylamino group will strengthen the sulfur-fluorine bonds thereby inhibiting fluorine shift from sulfur to metal. The cyclopentadienylmetal carbonyl systems of the group 6 metals chromium, molybdenum, and tungsten were chosen for this study since CpM(CO)₂SF₂NMe₂ (M = Cr, Mo, and W) derivatives with an intact Me₂NSF₂ ligand would be analogs of the very stable nitrosyls CpM(CO)₂(NO). However, for all of the CpM(CO)_nSF₂NMe₂ systems fluorine shift from sulfur to the metal atom occurred in all of the low-energy structures giving structures having separate Me₂NSF and fluorine ligands. Isomeric CpM(CO)₂SF₂NMe₂ structures with intact Me₂NSF₂ ligands bonded to the metal through both sulfur and nitrogen analogous to the known metal nitrosyls CpM(CO)₂(NO) lie 13–18 kcal/mol in energy above the lowest energy isomers with split Me₂NSF + F ligands.