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

Abstract

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.