Single and double fluorine migration in third row transition metal dialkylaminodifluorosulfane complexes

Abstract

Previous theoretical studies indicate that metal trifluorosulfane complexes are generally energetically disfavored with respect to fluorine migration from sulfur to the metal atom. This accounts for the limitation of currently known experimental metal trifluorosulfane chemistry to the single complex (Et3P)2Ir(CO)(Cl)(F)(SF3) having octahedral coordination of the central iridium atom. In a search for systems where such fluorine migrations are energetically disfavored, the density functional theoretical methods M06-L, BP86, and BP86-D3 have been used to study the related dimethylaminodifluorosulfane complexes of the third row transition metals, namely [M](SF2NMe2) ([M] = Ta(CO)5, CpW(CO)2, Re(CO)4, CpOs(CO), Ir(CO)3, CpPt). However, the complexes containing intact Me2NSF2 ligands, like the corresponding [M](SF3) complexes, are found to be energetically disfavored with respect to migration of one or two fluorine atoms from sulfur to the metal to give the monofluorides [M](SFNMe2)F and the difluorides [M](SNMe2)F2. Isomeric structures containing intact dihapto η2-Me2NSF2 ligands lie at significantly higher energies. Even higher energy [M](SF2)NMe2 structures with separate SF2 and NMe2 ligands are also found. An octahedral Re(CO)4(η2-SF2NMe2) structure with a relatively long SN bond can be viewed as a frozen intermediate in the rupture of an SN bond in an Re(CO)4(SF2NMe2) structure with an intact Me2NSF2 ligand to give a Re(CO)4(SF2)NMe2 structure with separate SF2 and Me2N ligands.