Synthesis and solution structure of desoxotungsten(IV) and monooxotungsten(VI) benzenedithiolate complexes containing two intramolecular NH⋯S hydrogen bonds

Abstract

Desoxotungsten(IV) and monooxotungsten(VI) benzenedithiolate complexes containing two intramolecular NH⋯S hydrogen bonds, (NEt4)[WIV{OSi(tBu)Ph2}(1,2-S2-3-tBuCONHC6H3)2] (1) and (NEt4)[WVIO{OSi(tBu)Ph2}(1,2-S2-3-tBuCONHC6H3)2] (2), were synthesized by silylation of the parent mono- and di-oxo compounds. The geometrical isomers, trans- and cis-1, were present at room temperature without any interconversion. 1H NMR spectra of 2 showed only one set of signals at room temperature, which were separated into two sets of distinct signals upon cooling down to lower temperatures. These results suggest that only one pair of enantiomers is present in solution, which are exchanged rapidly in the NMR time scale via Bailar twist at room temperature. Subsequent structural analysis demonstrates that the isomer is 2tc, where, one NH⋯S hydrogen bond is trans to the terminal WO and the other is cis to WO. Theoretical calculations revealed the contribution of the hydrogen bond to the molecular structure and indicate that 2tc is the most stable isomer.