Synthesis, structure, DFT calculations, and full vibrational analysis of the prototypical thioformaldehyde complex mer-[W(CO)3(Me2PC2H4PMe2)(??2-S???CH2)]The coordination chemistry of the C???S function, part 16. For part 15 see ref. 1.

Reaction of PPN[W(CO)(3)(dmpe)(SH)] 2 (PPN = Ph3PNPPh3, dmpe = Me2PC2 H4PMe2) with aqueous formaldehyde in the presence of trifluoroacetic acid gives the thioformaldehyde complex mer-[W(CO)(3)(Me2PC2H4PMe2)(eta(2)-S=CH2)] 3 in almost quantitative yield. The isotopomer mer-[W(CO)(3)(Me2PC2H4PMe2)(eta(2)-S=CD2)] 3-D-2 was obtained analogously. 3 has a slightly distorted pentagonal-bipyramidal structure with one carbonyl group, two P atoms and the C and S atoms of the thioformaldehyde ligand spanning the pentagonal plane. In solution, 3 is in equilibrium with fac-[W(CO)(3)(Me-2 PC2 H4PMe2)(eta(2)-S=CH2())] 4. The structures and energies of 3 and 4 and their rotamers 3' and 4' were calculated by DFT methods leading to a very good agreement with experimental data. FT-IR and FT-Raman spectra of 3 and 3-D-2 were recorded and assigned with the aid of DFT calculations. Calculated vibrational amplitudes emphasize the extensive mixing of modes, particularly in the low-wavenumber region. The HOMO of 3 can approximately be described as a lone-pair at sulfur and is 0.38 eV higher in energy than that of isomer 4. The LUMOs of both isomers are highly delocalized with that of 4 being 0.45 eV lower in energy. On this basis it is expected that electrophiles will add preferentially at the sulfur atom of 3 while nucleophiles if at all will add to the thiocarbonyl carbon of 4.