Selective synthesis of the missing tiara-like Ni10, Ni5 and Ni6 thiolates by the C–S bond cleavage of bis(thioether) molecules with a DFT study

Abstract

A series of new bis(phenylthioether) and bis(benzylthioether) compounds (L1–L5) having hexahydropyrimidine, imidazolidine and dihydroperimidine backbones were synthesized. Instead of giving NHC complexes, these compounds undergo facile C–S bond cleavages upon treatment with Ni(II) salts to selectively give new toroidal Ni(II) thiolates: [Ni₁₀(SPh)₂₀] (1) and [Ni₅(SCH₂Ph)₁₀] (5), and the known [Ni₆(SCH₂Ph)₁₂] (8), as confirmed by single crystal X-ray diffraction studies. By-products such as RSSR (R = Ph and CH₂Ph) and partially C–S bond cleaved starting compounds were isolated or detected as well from these reactions. The C–S bond cleavage does not take place with L5 having the dihydroperimidine backbone and a plausible mechanism is proposed based on by-products isolated or detected. DFT calculations give insights into the electronic structures of these ring systems and the nature of bonding with which a dichloromethane is present inside the cavity of 1. Experimentally observed absorption spectra of 1, 5 and 8 match with the calculated spectra.