New Perspectives in Phosphonodithioate Coordination Chemistry. Synthesis and X-ray Crystal Structure of Trans-bis-[O-ethyl(4-methoxyphenyl)phosphonodithioato] nickel(II)

Attempts to optimise the synthesis of a new class of nickel(ll) dithiolene complexes starting from 1,3-dialkylimidazolidine-2-thione-4,5- dione (1) and Lawesson's reagent (2) have afforded a new and easy one step synthesis of phosphonodithioate nickel(II) complexes. This consists of the direct reaction between NiCl2 and Lawesson's reagent in the appropriate alcohol R'OH (R=Me, Et, i-Pr, Bu, Bz) as solvent, to give the bis-[O-alkyl/aryl-(4-methoxyphenyl)phosphonodithioato] nickel(II) complexes (5a-e) with high yields (64-91%). Among them trans-bis-[O-ethyl-(4-methoxyphenyl) phosphonodithioato] nickel(II) (5b) was characterised by means of X-ray diffraction measurements on a single crystal. The compound crystallises in the triclinic, Pi space group with a= 6.4840(7), b = 7.6032(9), c= 13.055(2) Angstrom, alpha = 99.481(9), beta = 99.43(1), gamma = 104.487(9)degrees and Z = 1. The compound is centrosymmetric and exhibits discrete monomeric units with the ligand acting as S,S-bidentate. To explain the reactivity of Lawesson's reagent, the formation of 4-methoxyphenyldithiophospborane (6) as intermediate has been suggested. The reaction was also tested for Pd(II) and Pt(II), but in these cases the yields were not as satisfactory as for Ni(II).