Construction of a monoanionic S,N,S-pincer ligand with a pyrrole core by sequential [1,2] phospho-Fries rearrangement. Characterization of palladium and silver coordination complexes

The synthesis of an S,NH,S-pincer ligand possessing a pyrrole core and two O,O-diethylthiophosphonyl groups to design P=S lateral coordination sites is reported. The synthetic procedure to produce this ligand makes use of the nitrogen atom of the pyrrole heterocycle to successively functionalize the ortho-positions with the two O,O-diethylthiophosphonyl moieties. The ortho-functionalization arises from a repetition of a [1,2] base-induced rearrangement allowing the transformation of O,O-diethyl-N-pyrollylthiophosphoramidate to ortho-thiophosphonate. The coordination properties of this tridentate S,NH,S-ligand have been investigated with silver and palladium metals. Reaction of the monoanionic S,N,S-pincer ligand 4 (O,O,O,O-tetraethylpyrrol-2,5-yl-dithiophosphonate) with PdCl(2)(MeCN)(2) at room temperature in the presence of triethylamine gives rise to the formation of the eta(3)-complex [Pd(eta(3)-4')Cl] 5. Ligand 4 also reacts with silver oxide in dichloromethane to produce complex which, in the solid state, exists as a tetramer involving an almost linear arrangement of four silver atoms.