Reactions of halogens with Pt(ii) complexes of N-alkyl- and N,N-dialkyl-N′-benzoylthioureas: oxidative addition and formation of an I2inclusion compound

Abstract

The treatment of cis-[Pt^II(L^1a/b-S,O)₂] complexes of N,N-diethyl- (HL^1a) and N,N-di(n-butyl)-N’-benzoylthiourea (HL^1b) with I₂ or Br₂ in chloroform, leads to rapid oxidative addition to yield several geometric isomers of [Pt^IV(L-S,O)₂X₂] (X = I, Br); the reactions can be monitored by ¹⁹⁵Pt NMR and UV-visible spectrophotometry. The products cis-[Pt^IV(L^1a-S,O)₂I₂] 6 and cis-[Pt^IV(L^1a-S,O)₂Br₂] 7, which have been isolated and structurally characterized, are the first-reported crystal structures of complexes of Pt(IV) with this class of ligand. Molecules of 6 pack such that the I–Pt–I axes are essentially aligned, with unusually close nearest-neighbour iodide contacts (3.553(1) Å). These short I⋯I intermolecular interactions lead to infinite chains of weakly connected molecules in crystals of the compound. No such interactions are evident in the corresponding crystals of 7. Reaction of the Pt(II) complex of N-propyl-N’-benzoylthiourea (H₂L^2a) cis-/trans-[Pt^II(H₂L^2a-S)₂Br₂] with Br₂ also results in oxidative addition, to yield trans-Pt^IV(H₂L^2a-S)₂Br₄9. By contrast, treatment of cis-/trans-[Pt^II(H₂L^2a-S)₂I₂] with I₂ does not lead to an oxidative addition product, yielding instead an interesting iodine inclusion compound of Pt^II, trans-[Pt^II(H₂L^2a-S)₂I₂]·I₂8. In 8, short intermolecular I⋯I distances of 3.453(1) Å between I₂ and coordinated iodide ions in trans-[Pt^II(H₂L^2a-S)₂I₂] molecules, result in infinite chains of weakly linked trans-[Pt^II(H₂L^2a-S)₂I₂]⋯I₂ groups in the lattice. However, the empirically estimated bond order of 0.75 for the included I₂ molecules does not support the possible existence of discrete tetraiodide ions (I₄²⁻) in the lattice of compound 8.