Metallacyclic complexes. Part 4. Synthesis of platinathietane-3-oxide complexes, and the single-crystal X-ray structure of [Pt{CH(COPh)S(O)CH(COPh)}(PPh3)2]·2CH2Cl2

Abstract

Treatment of the complexes cis-[PtCl₂L₂] with diphenacyl sulphoxide, (PhCOCH₂)₂SO, and an excess of silver(I) oxide in refluxing dichloromethane affords high yields of the platinathietane-3-oxide complexes [[graphic omitted]H(COPh)}L₂](L = PPh₃, PMePh₂, or PMe₂Ph). A single-crystal X-ray diffraction study has been carried out on [[graphic omitted]H(COPh)}(PPh₃)₂](6a)·2CH₂Cl₂. The crystals are triclinic, space group P, Z= 2, in a unit cell with a= 13.824(1), b= 12.953(2), c= 19.248(6)Å, α= 118.0(2), β= 52.4(2), and γ= 113.56(5)°. The structure has been refined to R 0.0487 (R′ 0.0512) for 7 864 reflections with (I) 3σ(I). The complex contains a puckered platinathietane-3-oxide ring [fold angle 36.65(46)°] with the sulphinyl oxygen in the expected equatorial environment. The presence of short carbon–sulphur bonds is interpreted in terms of a contribution from a heteroallylic bonding representation. Room-temperature ¹H n.m.r. spectra for the platinathietane-3-oxide complexes indicate that the four-membered rings are puckered and non-fluxional in solution. The magnitude of the platinum-195 coupling to the axial and equatorial ring hydrogens of the platinathietane-3-oxide ring is dependent upon the orientation of the CH bonds with respect to the square-planar platinum function and the magnitudes of ³J(cis-PPtCH) are dihedral angle controlled. The reaction of [Pt₂Br₄(PEt₃)₂] with 1 equivalent of triphenylarsine and diphenacyl sulphoxide per platinum and an excess of silver(I) oxide in refluxing dichloromethane affords the mixed-ligand complex [[graphic omitted]H(COPh)}(AsPh₃)(PEt₃)], which exists as a mixture of two isomers, the major (76%) isomer having the triphenylarsine ligand trans to an axial COPh substituent.