Synthesis and characterisation of mixed ligand Pt(II) and Pt(IV) oxadiazoline complexes

The nitrile ligands in trans-[PtX2(PhCN)(2)] (X= Cl, Br, I) undergo sequential 1,3 dipolar cycloadditions with nitrones (RRC)-R-1-C-2=N+(Me)-O-(R-1 = H, R-2 = Ph; R-1 = CO2Et, R-2 = CH2CO2Et) to selectively form the Delta(4)-1,2,4-oxadiazoline complexes trans-[PtX2(PhCN) {N=C(Ph)-O-N(Me)-(CRR2)-R-1}] or trans-[PtX2{N= C(Ph)-O-N(Me)-(CRR2)-R-1}(2)] in high yields. The reactivity of the mixed ligand complexes trans-[PtX2(PhCN){N=C(Ph)-O-N(Me)-(CRR2)-R-1}] towards oxidation and ligand substitution was studied in more detail. Oxidation with Cl-2 or Br-2 provides the Pt(IV) species trans-[PtX2Y2-( PhCN){N=C(Ph)-O-N(Me)-CH(Ph)}] (X, Y= Cl, Br). The mixed halide complex (X = Cl, Y = Br) undergoes halide scrambling in solution to form trans-[PtX(4-n)Yn(PhCN){N= C(Ph)-O-N(Me)-CH( Ph)}] as a statistical mixture. Ligand substitution in trans-[PtCl2(PhCN){N= C(Ph)-O-N(Me)-(CRR2)-R-1}] allows for selective replacement of the coordinated nitrile by nitrogen heterocycles such as pyridine, DMAP or 1-benzyl-2-methylimidazole to produce mixed ligand Pt(II) complexes of the type trans-[PtX2(heterocycle){N= C(Ph)-O-N(Me)-(CRR2)-R-1}]. All compounds were characterised by elemental analysis, mass spectrometry, IR and H-1, C-13 and Pt-195 NMR spectroscopy. Single-crystal X-ray structural analysis of (R, S)-trans-[PtBr2{N= C(Ph)-O-N(Me)-CH(Ph)} 2] and trans-[PtCl2(C5H5N){N= C(Ph)-O-N(Me)-CH(Ph)}] confirms the molecular structure and the trans configuration of the heterocycles relative to each other.