Synthesis, molecular structure and stability of fused bicyclic Δ4-1,2,4-oxadiazoline Pt(II) complexes

Abstract

Abstract The reaction of trans-[PtCl2(NCR)2] (R1 = CH2CO2Me (1a), R2 = CH2Cl (1b)) with pyrroline N-oxide -O+NCHCH2CH2CMe2 (4), at room temperature for 15 min, furnishes via [3+2] cycloaddition the fused bicyclic Δ4-1,2,4-oxadiazoline Pt(II) complexes trans-[PtCl2{NC(R)ONC(H)CH2CH2CMe2}2] (R1 = CH2CO2Me (5a), R2 = CH2Cl (5b)). Compounds 5a and 5b were refluxed in CH2Cl2 for 1 week to afford the derived ketoimine Pt(II) complexes trans-[PtCl2{N(C(O)(R))CCH2CH2C(Me2)NH}2] (R1 = CH2CO2Me (6a), R2 = CH2Cl (6b)), respectively, as a result of the N-O bond cleavage of the oxadiazoline ring in 5. The complexes were characterized by IR, 1H and 13C NMR spectroscopies, ESI+-MS and elemental analyses. DFT calculations show that the Pt(II)-catalysed [3+2] cycloaddition reaction (4 + 10 → 11) is spontaneous and exergonic. In addition, the reaction is completely regioselective yielding a unique oxadiazoline. Moreover, the molecular structure, spectroscopic and electronic properties of complex 5b were predicted, and the optimized geometry showed a slightly distorted square planar arrangement around the Pt(II) centre.