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

The reaction of trans -[PtCl 2 (NCR) 2 ] (R 1 = CH 2 CO 2 Me ( 1a ), R 2 = CH 2 Cl ( 1b )) with pyrroline N -oxide − O + N CHCH 2 CH 2 C Me 2 ( 4 ), at room temperature for 15 min, furnishes via [3+2] cycloaddition the fused bicyclic Δ 4 -1,2,4-oxadiazoline Pt(II) complexes trans- [PtCl 2 { N C(R)O N C(H)CH 2 CH 2 C Me 2 } 2 ] (R 1 = CH 2 CO 2 Me ( 5a ), R 2 = CH 2 Cl ( 5b )). Compounds 5a and 5b were refluxed in CH 2 Cl 2 for 1 week to afford the derived ketoimine Pt(II) complexes trans- [PtCl 2 {N(C( O)(R)) C CH 2 CH 2 C(Me 2 ) N H} 2 ] (R 1 = CH 2 CO 2 Me ( 6a ), R 2 = CH 2 Cl ( 6b )), respectively, as a result of the N–O bond cleavage of the oxadiazoline ring in 5. The complexes were characterized by IR, 1 H and 13 C 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.