PtII versus PdII-assisted [2+3] cycloadditions of nitriles and nitrone. Synthesis of nitrile-derived arylamido platinum(II) and Δ4-1,2,4-oxadiazoline palladium(II) complexes

The reactions of bis(organonitrile) platinum(II) complexes trans-[PtCl2(NCR)2] (R = C6H4(p-HCO), CH2C6H4(p-CH3)) with pyrroline N-oxide −O+NCHCH2CH2CMe2 afford arylamido platinum(II) complexes trans-[PtCl2{(OCR)NCCH2CH2CMe2NH}2] (R = C6H4(p-HCO) (1), CH2C6H4(p-CH3) (2)). The spectral data of 1 and 2 show that the oxadiazoline rings in both cases have opened by a spontaneous NO bond cleavage to form (Z)-p-formyl-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide or (Z)-N-(5,5-dimethylpyrrolidin-2-ylidene)-2-p-tolylacetamide ligands, respectively, where the N-atoms of the benzamide or acetamide moieties coordinate to platinum(II) metal centre in trans positions. However, the reactions of bis(organonitrile) palladium(II) complexes trans-[PdCl2(NCR)2] with pyrroline N-oxide furnish Δ4-1,2,4-oxadiazoline palladium(II) complexes trans-[PdCl2{NC(R)ONC(H)CH2CH2CMe2}2] (R = C6H4(p-HCO) (3), CH2C6H4(p-CH3) (4)) as the exclusive detected products. Compounds 1–4 have been characterized by IR, 1H, 13C NMR spectroscopy, elemental analyses, ESI+-MS and also, in the case of 1, by single crystal X-ray diffraction analysis.