Pyrazine-bridged Pt(II)-sulfoxide complexes: multinuclear magnetic resonance spectroscopy and crystal structures of trans,trans-{Pt(R2SO)Cl2}2(μ-pyrazine)

A new type of pyrazine-bridged platinum(II) complexes, trans,trans-Pt(R2SO)Cl2(μ-pyrazine)Pt(R2SO)Cl2 was synthesized and characterized mainly by IR and multinuclear magnetic resonance spectroscopies (1H, 13C and 195Pt) and by crystallographic methods. Compounds with dimethylsulfoxide, tetramethylenesulfoxide, di-n-propylsulfoxide, di-n-butylsulfoxide, dibenzylsulfoxide and diphenylsulfoxide were prepared. The compounds were synthezised in good yields from the aqueous reaction of K[Pt(R2SO)Cl3] with pyrazine. IR spectroscopy showed only one ν(Pt–Cl) band suggesting trans isomers. The 195Pt NMR signals of the dimeric species were observed between −3041 and −3113 ppm. The resonance of the diphenylsulfoxide complex was found at higher fields than the other compounds. In 1H NMR, the pyrazine protons are more deshielded (ave. 0.52 ppm) than in free pyrazine. The coupling constants with the pyrazine protons 3J(195Pt–1H) are between 28 and 35 Hz. The crystal structures of three pyrazine-bridged dimers, {trans-Pt(R2SO)Cl2}2(μ-pyrazine) were studied by X-ray diffraction methods. The results confirmed the trans,trans configuration of the compounds. All the molecules contain an inversion centre.