Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(amine)2I2

Complexes of the types cis- and trans-Pt(amine)2I2 were studied by spectroscopic methods, especially by multinuclear NMR spectroscopy. In 195Pt NMR, the cis diiodo compounds with primary amines were observed between −3342 and −3357 ppm in acetone, while the trans compounds were found between −3336 and −3372 ppm. For the secondary amines, the chemical shifts were observed at lower fields. In 1H NMR, the trans complexes were observed at higher fields than the cis compounds, while in 13C NMR, the reverse was observed. The 2J(195Pt–1H) and 3J(195Pt–1H) coupling constants are larger for the cis compounds (ave. 67 and 45 Hz, respectively) than for the trans isomers (ave. 59 and 38 Hz). In 13C NMR, the values of 2J(195Pt–13C) and 3J(195Pt–13C) were also found to be larger for the cis complexes (ave. 17 and 39 Hz versus 11 and 28 Hz). There seems to be a slight dependence of the pKa values of the protonated amines or the proton affinity in the gas phase with the δ(Pt) chemical shifts. The crystal structures of eight diiodo complexes were determined. These compounds are cis-Pt(CH3NH2)2I2, cis-Pt(n-C4H9NH2)2I2, cis-Pt(Et2NH)2I2, trans-Pt(n-C3H7NH2)2I2, trans-Pt(iso-C3H7NH2)2I2, trans-Pt(n-C4H9NH2)2I2, trans-Pt(t-C4H9NH2)2I2 and trans-Pt(Me2NH)2I2. The Pt–N bond distances located in trans position to the iodo ligands were compared to those located in trans position to the amines. The Pt–N bond in cis-Pt(Et2NH)2I2 are much longer than the others, probably caused by the steric hindrance of the two very bulky ligands located in cis positions.