Multinuclear magnetic resonance spectroscopy and crystal structures of iodo-bridged dinuclear Pt(II) complexes with amines

Abstract

Complexes of the types cis-Pt(amine) 2I 2 were transformed into the iodo-bridged dimers, which were characterized mainly by multinuclear ( 195Pt, 1H and 13C) magnetic resonance spectroscopy. For bulby amines, the dinuclear species were synthesized directly from K 2[PtI 4]. Compounds with several primary aliphatic and cyclic amines and two secondary amines were studied. In 195Pt NMR, two signals were observed between −3899 and −4080 ppm in acetone. These species were assigned to the cis and trans dinuclear compounds I(amine)Pt(μ-I) 2PtI(amine). We suggest that the most shielded compound is the trans isomer. The difference between the two isomers is 12–13 ppm for the primary amine system and 26–27 ppm for the two secondary amines. There seems to be a slight dependence of the proton affinity in the gas phase of the amine (linear amines) with the δ(Pt) chemical shifts of the dinuclear Pt(II) compounds. The 2 J( 195Pt– 1HN) coupling constants are slightly larger for the trans isomers (average 67 Hz, vs. 56 Hz). The 3 J( 195Pt– 1H) coupling constants were detected only for the dimethylamine compounds, 46 Hz ( trans) and 44 Hz ( cis). In 13C NMR, the values of 2 J( 195Pt– 13C) and 3 J( 195Pt– 13C) were also found to be very slightly larger for the trans complexes (average 19 and 25 Hz vs. 15 and 18 Hz). The structures were confirmed by X-ray diffraction studies of the n-butylamine and diethylamine compounds. The two crystals were those of the trans dinuclear complexes.