Pt(II) nitrile complexes: new insights on old complexes from a combined experimental and theoretical study

The spectroscopic characterization of cis- and trans-[PtCl2(NCR)2] (R = CH3, Ph, CH2Ph) was reported in solid state and solution phase. Moreover, the X-ray structures of cis-[PtCl2(NCCH3)2], cis- and trans-[PtCl2(NCPh)2] were redetermined at low temperature. FT-IR and NMR showed a blue-shift and a slight shielding of the νCN and δ(13CCN) values, respectively, in a counterintuitive way with respect to the well known improved reactivity towards nucleophiles of nitriles ligands coordinated to platinum(II), when compared to their free forms. These spectroscopic behaviors were also confirmed by theoretical experiments at DFT level. Moreover, DFT approach showed that the increased reactivity of the nitrile ligands, after coordination to Pt(II), can be explained by the energy decreasing of the ligands’ LUMOs, instead of an increased polarization of the CN bond, accordingly with the orbital control model previously proposed for trans-[PtCl2(MeCN)2]. Finally, bond analysis also discarded the occurrence of Pt → N back-donation. The combined experimental and theoretical study herein reported, provides a rationale of the chemical and physical behavior for Pt(II)-acetonitrile and -benzonitrile complexes, proving to be a potential tool to set suitable based-nitrile intermediates for the synthesis of new organometallic derivatives.