Hydrogen Bonding in Transition Metal Complexes: Synthesis, Dynamics, and Reactivity of Platinum Hydride Bifluoride Complexes

Abstract

Platinum hydride bifluoride (FHF) complexes trans-[Pt(PR3)2H(FHF)] (R = Cy, iPr) were prepared from the reaction of the corresponding trans-dihydride complexes with NEt3·3(HF) in THF. They were also formed in C−F activation reactions of the same precursors with C6F6 in the presence of [Me4N]F. The low-temperature NMR spectra exhibit a complete network of coupling between the spin 1/2 nuclei, 1H, 31P, 19F, and 195Pt. At higher temperatures, fluxional behavior is observed which is principally associated with intermolecular exchange of HF between platinum centers. However, satisfactory simulation of the spectra also requires inclusion of intermolecular exchange of the distal fluoride. Addition of [Bu4N]FHF results in coalescence of the bifluoride proton resonance of the complex and the added bifluoride, demonstrating that the bifluoride ligand can exchange with free bifluoride, FHF-. The IR spectrum of trans-[Pt(PCy3)2H(FHF)] shows two broad bands at 2604 and 1832 cm-1 assigned to the H−F stretching modes and a sharp band at 2272 cm-1 for the Pt−H stretching mode. Bifluoride is a weakly coordinated ligand which can be replaced to give trans-[Pt(PCy3)2(H)X] complexes where X = N3, OTf. Hydrogen fluoride may be removed from trans-[Pt(PCy3)2H(FHF)] by treatment with CsOH in the presence of [NMe4]F, yielding trans-[Pt(PCy3)2(H)F]. In addition, these bifluoride complexes fluorinate organic compounds, such as CH3I, CH3COCl, and C6H5COCl, to give CH3F, CH3COF, and C6H5COF together with trans-[Pt(PCy3)2(H)X] (X = Cl, I). Reactions with PPh3 and pyridine yield trans-[Pt(PCy3)2(PPh3)H]FHF and trans-[Pt(PCy3)2(C5H5N)H]FHF.