[HPt(EtXantphos) 2](PF 6) (where EtXantphos is 9,9-dimethyl-4,5-bis(diethylphosphino)xanthene) can be prepared by the reduction of Pt(COD)Cl 2 (where COD is 1,4-cyclooctadiene) with hydrazine in the presence of 2 equiv of the diphosphine ligand followed by exchange of Cl - with PF 6 -. Deprotonation of [HPt(EtXantphos) 2](PF 6) (pK a = 27.3 in acetonitrile) leads to the formation of Pt(EtXantphos) 2, which has been characterized by an X-ray diffraction study. Pt(EtXantphos) 2 has a distorted tetrahedral geometry. The average chelate bite angle is 108.2°, and the dihedral angle between the two planes formed by the phophorus atoms of each diphophine ligand and platinum is 80.4°. Protonation of [HPt(EtXantphos) 2] - results in the formation of [(H) 2Pt(EtXantphos 2] 2+, which has a pK a of 6.8 in acetonitrile. Oxidation of Pt(EtXantphos) 2 with ferrocenium tetrafluoroborate produces [Pt(EtXantphos) 2] 2+. Pt(EtXantphos 2] 2- undergoes two reversible one-electron reductions (E 1/2/II/I) = -0.81 V versus ferrocene and E 1/2(I/0) = ∼0.97 V), and HPt(EtXantphos 2] - undergoes a reversible one-electron oxidation E 1/2(II/III) = -0.23 V). These half-wave potentials and the pK a values of [HPt(EtXantphos 2] - and [(H) 2Pt(EtXantphos 2] 2- have been used to calculate five additional homolytic and heterolytic bond-dissociation free energies for these two hydride species and for [HPt(EtXantphos 2] 2- The extensive thermodynamic characterization of this hydride system provides useful insights into the factors controlling the reactivity of these complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry