Relative hydride, proton, and hydrogen atom transfer abilities of [HM(diphosphine){sub 2}]PF{sub 6} complexes (M = Pt, Ni)
A series of [M(diphosphine){sub 2}]X{sub 2}, [HM(diphosphine){sub 2}]X, and M(diphosphine){sub 2} complexes have been prepared for the purpose of determining the relative thermodynamic hydricities of the [HM(diphosphine){sub 2}]X complexes (M - Ni, Pt; X - BF{sub 4}, PF{sub 6}; diphosphine = bis(diphenylphosphino)ethane (dppe), bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)ethane (dmpe), bis(dismethylphosphino)propane (dmpp)). Measurements of the half-wave potentials (E{sub 1/2}) for the M(II) and M(0) complexes and pK{sub a} measurements for the metal hydride complexes have been used in a thermochemical cycle to obtain quantitative thermodynamic information on the relative hydride donor abilities of the metal-hydride complexes. The hydride donor strengths vary by 23 kcal/mol and are influenced by the metal, the ligand substituents, and the size of the chelate bite of the diphosphine ligand. The best hydride donor of the complexes prepared is [HPt(dmpe){sub 2}](PF{sub 6}), a third-row transition metal with basic substituents and a diphosphine ligand with a small chelate bite. The best hydride acceptors have the opposite characteristics. X-ray diffraction studies were carried out on eight complexes: [Ni(dmpe){sub 2}](BF{sub 4}){sub 2}, [Ni(depe){sub 2}](BF{sub 4}){sub 2}, [Ni(dmpp){sub 2}](BF{sub 4}){sub 2}, [Pt(dmpp){sub 2}](PF{sub 6}){sub 2}, [Ni(dmpe){sub 2}(CH{sub 3}CN)](BF{sub 4}){sub 2}, [Ni(dmpp){sub 2}(CH{sub 3}CN)](BF{sub 4}){sub 2}, Ni(dmpp){sub 2}, and Pt(dmpp){sub 2}. The cations [Ni(dmpp){sub 2}]{sup 2+} and [Pt(dmpp){sub 2}]{sup 2+}exhibit significant tetrahedral distortions from a square-planar geometry arising from the larger chelate bite of dmpp compared to that of dmpe. This tetrahedral distortion produces a decrease in the energy of the lowest unoccupied molecular orbital of the [M(dmpp){sub 2}]{sup 2+} complexes, stabilizes the +1 oxidation state, and makes the [HM(dmpp){sub 2}]{sup +} complexes poorer hydride donors than their dmpe analogues. Another interesting structural feature is the shortening of the M-P bond upon reduction from M(II) to M(0).
- Research Organization:
- National Renewable Energy Lab., Golden, CO (US)
- Sponsoring Organization:
- US Department of Energy
- OSTI ID:
- 20017312
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 49 Vol. 121; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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