Halogen Oxidation and Halogen Photoelimination Chemistry of a Platinum鈥揜hodium Heterobimetallic Core

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• 作者：Timothy R. Cook ; Brian D. McCarthy ; Daniel A. Lutterman ; Daniel G. Nocera
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：May 7, 2012
• 年：2012
• 卷：51
• 期：9
• 页码：5152-5163
• 全文大小：594K
• 年卷期：v.51,no.9(May 7, 2012)
• ISSN：1520-510X

文摘

The heterobimetallic complexes, PtRh(tfepma)₂(CN^tBu)X₃ (X = Cl, Br), are assembled by the treatment of Pt(cod)X₂ (cod =1,5-cyclooctadiene) with {Rh(cod)X}₂, in the presence of tert-butylisonitrile (CN^tBu) and tfepma (tfepma = bis(trifluoroethoxyl)phosphinomethylamine). The neutral complexes contain Pt鈥揜h single bonds with metal鈥搈etal separations of 2.6360(3) and 2.6503(7) 脜 between the square planar Pt and octahedral Rh centers for the Cl and Br complexes, respectively. Oxidation of the XPt^IRh^IIX₂ cores with suitable halide sources (PhICl₂ or Br₂) furnishes PtRh(tfepma)₂(CN^tBu)X₅, which preserves a Pt鈥揜h bond. For the chloride system, the initial oxidation product orients the platinum-bound chlorides in a meridional geometry, which slowly transforms to a facial arrangement in pentane solution as verified by X-ray crystal analysis. Irradiation of the mer- or fac-Cl₃Pt^IIIRh^IICl₂ isomers with visible light in the presence of olefin promotes the photoelimination of halogen and regeneration of the reduced ClPt^IRh^IICl₂ core. In addition to exhibiting photochemistry similar to that of the chloride system, the oxidized bromide cores undergo thermal reduction chemistry in the presence of olefin with zeroth-order olefin dependence. Owing to an extremely high photoreaction quantum yield for the fac-ClPt^IRh^IICl₂ isomer, details of the X₂ photoelimination have been captured by transient absorption spectroscopy. We now report the first direct observation of the photointermediate that precedes halogen reductive elimination. The intermediate is generated promptly upon excitation (<8 ns), and halogen is eliminated from it with a rate constant of 3.6 脳 10⁴ s^鈥?. As M鈥揦 photoactivation and elimination is the critical step in HX splitting, these results establish a new guidepost for the design of HX splitting cycles for solar energy storage.