Homoleptic Tris-Diphosphine Re(I) and Re(II) Complexes and Re(II) Photophysics and Photochemistry

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• 作者：Jeramie J. Adams ; Navamoney Arulsamy ; B. Patrick Sullivan ; Dean M. Roddick ; Amelia Neuberger ; Russell H. Schmehl
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：December 7, 2015
• 年：2015
• 卷：54
• 期：23
• 页码：11136-11149
• 全文大小：596K
• ISSN：1520-510X

文摘

The ligand-to-metal charge transfer state (LMCT) of [(dmpe)₃Re]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) has been demonstrated to be a potent oxidant (E⁰(Re^2+*/Re⁺) = 2.61 V vs standard calomel electrode). This complex has been traditionally prepared by nontrivial routes in low yields, and very little has been achieved in optimizing the ground state and emission energy properties of the general class of complexes [(PP)₃Re]²⁺ (PP = chelating diphosphine) through phosphine modification. Improved syntheses for Re(I) tris-homoleptic diphosphine complexes [(PP)₃Re]⁺ (PP = 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), Me₂PCH₂PPh₂, 1,3-bis(dimethylphosphino)propane (dmpp), or 1,2-bis(dimethyl-phosphino)benzene (dmpb)) were achieved by single-pot reactions exploiting the reducing potential of the phosphines when reacted with Re^V oxo-complexes in 1,2-dichlorobenzene at 160鈥?80 掳C. Single-electron chemical oxidation of [(PP)₃Re]⁺ yields luminescent Re^II analogues; appropriate use of Ph₃C⁺, Cp₂Fe⁺, or (4-BrC₆H₄)₃N⁺ B(C₆F₅)₄^{鈥?/sup> salts produced [(PP)₃Re]2+ complexes in good yields. Crystallographic trends for the Re+/Re2+ pairs show significantly lengthened Re2+鈥揚 bonds for [(PP)₃Re]2+ relative to the corresponding [(PP)₃Re]+ system. The redox and luminescence behavior of the complexes indicates the luminescence is from a ligand P(蟽)-to-metal (Re(d蟺)) charge transfer (2LMCT) state for all the complexes. Structured luminescence at 77 K is postulated to originate from relaxation of the 2LMCT state into two spin鈥搊rbit coupled states: the ground state and a state 鈭?000 cm鈥? above the ground state. The excited-state reduction potential (Re(II*/I)) for [(depe)₃Re]2+ was determined from the free energy dependence of luminescence quenching rate constants. Yields for formation of charge separated ions were determined for three of the complexes with a variety of electron donors. Despite favorable electrostatics, no charge separated ions were observed for radical ion pairs for which the energy of back electron transfer exceeded 1.1 V.}