21127-91-3Relevant articles and documents
Electron Transfer Reactions: KO tBu (but not NaO tBu) Photoreduces Benzophenone under Activation by Visible Light
Nocera, Giuseppe,Young, Allan,Palumbo, Fabrizio,Emery, Katie J.,Coulthard, Graeme,McGuire, Thomas,Tuttle, Tell,Murphy, John A.
supporting information, p. 9751 - 9757 (2018/07/21)
Long-standing controversial reports of electron transfer from KOtBu to benzophenone have been investigated and resolved. The mismatch in the oxidation potential of KOtBu (+0.10 V vs SCE in DMF) and the first reduction potential of benzophenone (of many values cited in the literature, the least negative value is -1.31 V vs SCE in DMF), preclude direct electron transfer. Experimental and computational results now establish that a complex is formed between the two reagents, with the potassium ion providing the linkage, which markedly shifts the absorption spectrum to provide a tail in the visible light region. Photoactivation at room temperature by irradiation at defined wavelength (365 or 400 nm), or even by winter daylight, leads to the development of the blue color of the potassium salt of benzophenone ketyl, whereas no reaction is observed when the reaction mixture is maintained in darkness. So, no electron transfer occurs in the ground state. However, when photoexcited, electron transfer occurs within a complex formed from benzophenone and KOtBu. TDDFT studies match experimental findings and also define the electronic transition within the complex as n → π, originating on the butoxide oxygen. Computation and experiment also align in showing that this reaction is selective for KOtBu; no such effect occurs with NaOtBu, providing the first case where such alkali metal ion selectivity is rationalized in detail. Chemical evidence is provided for the photoactivated electron transfer from KOtBu to benzophenone: tert-butoxyl radicals are formed and undergo fragmentation to form (acetone and) methyl radicals, some of which are trapped by benzophenone. Likewise, when KOC(Et)3 is used in place of KOtBu, then ethylation of benzophenone is seen. Further evidence of electron transfer was seen when the reaction was conducted in benzene, in the presence of p-iodotoluene; this triggered BHAS coupling to form 4-methylbiphenyl in 74% yield.
Conformational studies by dynamic NMR.78.1 Stereonmutation of the helical enantiomers of trigonal carbon diaryl-substituted compounds: Dimesitylketone, dimesitylthioketone, and dimesitylethylene
Grilli,Lunazzi,Mazzanti,Casarini,Femoni
, p. 488 - 495 (2007/10/03)
The free energies of activation for the enantiomerization of the title compounds (Mes2C=X, Mes = 2,4,6,-trimethylphenyl) were determined by dynamic NMR to be 4.6, 6.5, and 9.2 kcal mol-1 for X= O, S, and CH2, respectively. Single-crystal X-ray diffraction showed that the structure of dimesitylketone is that of a propeller (C2 symmetry) with the mesityl rings twisted by 50° with respect to the plane of carbonyl. The same structure was predicted by molecular mechanics calculations, which also produced good agreement between computed and experimental barriers for a dynamic process where a disrotatory one-ring flip pathway reverses the helicity of the conformational enantiomers. Solid-state NMR spectra indicated that the enantiomerization barrier in the crystal must be much higher (at least 19 kcal mol-1) than that in solution. Contrary to the case of dimesitylketone, the calculated barrier of dimesitylethylene agrees better with the experimental value if the enantiomerization process is assumed to be a conrotatory two-ring flip pathway.
The Use of Chemical Probes To Differentiate between Polar and SET-Hydrogen Atom Abstraction Pathways Involved in the Reduction Reaction Promoted by an 8-Al-4 Anion
Tanner, Dennis D.,Yang, C. M.
, p. 5907 - 5914 (2007/10/02)
The mechanism for the reduction of aromatic ketones and alkyl halides with lithium tetrakis(N-dihydropyridyl)aluminate was found to proceed competitively by hydride reduction and by single electron transfer (SET)-hydrogen atom abstraction processes.A series of ketyl fragmentation probes were used to differentiate the two pathways.A SET process is the dominant pathway when the ketones involved are sterically hindered or when strong electron acceptors are used as the substrates.The observation that EPR-active intermediates can be detected, or that small amounts of radical derived products are formed, demonstrates only that a SET pathway is available but cannot be used to establish the mechanism of the major product-forming reactions.
Resolution and Enantiomerization Barrier of Tetramesitylethylene
Gur, Erez,Kaida, Yuriko,Okamoto, Yoshio,Biali, Silvio E.,Rappoport, Zvi
, p. 3689 - 3693 (2007/10/02)
The 1H NMR spectrum of tetramesitylethylene (2) was analyzed, and the signals were assigned by means of a 2D NOESY spectrum.Attempts to observe anisochrony of the enantiotopic groups of a racemic mixture of 2 in a chiral solvent by 1H NMR were unsuccesful.Molecular mechanics and MNDO calculations satisfactorily reproduce the ground-state conformation.The calculated barrier for the enantiomerization process is 21.8 (MM2) and 28.2 (MNDO) kcal mol-1. 2 was chromatographically resolved on a (+)-poly(triphenylmethyl)methacrylate (PTrMA) column.Its specific rotation is 25 = -12100 deg at 365 nm and -2300 deg at 589 nm (D line).The activation parameters for the enantiomerization of 2 in perhydrofluorene are ΔG = ΔH = 39.6 kcal mol-1 and ΔS = 0 cal mol-1 K-1.The barrier for 2 is the highest determined experimentally for a correlated rotation.
Evidence of Single Electron Transfer in the Reduction of Various OrganicSubstrates by Lithium Tetrakis(N-dihydropyridyl)aluminate
Ashby, E.C.,Goel, A.B.
, p. 3934 - 3936 (2007/10/02)
Aromatic ketones, polynuclear hydrocarbons, and alkyl halides with LiAl(PyH)4 by a single electron transfer process.
