- Electrochemical Ruthenium-Catalyzed C-H Hydroxylation of Amine Derivatives in Aqueous Acid
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The development of an electrochemically driven, ruthenium-catalyzed C-H hydroxylation reaction of amine-derived substrates bearing tertiary C-H bonds is described. The reaction is performed under constant current electrolysis in a divided cell to afford alcohol products in yields comparable to those of our previously reported process, which requires the use of stoichiometric H5IO6 for catalytic turnover. With aqueous acid as solvent, the cathodic electrode reaction simply involves the reduction of protons to evolve hydrogen gas. The optimized protocol offers a convenient, efficient, and atom-economical method for sp3-C-H bond oxidation.
- Robinson, Sophia G.,MacK, James B. C.,Alektiar, Sara N.,Du Bois,Sigman, Matthew S.
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supporting information
p. 7060 - 7063
(2020/06/05)
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- Mechanistic Study of Ruthenium-Catalyzed C-H Hydroxylation Reveals an Unexpected Pathway for Catalyst Arrest
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We have recently disclosed [(dtbpy)2RuCl2] as an effective precatalyst for chemoselective C-H hydroxylation of C(sp3)-H bonds and have noted a marked disparity in reaction performance between 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy)- and 2,2′-bipyridine (bpy)-derived complexes. A desire to understand the origin of this difference and to further advance this catalytic method has motivated the comprehensive mechanistic investigation described herein. Details of this reaction have been unveiled through evaluation of ligand structure-activity relationships, electrochemical and kinetic studies, and pressurized sample infusion high-resolution mass spectrometry (PSI-MS). Salient findings from this investigation include the identification of more than one active oxidant and three disparate mechanisms for catalyst decomposition/arrest. Catalyst efficiency, as measured by turnover number, has a strong inverse correlation with the rate and extent of ligand dissociation, which is dependent on the identity of bipyridyl 4,4′-substituent groups. Dissociated bipyridyl ligand is oxidized to mono- and bis-N-oxide species under the reaction conditions, the former of which is found to act as a potent catalyst poison, yielding a catalytically inactive tris-ligated [Ru(dtbpy)2(dtbpy N-oxide)]2+ complex. Insights gained through this work highlight the power of PSI-MS for studies of complex reaction processes and are guiding ongoing efforts to develop high-performance, next-generation catalyst systems for C-H hydroxylation.
- Mack, James B. C.,Walker, Katherine L.,Robinson, Sophia G.,Zare, Richard N.,Sigman, Matthew S.,Waymouth, Robert M.,Du Bois
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supporting information
p. 972 - 980
(2019/01/11)
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- Remote C(sp3)-H Oxygenation of Protonated Aliphatic Amines with Potassium Persulfate
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This letter describes the development of a method for selective remote C(sp3)-H oxygenation of protonated aliphatic amines using aqueous potassium persulfate. Protonation serves to deactivate the proximal C(sp3)-H bonds of the amine substrates and also renders the amines soluble in the aqueous medium. These reactions proceed under relatively mild conditions (within 2 h at 80 °C with amine as limiting reagent) and do not require a transition metal catalyst. This method is applicable to a variety of types of C(sp3)-H bonds, including 3°, 2°, and benzylic C-H sites in primary, secondary, and tertiary amine substrates.
- Lee, Melissa,Sanford, Melanie S.
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supporting information
p. 572 - 575
(2017/02/10)
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- Hydroquinones
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New hydroquinones have the formula: STR1 wherein p is 1 or 2 and q is 0 or 1, provided that p+q is 1 or 2; R is a residue of formula: STR2 wherein Q is (i) -OX or (ii) -PO(OR11)((O)x R11); and salts thereof with organic or inorganic acid bases. The groups X and R11 and x are defined hereinafter. The compounds of formula I are useful as stabilisers in photographic materials.
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- Benzo-1,4-quinones
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New benzo-1,4-quinones and salts thereof with organic or inorganic acid and bases have the formula I STR1 wherein p is 1 or 2 and q is 0 or 1, provided that p+q is 1 or 2, R is a residue of formula II STR2 wherein Q is selected from the residues --CO2 R4, --CON(R4)(R5), --OR5, --OCOR7, --N(R8)(R9), --PO(OR10)([O]x R11), --SO2 R12, --CN, Halogen, --NO2 or --COR13, n is an integer from 1 to 20, k is 1 or 2 and x is 0 or 1, and R1 to R5 and R7 to R13 are as defined in the specification. The compounds of formula I are useful in photographic materials such as bleaching inhibitors in films of photographic silver dye bleach materials.
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- Hydroquinone ether compounds
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New hydroquinone ether compounds of formula I are described: STR1 wherein p is 1 or 2 and q is 0 or 1, provided that p+q is 1 or 2, R is a residue of formula II STR2 and Ro, Roo, R1, R2, R3, Q, n and k are as defined in the specification. The new compounds are useful e.g. as stabilizers in photographic material.
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- Hydroquinones
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New hydroquinones having the formula: STR1 wherein p is 1 or 2 and q is 0 or 1, provided that p+q is 1 or 2; R is a residue of formula: STR2 wherein Q is selected from the residues --COZR4 wherein Z is 0 or NR5, --OX wherein X is R5 or --COR7, --NR8 R9, --PO(OR10)[O]x R11 wherein x is 0 or 1, --SO2 R12 or --CN, and salts thereof with organic or inorganic acid bases. The groups, R1, R2, R3, R4, R5, R7, R8, R9, R10, R11, R12, k and n are defined hereafter. These compounds are used as stabilizers in photographic materials.
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