Mild and Selective C(CO)–C(α) Bond Cleavage of Ketones by Rhodium(III) Porphyrins: Scope and Mechanism

Abstract

Rhodium(III) porphyrins were found to undergo selective C(CO)−C(α) bond activation (CCA) of ketones promoted by water at temperatures as low as 50 °C. The acyl group of the ketone was transferred to the rhodium center, and the alkyl fragment was oxidized to a carbonyl moiety accordingly. The hydroxyl group of water is transferred to the rhodium porphyrin through hydrolysis of the kinetic αcarbon−hydrogen bond activation (α-CHA) product to give Rh III (ttp)OH (ttp = 5,10,15,20-tetratolylporphyrinato dianion), which subsequently cleaves the C(CO)−C(α) bond of ketone.

From para‐Benziporphyrin to Rhodium(III) 21‐Carbaporphyrins: Imprinting Rh⋅⋅⋅η2‐CC, Rh⋅⋅⋅η2‐CO, and Rh⋅⋅⋅η2‐CH Coordination Motifs

“…[37] These feasible processes are facilitated by the specific C(25)H 3 ···Rh agostic interaction, which is rational for 4-Rh, reflected also by the extreme upfield positiono ft he methyl signali nt he 1 HNMR spectrum. The methyl resonance decreased in relative integral intensity and becames everely broadened when the temperature was gradually lowered from 230 to 180 K. The severe broadening of the methyl resonance (half linewidth:1 6, 160, and 590 Hz at 230, 200, and 190 K, respectively) results from slowerr otationa round the C(21)ÀC (25) bond, effectively hindered by the interaction with the Rh III center. Complex 4-Rh converts gradually into three hydride derivatives 5-Rh-H (200 K), identified by hydrider esonances split in doublets due to the scalar coupling with the rhodium center( d = À4.08, À6.31, and À20.06 ppm and 1 J RhH = 16.9, 19.3, and 12.9 Hz for 5-Rh-H 1 , 5-Rh-H 2 ,a nd 5-Rh-H 3 ,r espectively;i nset at Figure 2c).…”

“…The molecular structure of 2-Rh ( Figure 3) bears some resemblance to am etalloporphyrin modified by insertion of as ingle carbon atom into an MÀNb ond. [42,45] Such an architecture, which also incorporates some tetrahedral distortion from the trigonal idealized geometry around C(21),i mposes the Rh III ···h 2 -C(21)C(25) bonding mode, as reflectedb yt he RhÀC (25) and RhÀC(21) bond lengths (2.034(3) and 2.118(2) , respectively). [46,47] The C(21)ÀC(25) bond (1.529 (3) ) is markedly longert han typical in ethene or h 2 -ethene rhodium complexes.…”

“…The choiceo fm etal cationi ss trongly motivated by the extensive interest in reactions catalyzedb yr hodium(III)p orphyrins and in particular by their peculiar capability to contribute to processesi nw hich the activation of the single bond is of critical importance, whichi nvolves the formation of the CÀH, CÀC, and C=Ob onds unders ynthetic and catalytic conditions. [22][23][24][25][26][27][28][29][30][31][32][33][34] An impact on organorhodium chemistry,i mposed by the formation of carbametalacycles,c an also be noted. Such structuralm otivesa fford the stabilization of ap eculiar rhodium-carbon bonding situation, outstandingly reflected in the rhodiumo rganometallic chemistry in the surroundings of pincer-typeligands.…”

Chemoselective Oxidative C(CO)C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen

“…Aldehydes are an important class of compounds and widely used in all areas of chemistry; therefore, the development of new retrosynthetic disconnections of aldehydes is highly desirable. [5] The chemoselective C(CO) À C(a) bond cleavage of ketones is a fundamental reaction that has been extensively studied, and has been used for transformations into acids, [6] esters, [7] amides, [8] ketones, [9] and acyl-metal complexes [10] ( Figure 1). Very recently, Jiang and co-workers described an interesting oxidative cleavage and esterification of the C À C bonds of a-hydroxy ketones under metal-free conditions.…”

Copper‐Catalyzed Aerobic Oxidative CC Bond Cleavage for CN Bond Formation: From Ketones to Amides

“…(9)]. [17] In some cases, the aldehydes undergo a Schmidt reaction to produce the corresponding nitriles, which could be detected by GC-MS (see the Supporting Information for details). The substrate is initially attacked by the azide nucleophile to form unstable intermediate A in a potentially reversible process.…”