Alkyl Carbon–Oxygen Bond Cleavage of Aryl Alkyl Ethers by Iridium–Porphyrin and Rhodium–Porphyrin Complexes in Alkaline Media

Alkyl C–O bond cleavage in aryl alkyl ethers was achieved with Rh­(ttp)Cl (<b>1a</b>; ttp = 5,10,15,20-tetra­kis­(<i>p</i>-tolyl)­porphyrinato dianion) together with competitive alkyl C–H bond activation in alkaline media. In contrast, selective alkyl C–O bond cleavage occurred with the iridium–porphyrin Ir­(ttp)­(CO)Cl (<b>1b</b>)/KOH. Mechanistic investigations indicate the coexistence of M^I(ttp)⁻ and M₂^II(ttp)₂ (M = Rh, Ir) under basic conditions. With a weaker Rh­(ttp)–Rh­(ttp) bond, Rh^II(ttp)· metalloradical exists in an appreciable amount to cleave the alkyl C–H bond, competing with the alkyl C–O bond cleavage via Rh^I(ttp)⁻. In contrast, the more nucleophilic Ir^I(ttp)⁻ cleaves the alkyl C–O bond exclusively

K₂CO₃‑Promoted Consecutive Carbon–Hydrogen and Carbon–Carbon Bond Activation of Cycloheptane with Rhodium(III) Porphyrin Complexes: Formation of Rhodium Porphyrin Cycloheptyl and Benzyl

K₂CO₃-promoted carbon–hydrogen and carbon–carbon bond activations of cycloheptane are achieved with rhodium­(III) tetrakis­(4-tolyl)­porphyrin chloride (Rh­(ttp)­Cl) at 120 °C to give Rh­(ttp) cycloheptyl and benzyl complexes. On the basis of mechanistic studies, Rh­(ttp)Cl first reacts by ligand substitution to give Rh­(ttp)­OH, which then undergoes reductive elimination to give Rh^II₂(ttp)₂. The metalloradical Rh^II(ttp), formed via dissociation of Rh^II₂(ttp)₂, activates the CH bond of cycloheptane to form Rh­(ttp)­(cycloheptyl) and Rh­(ttp)­H. Rh­(ttp)­(cycloheptyl) slowly yields Rh­(ttp)­(cycloheptatrieneyl) by successive β-hydride elimination to olefins and Rh­(ttp)­H. K₂CO₃ promoted the dehydrogenation of Rh­(ttp)H to give Rh^II₂(ttp)₂ and H₂. Both Rh­(ttp)H and Rh^II₂(ttp)₂ activate the cycloheptatriene to give Rh­(ttp)­(cycloheptatrienyl), which further undergoes a Rh^II(ttp)-catalyzed skeletal rearrangement to form Rh­(ttp)­Bn with rate enhancement much faster than that of the analogous organic isomerization of cycloheptatriene to toluene

Base-Promoted Aryl Carbon–Iodine and Carbon–Bromine Bond Cleavage with Rhodium Porphyrin Complexes: Scope and Mechanism

Base-promoted aryl carbon–iodine and carbon–bromine bond (Ar–X, X = I, Br) cleavage by rhodium porphyrin complexes was achieved to give the rhodium­(III) porphyrin aryls Rh­(ttp)Ar (ttp = tetra-<i>p</i>-tolylporphyrinato dianion). Mechanistic studies showed that Rh^II₂(ttp)₂ is the intermediate for Ar–X (X = I, Br) cleavage. The Ar–X cleavage process goes through a rhodium­(II) porphyrin radical mediated ipso-substitution mechanism

Photocatalytic Carbon–Carbon σ‑Bond Anaerobic Oxidation of Ketones with Water by Rhodium(III) Porphyrins

Photocatalytic carbon–carbon σ-bond oxidation of unstrained ketones by water using rhodium­(III) porphyrin catalyst was accomplished. The catalysis yielded the corresponding one-carbon-less carbonyl compound and H₂ with up to 30 turnovers in both aliphatic and cyclic ketones with α substituents. No carbon loss was observed in aromatic ketone. Mechanistic studies suggest that (Ph₃P)­Rh^III(ttp)­OH (ttp = tetratolylporphyrinato dianion) is the key intermediate in the carbon–carbon σ-bond anaerobic oxidation

Catalytic Carbon–Carbon σ-Bond Hydrogenation with Water Catalyzed by Rhodium Porphyrins

The catalytic carbon–carbon σ-bond activation and hydrogenation of [2.2]­paracyclophane with water in a neutral reaction medium is demonstrated. The hydrogen from water is transferred to the hydrocarbon to furnish hydrogen enrichment in good yields

Mild and Selective C(CO)–C(α) Bond Activation of Ketones with Rhodium(III) Porphyrin β‑Hydroxyethyl

Rhodium­(III) porphyrin β-hydroxyethyl, Rh^III(ttp)­CH₂CH₂OH (ttp = 5,10,15,20-tetratolylporphyrinato dianion), was found to serve as a precursor of the highly reactive Rh^III(ttp)­OH for the C­(CO)–C­(α) bond activation (CCA) of ketones under mild and aerobic conditions of 25–50 °C

Base-Promoted Vinyl Carbon–Bromine Bond Cleavage by Group 9 Metalloporphyrin Complexes

Base-promoted vinyl carbon–bromine bond cleavage of styryl bromide by group 9 metalloporphyrin complexes was achieved to give the metal­(III) porphyrin styryls M­(ttp)­(styryl) (ttp = 5,10,15,20-tetra-<i>p</i>-tolylporphyrinato dianion). Mechanistic studies suggest that [M^II(ttp)]₂ (M = Rh, Ir) cleaves the vinyl C–Br bond via an addition–elimination mechanism. The much less reactive Co^II(ttp) undergoes a radical recombination with styryl radical which is generated by the hydroxide reduction of styryl bromide to give a radical anion with subsequent C–Br cleavage

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

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 α-carbon–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

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

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 α-carbon–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

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

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 α-carbon–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