Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles

Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H₂) evolution were examined. Our results showed that substituents at the <i>meso</i> positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. The copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)­corrole (<b>1</b>) was shown to have the best electrocatalytic performance among copper corroles examined. Complex <b>1</b> can electrocatalyze H₂ evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of <i>i</i>_cat/<i>i</i>_p = 303 (<i>i</i>_cat is the catalytic current, <i>i</i>_p is the one-electron peak current of <b>1</b> in the absence of acid) at a scan rate of 100 mV s^–1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that <b>1</b> has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry, and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by <b>1</b>. Doubly reduced <b>1</b> is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H₂

The Mechanism of E–H (E = N, O) Bond Activation by a Germanium Corrole Complex: A Combined Experimental and Computational Study

(TPFC)­Ge­(TEMPO) (<b>1</b>, TPFC = tris­(pentafluorophenyl)­corrole, TEMPO^• = (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl) shows high reactivity toward E–H (E = N, O) bond cleavage in R₁R₂NH (R₁R₂ = HH, ^<i>n</i>PrH, ^<i>i</i>Pr₂, Et₂, PhH) and ROH (R = H, CH₃) under visible light irradiation. Electron paramagnetic resonance (EPR) analyses together with the density functional theory (DFT) calculations reveal the E–H bond activation by [(TPFC)­Ge]⁰(<b>2</b>)/TEMPO^• radical pair, generated by photocleavage of the labile Ge–O bond in compound <b>1</b>, involving two sequential steps: (i) coordination of substrates to [(TPFC)­Ge]⁰ and (ii) E–H bond cleavage induced by TEMPO^• through proton coupled electron transfer (PCET)

Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles

Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H₂) evolution were examined. Our results showed that substituents at the <i>meso</i> positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. The copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)­corrole (<b>1</b>) was shown to have the best electrocatalytic performance among copper corroles examined. Complex <b>1</b> can electrocatalyze H₂ evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of <i>i</i>_cat/<i>i</i>_p = 303 (<i>i</i>_cat is the catalytic current, <i>i</i>_p is the one-electron peak current of <b>1</b> in the absence of acid) at a scan rate of 100 mV s^–1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that <b>1</b> has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry, and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by <b>1</b>. Doubly reduced <b>1</b> is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H₂

Production of Formamides from CO and Amines Induced by Porphyrin Rhodium(II) Metalloradical

It is of fundamental importance to transform carbon monoxide (CO) to petrochemical feedstocks and fine chemicals. Many strategies built on the activation of CO bond by π-back bonding from the transition metal center were developed during the past decades. Herein, a new CO activation method, in which the CO was converted to the active acyl-like metalloradical, [(por)­Rh­(CO)]^• (por = porphyrin), was reported. The reactivity of [(por)­Rh­(CO)]^• and other rhodium porphyrin compounds, such as (por)­RhCHO and (por)­RhC­(O)­NH^<i>n</i>Pr, and corresponding mechanism studies were conducted experimentally and computationally and inspired the design of a new conversion system featuring 100% atom economy that promotes carbonylation of amines to formamides using porphyrin rhodium­(II) metalloradical. Following this radical based pathway, the carbonylations of a series of primary and secondary aliphatic amines were examined, and turnover numbers up to 224 were obtained

Production of Formamides from CO and Amines Induced by Porphyrin Rhodium(II) Metalloradical

It is of fundamental importance to transform carbon monoxide (CO) to petrochemical feedstocks and fine chemicals. Many strategies built on the activation of CO bond by π-back bonding from the transition metal center were developed during the past decades. Herein, a new CO activation method, in which the CO was converted to the active acyl-like metalloradical, [(por)­Rh­(CO)]^• (por = porphyrin), was reported. The reactivity of [(por)­Rh­(CO)]^• and other rhodium porphyrin compounds, such as (por)­RhCHO and (por)­RhC­(O)­NH^<i>n</i>Pr, and corresponding mechanism studies were conducted experimentally and computationally and inspired the design of a new conversion system featuring 100% atom economy that promotes carbonylation of amines to formamides using porphyrin rhodium­(II) metalloradical. Following this radical based pathway, the carbonylations of a series of primary and secondary aliphatic amines were examined, and turnover numbers up to 224 were obtained

Production of Formamides from CO and Amines Induced by Porphyrin Rhodium(II) Metalloradical

It is of fundamental importance to transform carbon monoxide (CO) to petrochemical feedstocks and fine chemicals. Many strategies built on the activation of CO bond by π-back bonding from the transition metal center were developed during the past decades. Herein, a new CO activation method, in which the CO was converted to the active acyl-like metalloradical, [(por)­Rh­(CO)]^• (por = porphyrin), was reported. The reactivity of [(por)­Rh­(CO)]^• and other rhodium porphyrin compounds, such as (por)­RhCHO and (por)­RhC­(O)­NH^<i>n</i>Pr, and corresponding mechanism studies were conducted experimentally and computationally and inspired the design of a new conversion system featuring 100% atom economy that promotes carbonylation of amines to formamides using porphyrin rhodium­(II) metalloradical. Following this radical based pathway, the carbonylations of a series of primary and secondary aliphatic amines were examined, and turnover numbers up to 224 were obtained

Direct Borylation of Tertiary Anilines via C–N Bond Activation

The first successful catalytic borylation of unactivated aromatic C–N bonds of tertiary anilines without the preactivation or any directing groups is demonstrated. The reactivity of both <i>N,N</i>-dialkylarylamines and <i>N</i>-arylpyrroles were investigated systematically, and the targeted products were furnished in moderate to good yields. The DFT calculation results indicated that the catalytic cycle is furnished via a <i>five-membered cyclic transition-state</i> due to the steric hindrance of the Ni/NHC catalytic system

Rare-Earth Metalloligands for Low<b>-</b>Valent Cobalt Complexes: Fine Electronic Tuning <i>via</i> Co→RE Dative Interactions

Rare-earth metalloligand supported low-valent cobalt complexes were synthesized by utilizing a small-sized heptadentate phosphinomethylamine LsNH3 and a large-sized arene-anchored hexadentate phosphinomethylamine LlArH3 ligand precursors. The RE(III)-Co(−I)-N2 (RE = Sc, Lu, Y, Gd, La) complexes containing rare-earth metals including the smallest Sc and largest La were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The Co(−I)→RE(III) dative interactions were all polarized with major contributions from the 3dz2 orbital of the cobalt center, which was slightly affected by the identity of rare-earth metalloligands. The IR spectroscopic data and redox potentials obtained from cyclic voltammetry revealed that the electronic property of the Co(−I) center was finely tuned by the rare-earth metalloligand, which was revealed by variation of the ligand systems containing LsN, LmN, and LlAr. Unlike the direct alteration of the electronic property of metal center via an ancillary ligand, such a series of rare-earth metalloligand represents a smooth strategy to tune the electronic property of transition metals

Rare-Earth Metalloligands for Low<b>-</b>Valent Cobalt Complexes: Fine Electronic Tuning <i>via</i> Co→RE Dative Interactions

Rare-earth metalloligand supported low-valent cobalt complexes were synthesized by utilizing a small-sized heptadentate phosphinomethylamine LsNH3 and a large-sized arene-anchored hexadentate phosphinomethylamine LlArH3 ligand precursors. The RE(III)-Co(−I)-N2 (RE = Sc, Lu, Y, Gd, La) complexes containing rare-earth metals including the smallest Sc and largest La were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The Co(−I)→RE(III) dative interactions were all polarized with major contributions from the 3dz2 orbital of the cobalt center, which was slightly affected by the identity of rare-earth metalloligands. The IR spectroscopic data and redox potentials obtained from cyclic voltammetry revealed that the electronic property of the Co(−I) center was finely tuned by the rare-earth metalloligand, which was revealed by variation of the ligand systems containing LsN, LmN, and LlAr. Unlike the direct alteration of the electronic property of metal center via an ancillary ligand, such a series of rare-earth metalloligand represents a smooth strategy to tune the electronic property of transition metals

Synthesis, Electronic Structure, and Reactivity Studies of a 4‑Coordinate Square Planar Germanium(IV) Cation

A tetra-coordinate, square planar germanium­(IV) cation [(TPFC)­Ge]⁺ (TPFC = tris­(pentafluorophenyl)­corrole) was synthesized quantitatively by the reaction of (TPFC)­Ge–H with [Ph₃C]⁺[B­(C₆F₅)₄]^¯. The highly reactive [(TPFC)­Ge]⁺ cation reacted with benzene to form phenyl complex (TPFC)­Ge–C₆H₅ through an electrophilic pathway. The key intermediate, a σ-type germylium-benzene adduct, [(TPFC)­Ge­(η¹-C₆H₆)]⁺, was isolated and characterized by single-crystal X-ray diffraction. Deprotonation of [(TPFC)­Ge­(η¹-C₆H₆)]⁺ cation led to the formation of (TPFC)­Ge–C₆H₅. [(TPFC)­Ge]⁺ also reacted with ethylene and cyclopropane in benzene at room temperature to form (TPFC)­Ge–CH₂CH₂C₆H₅ and (TPFC)­Ge–CH₂CH₂CH₂C₆H₅, respectively. The observed electrophilic reactivity is ascribed to the highly exposed cationic germanium center with novel frontier orbitals comprising two vacant sp-hybridized orbitals that are not conjugated to π-system. The three electron-withdrawing pentafluorophenyl groups on the corrole ligand also enhance the electrophilicity of the cationic germanium corrole