Involvement of a Binuclear Species with the Re−C(O)O−Re Moiety in CO₂ Reduction Catalyzed by Tricarbonyl Rhenium(I) Complexes with Diimine Ligands: Strikingly Slow Formation of the Re−Re and Re−C(O)O−Re Species from Re(dmb)(CO)₃S (dmb = 4,4‘-Dimethyl-2,2‘-bipyridine, S = Solvent)

Excited-state properties of fac-[Re(dmb)(CO)3(CH3CN)]PF6, [Re(dmb)(CO)3]2 (where dmb = 4,4‘-dimethyl-2,2‘-bipyridine), and other tricarbonyl rhenium(I) complexes were investigated by transient FTIR and UV−vis spectroscopy in CH3CN or THF. The one-electron reduced monomer, Re(dmb)(CO)3S (S = CH3CN or THF), can be prepared either by reductive quenching of the excited states of fac-[Re(dmb)(CO)3(CH3CN)]PF6 or by homolysis of [Re(dmb)(CO)3]2. In the reduced monomer's ground state, the odd electron resides on the dmb ligand rather than on the metal center. Re(dmb)(CO)3S dimerizes slowly in THF, kd = 40 ± 5 M-1 s-1. This rate constant is much smaller than those of other organometallic radicals which are typically 109 M-1 s-1. The slower rate suggests that the equilibrium between the ligand-centered and metal-centered radicals is very unfavorable (K ≈ 10-4). The reaction of Re(dmb)(CO)3S with CO2 is slow and competes with the dimerization. Photolysis of [Re(dmb)(CO)3]2 in the presence of CO2 produces CO with a 25−50% yield based on [Re]. A CO2 bridged dimer, (CO)3(dmb)Re−CO(O)−Re(dmb)(CO)3 is identified as an intermediate. Both [Re(dmb)(CO)3]2(OCO2) and Re(dmb)(CO)3(OC(O)OH) are detected as oxidation products; however, the previously reported formato-rhenium species is not detected

Involvement of a Binuclear Species with the Re−C(O)O−Re Moiety in CO₂ Reduction Catalyzed by Tricarbonyl Rhenium(I) Complexes with Diimine Ligands: Strikingly Slow Formation of the Re−Re and Re−C(O)O−Re Species from Re(dmb)(CO)₃S (dmb = 4,4‘-Dimethyl-2,2‘-bipyridine, S = Solvent)

Excited-state properties of fac-[Re(dmb)(CO)3(CH3CN)]PF6, [Re(dmb)(CO)3]2 (where dmb = 4,4‘-dimethyl-2,2‘-bipyridine), and other tricarbonyl rhenium(I) complexes were investigated by transient FTIR and UV−vis spectroscopy in CH3CN or THF. The one-electron reduced monomer, Re(dmb)(CO)3S (S = CH3CN or THF), can be prepared either by reductive quenching of the excited states of fac-[Re(dmb)(CO)3(CH3CN)]PF6 or by homolysis of [Re(dmb)(CO)3]2. In the reduced monomer's ground state, the odd electron resides on the dmb ligand rather than on the metal center. Re(dmb)(CO)3S dimerizes slowly in THF, kd = 40 ± 5 M-1 s-1. This rate constant is much smaller than those of other organometallic radicals which are typically 109 M-1 s-1. The slower rate suggests that the equilibrium between the ligand-centered and metal-centered radicals is very unfavorable (K ≈ 10-4). The reaction of Re(dmb)(CO)3S with CO2 is slow and competes with the dimerization. Photolysis of [Re(dmb)(CO)3]2 in the presence of CO2 produces CO with a 25−50% yield based on [Re]. A CO2 bridged dimer, (CO)3(dmb)Re−CO(O)−Re(dmb)(CO)3 is identified as an intermediate. Both [Re(dmb)(CO)3]2(OCO2) and Re(dmb)(CO)3(OC(O)OH) are detected as oxidation products; however, the previously reported formato-rhenium species is not detected

Synthesis of 2‑Alkenyl- and 2‑Alkynyl-benzo[<i>b</i>]phospholes by Using Palladium-Catalyzed Cross-Coupling Reactions

Heck, Stille, and Sonogashira reactions of 2-bromobenzo[b]phosphole P-oxide afforded a series of 2-alkenyl- and 2-alkynyl-benzo[b]phosphole P-oxides. The charge-transfer character of the new benzo[b]phosphole π-systems in the excited state is enhanced by the terminal electron-donating substituents. Furthermore, the C–Sn cross-coupling of the bromide was applied to the facile synthesis of a new Stille-coupling precursor, 2-stannylbenzo[b]phosphole

Transesterification of Various Methyl Esters Under Mild Conditions Catalyzed by Tetranuclear Zinc Cluster

A new catalytic transesterification promoted by a tetranuclear zinc cluster was developed. The mild reaction conditions enabled the reactions of various functionalized substrates to proceed in good to high yield. A large-scale reaction under solvent-free conditions proceeded with a low E-factor value (0.66), indicating the high environmental and economical advantage of the present catalysis

Synthesis of 2‑Alkenyl- and 2‑Alkynyl-benzo[<i>b</i>]phospholes by Using Palladium-Catalyzed Cross-Coupling Reactions

Heck, Stille, and Sonogashira reactions of 2-bromobenzo[<i>b</i>]phosphole <i>P</i>-oxide afforded a series of 2-alkenyl- and 2-alkynyl-benzo[<i>b</i>]phosphole <i>P</i>-oxides. The charge-transfer character of the new benzo[<i>b</i>]phosphole π-systems in the excited state is enhanced by the terminal electron-donating substituents. Furthermore, the C–Sn cross-coupling of the bromide was applied to the facile synthesis of a new Stille-coupling precursor, 2-stannylbenzo[<i>b</i>]phosphole

Additive Effect of <i>N</i>-Heteroaromatics on Transesterification Catalyzed by Tetranuclear Zinc Cluster

A catalytic amount of 4-dimethylaminopyridine showed drastic additive effects on transesterification catalyzed by the μ4-oxo-tetranuclear zinc cluster Zn4(OCOCF3)6O, enhancing the catalytic activity by more than 15-fold. The new catalyst system facilitates transesterification of less reactive sterically demanding esters and alcohols

Synthesis and Oxidation of Iron(II) Ferrocenylacetylide Diphosphine Complexes. A Novel Type of Mixed-Valence Complex

Some Fe(II) ferrocenylacetylide complexes, [(Cp or Cp*)(PP)FeC⋮CFc], were prepared by the photolysis of the corresponding carbonyl complexes [(Cp or Cp*)(CO)2FeC⋮CFc] in the presence of diphosphines (PP = dppe, dppm, dmpe). The cyclic voltammograms showed two quasi-reversible waves at −0.47 to −0.84 and +0.08 to +0.12 V. The one-electron-oxidized species were isolated as relatively stable solids from the reaction of the neutral Fe(II) complexes with DDQ or FcHPF6. The oxidized complexes exhibited an intervalence transfer band at 1295−1595 nm, and the interaction parameters were calculated from the position (α2 = (0.98−2.44) × 10-2). This suggests that these are highly electron delocalized mixed-valence complexes. The IR spectra (νCC = 1956−1976 cm-1), the ESR spectra (appearance of one broad signal), and the Mössbauer spectra (QS = 2.00−2.26 mm s-1) support the above suggestion. The structure of [Cp(dppe)FeC⋮CFC] was determined by single-crystal X-ray diffraction

Synthesis and Oxidation of Iron(II) Ferrocenylacetylide Diphosphine Complexes. A Novel Type of Mixed-Valence Complex

Some Fe(II) ferrocenylacetylide complexes, [(Cp or Cp*)(PP)FeC⋮CFc], were prepared by the photolysis of the corresponding carbonyl complexes [(Cp or Cp*)(CO)2FeC⋮CFc] in the presence of diphosphines (PP = dppe, dppm, dmpe). The cyclic voltammograms showed two quasi-reversible waves at −0.47 to −0.84 and +0.08 to +0.12 V. The one-electron-oxidized species were isolated as relatively stable solids from the reaction of the neutral Fe(II) complexes with DDQ or FcHPF6. The oxidized complexes exhibited an intervalence transfer band at 1295−1595 nm, and the interaction parameters were calculated from the position (α2 = (0.98−2.44) × 10-2). This suggests that these are highly electron delocalized mixed-valence complexes. The IR spectra (νCC = 1956−1976 cm-1), the ESR spectra (appearance of one broad signal), and the Mössbauer spectra (QS = 2.00−2.26 mm s-1) support the above suggestion. The structure of [Cp(dppe)FeC⋮CFC] was determined by single-crystal X-ray diffraction

Additive Effect of <i>N</i>-Heteroaromatics on Transesterification Catalyzed by Tetranuclear Zinc Cluster

A catalytic amount of 4-dimethylaminopyridine showed drastic additive effects on transesterification catalyzed by the μ4-oxo-tetranuclear zinc cluster Zn4(OCOCF3)6O, enhancing the catalytic activity by more than 15-fold. The new catalyst system facilitates transesterification of less reactive sterically demanding esters and alcohols

Enzyme-Like Catalysis via Ternary Complex Mechanism: Alkoxy-Bridged Dinuclear Cobalt Complex Mediates Chemoselective O‑Esterification over N‑Amidation

Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt­(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co₄(OCOR)₆O]₂ (<b>2a</b>: R = CF₃, <b>2b</b>: R = CH₃, <b>2c</b>: R = ^<i>t</i>Bu) with nitrogen-containing ligands, such as 2,2′-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co₂(OCO^<i>t</i>Bu)₂­(bpy)₂(μ₂-OCH₂-C₆H₄-4-CH₃)₂ (<b>10</b>), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis–Menten behavior of the complex <b>10</b> through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester