Promising Routes of Application of Smart Allylborating Reagents

Among the known allylborating agents, amine adducts of allylic triorganoboranes can be considered as the most advanced smart reagents since they combine high activity with stability and selectivity. The new reactivity profile of these compounds offers additional opportunities for both the laboratory and industrial application of allylboranes. The current review presents a short analysis of the promising routes of application of the amine adducts, which include, for example, the catalytic synthesis of functionalized allylarenes, homoallylamines, and the synthesis of BN isosteres of carbon aromatic systems.

Ligand-Mediated Spin State Changes in a Cobalt-Dipyrrin-Bisphenol Complex

ABSTRACT: The influence of a redox-active ligand on spin changing events induced by coordination of exogenous donors is investigated within the cobalt complex <b>[Co^II(DPP^•2‒)]</b>, bearing a redox-active <b>DPP^2‒</b> ligand (DPP = dipyrrin-bis-(<i>o,p</i>-di-tert-butylphenolato) with a pentafluorophenyl moiety on the meso-position. This square planar complex was subjected to coordination of THF, pyridine, tBuNH₂ and AdNH₂ (Ad = 1‑adamantyl), and the resulting complexes were analyzed with a variety of experimental (XRD, NMR, UV-Vis, HRMS, SQUID, Evans’ method) and computational (DFT, NEVPT2-CASSCF) techniques to elucidate the respective structures, spin states and orbital compositions of the corresponding octahedral bis-donor adducts, relative to <b>[Co^II(DPP^•2‒)]</b>. This starting species is best described as an open-shell singlet complex containing a <b>DPP^•2‒</b> ligand radical that is antiferromagnetically coupled to a low-spin (S = ½) cobalt(II) center. The redox-active <b>DPP^n‒</b> ligand plays a crucial role in stabilizing this complex, and in its facile conversion to the triplet THF-adduct <b>[Co^II(DPP^•2‒)(THF)₂]</b> and closed-shell singlet pyridine and amine adducts <b>[Co^III(DPP^3‒)(L)₂]</b> (L = py, tBuNH₂ or AdNH₂). Coordination of the weak donor THF to <b>[Co^II(DPP^•2-)]</b> changes the orbital overlap between the <b>DPP^•2‒</b> ligand radical π-orbitals and the cobalt(II) metalloradical d-orbitals, which results in a spin-flip to the triplet ground state without changing the oxidation states of the metal or <b>DPP^•2‒</b> ligand. In contrast, coordination of the stronger donors pyridine, tBuNH₂ or AdNH₂ induces metal-to-ligand single-electron transfer, resulting in formation of low-spin (S = 0) cobalt(III)-complexes <b>[Co^III(DPP^3‒)(L)₂]</b> containing a fully reduced <b>DPP^3‒</b> ligand, thus explaining their closed-shell singlet electronic ground states.

Ligand-Mediated Spin State Changes in a Cobalt-Dipyrrin-Bisphenol Complex

ABSTRACT: The influence of a redox-active ligand on spin changing events induced by coordination of exogenous donors is investigated within the cobalt complex <b>[Co^II(DPP^•2‒)]</b>, bearing a redox-active <b>DPP^2‒</b> ligand (DPP = dipyrrin-bis-(<i>o,p</i>-di-tert-butylphenolato) with a pentafluorophenyl moiety on the meso-position. This square planar complex was subjected to coordination of THF, pyridine, tBuNH₂ and AdNH₂ (Ad = 1‑adamantyl), and the resulting complexes were analyzed with a variety of experimental (XRD, NMR, UV-Vis, HRMS, SQUID, Evans’ method) and computational (DFT, NEVPT2-CASSCF) techniques to elucidate the respective structures, spin states and orbital compositions of the corresponding octahedral bis-donor adducts, relative to <b>[Co^II(DPP^•2‒)]</b>. This starting species is best described as an open-shell singlet complex containing a <b>DPP^•2‒</b> ligand radical that is antiferromagnetically coupled to a low-spin (S = ½) cobalt(II) center. The redox-active <b>DPP^n‒</b> ligand plays a crucial role in stabilizing this complex, and in its facile conversion to the triplet THF-adduct <b>[Co^II(DPP^•2‒)(THF)₂]</b> and closed-shell singlet pyridine and amine adducts <b>[Co^III(DPP^3‒)(L)₂]</b> (L = py, tBuNH₂ or AdNH₂). Coordination of the weak donor THF to <b>[Co^II(DPP^•2-)]</b> changes the orbital overlap between the <b>DPP^•2‒</b> ligand radical π-orbitals and the cobalt(II) metalloradical d-orbitals, which results in a spin-flip to the triplet ground state without changing the oxidation states of the metal or <b>DPP^•2‒</b> ligand. In contrast, coordination of the stronger donors pyridine, tBuNH₂ or AdNH₂ induces metal-to-ligand single-electron transfer, resulting in formation of low-spin (S = 0) cobalt(III)-complexes <b>[Co^III(DPP^3‒)(L)₂]</b> containing a fully reduced <b>DPP^3‒</b> ligand, thus explaining their closed-shell singlet electronic ground states.

Free Radical Scavenging Activity of Carbonyl-Amine Adducts Formed in Soybean Oil Fortified with Phosphatidylethanolamine

Non-enzymatic browning reactions between lipid aldehydes and aminophospholipids might play an important role in the oxidative stability of cold-pressed vegetable oils. We, therefore, aimed to study the Maillard-type reaction between hexanal, a lipid oxidation product of linoleic acid, and phosphatidylethanolamine (PE (16:0/18:1)) at a ratio of 2:1 at conditions representative of the extraction of cold-pressed soybean oils (CPSBO) and determine the radical scavenging activity of the carbonyl-amine adducts with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The reaction product, 2-pentyl-3,5-dibutyl-dihydropyridine, could be identified by means of LC-ESI-QTOF-MS/MS. The formation of this nitrogen-containing heterocycle significantly increased with time and temperature (p < 0.05). The products formed during the carbonyl-amine reaction between PE (16:0/18:1) and hexanal at 60 °C showed a radical scavenging activity of approximately 20% (p < 0.05). The fraction, containing 2-pentyl-3,5-dibutyl-dihydropyridine, contributed to, but was not solely responsible for, the radical scavenging activity (p < 0.05). Incubation of CPSBO fortified with PE (16:0/18:1) at 60 °C for 60 min had the strongest radical scavenging activity of 85.1 ± 0.62%. Besides 2-pentyl-3,5-dibutyl-dihydropyridine, other carbonyl-amine adducts might impact the radical scavenging activity of CPSBO as well. The oxidative stability of CPSBO might be increased by promoting the formation of carbonyl-amine reaction products, such as 2-pentyl-3,5-dibutyl-dihydropyridine.