Discrete cyanide-bridged Co−Fe multinuclear complexes can be considered as functional units of bulk Co− Fe Prussian blue analogues, and they have been recognized as a new class of switching molecules in the last decade. The switching property of the cyanide-bridged Co−Fe complexes is based on intramolecular electron transfers between Co and Fe ions, and we herein refer to this phenomenon as an electron transfer-coupled spin transition (ETCST). Although there have been numerous reports on the complexes exhibiting ETCST behavior, the systematic study of the substituent effects on the thermal ETCST equilibrium in solution has not been reported yet, and the rational control of the equilibrium temperature remains challenging. We report here the syntheses and thermal ETCST behavior both in the solid state and solution for a series of tetranuclear [Co 2 Fe 2 ] complexes, [Co 2 Fe 2 (CN) 6 (L1) 2 (L2) 4 ]X 2 (L1 and L2: tri-and bidentate capping ligands for Fe and Co ions, X: counteranions). All complexes showed thermal ETCST equilibrium between high-spin ([(hs-Co II ) 2 (ls-Fe III ) 2 ]) and low-spin ([(ls-Co III ) 2 (ls-Fe II ) 2 ]) states in butyronitrile, and the equilibrium temperatures (T 1/2 ) showed systematic shifts by chemical modifications and chemical stimuli. The T 1/2 values were correlated with the redox potential differences (ΔE) of the Fe and Co ions in the constituent units, and the larger ΔE values led to the lower T 1/2 . The present result suggests that the thermal ETCST behavior in solution can be rationally designed by considering the redox potentials of the constituent molecules.

Silyl dienol ethers, prepared from α,β-unsaturated ketones, underwent proton sponge-catalyzed difluorocyclopropanation with trimethylsilyl 2,2-difluoro-2-fluorosulfonylacetate in a regioselective manner, leading to 1,1-difluoro-2-siloxy-2-vinylcyclopropanes in good yields. The cyclopropanes thus obtained were in turn subjected to fluoride-ion-catalyzed ring opening to afford 1-fluorovinyl vinyl ketones (i.e., Nazarov precursors). Treatment of the precursors with Me Si B(OTf) regioselectively promoted the Nazarov cyclization, the rate and regioselectivity of which were drastically enhanced by the fluoro substituent, which thus facilitated efficient synthesis of biologically promising α-fluorocyclopentenone derivatives.

A hydrogen‐bonding donor–acceptor system, [Co2Fe2(bpy*)4(CN)6(tp*)2](PF6)2⋅2ABA⋅4BN⋅2PE (1 solv), was prepared by co‐crystallization of an external stimuli‐responsive cyanide‐bridged tetranuclear [Co2Fe2] complex and bifunctional hydrogen‐bonding donors, p‐aminobenzoic acid. Compound 1 solv exhibited a gradual electron‐transfer‐coupled spin transition (ETCST), and the removal of solvent molecules led to an abrupt thermal ETCST behavior with increased transition temperature. X‐ray structural analysis revealed that the modification of ETCST was caused by a significant alteration of a hydrogen‐bonding mode between the tetranuclear [Co2Fe2]2+ cations and ABA molecules. Variable temperature IR measurements indicated that the desolvated form, 1 desolv, showed dynamic alteration of hydrogen‐bonding interactions coupled with thermal ETCST behavior. These results suggested that the tetranuclear [Co2Fe2] complex shows solid‐state modulations of hydrogen‐bond strengths by external stimuli.

The reaction of CoX2(X=Br, Cl) and pyrimidine (PM) in H2O gave crystals of CoPM2X2. The crystal structure analysis revealed a chiral three-dimensional network of the Co(II) ions. Weak ferromagnetism with relatively large spontaneous magnetization was observed below 5 K for both compounds.

Electrophilic difluoromethylidenation of dithioesters was achieved in high yields via the reaction with difluorocarbene. When aryl or alkyl dithiocarboxylates were treated with trimethylsilyl 2,2-difluoro-2-fluorosulfonylacetate in the presence of 5 mol % of a Proton Sponge catalyst, the in situ generated difluorocarbene reacted with the dithioesters to afford 2-sulfanylated 1,1-difluoro-1-alkenes via difluorothiiranes. This reaction can be considered as an electrophilic counterpart of the Wittig-type difluoromethylidenation of carbonyl compounds with nucleophilic difluoromethylene ylides.