Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

Abstract

cysteine-containing dipeptides in high yield and without significant loss of chirality at the C2-exomethine carbon atom. Finally, the application of this method to one-pot tandem dehydrocyclizations afforded a thiazole±thiazoline product in good overall yield and with excellent stereocontrol. Experimental SectionGeneral procedure for synthesis of thiazolines: Trifluoromethanesulfonic anhydride (50 mL, 0.3 mmol) was added slowly to a solution of triphenylphosphane oxide (167 mg, 0.6 mmol) in dry CH 2 Cl 2 (2 mL) at 0 8C. The reaction mixture was stirred for 10 min at 0 8C and then adjusted to the desired reaction temperature, followed by addition of the fully protected cysteine N-amide (0.2 mmol). The reaction progress was monitored by TLC. The reaction mixture was quenched with 10 % aqueous NaHCO 3 solution. The aqueous layer was extracted with CH 2 Cl 2 , and the combined organic layers were dried over Na 2 SO 4 , filtered, and concentrated. The resultant crude product was purified by flash chromatography with EtOAc/hexanes. More details and characterization data of the products can be found in the Supporting Information.

Efficient C–H bond activations via O2cleavage by a dianionic cobalt(ii) complex

“…S6†). This redox couple is more negative than that for cobalt complexes supported by salen 8 a ( E 1/2 = +0.25 V vs. NHE), porphyrin 8 b ( E 1/2 = +0.68 V vs. NHE), corrole 8 c ( E 1/2 = +0.03 V vs. NHE), 1,1′-(ethane-1,2-diyl)bis(3- tert -butylurea) 4 a ( E 1/2 = –0.086 V vs. NHE), and 2,2′,2′-nitrilo-tris( N -isopropylacetamide) 4 b ( E 1/2 = +0.44 V vs. NHE) ligands.…”

Dioxygen Binding and Activation: Reactive Intermediates

“…6.31) [81]. We found that high-spin [Co(II)(H 2 bade) 2 ] 2-reacts with excess dioxygen to initially produce a species that is formulated as a monomeric cobalt-dioxygen species based on its spectroscopic properties.…”

A New Domain of Reactivity for High‐Valent Dinuclear [M(μ‐O)2M′] Complexes in Oxidation Reactions

“…[1] Moreover, such studies can lead to the discovery of novel species [2] exhibiting reactivity patterns different from their homodinuclear counterparts. The illustrative example (Scheme 1 inset) is the recently reported [L 1 Ni(μ-O) 2 Cu(MeAN)] + ( 1; L 1 = [HC(CMeNC 6 H 3 ( i Pr) 2 ) 2 ]; MeAN = N,N,N ′ ,N ′ ,N ″-pentamethyl dipropylenetriamine), [3] complex which, in sharp contrast to the presence of electrophilic oxido groups in symmetric [M 2 (μ–O) 2 ] n+ (M = Ni, Co, Fe and Mn) analogues, [4] possesses nucleophilic oxido ligands and deformylates aldehydes.…”

“…Furthermore, the fully symmetric [L 1 Ni III (μ-O) 2 Ni III L 1 ] 2+ ( 3 ) complex demonstrates a nucleophilic property, which is in contrast to the observed electrophilic behavior of all homodinuclear bis(μ-oxido) cores reported to date. [4] This together with the self-decay of the heterodinuclear [L 1 Ni(μ-O) 2 CoL 3 ] species 2 (L 3 = [HC(CHNC 6 H 3 ( i Pr) 2 ) 2 ]) by an unprecedented hydroxylation mediated 1,3-migration of an aryl-nitrogen atom, represent a novel domain for high-valent bis(μ-oxido)dimetal reactivity.…”

“…The short metal-metal and metal-oxo distances found in 4 compare favorably to those in related “diamond core” structures. [4] A solution magnetic moment (μ eff , C 6 D 6 , 298 K) of 2.55 μB for 4 suggests population of a higher spin state at elevated temperatures. The Ni sites in 3 are, however, antiferromagnetically coupled at 298 K stabilizing the singlet (S=0) state.…”