A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

Abstract

A novel Co(II) hydroxo complex Co{HB(3- Prpz) 3 = hydrotris(3-tert-butyl-5-isopropylpyrazol-l-yl)borate} has been prepared and its molecular structure has been determined by X-ray crystallography. This complex is mononuclear with distorted tetrahedral geometry. The reaction of CO 2 with Co{HB(3- Prpz) 3 }] 2 (CO 3 ) wherein the carbonate group is bound to both metal centers in an asymmetrical manner. In order to explore the role of labile metal complexes in promoting ester hydrolysis, complexes [Co{HB(3,

Isolation of a Terminal Co(III)-Oxo Complex

“… Complex 1 has been characterized by a suite of spectroscopic techniques including X-ray diffraction (XRD) that confirm the assignment of a terminal, pseudotetrahedral, S = 3/2 Co II hydroxide complex with a Co–O bond length of 1.876(2) Å (Figure , Figures S1–S6). This bond length is comparable to other pseudotetrahedral Co II -hydroxide complexes. , Cyclic voltammetry of 1 in MeCN shows a quasi-reversible couple at −230 mV vs Fc/Fc + (Fc = ferrocene) which is assigned to the Co II /Co III redox couple and suggests a Co III –OH species may be chemically accessible (Figure S7). Monitoring the addition of one equivalent of [Fc]­[BF 4 ] to 1 in THF at −78 °C by UV–vis spectroscopy shows an isosbestic conversion from violet 1 to a green species assigned as the one-electron oxidized product, [PhB­( t BuIm) 3 Co III OH]­[BF 4 ] ( 2 , Figure S8).…”

“…This bond length is comparable to other pseudotetrahedral Co II -hydroxide complexes. 36,37 S8). This oxidation is also reversible as addition of cobaltocene to in situ generated 2 cleanly regenerates 1 (Figure S9).…”

Organometallic MFU-4l(arge) Metal–Organic Frameworks

“…The reactivity of 2-Me was confirmed by the fast hydrolysis reaction yielding 2-OH , which showed the same carbonic anhydrase mimicking behavior as the reported 1-OH . Usually the formation of carbonato-bridged binuclear complexes is observed for the reaction of scorpionate Co–OH complexes with carbon dioxide, which is not possible in the rigid MOF structure. − This could enable reactions not possible for the molecular complexes.…”

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

“…The FT-IR spectrum of the Co(III)-OH product obtained via precipitation had a peak at 3500 cm −1 , which is consistent with an O-H vibration. 31 The reactivity of 3 was further examined with para -substituted thioanisoles, para -X-Ph-SCH 3 (X = Me, F, H, Cl, Br), to investigate the electronic effect of para -substituents on the oxidation of thioanisoles by 3 (Figure 4d). The Hammet plot of the pseudo-first-order rate constants versus σ p + gave a ρ value of − 3.6(6).…”

“…In addition, [Co III (Me 3 -TPADP)­(OH)­(CH 3 CN)] 2+ was found in the reaction solution as a decomposed product of 3 (see the SI, Figure S12). The FT-IR spectrum of the Co­(III)–OH product obtained via precipitation had a peak at 3500 cm –1 , which is consistent with an O–H vibration . The reactivity of 3 was further examined with para -substituted thioanisoles, para -X-Ph-SCH 3 (X = Me, F, H, Cl, Br), to investigate the electronic effect of para -substituents on the oxidation of thioanisoles by 3 (Figure d).…”