Abstract
The mono- and binuclear Schiff base complexes [CoL3]·DMF (1) and [CoCdL3Cl2]·0.5H2O (2) were facilely synthesized using zerovalent cobalt and cadmium chloride (for 2) as starting materials and the pre-formed pro-ligand HL (2-methoxy-6-[(methylimino)methyl]phenol, the product of condensation of o-vanillin and methylamine) in air. The compounds were characterized by single crystal X-ray diffraction analysis and spectroscopic methods in solution and in the solid state. Both complexes demonstrate a profound catalytic activity in the stereoselective oxidation of cis-1,2-dimethylcyclohexane (model substrate) with m-CPBA (m-chloroperbenzoic acid) under mild conditions in the presence of promoters of various acidity (HNO3, TFA and HOAc). The heterometallic binuclear CoIIICdII pre-catalyst (2) was more active than the mononuclear CoIII one (1), exhibiting higher products yields up to 51% and excellent stereospecificity (up to 99.2% retention of stereoconfiguration). This result could be associated with a synergistic effect of two different metals in 2. Based on the large obtained kinetic isotope effect and H218O labeling studies, the overall reaction mechanism was proposed to proceed without the participation of free alkyl radicals. The acidity of the promoter was shown to influence catalytic parameters for both 1 and 2 so that the better parameters are achieved with the acid possessing lower pKa values (a stronger acid). The comparison of the catalytic behaviours of 1 and 2 is discussed in detail considering relevant examples from the literature.
| Original language | English |
|---|---|
| Pages (from-to) | 171-184 |
| Number of pages | 14 |
| Journal | Applied Catalysis A: General |
| Volume | 560 |
| DOIs | |
| Publication status | Published - 25 Jun 2018 |
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Stereospecific sp3 C–H oxidation with m-CPBA : A CoIII Schiff base complex as pre-catalyst vs. its CoIIICdII heterometallic derivative. / Nesterova, Oksana V.; Kasyanova, Katerina V.; Makhankova, Valeriya G.; Kokozay, Vladimir N.; Vassilyeva, Olga Yu; Skelton, Brian W.; Nesterov, Dmytro S.; Pombeiro, Armando J.L.
In: Applied Catalysis A: General, Vol. 560, 25.06.2018, p. 171-184.Research output: Contribution to journal › Article
TY - JOUR
T1 - Stereospecific sp3 C–H oxidation with m-CPBA
T2 - A CoIII Schiff base complex as pre-catalyst vs. its CoIIICdII heterometallic derivative
AU - Nesterova, Oksana V.
AU - Kasyanova, Katerina V.
AU - Makhankova, Valeriya G.
AU - Kokozay, Vladimir N.
AU - Vassilyeva, Olga Yu
AU - Skelton, Brian W.
AU - Nesterov, Dmytro S.
AU - Pombeiro, Armando J.L.
PY - 2018/6/25
Y1 - 2018/6/25
N2 - The mono- and binuclear Schiff base complexes [CoL3]·DMF (1) and [CoCdL3Cl2]·0.5H2O (2) were facilely synthesized using zerovalent cobalt and cadmium chloride (for 2) as starting materials and the pre-formed pro-ligand HL (2-methoxy-6-[(methylimino)methyl]phenol, the product of condensation of o-vanillin and methylamine) in air. The compounds were characterized by single crystal X-ray diffraction analysis and spectroscopic methods in solution and in the solid state. Both complexes demonstrate a profound catalytic activity in the stereoselective oxidation of cis-1,2-dimethylcyclohexane (model substrate) with m-CPBA (m-chloroperbenzoic acid) under mild conditions in the presence of promoters of various acidity (HNO3, TFA and HOAc). The heterometallic binuclear CoIIICdII pre-catalyst (2) was more active than the mononuclear CoIII one (1), exhibiting higher products yields up to 51% and excellent stereospecificity (up to 99.2% retention of stereoconfiguration). This result could be associated with a synergistic effect of two different metals in 2. Based on the large obtained kinetic isotope effect and H218O labeling studies, the overall reaction mechanism was proposed to proceed without the participation of free alkyl radicals. The acidity of the promoter was shown to influence catalytic parameters for both 1 and 2 so that the better parameters are achieved with the acid possessing lower pKa values (a stronger acid). The comparison of the catalytic behaviours of 1 and 2 is discussed in detail considering relevant examples from the literature.
AB - The mono- and binuclear Schiff base complexes [CoL3]·DMF (1) and [CoCdL3Cl2]·0.5H2O (2) were facilely synthesized using zerovalent cobalt and cadmium chloride (for 2) as starting materials and the pre-formed pro-ligand HL (2-methoxy-6-[(methylimino)methyl]phenol, the product of condensation of o-vanillin and methylamine) in air. The compounds were characterized by single crystal X-ray diffraction analysis and spectroscopic methods in solution and in the solid state. Both complexes demonstrate a profound catalytic activity in the stereoselective oxidation of cis-1,2-dimethylcyclohexane (model substrate) with m-CPBA (m-chloroperbenzoic acid) under mild conditions in the presence of promoters of various acidity (HNO3, TFA and HOAc). The heterometallic binuclear CoIIICdII pre-catalyst (2) was more active than the mononuclear CoIII one (1), exhibiting higher products yields up to 51% and excellent stereospecificity (up to 99.2% retention of stereoconfiguration). This result could be associated with a synergistic effect of two different metals in 2. Based on the large obtained kinetic isotope effect and H218O labeling studies, the overall reaction mechanism was proposed to proceed without the participation of free alkyl radicals. The acidity of the promoter was shown to influence catalytic parameters for both 1 and 2 so that the better parameters are achieved with the acid possessing lower pKa values (a stronger acid). The comparison of the catalytic behaviours of 1 and 2 is discussed in detail considering relevant examples from the literature.
KW - O isotopic labeling
KW - Homogeneous catalysis
KW - m-Chloroperbenzoic acid
KW - Metal complex catalysis
KW - Stereoselective C–H oxidation
UR - http://www.scopus.com/inward/record.url?scp=85047245395&partnerID=8YFLogxK
U2 - 10.1016/j.apcata.2018.05.004
DO - 10.1016/j.apcata.2018.05.004
M3 - Article
VL - 560
SP - 171
EP - 184
JO - APPLIED CATALYSIS A-GENERAL
JF - APPLIED CATALYSIS A-GENERAL
SN - 0926-860X
ER -