1H NMR and EPR Spectroscopic Monitoring of the Reactive Intermediates of (Salen)Mn(III) Catalyzed Olefin Epoxidation Full article
| Conference |
Physical Methods for Catalytic Research at the Molecular Level: International memorial K.I. Zamaraev conference 28 Jun - 2 Jul 1999 , Novosibirsk |
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| Journal |
Journal of Molecular Catalysis A: Chemical
ISSN: 1381-1169 |
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| Output data | Year: 2000, Volume: 158, Number: 1, Pages: 19-35 Pages count : 17 DOI: 10.1016/S1381-1169(00)00040-6 | ||||
| Tags | 1H NMR spectroscopy, Enantioselective epoxidation, EPR, Manganese salen complexes, Mechanism | ||||
| Authors |
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| Affiliations |
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Funding (1)
| 1 | Russian Foundation for Basic Research | 97-03-32495 |
Abstract:
Using 1H NMR and EPR spectroscopy, manganese species formed in the catalytic systems 1+iodosobenzene (PhIO) and 1+meta-chloroperoxybenzoic acid (m-CPBA), where 1 is (R,R)-(−)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino-manganese(III) chloride ([(Salen)MnIII]) were studied. Three types of manganese complexes were characterized in the catalytic system 1+PhIO (4–6). Complex 4 is very unstable and reacts with styrene at −20°C to afford styrene oxide. It exhibits three signals of tBu groups at 1.68, 1.64 and 1.42 ppm. This pattern closely resembles that for a model complex [(Salen)MnV≡N]. Based on these data, 4 was identified as d2 low-spin oxomanganese(V) complex [(Salen)MnV=O]+. Complexes 5 and 6 are relatively stable at −20°C and poorly reactive towards styrene at this temperature. They display 1H NMR spectra characteristic for antiferromagnetically coupled μ-oxo-dinuclear MnIV species and are identified as dinuclear complexes [(Salen)LMnIV-O-MnIV(Salen)L′] with L, L′=Cl− and PhIO. It was found by EPR that the acylperoxo complex (Salen)MnIII(OOCOAr) (7) was formed at the first stage of the interaction of 1 with m-CPBA in CH2Cl2. Complex 7 is unstable and converts into manganese(IV) oxo complex [(Salen)MnIV(O)] (8). The evaluated first order rate constant of this conversion is 0.25±0.08 min−1 at −70°C. Complex 7 reacts with styrene with the rate constant 1.1±0.4 M−1 min−1 at −70°C to give epoxide and restore 1. Complex 8 is inert towards styrene at low temperature. The effect of donor ligand N-methylmorpholine-N-oxide (NMO) on the epoxidation of styrene by the system 1+m-CPBA was studied. Addition of NMO (2–5 equiv.) to the solution of 1 in CH2Cl2 before interaction with m-CPBA was found to dramatically increase the rate of undesirable transformation of the reactive acylperoxo complex 7-NMO into relatively inert oxo complex-8-NMO. However, in the presence of styrene, such undesirable conversion is entirely suppressed by very rapid reaction of 8-NMO with styrene to afford styrene oxide and restore 1-NMO.
Cite:
Bryliakov K.P.
, Babushkin D.E.
, Talsi E.P.
1H NMR and EPR Spectroscopic Monitoring of the Reactive Intermediates of (Salen)Mn(III) Catalyzed Olefin Epoxidation
Journal of Molecular Catalysis A: Chemical. 2000. V.158. N1. P.19-35. DOI: 10.1016/S1381-1169(00)00040-6 WOS Scopus РИНЦ ANCAN OpenAlex
1H NMR and EPR Spectroscopic Monitoring of the Reactive Intermediates of (Salen)Mn(III) Catalyzed Olefin Epoxidation
Journal of Molecular Catalysis A: Chemical. 2000. V.158. N1. P.19-35. DOI: 10.1016/S1381-1169(00)00040-6 WOS Scopus РИНЦ ANCAN OpenAlex
Dates:
| Published online: | Jul 18, 2000 |
| Published print: | Sep 8, 2000 |
Identifiers:
| Web of science: | WOS:000089201200003 |
| Scopus: | 2-s2.0-0034623123 |
| Elibrary: | 13353136 |
| Chemical Abstracts: | 2000:498664 |
| Chemical Abstracts (print): | 133:349897 |
| OpenAlex: | W2016651664 |