Henry Reaction Revisited. Crucial Role of Water in an Asymmetric Henry Reaction Catalyzed by Chiral NNO Type Copper(II) Complexes

Larionov, V.A.; Yashkina, L.V.; Medvedev, M.G.; Smol’yakov, A.F.; Peregudov, A.S.; Pavlov, A.A.; Eremin, D.B.; Savel’yeva, T.F.; Maleev, V.I.; Belokon, Y.N.

Авторы: Larionov Vladimir A., Yashkina Lidiya V., Medvedev Michael G., Smol’yakov Alexander F., Peregudov Alexander S., Pavlov Alexander A., Eremin Dmitry B., Savel’yeva Tat'yana F., Maleev Victor I., Belokon Yuri N.
Журнал: Inorganic Chemistry
Том: 58
Номер: 16
Год издания: 2019
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 11051
Последняя страница: 11065
DOI: 10.1021/acs.inorgchem.9b01574
Аннотация: Chiral copper(II) and cobalt(III) complexes (1−5 and 6, respectively) derived from Schiﬀ bases of (S)-2 (aminomethyl)pyrrolidine and salicylaldehyde derivatives were employed in a mechanistic study of the Henry reaction-type condensation of nitromethane and o-nitro benzaldehyde in CH2Cl2 (CD2Cl2), containing diﬀerent amounts of water. The reaction kinetics was monitored by 1H and 13C NMR. The addition of water had a diﬀerent inﬂuence on the activity of the two types of complexes, ranging from a crucial positive eﬀect in the case of the copper(II) complex 2 to insigniﬁcant in the case of the stereochemically inert cobalt(III) complex 6. No experimental support was found by 1H NMR studies for the classical Lewis acid complexation of the carbonyl group of the aldehyde by the central copper(II) ion, and, moreover, density functional theory (DFT) calculations support the absence of such coordination. On the other hand, a very signiﬁcant complexation was found for water, and it was supported by DFT calculations. In fact, we suggest that it is the Brønsted acidity of the water molecule coordinated to the metal ion that triggers the aldehyde activation. The rate-limiting step of the reaction was the removal of an α-proton from the nitromethane molecule, as supported by the observed kinetic isotope eﬀect equaling 6.3 in the case of the copper complex 2. It was found by high-resolution mass spectrometry with electrospray ionization that the copper(II) complex 2 existed in CH2Cl2 in a dimeric form. The reaction had a second-order dependence on the catalyst concentration, which implicated two dimeric forms of the copper(II) complex 2 in the rate-limiting step. Furthermore, DFT calculations help to generate a plausible structure of the stereodetermining transition step of the condensation.
Добавил в систему: Ларионов Владимир Анатольевич

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Henry Reaction Revisited. Crucial Role of Water in an Asymmetric Henry Reaction Catalyzed by Chiral NNO Type Copper(II) Complexesстатья

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