Nitrous oxide ("laughing gas", N 2 O) is a potent oxidation agent, from a thermodynamic point of view. [1] Moreover, it is an environmentally benign oxidant, because the side product is dinitrogen. An obstacle in using N 2 O in oxidation reactions is the inert nature of the gas. Heterogeneous catalysts have been used with good success for the activation of N 2 O, but high temperatures and/or pressures are typically required to achieve acceptable reaction rates. [2] Thus far, N 2 O-based oxidation reactions with homogeneous catalysts in solution have met with only limited success. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. Some polyoxometalates [4] and ruthenium complexes [5] were shown to catalyze oxidation reactions with N 2 O, but the reactions require high temperatures (100-200 8C) and often elevated pressures. [6] Furthermore, the reported turnover numbers are modest ( 100). Herein, we describe oxidative carbon-carbon coupling reactions with N 2 O, which can be performed under mild conditions with good selectivity and unprecedented turnover numbers.Oxidative homo-and cross-coupling reactions of Grignard reagents [7,8] in the presence of metal catalysts can be achieved with different oxidants, including 1,2-dihaloethanes [9] and dioxygen. [10] The reactions are believed to involve low-valent organometallic complexes. [7][8][9][10] We hypothesized that these low-valent, nucleophilic complexes might be susceptible to oxidation by N 2 O. As a model reaction, we studied the homocoupling of phenylmagnesium chloride. The reactions were performed in THF at room temperature under an atmosphere of N 2 O using different transition-metal salts as potential catalysts (Li 2 CuCl 4 , Li 2 MnCl 4 , CoCl 2 , FeCl 3 , [Fe(acac) 3 ]). To avoid reactions caused by traces of dioxygen, we have used N 2 O of high purity (99.999 %). Test reactions with metal salt (1 mol %) gave the oxidative coupling product biphenyl after 1 h in yields of 30-95 % (Table 1, entries 1-5). The best results were found for FeCl 3 (94 % yield), [Fe(acac) 3 ] (94 % yield) and CoCl 2 (95 % yield). The latter two complexes were used for further studies.First, we examined the efficiency of the reaction. Lowering the amount of catalyst from 1.0 mol % to 0.1 mol % had no effect on the yield. Further reduction to 0.01 mol % gave a poor yield in the case of [Fe(acac) 3 ], even if the reaction time was prolonged. With CoCl 2 , however, the catalyst loading could be reduced to 0.004 mol % and biphenyl was still obtained in 83 % yield (Table 1, entry 7). Taking into account the small amount of product formed without catalyst (8 % after 18 h), and assuming that one catalytic cycle produces one biphenyl molecule, we can calculate a turnover number of 9.4 10 3 . This value greatly exceeds what has been reported thus far for metal-catalyzed oxidation reactions with N 2 O in homogeneous solution. [4,5] The groups of Lei [10c] and Cahiez [10d] have shown that Fe complexes ar...
1-Aryl-3,3-dialkyltriazenes have received considerable attention in the context of synthetic and medicinal chemistry. In contrast, the chemistry of other unsaturated triazenes is largely unexplored. The synthesis of 1-allenyltriazenes is described. This new class of compounds can be obtained by base-induced isomerization of 1-alkynyltriazenes. The latter are accessible by reaction of alkynyl Grignard reagents with lithium amides and nitrous oxide. 1-Allenyltriazenes were found to be thermally labile, but they can be stored without degradation at lower temperatures. In the presence of ZnCl, 1-allenyltriazenes rearrange into N-aminopyrazoles.
Nitrous oxide ("laughing gas", N 2 O) is a potent oxidation agent, from a thermodynamic point of view. [1] Moreover, it is an environmentally benign oxidant, because the side product is dinitrogen. An obstacle in using N 2 O in oxidation reactions is the inert nature of the gas. Heterogeneous catalysts have been used with good success for the activation of N 2 O, but high temperatures and/or pressures are typically required to achieve acceptable reaction rates. [2] Thus far, N 2 O-based oxidation reactions with homogeneous catalysts in solution have met with only limited success. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. Some polyoxometalates [4] and ruthenium complexes [5] were shown to catalyze oxidation reactions with N 2 O, but the reactions require high temperatures (100-200 8C) and often elevated pressures. [6] Furthermore, the reported turnover numbers are modest ( 100). Herein, we describe oxidative carbon-carbon coupling reactions with N 2 O, which can be performed under mild conditions with good selectivity and unprecedented turnover numbers.Oxidative homo-and cross-coupling reactions of Grignard reagents [7,8] in the presence of metal catalysts can be achieved with different oxidants, including 1,2-dihaloethanes [9] and dioxygen. [10] The reactions are believed to involve low-valent organometallic complexes. [7][8][9][10] We hypothesized that these low-valent, nucleophilic complexes might be susceptible to oxidation by N 2 O. As a model reaction, we studied the homocoupling of phenylmagnesium chloride. The reactions were performed in THF at room temperature under an atmosphere of N 2 O using different transition-metal salts as potential catalysts (Li 2 CuCl 4 , Li 2 MnCl 4 , CoCl 2 , FeCl 3 , [Fe(acac) 3 ]). To avoid reactions caused by traces of dioxygen, we have used N 2 O of high purity (99.999 %). Test reactions with metal salt (1 mol %) gave the oxidative coupling product biphenyl after 1 h in yields of 30-95 % (Table 1, entries 1-5). The best results were found for FeCl 3 (94 % yield), [Fe(acac) 3 ] (94 % yield) and CoCl 2 (95 % yield). The latter two complexes were used for further studies.First, we examined the efficiency of the reaction. Lowering the amount of catalyst from 1.0 mol % to 0.1 mol % had no effect on the yield. Further reduction to 0.01 mol % gave a poor yield in the case of [Fe(acac) 3 ], even if the reaction time was prolonged. With CoCl 2 , however, the catalyst loading could be reduced to 0.004 mol % and biphenyl was still obtained in 83 % yield (Table 1, entry 7). Taking into account the small amount of product formed without catalyst (8 % after 18 h), and assuming that one catalytic cycle produces one biphenyl molecule, we can calculate a turnover number of 9.4 10 3 . This value greatly exceeds what has been reported thus far for metal-catalyzed oxidation reactions with N 2 O in homogeneous solution. [4,5] The groups of Lei [10c] and Cahiez [10d] have shown that Fe complexes ar...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.