Mechanistische Einblicke in die Bindung und Aktivierung von N<sub>2</sub>O an Übergangsmetallzentren

Tolman, William B.

doi:10.1002/ange.200905364

Cited by 35 publications

(5 citation statements)

References 99 publications

(122 reference statements)

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“…Next, we examined the substrate scope. Aryl Grignard reagents containing different groups in the para position (CH 3 , F, OMe) or a sterically congesting methyl group in the ortho position could be coupled cleanly with [Fe(acac) 3 ] (0.1 mol %; Table 2, entries [1][2][3][4] or CoCl 2 (Table S4). For reactions with CoCl 2 , high turnover numbers of more than 10 3 could be achieved as well.…”

Section: Methodsmentioning

confidence: 99%

“…Further optimization was achieved by lowering the reaction temperature to 0 8C and using a 1:2 ratio of the starting materials (Table S3). Under these conditions, it was possible to obtain the cross-coupling products of phenylmagnesium chloride and different primary (n-butyl, n-decyl, phenethyl) and secondary alkyl Grignard reagents (cyclohexyl) in yields of 59-83 % ( Table 4, entries [1][2][3][4]. In line with the low reactivity of tert-butylmagnesium bromide in the homocoupling reactions, the cross-coupling with phenylmagnesium chloride was not very efficient ( Table 4, entry 5), whereas very good selectivities were obtained for oxidative alkenyl-alkyl cross-coupling reactions ( Table 4, entries [6][7][8].…”

Section: Methodsmentioning

confidence: 99%

“…

Nitrous oxide ("laughing gas", N 2 O) is a potent oxidation agent, from a thermodynamic point of view. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. An obstacle in using N 2 O in oxidation reactions is the inert nature of the gas.

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confidence: 99%

“…[1] Moreover, it is an environmentally benign oxidant, because the side product is dinitrogen. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. 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.…”

mentioning

confidence: 99%

“…[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.…”

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confidence: 99%

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Oxidative Coupling Reactions of Grignard Reagents with Nitrous Oxide

2013

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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...

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Section: Methodsmentioning

confidence: 99%