The gas-phase reactions of metal porphyrins with diazoacetate esters

Aldajaei, Jamal T.; Gronert, Scott

doi:10.1016/j.ijms.2011.12.012

Cited by 11 publications

(10 citation statements)

References 41 publications

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“…Figure both the quartet (oxidized) and triplet (reduced) species exhibit ferromagnetic coupling, with a singly occupied d yz , and the oxidized quartet state also has one electron removed from the a 2u /S orbital, compared to the reduced triplet state. 107 Experimental 9,10 and computational 107 studies suggest the oxidized carbene complex may exist in a bridged form (carbon bridging iron and a porphyrin meso nitrogen). These findings agree with previous work claiming there is spin density on the carbene carbon in terminal oxidized iron porphyrin carbenes.…”

Section: D Alternative Electronic Structuresmentioning

confidence: 99%

Computation Sheds Insight into Iron Porphyrin Carbenes’ Electronic Structure, Formation, and N–H Insertion Reactivity

et al. 2016

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Iron porphyrin carbenes constitute a new frontier of species with considerable synthetic potential. Exquisitely engineered myoglobin and cytochrome P450 enzymes can generate these complexes and facilitate the transformations they mediate. The current work harnesses density functional theoretical methods to provide insight into the electronic structure, formation, and N-H insertion reactivity of an iron porphyrin carbene, [Fe(Por)(SCH3)(CHCO2Et)](-), a model of a complex believed to exist in an experimentally studied artificial metalloenzyme. The ground state electronic structure of the terminal form of this complex is an open-shell singlet, with two antiferromagnetically coupled electrons residing on the iron center and carbene ligand. As we shall reveal, the bonding properties of [Fe(Por)(SCH3)(CHCO2Et)](-) are remarkably analogous to those of ferric heme superoxide complexes. The carbene forms by dinitrogen loss from ethyl diazoacetate. This reaction occurs preferentially through an open-shell singlet transition state: iron donates electron density to weaken the C-N bond undergoing cleavage. Once formed, the iron porphyrin carbene accomplishes N-H insertion via nucleophilic attack. The resulting ylide then rearranges, using an internal carbonyl base, to form an enol that leads to the product. The findings rationalize experimentally observed reactivity trends reported in artificial metalloenzymes employing iron porphyrin carbenes. Furthermore, these results suggest a possible expansion of enzymatic substrate scope, to include aliphatic amines. Thus, this work, among the first several computational explorations of these species, contributes insights and predictions to the surging interest in iron porphyrin carbenes and their synthetic potential.

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Section: D Alternative Electronic Structuresmentioning

confidence: 99%

Computation Sheds Insight into Iron Porphyrin Carbenes’ Electronic Structure, Formation, and N–H Insertion Reactivity

et al. 2016

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“…This is consistentw ith the formationof ac opper(I) carbenes pecies, but the product does not have typical metal-carbene behavior;i tg ives no reactions othert han adduct formationw ith electron-rich (ethyl vinyl ether) and electron-poor( trichloroethene) olefins. In analogy to our work with metalp orphyrins, [13] it is likely that the carbene inserted into aC u ÀNb ond in the complex resulting in ac opper(I) ylide complex on the millisecondt imescale of our experiments.I nD FT enthalpy calculations at the M06/6-311 + G** level (R = Me, R' = H, R'' = H), the barrier to insertion is just 15 kcal mol À1 above the carbene complex (2 kcal mol À1 below the energy of the separatedr eactants) and is favorable by almost 18 kcal mol À1 relative to the copper(I) carbene (Table 1, Figure1a). Therefore, it is not surprising that spontaneous metal-ligand insertion occurs, leading to the destruction of the carbene center.…”

Section: Resultsmentioning

confidence: 75%

“…The rigid phenanthroline ligand is capable of suppressing the insertion process,b ut the copper did not providee nough stabilization to prevent as pontaneous Wolffr earrangement. As we have now observed in cobalt, iron,g old, [14] and copper gas-phase systems, [13] the back-bonding in metal carbenes may not effectively inhibitc haracteristic unimolecular carbene chemistry.…”

Section: Resultsmentioning

confidence: 99%

“…Gas-phase studies have provent ob ee xtremely useful in identifying intermediatesi no rganometallic reaction processes and probing their characteristics. [7][8][9][10][11][12] In the past, we have examined the gas-phase formationof metal carbenes involving cobalt(III) and iron(III)porphyrins [13] as well as triphenylphosphine-ligated gold(I)c omplexes [14] and concluded that the carbene intermediatesa re unstable and spontaneously undergo insertionsi nto am etal-ligand bond to produceametal ylide producto ru ndergo other rearrangements. There is literature precedencef or the insertions and it is also supported by computational modelling.…”

Section: Introductionmentioning

confidence: 99%

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Are Copper(I) Carbenes Capable Intermediates for Cyclopropanations? The Case for Ylide Intermediates

Aldajaei

Keeffe

Swift

et al. 2015

Chemistry A European J

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A novel approach is used to synthesize a stable, ligated copper(I) carbene in the gas phase that is capable of typical metal carbenoid chemistry. However, it is shown that copper(I) carbenes generally undergo rapid unimolecular rearrangements including insertions into copper-ligand bonds and Wolff rearrangements. The results indicate that most copper(I) carbenes are inherently unstable and would not be viable intermediates in condensed-phase applications; an alternative intermediate that is less prone to rearrangements is required. Computational data suggest that ylides formed by the complexation of the carbene with solvent or other weak nucleophiles are viable intermediates in the reactions of copper(I) carbenes.

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“…11 Previously, we have reported the gas-phase synthesis of iron and cobalt carbene complexes by the reaction of a ligated metal with diazoacetate esters. 12,13 In those cases, the metal carbenes were prone to rearrangement processes, particularly metal−ligand insertions that converted the carbene to an ylide. Here we apply a variety of approaches to prepare and explore the reactivity of gold(I) carbene complexes in the gas phase.…”

Section: ■ Introductionmentioning

confidence: 99%

Formation and Reactivity of Gold Carbene Complexes in the Gas Phase

Swift

Gronert

2014

Organometallics

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A series of ligated gold(I) carbenes (where the ligand is Ph 3 P, Me 2 S, or an N-heterocyclic carbene, NHC) were formed in the gas phase by a variety of methods. Gold(I) benzylidenes could be formed using Chen's method of dissociating an appropriate phosphorus ylide precursor. The resulting carbene undergoes an addition reaction with olefins to give an adduct. The adduct undergoes a second gas-phase reaction with an olefin, where presumably a cyclopropanation product is displaced by the second olefin molecule. Both steps in the process were analyzed with linear free energy relationships (i.e., Hammett plots). Under collision-induced dissociation conditions, the adduct undergoes competing processes: (1) dissociation of the cyclopropanation product to give ligated gold(I) species and (2) metathesis to give a more stable gold(I) carbene. Attempts to form less stable gold(I) carbenes in the gas phase by Chen's approach or by reactions of diazo species with the ligated gold(I) cations were not successfulprocesses other than carbene formation are preferred or the desired carbene, after formation, rearranges rapidly to a more stable species. In accord with other recent work, the data suggest that coordination to a ligated gold(I) cation in the gas phase may not offer sufficient stabilization to carbenes to prevent competition from rearrangement processes.

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The gas-phase reactions of metal porphyrins with diazoacetate esters

Cited by 11 publications

References 41 publications

Computation Sheds Insight into Iron Porphyrin Carbenes’ Electronic Structure, Formation, and N–H Insertion Reactivity

Computation Sheds Insight into Iron Porphyrin Carbenes’ Electronic Structure, Formation, and N–H Insertion Reactivity

Are Copper(I) Carbenes Capable Intermediates for Cyclopropanations? The Case for Ylide Intermediates

Formation and Reactivity of Gold Carbene Complexes in the Gas Phase

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