Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Bhutto, Samuel M.; Hooper, Reagan; Mercado, Brandon Q.; Holland, Patrick L.

doi:10.26434/chemrxiv-2022-mk6fs

Cited by 4 publications

(22 citation statements)

References 77 publications

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“…These observations led to an initial indication that dimer dissociation may have occurred upon reduction to give a three-coordinate iron(I) center that can bind N2, by analogy to literature diketiminate-supported iron(I) aryl and alkyl complexes. [42][43]46 Scheme 3. Reduction of 1 to form the iron(I) complex 2 and reversible N2 binding at 2.…”

Section: Resultsmentioning

confidence: 99%

“…[39][40] Here, we use the ligand with methyl groups on the backbone 44 for a more direct comparison to aforementioned N2 functionalization system. [42][43] To start, we targeted the bulky tert-butylacetylide ligand with the goal of isolating a three-coordinate species and limiting the possibility of complex dimerization observed in previously reported alkynyl complexes (see Figure 1, right). The alkynyl ligands in 1 bridge the two iron centers in an η 1 :η 1 fashion unlike the previously reported iron(II) alkynyl dimers which bridge in an η 1 :η 2 fashion (see Figure 1, right).…”

Section: Resultsmentioning

confidence: 99%

“…of N2 binding to the reduced iron center of 2, we explored the potential for migratory insertion of the alkynyl ligand upon N2 silylation, based on the precedent from the phenyl analogue. [42][43] Addition of a solution of (OTf)Me2Si(CH2)2SiMe2(OTf) in Et2O to a mixture of 2-N2 and K(18crown-6)(C10H8) in Et2O at -116 °C gave an immediate color change from red to brown (Scheme 4). The 1 H NMR spectrum of the crude mixture after warming to ambient temperature showed the formation of a new Cs symmetric species in 54% spectroscopic yield.…”

Section: Silylation To Give a Formally Iron(iv) Hydrazido Complex Wit...mentioning

confidence: 99%

“…[36][37][38][39][40][41] Additionally, the reactivity of these reported alkynyl complexes is not well-explored. Inspired by recent findings from our group showing that reduced, three-coordinate iron(I) hydrocarbyl complexes can bind and functionalize N2 (Scheme 1), [42][43] we sought to explore similar reactivity with alkynyl complexes. Here, we report our findings on the synthesis and reactivity of monoalkynyl iron complexes supported by a b-diketiminate ligand, including the binding of N2 at an iron(I) alkynyl complex and isolation of a formally iron(IV) alkynyl hydrazido(2-) species.…”

Section: Introductionmentioning

confidence: 99%

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Dinitrogen Binding and Functionalization in Low-Coordinate Alkynyliron Complexes

Bhutto

Mercado

Holland

2022

Preprint

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Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and unusual bonding for reactivity. Here, we explore the capacity of iron(I) alkynyl complexes to bind N2, and isolate an N2 complex including its X-ray crystal structure. Silylation of this complex gives a formally iron(IV) complex with a disilylhydrazido(2–) ligand, but NBO analysis indicates that an iron(II) formulation is more accurate. The structure of this compound is similar to an earlier reported phenyl complex in which phenyl migration forms a new N–C bond, but the alkynyl group does not migrate. DFT calculations are used to test the possible reasons, and the most likely is the stronger Fe–C bond energy in the alkynyl complex.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Silylation To Give a Formally Iron(iv) Hydrazido Complex Wit...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dinitrogen Binding and Functionalization in Low-Coordinate Alkynyliron Complexes

Bhutto

Mercado

Holland

2022

Preprint

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“…Geometries were optimized using B3LYP/def2-TZVP in both the triplet and quintet states to probe possible spin-crossover behavior as observed in the aryl migration mechanism. 38…”

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confidence: 99%

Iron(IV) Alkyl Hydrazido Complexes: Electronic Structure, Fe–C Bond Homolysis, and N–C Bond Forming Migration Reactions

Bhutto

McWilliams

Hooper

et al. 2022

Preprint

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High-valent iron-alkyl complexes are rare, as they are typically prone to Fe–C bond homolysis. We show here an unusual way to access formally iron(IV) alkyl complexes through double silylation of iron(I) alkyl dinitrogen complexes to form an NNSi2 group. When the alkyl group is trimethylsilylmethyl, the formally iron(IV) compound is stable at room temperature. Spectroscopically validated computations show that the disilylhydrazido(2–) ligand stabilizes the formal iron(IV) oxidation state through a strongly covalent Fe–N -interaction, in which one -bond fits an "inverted field" description. This means that the two bonding electrons are localized on the metal and not the ligand, and an iron(II) resonance structure is a significant contributor as with the phenyl analogue. However, in contrast to the phenyl analogue which has an S = 1 ground state, the ground state of the alkyl complex is S = 2, and this places one electron in the * orbital and weakens the Fe–N bonding, leading to longer Fe–N bonds. The reactivity of these hydrazido(2–) complexes has an interesting dependence on the specific alkyl group. When the alkyl group is methyl, the formally iron(IV) species undergoes migration of the carbon-based ligand to the NNSi2 group to form a new N–C bond, followed by an intriguing isomerization of the hydrazido ligand. This reactivity is not observed with the bulkier trimethylsilylmethyl complex. When the alkyl group is benzyl, yet another reactivity pathway is evident: the Fe–C bond homolyzes to give a three-coordinate iron(III) complex with a hydrazido(2–) ligand. DFT calculations are used to explain the differences between the behavior with the different alkyl groups. Overall, these formally iron(IV) compounds display a diverse set of reaction pathways associated with the specific alkyl groups.

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Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

Landaeta,

Horsley Downie,

Wolf

2024

Chem. Rev.

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This review surveys the synthesis and reactivity of low-oxidation state metalate anions of the d-block elements, with an emphasis on contributions reported between 2006 and 2022. Although the field has a long and rich history, the chemistry of transition metalate anions has been greatly enhanced in the last 15 years by the application of advanced concepts in complex synthesis and ligand design. In recent years, the potential of highly reactive metalate complexes in the fields of small molecule activation and homogeneous catalysis has become increasingly evident. Consequently, exciting applications in small molecule activation have been developed, including in catalytic transformations. This article intends to guide the reader through the fascinating world of low-valent transition metalates. The first part of the review describes the synthesis and reactivity of d-block metalates stabilized by an assortment of ligand frameworks, including carbonyls, isocyanides, alkenes and polyarenes, phosphines and phosphorus heterocycles, amides, and redox-active nitrogen-based ligands. Thereby, the reader will be familiarized with the impact of different ligand types on the physical and chemical properties of metalates. In addition, ion-pairing interactions and metal−metal bonding may have a dramatic influence on metalate structures and reactivities. The complex ramifications of these effects are examined in a separate section. The second part of the review is devoted to the reactivity of the metalates toward small inorganic molecules such as H 2 , N 2 , CO, CO 2 , P 4 and related species. It is shown that the use of highly electron-rich and reactive metalates in small molecule activation translates into impressive catalytic properties in the hydrogenation of organic molecules and the reduction of N 2 , CO, and CO 2 . The results discussed in this review illustrate that the potential of transition metalate anions is increasingly being tapped for challenging catalytic processes with relevance to organic synthesis and energy conversion. Therefore, it is hoped that this review will serve as a useful resource to inspire further developments in this dynamic research field.

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Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Cited by 4 publications

References 77 publications

Dinitrogen Binding and Functionalization in Low-Coordinate Alkynyliron Complexes

Dinitrogen Binding and Functionalization in Low-Coordinate Alkynyliron Complexes

Iron(IV) Alkyl Hydrazido Complexes: Electronic Structure, Fe–C Bond Homolysis, and N–C Bond Forming Migration Reactions

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

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