Germanium(<scp>iii</scp>) corrole complex: reactivity and mechanistic studies of visible-light promoted N–H bond activations

Fang, Hanming; Ling, Zhen; Lang, Ke; Brothers, Penelope J.; Bruin, Bas de; Fu, Xuefeng

doi:10.1039/c3sc52326h

Cited by 46 publications

(53 citation statements)

References 40 publications

(17 reference statements)

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“…Coordination-induced bond weakening, whereby interaction of a ligand results in a considerable lowering of the X-H BDFE, has recently been identified or implicated in rare instances (18)(19)(20)(21)(22)(23) and has been applied by Knowles's group (24) and others (25)(26)(27) in reactions of organic molecules involving N-H and O-H bonds, respectively. Cuerva's group (26,27) and ours (28) have demonstrated the effectiveness of bis(cyclopentadienyl) titanium(III) complexes in weakening the O-H bonds of water and the N-H bonds of ammonia.…”

mentioning

confidence: 99%

Coordination-induced weakening of ammonia, water, and hydrazine X–H bonds in a molybdenum complex

Bezdek

Guo

Chirik

2016

Science

184

192

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Although scores of transition metal complexes incorporating ammonia or water ligands have been characterized over the past century, little is known about how coordination influences the strength of the nitrogen-hydrogen and oxygen-hydrogen bonds. Here we report the synthesis of a molybdenum ammonia complex supported by terpyridine and phosphine ligands that lowers the nitrogen-hydrogen bond dissociation free energy from 99.5 (gas phase) to an experimentally measured value of 45.8 kilocalories per mole (agreeing closely with a value of 45.1 kilocalories per mole calculated by density functional theory). This bond weakening enables spontaneous dihydrogen evolution upon gentle heating, as well as the hydrogenation of styrene. Analogous molybdenum complexes promote dihydrogen evolution from coordinated water and hydrazine. Electrochemical and theoretical studies elucidate the contributions of metal redox potential and ammonia acidity to this effect.A mmonia and water are ubiquitous small molecules with strong bonds between hydrogen and the central atom (1). For over a century, transition metal-ammine (NH 3 ) and -aquo (H 2 O) compounds have defined bonding paradigms in chemistry (2), found application in cancer therapy (3), and promoted important fundamental chemical reactions such as electron transfer that rely on the inertness of the N-H or O-H bonds in the supporting ligands ( Fig. 1) (4).Common strategies for activation of ammonia and water include oxidative addition to a transition metal center (5-7), deprotonation by transition metal hydrides (8), reaction with bimetallic compounds (9), cooperative chemistry between a transition metal and a supporting ligand (10-12), and element-hydrogen (X-H) bond cleavage through reaction with main group compounds (13-16). Using most of these strategies, activation of the strong X-H bond is not typically coupled to H-H bond formation. One exception is the observation of H 2 elimination following oxidative addition of ammonia to a tantalum(III) complex (17).An alternative and less commonly explored strategy is homolytic cleavage of the X-H bond. Because of the high gas-phase bond dissociation free energies (BDFEs; 99.5 and 111.0 kcal/mol for NH 3 and H 2 O, respectively) (1), interaction with a transition metal or other appropriate reagent is necessary to induce bond weakening. As shown in Fig. 1, most classical transition metal compounds with ammine (aquo) ligands have N-H (O-H) bond strengths that are only slightly perturbed from the gas-phase value. Because experimental data are lacking, we used density functional theory (DFT) to compute N-H BDFEs.Coordination-induced bond weakening, whereby interaction of a ligand results in a considerable lowering of the X-H BDFE, has recently been identified or implicated in rare instances (18-23) and has been applied by Knowles's group (24) and others (25-27) in reactions of organic molecules involving N-H and O-H bonds, respectively. Cuerva's group (26, 27) and ours (28) However, this strategy has not yet been shown to be capable of ...

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mentioning

confidence: 99%

Coordination-induced weakening of ammonia, water, and hydrazine X–H bonds in a molybdenum complex

Bezdek

Guo

Chirik

2016

Science

184

192

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“…Exploiting the concept of bond-weakening upon coordination to redox-active metals [223][224][225][226][227][228][229][230][231][232], our lab demonstrated that a redox-active titanium catalyst Cp* 2 Ti III Cl and a weak hydrogen atom acceptor TEMPO enable intramolecular additions of amides to Michael acceptors ( Figure 32) [223]. The substrate scope allows for N-H activation of amides, carbamates, thiolcarbamates, and ureas bearing phenyl or electron-rich arenes in uniformly high yield.…”

Section: Amidesmentioning

confidence: 99%

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Miller

Tarantino

Knowles

2016

Topics in Current Chemistry Collections

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Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter we aim to highlight the origins, development and evolution of PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups.

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“…40 (Figure 1b), distinct from most of the previously reported penta-coordinated germanium corrole complexes that exhibited a domed structure with the germanium atom significantly displaced from the N 4 plane. 36,43,44 This is ascribed to the more symmetric hexacoordination geometry and smaller radius of the cationic However, silicon and the heavier group 14 element cations are rarely observed to undergo this type of reaction. 6,37,45,46 Interestingly, the oily [(TPFC)Ge] + cation was observed to react with benzene quantitatively to form a new compound as brownish-black crystals at room temperature in a few days.…”

Section: ■ Results and Discussionmentioning

confidence: 92%

“…The Xray crystal structure of (TPFC)Ge−C 6 H 5 (Figure 2b) showed a domed geometry similar to that of other penta-coordinated germanium corroles. 36 54 whereas the Si−C arene (distances ranging from 2.089 to2.231 Å) bond orders in previously reported silylium-arene adducts were calculated to be only from 0.20 to 0.35 (the D(1) value of 1.817 Å used here was as reported for the Si−C Mes bond length in [Mes 3 Si] + , 5 Mes = 2,4,6-trimethylphenyl). 6,37,46,55,56 This result also indicates that [(TPFC)Ge(η 1 -C 6 H 6 )] + is best described as a σ-type germylium-benzene adduct rather than a π-type complex.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…4,27 This work presents a rare example of group 14 cations with vacant sphybridized orbitals illustrating its distinctive reactivity. Similarly, our previous studies 36,62 showed that the unpaired electron in the [(TPFC)Ge] 0 radical was mainly localized in a sphybridized orbital on the germanium center rather than in a pure p orbital as is typical of the traditional heavier group 14 radicals. 63,64 ■ CONCLUSIONS A square planar, tetra-coordinated Ge(IV) cation, [(TPFC)-Ge] + , was synthesized through the reaction of (TPFC)Ge−H with [Ph 3 C] + [B(C 6 F 5 ) 4 ] − .…”

Section: Journal Of the American Chemical Societymentioning

confidence: 85%

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Synthesis, Electronic Structure, and Reactivity Studies of a 4-Coordinate Square Planar Germanium(IV) Cation

et al. 2016

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A tetra-coordinate, square planar germanium(IV) cation [(TPFC)Ge](+) (TPFC = tris(pentafluorophenyl)corrole) was synthesized quantitatively by the reaction of (TPFC)Ge-H with [Ph3C](+)[B(C6F5)4](¯). The highly reactive [(TPFC)Ge](+) cation reacted with benzene to form phenyl complex (TPFC)Ge-C6H5 through an electrophilic pathway. The key intermediate, a σ-type germylium-benzene adduct, [(TPFC)Ge(η(1)-C6H6)](+), was isolated and characterized by single-crystal X-ray diffraction. Deprotonation of [(TPFC)Ge(η(1)-C6H6)](+) cation led to the formation of (TPFC)Ge-C6H5. [(TPFC)Ge](+) also reacted with ethylene and cyclopropane in benzene at room temperature to form (TPFC)Ge-CH2CH2C6H5 and (TPFC)Ge-CH2CH2CH2C6H5, respectively. The observed electrophilic reactivity is ascribed to the highly exposed cationic germanium center with novel frontier orbitals comprising two vacant sp-hybridized orbitals that are not conjugated to π-system. The three electron-withdrawing pentafluorophenyl groups on the corrole ligand also enhance the electrophilicity of the cationic germanium corrole.

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Germanium(iii) corrole complex: reactivity and mechanistic studies of visible-light promoted N–H bond activations

Abstract: Germanium(III) corrole complex: reactivity and mechanistic studies of visible-light promoted N-H bond activationsFang, H.; Ling, Z.; Lang, K.; Brothers, P.J.; de Bruin, B.; Fu, X.

Cited by 46 publications

References 40 publications

Coordination-induced weakening of ammonia, water, and hydrazine X–H bonds in a molybdenum complex

Coordination-induced weakening of ammonia, water, and hydrazine X–H bonds in a molybdenum complex

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Synthesis, Electronic Structure, and Reactivity Studies of a 4-Coordinate Square Planar Germanium(IV) Cation

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