N2Cleavage on d4/d4Molybdenum Centers and Its Further Conversion into Iminophosphorane under Mild Conditions

Zhang, Guoqiang; Liu, Tanggao; Song, Jinyi; Quan, Yingyu; Jin, Li; Si, Mengyue; Liao, Qian

doi:10.1021/jacs.1c11134

Cited by 18 publications

(16 citation statements)

References 72 publications

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“…34,97 A similar result is found for the R = tBu adduct (δ 37.2 ppm), and 50% 15 N labeling of the nitride results in an isotopic distribution in the positive-mode ESI-MS (PPh 3 P 14/15 NH 2 + = m/z 279) that is consistent with the incorporation of the nitride into the iminophosphorane product (Figure S41). In addition, 31 P{H} NMR of the 15 N-labeled iminophosphorane shows an unexpectedly small N−P coupling constant ( 1 J N−P = 2.9 Hz, Figure S41); 35,39 however, this compares to a recent report, 97 and relatively small 1 J N−P coupling constants have been observed in other related compounds. 98 We speculate that the initially formed Cr IV phosphoraneiminato adduct is unstable 99,100 and is easily reduced either by impurities or by excess PPh 3 to [Cr III Sal R ] + (R = tBu, CF 3 ) and the resulting iminophosphorane anion is protonated by trace water.…”

Section: ■ Introductionmentioning

confidence: 93%

Chromium Nitride Umpolung Tuned by the Locus of Oxidation

et al. 2022

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Oxidation of a series of CrV nitride salen complexes (Cr V NSal R ) with different para-phenolate substituents (R = CF3, tBu, NMe2) was investigated to determine how the locus of oxidation (either metal or ligand) dictates reactivity at the nitride. Para-phenolate substituents were chosen to provide maximum variation in the electron-donating ability of the tetradentate ligand at a site remote from the metal coordination sphere. We show that one-electron oxidation affords CrVI nitrides ([Cr VI NSal R ] + ; R = CF3, tBu) and a localized CrV nitride phenoxyl radical for the more electron-donating NMe2 substituent ([Cr V NSal NMe2 ] •+ ). The facile nitride homocoupling observed for the MnVI analogues was significantly attenuated for the CrVI complexes due to a smaller increase in nitride character in the MN π* orbitals for Cr relative to Mn. Upon oxidation, both the calculated nitride natural population analysis (NPA) charge and energy of molecular orbitals associated with the {CrN} unit change to a lesser extent for the CrV ligand radical derivative ([Cr V NSal NMe2 ] •+ ) in comparison to the CrVI derivatives ([Cr VI NSal R ] + ; R = CF3, tBu). As a result, [Cr V NSal NMe2 ] •+ reacts with B(C6F5)3, thus exhibiting similar nucleophilic reactivity to the neutral CrV nitride derivatives. In contrast, the CrVI derivatives ([Cr VI NSal R ] + ; R = CF3, tBu) act as electrophiles, displaying facile reactivity with PPh3 and no reaction with B(C6F5)3. Thus, while oxidation to the ligand radical does not change the reactivity profile, metal-based oxidation to CrVI results in umpolung, a switch from nucleophilic to electrophilic reactivity at the terminal nitride.

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Section: ■ Introductionmentioning

confidence: 93%

Chromium Nitride Umpolung Tuned by the Locus of Oxidation

et al. 2022

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“…The reaction was first discovered by Laplaza and Cummins in 1995 for [ 5 -Mo] 2 (μ-N 2 ) (Scheme B) upon treating the isolable three-coordinate fragment Mo(N t BuAr) 3 with N 2 . The reaction is of immense interest because it suggests distinct pathways in catalytic N 2 reduction and functionalization. ,,− In this section we show how Lewis structures can greatly simplify the discussion of this reaction, and even bring new insights to understanding it. Instead of continuing our presentation with the octahedral complex [ 1- Re] 2 (μ-N 2 ) which undergoes NN cleavage photolytically but not thermally, we chose to study Cummins’ original complex [ 5 -Mo] 2 (μ-N 2 ).…”

Section: Lewis Structure and The Splitting Of μ-N2 Complexesmentioning

confidence: 92%

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes

et al. 2023

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The activation of dinitrogen by coordination to transition metal ions is a widely used and promising approach to the utilization of Earth’s most abundant nitrogen source for chemical synthesis. End-on bridging N2 complexes (μ-η1:η1-N2) are key species in nitrogen fixation chemistry, but a lack of consensus on the seemingly simple task of assigning a Lewis structure for such complexes has prevented application of valence electron counting and other tools for understanding and predicting reactivity trends. The Lewis structures of bridging N2 complexes have traditionally been determined by comparing the experimentally observed NN distance to the bond lengths of free N2, diazene, and hydrazine. We introduce an alternative approach here and argue that the Lewis structure should be assigned based on the total π-bond order in the MNNM core (number of π-bonds), which derives from the character (bonding or antibonding) and occupancy of the delocalized π-symmetry molecular orbitals (π-MOs) in MNNM. To illustrate this approach, the complexes cis,cis-[(iPr4PONOP)MCl2]2(μ-N2) (M = W, Re, and Os) are examined in detail. Each complex is shown to have a different number of nitrogen–nitrogen and metal–nitrogen π-bonds, indicated as, respectively: WN–NW, ReNNRe, and Os–NN–Os. It follows that each of these Lewis structures represents a distinct class of complexes (diazanyl, diazenyl, and dinitrogen, respectively), in which the μ-N2 ligand has a different electron donor number (total of 8e–, 6e–, or 4e–, respectively). We show how this classification can greatly aid in understanding and predicting the properties and reactivity patterns of μ-N2 complexes.

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“…73 The reaction is of immense interest because it suggests distinct pathways in catalytic N2 reduction and functionalization. 32,69,[74][75][76][77][78][79][80] In this section we show how Lewis structures can greatly simplify the discussion of this reaction, and even bring new insights to understanding it. Instead of continuing our presentation with the octahedral complex [1-Re]2(µ-N2) which undergoes NN cleavage photolytically but not thermally, we chose to study Cummins' original complex [5-Mo]2(µ-N2).…”

Section: Lewis Structure and The Reaction Of [1-m]2(µ-n2mentioning

confidence: 99%

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes

Hasanayn

Holland

Goldman

et al. 2022

Preprint

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The activation of dinitrogen by coordination to transition metal ions is a widely used and promising approach to the utilization of Earth’s most abundant nitrogen source for chemical synthesis. End-on bridging N2 complexes (µ-N2) are key species in nitrogen fixation chemistry, but a lack of consensus on the seemingly simple task of assigning a Lewis structure for such complexes has prevented application of valence electron counting and other tools for understanding and predicting reactivity trends. The Lewis structures have traditionally been determined by comparing the experimentally observed NN distance to the bond lengths of free N2, diazene, and hydrazine. We introduce an alternative approach here, and argue that the Lewis structure should be assigned based on the total π-bond order in the MNNM core (number of π-bonds), which derives from the character (bonding or antibonding) and occupancy of the delocalized π-symmetry molecular orbitals (π-MOs) in MNNM. To illustrate this approach, the end-on bridging N2 complexes cis,cis-[(iPr4PONOP)MCl2]2(µ-N2) (M = W, Re and Os) are examined in detail. Each complex is shown to have a different number of nitrogen–nitrogen and metal–nitrogen π-bonds, indicated as, respectively: WN–NW, Re=N=N=Re and Os–NN–Os. It follows that each of these Lewis structures represents a distinct class of complexes in which the µ-N2 ligand has a different electron donor number (total of 4e-, 6e-, or 8e-). We show how this classification can greatly aid in understanding and predicting the properties and reactivity patterns of µ-N2 complexes.

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N₂Cleavage on d⁴/d⁴Molybdenum Centers and Its Further Conversion into Iminophosphorane under Mild Conditions

Cited by 18 publications

References 72 publications

Chromium Nitride Umpolung Tuned by the Locus of Oxidation

Chromium Nitride Umpolung Tuned by the Locus of Oxidation

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes

Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes

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