Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity ...(Inorg. Chem. 2022, 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π‐dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso‐substituent and report a iron(III) π‐dication bearing the meso‐tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, 2H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso‐substituent as a factor in catalyst design.
A key intermediate in bioinspired umpolung of nucleophiles is an iron(III) π‐dication. We identify that the meso‐substituent of the porphyrin controls its accessibility and report the detailed study of an iron(III) π‐dication with the meso‐tetraphenylporphyrin ligand. We investigate the dynamics of the system and extensively characterize the species, providing crucial information for future catalyst design. Finally, we correlate the meso‐substituent nature to catalytic chlorination reactivity.
How reduced are nucleophilic gold complexes? Leach, Isaac F; Sorbelli, Diego; Belpassi, Leonardo ...
Dalton transactions : an international journal of inorganic chemistry,
12/2022, Letnik:
52, Številka:
1
Journal Article
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Odprti dostop
Nucleophilic formal gold(-
i
) and gold(
i
) complexes are investigated
via
Intrinsic Bond Orbital analysis and Energy Decomposition Analysis, based on density functional theory calculations. The ...results indicate gold(0) centres engaging in electron-sharing bonding with Al- and B- based ligands. Multiconfigurational (CASSCF) calculations corroborate the findings, highlighting the gap between the electonic structures and the
oxidation state
formalism.
Nucleophilic formal gold(-
i
) and gold(
i
) complexes are investigated
via
Intrinsic Bond Orbital analysis and Energy Decomposition Analysis, based on density functional theory calculations.
We introduce here the spin-resolved version of the charge displacement function, which is applied to two competing pathways of proton-coupled electron transfer in oxidation catalysis (hydrogen-atom ...transfer, concerted proton-coupled electron transfer). The difference in charge displacement between the two mechanisms is directly observable and can be translated to electron flow using this new analysis tool.
The spin-resolved version of the charge displacement function is introduced as an intuitive tool for differentiating between hydrogen-atom transfer and concerted proton-coupled electron transfer.
A recent report on the crystal structure of the pentagonal‐pyramidal hexamethylbenzene dication C6(CH3)62+ by Malischewski and Seppelt Angew. Chem. Int. Ed. 2017, 56, 368 confirmed the structural ...proposal made in the first report of this compound in 1973 by Hogeveen and Kwant Tetrahedron Lett. 1973, 14, 1665. The widespread attention that this compound quickly gained led us to reinvestigate its electronic structure. On the basis of intrinsic bond orbital analysis, effective oxidation state analysis, ring current analysis, and comparison with well‐established coordination complexes, it is demonstrated that the central carbon atom behaves like a transition metal. The central (apical) carbon atom, although best described as a highly Lewis‐acidic carbon atom coordinated with an anionic cyclopentadienyl ligand, is also capable of acting as an electron‐pair donor to a formal CH3+ group. The different roles of coordination chemistry are discussed.
Carbon coordination chemistry: The electronic structure of the pentagonal‐pyramidal hexamethylbenzene dication C6(CH3)62+ is investigated through intrinsic bond orbital analysis, effective oxidation state analysis, ring current analysis, and comparison with well‐established coordination complexes. The central carbon atom behaves like a transition metal, and incorporates both possible modes of coordination chemistry at carbon, that is, serving as an electron‐pair donor and as an electron‐pair acceptor, all within a purely hydrocarbon framework.
We report the preparation and characterization of the dinuclear AuII hydroxide complex AuII2(L)2(OH)2 (L=N,N′‐bis (2,6‐dimethyl) phenylformamidinate) and study its reactivity towards weak X−H bonds. ...Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton‐coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au−Au σ‐bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)−H bond cleavage. We thus describe the oxidation event as a valence tautomerism‐induced PCET where the basicity of one reduced Au−OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical‐type reactivity by a closed shell AuII complex.
Proton‐Coupled electron transfer (PCET)‐type reactivity of the dinuclear AuII hydroxide complex AuII2(L)2(OH)2 (L=N,N′‐bis (2,6‐dimethyl) phenylformamidinate) towards weak X−H bonds is reported. For C(sp3)−H oxidation Au−Au σ‐bond polarization leads to an adjustment of oxidation levels for both Au centers prior to the PCET event. The oxidation event for C(sp3)−H bonds is therefore described as a valence tautomerism induced PCET, where a basic reduced Au−OH unit serves as proton acceptor and the second more oxidized Au center as an electron acceptor.
We herein report a computational study of the bonding in gold(I) vinylidene complexes and compare them to their carbene and CO analogues. The relevance of these intermediates is analysed for the ...intramolecular cyclisation leading to vinyl sulfonates.
Tight ion pair gold vinylidene complexes are studied as intermediates in the formation of vinyl sulfonates using computational methods (see scheme). The role of π‐backbonding in gold vinylidene complexes, such as the aforementioned tight ion pair, is analysed by using the intrinsic bond orbital method.
An H/D kinetic isotope effect (KIE) of 80 is found at −20 °C for the oxidation of 9,10-dihydroanthracene by FeIV(O)(TMCS)+, a complex supported by the tetramethylcyclam (TMC) macrocycle with a ...tethered thiolate. This KIE value approaches that previously predicted by DFT calculations. Other FeIV(O)(TMC)(anion) complexes exhibit values of 20, suggesting that the thiolate ligand of FeIV(O)(TMCS)+ plays a unique role in facilitating tunneling. Calculations show that tunneling is most enhanced (a) when the bond asymmetry between C–H bond breaking and O–H bond formation in the transition state is minimized, and (b) when the electrostatic interactions in the O---H---C moiety are maximal. These two factorswhich peak for the best electron donor, the thiolate ligandafford a slim and narrow barrier through which the H-atom can tunnel most effectively.
The preparation of 3,3-disubstituted oxindoles by a formal C−H, Ar−H coupling of anilides is described. Highly efficient conditions have been identified using catalytic (5 mol %) Cu(OAc)2·H2O with ...atmospheric oxygen as the reoxidant; no additional base is required, and the reaction can be run in toluene or mesitylene. Optimization studies are reported together with a scope and limitation investigation based on variation of the anilide precursors. The application of this methodology to prepare a key intermediate for the total synthesis of the anticancer, analgesic oxindole alkaloid Horsfiline is also described.
Au is known to be fairly redox inactive (in catalysis) and bind oxygen adducts only quite weakly. It is thus rather surprising that stable Au−OH complexes can be synthesized and used as oxidants for ...both one‐ and two‐electron oxidations. A charged AuIII−OH complex has been shown to cleave C−H and O−H bonds homolytically, resulting in a one‐electron reduction of the metal center. Contrasting this, a neutral AuIII−OH complex performs oxygen atom transfer to phosphines, resulting in a two‐electron reduction of the hydroxide proton to form a AuIII−H rather than causing a change in oxidation state of the metal. We explore the details of these two examples and draw comparisons to the more conventional reactivity exhibited by AuI−OH. Although the current scope of known Au−OH oxidation chemistry is still in its infancy, the current literature exemplifies the unique properties of Au chemistry and shows promise for future findings in the field.
Au is known to be rather redox‐inactive in catalysis with molecular catalysts and only binds oxygen weakly. Nevertheless, examples of Au−OH complexes in both the formal +I and +III oxidation states have recently been reported. Surprisingly, formal AuIII−OH complexes have shown to be promising oxidants for oxygen atom transfer and proton‐coupled electron transfer reactions. In this concept article the authors describe the known subtilities of these reactions and outline future possibilities for the field.
Recent desires to develop environmentally benign procedures for electrophilic chlorinations have encouraged researchers to take inspiration from nature. In particular, the enzyme chloroperoxidase ...(CPO), which is capable of electrophilic chlorinations through the umpolung of chloride by oxidation with hydrogen peroxide (H2O2), has received lots of attention. CPO itself is unsuitable for industrial use because of its tendency to decompose in the presence of excess H2O2. Biomimetic complexes (CPO active-site mimics) were then developed and have been shown to successfully catalyze electrophilic chlorinations but are too synthetically demanding to be economically viable. Reported efforts at generating the putative active chlorinating agent of CPO (an iron hypochlorite species) via the umpolung of chloride and using simple meso-substituted iron porphyrins were unsuccessful. Instead, a meso-chloroisoporphyrin intermediate was formed, which was shown to be equally capable of performing electrophilic chlorinations. The current developments toward a potential method involving this novel intermediate for environmentally benign electrophilic chlorinations are discussed. Although this novel pathway no longer follows the mechanism of CPO, it was developed from efforts to replicate its function, showing the power that drawing inspiration from nature can have.
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