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Iron(IV) Alkyl Hydrazido Complexes: Electronic Structure, Fe–C Bond Homolysis, and N–C Bond Forming Migration Reactions
No full textHigh-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
Nature-inspired radical pyridoxal-mediated C–C bond formation
No full textPyridoxal-5\u27-phosphate (PLP) and derivatives of this cofactor enable a plethora of reactions in both enzyme-mediated and free-in-solution transformations. With few exceptions in each category, such chemistry has predominantly involved two-electron processes. This sometimes poses a significant challenge for using PLP to build tetrasubstituted carbon centers, especially when the reaction is reversible. The ability to access radical pathways is paramount to broadening the scope of reactions catalyzed by this coenzyme. In this study, we demonstrate the ability to access a radical PLP-based intermediate and engage this radical intermediate in a number of C–C bond forming reactions. By selecting an appropriate oxidant, single-electron oxidation of the quinonoid intermediate can be achieved, which can subsequently be applied to C–C bond forming reactions. Through this radical reaction pathway, we synthesized a series of α-tertiary amino acids and esters to investigate the substrate scope and identify non-productive reaction pathways. Beyond the amino acid model system, we demonstrate that other classes of amine substrates can be applied in this reaction and that a range of small molecule reagents can serve as a coupling partner to the semiquinone radical. We anticipate that this versatile semiquinone radical species will be central to the development of a range of novel reactions
Pd-Catalyzed Asymmetric Hydrogenation of C=C Bond of a,b-Unsaturated Ketones
No full textPd-Catalyzed Asymmetric Hydrogenation of C=C Bond of a,b-Unsaturated Ketone
Manganese-Mediated C-C Bond Formation: Alkoxycarbonylation of Organoboranes
Get PDFAlkoxycarbonylations are important and versatile reactions that result in the formation of a new C-C bond. Herein, we report on a new and halide-free alkoxycarbonylation reaction that does not require the application of an external carbon monoxide atmosphere. Instead, manganese carbonyl complexes and organo(alkoxy)borate salts react to form an ester product containing the target C-C bond. The required organo(alkoxy)borate salts are conveniently generated from the stoichiometric reaction of an organoborane and an alkoxide salt and can be telescoped without purification. The protocol leads to the formation of both aromatic and aliphatic esters and gives complete control over the ester's substitution (e.g., OMe, OtBu, OPh). A reaction mechanism was proposed on the basis of stoichiometric reactivity studies, spectroscopy, and DFT calculations. The new chemistry is particularly relevant for the field of Mn(I) catalysis and clearly points to a potential pathway toward irreversible catalyst deactivation. ChemE/Inorganic Systems EngineeringChemE/Algemee
Recent Advancement in Palladium Catalysed C-C bond Activation of Strained Ring Systems: Three and four-membered carbocycles as prominent C3/C4 building blocks
No full textIn recent years, transition metal catalysed strong C-C bond activation has significantly attracted the attention of synthetic chemists. This enables simultaneous and direct functionalization of two different M-C bonds. Among different types of C-C bond activation strategies, strain-driven C-C bond activation has resulted in a variety of transformations, which is otherwise impossible. In this context, palladium catalyst has been extensively used and studied due to its robust nature in terms of its reactivity and selectivity. Herein, we have provided a brief discussion about palladium catalysed C-C bond activation of three and four-membered cycloalkane derivatives
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Once Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexes
No full textOnce Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexe
Once Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexes
No full textOnce Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexe
Once Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexes
No full textOnce Cleaved C−C Bond Was Reformed: Reversible C−C Bond Cleavage of Dihydroindenyltitanium Complexe
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