Synthesis and Prior Misidentification of 4-<i>tert</i>-Butyl-2,6-dinitrobenzaldehyde

Substituted 2,6-dinitrobenzaldehydes are valuable synthetic precursors and have been prepared by several methods. We report here that one reported synthetic method actually forms the 3,5-dinitro isomer, 4-tert-butyl-3,5-dinitrobenzaldehyde, instead of the claimed 2,6-isomer, 4-tert-butyl-2,6-dinitrobenzaldehyde. Improved syntheses for the large-scale preparation of both compounds and their single-crystal X-ray structures are described

Synthesis and Prior Misidentification of 4-<i>tert</i>-Butyl-2,6-dinitrobenzaldehyde

Substituted 2,6-dinitrobenzaldehydes are valuable synthetic precursors and have been prepared by several methods. We report here that one reported synthetic method actually forms the 3,5-dinitro isomer, 4-tert-butyl-3,5-dinitrobenzaldehyde, instead of the claimed 2,6-isomer, 4-tert-butyl-2,6-dinitrobenzaldehyde. Improved syntheses for the large-scale preparation of both compounds and their single-crystal X-ray structures are described

Synthesis and Prior Misidentification of 4-<i>tert</i>-Butyl-2,6-dinitrobenzaldehyde

Substituted 2,6-dinitrobenzaldehydes are valuable synthetic precursors and have been prepared by several methods. We report here that one reported synthetic method actually forms the 3,5-dinitro isomer, 4-tert-butyl-3,5-dinitrobenzaldehyde, instead of the claimed 2,6-isomer, 4-tert-butyl-2,6-dinitrobenzaldehyde. Improved syntheses for the large-scale preparation of both compounds and their single-crystal X-ray structures are described

Desulfurization and N₂ Binding at an Iron Complex Derived from the C–S Activation of Benzothiophene

Metal insertion into the C–S bonds of thiophenes is a facile route to interesting polydentate ligand scaffolds with C and S donors. Here, we describe iron-mediated C–S activation of a diphenylphosphine-functionalized benzothiophene proligand. Metalation of the proligand with Fe(PMe3)4 gives an initial five-coordinate, diamagnetic iron(II) species with two PMe3 ligands and a dianionic PCS pincer ligand. Upon one-electron reduction, a reactive anionic iron(I) complex is formed. This species then undergoes deep-seated changes, notably cleavage of C–S and C–P bonds in the supporting ligand. Substantial coordination sphere alterations accompany the ligand C–S bond activation, including loss of a sulfur anion from the S–Fe–C metallacycle and reorganization of the two PMe3 ligands. The resulting desulfurized six-coordinate PCC iron complex also has a N2 ligand trans to the vinyl carbon. Reducing this complex then cleaves a C–P bond in the appended diphenylphosphine, giving a phosphido arm. These ligand transformations demonstrate novel approaches to pincers with thiolates and phosphides, which would be difficult to synthesize using typical methods through free ligand salts

Desulfurization and N₂ Binding at an Iron Complex Derived from the C–S Activation of Benzothiophene

Metal insertion into the C–S bonds of thiophenes is a facile route to interesting polydentate ligand scaffolds with C and S donors. Here, we describe iron-mediated C–S activation of a diphenylphosphine-functionalized benzothiophene proligand. Metalation of the proligand with Fe(PMe3)4 gives an initial five-coordinate, diamagnetic iron(II) species with two PMe3 ligands and a dianionic PCS pincer ligand. Upon one-electron reduction, a reactive anionic iron(I) complex is formed. This species then undergoes deep-seated changes, notably cleavage of C–S and C–P bonds in the supporting ligand. Substantial coordination sphere alterations accompany the ligand C–S bond activation, including loss of a sulfur anion from the S–Fe–C metallacycle and reorganization of the two PMe3 ligands. The resulting desulfurized six-coordinate PCC iron complex also has a N2 ligand trans to the vinyl carbon. Reducing this complex then cleaves a C–P bond in the appended diphenylphosphine, giving a phosphido arm. These ligand transformations demonstrate novel approaches to pincers with thiolates and phosphides, which would be difficult to synthesize using typical methods through free ligand salts

Structure and Reactivity of Highly Twisted <i>N</i>‑Acylimidazoles

A modular and efficient synthesis of highly twisted N-acylimidazoles is reported. These twist amides were characterized via X-ray crystallography, NMR spectroscopy, IR spectroscopy, and DFT calculations. Modification of the substituent proximal to the amide revealed a maximum torsional angle of 88.6° in the solid state, which may be the most twisted amide reported for a nonbicyclic system to date. Reactivity and stability studies indicate that these twisted N-acylimidazoles may be valuable, namely as acyl transfer reagents

Dinitrogen Binding and Functionalization from a Low-Coordinate Alkynyliron Complex

Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and interesting bonding opportunities. Here, we explore the capacity of iron(I) alkynyl complexes to bind N2 and isolate a N2 complex including its X-ray crystal structure. Silylation of the N2 complex gives an isolable, formally iron(IV) complex with a disilylhydrazido(2−) ligand, but natural bond orbital analysis indicates that an iron(II) formulation is preferable. 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 why the alkynyl is resistant to migration, and these show that the large Fe–C bond energy in the alkynyl complex is a factor that could contribute to the lack of migration

Synthesis and Prior Misidentification of 4-<i>tert</i>-Butyl-2,6-dinitrobenzaldehyde

Substituted 2,6-dinitrobenzaldehydes are valuable synthetic precursors and have been prepared by several methods. We report here that one reported synthetic method actually forms the 3,5-dinitro isomer, 4-tert-butyl-3,5-dinitrobenzaldehyde, instead of the claimed 2,6-isomer, 4-tert-butyl-2,6-dinitrobenzaldehyde. Improved syntheses for the large-scale preparation of both compounds and their single-crystal X-ray structures are described

Dehydrogenative Synthesis of Carbamates from Formamides and Alcohols Using a Pincer-Supported Iron Catalyst

We report that the pincer-ligated iron complex (iPrPNP)­Fe­(H)­(CO) [1, iPrPNP– = N­(CH2CH2PiPr2)2–] is an active catalyst for the dehydrogenative synthesis of N-alkyl- and N-aryl-substituted carbamates from formamides and alcohols. The reaction is compatible with industrially relevant N-alkyl formamides, as well as N-aryl formamides, and 1°, 2°, and benzylic alcohols. Mechanistic studies indicate that the first step in the reaction is the dehydrogenation of the formamide to a transient isocyanate by 1. The isocyanate then reacts with the alcohol to generate the carbamate. However, in a competing reaction, the isocyanate undergoes a reversible cycloaddition with 1 to generate an off-cycle species, which is the resting state in catalysis. Stoichiometric experiments indicate that high temperatures are required in catalysis to facilitate the release of the isocyanate from the cycloaddition product. We also identified several other off-cycle processes that occur in catalysis, such as the 1,2-addition of the formamide or alcohol substrate across the Fe–N bond of 1. It has already been demonstrated that the transient isocyanate generated from dehydrogenation of the formamide can be trapped with amines to form ureas and, in principle, the isocyanate could also be trapped with thiols to form thiocarbamates. Competition experiments indicate that trapping of the transient isocyanate with amines to produce ureas is faster than trapping with an alcohol to produce carbamates and thus ureas can be formed selectively in the presence of alcohols. In contrast, thiols bind irreversibly to the iron catalyst through 1,2 addition across the Fe–N bond of 1, and it is not possible to produce thiocarbamates. Overall, our mechanistic studies provide general guidelines for facilitating dehydrogenative coupling reactions using 1 and related catalysts

Alkali Metal Control over N–N Cleavage in Iron Complexes

Though N₂ cleavage on K-promoted Fe surfaces is important in the large-scale Haber–Bosch process, there is still ambiguity about the number of Fe atoms involved during the N–N cleaving step and the interactions responsible for the promoting ability of K. This work explores a molecular Fe system for N₂ reduction, particularly focusing on the differences in the results obtained using different alkali metals as reductants (Na, K, Rb, Cs). The products of these reactions feature new types of Fe–N₂ and Fe-nitride cores. Surprisingly, adding more equivalents of reductant to the system gives a product in which the N–N bond is not cleaved, indicating that the reducing power is not the most important factor that determines the extent of N₂ activation. On the other hand, the results suggest that the size of the alkali metal cation can control the number of Fe atoms that can approach N₂, which in turn controls the ability to achieve N₂ cleavage. The accumulated results indicate that cleaving the triple N–N bond to nitrides is facilitated by simultaneous approach of least three low-valent Fe atoms to a single molecule of N₂