Grignard Reagents and Non-Precious Metals: Cheap and Eco-Friendly Reagents for Developing Industrial Cross-Couplings. A Personal Account

C-N, C-O and C-S Ullmann-Type Coupling Reactions of Arenediazonium o-Benzenedisulfonimides

Arenediazonium o-benzenedisulfonimides have been used as efficient electrophilic partners in Cu(I) catalysed Ullmann-type coupling. The synthetic protocols are mild and easy, and produced either N-alkylanilines, aryl ethers, or thioethers in fairly good yields (18 positive examples, average yield 66%). o-Benzenedisulfonimide was recovered at the end of the reactions and was reused to prepare the starting salts for further reactions. It is noteworthy that diazonium salts have been used as electrophilic partners in the Ullmann-type protocol for the first time.

Enantioselective Cross-couplings between Halide Derivatives and Organometallics by Using Iron and Cobalt Catalysts: Formation of C-C Bonds

This review highlights the recent achievements of iron- and cobalt-catalyzed enantioselective cross-couplings of halide derivatives with organometallic reagents for the construction of C-C bonds. Synthetic applications of enantioselective cross-couplings to natural products and biologically active compounds are also covered showing the power of these cross-couplings in organic synthesis.

Application of organometallic catalysts for the synthesis of o-tolyl benzonitrile, a key starting material for sartans

This review describes methods for the synthesis of o-tolyl benzonitrile, such as Pd-, Ni-catalyzed Suzuki, Negishi and Kumada couplings reactions.

A One-Pot Iodo-Cyclization/Transition Metal-Catalyzed Cross-Coupling Sequence: Synthesis of Substituted Oxazolidin-2-ones from N-Boc-allylamines

A one-pot iodo-cyclization/transition metal-catalyzed cross-coupling sequence is reported to access various C5-functionalized oxazolidin-2-ones from unsaturated N-Boc-allylamines. Depending on the Grignard reagents used for the cross-coupling, e.g., aryl- or cyclopropylmagnesium bromide, a cobalt or copper catalyst has to be used to obtain the functionalized oxazolidin-2-ones in good yields.

Iron-Catalyzed Cross-Coupling of Bis-(aryl)manganese Nucleophiles with Alkenyl Halides: Optimization and Mechanistic Investigations

Various substituted bis-(aryl)manganese species were prepared from aryl bromides by one-pot insertion of magnesium turnings in the presence of LiCl and in situ trans-metalation with MnCl₂ in THF at −5 °C within 2 h. These bis-(aryl)manganese reagents undergo smooth iron-catalyzed cross-couplings using 10 mol% Fe(acac)₃ with various functionalized alkenyl iodides and bromides in 1 h at 25 °C. The aryl-alkenyl cross-coupling reaction mechanism was thoroughly investigated through paramagnetic ¹H-NMR, which identified the key role of tris-coordinated ate-iron(II) species in the catalytic process.

Iron catalyzed stereoselective alkene synthesis: a sustainable pathway

Replacing expensive or toxic transition metals with iron has become an important trend. This article summarises the recent progresses of a wide range of Fe-catalyzed reactions for accessing various stereodefined alkenes.

Iron-Catalyzed Cross-Coupling of Alkynyl and Styrenyl Chlorides with Alkyl Grignard Reagents in Batch and Flow

Transition-metal-catalyzed cross-coupling chemistry can be regarded as one of the most powerful protocols to construct carbon-carbon bonds. While the field is still dominated by palladium catalysis, there is an increasing interest to develop protocols that utilize cheaper and more sustainable metal sources. Herein, we report a selective, practical, and fast iron-based cross-coupling reaction that enables the formation of Csp-Csp3 and Csp2 -Csp3 bonds. In a telescoped flow process, the reaction can be combined with the Grignard reagent synthesis. Moreover, flow allows the use of a supporting ligand to be avoided without eroding the reaction selectivity.

Iron-Catalyzed Reactions of 2-Pyridone Derivatives: 1,6-Addition and Formal Ring Opening/Cross Coupling

In the presence of simple iron salts, 2‐pyridone derivatives react with Grignard reagents under mild conditions to give the corresponding 1,6‐addition products; if the reaction medium is supplemented with an aprotic dipolar cosolvent after the actual addition step, the intermediates primarily formed succumb to ring opening, giving rise to non‐thermodynamic Z,E‐configured dienoic acid amide derivatives which are difficult to make otherwise. Control experiments as well as the isolation and crystallographic characterization of a (tricarbonyl)iron pyridone complex suggest that the active iron catalyst generated in situ exhibits high affinity to the polarized diene system embedded into the heterocyclic ring system of the substrates, which likely serves as the actual recognition element.

Oxidation States, Stability, and Reactivity of Organoferrate Complexes

We have applied a combination of electrospray-ionization mass spectrometry, electrical conductivity measurements, and Mössbauer spectroscopy to identify and characterize the organoferrate species R _nFe _m^- formed upon the transmetalation of iron precursors (Fe(acac)₃, FeCl₃, FeCl₂, Fe(OAc)₂) with Grignard reagents RMgX (R = Me, Et, Bu, Hex, Oct, Dec, Me₃SiCH₂, Bn, Ph, Mes, 3,5-(CF₃)₂-C₆H₃; X = Cl, Br) in tetrahydrofuran. The observed organoferrates show a large variety in their aggregation (1 ≤ m ≤ 8) and oxidation states (I to IV), which are chiefly determined by the nature of their organyl groups R. In numerous cases, the addition of a bidentate amine or phosphine changes the distributions of organoferrates and affects their stability. Besides undergoing efficient intermolecular exchange processes, several of the probed organoferrates react with organyl (pseudo)halides R'X (R' = Et, ⁱPr, Bu, Ph, p-Tol; X = Cl, Br, I, OTf) to afford heteroleptic complexes of the type R₃FeR'^-. Gas-phase fragmentation of most of these complexes results in reductive eliminations of the coupling products RR' (or, alternatively, of R₂). This finding indicates that iron-catalyzed cross-coupling reactions may proceed via such heteroleptic organoferrates R₃FeR'^- as intermediates. Gas-phase fragmentation of other organoferrate complexes leads to β-hydrogen eliminations, the loss of arenes, and the expulsion of organyl radicals. The operation of both one- and two-electron processes is consistent with previous observations and contributes to the formidable complexity of organoiron chemistry.

A Copper-Catalyzed Reductive Defluorination of β-Trifluoromethylated Enones via Oxidative Homocoupling of Grignard Reagents

An efficient copper-catalyzed reductive defluorination of β-trifluoromethylated enones via an oxidative homocoupling of Grignard reagents is reported. The reaction proceeded smoothly with a wide range of substrates, including the ones bearing aromatic heterocycles, such as furyl and thienyl ring systems in high yields (80-92%, except one example) under mild conditions. This provides a practical method for synthesis of gem-difluoroolefin ketones. It is also worth noting that this homocoupling process of Grignard reagents using β-trifluoromethylated enones as "oxidizing reagents" is effective for both the Csp²-Csp² and Csp³-Csp³ bond formations, including for substrates whose β-hydride elimination of the corresponding transition metal alkyl complex is particularly facile, affording coupling products with high yields (83-95%), simultaneously.

Grignard Reagents on a Tab: Direct Magnesium Insertion under Flow Conditions

An on-demand preparation of organomagnesium reagents is presented using a new flow protocol. The risks associated with the activation of magnesium are circumvented by a new on-column initiation procedure. Required amounts of solutions with a precise titration were obtained. Telescoped flow or batch reactions allow access to a diverse set of functional groups.

Intermediates and Reactivity in Iron-Catalyzed Cross-Couplings of Alkynyl Grignards with Alkyl Halides

Iron-catalyzed cross-coupling reactions using alkynyl nucleophiles represent an attractive approach for the incorporation of alkynyl moieties into organic molecules. In the present study, a multitechnique approach combining inorganic spectroscopic methods, inorganic synthesis, and reaction studies is applied to iron-SciOPP catalyzed alkynyl-alkyl cross-couplings, providing the first detailed insight into the effects of variation from sp2- to sp-hybridized nucleophiles on iron speciation and reactivity. Reaction studies demonstrate that reaction of FeBr2(SciOPP) with 1 equiv (triisopropylsilyl)ethynylmagnesium bromide (TIPS-CC-MgBr) leads to a distribution of mono-, bis-, and tris-alkynylated iron(II)-SciOPP species due to rapid alkynyl ligand redistribution. While solvents such as THF promote these complex redistribution pathways, nonpolar solvents such as toluene enable increased stabilization of these iron species and further enabled assessment of their reactivity with electrophile. While the tris-alkynylated iron(II)-SciOPP species was found to be unreactive with the cycloheptyl bromide electrophile over the average turnover time of catalysis, the in situ formed neutral mono- and bis-alkynylated iron(II)-SciOPP complexes are consumed upon reaction with the electrophile with concomitant generation of cross-coupled product at catalytically relevant rates, indicating the ability of one or both of these species to react selectively with the electrophile. The nature of the reaction solvent and Grignard reagent addition rate were found to have broader implications in overall reaction selectivity, reaction rate, and accessibility of off-cycle iron(I)-SciOPP species. Additionally, the effects of steric substitution of the alkynyl Grignard reagent on catalytic performance were investigated. Fundamental insight into iron speciation and reactivity with alkynyl nucleophiles reported herein provides an essential foundation for the continued development of this important class of reactions.

Facile routes to abnormal-NHC-cobalt(ii) complexes

Deprotonation of 1 with Co{N(SiMe₃)₂}₂ affords aNHC-Co(ii) complex 2, whereas carbene transfer from 3 to Co{N(SiMe₃)₂}₂ enables access to complex 4.

Cyclopentadienyl nickel(ii) N,C-chelating benzothiazolyl NHC complexes: synthesis, characterization and application in catalytic C–C bond formation reactions

CpNi(ii) N,C-chelating benzothiazolyl NHC complexes have been synthesized. They are efficient catalysts for the homo-coupling of benzyl bromide in the presence of MeMgCl at r.t. with good function group tolerance.

A practical cobalt-catalyzed cross-coupling of benzylic zinc reagents with aryl and heteroaryl bromides or chlorides

A catalytic system consisting of 5 mol% CoCl₂ and 10 mol% isoquinoline allows a convenient cross-coupling of benzylic zinc reagents with various aryl and heteroaryl bromides or chlorides leading to polyfunctionalized diaryl- and aryl-heteroaryl-methane derivatives.

Carbon-based two electron σ-donor ligands beyond classical N-heterocyclic carbenes

Recent advances in N-heterocyclic carbene-derived carbon-based two electron σ-donor ligands are presented in this perspective.

An organo-NHC catalyzed domino addition approach for the selective synthesis of 5-butynylisoxazoles and subsequent Sonogashira coupling

An organo-NHC catalysed domino addition approach for the selective synthesis of 5-butynylisoxazoles and the subsequent Sonogashira cross-coupling for the selective synthesis of corresponding internal alkynes is described.