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A Co(acac)3/PN precatalyst was developed and optimized for catalytic Kumada coupling of aryl Grignard reagents to sterically encumbered alkyl halides. The substrate scope demonstrates excellent yie...

International audience; This chapter describes recent developments in the manganese-catalyzed crosscoupling reactions for the formation of CC or C-heteroatom bonds, including C-N, CO , C-S and C-B bonds. The nature of the organic halide and the organometallic coupling partner (organolithium, Grignard or organostannyl reagents) are important parameters in these reactions. Mechanistic studies are discussed as well as the recently arisen question about the influence of trace-metal contamination in certain reactions.

Transition-metal-catalyzed cross-coupling has emerged as one of the most powerful and useful tools for the formation of C–C and C–heteroatom bonds. Given the shortage of resources of precious metals on Earth, the use of Earth-abundant metals as catalysts in developing cost-effective strategies for cross-coupling is a current trend in synthetic chemistry. Compared with the achievements made using first-row nickel, iron, cobalt, and even manganese catalysts, the group 6 metal chromium has rarely been used to promote cross-coupling. This perspective covers recent advances in chromium-catalyzed cross-coupling reactions in transformations of chemically inert C(aryl)–O, C(aryl)–N, and C(aryl)–H bonds, offering selective strategies for molecule construction. The ability of low-valent Cr with a high-spin state to participate in two-electron oxidative addition is highlighted; this is different from the mechanism involving single-electron transfer that is usually assigned to chromium-mediated transformations.1 Introduction2 Chromium-Catalyzed Kumada Coupling of Nonactivated C(aryl)–O and C(aryl)–N Bonds3 Chromium-Catalyzed Reductive Cross-Coupling of Two Nonactivated C(aryl)–Heteroatom Bonds4 Chromium-Catalyzed Functionalization of Nonactivated C(aryl)–H Bonds5 Conclusions and Outlook

Polythiophene derivatives synthesized by Kumada catalyst-transfer polycondensation (KCTP) have been intensively studied as potential candidates for low-cost organic solar cells (OSCs) due to their capability of scalable production. However, the power conversion efficiency (PCE) is still unsatisfactory so far. In this work, two regioregular polythiophene derivatives, P3SHT and PTST with thioalkyl chains, were prepared by KCTP. Compared to the analogue P3HT with alkyl chains, the new polymers show stronger absorption and downshifted energy levels due to the role of sulfur as a π-acceptor. The non-covalent interaction induced by sulfur also improves the crystallinity of the relevant polymers. However, the photovoltaic properties of P3SHT with thioalkyl chains are inferior to those of P3HT due to the severe phase separation in OSCs. PTST with alternating alkyl and thioalkyl chains exhibits the strongest crystallinity among these polymers since it mitigates the steric hindrance of sulfur atoms while retaining the merit of thioalkyl chains. More importantly, PTST is able to hierarchically pre-aggregate in solution, and then form a favorable morphology in OSCs, consequently yielding a superior PCE to P3HT.

Biaryl compounds are an important class of aromatic compounds used for the synthesis of antiviral, antihypertensive, and antifungal drugs. The familiar methods for the synthesis of biaryl compounds are Pd-, Ni-catalyzed couplings reactions, such as Suzuki, Negishi and Kumada reactions. Hypertension is a medical condition in which the blood pressure against artery wall is high enough to increase the risk of heart disease and stroke. Angiotensin receptor blockers (ARBs) are one of the most effective and commonly prescribed antihypertensive agents. o-Tolyl benzonitrile (OTBN) is the common building block for the synthesis of the sartan series of drug molecules (ARBs), such as candesartan, irbesartan, losartan, tasosartan, and valsartan. The classical methods for the synthesis of OTBN are Pd-catalyzed, Ni-catalyzed Suzuki coupling reactions. The other high yield methods for the synthesis of OTBN are Ni-catalyzed Kumada coupling, and desulfinating cross-coupling using Pd-catalyst. The Ni-catalysts could be an alternative to the expensive Pd-catalyst, as cost is a factor for bulk manufacturing of this building block. Although there are few reports of OTBN synthesis using desulfinating cross coupling, this method has opened a new avenue.

Suzuki–Miyaura catalyst transfer polymerization (SM CTP) is a versatile method to prepare conjugated polymers with control over molecular weight, sequence, and dispersity. This perspective aims to highlight some of the progress in using Suzuki–Miyaura coupling to prepare well-defined conjugated polymers via a chain-growth mechanism. We detail some of the advantages and challenges of this coupling to make aromatic polymers from monomers bearing two functional groups. The advances in arene borylation over the last twenty years are briefly highlighted, as these strategies should serve to diversify monomer scope in the future. The proposed mechanism for transmetalation in Suzuki–Miyaura polymerization is discussed, as it is different from the more typical Kumada coupling. We describe the versatility of the organoboron group used for this reaction and how it can be used tune polymerization behavior. Finally, some of the advances in catalyst design to prepare conjugated polymers using SM CTP are noted.

New PCNPy pincer nickel complexes have been synthesized through a short synthetic route. Incorporating pyridine as the nitrogen side arm facilitated the C–H activation in the PCN ligand and allowed the cyclometallation with nickel to take place at room temperature. Pyridine also enhanced the stability of β-hydrogen-containing alkyl complexes. Also, the symmetric NCN nickel complex with pyridine side arms was successfully obtained giving a rare example of such type of complexes to be prepared through direct C–H activation. Furthermore, preliminary results showed that the (PCNPy)Ni–Br is active in Kumada coupling reactions particularly the coupling of aryl halides with aryl Grignard reagents.

A new series of 3,3ʹ-disubstituted chiral (S)-BINOL derivatives 6a–6k has been synthesized via the Kumada and Suzuki–Miyaura coupling reactions using (S)-BINOL as the initial compound. The Kumada coupling has been found to be superior in terms of yields and reaction time. All the synthesized compounds have been screened for their antibacterial activity against Gram-positive and Gram-negative organisms using Penicillin and Streptomycin as standards. The most potent antibacterial activity has been determined for compounds 6a,6b, 6c, and 6d with MIC values ranging from 1.17 to 4.68 μg/mL against all bacterial strains tested. Molecular docking studies has presented an insight into the binding pattern of the top active ligands with the respective target protein.

A series of ester-functionalized benzimidazolium salts 2a–c were prepared by quaternization of 1-{(ethoxycarbonyl)methyl}benzimidazole (1) with 3,5-dimethylbenzyl bromide, 2,5-dimethylbenzyl chloride and 3-methoxybenzyl chloride, respectively. Refluxing 2a–c with nickelocene in THF yielded the neutral cyclopentadienyl NHC nickel(II) complexes 3a–c. Their structures were defined by NMR, IR and elemental analysis techniques. Molecular weights of 3a–c were affirmed by MALDI-TOF mass spectrometry. Catalytic tests of 3a–c were performed in Kumada coupling of some aryl chlorides with phenylmagnesium bromide at 25 °C.

1,3‐Disubstituted bicyclo[1.1.1]pentanes (BCPs) are important motifs in drug design as surrogates for p‐substituted arenes and alkynes. Access to all‐carbon disubstituted BCPs via cross‐coupling has to date been limited to use of the BCP as the organometallic component, which restricts scope due to the harsh conditions typically required for the synthesis of metallated BCPs. Here we report a general method to access 1,3‐C‐disubstituted BCPs from 1‐iodo‐bicyclo[1.1.1]pentanes (iodo‐BCPs) by direct iron‐catalyzed cross‐coupling with aryl and heteroaryl Grignard reagents. This chemistry represents the first general use of iodo‐BCPs as electrophiles in cross‐coupling, and the first Kumada coupling of tertiary iodides. Benefiting from short reaction times, mild conditions, and broad scope of the coupling partners, it enables the synthesis of a wide range of 1,3‐C‐disubstituted BCPs including various drug analogues., 1,3‐C‐disubstituted bicyclo[1.1.1]pentanes (BCPs) are accessed from 1‐iodo‐BCPs by direct iron‐catalyzed cross‐coupling with aryl and heteroaryl Grignard reagents. This represents the first general use of iodo‐BCPs as cross‐coupling electrophiles, and the first Kumada coupling of tertiary iodides in general. Benefiting from short reaction times, mild conditions, and broad scope, it enables the synthesis of a wide range of BCPs including drug analogues.

A series of nickel complexes in varying oxidation states were evaluated as precatalysts for the stereospecific cross-coupling of benzylic ethers. These results demonstrate rapid redox reactions of precatalysts, such that the oxidative state of the precatalyst does not dictate the oxidation state of the active catalyst in solution. These data provide the first experimental evidence for a Ni0 -NiII catalytic cycle for a stereospecific alkyl-alkyl cross-coupling reaction, including spectroscopic analysis of the catalyst resting state.

A supramolecular catalytic ensemble HP-T@Au-Fe3O4 supported by highly branched assemblies of hexaphenylbenzene (HPB) derivatives has been developed. The as-prepared HP-T@Au-Fe3O4 nanohybrid material serves as an efficient catalytic system to prepare biaryl derivatives through the Kumada cross-coupling reaction using aryl chlorides as one of the coupling partners under mild reaction conditions (visible light irradiation, aqueous media, aerial conditions, short reaction time). Through the cooperative effect of Au NPs and Fe3O4 NPs, dual activation of aryl chlorides for the generation of aryl radical intermediates is achieved. On the other hand, oligomeric assemblies contributed significantly to the enhancement of the reaction rate and yield of the product by facilitating the reductive elimination step. Different mechanistic studies confirm the involvement of Au NPs, Fe3O4 NPs and oligomeric assemblies in the synergistic and balanced operation of HP-T@Au-Fe3O4 nanohybrid materials in the efficient completion of the catalytic cycle of the Kumada coupling reaction. Being magnetic, the catalytic ensemble could be recycled for up to five catalytic cycles. The as-prepared supramolecular photocatalytic ensemble also works efficiently in Heck coupling reactions involving aryl chlorides and aryl iodides as the coupling partner.

X.-J.W., I.A., J.A., and T.N. would like to acknowledge the European Union for a Marie Curie ITN Grant (Photo4Future, Grant No. 641861). C.S. acknowledges the European Union for a Marie Curie European post-doctoral fellowship (FlowAct, Grant No. 794072). We would like to thank the Engineering and Physical Sciences Research Council for financial support (EP/M02105X/1). C. L. thanks the Prof. & Mrs Purdie Bequests Scholarship and AstraZeneca for his PhD Studentship. A continuous‐flow, visible‐light‐promoted method has been developed to overcome the limitations of iron‐catalyzed Kumada–Corriu cross‐coupling reactions. A variety of strongly electron rich aryl chlorides, previously hardly reactive, could be efficiently coupled with aliphatic Grignard reagents at room temperature in high yields and within a few minutes’ residence time, considerably enhancing the applicability of this iron‐catalyzed reaction. The robustness of this protocol was demonstrated on a multigram scale, thus providing the potential for future pharmaceutical application. Publisher PDF

Ni-catalyzed C(sp(3))-O bond activation provides a useful approach to synthesize enantioenriched products from readily available enantioenriched benzylic alcohol derivatives. The control of stereospecificity is key to the success of these transformations. To elucidate the reversed stereospecificity and chemoselectivity of Ni-catalyzed Kumada and cross-electrophile coupling reactions with benzylic ethers, a combined computational and experimental study is performed to reach a unified mechanistic understanding. Kumada coupling proceeds via a classic cross-coupling mechanism. Initial rate-determining oxidative addition occurs with stereoinversion of the benzylic stereogenic center. Subsequent transmetallation with the Grignard reagent and syn reductive elimination produces the Kumada coupling product with overall stereoinversion at the benzylic position. The cross-electrophile coupling reaction initiates with the same benzylic C-O bond cleavage and transmetallation to form a common benzylnickel intermediate. However, the presence of the tethered alkyl chloride allows a facile intramolecular S(N)2 attack by the benzylnickel moiety. This step circumvents the competing Kumada coupling, leading to the excellent chemoselectivity of cross-electrophile coupling. These mechanisms account for the observed stereospecificity of the Kumada and cross-electrophile couplings, providing a rationale for double inversion of the benzylic stereogenic center in cross-electrophile coupling. The improved mechanistic understanding will enable design of stereoselective transformations involving Ni-catalyzed C(sp(3))-O bond activation.

1,3-Disubstituted bicyclo[1.1.1]pentanes (BCPs) are important motifs in drug design as surrogates for p-substituted arenes and alkynes. Access to all-carbon disubstituted BCPs via cross coupling has to date been limited to use of the BCP as the organometallic component, which restricts scope due to the harsh conditions typically required for the synthesis of metallated BCPs. Here we report a general method to access 1,3-C-disubstituted BCPs from 1-iodo-bicyclo[1.1.1]pentanes (iodo-BCPs) by direct iron-catalyzed crosscoupling with aryl and heteroaryl Grignard reagents. This chemistry represents the first general use of iodoBCPs as electrophiles in cross-coupling, and of Kumada coupling of tertiary iodides in general. Benefiting from short reaction times, mild conditions, and broad scope of the coupling partners, it enables the synthesis of a wide range of 1,3-C-disubstituted BCPs including various drug analogues.

A nanoparticle (NP)-based precatalyst has been developed for organic synthesis: sulfur-modified Au-supported Fe (SAFe). The SAFe was easily prepared through a three-step procedure involving simultaneous in situ metal NP and nanospace organization (PSSO). This method avoids the need for preformed templates for immobilizing and stabilizing the metal nanoparticles. On account of the relative safety and enormous earth abundance of iron, SAFe potentially represents an ideal precatalyst for carbon–carbon bond-forming cross-coupling reactions. As such, it has been applied as a precatalyst to Kumada coupling under ligand-free conditions, proving to be capable of being recycled and used repeatedly for this reaction. Analysis of SAFe and of reaction mixtures suggested that the active species in these reactions are produced in situ by assemblies of iron-based NPs.

Heterodinuclear transition metal complexes with a direct metal–metal interaction offer the potential of unique reactivity compared with mononuclear catalysts. Heterodinuclear Co–Zr complexes with phosphinoamide ligands bridging Co and Zr metal centers are effective precatalysts for Kumada C–C bond coupling reactions between alkyl halides and alkyl Grignards. In contrast, the analogous mononuclear Co tris(phosphinoamine) complex without Zr provides very inefficient catalysis. Here we describe density functional theory calculations that reveal the mechanistic and reactivity impact of the Co–Zr metal–metal interaction and phosphinoamide ligands on alkyl halide–alkyl Grignard Kumada coupling catalysis. The Co–Zr interaction enables two-electron reduction of the precatalyst to form an active catalyst, which then promotes a low-energy electron-transfer alkyl halide oxidative addition mechanism. The Co–Zr interaction and the phosphinoamide ligands bridging the metal centers provide a dialkyl intermediate with a ...

A systematic study of the widely used, titled name reaction transition-metal-catalyzed cross-coupling reactions with attention to context with the directed ortho metalation (DoM) is reported. In general, the Suzuki–Miyaura and Negishi protocols show greater scope and better yields than the Corriu–Kumada variant, although the latter qualitatively proceeds at fastest rate but has low functional group tolerance. The Negishi process is shown to be useful for substrates with nucleophile and base-sensitive functionality and it is comparable to the Suzuki–Miyaura reaction in efficiency. The link of these cross-coupling reactions to the DoM strategy lends itself to the regioselective construction of diversely substituted aromatics and heteroaromatics.

We report here the chromium-catalyzed regioselective Kumada arylative cross-coupling of C(aryl)-O bonds at ambient temperature. By using a simple and low-cost chromium(II) chloride salt as a precatalyst, accompanied by a 2-pyridyl ligation, the catalytic cleavage and arylative coupling of C(aryl)-O bonds were achieved with a traceless activation strategy, overcoming the regioselectivity obstacle when several C-O bonds coexist in the Kumada coupling system.

The electron-rich silylene Co(I) chloride 5 was obtained through the reaction of CoCl(PMe3)3 with chlorosilylene. Complex 5 reacted with 1,3-siladiazole HSiMe(NCH2PPh2)2C6H4 to give the silylene Co(III) hydride 6 through chelate-assisted Si–H activation. To the best of our knowledge, complex 6 is the first example of Co(III) hydride supported by N-heterocyclic silylene. Complexes 5 and 6 were fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 6 was used as an efficient precatalyst for Kumada cross-coupling reactions. Compared with the related complex 3 supported by only trimethylphosphine, complex 6 as a catalyst supported by both chlorosilylene and trimethylphosphine exhibits a more efficient performance for the Kumada cross-coupling reactions. A novel catalytic radical mechanism was suggested and experimentally verified. As an intermediate silylene cobalt(II) chloride 6d was isolated and structurally characterized.

The synthesis and catalytic properties in Kumada C C coupling of the [Ni(BIPHEP)X2] complexes, X = Cl (1), Br (2), are described. The crystal structures of the BIPHEP ligand and 2 are also presented and compared with previously reported crystal structures of atropisomeric bidentate phosphine ligands (P,P) and related [M(P,P)X2] complexes (M = Ni, Pd, Pt). BIPHEP crystallizes in the C2/c space group, with both enantiomers present in the unit cell. This is consistent with BIPHEP being a “tropos” ligand. Complex 2 crystallizes in the P21/a space group. There are two symmetry-independent molecules in the asymmetric unit, namely 2a and 2b, in which the BIPHEP ligand adopts the S or the R configuration, respectively. Complexes 2a and 2b exhibit a severely tetrahedrally-distorted square planar NiP2Br2 coordination sphere, with a PNiP bite angle of 93.3° and 94.7°, respectively. The observed catalytic behavior of complexes 1 and 2 in the Kumada coupling between p-tert-butyl-halogenobenzene and p-tolylmagnesium chloride is benchmarked against that of [Ni(dppp)Cl2], dppp = 1,3-bis(diphenylphoshpino)propane. However, all three complexes are catalytically inactive in the Suzuki-Miyaura coupling reaction.

We have previously reported the synthesis of a polythiophene derivative (P2′) bearing pyridine and methoxy groups at the β-position, but the halogen–magnesium exchange reaction of the monomer did not proceed in a regioselective manner and resulted in a twisted polymer conformation. In the present paper, the halogen–magnesium exchange reaction of 4-(5″-hexylpyridine-2″-yl)-3-methoxy-2-(5′-bromothiophene-2′-yl)-5-bromothiophene (M3) and its Kumada coupling polymerization and optoelectronic characterization were investigated. The reaction of M3 with i-PrMgCl·LiCl gave a Grignard monomer (GM3a) in 79% yield, with the halogen–magnesium exchange reaction occurring exclusively at the bromine atom neighboring the pyridine group. Reflux temperature was required for the Kumada coupling polymerization of GM3a using Ni(dppp)Cl2 to proceed smoothly (72% conversion after 24 h) due to the sterically hindered monomer structure. On the other hand, the conversion of GM3a remained at 15% without the addition of LiCl. The number-average molecular weight of the tetrahydrofuran-soluble fraction of the regiocontrolled oligo(bithiophene) (P3′) was 2900 because of its poor solubility. Ultraviolet–visible and cyclic voltammogram measurements indicated that compared with P2′, P3′ has a more planar conformation, an increased highest occupied molecular orbital energy level and a narrower bandgap energy. A non-covalent S···O interaction was assumed to cause the planar conformation, which was supported by theoretical density functional theory calculations. The regioselective halogen–magnesium exchange reaction of 4-(5″-hexylpyridine-2″-yl)-3-methoxy-2-(5′-bromothiophene-2′-yl)-5-bromothiophene (M3) with i-PrMgCl·LiCl, Kumada coupling polymerization using Ni(dppp)Cl2 at the refluxing temperature and optoelectronic characterization of regiocontrolled oligo(bithiophene) (P3′) were investigated. The ultraviolet–visible and cyclic voltammogram measurements indicated that P3′ has the more planar conformation, increased highest occupied molecular orbital energy level and narrower bandgap energy as compared with a polythiophene derivative without the methoxy group. The non-covalent S···O interaction was supposed to be a reason for the planar conformation, which was supported by the theoretical density functional theory calculation.

Two 4-pyridylthiophene monomers M1 (2,5-dibromo derivative) and M2 (5-bromo-2-iodo derivative) having the methoxy group at the 3-position were synthesized. The Grignard metathesis reaction of M1 using i -PrMgCl·LiCl demonstrated the highest monomer conversion (87%) and regioselectivity ( GM1 / GM1′ = 76/24). The following Kumada coupling polymerization by Ni(dppe)Cl 2 gave P1-OMe with the number-averaged molecular weight ranging from 3000 to 4600. Likewise, P2-OMe was obtained from M2 . On the basis of 1 H-NMR spectra, the regiorandom structure of P1-OMe and P2-OMe were suggested. The transformation from the methoxy group to the hydroxy one was then carried out using P1-OMe by treating with BBr 3 to afford P1-OH . By measuring the UV-vis absorption spectra of polymers in CHCl 3 and film along with the DFT calculation of model compounds, it was found that 1) the formation of an intramolecular hydrogen bonding between the pyridine and hydroxy groups brings about the significant red-shift of the absorption maxima from 476 nm ( P1-OMe ) to 662 nm ( P1-OH ) and 2) P1-OH has the less planar conformation resulting in the ineffective π-π stacking of polymer chains in the solid state. The proton doping experiments and CV measurements revealed the hydrogen bonding characteristic in P1-OH .

A nickel-catalyzed Kumada coupling of aniline derivatives was developed by selective cleavage of aryl C–N bonds under mild reaction conditions. Without preinstallation of an ortho directing group on anilines, the cross-coupling reactions of Boc-protected aromatic amines with aryl Grignard reagents afforded unsymmetric biaryls. Mechanistic studies by DFT calculations revealed that the nickel-mediated C–N bond cleavage is the rate-limiting step.

A new amine functionalized double chelate NHC nickel complex 2 was synthesized and characterized. Complexes 4a and 4b were generated through an improved synthetic method. Catalytic ability of the three nickel complexes were tested in Kumada coupling reaction. Complex 2 showed the best catalytic activity among them. With only 0.5 mol% of complex 2, the coupling of aryl chlorides with Grignard reagents received good yields.

The macrocyclic core (35) of the marine natural product leiodermatolide (1) was synthesized from two key fragments, vinyl iodide 23 (C1-C11 part) and vinyl stannane 31 (C12-C18 part). A Stille coupling led to conjugated Z,Z-diene 32. The derived seco acid 34 was cyclized using a Yamaguchi macrolactonization. Key steps in the assembly of vinyl iodide 23 were a Paterson aldol reaction, and a Kumada coupling on a triflate derivative to create the C4-C5 trisubstituted double bond. The two stereocenters in fragment 31 were established by a Marshall-Tamaru reaction. The longest linear sequence comprises 20 steps.

We have developed a conceptually and methodologically novel self-assembled multilayer nickel nanoparticle (NP) catalyst – sulfur-modified gold-supported Ni NPs (SANi) – for organic synthesis. The SANi catalyst was easily prepared through a three-step procedure involving simultaneous in situ metal NP and nanospace organization. This unique method does not require any conventional preformed template for immobilizing and stabilizing NPs. SANi catalyzes carbon-carbon bond-forming cross-coupling, Kumada coupling, and Negishi coupling reactions under ligand-free conditions and can be used repeatedly for these reactions. Physical analysis of SANi showed that the active species in these reactions are self-assembled multilayer zerovalent Ni NPs with a size of ∼3 nm.

Pyridyl-substituted [2.2]paracyclophanes build a multifunctional structural motif that is useful in material chemistry, catalysis and for luminescent structures. Nonetheless, there is still a lack of general methods for the synthesis of these structures tolerating easily accessible bromides as well as different isomeric pyridyl groups. Hence the coupling of functionalized [2.2]paracyclophanes with various substituted and functionalized pyridyl derivatives was achieved using Stille, Suzuki and Kumada coupling conditions. Hereby the Stille coupling of a [2.2]paracyclophane is presented as a versatile reaction for the formation of heteromeric [2.2]paracyclophane-containing biaryl structures.

The new N-heterocyclic σ-silyl pincer ligand HSiMe(NCH2PPh2)2C6H4 (1) was designed. A series of tridentate silyl pincer Fe and Co complexes were prepared. Most of them were formed by chelate-assisted Si–H activation. The typical iron hydrido complex FeH(PMe3)2(SiMe(NCH2PPh2)2C6H4) (2) was obtained by Si–H activation of compound 1 with Fe(PMe3)4. The combination of compound 1 with CoMe(PMe3)4 afforded the Co(I) complex Co(PMe3)2(SiMe(NCH2PPh2)2C6H4) (3). The Co(III) complex CoHCl(PMe3)(SiMe(NCH2PPh2)2C6H4) (5) was generated by the reaction of complex 1 with CoCl(PMe3)3 or the combination of complex 3 with HCl. However, when complex 3 was treated with MeI, the Co(II) complex CoI(PMe3)(SiMe(NCH2PPh2)2C6H4) (4), rather than the Co(III) complex, was isolated. The catalytic performance of complex 5 for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex 5 displayed efficient catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard r...

A ligand-free Pd/Al(OH)3 nano-catalyst which is prepared by one-pot three-component method using Pd(PPh3)4, tetra (ethylene glycol), and aluminum tri-sec-butoxide exhibits excellent catalytic activity in Stille cross-couplings of (Het)aryl chlorides, arenediazonium tetrafluoroborate salts with phenyltributylstannane, respectively, and Kumada couplings of (Het)aryl chlorides with various Grignard reagents. More importantly, these two processes show excellent functional group compatibility with moderate to good yields and they are also versatile with respect to not only (Het)aryl chlorides, but also diazonium salts, and heteroaryl Grignard reagents. The nano-catalyst could also be recycled and reused 5 times without loss of activity and decrease of yield.

Quinolinamide-based pincer copper(II) complexes, κN,κN,κN-{C9H6N-(μ-N)-C(O)CH2NEt2}CuX [(QNNNEt2)CuX (X = Cl, 2; X = Br, 3; X = OAc, 4)], were synthesized by the reaction of ligand (QNNNEt2)-H (1) with CuX2 (X = Cl, Br or OAc) in the presence of Et3N. The reaction of (QNNNEt2)-H with CuX (X = Cl, Br or OAc) also afforded the Cu(II) complexes 2, 3 and 4, respectively, instead of the expected Cu(I) pincer complexes. The formation of Cu(II) complexes from Cu(I) precursors most likely occurred via the disproportionation reaction of Cu(I) into Cu(0) and Cu(II). A cationic complex [(QNNNEt2)Cu(CH3CN)]OTf (5) was synthesized by the treatment of neutral complex 2 with AgOTf. On the other hand, the reaction of (QNNNEt2)-H (1) with [Cu(MeCN)4]ClO4 produced cationic Cu(I) complex, [(QNN(H)NEt2)Cu(CH3CN)]ClO4 (6), in good yield. All complexes 2–5 were characterized by elemental analysis and HRMS measurements. Furthermore, the molecular structures of 2, 3 and 4 were elucidated by X-ray crystallography. Complex 4 crystallizes in a dimeric and catemeric pattern. The cationic complex 5 was found to be an efficient catalyst for the Kumada coupling reaction of diverse nonactivated alkyl chlorides and bromides with alkyl magnesium chloride under mild reaction conditions.

Replacement of a dimethyl amino group of the amidobis(amine) nickel(II) pincer complex (1), [((N2N)-N-Me)-Ni-Cl], by a pyrrolidino group resulted in a new nickel(II) pincer complex (2), [((PNNN)-N-yr-N-Me)Ni-Cl]. Complex 2 is an efficient catalyst for Kumada and Suzuki-Miyaura cross-coupling of nonactivated secondary alkyl halides, while complex 1 is largely inactive. The significant activity difference is tentatively attributed to a minimal structural difference, which leads to a more hemilabile ligand.

The ligand-exchange reaction between [Ni(PPh3)2Cl2] and (Ph2P)2N(CH2)3Si(OCH3)3 afforded the novel NiII complex [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P′}Cl2] (1) in which the square-planar NiP2Cl2 coordination sphere contains a four-membered Ni–P–N–P ring. Comparison of the structure of 1 and related NiII square-planar or Ni0 tetrahedral complexes containing similar P–N–P ligands shows that the magnitude of the P–Ni–P angle is controlled by the presence of the Ni–P–N–P ring, irrespective of the geometry of the nickel coordination sphere. Direct anchoring of 1 onto SBA-15 molecular sieves through the trimethoxysilyl end-group of the ligand afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/SBA-15 catalyze Kumada cross-coupling reactions, exhibiting similar activity and a slightly higher product selectivity than the [Ni{Ph2P(CH2)3PPh2-P,P′}Cl2] and [Ni{(Ph2P)2N-(S)-CHMePh-P,P′}X2] (X = Cl, Br) complexes described in the literature. The Grignard reagent employed is likely to induce leaching of the catalyst, which retains its activity in solution.

Iron(III) bisoxazolinylphenylamido (bopa) pincer complexes are efficient precatalysts for the cross-coupling of nonactivated primary and secondary alkyl halides with phenyl Grignard reagents. The reactions proceed at room temperature in moderate to excellent yields. A variety of functional groups can be tolerated. The enantioselectivity of the coupling of secondary alkyl halides is low.

Four silyl [P,Si]-chelate cobalt complexes (2–5) have been synthesized through the chelate-assisted Si−H activation of bidentate preligand ortho-HSi(Me)2(PPh2)C6H4 (1) with CoMe(PMe3)4 and CoCl(PMe3)3. The silyl CoI complex, Co(PMe3)3(1-Si(Me)2-2-(PPh2)C6H4) (2), was synthesized by Si−H activation of 1 with CoMe(PMe3)4 or by combining complex 5 with MeLi and PMe3. Complex 2 was treated with CH3I or EtBr, generating the silyl CoII products CoI(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4) (3) and CoBr(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4) (4). The silyl CoIII hydride, CoHCl(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4) (5), was obtained by the reaction of complex 1 with CoCl(PMe3)3. The catalytic performance of complex 5 was explored for Kumada coupling reactions, showing good to excellent catalytic efficiency with 2 mol % catalyst loading for the reactions of aryl chlorides or aryl bromides with Grignard reagents. It is noteworthy that the synthesis of 5 as a chelate complex is easier than that of previously reported [PSiP]-pincer cobalt hydride. With similar catalytic efficiency for Kumada reactions, the catalyst loading (2 %) of 5 was lower than that (5 %) of [PSiP]-pincer cobalt hydride.

A series of new 4,4-dialkyl- and 4,4-diaryl-4H-indeno[1,2-b]thiophenes and their 2-bromo derivatives were synthesized and characterized. An economical one-pot method for the preparation of the key starting material 2-(2-thienyl)benzoic acid and improved procedures for the synthesis of indeno[1,2-b]thiophen-4-one and 4,4-dialkyl-4H-indeno[1,2-b]thiophenes have been developed. The described methods were shown to be efficient for the preparation of the title compounds on a multigram scale.

Iron-catalyzed alkyl–aryl Kumada coupling has developed into an efficient synthetic method, yet its mechanism remains vague. Here, we apply a bis(oxazolinylphenyl)amido pincer ligand (Bopa) to stabilize the catalytically active Fe center, resulting in isolation and characterization of well-defined iron complexes whose catalytic roles have been probed and confirmed. Reactivity studies of the iron complexes identify an Fe(II) “ate” complex, [Fe(Bopa-Ph)(Ph)2]−, as the active species for the oxidative addition of alkyl halide. Experiments using radical-probe substrates and DFT computations reveal a bimetallic and radical mechanism for the oxidative addition. The kinetics of the coupling of an alkyl iodide with PhMgCl suggests that formation of the “ate” complex, rather than oxidative addition, is the turnover-determining step. This work provides insights into iron-catalyzed cross-coupling reactions of alkyl halides.

Poly[3-(5′-hexylpyridine-2′-yl)thiophene] (P3PT) (Mn = 13900, H-T content = 90%) was prepared by the regioselective Grignard metathesis reaction and the subsequent Kumada coupling polymerization. Likewise, poly(3-hexylthiophene)-b-poly[3-(5′-hexylpyridine-2′-yl)thiophene] (P3HT-b-P3PT) (Mn = 17,300) was synthesized in the one-pot and successive monomer addition protocol, in which the segment ratio was calculated to be 56 (P3HT)/44 (P3PT) base on the 1H NMR spectrum. The absorption and emission spectra of homopolymer P3PT(H), obtained by the protonation of the pyridine nitrogen, in THF/cyclohexane shifted to the longer wavelength as compared with those collected in THF, suggesting the aggregation in poor solvent. The aggregation of P3PT induced by the addition of Sc(OTf)3 could be controlled by the molar ratio of pyridine and scandium complex. The protonated block copolymer P3HT-b-P3PT(H) was also subjected to the aggregate formation. The absorption maximum in THF/CH3OH showed a bathochromic shift and the fluorescence emission was almost quenched. From the 1H NMR spectra and DLS measurements, P3HT-b-P3PT(H) forms nanometer scale aggregates particularly with the insolubility and stacking of non-ionic P3HT in alcohol as the driving force. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3383–3389

Conditions for the fast Ni-catalyzed Kumada-type cross-coupling of functionalized benzyl and allyl chlorides with alkylmagnesium reagents were discovered. The use of Ni(acac)2–TMEDA (acac = acetylacetonate, TMEDA = N,N,N′,N′-tetramethyl-1,2-ethylenediamine) allows the presence of reactive functional groups on the electrophile. On the other hand, the use of diallyl ether was shown to provide fast coupling at low temperature with a low catalyst loading. The reaction seems to follow a radical pathway.

Substituted polyacetylenes with alkylphenyl side groups and head-to-head regioregularity were prepared through anionic living polymerization of template monomers and subsequent dehydrogenation process. The template monomers have the structure of 2,3-disubstituted-1,3-butadienes prepared by palladium-catalyzed Kumada coupling of the corresponding vinyl bromides. Anionic polymerizations of the template monomers produced narrow disperse substituted polybutadiene precursors with exclusive 1,4-enchainment. The precursors were converted into soluble polyacetylene derivatives via two methods, e.g., bromination followed by elimination of HBr, and direct dehydrogenation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), both resulting in dark colored products with significant red shift in UV spectra. The obtained head-to-head polyacetylene derivatives exhibited highly thermal stability, possibly due to trans-rich and/or head-to-head chain configurations. The microstructures of the poly(2,3-dialkylphenyl butadiene...

Alkynes serve as prevalent intermediates in the synthesis of natural products and pharmaceuticals. We here described a new and efficient route to internal alkynes by Pd-catalyzed Kumada cross-coupling reactions of alkynyl halides with Grignard reagents. In the presence of Pd(PPh3)4 and N1,N1,N2,N2-tetramethylethane-1,2-diamine (TMEDA), a variety of alkynyl halides underwent Kumada coupling with Grignard reagents, giving the corresponding internal alkynes in moderate to good yields.

The controlled synthesis of branched polythiophenes via Ni-catalyzed Kumada type coupling of branched AB2 monomers prepared in situ from 5,5′′-dibromo-2,2′:3′,2′′-terthiophene (3TBr2) and 5,5′,5′′-tribromo-2,2′:3′,2′′-terthiophene (3TBr3) is presented. The access to highly branched polymer architectures with rather high molecular weights is a key benefit of this one-pot polymerization with respect to standard oxidative polymerization procedures. Our synthetic route further allows the in situ endgroup functionalization as shown exemplarily for pentene functionalized branched polythiophenes and eases thereby the access to branched polythiophenes with tailor-made properties. In particular a comparison of the optical properties allows conclusions about the architecture of the obtained materials with respect to linear and fully branched systems. Energy levels are obtained by cyclic voltammetry measurements in thin films. DFT calculations provide further guidance on the interpretation of the possible molecular structure of the polymer (i.e. branching density) in correlation with their properties.

Head-to-tail regioregular poly(4-alkylthiazole)s containing silylethers in the side-chains were synthesized via Kumada-Coupling polycondensation of “reversed” monomers, that were metalated at the sterically hindered 5-position. Their optical, electrochemical, and bulk properties have been studied, and evidence is presented that indicates the occurrence of quasi-living chain-growth behavior in the polymerization process. Two polymers, PTzTIP and PTzDIBO, featuring triisopropylsilyl and diisobutyloctadecylsilyl side chains, respectively, were prepared. PTzTIP is largely insoluble, while PTzDIBO is fully soluble in common organic solvents, including hexane, and readily gave number-averaged molecular weights exceeding 100 kDa, corresponding to an average degree of polymerization greater than 200, as determined via gel-permeation chromatography (GPC) in CHCl3. The formation of a regular head-to-tail regiostructure could be confirmed through comparison with a head-to-head–tail-to-tail regioregular polybithiazol...

The coordination behaviour of the aliphatic pincer ligand cis-1,3-bis-((di-tert-butylphosphino)methyl) cyclohexane with NiCl2 and NiBr2 was studied. Reflux in toluene afforded cyclometalated, tridentate PCsp3P pincer complexes, that were characterised by elemental analysis and NMR spectroscopy; the solid state structures were determined by X-ray diffraction showing an unusually long Ni-Br bond in the bromo complex. A preliminary account of their reactivity is reported and they were found to be unreactive towards base and hydride sources and to be poor catalysts in Kumada coupling reactions. (C) 2014 Elsevier B. V. All rights reserved.

The Grignard metathesis reaction of 2,5-dibromo-3-(5′-hexylpyridine-2′-yl)thiophene (M1) with i-PrMgCl afforded 5-bromo-2-chloromagnesio-3-(5′-hexylpyridine-2′-yl)thiophene (GM1) in the 86% selectivity. The Kumada coupling polymerization by Ni(dppp)Cl2 gave polyM1 having the roughly controlled molecular weight between 6700 and 23,400. The characterization using the gel permeation chromatographic and matrix-assisted laser desorption/ionization-time of flight mass spectra indicated the diffusion of the nickel catalyst from the propagating end. Based on the GC and 1H NMR spectra, the head-to-tail content of polyM1 was calculated to be 89%. The regioselective Grignard metathesis reactions of 5,5′-dibromo-4-(5″-hexylpyridine-2″-yl)-2,2′-bithiophene (M2) and 5,5′-dibromo-4-(5″-hexylpyrimidine-2″-yl)-2,2′-bithiophene (M3) also occurred at the ortho-position of the nitrogen heterocycle. The Kumada coupling polymerizations gave polyM2 and polyM3 having the head-to-tail content of 75% and 85%, respectively. The UV–vis spectra of polymers suggested that the polymer conformation becomes more planar in the order of polyM1 < polyM3 < polyM2, which was investigated by the theoretical calculation of the model oligomers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2166–2174

The reactions of iron chlorides with mesityl Grignard reagents and tetramethylethylenediamine (TMEDA) under catalytically relevant conditions tend to yield the homoleptic "ate" complex [Fe(mes)3 ](-) (mes=mesityl) rather than adducts of the diamine, and it is this ate complex that accounts for the catalytic activity. Both [Fe(mes)3 ](-) and the related complex [Fe(Bn)3 ](-) (Bn=benzyl) react faster with representative electrophiles than the equivalent neutral [FeR2 (TMEDA)] complexes. Fe(I) species are observed under catalytically relevant conditions with both benzyl and smaller aryl Grignard reagents. The X-ray structures of [Fe(Bn)3 ](-) and [Fe(Bn)4 ](-) were determined; [Fe(Bn)4 ](-) is the first homoleptic σ-hydrocarbyl Fe(III) complex that has been structurally characterized.

Externally initiated living catalyst-transfer polymerization based on Ni(II)-catalyzed Kumada coupling of aromatic halogen-substituted Grignard monomers is an established and highly efficient method for the controlled preparation of conjugated polymers such as polythiophenes and poly(p-phenylenes). In this contribution, we report a simple preparation of external catalytic initiators for such a polymerization based on oxidative addition between a readily available Ni(0) complex Ni(dppp)2 (where dppp is 1,3-bis(diphenylphosphino)propane) and various aryl halides. As a direct challenge to previous reports and established opinion that such a reaction would be impossible, this clean and efficient oxidative addition enables simple preparation of highly reactive catalytic initiators for the catalyst-transfer polymerization. In particular, we demonstrated that polymerization of 5-halo-2-thienylmagnesium monomers initiated by these catalysts produced highly regioregular, defect-free polythiophenes and block copoly...