The development of palladium catalysts for CC and Cheteroatom bond forming reactions of aryl chloride substrates

Highly Efficient Detection of Pd2+ in Aqueous Medium by an Elusive Mn(II) Coordination Polymer

Herein, we report the synthesis of a Mn(II)-based coordination polymer (CP); and its structure, phase consistency and thermal stability have been established by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD) and thermalgravimetric analysis (TGA) respectively. This is the first example of paramgnetic Mn(II)-based CP that acts as pH-dependent emitting material [λem=525 nm (pH=2.0-4.0) and 450 nm (pH=5.0-12.0)]. Its emission is quenched by Pd2+ in aqueous medium in presence of other thirteen cations with reasonably low pH-dependent limits of detection (LODs) [21.178 ppb (pH=3), 15.005 ppb (pH=7.0) and 59.940 ppb (pH=10.0)] as described by well-established mechanism. Therefore, urgency of such stable sensor remains high in regard to the environmental pollution.

Double Direct C-H Bond Arylation of Thiophenes with Aryl Chlorides Catalyzed by the N-Heterocyclic Carbene-PdCl2-1-methylimidazole Complex

With the combination of the N-heterocyclic carbene-PdCl2-1-methylimidazole complex and Cu2O, we succeeded in the first example of double direct C-H bond arylation reactions between thiophenes and aryl chlorides, giving the desired 2,5-diarylated thiophenes in moderate to high yields under suitable conditions, consistent with the density functional theory calculations.

Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde

The polynuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(μ-OAc)}]2 (I) reacts with tbbpy (4,4'-di-tert-butyl-2,2'-bipyridine) and TlOTf to form the dinuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(tbbpy)}2] (1). The hydrolysis of I with acetic acid in a 5:1 acetone/water mixture, in the presence of two equivalents of tbbpy and excess NaX (X = Br, I), yields the dipalladated terephthalaldehyde complexes [C6H2{PdX(tbbpy)}2-1,4-(CHO)2-2,5] [X = Br (2a), X = I (2b)], which are the first fully characterized complexes of this type. The reaction of 2a,b with CO results in the insertion of CO into both aryl-Pd bonds, forming [C6H2{C(O){PdX(tbbpy)}}2-1,4-(CHO)2-2,5] [X = Br (3a), X = I (3b)], which are the first examples of complexes with CO inserted into two separate aryl-metal bonds involving the same ligand. The bromo complex 2a reacts with excess XylNC in acetone, causing the precipitation of the dinuclear complex 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(=NXyl)-[PdBr(CNXyl)2]} (4), which is the result of the insertion of three molecules of the isocyanide into each aryl-Pd bond and the nucleophilic attack of one of them at each formyl group. When complex 4 reacts with TlOTf and residual water in 1,2-dichloroethane at 70 °C, depalladation occurs, and the organic compound 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c']dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(O)NHXyl} (5) can be isolated. The crystal structures of 1·4CHCl3, 4·2CH2Cl2·3hexane, and 5·2CDCl3 have been determined by X-ray crystallography.

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Nitron-derivative-based palladium carbene complexes: structural characterization, theoretical calculations, and catalytic applications in the Mizoroki-Heck coupling reaction

New palladium(0) and palladium(ii) complexes with N-heterocyclic carbene (NHC) ligands derived from nitron and its derivatives were synthesized. The structures of most of these complexes were established by single-crystal X-ray diffraction studies. Among the new complexes, the palladium complex with a monodentate NHC ligand derived from nitron demonstrated the highest efficacy as a catalyst precursor in the Mizoroki-Heck coupling reaction of aryl chlorides with alkenes. Theoretical calculations provide valuable insights into the electronic parameters of both the ligands and the palladium complexes, highlighting the significance of a robust Pd-C bond and the π-accepting property of the NHC ligand in achieving enhanced catalytic activity. Notably, catalyst activation occurred much more rapidly with the preformed palladium(0) complex compared to its palladium(ii) counterpart.

Synthesis of mono-, di- and tripalladated 1,3,5-benzenetristyryl complexes. CO insertion to give a dipalladated indenone

The tribrominated arenes 1,3,5-C₆(E-CHCHAr)₃Br₃ (Ar = Ph, (I), p-To (I')), add oxidatively to [Pd(dba)₂] ([Pd₂(dba)₃]·dba) in the presence of two equivalents of a phosphine (PPh₃ or PMe₂Ph) to form the monopalladated complexes trans-[Pd{C₆(E-CHCHAr)₃Br₂}Br(L)₂] (Ar = Ph, L = PPh₃ (1a), Ar = p-To, L = PPh₃ (1a'), Ar = Ph, L = PMe₂Ph (1b)), while the reaction in a 1 : 2 : 4 arene : Pd : PMe₂Ph molar ratio affords the dipalladated complex [{trans-PdBr(PMe₂Ph)₂}₂{μ₂-C₆(E-CHCHPh)₃Br}] (2b). Both I and I' add oxidatively to 3 equivalents of [Pd(dba)₂] in the presence of the chelating N-donor ligand tmeda (N,N,N',N'-tetramethylethylenediamine) to form the tripalladated complexes [{PdBr(tmeda)}₃{μ₃-C₆(E-CHCHAr)₃}] (Ar = Ph, (3c), p-To (3c')). Complex 3c reacts with PMe₃ to form [{trans-PdBr(PMe₃)₂}₃{μ₃-C₆(E-CHCHPh)₃}] (3d). Compound 3c also reacts with CO to give the novel dipalladated indenone [2-Ph-4,6-{PdBr(tmeda)}₂-5,7-(E-CHCHPh)₂-inden-1-one] (4). The crystal structures of 1a' and 1b were determined by X-ray diffraction studies.

A Dual Functional 2D MOF Exhibiting Rare Photosalient Effect as well as Selective Pd(II) Sensing in Aqueous Medium

A Zn(II) based two-dimensional metal-organic framework (2D MOF) [Zn₂(suc)₂(4-nvp)₂] (1) [H₂suc = succinic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] exhibits a "photosalient effect" under UV light as well as sunlight along with the release of a stereoselective cyclobutane ligand, 1,3-bis(4'-pyridyl)-2,4-bis(naphthyl)cyclobutane (rctt-4-pncb). Photolysis of in situ generated MOF in solution also leads to the formation of rctt-4-pncb crystals. Interestingly, compound 1 shows a high selectivity for Pd(II) sensing in aqueous medium.

Nickel(II) complexes containing tridentate ONCi ligands (i = abnormal N-heterocyclic carbene donors) and their catalytic application in Suzuki-Miyaura coupling reaction

New nickel complexes with tridentate phenoxy-amidate-aNHC donor groups were synthesized from the reactions between nickel acetate and imidazolium ligand precursors in net pyridine. An unusual degradation pathway was observed, leading to imidazole derivatives occupying the fourth coordination sites in these square planar complexes. A new imidazole-coordinated nickel complex was found to be efficient in catalyzing Suzuki-Miyaura cross-coupling with aryl chlorides under 3 mol% of catalyst loading. The catalytic activities were superior to those of its reported normal NHC counterpart. Instead of the common procedure of using additional phosphine, the addition of IMes·HCl significantly enhances the product yields of the catalytic reaction.

Dihydroquinazolinones as adaptative C(sp3) handles in arylations and alkylations via dual catalytic C-C bond-functionalization

C–C bond forming cross-couplings are convenient technologies for the construction of functional molecules. Consequently, there is continual interest in approaches that can render traditionally inert functionality as cross-coupling partners, included in this are ketones which are widely-available commodity chemicals and easy to install synthetic handles. Herein, we describe a dual catalytic strategy that utilizes dihydroquinazolinones derived from ketone congeners as adaptative one-electron handles for forging C(sp³) architectures via α C–C cleavage with aryl and alkyl bromides. Our approach is achieved by combining the flexibility and modularity of nickel catalysis with the propensity of photoredox events for generating open-shell reaction intermediates. This method is distinguished by its wide scope and broad application profile––including chemical diversification of advanced intermediates––, providing a catalytic technique complementary to existing C(sp³) cross-coupling reactions that operates within the C–C bond-functionalization arena.

Although derived from feedstock chemicals and therefore in principle abundant, ketones are not widely used as cross-coupling partners in organic synthesis. Herein, the authors use ketone derivatives as one-electron handles for forging C(sp3) architectures via dual photo- and nickel catalysis.

Sodium silylsilanolate enables nickel-catalysed silylation of aryl chlorides

Structurally diverse aryl chlorides were silylated with sodium silylsilanolate reagents in the presence of a Ni(cod)2 catalyst complexed with a phosphine ligand; PMe2Ph for electron-rich substrates, and PCy2Ph for electron-deficient ones. The mild reaction conditions allowed the silylation of various aryl chlorides including functionalised drug molecules.

Comparative study of aryl halides in Pd-mediated reactions: key factors beyond the oxidative addition step

The comparative experimental study of Ar–X (X = Cl, Br, I) reactivity and analysis reported herein suggest that oxidative addition cannot be considered the sole reason of the observed low reactivity of aryl chlorides.

Sunlight assisted SCSC dimerization of a 1D coordination polymer impacts the selectivity of Pd(II) sensing in water

A one-dimensional coordination polymer (1D CP) [Cd(4-nvp)2(5-ssa)]·(4-nvp) (1) [4-nvp = 4-(1-naphthylvinyl)pyridine and 5-ssa = 5-sulfosalicylic acid] undergoes topochemical [2+2] cycloaddition by sunlight irradiation to generate a two-dimensional (2D) CP [Cd(rctt-4-pncb)0.5(4-nvp)(5-ssa)]·(4-nvp) (1') [rctt-4-pncb = 1,3-bis(4'-pyridyl)-2,4-bis(naphthyl)cyclobutane] in a single-crystal to single-crystal manner. Interestingly, 1' can be reverted back to 1 by heating and both the CPs selectively recognize Pd2+ in aqueous medium; however, the limit of detection is improved after photodimerization.

Pd-catalyzed asymmetric Suzuki-Miyaura coupling reactions for the synthesis of chiral biaryl compounds with a large steric substituent at the 2-position

Pd-catalyzed asymmetric Suzuki-Miyaura couplings of 3-methyl-2-bromophenylamides, 3-methyl-2-bromo-1-nitrobenzene and 1-naphthaleneboronic acids have been successfully developed and the corresponding axially chiral biaryl compounds were obtained in very high yields (up to 99%) with good enantioselectivities (up to 88% ee) under mild conditions. The chiral-bridged biphenyl monophosphine ligands developed by our group exhibit significant superiority to the naphthyl counterpart MOP in both reactivity and enantioselectivity control. The large steric hindrance from π-conjugated ortho-substituents of the bromobenzene substrates and the Pd···O interaction between carbonyl and palladium seem essential to achieve high enantioselectivity.

Selectivity in carbon–carbon coupling reactions at palladium(IV) and platinum(IV)

The isomerization and reductive elimination reactions from octahedral organometallic complexes of palladium(IV) and platinum(IV) usually occur through five-coordinate intermediates that cannot be directly detected. This paper reports a computational study of five-coordinate complexes of formulae [PtMe3(bipy)]+, [PtMe2Ph(bipy)]+, and [PtMe(CH2CMe2C6H4)(bipy)]+ (M = Pd or Pt, bipy = 2,2′-bipyridine), particularly with respect to reactivity and selectivity in reductive elimination. All of the complexes are predicted to have square pyramidal structures with the bipy and two R groups in the equatorial positions and one R group in the axial position, and axial–equatorial exchange occurs by a pairwise mechanism, with the transition state having a pinched trigonal bipyramidal (PTBP) stereochemistry, with one nitrogen and two R groups in the trigonal plane. The activation energy for isomerization is lower than that for reductive elimination in all cases. For the complexes [MMe2Ph(bipy)]+, the activation energies for reductive elimination with Me–Me or Me–Ph coupling are similar. For the complexes [MMe(CH2CMe2C6H4)(bipy)]+, the reductive elimination with Me–C6H4 bond formation from the isomer with the methyl group in the axial position is predicted and is attributed to it having the best conformation of the Me and C6H4 groups for C–C bond formation. In all cases, the selectivity for reductive elimination is similar for M = Pd or Pt, but reactivity is higher for M = Pd. The relevance of this work to selectivity in catalysis is discussed.

Aminophosphine Palladium Pincer-Catalyzed Carbonylative Sonogashira and Suzuki-Miyaura Cross-Coupling with High Catalytic Turnovers

This work documents the first palladium pincer complex-catalyzed carbonylative Sonogashira (CS) and carbonylative Suzuki-Miyaura (CSM) cross-coupling. Compared to previous protocols, which employ hazardous and toxic solvents, the aminophosphine pincer complex {[C₆H₃-2,6-(NHP{piperidinyl}₂)₂]Pd(Cl)} (III) catalyzes both the cross-coupling reactions in propylene carbonate, an eco-friendly and sustainable polar aprotic solvent. Advantageously, employing III allows the CS cross-coupling to be carried out at a palladium loading of 10^-4 mol % and the CSM cross-coupling to be carried out at 10^-6 mol %, thus resulting in catalytic turnovers of 10⁵ and 10⁷, respectively. Relative comparison of the pincer complex with conventional palladium precursors Pd(OAc)₂ and PdCl₂(PPh₃)₂ shows the efficiency and robustness of the pincer complex in effecting higher catalytic activity at low palladium loadings.

Experimental and theoretical investigations of cyclometalated ruthenium(ii) complex containing CCC-pincer and anti-inflammatory drugs as ligands: synthesis, characterization, inhibition of cyclooxygenase and in vitro cytotoxicity activities in various cancer cell lines

The cyclometalated ruthenium(ii) complex was synthesized and studied for cytotoxicity. The interaction of Ru(ii) complex with COX-2 was studied by experimental and molecular docking.

Pd-catalyzed synthesis of α,β-unsaturated ketones by carbonylation of vinyl triflates and nonaflates

A general and highly chemoselective Pd-catalyzed protocol for the synthesis of α,β-unsaturated ketones by carbonylation of vinyl triflates and nonaflates is presented. Applying the specific monophosphine ligand cataCXium® A, the synthesis of various vinyl ketones as well as carbonylated natural product derivatives proceeds in good yields.

Palladium/phosphorus-functionalized porous organic polymer with tunable surface wettability for water-mediated Suzuki–Miyaura coupling reaction

A series of phosphorus-functionalized porous organic polymers supported palladium catalysts with tunable surface wettability were successfully prepared using an easy copolymerization and successive immobilization method. The obtained polymers were carefully characterized by many physicochemical methods. Characterization results suggested that the prepared materials featured hierarchically porous structures, high pore volumes, tunable surface wettability and strong electron-donating ability towards palladium species. We demonstrated the use of these solid catalysts for water-mediated Suzuki–Miyaura coupling reactions. It was found that the surface wettability of the prepared catalysts has an important influence on their catalytic activities. The optimal catalyst, which has excellent amphipathicity and relatively high phosphorus concentration, displayed superior catalytic activity compared to the other catalysts. Under ambient conditions, a variety of aryl chlorides can be efficiently transformed to biaryls in high yields. Moreover, the catalyst could be easily recovered and reused at least six times.

A palladium/phosphorus-functionalized porous organic polymer with tunable surface wettability was successfully prepared. The catalyst displayed high catalytic activity for the water-mediated Suzuki–Miyaura coupling reaction of aryl chlorides.

Phosphino-Triazole Ligands for Palladium-Catalyzed Cross-Coupling

Twelve 1,5-disubtituted and fourteen 5-substituted 1,2,3-triazole derivatives bearing diaryl or dialkyl phosphines at the 5-position were synthesized and used as ligands for palladium-catalyzed Suzuki-Miyaura cross-coupling reactions. Bulky substrates were tested, and lead-like product formation was demonstrated. The online tool SambVca2.0 was used to assess steric parameters of ligands and preliminary buried volume determination using XRD-obtained data in a small number of cases proved to be informative. Two modeling approaches were compared for the determination of the buried volume of ligands where XRD data was not available. An approach with imposed steric restrictions was found to be superior in leading to buried volume determinations that closely correlate with observed reaction conversions. The online tool LLAMA was used to determine lead-likeness of potential Suzuki-Miyaura cross-coupling products, from which 10 of the most lead-like were successfully synthesized. Thus, confirming these readily accessible triazole-containing phosphines as highly suitable ligands for reaction screening and optimization in drug discovery campaigns.

Pd/Pt metallacyclopropa[60]fullerene complexes bearing versatile phosphorous ylide ligands; a comprehensive multi-spectroscopic, electrochemistry, theoretical and catalytic studies

The synthesis of new Pd/Pt metallacyclopropa[60]fullerene complexes containing unsymmetrical phosphorus ylides [Ph₂P(CH₂)_nPPh₂ = C(H)C(O)C₆H₄-p-OMe] (n = 1, (Y¹); n = 2, (Y²)) has been reported. The synthesized complexes exhibit different structures, including two P,C- chelated [(η²-C₆₀)Pd(κ²-Y¹)] (1) and [(η²-C₆₀)Pt(κ²-Y¹)] (2) complexes and two P-coordinated [(η²-C₆₀)Pd(Y²)₂] (3) and [(η²-C₆₀)Pt(Y²)₂] (4) complexes with chain structures. Characterization of all compounds was performed by multi-neclear NMR spectroscopies (¹H, ¹³C and ³¹P NMR) and other conventional techniques such as IR, UV-Vis, SEM and cyclic voltammetry (CV) analyses. In this regard, the presence of all characteristic chemical shifts in the IR and NMR spectra proposed the formation of desired products. Also, theoretical studies were used to investigate the nature of metal-ligands in all complexes. In addition, a comparison between the catalytic activity of Pd complexes 1 and 3 was evaluated in the Suzuki-Miyaura reaction of various aryl chlorides with phenylboronic acid, which revealed a meaningful difference between the catalytic activity of complexes 1 and 3.

Preparation and Reactivation of Heterogeneous Palladium Catalysts and Applications in Sonogashira, Suzuki, and Heck Reactions in Aqueous Media

A new type of heterogeneous palladium catalyst, PdMgAl-LDH, was facilely prepared by the immobilization of Pd2+ species in the layers of a Mg-Al layered double hydroxide (LDH) with co-precipitation, and then fully characterized by using powder XRD, thermogravimetric differential thermal analysis, TEM, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. These catalysts can efficiently catalyze copper-free Sonogashira, Suzuki and Heck coupling reactions of various aryl iodides, bromides, and chlorides in aqueous media under phosphine-ligand- and organic-base-free conditions. These catalysts feature easy recovery through simple filtration and could be reused at least six times without a marked loss in activity. Notably, they can be facilely reactivated by a combination of nitrolysis with co-precipitation. The basic LDH skeletons could effectively stabilize the Pd0 species created in situ and donate electron density to the Pd0 center to facilitate the oxidative addition of aryl halides, thus the PdMgAl-LDH catalysts are stable during catalysis.

Glass wool: a novel support for heterogeneous catalysis

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material - glass wool - can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp3-Csp3 couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.