Ligated Palladium Complexes Research Articles

Thermally Stable P-Chiral Supramolecular Phosphines, their Self-Assembly and Implication in Rh-Catalyzed Asymmetric Hydrogenation.

P-chiral supramolecular phosphine ligands are crucial for asymmetric transformations, but their synthesis is tedious. We report a one-step synthesis of thermally stable P-chiral supramolecular phosphines and their performance in the asymmetric hydrogenation of functionalized alkenes. A rational designing and synthesis of (R, R)-QuinoxP* ligated palladium complex (Pd-2) in excellent yield is reported. This Pd-2 catalyzed a direct P-C coupling of 2,3-dihydro-1-H-phosphindole (A1)/1,2,3,4-tetrahydrophosphindoline (A2) with 1-(3-iodophenyl)urea (B1)/2-iodo /6-hydroxy pyridine (B2) and,produced corresponding ligands L1-L3. The P-C coupling between A1 and B2 produced 6-(2,3-dihydro-1H-phosphindol-1-yl)pyridine-2(1H)-one (L2) with an excellent enantiomeric excess of up to 99 %. L2 was found to be remarkably stable even at 150 °C and did not oxidize/hydrolyze for at least 24 hours in open air. Such thermal stability and an impediment to oxidation are unprecedented. L2 self-assembled and produced L2-C1 (Pt), L2-C2(Pd), and L2-C3(Rh) assemblies. The utility of the self-assembled P-chiral ligand was demonstrated in the Rh-catalyzed asymmetric hydrogenation (AH) of functionalized olefins. The L2-C3 catalyzed AH of functionalized alkenes and delivered chiral products with excellent enantioselectivity of >99 %. A small library of 16 substrates was subjected to AH using L2-C3 to produce chiral compounds with excellent conversion and ee.

Reactions of POCOP pincer palladium benzylthiolate complexes with BH3·THF: Isolation and characterization of unstable POCOP-Pd(η1-HBH3) complexes

In order to explore the boron mediated C-S bond activation of the thiolate ligand in transition metal thiolate complexes, several bis(phosphinite) (POCOP) pincer ligated palladium complexes bearing a benzylthiolate or mercapto auxiliary ligand, [2,6-(R2PO)2C6H3]PdY (Y = SCH2Ph, R = tBu, 1a, iPr, 1b; Y = SH, R = tBu, 2a, iPr, 2b), were synthesized and fully characterized by multinuclear NMR, FTIR, X-ray crystallography and elemental analysis. The reactions of complexes 1a-b or 2a-b with BH3·THF at room temperature produced exclusively the corresponding tetrahydroborate complexes, [2,6-(R2PO)2C6H3]Pd(η1-HBH3) (R = tBu, 3a; iPr, 3b), through Pd-S bond cleavage. Complexes 3a and 3b are air/moisture sensitive and thermally unstable. X-ray crystallography and FTIR spectra supported a η1-HBH3 monodentate coordination mode for the BH4 ligand in complexes 3a and 3b. The boron mediated C-S bond cleavage was not observed in the reactions of complexes 1a and 1b with BH3·THF perhaps due to the relatively weak Pd-S bond.

A Highly Efficient and Inexpensive Palladium-Salen Complex for Room Temperature Suzuki-Miyaura Reaction

The palladium catalysed Suzuki-Miyaura cross-coupling reaction is one of the most important strategy for the synthesis of biaryls, which are building blocks of numerous vital organic compounds used in pharmaceuticals, fineand agro-chemical industries. The Suzuki-Miyaura reaction relies on the cross-coupling between aryl halides and easily accessible organoborons in presence of catalytic amount of palladium-based salts or complexes. Many ideal developments have been attained till now to improve the efficiency of this reaction and to minimize the issues related to environment pollution. Conventionally, the C-C bond formation reactions are performed using phosphine ligated palladium complexes, which show excellent activity in this transformation. However most of the phosphine ligands are toxic and unstable in air or moisture, and are also known to increase the possibility of side reactions, thereby lowering the yield of desired cross-coupled products. Recently, different nitrogen based ligands such as N-heterocyclic carbenes, amines, oximes, amides and their co-ordination with palladium have attracted considerable attention for SuzukiMiyaura Cross-Coupling reaction with potentiality to overcome some of drawbacks face by traditional phosphine ligands. So attention has been given to design catalyst containing chelating multi-dentate Schiff-base ligands. The water insoluble property of these ligands restricts their use upto undesirable organic solvents such as DMF, toluene, THF etc. Thus, to practice the principles of green chemistry, researchers have developed efficient catalytic protocols to conduct Suzuki-Miyaura cross-coupling reaction under easily available and non-toxic aqueous media. Moreover, there has been a tremendous rise in interest for employing aryl chloride as substrates for Suzuki-Miyaura cross-coupling, as they are easily accessible economical compared to their bromide and iodide counterparts. Herein we wish to report a facile and efficient room temperature Suzuki-Miyaura cross-coupling reaction strategy using a unique Palladium salen complex as catalyst in greener solvent. It is notable to mention that these multidanted ligands, due to the presence of multiple bonding sites is expected to increase the steric congestion around the metal centre which is considered to be the vital step facilitating the reductive elimination step in the cross-coupling mechanism. Initially, we have synthesised and characterized two novel palladium complexes with a previously reported tetradentate Schiff-base ligand N,N'-bis(salicylidene)-phenylmethanediamine (L1) and its reduced form (L2), ligand (Scheme 1). The new palladium complexes C1 and C2 were prepared by refluxing methanolic solution of the corresponding tetradentate ligands L1 and L2 with equimolar amount of palladium acetate. The newly synthesized complexes C1 and C2 were characterized by elemental analysis, IR, Hand CNMR and mass spectral data. The spectral analysis of prepared complexes corroborates with the reported one. The value of elemental analyses and the appearances of molecular ion peaks in ESI-mass spectra of complexes C1 and C2 support their proposed composition. In the FTIR spectra of complexes, the value for ν (C=N) stretching vibration of the free ligand at about 1617 cm gets considerably shifted to lower frequency at 1606 cm after complexation, implying the coordination of imine nitrogen with palladium owing to the donation of electrons from nitrogen atom to the empty d-orbitals of the metal. This signal was absent in ligand L2 and in its corresponding complex C2, indicating the successful reduction of C=N bond. In complex C2 the band at 3160 cm due to the ν (NH) stretching frequency of the L2 undergoes a considerable shift towards 3080 cm after complexation. The complex C2 has been shifted about 80 cm, indicating strong coordination of nitrogen to palladium metal atom. The v (O-H) signal pertaining to free ligands (3425 cm in FTIR and 13.5 ppm in H NMR) was found to be absent in both complex C1 and C2, supporting the deprotonation of phenolic moiety and

Palladium(II)-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions

A series of general and selective Pd(II)-catalyzed Heck reactions were investigated under mild reaction conditions. The first protocol has been developed employing an imidazole-based secondary phosphine oxide (SPO) ligated palladium complex (6) as a precatalyst. The catalytic coupling of aryl halides and olefins led to the formation of the corresponding coupled products in excellent yields. A variety of substrates, both electron-rich and electron-poor olefins, were converted smoothly to the targeted products in high yields. Compared with the existing approaches employing SPO–Pd complexes in a Heck reaction, the current strategy features mild reaction conditions and broad substrate scope. Furthermore, we described the coupling of arylboronic acids with olefins, which were catalyzed by Pd(OAc)2 and employed N-bromosuccinimide as an additive under ambient conditions. The resulted biaryls have been obtained in moderate to good yields.

ChemInform Abstract: Thiopseudourea Ligated Palladium Complexes: Synthesis, Characterization and Application as Catalysts for Suzuki—Miyaura, Sonogashira, Heck and Hiyama Reactions.

AbstractSix palladium complexes of type (I) are prepared in 4 steps from commercially available benzoyl chlorides.

Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide–Palladium Complexes

The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.

Studies on Suzuki‐Miyaura Reactions Catalyzed by Ferrocenyl or Cobaltocenyl Phosphines Ligated Palladium Complexes

AbstractDFT studies on several dppf‐ and dppc‐derived bidentate phosphines ligated palladium complexes catalyzed Suzuki‐Miyaura coupling reactions were pursued. The catalytic reactions employing ligands, having two phosphine biting sites on different cyclpentadienyl or cyclobutadiene rings, such as 1,1′‐dmpf or 1,1′‐dmpc, have been verified to be energetically more favorable than those on the same ring provided that tetra‐coordinated palladium conformations for all transition states and intermediates are maintained. Apart from the purpose of storage, the application of phosphinous acid (R2P(OH)) in Suzuki‐Miyaura reaction is inferior to tertiary phosphine (R3P).

Thiopseudourea ligated palladium complexes: synthesis, characterization and application as catalysts for Suzuki–Miyaura, Sonogashira, Heck and Hiyama reactions

A series of new non-phosphine 1-(2-picolyl)-3-benzoylsubstituted-2-benzyl-2-thiopseudourea ligands 2a–2f have been synthesized in two steps from commercially available benzoyl chlorides. Treatment of these ligands with Pd(OAc)2 in a 1 : 1 molar ratio in dichloromethane (DCM) at room temperature provided convenient access to the corresponding N,N,O-tridentate palladium(II) complexes [Pd(OAc){ArCONHC(N(CH2Py)}SCH2C6H5] (Ar = C6H5 (3a); 4-F-C6H4 (3b); 4-Br-C6H4 (3c); 4-I-C6H4 (3d); 4-Me-C6H4 (3e); 3,4,5-(OMe)3-C6H2 (3f)) in almost quantitative yields. The new ligands and their palladium complexes were characterized by NMR, IR, ESIMS, and HRMS analysis. The molecular structure of complex 3c has been determined by X-ray single-crystal diffraction. These Pd(II) complexes have been used as catalysts for the Suzuki–Miyaura, Sonogashira, Heck and Hiyama cross-coupling reactions.

Facile Preparation of Aryl Sulfides Using Palladium Catalysis under Mild Conditions

A convenient method for C-S cross-coupling of aryl bromides with various thiols has been developed that involves the use of a 1,1′-bis(diphenylphosphino)ferrocene (DPPF)-ligated palladium complex with N,N-diisopropylethylamine (DIPEA) as the base. This coupling is tolerant of a wide range of functional groups, including hydroxy, amino, cyano, nitro, formyl, and carboxyl groups.

Preparation of a cobalt-containing P,N-bidentate ligand ligated palladium complex: Its applications in amination and Suzuki cross-coupling reactions

Abstract A cobalt-containing P,N-ligand, alkyne-bridged dicobalt phosphine [(μ-PPh2CH2PPh2)Co2(CO)4(μ,η-Me2NCH2C CP(Cy)2)] (4c), was prepared from the reaction of Me2NCH2C CPR2 (2c) with a dppm-bridged dicobalt complex [Co2(CO)6(μ-P,P-PPh2CH2PPh2)] (3). Further reaction of 4c with Pd(COD)Cl2 gave a 4c-chelated palladium dichloride complex (μ-PPh2CH2PPh2)Co2(CO)4(μ,η-Cy2PC CCH2NMe2)PdCl2 (5c). Compound 5c was characterized by spectroscopic methods and crystal structure of 5c was determined by single-crystal X-ray diffraction techniques. It shows that 4c is an authentic cobalt-containing P,N-bidentate ligand. Amination and Suzuki reactions employing either a 4c/palladium salt system or an isolated 5c as the catalytic precursor led to satisfactory results.

Preparation of monodentate phosphinite ligands: their applications in palladium catalyzed Suzuki reactions

Two phosphinites 2,6-OMe, 4-Me, 1-OPR 2C 6H 2 ( 5a: R=Ph; 5b: R= t Bu) were prepared in good yields. Two methoxy groups are placed on the 2,6 positions of the phosphinites deliberately thereby to avoid a plausible orthometallation process while coordinating toward palladium metal. Further reaction of 5a with PdCl 2 in the ratio of 2:1 and 1:1 gave 5a ligated palladium complexes {( 5a)PdCl(μ-Cl)} 2 7a and {( 5a) 2PdCl 2} 8a, respectively. As revealed from their crystal structures, the former is a dimeric complex with anticipated molecular arrangement; nevertheless, the latter is a monomeric complex with unexpected, energetically unfavorable cis form. By contrast, only dimeric form was observed from the reaction of 5b with PdCl 2. It is believed that the bulky substituents, t Bu, on 5b prevent the formation of a monomeric complex in cis form. Fair to good efficiencies were observed for the Suzuki–Miyaura cross-coupling reactions employed in situ-prepared 5/Pd(OAc) 2 as the catalytic precursor.

ChemInform Abstract: Weakly Ligated Palladium Complexes PdCl2(RCN)2 in Piperidine: Versatile Catalysts for Sonogashira Reaction of Vinyl Chlorides at Room Temperature.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Weakly ligated palladium complexes PdCl 2(RCN) 2 in piperidine: versatile catalysts for Sonogashira reaction of vinyl chlorides at room temperature

Copper iodide and weakly ligated palladium complexes PdCl 2(RCN) 2 (R=Ph, Me) catalyzed efficiently the coupling reaction of vinyl chlorides with 1-alkynes in the presence of piperidine to give the corresponding conjugated enynes in good to excellent yields. The reaction takes place rapidly and cleanly at room temperature. Application to the synthesis of terbinafine which exhibits strong antimycotic activity has been realized.

A two-step synthesis of terbinafine

An efficient and high yielding synthesis of terbinafine 1a and amino enyne derivatives 1b-f is described from amino vinyl chlorides 2a-b and 1-alkynes in the presence of a weak ligated palladium complex: PdCl 2(PhCN) 2 in piperidine.