Successive Replacement of Halogen Atoms in 4,6-Dihaloquinolines in Cross-coupling Reactions with Arylboronic Acids Catalyzed by Palladium and Nickel Complexes

Conditions were found where in 6-halo-4-quinolines (halogen = iodine, bromine, or chlorine) the halogen atoms were replaced in succession by similar or different aryl groups in cross-coupling reactions with arylboric acids catalyzed by palladium and nickel complexes. Basing on successive Suzuki reaction a convenient procedure was developed for preparation of diarylquinolines that did not require isolation of the intermediate monoarylation product and afforded almost quantitative yields of diarylquinolines.     

The CO/PC analogy in coordination chemistry and catalysis

This short account summarizes recent results obtained in the coordination chemistry of phosphinines and emphasizes their analogy with CO ligands. Reduced complexes can be easily assembled through the reaction of reduced 2,2′-biphosphinine dianions with transition metal fragments. Theoretical calculations were performed to establish the oxidation state of the metal in these complexes. Though many reduced complexes are available, phosphinines proved to be too sensitive toward nucleophiles to be used as efficient ligands in most catalytic processes. However, the high electrophilicity of the phosphorus atom can be exploited to synthesize phosphacylohexadienyl anions which exhibit a surprising coordination chemistry. When phosphino sulfide groups are incorporated as ancillary tridentate anionic SPS ligands can be easily produced. These ligands can bind different transition metal fragments such as M-X (M = group 10 metal, X = halogen), Rh-L (L = 2 electron donor ligand), Cu-X and Au-X (X = halogen). Palladium(II) complexes proved to be active catalyst in the Miyaura cross-coupling reaction. Bidentate anionic PS ligands were also synthesized following a similar approach. Their Pd(II) (allyl) derivatives showed a very good activity in the Suzuki catalyzed cross-coupling process that allows the synthesis of biphenyl derivatives through the reaction of phenylboronic acid with bromoarenes.     

Small cobaltacarborane clusters in synthesis. Peralkylation, perhalogenation, and macrocycle construction

Methods are described for achieving stepwise replacement of all BH terminal hydrogens in CoC₂B₄ clusters with halogen or alkyl groups, leading to complexes such as Cp*Co(2,3-Et₂C₂B₄X₄) (X=Me or I) and Cp*Co(2,3-Et₂C₂B₄IMe₂[O₃SCF₃]). Building on earlier work on B-functionalization of small metallacarboranes via metal-catalyzed cross-coupling, two- and three-dimensional macrocycles containing four to six metal centers have been constructed systematically from monomeric precursor complexes.     

Kumada coupling of aryl, heteroaryl, and vinyl chlorides catalyzed by amido pincer nickel complexes

A series of amido pincer complexes of nickel were examined for their catalysis in the Kumada cross-coupling reaction. The P,N,O-pincer nickel complexes tested are active catalysts for the cross-coupling of aryl, heteroaryl, and vinyl chlorides with aryl Grignard reagents. The reactions can proceed at room temperature and tolerate functional groups in aryl chlorides with the aid of LiCl and ZnCl(2) additives.     

Suzuki-Miyaura cross-coupling reactions of aryl tellurides with potassium aryltrifluoroborate salts

[reaction: see text] Palladium(0)-catalyzed cross-coupling between potassium aryltrifluoroborate salts and aryl tellurides proceeds readily to afford the desired biaryls in good to excellent yield. The reaction seems to be unaffected by the presence of electron-withdrawing or electron-donating substituents in both the potassium aryltrifluoroborate salts and aryl tellurides partners. Biaryls containing a variety of functional groups can be prepared. A chemoselectivity study was also carried out using aryl tellurides bearing halogen atoms in the same compound. In addition, this new version of the Suzuki-Miyaura cross-coupling reaction was monitored by electrospray ionization mass spectrometry where some reaction intermediates were detected and analyzed.     

Dual effect of halides in the Stille reaction: in situ halide metathesis and catalyst stabilization

Halide anions can increase or decrease the transmetallation rate of the Stille reaction through in situ halide metathesis. Although the influence of the halogen present in oxidative addition complexes on the transmetallation rate with organostannanes was already known, the application of in situ halide metathesis to accelerate cross-coupling reactions with organometallic reagents is not described in the literature yet. In addition a second unprecedented role of halides was discovered. Halide anions stabilize the [Pd(0)(L)(2)] catalyst in Stille reactions, by means of [Pd(0)X(L)(2)](-) formation (X=Cl, I), hereby preventing its leaching from the catalytic cycle. Both arene (iodobenzene) and azaheteroarene (2-halopyridine, halopyrazine, 2-halopyrimidine) substrates were used.     

Synthesis of ortho substituted arylboronic esters by in situ trapping of unstable lithio intermediates

[reaction: see text] Ortho lithiation-in situ boration using lithium 2,2,6,6-tetramethylpiperidide (LTMP) in combination with triisopropylborate (B(OiPr)(3)) is a highly efficient and experimentally straightforward process for the preparation of ortho substituted arylboronic esters. The mild reaction conditions allow the presence of functionalities such as ester or cyano groups or halogen substituents that are usually not compatible with the conditions used in directed ortho metalation of arenes. The arylboronic esters underwent Suzuki-type cross-coupling with a range of aryl halides, furnishing biaryls in 53-94% yield.     

S···X halogen bonds and H···X hydrogen bonds in H2CS-XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes: cooperativity and solvent effect

Using ab initio calculations, we have studied the structures, properties, and nature of halogen bonds in H(2)CS-XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes. The results show that the ring-shaped complexes are formed by a halogen bond (S···X) and a secondary hydrogen bond (H···X). We also analyzed the H(2)CS-ClF-ClF and FCl-H(2)CS-ClF complexes to investigate the cooperative and diminutive halogen bonding. The cooperative effect of halogen bonding is found in the former, while the diminutive effect is present in the latter. We finally considered the solvent effect on the halogen bond in H(2)CS-BrCl complex and found that the solvent has a prominent enhancing effect on it. The complexes have also been analyzed with natural bond orbital, atoms in molecules, and symmetry adapted perturbation theory method.     

含吡啶鎓阳离子的氮杂环卡宾Pd(Ⅱ)配合物的合成、结构及催化性能

合成了四个含吡啶鎓阳离子的氮杂环卡宾钯(II)三碘配合物. 通过核磁共振谱和元素分析对它们进行了表征. 同时利用X射线单晶衍射确定了其中两个配合物的晶体结构. 研究表明该系列配合物对Suzuki-Miyaura偶联具有催化活性.     

Catalytic activity of palladium(II) diaminocarbene complexes in the Sonogashira and Suzuki reactions

Palladium(II) complexes with chelating and non-chelating diaminocarbene ligands were assessed as catalysts in the cross-coupling reactions of haloarenes with oct-1-yne (Sonogashira reaction) and phenylboronic acid (Suzuki reaction). Both complexes exhibited a higher catalytic activity than traditional phosphine ligandbased systems in the Sonogashira reaction, and they ensured cross-coupling not only with iodoarenes but also with bromoarenes activated by electron-withdrawing substituents. The catalytic activities of the examined complexes in the Suzuki reaction were appreciably different: the palladium(II) complex with the chelating ligand turned out to be considerably less active than the complex with the non-chelating ligand.     

4-Halogeno-1,1,1-trifluorobut-3-yn-2-one [4+2] cycloadducts and their cross-coupling with organozinc compounds

The reactions of 4-chloro-1,1,1-trifluorobut-3-yn-2-one and 4-bromo-1,1,1-trifluorobut-3-yn-2-one with conjugated dienes afford [4+2] cycloadducts in high yields. The halogen atom in the products is readily replaced by a (het)aryl residue in the cross-coupling with organozinc compounds.     

Ab initio study of the complexes of halogen-containing molecules RX (X=Cl, Br, and I) and NH3: towards understanding the nature of halogen bonding and the electron-accepting propensities of covalently bonded halogen atoms

Ab initio calculations have been performed on a series of complexes formed between halogen-containing molecules and ammonia to gain a deeper insight into the nature of halogen bonding. It appears that the dihalogen molecules form the strongest halogen-bonded complexes with ammonia, followed by HOX; the charge-transfer-type contribution has been demonstrated to dominate the halogen bonding in these complexes. For the complexes involving carbon-bound halogen molecules, our calculations clearly indicate that electrostatic interactions are mainly responsible for their binding energies. Whereas the halogen-bond strength is significantly enhanced by progressive fluorine substitution, the substitution of a hydrogen atom by a methyl group in the CH(3)X...NH(3) complex weakened the halogen bonding. Moreover, remote substituent effects have also been noted in the complexes of halobenzenes with different para substituents. The influence of the hybridization state of the carbon atom bonded to the halogen atom has also been examined and the results reveal that halogen-bond strengths decrease in the order HC triple bond CX > H(2)C=CHX approximately O=CHX approximately C(6)H(5)X > CH(3)X. In addition, several excellent linear correlations have been established between the interaction energies and both the amount of charge transfer and the electrostatic potentials corresponding to an electron density of 0.002 au along the R-X axis; these correlations provide good models with which to evaluate the electron-accepting abilities of the covalently bonded halogen atoms. Finally, some positively charged halogen-bonded systems have been investigated and the effect of the charge has been discussed.     

Nickel(II) complexes of bidentate N-heterocyclic carbene/phosphine ligands: efficient catalysts for Suzuki coupling of aryl chlorides

Nickel(II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl(2)(L)], the stable nickel product isolated is the ionic [Ni(L)(2)]Cl(2). These Ni(II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh(3), and this suggests that the PPh(2) functionality of hybrid NHC ligand L can partially take on the role of free PPh(3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh(3) accelerates the reaction.     

Palladium-Catalyzed Arylation of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with Halogen-Substituted Phenols

Phenol functionalized 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives are synthesized via palladium-catalyzed arylation of DOPO with halogen-substituted phenols. 2-,3-, and 4-Substituted halogen phenols are successfully applied to the cross-coupling reactions. This method is mild, convenient, and leads to high yields (65–95%).     

Controlling the spin state of diphenylcarbene via halogen bonding: A theoretical study

Halogen bonding has recently become an effective tool to control the spin state of reactive carbenes. In this work, a series of the complexes of diphenylcarbene (DPC) that has a triplet ground state with several halogen bond donors RX were theoretically studied, and in particular, the influence of the formation of halogen bonding on the spin state of DPC was extensively explored. The spin flip depends on the difference of halogen bond energies between triplet and singlet, that is, when the difference is large enough a spin flip may occur. Furthermore, the variations of the geometries on complexation may induce the potential energy surfaces of different spin states to intersect, thus leading to intersystem crossing. Based on the energy analysis of the minimum energy crossing points (MECPs), the systems with a smaller MECP‐triplet energy barrier go through intersystem crossing more easily. Halogen bonds in the complexes, where a spin flip takes place, exhibit a partially covalent character, while other complexes show conventional behaviors of halogen bonding. According to charge decomposition analysis, the charge transfer from HOMO (DPC) to LUMO (RX) is identified as a prominent stabilizing interaction in the whole complexes.     

Phosphorus-nitrogen-phosphorus ligands: cooperative effects between nitrogen and phosphorus substituents on catalytic activity

A new generation of PNP compounds bearing different diarylphosphine groups were prepared and used as ligands in palladium-catalysed Suzuki cross-coupling reactions. Rates of oxidative addition of iodobenzene to (PNP)Pd[0] complexes were measured using UV spectroscopy. Synergistic effects between the N- and P- substituents were identified and correlated in redox and catalytic chemistry.     

Halogen Bonding or Hydrogen Bonding between 2,2,6,6-Tetramethyl-piperidine-noxyl Radical and Trihalomethanes CHX3 (X=Cl,Br, I)

The halogen and hydrogen bonding complexes between 2,2,6,6-tetramethylpiperidine-noxyl and trihalomethanes (CHX₃, X=Cl, Br, I) are simulated by computational quantum chem-istry. The molecular electrostatic potentials, geometrical parameters and interaction energy of halogen and hydrogen bonding complexes combined with natural bond orbital analysis are obtained. The results indicate that both halogen and hydrogen bonding interactions obey the order Cl相似文献   

Metal assisted synthesis of mono and diamino substituted pyridines

A microwave assisted Buchwald-Hartwig amination protocol is reported for a series of dihalopyridine precursors. Using this procedure, selective substitution of one halogen by aryl or alkylamines is possible in very short time, usually 30 min. Mild base (K₂CO₃) can be used successfully, which broadens the substrate scope. The second halogen can then be substituted using alkylamines under nucleophilic substitution condition or via a Suzuki-Miyaura cross-coupling reaction. The target compounds are potential inducers of cardiomyogenesis as innovative approach in regenerative medicine.     

Stereoselective Stille coupling of enantiopure haloallenes and alkenylstannanes for the synthesis of allenyl carotenoids. Experimental and computational studies

The stereoselectivity of the Stille cross-coupling of chiral enantiopure haloallenes and alkenylstannanes en route to allenic carotenoids is shown to depend on the nature of the halogen and palladium catalyst as well as on the presence of DMF as coordinating ligand and solvent. The results are consistent with DFT studies (B3LYP/6-31G*) on haloallene model systems, which compare the energetics of the competing oxidative addition to the allene-halogen bond (with retention of configuration) and the S(N)2' displacement of the haloallene (with inversion of configuration) by the palladium complex.     

New efficient approach to 2,2-diaryl-1,1-difluoro-1-alkenes and 1,1-difluoro-2-aryl-1,3-dienes via Suzuki coupling of alpha-halo-beta,beta-difluorostyrenes

[reaction: see text] Alpha-halo-beta,beta-difluorostyrenes [ArCX = CF2; X = Br, I; Ar = aryl, heteroaryl; synthesized by the Pd(0)-catalyzed coupling reaction of the corresponding alpha-halo-beta,beta-difluoroethenylzinc reagents (CF2=CXZnCl, X = Br, I) with aryl iodides] were functionalized at the halogen site with arylboronic acids under Pd(0)-catalyzed Suzuki-Miyaura coupling reaction conditions to obtain 2,2-diaryl-1,1-difluoro-1-alkenes (ArAr'C=CF2, Ar' = aryl, heteroaryl) in 51-91% isolated yield. The corresponding reaction with alkenylboronic acids produced 1,1-difluoro-2-aryl-1,3-dienes in 53-80% isolated yield. Alternatively, 2,2-disubstituted-1,1-difluoro-1-alkenes were synthesized in moderate yield by a zinc-insertion reaction at the halogen site of the alpha-halo-beta,beta-difluorostyrenes, followed by Pd(0)-catalyzed cross-coupling of the zinc reagent with aryl or alkenyl iodides.