Pd nanoparticles for C-C coupling reactions

The catalytic formation of C-C bonds is one of the most useful transformations in organic synthesis. Over the last decade, the use of transition metal nanoparticles (NPs) in catalysis has attracted much interest and their use in C-C bond formation reactions constitutes one of their most important applications, including the Suzuki, Heck, and Sonogashira reactions. This tutorial review highlights recent work in this active area, considering the stabilising agents used to prepare the NPs, the catalytic results and the recycling possibilities.     

Alpha-hydroxy esters via enantioselective hydrogen-mediated C-C coupling: regiocontrolled reactions of silyl-substituted 1,3-diynes

[reaction: see text] Catalytic hydrogenation of ethyl glyoxalate in the presence of 1,3-diynes 4a-9a using chirally modified rhodium catalysts enables formation of alpha-hydroxy esters 4c-9c in highly optically enriched form. Notably, for such trialkylsilyl-substituted 1,3-diynes, C-C coupling occurs exclusively at the carbon atom bearing silicon. Pi-back-bonding from low valent rhodium as described by the Dewar-Chatt-Duncanson model appears to direct the regiochemistry of C-C coupling, as corroborated by calculations of the diyne LUMO coefficients.     

Dialkyltitanium-mediated titanation of conjugated 1,3-butadiynes and its coupling reactions with aldehydes: a facile synthesis of stereodefined enynes and trans-enynols

A highly efficient and convenient method for the selective titanation of 1,3-butadiynes using Ti(OⁱPr)₄/ⁿBuLi reagent has been developed. The method provided a facile synthesis of enynes and trans-enynols in a well-stereodefined manner.     

Osmium-carbon multiple bonds: Reduction and C-C coupling reactions

This paper shows that the redox equilibria hydride-alkenylcarbyne/alkenylcarbene and alkenyl-alkenylcarbyne/dienylcarbene are readily governed by the electronic properties of the ligands of the complexes. Because we have learned to control the position of these equilibria, we are able to build, step by step, osmium derivatives with cyclic alkenylcarbene ligands and osmacyclopentapyrrole complexes. The dihydride OsH₂Cl₂(PⁱPr₃)₂ reacts with alkynols, allenes, enynes, and dienes to give hydride-alkenylcarbyne derivatives, OsHCl₂(CCR′CR₂)(PⁱPr₃)₂, which can be transformed into dicationic species by replacement of chloride ligands by acetonitrile molecules. The selective deprotonation of the alkenylcarbyne ligand of [OsH(CCHCPh₂)(CH₃CN)₂(PⁱPr₃)₂]²⁺ affords the hydride-allenylidene [OsH(CCCPh₂)(CH₃CN)₂(PⁱPr₃)₂]⁺, which undergoes the reduction of the C_α-C_β double bond of the cumulene in the presence of alcohols. The insertion of monosubstituted alkynes into the Os-H bond of the hydride-allenylidene complex leads to alkenyl-allenylidene derivatives, which are transformed into dienylcarbene compounds. The coordination of carbon monoxide to the osmium atom of the latter promotes the 4π-conrotation of the dienylcarbene ligand, to afford a cyclic alkenylcarbene complex via an η¹-cyclopentadienyl intermediate. Through a similar cyclization, in acetonitrile under reflux, the alkenyl-allenylidene complexes are converted into osmapyrrole derivatives by means of the formation of three C-C bonds involving the three carbon atoms of the cumulene, the alkenyl ligand, and an acetonitrile molecule.     

Transannular reactions of two parallel 1,3-butadiynes: syntheses,structures, and reactions of 1-azacyclotetradeca-3,5,10,12-tetrayne derivatives

The synthesis of 1-alkyl and 1-aryl-1-azacyclotetradeca-3,5,10,12-tetraynes was achieved in a stepwise approach. The key intermediate was 1,13-dibromotrideca-2,4,9,11-tetrayne (18). Reaction with methyl- (19 a), ethyl- (19 b), isopropyl- (19 c), n-butyl- (19 d), and tert-butylamine (19 e) as well as aniline (19 f) and p-methoxyaniline (19 g) gave the corresponding 14-membered tetraynes 20 a-20 g. The ring inversion process of 20 b was studied by variable temperature (1)H NMR spectroscopy. From these measurements a value of 10.6 kcal mol(-1) was calculated for DeltaG(not equal). X-ray investigations on single crystals of 20 b, 20 c, and 20 f revealed the axial position for the substituent at each nitrogen atom. For 20 b we encountered the chair conformation, for 20 c both chair and boat conformations, and for 20 f the boat conformation in the solid state. The reaction of 20 c with concentrated HCl in ethanol yielded 2,10-dichloro-6-isopropyl-6-azatricyclo[9.3.0.0(4,8)]tetradeca-1(11),2,4(8),9-tetraene (25 c). Compound 25 c was oxidized by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to 27 c. The structure of the latter was confirmed by X-ray investigations. The reaction of 20 c in aqueous HCl lead to the formation of 10-chloro-2-isopropyl-1,3,4,6,7,8-hexahydro-2H-benzo[g]isoquinolin-9-one (37 c). The structure of 37 c was verified by X-ray studies on single crystals.     

Synthesis of symmetrical 1,3-butadiynes by homocoupling reactions of alkynylboronates mediated by a copper salt

Alkynylboronates are employed as a practical and versatile precursor for a variety of π-conjugated organic compounds. In the presence of a Cu(I) or Cu(II) salt, transformation of alkynylboronates into the corresponding 1,3-diynes upon exposure to air takes place readily in aprotic polar solvents such as DMI.     

Phosphino imidazoles and imidazolium salts for Suzuki C-C coupling reactions

The consecutive syntheses of imidazoles 1-(4-X-C(6)H(4))-4,5-R(2)-(c)C(3)HN(2) (3a, X = Br, R = H; 3b, X = I, R = Me; 3c, X = H, R = Me; 5, X = Fc, R = H; 7, X = C≡CFc, R = H; 9, X = C(6)H(5), R = Me; Fc = Fe(η(5)-C(5)H(4))(η(5)-C(5)H(5))), phosphino imidazoles 1-(4-X-C(6)H(4))-2-PR'(2)-4,5-R(2)-(c)C(3)N(2) (11a-k; X = Br, I, Fc, FcC≡C, Ph; R = H, Me; R' = Ph, (c)C(6)H(11), (c)C(4)H(3)O), imidazolium salts [1-(4-X-C(6)H(4))-3-R'-4,5-R(2)-(c)C(3)HN(2)]I (16a; X = Br, R = H, R' = n-Bu; 16b, X = Br, R = H, R' = n-C(8)H(17); 16c, X = I, R = Me, R' = n-C(8)H(17), 16d, X = H, R = Me, R' = n-C(8)H(17)) and phosphino imidazolium salts [1-C(6)H(5)-2-PR'(2)-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)N(2)]PF(6) (17a, R' = C(6)H(5); 17b, R' = (c)C(6)H(11)) or [1-(4-P(C(6)H(5))(2)-C(6)H(4))-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)HN(2)]PF(6), (20) and their selenium derivatives 1-(4-X-C(6)H(4))-2-P([double bond, length as m-dash]Se)R'(2)-4,5-R(2)-(c)C(3)N(2) (11a-Se-f-Se; X = Br, I; R = H, Me; R' = C(6)H(5), (c)C(6)H(11), (c)C(4)H(3)O) are reported. The structures of 11a-Se and [(1-(4-Br-C(6)H(4))-(c)C(3)H(2)N(2)-3-n-Bu)(2)PdI(2)] (19) in the solid state were determined. Cyclovoltammetric measurements were performed with the ferrocenyl-containing molecules 5 and 7 showing reversible redox events at E(0) = 0.108 V (ΔE(p) = 0.114 V) (5) and E(0) = 0.183 V (ΔE(p) = 0.102 V) (7) indicating that 7 is more difficult to oxidise. Imidazole oxidation does not occur up to 1.3 V in dichloromethane using [(n-Bu)(4)N][B(C(6)F(5))(4)] as supporting electrolyte, whereas an irreversible reduction is observed between -1.2 - -1.5 V. The phosphino imidazoles 11a-k and the imidazolium salts 17a,b and 20, respectively, were applied in the Suzuki C-C cross-coupling of 2-bromo toluene with phenylboronic acid applying [Pd(OAc)(2)] as palladium source. Depending on the electronic character of 11a-k, 17a,b and 20 the catalytic performance of the in situ generated catalytic active species can be predicted. As assumed, more electron-rich phosphines with their higher donor capability show higher activity and productivity. Additionally, 11e was applied in the coupling of 4-chloro toluene with phenylboronic acid showing an excellent catalytic performance when compared to catalysts used by Fu, Beller and Buchwald. Furthermore, 11e is eligible for the synthesis of sterically hindered biaryls under mild reaction conditions. C-C Coupling reactions with the phosphino imidazolium salts 17b and 20 in ionic liquids [BMIM][PF(6)] and [BDMIM][BF(4)] were performed, showing less activity than in common organic solvents.     

Molecular iodine catalyzed coupling reactions of indole with 1,3-dicarbonyl compounds

The molecular iodine-catalyzed direct coupling of indoles with 1,3-dicarbonyl compounds is described. This new method for C–C bond formation allows high functional group tolerance, regioselectivity, and scope under mild conditions.     

Synthesis of new aminophosphine complexes and their catalytic activities in C-C coupling reactions

Two new aminophosphines, benzyl-N(Ph₂P)₂ and 2-picolyl-N(Ph₂P)₂, have been synthesized. Oxidation of the aminophosphines with either hydrogen peroxide, elemental sulfur and selenium gave the corresponding oxides, sulfides and selenides benzyl-N(Ph₂PE)₂ and 2-picolyl-N(Ph₂PE)₂, where E = O, S, or Se. Complexes [benzyl-N(Ph₂P)₂]MCl₂ and [2-picolyl-N(Ph₂P)₂]MCl₂, where M = Pd, Pt, were obtained by the reaction of the aminophosphines with MCl₂(cod). The new compounds were characterised by NMR, IR spectroscopy and microanalysis. Furthermore, representative solid-state structures of the palladium and platinum complexes were determined using single crystal X-ray diffraction analysis. The palladium complexes were further investigated as potential catalysts in C-C coupling reactions.     

间苯二酚保护的抗菌Pd纳米粒子催化C-C偶联反应活性(英文)

合成了新型四甲氧基间苯二酚-四酰肼(TMRTH),并作为还原剂和封端剂用于合成水分散性稳定的Pd纳米粒子(PdNPs).采用紫外-可见光谱、透射电镜、能量散射谱和粉末X射线衍射对所得TMRTH-PdNPs样品进行了表征.结果表明,所制纳米粒子具有多分散性,粒径为5±2 nm,并在Suzuki-Miyuara交叉偶联反应中可重复使用5次,具有较高的催化效率.该纳米催化剂在反应时间、催化剂用量和可重复使用性能等方面优于常规Pd催化剂.另外,TMRTH-PdNPs样品对革兰(氏)阳性菌具有较好的抗菌活性,因而有望用于一些生物领域.     

Mechanistic studies of thiourea-catalyzed cross-dehydrogenative C-P and C-C coupling reactions and their further applications

Thiourea-based hydrogen bond donor has been recently disclosed by our group to be an efficient organocatalyst for cross-dehydrogenative coupling (CDC) reactions. Here we present a detailed mechanistic study of this reaction using NMR spectroscopy and kinetic isotope effect experiment. The results revealed that α-amino peroxide is the true intermediate within the catalytic cycle, formed via a thiourea-catalyzed rate-determining hydrogen atom transfer (HAT) process. These experimental investigations not only provide somewhat insight into the mechanism of thiourea-catalyzed CDC reactions but also promote their further applications.     

Novel acetoxylation and C-C coupling reactions at unactivated positions in alpha-amino acid derivatives

[Structure: see text] Under special conditions, N-phthaloyl-alpha-amino acid amides of 8-aminoquinoline can be either acetoxylated or arylated selectively at the beta-carbon. In certain cases, arylation can be effected at the gamma-carbon.     

Novel triphenylarsinyl-functionalized N-heterocyclic carbene ligands in palladium-catalyzed C-C coupling reactions

Synthesis of novel triphenylarsinyl-functionalized N-heterocyclic carbene pre-ligands starting from N,N-dimethylbenzylamine, chlorodiphenylarsine and different 1-substituted imidazoles and their characterization by NMR and X-ray analysis is reported. Furthermore, these precursors are applied to different palladium-catalyzed reactions such as Heck-, hydro-Heck, π, σ domino-Heck and Suzuki reactions to give the C-C coupling products in good to excellent isolated yields.     

Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C-C coupling reactions

A series of new ethylene-bridged bis(imidazolium) halides with various N-substitutions were synthesized. Complexation of these imidazolium halides with Pd(OAc)₂ produced new Pd(II) ethylene-bridged bis(carbene) complexes. Crystallographic analyses of some of the new imidazolium salts and Pd(II) complexes were determined. Applications of these seven-member palladacycles in Suzuki and Heck coupling reactions produced comparable catalytic activities to those of six-member analogs.     

Regio- and stereoselective hydrohalogenation of ynamide components in 1,3-butadiynes with in situ generated HX

A simple protocol for regio-, and stereoselective hydrohalogenation of ynamide moieties in 1,3-butadiyne structures is described. The facile approach enables exact syn-addition of HX to the diyne components, giving just single isomer of the corresponding dienes and enynes.     

Luminescent atropisomeric N,N-chelating ligands from copper-catalyzed one-pot C-N and C-C coupling reactions

New atropisomeric N,N-chelating ligands with a 3,3'-bis[2-(2'-py)-indolyl] unit have been achieved via one-pot reactions that involve the formation of multiple C-N bonds between an indolyl and a brominated benzene and the indolyl 3,3'-C-C coupling. The new ligands display distinct blue intramolecular excimer emission (lambda(max) = 445 nm). Cu(I) ions bind to the new N,N-chelate ligands with a homochiral selectivity. The complex [Cu(bpib)2][BF(4)] (bpib = bis{3,3'-[N-phenyl-2-(2'-py)-indolyl]}) crystallizes as chiral crystals, thus allowing enantiomeric separation.     

Synthesis of unsymmetrically substituted 1,3-butadiynes and 1,3,5-hexatriynes via alkylidene carbenoid rearrangements

Unsymmetrically substituted 1,3-butadiynes and 1,3,5-hexatriynes are synthesized in four steps from commercially available aldehydes or carboxylic acids. The key step in this process involves a Fritsch-Buttenberg-Wiechell rearrangement, in which an alkylidene carbenoid intermediate subsequently rearranges to the desired polyyne. This rearrangement proceeds under mild conditions, and it is tolerant of a range of functionalities. In general, the procedurally facile formation of the dibromoolefinic precursors, in combination with the effectiveness of the rearrangement step, makes this procedure an attractive alternative to traditional methods for di- and triyne synthesis that utilize palladium or copper catalysis.