Stille-type Coupling Reactions Research Articles

Late-stage derivatization of a (B,O)2-doped perylene.

Regioselective di- and tetrabrominations of the (B,O)2-perylene 1 afford derivatives 2-4. Despite their poor solubility, 2 and 4 could be used in Stille-type coupling reactions to introduce two CCMe (5) or four CC(p-C6H4tBu) substituents (6), respectively. The alkynylated derivatives show blue-green photoluminescence with appreciable quantum efficiencies.

A Vicinal Electrophilic Diborylation Reaction Furnishes Doubly Boron-Doped Polycyclic Aromatic Hydrocarbons.

Ten examples of unsymmetrically benzannulated, boron-doped polycyclic aromatic hydrocarbons (B-PAHs) were prepared by a one-pot protocol using 4,5-dichloro-1,2-bis(trimethylsilyl)benzene (1), BBr3 , and selected PAHs-among them anthracene, benzo[a]pyrene, biphenylene, and fluoranthene. After mesitylation at the boron centers, the resulting air- and water-stable products were investigated by 1 H/11 B{1 H}/13 C{1 H} NMR spectroscopy, X-ray crystallography, cyclic voltammetry, and UV/Vis absorption/emission spectroscopy. The experiments were augmented by DFT calculations. Most of the B-PAHs are brightly luminescent (ΦPL up to 90 %) and undergo reversible reduction at moderate half-wave potentials. The two chloro substituents of 1 are not only mandatory for accomplishing efficient diborylation, but can subsequently be used for Stille-type coupling reactions to introduce 2-thienyl moieties. Alternatively, Cl/H exchange is achievable with HSiEt3 in a quantitative, Pd-catalyzed transformation.

Synthesis and characterisation of the complete series of B–N analogues of triptycene

The reaction between the bisborate Li2[o-C6H4(BH3)2] and 2 equivalents of an appropriate pyrazole derivative (Hpz(R)) in the presence of Me3SiCl yields o-phenylene-bridged pyrazaboles HB(μ-pz(R))2(μ-o-C6H4)BH (3a-3e; Hpz(R) = 4-iodopyrazole (3a), 4-(trimethylsilyl)pyrazole (3b), 3,5-dimethylpyrazole (3c), 3,5-di(tert-butyl)pyrazole (3d), 3,5-bis(trifluoromethyl)pyrazole (3e)). The synthesis approach thus provides access to uncharged B-N triptycenes bearing (i) functionalisable groups, (ii) electron-donating or -withdrawing substituents and (iii) pyrazole rings of varying steric demand. Treatment of p-R*C6H4BBr2 with the potassium tris(pyrazol-1-yl)borates K[HBpz3] or K[p-R*C6H4Bpz3] yields cationic pyrazolyl-bridged pyrazaboles [p-BrC6H4B(μ-pz)3BH]Br ([4a]Br) and [p-R*C6H4B(μ-pz)3Bp-C6H4R*]Br (R* = Br ([4b]Br), I ([4c]Br), SiMe3 ([4d]Br)), which can be regarded as full B-N analogues of triptycene. The B-H bonds of 3b and [4a]Br are unreactive towards tBuC[triple bond, length as m-dash]CH even at temperatures of 80 °C, thereby indicating an appreciable thermal stability of the corresponding B-N cage bonds. Most of the cage compounds are sufficiently inert towards water to allow quick aqueous workup. However, NMR spectroscopy in CD3OD solution reveals degradation of 3b or [4a]Br to the corresponding pyrazoles and o-C6H4(B(OCD3)2)2 or p-BrC6H4B(OCD3)2/B(OCD3)3. The diphenylated species [4b]Br is significantly more stable under the same measurement conditions; even after 76 d, most of the material degrades only to the stage of the syn/anti-pyrazaboles p-BrC6H4(CD3O)B(μ-pz)2B(OCD3)p-C6H4Br (11a/11b). A derivatisation of [4c]Br with nBu3SnC≡CtBu through Stille-type coupling reactions furnishes the alkynyl derivative [p-tBuC≡CC6H4B(μ-pz)3Bp-C6H4C≡CtBu]Br ([4e]Br). Larger B-N aggregates are also accessible: treatment of the tetrakisborate Li4[1,2,4,5-C6H2(BH3)4] with 4 equivalents of Hpz(R) in the presence of Me3SiCl leads to the corresponding B-N pentiptycenes (Hpz(R) = 3,5-bis(trifluoromethyl)pyrazole (14a), 4-(trimethylsilyl)pyrazole (14b), 3,5-dimethylpyrazole (14c), 3,5-di(tert-butyl)pyrazole (14d)).

Synthesis and characterization of 6,6″′-bis(anthracen-9-yl)-2,2′;6′,2″;6″,2″′-quaterpyridine

New bianthracene-quaterpyridine ligand 6,6″′-bis(anthracen-9-yl)-2,2′;6′,2″;6″,2″′-quaterpyridine L has been obtained in a multistep synthesis using Suzuki–Miyaura and Stille-type coupling reactions. The dianthracene ligand L has four nitrogen-donor atoms and can form different supramolecular architectures with transition metal ions. Ligand L and intermediate compounds have been characterized by spectroscopic methods and elemental analyses. 2-(Anthracen-9-yl)-6-bromopyridine and 6-(anthracen-9-yl)-6′-bromo-2,2′-bipyridine have been also characterized by X-ray crystallography.

Ferrocenes with Perfluorinated Side Chains and Ferrocenophanes with Fluorinated Handles

Trifluorovinyl groups are introduced onto the cyclopentadienyl ligands of ferrocene at the 1-, 1,1'-, and 1,2-positions by Negishi-type and Stille-type coupling reactions of trifluorovinylzinc chloride and tri-n-butyltrifluorovinyl stannane with several iodoferrocenes. Modification of the trifluorovinyl group by nucleophilic substitution and [2+2] cycloaddition make them versatile building blocks for synthetic transformations. 1,1'-Bis(trifluorovinyl) ferrocene reacts upon contact with silica or oxidizing agents and in the presence of a suitable nucleophile through a redox autocatalytic mechanism to afford ferrocenophanes with fluorinated handles. C(F)(H) and C(F)(OMe) moieties in α-positions allowed further modifications to be performed by nucleophilic substitution of the fluorine atoms. A series of ferrocenes with fluorinated side chains and ferrocenophanes with fluorinated handles were isolated and characterized. Several molecular structures were determined by single-crystal X-ray diffraction. The influence of the fluorine substituents on the redox properties of the iron center were studied by cyclic voltammetry.

Distannylated Isothianaphthene: A Versatile Building Block for Low Bandgap Conjugated Polymers

A novel 1,3-distannylated isothianaphthene (1) was synthesized in high yield by dilithiation of isothianaphthene (ITN) followed by treatment with trimethyltin chloride. Compound 1 is stable in the absence of oxygen and was fully characterized by multinuclear NMR spectroscopy, mass spectrometry, and elemental analysis. We used 1 as a building block for the synthesis of a series of conjugated polymers with alternating structures through Stille-type coupling reactions with dibromo and diiodo compounds. The resulting polymers were characterized by size exclusion chromatography, multinuclear NMR spectroscopy, mass spectrometry, and differential scanning calorimetry. The HOMO−LUMO energy bandgaps of these materials, estimated from UV−vis spectroscopy and cyclic voltammetry (CV), ranged from 1.66 to 2.56 eV depending on the chemical nature of the dihalogenated units. Bulk heterojunction photovoltaic (PV) devices constructed using blends of the ITN-containing copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) gave power conversion efficiencies ranging from 0.12% to 0.43%.

Development in Synthesis, Electrochemistry, LB Moieties of Phenothiazine Based Units

AbstractA convenient and higher yielding synthetic route to N‐alkyl‐bis(thiophene)phenothiazine derivatives is reported and their aggregation, electrochemical properties and polymerization are characterized. The key step in the synthesis of this group of compounds has been the Stille type coupling reaction between the N‐alkyldibromophenothiazine and tin derivatives of thiophene as the best way for preparation of conjugated N‐alkylphenothiazine derivatives. For this group of compounds we also present an electrochemical polymerization effect and widely adopted approach to prepare structurally ordered thin, electroconducting films by Langmuir–Blodgett technique.

Development in synthesis and electrochemical properties of thienyl derivatives of carbazole

A convenient and higher yielding synthetic route to N-alkyl-bis(thiophene)- and N-alkyl-bis(ethylenedioxythiophene) carbazole derivatives is reported and their aggregation, and electrochemical properties are characterized. The key step in the synthesis of this group of compounds has been the Stille-type coupling reaction between the N-alkyldibromocarbazole and tin derivatives of thiophene or ethylenedioxythiophene, as the best way for preparation of conjugated N-alkylcarbazole derivatives. For this group of compounds we also present an electrochemical polymerization effect.

Synthesis of Surface Organopalladium Intermediates in Coupling Reactions: The Mechanistic Insight

The design and synthesis of surface transient organometallic intermediates on nanopalladium supported on layered double hydroxides is conceived and developed for the first time. The formation of only one STO intermediate in all the Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions during their reaction sequences and the excellent isolated yields of each of the coupling products from the corresponding organometallic complexes not only validate the mechanism but also demonstrate the evolution of the single-site heterogeneous catalyst.

Layered double hydroxide supported nanopalladium catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes.

Layered double hydroxide and Merrifield resin supported nanopalladium(0) catalysts are prepared by an exchange of PdCl(4)(2-) followed by reduction and well characterized for the first time. The ligand-free heterogeneous layered double hydroxide supported nanopalladium (LDH-Pd(0)) catalyst using the basic LDH in place of basic ligands indeed exhibits higher activity and selectivity in the Heck olefination of electron-poor and electron-rich chloroarenes in nonaqueous ionic liquids (NAIL) over the homogeneous PdCl(2) system. Using microwave irradiation, the rate of the Heck olefination reaction is accelerated, manifold with the highest turnover frequency ever recorded in the case of both electron-poor and electron-rich chloroarenes. The basic LDH-Pd(0) shows a superior activity over a range of supported catalysts, from acidic to weakly basic Pd/C, Pd/SiO(2,) Pd/Al(2)O(3), and resin-PdCl(4)(2-) in the Heck olefination of deactivated electron-rich 4-chloroanisole. The use of LDH-Pd(0) is extended to the Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes in an effort to understand the scope and utility of the reaction. The catalyst is quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost consistent activity in all the coupling reactions. The heterogeneity studies provide an insight into mechanistic aspects of the Heck olefination reaction and evidence that the reaction proceeds on the surface of the nanopalladium particles of the heterogeneous catalyst. TEM images of the fresh and used catalyst indeed show that the nanostructured palladium supported on LDH remains unchanged at the end of the reaction, while the XPS and evolved gas detection by TGA-MS of the used catalyst identify ArPdX species on the heterogeneous surface. Thus, the ligand-free nanopalladium supported on LDH, synthesized by the simple protocol, displays superior activity over the other heterogeneous catalysts inclusive of nanopalladium in the C-C coupling reactions of chloroarenes.

Dialkylfluorene-Oligothiophene and Dialkylfluorene-Dithienylvinylene Alternating Copolymers

Well defined dialkylfluorene/oligothiophene and di-alkylfluorene/dithienylvinylene alternating copolymers have been synthesized via the polycondensation of 2,7-dibromo-(9,9-dialkyl-fluorene) with the appropriate distannylated (oligo)thienylene component according to a Stille-type coupling reaction using tetrakis(triphenylphosphine)palladium [Pd(PPh 3 ) 4 ] as catalyst. The alternate incorporation of the thienylene building blocks leads to the tunability of the photoluminescent properties of the alternating copolymers. The long wavelength absorption and photoluminescence maxima of the copolymers display a subsequent bathochromic shift upon increasing the size of the (oligo)thienylene building block.

Two-Level Self-Organisation of Arrays of [2×2] Grid-Type Tetranuclear Metal Complexes by Hydrogen Bonding

Here we report on the synthesis and characterisation of four new complexes of the [2×2] M4II grid-type (M = Co, Fe, Zn) with oligopyridine-derived ligands. The presence of aminopyrazine and aminopyrimidine moieties at the edge of the ligands potentially enables the formation of infinite hydrogen-bonded multi-grid networks. The ligands were synthesised by subsequent stannylations and Stille-type coupling reactions. The complexes were obtained by self-assembly of the ligand with the metal salt. The single-crystal X-ray structure was determined for the Co complex 7 containing aminopyrimidine as the hydrogen-bonding moiety [P1¯; a = 15.4976(4), b = 18.2114(6), c = 31.9538(10) A, α = 86.9809(13), β = 83.4137(18), γ = 67.2828(16)°]. The crystal structure reveals hydrogen bonding in one direction, thus forming infinite chains of grids, whereas in the second direction of a layer, only weak attractive interactions are found. Anions and solvent molecules are situated between the layers, thus inhibiting any direct interaction between them. Cocrystallisation of the complementary complexes should enable the recognition-controlled alternating arrangement of grids incorporating different metal ions in a chessboard-like manner.

Synthesis and Applications of Palladium-Coated Poly(vinylpyridine) Nanospheres

Monodisperse poly(4- and poly(2-vinylpyridine) nanospheres in the 500 nm diameter range were prepared by emulsifier-free emulsion polymerization techniques under free radical initiation of the respective monomers with 4 wt % divinylbenzene as the cross-linking agent. The size, integrity, and nature of the nanospheres were investigated by Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, Auger spectroscopy, and Fourier-transform infrared spectroscopy measurements. The rigid and highly stable nanospheres with exposed pyridine nitrogen on the surface serve as an excellent support for Pd0 nanoparticles in the range of 1−4 nm. The Pd-coated nanospheres were also characterized by transmission electron microscopy and inductively coupled plasma mass spectrometry measurements. Four weight percent palladium-coated nanospheres serve as good catalysts for Suzuki-, Heck-, and Stille-type coupling reactions for carbon−carbon bond formation.

Regioselective halogenation and palladium-catalysed couplings on 5,15-diphenylporphyrin

5,15-Diphenylporphyrin was regiospecifically halogenated in high yield to give 5-iodo-15-bromo-10,20-diphenylporphyrin, which was then subjected to Heck and Stille-type coupling reactions to form unsymmetrically substituted porphyrins. The regioselectivity of the iodination of diphenylporphyrins and subsequent formation of amphiphilic porphyrins via palladium-based methodology was also studied. The utility of this method for the synthesis of photodynamic sensitisers has been demonstrated on AR4-2J rat pancreatic carcinoma cells.

Azadiradione Analogs from 13α- and 13β-Dehydro-epi-androsterone

The synthesis of diketones 6, 11 and 17 related to the limonoid antifeedant azadiradione is achieved in 5, 4 and 5 steps, respectively, involving a Stille type coupling reaction and a stereoselective epoxide rearrangement.

Palladium(0) mediated coupling of bromophosphaalkenes with Grignard reagents

Attempts to subject the phosphaalkene Mes * P CBr 2 ( 1) (Mes * = supermesityl = 2,4,6-tri- tert-butylphenyl) to a palladium(0) catalyzed Stille-type coupling reaction with phenylmagnesium chloride failed due to elimination of palladium bromide and rearrangement to the phosphaacetylene Mes * C P ( 2). To prevent this undesired reaction, the monobromophosphaalkene Mes * P C(H)Br ( 6) was used. Although both isomers are known, a new method for the synthesis of ( E)-Mes * P C(H)Br (( E)- 6) has been developed and the compound tested in Stille-type coupling reactions with organometallic reagents. Best results were obtained in combination with Grignard reagents; aromatic, olefinic and alkynyl groups could be introduced. Most unexpected was the result when ( Z)-Mes * P C(Br)H (( Z)- 6) was subjected to this coupling reaction: in all cases, isomerization occurred to give ( E)-Mes * P C(H)R ( 7–17) in high yield and purity. This method offers a convenient access to a variety of new functionalized phosphaalkenes with potentially interesting coordinating properties. The mechanism of the coupling reaction appears not to involve the usual oxidative addition step, assumed to occur in the normal Stille coupling. Attempts to elucidate the mechanism are reported and the η 2-palladium complex 19 has been tentatively identified as an intermediate.