Dimerization of isoprene in methanol using palladium complexes

Conclusions The systems Pd(acac)₂-Ph₃P and Pd(OAc)₂-Ph₃P cause the dimerization and telomerization of isoprene in methanol to give linear isoprene dimers and methoxydimethyloctadienes. In isopropanol these systems dimerize isoprene to 2,7-dimethyl-1,3,7-octatriene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2099–2100, September, 1976.     

Solvent dependence of the palladium catalyzed telomerization of isoprene with methanol

The palladium catalyzed telomerization of isoprene with methanol as a nucleophilic agent has been investigated, applying the reaction system Pd-complex, tributylphosphine, sodium methylate, isoprene and methanol in a ratio of 1232002000. Two main products were found: 1-methoxy-3,6-dimethylocta-2,7-diene with a head-head coupling (I) and 1-methoxy-2,6-dimethylocta-2,7-diene with a tail-head-coupling (II). By substituting part of the methanol by different solvents the formation of I and II, respectively, can be controlled to a large extent.     

NHC copper complexes functionalized with sulfoxide and sulfone moieties

A series of N‐heterocyclic copper carbene complexes bearing sulfoxide and sulfone moieties have been prepared. In case of new copper compounds with sulfone ligand, the solid‐state structures were determined using X‐Ray crystallography. Obtained complexes were investigated as catalysts in such transformations as: 1,3‐dipolar cycloaddition of alkynes and azides (CuAAC), A³ coupling reaction and β‐hydroboration and compared with standard copper catalytic systems.     

NHC triggered cascade metal-free synthesis of 2,3-diarylated indoles under solvent-free conditions

A new cascade strategy to the synthesis of 2,3-diarylated indoles via the metal-free reaction of aryl aldehyde and aryl amine triggered by N-heterocyclic carbene (NHC) under solvent-free conditions, has been disclosed. The protocol has the advantages of easy work-up, high yields, wide application scope, and an environmentally benign procedure compared with the reported methods.     

Synthesis and characterization of asymmetric NHC complexes

New chiral and non-chiral rhodium(I)–NHC complexes were synthesized. The first attempt by deprotonation of an imidazolinium salt with KOtBu and reaction with [Rh(COD)Cl]₂ leads to the corresponding rhodium(I) complex. Due to the basic conditions during the reaction a loss of chirality occurs. An alternative transmetallation reaction with a silver(I)–NHC complex yields the desired rhodium(I)–NHC complex under retention of chirality. Both Rh complexes were fully characterized by analytical methods.     

Iridium complexes of the doubly cyclometalated NHC ligand IMes'

Two consecutive C-H bond activations at the coordination sphere of Ir transform the commonly employed NHC ligand IMes into the new κ(3)-C fac-coordinating ligand IMes'. The preparation and structure of Ir(III) complexes featuring this ligand together with selected reactions toward small molecules that illustrate their reactivity keys are described.     

Synthesis and catalytic activity of histidine-based NHC ruthenium complexes

Main-chain C,N-protected histidine has been successfully alkylated at both side-chain nitrogens. The corresponding histidinium salt was metallated with ruthenium(II) by a transmetalation procedure, thus providing histidine-derived NHC ruthenium complexes. These bio-inspired complexes show appreciable activity in the catalytic transfer hydrogenation of ketones.     

Olefin metathesis featuring ruthenium indenylidene complexes with a sterically demanding NHC ligand

The synthesis and characterization of two new ruthenium indenylidene complexes [RuCl(2)(SIPr)(Py)(Ind)] 6 and [RuCl(2)(SIPr)(3-BrPy)(Ind)] 7 featuring the sterically demanding N-heterocyclic carbene 1,3-bis(2,6-di isopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) are reported. Remarkable activity was observed with these complexes in ring closing, enyne, and cross metathesis of olefins at low catalyst loadings. The performance of SIPr-bearing complexes 6 and 7 as well as [RuCl(2)(SIPr)(PCy(3))(Ind)] 5 in ring opening metathesis polymerization is also disclosed. This work highlights the enormous influence of the neutral "spectator" ligands on catalyst activity and stability.     

Synthesis of NHC complexes by oxidative addition of 2-chloro-N-methylbenzimidazole

The oxidative addition of 2-chloro-N-methylbenzimdazole to complexes of type [M(PPh(3))(4)] yields after N-protonation compounds with NH,NMe-substituted NHC ligands. For M = Pd complex compound trans-[3]BF(4) was obtained, while the oxidative addition for M = Pt yielded a mixture of cis-[4]BF(4) (major) and trans-[4]BF(4) (minor).     

Synthesis of new iron–NHC complexes as catalysts for hydrosilylation reactions

A series of new piano‐stool iron(II) complexes comprising N‐heterocyclic carbene ligands [Fe(Cp)(CO)₂(NHC)]I (NHC = 1,3‐disubstituted imidazolidin‐2‐ylidene) have been synthesized and analyzed by ¹H NMR, ¹³C NMR, IR, elemental analysis and mass spectrometric techniques. These compounds were easily prepared from the reaction of disubstituted imidazolidin‐2‐ylidene with [FeI(Cp)(CO)₂] in toluene at room temperature. These complexes were tested in the catalytic hydrosilylation reaction of aldehydes and ketones with phenylsilane in solvent‐free conditions. After a basic hydrolysis step, the corresponding alcohols were obtained in good yields. Copyright © 2013 John Wiley & Sons, Ltd.     

Isolated-palladium complexes for catalyzed telomerization of butadiene with methanol in the presence of water

In order to study the performance of organometallic complexes in the telomerization of butadiene with methanol in aqueous medium, we synthesized and characterised hydrosoluble palladium complexes. [(π-allyl)Pd(TPPTS)₂]⁺Cl⁻ complex exhibited strong stability as no degradation was observed after storage at room temperature under air atmosphere for weeks. TON’s up to 36 000 were achieved at 50 °C.     

Well-defined phosphate yttrium dialkyl complexes for catalytic stereo-controllable 1,4-polymerization of isoprene

Oxygen ligation is envisioned to provide a stable and distinctive coordination environment to the strongly oxophilic rare-earth metals. However, the well-defined dialkyl complexes bearing oxyanion ancillary ligand had been rarely addressed for the instability of the complexes and the shortage of easily available ligands. Herein, we report the synthesis of phosphate ligated dialkyl yttrium complexes（PYR2） featuring a high stability and a tunable ligand. Treated with the borate reagent, the phosph...     

The mechanism of formation of π-allyl complexes: The reaction of PdCl2−4 with isoprene in methanol

A kinetic study of the reaction between PdCl^2?₄ and isoprene is described. The results are interpreted in terms of the formation of two π-complexes between palladium(II) and isoprene, one having only one double bond coordinated to the metal, the other being a chelated diene compound. Nucleophilic attack of solvent methanol on these intermediate complexes gives the methoxy π-allyl complex.     

Multiphase telomerisation of butadiene with acetic acid and acetic anhydride

Two different routes to acetoxyoctadiene are presented. The first one uses the well-known telomerisation of butadiene with acetic acid operating in a multiphase semi-batch mode. The second reaction involves the cleavage of acetic anhydride, hydrogen transfer via ketene formation and thus a telomerisation as well.     

Modified (NHC)Pd(allyl)Cl (NHC = N-heterocyclic carbene) complexes for room-temperature Suzuki-Miyaura and Buchwald-Hartwig reactions

A series of (NHC)Pd(R-allyl)Cl complexes [NHC: IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = N,N'-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me2, Ph] have been synthesized and fully characterized. When compared to (NHC)Pd(allyl)Cl, substitution at the terminal position of the allyl scaffold favors a more facile activation step. This translates into higher catalytic activity in the Suzuki-Miyaura and Buchwald-Hartwig reactions, allowing for the coupling of unactivated aryl chlorides at room temperature in minutes. In the Suzuki-Miyaura reaction, aryl triflates, bromides, and chlorides react with boronic acids using very low catalyst loading. In the N-aryl amination reaction, a wide range of substrates has been coupled efficiently; primary-, secondary-, alkyl-, or aryl-amines react in high yields with unactivated, neutral, and activated aryl chlorides and bromides. In both reactions, extremely hindered substrates such as tri-ortho-substituted biaryls and tetra-ortho-substituted diarylamines can be produced without loss of activity. Finally, the present catalytic system has proven to be efficient with as low as 10 parts-per-million (ppm) of precatalyst in the Buchwald-Hartwig reaction and 50 ppm in the Suzuki-Miyaura reaction.     

Low valent and hydride complexes of NHC coordinated gallium and indium

The reactions of the N-heterocyclic carbene 1,3-dimesitylimidazol-2-ylidene (IMes) with Ga[GaCl(4)], "GaI", InCl(2) and GaBr(3) have been examined. All reactions using a low valent gallium or indium starting material led to species of the form [{MX(2)(IMes)}(2)], where M = Ga, X = Cl (1), I (2); M = In, X = Cl (3), with disproportionation and loss of gallium metal in the case of 2. Reaction of IMes with gallium tribromide yields the air and moisture stable complex [GaBr(3)(IMes)] (4), which has been used as a precursor to the mixed bromohydrides [GaBrH(2)(IMes)] (5) and [GaBr(2)H(IMes)] (6) by (i) ligand redistribution with [GaH(3)(IMes)], (ii) hydride-bromide exchange with triethylsilane, and (iii) alkylation with (n)butyllithium followed by β-hydride elimination (6 only). Attempts to prepare 1, or monovalent analogues such as [{GaCl(IMes)}(n)], by thermally induced reductive elimination of dihydrogen from the chlorohydride congeners of 5 and 6 resulted in isolation of the known compounds [IMesCl][Cl] (IMesCl = 1,3-dimesityl-2-chloroimidazolium), and/or 1,3-dimesityl-2-dihydroimidazole, and gallium metal. Preliminary photochemical NMR spectroscopy and catalytic studies of 5 and 6 aimed at reductive dehydrogenation under milder conditions are reported. Compounds 1 and 4 have been characterised by single crystal X-ray structure determination.     

Synthesis and characterization of para-pyridine linked NHC palladium complexes and their studies for the Heck-Mizoroki coupling reaction

This paper describes the synthesis of 1-(pyridine-4-ylmethyl) NHC and their Pd(II) and Ag(I) complexes, which are fully characterized. Interestingly, we have also synthesized a Pd complex 3a-CO(3) using a more direct treatment of K(2)CO(3) with PdCl(2). 3a-CO(3) represents the first reported solid structure of a Pd η(2)-carbonato complex stabilized by an NHC framework. 3a-CO(3) can be easily converted to a PdCl(2) derivative by treating it with chloroform. We have found these palladium complexes mediate the Heck-Mizoroki coupling with a low catalyst loading. Furthermore, we also expand such catalytic manifold toward constructing fused polyaromatic substrates, a highly useful class of compounds in optoelectronic chemistry.     

Thermal properties of chitin ammonophosphates and their complexes with methanol

The thermal properties of chitin ammonosphosphate complexes with methanol are discussed. The endothermic effect of chitin ammonophosphate decomposition is dependent on the substitution degree. The chitin ammonophosphates have a lower ability to form complexes with methanol than chitin itself. The bonding energy of methanol with chitin ammonophosphates is dependent on the substitution degree of the ammonophosphate group. As the substitution degree increases, the quantity of methanol bonded to the chitin ammonophosphate decreases, as does the bonding energy of the methanol; this is manifested in a lower endothermic effect and a lower temperature of the maximum of this effect.