Cationic iridium-BINAP complex-catalyzed addition of aryl ketones to alkynes and alkenes via directed C-H bond cleavage

Cationic Ir complex ([Ir(cod)₂]BF₄ + BINAP) catalyzed the addition of ortho-C-H bonds in aryl ketones to alkynes, which gave alkenylated products in good to high yield. Styrene derivatives were good substrates, and the enantioselective addition to norbornene was also described.     

Recent advances in the synthetic and mechanistic aspects of the ruthenium-catalyzed carbon-heteroatom bond forming reactions of alkenes and alkynes

The group’s recent advances in catalytic carbon-to-heteroatom bond forming reactions of alkenes and alkynes are described. For the C-O bond formation reaction, a well-defined bifunctional ruthenium-amido catalyst has been successfully employed for the conjugate addition of alcohols to acrylic compounds. The ruthenium-hydride complex (PCy₃)₂(CO)RuHCl was found to be a highly effective catalyst for the regioselective alkyne-to-carboxylic acid coupling reaction in yielding synthetically useful enol ester products. Cationic ruthenium-hydride catalyst generated in-situ from (PCy₃)₂(CO)RuHCl/HBF₄·OEt₂ was successfully utilized for both the hydroamination and related C-N bond forming reactions of alkenes. For the C-Si bond formation reaction, regio- and stereoselective dehydrosilylation of alkenes and hydrosilylation of alkynes have been developed by using a well-defined ruthenium-hydride catalyst. Scope and mechanistic aspects of these carbon-to-heteroatom bond forming reactions are discussed.     

Synthesis of 2-boryl-1,3-butadienes from tributylphosphine stabilized zirconacyclopropenes and alkynes

Boryl zirconacycopropenes stabilized with tributylphosphine react with alkynes (terminal and internal) to give predominately 2-boryl-1,3-butadienes, 5, in 40-81% isolated yields. Products 5 are accompanied by 4-boryl-1,3-butadienes in 7-23% when terminal alkynes are inserted. However, the use of an internal alkyne (3-hexyne) gave predominantly 6c.     

Arylcyanation of alkynes catalyzed by nickel

A nickel catalyst prepared from Ni(cod)₂ and PMe₃ is found to effect arylcyanation reaction of alkynes, namely, cleavage of a C-CN bond of an aryl cyanide followed by addition of each fragment across an alkyne. A wide range of functional groups in aryl cyanides tolerated the catalysis, giving variously functionalized β-arylalkenenitriles stereoselectively.     

Copper-free Sonogashira reactions of 4-hydroxycoumarins with alkynes

The palladium-catalyzed direct coupling reactions of 4-hydroxycoumarins with various alkynes under copper-free conditions are described. This transformation is highly effective under mild conditions and the desired products are obtained in good yields.     

Alkynylcyanation of alkynes and dienes catalyzed by nickel

Alkynyl cyanides are found to add across alkynes and 1,2-dienes in the presence of a catalyst prepared in situ from Ni(cod)₂, xantphos, and BPh₃. A range of functionalized conjugated cis-enynes are obtained with high regioselectivity. The addition reaction across norbornadiene proceeds in the absence of BPh₃ to give exo-cis adduct exclusively. A stoichiometric reaction of an alkynyl cyanide, Ni(cod)₂, xantphos, and BPh₃ gives trans-(xantphos)Ni(CNBPh₃)(CCSiMe₂t-Bu), which is suggested to be a plausible reaction intermediate of the alkynylcyanation reaction.     

Indium(III)-catalyzed intramolecular addition of silyl enolates to alkynes

In the presence of water and a catalytic amount of InBr₃, intramolecular trans-addition of silyl enolates derived from ketones and an aldehyde to alkynes proceeded smoothly to give 4 to 7-membered carbocycles bearing an acyl group. When carboxylic anhydrides were used as electrophiles instead of water, the cyclized products could be functionalized with an additional acyl group.     

Methyl-oxygen bond cleavage in hemilabile phosphine-ether ligand of ruthenium(II) complexes

The preparation and characterization are described for four ruthenium(II) complexes containing hemilabile phosphine-ether ligand o-(diphenylphosphino)anisole (Ph₂PC₆H₄OMe-o) and/or bidentate ligand diphenylphosphino-phenolate ([Ph₂PC₆H₄O-o]⁻) Ru(RCN)₂(κ²-Ph₂PC₆H₄O-o)₂ (1a: R = Me; 1b: R = Et) and [Ru(RCN)₂(κ²-Ph₂PC₆H₄O-o)(κ²-Ph₂PC₆H₄OMe-o)](PF₆) (2a: R = Me; 2b: R = Et). The ruthenium(II) phosphine-ether complexes undergo mild methyl-oxygen bond cleavage. Two different kinds reaction mechanism are proposed to describe the methyl-oxygen bond cleavage, one involving attack of anionic nucleophiles and another involving the phosphine. The new reactions define novel routes to phosphine-phenolate complexes. The structures of complexes 1a, 1b and 2a were confirmed by X-ray crystallography.     

Pt-catalyzed regio- and stereoselective pyridylthiolation of terminal alkynes

Three-component cross-coupling reactions among 3-iodopyridynes, terminal alkynes and ArSK took place in the presence of Pt-catalyst to give pyridine derivatives with conjugated vinyl groups in moderate yields.     

Synthesis and evaluation of P-chirogenic monodentate binaphthyl phosphines

P-Chirogenic monodentate binaphthyl phosphines were prepared in five steps from enantiomerically pure BINOL. This approach supposes the utilization of two methods previously developed in our group, the formation of secondary phosphine oxide, and the reduction of tertiary phosphine oxide using the association of tetramethyldisiloxane and Ti(OⁱPr)₄. During the last reduction step, only the formation of the more stable diastereoisomer was observed. This product was employed as a ligand for the palladium catalyzed hydrosilylation of styrene to afford the corresponding alcohol with high yield and enantiomeric excess.     

Synthesis of new tricyclic phosphines and phosphinites by intramolecular Diels-Alder reactions of trivalent phospholes

Phospholes bearing an allyl-X substituent at phosphorus tend to undergo an intramolecular Diels-Alder cycloaddition (IMDA) leading to the corresponding tricyclic derivative. When X = O or NR, the IMDA easily takes place at room temperature. When X = CH2, the IMDA slowly takes place around 110-140 degrees C, as a function to the substitution pattern of the dienic system. Two tricyclic derivatives (X = O and CH2) have been characterized by X-ray crystal structure analysis of the P-sulfides.     

The Coordination and Derivative Chemistry of Phosphinoalkynes on Polymetallic Frameworks and Related Systems

Some aspects of the coordination chemistry of phosphinoalkynes on polymetallic cluster frameworks are reviewed and illustrated with selected examples. Topics covered include the preparation of phosphinoalkynes, alkyne coordination, phosphine coordination, coordination in the absence of P–C bond cleavage, P–C bond cleavage and subsequent transformations of the resulting acetylide ligands, and the use of metal complexes of phosphinoalkynes as metalloligands in catalytic applications. Dedicated to the memory of Professor F.A. Cotton.     

Gallium(III) halide complexes with phosphines,arsines and phosphine oxides – a comparative study

The phosphine oxide complexes [GaX₃(Me₃PO)] and [(GaX₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] have been prepared and characterised by microanalysis, IR and multinuclear NMR (¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷¹Ga) spectroscopy. The structures of [GaCl₃(Me₃PO)], [(GaBr₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] and of the ionic product [GaI₂(Me₃PO)₂][GaI₄] have been determined and show that the Lewis acidity of the gallium halides towards phosphinoyl ligands diminishes as the halogen becomes heavier. The [GaX₃(Ph₃E)] (X = Cl, Br or I; E = P or As) and [(GaX₃)₂{μ-o-C₆H₄(CH₂PPh₂)₂}] (X = Br or I) have been prepared and their structural and spectroscopic properties compared with those of the phosphinoyl complexes. The results, and competitive solution NMR studies, show that Ga(III) binds the hard R₃PO in preference to the softer phosphine or arsine ligands. Hydrolysis of gallium(III) phosphines is shown to lead to [R₃PH][GaX₄], but in contrast to some other p-block halides, GaX₃ do not promote air-oxidation of R₃P to R₃PO.     

Activation of tri(2-furyl)phosphine at a dirhenium centre: Formation of phosphido-bridged dirhenium complexes

Reaction of tri(2-furyl)phosphine (PFu₃) with [Re₂(CO)_10−n(NCMe)_n] (n = 1, 2) at 40 °C gave the substituted complexes [Re₂(CO)_10−n(PFu₃)_n] (1 and 2), the phosphines occupying axial position in all cases. Heating [Re₂(CO)₁₀] and PFu₃ in refluxing xylene also gives 1 and 2 together with four phosphido-bridged complexes; [Re₂(CO)_8−n(PFu₃)_n(μ-PFu₂)(μ-H)] (n = 0, 1, 2) (3-5) and [Re₂(CO)₆(PFu₃)₂(μ-PFu₂)(μ-Cl)] (6) resulting from phosphorus-carbon bond cleavage. A series of separate thermolysis experiments has allowed a detailed reaction pathway to be unambiguously established. A similar reaction between [Re₂(CO)₁₀] and PFu₃ in refluxing chlorobenzene furnishes four complexes which include 1, 2, 6 and the new binuclear complex [Re₂(CO)₆(η¹-C₄H₃O)₂(μ-PFu₂)₂] (7). All new complexes have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction studies.     

Addition of alkynes at bridging vinyliminium ligands in diiron complexes: Unprecedented diene formation by enyne-like metathesis

The zwitterionic bridging vinyliminium complex [Fe₂{μ-η¹:η³-C(Tol)C(CS₂)CN(Me)₂}(μ-CO)(CO)(Cp)₂] (5a) undergoes the addition of two equivalents of MeO₂C-CC-CO₂Me affording the bridging bis-alkylidene complex [Fe₂{μ-η¹:η³-C(Me)C{C(CO₂Me)C(CO₂Me)CSC(CO₂Me)C(CO₂Me)S}CNMe₂}(μ-CO)(CO)(Cp)₂] (6). One alkyne unit inserts into a C-CS₂ bond of the bridging ligand, with consequent rearrangement that leads to the formation of a diene. The reaction shows analogies with the enyne metathesis. The second alkyne is incorporated into the bridging frame via cycloaddition at the thiocarboxylate function, affording a 1,3-dithiolene. The complexes [Fe₂{μ-η¹:η³-C(R′)C(CS₂)CN(Me)(R)}(μ-CO)(CO)(Cp)₂] (R = Xyl, R′ = Tol, 5b; R = p-C₆H₄OMe, R′ = Me, 5c; Xyl = 2,6-Me₂C₆H₃), treated with MeO₂C-CC-CO₂Me and then with HBF₄, undergo the cycloaddition of the alkyne with the dithiocarboxylate group and protonation of the dithiocarboxylate carbon, affording the complexes [Fe₂{μ-η¹:η³-C(R′)C{C(H)SC(CO₂Me)C(CO₂Me)S}CN(Me)(R)}(μ-CO)(CO)(Cp)₂][BF₄] (R = Xyl, R′ = Tol, 7a; R = p-C₆H₄OMe, R′ = Me, 7b), respectively.The X-ray molecular structure of 6 has been determined.     

A general and efficient method for the palladium-catalyzed cross-coupling of thiols and secondary phosphines

The general and efficient cross-coupling of thiols with aryl halides was developed utilizing Pd(OAc)₂/1,1′-bis(diisopropylphosphino)ferrocene as the catalyst. The substrate scope is broad and includes a variety of aryl bromides and chlorides, which can be coupled to aliphatic and aromatic thiols. This catalyst system has the widest substrate scope of any reported to date. The present catalyst system also enables the palladium-catalyzed coupling of secondary phosphines with aryl bromides and chlorides.     

Visible-light promoted one-pot synthesis of pyrazoles from alkynes and hydrazines

A visible-light promoted cascade of Glaser coupling/annulation has been developed for one-pot synthesis of polysubstituted pyrazoles from alkynes and hydrazines. The method features mild reaction conditions, readily availible starting materials and green oxidant (O₂). It works for a wide range of substituted phenyl acetylene and hyrazines with good functional group tolerance and efficiency. Mechanistic pathways including photochemical irridiation, intramolecular hydrogen-atom-abstraction (HAT) and enamine-to-imine tautomerization was proposed for the transformation.     

Reactivity of cyclopalladated compounds derived from biphenyl-2-ylamine towards carbon monoxide, butyl isocyanide and alkynes

The reactivity of the dimeric cyclopalladated compounds derived from biphenyl-2-ylamine (μ-X)₂[κ²-N2′,C1-1-Pd-2-{(2′-NH₂C₆H₄)C₆H₄}]₂ [X = OAc (1), X = Cl (2)] towards unsaturated organic molecules is reported. Compound 1 reacted with carbon monoxide and ^tbutyl isocyanide producing phenanthridin-6(5H)-one and N-tert-butylphenanthridin-6-amine in 63% and 88% yield, respectively. Compound 2 reacted separately with diphenylacetylene and 3-hexyne, affording the mononuclear organopalladium compounds [κ²-N2″,C1-η²-C2,C3- 1-Pd{(R-CC-R)₂-2′-(2″-NH₂C₆H₄)C₆H₄}Cl] [R = Ph (5), R = Et (6)] in 50-60% yield, which derived from the insertion of two alkyne molecules into the C-Pd σ bonds of 2. The crystal structure of compounds 5 and 6 has been determined. Compound 5 crystallized in the monoclinic space group P2₁/n with a = 13.3290(10) Å, b = 10.6610(10) Å and c = 22.3930(10) Å and β = 100.2690(10)°. Compound 6 crystallized in the triclinic space group with a = 7.271(7) Å, b = 10.038(3) Å and c = 16.012(5) Å, and α = 106.79(3)°, β = 96.25(4)° and γ = 99.62(4)°. The crystal structures of 5 and 6 have short intermolecular Pd-Cl?H-N-Pd non-conventional hydrogen bonds, which associated the molecules in chains in the first case and in dimers in the second.