Bis(triphenylphosphan)Palladium-Komplexe mit Schwefeloxid-Liganden

Bis(triphenylphosphine)Palladium Complexes with Sulfur Oxide Ligands New examples in the series of sulfur oxide complexes of the type (PPh₃)₂Pd(S_nO_m) (n = 1,2; m 1–4) were found by the synthesis of (PPh₃)₂Pd(SO) and (PPh₃)₂Pd(S₂O₃. The SO complex is obtained by the reaction of Pd(PPh₃)₄ or (PPh₃)₂Pd(RCCR) (R=COOMe) and thiirane-S-oxide. The thiosulfato complex (PPh₃)₂Pd(S₂O₃) is formed from (PPh₃)₂Pd(SO) and SO₂ or, alternatively, from (PPh₃)₃Pd(SO₂) and C₂H₄SO. Both SO und SO₂ complexes can be oxidized to the corresponding sulfato compound (PPh₃)₂)Pd(SO₄). The SO complex is used as a SO-source for the formation of 3,4-dimethyldihydrothiophene-S-oxide from 2,3-dimethyl-1,3-butadiene.     

Metal-thiophen derivatives. Organometallic compounds of palladium and platinum

Thienylmercury(II)chloride reacts with [Pd(PPh₃)₂Cl₂], [Pd(PPh₃)₄] and [Pt(PPh₃)₄] to afford new compounds containing a metal-2-thienyl linkage. The compound [Pd(PPh₃)₂(2-C₄H₃S)Cl] probably has trans stereochemistry.2-Bromothiophen undergoes oxidative addition with [Pd(PPh₃)₄] and [Pt(PPh₃)₄], probably via a radical mechanism. With [Pd(CO)(PPh₃)₃], a carbonyl inserted product is obtained. The bromo-metal(II) complexes have trans stereochemistry. The course of the reaction between 3-methyl-2-bromothiophen and Pd(PPh₃)₄ is more complex. Thus, there is evidence of some cis bromopalladium(II) compounds amongst the products, also there is good evidence to support the view that some isomerisation of 3-methyl-2-thienyl to 4-methyl-2-thienyl occurs during the reaction, thus giving greater molar quantities of [Pd(PPh₃)₂(4-CH₃-2-C₄H₂S)Br] than can be accounted for from any initial 4-methyl-2-bromothiophen impurity.The metallation of the thiophen ring, probably in the 4-position, with palladium(II) is described for 3-theylidene-4-methylaniline.     

Route selection in the synthesis of C-4 and C-6 substituted thienopyrimidines

Three different routes have been investigated for the preparation of 6-aryl-N-(1-arylethyl)thienopyrimidin-4-amines. First the possibilities of selective Suzuki reactions on 6-bromo-4-chlorothienopyrimidine were investigated. The preference for mono arylation at C-6 could be increased, in the case of Pd(PPh₃)₄ catalysis, by reducing the water content of the reaction, or by using less electron rich Pd-ligands. The highest selectivity was obtained with Pd(OAc)₂ or Pd₂(dba)₃, while reactions with the more electron rich Pd(PPh₃)₄ and especially XPhos gave a lower mono- to dicoupled product ratio. Secondly, two alternative strategies avoiding this selectivity issue were tested. Suzuki reaction on C-6 of 6-bromothienopyrimidin-4(3H)-one (three examples) proceeded in 70-89% yield using Pd(PPh₃)₄ in dioxane/water. Similar conditions on 4-amino-6-bromo-thienopyrimidine (eight examples) gave 67-95% yield. The reaction could be performed with boronic acids containing nonprotected phenolic groups in the ortho, meta and para positions. By prolonging the reaction time, coupling with sterically crowded arylboronic acids was also efficient. Diarylation of 6-bromo-4-chlorothienopyrimidine gave the corresponding 4,6-diarylated derivatives in 71-80% yield depending on the nature of the arylboronic acid.     

Preparation of Pd(PPh<Subscript>2</Subscript>H)<Subscript>2</Subscript>(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript> and its Role as a Precursor of a Dinuclear Complex with Bridging Phosphide Ligands

Reaction of PPh₂H with Pd(PPh₃)₄ in a 4:1 molar ratio produced the Pd complex with two diphenylphosphine ligands, Pd(PPh₂H)₂(PPh₃)₂ (1). Complex (1) was characterized by n.m.r. (¹H and ³¹P{¹H}) spectra as well as by elemental analysis. Reaction of (1) with RhCl(PPh₃)₃ yielded a Pd–Rh heterobimetallic complex with bridging phosphide ligands, formulated as [(Ph₃P)₂Pd(μ-PPh₂)₂Rh(PPh₃)₂]Cl (2).     

Syntheses and characterization of some new 2-picolylpalladium(II) complexes

The 2-picolylpalladium(II) complex [{Pd(CH₂Py)Cl(PPh₃)}₂] (CH₂Py=2-picolyl) (I), prepared from 2-picolyl chloride and [Pd(PPh₃)₄], was treated with lithium bromide, silver acetate, 4-picoline (pic) and silver perchlorate, thallium acetylacetonate{Tl(acac)}, sodium dimenthyldithiocarbamate-water-(1/2) {Na(dmdc). 2 H₂O}, and 1,2-bis(diphenylphospino)ethane (dppe) to yield [{PdBr(CH₂Py)(PPh₃)}₂] (II), [{Pd(CH₂Py)OAc(PPh₃)}₂] (III), [{Pd(Ch₂Py)(pic)(PPh₃)}₂](ClO₄)₂ (IV), [Pd(CH₂Py)(acac)(PPh₃)] (V), [Pd(CH₂Py)(dmdc)(PPh₃)] (VI), and [Pd(Ch₂Py)Cl(dppe)] (VII), respectively. Halogen abstraction from VII using silver perchlorate afforded an ionic complex [{Pd(CH₂Py)(dppe)}₂](ClO₄)₂ (VIII). It was concluded that the 2-picolyl groups in these eight complexes are σ-bonded to palladium, and that in the dinuclear complexes I, II, III, IV, and VIII, they serve as bridging ligands.     

On the Synthesis and Characterization of Pd (CO) (PPh3)3

Pd (CO) (PPh₃)₃ could be isolated from the reaction mixture arising from cyclohexene hydrocarboxylation by PdCl₂ (PPh₃)₂ as the catalyst precursor; furthermore, it has also been prepared through direct reaction of Pd (PPh₃)₄ with CO in benzene. For this complex, ³¹P- and ¹³C-NMR. spectra suggest a rapid dissociation of PPh₃ at room temperature and a tetrahedral structure at – 70° in solution.     

Palladium-catalyzed Sonogashira cross-coupling of organic tellurides with alkynes

Alkyl aryl tellurides and a tellurol ester were used as coupling partners in Pd(0)-catalyzed Sonogashira reactions. Microwave-assisted reactions of alkyl aryl tellurides with alkynes in the presence of CuI and catalytic amounts of Pd(PPh₃)₄ produced alkynyl arenes. Similarly, a tellurol ester on reaction with alkynes afforded alkynyl phenyl ketones in the presence of CuI and a catalytic amount of Pd(PPh₃)₄ at room temperature.     

Kinetics and mechanism of cyclohexene hydrocarbomethoxylation catalyzed by a Pd(II) complex

The kinetics of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid (TSA) is reported. The reaction is first-order with respect to cyclohexene and TSA and of order 0.5 with respect to Pd(PPh₃)₂Cl₂. The reaction rate as a function of CO pressure or methanol or PPh₃ concentration passes through an extremum. The chloride anion inhibits the reaction. A mechanism involving cationic hydride complexes as intermediates is suggested. A rate equation is set up by the quasi-steady-state treatment of experimental data.     

A new type of palladium(0) complex having both electron-withdrawing and -donating sites in a ligand: 5,8-dihydro- and 5,8,9,10-tetrahydro-1,4-naphthoquinone complexes

A new type of palladium(0) complex, (5,8-dihydro-1,4-naphthoquinone)Pd(PPh₃)₂ and (5,8,9,10-tetrahydro-1,4-naphthoquinone)Pd(PPh₃)₂, having both olefin and quinone or dihydro-quinone sites in a ligand molecule was prepared. IR and ¹H NMR spectroscopic studies of these complexes suggested that it is the quinone or dihydro-quinone CC bond which is complexed to Pd. Ligand exchange reactions showed that the stability order of the olefinic quinone complexes was as follows: (1,4-naphthoquinone)Pd(PPh₃)₂ > (5,8-dihydro-1,4-naphthoquinone) Pd(PPh₃)₂>(5,8,9,10-tetrahydro-1,4-naphthoquinone)Pd(PPh₃)₂.     

Regioselective synthesis of allylic sulfones by palladium-catalyzed denitro-sulfonylation of allylic nitro compounds

Allylic nitro compounds undergo denitro-sulfonylation catalyzed by Pd(PPh₃)₄ or Pd(PPh₃)₄ +NaNO₂ with PhSO₂Na·2H₂O to afford allylic sulfones regioselectively.     

Convenient laboratory synthesis of vinylic silicon compounds via the reactions of acetylene with hydrosilanes catalyzed by group-VIII metal phosphine complexes

The hydrosilylation of acetylene (HCCH) with trichlorosilane, triethoxysilane, methyldichlorosilane, methyldiethoxysilane and $\text{n}$-hexyldichlorosilane in an inert solvent in the presence of various phosphine complexes of Group-VIII metals such as Ru, Rh, Pd and Pt, as well as chloroplatinic acid, was investigated. Among the complexes studied, RuCL₂ (PPh₃)₃, PtCl₂ (PPh₃)₂, RhCl (PPh₃)₃, RhH(PPh₃)₄ and Pt(PPh₃)₄ were found to be the catalysts of choice for the selective syntheses of vinyltrichlorosilane, vinyltriethoxysilane, methylvinyldichlorosilane, methylvinyldiethoxysilane and $\text{n}$-hexylvinyldichlorosilane, respectively.     

Reactions of a 2-picolyl-bridged palladium(ii) complex with some pyrazole derivatives

A 2-picolyl-bridged dinuclear complex, [Pd(2-picolyl)Cl(PPh₃)₂] (I) reacted with alkali metal salts of poly(1-pyrazolyl)borates, Na(BPz₄) (Pz = 1-pyrazolyl), Na(HBPz₃),and K(H₂BPz₂) to afford the complexes, [Pd(2-picolyl)(BPz₄)₂] (II), [Pd(2-picolyl)(HBPz₃)(PPh₃)] (III), and [Pd(2-picolyl)(H₂BPz₂)₂] (V), respectively. Complexes II and V retained the 2-picolyl bridge, whereas III was mononuclear without the bridge. Complex I was treated with hydrated silver perchlorate in the presence of tris(1-pyrazolyl)methane to give [Pd(2-picolyl)(OH₂)(PPh₃)₂](ClO₄)₂ (VI) without incorporating the neutral ligand.     

Reactions of palldium(II) compounds with carbon monoxide in alcohol/amine systems : a new route to palladium(O) carbonyl and carboalkoxy-palladium(II) complexes

Palladium(O) carbonyl complexes, Pd(CO)(PPh₃)₃ Pd₃(CO)₃(PPh₃)₃ and Pd₃(CO)₃(PPh₃)₄, can conveniently be prepared by the reaction of (PPh₃)₂PdCl₂ with carbon monoxide at room temperature in methanol/amine systems involving primary and secondary amines such as diethylamine and cyclohexylamine. These carbonyl complexes are interconvertible under suitable conditions. On the other hand, use of tertiary amine such as triethylamine and tri-n-butylamine in place of the above amines give selectively a carbomethoxy complex (PPh₃)₂PdCl(COOCH₃).     

Structures and Reaction Mechanism of Novel Metal-Carbene Complexes Derived from Hypervalent Diazadiselenathiapentalenes

Abstract

Novel metal-carbene complexes (4) with a metallapentalene framework have been obtained from hypervalent diazadiselenathiapentalenes (3) by treating with Pt(PPh₃)₄, Pd(PPh₃)₄ and RhCl(PPh₃)₃. X-Ray investigations revealed that the central hypervalent sulfur atom in 3 was substituted by a metal atom to form M-Se bonds in the resultant metallapentalene framework.     

Sulfur‐assisted Chloride and Triphenylphosphine Dissociation of Palladium(II) Complex with Phenyloxythiocarbonyl,PhOC(S), Containing Ligand: X‐Ray Structure of [Pd(PPh3)2{η1‐C(S)OPh}(Cl)]

Treatment of Pd(PPh₃)₄ with phenylchlorothionoformate, PhOC(S)Cl, in dichloromethane at ?20 °C produces the phenyloxythiocarbonyl complex [Pd(PPh₃)₂{η¹‐C(S)OPh}(Cl)], 1 . The ³¹P{¹H} NMR spectrum of 1 shows the dissociation of either the chloride or the triphenylphosphine ligand to form complex [Pd(PPh₃)₂(η²‐SCOPh)][Cl], 2 or the dipalladium complex [Pd(PPh₃)Cl]₂(μ,η²‐SCOPh)₂, 3 . Continuous stirring of the dichloromethane solution of 1 at room temperature for 4 h forms the dipalladinum complex [Pd(PPh₃)Cl]₂(μ,η²‐SCOPh)₂, 3 as the final product. Respective reactions of 1 and Et₂NCS₂Na or dppa {bis(diphenylphosphino)amine} gives complex [Pd(PPh₃){η¹‐C(S)OPh}(η²‐S₂CNEt₂)], 4 or [Pd(PPh₃){η¹‐C(S)OPh}(η²‐dppa)][Cl], 5 . Complex 1 is determined by single‐crystal X‐ray diffraction and crystallized in the monoclinic space group P2₁ with Z = 4. The cell dimensions of 1 are as follows: a = 9.5613(1) Å, b = 33.6732(3) Å, c = 12.2979(1) Å.     

Binuclear hydroxo-monopentahalophenyl complexes of palladium(II)

The novel binuclear hydroxo-bridged complexes trans-[R(PPh₃)Pd(μ-OH)₂Pd(PPh₃)R] and cis-[R(PPh₃)Pd(μ-OH)(μ-pz)Pd(PPh₃)R] (R = C₆F₅ or C₆Cl₅; pz = pyrazolate) have been prepared, and their structures assigned on the basis of NMR data.     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Synthesis of α,α-disubstituted amino acids based on tandem reaction of dehydroamino acid derivatives

The formation of all-substituted sp³-hybridized carbon-center was investigated via tandem reaction of dehydroamino acid derivatives. The diethylzinc-promoted reaction of dehydroamino acid derivatives with acid anhydride or π-allyl palladium complex proceeded smoothly to afford α,α-disubstituted amino acids via a radical and anionic carbon-carbon bond-forming processes. The tandem reductive reaction of N-phthaloyl dehydroalanine also proceeded effectively by using Bu₃SnH and Pd(PPh₃)₄.     

Synthesis of regioregular poly(3‐octylthiophene)s via Suzuki polycondensation and end‐group analysis by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Regioregular poly(3‐octylthiophene)s were synthesized through a palladium‐catalyzed Suzuki polycondensation of 2‐(5‐iodo‐4‐octyl‐2‐thienyl)‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane. The effects of the palladium catalyst {tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄], palladium(II) acetate [Pd(OAc)₂], [1, 1′‐bis(diphenylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl₂], tris(dibenzylideneacetone)dipalladium(0), or bis(triphenylphosphine)palladium(II) dichloride [Pd(PPh₃)₂Cl₂]} and the reaction conditions (bases and solvents) were investigated. NMR spectroscopy revealed that poly(3‐octylthiophene)s prepared via this route were essentially regioregular. According to size exclusion chromatography, the highest molecular weights were obtained with in situ generated Pd(PPh₃)₄ and tetrakis(tri‐o‐tolylphosphine]palladium(0) {Pd[P(o‐Tol)₃]₄} catalysts or more reactive, phosphine‐free Pd(OAc)₂. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry was used to analyze end groups and allowed the determination of some mechanistic aspects of the Suzuki polycondensation. The polymers were commonly terminated with hydrogen or iodine as a result of deboronation and some deiodination. Pd(PPh₃)₄, Pd(PPh₃)₂Cl₂, and Pd[P(o‐Tol)₃]₄ induced aryl–aryl exchange reactions with the palladium center and resulted in some chains having phenyl‐ and o‐tolyl‐capped chain ends. Pd(dppf)Cl₂ yielded only one type of chain, and it had hydrogen end groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1454–1462, 2005     

Neutral and cationic orthopalladated ( ) complexes ( = phenylazophenyl, dimethylbenzylamine, 8-methylquinoline, 2-methoxy-3-N,N-dimetrylaminopropyl)

By reacting [Pd( )(μ-Cl)]₂ with AgClO₄ in NCMe, the corresponding cationic complexes [Pd( )(NCMe)₂]ClO₄ ( = phenylazophenyl-C²,N¹; dimethylbenzylamine-C²,N; 8-methylquinoline-C⁸,N) can be obtained. Solutions containing the cations [Pd( )(S)₂]⁺ are obtained when the reaction is carried out in tetrahydrofuran or acetone (S). The treatment of these solutions with bidentate ligands (L—L) (Ph₂PCH₂PPh₂,Ph₂PNHPPh₂ or Ph₂PCH₂PPh₂CHC(O)Ph) gives the mononuclear [Pd( )(L3l)]ClO₄ complexes, with L3l acting as a chelate ligand. On the other hand [Pd( (μ-Cl)]₂ reacts with L3l (Ph₂PCH₂PPh₂, Ph₂PNHPPh₂) yielding [Pd( )Cl(L3l)] with L3l acting as monodentate. The reactions between [Pd( )(NCMe)₂]ClO₄ and 2,2′-bipyrimidyl give rise to the formation of the mononuclear [Pd( ) (bipym)]ClO₄ or binuclear [Pd₂( )₂(μ-bipym)](ClO₄)₂, [( )Pd(μ-bipym)Pd( )](ClO₄)₂ derivatives. Finally [Pd( )Cldppm] (dppm = Ph₂PCH₂PPh₂) react with NaH producing the neutral complexes [Pd( )(ddppm)] (ddppm = Ph₂PCHPPh₂) which by reaction with HCl lead again to the starting materials [Pd( )Cl(dppm)].