Palladium complexes benzene

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

An aromatic C-H functionalization involving the m-addition of benzene to internal alkynes is mediated by a bimetallic palladium complex in the presence of catalytic amounts of a borane. The mechanism of process remains to be clarified (Equation (77)).73... 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

Substituting the benzene ring with a double bond, Pd-catalyzed intramolecular alkoxylation of alkyne 122 also proceeded via an alkenyl palladium complex to form furan 123 instead of a benzofurans [99, 100]. In addition, 3-hydroxyalkylbenzo[fc]furans was prepared by Bishop et al via a Pd-catalyzed heteroannulation of silyl-protected alkynols with 2-iodophenol in a fashion akin to the Larock indole synthesis, [101]. 

Finally, a few cyclizations of unsaturated side chains on o-halogeno-anilines or -benzenes have been catalyzed by transition metal complexes. Cyclization of the cinnamylbenzylamine (245) by palladium gives some 4-benzylisoquinoline and some of compound (246) (77TL1037). Acryloylanilines (247) and (248) can be cyclized by a nickel complex (75MI20800) or by a palladium complex (79JA5281). The mechanism for the latter reaction is given in equation (50). 

The reaction is carried out under a dry nitrogen atmosphere. To a mixture of 7.32 g (40 mmol) of ( )-bromophenylethcnc and 0.20 mmol of the palladium complex are added 100 mL (80 mmol) of a 0.8 M solution of [a-(trimethylsilyl)benzyl]magnesium bromide in diethyl ether at —78 °C. The mixture is allowed to warm and stirred at 0 "C for 2 d and then hydrolyzed with 10% HCI at 0 C. The organic layer and ether extracts from the aqueous layer are combined, washed with aq NaHCG3 and then water, and dried over anhyd MgS04. The solvent is evaporated and the product isolated by distillation yield 10.1 g (93% ) bp 135-139 JC/0.9 Torr [a]p° —43.9 (c = 1.0, benzene) 95% op (determined by hydrogenation and direct comparison with an authentic sample prepared via asymmetric hydrosilylation and correlated with 1,3-diphenyl-t -propanol). 

Nickel(O) or palladium(II) compounds in stoichiometric amounts promote the ring enlargement of simple alkyl-substituted 1,2-divinylcyclobutanes in benzene at room temperature to give 1 1 metal complexes of cycloocta-1,5-dienes.119 Destruction of the palladium complexes with potassium cyanide affords the free cycloocta-1,5-dienes. The stereochemistry observed is the same as in the thermal reaction at 150°C. 

Rodriguez CJ, Foster DF, Eastham GR, Cole-Hamilton DJ (2004) Highly selective formation of linear esters from terminal and internal alkenes catalysed by palladium complexes of bis-(di-tert-butylphosphinomethyl) benzene. Chem Comm 10(15) 1720-1721... 

During their work on the arylation of aromatic compounds by substitution, Fujiwara, et al. observed biaryl formation when aromatic compounds were placed in the presence of olefin-palladium complexes and silver nitrate.80 Developing this reaction as a method for biphenyl synthesis, these authors showed that the more stable the olefin-palladium complex was, the lower the yield. Ethylene dichloropalladium proved to be the best choice, when used with silver nitrate. However, the reaction required stoichiometric amounts of both catalysts (Scheme 10.47). Benzene derivatives substituted by electron-donating or -withdrawing groups reacted as well, but a mixture of regioisomers was produced, except for nitrobenzene, which only gave m,m -dinitrobiphenyl. 

We reported that the palladium-catalyzed reaction of arynes with bis-jr-allyl palladium complex afforded 1,2-diallylated derivatives of benzene in good yields (Scheme 32) [77]. The reaction of 104 with allyltributylstan-nane 3a and allyl chloride 11 in acetonitrile in the presence of 2.5 mol % Pd2(dba)3.CHCl3/dppf catalyst at 40 °C for 12 h afforded 1,2-diallyl benzene 105 in 76% yield. The generation of benzyne 106 takes place presumably first from 104 under the conditions of the palladium catalysis, which reacts with the complex 2 in a manner similar to the diallylation of activated olefins (refer Scheme 29). 

Reaction of the palladium complex of ligand la with 10a in the presence of Af,0-bis(trimethylsilyl)acetamide (BS A), catalytic KOAc as the base, and dimethyl malonate results in good yield and high selectivities for 12a (eq 4). The most efficient ligand in terms of regio- and enantioselectivity is la. In benzene, the regio-and enantioselectivity are further improved (Table 1). 

C,H,N, Benzene, 2-isocyano-l,3-dimethyl-, iron complexes, 26 53 57 C,H jN, Benzenemethanamine, N,N-di-methyl-, lithium complex, 26 152 Iutetium complex, 27 153 palladium complex, 26 212 QHijP, Phosphine, cthylmethylphenyl-, lithium complex, 27 178 C,H,3P, Phosphorane, dimethylmethylene-diphenyl-, uranium complex, 27 177 C,H P, Phosphine, triisopropyl-, rhodium complex, 27 292 tungsten complex, 27 7 C,Hj7PSi3, Phosphine, tris(trimethylsilyl)-, 27 243... 

C12H111N2, Azobenzene, cobalt and palladium complexes, 26 175, 176 manganese complex, 26 173 C12H11N, Pyridine, 2-(phenylmethyl)-, palladium complex, 26 208-210 C12H11P, Phosphine, diphenyl-, manganese complex, 26 158, 226-230 ruthenium complex, 26 264 Ci2H,20,S, Thiophenetetracarboxylic acid, tetramethyl ester, 26 166 C 2H,5N, Naphthalenamine, A ,iV-dimethyl-, lithium complex, 26 154 Cj2Hih, Benzene, hexamethyl-, ruthenium complex, 26 181, 182... 

To a suspension of Pdfdbalj (0.68 g, 1.2 mmol) in benzene (20 mL) was added i-PrjP (0.19 g, 1.2 mmol). After stirring for 15 min at rt, the palladium complex was dissolved to form a yellow-reddish solution. Within 45 min, 3,3-dimethylcyclopropene (16.0 g, 0.236 mol) cooled to — 78 C was added. The reaction temperature was kept at 45 C or lower by external cooling with water. The yellow solution was stirred at rt for 1 h and evaporated. After distilling off 17.0g of benzene (25°C/0.1 Torr), 17 was obtained by distillation at 45-50 C/0.1 Torr yield 15.6 g (97.2%) GC 99.2% purity. The product crystallized mp 30°C. The red powder cataly.st, remaining as distillation residue, showed activity for further cyclotrimer-ization. 

In several cases, the in situ formation of hydrogen peroxide is the first step of the process. Thus, phenol can be obtained from benzene, carbon monoxide (5 atm) and oxygen (65 atm) at 70 °C in a benzene-water-methyl isobutyl ketone mixture, with TS-1 and a palladium complex as catalysts [26]. Despite a 91% selectivity to phenol, benzene conversion (3.2%) and productivity are still too low for industrial application. The palladium complex is required to promote hydrogen peroxide formation upon reaction of oxygen, carbon monoxide and water [27[. 

As revealed in our previous study, palladium complexes with heteropolytungstate anion PWnOag do catalyze oxidation of benzene with O2/H2 mixture. Water soluble palladium complexes operate in a two-phase liquid medium. This paper describes preparation, characterization and catalytic performance of Si02 supported palladium complexes with heteropolytungstates. 

In general for carbonylations, palladium as catalyst metal is preferable to nickel with respect of catalyst efficiency. Thus, Okano, Kiji, and co-workers described some other efficient palladium-catalyzed carbonylations of allyl chloride and substituted allyl halides (Eqs. 5-10). In greater detail, the water-soluble palladium complex PdCl2[Ph2P(w-C6H4S03Na)]2 has been used in a two-phase system (e.g., aqueous NaOH/benzene medium) at atmospheric carbon monoxide pressure, giving 3-butenoic acids [20], In the carbonylation of allyl chloride a mixture of 2-bute-noic acid, which was formed by base-catalyzed isomerization, and 3-butenoic acid was obtained in up to 90% yield (TON = 135), albeit at moderate selectivity (24 76). Clearly, the isomerization depends on the concentration of the base and was therefore suppressed by a method of continuous addition to the aqueous medium. 

The solvent may determine the stereochemistry in the stoichiometric formation of 7r-allyl-palladium complexes from allyl halides. Strong donor solvents such as acetonitrile and dimethylsulfoxide lead to the expected m-ir-allyl complexes cis-16, whereas benzene, dichloro-methane or tetrahydrofuran give the. vva-addition product Irans-1639. Using soft carbanions in tetrahydrofuran. both complexes are converted to the corresponding alkylated products 17 with clean inversion of configuration. 

Preparation. - Fluorophosphines have been obtained from the reactions of the related chlorophosphines with trimethyl tin fluoride. Phenyl(isopropyl)-fluorophosphine has been resolved via a chiral amine-palladium(II) complex, providing the first example of the resolution of a free fluorophosphine chiral at phosphorus. This compound racemises at 20 °C in benzene solution over six hours. The neat compound rapidly decomposes by redox disproportionation. The same approach has been used for the resolution of the related chloro-phosphine, but the optically active compound could not be liberated unchanged from the crystallised diastereoisomeric palladium complex. The dihalo-genophosphines... 

Analogously, in the presence of silica-supported palladium catalysts, benzene is oxidized under ambient conditions to give phenol, benzoquinone, hydroquinone and catechol [37b]. Palladium chloride, used for the catalyst preparation, is believed to be converted into metallic palladium. The synthesis of phenol from benzene and molecular oxygen via direct activation of a C-H bond by the catalytic system Pd(OAc)2-phenanthroline in the presence of carbon monoxide has been described [38]. The proposed mechanism includes the electrophilic attack of benzene by an active palladium-containing species to to produce a a-phenyl complex of palladium(ll). Subsequent activation of dioxygen by the Pd-phen-CO complex to form a Pd-OPh complex and its reaction with acetic acid yields phenol. The oxidation of propenoidic phenols by molecular oxygen is catalyzed by [A,A"-bis(salicylidene)ethane-l,2-diaminato]cobalt(ll)[Co(salen)] [39]. 

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