Butadiene linear dimerization

Pi 2 NiBr2(PPh3)2/NaBH4 Butadiene Linear dimerization 40... 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Butadiene-ethylene dimerization (example 3, Table II) has been shown to proceed via a croty 1-nickel complex formed by protonation (54). It should be observed at this point that it cannot be excluded that linear cooligomerization of butadiene with ethylene to give 1,4,9-decatriene... 

Dimerization of conjugated dienes and trienes is generally accomplished at elevated temperatures or in the presence of metal catalysts. Linear dimerization of butadiene occurs readily at room temperature on nickel catalysts bearing aminophosphinite (AMP) ligands, and the reaction rate is reportedly twice that observed in other nickel systems employing either morpholine, ethanol or P-methyloxaphospholidines as modifiers62. 1,3-Pentadiene dimerizes in the presence of 1 mol% nickel catalyst to give a diastereomeric mixture of 4,5-dimethyl-l,3,6-octatriene as shown in equation 42. 

Linear dimerization and oligomerization of butadiene can be achieved by using a number of catalyst systems based on Pd, Ni (158—161), and Fe (162). 1,7-Octadiene can be obtained selectively when the dimerization is carried out in the presence of a reducing agent such as formic acid (163—165) or... 

The bis(ir-allyl) complex derived from the linear dimerization of butadiene can be trapped with phe-nylhydrazones in a process involving C—N insertion into a ir-allyl intermediate.265 Predominant insertion into the more substituted terminus is observed (equation 304). 

The linear dimers 89-91 are formed by Ni [32], Co [33], Fe [34] and Pd [35] catalysts. Linear dimers 90 and 91 are produced via the formation of metal M—H, accompanying migration of hydrogen. The formation of 89 is discussed later. The mechanism of the formation of 91 was studied by an experiment using butadiene 92 deuterated at the terminal carbons. In the formation of the branched dimer 91 from the deuterated butadiene 92, catalysed by Co or Fe complexes, insertion of the second butadiene occurs at the substituted side of the 7r-allyl complex 93 to give 94. Finally, the triene 96 is formed from 95 and Fe—H(D) is regenerated. 

Unique linear dimerization of butadiene is catalysed by a Pd—PI13P complex [50]. This Pd-catalysed linear dimerization affords 1,3,7-octatriene (89) by //-elimination of 128 and reductive elimination of 129. Transfer of H from C(5) to C(3) in the intermediate bis-7r-allylpalladium 68 occurs to give 1,3,7-octatriene (89). 

The 1,5 cyclooctadiene complex [Cp Ru(jj rf--C Yiu) (CO)]OTf was isolated upon treatment of Cp Ru(j)" -butadiene)X (X = Cl, Br) with butadiene, AgOTf, and CO. A similar [4-1-4] cycloaddition (a thermally forbidden reaction see Woodward-Hoffmann Rules)) is observed when Cp Ru(isoprene)Cl is treated with iso-prene, AgOTf, and CO. Likewise, the reaction of 1,3-pentadiene with Cp Ru( ) -l,3-pentadiene)Cl results in linear dimerization to form [Cp Ru(4-methyl-(l,3-jj 6-8-j) )-nonadienediyl)]OTf. These types of dimerization occur with both stoichiometric and catalytic amounts of the ruthenium complex. ... 

Mixed cyclopentadienyl-diene titanium complexes, Cp TiX(diene)(X = Cl, Br, I), have been prepared in 30-60% yield by the stoichiometric reaction of CpTiXs with (2-butene-l,4-diyl)magnesium derivatives or by the reduction of CpTiXs with RMgX (R = i-Pr, f-Bu, Et X = Cl, Br, I) in the presence of conjugated dienes, as shown in Scheme 4. The butadiene, 1,3-pentadiene, and 1,4-diphenylbutadiene complexes of Cp TiX exhibit a unique prone (endo) conformation (13), while the isoprene, 2,3-dimethylbutadiene, and 2,3-diphenylbutadiene complexes prefer the supine (exo) conformation (14). Reduction of Cp TiX(diene) with RMgX or Mg gives a low-valent species, which catalyzes a highly selective (>99%) tail-to-head linear dimerization of isoprene and 2,3-dunethylbutadiene. " ... 

Cyclo- and linear-dimerizations of 1,3-dienes were accomplished by means of a cationic ruthenium catalyst derived from [Cp RuCl(l,3-diene)] and AgOTf (Scheme 4.48) [96]. In THF, 1,3-butadiene was treated with the cationic ruthenium catalyst at 70 °C for 10 h to afford 1,5-cyclooctadiene in 89% yields. Similarly, isoprene underwent [4 -I- 4] cycloaddition in a head-to-tail fashion to yield quantitatively 2,6-dimeth-yl-l,3-cyclooctadiene and 3,7-dimethyl-l,5-cydooctadiene in a ratio of 21 79. On the O ther hand, a head-to-tail linear dimer was obtained in 95% yield from 1,3-pentadiene. 

Unlike nickel catalysts which form cyclic dimers and trimers (1,5-cyclooctadiene and 1,5,9-cyclododecatriene), palladium compounds catalyze linear dimerization of conjugated dienes. 1,3-Butadiene itself is converted to 1,3,7-octatriene. The reaction most characteristic of palladium is the formation of various telomers. 1,3-Buta-diene dimerizes with incorporation of various nucleophiles to form telomers of the following type ... 

Linear dimerization of 1,3-butadiene. Butadiene is dimerized to (E,E)-1,3,6-octatriene in 95% yield by a catalyst system composed of NaBH4 and [P(CgH5)3]2NiBr2 in a ratio of 2 1. The polymer-bound analogue (2) of... 

The 1,3-butadiene cyclo-dimerization reaction can be performed by iron complexes, prepared in situ by the reduction of [Fe2(NO)4Gl2l with metallic zinc, dissolved in [G4GiIm][BF4] or [G4GiIm][PF6] ILs (Scheme 30). The linear dimerization of 1,3-butadiene can also be performed with Pd(ii) salts (chloride or acetate)/PPh3 catalyst precursor dissolved in [G4GiIm]BF4 or [G4GiIm]PF6 to produce 1,3,6-octatriene (Scheme 31). ... 

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

The Pd-catalyzed linear dimerization of butadiene or isoprene in the absence of trapping reagent affords the linear dimer 1,3,7-octatriene (4) or its methylated derivative. Hagihara and co-workers originally reported that, in the absence of trapping reagent, treatment of butadiene with the bis(triphenylphosphine)(maleic anhydride)palladium(0) complex (0.01 mol %, acetone, 115 °C) affords 1,3,7-octatriene in 85% yield. NickeP " and cobaltf" " catalyst systems have also been described. 

While the intermolecular reactions of butadiene and related methyl or simple alkyl-substituted dienes have been investigated extensively, relatively few examples of the Pd-catalyzed linear dimerization of higher dienes have been reported. Brun and co-work-ers in an isolated paper reported that, under palladium catalysis, reaction of methyl 2,4-pentadienoate (Scheme 9, 28) affords the linear dimer 29 in high yield (95%). Two aspects of this reaction are of particular interest, (i) The dimerization yields essentially only the tail-to-tail dimer 29, not the head-to-tail or head-to-head isomers (30 or 31, respectively). This is in contrast to the behavior of alkyl-substituted dienes under similar conditions vide infra), (ii) Although no details are given, the authors imply that 29 is... 

Metal-mediated cyclizations that rely on the initial complexation of an alkene or alkyne around a low oxidation state metal center are often sensitive to the presence of additional substituents (particularly electron-donating substituents), and relatively more stringent reaction conditions are often required for successful cychzation. This effect was noted in the Ni-catalyzed formal [4 -I- 4] cycloaddition reactions developed by Wender and Tebbe and is apparent when one compares the reported facility of Pd-catalyzed linear dimerization of 1,3-butadiene versus that of substituted 1,3-dienes. Similarly, the initial attempts at Pd-catalyzed cyclization of bisdiene 70a (Scheme 22) were rather disappointing. Using 0.05 equiv of [Pd(OAc)2/3 PhjP] (THF, 65 °C, 12 h), only a small... 

The linear dimerization of isoprene often affords mixtures of head/tail dimers. For example, [Pd(OAc)2, P(CH2CH2CN)3l catalyzes dimerization of isoprene with triethylammo-nium formate in dimethylacetamide (55 °C, 3 h), affording dimers in 91% yield as a 10 49 37 98/99/100 mixture of head/tail coupling regioisomers (Scheme 30). It is interesting to note that, as in the case of butadiene and formic acid in the presence of phosphine-modified Pd(OAc)2, only 1,7-dienes are formed in this reaction of isoprene with formic add. 

Butadiene undergoes efficient Pd-catalyzed linear dimerization followed by trapping with many primary and secondary amines to give predominantly l-amino-2,7-octadi-... 

Under certain conditions less activated ketones (e.g., acetone, cyclopentanone, cyclohexanone, and cyclohexenone) can participate in the reaction with butadiene or iso-prene, ° but more commonly enamine derivatives are anployed. For example, Tsuji reported that butadiene undergoes Pd-catalyzed linear dimerization with trapping by the pyrrolidoyclohexene 126 (Scheme 39) (Pd(OAc)2, PhjP, CH3CN, 80 °C, 3 h) to afford the octadienyl derivative 127 in 66% yield after hydrolysis (aq. HCl, 50 C, 0.5 h). In addition, 22% of the a,a -dialkylated product was isolated. 

While relatively few examples have been reported, nitroalkanes can serve as efficient carbon nucleophiles in the Pd-catalyzed linear dimerization reaction.t For example, butadiene reacts with 2-nitropropane (137, (Ph3P)2PdCl2, KOH, i-PrOH, 50 °C, 4 h) to afford 9-methyl-9-nitro-l,6-decadiene (138 R , = Me) in 89% yield (Scheme 44). Nitromethane... 

Disilane trapping reagents behave in a conceptually similar fashion. Tsuji and coworkers found that a variety of simple dienes (143, e.g., butadiene, isoprene, 2-phenyl-l,3-butadiene, 2-trimethylsilyloxy-l,3-butadiene) undergo efficient Pd(dba)2-catalyzed linear dimerization disilane trapping with a variety of simple disilanes 144 to afford bis(allylsi-lane) products 145 (41-92% yield) (Scheme 47). Cyclic disilanes afford macrocyclic bis(allylsilane) products. ... 

---