Telomerization of diene

Takacs JM (1995) Transition metal allyl complexes Telomerization of dienes. In Hegedus LS (ed) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford... 

From the beginning of the 1970s unhl the mid 1980s, several examples of the telomerization of dienes with water [76, 77] or methanol [78, 79] to isomeric mixtures of dienols or dienol ethers catalyzed by palladium-phosphine complexes in the presence of carbon dioxide have been reported. Neither the yield nor the selectivity were very high. However, when allene was employed as a diene , 3-methyl-2-meth-ylene-3-buten-l-ol was obtained with fairly good selectivity (up to 98%) (Eq. 6.43) [78]. 

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

The telomerization of dienes in a two-phase system was first described in a patent (100). Water was used as the solvent for the catalyst, with sulfonated phosphane ligands providing the water solubility. Water, alcohols, phenols, acids, amines, and acetylacetic add were used as nucleophiles. 

Although the telomerization of dienes in a two-phase system has been intensively investigated with compounds containing active hydrogen such as alcohols, amines, phenols, acids, etc., the selective and productive telomerization of butadiene continues to be a challenge. It is only recently that primary octadi-enylamines have been obtained with selectivity up to 88% in the telomerization of butadiene with ammonia using a two-phase toluene/water system and Pd(OAc)2/tppts as the catalyst [Eq. (23)] [125]. 

In a similar fashion, palladium- or nickel-catalyzed hydrosilylative cyclization of bis-diencs 6 stereoselectively leads to //( / .< -1,2-disubstituted cyclopentanes 761. This reaction resembles telomerization of dienes with 1,4-carbosilylation of one of the diene subunits, leading to allylsilanes. Both stereoisomers are formed with the same relative configuration of the ring substituents, solely differing with respect to the Z/E configuration of the (wo different unsaturated side chains. 

These unusual properties were the basis of the fluorous biphasic catalysis process (FBC) first published in 1994 by Horvdth and Rdbai and demonstrated using hydroformylation chemistry as a pertinent example (7, 2) in a 1991 Ph.D. thesis, that was unfortunately not readily available to the homogeneous catalysis community nor published in the open literature, M. Vogt, under the guidance of his Ph.D. advisor, W. Keim, of the Rheinisch-WestflUischen Technischen Hochschule in Aachen, Germany, presented the first conceptual aspects of the FBC approach with an emphasis on oligomerization of alkenes, oxidation of alkenes, hydroformylation of olefins, and telomerization of dienes (5, 4). 

Allyl ligands are reactive groups in catalytic processes, such as allylic substitution (Chapter 20) and transition-metal-catalyzed additions of allyl groups to carbonyl compounds (Chapter 12). They are also intermediates in a variety of catalytic processes involving dienes, including the hydroamination (Chapter 16) and telomerization of dienes (Chapter 22). They are also formed by cleavage of the allylic C-H bonds of olefins to form intermediates in allylic oxidation chemistry and as stable species that inhibit the polymerization of a-olefins (Chapter 22). The synthesis, structure, and occurrence of -rj -allyl complexes have been reviewed. ... 

The telomerization of dienes with alcohols as the nucleophile has now been conducted in a practical fashion. A palladium catalyst containing an N-heterocyclic carbene ligand has been shown to form linear dimeric ethers selectively from alcohols and butadiene with remarkably high turnover numbers (Equation 22.40). The activity of this catalyst is significantly higher than that of the more classical catalysts generated from Pd(OAc)j and PPhj. Under optimized conditions involving some added carbene precursor, presumably to... 

Aqueous and aqueous-organic biphasic systems would constitute straightforward reaction mixtures for catalyzed hydration of olefins and alkynes. In fact, water is chemically utilized in telomerization of dienes with H2O (179) and hydration of alkynes has also gained synthetic importance (222). However, these reactions are usually run in homogeneous solutions making the olefin or alkyne soluble by using a water-miscible organic cosolvent (alcohols, THF). 

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