Vinylidene olefins

The prevailing chirality of the aldehyde produced using ( — )-DIOP as the asymmetric ligand is [ (R) ] for vinyl olefins where the asymmetric carbon atom arises from the attack of carbon monoxide at the carbon atom in position 2. The same chirality [ (R) ] is found also for vinylidene olefins where the asymmetric carbon atom arises from the attack of a hydrogen atom on the same carbon atom. 

For vinyl olefins the face prevailingly attacked by carbon monoxide and hydrogen is always the same and, as shown in Table VI, has the same name according to the Hanson s nomenclature (35). For vinylidene olefins, faces having different names according to Hanson are preferentially attacked (Table VI). As shown in the Scheme 6, if we equally... 

The same simple model predicts in a qualitatively correct way the isomeric composition of the reaction products with the exception of styrene and rans-/ -methylstyrene, in which the double bond is obviously conjugated with the phenyl ring. The predictions using the same model are contradictory for the vinylidene olefins. This is not surprising as the asymmetric induction in these olefins is always very small. 

The enantioselective hydroformylation process confronts a series of challenges. First, the hydroformylation of alkenes tends to form linear over branched products. Thus, enantioselective hydroformylation of alkenes must be conducted with uns)rmmetrical "vinylidenic" olefins (2,2-disubstituted) that establish a stereocenter at the carbon p to the carbonyl group, or with mono-substituted olefins that form the branched product. As noted above, vinylarenes, vinyl acetates, and other olefins bearing electron-withdrawing groups, form branched products. Thus, reactions of these olefins have been the greatest focus of enantioselective hydroformylations. 

The impurities contained in the AO obtained by these processes consist of vinylidene olefins (branched isomers), internal olefins, paraffins, and diolefins. 

In all the eases, the first step of the reaetion leads to the formation of eyelie intermediates (P-sultones), whieh rapidly undergo isomerization to unsaturated sulfonie aeids and (in the ease of linear and internal, but not vinylidene olefins) the more stable y- and 8-sultones. These sultones ean be hydrolyzed to hydroxyalkane sulfonates. 

Alpha-olefins are a potential replacement for alkylbenzenes in detergent applications. Then-exploitation, however, is largely limited to the Far East, centred on Japan, at present. Commercial supplies of alpha-olefins are produced by the oligomerisation of ethylene with the main exponents being Shell, Gulf and Ethyl. The material contains quantities of internal and vinylidene olefins but only when the level of internal olefins becomes excessive is this likely to have an effect on feedstock conversion. 

When developing a specification for the supply of alpha-olefins the following guidelines may be applied, although it should be remembered that the distribution of alpha, internal and vinylidene olefins are supplier-specific depending upon the manufacturing process ... 

Isoolefins with branchings adjacent to the double bond cannot be homopolymerized by active centers of the Ziegler-Natta type. Corresponding olefins with vinylidene double bonds, however, are classical monomers for cationic polymerization [556]. In this context Ziegler catalysts can act as cationic catalysts [557]. In the group of vinylidene olefins, isobutene is the one of greatest importance. It is obtained as the major component (45 to 50 vol%) of the C4 fraction in the naphtha cracking process [558]. The first polymerization was carried out by Lebedew [559]. 

TiCl,-(C2H5)3AUCl3 1-hexene vinyliden olefins 834... 

Olefins ean be eategorized as linear alpha- or 1-olefins, (H(CH2) CH = CH2 (Tables 1 ) branched 1-olefins, RCH = CH2 (R, branched alkyl) (Table 5) vinylidene olefins, R2C = CH2 internal olefins, RCH=CHR cyclic olefins and vinylcycloalkanes [7]. 

In trans, trisubstituted, and tetrasubstituted olefins In vinyl, cis, and vinylidene olefins... 

In the reactions of the fluoro-olefins, steric factors are of lesser importance because of the relatively small size of the fluoro-substitucnt.3 Fluorine and hydrogen are of similar bulk. In these circumstances, it should be expected that polar factors could play a role in determining regiospecificity. Application of the usual rules to vinylidene fluoride leads to a prediction that, for nucleophilic... 

Propagation reactions involving the fluoro-olefins, vinyl fluoride (VF)6Q 7 vinylidene fluoride (VF2)69 7""74 and trifluoroethylene (VF3),75 show relatively poor rcgiospccificity. This poor specificity is also seen in additions of small... 

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

The first explicit information appeared in 1953 in two U.S. patents (9) which showed that platinum black as well as platinized asbestos or silica were effective for addition of trichlorosilane to olefins. Platinum on charcoal was unusually active with trichlorosilane and acetylene, ethylene, butadiene, vinyl chloride, or vinylidene fluoride. Temperatures as low as 130°C were sometimes employed. 

As exemplified in Eq. 8.38, thermal [2 + 2] cycloadditions of 4-vinylidene-2-oxazoli-dinone 287 and alkynes such as phenylacetylene result in the formation of 3-phenyl-substituted methylenecyclobutene 288 [149]. The authors confirmed by NMR analysis that only the Z-configuration isomer was formed. It is worth noting that the [2 + 2] cycloaddition of allenes 287 is not restricted to alkynes even olefins such as acrylic esters or silyl enol ethers furnish the corresponding methylenecyclobutanes... 

On the other hand, 4-vinylidene-l,3-oxazolidin-2-one 26 undergoes a facile [2 + 2]-cycloaddition with electron-deficient olefins regioselectively at the terminal double bond to furnish methylenecyclobutane derivatives [25]. 

DFT calculations confirmed the similarities with the alkyne/vinylidene transformation but have revealed that additional parameters were essential to achieve the isomerization [8, 20-23]. The hydride ligand on the 14-electron fragment RuHC1L2 opens up a pathway for the transformation similar to that obtained for the acetylene to vinylidene isomerization. However, thermodynamics is not in favor of the carbene isomer for unsubstituted olefins and the tautomerization is observed only when a re electron donor group is present on the alkene. Finally the nature of the X ligand on the RuHXL2+q (X = Cl, q=0 X = CO, q=l) 14-electron complex alters the relative energy of the various intermediates and enables to stop the reaction on route to carbene. 

Water-soluble mthenium vinyUdene and aUenylidene complexes were also synthetized in the reaction of [ RuCl2(TPPMS)2 2] and phenylacetylene or diphenylpropargyl alcohol [29]. The mononuclear Ru-vinylidene complex [RuCl2 C=C(H)Ph)(TPPMS)2] and the dinuclear Ru-aUylidene derivative [ RuCl(p,-Cl)(C=C=CPh2)(TPPMS)2 2] both catalyzed the cross-olefin metathesis of cyclopentene with methyl acrylate to give polyunsaturated esters under mild conditions (Scheme 7.10). 

Ruthenium vinylidene species can be transformed into small carbocyclic rings via carbocyclization reactions. Ruthenium vinylidene complex 2, generated from the electrophilic reaction of alkyne complex 1 with haloalkanes, was deprotonated with "BU4NOH to give the unprecedented neutral cyclopropenyl complex 3 (Scheme 6.2) [5]. Gimeno and Bassetti prepared ruthenium vinylidene species 4a and 4b bearing a pendent vinyl group when these complexes were heated in chloroform for a brief period, cyclobutylidene products 5a and Sb formed via a [2 + 2] cycloaddition between the vinylidene Ca=Cp bond and olefin (Scheme 6.3) [6]. 

---