Alkyl-allyl complex

As a mechanistic hypothesis, the authors assumed a reduction of the Fe(+2) by magnesium and subsequent coordination of the substrates, followed by oxidative coupling to form alkyl allyl complex 112a. A ti—c rearrangement, followed by a syn p-hydride elimination and reductive elimination, yields the linear product 114 with the 1,2-disubstituted ( )-double bond (Scheme 29). This hypothesis has been supported by deuterium labeling experiments, whereas the influence of the ligand on the regioselectivity still remains unclear. 

Itoh and co-workers prepared the first Ru(IV) alkyl-allyl complexes by the alkylation of RuCl2[(l-3- 6,7- 10-12- )-Ci2Hi8] by means of CHsMgX or an equimolar amount of CHsLi (Eq. 5.12) [21]. 

In selected cases, l-/ -alkyl-3,4,5-t -allyl complexes can be obtained via nucleophilic attack of carbanions at an internal carbon of pentadienyl ligands. Thus, in contrast to a previous communication, nucleophilic attack of the malonate carbanion does not occur at the terminal position of a pentadienyltricarbonyliron cation complex 1 to give a diene complex product 2 as the major product. Instead, the internal position is attacked to give an alkyl-allyl complex 3, which upon oxidative decomposition aifords a vinylcyclopropane product X ... 

Addition of alkenes to a tricarbonylvinylketeneiron complex 7 leads to an alkyl-allyl complex 8, which upon oxidative decomposition yields a vinylcyclopropane 9. ... 

Teatment of cyclooctatetraenetricarbonyliron complexes 10 with anhydrous aluminum trichloride in benzene gives tricarbonyl(2,4- j-8-or-9-oxabicyclo[3.2.2]nona-2,6-dien-8-yl)iron (11), which was previously obtained from tricyclo[3.3.1.0 ]nona-3,6-dien-9-one (12 barbaralone) with nonacarbonyldiiron. Conversion of this product 11 with carbon monoxide (100 atm, 120°C) yields barbaralone (12) in 95% yield. Thus, a high yielding (95%), short synthesis of barbaralone (12, R = H) from cyclooctatetraene via an alkyl-allyl complex intermediate 11 is available. 

Alkyl-allyl complexes of isomeric systems can be interconverted and thus be used in isomerization of vinylcyclopropanes. Ethyl 4-azabicyclo[5.1.0]octa-2,5-diene-4-carboxylate (20) reacts with pentacarbonyliron to give complex 21, which photochemically rearranges to complex 23. Carbonylation of both products 21 and 23 leads to ethyl 9-oxo-2-aza-bicyclo[3.3.1]nona-3,7-diene-2-carboxylate (22). While complex 21 upon heating regenerates the starting material, complex 23 gives the isomeric product 24. In contrast to iron, with rhodium only the endo-complex 25 is formed. ... 

The telomerization reactions are thought to occur by the mechanism in Scheme 22.20. In this mechanism, the two dienes couple to form the tethered alkyl allyl complex. The isolation of this class of complex was reported by Jolly and Wilke during mechanistic studies of diene oligomerization and later by others. Reaction of this complex with methanol would then protonate the olefinic C-3 carbon, and the resulting methoxide would attack the terminal position of the coordinated allyl to generate the resulting diene complex. Replacement of the dienyl ether ligand by two equivalents of butadiene restarts the catalytic process. 

Nickel-allyl complexes prepared from Ni(CO)4 and allyl bromides are useful for the ole-fination of alkyl bromides and iodides (E.J. Corey, 1967 B A.P. Kozikowski, 1976). The reaction has also been extended to the synthesis of macrocycles (E.J. Corey, 1967 C, 1972A). 

Allyl Complexes. Allyl complexes of uranium are known and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a uranium halide and an allyl grignard reagent. This synthetic method was utilized to obtain a rare example of a "naked" homoleptic allyl complex, U(T -C2H )4 [12701 -96-17, which decomposes at 0°C. Other examples, which are more stable than the homoleptic allyl complex have been synthesized, ie, U(allyl)2(OR)2 (R = alkyl), U(allyl)2X (X = halide), and U(allyl)(bipy)2. 

Thermal insertion occurs at room temperature when R is XCH2CHAr-, at 40° C when R is benzyl, allyl, or crotyl (in this case two isomeric peroxides are formed), but not even at 80° C when R is a simple primary alkyl group. The insertion of O2 clearly involves prior dissociation of the Co—C bond to give more reactive species. The a-arylethyl complexes are known to decompose spontaneously into CoH and styrene derivatives (see Section B,l,f). Oxygen will presumably react with the hydride or Co(I) to give the hydroperoxide complex, which then adds to the styrene. The benzyl and allyl complexes appear to undergo homolytic fission to give Co(II) and free radicals (see Section B,l,a) in this case O2 would react first with the radicals. 

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). 

Alkyl, aryl and allyl complexes of 5 some metallocenes (43)... 

Allylic alkylation of 3-acetoxy-l,3-diphenylpropene by sodium dimethytmalonate, catalysed by the Pd-allyl complex 115, bearing the non-symmetric phosphonium ylide NHC ligand (5 mol%), proceeds to completion with 100% regioselectivity. 

Another interesting example of dehydrative C-C coupling involves the alkylation of benzimidazole 36 with allyl alcohol 37, which is catalysed by complex 39 [15], The reaction is believed to proceed by alkene complex formation with the allyl alcohol 37 with loss of water from the NH proton of the NHC ligand and OH of the allyl alcohol to give an intermediate Ji-allyl complex. The initially formed 2-allylbenzimidazole isomerises to a mixture of the internal alkenes 38 (Scheme 11.9). 

Attempts to synthesize transition metal alkyl compounds have been continuous since 1952 when Herman and Nelson (1) reported the preparation of the compound C H6>Ti(OPri)3 in which the phenyl group was sigma bonded to the metal. This led to the synthesis by Piper and Wilkinson (2) of (jr-Cpd)2 Ti (CH3)2 in 1956 and a large number of compounds of titanium with a wide variety of ligands such as ir-Cpd, CO, pyridine, halogen, etc., all of which were inactive for polymerization. An important development was the synthesis of methyl titanium halides by Beerman and Bestian (3) and Ti(CH3)4 by Berthold and Groh (4). These compounds show weak activity for ethylene polymerization but are unstable at temperatures above — 70°C. At these temperatures polymerizations are difficult and irreproduceable and consequently the polymerization behavior of these compounds has been studied very little. In 1963 Wilke (5) described a new class of transition metal alkyl compounds—x-allyl complexes,... 

Alkyl, allyl, and aryl bromides are dehalogenated mainly with the formation of R R dimers in the presence of polypyridyl complexes of the metals of Group VIII. It has been demonstrated that the complexes [Co(bpy)3] + 203-204 [Ni(bpy)3]2+,205 and [Ni(phen)3]2+206 catalyze the reductive dimerization of allyl and alkyl bromides in organic 203 205 206 and aqueous micellar 204 solution. 

One of the most recent developments in the field of Ni-catalyzed reactions of alkyl halides with organozinc derivatives is a study of Terao et al.411 They reported the use of three additives in the couplings 1,3-butadiene, N,N-bis(penta-2,4-dienyl)benzylamine 308a, and 2,2-bis(penta-2,4-dienyl)malonic acid dimethyl ester 308b. Addition of tetraene 308b to the reaction mixtures significantly increased the product yields (Scheme 157). The remarkable effect of these additives was explained by the formation of the bis-7r-allylic complex 309 as the key intermediate (Scheme 158). 

Remarkably high reactivity of cationic alkyl complexes of Group 4 metals with 1-alkenes has been observed in gas-phase reactions [129]. Typical ionic species such as TiCl2Me+ react with ethylene, and the insertion followed by H2 elimination gives rise to a cationic allyl complex TiCl2C3H5, which does not react further with ethylene. 

Jordan RF, LaPointe RE, Bradley PK, Baenziger N (1989) Synthesis and chemistry of cationic alkyl, alkenyl, and allyl complexes derived from the soluble, cationic hydride (CH4Me)2Zr(H) (THF)+. Organometallics 8 2892-2903... 

Our calculations show that the isomerization of the silyl-alkyl complex to form a V-allyl complex affords a significant stabilization as summarized in Figure 11. TheiV toil3 isomerization of 9a to the anti silyl-allyi complex, 10a-anti, results in a 9.5 kcal/mol stabilization and isomerization to the syn isomer, lOa-syn, results in a 7.2 kcal/mol stabilization. Isomerization of 9b to the anti silyl-allyi complex, 10b-anti, results in a 6.1 kcal/mol stabilization and isomerization to the syn isomer, lOb-.vyn results in a 5.4 kcal/mol stabilization. High temperature (500 °C) molecular dynamics simulations initiated at the V complex, 9a, reveal that the rj1 to T 3 isomerization has a minimal barrier and occurs in the sub-pico time frame. The inter-conversion between the syn and anti isomers has not been examined since both isomers are stereochemically equivalent, however, we expect the barrier to be small. 

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