Tt-allylic complexes, with

In the catalytic reaction this diastereoselectivity drops, and it was demonstrated that the TT-allyl complex with the cis tetrahydrofuran is kinetically favored and is trapped by the... 

A related Pd-catalyzed allylation relied on the excellent leaving group ability of the H-phosphinate anion. Instead of the allyl acetate shown in Scheme 53, unfunctionalized allyl alcohol was used directly. Transesterification yields an allyl phos-phonate, whose oxidative addition to a Pd(Xantphos) catalyst yields a tt-allyl complex, with the H-phosphinate group present as a counter ion or bound to Pd. P-C bond formation might then take place either by nucleophilic attack, or by P-C reductive elimination (Scheme 55) [91]. A similar mechanism was suggested for cross-coupling of H3PO2 with benzylic alcohols [92]. 

These TT-allyl complexes are moderately electrophilic 101 in character and react with a variety of nucleophiles, usually at the less-substituted allylic terminus. After nucleophilic addition occurs, the resulting organopalladium intermediate usually breaks down by elimination of Pd(0) and H+. The overall transformation is an allylic substitution. 

Nucleophilic Substitution of xi-Allyl Palladium Complexes. TT-Allyl palladium species are subject to a number of useful reactions that result in allylation of nucleophiles.114 The reaction can be applied to carbon-carbon bond formation using relatively stable carbanions, such as those derived from malonate esters and (3-sulfonyl esters.115 The TT-allyl complexes are usually generated in situ by reaction of an allylic acetate with a catalytic amount of fefrafcz s-(triphenylphosphine)palladium... 

The early synthetic processes using organonickel compounds involved the coupling of allylic halides, which react with nickel carbonyl, Ni(CO)4, to give TT-allyl complexes. These complexes react with a variety of halides to give coupling products.255... 

A final example concerns the question of 7r-allyl and related complexes with hydrogen. Again the evidence cited in the preceding section suggests that the principal reaction of jr-allyl complexes with hydrogen is to yield olefins, desorbed from the surface, although the possibility that a TT-bonded olefin is formed first is a geometrically feasible process (Fig. 25). 

It was later found that stable organometallic compounds of transition metals exhibiting very low polymerization activity could be transformed into high-activity catalysts when deposited on silica, alumina, or silica-alumina.287-289 Interaction of surface hydroxyl groups with the organometallic compounds such as chromocenes, benzyl, and Tt-allyl complexes results in the formation of surface-bound organometallic complexes (41-43) 289-291... 

The Tsuji-Trost reaction is the palladium-catalyzed allylation of nucleophiles [110-113]. In an application to the formation of an A-glycosidic bond, the reaction of 2,3-unsaturaled hexopyranoside 97 and imidazole afforded iV-glycopyranoside 99 regiospecifically at the anomeric center with retention of configuration [114]. Therefore, the oxidative addition of allylic substrate 97 to Pd(0) forms the Tt-allyl complex 98 with inversion of configuration, then nucleophilic attack by imidazole proceeds with a second inversion of configuration to give 99. 

The adoption of reaction models available for the polymerization of conjugated dienes by Ni- and Ti-catalysts to the polymerization of BD by Nd catalysis is justified by the similarities of the respective metal carbon bonds. In each of these mechanistic models the last inserted monomer is bound to the metal in a 3-allyl mode. The existence of Ni- -allyl-moieties was demonstrated by the reaction of the deuterated nickel complex [ rf- C4D6H)NiI]2 with deuter-ated BD (deuterated in the 1- and 4-position). After each monomer insertion a new 3-allyl-bond is formed [629]. As TT-allyl-complexes are known for Ti and Ni this knowledge has been adopted for Nd-based polymerization catalysts [288,289,293,308,309,630-636,638-645]. 

Reports of complexes of this class bearing phosphorus ligands also exist. The oxidative addition of allyl bromides and iodides to Fe(Pp3)5 gives the analogous -allyl complexes (136). The reaction of (j7" -diene)Fe(PMe3)3 with CO2 under pressure gives chelated tt-allyl complex (137). ... 

The parent TMM complex (190 R = H) undergoes photochemical ligand substitution with trifluorophosphine or trimethylamine Al-oxide assisted substitution with tertiary phosphines or t-butyl isocyanide (Scheme 5A) Trimethylamine A-oxide assisted substitution using isoprene as the incoming ligand results in C-C bond formation to afford the bis-TT-allyl complex (197). An intramolecular version of this reaction is also known.The parent complex (190 R = H) reacts with electrophiles. Addition of HCl or Br2 gives the methallyl complexes (192) and (198), respectively. Tetrafluoroethylene adds across the Fe bond to afford (199) under photochemical conditions. Complex (190) undergoes Friedel-Crafts-type acylation with... 

However, as the temperature rises this is rapidly converted to the TT-allylic complex. Similar complexes of conjugated dienes involving complexing of only one double bond have been observed with trans-1,3-pentadiene, cis,trans-2, i-hexadiene, and 1,3-cyclooctadiene. 

Treatment of [WICO) ] with allyl halides under UV radiation gives the TT-allyl complexes[W2Cl3(CO)6(Tj -allyl)], [WBr(CO)4(Tj -allyl)], and [WI (CO)4(Tj -allyl)], respectively. A large series of 7r-allyl complexes of the type [MX(CO)2L2(T7 -allyl)] have been prepared by reaction of the zero-valent complexes [M(CO)4L2] with ally halides. ... 

In 1991, Shin et and Sarkar et reported the reactions of zero-valent bis(3,5-dimethylpyrazolyl)methane type complexes [Mo (C0)4(N"N)] with allyl halides to give a series of TT-allyl complexes [MoX (CO)2(N N)(TjCallyl)] (N N = H2CPZ2, H2CPz 2, PhHCPz2, PhHCPz 2). These complexes also can be made by reaction of [MoBr(CO)2(NCMe)2 (r/Callyl)] with... 

Starting from our ferrocene investigations, we (Kritskaya and the author, in collaboration with Yu. Ustynyuk and Struchkov) studied TT-allyl complexes of iron. 

Metal 77-cyclopentadienyls somewhat resemble the rr-allyl complexes. Initially, when the nature of the metal-allyl bond was not sufficiently clear, the similarity was emphasized many times [see the review by E. O. Fischer (425)]. The similarity shows itself, for example, in the equal antisymmetric C—C stretching frequencies (1640 cm ), which indicate that the force constants, hence the bond orders, are close. The central rr-allyl proton absorbs in the same NMR region as do the protons of coordinated cyclopentadienyl. Both ligands display the symmetrical sandwichlike bond with their metals. Today, however, it is clear that the complexes differ significantly in type, the difference being associated first of all with the fact that TT-allyl complexes are much more efficient than 77-cyclopentadienyls at transforming to o-allyl or 77-olefin compounds. This may be due to the difference between the delocalization energies, 2.472 and 0.828 eV for cyclopentadienyl and allyl anions, respectively (426). 

If the unsaturated hydrocarbon is a diene, both double bonds may coordinate to pal-ladium(ll). (Diene)palladium(ii) complexes have been isolated and characterized. For example, 2 and 3 are stable complexes in which both double bonds are coordinated to the metal . Conjugated dienes constitute a special case and although -diene complexes, e.g. 4, are postulated as intermediates, they have not yet been isolated. The butadiene complex 4 is in equilibrium with the Tt-allyl complex 5 in solution, and attempts to isolate the diene complex from this mixture lead to formation of a yellow crystalline complex 5. ... 

Reaction of alienes with PdCi2(PhCN)2 in benzene leads to the formation of 2-chloro TT-allyl complexes 69 (equation 30) ... 

In the first stage Lewis acids are absent and further hydroeyanation of the monoolefm products 3-PN 40 and 2M3BN 41 does not readily oeeur. The monoeyanation of butadiene is similar to HCN addition to olefins. An individual feature of hydrocyanation of conjugated dienes is the intermediate appearance of TT-allylic complexes 43, which participate in the successive carbon-carbon coupling. Equations (12) and (13) demonstrate the reaction of butadiene with the hydrido-nickel complex 42 leading to formation of nitrile 40 (a) and explain the generation of byproducts, i.e., the branched nitrile 41 via an alternative pathway (b) [68-70]. 

The acrylonitrile content in the fraction of acrylonitrile plus acrolein can therefore be interpreted as the probability of a NH-insertion instead of an oxygen insertion in the TT-allyl complex. The increase with time on stream in the acrylonitrile content then means an increase in the probability of insertion of... 

The cis-pentadienyl cation [C6H7Fe(CO)3] (387) and its 1-methyl-substituted analog (386) upon reaction with water undergo geometrical inversion leading to formation of the corresponding trans alcohol (84) (R = H and CHg, respectively). A mechanism involving a hydrated tt-allylic complex as intermediate has been postulated (386). Solvolysis... 

The TT-allyl complexes of Pd , e.g. [Pd( j -C3Hs)X]2 (X = Cl, Br, I), are very stable and more numerous than for any other metal, and neither Ni nor Pt form as many of these complexes. Indeed, the contrast between Pd and Pt is such that in reactions with alkenes, where a particular compound of Pt is likely to form an alkene complex, the corresponding compound of Pd is more likely to form a rr-allyl complex. The role of the Pd and Ni complexes as intermediates in the oligomerization of conjugated dienes (of which 1,3-butadiene, C4H6, is the most familiar) have been extensively studied, particularly by... 

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