Complex, TT-Allyl

Another difference between the two mechanisms is that the former involves 1,2 and the latter 1,3 shifts. The isomerization of 1-butene by rhodium(I) is an example of a reaction that takes place by the metal hydride mechanism, while an example of the TT-allyl complex mechanism is found in the Fe3(CO)i2 catalyzed isomerization of 3-ethyl-l-pentene. " A palladium acetate or palladium complex catalyst was used to convert alkynones RCOCSCCH2CH2R to 2,4-alkadien-l-ones RCOCH= CHCH = CHCHR. ... 

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... 

When we used asymmetric nucleophilic addition of malonate to the Mo tt-allyl complex in our first delivery, the Mo chemistry was not so clearly understood, and our application would be the first large scale example, to the best of our knowledge. Initially our contributions to Mo chemistry were two-fold (i) replacement of non-commercially available (EtCN)3Mo(CO)3 or (C7H8)Mo(CO)3 by more stable and inexpensive Mo(CO)6 by incorporation of proper pre-activating time (ii) simplified preparation of the chiral ligand. Even after we completed the project, we still had a strong interest in Mo chemistry. 

The other mechanism, called the tt-allyl complex mechanism, does not require external hydrogen ... 

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 mechanism of coordination polymerization of 1,3-butadiene and, in general, that of conjugated dienes follows the same pathway discussed for alkene polymerization that is, monomer insertion into the transition metal-carbon bond of the growing polymer chain occurs. One important difference, however, was recognized very early.47,378,379 In the polymerization of dienes the growing chain end is tt-allyl complexed to the transition metal ... 

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. 

Nucleophilic attack at tt- allylic complexes may also occur from (a) external trans addition or (b) internal cis addition, resulting in the formation of allylic oxidation products (equation 153).398,399... 

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]. 

The Pd-catalyzed allylic substitution reactions proceed via TT-allyl complex, so that branched and linear substrates yield the same products (Scheme 5.7). 

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... 

The addition of nucleophiles to the terminal carbons of the ITT-allyl group leads to allylation of the nucleophile (equation 59). The nucleophiUc group normaUy bonds to the less-hindered terminal carbon. However, this preference depends on the other ligands coordinated to paUadium. In the case of the tt-allyl complex derived from methylenecyclohex-ane, the nucleophile LiCH(S02Me)C02Me gives the product... 

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). 

---