Allyl complexes preparation

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). 

Manganese allyl complexes, preparation, 5, 826 Manganese arenes, preparation and characteristics, 5, 830 Manganese aryl complexes, preparation and characteristics,... 

TT-Aliylpalladium chloride reacts with a soft carbon nucleophile such as mal-onate and acetoacetate in DMSO as a coordinating solvent, and facile carbon-carbon bond formation takes place[l2,265], This reaction constitutes the basis of both stoichiometric and catalytic 7r-allylpalladium chemistry. Depending on the way in which 7r-allylpalladium complexes are prepared, the reaction becomes stoichiometric or catalytic. Preparation of the 7r-allylpalladium complexes 298 by the oxidative addition of Pd(0) to various allylic compounds (esters, carbonates etc.), and their reactions with nucleophiles, are catalytic, because Pd(0) is regenerated after the reaction with the nucleophile, and reacts again with allylic compounds. These catalytic reactions are treated in Chapter 4, Section 2. On the other hand, the preparation of the 7r-allyl complexes 299 from alkenes requires Pd(II) salts. The subsequent reaction with the nucleophile forms Pd(0). The whole process consumes Pd(ll), and ends as a stoichiometric process, because the in situ reoxidation of Pd(0) is hardly attainable. These stoichiometric reactions are treated in this section. 

Complexes with unsaturated ligands (a-vinyl. a-allyl, and alkynyl) have been reported, each prepared from Fe(TPP)CI with the appropriate Grignard (vinyl, 2- methylvinyl.2,2-dimethylvinyl,allyl,or2-methylallyl)orlithiumreagent(LiC= C-n-Pr or LiC CPh) and observed by NMR spectroscopy (Scheme 4). The vinyl and alkynyl complexes are stable in solution at 25 C, whereas the allyl species decompose quickly if allowed to warm to room temperature. All were too reactive to be purihed by chromatography. The vinyl and allyl complexes show characteristic low spin behavior, although the temperature dependence of the vinyl... 

It was suggested that this change in product distribution was due to the existence of an equilibrium between two types of complex, viz., a cr-butenyl-pentacyanocobaltate(III) and a 7r-butenyltetracyanocobaltate(III) 107, 109). However, further study of the kinetics and product distribution suggested the presence of two o-bonded complexes, viz., cr-but-l-en-3-yl and a-but-2-en-l-yl 24a). Direct evidence for the existence of a cyanide-dependent equilibrium between the a- and rr-bonded organocyanide complexes has been obtained from NMR studies of the complex prepared by the reaction of allyl halides with Co—H 109) (see also Section V,C). Both butadiene and crotyl chloride react with Co—H to give the same... 

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. 

Nitronate anions react with (jl-allyl)cobalt complexes prepared from acylation of 1,3-dienes by acetylcobalt tetracarbonyl to produce nitro enones (Eq. 5.50).74... 

Summary Several lithium l,3-diphospha-2-sila-allyl complexes 3a-f and the diphosphino-dichlorosilane 2 have been prepared and characterized. The hydrolysis and substitution reactions of these compounds are described yielding a number of phosphino- and diphosphino-silaphosphenes 5a-d, 4a,b and 6. The compounds have been characterized by NMR and by X-ray analyses in the cases of 2, 3a-c and 4a. 

Related bimetallic systems were also prepared with M = Ni, Pd, Pt or Ag [3-5]. This unprecedented Tl2- t2-SiO bonding mode is also found in the siloxane-substituted complex 4 [6], and may assist the rapid c-Ji-isomerization observed in the allylic complex 5. 

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,... 

The general interligand C—C coupling reaction shown in Eq. (8) for (metalla-/3-diketonato)BF2 compounds also occurs directly with metalla-/3-diketonate anions, thereby precluding the need to prepare the neutral difluoroboron complexes (53). As a one-pot synthesis, metal carbonyl acetyl compounds can be converted to neutral 77-allyl complexes [Eq. (12)]. 

Iridium-catalyzed transfer hydrogenation of aldehyde 73 in the presence of 1,1-dimethylallene promotes tert-prenylation [64] to form the secondary neopentyl alcohol 74. In this process, isopropanol serves as the hydrogen donor, and the isolated iridium complex prepared from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS is used as catalyst. Complete levels of catalyst-directed diastereoselectivity are observed. Exposure of neopentyl alcohol 74 to acetic anhydride followed by ozonolysis provides p-acetoxy aldehyde 75. Reductive coupling of aldehyde 75 with allyl acetate under transfer hydrogenation conditions results in the formation of homoallylic alcohol 76. As the stereochemistry of this addition is irrelevant, an achiral iridium complex derived from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and BIPHEP was employed as catalyst (Scheme 5.9). 

Because of the exceptional C-F bond strength, the successful preparation of a-halocyclopropyl c-complexes is realized by substitution of 1-bromo-l-fluoro-trans-2,3-dimethylcyclopropane 179 with Fp [90], Silica gel column chromatography of the thus obtained cr-complex 180 results in ring opening to the alcohol 181 as a single stereoisomer. The allene complex 182 is produced by treatment with BF3OEt2, indicating that 181 is derived from 182 and water. The 7i-allyl complex 183 is formed by photolysis via a disrotatory process. 

Similar reactions can be utilized to prepare allyl complexes of platinum and palladium. In this case, the product can exist in two isomers as described earlier. Analogous reactions can be used to prepare the tris allyl complexes of several metals. 

Another easily available palladium compound is PdCl2 however, it has low or no activity. The chloride ion in the coordination sphere of palladium seems to inhibit the coordination of two moles of butadiene to form the bis-77-allylic complex. However, PdCl2 can be used in the presence of an excess of bases, such as KOH, NaOH, sodium phenoxide, sodium acetate, potassium acetate, sodium methoxide, or tertiary amines. These bases deprive the chloride ion from the coordination sphere of palladium to form the active species. Thus, very stable and easily prepared... 

The stereoselective isomerization of allyl silyl ethers to (E)- or (Z)-silyl enol ethers was carried out in the presence of a cationic iridium(i) catalyst. The complex, prepared in situ by treating [Ir(cod)2]PFf,/2PPi3 with hydrogen was... 

Liebeskind and coworkers have examined the reactivity of (2//-pyran)Mo(CO)2Cp+ cations 210, which may be prepared in optically active form from carbohydrate precursors. Nucleophilic attack on cation 210 occurs at the diene terminus bonded to the ring oxygen to give jr-allyl complexes 51 (Scheme 53)85. Hydride abstraction from 51 gives the cation 54 addition of a second nucleophilie occurs regioselectively to give... 

Some of the evidence for such structures comes from the change in product distribution of the butenes as a function of cyanide concentration when butadiene is hydrogenated with pentaeyanocobaltate(II) catalyst or when the a butenyl complex is reduced with the hydride complex [HCo(CN)5] . Thus 1-butene is the major product in the presence of excess CN, and major product in the absence of excess cyanide. The 1-butene presumably arises from the cleavage of a tr complex, and the 2-butene via an intermediate w-allyl complex. The Tr-allyl complexes of cobalt tricarbonyl are well-characterized and can be prepared either from butadiene and HCo(CO)4 or from methallyl halide and NaCo(CO)4 [49). 

The protonation of the a-allylic cyanocobaltate complexes has been reported by Kwiatek and Seyler 50) to proceed with the liberation of the corresponding olefin. Thus the complex prepared from butadiene [Eq. (35)] on treatment with aqueous HCl liberates 1-butene. The carbonium ion which probably forms first can cleave directly to 1-butene or it may first rearrange to a Tr-olefin complex, from which the olefin is then displaced with either HgO or chloride ... 

Additional mechanistic insights were gained when Hartwig and coworkers isolated and characterized the first 7t-allyl complexes that are chemically and kinetically competent to be intermediates in iridium-catalyzed allylic substitution [46]. These complexes were prepared independently from allylic electrophiles that are more reactive than allylic carbonates. The isolation and structural characterization of these species provided a detailed view into the origins of enantioselectivity. 

Many of the studies on the asymmetric Ir-catalyzed allylic subshtuhon have been carried out with complexes prepared from [Ir(COD)Cl]2 and a phosphoramidite ligand. While numerous phosphoramidites have been inveshgated, those considered to be the most useful are shown in Figure 9.2. 

OR tHF Scheme 9.8 Steric course of all known allylic substitutions catalyzed by Ir complexes prepared from phosphoramidites L1-L5. 

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