Metal allylic

Dienes and allylarcncs can be prepared by the Pd-catalyzcd coupling of allylic compounds with hard carbon nucleophiles derived from alkenyl and aryl compounds of main group metals. Allylic compounds with various leaving groups can be used. Some of them are unreactive with soft nucleophiles, but... 

Addition of Metalated Allylic Phosphine Oxides, Phosphonates, Sulfones, and Sulfoxides and Sulfoximines to a,/i-l nsaturated Carbonyl Compounds... 

Metalated Allylic Phosphine Oxides and Phosphonates Simple Diastcreoselection... 

Volume F, 21 D.1.5.2.2. Addition of Metalated Allylic Phosphorus and Sulfur Compounds 2071... 

Unlike many other metal-allyl systems, allylsilanes are rcgio-stable at inormal temperatures, with 1,3-sigmatropic shifts occurring at a significant Irate only at temperatures in excess of 300°C. 5-Trimethylsilylcyclo-Ipentadiene provides an exception to this generalization, but it can still be lhandled quite readily. 

Takacs JM (1995) Transition metal allyl complexes Telomerization of dienes. In Hegedus LS (ed) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford... 

Compounds of the type Zr(7r-Cpd)2, Ti(Tr-Cpd)2, and Cr(CaH6)2, were found to be completely inactive with all monomers whereas a significant number of transition metal allyl compounds were found to have weak activity for ethylene polymerization. The latter results are summarized in Table I. Despite the fact that many transition metal allyl compounds are unstable above 0°C, in the presence of monomer, the metal allyl structure... 

Metal allyls that were found not to have any polymerization activity at all, despite extreme care in preparation and polymerization, wereNi(allyl)s, Pd(allyl)2, and Mn(aHyl)s (9) and these are probably not polymerization... 

The activity of transition metal allyl compounds for the polymerization of vinyl monomers has been studied by Ballard, Janes, and Medinger (10) and their results are summarized in Table II. Monomers that polymerize readily with anionic initiators, such as sodium or lithium alkyls, polymerize vigorously with allyl compounds typical of these are acrylonitrile, methyl methacrylate, and the diene isoprene. Vinyl acetate, vinyl chloride, ethyl acrylate, and allylic monomers do not respond to these initiators under the conditions given in Table II. 

Polymerization of Substituted Transition Metal Allyl Compounds Temperature 50°C, Ethylene Pressure Jfi aims, Ethylene. Catalyst Concentration 24 X 10 M... 

In addition to the simple chemical methods for following these processes, infrared spectroscopy may also be used. In Fig. 9 is shown the spectrum of silica dried at 200°C before and after reaction with Zr(allyl)4- The characteristic absorption bands of the transition metal-allyl group are clearly displayed, also a significant reduction in the number of hydroxyl groups (3740 cm-1) is also clearly evident. 

Initial studies of the polymerization of propylene with transition metal allyl compounds suggested that this monomer could not be polymerized by any of the soluble catalysts available. Subsequent work (16) has revealed, however, that the propylene polymerization is much more susceptible to impurities, in particular traces of ether which compete with the monomer for the coordination sites. When this and other impurities are removed, weak activity is detected. These results are summarized in Table XIII. 

A detailed study of the mechanism of the insertion reaction of monomer between the metal-carbon bond requires quantitative information on the kinetics of the process. For this information to be meaningful, studies should be carried out on a homogeneous system. Whereas olefins and compounds such as Zr(benzyl)4 and Cr(2-Me-allyl)3, etc. are very soluble in hydrocarbon solvents, the polymers formed are crystalline and therefore insoluble below the melting temperature of the polyolefine formed. It is therefore not possible to use olefins for kinetic studies. Two completely homogeneous systems have been identified that can be used to study the polymerization quantitatively. These are the polymerization of styrene by Zr(benzyl)4 in toluene (16, 25) and the polymerization of methyl methacrylate by Cr(allyl)3 and Cr(2-Me-allyl)3 (12)- The latter system is unusual since esters normally react with transition metal allyl compounds (10) but a-methyl esters such as methyl methacrylate do not (p. 270) and the only product of reaction is polymethylmethacrylate. Also it has been shown with both systems that polymerization occurs without a change in the oxidation state of the metal. 

It is more difficult to study equilibria between transition metal allyl compounds and bases, olefins, etc. In the case of Zr (allyl) 4 and pyridine, a valency change occurs as shown by Eq. (8), and the process is irreversible. The polymerization is considered to be preceded by displacement of one allyl group by the monomer (12) as shown in Eq. (1). In the methyl methacrylate/Cr(allyl)3 system it was not possible to detect any interaction between the olefin and catalyst with infrared radiation, even with equimolar concentrations because of the strong absorption by the allyl groups not involved in the displacement processes. Due to the latter, evidence for equilibrium between monomer and catalyst is less likely to be found with these compounds than with the transition metal benzyl compounds. 

The deprotonation of alkenes by organometallic reagents affords allyl species. As the simplest example of delocalized organometallic systems, the alkali metal allyl system has been studied in solution and the solid state in quite some detail this work has been further supported by theoretical studies. Allyl species are usually very reactive undergoing complex rearrangement reactions, and often, the reaction products cannot be directly characterized. Instead, they are often identified by their reaction products. 

The study of solvated alkali metal allyl species remains a complex topic due to a variety of reorganization processes. Structural data on alkali metal allyl derivatives include [G3H5Li(TMEDA)] 133,139 where solvated lithium ions act as... 

Calculations of alkali metal allyl derivatives involving all alkali metals (Li-Cs) indicate a preferred geometry with the metal symmetrically bound in a predominantly electrostatic manner to all three carbon atoms.143 Solution studies of allyllithium in ether indicate the compounds to be highly aggregated in THF complex dynamic behavior is observed. 

The effects of altered hapticity can be seen by comparing the q3, four-electron allyl complex of Ir+ (Fig. 4.86(c)) with the corresponding complex of Au+ (Fig. 4.87(c)). Because Au+ requires only two electrons to complete its formal duodectet, the metal-allyl complexation now involves only the anionic nc center of a localized allylic H2C—CH=CH2 moiety, and the hapticity slips from q3 to q1 ... 

Table 4.48. Comparison bond lengths Rm and bond orders 6Ab in r 3,four-electron (M = Ir+) versus ri1, two-electron (M = Au+) metal allyl complexes (see Figs. 4.85(c) and 4.86)...

Oppolzer, W. Transition Metal Allyl Complexes Intramolecular Alkene and Alkyne Insertions. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 905-921. 

Recently, the electrochemical recycKng of allyltin reagents has been realized for the first time in protic solvents. Difhculties in the recycling of metallic allyl reagents in situ are due to the fact that reaction conditions that allow... 

The allyl group is able to form both a- and jr-bonded complexes with the actinides. The 71 complexes will be considered here because of the similarities of the homoal-lyls with the lanthanide and actinide homoalkyls. The limiting modes of bonding in metal allyl complexes and the ratio of PMR intensities from magnetically equi valent protons are illustrated in Fig. 14. 

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