Insertion reactions metal alkyl

The study of stoichiometric CO insertions into transition metal complexes is of great importance because this reaction is the first step m the catalytic conversion of carbon dioxide. Hence, these investigations can lead to the possibility of introducing carbon dioxide into transition metal-catalyzed synthetic processes. Analogies with carbon monoxide chemistry may be drawn, for instance. from the CO insertion into metal alkyl bonds leading to such important industrial processes as hydroformylation and carbonylalion. 

A special case of substitution reaction is the migratory insertion (see Migratory Insertion) reaction of alkyl or aryl metal carbonyls (see equation 58), by which an alkyl or aryl metal carbonyl is converted into an acyl or aroyl metal carbonyl by the action of a Lewis base. This reaction has been studied extensively, and in the case of Mn(Me)(CO)5 is found to proceed through a coordinatively unsaturated tetracarbonyl resulting from methyl migration on to one of the terminal CO groups in a cis position, (see equation 59). ... 

Metal insertion reactions of alkyl halides produce organometal-lic derivatives such as Grignard reagents, which are synthetically useful sources of carbanions and change the reactive character of the carbon atom of the alkyl halide. 

Cossee was the first to analyze theoretically olefin insertion into metal-alkyl bonds (reaction (30), step B) assuming that it was the rate-determining step of the... 

As for CO insertions into metal-alkyl bonds, it has been proposed that the alkyl group migrates with retention of configuration. More tests of the stereochemical outcome of olefin insertion reactions are needed. 

If a group, such as (C(0)0CH2CH2CH2CH=CH2), was used, the olefin was conforma-tionally constrained to bind perpendicular to the Pd—C bond and insertion-cyclization did not occur. Alkene insertion reactions into metal-acyl bonds usually occur more rapidly than insertions into metal-alkyl bonds. 

Olefin insertion into metal alkyls is involved in many valuable catalytic and stoichiometric organometalic syntheses. The high reactivity of most transition-metal alkyls causes them to react further under the conditions required for their formation, and the intermediate alkyls often have not been identified. Nevertheless, insertions into metal alkyls are important steps in many reactions. 

The transformation of an alkylmetal carbonyl complex into a metal-acyl complex is one of the most common types of migratory insertion reactions (Equation 9.3). Examples of CO insertion into metal-alkyl complexes are known for all of the transition elements. This reaction class has been the subject of review articles. These reactions occur by a family of diverse, delicately balanced reaction pathways the dominant mechanism depends on the reaction conditions, especially the solvent. Although these pathways are now imderstood in considerable detail, the precise identities of the intermediates in some of these reaction pathways are unknown. 

CO shows a strong tendency to insert into metal alkyl bonds to give metal acyls. The reaction has been carefully studied for a number of systems. Although the details may differ, most follow the pattern set by the best-known... 

Olefins can insert into metal-alkyl bonds as well as into metal-hydride bonds provided that a vacant coordination site is available on the metal center. This reaction can thus be repeated even when the alkyl ligand lengthens, which makes the proposed mechanism a Ziegler-Natta olefin polymerization. This type of polymerization is detailed in Chap. 15.1 ... 

The chemistry of metalated aziridines is far less developed than the chemistry of metalated epoxides, although from what is known [lb], it is obvious that their chemistry is similar. Like metalated epoxides, metalated aziridines can act as classical nucleophiles with a variety of electrophiles to give more highly substituted aziridines (Scheme 5.56, Path A). A small amount is known about how they can act as electrophiles with strong nucleophiles to undergo reductive alkylation (Path B), and undergo C-H insertion reactions (Path C). 

The insertion of a carbonyl group into a metal-alkyl or metal-aryl bond, and the reverse reaction involving decarbonylation of an acyl complex, have been studied from both the synthetic and mechanistic points of view. The mechanism proposed for this type of reaction seems well established and is... 

Few quantitative data are available on the relative nucleophilicities of L toward various alkyl carbonyls. The rates of the reaction of CpMo(CO)3Me with L in toluene (Table II) decrease as a function of the latter reactant P( -Bu)3 > P( -OBu)j > PPhj > P(OPh)j, but the spread is relatively small (<8). The above order is that customarily observed for 8 2 reactions of low-valent transition metal complexes (J, 214). Interestingly, neither CpMo(CO)3Me nor CpFe(CO)2Me reacts with 1 or N, S, and As donor ligands 28, 79). This is in direct contrast to the insertion reactions of MeMn(CO)5 which manifest much less selectivity toward various L (see Section VI,B,C,D for details). 

No comparative kinetic study has been made on the same alkyl carbonyl system for two members of a given transition metal triad. Qualitative data show that the middle member is more reactive than the heaviest one e.g., CpMo(CO)jR > CpW(CO)jR (Section VI,B), Rh(III) > Ir(III) (Section VI,E), and Pd(II) > Pt(II) (Section VI,F). However, the extreme unreactivity of CpW(CO)jR and a considerable difference in lability between most alkyls of Rh(III) and Ir(III), as well as those of Pd(II) and Pt(II), have prevented detailed investigations. Surprisingly, no kinetic studies have been conducted on insertion reactions of RRe(CO)5, which would seem readily amenable to such investigations. 

Reactions of carbon subsulphide and of elementary phosphorus, sulphur and selenium with complexes of the platinum metals Sulphur dioxide insertion reactions of transition metal alkyls and related complexes... 

Insertion reactions of stannylenes, even of unstable ones, into metal-metal bonds have attracted considerable attention 156 158>. In this context, it is very astonishing that the reaction (28) between the alkyl-substituted stannylene 14 and Fe2(CO)9 does not lead to a product of type 66 (X2Sn Fe(CO)4)2 (an X-ray structural analysis indicates an Sn2Fe2-ring167)) but to a three-membered ring, as determined by elemental analysis and from IR-spectral data133). 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

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