Alkyl complexes carbon monoxide insertions

Reductive coupling reactions, titanium complexes Carbon monoxide insertion, titanium complexes Acetylene insertion, titanium complexes Carbon dioxide insertion, titanium complexes Isocyanide insertion, titanium complexes Carbonylatlon, titanium alkyls... 

A simplified mechanism for the hydroformylation reaction using the rhodium complex starts by the addition of the olefin to the catalyst (A) to form complex (B). The latter rearranges, probably through a four-centered intermediate, to the alkyl complex (C). A carbon monoxide insertion gives the square-planar complex (D). Successive H2 and CO addition produces the original catalyst and the product ... 

The results do not prove that in the reaction conditions used the alkyl formation is not reversible, but only that, if it is reversible, the carbon monoxide insertion on both diastereomeric rhodium-alkyls must be much faster than the rhodium-alkyls decomposition. Restricting this analysis of the asymmetric induction phenomena to the rhodium-alkyl complexes formation, two 7r-olefin complexes are possible for each diastereomer of the catalytic rhodium complex (see Scheme 11). The induction can take place in the 7r-olefin complexes formation (I — II(S) or I — II(R)) or in the equilibrium between the diastereomeric 7r-olefin complexes (II(r) and... 

From the results of the asymmetric hydroformylation of the isomeric straight-chain butenes we have concluded that asymmetric induction in the case of Rh/(—)-DIOP catalytic complexes does not result either in carbon monoxide insertion or in the following steps described in Fig. 12 but either in the 7t-eomplex formation or the alkyl-complex formation 15) (Fig. 13). 

Compared in this section are the activation parameters and the relative reactivities toward SO2 of the various types of transition metal alkyl and aryl complexes. As shown in Table IV, the values of AS and AH range from — 63 to — 43 e.u. and from 2.7 to 8.7 kcal/mole, respectively. These entropies of activation are more negative than those for the solvent-assisted carbon monoxide insertion [—33 to —17 e.u. (1J7)] or for the SO2 insertion into the Sn—R (R = Ph and CHaPh)... 

Carbon monoxide insertion into the copper-alkyl bond is indirectly shown by reaction of CO with dibutylcuprate(I), an anionic dialkyl derivative of dicoordinated copper(I). The product of the reaction, dibutylketone, may be rationalized by assuming carbon monoxide coordination to the anionic copper complex, followed by alkyl migration to the unstable anionic complex Cu[C(0)Bu](Bu) , with subsequent reductive elimination to the observed organic product. 

The dibutyl derivative Ti(r7 -C5H5)2Bu2 decomposes upon treatment with CO, but the dibenzyl compound gives dibenzylketone, suggesting that the relatively slow carbon monoxide insertion reaction [reaction (b)] is followed by fast reductive elimination from the intermediate alkyl-acyl complex. 

Furthermore, the phosphine-dihydrooxazole hgands show an unusual behavior with respect to ethene and styrene. The productivity of those systems is larger for styrene than for ethene under equal reactions conditions nevertheless, in the terpolymerization experiments ethene, and not styrene, is prevailingly inserted. Considering that ethene was inserted more rapidly than styrene into model acetyl complexes [103], the poisoning" effect of ethene can be explained by assuming that ethene is coordinated more easily, without rapid olefin dissociation, and that rate-determining carbon monoxide insertion into the two different alkyl intermediates occurs. 

Reactions of halogen-containing compounds with Ni(CO)4, Fe(CO)s, or Fe3(CO)12 are widely observed. In these reactions, the formation of intermediate a-alkyl complexes by the addition reaction, followed by carbon monoxide insertion to form acyl complexes, is assumed. From these acyl complexes, many useful carbonyl compounds can be synthesized. Compounds having relatively active halogens such as... 

With carbonyl complexes, alkyl exchange often takes place with carbon monoxide insertion. 

One possible mechanistic sequence for the present reaction is shown in Scheme 7.1. The carbon monoxide insertion into the carbon-metal o bond of alkyltransition metal complexes is well known [88]. Thus, the oxidative addition of benzyl halide to metallic nickel gives benzylnickel (II) halide 4, and the insertion of carbon monoxide, which is formed by decarbonylation of alkyl oxalyl chloride into the benzyl-nickel bond of complex 4, would afford arylacetyl (II) complex 5. The metathesis of complexes 4 and 5 seems to give (arylacetyl)benzylnickel complex 6, which undergoes reductive elimination to yield l,3-diarylpropan-2-one, 3. The formation of 1,2-diarylethane may be explained by the reductive elimination of bisbenzylnickel complex 7 formed by metathesis of benzylnickel complex 4 [89]. It is also possible that the reaction of benzyl halide with complex 4 or 5 gives homocoupled product or ketone, respectively. 

Alkylation of the anion 2 with iodomethane or other haloalkanes provides alkyldicarbonyl(t/5-cyclopentadienyl)iron complexes such as 53,0 (see also Houben-Weyl, Vol. 13/9a, p 209). Migratory insertion of carbon monoxide occurs on treatment with phosphanes or phosphites9 -11 (see also Houben-Weyl, Vol. d3/9a, p257) to provide chiral iron-acyl complexes such as 6. This is the most commonly used preparation of racemic chiral iron-acyl complexes. 

Another route to enantiomcrically pure iron-acyl complexes depends on a resolution of diastereomeric substituted iron-alkyl complexes16,17. Reaction of enantiomerically pure chloromethyl menthyl ether (6) with the anion of 5 provides the menthyloxymethyl complex 7. Photolysis of 7 in the presence of triphenylphosphane induces migratory insertion of carbon monoxide to provide a racemic mixture of the diastereomeric phosphane-substituted menthyloxymethyl complexes (-)-(/ )-8 and ( + )-( )-8 which are resolved by fractional crystallization. Treatment of either diastereomer (—)-(/J)-8 or ( I )-(.V)-8 with gaseous hydrogen chloride (see also Houben-Weyl, Vol 13/9a, p437) affords the enantiomeric chloromethyl complexes (-)-(R)-9 or (+ )-(S)-9 without epimerization of the iron center. 

Complexes of the type RMn(CO)5, where R is a primary alkyl group, undergo facile CO insertion at room temperature. Carbonylated to the corresponding acyls have been the pentacarbonyls with R = Me 50, 69), Et 51, 70), n-Pr 51), and CHjSiMe, 243). The phenyl compound, PhMn(CO)j, also inserts CO, but the benzyl analog does not 51). The claim 194) that CX3Mn(CO)5 (X = H, D, or F) converts to CX3COMn-(CO) ( < 5) upon irradiation in an Ar matrix at 17°K has been disputed 209). Carbon monoxide dissociation and recombination have been proposed instead for MeMn(CO)5. 

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... 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

Insertion of CO is therefore always kinetically controlled. When an alkyl palladium species has formed, the open site will be occupied by a coordinating CO molecule. Carbon monoxide coordinates more strongly to palladium than ethene, even when the palladium centre is cationic. The reason for this is steric the cone angle of ethene is much larger than that of CO and the steric hindrance in the ethene complex is therefore much larger. If the barriers of activation for the insertion processes of ethene and CO are of the same order of... 

Fig. 2.5. Preparation of hydroxy- and alkoxycarbene complexes from alkyl complexes by 1,1-insertion of carbon monoxide [106-108].

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