Insertion into iron-carbon bonds

Xlld does not involve the chiral center, so if the reaction takes place by this pathway, the migration of the alkyl group from sulfur to palladium (with the concomitant or subsequent loss of sulfur dioxide) must take place with inversion of configuration at carbon. Inversion of configuration at carbon has been observed in the reverse-type reaction, the sulfur dioxide insertion into a carbon-iron sigma bond (49). Nucleophilic displacement at carbon in compounds of type Xld is unusually difficult, so the reaction via the sulfite intermediate Xlld would appear to be more likely. Conversion of the tosylate of l-phenyl-2,2,2-trifluoroethanol to the corresponding chloride, a reaction which takes place in the presence of tetra- (n-butyl) ajnmonium chloride with inversion of configuration at carbon, requires 100°C for 24 hrs in dimethylsulfoxide. 

Sulfur dioxide readily inserts into metal-carbon tr bonds (136, 137). The reaction is stereospecific with respect to the configuration at the a-carbon atom of the alkyl group (138) and proceeds with inversion of configuration at the a-carbon atom (139-142). The stereospecificity of the S02 insertion with respect to the metal center was demonstrated with diastereoisomeric pairs of enantiomers of Fe compounds (143-146). Also, the stereochemistry of the S02 insertion at the iron atom was studied by starting with the optically active iron alkyl derivative 26a (see Scheme 18). Retention of configuration was concluded from the similarity in the... 

Support for the proposal of M+ insertion into the carbon-halogen bond came from later work in which the reactivity of the Fe(CO) + ions (n = 0 - 5) towards allyl chloride was investigated using a MS/MS/MS multiquadrupole spectrometer60. Thus, while with the naked Fe+ the only observed products were FeCl+ (minor) and C3H5+ (and the secondary products derived from its reaction with neutral allyl chloride), with the iron carbonyl... 

On the other hand, t/ireo-Fe(f7 -C5H5)(CHDCHDCMe3)(CO)2 reacts with sulfur dioxide with > 95% inversion of configuration at carbon. Thus, sulfur dioxide insertion into the iron-carbon bond proceeds differently from carbon monoxide insertion, which is characterized by retention of configuration at carbon" . 

The polymer yield in early stages is higher with a lower ratio Al/Fe. This indicates that alkyl exchange between iron and aluminum is more rapid than ethene insertion into the iron carbon bond. This results in very short chains on aluminum that do not precipitate in methanol. This follows also from the molecular weight of the polymers obtained with various ratios of Al/Fe in time (Fig. 3.12) the higher the ratio, the lower the molecular weight With a ratio of Al/Fe of 8000, the chain length of the polymer increases linearly with time. 

In Eq. (7) the results of the insertion of the low valent elements in 1 and 2 into an iron-carbon bond are summarized. The two products 14 and 15 are obtained in almost quantitative yield and are similar in structure. 

Ockam s razor, we concluded that an intemiediate was fonned at both sec, and tert, positions. We postulated that this was formed by insertion of an Fe oxenoid species into the carbon-hydrogen bond. At the secondary position, the iron-carbon bond was stable, but at the tertiary position, the weaker bond fragmented into radicals which coupled with pyridine in the ordinary way. All the appropriate blank experiments were carried out to show that secondary radicals, had they been formed at the lower oxygen pressures, would have been captured by the solvent pyridine. [6]... 

The insertion of dimethyl acetylenedicarboxylate into the iron-carbon bond of the erythro- and threo- somers of [FeCCHDCHDCMesXn -QHjXCOla] occurs with 80% retention of configuration at carbon. ... 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

It was found that radicals are not involved in ketone formation in Gif oxidation.164,165 As a minor route, in contrast, tertiary alcohols are formed through carbon radicals. Key intermediates164 are the Fe(V)=0 species 11, formed from a p-oxoiron dimer that inserts into the C—H bond, and the alkoxy-iron species 12 ... 

Tetrahydropyridine 152 can be inserted into the iron-acyl carbon bond of the Fe(CO)3-bound vinyl ketene 158 to give the iron complex 159, which can be oxidatively cleaved to give bicyclic lactam 160 (Scheme 42)... 

Recently, carbon dioxide complexes have attracted increasing attention for preparative and catalytic application.17 However, the number of known simple and reasonably stable C02 adducts is limited.1611 17,18 Because of the isomerization behavior of the previously described complex, [(CH3)3P]4Fe (Sec. B), a variety of very different compounds is obtained on reaction with C02, depending on the reaction conditions. For example, insertion into the iron-carbon and iron-hydrogen bonds may occur, as well as disproportionation to C032- and... 

Insertion of isocyanide carbon atoms into the Cr—carbene bond of [(CO)5CrC(OMe)Me] gave aziridinylcarbene complexes (CIV), some reactions of which are summarized in Scheme 2 28, 198). Cyclic carbene groups (CV)-(CVIII), in which the carbene carbon atom is part of an aromatic six-electron Tr-system, have been reported to form pentacarbonyl chromium and tetracarbonyl iron complexes 383, 384). Related to carbene... 

The sulfur ylid Me2S(0)CH2 is a very weak base, and, when coordinated to nickel in the complex [Ni( / -C2H4)2CH2S(0)Me2] (91), spontaneous decomposition to ethane, cyclopropane, and methane occurs (93). In another reaction, compound 92 rearranges under UV irradiation to yield, with insertion of iron into a phenyl-carbon bond, a cyclic carbene complex, 93 94). 

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