Tricarbonyl iron complexes fragmentation

The molecular ion of the tricarbonyl (dienamine) iron complex 25 (cross-conjugated) is more abundant than that of 26 (linear) (Scheme 20) confirming their different relative stabilities18. They fragment essentially by successive losses of 3 CO and CH4 molecules leading to an abundant ion m/z 231 [Fe(C12H17N)] + ... 

Reaction of hexacarbonyldicobalt complexes of ene-ynes or hetero-ene-ynes with (biscyclooctene)(tricarbonyl)iron results in formation of [FeCo2 (p.-alkyne)(CO)9] (Scheme 15).142 In both cases the free double bond in the vicinity of the Co2C2 unit facilitates the incorporation of the incoming Fe(CO)3 fragment. 

Alternatively, (trimethylenemethane)iron complexes can be synthesized by disproportionation of tricarbonyl(2-methallyl)ironJ Enantiomerically pure tricarbonyl-(trimethylenemethane)iron complexes can be obtained by resolution of the racemic mixture via diastereomeric esters or amides. (5)-(-)-Ethyl lactate and (/ I)-(+)-a-methyl-benzylamine are employed as resolving reagents for this piupose. The chiral auxiliaries can be removed by a variety of reagents leaving the (trimethylenemethane)iron fragment unaffected. Treatment of both the corresponding Boc-protected amides and the chiral esters with diisobutylaluminum hydride (DIBAL) or methyllithium provides the primary or tertiary alcohols, respectively. Saponification of the ester with lithium hydroxide in methanol and subsequent acidification of the mixture affords the methyl ester. Treatment of the ester with triethylsilane leads to complete reduction of the functionality to leave a methyl group (Scheme 4—85). ... 

A number of natural products or fragments of them have become available by nucleophilic additions to the aldehyde group of tricarbonyl(T -dienal)iron complexes. This includes ( )-5-hydroxy-6 , 8Z,l lZ,14Z-icosatetraenoic acid (5-HETE) methyl ester,(-)-LTA4 methyl ester, halicholactone, racemic lipoic acid methyl ester,macrolactin A fragments, the as-indacene unit of ikarugamycin, 1 l-(Z)-retinal, and the C11-C17 segment of soraphen Asymmetric variations... 

Cyclohepta-3,5-dienone)iron complexes can be stereoselectively methylated and hydroxylated. The electrophile adds exclusively anti to the tricarbonyliron fragment. Double methylation or hydroxylation of the a and a positions is accomplished in high overall yield (Scheme 4-146). Silyl enol ethers adjacent to tricarbonyl(Ti -diene)iron units can be subjected to Mukaiyama aldol reaction with aldehydes to provide aldol adducts with varying diastereoselectivity. This methodology has, for example, been applied to the enantioselective synthesis of the dienetriols streptenol C and D (Scheme 4-147). ... 

The synthesis of the trismethylenemethane iron tricarbonyl complex [(CH2)3C]-Fe(CO)3 was reported by Emerson et al. in 1966 (27). The geometry of this compound in the gas phase was investigated by Almenningen et al. (28) using electron diffraction methods. These authors pointed out some structural peculiarities which were not amenable to a simple explanation, in particular, why the hypothetical planar (CH2)3C radical is distorted when bound to the Fe(CO)3 conical fragment in such a way that the carbon atoms of the CH2 groups are displaced toward — the iron atom (Fig. 9). 

Haas and Wilson (117) have studied a number of substituted butadiene-iron tricarbonyl complexes, finding that in most cases loss of three CO groups precedes fragmentation of the ligand. Compared with the ligands the spectra of the complexes show a number of instances where the iron atom tends to stabilize odd-electron ions. In (XV), the presence of the ion... 

Another aspect of the chemistry of M(CO) fragments that the computed molecular orbital diagram could help to explain was the structure of the cyclooctatetraene complexes of iron and chromium tricarbonyl.10 Chromium tricarbonyl was shown to have three relatively low-lying vacant orbitals, with the right spatial characteristics to be able to accept electron donation from three of the double bonds of cyclooctatetraene, and accordingly adopts the r geometry shown in Figure 10.4. In iron... 

As with acyclic dienes, methods have been developed for enantioselective and diastereoselective complexation of prochiral and chiral cyclic dienes. An approach has been developed for the asymmetric catalytic complexation of prochiral eyelohexa-1,3-dienes nsing (1) in the presence of catalytic amounts of l-azabuta-l,3-dienes such as (232) or (233) an enantiomeric excess as high as 86% has been reported. By contrast, attempts to effect diastereoselective complexations using cyclic diene systems eqnipped with chiral auxiliaries have met with limited success. On the other hand, direct complexation of chiral cyclic dienes snch as (234) and (235) proceed with a high degree of diastereoselectivity, where the iron tricarbonyl fragment is directed syn to alcohols or ethers by transient coordination ( heteroatom dehvery ) (Scheme 66). ... 

Cyclobutadiene complexes are prepared by the method described in equation (8) some members of the series can also be synthesized by dimerization of an acetylene on an iron tricarbonyl fragment (eq (16)) [50]. 

The iron-carbonyl complexes can be viewed as a protected form of the diene, as the complexes do not undergo typical diene or alkene reactions. Complexation to iron-tricarbonyl fragments has been used in dendralene chemistry in this way. When the [3]dendralene 10.14 was complexed to iron tricarbonyl, employing a cinnamaldehyde imine as a catalyst, the two complexed alkenes lost typical alkene reactivity, while the uncomplexed alkene retained it (Scheme 10.6). Cyclopropanation, dihydroxylation and crossmetathesis of the uncomplexed alkene proceeded as expected. The monocomplexed [4]dendralene 10.19 underwent Diels-Alder reactions at the uncomplexed alkenes (Scheme 10.7). ... 

A wide range of metals form ti -arene complexes, but the best-known complexes are with chromium tricarbonyl. Complexes of iron, manganese and ruthenium have also been used. These complexes have the Cr(CO)3 moiety or other metallic fragment above the -ir-system of the aromatic ring (Figures 10.2 and 10.3), thereby making the two faces distinct. This can be exploited for stereochemical control purposes. 

Retinaldehyde (2) reacted with iron dodecacarbonyl to form the complex (57), in which an iron tricarbonyl fragment is bonded to the polyene chain (Birch et al., 1966 Birch and Fitton, 1966 Brodie et aL, 1973). 

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