Iron complexes, with tropone

It is interesting that iron carbonyl can be used as a protecting group for dienes. Iron diene complex 491, for example, reacted with 492 in a Mukaiyama aldol reaction (sec. 9.4,C), giving an 81% yield of 493 and 494 in an 84 16 ratio.32 in a synthesis of heptitol derivatives,322 Pearson protected tropone as the iron tricarbonyl derivative (495), and prepared 496 using a multistep sequence before deprotecting the diene to give 497. 

Similarly, (tropone)iron complexes can also be subjected to this reaction (Scheme 4-25). Treatment of an (T -tropone)iron complex with trimethylsilyl triflate provides an Tj -dienyliumiron complex salt with an additional silyl enol ether moiety. 

Annulation of tricarbonyl cyclobutadiene iron to tropone and tropylium ion to give complexes 282 and 285 is achieved by Wittig cycloolefination of dialdehyde 281 with biphosphonium salts, 280 and 283, respectively (Scheme 71 77JA513 78AJC1607). 

Access to alkyl substituted derivatives of the homotropylidene complexes is provided via the >j4-tropone iron complex by reaction with diazoalkanes, followed by mild thermolysis of the 3+2 py razoline adduct to give the corresponding homotropone complexes (equation 149)217,218. The 8,8-dimethyl derivative was used as starting material for the preparation of the fluxional ( 5-2,8,8-trimethylbicyclo[5.1.0]octa-2,4-dienylium)Fe(CO)3 cation complex219. More recently (homotropone)Fe(CO)3 was used for the synthesis of unique chiral 1,2-homoheptafulvene iron complexes220 221. 

A similar phenomenon has been observed in the spectra of some diene-iron tricarbonyl compounds (136). The anisolechromium tricarbonyl complex shows loss of 2 H from the [M - 3 CO]+ ion, giving C7H6OCr+, which could have the tropone structure (XIV) while the analogous iso-propoxy complex loses propylene with the probable rearrangement to give... 

Comparison of the tropone ring geometry in iron complex 282 with that of the parent tropone shows that the double bond character of the carbonyl group and the bond between C-2 and C-3 in 282 is even higher, probably as a result of dominant contributions from two cyclobutadiene resonance... 

This complex contains six terminal carbonyl groups and three carbonyl groups bridging the two atoms of iron. When the complex is treated with acetylene at 20-25° and 20-24 atm., acetylene displaces the bridging carbonyls with formation of tropone iron tricarbonyl (2), which is an orange solid of double melting point (63.5-64° and 83-84°). This complex is obtained in only trace amounts with Fe(CO)s and Fe(CO)i. Treatment of the complex (2) with triphenylphosphine affords free tropone (3,69% yield) and a new complex (4), tropone iron dicarbonyltriphenylphosphine. Tropone can also be obtained, if in low yield, by oxidation of (2) with ferric chloride ... 

Reaction of tricarbonyl(tropone)iron with tetracyanoethylene gave the 1 1 adduct (602) the similar reaction of the 2-deuteriotropone complex gave exclusively (603). It is concluded that electrophilic attack by TCNE occurs exo to the iron atom and at a non-co-ordinated double bond of the substrate. The tricarbonyl(bicyclo[6,l,0]nona-2,4,6-triene)chromium complex is reported to rearrange at 100 °C almost completely to (604). 2... 

Early applications of iron cationic species resulted from the facile reaction of a, a -dibromo-(and tetrabromo) acetone with Fe2(CO)9 with formation of the cation (A). Such cationic complexes can be efficiently trapped by olefin with formation of five-membered ketones. The reaction with conjugated dienes affords a straightforward access to tropones. Furan is a particularly good acceptor of these cationic complexes whereas their addition to enamines constitutes a potentially useful pathway to prostaglandins (cyclopentenones being thus obtained). 

The stepwise formation of tropones upon insertion of GO into alkyne dimers coordinated to diiron centers is a commonly found process in iron carbonyl chemistry no triiron complexes are isolated during these processes (e.g., see Refs 14 and 14a). Finally, GO insertion is observed when diiron dimers linked by diacetylene moieties are reacted with diethylamine to give the complexes 6 and 7 (Figure 2) these complexes also contain iron-carbon-nitrogen and iron-carbon-phosphorus bonds. 

Reactions with Alkynes. Fe2(CO)9 reacts with acetylene by carbonylation/cyclotrimerization leading to the formation of tri-carbonyl(tropone)iron(0) (51) (eq 32). (For comparison with direct complexation of tropone, see eq 6.) This complex is obtained in low yield (28%) with Fe2(CO)9, but this represents a significant improvement on results obtained with Fe(CO)5. ... 

As noted in the introduction, the complexes formed by the reactions between acetylenes and iron carbonyls depend markedly on the conditions employed. Treatment of Fe3(CO)i2 with substituted acetylenes at 80°C in inert hydrocarbon solvents gives reasonable yields of substituted tropone iron carbonyl complexes and tropone iron tricarbonyl is formed from acetylene and Fe2(CO)9 at room temperature. Tropone iron tricarbonyl [69, 70], which has a structure similar to that shown in Figure 80, for the... 

Phenylacetylene and Fe3(CO)i2 give, as the main products, isomeric triphenyltropone iron tricarbonyl complexes. Both complexes liberate 2,4,6-triphenyltropone when the complex is treated with Ph3P [52a]. Therefore it may be assumed that both complexes contain this tropone. The X-ray structure of one isomer has been determined [72] and is shown in Figure 80. In this molecule, the tropone ring is attached to the iron by a diene system and the third double bond is bent out of the plane of thediene carbons, away from the iron. The other isomer of this complex is presumably that in which the tropone bonds to the iron by the alternative diene system of the ligand [52]. 

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