Tropone-iron tricarbonyl complexes

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 ... 

Phenylacetylene and Fe3(CO)i2 in inert hydrocarbon solvents at 80°C give, as the main products isomeric triphenyltropone iron tricarbonyl complexes. The triphenyltropone ligand can be derived from three acetylene molecules and one carbonyl group (cf. the formation of cyclopenta-dienone complexes p 229). The X-ray structure of one isomer 9.6, shows that the tropone ring is attached to the iron atom by a diene system, the third double bond being bent out of the plane of the diene carbon atoms, away from the iron (cf. structure of GgH8Fe(CO)3 p 166). 

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... 

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... 

Cyclopropanation of tricarbonyl(tropone)iron 18 via cycloaddition of diazomethane, diazoethane or diazopropane and thermal dinitrogen extrusion gave bicyclo[5.1.0]octadienone ( homotropone ) complexes which decomposed to form the free ligand 20 in high yield. When the same procedure was applied to the free ligand 16, a substituted cyclooctatrienone system 17 was obtained via ring expansion. 

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. 

The seven-membered cyclic ketone, tropone, C7H7O, might be expected to form complexes like those of cycloheptatriene. Only the iron carbonyl complexes have been studied in any detail. Troponeiron tricarbonyl is one of the products of the reaction between acetylene and Fe2(CO)9 131a) this reaction, and the properties of the complex, have been summarized by Pettit and Emerson (118). Reaction betvreen Fc3(CO)i2 and phenylacetylene gives two isomeric complexes of formula (2,4,6-triphenyltropone)Fe(CO)3, which are assigned structures (VIII) and (IX) IS). 

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... 

Similar results have been found by Smith and Dahl who showed, from X-ray studies, that in the complex 2,4,6-triphenyltropone-iron tricarbonyl the tropone ring was no longer planar (2J). The arrangement of the atoms of the tropone ring and the Fe(CO)3 are as shown in Fig. 4. 

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). 

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