Tropone iron complexes

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. 

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 ... 

A useful method for the release of organic ligands from iron complexes has been developed using trimethylamine oxide. It is suitable for releasing ligands which are easily oxidized and which cannot be released by the more conventional oxidizing agents examples include the release of tropone and cyclo-octatetraene from their iron carbonyl complexes. ... 

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. 

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... 

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