Iron tricarbonyl derivatives

In the case of tt complexes of substituted cyclopentadienones, such as the iron tricarbonyl derivatives prepared by Weiss and H libel (30), qualitative molecular-orbital theory (20) predicted a considerable reduction of the ketonic carbonyl bond order. It was observed that the ketonic carbonyl frequency dropped by as much as 65 cm-1, in agreement with theory. A similar explanation can also be provided in terms of valence bond theory (Fig. 14). It has been suggested that n complexing of arenes such as benzene results in loss of aromaticity of the ring in contrast to the dicyclopentadienyl... 

Recently, in a study of a large number of organo-iron compounds 120), it has been found possible to treat the isomer shift as being due to a sum of partial isomer shifts 8,. from individual ligands which for 7r-cyclopentadienyl derivatives could be correlated with proton NMR chemical shifts in the same compounds. The Mossbauer spectra of two cases of theoretical interest are worthy of mention. First, the spectra of both the mono- and binuclear iron tricarbonyl derivatives of cyclooctatetraene 115) show similar 8 and A values. The small 8 values are consistent with zero oxidation state for the iron atom and essentially complete covalent bonding between the iron and the tt electrons of the ring, so that, at least for the mononuclear... 

The mass spectra of some iron tricarbonyl derivatives of -ionone and related compounds (CVIII)-(CX) show the usual stepwise loss of CO groups from the molecular ion, but further analysis of the spectra was not attempted because of the complex nature of the ligands (36). Vitamin A... 

Much less attention was devoted to organometallic liquid crystals, even though the first examples, diarylmercury derivatives, were described as early as 1923 by Vorlander [6]. Recently, Ziminski and Malthete [7] reported the first mesomorphic (butadiene)iron-tricarbonyl derivatives. 

Initial attempts to prepare 7r-cycloheptatrienyl-iron tricarbonyl complexes were not successful—the products often being 7r-cycloheptadienyl-iron tricarbonyl derivatives (60). In 1964 Mahler, Jones, and Pettit (162) reported the synthesis of a complex [(C7H7)Fe(CO)3] BF4 by the following route ... 

Although few examples of acylations of 1,3-butadienes have been described, Friedel-Crafts acylations of diene complexes, in particular iron tricarbonyl derivatives, can give synthetically useful yields. In acylations of iron tricarbonyl complexes with the Perrier reagent from acetyl chloride and aluminum chloride, acylation occurs only at unsubstituted terminal carbons (Scheme 18). ° The primary product is... 

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. 

M. Xu and C.D. Tran, High-performance Liquid Chromatographic Separation of Racemic and Diastereomeric Mixtures of 2,4-Pentadienoate Iron Tricarbonyl Derivatives, /. Chromatogr., 543(1991) 233. 

It was suggested that the cyclobutene ring opened to give an o,p -benzene dimer, which underwent a retro Diels-Alder reaction to benzene. Support for this proposal was the isolation of an iron tricarbonyl derivative of the benzene dimer when the reaction was run in the presence of iron pentacarbonyl. Subsequently, the o,p -benzene dimer was prepared independently and found to readily give benzene with log = 11.78 - 14 700/2.3i r, so it is a likely intermediate in the overall... 

Dienes. l,5-Cyclo6ctadiene heated 7 hrs. at 115° with iron pentacarhonyl l,3-cyclo6ctadiene. Y 94%.—In most other cases the product is a stable diene-iron tricarbonyl derivative. J. E. Arnet and R. Pettit, Am. Soc. 83, 2954 (1961). 

The spontaneous decomposition of (XLV) to (XLVI) has been suggested from separate studies 28). Reduction of the cation (XLVII) with NaBH4 produces (XLVI) rather than (XLV) the compound (XLVI), in turn, readily decomposes at room temperature to produce (XLIV), with loss of hydrogen. It is interesting to note that whereas the iron tricarbonyl derivative of cyclopentadiene appears too unstable to allow isolation, the iron dicarbonyl-phosphine derivative (XLVIII) can be isolated by reduction of the corresponding cation (XLIX) 28). These reactions are outlined in Eq. S. 

The acetylene PhC=CC02Me reacts with FeifCOjg forming, as by now would be expected, substituted-cyclobutadiene- mid substituted-cyclopen-tadienone iron tricarbonyl derivatives. An unexpected product of the reaction is the jr-cyclopentadienyl compound, 8.19, whose crystal structure has been determined [72a]. 

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