Cyclopentadiene, iron derivative

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

In similar investigative studies for bimetalhc single-source precursors, an iron indane derivative was synthesized by the reaction Na[(Cp)(CO)2Fe]0.5THF with BrIn[(CH2)3NMe2]2 in THF (Scheme 18)). The analogous Ni, Co, and Mn intermetallic complexes were also successfully prepared with either cyclopentadiene or carbonyl ligands. Photolysis of the indium-iron derivative [ Cp(CO)2Fe 2ln(CH2)3NMe2)2]... 

FIGURE 1. Possible orientations of phosphine derivatives of cyclopentadiene iron and nickel complexes. The Fe(II) and Ni(II) ions lie behind the circle of Newman s rendition of the complexes... 

Bis(cyclopentadienyl)iron derivatives, ferrocenes, are remarkably stable against heat and air and undergo various kinds of chemical reactions. They are usually prepared by the reaction of FeCh with an alkali metal salt of cyclopentadienyl or cyclopentadiene in the presence of base [51]. Although ferrocene derivatives basically have chemical reactivities similar to those of aromatic compounds, they have found only limited applications to organic synthesis so far. However, because chiral ferrocenylphosphines are capable of having both planar chirality and an asymmetry in the side chain in their rigid framework, they have been used recently in a number of asymmetric reactions. In this section, synthesis and developments of monocyclopentadienyl complexes and ferrocenylphosphines are described. The general chemistry of ferrocenes and half metallocene complexes is reviewed elsewhere [52-53]. 

Reactions of acetylene and iron carbonyls can yield benzene derivatives, quinones, cyclopentadienes, and a variety of heterocycHc compounds. The cyclization reaction is useful for preparing substituted benzenes. The reaction of / fZ-butylacetylene in the presence of Co2(CO)g as the catalyst yields l,2,4-tri-/ f2 butylbenzene (142). The reaction of Fe(CO) and diphenylacetylene yields no less than seven different species. A cyclobutadiene derivative [31811 -56-0] is the most important (143—145). 

Dihydro-lH-l,2-azaboroles derive from cyclopentadiene by the isoelectronic replacement of a C=C group by a BN moiety ". The neutral rings react in xs boiling Fe(CO)j without any other solvent to form red-brown iron-dihydro-1,2-azaborolyldi-carbonyl dimers as their cis and transisomers in 56% yield, or with CojfCOg in petroleum ether at 60-80°C to the half-sandwich complex (dihydro-1,2-azaborolyl)Co(CO)2 (40%). The CO group can easily be substituted by olefins ... 

A titanium complex derived from chiral /V-arencsulfonyl-2-amino-1 -indanol [20], a cationic chiral iron complex [21], and a chiral oxo(salen)manganese(V) complex [22] have been developed for the asymmetric Diels-Alder reaction of oc,P-unsaturated aldehydes with high asymmetric induction (Eq. 8A.11). In addition, a stable, chiral diaquo titanocene complex is utilized for the enantioselective Diels-Alder reaction of cyclopentadiene and a series of a.P Unsaturated aldehydes at low temperature, where catalysis occurs at the metal center rather than through activation of the dienophile by protonation. The high endo/exo selectivity is observed for a-substituted aldehydes, but the asymmetric induction is only moderate [23] (Eq. 8A. 12). 

The former is prepared (Expt 6.15) by the reaction of cyclopentadiene with iron(n) chloride in the presence of diethylamine. Iron(n) chloride is prepared in situ from iron(m) chloride in tetrahydrofuran by reduction with iron metal. This preparation is one of the simplest for ferrocene, although not of general application for substituted ferrocenes. The acetylation of ferrocene in a Friedel-Crafts manner to yield the monoacetyl derivative is described in Expt 6.122. 

The ligands used in the iron-based catalyst systems and the best results for the respective catalytic system in the reaction of the acrylate derivative 34 with cyclopentadiene are summarized in Figure 9.3. 

A very remarkable series of organometallic compounds, derived principally from the hydrocarbon cyclopentadiene, (III), and having sandwichlike structures, was first synthesized in the 1950 s, chiefly by G. Wilkinson. The first member of the series, ferrocene (biscyeiopentadienyl-iron), abbreviated Fe(cpd)2, may be made by heating cyclopentadiene... 

By this method, which had formerly been employed only for the alkali metals and iron, the magnesium derivative, Mg(C5H6)2, has recently been prepared in the vapor phase. Cyclopentadiene vapor was passed over magnesium powder at 500-600° and under suitable conditions crystals of mp 176° were obtained (4). Thallium and indium reacted similarly with cyclopentadiene vapor at 350°, giving the compounds TlCsHs and InCgH (55). Attempts to develop a more general method of preparation from cyclopentadiene and molten metals met with no success 121). 

Klin dig s cationic iron(II) complex 39a, derived from tra s-l,2-cyclopentanedi-ol, is a stable, isolable brown solid that possesses sufficient Lewis acidity to catalyze Diels-Alder reactions between unsaturated aldehydes and dienes [95]. The highest selectivities and yields were realized using bromoacrolein as the dienophile (Scheme 32). Further inspection reveals that dienes less reactive than cy-clopentadiene give cycloadducts in higher yield and enantioselectivity, a characteristic that is even more impressive when one considers that the endo and exo transition states produce enantiomeric products for isoprene and 2,3-dimethyl-butadiene. Cyclohexadiene may be used in the reaction with bromoacrolein to afford the cycloadduct in 80% de and >99% ee. In the case of cyclopentadiene. 

The chiral iron(III) Lewis acid 3, derived from an oxazoline ligand, catalyzes Diels-Alder reactions of A -acryloyl-l,3-oxazolidinone (1) and cyclopentadiene (2) with good enantiomeric excess30. Nickel complexes of chiral phosphanes also catalyze Diels-Alder reactions albeit with low enantiomeric excess, not exceeding 15% cc31. Much better results are achieved for cobalt complexes with chiral phosphanes in the presence of a Lewis acid31,32. 

Decomplexation of 2-ethoxycarbonyl-l,3-butadiene-tricarbonyl iron complex 67 in the presence of an excess of cyclopentadiene affords the endo-adduct 68 stereospecifically, which readily undergoes Cope rearrangement to the bicyclo[4.3.0] derivative 69l073. 

The technical product contains 60% of -chlordane and 25-40% of other chlorinated cyclopentadiene derivatives, including heptachlor (44) (Riemschneider, 1950 March, 1952). It is a yellow or brown viscous liquid smelling slightly of camphene. The technical product is very sensitive to alkali action, and the presence of iron compounds may accelerate decomposition. 

A,ii, Cyclopentadienylirondicarbonyl (Fp) Compounds. A common organoiron reagent is cyclo-pentadienylbis(carbonyliron) (Fp, 711). " This derivative can be converted to an alkyl derivative (713, where R = alkyl) by reaction with an alkyl halide, or to the protio derivative (713, R = H) by reaction with an acid. The anionic reagent 712 is prepared by reaction of iron pentacarbonyl with the dimer of cyclopentadiene (710 - sec. 115.B) at 200°C to give the dimeric species 711. Treatment of 711 with base leads to loss of cyclopentadiene and formation of 712. A byproduct of this process is ferrocene (71 4) formed by extrusion of carbon monoxide from 711.595... 

The [4+2] cycloaddition of chiral a,P-unsaturated ketones, derived from optically pure 2-hydroxy-3,3-dimethylbutyric acid, proceed with high selectivities and in excellent yield at low temperature in the presence of a Lewis acid, e.g. ZnCl2 or BF3-OEt2. Cycloaddition reactions of chiral at iron aciyloyl complexes with cyclopentadiene in the presence of ZnCl2 have been studied by Davies et al... 

The third type of single-site catalyst is best described as a nonmetallocene type of catalyst system, where a ligand system is used that is not based on a cyclopentadiene derivative. This third type of single-site catalyst may utilize a very wide variety of ligands and an early or late transition metal (i.e., iron, cobalt or nickel) maybe utilized as the active center [9-13]. 

It works well for instance with the metal-vapor technique that consists in vaporizing metal atoms at low temperature and pressure. In fact, the most practical method for the syntheses of ferrocene and its derivatives consists in the in situ deprotonation of cyclopentadiene pKa = 15) or its derivative by diethylamine, the solvent, in the presence of anhydrous FeCl2 or FeCls. The iron chloride can be generated in situ from iron powder and the amine chlorohydrate ... 

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