Cyclopentadiene with metal carbonyls

Reaction of Cyclopentadienes with Metal Carbonyls (Method 3)... 

The methods of preparation of ferrocene have been reviewed by Pauson and by Fischer. Ferrocene has been made by the reaction of ferric chloride with cyclopentadienylmagnesium bromide, by the direct thermal reaction of cyclopentadiene with iron metal, by the direct interaction of cyclopentadiene with iron carbonyl, by the reaction of ferrous chloride with cyclopentadiene in the presence of organic bases such as diethyl-amine, by the reaction of ferrous chloride with sodium cyclo-[lentadienide in liquid ammonia, and from cyclopentadiene and... 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Some heterocyclic cyclopentadiene derivatives form n complexes with metal carbonyls (47, 55, 373, 384) ... 

During reactions with metal carbonyls, cyclopentadiene complexes are probably first formed which subsequently undergo rearrangement to hydridocyclopentadienyl compounds followed by decomposition with hydrogen evolution ... 

Cyclopentadiene reacts directly with metal carbonyls to form two classes of compounds, each with cyclopentadienyl-metal bonds. Under mild conditions cyclopentadienyl metal carbonyls, C5H5M(CO), are formed, and this is the preferred method for preparing many of them. Under more vigorous conditions dicyclopentadienyl metal compounds, (C5Hs)2M, are formed. Because, however, yields of dicyclopentadienyl metals are low, this is not an important method for their preparation except possibly in the case of ferrocene (40). This reaction under mild conditions, is carried out in the liquid phase in refluxing dicyclopentadiene. OccasionaUy, a solvent of high... 

Methylcyclopentadiene readily undergoes reaction with metal carbonyls 47) and even 1,3-diphenylcyclopentadiene reacts with iron carbonyl 4S). A novel method for obtaining a ferrocene with one substituted ring, is the reaction of 1,3-diphenylcyclopentadiene with the dimer of cyclopentadienyl-iron dicarbonyl at 170° C to produce 1,3-diphenylferrocene in 15% yield. Other substituted cyclopentadienes which have been used are tetraphenyl-cyclopentadienone in the preparation of tetraphenyl(hydroxy)cyclopenta-dienylmanganese tricarbonyl 49) and indene in the preparation of the dimer of indenylmolybdenum tricarbonyl (50). A variety of substituted fulvenes have been used in the preparation of substituted cyclopentadienyl metal tricarbonyl compounds of Cr, Mo, and W (57, 52). This latter reaction proceeds best in the presence of a solvent, such as 1,2-dimethoxyethane, to permit easy abstraction of hydrogen. 

Cyclopentadiene reacts readily with metal carbonyls in a variety of ways. With iron pentacarbonyl under reflux the binuclear complex [jr-CpFe(CO)2]2 is formed in good yields. The following mechanism for the reaction has been proposed [25, 26] ... 

This review deals with metal-hydrocarbon complexes under the following headings (1) the nature of the metal-olefin and -acetylene bond (2) olefin complexes (3) acetylene complexes (4) rr-allylic complexes and (5) complexes in which the ligand is not the original olefin or acetylene, but a molecule produced from it during complex formation. ir-Cyclopentadienyl complexes, formed by reaction of cyclopentadiene or its derivatives with metal salts or carbonyls (78, 217), are not discussed in this review, neither are complexes derived from aromatic systems, e.g., benzene, the cyclo-pentadienyl anion, and the cycloheptatrienyl cation (74, 78, 217), and from acetylides (169, 170), which have been reviewed elsewhere. 

Caution. Diazo compounds are potentially explosive. Although neat 5-diazo-l,3-cyclopentadiene is known to be highly explosive,6 it may be handled conveniently and safely in a pentane solution.2,1 Tetrachloro-5-diazo-l,3-cyclopentadiene is reported to be stable, but due caution should be exercised in the manipulation of this compound. Carbon monoxide, volatile metal carbonyls, and some diazo compounds are highly toxic, and reactions with these species should be conducted in a well-ventilated fume hood. Avoid inhalation or contact with skin. 

Cyclopentadiene, CsHg, is a colourless liquid which readily forms a monosodium derivative. This in turn reacts with anhydrous transition-metal halides to form derivatives M(CsHs) , some of which may be made direct from the hydrocarbon and the metal carbonyls at about 300°C. Some of these compounds, including Fe(CsHj)2 ( ferrocene ) can be oxidized to cations. The following are examples of cyclopentadienyl compounds ... 

Cyclopentadienyl carbonyls of several transition metals have been reported during the last decade, and these compounds have been shown to undergo a variety of interesting reactions. Two general methods have been used to prepare these materials treatment of metal carbonyls with cyclopentadiene or cyclopentadienylsodium, and the reac-... 

Halides and other salts as well as metal carbonyls sometimes react with cyclopentadiene to afford cyclopentadienyl complexes with concomitant evolution of hydrogen, hydrogen chloride, or other reduction products, such as CjHg. These reactions take place under relatively severe conditions at high temperatures and often under elevated pressures ... 

The strong acidity of cyclopentadiene, estimated as approximately = 17 (3), was first recognized by Thiele, who took advantage of this property in the preparation of potassium cyclopentadienide from potassium metal and cyclopentadiene (4). While direct reaction with cyclopentadiene is limited in scope to the elements of Groups lA and IIA, to their strongly basic compounds, and to a few other elements, it is the only approach for the synthesis of the ionic cyclopentadienides of elements of Groups lA and IIA. Direct reaction of cyclopentadiene is also applicable to the preparation of certain compounds of the (C5H5) M(CO), class from metal carbonyls and is often the preferred method. 

The utility of bis(oxazoline)-Cu(II) complexes as catalysts for the Diels-Alder reaction has been examined in a number of other systems. Aggarwal et al. (205) demonstrated that a-thioacrylates behave as effective two-point binding substrates for these catalysts. With cyclopentadiene, catalyst 271d induces the reaction at -78°C to provide the cycloadduct in 94 6 diastereoselectivity and >95% ee. Aggarwal proposes that the metal binds to the carbonyl oxygen and to the sulfur atom. The sulfur substituent is placed opposite the ligand substituent thereby shielding the bottom face of the alkene. Considerably lower selectivities are observed with 5-Me substrates. 

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