Cyclopentadienides metal

The cyclopentadienide ion, C H , is a common organic anion that forms very stable complexes with metal cations. The anion is derived by removing a proton from cyclopentadiene, QH, with strong base. The molecule has a five-memhered ring of carbon atoms, with four carbon atoms attached to only one proton and one carbon atom bonded to two. Draw the Lewis... 

Aryl-l,2-dithiolium salts are a source of either dithiatricyclodecadienes (29) or cyclopenta[fc]thiopyrans (30) depending on whether the initial ring opening resulting from reaction with a metal cyclopentadienide is followed by an intramolecular cycloaddition or a condensation <96LA109>. 

Verdet and Stille1 employed brominated poly(phenylene oxide) intermediates in an effort to synthesize more stable catalyst supports containing (cyclopentadienyl)metal complexes. Treatment of poly(oxy-2,6-dimethyl-l,4-phenylene) with N-bromosuccinimide under photolytic conditions produced only the bromomethyl derivative if the D.F. did not exceed 0.35. Subsequent treatment of the bromomethylated polymer with sodium cyclopentadienide afforded the cyclopentadienyl functionalized polymer, 5, but the reaction was accompanied by crosslinking and it was not possible to remove the bromomethyl substituents quantitatively. 

Alkali metal boratabenzenes have a wide synthetic applicability just like alkali metal cyclopentadienides. Two syntheses have been developed Ashe s synthesis via organotin intermediates (23) and our cyanide degradation of bis (boratabenzene) cobalt complexes (61). 

Studies of CpLi solutions showed high conductivity, suggesting ionic particles in solution.91 Ionic particles could consist of the free ions, but anionic cyclopentadienides MCp2- particles isoelectronic to the well-known alkaline earth cyclopentadienides Cp2M (M = alkaline earth metal),103 could also be envisioned. Moreover, the structural motif of a sandwich complex where two Cp ligands bind to a metal center is well established throughout the periodic table. Indeed, the Cp2 Li anion was suggested based on NMR techniques,114-116 and... 

Bis[(tris(isopropyl)cyclopentadienyl)]zinc (Zn C5(Pr1)3H2 2, 21) and bis[(tetrakis(isopropyl)cyclopentadienyl)]zinc (Zn C5(Pr1)4H 2, 22) were synthesized from the respective potassium cyclopentadienides and zinc iodide as shown in Scheme 18.50 The same slipped sandwich compounds were also isolated from zinc-reduced VC13 solutions when they were treated with these alkali metal cyclopentadienides at room temperature.51 The outcomes of these reactions suggest that zincocenes are likely intermediates in the syntheses of transition metal metallocenes, in which the metal halides have been pre-reduced with zinc. The solid-state structure of Zn G5(Pr1)4H 2 is shown in Figure 10. The sole... 

This is remarkable, since the reduction potential of Th(IV) to Th(III) recently has been estimated as —3.7 volts 73) and direct reduction of U(C5H5)4 and Pu(C5Hs)3 with potassium metal produces the actinide metals. The ei/z for naphthalene in acetonitrile is —2.63 V (nearly the same as the aLkaJi metals). Since this is much smaller than the Th(IV) to Th(III) reduction potential, it would seem to imply substantial stabilization of the +3 state by cyclopentadienide. The observed room temperature magnetic moment of Th(C 5115)3 (0.403 BM) is consistent with the Th(III) (5/ ) assignment. Thorium triscyclopentaxhenide is similar in behavior to U(C5H5)3, forms adducts with both THF and cyclohexyhso-nitrile and has been shown to be isostructural with the other tris (cyclopentadienyl) actinides and lanthanides. 

The preparation of Th, U and Np tetracyclopentadienides were accomplished by the straightforward reaction of the anhydrous metal tetrachloride with potassium cyclopentadienide in benzene (6). Tetrakis(cyclopentadienyl) pro-tactinium(IV) was prepared using Be(CsH5)2 and Pads prepared in situ (6). Infrared data suggest that aU of the tetracyclopentadienides possess similar molecular structures the Th, U and Np complexes were found to be isostmctural by powder techniques (79, 80). 

The first weU-characterized organometallic compounds of the lanthanides or actinides were the tricyclopentadienides of various lanthanide ions S3mthesized by Birmingham and Wilkinson in 1954 (97—98). Anhydrous metal chlorides were reacted with sodium cyclopentadienide in tetrahydrofuran as follows ... 

Complexes 88—91 catalyzed the polymerization of ethene upon activation with MAO. Every dendritic catalyst displayed a lower activity than its reference complex Cp2ZrCl2 or Cp2TiCl2. It was found that the replacement of a C5HJ ligand by a dendritic cyclopentadienide (88 or 89) caused a moderate decrease in activity (4,320 2,064 and 1,720 kg/mol/h for CpTiCls, 88, and 89, respectively), which could be attributed to steric hindrance. The bis-dendritic Cp system 90 gave a lower activity (576kgmor h ). Interaction between a pair of dendritic wedges may restrict the conformations in which they are kept far away from the metal center. 

With transition metal reagents, Cgo undergoes either hydrometalations or forms T] - rather than t] - or Tj -Tt-complexes (see Chapter 7). The latter would be typical reactions for planar aromatics (Scheme 14.2). Conversely, Tj -Tt-complexes can be obtained with fullerene derivatives, where due to a specific addition pattern an isolated cyclopentadienide substructure is present (see Chapter 7) [76-78]. 

Use of the r]n- prefix in organometallic complexes is explained in Chapter 18. The superscript n gives the number of atoms (usually carbon atoms) in a ligand that are directly bonded to the metal center for example, rf-cyclopentadienide means that all five carbons in a CsHs- ligand are bonded to the metal atom. 

Another type of five-membered aromatic compound is the metallocenes (also called sandwich compounds), in which two cyclopentadienide rings form a sandwich around a metallic ion. The best known of these is ferrocene, although others have been prepared... 

In the early 1960s it was recognized (6,187) that there were bonding similarities between the pentagonal face of the isomeric [nirio-(y HjJ2- ions and the well-known cyclopentadienide ion (Cp ) [CydJ- (Fig. 16). The isomeric nido-C2B9H1 J2- ions, which are commonly known as dicarbollide ions, and many other carborane anions, form stable complexes with most of the metallic elements. Indeed nearly all metals can be combined with polyborane hydride clusters to produce an apparently limitless variety of cluster compounds. 

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