Cyclopentadienyl halide

Mono(cyclopentadienyl) halides, with Ti(IV) alkyl- and alkenyl-substituted Cp ligands, 4, 383 boryl-Cp ligands, 4, 392 halide abstraction reactions, 4, 405 hydrolysis reactions, 4, 398 metathesis reactions, 4, 400... 

Cyclopentadienyl halide complexes have been prepared from the reaction of NaCp or LiCsMes and BiCb. As described earlier, CpBiCb, in its red crystal morphology, has been structurally characterized (5) and shows a chain polymeric structure containing both if-- and f-coordination of the Cp ring to bismuth. In (C5Me5)2BiCl, the... 

Allyl, propargyl, and cyclopentadienyl halides are more reactive than alkyl halides, and LiBr,73 Cu(I),74 Cu(II),75-76 and R4N+ X salts have been used as promoters.73-74 76... 

Bis(pentamethylcyclopentadienyl)tin dibromide103 and pentaphenylcyclopentadi-enyltin trichloride104 105 (though not the tribromide) can be prepared by oxidative addition of the cyclopentadienyl halide to Sn or Sn(II) as appropriate. 

Fig. 13a-c. Photoelectron spectra of lanthanide and actinide cyclopentadienyl halides a Gdtp-CsHcGCl b U(t,-CsHs)3C1 c U(r -C5Me5)2Cl2... 

A slightly dated, but exhaustive, review is available on complexes of the type [CpMoX j. Cyclopentadienyl halide complexes of molybdenum in the -E6 and +2 oxidation states are not known. 

In contrast, the less-strained four-rr-electron cyclopentadienyl cation is very unstable. The p R+ has been estimated as -40, using an electrochemical cycle. Solvolysis of cyclopentadienyl halides assisted by silver ion is extremely slow, even though the halide is in an allylic position. " When the bromide and antimony pentafluoride react at -78°C, the product has an EPR spectrum indicating that the cyclopentadienyl cation is a triplet, in agreement with HMO and more sophisticated MO calculations. The pentachloro derivative is also a triplet, but the pentaphenyl ion is a singlet. ... 

Palladium complexes with an heterocyclic N-containing ligand have been used in the carbonylation of aromatic nitro compounds with cocatalysts such as cyclopentadienyl halides or oxyhalides of transition metals belonging to group V e.g. CP2VCI) [168], a cyclopentadienyl halide or oxyhalide together with phosphorus oxytrichloride [169], or a 1,3-diketone derivative of vanadium [170], even also in the presenee of phosphorus oxychloride [171]. 

The reaction of 2,4-cyclopentadienyl iodide with silver ion is extremely slow. When the carbocation corresponding to ionization of a 2,4-cyclopentadienyl halide is generated at low temperature it gives an EPR spectrum that indicated that the molecule is a ground state triplet, that is, it has two unpaired electrons. A quantitative measure of carbonium ion stability is called p/ R+ and is equal to log K for the reaction ... 

Tris(cyclopentadienyl) halides of thorium and neptunium have also been prepared. For thorium, the TlCp methodology is the most convenient synthetic approach [54] ... 

The general recognition of the difference between the 4/3 + 2 and 4/3 r-systems led to many studies of the cyclopentadienyl cation. In an early observation, Breslow et al. reported that cyclopentadienyl halides are remarkably resistant to solvolysis. Thus, cyclopentadienyl iodide does not react with silver perchlorate in propionic acid solution. Subsequently, it has been possible to prepare substituted cyclopentadienyl derivatives which undergo solvolysis, but the rates of reaction are very low. ° Cyclopropyl substituents appear to be particularly effective in stabilizing the cation. ... 

Frequently the bis-Tt-cyclopentadienyl halides are thermally stable above 200°C and are stable to oxidation in dry air. They are rather less rapidly hydrolysed than the corresponding metal halides although partial hydrolysis or oxyhalide formation can occur. Thus contrast the rapid hydrolysis reactions of titanium and zirconium tetrachlorides with the reactions... 

The mono-7t-cyclopentadienyl halides are usually more readily hydrolysed and are less stable to heat than the bis- r-cyclopentadienyl halides. 

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