Lanthanoids cyclopentadienyl complexes

Cyclopentadienyl complexes of lanthanoids(II) are known for samarium, europium and ytterbium [1-24] (Table III.L) One compound of Nd(II) is claimed as well [25], but its exact structure and the valent state of the neodymium atom apparently needs additional proves. Samarium derivatives are isolated as tetrahydrofuranates Cp2Sm(THF). In the case of europium and ytterbium solvent-free complexes are obtained. 

The redox transmetallation method is a simple and convenient preparative route. Cp2Hg and cyclopentadienyl complexes of T1(I) are used as a source of cyclopentadienyl ligands [19]. The reactions of dicyclopentadienylmercury are carried out in THF at 0-20 C with 4-5-fold excess of lanthanoid finely divided and activated by mercury chloride. 

Cyclopentadienyl complexes of lanthanoids can be used as catalysts for the hydro-amination/cyclization of aminoolefines [90], the hydroformylation of olefines [89, 135], the cyclization of alkynes [68] and other processes. 

The introduction of substituted cyclopentadienyl ligands has only been successful in two instances. Thus, all lanthanoides form tris-(methylcyclopentadienyl)lanthanoide complexes, Ln(C5HI CH3)3, as well as niimerous adducts of them with Lewis bases (28,37 to 4o). Furthermore, lanthanum, praseodymium and neodymium form compoimds of the type Ln(C5Hif-i-C3H7) 3 (4l). With the more bulky ligands, such as the penta-methylcyclopentadienyl- or even the bis(trimethylsilyl)cyclopentadienyl ligand, only the disubstituted derivatives can be obtained. 

Organolanthanoide hydrides (1 11,1 8,215,221), cyclopentadienyl-ytterbium(ll) complexes (190) as well as the cocondensation products of lanthanoides with acetylenic derivatives (137,216,222) catalyze the hydrogenation of olefins and acetylenes. 

Table 1.13 Cyclopentadienyl lithium-lanthanoid complexes (continued). 

The infra red spectra of bridging methyl complexes are practically identical, just as the spectra of ethyl analogues. It allows to use IR spectroscopy for identification of new bridging alkyl lanthanoid complexes. The frequencies of cyclopentadienyl ring in the spectra of all complexes are observed at 3100 m., 1446 m., 1020 s. and 800 v.br. cm... 

This method allows to obtain the compounds with substituted and unsubstituted cyclopentadienyl ligands practically for all lanthanoids, including hardly accessible compounds of early REM [270], and the triflate complex CpLn(0S02CF3)2(THF)3 as well [241]. 

Especially it is important to note the formation of mono- and disubstituted complexes of "light" lanthanoids (La and Nd). As has been already noted, such compounds of the cyclopentadienyl derivatives series either have not been received or they have a poor solubility. 

Table VI.2. Mixed cyclopentadienyl/amides of lanthanoids and relative complexes.

A suitable route to REM cyclopentadienyl alkoxides is the alcoholysis of a Ln-R bond, in which R is H or an alkyl group, in complexes of the Cp2LnR type [76, 77, 91], As a rule cyclopentadienyl- lanthanoid bonds are not involved in the reaction and Cp2LnOR alkoxides are isolated in a good yield ... 

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