Cyclopentadienyl rare-earth complexes

The properties of cyclopentadienyl lanthanide compounds are influenced markedly by the relationship between the size of the lanthanide atoms and the steric demand of the Cp group. The former varies from La to Lu according to lanthanide contraction, while the latter varies from the least bulky Cp to highly substituted Cp, which is appreciably larger. The Sc and Y complexes are very similar to those of lanthanides with proper allowance for the relative atomic sizes. 

Structural formulas and geometries of LnCp3 complexes (a) LaCp3, (b) SmCp3, and (c) LuCp3. 

Structures of some biscyclopentadienyl rare-earth complexes (a) (Cp2ScCl)2, (b) Cp Yb(MeBeCp ), (c) 

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Crystallographic data, bonding distances and angles in bis(trimethylsilyl)cyclopentadienyl rare earth complexes Cp = (Me3Si)2C5H3. 

Ring-bridged bis(cyclopentadienyl)rare earth complexes have been synthesized with Ln = La or Ce in THF (51,52). The derivatives of Pr,... 

Fieser ME, Bates JE, ZiUerJW, Furche F, Evans WJ. Dinitrogen reduction via photochemical activation of heteroleptic tris(cyclopentadienyl) rare-earth complexes. 

CHART 2 Non-cyclopentadienyl rare earth complexes reported by various groups (abbrevia-tirms are the same as in text). 

CHART 10 Examples of reduced tris-cyclopentadienyl rare earth complexes reported by Lappert s and Evans s groups. 

Two classes of material will be described here - the metal dithiolenes and rare earth metallocenes. In the metal dithiolenes a strong, low energy pi-pi transistion occurs in the near IR (9.10). This can be tuned from about 700 nm to 1400 nm by altering the metal ion, substituents or charge state of the dithiolene. The dithiolenes are particularly attractive because of their optical stability which has been exploited in their use as laser Q-switch materials. In the rare earth complexes the near IR band is provided by/-/transistions of the rare earth ion rather than the cyclopentadienyl ring structure various nonlinear optical phenomena have been observed in glasses incorporating similar ions. Previous studies have shown that dicyclopentadienyl complexes such as ferrocene have off-resonant nonlinearities similar to nitrobenzene or carbon disulphide (11-13)... 

The organometalhc chemistry of the rare earths deals mainly with bis(cyclopentadienyl) derivatives due to the easy available bis(cyclopentadienyl) rare earth chlorides and other halides via reaction of the rare earth trichlorides with two equivalents of a cyclopentadienyl alkali salt. Bis(cyclopentadienyl)lanthanide chlorides are formed as chloride-bridged dimers (Figure 28a), as monomers stabihzed by a donor molecule like THF (Figure 28b) or as ate complexes with alkali hahdes (Figure 28c). 

Tricyclopentadienyl rare earth cyclohexyl isonitrile complexes have been prepared by addition of cyclohexyl isonitrile to the corresponding tris(cyclopentadienyl) rare earth compounds in benzene. They show definite melting points and are sublimable in vacuum at about 150 to 160°C (E.O. Fischer and H. Fischer, 1965a, 1966 Von Ammon and Kanellakopulos, 1972) ... 

Solvent-free cyclopentadienyl rare earth dichlorides have not been prepared. Only the cyclopentadienyl lanthanide dichlorides coordinated by three tetrahydrofuran molecules of the heavier lanthanides could be isolated and some of their properties were investigated (Manastyrskyj et al., 1963 Ely and Tsutsui, 1975). The corresponding yttrium complex was mentioned in a paper by Jamerson et al. (1974), but no characterization of the compound was given. The preparation of the cyclopentadienyl rare earth dichloride complexes with 2 coordinated tetrahydrofuran Ugands of Eu, with 3 THE ligands of La and TM and with 4 THE ligands of La, Sm, Eu, Tm, and Yb was also described in the meantime (Suleimanov et al., 1982c, d). 

Iodine cleaves one erbium-cyclopentadienyl bond in tricyclopentadienyl erbium with formation of pink dicyclopentadienyl erbium iodide (Maginn et al., 1963), and the tricyclopentadienyl complexes of neodymium and ytterbium are cleaved by hydrogen cyanide with formation of the corresponding dicyclopentadienyl lanthanide cyanide (Kanellakopulos et al., 1974). The colors and some physical data of the cyclopentadienyl rare earth halides and cyanides are given in table 4. 

The cyclohexyl isonitrile complexes of the tris(methylcyclopentadienyl) cerium, praseodymium, and neodymium compounds have been mentioned in a discussion of the NMR spectra of these and the corresponding tricyclopentadienyl rare earth complexes, which showed that the AG values of the fluxionality of the cyclohexyl ligands decreased in contrast to those of the unsubstituted cyclopentadienyl derivatives (R.D. Fischer, 1979). 

Mixed sandwich complexes of the rare earths containing cyclopentadienyl and cyclooctatetraenyl ligands were prepared either by the reaction of cyclopentadienyl rare earth dichlorides with dipotassium cyclooctatetraenide or form cyclooctatetraenyl rare earth chlorides and sodium cyclopentadienide in tetrahydrofuran (Jamerson et al., 1974) ... 

Cyclopentadienyl rare earth alkyl and aryl complexes... 

The reaction of di- u-alkyl-bis(cyclopentadienyl) rare earth dialkylaluminum complexes with equimolar amounts of pyridine in toluene at room temperature gives dimeric dicyclopentadienyl rare earth methyl complexes, which are isolated in about 80% yield as air-sensitive crystalline solids. They are stable for short periods up to 150°C, soluble in CH2CI2, hot toluene or benzene, partly soluble in cold toluene or benzene, but insoluble in saturated hydrocarbons (Holton et al., 1976a and 1979c). The similar reaction of the corresponding scandium derivative with pyridine or tetrahydrofuran does not give the bridging dimer, but a monomer with coordinated pyridine or tetrahydrofuran ... 

The preparation of cyclopentadienyl rare earth dichloride complexes with two coordinated THF ligands of Eu, and with four THF ligands of La, Sm, Eu, Tm, and Yb was also described (68,69). Figure 6 shows the ligand arrangement of C5H5ErCl2(THF)3 (70). 

Scheme 1 Generic reaction for the formation of />w(cyclopentadienyl) rare earth ate complexes...

Scheme 2 Utility of w(cyclopentadienyl) rare earth ate complexes in the S3mthesis of alkyl and hydride derivatives...

Trivalent Chemistry Cyclopentadienyl Rare Earth Metal Cluster Complexes Lanthanide Oxide/Hydroxide Complexes Oxide and Sulfide Nanomaterials Near-Infrared Materials. 

Rare earth organometallic chemistry has witnessed remarkable advances since the first paper that appeared 60 years ago on cyclopentadienyl compounds, authored by Wilkinson and Birmingham. In particular, ancillary ligands other than cyclopentadienyl derivatives have been introduced and their complexes exhibit distinct reactivity and properties compared to the metallocene or half-sandwiched analogues. The chapter reviews arene-bridged rare-earth complexes with emphasis on compounds obtained by reduction... 

Sterically hindered ligands (30) were synthesized and their rare earth complexes (31) prepared and characterized. The rare earth metal ion is bound in a rj fashion to the 5-membered cyclopentadienyl ring, along with coordination to nitrogen. ... 

Immobilization of Rare-Earth Metal Hydride, Alkyl, and Cyclopentadienyl Complexes... 

Cyclopentadienyl compounds have been thoroughly investigated as suitable precursors to rare earth doped semiconductors in MOCVD (metal-organic chemical vapor deposition) or MOVPE (metal-organic vapor phase epitaxy) processes [283]. The use of btsa complexes for the same purpose has appeared in the literature very recently [285]. Typical process conditions are shown in Scheme 14. It was found that the carbon contamination of the deposited metal is less in the btsa case. 

A rare example of isospecific 3,4-polymerization of isoprene mediated by a constrained-geometry rare-earth metal initiator was reported by Z. Hou [270]. Binuclear silyl-linked cyclopentadienyl phosphido lanthanide dialkyl complexes were synthesized in good yields and activated with an equimolar amount of [Ph3C] [B(C6Fs)4] (Scheme 68). Cationic alkyl species were proposed as intermediates and an activation scenario was presented based on DFT calculations [270]. 

Roesky introduced bis(iminophosphorano)methanides to rare earth chemistry with a comprehensive study of trivalent rare earth bis(imino-phosphorano)methanide dichlorides by the synthesis of samarium (51), dysprosium (52), erbium (53), ytterbium (54), lutetium (55), and yttrium (56) derivatives.37 Complexes 51-56 were prepared from the corresponding anhydrous rare earth trichlorides and 7 in THF and 51 and 56 were further derivatised with two equivalents of potassium diphenylamide to produce 57 and 58, respectively.37 Additionally, treatment of 51, 53, and 56 with two equivalents of sodium cyclopentadienyl resulted in the formation of the bis(cyclopentadienly) derivatives 59-61.38 In 51-61 a metal-methanide bond was observed in the solid state, and for 56 this was shown to persist in solution by 13C NMR spectroscopy (8Ch 17.6 ppm, JYc = 3.6 2/py = 89.1 Hz). However, for 61 the NMR data suggested the yttrium-carbon bond was lost in solution. DFT calculations supported the presence of an yttrium-methanide contact in 56 with a calculated shared electron number (SEN) of 0.40 for the yttrium-carbon bond in a monomeric gas phase model of 56 for comparison, the yttrium-nitrogen bond SEN was calculated to be 0.41. 

Cyclopentadienylthallium compounds have demonstrated tremendous preparative potential as mild reagents for the synthesis of cyclopentadienyl derivatives of Main Group Elements, Transition Metals, md Rare Earth Elements. In fact, some aUcyl-substituted cyclopentadienyl metal complexes can be obtained only from the analogous T1(I) compounds. 

Arndt, S. andOkuda, J. (2002) Mono(cyclopentadienyl) complexes of the rare-earth metals. Chemical Reviews, 102, 1953. 

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