Tricyclopentadienyl complexes

The discovery of ferrocene and of the other sandwich complexes initiated a new field of organometallic chemistry, the chemistry of the w-complexes. Wilkinson and Birmingham (1954) prepared the first organometallic w-complexes of the rare earths, the tricyclopentadienyl complexes of Sc, Y, La, Ce, Pr, Nd, Sm and Gd. It was not until 14 years later with the synthesis of triphenyl scandium (Hart and Saran, 1968) that the first a-bonded aryl-rare-earth compound was made. 

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 displacement of tetrahydrofiiran by triphenylmethylenephosphorane in CpjLuCTHF) gives a new tricyclopentadienyl complex, containing ylide as a coordinative ligand [243] ... 

In the reactions with CpjHg and CpTl, samarium, unlike Yb and Eu, gives only the tricyclopentadienyl complex even with the use of a large excess of Sm [9]. 

Lanthanoid halides LnCl3 and Lnp3 form tricyclopentadienyl complexes when alloyed with Cp2Mg (ca. 200°C) [122] or Cp2Be (ca. 70°C) [111]. The latter method has been developed for microgram quantities and has been used to prepare the promethium derivative ... 

All tricyclopentadienyl complexes of REM have similar chemical properties [91, 119]. In the crystalline state all they decompose in air with a remarkable rate. The Cp3Ce [91] and CP3EU [112] are especially unstable. The oxidation of the complexes is accompanied by chemiluminescence [131], In an inert atmosphere or in vacuum the complexes are stable up to 250-450 C. The only exclusion is CP3EU, which decomposes on heating over 100 C [112]. The measurement of temperature of triple point for CpgLn has shown [99] that the melting temperature noticeably diminishes simultaneously with the Ln "" ionic radius decrease (Fig. III. 14). 

Tricyclopentadienyl rare earth complexes ([M(7j5-CSH5)3] M = Er, Nd, Pr, Yb) have been measured by DFWM at a fundamental frequency corresponding to A = 1064 nm.29 They possess moderate nonlinearities despite having electronic transitions in the range 800-1550 nm, which might have been expected to result in dispersively enhanced values. Solution / ul for [Yb(T75-C5H5)3] [the largest nonlinearity of the series, and the complex with Amax (1030 nm) closest to ] is only about half that of CS2. 

Third-Order NLO Measurements of Other Metallocene Complexes and Tricyclopentadienyl Rare Earth Complexes... 

Tetrakis-cyclopentadienyl cerium (CeCp4) has been reported to be formed by the reaction of bis(pyridinium) hexachlorocerate with sodium cyclopentadienide [17]. Similarly indenyl and fluorenyl derivatives were prepared. Later work showed the same reactants in tetrahydrofurane to yield, Ce(Cp3), tricyclopentadienyl cerium complex instead of Ce(Cp4) [18]. 

The rare earth tricyclopentadienyls are insoluble in aliphatic hydrocarbons, and only sparingly soluble in aromatic hydrocarbons. They dissolve in polar solvents like tetrahydrofuran with complexation. Similarly, numerous bases like ethers, amines, isonitriles, phosphines and other compounds react with CP3R, yielding stable 1 1... 

Tricyclopentadienyl rare earth compounds form stable 1 1 adducts with many bases. THF adducts have been described for yttrium, lanthanum and nearly all lanthanides (Manastyrskyj and Dubeck, 1964 Calderazzo et al., 1966 E.O. Fischer and H. Fischer, 1966 R.D. Fischer and H. Fischer, 1967 Pappalardo, 1969 Raymond and Eigenbrodt, 1980 Rogers et al., 1981 Deacon et al., 1982). Tetrahydrofuran can be removed in high vacuum from all the complexes except for... 

C5H5)3Eu THF. The THF complexes exhibit a bathochromic shift in their color because of the coordination of the oxygen to the rare earth metal. Tetrahydrofurane adducts with 2 and 3 THF coordinated to the tricyclopentadienyl lanthanide complex are also known (Suleimanov et al., 1982c). 

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) ... 

Tricyclopentadienyl ytterbium reacts with liquid ammonia with formation of a stable 1 1 complex, which can be sublimed, but which decomposes above 200°C with formation of dicyclopentadienyl ytterbium amide and cyclopentadiene (E.O. Fischer and H. Fischer, 1966). The corresponding 1 1 adducts of NH3 could also be isolated for (C5Hj)3Pr and (C5H5)3Sm (Birmingham and Wilkinson, 1956), as well... 

Tricyclopentadienyl ytterbium reacts with tricyclopentadienyl uranium fluoride in benzene with formation of an adduct with a fluorine bridge between ytterbium and uranium. Tricyclopentadienyl thulium does not give an analogous complex with CpjUF. These reactions are unique to the uranium fluorine bond for CpjUCI fails to give an adduct with CpjYb (Kanellakopulos et al., 1970). 

The isolated complexes of tricyclopentadienyl rare earth compounds are shown in table 3. 

Unit cell parameters, bond lengths and angles of tricyclopentadienyl rare earth complexes. 

The optical absorption spectra for many tricyclopentadienyl and dicyclopenta-dienyl rare earth complexes have been reported. An excellent review with a detailed discussion of the work in this area done until 1970 is given by Hayes and Thomas (1971). An interpretation of the energy level structure of these complexes derived from the optical spectra is given by Carnall (1979). 

The diamagnetic (C5H,)2ScCl shows a chemical shift for the cyclopentadienyl protons of 5 = 6.16 ppm in tetrahydrofuran solution (Coutts and Wailes, 1970) the signal for the tetrahydrofuran complex in benzene solution appears at 5 = 6.25 ppm (Manzer, 1976a). The chemical shift for tricyclopentadienyl lutetium is 5 = 5.83 ppm in tetrahydrofuran and 6 = 5.90 ppm in benzene solution (E.O. Fischer and H. Fischer, 1965b). 

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). 

Tricyclopentadienyl lutetium reacts with triphenylmethylenephosphorane in tetra-hydrofuran with formation of a 1 1 complex, which precipitates from the solvent in colorless crystals, decomposing above 108°C (Schumann and Reier, 1984b). Di-cyclopentadienyl lutetium chloride forms in the same way in toluene an 1 1 complex with triphenylmethylenephosphorane, which is zwitterionic containing a ij -Lu-C bond (Schumann and Reier, 1981) ... 

The tetrahydrofuran complex of dicyclopentadienyl samarium is made by reduction of tricyclopentadienyl samarium with KCjgHg in naphthalene in the presence of tetrahydrofuran and was isolated as a purple pyrophoric product (Watt and Gillow, 1969). Ytterbium also reacts with thallous cyclopentadienide in dimethoxyethane in the presence of a little metallic mercury with formation of Cp2Yb DME (Deacon et al., 1982a). 

The base-free compounds of CpjLn type are known for all metals of the being considered block including radioactive promethium (Table III.3.). The cyclopentadienyl complexes of trivalent Sc, Y, La, Ce, Pr, Nd, Sm and Gd prepared in 1954 by Wilkinson and Birmingham in the reaction of anhydrous metal chlorides with CpNa were the first REM organoderivatives [119]. Later this method has been modified and applied to Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu [88, 91, 120, 121]. Up to now it remains to be the main way to the tricyclopentadienyl REM complexes. Besides CpNa, cyclopentadienides or substituted cyclopentadienides of lithium and potassium are used in these reactions [31,95, 100,101, 111, 116] ... 

The tricyclopentadienyl derivatives belong to the series of volatile REM derivatives. Except the less thermostable europium complex, all of them sublime on heating up to 150-250°C in vacuum lO -s-lO mm Hg. 

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