Dicyclopentadienyl ytterbium complexes

Structural studies by Baker, Brown, and Raymond (42) have shown the dimeric nature of lanthanide dicyclopentadienyl halides. They reported that the molecular structure of [Y (C H CH ) Cl] consists of two ytterbium atoms, each with two n -bound methyl-cyclopentadienyl rings, which are nearly symmetrically bridged by the two chlorine atoms. The crystal structure of Yb(C(.H Me was reported by Halton et al. (43). The complex actually nas a dimeric structure, Cp2YbMe2YbCp2, remarkably similar to Me2ALMe2 AlMe2 The overall molecular geometry is identical with that or the chloride analogue Yb(C H CH )2CI. 

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... 

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. 

Dicyclopentadienyl erbium methyl and dicyclopentadienyl ytterbium methyl react with alkynes like HC CC(CH3)3 with formation of dimeric alkynide-bridged complexes of the type [Cp2RC=CC(CH3)3]2 (Atwood et al., 1981). 

Investigations by Bielang and R.D. Fischer (1978) demonstrate that the reactions of dicyclopentadienyl ytterbium chloride with lithium di(cyclohexyI)phosphide, lithium cyclohexylphosphide and lithium phenylphosphide are rather complicated. The decomposition behavior of these very sensitive substances is complex. It was possible to isolate Cp2YbP(QHji)2, but Cp2YbPHPh and Cp2YbPHQH decompose with formation of polymeric species [CpYbPPh] and [CpYbPQH,] . 

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). 

A metal vapor technique provides a very interesting route to the preparation of Sm(II) or Yb(II) organometallic species. Thus W.J. Evans et al. (1980, 1981a, 1982) were able to prepare several substituted dicyclopentadienyl samarium and ytterbium complexes. Sm(C5Mes)2 was the first known soluble divalent organosamarium complex. 

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