Tris(cyclopentadienyl)cerium and -uranium: Relative basicity, structure, and reactions
The trivalent cerium complexes (RC/sub 5/H/sub 4/)/sub 3/Ce /center dot/ L have been prepared and structurally characterized in order to study the relative basicity of neutral donor ligands toward (RC/sub 5/H/sub 4/)/sub 3/Ce. The steric properties of the metal environment and the steric and electronic properties of the donor ligand influence complex stability. The base-free metallocenes, (RC/sub 5/H/sub 4/)/sub 3/Ce, react with a number of protic reagents to form stable ((RC/sub 5/H/sub 4/)/sub 2/CeX)/sub 2/ complexes via a ring protonation reaction. The reagent pKa values govern the thermodynamics of the reaction. The steric bulk of the protic substrate and the cyclopentadienyl ligands can be altered to achieve kinetically stable compounds. In contrast, the analogous uranium complexes, (RC/sub 5/H/sub 4/)/sub 3/U, react in an oxidative manner with protic reagents to form (RC/sub 5/H/sub 4/)UX complexes. The base-free cerium metallocenes also react with methyllithium to afford bis(cyclopentadienyl)cerium methyl complexes. Other alkyl complexes cannot be prepared in a similar manner. The cerium methyl complexes readily polymerize ethylene, and they react with phenylacetylene, hydrogen, and ammonia to yield the bridging acetylide, hydride, and amide complexes, respectively. The uranium metallocene, (MeC/sub 5/H/sub 4/)/sub 3/U /center dot/ thf, reacts with methyllithium at low temperature (/minus/30/degree/C) in the presence of Me/sub 2/NCH/sub 2/CH/sub 2/NMe/sub 2/ (tmed) to form a complex that contains a methyl group that is linearly and symmetrically bridging between two (MeC/sub 5/H/sub 4/)/sub 3/U groups, and a MeC/sub 5/H/sub 4/ group that is sandwiched between two Li(tmed) fragments. 149 refs., 35 figs., 40 tabs.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6597490
- Report Number(s):
- LBL-26124; ON: DE89002946
- Country of Publication:
- United States
- Language:
- English
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ACTINIDE COMPLEXES
BASES
BOND ANGLE
BOND LENGTHS
CERIUM COMPLEXES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMICAL STATE
COMPLEXES
CRYSTALS
DIMENSIONS
ELECTRONIC STRUCTURE
HYDROGEN 1
HYDROGEN ISOTOPES
INFRARED SPECTRA
ISOTOPES
KINETICS
LENGTH
LEWIS BASES
LIGANDS
LIGHT NUCLEI
MOLECULAR STRUCTURE
NMR SPECTRA
NUCLEI
ODD-EVEN NUCLEI
PH VALUE
PHYSICAL PROPERTIES
RARE EARTH COMPLEXES
REACTION KINETICS
SPECTRA
STABILITY
STABLE ISOTOPES
SYNTHESIS
URANIUM COMPLEXES