The Coordination Chemistry of Divalent Bis(pentamethylcyclopentadienyl)lanthanide Complexes With Non-classical Ligands
Year: 1987
Type: article
Abstract: Divalent complexes of the formula (Ne 5 C5 ) 2M (H = Eu, Sm, Yb, Ca, Sr, and Ba) have been isolated free of coordinating Lewis bases.X-Ray crystallography and gas-phase electron diffraction reveal that these complexes have a "bent-sandwich" geometry.UV-Photoelectron spectroscopy suggests that the bonding in the compounds is ionic, and a model consistent with this observation is proposed to rationalize the bending of the molecules.Divalent lanthanide and alkaline earth cations of similar ionic radii demonstrate similar coordination chemistry with simple Lewis bases.Isolation of the base-free species allows the synthesis of coordination compounds of weak bases, such as electron-rich olef ins and acetylenes.The complexes (Me 5 C 5 ) 2 Yb(p-C 2 H 4 )Pt(PPh 3 ) 2 and (!e 5C 5 ) 2Yb(,? 2-MeCDCHe) have been structurally characterized, and in each case the neutral organic molecule is i 2 -coordinated to the lanthanide.Ethylene is rapidly polymerized by (He 5 C5 ) 2 Yb, and methylallene is catalytically isomerized to 2-butyne.Both of these processes are proposed to be involve initial reduction of the organic substrate by the ytterbium.Fluoro-olef ins and -arenes undergo reduction followed by fluoride abstraction to give the mixed-valence compound [(Ne5C5)2Yb)2(p-F) , which is converted thermally to the tetranuclear species (Ne 5 C5 ) 6Yb 4 (p-F) 4 .The reaction of (Me 5•C 5 ) 2Yb with polar compounds such as (Xe 5 C 5 )BeMe and BR 3 PMe 3 results in the formation of coordination compounds which may be viewed as models for the coordination of the small molecules CH 4 and 8H3 .Zinc alkyl and aryl compounds undergo reduction, yielding zincate complexes of the formula (Me 5 C 5 ) 2Yb(p-R) 2 ZnR.The trimethylzincate compound displays symmetrically bridging methyl groups, while in the phenyl analog, the bridging geometry is markedly unsymmetric.Sterically demanding polar molecules such as carboranes react with (Me 5 C 5 ) 2Yb to form inclusion compounds, with no close host-guest contacts in the solid state.First-row transition metal metallocenes, however, form 1:2 adducts with (fle 5 C5 ) 2Yb, in which the ytterbium atoms coordinate to the cyclopentadienyl rings of the metallocene.
Author: Christopher J. Burns
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Funder: U.S. Department of Energy
Awards: G1398330795, G1643223109, G193590374
OpenAlex ID: W2771605089