Hydride pentamethylcyclopentadienyl lanthanide

The highly syndiospecific-living polymerization of methyl methacrylate has been initiated by the neutral bis(pentamethylcyclopentadienyl)lanthanide-alkyl or -hydride complexes [215,216]. The plausible reaction mechanism is shown in Scheme XI. 

Bi(pentamethylcyclopentadienyl) lanthanide hydride and methyl complexes [(C5Me5)2Ln(p.-R)]2 (R = H, CH3) were the first to be reported as excellent initiators for the highly... 

The dissociation of the dimer [Cp 2Y(/i-H)]2 to the Cp 2YH monomer is an important process in the reactions of the dimer with alkenes. The kinetics and formation of yttrium alkyl complexes from [Cp 2Y(//-I I)]2 and alkenes have been investigated.587 In situ prepared dimeric bis(pentamethylcyclopentadienyl)yttrium hydride reacted rapidly with 3,3-dimethyl-l,4-pentadiene in methylcylohexane-r/ at — 78 °C and formed a bright yellow solution of the t/°-yttrium(m)pentenyl chelate complex Cp 2Y[7/,7/2-CI I2CI I2CMc2CI I=CH2] in 98% yield (Scheme 130). This pentenyl chelate complex was also prepared in toluene-// in 84% yield. The chelate complex was stable for about 2 weeks at — 78 °C but decomposed after a few hours at —50 °C. The complex was characterized without isolation by 1H and 13C NMR spectroscopy at —100 °C such complexes can be regarded as models for the coordination of alkenes to lanthanide and isoelectronic grouop 4 polymerization catalysts.588 Agostic interactions in yttrium alkyls of the type... 

The lanthanides and actinides are also active in electrophilic attack on arenes. Bis(pentamethylcyclopentadienyl)lutetium methyl or hydride complexes react readily with benzene to give phenyl complexes and methane or dihydrogen . Similar reactions are observed for Sc and Th In a remarkable reaction benzene can be dimetallated by Lu, yielding II ... 

The lanthanide hydrides are exceedingly sensitive towards air and moisture. In the absence of added reagents, the electron-rich pentamethylcyclopentadienyl hydrides, Cp 2LnH, react with themselves by intermolecular H abstraction from a Cp ligand. Aromatic solvents and a large variety of unsaturated substrates (carbon monoxide, aldehydes, ketones, imines, alkynes, olefins) also readily react with these hydrides (Scheme 9) [20]. The high electrophilic nature of these metals... 

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