Agostic interactions lanthanide complexes

Very similar Si H M agostic interactions, characterized by a red shift of the Si-H absorption (IR), a high-field shift of the Si-H resonance ( H NMR), reduced Si-H coupling constants, and acute M-N-Si bond angles, were thoroughly studied by Anwander et for a range of d lanthanide complexes. In particular, the series... 

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... 

This article has reviewed the synthesis and reactivity towards small molecules of a range of U(lll) cyclooctatetraene and pentalene complexes. It is evident that in many cases the uranium centre is capable of tt back-bonding through the 5/ orbitals additionally, a C - C agostic interaction between a bound substrate and a U(IV) centre has been observed. Clearly uranium is capable of bonding with a degree of covalency , and this is perhaps why the reduction chemistry of U(III) is so rich and diverse, and not simply an iteration of low-valent lanthanide chemistry. 

Compounds which accommodate agostic interactions of Si-H moieties with transition metals may also be considered as a special type of higher-coordinated silicon compounds. A few reviews on this matter are also available [36]. These include a recent general overview [37] and further publications on selected sub-topics such as platinum compounds [38] or niobium and tantalum complexes [39]. Complexes of this type are also discussed in comparison to C-H and H-H interactions with lanthanides [40]. 

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