Synthesis and Reactivity of Lanthanide Hydride Complexes

A metathesis reaction is a convenient route to lanthanide tetrahydroaluminate and lanthanide tetrahydroborate complexes. Using tetrahydroaluminate complexes as the hydride source, a number of structurally characterized lanthanide tetrahydroaluminate complexes are prepared via metathesis reactions in the presence of an excess of a Lewis base (Equation 8.24) [79]. Metathesis reaction of organolanthanide chlorides with alkali metal tetrahydroborate generates the corresponding lanthanide tetrahydroborate. The same reaction with sodium hydride in THE is reported to afford a lanthanide hydride however, no molecular structure for the hydride has been presented up till now. 

Cleavage of Ln-C a-bonds of lanthanide alkyls and aryls by a hydrogen molecule at ambient pressure and room temperature is a popular method for the synthesis of neutral lanthanide hydride complexes (Equation 8.25). The first structurally characterized neutral lanthanide hydrides were prepared by hydrogenolysis of bi(cyclopentadienyl) lanthanide alkyl 

Lanthanide alkyl and aryl complexes react with organoelement hydride compounds, such as hydrides of silicon, germanium, and tin, and so on, resulting in a hydride transfer to the lanthanide metal atom. Among the organoelement hydrides, organosilanes are the most popular source of the hydride. 

Lanthanide hydride complexes are highly active species. They can activate unsaturated C-C, C-N, and even saturated C-H and C-O bonds. 

Reaction of tetranuclear lanthanide octahydrides with styrene provides lanthanide benzylic allyl heptahydride complexes through the insertion of a styrene molecule into one Ln-H bond. The lanthanide benzylic allyl complexes can be considered as the intermediates of styrene hydrogenation. Indeed, both the lanthanide octahydrides and the lanthanide benzylic allyl complexes can catalyze styrene hydrogenation efficiently in the presence of H2 [89]. Lanthanide hydrides react with 1,3-cyclohexadiene to form lanthanide allylic complexes via 1,4-addition [90]. However, these lanthanide hydride clusters can not catalyze the polymerization of styrene and 1,4-cyclohexadiene. 

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