Lanthanide complex with hydride

Hunt s group (50, 51) have pioneered the application of the Cl source to organometallics such as the iron tricarbonyl complex of heptafulvene, whose electron impact spectrum shows (M—CO)+ as the heaviest ion, in contrast to the methane Cl spectrum with the ion as base peak. Boron hydrides (52) and borazine (53) have also been studied. The methane Cl spectrum of arenechromium and -molybdenum (54) show protonation at the metal giving a protonated parent or molecular ion. Risby et al. have studied the isobutane Cl mass spectra of lanthanide 2,2,6,6-tetramethylheptane-3,5-dionates[Ln(thd)3] (55) and 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-oetanedione [H(fod)] lanthanide complexes (56). These latter complexes have been suggested as a means of analysis for the lanthanide elements. 

The potential use of non-solvated lanthanide cyclopentadienyl hydride complexes as catalysts in alkene C-H bond activation, hydrogenation of alkynes led to synthesis of aluminum hydride organo lanthanide complexes. Examples of such complexes with polymeric structure and chain structure have been characterized [251]. 

Lanthanide monohydride complexes, such as bi(cyclopentadienyl) lanthanide hydrides, can be conveniently prepared by the reactions of lanthanide mono-alkyl or -aryl complexes with organosilanes under mild reaction conditions (Figure 8.27) [82]. 

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. 

Chiral lanthanide bistrifylamides were prepared through the reaction of lan-thanide(III) triflates and chiral bistrifylamides, which are deprotonated with 2 equivalents of sodium hydride in THF for 1 h. Dichloromethane or toluene was introduced, after evaporation of THF, to the residual complex. The resultant suspension of the lanthanide complex was then used for the hetero-Diels-Alder reaction (Scheme 16). 

The mechanism of the reaction was studied for cyclopentadienyl lanthanide complexes, [26, 29, 31]. A monomeric metal hydride is proposed to be the active species. The catalytic cycle turns via a fast and irreversible insertion of the olefin into the metal hydrogen bond to form an alkyl species which reacts with the silane in the rate determining step with regeneration of the hydride (Scheme 12). 

In conclusion, one can look at the silyl hydride complexes in a number of ways, either as coordinated silane with a very elongated Si- -H bond or as complexes of hypervalent silicon moieties with an agostic Si-H bond [109]. It should be pointed out that the ability of Si to become hypervalent in the vicinity of a transition metal fragment has some important consequence on the reactivity of silane derivative in metathesis reaction with lanthanide complexes [115]. 

---