Reactivity of Lanthanide and Yttrium Hydrides and Hydrocarbyls toward Organosilicon Hydrides and Related Compounds

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Abstract

The reaction of lanthanide and yttrium hydrocarbyls {Cp*2Ln(μ-Me)}2 (Cp* = tBuC5H4 (Cp‘), Ln = Y (1), Tb (2), Yb (3), Lu (4); Cp* = Me3SiC5H4 (Cp‘‘), Ln = Lu (5)), one of which, 2, has been characterized by X-ray crystal analysis, with various organosilicon, -germanium, and -tin hydrides (as well as some organoaluminum and -gallium hydrides) in hydrocarbon solution was found to yield the corresponding unsolvated dimeric lanthanide and yttrium hydrides {Cp*2Ln(μ-H)}2 rather than compounds with lanthanide−element (Si, Ge, Sn) bonding. Thus, the reaction involves hydride transfer to Ln rather than the silyl transfer studied earlier for pentamethylcyclopentadienyllanthanide hydrocarbyls. Dimeric compounds Cp*2Ln(μ-H)(μ-Me)LnCp*2 with different bridging ligands were isolated; they are intermediates in this reaction. Dimeric lanthanide and yttrium hydrides catalyze the H/D exchange in silanes. This catalytic reaction is most correctly described by a mechanism involving nucleophilic substitution at the silicon atom. Yttrium and lutetium hydrocarbyls 1 and 4 react with various alkoxysilanes to produce the dimeric alkoxides {Cp‘2Ln(μ-OR)}2 or the hydrocarbyl alkoxides Cp‘2Ln(μ-Me)(μ-OR)LnCp‘2 (R = Me, Et), depending on the reaction conditions. The reaction of 4 with (MeO)4Si provided Cp‘2Lu(μ-Me)(μ-OMe)LuCp‘2, which has been characterized by X-ray crystal analysis. This compound contains one methyl bridge (Lu−C 2.57(2) and 2.58(2) Å) and nonsymmetrically bonded μ-OMe ligand (Lu−O 2.20(2) and 2.12(2) Å). The reaction of 1 and 4 with Me3SiCl leads to the corresponding dimeric chlorides {Cp‘2Ln(μ-Cl)}2 only. Thus, the reaction of lanthanide and yttrium hydrocarbyls with various heterosubstituted organosilanes R3SiX, where X = H, OR, or Cl, is a selective and convenient synthetic method in the chemistry of the group 3 elements. Complexes with Ln(μ-H)(μ-Me)Ln and Ln(μ-H)(μ-Cl)Ln bridging were prepared in high yield by the exchange reactions between the corresponding dimeric compounds {Cp*2Ln(μ-X)}2 (X = H, Me, Cl) in a hydrocarbon solution. The capacities of various bridging fragments to undergo reversible cleavage (dissociation) in the hydrocarbon solution increase in the sequence Ln−O(Me)−Ln ≪ Ln−Cl−Ln < Ln−H−Ln < Ln−Me−Ln.

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