Reactivity of Ln(II) Complexes Supported by (C₅H₄Me)^1– Ligands with THF and PhSiH₃: Isolation of Ring-Opened, Bridging Alkoxyalkyl, Hydride, and Silyl Products

Reduction of CpMe3Ln­(THF), 1-Ln (Ln = La and Gd; CpMe = C5H4Me), with KC8 in the presence of 2.2.2-cryptand (crypt) generates dark solutions, 2-Ln, with EPR spectra consistent with Ln­(II) complexes: an eight-line hyperfine pattern for La at g = 1.971 and a broad single line for Gd at g = 1.988. The solutions decompose within minutes, and in the La system, a decomposition product was isolated in which a molecule of THF had been reduced by two electrons and ring-opened to generate an alkoxyalkyl-bridged bimetallic La­(III) complex, [K­(crypt)]2­[(CpMe3La)2­(μ-OCH2­CH2CH2­CH2)], 3-La. An analogous Pr complex, 3-Pr, was also crystallographically characterized. Since decomposition products were not readily isolated from the analogous yttrium CpMe3­Y­(THF)/​KC8/​crypt reaction, the composition of the solution of 2-Y was probed by addition of the hydrogen delivery reagent, PhSiH3, which had previously been reported to form U­(III) hydrides from tris­(cyclo­pentadienyl) U­(II) complexes. This generated an Y­(III) silyl complex, [K­(crypt)]­[CpMe3­Y­(SiH2Ph)], 4, in addition to a hydride product, [K­(crypt)]­[(CpMe3­Y)2­(μ-H)], 5. The retention of three CpMe ligands per metal in 3-Ln, 4, and 5 is consistent with the presence of a (CpMe3­Ln)1– species in 2-Ln.