Reductive C-O Cleavage of Ethereal Solvents and 18-Crown-6 in Ln(NR2)3/KC8 Reactions (R = SiMe3)

Abstract

The high reactivity accessible from the reduction of the tris(amide) complexes Ln(NR₂)₃ (R = SiMe₃) with potassium graphite in the presence of a variety of ethers is demonstrated by crystal structures of six different types of products of C-O bond cleavage reactions with Ln = Y, Ho, Er, and Lu. Specifically, 1,2-dimethoxyethane (DME) can be cleaved in Ln(NR₂)₃/KC₈ reactions as shown by three different types of crystals: [K (crypt)][(R₂N)₃Y(OCH₂CH₂OCH₃)], 1-Y, [(R₂N)₂Y(μ-OCH₂CH₂OCH₃-κO,κO')]₂, 2-Y, and [K₂(18-c-6)₃]{[(R₂N)₃Lu]₂[(μ-OCH₂CH₂O)]}, 3-Lu (18-c-6 = 18-crown-6; crypt = 2.2.2-cryptand). THF can be ring opened by the Y(NR₂)₃/KC₈ reaction system, as shown by crystals of the butoxide, [K(crypt)][(R₂N)₃Y(OCH₂CH₂CH₂CH₃)], 4-Y. The cyclic ether, oxetane, OC₃H₆, ring opens in Ln(NR₂)₃/KC₈ reactions to form crystals of the propoxide, [K(18-c-6)(OC₃H₆)][(R₂N)₃Ln(OCH₂CH₂CH₃)], 5-Ln, for Ln = Ho and Er. In Et₂O, the Y(NR₂)₃/KC₈ reactions do not attack the solvent, but C-O cleavage of 18-c-6 is observed to form {[(R₂N)₂]Y[μ-η¹:η¹-O₂(C₁₀H₂₀O₄)K]}₂, 6-Y. These Ln(NR₂)₃/KC₈ C-O cleavage reactions are typically accompanied by C-H bond activation reactions, which form cyclometalates such as [K(crypt)]{(R₂N)₂Ln[N(SiMe₃)(SiMe₂CH₂)-κC,κN]}, 7-Ln (Ln = Y, Ho, Er), and [K(18-c-6)]{(R₂N)₂Y[N(SiMe₃)(SiMe₂CH₂)-κC,κN]}, 8-Y, which are common decomposition products of Ln(NR₂)₃ reactions. In addition, in this study, the hydride complex, [K(18-c-6)][(R₂N)₃YH], 9-Y, was isolated. NMR analysis indicates that the yttrium reactions form mixtures that consistently contain the yttrium cyclometalates 7-Y and 8-Y as major components. These results show the diversity of available reaction pathways for the Ln(NR₂)₃/KC₈ system and highlight the inherent difficulties in isolating Ln(II) complexes containing the [Ln(NR₂)₃]^1- anion.