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

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.

Solid-State End-On to Side-On Isomerization of (N═N)2- in {[(R2N)3Nd]2N2}2- (R = SiMe3) Connects In Situ LnIII(NR2)3/K and Isolated [LnII(NR2)3]1- Dinitrogen Reduction.

Examination of the reduction chemistry of Nd(NR2)3 (R = SiMe3) under N2 has provided connections between the in situ Ln(III)-based LnIII(NR2)3/K reductions of N2 that form side-on bound neutral (N=N)2- complexes, [(R2N)2(THF)Ln]2[µ-η2:η2-N2], and the Ln(II)-based [LnII(NR2)3]1- reductions by Sc, Gd, and Tb that form end-on bound (N=N)2- complexes, {[(R2N)3Ln]2[µ-η1:η1-N2]}2-, which are dianions. The reduction of Nd(NR2)3 by KC8 under dinitrogen in Et2O in the presence of 18-crown-6 (18-c-6) forms dark yellow solutions of [K2(18-c-6)3]{[(R2N)3Nd]2N2} at low temperatures that become green as they warm up to -35 °C in a glovebox freezer. Green crystals obtained from the solution turn yellow-brown when cooled below -100 °C, and the yellow-brown compound has an end-on Nd2(µ-η1:η1-N2) structure. The yellow-brown crystals isomerize in the solid state on the diffractometer upon warming, and at -25 °C, the crystals are green and have a side-on Nd2(µ-η2:η2-N2) structure. Collection of X-ray diffraction data at 10 °C intervals from -50 to -90 °C revealed that the isomerization occurs at temperatures below -100 °C. In the presence of tetrahydrofuran (THF), the dianionic {[(R2N)3Nd]2N2}2- system can lose an amide ligand to provide the monoanionic [(R2N)3NdIII(µ-η2:η2-N2)NdIII(NR2)2(THF)]1-, characterized by X-ray crystallography. These data suggest a connection between the in situ Ln(III)/K reductions and Ln(II) reductions that depends on solvent, temperature, the presence of a chelate, and the specific rare-earth metal.

Reductive Reactivity of the 4f75d1 Gd(II) Ion in {GdII[N(SiMe3)2]3}-: Structural Characterization of Products of Coupling, Bond Cleavage, Insertion, and Radical Reactions.

The reductive reactivity of a Ln(II) ion with a nontraditional 4fn5d1 electron configuration has been investigated by studying reactions of the {GdII(N(SiMe3)2)3]}- anion with a variety of reagents that survey the many reaction pathways available to this ion. The chemistry of both [K(18-c-6)2]+ and [K(crypt)]+ salts (18-c-6 = 18-crown-6; crypt = 2.2.2-cryptand) was examined to study the effect of the countercation. CS2 reacts with the crown salt [K(18-c-6)2][Gd(NR2)3] (1) to generate the bimetallic (CS3)2- complex {[K(18-c-6)](µ3-CS3-κS,κ2S',S'')Gd(NR2)2]}2, which contains two trithiocarbonate dianions that bridge Gd(III) centers and a potassium ion coordinated by 18-c-6. In contrast, the only crystalline product isolated from the reaction of CS2 with the crypt salt [K(crypt)][Gd(NR2)3] (2) is [K(crypt)]{(R2N)2Gd[SCS(CH2)Si(Me2)N(SiMe3)-κN,κS]}, which has a CS2 unit inserted into a cyclometalated amide ligand. Complexes 1 and 2 reductively couple pyridine to form bridging dipyridyl moieties, (NC5H4-C5H4N)2-, that generate bimetallic complexes differing only in the countercation, {[K(18-c-6)(C5H5N)2]}2{[(R2N)3Gd]2[µ-(NC5H4-C5H4N)2]} and [K(crypt)]2{[(R2N)3Gd]2[µ-(NC5H4-C5H4N)2]}. Complexes 1 and 2 also show similar reactivity with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to form the (TEMPO)- complexes [K(18-c-6)][(R2N)3Gd(η1-ONC5H6Me4)] and [K(crypt)][(R2N)3Gd(η1-ONC5H6Me4)], respectively. The first example of a bimetallic coordination complex containing a Bi-Gd bond, [K(crypt)][(R2N)3Gd(BiPh2)], was obtained by treating 2 with BiPh3.

Reductive cleavage of N,N'-di-tert-butyl-carbodi-imide generates tert-butyl-cyanamide ligands, (Me3CNCN)-, that bind potassium both end-on and side-on in the same single crystal.

N,N'-Di-tert-butyl-carbodi-imide, Me3CN=C=NCMe3, undergoes reductive cleavage in the presence of the GdII complex, [K(18-crown-6)2][GdII(NR 2)3] (R = SiMe3), to form a new type of ligand, the tert-butyl-cyanamide anion, (Me3CNCN)-. This new ligand can bind metals with one or two donor atoms as demonstrated by the isolation of a single crystal containing potassium salts of both end-on and side-on bound tert-butyl-cyanamide anions, (Me3CNCN)-. The crystal contains [K(18-crown-6)(H2O)][NCNCMe3-kN], in which one ( t BuNCN)- anion is coordinated end-on to potassium ligated by 18-crown-6 and water, as well as [K(18-crown-6)][η2-NCNCMe3], in which an 18-crown-6 potassium is coordinated side-on to the terminal N-C linkage. This single crystal also contains one equivalent of 1,3-di-tert-butyl urea, (C9H20N2O), which is involved in hydrogen bonding that may stabilize the whole assembly, namely, aqua-(tert-butyl-cyanamidato)(1,4,7,10,13,16-hexa-oxa-cyclo-octa-deca-ne)potas-sium(I)-(tert-butyl-cyanamidato)(1,4,7,10,13,16-hexa-oxa-cyclo-octa-deca-ne)potas-sium(I)-N,N'-di-tert-butyl-carbodi-imide (1/1/1) [K(C5H9N2)(C12H24O6)]·[K(C5H9N2)(C12H24O6)(H2O)]·C9H20N2.