Screening of the Relaxivity of Gadolinium-Loaded Periodic Mesoporous Silica Functionalized by Means of Soft Metalorganic Silylamide Grafting

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

The number of rare earth (RE) starting materials used in synthesis is staggering, ranging from simple binary metal-halide salts to borohydrides and "designer reagents" such as alkyl and organoaluminate complexes. This review collates the most important starting materials used in RE synthetic chemistry, including essential information on their preparations and uses in modern synthetic methodologies. The review is divided by starting material category and supporting ligands (i.e., metals as synthetic precursors, halides, borohydrides, nitrogen donors, oxygen donors, triflates, and organometallic reagents), and in each section relevant synthetic methodologies and applications are discussed.

Variation of electronic transitions and reduction potentials of cerium(IV) complexes

The trivalent compound K[Ce[N(SiHMe2)2]4] was synthesized and oxidized, providing a convenient route to the reported cerium(IV) compound Ce[N(SiHMe2)2]4. Protonolysis reactions of Ce[N(SiHMe2)2]4 with tert-butanol, substituted benzyl alcohols, and 2,6-diphenylphenol yielded the neutral tetravalent compounds Ce(O(t)Bu)4(py)2, Ce2(OCH2C6R5)8(thf)2 (R = Me, F), and Ce(Odpp)4 (dpp = 2,6-(C6H5)2-C6H3). Spectroscopic and electrochemical characterization of the monometallic cerium(IV) silylamide, alkoxide, and aryloxide compounds revealed variable ligand-to-metal charge transfer transitions and metal-based reduction potentials. Computational bonding analyses were performed to complement the physical characterization of the complexes.

Recent advances in hybrid periodic mesostructured organosilica materials: opportunities from fundamental to biomedical applications

Periodic mesoporous organosilica nanostructures functionalized with various active functional groups: from design to biomedical applications.

Europium bis(dimethylsilyl)amides including mixed-valent Eu3[N(SiHMe2)2]6[μ-N(SiHMe2)2]2

Trivalent Eu[N(SiHMe2)2]3(THF)2 can easily be synthesized by applying a routine salt metathesis protocol (EuCl3(THF)2 and 3 equiv. of Li[N(SiHMe2)2] in n-hexane) which crystallizes isotypically to its analogues of the rare-earth metal series (space group P21/c). Transsilylamination of Eu[N(SiMe3)2]2(THF)2 with a slight excess of HN(SiHMe2)2 in n-hexane-THF yields the divalent trinuclear compound Eu{[μ-N(SiHMe2)2]2Eu[N(SiHMe2)2](THF)}2, the solid-state structure of which differs significantly from the samarium and ytterbium analogues by showing three unique molecules in the asymmetric unit of which one is related to the two others by an inversion. Using crude Eu[N(SiMe3)2]3 in transsilylamination reactions with HN(SiHMe2)2 in n-hexane afforded n-hexane-insoluble trivalent ate complexes {MEu[N(SiHMe2)2]4}n (M = Na, K) depending on the synthesis conditions of Eu[N(SiMe3)2]3. Performing the transsilylamination of Eu[N(SiMe3)2]3 with a large excess of HN(SiHMe2)2 at elevated temperatures gave reproducibly the donor-free, mixed-valent, trinuclear compound Eu(II){[μ-N(SiHMe2)2]Eu(III)[N(SiHMe2)2]3}2 in good yield.

Silylamide complexes of chromium(II), manganese(II), and cobalt(II) bearing the ligands N(SiHMe2)2 and N(SiPhMe2)2

Bis(dimethylsilyl)amide and bis(dimethylphenylsilyl)amide complexes of the divalent transition metals chromium, manganese, and cobalt were synthesized. Dimeric, donor-free {Mn[N(SiHMe2)2]2}2 could be obtained via two different pathways, a salt metathesis route (utilizing MnCl2(thf)1.5 and LiN(SiHMe2)2) and a transsilylamination protocol (utilizing Mn[N(SiMe3)2]2(thf) and HN(SiHMe2)2). Addition of 1,1,3,3-tetramethylethylendiamine (tmeda) to {Mn[N(SiHMe2)2]2}2 yielded the monomeric adduct Mn[N(SiHMe2)2]2(tmeda). The syntheses of Cr[N(SiHMe2)2]2(tmeda), Co[N(SiMe3)2][N(SiHMe2)2](tmeda), and Co[N(SiHMe2)2]2(tmeda) were achieved by transsilylamination from Cr[N(SiMe3)2]2(tmeda) and {Co[N(SiMe3)2]2}2(μ-tmeda), respectively. Bis(dimethylphenylsilyl)amide complexes Mn[N(SiMe2Ph)2]2, Cr[N(SiMe2Ph)2]2, and Co[N(SiMe2Ph)2]2(thf) were obtained via salt metathesis employing MCl2(thf)x (M = Cr, Mn, Co) with equimolar amounts of LiN(SiMe2Ph)2 in n-hexane. Treatment of CrCl2 with LiN(SiMe2Ph)2 in thf gave Cr[N(SiMe2Ph)2]2(thf)2, featuring an almost square planar trans-coordination. All complexes were examined by elemental analyses, DRIFT and UV-vis spectroscopy, as well as X-ray structure analysis, paying particular attention to secondary M---SiH β-agostic and M---π(arene) interactions. Magnetic moments were determined by Evans' method.