Samarium- and Ytterbium-Grafted Periodic Mesoporous Silica for Carbon Dioxide Capture and Conversion.

Immobilized coordination compounds of Lewis acidic metals are powerful catalytic components of systems for the cycloaddition of CO2 to epoxides that do not require sophisticated coordination frameworks to harness the metal center and modulate its activity. Surface organometallic chemistry (SOMC) is a valuable methodology to prepare well-defined and site-isolated surface complexes and coordination compounds on metal oxides, with ligand environments easily adjustable to a targeted catalytic reaction. In this work, the SOMC methodology is applied to prepare SmII, YbII, and SmIII alkoxide surface complexes on periodic mesoporous (organo)silica of distinct pore symmetry/size for application in the CO2 cycloaddition reaction. The surface complexes are readily accessible by the grafting of the bis(trimethylsilyl)amide precursors LnII[N(SiMe3)2]2(THF)2 (Ln = Sm, Yb) and SmIII[N(SiMe3)2]3, followed by ligand exchange with alcohols (ethanol and neopentanol). The use of periodic mesoporous supports led to hybrid materials with relatively high surface areas and pore sizes, affording good performance in CO2 capture and in the cycloaddition of CO2 to epoxides under mild conditions (60-80 °C, 1-10 bar). In terms of catalytic performance, recyclability, and low amount of added nucleophile TBAX (X = Br, I), the most active materials prepared in this work compare well to a variety of previously reported SOMC-derived surface complexes and to other heterogeneous Lewis acids displaying more elaborate ligand environments.

[(CH3 )Al(CH2 )]12 : Methylaluminomethylene (MAM-12).

The molecular structure of enigmatic "poly(aluminium-methyl-methylene)" (first reported in 1968) has been unraveled in a transmetalation reaction with gallium methylene [Ga8 (CH2 )12 ] and AlMe3 . The existence of cage-like methylaluminomethylene moieties was initially suggested by the reaction of rare-earth-metallocene complex [Cp*2 Lu{(µ-Me)2 AlMe2 }] with excess AlMe3 affording the deca-aluminium cluster [Cp*4 Lu2 (µ3 -CH2 )12 Al10 (CH3 )8 ] in low yield (Cp*=C5 Me5 ). Treatment of [Ga8 (CH2 )12 ] with excess AlMe3 reproducibly gave the crystalline dodeca-aluminium complex [(CH3 )12 Al12 (µ3 -CH2 )12 ] (MAM-12). Revisiting a previous approach to "poly(aluminium-methyl-methylene" by using a (C5 H5 )2 TiCl2 /AlMe3 (1 : 100) mixture led to amorphous solids displaying solubility behavior and spectroscopic features similar to those of crystalline MAM-12. The gallium methylene-derived MAM-12 was used as an efficient methylene transfer reagent for ketones.

Organomagnesia: Reversibly High Carbon Dioxide Uptake by Magnesium Pyrazolates.

A series of new pyrazolate and mixed pyrazolate/pyrazole magnesium complexes is described and their reactivity toward carbon dioxide is examined. The dimeric complex [Mg(pzt Bu, t Bu)2]2 inserts CO2 instantly and quantitatively forming the tetrameric complex [Mg(CO2·pzt Bu, t Bu)2]4 and monomeric donor-stabilized [Mg(CO2·pzt Bu, t Bu)2(thf)2]. Complexes of the type [Mgx(pzR,R)2 x(HpzR,R)y]n (R = iPr, tBu) engage in similar insertion reactions involving dissociation of the carbamic acid HOOCpzR,R. Even solid polymeric derivatives [Mg(pzR,R)2]n (R = Me, H) react instantaneously and exhaustively with CO2, the resulting [Mg(CO2·pz)2]m featuring a CO2 capacity of 35.7 wt% (8.2 mmol g-1). All described magnesium pyrazolates display completely reversible CO2 uptake in solution and in the solid state, respectively, as monitored via VT 1H NMR and in situ FTIR spectroscopy as well as thermogravimetric analysis. Fluorinated [Mg2(pzCF3,CF3)4(thf)3] does not yield any isolable CO2 insertion product but exhibits the highest activity in the catalytic transformation of epoxides and CO2 to cyclic carbonates.

Potential precursors for terminal ytterbium(II) imide complexes bearing the hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand.

Monomeric, divalent ytterbium primary amides TptBu,MeYb(NHR)(thf)x (R = C6H3iPr2-2,6 = AriPr = Dipp, C6H3(CF3)2-3,5 = ArCF3, SiPh3) supported by the bulky hydrotris(3-tBu-5-Me-pyrazolyl)borato scorpionate ligand are synthesized acccording to salt metathesis and protonolysis protocols, respectively. Yb(II) precursors comprise YbI2(thf)2, Yb[N(SiMe3)2]2(thf)2 and TptBu,MeYb[N(SiMe3)2]. Complexes TptBu,MeYb(NHR)(thf)x readily engage in donor (thf) exchange with nitrogen donors like DMAP (4-dimethylaminopyridine) and pyridine. Treatment of TptBu,MeYb(NHArCF3)(thf)2 with the Lewis acids AlMe3 and GaMe3 results in the heterobimetallic complexes TptBu,MeYb(NHArCF3)(MMe3) (M = Al, Ga). Reactions of TptBu,MeYb(NHR)(thf)x (R = AriPr, ArCF3) with the halogenating agents C2Cl6 and TeBr4 give access to trivalent complexes [TptBu,MeYb(NHR)(X)] (X = Cl, Br). The ytterbium(II) complexes under study display 171Yb NMR chemical shifts in the range 582 ppm for TptBu,MeYb(NHArCF3)(GaMe3) to 954 ppm for TptBu,MeYb(NHSiPh3)(dmap). The salt-metathesis route is also applicable for the synthesis of complexes TptBu,MeLn(NHAriPr)(thf) (Ln = Sm, Eu) and TptBu,MeYb(NHArMe) (ArMe = C6H3Me2-2,6).

Rare-earth-metal trimethylsilylmethyl ate complexes.

En route to putative rare-earth-metal alkylidene complex Li[Lu(CH2SiMe3)2(CHSiMe3)], according to Schumann's original protocol, the reaction of YCl3 with LiCH2SiMe3 in a mixture of diethyl ether and n-pentane afforded a neosilyl ate complex of composition Li3Y(CH2SiMe3)6. Tetrametallic complex Li3Y(CH2SiMe3)6 shows an unprecedented structural motif in the solid state and was further characterized by heteronuclear 1H/13C/7Li/29Si/89Y, as well as VT NMR and DRIFT spectroscopies. Analysis of the thermolysis product via heteronuclear NMR spectroscopy and its reactivity towards benzophenone gave strong evidence for an alkylidene formation upon decomposition. Application of a similar protocol for the smallest rare-earth-metal scandium led to the isolation of ate complex [Li(thf)4][LiSc2(CH2SiMe3)8] as the preferred crystallized product. Here, the reaction of adduct ScCl3(thf)3 and LiCH2SiMe3 was performed in Et2O/n-hexane, in the absence of additional THF. The reaction of LaCl3(thf) with 3 equiv. of LiCH2SiMe3 in THF/Et2O at -40 °C yielded the ate complex [Li(thf)4][La(CH2SiMe3)4(thf)], which is the first of its kind.

Prevalence of renal cysts and association with risk factors in a general population: an MRI-based study.

PURPOSE: To assess the prevalence and size of renal cysts and to analyze associated risk factors in a general population using magnetic resonance imaging (MRI). METHODS: Data of 2063 participants (1052 women) of the Study of Health in Pomerania who underwent whole-body MRI were included. Renal cyst prevalence was calculated separately for men and women and for 10-year age groups. The association between risk factors and occurrence of renal cysts was estimated. RESULTS: The prevalence of renal cysts was 27% and higher in men (34%) than in women (21%; p < 0.001). Renal cyst prevalence increased from 14% in the youngest age group (20-29 years) to 55% in the oldest age group (≥ 70 years) for men and from 7% to 43% for women (both p < 0.001). In the subset of participants with renal cysts, the total mean number was higher in men (1.9) compared to women (1.6, p = 0.012) and was significantly associated with age. Mean renal cyst size was higher in men (1.50 cm) compared to women (1.18 cm, p < 0.001). Male sex (OR 1.83, 95% CI 1.47; 2.26), older age (OR 1.05, 95% CI 1.04; 1.06, per 1-year increment), and hypertension (OR 1.27, 95% CI 1.00; 1.61) were associated with higher renal cyst prevalence. In additional analyses, current smoking and ex-smoking showed a significantly higher risk for renal cysts (OR 1.47, 95% CI 1.05; 2.05 and OR 1.38, 95% CI 1.04; 1.82, respectively). CONCLUSIONS: The prevalence, number, and mean size of renal cysts are higher in men compared to women and are associated with age. In addition, renal cyst prevalence is higher in hypertensive and smoking subjects.