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Reiner Anwander

Publications and source records attributed to Reiner Anwander.

14 recordsLinked to original sources
PubMed2007

A general strategy for the rational design of size-selective mesoporous catalysts.

A series of functionalized mesoporous silicas with cagelike pore topology has been synthesized and screened for size-selective catalytic transformations. The aluminum-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction of differently sized aromatic aldehydes (benzaldehyde and 1-pyrenecarbox-aldehyde) has been investigated as a test reaction. The catalysts were synthesized in a two-step grafting sequence comprising pore-size engineering of mesoporous silicas (SBA-1, SBA-2, SBA-16) with long-chain alkyl dimethylaminosilanes and surface organoaluminum chemistry with triethylaluminum [{Al(CH(2)CH(3))3}2]. Size-selective reaction behavior was found for small pore SBA-1 materials, and the selectivity could be efficiently tuned by selecting a silylating reagent of appropriate size. The results are compared with the catalytic performance of a large-pore periodic mesoporous organosilica PMO[SBA-1] and the nonporous high-surface-area silicas Aerosil 300/380.

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PubMed2006

Advanced surface functionalization of periodic mesoporous silica: Kinetic control by trisilazane reagents.

The surface reactions of mesoporous silica MCM-41 with a series of new trisilylamines (trisilazanes) (SiHMe2)2NSiMe2R and (SiMe2Vin)2NSiMe2R (R = indenyl, norpinanyl, chloropropyl, 3-(N-morpholin)propyl; Vin = vinyl), disilylalkylamine (SiHMe2)iPrNSiMe2(CH2)3Cl, and monosilyldialkylamines Me2NSiMe2R (R = indenyl, chloropropyl, 3-(N-morpholin)propyl) were investigated. 1H, 13C, and 29Si MAS NMR spectroscopy, nitrogen adsorption/desorption, infrared spectroscopy, and model reactions with calix[4]arene as a mimic for an oxo surface were used to clarify the chemical nature of surface-bonded silyl groups. The trisilylamines exhibited a comparatively slow surface reaction, which allowed for the adjustment of the amount of silylated and nonreacted SiOH groups and led to a stoichiometric distribution of surface functionalities. The 2:1 integral ratio of SiHMe2 and SiMe2R moieties of such trisilazanes was found to be preserved on the silica surface as indicated by microanalytical as well as 13C and 29Si MAS NMR spectroscopic data of the hybrid materials. For example, the reaction of MCM-41 with (SiHMe2)2NSiMe2(CH2)3Cl, (SiHMe2)iPrNSiMe2(CH2)3Cl, and Me2NSiMe2(CH2)3Cl provided bi- and monofunctional hybrid materials with one-third, one-half, or all chemically accessible silanol groups derivatized by chloropropyl groups, respectively. Thus, a molecular precursor strategy was developed to efficiently control the relative amount of three different surface species, SiHMe2 (or SiVinMe2), SiMe2R, and SiOH, in a single reaction step. The reaction behavior of indenyl-substituted monosilazanes and trisilazanes (R = Ind) with calix[4]arene proved that the indenyl substituent can act as a leaving group forming a dimethylsilyl species, which is anchored bipodally on the silica surface, that is, via two Si-O bonds.

Amines↗
PubMed2006

"Ionic carbenes": synthesis, structural characterization, and reactivity of rare-Earth metal methylidene complexes.

Treatment of mixed chloride tetramethylaluminate polynuclear clusters {Cp*Y[(mu-Me)2AlMe2](mu-Cl)}2 and {Cp*6La6[(mu-Me)3AlMe]4(mu3-Cl)2(mu2-Cl)6} with toluene/THF solutions produces "aluminum-free" methylidene complexes [Cp*3Ln3(mu-Cl)3(mu3-Cl)(mu3-CH2)(THF)3] (Ln = Y, La). The trinuclear methylidene complexes are isostructural in the solid state and feature a sterically well-shielded Schrock-type nucleophilic CH22- unit, which is prone to Tebbe-like methylenation reactions with ketones and aldehydes. The rapid polymerization of gamma-valerolactone reveals intrinsic rare-earth metal reactivity.

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PubMed2006

Organometallic chemistry on periodic mesoporous organosilicas: generation of surface-confined zinc and yttrium centres.

Periodic mesoporous ethylenesilicas with hexagonal P6mm and cubic Fm3m/Pm3n symmetry were prepared by using divalent surfactant C(16-3-1) and binary surfactant mixtures C(18-3-1) and C18TABr as structure-directing agents, respectively, under basic conditions. A tetramethyldisilazane-based surface silylation was carried out under mild conditions affording hybrid materials SiHMe2@PMO[MCM-41], SiHMe2@PMO[KIT-5] and SiHMe2@PMO[SBA-1], corresponding to silanol group populations of ca. 1.46, 0.67 and 1.63 mmol g(-1), respectively. New molecular zinc precursor compounds Zn[N(SiHMe2)2]2 and EtZn(OSiHtBu2) were synthesized via salt metathesis and alkane elimination procedures from ZnCl2 and LiN[SiH(CH3)2]2, HOSiHtBu2 and ZnEt2, respectively. Organozinc and organoyttrium complexes were reacted with the surface silanol groups according to a heterogeneously performed silylamide route, aswell as an alkane elimination reaction, yielding Zn[N(SiHMe2)2]@PMO[MCM-41], Zn[N(SiHMe2)2]@PMO[KIT-5], Zn[N(SiHMe2)2]@PMO[SBA-1], Zn[N(SiMe3)2]@PMO[MCM-41], Zn[N(SiMe3)2]@PMO[KIT-5], Zn[N(SiMe3)2]@PMO[SBA-1], Y[N(SiHMe2)2]x(THF)y@PMO[MCM-41], Y[N(SiHMe2)2]x(THF)y@PMO[KIT-5], Y[N(SiHMe2)2]x(THF)y@PMO[SBA-1] and Zn(OSiHtBu2)@PMO[MCM-41]. The metal loading mainly depended on the surface silanol group population, size and shape of metal-coordinated ligand, and reaction time as shown for Zn contents in the range of 4.2 to 10.6 wt%. In addition, a preferred N(SiHMe2)2/OC6H2tBu2-2,6-Me-4 ligand exchangeability was found for the large yttrium surface centres. The parent and functionalized materials were characterized by powder X-ray diffraction, elemental analysis, N2 physisorption, FTIR, 13C CP and 1H MAS NMR spectroscopy.

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PubMed2006

Multiple C-H bond activation in group 3 chemistry: synthesis and structural characterization of an yttrium-aluminum-methine cluster.

Complete donor-induced alkylaluminate cleavage of halfmetallocene complex Cp*Y(AlMe4)2, that is, treatment of Cp*Y(AlMe4)2 with 2 equiv of diethyl ether, produces [Cp*Y(mu2-Me)2]3 in high yield (95%). In contrast, the equimolar reaction of Cp*Y(AlMe4)2 with diethyl ether reproducibly formed complex [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] in low yield (10-30%) via a multiple C-H bond activation. The synthesis of the heterooctametallic yttrium-aluminum-methine cluster was also accomplished in moderate yield (47%) by the equimolar reaction of discrete Cp*Y(AlMe4)2 and [Cp*Y(mu2-Me)2]3 in the absence of any donor solvent and "free" AlMe3. This gives strong evidence that preformed heterometal-bridged Y-CH3-Al moieties are prone to multiple hydrogen abstraction in the presence of a highly basic reagent such as [Cp*Y(mu2-Me)2]3. The monocylopentadienyl complexes [Cp*Y(mu2-Me)2]3 and [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] were structurally characterized.

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PubMed2005

Synthesis and structural characterization of scandium SALEN complexes.

A series of heteroleptic scandium SALEN complexes, [(SALEN)Sc(mu-Cl)]2 and (SALEN)Sc[N(SiHMe2)2] is obtained via amine elimination reactions using [Sc(N(i)Pr2)2(mu-Cl)(THF)]2 and Sc[N(SiHMe2)2]3(THF) as metal precursors, respectively. H(2)SALEN ligand precursors comprising H2Salen [(1,2-ethandiyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol], H2Salpren [(2,2-dimethylpropanediyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol], H2Salcyc [(1R,2R)-(-)-1,2-cyclohexanediyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol] and H2Salphen [((1S,2S)-(-)-1,2-diphenylethandiyl)bis(nitrilomethylidyne)bis(2,4-di-tert-butyl)phenol] are selected according to solubility and ligand backbone variation ("=N-(R)-N=" bite angle) criteria. Consideration is given to the feasibility of [Cl --> NR2] and [N(SiHMe2)2--> OSiR3] secondary ligand exchange reactions. X-ray crystal structure analyses of donor-free (Salpren)Sc(N(i)Pr2), (R,R)-(Salcyc)Sc[N(SiHMe2)2], (Salen)Sc(OSi(t)BuPh2) and (Salphen)Sc(OSiH(t)Bu2) reveal (i) a very short Sc-N bond distance of 2.000(3) A, (ii) weak beta(Si-H)(amido)-Sc agostic interactions and (iii) an exclusive intramolecularly tetradentate and intrinsically bent coordination mode of the SALEN ligands with angle(Ph,Ph) dihedral angles and Sc-[N(2)O(2)] distances in the 124.27(9)-127.7(3) degrees and 0.638(1)-0.688(1) A range, respectively.

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PubMed2005

[LnIIAlIII2(alkyl)8]x: donor addition instead of donor-induced cleavage.

(SmAl2Me8)x and (SmAl2Et8)x are obtained via a silylamide elimination reaction from Sm[N(SiMe3)2]2(THF)2 and excess AlR3 (R = Me, Et); (LnAl2Et8)x (Ln = Sm, Yb) react with THF, pyridine, and 1,10-phenanthroline to form the first donor adducts of homoleptic peralkylated Ln-Al heterobimetallic complexes.

Journal Article↗
PubMed1997

Volatile Donor-Functionalized Alkoxy Derivatives of Lutetium and Their Structural Characterization(1).

Reaction of beta-functionalized alcohols of type HOCR(2)CH(2)do (1a, do = OMe, R = Me; 1b, do = OMe, R = Et; 1c, do = NMe(2), R = Me) with Ln[N(SiMe(3))(3)](3) yields highly volatile (sublimation < 100 degrees C/10(-)(3) Torr) and n-hexane-soluble homoleptic alkoxide complexes [Ln(OCR(2)CH(2)do)(3)] (2a-d, Ln = Y, Lu). A single-crystal X-ray diffraction study of Lu(OCMe(2)CH(2)OMe)(3) (2a) revealed a dinuclear complex with significantly polarized metal centers originating from asymmetrical ligand association (triple-bridging). Unintentional employment of "water-contaminated" alcohol 1a resulted in the formation of n-hexane-soluble 3 exhibiting a substantially increased sublimation temperature (>220 degrees C/10(-)(3) Torr). Crystallization of 3 affords single crystals 3a featuring the tetranuclear constitution Lu(4)(O)(OH)(OCMe(2)CH(2)OMe)(9). 3a represents an unprecedented lanthanide alkoxide comprising both oxo and hydroxo units in addition to alkoxide ligands. The Lu(4)O(15)-core structure of 3a adopts a "butterfly" rather than a tetrahedral geometry. Potentially tridentate alcohols HOCtBu(CH(2)OiPr)(2) (4) and HOCiPr(2)CH(2)OCH(2)OMe (5) afford alkoxide complexes "Nd(OR)(3)" (6, 7) of reduced volatility. 2a crystallizes from n-hexane at ambient temperature in space group P2(1)/n with a = 13.510(1) Å, b = 15.130(1) Å, c = 38.953(4) Å, beta = 93.11(1) degrees, V = 7950 Å(3), and Z = 8. Least-squares refinement of the model based on 11 747 reflections (I > 2.0 sigma(I)) converged to a final R = 3.5%. 3a crystallizes from n-hexane at -35 degrees C in space group Cc with a = 21.63(1) Å, b = 14.49(3) Å, c = 21.04(2) Å, beta = 109.70(3) degrees, V = 6209 Å(3), and Z = 4. Least-squares refinement of the model based on 6057 reflections (I > 3.0 sigma(I)) converged to a final R = 6.7%.

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