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Dive into the research topics where Clemens Krempner is active.

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Featured researches published by Clemens Krempner.


Journal of the American Chemical Society | 2013

A Zwitterionic Carbanion Frustrated by Boranes – Dihydrogen Cleavage with Weak Lewis Acids via an “Inverse” Frustrated Lewis Pair Approach

Hui Li; Adélia J. A. Aquino; David B. Cordes; Fernando Hung-Low; William L. Hase; Clemens Krempner

The synthesis, structural characterization, and acid-base chemistry of [C(SiMe2OCH2CH2OMe)3]Na (2), a sterically encumbered zwitterionic organosodium compound, is reported. 2 is a strong Brønsted base that forms frustrated Lewis pairs (FLPs) with a number of boron-containing Lewis acids ranging from weakly Lewis acidic aryl and alkyl boranes to various alkyl borates. These intermolecular FLPs readily cleave H2, which confirms that even poor Lewis acids can engage in FLP-mediated H2 cleavage provided that the present bulky base is of sufficiently high Brønsted basicity.


Chemistry: A European Journal | 2014

A Well‐Defined Monomeric Aluminum Complex as an Efficient and General Catalyst in the Meerwein–Ponndorf–Verley Reduction

Brian McNerney; Bruce R. Whittlesey; David B. Cordes; Clemens Krempner

The metal-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction allows for the mild and sustainable reduction of aldehydes and ketones but has not found widespread application in organic synthesis due to the high catalyst loading often required to obtain satisfactory yields of the reduced product. We report here on the synthesis and structure of a sterically extremely overloaded siloxide-supported aluminum isopropoxide capable of catalytically reducing a wide range of aldehydes and ketones (52 examples) in excellent yields under mild conditions and with low catalyst loadings. The unseen activity of the developed catalyst system in MPV reductions is due to its unique monomeric nature and the neutral donor isopropanol weakly coordinating to the aluminum center. The present work implies that monomeric aluminum alkoxide catalysts may be attractive alternatives to transition-metal-based systems for the selective reduction of aldehydes and ketones to primary and secondary alcohols.


Inorganic Chemistry | 2015

Synthesis, Structure, and Reactivity of Zwitterionic Divalent Rare-Earth Metal Silanides

Vidura D. Thalangamaarachchige; Daniel K. Unruh; David B. Cordes; Clemens Krempner

The synthesis and structures of the first zwitterionic divalent rare-earth metal silanides of the formula [Si(SiMe2OMe)3-κ(3)]2M (M-3), where M = Eu, Yb, and Sm, are reported. M-3 compounds feature spirocyclic bicyclooctane structures in which the central rare-earth metal ions are being octahedrally coordinated by six methoxy groups. The reaction of Yb-3 with BPh3 and W(CO)6 respectively generated the trinuclear zwitterions [Ph3BSi(SiMe2OMe)3-κ(3)]2Yb (Yb-4) and [(CO)5WSi(SiMe2OMe)3-κ(3)]2Yb (Yb-5) in good yield.


Chemical Communications | 2006

Novel double-cored oligosilane dendrimers-conformational dependence of the UV absorption spectra

Clemens Krempner; Martin Köckerling; Constantin Mamat

The novel double-cored oligosilane dendrimers {[Me(Me3Si)2Si-Me2Si]2SiMe-SiMe2}2 (4) and {[Me(Me3Si)2Si-Me2Si]2SiMe}2 (5) have been shown to display unusual UV absorption behaviour as a function of conformation and steric interaction in the longest oligosilane chains.


Inorganic Chemistry | 2017

Interactions of Verkade’s Superbase with Strong Lewis Acids: From Labile Mono- and Binuclear Lewis Acid–Base Complexes to Phosphenium Cations

Suresh Mummadi; Dustin Kenefake; Rony Diaz; Daniel K. Unruh; Clemens Krempner

A series of mono- and binuclear Lewis acid-base complexes of the formulas N[CH2CH2N(Pri)]3P→LA [LA = BH3 (8), Ga(C6F5)3 (10), GaCl3 (11)], LA←N[CH2CH2N(Pri)]3P [LA = Al(C6F5)3 (6a), AlMe3 (6b), AlEt3 (6c), AlBui3 (6d), BF3 (13)], and LA←N[CH2CH2N(Pri)]3P→LA [Lewis acid (LA) = Al(C6F5)3 (7a), AlMe3 (7b), AlEt3 (7c), AlBui3 (7d), AlCl3 (7e), BH3 (9)] were generated from reactions of Verkades base, N[CH2CH2N(Pri)]3P (1), with various boron-, aluminum-, and gallium-containing Lewis acids, and characterized by multinuclear NMR spectroscopy. {N[CH2CH2N(Pri)]3P→C7H7}[BF4] (5) was synthesized via the treatment of 1 with [C7H7][BF4]. The reaction of 1 with B(C6F5)3, followed by the addition of [Ph3C]2[B12Cl12], gave rise to the rearranged borate salt [PN4C9H17(Pri)2][B12Cl12] (3), while treating 1 with [Ph3C]2[B12Cl12] exclusively afforded {N[CH2CH2N(Pri)]3PH}2[B12Cl12] (4). Reactions of 1 with 2 equiv of GaCl3 and BF3, respectively, afforded the novel phosphenium gallate and borate salts 12a, 12b, and 15. The solid-state structures of 1, 3-5, 6b, 7a, 7b, 7e, 8, 10, 11, 12b, 13, and 15 were determined by X-ray crystallography.


European Journal of Inorganic Chemistry | 2011

Role of Siloxides in Transition Metal Chemistry and Homogeneous Catalysis

Clemens Krempner


Journal of the American Chemical Society | 2016

Inverse Frustrated Lewis Pairs--Activation of Dihydrogen with Organosuperbases and Moderate to Weak Lewis Acids.

Suresh Mummadi; Daniel K. Unruh; Jiyang Zhao; Shuhua Li; Clemens Krempner


Chemical Communications | 2011

Homoleptic tris(methoxydimethylsilyl)silanides of the alkaline earth metals: first zwitterionic silanides with two naked silyl anions

Bryan Carlson; Adélia J. A. Aquino; Louisa J. Hope-Weeks; Bruce R. Whittlesey; Brian McNerney; William L. Hase; Clemens Krempner


Chemical Communications | 2011

A supramolecular approach to zwitterionic alkaline metal silanides and formation of heterobimetallic silanides

Hui Li; Louisa J. Hope-Weeks; Clemens Krempner


Inorganic Chemistry | 2006

Trisilane-1,3-diolato Complexes of Ti and Zr: Syntheses and X-ray Crystal Structures

Clemens Krempner; Martin Köckerling; Helmut Reinke; Weichert K

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Hui Li

Texas Tech University

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