Experimental and theoretical treatment of hydrogen splitting and storage in boron–nitrogen systems

Sumerin, Victor; Schulz, Felix; Nieger, Martin; Atsumi, Michiko; Wang, Cong; Leskelä, Markku; Pyykkö, Pekka; Repo, Timo; Rieger, Bernhard

doi:10.1016/j.jorganchem.2009.03.023

Cited by 89 publications

(59 citation statements)

References 44 publications

(19 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[39] In a similar fashion, the research groups of Repo and Rieger have very recently reported a linked amine-borane system 68/69 derived from tetramethylpiperidine . [40] This system exhibits the ability to effect reversible H 2 activation and will be discussed in Section 6.3.…”

Section: Imines and Amines In Flp Activation Of Hmentioning

confidence: 99%

Frustrated Lewis Pairs: Metal‐free Hydrogen Activation and More

2009

View full text Add to dashboard Cite

Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter- or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C(6)F(5))(2) components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H(+)/H(-) pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal-free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three-component reactions, offering new strategies for synthetic chemistry.

show abstract

Section: Imines and Amines In Flp Activation Of Hmentioning

confidence: 99%

Frustrated Lewis Pairs: Metal‐free Hydrogen Activation and More

2009

View full text Add to dashboard Cite

show abstract

“…There have been many calculations on FLPs and the mode of their reaction with H 2 (43)(44)(45)(46). For instance, Zeonjuk et al (47) investigated six combinations of Lewis acids (boranes) and Lewis bases (phosphines) that showed different reactivity in H 2 activation.…”

Section: Sidewaysmentioning

confidence: 99%

Stabilizing a different cyclooctatetraene stereoisomer

Lei

Xie

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

An unconventional cis-cis-cis-trans or (Z,Z,Z,E) structure B of cyclooctatetraene (COT) is calculated to lie only 23 kcal/mol above the well-known tub-shaped (Z,Z,Z,Z) isomer A; one example of this type of structure is known. The barrier for B returning to A is small, 3 kcal/mol. However, by suitable choice of substituents, the (Z,Z,Z,E) isomer can be made to lie in energy below the tub-shaped structure. Steric, clamping, and electronic strategies are proposed for achieving this. In the steric strategy, the C 8 H 4 (CH 3 ) 2 (C( t Bu) 3 ) 2 structure B is predicted to lie 21 kcal/mol below structure A, which is separated from form B only by a small barrier. A simple clamping strategy, effective for COT planarization, does not influence the A/B isomerization much. But, if the clamping group is aromatic (a fused benzene, pyrrole, thiophene, furan), the subtle interplay of potential aromaticity with clamping can be used to confer persistence if not stability on the (Z,Z,Z,E) isomer. An electronic strategy of a different kind, push-pull substitution on the COT ring, was not very effective in stabilizing the B form. However, it led us to vicinal amine-borane-substituted normal COTs that proved to be quite good at activating H 2 in a frustrated Lewis pair scenario. The molecule is most certainly not aromatic, in accord with Hückel's rule (2). It features four cis-or Z double bonds in a characteristic nonplanar D 2d tub shape (3). From a combined femtosecond rotational coherence spectroscopy and theoretical study we have the molecule's precise gas-phase structure, with bond lengths r e (C-C) = 1.470, r e (C=C) = 1.337, and r e (C-H) = 1.079 Å (4). Potential ring inversion and bond-bond switching in COT have fascinated the organic community for decades (5-7). The planar D 4h structure of COT is a transition state (TS) for the ring inversion (calculated barrier height of 10-14 kcal/mol) (8-12). The D 8h bondswitching TS lies a few kilocalories per mole higher. The accepted automerization surface is summarized schematically in Fig. 1.Motivated by the recent determination of the structures of some asymmetrically substituted COTs (13), we began a systematic study of COTs. Some peculiar geometries, far away from the tub shape, emerged; in time we identified them as cis-cis-cistrans (Z,Z,Z,E) isomers of COT. Stabilizing these structures is the aim of this article.(Z,Z,Z,E)-COT structures already appear in the theoretical and experimental literature. Conesa and Rzepa in 1998 predicted this isomer to lie 21-29 kcal/mol above the conventional all-Z structure, with a small barrier to return to all-Z COT (14). In their studies of Möbius aromaticity, Havenith et al. (15) optimized a C 8 H 8 (Z,Z,Z,E) structure, finding it again 21-29 kcal/mol above (Z,Z,Z,Z). And, in a comprehensive paper on the photochemistry and thermal rearrangements of COT, Garavelli et al. (16) found the (Z,Z,Z,E) isomer as a reaction intermediate, 24 to 25 kcal/mol above normal COT. The primary interest in their wideranging paper was in the photochemistry o...

show abstract

“…[5] Most notably such systems have been used for the heterolytic activation of dihydrogen and concomitantly for metal-free catalytic hydrogenation of several functionalized alkenes [6] and bulky imines. [7][8][9] Frustrated Lewis pairs have been shown to add to olefinic substrates, [10,11] to terminal alkynes, [11,12] to N 2 O, [13] to organic carbonyl compounds [11,14] and even to carbon dioxide. [15] The intramolecular frustrated Lewis pair 1 (Scheme 1) was shown to be especially reactive in some of these binding or activation reactions of small molecules.…”

Section: Dedicated To Professor Günther Wilke On the Occasion Of His mentioning

confidence: 99%