5 research outputs found
Lewis Acid-Lewis Base Mediated Metal-Free Hydrogen Activation and Catalytic Hydrogenation
Organocatalysis, the use of organic molecules as catalysts, is attracting increasing attention as one of the most modern and rapidly growing areas of organic chemistry, with countless research groups in both academia and the pharmaceutical industry around the world working on this subject.
The literature review of this thesis mainly focuses on metal-free systems for hydrogen activation and organocatalytic reduction. Since these research topics are relatively new, the literature review also highlights the basic principles of the use of Lewis acid-Lewis base pairs, which do not react irreversibly with each other, as a trap for small molecules.
The experimental section progresses from the first observation of the facile heterolytical cleavage of hydrogen gas by amines and B(C6F5)3 to highly active non-metal catalysts for both enantioselective and racemic hydrogenation of unsaturated nitrogen-containing compounds. Moreover, detailed studies of structure-reactivity relationships of these systems by X-ray, neutron diffraction, NMR methods and quantum chemical calculations were performed to gain further insight into the mechanism of hydrogen activation and hydrogenation by boron-nitrogen compounds.Organokatalyysi, eli pienten orgaanisten molekyylien kÀyttö katalyytteinÀ, herÀttÀÀ yhÀ enemmÀn kiinnostusta ja on yksi nopeimmin kasvavista modernin orgaanisen kemian tutkimusaloista. Tutkimusta tehdÀÀn kansainvÀlisesti lukuisissa ryhmissÀ, niin akateemisessa maailmassa kuin lÀÀketeollisuudessa.
TÀmÀn vÀitöskirjan kirjallisuuskatsaus kÀsittelee metallittomia menetelmiÀ vedyn aktivoinnissa sekÀ organokatalyyttistÀ pelkistystÀ. Koska nÀmÀ tutkimusaiheet ovat suhteellisen uusia, kirjallisuustarkastelu sisÀltÀÀ myös pÀÀperiaatteet reversiibelisti reagoivien Lewis happo- Lewis emÀs-parien kÀytöstÀ pienten molekyylien loukkuina.
Kokeellisessa osassa esitellÀÀn kaasumaisen vedyn heterolyyttinen pilkkominen amiineilla ja B(C6F5)3:lla, erittÀin aktiivisia metallittomia katalyyttejÀ sekÀ enantioselektiivisten ja raseemisten tyydyttymÀttömien typpiyhdisteiden vedytys. NÀiden menetelmien reaktiivisuuden riippuvuutta rakenteista tutkittiin yksityiskohtaisesti röntgendiffraktiolla, neutronidiffraktiolla, NMR-spektroskopialla ja kvanttikemiallisten laskujen avulla. NÀin saatiin tarkempi kuva reaktiomekanismeista vedynaktivoinnissa ja pelkistyksissÀ boori-typpi yhdisteillÀ
Vanadyl calix[6]arene complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability
Treatment of p-tert-butylcalix[6]areneHâ (Lâ¶Hâ) with in situ [LiVO(Ot-Bu)â] afforded, after work-up, the dark green complex [Li(MeCN)â][Vâ(O)âLi(MeCN)(Lâ¶Hâ)â]·8MeCN (1·8MeCN). On one occasion, the reaction led to the formation of a mixture of products, the bulk of which differing from 1 only in the amount of solvate, viz.2·9.67MeCN. The second minor, yellow product has the formula {[(VOâ)â(Lâ¶Hâ)(Li(MeCN)â)â]·2MeCN}n (3·2MeCN), and comprises a 1D polymeric structure with links through the Lâ¶Hâ ligand and LiâOâ units. When the reverse order of addition was employed such that lithium tert-butoxide (7.5 equivalents) was added to Lâ¶Hâ, and subsequently treated with VOClâ (2 equiv.), the complex {[VO(THF)][VO(ÎŒ-O)]âLi(THF)(EtâO)][Lâ¶]}·2EtâO·0.5THF (4·2EtâO·0.5THF), which contains a trinuclear motif possessing a central, octahedral vanadyl centre linked via oxo bridges to two tetrahedral (Câv) vanadyl centres, was isolated. The calix[6]arene in 4 is severely twisted and adopts a âdown, down, down, down, out, outâ conformation. Use of excess lithium tert-butoxide led to a complex very similar to 4, differing only in the solvent of crystallization, namely 5·EtâO·2THF. The ability of 1 and 5 to act as pre-catalysts for ethylene polymerization in the presence of a variety of co-catalysts and under various conditions has been investigated. Co-polymerization of ethylene with propylene and with 1-hexene have also been conducted; results are compared versus VO(OEt)Clâ
Tweezers for Parahydrogen: A Metal-Free Probe of Nonequilibrium Nuclear Spin States of H<sub>2</sub> Molecules
To date, only metal-containing hydrogenation
catalysts have been
utilized for producing substantial NMR signal enhancements by means
of parahydrogen-induced polarization (PHIP). Herein, we show that
metal-free compounds known as molecular tweezers are useful in this
respect. It is shown that <i>ansa</i>-aminoborane tweezers
QCAT provided (20â30)-fold signal enhancements of parahydrogen-originating
hydrogens in <sup>1</sup>H NMR spectra. Nuclear polarization transfer
from the polarized hydrogens to <sup>11</sup>B nuclei leads to a 10-fold
enhancement in the <sup>11</sup>B NMR spectrum. Moreover, our results
indicate that dihydrogen activation by QCAT and CAT tweezers is carried
out in a pairwise manner, and PHIP can be used for understanding the
activation mechanism in metal-free catalytic systems in general