Gregory Leitus | Weizmann Institute of Science (original) (raw)

Papers by Gregory Leitus

Molecules

Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and p... more Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(...

Angewandte Chemie (International ed. in English), Jan 2, 2017

The first example of base-metal-catalyzed synthesis of amides from the dehydrogenative coupling o... more The first example of base-metal-catalyzed synthesis of amides from the dehydrogenative coupling of primary amines with alcohols or esters is reported. The reactions are catalyzed by a new manganese pincer complex and generate hydrogen gas as the sole by-product, making the overall process atom economical and sustainable.

Science

Biological incorporation of functional molecules into cotton fibers adds magnetic or optical prop... more Biological incorporation of functional molecules into cotton fibers adds magnetic or optical properties.

ACS catalysis, Jan 2, 2016

Azines (2,3-diazabuta-1,3-dienes) are a widely used class of compounds with conjugated C=N double... more Azines (2,3-diazabuta-1,3-dienes) are a widely used class of compounds with conjugated C=N double bonds. Herein, we present a direct synthesis of azines from alcohols and hydrazine hydrate. The reaction, catalyzed by a ruthenium pincer complex, evolves dihydrogen and can be run in a base-free version. The dehydrogenative coupling of benzylic and aliphatic alcohols led to good conversions and yields. Spectroscopic evidence for a hydrazine-coordinated dearomatized ruthenium pincer complex was obtained. Isolation of a supramolecular crystalline compound provided evidence for the important role of hydrogen bonding networks under the reaction conditions.

The journal of physical chemistry. B, May 4, 2017

Xanthorhodopsin (xR) is a member of the retinal protein family and acts as a proton pump in the c... more Xanthorhodopsin (xR) is a member of the retinal protein family and acts as a proton pump in the cell membranes of the extremely halophilic eubacterium Salinibacter ruber. In addition to the retinal chromophore, xR contains a carotenoid, which acts as a light-harvesting antenna as it transfers 40% of the quanta it absorbs to the retinal. Our previous studies have shown that the CD and absorption spectra of xR are dramatically affected due to the protonation of two different residues. It is still unclear whether xR can bind cations. Electron paramagnetic resonance (EPR) spectroscopy used in the present study revealed that xR can bind divalent cations, such as Mn(2+) and Ca(2+), to deionized xR (DI-xR). We also demonstrate that xR can bind 1 equiv of Mn(2+) to a high-affinity binding site followed by binding of ∼40 equiv in cooperative manner and ∼100 equiv of Mn(2+) that are weakly bound. SQUID magnetic studies suggest that the high cooperative binding of Mn(2+) cations to xR is due t...

Journal of the American Chemical Society, Aug 10, 2017

The first example of base-metal-catalyzed dehydrogenative coupling of diols and amines to form cy... more The first example of base-metal-catalyzed dehydrogenative coupling of diols and amines to form cyclic imides is reported. The reaction is catalyzed by a pincer complex of the earth abundant manganese and forms hydrogen gas as the sole by-product, making the overall process atom economical and environmentally benign.

Angewandte Chemie (International ed. in English), Jan 3, 2017

The first example of a base metal (manganese) catalyzed acceptorless dehydrogenative coupling of ... more The first example of a base metal (manganese) catalyzed acceptorless dehydrogenative coupling of methanol and amines to form formamides is reported herein. The novel pincer complex (iPr-PN(H) P)Mn(H)(CO)2 catalyzes the reaction under mild conditions in the absence of any additives, bases, or hydrogen acceptors. Mechanistic insight based on the observation of an intermediate and DFT calculations is also provided.

Angewandte Chemie, 2017

The first example of a base-metal-catalyzed homogeneous hydrogenative coupling of nitriles and am... more The first example of a base-metal-catalyzed homogeneous hydrogenative coupling of nitriles and amines to selectively form secondary cross-imines is reported. The reaction is catalyzed under mild conditions by a well-defined (iPr-PNP)Fe(H)Br(CO) pincer pre-catalyst and catalytic tBuOK.

Nature Chemistry, 2016

How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly u... more How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly understood phenomenon. The classical mechanism of homogeneous crystal nucleation proceeds via the spontaneous random aggregation of species from liquid or solution. However, a non-classical mechanism suggests the formation of an amorphous dense phase that reorders to form stable crystal nuclei. So far it has remained an experimental challenge to observe the formation of crystal nuclei from five to thirty molecules. Here, using polyoxometallates, we show that the formation of small crystal nuclei is observable by cryogenic transmission electron microscopy. We observe both classical and non-classical nucleation processes, depending on the identity of the cation present. The experiments verify theoretical studies that suggest non-classical nucleation is the lower of the two energy pathways. The arrangement in just a seven-molecule proto-crystal matches the order found by X-ray diffraction of a single bulk crystal, which demonstrates that the same structure was formed in each case.

Chemistry - A European Journal, 2016

Homogeneous catalytic hydrogenation of esters to alcohols is an industrially important, environme... more Homogeneous catalytic hydrogenation of esters to alcohols is an industrially important, environmentally benign reaction. While precious metal-based catalysts for this reaction are now well known, only very few catalysts based on first-row metal complexes were reported. Here we present the hydrogenation of esters catalyzed by a complex of earth-abundant manganese. The reaction proceeds under mild conditions and insight into the mechanism is provided based on an NMR study and the synthesis of novel Mn complexes postulated as intermediates.

Journal of the American Chemical Society, 2016

Journal of the American Chemical Society Jacs, 2006

Russian Metallurgy (Metally)

ABSTRACT

Journal of the American Chemical Society, Jan 13, 2014

A compound combining the features of a molecular rotor and a photoswitch was synthesized and was ... more A compound combining the features of a molecular rotor and a photoswitch was synthesized and was shown to exist as three diastereomers, which interconvert via a reversible cyclic reaction scheme. Each of the three diastereomers was isolated, and by following the equilibration kinetics, activation barriers for all reactions were calculated. The results indicate that the properties of molecular switches depend heavily on their immediate chemical environment. The conclusions are important in the context of designing new switchable molecules and materials.

Inorganic chemistry, Jan 19, 2015

We report on Ru((II))(μ(2)-O2) nitrosyl pincer complexes that can return to their original Ru(0) ... more We report on Ru((II))(μ(2)-O2) nitrosyl pincer complexes that can return to their original Ru(0) state by reaction with mono-oxygen scavengers. Potential intermediates were calculated by density functional theory (DFT) and a mechanism is proposed, revealing a new type of metal-ligand cooperation consisting of activation of the O2 moiety by both the metal center and the NO ligand. Reaction of the Ru(0) nitrosyl complex 1 with O2 quantitatively yielded the crystallographically characterized Ru((II)) (μ(2)-O2) nitrosyl complex 2. Reaction of 2 with the mono-oxygen scavengers phosphines or CO gave the Ru(0) complex 1 and phosphine oxides, or the carbonyl complex 3 (1 trapped by CO) and CO2, respectively. Reaction of 2 with 1 equiv of phosphine at room temperature or -40 °C resulted in immediate formation of half an equivalent of 1 and 1 equiv of phosphine oxide, while half an equivalent of 2 remained unchanged. Overnight reaction at room temperature of 2 with excess CO (≥3 equiv) result...

Journal of Superconductivity, 2000

WO3 crystals were doped with Na on the surface to ~7% nominal atomic concentration. Scanning tunn... more WO3 crystals were doped with Na on the surface to ~7% nominal atomic concentration. Scanning tunneling microscopy and spectroscopy were employed, together with magnetization measurements, in the study of these crystals. Tunneling experiments reveal superconducting islands, 20–150 nm in size, covering about 10% of the surface, the rest of which is insulating. Magnetization measurements show that the superconducting phase formed

The Journal of Physical Chemistry B, 2010

The Journal of Physical Chemistry B, 2009

We model the interaction of side-chain and end-chain groups of poly(4-vinylpyridine) by a 5:1 mol... more We model the interaction of side-chain and end-chain groups of poly(4-vinylpyridine) by a 5:1 molar ratio mixture of 4-isopropylpyridine (side-chain model) and 4-propylpyridine (end-chain model). We find that the 4-isopropylpyridine in the mixture is oxidized in a slow air flow to produce 4-isopropylpyridine hydroperoxide which in turn precipitates as lamellar crystals with monoclinic structure. The fact that the peroxide group is exchanged for the hydrogen of the tertiary carbon demonstrates the high activity of the latter and gives strong support for its involvement in the self-protonation mechanism proposed earlier for the poly(4-vinylpyridine)/pyridine gel.

physica status solidi (b), 2006