Cohen S, Bilyachenko AN, Gelman D. Bifunctional Pincer Catalysts for Chemoselective Transfer Hydrogenation and Related Reactions. Eur. J. Inorg. Chem. [Internet]. 2019 :in press. Publisher's VersionAbstract

A comparative study on the chemoselective transfer hydrogenation of nitroarenes to anilines and related processes using FA as the hydrogen source is described; these processes are catalyzed by a series of pincer catalysts equipped with different functional groups in the secondary coordination sphere. Some new (4 and 5) as well as previously reported (1?3) catalysts belonging to the family of bifunctional PC(sp3)P pincer complexes were employed in this study The reported compounds exhibited remarkably different catalytic activity behavior, depending on the nature of the functional groups. Transfer hydrogenation of nitrobenzene with FA as a hydrogen source was probed using iridium complexes 3 or 4 as a catalyst. Under the same conditions, the analogous palladium complex was found to be useful for the selective amidation of aniline with light carboxylic acids.

Cohen O, Gelman D, Avnir D. Optical rotation kinetics study of the polycondensation of chiral sol-gel precursors. J. Sol-Gel Sci. Technol.Journal of Sol-Gel Science and Technology. 2018 :Ahead of Print.Abstract
We show that the polycondensation of chiral sol-gel precursors can be efficiently followed up by optical rotation measurements. Three silanes were studied, namely, the hexaethoxysilane derivs. of L-threonine, L-isoleucine, and dimethyl-L-tartrate. Two main sol-gel polycondensation mechanisms were identified, namely, linear kinetics product growth and second-order cluster-cluster growth. Dynamic light scattering measurements are used to support the proposed mechanisms. [Figure not available: see fulltext.]. [on SciFinder(R)]
Zoabi A, Santiago MG, Gelman D, Rosenblatt C, Avnir D, Abu-Reziq R. Chiral Polymeric Nanocapsules and Their Use for Conformational Deracemization of Liquid Crystals. J. Phys. Chem. C. 2018;122 (31) :17936 - 17941.Abstract

We present the first prepn. and properties of chiral nanocapsules. The chiral shell, a polyurea deriv., was obtained by interfacial emulsion polymn. of L-lysine with polymethylene polyphenyl isocyanate. The chirality of these nanocapsules was manifested by its ability to induce conformational deracemization of a liq. crystal. This induced chirality was measured using the "Raynes' expt.", in which the boundary conditions of cells impose a ±90° rotation of the liq. crystal director from one surface to the other. Both left- and right-handed director twist domains appear on cooling from the isotropic to the nematic phase. Owing to the weak induced chirality of the liq. crystal, one sense of director rotation is energetically more favorable and its domain size expands, resulting in curvature of the domain walls. The curvature was measured as a function of capsule concn. and serves as a metric of the induction of chirality in the surrounding liq. crystal. [on SciFinder(R)]

De-Botton S, Cohen S, Gelman D. Iridium PC(sp3)P Pincer Complexes with Hemilabile Pendant Arms: Synthesis, Characterization, and Catalytic Activity. Organometallics. 2018;37 (8) :1324 - 1330.Abstract

New PC(sp3)P pincer ligands possessing hemilabile alkoxyl side arms as well as their Ir complexes are reported. All new organometallic compds. were structurally characterized including x-ray anal. The hemilability of the side arms was probed by reactions with CO, revealing the reversible coordination. The catalytic activity of the new complexes was tested by Ir-catalyzed transfer dehydrogenation of alkanes, THF, and chroman under mild conditions. [on SciFinder(R)]

Cohen O, Ferris AJ, Adkins R, Lemieux RP, Avnir D, Gelman D, Rosenblatt C. Chiral organosilica particles and their use as inducers of conformational deracemization of liquid crystal phases. Chem. Phys. Lett. 2018;696 :112 - 118.Abstract

Chiral organosilica particles of size ∼200 nm were synthesized from an enantio-pure multi-armed chiral D-maltose organosilane precursor in the absence of co-condensation with an achiral monomer. Two distinct expts. were performed to demonstrate the particles' ability to induce conformational deracemization of a host liq. crystal. The first involves an elec. field-induced tilt of the liq. crystal director in the deracemized smectic-A phase. The other involves domain wall curvature sepg. left- and right-handed liq. crystal helical pitch domains imposed by the cells' substrates. The results demonstrate unequivocally that enantio-pure organosilica nanoparticles can be synthesized and can induce chirality in a host. [on SciFinder(R)]

Kisets I, Gelman D. Carbometalated Complexes Possessing Tripodal Pseudo-C3-Symmetric Triptycene-Based Ligands. Organometallics. 2018;37 (4) :526 - 529.Abstract

New air-stable tripodal triphosphine ligands 1,8,13-tris(diisopropylphosphino)-2,3-dimethoxytriptycene (P3T1) and 1,8,13-tris(diphenylphosphino)-2,3-dimethoxytriptycene (P3T2) are presented and discussed. Their synthesis is based on the 1st practical synthesis of 1,8,13-tribromotriptycene. Reaction with Pd gives new pseudo-C3-sym. carbometalated complexes: namely, Pd(P3T1)Cl and Pd(P3T2)Cl. The catalytic activity of the new ligands and complexes was tested in the Pd-catalyzed chemoselective transfer hydrogenation of α,β-unsatd. ketones. [on SciFinder(R)]

Biniuri Y, Albada B, Wolff M, Golub E, Gelman D, Willner I. Cu2+ or Fe3+ Terpyridine/Aptamer Conjugates: Nucleoapzymes Catalyzing the Oxidation of Dopamine to Aminochrome. ACS Catalysis [Internet]. 2018 :1802 - 1809. Publisher's Version
Cohen S, Borin V, Schapiro I, Musa S, De-Botton S, Belkova NV, Gelman D. Ir(III)-PC(sp3)P Bifunctional Catalysts for Production of H2 by Dehydrogenation of Formic Acid: Experimental and Theoretical Study. ACS Catal. 2017;7 (12) :8139 - 8146.Abstract

Reversible storage of hydrogen in the form of stable and relatively harmless chem. substances such as formic acid (FA) is one of the cornerstones of a fossil-fuel-free economy. Recently, Ru(III)-PC(sp3)P (where PC(sp3)P = modular dibenzobarrelene-based pincer ligand possessing a pendant functional group) complex 1 has been reported as a mild and E-selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid. Discovery of the additive-free protocol for dehydrogenation of FA launched further studies aiming at the rational design of highly efficient catalysts for this reaction operating under neutral conditions. We now report the results of our investigation on a series of bifunctionl PC(sp3)P complexes equipped with different outer-sphere auxiliaries, that allowed us to identify an amine-functionalized Ir(III)-PC(sp3)P complex 3, as a clean and efficient catalyst for the FA dehydrogenation. The catalyst is suitable for fuel-cell applications demonstrating a TON up to 5 × 105 and TOF up to 2 × 104 h-1 (3.8 × 105 and 1.2 × 104 h-1 with no additives). In addn. to the practical value of the catalyst, exptl. and computational mechanistic studies provide rationale for the design of improved next-generation catalysts. [on SciFinder(R)]

Cohen O, Abu-Reziq R, Gelman D. Chiral enantiopure organosilane precursors for the synthesis of periodic mesoporous organosilicas. Tetrahedron: Asymmetry. 2017;28 (12) :1675 - 1685.Abstract

The manuscript describes synthesis of new chiral organosilica networks starting from modified readily available enantiopure substances such as sugars and amino acids. We report on the successful prepn. of robust all-chiral organosilicas by polymn. of the homochiral monomers. When the homochiral organosilane monomers were polymd. in mixts. of polar org. solvents and water in the presence of hydrochloric acid or tetrabutylammonium fluoride as catalysts, mainly spherical microparticles were obtained due to emulsification of the hydrophobic monomers in these mixts. Polycondensation of the chiral organosilanes in the presence of Pluronic P123 as a template produced ordered mesoporous networks. The new all-chiral materials were characterized by SEM, STEM, BET, SAXS, IR, NMR and TGA. [on SciFinder(R)]

Warratz S, Burns DJ, Zhu C, Korvorapun K, Rogge T, Scholz J, Jooss C, Gelman D, Ackermann L. meta-C-H Bromination on Purine Bases by Heterogeneous Ruthenium Catalysis. Angew. Chem., Int. Ed. 2017;56 (6) :1557 - 1560.Abstract

Methods for positionally selective remote C-H functionalizations are in high demand. Herein, we disclose the first heterogeneous ruthenium catalyst for meta-selective C-H functionalizations, which enabled remote halogenations with excellent site selectivity and ample scope. The versatile heterogeneous Ru@SiO2 catalyst was broadly applicable and could be easily recovered and reused, which set the stage for the direct fluorescent labeling of purines. In contrast to palladium, rhodium, iridium, or cobalt complexes, solely the ruthenium catalysis manifold provided access to meta-halogenated purine derivs., illustrating the unique power of ruthenium C-H activation catalysis. [on SciFinder(R)]

De-Botton S, Romm R, Bensoussan G, Hitrik M, Musa S, Gelman D. Coordination versatility of p-hydroquinone-functionalized dibenzobarrelene-based PC(sp3)P pincer ligands. Dalton Trans. 2016;45 (40) :16040 - 16046.Abstract

The manuscript describes the synthesis and coordination chem. of a novel diphosphine pincer ligand based on a p-hydroquinone-functionalized dibenzobarrelene scaffold. The p-hydroquinone fragment of the ligand is oxidatively and coordinatively non-innocent and may render new reactivity to the metal center due to implied reversible redox behavior, tautomeric interconversion and metal-hydroxyl/alkoxide coordination switch of the pendant hydroxyl side-arm. Palladium, platinum and iridium complexes were prepd. and characterized. Investigation of their coordination chem. revealed that while tautomeric equil. exists in free ligands and in the chelate non-metalated complexes, it is essentially blocked in the corresponding C(sp3)-pincer compds. due to stabilizing hemilabile coordination of the hydroxyl group. However, its presence in close proximity to the metal center is essential for catalyzing acceptorless dehydrogenation of alcs. by the iridium complexes via the outer-sphere hydrogen transfer mechanism. Remarkably, authors found a similar activity for the analogous palladium complexes, which is not characteristic of this metal. This unprecedented reactivity of palladium stresses the fact that besides the choice of an active metal, transformation-oriented design of the ligand is crucial for catalysis. [on SciFinder(R)]

Ballerini E, Maggi R, Pizzo F, Piermatti O, Gelman D, Vaccaro L. An Efficient and Waste-Minimized One-Pot Procedure for the Preparation of N-Boc-γ-amino Alcohols Starting from α,β-Unsaturated Ketones in Flow. Org. Process Res. Dev. 2016;20 (2) :474 - 479.Abstract

We report herein a clean multistep flow process that starts from α,β-unsatd. ketones, e.g., MeCOCH:CHCH2CH2Me, and allows the prepn. of N-Boc-γ-amino alcs., e.g., cis/trans-MeCH(OH)CH2CH(NHBoc)CH2CH2Me, in high yields. The final products have been isolated in pure form without any addnl. purifn. step. The cleanness and environmental efficiency achieved using our protocol are proven by the calcn. of green metrics such as E-factors. [on SciFinder(R)]

Zell D, Warratz S, Gelman D, Garden SJ, Ackermann L. Single-Component Phosphinous Acid Ruthenium(II) Catalysts for Versatile C-H Activation by Metal-Ligand Cooperation. Chem. - Eur. J. 2016;22 (4) :1248 - 1252.Abstract

Well-defined ruthenium(II) phosphinous acid (PA) complexes enabled chemo-, site-, and diastereoselective C-H functionalization of arenes and alkenes with ample scope. The outstanding catalytic activity was reflected by catalyst loadings as low as 0.75 mol %, and the most step-economical access reported to date to angiotensin II receptor antagonist blockbuster drugs. Mechanistic studies indicated a kinetically relevant C-X cleavage by a single-electron transfer (SET)-type elementary process, and provided evidence for a PA-assisted C-H ruthenation step. [on SciFinder(R)]

Silantyev GA, Titova EM, Filippov OA, Gutsul EI, Gelman D, Belkova NV. Hydrogen bonds, coordination isomerism, and catalytic dehydrogenation of alcohols with the bifunctional iridium pincer complex IrHCl. Russ. Chem. Bull. 2015;64 (12) :2806-2810.Abstract

The reaction of iridium(iii) hydride complex 1 based on the pincer dibenzobarrelene ligand with pyridine proceeds stepwise to show different reactivities of the starting fac-isomers 1A and 1B. The kinetic product of the reaction is mer-complex 2 with a trans disposition of the pyridine and hydride ligands. Isomerization into the thermodynamic product 2' containing pyridine in the cis-position with regard to hydride proceeds slowly. The estimation of activation parameters (Delta H (not equal) and Delta S (not equal)) shows that the change in the geometry of fac-complexes upon coordination of pyridine occurs through an associative transition state, while isomerization of the mer-complexes is a dissociative process. The isomers of complex 1 and its pyridine-containing derivatives 2 and 2' are shown to exhibit different reactivities in the formation of dihydrogen bond and the catalytic dehydrogenation of (PrOH)-O-i under model conditions.

Moselage M, Sauermann N, Koeller J, Liu W, Gelman D, Ackermann L. Cobalt(III)-Catalyzed Allylation with Allyl Acetates by C-H/C-O Cleavage. Synlett. 2015;26 (11) :1596 - 1600.Abstract

Versatile cobalt-catalyzed C-H allylations on arenes, indoles, and pyrroles were accomplished with allyl acetates. The C-H/C-O functionalization process was characterized by a broad substrate scope as well as an excellent functional-group tolerance and occurs by initial C-H cobaltation. [on SciFinder(R)]

Musa S, Ghosh A, Vaccaro L, Ackermann L, Gelman D. Efficient E-Selective Transfer Semihydrogenation of Alkynes by Means of Ligand-Metal Cooperating Ruthenium Catalyst. Adv. Synth. Catal. 2015;357 (10) :2351 - 2357.Abstract

This paper describes an efficient protocol for the E-selective transfer semihydrogenation of internal alkynes employing a previously described bifunctional ruthenium-based PC(sp3)P complex, 20 mol% of sodium formate and nearly stoichiometric formic acid. Semihydrogenation of the terminal alkynes resulted in the formation of the corresponding styrenes. The mechanism of the reaction included stepwise transfer of both the hydride and the proton of the formic acid to the substrate. This fact allowed for the development of a facile protocol for the synthesis of monodeuterated alkenes by simply applying formic acid/sodium formate/D2O mixt. as a hydrogen source. High yields, selectivity and functional group compatibility were generally achieved. [on SciFinder(R)]

Ballerini E, Curini M, Gelman D, Lanari D, Piermatti O, Pizzo F, Santoro S, Vaccaro L. Waste Minimized Multistep Preparation in Flow of β-Amino Acids Starting from α,β-Unsaturated Carboxylic Acids. ACS Sustainable Chem. Eng. 2015;3 (6) :1221 - 1226.Abstract

An efficient protocol for the synthesis of β-amino acids starting from easily accessible α,β-unsatd. carboxylic acids based on the combination of two heterogeneous catalytic systems is reported. This multistep approach is based on the direct β-azidation of α,β-unsatd. carboxylic acids and subsequent azido group redn. performed in flow conditions. It has been demonstrated that the catalysts can be easily recovered and reused conserving its complete efficiency. The green metrics calcns. proved the high environmental efficiency of the protocol characterized by very low waste prodn. [on SciFinder(R)]

Silantyev GA, Filippov OA, Musa S, Gelman D, Belkova NV, Weisz K, Epstein LM, Shubina ES. Conformational Flexibility of Dibenzobarrelene-Based PC(sp3)P Pincer Iridium Hydride Complexes: The Role of Hemilabile Functional Groups and External Coordinating Solvents. Organometallics. 2014;33 (21) :5964 - 5973.Abstract

Bifunctional dibenzobarrelene-based PC(sp3)P pincer Ir complex 1 is known as an efficient catalyst in acceptorless dehydrogenation of alcs. and hydrogenation/hydroformylation of alkenes. To shed light on the mechanism of the H formation/activation, the authors performed variable-temp. IR and NMR (1H, 31P) anal. of intra- and intermol. interactions involving a hydride ligand and hydroxymethyl cooperating group in 1 and its analogs. The results of the spectroscopic measurements in different media (CH2Cl2, toluene, DMSO, and mixed solvents) were compared with the quantum chem. (DFT/M06 and B3PW91) calcns. The obtained data imply flexibility of the dibenzobarrelene-based scaffold, unprecedented for conventional pincer ligands. Both the CH2OH-substituted complex 1 and its COOEt analog 3 prefer facial configuration of the PCP ligand with a P-Ir-P angle of ∼100°. Such geometries are stabilized by Ir···O interaction with the dangling functional group and differ by the mutual arrangement of the H and Cl ligands. The complexes show dynamic equil. between the two most stable fac-isomers, which can be transformed into the meridional ones in the presence of coordinating additives (CH3CN, DMSO, or CO, but not Et3N). The process is reversible for MeCN but irreversible for DMSO and CO, in agreement with the Lewis basicity of these mols. [on SciFinder(R)]

Cohen O, Grossman O, Vaccaro L, Gelman D. Synthesis of chiral nonracemic PC(sp3)S pincer ligands. J. Organomet. Chem. 2014;750 :13 - 16.Abstract

The manuscript describes a straightforward synthetic route toward a new family of chiral nonracemic dibenzobarrelene-based PC(sp3)S pincer ligands. The target mols. were synthesized via lithiation of the racemic 1-bromo-8-diphenylphosphinotriptycene (2) and subsequent quenching with diastereomerically pure (1R,2S,5R)-(-)-menthyl (S)-p-toluenesulfinate. The resulting mixt. of diastereomers was resolved using conventional column chromatog. Hydrogenation of the diastereomerically pure compds. gave enantiopure PCS pincer ligands. [on SciFinder(R)]

Ismalaj E, Strappaveccia G, Ballerini E, Elisei F, Piermatti O, Gelman D, Vaccaro L. γ-Valerolactone as a Renewable Dipolar Aprotic Solvent Deriving from Biomass Degradation for the Hiyama Reaction. ACS Sustainable Chem. Eng. 2014;2 (10) :2461 - 2464.Abstract

γ-Valerolactone (GVL) can be a valid biobased replacement for toxic dipolar aprotic solvents esp. in widely used cross-coupling reactions. In this contribution, we have proved that GVL can be a useful medium for the Hiyama reaction, and we developed a practical and efficient protocol for the Hiyama coupling using a nonexpensive and com. available heterogeneous palladium catalyst without the use of any ligand or additive. Desired cross-coupling products have been obtained in good to excellent yields (74-94%). [on SciFinder(R)]