Evolution of a ‘privileged’ P-alkene ligand: added planar chirality beats BINOL axial chirality in catalytic asymmetric C–C bond formation

Calderón J.C., Herrera A., Heinemann F.W., Langer J., Linden A., Chelouan A., Grasruck A., Añez R., Clark T., Dorta R.

Adhikari A.S., Pandit S., Kant R., Majumdar N.

Galushko A.S., Boiko D.A., Pentsak E.O., Eremin D.B., Ananikov V.P.

An approach to the spatially localized characterization of supported catalysts over a reaction course is proposed. It consists of a combination of scanning, transmission, and high-resolution scanning transmission electron microscopy to determine metal particles from arrays of surface nanoparticles to individual nanoparticles and individual atoms. The study of the evolution of specific metal catalyst particles at different scale levels over time, particularly before and after the cross-coupling catalytic reaction, made it possible to approach the concept of 4D catalysis–tracking the positions of catalytic centers in space (3D) over time (+1D). The dynamic behavior of individual palladium atoms and nanoparticles in cross-coupling reactions was recorded with nanometer accuracy via the precise localization of catalytic centers. Single atoms of palladium leach out into solution from the support under the action of the catalytic system, where they exhibit extremely high catalytic activity compared to surface metal nanoparticles. Monoatomic centers, which make up only approximately 1% of palladium in the Pd/C system, provide more than 99% of the catalytic activity. The remaining palladium nanoparticles changed their shape and could move over the surface of the support, which was recorded by processing images of the array of nanoparticles with a neural network and aligning them using automatically detected keypoints. The study reveals a novel opportunity for single-atom catalysis─easier detachment (capture) from (on) the carbon support surface is the origin of superior catalytic activity, rather than the operation of single atomic catalytic centers on the surface of the support, as is typically assumed.

Shimamoto R., Tsurusaki A., Kamikawa K.

Zhou L., Zanda N., Chaudhari M., Da Silva M.F., Pericàs M.A.

Oka N., Yamada T., Sajiki H., Akai S., Ikawa T.

A wide range of aryl boronic 1,1,2,2-tetraethylethylene glycol esters [ArB(Epin)s] were readily synthesized. Purifying aryl boronic esters by conventional silica gel chromatography is generally challenging; however, these introduced derivatives are easily purified on silica gel and isolated in excellent yields. We subjected the purified ArB(Epin) to Suzuki-Miyaura couplings, which provided higher yields of the desired biaryl products than those obtained using the corresponding aryl boronic acids or pinacol esters.

Chuchelkin I.V., Gavrilov K.N., Gavrilov V.K., Zheglov S.V., Firsin I.D., Perepukhov A.M., Maximychev A.V., Borisova N.E., Zamilatskov I.A., Tyurin V.S., Dejoie C., Chernyshev V.V., Zimarev V.S., Goulioukina N.S.

A large family of P,S-bidentate diamidophosphite ligands were readily synthesized from accessible hydroxyl-thioether compounds. One type of Pd(II) cationic allylic complex with these diamidophosphites fulfilling a P-monodentate function, and three types, where the ligands act as P,S-bridging ligands (coordination polymer and head-to-head and head-to-tail dimers), were obtained. In addition, neutral Pd(II) halide complexes were generated in situ as common intermediates for both groups of cationic dimers. The structures of the ligands and complexes were elucidated by means of 2D-NMR and were confirmed by powder X-ray diffraction, as well as by DFT calculations. Asymmetric inducers of this type exhibited up to 94% ee in the Pd-mediated allylic substitution of (E)-1,3-diphenylallyl acetate with various C- and N-nucleophiles. Ee values of up to 80% were obtained in the Pd-catalyzed allylic alkylation of cinnamyl acetate with β-ketoesters. In addition, up to 61% ee was achieved in the asymmetric amination of 2-(diethoxyphosphoryl)-1-phenylallyl acetate with aniline. The effects of the diamidophosphite and thioether moieties on the catalytic activity and enantioselectivity were investigated.

Chuchelkin I.V., Gavrilov K.N., Borisova N.E., Perepukhov A.M., Maximychev A.V., Zheglov S.V., Gavrilov V.K., Firsin I.D., Zimarev V.S., Mikhel I.S., Tafeenko V.A., Murashova E.V., Chernyshev V.V., Goulioukina N.S.

Novel diamidophosphites based on β-hydroxyamides were prepared, and their individual and in situ formed complexes were tested in Pd-mediated allylations.

Nikol A., Zhang Z., Chelouan A., Falivene L., Cavallo L., Herrera A., Heinemann F.W., Escalona A., Frieß S., Grasruck A., Dorta R.

We thank Prof. Anthony Linden (University of Zurich) for solving the crystal structure of 8 and Ms. Christina Wronna for carrying out the elemental analyses. Financial support by Friedrich–Alexander University and King Abdullah University of Science and Technology (KAUST) is acknowledged. For computer time, this research used the resources of the Supercomputing Laboratory (KSL) at KAUST.

Frieß S., Herrera A., Linden A., Heinemann F.W., Dorta R.

Dibenzazepinyl dichlorophosphine 2 reacts with (R,R)-2,3-O-isopropylidene-threitol (3) in Et2O solution to afford gram-quantities of the enantiopure macrocylic phosphoramidite (all-R)-6, which may be seen as a formal dimer of classic phosphoramidite P-alkene hybrid ligands. Complexation experiments with PdCl2 reveal highly selective formation of the trans-dinuclear complex (all-R)-11. The corresponding bulkier and rigidly trans-eclipsed 1,4-diol (S,S)-bis-hydroximethyl-9,10-dihydro-9,10-ethaneanthracene (4), does not favor macrocycle formation and exclusively leads to the new dibenzazepinyl phsophormaidite P-alkene ligand 7, which in Pd-catalyzed asymmetric allylic amination comes the well-known ‘privileged’ binol-derived P-alkene analogue 1 close in terms of enantioselection.

Chelouan A., Bao S., Frieß S., Herrera A., Heinemann F.W., Escalona A., Grasruck A., Dorta R.

A stereodivergent synthesis using inexpensive reagents, i.e., dibenzazepine and glucose-derived t-Bu-sulfinate diastereomers (RS)-6 or (SS)-6, affords respective S(O)-alkene hybrid ligands (S)-7 and (R)-7 on gram scales and in excellent optical purity (ee > 99%). Phenyl substitution of the dibenzoazepine backbone generates planar chirality to give epimerization-resistant (pS,RS)-10 diastereoisomer in high isomeric purity. Furthermore, the crystal structure of widely used sulfinate (RS)-6 is disclosed for the first time since its discovery a quarter of a century ago. Ligands 7 and 10 coordinate Rh(I) in a bidentate fashion through the S atoms and the alkene functions as evidenced by the crystal structures of complexes (R)-11 and (SN,SS)-12. (R)-11 catalyzes the conjugate addition of arylboronic acids to enones with enantioselectivities of up to 77% ee. The reaction proceeds smoothly also under base-free conditions at 40 °C. The planar chirality in ligand (pS,RS)-10 is shown to override and invert the sense...

Kawashima K., Sato T., Ogasawara M., Kamikawa K., Mori S.

Recently, planar-chiral phosphine-olefin ligands based on (η6 -arene)chromium(0) and (η5 -cyclopentadienyl)manganese(I), which are known as first- and second-generation, respectively, have been developed. These ligands were employed for Rh-catalyzed asymmetric 1,4-addition to enones. First-generation ligands involve high enantioselectivity for cyclic enones (>98% ee). Second-generation ligands involve high enantioselectivity for not only cyclic enones but also for acyclic enones (>98% ee). In this study, we have performed DFT calculations to investigate the origin of enantioselectivity. The theoretical values of enantioselectivities were found to be in good agreement with the experimental values obtained for a cyclic enone, 2-cyclopenten-1-one, using both the first- and second-generation ligands. Regarding an acyclic enone, 3-penten-2-one, it was found that the s-cis type decreases the enantioselectivity because the transition states in the s-cis type have a large steric repulsion. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis indicate that it is important to study the orbital interactions in the transition states of the insertion step for the acyclic enone attacked from si-face with the second-generation ligand. © 2018 Wiley Periodicals, Inc.

Rössler S.L., Krautwald S., Carreira E.M.

Experimental mechanistic studies of iridium-catalyzed, enantioselective allylic substitution enabled by (phosphoramidite,olefin) ligands are reported. (η2-Allylic alcohol)iridium(I) and (η3-allyl)iridium(III) complexes were synthesized and characterized by NMR spectroscopy as well as X-ray crystallography. The substrate complexes are catalytically and kinetically competent to be intermediates in allylic substitutions of branched, racemic allylic alcohols with various nucleophiles. In addition, we have identified an off-cycle pathway involving reversible binding of molecular oxygen to iridium, which contributes to the air tolerance of the catalyst system.

Herrera A., Grasruck A., Heinemann F.W., Scheurer A., Chelouan A., Frieß S., Seidel F., Dorta R.

10-Phenyl-5H-dibenz[b,f]azepine (5) is synthesized by Suzuki cross coupling of the protected bromo alkene 4 with PhB(OH)2. 5 reacts with PCl3 to afford the dichlorophosphanyl-azepine 6 in >90% yield. Alkylation of 6 with 1 equiv of t-BuMgBr leads, after recrystallization in Et2O, to the diastereomerically enriched (dr > 98:2) chloride rac-7, which the crystal structure reveals to be the (pS,RP)/(pR,SP) pair. The fact that rac-7 crystallizes in the Sohncke space group P212121 opens up the possibility of a mechanical separation of the enantiomers. Methylation of rac-7 is perfectly stereoselective with inversion of configuration at the P atom to yield the new ligand rac-8 as the (R,R)/(S,S) pair. The corresponding BH3-protected diastereomer rac-9 (i.e., the (R,S)/(S,R) pair), is isolated after flash column chromatography in 73% yield. Compounds 5–9 are accessible in multigram quantities. X-ray crystal structures of Ru(II) complexes demonstrate the ambidentate nature of ligand rac-8: Complex 10 is exclusively...

Kamikawa K., Tseng Y., Jian J., Takahashi T., Ogasawara M.

A series of 2-methyl-1,3-propenylene-bridged (η5-diarylphosphinocyclopentadienyl)(phosphine)manganese(I) dicarbonyl complexes 2 have been developed as a new class of phosphine-olefin ligands based on a planar-chiral transition-metal scaffold, which show better robustness as well as higher enantioselectivity over phosphine-olefin ligands 1 with a planar-chiral (η6-arene)chromium(0) framework. The practical enantiospecific and scalable synthesis of 2 has been established. Phosphine-olefin ligands 2 enable construction of an effective chiral environment around a transition-metal center upon coordination, and thus their rhodium(I) complexes exhibit excellent catalytic performance in the various asymmetric addition reactions of arylboron nucleophiles. Complex 2b, which has a bis(3,5-dimethylphenyl)phosphino group on the cyclopentadienyl ring, is found to be a superior chiral ligand in the rhodium-catalyzed asymmetric 1,4-addition reactions of arylboronic acids to various cyclic/acyclic enones giving the corresponding arylation products in over 99% ee. On the other hand, 2c and 2d, which have bis[3,5-bis(trifluoromethyl)phenyl]phosphino and bis(3,5-di-tert-buthyl-4-methoxyphenyl)phosphino groups, respectively, are highly efficient chiral ligands in the rhodium-catalyzed asymmetric 1,2-addition reactions of the arylboron nucleophiles to imines or aldehydes showing up to 99.9% ee. The X-ray crystallographic studies of (R)-2b and [RhCl((S*)-2b)]2 reveal the absolute configuration of 2b and its phosphine-olefin bidentate coordination to a rhodium(I) cation. Structural comparison with [RhCl((R*)-1b)]2 postulates the origins of the higher enantioselectivity of newly developed phosphine-olefin ligands 2.

Grasruck A., Schall K., Heinemann F.W., Langer J., Herrera A., Frieß S., Schmid G., Dorta R.

A new Dibenzoazepine-hydrazine is a versatile building block for the synthesis of potentially hemilabile hydrazone N–alkene ligands for the formation of main group and transition metal complexes.