Roof-Shaped Halide-Bridged Bimetallic Complexes via Ring Expansion Reaction

Hydrogenation of CO2 by a Bifunctional PC(sp3 )P Iridium(III) Pincer Complex Equipped with Tertiary Amine as a Functional Group

Reversible hydrogen storage in the form of stable and mostly harmless chemical substances such as formic acid (FA) is a cornerstone of a fossil fuels-free economy. In the past, we have reported a primary amine-functionalized bifunctional iridium(III)-PC(sp3 )P pincer complex as a mild and chemoselective catalyst for the additive-free decomposition of neat formic acid. In this manuscript, we report on the successful application of a redesigned complex bearing tertiary amine functionality as a catalyst for mild hydrogenation of CO2 to formic acid. The catalyst demonstrates TON up to 6×104 and TOF up to 1.7×104  h-1 . In addition to the practical value of the catalyst, experimental and computational mechanistic studies provide the rationale for the design of improved next-generation catalysts.

Stereoisomerism as an Origin of Different Reactivities of Ir(III) PC(sp3)P Pincer Catalysts

Two stereoisomers of pentacoordinate iridium(III) hydridochloride with triptycene-based PC(sp³)P pincer ligand (1,8-bis(diisopropylphosphino)triptycene), 1 and 2, differ by the orientation of hydride ligand relative to the bridgehead ring of triptycene. According to DFT/B3PW91/def2-TZVP calculations performed, an equatorial Cl ligand can relatively easily change its position in 1, whereas that is not the case in 2. Both complexes 1 and 2 readily bind the sixth ligand to protect the empty coordination site. Variable temperature spectroscopic (NMR, IR, and UV-visible) studies show the existence of two isomers of hexacoordinate complexes 1·MeCN, 2·MeCN, and 2·Py with acetonitrile or pyridine coordinated trans to hydride or trans to metalated C(sp³), whereas only the equatorial isomer is found for 1·Py. These complexes are stabilized by various intramolecular noncovalent C-H···Cl interactions that are affected by the rotation of isopropyls or pyridine. The substitution of MeCN by pyridine is slow yielding axial Py complexes as kinetic products and the equatorial Py complexes as thermodynamic products with faster reactions of 1·L. Ultimately, that explains the higher activity of 1 in the catalytic alkenes' isomerization observed for allylbenzene, 1-octene, and pent-4-enenitrile, which proceeds as an insertion/elimination sequence rather than through the allylic mechanism.

Mechanistic insights into the tropo-inversion of the biphenyl moiety in chiral bis-amido phosphites and in their palladium(ii) complexes

Chiral bis-amido phosphites L1 and L2 containing a diaminobiphenyl unit and a chiral alkoxy group derived from either (-)-menthol or 3-acetoxy deoxycholic methyl ester have been synthesised. Both L1 and L2 react with PdCl₂(NCPh)₂ affording di- or mononuclear derivatives with formula trans-[Pd(μ-Cl)Cl(L)]₂ (1a, L = L1; 1b, L = L2) or trans-PdCl₂(L)₂ (2a, L = L1; 2b, L = L2) depending on the Pd : L molar ratio. The crystal structure of (M,P)-1a confirms the trans arrangement of the ligand L1 and shows an unusual puckering of the Pd₂(μ-Cl)₂ core (θ 46°). Both the ligands L1 and L2 and their complexes (1 and 2) are fluxional in solution as a consequence of the tropo-inversion of the diaminobiphenyl unit. For L1, L2, 1a and 2a a combined study including variable temperature ³¹P{¹H} NMR spectroscopy and line shape analysis, Eyring plots and DFT calculations have shed light on the mechanism of the tropo-inversion.

Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors

Reactions between 1,8‐dichloroanthracenes with substituents in position 10 and ortho‐chloroaryne afford mixtures of 1,8,13‐ (syn) and 1,8,16‐trichlorotriptycenes (anti). The syn/anti ratio is dependent on these substituents. Electropositive substituents like SiMe₃ and GeMe₃ lead to preferred formation of the syn‐isomer, whereas CMe₃ groups exclusively afford the anti‐isomer. Different quantum chemical calculations including location of transition states give conflicting results, but indicate the importance of dispersion forces for an at least qualitative prediction of results. The syn‐trichlorotriptycenes with SiMe₃ and GeMe₃ substituents were characterized by using NMR spectroscopy, mass spectrometry, and X‐ray diffraction experiments.

Coordination versatility of p-hydroquinone-functionalized dibenzobarrelene-based PC(sp3)P pincer ligands

Bifunctional hydroquinone-based PC(sp³)P pincer complexes.

Cyclodextrin and phosphorus(iii): a versatile combination for coordination chemistry and catalysis

The relevance of cyclodextrins equipped with P(iii) atoms in coordination chemistry and homogeneous catalysis is discussed.

Ridge-tile-like chiral topology: synthesis, resolution, and complete chiroptical characterization of enantiomers of edge-sharing binuclear square planar complexes of Ni(II) bearing achiral ligands

Binuclear square planar Ni(II) complexes are described, formed by two tridentate ligands with two imine-nitrogens coordinating two nickel atoms. Such complexes are synthetically readily available with great structural variety and present new types of ridge-tile-like chiral compounds that are reasonably stable in the appropriate "bent" conformation. Enantiomerically pure samples of these compounds have been obtained for the first time using HPLC with a chiral stationary phase. Absolute configurations and chiroptical properties are fully characterized by ECD, VCD, ORD spectroscopy, and theoretical calculations. These new compounds with ridge-tile-like chiral topology are configurationally reasonably stable [DeltaG(double dagger) = 121.4 kJ mol(-1), t(1/2) = 14.9 h (78 degrees C, ethanol)], and therefore their chemistry, physical properties, and applications can be systematically studied.

An approach to bimetallic catalysts by ligand design

New diphosphines based on benzofurobenzofuran and dibenzodioxocin backbones, forming exclusively bimetallic complexes were designed and synthesized. Depending on the ligand to metal ratio, face-to-face bimetallic complexes or syn-chloride bridged dimeric complexes were formed as main reaction products. The structures of the rhodium complexes of the new ligands 4, 7, 10, 13, 16 were established in solution by NMR, IR, and MS spectroscopy. The molecular structures of the syn-chloride bridged dimeric complexes [Rh(2)(CO)(2)(mu-Cl)(2)(4)] (22), [Rh(2)(CO)(2)(mu-Cl)(2)(10)] (24), and the face-to-face bimetallic complexes [Rh(CO)Cl(4)](2) (17), [Rh(CO)Cl(10)](2) (19), and [Rh(CO)Cl(13)](2) (20) were confirmed by X-ray crystallography. Ligands 4, 7, 10, 13, 16, and SPANphos were tested in rhodium catalyzed methanol carbonylation at 150 degrees C and 22 bar of CO gas, showing high activities under catalytic conditions.