Rhodium‐Catalyzed Enantioselective Intramolecular CH Silylation for the Syntheses of Planar‐Chiral Metallocene Siloles

Reported herein is the rhodium‐catalyzed enantioselective C? H bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)‐TMS‐Segphos, the reactions took place under very mild conditions to afford metallocene‐fused siloles in good to excellent yields and with ee values of up to 97 %. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C? H silylations.     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Regulating Molecular Recognition with C‐Shaped Strips Attained by Chirality‐Assisted Synthesis

Chirality‐assisted synthesis (CAS) is a general approach to control the shapes of large molecular strips. CAS is based on enantiomerically pure building blocks that are designed to strictly couple in a single geometric orientation. Fully shape‐persistent structures can thus be created, even in the form of linear chains. With CAS, selective recognition between large host and guest molecules can reliably be designed de novo. To demonstrate this concept, three C‐shaped strips that can embrace a pillar[5]arene macrocycle were synthesized. The pillar[5]arene bound to the strips was a better host for electron‐deficient guests than the free macrocycle. Experimental and computational evidence is provided for these unique cooperative interactions to illustrate how CAS could open the door towards the precise positioning of functional groups for regulated supramolecular recognition and catalysis.     

Surface-enhanced Raman spectroscopy based on conical holed enhancing substrates

In this contribution, surface-enhanced Raman spectroscopy (SERS) based on conical holed glass substrates deposited with silver colloids was reported for the first time. It combines the advantages of both dry SERS assays based on plane films deposited with silver colloids and wet SERS assays utilizing cuvettes or capillary tubes. Compared with plane glass substrates deposited with silver colloids, the conical holed glass substrates deposited with silver colloids exhibited five-to ten-folds of increase in the rate of signal enhancement, due to the internal multiple reflections of both the excitation laser beam and the Raman scattering photons within conical holes. The application of conical holed glass substrates could also yield significantly stronger and more reproducible SERS signals than SERS assays utilizing capillary tubes to sample the mixture of silver colloids and the solution of the analyte of interest. The conical holed glass substrates in combination with the multiplicative effects model for surface-enhanced Raman spectroscopy (MEM_SERS) achieved quite sensitive and precise quantification of 6-mercaptopurine in complex plasma samples with an average relative prediction error of about 4% and a limit of detection of about 0.02 μM using a portable i-Raman 785H spectrometer. It is reasonable to expect that SERS technique based on conical holed enhancing substrates in combination with MEM_SERS model can be developed and extended to other application areas such as drug detection, environmental monitoring, and clinic analysis, etc.     

Two CdII/CoII‐Imidazolate Coordination Polymers: Syntheses,Crystal Structures,Stabilities, and Luminescent/Magnetic Properties

Cadmium(II) based 2D coordination polymer [Cd(L1)₂(DMF)₂] ( 1 ) (L1 = 4,5‐dicyano‐2‐methylimidazolate, DMF = N,N′‐dimethylformamide) and 2D cobalt(II)‐imidazolate framework [Co(L3)₄] ( 2 ) (L3 = 4,5‐diamide‐2‐ethoxyimidazolate) were synthesized under solvothermal reaction conditions. The materials were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction measurement (PXRD) and single‐crystal X‐ray diffraction. Compound 1 has hexacoordinate Cd^II ions and forms a zigzag chain‐like coordination polymer structure, whereas compound 2 exhibits a 2D square grid type structure. The thermal stability analysis reveals that 2 showed an exceptional thermal stability up to 360 °C. Also, 2 maintained its fully crystalline integrity in boiling water as confirmed by PXRD. The solid state luminescent property of 1 was not observed at room temperature. Compound 2 showed an independent high spin central Co^II atom.     

Syntheses,Crystal Structures,and Properties of the Isotypic Pair [Cr(H2O)6]2[B12H12]3·15H2O and [In(H2O)6]2[B12H12]3·15H2O

Single crystals of [Cr(H₂O)₆]₂[B₁₂H₁₂]₃ · 15H₂O and [In(H₂O)₆]₂[B₁₂H₁₂]₃ · 15H₂O were obtained by reactions of aqueous solutions of the acid (H₃O)₂[B₁₂H₁₂] with chromium(III) hydroxide and indium metal shot, respectively. The title compounds crystallize isotypically in the trigonal system with space group R$\bar{3}$ c (a = 1157.62(3), c = 6730.48(9) pm for the chromium, a = 1171.71(3), c = 6740.04(9) pm for the indium compound, Z = 6). The arrangement of the quasi‐icosahedral [B₁₂H₁₂]^2– dianions can be considered as stacking of two times nine layers with the sequence …ABCCABBCA… and the metal trications arrange in a cubic closest packed …abc… stacking sequence. The metal trications are octahedrally coordinated by six water molecules of hydration, while another fifteen H₂O molecules fill up the structures as zeolitic crystal water or second‐sphere hydrating species. Between these free and the metal‐bonded water molecules, bridging hydrogen bonds are found. Furthermore, there is also evidence of hydrogen bonding between the anionic [B₁₂H₁₂]^2– clusters and the free zeolitic water molecules according to B–H^δ– ··· ^δ+H–O interactions. Vibrational spectroscopy studies prove the presence of these hydrogen bonds and also show slight distortions of the dodecahydro‐closo‐dodecaborate anions from their ideal icosahedral symmetry (I_h). Thermal decomposition studies for the example of [Cr(H₂O)₆]₂[B₁₂H₁₂]₃ · 15H₂O gave no hints for just a simple multi‐stepwise dehydration process.     

The Syntheses,Structures, and Magnetic Properties of Four 2D Lanthanide(III)‐naphthalenedicarboxylic Complexes

Four Ln‐NDC coordination polymers [Ln(NDC)(HNDC)(H₂O)] (Ln = La ( 1 ), Pr ( 2 ), Nd ( 3 ), Sm ( 4 ), H₂NDC = 1,4‐naphthalenedicarboxylic acid) were hydrothermally synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single‐crystal X‐ray diffraction. Compounds 1 – 4 are isomorphous, and their structures display a layer constructed from a Ln‐organic chain and NDC^2– ligand, in which the H₂NDC ligands adopt two different acidity‐dependent types and coordination modes: HNDC^1– with μ‐η¹:η¹ and NDC^2– with μ‐η¹:η²:η¹:η². The 3D supramolecular networks of 1 – 4 are mainly controlled by hydrogen bonds interactions. The magnetic susceptibilities of complexes 2 – 4 reveal overall antiferromagnetic interactions between the Ln^III ions. In addition, thermogravimetric analysis of compound 2 is described.     

Two Coordination Polymers based on 2‐Ethyl‐1H‐imidazole‐4,5‐dicarboxylic Acid and 1,3‐Bis(4‐pyridyl)propane: Synthesis,Crystal Structures,and Photoluminescent Properties

Two coordination polymers, [Cd(Heidc)(bpp)]_n ( 1 ) and [Zn₃ (eidc)₂(bpp)(H₂O)₂] · 2H₂O}_n ( 2 ) (H₃eidc = 2‐ethyl‐4,5‐imidazole dicarboxylic acid, bpp = 1,3‐bis(4‐pyridyl)propane) were hydrothermally synthesized and characterized by elemental analysis, IR, spectroscopy single‐crystal X‐ray diffraction, and thermogravimetric analyses. Compound 1 features a 2D layer formed by C–H ··· π stacking interactions between adjacent chains, whereas compound 2 shows a 3D (8³)₂(8⁵.10)‐tfc framework constructed of the 2D (6,3) layer. The result demonstrates that the central metal atoms play a key role in governing the coordination motifs. Moreover, solid‐state properties such as thermal stabilities and photoluminescence of 1 and 2 were also investigated.     

Four Metal Complexes Based on Bulky Imidazole Ligands: Solvothermal Syntheses,Crystal Structures,and Fluorescence Properties

In order to explore the influences of (de‐)protonation of the imidazole ring on the structural diversity of the resulting complexes, the imidazole‐based ligands 4, 5‐diphenylimidazole (Hdpi) and 1H‐phenanthro[9, 10‐d]imidazole (Hpi) were utilized as bulky building blocks to construct four complexes by solvothermal reactions, i.e. [Ag(Hdpi)₂](NO₃) · (H₂O) ( 1 ), [Cu(dpi)]_∞ ( 2 ), [Cu(Hpi)(NO₃)]_∞ ( 3 ), and [(H₂pi)(NO₃)] · H₂O ( 4 ). In complex 1 , two Hdpi ligands adopt a monodentate pattern and coordinate with one Ag^I ion to form a mononuclear unit, which is further connected by hydrogen bonds into a 1D supramolecular helix. The deprotonated dpi ligand of 2 acts in bidentate mode, and bridges Cu^I ions to afford a 1D chain. In 3 , the NO₃^– ion, acts as a monodentate bridging ligand and joins Cu^I ions to generate a 1D chain. The Hpi ligand employs a monodentate mode to bond with Cu^I ions of the 1D chain. 4 is protonated and two H₂pi nitrogen atoms are free of coordination. Interestingly, hydrogen bonds among the NO₃^– ion, the H₂pi ligand, and the water molecule yield a macro ring R⁴₄(14). The resulting structural diversity reveals that the (de‐)protonation of imidazole ring directly steers the coordination number of ligand, and thus causes a significant effect on the structure, especially the dimensionality. Furthermore, the solid‐state fluorescence properties of the free ligands and compounds 1 – 4 were studied at room temperature.