Bulky Adamantyl Research Articles

Adamantylated Calix[4]arenes Bearing CuAAC-Ready 2-Azidoethyl or Propargyl Functionalities

1,3-Alternate calix[4]arenes were prepared, having bulky adamantyl groups in the p-positions of all four aromatic units of the macrocycles and pairs of propargyl or 2-azidoethyl groups alternating with n-propyl groups at the phenol oxygen atoms. The step-wise syntheses were carried out through a selective distal alkylation of the parent p-adamantylcalix[4]arene with propargyl bromide or 1,2-dibromoethane, resulting in calix[4]arenes bearing pairs of propargyl or 2-bromoethyl groups at their narrow rims. The bromine atoms were replaced by azide groups, and then both calix[4]arene diethers were exhaustively alkylated at the remaining OH-groups with 1-iodopropane under stereoselective conditions to fix the macrocycles in an 1,3-alternate shape. The structures of the prepared p-adamantylcalix[4]arenes were confirmed by NMR and HRMS data, and, for the 1,3-alternate dipropargyl ether, the X-ray diffraction data were also collected. Preliminary data on the reactivity of the prepared calixarenes under the CuAAC conditions suggested a strong steric hampering created by the adamantane units nearby the reacting alkyne or azide groups that affected the outcome of the two-fold cycloaddition involving the calixarene bis(azides) or bis(alkynes) as complementary partners.

Palladium(II) NCS‐Pincer Complexes Mediated Regioselective Cross Dehydrogenative Alkenation of 2‐Arylthiophenes

AbstractIn this report, we have synthesized two new NCS pincer ligands by the Schiff base reaction of 3‐((phenylthio)methoxy)benzaldehyde (P) with alkyl amines (tbutylamine (L1) and 1‐adamantylamine (L2)). The palladium pincer complexes (tbutylamine=C1 and 1‐adamantylamine=C2) of these ligands were synthesized by their reaction with PdCl2(CH3CN)2 precursor. The newly synthesized ligands and complexes were characterized using various analytical and spectroscopic techniques such as 1H, 13C{1H} Nuclear Magnetic Resonance (NMR), Ultraviolet–visible (UV‐Visible), Fourier Transform Infrared (FTIR) Spectroscopy, and High‐Resolution Mass Spectrometry (HRMS). The structure of the ligand and its coordination mode with palladium precursor were studied with the help of single‐crystal X‐ray diffraction. The complexes showed distorted square planar geometry around the palladium center. The palladium pincer complexes were used as catalysts for the regioselective cross‐dehydrogenative alkenation of 2‐arylthiophene derivatives. The complex C2, where sterically bulky adamantyl ligand is part of the side arm showed a higher yield of alkenation reaction. Only 2.5 mol% catalyst loading was sufficient to achieve 74–95 % yields of desired products with excellent functional group tolerance under mild reaction conditions. The poisoning experiments (PPh3 and Hg) showed the homogeneous nature of the catalytic process. The plausible mechanism of the reaction was proposed based on the control experiments and time‐dependent HRMS studies.

Silica Immobilised Chloro- and Amido-Derivatives of Eremomycine as Chiral Stationary Phases for the Enantioseparation of Amino Acids by Reversed-Phase Liquid Chromatography.

Macrocyclic glycopeptide antibiotics immobilized on silica are one of the effective classes of stationary phases for chiral recognition and HPLC separation of a wide range of optically active compounds. Enantioselectivity primarily depends on the chemical structure of the chiral ligand, immobilization chemistry, and separation conditions. In the present work, three new chiral stationary phases (CSPs) based on macrocyclic antibiotic eremomycin were prepared and investigated for enantioseparation of amino acids. Two eremomycin derivatives, including simple non-substituted amide and bulky adamantyl amide, provided important information on the role of the carboxylic group in the eremomycin structure in the chiral recognition mechanism concerning amino acid optical isomers. One more CSP having a chlorine atom in the same position elucidates the role of the first aromatic ring in the eremomycin structure as a crucial point for chiral recognition. CSP with immobilized chloreremomycin was the most successful among the phases prepared in this work. It was additionally investigated under various separation conditions, including the type and content of the organic solvent in the eluent, the effects of different additives, and the concentration and pH of the buffer. Importantly, an efficient enantioselective separation of amino acids was achieved with pure water as the eluent.

Novel adamantane substituted polythiophenes as competitors to Poly(3-Hexylthiophene)

The investigation of poly(3-alkylthiophenes) (P3ATs) has gained great attention in the last decades. Here, we present the synthesis, experimental and theoretical study of the novel regioregular poly(3-adamantylmethylthiophene) (PMAT) and poly(3-adamantylethylthiophene) (PEAT) , characterised by a bulky adamantane side group. The prepared compounds are solution-processable in common organic solvents, possess excellent thermal stability up to 491 °C and have unique chemical endurance. The molecular ordering of the polymers was investigated by the GIWAXS technique, and PMAT was found to have the higher content of crystalline phase. The experimental absorption and fluorescence spectra of investigated polymers indicate a higher rigidity of the adamantane side group with respect to torsional rotation in solutions and in thin layers. Electrical measurements exhibit charge carrier mobilities comparable to poly(3-hexylthiophene) (P3HT) . In contrast to P3HT , adamantyl-substituted polymers show quasi-reversible reduction alongside the expected quasi-reversible oxidation, which in theory supports the ability to transport both types of electric charges. The newly synthetized regioregular adamantane substituted polythiophenes are serious competitors for a wide range of applications in electronics and optoelectronics. • Novel derivates of polythiophene, featuring the bulky adamantyl groups were synthesized. • These materials exhibit high thermal stability as well as electrical conductivity comparable to poly(3-hexylthiophene). • The materials absorb light in the 400 – 500 nm wavelength range, making them serious candidates for use in optoelectronics.

Design, Synthesis, and Application of Chiral Bicyclic Imidazole Catalysts.

Asymmetric organocatalysis has been considered to be an efficient and reliable strategy for the stereoselective preparation of optically active chemicals. In particular, chiral tertiary amines as Lewis base organocatalysts bearing core structures including quinuclidine, dimethylaminopyridine (DMAP), N-methylimidazole (NMI), amidine, etc. have provided new and powerful tools for various chemical transformations. However, due to the limitations in structural complexity, synthetic difficulty, low catalytic efficiency, and high cost, the industrial application of such catalysts is still far from being widely adopted. Therefore, the development of new chiral tertiary amine catalysts with higher activity and selectivity is greatly desired.In order to address the contradiction between activity and selectivity caused by the ortho group, a bicyclic imidazole structure bearing a relatively large bond angle ∠θ was designed as the skeleton of our new catalysts. 6,7-Dihydro-5H-pyrrolo[1,2-a]imidazole (abbreviated as DPI) and 5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (abbreviated as TIP) are two of the utilized skeletons. In addition to obtaining satisfactory catalytic activity, excellent enantioselectivity would also be expected because the stereocontrol R group is neither far nor close to the catalytic active site (sp2-N atom) and is adjustable. Based on this skeleton, a family of chiral bicyclic imidazole catalysts were easily prepared and successfully applied in several enantioselective reactions for the synthesis of a variety of valuable chiral compounds.6,7-Dihydro-5H-pyrrolo[1,2-a]imidazole (abbreviated as DPI) is the predominantly utilized skeleton. First, HO-DPI, the key intermediate of the designed chiral bicyclic imidazole catalysts, could be efficiently synthesized from imidazole and acrolein, then separated by kinetic resolution or optical resolution. Second, Alkoxy-DPI, the alkyloxy-substituted chiral bicyclic imidazole catalysts, were synthesized by a one-step alkylation from HO-DPI. This type of catalyst has been successfully applied in asymmetric Steglich rearrangement (C-acylation rearrangement of O-acylated azlactones), asymmetric phosphorylation of lactams, and a sequential four-step acylation reaction. Third, Acyloxy-DPI, the acyloxy-substituted chiral bicyclic imidazole catalysts, were synthesized with a one-step acetylative kinetic resolution from racemic HO-DPI or acylation from enantiopure HO-DPI. The catalyst AcO-DPI has been successfully applied in enantioselective Black rearrangement and in direct enantioselective C-acylation of 3-substituted benzofuran-2(3H)-ones and 2-oxindoles. Fourth, Alkyl-DPI was synthesized via a two-step reaction from racemic HO-DPI and separated easily by resolution. The catalyst Cy-DPI has been successfully applied in dynamic kinetic resolution of 3-hydroxyphthalides through enantioselective O-acylation. Cy-PDPI was synthesized through a Cu-catalyzed amidation from Cy-DPI and successfully applied in the kinetic resolution of secondary alcohols with good to excellent enantioselectivities. Finally, the carbamate type chiral bicyclic imidazole catalysts, Carbamate-DPI, were readily synthesized from HO-DPI, and the catalyst Ad-DPI bearing a bulky adamantyl group was successfully applied in the synthesis of the anti-COVID-19 drug remdesivir via asymmetric phosphorylation. Alongside our initial work, this Account also introduces four elegant studies by other groups concerning asymmetric phosphorylation utilizing chiral bicyclic imidazole catalysts.In summary, this Account focuses on the chiral bicyclic imidazole catalysts developed in our group and provides an overview on their design, synthesis, and application that will serve as inspiration for the exploration of new organocatalysts and related reactions.

Orange-red emissive Cu(I) complexes bearing Schiff base ligands: Synthesis, structures, and photophysical properties

Herein, the three novel copper (I) complexes bearing Schiff base ligands of the types [Cu(Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P1), [Cu(Methoxyl-Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P2), and [Cu(TriflMethyl-Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P3) (Phen-PyMethylene-Adam-Amine = ((5-phenylpyridin-2-yl)methylene)adamantan-1-amie, Methoxyl-Phen-PyMethylene-Adam-Amine = ((5-(4-methoxyphenyl)pyridin-2-yl)methylene)adamantan-1-amine, TriflMethyl-Phen-PyMethylene-Adam-Amine = ((5-(4-(trifluoromethyl)phenyl)pyridin-2-yl)methylene)adamantan-1-amine, POP=bis[2-diphenylphosphino]-phenyl)ether) have been prepared and investigated. Incorporation of the bulky adamantyl group into the complexes can enhance the stability of the complexes. The different electron-donating/withdrawing groups such as –H, –OCH3, and –CF3 substituents were functionalized onto the pyridine ring part of Schiff base ligands to tune the emission behavior of the resulting Schiff base Cu(I) complexes. All complexes exhibit the lowest energy metal-to-ligand charge transfer (MLCT) characters in 400–450 nm region showing a slight blue-shift of the absorption wavelengths in the order P3 > P1 > P2. Organe-red emissions in the region of 611-619 nm with photoluminescence quantum yields (PLQY) of 1.0–1.3% can be observed in the solid state. Additionally, the photophysical properties are also investigated theoretically using density functional theory (DFT) and time dependent DFT.

Reactions of Iso(thio)cyanates with Dialanes: Cycloaddition, Reductive Coupling, or Cleavage of the C═S or C═O Bond.

The dialanes [(dpp-Bian)Al-Al(dpp-Bian)] (1) and [(dpp-dad)Al(THF)-(THF)Al(dpp-dad)] (2) (dpp-Bian = 1,2-[(2,6-iPr2C6H3)NC]2C12H6, dpp-dad = [(2,6-iPr2C6H3)NC(CH3)]2) react with some isothiocyanates, isocyanates, and diphenylketene via [2 + 4] cycloaddition of the C═O or C═S bond across the C═C-N-Al fragment to afford complexes [L(X═C-Y)Al-Al(X═C-Y)L] with an intact Al-Al single bond (3, L = dpp-Bian, X = PhN, Y = O; 4, L = dpp-Bian, X = Ph2C, Y = O; 6, L = dpp-dad, X = BnN, Y = S; 7, L = dpp-dad, X = tBuN, Y = O; 8, L = dpp-dad, X = iPrN, Y = S; and 9, L = dpp-dad, X = CyN, Y = S). A mixed C═N and C═O mode cycloadduct, [(dpp-Bian)(TosN═C-O)Al-Al(TosN-C═O)(dpp-Bian)] 5, was obtained in the reaction of 1 with tosylisocyanate. Heating the solution of 3 resulted in a thermal transformation and a change of the cycloaddition mode from C═O to C═N to give the product [(dpp-Bian)(PhN-C═O)Al(O)Al(PhN-C═O)(dpp-Bian)] 10. The reduction of 7 and 8 with Na yielded the products [Na(THF)n]2[(dpp-dad-H)(X═C-Y)Al]2 (12, X = iPrN, Y = S, n = 2 and 13, X = tBuN, Y = O, n = 3) in which one of the methyl groups of the backbone of the initial dpp-dad ligand was dehydrogenated. When 2 was reacted with the bulky adamantyl isocyanate AdNCO, the C-C coupling of two substrates occurred to form 14 [(dpp-dad)Al(O═C-NAd)2Al(dpp-dad)] in which the coupled dianionic oxamide ligand bridged two Al atoms in a μ,η4-N,O/N,O mode. Moreover, in the presence of 2.0 equiv of Na metal, precursor 2 reacts with tBuNCS, p-TolylNCS, or Me3SiNCO, possibly through the reduced AlI intermediate, to yield the sulfur- or oxygen-bridged dimer [Na(solv)n]2[(dpp-dad)Al(μ-E)]2 (15, E = S, solv = THF, n = 3 and 16, E = O, solv = DME, n = 2) upon C═S or C═O bond cleavage. Dialane 1 reacts with dimethylsulfone to give a Lewis adduct [(dpp-Bian)(Me2SO2)Al]2 (17), which releases dimethylsulfone upon heating. The diamagnetic compounds 3-10 and 12-17 were characterized by NMR and IR spectroscopy. The molecular structures of 3-17 were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds and possible isomers have been examined by DFT calculations.

Highly Efficient Deep Blue Phosphorescent OLEDs Based on Tetradentate Pt(II) Complexes Containing Adamantyl Spacer Groups

AbstractTetradentate Pt(II) complexes are promising emitters for deep blue organic light‐emitting diodes (OLEDs) due to their emission energy and high photoluminescence efficiency. However, to obtain a pure blue color, spectral red‐shifts, and additional emission peaks at longer wavelengths, originating from strong intermolecular interactions between parallel Pt(II) complexes, must be avoided. Herein, a new class of deep‐blue emitting tetradentate Pt(II) complexes consisting of a non‐planar ligand and a bulky adamantyl group is reported. The six‐membered metallacycle structure renders the Pt(II) complex non‐planar. In addition, the bulky adamantyl groups increase intermolecular distances and decrease red‐shifts in the emission originating from strong dipole–dipole interactions. Therefore, these Pt(II) complexes exhibit little change in emission color with increasing dopant concentration. OLEDs incorporating these new Pt(II) complexes as emitters exhibit deep blue emission with a Commission International de L'Eclairage (CIE) y under 0.13 and a maximum external quantum efficiency of 22.6%, which is one of the highest observed for deep blue (CIE y < 0.15) phosphorescent OLEDs using Pt(II) complexes. These results provide a new approach for designing Pt(II) complexes for high efficiency deep blue OLEDs.

Synthesis of non-racemic dihydrofurans via Ni(II)-catalyzed asymmetric Michael addition

Abstract A highly efficient strategy for the enantio- and diastereoselective synthesis of 4,5-dihydrofuran derivatives was developed. Addition of carbonyl compounds which contain bulky adamantyl substituent and β-keto or phosphonate group to conjugated α-bromonitroolefins in the presence of a chiral Ni(II) complex gave corresponding non-racemic products of Michael reaction. These adducts were used for intramolecular cyclization leading to trans-4,5-dihydrofurans with two stereocenters. Resulting trans-4,5-dihydrofurans were obtained in good yields with moderate to high enantioselectivities (84–99% ee) and excellent diastereoselectivities (dr >99%).

Adamantane-containing poly(dialkyl fumarate)s with rigid chain structures

Four dialkyl fumarates containing bulky adamantyl ester groups, i.e., di(1-adamantyl) fumarate (1), bis(3,5-dimethyl-1-adamantyl) fumarate (2), 1-adamantyl isopropyl fumarate (3), and 3,5-dimethyl-1-adamantyl isopropyl fumarate (4), were polymerized to obtain poly(dialkyl fumarate)s (PDRFs) with rigid chain structures. We carried out the conventional radical polymerization of these adamantane-containing DRFs in the presence of a radical initiator either in toluene or in bulk at 80 or 60 °C. Reversible addition-fragmentation chain transfer (RAFT) polymerization was also performed using 1,1′-(1,2-ethanediyl) bis[2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate] and 2,2,2-trifluoroethyl 2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate as the chain transfer agents (CTAs). Triblock copolymers consisting of rigid and flexible segments were synthesized by the polymerization of 2-ethylhexyl acrylate, which was used as the second monomer, using the PDRFs as the macro-CTA containing trithiocarbonate groups at the chain ends. The excellent thermal stability of the adamantane-containing PDRFs was confirmed by thermogravimetric analysis in a nitrogen stream. The alignment of the rigid PDRF chains in the solid-state was revealed based on the appearance of a peak in the small angle regions of the X-ray diffraction profiles. We carried out the conventional radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization of di(1-adamantyl) fumarate, bis(3,5-dimethyl-1-adamantyl) fumarate, 1-adamantyl isopropyl fumarate, and 3,5-dimethyl-1-adamantyl isopropyl fumarate. Triblock copolymers consisting of rigid and flexible segments were synthesized by the RAFT polymerization of 2-ethylhexyl acrylate using poly(dialkyl fumarate)s as the macro-chain transfer agents. The excellent thermal stability of the adamantane-containing poly(dialkyl fumarate)s was confirmed by thermogravimetric analysis. The alignment of the rigid poly(dialkyl fumarate)s chains in the solid-state was revealed by X-ray diffraction.

Mechanistic Insights into the Reaction of N‐Propargylated Pyrrole‐ and Indole‐Carbaldehyde with Ammonia, Alkyl Amines, and Branched Amines: A Synthetic and Theoretical Investigation

The reaction of pyrrole‐ and indole‐carbaldehydes having a propargyl group attached to the nitrogen atom with various amines was studied. The reaction with ammonia formed pyrrolo[1,2‐a]pyrazine and pyrazino[1,2‐a]indole while the reaction with alkylamines such as methyl, ethyl, hexyl, and benzylamines formed the corresponding pyrazinone derivatives. Unexpectedly, the reaction with allylamine and propargylamine formed pyrazine derivatives in which the allyl and propargyl groups were removed from the molecule. On the other hand, the reaction of N‐propargylated pyrrole‐carbaldehyde formed indolizine derivatives upon reaction with sterically bulky adamantyl‐ and tert‐butylamines. To understand the main factors causing these differences in reactivity, the reaction mechanisms were studied by means of computational methods. Our calculations showed that bulky amines tend to attack the central carbon of allene formed by the isomerization of N‐propargyl functionality, while the attack on the carbonyl carbon by aliphatic amines is more profound.

Crystal Correlation Of Heterocyclic Imidazo[1,2-a]pyridine Analogues and Their Anticholinesterase Potential Evaluation

Imidazo[1,2-a]pyridine-based compounds are clinically important to the treatments of heart and circulatory failures, while many are under development for pharmaceutical uses. In this study, a series of imidazo[1,2-a]pyridine-based derivatives 2(a–o) were synthesized by reacting a-haloketones with 2-aminopyridines in a basic media at ambient temperature. Single crystal X-ray diffraction studies suggest that with low degree-of-freedom, the introduction of bulky adamantyl or electron-rich biphenyl moiety into the imidazopyridine derivatives will not affect its structural occupancy. Imidazo[1,2-a]pyridine-based derivatives with biphenyl side chain are potential AChE inhibitors. Compound 2h which bears a biphenyl side chain and methyl substituent at the position R4 of the imidazo[1,2-a]pyridine ring showed the strongest AChE inhibition with an IC50 value of 79 µM. However, imidazo[1,2-a]pyridine derivatives with phenyl side chain exhibit better BChE inhibition effect among the series. Compound 2j with 3,4-dichlorophenyl side chain and unsubstituted imidazo[1,2-a]pyridine ring appears to be the strongest BChE inhibitor with an IC50 value of 65 µM and good selectivity. The inhibitory effects of active compounds were further confirmed by computational molecular docking studies. The results unveiled that peripheral anionic sites of AChE and acyl pocket of BChE were the predominated binding sites for the subjected inhibitors.

Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the...

Living Anionic Polymerization of 1‐Adamantyl 4‐vinylphenyl ketone

The anionic polymerization of 1‐adamantyl 4‐vinylphenyl ketone (1), a styrene derivative carrying an electrophilic carbonyl group, is carried out in tetrahydrofuran (THF). Although no polymerization of 1 occurs with sec‐BuLi at −78 °C for 48 h, a polymeric product of 1 is obtained with diphenylmethyllithium in 10% yield under similar conditions. The resulting poly(1) has a very broad molar‐mass dispersity (Đ M = M w/M n = 1.72) and a molecular weight higher than the calculated value based on the molar ratio of the monomer and initiator and the conversion. On the other hand, the polymerization of 1 with diphenylmethylpotassium or diphenylmethylcesium quantitatively proceeds in THF at −78 °C within 48 h to form the polymers with predicted molecular weights and narrow molecular weight distributions (M w/M n < 1.1). The stability of the propagating carbanion derived from 1 is demonstrated by the quantitative efficiency of the postpolymerization (sequential monomer addition). The reaction of the adamantyl ketone moieties of poly(1) with methylmagnesium iodide quantitatively proceeds in THF/diethyl ether at room temperature, indicating the high electrophilicity of ketone groups. The resulting poly(1) has a high glass transition temperature at 193 °C, indicating the effect of the bulky adamantyl substituent. image

Triple adamantane expands the boundary of phosphine ligands

Phosphine ligands have played a supporting role in the success of many a transition-metal catalyst, helping to tune their activity, selectivity, and stability. Among the examples, tri(tert-butyl)phosphine has long been characterized as the most electron-releasing alkylphosphine ligand for metals. Liye Chen, Peng Ren, and Brad P. Carrow of Princeton University have succeeded in raising the bar with tri(1-adamantyl)phosphine, PAd3, a ligand that now provides a bridge between trialkylphosphines and the stronger electron-releasing N-heterocyclic carbene ligands (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b03215). Adamantane is an unusual rigid C10 tricyclic alkane. Researchers have made phosphine ligands containing two adamantyl groups before, and adamantane is occasionally used as a bulky substituent for N-heterocyclic carbenes. But installing a third bulky adamantyl group on phosphorus has been a challenge, one that researchers took on with complex approaches. Carrow’s group pulled it off with a simple subs...

Internal dynamics and guest binding of a sterically overcrowded host.

Substituent control in self-assembled host systems allows for a fine-tuning of structure, dynamics and guest preference. Flat banana-shaped ligands L1 assemble with Pd(ii) cations into the interpenetrated coordination cage dimer [3BF4@Pd4L18], capable of sequential guest uptake. In contrast, the introduction of bulky adamantyl groups in ligand L2 prevents dimerization and results in the clean formation of monomeric cage species [Pd2L24]. Owing to steric crowding, the adamantyl substituent is considerably bent sideways with respect to the ligand backbone, and is rapidly flipping between both faces of the free ligand giving rise to two energetically degenerate conformers. Surprisingly, the flipping is preserved in the cage, albeit at a lower rate due to entropic reasons. Despite the very dense packing within the self-assembled structure, the cage is able to encapsulate a series of bis-anionic guests in an induced-fit fashion. Electronic structure calculations revealed a substantial contribution from dispersion interactions between the guest and the surrounding adamantyl groups that stabilize the host-guest complex. Guest exchange kinetics were quantified and the influence that encapsulated guests imparted on the ligand flipping dynamics was examined by a series of 2D NMR experiments. Four synchrotron X-ray structures of the cage and its host-guest complexes are presented, allowing for unprecedented insight into the host-guest interactions of a sterically overcrowded host and its guest-induced distortion.

Living Anionic Polymerization of N-(1-Adamantyl)-N-4-vinylbenzylideneamine and N-(2-Adamantyl)-N-4-vinylbenzylideneamine: Effects of Adamantyl Groups on Polymerization Behaviors and Thermal Properties

The anionic polymerization of N-(1-adamantyl)-N-4-vinylbenzylideneamine (1) and N-(2-adamantyl)-N-4-vinylbenzylideneamine (2) was performed using various initiators, such as oligo(α-methylstyryl)dipotassium, potassium naphthalenide, diphenylmethylpotassium, and diphenylmethyllithium, in THF at −78 °C for 1 h to investigate the effects of adamantyl groups on the polymerization behaviors and thermal properties of the resulting polymers. The well-defined poly(1) and poly(2) with predictable molecular weights and narrow molecular weight distributions were successfully obtained, indicating that the bulky adamantyl groups effectively protected the carbon–nitrogen double bond (C═N) from the nucleophilic attack of the initiators and the propagating chain ends. The stability of the propagating chain end of poly(1) was confirmed by the quantitative efficiencies in the postpolymerization and the sequential copolymerization with tert-butyl methacrylate. A poly(4-formylstyrene) was quantitatively formed by the acidic ...

Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in PtII Phosphors

AbstractPhosphorescent PtII complexes featuring pincer luminophores of 2,6‐bis(1,2,4‐triazolyl)pyridine (H2L1) and 2,6‐bis(pyrazolyl)pyridine (H2L3) with a bulky adamantyl or tolyl substituent (H2L4) are systematically compared, and their structural features are correlated with their photophysical properties. The combination with 4‐amylpyridine (Py), triphenylphosphine (P) or benzimidazol‐2‐ylidene (N‐heterocyclic carbene, NHC) donors as monodentate ancillary ligands gave a series of highly luminescent triplet emitters with variable aggregation properties. The molecular structures of four of these complexes, namely, Pt‐L1‐P, Pt‐L1‐NHC, Pt‐L3‐P, and Pt‐L4‐P were garnered from single‐crystal X‐ray diffraction analysis. The coordination complexes displayed green phosphorescence in solution and in the solid state. In doped poly(methyl methacrylate) (PMMA) matrices, most of the complexes exhibited high phosphorescence quantum yields, which reached 59 % for Pt‐L3‐P. A comparative analysis between the spectroscopic data and the computed parameters derived from time‐dependent density functional theory (TD‐DFT) calculations suggests that the emission originates from metal‐perturbed ligand‐centered excited triplet states (3MP‐LC). The radiationless deactivation rate constants of the emissive states can be correlated with the aggregation properties derived from the substitution pattern at the tridentate luminophores and the ancillary ligands, whereas the radiative rate constants are determined by the electronic structures of the complexes. We found that PtII complexes containing pyrazolate donors showed an enhanced charge‐transfer character in the excited state, whereas bulky adamantyl moieties and triphenylphosphine ancillary ligands suppress bimolecular aggregation and quenching phenomena.

Helix-Sense-Selective Precipitation Polymerization of Achiral Monomer for Preparing Optically Active Helical Polymer Particles

Optically active polymer particles constitute a unique type of polymer particle. However, nearly all the particles of this kind so far reported in the literature were prepared from chiral monomers. On the other hand, helix-sense-selective polymerization (HSSP) techniques were majorly applied in solution polymerization systems for preparing helical polymers adopting predominant one-handed helicity. In the present study, we report the first HSSP in precipitation polymerization systems, by which optically active helical polymer particles were constructed from an achiral monomer. Achiral acetylenic monomer with bulky adamantyl group smoothly underwent helix-sense-selective precipitation polymerization (HSSPP) with (nbd)Rh+B–(C6H5)4 as catalyst in the presence of Boc-l- or Boc-d-alanine as chiral additive. The HSSPPs provided optically active polymer particles consisting of helical polymer forming predominantly one-handed screw sense. SEM images show that the resulting polymer particles were obtained in high y...

Bidentate NHC^pyrozolate ligands in luminescent platinum(II) complexes.

A bidentate C^N donor set derived from an N-heterocyclic carbene (NHC) precursor linked to a trifluoromethyl (CF3) functionalized pyrazole ring is described for the first time. The ligands have been employed to prepare four new phosphorescent complexes by the coordination of platinum(II) centres bearing cyclometalated phenyl-pyridine/triazole-pyridine chelates. The electronic and steric environments of these complexes were tuned through the incorporation of suitable substituents in the phenyl-pyridine/triazole-pyridine ligands, wherein the position of the phenyl-ring substituent (a CF3 group) also directs the selective adoption of either a trans or a cis configuration between the C(NHC) and the C(phenyl) donor atoms. Molecular structures obtained by X-ray diffraction for three of the complexes confirm a distorted square-planar configuration around the platinum centre, and DFT calculations show that the substituents have a significant influence on the energies of the frontier orbitals. Moreover, a platinum(II) complex featuring the new bidentate NHC^pyrazolate ligand and a bulky adamantyl functionalized pyridine-triazole luminophore was observed to be highly emissive and exhibiting a sky-blue luminescence (λ(Em) = 470 nm) with photoluminescence quantum yields as high as 50% in doped PMMA matrices. A complete photophysical investigation of all of the complexes in solution as well as in the solid state is herein reported.