Various aryl and heteroaryl monomers for polysiloxane materials are finally accessible by intermolecular dehydrogenative C-H silylation between commercial (hetero)arenes and the industry-relevant triethoxysilane. The development of well-defined rhodium catalysts enables the silylation of triethoxysilane, which is known for poor reactivity in this silylation and prone to undergo the redistribution side reaction. For the silylation of electronically unactivated arenes, portionwise addition of the silane is necessary to ensure a high efficiency. Mechanistic investigation including computational study led to the isolation of two important catalytic intermediates and their dynamic interconversion, which provide mechanistic insight into the importance of portionwise addition and the intrinsic difference between arenes and heteroarenes in the silylation. In addition to their monomer roles, (hetero)aryl triethoxysilanes can be broadly utilized as versatile intermediates or coupling agents in chemical synthesis.

Advances in genome sequencing and bioinformatics methods have identified a myriad of biosynthetic gene clusters (BGCs) encoding uncharacterized molecules. By mining genomes for BGCs containing a prevalent peptide-binding domain used for the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), we uncovered a new compound class involving modifications installed by a cytochrome P450, a multinuclear iron-dependent non-heme oxidative enzyme (MNIO, formerly DUF692), a cobalamin- and radical S-adenosyl-l-methionine-dependent enzyme (B12-rSAM), and a methyltransferase. All enzymes were functionally expressed in Burkholderia sp. FERM BP-3421. Structural characterization demonstrated that the P450 enzyme catalyzed the formation of a biaryl C-C cross-link between two Tyr residues with the B12-rSAM generating β-methyltyrosine. The MNIO transformed a C-terminal Asp residue into aminopyruvic acid, while the methyltransferase acted on the β-carbon of this α-keto acid. Exciton-coupled circular dichroism spectroscopy and microcrystal electron diffraction (MicroED) were used to elucidate the stereochemical configuration of the atropisomer formed upon biaryl cross-linking. To the best of our knowledge, the MNIO featured in this pathway is the first to modify a residue other than Cys. This study underscores the utility of genome mining to isolate new macrocyclic RiPPs biosynthesized via previously undiscovered enzyme chemistry.

Advances in genome sequencing and bioinformatics methods have identified a myriad of biosynthetic gene clusters (BGCs) encoding uncharacterized molecules. By mining genomes for BGCs containing a prevalent peptide-binding domain used for the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), we uncovered a new class involving modifications installed by a cytochrome P450, a multi-nuclear iron-dependent non-heme oxidative enzyme (MNIO, formerly DUF692), a cobalamin- and radical

Control of polymorphic behavior is crucial for designing functional organic semiconductor devices as even a slight structural difference may translate to dramatically different electronic properties. One route to controlling structure is through stimulus-induced polymorph transitions, which allows for switching those electronic properties. However, despite advances in predicting crystal structures, the molecular design characteristics governing the polymorphic transition mechanism remains unknown. Here, we systematically investigate a series of n-type organic semiconductor molecules based on 2-dimensional quinoidal terthiophene with varying alkyl side chain lengths to modulate two distinct polymorph transitions, one cooperative martensitic transition and the other non-cooperative nucleation and growth transition. In the three molecular systems, we observe that shortening the alkyl chain past a critical length suppresses the cooperative polymorph transition by limiting the alkyl chain conformation change. On the other hand, the nucleation and growth transition temperature increases as the side chain length decreases, possibly driven by the increase in the melting point of the alkyl chains. We also found that tuning the alkyl chain length modulates the associated quinoidal to aromatic biradical switching that drives the nucleation and growth transition, suggesting a synergy between the crystal structure and electronic structure. Ultimately depending on the exact mechanism of the polymorph transition, adjusting the alkyl chain length may lead to tuning of the polymorph transition temperature or suppression of the transition altogether. This offers a potential molecular design rule to target a particular transition mechanism based on the desired behavior for the system.

Fully automated synthetic chemistry would substantially change the field by providing broad on-demand access to small molecules. However, the reactions that can be run autonomously are still limited. Automating the stereospecific assembly of C sp 3 –C bonds would expand access to many important types of functional organic molecules 1 . Previously, methyliminodiacetic acid (MIDA) boronates were used to orchestrate the formation of C sp 2 –C sp 2 bonds and were effective building blocks for automating the synthesis of many small molecules 2 , but they are incompatible with stereospecific C sp 3 –C sp 2 and C sp 3 –C sp 3 bond-forming reactions 3 – 10 . Here we report that hyperconjugative and steric tuning provide a new class of tetramethyl N -methyliminodiacetic acid (TIDA) boronates that are stable to these conditions. Charge density analysis 11 – 13 revealed that redistribution of electron density increases covalency of the N–B bond and thereby attenuates its hydrolysis. Complementary steric shielding of carbonyl π-faces decreases reactivity towards nucleophilic reagents. The unique features of the iminodiacetic acid cage 2 , which are essential for generalized automated synthesis, are retained by TIDA boronates. This enabled C sp 3 boronate building blocks to be assembled using automated synthesis, including the preparation of natural products through automated stereospecific C sp 3 –C sp 2 and C sp 3 –C sp 3 bond formation. These findings will enable increasingly complex C sp 3 -rich small molecules to be accessed via automated assembly.

The synthesis and characterization of the conjugated macrocycle trioxazolo[23]metacyclophane, C27H15N3O3 (M), is reported. The macrocycle was synthesized in three steps by the multicomponent van Leusen reaction and consists of meta-linked phenylenes connected through positions 4 and 5 of an oxazole heterocyclic ring. The molecular structure was investigated by NMR spectroscopy, mass spectrometry, gel permeation chromatography (GPC), and single-crystal X-ray crystallography. X-ray diffraction (XRD) analysis shows that M possesses a twisted saddle-like shape and interacts with nearby molecules by various π-π interactions. Absorption and emission spectroscopy and density functional theory (DFT) calculations were further used to study the electronic properties of M.

Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulky N-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promoting cis C=O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulky N-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures.

Active site hydrogen-bond (H-bond) networks represent a key component by which metalloenzymes control the formation and deployment of high-valent transition metal-oxo intermediates. We report a series of dinuclear cobalt complexes that serve as structural models for the nonheme diiron enzyme family and feature a Co2(μ-OH)2 diamond core stabilized by intramolecular H-bond interactions. We define the conditions required for the kinetically controlled synthesis of these complexes: [Co2(μ-OH)2(μ-OAc)(κ1-OAc)2(pyR)4][PF6] (1R), where OAc = acetate and pyR = pyridine with para-substituent R, and we describe a homologous series of 1R in which the para-R substituent on pyridine is modulated. The solid state X-ray diffraction (XRD) structures of 1R are similar across the series, but in solution, their 1H NMR spectra reveal a linear free energy relationship (LFER) where, as R becomes increasingly electron-withdrawing, the intramolecular H-bond interaction between bridging μ-OH and κ1-acetate ligands results in increasingly "oxo-like" μ-OH bridges. Deprotonation of the bridging μ-OH results in the quantitative conversion to corresponding cubane complexes: [Co4(μ-O)4(μ3-OAc)4(pyR)4] (2R), which represent the thermodynamic sink of self-assembly. These reactions are unusually slow for rate-limiting deprotonation events, but rapid-mixing experiments reveal a 6000-fold rate acceleration on going from R = OMe to R = CN. These results suggest that we can tune reactivity by modulating the μ-OH pKa in the presence of intramolecular H-bond interactions to maintain stability as the octahedral d6 centers become increasingly acidic. Nature may similarly employ dynamic carboxylate-mediated H-bond interactions to control the reactivity of acidic transition metal-oxo intermediates.

This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (S N Ar) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1 H- 1 H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C–H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.

One of the more active areas in bioorganometallic chemistry is the preparation and reactivity studies of active site mimics of the [NiFe]-hydrogenases. One area of particular recent progress involves reactions that interconvert Ni(μ-X)Fe centers for X = OH, H, CO, as described by Song et al. Such reactions illustrate new ways to access intermediates related to the Ni-R and Ni-SI states of the enzyme. Most models are derivatives of the type (diphosphine)Ni(SR)2Fe(CO)3-n(PR'3)n. In recent work, the methodology has been generalized to include FeII(diphosphine) derivatives of Ni(N2S2), where N2S22- is the tetradentate diamine-dithiolate (CH2N(CH3)CH2CH2S-)2. Indeed, models based on Ni(N2S2) have proven valuable, but these studies also highlight challenges in working with heterobimetallic complexes, specifically the tendency of some such Ni-Fe complexes to convert to homometalliic Ni-Ni derivatives. This kind of problem is not readily detected by X-ray crystallography. With this caution in mind, we argue that one series of complexes recently described in this journal are almost certainly misassigned.

Polymorphism has emerged as an important design consideration in organic semiconductors (OSCs). Previously, in many OSCs, even small changes in molecular stacking can cause drastic changes to the optical and electronic properties. However, investigation into n-type semiconductors has significantly lagged behind their p-type counterparts. In this work, we present the prolific polymorphism of 2-dimensional quinoidal terthiophene (2DQTT-o-B) and systematically investigate each of 5 polymorphs, 3 of which have been previously unreported. Grazing incidence X-ray diffraction provided a key method to understanding the structure of each polymorph. Via the polymorphic transitions mapped, we tuned the electron mobility by 5 orders of magnitude, from 5.63 X 10(-5) to 0.22 cm(2) V-1 s(-1). These were accompanied by modifications to the optical properties, namely we observed substantial differences in the refractive index noted by intensity differences under polarized optical microscopy and a large shift in optical band gap from 1.18 eV up to 1.40 eV. Finally, we suggest that changes to these properties may be related to the unique quinoidal to aromatic transition observed in quinoidal molecules.

In order to further understand the role of the secondary coordination sphere in biomimetic systems, a series of cobalt(II) and iron(II) complexes bearing the non-heme bis(5-cyclohexyliminopyrrol-2-ylmethyl)-2-pyridylmethylamine (N-Py(pi(Cy))(2)) ligand were synthesized. This platform, based on the tris(5-cyclohexylimino-pyrrol-2-ylmethyl)amine (N(pi(Cy))(3)) platform, reduces the number of possible hydrogen-bonding interactions from three (in N(pi(Cy))(3)) to two, while maintaining the ability of the ligand to datively coordinate to a metal center. The secondary coordination spheres of the family of dative and anionic cobalt(II) and iron(II) complexes were characterized in the solid-state using X-ray crystallography and IR spectroscopy. Moreover, oxidation of an iron(II) complex was explored to compare its reactivity to that of the analogous iron(II) complex of the N(pi(Cy))(3)platform.

We describe the synthesis and characterization of three platinum(II) omega-alkenyl complexes of stoichiometry Pt-[CH2CMe2(CH2)(2)CH=CH2](2) where x is 0, 1, or 2, as well as some related platinum(II) compounds formed as byproducts during their synthesis. The omega-alkenyl ligands in all three complexes, cis-bis(eta(1),eta(2)-2,2-dimethylbut-3-en-1-yl)platinum (2), cis-bis(eta(1),eta(2)-2,2-dimethylpent-4-en-1-ypplatinum (3), and cis-bis(eta(1),eta(2)-2,2-dimethylhex-5-en-1-ypplatinum (4), bind to Pt by means of a Pt-alkyl sigma bond at one end of the ligand chain and a Pt-olefin pi interaction at the other; the olefins reversibly decomplex from the Pt centers in solution. The good volatility of 3 (10 mTorr at 20 degrees C), its ability to be stored for long periods without decomposition, and its stability toward air and moisture make it an attractive platinum chemical vapor deposition (CVD) precursor. CVD of thin films from 3 shows no nucleation delay on several different substrates (SiO2/Si, Al2O3, and VN) and gives films that are unusually smooth. At 330 degrees C in the absence of a reactive gas, the precursor deposits platinum containing 50% carbon, but in the presence of a remote oxygen plasma, the amount of carbon is reduced to below the Rutherford backscattering spectroscopy (RBS) detection limit without affecting the film smoothness. Under hot wall CVD conditions at 250 degrees C in the absence of a co-reactant, 72% of the carbon atoms in 3 are released as hydrogenated products (largely 4,4-dimethylpentenes), 22% are released as dehydrogenated products (all of which are the result of skeletal rearrangements), and 6% remain in the film. Some conclusions about the CVD mechanism are drawn from this product distribution.

We describe the first crystallographically characterized example of a nonconjugated olefin bound in a simple dihapto fashion to a lithium center, as part of a study of two alkyllithium compounds that contain C=C double bonds at the alkyl chain terminus: (2,2-dimethylbut-3-en-1-yl)lithium (1) and the related pentenyl compound (2,2-dimethylpent-4-en-1-yl)lithium (2). The Liolefin interactions in the crystal structure of 2 serve as a model for those proposed to be present in the [RLi...olefin] intermediate in olefin carbolithiation reactions. As seen in other systems, the Li-olefin interaction is correlated with deshielding of the H-1 NMR resonances of the olefinic hydrogen atoms. DOSY and NOE measurements show that 1 and 2 remain tetrameric in cyclohexane and that the lithium-olefin interactions persist in solution. Addition of a Lewis base such as THF to these ?-alkenyllithium species has two effects: the THF displaces the lithium-olefin interactions while accelerating the rate of carbolithiation. A deuteration experiment shows that compound 2 undergoes reversible carbolithiation to the corresponding cyclobutylmethyllithium species in the presence of Lewis bases, but this transformation is thermodynamically uphill owing to ring strain. In comparison, the longer chain hexenyl species (2,2-dimethylhex-5-en-1-yl)lithium is thermodynamically unstable with respect to the intramolecular carbolithiation product [(3,3-dimethylcyclopentyl)methyl]lithium (3). We suggest that rate-determining step in carbolithiation reactions may not always be formation of the C-C bond, as is often assumed, but in some cases may be formation of the lithium-olefin complex; the coordination of the olefin to lithium may occur in a concerted fashion with disaggregation of lithium clusters. Finally, we point out that activation enthalpies can be obtained solely from NMR line shapes above the coalescence point.

The unit cell defines the smallest building block of the crystalline structure such that when translation symmetry is applied in a, b and c lattice directions the whole of the crystal can be built.Disorder occurs when atoms or molecules are shifted rotated or occupationally absent as compared to their neighbors within the unit cell in such a way that translational symmetry in the 3 lattice directions is ruined.When these shifts are not random, but instead have an ordered periodicity that can be defined by an atomic modulation function we observe diffraction in reciprocal space.This diffraction appears as a projection on the 3 reciprocal lattice directions that does not have the same periodicity as the basic unit cell.

We report the single-crystal growth and characterization of a new hexagonal phase, Cu_0.82Mn_1.18As, in the Cu-Mn-As system. This compound contains the same square-pyramidal MnAs_5 units as the tetragonal and orthorhombic polymorphs of CuMnAs. Calorimetry, magnetometry, and neutron diffraction measurements reveal antiferromagnetic ordering at 270 K. The magnetic structure consists of a triangular arrangement of spins in the ab plane. Hexagonal Cu_0.82Mn_1.18As shows resistivity that varies only weakly from 5 K to 300 K, and is many times higher than tetragonal CuMnAs, indicative of a strongly-scattering metal. First-principles calculations confirm the metallic band structure with a small density of states at the Fermi energy. The neutron-refined magnetic ground state is close to the computationally-determined minimum energy configuration. This compound should serve as a clear control when disentangling the effects of current-driven Néel switching of metallic antiferromagnets since it exhibits in-plane spins but the magnetic ordering does not break degeneracy along the a and b directions, unlike tetragonal CuMnAs.

Efforts to quantitatively reduce CfIII → CfII in solution as well as studies of its cyclic voltammetry have been hindered by its scarcity, significant challenges associated with manipulating an unusually intense γ emitter, small reaction scales, the need for nonaqueous solvents, and its radiolytic effects on ligands and solvents. In an effort to overcome these impediments, we report on the stabilization of CfII by encapsulation in 2.2.2-cryptand and comparisons with the readily reducible lanthanides, Sm3+, Eu3+, and Yb3+. Cyclic voltammetry measurements suggest that CfIII/II displays electrochemical behavior with characteristics of both SmIII/II and YbIII/II. The °E1/2 values of -1.525 and -1.660 V (vs Fc/Fc+ in tetrahydrofuran (THF)) for [Cf(2.2.2-crypt)]3+/2+ and [Sm(2.2.2-crypt)]3+/2+, respectively, are similar. However, the ΔE values upon complexation by 2.2.2-cryptand for CfIII/II more closely parallels YbIII/II with postencapsulation shifts of 705 and 715 mV, respectively, whereas the shift of SmIII/II (520 mV) mirrors that of EuIII/II (524 mV). This suggests more structural similarities between CfII and YbII in solution than with SmII that likely originates from more similar ionic radii and local coordination environments, a supposition that is corroborated by crystallographic and extended X-ray absorption fine structure measurements from other systems. Competitive-ion binding experiments between EuIII/II, SmIII/II, and YbIII/II were also performed and show less favorable binding by YbIII/II. Connectivity structures of [Ln(2.2.2-cryptand)(THF)][BPh4]2 (Ln = EuII, SmII) are reported to show the important role that THF plays in these redox reactions.