Aromatic nitrogen scanning by ipso-selective nitrene internalization.

Nitrogen scanning in aryl fragments is a valuable aspect of the drug discovery process, but current strategies require time-intensive, parallel, bottom-up synthesis of each pyridyl isomer because of a lack of direct carbon-to-nitrogen (C-to-N) replacement reactions. We report a site-directable aryl C-to-N replacement reaction allowing unified access to various pyridine isomers through a nitrene-internalization process. In a two-step, one-pot procedure, aryl azides are first photochemically converted to 3H-azepines, which then undergo an oxidatively triggered C2-selective cheletropic carbon extrusion through a spirocyclic azanorcaradiene intermediate to afford the pyridine products. Because the ipso carbon of the aryl nitrene is excised from the molecule, the reaction proceeds regioselectively without perturbation of the remainder of the substrate. Applications are demonstrated in the abbreviated synthesis of a pyridyl derivative of estrone, as well as in a prototypical nitrogen scan.

Fast and programmable locomotion of hydrogel-metal hybrids under light and magnetic fields.

The design of soft matter in which internal fuels or an external energy input can generate locomotion and shape transformations observed in living organisms is a key challenge. Such materials could assist in productive functions that may range from robotics to smart management of chemical reactions and communication with cells. In this context, hydrated matter that can function in aqueous media would be of great interest. Here, we report the design of hydrogels containing a scaffold of high-aspect ratio ferromagnetic nanowires with nematic order dispersed in a polymer network that change shape in response to light and experience torques in rotating magnetic fields. The synergistic response enables fast walking motion of macroscopic objects in water on either flat or inclined surfaces and also guides delivery of cargo through rolling motion and light-driven shape changes. The theoretical description of the response to the external energy input allowed us to program specific trajectories of hydrogel objects that were verified experimentally.

Orbital energy mismatch engenders high-spin ground states in heterobimetallic complexes.

The spin state in heterobimetallic complexes heavily influences both reactivity and magnetism. Exerting control over spin states in main group-based heterobimetallics requires a different approach as the orbital interactions can differ substantially from that of classic coordination complexes. By deliberately engendering an energetic mismatch within the two metals in a bimetallic complex we can mimic the electronic structure of lanthanides. Towards this end, we report a new family of complexes, [Ph,MeTpMSnPh3] where M = Mn (3), Fe (4), Co (5), Ni (6), Zn (7), featuring unsupported bonding between a transition metal and Sn which represent an unusual high spin electronic structure. Analysis of the frontier orbitals reveal the desired orbital mismatch with Sn 5s/5p primarily interacting with 4s/4p M orbitals yielding localized, non-bonding d orbitals. This approach offers a mechanism to design and control spin states in bimetallic complexes.

Supramolecular Tessellations by a Rigid Naphthalene Diimide Triangle.

Tessellation of organic polygons though [π···π] and charge-transfer (CT) interactions offers a unique opportunity to construct supramolecular organic electronic materials with 2D topologies. Our approach to exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (NDI-Δ) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations. Utilization of nonhalogenated solvents, combined with careful tailoring of the concentrations, results in NDI-Δ self-assembling though [π···π] interactions into 2D honeycomb triangular and hexagonal tiling patterns. Cocrystallization of NDI-Δ with tetrathiafulvalene (TTF) leads systematically to the formation of 2D tessellations as a result of superstructure-directing CT interactions. Different solvents lead to different packing arrangements. Using MeCN, CHCl3, and CH2Cl2, we identified three sets of cocrystals, namely CT-A, CT-B, and CT-C, respectively. Solvent modulation plays a critical role in controlling not only the NDI-Δ:TTF stoichiometric ratios and the molecular arrangements in the crystal superstructures, but also prevents the inclusion of TTF guests inside the cavities of NDI-Δ. Confinement of TTF inside the NDI-Δ cavities in the CT-A superstructure enhances the CT character with the observation of a broad absorption band in the NIR region. In the CT-B superstructure, the CHCl3 lattice molecules establish a set of [Cl···Cl] and [Cl···S] intermolecular interactions, leading to the formation of a hexagonal grid of solvent in which NDI-Δ forms a triangular grid. In the CT-C superstructure, three TTF molecules self-assemble, forming a supramolecular isosceles triangle TTF-Δ, which tiles in a plane alongside the NDI-Δ, producing a 3 + 3 honeycomb tiling pattern of the two different polygons. Solid-state spectroscopic investigations on CT-C revealed the existence of an absorption band at 2500 nm, which on the basis of TDDFT calculations, was attributed to the mixed-valence character between two TTF•+ radical cations and one neutral TTF molecule.

Magnetic Anisotropy in Heterobimetallic Complexes.

Control of spin-orbit coupling enables the targeted modulation of coherence, catalytic, and magnetic properties in metal complexes. In this Forum, we describe our approach to exerting synthetic control over spin-orbit coupling by using heavy diamagnetic main-group metals as an external source of spin-orbit coupling. By binding these elements to first-row transition metals, we can probe the manifestation of spin-orbit coupling in their properties, by breaking spin-orbit coupling into a two-atom phenomenon. Within this approach, we focus on metal-ligand covalency and the importance of covalency in spin-orbit coupling transfer. To fully understand these systems, we need to design molecules that support careful decoupling of the influences of ligand field geometry and ligand-derived spin-orbit coupling on the magnetic anisotropy of paramagnetic transition metals. These design criteria, along with the advantages of bimetallic species, are described. We anticipate this perspective will offer a fundamental model for using two-metal systems for engendering spin-orbit coupling.

Octacyanometallate qubit candidates.

We report the temperature dependence of the spin dynamics of the octacyanometallates [Mo(CN)8]3- and [W(CN)8]3-. At 5 K, these complexes display remarkably long spin-lattice relaxation times of 1.05 s, and 0.63 s, respectively. We probe the contributing factors to the spin relaxation and demonstrate the impact of spin-orbit coupling as a handle to tune vibrationally mediated spin-lattice relaxation.

Enhancement of magnetic anisotropy in a Mn-Bi heterobimetallic complex.

A novel Mn2+Bi3+ heterobimetallic complex, featuring the closest MnBi interaction for a paramagnetic molecular species, exhibits unusually large axial zero-field splitting. We attribute this enhancement to the proximity of Mn2+ to a heavy main group element, namely, bismuth.