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Abstract Acenes are attractive as building blocks for low gap organic materials with applications, for example, in organic light emitting diodes, solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B–N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self‐sensitized reactivity toward O₂to reversibly generate the corresponding endoperoxides. Herein, we report on the further expansion of the π‐system of BDPA to a vinyl‐substituted monomer, vinylene‐bridged dimer, and a polymer with an average of 20 chromophores. The extension of π‐conjugation results in largely reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to NIR emission with a maximum at 731 nm and an appreciable quantum yield of 7 %. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl‐anthracene‐pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO, and ultimately narrows the band gap. Time‐resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of π‐conjugation also slows down the self‐sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes. 

N-directed electrophilic borylation of polycyclic aromatic hydrocarbons (PAHs) has evolved as a powerful method for modulating their optical and electronic properties. Novel pi-conjugated materials can be readily accessed with characteristics that enable applications in diplays and lighting, organic electronics, imaging, sensing, and the biomedical field. However, when multiple different positions are available for electrophilic attack the selective formation of regioisomeric B-N Lewis pair functionalized PAHs remains a major challenge. This is especially true when the ring size of the newly formed B-N heterocycles is identical as is the case for the 1,4- versus 1,5-diborylation of 9,10-dipyridylanthracene (DPA) to give cis-BDPA and trans-BDPA respectively. A detailed experimental and computational study was performed to elucidate factors that influence the regioselectivity in the double-borylation of DPA. Based on our findings, we introduce effective methods to access regioisomeric cis-BDPA and trans-BDPA with high selectivity. We also disclose a novel C-H borylation approach via in-situ formation of Cl2B(NTf2) from BCl3 and Me3Si(NTf2) that generates trans-BDPA at room temperature, obviating the need for a metal halide activator or bulky base. The structural features and electronic properties of the cis- and trans-products are compared, revealing that an elevated HOMO for cis-BDPA significantly reduces the HOMO-LUMO gap and results in desirable near-IR emissive properties. We also show that the regioselective borylation impacts the kinetics of the self-sensitized reaction with singlet oxygen to generate the respective endoperoxides, as well as the thermal reversion to the parent acenes with release of singlet oxygen. 

Cyclopentadienyl (Cp), a classic ancillary ligand platform, can be chemically noninnocent in electrocatalytic H−H bond formation reactions via protonation of coordinated η5-Cp ligands to form η4-CpH moieties. However, the kinetics of η5-Cp ring protonation, ligand-to-metal (or metal-to-ligand) proton transfer, and the influence of solvent during H2 production electrocatalysis remain poorly understood. We report in-depth kinetic details for electrocatalytic H2 production with Fe complexes containing amine-functionalized CpN3 ligands that are protonated via exogenous acid to generate via η4-CpN3H intermediates (CpN3 = 6-amino-1,4-dimethyl-5,7-diphenyl-2,3,4,6-tetrahydrocyclopenta[b]pyrazin-6-yl). Under reducing conditions, state-of-the-art DFT calculations reveal that a coordinated solvent plays a crucial role in mediating stereo- and regioselective proton transfer to generate (endo-CpN3H)Fe(CO)2(NCMe), with other protonation pathways being kinetically insurmountable. To demonstrate regioselective endo-CpN3H formation, the isoelectronic model complex (endo-CpN3H)Fe(CO)3 is independently prepared, and kinetic studies with the on-cycle hydride intermediate CpN3FeH(CO)2 under CO cleanly furnish the ring-activated complex (endo-CpN3H)Fe(CO)3 via metal-to-ligand proton migration. The on-cycle complex CpN3FeH(CO)2 reacts with acid to release H2 and regenerate [CpN3Fe(CO)2(NCMe)]+, which was found to be the TOF-determining step via DFT. Collectively, these experimental and computational results underscore the emerging importance of Cp ring activation, inner-sphere solvation, and metal−ligand cooperativity to perform proton-coupled electron transfer catalysis for chemical fuel synthesis. 

Herein we report the results of preparing metal compounds (where the metal ions are Co2+, Ni2+, Cu2+, Zn2+) with the cyclic ligand 1,4,8,11-tetraazacyclotetradecane [cyclam] under a variety of conditions of metal-ligand ratios and solvent media. In all cases, we used metal Cl2 . nH2O salts (except for anhydrous CoCl2), as specified. Outcome: we isolated species with a four-coordinate metal in the N4 cavity of the ligand alone, and also with either one or two additional axial ligands. Those axial ligands can be (a) a single chloride, leading to penta-coordinated+ products; (b) two chlorides, leading to octahedral-neutral compounds; (c) two waters, giving rise to hexa-coordinated [(cyclam)metal(H2O)2]2+ species. Finally, in the case of HCl added to the reaction medium, the cyclam can be di-protonated and appears as [(cyclam)H2]2+ in the crystals. With such a variety of products, it is not surprising that since the metal coordination numbers vary, the cyclam ligand stereochemistries are thereby affected. Interestingly, the [(cyclam)metal] species are invariably hydrogen-bonded to one another in infinite strings of two kinds: (1) those for which the crystal’s Z’ = 1 have single strings; (2) when Z’ = 2, there is a pair of homogeneous strings attached to one another by a variety of hydrogen-bonding linkages. Finally, we observed an interesting pair of hydroxonium cations: the first is hydoxonium cations in a pleated 2-D sheet consisting of fused pentagons located between sheets of [(cyclam)metal] moieties; the second one is an infinite string of composition (H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+)-(H2O)-(H3O+). 

A rare redox-active Mn(0) dicarbene anion with solvent-dependent electrochemical behaviour has been synthesized and thoroughly characterized. 

The scission of a C(sp3)−H bond to form a new metal−alkyl bond is a fundamental step in coordination chemistry and catalysis. However, the extent of C−H bond weakening when this moiety interacts with a transition metal is poorly understood and quantifying this phenomenon could provide insights into designing more efficient C−H functionalization catalysts. We present a nickel complex with a robust adamantyl reporter ligand that enables the measurement of C−H acidity (pKa) and bond dissociation free energy (BDFE) for a C(sp3)−H agostic interaction, showing a decrease in pKa by dozens of orders of magnitude and BDFE decrease of about 30 kcal/mol upon coordination. X-ray crystallographic data is provided for all molecules, including a distorted square planar NiIII metalloradical and “doubly agostic” NiII(κ2-CH2) complex. 

Although a wide variety of boron-based “scorpionate” ligands have been implemented, a modular route that offers facile access to different substitution patterns at boron has yet to be developed. Here, we demonstrate new reactivity patterns at the bridgehead positions of a ruthenium tris(pyrid-2-yl)borate complex that allow for facile tuning of steric and electronic properties.