Glenn P. A. Yap

All previously reported Ge(II) dications have remained chemically dormant, their reactivity confined to simple coinage metal coordination—a consequence of cationization‐induced lone pair contraction that renders the Ge center inaccessible to substrates. We report that dual σ/π‐donating carbodicarbene (CDC) ligands directly counteract this contraction, yielding [(CDC) ₂ Ge][OTf] ₂ ( 4 ), the first two‐coordinate Ge(II) dication to display broad reactivity beyond coinage metal coordination. Crystallographic and computational analysis reveal a delocalized 3c‐4e C‐Ge‐C moiety and a less contracted Ge lone pair with retained Ge‐centered LUMO, underpinning an unprecedented reactivity profile encompassing 1,1‐oxidative addition, [1 + 4] cycloaddition, selenium insertion, and cooperative C–S bond activation. As a Ge‐donor ligand, 4 coordinates to Rh, Ir, and Ag with donor strength comparable to that of IMes and forms geminal bimetallic complex 8 , featuring a rare noncluster Ag–Ge–Ag three‐center two‐electron bonding motif. These results establish CDC‐based low‐coordination stabilization as a productive strategy for accessing structurally simple yet reactive main‐group dications.

All previously reported Ge(II) dications have remained chemically dormant, their reactivity confined to simple coinage metal coordination—a consequence of cationization‐induced lone pair contraction that renders the Ge center inaccessible to substrates. We report that dual σ/π‐donating carbodicarbene (CDC) ligands directly counteract this contraction, yielding [(CDC) ₂ Ge][OTf] ₂ ( 4 ), the first two‐coordinate Ge(II) dication to display broad reactivity beyond coinage metal coordination. Crystallographic and computational analysis reveal a delocalized 3c‐4e C‐Ge‐C moiety and a less contracted Ge lone pair with retained Ge‐centered LUMO, underpinning an unprecedented reactivity profile encompassing 1,1‐oxidative addition, [1 + 4] cycloaddition, selenium insertion, and cooperative C–S bond activation. As a Ge‐donor ligand, 4 coordinates to Rh, Ir, and Ag with donor strength comparable to that of IMes and forms geminal bimetallic complex 8 , featuring a rare noncluster Ag–Ge–Ag three‐center two‐electron bonding motif. These results establish CDC‐based low‐coordination stabilization as a productive strategy for accessing structurally simple yet reactive main‐group dications.

Compared to first-row transition metal complexes, such as Mn, Fe, Co, and Ni, the development of molecular copper electrocatalysts for CO2 reduction has been plagued by the instability of low-valent Cu intermediates, which are prone to undergo demetallation or aggregation. A series of rational and systematic ligand modifications was employed to transform a CO2-fixing yet electrochemically unstable pyridine-2,6-dicarboxamide copper complex into a stable electrocatalytic system. Guided by the Hard–Soft Acid–Base principle, incorporation of a thioether donor into the nitrogen-based pincer framework stabilized Cu(I) intermediates, thereby promoting reversible electron transfer and mitigating the instability of the hard nitrogen-donor environment. Furthermore, the introduction of a macrocyclic structure not only enhances the overall stability of the complex but also minimizes structural reorganization to support the redox reversibility of the redox-active ligand. The resulting complex mediated the electroreduction of CO2 to CO through an alternating sequence of electron-transfer (E) and chemical (C) steps (ECEC mechanism). The mechanistic studies identified the key CO2-bound and protonated HCO2-bound copper intermediate species using a combination of spectroscopic tools, complementary in situ electrochemical methods, and isotopic labeling. In addition, comparative experimental and computational analyses of the copper complexes further revealed the factors governing catalyst stability. These results demonstrate that the interplay among the coordination sphere, redox-active ligand, and ligand rigidity dictates the electrocatalytic performance and stability of molecular copper complexes. This work provides design principles and mechanistic insights applicable to both homogeneous electrocatalysts and copper-complex-derived heterogeneous systems for CO2 reduction.

Monomeric heptazines have recently attracted significant attention for applications in photocatalysis, optics, and organic electronics. Many heptazine derivatives are known to have high triplet energies that are close or even above their singlet energy (anti‐Hund) that can be useful for applications in high efficiency organic light‐emitting diodes (OLEDs). We report a convenient synthetic route to asymmetric bis‐diarylamino carbazole‐substituted heptazines obtained in high yields via sequential nucleophilic substitutions of trichloroheptazine. These materials were thoroughly characterized by NMR spectroscopy and single‐crystal X‐ray crystallography. Furthermore, their photophysical properties were systematically examined to determine the energies of excited singlet/triplet states. Photophysical measurements and high‐level quantum chemical calculations demonstrate that bis‐diarylamino carbazole‐substituted heptazines are triplet wide bandgap materials that obey Hund's rule with T ₁ lying lower in energy than S ₁ . Detailed analysis of the electronic structure of the excited states reveals that their nature differs significantly from that of anti‐Hund heptazines with substantial localization/contribution of charge transfer character to carbazole and diarylamine moieties, which is responsible for Hund order of excited singlet/triplet states. Finally, application of bis‐diarylamino carbazole‐substituted heptazine 1 as wide bandgap host material for OLEDs does not interfere with triplet dynamics of emissive phosphor consistently with Hund order of excited singlet/triplet states

Schiff base complexes of Mn have garnered significant attention as homogeneous catalysts. Among that class of compounds, bis(imino)pyridine-supported variants feature prominently. Synthesis of these species typically entails multistep, multiday processes and often under forcing conditions to drive condensation of less favorable nucleophiles. We report the multigram-scale one-pot, one-step synthesis of bis(imino)pyridine-Mn complexes using ultrasound-assisted synthesis, or sonochemistry, via acoustic cavitation. Complexes are assembled from their ligand components (diacetylpyridine, anilines, and MnCl2·(H2O)4), without the aid of an additional acid catalyst, using methanol as a solvent, and without any effort to remove H2O, in only 30 min of reaction time. The process is additionally amenable to electron-poor fluorinated anilines, giving rise to new complexes with novel steric and electronic environments around the Mn center.

Salen-type tetradentate Schiff base ligands are ubiquitous in coordination chemistry because of their straightforward synthesis, derivatization, and versatility as ligands for metals across the periodic table. The present work was motivated by our interest in expanding the library of bifunctional salophen systems, where basic sites are incorporated in the secondary coordination sphere of salophen-ligated metals. Here, we report and describe seven previously unreported structures of nickel–, copper–, and zinc–salophen derivatives, including two complexes that integrate amine bases in the ligand periphery. These are {4,4′-di- tert -butyl-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}nickel(II) toluene 1.33-solvate, [Ni(C ₂₈ H ₃₀ N ₂ O ₂ )]·1.33C ₇ H ₈ or ( ^t Bu-salophen)Ni·1.33C ₇ H ₈ , {4,4′-di- tert -butyl-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}copper(II), [Cu(C ₂₈ H ₃₀ N ₂ O ₂ )] or ( ^t Bu-salophen)Cu, aqua{4,4′-di- tert -butyl-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}zinc(II) tetrahydrofuran monosolvate, [Zn(C ₂₈ H ₃₀ N ₂ O ₂ )(H ₂ O)]·C ₄ H ₈ O or ( ^t Bu-salophen)Zn(OH ₂ )·THF, {4,4′-bis(trifluoromethyl)-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}nickel(II), [Ni(C ₂₂ H ₁₂ F ₆ N ₂ O ₂ )] or (CF ₃ -salophen)Ni, {4,4′-bis(trifluoromethyl)-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}(pyridine)zinc(II), [Zn(C ₂₂ H ₁₂ F ₆ N ₂ O ₂ )(C ₅ H ₅ N)] or (CF ₃ -salophen)Zn(py), {4,4′-di- tert -butyl-6,6′-bis[(diisopropylamino)methyl]-2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolato}nickel(II), [Ni(C ₄₂ H ₆₀ N ₄ O ₂ )] or ( ^t Bu-salophen-N ⁱ Pr ₂ )Ni, and {4,4′-di- tert -butyl-6,6′-bis[(diphenylamino)methyl]-2,2′-[(pyridine-3,4-diyl)bis(nitrilomethylidyne)]diphenolato}(pyridine)zinc(II) pyridine monosolvate, [Zn(C ₅₃ H ₅₁ NO ₂ )(C ₅ H ₅ N)]·C ₅ H ₅ N or ( ^t Bu-salpyr-NPh ₂ )Zn(py)·py. The metal centers in these compounds adopt structures consistent with what has been observed for other salen-type ligands described in the literature, with near ideal square-planar structures around nickel or copper, and a distorted square-pyramidal structure for the zinc complexes. The primary coordination sphere around these metals expands slightly across the row, as anticipated based on the increase in d -electron count from nickel to zinc. The solid-state packing of these compounds is also discussed, including the tendency for their flat extended π-systems to pack parallel to one another. Differences in packing are observed as functional groups at the ligand periphery are varied or where the compounds cocrystallize with solvent molecules.

A stepwise sequence for the hydrodefluorination of a fluorobenzene equivalent has been described. By utilization of a P(III)/Pd(II)-P(V)/Pd(0) redox couple, pyramidalized P-CF₃-functionalized benzazaphosphole 1 accepts Ph-F from Pd(II) complexes B/C, resulting in the formation of trigonal bipyramidal (TBP) 2 featuring new P-Ph and P-F bonds. The desired release of Ph-H and regeneration of trivalent 1 from pentavalent 2 was silane-dependent. Using smaller silanes, fluoride abstraction forms phosphonium cation 3 with a hydridosilicate counterion, which delivers hydride to the cationic P-center, affording TBP analogues of Type 4. These observable P-H derivatives like 4x selectively expel H-CF₃ and P-Ph-functionalized 5 via a highly asynchronous transition state, resembling a heterolytic P-CF₃ bond cleavage/deprotonation event. If larger silanes like Ph₃Si-H are employed, the targeted Ph-H/1 product pair is generated directly from 2, closing the stoichiometric hydrodefluorination process. The P(III)/Pd(II)-P(V)/Pd(0) mechanism, silane-dependent product formation, and loss of H-CF₃ from 4x redox reaction were evaluated by DFT calculations.

We report our discovery that tricyclohexyl phosphine is a privileged ligand that enables highly efficient Pd-catalyzed B-C(sp) bond formation on iodinated carborane precursors. We display the generality and utility of our reaction framework in the alkynylation of 9-I-m-carborane and demonstrate the first examples of monoalkynylation and symmetric dialkynylation on 9-I-o-carborane and 9,10-I₂-m-carborane, respectively, under Sonogashira-type cross-coupling conditions across a broad range of diverse and complex alkyne-terminated coupling partners.

Organobismuth-catalyzed 1,1-difluorocyclopropanation is an efficient method due to the ability to release CF ₂ in a controlled manner. Transmetallation step is more challenging to address with catalyst tuning than CF ₂ release.

Platinum complexes have now been used in chemotherapy regimens for almost half a century to treat a variety of cancers. The most clinically significant of these compounds to date is cisplatin, cis-di­ammine­dichloro­platinum­(II), whose clinical application has significantly reduced the mortality rate of several cancers. Despite this development, there is still a push to find new compounds that have improved efficacy, that can be administered at lower doses, and that produce less severe side-effects compared to current options. One class of molecules that may fill that role is phosphaplatins, an underexplored class of platinum­(II) complexes that contain a bidentate pyrophosphate ligand. These compounds are anionic at physiological pH and display reduced DNA-binding compared to cisplatin. This study expands on the list of known phosphaplatins by introducing two new compounds, di­cyclo­butyl­amine­dihydrogen­pyro­phosphato­platinum­(II) and dicyclo­pentylamine­dihydrogen­pyrophosphato­platinum­(II). Here we report complete synthetic details, as well as cell viability data in response to these compounds using two cancer cell lines, a human lung adenocarcinoma and a triple-negative human breast cancer. While these compounds inhibit cell viability less than the leading phosphaplatin drug candidate, trans-(1R,2R)-diamino­cyclo­hexane­dihydrogen­pyro­phosphato­platinum­(II), this work represents an important step in elucidating structure–activity relationships for this class of molecules.