Gregor Schnakenburg

The Ni–Mg system can stoichiometrically and catalytically activate the ortho C–H bonds of pyridine.

Mononuclear bis(carbyne) complexes featuring two multiply bonded carbyne ligands at a single metal center, are an exceptionally rare class of organometallic compounds. Despite considerable advances in multiple bonding involving heavier group 14 elements, the synthesis of their heavier congeners, bis(tetrylidyne) complexes [L _n M(ER) ₂ ] (E = Si–Pb), remains extremely challenging owing to the lack of suitable synthetic strategies. Herein we report experimental and theoretical studies of the Rhodium bis(tetrylidyne) complex salts [Rh(ETbb) ₂ (PMe ₃ ) ₂ ][B(Ar ^F ) ₄ ] ( [2-E][B(Ar ^F ) ₄ ] ; E = Si, Ge; Tbb = C ₆ H ₂ -4- t Bu-2,6-(CH(SiMe ₃ ) ₂ ) ₂ ; Ar ^F = C ₆ H ₃ -3,5-(CF ₃ ) ₂ ). The complexes [2-E][B(Ar ^F ) ₄ ] were obtained by chloride abstraction of the tetrylidyne-chlorotetrylidene complexes [Rh(ETbb)(EClTbb)(PMe ₃ ) ₂ ] ( 1-E ) with Na[B(Ar ^F ) ₄ ]. Complexes 1-E were prepared by a E≡E triple bond cleavage reaction of the ditetrylynes E ₂ (Tbb) ₂ with [RhCl(PMe ₃ ) ₂ ] ₂ . The molecular structures of [2-E] ⁺ feature two almost linearly coordinated tetrel centers, that are bonded to the Rh center via two very short Rh−E bonds (Rh−Si1 = 2.1310(7) Å, Rh−Si2 = 2.1240(7) Å; Rh−Ge1 = 2.2093(2) Å, Rh−Ge2 = 2.1976(2) Å). The electronic structure calculations in combination with the assessment of the thermochemical properties corroborate the presence of two highly polar Rh≡E triple bonds in [2-E][B(Ar ^F ) ₄ ] . Cyclic voltammetric studies show a reversible electrochemical oxidation and reduction of the cations [2-E] ⁺ . The electrophilic character of the tetrel center is reflected in the reactions of [2-E][B(Ar ^F ) ₄ ] ] with LiMe yielding the tetrylidyne-methyltetrylidene complexes [Rh(ETbb)(EMeTbb)(PMe ₃ ) ₂ ] ( 5-E ).

The synthesis of small metallacycles of early transition metals and heavy pnictogens has been primarily achieved by reductive coupling of the pnictane moiety with a transition metal fragment. Herein, we report a light-enhanced synthesis of titanocene Sb2 and Bi2 metallacycles starting from the dipnictene (RSb=SbR, RBi=BiR) and a suitable titanocene synthon Cp2Ti(btmsa) (Cp = C5H5, btmsa = bistrimethylsilylacetylene). We further explored the reactivity of the TiSb2 complex by employing a diazoolefin, leading to the formation of an unusual six membered heterocycle. These findings were supported by thorough theoretical analysis of the electronic features of these complexes and expand upon previous studies of 3d transition metal dipnictene complexes.

We report the development of an iron‐photocatalyzed 1,2‐chloroaminoxylation of alkenes that installs two orthogonal and independently activatable synthetic handles, a chlorine atom and an alkoxyamino group, across a diverse range of alkene substrates. The reaction is driven by iron's ability to generate chlorine radicals via photoinduced chloride‐to‐iron charge transfer, followed by addition across the carbon–carbon double bond and subsequent trapping by TEMPO derivatives. This operationally simple protocol exhibits broad functional group tolerance, exquisite chemo‐ and regioselectivity and efficiently converts a wide range of C═C bonds, such as styrene derivatives, unactivated alkenes, and Michael acceptors, into synthetically valuable chlorooxygenated scaffolds. The resulting products can be engaged with various nucleophiles through distinct modes of reactivity: the TEMPO‐derived alkoxyamino moiety undergoes photoredox activation, while the C–Cl bond participates in nucleophilic substitution. This dual‐reactivity platform enables a programmable incorporation of two different nucleophiles under complementary activation conditions, providing streamlined access to structurally diverse architectures. Comprehensive mechanistic studies, integrating reaction kinetics, UV–vis spectroscopy, high‐resolution mass spectrometry (HRMS), x‐ray crystallographic characterization of key catalytic intermediates, cyclic voltammetry (CV), and chronoamperometry, elucidate the underlying reaction pathway and reveal key features of the iron catalytic cycle.

We report the development of an iron‐photocatalyzed 1,2‐chloroaminoxylation of alkenes that installs two orthogonal and independently activatable synthetic handles, a chlorine atom and an alkoxyamino group, across a diverse range of alkene substrates. The reaction is driven by iron's ability to generate chlorine radicals via photoinduced chloride‐to‐iron charge transfer, followed by addition across the carbon–carbon double bond and subsequent trapping by TEMPO derivatives. This operationally simple protocol exhibits broad functional group tolerance, exquisite chemo‐ and regioselectivity and efficiently converts a wide range of C═C bonds, such as styrene derivatives, unactivated alkenes, and Michael acceptors, into synthetically valuable chlorooxygenated scaffolds. The resulting products can be engaged with various nucleophiles through distinct modes of reactivity: the TEMPO‐derived alkoxyamino moiety undergoes photoredox activation, while the C–Cl bond participates in nucleophilic substitution. This dual‐reactivity platform enables a programmable incorporation of two different nucleophiles under complementary activation conditions, providing streamlined access to structurally diverse architectures. Comprehensive mechanistic studies, integrating reaction kinetics, UV–vis spectroscopy, high‐resolution mass spectrometry (HRMS), x‐ray crystallographic characterization of key catalytic intermediates, cyclic voltammetry (CV), and chronoamperometry, elucidate the underlying reaction pathway and reveal key features of the iron catalytic cycle.

π‐Extended conjugation offers the opportunity to unveil new frontiers in materials, coupling redox activity with tunable photophysical properties. Here, we report a new family of π‐conjugated salen ligands bearing phenylene bridges and tunable substituents, together with their corresponding boron difluoride complexes. Owing to the extended π‐delocalization, these new compounds show promising results in electrochemical CO ₂ reduction to CO, achieving a remarkable Faradaic efficiency for an organocatalyst (up to 56%). Electrochemical, spectroscopic, and computational analyses support a ligand‐centered mechanism in which single‐electron reduction activates the framework for CO ₂ binding at the imine nitrogen, forming an N‐bound CO ₂ H intermediate. Beyond electrocatalysis, coordination to boron rigidifies the π‐framework, producing emissive boron‐salphen complexes with large Stokes shifts (>7000 cm ^{− 1} ). These complexes function as efficient photosensitizers for singlet‐oxygen generation, enabling mild oxidative cleavage of alkenes under blue‐light irradiation. This work demonstrates that π‐extension transforms the traditional salphen framework into a redox‐active engine for small‐molecule activation, bypassing the need for transition metals in CO ₂ electroreduction while simultaneously unlocking good photosensitizing capabilities.

Various Ni‐based metalloenzymes employ synergistic heterometallic cooperativity where a Ni center and a second metal ion cofacilitate small‐molecule conversion. Inspired by these biological systems, synthetic model complexes have been developed that exploit bimetallic cooperativity to achieve analogous reactivity. In this work, we report a bimetallic Ni−Zn complex comprising a pincer‐type diamido‐diaminodiphosphine ligand, in which a weakly Lewis acidic Zn(II) center stabilizes a T‐shaped Ni(0) site. Subsequent reactivity with H ₂ led to the isolation of a rare Ni dihydride complex, which dynamically interconverts between Zn( μ ‐H)Ni(H) and trans ‐Ni(H) ₂ motifs via rotational rocking about the P−Ni−P axis. The Ni dihydride complex is a competent alkene hydrogenation catalyst (5 mol% loading, 70°C, 2 bar H ₂ ) for terminal olefins. Also, the Ni dihydride inserts CO ₂ to give a rare Ni hydrido formate. This product further reacts with a second equivalent of CO ₂ through a carboxylate shift mechanism that unveils a nucleophilic Zn(II) amide group that inserts CO ₂ to give carbamate. Collectively, our experimental and computational results highlight the role of Zn(II) as a weakly Lewis acidic partner, which promotes the dual activation of H ₂ and CO ₂ by a single Ni center in the absence of any external base.

Various Ni‐based metalloenzymes employ synergistic heterometallic cooperativity where a Ni center and a second metal ion cofacilitate small‐molecule conversion. Inspired by these biological systems, synthetic model complexes have been developed that exploit bimetallic cooperativity to achieve analogous reactivity. In this work, we report a bimetallic Ni−Zn complex comprising a pincer‐type diamido‐diaminodiphosphine ligand, in which a weakly Lewis acidic Zn(II) center stabilizes a T‐shaped Ni(0) site. Subsequent reactivity with H ₂ led to the isolation of a rare Ni dihydride complex, which dynamically interconverts between Zn( μ ‐H)Ni(H) and trans ‐Ni(H) ₂ motifs via rotational rocking about the P−Ni−P axis. The Ni dihydride complex is a competent alkene hydrogenation catalyst (5 mol% loading, 70°C, 2 bar H ₂ ) for terminal olefins. Also, the Ni dihydride inserts CO ₂ to give a rare Ni hydrido formate. This product further reacts with a second equivalent of CO ₂ through a carboxylate shift mechanism that unveils a nucleophilic Zn(II) amide group that inserts CO ₂ to give carbamate. Collectively, our experimental and computational results highlight the role of Zn(II) as a weakly Lewis acidic partner, which promotes the dual activation of H ₂ and CO ₂ by a single Ni center in the absence of any external base.

Light propels a dynamic mixture of photoswitchable, metallo-supramolecular Pd ^II capsules away from the thermodynamic equilibrium via a molecular ratchet mechanism.

Through functionalization with enantiomerically pure substituents, semiconducting dye molecules such as squaraines can be directed into homochiral arrangements, in which molecular chirality is transferred to a supramolecular level resulting in excitonic circular dichroism. Replacing the sterically demanding CMe groups in indolenine‐derived squaraines with sulfur atoms promotes aggregation and structural order in otherwise homogeneous thin films of benzothiazole‐derived squaraines. Here, we investigate solvent‐processed and thermally annealed thin films of a benzothiazole‐derived squaraine functionalized with homochiral citronellyl groups. The crystalline arrangement of the thin films does not correspond to the single crystal structure found, which consists of a solvent‐containing pseudo‐polymorph. The spectral shape of the excitonic circular dichroism in spin‐cast thin films is sensitive to the processing solvent and annealing temperature. Uniaxial anisotropy, evidenced by X‐ray diffraction and spectroscopic ellipsometry, shows excitonic transitions that are exclusively polarized either in the plane or perpendicular to the plane of the thin film. We interpret this in terms of a Davydov splitting into spatially separated upper (in‐plane) and lower (out‐of‐plane) Davydov components. This rarely documented arrangement changes our reading of optical spectra, including circular dichroism, recorded under standard normal incidence conditions, which probe only transitions with an in‐plane dipole‐moment component.