Initial Radical Cation Pathway in the Mo2Cl10-Mediated Dehydrogenative Arene Coupling

Molecular Rubies in Photoredox Catalysis

The molecular ruby [Cr(tpe) ₂ ] ³⁺ and the tris(bipyridine) chromium(III) complex [Cr(dmcbpy) ₃ ] ³⁺ as well as the tris(bipyrazine)ruthenium(II) complex [Ru(bpz) ₃ ] ²⁺ were employed in the visible light-induced radical cation [4+2] cycloaddition (tpe = 1,1,1-tris(pyrid-2-yl)ethane, dmcbpy = 4,4'-dimethoxycarbonyl-2,2'-bipyridine, bpz = 2,2'-bipyrazine), while [Cr(ddpd) ₂ ] ³⁺ serves as a control system (ddpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine). Along with an updated mechanistic proposal for the Cr^III driven catalytic cycle based on redox chemistry, Stern-Volmer analyses, UV/Vis/NIR spectroscopic and nanosecond laser flash photolysis studies, we demonstrate that the very weakly absorbing photocatalyst [Cr(tpe) ₂ ] ³⁺ outcompetes [Cr(dmcbpy) ₃ ] ³⁺ and even [Ru(bpz) ₃ ] ²⁺ in particular at low catalyst loadings, which appears contradictory at first sight. The high photostability, the reversible redoxchemistry and the very long excited state lifetime account for the exceptional performance and even reusability of [Cr(tpe) ₂ ] ³⁺ in this photoredox catalytic system.

Molecular flattening effect to enhance the conductivity of fused porphyrin tape thin films

The straightforward synthesis of directly fused porphyrins (porphyrin tapes) from 5,15-diphenyl porphyrinato nickel(ii) complexes with different substituents on the phenyl rings is achieved while processing from the gas phase. The porphyrin tapes, exhibiting NIR absorption, are readily obtained in thin film form. The gas phase approach cuts the need for solubilizing groups allowing for the first time the study of their conductivity according to the substituent. 2-Point probe and conductivity AFM measurements evidence that reducing the size of the meso substituents, phenyl < mesityl < di(3,5-tert-butyl)phenyl < di(2,6-dodecyloxy)phenyl, improves the thin film conductivity by several orders of magnitude. Density functional theory and gel permeation chromatography, correlate this improvement to changes in the intermolecular distances and molecular geometry. Furthermore, the oCVD of porphyrins with free ortho-phenyl positions causes intramolecular dehydrogenative side reactions inducing a complete planarization of the molecule. This molecular flattening drastically affects the π–π stacking between the porphyrins further enhancing the electronic properties of the films.

This work reports the strong correlation between the conductivity of fused porphyrins thin films and the porphyrin substituents.

Reactivity of Nickel(II) Porphyrins in oCVD Processes-Polymerisation, Intramolecular Cyclisation and Chlorination

Oxidative chemical vapour deposition of (5,15‐diphenylporphyrinato)nickel(II) (NiDPP) with iron(III) chloride as oxidant yielded a conjugated poly(metalloporphyrin) as a highly coloured thin film, which is potentially useful for optoelectronic applications. This study clarified the reactive sites of the porphyrin monomer NiDPP by HRMS, UV/Vis/NIR spectroscopy, cyclic voltammetry and EPR spectroscopy in combination with quantum chemical calculations. Unsubstituted meso positions are essential for successful polymerisation, as demonstrated by varying the porphyrin meso substituent pattern from di‐ to tri‐ and tetraphenyl substitution. DFT calculations support the proposed radical oxidative coupling mechanism and explain the regioselectivity of the C−C coupling processes. Depositing the conjugated polymer on glass slides and on thermoplastic transparent polyethylene naphthalate demonstrated the suitability of the porphyrin material for flexible optoelectronic devices.

The role of steric hindrance in the intramolecular oxidative aromatic coupling of pyrrolo[3,2-b]pyrroles

The presence of steric hindrance triggers different reaction pathways in the intramolecular oxidative aromatic coupling of tetraaryl-pyrrolo[3,2-b]pyrroles and leads to the formation of a fluorene moiety and a new cationic π-system linked together by a spiro carbon atom. Computational studies elegantly rationalized these results. These previously unknown functional dyes emit red light with reasonable efficiency.

Activation of CN bonds by high-valent group 6 metal chlorides, including the conversion of an α-diimine into a functionalized imidazolium

The direct interactions of WCl₆and MoCl₅with α-diimines (and also a carbodiimide in the case of MoCl₅) have been explored, leading to unusual reaction pathways.

Unusual activation pathways of amines in the reactions with molybdenum pentachloride

Both single electron reduction and oxidation of Mo(v) guide the activation of a series of aliphatic amines when these are allowed to react with MoCl₅.

Intermolecular oxidative dehydrogenative 3,3′-coupling of benzo[b]furans and benzo[b]thiophenes promoted by DDQ/H+: total synthesis of shandougenine B

A synthetic method applied to the synthesis of shandougenine B.

Over-Oxidation as the Key Step in the Mechanism of the MoCl5-Mediated Dehydrogenative Coupling of Arenes

Molybdenum pentachloride is an unusually powerful reagent for the dehydrogenative coupling of arenes. Owing to the high reaction rate using MoCl5, several labile moieties are tolerated in this transformation. The mechanistic course of the reaction was controversially discussed although indications for a single electron transfer as the initial step were found recently. Herein, based on a combined study including synthetic investigations, electrochemical measurements, EPR spectroscopy, DFT calculations, and mass spectrometry, we deduct a highly consistent mechanistic scenario: MoCl5 acts as a one-electron oxidant in the absence of TiCl4 and as two-electron oxidant in the presence of TiCl4, but leads to an over-oxidized intermediate in both cases, which protects it from side reactions. In the course of aqueous work-up the reagent waste (Mo(III/IV) species) acts as reducing agent generating the desired organic C-C coupling product.