Olivier Jarjayes

The square-planar Cu( ii )/Ni( ii ) complexes of three pyridine–phenol ligands show ligand-centred oxidations, with potentials spanning 0.62 V and a linker-dependent spin delocalization. The Cu complexes catalyse chemoselective benzyl alcohol oxidation.

The synthesis of Mn^V and Cr^V nitride complexes of a pro-radical tetradentate bis-phenol bis-N-heterocyclic carbene ligand H2LC2O2 was investigated.

The sterically hindered salen ligands featuring biphenyl and tetramethyl putrescine linkers were synthesized and chelated to copper. The resulting complexes CuL^bp,tBu, CuL^bp,OMe, CuL^pu,tBu and CuL^pu,OMe were structurally characterized, showing a significanty tetrahedrally distorted metal center. The complexes show two reversible oxidation waves in the range 0.2 to 0.8 V vs. Fc⁺/Fc. A further reduction wave is detected in the range −1.4 to −1.7 V vs. Fc⁺/Fc. It is reversible for CuL^bp,tBu and CuL^bp,OMe and assigned to the Cu^II/Cu^I redox couple. One-electron oxidation of CuL^bp,OMe, CuL^pu,tBu and CuL^pu,OMe was performed chemically and electrochemically. It is accompanied by a quenching of the EPR resonances. Phenoxyl radical formation was established by X-Ray diffraction on the cations [CuL^bp,OMe]⁺ and [CuL^pu,OMe]⁺, whereby the coordination sphere is elongated upon oxidation with quinoidal distributions of bond distances. The cations exhibit a NIR band of moderate intensity in their optical spectrum, supporting their classification as class II mixed-valent radical species according to the Robin Day classification. The proposed electronic structures are supported by DFT calculations. The cations [CuL^bp,OMe]⁺, [CuL^pu,tBu]⁺ and [CuL^pu,OMe]⁺ were active towards aerobic oxidation of the unactivated alcohol 2-phenylethanol, with TON numbers up to 58 within 3 h.

The tripodal ligand TREN-(3,5-di-tert-butylsalicylidene)₃ (H₃L) was synthesized and its tris(phenolato) lanthanide complexes L-Ln (Ln = Nd^III, Eu^III, Tb^III, Gd^III, Er^III, Yb^III and Lu^III) were prepared. The X-Ray crystal structures confirm that each metal ion resides in a similar monocapped octahedral geometry, excluding water molecules from the coordination sphere. The coordination bond distances are in agreement with the lanthanide contraction, with Ln–O bond lengths in the range 2.139–2.216 Å. The complexes show three reversible monoelectronic oxidation waves, which are assigned to the successive oxidation of the phenolate moieties to phenoxyl radicals. The L-Nd complex is the easiest to oxidize, with E¹ _1/2 = 0.11, E² _1/2 = 0.21 and E³ _1/2 = 0.34 V vs. Fc⁺/Fc, due to the larger size of the lanthanide ion. The ΔE_1/2 value (ΔE_1/2 = E² _1/2 − E¹ _1/2) is correlated to the lanthanide radius, with values of 0.10 V for L-Nd and 0.22 V for L-Lu. The monoradical species were persistent in solution, allowing for their characterisation. All exhibit a distinct absorption band at around 445 nm due to the phenoxyl π–π* transitions. The EPR spectrum of L-Lu⁺ consists of a single resonance at g_iso = 1.999, confirming the radical nature of the oxidized product. Most of the other complexes (L-Gd, L-Er, L-Yb) show a quenching of the Ln^III-based resonances upon oxidation, indicative of magnetic interactions between the metal and the radical spins. The L-Ln (L = Nd, Er, Yb) complexes exhibit a metal-based luminescence upon excitation of the ligand. A significant quenching of the luminescence was observed upon radical formation: 92%, 83% and 79% respectively for L-Nd⁺, L-Er⁺ and L-Yb⁺.

Three copper(II) complexes of the (R,R)‐N,N′‐bis(3,5‐di‐tert‐butyl‐2‐aminobenzylidene)‐1,2‐diaminocyclohexane ligand, namely [Cu(^NL)], [Cu(^NLH)]⁺ and [Cu(^NLH₂)]²⁺, were prepared and structurally characterized. In [Cu(^NLH₂)]²⁺ the copper ion lies in an octahedral geometry with the aniline groups coordinated in equatorial positions. In [Cu(^NL)] the anilines are deprotonated (anilido moieties) and coordinated to an almost square‐planar metal ion. Complex [Cu(^NL)] displays two oxidation waves at E_1/2^ox, 1=−0.14 V and E_1/2^ox, 2=0.36 V vs. Fc⁺/Fc in CH₂Cl₂. Complex [Cu(^NLH₂)]²⁺ displays an irreversible oxidation wave at high potential (1.21 V), but shows a readily accessible and reversible metal‐centered reduction at E_1/2^red=−0.67 V (Cu^II/Cu^I redox couple). Oxidation of [Cu(^NL)] by AgSbF₆ produces [Cu(^NL)](SbF₆), which was isolated as single crystals. X‐ray structure analysis discloses a contraction of the coordination sphere by 0.05 Å upon oxidation, supporting a metal‐centered process. Complex [Cu(^NL)](SbF₆) displays an intense NIR band at 1260 nm corresponding to an anilido‐to‐copper(III) charge transfer transition. This compound slowly evolves in CH₂Cl₂ solution towards [Cu(^NLH)](SbF₆), which is a copper(II) complex comprised of both anilido and aniline groups coordinated to the metal center. The copper(III) complex [Cu(^NL)](SbF₆) is an efficient catalyst for benzyl alcohol oxidation, with 236 TON in 24 h at 298 K, without additives other than oxygen and a base.

G‐rich DNA oligonucleotides derived from the promoter region of the HIV‐1 long terminal repeat (LTR) were assembled onto an addressable cyclopeptide platform through sequential oxime ligation, a thiol‐iodoacetamide SN2 reaction, and copper‐catalyzed azide–alkyne cycloaddition reactions. The resulting conjugate was shown to fold into a highly stable antiparallel G4 architecture as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. The binding affinities of six state‐of‐the‐art G4‐binding ligands toward the HIV‐G4 structure were compared to those obtained with a telomeric G4 structure and a hairpin structure. Surface plasmon resonance binding analysis provides new insights into the binding mode of broadly exploited G4 chemical probes and further suggests that potent and selective recognition of viral G4 structures of functional significance might be achieved.

The tetradentate ligand dppH₃, which features a half-porphyrin and two electron-rich phenol moieties, was prepared and chelated to manganese. The mononuclear Mn(III)-dipyrrophenolate complex 1 was structurally characterized. The metal ion lies in a square pyramidal environment, the apical position being occupied by a methanol molecule. Complex 1 displays two reversible oxidation waves at 0.00 V and 0.47 V vs. Fc⁺/Fc, which are assigned to ligand-centered processes. The one-electron oxidized species 1⁺ SbF₆⁻ was crystallized, showing an octahedral Mn(III) center with two water molecules coordinated at both apical positions. The bond distance analysis and DFT calculations disclose that the radical is delocalized over the whole aromatic framework. Complex 1⁺ SbF₆⁻ exhibits an S_tot = 3/2 spin state due to the antiferromagnetic coupling between Mn(III) and the ligand radical. The zero field splitting parameters are D = 1.6 cm⁻¹, E/D = 0.18(1), g_⊥ = 1.99 and g_∥ = 1.98. The dication 1²⁺ is an integer spin system, which is assigned to a doubly oxidized ligand coordinated to a Mn(III) metal center. Both 1 and 1⁺ SbF₆⁻ catalyze styrene oxidation in the presence of PhIO, but the nature of the main reaction product is different. Styrene oxide is the main reaction product when using 1, but phenylacetaldehyde is formed predominantly when using 1⁺ SbF₆⁻. We examined the ability of complex 1⁺ SbF₆⁻ to catalyze the isomerization of styrene oxide and found that it is an efficient catalyst for the anti-Markovnikov opening of styrene oxide. The formation of phenylacetaldehyde from styrene therefore proceeds in a tandem E–I (epoxidation–isomerization) mechanism in the case of 1⁺ SbF₆⁻. This is the first evidence of control of the reactivity for styrene oxidation by changing the oxidation state of a catalyst based on a redox-active ligand.

Four nickel(II)–salophen complexes containing alkyl‐imidazolium chains connected at the ortho or meta positions were prepared: N,N′‐bis(2‐hydroxy‐4‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)phenylenediamine (1), N,N′‐bis(2‐hydroxy‐3‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)phenylenediamine (2), N,N′‐bis(2‐hydroxy‐3‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)methyl‐3H‐imidazol‐1‐iumphenylenediamine (3), and N,N′‐bis(2‐hydroxy‐4‐methyl‐3H‐imidazol‐1‐iumbenzylideneamino)methyl‐3H‐imidazol‐1‐iumphenylenediamine (4). They protect G‐quadruplex DNA (G₄‐DNA) against thermal denaturation and show K_A values in the range of 7.4×10⁵ to 4×10⁷ m⁻¹ for G₄‐DNA models. Complex 4 exhibits an IC₅₀ value of 70 nm for telomerase inhibition.