Studies on Three-Coordinate [Co{N(SiMe₃)₂}₂L] Complexes, L = N‑Heterocyclic Carbene

A series of three-coordinate N-heterocyclic carbene bis­(trimethylsilyl)­amide complexes of cobalt, [Co­{N­(SiMe₃)₂}₂(NHC)] (NHC = <i>N</i>,<i>N</i>′-diarylimidazolin-2-ylidene, aryl = 2,6-diisopropylphenyl, SIPr (<b>1</b>), aryl = mesityl, SIMes (<b>2</b>); κ¹-<i>N</i>,<i>N</i>′-diphosphanylimidazol-2-ylidene, PCP (<b>5</b>); κ¹-<i>N</i>-phosphanyl-<i>N</i>′-2,6-diisopropylphenylimidazol-2-ylidene, PC (<b>6</b>); cyclic alkyl amino carbene :C­(Cy)­CH₂CMe₂N-2,6-Prⁱ₂C₆H₃, cAAC^Cy (<b>7</b>)) were prepared by the reaction of [Co­{N­(SiMe₃)₂}₂] with the corresponding NHCs. The complexes exhibited interesting transamination reactivity in reactions with bulky 2,6-diisopropylaniline (NH₂(DiPP)), where adjustment of the stoichiometry and reaction conditions resulted in the substitution of one or two N­(SiMe₃)₂ ligands by the anilido ligand NH­(DiPP), giving [Co­{N­(SiMe₃)₂}­{NH­(DiPP)}­(NHC)] (NHC = <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene, IPr (<b>8</b>)) and [Co­{NH­(DiPP)}₂(NHC)] (NHC = SIPr (<b>9</b>); IPr (<b>10</b>); PCP (<b>11</b>)). X-ray crystallography revealed trigonal-planar coordination geometry at Co for all of the new complexes and long Co–C_NHC bond lengths; in the cases of <b>5</b>, <b>8</b>, <b>9</b>, <b>10</b>, and <b>11</b>, intramolecular Co···H and/or H···P interactions may provide further stabilization of specific conformations. Magnetic and electron paramagnetic resonance studies showed that the three-coordinate Co­(II) centers in <b>1</b>–<b>7</b> behave as <i>S</i> = ³/₂ spins with strong anisotropy arising from the low symmetry of the coordination site (<i>C</i>_2<i>v</i>). The anisotropy results in large values of the zero-field splitting parameter <i>D</i>

Studies on Three-Coordinate [Co{N(SiMe₃)₂}₂L] Complexes, L = N‑Heterocyclic Carbene

A series of three-coordinate N-heterocyclic carbene bis­(trimethylsilyl)­amide complexes of cobalt, [Co­{N­(SiMe₃)₂}₂(NHC)] (NHC = <i>N</i>,<i>N</i>′-diarylimidazolin-2-ylidene, aryl = 2,6-diisopropylphenyl, SIPr (<b>1</b>), aryl = mesityl, SIMes (<b>2</b>); κ¹-<i>N</i>,<i>N</i>′-diphosphanylimidazol-2-ylidene, PCP (<b>5</b>); κ¹-<i>N</i>-phosphanyl-<i>N</i>′-2,6-diisopropylphenylimidazol-2-ylidene, PC (<b>6</b>); cyclic alkyl amino carbene :C­(Cy)­CH₂CMe₂N-2,6-Prⁱ₂C₆H₃, cAAC^Cy (<b>7</b>)) were prepared by the reaction of [Co­{N­(SiMe₃)₂}₂] with the corresponding NHCs. The complexes exhibited interesting transamination reactivity in reactions with bulky 2,6-diisopropylaniline (NH₂(DiPP)), where adjustment of the stoichiometry and reaction conditions resulted in the substitution of one or two N­(SiMe₃)₂ ligands by the anilido ligand NH­(DiPP), giving [Co­{N­(SiMe₃)₂}­{NH­(DiPP)}­(NHC)] (NHC = <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene, IPr (<b>8</b>)) and [Co­{NH­(DiPP)}₂(NHC)] (NHC = SIPr (<b>9</b>); IPr (<b>10</b>); PCP (<b>11</b>)). X-ray crystallography revealed trigonal-planar coordination geometry at Co for all of the new complexes and long Co–C_NHC bond lengths; in the cases of <b>5</b>, <b>8</b>, <b>9</b>, <b>10</b>, and <b>11</b>, intramolecular Co···H and/or H···P interactions may provide further stabilization of specific conformations. Magnetic and electron paramagnetic resonance studies showed that the three-coordinate Co­(II) centers in <b>1</b>–<b>7</b> behave as <i>S</i> = ³/₂ spins with strong anisotropy arising from the low symmetry of the coordination site (<i>C</i>_2<i>v</i>). The anisotropy results in large values of the zero-field splitting parameter <i>D</i>

Diarylethene-Containing Carbon-Rich Ruthenium Organometallics: Tuning of Electrochromism

The association of a dithienylethene (DTE) system with ruthenium carbon-rich systems allows reaching sophisticated and efficient light- and electro-triggered multifunctional switches R-[Ru]-CC-DTE-CC-[Ru]-R, featuring multicolor electrochromism and electrochemical cyclization at remarkably low voltage. The spin density on the DTE ligand and the energetic stabilization of the system upon oxidation could be manipulated to influence the closing event, owing to the noninnocent behavior of carbon-rich ligands in the redox processes. A combination of spectroscopic (UV–vis–NIR–IR and EPR) and electrochemical studies, with the help of quantum chemical calculations, demonstrates that one can control and get a deeper understanding of the electrochemical ring closure with a slight modification of ligands remote from the DTE unit. This electrochemical cyclization was established to occur in the second oxidized state (EEC mechanism), and the kinetic rate constant in solution was measured. Importantly, these complexes provide an unprecedented experimental means to directly probe the remarkable efficiency of electronic (spin) delocalization between two <i>trans</i> carbon-rich ligands through a metal atom, in full agreement with the theoretical predictions. In addition, when no cyclization occurs upon oxidation, we could achieve a redox-triggered magnetic switch

Dietary intervention targeting increased fiber consumption for metabolic syndrome

Metabolic Syndrome is highly prevalanet in the United States and is a harbinger of diabetes and cardiovascular disease. With the staggering rise in diet-related chronic diseases such as diabetes and cardiovascular disease, simple and effective dietary intervention strategies are needed. National dietary recommendations are ever-changing and complex, which can be overwhelming and confusing for individuals who are trying to prevent or manage a chronic condition. Some evidence suggests that healthy changes in one area of diet are associated with healthy changes in other untargeted areas of diet. There is an opportunity to bridge a dietetics research gap by testing a simple dietary message focusing on fiber intake to improve risk factors for metabolic syndrome

New Metal Phthalocyanines/Metal Simple Hydroxide Multilayers: Experimental Evidence of Dipolar Field-Driven Magnetic Behavior

A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu^II, Co^II, Ni^II, and Zn^II) tetrasulfonato phthalocyanines between layers of Cu^II and Co^II simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (<i>B</i>_dipolar ≈ 30 mT)

Redox and Luminescent Properties of Robust and Air-Stable N‑Heterocyclic Carbene Group 4 Metal Complexes

Robust and air-stable homoleptic group 4 complexes of the type M­(L)₂ [<b>1</b>–<b>3</b>; M = Ti, Zr, Hf; L = dianionic bis­(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis­(3,5-di-<i>tert</i>-butyl-2-hydroxyphenyl)­imidazolinium chloride (<b>H</b>_<b>3</b><b>L,Cl</b>) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes <b>2</b> and <b>3</b> can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative <b>2</b> (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes <b>1</b>–<b>3</b> agree with the formation of ligand-centered species. Compounds <b>2</b> and <b>3</b> are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (ϕ = 0.08 and 0.12) for <b>2</b> and <b>3</b>, respectively. In contrast, the titanium complex <b>1</b> does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes <b>2</b> and <b>3</b> constitute the first examples of emissive nonmetallocene group 4 metal complexes

Ring-Oxidized Zinc(II) Phthalocyanine Cations: Structure, Spectroscopy, and Decomposition Behavior

A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn­(solvent)]^•₂[BAr^F₄]₂ (<b>1</b>·solvent), in good yield. This material is dimeric in the solid state with one axially coordinated solvent [tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME)] and close intradimer ring–ring distances of 3.18 and 3.136 Å (THF and DME respectively); this proximity facilitates strong antiferromagnetic coupling to yield diamagnetic dimers. <b>1</b>·THF is present in solution as a monomer and a dimer. In CH₂Cl₂, the dimer is favored above 0.1 mM, and it is almost exclusively present in solvents with a high dielectric constant such as acetonitrile. The material <b>1</b>·THF/DME decomposes in DME to a <i>meso</i>-nitrogen-protonated species, [HPcZn­(DME)₂]­[BAr^F₄] (<b>2</b>), which was isolated and represents the first example of such a structurally characterized, protonated, unsubstituted PcM complex. A partially oxidized dimer or “pimer” [(PcZn­(DME))₂]^•[BAr^F₄] (<b>3</b>) was also structurally characterized and has a intradimer ring–ring distance of 3.192 Å, similar to <b>1</b>·THF/DME. Dimer <b>3</b> also represents the first isolated PcM-based pimer. Electron paramagnetic resonance analysis of a 1.0 mM solution of <b>1</b>·DME in DME showed the production of <b>3</b> over hours by the combination of <b>1</b>·DME and <b>2</b> in solution

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph–CC−)_2–<i>n</i>Ru­(dppe)₂(−CC-bipyM­(hfac)₂)_<i>n</i>] (<i>n</i> = 1, 2; M = Cu^II, Mn^II; bipy = 2,2′-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic Cu^II units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.3 Å between adjacent Cu and Ru centers, 16.6 Å between external Cu centers) and compared at two different redox states. Surprisingly, oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to weaker magnetic interactions. In contrast, in the simpler parent complexes bearing only one paramagnetic metal unit [Ph–CC–Ru­(dppe)₂-CC–bipyCu­(hfac)₂], one-electron oxidation of the ruthenium bis­(acetylide) unit generates an interaction between the Cu and Ru spin carriers of magnitude comparable to that observed between the two far apart Cu ions in the above corresponding neutral trimetallic system. Evaluation and rationalization of this coupling with theoretical tools are in rational agreement with experiments for such complex systems

Inexpensive and Efficient Ullmann Methodology To Prepare Donor-Substituted Porphyrins

The preparation of porphyrins functionalized with one or two carbazoles (or phenoxazines) is described. The electron donors were introduced into one or two porphyrin <i>meso</i> positions by using the inexpensive Ullmann coupling procedure. Very good yields were obtained, and for two new compounds, the X-ray structures were solved. Preliminary electrochemical data coupled with electronic spectroscopy are also reported