Going Up the Ladder: Stacking Four 4,4′-Bipyridine Moieties within a Ti(IV)-Based Tetranuclear Architecture

Biphenol-based ligands have proven their ability to bind titanium(IV) centers and generate sophisticated self-assembled structures in which auxiliary nitrogen ligands often complete the coordination sphere of the metal and improve stability. Here, a central 4,4′-bipyridine, which acts as both a spacer and a source of monodentate nitrogen to complete the coordination sphere of the Ti(IV) complex, was incorporated within two bis-2,2′-biphenol strands, 3H4 and 4H4. Both proligands possess structural features that are well adapted to form self-assembled structures built from titanium–oxygen–nitrogen units; however, their different degrees of torsional freedom strongly influenced the nuclearity of the complexes formed. The presence of a phenyl spacer between the bipyridine and the biphenol moieties of 3H4 provided enough flexibility for the ligand to wrap around one titanium(IV) center to form a mononuclear complex Ti(3)(DMF)2 in the presence of dimethylformamide (DMF). Assembly of the more rigid ligand 4H4 with Ti(OiPr)4 afforded a tetranuclear complex Ti4(4)2(4H)2(OEt)2 containing four stacked 4,4′-bipyridine units as shown by the X-ray structure of the complex. Density functional theory studies suggested that the assembly of this tetrametallic complex involves a dimetallic intermediate with TiO6 nodes that is converted to the thermodynamically stable tetranuclear complex with two TiO6 nodes and two TiO5N units with enhanced covalent character

Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

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

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