Three-dimensional molecular barrels Ru6-4 and Ru6-5 were synthesized in high yields from dinuclear ruthenium-vinyl clamps and tritopic triphenylamine-derived carboxylate linkers and characterized by multinuclear NMR spectroscopy including 1H-1H COSY and 1H DOSY measurements, high-resolution electrospray ionization mass spectrometry, and X-ray crystallography. The metal frameworks of the cages adopt the shape of twisted trigonal prisms, and they crystallize as racemic mixtures of interdigitating Δ- and Λ-enantiomers with a tight columnar packing in Ru6-4. Electrochemical studies and redox titrations revealed that the cages are able to release up to 11 electrons on the voltammetric timescale and that their cage structures persist up to the hexacation level. IR and UV-vis-near-infrared spectroelectrochemical studies confirm substituent-dependent intramolecular electronic communication within the π-conjugated 1,3-divinylphenylene backbone in the tricationic states, where all three divinylphenylene-bridged diruthenium clamps are present in mixed-valent radical cation states. The formation of 1:3 charge-transfer salts with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as the electron acceptor is also demonstrated.

Redox-active metallamacrocycles were built from 1,4-divinylphenylene-bridged diruthenium complexes and benzene-1,3-dicarboxylates. The nodal properties of the dicarboxylate ligands and the side-by-side placement of the phenylene linkers mutually insulate the conductive diruthenium building blocks. This has the interesting consequence of rendering the oxidized forms paramagnetic, while the polyelectrochromism of the individual building blocks is fully retained. More information can be found in the Full Paper by F. Pauly, R. F. Winter et al. on page 9574 ff.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Metallamacrocylic tetraruthenium complexes were generated by treatment of 1,4-divinylphenylene-bridged diruthenium complexes with functionalized 1,3-benzene dicarboxylic acids and characterized by HR ESI-MS and multinuclear NMR spectroscopy. Every divinylphenylene diruthenium subunit is oxidized in two consecutive one-electron steps with half-wave potential splittings in the range of 250 to 330 mV. Additional, smaller redox-splittings between the +/2+ and 0/+ and the 3+/4+ and 2+/3+ redox processes, corresponding to the first and the second oxidations of every divinylphenylene diruthenium entity, are due to electrostatic effects. The lack of electronic coupling through bond or through space is explained by the nodal properties of the relevant molecular orbitals and the lateral side-by-side arrangement of the divinylphenylene linkers. The polyelectrochromic behavior of the divinylphenylene diruthenium precursors is retained and even amplified in these metallamacrocyclic structures. EPR studies down to T=4 K indicate that the dications 1-H(2+) and 1-OBu(2+) are paramagnetic. The dications and the tetracation of macrocycle 3-H display intense (dications) or weak (3-H(4+) ) EPR signals. Quantum chemical calculations indicate that the four most stable conformers of the macrocycles are largely devoid of strain. Bond parameters, energies as well as charge and spin density distributions of model macrocycle 5-H(Me) were calculated for the different charge and spin states.

Cyclic oligomers comprising strongly interacting redox-active monomer units represent an unknown, yet highly desirable class of nanoscale materials. Here we describe the synthesis and properties of the first family of molecules belonging to this compound category—differently sized rings comprising only 1,1′-disubstituted ferrocene units (cyclo[ n ], n = 5–7, 9). Due to the close proximity and connectivity of centres (covalent Cp–Cp linkages; Cp = cyclopentadienyl) solution voltammograms exhibit well-resolved, separated 1 e – waves. Theoretical interrogations into correlations based on ring size and charge state are facilitated using values of the equilibrium potentials of these transitions, as well as their relative spacing. As the interaction free energies between the redox centres scale linearly with overall ring charge and in conjunction with fast intramolecular electron transfer (∼10 7 s −1 ), these molecules can be considered as uniformly charged nanorings (diameter ∼1–2 nm).

We report here on ruthenium alkenyl complexes 2 and 3 derived from 2,2'-bipyridine and their Re(CO)3X adducts 4a,b and 5. Detailed electrochemical studies on these complexes and spectroscopic characterization of their oxidized forms by IR, UV/vis/NIR, and electron paramagnetic resonance spectroscopies as well as quantum chemical studies reveal sizable (bridging) ligand contributions to the redox orbitals. Engagement of the free bipy functions of complexes 2 and 3 in binding to the electron-withdrawing fac-Re(CO)3X (X = Br, Cl) moiety enhances the metal-to-ligand charge-transfer character of the optical excitations, causes sizable anodic shifts of the redox potentials, and decreases the number of observable anodic redox waves by one when compared to complexes 2 and 3. Despite the decreasing electron density at the terminal or bridging alkenyl bipyridine ligand, the anodic redox processes still maintain appreciable ligand character as is seen by the shifts of the Ru(CO) and Re(CO)3 stretching frequencies on oxidation. Binding of the fac-Re(CO)3X moiety also attenuates the degree of ground-state delocalization in the mixed-valent states.

This paper focuses on the stable, ferrocene-based N-heterocyclic carbene (NHC) rac-[Fe{(η(5)-t-BuC5H3)NpN}2C:] (A'-Np, Np = neopentyl), which is planar-chiral due to the two tert-butyl substituents in 3,3'-positions. A'-Np was synthesized in nine steps starting from 1,1'-di-tert-butylferrocene (1), the first step being its 3,3'-dilithiation to afford rac-[Fe(η(5)-t-BuC5H3Li)2] (rac-fc'Li2, 2). The structures of rac-fc'(SiMe3)2 (3), rac-fc'Br2 (4), rac-fc'(N3)2 (5), and the immediate carbene precursor [A'-NpH]BF4 were determined by single-crystal X-ray diffraction (XRD). The chemical properties of A'-Np were found to be very similar to those of its tert-butyl-free congener A-Np, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. -4.0 eV) and low singlet-triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm(-1) was derived from IR data of cis-[RhCl(A'-Np)(CO)2], indicating the high donicity of A'-Np as a ligand. Consistent with its ambiphilic nature, A'-Np was found to react readily with carbon monoxide, affording the betainic enolate (A'-Np)2CO as four stereoisomers, viz. (RpRp-A'-Np)═C(O(-))(RpRp-A'-Np(+)), (SpSp-A'-Np)═C(O(-))(SpSp-A'-Np(+)), (RpRp-A'-Np)═C(O(-))(SpSp-A'-Np(+)), and (SpSp-A'-Np)═C(O(-))(RpRp-A'-Np(+)). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. A'-Np was found to react swiftly with dichloromethane, affording the addition product A'-NpH-CHCl2 in a reaction that is unprecedented for diaminocarbenes. A-NpH-CHCl2 was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of A'-Np by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of -0.310 vs ferrocene/ferrocenium (THF/NBu4PF6). The electrochemical data previously published for A-Np were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording A-Np(H2O). The hydrolysis products of A-Np and A'-Np were found to be reversibly oxidized at half-wave potentials of -0.418 and -0.437 V, respectively.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Tropolone and its N-derivatives isopropylaminotropone and diisopropylaminotroponimine react with [Cp*Ru(CH3CN)(3)]PF6 as the source of the electron-rich Cp*Ru+ synthon in a simple "capping reaction" to the first cyclopentadienyl/cycloheptatrienyl sandwich complexes containing two vicinal oxo or amino substituents. These heteroleptic, cationic C-5/C-7 pi-complexes, [Cp*Ru(C7H5)O2H](+) (4), [Cp*Ru(C7H5)O((NPr)-Pr-i)H](+) (5), and [Cp*Ru(C7H5)((NPr)-Pr-i)(2)H](+) (6), are air-stable 18-electron metallocenes without precedence. In solution, NMR spectroscopy proves the principal pi-coordination of the substituted eta(7)-cycloheptatrienyl ligands, whereas in the solid state a eta(5)-cycloheptatrienyl coordination mode with bent oxo/imino moieties prevails, as shown by X-ray single-crystal structure analyses. Chemically, these compounds are the conjugate Bronsted acids of neutral [O,O]-, [N,O]-, or [N,N]- metalloligands. Reaction with metal acetates or acetylacetonates by in situ deprotonation and complex formation gives access to trimetallic (M = Cu2+, 10-12) or tetrametallic (M = Fe3+, 13) complex cations. Their single-crystal structure analyses show square-planar or square-pyramidal (M = Cu2+) or octahedral (M = Fe3+) coordination motifs with peripheral, eta(5)-coordinated Cp*Ru moieties. Electrochemical studies on the trorucenes 4-6 showed a likely metal-based chemically reversible (4) or irreversible one-electron reduction (5, 6) as well as an irreversible one-electron oxidation for the N-substituted compounds 5 and 6. The behavior of the heterotri- and tetrametallic complexes 10, 11, and 13 was rationalized by a combination of cyclic and square-wave voltammetry as well as the combination of chronocoulometry and linear-sweep voltammetry and by comparison with the mononuclear copper or iron tropolone and topolonimine precursors 14-16. These studies indicate that in 10 and 11 the trorucene moieties are reduced first in two coincident or slightly separated one-electron reductions with the Cu2+ reduction at very negative potential, whereas in 13 the central Fe(III)-tris(troponolato) moiety is reduced prior to the trorucene appendices. An in vitro anticancer screening in MDA-MB-231 breast adenocarcinoma and HT-29 colon carcinoma cell lines showed enhanced antiproliferative activity for the [O,O]-coordinated iron and copper complexes.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.