Search

The known (tetraphenyl-η4-cyclobutadiene)-η5-cyclopentadienylcobalt (1) and a series of its new substituted derivatives have been prepared. The electronic states of a few representatives have been characterized by absorption and magnetic circular dichroism. Time-dependent density functional theory has been used to arrive at spectral assignments for several prominent low-energy bands. The absorption spectra of the radical ions of 1 have also been recorded.

The trinuclear [{Ru(NH3)4(py-COOH)}(μ-CN){Ru(bpy)2}(μ-CN){Ru(NH3)4(py-COOH)}]6+ (py-COOH = isonicotinic acid, bpy = 2,2'-bipyridine) (1) and dinuclear [{Ru(dcb)2}2L]7- (dcb = 2,2'-bipyridine-4,4'-dicarboxylic acid, H3L = 9-phenyl-2,3,7-trihydroxy-6-fluorone) (2) complexes were prepared and their spectroelectrochemical behaviour characterised in solution and on conductive glass electrodes layered with Sb-doped nanocrystalline SnO2. The systems display a reversible redox response in a narrow potential range (-0.5 to +0.5 V vs SCE) and offer the possibility of controlling colour changes of electrochromic devices through variations of the coordinated and bridging ligands at the metal centres. SnO2(Sb) electrodes loaded with these dyes show switching times of the order of ms.

We describe a convergent synthesis of eight 1,3,5- and 1,2,4,5-substituted benzene derivatives with long rigid arms containing 4-pyridyl, 2,2'-bipyridyl, and 2,2'-bipyrimidyl termini, meant to be used as trigonal or tetragonal connectors for the construction of large molecular structures. The synthesis involved copper-free Pd-mediated coupling of terminal acetylenes to aryl halides. First, one of the termini of 1,3-diethynylbicyclo[1.1.1]pentane was coupled with a brominated aza heterocycle, and second, 3 equiv of the resulting extended arm were coupled with 1,3,5-triiodobenzene or 4 with 1,2,4,5-tetraiodobenzene. An improved large-scale synthesis for 1,3-diethynylbicyclo[1.1.1]pentane is described. The structures of two of the arms were determined by single-crystal X-ray analysis. Several long molecular rods with 4-pyridyl termini were obtained as byproducts, and a single-crystal X-ray structure is reported for the shortest of these.

Efficient syntheses of 5-brominated and 5,5'-dibrominated 2,2'-bipyridines and 2,2'-bipyrimidines, useful for the preparation of metal-complexing molecular rods, have been developed. 5-Bromo-2,2'-bipyridine, 5-bromo-5'-n-butyl-2,2'-bipyridine, and 5-bromo-5'-n-hexyl-2,2'-bipyridine were obtained by Stille coupling of 2,5-dibromopyridine with 2-trimethylstannylpyridine or the requisite 5-alkyl-2-trimethylstannylpyridine, obtained via regioselective zincation of a 3-alkylpyridine.BF(3) complex in the less hindered of the two reactive positions with lithium di-tert-butyl-(2,2,6,6-tetramethylpiperidino)zincate. 5,5'-Dibromo-2,2'-bipyridine was obtained by the reductive symmetric coupling of 2,5-dibromopyridine with hexa-n-butyldistannane. The yields of these coupling reactions ranged from 70 to 90%. 5-Bromo- and 5,5'-dibromo-2,2'-bipyrimidines were obtained in yields of 30 and 15%, respectively, by bromination of 2,2'-bipyrimidine, prepared from 2-chloropyrimidine in 80% yield by an improved reductive symmetric coupling procedure.

A synthetic approach to a two-dimensional grid polymer is proposed and the execution of initial steps is described. Pd-catalyzed coupling of (1,12-dicarba-closo-dodecaboran-1-yl)copper (10) with iodobenzene, m-diiodobenzene, and 1,3,5-triiodobenzene yielded the known 1,12-dicarba-closo-dodecaboran-1-ylbenzene (3) and the new m-bis(1,12-dicarba-closo-dodecaboran-1-yl)benzene (4) and 1,3,5-tris(1,12-dicarba-closo-dodecaboran-1-yl)benzene (1), respectively. Each arm of the trigonal connector 1 was provided with one or two sticky tentacles by conversion to 1,3,5-tris[12-((3-(ethylthio)propyl)dimethylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]benzene (7) and 1,3,5-tris[12-(bis(3-(ethylthio)propyl)methylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]benzene (8). Linear coupling of carboranyl CH terminals through a mercury atom produced very stable dimeric structures from 3 and 4. The carborane 3, its mercury-linked dimer 13, the 1:1 complex of 13 with 2,2‘-bipyridyl, and the 2:1 complex of 13 with 2,2‘-bipyrimidyl ...

The first example of a binuclear ruthenium complex involving the p-carborane framework in the bridging ligand is reported. The bridging ligand is a symmetric linear array comprising a central p-carborane unit, two p-phenylene spacers, and two 5-yl-2,2'-bipyridine coordinating units. A homobinuclear Ru(II) complex, with 2,2'-bipyridine as peripheral ligands, was synthesized and characterized. The Ru(II)-Ru(III) mixed-valence species, obtained by partial oxidation, has been investigated with steady-state and time-resolved techniques in CH3CN. The rate of photoinduced electron transfer is 2.3 x 10(8) s(-1).

A series of Ru(bpy)(2)-dioxolene complexes 1-4 (bpy = 2,2'- bipyridine) and corresponding Ru(dcb)(2)-dioxolene complexes 5-8 (dcbH(2) = 2,2'-bipyridine-4,4'-dicarboxylic acid) have been prepared, and their spectroelectrochemical behavior in solution has been investigated. The complexes show reversible electrochemical behavior accompanied by a strong NIR absorption in their semiquinone forms due to a Ru(dpi) --sq(pi) MLCT band. Complete quenching of the NIR absorption occurs both upon oxidation (to the quinone form) and upon reduction (to the catechol form) very close to 0 V. The color of the systems can be tuned by using a wide range of ligands. The complexes 5-8 can be anchored onto nanocrystalline inorganic semiconductors allowing incorporation into potential electrochromic devices. As a proof of principle, compound 8 has been adsorbed on nanocrystalline Sb-doped SnO(2) supported on FTO glass, and it displays reversibly switchable electrochromic behavior in the NIR.

A series of cyano-bridged binuclear mixed valence complexes of the general formula M-Ru(III)(NH(3))(4)pyCOOH [pyCOOH = isonicotinic acid; M = cis-Ru(bpy)(2)(CN)(2), 1 (bpy = 2,2' bipyridine); trans-Ru(py)(4)(CN)(2), 2 (py = pyridine); [Ru(CN)(6)](4)(-), 3; [Fe(CN)(6)](4)(-), 4] have been prepared and anchored through the carboxylic function to nanocrystalline TiO(2) or SnO(2) electrodes. The complexes display a reversible electrochromic behavior in the range of applied potential from -0.5 to +0.5 V, versus SCE. Tuning of the electronic transitions in the visible and near-infrared spectral regions is achieved through changes of the solvent and of the cyano-bridged metal moiety M.