Synthesis,Structure, and Reactivity of Lewis Base Stabilized Plumbacyclopentadienylidenes

Plumbacyclopentadienylidenes, in which the lead atoms have divalent states and are coordinated by THF, pyridine and N‐heterocyclic carbene, were synthesized and characterized. The THF‐ and pyridine‐stabilized compounds can be regarded as rare examples of hypervalent 10‐X‐4 species. The equilibrium between the THF adduct and the free plumbacyclopentadienylidene was evidenced by spectroscopic analysis and theoretical calculations. The THF adduct in benzene converted into a plumbylene dimer, where one of the lead centers is coordinated by THF and the other lead atom is coordinated by a divalent lead atom, the dimer gradually decomposing into spiroplumbole. The THF adduct unexpectedly reacted with trifluoroborane and trichlorogallane to afford fluoroborole and chlorogallole, which are the first examples of non‐annulated fluoroborole and gallole, respectively.     

Facile Synthesis of Dibenzopentalene Dianions and Their Application as New π‐Extended Ligands

Reduction of phenyl(silyl)ethynes with potassium followed by quenching with iodine gave dibenzopentalenes in moderate yields. The intermediates of the reactions, dipotassium dibenzopentalenides, were isolated. The first dibenzopentalene–transition‐metal complex was successfully synthesized. The ruthenium atoms are located above the six‐membered rings. However, X‐ray diffraction analysis and theoretical calculations revealed that the aromatic nature of the five‐membered rings was retained. The cyclic voltammetry of the Ru complex revealed two oxidation waves with relatively large separation.     

Formation of the first monoanion and dianion of stannole

The first syntheses of mono- and dianions of stannole were accomplished by transmetallation or reduction of the novel bi(1,1-stannole).     

New reactions of a dibenzo[a,e]pentalene

Reduction of dibenzo[a,e]pentalene 3 (denoted as dibenzopentalene hereafter) with excess lithium gave dilithium dibenzopentalenide 1. Since oxidation of 1 with iodine gave 3, redox behavior between 1 and 3 is controllable and reversible. Reaction of 3 with methyllithium gave lithium 5-methyldibenzopentalenide 5, the formation of which was evidenced by some trapping experiments and X-ray crystallographic analysis. Reactions of 3 with halogens gave 5,10-dihalodibenzopentalenes, 8 and 9. Some optical properties of novel dibenzopentalene derivatives are also demonstrated.     

Arching a bay area of triphenyleno[1,12-bcd]thiophene with group 14 functionalities: Synthesis of the first triphenylene derivatives having thiophene and metallafluorene moieties

Arching a bay area of triphenyleno[1,12-bcd]thiophene with group 14 functionalities gave the first triphenylene derivatives whose two pairs of bay carbons are connected by two different heteroatom functionalities. Triphenyleno[1,12-bcd:4,5-b′c′d′]dithiophene, which had been only accessible through the very severe reaction conditions, was synthesized under the mild reaction conditions. Photophysical properties of newly-obtained heterolotriphenylene derivatives are discussed with theoretical calculations.     

Reduction of dichlorodiphenylstannane

Reduction of dichlorodiphenylstannane with lithium followed by treatment with methyl iodide gave methyltriphenylstannane, dimethyldiphenylstannane and 1,2‐dimethyldistannane. 1,2‐Dilithiodistannane and triphenylstannyllithium were intermediates of this reaction. Copyright © 2005 John Wiley & Sons, Ltd.     

Assessment of ESR-CT imaging by comparison with autoradiography for the distribution of a blood-brain-barrier permeable spin probe, MC-PROXYL, to rodent brain

Blood-brain-barrier (BBB)-permeable, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy (MC-PROXYL) and BBB-impermeable carbamoyl-PROXYL were used to assess the ESR imaging technique by comparing with autoradiography. For this purpose, spin probes, 14C-labeled at their five-membered ring, [14C]MC-PROXYL and [14C]carbamoyl-PROXYL, were newly synthesized. These probes were i.p. or i.v. injected into rats and autoradiograms were recorded. The autoradiograms of rat head showed that [14C]MC-PROXYL distributed well in the brain compared to [14C]carbamoyl-PROXYL. In vivo ESR spectra and two-dimensional ESR images of isolated rat brain treated with MC- or carbamoyl-PROXYL also indicated the extensive distribution of MC-PROXYL but not carbamoyl-PROXYL in the rat brain. The three-dimensional ESR images of the head of rats and mice were consistent with the fact that MC-PROXYL but not carbamoyl-PROXYL is incorporated into the brain. The ESR-CT images were better for mice than rats. However, the quality of the ESR-CT images was still not satisfactory. Although the resolution and sensitivity of the ESR-CT images were worse than those of the autoradiographic images, the former technique has unique features and advantages; e.g., functional, noninvasive and three-dimensional detection.