Synthesis of Tetracyclic 2,3-Dihydro-1,3-diazepines from a Dinitrodibenzothiophene derivative

Triply fused 1,3-diazepine derivatives have been obtained by acidic reduction of rotationally locked and sterically hindered nitro groups in the presence of an aldehyde or ketone. The nitro groups are sited on adjacent rings of a dicyanodibenzothiophene-5,5-dioxide, which also displays fully reversible two-electron-accepting behavior. The synthesis, crystallographically determined molecular structures, and aspects of the electronic properties of these new molecules are presented

Conformationally-restricted bicarbazoles with phenylene bridges displaying deep-blue emission and high triplet energies: systematic structure-property relationships

The synthesis is reported of twelve new symmetrical carbazole dimers in which the carbazole units are linked via 1,4-phenylene spacers. There are two distinct series of compounds based on the position on the carbazole ring where the phenylene spacer is attached: this is either at carbazole C(3) (series 1a-1f) or at C(2) (series 2a-2f). The central phenylene ring is substituted with either two methyl, two methoxy or two cyano substituents which impart an intramolecular torsional angle between the phenylene and carbazole rings, thereby limiting the extent of π-conjugation between the carbazole units, and raising the triplet energies of the molecules to ET 2.6-3.0 eV, as determined from their phosphorescence spectra at 80 K. Structure-property relationships were studied by UV-vis and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. A notable observation is that substitution at the 2-position of carbazole (linear conjugation) exerts control over the position of the HOMO, while substitution at the 3-position of carbazole (meta conjugation) allows greater control over the LUMO. X-ray crystal structures are reported for two of the bicarbazoles. Compound 2d is shown to be a suitable host for the sky-blue emitter FIrpic in PhOLEDs, with improved device performance compared to CBP as host

Mechanistic Studies on the Heck−Mizoroki Cross-Coupling Reaction of a Hindered Vinylboronate Ester as a Key Approach to Developing a Highly Stereoselective Synthesis of a C1−C7 <i>Z</i>,<i>Z</i>,<i>E</i>-Triene Synthon for Viridenomycin

Mechanistic studies of the Heck−Mizoroki reaction of a vinylboronate ester with electronically different (four-substituted) aryl iodides shows that electron donors accelerate the cross-coupling, demonstrating that the oxidative addition step is not rate determining and that there is development of some degree of positive charge in the rate determining step. These results were used as a basis to allow the development of reaction conditions for the Heck−Mizoroki coupling of a hindered vinylboronate ester with electron deficient methyl cis-2-iodoacrylate. The resulting dienylboronate ester was converted through a series of highly stereoselective iodo-deboronations and Heck−Mizoroki reactions into a trienyl iodide precursor for further application in the total synthesis of viridenomycin

Convergent Synthesis of 10 nm Aryleneethynylene Molecular Wires by an Iterative Regioselective Deprotection/Sonogashira Coupling Protocol

The synthesis of a new series of rigid-rod aryleneethynylene derivatives of up to ca. 10 nm molecular length (compounds 16 and 17) is reported using iterative Pd-mediated Sonogashira coupling methodology combined with regioselective removal of the different protecting groups (namely, trimethylsilyl and 2-hydroxyprop-2-yl groups) from the terminal alkyne units. Additionally, the TMS−acetylene unit has been cleanly deprotected to afford a terminal alkyne in the presence of a cyanoethylsulfanyl group. Some of these molecular wires are functionalized with terminal protected thiophenol units for attachment to metal surfaces (compounds 16 and 17). Internal electron-acceptor units have been incorporated into their structures, namely, 9-[di(4-pyridyl)methylene]fluorene (compound 17) or fluorenone (compounds 19−22). Optical absorption and photoluminescence spectra reveal a red shift in the value of λmax with increasing molecular length, which approaches saturation at an effective conjugation length of ca. 15−20 π-units in the molecules, where each phenyl ring or a triple bond is counted as one π-unit

Mechanistic Studies on the Heck−Mizoroki Cross-Coupling Reaction of a Hindered Vinylboronate Ester as a Key Approach to Developing a Highly Stereoselective Synthesis of a C1−C7 <i>Z</i>,<i>Z</i>,<i>E</i>-Triene Synthon for Viridenomycin

Mechanistic studies of the Heck−Mizoroki reaction of a vinylboronate ester with electronically different (four-substituted) aryl iodides shows that electron donors accelerate the cross-coupling, demonstrating that the oxidative addition step is not rate determining and that there is development of some degree of positive charge in the rate determining step. These results were used as a basis to allow the development of reaction conditions for the Heck−Mizoroki coupling of a hindered vinylboronate ester with electron deficient methyl cis-2-iodoacrylate. The resulting dienylboronate ester was converted through a series of highly stereoselective iodo-deboronations and Heck−Mizoroki reactions into a trienyl iodide precursor for further application in the total synthesis of viridenomycin

Unusual Dinuclear and Mononuclear Cyclometalated Iridium Complexes of 2,5-Diaryl-1,3,4-oxadiazole Derivatives

A family of new 2,5-diphenyl-1,3,4-oxadiazole (OXD) derivatives 8−11 bearing ortho-alkyl substituents on one of the phenyl rings is reported. The reactions of these OXDs with IrCl3 under standard cyclometalating conditions did not give the usual μ-dichloro bridged diiridium OXD complexes. Instead, the novel diiridium complexes 12−14 and the monoiridium complex 15 were isolated and characterized by X-ray crystallography. It is proposed that the unusual structures arise because of the ortho-alkyl substituents leading to a substantial twisting of part of the OXD system which, for steric reasons, changes the normal course of the metal−ligand coordination reactions. Subsequent reactions of 13 and 15 gave the mononuclear complexes 16−18 with acac and picolinate anciliary ligands. The crystal structures of 16 and 18 are reported. Photoluminescence is observed in the green (16) and blue-green regions (17 and 18) at room temperature. Complexes 16−18 are phosphorescent at low temperature, with triplet lifetimes of 4.2−5.7 μs at 77 K

Calix[6]arene Derivatives Selectively Functionalized at Alternate Sites on the Smaller Rim with 2-Phenylpyridine and 2-Fluorenylpyridine Substituents to Provide Deep Cavities

The synthesis is described of calix[6]arene derivatives 4, 9, and 14 functionalized at alternate sites on the smaller rim with 4‘-(pyrid-2‘ ‘-yl)phenylmethoxy, (6‘-phenylpyrid-3‘-ylmethoxy), and {6‘-[2-(9,9-di-n-hexylfluorenyl)]pyrid-3‘-ylmethoxy} substituents, respectively. They were obtained by 3-fold reactions of 2-[4-(bromomethyl)phenyl]pyridine (3), 5-(bromomethyl)-2-phenylpyridine (8), and 5-(bromomethyl)-2-(9,9-di-n-hexylfluorenyl)pyridine (13) with the 1,3,5-trimethylether of the t-Bu-calix[6]arene in the presence of sodium hydride in THF in 56−75% yields. Detailed analysis of the 1H NMR spectra (including variable-temperature data for 4) has established that 4, 9, and 14 exist predominantly in the C3v cone conformation with minor Cs isomers also observed. The X-ray crystal structure of 4 reveals two molecules of similar cone conformation, with all three 4‘-(pyrid-2‘ ‘-yl)phenylmethoxy substituents stretched in the axial direction. Molecule I has a dimeric capsule structure with (pyrid-2‘ ‘-yl)phenylmethoxy substituents of one molecule interpenetrating those of its inversion equivalent to form a deep enclosed intermolecular cavity, which contains a CH2Cl2 guest molecule. Molecule II forms no such pair:  the intramolecular cavity is filled with solvent molecules

Unusual Dinuclear and Mononuclear Cyclometalated Iridium Complexes of 2,5-Diaryl-1,3,4-oxadiazole Derivatives

A family of new 2,5-diphenyl-1,3,4-oxadiazole (OXD) derivatives 8−11 bearing ortho-alkyl substituents on one of the phenyl rings is reported. The reactions of these OXDs with IrCl3 under standard cyclometalating conditions did not give the usual μ-dichloro bridged diiridium OXD complexes. Instead, the novel diiridium complexes 12−14 and the monoiridium complex 15 were isolated and characterized by X-ray crystallography. It is proposed that the unusual structures arise because of the ortho-alkyl substituents leading to a substantial twisting of part of the OXD system which, for steric reasons, changes the normal course of the metal−ligand coordination reactions. Subsequent reactions of 13 and 15 gave the mononuclear complexes 16−18 with acac and picolinate anciliary ligands. The crystal structures of 16 and 18 are reported. Photoluminescence is observed in the green (16) and blue-green regions (17 and 18) at room temperature. Complexes 16−18 are phosphorescent at low temperature, with triplet lifetimes of 4.2−5.7 μs at 77 K

Convergent Synthesis of 10 nm Aryleneethynylene Molecular Wires by an Iterative Regioselective Deprotection/Sonogashira Coupling Protocol

The synthesis of a new series of rigid-rod aryleneethynylene derivatives of up to ca. 10 nm molecular length (compounds 16 and 17) is reported using iterative Pd-mediated Sonogashira coupling methodology combined with regioselective removal of the different protecting groups (namely, trimethylsilyl and 2-hydroxyprop-2-yl groups) from the terminal alkyne units. Additionally, the TMS−acetylene unit has been cleanly deprotected to afford a terminal alkyne in the presence of a cyanoethylsulfanyl group. Some of these molecular wires are functionalized with terminal protected thiophenol units for attachment to metal surfaces (compounds 16 and 17). Internal electron-acceptor units have been incorporated into their structures, namely, 9-[di(4-pyridyl)methylene]fluorene (compound 17) or fluorenone (compounds 19−22). Optical absorption and photoluminescence spectra reveal a red shift in the value of λmax with increasing molecular length, which approaches saturation at an effective conjugation length of ca. 15−20 π-units in the molecules, where each phenyl ring or a triple bond is counted as one π-unit

Extreme Conformational Constraints in π-Extended Tetrathiafulvalenes: Unusual Topologies and Redox Behavior of Doubly and Triply Bridged Cyclophanes

Doubly and triply bridged 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (ex-TTF) derivatives have been synthesized. Key steps are the generation and macrocyclization reactions of ex-TTF-dithiolate reagents. The X-ray crystal structures of the doubly bridged cyclophanes 15 and 16 and the triply bridged system 23 show that the saddle-like conformation of the ex-TTF framework is enhanced by the short bridges between the dithiole rings. Unlike all previous ex-TTF derivatives (which display a single quasi-reversible two-electron oxidation wave, D0 → D2+), cyclic voltammetry of the cyclophanes reveals two reversible, one-electron oxidation steps (D0 → D•+ → D2+), with differences between the half-wave potentials (E21/2 − E11/2) of 0.22−0.26 V. The conformational changes and gain in aromaticity which drive the second oxidation process in unrestricted ex-TTF systems (including singly bridged cyclophanes) have been prevented by multiple bridging. The radical cation species gives rise to a very broad, low-energy band (λmax = 2175 and 2040 nm for 15 and 21, respectively), assigned to an intramolecular interaction. The steric constraints imposed by multiple bridging have become so extreme that the π-framework of 15, 16, 21, and 23 exhibits remarkable optical and redox behavior which is not characteristic of ex-TTF systems