Multistimuli-Responsive Chromism of Vinylene-Linked Bisflavin Based on the Aggregation and Redox Properties.

Multistimuli-responsive chromism was observed for vinylene-linked bisflavin 1 a with an extended π-conjugated platform. The yellow emission of a dilute solution of 1 a in CHCl3 (0.2 mM) observed at 298 K under UV excitation was changed to orange or red emission upon (1) an increase of concentration, (2) a decrease of temperature, and (3) variation of the solvent. This is in contrast to the almost non stimuli-responsive chromism of the N-methylated bisflavin analogue 1 b and monoflavin 2 a. Mechanistic investigation by 1 H NMR analysis under various conditions revealed that the extended π-conjugation platform and imide moiety of 1 a generate controllability in the formation of lower- and higher-ordered aggregates, which induce variation of the emission color upon change. Bisflavin 1 a also exhibited redox-induced chromism, where the orange emission of 1 a was quenched by the addition of hydrazine under anaerobic conditions, and changed back to the original emission upon subsequent bubbling of O2 gas.

Phosphorescent Molecules That Resist Concentration Quenching in the Solution State: Concentration-Driven Emission Enhancement of Vaulted trans-Bis[2-(iminomethyl)imidazolato]platinum(II) Complexes.

In this paper, we describe the first phosphorescent molecules that do not exhibit the concentration quenching in the homogeneous solution state throughout the entire range of concentrations. A series of newly designed polymethylene-vaulted trans-bis[2-(iminomethyl)imidazolato]platinum(II) complexes (1a, n = 10; 1b, n = 12; 1c, n = 14) was prepared by treating [PtCl2(CH3CN)2] with the corresponding N,N'-bis[(1H-imidazol-2-yl)methylene]-1,ω-alkanediamines. The trans coordination and vaulted structures of 1 have been unequivocally established from X-ray diffraction studies. When the concentration of a clear homogeneous solution of 1a-c in organic solvents increases from the diluted to the saturated state, the emission intensity and quantum efficiency increase continuously without concentration quenching at ambient temperature. This is in contrast to the emission profiles of other analogues 2-4 and typical AIEgens, which show ordinary concentration quenching under the same measurement conditions. The present concentration-driven emission enhancement is observed more intensely in a solution of a racemic mixture of 1 in comparison to that of the optically pure solution. Kinetic studies, 1H NMR, XRD analyses, and DFT calculations revealed that this specifically intense emission enhancement of 1 is attributed to an increase in the contribution of a 3MMLCT to 1GS transition, which is caused by the specific ability for the formation of a cofacial association dimer of 1.

Single-Point Remote Control of Flapping Motion in Clothespin-Shaped Bimetallic Palladium Complexes Based on the N(sp(2))-N(sp(3)) Interconversion in Amide Functionalities.

The synthesis, structure, and flapping motion of clothespin-shaped binuclear trans-bis(salicylaldiminato)palladium(II) complexes (anti-1) with 4-azaheptamethylene linkers bearing amide (a-g), urethane (h), or urea (i) functionalities are described in this report. Various 2D (1)H NMR experiments and XRD analyses indicate that the amide- and urethane-linked anti-1 a,b,d-h complexes exist as equilibrated mixtures of major and minor conformers I and II in CDCl3, whereas the complexes anti-1 c and i were observed as a single species. The mapping of NOESY cross-peaks between conformers I and II revealed that the equilibration of the major and minor conformers of anti-1 a,b,d-h proceeds by two pathways, namely a nonrotatory flapping motion of the coordinated blades and a nonflapping rotation of C-N bonds, whereas the equilibration of anti-1 c proceeds by simultaneous flapping and rotation motions. Kinetic studies carried out by means of (1)H-(1)H EXSY experiments revealed that 1) the ΔG(≠) 298K values for the flapping motion are controlled remotely by the steric and electronic effects of the RCON functionalities and 2) the activation parameters for the nonrotatory flapping process are identical to those for the nonflapping peptide rotation in the complexes anti-1 a,b,d-h, which indicates that the present multistep conformational transformation induced by the flapping motion is controlled by the rate-determining pyramidalization/depyramidalization (i.e., sp(2)/sp(3) interconversion) of the nitrogen atoms of the functionalities. The static and controllable molecular mobility of anti-1 bearing peptide linkers has been discussed by comparison with the dynamic behavior of its analogues anti-2-4 with flexible polymethylene linkers.

Highly fluorescent flavins: rational molecular design for quenching protection based on repulsive and attractive control of molecular alignment.

Unprecedented intense fluorescent emission was observed for a variety of flavin compounds bearing a perpendicular cyclic imide moiety at the C7 position of an isoalloxazine platform. A series of alloxan-substituted flavins was prepared selectively by reduction of the corresponding N-aryl-2-nitro-5-alkoxyanilines with zinc dust and subsequent reaction with alloxan monohydrate in the presence of boric acid. Analogues bearing oxazolidine-2,4-dione functionality were obtained on methylation of the alloxan-substituted flavins with methyl iodide and subsequent rearrangement in the presence of an inorganic base. The flavin compounds exhibit intense white-green fluorescent emission in the solution state under UV excitation at 298 K, with emission efficiencies Φ298 K greater than 0.55 in CH3 CN, which are higher than the values for all reported flavin compounds under similar conditions. The highest Φ298 K value of 0.70 was obtained in CH3 CN for isoalloxazine bearing C7-alloxan and N10-2,6-diisopropylphenyl groups. The temperature dependence of the emission intensities indicates that the pronounced emission properties at 298 K are attributable to the highly heat resistant properties towards emission decay with increasing temperature. Mechanistic studies, including X-ray diffraction analysis, revealed that the good emission properties and high heat resistance of the alloxan-substituted flavins are due to a synergetic effect of the associative nature of the C7-alloxan unit and the repulsive nature of the perpendicular bulky substituents at the C7 and N10 positions.

Control of Metal Arrays Based on Heterometallics Masquerading in Heterochiral Aggregations of Chiral Clothespin-Shaped Complexes.

Heterometal arrays in molecular aggregations were obtained by the spontaneous and ultrasound-induced gelation of organic liquids containing the chiral, clothespin-shaped trans-bis(salicylaldiminato) d8 transition-metal complexes 1. Heterometallic mixtures of complexes 1 a (Pd) and 1 b (Pt) underwent strict heterochiral aggregation entirely due to the organic shell structure of the clothespin shape, with no effect of the metal cores. This phenomenon provides an unprecedented means of generating highly controlled heterometallic arrangements such as alternating sequences [(+)-Pd(-)-Pt(+)-Pd(-)-Pt⋅⋅⋅] as well as a variety of single metal-enriched arrays (e.g., [(+)-Pt(-)-Pd(+)-Pd(-)-Pd(+)-Pd(-)-Pd⋅⋅⋅] and [(+)-Pd(-)-Pt(+)-Pt(-)-Pt(+)-Pt(-)-Pt⋅⋅⋅]) upon the introduction of an optically active masquerading unit with a different metal core in the heterochiral single-metal sequence. The present method can be applied to form various new aggregates with optically active Pd and Pt units, to allow 1) tuning of the gelation ultrasound sensitivity based on the different hearing abilities of the metal units; 2) aggregation-induced chirality transfer between heterometallic species; and 3) aggregation-induced chirality enhancement. A mechanistic rationale is proposed for these molecular aggregations based on the molecular structures of the units and the morphologies of the aggregates.

Synthesis of primary and secondary alkylboronates through site-selective C(sp3)-H activation with silica-supported monophosphine-Ir catalysts.

The site-selective activation and borylation of unactivated C(sp(3))-H bonds in 2-alkylpyridines to form primary and secondary alkylboronates was achieved using silica-supported monophosphine-Ir catalysts. This borylation occurs selectively at C-H bonds located γ to the pyridine nitrogen atom. The site-selectivity of this reaction suggests that the C-H bond cleavage occurs with the assistance of a proximity effect due to N-to-Ir coordination.

Rh-catalyzed borylation of N-adjacent C(sp3)-H bonds with a silica-supported triarylphosphine ligand.

Direct C(sp(3))-H borylation of amides, ureas, and 2-aminopyridine derivatives at the position α to the N atom, which gives the corresponding α-aminoalkylboronates, has been achieved with a heterogeneous catalyst system consisting of [Rh(OMe)(cod)]2 and a silica-supported triarylphosphine ligand (Silica-TRIP) that features an immobilized triptycene-type cage structure with a bridgehead P atom. The reaction occurs not only at terminal C-H bonds but also at internal secondary C-H bonds under mild reaction conditions (25-100 °C, 0.1-0.5 mol % Rh).

Rh-catalyzed ortho-selective C-H borylation of N-functionalized arenes with silica-supported bridgehead monophosphine ligands.

Supported phosphine-Rh systems, prepared in situ from silica-supported bridgehead monophosphines and [Rh(OH)(cod)](2), have enabled ortho-selective C-H borylation for a range of arenes containing nitrogen-based directing groups. The regioselectivity was excellent with various N-directing groups, including saturated and unsaturated N-heterocycles, tert-aminoalkyl groups, and imine-type C-N double bonds. The reaction showed significant tolerance toward steric repulsion around the reacting C-H bond. This Rh catalysis complements the Ir-catalyzed ortho-borylation, which is effective for arenes with oxygen-based directing groups.

Ester-directed regioselective borylation of heteroarenes catalyzed by a silica-supported iridium complex.

The ester-directed regioselective borylation of arenes catalyzed by a silica-supported monophosphine-Ir complex displayed a significantly broad substrate scope toward heteroaromatic compounds, including thiophene, pyrrole, furan, benzothiophene, benzofuran, indole, and carbazole derivatives. The regioselectivity is complementary to the selectivities observed in the heteroarene C-H borylation with the dtbpy-Ir catalyst system.

Emission Control by Molecular Manipulation of Double-Paddled Binuclear PtII Complexes at the Air-Water Interface.

Molecular functions depend on conformations and motions of the corresponding molecular species. An air-water interface is a suitable asymmetric field for the control of molecular conformations and motions under a small applied force. In this work, double-paddled binuclear PtII complexes containing pyrazole rings linked by alkyl spacers were synthesized and their orientations and emission properties dynamically manipulated at the air-water interface. The complexes emerge from water with concurrent variation of interface orientation of the planes of the PtII complexes from perpendicular to parallel during mechanical compression suggesting a unique 'submarine emission'. Phosphorescence of the complexes is quenched at the air-water interface prior to monolayer formation with intensities subsequently rapidly increasing during monolayer compression. These results indicate that asymmetric reactions and motions might be controlled by applying mechanical force at the air-water interface.

Directed ortho borylation of functionalized arenes catalyzed by a silica-supported compact phosphine-iridium system.

An immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine, showed high activities and selectivities for the borylation of aromatic C-H bonds with bis(pinacolato)diboron. This system was effective not only for the borylation of benzene but also for the ortho borylation of arenes with directing groups, such as ester, amide, sulfonate, acetal, alkoxymethyl, and chloro groups, under mild reaction conditions.

Data on the characterization of (N-alkylsalicylaldiminato)bis(2-phenylpyridinato)iridium(III).

Herein we report the synthesis, characterization data and photophysical properties of iridium(III) complexes having N-alkylated salicylaldimine and 2-phenylpyridine ligands. The structures of novel iridium complexes were assigned by 1H and 13C NMR, 1H-1H COSY, NOESY, HMQC, HMBC, HRMS, IR and XRD analysis. For further information, we obtained photophysical properties in solution and crystalline states.

Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(ii) coordination platforms.

The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldiminato)Pt(ii) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone ligands. A series of non-vaulted and vaulted Pt complexes (1-5) with salicylaldehyde hydrazones as trans-coordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of the trans-bis(salicylaldiminato)Pt(ii) coordination platforms. X-ray diffraction and 2D NMR data demonstrated that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neighbouring N(2) lone pairs in the d-π conjugation of the trans-bis(salicylaldiminato)Pt(ii) platforms owing to conformational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-dimethyl analogues 2 made a much less significant contribution to the extension of the d-π conjugation, due to their high conformational mobility. Complexes 1-5 were found to have structure-dependent chromogenic properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes 1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and 5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(ii) complex 6. The introduction of MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic and bathochromic shifts, respectively. In addition, νmax - ET(30) plots for various solvents revealed that complexes 1-5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochromically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5. Complexes 1-5 also exhibit emission enhancement upon addition of excess CH3SO3H in dimethyl sulfoxide, and a significant effect of the linker on quantum yields (Φ77 K) was observed in the case of the vaulted complexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure dependence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone complexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d-π conjugation on the trans-bis(salicylaldiminato)Pt(ii) coordination platforms.

Site-selective C-H borylation of quinolines at the C8 position catalyzed by a silica-supported phosphane-iridium system.

Site-selective C-H borylation of quinoline derivatives at the C8 position has been achieved by using a heterogeneous Ir catalyst system based on a silica-supported cage-type monophosphane ligand SMAP. The efficient synthesis of a corticotropin-releasing factor1 (CRF1) receptor antagonist based on a late-stage C-H borylation strategy demonstrates the utility of the C8 borylation reaction.

Directed ortho borylation of phenol derivatives catalyzed by a silica-supported iridium complex.

The directed ortho borylation of phenol derivatives protected with an N,N-diethylcarbamoyl group was efficiently catalyzed by an immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine. The utility of the carbamoyloxy group as a leaving group for metal-catalyzed cross-coupling reactions was demonstrated by its utilization in the synthesis of a terphenyl derivative.

Hydrogenation of hindered ketones catalyzed by a silica-supported compact phosphine-Rh system.

A heterogeneous mono(phosphine)-Rh catalyst system silica-SMAP-Rh(OMe)(cod), where silica-SMAP stands for a caged, compact trialkylphosphine (SMAP) supported on silica gel, showed broad applicability toward the hydrogenation of hindered ketones. Doubly alpha-branched ketones such as diisopropyl ketone was hydrogenated under nearly atmospheric conditions. Di-tert-butyl ketone could be hydrogenated under more forcing conditions.