高尾（稲垣） 昭子

A pair of chiral Pt(ii) complexes exhibiting aggregation-induced phosphorescence and circularly polarized luminescence have been synthesized and characterized.

A series of novel metal complexes were synthesized containing an Ir-cyclometalated bichromophore as a visible-light sensitizer. A new bichromophoric unit containing a naphthyl substituent and methyl substituents on the 2-phenylpyridine chelating ligand was synthesized and characterized for the first time. According to the increased crystallinity of the bichromophoric unit, novel Ir-M metal complexes (M = Pd, Mn, and Ir) were synthesized and fully characterized. The novel Ir-Pd complex maintained photocatalytic activity toward styrenes under visible-light irradiation, and polymerization with p-chlorostyrene, copolymerization with styrene and p-chlorostyrene furnished corresponding polymers.

A highly efficient photo-Fenton catalyst iron silicate glass was successfully prepared by a simple sol–gel method.

<p>Light-active dinuclear iridium complexes catalyze the decomposition of formic acid to generate H₂ under ambient temperature and base-free conditions. The catalyst activity is sensitive to light demonstrating the ON/OFF switching ability.</p>

<p>Under irradiation conditions, low-pressure and room-temperature hydrogenation of carbon dioxide (CO₂) has been achieved using a trinuclear iridium hexahydride complex <bold>1</bold>.</p>

To examine the effect of tuning the electron transfer ability between photosensitizers and reaction centers on the activity of visible-light-driven catalysts, a series of trinuclear Ru photo-catalysts containing two Ru(II) photosensitizers and a Ru(II) reaction center bridged by a substituted bipyrimidine was prepared. The introduction of electron-donating or electron-withdrawing groups on the ligands was found to affect the photophysical and electrochemical properties of these catalysts. Density functional theory calculations of the mononuclear Ru complexes with nonsubstituted and substituted bipyrimidine ligands, which correspond to the reaction center of the trinuclear complexes, revealed how the electronic effect of the substituents affect the frontier orbital energies. For photocatalytic oxygenation of a sulfide and terminal alkenes, the catalyst with a 5,5'-dibromo-2,2'bipyrimidine ligand showed higher activity than the catalyst with 5,5'-dimethyl-2,2'-bipyrimidine and nonsubstituted bipyrimidine ligands, as expected according to the electronic effects of these ligands. In contrast, the catalyst with the nonsubstituted bipyrimidine ligand showed the highest activity toward inner alkenes, which may be due to steric effects.

Syntheses and structural determination of rhodium complexes ligated by diphosphines containing light-harvesting fluorene backbones are presented. In these rhodium complexes, the rhodium center is surrounded by a light-absorbing diphosphine unit. The presence of Rh-Rh bonding interactions is suggested by density functional theory studies.

Precise, one-pot synthesis of end-functionalized conjugated polymers, poly(9,9-di-n-octyl-fluorene vinylene)s (PFVs), have been prepared by acyclic diene metathesis (ADMET) polymerization followed by Wittig-type coupling with aldehyde in the presence of molybdenum-alkylidene catalyst, Mo(CHMe2Ph)(N-2,6-Me2C6H3) [OC(CH3)(CF3)(2)](2) (Mo cat.). Further addition of Mo cat. after the ADMET polymerization was necessary for completion of olefin metathesis (with the vinyl chain end) and for exclusive end-functionalization by the subsequent coupling. Various end-functionalities could be introduced without purification or isolation by this one pot methodology.

[Ru(bpy)(3)](2+) is well-known as a prototype for the Ru(II) complexes used in a wide variety of photofunctional materials. The triplet metal-centered ((MC)-M-3) state is important in this complex, since it dominates the phosphorescence lifetime and photoreaction processes. Despite this, the (MC)-M-3 state has not yet been observed by spectroscopic methods. In the present study, we demonstrated that time-resolved infrared vibrational spectroscopy enables observations of the (MC)-M-3 state. A vibrational band at 1599 cm(-1) was found to exhibit unique temporal behavior that differed from that of other bands assignable to the triplet metal-to-ligand charge-transfer ((MLCT)-M-3) state. This unique behavior was assessed under various experimental conditions and it was concluded that the band arises from the short-term population (similar to 23 ps) of the (MC)-M-3 state during relaxation to the bottom of the (MLCT)-M-3 state. These results agree with [Fe(bpy)(3)](2+) spectra, which show that the (MC)-M-5 state is the most stable excited state.

Trinuclear Ru cluster photocatalysts that contain two Ru(II) photo-sensitizers and a Ru(II) reaction center are prepared, and their activity in the photo-catalytic oxygenation of a sufide and alkenes is investigated. Photoirradiation (visible light) and the use of a Co salt ([Co(NH3)(5)Cl]Cl-2, as an electron acceptor) are found to be essential for these catalytic reactions. The 0 atom of the water solvent (pH 6.8) is transferred to the substrate by a stepwise electron transfer and deprotonation of an aqua ligand at the reaction center. Through these processes, the aqua ligand coordinated at the reaction center is converted to a Ru-V=O species, which is the active intermediate in the sulfide and alkene oxygenation.

A novel light-active Pd complex having a BINAP ligand with 2-naphthyl substituents on the phosphines was synthesized and characterized. The complex showed good polymerization activity toward 4-methoxystyrene during irradiation (lambda = 395 nm) and the reaction progress can be controlled by ON-OFF switching of the light source. Mechanistic investigations strongly suggest a coordination-insertion mechanism.

Oligo(2,5-dialkoxy-1,4-phenylenevinylene)s containing three different chiral alkoxy substituents on the phenyl end groups with structurally regular (all trans) controlled repeat units have been prepared; these compounds showed highly enhanced aggregation-induced circular dichroism (AICD; formation of supramolecular polymers), and an inversion of the CD signal was observed even with the same end groups under certain conditions.

A series of dinuclear Pt(II) bis-aryl complexes with visible-light-absorbing Ir(III)-cyclometalate units were synthesized, and their molecular structure and photophysical and electrochemical properties were investigated. The dinuclear complexes underwent reductive elimination upon visible-light irradiation at ambient temperature to afford the corresponding biaryls. The photoredox process at the Ir center induces the oxidation of the Pt(II)-Ar-2 center to [Pt-Ar-2] (III) to accelerate reductive elimination.

Time-resolved fluorescence study has been explored for end-functionalized conjugated triblock copolymers consisting of poly(9,9-di-n-octylfluorene-2,7-vinylene)s (PFVs, FV repeat units ca. 10 or 20) and oligo(2,5-dialkoxy-1,4-phenylenevinylene)s [OPV, alkoxy = O(CH2)(2)OSiPr3, 3 or 7 PV repeat unit] as the middle segment. Unit (FV and PV) length dependence of each block on fluorescence was examined. The polymer sample having three PV repeat units as the middle segment with C6F5 end-groups, [10PFV-relative intensities of the vibronic bands increase in later delay time, 3PV]F-2, showed time-dependent fluorescence spectra, in which whereas similar observations were not seen in the other polymer samples containing 7PV as the middle segment even by varying the PFV chain lengths (ca. 20) or the end-group (C6F5 vs C6H5). Time-resolved of fluorescence signals for [10PFV-3PV]F-2 can be analyzed by assuming two components: one is a faster decay component and the other is a slower red component, which rises with the time constant of the former one. On the other hand, the other three polymer samples showed single-exponential decays without significant wavelength dependence. Dynamical structural relaxation in the excited state is proposed as the origin of time dependence of the fluorescence spectra in the polymer having 3PV repeat unit on the basis of analysis of time-resolved fluorescence signals as well as viscosity dependence.

A facile, precise one-pot synthesis of end-functionalized star (triarm) polymers consisting of poly(9,9-di-n-octylfluorene-2,7-vinylene)s (PFVs), the triblock copolymers [by incorporation of tri(2,5-dialkoxy-1,4-phenylene vinylene) or terthiophene units as the middle segment], has been achieved by olefin metathesis followed by Wittig-type coupling; effects of the PFV conjugation length, the middle segment and the end groups on the emission properties have been studied.

Comprehensive analyses of the excited states of prototypical ruthenium complexes using time-resolved infrared vibrational spectroscopy reveal a peak that can be assigned to the dark (MC)-M-3 (metal centered) state, which plays an important role for their photofunctions.

Visible-light-controlled polymerization was achieved by a bichromophoric organopalladium catalyst which possesses a naphthyl-substituted cyclometallated Ir(III) light-absorbing moiety. The complex was highly active toward styrene polymerization upon visible-light irradiation, and its photoactivity toward polymerization and dimerization was switchable. On the basis of the switching activity, controlled copolymerization of styrene and vinyl ether was achieved upon photo-irradiation to give the corresponding copolymers.

Defect-free, highly trans oligo(2,5-dialkoxy-1,4-phenylene vinylene)s [alkoxy = O(CH2)(2)(OSiPr3)-Pr-i] with both repeat units (ex. 9, 15, and 31 repeat units) and end groups (aldehyde, C6F5, terthiophene, ferrocene) well-defined are prepared by a stepwise combined olefin metathesis using Mo(CHCMe2Ph)(N-2,6-Me2C6H3)[OCCH3(CF3)(2)](2) with subsequent Wittig-type coupling. End-functionalized oligomers with uniform distributions are also prepared by acyclic diene metathesis (ADMET) condensation using a ruthenium-carbene catalyst, followed by the above combined olefin metathesis and Wittig coupling. The effects of the repeat units and the end functional groups on the optical properties are explored; the photoluminescence quantum yields in the end-functionalized oligomers (e.g., 9 mers) are affected by the end groups.

Organometallic photocatalysis developed in the authors' laboratory, which is mediated by [Ru(bipy)(3)](2+) (TB)-type sensitizers, is reviewed. After characteristics of photophysical properties of TB ( (1) effective MLCT transition caused by visible light, (2) long lifetime of the excited triplet states, and (3) redox activities of the excited states) are briefly summarized, discussion is devoted to two types of catalytic systems. One is "photoredox catalysis", where the photoexcited TB species serves as a 1e-oxidant as well as a 1e-reductant (SET (single electron transfer) processes) in a single catalytic cycle. The reactions are further divided into two types: reductive and oxidative quenching cycles. The former is effective for generation of radical species from electron-rich substrates such as amine and organoborate, whereas the latter providing carbon-centered radicals is effective for C-C bond formation, in particular, C-CF3 bond formation by the action of electrophilic trifluoromethylating reagents. The present photoredox-catalytic system turns out to be very green in terms of (1) generation of organic radicals under mild conditions without use of harmful reagents, (2) no need of special equipment, (3) no need of sacrificial redox reagent (redox-neutral and atom-economic), and (4) sunlight-promoted reactions (no need of energy from oil and coal). The other catalytic system is "difunctional dinuclear catalyst system" consisting of a TB-type photo-harvesting unit and a reactive Pd center connected by a bipyrimidine bridge. The dinuclear catalyst turns out to be effective for dimerization/oligomerization/polymerization of olefins, and the photoexcitation promotes insertion of olefin into the Pd-C bond. Studies on the substituent effects and DFT analysis reveal that photoexcitation at the TB-like moiety induces MLCT transition toward the bridging bmp part, which causes perturbation of the electronic structure of the reactive Pd center to promote the insertion.

Ru-porphyrin complexes with pyridylpyrazine as metal coordination sites were synthesized. Introduction of Pd-alkyl units to the binding site led to the formation of a novel Pd-Ru-Pd trinuclear complex. The metalation causes drastic changes in the electrochemical and photophysical properties. The trinuclear complex exhibited a prominent metal-to-axial ligand charge transfer band in the visible region due to small energy gap between the Ru-based HOMO and the axial ligand-based LUMO. These changes resulted in the drastic color change from orange to green. (C) 2013 Elsevier B.V. All rights reserved.

Highly conjugated dinuclear Ru complexes bridged by a novel N2-N3 ligand were synthesized. The dinuclear Ru complexes were active toward photoredox-mediated catalytic sulfide oxygenation via proton-coupled oxidation in neutral conditions. Various control experiments have shown that both dinuclear motif and light are essential for the reaction.

This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)(2)(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)(3)](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)(2)(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)(3)](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes.

A series of (imido)vanadium(V) dichloride complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type V(NR)Cl-2[8-(2,6-Me2C6H3)N(C9H10N)] (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (Ar, 5)) have been prepared and identified, and their structures have been determined by X-ray crystallographic analysis. The ethylene dimerization catalyst generated from complex 3 upon treatment with an excess amount of MAO exhibited remarkable catalytic activities (e.g. TOF = 9600000 h(-1) (2670 s(-1)), Al/V = 4000 (molar ratio)), affording 1-butene as the major product (95.0-99.4%). The activities of 3 and 4 were higher than those exhibited by the corresponding 2-(anilide)methylpyridine analogues; 3 showed higher 1-butene selectivity than the others and the activity did not decrease remarkably at 50 degrees C. Complex 5 afforded a mixture of polymer and oligomers with low activities, suggesting that a fine tuning of both the imido and the anionic donor ligands plays an essential role in this catalysis.

We comprehensively studied the excited states of prototypical ruthenium complexes using time-resolved infrared vibrational spectroscopy and found a band assigned to the dark 3MC (metal centered) state, which plays an important role for their photofunctions. © 2014 OSA.

A series of (imido)vanadium(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V(NR')Cl-2(L) [R' = 2,6-Me2C6H3, L = 1,3-R-2(CHN)(2)C=N (1a-c,e) or 1,3-R-2(CH2N)(2)C=N (2a-d), R = Bu-t (a), 2,6-Me2C6H3 (b), 2,6-(Pr2C6H3)-Pr-i (c), C6H5 (d), 2,6-(Ph2CH)(2)-4-MeC6H2 (e); L = 1,3-(2,6-(Pr2C6H3)-Pr-i)(2)(CHN)(2)C=N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(Pr2C6H3)-Pr-i)(2)(CH2N)(2)C=N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et2AlCl cocatalyst; the 2,6-R2C6H3 analogues (R = Me, Pr-i; 1b,c, 2b,c) exhibited higher catalytic activities than the Bu-t analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the V-51 NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-(Pr2C6H3)-Pr-i analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).

A precise, one-pot synthesis of end-functionalized block copolymers consisting of poly(9,9-di-n-octylfluorene-2,7-vinylene)s (PFVs) and oligo(2,5-dialkoxy-1,4-phenyl-enevinylene) or terthiophene units as the middle segment have been prepared by olefin metathesis of the vinyl group in the PFV chain ends followed by subsequent Wittig-type coupling. Formation of the block copolymers and the quantitative efficiency in the end-functionalization can be confirmed by synthesis of amphiphilic block copolymers containing poly(ethylene glycol) at the both polymer chain ends. Effect of PFV conjugation length, middle segment, and the end groups toward the emission properties have been studied: the polymers containing ferrocene moiety at the chain ends displayed unique emission/quenching properties.

Poly(9,9-di-n-octylfluorene-2,7-vinylene)s containing F-BODIPY [PFV-(F-BODIPY)(2)] and Zn(II)-porphyrin have been prepared by olefin metathesis of the vinyl group in the PFV chain ends followed by subsequent Wittig-type coupling. An introduction of tris(2,S-dialkoxy-1,4-phenylene vinylene) into PFV-(F-BODIPY)(2) has also been achieved. The emission properties can be modified by the PFV chain length, chromophore, and the middle segment: PFV-(F-BODIPY)(2) exhibits white-light emission with high quantum efficiency.

A quantum chemical study of the photocatalytic dimerization of alpha-methylstyrene catalyzed by a dinuclear ruthenium-palladium complex was performed at the DFT/TD-DFT level in order to find the key steps of the catalytic reaction. This study reveals that the second insertion of alpha-methylstyrene is the rate-determining step and that it proceeds via triplet excited states of an intermediate complex. These excited states have geometries significantly different from that of the reactant, especially within the coordination sphere of the Pd unit. Indeed, one Pd-carbon bond is considerably lengthened, favoring the insertion process. These results open up the possibilities to optimize the process by fine modulation of the catalyst structure.

A series of novel bichromophoric Ru(II) complexes bearing a naphthyl chromophore linked with 2,2'-bipyridyl (bpy) and 2,2'-bipyrimidine (bpm) ligands were synthesized. Complexation with a Pd-alkyl unit led to the formation of bichromophoric Ru-Pd catalysts. The photochemical and electrochemical properties of the newly synthesized compounds were studied. It has been shown that the UV-light energy absorbed at the pendant naphthyl moiety is effectively transferred to the Ru(II) center; this is supported by the observation of metal-to-ligand charge-transfer luminescence through excitation of the naphthyl unit, which is identical to the luminescence observed through visible light excitation. The luminescence lifetime of the complex bearing a naphthyl moiety directly connected to the bpy ligands was lengthened to ca. 1000 ns. When a Pd complex containing the bichromophoric unit with an extended lifetime was used as a catalyst, styrene polymerization under visible or UV light irradiation was observed, in clear contrast to dimerization using other catalysts. These results indicate the formation of an excited-state with a prolonged excited-state lifetime, which promotes an insertion step in preference to the competing beta-H elimination step.

A series of Pd complexes containing a visible-light harvesting moiety with various combination of substituents (R, X) were synthesized. The variation of the substituents resulted in significant change in the electrochemical and photophysical properties of the complexes. Additionally, photocatalytic activity drastically increased through the introduction of an electron-donating group on R and an electron-withdrawing group on X, respectively. The molecular orbital analysis based on density functional theory (DFT) calculation suggested that the enhancement of the catalytic activity is due to the effective Metal-to-Ligand Charge-Transfer (MLCT) localization on the bridging ligand.

The reaction of the novel bichromophoric Pd complexes with styrene resulted in the formation of polymer or dimer by UV-vis light irradiation, depending upon the connectivity of the naphthyl moiety. The Pd complex having the bichromophore with a Ru(II)-polypyridyl and a naphthyl moiety connected by a single a bond contained long-lived (MLCT)-M-3 emitting species.

Dinuclear acetylide-type complexes bridged by a photochromic dithienylethene unit (DTE), [Y-C C- DTE-C C-Y] 1 (Y = {MCp*(dppe)}; Cp* = pentamethylcyclopentadienyl, M = Fe (1(Fe)), Ru (1(Ru))) have been prepared, and their wirelike and switching behavior, as well as their oxidation chemistry has been investigated. The DTE complexes 1 exhibit photochromic behavior in a manner similar to organic DTE derivatives; UV irradiation causes ring closure of the open isomer 10 to form the closed isomer 1C and visible-light irradiation of the resultant 1C causes reverse ring opening to regenerate 10. But the performance is dependent on the metals. With respect to the interconversion rates and the 1C content at the photostationary state under UV irradiation, the ruthenium complex 1(Ru) is superior to the iron analogue 1(Fe). The wirelike performance is associated with the photochromic processes, and the efficient switching performance has been verified for 1(Fe) as characterized by the V-ab values [V-ab is the electronic coupling derived from intervalence charge-transfer (IVCT) bands: V-ab(1(Fe)C; ON) = 0.047 eV versus V-ab(1(Fe)O; OFF) = 0 eV], and are also supported by the large switching factor (SF = K-C(C; ON)/K-C(O; OFF) = 39; K-C = comproportionation constant). SF for 1(Ru) is determined to be 4.2. The remarkable switching behavior arises from the different pi-conjugated systems in the two isomeric forms, that is, cross-conjugated (10) and fully conjugated pi-systems (1C). It was also found that, in contrast to the reversible redox behavior of the iron complex 1(Fe), the ruthenium complex 1(Ru)O undergoes oxidative ring closure to form the dicationic species of the closed isomer 1(Ru)C(2+) and, thus, the ruthenium system 1(Ru) shows dual photo- and electrochromism. The distinct oxidation behavior of 1(Fe) and 1(Ru) can be ascribed to the spin distribution on the diradical intermediates 1(Fe)O(2+) and 1(Ru)O(2+), as supported by DFT calculations.

Novel Ru(II) polypyridyl complexes possessing pyridylpyrazolyl tethers were synthesized. Reactions with various organometallic precursors readily afforded multinuclear complexes which possess a light-harvesting Ru(II) core and (pyridylpyrazolyl) metal fragments in high yields. Analysis of the photophysical properties of the obtained multinuclear complexes revealed that the complexes had similar absorption and emission characteristics; however, their emission quantum yields decreased in proportion to the number of metal fragments. The di- and trinuclear complexes were stable under donating solvent such as CH(3)CN. (C) 2009 Elsevier B.V. All rights reserved.

A series of bipyridyl-Pd and Rh complexes containing a [(bpy)(3)Ru](2+) or [(bpy)(2)Ru(phen)](2+) (bpy = 2,2'-bipyridyl, phen = 1,10-phenanthroline) moiety as visible-light absorbing unit was synthesized. The complexes were synthesized via a Suzuki-Miyaura coupling reaction between the Ru complexes having a 4-bromo-2,2'-bipyridyl ligand and a 2,2'-bipyridyl-4-boronic acid and a subsequent reaction with various mononuclear Pd and Rh precursors. There was a noticeable structural difference between the QP (2,2':4',4'':2'',2'''-quaterpyridyne) and PB (5-(2,2'-bipyridyl)-yl-1,10-phenanthroline) complexes, which involved the dihedral angles within the bridging ligand; the PB complexes possessed large dihedral angles but the QP complexes showed small values. This structural difference clearly indicated a strong pi-conjugation through the QP ligand. The electrochemical and photophysical properties of the QP and PB complexes were compared with the parent mononuclear Ru complexes, such as [(bpy)(3)Ru](2+), [(bpy)(2)Ru(phen)](2+), and [(bpy)(2)Ru(bpm)](2+) (bpm = 2,2'-bipyrimidine). The QP and PB complexes showed a (3)MLCT life time that was similar to [(bpy)(3)Ru](2+) and [(bpy)(2)Ru(phen)](2+), which was about 10 times longer (ca. 1 mus) than the corresponding bpm complexes. Reactivity studies with Pd complexes toward styrene dimerizations were examined. The reaction proceeded under visible-light irradiated conditions and the reactivity of the QP complexes was much higher than the corresponding PB complexes. Substantial acceleration of the reaction was observed with the introduction of an Me substituent on the bipyridyl ligand.

A series of di- and trinucleating ligands with a 1,3,5-triethylbenzene core connected to N,N-bidentate tethers was synthesized. The ligands readily reacted with monuclear Rh and Pd precursors to give the corresponding di- and trinuclear complexes, which were characterized by using NMR and ESI mass spectroscopy. In the solid state, the trinuclear complexes with ligands having pyridylpyrazolyl tethers adopt the most stable ababab configuration, in which the organometallic fragments are on the same side of the benzene plane. On the other hand, in solution, the linker moieties between the benzene core and the metals are flexible enough to interconvert between other configurations, that is, they exhibit dynamic behavior, and the rotational barrier was dependent on the length of the linkers. From variable temperature (VT) H-1 NMR measurements, the rotational barrier for a trinuclear Rh-CO complex with a ligand having methylene linkers was estimated to be similar to 12.6 kcal mol(-1). However, no spectral changes were observed for the ethylene derivative in the temperature range of -60 degrees C to 50 degrees C, indicating that the rotation was not frozen out on the H-1 NMR timescale, even at - 60 C.

Mononuclear ruthenium complexes and dinuclear Ru center dot center dot center dot Pd complexes having a series of 2,2'-bipyrimidine ligands, [(bpy)(2)Ru(L-n)](2+) [L-n = 2,2'-bipyrimidine (L1), 5,5'-dimethyl-2,2'-bipyrimidine (L2), 5,5'-dibromo-2,2'-bipyrimidine (L3), 4,4'-dimethyl-2,2'-bipyrimidine (L4), and 4,4',6,6'-tetramethyl- 2,2'-bipyrimidine (L5)] and [(bpy)(2)Ru(L-n)PdL](m+) [L-n = L1-L3; PdL = PdMeCl (m = 2) and PdMe(solvent) (m = 3)], are prepared, and the obtained complexes are characterized by means of spectroscopic and crystallographic methods. Introduction of the substituents on the bipyrimidine ligands led to the substantial differences in their electrochemical and photophysical properties. Density functional theory calculations have been performed to understand the substituent effect on the ground-state molecular orbital energy level. Reactivity studies on the catalytic dimerization of alpha-methylstyrene revealed that the Pd complex having a Br-substituted bipyrimidine ligand were much more active than those of the corresponding Pd complexes having methyl-substituted or nonsubstituted bipyrimidine ligands.

A series of ruthenium and chromium complexes bearing pH indicators as the eta(6)-arene ligand, (eta(6)-X)(MLn)(y) [X = methyl yellow, crystal violet lactone, phenolphthalein; MLn = RuCp*(+), RuCl2(L), Cr(CO)(3); y = 1, 2] is prepared and characterized by spectroscopic and crystallographic methods. Of the plural arene rings in the indicators, a specific arene ring can be successfully coordinated to the metal center in a selective manner under appropriate conditions (i.e. use of the precursors of different oxidation states and reaction with the non-protonated and protonated pH indicator). The obtained indicator complexes show halochromic behavior depending on pH as observed for the parent molecules but the transition pH ranges are shifted to the more acidic side because of the attachment of the electron-withdrawing metal fragments, which decrease the basicity of the attached pH indicators. (c) 2006 Elsevier B.V. All rights reserved.