Akiko Takao (Inagaki)

Visible-light promoted molecular transformations catalyzed by bimetallic species containing a [Ru(bipy)(3)](2+) (TB)-like fragment as the photosensitizing unit are reviewed. Catalytic reactions are classified according to the following two criteria: (1) electron transfer (A)/energy transfer (B) from TB and (2) intra- (I) and inter-molecular catalyst systems (II). Reactions promoted by electron transfer (A) involve reductive processes such as W-reduction giving H(2) and CO(2)-reduction giving CO, which have been extensively studied also by using mononuclear catalysts. The catalytic H(+)- and CO(2)-reductions have been considerably improved by the use of II-A- and I-A-type bimetallic catalysts, respectively. Furthermore, as recently reported by our research group, photocatalysis is extended to organic transformations, which have been much less explored compared to transformations of small inorganic molecules mentioned above. While Sonogashira coupling is mediated by II-A-type catalysts, up-hill trans-to-cis isomerization of cyanostilbene and dimerization of alpha-methylstyrene follow the energy transfer processes (B). Thus new aspects of the photochemical bimetallic catalysis have been unveiled as mentioned above but catalyst design is still in its infancy. Continued accumulation of reaction data and mechanism analysis will lead to development of practical bimetallic photocatalysts, which promote unique reactions including up-hill reactions. (C) 2009 Elsevier B.V. All rights reserved.

A series of organoruthenium complexes containing photochromic 1,2-di(2-methylthien-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene fragments (DTE), DTE-(RRuLm)(n) (RRuLm = (eta(6)-C6H5)Ru(eta(5)-C5Me5) (I): n = 1 (3), 2 (4); (eta(6)-C6H5)RuCl2(PPh3) (II): n = 1 (10), 2 (11); (eta(5)-C5Me4)Ru(CO)(2) (III): n = 1 (25), 2 (24); substituted at the 5-position of the thiophene ring), are prepared and characterized by H-1 NMR and UV-vis spectroscopy, and molecular structures of the 1:2 adducts 4, 11, and 24 are determined by X-ray crystallography, which reveals the antiparallel conformation of the two thiophene rings suitable for photocyclization, causing the photochromism. It is revealed that the metalated DTE derivatives show photochromic behavior through the photochemical, electrocyclic conrotatory ring-closing and -opening processes in a manner analogous to the organic counterparts, but the efficiency of the photochromic processes is dependent on the attached metal fragments. The cationic Cp*Ru(eta(6)-arene)-type (I) and neutral Cp*Ru(CO)(2)Cl-type complexes (III) show photochromic behavior (content of the closed isomers at the UV photostationary states: 25-88%), and subsequent visible light irradiation of the equilibrated mixtures reverts the process to afford the open forms quantitatively. The ring-closing and -opening processes are reversible and can be repeated without notable deterioration. As for the series of Ph derivatives of I (1, 3, and 4), metalation improves the efficiency of the ring-closing process. In contrast to these derivatives, no significant photochromic behavior is noted for the benzo-fused derivatives of I, and UV irradiation of II (10 and 11) causes irreversible dissociation of the arene ligand (DTE).

A series of organoruthenium complexes containing photochromic 1,2-di(2-methylthien-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene fragments (DTE), DTE-(RRuLm)(n) (RRuLm = (eta(6)-C6H5)Ru(eta(5)-C5Me5) (I): n = 1 (3), 2 (4); (eta(6)-C6H5)RuCl2(PPh3) (II): n = 1 (10), 2 (11); (eta(5)-C5Me4)Ru(CO)(2) (III): n = 1 (25), 2 (24); substituted at the 5-position of the thiophene ring), are prepared and characterized by H-1 NMR and UV-vis spectroscopy, and molecular structures of the 1:2 adducts 4, 11, and 24 are determined by X-ray crystallography, which reveals the antiparallel conformation of the two thiophene rings suitable for photocyclization, causing the photochromism. It is revealed that the metalated DTE derivatives show photochromic behavior through the photochemical, electrocyclic conrotatory ring-closing and -opening processes in a manner analogous to the organic counterparts, but the efficiency of the photochromic processes is dependent on the attached metal fragments. The cationic Cp*Ru(eta(6)-arene)-type (I) and neutral Cp*Ru(CO)(2)Cl-type complexes (III) show photochromic behavior (content of the closed isomers at the UV photostationary states: 25-88%), and subsequent visible light irradiation of the equilibrated mixtures reverts the process to afford the open forms quantitatively. The ring-closing and -opening processes are reversible and can be repeated without notable deterioration. As for the series of Ph derivatives of I (1, 3, and 4), metalation improves the efficiency of the ring-closing process. In contrast to these derivatives, no significant photochromic behavior is noted for the benzo-fused derivatives of I, and UV irradiation of II (10 and 11) causes irreversible dissociation of the arene ligand (DTE).

A tetranuclear C-2 (dicarbide) cluster complex with a permetallated ethene structure, (mu(4)-CC)Ru-2(FeCp*)(2)(CO)(10) (2), reacts with alkynes in refluxing THF to give a variety of adducts resulting from C-C coupling and oxidative metallacyclization with the C-2 ligand in addition to a unique mu(4)-dicarbyne complex with a dimetallacyclobutatriene core, (mu(4)-C-C)Ru-2(FeCp*)(2)(CO)(6)(mu-eta(2):eta(2)-PhCCPh). The reactions are initiated by decarbonylation, as confirmed by the reactions of an isolated, labile species lightly stabilized by MeCN, (mu(4)-CC)Ru-2(FeCp*)(2)(CO)(8)(NCMe)(2), which undergoes the reactions at room temperature and provides the same types of products as those obtained from 2.

Redox active polyiron complexes with higher dimensional spacers, the tetrairon complex with the two-dimensional tetra( ethynylphenyl) ethene spacer, (C=C)[p-C6H4-C = C-FeCp*(dppe)]4, and the diiron complex with the three-dimensional spacer (pseudo-m-[2,2] paracyclophane)[C equivalent to C-FeCp*(dppe)](2), are prepared, and their performance as molecular wires is evaluated on the basis of their comproportionation constants for the mixed valence state.

A redox-active diiron complex with the diethynylated dithienyl-ethene (DTE) linker, (dppe)(eta(5)-C5Me5)Fe-C C-DTE-C C-Fe( eta(5)-C5Me5)(dppe), shows photochromic behaviour, which switches on and off the communication performance between the two metal centres.

A tetranuclear C-2 (dicarbide) cluster complex with a permetallated ethene structure, (mu(4)-CC)Ru-2(FeCp*)(2)(CO)(10) (2), reacts with alkynes in refluxing THF to give a variety of adducts resulting from C-C coupling and oxidative metallacyclization with the C-2 ligand in addition to a unique mu(4)-dicarbyne complex with a dimetallacyclobutatriene core, (mu(4)-C-C)Ru-2(FeCp*)(2)(CO)(6)(mu-eta(2):eta(2)-PhCCPh). The reactions are initiated by decarbonylation, as confirmed by the reactions of an isolated, labile species lightly stabilized by MeCN, (mu(4)-CC)Ru-2(FeCp*)(2)(CO)(8)(NCMe)(2), which undergoes the reactions at room temperature and provides the same types of products as those obtained from 2.

Systematic evaluation of method and basis set on the structure and energetics of organocuprate(l) and organocopper(III) species has been carried out. Various structures of organocuprate(l) and organocuprate(III) complexes were optimized with the HF, MP2, and B3LYP methods, and compared with the structures determined by X-ray crystallography (i.e., Me2Cu(I)(-), (CF3)(4)Cu(III)(-)). Both the MP2 and B3LYP methods reasonably reproduce the X-ray structures while the HF method does not. Using larger basis set and incorporating the relativistic effects for Cu afford the best results. In the studies on the energetics of a Li-Cu cluster model (Me2CuLi (.) LiCI) and Me3Cu model with the MP2, MP3. MP4DQ, MP4SDQ, CCSD(T), and B3LYP methods, the B3LYP method gives energetics similar to those obtained with the CCSD(T) method with much less cost, and hence, is judged to be the best practical method. The studies have shown that B3LYP method with the basis set incorporating the relativistic effective core potentials for Cu and the 6-31G* basis set for the rest is the theoretical method that is the most cost-effective for the studies of the structure and energetics of organocuprate(I) and organocopper(III) species. (C) 2003 Wiley Periodicals, Inc.

Systematic evaluation of method and basis set on the structure and energetics of organocuprate(l) and organocopper(III) species has been carried out. Various structures of organocuprate(l) and organocuprate(III) complexes were optimized with the HF, MP2, and B3LYP methods, and compared with the structures determined by X-ray crystallography (i.e., Me2Cu(I)(-), (CF3)(4)Cu(III)(-)). Both the MP2 and B3LYP methods reasonably reproduce the X-ray structures while the HF method does not. Using larger basis set and incorporating the relativistic effects for Cu afford the best results. In the studies on the energetics of a Li-Cu cluster model (Me2CuLi (.) LiCI) and Me3Cu model with the MP2, MP3. MP4DQ, MP4SDQ, CCSD(T), and B3LYP methods, the B3LYP method gives energetics similar to those obtained with the CCSD(T) method with much less cost, and hence, is judged to be the best practical method. The studies have shown that B3LYP method with the basis set incorporating the relativistic effective core potentials for Cu and the 6-31G* basis set for the rest is the theoretical method that is the most cost-effective for the studies of the structure and energetics of organocuprate(I) and organocopper(III) species. (C) 2003 Wiley Periodicals, Inc.

Thermolysis of a triruthenium complex containing a nido-ruthenacyclopentadiene ligand {Cp*Ru-(mu-H)}(3)(CH=CMe-CR=CH) (3a, R = H; 3b, R = Me, Cp* = eta(5)-C5Me5) affords an open-form Ru-3 cluster (Cp*Ru)(2)-{Cp*Ru(CH=CMe-CR=CH)}(mu-H) (4a, R = H, 4b, R = Me) as a result of partial Ru-Ru bond cleavage. Reformation of an Ru-3 triangle accompanied with C-C bond cleavage of the C-4 fragment was performed by prolonged heating of 4 to afford a mu(3)-methylidyne-mu(3)-diruthenaallyl complex (Cp*Ru)(3)(mu-H)(mu(3)-CH)(mu(3)-CRC-MeCH) (5a, R = H, 5b, R = Me).

Thermolysis of a triruthenium complex containing a nido-ruthenacyclopentadiene ligand {Cp*Ru-(mu-H)}(3)(CH=CMe-CR=CH) (3a, R = H; 3b, R = Me, Cp* = eta(5)-C5Me5) affords an open-form Ru-3 cluster (Cp*Ru)(2)-{Cp*Ru(CH=CMe-CR=CH)}(mu-H) (4a, R = H, 4b, R = Me) as a result of partial Ru-Ru bond cleavage. Reformation of an Ru-3 triangle accompanied with C-C bond cleavage of the C-4 fragment was performed by prolonged heating of 4 to afford a mu(3)-methylidyne-mu(3)-diruthenaallyl complex (Cp*Ru)(3)(mu-H)(mu(3)-CH)(mu(3)-CRC-MeCH) (5a, R = H, 5b, R = Me).

Oxidation of the triruthenium cluster 2 bearing a face-bridging allyl fragment results in the formation of a mu(3)-C-3 ring on the Ru-3 plane as a consequence of bimetallic reductive C-C coupling. Both structural and spectral data of 5 indicate carbenic character of the carbon atoms within the newly formed face-bridging C-3 ring.

Oxidation of the triruthenium cluster 2 bearing a face-bridging allyl fragment results in the formation of a mu(3)-C-3 ring on the Ru-3 plane as a consequence of bimetallic reductive C-C coupling. Both structural and spectral data of 5 indicate carbenic character of the carbon atoms within the newly formed face-bridging C-3 ring.

Trinuclear polyhydrido complex of ruthenium effectively activates alkanes to cleave C-H bonds in a selective manner due to cooperative action of the metal centers. The reaction of (Cp 'Ru)(3)(mu -H)(3)(mu (3)-H)(2)(1) (Cp' = eta (5)-C5Me5) with n-alkane at 170 degreesC leads to the formation of a trinuclear closo-ruthenacyclopentadiene complex as a result of a successive cleavage of sis C-H bonds. Introduction of a mu (3)-sulfido ligand into the Ru-3 core Of the trirutheniumpolyhydrido cluster significantly modifies the regioselectivity of the alkane C-H activation. Heating of a solution of (Cp'Ru)(3)(mu (3)-S)(mu -H)(3) (4) in alkane exclusively gives a trinuclear mu (3)-alkylidyne complex via a selective C-H bond cleavage at the less-hindered terminus of alkane molecule.

Trinuclear polyhydrido complex of ruthenium effectively activates alkanes to cleave C-H bonds in a selective manner due to cooperative action of the metal centers. The reaction of (Cp 'Ru)(3)(mu -H)(3)(mu (3)-H)(2)(1) (Cp' = eta (5)-C5Me5) with n-alkane at 170 degreesC leads to the formation of a trinuclear closo-ruthenacyclopentadiene complex as a result of a successive cleavage of sis C-H bonds. Introduction of a mu (3)-sulfido ligand into the Ru-3 core Of the trirutheniumpolyhydrido cluster significantly modifies the regioselectivity of the alkane C-H activation. Heating of a solution of (Cp'Ru)(3)(mu (3)-S)(mu -H)(3) (4) in alkane exclusively gives a trinuclear mu (3)-alkylidyne complex via a selective C-H bond cleavage at the less-hindered terminus of alkane molecule.

Trinuclear ruthenium pentahydride complex (Cp'Ru)(3)(mu- H)(3)(mu(3)-H)(2) (1: Cp' = eta(5)-C5Me5) reacts with a series of acyclic conjugated dienes such as butadiene, isoprene, or penta-1,3-diene to form trinuclear mu(3)-1,3-dimetalloallyl complexes 2 by way of an intermediary mu(3)-eta(2):eta(2)-s-cis-1,3- diene complex. In the reactions with butadiene and isoprene, an agostic intermediate, in which three ruthenium centers concertedly activate a 1,3-diene by taking the role of coordination sites and an activation site, is detected by H-1 and C-13 NMR. The intermediary 1,3-diene complexes with agostic interaction undergo C(sp(2))-H bond cleavage at room temperature to generate 1,3-dimetalloallyl complexes. The reaction of 1 with cyclopentadiene generates a trinuclear mu(3)-2-methylruthenacyclopentadiene complex 4 as a result of cleavage of the unactivated C(sp(3))-C(sp(2)) bond. In the reaction of 1 with 1,3-cyclohexadiene, cleavage of an allylic C-H bond followed by the beta-H elimination affords a mu(3)-eta(2):eta(2):eta(2)-benzene complex.

Trinuclear ruthenium pentahydride complex (Cp'Ru)(3)(mu- H)(3)(mu(3)-H)(2) (1: Cp' = eta(5)-C5Me5) reacts with a series of acyclic conjugated dienes such as butadiene, isoprene, or penta-1,3-diene to form trinuclear mu(3)-1,3-dimetalloallyl complexes 2 by way of an intermediary mu(3)-eta(2):eta(2)-s-cis-1,3- diene complex. In the reactions with butadiene and isoprene, an agostic intermediate, in which three ruthenium centers concertedly activate a 1,3-diene by taking the role of coordination sites and an activation site, is detected by H-1 and C-13 NMR. The intermediary 1,3-diene complexes with agostic interaction undergo C(sp(2))-H bond cleavage at room temperature to generate 1,3-dimetalloallyl complexes. The reaction of 1 with cyclopentadiene generates a trinuclear mu(3)-2-methylruthenacyclopentadiene complex 4 as a result of cleavage of the unactivated C(sp(3))-C(sp(2)) bond. In the reaction of 1 with 1,3-cyclohexadiene, cleavage of an allylic C-H bond followed by the beta-H elimination affords a mu(3)-eta(2):eta(2):eta(2)-benzene complex.