Ruthenium complexes dicarboxylates

Bedja, I. Hotchandani, S. Kamat, P. V. Preparation and characterization of thin Sn02 nanocrystalline semiconductor films and their sensitization with bis(2,2 -bipyridine)(2,2 -bipyridine-4-4 -dicarboxylic acid)ruthenium complex, J. Phys. Chem. 1994, 98, 4133. 

Rhodium-based catalysis suffers from the high cost of the metal and quite often from a lack of stereoselectivity. This justifies the search for alternative catalysts. In this context, ruthenium-based catalysts look rather attractive nowadays, although still poorly documented. Recently, diruthenium(II,II) tetracarboxylates [42], polymeric and dimeric diruthenium(I,I) dicarboxylates [43], ruthenacarbor-ane clusters [44], and hydride and silyl ruthenium complexes [45 a] and Ru porphyrins [45 b] have been introduced as efficient cyclopropanation catalysts, superior to the Ru(II,III) complex Ru2(OAc)4Cl investigated earlier [7]. In terms of efficiency, electrophilicity, regio- and (partly) stereoselectivity, the most efficient ruthenium-based catalysts compare rather well with the rhodium(II) carboxylates. The ruthenium systems tested so far seem to display a slightly lower level of activity but are somewhat more discriminating in competitive reactions, which apparently could be due to the formation of less electrophilic carbenoid species. This point is probably related to the observation that some ruthenium complexes competitively catalyze both olefin cyclopropanation and olefin metathesis [46], which is at variance with what is observed with the rhodium catalysts. 

Ohta, T., Takaya, H., Noyori, R. Stereochemistry and mechanism of the asymmetric hydrogenation of unsaturated carboxylic acids catalyzed by BINAP-ruthenium(ll) dicarboxylate complexes. Tetrahedron Lett. 1990, 31,7189-7192. 

Ruthenium complexes attract recent interest as new promising candidates for efficient, specific and environmentally benign allylation catalysts. It is noticeable that some J7 -allylruthenium(II) complexes have an ambiphilic property in catalysis involving the C-0 bond activation [52]. When allyl carboxylates or carbonates are treated with nucleophilic 1,3-dicarboxylates or electrophilic aldehyde in the presence of Ru complexes, catalytic allylations of nucleophiles or electrophiles take place [53]. In both reactions, J7 -allylruthenium complexes are assumed to be intermediates. Independent synthesis and reactions of the model compounds support this observation (Scheme 3.28). This ambiphilicity of the allylruthenium(II) may arise from the different reactivity of and rf forms in the allylic moiety [54]. 

Polyamides and polyesters containing ruthenimn bipyridine complexes in their structures have been synthesized by Chan and coworkers." " Scheme 14 depicts the synthesis of polymer 64 by reaction of the metal-containing dicarboxylic acid complex 61 and the organic dicarboxylic acid (62) with an aromatic or aliphatic diamine (63). These polymers were thermally stable to temperatures between 320 and 500°C. Many of the polymers exhibited liquid crystalline characteristics. The photoconductivity of this class of polymer increased with increasing metal content." Chan also reported that polybenzo-bw-oxazoles and polybenzo-Z>w-thiazoles that contain ruthenium complexes coordinated to 2,2 bipyridyl units in the backbone... 

Ohta T, Takaya H, Noyori R. Bis(diarylphosphino)-l,l binaphthyl (BINAP)-ruthenium(II) dicarboxylate complexes new, highly efficient catalysts for asymmetric hydrogenations. Inorg. Chem. 1988 27(3) 566-569. 

BINAP-ruthenium dicarboxylate complexes are also efficient catalysts for asymmetric hydrogenation of enamides, a,p- and p,y-unsatu rated carboxylic acids, a-amino ketones, and a-acylaminoacrylic acids.1 2 3 4 5... 

Ruthenium bipyridyl complexes are suitable photosensitizers because then-excited states have a long lifetime and the oxidized Ru(III) center has a longterm chemical stability. Therefore, Ru bipyridyl complexes have been studied intensively as photosensitizers for homogeneous photocatalytic reactions and dye-sensitization systems. The Ru bipyridyl complex, bis(2,2 -bipyridine)(2,2 -bipyri-dine-4, 4,-dicarboxylate)ruthenium(II), having carboxyl groups as anchors to the semiconductor surface was synthesized and single-crystal Ti02 photoelectrodes sensitized by this Ru complex were studied in 1979 and 1980 [5,6]. 

J. Acid-Base Equilibria of C/s-dithiocyanato Bis(2,2-bipyridine-4,4 -dicarboxylate)ruthenium(ll) Complex (22)... 

The effect of the salt bridge on electron transfer can be determined directly by a comparative kinetics study of a D—[amidinium-carboxylate]—A complex and its switched interface D—[carboxylate-amidinium]—A congener. We have reported such a study for a supramolecular series of complexes where the donor is a ruthenium(II) polypyridyl with one bipyridine (bpy) ligand modified by either amidinium or carboxylate and the acceptor is the complementarity modified 3,5-dinitrobenzene (DNB) [162, 163]. The same donor-acceptor pair bridged by a symmetrical dicarboxylic acid interface has also been examined. 

Several properties of these ruthenium(II) complexes are shown in Table 2. Apparently, the absorption and emission maxima of [Ru((-)-menbpy)3l and [Ru(S( - )-PhEtbpy)3l + exhibit considerably large red shifts, compared to those of [Ru(bpy)3l. A similar red shift was observed in [Ru(dmp)n(dcbpy)3 n] (dcbpy = 2,2 -bipyridyl-4,4 -dicarboxylic acid), as was shown in Table 1. These red shifts are easily understood in terms of the introduction of electron-withdrawing substituents at the 4 and 4 positions of 2,2 -bipyridine. The other important feature is that the lifetime of the MLCT excited state becomes much longer than that of [Ru(bpy)3l +. One of the important reasons is the increase in the energy difference between the triplet d-d ( d-d) and MLCT excited states, as follows [13,29] Since the electron-withdrawing substituent of 2,2 -bipyridine stabilizes the TT orbital of 2,2 -bipyridine, the MLCT excited state becomes lower in energy, but the d-d excited state is little influenced in energy by the substiment. 

In early work in 1995, just before the concept of dynamic combinatorial chemistry was first explicitly recognized, Hamilton et al. screened a combinatorial library of ruthenium A(terpyridyl) complexes.From five differently substituted terpyridine ligands, a series of 15 different coordination complexes was synthesized and isolated. The library was screened for affinity for dicarboxylate or diammonium guests using microcalorimetry or picrate extraction, and several receptors were identified (Fig. 2). 

To illustrate the tuning aspects of the MLCT transitions in ruthenium polypyridyl complexes, the well known [RuLs] (L = 4,4 dicarboxylic acid-2,2 -bi-pyridine) type of complex can be considered. This complex shows strong visible band at 466 nm, because of CT transition from metal t2g highest occupied molecular orbitals (HOMO) to jr -lowest unoccupied molecular orbitals (LUMO) of the ligand (Fig. 3). The Ru(II)/(III) oxidation potential is at 1.3 V, and the ligand based reduction potential is at —1.5V... 

Influence of the Position of Carboxyl Croups on M LCT Transitions Ruthenium polypyridyl compounds, of the type [RuL2(X)2], (where L = 4,4 -dicarboxylic acid-2,2 -bipyridine, 5,5 -dicarboxylic acid-2,2 -bipyridine, and 6,6 -dicarboxylic acid-2,2 -bipyridine X = Cl , CN and NCS ) have been reported [41-43]. The lowest M LCT absorption maxima of [RuL2(NCS)2] complex (L = 2,2 -bipyridine) is seen at 510 nm in ethanol. By substituting two... 

Tab. 4 Electronic Spectral Data of the cis- and trons-bis(4,4 -dicarboxylic acid-2,2 -bipyridine)Ruthenium (X2) Complexes (X = CP, H2O, NCS ) in DMF...

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