Ru 0 Complexes

The only oxidation state not represented in this snrvey between Rn(Vin) and Rn(0) is Rn(I) the latter and Ru(-l) are the rarest oxidation states of rutheninm, represented mainly by nitrosyl complexes. There are many Rn(0) complexes, mostly containing the carbonyl ligand, but few have been used for oxidation catalysis. 

Medium composition Electrolysis time (h) Volume of CO produced (ml) Coulombs consumed Average current efficiency (%)c 

Re(bpy)(CO)3Cl-modified electrodes has not yet been explained. However, from the cyclic voltammograms of fac-Re(bpy)(CO)3Cl (Fig. 14) and from the intermediate complexes formed by electrolysis in acetonitrile in the presence and absence of C02, two different electrocatalytic pathways (Fig. 15) were suggested144 initial one-electron reduction of the catalyst at ca. -1.5 V versus SCE followed by the reduction of C02 to give CO and C03, and initial two-electron reduction of the catalyst at ca. -1.8 V to give CO with no C03. The electrochemistry of [Re(CO)3(dmbpy)Cl] (dmbpy = 4,4 -dimethyl-2,2 -bipyridine) was investigated145 to obtain mechanistic information on C02 reduction, and the catalytic reac- 

it would be worthwhile to investigate catalysts developed for C02 reduction in other fields with regard to their possible application to electrochemical and photoelectrochemical reduction of C02, and vice versa in fact, catalysts developed for a particular system have been applied successfully in various related systems as described above. 

Rhodium and ruthenium complexes have also been studied as effective catalysts. Rh(diphos)2Cl [diphos = l,2-bis(diphenyl-phosphino)ethane] catalyzed the electroreduction of C02 in acetonitrile solution.146 Formate was produced at current efficiencies of ca. 20-40% in dry acetonitrile at ca. -1.5 V (versus Ag wire). It was suggested that acetonitrile itself was the source of the hydrogen atom and that formation of the hydride HRh(diphos)2 as an active intermediate was involved. Rh(bpy)3Cl3, which had been used as a catalyst for the two-electron reduction of NAD+ (nicotinamide adenine dinucleotide) to NADH by Wienkamp and Steckhan,147 has also acted as a catalyst for C02 reduction in aqueous solutions (0.1 M TEAP) at -1.1 V versus SCE using Hg, Pb, In, graphite, and n-Ti02 electrodes.148 Formate was the main 

Run Cathode E (V versus SCE) Rh complex6 (mM) Q ( c) HCOOH (/Amol) Current efficiency (%) Volume of gas produced (ml) 

Compound Time (Hrs) Tumor Blood Muscle (Tumor/Tissue Ratios in Liver Kidney Parentheses) TCI 

TCI (Tumor Concentration Index) = I Injected Dose/o op Tumor Z Injected Dose/o in Whole Bout  

Tissue from EMT-6 sarcoma bearing mice. Date given as % dose/g of tissue.  

ACS Symposium Series Ameriean Chemical Society Washington, DC, 1980. 

A number of Ru(III) complexes have exhibited antitumor activity and It is likely that redox assisted substitution Is Involved In causing the metal to Interact with genetic 

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In earlier studies (24), the reaction was carried out at temperatures above 200°C under autogenous pressure conditions usiag alkaU metal hydroxide or alkoxide catalysts significant amounts of carboxyUc acid, RCH2COOH, were formed as were other by-products. More recent reports describe catalysts which minimize by-products MgO—K CO —CUC2O2 (25), less basic but stiU requiring high temperatures Rh, Ir, Pt, or Ru complexes (26) and an alkaU metal alkoxide plus Ni or Pd (27), effective at much lower temperatures. 

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

Martin et al. [69] undertook a study of the kinetics and mechanism of NBR hydrogenation using various Ru complexes. They examined the activity of RuXCl-(C0)L2 (X = H, Ph, or CH=CHPh L = PCy3, PPr,... 

In the preceding section, it has been shown that considerable attention has been devoted to palladium as a heterogeneous catalyst. The present section describes the homogeneous palladium catalysts developed for hydrogenation of NBR. The main drive behind the development of various catalyst systems is to find suitable substituents of the Rh catalyst. Palladium complexes are much cheaper as compared with Rh and exhibit comparable activity and selectivity to Rh and Ru complexes. 

The back ET between the reduced Ru complex in 26 and the oxidized donor moiety in 27 was strikingly slow. Figure 14 shows the decays of reduced 26 at 510 nm and oxidized 27 at 606 nm after irradiation with 450-nm light for... 

ZnO instead of T1O2 because ZnO provides a 220 times higher mobility for photoinjected electrons, which would allow reduction of the exciting laser intensity. The slow PMC decay of TiOrbased nanostructured sensitization solar cells (the Ru complex as sensitizer), which cannot be matched by a single exponential curve and is influenced by a bias illumination, is strongly affected by the concentration of iodide in the electrolyte (Fig. 38). On the basis of PMC transients and their dependence on the iodide concentration, a kinetic mechanism for the reaction of photoinjected electrons could be elaborated.40... 

Figure 4.8 DKR of seoalcohols catalyzed by a lipase and Ru complexes at ambient temperature.

Reactions of hydrides are therefore similar to those of carbonyls, and by appropriate choice of reactants a product often can be made by either route, as is shown for the mercuration of trinuclear Ru complexes ... 

Dehydrohalogenation of (Ar)MCl2(Mes PH2) has also been explored in the absence of a stabilizing ligand and shown to result in the formation of 66 in the case of the Ru complex, presumable via the RU2P2 dimer 65 [104]. The formation of 68 was shown to result when the dehydrohalogenation was executed in the presence of 2-butyne, which has metallocycle 67 as likely intermediate [104]. 

The same type of porphyrin-Ru complex was immobilized by coordina-tive adsorption on aminopropylsilicas (Fig. 26) as either amorphous or crystalline supports [79]. Mesoporous crystalline MCM-48 was the best support, as shown by the improved results obtained in the epoxidation of styrene with 2,6-dichloropyridine N-oxide (TON > 13 000 and 74% ee). The versatility of this catalyst was demonstrated in the intramolecular cyclopropanation of frans-cinnamyl diazoacetate. TON was ten times higher than that obtained in solution and 85% ee was observed. The solid was recycled and reused, although partial loss of selectivity occurred. 

Other chiral ligands such as BINAP (where BINAP is bis(diarylphosphino)-1,1 binaphthyl) or aminophosphines are also efficient for stereoselective synthesis of chiral-at-metal Ru complexes [39-41]. 

The reactions of the butadiynediyldimetal(Fe, Ru) complexes with Fe2(CO)ci at room temperature afforded mixtures of products, from which three types of products, viz. the ps-acetylide cluster compound 4, the pj-ti -propargylidene-ketene compound 5 and zwitterionic cluster compound 6, were isolated. While the reaction with an excess amount of Co2(CO)g results in addition to the sterically congested Fp -C=C part [6]. The distributions of the products were dependent on the metal fragments situated at the other end of the conjugated carbon rod. The cluster compounds so obtained were characterized by spectroscopic and... 

All the Ru-based racemization catalysts described earUer are air-sensitive and thus difficult to reuse. We found that a modified Ru complex 7 was air-stable and recyclable, in particular, in a polymer-supported form 8. The racemization of secondary alcohols with 7 took place equally well under both oxygen and argon atmospheres. The subsequent DKRs of several alcohols using 7 or 8 under aerobic... 

The measurement of these angles for a series of [PdClj(NHC) P(OR)3 ] complexes permitted to evidence the remarkable flexibility of NHCs due to rotations aronnd the iV-substituent bonds [82]. This flexibility, captured by the allows NHCs to respond actively to the steric requirements of co-ligands. This is further confirmed by ab initio molecular dynamics simulations aimed at understanding the variability of ( )j and in a series of NHCs containing Ru-complexes relevant to olefin metathesis [83]. 

However, similar NHC architectures employing aromatic side chains have shown more encouraging results. In 2000, Nolan and co-workers reported the synthesis and characterisation of the NHC-Ru complex 20 bearing a sterically more demanding N,N -bis-[2,6-(di-/xo-propyl)phenyl]imidazol-2-ylidene (IPr) ligand [27, 28] (Fig. 3.5). Standard RCM substrate 1 was used to test the catalytic performance of 20. The ring closure was found to be complete after 15 min by using 5 mol% 20 as catalyst at room temperature. Under identical conditions, 15... 

In 2001, Furstner reported the preparation and characterisation of the NHC-Ru complex 22 containing iV,iV -bis[2,6-(diisopropyl)phenyl]imidazolidin-2-ylidene (SIPr) [29] (Fig. 3.6), which is the congener of complex 20. Subsequently, Mol and co-workers revealed that complex 22 was a highly active metathesis initiator [30]. More recent comparative studies showed that catalyst 22 could catalyse the RCM of 1 faster than any other NHC-Ru catalyst, while it was not stable enough to obtain complete conversion in the RCM of 3 and was inefficient for the construction of the tetrasubstituted double bond of cyclic olefin 6 [31]. 

Some attempts have also been made to vary the para- or meta-substituents on the phenyl ring of the SlMes ligand, however none of the resulting NHC-Ru complexes showed better RCM activity than the original Grubbs 1114 when tested with standard substrates 1 and 7 [37 0]. 

Fig. 3.13 Examples of Ru-complexes bearing NHCs with phenyl side chains...

The use of unsymmetrically substituted Ru-complexes can lead to some interesting selectivities in CM [154]. The modified Hll-catalysts Ru4 and Ru5, where... 

A NHC-Cu complex 9 has also been used in the cyclopropanation of 5 and cyclooctene 8 using EDA 6 (Scheme 5.3) [5]. Complex 9 was isolated prior to use and, as in the case of NHC-Ru complex, the cyclopropanation reaction did not display high diastereoselectivity. However, products 7 and 10 were obtained in good to excellent yields depending on the ratio between the alkenes and EDA. Improved yields were obtained when alkenes were used in six- or ten-fold excess. 

For the last 2 decades ruthenium carbene complexes (Grubbs catalyst first generation 109 or second generation 110, Fig. 5.1) have been largely employed and studied in metathesis type reactions (see Chapter 3) [31]. However, in recent years, the benefits of NHC-Ru complexes as catalysts (or pre-catalysts) have expanded to the area of non-metathetical transformations such as cycloisomerisation. 

A chiral NHC-Ru complex 158 was used in the Diels-Alder reaction between methacrolein 156 and cyclopentadiene 157 (Scheme 5.41) [47]. The adduct 159 was obtained in an excellent yield under mild conditions, albeit with low enantioselectivity. 

The oxidative cleavage of alkenes is a common reaction usually achieved by ozonolysis or the use of potassium permanganate. An example of NHC-coordina(ed Ru complex (31) capable of catalysing the oxidative cleavage of alkenes was reported by Peris and co-workers (Table 10.9) [44]. Despite a relatively limited substrate scope, this reaction reveals an intriguing reactivity of ruthenium and will surely see further elaboration. 

In some ca.ses the use of a two-phase system may allow a change in the selectivity. Thus, Joo et al. (1998) have shown that water-soluble Ru hydrides (sulphanatophenylphosphine Ru complexes) give different products in the hydrogenation of cinnamaldehyde with variation in the pH of the aqueous media. At a pH greater than 7.2, cinnamyl alcohol is formed and at a pH less than 5 saturated aldehyde is formed. 

All these results indicate that one is just at the beginning of understanding the function of catalysts being deposited on a semiconductor. There is still quite a confusion in many papers published in this field. Therefore the catalytic properties depend so much on the procedure of deposition . It seems to be rather difficult to produce a catalyst for 02-formation, as shown by results obtained with Ti02 (see e.g.) . Rather recently new concepts for the synthesis of new catalysts have been developed applicable for multielectron transfer reactions. Examples are transition metal cluster compounds such as M04 2RU1 gSeg and di- and trinuclear Ru-complexes . 

The authors confirmed the formation of vinyl Ru-complex 21 by the reaction of [Cp Ru(SBu-t)]2 with methyl propiolate (Eq. 7.15). To my knowledge, this is the first observation of the insertion of an alkyne into the M-S bond within a catalytically active metal complex. In 2000, Gabriele et al. reported the Pd-catalyzed cycloisomerization of (Z)-2-en-4-yne-l-thiol affording a thiophene derivative 22 (Eq. 7.16) [26]. 

The enantiopure l-chloro-2,5-dimethylphospholane 2 is now available from the corresponding 1-trimethylsilylphospholane 1. The new phospholane 2 was used as an electrophilic building block in a wide range of coupling reactions giving rise to new phospholanes. These proved to be valuable as chiral ligands in transition metals catalysis with Rh, Ir or Ru complexes. 

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