Ruthenium phosphine ligands

Ruthenium hydride complexes, e.g., the dimer 34, have been used by Hofmann et al. for the preparation of ruthenium carbene complexes [19]. Reaction of 34 with two equivalents of propargyl chloride 35 gives carbene complex 36 with a chelating diphosphane ligand (Eq. 3). Complex 36 is a remarkable example because its phosphine ligands are, in contrast to the other ruthenium carbene complexes described so far, arranged in a fixed cis stereochemistry. Although 36 was found to be less active than conventional metathesis catalysts, it catalyzes the ROMP of norbornene or cyclopentene. 

Third generation initiators are based on the NHC system of second generation initiators, but do not contain any phosphine ligand. Instead, one or two pyridine ligands are weakly bound to the ruthenium centre (c/. Fig. 3.28, complexes 73 and 74c). Pyridine dissociates very easily and hardly competes with the olefin for the coordination site. As a result, complete initiation and fast propagation are enabled, therefore living polymerisation is rendered possible. 

The homo- and cross-addition of alkenes catalyzed by a transition-metal provided another economical way of forming C-C bonds.155 These reactions are carried out by using nickel, palladium, or ruthenium phosphine complexes to yield vinylarenes and some can occur in aqueous media. By using carbohydrate-derived ligands, asymmetric hydrovinylations can be carried out in aqueous conditions.156... 

More recently, a new metathesis catalyst involving a ruthenium-alkylidene complex with a sterically bulky and electron-rich phosphine ligand has been synthesized and applied to RCM in aqueous media (Figure 3.5).197 This catalyst has the benefit of being soluble in almost... 

In an effort to apply the cooperative principles of metalloenzyme reactivity, involving a combination of metal-ligand and hydrogen bonding, we have reported a ruthenium catalyst incorporating imidazolyl phosphine ligands that efficiently and selectively hydrates terminal alkynes (5). We subsequently found that application of pyridyl phosphines to the reaction resulted in a >10-fold rate enhancement and complete anti-Markovnikov selectivity, even in the... 

Although palladium or platinum on charcoal are widely used, there is a preference for homogeneous reactions on both the laboratory and the industrial scale. Complexes of ruthenium (II) and rhodium (I), particularly with phosphine ligands, do have some importance in special applications [4], but... 

The plausible mechanism of this ruthenium-catalyzed isomerization of allylic alcohols is shown in Scheme 15. This reaction proceeds via dehydrogenation of an allylic alcohol to the corresponding unsaturated carbonyl compound followed by re-addition of the metal hydride to the double bond. This mechanism involves dissociation of one phosphine ligand. Indeed, the replacement of two triphenylphosphines by various bidentate ligands led to a significant decrease in the reactivity.37... 

The formation as well as the reactivity of (7r-allyl)ruthenium(ll) complexes bearing phosphine ligands have been described in a series of articles. However, the main drawback in these cases is the use of non-catalytic... 

Ruthenium complexes are active hydrogenation catalysts for the reduction of dienes to monoenes. Both zerovalent and divalent ruthenium complexes containing various (alkene, diene and phosphine) ligands have been employed as catalysts that have met with different degrees of success. 

As already mentioned earlier, the ruthenium complex [Ru(bdmpza) Cl(PPh3)2l (24) easily releases one of the two phosphine ligands and allows the substitution not only of a chlorido but also of a triphenylphosphine ligand for K -coordinating carboxylato or 2-oxocarboxylato ligands (58). The purpose of these studies was to find structural ruthenium models for the active site of 2-OG dependent iron enzymes, since ruthenium(II) complexes are low spin and thus suitable for NMR characterization, whereas ferrous iron complexes with NJV,0-ligands are often difficult to investigate, due to their... 

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). 

Ruthenium complexes B are stable in the presence of alcohols, amines, or water, even at 60 °C. Olefin metathesis can be realized even in water as solvent, either using ruthenium carbene complexes with water-soluble phosphine ligands [815], or in emulsions. These complexes are also stable in air [584]. No olefination of aldehydes, ketones, or derivatives of carboxylic acids has been observed [582]. During catalysis of olefin metathesis replacement of one phosphine ligand by an olefin can occur [598,809]. 

Ruthenium complexes of a novel silsesquioxane-based tridentate phosphine ligand have been prepared and characterized by Mitsudo et al The synthesis of the ligand 178 is depicted in Scheme 60. Reactions of 178 with several late transition metal complexes were examined. A typical example is the reaction with three equivalents of [RuCl2(cymene)]2, which produced the red triruthenium complex (c-C5H9)7Si709[0SiMe2CH2CH2PPh2RuCl2(cymene)]3 (179) in almost quantitative yield. 

In situ deprotonation combined with a substitution of a phosphine ligand was reported as a convenient way for the synthesis of ruthenium-alkylidene complexes (Scheme For imidazolidin-2-ylidenes, this is the only way... 

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