Ruthenium complexes centers

One other study of group 14 heteroallenes involving transition metals was reported in 1995. Jones et al. described the isolation of a ruthenium complex of a 1-silaallene (132—Scheme 32). The 1-silaallene also interacts with a hydrogen atom as well as the ruthenium metal center. Jones et al. describe this view... 

There are more examples of a second type in which the chirality of the metal center is the result of the coordination of polydentate ligands. The easiest case is that of octahedral complexes with at least two achiral bidentate ligands coordinated to the metal ion. The prototype complex with chirality exclusively at the metal site is the octahedral tris-diimine ruthenium complex [Ru(diimine)3 with diimine = bipyridine or phenanthroline. As shown in Fig. 2 such a complex can exist in two enantiomeric forms named A and A [6,7]. The bidentate ligands are achiral and the stereoisomery results from the hehcal chirality of the coordination and the propeller shape of the complex. The absolute configuration is related to the handness of the hehx formed by the hgands when rotated... 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

Later in 1965, Chart and Davidson [2] reported the first example of cyclometal-lation of an sp C—H bond in [Ru(dmpe)2] (3) dmpe = dimethyl phosphinoethane. These authors found not only that this complex spontaneously cyclometaUates at the phosphorus methyl groups to produce complex [Ru(H)(CH2P(Me)CH2CH2PM 62)(dmpe)] (4 see Scheme 13.4) (a later examination by Cotton and coworkers [9] of this compound provided crystallographic evidence that the cyclometalated form of [Ru(dmpe)2] is in fact a dimer (5) of the type shown in Scheme 13.3), but also that the system reacts with free naphthalene via the oxidative addition of a C—H bond to the zero-valent rathenium center to produce complex [cis-Ru(H)(2-naphthyl)(dmpe)2] (6). This species was in equilibrium with the r-coordinated naphthalene ruthenium complex [Ru(naphthalene)(dmpe)2] (7) (Scheme 13.4). 

A special application of bimetallic ruthenium complexes was found in the olefin metathesis reaction vide infra) The two metal centers were closely attached to one another through /r-halide anions. The labile assembly was the key feature to the formation of highly active catalysts. 

The CVs of alkynylbipyridyl-ruthenium complexes, such as [Ru(bpy)2(5-HC= C-bpy)] " and the related terpy complex, [Ru(terpy)(4-HC=C-terpy)] +, contain reversible metal-centered oxidation waves and several ligand-dependent reduction... 

The synthesis introduced by Bruce et al. starts from butadiynyl lithium [14]. The addition of HBF4 to solutions of buta-l,3-diynyl ruthenium complex 3 was proposed to afford the butatrienylidene cation 4 by protonation of the terminal carbon atom of the butadiynyl ligand. Complex 4 could neither be isolated nor spectroscopically detected. It readily decomposed by reaction with even traces of water in the air by nucleophilic attack of H2O on the cationic center (Scheme 3.2). 

Trust s group has shown that another selective reaction involving C—O bond formation followed by rearrangement and C—C bond formation occurred when Cp-containing ruthenium complexes were used as catalytic precursors. With RuCl(Cp)(PPh3)2 in the presence of NH4PF6, an additive known to facilitate chloride abstraction from the metal center, the addition of allylic alcohols to terminal alkynes afforded unsaturated ketones [46, 47]. It has been shown that the key steps are the... 

Terminal alkynes can undergo several types of interaction with ruthenium centers. In addition to the formation of ruthenium vinylidene species, a second type of activation provides alkynyl ruthenium complexes via oxidative addition. 

Several 7] -allylic ruthenium complexes can function as both a nucleophile and an electrophile, as Watanabe and his co-workers observed. Namely, these ruthenium complexes smoothly react with a variety of carbon-centered nucleophiles such as aldehydes, alcohols, and /3-diketones under mild reaction conditions and give the corresponding allylated compounds (Scheme 22). 

In 2002, Trost and his co-workers reported a stereospecific ruthenium-catalyzed allylic alkylation reaction (Equation (58)). Treatment of an optically active allylic carbonate with carbon-centered nucleophiles in the presence of a ruthenium complex gives the corresponding allylic alkylated compounds with enantiomeric purity being completely maintained. Additionally, the regioselectivity is revealed not to be highly dependent on the nature of the starting carbonates. 

In contrast to ferrocenes, osmium and ruthenium complexes are capable of forming coordinative bonds with donor centers of GO including histidine imidazoles. There are therefore two ways of bringing coordinated transition metals onto enzyme surfaces, i.e., via natural and artificial donor sites. Artificial centers are commonly made of functionalized pyridines or imidazoles, which must be covalently attached to GO followed by the complexation of an osmium or... 

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