Ruthenium complexes configuration

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 correlation of isomer shift, electronic configuration, and calculated -electron densities for a number of ruthenium complexes in analogy to the Walker-Wertheim-Jaccarino diagram for iron compounds has been reported by Clausen et al. [ 127]. Also useful is the correlation between isomer shift and electronegativity as communicated by Clausen et al. [128] for ruthenium trihalides where the isomer shift appears to increase with increasing Mulliken electronegativity. 

In order to verify the enhancement provided by the cones, a sol-gel layer doped with a fluorescent ruthenium complex was deposited onto a chip in a configuration similar to that shown in Figure 15. Blue LED excitation of the fluorescent sol-gel layers was employed. The resultant fluorescence was recorded using a CMOS camera and the resultant image is shown in Figure 16. 

It is clear from the preceding section that the field of tethered arene-metal complexes is dominated by ruthenium and by arene-phosphines as ligands. In part, this situation has arisen because of the current surge of interest in the catalytic properties of ruthenium complexes in organic synthesis.85,86 Moreover, the tethered arene complexes are usually air-stable, crystalline solids with a well-defined, half-sandwich molecular geometry that, in principle, can lock the configuration at the metal centre. These compounds should, therefore, be ideal both for the study of the stereospecificity of reactions at the metal centre and for stereospecific catalysis. 

The catalytic activation of allylic carbonates for the alkylation of soft car-bonucleophiles was first carried out with ruthenium hydride catalysts such as RuH2(PPh3)4 [108] and Ru(COD)(COT) [109]. The efficiency of the cyclopen-tadienyl ruthenium complexes CpRu(COD)Cl [110] and Cp Ru(amidinate) [111] was recently shown. An important catalyst, [Ru(MeCN)3Cp ]PF6, was revealed to favor the nucleophilic substitution of optically active allycarbonates at the most substituted allyl carbon atom and the reaction took place with retention of configuration [112] (Eq. 85). The introduction of an optically pure chelating cyclopentadienylphosphine ligand with planar chirality leads to the creation of the new C-C bond with very high enantioselectivity from symmetrical carbonates and sodiomalonates [113]. 

Consiglio and Morandini and co-workers (67) have investigated the stereochemistry involved in the addition of acetylenes to chiral ruthenium complexes. Reaction of propyne with the separated epimer of the chiral ruthenium phosphine complex 34 at room temperature results in the chemo- and stereospecific formation of the respective propylidene complex 64. An X-ray structure of the product (64) proves that the reaction proceeds with retention of configuration at the ruthenium center. The identical reaction utilizing the epimer with the opposite configuration at ruthenium (35) also proceeded with retention of configuration at the metal center, proving that the stereospecificity of the reaction in not under thermodynamic control [Eq. (62)]. 

An interesting aspect of the bis(methyl)ruthenium complexes 33 is their tendency to allow hydride abstraction with (Ph3C)PF6. They lead to ethylene complexes 55 and 56 (46,47).The X-ray structure of 55 shows bond distances of 1.411(13) A for C=C and 1.50 A for Ru—H (46,47). The reaction probably proceeds via intermediates 53 and 54, although it was not established whether the transformation 33 - 53 involves a mono-electronic process as with WMe2(C5H5)2 (48). A similar reaction from the deuterated derivative 57 gives exclusively complex 58, configurationally... 

Platinum and palladium complexes of thietane and 3,3-dimethylthietane have been prepared as illustrated for 90. The platinum complexes exist in cis and trans configurations, but no cis-trans isomerization of the palladium complexes in the solid state was observed. Stability constants of thietane with Mn(ll), Co(II), and Ni(II) chelates have been determined. Proton nmr studies show that the absorption of the a-methylene protons, which are syn to the metal, is shifted downfield (about 0.7 ppm) more than the absorption of the protons anti to the metal (about 0.4 ppm downfield). Energies of activation for pyramidal inversion were determined. Bis-ruthenium complexes of di-, tri- and tetraspirothietanes (e.g., 90a) show rapid electron transfer between the ruthenium ions long-range electron tunneling was proposed. ... 

For cobalt, iron, and ruthenium sarcophaginates, the Log kn values increase with an increase in the redox potentials. This is the case when the main factor affecting a variation in both values in the same direction is the electronic configuration. The increase in E values in a series of clathrochelates from cobalt to ruthenium is attributed to differences in spin states Is > hs for cobalt. Is > hs, Is for iron. Is > Is for ruthenium complexes. The increase in Logftii values correlates with ALFSE for +3 and +2 oxidation states. 

The appropriate representation of a molecule with RDF descriptors finally depends on the question of what the term similarity should describe in the given context. Let us have a look at the following example. Figure 5.8 shows three possible configurations of stereoisomers for a Ruthenium complex with sulfur dominated coordination sphere, a compound that serves as a model for nitrogenase. 

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