Arene-metal distance

Oxidation of M(CO)6 with halogens affords M2(CO)gXj anions, but in the presence of PMe3, neutral mononuclear species MX(CO)3(PMe3)3 are formed. The former contain three bridging halide atoms, which can be substituted by MeO or CH3C02 by reaction with methanol or acetic acid. The metal-metal distance of over 3.5 A precludes direct interaction. The dinuclear chloro anions are converted to CpM(CO)4 by reaction with LiCp and to (i76-arene)M(CO)4+ in the presence of arene and AlBr3. 

Plots of EM vs. the carboxylate-carbonyl distances in the ester substrates, taken as a gross measure of their size, are shown in Figure 8.1. It is apparent that the dinuclear catalyst 14-Ba2, in which the azacrown units are linked to vicinal positions of the calix[4] arene scaffold, is not only far superior to its diagonal regioisomer 15-Ba2 in all cases, but it is also superior to 16-Ba2 in the reactions of esters 18-20. The EM profile shows that the catalytic efficiency of 14-Ba2 reaches its maximum value in the reaction of ester 19, and drops to a very low value in the reaction of the longest ester 21. This indicates that 14-Ba2 cannot expand its intermetal distance to fit the long carboxylate-carbonyl distance in 21. In conclusion, reactivity data obtained for the various catalyst-substrate combinations indeed show that a close fit of ester size to metal-to-metal distance is an important prerequisite for catalysis. However, the marked superiority of 14-Ba2 over... 

Axial interaction of an aryl unit with the [Ru-Ru] bond tends to increase the metal-metal distances. Petrukhina et al. isolated two complexes by codeposition of 2 and 8 with [2.2]paracyclophane to yield (17) and (18), respectively (Scheme 11) [68]. A sandwich structure with the aromatic moiety entrapped between two dimetal imits is observed. The [Ru-Ru] distance increases from 2.627(9) A in 8 to 2.656(3) A in 18 on axial coordination of the arene moiety. Similarly, a change of [Ru-Ru] distance from 2.673(1) A in 2 to 2.678(3) A in 17 was also observed. The inter-centroid distances between the two rings in [2.2]paracyclophane group are shorter (2.974(4) A in 17 and 2.982(5) A in 18) compared to the free [2.2] paracyclophane ligand (3.09 A). This supports the hypothesis that coordination of aryl group to the electrophilic ruthenium centers allows the aromatic decks to move closer which also increases the [Ru-Ru] bond distances. 

Table 10.7. Interatomic Distances in Arene Metal Complexes...

Finally, a metal- -T 6-arene interaction that generates a supramolecular onedimensional array has been reported in the solid-state structure of the (2,6-diphe-nylpyridine)gold(III) derivative [Au(CN) 2,6-NC5H3(C6H4)2-C,C, N [ [66]. Its crystal structure shows that the planes of the planar molecules are parallel, but slip-stacked via intermolecular Au- -T 6-arene contacts in which the distance between the gold atom and the centroid of the arene is 3.428 A. A representation of this structure is shown in Figure 5.35. 

Jote the greater complexity of defining adsorption here in studies of electric double layers than, e.g., for metal-gas systems. With electric double layers, one is concerned with the whole interphasial region. The total adsorption is the sum of the increases of concentration over a distance, which in dilute solutions may extend for tens of nanometers. Within this total adsorption, there are, as will be seen, various types of adsorptive situations, including one, contact adsorption, which counts only Arose ions in contact with the electronically conducting phase (and is Aren, like the adsorption referred to in metal-gas systems, the particles on Are surface). Metal-gas systems deal with interfaces, one might say, whereas metal-electrolyte systems deal primarily with interphases and only secondarily with interfaces. 

The complexed arene rings in tethered complexes of ruthenium(II) are close to planar, though the ipso-carbon atom is often pulled slightly towards the metal atom. In the phosphine complexes, the Ru-C(arene) distances trans to the P-donor (2.22-2.29 A) are significantly greater than those trans to the Ru-Cl bonds (2.15-2.25 A). This feature is also evident in non-tethered complexes of the type [RuCl2(r 6-arene)(PR3)] and can be attributed to the higher trans-influence of PR3 relative to that of Cl-.88... 

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