Silver Arene Cationic Complexes

Recently, Lacour, Sauvage and coworkers were able to show that the association of chiral [CuL2] complexes (L=2-R-phen,6-R-bpy and2-iminopyridine) with TRISPHAT 8 leads to an NMR enantiodifferentiation, which allows the determination of the kinetics of racemization of the complexes (bpy=2,2 -bipyri-dine phen=l,10-phenanthroline) [119]. This type of application has recently been reported in conjunction with chiral sandwich-shaped trinuclear silver(l) complexes [122]. Several reports, independent from Lacour s group,have confirmed the efficiency of these chiral shift agents [123-127]. Finally, TRISPHAT can be used to determine the enantiomeric purity of (r] -arene)chromium complexes. These results broaden the field of application of 8 to chiral neutral, and not just cationic, species [114,128,129]. 

Cyclopentadienyl dicarbonyl ruthenium dimer 132 reacts with silver tetrafluoroborate and diphenylacetylene to afford the cyclobutadiene ruthenium complex 133 (Scheme 12). Irradiation of 133 in dichloro-methane in the presence of several alkynes leads to the arene cyclopentadienyl ruthenium complexes 125 in high yield. This reaction appears to be a general route to sterically crowded ruthenium arene cations (55). 

Silver(I) cations form only rather labile rr-complexes with aromatic hydrocarbons. The nature of the complex formation may be described as solvation of silver salts in arene solution. Supramolecular framework structures can be isolated upon concentration, and the structure of many of these solvates has been determined. The Ag(I) cations are found to be mostly or bound to the arene, but the coordination is weak and arene may be removed already at ambient temperature in a vacuum. This class of compounds for which no synthetic strategy is required, is no longer considered in this chapter which is orientated towards preparative methods. The adducts have not yet found any significant applications. 

Haino and co-workers have reported the synthesis of a self-assembling dimeric capsule via metal-coordination utilizing two octadentate resorcin[4]arene cavitands possessing four bipyridyl groups (13) which complex four silver cations (Ag+) in a tetrahedral fashion (Fig. 4) [46, 47]. A detailed computational study of the dimeric metallo-capsule 14 revealed a large and elaborate three-dimensional inner capsular... 

The synthesis of cahx[4]arene dimelamines with different functionalities and their self-assembly with barbituric and cyanuric acid to hydrogen-bonded nanostructures have been published <05OBC3727> Unique ionophores of penta-crown ethers have been prepared by the reaction of l,3,5-triacryloylhexahydro-l,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by Michael addition, and their binding capabilities towards alkali metal cations studied <05SL2257>. New silver complexes of polydentate ligands including a derivative of pyrazol-l-yl-l,3,5-triazine have been reported <05EJ14370>. 

L2 = hexadiene, nbd). Bis(2,2 -bipyridine)binaphtholate reacts with [(j -COE)2Rh]2 followed by hexadiene and then silver tetrafluoroborate or with [(/ -nbd)2Rh](BF4) to give cationic dinuclear 36 (L2 = hexadiene, nbd). With [(/ -cod)IrCl]2 this ligand produces neutral 37. Into this category falls the complex similar to 34 with L2 = nbd and polypyridine ligand h s(2,2 -bipyridine)calyx[4]arene (03IC3160). 

Let us now consider metal complexes. Transition metal complexes of olefins, alkynes, and arenes and other organic 7T systems have become quite common in both the textbook and research literature some exotica of this type will be discussed in a later section. We start with an ethylene complex with the simplest metal ion, Li+. The cation is definitionally electrophilic, the olefin has an energetically accessible pair of electrons, and the complex is really quite sensible. We may recognize it as analogous to the better known olefin-silver complexes... 

Following up on their previous work [73] with covalently-linked double calix[5] arenes, Fukazawa and coworkers [74] reported the fullerene complexation of other related double calix[5]arene receptors in a series of studies published in 2001-2010. A fullerene (Fig. 33.34) receptor which they produced was based on a silver-cation assisted self-assembled pair of upper-rim mono-2,2 -bispyridyl-functionalized tetra-p-methylcalix[5]arenes 49. The cavity thus produced formed quaternary complexes C6o 49 Ag 49 and C7o 49 Ag 49 with the respective fullerenes in 1,1,2,2-tetrachloroethane ( TCE ) and which were established by using ESI MS. The relative intensities of the mass signals also suggested a preference for Ceo over C70. Later, these authors prepared a double calix[5]arene derivative 50 which was based upon linking two molecules of 49 covalently via their bipyridines. As measured by UV-Vis titration, treatment of Cgo with the complex of 50 with [Cu... 

Self-assembly of a diruthenium precursor 285 as a bimetallic connector with tris-pyridyl ligand syntone 241 in the presence of silver(l) ions by Scheme 4.35 afforded a cationic TP (arene)ruthe-ninm Rne Ls La coordination capsule 540 [36]. This capsule encapsulates palladium and platinnm(ll) acetylacetonates to give the corresponding 1 1 cage complexes [36]. In the platinum-... 

---