Silver coordination

One of the sulfur atoms is linked to one and the other to two silver atoms. The silver coordination is threefold but not planar, the metal atoms being situated inside the plane of the coordinating sulfur atoms 144). 

In pyridine solution the cuprous or silver acetate molecules probably exist as the solvated complexes CuPy3OAc and AgPy3OAc, (In the case of silver, coordination with less than four groups may also occur.) Presumably one of the coordinated solvent molecules is displaced when the activated complex with hydrogen is formed. This will not change the electronic configuration about the metal ion, provided that either two hydrogen atoms or a hydride ion become attached to the metal in either case, the 3d, 4s, and 4p (4d, 5s, and 5p for silver) orbitals remain filled. 

Further mechanistic work with optically active and labeled compounds confirmed that the rate-determining step in such rearrangement was the silver coordination to the alkyne moiety and revealed that the silver-catalyzed allene epimerization was 2-40 times faster than the propargyl ester rearrangement.53... 

In contrast to the preceding mechanisms proposed for [3,3]-sigmatropic shifts, the mechanism of the silver-catalyzed oxy-Cope rearrangement was proposed as a stepwise process (Scheme 3.37). As usual, the reaction would be initiated by silver coordination to the alkyne moiety. Nucleophilic attack of this complex by the double bond would then lead to a cyclic cationic vinylsilver intermediate. Fragmentation would then give the dienone. 

Although not the best catalyst, AgSbF6 led to the rearranged product in 50% yield. This cascade reaction probably started with the well-known cyclization of the ketone to the alkyne on silver coordination, giving a cyclic oxonium intermediate that rearranged to furanone via an alkyl 1,2-migration (Scheme 3.54).82... 

SILVER COORDINATION POLYMERS WITH SPECIFIC TOPOLOGY... 

In addition to the infinite tubes, polycatenanes, and polyrotaxanes, all of which are polymeric complexes, a great number of silver coordination polymers with ID, 2D and 3D framework structures have been reported more recently. Selected examples and their specific topologies of some of these are listed in Table 11.1. Schematic structures of the corresponding organic ligands are shown in Figure 11.23.9,58-75... 

TABLE 11.1. Selected Silver Coordination Polymers with Specific Topology... 

Schmaltz et al (2001) Double stranded interwound infinite silver coordination network. Chem Commun 1242-1243... 

Product analysis shows that the thermal and metal induced reactions follow similar courses. The former reaction may proceed by opening of one ring to produce a formal vinyl carbene, followed by ring expansion the latter may be rationalised in terms of electrophilic attack by silver ion at one of the cyclopropenes to produce a carbenium ion (355) — that is a silver-coordinated equivalent of the carbene — followed by ring expansion of the second cyclopropene. 

A third structural motif for silver(l) pincer carbene complexes is the dimer observed by Nielsen et al. [490] (see Figure 3.169). This dimeric structure becomes possible because of the flexibility introduced into the pincer structure by the linker unit, which acts as a hinge. It makes it possible for the NHC donor ligands to align themselves parallel to each other and perpendicular to the C-Ag-C vector of the silver coordination sphere. The dimer is considered to possess no argentophilic interactions as the Ag-Ag distance is 31 pm longer than the sum of the van der Waal s radii (340 pm) [20]. 

The ligand (25) (Scheme 22) consists, in the solid state, of discrete molecules without significant intermolecular association. Within each HC(pz)3 unit the orientation of the three pyrazolyl ring is a propeller arrangement. This ligand supports the supramolecular architecture of a silver coordination polymer.258... 

Double stranded interwound infinite linear silver coordination network, B. Schmaltz, A. Jouaiti, M. W. Hosseini and A. De Cian, Chem. Commun., 2001, 1242. 

Prochazka et al. demonstrated the suitability of surface-enhanced resonance Raman scattering (SERRS) spectroscopy to monitor silver coordination of free base 5,10,15,20-tetrakis(l-methyl-4-pyridyl) porphyrin adsorbed on the Ag colloidal surface. The approach was based on factor analysis (FA) which allows the analysis of the time development of SERRS spectra in terms of varying content of particular porphyrin forms. Their SERRS spectra can be isolated even if none of them is present singularly in any SERRS spectmm. Depending on the chemical properties of the molecular systems, SERRS spectra of two different porphyrin metalated forms have been obtained Ag+ and Ag metalated. The latter form was found to be evoked by pre-treatment of the laser-ablated Ag colloids by the thiosulphate ions. The metalation kinetics obtained show a substantially slower metalation by Ag than that by Ag+ cations. 

Gordon O, Vig Slenters T, Brunetto PS, VUlaruz AE, Sturdevant DE, Otto M, et al. Silver coordination polymers for prevention of implant infection thiol interaction, impact on respiratory chain enzymes, and hydroxyl radical induction. Antimicrob Agents Chemother 2010 54 4208-18. 

Gold-silver coordination compounds and decorating compositions containing same, R. C. Langley and H. M. Fitch, GB patent, 1009539, 1963. 

Silver coordination compounds of oxadiazole (69) were formed with both the nitrate and triflate salts of the metal. The phosphazene was formed by assembly of the ligand followed by attachment to bis(2,2-phenylenedioxy)-bis-chlorocyclotriphosphazene. 

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