Silver five coordinate complex

Reaction of the Schiff base ligand A,Ar -bis(o-diphenylphosphinobenzylidene)(ethylene-diamine (49 en=P2) with AgBF4 produced a pale yellow salt. The IR spectrum of this complex showed strong bands due to the imino and BF4 group (v(C=N) 1653 cm-1, v(BFj) 1080 cm-1). The crystal structure of the Cu1 analogue was reported and the copper ion was found to adopt a severely distorted tetrahedral geometry. This strain was manifested in its reactivity since both the copper and silver complex reacted with f-butyl isocyanide. In the case of silver(I) a five-coordinate adduct was obtained, [Ag(en=P2)(Bu NC)]BF4.396... 

In terms of its coordination chemistry, the silver(I) ion is typically characterized as soft . Although originally believed to only bind ligands in a linear arrangement, it was soon shown that it can adopt a variety of coordination environments, the most common one being a four-coordinate tetrahedral geometry. Square-planar complexes are not rare, and various silver(I) cluster complexes also contain three-and five-coordinate sUver(I) ions. 

On addition of AgN03 to a solution of 16, 17 or 18 in acetonitrile, the d-d transition at ca. 440 nm showed a hypsochromic shift and a decrease in absorbance indicative of 1 1 complex formation [38]. An X-ray crystal structure of the 1 1 silver perchlorate complex of 17 revealed a five-coordinate Ag" ion bound within a distorted square pyramid to four sulfur atoms and a perchlorate ligand [39]. 

Interestingly most of the catalytic systems based on Tp M units contain a coinage metal such as copper or silver. This is also observed for NHC-based catalytic systems, with the addition of gold to those metals. This similarity can be explained in terms of a common feature of both Tp M and (NHC)M moieties with those metals they leave just one coordination site for the catalytic reaction to occur. A second coordination site may also accessible in some cases, for example with Cu(ll)-based systems where five-coordinate geometries are available. In the case of (NHC)M systems (M = Cu, Ag, Au), the linear complexes can accept an incoming ligand (reactant) through the transient formation of three-coordinate intermediates (Scheme 2). 

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

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