Silver complexes pincer

Silver(I) carbene complexes are characterised by a broad range of different structures [314]. Hence, it is not surprising that Melaiye et al. [488] found an infinite chain structure as the underlying motif in a water soluble silver(l) pincer carbene complex (see Figure 3.168). Water solubility was achieved by the introduction of pendant hydroxyalkyl wingtip groups. Water solubility of the silver(l) pincer carbene is desirable when the compound is used as an antimicrobial agent in medical applications [489]. 

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]. 

Figure 3.169 A silver I) pincer carbene complex with dimer structure.

Youngs and co-workers extended the chemistry toward synthesizing water-soluble silver carbene complexes 68a-68c (Figure 28) by using hydroxyl-containing pincer-type iV-heterocyclic carbenes as ligands.1 4 It is interesting... 

Nielsen et al. have introduced a monoether linked bis-carbene [209] modelled on an amino linked bis-carbene ligand that acts as a C,N,C pincer ligand in a corresponding palladium(II) complex [156]. Synthesis of the ether linked bis-carbene is facile and involves the reaction of the l-co-dichloro-diethylether with 2 equiv. of methylimidazole. Subsequent reaction with silver oxide and carbene transfer to suitable transition metal precursor complexes affords the corresponding complexes (see Figure 3.73). 

Simons et al. [487] used these pincer carbene ligands in the synthesis of silver(I), palladium(II) and rhodium(l) pincer carbene complexes (see Figure 3.167). Similar to the Anker-free pincer carbene ligands, [Rh(cod)Cl]2 proved to be an unsuitable starting material to synthesise a rhodium(l) pincer carbene complex [462]. The ligand acted as bridging ligand to two [Rh(cod)Cl] units instead. 

Formation of the palladium(n) complex does not require the silver(I) complex, but can be achieved by reaction of the pincer imidazolium salt with [PdjCdbalj] [136]. As already described for the corresponding CT4,C pincer complex, the C,C,C palladium(ll) complex displays a conformational flexibility with 8// of 51.6 kJ/mol for the C,N,C pincer complex and 74.5 kJ/mol for the C,C,C pincer complex. This difference in enthalpies is unexpected and was explained later by the same authors [503] as stemming from a counter anionic... 

Figure 3.173 The silver(l) complex of a potential C,C,C pincer carbene ligand.

Fig. 11 A pincer silver(I)-carbene complex designed for the controlled release of Ag ions to fight bund wounds...

In the same way that the controlled release of silver ions is important in the antibacterial activity of silver nitrate and silver(I) n-pincer-type heterocyclic carbene complexes, the release of carbon monoxide in a controlled... 

Nielsen, D.J., CaveU, K.J., Skelton, B.W. and White, A.H. (2006) Silver(l) and palladium(II) complexes of an ether-functionalized quasi-pincer bis-carbene ligand and its alkyl analogue. Organometallics, 25,4850-6. 

Further examples of palladium picolyl- and pyridyl-functionalized carbene complexes, and also a methoxy ether-functionalized complex have been reported.The synthesis of C-N chelating and N-C-N pincer carbene complexes of palladium have been described.Complexes were generally prepared by a silver-transfer route, although several were prepared via the free carbene method. Structural studies were undertaken on a number of the complexes. Air and thermally stable tridentate carbene C-N-C 92, 93 and C-C-C 94 palladium pincer complexes have been prepared.Complex 94 is formed by the reaction of the appropriate aryl-bridged precursor with... 

Pyridine-bridged bisimidazolium salts also afforded the preparation of dimetallic Rh(l) species by transmetallation from a silver(l)-NHC complex and deprotonation with a weak base. A pincer pyridine-bis-NHC Rh(lll) complex 330 was obtained from the reaction of the corresponding bisimidazolium salt and [Rh(/r-Cl)(cod)]2 in the presence of... 

Another type of potential pincer ligand with an anionic central moiety has been proposed by Poethig and Strassner. The ligands have the structure displayed in 12 and feature an anionic triazinone central moiety. Such moiety is actually a very weak electron donor hence, these ligands have not been employed up to now to prepare pincer complexes, but rather dinuclear complexes of silver(I) and gold(I), in which the central triazinone moiety remains uncoordinated. The resulting complexes are emissive in the sofid state and are neutral, which facifitates their dispersion into, e.g., polymer films for photophysical appHcations. 

Huckaba AJ, Hollis TK, Howell TO, Valle HU, Wu Y. Synthesis and characterization of a 1,3-phenylene-bridged N-alkyl bis(benzimidazole) CCC-NHC pincer ligand precursor homobimetaUic silver and rhodium complexes and the catalytic hydrosilylation of phenylacetylene. Organometallics. 2013 32 63-69. 

The use of silver as an antimicrobial agent dates back to antiquity, with reports of ancient civilizations storing their water in silver urns. Silver metal Ag readily ionizes in the presence of water to generate Ag, thought to be the bioactive species. The broad history of silver as an antibiotic provided the rationale for the first NHC-Ag complexes." In a 2004 report by Youngs et al., the antimicrobial properties of the pyridine-linked pincer complexes... 

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