Silver sources

Of the 19 elements determined in Sasanian silver objects, only gold and iridium seem to indicate the silver source used. Indirectly through their concentration ratios zinc, tin, arsenic, antimony, and selenium might provide some additional information on the silver source used, and their absolute concentrations, together with those of other elements might be useful in obtaining information on metallurgical techniques used. 

Of course, the heteroaromatic sidegroup is usually not strong enongh as a donor ligand to replace chloride from a palladinm(II) centre [31,34], Coordination of the sidearm can be achieved by silver halide abstraction nsing a snitable silver salt [31], using a silver carbene complex as the silver source [31,34,35] or reacting the imidazolium salt directly with [Pd(OAc)2] [36] and therefore in the absence of halide (PF - was nsed as the imidazolium counterion). 

A quantitative measurement of the depth of penetration of the diffracted electrons has been made previously by the author (1) by depositing silver vapor onto a gold crystal surface, using a calibrated silver source. Since the lattice structures are the same and the lattice constants differ by less than 0.4%, the silver was found to deposit as a thin crystal on the gold surface. Because of the different indices of refraction and certain fine-structure characteristics for the two metals, the diffraction beams from silver and gold were readily distinguished. 

The use of an Ag-exchanged zeolite also appears to give somewhat better results than the more usual Ag3P04 silver source. The desired indolizidine 30 is obtained as a mixture (94% yield, 86% ee) with the isomer 29 however, treatment of the mixture with catalytic Pd/C in MeOH at room temperature gives clean isomerization to 30 in essentially quantitative yield. Compound 30 has been converted to the natural products lentiginosine 32,1,2-diepilentiginosine, and ge-phyrotoxin 209D 33 [38]. 

Figure 6.4 Generalized schematic of silver source/inorganic resist systems.

The title compound produced superior conversions and better C4 selectivity compared with other silver sources such as AgBFq and AgOTf. Of note, AgF performed comparably to Ag20 (90% yield, 92 8 (C4 C2/C5) for AgF vs. 91%, 93 7 (C4 C2/C5) for Ag20). 

The synthesis of 1-amino-isoquinoline-A-oxides from 2-alkynylbenzaldoxime and related compounds has been achieved using a silver/copper-cocatalyzed reaction in air (Scheme 3.58) [64]. While silver triflate was used as the silver source, a range of copper salts were screened for activity, and copper iodide was found to be an effective cocatalyst... 

An incomplete cubane cluster, [V2Ag(p -S)(p-S)3(S2CNMe2)2(PPh3)] (68) (Fig. 66), has also been synthesized in low yield using [Ag(PPh3)2Cl] as both the silver source and reductant (703). Both vanadium ions possess identical coordination environments and all metal-metal distances are shorter than found... 

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