10. Scavenging A Tin Catalyst
A metal scavenging study using SiliaBond® Metal Scavengers products was conducted on a tin catalyst (Sn(OTf)2) commonly used in organic synthesis.
Various parameters were studied for their influence on the scavengers' robustness as well as to establish the best conditions to bring the level of metal down to an acceptable level for the pharmaceutical industry (i.e.: solvent, number of equivalents, temperature, and reaction time).
Tin Scavenging with SiliaMetSOrganotin compounds are versatile reagents commonly used in organic synthesis. The two main applications are in Stille couplings or in radical reactions. The removal of tin residues can often be an issue due to the well known high toxicity of this metal.
Traditional removal methods for this particular type of impurity are treatment with an aqueous solution of KF, NH4OH or NaOH, or with bases such as DBU. However, the efficiency of these methods can vary and may be inapplicable for particular compounds.
SiliaMetS Cysteine & TAAcONa can be used as an efficient method to remove tin residues from organic mixtures as demonstrated by the exemples below.
|Tin Scavenging using SiliaMetS Cysteine (TAAcONa)|
|SiliaMetS Cysteine||SiliaMetS TAAcONa|
|4 eq., 4 h, 22°C [2 treatments]||8 eq., 4 h, 22°C||4 eq., 4 h, 22°C [2 treatments]||8 eq., 4 h, 22°C||4 eq., 16 h, 22°C|
|Stille coupling #11||3 385 ppm||99 %||64 %||96 %||62 %||-|
|Stille coupling #21||981 ppm||90 %||66 %||66 %||50 %||-|
|Radical Reduction||4 090 ppm||92 %||88 %||90 %||90 %||90 %|
|1Pd residues were completely removed after only one treatment with SiliaMetS Cysteine.|
SiliaMetS® TAAcONa or (or SiliaMetS Triaminetetraacetate, sodium salt) is a silica bound metal scavenger for Pd(II), Ni(II) and Cu. It is the supported version of EDTA in its sodium salt form. It is an effective scavenger for metals in higher oxidation state, 2+ or higher.