## 1 Introduction  
While homogeneous catalysis using transition metals is now commonly used in synthesis of most drugs and chemical intermediates [1; 2], the separation of the metal catalysts from the desired products remains a problem. This issue has been addressed in a variety of ways [3; 4], and the oldest approach is to use solid state sequestrants. There is an immense arsenal of ion exchange resins and functionalized inorganic supports that can sequester metals or metal catalyst residues [5; 6; 7; 8; 9; 10; 11]. These materials like ion exchange resins are insoluble and have the advantage that they are physically separable from product solutions. However, metal catalyst residues are often present with other ligands that make insoluble sequestrants less effective. In other cases, catalyst residues are present in the form of colloids that might not be as effectively sequestered by solid supported scavengers. Thus, it is not surprising that there is still ongoing work to develop better metal scavenging systems. This includes developing novel homogeneous scavenging agents. Indeed, recent reports have suggested that soluble sequestrants that can be separated by liquid/liquid or liquid/solid separations can be more effective than conventional solid sequestrants. For example, [PERSON] and [PERSON] showed that copper catalyst residue sequestration by water soluble dithiocarbamate sequestrants was more effective in large scale pharmaceutical synthesis than solid sequestrants [12]. [PERSON] et al. reported a homogeneous isocyanate scavenger that was extremely efficient at precipitation of ruthenium catalyst residues followed by simple filtration [13]. Similarly, [PERSON] et al. prepared a perfluorinatedketone with temperature dependent solubility for heavy metal removal [14]. In another report, [PERSON] et al. demonstrated that in the case of cephalospororin antibiotic synthesis, solid state scavengers had only limited success in palladium sequestration in comparison with homogeneous organosulfur scavengers [15]. Those successes and our past work where we developed phase selectively soluble polymeric ligands that immobilize transition metal catalysts suggested to us that alkane phase selectively soluble sequestrants would be practical sequestrating agents too [5; 6; 15; 16; 17; 18; 19; 20; 21; 22]. Based on that prior work, we reasoned that polyisobutylene (PIB) could be functionalized to make it a capable sequestrant. Commercially available alkene-terminated PIB oligomers have a reactivity identical to that of low molecular weight analogs that enables their efficient functionalization [23]. Moreover, if dilute heptane solution of such functional PIB were used in a liquid/liquid extraction in a water/heptane biphasic mixture, it would be expected to lead to essentially no PIB leaching to the aqueous phase. Heptane has a known solubility in water of 3.37 ppm under ambient conditions [24]. If we assume polyisobutylene solubility in heptane equal to that in water, addition of 1000 ppm solution of PIB in heptane to water would lead to ca. 3 ppb solubility of PIB in water. Since hydrocarbon solubility in water decreases dramatically with increase of molecular weight, PIB solubility in water is extremely low. Hence, its leaching in water is also negligibly low. Such quantitative phase separation was further demonstrated in our previous studies [25]. The work described below confirms that simple oligomer PIB derivatives are excellent sequestrants that quantitatively phase separate and sequester transition metals from aqueous or polar organic solutions. Readily available polyisobutylene thioether thiol was successfully utilized for the liquid-liquid extractions of transition metals such as Co\({}^{2+}\), Ni\({}^{2+}\), Cu\({}^{2+}\), Pd\({}^{2+}\) and Ru\({}^{3+}\) from aqueous or polar organic solutions.