Phosphinimines as potential technetium environmental sensors

Abstract

Phosphinimines, R₃P=NSiMe₃, undergo hydrolysis to form the phosphiniminiumcation, R₃P=NH₂+, which forms the ion pair [R₃P=NH₂+][X-] in the presence of an anion.Preliminary studies show that in the presence of TcO₄-, Ph₃P=NSiMe₃ forms [Ph₃P=NH₂+][TcO₄-] and [Ph₃P=NH₂+] is selective for TcO₄- over other anions.Technetium-99 is present as environmental contamination in the form of ⁹⁹TcO₄-, which is extremely mobile. Currently available methods to measure this contamination are time consuming and tedious. A method to preconcentrate and measure ⁹⁹Tc environmental contamination in a quick and efficient manner is needed. The selectivity of the phosphiniminium cation for TcO₄- may make phosphinimines suitable for such preconcentration and possibly for measurement. Several phosphinimines were synthesized and characterized for their stability and selectivity with ⁹⁹TcO₄-, including Ph₃P=NSiMe₃, (9-anthracenyl)Ph₂P=NSiMe₃, (1-napthyl)Ph₂P=NSiMe₃, and (p-COOMe)C₆H₄Ph₂P=NSiMe₃. (9-anthracenyl)Ph₂P=NSiMe₃ and (1-napthyl)Ph₂P=NSiMe₃ include possible reporter groups and (p-COOMe)C₆H₄Ph₂P=NSiMe₃ contains a linking moiety for incorporating reporter groups or attaching the phosphinimine to a polymer support. The use of internal and external reporter groups to generate a signal in the presence of TcO₄- is also investigated.