The Sterically Mediated Reaction of Some Triorganotins with Picolinic Acid N-Oxide

Undergraduate #43
Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)

Adewola Osunsade - University of the District of Columbia
Co-Author(s): Xueqing Song, University of the District of Columbia, Washington, DC

---

Previous work in our laboratory examined the preferred mechanism in the reaction of Triphenyltin Hydroxide with Picolinic Acid N-Oxide. In this case, the tin had the option of either bonding covalently with the oxygen from the acid’s deprotonated carboxyl group via a substitution mechanism to form a 4-coordinated product, or coordinating with the oxygen from the N-Oxide of the ligand via an addition mechanism. We were able to show that both mechanisms were observed, and the product formed was a loosely associated 5-coordinated polymer that dissociated in solution into the substitution product. We hypothesize that this reaction is sterically mediated, and that the extent of association seen in the polymer – or whether a polymer forms at all – is dependent on the size of the organic groups bonded to the tin atom. We predict smaller R groups will result in a chain of tightly bound monomer units, while larger ones will form a more weakly linked product. A better understanding of the preferred reaction pathways of various triorganotins will increase the ease with which they can be functionalized in order to enhance their innate biocidal activity.

Picolinic Acid N-Oxide was reacted with a series of triorganotin chlorides (R = Pr, Bu, Cy, Ph, and Bn) in a 1:1 molar ratio in the presence of 1 molar equivalent of either triethylamine or dicyclohexylamine; the resulting products were purified. Characterization by FT-IR and NMR spectroscopies is underway. Preliminary data suggest the tripropyl- and tributyl-tin products in this case exist as liquids, while the triphenyltin complex is solid. The tribenzyltin complex is still being characterized, while the tricyclohexyltin reaction seems unlikely to proceed. X-ray crystallographic results will be discussed. Thorough structural analysis of our complexes will allow us to confirm or refute the validity of our hypothesis.

As the toxicity of triorganotins against a particular species is thought to be dependent on the R groups on the tin, this series will also be screened against different species of bacteria.

Funder Acknowledgement(s): Financial support from the Science, Technology, Engineering and Mathematics (STEM) Program at UDC is gratefully acknowledged (NSF/HBCU-UP-HRD-0928444).

Faculty Advisor: Xueqing Song,