Degradatiom of environmental pollutants using rhodium hydrides.

Abstract

The objective of this work was to study the dehalogenation of environmental pollutants mediated by rhodium hydrides. The product distribution and mechanism of dehalogenation was explored and the information obtained can possibly be applied to improve future remediation strategies. In Chapter 2, the dehalogenation of chlorinated and fluorinated ethylenes was explored using (PPh 3 ) 3 RhCl and Et 3 SiH, and counter-intuitively, vinyl fluoride was dehalogenated 6 times faster than vinyl chloride. This study established substrate scope and preferences for the Et 3 SiH and (PPh 3 ) 3 RhCl catalytic system. In Chapter 3, the mechanism for dehalogenation of chlorinated and fluorinated ethylenes was elucidated using H 2 as the reducing agent with the pre-catalyst (PR 3 ) 3 RhCl. These results were compared to those from using Et3SiH as the reducing agent. Dehalogenation using (PPh 3 ) 3 RhCl and either H 2 or Et 3 SiHsupport an insertion/β-chloride elimination mechanism; however the two systems display distinct differences. Based on these differences, the dominant pathway for Et 3 SiH is proposed to involve rhodium(I), while the H 2 system is proposed to primarily involve rhodium(III). In Chapter 4, a heterogeneous catalytic system using Rh/Al 2 O 3 as the catalyst and H 2 as the reducing agent was investigated. Consistent with the homogenous system of (PPh 3 ) 3 RhCl and H 2 , the data from this system also supports an insertion/β-Cl-elimination mechanism as the dominant degradation pathway. Ultimately, the goal of this work was to facilitate the preparation of engineered pump-and-treat strategies that will function to effectively degrade environmental pollutants to benign products with no halogen substituents.