Asymmetric Synthesis of Borylated Amines via Rhodium Catalyzed Hydroboration of Allylamine Derivatives: Surprising Role of Counterions and Accelerators

Authors

• Rukshani Wickrama Arachchilage, University of Nebraska-LincolnFollow

First Advisor

James Takacs

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Barry Cheung, Jiantao Guo, Li Tan, Patrick Dussault

Department

Chemistry

Date of this Version

5-6-2026

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy

Major: Chemistry

Under the supervision of Professor James Takacs

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Rukshani Wickrama Arachchilage. Used by permission

Abstract

The Catalytic Asymmetric Hydroboration (CAHB) reaction is a valuable method for synthesizing chiral organoboron compounds. Nevertheless, key mechanistic details, including catalyst activation, ligand effects, and rate-determining steps, are difficult to generalize and remain not fully understood. Building on previous research from the Takacs group, this work explores acyclic N-acyl allylamines as substrates in rhodium-catalyzed hydroboration and investigates the formation of active catalysts from various rhodium precursors, the role of counterions (e.g. BF₄, BArF-), ligand-to-metal ratios, and the impact of external fluoride additives (e.g. TBAT). Hydroboration of acyclic N-acyl allylamines achieves up to 90% yield and 99 : 1 enantioselectivity. Mechanistic insights show that counterions strongly affect reactivity, with TBAT notably accelerating the process. A kinetic isotope effect close to unity with Rh(nbd)₂BF₄ suggests B–H bond cleavage is less significant in the rate-limiting step. The findings, notably the influence of counterions, ligand ratios, and fluoride additives on catalyst efficiency, elucidate essential mechanistic aspects of the CAHB reaction. Overall, the results support a catalytic cycle that starts with a rhodium(I)-monohydride species generated via borane activation by the counterion. Proposing this novel rhodium(I)-monohydride pathway offers fresh perspectives for catalyst development and reaction enhancement.

Recommended Citation

Wickrama Arachchilage, Rukshani, "Asymmetric Synthesis of Borylated Amines via Rhodium Catalyzed Hydroboration of Allylamine Derivatives: Surprising Role of Counterions and Accelerators" (2026). Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–. 504.
https://digitalcommons.unl.edu/dissunl/504