Palladium-catalyzed C-N cross-coupling and application to the synthesis of delayed singlet emitters for OLED development

Abstract

The studies in the present dissertation were aimed at developing and applying synthetic methods mediated by palladium catalysis. In Chapters 1 and 2, the palladium-catalyzed amidation and amination of five-membered heterocyclic bromides containing multiple heteroatoms are described. These methods provide efficient access to N-arylated imidazoles and pyrazoles in moderate to excellent yields. In Chapter 3, a series of novel triptycene-based compounds were synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Experimental results suggest that this series of compounds could potentially be used as delayed singlet emitters for organic light emitting devices. Chapter 1. Palladium-Catalyzed Amidation of Five-Membered Heterocyclic Bromides Palladium-catalyzed C-N cross-coupling between primary amides and five-membered heterocyclic bromides that contain multiple heteroatoms was achieved for the first time using the Pd/AdBrettPhos catalyst system. This system allows for efficient access to Narylated imidazoles, pyrazoles, thiazoles, pyrroles, and thiophenes in moderate to excellent yield. Experimental results and DFT calculations point to the need for electronrich and especially sterically demanding biaryl dialkylphosphine ligands to promote these difficult cross-coupling reactions. The same protocol was also extended to forming tertiary amides from secondary amides and five-membered heterocyclic bromides. Preliminary studies showed promising results using a Pd/AdRockPhos catalyst system. Chapter 2. Palladium-Catalyzed Amination of Unprotected Five-Membered Heterocyclic Bromides An efficient method for the palladium-catalyzed amination of unprotected bromoimidazoles and bromopyrazoles is presented. The transformation is facilitated by the use of our newly developed Pd-precatalyst based on the bulky biarylphosphine ligand, tBuBrettPhos. The mild reaction conditions employed allow for the preparation of a broad scope of aminoimidazoles and aminopyrazoles in moderate to excellent yields. Chapter 3. Synthesis of Delayed Singlet Emitters for OLED Development The development of novel thermally activated delayed fluorescence (TADF) materials for use in organic light emitting devices (OLEDs) is reported. A series of triptycenebased delayed singlet emitters have been synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Preliminary investigations have demonstrated that these compounds could serve as delayed singlet emitters at a range of wavelengths from orange to blue, which is highly desirable for organic electronics applications.