UC San Diego

Cyclic (alkyl)(amino)carbenes (CAACs) have been recognized as a class of carbenes adept at activating small molecules and stabilizing a wide array of highly reactive compounds. Herein, we outline the impact of CAACs in a variety of applications, e.g., as a catalyst replacing metals, and as ligands promoting metal replacement. Moreover, we delineate that in some transformations, and in marked contrast with the literature, CAACs, or any ligand for that matter, are superfluous in achieving high catalytic activity.

Unlike traditional carbene-catalysts that act as Lewis bases, CAACs are ambiphilic enough to activate carbon monoxide, thus mimicking the behavior of metals. In chapter two, we demonstrate that, without the need for a metal, sterically encumbered CAACs can catalytically transform and transfer CO in carbonylation. This highlights that ambiphilic carbenes can open new avenues in carbene-organocatalysis.

Next, light emitting devices are traditionally made using scarce heavy metals (e.g., Ir, and Pt). The use of copper, however, would constitute a major innovation by replacing those metals, but it is plagued by weak spin-orbit coupling as well as high reorganization energies. In chapter three, we demonstrate that having copper sandwiched between an electron-donor (carbazole) that is rigidly pointed at an electron-acceptor (CAAC) enables record photoluminescent properties akin to heavy metals. Significantly, we exploited this copper system to fabricate a rare example of a high energy blue OLED device.

In chapter four, upon taking advantage of CAAC’s ambiphilicity, we stabilized an active copper cluster and used it as a template via absolute galvanic metal replacement to isolate the coinage metal family of clusters. Moreover, analogous to M(111) surfaces, we demonstrated that copper is unique among coinage metals as it can transform CO2 into CO, further delineating the intermediacy of clusters between homogenous and heterogeneous processes.

In the last chapter, we discuss the challenges of the parent hydrazine in catalytic transformations. As a substrate, it typically requires gold catalysts stabilized by strongly donating carbene ligands. Although we found that (CAAC)Cu cationic complexes could catalyze this difficult transformation, we discovered that commercially available copper salts, unlike gold, were highly efficient catalyst precursors in the absence of ancillary ligands.