Iodonium ylides as alternative precursors for cobalt- and iron carbene radical transfer

Carbon-carbon bond formation is at the heart of synthetic organic chemistry. As highly versatile carbon-based synthons, transition metal Fischer-type carbenes have seen increasing use over several decades to directly access numerous challenging motifs. In this perspective, square planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for a wide variety of (hetero)cyclic structures, operating via a redox non-innocent cobalt(III)-carbene radical intermediate. Despite their unique, alternative stepwise reactivity, current systems were limited largely to mono-substituted carbenes derived from diazo compounds.
In this dissertation, I have investigated the use of iodonium ylides as alternative carbene precursors for the analogous diazo compounds. Using the contemporary cobalt(II)-tetraphenylporphyrin catalyst, I found that the increased reactivity of the ylides leads to bis-carbenoid formation and subsequent rearrangement to an N-enolate carbene. Most notably, these results reveal that these N-enolate carbenes are catalytically active and their formation is reversible in contrast to previous reports. Using a newly developed redox-active platform, PhenTAA, the reactivity of iodonium ylides was further explored using an iron-based catalyst. In contrast to other isoelectronic square planar iron(II)-systems, the FeH₂PhenTAA and iodonium ylide system exhibited purely radical reactivity with the unique N-enolate carbene moiety as a catalytically active species. The results described in this thesis provide novel insights in carbene formation and deactivation and a platform for further application of iodonium ylides in carbene radical transfer.