Catalytic Acyloin-Type Heterocoupling of Thioesters via a Putative Cobalt Siloxycarbene

α-Oxy-metallocarbenes exemplify Fischer carbenes and find use in the synthesis of diverse materials. Most, however, arise from the additions of reactive organometallics to toxic metal carbonyls. Here we report a method to instead access α-siloxycarbenes from thioesters via reductive silylation of cobalt acyls. The reaction effects carbonyl dimerization with unprecedented hetero- and stereoselectivity to yield unsymmetrical tetrasubstituted disiloxyalkenes, while avoiding competitive decarbonylation. These products could be further elaborated to new functionalized fragments, heterocycles, and challenging enolsilanes. Several different reactivity patterns combined with mechanistic interrogation converged on α-oxycarbenes as fleeting catalytic intermediates, indicating a novel way to generate and harness these reactive species using mild conditions. To the best of our knowledge, these are the first studies to generate carbenes from carboxylate derivatives, enabling a trove of new reactivities.