Chemistry - A European Journal
Chemistry - A European Journal
5 years ago

Rhodium-Catalyzed Silylative and Germylative Cyclization with Dehydrogenation Leading to 9-Sila- and 9-Germafluorenes: A Combined Experimental and Computational Mechanistic Study

Rhodium-Catalyzed Silylative and Germylative Cyclization with Dehydrogenation Leading to 9-Sila- and 9-Germafluorenes: A Combined Experimental and Computational Mechanistic Study
Ryo Okada, Masahito Murai, Sobi Asako, Kazuhiko Takai
Stoichiometric amounts of oxidants are widely used as promoters (hydrogen acceptors) in dehydrogenative silylation of C−H bonds. However, the present study demonstrates that silylative and germylative cyclization with dehydrogenation can proceed efficiently, even without hydrogen acceptors. The combination of [RhCl(cod)]2 and PPh3 was effective for both transformations, and allowed a reduction in reaction temperature compared with our previous report. Monitoring of the reactions revealed that both transformations had an induction period for the early stage, and that the rate constant of dehydrogenative germylation was greater than that of dehydrogenative silylation. Competitive reactions in the presence of 3,3-dimethyl-1-butene indicated that the ratio of dehydrogenative metalation and hydrometalation was affected by reaction temperature when a hydrosilane or hydrogermane precursor was used. Further mechanistic insights of oxidant-free dehydrogenative silylation, including the origin of these unique reactivities, were obtained by density functional theory studies. Activating the unactivated: The combination of [RhCl(cod)]2 and PPh3 is used to catalyze the oxidant-free dehydrogenative silylation and germylation of unactivated C(sp2)−H bonds under neutral conditions (see scheme). The experimentally obtained unique reactivity is supported by the results of theoretical calculations, and a plausible reaction mechanism, including insights into why the current transformation does not require hydrogen acceptors and heteroatom-containing directing groups, is proposed.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701579

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