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Ligand Postsynthetic Functionalization with Fluorinated Boranes and Implications in Hydrogenation Catalysis
Macarena G Alférez1, Juan J Moreno1, Miguel A Gaona1
1Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Consejo Superior de Investigaciones, Científicas (CSIC) and Universidad de Sevilla, Avenida Américo Vespucio 49, 41092 Sevilla, Spain.
Abstract:
The incorporation of boron functionalities into transition-metal catalysts has become a promising strategy to improve catalytic performance, although their synthesis typically entails the preparation of sophisticated bifunctional ligands. We report here the facile and direct postsynthetic functionalization of rhodium(I) compound [(η5-C9H7)Rh(PPh3)2] (1) by treatment with perfluorinated boranes. Borane addition to 1 results in an unusual C(sp2)-H hydride migration from the indenyl ligand to the metal with the concomitant formation of a C-B bond. In the case of Piers' borane [HB(C6F5)2], this is followed by a subsequent hydride migration that leads to an unprecedented 1,2-hydrogen shift reminiscent of Milstein's cooperative dearomatization pathways. Computational investigations provide a mechanistic picture for the successive hydride-migration steps, which enriches the non-innocent chemistry of widespread indenyl ligands. Moreover, we demonstrate that the addition of Piers' borane is highly beneficial for catalysis, increasing catalyst efficiency up to 3 orders of magnitude.
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