Directed Synthesis and Chemistry of Unsymmetric Dicationic Diboranes and Their Use in Frustrated Lewis Pair-like Chemistry |
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Authors: | Lucas Kistner Dario Kowatsch Andreas Marz Dr. Elisabeth Kaifer Prof. Hans-Jörg Himmel |
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Affiliation: | Anorganisch-Chemisches Institut, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany |
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Abstract: | The chemistry of dicationic diboranes with two BII atoms that are engaged in direct B−B bonding is by enlarge unexplored, although these molecules have intriguing properties due to their combined Lewis acidic and electron-donor properties. Unsymmetric dicationic diboranes are extremely rare, but especially attractive due to their polarized B−B bond. In this work we report the directed synthesis of several stable unsymmetric dicationic diboranes by reaction between the electron-rich ditriflato-diborane B2(hpp)2(OTf)2 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-α]pyrimidinate) and phosphino-pyridines, establishing B−N and B−P bonds with the diborane concomitant with triflate elimination. In the case of 2-((ditertbutylphosphino)methyl)pyridine, the B−N bond is formed instantly, but the B−P bond formation requires (due to steric constraints) several days at ambient conditions for completion, creating an intermediate that could be used for frustrated Lewis pair (FLP)-like chemistry. Here we test its reaction with an aldehyde, and propose a new type of FLP-like chemistry. |
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Keywords: | boron diborane dication frustrated Lewis pair Lewis acid |
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