Formation of a radical tricationic tetraborane(4) by hydride abstraction from sp3-sp3-hybridized diboranes

• Verfasst von: Litters, Sebastian [VerfasserIn]
• Verfasst von: Kaifer, Elisabeth [VerfasserIn]
• Verfasst von: Himmel, Hans-Jörg [VerfasserIn]
• Titel: Formation of a radical tricationic tetraborane(4) by hydride abstraction from sp3-sp3-hybridized diboranes
• Verf.angabe: Sebastian Litters, Elisabeth Kaifer, and Hans-Jörg Himmel
• E-Jahr: 2016
• Jahr: 06 August 2016
• Umfang: 9 S.
• Fussnoten: Im Titel ist die Zahl "3" jeweils hochgestellt ; Gesehen am 27.05.2020
• Titel Quelle: Enthalten in: European journal of inorganic chemistry
• Ort Quelle: Weinheim : Wiley-VCH, 1998
• Jahr Quelle: 2016
• Band/Heft Quelle: (2016), 25, Seite 4090-4098
• ISSN Quelle: 1099-0682
• DOI: doi:10.1002/ejic.201600629
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: Boron
• Sach-SW: Hydride abstraction
• Sach-SW: Multiple-center bonding
• Sach-SW: Radicals
• K10plus-PPN: 1698884052

Abstract

The formation, electronic structure, and reactivity of the recently-reported radical tricationic tetraborane [B4(hpp)4]·3+ (hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), which features a planar rhomboid B4 unit and bridging bicyclic guanidinate (hpp) substituents, is reported. New experiments show that the tetraborane could be synthesized by hydride abstraction either in a very fast reaction from the electron-rich sp3?sp3-hybridized diborane [HB(hpp)]2, or in a very slow reaction from the cationic, less electron-rich sp3?sp3-hybridized diborane [HB(hpp)2BPCy3]+. The results argue for an electron-transfer in the rate-determining step of a complex reaction sequence. Quantum chemical calculations highlight the role of the hpp substituents for the stabilization of the radical tricationic tetraborane [B4(hpp)4]·3+. Further analysis shows that [B4(hpp)4]·3+ is highly reactive, and especially a very strong electrophile. This reactivity makes the compound very interesting because boron atoms in such a low oxidation state (<2) are expected to be strong nucleophiles.