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Formation of a Radical Tricationic Tetraborane(4) by Hydride Abstraction from sp 3 –sp 3 ‐Hybridized Diboranes
Author(s) -
Litters Sebastian,
Kaifer Elisabeth,
Himmel HansJörg
Publication year - 2016
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201600629
Subject(s) - chemistry , diborane , electrophile , reactivity (psychology) , hydride , nucleophile , cationic polymerization , medicinal chemistry , hydrogen atom abstraction , boranes , computational chemistry , stereochemistry , boron , radical , organic chemistry , hydrogen , medicine , alternative medicine , pathology , catalysis
The formation, electronic structure, and reactivity of the recently‐reported radical tricationic tetraborane [B 4 (hpp) 4 ] · 3+ (hpp = 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidinate), which features a planar rhomboid B 4 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 sp 3 –sp 3 ‐hybridized diborane [HB(hpp)] 2 , or in a very slow reaction from the cationic, less electron‐rich sp 3 –sp 3 ‐hybridized diborane [HB(hpp) 2 BPCy 3 ] + . 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 [B 4 (hpp) 4 ] · 3+ . Further analysis shows that [B 4 (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.