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Systematic Investigation of the Ring‐Expansion Reaction of N‐Heterocyclic Carbenes with an Iminoborane Dihydride
Author(s) -
Franz Daniel,
Inoue Shigeyoshi
Publication year - 2014
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201402233
Subject(s) - carbene , yield (engineering) , steric effects , ring (chemistry) , chemistry , borane , hydride , boron , medicinal chemistry , photochemistry , polymer chemistry , catalysis , organic chemistry , materials science , hydrogen , metallurgy
Conversions of iminoboranes with an N‐heterocyclic carbene (NHC) result in borane dihydride formation (BDF) concomitant with dihydrogenated NHC. The iminoborane dihydrides are prone to a hydride‐mediated ring‐expansion reaction (RER) at elevated temperature, that is, the insertion of the boron atom into the adjacent CN bond of the NHC to yield boracycles. Upon conversion of a saturated‐backbone NHC with respective iminoborane precursors RER yet occurs at ambient temperature to yield the ring‐expanded products. When a less bulky iminoborane is brought in contact with sterically unhindered NHC neither the iminoborane dihydride is stable at room temperature nor is the RER observed to take place upon heating. The conversions of iminoboranes with very bulky NHC do not show BDF at ambient temperature and only in the case of the less hindered borane precursor the RER is found to proceed in a controlled fashion upon heating.