TY - JOUR
T1 - Room temperature ring expansion of N-heterocyclic carbenes and B-B bond cleavage of diboron(4) compounds
AU - Pietsch, Sabrina
AU - Paul, Ursula
AU - Cade, Ian A.
AU - Ingleson, Michael J.
AU - Radius, Udo
AU - Marder, Todd B.
PY - 2015/5/8
Y1 - 2015/5/8
N2 - We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2cat2). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2neop2) is much more reactive than B2cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis. Bor-rings are anything but boring: The isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2cat2) is reported. The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable, see scheme (B2neop2=bis(neopentylglycolato)diboron).
AB - We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2cat2). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2neop2) is much more reactive than B2cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis. Bor-rings are anything but boring: The isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2cat2) is reported. The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable, see scheme (B2neop2=bis(neopentylglycolato)diboron).
KW - B-B bond activation
KW - boron compounds
KW - C-N bond cleavage
KW - N-heterocyclic carbene
KW - ring expansion reaction
UR - http://www.scopus.com/inward/record.url?scp=84930617467&partnerID=8YFLogxK
U2 - 10.1002/chem.201501498
DO - 10.1002/chem.201501498
M3 - Article
AN - SCOPUS:84930617467
VL - 21
SP - 9018
EP - 9021
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 25
ER -