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One‐Electron Reductions of Organodiborane(4) Compounds: Singly Reduced Anions and Rearrangement Reactions
Author(s) -
Grigsby Warren J.,
Power Philip
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030308
Subject(s) - chemistry , medicinal chemistry , electron paramagnetic resonance , ether , diethyl ether , lithium (medication) , solvent , stereochemistry , crystallography , molecule , ion , organic chemistry , medicine , physics , nuclear magnetic resonance , endocrinology
One‐electron reductions of the tetraaryldiborane(4) compound Mes 2 ‐BBMes(Ph) ( 1 ) (Mes = 2,4,6‐Me 3 C 6 H 2 ) with KC 8 to afford the singly reduced radical anions [K(DME) 3 ][Mes 2 BBMes(Ph)] ( 2 ) and [K([18]crown‐6)(THF) 2 ][Mes 2 ‐BBMes(Ph)] ( 3 ) are described. Both 2 and 3 were characterized by IR and EPR spectroscopy, and X‐ray diffraction studies of 3 showed it to be a solvent‐separated ion pair. Similarly, reduction of Mes(MeO)‐BB(OMe)Mes with lithium in diethyl ether under controlled conditions furnished the radical anion [Li(OEt 2 ) 2 ]‐[Mes(MeO)BB(OMe)Mes] ( 4 ), which has a contact‐ion‐pair structure in which lithium is solvated by oxygen atoms from ether molecules and methoxy groups. The X‐ray crystallographic studies of [K([18]‐crown‐6)(THF) 2 ][Mes 2 BBMes(Ph)] ( 3 ) and [Li(OEt 2 ) 2 ][Mes(MeO)BB(OMe)‐Mes] ( 4 ) revealed shortened B–B bond lengths in both compounds, consistent with the presence of partial (bond order 0.5) B–B π bonds. Interestingly, the B–B distances in the singly reduced species are very similar to those in the doubly reduced dianions [R 2 BBR 2 ] 2‐ , which have formal π‐bond orders of unity. The synthesis and characterization of 2,6‐Mes 2 ‐C 6 H 3 (MeO)BB(OMe) 2 ( 5 ) and 2,6‐Mes 2 ‐C 6 H 3 (MeO)BB(OMe)Mes ( 6 ) are also reported. Reduction of 6 or 5 with lithium in diethyl ether solution did not lead to multiply bonded B–B species, but to the isolation of the rearranged products [(Et 2 ‐O)Li][1‐mesityl‐5,7, and 8 are also described.