The synthesis and characterization of bis-substituted derivatives of the [a2-B20H18]4- anion and the interconversion of isomers.
The apical-apical (a2) isomer of [Et4N]4[B20H18] reacts with oxalyl chloride in dichloromethane to produce a protonated bis-substituted carbonyl species, [Et4N][a2-B20H17(CO)2] ([Et4N][H1]), in 60% yield. Removal of the bridging hydrogen of the [H1]- anion in aprotic media results in rearrangement to form the equatorial-equatorial [e2-B20H16(CO)2]2- anion ([e2-1]2-). The reaction of [Et4N][H1] with sodium azide in acetonitrile produces [Et4N]3- [a2-B20H17(NCO)2] ([Et4N]3[H2]) in 53% yield, which subsequently reacts with isopropylamine in acetonitrile to provide the urea derivative [a2-B20H16(NH2C(O)NH(i-Pr))2]2- ([Et4N]2[4]) in 89% yield. The [H1]- ion is hydrolyzed in aqueous acetonitrile to give a protonated [a2-B20H17(CO2H)2]3- ion ([H3]3-) in 61% yield. The a2 isomers of the bis-substituted species [B20H16(CO2H)2]4- ([3]4-), [B20H16(NCO)2]4- ([2]4-), and [B20H16(NH2C(O)NH(i-Pr))2]2- ([4]2-), formed by the removal of the bridging proton from their protonated precursors, rearrange to form a mixture of ae isomers in solution.
Watson-Clark
R A
RA
Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California 90095-1569, USA.
Shelly
K
K
Hawthorne
M F
MF
D000838:Anions; D001896:Boron Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D016754:Boron Neutron Capture Therapy; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods
D000838:Anions; D001896:Boron Compounds