Regioselective Functionalization of the [ closo-1-CB9H10]- Anion through Iodonium Zwitterions

Reactions of [closo-1-CB9H9-1-R]- (2, R = H, COOH, C5H11) with PhI(OAc)2 lead to mixtures of regioisomers [closo-1-CB9H8-1-R-6-IPh] (5[6]) and [closo-1-CB9H8-1-R-10-IPh] (5[10]) in ratios of 3:1 to 1:1, of which the former isomer undergoes selective reactions with nucleophiles (MeCN, pyridine, MeC(=NH)NH2, CN-). The products and the unreacted 10-isomers 5[10] are separated achieving kinetic resolution of the isomeric iodonium zwitterions. Pure 5[10] is reacted with nucleophiles (pyridine, 4-C7H15OPyridine, Me2NCHS, PhCO2 -, CN-, N3 -, I-, MeC(=NH)NH2, and MeCN), giving substitution products. The mechanism of the substitution is investigated with density functional theory (DFT) methods. Some of the nucleophilic substitution products are transformed further, expanding the scope of available functional groups for the [closo-1-CB9H10]- anion. Four derivatives are characterized with single-crystal XRD methods: [closo-1-CB9H9-10-N2] (4[10]a), [closo-1-CB9H9-6-NC5H5] (9[6]a), [closo-1-CB9H9-10-NC5H5] (9[10]a), and [closo-1-CB9H9-10-NHC(NH2)Me] (10[10]a). Spectroscopic data for selected derivatives are interpreted in terms of transmission of electronic effects through the {closo-1-CB9} cluster (NMR) and interaction with substituents (IR, UV). The latter results are compared to those of TD-DFT computational methods. Copyright © 2018 American Chemical Society.