Syntheses and structural characterization of o-carboranylamides with direct cage–amide bond

Abstract

Reactions of lithio-o-carborane with isocyanates under various conditions were studied, and the structural features of the resulting carboranylamides are described. The reactions of o-carborane (o-C2B10H12), n-BuLi (two equiv.) and two equiv. of (substituted) phenylisocyanate, pentylisocyanate and p-ethylphenylthioisocyanate in diethyl ether, respectively, led, after workup, to the corresponding mono-substituted carboranylamide 2a-g and carboranylthioamide 5 in low to moderate yields, and only with RNCO (R = Ph, m-MeOC6H4, pentyl) could disubstituted products 3a-c be isolated. The reaction with phenylisocyanate afforded the mono-amide and di-amide products in a ratio of approximately 1 : 2, whereas in the other two reactions the ratios are approximately 4 : 1 and 3 : 2, respectively. In tetrahydrofuran all the reactions attempted with RNCO (R = Ph, p-IC6H4, m-NCC6H4 and pentyl) gave more monoamide products than those in diethyl ether. With phenylisocyanate no diamide product was isolated and with pentylisocyanate the ratio between monoamide and diamide is approximately 3.5 : 1. The new carboranylamides were characterized by means of elemental analyses, IR and NMR spectroscopy and mass spectrometry, as well as single-crystal X-ray diffraction analyses of 2a-f, 3a and 5.

Facile Deboronation of Some o‐Carboranylamides

“…The main difference between the two molecules of 3 lies in the relative positions of the exo ‐cluster amide/phenyl groups and the cage. The C cage – C cage and other bond lengths in 3 are very similar to that in 1,2‐( m ‐CH 3 OC 6 H 4 NHCO) 2 C 2 B 10 H 10 [1.659(3) Å]. In molecule 1 (C1, C2), the dihedral angle between the amide moiety (C10, N2, O2) and the plane C1–C2–C10 is 25.2(1)°, and the dihedral angle between C3–C1–C2/N1–C3–O1 is 71.1(2)°, whereas the corresponding dihedral angles in molecule 2 (C17, C18) are 18.8(1)° [amide (C19, N3, O3)/plane C19–C17–18] and 74.6(1)° (amide C17–C18–C26/N4–C26–O4).…”

“…In a separate reaction of dilithio‐ o ‐carborane (Li 2 C 2 B 10 H 12 ) with two equivalents of phenylisocyanate in toluene, a small amount of colorless plate crystals was isolated as ( 3 ) 2 · H 2 O · 2C 7 H 8 after the reaction was quenched with dilute HCl, then neutralized with aqueous NaOH solution, and the resulting mixture was left at room temperature. After further workup both the monoamide 2 and diamide 3 were isolated but in lower yields than those of the same reaction in Et 2 O or THF …”

“…We have recently studied the one‐pot reactions of o ‐carborane (C 2 B 10 H 12 , 1 ), n BuLi (2 equiv. ), and two equivalents of isocyanates in diethyl ether or tetrahydrofuran (THF), and found that there are interesting substituent and solvent effects on the distribution of the carboranylamide products In particular, with phenylisocyanate the reaction gave both the monosubstituted carboranylamide 1‐PhNHCO‐ closo ‐C 2 B 10 H 11 ( 2 ) and the disubstituted 1,2‐(PhNHCO) 2 ‐ closo ‐C 2 B 10 H 10 ( 3 ) (Scheme ) , . Contrarily, in the case of substituted phenylisocyanates, the reactions all led to monoamide compounds as the major or only carborane products.…”

Selective B(4)−H Activation of an o‐Carboranylthioamide Based on a Palladium Precursor

“…All density functional theory (DFT) calculations were carried out using the SIESTAp ackage with numerical atomic orbital basis sets and Troullier-Martins norm-conserving pseudopotentials. [17,18] The DFT functional utilized was the PBE functional, [19] ageneralized gradient approximation DFT method. Ad ouble-z plus polarization (DZP) basis set was employed.…”

Synthesis and characterization of carboranyl Schiff base compounds from 1-amino- o -carborane

“…Similar to this finding, we recently studied the reactions of dilithio-o-carborane with two equivalents of various aryl isocyanates, the major or single carborane products are the mono-substituted carboranylamides with direct cage-amide bond [9].…”