The [closo-B12H11-1-IAr]− zwitterion as a precursor to monosubstituted derivatives of [closo-B12H12]2−

Abstract

Reactions of [closo-B 12 H 12 ] 2with ArI(OAc) 2 in aqueous AcOH in the presence of [NEt 4 ] + or [NHEt 3 ] + give [closo-B 12 H 11-1-IAr]-(1) in 74-95% yield as a white precipitate. The zwitterions decompose in CD 3 CN solutions with rates k = 3.30±0.04×10-4 s-1 (Ar = Ph, 1a[NEt 4 ]) and k = 1.96±0.01×10-4 s-1 (Ar = C 6 H 4 OMe-4, 1b[NEt 4 ]) at 0 o C. Reactions of the zwitterion with Me 2 NCHS and pyridine gave the corresponding products [closo-B 12 H 11-1-SCHNMe 2 ]-(2) and [closo-B 12 H 11-1-NC 5 H 5 ]-(3) isolated in 25-27% and up to 44% yield, respectively. The former anion is a protected thiol derivative, which was transformed to the sulfonium derivative [closo-B 12 H 11-1-S(CH 2) 5 ]-(8). The molecular structure and spectroscopic properties of pyridinium zwitterion 3 were analyzed experimentally and computationally (B3LYP), and results compared with those for the [closo-B 10 H 9-1-NC 5 H 5 ]-(4) analogue. Mechanisms of formation of 2-4 from appropriate aryliodonium zwitterions were analyzed with the M06-2x computational method.

Thermal and Photophysical Properties of Highly Quadrupolar Liquid‐Crystalline Derivatives of the [closo‐B12H12]2− Anion

“…The initial suspension gradually dissolved and the resulting isomeric pyridinium bis‐zwitterions, 1B[ n ]‐ p and 1B[ n ]‐ m , were separated by means of chromatography to give pure products in overall yields of about 14 and 7 %, respectively (Scheme ). The low overall yield is presumably due to the competing rearrangement process and formation of ionic byproducts (cage arylation products), which were immobile on chromatographic supports and were not investigated further.…”

“…The preparation of derivatives 2B[ n ]‐ p was accomplished by starting with either mercaptan [ closo ‐B 12 H 11 ‐1‐SH] 2− ( 4 a ) or its protected forms 4 b and 4 c (Scheme ). Thus, the alkylative cyclization reaction of 4 a ‐[Na], 4 b ‐[Et 4 N], or 4 c ‐[Me 4 N] with dibromide 5 in the presence of an appropriate base, [R 4 N]OH, gave the 4‐pentylthianium derivatives 6 ‐[Et 4 N] or 6 ‐[Me 4 N] in 75–80 % yield, based on 4 a , or about 50 % based on 4 b and 4 c (Scheme ). Subsequent treatment of 6 ‐[R 4 N] with 4‐MeOC 6 H 4 I(OAc) 2 in 70 % aqueous TFA gave a mixture of bis‐zwitterions 7‐ m and 7‐ p (Ar=4‐anisyl).…”

“…A literature search revealed that there were only a handful of derivatives of anion B with π substituents (phenyl, naphthyl, ethynyl, and ferrocenylethynyl), typically introduced through Pd‐catalyzed C−B cross‐coupling of the appropriate iodoborane with an organometallic reagent, and π‐zwitterionic derivatives that included tropylium and pyridinium . Consequently, there are even fewer photophysical studies of such derivatives, and these concentrate mainly on the zwitterions . For instance, tropylium and pyridinium derivatives, [ closo ‐B 12 H 11 ‐1‐C 7 H 6 ] − and [ closo ‐B 12 H 11 ‐1‐NC 5 H 5 ] − , respectively, show intense CT bands at 384 (log ϵ =4.07) and 266.5 nm (3.87), respectively, in MeCN; the former zwitterion exhibits solvatochromic behavior .…”

“…Consequently, there are even fewer photophysical studies of such derivatives, and these concentrate mainly on the zwitterions . For instance, tropylium and pyridinium derivatives, [ closo ‐B 12 H 11 ‐1‐C 7 H 6 ] − and [ closo ‐B 12 H 11 ‐1‐NC 5 H 5 ] − , respectively, show intense CT bands at 384 (log ϵ =4.07) and 266.5 nm (3.87), respectively, in MeCN; the former zwitterion exhibits solvatochromic behavior . The recent discovery of very intriguing properties, such as intramolecular CT, strong emission, and thermochromic fluorescence, in the bis‐pyridinium derivative of the [ anti ‐B 18 H 22 ] 2− anion, a cluster related to B , provides further impetus to study the photophysical properties of zwitterionic polyhedral boron clusters.…”

The chemical bonding and spectral assignments of rhodium(III)-catalyzedcloso-dodecaborate complexes: Ab initio study

“…Up to now, there are many previous theoretical and experimental studies on the derivatives of the icosahedral [B 12 H 12 ] 2− cluster . For example, Dávalos et al investigated the structures of Li 2 [B 12 H 12 ] (I) and Li[CB 11 H 12 ] (II) using the ESI‐TQ‐FT‐ICR mass spectrometer and computational modeling, and revealed that the oligomerization process of the I and II species has the similar phenomena in the anionic mode.…”