The Synthesis of Carboracycles Derived from B,B′-Bis(aryl) Derivatives of Icosahedral ortho-Carborane

• Published in: Chemistry : a European journal Vol. 9; no. 12; pp. 2732 - 2744
• Main Authors: Bayer, Michael J., Herzog, Axel, Diaz, Martin, Harakas, George A., Lee, Hans, Knobler, Carolyn B., Hawthorne, M. Frederick
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 16.06.2003; WILEY‐VCH Verlag
• Subjects: boron; carboracycles; carboranes; host-guest chemistry; macrocycles
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200304803

Reactions of both closo‐9,12‐I2‐1,2‐C2B10H10 and closo‐9,10‐I2‐1,7‐C2B10H10 with an excess of aryl magnesium bromide in the presence of [PdCl2(PPh3)2] afford the corresponding closo‐9,12‐(4‐R‐C6H4)2‐1,2‐C2B10H10 [R=H (1), Me (2), OMe (3), SMe (4), N(CH3)2 (5), Cl (6)] and closo‐9,10‐(4‐R′‐C6H4)2‐1,7‐C2B10H10 [R′=Me (7), OMe (8), N(CH3)2 (9), Cl (10), and ‐C[(OCH2)2]CH3 (11)] compounds in high yields. The anisole derivatives 3 and 8 were deprotected to yield the corresponding bis‐phenols 12 and 13, respectively. Structural analyses of compounds 1, 3, 6, and 12 are reported. Re‐etherification of compound 12 by using γ‐bromotriethyleneglycol methyl ether provided 14 (R=(CH2CH2O)3CH3). Oxidation of 4 with ceric(IV) ammonium nitrate (CAN) generated the bis‐sulfoxide 15 (R=S(O)Me). Deprotection of compound 11 led to the corresponding acetyl derivative 18 (R′=C(O)Me). Bis‐anisole 3 was tethered with 1,3‐dibromopropane, 1,6‐dibromohexane, 1,8‐dibromooctane, 4,4′‐bis(iodomethyl)‐1,1′‐biphenyl, and α,α′‐dibromo‐2,6‐lutidine to afford the dimers 20 b, 21 b, 22 b, 23 b, and 24 b, respectively. The tetrameric carboracycles 27 a and 30 a, as well as the dimeric 29 c were obtained through repetitive coupling of the dimeric compounds 20 b, 24 b, and 22 b with 1,3‐dibromopropane, α,α′‐dibromo‐2,6‐lutidine, and 1,8‐dibromooctane, respectively. The tetrameric carboracycle 28 a was obtained upon consecutive reactions of 1 with 1,4‐dibromobutane. Hexameric carboracycle 28 b was identified as a byproduct. Exhaustive ether cleavage of 27 a generated octaphenol 31 a. Re‐etherification of 31 a with trimethylenesultone provided the octasulfonate 32 a, the first example of a water‐soluble carboracycle. Linkage of dimer 23 b with α,α′‐dibromolutidine yielded the cyclic tetrameric tetrapyridyl derivative 30 a in low yield. The structures of the carboracycles 27 a, 28 a, 28 b, and 30 a have been confirmed by Xray crystallography. In addition, the compounds 28 a,b are the first reported carboracycles that interact with solvent molecules in a host–guest fashion. Multifunctional carborane‐based macrocycles (carboracycles) are obtained upon linkage of 9,12‐(4‐R‐C6H4)‐1,2‐C2B10H10 (R = H, OCH3) with organic moieties, which are variable in polarity and size (R1 = CH2, (CH2)2, 2,6‐py). An example of such a potential carboracycle host species is 1 (R1 = (CH2)2) in which the aryl substituents R (R = (CH2)3SO3Li) are chemically modified to provide water‐solubility for the entire array.