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

Reactions of both closo ‐9,12‐I 2 ‐1,2‐C 2 B 10 H 10 and closo ‐9,10‐I 2 ‐1,7‐C 2 B 10 H 10 with an excess of aryl magnesium bromide in the presence of [PdCl 2 (PPh 3 ) 2 ] afford the corresponding closo ‐9,12‐(4‐R‐C 6 H 4 ) 2 ‐1,2‐C 2 B 10 H 10 [R=H ( 1 ), Me ( 2 ), OMe ( 3 ), SMe ( 4 ), N(CH 3 ) 2 ( 5 ), Cl ( 6 )] and closo ‐9,10‐(4‐R′‐C 6 H 4 ) 2 ‐1,7‐C 2 B 10 H 10 [R′=Me ( 7 ), OMe ( 8 ), N(CH 3 ) 2 ( 9 ), Cl ( 10 ), and ‐C[(OCH 2 ) 2 ]CH 3 ( 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=(CH 2 CH 2 O) 3 CH 3 ). 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.