Organic syntheses on an icosahedral borane surface: closomer structures with twelvefold functionality.

The syntheses of a series of novel ester-linked derivatives of the icosahedral [closo-B12(OH)12]2- boron cluster (closomer esters) are described using several synthetic methods. The reaction of bis(tetrabutylammonium)-closo-dodecahydroxy-dodecaborate, [NBu4]2 1, with carboxylic acid chlorides and anhydrides, vinyl esters with a Y5(OiPr)13O catalyst and 1,1'-carbonyldiimidazole-activated carboxylic acids yields the corresponding dianionic dodeca-ester closomers. The method using 1,1'-carbonyldiimidazole-activated carboxylic acids may be employed as a general synthetic strategy. The use of elevated reaction temperatures, achievable under pressure, to expedite syntheses is described. An attractive methodology using immobilized scavenger reagents for the expeditious purification of the closomer esters was employed. The developed methodology is compatible with a variety of peripheral functional groups attached to the termini of densely packed, carboxylate ester-linked radial arms bonded to the icosahedral borane surface. A closomer ester having twelve terminal amino groups was prepared, and without isolation, fully acetylated in good yield.

An improved method for the synthesis of [closo-B12(OH)12]-2.

The dicesium salt of the icosahedral borane anion dodecahydroxy-closo-dodecaborate(2-), closo-Cs(2)B(12)(OH)(12), Cs(2)4, was prepared using an improved synthetic pathway. Heating cesium dodecahydro-closo-dodecaborate, closo-Cs(2)B(12)H(12), Cs(2)1, with 30% hydrogen peroxide added in successive increments at 105-110 degrees C provided Cs(2)4 in 95% yield. Reaction progress was monitored using (1)H-decoupled (11)B NMR while (17)O NMR provides the most reliable way to detect the presence of peroxides in the reaction solution. The reaction may be safely increased in scale to afford Cs(2)4 in multigram quantities.

Electrical or photocontrol of the rotary motion of a metallacarborane.

Rotary motion around a molecular axis has been controlled by simple electron transfer processes and by photoexcitation. The basis of the motion is intramolecular rotation of a carborane cage ligand (7,8-dicarbollide) around a nickel axle. The Ni(III) metallacarborane structure is a transoid sandwich with two pairs of carbon vertices reflected through a center of symmetry, but that of the Ni(IV) species is cisoid. The interconversion of the two provides the basis for controlled, rotational, oscillatory motion. The energies of the Ni(III) and Ni(IV) species are calculated as a function of the rotation angle.

The synthesis of carboacycles derived from B,B'-bis(aryl) derivatives of icosahedral ortho-carborane.

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 gamma-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 alpha,alpha'-dibromo-2,6-lutidine to afford the dimers 20b, 21b, 22b, 23b, and 24b, respectively. The tetrameric carboracycles 27a and 30a, as well as the dimeric 29c were obtained through repetitive coupling of the dimeric compounds 20b, 24b, and 22b with 1,3-dibromopropane, alpha,alpha'-dibromo-2,6-lutidine, and 1,8-dibromooctane, respectively. The tetrameric carboracycle 28a was obtained upon consecutive reactions of 1 with 1,4-dibromobutane. Hexameric carboracycle 28b was identified as a byproduct. Exhaustive ether cleavage of 27a generated octaphenol 31a. Re-etherification of 31a with trimethylenesultone provided the octasulfonate 32a, the first example of a water-soluble carboracycle. Linkage of dimer 23b with alpha,alpha'-dibromolutidine yielded the cyclic tetrameric tetrapyridyl derivative 30a in low yield. The structures of the carboracycles 27a, 28a, 28b, and 30a have been confirmed by Xray crystallography. In addition, the compounds 28a,b are the first reported carboracycles that interact with solvent molecules in a host-guest fashion.

A "tetrameric" 3,4-di-p-tolyl-1,2,5-oxadiborole derivative.

In the title compound, 1,1,6a,7,9a,10-hexachloro-2,3,5,6,8,9,11,12-octa-p-tolyl-1,6a,9a,12a-tetraborata-3a,4a,7,10-tetrabora-4a(1),6b,9b,12b-tetraoxonia-4-oxatetracyclopenta[1,2-a:2,1,5-de:1,2-g:1,2-i]naphthalene dichloromethane pentasolvate, C(64)H(56)B(8)Cl(6)O(5).5CH(2)Cl(2), two condensed oxadiborole rings are attached to two further oxadiborole rings in a type of donor-acceptor bonding, thus forming a ten-membered alternating (B-O)(5) naphthalene-like arrangement as the central building block.