Abstract
Two C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes, 1-(BMes2)-2-R-1,2-C2B10H10 (1, R = H, 2, R = Ph), were synthesised by lithiation of 1,2-dicarba-closo-dodecaborane and 1-phenyl-1,2-dicarba-closo-dodecaborane, respectively, with n-butyllithium and subsequent reaction with fluorodimesitylborane. These novel compounds were structurally characterised by X-ray crystallography. Compounds 1 and 2 are hydrolysed on prolonged exposure to air to give mesitylene and boronic acids 1-(B(OH)2)-2-R-1,2-C2B10H10 (3, R = H, 4, R = Ph respectively). Addition of fluoride anions to 1 and 2 resulted in boryl-carborane bond cleavage to give dimesitylborinic acid HOBMes2. UV absorption bands at 318-333 nm were observed for 1 and 2 corresponding to local π-π*-transitions within the dimesitylboryl groups while visible emissions at 541-664 nm with Stokes shifts of 11 920-16 170 cm(-1) were attributed to intramolecular charge transfer transitions between the mesityl and cluster groups. Compound was shown by cyclic voltammetry to form a stable dianion on reduction. NMR spectra for the dianion [](2-) were recorded from solutions generated by reductions of 2 with alkali metals and compared with NMR spectra from reductions of 1,2-diphenyl-ortho-carborane 5. On the basis of observed and computed (11)B NMR shifts, these nido-dianions contain bowl-shaped cluster geometries. The carborane is viewed as the electron-acceptor and the mesityl group is the electron-donor in C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes.
Highlights
IntroductionTri-coordinate boron compounds have been intensely investigated in the past two decades in view of potential applications as functional materials
Tri-coordinate boron compounds have been intensely investigated in the past two decades in view of potential applications as functional materials.1 The most widely employed functional moiety containing a tri-coordinate boron atom is the dimesitylboryl group (BMes2; Mes = 2,4,6-Me3C6H2) in which the unsaturated boron centre is kinetically stabilised by steric shielding of the mesityl groups
As many organic dimesitylboranes have been explored as fluoride sensors,7,29 the reactivity of 1 and 2 towards fluoride ions was of interest
Summary
Tri-coordinate boron compounds have been intensely investigated in the past two decades in view of potential applications as functional materials.. The most widely employed functional moiety containing a tri-coordinate boron atom is the dimesitylboryl group (BMes; Mes = 2,4,6-Me3C6H2) in which the unsaturated boron centre is kinetically stabilised by steric shielding of the mesityl groups. Other boron-containing compounds that have gained considerable interest in the last seven years in the field of optoelectronic materials are derivatives of the dicarba-closo-dodecaborane isomers (1,2-, 1,7- and 1,12-C2B10H12 which are ortho-, meta- and para-carborane, respectively).. Other boron-containing compounds that have gained considerable interest in the last seven years in the field of optoelectronic materials are derivatives of the dicarba-closo-dodecaborane isomers (1,2-, 1,7- and 1,12-C2B10H12 which are ortho-, meta- and para-carborane, respectively).12,13 Due to their delocalised σ-electron systems (‘3D aromaticity’), these clusters possess high thermal and chemical stabilities.. Other boron-containing compounds that have gained considerable interest in the last seven years in the field of optoelectronic materials are derivatives of the dicarba-closo-dodecaborane isomers (1,2-, 1,7- and 1,12-C2B10H12 which are ortho-, meta- and para-carborane, respectively). Due to their delocalised σ-electron systems (‘3D aromaticity’), these clusters possess high thermal and chemical stabilities. The orthocarborane is a unique electron-acceptor when connected to a donor at one or both cluster carbon atoms (at C1 and/or C2 in 1,2-C2B10H12) due to the elasticity of the cluster C1–C2 bond. The ortho-carborane unit can play an active role as the acceptor in donor–acceptor molecules (dyads)
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