Dimesitylboryl groups

End-capping of oligothiophenes with electron-deficient dimesitylboryl groups resulted in amorphous electron transporting materials 39 (n = 2, 3), for which extremely high brightness (up to 23,200 cd m ) OLEDs were fabricated [74]. 

EFISH measurements revealed large molecular hyperpolarizabilities of 31 and 37 x 10 esu for the pyrrolidine and dithionylidene derivatives, respectively. These investigations again confirmed the good electron-accepting character of the dimesitylboryl group. 

In the nitrogen and boron analogs depicted in Scheme 3-52, two methyl groups provide a sufficient shielding at the NR2 centers (R = Me), while two mesityl groups are needed for protection of the BR2 centers (R = 2,4,6-trimethyl phenyl). Electrochemical studies of l,4-bis(dimesitylboryl)benzene have shown two well-separated one-electron reduction processes, with the formation of the corresponding anion radicals and dianions, respectively (Fiedler et al. 1996). According to UV/vis/near-IR and ESR spectroscopic data... 

The production of boron-stabilized caibanions using steric hindrance on the borane to inhibit borate formation was first demonstrated as part of a study of the properties of dimesitylboryl derivatives. Unlike the situation with dialkoxyboryl derivatives, it was possible to carry out the deprotonation with only one boron atom present and with no extra stabilizing groups. Either LDA or lithium dicyclohexylami may be used as base, the latter being rather more efficient (equation 17). The initial study showed that the reaction with MeS2BCHR R was successful with R, R = H R = H, R = Me R = H, R = Ph and R, R = Me. 

As much recent work has concerned dimesitylboryl species, it is worth remarking that the related compounds (22)-(24) also readily yield carbanions. Unlike mesityl compounds, (22) cannot be deproton-ated at the 4 -methyl group, while compounds (23) have some special properties due to the great increase in steric hindrance around boron. Compounds (24) promise to be of utility due to their very ready solvolysis with water or alcohols in the presence of caudytic quantities of mineral acid. n>ey are even selectively hydrolyzed in preference to vinyl as well as alkyl groups (equation 23). ... 

In general, all types of boron-stabilized carbanions are readily alkylated by primary alkyl halides. The situation for the i ylation of dimesitylboryl compounds is sununarized in Scheme 2. These reactions represent highly efficient homologation processes. Oxidation of the tertiary all l organoboranes is slow, but use of 4-methoxy-2,6-dimethylphenyl groups instead of mesityl groups renders the products sensitive to solvolysis. ... 

In 1997, the same working group (Branger et al., 1997) published results with an azo-dye containing dimesitylboryl units used in the side chains in a polyurethane matrix (Scheme 13.2). The main... 

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