Dodecahydro-closo-dodecaboratderivate für die Anwendung in der nichtlinearen Optik

Abstract

Previously investigated and calculated properties of the dodecahydro-closo-dodecaborate(2-) derivatives predict a high probability that they are applicable for nonlinear optical materials for compounds in which the B12-cluster acts as a donor and is connected via a Pi-conjugated system to an acceptor substituent. For this reason it was of interest to prepare new dodecaborate containing nonlinear optical molecules.Palladium catalyzed coupling reactions were carried out and new coupling products could be achieved, which could serve as intermediates for further reactions. Alkynyl derivatives of the dodecaborate are described, [B12H11C6H4CCH](2-),[B12H11CCPh](2-), [B12H11CCSi(CH3)3](2-)and the resulting ethynyl derivative. Also coupling-products with double bonds could be achieved([B12H11C6H4CCH2](2-)). [B12H11C6H4CCH](2-) was able to be connected via Sonogashira coupling to acceptor containing molecules, 1-bromo-4-nitrobenzene, trans-2,3,4,5,6-pentafluoro-4'-bromostilben, and 1-(4-bromophenyl)-2-phenyl-o-carborane. The resulting compounds (16, 18, 22) might have nonlinear optical properties. The advantage of the compound which contains the dodecaborate and the o-carborane is a high transparency in the region above 400 nm. Dodecaborates should be also connected via an amino group to an acceptor substituted aromatic compound, to increase the donor properties of the amino group by the cluster and to prevent a centrosymmetric crystallization.The nucleophilic aromatic substitution with [B12H11NH2](2-) on aromatic systems with electron withdrawing substituents, such as 4-nitrophthalonitrile, which results in two different products (33, 34), and 1-chloro-2,4-dinitrobenzene (32), was successful. In the case of the dinitrophenyl derivative 32 single crystals for X-ray analysis could be obtained. Another possibility for a boron-nitrogen-aryl linkage is the reaction of TBA2B12H12 with arylamines, such as aniline and N,N-dimethylaniline, which results in the expected arylammonium derivatives (35, 36) of the cluster.Mass spectral analyses helped to explain the as yet unknown mechanistic pathway: in the case of N,N-dimethylaniline, and 4-(dimethylamino)pyridine, Hofmann elimination of the tetrabutylammonium ion at high temperatures takes place, initiated by the abstraction of a hydride from the cluster. The structure of the N,N-dimethylaniline derivative could be elucidated by X-ray analysis. In the case of aniline and 4-aminopyridine (the latter is described by Koch and Preetz (1997b)), the formed hydride reacts with a proton of the amino group to form dihydrogen. The nucleophilic attack at the electropositive boron atom occurs by the amino nitrogen. This could also be the mechanisms of the reactions resulting in a linkage to nitrogen (Koch and Preetz 1997a and 1997b), or carbon (Preetz and von Bismarck 1991). Overnight reaction of aniline and TBA2B12H12 leads to dodecaborate derivatives, substituted with one up to three aniline moieties. Interestingly, hydroamination products of these compounds with butene could be observed.