Albrecht Krämer

Synthese und Umlagerung von 2,3,5,6-Tetrakis(isopropyliden)-und 2.3-Bis(isopropyliden)-1,4-diboracycIohexan-Derivaten / Synthesis and Rearrangement of 2,3,5,6-Tetrakis(isopropylidene)-and 2.3-Bis(isopropylidene)-1,4-diboracyclohexane Derivatives

2,3,5,6-Tetrakis(isopropylidene)-1,4-dimethyl-1,4-diboracyclohexane (1c) is formed in 66% yield from 3,4-bis(chloromethylboryl)-2,5-dimethyl-2,4-hexadiene (4a) and (Me2C=CLi)2. Surprisingly, 1,4-dichloro-2,3,5,6-tetrakis(isopropylidene)-1,4-diboracyclohexane (1d) is obtained in 38% yield, when tetrabutyltin and 3,4-bis(dichloroboryl)-2,5-dimethyl-2,4-hexadiene (4b) are heated. Reactions of 1,2-bis(chloromethylboryl)ethane derivatives 5a, b with (Me2C=CLi)2 lead to the 2,3-bis(isopropylidene)-1,4-diboracyclohexanes 6a, b in 41 and 35% yield. The irradiation of 6a, b and 1c,d with ultraviolet light induces an antarafacial [1,5]-Hshift which leads to the formation of the diboracyclohexenes 7a, b and 8a, b, as indicated by NMR studies. On further irradiation 8a, b rearrange to form the corresponding nido-C4B2 carboranes 9a, b. The constitutions of the compounds are derived from spectroscopic data and are proven by X-ray structure analyses of 1c, d, e.

Intramolekular verbrückte Organo-bis[dialkylaminochlorborane] / Intramolecularly Bridged Organo-bis[dialkylaminochloroboranes]

The synthesis and structural properties of organo-bis-dialkylaminochlorboranes X(BNR2Cl)2, X = R2NB(CHCH3)2, o-C6H4, 1-α-C6H4CH2, and 1.8-C10H6 are reported. The steric influence of the alkylamino group and the geometrical situation caused by a chain of sp2 or sp3 hybridized carbon atoms control the formation of intramolecular donor-acceptor bonds. In o-(C6H4)(BNMe2Cl)2 (5) only one amino-boron donor-acceptor bond is observed. The steric influence of the alkyl groups in R2NB(CHCH3BClNR2)2 is discernible from the formation of two donor-acceptor bonds in 7a (R = Me), whereas 7b (R = iPr) is a non-bridged species. The reaction of benzomagnesacyclobutene with chlorbis(dimethylamino)borane yields cyclic 1-α(C6H4CH2)(BNMe2Cl)2 (9). 1,8-Dilithionaphthalene reacts with ClB(NR2)2 (R = Me, Et, iPr) to yield 1,8-(C10H6)[B(NR2)2]2 (10a-c), its reaction with BCl3 gives 1,8-(C10H6)(BClNR2)2 (11a: R = Me; 11b: R = Et; 11c: R = iPr). In 11a,b two tetracoordinate boron atoms are observed, in 11c the steric hinderance of the isopropyl substituents prevents donor-acceptor bonding.