PUB - Publikationen an der Universität Bielefeld

The reduction of 2-bromo-1,3,2-diazaborole tBuNCH=CH(tBu)BBr (4c) with a potassium mirror in 1,2-dimethoxyethane afforded a non-separable 1 : 2 : 1 mixture of the compounds tBuNCH=CHN(tBu)BH (5), tBuNCH=CHN(tBu)BOCH3 (6) and {tBuNCH=CHN(tBu)B}(2)O (7). Reaction of 4c with a potassium-sodium alloy in N,N,N',N'-tetramethylethylenediamine led to 5 as the major product. 1,3,2-Diazaboroles tBuNCH=CHN(tBu)BN-Me-2 (8) and {tBuNCH=CHN(tBu)B}(2) (9) were spectroscopically identified as minor products. The treatment of 4c with potassium-sodium alloy in toluene solution in the presence of [15]crown-5 yielded a 1 : 1 mixture of 5 and the benzyl derivative tBuNCH=CHN( tBu)BCH2Ph (12). The same reaction in toluene-d(8) produced the deuterated species 5-d(1) and 12-d(7). tBuNCH=CHN(tBu)BCH3 (17) and 1,4-diazabutadiene (tBuN=CH)(2) (18) resulted from the treatment of tBuNCH=CHN(tBu)BSCH3 (15) with potassium-sodium alloy in n-hexane. In contrast to this, compound 9 was obtained as the main product of the reduction of tBuNCH=CHN(tBu)BStBu (16) under similar conditions. The reduction of the 1-bromo-2-tert-butyl-1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridine (19) smoothly produced the respective diborane(4) derivative (20) which was subjected to X-ray diffraction analysis.