The Borane Complexes Htbo•BH3 and Htbn•BH3 (Htbo=1,4,6-Triazabicyclo[3.3.0]oct-4-ene, Htbn=1,5,7-Triazabicyclo[4.3.0]non-6-ene): Synthesis and Dehydrogenation to Dinuclear Boron Hydrides

Herein we report on the synthesis and characterization of the new borane adducts Htbo center dot BH3 and Htbn center dot BH3 (two isomers), where Htbo = 1,4,6-triazabicyclo[3.3.0]oct-4-ene and Htbn = 1,5,7-triazabicyclo[4.3.0]non-6-ene. Thermal treatment of these adducts leads to dihydrogen elimination and the formation of dinuclear boron hydrides with bridging guanidinate ligands, namely [BH2(mu-tbo)](2) and [BH2(mu-tbn)](2), which both adopt boat-type conformations in the solid state. The experimental studies are accompanied by quantum-chemical calculations, and we also analyse the possibility of further reductive dehydrogenation to give the double base-stabilized diboranes(4) [BH(mu-tbo)](2) and [BH(mu-tbn)](2) or oligomeric H2B(mu-tbn)(2)BH[BH(mu-tbn)(2)BH),BH(mu-tbn)(2)BH2 (n = 0, 1, 2, ...). Furthermore we synthesized the dinuclear dicationic boron(II) compound [HMe2NB(mu-tbn)](2)(2+) featuring a long B-B bond length of 180.1(5) pm. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)