The 1,1,3,3-tetramethylguanidine-borane adduct: Theoretical comparison of the bonding properties in amine- and guanidine-borane adducts

Herein we report on the synthesis and characterization of the adduct 1,1,3,3-tetramethylgudnidine-borane, H3B center dot N(H)C(NMe2)(2), and a general inspection of the bonding properties of guanidine adducts to BH3. The new compound was characterized by its vibrational, NMR and mass spectra as well as single-crystal X-ray diffraction. Quantum chemical calculations match the experimental results. Particular attention was devoted to the evaluation of the dimeric assembly through H center dot center dot center dot H contacts of the molecules in the crystalline phase. The adduct is formed at 80 degrees C, but it also decomposes slowly at this temperature. The bonding properties in amine- and guanidine-borane adducts are compared in general on the basis of quantum chemical calculations carried out for several representative amine-borane adducts, namely H3B center dot NH3, H3B center dot NMe3 and H3B-quinuclidine, and guanidine-borane adducts, namely H3B center dot N(H)C(NH2)(2), H3B center dot N(H)C-(NMe2)(2) and H3B-hppH, as well as the available experimental data for these species. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).