Synthesis and characterization of a new guanidine-borane complex and a dinuclear boron(II) hydride with bridging guanidinate ligands

We report the synthesis and structural characterization of the new monomeric borane complex H3B center dot hppH (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), which represents the first example of a structurally characterized 1:1 complex between hppH and a group 13 element hydride. Significant intramolecular and, in the crystalline phase, intermolecular H center dot center dot center dot H contacts are established in this complex. It is shown that the complex can be used as a precursor to new dinuclear boron(II) compounds featuring a B-B single bond. Thus H-2 elimination followed by dimerization of H3B center dot hppH leads to [(hpp)BH](2) with two bridging hpp units. The structural details derived from X-ray diffraction measurements are reported. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).