Binuclear magnesium amidoborane complexes: characterization of a trinuclear thermal decomposition product

The bis-beta-diketimine with a meta-phenylene bridge (META-H-2: DIPPN(H)CMeCHCMeN-C6H4-NCMeCHCMeN(H)DIPP; DIPP = 2,6-iPr-C6H3) reacted with two equivalents of nBu(2)Mg to give the bis-beta-diketiminate complex META-(MgnBu)(2). The latter binuclear magnesium complex was converted to META-[MgNH(iPr)BH3](2) by reaction with H2N(iPr)BH3. The thermal decomposition of this binuclear iPr-substituted magnesium amidoborane complex has been investigated. In benzene it starts to eliminate H-2 at 90 degrees C. Two decomposition products could be obtained by fractional crystallization of the residue. The first product is the trinuclear magnesium complex META-Mg-3[iPrNB(H)N(iPr)BH3](2) and the second product is (META-Mg)(2). These products have been formed by ligand exchange reactions of the expected complex META-Mg-2[iPrNB(H)N(iPr)BH3] and were characterized by single crystal X-ray diffraction. The central Mg2+ ion in META-Mg-3[iPrNB(H) N(iPr) BH3](2) is not connected to the ligand system and its coordination geometry could be representative of that in a solid-state magnesium salt containing the RNB(H)N(R)BH32- ion.