Si-O bond fission in a siloxamine by aluminium hydride

When the alkoxyaminosilane tBu-O[tBuN(H)]SiMe2 (1) reacts with aluminium hydride the expected cyclic alkoxyaluminosilane tBuO(tBuN)(AlH2)SiMe2 (2) is not obtained. Instead 1 reacts directly with two equivalents of aluminiumhydride to the alkoxyaminodialane 3, (tBuO) (AlH2)[N(SiMe2H)tBu](AlH2). The compound 3 is characterized by spectroscopic methods and by a single crystal X-ray diffraction analysis: the molecule has a four-membered OAl2N cycle (Al-O 1.817(2) Angstrom, Al-N 1.970(1) Angstrom) as central unit. On the oxygen and nitrogen atom a tert-butyl or a tert-butyl and HMe2Si group are attached, while the aluminium atoms have exclusively hydrogen as further ligands. The Si-O bond in the starting compound 1 has thus been cleaved, the oxygen atom being coordinated by aluminium and the silicon atom by hydrogen.