Synthesis and hydrolysis of a fluorosilyl-t-butylaminodichloroalane. Crystal structures of the cyclic compounds [(Me3SiNMe)2SiNCMe3]2 and (Me3CNHAlCl2)2

The lithium salt of t-butylaminofluorobis(methyltrimethylsilylamino)silane, (Me3SiNMe)2SiFNLiCMe3, reacts with aluminium trichloride to form a dimeric silylaminodichloroalane, [(Me2SiNMe)2SiFNCMe3AlCl2]2 (I); the cyclodisilazane [(Me3SiNMe)2SiNCMe3]2 (II) is formed as a by-product. Hydrolysis of I cleaves the SiN bonds to produce the four-membered ring compound (Me3CNHAlCl2)2 (III). II forms monoclinic crystals, space group P21/n, with a 10.721(2), b 10.099(2), c 17.166(3) Å, β 93.46(2)°, Z = 2. III also crystallises in P21/n, with a 6.500(2), b 11.957(2), c 10.802(2) Å, β 96.31(2)°, Z = 2. The structures were determined from 2655 and 1382 diffractometer-measured intensities, and refined to R = 0.046 and 0.032, respectively. Molecules of both compounds have crystallographic inversion centres, requiring planar four-membered rings (Si2N2 and Al2N2, respectively), and additionally a trans arrangement of the nitrogen substituents in III.