Hexakis(dimethylaminoxy)disiloxane: Insertion of an Oxygen Atom into the Si-Si Bond of a Disilane by Dimethylaminoxy Lithium

Abstract

The compound (Me2NO)3SiOSi(ONMe2)3 was prepared by the reaction of LiONMe2 with Si2Cl6, a reaction in which oxygen is inserted into the Si-Si bond. The crystal structure of (Me2NO)3SiOSi(ONMe2)3 was determined and shows the compound to have a linear siloxane core and SiON units with small valence angles at oxygen, caused by weak Si (-N interactions leading to partially hypercoordinate Si centres.Our recent studies on aminoxysilanes R^Si-O-NR'2 have shown that attractive interactions be tween the silicon and nitrogen atoms lead to hy percoordinate Si centres and three-membered ring systems in extreme cases [1]. Thus, exceptionally strong interactions of this type have been found in ClH2SiONMe2 [2] and F3SiONMe2 [3], The strength of such interactions is dependent on the na ture of the substituents at the silicon atoms, their ori entation relative to the SiON skeletons and the steric congestion about the silicon centre. The knowledge about such interactions is important, as aminoxysi lanes have found applications as cold curing cata lysts [4], i. e. crosslinking agents [51 for silicone polymers. Representative examples are the tris-C/V,N-dialkylaminoxy)organosilanes, but also oximatosilanes. These have the advantage of being highly active and applicable without addition of toxic organotin catalysts. The formation of SiON units is also seen as an intermediate step of the hydroxylamine catalysed alkoholysis of Si-H func tionalities in polylsilanes applied for tailoring their properties [6],Here we report a method to prepare hexakis-(N,N-dimethylaminoxy)disiloxane (Me2NO)3 SiOSi(ONMe2)3 , in one step from hexachlorodisilane, Si2Cl6, and the determination of its crystal struc ture. Initially, we intended to react N,N-dimethylaminoxylithium, LiONMe2, with hexachloro disilane in order to obtain hexakis(N,N-dimethylaminoxy)disilane, (Me2NO)3 SiSi(ONMe2)3 . How ever, the reaction yielded unexpectedly (Me2NO)3 -SiOSi(ONMe2)3 , which means that the Si-Si bond was broken and an oxidation has taken place under the conditions applied.As we could not identify other reaction products, we have to assume that the hydroxylamine link ages have served as oxidative agent. This is possi ble if LiONMe2 acted as an "oxenoid", analogous to lithium peroxides as has been reported by Boche et al. for LiOOC(CH3)3,[7] which reacts to give LiOC(CH 3)3 under extrusion of oxygen atoms.The compound (Me2NO)3 SiOSi(ONMe2)3 was characterised by elemental analysis, mass spectro metry and N M R spectroscopy of the nuclei ]H, I3C, 15N and 29Si. The 'H N M R shows a single line, while the splitting of the 13C NMR signal into a quartet of quartets proves the presence of the NMe2 group. The 15N N M R spectrum shows a singlet at -257.1 ppm, which is shifted to lower fre quencies as compared to Si(ONMe2)4 (-249.2 ppm) [8] or HSi(ONMe2)3 (-248.1 ppm) [9]. The signal in the 29Si N M R spectrum is found at -85.8 ppm, which is quite different from those in Si(ONMe2)4 (-73.7 ppm) and in Si(ONEt2)4 (-59.9 ppm), but similar to the value for Si(OiPr)4 at -85.7 ppm. Th...