Thermal Isomerisation of Tris(silyl)hydroxylamines to Silylaminodisiloxanes − Experimental and Quantum Chemical Results

Abstract

O‐Lithio‐N,N‐bis(trimethylsilyl)hydroxylamide, LiO−N(SiMe3)2, reacts with ClSiMe2H to give HMe2Si−O−N(SiMe3)2 (1), while LiO−N(SiMe2CMe3)2 reacts with C6H5SiF3 to give C6H5SiF2−O−N(SiMe2CMe3)2 (2). 2 isomerises in solution to give N,O‐bis(tert‐butyldimethylsilyl)‐N‐[difluoro(phenyl)silyl]hydroxylamine (3). Boiling of 1 leads to the structurally isomeric silylaminodisiloxane, Me3Si−O−SiMe2−NH−SiMe3 (4), while boiling of 3 leads to the isomeric Me3CSiMe2−O−Si(Me)CMe3−NMe−SiF2C6H5 (5). Quantum chemical calculations (B3LYP) on the thermal rearrangement of tris(silyl)hydroxylamines to silylaminodisiloxanes for the model compounds H3Si−O−N(SiMe3)2 (A), Me3Si−O−N(SiH3)2 (B), Me3Si−O−N(SiH3)SiMe2F (C), and Me3Si−O−N(SiMe2F)SiMeF2 (D) demonstrate that N‐bonded silyl units, e.g. SiH2 in model compound B or SiFMe in model compound D, preferentially insert into the N−O bond. The reaction mechanisms and the structures of the transition states are discussed in detail. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Structure and Rearrangement Reactions of Bis(organosilyl)(organostannyl)hydroxylamines: A Joint Theoretical/Experimental Study

“…It is not self-evident that similar dyotropic rearrangement reactions may take place in hydroxylamines containing germyl or stannyl groups, because these groups are much bulkier than silyl groups so that the acute angles in the corresponding dyotropic transition states are even smaller. It may be anticipated that these transition states are higher in energy than those reported in ref , so that a thermal dyotropic rearrangement is less favorable for stannylhydroxylamines. In this paper we present the synthesis and the X-ray structure of the first N , O -bis(silyl)- N -stannylhydroxylamine.…”

“…Attempts to carry out insertion reactions of a dimethylstannyl group or a dimethylsilyl group into the N−O bond under the right reaction conditions, which was successfully done in tris(silyl)hydroxylamine chemistry, , failed until now. In a not transparent, complex reaction we were able to isolate bis(trimethylstannyl)carbodiimide ( 2 ), which was described in 1971, and the dimeric 1,7,9-trisilyl-3,5-distannyl-2,4,6,8-tetraoxane 3 .…”

“…These first-order saddle points on the potential energy surface can be described as bicyclic structures with the N−O unit bridged by two silyl groups. Recently, several model compounds were investigated, and trends for the migration of differently substituted silyl groups via dyotropic transition states were reported . It is not self-evident that similar dyotropic rearrangement reactions may take place in hydroxylamines containing germyl or stannyl groups, because these groups are much bulkier than silyl groups so that the acute angles in the corresponding dyotropic transition states are even smaller.…”

“…The insertion of silyl groups into the N−O bond, yielding disiloxane, was studied both experimentally 1 and theoretically, emphasizing the reaction mechanisms and the pertinent transition states. Preferences for insertion were discussed in detail.…”

Stable O,O‘-Bis(hydroxylamino)silanes R2Si(ONH2)2 and Isomeric N,N‘- and O,O‘-Bis(silylhydroxylamino)silanes R2Si(NHOSiR3)2 and R2Si(ONHSiR3)2

“…It was found that no other class of compounds is comparably rich in isomerization reactions as silylhydroxylamines. Anionic, radicalic, and neutral silyl group migrations and silyl group insertions into the N−O bond have been described. ,− However, bis(hydroxylamino)silanes have not been isolated so far. Knowing that in contrast to carbon chemistry it is possible to stabilize compounds with two or three electronegative groups such as OH, NH 2 , and PH 2 bonded to one silicon atom, we tried to prepare bis(hydroxylamino)silanes and report our recent results.…”