Asymmetric Tris- and Cyclic Silylhydroxylamines from Trimeric and Tetrameric Lithium N,N-Bis(silyl)hydroxylamides

Abstract

The fluorosilylhydroxylamine tBuSiF(Me)−ONH2 (2) is obtained in the reaction of tBuSiF(Me)−NHtBu (1) and HONH2·HCl. The reaction of tBuSiMe2−ONH2 with butyllithium leads to the formation of the bis(silyl)hydroxylamine tBuSiMe2−NH−O−SiF(Me)tBu (3). Depending on the bulkiness of the substituents and the solvent, lithium salts of N,O-bis(silyl)hydroxylamines crystallize as dimeric, trimeric, or tetrameric O-lithium-N,N-bis(silyl)hydroxylamides, e.g., [(tBuSiMe2)2N−OLi·THF]2, [(tBuSiMe2)2N−OLi]3 (4), and [tBuSiMe2(Me3Si)N−OLi]4 (6). Lithiation of tBuSiMe2ONHSiMe2 tBu in the presence of TMEDA leads to a cleavage of the N−O bond. The hexameric lithium silanolate (tBuSiMe2O−Li)6 (5) is obtained. Above 0 °C the lithium derivative of 3 (3a) reacts with LiF and the cyclic silylhydroxylamine (tBuSiMe-O−N−SiMe2 tBu)2 (7). In the reactions of 3a and 6 with F2SiMe2 and F3SiMe the first asymmetrical tris(silyl)hydroxylamines N,N-tBuSiMe2(FSi(Me)tBu)N−O−SiFMe2 (8), N,N-tBuSiMe2(SiMe3)N−O−SiFMe2 (9), N,N-tBuSiMe2(SiMe3)N−O−SiF2Me (10), and the bis((bis)(silyl)hydroxylamino)silane [N,N-tBuSiMe2(SiMe3)]2−O−SiFMe (11) are isolated. Chlorodimethylalane reacts with the trimeric O-lithium-N,N-bis(tert-butyldimethylsilyl)hydroxylamide to give LiCl and the four-membered ring system 2,4-bis-N,N-bis(tert-butyldimethylsilylhydroxylamide)-1-dimethylalano-3-lithio-2,4-dioxocyclobutane (12). Crystal structures of 4−7 and 12 are reported.

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

“…(5) The lithium salt of N,O-bis(tert-butyldimethylsilyl)hydroxylamine crystallises from THF as dimeric N,N-bis(tertbutyldimethylsilyl)hydroxylamide [7] and reacts with trifluoro-(phenyl)silane at 0°C with formation of N,N-bis(tert-butyldimethylsilyl)-O-[difluoro(phenyl)silyl]hydroxylamine (2). (6) Product 2 could be isolated following the removal of LiF in a centrifuge by virtue of the low reaction temperature and the bulky SiMe 2 CMe 3 groups.…”

“…The softer Lewis acid F 2 SiPh migrates to the softer Lewis base nitrogen, while the harder Lewis acid SiMe 2 CMe 3 migrates to the harder Lewis base oxygen. (7) When heated under reflux for 3 d, 1 and 3 undergo a thermal rearrangement to form the silylaminodisiloxanes 4 and 5, respectively. The conversion of 1 to 4 was monitored by 1 H NMR spectroscopy.…”

“…[1,2,8] Although lithiobis(silyl)hydroxylamines have been successfully used in the synthesis of tris(silyl)hydroxylamines since the end of the 1960s, the first crystal structures of these compounds were described only two years ago. [6,7] It was found that lithium derivatives of N,O-bis(silyl)hydroxylamines form Olithio-N,N-bis(silyl)hydroxylamides in the solid state.…”

“…Depending on the bulkiness of the silyl groups and on the solvent used, (LiϪO) 2,3,4 four-, six-, or eight-membered rings were formed, [6,7] and dimeric, trimeric, or tetrameric O-lithio-N,N-bis(silyl)hydroxylamides could be isolated. This indicated that silyl group migration from the oxygen atom to the nitrogen atom had occurred.…”

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“…Lithiation of Bu t SiMe 2 ONHSiMe 2 Bu t in the presence of tmen results in cleavage of the N-O bond and formation of (Bu t SiMe 2 OLi) 6 . 81 An Xray diffraction study revealed a rare example of an (LiO) 4 ladder in the structure of {[PhC(O)N(Me)Al(Me)(Bu t )OMe]Li[PhC(O)N(Me)Al(Me)(OBu t )OMe]Li} 2 . 82 Reaction of a-cyanophosphonates (RO) 2 P(O)CH 2 CN (R = Et or Pr i ) with LiNPr i 2 in thf has yielded the Wittig-type reagents [N•CCH(RO) 2 P(O)Li(thf)] H the structures of which are based on Li 2 O 2 rings which link up through inter-dimer association via the nitrile group to form cross-linked polymeric networks.…”