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 tBuSiMe2ONHSiMe2tBu 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−SiMe2tBu)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.

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