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Synthese und Kristallstrukturen von Cyclosilazanen mit ungewo¨hnlichen Konformationen

1996; Elsevier BV; Volume: 524; Issue: 1-2 Linguagem: Inglês

10.1016/s0022-328x(96)06393-0

1872-8561

Hans-Jo ̈rg Rakebrandt, Uwe Klingebiel, Mathias Noltemeyer, U Wenzel, Dietrich Mootz,

Organometallic Complex Synthesis and Catalysis

The 1,3-disilazanes, (Me 3 C) 2 SiNH 2 NHSiFR 2 , R = Me ( 1 ), CHMe 2 ( 2 ) and the 1,3,5-trisilazane, (Me 3 C) 2 Si(NHSiFMe 2 ) 2 ( 3 ), are formed in the reaction of lithiated diamino-di- tert -butylsilane with F 2 SiMe 2 and F 2 Si(CHMe 2 ) 2 . 1 and 2 react with BuLi to give the cyclodisilazanes 4 and 5 , (Me 3 C) 2 Si(NH) 2 SiR 2 , R = Me ( 4 ), CHMe 2 ( 5 ), and the cyclotetrasilazane 6 , [(Me 3 C) 2 SiNH SiMe 2 NH] 2 . In the reaction of fluorosilanes with the lithium derivatives of 4 and 5 the silylsubstituted cyclodisilazanes 7, 8, 10 and 11 are obtained: 7 , (Me 3 C) 2 SiNH(NSiFMe 2 )SiMe 2 ; 8 , (Me 3 C) 2 Si(NSiFMe 2 )SiMe 2 ; 10 , (Me 3 C) 2 SiNH(NSiF 2 CMe 3 )Si(CHMe 2 ) 2 ; 11 , (Me 3 C) 2 Si(NSiF 2 C 6 H 5 )(NSiF 2 CMe 3 )Si(CHMe 2 ) 2 . The reaction of dilithiated diamino- tert -butylmethylsilane with dichloro- tert -butylmethylsilane leads to the formation of the cyclotetrasilazane 9 , (Me 3 CMeSi NH) 4 . The crystal structures of 4, 6 and 11 have been determined. 4 forms monoclinic crystals, space group P 2 1 /m, Z = 2. The four-membered ring is planar. The NSiN angles are smaller than 90°, and the SiNSi angles are bigger than 90°. 6 forms crystals, space group P1, Z = 2. The ring has a saddle conformation. with the Si atoms approximately coplanar and the N atoms alternatively above and below this plane. The N atoms have an almost planar environment (sum of angles 357.4–359.0°) with SiNSi angles between 139.8–142.8°. 11 forms monoclinic crystals, space groupC2/c, Z = 8. The angle between the lines of the atoms N1-N2/N2-Si4 is 166.5° and between N2-N1/N1-Si3 is 176.4°. The N2 atom has a pyrimidal environment (sum of angles 355.1°), a very rare example of a nitrogen atom bonded to three silicon atoms. The exocyclic silyl groups have cis position. The electron-withdrawing effect of the fluorine atoms leads to a shortening of the exocyclic Si N bonds.