Preparative, spectroscopic, and structural studies on some new silylamines

Abstract

The synthesis and characterization of two complete series of trimethylsilane. Crystal structure analyses reveal that dibenbenzyl(phenylsily1)amines (PhHzSi),(PhH2C)3 -,N, benzyl(p-zyl(p-tolylsily1)amine (7) and 10 contain planar nitrogen atoms. tolylsily1)amines (p-H3CC6H4H2Si),(PhHzC)3 -,N, and of bis-Heteronuclear NMR spectra ('H, I3C, I5N, and "Si) have been (p-tolylsily1)amine are described. The compounds have measured for all compounds. The 15N chemical shifts are been prepared from the corresponding arnines and chlorosishown to be sensitive to variations of the geometry at the lanes with triethylamine as the auxiliary base. Bis(pheny1si-nitrogen atom. The coupling constants 1J('5Nz9Si ) show a linlyl)(trimethylsilyl)amine, (PhH2Si),NSiMe3 (lo), was obtained ear correleation with the N-Si bond lengths.by the reaction of lithium bis(phenylsily1)amide with chloro-The planarity of nitrogen coordination in silylamines continues to be a frequently discussed issue [']. This unique structural feature -as compared to the carbon analogs -was first discovered for trisilylamine, (H3Si)3N, in a gas-phase electron diffraction study by Hedbergl2] in 1955 and confirmed for the crystalline state by Barrow and Ebsworth in 1984[31. All doubly and triply silylated amines whose structures have been elucidated are planar at nitrogen r41. It is only for selected monosilylated amines, like dimethylsilylamine, (H3C)2NSiH3r that pyramidal nitrogen has been observed in the gas phaseL5]. In the crystalline phase, (H3S& NCH3 is associated to give pentamers with tetrahedral coordination at nitrogen and trigonal-bipyramidal coordination at siliconL6]. These results have prompted a large number of theoretical studies [',*]. In a series of calculations the configurational effect in the Si3N, Si,NC, and SiNC2 units has been interpreted initially in terms of d-orbital participation [(p+d)n bonding], but a more sophisticated treatment has shown that such contributions should be only marginal. Other approaches have focused on o/n-hyperconjugative effects and on electrostatic effects originating from the special force field for longer bond distances and higher polarity of SiN as compared to CN linkages, and on steric effects. All of these studies agree with the prediction that the inversion barrier at nitrogen -if any -should be flat and that only a few kJ/mol are necessary for nitrogen inversion in silylamines. Recent findings that tertiary amines with bulky alkyl groups are also flat at nitrogen19], and that silylated primary amines R3SiNH2 appear to be pyramidal ["], have added to the current uncertainties, if not confusion.In an attempt to contribute to the discussion with more experimental data, we have described in preceding papers the synthesis and structure of tris(phenylsilyl)amine['l~lzl. In contrast to the pyramidal benzylamine analog['91, this molecule has been shown to be completely planar at nitrogen. Since there is no reason to invoke steric effects for (PhH2Si)3N with six small hydrogen substituents at the silicon atoms and virt...

Hydrosilylation of an Iron(IV) Nitride Complex

“…Taken together, the synthesis results suggest that the formation of 1 occurs by the initial insertion of PhB­(MesIm) 3 FeN into the Si–H bond of PhSiH 3 to provide the corresponding iron­(II) silylamido complex, which reacts in turn with additional PhSiH 3 to provide 1 , presumably with the concomitant formation of the aminosilane, PhSi­(N­(H)­SiH 2 Ph)­H 2 . However, we have been unable to determine the ultimate fate of the nitride ligand in either of the silylation reactions discussed above . For example, the reaction of PhB­(MesIm) 3 FeN with 2 equiv of PhSiH 3 results in the formation of multiple iron hydride products, suggesting that the putative aminosilane byproducts are reactive toward the iron­(IV) nitride or iron­(II) amido complexes.…”

Molecular structure of N-trimethylsilylaziridine in the gas phase

“…This interpretation is confirmed by data from 15 N NMR spectroscopy which gave a signal at δ Ϫ348.5, which bears two pairs of satellites identified by their relative intensities as coupling to the ring carbon atoms with 1 J NC = 2.9 Hz and a coupling to the silicon centre with 1 J SiN = 4.8 Hz. The latter value is exceptionally low for a monosilylamine (coupling constants of about 20 Hz are seen normally 14 ) suggesting the presence of a weak and relatively long Si-N bond. Such small 1 J SiN coupling constants have, however, been observed for N-silylhydroxylamines, which have been shown to have pyramidal nitrogen containing cores and weak Si-N bonds.…”

Ammonolysis of 1,2‐Bis[dichloro(methyl)silyl]ethane. On the Structure of 1,3,6,8‐Tetramethyl‐2,7,11,12‐tetraaza‐1,3,6,8‐tetrasila‐tricyclo[6.2.1.13,6]‐dodecane

“…The normal at the planes Si1, N1, Si2A, N2A (or N2, Si2, N1A, Si1A) and at N2, Si1, N2A, Si1 enclose an angle of 120.2° and the Si–N bond lengths in 1 are in the expected range (171–173 pm). For example the corresponding values in N(SiMe 3 ) 3 , N(SiH 3 ) 3 and HNMe(SiMe 3 ) are 175.5 29, 172.9 20 and 172.0 pm 30, whereas in the cyclic compounds [ R 2 SiN R ′] 4 with R = Me, R ′ = H 172.0 (bowl) and 173.0 (chair) 28, R = R ′ = Me 173.0 (bowl) 31 and R = i Pr, R ′ = H 171.4 pm (bowl) 32 were found. The significant shortening of the Si–N bond lengths in comparison with the sum of the covalent radii (191 pm 33) is typical of aminosilanes 34.…”