Are There Structurally Relevant Attractive Interactions between Nitrogen Atoms and Group 14 Elements in Their Aminomethyl Compounds?

Abstract

The three compounds H3SiCH2NMe2, Me3GeCH2NMe2, and Me3SnCH2NMe2 have been prepared for the purpose of the determination of their molecular structures. The gas-phase structure of H3SiCH2NMe2 has been established by electron diffraction (GED) and ab initio calculations up to the MP2/6-311G** level of theory. The geometry of Me3GeCH2NMe2 could be studied only by theoretical methods, while the structure of Me3SnCH2NMe2 has been determined by single-crystal X-ray diffraction (XRD) and computational methods. The E−C−N units (E = Si, Ge, Sn) in all three compounds adopt angles that are larger than the tetrahedral angle (H3SiCH2NMe2 GED 114.7(3)°, MP2/6-311G** 111.4°; Me3GeCH2NMe2 SCF/6-31G* 116.1°; Me3SnCH2NMe2 XRD 113.0(2)°, SCF/dzp 115.4°), and all three compounds adopt gauche conformations; that is, the lone pairs at nitrogen are declined away from the plane E−C−N. These facts are interpreted in terms of the absence of an earlier postulated α-effect, which should lead to an attractive interaction between E and N centers. The structures, energies, and orbital interactions in the natural bond orbital (NBO) model for three possible conformations of the SiCH2NC2 skeleton (lone pairs at N vs Si atom) of H3SiCH2NMe2 have been calculated ab initio and show the gauche conformer to be the ground state and the syn form (+6.6 kJ mol-1) as well as the anti form (+10.2 kJ mol-1) to be transition states to rotation about the N−C(H2) bond. The NBO calculations do not confirm the earlier postulated lp(N) → d(E), σ(NC) → d(E), or lp(N) → σ*(EX) interactions as important contributors to electron delocalization. Calculations on the model system FH2SiCH2NMe2 predict a tendency of SiCN units to adopt small bond angles if very electronegative groups are bound to silicon. The conformational preferences of the unsubstituted H3SiCH2NMe2 are overridden in favor of a conformation bringing the lone pair of electrons closer to the electrophilic Si center. This compound is predicted to have significant lp(N) → σ*(SiF) interactions.

N,N‐Dimethylaminopropylsilane: A Case Study on the Nature of Weak Intramolecular Si⋅⋅⋅N Interactions

“…The intramolecular Si···N distance of 2.712(2) is shorter than in the gasphase structure of H 3 SiCH 2 NMe 2 (2.828 (7) ). [12] The H2AA-Si1-N1 angle is very close to 1808 (179.6(13)8). These are important structural features consistent with an attractive Si···N interaction.…”

“…Compound 1 was analysed and described earlier, [12] but we list some of its properties here for the sake of discussion. Compounds 2 and 3 are liquids at ambient temperature with boiling points of 47 8C at 530 mbar for 2 and 60 8C at 200 mbar for 3.…”

“…1: n = 1 [12] C 6 van der Waals radii of the respective atoms. The intramolecular Si···N distance of 2.712(2) is shorter than in the gasphase structure of H 3 SiCH 2 NMe 2 (2.828 (7) ).…”

“…This paper therefore presents a detailed investigation of the structure and conformational preference of H 3 SiA C H T U N G T R E N N U N G (CH 2 ) 3 NMe 2 (3), in which the presence of three CH 2 spacer groups allows greater freedom for the Si···N interaction. Where relevant, the results are also compared with related compounds H 3 SiCH 2 NMe 2 (1), which was described earlier, [12] and H 3 SiA C H T U N G T R E N N U N G (CH 2 ) 2 NMe 2 (2), which we prepared for spectroscopic comparison. Note that, in contrast to earlier studies on compounds with rigid backbones between the Si and N atoms, such as 1,8-naphthyl groups,…”

(Dimethylaminomethyl)trifluorosilane, Me2NCH2SiF3—A Model for the α‐Effect in Aminomethylsilanes

“…The most intriguing examples are ClH 2 SiONMe 2 [7] and F 3 SiONMe 2 [8] for the SiON systems and F 3 SiN(SiMe 3 )NMe 2 and F 3 SiN(SnMe 3 )NMe 2 for the SiNN systems. [9] Our investigations into the SiCN systems have so far been restricted to the parent systems H 3 SiCH 2 NMe 2 [10] and Cl 3 SiCH 2 NMe 2 , [11] but these compounds do not show significant attractive interactions between the Si and N atoms, which would lead to compression of the Si-C-N angle. However, some calculations on electronegatively substituted systems have predicted the compound FH 2 SiCH 2 NMe 2 to show deformation of this angle, [10] which could be the first proof of the existence of such an effect.…”