Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds?

Mitzel NW, Kiener C, Rankin DWH (1999)
ORGANOMETALLICS 18(17): 3437-3444.

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The three compounds H3SiCH2NMe2, Me8GeCH2NMe2, 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)degrees, MP2/6-311G** 111.4 degrees; Me3GeCH2NMe2 SCF/6-31G* 116.1 degrees; Me3SnCH2NMe2 XRD 113.0(2)degrees, SCF/dzp 115.4 degrees), 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 alpha-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(H-2) bond. The NBO calculations do not confirm the earlier postulated lp(N) --> d(E), sigma(NC) --> d(E), or lp(N) --> sigma*(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) --> sigma*(SiF) interactions.
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Mitzel NW, Kiener C, Rankin DWH. Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds? ORGANOMETALLICS. 1999;18(17):3437-3444.
Mitzel, N. W., Kiener, C., & Rankin, D. W. H. (1999). Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds? ORGANOMETALLICS, 18(17), 3437-3444. doi:10.1021/om990166c
Mitzel, N. W., Kiener, C., and Rankin, D. W. H. (1999). Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds? ORGANOMETALLICS 18, 3437-3444.
Mitzel, N.W., Kiener, C., & Rankin, D.W.H., 1999. Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds? ORGANOMETALLICS, 18(17), p 3437-3444.
N.W. Mitzel, C. Kiener, and D.W.H. Rankin, “Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds?”, ORGANOMETALLICS, vol. 18, 1999, pp. 3437-3444.
Mitzel, N.W., Kiener, C., Rankin, D.W.H.: Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds? ORGANOMETALLICS. 18, 3437-3444 (1999).
Mitzel, Norbert W., Kiener, C, and Rankin, DWH. “Are there structurally relevant attractive interactions between nitrogen atoms and group 14 elements in their aminomethyl compounds?”. ORGANOMETALLICS 18.17 (1999): 3437-3444.
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