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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Abstract
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.
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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