Crystal structures and Hirshfeld surface analyses of bis(4,5-dihydrofuran-2-yl)dimethylsilane and (4,5-dihydrofuran-2-yl)(methyl)diphenylsilane

The molecular and crystal structures of two dihydrofurylsilanes are reported. A Hirshfeld surface analysis was performed to investigate the intermolecular interactions.


Chemical context
Dihydrofurylsilanes are interesting starting materials for tailor-made silicon compounds. First presented in the 1980s by Lukevics (Lukevics et al., 1985), they turned out to be versatile building blocks for multiple silicon compound classes. Tetrasubstituted silicon compounds are obtainable as a result of the excellent nature of the dihydrofuryl (DHF) substituent as a leaving group in various nucleophilic substitutions at the silicon atom. Si-C(DHF) bond cleavages under substitution of the dihydrofuryl group was observed for the reactions with C-nucleophiles (e.g. organolithium compounds) (Gevorgyan et al., 1992), H-nucleophiles (e.g. LiAlH 4 , NaH, NaBH 4 ) (Gevorgyan et al., 1989(Gevorgyan et al., , 1990, O-nucleophiles (e.g. t-butanol) and N-nucleophiles [e.g. LiN(Et) 2 ] . By means of this efficient pathway, a noteworthy approach to pentacoordinated organyl silatranes has been made , as well as for (-aminomethyl)silanes (Labrecque et al., 1994). Along with their easy preparation and hydrolytical and chromatographical stability , dihydrofurylsilanes offer the potential to be useful reagents as protecting groups for the synthesis of aminomethylsilazanes (Colquhoun et al., 2011;Colquhoun & Strohmann, 2012).

Structural commentary
The molecular structure of 1 is given in Fig. 1 and selected bond lengths and angles are given in Table 1. Compound 1 shows C 2 molecular symmetry. The lengths of the Si-C(DHF) bonds are similar but slightly longer than the lengths of the Si-C(Me) bonds. However, all bonds have characteristic dimensions (Allen et al., 1987). Furthermore, the length of the C C double bond corresponds well with literature values (Allen et al., 1987) and is clearly shortened in comparison to the C-C single bonds in the dihydrofuranyl substituent. The silicon atom is tetrahedrally surrounded by its substituents, however slightly distorted as evident from the slight deviations from the ideal angle of 109.47 . These deviations are congruent with a former publication on dihydrofurylsilanes (Krupp et al., 2020). Both DHF planes display planarity while the C1-C4/O1 ring has an r.m.s. deviation of 0.0197 Å from an ideal least-squares plane with atom C4 showing the largest deviation of À0.0269 (2) Å . The C5-C8/O2 ring deviates more strongly from an ideal least-square plane with an r.m.s. deviation of 0.0608 Å , with the C8 atom deviating the most by 0.0838 (2) Å . The angle between the normals of the leastsquares planes through the DHF rings is 78.943 (15) .
The molecular structure of 2 is given in Fig. 2 and selected bond lengths and angles are given in Table 2. The length of the Si-C(DHF) bond is in the range of the lengths of the Si-C(Ph) bonds, which are again slightly longer than the Si-C(Me) bond. The bond lengths of the dihydrofuran ring are consistent with those of structure 1. Again, a slightly distorted tetrahedral environment at the silicon atom is observed. The DHF ring is less planar than the phenyl rings, with an r.m.s. deviation from the least-squares plane of 0.0426 Å with the C4 atom having the largest deviation of À0.0582 (7) Å . The phenyl rings show r.m.s. deviations of 0.0066 and 0.0047 Å . The angle between the normals of the least-squares planes of the DHF ring and the C5-C10 phenyl ring is 87.68 (4) and the angle between the normals of the least-squares planes of the phenyl rings is 60.03 (4) .

Supramolecular features
The crystal packing of compound 1 is defined by C10-H10AÁ Á ÁC2 i van der Waals interactions as can be seen in Fig. 3

Figure 2
The molecular structure of compound 2 with displacement ellipsoids drawn at the 50% probability level. Table 2 Selected geometric parameters for compound 2 (Å , ).

Figure 1
The molecular structure of compound 1 with displacement ellipsoids drawn at the 50% probability level.
H10AÁ Á ÁC2 i = 148.4 (8) ; symmetry code: (i) Àx + 1, Ày + 2, Àz]. As a result of the interactions between carbon atom C2 and hydrogen atom H10A, a polymeric chain structure along the [011] direction is formed (Fig. 4). The interactions can be displayed by a Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) generated by CrystalExplorer21 (Spackman et al., 2021), here indicated by the red spots (Fig. 5). The Hirshfeld surface mapped over d norm is in the range from À0.0783 to 1.0981 a.u. The contributions of the different types of intermolecular interactions for 1 are shown in the two-dimensional fingerprint plots (McKinnon et al., 2007) in Fig. 6. The contribution of the HÁ Á Á H interactions, with a value of 76.4%, has the largest share of the crystal packing of 1. The OÁ Á ÁH/ HÁ Á ÁO interactions have a smaller share with a 15% contribution and the CÁ Á ÁH/HÁ Á ÁC interactions with a 8.6% contribution. Both heteronuclear interactions appear as spikes. The structure of compound 2 is more strongly defined by C-HÁ Á ÁO hydrogen bonds (Fig. 7, Table 3). Two different layers are formed along the b-axis direction and interconnected by hydrogen bonds between the O1 atom and the H17C atom. An additional interaction in each of the layers is observed by C-HÁ Á ÁO hydrogen bonds between the O1 atom The crystal packing of compound 1 with the (011) plane shaded in blue. C-HÁ Á ÁC van der Waals interactions are shown as dashed lines.

Figure 5
Hirshfeld surface analysis of 1 showing close contacts in the crystal. The van der Waals interaction between carbon atom C2 and the H10A hydrogen atom is labeled. [Symmetry code: (i) Àx + 1, Ày + 2, Àz].   The crystal packing of compound 1. C-HÁ Á ÁC van der Waals interactions are shown as dashed lines.

Figure 7
The crystal packing of compound 2. C-HÁ Á ÁO hydrogen bonds are shown as dashed lines. and the H15 atom. The C17-H17CÁ Á ÁO1 ii hydrogen bond can be described by the R 2 2 (10) graph-set motif and the C15-H15Á Á ÁO1 i hydrogen bond by the C 1 1 (7) graph-set motif (Etter et al., 1990). Both C-HÁ Á ÁO hydrogen bonds can be identified as weak interactions according to Desiraju & Steiner (2001). A Hirshfeld analysis, carried out analogously as for structure 1, was used to further study the crystal packing. In Fig. 8, the nearest contacts are shown in red. The Hirshfeld surface mapped over d norm is in the range from À0.0717 to 1.0768 a.u. By analysis of the two-dimensional fingerprint plots ( Fig. 9), again, the biggest contribution to the crystal packing can be assigned to HÁ Á ÁH interactions (66%). Although the closest contacts were identified as C-HÁ Á ÁO hydrogen bonds, OÁ Á ÁH/ HÁ Á ÁO interactions contribute only 6.4% to the crystal packing, while CÁ Á ÁH/HÁ Á ÁC interactions have a larger share of 27%.

Figure 8
Hirshfeld surface analysis of 2 showing close contacts in the crystal. The weak hydrogen bond between oxygen atom O1 and the H15 hydrogen atom, as well as the weak hydrogen bonds between the oxygen atom O1 and the H17C hydrogen atom are labeled. [Symmetry codes: (i) x, y + 1, z; (ii) Àx + 2, Ày + 1, Àz + 1].

Figure 9
Two-dimensional fingerprint plots for compound 2, showing (a) all contributions, and (b)-(d) delineated showing the contributions of atoms within specific interacting pairs (blue areas).
was synthesized by adding t BuLi (1.9 M in pentane, 8.16 mL, 15.5 mmol, 2.0 eq.) to a solution of 2,3-dihydrofuran (1.09 g, 15.5 mmol, 2.0 eq.) in diethyl ether at 243 K and subsequent stirring for an hour. Dichlorodimethylsilane (1.00 g, 7.75 mmol, 1.0 eq.) was added at 243 K and warmed to room temperature under stirring for 2 h. All solids were filtered off inertly and all volatile components were removed in vacuo.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. H atoms were positioned geometrically (C-H = 0.95-1.00 Å ) and were refined using a riding model, with U iso (H) = 1.2U eq (C) for CH 2 and CH hydrogen atoms and U iso (H) = 1.5U eq (C) for CH 3 hydrogen atoms. Hydrogen atoms H2 and H6 for compound 1 and H2, H15 and H17C for compound 2 were refined independently.

Funding information
Funding for this research was provided by: Fonds der Chemischen Industrie (scholarship to ERB).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq