Nitrogen-silicon bonds lengths

Figure 3.7 Molecular structure of [(Cp )Ca N(SiMe t)2l(thf>l calcium, nitrogen and silicon atoms are shown as black spheres, oxygen and carbon atoms are white. Selected bond lengths Ca-N 2.30(1), Ca-O 2.35(1), Ca-M 2.397A...

Figure 3.10 The structure of [BalNiSiMc il hlthfi ] Barium and nitrogen atoms are shown as black spheres, silicon atoms are grey and carbon and oxygen atoms are white. Selected bond lengths Ba-NI 2.587(6), Ila i 2 2.596(6), Ba-OI 2.745(6), Ba 02 2.717(6)A...

Figure 6.6 Illustration of the phosphinidene complex ll(MciSiN)jN Ta — PCy]. Tantalum and nitrogen atoms are shown as black spheres, silicon and phosphorus atoms are grey and carbon atoms are indicated in white shadow. The Ta=P bond length is 2. ISA...

Figure 8.1 Illustration of the structure of crystallized [flMe, Si)2Al(NH2)2 3AII. Aluminium atoms are shown as black spheres, silicon atoms are dark grey and nitrogen and carbon atoms are white. Selected bond lengths AI1-N1 2.022(4), AII-N2 2.017(5), AI1-N3 2.022(3), AI2-N1 1.935(4), AI3-N2 1.936(4), AI3-N3 1.923(5), AII-AI2 2.911(3), AI1-AI3 2.905(2) A...

Figure 8.14 Representation of ITCdH) HiCC(CH2NSiMei)il2l highlighting the central TIr core in bold. Thallium, nitrogen and silicon atoms are shown as black spheres and carbon atoms arewhite. Selected bond lengths Til-TI2 3.707(3), Til-TI3 3.837(3), TI 2-TI3 3.756(3), T14-TI1 3.409(3), TI4-TI2 3.541(3), TI4-TI3 3.479(3), TI4-TI5 3.403(3), TI1/4-N1/5 2.39(1)-2.49(l), T15-hyphen N6 2.62(2) A...

FIGURE 11. Histogram of Si—N bond lengths in compounds with tetracoordinate silicon and dicoordinate nitrogen atoms... 

Pentacoordinate silicon forms two types of bonds with tricoordinate nitrogen atoms, a pure covalent bond and a N - Si dative bond. The first is significantly shorter than the second. The average covalent Si—N bond length in compounds where pentacoordinate silicon atom is bonded to tricoordinate nitrogen atom was calculated from 48 XRD experimental values to be 1.761 A (s.d. 0.06 A, s.m. 0.009 A). An example of the difference in bond length is shown in 127141 where the covalent Si—N bond lengths are 1.766 and 1.770 A and the dative bond is 2.333 A. 

The coordination of donors lengthens the Si=N bond and leads to pyramidalization at the silicon centre, as can be seen from the deviation of the sum of angles around the silicon atom from 360° (see examples in Table 17). Coordination of silanimines to transition metal centres also increases the silicon-nitrogen bond length to 1.66-1.69 A, which corresponds to a Si—N single bond. It has already been mentioned above that these metal compounds are best described as metallacycles349,350. 

The chromium complexes are proved to be silanediyl complexes, as shown by the silicon-transition metal bond lengths (Table 5) and by the extreme low field shift of the 29Si NMR signals (124.9 and 121.2) at 22 °C for R = H and CH2NMe2, respectively (Table 6). The 29Si NMR shifts of these complexes are temperature-dependent due to the hindered rotation of the phenyl ring and dynamic coordination of the nitrogens to the Si atom. 

Electron donation from nitrogen to silicon is undoubtedly important in stabilizing all of these molecules. Partial double-bonding between N and Si will tend to occupy the vacant p-orbital on silicon, which is the usual site of electrophilic reactivity of silylenes. This stabilization is shown in resonance drawings in Scheme 16. Greater --donation from N to Si would be expected for 60 than for 59 or 61, since in 60 the nitrogens are more basic. The Si—N bond lengths are consistent with this model, as mentioned above. 

Table VIII lists various bond lengths and angles extracted from the X-ray crystallographic determinations for 30-38. Examination of the silicon-nitrogen distances shows that octahedral complexes are characterized by relatively short Si-N bond distances ( 1.95-2.2 A), while in the bicapped-tetrahedral structures the Si-N distances are greater than 2.5 A.53-56...

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