Si-H bond distance

For this reaction, the reaction coordinate is simply the Si-H bond distance. Since the reverse of this reaction is radical-radical recombination and should have no activation energy barrier, the E for forward reaction would be expected to be AH,. 

As seen from Fig. 12, quantum chemical calculations indeed support the fact that the activation energy for the SiHj-H bond scission reaction corresponds to the bond dissociation energy or the heat of reaction, i.e., AH, % s 90 kcal/mol. In addition, at the transition state, the Si-H bond distance is calculated to be about 2.5 A, a clear indication of the loosness and the increase in entropy associated with the formation of the transition state. 

Table 4 Enthalpy differences between equatorial and axial conformers (AH), Si-H bond distances (r(Si-H)), and the percentage of the axial conformer based on IR data...

The four fundamental vibrational frequencies and the Si-H bond distance are the result of gas-phase infrared and Raman spectral studies by Kattenberg and Oskam (8). They are in excellent agreement with values selected from earlier work as given in the compilations of Janz and Mikawa (9) and Shiraanouchi (1 ). The heat capacity and entropy calculations are based on a tetrahedral structure. The S°(298.15 K) = 48.89 0.01 cal K mol is in good agreement with another evaluation ( ). 

While the majority of J7 -silane complexes characterized to date are mononuclear species, there are several dinuclear or polynuclear metal complexes with bridging M-H-Si interaction. A Si-H-M interaction was unambiguously identi-hed in compound 25 by X-ray structure determination, showing the Si-H bond distance of 1.58 A. This is 7% longer than in free silane and represents a rare case of unstretched silane a complex [84]. The unique unstretched silane o bond is further documented in the tetrahedral geometry around the silicon atom, which is largely retained, as opposed to the more distorted geometry at the Si atom in the extensively studied mononuclear Mn complexes. 

Problem 14.8 Compare the bond distances in the most stable form of Si2H2 with the Si-H bond distance in S1H4, 148 pm, and the Si-Si distance in Si2H6, 233 pm, and suggest a description of the bonding in terms of 2c and 3c molecular orbitals. 

Silane, SiH4, has a tetrahedral geometry and a rovibrational spectrum consisting of lines spaced by 5.92 cm . Calculate the Si-H bond distance in silane. Could this information be obtained by pure rotational spectroscopy Why or why not ... 

With the compound (2-Me2NCH2C6H4)PhSi(H)(03SCF3) 786, it was demonstrated that more than one built-in ligand is needed for the stabilization of trivalent silicon cations as, in this structure, the triflate anion is involved in the coordination to the silicon atoms.810 The related Si-O bond distance of 1.951(1) A is longer than the standard Si-O bond length (approx. 1.6 A) and therefore compound 786 might be best described as contact ion pairs (Figure 5). 

In an earlier review article Schubert suggested that the shortest nonbonding Si-H contact can be estimated as 2.0 A, with the inexplicit assumption that any distance above this value is nonbonding, whereas shorter contacts correspond to the presence of some kind of Si-H bond. Schubert s structural criterion has been widely used in the 1990s to identify silane a-complexes both in experimental and theoretical stud-This criterion was obtained by summing up half of the nonbonding Si-Si... 

To summarize, the Si-H distance can serve as a criterion of the Si-H interaction when it does not differ much from the normal Si-H bond and is determined by an accurate method such as ND and high-level quantum mechanic calculations. The discussion of other structural parameters requires the proper choice of a reference system. In systems with elongated Si-H interactions a justified conclusion can be made only on the basis of a combined application of several independent structural, spectroscopic, and computational methods. 

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

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