Group 14 hydrides

Synthetically useful stereoselective reductions have been possible with cyclic carbonyl compounds of rigid conformation. Reduction of substituted cyclohexanone and cyclopentan-one rings by hydrides of moderate activity, e.g. NaBH (J.-L. Luche, 1978), leads to alcohols via hydride addition to the less hindered side of the carbonyl group. Hydrides with bulky substituents 3IQ especially useful for such regio- and stereoselective reductions, e.g. lithium hydrotri-t-butoxyaluminate (C.H. Kuo, 1968) and lithium or potassium tri-sec-butylhydro-borates or hydrotri-sec-isoamylborates (=L-, K-, LS- and KS-Selectrides ) (H.C. Brown, 1972 B C.A. Brown, 1973 S. Krishnamurthy, 1976). 

Main group hydrides 15 PH3, AsH3 Conventional group 15 sources in MOCVD... 

Main group hydrides which include borohydride species.12... 

Another application of an isomerisation reaction can be found in the production of the third monomer that is used in the production of EPDM rubber, an elastomeric polymerisation product of Ethene, Propene and a Diene using vanadium chloride catalysts. The starting diene is made from vinylnorbomene via an isomerisation reaction using a titanium catalyst. The titanium catalyst is made from tetravalent salts and main group hydride reagents, according to patent literature. 

Rivard E, Fischer RC, Wolf R et al (2007) Isomeric forms of heavier main group hydrides experimental and theoretical studies of the Sn(Ar)H (2) (Ar=terphenyl) system. J Am Chem Soc 129 16197-16208... 

Calculated equilibrium geometries for hydrogen and main-group hydrides containing one and two heavy (non-hydrogen) atoms are provided in Appendix A5 (Tables A5-1 and A5-10 for molecular mechanics models, A5-2 and A5-11 for Hartree-Fock models, A5-3 and A5-12 for local density models, A5-4 to A5-7 and A5-13 to A5-16 for BP, BLYP, EDFl and B3LYP density functional models, A5-8 and A5-17 for MP2 models and A5-9 and A5-18 for MNDO, AMI and PM3 semi-empirical models). Mean absolute errors in bond lengths are provided in Tables 5-1 and 5-2 for one and two-heavy-atom systems, respectively. 

The Hartree-Fock STO-3G model provides a generally reasonable account of equilibrium geometry in main-group hydrides. The worst results are for alkali metal compounds where, with the exception of NaH, calculated bond distances are significantly shorter than experimental values. Significant errors also appear for systems with two highly electronegative elements, e.g., for F2, where calculated bond distances are shorter than experimental values. 

Figure 5-1 6-311+G vs. Experimental Heavy-Atom Bond Distances in Two-Heavy-Atom, Main-Group Hydrides... 

Semi-empirical models do not account for the geometries of main-group hydrides as well as any of the other quantum chemical models, with the notable exception of the STO-3G model. Overall, MNDO... 

Carbon-carbon bond lengths for a selection of hydrocarbons obtained from molecular mechanics calculations, Hartree-Fock calculations, local density calculations, density functional calculations, MP2 calculations and semi-empirical calculations are compared with experimental distances in Table 5-3. The same basis sets considered for main-group hydrides are utilized here. Mean absolute errors for each method have also been tabulated. 

Calculated vibrational frequencies for main-group hydrides containing one first or second-row element are provided in Appendix A7 (Tables A7-1 to A7-8), and compared both with experimentally measured values and, where available, with harmonic experimental frequencies. The same theoretical models considered for diatomic molecules are also examined here. A summary of mean absolute errors for symmetric stretching frequencies (only) is provided in Table 7-2. 

CH3X molecules provide an excellent opportunity to assess the ability of the calculations both to reproduce gross trends in measured vibrational frequencies, for example, trends in CX stretching frequencies, as well as to account for what are presumed to be subtle differences associated with the methyl rotor with change in X. Data are provided in Appendix A7 (Tables A7-9 to A7-16) for the usual collection of theoretical models. The reader can easily verify that the same comments made for diatomic molecules and for one-heavy-atom, main-group hydrides generally apply here as well. 

The commonly used reducing agents AlH and BH will reduce aldehydes and ketones to primary and secondary alkoxides.109 Similar reactivity is found for some other main group hydrides, e.g. gallium (equation 33).110... 

Main group hydrides are of particular interest in themselves but are relevant to coordination chemistry only to the extent that they are used to prepare transition metal hydrides or act as ligands. 

E. Magnusson,/. Am. Chem. Soc., 106, 1177 (1984). sp Hybridization Reconsidered The Composition of Orbitals in Main-Group Hydrides. 

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