REACTION STUDIES ON HYPERVALENT SILICON HYDRIDE COMPOUNDS

The versatile reaction chemistry of penta-coordinated silanes of type [C6H4CH2N(CH3)(2)-2](H2C=CH)(CH3)SiH (1a) and [C6H4CH2N(CH3)(2)-2](H2C =CH)SiH2 (1b) with different substrates is described. The reaction beh avior along with the structure and bonding of the compounds obtained i s compared with tetravalent silicon molecules. Hypervalent 1a and 1b r eact, without added catalysts, with alcohols, water and benzoylic acid to produce alcoxysilanes, siloxanes and carboxysilanes, respectively. Compounds [C6H4CH2N(CH3)(2)-2](H2C=CH)(CH3)Si(OCH3) (3), [C6H4CH2N(CH 3)(2)-2](H2C=CH)Si(OR)(2) (4a: R = CH3, 4b: R = C2H5, 4c: R = (C3H7)-C -i, 4d: R = CH2C=CH), {[C6H4CH2N(CH3)(2)-2](H2C=CH)(CH3)Si}(2)O (5a), {[C6H4CH2N(CH3)(2)-2](H2C=CH)SiO}(n) (5b) as well as [C6H4CH2N(CH3)(2) -2](H2C=CH)Si(H)[OC(O)C6H5] (8) are formed in quantitative yields. The carboxysilane 8 reacts with C6H5CO2H (7) further to give the polymeri c siloxane 5b and benzoylic anhydride. Moreover, H2PtCl6-catalyzed hea d-tail polymerization of 1b yields the oligomeric carbosilane {[C6H4CH 2N(CH3)(2)-2](H)Si-CH2CH2-}(n) (6). Due to the intramolecular nitrogen -silicon interaction in hypervalent la as well as Ib, the hydrosilylat ion reaction with C6H5N=C=X (11a: X = S, 11b: X = O) takes place witho ut a catalyst added, whereas hydrosilylation of isocyanates and isothi ocyanates does not occur with tetravalent silanes. The obtained produc ts [C6H4CH2N(CH3)(2)-2](H2C=CH)(R)Si(C6H5NCHX) (12a: R = CH3, X = S; 1 2b: R = H, X = S; 12c: R = H, X = O) are suitable catalysts for the cy clooligomerization of isocyanates and isothiocyanates. While compounds 12a-12c are stable in the solid state, 12c starts to rearrange in sol ution to afford oligomeric 5b along with 1,3,5-triphenylhexahydro-1,3, 5-triazine (13). A possible mechanism for the formation of the latter compounds is discussed. An example for an insertion-elimination proces s of compound Ib is given by the insertion of sulfur into the silicon- hydrogen bonds, yielding [C6H4CH2N(CH3)(2)-2](H2C=CH)Si(SH)(2) (15) as an intermediate first; elimination of H2S affords the intermolecular donor-stabilized silanethion [C6H4CH2N(CH3)(2)-2](H2C=CH)Si=S (16). Th e X-ray structure analysis of compound 12b is reported. Crystals of 12 b are monoclinic, space group P2(1)/n with the cell constants a = 9.35 6(3), b = 10.890(4), c = 17.236(6) Angstrom, beta = 99.80(3)degrees, V = 1730(1) Angstrom(3) and Z = 4. (C) 1998 Elsevier Science S.A. All r ights reserved.