PENTACOORDINATED CHLOROSILANES - REACTION CHEMISTRY, STRUCTURE AND BONDING

The synthesis and reaction behavior of the penta-coordinated chlorosil anes [C6H4CH2N(CH3)(2)-2]Si(Cl)(R)(R') [3a: R=R'=Cl; 3b: R=R'=CH3; 3c: R=Cl, R'=CH3; 3d: R=Cl, R'=CH=CH2,; 3e: R=CH3, R'=CH=CH2] are discuss ed. Compounds 3a-e can be obtained by the reaction of LiC(6)H4CH(2)N(C H3)(2)-2 (1) with stoichiometric amounts of (R)(R')SiCl2 (2) in high y ields and give access to a versatile reaction chemistry on substitutio n of the chlorine atoms by many of the diverse nucleophiles used. Hydr olysis of compound 3d produces oligomeric {[C6H4CH2N(CH3)(2)-2](CH2=CH )SiO}(n) (4a), whereas 3e yields the disiloxane {[C6H4CH2N(CH3)(2)-2]( CH2=CH)(CH3)Si}(2)O (4b). Alcoholysis of compounds 3d and 3e in presen ce of NEt3 affords [C6H4CH2N(CH3)(2)-2](CH2=CH)(CH3)Si(OCH3) (5a) or [ C6H4CH2N(CH3)(2)-2](CH2=CH)Si(OR)(2) [5b: R=CH3, 5c: R=C2H5, 5d: R=(C3 H7)-C-i], respectively. Compound 5b can be transferred to the difluoro silane derivative [C6H4CH2N(CH3)(2)-2](CH2=CH)SiF2 (6) by its reaction with BF3O(C2H5)(2), while treatment with LiAlH4 produces the silane [C6H4CH2N(CH3)(2)-2](CH2=CH)SiF2 (7a). Moreover, hypervalent silanes a re accessible by the reaction of chloro-functionalized 3d or 3e with L iAlH4 whereby compounds [C6H4CH2N(CH3)(2)](H2C=CH)Si(H)(R) (7a: R=H; 7 b: R=CH3) are formed in good yields. Metathesis reaction of compounds 3b-e with LiR reagents [R=C=CR', NHC6H2(CH3)(3)-2,4,6, P(C6H5)(2)] pro duces [C6H4CH2N(CH3)(2)-2](CH3)(R)(SiC=CR') [reaction of 3b or 3e with LiC=CR'; 8a: R=CH3, R'=C6H5; 8b: R=CH3, R'=Si(CH3)(3); 8c: R=CH=CH2, R'=C6H5; 8d: R=CH=CH2, R'=Si(CH3)(3)], [C6H4CH2N(CH3)(2)-2](R)Si(C=CR' )(2) [reaction of 3c or 3d with LiC=CR'; 9a: R=CH3, R'=C6H5; 9b: R=CH= CH2, R'=C6H5; 9c: R=CH=CH2, R=Si(CH3)(3)], CH2N(CH3)(2)-2](H2C=CH)Si[H NC6H2(CH3)(3)-2,4,6](2) [reaction of 3d with LiNHC6H2(CH3)(3)-2,4,6; 1 0] or [C6H4CH2N(CH3)(2)-2](H2C=CH)Si[P(C6H5)(2)](2) [reaction of 3d wi th LiP(C6H5)(2); 11]. The solid state structures of 3c and 3d are repo rted. Complex 3e crystallizes in the monoclinic space group P2(1)/c wi th a=8.918(5), b=11.557(3), c=12.830(7) Angstrom; beta=108. 17(4)degre es, V=1256(5) Angstrom(3) and Z=4; 3d crystallizes in the monoclinic s pace group P2(1) with a=6.625(3), b=8.574(6), c=11.281(8) Angstrom; be ta=88.16(5)degrees, V=640.5(7) Angstrom(3) and Z=2. The central silico n atom in compounds 3c and 3d shows an essentially distorted trigonal- bipyramidal coordination sphere, with the axial positions occupied by the nitrogen donor atom and one chloro ligand. Dynamic H-1-NMR studies confirm that the same geometry is adopted in solution. (C) 1998 Elsev ier Science S.A. All rights reserved.