Penta-coordinated chlorosilanes: reaction chemistry, structure and bonding

Abstract

The synthesis and reaction behavior of the penta-coordinated chlorosilanes [C 6H 4CH 2N(CH 3) 2-2]Si(Cl)(R)(R′) [ 3a: R=R′=Cl; 3b: R=R′=CH 3; 3c: R=C1, R′=CH 3; 3d: R=Cl, R′=CHCH 2; 3e: R=CH 3, R′=CHCH 2] are discussed. Compounds 3a–e can be obtained by the reaction of LiC 6H 4CH 2N(CH 3) 2-2 ( 1) with stoichiometric amounts of (R)(R′)SiCl 2 ( 2) in high yields and give access to a versatile reaction chemistry on substitution of the chlorine atoms by many of the diverse nucleophiles used. Hydrolysis of compound 3d produces oligomeric {[C 6H 4CH 2N(CH 3) 2-2](CH 2CH)SiO} n ( 4a), whereas 3e yields the disiloxane {[C 6H 4CH 2N(CH 3) 2-2](CH 2CH)(CH 3)Si} 2O ( 4b). Alcoholysis of compounds 3d and 3e in presence of NEt 3 affords [C 6H 4CH 2N(CH 3) 2-2](CH 2CH)(CH 3)Si(OCH 3) ( 5a) or [C 6H 4CH 2N(CH 3) 2-2](CH 2CH)Si(OR) 2 [ 5b: R=CH 3, 5c: R=C 2H 5, 5d: R= i C 3H 7], respectively. Compound 5b can be transferred to the difluorosilane derivative [C 6H 4CH 2N(CH 3) 2-2](CH 2CH)SiF 2 ( 6) by its reaction with BF 3*O(C 2H 5) 2, while treatment with LiAlH 4 produces the silane [C 6H 4CH 2N(CH 3) 2-2](CH 2CH)SiH 2 ( 7a). Moreover, hypervalent silanes are accessible by the reaction of chloro-functionalized 3d or 3e with LiAlH 4 whereby compounds [C 6H 4CH 2N(CH 3) 2](H 2CCH)Si(H)(R) ( 7a: R=H; 7b: R=CH 3) are formed in good yields. Metathesis reaction of compounds 3b–e with LiR reagents [R=CCR′, NHC 6H 2(CH 3) 3-2,4,6, P(C 6H 5) 2] produces [C 6H 4CH 2N(CH 3) 2-2](CH 3)(R)(SiCCR′) [reaction of 3b or 3e with LiCCR′; 8a: R=CH 3, R′=C 6H 5; 8b: R=CH 3, R′=Si(CH 3) 3; 8c: R=CHCH 2, R′=C 6H 5; 8d: R=CHCH 2, R′=Si(CH 3) 3], [C 6H 4CH 2N(CH 3) 2-2](R)Si(CCR′) 2 [reaction of 3c or 3d with LiCCR′; 9a: R=CH 3, R′=C 6H 5; 9b: R=CHCH 2, R′=C 6H 5; 9c: R=CHCH 2, R=Si(CH 3) 3], [C 6H 4CH 2N(CH 3) 2-2](H 2CCH)Si[HNC 6H 2(CH 3) 3-2,4,6] 2 [reaction of 3d with LiNHC 6H 2(CH 3) 3-2,4,6; 10] or [C 6H 4CH 2N(CH 3) 2-2](H 2CCH)Si[P(C 6H 5) 2] 2 [reaction of 3d with LiP(C 6H 5) 2; 11]. The solid state structures of 3c and 3d are reported. Complex 3c crystallizes in the monoclinic space group P2 1/ c with a=8.918(5), b=11.557(3), c=12.830(7) Å; β=108.17(4)°, V=1256(5) Å 3 and Z=4; 3d crystallizes in the monoclinic space group P2 1 with a=6.625(3), b=8.574(6), c=11.281(8) Å; β=88.16(5)°, V=640.5(7) Å 3 and Z=2. The central silicon 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 1H-NMR studies confirm that the same geometry is adopted in solution.