Raman Spectroscopic Investigation and Coordination Behavior of the Polyimido SVI Anions [RS(NR)3]− and [S(NR)4]2−
摘要:
On the basis of Raman spectroscopic experiments and the computational assignment of the SN vibrations to small wavenumbers (640-920 cm(-1)), the bonding in sulfur triimides is interpreted to be mainly electrostatic (>S+-Ne--) rather than covalent (S(=NR)(3)). The coordination of the S-alkyldiiminosulfonamide [RS(NR')(3)](-) and tetraazasulfate [s(NR)(4)](2-) to barium is elucidated. In the anions presented here the central sulfur atom adopts the oxidation state vl They can be readily synthesized from sulfur triimides, by nucleophilic addition of organolithium species or lithium amides to the S=N formal double bond. Although three or four nitrogen donor centers are present, tripodal coordination to barium was not observed in any case. In the [S(NtBu)(3)](2-) dianion, tripodal coordination is facilitated by all tert-butyl groups pointing towards the lone pair of the sulfur atom, leaving all lone pairs of the nitrogen atoms pointing in the opposite direction. However, in [(thf)(2)Ba{(NtBu)(3)SMe}(2)] (4) the steric demand of the S-methyl group in the [MeS(NtBu)(3)](-) ion forces one tert-butyl group to the open site of the anion, and the third nitrogen atom is blocked. Within the [S(NtBu)(4)](2-) ion in [(thf)(4)Ba-2{N-(SiMe3)(2)}(2){(NtBu)(4)S}] (7), tripodal coordination to barium is precluded by the bent SN-tBu arrangement. In the known isoelectronic complex [Li-2{(NtBu)(4)W}(2)] with a linear W=N-tBu group tripodal coordination was observed.
On the basis of Raman spectroscopic experiments and the computational assignment of the SN vibrations to small wavenumbers (640-920 cm(-1)), the bonding in sulfur triimides is interpreted to be mainly electrostatic (>S+-Ne--) rather than covalent (S(=NR)(3)). The coordination of the S-alkyldiiminosulfonamide [RS(NR')(3)](-) and tetraazasulfate [s(NR)(4)](2-) to barium is elucidated. In the anions presented here the central sulfur atom adopts the oxidation state vl They can be readily synthesized from sulfur triimides, by nucleophilic addition of organolithium species or lithium amides to the S=N formal double bond. Although three or four nitrogen donor centers are present, tripodal coordination to barium was not observed in any case. In the [S(NtBu)(3)](2-) dianion, tripodal coordination is facilitated by all tert-butyl groups pointing towards the lone pair of the sulfur atom, leaving all lone pairs of the nitrogen atoms pointing in the opposite direction. However, in [(thf)(2)Ba(NtBu)(3)SMe}(2)] (4) the steric demand of the S-methyl group in the [MeS(NtBu)(3)](-) ion forces one tert-butyl group to the open site of the anion, and the third nitrogen atom is blocked. Within the [S(NtBu)(4)](2-) ion in [(thf)(4)Ba-2N-(SiMe3)(2)}(2)(NtBu)(4)S}] (7), tripodal coordination to barium is precluded by the bent SN-tBu arrangement. In the known isoelectronic complex [Li-2(NtBu)(4)W}(2)] with a linear W=N-tBu group tripodal coordination was observed.