Intramolecular Chalcogen−Nitrogen Interactions: Molecular and Electronic Structures of Geometrical Isomers of the Diazenes RSNC(R‘)NNC(R‘)NSR
1996; American Chemical Society; Volume: 35; Issue: 20 Linguagem: Inglês
10.1021/ic960465j
ISSN1520-510X
AutoresT. Chivers, Ian H. Krouse, Masood Parvez, Ignacio Vargas‐Baca, Tom Ziegler, Peter Zoricak,
Tópico(s)Chemical Reactions and Mechanisms
ResumoThe sulfur-containing diazenes ArSNC(Ar')NNC(Ar')NSAr (1d, Ar = Ar' = 4-CH3C6H4; 3b, Ar = Ph, Ar' = 2-BrC6H4; 3c, Ar = Ph, Ar' = 2-CF3C6H4) are obtained by the reaction of Ar'CN2(SiMe3)3 with 3 molar equivs of ArSCl in CH2Cl2. X-ray structural determinations have shown that 1d exists as a Z,E,Z isomer with a weak intramolecular S···N interaction [2.607(10) Å], whereas 3b adopts an E,E,E configuration. Crystals of 1d are monoclinic, space group P21/n, with a = 6.140(2) Å, b = 10.492(6) Å, c = 20.728(9) Å, β = 96.56(4)°, V = 1325(1) Å3, Z = 2, R = 0.056, and Rw = 0.052. Crystals of 3b are orthorhombic, space group Ccca, with a = 13.884(5) Å, b = 24.763(7) Å, c = 14.500(3) Å, V = 4985(2) Å3, Z = 8, R = 0.043, and Rw = 0.044. Density functional theory calculations for the model diazenes HENC(H)NNC(H)NEH (E = S, Se, Te) show that (a) Z,E,Z isomers with an intramolecular E···N interaction are more stable than the E,E,E isomers, (b) the intramolecular interaction involves donation from the σ(N) lone pairs into both σ*(S−H) and σ*(S−N) and back-donation from a chalcogen π lone pair into the π*(NN) orbital, and (c) the intense visible absorption bands (λmax 500−550 nm, ε = 1 × 104 M-1 cm-1) can be attributed to the π-HOMO (3au) → π*-LUMO (3bg) transition. Variable-temperature 1H NMR spectra of PhSNC(H)NNC(H)NSPh in toluene-d8 and in CD2Cl2 provide evidence for the co-existence and interconversion of several geometrical isomers.
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