Molecular and electronic structures of the purple chromophore RC(NH₂)(NSePh) (R = H, 4-CH₃C₆H₄)

Abstract

The reaction of Li[4-CH3C6H4C(NSiMe3)2] with PhECl (E = S, Se) in a 1:1 molar ratio produces the monosubstituted derivatives 4-CH3C6H4C(NEPh)[N(SiMe3)2] (3b, E = Se; 3d, E = S). The thermolysis of 3b at 130 °C produces PhSeN(SiMe3)2 and 4-CH3C6H4CN. Crystals of 3b slowly acquire a purple stain upon prolonged standing at 23 °C owing to the formation of 4-CH3C6H4C(NH2)(NSePh) (4c, λmax = 551 nm). The formamidine derivative HC(NH2)(NSePh) (4a, λmax = 472 nm) was isolated from the reaction of HCN2(SiMe3)3 with PhSeCl (1:3 molar ratio) in dichloromethane. The structure of 4a was shown by X-ray crystallography to involve a syn configuration at the [Formula: see text] bond and hydrogen bonding between amino nitrogen atoms. The crystals of 4a are monoclinic, space group P21 (No. 4), with a = 7.514(1), b = 5.575(1), c = 8.925(1) Å, β = 100.71(1)°, V = 367.40(6) Å3, and Z = 2. The final R and Rw values were 0.055 and 0.060, respectively. The 1H and 77Se NMR spectra indicate that both 4a and 4c exist as a mixture of tautomers in THF solution. DFT calculations for the model tautomers HC(NH2)(NER) and HC(NH)(NHER) (E = S, Se; R = H, Ph) show that the former is more stable in all cases, but the difference in total bonding energy is smaller for selenium than for sulfur (17.5 vs. 29 kJ mol−1). The visible absorption band for 4a is assigned to the HOMO–LUMO transition (ΔE = 2.90 eV, λmax = 427 nm) of the minor tautomer. Keywords: formamidine, tautomer, selenium, purple chromophore.

Intramolecular Chalcogen−Nitrogen Interactions: Molecular and Electronic Structures of Geometrical Isomers of the Diazenes RSNC(R‘)NNC(R‘)NSR

“…(d) What is the nature of the intramolecular E···N interaction, and why is it so much stronger in the halogeno derivative 2a compared to 1a ? Approximate density functional theory (DFT) has proven to be an efficient method for modeling the structures and properties of chalcogen−nitrogen compounds. − In this paper we report the X-ray structures of the Z , E , Z isomer 1d and the E , E , E isomer 3b and we address questions (a) and (c) by means of DFT theory.…”

Formation and X-ray Structures of Eight- and Sixteen-Membered Rings (ArC)nN2n(SPh)n[n= 2, Ar = 4-XC6H4(X = Br, CF3);n= 4, Ar = 4-BrC6H4] and the Electronic Structures of (HC)2N4(SH)2and (HC)2N4(SH)22-

“…2.9 Å for 1b and 1c , it was of interest to determine the relative stabilities of the chair and boat conformers of the C 2 N 4 S 2 ring in the model system (HC) 2 N 4 (SH) 2 ( 1d ). Approximate DFT theory has been applied successfully to modeling the properties of a variety of chalcogen−nitrogen compounds. ,, In this study the structure of 1d was optimized on the basis of the C 2 v structure determined for 1b by X-ray crystallography. The calculated structure for 1d is in reasonable agreement with the experimental data (see Table ); the largest deviations are for parameters involving S atoms.…”

Structural control of dithiazolyl radicals: Case studies on 3′- and 4′-cyano-benzo-1,3,2-dithiazolyl, NCC6H3S2N

“…Notably in both PDTA and QDTA the corresponding pyridyl-NÁ Á ÁH-C interactions appeared structuredirecting. Whilst the CNÁ Á ÁH-C motif persists in both 3-NCBDTA and 4-NCBDTA, the centrosymmetric SÁ Á ÁN dimer motif (common to thiazyl systems) [12] is present in 3-NCBDTA but absent in 4-NCBDTA. This would suggest that the CNÁ Á ÁH-C contact is more favourable.…”

“…In the case of thiazyl chemistry, SÁ Á ÁN contacts are prevalent and SÁ Á ÁN contacts between heterocyclic rings e.g. in thiadiazolyl rings [12] and CNÁ Á ÁS interactions in dithiadiazolyl rings have been successfully used as structure-directing motifs [13].…”