Zinc(ii), iron(ii/iii) and ruthenium(ii) complexes of o-phenylenediamine derivatives: oxidative dehydrogenation and photoluminescence

Abstract

Reactions of benzoyl pyridine, o-phenylenediamine and anhydrous ZnX2 in methanol afford imine complexes [Zn(L1)X2] (X = Cl, 1; X = Br, 2) in good yields (L1 = (E)-N(1)-(phenyl(pyridin-2-yl)methylene)benzene-1,2-diamine). The reduction of 1 with NaBH4 affords (E)-N(1)-(phenyl(pyridine-2-yl)methylene)benzene-1,2-diamine (L2H). The reaction of L2H with [Ru(II)(PPh3)3Cl2] results in the oxidative dehydrogenation to L1 generating cis-[Ru(II)(L1)(PPh3)Cl2] (3). The reaction of L2H with salicylaldehyde affords (E)-2-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)phenol (L3H2). The reaction of L3H2 with anhydrous FeCl3 in CH3OH affords cis-[Fe(III)(L3H(-))Cl2] (4). Reaction of L3H2 with [Ru(II)(PPh3)3Cl2] results in the oxidative dehydrogenation to diimine, L4H, affording trans-[Ru(II)(L4(-))(PPh3)2](+), which is isolated as trans-[Ru(II)(L4(-))(PPh3)2]PF6 (5(+)PF6(-)) (L4H = 2-((E)-(2-((E)-phenyl(pyridin-2-yl)methyleneamino)phenylimino)methyl)phenol). The reduction of L3H2 with NaBH4 produces 2-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)amino)methyl)phenol (L5H3). With iron(III) L5H3 undergoes oxidative dehydrogenation to L3H2 affording 4, while with [Ru(II)(PPh3)3Cl2], L5H3 undergoes 4e + 4H(+) transfer giving 5(+). A fluid solution of L3H2 at 298 K exhibits an emission band at 470 nm (λ(ex) = 330 nm, τ1 = 3.70 ns) and a weaker band at 525 nm (λ(ex) = 330, 390 nm, τ1 = 1.1 ns) at higher concentrations due to molecular aggregation, which are temperature dependent. 4 is brightly emissive (λ(ex) = 330 nm, λ(em) = 450 nm, Φ = 0.586, τ1 = 3.70 ns). Time resolved emission spectra (TRES) and lifetime measurements confirm that the lower energy absorption band of L3H2 at 390 nm, which is absent in complex 4, has a larger non-radiative rate constant (k(nr)). The redox innocent Al(III) adduct of L3H2 is fluorescent (λ(ex) = 330 nm, λ(em) = 450 nm, τ1 = 3.70 ns). On the contrary, the cis-[Fe(II)(L3H(-))Cl2](-) and cis-[Co(L3H(-))Cl2](-) analogues are non emissive. Density function theory (DFT) calculations, redox potentials and the near infra-red (NIR) absorption data prove that 4 is emissive due to the stable [Fe(III)(L3H(-)*)] state, while 3, 5(+), cis-[Fe(II)(L3H(-))Cl2](-) and cis-[Co(L3H(-))Cl2](-) are non-emissive due to transformations of the [M(II)(L*)] to [M(III)(L˙(-)*)] states.

Oxidovanadium(iv), oxidomolybdenum(vi) and cobalt(iii) complexes of o-phenylenediamine derivatives: oxidative dehydrogenation and photoluminescence

“…o-Phenylene derivatives are synthesized using the reported procedures. 7 L 3 t-Bu H 2 and 3-6 are characterized by the elemental analyses and IR, mass, EPR and 1 H NMR spectra. The VvO stretching vibrations of 3 and 4 are at 966 and 959 cm −1 , while the symmetric and asymmetric stretching vibrations of two cis MovO 25 resonate at 901 and 915 cm −1 .…”

“…It was recorded that 1 has eighty fold stronger emission than L 3 H 2 itself, while the ketimine analogue 2 + ion is non-emissive. 7 The fluid solution fluorescence features of 3, 4, 5 and 6 are also recorded at 298 K. It is found that 3 and 4 in fluid solutions at 298 K are non-emissive while the electrogenerated one-electron oxidized analogues,…”

“…The solution was evaporated under low pressure and the residue was extracted with diethyl ether. After evaporation of the ether, a yellow oily liquid of L 2 H was obtained 7 To L 2 H, MeOH (10 ml) followed by 3,5-di-tert-butyl-2-hydroxybenzaldehyde (240 mg, 1 mmol) were added and the resulting solution was refluxed for 30 min and then cooled to 298 K. A yellow crystalline solid of L )] (5). To a MeOH solution (30 ml) of L 3 H 2 (380 mg, 1 mmol), (NH 4 ) 2 [MoO 4 ] (175 mg, 1 mmol) was added and the resulting solution was heated at 327 K for 60 min.…”

“…11 It is observed that L 3 H 2 is fluorescent due to the internal charge transfer (ICT) from the π phenolato to the π aldimine * orbital (λ ex = 330; λ em = 470 nm). 7 Lifetimes measurements and time resolved emission spectra (TRES) have confirmed that the lower energy excited state at 390 nm has a higher non-radiative rate constant (k nr ). It was noted that due to molecular aggregation at higher concentration, the fluid solution fluorescence spectra of L 3 H 2 depend on concentration, which has been investigated by 1 H NMR and temperature dependent fluorescence spectra.…”

“…It was noted that due to molecular aggregation at higher concentration, the fluid solution fluorescence spectra of L 3 H 2 depend on concentration, which has been investigated by 1 H NMR and temperature dependent fluorescence spectra. 7 An interesting observation is that the molecular aggregation of L 3 H 2 depends reversibly on temperature. At higher concentration, in addition to the emission band at 470 nm, L 3 H 2 displays a lower energy emission band at 525 nm, which disappears upon dilution.…”