Fe -l,2,4-triazole

Aminothiazole[3,2-fe][l,2,4]triazoles are readily bis-N-acylated (Ae20, reflux). The 5-alkylation of thiazolo[3,2-b][l,2,4]triazoles with chloro- and aeetoxymethylcephem was also reported (91MI2). An 5-alkylated thia-zolo[3,2-fe][l,2,4]triazole was converted to a sulfonyl ehloride and aminated (88EUP244098). 

The reaction of l-arylamino-4,4-dimethyl-5-methylene-2,3,4,5-tetrahydro-l//-imidazol-2-one (338 Y = O) and -2-thione (338 Y = S) with protic heterocumulenes affords 7,7,7a-trimethyl-3-aryl-2,3,5,6,7,7a-hexahydro-l/7-imidazo[l,5-fe][l,2,4]triazol-2,5-diones (339 X = Y = 0), and N-and 5-derivatives of these functions in 2- and 5-positions (Equation (104)) <93TH 805-oi, 95FES379>. 

Benzoin cyclocondenses with 3-amino-5-methyl-4/7[l,2,4]triazole to give 2-methyl-5,6-diphenyl-47/-imidazo[2,l-fe][l,2,4]triazole (354) (Equation (113)) <88IJC(B)421>. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

The ketoxime, 3-[a-hydroxymrino-a-(5-methyl-l,2,4-triazol-3-yhnethyl)]-2(lfl)-quinoxalinone (218), gave 3-(5-methyl-l,2,4-triazol-3-yl)isoxazolo[4,5-fe]-quinoxaline (219) (POCI3, dioxane, reflux, h 88%).417... 

Fe(abpt)2(TCNQ)2], (Fig. 7 abpt = 3,5-bis(pyridin-2-yl)-4-amino-l,2,4-triazole) synthesized in 1996 by Kunkeler et al. [98] is the first compound containing a possible conductive unit (TCNQ) and an SCO moiety (Fen(abpt)2). However,... 

This is consistent with the relative values for Dq(Ni2+) (1160 and 1170 cm-1 for 23 and 24, respectively) [36]. For 2-(l,2,4-triazol-3-yl)pyridine 26 Dq(Ni2+) is somewhat smaller,1130 cm-1, and for this and certain substituted derivatives the spin transitions in the [Fe N6]2+ derivatives are observed below room temperature [29]. This and related triazole systems are discussed more fully in chapter 5 by van Koningsbruggen. 

Among all Fe(II) spin crossover compounds known to date, the extensively studied polymeric [Fe(4-R-l,2,4-triazole)3](anion)2 systems (R=amino, alkyl, hydroxyalkyl) appear to have the greatest potential for technological applications, for example in molecular electronics [1, 24, 25] or as temperature sensors [24, 26]. This arises because of their near-ideal spin crossover characteristics pronounced thermochromism, transition temperatures near room temperature, and large thermal hysteresis [1, 24, 27]. 

The crystal structure of [Fe2(totrz)5(NCS)4]2[Fe(totrz)2(NCS)2(H20)2]-n-H20, a compound obtained by self-assembly of 4-(p-tolyl)-l,2,4-triazole... 

In these polymeric species, the M,AT2-1,2,4-triazole linkage is rigid, and allows an efficient transmission of cooperative effects. Consequently, abrupt ST with broad thermal hysteresis loops have been observed [26, 32-34]. The absorption spectra of these compounds show a broad band at 520 nm corresponding to the Aig Trg d-d transition in the LS state whereas no band is found in the visible region in the HS state, the 5T2g-5Eg transition being located around 850 nm [7a]. The ST is thus accompanied by a thermochromic effect, purple (LS) and white (HS). These characteristics make these compounds potential candidates for practical applications, e.g. thermal display devices [7, 8, 17]. Such behaviour has been observed, for example, in the compound [Fe(4-amino-l,2,4-triazole)3](NC>3)2 [32] whose SCO is associated with a hysteresis loop of width 35 K, centred above room temperature [8]. 

The influence of pressure has also been used to tune the ST properties of these ID chain compounds. Application of hydrostatic pressure ( 6 kbar) on [Fe(hyptrz)3] (4-chlorophenylsulfonate)2 H20 (hyptrz=4-(3 -hydroxypro-pyl)-l,2,4-triazole) provokes a parallel shift of the ST curves upwards to room temperature (Fig. 5) [41]. The steepness of the ST curves along with the hysteresis width remain practically constant. This lends support to the assertion that cooperative interactions are confined within the Fe(II) triazole chain. Thus a change in external pressure has an effect on the SCO behaviour comparable to a change in internal electrostatic pressure due to anion-cation interactions (e.g. changing the counter-anion). Both lead to considerable shifts in transition temperatures without significant influence on the hysteresis width. Several theoretical models have been developed to predict such SCO behaviour of ID chain compounds under pressure [50-52]. Figure 5 (bottom) also shows the pressure dependence of the LS fraction, yLS, of... 

The reaction of 2-amino-l,3,4-thiadiazole 470 and 3-amino-l,2,4-triazole 472 with benzaldehyde and fe/V-butylisoni-trile gives imidazo[2,l-A [l,3,4]thiadiazoles 471 and imidazo[l,2- ][l,2,4]triazoles 473, respectively, in a one-pot process (Equation 110) <1998AG(E)2234>. 

M(trpn)(abpt)]2+ (M = Fe, Ni, trpn = tris(3-aminopropyl)amine, abpt = 4-amino-3,5-bis(pyridine-2-yl)-l,2,4-triazole) ( H) 255 (acac)2Fe(p-ox)Fe(acac)2... 

Figure 2.65 Mesogenic triazole ligand forming complexes of the type [Fe(L)2](4-...

Figure 3.27 General structure of coordination polymer chains in the spin crossover species [Fe(Rtrz)3][X]2, R = NH2, Rtrz = 4-R-l,2,4-triazole (X = various counterions or mixed counterions)...

Studies of the crystal structure of 3,7-dibromo-2,6-dimethyl-[l,2,3]triazolo[l,2-fe][l,2,3]triazole show that this dibromo derivative has a geometry consistent with its representation as a mesomeric betaine, havingN(l)—C, 1.37 A,C—C, 1.33 A, N(4) C, 1.40A,andN(4 N(8), 1.36 A <63G1571>. Similar results have been obtained also for rubidium salts of 2,6-dimethyl-1,2,3-triazolo[ 1,2-6][l,2,3]triazole-3,7-dicarboxylic acid and l,2,3-triazolo[l,2-fe][l,2,3]triazole-2,6-dicarboxylic acid <63G1556>. The dibenzo derivative of (53) has been shown by x-ray analysis to be planar <76AX(B)2518, 76AX(B)2614>. 

Condensation of 3-(2-thienyl)-4-amino-5-thiol-l,2,4-triazole (174) with 2-chloronicotinic acid (175) in refluxing ethanol in the presence of sodium acetate produced the sulfide (176), which was treated with phosphorus oxychloride to result in cyclization giving rise to the triazolo[3,4-fe]pyrido[3,2-/]-l,3,4-thiadiazepine (177) (45% yield). The triazole (174) also reacted with the a,jS-unsaturated ketones (178) to give the triazolo-l,3,4-thiadiazepines (179) (75% yield) (Scheme 32) <91SUL201>. 

Sanina NA, Rakova OA et al (2004) Structure of the neutral mononuclear dinitrosyl iron complex with l,2,4-triazole-3-thione[Fe(SC2H3N3)(SC2H2N3)(NO)2]-0.5 H2O. Mendeleev Commun 14 7-8... 

Various synthetic protocols were available for the preparation of 1,2,4-triazoles and derivatives thereof Efhcient synthesis of 3,4,5-tri-substituted 1,2,4-triazoles 171 was accompHshed from the reaction of guanidines 169 with 2,2,2-tri-chloroethylimidates 170 in PEG-400 (14TL177). 3,5-Diaryl-l,2,4-triazoles 173 were synthesized from a domino nucleophilic substitution/ oxidative cycfr-zation sequence from 2 equivalents of amidines 172 with copper catalyst, sodium bicarbonate as base, 1,10-phenanthroline as an additive, and K3[Fe(CN)6]/air as the oxidant (14T1635). Sulfur-substituted 1,2,4-triazoles... 

The IR spectra of the spin-transition complexes [Fe(L)3] , where L = IH-l,2,4-triazole and derivatives, showed characteristic shifts in vFeN modes between the high-spin and low-spin states. A resonance Raman band (180-250 cm" ) was ascribed to iron-ligand out-of-plane modes in mutant H93G myoglobin - its position is markedly dependent on the nature of the axial ligand. A normal-coordinate analysis shows that this band has vFe-L character, but also a significant contribution from iron-haem doming. ... 

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