Job/Unit: Z12322 /KAP1 Date: 21-09-12 10:34:49 Pages: 5

SHORT COMMUNICATION

DOI: 10.1002/zaac.201200322

N-Triazolylpropanamide – an Acrylamide-Derived Multifunctional Ligandfor the Construction of Supramolecular Hydrogen-Bonded Networks

Thomas Wagner,[a] Cristian G. Hrib,[a] Volker Lorenz,[a] Frank T. Edelmann,*[a]

Jianfeng Zhang,*[b] and Qiaohua Yi[b]

Keywords: N-Triazolylpropanamide; Acrylamide; Michael addition; Iron; Hydrogen bonds; Crystal structure

Abstract. The synthesis and single crystal X-ray structure of the multi-functional acrylamide-derived ligand N-triazolylpropanamide (1, =NTPA) are reported. The title compound was prepared in 72% yieldby Michael addition of 1,2,4-triazole and acrylamide in the presenceof Triton B (= trimethylbenzylammonium hydroxide) as catalyst.Treatment of 1 with FeCl3(H2O)6 in MeOH/MeCN led to reduction

Introduction

Currently there is considerable interest in the use of multi-functional ligands containing substituted pyrazole groups be-cause of their potential applications in catalysis and their abil-ity to form complexes that mimic structural and catalytic func-tions in metalloproteins.[1] As part of our continuing interestin the coordination chemistry of acrylamide[2] and acrylamide-based ligands we have earlier synthesized and characterized anacrylamide-derived pyrazole ligand, N-pyrazolylpropanamideand its complexes with various transition metals such as iron,cobalt, nickel, copper, and silver.[3,4] Thus, we reasoned thatthe corresponding N-triazolyl derivative would represent avaluable addition to this chemistry.

Prior to our work, there had been only one earlier paper inthe literature mentioning the title compound N-triazolylpropan-amide (1), and no coordination compounds of this potentiallymultifunctional ligand have ever been prepared. More than 20years ago, de la Cruz et al. reported the syntheses and spectro-scopic properties of a series of N-azolylpropanamides includ-ing N-triazolylpropanamide (1) obtained by Michael additionfrom acrylamide and the corresponding azoles.[5] Moreover,compound 1 has been mentioned in two patents as a potentialfungicide[6] or as a crosslinking agent for epoxy resin composi-tions.[7] We report here an improved synthesis of 1 as well as

* Prof. Dr. F. T. EdelmannFax: +49-391-6712933E-Mail: frank.edelmann@ovgu.de

* Prof. Dr. J. ZhangFax: +86-574-87609983E-Mail: zhangjianfeng1@nbu.edu.cn

[a] Chemisches InstitutOtto-von-Guericke-Universität Magdeburg39106 Magdeburg, Germany

[b] Faculty of Materials Science and Chemical EngineeringNingbo UniversityNingbo, Zhejiang 315211, P. R. China

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and formation of the iron(II) complex (NTPA)2FeCl2(MeOH)2 (2, yel-low prisms, 52% yield). Both 1 and 2 were structurally characterizedby X-ray diffraction. Surprisingly, the NTPA ligands in 2 are coordi-nated to iron in a monodentate fashion through a triazole ring nitrogenatom. In the crystal, both compounds form supramolecular hydrogen-bonded networks.

a first coordination compound with iron(II) dichloride. Bothcompounds have been structurally characterized by X-ray dif-fraction.

Results and Discussion

The originally reported Michael addition between acrylam-ide and various azoles employed pyridine/sodium methoxideas a basic catalyst.[5] We used instead the easier to handle tri-methylbenzylammonium hydroxide (= Triton B, 40 % in meth-anol). This improved method provided N-triazolylpropanamide(1) in high yield (72%) and in a straightforward manner(Scheme 1).

Scheme 1.

N-Triazolylpropanamide forms colorless, needle-like crys-tals (m.p. = 122–124 °C) which are soluble in common organicsolvents. The purity of the material was readily established byelemental analysis and its spectroscopic data (IR, 1H and 13CNMR). The IR spectrum of 1 shows characteristic bands of theamide group. Bands at 3298 cm–1 as well as 1694 cm–1 and1660 cm–1 can be assigned to N–H stretching vibration, theamide I absorption band (mainly due to the CO absorption ofthe amide group) and the ν(C=N) bands of the pyrazolegroups, respectively. The 1H NMR spectrum reveals four well-resolved signals and two weak broad singlets (7.51 and 6.89ppm, NH2) in the region of 0–9 ppm. The methylene groupsshow triplets at 2.66 ppm (β-CH2) and 4.37 ppm (α-CH2). Thetwo remaining signals at 7.51 ppm and 8.41 can be assignedto the two protons in the triazolyl ring. Signals at 34.9 (Cβ),

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T. Wagner, C. G. Hrib, V. Lorenz, F. T. Edelmann, J. Zhang, Q. YiSHORT COMMUNICATION45.2 (Cα), 144.4 (C=N), 138.58 (C=N), and 171.9 (C=O) ppmare observed in the 13C NMR spectrum.

The molecular structure of 1 was verified by single-crystalX-ray diffraction. Colorless single crystals of 1 were obtainedby slow cooling of a saturated solution in THF to room tem-perature. The compound crystallizes in the triclinic spacegroup P1̄. Table 1 summarizes the crystallographic data. Themolecular structure of 1 together with selected bond lengthsand angles are shown in Figure 1. The C=O and C–NH2 bondlengths of the amide group are 1.233(1) Å and 1.328(1) Å,respectively. The molecule contains a conjugated N-propyl-amide moiety which can adopt conformational changes cen-tered at the β-carbon atom suggesting that the bidentate ligandis flexible and can accommodate metals for coordination. TheC–N bond lengths in the triazolyl ring fall in the narrow rangeof 1.315(1)–1.350(1), whereas the N(1)–N(2) bond lengthwithin the ring is 1.355(1) Å. It has recently been pointed outthat primary carboxylic amides with their two hydrogen donorsand two hydrogen acceptors are unique supramolecular syn-thons.[8] Primary amides can form hydrogen bonds in two di-rections due to the presence of two hydrogen atoms connectedto each nitrogen atom. This is why primary amides reliablygenerate two-dimensional hydrogen-bonded networks in thesolid state. These differ significantly from related hydrogen-bonded networks such as carboxylic acid dimers or the one-dimensional polymeric chains formed by secondary amides.This has led to the design of various sophisticated supramolec-ular assemblies based on primary carboxylic amides. The fieldof crystal engineering has greatly benefitted from the use ofprimary amides, as the hydrogen-bonded networks stronglyfavor crystallization.[8] In view of these considerations it washardly surprising that in the crystalline state N-triazolylpropan-amide (1) also forms such a supramolecular hydrogen-bondednetwork. A view of the crystal packing and hydrogen-bondingis shown in Figure 2. The hydrogen-bonding pattern in thecrystal structure of 1 can be described by a combination of twosupramolecular synthons:[8] first a cyclic dimer utilizing a syn-oriented hydrogen atom (Hsyn) to form face-to-face N–H···Ohydrogen bonds, and then a chain structure resulting from N–H···N hydrogen-bonding between the anti-oriented hydrogenatom (Hanti) and an nitrogen atom of the triazolyl ring to formside-to side hydrogen bonds. The overall result is a two-dimen-sionally extended ladder-type network as shown in Figure 2.

For a first complexation test, the ligand 1 was treated withhydrated iron(III) trichloride in a mixture of methanol and ace-tonitrile according to Scheme 2. The resulting yellow productwas shown by X-ray diffraction (vide infra) to be the divalentiron complex (NTPA)2FeCl2(MeOH)2 (2). This is the first ex-ample of a reduction process induced by a ligand like 1 or N-pyrazolylpropanamide. However, it remains unclear why thisredox reaction takes place and what the oxidation product is.It can be assumed, however, that the reduction to the Fe2+ stateaccounts for the fairly low isolated yield of only 52%.

The new iron(II) complex 2 forms yellow crystals which aresoluble only in polar organic solvents such as methanol, eth-anol, or acetonitrile. The IR spectrum of 2 shows strong bandstypical for the amide functionality of the N-triazolylpropanam-

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Table 1. Crystallographic Data for 1 and 2.

1 2

empirical formula C5H8N4O C12H24Cl2FeN8O4

a /Å 4.7472(9) 10.5657(5)b /Å 7.9431(6) 7.2793(3)c /Å 9.8953(7) 13.7487(8)α /° 109.009(6) 90β /° 96.760(6) 109.173(4)γ /° 105.211(6) 90V /Å3 331.87(7) 998.77(9)Z 2 2formula weight 140.15 471.14space group P1̄ P21/nT /°C –100 –123λ /Å 0.71073 0.71073Dcalcd /g·cm–3 1.403 1.567μ /mm–1 0.104 1.058F(000) 148 488data / restraints / parameters 1785 / 0 / 123 2680 / 0 / 172goodness-of-fit on F2 1.044 1.250R(Fo or Fo

2) 0.0405 0.0238Rw(Fo or Fo

2) 0.0887 0.0845

Figure 1. ORTEP view of 1 with thermal ellipsoids at the 50% prob-ability level. Selected distances /Å and angles /°: O(1)–C(5) 1.233(1),N(1)–C(1) 1.327(1), N(1)–N(2) 1.355(1), N(1)–C(3) 1.459(1), N(2)–C(2) 1.315(1), N(3)–C(1) 1.319(1), N(3)–C(2) 1.350(1), N(4)–C(5)1.331(1), C(3)–C(4) 1.511(2), C(4)–C(5) 1.509(1), C(1)–N(1)–N(2)109.50(9), C(1)–N(1)–C(3) 129.58(9), N(2)–N(1)–C(3) 120.92(9),C(2)–N(2)–N(1) 102.26(8), C(1)–N(3)–C(2) 102.16(9), N(3)–C(1)–N(1) 110.88(9), N(2)–C(2)–N(3) 115.20(10), N(1)–C(3)–C(4)112.65(9), C(5)–C(4)–C(3) 114.53(9), O(1)–C(5)–N(4) 123.04(9),O(1)–C(5)–C(4) 122.03(9), N(4)–C(5)–C(4) 114.92(8).

Figure 2. Packing diagram of 1. Short contacts: N(4)–H(4NB)···O(1)#1 2.936(1), N(4)–H(4NA)···N(3)#2 2.991(1) (#1 –x, –y+1, –z+1 #2 x,y–1, z).

ide ligand. The C=O absorption appears as very strong bandat 1655 cm–1, while a band attributable to the N–H strectching

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N-Triazolylpropanamide – Ligand for the Construction of Supramolecular Networks

Scheme 2.

vibration is observed at 3413 cm–1. Yellow, prism-shaped sin-gle-crystals of 2 suitable for X-ray diffraction were obtainedby crystallization directly from the reaction mixture (cf. Exper-imental Section). The X-ray analysis revealed the presence ofthe mononuclear iron(II) complex (NTPA)2FeCl2(MeOH)2

with all three different ligands being pairwise coordinated intrans-positions. A surprising structural feature of the molecularstructure of 2 is the monodentate N-coordination of the poten-tially multifunctional N-triazolylpropanamide ligand throughthe triazolyl ring. This is quite in contrast to the previouslyreported iron(II) complex [(NPPA)2Fe(EtOH)2](ClO4)2 (NPPA= N-pyrazolylpropanamide),[4] which contains the closely re-lated N-pyrazolylpropanamide ligands in an O,N-chelatingfashion. A plausible explanation for the different coordinationmodes is the use of the poorly coordinating perchlorate ion in[(NPPA)2Fe(EtOH)2](ClO4)2 in contrast to the chloride ions in2 which remain coordinated and thereby prevent chelation ofthe N-triazolylpropanamide ligands. The coordination geome-try around the central Fe2+ ion in 2 is almost ideally octahedral(O(1)–Fe(1)–N(3) 89.37(4)°, O(1)–Fe(1)–Cl(1) 89.64(3)°,N(3)–Fe(1)–Cl(1) 90.07(3)°). The Fe–N(triazole) distance in 2is 2.187(1) Å, which is only slightly longer than the 2.137(2)reported for [(NPPA)2Fe(EtOH)2](ClO4)2.[4] While the molec-ular structure of 2 is simple and highly symmetrical (Figure 3),the crystal structure comprises an intricate three-dimensionalhydrogen-bonded network as shown in Figure 4. As in thecrystal structure of 1 we find again the association into chainsthrough cyclic dimers utilizing the syn-oriented hydrogen atom(Hsyn) of the amide functionality to form face-to-face N–H···Ohydrogen bonds. In addition, the OH groups of the methanolligands engage in O–H···N hydrogen-bonding interactions withthe triazole rings of neighboring molecules. Finally, the chainsare interconnected into a three-dimensional network though theof N–H···Cl hydrogen bonds between Hanti of the amide moie-ties and chloro ligands of adjacent molecules. A similar situa-tion has recently been found for the nickel(II) N-pyrazolylpro-panamide complex [(NPPA)2Ni(H2O)4]Cl2,[4] underliningagain the utility of these ligands for the construction of supra-molecular hydrogen-bonded networks.

In summarizing the results reported here, the multifunctionalacrylamide-derived ligand N-triazolylpropanamide (1, =NTPA) was prepared in good yield by Michael addition of1,2,4-triazole and acrylamide in the presence of Triton B ascatalyst. Treatment of 1 with FeCl3(H2O)6 in MeOH/MeCNlead to reduction and formation of the yellow iron(II) complex(NTPA)2FeCl2(MeOH)2 (2). Both 1 and 2 were structurallycharacterized by X-ray diffraction. Surprisingly, the NTPA li-

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Figure 3. ORTEP view of 2 with thermal ellipsoids at the 50% prob-ability level. Selected distances /Å and angles /°: Fe(1)–O(1) 2.157(1),Fe(1)–N(3) 2.187(1), Fe(1)–Cl(1) 2.4596(3), N(1)–C(2) 1.330(2),N(1)–N(2) 1.362(2), N(1)–C(3) 1.462(2), N(2)–C(1) 1.317(2), N(3)–C(2) 1.333(2), N(3)–C(1) 1.362(2), N(4)–C(5) 1.328(2), O(1)–C(6)1.425(2), O(2)–C(5) 1.236(2), C(3)–C(4) 1.515(2), C(4)–C(5)1.516(2), O(1)–Fe(1)–N(3) 89.37(4), O(1)–Fe(1)–Cl(1) 89.64(3),N(3)–Fe(1)–Cl(1) 90.07(3).

Figure 4. Packing diagram of 2. Short contacts: O(1)–H(1O)···N(2)#1 2.879(2), N(4)–H(4NY)···O(2)#2 2.867(2), N(4)–H(4NP)···Cl(1)#33.245(2) (#1 –x+1/2, y+1/2, –z+1/2 #2 –x+1, –y–1, –z #3 –x+1/2, y–1/2,–z+1/2).

gands in 2 are coordinated to iron in a monodentate fashionthrough a triazole ring nitrogen atom. The crystal structuresof both compounds comprise supramolecular hydrogen-bondednetworks, double chains in the case of 1 and a three-dimen-sional array in the case of 2. Future work will show if thetriazolyl-substituted ligand is as versatile in coordinationchemistry as N-pyrazolylpropanamide.[3,4]

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T. Wagner, C. G. Hrib, V. Lorenz, F. T. Edelmann, J. Zhang, Q. YiSHORT COMMUNICATION

Experimental Section

General Procedures

All starting materials used in this study were obtained from commer-cial suppliers and used as received. Microanalyses of the compoundswere performed using a Leco CHNS 923 apparatus. Melting pointswere determined with a Büchi B-450 digital melting point apparatus.IR spectra were recorded using KBr pellets on a Perkin Elmer FT-IRspectrometer system 2000 or ThermoNicolet Avatar 370 FT-IR be-tween 4000 cm–1 and 400 cm–1. The intensity data of 1 and 2 werecollected with a Stoe IPDS 2T diffractometer with Mo-Kα radiation.The data were collected with the Stoe XAREA[9] program using ω-scans. The structure was solved by direct methods (SHELXS-97) andrefined by full matrix least-squares methods on F2 using SHELXL-97.[10]

Syntheses

N-Triazolylpropanamide (1): A mixture of 1,2,4-triazole (5.00 g,74 mmol), acrylamide (5.00 g, 70 mmol) and Triton B (trimethylbenz-ylammoniumhydroxide solution 40% in methanol, 2 mL) was stirredat reflux temperature for 7 h. Upon cooling to room temperature acrystal cake formed, which was broken up by addition of a smallamount (ca. 10–20 mL) of diethyl ether. The product was isolated byfiltration, dried in vacuo, and recrystallized from a minimum amountof hot THF to give 7.20 g (72 %) of spectroscopically pure N-triazolyl-propanamide (1) (m.p. = 122–124 °C). Elemental Anal. Calcd forC5H8N4O (Mr = 140.14): C 42.85%; H 5.75%; N 39.98%. Found: C42.59%; H 5.61%; N 40.27%. IR (KBr, cm–1): 3298vs, 3123vs,2998m, 2967m, 2960m, 2941m, 2820m, 1759m, 1694vs, 1660(sh)s,1620(sh)m, 1530(sh)m, 1512vs, 1434vs, 1418s, 1399s, 1371m, 1345m,1336m, 1315s, 1294m, 1286m, 1272vs, 1257m, 1209m, 1143vs,1065m, 1010vs, 968s, 937m, 880s, 812m, 708m, 692m, 674s, 648s,630m, 549m, 508m. 1H NMR ([D6]DMSO, 20 °C, 400.13 MHz): 8.41(s, 1H, N–CH=N), 7.94 (s, 1H, N–CH=N), 7.51 (s, br, 1H, NH2), 6.97(s, br, 1H, NH2), 4.37 (t, 2H, N–CH2), 2.66 (t, 2H, CH2) ppm. 13CNMR ([D6]DMSO, 20 °C, 100.6 MHz): 171.9 (–CO–NH2), 151.5 (N–CH=N), 144.4 (N–CH=N), 45.2 (N–CH2), 34.9 (CH2) ppm.

(NTPA)2FeCl2(MeOH)2 (2): To a solution of 1 (2.75 g, 10.2 mmol)in acetonitrile (25 mL) was added a methanol solution (25 mL) ofiron(III) trichloride hexahydrate (2.75 g, 10.2 mmol). The mixture wasstirred at room temperature for 1 h and concentrated in vacuo to a totalvolume of ca. 10 mL. Crystallization at room temperature afforded(NTPA)2FeCl2(MeOH)2 (2) (2.50 g, 52%) in the form of yellow,prism-shaped crystals. Elemental Anal. Calcd. for C12H24Cl2FeN8O4

(Mr = 471.12): C 30.59%; H 5.13%, N 23.78%, Cl 15.05%, Fe11.85%, O 13.58 %. Found: C 30.22%; H 5.04%; N 24.11%. IR (KBr,

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cm–1): 3413vs, 3138vs, 1655vs, 1577(sh)s, 1531s, 1449m, 1284m,1209m, 1172w, 1126s, 997m, 939w, 825m, 641s.

Crystallographic data for the crystal structures reported in this papercan be obtained from the Cambridge Crystallographic Data Center, 12Union Road, Cambridge CB21EZ, UK (Fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/) by re-ferring to the CIF deposition codes CCDC-889114 (1) and CCDC-889115 (2).

Acknowledgment

This work was financially supported by the Otto-von-Guericke-Uni-versität Magdeburg.

References[1] a) R. Mukherjee, Coord. Chem. Rev. 2000, 203, 151; b) S. Pal,

A. K. Barik, S. Gupta, A. Hazra, S. K. Kar, S.-M. Peng, G.-H.Lee, R. J. Butcher, M. S. El Fallah, J. Ribas, Inorg. Chem. 2005,44, 3880; c) J. L. Shaw, T. B. Cardon, G. A. Lorigan, C. J. Ziegler,Eur. J. Inorg. Chem. 2004, 1254; d) G. Gracia-Anton, J. Pons, X.Solans, M. Font-Bardia, J. Ros, Eur. J. Inorg. Chem. 2003, 2992.

[2] a) K. B. Girma, V. Lorenz, S. Blaurock, F. T. Edelmann, Coord.Chem. Rev. 2005, 249, 1283; b) K. B. Girma, V. Lorenz, S. Blaur-ock, F. T. Edelmann, Z. Anorg. Allg. Chem. 2005, 631, 1419; c)K. B. Girma, V. Lorenz, S. Blaurock, F. T. Edelmann, Z. Anorg.Allg. Chem. 2005, 631, 1843; d) K. B. Girma, V. Lorenz, S. Blaur-ock, F. T. Edelmann, Z. Anorg. Allg. Chem. 2005, 631, 2763; e)K. B. Girma, V. Lorenz, S. Blaurock, F. T. Edelmann, Inorg.Chim. Acta 2006, 359, 364; f) K. B. Girma, V. Lorenz, S. Blaur-ock, F. T. Edelmann, Z. Anorg. Allg. Chem. 2006, 632, 1974.

[3] K. B. Girma, V. Lorenz, S. Blaurock, F. T. Edelmann, Z. Anorg.Allg. Chem. 2008, 634, 267.

[4] T. Wagner, C. G. Hrib, V. Lorenz, F. T. Edelmann, D. S. Amenta,C. J. Burnside, J. W. Gilje, Z. Anorg. Allg. Chem. 2012, 638, pub-lished online, DOI:10.1002/zaac.201200139.

[5] A. de la Cruz, J. Elguero, P. Goya, A. Martinez, J. Heterocycl.Chem. 1988, 25, 225.

[6] M. B. Gravestock, Eur. Pat. Appl. 1983, EP 69448 A1 19830112.[7] A. Kotone, M. Hoda, T. Hori, Jpn. Kokai Tokkyo Koho 1976, JP

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(XRED32 included in XAREA), Stoe, 2002.[10] a) G. M. Sheldrick, SHELXL-97, Program for Crystal Structure

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Received: July 10, 2012Published Online: �

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N-Triazolylpropanamide – Ligand for the Construction of Supramolecular Networks

T. Wagner, C. G. Hrib, V. Lorenz, F. T. Edelmann,*J. Zhang,* Q. Yi ................................................................ 1–5

N-Triazolylpropanamide – an Acrylamide-Derived Multifunc-tional Ligand for the Construction of Supramolecular Hydro-gen-Bonded Networks

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