摘要:
1972 1311Complexes of Thiazoles. Part 1V.l Acetamido-thiazoles as AmbidentateLigandsBy M. N. Hughes and K. J. Rutt, Department of Chemistry, Queen Elizabeth College, Campden Hill, LondonW8 7AHSome complexes of 2-acetamidothiazole and 2-acetamidobenzothiazole with Nil1 and Cu” have been preparedand three types of co-ordination behaviour distinguished on the basis of their i.r. spectra. The organic ligand donoratoms may be (a) carbonyl oxygen and thiazole nitrogen, ( b ) amide nitrogen and thiazole nitrogen, or (c) carbonyloxygen, amide nitrogen, and thiazole nitrogen. Types ( b ) and (c) are of interest as examples of co-ordination viaa non-deprotonated amide nitrogen atom.As part of our work on thiazoles as ligandsl we have RESULTSprepared the compounds 2-acetamidothiazole (acam) The complexes fall into three groups in terms of theand 2-acetamidobenzothiazole (acamb) and have ex- behaviour of the ligand as indicated by a study of theiramined their co-ordination behaviour.This was of i.r. spectra (Table 1). Details of electronic spectra,ComplexNi(acamb) ,C1,Ni(acamb) ,Br2Ni(acamb),I,Ni (acam) ,C12H20Ni (acam) ,(NO3) ,Cu (acamb) ,C1,Cu (acam) BrCu (acamb),(CIO,)Cu (acam) ,CI,Cu (acam) C1,Cu (acam) ,Br,Cu(acam)Br,Cu(acam),(ClO,),“i(acamb) 2(H,O) ,112“Warn) 2(H,O) 21 Br,Cu(acam)2(N03)2TABLE 1Far-infrared spectra (660-222 cm-1) and v(C=O) frequencies (cm-1)* v(c=O) Ligand modes v(M-0) v(M-N)1659s 429s, 412sh 352s, 315sh1675m 429s, 412sh 352s, 314m1658m 430m 350s1661m 429m 351s1660m 355s, 319m 392m 269s, 233s1660m 365s, 317m 394m1668ni 355s, 321m 392m 260m, 226m1710m 429m1708m 433m1653m 427s, 416sh 361m, 318m1714m 320w 288s, 247m1658ni 370m, 311w 405m 278m, 246m1648m 368s, 318m 408s 276s, 2451111652m 370m, 31Ow 405m 280m1663m 374s, 319w 412m 282s1640m 377% 320m 410s 286s, 249m* v(C=O) in acamb = 1704 cm-l, acam = 1708 cm-l.0 thersv(Ni-C1) ca.230brv(Ni-OH,) 463mv(Ni-OH,) 463m292s, 282s278m, 267m279m, 245mv(Cu41) 331sv(CuBr) 260s309mTABLE 2Magnetic moments, conductances, and electronic spectraComplex (Q-l) Ileu (B.M.) Absorption maxima (kK)Ni (acamb) ,C1, 18.7 * 3-27 25.8s, 24.2sh, 14.5m, ca. 13-0sh, ca. 9.8sh, 8.0mNi(acamb),Br, 14-2 * 3-19 25.6s, 23.6sh, 14.4m, ca.12*8sh, ca. 9.3w, 7.5mNi(acamb),I, 21.6 * 3-06 25.5s, 19*8sh, 14.5m, ca. 12.8sh, 10.3w, 7.3mNi (acainb) ,I2,2H,O 139 * ca. 26-6sh, 15-5m, ca. 14-0sh1 9.6mNi(acam) ,Cl,,H,O 74- 1 3-16 ca. 26.5sh, 16.5m, 10-5m, ca. 8.9shNi (acam) ,Br2,2H,0 75.8 3.08 16-6m, 10.7m, ca. 9.4shNi(acam) ,(NO,), 76.3 2.87 ca. 26.5sh, 16.2m, 10-4m, ca. 8.lshCu (acamb),Cl, 11.1 * 1.86 1 3-0s,brCu(acamb)Br 47-6 * DiamagneticCu(acamb),(C10,), 14-8 * 1.83Cu (acam) ,C1, 22.3 1.90 ca. 24.0sh, 14.6mCu (acam) C1, 16.3 1.84 24*ls, br, 9.4s,brCu (acam),Br, 46.9 1-92 ca. 26-0sh, 14.7m, ca. 10.8shCu (acam) Br, 14-4 1-87 18-9~, 16-7~, 9-5sc u @cam) ,(NO,) 2 72-3 1.94 15-2sCu (acam) ,(C10,) , 76.4 1.91 16-9sConductances in Me,SO (1 : 1 = 40 R-l, 1 : 2 = 80 a-l) or nitromethane * (1 : 1 = 80 R-l, 1 : 2 = 130 a-1).interest partly because of, their close similarity to theanti-parasitic compound Aminotrozal (2-acetamido-5- in Table 2.nitrothiazole). We now report a study of the complexesof these ligands with nickel(I1) and copper(11) halides,nitrates, and perchlorates.A number of different typesof ligand behaviour have been observed.magnetic moments, and molar conductances are givenThe co-ordination behaviour of the ligands may berelated to that of amides and peptides, although onefamiliar form of co-ordination in peptides, involvingdeprotonated amide nitrogen atoms is clearly notPart 111, M. N. Hughes and K. J. Rutt, J. Chem. Soc. ( A ) , E. F. Elslager, Reviews in Ann. Rep. Medicin. Chem., 1965,1970, 3015.19661312 J.C.S. Daltoninvolved in our complexes. We must, however, considerthe possibility that the ligand is co-ordinated in the enolform.The free ligand exists in the keto-form [vcl=o at 1708cm-l for acam and at 1704 cm-l for acamb, v(N-H) at3240 and 3237 cm-l respectively]. On complexformation the spectrum is largely unaffected apartfrom shifts in certain bands and intensity changes whichcan be rationalised in terns of co-ordination. Thesechanges occur in regions associated with the v H andvN-H bands of the free ligand.We include here the complexes of acamand acainb with NiII halides and copper bromide and acomplex of acam with copper chloride, of stoicheiometryNi(acamb),X, (X = C1, Br, or I), Ni(acamb),I,,2H20,Ni(acam) ,Cl,, H20, Ni( acam) ,Br,, H20, Cu(acam) 2Br2, andCu(acam)X, (X = C1 or Br).The magnetic momentsand electronic spectra of the 1 : 2 complexes are character-istic of distorted octahedral structures. Conductancedata suggest that the aquo-complexes in nitromethaneor dimethyl sulphoxide solution have unco-ordinatedanions, while in the solid state the i.r. spectra indicatethat the water molecules are probably co-ordinated.The conductance of Cu(acam),Br, is fairly high but weattribute this to dissociation since the solution spectrumindicates considerable decomposition of the complex.The remainder of the complexes were non-electrolytesin nitromethane or dimethyl sulphoxide.The electronic spectrum of Cu(acam)Cl, is consistentwith a tetrahedral geometry, whereas the correspondingbromo-complex has a more complicated spectrum whichwe are unable to account for by any single structure.This spectrum shows strong bands at 18.9, 16.7, and9.5 k K which might be due to a mixture of planar andtetrahedral species; however, adjustments to theconditions of preparation of Cu(acam)Br, did not alterthe intensities of the bands in its electronic spectrum.The f ar4.r.spectra of the chloro- and bromo-complexeseach show only one metal-halogen stretching frequency(331 cm-l in chloro, 260 cm-l in bromo) instead of thedoublet expected for a tetrahedral species and multipletfor a mixture.In the i.r. spectra of all the complexes in this groupthe v(C=O) mode of the ligand was shifted ca. 30 cm-l tolower frequencies, suggesting that co-ordination occursvia the carbonyl oxygen.We discount the possibilitythat this band is the ' v(C=N) ' band of the enol form asthere is no change in the vX-H region. The complexes allshow bands at ca. 350 cm-l (acamb) or ca. 400 cm-l(acam) in their €ar-i.r. spectra which we assign4 asv(M-0) (carbonyl). The diaquo-complexes have anadditional band in their far4.r. spectra at 463 cm-l forwhich a tentative assignment of v(Ni-OH2) is made.In the case of acam Complexes, bands were observed atca. 260 and 230 cm-l which are probably1 v(M-N)Type a.8 E. W. Randall, C. M. Silcox Yoder, and J. J. Zuckerman,4 J . Fujita, A. E. Martell, and K. Nakamoto, J . Chem. Phys.,Inorg. Chem., 1966, 5, 2240.1962, 36, 324.(thiazole) modes, the corresponding bands for acambcomplexes being expected6 below the limit of ourinstrument (222 cm-l).We conclude that the acet-amido-thiazoles act as bjdentate ligands, chelating viathe carbonyl oxygen and thiazole nitrogen atoms.There is no evidence for co-ordination of the thiazolesulphur atom in these complexes and in other cases1thiazoles have been found to co-ordinate preferentiallyvia the nitrogen atom.Attempts were made to dehydrate Ni(acam),Cl,,H,Oand Ni(acam),Br2,2H,0 by heating them in vacuo,whereupon it was found that the compounds changedcolour from blue to green. However neither consistentweight losses were obtained nor reproducible analysesfor the products. The analytical figures suggest thatthe effect of heating is more complicated than theelimination of water.Another compound which we include here isCu(acamb)Br, which is rather different from the others.We were unable to prepare consistently a pure com-pound from the CuBr,-acamb system and obtained awhite product analysing only approximately asCu(acamb)Br.This diamagnetic species shows noabsorptions in its electronic spectrum between 27-5 k Kand appears to contain CuI.This reduction takes place in the presence of an excessof acamb, but we have not isolated the oxidised species.The v(C=O) mode in the i.r. spectrum of this complex isnot shifted to lower frequency, and no ~(CU-0) modescould be identified in the far4.r. region. It appears thatthe carbonyl oxygen is not co-ordinated. Since CuI isfairly ' soft ' it is possible that it complexes with thethiazole sulphur atom in this case.Cupric chloride with acetone solutions ofacamb gave the compound Cu(acarnb),Cl,,acetone.Theacetone is readily removed by heating to 100" for a fewminutes and the properties of the desolvated complexare very similar to the original compound. The ligandacam gave the compound Cu(acam),Cl, with cupricchloride. Both of these complexes are non-electrolytesin nitromethane or Me,SO. Their electronic spectra arevery similar and support their formulation as octahedralCuII complexes. These Complexes differ from theothers in that the v(C=O) mode in the i.r. spectrum is notshifted down from the free ligand, but by ca. 5 c.m-l tohigher frequencies. This strongly suggests that thecarbonyl oxygen is not co-ordinated, corroborativeevidence being provided by the far4.r.spectra whichshow no bands assignable as ~(CU-0) modes. Again thei.r. spectra eliminate the possibility of the ligand beingin the enol form. We have assigned v(Cu-N) (thiazole)at 288 cm-1 in the far4.r. spectrum of Cu(acam),Cl,.Another feature of the i.r. spectra is the ca. 10-foldenhanced intensity of the v(N-H) mode at 3240 cm-lwhich implicates the amide nitrogen in co-ordination.We suggest that the structures involve the organic ligandType b.G. Blyholder and S. Vergez, J . Phys. Chem., 1963, 61, 2149.E. J. Duff, M. N. Hughes, and K. J. Rutt, J . Chem. SOC. ( A ) ,1969, 21011972 1313bridging Cu atoms via thiazole and amide nitrogenatoms, with chloride ions in axial positions.The metal complexes involving oxy-anionsappear to be structurally similar.The compoundsprepared were Ni(acam),(NO,),, Cu(acam),X, (X =NO, or C10,) and Cu(acamb),(C104),. Their electronicspectra and magnetic moments are consistent with theirformulation as octahedral complexes. The oxy-anionsare not co-ordinated, as shown by i.r. and conductancedata. The i.r. and far4.r. spectra of the compoundsshow that the carbonyl oxygen of the ligand is co-ordinated, while bands assignable as v(M-N) (thiazole)are observed for acam complexes. In addition howeverthe ligand v(N-H) band at 3240 cm-l shows a muchgreater intensity in the spectra of the complexes. Againwe suggest that its enhanced intensity is due to co-ordination of the amide nitrogen atom.The resultingstructure is then one in which the ligand is chelatingvia carbonyl oxygen and thiazole nitrogen, with theamide nitrogen atom linking the unit to an adjacentmetal atom. The i.r. evidence in this case is not soclear cut, but in view of the way in which it fits into thepattern shown by type (a) and (b) complexes it isprobable that our assignments axe correct.Type c.DISCUSSIONThe complexes appear to fall into three well-definedcategories. The first group has the intuitively expectedstructure where the ligand chelates via the thiazolenitrogen and carbonyl oxygen to form a six-memberedring. Those complexes having oxy-anions are ionic andhave terdentate ligands, the third donor atom being theamide nitrogen.Thus it seems that the amide nitrogenis a better donor than the oxy-anions, but poorer thanwater or halide. The cupric chloride complexes are ofinterest ; there is no ready explanation of why the amidenitrogen appears to co-ordinate in preference to theoxygen atom and the stable chelate ring is not formed.There have been a number of studies on complexes ofpeptides, amides, and substituted amides with a rangeof metal ions. In all cases where crystal structures havebeen determined the amide nitrogen is co-ordinatedonly if deprotonated, while many other papers 8 citeinstances in which a deprotonated amide nitrogen isco-ordinated. In this system the amide nitrogen atomapparently co-ordinates quite readily without deproton-ation and in two cases does so at the expense of thecarbonyl oxygen.EXPERIMENTALPhysical measurements were made as described previ-Preparations.-(Calculated C, H, and N analyses are shownin parentheses after the analytical figures for each complex.)2-Acetamidothiazole was prepared by warming 2-amino-thiazole (Koch-Light) with an excess of acetic anhydrideand pouring the mixture into water.The solid formed wasfiltered off, washed well with water, and then recrystallisedously.1twice from acetone and dried in VUGUO, m.p. 203" (lit. 203")[Found: C, 42.4 (42-3); H, 4.43 (4-23); N, 19.7% (19-7)].2-Acetamidobenzothiazole was prepared as above from2-aminobenzothiazole; it had m.p. 186" (lit., 186") [Found:Ni(acamb),X, (X = C1 or Br) and Ni(acamb)21,,2H,0.-A solution of the appropriate hydrated nickel salt (5 mmol)in the minimum volume of ethanol (acetone for NiI,) wasadded to an acetone solution of acamb (10 mmol); themixture was warmed and stirred for 1 h.The green solidswhich deposited were filtered off and washed with acetoneand light petroleum. Ni(acamb),Cl, [Found : C, 42.0;(42.0); H, 3-2 (3.1); N, 10.5% (10.9)], Ni(acamb),Br,[Found: C, 35.6 (35.8); H, 2.7 (2.65); N, 9.0% (9-28)],Ni(acamb),I2,2H,O [Found: C, 29.3 (29-5) ; H, 2.3 (2.2) ;N, 7.6% (7-65)].Ni(acamb) ,I,.-This compound was prepared as aboveexcept that the mixture was refluxed vigorously for 1 h[Found: C, 31.1 (31.0); H, 2.3 (2-3); N, 8.03% (8.05)].Ni(acam) ,C12,H20, Ni(acam) 2Br,, 2H,O, and Ni(acam),-(NO,),.-These compounds were prepared by a similarmethod to that for Ni(acamb),Cl,. Ni(acam),Cl,,H,O[Found: C, 27.8 (27.8); H, 3.3 (3.25); N, l%8Y0 (12-9)],Ni(acam),Br,,2H20 [Found: C, 22.6 (22-3) ; H, 3-3 (2.95) ;N, 10.3% (10-4)], Ni(acam),(NO,), [Found: C, 25.4 (25.7) ;H, 2.70 (2.55); N, 17.6% (18.0)].Cu (acamb) ,Cl,,acetone, Cu(acamb)Br, Cu(acamb),(ClOJ,,Cu(acam),X, (X = C1, Br, NO,, or C104).-A minimumvolume solution of the appropriate hydrated metal salt(5 mmol) in ethanol was added to an acetone solution of theligand (10 mmol) and the mixture was stirred for Q h.Theprecipitates formed were filtered off and washed withacetone and light petroleum. Cu(acamb),C1,,acetone[Found: C, 43-3 (43.7); H, 3-6 (3.85); N, 10.21% (9-7)],Cu(acamb)Br [Found: C, 32.1 (32.2); H, 2.45 (2.4); N,8.4% (8.35)], Cu(acamb),(C10,), [Found: C, 33.2 (33.8) ;H, 2.55 (2-5); N, 8.7% (8.7)], Cu(acam),Cl, [Found: C,28.7 (28.7) ; H, 2-5 (2.85) ; N, 13.4% (13.4)], Cu(acam),Br,[Found: C, 23.8 (23.6); H, 2.55 (2.35); N, 11.0% (11-0)],Cu(acam),(NO,), [Found: C, 25-5 (25.5); H, 2.55 (2.55);N, 17.6% (17.8) 3, Cu(acam),(ClO,), [Found : C, 22-3 (22.0) ;Cu (acamb) ,Cl,.-The acetone adduct, prepared as above,was heated at 100" for + h [Found: C, 41.5 (41-6); H, 3-0(3.1); N, 10.6% (10-S)].Cu(acam)Cl,.-An acetone solution of acam (5 mmol) wasadded to a solution of the metal salt (50 mmol) in ethanol(minimum).The mixture was refluxed for Q 11, cooled, andfiltered. The product was washed with ethanol and lightpetroleum [Found: C, 21.7 (21.7); H, 2.25 (2.25); N,Cu(acam)Br,.-A solution of CuBr, (5 mmol) in ethanolwas added to an acetone solution of the ligand and thesuspension refluxed for 1 h. The product was filtered offand washed with ethanol and light petroleum [Found: C,C, 56.1 (56.2); H, 4.33 (4.19) ; N, 14.6% (14.6)].H, 2-35 (2.2); N, 10.2% (lO*Z)].10.0% (10.1).16.5 (16.4); H, 1.6 (1.35); N, 7.55% (7.66)].[1/1579 Received, 18th September, 19711H. C . Freeman, Adv. Protein Chem., 1968, 257.8 E.g. H. A. 0. Hill and K. A. Raspin, J . Chem. SOC. ( A ) ,1968, 3036; R. B. Martin, M. Chamberlin, and J. T. Edsall,J . Amer. Chem. SOC., 1960,82,496; M. F. Kim and A. E. Martell,ibid., 1966, 89, 914; W. L. Koltun, M. Fried, and F. R. N. Gurd,ibid., 1960, 82, 233
ISSN:1477-9226
DOI:10.1039/DT9720001311
出版商:RSC
年代:1972
数据来源: RSC