摘要:
1972 24514N Nuclear Magnetic Resonance of Covalent AzidesBy W. Beck and W. Becker, lnstitut fur Anorganische Chemie der Universitat Munchen, 8000 Munchen 2,K. F. Chew, W. Derbyshire, N. Logan,' D. M. Revitt, and D. B. Sowerby, Departments of Chemistry andMeiserstrasse 1, W. GermanyPhysics, University of Nottingham, University Park, Nottingham NG7 2RD14N Chemical shifts are reported for hydrazoic acid, certain organic and organoarsenic azides, and a number ofmetal azido-complexes. The shifts are related where possible to the electronic characteristics of the atom or groupto which the azide is covalently attached and to the mode of attachment.No spin-spin coupling effects are observed but the shifts provide some evidence for molecular association orazide exchange in the compounds Me2AsN, and Et,AsN,.The covalent character of the metal-azide bond i sdemonstrated by the appearance of three distinct 14N n.m.r. signals for each of the azido-complexes studied.THE linear azide ion, N3-, in aqueous solution gives riseto two 14N resonances with integrated intensities of1 : 2 at 128 and 277 p.p.m. upfield from aqueous nitrateion as standard.l? These resonances are attributableto the differing electronic arrangements at the centralatom and the two outer equivalent atoms respectively.Spin-spin splitting is not observed, presumably as aresult of the large quadrupole moment of 14N. It hasbeen estimated, however, that the 14N-14N couplingconstant in the azide ion must be less than 30 Hz.,Correspondingly, covalent e.g.organic azides, RN,,are expected to furnish a distinct 14N signal from eachof the non-equivalent nitrogen sites in the structure (1)and three well-resolved resonances are indeed found formethyl and ethyl azides (Table). Again, however,no spin-spin splitting was observed. In the work re-ported here the 14N n.m.r. study of covalent azides hasbeen extended to include hydrazoic acid and a furthergroup of organic azides as well as certain organo-arsenic azides and metal azido-complexes. Chemicalshifts for these compounds are recorded in the Tableand assignment of the individual resonances to N,,Nb, and N, is made on the basis of the arguments givenby Witanowski.4 These will be summarised brieflyhere. The signal at ca. 130-140 p.p.m.is assignedto the central nitrogen atom (Nb) since the shift isclosely similar to that of the central atom of the azideion. One of the other two signals is at higher field(ca. 300 p.p.m.) and shows a downfield shift from methylto ethyl azide. Organic isocyanates 4 9 5 and isothio-cyanates show a corresponding value with the samedependence on R, indicating that it is the resonanceof the nitrogen atom adjacent to the alkyl group (NJ.The remaining signal at ca. 170 p.p.m. is thus assignedto the terminal nitrogen atom (NJ.Hydrazoic Acid, HN,.-A dilute solution of hydrazoicacid in diethyl ether gave the expected three-line14N spectrum, the resonance positions correspondingclosely to those in methyl and ethyl azides (Table).In contrast to the situation in HNC0,5 no splitting ofT.Kanda, Y. Saito, and K. Kawamura, Bull. Chem. SOC.Japan, 1962, 35, 172.R. A. Forman, J . Chem. Phys., 1963, 89, 2393.the N, signal into a doublet as a result of l4N--lH coup-ling was observed for HN,. A solution of HN, in diethylether containing some water shows two resonances only,the high-field signal being of relative intensity 2 posi-tioned at the mean value of the bonded and terminalshifts of the acid in anhydrous ether. The evidentequivalence of the outer nitrogens of the azide groupin this case is presumably achieved via proton exchangewith water molecules. An acidified aqueous sampleof the sodium salt also shows only two resonances.The positions of the resonances obtained from in-creasingly acidified (H,S04) aqueous solutions ofsodium azide indicate that here, the line of intensity 2to high field of the practically immobile central atomresonance is an exchange peak intermediate betweenthe positions of the terminal azide ion resonance and themean of the terminal and bonded resonances of thehydrazoic acid molecule.When an excess of strong acidis present, no azide ion remains in the solution and thefinal resonance position again corresponds to the meanof the two outer nitrogen shifts in the acid.Organic Axides.-Predictably, in the organic speciesRN,, the N, chemical shift is most markedly affectedby the nature of R. As found for RNCO and RNCS,there is a correlation between the chemical shift andthe electronegativity of the substituent R, i.e. a shiftto lower field is observed with decreasing electronega-tivity of R4.Of the aryl azides studied, PhN, showsthe lowest field N, resonance. Higher field N, shiftsin the other three aryl azides examined are attributableto the electron-withdrawing effects of -CO-, -SO,-and -NO, groups respectively. The signals arisingfrom Nb and N, in organic azides show no similardependence on the nature of the attached organicgroup which is separated from these atoms by two orthree bonds.Organoarsenic (111) hides.-Each of the disubstitutedazidoarsines listed in the Table gave rise to the clearlydefined and relatively sharp resonance line at ca. 130p.p.m. (attributable to Nb) which is characteristic ofall 14N n.m.r.spectra of azides, examined to date.The resonances arising from N, and N, are almost3 D. Herbison-Evans and R. E. Richards, Mol. Phys., 1964,4 M. Witanowski, J . Amer. Chem. SOC., 1968, 90, 5683.5 K. F. Chew, W. Derbyshire, N. Logan, A. H. Norbury, and7, 515.A. I. P. Sinha, Chem. Comm., 1970, 1708J.C.S. Daltoninvariably broader, particularly that due to N,, andneither could be observed for certain of the azido-arsines, e.g. Ph(Et)AsN,, either in the pure liquid formor when diluted with carbon tetrachloride. In the di-phenyl, chlorophenyl, and bromophenyl derivatives,resonances assignable to Nb and N, were observed, butthe N, resonance was presumed to be so broad as to beis achieved in some fashion. This could conceivablyarise from association of molecules by azide bridgingof arsenic atoms as shown in (11).However, in order to explain the occurrence of asingle resonance for N, and N, it would be necessary toassume either that all As-N bonds in such a system areequally strong, or that easy exchange of N, groups14N Chemical shifts of covalent azides *WO3-)f \ Coinpound Na Nb Nc Solvent Ref.to prepn.Na+N,- 277 t (55) 128 (22) 277 t H2ONa+N,- 277 t 129 (23) 277 t H W 4 aHN,3 245 -+ 245HN, 240 t (100) 129 (30) 240 t E t,O-H,O b300 (100) 129 (24) 165 (100) Et,O bMeN, 320 (101) 128 (17) 170 (19) MeNO, cEtN, $ 305 (122) 129 (22) 167 (28) MeNO, c$-MeC,H,SO,N, 304 (410) 152 (260) 209 (120) Liquid cMe, AsN, 253 t (80) 132 (37) 253 t Liquid dEt,AsN, 251 t (85) 133 (40) 251 7 Liquid dEt,AsN, 130 (23) CC14Ph, AsN, 134 (94) Liquid dPh,AsN, 132 (37) 188 (75) CCI,Ph( Et) AsN, 134 (100) Liquid dPh(Et) AsN, 131 (30) CC14Ph(Br)AsN, 134 (87) 170 (200) Liquid d293 (800) 143 (90) 225 (90) CH,C12 e(Ph4As) 2Sn(N3)6 200 (185) CH,CI, 280 (328) 143 (185) eCH2C1, (Ph,As)Au(N,), 310 (410) 140 (55) 183 (127) e336 (180) 140 (75) 248 (75) CH,CI,334 (246) 143 (110) 225 (125) CH,Cl, e345 (180) 130 (110) 237 (250) CH,Cl, e230 (324) CH,C12 (Ph4As) 2Pd2(N3)6 355 (218) 135 (145) eg cis-(Bu,P),Pt(Ns), 326 (220) 135 (145) 226 (1 10) CH,C12g 230 (360) CH,Cl, ~is-(PhBu,P),Pt(Ns) 2 344 (180) 130 (290) CI2g cis-(Ph,B~P)~Pt(N3)2 365 (73) 135 (220) 230 (220)cis-( Ph,P) 2Pt(N3) , 351 (110) 131 (180) 225 (250) CH,C1, e140 (110) 230 (75) CH,C1, 363 (145) e374 (218)PhN, 286 (1200) 135 (180) 194 (55) C6H6 cPhCON, 322 (430) 140 (300) 237 (73) C6HL3 Cp-N0!2C6H4N3 310 (270) 139 (75) 211 (45) 'eH6 cPh (CI) AsN, 134 (43) 170 (86) Liquid d(Ph4As)2Pb(N3)6(Ph4As) Au(N3)2 e(Ph4As) 2Pd(N3)4(Ph4As) 2Pt(N3)4Ph,PAuN, 315 (330) 132 (110) 229 (290) CH,Cl2 f134 (145) 255 (320) CH,C12 f(ph3p) *pd2!N3) 2(BF4) 2 365 (110) 129 (40) 192 (92) CH,CI2 f(Ph3P)2Pd(N3)2(ph3p) 2pd2(N3) 4* Line widths (Hz) at half peak height in parentheses.4 Solution prepared by careful addition of conc.H2S04 to a cooled aqueous solution of NaN,.t Resonance of intensity 2 relative to the Nt, signal. Data fromref. 4.G. Brauer, ' Handbook ofPreparative Inorganic Chemistry,' vol. I, 1963, p.472. c C. Grundmann in Houben-Weyl: Methoden der organischen Chemie,Bd. X/3, p. 777, Thieme, Stuttgart, 1965. 6 Ref. 8. f W. P. Fehlhammer, W. Beck, and P. Pollmann, Chem. Ber.,1969,102, 3903; W. Beck, P. Kreutzer, and K. v. Werner, Chem. Ber., 1971,104, 528; W. Beck, W. P. Fehlhammer, P. Pollmann,and R. S. Tobias, Inorg. Chim. Acta, 1968, 2, 467.d Ref. 6.I P. Kreutzer, Dissertation, Miinchen, 1971.indistinguishable from the noise level. The failure toobserve the three possible resonances in the abovecompounds may be attributed to viscosity broadeningof signals from the pure liquids and insufficient intensityfrom solutions in carbon tetrachloride. In the caseof the dimethyl and diethyl compounds however adifferent phenomenon was encountered.When runas pure liquids, two resonances were again observed,but the high-field signal had twice the intensity of theNb line and was situated [8(NO,-) ca. 250 p.p.m.1approximately at the mean position of the N, and N,resonances observed in RN, compounds (see Table).This implies that environmental equivalence of bondedand terminal nitrogen atoms in Me,AsN, and Et,AsN,D. M. Revitt and D. B. Sowerby, Inorg. Nuclear Chem.Letters, 1969, 5, 459.between R,As moieties can occur. Two related ob-servations may be cited in support of these proposals.First, the significantly higher boiling point of Me,AsN,/N-N-: /N-N-Nt \ R As AsR, R,As# ' 7 ;9N-N-N(82-84 "C at 125 mmHg) compared to Me,AsCl (57-59 "C at 125 mmHg) may be a reflection of associationin the liquid state.Secondly, the organoarsenic azidesstudied here were prepared as possible precursors ofAs-N ring compounds via thermal decomposition ,1972 247e.g. the first example of a simple arsenic(v)-nitrogenring compound (Ph,AsN), had been previously obtainedfrom the thermal decomposition of Ph,AsN,.' How-ever the thermal decomposition of Me,AsN, and Et,AsN,gave only nitrogen-free products, indicating thatcleavage of the As-N bond occurs more readily in thesemolecules as would be necessary to facilitate N, ex-change between R,As groups. The observation ofthe N, resonance a t ca. 170 p.p.m. in Ph,AsN,, Ph(C1)-AsN,, and Ph(Br)AsN, can be rationalised in terms ofthe greater steric hindrance of arsenic atoms by phenylor substituted phenyl groups, resulting in a diminishedtendency towards molecular association or exchangeof N, groups.In an attempt to ascertain whether association orexchange was still indicated in the presence of a solvent,spectra of Et,AsN, were also recorded in CCI, solution.Unfortunately, the attendant dilution resulted in theobservance of only the single, sharp Nb resonance.Axido-complexes of Metals.-Each of the metal azido-complexes displays the three 14N resonances expectedfor co-ordinated azide ligands (see Table). The observedchemical shifts indicate that the bonding is very similarto that in the organic azides.The covalent characterof metal azide bonds in such complexes has also beenestablished by vibrational and electronic spectro-s c ~ p y , ~ and X-ray structural determinations of a numberof azido-complexes 9-1, revealed significantly differentN-N bond distances within each azide ligand.Incommon with the organic azides and other complexeswhich have been studied by 14N n.m.r.5J3-15 each ofthe azide complexes listed in the Table shows a chemicalshift for the bonded nitrogen (N,) atom to high fieldof that observed for the free ligand. These ' co-ordination shifts' for the N, atom increase for theanionic azide complexes in the following order of themetal oxidation state involved: PbIV < SnIV < AuIII< AuI - PdII < PtII. This order corresponds closelyto increasing ' class (b) ' behaviour l6 (' softness ' 17)along this series.In the complexes Pd2(N,),2- and (Ph,P),Pd,(N,),which contain both terminal and bridging azide ligandsonly one N, signal could be observed.Also the N, co-ordination shift of (Ph,P),Pd(N,),2+ which possessesonly azide bridges is close to that of the terminal azideW. T. Reichle, Tetrahedrou Letters, 1962, 61. * W. Beck, W. P. Fehlhammer, P. Pollmann, E. Schuierer, andand K. Feldl, Chem. Ber., 1967, 100, 2335; H. Schmidtke andG. Garthoff, J . Amer. Chem. SOC., 1967, 89, 1317.G. J. Palenik, Acta Cryst., 1964, 17, 360.lo I. Agrell, Acta Chem. Scand., 1966, 20, 1281.l1 2. Dori, Chem. Comm., 1968, 714.l2 W. P. Fehlhammer and L. F. Dahl, J . Amer. Chem. SOC., inthe press.groups in (Ph,P),Pd(N,),. Actually a recent X-raystructural determination l2 of (N,),Pd(N,),Pd(N,),2-showed a surprising similarity of the N-N distancesand Pd-N, angles in both terminal and bridging N,ligands.The azide bridges in these complexes provedto be of N-diazonium type (111) 12*18; obviously attach-ment of a second metal to the lone pair of the Na atomdoes not significantly alter the bonding within the azidegroup-The Nb resonances change very little from the valuein the free azide ion and are remarkably constant in allcovalent azides, indicating high electronic mobility inthe x-bonded structure of the azide group. Electronwithdrawal via the bonded atom is compensated by amovement of electrons from the terminal atom regiontowards the central nitrogen. The terminal N, shows adownfield shift from the value in free azide ion as isusually observed for linear triatomic nitrogen-containingligands which are not directly bonded via the nitrogento an organic group or a metal, e.g.in ROCN 5915 andMSCN.13EXPERIMENTALReference to preparative methods for the compoundsstudied here is made in the Table. Spectra were recordedat ca. 30 "C on a Varian HA 100 n.m.r. spectrometeroperating at 7.226 MHz using standard 5 mm sampletubes (8 mm sample tubes for the metal azido-complexes)and concentrated (preferably saturated) solutions or pureliquid samples due to the low sensitivity of 14N to n.m.r.detection. Chemical shifts were measured by the sample-substitution method relative to NO,' ion in a saturatedaqueous solution of NaNO, or NH,NO,.We thank the S.R.C. for the award of studentships (toK. F. C. and D. M. R.) and the Deutsche Forschungsgemeinschaft and Fonds der chemischen Industrie forfinancial support. We are grateful to Mr. M. A. Healyfor experimental assistance.[1/1069 Received, June 28th, 19711I3 0. W. Howarth, R. E. Richards, and L. 31. Venanzi, J .l4 R. Bramley, B. N. Figgis, and R. S. Nyholm, J . Chem. SOC.I5 W. Becker and W. Beck, 2. Naturforsch., 1970, 25b, 101.l6 S. Ahrland, J. Chatt, and N. R. Davies, Quart. Rev., 1958,l8 R. Mason, G. A. Rusholme, W. Beck, H. Engelmann, K.Joos, B. Lindenberg, and H. S. Smedal, Chem. Comm., 1971,496.Chem. Soc., 1964, 3335.( A ) , 1967, 861.12, 265.R. G. Pearson, J . Chem. Educ., 1968, 45, 581, 643
ISSN:1477-9226
DOI:10.1039/DT9720000245
出版商:RSC
年代:1972
数据来源: RSC