1976 1525Simple Halogenonitrosyl Anions of IronBy Neil G. Connelly and Christopher Gardner, Department of Inorganic Chemistry, University of Bristol,Bristol BS8 1TSThe complex [N(PPh,),] [Fe(CO),(NO)] reacts with a(kyl halides to afford [N(PPha),] [FeX,(NO),] (X =CI, Br.or I) and with halogens to afford [N(PPh,),][FeX,(NO)] (X = CI or Br) and [N(PPh,)?][Fel,(NO),]. Therelations between the two sets of paramagnetic anions, their reactivity, and their magnetic and e.s.r. spectralproperties are discussed.IT is somewhat surprising that no simple halogeno-nitrosyl anions of iron have been fully characterised,particularly in view of the existence of the rutheniumand osmium species [MX,(N0)l2- (M = RuX = C1, Br, or I). The e.s.r. spectra of mixtures ofiron(@ salts, NO, and halide ions in aqueous ethanolhave been interpreted3 in terms of the existence of[FeX,(NO)d- and [FeX(NO),(OH,)], and [FeCl,(NO)d-was suggested as the product of reductive nitrosylationof FeCl, by NO.* In neither case, however, was astable complex prepared.In addition, although thereaction of iron(I1) salts, NO, and o-phenylenebis-(dimethylarsine) (pdma) gave [Fe(pdma),X(NO)] peX,-(NO),] (X = Br or I), the identity of the anion was notunequivocally e~tablished.~ We now report the isol-ation and complete characterisation of two series ofhalogenonitrosyliron anions, [FeX,(NO),]- (X = I, Br,or C1) and [FeX,(NO)]- (X = Br or Cl), stabilised by thebis (trip hen y lp h osp hine) iminium cat ion.and 0 s ;RESULTS AND DISCUSSIONIt has been shown previously that Na[Fe(CO),(NO)]reacts with cyclopentadiene or cyclohexadiene in thepresence of methyl iodide to afford acetyl-substitutedred-brown crystalline solids, by allowing EtBr or PrXlto react with [N(PPh,),][Fe(CO),(NO)] in refluxingP COMe 111)CH,Cl,.The i.r. spectrum of each of the new complexesexhibited two bands in the nitrosyl-stretching region.The positions of the absorptions for the dichloride arevirtually identical with those reported by Caulton:thus confirming the formulation, [NEt,H] [FeCl,(NO)d,proposed for the product of the reaction between FeC1,and NO in the presence of NEt,. That [FeX,(NO)a-has not previously been recognised in the reaction of[Fe(CO),(NO)]- with alkyl halides, RX, and that wehave found no evidence for the usually formed acyl[Fe(COR)(CO),(NO)], results from the use of the [N-(PPh3)J + cation, which stabilises the dinitrosyl anion,and of CH,Cl, in which the acyl is unstable.In order to optimise the yields of the dinitrosyl anions,TABLE 1I.r., analytical, m.p., and conductance data for [N(PPh,)J[FeX,(NO),], (I), and [N(PPh,),][FeX,(NO)], (11);(NO) Ad Analyses (76)t - Complex X M.p.(O,/"C) Yield ("/o) C H N cm-1 S cm2 mol-1I 160-161 97 47.8 (47.6) 3.7 (3.3) 4.4 (4.6) 1778, 1719 171Br 176-178 23 53.8 (63.1) 4.0 (3.7) 5.1 (5.2) 1780, 1710 176c1 2 12-21 3 50 59.6 (59.6) 4.2 (4.2) 5.6 (5.8) 1781, 1708 168Br 22 1-222 65 50.0 (60.0) 3.5 (3.5) 3.5 (3.2) 1 802 194c1 237-239 66 58.9 (69.2) 4.1 (4.1) 3.4 (3.8) 1 802 192(1)(11)a Calculated values are given in parentheses.a In CH,CI,. lo-$ mol dm3 solutions in pure acetone.ally1 complexes such as (I). We now find that reactionof [N(PPh,),][Fe(CO),(NO)] with Me1 and cyclo-octatetraene (cot) in CH,Cl, does not afford the analogouscyclo-octatrienyl complex but, instead, yields blackcrystalline [N(PPh,)d[FeI,(NO)J (Table 1) and smallamounts of [Fe(q-C,H,)(CO),]. In the absence of cotthe di-iodo-complex wa.s still isolated, but apparently ina slightly decreased yield. The corresponding dibromo-and dichloro-complexes were also prepared, as dark1 J. R. Durig, W. A. McAllister, J. N. Willis, jun., and E. E.Mercer, Spectrochim. Ada, 1966, 22, 1091.K. A. Bol'shakov, N. M. Sinitsyn, V. F. Trafkin, and 2.B.Itkina, Doklady Chem., 1972, 206, 688.a L. Burlamacchi, G. Martini, and E. Tiezzi, Inorg. Chew.,1969, 8, 2021.the reactions of the tricarbonyl with halogens and withnitrosyl halides were examined. Addition of I, t a[N(PPh,)d [Fe(CO),(NO)] in CH,Cl, very rapidly gave adeep brown-black solution from which the di-iodo-complex was isolated in excellent yield. The dichlorideis, however, best prepared by dropwise addition of NOCtin CH2Cl, to [N(PPh,)J[Fe(CO),(NO)] in the samesolvent. It is interesting to note that the initial form-ation of [Fe(CO),(NO)J in this reaction may be detectedby i.r. spectroscopy. The isolation of [Fe(CO),(NO),ID. Gwost and K. G. Caulton, Inorg. Chem., 1973, 12, 2095.W. Silverthorn and R. D. Feltham, Inoug.Chem., 1967, 6,F. M. Chaudhari, G. R. Knox, and I?. L. Pauson, J . Chem.1662.Soc. (C), 1967, 22551526 J.C.S. Daltonfrom [Fe(C0),l2- and NOCl has recently been reported;there is no doubt, therefore, that [Fe(CO),(NO)]- isformed as an intermediate.In contrast to the reaction of I, with [N(PPh,),]-[Fe(CO),(NO)], addition of Br, or C1, in CH,C1, to thecarbonyl anion afforded deep green solutions from whichdark green crystals of [N(PPh,),][FeX,(NO)] (X =Br or C1) (Table 1) were isolated. The solid complexesare stable for at least several weeks, but their solutionsin air are fairly rapidly decomposed to give [N(PPh,)J-[FeX,] (as confirmed by the isolation of small amounts of[N (PPh,),] [FeBr,] ). Although the anionic trihalogeno-nitrosyls have never been characterised before it ispossible that they have been generated.We were,however, unable to isolate them from the deep greensolutions prepared from NO and FeC1, in methanol[v(NO) at 1802 cm-I],4 FeCl, in ethanol [v(NO) 1775cm-l],8 and FeBr, in tetrahydrofuran (thf) [v(NO)1 800 cm-lI.5Although [FeX,(NO)]- are the only nitrosyl complexesisolable from the reactions between [Fe(CO),(NO)]-and Br, or Cl,, it is possible that they are formed viathe dinitrosyls [FeX,(NO),]-. Solutions of the latterslowly afford the trihalides on standing, and do so morerapidly in the presence of the appropriate halide ion, X-.The non-isolation of the tri-iodo-complex from [N-(PPh,),][Fe(CO),(NO)] and 1, is probably a result ofsteric factors.In the presence of I- only [N(PPh,),][I,]could be isolated from [N(PPh3)2][Fe12(NO)2]. WithBr-, however, the di-iodo-complex slowly gave a mono-nitrosyl, identified only by i.r. spectroscopy, which waspossibly [N (PPh,) ,] [FeBrI, (NO)].As precursors to iron nitrosyl complexes the two seriesof anions are somewhat disappointing. For examplethe reactions of [FeI,(NO),]- with PPh,, and of [N-(PPh,) 2] [FeBr, (NO)] with 1,2-bis (diphenylphosphino) -ethane (dppe) gave only low yields of [Fe(NO),(PPh,),]and [Fe(NO),(dppe)] respectively. In addition, al-though the nitrosyl group of the dihalogeno-anion isapparently labile, it has not been possible to transfer it toan organic substrate. The complex [Co(CO),I(NO)]-reacts with, benzyl halides to afford benzaldoximes,9but a similar reaction with [FeI,(NO),]- did not give anyorganonitrogen compounds.MagNetic m d E.S.R. Studies.-Both [N(PPh,)&[FeX,(NO),] and "(PPh,),] [FeX,(NO)] are paramag-netic. Measurement of the magnetic susceptibilities ofthese species, by a variation of Evans' n.m.r.rnethod,lOshows that the dihalides have one unpaired electronwhile the trihalides have three (Table 2). That pd.for the dibromo- and dichloro-complexes are slightlyhigher than the calculated spin-only value of 1.73 B.M.is probably due to the presence of small amounts oftrihalide impurity. * Although analytically pure sam-* 1 B.M. z 9.27 x 10-24 A m2.P. Legzdins, cited as ref. 247, Co-ordination Chem. Rev.,a W. P. Griffith, J. Lewis, and G.Wilkinson, J . Chem. SOC.,1975, 14, 317.1968, 3993.ples were used for all the susceptibility measurements,slow formation of [FeX,(NO)]- from [FeX,(NO),]-(X = Br or C1) occurred in solution even under nitrogen.As [FeI,(NO),]- does not transform to [FeI,(NO)]- (seeabove), the measured value of p e ~ . is close to the cal-culated value for one unpaired electron. In the case ofTABLE 2Magnetic moments and e.s.r.a spectral values for [FeX,-(N0)21-, (I), and [FeX,(NO)]-, (11)Complex X ks./B.M. <A)/G <g>I 1.72 19.2 2.072Br 1.75 18.9 2.049c1 1.81 2.033Br 3.82a In CH,Cl, a t room temperature.(1)4.77, 4.84b(11) c1b See text.the trihalides the measured susceptibility of [N(PPh,),]-[FeBr,(NO)] is in good agreement with the spin-onlyvalue for three unpaired electrons.For the trichloro-complex, however, two measurements of peS. gavevalues of 4.77 and 4.84 B.M. which are considerablyhigher than the expected value. It seems likely thatsuch high values arise from the formation in solution of[N(PPh,),][FeCl,] which, with five unpaired electrons,would cause the measured peff. to be raised.While nitrosyl-stretching frequencies are a poor aid tothe assignment of either bent (formally NO-) or linear(formally NO+) structures to metal nitrosyl complexes,in both sets of anions reported here the frequencies are,for negatively charged nitrosyls, relatively high. Themetal nitrosyl groups are, therefore, probably linear andbest regarded as containing the NO+ ligand.The assign-ment of the nitrosyl ligand as NO+ leads to the assign-ment of oxidation states -I and +I to the iron atoms in[FeX,(NO),]- and [FeX,(NO)]- respectively. The meas-ured magnetic susceptibilities are then in good agreementwith the iron atoms having basically tetrahedral geo-metry with d9 and d7 configurations respectively.In CH,C1, at room temperature and at -196 OC, thetrihalides showed no detectable e.s.r. signals. Thedihalides, however, showed well resolved spectra atroom temperature. Burlamacchi et aL3 previouslyreported the e.s.r. spectra of aqueous alcoholic solutionsof iron(I1) salts and halide ions saturated with nitrogenmono-oxide. In each case spectra were observed whichwere dependent on the concentration of X- and whichwere interpreted as indicating the presence of mixturesof [FeX(NO),(OH,)] and [FeX,(NO),]-.In the case ofX = I the spectrum of the anion, free of the neutralspecies, was seen at high iodide concentration. ForX = C1 or Br, however, only spectra of the mixtureswere observed. The di-iodo- and dibromo-complexesreported here each showed an e.s.r. spectrum withhyperfine coupling to two halogen atoms, but, as foundpreviously, not to nitrogen. In each case the (g) and( A ) values (Table 2) are close to those assigned byBurlamacchi for the anionic dihalogeno-species in themixtures studied. Thus, the di-iodide showed an 111976 1527line spectrum due to coupling with two equivalentiodine atoms [ I (12’1) = &I, and the dibromide aseptet due to coupling with two equivalent brominenuclei [1(79Br) = I(*lBr) = $1.In the case of [N-(PPh,)J [FeCl,(NO),] we only observed a single linewith no hyperfine coupling to either 35Cl or 37Cl (I = s).The (g) value is, however, in good agreement withthat previously measured. It is probable that the non-observation of coupling is due to poor resolution inCH,Cl,; the insolubility of the complex prevented theuse of aqueous ethanol as the solvent for e.s.r. studies.EXPERIMENTALThe preparation and purification of the complexes de-scribed were carried out under an atmosphere of drynitrogen.Infrared spectra were recorded on Perkin-Elmer PE257or PE457 spectrophotometers and were calibrated againstthe 1601 cm-1 absorption of polystyrene.X-Band e.s.r.spectra were recorded on a Vanan Associates 4502/15instrument and were calibrated against a solid sample of thediphenylpicrylhydrazyl radical. Magnetic-susceptibilitymeasurements were carried out, using a modification ofEvans’ n.m.r. method,”’ on a Varian Associates HA100instrument. Bulk susceptibilities were calculated from thedifference between the chemical shift of pure CH2C1, andthat of the CH,C12 proton resonance of ca. 0.05 mol dm-3solutions of the paramagnetic complexes. Both shiftswere measured relative to an internal cyclohexane reference.Microanalyses were by the Microanalytical Service of theSchool of Chemistry, University of Bristol. Melting pointsare uncorrected.Tricarbony lnitrosylir~,[N(PPh,)J[Fe(CO),(NO)].-To sodium ( 4 g) in methanol(270 cm3) were added Na[N02] (5.2 g) and [Fe(CO),] (10cm3).After refluxing for 90 min, [N(PPh,)&l*CH,Cl,,(49.0 g) in CH2C12 (150 cm3) was added. After partialevaporation the crude product was filtered from the reac-tion mixture and recrystallised from acetone-hexane toafford bright yellow crystals of [N(PPh,)J[Fe(CO),(NO)](31.5 g) {yield 60% based on [Fe(CO),]}. The cowzplex issoluble in polar solvents such as acetone and CH2C12 togive deep yellow solutions which only slowly decompose inair. The solid complex is stable in air for at least severalmonths.Dich lorodinitrosy liron,g) in CH,Cl, (100 cm3) was added dropwise a dilute solutionof NOCl in CH,C12. The reaction was judged to be completewhen the carbonyl absorptions of [Fe(CO),(NO)]- and of theintermediate [Fe(CO),(NO),] were absent from the i.r.spectrum. The brown solution was then evaporated toAll solvents were dried and distilled before use.Bis (tripheny lphosphine) iminiumBis (trip heny lphosphine) iminium“(PPh,),I[FeC12(NO)zI.--To “(PPh,),ICFe(CO),(NO)I (1.0dryness and the residue recrystallised from dichloromethane-ethanol to give red-brown crystals of [N( PPh,) 2] [FeCl,-(NO),] (0.51 g) {yield 50% based on [N(PPh,),][Fe(CO),-(NO)]).The complex is soluble in polar solvents such asacetone and CH2C12 to give red-brown solutions whichdecompose slowly in air. The solid complex is stable inair for a period of weeks.Bis(tripheny1phosfihine)iminiurn Dibromodinitrosyliron,[N( PPh,) ,J [FeBr,(NO) J.-The complex [N(PPh,) ,] [Fe (CO) 3-(NO)] (2.0 g), cyclo-octatetraene (1 cm3), and EtBr (5 cm3)were heated under reflux in CH2C12 (75 cm3) for 26 h.Thebrown solution was then evaporated to dryness and theresidue recrystallised from dichloromethane-ethanol to givedark red-brown crystals of [N(PPh,)J[FeBr,(NO),] (0.52 g){yield 45% based on the nitrosyl group of [N(PPh,),][Fe-(CO),(NO)]}. The solid complex is reasonably stable in air;brown solutions in polar solvents such as acetone and CH2-C1, slowly decompose.Bis(tripheny1phosphine)iminium Di-iododinitrosyliron,g) in CH2C12 (50 cm3) was added I, (1.79 g). After stimnguntil the carbonyl absorptions of [Fe(CO),(NO)]- haddisappeared from the i.r. spectrum of the reaction mixture(ca.30 min) the brown solution was evaporated to dryness.Recrystallisation from dichloromethane-ethanol gave blackcrystals of [N(PPh3)2][Fe12(NO)2] {yield 98% based on thenitrosyl group of [N(PPh,),][Fe(CO),(NO)]). The solidcomplex is stable for some weeks in air, slowly decomposingwith loss of iodine. Dark brown solutions of the complexin polar solvents such as acetone and CH,Cl, slowly decom-pose in air.Bis(triphenyl~hos~hine)i~i~ium Trichlormitrosyliron,[N(PPh,)J[FeCl,(NO)] .-TO [N( PPh,) 2] [Fe(CO),( NO)] ( 1 .Og) in CH2Clz (50 cm3) was added dropwise a solution ofchlorine in CH,Cl,, until the carbonyl absorptions of [Fe-(CO),(NO)]- were absent from the i.r. spectrum. Onaddition of ethanol and evaporation at the water pump,dark green crystals of [N(PPh,),][FeCl,(NO)] (0.68 g) weredeposited (yield 66% based on [N(PPh,)JFe(CO),(NO)]).The complex dissolves in polar solvents such as CH2C12 andacetone to give green solutions which decompose fairlyrapidly in air. The solid complex is stable in air for severalweeks. The complex [N(PPh,)J[FeBr,(NO)] may besimilarly prepared as dark green crystals (yield 65% afterrecrystallisation from dichloromethane-ethanol) .“ (PPh,) 21 P I , (NO) 23 --To “ (PPh,) 21 [Fe (CO) 3 (NO) 1 (5 * 0We thank the S.R.C. for a studentship (to C. G.), and Dr.R. J. Goodfellow for assistance with magnetic-susceptibilitymeasurements.[5/2137 Received, 3rd Novembev, 19751@ M. Foh and L. Cassar, J . Organometallic Chem., 1971, 30,lo D. F . Evans, J . Chem. Soc., 1959, 2003.123