1973 1329Synthetic Applications of the Reaction of Silver(i) Salts with the Bis-[d icarbonyl (z-cyclopentadienyl) iron] ComplexBy William E. Williams and Fergus J. Lalor,' Department of Chemistry, University College, Cork, frelandIn polar solvents the iron-iron bond of the dimeric complex [(cp),Fe,(CO),] (cp = x-cyclopentadienyl) is smoothlyoxidised by Ag' ions to give diamagnetic cations containing a co-ordinated solvent molecule, and metallic silver.Using acetone as solvent. the cation [(cp) Fe(CO),(acetone)]+ has been isolated and fully characterised as thehexafluorophosphate salt. The use of Ag' salts as convenient reagents for the synthesis of a wide variety of[(cp) Fe(CO),R] [R = N03,CF3C0,, SCN. NCO, PhC0,,p-Me-C6H,S0,. and OP(0) (OPh),],and [ (cp) Fe(CO),L] +(L = CO.Ph,P. Ph3As, Ph,Sb. MeCN. PhCHJN, Ph,CHCN. PhSMe, and [(cp)Fe(CO),I]) complexes is described.Some mechanistic implications of the reaction are briefly discussed.MUCH attention has recently centred on the oxidationof the iron-iron bond in the dimeric complex [(cp),Fe,-(CO),] (I) (cp = x-cyclopentadienyl) and its derivatives. 1-4Electrochemical oxidation has established that, for theditertiary phosphine bridged complex [{ (cp)Fe(CO)),-{Ph,P(CH,),PPh,)], an initial one-electron oxidationstep gives a novel paramagnetic cation [{(cp)Fe(CO)},-(Ph,P(CH2)3,PPh,)] + involving a ' one-electron metal-metal bond. A similar cation has been produced fromthe phosphine derivative via chemical oxidation withiodine, AgCIO,, or AgSbFG4 but the analogous cationderived from (I) has not been detected under similarconditions. However anhydrous iron(II1) perchloratereacts with complex (I) to produce diamagneticcations of the type [(cp)Fe(CO),S]+ (S = solvent).Reaction of such complexes, generated irt situ, withneutral or anionic ligands has proved to be a usefulsynthetic route for iron complexes of the type [(cp)Fe-(CO),L]+ or [(cp)Fe(CO),R] respectively? Apart fromthe work of Ruff with Group VI metal decacarbonyl(XII) (Iv); L = Ph3P, x = PF,(VI); L = Ph,Sb, X = PF,(a); Y = C1 (V); L = Ph,As, X = SbF,(b); Y = I (VII); L = MeCN, X = PF, (vm) ; L = PhCH,CN, x =-PF,(IX) ; L = Ph,CHCN, X = PF6 (x); L = PhSMe, = P1'6(XI); L = [(cp)Fe(CO),I], x = SbF,dianions, there has been little general synthetic ex-ploitation of the oxidising power of silver(1) salts.WeJ. A. Ferguson and T. J. Meyer, Iviorg. Chem., 1971, 10,2 J. A. Ferguson and T. J. Meyer, Chem. Comm., 1971, 1544.3 E. C. Johnson, T. J. Meyer, and N. Winterton, Inorg. Chem.,1025.1971, 10, 1673.present here evidence that silver(1) salts are at least asuseful synthetic reagents vis d vis complex (I) as iron(m)perchlorate, and in several cases have distinct advantagesover the latter [equations (1) and (2)].2AgR[(cP)2Fe,(C0)41 21.(cP)Fe(CO),Rl + 2Ag" (2)(XIII); R = NO,(XIV); R = CF&02(XV); R = SCN(XVI); R = NCO(XVII); R = PhCO,(XIX); R = OP(O)(OPh),XVIII) ; R = ~-Me-C,H,SO,RESULTS AND DISCUSSIONAddition of a soluble silver salt AgX (X = ClO,-,PF6-, or SbF,-) to an acetone solution of complex (I)resulted in rapid discharge of the maroon colour and itsreplacement by a deep red hue.The progress of thereaction was conveniently followed by monitoring thedisappearance of the i.r. absorption below 2000 cm-lcharacteristic of (I). Oxidation was essentially com-plete within a few minutes. Metallic silver was depositedas a silver mirror or, less commonly, as silver powder.Using silver( 11) hexafluorophosphate or silver( I) hexa-fluoroantimonate(v) as oxidant , the reaction mixturecould be worked up to yield red crystalline salts (IIb)and (IIc) which contained a co-ordinated acetone mole-cule. In the case of the hexafluorophosphate derivative,the salt has been fully characterised as the complex[(cp)Fe(CO),(acetone)]+PF,- (IIb).Microanalyticaldata (Table) are in agreement with this formulation andthe n.m.r. spectrum (in acetone solution) shows, besidessolvent absorptions, two resonances of relative area 5 : 6corresponding to the cyclopentadienyl and acetone ligandprotons respectively.Complex (IIb) is stable for at least a day in dry airand even after several days decomposition is not exten-sive. Solutions of the complex appear to be rather lessstable. The cation of (11) has been assumed to inter-vene in the oxidation of complex (I) using either electro-chemical means or iron(II1) perchlorate? but solidR. J. Haines and A. L. du Preez, Inorg. Clrem., 1972, 11,6 W. J. Schlientz and J. K. Ruff, Sytdhetic Inorg.Matal-Org.330.Chem., 1971, 1, 2151330 J.C.S. Daltonsalts of the cation have not previously been charac-tei-ised. Although Silverthorn has recently charac-terised the related cation [(cp)Fe(dmpe) (acetone)]+[dmpe = 1,2-bis(dimethylphosphino)ethane], the stab-ility of complex (IIb) is rather unexpected and mayinvolve resonance with an oxo-carbenium canonical for1[equation (3)].Dilution of an acetone solution of complex (11) witacetone-d, resulted in a considerable reduction inintensity of the acetone ligand n.m.r. resonance. Simi-larly a solution of the solid complex in acetone-d,showed no resonance due to the complexed acetoneniolecule. Both observations indicate that the iron-bonded acetone molecule exchanges with solvent, butthat this exchange is slow on the n.m.r.time-scale sinceresonances due to both co-ordinated and free solvent areobserved in acetone solution.Reactions in which the smooth oxidation of complex(I) by silver(1) salts was harnessed for synthetic pur-poses may be classified in three distinct groups as follows.( A ) Reaction of CompZex (I) with AgX (X is a N o wco-ordiaabing Anion) followed by Addition of a Neutralor A~zzioizic Ligmzd-This route, which parallels the iron-(111) perchlorate route of Meyer? was used to synthesisea wide variety of iron complexes [(II)-(V) and (VI1)-(XI)], some of which [(VII)-(X)] are reported for thefirst time. Under the appropriate conditions (videiizfra), the reaction is rapid and yields are high (often70--80y0).In one case, the synthesis of the iodonium-bridged complex (XI), CH,C1, was successfully used assolvent. This simple route to this complex represents auseful addition to published synthetic procedures.’Rather disappointingly, the reaction of complex (IIb)with iodobenzene to give the asymmetric iodonium salt[(cp)Fe(CO),-I--Ph]+PF,- did not take place. Suitablesilver(1) salts for procedure (A) are the perchlorate, hexa-fluorophosphat e, or hexafluoroantimonate (v) .Despite the formal similarity with Meyer’s use ofiron(I11) perchlorate? the reaction of complex (I) withsilver(1) perchlorate shows some significant differences.In contrast to Meyer’s method, the present reaction israpid only if the ligand is added before the oxidant andis otherwise quite slow.Thus in the oxidation of (I)with AgClO, or AgPF, the yellow colour and characteris-tic i.r. spectrum of the acetonitrile complex (VIII)appeared virtually instantaneously if the ligand wasadded before the oxidant. If acetonitrile was addedafter the silver@) salt it was several hours before thepresence of complex (VIII) could be detected. Simplecompetition between acetonitrile and the solvent fortransient unsolvated [ (cp)Fe(CO),]+ is unlikely to beinvolved since the FeIII oxidation is not similarly sensitiveto reaction conditions. In the AgI-induced redox pro-cess the oxidant is cleanly removed from the reactionmixture as metallic silver. It seems reasonable toenvisage that, in the absence of external ligand, theinitially formed cation containing a co-ordinated solventmolecule could interact with perchlorate or hexafluoro-phosphate anions to form tightly bound ion-pairs.Slowreaction of either of these possible intermediates with theligand would account for the slow formation of the ulti-mate product. When iron(n1) is the oxidant, theiron(n) cation produced remains in solution and mayreasonably be assumed to complete successfully foranions with the cation containing the co-ordinatedsolvent molecule, hence preventing formation of arelatively inert intermediate.(B) Reaction of Co~zplex (I) with AgR (R i s a Co-ordinatiqg Anion) .-Several interesting complexcs[(XIII)-(XIX)] have been prepared by this method.The novel O-bonded benzoato- (XVII), toluene-$-sulphonato- (XVI II) , and diphenyl phosphato-com-plexes (XIX) are here reported for the first time andwould probabIy be difficult to prepare by any otherroute.In the case of tlie known nitrato-complex(XIII), the yield by the present method is considerablybetter than that obtained in the previously reportedsynthesis3 The ready availability of the silver( I)nitrate oxidant should make the new route the methodof choice. Use of silver(1) isocyanate makes availablefor the first time it simple one-step synthesis of theisocyanato-complex (XVI). Of all the complexes re-ported in this paper, the diphenyl phosphato-complex(XIX) alone did not survive recrystallisation and ischaracterised by its i.r. spectrum.The only limitation to this versatile method wouldappear to be the solubility of the silver salt involved.Insolubility of the latter doubtless accounts for thefailure of complex (T) to react with either silver(1)sulphate or silver(r) cyanide.While complex (I) reactsrapidly with silver(1) nitrite, the product was not theexpected [ (cp)Fe(CO),ONO] complex. This anomalousreaction is currently under investigation.( C ) Reaction of Ligand with Preformed Complex (11)2.12 a?z Indifferent Solvent .-The isolation and characteris-ation of the solid complex containing a co-ordinatedsolvent molecule makes it possible to enhance thereactivity of complex (11) by carrying out subsequentreactions with ligands in solvents of low co-ordinatingability. Thus the ligand Ph,Sb, which fails to react with(11) according to procedure (A), gives the complex (VI)in 40% yield when reacted with (11) in methylenechloride.This route promises to be of particular usefor ligands of low reactivity. On treatment withnitrogen, Silverthorn’s complex [(cp)Fe(dmpe)-(acetone)] + gives the novel dimeric p,-dinitrogen-cation[(cp),Fe,(drnpe),N,]+. When the complex (IIb) wasshaken for several hours in CH,Cl, solution under anatniosphere of nitrogen gas (25 p.s.i.), a red oil wasrecovered which appeared to contain some (ca. 2%)W. E. Silverthorn, Clzein. Coiizni., 1971, 1310.R. J. Haines and A. L. du Preez, J. Clzem. Soc. ( A ) , 1970.2341 and references therein1973 1331.nitrogen ; however, no characterisable products couldbe isolated.Some preliminary experiments were carried out toextend this synthetic route to other oxidants and metal-metal bonded systems.Thus complex (I) reacts withtris(9-bromophenyl) amminium hexachloroantimonateto give a 30% yield of the chloro-complex (XIIa). Thechlorine atom of the latter presumably originates inthe SbC1,- anion but the precise mechanism of thereaction is not yet clear. The dimeric molybdenumcomplex [(~p)~nlro,(CO),] reacts with silver(1) trifluoro-of the synthetic procedures are described below. Pre-viously known complexes were identified by microanalysisand by comparison of i.r. and n.m.r. spectra with thepublished data. Spectroscopic and iiiicroanalytical datafor the new complexes are collected in the Table.Pracedwe.-(A).A solution of complex (I) and anexcess of neutral ligand in oxygen-free acetone was treatedwith the appropriate silver(1) salt (ClO,-, PF,-, or SbF,-).When the i.r. spectrum of the reaction mixture indicatedthat the reaction had proceeded to completion, the reactionmixture was either reduced to a small volume and aqueousNH,PF, added (AgClO,), or evaporated to dryness (AgPl?,Analytical and spectroscopic data.A v(c-0) aFound (7;) Calc. (%)r , r--, - M:P.Complex C H N C H N OC cm-18 bp.p.m.(IIb) 31.3 3.0 31.6 8.9 50 2075, 2030 C 2.38(s) (co-ordinated acetone) , 5.61 (s)(VIII) 41.0 2-9 3-3 41-0 2.7 3.2 161 2082, 2040 4.33(~) (CH,), 5 . 6 0 ( ~ ) (C,H,). 7-38(~)(C5HJ(decomp .) (C6HS)(IX) 48.7 3-1 2.8 48.9 3.1 2.7 170 2083, 2042 5-68(s) (C,H,), 5-95(s) (CH).7-41(s)(decomp.) (C,H,)(Cia,)(C,HJ(X) 37-6 3.1 37.6 2.9 145 2070, 2030 2.97(~), (CH,), 5-66(~) (C,H,), 7-60(~)(XVII) 56.0 3.4 56.4 3.4 97-98 2059, 3017 5-27(s) (C,H,), 7.0-8.0(m) C,H,)(XVIII) 48-6 3.8 48-3 3.4 94 3028, 2076 4-35(s) (CH,), 5-30(s) (C5H,), ‘im3(In)W X ) 2010, 2062 6In CHC1, solution, except for complex (11) which was in CH,CI,.acetone-d, except for that of complex (11) in acetone.correctly. Assignments in parentheses.molecule occurs a t ca. 1635 c1n-l. d Solvent acetone absorbs a t 2.07 p.p.m.appear to be in error. * The carbonyl group of the benzoate ligand absorbs a t 1707 cm-l.(XVIII) must contain traces of paramagnetic impurity.lised samples and even here considerable broadening was c\-idcnt.for accurate determination of the resonance positions.6 TMS internal standard.All spectra were measured inAll spectra except that of complex (XVIII) (see footnote f) integratedc The carbonyl absorption of the co-ordinated acetoncThe resonances reported in ref. 3 for cation (11)f Although analytically pure, complexReasonably well resolved spectra were recorded only for freshly recrystal-I Paramagnetic impurity evident, thc spectrum was too broads = Singlet, m = multiplet.acetate to give the known1* trifluoroacetato-derivative inlow yield. However, tlie dimeric molybdenum complexis decomposed by either silver(1) nitrate or silver(1)hexafluoroantimonate.Despite the adverse price-factor involved in the useof silver-containing reagents, the synthetic routesdescribed. have much to recommend them.The oxida-tion is rapid and clean (removal of silver metal, the onlyby-product, by deposition from solution eliminates thenecessity for tedious work-up procedures) and, in manycases, product yields are higher than those obtainableby other methods. This method should prove a usefulsupplement to the established synthetic procedures.Further extensions of the method are under study.EXPERIMENTALReagents and ligancls were commercially available aiidwere used as received without further purification. Re-actions were carried out under an atmosphere of oxygen-freenitrogen, although this precaution could probably be dis-pensed with in most cases. N.m.r. spectra were measureda t 60 MHz on a Perkin-Elmer-Hitachi R20A spectrometerand i.r.spectra were recorded using a Perkin-Elmer 257spectrophotometer with grating optics. The essentialsF. A. BeIl, A. Ledwith, and D. C. Sherrington, J. Chenz. SOC.(C), 1969, 2719.D. Csshman and F. J. Lalor, J . Ovganomctallic Chrrri.,1971, 32, 351.and AgSbF,) and the product recrystaked from acetone-ether or inethylene chloride4Aier. In the case of tlieiodo-complex (XIIb) alone, the ligand (as aqueous KT)was added after oxidation was complete. For the synthesisof the tricarbonyl cation (111), a solution of (I) in acetonewas saturated with CO before addition of the oxidant and astream of CO gas was maintained for 45 min after theaddition. In this manner the following complexes wereprepared (yields in parentheses) : (IIb), 7 1 ; (111) , 57 ; (IV),85; (V), GO; (VII), 75; (VIII), 87; (IX), 62; ( X ) , 74; (XI),70; and (XIIb), 53%.Complex (I) and the appropriate silver(1) salt werestirred at room temperature in acetone solution until i.r.measurements indicated that reaction mas complete.Thetime required varics from ca. 30 inin for the nitrato-complex(XIII) to ca. 2 days for the benzoato-complex (XVII).After filtration the solution was concentrated to drynessand the residue recrystallised from inethylene chloride-liesane. In one case, the thiocyanato-complex (XV) ,heating under reflux for 24 11 was necessary to inducereaction. Rather surprisingly, the AT-bonded isomer wasnot isolated under these conditions. In this manner thefollowing complexes were prepared (yields in parcntheses) :(XIII), 60; (XIV), 87; (XV), 50; (XVl), 70; (XVII),42 ; and (XVIII), 75‘7;. The diphenyl phospliato-complex(XIX) prepared in this fashion was unstable, could not bepurified, and was identified on the basis of its i.r. spectrum.lo R. R. King and R. N. Kapoor, J. Organometallic Chem.,1968, 15, 457.( B ) 1332 J.C.S. DaltonA similar procedure was used to prepare the complex[(cp)Mo(CO),02CCF3) (in ca, 40% yield) from [(cp),Mo,-(CO),] and AgO,CCF,.(C) . Preparation of the Complex [(cp)Fe(CO),(SbPh,)]+-PF,- (VI). Complex (IIb) (0.5 g, 1.3 mmol) was dissolvedin oxygen-free CH,Cl, (40 ml). Ph,Sb (1.0 g, ca. 2-8 [2/2113 Received, 8th September, 19721mmol) was then added and the solution stirred overnight.After filtration through Celite the solution was concentratedand diluted with ether, giving yellow crystals of the corn-plex [(cp)Fe(CO),SbPh,]+PF,- in 40% yield