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~~ournaZof Orgcmometallic~Chemistgy, 157 (2976) C64466 I ~@Ekevier-Sequoia &A., Lausanne -Pri~riqted in.we Net&erla+s

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Prelimimry communication

SUBSti~ON &ACTIONS dF DICYCLOOCTATEiTRAENEIRON. A sIm?LERouTE TOZEROV AIiNWRON-ORGANOPHOSPHORUS coMPouNDs

E=UGH FELKIN, PETER W. LEDNOR”, JEAN-MICHEL NORMANT and ROBIN k3. sMITH**

I~Miiuf de Chimie des Substances Naturelies, C.N.R.S., 91190 Gif-sur-Yvette. France

(Received July 6th, 1978)

Fe(cot), (cot = cyclooctatetraen~e) rea&s with certain phosphines and phos- phites to give Fe(cot)L, compounds in gotid yield. Reaction of Fe(cot)2 with Ph2PCH2CH2PPh2 under N2 gives a complex containing coordinated dinitiogen, which isconverted into Fe(cot)(Fh,FCH&HzPPhz )(CO) on reaction with CO or formate esters.

The chemistry of low-vdent iron is dominated by the carbony derivatives; analogous species with crganophosphorus ligands are less well known but are of currefit‘ interest because of the possibility of (a) establishing a high electron density on the metal (cf. reactions of Fe[P(OMe)3]5 [l] or “Fe(PMe&” [2,3]) (b) observing dynamic behaviour, including inter- and intra-molecular ligand ex- change (cf. Fe(l,8cod) [P(OR),], [4]) (cod = cyclooctadiene and (c) obtain- ing potential hydrogenation catalysts. Previous synthetic routes to this class of compounds have involved reductive [l--3] or metal-atom [4, 5) techniques. We now report that substitutitin reactions of Fe(cot), (I) 161 provide a simple route to novel zerovalent phosphine- and phosphite-iron compounds.

The 1%electron complex I [S], which contains fluxional v4- and v6-cot rings, gives a single ‘H NMR absorption at T 4.96 ppm (benzene-d,, 34°C). No change in the spectrum is observed on treatment of the solution in benzene-& with PPh,, confirming the original report [7] _ However, a benzene solution of I containing one equivalent of Ph2PCH,CH,PPh, (diphos) under N2 or Ar gives solutions, the ‘II NMR spectra of which show signals for uncomplexed cot (s, T 4.37 ppm) and coordinated cot (broad s, T 5.06 ppm) in a l/l ratio. No absorption for I could be detected in these solutions. The IR spectrum of this solution under N2 shows

*Present address: Kooinldijke/Shell LabOratorillm. Amsterdam <SlM.I Research, B-V.), Badhukweg 3. _Amstmdzm <The Netherlands).

**Present add==: Department of Chemistry, University of Otago. Dunedin (New Zealand).

C65

an absorption at 2105 cm-‘, assigned to coordinated dinitrogen. The IR spectrum of the reaction mixture prepared under Ar showed no peak in this range. The product is thus formulated as Fe(cot)(diphos)(N,) (II) and although efforts to obtaina pure solid sample have been unsuccessful, treatment of the solution with CO yields the red crystalline Fe(cot)(diphos)(CO) (III)* (v,, 1900 cm-‘, nujol).

In contrast, the reaction of I with one equivalent of Me,PCH,CH,PMe, (dimos) under N2 gave e solution containing no IR band assignable to coordinated di- nitrogen. ‘H NMR studies of this reaction showed that complete consumption of I required 1.5 equivalents of dimes and the crystalline product is accordingly formulated as Fe,(cot),(dimos), (IV) (cot, 7 5.08 ppm). Cryoscopic measure- ment in benzene indicated a molecular weight of 700 f 100, in accordance with this formulation, and a crystal structural determination** [S] shows that the com- piex is [Fe(~4-cot)(dimos)(Me,PCH,)],, with a single dimos bridge between the two iron atoms.

‘lkeatment of I with one equivalent of PhP(CH,Cl$PPh2 )z (triphos) or t’hree equivalents of P(OMe), gave the crystalline compounds Fe(cot)(triphos) (V) and

SCHEME 1. cot = cyclooctatetraene; diphos = Ph,PCH,CH,PPh,. - dimes = Me,PCH2 CH,PMe, ; triphos =

PhP(CH,CqPPh, It _

co Fe(cot) (diphosl(N~)

or HCOOR - Fe (cot) (diphosl (CO)

(Ii) tm,

I diphos/Nz

Fe Lot), dimos 4

Fekot) (triphos)

(PI

Fe2(cot12(dimos13

tm,

Fe(cot)[P(OMe)J 3 (VI). Both compounds show a broadened ‘H NMR singlet resonance for coordinated cot (7 5.11 and 4.64 ppm, respectively), indicating that the cot is fluxional and presumably q4-coordinated. The ‘H NMR cot resonance in V was unchanged at -85°C (CD&l, ).

These reactions of Fefcot), are summarized in Scheme 1. Fe [P(OMe) ] 3 s is known [l], but addition of 2 equivalents of P(OMe), to a

benzene solution of VI gave no evidence of further cot substitution. No reaction was observed foilowing the addition of ‘PPhs to a benzene solution of II.

*The new compounds gave satisfactory elemental analyses. **By c. Pascard.

1 -~z&bl&+rn$+&re ?P{fH) NMR studies on III, V and VI indicated the fiuxion~,natuqof-the phosphorusligands; Compounds III and. VI showed only a-singk-sharppe& at 6 -93.6 and +188;8 ppm.* (CD&) respectively, and the spectti-were unchanged at -80°C. These r&u&s are in contrast to the reports [4; 9J that the~hmiting,structures of the closely related compounds Fe(l,S-cod)- [P(Oi%ie)s]3 (VII) and Fe(l,3:butadiene)(diphcs)(CO) can be observed in the -60.to -8O‘%temperaturerange. In accord with the results for VII 141, however, rapid intcrmoiecuk phosphite exchange was not observed, since the spectrum of a mixture of P(OMe), and VI at 25°C showed two sharp peaks at 6. -141.0 and -188.8 ppm. The 31P(1H) NMR.spectrum of V at 0°C showed two absorp- tionsat -94.9 (d, J.9 Hi) and -117.4 (t,.J9 I-&)-in an intensity ratio of 2/l. On cooling, the spectrum of V changed considerably until, at the lowest temperature limit (-80°C) of the most suitable inert solvent-(CD2C12), a non-limiting spectrum was observed containing tlhree broad signals of comparable intensity at 6 -92, -95 and -188 ppm,

The chemistry of these new phospho rus-iron compounds is at present being investigated. Attempts to use them as hydrogenation catalysts have been un- SuccessfuI, although it has been shown that I will react with phosphines or phos- phi& and &I* sunder vigorous conditions (- lOO”C, 100 atm) to give FeH,P4 corn-- pounds {lo]. The dinitrogen complex II decarbocylates ethyl formate; the car- bonyl complex (III) was isolated in 56% yield and ethanol was identified by ‘II NMR. Ihis decarbonylation reaction appears to be specific for formate esters as no reaction was noted with CsH,,CHO, MeCOOEt, MeCOOCH,Ph, p-Me&H&HO, (COOMe), , HCONMez or HC(OMe), . The reaction is somewhat unusual, and to our knowledge has only been reported previously with tran.s-Mo(diphos),(& )Z 1113.

Acknowledgements

We thank B.A.S.F. (Ludwigshafen) for a generous gift of cyclooctatekaene and Professor M. F&izon for access to 31P NMR facilities.

References

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*Negative “P chemical shifts are downfield from exter;lal85% H,PO,.