1975 1109Reactions of Co-ordinated Ligands. Part V.l The Addition of Tetra-fluoroethylene to Tricarbonyl(diene)iron, Tricarbonyl(trans-cinnamalde-hyde) i ron, and Trica rbonyl (o-styryld iphenyl phosph h e ) iron Complexes tBy Alan Bond, Brian Lewis, and Michael Green,' Department of Inorganic Chemistry, The University, BristolBS8 1TSTetrafluoroethylene reacts with tricarbonyl(buta-I ,3-diene, trans-penta-I ,3-diene, isoprene, or 2,3-dimethylbuta-1.3-diene)iron on U.V. irradiation to afford 1 : 1 adducts formulated as x-allylic iron(l1) complexes, in which theC,F, links the metal and diene, the linking reaction occurring preferentially a t the least-substituted end of thediene. Similar reactions are observed with tricarbonyl(cyc1ohexa-1.3-diene or bicyclo[4.2.0]octa-l,3-diene)ironto give x-allylic adducts.The corresponding reaction with tricarbonyl (cyclo-octa-I ,3-diene) iron affords twocomplexes, a n-allylic adduct and a tetracarbonylferracyclopentane. Tetra- and tri-carbonyl (trans-cinnamalde-hyde) iron react with C2F4 to give tetracarbonylferracyclopentanes, in which the aldehyde and phenyl groups havea re I at i v e cis - c o n f i g u ratio n . T r i ca r b o n y I ( nor b o r n ad i e n e ) i ro n a n d t r i c a r b o n y I (0 - sty r y I d i p hen y I p h o s phi n e ) i r o n a I s oform adducts with C2F4, the former giving a nortricyclene tetracarbonyl species. The n.m.r. spectra of thesecomplexes and possible modes of formation are discussed.IN previous papers in this series the reaction of neutralelectrophilic molecules with tricarbonyl(cyc1obutadieneand tetramethylcyclobutadiene)iron,2 tricarbonyl(cyc1o-hept atriene) iron,3 tricarbonyl( N-met hoxycarbonylaze-pine)iron ,4 and tricarbonyl(c yclo-oct atet raene) iron havebeen described.In the photochemical reaction offluoro-olefins with, for example, [Fe(x-C4Me,) (CO),] a x-tetramethylcyclobutenyl complex is formed, in which thefluoro-olefin links the C, ring and iron atom, a reactionwhich involves a formal endo-attack and a change in theoxidation state of the iron from (0) to (2+). In contrast,tetracyanoethylene and related molecules such as hexa-fluoroacetone react thermally with [Fe(C,H,) (CO),],[Fe(C,(NCO,Me)H,)(CO),], and [Fe(C,H,) (C0)J to form1 : 1 adducts, in which the electrophile adds exo-1,3- tothe co-ordinated olefinic species.In an effort to under-stand the factors controlling these reactions, relatedprocesses have been examined, and in this paper thephotochemical reaction of tetrafluoroethylene with tri-carbonyl( 1,3-diene)iron, tricarbonyl(norbornadiene)iron,tetracarbonyl (cinnama1dehyde)iron , and tricarbonyl( o-styryldipheny1phosphine)iron are reported. The com-plexes obtained have been characterised by elementalanalysis, mass spectroscopy, and i.r. and n.m.r. spectro-scopy.RESULTSU.V. irradiation of hexane solutions of an excess of tetra-fluoroethylene and the compounds tricarbonyl( 1,3-diene) -iron (diene = buta- 1,3-diene, trans-penta- 1,3-diene, iso-prene, or 2,3-dimethylbuta-l , 3-diene) affords moderateyields of the air-stable crystalline adducts (I), (II), (111), and(IV), respectively.The adducts are assigned the illustratedstructures, in which a formal eado-oxidative linking reactionoccurs resulting in the hydrocarbon fragment being bondedto the metal in the 1,2,3--q mode with one end of the fluoro-carbon being attached to the iron via an Fe-C Q bond. Bothisoprene and tram-penta- 1,S-diene are unsymmetrical dienesand it has been firmly established, on the basis of the n.m.r.data, that the linkage reaction of tricarbonyl(tmns-penta-No reprints available.* Part IV, P. K. Maples, &I. Green, and F. G. A. Stone, J.C.S.Dalton. 1973. 2069.1,3-diene)iron with C,F, proceeds specifically a t the un-substituted end of the co-ordinated diene affording (11) asthe only product.The reaction of tricarbonyl(isoprene)ironis not as specific but attack at the unsubstituted end of thediene, affording (IIIa), occurs approximately five times asreadily as does reaction to give (IIIb) (see below).The i.r. spectra of (1)-(IV) each show three sharp bandsassignable to terminal carbonyl groups, one band appearingin the range 2083-2086 cm-1 and the other two in the range2009-2032 cm-l. This is consistent with an Fe(CO), group,i I I I I I IT5 6 7 8 9 10FIGURE 1 lH N.m.r. spectrum of complex (IIIa) in CDCl,and the presence of this structural feature was confirmed bythe mass spectra.The IH and 19F n.m.r. spectra of the four adducts showvery similar features, and therefore a detailed discussion isrestricted to the tricarbonyl(isoprene)iron adduct.In thelH spectrum of (IIIa) (Figure l), H1 appears as a doublet ofdoublets a t T 7.31 and H2 as an apparent triplet centred atz 6.66; IH-lH decoupling established a value for J1,2 of2.5 Hz, leaving a coupling of 4-0 Hz on H1 to be assigned,which further decoupling revealed was not due to a proton.M. Green, S. M. Heathcock, and D. C. Wood, J.C.S. Dalton,1973. 1564..M. Green, S. M. Heathcock, J, Weaver, D. C. Wood, and P.Woodward, Chem. Comm., 1971, 222.~~. .a A: Bond and M. Green, J.C.S. Dalton, 1972, 7631110 J.C.S. DaltonThe resonance due to H4 appears as an apparent triplet atIC 5.54 and irradiation of this signal showed coupling to Ha,H5, and H6; JZs4 is small (2.5 Hz) but J4,5 (7.5 Hz) and J4,&(8.0 Hz) are larger and almost equal.The signal due to H6appears as seven equally spaced lines of relative intensity1 : 2 : 3 : 4 : 3 : 2 : 1 centred at T 7-58; the H6 resonanceH 5 u 5signal takes the form of a double triplet of doublets with acoupling of 35.0, 15.0, 14.0, and 3.0 Hz; the large couplingis clearly J(F3H6). The resonances at 76.6 and 88-7 p.p.m.are assigned to F1 and F2 respectively, where Jl,z is 236 Hzand each half of F1 appears as a doublet of triplets, while F Zcorrespondingly takes the form of multiplets.H7,,H6appears as a complex doublet a t 7 8.95. It was onlypossible to make firm assignments for the 135 and H6resonances by examination of a molecular model.The H5resonance structure arises from four doublet couplings of14.0, 14.0, 7.6, and 7.0 Hz. One of these (7.5 Hz) wasassigned to J4,5 and irradiation of H5 showed that another isdue to J5,6; H5 is coupled to no other proton. At this stagein the analysis no precise value could be assigned to J5,6.The only coupling constant immediately apparent from theH* resonance is a large (35.0 Hz) coupling, clearly due to1H-19F coupling.The 19F n.m.r. spectrum of (IIIa) shows that all fourfluorine nuclei are chemically inequivalent and that eachCF, group forms an AB system. One CF, group has reson-ances at 76.6 and 88.7 p.p.m. while the other two resonancesoccur a t higher field, 113.6 and 116.9 p.p.m. The higherfield signals are assigned to the CF, group p to the iron atom.5This assignment is supported by the 19F spectrum of thecorresponding adduct of tricarbonyl (isoprene)iron and hexa-fluoropropene, whose structure has been established byX-ray crystallography, which showed resonances at 101.2p.p.m.and 117.0 assignable to FeCF(CF,)CF,.6 In both(IIIa) and the hexafluoropropene adduct the higher fieldresonance of the P-CF, group displays a large J(HF)coupling (36.0 Hz) to the adjacent methylene group.Examination of a molecular model of (IIIa) suggests that thesignal a t 116.9 p.p.m. be assigned to F3, and therefore theresonance at 113.6 p.p.m. to F4; regarding F3, the large J3,4coupling (222 Hz) is readily assigned and each half ’ of theE. Pitcher, A. D. Buckingham, and F.G. A. Stone, J . Chenz.Phys., 1962, 36, 124.Heteronuclear lH-19F decoupling experiments (Figures2 and 3) facilitated firm allocation of the remaining couplingconstants. In Figure 3 the decoupling results concerning F3and F 4 are detailed. Simultaneous irradiation of H6 and Hacollapses each half of F3 to a doublet of doublets. The 35.0and 14.0 Hz couplings are removed, giving J(F3H5) as 14.0Hz, and leaving vicinal FF couplings of 15.0 and 3.0 Hz.A t the same time each half of F4 is reduced to show only thevicinal FF couplings 7-0 and 4.0 Hz. Irradiation of H6 onlyremoves the 35-0 Hz coupling from F3, providing confirm-ation of the J(F3H6) assignment; this also reduced each‘ half ’ of F4 to a doublet of doublets. Irradiation of H5only reduced each half’ of the F3 resonance t o threedoublet coupling, and also caused F4 to revert to its originalcomplexity, demonstrating that J(F4H6) is 3.0 Hz.Similarly, in Figure 2 the decoupling experiments con-cerned with F1 and F2 are illustrated.Simultaneousirradiation of H6 and H6 collapsed each ‘ half ’ of the F1resonance to a doublet of doublets by removal of a 7.0 Hzcoupling, which irradiation of Ii5 only confirms is due toJ(F1H5). Thus, three of the four couplings to H5 have beenallocated: J4,6 7.5, J(F1H5) 7.0, and J(F3H5) 14.0 Hz givingJ5,6 as 14.0 Hz, by elimination. A7icinal FF couplings of15.0 and 7.0 Hz remain on F1, and clearly J1,3 = 15.0 andJ1,4 = 7.0 Hz. Thus, the two outstanding vicinal FFcouplings may be assigned as J2,4 4.0 and Jz,3 3.0 Hz.Simultaneous irradiation of both H5 and H6 does not, how-ever, affect the F2 resonance, suggesting that this fluorine isthe one coupled to H1 by 4.0 Hz.A model of the complex6 M. Green, B. Lewis, J. J . Daly, and F. Saw, followingpaper1975 1111demonstrates the close proximity of H1 and F2 suggesting athrough- space coupling.Further support for these assignments was provided by astudy of the reaction of (IIIa) with trimethyl phosphite.The thermal reaction afforded the crystalline complex (XI),which showed two strong bands in the i.r. spectrum suggest-ing the reaction involves displacement of carbon monoxideby phosphite. Although the 1H and l9F n.m.r. spectra of(XI) closely resemble those of (IIIa) significant changesFIGURE 2 F1 (a) and F2 (b) resonances of complex (IIIa) inCDCl,; (c) shows F1 with €I5 and K6 decoupled; (d) shows F2with H5 and H6 decoupledI g IFIGURE 3 F3 (f) and F4 (e) resonances of (IIIa) (CDCI,); (g)shows F4 with H6 and H6 decoupled; (h) shows F3 under thesame conditions; (i) shows one half of F3 with HS decoupled;(j) shows F3 with Hs decoupledoccur in both the chemical shifts and resonance widths of thelow-field pair of lSF resonances, thus providing support forthe suggestion that these are due to the FeCF, group.As required by the illustrated structure of (11), in whichthe C2F4 links to the unsubstituted end of the pentadiene,comparison of the lH spectra of (I) and (11) show only smallvariation in both the chemical shifts and splitting patternsof the €3" and H6 resonances.The 1H-lH couplings withinthe allylic group also indicate the presence of a syn-methylsubstituent a t the terminal carbon atom. In agreement, theresonance assigned to HI, which differs in chemical shiftfrom its counterpart in (I) and (IIIa) has a coupling to F2(6.0 Hz) associated with it. Interestingly, the H3 resonanceof (11) displays, in addition to the typical allylic couplingsto H1 and H4, two equal couplings (3.5 Hz), which lH-lHdecoupling experiments showed did not arise from couplingwith any other protons. This is supported by the fact thatthe H3 signal of the corresponding adduct of CF3C,CF3 andbuta- 1,3-diene(tricarbonyl)iron, where HF coupling isrestricted to the methylene protons, shows only threecouplings, all of the expected allylic type.Since thesplitting patterns of the F1 and F3 signals of (11) are identicalwith their counterparts in (I), whereas those of FZ and F4are not, it is concluded that the latter nuclei must be coupledto H3. These unusual couplings are also a feature of thecentral allylic proton of (I) and the adduct from C,F, andIt was demonstrated that the fluoro-olefin oxidative link-ing reaction is not restricted to open-chain diene complexesof Fe(CO), by studying the reaction of C2F4 with tricarbonyl-(cyclohexa- 1 , 3-dieneJ bicyclo[4. 2.0Jocta-2,4-dieneJ or cyclo-octa- 1,3-diene)iron.U.V. irradiation of a hexane solution of C2F, and tri-carbonyl(cyclohexa-1,3-diene)iron afforded the crystalline1 : 1 adduct (V), which showed the expected i.r.and massspectra. Examination of the n.m.r. spectra with the aid of1H-1H decoupling experiments and reference to a molecularmodel led to the assignment of resonances due to a n-allylicgroup and a C,F4 linked system.In the lH n.m.r. spectrum of (V), H2 appears a t T 4-52 asan apparent doublet of triplets, with coupling constants of6.5, 6.5, and 4.0 Hz, and H3 resonates as a triplet of doubletscentred a t T 5.03 with associated couplings of 6-5, 6.5, and2.0 Hz. The remaining allylic proton, HI, occurs as a com-plex multiplet centred at T 5.58. Double irradiation of H2removed a doublet coupling of 6-5 Hz from both H1 and H3;this irradiation has no affect on the other protons, leaving H2with a 4.0 Hz lH-19F coupling. When H1 was irradiatedthe H3 signal collapsed to a triplet giving J1,3 2.0 Hz.Thus, H1 can be allocated Jl,$ 6-5 and J1,3 2.0 Hz, andfurther double-irradiation experiments showed that HI isalso coupled equally (5.0 Hz) to the adjacent methyleneprotons H7 and H8.The H4 resonance appeared as a six-line multiplet a t 7 7.26; irradiation of this signal affectsthree resonances, H3 and the methylene signals, leading tothe assignments J4,5 = J4,6 7.0, and J3,4 6.5 Hz. Thissuggested that the remaining coupling (15-0 Hz) on H4 mustbe due to lH-lsF coupling.The l9F spectrum of (V) shows two AB systems; signalsdue to the a-CF, group appear at 63.0 and 97.2 p.p.m. Boththese signals are well resolved and one of them (97.2 p.p.rn.1exhibits, in addition to a large geminal FF coupling (247Hz), only one other vicinal FF coupling (7-5 Hz).In con-trast, the resonance at 63.0 p.p.m. exhibits couplings of 247,12.0, and two of 7.5 Hz; of these, two (12.0 and 7.5 Hz) arevicinal FF couplings while the remaining (7-5 Hz) couplingmust arise from a through-space interaction with a nearbymethylenic proton, implying that this fluorine resonancecorresponds to F2. Examination of a molecular model sup-ports this interpretation and suggests that the proton in-volved is HS. Therefore, it appears that in (V), F 2 resonatesat higher field than F1, a reversal of the trend found with therelated acyclic system. The signals due to F3 and F4 occurat above 100 p.p.m., in line with the shifts observedwith (1)-(IV).Allocation of the vicinal FF couplings, withthe exception of J1.4, was possible; the latter must be <0.8CFe (X-C4H4) (CO) 31 *' M. Green and B. Lewis, unpublished observations1112 J.C.S. DaltonHz. In addition, the lH-19F couplings J(F3H4) 15-0 andJ(F4H2) 4.0 Hz were established, the latter comparingfavourably with the corresponding couplings in (I) and (11).The corresponding reaction between C2F4 and tricarbonyl-(bicyclo[4.2.0]octa-2,4-diene)iron afforded the 1 : 1 adduct(VI), which was assigned the illustrated structure on thebasis of the analytical and spectroscopic data. The n.m.r.data closely corresponded to that found for (V). There wasno evidence for the formation of a C, ring-opened adduct.Reaction of C2F, and tricarbonyl(cyc1o-octa- 1,3-diene)ironoccurred on irradiation to give a mixture (3 : 1) of two crystal-line compounds (VII) and (VIII) which were separated byfractional crystallisation. The i.r.spectrum of (VII) showsthree strong terminal bands in agreement with the illustratedx-allylic structure containing an Fe(C0) group.The 1H n.m.r. spectrum of (VII) shows low-field resonancesa t T 5.00 (2H) and 5.82 (lH), which, although not typical of( X a 1In the n.m.r. spectrum of (VIII) the unco-ordinateddouble-bond protons, H3 and H4, appear at low field ( T 4.02-4.40) as overlapping multiplets with a cis-coupling of 7.5 Hz.Apart from a complex resonance (9H) in the methylenicregion the only other signal in the spectrum is a multiplet(1H) at T 6.48.The latter cannot be due to HI, because oneof the P-CF, fluorines bears a J(HF) coupling of 37.0 Hz(clearly to H1) which is present in this signal, therefore, byelimination this signal must correspond to H2. This is sup-ported by the fact that irradiation of the Ha94 signal removesa 10.5 Hz splitting from the resonance at T 6.48, which alsoallows the allocation of the unco-ordinated double-bondposition.Thus, the complex (VIII) is a ferracyclopentane, formedfrom (VII) by displacement by carbon monoxide of the co-ordinated double bond. An alternative conformation forthe C, ring in (VIII), in which the ring is bent towards thecoa x-ally1 group contained in an acyclic system, may beassigned to an allylic group bonded in the o,x-mode.De-coupling experiments confirm this interpretation, and deter-mination of cis J(H2H2) gave a typical value of 7-5 Hz.Two of the methylene proton resonances occur at lowerfield than the others, and from examination of a molecularmodel i t is assumed that these are due to Hll and H12, thelow-field shift arising due to close proximity of the a-CF,group. Further study of the model demonstrated thatseveral other methylene protons are quite close to theFeCF,CF, chain suggesting the possibility of widespreadthrough-space 1H-19F coupling. In agreement, the l9Fn.m.r. spectrum, although exhibiting typical chemical shifts,shows complex multiplets unlike the other adducts.The i.r. spectrum of the other product (VIII) showed, inaddition to a weak band a t 1624 cm-l assigned to v c s , fourterminal carbonyl bands, suggesting the presence of anFe(CO), group.This was supported by the mass spectrum.ocCO F '( X b 1FeCF,CF, group, is considered unliltely due to the presencein a model of considerable non-bonding interactions. Thel9F n.m.r. spectrum, which exhibited typical chemical shiftsand coupling constants, showed no evidence of through-space 1H-19F coupling, which might be expected if this wasthe preferred conformation in solution.Irradiation of a solution of tricarbonyl(norb0rnadiene)ironand tetrafluoroethylene leads to the formation of anFe(CO), species (IX), which is assigned a nortricyclenestructure. The i.r. and mass spectra show the expectedfeatures for such a structure.In the 1H n.m.r.spectrum of (IX) all the resonances occurin the range T 7-5-8.7, there being no evidence for reson-ances corresponding to protons attached to either a co-ordinated or unco-ordinated double bond. Comparison ofchemical shifts with those reported for other nortricyclenesand decoupling experiments allowed the assignments to bemade, which are listed in the Experimental section1975 1113It has been observed 8 that in nortricyclene systems bear-ing electronegative groups a t C3 and at C6 noticeable para-magnetic shifts are experienced by all protons, especially thebridgehead hydrogen, H4. Accordingly, the slightly broadsinglet (1H) at T 7.53 is assigned to this proton and a sharpersinglet (1H) at T 7.96 is attributed to H1.The correspond-ing resonance in nortricyclene itself occurs 8 at T 8.09. TheQ .*-Pcobroad multiplet (1H) at T 7-79 is assigned to H6, the signalshowing HF coupling. The methylene protons H7 and Haresonate as a sharp multiplet (2H) at T 8-55 with only asmall coupling to the bridgehead protons. The multiplet(1H) at T 8.68 is assigned to H3, the high-field position beingattributed to shielding by the metal.9 Finally, the multiplet(2H) at 7 8.41 is assigned to H2 and H8; the chemical shiftsbeing similar to those observed lo in related electronegativelysubstituted nortricyclenes.The l9F n.m.r. chemical shifts are not the same as thosefound in the other complexes described, the a-CF, fluorineshaving very similar (within 3 p.p.m.) chemical shifts a trather low field.The P-CF, shifts are more typical.Examination of molecular models shows that this complexcan exist in either a boat or a chair conformation, however, itis not possible on the present evidence to distinguish firmlybetween these two alternatives. It may be noted that F2 isequally coupled (5.5 Hz) to F3 and F 4 , an observation whichis more readily accommodated by the chair form.Both tetra- and tri-carbonyl(trans-cinnamaldehyde)iron 11, l2 react with tetrafluoroethylene on irradiation toafford a pale yellow crystalline material which is formulatedas a mixture ( 4 : 5) of the tetracarbonyl species (Xa) and(Xb). The presence in the i.r. spectrum of a band at 1667scm-l (CHO) in addition to four terminal carbonyl bandssuggested that in the reaction leading to the formation of theisomeric ferracyclopentanes the co-ordinated cinnamalde-hyde behaves as a mono-olefin.This is supported by boththe lH and 19F n.m.r. spectra.Proton-proton decoupling experiments enable theCH(CH0) resonance, which is coupled (3.0 Hz) to thealdehydic proton, to be distinguished for both isomers in aspectrum of the mixture. This allowed CHPh to beassigned for each isomer. It is clear that the isomerism in(Xa) and (Xb) arises from formal attack by C2F, at oppositeends of the co-ordinated olefinic bond of unidentate cin-D. J. Thecker and J. P. Henry, J . A itzer. Chem. SOC., 1963,85,3204.J. K. Coulson, J . Amel.. Chem. SOC., 1969, 91, 200.lo I<.S. Neale and E. B. Whipple, J . Anzer. Chem. Soc., 1964,l1 12. Weiss, K. Stark, J. G. Lancaster, and H. D. Murdoch,l2 E. Weiss, K. Stark, J. G. Lancaster, and H. D. Nurdoch, 2.86, 3130.Helv. Chim. Acta, 1963, 46, 288.Natiwforsch (B), 1964, 19, 284.namaldehyde. Such isomerism also accounts for the com-plex nature of the F3 and F4 resonance in the lDF spectrumof the mixture. Although the 1H-fH coupling (Jl,2) con-stant cannot be accurately extracted from the spectrum, anapproximate value of 4.0 Hz can be assigned for bothisomers, suggesting that in both (Xa) and (Xb) the phenyland CHO group have a relative cis-configuration.HcoSince in a previous investigation it was found that thezerovalent species [M(CO),L,] (L = phosphine or phos-phite; M = Fe,13 Ru,13 or 0 s l*) react on U.V.irradiationwith tetrafluoroethylene to form the complexes [MCF2CF2-(CO),L,J, and in contrast a variety of zerovalent tricarbonyl-(o1efin)iron complexes undergo an oxidative linking reactionwith C2F4, it was clearly important to examine the reactionof C,F, with tricarbonyl(0-styryldiphenylphosphine)iron,i.e. [Fe(sp) (CO),].15*16Irradiation of a solution of [Fe(sp)(CO),] in the presenceof an excess of tetrafluoroethylene gave the yellow crystal-line 1 : 1 adduct (XII), which showed, in the i.r. spectrum,three terminal carbonyl bands with similar frequencies tothose observed in the complexes discussed above. How-ever, the relative intensities of the bands are not the same.In (XII) the highest band is weak, whereas in the othercomplexes this band is strong.The lH n.m.r. spectrum of (XII) shows three resonancesin addition to a broad complex multiplet at low field due tothe aromatic protons of the Ph2P group. A signal at T 6.1 1is assigned to H1 of the illustrated structure, and appears asa doublet of doublets due to lH-lH couplings, which areeasily measured (12.0 and 6.0 Hz) and assigned, with the aidof decoupling experiments, to J1, 3 and J1, respectively. Inagreement with this assignment this signal does not displayHF coupling. The two remaining resonances (7 7.10 and7.40), due to the methylene protons H2 and H3, are morecomplex. However, decoupling experiments showed thatthe signal at T 7.10 is coupled to H1 by 12.0 Hz, and thisfinding, in conjunction with examination of dihedral anglesin a molecular model, permits its allocation to proton H3.The l9F n.m.r. spectrum shows four AB type resonanceswith chemical shifts typical of a ferracyclopentane. Sig-nificantly, both F1 and F2 show a PF coupling (16.5 and 18-0Hz respectively) ; in addition, F1 is coupled (5.5 Hz) to Ha.These observations are comparable with either of the twor--ll3 R. Burt, &I. Cooke, and &I. Green, J . Ckem. Soc. ( A ) , 1970,l4 M. Cooke, NI. Green, and T. A. Kuc, J . Chem. Soc. ( A ) , 1971,2975.1200.14. A. Bennett, R. S. Nyholm, and J. D. Saxby, J . Ovgano-l6 M. A. Bennett, G. B. Robertson, I. B. Tomkins, and P. 0.metallic Chem., 1966, 10, 301.Whimp, Chem. Comm., 1971, 341