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Synthesis of Cyclopentadienyl Iron Alkoxycarbene Complexes via Vinylidene Intermediates: X-ray Structures of [Fe{C(OMe)Me}(dppe)Cp][I] and [Fe{C(CH2)3O}(dppe)Cp][PF6] Sarah El-Tarhuni,a Letícia M. Manhães,a Charlotte Morrill,a James Raftery,a Jaskirit K. Randhawaa and Mark W. Whiteleya* a School of Chemistry, University of Manchester, Manchester M13 9PL, UK Corresponding Author. Email [email protected] Tel. +441612754634 Abstract The reaction of [FeI(dppe)Cp], 1 (dppe = Ph2PCH2CH2PPh2) with HC≡CSiMe3 in refluxing methanol results in formation of a mixture of the vinylidene complex [Fe(=C=CH2)(dppe)Cp]+, 2 and the heteroatom stabilised alkoxycarbene [Fe{C(OMe)Me}(dppe)Cp]+, 3. The carbene 3 is formed by addition of the alcohol solvent to the reaction intermediate vinylidene 2, and prolonged reflux in methanol (4 days) resulted in complete conversion of 2 to 3. The methoxycarbene, 3 was isolated as a stable solid and fully characterised by spectroscopic and structural methods. Vinylidene 2 also reacts with ethanol to give the ethoxycarbene [Fe{C(OEt)Me}(dppe)Cp]+, 4 but no reaction was observed in refluxing isopropanol, thus providing a specific synthesis of vinylidene 2 from 1 and HC≡CSiMe3. An example of an alcohol based, intramolecular nucleophilic addition to a mono-substituted vinylidene [Fe(=C=CHR)(dppe)Cp]+ was uncovered in the reaction of 1 with 3-butyn-1-ol which leads to the synthesis of the cyclic oxacarbene complex [Fe{C(CH2)3O}(dppe)Cp][PF6], 5. X-ray crystallographic investigations on 3[I] and 5[PF6] determine Fe-Cα bonds lengths of 1.851(5) and 1.834(2) Å respectively, intermediate between previously reported Fe-Cα distances for the amino carbene [Fe{C(NH2)Me}(dppe)Cp][PF6] and [Fe{=C(H)Me}(dppe)Cp*][PF6]. Keywords Iron; Vinylidene; Nucleophilic addition; Alcohol; Alkoxycarbene 1 the alkylidene complex Introduction Metal cumulenylidene complexes have important applications as intermediates in the functionalization of terminal alkynes [1]. Experimental and theoretical investigations demonstrate that the regioselectivity of nucleophilic and electrophilic addition to vinylidene [2,3], allenylidene [4,5] and higher cumulenylidene [6] ligands can be controlled to give a wide range of products. Nucleophilic addition at the alpha carbon of a metal vinylidene complex is a well-established process and reactions with a range of nucleophiles have been investigated [2,7,8]. A frequently employed protocol involves reaction of a metal halide M-X with a terminal alkyne HC≡CR in an alcohol solvent R’OH to give the vinylidene intermediate [M(=C=CHR)]+ followed by addition of R’OH to the vinylidene C=C bond to give the heteroatom-stabilised, Fischer carbene type complex [M{C(OR’)CH2R}]+ [9-16]. Investigations where M = RuL2Cp (L2 = dppe or 2PPh3) or RuL2(η-indenyl) (L2 = dppe, 2PPh3, or PPh3/ P(OEt)3) indicate that the process is sensitive to both steric and electronic factors and is promoted by low steric demand of M, R and R’ and by electron poor M and R centres which enhance electron deficiency at the vinylidene Cα carbon. In view of the established reactivity of ruthenium complexes [Ru(=C=CHR)L2(η-L’)]+ (L’ = Cp or indenyl) towards solvent-based nucleophilic addition, the very limited development of an analogous chemistry of the corresponding iron system [Fe(=C=CHR)L2Cp]+ (L2 = P-donor ligand) is surprising. Mixed carbonyl phosphine derivatives [Fe(=C=CHR)(CO)(PPh3)Cp]+ do react with R’OH [11] and the dppm (dppm = Ph2PCH2PPh2) substituted vinylidene complex [Fe(=C=CH2)(dppm)Cp]+ has been reported to react with methanol to give [Fe{C(OMe)Me}(dppm)Cp]+ although, to our knowledge, supporting data were not provided [17]. Very recently, addition of NH3 to [Fe(=C=CH2)(dppe)Cp]+ to give the amino carbene [Fe{C(NH2)Me}(dppe)Cp]+ has been described [8] but an analogous direct reaction of [Fe(=C=CHR)(dppe)Cp]+ and related disubstituted vinylidene derivatives with R’OH or water is reported not to proceed [18, 19]. In this article, we demonstrate that in fact, in very specific cases, vinylidene complexes of the type [Fe(=C=CHR)(dppe)Cp]+ can be induced to undergo addition at Cα with R’OH based 2 nucleophiles to give synthetically useful [20], heteroatom stabilised carbenes [Fe{C(OR’)CH2R}(dppe)Cp]+, albeit with much reduced reactivity by comparison with Ru analogues. Results and discussion 1. Synthetic Studies. In view of the steric constraints to the addition of alcohols R’OH to vinylidenes [Fe(=C=CR2)(dppe)Cp]+, the search for a stable alkoxycarbene derivative of the Fe(dppe)Cp system commenced with an investigation of the reaction of MeOH with the unsubstituted vinylidene [Fe(=C=CH2)(dppe)Cp]+ (2). Several protocols for the synthesis of 2 have been developed [18, 21, 22], including the reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in an alcohol solvent [22]. In the initial investigation [Fe(=C=CH2)(dppe)Cp][PF6] was reported to be formed in high yield from the reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in MeOH [22a] although a later, independent synthesis employed ButOH as solvent with the explicit purpose of impeding the formation of an alkoxycarbene by-product [22b]. The reaction of [FeCl(dppe)Cp*] with HC≡CSiMe3 in refluxing MeOH has also been investigated [23] but again, only the vinylidene [Fe(=C=CH2)(dppe)Cp*][PF6] was isolated, consistent with the increased steric demand of the Cp* ring. The reaction of [FeI(dppe)Cp] (1) [24], with HC≡CSiMe3 and K[PF6] in refluxing methanol (Scheme 1) was allowed to progress for 3 hours following which the initially brown reaction mixture had changed to orange-red in colour. A sample of the product was isolated as an orange solid and spectroscopic characterisation by 1H, 31P{1H} NMR and mass spectrometry confirmed the successful formation of 2 (identified by comparison with previously reported data). However, in addition to the spectroscopic data characteristic of vinylidene 2, the isolated reaction product contained a second, unidentified complex, most apparent in the 31P{1H} NMR spectrum recorded in CD2Cl2 as a singlet resonance at 113.3 ppm. To explore the possible involvement of this unidentified complex in an extended reaction sequence, the methanol reflux was continued with periodic monitoring of the reaction mixture by 31P{1H} NMR spectroscopy. After a total reflux time of 4 days, the 31P{1H} resonance at 97.1 ppm for vinylidene complex 2 3 was totally absent and only the resonance at 113.3 ppm associated with the unknown remained. The reaction product was isolated as a yellow solid and was identified by subsequent spectroscopic and structural (see below) characterisation as the iodide salt of the target methoxycarbene complex [Fe{C(OMe)Me}(dppe)Cp][I] (3). The formulation as a carbene complex is supported by a triplet resonance in the 13C{1H} NMR spectrum at 321.6 ppm for the Cα carbene carbon (shifted to high field by comparison with Cα of vinylidene 2, δ 13C{1H} 354.7 ppm [22]) and by the appearance of resonances at 59.6 and 42.7 ppm consistent with the OMe and Me substitutents respectively of the methoxycarbene ligand. The low field shift of 16 ppm in the 31P{1H} spectrum on conversion of 2 to 3 is closely comparable to the equivalent shift for the Cp* analogues [Fe(=C=CH2)(dppe)Cp*][PF6] and [Fe{C(OMe)Me}(dppe)Cp*][PF6] (δ 31 P{1H}, 90.7 (CDCl3) and 111.9 (CD2Cl2) ppm respectively) [23,25]. Scheme 1: Reagents and conditions (i) HC≡CSiMe3/K[PF6], reflux in R’OH (R’ = Me, Et, Pri), 3 h.; (ii) prolonged reflux in MeOH or EtOH; (iii) HC≡CCH2CH2OH/K[PF6], reflux in MeOH, 2 h. 4 The isolation of 3 principally as an iodide salt rather than as a hexafluorophosphate salt was unexpected given the inclusion of excess K[PF6] in the reaction mixture. However the iodide salt 3[I] was obtained in two independent ‘one-pot’ preparations and the presence of the iodide counter-ion was inferred from microanalytical data for iodine and phosphorus (see experimental section) and was further confirmed by an X-ray structural investigation. Moreover, under similar reaction conditions (see below), the vinylidene complex 2 was also isolated as an iodide salt starting from [FeI(dppe)Cp], HC≡CSiMe3 and K[PF6]. As reported previously [8], use of [NH4][PF6] as an alternative source of the hexafluorophosphate counter-ion led to the formation of small quantities of the aminocarbene [Fe{C(NH2)Me}(dppe)Cp]+ as a reaction by-product. However by-products resulting from the iodide-promoted dealkylation of an alkoxycarbene [26, 27] were not observed in the synthesis of 3[I]. The conversion of vinylidene 2 to methoxycarbene 3 represents a new reaction type in the Fe(dppe)Cp system. However the rate of reaction is very slow (even with the low steric protection afforded to Cα by the H substituents at Cβ of 2). By comparison [Ru(=C=CH2)L2Cp]+ (L2 = 2PPh3 or dppe) are reported to react rapidly with methanol under mild conditions [12]. To examine the extent of the reactivity exhibited by [Fe(=C=CH2)(dppe)Cp]+ towards R’OH, the effect of variation of R’ was investigated. An isolated sample of vinylidene 2 was dissolved in EtOH and refluxed for 24 h. Subsequent work up led to the isolation of a mixture of unreacted 2, and the new ethoxycarbene complex [Fe{C(OEt)Me}(dppe)Cp]+, (4); partial separation was achieved by fractional recrystallization from CH2Cl2/ diethyl ether from which 4 was precipitated preferentially as the first fraction. The identity of 4 as an ethoxycarbene complex was confirmed by a triplet resonance in the 13C{1H} NMR spectrum at 321.5 ppm for the Cα carbene carbon, by the appearance of resonances at 70.3, 12.9 ppm and 43.7 ppm consistent with the OEt and Me substitutents respectively of the ethoxycarbene ligand and by a characteristic low field shift in the 31P{1H} NMR resonance (113.6 ppm). However when the reaction of 1 with HC≡CSiMe3 was carried out in 2-propanol, a clean sample of vinylidene 2 was isolated (as the iodide salt [Fe(=C=CH2)(dppe)Cp][I]) with no evidence observed for the formation of a secondary alkoxycarbene product. The use of 2-propanol as reaction solvent therefore provides a reliable protocol for the synthesis of pure samples of vinylidene complex 2 from 1; as discussed above, an equivalent reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in ButOH is also reported to give only vinylidene 2 in high yield [22b]. 5 Our attempts to isolate an alkoxycarbene derivative from the extended reaction (18 hours) of the monosubstituted vinylidene [Fe(C=CHPh)(dppe)Cp][PF6] with refluxing MeOH have been unsuccessful although mass spectrometry of the isolated product revealed a weak peak with m/z = 653, consistent with formation of the known complex [Fe{C(OMe)Ph}(dppe)Cp]+, [28]. An alternative strategy to facilitate the conversion of a monosubstituted vinylidene to an alkoxycarbene is the promotion of an intramolecular process involving the formation of a hydroxyvinylidene intermediate [M{=C=CH(CH2)nOH}]+ which subsequently undergoes intramolecular addition at Cα to give a cyclic oxacarbene product [27, 29-31]. This method has proved to be effective even at the electron-rich Mo(dppe)(η-C7H7) centre where the large cycloheptatrienyl ring affords additional steric protection to the vinylidene alpha carbon atom [30]. The reaction of [FeI(dppe)Cp] with 3-butyn-1-ol, HC≡C(CH2)3OH, in refluxing methanol in the presence of K[PF6] resulted in a rapid colour change (15 min.) from brown to pale yellow and subsequent work up led to the isolation of the 2-oxacyclopentylidene (ocp) complex [Fe{C(CH2)3O}(dppe)Cp][PF6], (5). The carbene character of complex 5 is implicit in the observation of a triplet resonance at 313.0 ppm for Cα in the 13C{1H} NMR spectrum and the molecular structure was confirmed by a single crystal X-ray structure determination (see below). 2. X-Ray Structural Investigations Although a wide range of carbene complexes supported by Ru(dppe)Cp and Ru(PPh3)2Cp auxiliaries has been structurally characterised, [13, 32-35], structural investigations of analogues based on the Fe(dppe)Cp’ (Cp’ = Cp or Cp*) system appear to be restricted to [Fe{C(NH2)Me}(dppe)Cp][PF6], [8] and the alkylidene complex [Fe{=C(H)Me}(dppe)Cp*][PF6], [25]. The X-ray crystal structures of the oxygen heteroatomstabilised carbene complexes 3[I] and 5[PF6] have therefore been determined and important bond lengths and angles are summarised in Table 1 together with comparative data for related cyclopentadienyl iron and ruthenium carbene complexes. The molecular structures of 3[I] (as a CH2Cl2 solvate) and 5[PF6], annotated with atomic numbering schemes are shown in Figures 1 and 2 respectively. 6 Figure 1. Molecular structure of 3[I].CH2Cl2 with thermal ellipsoids plotted at 50% probability. Figure 2. Molecular structure of 5[PF6] with thermal ellipsoids plotted at 50% probability. 7 Table 1: Key structural data for carbene complexes [M{C(ER’x)R}L2Cp’]+ 3[I] Complex ML2Cp’ Fe(dppe)Cp C(ER’x)R C(OMe)Me Bond Lengths (Å) M-Cα 1.851(5) 5[PF6] Fe(dppe)Cp ocp a Cα-E 1.333(6) 1.328(2) Cα-C(R) 1.495(7) 1.518(3) M-P 2.1859(12) 2.1991(13) 2.1924(6) 2.2028(6) 1.834(2) Bond Angles (°) M-Cα-E 119.0(3) 123.72(14) M-Cα-C(R) 126.9(4) 129.29(16) E-Cα-C(R) 114.0(4) 106.92(17) Data This work This work a ocp Fe(dppe)Cp C(NH2)Me Fe(dppe)Cp* C(H)Me Ru(PPh3)2Cp C(OMe)Me Ru(dppe)Cp ocp a 1.9272(15) 1.9251(15) 1.312(2) 1.310(2) 1.518(2) 1.519(2) 2.1756(4) 2.1829(4) 2.2032(4) 2.1860(4) 1.787(8) 1.931(9) 1.92(1) - 1.321(9) 1.32(1) 1.49(1) 1.50(1) 1.51(1) 2.221(2) 2.239(7) 2.333(2) 2.336(2) 2.267(3) 2.273(3) 128.32(11) 128.61(12) 122.21(11) 121.78(11) 109.4(1) 109.5(1) ref.8 - 120.9(6) 126.5(7) 141.3(6) 124.8(7) 127.1(8) - 114.3(8) 106.3(9) ref. 25 ref. 32 ref. 35 = 2-oxacyclopentylidene 8 The character of the iron to C-alpha bond in a series of alkylidenes and heteroatom (E) stabilised carbenes has been the focus of a series of theory investigations on complexes of the type [Fe{C(ER’x)R}L2Cp]+ [36,37]. There is a clear correlation between the extent of heteroatom stabilisation and the length of the iron to C-alpha bond; heteroatom stabilisation leads to a longer metal to carbene carbon distance as the acceptor character of the carbene ligand is reduced. The data in Table 1 permit a direct experimental confirmation of these investigations. The alkylidene complex [Fe{=C(H)Me}(dppe)Cp*][PF6] exhibits a short Fe-Cα distance (1.787(8) Å), similar to that reported for the vinylidene [Fe(=C=CH2)(dppe)Cp*][PF6] (1.763(7)Å, [38]) and consistent with a significant degree of multiple bond character in the Fe-Cα bond. By contrast the amino carbene ligand of [Fe{C(NH2)Me}(dppe)Cp][PF6] represents the opposite extreme of the range with a Fe-Cα distance of 1.9272(15), 1.9251(15) Å consistent with extensive N=Cα double bond character in the heteroatom stabilised carbene and a Fe-Cα bond with little, if any multiple character [8]. The Fe-Cα distances for 3[I] and 5[PF6] (1.851(5), 1.834(2) respectively) lie intermediate between the two previously reported examples and agree well with the computed value of 1.873 Å determined for [Fe{C(OMe)Me}(CO)(PMe3)Cp]+ [36]. The Fe-Cα distances of 3[I] and 5[PF6] indicate that the oxygen heteroatom stabilised carbene ligands are also relatively poor acceptor systems with a large contribution from a O=Cα double bond in the overall structure. In addition to Fe-Cα and O-Cα distances, the Fe-P bond lengths provide an indirect indicator of the character of the Fe-Cα bond by acting as a monitor of electron density at the Fe centre. For the alkylidene complex [Fe{=CH(Me)}(dppe)Cp*][PF6], the average Fe-P distance is 2.23 Å; this quite long bond reflects a reduction in Fe to P back bonding effects as electron density at the Fe centre is depleted by the strongly accepting alkylidene ligand. By contrast, average Fe-P distances in the heteroatom stabilised carbene complexes (2.193, 2.198, 2.187 Å for 3[I], 5[PF6] and [Fe{C(NH2)Me}(dppe)Cp][PF6] respectively) are much shorter, consistent with enhanced Fe-P back bonding and a corresponding reduction in the electron acceptor capacity of the heteroatom stabilised carbenes. Finally the geometry of the {C(OMe)Me} and ocp ligands in 3[I] and 5[PF6] may be compared with Ru analogues. With the obvious exception of M-Cα bond lengths, the bond lengths and angles defining the alkoxycarbene ligands compare very closely with the corresponding parameters in the analogous Ru complexes (see Table 1). 9 Conclusions The nucleophilic addition of alcohols R’OH to Cα of group 8 metal, half-sandwich vinylidene complexes [M(=C=CHR)L2(η-L’)]+ (M = Fe, Ru, Os) to give heteroatom stabilised alkoxycarbene products [M{C(OR’)CH2R}L2(η-L’)]+ is controlled by a complex interplay of steric and electronic factors and dependent upon all the variables M, R, R’, L and L’[11-16, 39]. Where L2 = dppm, dppe or 2PPh3, successful reactions are generally limited to less sterically demanding options (R = H, R’ = Me, Et) but, as highlighted in the current report, the contrast in reactivity between cyclopentadienyl iron and ruthenium analogues is quite marked. Thus for iron complexes [Fe(=C=CHR)L2Cp]+ (L2 = dppm [17], dppe) observation of this reactivity type is currently limited essentially to R = H, R’ = Me, Et with a prolonged reaction time required where L2 = dppe. By contrast Ru analogues [Ru(=C=CHR)L2Cp]+ (L2 = dppe, 2PPh3) either react much more rapidly (R = H, R’ = Me) or show an extended reactivity pattern (R = Me, Ph, CO2Me, R’ = Me). The X-ray structural characterisations of [Fe{C(OMe)Me}(dppe)Cp][I], 3[I], and [Fe{C=C(CH2)3O}(dppe)Cp][PF6], 5[PF6], complete a dataset that permits examination of the structural differences arising from transition of the series alkylidene, alkoxycarbene, aminocarbene, against a common support unit. The elongation in the Fe-Cα distance along the series [Fe{=C(H)Me}(dppe)Cp*][PF6], (1.787(8) Å), [Fe{C(OMe)Me}(dppe)Cp][I], (1.851(5) Å) and [Fe{C(NH2)Me}(dppe)Cp][PF6], (1.9272(15), 1.9251(15) Å) is consistent with a reduction in the metal to carbene π-interaction and an increased degree of heteroatom to Cα multiple bond character. 10 Experimental General Procedures. The preparation, purification and reactions of the complexes described were carried out under dry nitrogen. All solvents were dried by standard methods, distilled and deoxygenated before use. NMR spectra were recorded on a Bruker Avance III HD (500 MHz 1H, 125 MHz 13C{1H}, 202 MHz 31P{1H}) spectrometer. Infrared spectra (solid state) were obtained on a Nicolet iS5 FT-IR spectrometer fitted with an ATR attachment. Electrospay mass spectra were obtained on a Waters SQD2 instrument and MALDI mass spectra were recorded using a Shimadzu Axima Confidence spectrometer. Microanalyses were conducted by the staff of the Microanalytical Service of the School of Chemistry, University of Manchester. Preparation of [Fe(=C=CH2)(dppe)Cp][I], 2[I] A solution of [FeI(dppe)Cp] (0.75 g, 1.16 mmol), trimethylsilylacetylene (0.57 g, 5.80 mmol) and K[PF6] (0.43 g, 2.32 mmol) in isopropanol (40 cm3) was refluxed with stirring for 3h to give a dark red solution. Reduction of solvent volume in vacuo and cooling resulted in precipitation of the crude product which was recrystallized from dichloromethane/diethyl ether to give the product 2[I].CH2Cl2 as a red solid; yield 0.21 g (24%). 1H NMR (CDCl3): δ 3.08, 3.11 (br, 4H, CH2, dppe), 3.92 (t, J(P-H) 3Hz, 2H, C=CH2), 4.93 (s, 5H, Cp), 7.18, 7.41, 7.47 (m, 20H, Ph, dppe). 31P{1H} NMR (CDCl3): δ 97.1. IR: (solid state) ν(C=C)/cm-1, 1624. MALDI/MS (m/z): 545 [M]+. Anal. 2[I].CH2Cl2: Calcd. (%) for C33H31P2FeI.CH2Cl2: C, 53.9; H, 4.4; P, 8.2; I, 16.8. Found, C, 54.8; H, 4.6; P, 8.7; I, 14.3. Anal. 2[I] (after recrystallization from acetone/ether): Calcd. (%) for C33H31P2FeI: C, 58.9; H, 4.6. Found, C, 58.4; H, 4.5. Preparation of [Fe{C(OMe)Me}(dppe)Cp][I], 3[I] A solution of [FeI(dppe)Cp] (4.48 g, 6.93 mmol), trimethylsilylacetylene (3.20 g, 32.7 mmol) and K[PF6] (2.51 g, 13.6 mmol) in methanol (100 cm3) was refluxed with stirring for 4 days to give an orange solution. Methanol was removed in vacuo and the residue was recrystallized from CH2Cl2/diethylether to give 3[I].CH2Cl2 as a bright yellow solid; yield 1.65 g (30%). 1H NMR (CD2Cl2): δ 2.43 (s, 3H, Cα-Me), 2.66 (s, 3H, Cα-OMe), 2.80 (br, 2H, 11 CH2, dppe), 2.96 (br, 2H, CH2, dppe), 4.48 (s, 5H, Cp), 7.10, 7.37, 7.45, (m, 20H, Ph, dppe). 13 C{1H} NMR (CD2Cl2): 321.6 (t, JC-P 27 Hz), Cα; 139.6, m, 134.8, m, Phi; 131.9, m, 130.5, m, Pho; 130.8, s, 130.2, s, Php; 129.0, m, 128.9, m, Phm; 87.1, s, Cp; 59.6, s, Cα-OMe; 42.7, s, Cα-Me; 29.8, m, CH2 (dppe). 31P{1H} NMR (CD2Cl2): δ 113.3. IR: (solid state) ν(C-O)/cm-1, 1222, 1172. ES(+)/MS (m/z): 577 [M]+. Anal. 3[I].CH2Cl2: Calcd. (%) for C34H35P2OFeI.CH2Cl2: C, 53.2; H, 4.7. Found, C, 53.0; H, 4.6. A small sample of 3[I].CH2Cl2 was dissolved in acetone (in which it was only sparingly soluble) and precipitated with diethylether to give 3[I] free from CH2Cl2 of crystallisation. Anal. 3[I]: Calcd. (%) for C34H35P2OFeI: C, 58.0; H, 5.0; P, 8.8; I, 18.0; Found, C, 57.2; H, 5.3; P, 7.7; I, 15.2. Preparation of [Fe{C(OEt)Me}(dppe)Cp][I], 4[I] A solution of [Fe(=C=CH2)(dppe)Cp][I], 2[I], (0.15 g, 0.22 mmol), in ethanol (40 cm3) was refluxed with stirring for 24 h. Ethanol was removed in vacuo and the residue was recrystallized from CH2Cl2/diethylether. The first precipitate was collected as a yellow solid and recrystallized a second time from CH2Cl2/diethylether to give 4[I] as a bright yellow solid; yield 0.02 g (13%). 1H NMR (CD2Cl2): δ 0.27 (br, 3H, Cα-OCH2Me), 2.51 (s, 3H, CαMe), 2.93 (br, 2H, Cα-OCH2Me), 2.84 (br, 2H, CH2, dppe), 2.98 (br, 2H, CH2, dppe), 4.47 (s, 5H, Cp), 7.09, 7.36, 7.45, (m, 20H, Ph, dppe). 13C{1H} NMR (CD2Cl2): 321.5 (t, JC-P 27 Hz), Cα; 139.8, m, 134.5, m, Phi; 132.2, m, 130.5, m, Pho; 130.9, s, 130.1, s, Php; 129.0, m, 128.9, m, Phm; 87.1, s, Cp; 70.3, s, Cα-OCH2Me; 43.7, s, Cα-Me, 12.9, Cα-O-CH2Me; 29.8, m, CH2 (dppe). 31P{1H} NMR (CD2Cl2): δ 113.6. ES(+)/MS (m/z): 591 [M]+. Preparation of [Fe{C(CH2)3O}(dppe)Cp][PF6], 5[PF6] A solution of [FeI(dppe)Cp] (0.75 g, 1.16 mmol), 3-butyn-1-ol (0.41 g, 5.86 mmol) and K[PF6] ( 0.43 g, 2.32 mmol) in methanol (40 cm3) was refluxed with stirring for 2h resulting in the precipitation of a bright yellow solid. The solution was then cooled and reduced to half of its volume in vacuo and the resulting precipitate collected. The crude product was recrystallized from dichloromethane/diethylether, then acetone/diethylether to give the product 5[PF6], as a bright yellow solid; yield 0.40 g (47%). 1H NMR (CD2Cl2): δ 1.11 (br, 2H, Hγ), 2.72 (br, 2H, CH2, dppe), 2.99 (br, 2H, CH2, dppe), 3.20 (br, 4H, Hβ, Hδ), 4.53 (s, 5H, Cp), 7.11, 7.37, (m, 12 20H, Ph, dppe). 13C{1H} NMR (CD2Cl2): 313.0 (t, JC-P 26 Hz), Cα; 139.2, m, 134.7, m, Phi; 131.8, m, 130.6, m, Pho; 130.8, s, 130.3, s, Php; 129.0, m, 128.8, m, Phm; 86.6, s, Cp; 80.5, Cδ; 58.3, Cβ; 29.4, m, CH2 (dppe); 21.8, s, Cγ. P{1H} NMR (CD2Cl2): δ 111.0. IR: (solid 31 state) ν(C-O)/cm-1, 1192, 1153. MALDI/MS (m/z): 589 [M]+. Anal. 5[PF6]: Calcd. (%) for C35H35P2OFePF6: C, 57.2; H, 4.8; P, 12.7; Found, C, 57.3; H, 4.5; P, 12.3. Crystallography Single crystals of 3[I] (as a CH2Cl2 solvate) were obtained as yellow plates by vapour diffusion of diethyl ether into a CH2Cl2 solution of the complex at 4°C; yellow-brown blocks of 5[PF6] were obtained by vapour diffusion of diethyl ether into an acetone solution of the complex at 4°C. Single crystal X-ray data were collected at 100 K on a Bruker APEX-II CCD Diffractometer, by a means of Cu-Kα (λ = 1.54178 Å) radiation. SHELXS-97 [40] was employed for the computing structure solution and SHELXL-97 [41] for the computing structure refinement. The structure was solved by direct methods with refinement based on F2. The non-hydrogen atoms were refined anisotropically and H atoms were included in calculated positions. Crystal Data for 3[I].CH2Cl2: C35H37P2FeOCl2I, Mr = 789.24, monoclinic, space group P1 21/n1 , a = 14.1508(3) Å, b = 15.8415(4) Å, c = 15.6359(3) Å, β = 101.2849(18)°, U = 3437.32(12) Å3, Z = 4, μ = 13.082 mm-1, 24787 reflections collected, final wR2(F2) = 0.1421 for all data, conventional R1 = 0.0491 for 5616 reflections with I>2σ(I), S = 0.993 Crystal Data for 5[PF6]: C35H35P3FeOF6, Mr = 734.39, monoclinic, space group P2(1)/n , a = 12.8715(6) Å, b = 15.1195(8) Å, c = 16.6047(8) Å, β = 95.825(3)°, U = 3214.8(3) Å3, Z = 4, μ = 5.736 mm-1, 21892 reflections collected, final wR2(F2) = 0.0857 for all data, conventional R1 = 0.0337 for 5537 reflections with I>2σ(I), S = 1.032 Appendix. Supplementary material CCDC 1425807 and CCDC 1425808 contain the supplementary crystallographic data for complexes 3[I] and 5[PF6] respectively. 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