Synthesis and characterisation of halide, separated ion pair, and hydride cyclopentadienyl iron bis(diphenylphosphino)ethane derivatives

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Synthesis and characterisation of halide, separated

ion pair, and hydride cyclopentadienyl iron

bis(diphenylphosphino)ethane derivatives†

Cite this: DOI: 10.1039/c5dt00704f

Dipti Patel,^aAshley Wooles,^aAndrew D. Cornish,^aLindsey Steven,^a

E. Stephen Davies,^aDavid J. Evans,*^bJonathan McMaster,^aWilliam Lewis,^a

Alexander J. Blake^aand Stephen T. Liddle*^a

Treatment of anhydrous FeX₂(X = Cl, Br, I) with one equivalent of bis(diphenylphosphino)ethane (dppe) in

reﬂuxing THF aﬀorded analytically pure white (X = Cl), light green (X = Br), and yellow (X = I) [FeX₂(dppe)]_n

(X = Cl, I; Br, II; I, III). Complexes I–III are excellent synthons from which to prepare a range of cyclopenta-

dienyl derivatives. Speciﬁcally, treatment of I–III with alkali metal salts of C₅H₅(Cp, series 1), C₅Me₅

(Cp*, series 2), C₅H₄SiMe₃(Cp’, series 3), C₅H₃(SiMe₃)₂(Cp’’, series 4), and C₅H₃(Bu^t)₂(Cp^tt, series 5)

aﬀorded [Fe(Cp^†)(Cl)(dppe)] 1Cl–5Cl, [Fe(Cp^†)(Br)(dppe)] 1Br–5Br, and [Fe(Cp^†)(I)(dppe)] 1I–5I (Cp^†= Cp,

Cp*, Cp’, Cp’’, or Cp^tt). Dissolution of 1I–5I in acetonitrile, or treatment of 1Cl–5Cl with Me₃SiI in aceto-

nitrile (no halide exchange reactions were observed in other solvents) aﬀorded the separated ion pair

complexes [Fe(Cp^†)(NCMe)(dppe)][I] 1SIP–5SIP. Attempts to reduce 1Cl–5Cl, 1Br–5Br, and 1I–5I with a

variety of reductants (Li-Cs, KC₈, Na/Hg) were unsuccessful. Treatment of 1Cl–5Cl with LiAlH₄gave the

hydride derivatives [Fe(Cp^†)(H)(dppe)] 1H–5H. This report provides a systematic account of reliable

methods of preparing these complexes which may ﬁnd utility in molecular wire and metal–metal bond

chemistries. The complexes reported herein have been characterised by X-ray diﬀraction, NMR, IR,

UV/Vis, and Mössbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and

elemental analyses, which have enabled us to elucidate the electronic structure of the complexes and

probe the variation of iron redox properties as a function of varying the cyclopentadienyl or halide ligand.

Received 16th February 2015,

Accepted 7th July 2015

DOI: 10.1039/c5dt00704f

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fragments that are supported by two monodentate or one

bidentate phosphine ligand[s]. This approach has enabled the

Introduction

One of the most popular and widely used organometallic tran- isolation of a range of novel linkages and has also been

sition metal anions in the literature is [FeCp(CO)₂]⁻(Fp⁻).¹implemented in rare earth-ruthenium chemistry.⁵

The Fp⁻anion has been used extensively in nucleophilic dis-

Recently, we reported four uranium–ruthenium bonds

placement reactions and in the preparation of metal–metal using the ruthenium analogue of Fp.⁶As part of that study we

bonds.²Regarding the latter point, although the nucleophili- found that the corresponding uranium–iron (Fp) linkages

city of the Fp anion should favour M–Fe bond formation, there could not be isolated. We reasoned that substitution of the

is a significant possibility of iso-carbonyl bond formation with carbonyl groups with phosphines might increase the steric

early, electropositive and oxophilic metals,³an area which we protection and thus stability of uranium–iron linkages which

have been investigating in recent years.⁴One approach to would necessitate the preparation of the corresponding iron

avoid iso-carbonyl bridges is to employ cyclopentadienyl iron precursors. Since substitution of the carbonyl groups in situ is

not feasible, it would be necessary to start with a cyclopenta-

dienyl–phosphine ligand set before constructing the uranium–

iron bond.

^aSchool of Chemistry, University of Nottingham, University Park, Nottingham,

NG7 2RD, UK

^bDepartment of Chemistry, University of Hull, Hull, HU6 7RX, UK.

Two methods of preparing uranium–iron bonds could be

envisaged, either reductive cleavage of a Fe–Fe species, as has

been accomplished with cobalt,¹⁰or protonolysis of a uranium

alkyl or amide with an iron hydride.⁴One approach to iron

cyclopentadienyl ligand derivatives would be to prepare the

relevant iron cyclopentadienyl dicarbonyl halide or hydride

E-mail: stephen.liddle@nottingham.ac.uk, david.evans@hull.ac.uk

†Electronic supplementary information (ESI) available: Electrochemical, DFT,

and Mössbauer data for 1Cl–5Cl, 1Br–5Br, 1I–5I, 1SIP–5SIP, and 1H–5H, and

X-ray data for I–III, 1Cl, 3Cl–5Cl, 1Br, 3Br–5Br, 2I–5I, 1SIP–5SIP, and 1H–5H.

CCDC 1049712–1049737. For ESI and crystallographic data in CIF or other elec-

tronic format see DOI: 10.1039/c5dt00704f

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then substitute the carbonyl with phosphines, but it is known

that this approach can be complicated by the formation of

mono-substituted complexes,⁷or the formation of chelated

Results and discussion

Synthesis of iron(II) halide dppe adducts

derivatives with the retention of one CO ligand and expulsion We began by preparing dppe adducts of iron(^II) halides

of the halide ligand from the primary coordination sphere of from the reaction between anhydrous FeX₂(X = Cl, Br, I) and

iron.⁸We therefore decided to prepare phosphine chelated one equivalent of dppe in refluxing THF, Scheme 1. Following

iron(^II) halides, introduce the cyclopentadienyl ligand, then filtration, removal of solvent, washing with toluene, and

either reduce or substitute the halide with hydride. This meth- drying, analytically pure white (X = Cl), light green (X = Br),

odology has been shown to work in a few cases,⁷but the data and yellow (X = I) solids were obtained in ∼95% yield in each

in the literature are fragmented and sometimes incomplete. In case. It is notable that although these simple coordination

particular, solid state structures are often missing but would complexes [FeX₂(dppe)]_n(X = Cl, I; Br, II; I, III) are often men-

provide valuable benchmarking for previously reported spectro- tioned in the literature,⁷detailed descriptions of their syn-

scopic and computational studies. Given the importance of thesis and characterisation are scant and the structure of II is

cyclopentadienyl iron bis(diphenylphosphino)ethane (dppe) unknown. In all three cases we were able to determine the

fragments in assembling molecular wires⁹as well as represent- solid state structures by X-ray crystallography (Fig. 1). The solid

ing synthons to iron–metal bonds it would be desirable to state structures of I and III were determined from crystals

draw together a cohesive and comprehensive description of a grown from THF, for I, an infinite polymer is observed in the

reliable general methodology for the preparation of a range of solid state with tetrahedral iron centres and bridging dppe

well characterised and understood functionalised iron cyclo- ligands whereas in III a dimer is formed containing two tetra-

pentadienyl dppe derivatives where the steric and electronic hedral iron centres which are each bridged by two dppe ligands.

properties can be systematically varied.

In contrast, the bromide compound II could be isolated as

Here, we report the synthesis of three iron(^II) halide dppe the polymeric (II) or dimeric (IIa) forms from THF/hexane

complexes, and their utility in preparing a range of cyclopenta- or toluene solutions, respectively. Langer and co-workers have

dienyl derivatives. We describe attempts to reduce these cyclo- recently independently found that

I co-crystallises with

pentadienyl dppe halide complexes to the corresponding [FeCl₂(dppe)₂] from a chloroform/acetone mixture in a poly-

diiron derivatives, and also the synthesis of hydride congeners. meric chain similar to our findings, and also solely if the reac-

In all, we describe the synthesis of twenty five iron cyclopenta- tion is completed in the correct stoichiometry, with similar

dienyl dppe complexes as either halide, separated ion pair, or bond lengths and angles to those found in I.⁷Pohl et al. eluci-

hydride derivatives which has enabled us, through a structural dated the solid state structure of [Fe₂I₂(dppe)₄] from toluene

and spectroscopic benchmarking study, to provide reliable syn- solution and also found it to be dimeric in nature, with

thetic methods and a detailed understanding of the electronic similar bond lengths and angles to those found in III which

structure of these compounds. This report thus constitutes a crystallised from THF solvent,⁷suggesting that the isolation of

cohesive account of compounds which could find extensive polymeric or dimeric forms of I–III is due to the halide and

utility in molecular wire and metal–metal bond chemistries.

not solvent eﬀects.

Scheme 1 Synthesis of I, II, III, 1Cl–5Cl, 1Br–5Br, 1I–5I. Reagents and conditions: (a) THF, Δ; (b) LiCp/NaCp/KCp^†, toluene, −78 °C, –LiCl/KCl/NaI/

KCl/KBr/KI.

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Fig. 1 Solid state asymmetric unit structures of (a) I (polymer), (b) II (polymer), (c) IIa (dimer), (d) III (dimer) with ellipsoids set at 40% probability.

Hydrogen atoms and minor disorder components are omitted for clarity. Selected bond lengths (Å) and angles (°): (a) Fe1–Cl1 2.2416(16), Fe1–Cl2

2.2403(15), Fe1–P1 2.4422(16), Fe1–P2 2.4849(16), Cl1–Fe1–Cl2 127.14(6), Cl1–Fe1–P1 104.65(6), Cl1–Fe1–P2 100.74(6), Cl2–Fe1–P1 100.80(6),

Cl2–Fe1–P2 111.50(6), P1–Fe1–P2 111.80(5); (b) Fe1–Br1 2.368(8), Fe1–Br2 2.370(9), Fe1–P1 2.468(12), Fe1–P2 2.454(13), Br1–Fe1–Br2 121.22(3),

Br1–Fe1–P1 100.24(4), Br1–Fe1–P2 114.25(4), Br2–Fe1–P1 108.10(4), Br2–Fe1–P2 105.65(4), P1–Fe1–P2 107.54(4); (c) Fe1–Br1 2.375(2), Fe1–Br2

2.372(2), Fe1–P1 2.429(4), Fe1–P2 2.464(4), Br1–Fe1–Br2 119.38(9), Br1–Fe1–P1 108.77(12), Br1–Fe1–P2 107.56(12), Br2–Fe1–P1 108.65(13), Br2–

Fe1–P2 111.71(12), P1–Fe1–P2 98.77(12); (d) Fe1–I1 2.5856(9), Fe1–I2 2.5659(9), Fe1–P1 2.4748(18), Fe1–P2 2.4963(18), I1–Fe1–I2 116.98(3), I1–Fe1–

P1 106.75(4), I1–Fe1–P2 110.21(4), I2–Fe1–P1 113.32(5), I2–Fe1–P2 109.30(4), P1–Fe1–P2 99.81(5).

Synthesis and characterisation of halide and separated ion

pair complexes

(dppe)] (5Br), [Fe(Cp)(I)(dppe)] (1I), [Fe(Cp*)(I)(dppe)] (2I),

[Fe(Cp′)(I)(dppe)] (3I), [Fe(Cp″)(I)(dppe)] (4I), and [Fe(Cp^tt)(I)-

(dppe)] (5I), in crystalline yields of ca. 50–70%. We note that

With the synthesis of I–III in-hand we first targeted cyclopenta- apart from some minor decomposition, the bulk products are

dienyl derivatives using C₅H₅(Cp, series 1), C₅Me₅(Cp*, series fairly pure (ca. 90%) and that the crystalline yields principally

2), C₅H₄SiMe₃(Cp′, series 3), C₅H₃(SiMe₃)₂(Cp″, series 4), and reflect the solubility of the cyclopentadienyl derivatives.

C₅H₃(Bu^t)₂(Cp^tt, series 5) since this selection provides a wide During this work we noted that the temperature of the initial

variation of steric and electronic (σ-donor, π-acceptor) pro- salt elimination reaction is important since the formation of

perties. Thus, treatment of I–III with one equivalent of the rele- ferrocenes and free dppe from ligand scrambling is a compet-

vant lithium/sodium/potassium (Cp) or potassium (Cp*^/′/″/tt

)

ing side reaction which becomes a major by-product at room

cyclopentadienyl reagent in toluene at −78 °C aﬀorded, after temperature. However, ferrocenes formation is suppressed and

filtration and removal of toluene, generally black solids, indeed essentially eliminated if reactions are initially conducted

Scheme 1. Recrystallisation from toluene or dichloromethane at −78 °C. Compound 1I can also be prepared from [Fe-

layered with hexane (1Cl) aﬀorded the target complexes (CO)₂(Cp)]₂with treatment with iodine followed by addition of

[Fe(Cp)(Cl)(dppe)] (1Cl), [Fe(Cp*)(Cl)(dppe)] (2Cl), [Fe(Cp′)(Cl)- dppe in refluxing toluene, however in lower yields of 48% com-

(dppe)] (3Cl), [Fe(Cp″)(Cl)(dppe)] (4Cl), [Fe(Cp^tt)(Cl)(dppe)] pared to the above method in which yields of 1I reach 67%.¹¹

(5Cl), [Fe(Cp)(Br)(dppe)] (1Br), [Fe(Cp*)(Br)(dppe)] (2Br), [Fe-

Halide exchange in iron cyclopentadienyl phosphine deriva-

(Cp′)(Br)(dppe)] (3Br), [Fe(Cp″)(Br)(dppe)] (4Br), [Fe(Cp^tt)(Br)- tives has previously been eﬀected by mixing complexes such as

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2Cl with, for example, KI,¹²whereas the approach outlined Cp″ derivatives 3H and 4H are notably low (35 and 41%,

above gives direct access to chloride, bromide, and iodide respectively). It should be noted that 3H and 4H are far less

derivatives. In an attempt to ascertain whether any other stable than the other three hydride derivatives and decompose

methods have applicability here, we screened the reactivity of in solution over a few hours, which is, in part, reflected in

the chlorides with trimethylsilyl iodide. Interestingly, although their crystalline yields. Complexes 1H and 2H have been pre-

1Cl–5Cl are inert with respect to halide exchange in THF, viously reported, however, in the preparation of 1H an excess

toluene, and dichloromethane, in acetonitrile spontaneous of NaBH₄was reacted with the chloroform adduct of 1Cl

displacement of the chloride ligand by acetonitrile and facile giving only a 50% yield¹³and 2H was reported to have been

halide exchange occurs to aﬀord the separated ion pair (SIP) synthesised by the same method outlined above or alterna-

complexes [Fe(Cp)(NCMe)(dppe)][I] (1SIP), [Fe(Cp*)(NCMe)- tively by reacting I with Cp*H in a colloidal dispersion of

(dppe)][I] (2SIP), [Fe(Cp′)(NCMe)(dppe)][I] (3SIP), [Fe(Cp″)- potassium metal in THF; a reaction which reportedly proceeds

(NCMe)(dppe)][I] (4SIP), and [Fe(Cp^tt)(NCMe)(dppe)][I] (5SIP) via the formation of a “Fe(dppe)” intermediate followed by

as red powders following work-up (Scheme 2). Recrystallisation oxidative addition of Cp*H.¹⁴

of these powders from acetonitrile aﬀorded 1SIP–5SIP in crys-

talline yields of typically 65–75%, although 3SIP is a notable

Solid state structures

outlier (36% crystalline yield). Since SIPs form readily we did

not investigate this avenue further with the bromides, but it is

germane to note that complexes 1SIP–5SIP represent valuable

precursors to a range of separated ion pair species such as

known PF₆-derivatives.

We investigated the reduction of 1Cl–5Cl, 1Br–5Br, and

1I–5I with a variety of reductants (Li-Cs, KC₈, Na/Hg), but in all

cases either no reaction occurred, or on extended stirring

decomposition was observed. This might be attributed to the

iron centres being electron rich, and more so than in Fp

because of less eﬀective back-bonding to dppe compared to

two CO ligands. This would also be consistent with the relative

ease of oxidising these complexes (see below). We therefore

focussed on preparing the hydrides.

The solid-state structures of 1Cl, 3Cl–5Cl, 1Br, 3Br–5Br, 2I–5I

were determined by single-crystal X-ray diﬀraction studies and

are illustrated in Fig. 2–4, respectively, and key metrical data

are presented in Table 1. The structures of 2Cl¹⁴and 1I¹⁵were

determined previously and the experimental data obtained of

crystals of 2Br were of insuﬃcient quality to determine mean-

ingful metrical parameters. Each complex displays a piano-

stool geometry, and in comparison to the ideal bond angle

of a classical tetrahedral geometry of 109.5°, the X1–Fe1–P1,

X1–Fe1–P2, P1–Fe1–P2 angles span the ranges 86.03(4)–

93.12(2), 84.18(4)–92.12(10) and 80.78(5)–86.22(3)° in 1Cl–5Cl,

1Br–5Br and 1I–5I respectively, due in part to the restrictive

bite angle of the dppe ligand but mainly due to the large size

of the various substituted Cp ligands forcing the other ligands

closer together. This results in large Ct–Fe1–X1, Ct–Fe1–P1,

Ct–Fe1–P2 angles ranging 118.97(9)–123.9(9), 126.37(7)–

Synthesis of hydride complexes

With the aforementioned halide complexes in hand we exam- 132.6(11) and 124.8(2)–132.98(13)° respectively. The Fe1–Ct

ined their conversion to the corresponding hydrides. Accord- bond lengths span the narrow range of 1.699(3)–1.743(12) Å in

ingly, treatment of the chloride series 1Cl–5Cl with

5

all of the complexes, which compares well to the Fe–Cp_centroid

equivalents of lithium aluminium hydride in THF aﬀorded, average distance of 1.740 Å in complexes containing both dppe

after removal of solvent, extraction into hexane, filtration and and Cp ligands.¹⁶The Fe–P bond distances span the narrow

removal of solvent, the hydride complexes [Fe(Cp)(H)(dppe)] range of 2.184(2)–2.2580(9) Å, which compares to Fe–P bond

(1H), [Fe(Cp*)(H)(dppe)] (2H), [Fe(Cp′)(H)(dppe)] (3H), [Fe(Cp″)- distances in complexes containing both Cp and dppe ligands

(H)(dppe)] (4H), and [Fe(Cp^tt)(H)(dppe)] (5H) as orange solids in the range 2.1168(19)–2.3105(14) Å.¹⁶The Fe–Cl, Fe–Br,

that are approximately 90% pure, Scheme 2. Recrystallisation Fe–I distances of 2.294(2)–2.346(1), 2.2464(6)–2.481(3) and

of 1H–5H from hexane aﬀorded orange crystalline materials in 2.643(1)–2.661(2) Å respectively increase as expected according

yields typically ranging from 41 to 73%, but, as was the case to increasing ion size in the order I > Br > Cl. Although a range

for the SIP complex 3SIP, the crystalline yield of the Cp′ and of diﬀerent substituted Cp ligands have been studied and

Scheme 2 Synthesis of 1SIP–5SIP, 1H–5H. Reagents and conditions: (a) TMSI, MeCN, –TMSCl; (b) excess LiAlH₄, THF, –LiCl.

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Fig. 2 Solid state structures of (a) 1Cl, (b) 3Cl, (c) 4Cl, (d) 5Cl with ellipsoids set at 40% probability. Hydrogen atoms are omitted for clarity.

Fig. 3 Solid state structures of (a) 1Br, (b) 3Br, (c) 4Br, (d) 5Br with ellipsoids set at 40% probability. Hydrogen atoms are omitted for clarity.

characterised the diﬀerence in their steric properties appears lengths range 1.709(4)–1.732(4) Å and are comparable to those

to have no major eﬀect on the bond angles and lengths of the found in 1I–5I (1.707(3)–1.743(12) Å) and the Fe–P bond

other ligands.

lengths range from 2.1986(12)–2.247(2) Å and are comparable

The solid-state structures of 1SIP–5SIP were determined by to those found in 1I–5I (2.188(1)–2.2580(9) Å. The Fe–N bond

single-crystal X-ray diﬀraction studies and are illustrated in lengths range from 1.892(7)–1.908(4) Å and are comparable to

Fig. 5 with key bond distances listed in Table 1. The geo- those found in the literature with complexes containing dppe

metries of these complexes are similar to those featured in the and Cp ligands (1.881(5)–1.909(8) Å).¹⁶The Ct–Fe–N and

halide complexes except that an acetonitrile, not a halide, Ct–Fe–P angles range 120.8(15)–123.4(10) and 124.27(13)–

ligand is coordinated to the iron centres. The Fe1–Ct bond 132.27(12)° respectively, and are comparable with the Ct–Fe–I

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Fig. 4 Solid state structures of (a) 2I, (b) 3I, (c) 4I, (d) 5I with ellipsoids set at 40% probability. Hydrogen atoms are omitted for clarity.

Although complexes 1H and 2H were synthesised previously

their solid-state structures were not reported and hence the

solid-state structures of 1H–5H were also determined by

single-crystal X-ray diﬀraction studies and are illustrated in

Table 1 Selected bond lengths (Å) for the new crystal structures 1Cl,

3Cl–5Cl, 1Br, 3Br–5Br, 2I–5I, 1SIP–5SIP and 1H–5H^a

Compound

Fe–Ct

Fe–X

Fe1–P1

Fe1–P2

1Cl

3Cl

4Cl

5Cl

1Br

3Br

4Br

5Br

2I

3I

4I

5I

1SIP

2SIP

3SIP

4SIP

5SIP

1H

1.699(3)

1.716(5)

1.704(7)

1.739(4)

1.699(5)

1.709(18)

1.720(5)

1.734(4)

1.743(12)

1.712(2)

1.728(2)

1.734(3)

1.713(3)

1.732(4)

1.709(4)

1.730(2)

1.727(7)

1.702(4)

1.712(7)

1.698(3)

1.701(5)

1.707(8)

2.3317(9)

2.3298(16)

2.294(2)

2.3423(10)

2.4647(6)

2.481(3)

2.464(8)

2.476(8)

2.661(2)

2.6478(4)

2.6464(4)

2.6603(5)

1.900(2)

1.896(3)

1.908(4)

1.9063(19)

1.892(7)

1.60(4)

2.1963(10)

2.1980(16)

2.184(2)

2.2107(11)

2.1909(10)

2.1909(5)

2.201(13)

2.2273(13)

2.221(3)

2.1874(7)

2.2018(7)

2.2266(10)

2.2188(7)

2.2034(13)

2.1986(12)

2.2392(7)

2.240(2)

2.1455(1)

2.1255(18)

2.1404(9)

2.1333(13)

2.142(2)

2.1846(10) Fig. 6 with pertinent bond lengths compiled in Table 1. In

2.1881(15)

each instance the hydride atom was located in the diﬀerence

2.194(2)

2.2358(10)

map and was allowed to refine freely. In each complex the Fe^II

2.1958(10) centre adopts a classical piano stool geometry. The Fe–H bond

2.2059(5)

2.210(13)

2.2578(13)

distances in 1H–5H span the range 1.39(2)–1.60(4) Å. There are

only two other examples of terminal iron hydride bonds

2.208(3)

with bidentate phosphine and cyclopentadienyl ligands with

which to compare these values; [Fe(Cp*)(H)₂(dppe)][BF₄]

has Fe–H_hydridedistances of 1.48 and 1.50 Å ¹⁷and [Fe(Cp*)-

2.1956(7)

2.2116(7)

2.2580(9)

2.2194(7)

2.2214(11)

2.1940(12)

2.2429(7)

2.247(2)

(H)₂(dippe)][BPh₄], where dippe = 1,2-bis(diisopropylphos-

phino)ethane, has Fe–H_hydridedistances of 1.41(5) and 1.35(6)

Å.¹⁸The Fe–H bond distance in 4H of 1.39(2) Å, is significantly

shorter than those in the rest of the series; however, it is

not outside the limited range reported for Fe–H_hydridebonds

in complexes containing the dppe ligand (1.28(8)–

2.1292(10)

2.1448(19)

2.1196(9)

2H

3H

4H

5H

1.56(7)

1.50(4)

1.39(2)

1.52(14)

2.1302(13) 1.65(9) Å).^17,19–35

2.153(2)

Electrochemical investigations

^aCt = centroid of the cyclopentadienyl ring; X = Cl, Br, I, acetonitrile N

or H.

Cyclic voltammetric studies were performed on 1Cl–5Cl, 1Br–

5Br, 1I–5I and 1H–5H as THF solutions containing 0.5 M of

electrolyte, [NBuⁿ₄][BF₄], in the potential range from −2.55 to

1.2 V vs. Fc⁺/Fc. The results of these studies are summarised in

Table 2 and plotted in Fig. 7. THF was chosen as the solvent as

it provides good solubility for all of the complexes and

remains relatively inert with respect to nucleophilic attack on

electrogenerated cations.

and Ct–Fe–P bond angles of 118.97(7)–123.78(7), 126.37(7)–

133.93(4)° respectively found in 1I–5I. The N–Fe–P and P1–Fe–

P2 bond angles of 88.79(10)–93.24(12) and 85.48(4)–86.47(4)°

respectively lie within the range shown for the I–Fe–P and P1–

Fe–P2 angles in 1I–5I (88.82(2)–93.12(2), 80.85(3)–86.22(3)°

respectively).

The potentials obtained from cyclic voltammetric studies

are consistent with results of square wave voltammetry ( 0.01

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Fig. 5 Solid state structures of (a) 1SIP, (b) 2SIP, (c) 3SIP, (d) 4SIP, (e) 5SIP with ellipsoids set at 40% probability. Hydrogen atoms are omitted for

clarity.

V, except 4H, see below) for the process designated OX and in cationic species, [Fe(Cp*)(X)(dppe)].³⁶Our results are consistent

all cases the potentials are quoted against an appropriate with these, albeit with a small diﬀerence in reported poten-

internal standard (see Table S1†). For OX, analysis of the tials, therefore we assign OX for the series of compounds 1Cl–

current response in a range of scan rates between 0.02 and 5Cl, 1Br–5Br, 1I–5I and 1H–5H as a one-electron oxidation of

0.3 V s⁻¹suggest that this process is, in general, electro- Fe(^II) to Fe(III) corresponding to a [Fe(Cp^†)(X)(dppe)]^+/0couple.

chemically reversible under these conditions, 4H being an The negative values of these potentials, particularly noticeable

notable exception. At slow scan rates (<0.1 V s⁻¹), the cyclic when referenced against the Fe(^III)/Fe(II) couple of ferrocene,

voltammogram of 4H has no reduction wave associated with are evidence of an electron rich Fe centre, where the loss of an

this oxidation suggesting that the electrogenerated cation is electron is facile. The trend in OX for [Fe(Cp^†)(X)(dppe)] (X =

unstable. This was confirmed at faster scan rates (1 V s⁻¹), H, Cl, Br and I) always follows H < Cl < Br < I, and it is worthy

corresponding to shorter timescales, when OX appeared as a of note that the diﬀerence between OX for [Fe(Cp^†)(Cl)(dppe)]^+/0

redox couple. Data for [Fe(Cp*)(X)(dppe)] (X = Cl, Br, I, and H) and [Fe(Cp^†)(Br)(dppe)]^+/0and between [Fe(Cp^†)(Br)(dppe)]^+/0

have been reported previously wherein this process was and [Fe(Cp^†)(I)(dppe)]^+/0is +0.04 V and that this diﬀerence is

assigned as a one electron oxidation to give the corresponding independent of the substitutents on the cyclopentadienyl ring.

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Fig. 6 Solid state structures of (a) 1H, (b) 2H, (c) 3H, (d) 4H, (e) 5H with ellipsoids set at 40% probability. All hydrogen atoms except those for the

hydride atoms are omitted for clarity.

This trend does not extend to the hydrides, where diﬀerences Cp^tt) follow the series Cp* < Cp^tt< Cp′ < Cp″ < Cp and com-

between potentials for [Fe(Cp^†)(H)(dppe)]^+/0and [Fe(Cp^†)(Cl)- pounds containing Cp* are −0.05 V easier to oxidise than com-

(dppe)]^+/0vary between +0.05 (Cp′) and +0.12 (Cp*).

pounds containing Cp^tt, Cp^ttcompounds are −0.09 V easier to

The trend in OX for each halide series appears to be inver- oxidise than compounds containing Cp′, Cp′ compounds are

sely correlated with the electronegativity of the halide thus −0.01 V easier to oxidise than compounds containing Cp″, and

making the chlorides easiest to oxidise and indicating an Cp″ compounds are −0.02 V easier to oxidise than compounds

increase in electron density on the iron centre relative to the containing Cp. Hence compounds containing Cp*, with five

corresponding bromides and iodides. This has been rational- electron donating methyl groups are easiest to oxidise whilst

ised by the involvement of π-based orbitals in the bonding of compounds containing Cp are most diﬃcult. The latter result

the halide to the iron centre (see DFT calculations below) thus is unexpected since TMS is electron withdrawing³⁷relative to

allowing donation of electron density from the halide to the hydrogen (in Cp) and would be expected to reduce the electron

metal centre. The hydrides should have no contribution from density at iron, thus making oxidation more diﬃcult (hence

π-bonding so the relatively negative values for OX in [Fe(Cp^†)- occurring at a higher potential). However, the diﬀerence in OX

(H)(dppe)] compounds reflect the purely σ-bonded nature of between [Fe(Cp′)(X)(dppe)] and [Fe(Cp″)(X)(dppe)] (X = Cl, Br

the hydrides. The trend in OX for [Fe(Cp^†)(Cl)(dppe)], [Fe(Cp^†)- and I) is only 0.01 V for the addition of a second TMS group

(Br)(dppe)] and [Fe(Cp^†)(I)(dppe)] (Cp^†= Cp, Cp*, Cp′, Cp′′, therefore the inductive eﬀect of these substitutents may not be

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cyclic and square wave voltammetries and the results of these

investigations are presented in Table 2 and Fig. S1.† The separ-

ated ion pairs were generated in situ by dissolving the corres-

ponding [Fe(Cp^†)(I)(dppe)] (Cp^†= Cp, Cp*, Cp′, Cp″, Cp^tt)

compound in MeCN containing 0.1 M [NBuⁿ₄][BF₄] as the sup-

porting electrolyte. Analysis of these solutions showed an

absence of redox chemistry associated with [Fe(Cp^†)(I)(dppe)]

indicating that the equilibrium exclusively favours the for-

mation of the separated ion pair under these conditions. We

confirmed the electrochemistry obtained by this method was

that associated with a separated ion pair in MeCN solution by

dissolving crystals of 2SIP in MeCN containing 0.1 M [NBuⁿ₄]-

[BF₄] and repeating the electrochemical experiment; the

results of this experiment are essentially identical to those

obtained starting from [Fe(Cp*)(I)(dppe)] (Fig. S1†). The displa-

cement of iodide from coordination at the metal centre into

the outer sphere significantly complicates the electrochemistry

of these compounds since both iodide and [Fe(Cp^†)(NCMe)-

(dppe)]⁺exhibit oxidation chemistry in the range of potentials

from ca. 0 to +0.5 V. Fig. S1† shows the cyclic voltammetry of

the separated ion pairs and [NBuⁿ₄][I]. The electrochemistry of

iodide gives two oxidation processes (−0.02 and +0.31 V) and a

broad reduction, centred around ca. −0.6 V and these may rep-

resent electrochemical processes resulting from components

of an [I⁻]/[I₂]/[I₃⁻] equilibrium.³⁸The electrochemistry of [Fe-

(Cp^†)(NCMe)(dppe)]⁺(Cp^†= Cp, Cp*, Cp′, Cp″, Cp^tt) appears as

a redox couple in the range of potentials between +0.06 V

(Cp*) and +0.26 V (Cp and Cp″). These potentials are consist-

ent with results of square wave voltammetry ( 0.01 V) for the

process designated OX (Table S1†). The nature of the electron

transfer process in these compounds is diﬃcult to determine

given the presence of OX′, a process we assign to iodide oxi-

dation, however it is noted that the separation between E^a_pand

E^c_pfor OX in [Fe(Cp^†)(NCMe)(dppe)]⁺(Cp^†= Cp, Cp*, Cp′, Cp″,

Cp^tt) compounds (0.09–0.10 V at 0.1 V s⁻¹) is greater than that

for the decamethylferrocene couple (0.07 V) used as the

internal standard and this suggest that the process is not

simply diﬀusion controlled. For 2SIP, the electron donating

eﬀect of the five methyl groups shift OX to a more negative

potential than others in the series and result in OX over-

lapping with OX′. For the other members of the series OX over-

laps with the second oxidation process of the iodide anion.

Redox potentials for the separated ion pair complexes are con-

siderably more positive (ca. 0.5 V) than those of their [Fe(Cp^†)-

(I)(dppe)] precursors since oxidation involves the loss of an

electron from an already cationic species i.e. the [Fe(Cp^†)-

(MeCN)(dppe)]^2+/+redox couple however these potentials

are significantly lower than those obtained previously for the

16-electron cationic complex [Fe(Cp*)(dppe)][PF₆]³⁹(0.64 V vs.

Fc⁺/Fc in THF) cf. 0.06 V for [Fe(Cp*)(NCMe)(dppe)] in MeCN.

Table 2 Electrochemical and highest occupied molecular orbital ener-

gies for 1Cl–5Cl, 1Br–5Br, 1I–5I, 1H–5H and 1SIP–5SIP^a

E_1/2

(V)

HOMO

(eV)

E_1/2

(V)

HOMO

(eV)

Compound

1Cl

2Cl

3Cl

4Cl

5Cl

1Br

2Br

3Br

4Br

5Br

1I

−0.42

−0.59

−0.45

−0.44

−0.54

−0.38

−0.55

−0.41

−0.40

−0.50

−0.34

−0.51

−0.37

−3.732

−3.537

−3.694

−3.747

−3.545

−3.788

−3.561

−3.741

−3.787

−3.665

−3.836

−3.625

−3.781

4I

5I

1H

2H

3H

4H

5H

1SIP

2SIP

3SIP

4SIP

5SIP

−0.36

−0.46

−0.50

−0.71

−0.50

−0.53

−0.62

0.26

0.06

0.25

0.26

0.20

−3.868

−3.741

−3.838

−3.616

−3.789

−3.706

−3.638

−7.218

−6.958

−7.125

−7.073

−6.997

2I

3I

^aSolutions were ca. 0.1 mM of the complex in THF containing 0.5 M

[NBuⁿ₄][BF₄] as the electrolyte for 1Cl–5Cl, 1Br–5Br, 1I–5I and 1H–5H

and ca. 0.1 mM of 1I–5I in MeCN containing 0.1 M [NBuⁿ₄][BF₄] as the

electrolyte for 1SIP–5SIP. The working electrode was glassy carbon

and potentials are reported against the Fc⁺/Fc redox couple at

ambient temperature. The HOMO energies are derived from the DFT

analyses (see below) and are in the gas-phase with no solvent-shell

correction.

Fig. 7 Cyclic voltammograms showing OX for (a) [Fe(Cp^†)(Cl)(dppe)],

(b) [Fe(Cp^†)(Br)(dppe)], (c) [Fe(Cp^†)(I)(dppe)] and (d) [Fe(Cp^†)(H)(dppe)]

(Cp^†= Cp (black), Cp* (violet), Cp’ (blue), Cp’’ (green), Cp^tt(red)). In THF

containing [ⁿBu₄N][BF₄] (0.5 M) as supporting electrolyte, at 0.1 V s⁻¹

(except 4H, at 1 V s⁻¹). Currents are normalised to I^a_pfor clarity. Typical

currents obtained from CV experiments for [Fe(Cp^†)(X)(dppe)] com-

pounds are shown in Fig. S2† for 1Cl, as are designations of OX, OX’,

OX’’ and RED for 1Cl–5Cl, 1Br–5Br, 1I–5I and 1H–5H used in Table S1.†

Mössbauer studies

transferred eﬀectively to the redox centre, which is reflected by

only minor changes in the energies of the HOMO orbitals of

the Cp′ and Cp″ derivatives of 1Cl, 1Br, and 1I.

The Mössbauer parameters at 80 K for all of the compounds

are collected in Table 3. The isomer shift (I.S.) and quadruple

splitting (Q.S.) values for all compounds are fully

consistent with derivatives of iron(^II)–cyclopentadienyl in a

The electrochemistry of the separated ion pairs, [Fe(Cp^†)-

(NCMe)(dppe)][I] (Cp^†= Cp, Cp*, Cp′, Cp″, Cp^tt) was studied by

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Table 3 Mössbauer data for compounds 1Cl–5Cl, 1Br–5Br, 1I–5I,

1SIP–5SIP and 1H–5H at 80 K^a

Compound

I.S. (mms⁻¹

)

Q.S. (mms⁻¹

)

H.W.H.M. (mms⁻¹

)

1Cl

2Cl

3Cl

4Cl

5Cl

1Br

2Br

3Br

4Br

5Br

1I

2I

3I

4I

5I

1SIP

2SIP

3SIP

4SIP

5SIP

1H

2H

3H

4H

5H

0.44

0.48

0.46

0.48

0.50

0.44

0.50

0.47

0.48

0.53

0.43

0.52

0.45

0.49

0.53

0.39

0.42

0.39

0.44

0.45

0.26

0.25

0.26

0.28

0.27

1.92

2.04

1.88

1.73

2.08

1.94

2.10

1.84

1.70

2.00

1.89

2.09

1.85

1.69

1.95

2.01

2.00

1.91

1.86

1.97

1.91

1.92

1.70

1.71

1.96

0.13

0.15

0.13

0.15

0.13

0.14

0.12

0.13

0.14

0.12

0.13

0.12

0.13

0.14

0.13

0.14

0.13

0.14

0.16

0.15

^aI.S. = isomer shift; Q.S. = quadrupole splitting; H.W.H.M = half-width

at half-maxima with errors ≤ 0.01 mms⁻¹

.

Fig. 8 (a) UV-vis spectra of 2Cl at 1.25 mM and 0.0125 mM (insert) in

THF solution. (b) Predicted UV-vis spectrum of 2Cl showing the individ-

ual electronic transitions and the combined total in the gas phase.

piano-stool geometry.^13,14,40As expected the I.S. decreases

and the Q.S. is invariant on raising the temperature from 80 to

298 K.^41,42On changing halide from chloride to bromide to

iodide and on varying substituents on the cyclopentadienyl

ligand there are only slight changes in I.S. and Q.S. When

halide is replaced by acetonitrile to form a separated ion

pair there is a slight decrease in I.S. but a much larger

decrease is observed when halide is replaced by hydride; this

can be attributed to the higher σ-donor ability of the hydride

ligand increasing the relative electron density at the iron

centre.

the calculations are a good approximation of the experimental

spectra. With this in hand it is then possible to assign these

absorptions from the calculated spectra, and calculations

suggest that the band at 40 816 cm⁻¹, is a result of π–π* tran-

sitions in the aromatic carbon systems; and the bands in the

visible region can be predominantly ascribed to metal–ligand

charge transfer (MLCT) from the Fe 3d orbitals to the phenyl

rings and the Cp* ligand.

UV-Vis spectroscopic studies

The UV-vis spectra of all the complexes were recorded in THF

The UV-vis spectra for the bromide and iodide series of

solutions at two diﬀerent concentrations (1.25 mM and complexes present similar observations as found in the spectra

0.0125 mM) to enable observation of all the relevant tran- of the chloride series where variation of the Cp ligands has an

sitions without interference from solvent overtones. Theore- eﬀect on the absorptions observed in the visible region (see

tical UV-vis spectra have also been plotted from time ESI† for further spectra). However, there is no obvious trend in

dependant DFT (TD-DFT) calculations. The representative the electronic absorptions observed upon change in halide

experimental and calculated UV-vis spectra of 2Cl are illus- across the series, therefore we can conclude that the Fe to Cp

trated in Fig. 8. At dilute concentration an intense band is MLCT bands are the dominant features in the visible region

observed at 40 816 cm⁻¹(ε = 20 300 M⁻¹cm⁻¹) in the UV and the halide has very little eﬀect on the absorptions,

region, and at higher concentrations relatively weak bands can Table 4. Although one notable feature is the value of the

be observed in the visible region at 16 502 (ε = 221 M⁻¹cm⁻¹

)

extinction coeﬃcient for the π–π* transitions in the bromide

and 18 587 cm⁻¹(ε = 352 M⁻¹cm⁻¹). By comparison of these complexes (1Br–5Br) are on average larger than their chloride

experimental data with the combined total of the calculated and iodide counterparts. For example the π–π* transition in

data it can be seen that they are in good agreement, and that 4Br at 41 152 cm⁻¹has a molar absorptivity of 46 300 M⁻¹

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Table 4 Experimental (in THF solution) and calculated (in gas phase) UV-vis absorptions and extinction coeﬃcients for 1Cl–5Cl, 1Br–5Br, 1I–5I,

1SIP–5SIP and 1H–5H^a

Compound

1Cl

2Cl

3Cl

4Cl

5Cl

Experimental/cm⁻¹(ε/M⁻¹cm⁻¹

)

17 007 (247)

19 880 (307)

40 323 (21 000)

16 200 (478)

18 400 (1150)

37 100 (9590)

1Br

16 502 (221)

18 587 (352)

40 816 (20 300)

15 900 (1340)

17 600 (1650)

39 200 (22 600)

2Br

15 456 (156)

18 587 (283)

40 000 (21 900)

15 300 (577)

18 400 (1320)

34 800 (11 100)

2I

15 106 (264)

18 519 (500)

40 486 (25 000)

15 400 (441)

18 200 (1090)

33 400 (10 300)

2SIP

15 244 (160)

18 553 (368)

22 750 (809)

40 323 (32 700)

19 900 (705)

25 400 (2030)

32 500 (11 900)

37 600 (14 900)

2H

16 978 (376)

19 417 (463)

41 152 (15 000)

16 400 (1170)

19 100 (1310)

35 300 (11 500)

3Br

15 500 (191)

18 903 (339)

39 682 (13 200)

16 600 (1460)

18 400 (1340)

35 600 (11 500)

4Br

15 898 (334)

18 939 (621)

41 152 (46 300)

16 600 (1310)

18 900 (1450)

34 500 (9930)

4I

15 000 (172)

19 048 (445)

40 486 (19 100)

16 300 (1140)

19 100 (1360)

34 300 (10 700)

4SIP

15 015 (123)

19 120 (391)

23 000 (458)

40 000 (26 700)

21 000 (1530)

27 600 (1800)

31 900 (10 100)

38 100 (12 500)

4H

15 000 (113)

18 148 (183)

39 682 (21 900)

15 400 (412)

18 500 (1580)

35 500 (11 300)

5Br

15 456 (271)

18 051 (425)

41 152 (30 200)

15 400 (1260)

18 200 (1810)

34 700 (10 300)

5I

14 500 (202)

18 051 (448)

40 323 (21 000)

15 000 (949)

18 500 (1880)

35 000 (10 900)

5SIP

14 514 (221)

18 083 (491)

22 500 (715)

40 000 (28 100)

21 400 (1050)

26 900 (1830)

33 800 (12 100)

38 500 (12 200)

5H

Theoretical/cm⁻¹

Compound

Experimental/cm⁻¹(ε/M⁻¹cm⁻¹

16 155 (200)

19 960 (391)

15 898 (389)

19 417 (617)

Theoretical/cm⁻¹

16 200 (921)

19 200 (1390)

34 800 (11 100)

3I

15 848 (199)

19 569 (421)

40 486 (25 900)

15 500 (556)

18 800 (1180)

34 000 (10 700)

3SIP

18 600 (1030)

36 900 (8390)

1I

16 000 (134)

20 120 (238)

40 323 (19 100)

15 800 (219)

19 200 (982)

34 500 (7060)

1SIP

16 000 (95)

20 202 (392)

24 500 (552)

40 323 (22 900)

21 200 (1180)

25 100 (1170)

32 700 (10 900)

39 600 (12 400)

1H

Compound

Experimental/cm⁻¹(ε/M⁻¹cm⁻¹

Theoretical/cm⁻¹

Compound

Experimental/cm⁻¹(ε/M⁻¹cm⁻¹

20 921 (658)

40 323 (25 300)

Theoretical/cm⁻¹

21 300 (1440)

26 000 (1530)

32 400 (10 600)

38 700 (15 700)

3H

24 000 (805)

40 161 (8730)

Compound

Experimental/cm⁻¹(ε/M⁻¹cm⁻¹

)

28 011 (2760)

39 841 (27 900)

16 400 (1190)

18 600 (2590)

21 600 (2520)

26 400 (1210)

31 300 (5950)

24 096 (1660)

39 683 (14 200)

23 474 (2610)

39 683 (20 500)

39 683 (27 900)

Theoretical/cm⁻¹

20 600 (3640)

27 300 (1050)

37 700 (13 600)

20 200 (3550)

26 700 (1790)

36 700 (12 300)

20 300 (3430)

25 600 (2130)

36 400 (12 600)

17 900 (2190)

22 900 (2110)

27 200 (1620)

36 000 (15 700)

^aEpsilon is quoted to 3 significant figures.

cm⁻¹which is at least twice as large as the analogous tran- DFT calculations

sition in 4Cl of ε = 13 200 M⁻¹cm⁻¹at 39 682 cm⁻¹, and 4I of

We have undertaken DFT calculations for 1Cl–5Cl, 1Br–5Br,

1I–5I, 1SIP–5SIP and 1H–5H to provide a qualitative descrip-

tion of the structure and bonding within these complexes and

to provide a framework to interpret the electrochemical pro-

perties of these compounds. The DFT calculations reproduce

the magnitude of the crystallographically determined bond

lengths and the interbond angles of these complexes to within

∼0.05 Å and ∼1.5°, respectively. We therefore conclude that

the calculations aﬀord reliable qualitative descriptions of the

electronic manifolds of 1Cl–5Cl, 1Br–5Br, 1I–5I, 1SIP–5SIP and

1H–5H.

The frontier orbital manifolds of 1Cl–5Cl, 1Br–5Br and

1I–5I are similar with the HOMO, HOMO−1 and HOMO−2

orbitals in each compound possessing dominant Fe character

derived from the 3d orbitals that form the t_2gset in O_hsym-

metry (for representative frontier orbitals see Fig. 9).⁴⁴These

orbitals are non-bonding with respect to σ-interactions but can

ε = 19 100 M⁻¹cm⁻¹at 40 486 cm⁻¹

.

IR spectroscopic studies

The IR spectra of all the complexes studied in this work were

recorded as Nujol mulls. The IR spectra of 1H–2H contain

bands at 1845, 1844, 1849, 1854 and 1872 cm⁻¹respectively

and these absorptions can be assigned to the ν_Fe–Hstretching

absorptions for the terminally bonded metal hydride. All these

bands are very weak, and are comparable to the ν_Fe–Hreported

for other structurally authenticated iron terminal hydride com-

plexes containing the dppe ligand which span the range

1833–1919 cm^{−1 20,30,34}

The only other example of an iron

.

hydride complex with both dppe and cyclopentadienyl ligands

with which to compare is [Fe(Cp*)(H)(dppe)][PF₆] that has a

comparable band at 1869 cm^{−1 43}

.

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Fig. 9 Frontier Kohn Sham molecular orbitals of 1Cl: (a) HOMO, (b) HOMO−1, (c) HOMO−2. The models were orientated such that the Fe–X vector

corresponded to the z-axis and, looking down the Fe–X vector, the left and right Fe-P bonds were aligned along the x and y axes, respectively.

1

Fig. 10 Plot of HOMO energy vs. E for 1Cl–5Cl, 1Br–5Br and 1I–5I.

2

exhibit π-interactions with X = Cl, Br, I. Thus, in each 1Cl–5Cl, noted previously,³⁹and has been ascribed to the ionic nature

1Br–5Br and 1I–5I the HOMO possess Fe and X character of the Fe–X bond, in which the X-ligand may be viewed as

(61.9–74.0% and 10.7–24.9%, Table S3†) and for a homo- acting as a point negative charge that destabilizes the t_2gset of

geneous series with a fixed cyclopentadienyl-derived ligand the orbitals which results in an inverse of the energy order

contribution to the HOMO typically varies as I > Br > Cl as expected from π-donor eﬀects alone.^45–50

would be expected from the π-donor ability for each halogen

donor. These calculations are in broad agreement with those

accomplished previously for CpFe(dpe)X (dpe = 1,2-diphospino-

Conclusions

ethane; X = Cl, Br, I).²⁸The energies of the HOMO orbital for a

1

fixed Cp ligand and

E

for the oxidation process (see

To conclude, we have reported the synthesis of three iron(II)

halide dppe complexes, and their utility in preparing a range

of cyclopentadienyl derivatives. In all, we describe the syn-

thesis of twenty five iron cyclopentadienyl dppe complexes as

either halide (Cl, Br, I), separated ion pair, or hydride deriva-

tives, thus providing a cohesive and reliable approach to the

preparation of such molecules. This report has enabled a com-

prehensive structural and spectroscopic benchmarking study,

providing a detailed understanding of the electronic structure

of these compounds in one common framework. The Möss-

bauer studies suggest that the bonding is these complexes is

2

above) show clear trends as X is varied (Fig. 10). Thus, the

energy of the HOMO varies as Cl > Br > I with a reduction

potential order of Cl < Br < I. Thus, for a fixed cyclopenta-

dienyl-derived ligand complexes with X = Cl are more readily

oxidised to their cationic counterparts and this observation is

borne out by the relative energies of the HOMO orbitals in this

series of compounds. The variation in energy of the HOMO

with X-ligand appears counterintuitive given the percentage

X-ligand character in the HOMO and the relative π-donor abil-

ities of the halide donors. This inverse halide order has been

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predominantly ionic. Nevertheless, it is evident that the cyclo- from Sigma Aldrich and were used without any further purifi-

pentadienyl and X-ligands modulate the electronic structure cation. Compounds II, III, 2Cl, 1I, and 1H have previously

and redox properties of iron. Surprisingly, it is clear that been reported and are well characterised, the syntheses

although the cyclopentadienyl substituents do influence the described for these compounds below are for completeness

redox properties of the iron centre, their influence is modest, and to report any additional characterisation.

and does not follow the trend that might be anticipated. In the

NMR spectra were recorded on either a Bruker DPX300

pantheon of cyclopentadienyl ligands, taking C₅H₅as the refer- spectrometer [operating at 300.1 MHz (¹H), 75.5 MHz (¹³C{¹H})

ence point, the pentamethyl and di-tert-butyl variants are and 121.5 MHz (³¹P{¹H})] or a Bruker DPX400, AV400 spectro-

usually described as better donor and poorer acceptor ligands, meter [operating at 400.2 MHz (¹H), 100.6 MHz {¹³C{¹H}),

whereas the silyl-substituted variants are often viewed as 162.0 MHz (³¹P{¹H}) and 79.5 MHz (²⁹Si{1H})]. Chemical shifts

poorer donors and better acceptor ligands. This should result are quoted in ppm and are relative to TMS (¹H, ¹³C{¹H} and

in pentamethyl and di-tert-butyl cyclopentadienyl ligands ²⁹Si{¹H}) and external 85% H₃PO₄(³¹P{¹H}). IR spectra were

leading to more electron rich iron centres whereas the silyl- recorded on a Bruker Tensor 27 FTIR spectrometer, where

substituted variants should give more electron deficient iron samples were prepared in the glovebox using a Nujol mull

centres. However, on the basis of the electrochemical data pre- between two KBr discs. UV-Vis/NIR spectra were recorded on a

sented here although the alkyl-cyclopentadienyls do fit this Perkin Elmer LAMBDA 750 spectrometer. Data were collected

trend, this view is clearly overly simplistic where the silyl-sub- in THF in 1 cm path length quartz cuvettes which were pre-

stituted variants are concerned since their behaviour more pared in the glovebox. Elemental microanalyses were carried

closely resembles that of C₅H₅. This observation helps to out by Mr Stephen Boyer at the Microanalysis Service, London

codify the unpredictability of cyclopentadienyl-substituent Metropolitan University, UK or Dr Tong Liu, University of Not-

eﬀects on the redox potentials of transition metal complexes tingham. Mössbauer spectra were recorded in a zero magnetic

for a widely employed ligand class. The identity of the field at 80 K or 298 K on an ES-Technology MS-105 Mössbauer

X-ligand, however, has a substantial and direct eﬀect on the spectrometer with a 25 MBq ⁵⁷Co source in a rhodium matrix

redox properties of the iron centre, which reflects the potential at ambient temperature. Spectra were referenced against a

π-donor capcacity of the halides and their direct negative point 25 μm iron foil at 298 K and spectrum parameters were

charge to iron; indeed for the halides there is an essentially obtained by fitting with Lorentzian lines. Samples were pre-

linear electrochemical relationship on moving from Cl to Br to pared by grinding with boron nitride before mounting.

I and these studies support the notion of hydride as a strong

Preparation of [FeBr₂(dppe)], II

donor ligand. The complexes reported in this study could find

extensive utility in molecular wire and metal–metal bond THF (40 mL) was added to a mixture of FeBr₂(3.45 g,

chemistry, where control of redox properties is important; the 16.0 mmol) and dppe (6.43 g, 16.0 mmol) at room temperature

data presented here provide a database that enables the selec- and then refluxed overnight. The mixture was filtered, the

tion of a particular iron complex with an appropriate reduction solids washed with toluene and dried in vacuo to yield a light

potential for a given application. We are currently investigating green solid in excellent yield (9.28 g, 94%).

the utility of the iron-hydride complexes presented here for the

Preparation of [FeI₂(dppe)], III

synthesis of uranium–iron bonds by alkane or amine elimin-

ation routes.

THF (40 ml) was added to a mixture of FeI₂(5.00 g,

16.0 mmol) and dppe (6.43 g, 16.0 mmol) at room temperature

and stirred for 18 hours. The mixture was filtered and the

solids were dried in vacuo to yield a yellow solid in excellent

yield (10.8 g, 95%).

Experimental

General experimental details

General preparative method for 1Cl–5Cl, 1Br–5Br, 1I–5I

All manipulations were carried out using standard Schlenk

techniques or an MBraun UniLab glovebox, under an atmos- Toluene (20 ml) was added dropwise to

a mixture of

phere of dry nitrogen. THF, toluene, hexane and diethyl ether FeX₂(dppe) (where X = Cl, Br or I) and MCp^†(where M = Li, K

were dried by passage through activated alumina towers and or Na, Cp = C₅H₅, M = K, Cp = C₅Me₅, C₅H₄(SiMe₃),

degassed before use and then were stored over potassium C₅H₃(SiMe₃)₂or C₅H₃(^tBu)₂) in a 1 : 1 molar ratio at −78 °C

mirrors (except THF which was stored over activated 4 Å mole- with stirring, the resultant mixture was allowed to warm to

cular sieves). Acetonitrile and dichloromethane were distilled room temperature slowly over 18 hours. The mixture was fil-

from CaH₂and stored over 3 Å (DCM) or 4 Å (MeCN) activated tered and the solids washed with toluene (2 × 5 ml), the vola-

molecular sieves. Benzene-d₆was dried over potassium, dis- tiles were removed in vacuo and the resulting solids were

tilled, degassed and stored under nitrogen. The compounds recrystallized from the minimum amount of toluene with

CpH*,^51,52KCp*,⁵³C₅H₅(SiMe₃),⁵⁴KC₅H₄(SiMe₃),⁵⁴C₅H₄- storage at −30 °C, with the exception of 1Cl which is best

(SiMe₃)₂,⁵⁴KC₅H₃(SiMe₃)₂,⁵⁴C₅H₄(^tBu)₂,⁵⁵KC₅H₃(^tBu)₂,⁵⁵and recrystallized from a DCM/hexane layer (1 : 3 ratio) with storage

[FeCl₂(dppe)]⁵⁵were synthesised according to published pro- at −30 °C. The black crystals were isolated by filtration,

cedures. The compounds LiCp, NaCp and KCp were purchased washed with hexanes (2 × 1–2 mL) and dried in vacuo.

This journal is © The Royal Society of Chemistry 2015

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Dalton Transactions

1Cl: I (2.63 g, 5.0 mmol) and LiCp (0.36 g, 5.0 mmol), yield:

5Cl:

I

(1.05 g, 2.0 mmol) and KC₅H₃(^tBu)₂(0.43 g,

1.75 g, 66%. Anal. calc’d for C₃₁H₂₉FeClP₂: C, 67.11; H, 5.27%. 2.0 mmol), yield: 0.76 g, 57%. Anal. calc’d for C₃₉H₄₅FeClP₂: C,

1

Found: C, 66.85; H, 5.16%. H NMR (C₆D₆, 298 K): δ_H2.29 (m, 70.23; H, 6.80%. Found: C, 70.39; H, 6.72%. H NMR (CDCl₃,

4H, CH₂), 4.28 (s, 5H, C₅H₅), 7.01–8.23 (m, 20H, Ar–H). ¹³C{¹H} 298 K): δ_H0.94 (s, 18H, CH₃), 2.26 (s, 4H, CH₂), 3.14 (s, 2H,

NMR (C₆D₆, 298 K): δ_C27.65 (t, CH₂, J_CP= 81 Hz), 76.94 CvCH), 3.99 (d, 1H, CvCH), 7.30–7.68 (m, 20H, Ar–H). ¹³C

1

(C₅H₅), 127.88 (Ar–C), 128.22 (Ar–C), 128.90 (Ar–C), 129.60 (Ar– {¹H} NMR (C₆D₆, 298 K): δ_C1.18 (CH₃), 31.25 (CH₂), 61.21

C), 132.31 (t, Ar–C, ²J_CP= 18 Hz), 134.62 (t, Ar–C, ²J_CP= 18 Hz), (CH), 63.14 (CH), 76.27 (C^tBu), 109.55 (CMe₃), 126.12 (Ar–C),

142.31 (Ar–C), 142.67 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P129.00 (Ar–C), 130.15 (Ar–C), 134.34 (Ar–C), 139.80 (Ar–C). ³¹P

111.31. FTIR ν/cm⁻¹(Nujol): 1403 (s), 861 (s), 694 (s), 667 (s) {¹H} NMR (CDCl₃, 298 K): δ_P85.6. FTIR ν/cm⁻¹(Nujol): 1433

651 (s), 588 (s), 529 (s) 518 (s), 491 (s), 462 (s) and 438 (s). UV- (s), 1183 (s), 1160 (s), 937 (s), 919 (s), 875 (s), 833 (s), 748 (s),

vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 17 007 (247), 19 881 (307), 694 (s), 671 (s), 648 (s), 636 (s), 616 (s), 528 (s), 517 (s), 508 (s),

40 323 (21 000). Mössbauer (80 K, mm s⁻¹) I.S. = 0.44, Q.S. = 489 (s), 475 (s) and 438 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹

1.92. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.42 V.

cm⁻¹) 15 000 (114), 18 149 (183), 39 683 (21 900). Mössbauer

2Cl: I (2.63 g, 5.0 mmol) and KCp* (0.87, 5.0 mmol), yield: (80 K, mm s⁻¹) I.S. = 0.50, Q.S. = 2.08. CV (298 K, THF, [NBu₄ⁿ]-

2.28 g, 73%. ¹H NMR (C₆D₆, 298 K): δ_H1.40 (s, 15H, CH₃), 2.75 [[BF₄], 1 mM) E_1/2= −0.54 V.

(m, 4H, CH₂), 7.00–8.05 (m, 20H, Ar–H). ¹³C{¹H} NMR (C₆D₆,

1Br: II (1.23 g, 2.0 mmol) and KCp (0.21 g, 2.0 mmol),

298 K): δ_C30.2 (CH₂), 83.60 (C₅H₅), 131.3–140.2 (Ar–C). ³¹P{¹H} yield: 0.52 g, 68%. Anal. Calc’d for C₃₁H₂₉P₂FeBr: C, 62.13;

NMR (C₆D₆, 298 K): δ_P91.6. FTIR ν/cm⁻¹(Nujol): 1483(w), H, 4.88%. Found: C, 62.25; H, 5.03%. H NMR (C₆D₆, 298 K):

1

1432 (s), 1091 (s), 1068 (w), 1027 (m), 787 (w), 471 (s), 694 (vs), δ_H2.40 (m, 4H, CH₂,), 4.28 (s, 5H, CH), 7.01–8.23 (m, 20H,

658 (s), 616 (w), 528 (vs), 519 (w), 484 (vs), 450 (w) and 428 (s). CH). ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C76.64 (CH), 128.57 (Ar–C),

UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹

)

16 502 (221), 129.37 (Ar–C), 131.97 (Ar–C), 134.43 (Ar–C). ³¹P{¹H}

18 587 (352), 40 816 (20 300). Mössbauer (80 K, mm s⁻¹) I.S. = NMR (C₆D₆, 298 K): δ_P98.2. FTIR ν/cm⁻¹(Nujol): 1433 (s),

0.48, Q.S. = 2.04. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2

−0.59 V.

=

1179 (s), 1156 (s), 861 (s), 846 (s), 831 (s), 812 (s), 787 (s),

743 (s), 727 (s), 694 (s), 669 (s), 652 (s), 588 (s), 528 (s), 518 (s),

3Cl: I (1.05 g, 2.0 mmol) and KC₅H₄(SiMe₃) (0.35 g, 489 (s) and 461 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹

)

2.0 mmol), yield: 0.66 g, 48%. Anal. calc’d for C₃₃H₃₇FeClP₂Si: 16 155 (200), 19 960 (392). Mössbauer (80 K, mm s⁻¹) I.S. =

C, 65.13; H, 5.95%. Found: C, 64.85; H, 6.12%. ¹H NMR 0.44, Q.S. = 1.94. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2

(CDCl₃, 298 K): δ_H0.08 (s, 9H, CH₃), 2.39 (m, 4H, CH₂), 4.09 (t, −0.38 V.

=

2H, CH), 4.31 (t, 2H, CH), 7.27–8.14 (m, 20H, Ar–H). ¹³C{¹H}

2Br: II (1.23 g, 2.00 mmol) and KCp* (0.35 g, 2.00 mmol),

NMR (CDCl₃, 298 K): δ_C1.03 (SiCH₃), 27.20 (CH₂), 68.95 (CH), yield: 0.40 g, 30%. Anal. Calc’d for C₃₆H₃₉P₂FeBr: C, 64.60; H,

1

77.25 (CSiMe₃), 88.78 (CH), 127.86 (Ar–C), 127.97 (Ar–C), 5.87%. Found: C, 64.52; H, 6.02%. H NMR (C₆D₆, 298 K): δ_H

129.12 (Ar–C), 129.41 (Ar–C), 132.29 (Ar–C), 134.24 (Ar–C). ³¹P- 1.58 (s, 15H, CH₃), 2.35 (m, 4H, CH₂), 7.11–7.40 (m, 20H, Ar–

{¹H} NMR (CDCl₃, 298 K): δ_P93.9. ²⁹Si{¹H} (CDCl₃, 298 K): δ_SiH). ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C11.24 (CH₃), 31.90 (CH₂),

−21.94. FTIR ν/cm⁻¹(Nujol): 1658 (s), 1433 (s), 1304 (m), 1245 83.30 (CH), 127.09 (Ar–C), 127.18 (Ar–C), 128.68 (Ar–C), 129.08

2

(s), 1180 (s), 1158 (s), 1070 (s), 1041 (s), 900 (s), 871 (s), 817 (s), (Ar–C), 134.45 (t, Ar–C, J_CP= 20 Hz), 135.00 (t, Ar–C, J_CP

=

737 (s), 697 (s) 669 (s), 645 (s), 635 (s), 609 (s), 530 (s), 520 (s), 16 Hz), 140.20 (Ar–C), 140.50 (Ar–C). ³¹P{¹H} NMR (C₆D₆,

489 (s), 452 (s), 436 (s) and 424 (s). UV-vis (THF): λ_max/cm⁻¹298 K): δ_P95.0. FTIR ν/cm⁻¹(Nujol): 1432 (s), 1179 (s), 1153

(ε/mol⁻¹cm⁻¹) 16 978 (376), 19 417 (463), 41 152 (15 000). (s), 1067 (s), 865 (s), 740 (s), 699 (s), 662 (s), 617 (s), 528 (s), 490

Mössbauer (80 K, mm s⁻¹) I.S. = 0.46, Q.S. = 1.88. CV (298 K, (s), 468 (s) and 433 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹

)

THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.45 V.

15 455 (157), 18 587 (284), 40 000 (21 900). Mössbauer (80 K,

4Cl: I (0.53 g, 1.0 mmol) and KC₅H₃(SiMe₃)₂(0.25 g, mm s⁻¹) I.S. = 0.52, Q.S. = 2.09. CV (298 K, THF, [NBu₄ⁿ][[BF₄],

1.0 mmol), yield: 0.36 g, 51%. Anal. calc’d for C₃₇H₄₅FeClP₂Si₂: 1 mM) E_1/2= −0.55 V.

C, 63.56; H, 6.49%. Found: C, 60.26; H, 6.61%. ¹H NMR

3Br: II (1.23 g, mmol) and KC₅H₄(SiMe₃) (0.35 g, 2.0 mmol),

(CDCl₃, 298 K): δ_H0.25 (s, 18H, CH₃), 2.75 (m, 4H, CH₂), 4.31 yield: 0.52 g, 39%. Anal. Calc’d for C₃₄H₃₆P₂SiFeBr: C, 60.82;

1

(d, 2H, CH), 4.85 (s, 1H, CH), 7.25–7.94 (m, 20H, Ar–H). ¹³C H, 5.55%. Found: C, 61.95; H, 5.40%. H NMR (C₆D₆, 298 K):

1

{¹H} NMR (C₆D₆, 298 K): δ_C0.04 (CH₃), 28.95 (t, CH₂, J_CP

=

δ_H0.39 (9H, s, CH₃), 2.41 (m, 4H, CH₂), 3.29 (d, 2H, CH), 5.15

36 Hz₎, 77.04 (CH), 81.43 (CSiMe₃), 102.97 (CH), 127.74 (Ar–C), (d, 2H, CH), 7.02–8.18 (m, 20H, Ar–H). ¹³C{¹H} NMR (C₆D₆,

129.29 (Ar–C), 133.38 (Ar–C), 134.33 (Ar–C), 140.13 (Ar–C). ³¹P- 298 K): δ_C0.15 (CH₃), 27.93 (t, CH₂, J_CP= 76 Hz), 70.42 (CH),

1

{¹H} NMR (C₆D₆, 298 K): δ_P93.6. ²⁹Si{¹H} (CDCl₃, 298 K): δ_Si86.86 (CH), 128.68 (Ar–C), 129.34 (Ar–C), 132.39 (Ar–C), 134.51

−2.79. FTIR ν/cm⁻¹(Nujol): 1434 (s), 1401 (s), 1251 (s), 1188 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P95.9. ²⁹Si{¹H} NMR

(s), 1156 (s), 916 (s), 883 (s), 834 (s), 762 (s), 751 (s), 738 (s), 696 (C₆D₆, 298 K): δ_Si−2.3. FTIR ν/cm⁻¹(Nujol): 1245 (s), 1180 (s),

(s), 661 (s), 632 (s), 616 (s), 598 (s), 530 (s), 518 (s), 485 (s), 459 1154 (s), 914 (s), 885 (s), 831 (s), 740 (s), 659 (s), 655 (s), 635 (s),

(s), 443 (s) and 426 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹

)

532 (s), 517 (s), 482 (s) and 455 (s). UV-vis (THF): λ_max/cm⁻¹

15 500 (191), 18 904 (339), 39 683 (13 200). Mössbauer (80 K, (ε/mol⁻¹cm⁻¹) 15 898 (390), 19 417 (618). Mössbauer (80 K,

mm s⁻¹) I.S. = 0.48, Q.S. = 1.73. CV (298 K, THF, [NBu₄ⁿ][[BF₄], mm s⁻¹) I.S. = 0.47, Q.S. = 1.84. CV (298 K, THF, [NBu₄ⁿ][[BF₄],

1 mM) E_1/2= −0.44 V.

1 mM) E_1/2= −0.41 V.

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1

4Br: II (1.23 g, 2.0 mmol) and KC₅H₃(SiMe₃)₂(0.50 g, (C₆D₆, 298 K): δ_C0.59 (SiCH₃), 28.78 (t, CH₂, J_CP= 84 Hz),

2

2.0 mmol), yield: 0.69 g, 46%. Anal. Calc’d for C₃₇H₄₅P₂Si₂- 71.71 (CH), 81.94 (t, CSiMe₃, J_CP= 8 Hz), 86.50 (CH), 127.63

1

FeBr: C, 59.76; H, 6.10%. Found: C, 59.85; H, 5.91%. H NMR (Ar–C), 127.73 (Ar–C), 128.58 (Ar–C), 129.32 (Ar–C), 132.35 (t,

2

(C₆D₆, 298 K): δ_H0.22 (s, 18H, CH₃), 2.35 (m, 4H, CH₂), 4.02 (s, Ar–C, ²J_CP= 16 Hz), 132.90 (t, Ar–C, J_CP= 32 Hz) 134.48 (t, Ar–

2H, CH), 5.43 (s, 1H, CH), 7.08–7.40 (m, 20H, Ar–H). ¹³C{¹H} C, J_CP= 16 Hz), 139.33 (t, Ar–C, J_CP= 24 Hz), 139.74 (t, Ar–C,

NMR (C₆D₆, 298 K): δ_C0.41 (CH₃), 29.45 (CH₂), 78.61 (CH), ²J_CP= 20 Hz) 142.00 (t, Ar–C, ¹J_CP= 52 Hz), 142.33 (t, Ar–C, ¹J_CP

81.12 (CH), 101.60 (Ar–C), 127.56–134.67 (Ar–C). ³¹P{¹H} NMR = 52 Hz). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P96.8. ²⁹Si{¹H} (C₆D₆,

(C₆D₆, 298 K): δ_P90.2. ²⁹Si{¹H} NMR (C₆D₆, 298 K): δ_Si−2.6. 298 K): δ_Si−1.79. FTIR ν/cm⁻¹(Nujol): 1482 (w), 1431 (s), 1308

FTIR ν/cm⁻¹(Nujol): 1432 (s), 1366 (s), 1331 (s), 12 580 (s), (w), 1243 (m), 1156 (m), 1096 (m), 1069 (sh), 1037 (sh), 1026

1238 (s), 1187 (s), 1161 (s), 1068 (s), 1051 (s), 968 (s), 956 (s), (w), 999 (w), 900 (w), 890 (w), 833 (s), 741 (s), 693 (vs), 661 (s),

923 (s), 887 (s), 833 (s), 751 (s), 733 (s), 692 (s), 656 (s), 629 (s), 632 (m), 617 (sh), 566 (w), 518 (vs), 485 (s) and 436 (s). UV-vis

611 (s), 585 (s), 532 (s), 519 (s), 483 (s), 448 (s), 438 (s) and 425 (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 15 848 (199), 19 569 (421),

(s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 15 898 (334), 40 486 (25 900). Mössbauer (80 K, mm s⁻¹) I.S. = 0.45, Q.S. =

18 939 (622), 41 152 (46 300). Mössbauer (80 K, mm s⁻¹) I.S. = 1.85. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.37 V.

2

0.49, Q.S. = 1.69. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2

−0.40 V.

=

4I: III (0.71 g, 1.0 mmol) and KC₅H₃(SiMe₃)₂(0.25 g,

1.0 mmol), yield: 0.41 g, 52%. Anal. calc’d for C₃₇H₄₅FeIP₂Si₂:

5Br: II (1.23 g, 2.0 mmol) and KC₅H₃(^tBu)₂(0.42 g, C, 56.21; H, 5.74%. Found: C, 56.30; H, 5.65%. ¹H NMR (C₆D₆,

2.0 mmol), yield: 0.79 g, 56%. Anal. Calc’d for C₃₉H₄₅P₂FeBr: 298 K): δ_H0.24 (s, 18H, CH₃), 2.50 (m, 4H, CH₂), 4.04 (s, 2H,

C, 65.82; H, 6.38%. Found: C, 65.67; H, 6.36%. ¹H NMR (C₆D₆, CH), 5.56 (s, H, CH), 6.95–8.28 (m, 20H, Ar–H). ¹³C{¹H} NMR

298 K): δ_H1.26 (s, 18H, CH₃), 2.23 (m, 4H, CH₂), 3.39 (s, 2H, (C₆D₆, 298 K): δ_C0.70 (SiCH₃), 30.46 (CH₂), 79.00 (CH), 79.61

CH), 5.29 (s, 1H, CH), 7.12–7.27 (m, 20H, Ar–H). ¹³C{¹H} NMR (CH), 101.70 (CSiMe₃) 127.70 (Ar–C), 127.94 (Ar–C), 128.55 (Ar–

1

(C₆D₆, 298 K): δ_C1.17 (CH₃), 31.54 (t, CH₂, J_CP= 278 Hz), C), 129.51 (Ar–C), 133.14 (t, Ar–C, ²J_CP= 16 Hz), 134.73 (t, Ar–C,

60.93 (CH), 80.63 (CH), 107.06 (Ar–C), 127.88 (Ar–C), 129.01 ²J_CP= 16 Hz). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P92.3. ²⁹Si{¹H}

(Ar–C), 134.26 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P82.7. (C₆D₆, 298 K): δ_Si−2.34. FTIR ν/cm⁻¹(Nujol): 915 (s), 886 (s),

FTIR ν/cm⁻¹(Nujol): 1659 (s), 1433 (s), 1286 (s), 1251 (s), 1187 696 (s), 661 (s), 635 (s), 532 (s), 517 (s), 484 (s) and 454 (s). UV-

(s), 1160 (s), 1047 (s), 998 (s), 934 (s), 919 (s), 872 (s), 843 (s), vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 15 500 (172), 19 048 (445),

832 (s), 791 (s), 741 (s), 691 (s), 664 (s), 655 (s), 642 (s), 615 (s), 40 486 (19 100). Mössbauer (80 K, mm s⁻¹) I.S. = 0.49, Q.S. =

528 (s), 482 (s), 450 (s) and 428 (s). UV-vis (THF): λ_max/cm⁻¹1.69. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.36 V.

(ε/mol⁻¹cm⁻¹) 15 456 (271), 18 051 (425), 41 152 (30 200).

Mössbauer (80 K, mm s⁻¹) I.S. = 0.53, Q.S. = 1.95. CV (298 K, 1.0 mmol), yield: 0.37 g, 49%. Anal. calc’d for C₃₉H₄₅FeIP₂: C,

THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.50 V. 61.76; H, 5.98%. Found: C, 61.65; H, 6.06%. ¹H NMR (C₆D₆,

5I: III (0.71 g, 1.0 mmol) and KC₅H₃(^tBu)₂(0.22 g,

1I: III (1.42 g, 2.0 mmol) and NaCp (0.16 g, 2.0 mmol), 298 K): δ_H1.29 (s, 18H, CH₃), 2.50 (m, 4H, CH₂), 3.45 (s, 2H,

yield: 0.84 g, 67%. ¹H NMR (C₆D₆, 298 K): δ_H2.60 (m, 4H, CH), 5.38 (s, H, CH), 6.95–8.36 (m, 20H, Ar–H). ¹³C{¹H} NMR

1

CH₂), 4.30 (s, 5H, C₅H₅), 6.99–8.05 (m, 20H, Ar–H); ³¹P{¹H} (C₆D₆, 298 K): δ_C21.20 (CMe₃), 31.91 (t, CH₂J_CP= 132 Hz),

NMR (C₆D₆, 298 K): δ_P99.1. UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹62.69 (CH), 83.77 (CH), 104.20 (C^tBu), 127.41 (Ar–C), 128.32

cm⁻¹) 16 000 (69.2), 20 120 (219), 40 323 (19 300). Mössbauer (Ar–C), 129.09 (Ar–C), 133.57 (Ar–C), 134.64 (Ar–C), 140.26 (Ar–

(80 K, mm s⁻¹) I.S. = 0.43, Q.S. = 1.89. CV (298 K, THF, [NBu₄ⁿ]- C), 140.57 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P80.5. FTIR

[[BF₄], 1 mM) E_1/2= −0.34 V.

ν/cm⁻¹(Nujol): 1157 (s), 880 (s), 842 (s), 738 (s), 696 (s), 657

2I: III (0.71 g, 1.0 mmol) and KCp* (0.17 g, 1.0 mmol), (s), 528 (s), 517 (s), 489 (s) and 467 (s). UV-vis (THF): λ_max/cm⁻¹

yield: 0.46 g, 64%. Anal. calc’d for C₃₆H₃₉FeIP₂: C, 60.36; H, (ε/mol⁻¹cm⁻¹) 14 500 (202), 18 051 (448), 40 323 (210 000).

5.49%. Found: C, 60.26; H, 5.37%. H NMR (C₆D₆, 298 K): δ_HMössbauer (80 K, mm s⁻¹) I.S. = 0.53, Q.S. = 1.95. CV (298 K,

1

1.17 (s, 15H, CH₃), 2.50 (m, 4H, CH₂), 6.82–8.14 (m, 20H, Ar– THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.46 V.

H); ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C−11.24 (CH₃), 31.90 (t, CH₂)

General preparative method for 1SIP–5SIP

83.30 (HCvC) 128.81 (p-Ar–C), 129.48 (m-Ar–C), 133.14 (o-Ar–

C), 134.73 (i-Ar–C); ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P95.0. FTIR To a solution of 1Cl–5Cl in MeCN (10 ml), TMSI (1 : 1 molar

ν/cm⁻¹(Nujol): 1179 (s), 1153 (s), 1069 (s), 893 (s), 863 (s), 739 ratio) was added dropwise at −30 °C with stirring, the mixture

(s), 699 (s), 660 (s), 618 (s), 527 (s), 518 (s), 490 (s), 468 (s), 451 was allowed to warm to room temperature slowly over

(s) and 431 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 15 106 18 hours. Volatiles were removed in vacuo to yield red solids

(264), 18 518 (500), 40 486 (35 000). Mössbauer (80 K, mm s⁻¹

I.S. = 0.52, Q.S. = 2.09. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) with storage at −30 °C to aﬀord red crystals. The crystals were

)

which were recrystallized from the minimum amount of MeCN

E_1/2= −0.51 V.

isolated by filtration and dried in vacuo.

3I: III (0.71 g, 1.0 mmol) and KC₅H₄(SiMe₃) (0.18 g,

1SIP: 1Cl (0.46 g, 0.8 mmol) and TMSI (0.12 mL, 0.8 mmol),

1.0 mmol), yield: 0.26 g, 36%. Anal. calc’d for C₃₄H₃₇FeIP₂Si: yield: 0.35 g, 65%. Anal. calc’d for C₃₃H₃₂FeINP₂: C, 57.67; H,

C, 56.84; H, 5.19%. Found: C, 57.50; H, 5.18%. ¹H NMR (C₆D₆, 4.69; N, 2.04%. Found: C, 57.50; H, 4.78; N, 2.18%. ¹H NMR

298 K): δ_H0.38 (s, 9H, CH₃), 2.57 (m, 4H, CH₂), 3.45 (s, 2H, (CDCl₃, 298 K): δ_H0.08 (s, 3H, CH₃), 2.02 (s, 3H, CH₃), 2.18 (m,

CH), 5.14 (s, 2H, CH), 6.99–8.14 (m, 20H, Ar–H). ¹³C{¹H} NMR 4H, CH₂), 4.41 (s, 5H, C₅H₅), 7.31–7.86 (m, 20H, Ar–H). ¹³C{¹H}

Dalton Trans.

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Dalton Transactions

1

NMR (CDCl₃, 298 K): δ_C6.25 (CH₃), 28.22 (t, CH₂, J_CP= 88 135.67 (NCMe), 136.58 (Ar–C). ³¹P{¹H} NMR (CDCl₃, 298 K): δ_P

2

Hz), 78.87 (C₅H₅), 129.10 (t, Ar–C, J_CP= 20 Hz), 129.26 (t, Ar– 89.1. ²⁹Si{¹H} (CDCl₃, 298 K): δ_Si−2.76. FTIR ν/cm⁻¹(Nujol):

2

C, J_CP= 18 Hz), 130.48 (Ar–C), 130.72 (Ar–C), 131.22 (t, Ar–C, 2273 (s), 1432 (s), 1193 (s), 1178 (s), 1079 (s), 944 (s), 914 (s),

2

²J_CP= 20 Hz), 132.72 (t, Ar–C, J_CP= 20 Hz), 134.06 (NuCMe), 896 (s), 873 (s), 832 (s), 751 (s), 700 (s), 675 (s), 649 (s), 632 (s),

136.49 (t, Ar–C, ¹J_CP= 80 Hz), 136.90 (t, Ar–C, ¹J_CP= 80 Hz). ³¹

P

526 (s), 513 (s), 493 (s) and 436 (s). UV-vis (THF): λ_max/cm⁻¹

{¹H} NMR (CDCl₃, 298 K): δ_P97.9. FTIR ν/cm⁻¹(Nujol): 2266 (ε/mol⁻¹cm⁻¹) 15 015 (124), 19 120 (392), 23 000 (458), 40 000

(s), 1432 (s), 1175 (s), 1157 (s), 1073 (s), 998 (s), 951 (s), 919 (s), (26 700). Mössbauer (80 K, mm s⁻¹) I.S. = 0.44, Q.S. = 1.86. CV

873 (s), 859 (s), 836 (s), 812 (s), 748 (s), 712 (s), 699 (s), 672 (s), (298 K, MeCN, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= 0.26 V.

648 (s), 617 (s), 532 (s), 520 (s), 496 (s) 454 (s), 440 (s) and

5SIP: 5Cl (0.30 g, 1.0 mmol) and TMSI (0.14 Ml, 1.0 mmol),

429 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 16 000 (95.4), yield: 0.55 g, 69%. Anal. calc’d for C₄₁H₄₈FeINP₂: C, 61.59; H,

20 202 (392), 24 500 (553), 40 323 (22 900). Mössbauer (80 K, 6.05; N, 1.75%. Found: C, 61.42; H, 5.84; N, 1.73%. ¹H NMR

mm s⁻¹) I.S. = 0.39, Q.S. = 2.01. CV (298 K, MeCN, [NBu₄ⁿ]- (CDCl₃, 298 K): δ_H0.80 (s, 18H, CH₃), 2.02 (s, 3H, CH₃), 2.18

[[BF₄], 1 mM) E_1/2= 0.26 V.

(m, 4H, CH₂), 4.11 (s, 2H, CH), 4.78 (s, 1H, CH), 7.28–7.80 (m,

2SIP: 2Cl (0.62 g, 1.0 mmol) and TMSI (0.14 mL, 0.8 mmol), 20H, Ar–H). ¹³C{¹H} NMR (CDCl₃, 298 K): δ_C2.65 (CH₃), 8.29

1

yield: 0.57 g, 75%. Anal. calc’d for C₃₈H₄₂FeINP₂: C, 60.26; H, (CH₃), 31.21 (t, CH₂, J_CP= 88 Hz), 70.31 (CH), 74.89 (CH),

5.59; N, 1.85%. Found: C, 60.36; H, 5.46; N, 1.86%. ¹H NMR 109.72 (C^tBu), 129.10 (Ar–C), 129.35 (Ar–C), 130.51 (Ar–C),

(CDCl₃, 298 K): δ_H1.32 (s, 15H, CH₃), 2.17 (s, 3H, CH₃), 2.18 130.64 (Ar–C) 132.29 (Ar–C), 133.14 (Ar–C), 136.43 (NCMe),

(m, 4H, CH₂) 7.39–7.61 (m, 20H, Ar–H). ¹³C{¹H} NMR (CDCl₃, 137.43 (t, Ar–C, J_CP= 60 Hz), 137.80 (t, Ar–C, J_CP= 60 Hz). ³¹P

298 K): δ_C7.13 (CH₃), 9.89 (CH₃) 28.57 (t, CH₂, J_CP= 78 Hz), {¹H} NMR (CDCl₃, 298 K): δ_P84.6. FTIR ν/cm⁻¹(Nujol): 2267

1

87.21 (C₅Me₅), 128.56 (t, Ar–C, J_CP= 18 Hz), 129.09 (t, Ar–C, (s), 1432 (s), 1411 (s), 1364 (s), 1293 (s), 1248 (s) 1179 (s), 1164

J_CP= 18 Hz), 130.66 (Ar–C), 130.87 (Ar–C) 132.34 (t, Ar–C, J_CP

=

(s), 1127 (s), 998 (s), 951 (s), 923 (s), 892 (s), 866 (s), 758 (s), 741

18 Hz), 133.34 (t, Ar–C, J_CP= 21 Hz). ³¹P{¹H} NMR (CDCl₃, (s), 716 (s), 701 (s), 678 (s), 654 (s), 520 (s), 505 (s), 471 (s) and

298 K): δ_P89.9. FTIR ν/cm⁻¹(Nujol): 2248 (s), 1403 (s), 1156 438 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 14 514 (221),

(s), 949 (s), 890 (s), 861 (s), 786 (s), 759 (s), 742 (s), 695 (s), 661 18 083 (491), 22 500 (716), 40 000 (28 100). Mössbauer (80 K,

(s), 640 (s), 528 (s), 516 (s), 483 (s) and 456 (s). UV-vis (THF): mm s⁻¹) I.S. = 0.45, Q.S. = 1.97. CV (298 K, MeCN, [NBu₄ⁿ]-

λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 15 244 (161), 18 553 (369), 22 750 [[BF₄], 1 mM) E_1/2= 0.20 V.

(810), 40 323 (32 700). Mössbauer (80 K, mm s⁻¹) I.S. = 0.42, Q.

S. = 2.00. CV (298 K, MeCN, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= 0.06 V.

General preparative method for 1H–5H

3SIP: 3Cl (1.14 g, 1.8 mmol), and TMSI (0.25 mL, THF (10 ml) was added dropwise to a mixture of 1Cl–2Cl and

1.8 mmol), yield: 0.47 g, 36%. Anal. calc’d for C₃₆H₄₀FeINP₂Si: LiAlH₄(1 : 5 molar ratio) at −78 °C with stirring, the suspen-

C, 56.93; H, 5.31; N, 1.84%. Found: C, 54.54; H, 5.30; N, sion was allowed to warm to 0 °C and stirred for a further

1

2.08%. H NMR (CDCl₃, 298 K): δ_H0.25 (s, 9H, CH₃), 2.03 (s, 3 hours. At 0 °C degassed deionised water was added dropwise

3H, CH₃), 2.61 (m, 4H, CH₂), 4.31 (d, 2H, CH) 4.85 (s, 2H, CH), until the evolution of gas ceased and the volatiles were

7.38–7.86 (m, 20H, Ar–H). ¹³C{¹H} NMR (CDCl₃, 298 K): δ_Cremoved in vacuo to yield orange solids which were extracted

1

−0.53 (CH₃) 6.81 (CH₃), 28.45 (t, CH₂, J_CP= 80 Hz), 71.06 and recrystallized from hexanes to aﬀord orange crystals. The

2

(CH), 72.77 (CH), 74.79 (CH), 88.29 (CH) 129.08 (t, Ar–C, J_CP

=

crystals were collected by filtration and dried in vacuo.

2

20 Hz), 129.30 (t, Ar–C, J_CP= 20 Hz), 130.70 (Ar–C), 130.80

1H: 1Cl (0.56 g, 1.0 mmol) and LiAlH₄(0.19 g, 5.0 mmol),

(Ar–C), 131.72 (t, Ar–C, J_CP= 20 Hz), 132.72 (t, Ar–C, J_CP= 18 yield: 0.41 g, 73%. ¹H NMR (C₆D₆, 298 K): δ_H−15.94 (t, 1H,

2

1

2

Hz), 134.61 (NCMe), 136.24 (t, Ar–C, J_CP= 76 Hz), 136.65 (t, FeH, J_PH= 72 Hz) 1.87 (2H, CH₂), 2.10 (m, 4H, CH₂), 4.31 (s,

Ar–C, J_CP= 88 Hz). ³¹P{¹H} NMR (CDCl₃, 298 K): δ_P95.3. ²⁹Si 5H, C₅H₅), 7.16–7.97 (m, 20H, Ar–H). ¹³C{¹H} NMR (C₆D₆,

1

{¹H} (CDCl₃, 298 K): δ_Si−3.12. FTIR ν/cm⁻¹(Nujol): 2268 (s), 298 K): δ_C33.02 (t, CH₂, J_CP= 60 Hz), 75.47 (CH), 127.21 (Ar–

1

2

1165 (s), 1065 (s) 1031 (s), 950 (s), 899 (s), 871 (s), 832 (s), 746 C), 128.48 (Ar–C), 133.27 (Ar–C), 132.90 (t, Ar–C, J_CP= 40 Hz),

2

(s) 698 (s), 674 (s), 616 (s) 527 (s), 517 (s), 490 (s), 455 (s). UV- 133.27 (t, Ar–C, J_CP= 16 Hz), 133.92 (t, Ar–C, J_CP= 20 Hz),

vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 20 920 (658), 40 323 139.33 (t, Ar–C, J_CP= 36 Hz), 140.11 (t, Ar–C, J_CP= 28 Hz),

2

(25 300). Mössbauer (80 K, mm s⁻¹) I.S. = 0.39, Q.S. = 1.91. CV 141.85 (Ar–C), 142.23 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P

(298 K, MeCN, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2= 0.25 V.

111.6. FTIR ν/cm⁻¹(Nujol) 1845 (s), 1621 (w), 1584 (w), 1301

4SIP: 4Cl (0.35 g, 0.5 mmol) and TMSI (0.14 mL, 1.0 mmol), (w), 1260 (w), 1087 (s), 1065 (w), 1027 (w), 812 (w), 740 (w), 695

yield: 0.27 g, 64%. Anal. calc’d for C₃₉H₄₈FeINP₂Si₂: C, 56.32; (vs), 672 (s), 530 (vs), 493 (s), 474 (w) and 439 (w). UV-vis

H, 5.82; N, 1.68%. Found: C, 56.66; H, 5.69; N, 1.63%. ¹H NMR (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 39 683 (27 900). Mössbauer

(CDCl₃, 298 K): δ_H−0.13 (s, 18H, CH₃), 1.77 (s, 3H, CH₃), 2.51 (80 K, mm s⁻¹) I.S. = 0.26, Q.S. = 1.91. CV (298 K, THF, [NBu₄ⁿ]-

(m, 4H, CH₂), 4.46 (d, 2H, CH) 4.85 (s, 1H, CH), 7.46–7.84 (m, [[BF₄], 1 mM) E_1/2= −0.50 V.

20H, Ar–H). ¹³C{¹H} NMR (CDCl₃, 298 K): δ_C0.03 (CH₃) 7.79

2H: 2Cl (0.62 g, 1.0 mmol) and LiAlH₄(0.19 g, 5.0 mmol),

1

(CH₃), 29.18 (t, CH₂, J_CP= 72 Hz), 83.91 (CH), 84.41 (CH), yield: 0.40 g, 68%. Anal. calc’d for C₃₆H₄₀FeP₂: C, 73.22; H,

2

1

98.48 (CSiMe₃), 129.13 (t, Ar–C, J_CP= 18 Hz), 129.36 (t, Ar–C, 6.83%. Found: C, 73.34; H, 6.85%. H NMR (C₆D₆, 298 K): δ_H

²J_CP= 18 Hz), 130.77 (Ar–C), 130.83 (Ar–C) 130.83 (Ar–C), −16.66 (t, 1H, FeH, ²J_PH= 80 Hz) 1.73 (15H, CH₃), 1.84 (m, 4H,

2

132.36 (t, Ar–C, J_CP= 18 Hz), 133.29 (t, Ar–C, J_CP= 18 Hz), CH₂), 7.08–7.91 (m, 20H, Ar–H). ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C

Dalton Trans.

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Dalton Transactions

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1

11.35 (CH₃), 33.02 (t, CH₂, J_CP= 64 Hz) 84.88 (CMe₃), 127.21 (s), 1047 (2), 939 (s), 918 (s), 911 (s), 874 (s), 842 (s), 743 (s),

2

(Ar–C), 127.43 (Ar–C), 132.89 (t, Ar–C, J_CP= 36 Hz), 133.27 (t, 696 (s), 676 (s), 657 (s), 617 (s), 588 (s), 524 (s), 514 (s), 496 (s)

Ar–C, ²J_CP= 16 Hz), 133.92 (t, Ar–C, ²J_CP= 20 Hz), 138.89 (t, Ar– and 475 (s). UV-vis (THF): λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 23 474

2

C, J_CP= 35 Hz), 139.93 (t, Ar–C, J_CP= 32 Hz) 140.11 (t, Ar–C, (2610), 39 683 (20 500). Mössbauer (80 K, mm s⁻¹) I.S. = 0.27,

²J_CP= 35 Hz), 141.85 (t, Ar–C, J_CP= 68 Hz), 142.23 (t, Ar–C, Q.S. = 1.96. CV (298 K, THF, [NBu₄ⁿ][[BF₄], 1 mM) E_1/2

¹J_CP= 68 Hz). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_P107.7. FTIR −0.62 V.

=

1

ν/cm⁻¹(Nujol): 1844 (s), 1153 (s), 1064 (s), 876 (s), 740 (s), 695

X-ray crystallographic details

(s), 672 (s), 529 (s), 493 (s) and 474 (s). UV-vis (THF): λ_max/cm⁻¹

(ε/mol⁻¹cm⁻¹) 28 011 (2760), 39 683 (27 900). Mössbauer Crystallographic data can be found in the ESI in cif format.†

(80 K, mm s⁻¹) I.S. = 0.25, Q.S. = 1.92. CV (298 K, THF, [NBu₄ⁿ]- Crystals were examined variously on: (a) a Bruker AXS CCD

[[BF₄], 1 mM) E^a_p= −0.67 V, E_1/2= −0.71 V.

area detector diﬀractometer operating at 90 K/150 K using

3H: 3Cl (1.01 g, 1.5 mmol) and LiAlH₄(0.28 g, 7.5 mmol), graphite-monochromated Mo Kα radiation (λ = 0.71073 Å),

yield: 0.31 g, 35%. No satisfactory elemental analysis could be with intensities integrated from a sphere of data recorded on

obtained for 3H due to contamination of samples with free 0.3° frames by rotation of ω, or (b) an Oxford Diﬀraction CCD

dppe ligand. ¹H NMR (C₆D₆, 298 K): δ_H−15.31 (t, 1H, FeH, area detector diﬀractometer operating at 90 K using mirror-

²J_PH= 72 Hz), 0.35 (s, 9H, CH₃), 1.92 (m, 4H, CH₂), 4.22 (m, monochromated Cu Kα radiation (λ = 1.5418 Å) with intensities

4H, CH), 7.21–7.89 (m, 20H, Ar–H). ¹³C{¹H} NMR (C₆D₆, integrated from a sphere of data recorded on 1° frames by

1

298 K): δ_C0.34 (CH₃), 31.01 (t, CH₂, J_CP= 92 Hz), 71.27 (CH), rotation of ώ. Cell parameters were refined from the observed

72.91 (CH), 80.84 (CSiMe₃), 127.69 (Ar–C), 128.32 (Ar–C), positions of all strong reflections in the data set. The struc-

2

132.14 (t, Ar–C, J_CP= 16 Hz), 132.82 (t, Ar–C, J_CP= 16 Hz), tures were solved by either direct methods or heavy atom

143.00 (Ar–C), 143.52 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_Pmethod and refined by least-squares methods on all unique F²

110.1. ²⁹Si{¹H} (C₆D₆, 298 K): δ_Si−4.77. FTIR ν/cm⁻¹(Nujol): values, with all non-H non solvent atoms being anisotropic.

1245 (s), 1160 (s), 1066 (s), 1036 (s), 969 (s), 918 (s), 903 (s), 872 The largest residual electron densities in final diﬀerence synth-

(s), 862 (s), 834 (s), 813 (s), 743 (s), 693 (s), 675 (s), 646 (s), 627 eses were close to heavy atoms unless stated otherwise.

(s), 525 (s), 499 (s), 468 (s), 437 (s) and 422 (s). UV-vis (THF): Absorption correction was performed by multi-scan methods.

λ_max/cm⁻¹(ε/mol⁻¹cm⁻¹) 24 000 (805), 40 161 (8730). Möss- Criterion for observed reflections is I > 2σ(I) and weighting

bauer (80 K, mm s⁻¹) I.S. = 0.26, Q.S. = 1.70. CV (298 K, THF, scheme used is W = 1/[σ²(F_o) + (xP)²+ yP] where P = (F_o

+

2

[NBu₄ⁿ][[BF₄], 1 mM) E_1/2= −0.50 V.

2F_c)/3. Programs used for Bruker AXS were SMART (control),

4H: 4Cl (1.37 g, 2.0 mmol) and LiAlH₄(0.38 g, 10.0 mmol), SAINT (integration) and SHELXTL for structure solution and

yield: 0.54 g, 41%. Anal. calc’d for C₃₇H₄₆FeP₂: C, 66.86; H, refinement. Programs used for Oxford diﬀraction were Crysalis-

1

6.98%. Found: C, 66.98; H, 7.05%. H NMR (C₆D₆, 298 K): δ_HPro CCD (control), CrysalisPro RED (integration), SHELXTL for

−16.54 (t, 1H, FeH, ²J_PH= 72 Hz), −0.11 (s, 18H, CH₃), 2.60 (m, structure solution and refinement.⁵⁶

4H, CH₂), 4.45 (d, 2H, CH), 4.88 (s, 1H, CH), 7.49–7.89 (m,

Cyclic voltammetry experimental details and ESI†

20H, Ar–H). ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C0.43 (CH₃), 31.25 (t,

1

CH₂, J_CP= 88 Hz), 82.16 (CSiMe₃), 83.71 (CH), 87.01 (CH), Electrochemical measurements were performed using an

127.51 (t, Ar–C, J_CP= 16 Hz), 127.73 (t, Ar–C, J_CP= 16 Hz), Autolab PGSTAT20 potentiostat with a three-electrode configur-

2

128.40 (Ar–C), 128.50 (Ar–C), 132.31 (t, Ar–C, J_CP= 18 Hz) ation consisting of a saturated calomel electrode (SCE) refer-

132.77 (t, Ar–C, J_CP= 20 Hz), 146.94 (Ar–C). ³¹P{¹H} NMR ence electrode, Pt wire secondary electrode and a glassy

2

(C₆D₆, 298 K): δ_p104.8. ²⁹Si{¹H} (C₆D₆, 298 K): δ_Si−5.01. FTIR carbon working electrode. All voltammograms were recorded

ν/cm⁻¹(Nujol): 1245 (s), 1184 (s), 1155 (s), 1074 (s), 968 (s), at ambient temperatures for solutions of the sample at ca.

924 (s), 911 (s), 864 (s), 832 (s), 742 (s), 696 (s), 669 (s), 634 (s), 1 mM in tetrahydrofuran (THF) or acetonitrile (MeCN) contain-

522 (s), 494 (s), 479 (s), 444 (s) and 427 (s). UV-vis (THF): λ_max

/

ing 0.5 M or 0.1 M [NBuⁿ₄][BF₄], respectively, as the supporting

cm⁻¹(ε/mol⁻¹cm⁻¹) 24 096 (1660), 39 683 (14 200). Mössbauer electrolyte. Samples were prepared in a glove box and main-

(80 K, mm s⁻¹) I.S. = 0.28, Q.S. = 1.71. CV (298 K, THF, [NBu₄ⁿ]- tained under an argon atmosphere using Schlenk line tech-

[[BF₄], 1 mM) E_1/2= −0.53 V.

niques during the experiment. All electrochemical potentials

5H: 5Cl (0.63 g, 1.0 mmol) and LiAlH₄(0.19 g, 5.0 mmol), were measured relative to SCE and were corrected for liquid-

yield: 0.46 g, 53%. Anal. calc’d for C₃₉H₄₆FeP₂: C, 74.05; H, junction potentials via the use of the [(η⁵-C₅H₅)₂Fe]⁺/[(η⁵-

1

7.33%. Found: C, 72.03; H, 7.15%. H NMR (C₆D₆, 298 K): δ_HC₅H₅)₂Fe] ([Cp₂Fe]⁺/[Cp₂Fe]) couple as an internal redox stan-

2

−15.65 (t, 1H, FeH, J_PH= 84 Hz) 1.19 (s, 18H, CH₃), 1.98 (m, dard. When the potential of a redox process of the compound

4H, CH₂), 4.05 (d, 2H, CH), 4.09 (s, 1H, CH), 7.17–8.02 (m, of interest overlapped with that of the ([Cp₂Fe]⁺/[Cp₂Fe])

20H, Ar–H). ¹³C{¹H} NMR (C₆D₆, 298 K): δ_C22.54 (CMe₃), 30.72 couple, either the [(η⁵-Me₅)₂Fe]⁺/[(η⁵-C₅Me₅)₂Fe] or ([Cp₂Co]⁺/

5

(CH₃), 32.06 (CH₂) 69.93 (CH), 71.17 (CH), 108.73 (C^tBu), [Cp₂Co]) couples was used as a standard. Under these circum-

127.46 (Ar–C), 127.66 (Ar–C), 128.20 (Ar–C), 128.26 (Ar–C), stances, the redox processes of the compound were referenced

2

132.26 (t, Ar–C, J_CP= 24 Hz) 132.65 (t, Ar–C, J_CP= 16 Hz), to the [Cp₂Fe]⁺/[Cp₂Fe] couple by an independent calibration

144.19 (Ar–C), 144.39 (Ar–C). ³¹P{¹H} NMR (C₆D₆, 298 K): δ_Punder identical conditions; E_1/2[Cp₂Co]⁺/[Cp₂Co] was −1.358 V

104.5. FTIR ν/cm⁻¹(Nujol): 1431 (s), 1360 (s), 1198 (s), 1162 vs. [Cp₂Fe]⁺/[Cp₂Fe] in THF at 1 V s⁻¹(used for 4H only) and

Dalton Trans.

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Dalton Transactions

E_1/2[(η⁵-C₅Me₅)₂Fe]⁺/[(η⁵-C₅Me₅)₂Fe] was −0.505 V vs. [Cp₂Fe]⁺/

[Cp₂Fe] in MeCN at 0.1 V s⁻¹(used for 1SIP–5SIP).

6 B. M. Gardner, D. Patel, A. D. Cornish, J. McMaster,

W. Lewis, A. J. Blake and S. T. Liddle, Chem. – Eur. J., 2011,

17, 11266.

DFT experimental and ESI†

7 M. J. Mays and P. L. Sears, J. Chem. Soc., Dalton Trans.,

1973, 1873; G. Hata, H. Kondo and A. Miyake, J. Am. Chem.

Soc., 1968, 90(9), 2278–2281; J. E. Barclay, G. J. Leigh,

A. Houlton and J. Silver, J. Chem. Soc., Dalton Trans., 1988,

2865–2870; S. Pohl, U. Opitz, D. Hasse and W. Saak,

Z. Anorg. Allg. Chem., 1995, 621, 1140–1146; R. Langer,

F. Bönisch, L. Maser, C. Pietzonka, L. Vondung and

T. P. Zimmermann, Eur. J. Inorg. Chem., 2015, 141–

148.

8 J. Niemeyer, D. A. Addy, I. Riddlestone, M. Kelly,

A. L. Thompson, D. Vidovic and S. Aldridge, Angew. Chem.,

Int. Ed., 2011, 50, 8908; J. A. van Rijn, E. Gouré,

M. A. Siegler, A. L. Spek, E. Drent and E. Bouwman, J. Orga-

nomet. Chem., 2011, 696, 1899; S. G. Davies, J. Organomet.

Chem., 1979, 179, C5.

9 E. C. Fitzgerald, A. Ladjarafi, N. J. Brown, D. Collison,

K. Costuas, R. Edge, J.-F. Halet, F. Justaud, P. J. Low,

H. Meghezzi, T. Roisnel, M. W. Whiteley and C. Lapinte,

Organometallics, 2011, 30, 4180; Y. Tanaka, J. A. Shaw-

Taberlet, F. D. R. Justaud, O. Cador, T. Roisnel, M. Akita,

J.-R. Hamon and C. Lapinte, Organometallics, 2009,

28, 4656; L. Medei, L. Orian, O. V. Semeikin,

M. G. Peterleitner, N. A. Ustynyuk, S. Santi, C. Durante,

A. Ricci and C. Lo Sterzo, Eur. J. Inorg. Chem., 2006, 2582;

M. I. Bruce, K. Costuas, T. Davin, B. G. Ellis, J.-F. Halet,

C. Lapinte, P. J. Low, M. E. Smith, B. W. Skelton, L. Toupet

and A. H. White, Organometallics, 2005, 24, 3864; F. de

Montigny, G. Argouarch, K. Costuas, J.-F. Halet, T. Roisnel,

L. Toupet and C. Lapinte, Organometallics, 2005, 24, 4558;

N. Le Narvor and C. Lapinte, C. R. l’Académie. Sci., Ser. IIC

Chem., 1998, 1, 745; T. Weyland, C. Lapinte, G. Frapper,

M. J. Calhorda, J.-F. Halet and L. Toupet, Organometallics,

1997, 16, 2024; F. Coat and C. Lapinte, Organometallics,

1996, 15, 477; N. Le Narvor and C. Lapinte, Organometallics,

1995, 14, 634.

Restricted gas-phase DFT calculations were performed using

the Amsterdam Density Functional (ADF) suite version 2012.01

with initial models of were derived from the X-ray crystal struc-

tures of 1Cl–5Cl, 1Br–5Br, 1I–5I, 1SIP–5SIP and 1H–5H.^57–59

The DFT calculations employed a Slater-type orbital (STO) all-

electron triple-ζ-plus one polarization function basis set from

the ZORA/TZP database of the ADF suite for all atoms. The

scalar relativistic (SR) approach was used within the ZORA

Hamiltonian for the inclusion of relativistic eﬀects. The calcu-

lations employed the local density approximation (LDA) with

the correlation potential due to Vosko et al.⁶⁰Gradient correc-

tions were performed using the functionals of Becke⁶¹and

Perdew.⁶²Pictorial representations of the MOs were generated

using MOLEKEL⁶³and the orbital compositions were calcu-

lated using AOMIX.⁶⁴

Acknowledgements

We thank the Royal Society, EPSRC, ERC, and University of

Nottingham for supporting this work.

References

1 R. D. Theys, M. E. Dudley and M. M. Hossain, Coord. Chem.

Rev., 2009, 253, 180.

2 A search of the Cambridge Strucutral Database v1.17,

accessed on 15–01–2015, reveals over six hundred com-

plexes containing a CpFe(CO)₂fragment bonded to a d- or

f-block metal.

3 M. P. Blake, N. Kaltsoyannis and P. Mountford, Chem.

Commun., 2013, 49, 3315; B. Oelkers, M. V. Butovskii and

R. Kempe, Chem. – Eur. J., 2012, 18, 13566; S. T. Liddle and

D. P. Mills, Dalton Trans., 2009, 5569; S. T. Liddle, Philos. 10 D. Patel, F. Moro, J. McMaster, W. Lewis, A. J. Blake and

Trans. R. Soc. London, Ser A, 2009, 465, 1673; P. Beletskaya, S. T. Liddle, Angew. Chem., Int. Ed., 2011, 50, 10388.

A. Z. Voskoboynikov, E. B. Chuklanova, N. I. Kirillova, 11 S. El-Tarhuni, M. Ho, M. H. Kawser, S. Shi and

A. K. Shestakova, I. N. Parshina, A. I. Gusev and

G. K.-I. Magomedov, J. Am. Chem. Soc., 1993, 115, 3156.

4 B. M. Gardner, J. McMaster, F. Moro, W. Lewis, A. J. Blake

M. W. Whiteley, J. Organomet. Chem., 2014, 752, 30.

12 P. Hamon, L. Toupet, J.-R. Hamon and C. Lapinte, Organo-

metallics, 1996, 15, 10.

and S. T. Liddle, Chem.

B. M. Gardner, W. Lewis, A. J. Blake and S. T. Liddle, Inorg.

Chem., 2011, 50, 9631; D. Patel, D. M. King, B. M. Gardner, 14 C. Roger, P. Hamon, L. Toupet, H. Rabaa, J. Y. Saillard,

–

Eur. J., 2011, 17, 6909; 13 M. J. Mays and P. L. Sears, J. Chem. Soc., Dalton Trans.,

1973, 1873.

J. McMaster, W. Lewis, A. J. Blake and S. T. Liddle, Chem.

Commun., 2011, 47, 295; S. T. Liddle, D. P. Mills,

B. M. Gardner, J. McMaster, C. Jones and W. D. Woodul,

J. R. Hamon and C. Lapinte, Organometallics, 1991, 10,

1045; Y.-P. Ou, D. Feng and J.-J. Yuan, Acta Crystallogr.,

Sect. E: Struct. Rep. Online, 2010, 66, m921.

Inorg. Chem., 2009, 48, 3520; B. M. Gardner, J. McMaster, 15 D. H. Hill, M. Parvez and A. Sen, Acta Crystallogr., Sect. C:

W. Lewis and S. T. Liddle, Chem. Commun., 2009, 2851; Cryst. Struct. Commun., 1990, 46, 133.

S. T. Liddle, J. McMaster, D. P. Mills, A. J. Blake, C. Jones 16 As determined by a search of the Cambridge Structural

and W. D. Woodul, Angew. Chem., Int. Ed., 2009, 48, 1077. Database v1.17, accessed on the 15-01-2015.

5 A. P. Sobaczynski, T. Bauer and R. Kempe, Organometallics, 17 J.-R. Hamon, P. Hamon, L. Toupet, K. Costuas and

2013, 32, 1363. J.-Y. Saillard, C. R. Chim., 2002, 5, 89.

Dalton Trans.

View Article Online

Dalton Transactions

Paper

18 M. Jimenez-Tenorio, M. C. Puerta and P. Valerga, Organo- 41 V. Guillaume, P. Thominot, F. Coat, A. Mari and C. Lapinte,

metallics, 1994, 13, 3330. J. Organomet. Chem., 1998, 565, 75.

19 E. B. Lobkovskii, M. Y. Antipin, A. P. Borisov, 42 P. Hamon, L. Toupet, J. R. Hamon and C. Lapinte, Organo-

V. D. Makhaev, K. N. Semenenko and Y. T. Struchkov,

Koord. Khim., 1980, 6, 1267.

20 R. H. Morris, J. F. Sawyer, M. Shiralian and J. Zubkowski,

J. Am. Chem. Soc., 1985, 107, 5581.

21 M. Knorr, J. Mueller and U. Schubert, Chem. Ber., 1987,

120, 879.

22 J. S. Ricci, T. F. Koetzle, M. T. Bautista, T. M. Hofstede,

metallics, 1992, 11, 1429.

43 T. A. Albright, J. K. Burdett and M.-H. Wangbo, Orbital

Interactions in Chemistry, John Wiley, New York, 1985.

44 G. M. Aston, S. Badriya, R. D. Farley, R. W. Grime,

S. J. Ledger, F. E. Mabbs, E. J. L. McInnes, H. W. Morris,

A. Ricalton, C. C. Rowlands, K. Wagner and

M. W. Whiteley, J. Chem. Soc., Dalton Trans., 1999, 4379.

R. H. Morris and J. F. Sawyer, J. Am. Chem. Soc., 1989, 111, 45 I. M. Bartlett, S. Carlton, N. G. Connelly, D. J. Harding,

8823.

O. D. Hayward, A. G. Orpen, C. D. Ray and P. H. Reiger,

23 P. B. Hitchcock, M. A. N. D. A. Lemos, M. F. Meidine,

Chem. Commun., 1999, 2403.

J. F. Nixon and A. J. L. Pombeiro, J. Organomet. Chem., 46 S. T. Krueger, R. Poli, A. L. Rheingold and D. L. Staley,

1991, 402, C23. Inorg. Chem., 1989, 28, 4599.

24 M. F. Meidine, M. A. N. D. A. Lemos, A. J. L. Pombeiro, 47 T. C. Zietlow, M. D. Hopkins and H. B. Gray, J. Am. Chem.

J. F. Nixon and P. B. Hitchcock, J. Chem. Soc., Dalton Trans.,

Soc., 1986, 108, 8266.

1998, 3319.

48 T. Hascall, D. Rabinovich, V. J. Murphy, M. D. Beachy,

R. A. Friesner and G. Parkin, J. Am. Chem. Soc., 1999, 121,

11402.

25 J.-G. Lee, G.-S. Jung and S. W. Lee, Bull. Korean Chem. Soc.,

1998, 19, 267.

26 S. S. P. R. Almeida, M. F. C. G. da Silva, J. J. R. Fraustoda 49 S. T. Krueger, B. E. Owens and R. Poli, Inorg. Chem., 1990,

Silva and A. J. L. Pombeiro, J. Chem. Soc., Dalton Trans.,

1999, 467.

27 J. G. Lee, B. S. Yoo, N. S. Choi, K. I. Park, S. I. Cho, C. Lee

and S. W. Lee, J. Organomet. Chem., 1999, 589, 138.

29, 2001.

50 C. M. Fendrick, L. D. Schertz, E. A. Mintz, T. J. Marks,

T. E. Bitterwolf, P. A. Horine, T. L. Hubler, J. A. Sheldon

and D. D. Belin, Inorg. Synth., 1992, 29, 193.

28 L. M. D. R. S. Martins, J. J. R. Frausto Da Silva, 51 F. X. Kohl and P. Jutzi, J. Organomet. Chem., 1983, 243,

A. J. L. Pombeiro, R. A. Henderson, D. J. Evans, 119.

F. Benetollo, G. Bombieri and R. A. Michelin, Inorg. Chim. 52 H. Schumann, I. Albrecht, J. Loebel, E. Hahn,

Acta, 1999, 291, 39.

29 J. Y. Baeg, W. S. Han and S. W. Lee, J. Korean Chem. Soc.,

2002, 46, 427.

30 B.-S. Yoo, N.-S. Choi, C. Y. Shim, Y. Son and S. W. Lee,

Inorg. Chim. Acta, 2000, 309, 137.

M. B. Hossain and D. Van der Helm, Organometallics, 1986,

5, 1296.

53 C. Ting, J.-C. Tsai, Y.-C. Chen, S.-S. Hua, T.-T. Su and

Y.-S. Chao, Pat. No US6207773B1, 2001, Metallocene cata-

lyst for preparing olefin polymer.

31 J. H. Lee, B. S. Yoo and S. W. Lee, Inorg. Chim. Acta, 2001, 54 M. D. Walter, C. D. Sofield, C. H. Booth and

321, 75. R. A. Andersen, Organometallics, 2009, 28, 2005.

32 S. S. P. R. Almeida, M. F. C. Guedes da Silva, 55 D. J. Evans, P. B. Hitchcock, G. J. Leigh, B. K. Nicholson,

L. B. Jerzykiewicz, P. Sobota and A. J. L. Pombeiro, Inorg.

Chim. Acta, 2003, 356, 259.

A. C. Niedwieski, F. S. Nunes and J. F. Soares, Inorg. Chim.

Acta, 2001, 319, 147.

33 H. V. Nanishankar, M. Nethaji and B. R. Jagirdar, Indian 56 Bruker SMART and SAINT Bruker AXS Inc., Madison, Wis-

J. Chem., Sect. A: Inorg., Bio-inorg., Phys., Theor. Anal. Chem.,

2003, 42A, 2332.

34 M. P. Rabalo, A. P. S. Teixeira, M. H. Garcia, M. F. Minas da

consin, 2001; G. M. Sheldrick, SHELXTL, version 5, Bruker

AXS Inc., Madison, WI; SHELXTL, version 5, Bruker AXS

Inc., Madison, WI, 2001.

Piedade, M. T. Duarte, A. R. Dias, J. Campo, W. Wenseleers 57 G. t. Velde, F. M. Bickelhaupt, S. J. A. v. Gisbergen,

and E. Goovaerts, Eur. J. Inorg. Chem., 2006, 2175.

35 J. G. Cordaro, D. Stein and H. Gruetzmacher, J. Am. Chem.

Soc., 2006, 128, 14962.

C. F. Guerra, E. J. Baerends and S. J. G. Ziegler, J. Comput.

Chem., 2001, 22, 931.

58 C. F. Guerra, J. G. Snijders, G. t. Velde and E. J. Baerends,

Theor. Chem. Acc., 1998, 99, 391.

36 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165.

37 G. Boschloo and A. Hagfeldt, Acc. Chem. Res., 2009, 42, 59 ADF2014, Theoretical Chemistry, Vrije Universiteit, Amster-

1819. dam, The Netherlands, http://www.scm.com.

38 M. Tilset, I. Fjeldahl, J.-R. Hamon, P. Hamon, L. Toupet, 60 S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58,

J.-Y. Saillard, K. Costuas and A. Haynes, J. Am. Chem. Soc.,

2001, 123, 9984.

1200.

61 A. D. Becke, Phys. Rev. A, 1988, 38, 3098.

39 F. Paul and C. Lapinte, Coord. Chem. Rev., 1998, 178–180, 62 J. P. Perdew, Phys. Rev. B: Condens. Matter, 1986, 33, 8822.

431. 63 S. Portmann and H. P. Lüthi, Chimia, 2000, 54, 766.

40 N. N. Greenwood and T. C. Gibb, Mössbauer Spectroscopy, 64 S. I. Gorelsky and A. B. P. Lever, J. Organomet. Chem., 2001,

Chapman and Hall Ltd, London, 1971.

635, 187.

Dalton Trans.

Article Doi

Synthesis and characterisation of halide, separated ion pair, and hydride cyclopentadienyl iron bis(diphenylphosphino)ethane derivatives

DOI: 10.1039/c5dt00704f

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