Ferrocenyl-phosphonium ionic liquids-synthesis, characterisation and electrochemistry

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Ferrocenyl-phosphonium ionic liquids – synthesis,

characterisation and electrochemistry†

Cite this: Dalton Trans., 2014, 43,

3750

Paul Kübler and Jörg Sundermeyer*

New unsymmetrically substituted ferrocenyl-phosphonium ionic liquids (ILs) [FcPR₂R’]NTf₂5a–j are syn-

thesized by two or three step syntheses starting from ferrocene, Fc = (C₅H₅)Fe(C₅H₄); R = Me, ⁿBu, ⁿHex,

Ph; R’ = Me, ⁿPr, ⁿBu, Ph; NTf₂= N(SO₂CF₃)₂. The selective synthesis of alkyl phosphines FcPR₂via a

Friedel–Crafts phosphorylation is highlighted as an alternative for the standard protocol commonly used

for ferrocenyl arylphosphines involving lithiation of FcH followed by phosphorylation. The inﬂuence of the

P-substituents on thermal stability, electrochemical potential, chemical shift, and UV-Vis absorption be-

havior of the ILs is studied. The phosphonium group acts both as an ionic tag and as an electron-with-

drawing substituent directly bound at the Cp-ring position. Therefore the title compounds are attractive

for further studies to use them as tunable redox mediators for (photo)electrochemical devices such as

dye sensitized solar cells (DSSCs) or redox ﬂow batteries.

Received 3rd December 2013,

Accepted 19th December 2013

DOI: 10.1039/c3dt53402b

www.rsc.org/dalton

Introduction

In recent years a number of ferrocene based ionic liquids have

been reported and their electrochemical properties have been

examined (Scheme 1).

First applications for these redox-active compounds include

surface structuring of precious metals⁶like platinum, silver

and gold, electron transfer across the interface between two

phases⁷as well as additives for lithium-ion batteries⁸to

prevent overcharging/discharging. Furthermore, a ferrocene

based supported ionic liquid phase (SILP) catalyst⁹has been

used in a multi-component synthesis. Ionic liquids based

on organosubstituted ferrocenium cations [FcR]X have been

investigated, which however after reduction lose their ionic

character and retention properties in electrolytes.¹⁰Further-

more low-melting heteroleptic sandwich compounds of the

form [(C₅H₄R)Fe(arene)]X came into focus¹¹but they tend to

be not robust enough against light.

Scheme 1 Literature-known ferrocene based ionic liquids (A,¹B,²C,²

D,³E,⁴F⁵).

properties have been studied (e.g. [FcPPh₂Me]I, E_1/2= 1.01 V

(vs. SCE in DCM)¹³). Probably due to the synthetic challenge

the influence of a set of diﬀerent alkyl groups at the phos-

phorus atom on the physical properties has not yet been

investigated.

In the field of ferrocenyl-phosphonium ILs only a few com-

pounds of the form [FcPR₃]X (R = alkyl, aryl; X = halide, BF₄)

are known.¹²These are typically based on quaternized diphe-

nylferrocenylphosphine (2d) which results in melting points

between 175 °C and 222 °C. In rare cases the electrochemical

The synthetic access to diphenylphosphino derivative 2d

includes salt elimination¹⁴from in situ generated monolithio-

ferrocene (FcLi) with Ph₂PCl (1d), the visible-light photolysis¹⁵

of [(C₅H₅)Fe(arene)]PF₆in the presence of Li[C₅H₄PPh₂] or

Friedel–Crafts phosphorylation¹⁶of ferrocene (FcH) with 1d.

In the case of alkyl-substituted ferrocenylphosphines only

salt elimination from in situ generated FcLi with R₂PCl has

been described; however, with decreasing steric bulk of the

Philipps-Universität Marburg, Fachbereich Chemie und Zentrum für

Materialwissenschaften, Hans-Meerwein-Straße, 35043 Marburg, Germany.

E-mail: jsu@staﬀ.uni-marburg.de; Fax: +49 (0)6421 28-25711;

Tel: +49 (0)6421 28-25693

†Electronic supplementary information (ESI) available. CCDC 974963 and

974964. For ESI and crystallographic data in CIF or other electronic format see

DOI: 10.1039/c3dt53402b

t

alkyl group the yield is dropping strongly (R = Bu (45–78%),¹⁷

Cy (44–70%),¹⁸Et (30%),¹⁹Me (23%)²⁰). Another disadvantage

3750 | Dalton Trans., 2014, 43, 3750–3766

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of this synthetic route is the necessary chromatographic separ- cation [ⁿBu₂(Cl)P–PⁿBu₂]⁺II under the prevailing conditions.

ation of the obtained product mixture (FcH, FcPR₂, Fc′(PR₂)₂This behavior has been described in the literature for a

(Fc′ = (C₅H₄)₂Fe)) under an inert-gas atmosphere.

number of R₂PCl and several Lewis acids.²²Nucleophilic

Here we present a selective synthesis of FcPR₂(R = Me, ⁿBu, attack of FcH at these positively charged phosphorus atoms

ⁿHex) via Friedel–Crafts phosphorylation of FcH with R₂PCl. under release of hydrogen chloride detected as a gaseous by-

Related phosphonium-ILs can either be prepared by alkylation product and AlCl₃yields the desired phosphine 2b. This phos-

with alkylhalides (MeI, ⁿPrBr, ⁿBuBr) and subsequent anion phine reacts with in situ generated HCl in the presence of

exchange or by direct alkylation with methyl bis(trifluoro- AlCl₃to [FcP(H)ⁿBu₂]AlCl₄3c which was isolated from the reac-

methanesulfonyl)imide 6.

tion mixture and characterized by NMR spectroscopy as well as

mass spectrometry. The phosphine 2b may also react with an

excess of ⁿBu₂PCl 1b to the phosphinophosphonium cation

[FcⁿBu₂P–PⁿBu₂]⁺, which was independently confirmed by reac-

tion of 2b, 1b and AlCl₃in DCM displaying NMR signals

Results and discussion

Synthesis of dialkylferrocenylphosphines 2a–c

1

δ_P(CD₂Cl₂) = 27.7; −45.3 ppm; J_PP= 300.0 Hz. The cation

[FcⁿBu₂P–PⁿBu₂]⁺is converted to 3c by reaction with in situ

generated HCl/AlCl₃and can be separated from the unreacted

starting material (FcH, ⁿBu₂PCl) by washing with n-pentane.

The cation [FcP(H)ⁿBu₂]⁺is a weak acid (pK_BH+(3a) = 7.51)

The preparation of the dialkylchlorophosphines 1a–c, required

for the Friedel–Crafts phosphorylation, was implemented

either by a literature-known, four-step synthesis²¹or via one-

pot synthesis based on PCl₃. The method presented here pro-

ceeds from a direct alkylation of PCl₃with organolithium com-

pounds RLi (R = ⁿBu, ⁿHex). Slow addition of the pre-cooled

(−78 °C) organolithium compounds is crucial to avoid unde-

sired by-products (RPCl₂, R₃P, phosphinophosphonium

compounds²²).

We found that by variation of the reaction conditions the

Friedel–Crafts phosphorylation of FcH with aromatic Ph₂PCl

1d¹⁶can be also applied for dialkylchlorophosphines R₂PCl

(R = Me, ⁿBu, ⁿHex). Based on ³¹P NMR monitoring of the

conversion of ferrocene with ⁿBu₂PCl 1b and AlCl₃a reaction

pathway is proposed (Scheme 2).

which was determined by NMR titration of 2b with [PhP-

24

(H)ⁿBu₂]NTf₂3b of literature-known pK_BH+

;

thus 3c can be

deprotonated by degassed water yielding phosphine 2b of high

purity.²⁵

In contrast to the selective Friedel–Crafts phosphorylation a

product mixture was obtained during the reaction from in situ

generated FcLi with Me₂PCl 1a.²⁶

Synthesis of ferrocenyl-phosphonium ILs 5a–j

Diﬀerent synthetic routes to phosphonium compounds 5a–j

are presented in Scheme 3 and received products in Table 1.

Two of these strategies are based on the phosphines 2a–d and

diﬀer only in the employed alkylating agents (method A and B).

In method C the phosphonium moiety is inserted through a

photolytic conversion of heteroleptic sandwich compounds of

the form [(C₅H₅)Fe(arene)]NTf₂with cyclopentadienylidene

phosphoranes.

n

In the first step the Lewis acid AlCl₃reacts with Bu₂PCl 1b

yielding a mixture of the complex ⁿBu₂(Cl)P–AlCl₃I and the

tetrachloro-aluminate salt of the phosphinophosphonium

The very nucleophilic alkyl phosphines 2a–c can be quater-

nized with any alkyl halides in high yields. However, the result-

ing phosphonium halides 4a–f exhibit high melting points

and a small electrochemical window. Therefore, via anion-

metathesis with LiNTf₂they are converted into the corres-

ponding NTf₂salts. The main drawback of this two-step syn-

thesis is the anion-metathesis. In the case of incomplete

conversion remaining redox-active halide ions or lithium

halide would contaminate the product leading to an additional

Scheme 2 Proposed reaction mechanism (top); observed ³¹P NMR

spectrum of the reaction of FcH, ⁿBu₂PCl and AlCl₃in CD₂Cl₂after 1 h

(bottom).²³

Scheme 3 Synthetic routes to 5a–j; method A: (1) R’X, MeCN; (2)

LiNTf₂, MeOH–H₂O; method B: MeNTf₂, MeCN; method C: CpPR₂R’

(R = R’ = Ph 8a, R = R’ = ⁿBu 8b), MeCN, hν.

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spontaneously, it was possible to monitor the conversion

at 25 °C and 40 °C by ³¹P NMR spectroscopy in the case of

MeNTf₂(Scheme 4).

Table 1 Compound numbering for [FcPR₂R’]X

FcPR₂

R′

Anion [X]

Nevertheless, all phosphines 2a–d could selectively be

methylated with 6, and pure ionic liquids 5a, 5d, 5g and 5h

were obtained directly. Furthermore it was possible to methy-

late dppf at both phosphorus atoms with 2.0 eq. of 6. However,

due to its lower nucleophilicity and poor solubility of dppf and

its monoalkylated intermediate in MeCN the alkylation took

4 d (78% yield).

An alternative strategy for the preparation of ferrocenyl-

phosphonium ILs is the visible-light photolysis of [(C₅H₅)-

Fe(arene)]NTf₂with cyclopentadienylidene phosphoranes

8a–b. While phenylphosphorane 8a is literature-known,³¹

alkylphosphoranes such as 8b can be obtained from cyclopen-

tadienyl substituted phosphines in straightforward protocols

either by deprotonation of the related phosphonium halides³²

or via reaction of cyclopentadienides with alkyl halides³³

(Scheme 5).

FcPMe₂2a

Me

ⁿPr

ⁿBu

H

Me

ⁿPr

ⁿBu

Me

Ph

I 4a, NTf₂5a

Br 4b, NTf₂5b

Br 4c, NTf₂5c

NTf₂3a, AlCl₄3c

I 4d, NTf₂5d

Br 4e, NTf₂5e

Br 4f, NTf₂5f

NTf₂5g

FcPⁿBu₂2b

FcPⁿHex₂2c

FcPPh₂2d

NTf₂5h

NTf₂5i

NTf₂5j

Fc′(PPh₂)₂

Me

The self-evident quaternization of dibutylcyclopentadienyl

phosphine 9 with 1-bromobutane turned out to be unselective.

An observed side reaction proven by ESI-HRMS is the dimeriza-

tion by the Diels–Alder addition of the two dienes.³⁴However,

reaction of potassium dibutylphosphinocyclopentadienide 10

with 1-bromobutane was directly leading to the new phosphor-

ane 8b (Scheme 5). Finally a straightforward one-pot synthesis

based on sodium cyclopentadienide gave 8b in 78% yield

(Scheme 5, bottom). 8b will turn out to be a very nice synthon

for the preparation of zwitterionic and soluble metal com-

plexes in general.

Scheme 4 Synthetic approach for MeNTf₂(top); methylation of

FcPⁿBu₂2b with MeNTf₂6 in CDCl₃at various temperatures. The reac-

tion progress was monitored by ³¹P NMR spectroscopy (bottom).

The photolysis of [(C₅H₅)Fe(arene)]PF₆with substituted

cyclopentadienide salts is literature-known and delivers in

high yield functionalized ferrocenes.¹⁵Here we present the

implementation of this promising method on the use of cyclo-

pentadienylidene phosphoranes. Visible light photolysis

(Osram Ultra Vitalux 300W) of [(C₅H₅)Fe(arene)]NTf₂with 8a

and 8b in MeCN proceeds readily to give the expected ferro-

cenyl-phosphonium ILs in quantitative yields. In this way, 5i is

available, which is not accessible via quaternization of 2d

(Scheme 6).

expenditure in purifying the redox-active IL up to electrochemi-

cal grade. Furthermore, the resulting product has to be dried

under high-vacuum for an extended period of time in order to

remove traces of water.

For these reasons the strategy was varied in order to obtain

the desired IL by direct alkylation with MeNTf₂6 in one step. 6

is literature-known, but so far only its application as an alkylat-

ing agent has been described.²⁷To the best of our knowledge,

no synthetic procedure for 6 is given in the literature; there-

fore, we present two possible syntheses (Scheme 4). Both are

based on a salt elimination reaction of AgNTf₂with MeI. In

the first case AgNTf₂is prepared by a literature-known²⁸syn-

thesis of HNTf₂with Ag₂O, subsequently isolated and further

implemented. An additional possibility is the reaction of

LiNTf₂with AgNO₃in MeCN, forming the room temperature

ionic liquid (RTIL) [Ag(MeCN)₄]₂[Ag(NTf₂)₃].²⁹From this com-

pound MeNTf₂6 can be prepared by reaction with MeI fol-

lowed by removal of surplus MeCN by distillation.

Alternatively, MeCN can be removed under vacuum (120 °C/

0.02 mbar) to form solvent-free AgNTf₂prior reaction with

MeI.³⁰

All phosphonium compounds 4a–g and 5a–j are soluble in

polar organic solvents (DCM, THF, MeCN, MeOH, etc.) but

A reactivity study showed that MeNTf₂is not such a power-

ful methylating agent as MeI or Me₂SO₄, respectively: while

reaction of 2b with MeI or Me₂SO₄in CDCl₃at 25 °C proceeds

Scheme 5 Step by step reaction to 8b; (i) ⁿBu₂PCl, n-pentane, 0 °C; (ii)

benzyl potassium, Et₂O, 0 °C; (iii) ⁿBuBr, Et₂O, r.t.; (iv) HCl_(g), CDCl₃

(top); one-pot synthesis of 8b (bottom).

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Scheme 6 Photolysis of [(C₅H₅)Fe(arene)]NTf₂7a–b with cyclopenta-

dienylidene phosphoranes 8a–b. R = Ph, ⁿBu, R’’ = H, Me.

insoluble in water and nonpolar organic solvents like toluene,

Et₂O and hydrocarbons.³⁵While the halides 4 were obtained

as amorphous solids, the ionic liquids 5 reveal either a honey-

like consistency (5b, 5e) or are isolated as a wax (5a, 5c, 5d).

The only exception is 5f which was obtained as a solid. In

addition, all NTf₂salts are insensitive to oxygen and moisture

in the air, which was determined by NMR spectroscopy over a

period of five months.

Fig. 1 ³¹P NMR spectra of 2a–d (left); ¹H NMR changes in chemical

shift for α, β and C₅H₅positions of 2b and 5d, respectively (right).

atoms and protons of the Cp-rings. This might be explained by

the increasing electron-donating character with increasing

length of the alkyl chain. In comparison with 2d there is a

stronger downfield shift due to the significantly stronger elec-

tron-donating property of the phenyl groups (δ_P(2a) ≪ δ_P(2b) <

δ_P(2c) ≪ δ_P(2d); Fig. 1, left side).

Melting points and glass-transition temperatures

The melting points of most of the halides are in the range

By alkylation of the phosphorus atoms the electron-donat-

ing phosphine moieties are converted into electron-withdraw-

ing phosphonium groups, which can be related to the

electrochemical potential and to strong downfield shifts in the

³¹P NMR (Δδ_P(2a vs. 5b) = 83.9 ppm; Δδ_P(2b vs. 5e) =

68.0 ppm). The same deshielding eﬀect can be observed in the

corresponding ¹H NMR spectrum (Fig. 1, right side). This is in

accordance with former studies on substituent eﬀects on

chemical shifts in monosubstituted ferrocenes.⁴⁰

UV-Vis spectroscopy. If these redox-active electrolytes are

thought to be used as redox mediators in dye-sensitised solar

cells, they should not have strong absorption bands in the

visible light. As expected the absorption and extinction coeﬃ-

cient of each phosphonium compound is in the range of ferro-

cene (λ_FcH= 225 nm (ε = 5250 M⁻¹cm⁻¹) in EtOH).⁴¹In this

from 106.7 °C (4e) to 155.0 °C (4c). Exceptions are 4a (T_m

=

276.9 °C) and 4d (glassy undercooled melt at r.t.). Interest-

ingly, the trend in melting points for methyl derivative 4a

(276.9 °C) ≫ n-butyl derivative 4c (155.0 °C) > n-propyl deriva-

tive 4b (125.6 °C) is also found in the corresponding phenyl

phosphonium halides [PhPMe₂R]X (R = Me, T_m: 238.9 °C;³⁶

R = ⁿPr, T_m: 118 °C;³⁷R = ⁿBu, T_m: 132 °C³⁸).

The conversion of the halide salts 4 into the NTf₂salts 5

results in a decrease of the melting points. However an exact

trend cannot be described since most of the compounds were

obtained as glassy undercooled melts and no melting point

could be determined by DSC.

The thermal stability of phosphonium compounds is gener-

ally very high and can be increased by substitution of the

halides by weakly nucleophilic NTf₂.³⁹This trend can also be

observed for the trisalkylferrocenyl-phosphonium compounds

discussed here. For the halides 4a–f all decomposition temp-

eratures T_dare below 300 °C and for the NTf₂salts 5a–f signifi-

cantly higher than 300 °C (Table 2).

regard the alkyl-substituted Fc-phosphonium IL 5d, λ_5d

=

259 nm (ε = 4481 M⁻¹cm⁻¹), has a much lower extinction

coeﬃcient than the phenyl-substituted ferrocenyl-phosphonium

ILs 5h and 5i: λ_5h= 261 nm (ε = 6281 M⁻¹cm⁻¹); λ_5i= 261 nm

(ε = 6499 M⁻¹cm⁻¹). In the visible region all three compounds

show very low extinction coeﬃcients (Table 3). In addition to

the main absorption around 260 nm and the minor absorption

in the visible light region, phenyl phosphonium salt 5i shows a

third absorption maximum at λ_5i= 308 nm with an extinction

Spectroscopic properties

NMR spectroscopy. The ³¹P and ¹H NMR spectra of the

phosphines 2a–c show a small influence of the length of the

alkyl chain on the chemical shift of the respective phosphorus

coeﬃcient of ε = 1628 M⁻¹cm⁻¹

.

Comparing these results with the absorption properties of

[Me₄N][I₃], it can be seen that ferrocenyl-phosphonium ionic

liquids have an up to ten times lower extinction coeﬃcient in

the near UV region and over a hundred times lower in the visible

Table 2 Phase transition and thermal decomposition temperatures

Compd

T_m^a/°C

T_d^a/°C

Compd

T_m(T_g)^c/°C

T_d^d/°C

−

light region than the I⁻/I₃redox couple often used in DSSCs⁴²

4a

4b

4c

4d

4e

4f

276.9

125.6

155.0

—

106.7

129.3

299.7

200.4

217.2

—

245.2

268.7

5a

5b

5c

5d

5e

5f

—^b(−30.6)

40.3 (−41.7)

—^b(−42.0)

—^b(−38.6)

43.7 (−41.5)

72.4 (—^e)

353.4

356.1

361.4

359.1

343.7

329.8

(Fig. 2). They do not compete that much for light absorbance.

Cyclic voltammetry. It is well-known that diﬀerent substitu-

ents at the ferrocene backbone result in an alteration of its

electrochemical potential.⁴³The potential gets more negative

by introducing electron-donating groups and more positive by

electron withdrawing groups.⁴⁴The electron-withdrawing char-

acter of diﬀerent phosphonium groups leads to a more or less

b

^aOptical melting point determination. ^bNot measurable due to glassy

undercooled melt. ^cMeasured by diﬀerential scanning calorimetry.

^dT_dwas recorded as the 5% weight loss temperature. ^eNot measured.

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Table 3 Selected absorption characteristics

Compd

λ_max/nm

ε/M⁻¹cm⁻¹

λ_max/nm

ε/M⁻¹cm⁻¹

c

5d^a

259

261

292

4481

6281

6499

450

447

362

5h^a

241

230

25 000

5i^a

[Me₄N][I₃]^b

45 800

^aMeasured in DCM. ^bMeasured in 1,2-dichloroethane (see ref. 42).

^cNot determined.

Fig. 3 CV scans for some ferrocenyl-phosphonium compounds in

comparison with ferrocene; approx. 5 mM in [EMIM]NTf₂at 50 mV s⁻¹

vs. Ag/AgNTf₂as a reference electrode; 11: [FcCHMePBu₃]NTf₂.

5e has a reversible stability from −2.45 V to 2.10 V, which cor-

responds to a remarkable chemical window of 4.55 V. The

chemical window of 11 (−2.45 V to 1.81 V) is a little bit smaller

due to the predetermined P–C bond cleavage at the alkylene

spacer forming the privileged cation [FcCHMe]⁺which was

also proven by ESI-HRMS.

Crystal structures. Single-crystal analyses could be obtained

for 4a and 5f either from a saturated chloroform solution or by

slow diﬀusion of Et₂O into an acetonitrile solution.

Crystallographic data are listed in Table 6, selected bond

distances and angles are shown in Table 5, and for compari-

Fig. 2 UV-Vis spectra obtained from 0.2 mM solution of 5d, 5h and 5i

in DCM; inset shows spectral range of the visible spectrum.

positive equilibrium potential vs. FcH for all the ferrocenyl- son, the corresponding data for two closely related salts,

[FcPPh₂(CH₂Ph)]Cl¹²VII and [FcPPh₂(CH₂C₆H₄OMe)]BF₄

48

phosphonium ILs 5a–j.

As shown in Table 4 and Fig. 3 the potential shift is higher VIII, are also included. Full details are available via ESI.†

in case two phenylphosphonium groups are attached to ferro-

5g crystallizes monoclinic (P2₁/c), while crystals of 4a are

ˉ

cene (5j), while it is lower with one alkylphosphonium group cubic (Pa3). The packing of 4a shows weak C–H⋯I contacts

and lowest if an alkyl spacer is inserted between the Cp moiety with a minimum distance of 311.4 pm, which is lower than

and the phosphonium group, e.g. in 11. In this respect the the sum of the van der Waals radii of 335 pm.⁴⁶The P⋯I dis-

potential can be tuned.

tances vary from 480.0 pm to 800.0 pm. Similar to other qua-

CV measurements also allow one to control the purity of ternary phosphonium salts, there is no direct P⋯I anion

the products, e.g. the CV of 5j shows very small redox waves cation interaction.^36,47

next to the reversible redox process at E_1/2(5j) = 983 mV

Phosphorus–alkyl bond distances for both compounds are

attributable to a trace contamination of monoalkylated dppf, approximately constant (4a: 177.2 0.5 pm; 5f: 179.7 0.5 pm)

which independently was detected by ESI-HRMS. Due to the and a bit shorter than the average value of 184 pm reported

presence of the two lone pairs of electrons an electrochemical for the P–C(sp³) bond.⁴⁹The same situation is found for the

dimerization during the CV measurement has been discussed P–C_Cpbond distances (176.4 and 177.2 pm for 4a and 5f,

for dppf.⁴⁵Similar reactions can be assumed for the mono- respectively).

alkylated dppf.

These are larger in comparison with cyclopentadienylidene

The electrochemical stability of the alkyl-substituted com- phosphoranes (C₅H₄PPh₂Me:³²172.7 pm; C₅H₄PPh₃:⁵⁰

pounds was confirmed by a measurement of neat 5e at 60 °C. 171.8 pm; Cp™PPh₂Me:³³171.4 pm). In η⁵-coordinated

Table 4 Cyclic voltammetry of ferrocenyl-phosphonium compounds^a

Compound

5a

5b

5c

5d

5e

5f

5g

5h

5i

5j

11

E [mV] vs. Fc/Fc⁺

458

463

454

453

454

453

504

523

983

164

^aApprox. 5 mM in [EMIM]NTf₂at 50 mV s⁻¹vs. Ag/AgNTf₂as a reference electrode.

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Table 5 Selected bond distances (pm) and angles (°) for 4a, 5f and

related compounds [FcPPh₂(CH₂Ph)]Cl (VII) and [FcPPh₂(CH₂C₆H₄OMe)]-

BF₄(VIII)

4a

5f

VII^a

VIII^a

C

_Cp–P

176.4(6)

177.0(6)

176.7(4)

177.7(6)

144.3(8)

142.6(8)

142.3(9)

142.2(9)

141.6(9)

142.6(9)

143.0(9)

141.1(9)

139.1(9)

142.5(9)

163.7(1)

165.5(1)

177.2(3)

180.1(4)

179.2(3)

180.2(3)

142.6(5)

141.1(6)

141.0(6)

141.6(6)

143.9(5)

141.1(6)

141.4(6)

140.2(6)

139.8(6)

142.5(6)

164.3(1)

164.9(1)

176.7(5)

181.9(5)

177.9(4)

181.3(4)

C_alkyl–P

C_Cp–C_Cp

143.2(3)

142.6(4)

140.6(3)

141.8(4)

145.3(4)

140.1(3)

141.5(4)

137.4(3)

138.0(3)

138.4(4)

164.5(4)

165.9(4)

142.8(6)

141.8(6)

141.6(8)

140.9(6)

142.3(7)

137.6(8)

137.3(8)

137.8(11)

139.6(8)

138.1(9)

164.5(2)

166.3(2)

C_Cp′–C_Cp′

Fig. 5 Molecular structure of 5f. Displacement ellipsoids are shown for

50% probability, hydrogen atoms are omitted for clarity.

C

_Cp,i–Fe

_Cp′,i–Fe

C

_Cp,i–Fe–C_Cp′,i

_Cp,i–C_Cp–P

_Cp–P–C_alkyl

174.2(6)

176.0(5)

110.3(3)

110.7(3)

109.1(3)

107.2(3)

108.2(3)

111.3(3)

174.2(3)

172.9(2)

106.7(2)

111.2(1)

111.5(1)

109.1(2)

107.3(2)

110.9(2)

174.9(2)

175.2(1)

111.6(1)

176.3(1)

175.5(3)

108.0(2)

4a and 5.5° for 5f, which is slightly higher than for the known

compounds (VII: 4.7°; VIII: 3.6°). Both phosphorus atoms are

displaced 13.3 pm and 21.0 pm (for 4a and 5f, respectively)

out of the plane defined by the Cp rings.

For the literature-known compounds VII (deviation: 2.3°)

and VIII (deviation: 4.0°) a nearly perfect eclipsed structure for

the arrangement of the Cp rings is found. For the new com-

pounds the same trend is observed, but the deviation is higher

(9.4°) for 4a and smaller (0.1°) for 5f.

C_alkyl–P–C_alkyl

^aVII: see ref. 12, VIII: see ref. 48.

Conclusions

A new series of unsymmetrically substituted trisalkylferrocenyl-

phosphonium ILs were prepared by various synthetic strat-

egies using cheap starting materials. For this purpose a

selective Friedel–Crafts phosphorylation in the preparation of

dialkylferrocenylphosphines has been established as a more

selective alternative to FcH lithiation and subsequent reaction

with R₂PCl. Furthermore, the purity of the desired phos-

phonium ILs has been increased and the number of synthetic

steps could be reduced by the use of MeNTf₂as an alkylating

agent. A simple synthesis for MeNTf₂based on commercially

available LiNTf₂has been described. Another synthon useful

for many further studies, the new tributyl-cyclopentadienyli-

dene phosphorane 8b, has been obtained in a simple one-pot

synthesis.

The influence of the substituents at the phosphorus atom

on the thermal stability, the electrochemical potential, the

melting points as well as the absorption behavior has been

investigated. Generally all phosphonio-substituted ferrocenes

showed a shift to more positive potentials, as phosphonium

groups are electron-withdrawing substituents. This tunable

redox potential and low absorption coeﬃcients make these

new compounds attractive for the use as redox mediators in

dye sensitized solar cells (DSSCs). Due to the fact that the

overall eﬃciency of the cell is proportional to the open circuit

Fig. 4 Molecular structure of 4a. Displacement ellipsoids are shown for

50% probability, hydrogen atoms are omitted for clarity; the four iodide

ions present in the unit cell are symmetry independent, and therefore

cannot be distinguished. For clarity, only one iodide ion is displayed.

cyclopentadienylidene phosphoranes much less negative

charge is delocalized into empty orbitals of the phosphonio

group than in non-coordinated ones. As a consequence no sig-

nificant P–C_Cpbond shortening and no C_Cp–C_Cpbond length

alteration (4a: 142.6 1 pm; 5f: 142.0 1 pm) is observed in

the η⁵-coordinated cyclopentadienyl units (Fig. 4 and 5).

Interestingly, despite steric aspects the distances of the iron

atom to the centroid of the phosphonio-substituted Cp rings

(4a: 163.7 pm; 5f: 164.3 pm) are shorter compared to the

unsubstituted Cp rings (4a: 165.5 pm; 5f: 164.9 pm). The di-

hedral angle between the planes of the two Cp rings is 5.3° for

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Dalton Transactions

voltage⁵¹(V_OC), a lowering of the potential of the redox

IR spectra were recorded on a Bruker Alpha FT-IR spectro-

meter using neat samples with an ATR measurement setup

(diamond cell) at room temperature.

mediator leads to an increase of V_OC

.

Elemental analysis was done on an Elementar vario MICRO

cube. Values are given in weight percent. In the case of the pre-

pared phosphines elemental analysis was not possible due to

high sensitivity; thus, the purity of the compounds is demon-

strated by NMR spectroscopy and high resolution EI spec-

trometry (see ESI†).

UV-Vis spectra were taken on an Avantes AvaSpec-2048 spec-

trophotometer at room temperature. All measurements were

carried out in a glovebox.

Experimental

General remarks

Synthesis and handling of air- and moisture-sensitive sub-

stances was carried out using standard Schlenk- and glovebox-

techniques. Solvents were dried using standard procedures⁵²

and stored over an Al₂O₃/molecular sieve 3 Å/R3-11G catalyst

(BASF).

Melting points (T_mor T_g) were measured by diﬀerential

scanning calorimetry (DSC) using a Mettler Toledo DSC 821e

calorimeter with a heating rate of 10 °C min⁻¹or via optical

melting point determination using a Büchi melting point

B-540 with a heating rate of 10 °C min⁻¹. Thermogravimetric

analysis (TGA) was performed using a Mettler Toledo TGA/

SDTA 851e apparatus between 25 and 800 °C; the heating rate

The following starting materials were prepared according to

literature procedures: dimethylchlorophosphine (1a),²¹diphe-

nylferrocenylphosphine (2d),¹⁶1,1′-bis(diphenylphosphino)-

ferrocene (dppf),¹⁴silver bis(trifluoromethanesulfonyl)imide

(AgNTf₂),²⁸bis(trifluoromethanesulfonyl)amine (HNTf₂),²⁸

sodium cyclopentadienide (NaCp),⁵³triphenylcyclopentadieny-

lidene phosphorane (CpPPh₃),⁵⁴[(C₅H₅)Fe(η⁶-toluene)]NTf₂,⁵⁵

benzyl potassium (BzK),⁵⁶dibutylphenylphosphine,⁵⁷1-hydro-

xyethylferrocene (FcCHMeOH),⁵⁸tributylphosphine hydro-

bromide.⁵⁹AlCl₃(98%, Merck) was sublimated, 1-bromobutane

(99%, Acros Organics) was dried over calcium hydride and puri-

fied by vacuum distillation before use. [EMIM]NTf₂(electro-

chemical grade, IoLiTec) was degassed and dried in a vacuum

at 60 °C/3 × 10⁻⁵mbar. Other starting materials were obtained

from commercial sources (Sigma-Aldrich, Merck, Acros Organ-

ics) and used as received. All reactions involving silver salts

were carried out under exclusion of light.

was 10 °C min⁻¹

.

Cyclic voltammetry (CV) experiments were performed using

a RHD Instruments Microcell HC and an Ivium Technologies

Iviumstat in a glovebox (N₂-atmosphere, O₂and water content

below 2 ppm and 1 ppm respectively). Experiments were per-

formed at ambient temperature (25.0 °C) with an analyte con-

centration of 4.5–7.5 mM in [EMIM]NTf₂as the supporting

electrolyte unless otherwise specified. A three-electrode setup

was used, where a ∅ = 0.25 mm Pt-wire was used as a working

electrode and a 70 µl platinum crucible acted as a sample con-

tainer as well as a counter electrode. Both were polished with

Kemet diamond paste 0.25 µm direct prior to measurements.

The reference electrode was 100 mM Ag/AgNTf₂in [EMIM]-

NTf₂.⁶⁰The reference electrode potential was determined with

a ferrocene solution (6.22 mM in [EMIM]NTf₂) prior to and

after measurement. Data were collected at 50 mV s⁻¹unless

otherwise specified.

NMR spectra were recorded at 300 K on a Bruker AC 300,

DRX 400 or DRX 500 using CD₃CN, CDCl₃, CD₂Cl₂, C₆D₆or

THF-d₈as solvent. Chemical shifts are given with respect to

tetramethylsilane (¹H, ¹³C), phosphoric acid (³¹P) and CFCl₃

1

(¹⁹F), respectively. Calibration of H and ¹³C NMR spectra was

accomplished with the solvent signals; ³¹P and ¹⁹F NMR

spectra were calibrated externally unless otherwise specified.

The applied numbering scheme is shown beneath. If no

assignment was possible for the resonances of positions α and

β, they are mentioned with H_Cpor C_Cp, respectively (Scheme 7).

ESI and APCI mass spectra were recorded on a Thermo

Fisher Scientific LTQ FT Ultra using methanol or dichloro-

methane as solvents. EI mass spectra were recorded on a

Finnigan MAT95. The m/z values are given together with their Chemical formula

Table 6 Crystallographic data

4a

5f

C₁₃H₁₈FeIP

388.01

C₂₄H₃₆F₆FeNO₄PS₂

667.11

M/g mol⁻¹

relative intensities. Isotopic patterns were in all cases consist-

ent with natural abundance.

Crystal system

Space group

Cubic

Pa3

Monoclinic

P2₁/c

ˉ

a/Å

b/Å

c/Å

α/°

β/°

γ /°

V/Å³

T/K

Z

20.3608(13)

90

8440.8(9)

100(2)

24

10.6934(3)

14.4249(6)

20.1051(7)

90

97.508(3)

90

3074.65(19)

100(2)

4

No. reflections measured

7968

23 096

No. independent reflections

R_int

Final R₁values (I > 2σ(I))

Final wR(F²) values (all data)

2978

6538

0.1064

0.0568

0.1411

0.0941

0.0296

0.0417

Scheme 7 Example of numbering of compounds.

3756 | Dalton Trans., 2014, 43, 3750–3766

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Dalton Transactions

Paper

Crystallographic data are provided in Table 6 and full

Preparation of dihexylchlorophosphine (1c) (ⁿHex₂PCl).

details are available in ESI.† X-Ray data collection was 17.42 g phosphorus trichloride (0.13 mol, 1.0 eq.) was dis-

performed via a STOE IPDS I or IPDS II area detector using solved in 500 mL n-pentane and cooled to −78 °C. A cooled

Mo-K_α-radiation (λ = 71.073 pm). STOE IPDS software⁶¹was (−78 °C) solution of 47.4 mL n-hexyllithium (2.68 M in n-

used for integration and data reduction; structure solution and hexane, 0.13 mol, 1.0 eq.) dissolved in 100 mL n-pentane was

refinement was done with the WinGX program suite⁶²using added dropwise over a period of 80 min. The resulting suspen-

SIR92⁶³and SHELX-97.⁶⁴

sion was stirred for 2 h at −78 °C and a second equivalent

n-hexyllithium (47.4 mL, 0.13 mol, 1.0 eq.) dissolved in

100 mL n-pentane and cooled to −78 °C was slowly added over

Synthesis of compounds

Preparation of dibutylchlorophosphine (1b) (ⁿBu₂PCl). a period of 3 h. The reaction mixture was stirred over 15 h

Method A: 5.00 g Mg-powder (0.21 mol, 3.3 eq.) was activated whereby the solution warmed up to −64 °C. A reaction control

by heating in a vacuum and afterwards suspended in 60 mL via ³¹P NMR spectroscopy presented an 87% conversion for

Et₂O. To this suspension 30.14 g 1-bromobutane (0.22 mol, which reason additional n-hexyllithium (6.16 mL, 16.51 mmol,

3.5 eq.) in 30 mL Et₂O was slowly added until the solvent 0.13 eq.) was added over 15 min. After stirring for 1 h

started boiling. The mixture was heated to reflux for 2.5 h. At n-pentane was removed at 60 °C/ambient pressure and the

0 °C 10.75 g thiophosphoryl chloride (63.45 mmol, 1.0 eq.) in resulting residue was recondensed at 130 °C/0.02 mbar to

15 mL Et₂O was added dropwise and after complete addition obtain the crude product (21.97 g, 92.79 mmol, 73%) as a

heated to reflux for 1 h. The reaction mixture was brought to slightly yellow liquid. To receive 1c (16.90 g, 71.39 mmol, 56%)

ambient temperature and poured slowly into 150 mL ice water. distillation at 150 °C/0.1 mbar has been implemented. ³¹P{¹H}

1

The aqueous phase was acidified with hydrochloric acid and NMR (121.5 MHz, C₆D₆) δ = 113.6 ppm; H NMR (300.1 MHz,

3

extracted five times with 50 mL Et₂O. The combined ether C₆D₆) δ = 0.86 (t, 6H, J_HH= 7.0 Hz, P(CH₂)₅Me), 1.09–1.30 (m,

phases were dried over MgSO₄, filtered and after removing the 12H, P(CH₂)₄CH₂Me, P(CH₂)₃CH₂Et, P(CH₂)₂CH₂ⁿPr), 1.43–1.53

solvent in a vacuum 11.02 g tetrabutyldiphosphine disulfide (m, 4H, PCH₂CH₂ⁿBu), 1.55–1.65 (m, 4H, PCH₂ⁿPent) ppm; ¹³

C

(31.09 mmol) was received as a slightly yellow solid. The {¹H} NMR (75.5 MHz, C₆D₆) δ = 14.2 (s, P(CH₂)₅Me), 22.9 (s,

yellow solid was redissolved in 20 mL benzene. 8.39 g sulfuryl P(CH₂)₄CH₂Me), 24.9 (d, ²J_CP= 13.1 Hz, PCH₂CH₂ⁿBu), 30.8 (d,

chloride (62.18 mmol, 0.98 eq.) in 10 mL benzene was slowly ³J_CP= 10.5 Hz, P(CH₂)₂CH₂ⁿPr), 31.8 (s, P(CH₂)₃CH₂Et), 35.5 (d,

added at 0 °C. After addition the reaction mixture was stirred ¹J_CP= 29.8 Hz, PCH₂ⁿPent) ppm.

for 12 h at ambient temperature and the solvent was removed

by distillation under ambient pressure. The residue was dis-

General procedure for the preparation of 2

tilled at 145 °C/1 mbar to get 10.32 g dibutylthiophosphinyl Ferrocene (1.0 eq.) and AlCl₃(1.1–1.2 eq.) were suspended in a

chloride (48.50 mmol) as a brown liquid. 10.32 g dibutylthio- suﬃcient amount of n-hexane (5 mL mmol⁻¹ferrocene). The

phosphinyl chloride (48.50 mmol, 0.76 eq.) and 15.27 g PPh₃appropriate dialkylchlorophosphine 1 (1.0–1.2 eq.) was added

(58.2 mmol, 0.92 eq.) were heated for 1 d at 140 °C and sub- via a syringe and the reaction mixture was heated to reflux for

sequent distillation at 150 °C/1 mbar gave 8.06

g 1b 12 h whereupon a dark green oil was formed. The oil was

(44.62 mmol, 70%) as a colorless liquid. Method B: 13.65 g washed with n-hexane several times until unreacted starting

phosphorus trichloride (99.40 mmol, 1.0 eq.) was dissolved in materials had been separated. The oil was suspended in 20 mL

500 mL n-pentane and cooled to −78 °C. A cooled (−78 °C) n-pentane and 20 mL degassed H₂O was added. After vigorous

solution of 63.7 mL n-butyllithium (1.60 M in n-hexane, stirring the orange discolored organic phase was separated

99.40 mmol, 1.0 eq.) dissolved in 100 mL n-pentane was added and the aqueous solution was extracted with n-pentane until

dropwise over a period of 105 min. The resulting suspension no coloration could be obtained. The solvent of the combined

was stirred for 1 h at −78 °C and a second equivalent n-butyl- organic phases was removed in a vacuum yielding the desired

lithium (63.7 mL, 99.40 mmol, 1.0 eq.) dissolved in 100 mL phosphine as a red oil.

n-pentane and cooled to −78 °C was slowly added over a

Dimethylferrocenylphosphine (2a) FcPMe₂. Prepared from

period of 105 min. The reaction mixture was stirred over 24 h ferrocene (1.12 g, 6.03 mmol, 1.0 eq.), AlCl₃(965 mg,

at −55 °C. The suspension was filtered at −30 °C over Celite® 7.24 mmol, 1.2 eq.) and 1a (2 M in toluene, 3.0 mL,

and washed two times with 60 mL n-pentane. The n-pentane 6.03 mmol, 1.0 eq.); 705 mg (2.87 mmol, 48%), red oil. The

was removed by distillation under ambient pressure yielding a observed analytical results were in accordance with previously

yellow suspension. The crude product was distilled at 54 °C/ published data.²⁰

0.02 mbar to obtain 7.70 g 1b (42.60 mmol, 43%). ³¹P{¹H}

Dibutylferrocenylphosphine (2b) FcPBu₂. Prepared from

1

NMR (121.5 MHz, C₆D₆) δ = 112.9 ppm; H NMR (300.1 MHz, ferrocene (1.04 g, 5.60 mmol, 1.0 eq.), AlCl₃(820 mg,

3

C₆D₆) δ = 0.79 (t, 6H, J_HH= 7.3 Hz, P(CH₂)₃Me), 1.17–1.31 (m, 6.15 mmol, 1.1 eq.) and 1b (1.21 g, 6.72 mmol, 1.2 eq.); 1.63 g

4H, P(CH₂)₂CH₂Me), 1.36–1.50 (m, 4H, PCH₂CH₂Et), 1.51–1.72 (4.93 mmol, 88%), red oil. ³¹P{¹H} NMR (121.5 MHz, CDCl₃):

(m, 4H, PCH₂ⁿPr) ppm; ¹³C{¹H} NMR (75.5 MHz, C₆D₆) δ = δ = −35.9 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.93 (t, ³J_HH

=

3

13.9 (s, P(CH₂)₃Me), 24.2 (d, J_CP= 10.8 Hz, P(CH₂)₂CH₂Me), 6.9 Hz, 6H, P(CH₂)₃Me), 1.39–1.46 (m, 8H, P(CH₂)₂CH₂Me,

2

1

27.0 (d, J_CP= 13.0 Hz, PCH₂CH₂Et), 35.1 (d, J_CP= 29.7 Hz, PCH₂CH₂Et), 1.59–1.64 (m, 4H, PCH₂ⁿPr), 4.18 (s, 5H, H_Cp′),

3/4

PCH₂ⁿPr) ppm.

4.22 (q,

J

HH

= 1.8 Hz, 2H, H_Cp), 4.30 (t,

J

HH

= 1.8 Hz, 2H,

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Dalton Transactions

H_Cp) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = 13.8 (s, 52.9 (d, overlain by CD₂Cl₂-signal, C_Cp,ipso), 71.1 (s, C_Cp′), 72.6

1

2/3

2

3

P(CH₂)₃Me), 24.4 (d, J_CP= 11.8 Hz, C-4a), 28.3 (d,

J

=

(d, J_CP= 13.2 Hz, C_α), 74.9 (d, J_CP= 10.6 Hz, C_β) ppm,

CP

2/3

9.8 Hz, P(CH₂)₂CH₂Me/PCH₂CH₂Et), 28.5 (d,

P(CH₂)₂CH₂Me/PCH₂CH₂Et), 68.8 (s, C_Cp′), 69.7 (d,

3.4 Hz, C_Cp), 71.1 (d,

J

= 14.4 Hz, CF₃-resonance has not been obtained; ¹⁹F NMR (282.4 MHz,

CP

2/3

J

=

CD₂Cl₂): δ = −79.6 ppm. MS (APCI+, DCM) m/z (%) = 331.1271

CP

2/3

1

J

= 13.0 Hz, C_Cp), 79.0 (d, J_CP

CP

(100, [M − NTf₂]⁺requires 331.1272); MS (APCI−, DCM) m/z

12.2 Hz, C_Cp,ipso) ppm. MS (EI+) m/z = 330.1202 (C₁₈H₂₇FeP (%) = 279.9178 (100, [NTf₂]⁻requires 279.9178). IR (neat): ν =

requires 330.1200). IR (neat): ν = 3094 (w), 2954 (m), 2926 (s), 3108 (w), 2964 (m), 2936 (m), 2876 (m), 1466 (m), 1440 (m),

2870 (m), 2856 (m), 1463 (m), 1412 (m), 1377 (m), 1261 (w), 1416 (s), 1329 (s), 1225 (m), 1178 (vs), 1132 (s), 1051 (s),

1193 (w), 1159 (m), 1106 (m), 1091 (m), 1024 (m), 1001 (m), 935 (m), 875 (m), 829 (m), 788 (m), 762 (m), 738 (m), 653 (m),

967 (m), 887 (m), 816 (s), 718 (m), 641 (w), 626 (w), 485 (s), 599 (s), 569 (s), 508 (s), 462 (m) cm⁻¹

454 (m), 436 (m) cm⁻¹

Dibutylphenylphosphonium bis(trifluoromethanesulfonyl)-

.

Dihexylferrocenylphosphine (2c) FcPHex₂. Prepared from imide (3b). Prepared from dibutylphenylphosphine (765 mg,

ferrocene (939 mg, 5.05 mmol, 1.0 eq.), AlCl₃(740 mg, 3.44 mmol, 1.1 eq.) and bis(trifluoromethanesulfonyl)amine

5.55 mmol, 1.1 eq.) and 1c (1.43 g, 6.06 mmol, 1.2 eq.); 1.31 g (879 mg, 3.13 mmol, 1.0 eq.); 1.49 g (2.96 mmol, 95%) color-

(3.38 mmol, 67%), red oil. ³¹P{¹H} NMR (121.5 MHz, C₆D₆): δ = less oil. Anal. calc. for C₁₆H₂₄F₆NO₄PS₂(503.46 g mol⁻¹) C

3

−35.5 ppm; ¹H NMR (300.1 MHz, C₆D₆): δ = 0.88 (t, J_HH

=

38.17, H 4.80, N 2.78%; found C 38.28, H 4.66, N 2.77%. ³¹P

1

6.9 Hz, 6H, P(CH₂)₅Me), 1.19–1.31 (m, 8H, P(CH₂)₄CH₂Me, NMR (121.5 MHz, CDCl₃): δ = 14.2 (dm, J_PH= 490.2 Hz) ppm;

P(CH₂)₃CH₂Et), 1.34–1.45 (m, 4H, PCH₂CH₂ⁿBu), 1.48–1.62 (m, ¹H NMR (300.1 MHz, CDCl₃): δ = 0.87 (t, J_HH= 7.1 Hz, 6H,

3

4H, P(CH₂)₂CH₂ⁿPr), 1.63–1.72 (m, 4H, PCH₂ⁿPent), 4.10 (s, P(CH₂)₃Me), 1.37–1.64 (m, 8H, P(CH₂)₂CH₂Me, PCH₂CH₂Et),

1

5H, H_Cp′), 4.10–4.11 (m, 2H, H_β), 4.19–4.21 (m, 2H, H_α) ppm; 2.43–2.57 (m, 4H, PCH₂ⁿPr), 6.90 (dquint, J_PH= 489.7 Hz,

¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = 14.3 (s, P(CH₂)₅Me), 23.0 ⁴J_HH= 6.5 Hz, 1H, PH) 7.64–7.68 (m, 2H, H_o-Ph), 7.76–7.86 (m,

(s, P(CH₂)₄CH₂Me/P(CH₂)₃CH₂Et), 26.9 (d, J_CP= 15.1 Hz, 3H, H_m-Ph, H_p-Ph) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ =

3

P(CH₂)₂CH₂ⁿPr), 29.4 (d, J_CP= 11.9 Hz, PCH₂ⁿPent), 31.5 (d, 13.0 (s, P(CH₂)₃Me), 19.1 (d, J_CP= 46.6 Hz, PCH₂ⁿPr), 23.2 (d,

1

²J_CP

=

11.2 Hz, PCH₂CH₂ⁿBu), 32.0 (s, P(CH₂)₄CH₂Me/ ³J_CP= 15.7 Hz, P(CH₂)₂CH₂Me), 24.6 (d, J_CP= 4.7 Hz,

2

P(CH₂)₃CH₂Et), 69.2 (s, C_Cp′), 70.1 (d, ³J_CP= 3.1 Hz, C_β), 71.4 (d, PCH₂CH₂Et), 114.4 (d, J_CP= 82.5 Hz, C_Ph,ipso), 119.8 (q, J_CF

=

1

²J_CP= 13.1 Hz, C_α), 80.1 (d, J_CP= 15.5 Hz, C_Cp,ipso) ppm. MS 321.4 Hz, CF₃), 130.5 (d, J_CP= 12.7 Hz, C_o-Ph), 132.8 (d, J_CP

1

2

3

(EI+) m/z = 386.1818 (C₂₂H₃₅FeP requires 386.1826). IR (neat): 10.2 Hz, C_m-Ph), 135.2 (d, J_CP= 2.3 Hz, C_p-Ph) ppm; ¹⁹F NMR

ν = 3096 (w), 2954 (m), 2921 (s), 2853 (s), 1457 (m), 1412 (w), (282.4 MHz, CDCl₃): δ = −78.9 ppm. MS (ESI+, MeOH) m/z (%)

1378 (w), 1192 (w), 1159 (m), 1106 (m), 1052 (m), 1025 (m), = 223.1608 (100, [M − NTf₂]⁺requires 223.1610); MS (ESI−,

1001 (m), 975 (m), 889 (w), 816 (s), 718 (m), 486 (s), 445 (m) MeOH) m/z (%) = 279.9179 (61, [NTf₂]⁻requires 279.9178). IR

4

cm⁻¹

.

(neat): ν = 2965 (m), 2937 (m), 2877 (w), 1467 (w), 1442 (m),

1346 (s), 1328 (s), 1225 (m), 1178 (s), 1131 (s), 1051 (s),

999 (m), 965 (w), 937 (m), 876 (w), 788 (m), 739 (m), 722 (m),

691 (m), 653 (m), 612 (s), 599 (s), 569 (s), 480 (m), 452 (m)

General procedure for the protonation of phosphines with

bis(trifluoromethanesulfonyl)amine (3)

To a dichloromethane solution of the appropriate phosphine cm⁻¹

(1.1 eq.) bis(trifluoromethanesulfonyl)amine (1.0 eq.) was

.

Dibutylferrocenylphosphonium tetrachloroaluminate (3c).

added and the resulting solution was stirred at ambient temp- 100 mg ferrocene (0.54 mmol, 1.0 eq.) and 79 mg AlCl₃

erature for 2 h. The reaction mixture was evaporated to dryness (0.59 mmol, 1.1 eq.) were suspended in 15 mL n-heptane.

and the crude product was washed several times with 117 mg 1b (0.65 mmol, 1.2 eq.) were added via a syringe and

n-pentane. After drying in a vacuum the desired phosphonium the reaction mixture was heated to reflux for 1.5 h whereupon

compounds were obtained as viscous oils.

a dark green oil was formed. The oil was washed with

Dibutylferrocenylphosphonium bis(trifluoromethanesulfonyl)- n-pentane several times until unreacted starting materials had

imide (3a). Prepared from 2b (217 mg, 0.66 mmol, 1.1 eq.) been separated forming a deep orange solid. The solid was

and bis(trifluoromethanesulfonyl)amine (131 mg, 0.60 mmol, dried in a vacuum yielding 251 mg 3c (0.50 mmol, 93%). ³¹P

1.0 eq.); 310 mg (0.51 mmol, 85%) orange oil. Anal. calc. for NMR (121.5 MHz, CD₂Cl₂): δ = 13.1 (dm, ¹J_PH= 489.4 Hz) ppm;

C₂₀H₂₈F₆FeNO₄PS₂(611.39 g mol⁻¹) C 39.29, H 4.62, N 2.29%; ¹H NMR (300.1 MHz, CD₂Cl₂):

δ = 0.87–1.10 (m, 6H,

found C 39.48, H 4.28, N 2.61%. ³¹P NMR (121.5 MHz, P(CH₂)₃Me), 1.41–1.64 (m, 4H, P(CH₂)₂CH₂Me), 1.65–1.87 (m,

CD₂Cl₂): δ = 10.6 (dm, J_PH= 496.1 Hz) ppm; ¹H NMR 4H, PCH₂CH₂Et), 2.28–2.56 (m, 4H, PCH₂ⁿPr), 4.44 (s, 5H,

1

3

1

(300.1 MHz, CD₂Cl₂): δ = 0.98 (t, J_HH= 7.2 Hz, 6H, H_Cp′), 4.46 (s, 2H, H_α), 4.83 (s, 2H, H_β), 6.90 (dm, J_PH

=

P(CH₂)₃Me), 1.46–1.58 (m, 4H, P(CH₂)₂CH₂Me), 1.59–1.73 (m, 487.0 Hz, 1H, PH) ppm; ¹³C{¹H} NMR (75.5 MHz, CD₂Cl₂): δ =

4H, PCH₂CH₂Et), 2.28–2.42 (m, 4H, PCH₂ⁿPr), 4.41 (s, 5H, 13.6 (s, P(CH₂)₃Me), 20.9 (d, J_CP= 48.0 Hz, PCH₂ⁿPr), 24.2

1

3

4

3

2

H_Cp′), 4.63 (quart, J_HH= 1.9 Hz, 2H, H_α), 4.79 (quart, J_HH

=

(d, J_CP= 15.5 Hz, P(CH₂)₂CH₂Me), 25.5 (d, J_CP= 3.7 Hz,

1

4

1.8 Hz, 2H, H_β), 6.90 (dquint, J_PH= 496.0 Hz, J_HH= 5.3 Hz, PCH₂CH₂Et), 52.8 (d, overlain by CD₂Cl₂-signal, C_Cp,ipso), 71.4

1H, PH) ppm; ¹³C{¹H} NMR (75.5 MHz, CD₂Cl₂): δ = 13.4 (s, (s, C_Cp′), 73.1 (d, ²J_CP= 13.3 Hz, C_α), 75.2 (d, ³J_CP= 10.6 Hz, C_β)

1

3

P(CH₂)₃Me), 20.2 (d, J_CP= 49.4 Hz, PCH₂ⁿPr), 24.0 (d, J_CP

=

ppm;²⁷Al NMR (104.2 MHz, CD₂Cl₂): δ = 103.8 ppm. MS

15.6 Hz, P(CH₂)₂CH₂Me), 25.1 (d, J_CP= 4.4 Hz, PCH₂CH₂Et), (APCI+, DCM) m/z (%) = 331.1271 (100, [M − AlCl₄]⁺requires

2

3758 | Dalton Trans., 2014, 43, 3750–3766

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Dalton Transactions

Paper

331.1272); MS (APCI−, DCM) m/z (%) = 168.8546 (15, [AlCl₄]⁻and 1-bromobutane (140 mg, 1.02 mmol, 1.5 eq.); 218 mg

requires 168.8545). IR (neat): ν = 3105 (w), 2961 (m), 2932 (m), (0.57 mmol, 84%) orange solid. ³¹P{¹H} NMR (121.5 MHz,

2873 (m), 1464 (m), 1414 (m), 1383 (m), 1347 (m), 1310 (w), CDCl₃): δ = 26.5 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.85 (t,

1187 (m), 1095 (m), 1036 (m), 1002 (m), 963 (m), 907 (m), 834 ³J_HH= 6.9 Hz, 3H, H-1b), 1.33–1.45 (m, 4H, H-2b, H-3b), 2.35

2

(m), 717 (m), 562 (m), 477 (vs) cm⁻¹

.

(d, J_HP= 14.0 Hz, 6H, H-1a), 2.47–2.57 (m, 2H, H-4b), 4.33 (s,

5H, H_Cp′), 4.65 (s, 2H, H_Cp), 4.66 (s, 2H, H_Cp) ppm; ¹³C{¹H}

NMR (75.5 MHz, CDCl₃): δ = 9.9 (d, J_CP= 57.6 Hz, C-1a), 13.5

General procedure for the preparation of trialkylferrocenyl-

phosphonium halides (4)

1

2

3

(s, C-1b), 23.5 (d, J_CP= 16.3 Hz, C-2b), 24.0 (d, J_CP= 4.5 Hz,

1

The appropriate phosphine 2 (1.0 eq.) was dissolved in a C-3b), 25.7 (d, J_CP= 52.8 Hz, C-4b), 61.2 (d, J_CP= 96.6 Hz,

suﬃcient amount of acetonitrile and the corresponding alkyl- C_Cp,ipso), 70.2 (s, C_Cp′), 71.5 (d,

2/3

J

CP

= 12.8 Hz, C_Cp), 73.6 (d,

2/3

halide (1.2 eq.) was added. The reaction mixture was heated to

J

= 10.3 Hz, C_Cp) ppm. MS (ESI+, MeOH) m/z (%) =

CP

60 °C for 12 h (in case of methyl iodide as an alkylation agent 303.0955 (100, [M − Br]⁺requires 303.0960). IR (neat): ν = 3098

the reaction was carried out at ambient temperature). All vola- (w), 3053 (m), 2955 (m), 2931 (m), 2863 (m), 1464 (w), 1412

tile components were removed in a vacuum and the crude (m), 1390 (m), 1367 (w), 1314 (m), 1301 (m), 1231 (w), 1188 (s),

product was washed two times with 20 mL n-pentane. The 1106 (m), 1073 (m), 1035 (m), 1001 (m), 967 (s), 950 (s), 890

desired trialkylferrocenyl-phosphonium halides 4 were dried (vs), 877 (m), 846 (m), 823 (s), 777 (vs), 762 (m), 723 (m), 695

in a vacuum (0.01 mbar) for one day.

Trimethylferrocenylphosphonium iodide (4a) [FcPMe₃]I. 155.0 °C (T_d: 217.2 °C).

Prepared from 2a (83 mg, 0.34 mmol, 1.0 eq.) and methyl Dibutylmethylferrocenylphosphonium

(m), 618 (w), 510 (m), 483 (vs), 443 (s), 427 (m) cm⁻¹. T_m:

iodide

(4d)

iodide (72 mg, 0.51 mmol, 1.5 eq.); 113 mg (0.27 mmol, 85%) [FcPBu₂Me]I. Prepared from 2b (156 mg, 0.47 mmol, 1.0 eq.)

yellow solid. ³¹P{¹H} NMR (121.5 MHz, CD₃CN): δ = 25.0 ppm; and methyl iodide (80 mg, 0.57 mmol, 1.2 eq.); 199 mg

2

¹H NMR (300.1 MHz, CD₃CN): δ = 2.07 (d, J_HP= 14.4 Hz, 9H, (0.58 mmol, 89%) orange highly viscous oil. ³¹P{¹H} NMR

3

H-1a), 4.42 (s, 5H, H_Cp′), 4.67 (q, J_HH= 1.8 Hz, 2H, H_Cp), 4.75 (121.5 MHz, CDCl₃): δ = 29.4 ppm; ¹H NMR (300.1 MHz,

3

(q, J_HH= 1.8 Hz, 2H, H_Cp) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = 0.96 (t, J_HH= 6.9 Hz, 6H, H-1a), 1.47–1.62 (m, 8H,

1

2

CD₃CN): δ = 11.5 (d, J_CP= 58.7 Hz, C-1a), 62.9 (d, J_CP

=

H-2a, H-3a), 2.41 (d, J_HP= 13.3 Hz, 3H, H-1b), 2.47–2.74 (m,

2/3

3/4

100.9 Hz, C_Cp,ipso), 71.0 (s, C_Cp′), 72.1 (d,

J

CP

= 13.7 Hz, C_Cp), 4H, H-4a), 4.39 (s, 5H, H_Cp′), 4.70 (quint,

J

HH

= 1.8 Hz, 2H,

74.5 (d, ^2/3J_CP= 10.6 Hz, C_Cp) ppm. MS (ESI+, MeOH) m/z (%) =

H

_Cp), 4.72 (quint,

J

HH

= 1.8 Hz, 2H, H_Cp) ppm; ¹³C{¹H} NMR

3/4

261.0486 (100, [M − I]⁺requires 261.0490). IR (neat): ν = (75.5 MHz, CDCl₃): δ = 8.6 (d, J_CP= 56.4 Hz, C-1b), 13.6 (s,

1

2/3

3054 (m), 2959 (m), 2895 (m), 2880 (m), 1409 (m), 1364 (w), C-1a), 23.3 (d, J_CP= 42.4 Hz, C-4a), 23.8 (d,

1304 (m), 1295 (m), 1188 (s), 1106 (m), 1073 (w), 1040 (s), C-2a/C-3a), 24.1 (d,

J

CP

= 6.5 Hz,

2/3

1

J

= 4.5 Hz, C-2a/C-3a), 60.6 (d, J_CP=

CP

2/3

999 (m), 966 (vs), 953 (vs), 889 (m), 867 (m), 841 (vs), 807 (s), 95.0 Hz, C_Cp,ipso), 70.3 (s, C_Cp′), 71.6 (d,

J

= 12.2 Hz, C_Cp),

CP

784 (m), 770 (s), 688 (m), 613 (m), 506 (s), 484 (vs), 442 73.6 (d, ^2/3J_CP= 10.1 Hz, C_Cp) ppm. MS (ESI+, MeOH) m/z (%) =

(vs) cm⁻¹. T_m: 276.9 °C (T_d: 299.7 °C). Single crystals suitable 345.1423 (100, [M − I]⁺requires 345.1429). IR (neat): ν = 3052

for XRD obtained from a saturated chloroform solution at (m), 2955 (s), 2929 (s), 2869 (s), 1461 (m), 1410 (m), 1391 (m),

ambient temperature.

1368 (m), 1308 (m), 1226 (m), 1185 (vs), 1105 (m), 1036 (s),

Dimethylpropylferrocenylphosphonium

bromide

(4b) 1002 (m), 969 (m), 931 (s), 883 (s), 823 (vs), 720 (m), 616 (w),

[FcPMe₂Pr]Br. Prepared from 2a (189 mg, 0.77 mmol, 1.0 eq.) 486 (vs), 465 (vs) cm⁻¹

.

and 1-bromopropane (142 mg, 1.15 mmol, 1.5 eq.); 232 mg

Dibutylpropylferrocenylphosphonium

bromide

(4e)

(0.63 mmol, 82%) orange solid. ³¹P{¹H} NMR (121.5 MHz, [FcPBu₂Pr]Br. Prepared from 2b (173 mg, 0.52 mmol, 1.0 eq.)

1

CDCl₃): δ = 26.2 ppm; H NMR (300.1 MHz, CDCl₃): δ = 1.00 and 1-bromopropane (77 mg, 0.63 mmol, 1.2 eq.); 203 mg

3

4

(dt, J_HH= 7.0 Hz, J_HP= 1.1 Hz, 3H, H-1b), 1.42–1.58 (m, 2H, (0.45 mmol, 87%) orange solid. ³¹P{¹H} NMR (121.5 MHz,

H-2b), 2.35 (d, J_HP= 14.0 Hz, 6H, H-1a), 2.45–2.55 (m, 2H, CDCl₃): δ = 30.7 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.97 (t,

2

H-3b), 4.33 (s, 5H, H_Cp′), 4.64–4.70 (m, 4H, H_Cp) ppm; ¹³C{¹H} ³J_HH= 7.1 Hz, 6H, H-1a), 1.17 (dt, J_HH= 7.1 Hz, J_HP= 1.5 Hz,

3

4

1

NMR (75.5 MHz, CDCl₃): δ = 9.9 (d, J_CP= 57.6 Hz, C-1a), 15.2 3H, H-1b), 1.51–1.63 (m, 8H, H-2a, H-3a), 1.65–1.76 (m, 2H,

2

3

(d, J_CP= 16.9 Hz, C-2b), 15.9 (d, J_CP= 4.2 Hz, C-1b), 27.8 (d, H-2b), 2.60–2.72 (m, 6H, H-4a, H-3b), 4.37 (s, 5H, H_Cp′), 4.71 (s,

¹J_CP= 52.5 Hz, C-3b), 61.2 (d, J_CP= 96.6 Hz, C_Cp,ipso), 70.2 (s, 2H, H_Cp), 4.71 (s, 2H, H_Cp) ppm; ¹³C{¹H} NMR (75.5 MHz,

1

2/3

C_Cp′), 71.5 (d,

J

= 12.9 Hz, C_Cp), 73.6 (d,

J

CP

= 10.3 Hz, CDCl₃): δ = 13.6 (s, C-1a), 15.6 (d, ³J_CP= 16.6 Hz, C-1b), 16.2 (d,

CP

C

_Cp) ppm. MS (ESI+, MeOH) m/z (%) = 289.0798 (100, [M − ²J_CP= 4.3 Hz, C-2b), 21.8 (d, ¹J_CP= 50.4 Hz, C-4a), 23.9 (d, ²J_CP

=

Br]⁺requires 289.0803). IR (neat): ν = 3048 (m), 2958 (m), 2874 15.7 Hz, C-3a), 24.0 (d, J_CP= 50.7 Hz, C-3b), 24.3 (d, J_CP

1

3

1

(m), 1456 (m), 1411 (m), 1391 (m), 1367 (m), 1350 (w), 1311 4.8 Hz, C-2a), 60.1 (d, J_CP= 91.9 Hz, C_Cp,ipso), 70.3 (s, C_Cp′),

2/3

(m), 1299 (m), 1244 (w), 1216 (w), 1187 (s), 1105 (m), 1083 (m), 71.9 (d,

J

CP

= 11.3 Hz, C_Cp), 73.5 (d,

J

= 9.7 Hz, C_Cp)

CP

1055 (s), 1037 (s), 1002 (m), 964 (m), 941 (vs), 884 (s), 782 (s), ppm. MS (ESI+, MeOH) m/z (%) = 373.1735 (100, [M − Br]⁺

723 (m), 656 (m), 617 (m), 484 (vs), 459 (s), 439 (s) cm⁻¹. T_m: requires 373.1742). IR (neat): ν = 3055 (m), 2956 (s), 2929 (s),

125.6 °C (T_d: 200.4 °C).

2868 (s), 2797 (m), 1460 (m), 1411 (m), 1393 (w), 1372 (m),

Dimethylbutylferrocenylphosphonium

bromide

(4c) 1351 (w), 1311 (w), 1234 (m), 1184 (s), 1106 (s), 1088 (m), 1067

[FcPMe₂Bu]Br. Prepared from 2a (168 mg, 0.68 mmol, 1.0 eq.) (m), 1045 (m), 1001 (m), 971 (w), 896 (m), 846 (m), 819 (vs),

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733 (s), 619 (w), 520 (w), 483 (vs), 464 (vs) cm⁻¹. T_m: 106.7 °C bis(trifluoromethanesulfonyl)imide (98 mg, 0.34 mmol,

(T_d: 313.6 °C).

1.2 eq.); 114 mg (0.20 mmol, 74%) orange oil. Anal. calc. for

Tributylferrocenylphosphonium bromide (4f) [FcPBu₃]Br. C₁₅H₁₈F₆FeNO₄PS₂(541.25 g mol⁻¹) C 33.29, H 3.35, N 2.59%;

Prepared from 2b (177 mg, 0.54 mmol, 1.0 eq.) and 1-bromo- found C 33.63, H 3.15, N 2.58%. ³¹P{¹H} NMR (121.5 MHz,

1

butane (88 mg, 0.64 mmol, 1.2 eq.); 193 mg (0.41 mmol, 76%) CD₃CN): δ = 25.0 ppm; H NMR (300.1 MHz, CD₃CN): δ = 2.00

orange solid. ³¹P{¹H} NMR (121.5 MHz, CDCl₃): δ = 31.6 ppm; (d, J_HP= 14.4 Hz, 9H, H-1a), 4.41 (s, 5H, H_Cp′), 4.63 (q, J_HH

=

2

3

¹H NMR (300.1 MHz, CDCl₃): δ = 0.93 (t, J_HH= 6.9 Hz, 9H, 1.9 Hz, 2H, H_Cp), 4.75 (q, ³J_HH= 1.9 Hz, 2H, H_Cp) ppm; ¹³C{¹H}

3

1

H-1a), 1.48–1.61 (m, 12H, H-2a, H-3a), 2.58–2.68 (m, 6H, H-4a), NMR (75.5 MHz, CD₃CN): δ = 11.3 (d, J_CP= 58.7 Hz, C-1a),

4.31 (s, 5H, H_Cp′), 4.66 (s, 2H, H_Cp), 4.67 (s, 2H, H_Cp) ppm; ¹³C 62.1 (C_Cp,ipso),⁶⁵71.1 (s, C_Cp′), 72.0 (d,

J

= 13.8 Hz, C_Cp),

CP

2/3

{¹H} NMR (75.5 MHz, CDCl₃): δ = 13.7 (s, C-1a), 22.0 (d, J_CP

=

74.7 (d,

J

= 10.7 Hz, C_Cp) ppm; ¹⁹F NMR (282.4 MHz,

CP

1

2/3

2

3

50.5 Hz, C-4a), 24.0 (d, J_CP= 15.7 Hz, C-3a), 24.4 (d, J_CP

CDCl₃): δ = 79.5 ppm. MS (ESI+, MeOH) m/z (%) = 261.0487

4.7 Hz, C-2a), 60.2 (d, J_CP= 91.9 Hz, C_Cp,ipso), 70.4 (s, C_Cp′), (100, [M − NTf₂]⁺requires 261.0490); MS (ESI−, MeOH) m/z

1

2/3

72.0 (d,

J

= 11.1 Hz, C_Cp), 73.5 (d,

J

CP

= 9.5 Hz, C_Cp), (%)

=

279.9177 (100, [NTf₂]⁻requires 279.9178). IR

CP

ppm. ESI-HRMS (MeOH): pos.: m/z (%) = [M − Br]⁺ber. (neat): ν = 3111 (w), 3004 (w), 2925 (w), 1421 (m), 1346 (s),

387.1899, gef. 387.1892 (100). IR (neat): ν = 3053 (w), 2955 (s), 1330 (s), 1304 (m), 1225 (m), 1175 (vs), 1132 (vs), 1108 (m),

2929 (s), 2868 (s), 2797 (m), 1460 (m), 1411 (m), 1393 (m), 1050 (vs), 1004 (m), 958 (s), 889 (m), 870 (m), 831 (m), 787 (m),

1377 (m), 1351 (m), 1311 (m), 1227 (m), 1184 (w), 1106 (m), 763 (m), 739 (m), 685 (m), 653 (m), 612 (s), 599 (s), 568 (vs),

1094 (m), 1066 (m), 1044 (m), 1001 (m), 971 (m), 897 (m), 506 (vs), 484 (s), 436 (s) cm⁻¹. E_1/2([EMIM]NTf₂) = 458 mV

845 (s), 818 (vs), 783 (s), 618 (w), 482 (s), 466 (vs) cm⁻¹. T_m: vs. Fc/Fc⁺.

129.3 °C (T_d: 339.6 °C).

Dimethylpropylferrocenylphosphonium bis(trifluoromethane-

sulfonyl)imide (5b) [FcPMe₂Pr]NTf₂. 5b was prepared

according to method A. 4b (232 mg, 0.63 mmol, 1.0 eq.) and

General procedure for the preparation of ferrocenyl-

phosphonium bis(trifluoromethanesulfonyl)imides (5)

lithium

bis(trifluoromethanesulfonyl)imide

(217

mg,

Method A: The appropriate trisalkylferrocenylphosphonium 0.76 mmol, 1.2 eq.); 347 mg (0.61 mmol, 97%) orange oil.

halide 4 (1.0 eq.) was suspended in a 1 : 1 mixture of metha- Anal. calc. for C₁₇H₂₂F₆FeNO₄PS₂(569.30 g mol⁻¹) C 35.87,

nol–water and lithium bis(trifluoromethanesulfonyl)imide H 3.90, N 2.46%; found C 35.58, H 3.96, N 2.65%. ³¹P{¹H}

1

(1.1 eq.) was added. The resulting yellow suspension was NMR (121.5 MHz, CDCl₃): δ = 26.9 ppm; H NMR (300.1 MHz,

3

4

stirred vigorously at 40 °C for 12 h. Under inert conditions the CDCl₃): δ = 1.04 (dt, J_HH= 7.3 Hz, J_HP= 1.3 Hz, 3H, H-1b),

2

reaction mixture was extracted four times with 20 mL dichloro- 1.46–1.58 (m, 2H, H-2b), 2.09 (d, J_HP= 13.7 Hz, 6H, H-1a),

3

methane until the organic phase stayed colorless. The volume 2.15–2.23 (m, 2H, H-3b), 4.37 (s, 5H, H_Cp′), 4.57 (q, J_HH

=

of the combined organic phases was reduced to 30 mL and 1.9 Hz, 2H, H_Cp), 4.73 (q, ³J_HH= 1.8 Hz, 2H, H_Cp) ppm; ¹³C{¹H}

1

washed three times with 20 mL ultrapure water (σ = 0.054 µS). NMR (75.5 MHz, CDCl₃): δ = 8.5 (d, J_CP= 58.2 Hz, C-1a),

3

The organic phase was evaporated to dryness and washed two 14.9 (d, ²J_CP= 17.0 Hz, C-2b), 15.7 (d, J_CP= 4.1 Hz, C-1b), 27.4

1

times with 20 mL Et₂O and three times with 20 mL n-pentane. (d, J_CP= 52.6 Hz, C-3b), 60.3 (d, J_CP= 98.4 Hz, C_Cp,ipso), 70.3

The desired product was dried under high vacuum (5 × 10⁻⁵

7 × 10⁻⁶mbar). Method B: The appropriate phosphine 2

–

(s, C_Cp′), 71.0 (d, ^2/3J_CP= 13.2 Hz, C_Cp), 74.0 (d, ^2/3J_CP= 10.5 Hz,

_Cp), 120.0 (q, J_CF

1

C

=

321.4 Hz, CF₃) ppm; ¹⁹F NMR

(1.0 eq.) was dissolved in a suﬃcient amount of acetonitrile (282.4 MHz, CDCl₃): δ = −78.8 ppm. MS (ESI+, MeOH) m/z (%)

and MeNTf₂(1.1 eq. and 2.0 eq. for 2e) was added. The reac- = 289.0799 (100, [M − NTf₂]⁺requires 289.0803); MS (ESI−,

tion mixture was stirred for 12 h at ambient temperature MeOH) m/z (%) = 279.9177 (100, [NTf₂]⁻requires 279.9178).

(in case of 2d and 2e the reaction was carried out at 60 °C for IR (neat): ν = 3109 (w), 2972 (m), 2928 (m), 2881 (w), 1463 (w),

12 h and 3 d, respectively). All volatile components were 1416 (m), 1346 (s), 1330 (s), 1225 (m), 1176 (vs), 1133 (vs),

removed in a vacuum and the crude product was washed two 1108 (m), 1050 (vs), 1004 (m), 956 (s), 936 (m), 886 (m),

times with 20 mL n-pentane. The desired product was dried in 830 (m), 787 (m), 762 (m), 739 (m), 653 (m), 612 (s), 599 (s),

a vacuum (0.01 mbar) at 40 °C for one day. Method C: 568 (s), 508 (s), 485 (s), 458 (m), 444 (s) cm⁻¹. E_1/2([EMIM]-

The appropriate heteroleptic sandwich complex [(η⁵-C₅H₅)- NTf₂) = 458 mV vs. Fc/Fc⁺.

Fe(η⁶-arene)]NTf₂(1.0 eq.) and the cyclopentadienylidene

Dimethylbutylferrocenylphosphonium bis(trifluoromethane-

phosphorane (1.0 eq.) were dissolved in a suﬃcient amount of sulfonyl)imide (5c) [FcPMe₂Bu]NTf₂. 5c was prepared accord-

acetonitrile. The solution was irradiated with visible light ing to method A. 4c (218 mg, 0.57 mmol, 1.0 eq.) and lithium

(Osram Ultra Vitalux 300W) for 12 h. On subsequent removing bis(trifluoromethanesulfonyl)imide (196 mg, 0.68 mmol,

the solvent in a vacuum the crude product was washed two 1.2 eq.); 247 mg (0.42 mmol, 74%) orange oil. Anal. calc. for

times with Et₂O and two times with n-pentane to obtain the C₁₈H₂₄F₆FeNO₄PS₂(583.34 g mol⁻¹) C 37.06, H 4.15, N 2.40%;

desired product after drying in a vacuum (0.01 mbar) for one found C 37.36, H 4.18, N 2.60%. ³¹P{¹H} NMR (121.5 MHz,

day.

CDCl₃): δ = 27.3 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.85 (t,

Trimethylferrocenylphosphonium bis(trifluoromethanesul- ³J_HH= 6.8 Hz, 3H, H-1b), 1.33–1.45 (m, 4H, H-2b, H-3b), 2.35

2

fonyl)imide (5a) [FcPMe₃]NTf₂. 5a was prepared according (d, J_HP= 14.0 Hz, 6H, H-1a), 2.47–2.57 (m, 2H, H-4b), 4.33 (s,

to method A. 4a (113 mg, 0.27 mmol, 1.0 eq.) and lithium 5H, H_Cp′), 4.65 (s, 2H, H_Cp), 4.66 (s, 2H, H_Cp) ppm; ¹³C{¹H}

3760 | Dalton Trans., 2014, 43, 3750–3766

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1

2/3

NMR (75.5 MHz, CDCl₃): δ = 8.5 (d, J_CP= 58.2 Hz, C-1a), 13.2 ¹J_CP= 93.2 Hz, C_Cp,ipso), 70.4 (s, C_Cp′), 71.3 (d,

J

= 11.5 Hz,

CP

2

3

2/3

1

(s, C-1b), 23.4 (d, J_CP= 16.2 Hz, C-2b), 23.7 (d, J_CP= 4.5 Hz,

C_Cp), 73.8 (d,

J

CP

= 9.8 Hz, C_Cp), 120.0 (q, J_CF= 321.5 Hz,

C-3b), 25.4 (d, J_CP= 53.0 Hz, C-4b), 60.3 (d, J_CP= 98.5 Hz, CF₃) ppm; ¹⁹F NMR (282.4 MHz, CDCl₃): δ = −78.8 ppm. MS

1

2/3

C_Cp,ipso), 70.3 (s, C_Cp′), 71.1 (d,

J

= 13.1 Hz, C_Cp), 74.0 (d, (ESI+, MeOH) m/z (%) = 373.1737 (100, [M − NTf₂]⁺requires

CP

2/3

1

J

= 10.5 Hz, C_Cp), 120.0 (q, J_CF= 321.4 Hz, CF₃) ppm; ¹⁹F 373.1743); MS (ESI−, MeOH) m/z (%) = 279.9177 (100, [NTf₂]⁻

CP

NMR (282.4 MHz, CDCl₃): δ = −78.8 ppm. MS (ESI+, MeOH) requires 279.9178). IR (neat): ν = 3110 (w), 2965 (m), 2937 (m),

m/z (%) = 303.0956 (100, [M − NTf₂]⁺requires 303.0960); MS 2877 (m), 1465 (w), 1414 (w), 1383 (w), 1346 (s), 1330 (s),

(ESI−, MeOH) m/z (%) = 279.9176 (100, [NTf₂]⁻requires 1225 (m), 1176 (vs), 1134 (s), 1108 (m), 1098 (m), 1051 (s),

279.9178). IR (neat): ν = 3109 (w), 2964 (w), 2932 (m), 2877 (w), 1004 (m), 911 (w), 830 (m), 787 (m), 761 (m), 738 (m), 652 (m),

1467 (w), 1416 (w), 1346 (s), 1330 (s), 1225 (m), 1176 (vs), 613 (s), 599 (s), 568 (s), 509 (s), 486 (s), 465 (s) cm⁻¹. E_1/2

1133 (vs), 1108 (m), 1051 (vs), 1004 (m), 944 (s), 886 (m), ([EMIM]NTf₂) = 453 mV vs. Fc/Fc⁺.

869 (m), 830 (s), 787 (s), 761 (m), 739 (m), 653 (m), 612 (s),

599 (s), 569 (s), 508 (s), 485 (s), 459 (m), 444 (m) cm⁻¹. E_1/2nyl)imide (5f) [FcPBu₃]NTf₂. 5f was prepared according to

([EMIM]NTf₂) = 463 mV vs. Fc/Fc⁺.

method A and C. Method A: 4f (193 mg, 0.41 mmol, 1.0 eq.)

Tributylferrocenylphosphonium bis(trifluoromethanesulfo-

Dibutylmethylferrocenylphosphonium bis(trifluoromethane- and lithium bis(trifluoromethanesulfonyl)imide (119 mg,

sulfonyl)imide (5d) [FcPBu₂Me]NTf₂. 5d was prepared accord- 0.41 mmol, 1.0 eq.); 244 mg (0.37 mmol, 89%) orange solid.

ing to method A. 4d (199 mg, 0.58 mmol, 1.0 eq.) and lithium Method C: 8b (222 mg, 0.83 mmol, 1.2 eq.) and [(C₅H₅)Fe(η⁶-

bis(trifluoromethanesulfonyl)imide (167 mg, 0.58 mmol, toluene)]NTf₂(343 mg, 0.70 mmol, 1.0 eq.); 444 mg

1.0 eq.); 264 mg (0.42 mmol, 72%) orange oil. Anal. calc. for (0.67 mmol, 95%) orange solid. Anal. calc. for C₂₄H₃₆F₆Fe-

C₂₁H₃₀F₆FeNO₄PS₂(625.42 g mol⁻¹) C 40.33, H 4.83, N 2.24%; NO₄PS₂(667.50 g mol⁻¹) C 43.19, H 5.44, N 2.10%; found C

found C 40.68, H 5.01, N 2.55%. ³¹P{¹H} NMR (121.5 MHz, 43.47, H 5.55, N 2.45%. ³¹P{¹H} NMR (121.5 MHz, CDCl₃): δ =

3

CDCl₃): δ = 30.0 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.95 (t, 32.1 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.97 (t, J_HH

=

³J_HH= 6.8 Hz, 6H, H-1a), 1.43–1.55 (m, 8H, H-2a, H-3a), 2.07 6.8 Hz, 9H, H-1a), 1.47–1.62 (m, 12H, H-2a, H-3a), 2.24–2.33

2

3

(d, J_HP= 13.2 Hz, 3H, H-1b), 2.20–2.32 (m, 4H, H-4a), 4.37 (s, (m, 6H, H-4a), 4.36 (s, 5H, H_Cp′), 4.54 (d, J_HH= 1.6 Hz, 2H,

3/4

3

5H, H_Cp′), 4.56 (q,

J

HH

= 1.8 Hz, 2H, H_Cp), 4.74 (q,

J

=

HH

H

_Cp), 4.76 (d, J_HH= 1.6 Hz, 2H, H_Cp) ppm; ¹³C{¹H} NMR

1.8 Hz, 2H, H_Cp) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = (75.5 MHz, CDCl₃): δ = 13.3 (s, C-1a), 21.3 (d, J_CP= 51.0 Hz,

1

2

3

6.6 (d, J_CP= 57.3 Hz, C-1b), 13.3 (s, C-1a), 22.9 (d, J_CP

52.2 Hz, C-4a), 23.6 (d, J_CP= 15.9 Hz, C-2a), 23.8 (d, J_CP

4.5 Hz, C-3a), 59.8 (d, J_CP= 96.1 Hz, C_Cp,ipso), 70.3 (s, C_Cp′),

71.2 (d,

=

C-4a), 23.7 (d, J_CP= 15.7 Hz, C-3a), 24.0 (d, J_CP= 4.6 Hz,

C-2a), 59.3 (d, J_CP= 93.3 Hz, C_Cp,ipso), 70.4 (s, C_Cp′), 71.3 (d,

3

2

1

2/3

J

= 11.5 Hz, C_Cp), 73.8 (d,

J

CP

= 9.8 Hz, C_Cp), 120.0 (q,

CP

2/3

J

= 12.3 Hz, C_Cp), 73.9 (d,

J

= 10.2 Hz, C_Cp), ¹J_CF= 321.9 Hz, CF₃) ppm; ¹⁹F NMR (282.4 MHz, CDCl₃): δ =

CP

120.0 (q, J_CF= 321.5 Hz, CF₃) ppm; ¹⁹F NMR (282.4 MHz, −78.8 ppm. MS (ESI+, MeOH) m/z (%) = 387.1894 (100, [M −

CDCl₃): δ = −78.8 ppm. MS (ESI+, MeOH) m/z (%) = 345.1425 NTf₂]⁺requires 387.1899); MS (ESI−, MeOH) m/z (%) =

(100, [M − NTf₂]⁺requires 345.1429); MS (ESI−, MeOH) m/z 279.9177 (100, [NTf₂]⁻requires 279.9178). IR (neat): ν =

(%) = 279.9177 (100, [NTf₂]⁻requires 279.9178). IR (neat): ν = 3114 (w), 2966 (m), 2937 (m), 2877 (w), 1466 (w), 1409 (w),

3109 (w), 2964 (m), 2936 (m), 2876 (m), 1720 (vw), 1466 (w), 1383 (w), 1348 (s), 1336 (s), 1222 (m), 1180 (vs), 1138 (s),

1415 (w), 1347 (s), 1330 (s), 1225 (s), 1176 (vs), 1134 (vs), 1107 (m), 1099 (m), 1051 (s), 1036 (s), 1003 (m), 968 (w),

1108 (m), 1051 (vs), 1004 (m), 969 (w), 928 (m), 882 (m), 907 (m), 894 (w), 850 (m), 824 (s), 789 (m), 761 (w), 738 (m),

1

830 (m), 787 (m), 761 (m), 739 (m), 652 (m), 613 (s), 599 (s), 724 (m), 613 (s), 568 (s), 512 (s), 486 (s), 467 (s), 407 (m) cm⁻¹

569 (s), 509 (s), 486 (s), 463 (s) cm⁻¹. E_1/2([EMIM]NTf₂) = T_m: 72.4 °C (T_d: 327.4 °C). Single crystals suitable for

454 mV vs. Fc/Fc⁺.

XRD obtained by slow diﬀusion of Et₂O into an acetonitrile

Dibutylpropylferrocenylphosphonium bis(trifluoromethane- solution. E_1/2([EMIM]NTf₂) = 454 mV vs. Fc/Fc⁺.

.

sulfonyl)imide (5e) [FcPBu₂Pr]NTf₂. 5e was prepared accord-

Dihexylmethylferrocenylphosphonium bis(trifluoromethane-

ing to method A. 4f (203 mg, 0.45 mmol, 1.0 eq.) and lithium sulfonyl)imide (5g) [FcPHex₂Me]NTf₂. 5g was prepared accord-

bis(trifluoromethanesulfonyl)imide (129 mg, 0.45 mmol, ing to method B. 2c (570 mg, 1.48 mmol, 1.0 eq.) and MeNTf₂

1.0 eq.); 240 mg (0.37 mmol, 82%) orange oil. Anal. calc. for (479 mg, 1.62 mmol, 1.1 eq.); 860 mg (1.26 mmol, 85%) red

C₂₃H₃₄F₆FeNO₄PS₂(653.47 g mol⁻¹) C 42.27, H 5.24, N 2.14%; oil. Anal. calc. for C₂₅H₃₈F₆FeNO₄PS₂(681.51 g mol⁻¹) C 44.06,

found C 42.48, H 5.35, N 2.35%. ³¹P{¹H} NMR (121.5 MHz, H 5.62, N 2.06%; found C 44.39, H 5.69, N 2.30%. ³¹P{¹H}

1

CDCl₃): δ = 31.8 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.97 (t, NMR (121.5 MHz, CDCl₃): δ = 29.9 ppm; H NMR (300.1 MHz,

3

4

3

³J_HH= 6.9 Hz, 6H, H-1a), 1.15 (dt, J_HH= 7.2 Hz, J_HP= 1.5 Hz, CDCl₃): δ = 0.88 (t, J_HH= 6.9 Hz, 9H, H-1a), 1.23–1.35 (m, 8H,

2

3H, H-1b), 1.46–1.57 (m, 8H, H-2a, H-3a), 1.60–1.72 (m, 2H, H-2a, H-3a), 1.40–1.60 (m, 8H, H-4a, H-5a), 2.07 (d, J_PH

=

H-2b), 2.22–2.32 (m, 6H, H-4a, H-3b), 4.36 (s, 5H, H_Cp′), 4.53 13.2 Hz, 3H, H-1b), 2.16–2.34 (m, 4H, H-6a), 4.37 (s, 5H, H_Cp′),

3

(q, J_HH= 1.89 Hz, 2H, H_Cp), 4.75 (q, J_HH= 1.9 Hz, 2H, H_Cp

)

4.55 (q, J_HH= 1.8 Hz, 2H, H_Cp), 4.74 (q, J_HH= 1.8 Hz, 2H,

ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = 13.3 (s, C-1a), 15.3

H

_Cp) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = 6.6 (d, J_CP

=

1

3

2

(d, J_CP= 16.7 Hz, C-1b), 15.9 (d, J_CP= 4.4 Hz, C-2b), 21.3 (d, 57.3 Hz, C-1b), 13.8 (s, C-1a), 21.8 (d, J_CP= 4.3 Hz, C-5a),

¹J_CP= 51.0 Hz, C-4a), 23.5 (d, J_CP= 50.7 Hz, C-3b), 23.7 (d, 22.3 (s, C-2a), 23.1 (d, J_CP= 51.9 Hz, C-6a), 30.1 (d, J_CP

=

1

3

²J_CP= 15.7 Hz, C-3a), 24.0 (d, J_CP= 4.5 Hz, C-2a), 59.2 (d, 15.4 Hz, C-4a), 30.9 (s, C-3a), 59.8 (d, J_CP= 95.9 Hz, C_Cp,ipso),

3

1

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70.3 (s, C_Cp′), 71.1 (d,

J

CP

= 12.2 Hz, C_Cp), 73.9 (d, 1134 (s), 1111 (s), 1048 (vs), 1034 (s), 998 (m), 911 (w), 841 (m),

2/3

J

= 10.1 Hz, C_Cp), ppm, CF₃-resonance has not been 830 (m), 789 (m), 759 (m), 749 (m), 739 (m), 726 (s), 693 (s),

CP

obtained; ¹⁹F NMR (282.4 MHz, CDCl₃): δ = −78.7 ppm. MS 613 (w), 563 (s), 532 (s), 513 (s), 492 (s), 460 (m), 447 (m). E_1/2

(ESI+, MeOH) m/z (%) = 401.2052 (100, [M − NTf₂]⁺requires ([EMIM]NTf₂) = 523 mV vs. Fc/Fc⁺.

401.2054); MS (ESI−, MeOH) m/z (%) = 279.9177 (100, [NTf₂]⁻

1,1′-Bis(diphenylmethyl)ferrocendiylphosphonium bis(tri-

requires 279.9178). IR (neat): ν = 3108 (w), 2957 (m), 2931 (m), fluoromethanesulfonyl)imide (5j) [Fc(PPh₂Me)₂][NTf₂]₂. 5j

2862 (m), 1466 (w), 1415 (w), 1347 (s), 1331 (s), 1225 (m), was prepared according to method B. dppf (400 mg,

1177 (vs), 1134 (s), 1108 (m), 1052 (s), 1004 (m), 912 (m), 0.72 mmol, 1.0 eq.) and MeNTf₂(425 mg, 1.44 mmol, 2.0 eq.);

882 (m), 830 (m), 787 (m), 761 (m), 738 (m), 652 (m), 614 (s), 643 mg (0.56 mmol, 78%) pale brown solid. Anal. calc. for

599 (s), 569 (s), 510 (s), 485 (m), 407 (w). E_1/2([EMIM]NTf₂) = C₄₀H₃₄F₁₂FeN₂O₈P₂S₄(1144.74 g mol⁻¹) C 41.97, H 2.99, N

453 mV vs. Fc/Fc⁺.

2.45%; found C 42.02, H 3.07, N 2.60%. ³¹P{¹H} NMR

Diphenylmethylferrocenylphosphonium bis(trifluorometha- (121.5 MHz, CD₃CN): δ = 21.9 ppm; ¹H NMR (300.1 MHz,

2

3

nesulfonyl)imide (5h) [FcPPh₂Me]NTf₂. 5h was prepared CD₃CN): δ = 2.59 (d, J_PH= 13.8 Hz, 6H, H-1b), 4.60 (q, J_HH

=

3

according to method B. 2d (507 mg, 1.37 mmol, 1.0 eq.) and 1.9 Hz, 4H, H_Cp), 4.80 (q, J_HH= 1.9 Hz, 4H, H_Cp), 7.55–7.71

MeNTf₂(485 mg, 1.64 mmol, 1.2 eq.); 875 mg (1.32 mmol, (m, 16H, H_o-Ph, H_m-Ph), 7.81–7.87 (m, 4H, H_p-Ph) ppm; ¹³C{¹H}

96%) red oil. Anal. calc. for C₂₅H₂₂F₆FeNO₄PS₂(664.39 g NMR (75.5 MHz, CD₃CN): δ = 8.5 (d, ¹J_CP= 60.4 Hz, C-1b), 65.1

mol⁻¹) C 45.13, H 3.33, N 2.11%; found C 45.46, H 3.34, (d, ¹J_CP= 101.6 Hz, C_Cp,ipso), 75.3 (d, ^2/3J_CP= 12.4 Hz, C_Cp), 77.4

N 2.37%. ³¹P{¹H} NMR (121.5 MHz, CD₃CN): δ = 22.6 ppm; H (d,

J

= 10.2 Hz, C_Cp), CF₃resonance overlain by CD₃CN-

CP

1

2/3

2

1

2

NMR (300.1 MHz, CD₃CN): δ = 2.73 (d, J_PH= 13.8 Hz, 3H, signal, 121.4 (d, J_CP= 91.0 Hz, C_Ph,ipso), 131.0 (d, J_CP

=

3

4

H-1b), 4.25 (s, 5H, H_Cp′), 4.59 (q, J_HH= 1.9 Hz, 2H, H_Cp), 4.89 13.1 Hz, C_o-Ph), 133.4 (d, J_CP= 11.0 Hz, C_m-Ph), 136.1 (d, J_CP

3

(q, J_HH= 1.9 Hz, 2H, H_Cp), 7.64–7.72 (m, 8H, H_o-Ph, H_m-Ph), 3.0 Hz, C_p-Ph) ppm; ¹⁹F NMR (282.4 MHz, CD₃CN): δ =

7.79–7.86 (m, 2H, H_p-Ph) ppm; ¹³C{¹H} NMR (75.5 MHz, −80.9 ppm. MS (ESI+, MeOH) m/z (%) = 292.0732 (100, [M −

1

CD₃CN): δ = 9.5 (d, J_CP= 61.6 Hz, C-1b), 61.1 (d, J_CP

105.0 Hz, C_Cp,ipso), 71.5 (s, C_Cp′), 73.6 (d,

=

(NTf₂)₂]²⁺requires 292.0737), 864.0654 (47, [M − (NTf₂)]⁺

= 13.2 Hz, C_Cp), requires 864.0653); MS (ESI−, MeOH) m/z (%) = 279.9178 (66,

2/3

J

CP

2/3

1

75.7 (d,

J

CP

= 10.8 Hz, C_Cp), 120.9 (q, J_CF= 320.9 Hz, CF₃), [NTf₂]⁻requires 279.9178). IR (neat): ν = 3109 (w), 3010 (w),

1

2

122.7 (d, J_CP= 90.7 Hz, C_Ph,ipso), 130.8 (d, J_CP= 12.8 Hz, 2932 (w), 1486 (w), 1440 (m), 1420 (w), 1397 (w), 1349 (s),

3

4

C

_o-Ph), 133.4 (d, J_CP= 10.8 Hz, C_m-Ph), 135.6 (d, J_CP= 3.0 Hz, 1179 (vs), 1138 (s), 1111 (s), 1049 (s), 997 (m), 896 (m), 865 (m),

_p-Ph) ppm; ¹⁹F NMR (282.4 MHz, CD₃CN): δ = −79.4 ppm. MS 838 (m), 786 (m), 753 (m), 740 (m), 719 (m), 687 (m), 608 (s),

(ESI+, MeOH) m/z (%) = 385.0794 (100, [M − NTf₂]⁺requires 568 (s), 536 (m), 511 (m), 483 (m), 464 (m), 443 (m), 424 (m).

385.0803); MS (ESI−, MeOH) m/z (%) = 279.9178 (61, [NTf₂]⁻E_1/2([EMIM]NTf₂) = 983 mV vs. Fc/Fc⁺.

requires 279.9178). IR (neat): ν = 3103 (w), 3064 (w), 3000 (w),

Preparation of methyl bis(trifluoromethanesulfonyl)imide

2925 (w), 1439 (m), 1416 (w), 1348 (s), 1330 (s), 1176 (vs), (6) MeNTf₂. Method A: 570 mg methyl iodide (4.02 mmol,

1133 (vs), 1110 (s), 1050 (vs), 998 (m), 895 (m), 881 (m), 1.0 eq.) was condensed onto 2.00 g silver bis(trifluoromethane-

833 (m), 785 (m), 740 (s), 718 (m), 689 (s), 652 (m), 609 (s), sulfonyl)imide (5.15 mmol, 1.3 eq.). The reaction mixture was

568 (s), 538 (s), 510 (m), 465 (s), 443 (m). E_1/2([EMIM]NTf₂) = stirred for 12 h at ambient temperature. The crude product

504 mV vs. Fc/Fc⁺.

was cleaned by recondensation. The desired product (984 mg,

Triphenylferrocenylphosphonium bis(trifluoromethanesul- 3.33 mmol, 83%) was achieved as a colorless liquid. Method B:

fonyl)imide (5i) [FcPPh₃]NTf₂. 5i was prepared according to 4.76 g silver nitrate (28.0 mmol, 1.11 eq.) was dissolved in a

method C. 8a (230 mg, 0.70 mmol, 1.0 eq.) and [(C₅H₅)Fe(η⁶- minimum amount acetonitrile and added to 8.04 g lithium

toluene)]NTf₂(379 mg, 0.70 mmol, 1.0 eq.); 490 mg bis(trifluoromethanesulfonyl)imide (28.0 mmol, 1.11 eq.) dis-

(0.67 mmol, 96%) yellow solid. Anal. calc. for C₃₀H₂₄F₆Fe- solved in a minimum amount acetonitrile. The reaction

NO₄PS₂(727.46 g mol⁻¹) C 49.53, H 3.33, N 1.93%; found C mixture was stirred at ambient temperature for 2 h and the

49.31, H 3.33, N 2.16%. ³¹P{¹H} NMR (121.5 MHz, CDCl₃): δ = solvent was removed in a vacuum at 50 °C. The in situ gener-

1

28.1 ppm; H NMR (300.1 MHz, CDCl₃): δ = 4.15 (s, 5H, H_Cp′), ated [Ag(MeCN)₄]₂[Ag(NTf₂)₃] was treated slowly at −78 °C with

4.51 (s, 2H, H_Cp), 4.91 (s, 2H, H_Cp), 7.51–7.95 (m, 10H, H_o-Ph

,

3.58 g methyl iodide (25.2 mmol, 1.0 eq.) and stirred at

H

_m-Ph, H_p-Ph) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ = 59.7 ambient temperature for 12 h. The crude product was cleaned

1

2/3

(d, J_CP= 105.0 Hz, C_Cp,ipso), 71.0 (s, C_Cp′), 74.2 (d,

J

CP

=

by distillation under ambient pressure to obtain 4.73 g 6

(16.02 mmol, 57%). ¹H NMR (300.1 MHz, C₆D₆): δ = 2.61 (s,

2/3

1

13.1 Hz, C_Cp), 75.0 (d,

J

= 10.9 Hz, C_Cp), 120.0 (d, J_CP

CP

91.9 Hz, C_Ph,ipso), 130.4 (d, J_CP= 12.9 Hz, C_o-Ph), 133.5 (d, 3H, Me); ¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = 38.1 (s, Me),

2

³J_CP= 10.5 Hz, C_m-Ph), 135.4 (d, J_CP= 2.7 Hz, C_p-Ph) ppm, CF₃- 119.4 (q, ¹J_CF= 324.0 Hz, CF₃); ¹⁹F NMR (C₆D₆) δ = −73.9 ppm.

4

resonance has not been obtained; ¹⁹F NMR (282.4 MHz, IR (neat): ν = 1448 (s), 1419 (s), 1337 (w), 1203 (vs), 1117 (vs),

CDCl₃): δ = −77.8 ppm. MS (ESI+, MeOH) m/z (%) = 447.0964 1042 (m), 834 (vs), 767 (m), 688 (m), 598 (vs), 568 (s), 501 (vs)

(100, [M − (NTf₂)]⁺requires 447.0960); MS (ESI−, MeOH) m/z cm⁻¹

(%) = 279.9179 (13, [NTf₂]⁻requires 279.9178). IR (neat): ν =

.

Preparation of [iron-cyclopentadienyl-η⁶-benzene]bis(tri-

3106 (w), 3065 (w), 1588 (w), 1485 (w), 1439 (m), 1414 (w), fluoromethanesulfonyl)imide (7a) [(C₅H₅)Fe(η⁶-C₆H₆)]NTf₂.

1394 (w), 1348 (s), 1331 (s), 1221 (m), 1194 (s), 1175 (vs), 1.48 g ferrocene (7.95 mmol, 1.0 eq.), 4.24 g AlCl₃(33.2 mmol,

3762 | Dalton Trans., 2014, 43, 3750–3766

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Dalton Transactions

Paper

4.2 eq.) and 215 mg aluminium powder (7.95 mmol, 1.0 eq.) 1276 (w), 1225 (m), 1094 (m), 1037 (s), 1007 (m), 969 (w),

were suspended in 25 mL benzene and heated to reflux for 889 (m), 791 (m), 701 (s), 612 (m), 531 (w), 504 (m), 469 (m),

1 h. 0.2 mL water (11.1 mmol, 1.4 eq.) was added at ambient 441 (w) cm⁻¹

.

temperature and subsequently heated again to reflux for 12 h.

Preparation of dibutylcyclopentadienyl phosphine (9).

The reaction mixture was hydrolysed with 40 mL ice water, fil- 1.72 g sodium cyclopentadienide (19.53 mmol, 1.2 eq.) was

tered and washed three times with 20 mL Et₂O. The aqueous suspended in 100 mL n-pentane and treated at 0 °C with

phase was adjusted to an initial pH of 9 using aqueous 2.93 g 1b (16.22 mmol, 1.0 eq.). After stirring at ambient temp-

ammonia, the precipitate was filtered and the solution was erature for 12 h the volume was reduced to half the original

treated with an aqueous solution of 2.28 g lithium bis(trifluoro- volume and filtered. The residue was extracted two times with

methanesulfonyl)imide (7.95 mmol, 1.0 eq.). The resulting 20 mL n-pentane and after removing the solvent in a vacuum

yellow precipitate was filtered and washed with Et₂O and 2.96 g 9 (14.08 mmol, 87%) was obtained as a slightly yellow

n-pentane to obtain 1.57

g

[(C₅H₅)Fe(η⁶-C₆H₆)]NTf₂oil. 9 was isolated as a mixture of three isomers. Dibutylcyclo-

(3.07 mmol, 39%). Anal. calc. for C₁₃H₁₁F₆FeNO₄S₂(479.20 g penta-2,4-dienyl phosphine: ³¹P{¹H} NMR (121.5 MHz, C₆D₆):

mol⁻¹) C 32.58, H 2.31, N 2.92%; found C 32.69, H 2.27, δ = −20.8 ppm (4%); H NMR (300.1 MHz, C₆D₆): δ = 0.83 (t,

1

N 3.10%. ¹H NMR (300.1 MHz, acetone-d⁶): δ = 5.24 (s, 5H, ³J_HH

=

7.0 Hz, 6H, P(CH₂)₃Me), 1.27–1.43 (m, 8H,

H

_Cp), 6.50 (s, 6H, H_arom) ppm; ¹³C{¹H} NMR (75.5 MHz, P(CH₂)₂CH₂Me, PCH₂CH₂Et), 1.45–1.60 (m, 4H, PCH₂ⁿPr),

acetone-d⁶): δ = 77.61 (s, C_Cp), 89.40 (s, C_arom) ppm; ¹⁹F NMR 3.39–3.42 (m, 1H, H_Cp,ipso), 6.46–6.50 (m, 4H, H_α, H_β) ppm; ¹³

C

(282 MHz, acetone-d⁶): δ = −78.9 ppm. MS (ESI+, MeOH) m/z {¹H} NMR (75.5 MHz, C₆D₆): δ = 14.0 (s, P(CH₂)₃Me), 26.3 (d,

(%) = 199.0205 (100, [M − NTf₂]⁺requires 199.0205); MS (ESI−, ³J_CP= 17.7 Hz, P(CH₂)₂CH₂Me), 28.0 (d, J_CP= 11.4 Hz,

1

MeOH) m/z (%) = 279.9179 (60, [NTf₂]⁻requires 279.9178). PCH₂ⁿPr), 29.4 (d, J_CP= 16.8 Hz, PCH₂CH₂Et), 52.7 (d, J_CP

=

2

1

3

2

IR (neat): ν = 3116 (w), 3093 (w), 1450 (w), 1422 (w), 1348 (s), 24.0 Hz, C_Cp,ipso), 132.0 (d, J_CP= 3.4 Hz, C_β), 135.1 (d, J_CP

1333 (s), 1177 (s), 1134 (s), 1050 (s), 918 (w), 856 (m), 828 (m), 4.8 Hz, C_α) ppm. Dibutylcyclopenta-1,4-dienyl phosphine: ³¹P

788 (m), 762 (w), 739 (m), 610 (s), 568 (s), 512 (s), 468 (s), {¹H} NMR (121.5 MHz, C₆D₆): δ = −37.5 ppm (68%); H NMR

1

408 (w) cm⁻¹

.

(300.1 MHz, C₆D₆): δ = 0.83 (t, J_HH= 7.0 Hz, 6H, P(CH₂)₃Me),

3

Preparation of tributylcyclopentadienylidene phosphorane 1.27–1.43 (m, 8H, P(CH₂)₂CH₂Me, PCH₂CH₂Et), 1.45–1.60 (m,

(8b). Method A: 1.00 g sodium cyclopentadienide (11.35 mmol, 4H, PCH₂ⁿPr), 2.84–2.87 (m, 2H, C_βH₂), 6.42–6.44 (m, 2H,

3

2/3

1.2 eq.) was suspended in 60 mL n-hexane and treated at 0 °C C_αH), 6.76–6.80 (dquint, J_PH= 5.0 Hz,

J

HH

= 1.5 Hz, C_βH)

with 1.71 g 1b (9.46 mmol, 1.0 eq.). After stirring for 12 h at ppm; ¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = 14.0 (s, P(CH₂)₃Me),

3

1

ambient temperature the resulting suspension was treated 24.7 (d, J_CP= 11.6 Hz, P(CH₂)₂CH₂Me), 28.3 (d, J_CP= 11.0 Hz,

2

3

at 0 °C with 3.7 mL n-butyllithium (2.55M in n-hexane, PCH₂ⁿPr), 28.9 (d, J_CP= 14.1 Hz, PCH₂CH₂Et), 42.8 (d, J_CP

=

2

9.46 mmol, 1.0 eq.) and after stirring for 6 h at 0 °C the reac- 5.0 Hz, C_CpH₂), 133.1 (d, J_CP= 8.0 Hz, C_α), 136.4 (d, J_CP

3

1

tion mixture was treated with 1.94

g 1-bromobutane 2.1 Hz, C_α), 140.2 (d, J_CP= 25.2 Hz, C_β), 147.0 (d, J_CP

(14.19 mmol, 1.5 eq.). The suspension was stirred for 1 d at 19.7 Hz, C_Cp,ipso) ppm. Dibutylcyclopenta-1,3-dienyl phosphine:

ambient temperature and after filtration and extraction with ³¹P{¹H} NMR (121.5 MHz, C₆D₆): δ = −40.3 ppm (28%); ¹H

3

four times 10 mL n-hexane and removing the solvent in a NMR (300.1 MHz, C₆D₆): δ = 0.83 (t, J_HH= 7.0 Hz, 6H,

vacuum 1.97 g 8b (7.40 mmol, 78%) was obtained. Method B: P(CH₂)₃Me), 1.27–1.43 (m, 8H, P(CH₂)₂CH₂Me, PCH₂CH₂Et),

948 mg 10 (3.82 mmol, 1.0 eq.) was suspended in 30 mL Et₂O 1.45–1.60 (m, 4H, PCH₂ⁿPr), 2.74–2.78 (m, 2H, C_αH₂) 6.30–6.35

and treated with 576 mg 1-bromobutane (4.20 mmol, 1.1 eq.). (m, 1H, C_αH), 6.52–6.57 (m, 1H, C_βH), 6.59–6.64 (m, 1H, C_βH)

After stirring for

1

d

at ambient temperature the ppm; ¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = 14.0 (s, P(CH₂)₃Me),

3

1

reaction mixture was filtered using a syringe filter (Phenex, 24.7 (d, J_CP= 11.6 Hz, P(CH₂)₂CH₂Me), 27.2 (d, J_CP= 11.1 Hz,

2

PTFE; pore size: 0.45 µm). The solvent was removed in PCH₂ⁿPr), 28.8 (d, J_CP= 13.8 Hz, PCH₂CH₂Et), 43.1 (d, J_CP

=

3

2

a vacuum to obtain 835 mg 8b (3.13 mmol, 82%). Anal. calc. 7.1 Hz, C_αH₂), 133.5 (d, J_CP= 7.6 Hz, C_βH), 133.8 (d, J_CP

for C₁₇H₃₁P (266.40 g mol⁻¹) C 76.64, H 11.73%; found 3.3 Hz, C_αH), 139.6 (d, J_CP= 23.1 Hz, C_βH), 145.3 (d, J_CP

3

1

C 76.42, H 11.51%. ³¹P{¹H} NMR (121.5 MHz, CDCl₃): δ = 18.0 Hz, C_Cp,ipso) ppm. MS (EI+) m/z = 210.1539 (C₁₃H₂₃P

13.6 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.96 (t, J_HH

=

requires 210.1537). IR (neat): ν = 3091 (w), 3070 (w), 2956 (s),

3

7.2 Hz, 9H, P(CH₂)₃Me), 1.41–1.50 (m, 6H, P(CH₂)₂CH₂Me), 2925 (s), 2871 (m), 2858 (m), 1463 (m), 1416 (m), 1375 (m),

1.52–1.62 (m, 6H, PCH₂CH₂Et), 1.98–2.08 (m, 6H, PCH₂ⁿPr), 1345 (m), 1295 (w), 1260 (w), 1221 (w), 1199 (w), 1092 (m),

6.28–6.31 (m, 2H, H_Cp), 6.33–6.36 (m, 2H, H_Cp) ppm; ¹³C{¹H} 1066 (m), 993 (m), 968 (w), 948 (m), 928 (w), 893 (s), 863 (w),

NMR (75.5 MHz, CDCl₃): δ = 13.4 (s, P(CH₂)₃Me), 23.1 (d, 841 (vw), 810 (m), 788 (m), 717 (m), 678 (s), 585 (m), 463 (w),

¹J_CP= 54.2 Hz, PCH₂ⁿPr), 24.0 (s, P(CH₂)₂CH₂Me), 24.1 (d, 436 (w) cm⁻¹

.

1

²J_CP= 10.5 Hz, PCH₂CH₂Et), 79.2 (d, J_CP= 105.0 Hz, C_Cp,ipso),

Preparation of potassium dibutylphosphinocyclopentadie-

= 16.7 Hz, nide (10). 968 mg 9 (4.60 mmol, 1.0 eq.) was dissolved in

CP

2/3

112.1 (d,

J

CP

= 14.5 Hz, C_Cp), 112.8 (d,

J

C_Cpppm. MS (EI+) m/z

)

= 266.2169 (C₁₇H₃₁P requires 20 mL Et₂O and treated in portions at 0 °C with 599 mg benzyl

266.2163); MS (ESI+, MeOH) m/z (%) = 267.2236 (100, [M + H]⁺potassium (4.60 mmol, 1.0 eq.). After complete addition of

requires 267.2236). IR (neat): ν = 3067 (w), 2956 (m), 2928 (m), benzyl potassium the color of the reaction mixture turned from

2870 (m), 1463 (m), 1437 (m), 1409 (w), 1378 (w), 1345 (w), dark red to slightly orange and a slightly orange precipitate was

Dalton Trans., 2014, 43, 3750–3766 | 3763

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Paper

Dalton Transactions

formed. The residue was filtrated and washed two times

with 10 mL Et₂O and two times with 20 mL n-pentane. After

drying 948 mg 10 (3.82 mmol, 83%) obtained as a colorless

solid. ³¹P{¹H} NMR (121.5 MHz, THF-d⁸): δ = −38.6 ppm; ¹H

Notes and references

1 J. E. F. Weaver, D. Breadner, F. Deng, B. Ramjee,

P. J. Ragogna and R. W. Murray, J. Phys. Chem. C, 2011, 115,

19379–19385.

3

NMR (300.1 MHz, THF-d⁸): δ = 0.93 (t, J_HH= 6.9 Hz, 6H,

P(CH₂)₃Me), 1.29–1.58 (m, 12H, P(CH₂)₂CH₂Me, PCH₂CH₂Et,

2 Y. Gao, B. Twamley and J. M. Shreeve, Inorg. Chem., 2004,

43, 3406–3412.

3 V. O. Nyamori, M. Gumede and M. D. Bala, J. Organomet.

Chem., 2010, 695, 1126–1132; J.-L. Thomas, J. Howarth,

K. Hanlon and D. McGuirk, Tetrahedron Lett., 2000, 41,

413–416.

4 R. Balasubramanian, W. Wang and R. W. Murray, J. Am.

Chem. Soc., 2006, 128, 9994–9995.

5 Y. Miura, F. Shimizu and T. Mochida, Inorg. Chem., 2010,

49, 10032–10040.

n

PCH₂Pr), 5.64–5.69 (m, 2H, H_Cp), 5.76–5.81 (m, 2H, H_Cp

)

ppm; ¹³C{¹H} NMR (75.5 MHz, THF-d⁸):

δ

=

15.1 (s,

3

P(CH₂)₃Me), 26.2 (d, J_CP= 11.6 Hz, P(CH₂)₂CH₂Me), 31.0 (d,

n

2

¹J_CP= 16.1 Hz, PCH₂Pr), 32.7 (d, J_CP= 11.7 Hz, PCH₂CH₂Et),

2/3

108.1 (d,

J

CP

= 7.9 Hz, C_Cp), 111.5 (d,

J

CP

= 18.7 Hz, C_Cp),

1

111.8 (d, J_CP= 1.8 Hz, C_Cp,ipso) ppm. IR (neat): ν = 3059 (w),

2956 (m), 2923 (m), 2871 (m), 2856 (m), 1463 (m), 1432 (m),

1377 (w), 1343 (w), 1202 (w), 1178 (w), 1092 (w), 1029 (m), 967

(w), 889 (w), 779 (m), 729 (s), 716 (s), 644 (m), 496 (w), 472 (m),

446 (w), 425 (w) cm⁻¹

.

6 O. Fontaine, C. Lagrost, J. Ghilane, P. Martin, G. Trippé,

(1-Ferrocenylethyl)tributylphosphonium bis(trifluoromethane-

sulfonyl)imide (11) [FcCHMePBu₃]NTf₂. 350 mg 1-hydroxy-

ethylferrocene (1.52 mmol, 1.0 eq.) was dissolved in 20 mL

chloroform and treated with 430 mg tributylphosphine hydro-

bromide (1.52 mmol, 1.0 eq.) and heated to reflux for 2 h. Sub-

sequently the solvent was removed in a vacuum. The residue

was washed two times with 10 mL Et₂O and two times with

20 mL n-pentane. After drying (1-ferrocenylethyl)tributyl-

phosphonium bromide was obtained as a orange oil. The

bromide and 479 mg LiNTf₂(1.67 mmol, 1.1 eq.) were sus-

pended in a water–methanol mixture (20 mL, 1 : 1) and stirred

at 40 °C for 1 d. The reaction mixture was extracted with 20 mL

C.

Fave,

J.

C.

Lacroix,

P.

Hapiot

and

H. N. Randriamahazaka, J. Electroanal. Chem., 2009, 632,

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135, 4722–4728.

7 J. Langmaier, A. Trojánek and Z. Samec, Electrochem.

Commun., 2010, 12, 1333–1335; J. Langmaier and Z. Samec,

Electrochim. Acta, 2011, 58, 606–613.

8 J. C. Forgie, S. El Khakani, D. D. MacNeil and

D. Rochefort, Phys. Chem. Chem. Phys., 2013, 15, 7713–

7721.

9 G. Rashinkar and R. Salunkhe, J. Mol. Catal. A: Chem.,

2010, 316, 146–152.

portions of DCM until the organic phase does not turn orange. 10 T. Inagaki and T. Mochida, Chem. Lett., 2010, 39, 572–573;

The solvent was removed in a vacuum and the received crude

product was washed two times with 10 mL Et₂O. After drying

681 mg 11 (0.98 mmol, 64%) was obtained as a orange

Y. Funasako, T. Inagaki, T. Mochida, T. Sakurai, H. Ohta,

K. Furukawa and T. Nakamura, Dalton Trans., 2013, 42,

8317–8327.

oil which solidified after several months. Anal. calc. for 11 A. Chakraborty, T. Inagaki, M. Banno, T. Mochida and

C₂₆H₄₀F₆FeNO₄PS₂(695.54 g mol⁻¹) C 44.90, H 5.80, N 2.01%;

found C 45.17, H 6.15, N 2.07%. ³¹P{¹H} NMR (121.5 MHz,

CDCl₃): δ = 34.7 ppm; ¹H NMR (300.1 MHz, CDCl₃): δ = 0.93 (t,

K. Tominaga, J. Phys. Chem. A, 2011, 115, 1313–1319;

T. Inagaki, T. Mochida, M. Takahashi, C. Kanadani,

T. Saito and D. Kuwahara, Chem.–Eur. J., 2012, 18, 6795–

6804.

³J_HH

= 7.0 Hz, 9H, P(CH₂)₃Me), 1.36–1.48 (m, 12H,

2

3

P(CH₂)₂CH₂Me, PCH₂CH₂Et), 1.74 (dd, J_PH= 16.9 Hz, J_HH

=

12 G. P. Sollott, H. E. Mertwoy, S. Portnoy and J. L. Snead,

J. Org. Chem., 1963, 28, 1090–1092; W. E. McEwen,

J. E. Fountaine, D. N. Schulz and W. I. Shiau, J. Org. Chem.,

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C. Imrie, T. A. Modro and P. H. Van Rooyen, Polyhedron,

1994, 13, 1677–1682.

7.1 Hz, 3H, CHMe), 1.94–2.00 (m, 6H, PCH₂ⁿPr), 3.51–3.58 (m,

1H, CHMe), 4.10 (s, 1H, H_α), 4.25 (s, 6H, H_α, H_Cp′), 4.28 (s, 1H,

H_β), 4.30 (s, 1H, H_β) ppm; ¹³C{¹H} NMR (75.5 MHz, CDCl₃): δ =

1

13.1 (s, P(CH₂)₃Me), 14.2 (s, CHMe), 17.3 (d, J_CP= 44.7 Hz,

PCH₂ⁿPr), 23.6 (d, ³J_CP= 5.0 Hz, P(CH₂)₂CH₂Me), 23.9 (d, ²J_CP

=

1

14.9 Hz, PCH₂CH₂Et), 27.9 (d, J_CP= 41.5 Hz, CHMe), 66.0

(d, J_CP= 0.9 Hz, C_α), 68.8 (d, J_CP= 1.3 Hz, C_α), 69.0 (s, C_β), 13 J. C. Kotz, C. L. Nivert, J. M. Lieber and R. C. Reed,

3

1

69.1 (s, C_β), 69.4 (s, C_Cp′), 82.8 (s, C_Cp,ipso), 120.0 (q, J_CF

=

J. Organomet. Chem., 1975, 91, 87–95.

321.6 Hz, CF₃) ppm; ¹⁹F NMR (282.4 MHz, CDCl₃): δ = 14 D. Guillaneux and H. B. Kagan, J. Org. Chem., 1995, 60,

−79.2 ppm. MS (ESI+, MeOH) m/z (%) = 415.2211 (15, [M −

(NTf₂)]⁺requires 415.2212), 213.0361 (100, [FcCHMe]⁺

requires 213.0361); MS (ESI−, MeOH) m/z (%) = 279.9179

(90, [NTf₂]⁻requires 279.9178). IR (neat): ν = 3099 (w), 2962 (m),

2936 (m), 2876 (m), 1466 (m), 1411 (w), 1383 (w), 1348 (s),

1330 (s), 1225 (m), 1177 (vs), 1134 (s), 1105 (m), 1051 (s),

2502–2505; B. Milde, M. Lohan, C. Schreiner, T. Rüﬀer and

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652 (m), 614 (s), 599 (s), 569 (s), 507 (s), 483 (m), 431 (m).

1913–1920; A. K. Diallo, J. Ruiz and D. Astruc, Org. Lett.,

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E_1/2([EMIM]NTf₂) = 164 mV vs. Fc/Fc⁺.

3764 | Dalton Trans., 2014, 43, 3750–3766

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Dalton Transactions

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[ⁿBu₂(H)P–PⁿBu₂]⁺is not clarified until now. However, it

5251–5254.

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3766 | Dalton Trans., 2014, 43, 3750–3766

Article Doi

Ferrocenyl-phosphonium ionic liquids-synthesis, characterisation and electrochemistry

DOI: 10.1039/c3dt53402b

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