The dichloromethane induced fragmentation of ferrocenylmethyldimethylamine. Mechanistic aspects and crystallographic and electrochemical investigation of the (FcCH2)2NMe2(+) and FcCH2NMe2H(+) ions

Journal of Organometallic Chemistry 570 (1998) 201–218

The dichloromethane induced fragmentation of

ferrocenylmethyldimethylamine. Mechanistic aspects and

crystallographic and electrochemical investigation of the

(FcCH₂)₂NMe₂⁺and FcCH₂NMe₂H⁺ions¹

Rainer F. Winter ^a,*, Gotthelf Wolmersha¨user ^b

^aInstitut fu¨r Anorganische Chemie der Uni6ersita¨t Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany

^bFachbereich Chemie der Uni6ersita¨t Kaiserslautern, Erwin-Schro¨dinger-Str., D-67653 Kaiserslautern, Germany

Received 16 March 1998

Abstract

Ferrocenylmethyldimethylamine, FcCH₂NMe₂, reacts with CH₂Cl₂in either the presence or absence of non-coordinating

counterions to give equimolar amounts of the bis(ferrocenylmethyl)dimethyl ammonium salts (FcCH₂)₂NMe₂⁺X⁻(X⁻=PF₆⁻

,

SbF₆⁻, BPh₄⁻or Cl⁻, 1a–d) and the corresponding protonated ammonium salts FcCH₂NMe₂H⁺which have been isolated as

the SbF₆⁻and Cl⁻salts 2b,d. The reaction proceeds via fragmentation of an intermediate quaternary chloromethylated

ammonium ion to chloromethylferrocene, FcCH₂Cl, and dimethyliminium chloride NMe₂CH₂⁺Cl⁻. The parent amine acts as a

nucleophile toward FcCH₂Cl to give 1a–d and as a base toward NMe₂CH₂⁺to give FcCH₂NMe₂H⁺, NMe₂H and (Me₂N)₂CH₂.

The FcCH₂Cl intermediate is intercepted by NEt₃while KCN or LiH do not successfully compete with FcCH₂NMe₂. A new,

non-toxic, selective, high-yield route to 1d is also presented. Electrochemistry and UV–vis spectroelectrochemistry reveal, that the

two identical redox centers in 1a–d are essentially non-interacting. Individual E_1/2values have been determined for different

solvents by digital simulation. The corresponding ferrocenium salts were prepared by either chemical or electrochemical means

and accordingly characterized. Our studies are augmented by X-ray structure analyses of 1b, 1d and 2d. 1d contains three different

cation conformers and four molecules of water per unit cell. The latter are hydrogen bonded to the chloride counterions to form

Keywords: Ferrocenes; Ferrocenium salts; Dichloromethane; Desamination; Voltammetry; X-ray structures

1. Introduction

cenylmethyldimethylamine, FcCH₂NMe₂, as an addi-

tional reversible redox center into such molecules. An

inseparable variety of phosphorus containing products

was, however, obtained from which the binuclear am-

monium ion (FcCH₂)₂NMe₂⁺was isolated as an orange

solid. This was our incentive for initiating an in-

depth study of the reactivity of FcCH₂NMe₂with

CH₂Cl₂itself.

The fact that certain amines are reactive toward

CH₂Cl₂, and the factors governing their reactivity, have

already been well established [2,3]. N-methylated tertiary

amines of sufﬁcient nucleophilicity readily give the Men-

schutkin reaction and form crystalline chloromethylam-

monium salts which directly precipitate from solution

We have recently reported that the putative cationic

ruthenium butatrienylidene intermediate [Ru]ꢀCꢀCꢀ

CꢀCH₂⁺may be trapped with tertiary amine nucleo-

philes to give novel Ru-ammoniobutenynyl complexes

[Ru]–CꢁC–C(NR₃)ꢀCH⁺₂PF₆⁻([Ru]=trans-Ru(dppm)₂

Cl, R=Et, Pr) in CH₂Cl₂as solvent [1]. Following this

line of work we have attempted to incorporate ferro-

* Corresponding author. Tel.: +49 711 6854193; fax: +49 711

6854165; e-mail: winter@iac.uni-stuttgart.de

¹Dedicated to Professor Dr Otto J. Scherer on the occasion of his

65th birthday.

PII S0022-328X(98)00866-3

202

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

[2–5]. With secondary amines the reaction is more

complex. The corresponding hydrochlorides and bis(di-

amino)methylene derivatives (aminals) are the most

frequently encountered products and usually both are

found in the crude reaction mixture. It has been con-

cluded that both evolve from N-methylene iminium

intermediates R₂NꢀCH₂⁺which, under the reaction

conditions, cannot directly be detected [2,6]. This

thought is supported by the frequent observation of

typical Mannich products as minor or even the major

components. More recently the reaction of secondary

amines with CH₂Cl₂has evolved into a stratagem for

the in situ preparation of iminium salts and their con-

version to Mannich products [7–9].

aimed at attaching the ferrocenylmethyldimethylamine

nucleophile (FcCH₂NMe₂) as a reversible redox center

to the electrophilic C_kof an in situ prepared

[Ru]ꢀCꢀCꢀCꢀCH₂⁺intermediate ([Ru]=trans-Ru-

Cl(dppm)₂,

dppm=bis(diphenylphosphino)methane)

[1,12]. (FcCH₂)₂NMe₂⁺SbF₆⁻(1b) proved to be the only

isolable compound and was subsequently characterized

by NMR, IR and UV–vis spectroscopy as well as by C,

H, N analysis. Made curious by this unexpected out-

come we decided to investigate this reaction in more

detail. To these ends we ﬁrst reacted the parent amine

FcCH₂NMe₂with a suspension of NaSbF₆or NaPF₆in

CH₂Cl₂under ambient conditions. 1b and 1a were

readily identiﬁed and isolated as one of the two prod-

ucts detected by NMR investigation of the crude reac-

tion mixture. We were now concerned that the

chemically somewhat unstable suspensions of hex-

aﬂuoro-ate anions in CH₂Cl₂, and more speciﬁcally, the

ﬂuoride liberated upon their decomposition [13] might

be involved in this process and therefore turned to the

BPh₄⁻anion. When FcCH₂NMe₂was treated with

NaBPh₄in CH₂Cl₂, (FcCH₂)₂NMe₂⁺BPh₄⁻(1c) was

obtained in good yield as an orange, analytically pure

precipitate. The mother liquor still contained some 1c

and again the same by-product as in the case of 1a,b as

detected by NMR. All our initial attempts to isolate

this second component by crystallization from

chlorobenzene or chlorobenzene/CH₃CN mixtures

failed and lead to either pure 1a–c, mixtures of the two

products or, especially upon warming, decomposition

as indicated by the precipitation of some dark brown

insoluble powder.

The ammonium cations present in 1a–c exhibit es-

sentially identical spectroscopic properties and, in their

IR spectra, besides identical absorptions of the cation

those of the respective counterion. Integration of the

¹H-NMR signals indicates that in 1a–c NMe and fer-

rocenylmethyl groups are present in a 1:1 ratio. While

all signals are shifted downﬁeld with respect to the

parent amine this effect is most pronounced for the

methyl and methylene groups which are directly at-

tached to nitrogen (see Table 1). The same holds for

the ¹³C resonances with the notable exception of the

ipso carbon of the substituted ferrocene ring which in

contrast is shifted by more than 11 ppm toward a

higher ﬁeld. All carbon atoms directly attached to

nitrogen are split into non-binomial triplets with cou-

plings to the ¹⁴N nucleus that amount to 4.4 Hz for

the NMe groups and 2.2 Hz for the CH₂units of the

ferrocenylmethyl moiety. Such splitting patterns are

characteristic of quaternary ammonium ions [14]. The

UV–vis spectra may be regarded as archetypical of

the ferrocenyl chromophore with molar absorptivities

that are approximately twice as high as for derivatives

with only one ferrocenyl moiety per molecule [15]

(Table 1). While these observations left little doubt

In the course of our investigations we became aware

that we had discovered a highly unusual CH₂Cl₂in-

duced fragmentation of

a tertiary organometallic

amine. Equal proportions of the binuclear

(FcCH₂)₂NMe₂⁺and the protonated starting material

FcCH₂NMe₂H⁺are formed in the overall process. It

should be noted that none of these cations is really new.

The protonated amine is easily available from the reac-

tion with an appropriate dilute acid [10] whereas

(FcCH₂)₂NMe₂⁺Br⁻has already been obtained by the

von Braun cleavage reaction of the parent amine (i.e. its

reaction with BrCN) [11]. Thus, it is not the products

but rather the underlying reaction pathway relating

them that constitutes the novelty of our ﬁndings. As we

will point out, the bis(ferrocenyl-methyl)dimethyl am-

monium salt results from the fragmentation of a qua-

ternary chloromethyl ammonium intermediate and the

subsequent trapping of the liberated FcCH₂Cl by the

parent amine. In addition we have investigated two of

the (FcCH₂)₂NMe₂⁺salts as well as the hydrochloride

FcCH₂NMe₂H⁺Cl⁻by X-ray structure analyses. Re-

markably, (FcCH₂)₂NMe₂⁺Cl⁻·4/3H₂O contains pairs

of three different cation conformers and eight molecules

of water that are hydrogen bonded to the Cl⁻counter-

ions per unit cell. Our studies are augmented by electro-

chemical investigations which reveal two very weakly

coupled, reversible redox centers in (FcCH₂)₂NMe₂⁺

and its reductively induced fragmentation as well as the

cathodic deprotonation of the hydrochloride. The radi-

cal tri- or dications have also been prepared and inves-

tigated by ESR and UV–vis spectroscopy. In addition

an alternative, non-toxic, high-yield route to (FcCH₂)₂

NMe₂⁺Cl⁻has been elaborated.

2. Results and discussion

2.1. Formation of the bis( ferrocenylmethyl)dimethyl

ammonium salts (FcCH₂)₂NMe⁺₂X⁻(X⁻=PF⁻₆,

SbF⁻₆, BPh⁻₄(1a–c))

Our entry into this chemistry came from a reaction

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

203

204

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Scheme 1.

as to the identity of 1a–c the ﬁnal proof came from an

X-ray analysis of 1b (vide infra).

of the parent amine and excess NaSbF₆for 2 days in this

solvent an orange suspension gradually formed. After

workup a pure compound was obtained which proved to

be identical with the as yet unidentiﬁed second product

of the CH₂Cl₂reaction. It was ﬁnally characterized as the

protonated ammonium salt FcCH₂NMe₂H⁺SbF₆⁻(2b).

The hydrochloride 2d was similarly obtained in the

absence of NaSbF₆. For comparison purposes with 1b its

molecular structure in the solid state was established by

X-ray structure analysis (vide infra). The same reaction

was also observed in the considerably less acidic CH₃CN

and CH₃NO₂, albeit on a much longer time scale (ca. 1

2.2. In6estigations into the reaction mechanism

The identical outcome of all reactions regardless of the

speciﬁc counterion ﬁnally brought the role of the solvent

into focus. We indeed observed the same reaction as

above upon stirring the parent amine in neat CH₂Cl₂. The

crude product contained a second component with

identical NMR signals as before but again only the

chloride salt 1d was obtained in moderate yield by

crystallization from chlorobenzene/CH₃CN mixtures.

This spurred our curiosity whether this reaction is unique

for CH₂Cl₂. In only a brief survey we found that

ferrocenylmethyldimethylamine possesses a long term

stability in methanol, while it is reactive toward CHCl₃,

CH₃CN and CH₃NO₂. The reaction with CHCl₃proved

to be of special signiﬁcance to us. Upon stirring a mixture

1

week). In their H-NMR-spectra 2b,d exhibit resonance

signals of N-methyl and ferrocenylmethyl groups in a 2:1

integral ratio. All signals are shifted to a lower ﬁeld with

respect to the parent amine. This also holds for the

¹³C-NMR spectra with again the exception of the ipso

carbon of the substituted ferrocenyl ring and, remark-

ably, the NMe groups for which, in turn, signiﬁcant

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

205

upﬁeld shifts are observed (Table 1). In 2b,d the methyl

and methylene carbons appear as singlets without any

detectable coupling to nitrogen. The NH proton gives

rise to a weak, rather broad signal in the ¹H-NMR

spectrum and a band at 3235 cm⁻¹in the IR (KBr)

spectrum. UV–vis spectra of 2b,d are very similar to

1a–d but with roughly only half the molar absorptivity.

Having identiﬁed both products we then found that

these were present in basically equal amounts in each of

the crude reaction mixtures obtained from CH₂Cl₂. This

was further substantiated by following the conversion of

ferrocenylmethyldimethylamine to 1d and the hydro-

chloride 2d by means of in situ NMR spectroscopy in

CD₂Cl₂. Within 30 min the signals of the binuclear

(FcCH₂)₂NMe₂⁺ion were discernible and slowly in-

creased in intensity. The progress of the reaction was

accompanied by a continuous downﬁeld shift of the

signals pertinent to the starting material indicating the

concomitant formation of its conjugate acid and the

appearance of new signals in the aliphatic region of the

¹H- and ¹³C-NMR spectra. Two additional small triplet

signals for the Cp-protons of a ring substituted ferrocene

were observed at l=4.77 and 4.60 ppm with a coupling

constant of 1.96 Hz as well as a signal in the ¹³C-NMR

at l=70.4 ppm which we tentatively attribute to the

elusive chloromethylferrocene (vide infra). We also noted

a distinct broadening of the methyl resonance of the

FcCH₂NMe₂/FcCH₂NMe₂H⁺exchange signal, espe-

cially at some intermediate stage. This signal also ap-

peared to be of larger intensity, as expected, and to be

slightly shifted with respect to the pure compound. After

about 3 days the reaction had gone to completion as

indicated by the constant shift values and integral ratios

of the individual components in the reaction mixture. 1d

and 2d were indeed formed in essentially equimolar

amounts.

starting material to its conjugate acid. The feasibility of

this step was suggested to us by previous ﬁndings in-

dicating that the iminium ion reacts with amines with a

pK_asmaller than 10.8 by deprotonation but usually adds

to tertiary amines of lower basicity and low steric demand

to give monoquaternary salts of monoalkylated aminals

Me₂NCH₂NR₃⁺[19]. While ferrocenylmethyldimethyl-

amine (pK_ain H₂O=9.84 [20], but note that the pK_ain

media of low dielectric constant may be signiﬁcantly

lower [21]) still lies below this limit, the formation of

FcCH₂NMe₂H⁺presents clear evidence that in our case

deprotonation occurs. Bis-(N,N-dimethylamino)me-

thane, dimethylamine and 1,2-bis(dimethylamino)ethene

have been identiﬁed as deprotonation products of the

iminium salt [19] and this ﬁnally reminded us of the small

additional signals in the aliphatic region that we had

noted during our in situ NMR spectroscopic investiga-

tions.

In order to lend more credibility to this ﬁnal reaction

step and to positively identify the products arising from

the proposed iminium intermediate we independently

synthesized Me₂NꢀCH₂⁺Cl⁻and checked its reaction

with equimolar amounts of FcCH₂NMe₂. Upon mixing,

the iminium chloride which is only sparingly soluble in

CD₂Cl₂gradually dissolves, forming an orange suspen-

sion. At no time did the supernatant exhibit the charac-

1

teristic low ﬁeld H and ¹³C signals of the iminium ion

[18,19] and only the resonances of the FcCH₂NMe₂/

FcCH₂NMe₂H⁺couple and a small additional proton

signal at 2.32 ppm, a region typical for aliphatic amines,

were observed. When this reaction was monitored in

CD₃CN which dissolves the iminium salt, the low ﬁeld

signals of Me₂NꢀCH₂⁺immediately disappeared upon

addition of FcCH₂NMe₂. In CD₂Cl₂the NMe groups of

the equilibrated ferrocenylamine and its conjugate acid

again appeared as a broad signal of higher intensity than

expected by integration of the remaining signals. Fur-

thermore, all resonances of the FcCH₂NMe₂H⁺salt in

the fully equilibrated NMR sample were shifted slightly

upﬁeld with respect to those of pure isolated samples

recorded under otherwise identical conditions. The ¹³C-

NMR signals ﬁnally lead to the identiﬁcation of bis(N,N-

dimethylamino)methane and dimethylamine in the

reaction mixture [22]. The aminal gave somewhat broad-

ened signals at l=87.6 and 44.3 ppm for the methylene

and N-methyl groups, respectively. Both are shifted

downﬁeld compared to those of an authentic sample. The

broadening of all signals as well as the opposite direction

of the shifts for the aminal and the FcCH₂NMe₂H⁺salt

indicate that these components engage in an acid/base

equilibrium as indicated in Eq. (1). This was indeed

shown to be the case by NMR spectroscopy. Upon

addition of increasing amounts of Me₂NCH₂NMe₂to a

solution of FcCH₂NMe₂H⁺in CD₂Cl₂all signals are

shifted just in the manner indicated above.

Scheme 1 outlines an overall mechanism which is in

accordance with all our observations. The initial, and

obviously rate determining step [3,6] is the nucleophilic

attack of the amine on the electrophilic carbon atom of

the CH₂Cl₂solvent molecule which has been attributed

a carbonyl like character [3]. This step, the so called

Menschutkin reaction, has ample literature precedent

[2–5,14]. Unlike any other case known to us, the resulting

quaternary

chloromethyldimethylammonium

salt

[FcCH₂NMe₂CH₂Cl]⁺Cl⁻(A) is unstable and breaks

down liberating chloromethylferrocene. Its subsequent

reaction with a molecule of the starting material to give

1a–d is also a key step of the original high yield synthesis

of (FcCH₂)₂NMe₂⁺Br⁻[11]. Let us now turn to the

second fragment resulting from the decomposition of A.

From stoichiometry reasons we were soon pointed to

N,N-dimethylchloromethyl amine which, according to

the literature, is more adequately described as the

iminium chloride Me₂NꢀCH₂⁺Cl⁻[16–18]. If so, this

compound must be acidic enough to protonate the

When the reaction between equimolar amounts of

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R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Me₂NꢀCH₂⁺Cl⁻and FcCH₂NMe₂was investigated in

more detail one further side process was uncovered. The

orange solid obtained from treating the equilibrated

mixture with Et₂O consists of an approximately 20:1

2.3. Attempted trapping of the FcCH⁺₂intermediate

with other nucleophiles

Having proposed the intermediacy of chloromethylfer-

rocene (Scheme 1) we were now striving to trap this

species with nucleophiles other than the parent amine.

Attempts to employ LiH, NaBH₄or KCN were, how-

ever, not met by success. Instead, (FcCH₂)₂NMe₂⁺Cl⁻

(1d) and the hydrochloride 2d were isolated in good to

excellent yields after chromatographic workup of the

crude reaction mixtures. Since CH₃CN/H₂O mixtures

were employed as eluants the isolated samples of 1d all

contain variable amounts of water as shown by a broad

signal in the ¹H-NMR at l=2.20–2.25 ppm and a

broad, very intense, structured absorption band in the

3600–3300 cm⁻¹region in the IR spectra. Both are

absent in water free samples of 1d. Moreover, small shift

differences as compared to water free samples are found

in the NMR spectra (see Table 1). Thus, they are best

formulated as 1d·nH₂O with n ranging from 1 to 3.

Orange-brown crystals grown from one of these samples

were also investigated by X-ray analysis (vide infra).

Remarkably, samples of 2d obtained by this protocol do

not incorporate water. During workup, traces of a low

polarity ferrocene derivative were noted in each case.

They exhibit the same NMR signals as those found

during our in situ experiments (¹H: l=4.78, 4.63 (each

mixture

of

FcCH₂NMe₂H⁺Cl⁻

(2d)

and

(FcCH₂)₂NMe₂⁺Cl⁻(1d). In the above NMR experi-

ment, the signals of 1d are masked by the shifted,

broadened signals of 2d. To explain this ﬁnding one must

additionally envoke the reaction outlined in Eq. (2). This

side process must also be operative in the overall reaction

of the parent amine with CH₂Cl₂and is consequently

added in Scheme 1. We could, however, obtain no ﬁrm

evidence for the formation of bis(dimethylamino)ethene.

If formed at all, it is most probably only a minor

component [19] and may be obscured by other resonance

signals.

FcCH₂NMe₂H⁺+Me₂NCH₂NMe₂

X FcCH₂NMe₂+Me₂NCH₂NMe₂H⁺

(1)

NMe₂CH₂⁺+2FcCH₂NMe₂

Me₂NCH₂NMe₂+(FcCH₂)₂NMe₂⁺

(2)

Let us now discuss some of the more immediate

implications of the overall conversion. First, regarding

the reactions of similar amines with dihalomethane

solvents, ferrocenylmethyldimethylamine sticks out as

highly unusual in that its quaternary chloromethylam-

monium salt (intermediate A in Scheme 1) readily frag-

ments into chloromethylferrocene, FcCH₂Cl, and

N,N-dimethyliminium chloride, even under ambient con-

ditions. In contrast, the corresponding trimethylammo-

nium ion FcCH₂NMe₃⁺is perfectly stable, its iodide

being commercially available in large quantities. While

this compound has evolved into a key synthon for the

synthesis of substituted ferrocenes FcCH₂R [23], it is

revealing to note that the conditions required to substi-

tute the NMe₃group are rather harsh compared to those

applied in our case. Obviously the substitution of one

proton by a chlorine atom is sufﬁcient to destabilize the

quaternary ammonium ion toward fragmentation. Both

fragments may be regarded as rather high energy

molecules. In fact, FcCH₂Cl is a rather labile ferrocene

derivative known as a source of the resonance stabilized

ferrocenylmethylene cation FcCH₂⁺[24,25]. Its Diels-

Alder reaction with cyclopentadiene in CH₂Cl₂at −

78°C constitutes the most striking example for such a

behavior [26] and implies that appreciable amounts of the

ferrocenylmethylene cation are formed from FcCH₂Cl

even at low temperatures in low dielectricity media. The

ferrocenylmethylene carbenium ion on the other hand is

an extremely well investigated and easy to prepare species

[27]. Its high intrinsic stability has been ascribed to

resonance effects and the coordination of the exo double

bond to the Fe nucleus in a fulvalenyl type structure [28].

3

2H, J_H–H=1.96 Hz), 4.28 (s, 7H, Cp and CH₂); ¹³C:

75.4, 74.1, 70.4 (C_ipso, C_h,iof the substituted Cp-ring),

70.5 (Cp_unsubst.)) but the low yields and our inability to

crystallize the oily residue precluded their ﬁrm identiﬁca-

tion. We nevertheless believe that these samples are

FcCH₂Cl. Our failure to isolate FcCH₂X (X=H, CN)

from these reactions may be due to either the rather

limited solubility of the applied nucleophile salts in

CH₂Cl₂and/or the higher nucleophilicity of the parent

amine.

We therefore decided to react FcCH₂NMe₂with

CH₂Cl₂in the presence of a 15-fold excess of NEt₃. This

amine reportedly does not react with CH₂Cl₂to an

appreciable extent during the typical time scale of our

experiments [3] but is still a potent nucleophile. Thus, it

may serve as both a trapping reagent and a base [19],

capturing the proton from NMe₂CH₂⁺Cl⁻liberated

upon the fragmentation of A. Indeed, FcCH₂NEt⁺₃SbF₆⁻

(3) was formed beside roughly equal amounts of 1b in

such a competition experiment, further supporting the

mechanism depicted in Scheme 1. Attempts to separate

1b and 3 by column chromatography or fractional

crystallization were unsuccessful but the spectroscopic

data of 3 could nevertheless be established (Table 1).

2.4. A non-toxic, high-yield route to

(FcCH₂)₂NMe⁺₂Cl⁻(1d)

The reactivity of FcCH₂NMe₂toward CH₂Cl₂is very

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

207

(3)

(4)

reminiscent of the von Braun cleavage reaction, which,

Me₂NCH₂NMe₂+CH₃COCl

however, utilizes a much stronger electron acceptor (i.e.

the CN group) than the chloromethyl moiety. The ease

of fragmentation of intermediate A suggested to us that

a similar reaction might be induced by treating

FcCH₂NMe₂with a more powerful electrophile than

CH₂Cl. If chosen properly, such a reaction would then

provide an alternative, high-yield route to the binu-

clear (FcCH₂)₂NMe₂⁺Cl⁻(1d) without the necessity to

employ the toxic BrCN [11], or sacriﬁcing one third of

the starting material with the additional hazzle to sepa-

rate 1d from equimolar amounts of the hydrochloride

2d.

In general, the conversion of aliphatic tertiary amines

to alkyl halides (halo-de-amination) may be effected by

either the von Braun cleavage reaction [29,30], by treat-

ing tertiary amines with phosgene [31] or certain chlo-

roformates ROCOCl ([30,34] or upon heating the

halogenides (preferably the iodides) of quaternary am-

monium salts [35]). The acyl substituent, on the other

hand, is generally too weak an electron acceptor to

induce the de-amination of quaternary salts

R₃NCOR%⁺. One exception are aminals which are

readily cleaved by acetyl chloride [17–19]. This reaction

provides the perhaps most general and easiest access to

iminium salts (Eq. (3)). Since FcCH₂⁺and Me₂NꢀCH₂⁺

are liberated from FcCH₂NMe₂CH₂Cl⁺with excep-

tional ease, we hoped that ferrocenylmethyldimethy-

lamine might parallel the high reactivity of aminals.

As outlined in Eq. (4) our expectations were indeed

met by success. Upon simply adding half an equiva-

lent of acetyl chloride dissolved in Et₂O to a suspen-

sion of FcCH₂NMe₂in the same solvent, the dinu-

clear 1d was obtained as an analytically pure orange

precipitate. The ready availability of acetyl chloride

and its non-toxicity constitute a major advantage over

the original route while providing the same high yield

[11].

Me₂NCH₂⁺Cl⁻+CH₃CONMe₂

2FcCH₂NMe₂+CH₃COCl

(FcCH₂)₂NMe₂⁺Cl⁻+CH₃CONMe₂

2.5. X-ray structural studies of FcCH₂NMe₂H⁺

Cl⁻(2d), (FcCH₂)₂NMe⁺₂SbF⁻₆(1b) and

(FcCH₂)₂NMe⁺₂Cl⁻(1d)

The bis(ferrocenyl-methyl)dimethyl ammonium salts

1b and 1d and the mononuclear hydrochloride 2d were

investigated by X-ray structure analysis. Tables 2 and 3

list the bond lengths and relevant bond angles while

fractional atomic coordinates and U_eqare provided in

Tables S1–S3 in the Supporting Information. ORTEP

plots of the respective cations are depicted in Figs. 1–3.

The molecular structure of the FcCH₂NMe₂H⁺cation

in the chloride salt 2d is very similar to that observed in

either its tetrachlorozincate [39] or B₁₂H₁⁻₂borane clus-

ter salt [40] and also resembles that of the

FcCH₂NMe₃⁺[41–43] and FcCH₂NMe₂Et⁺cations

[44]. As usually found for ferrocene derivatives, the two

carbocyclic ligands are planar and parallel and exhibit a

close to eccliptic conformation (Table 4). The short

˚

NH···Cl distance of 2.18 A suggests the presence of a

˚

rather strong H-bridge and compares well to the 2.13 A

found for NH···O contacts to perchlorate in a ferrocene

with an appended protonated oxoaza crown ether [45].

It is much shorter than the 3.11 A observed in the

tetrachlorozincate salt, where the chloride is part of a

complex counterion and additional hydrogen bonding

˚

to cocrystallized water exists (d_NH···O=2.76 A) [39].

Besides this structural evidence, the relevance of the

NH···Cl interaction in FcCH₂NMe₂H⁺Cl⁻(2d) is

demonstrated by a broad, intense and richly structured

band in the IR that stretches from 2650 to 2350 cm⁻¹

.

This band is shifted to lower energies by a considerable

amount as compared to the analogous SbF₆⁻salt 2b

where a much weaker and sharper absorption band at

3235 cm⁻¹is found instead.

Table 2

Bond distances and selected bond angles for FcCH₂NMe₂H⁺Cl⁻

(2d)

Both, the SbF₆⁻and the Cl⁻salts of

(FcCH₂)₂NMe₂⁺cocrystallize with solvent molecules.

In 1b one rotationally disordered molecule of

chlorobenzene is found for each cation. 1d·4/3H₂O

contains pairs of three different cation conformers

(Z=6) and eight molecules of water in the unit cell.

The four different (FcCH₂)₂NMe₂⁺cations in the struc-

tures of 1b and 1d·4/3H₂O are rather similar. Relevant

structural data are combined in Table 4 such that

related bond parameters appear in the same row. Each

of the cations display a cisoid arrangement of the two

ferrocenyl subunits. The main differences originate

from the interplanar angles between the substituted

cyclopentadienyl ligands (Cp^R) on adjacent Fe atoms.,

Fe(1)–C(1)

Fe(1)–C(2)

Fe(1)–C(3)

Fe(1)–C(4)

Fe(1)–C(5)

Fe(1)–C(6)

Fe(1)–C(7)

Fe(1)–C(8)

Fe(1)–C(9)

Fe(1)–C(10)

C(1)–C(11)

N(1)–C(11)

2.033(2)

2.046(2)

2.050(2)

2.051(2)

2.040(2)

2.045(2)

2.036(2)

2.050(2)

2.045(2)

2.035(2)

1.492(2)

1.503(2)

C(1)–C(2)

C(2)–C(3)

C(3)–C(4)

C(4)–C(5)

C(1)–C(5)

C(6)–C(7)

C(7)–C(8)

C(8)–C(9)

C(9)–C(10)

C(6)–C(10)

N(1)–C(12)

N(1)–C(13)

1.434(2)

1.427(2)

1.424(2)

1.425(2)

1.431(2)

1.425(4)

1.409(4)

1.406(3)

1.408(3)

1.424(3)

1.486(2)

1.485(2)

C(12)–N(1)–C(11) 109.81(12)

C(13)–N(1)–C(11) 112.77(13)

C(12)–N(1)–C(13) 110.9(2)

C(1)–C(11)–N(1) 113.18(12)

208

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Table 3

Bond distances and selected bond angles for the (FcCH₂)₂NMe₂⁺cations in the SbF₆⁻salt 1b and the Cl⁻salt 1d·4/3H₂O (3 independent cations)

1b

1d (cation 1)

1d (cation 2)

1d (cation 3)

Fe(1)–C(11)

Fe(1)–C(12)

Fe(1)–C(13)

Fe(1)–C(14)

Fe(1)–C(15)

Fe(1)–C(31)

Fe(1)–C(32)

Fe(1)–C(33)

Fe(1)–C(34)

Fe(1)–C(35)

Fe(2)–C(21)

Fe(2)–C(22)

Fe(2)–C(23)

Fe(2)–C(24)

Fe(2)–C(25)

Fe(2)–C(41)

Fe(2)–C(42)

Fe(2)–C(43)

Fe(2)–C(44)

Fe(2)–C(45)

C(31)–C(32)

C(32)–C(33)

C(33)–C(34)

C(34)–C(35)

C(11)–C(12)

C(12)–C(13)

C(13)–C(14)

C(14)–C(15)

C(11)–C(15)

C(21)–C(22)

C(22)–C(23)

C(23)–C(24)

C(24)–C(25)

C(41)–C(42)

C(42)–C(43)

C(43)–C(44)

C(44)–C(45)

C(41)–C(45)

C(1)–C(11)

C(2)–C(21)

N(1)–C(1)

2.024(6)

2.029(6)

2.045(7)

2.051(8)

2.045(7)

2.047(8)

2.040(8)

2.014(8)

2.023(8)

2.039(7)

2.030(6)

2.040(7)

2.043(8)

2.059(8)

2.044(7)

2.041(9)

2.035(8)

2.052(8)

2.039(8)

2.031(9)

1.357(13)

1.411(16)

1.426(16)

1.349(14)

1.421(9)

1.411(11)

1.430(13)

1.414(11)

1.429(9)

1.437(9)

1.429(11)

1.398(14)

1.424(12)

1.392(15)

1.374(14)

1.397(12)

1.394(14)

1.407(13)

1.498(8)

1.476(8)

1.521(7)

1.534(8)

1.511(7)

1.509(7)

Fe(1)–C(11)

Fe(1)–C(12)

Fe(1)–C(13)

Fe(1)–C(14)

Fe(1)–C(15)

Fe(1)–C(16)

Fe(1)–C(17)

Fe(1)–C(18)

Fe(1)–C(19)

Fe(1)–C(110)

Fe(2)–C(115)

Fe(2)–C(116)

Fe(2)–C(117)

Fe(2)–C(118)

Fe(2)–C(119)

Fe(2)–C(120)

Fe(2)–C(121)

Fe(2)–C(122)

Fe(2)–C(123)

Fe(2)–C(124)

C(11)–C(12)

C(12)–C(13)

C(13)–C(14)

C(14)–C(15)

C(11)–C(15)

C(16)–C(17)

C(17)–C(18)

C(18)–C(19)

C(19)–C(110)

C(16)–C(110)

C(115)–C(116)

C(116)–C(117)

C(117)–C(118)

C(118)–C(119)

C(115)–C(119)

C(120)–C(121)

C(121)–C(122)

C(122)–C(123)

C(123)–C(124)

C(120)–C(124)

C(110)–C(111)

C(114)–C(115)

N(1)–C(111)

N(1)–C(114)

N(1)–C(112)

N(1)–C(113)

2.045(5)

2.038(5)

2.045(5)

2.024(5)

2.036(5)

2.040(4)

2.052(4)

2.046(5)

2.026(4)

2.019(5)

2.031(5)

2.032(5)

2.041(5)

2.034(5)

2.028(5)

2.024(5)

2.032(5)

2.039(5)

2.052(6)

2.034(5)

1.398(9)

1.419(7)

1.403(9)

1.419(10)

1.410(9)

1.419(7)

1.413(7)

1.438(7)

1.424(6)

1.429(6)

1.433(7)

1.416(7)

1.428(7)

1.413(7)

1.430(6)

1.485(9)

1.400(8)

1.376(8)

1.360(9)

1.396(9)

1.491(6)

1.483(6)

1.523(5)

1.532(5)

1.491(5)

Fe(3)–C(21)

Fe(3)–C(22)

Fe(3)–C(23)

Fe(3)–C(24)

Fe(3)–C(25)

Fe(3)–C(26)

Fe(3)–C(27)

Fe(3)–C(28)

2.037(4)

2.036(5)

2.040(5)

2.040(4)

2.035(4)

2.023(4)

2.045(4)

2.036(4)

2.043(4)

2.028(4)

2.026(4)

2.040(4)

2.049(5)

2.035(5)

2.026(5)

2.037(6)

2.036(6)

2.042(5)

1.427(7)

1.415(7)

1.419(7)

1.422(7)

1.398(7)

1.420(7)

1.418(7)

1.434(6)

1.438(6)

1.428(6)

1.421(7)

1.410(8)

1.412(7)

1.439(6)

1.396(8)

1.409(9)

1.351(10)

1.416(9)

1.433(8)

1.481(6)

1.499(6)

1.531(5)

1.523(5)

1.491(5)

1.494(5)

108.2(3)

109.6(3)

109.1(3)

110.3(3)

111.8(3)

113.0(3)

Fe(5)–C(31)

Fe(5)–C(32)

Fe(5)–C(33)

Fe(5)–C(34)

Fe(5)–C(35)

Fe(5)–C(36)

Fe(5)–C(37)

Fe(5)–C(38)

2.044(5)

2.037(5)

2.040(5)

2.045(5)

2.040(5)

2.045(4)

2.052(5)

2.045(5)

2.033(4)

2.027(4)

2.017(4)

2.024(5)

2.047(5)

2.043(5)

2.027(5)

2.032(5)

2.044(5)

2.039(5)

2.023(6)

2.031(6)

1.424(7)

1.418(7)

1.399(8)

1.428(8)

1.404(8)

1.409(6)

1.414(7)

1.419(7)

1.430(6)

1.421(7)

1.418(7)

1.412(9)

1.411(8)

1.431(6)

1.389(8)

1.401(8)

1.372(10)

1.422(10)

1.423(9)

1.480(6)

1.487(6)

1.531(5)

1.528(5)

1.500(5)

1.489(5)

107.9(3)

110.7(3)

108.8(3)

109.4(3)

110.5(3)

112.6(3)

113.2(3)

Fe(3)–C(29)

Fe(5)–C(39)

Fe(3)–C(210)

Fe(4)–C(215)

Fe(4)–C(216)

Fe(4)–C(217)

Fe(4)–C(218)

Fe(4)–C(219)

Fe(4)–C(220)

Fe(4)–C(221)

Fe(4)–C(222)

Fe(4)–C(223)

Fe(4)–C(224)

C(21)–C(22)

C(22)–C(23)

C(23)–C(24)

C(24)–C(25)

C(21)–C(25)

C(26)–C(27)

C(27)–C(28)

C(28)–C(29)

C(29)–C(210)

C(26)–C(210)

C(215)–C(216)

C(216)–C(217)

C(217)–C(218)

C(218)–C(219)

C(215)–C(219)

C(220)–C(221)

C(221)–C(222)

C(222)–C(223)

C(223)–C(224)

C(220)–C(224)

C(210)–C(211)

C(214)–C(215)

N(2)–C(211)

N(2)–C(214)

N(2)–C(212)

N(2)–C(213)

C(214)–N(2)–C(211)

C(212)–N(2)–C(211)

C(213)–N(2)–C(211)

C(212)–N(2)–C(214)

C(213)–N(2)–C(214)

C(210)–C(211)–N(2)

C(215)–C(214)–N(2)

Fe(5)–C(310)

Fe(6)–C(315)

Fe(6)–C(316)

Fe(6)–C(317)

Fe(6)–C(318)

Fe(6)–C(319)

Fe(6)–C(320)

Fe(6)–C(321)

Fe(6)–C(322)

Fe(6)–C(323)

Fe(6)–C(324)

C(31)–C(32)

C(32)–C(33)

C(33)–C(34)

C(34)–C(35)

C(31)–C(35)

C(36)–C(37)

C(37)–C(38)

C(38)–C(39)

C(39)–C(310)

C(36)–C(310

C(315)–C(316)

C(316)–C(317)

C(317)–C(318)

C(318)–C(319)

C(315)–C(319)

C(320)–C(321)

C(321)–C(322)

C(322)–C(323)

C(323)–C(324)

C(320)–C(324)

C(310)–C(311)

C(314)–C(315)

N(3)–C(311)

N(3)–C(314)

N(3)–C(312)

N(3)–C(313)

C(314)–N(3)–C(311)

C(312)–N(3)–C(311)

C(313)–N(3)–C(311)

C(312)–N(3)–C(314)

C(313)–N(3)–C(314)

C(310)–C(311)–N(3)

C(315)–C(314)–N(3)

N(1)–C(2)

N(1)–C(3)

N(1)–C(4)

C(1)–N(1)–C(2) 107.7(4)

C(3)–N(1)–C(1) 110.2(5)

C(4)–N(1)–C(1) 110.2(5)

C(4)–N(1)–C(2) 108.7(5)

C(3)–N(1)–C(2) 109.6(5)

C(11)–C(1)–N(1) 113.9(4)

C(21)–C(2)–N(1) 113.8(5)

C(111)–N(1)–C(114) 107.1(3)

C(112)–N(1)–C(111) 110.7(3)

C(113)–N(1)–C(111) 109.7(3)

C(112)–N(1)–C(114) 109.9(3)

C(113)–N(1)–C(112) 109.4(3)

C(110)–C(111)–N(1) 115.6(3)

C(115)–C(114)–N(1) 115.1(3)

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

209

Fig. 3. ORTEP drawing of one of the three independent cations of

(FcCH₂)₂NMe₂⁺in the Cl⁻salt 1d·4/3H₂O (cation 2) with 30%

thermal ellipsoids. Hydrogen atoms are omitted.

Fig. 1. ORTEP drawing of complex 2a. All hydrogens but the one

attached to N(1) are omitted. Thermal ellipsoids are shown on a 30%

probability level.

depicted in Fig. 4a. As shown in the packing diagram in

Fig. 4b, the chains occupy channels that penetrate the

cation sublattice. Contacts between the hydrophilic

chains and the mostly hydrophobic cations are made via

the roughly tetrahedral N(CH₃)₂(CH₂R)₂⁺subunits with

the Cl⁻ions pointing toward two (Cl(1), Cl(2)) or three

(Cl(3)) triangular faces of the NR₄⁺units of neighboring

cations. Again, the presence of such interactions is

indicated by an intense structured OH band centered at

3450 cm⁻¹in the IR. It has already been suggested that

hydrogen bridging between the methylene or methyl

groups bound to a quaternary nitrogen and the counter-

ion plays a certain role in such structures [39,42]. The

shortest contacts CH···X (X=F in SbF₆⁻or Cl⁻) are

the rotational angles between the two ring ligands

coordinated to the same Fe atom and the dihedral angles

as deﬁned by the two axes Fe-centroid of the respective

Cp^Rand a line connecting these centroids (Table 4). The

scatter of individual values suggests a fair amount of

conformational ﬂexibility within the binuclear cations. In

all four cases the Fe atom binds somewhat asymmetri-

cally to the two different carbocyclic ligands. While the

mean Fe–C distances are almost identical for the substi-

tuted and the unsubstituted rings, the substituted ring

ligand is slightly expanded and possesses the larger

intraring C–C bond distances. This draws the less

electron rich Cp^Rligand closer to the metal (Table 4). A

closer inspection of the data available for similar systems

[39–42] reveals the same overall picture which seems to

be of more general validity.

˚

3.33 and 3.48 A for methylene and 3.19 A for methyl

˚

groups in 1b and 3.59 and 3.75 A, respectively, for the

methylene carbons in 1d. These values are in the same

range as those found for the ZnCl²₄⁻salt of

In the chloride salt 1d·4/3H₂O hydrophilic domains

exist. They are formed by water molecules that are

hydrogen bonded to the Cl⁻counterions with Cl···O

FcCH₂NMe₂H⁺

(CH···Cl=3.56

A

[39]) and

˚

FcCH₂NMe₃⁺I⁻or Fc(CH₂NMe₃⁺)₂2I⁻(CH···I=3.73

˚

to 4.27 A [42]). The relatively longer C···Cl contacts in

˚

distances ranging from 3.19 to 3.29 A. Cl(1) and Cl(2)

1d may be due to the additional hydrogen bonding to the

cocrystallized water molecules.

form short contacts to three water molecules whereas

Cl(3) is bonded to O(4) only. Due to the statistical

replacement of Cl(3) by CN⁻and the cyanide nitrogen

being disordered there are, however, some uncertainties

in the structure pertaining to the vicinity of O(4). The

(H₂O)₄(Cl)₃entities are linked via shorter O(4)···O(2)

2.6. Electrochemistry

The anodic electrochemistry of FcCH₂NMe₂H⁺has

already been explored [23,45] and our data are in

complete agreement with previous ﬁndings. The fer-

rocene/ferrocenium couple exhibits Nernstian behavior

and, upon protonation, is shifted anodically by 0.185 V

with respect to the parent amine. Full reversibility also

prevails on the somewhat extended timescale of

chronoamperometric or chronocoulometric experiments.

We also observed a totally (chemically and electrochem-

ically) irreversible one electron reduction wave. The peak

potential depends on the electrode material and changes

from −1.44 V at platinum and −1.58 V at gold to

−1.84 V at glassy carbon. The chemical irreversibility

does not allow for the observation of an associated

anodic return wave. The electrochemical irreversibility

leads to a broadening of the wave and a signiﬁcantly

˚

hydrogen bridges of 2.94 A to one dimensional inﬁnite

chains that run parallel the a axis. One isolated chain is

Fig. 2. ORTEP drawing of the cation (FcCH₂)₂NMe₂⁺in the SbF₆⁻

salt 1b with 30% thermal ellipsoids. Hydrogen atoms are omitted.

210

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Table 4

Selected structural parameters for 2d, 1b and the three independent cations of 1d·4/3H₂O

2d

1b

1d (cation 1)

1d (cation 2)

1d (cation 3)

Fe–C (Cp^R) (av.)^a

Fe–C (Cp) (av.)^a

C (Cp^R)–C (Cp^R) (av.)

C (Cp)–C (Cp) (av.)

Fe–Cp^R(centroid)^b

Fe–Cp (centroid)^b

Dihedral angle^c

2.042

2.044

1.428

1.414

1.643

1.650

—

2.1

—

3.8

2.041

2.038

1.422

1.389

1.641; 1.646

1.656; 1.660

10.9

0.9; 1.1

55.4

2.035

2.037

1.427

1.406

1.637; 1.633

1.647; 1.649

16.4

1.5; 0.8

51.8

2.035

2.036

1.422

1.410

1.637; 1.637

1.641; 1.647

5.8

1.8; 3.4

52.8

2.037

2.036

1.420

1.408

1.644;1.634

1.649; 1.648

7.4

0.8; 2.4

61.4

Interplanar angle^d

Interplanar angle^e

Rot. Angle^f

3.6; 34.6

1.4; 5.7

14.2; 18.6

16.0; 8.9

^aCp^Rdenotes the monosubstituted and Cp the unsubstituted carbocyclic ligands.

^bDeﬁned by the distance of the Fe atom to the mean plane of the ring.

^cDeﬁned as the angle between the axes Fe–Cp^R-centroid and a line connecting the two centroids.

^dInterplanar angle between the Cp and the Cp^Rligands coordinated to the same Fe atom.

^eInterplanar angle between Cp^Rligands coordinated to adjacent Fe-atoms.

^fTaken as the average of all angles C (Cp^R)–Cp^R(centroid)–Cp (centroid)–C (Cp) for the ring C-atoms.

larger cathodic shift of the peak potential with increasing

sweep rate as is accounted for by chemical irreversibility

alone. From these data the electron transfer coefﬁcient

h, a dimensionless parameter that describes the symmetry

of the transition state of the electron transfer reaction,

was determined as 0.43 (0.02) [46]. If, after reduction, the

sweep is continued to anodic potentials a new chemically

reversible wave at ca. −0.19 V with respect to the

FcCH₂NMe₂H^+/2+couple appears. Since this feature is

absent if the anodic sweep is performed ﬁrst, the electro-

chemical reduction must be followed by a fast chemical

reaction which in turn generates the new electroactive

product detected on the reverse scan (ECE process, where

E and C denote elctrochemical and chemical steps,

respectively). The electrogenerated reduction product

was readily identiﬁed as the parent amine FcCH₂NMe₂.

When increasing amounts of the amine were added to the

analyte solution, this new feature gained in height as

conveniently shown by square wave voltammetry (Fig.

5). The one electron reduction of FcCH₂NMe₂H⁺is thus

accompanied by the loss of hydrogen. This reaction is

well known for tertiary ammonium salts [47] and explains

the electrode material dependent reduction potentials

and the sluggishness of the electron transfer.

between the two identical redox sites [48,51]. The satu-

rated CNC bridge is only a very poor delocalizer and so

we expected to see only small differences in the E_1/2

values. In fact, both one electron steps occur in a single,

slightly broadened wave of almost identical peak height

as was observed for an equimolar quantity of the

ferrocene standard. The close resemblance of the peak

heights is due to a broadening of the wave caused by

slight differences of the individual E_1/2values and the

opposite effects of the number of the transferred elec-

trons n and the diffusion coefﬁcient D. In cyclic voltam-

metry, the peak current is proportional to n^3/2·D^1/2

.

Once n is known, D is easily accessible from chronoam-

perometry by determining the slope of i(t) versus t^−1/2

plots. We obtained a value of 0.86×10⁻⁵(0.02) cm²s⁻¹

which is about one third the value reported for ferrocene

by Kochi et al. [52,53]. The two electron nature of this

wave was independently conﬁrmed by comparing the

diffusion controlled currents in a large amplitude poten-

tial step experiment and the limitting currents from

steady state voltammetry for (FcCH₂)₂NMe₂⁺with those

of the ferrocene standard as suggested by Baranski et al.

[54] and ﬁnally by controlled potential electrolysis. Fer-

rocene was also employed as an internal redox standard

to determine the exact degree of wave broadening in

terms of the differences in peak potentials DE_pand half

widths E_p−E_p/2. These parameters are diagnostic tools

that give access to the individual E_1/2values [55]. Our

ﬁndings were additionally supported by digital simula-

tion. Best ﬁt parameters are listed in Table 5 and were

obtained over a 10-fold increase in 6 for either CH₃CN,

propylene carbonate or DMF solutions. We expect these

data to be accurate within a 91 mV range for CH₃CN

and propylene carbonate and 92 mV for DMF since the

experimental results and the best ﬁt data differed by no

more than that from each other. According to Eq. (5),

DE_1/2values can be translated into equilibrium constants

The (FcCH₂)₂NMe₂⁺cations present in 1a–d comprise

two electrochemically well behaved ferrocene subunits

that are connected via a saturated CNC spacer. Related

dinuclear systems have been extensively studied in view

of the electronic communication between the identical

redox centers. The degree of such interactions is a

function of mainly two parameters: the electron delocal-

izing abilities of the bridging unit and the spatial separa-

tion and relative orientation of the two redox centers

imposed by the bridge [48–50]. The differences in half

wave potentials of the individual one electron events as

determined by voltammetry constitutes one, however

only qualitative, indicator for electronic interactions

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

211

Fig. 4. (a) View of a one dimensional chain comprised of hydrogen bonded Cl⁻and H₂O in the structure of 1d·4/3H₂O. (b) Packing diagram

of (1d·4/3H₂O). One of the Cl⁻ions is statistically replaced by CN⁻(not shown).

K_cfor the comproportionation reaction in Eq. (6). These

values are also listed in Table 5. One should, however,

note that the wave splitting may rather be due to

coulombic interactions between the increasingly charged

redox centers than to electronic interactions between the

two sites. This thought is strongly supported by UV–vis/

NIR spectro-electrochemical experiments in an optical

transparent thin layer electrolysis (OTTLE) cell. From

simple statistics one may deduce that after passage of

only one equivalent of charge the monooxidized, mixed

valent form must be the predominant species. The

presence and strength of the electronic coupling between

the two different redox sites can be inferred from the

appearance and shape of an intervalence charge transfer

band in the near IR [56]. Even when concentrated

solutions were electrolysed gradually and slowly we were

never able to detect any absorption in the NIR region

down to 2600 cm⁻¹. This result argues against any

signiﬁcant electronic interactions between the two ferro-

cenyl subunits in 1a–d.

K_c=exp(DE_1/2nF/RT)

(FcCH₂)₂NMe₂⁺+(FcCH₂)₂NMe³₂⁺

(5)

(6)

X 2FcCH₂)₂NMe²₂⁺

The reduction of the (FcCH₂)₂NMe₂⁺cation occurs

outside the potential range accessible in CH₃CN but may

well be studied in propylene carbonate or DMF (see Fig.

6). Again, the reduction is a chemically irreversible

process. Unlike for the protonated FcCH₂NMe₂H⁺,

however, the peak potential does not depend on the

electrode material and the electron transfer rate is much

higher with K_sin the range of ca. 0.1 cm·s⁻¹. An even

more striking difference is its two electron nature. This

is evident from the only slightly decreased peak heights

and the identical slopes of i(t) versus t^−1/2plots in

chronoamperometry for the oxidation and the reduction

waves. According to digital simulations the individual

212

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Fig. 5. Square wave voltammograms of FcCH₂NMe₂H⁺. The sweep

is initiated negative of the irreversible reduction peak A. Peak B is

due to the reversible oxidation. The lower trace represents the

voltammogram obtained from the pure compound while the two

upper traces were recorded after addition of increasing amounts of

N,N-(dimethylaminomethyl)ferrocene.

Fig. 6. Cyclic voltammograms of the (FcCH₂)₂NMe₂⁺ion; (a) initial

sweep in the anodic direction, (b) initial sweep in the cathodic

direction. The new reversible feature in curve (b) is due to an

electrogenerated product following reduction.

E^ovalues for the two one electron uptake events can not

be separated by more than 20 mV. This is rather

surprising since quaternary ammonium salts usually

undergo a one electron reduction followed by the cleav-

age of one of the C–N bonds according to Eq. (7) [47].

In the (FcCH₂)₂NMe₂⁺cation the bond rupture can

occur in two different ways with either the loss of a

methyl or a ferrocenyl substituent. Since earlier work

points to the preferential formation of the more stable

fragments [48] one may expect to see FcCH₂NMe₂

resulting from the reduction of (FcCH₂)₂NMe₂⁺. If after

sweeping past the peak of the cathodic wave the scan is

reversed a new reversible feature does indeed appear at

0.185–0.245 V negative of the oxidation wave, depending

on the solvent. The peak potentials agree well with those

of the FcCH₂NMe⁰₂^/+couple in the respective solvents.

Addition of this amine to the analyte solution causes the

new feature to gain in peak height but also induces a

slight anodic displacement of the wave. At the present

stage we can therefore not exclude that the C–N bond

cleavage, in part or even completely, occurs in the

opposite sense nor can we explain the two electron nature

of the reduction wave. In view of the electrochemical

behavior of (FcCH₂)₂NMe₂⁺one may reasonably expect

the two ferrocenyl subunits of a neutral biferrocenyl-

amine (FcCH₂)₂NMe that would result from the latter

cleavage reaction to be oxidized in a single wave at

potentials not much different from those of

FcCH₂NMe₂.

R%NR₃⁺+e⁻R% +NR₃

(7)

2.7. Preparation and spectroscopic characterization of

the corresponding ferrocenium salts

The oxidized monoferrocenium ion FcCH₂NMe₂H²⁺

and the dioxidized bisferrocenium ion (FcCH₂)₂NMe₂³⁺

are accessible by a variety of methods, including electro-

chemical oxidation in a preparative three compartment

cell or a thin layer cell and chemical oxidation. As

oxidizing agents Ag⁺or NO⁺in CH₂Cl₂or CH₃NO₂

or H₂SO₄or triﬂic acid in the presence of H₂O₂and

oxygen in water were successfully employed ([10]b). For

the ease of preparation and puriﬁcation, the oxidation of

FcCH₂NMe₂H⁺with NO⁺in CH₃CN and of

(FcCH₂)₂NMe₂⁺with Ag⁺in CH₃NO₂is recommended.

The oxidized species are only sparingly soluble or insol-

uble in CH₂Cl₂, but dissolve very well in CH₃NO₂,

Table 5

Redox potentials for (FcCH₂)₂NMe₂^+a,b

+/2+

1/2

2+/3+

1/2

ECE

Solvent

E

(V)

E

(V)

DE (V)

K_c

E^r_p^ed(V)

E

1/2

(V)^c

CH₃CN

PC

DMF

0.180 (1)

0.164 (1)

0.150 (2)

0.243 (1)

0.234 (1)

0.224 (2)

0.063 (2)

0.070 (2)

0.074 (4)

12 (1)

16 (1)

19 (3)

—

−2.89

−2.94

—

−0.04

−0.06

^aValues in brackets are standard deviations.

^bAll potentials referenced to the Fc^0/+couple as internal redox standard.

^cE_1/2of the new species generated by the ECE reduction process.

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

213

CH₃CN or CH₃OH, forming quite air stable, intense blue

to blue-green solutions with red to purple dichroism.

Solutions of FcCH₂NMe₂H²⁺in CH₃NO₂or CH₃CN

slowly decompose even under an argon atmosphere.

Solid (FcCH₂)₂NMe³₂⁺salts of weakly coordinating

cations may be stored for weeks under ambient condi-

tions without any detectable degradation. The ferroce-

nium salts were characterized by UV–vis, IR and ESR

spectroscopy. ESR spectra were recorded at 4 K and

closely resemble those of other substituted ferrocenium

salts ([10]a). They exhibit axial patterns with g_II=4.35

(DH_II=120 G), g_Þ=1.42 (DH_Þ=1200 G) for

FcCH₂NMe₂H²⁺and g_II=4.15 (DH_II=250 G), g_Þ=

1.48 (DH_Þ=1200 G) for the fully oxidized

(FcCH₂)₂NMe³₂⁺. UV–vis spectra were obtained from

either electrochemical oxidation in an OTTLE cell or

from the isolated oxidation products themselves (Fig. 7).

Upon gradual oxidation of 2b and 1b the characteristic

intense absorptions of the ferrocenium chromophore

[57]. In the visible region the spectra are dominated by

a fairly intense charge transfer band at u_max=627 nm

2

with several ligand ﬁeld transitions based on the E_2g

ground state superimposed as shoulders on the high

energy part of this band or discernable as discrete peaks

(see Section 3). As in other ferrocenium systems, the IR

spectra are less well resolved than those of the reduced

counterparts and exhibit considerably fewer peaks. We

note that air stable (FcCH₂)₂NMe³₂⁺salts are available

from commercial products in an easy, high-yield, two-

step synthesis. They are capable of transferring two

electrons at virtually the same potential and may be

useful as a convenient oxidizing agent with an oxidizing

power comparable to that of the acetylferrocenium ion.

3. Experimental

1

¹A_1g¹E_1gand A_1g¹E_1g,¹E_2gbands centered at ca.

325 and 435 nm (Table 1) are displaced by much more

All manipulations apart from those involving

Me₂NꢀCH₂⁺Cl⁻and oxidation reactions with NO⁺

were performed in undried solvents without any pre-

cautions to exclude moisture or air. Ferrocenyl-

methyldimethylamine was purchased from Lancaster

and used as received. The deuterated solvents were

supplied by Aldrich. Infrared spectra were obtained on

a Perkin Elmer Paragon 1000 PC FT-IR instrument. ¹H

(250.13 MHz) and ¹³C (62.90 MHz) NMR spectra were

recorded on a Bruker AC 250 spectrometer at 303 K in

CD₃CN unless stated otherwise. For the in situ reac-

tions of FcCH₂NMe₂in CD₂Cl₂the NMR tubes were

sealed to maintain a constant solvent volume. The

spectra were referenced to the residual protonated sol-

vent (¹H) or the solvent signal itself (¹³C). If necessary,

the assignment of ¹³C-NMR spectra was aided by ap-

propriate DEPT measurements [58]. UV–vis experi-

ments were performed with a Shimadzu UV-160

spectrometer in HELMA quartz cuvettes with 1 cm

optical path lengths. The ESR equipment consists of a

Bruker ESP 3000 spectrometer equipped with a HP

frequency counter 5350 B, a Bruker NMR gaussmeter

ER 035 M and a continuous ﬂow cryostat ESR 900

from Oxford Instruments for low temperature work.

Elemental analyses (C, H, N) were performed at in-

house facilities. Theoretical yields are calculated based

on the overall reaction stoichiometry in Scheme 1.

All electrochemical experiments were performed in a

home-built cylindrical vacuum tight one compartment

cell. A spiral shaped Pt wire and a Ag wire as the

counter and reference electrodes were sealed directly

into opposite sides of the glass wall while the respective

working electrodes (Pt 350 mm, glassy carbon 1.1 mm,

Au 60 mm diameter, polished with 0.25 mm diamond

paste (Buehler-Wirtz) before each experiment) were in-

troduced via a teﬂon screw cap with a suitable ﬁtting.

The cell may be attached to a conventional Schlenk line

Fig. 7. UV–vis traces during the oxidation of the FcCH₂NMe₂H⁺

ion (top) and the (FcCH)₂NMe₂⁺ion (bottom) in an OTTLE cell. In

both cases the lowest curve represents the spectra before oxidation

and the uppermost trace the spectra after complete oxidation to the

ferrocenium ions.

214

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

via two sidearms equipped with teﬂon screw valves and

allows experiments to be performed under an atmosphere

of argon with approximately 2.5 ml of analyte solution.

The solvents were obtained in the highest available purity

from commercial sources (CH₂Cl₂and propylene car-

bonate from Fluka (Burdick and Jackson), CH₃CN

(HPLC Gradient Grade) from Roth) and treated with

alumina (2–5 mm particles for drying purposes from

Fluka) while being freeze–pump–thaw degassed (three

times) or purged with argon (at least 20 min). NBu₄PF₆

(CH₂Cl₂, CH₃CN) or NBu₄ClO₄(propylene carbonate,

0.25 mM each) were used as the supporting electrolytes.

All potentials are referenced versus ferrocene. All electro-

chemical data were acquired with a computer controlled

EG&G model 273 potentiostat utilizing the EG&G 250

software package. Controlled potential electrolyses were

performed in a home built, air-tight three compartment

cell with electrodes (working electrode: Pt-basket, 3 cm

diameter, auxiliary electrode: Pt-basket 1 cm diameter,

reference electrode: Ag-rod, 3 mm diameter) sealed

directly into the glass. The OTTLE cell was also home

built and comprised a Pt-mesh working and counter

electrode and a thin silver wire as a pseudo-reference

electrode sandwiched between the CaF₂windows of a

conventional liquid IR cell. The working electrode was

positioned in the center of the spectrometer beam. Digital

simulations of experimental CVs were performed with

DigiSim^®(version 2.1) available from BAS.

1b: 0.154g, 67%. Anal. found: C, 42.39; H, 3.84; N,

2.11. C₂₄H₂₈F₆Fe₂Sb requires C, 42.27, H, 4.13; N, 2.05.

IR spectra display besides the signals of the cation those

of the SbF₆⁻anion: IR w 657(vs), 291(s).

3.2. Synthesis of (FcCH₂)₂NMe⁺₂BPh⁻₄(1c)

FcCH₂NMe₂(0.243 g, 1.0 mmol) was dissolved in

CH₂Cl₂(20 ml) and solid NaBPh₄(0.358 g, 1.05 mmol)

added. The yellow-orange suspension was stirred for 3

days under ambient conditions. The resulting orange

solid was allowed to settle and isolated by removing the

mother liquor via ﬁlter cannula. It was washed with two

additional 3 ml portions of cold CH₂Cl₂and dried in

vacuo. Yield: 0.185 g, 0.24 mmol, 72%. The mother

liquor still contains appreciable amounts of the product

and FcCH₂NMe₂H⁺BPh₄⁻. Attempts to separate the

two components by fractional crystallization were unsuc-

cessful. Anal. found: C, 75.56; H, 6.28; N, 1.90.

C₄₈H₄₈BFe₂N requires C, 75.71. H, 6.35; N, 1.84. NMR

and IR spectra show in addition to the cation signals

those characteristic of the BPh₄⁻anion (¹H d 7.27 (br,

8H); 7.00 (t, ³J_HH=7.40 Hz, 8H); 6.84 (t, ³J_HH=7.40 Hz,

4H). ¹³C d 160.9 (non-binomial q, J_BC=60 Hz); 131.0,

129.4, 127.8(all s). IR n 1580(m), 1428(s), 1261(m), 1183

(m), 1152(m), 866(m), 850(s), 737(vs), 729(vs), 708(vs))

[59].

3.3. Synthesis of (FcCH₂)₂NMe²⁺Cl⁻(1d)

3.1. Syntheses of (FcCH₂)₂NMe⁺₂X⁻(X⁻=PF⁻₆

(1a), SbF⁻₆(1b))

A solution of FcCH₂NMe₂(0.128 g, 0.53 mmol) in 10

ml CH₂Cl₂was stirred at room temperature for 3 days,

the solvent evaporated and the tarry residue dissolved in

a minimum amount of warm CH₃CN. After ﬁltration,

the solvent was allowed to slowly evaporate until small

amber crystals had formed. One more crop was obtained

upon further concentration of the mother liquor. Com-

bined yield: 0.059 g (0.165 mmol), 70%. Anal. found: C,

59.93; H, 6.00; N, 2.91. C₂₄H₂₈ClFe₂N requires C, 60.34,

H, 5.91; N, 2.95.

FcCH₂NMe₂(0.245 g, 1.01 mmol) was dissolved in

CH₂Cl₂(25 ml) and an equimolar amount of NaEF₆

(E=P, 0.171 g; E=Sb, 0.265 g) added as a solid. The

suspension was stirred for 3 days under ambient condi-

tions. The solution was then transferred to a ﬂask by ﬁlter

cannula and the solvent removed in vacuo. The resultant

tarry residue was extracted into a warm 2:1 chloroben-

zene/CH₃CN mixture (10 ml; caution: extensive warming

will result in decomposition as indicated by the formation

of a dark brown insoluble material). The solution was

ﬁltered, slowly cooled and concentrated. After 2–3 days

(FcCH₂)₂NMe₂⁺EF₆⁻crystallized as orange-yellow

needles (PF₆⁻) or large hexagonal plates (SbF₆⁻). Yields:

1a: 0.116 g, 0.24 mmol, 59%. Anal. found: C, 48.56; H,

4.88; N, 2.34. C₂₄H₂₈F₆Fe₂P requires C, 49.09, H, 4.81;

N, 2.40. NMR and IR spectra display besides the signals

of the cation (for NMR data see Table 1) those of the

PF₆⁻anion: ³¹P l −143.9 (hept, J_PF=706.6 Hz). ¹⁹F l

−67.6 (d, J_PF=706.6 Hz). IR w 838(vs), 557(m). Bands

of the cation: w 3096(m), 3086(m), 3046(w), 3038(w),

2964(m), 1580(w), 1478(s), 1450(m), 1444(m), 1430(m),

1406(m), 1375 (w), 1331(m), 1261(w), 1238(m), 1105(s),

1043(m), 1032(m), 1012(m), 1000(m), 980(w), 920(w),

845(sh), 825(vs), 547(m), 485(s, br), 451(w), 420(w).

3.4. Synthesis of FcCH₂NMe₂H⁺SbF⁻₆(2b)

FcCH₂NMe₂(0.577 g, 2.37 mmol) was dissolved in a

suspension of NaSbF₆(1.24 g, 5.75 mmol) in 20 ml

CHCl₃and stirred for 2 days at room temperature. The

resulting orange solid was ﬁltered off, dried in vacuo and

extracted into 15 ml of CH₂Cl₂. The yellow-orange

solution was put to dryness to leave an orange powder.

The mother liquor was concentrated in vacuo and

puriﬁed by column chromatography (neutral alumina,

15×3 cm, 4% H₂O in CH₃CN as eluant). The product

was obtained as an orange fraction. Combined yields

0.657 g, 1.38 mmol, 58%. Anal. found: C, 32.65; H, 3.78;

N, 2.88. C₁₃H₁₈F₆FeNSb requires C, 32.54, H, 3.78; N,

2.92. IR: w (cation) 3235(m), 3100(w), 2960(w), 2734(w),

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

215

3.8. Trapping experiments with LiH, NaBH₄and KCN

1475(vs), 1450(m), 1430(s), 1421(s), 1401(m), 1382 (m),

1332(w), 1292(w), 1261(vw), 1235(m), 1165(m), 1123(m),

1105(s), 1060(m), 1040(m), 1022(m), 1014(m), 1001(m),

947(m), 920(s), 845(m), 820(vs), 516(m), 500(m), 485(s),

446(m), 313(m).

These reactions were performed on a 1 mmol scale in

25 ml of CH₂Cl₂with a 4- to 5-fold excess of the trapping

reagent. After 3 days of stirring under ambient condi-

tions, the orange suspensions were ﬁltered with a paper

tipped cannula and the solvent stripped off in vacuo. The

oily or tarry residues were puriﬁed by column chro-

matography on neutral alumina with a 5% H₂O/CH₃CN

mixture as the eluant. A dark orange zone was rapidly

eluted followed by two well separated yellow-orange

fractions. The fractions were collected, stirred over

anhydrous MgSO₄for 1 h, ﬁltered and the solvents

removed on a rotary evaporator. The ﬁrst fraction

yielded a small amount of a dark orange oil, whereas the

second and third fractions were obtained as orange

microcrystals. Yields: Fraction 1: 6–10 mg. Fraction 2:

(FcCH₂)₂NMe₂⁺Cl⁻(1d·4/3H₂O) 0.094–0.113 g, 0.19–

0.22 mmol, 56–67%. Anal. found: C, 57.47; H, 6.27; N,

2.83. C₂₄H₂₈ClFe₂N·4/3H₂O requires C, 57.46, H, 6.16;

N, 2.79. NMR spectra of the hydrated samples are given

in Table 1. Fraction 3: FcCH₂NMe₂H⁺Cl⁻(2d) 0.087–

0.091 g, 94–98%. Anal. found: C, 55.79; H, 6.49; N, 5.00.

C₁₃H₁₈ClFeN requires C, 55.85, H, 6.49; N, 5.00. Crys-

tals were obtained by slow concentration of solutions in

CH₃CN.

3.5. NMR spectroscopic in6estigation of the reaction of

FcCH₂NMe₂in CD₂Cl₂

FcCH₂NMe₂(54 mg, 0.22 mmol) was balanced into a

screw cap NMR tube and CD₂Cl₂(1.21 g, 0.9 ml) added.

The NMR tube was tightly closed and NMR spectra

recorded continuously over a 28 h period after mixing

(¹H initially every 30, then every 90 min with intermediate

recording of ¹³C-NMR spectra; additional spectra were

acquired after 2 and 3 days, respectively). The reaction

was accompanied by the growth of the signals of

(FcCH₂)₂NMe₂⁺and a continuous downﬁeld shift of the

signals due to the starting material. At the end of the

reaction the shift data for this second set of signals almost

match those of pure 2d. In the course of the reaction new

1

3

NMR signals appeared: H l 4.77 (t, J_HH=1.96 Hz),

4.60 (t, ³J_HH=1.96 Hz), 4.27(s), 2.57(s), 2.36(s), 2.32(s);

¹³C l 78.0(br), 73.5, 70.2, 45.0, 41.5.

3.6. Reaction of FcCH₂NMe₂with Me₂NꢀCH⁺₂Cl⁻

Under Ar, Me₂NꢀCH₂⁺Cl⁻(27 mg, 0.288 mmol) were

balanced into an NMR tube and a solution of 72 mg (0.29

mmol) FcCH₂NMe₂in CD₂Cl₂added. The NMR tube

was closed with an air tight screw cap and NMR spectra

acquired over the course of 4 h. An additional experiment

was performed in CD₃CN on a 0.225 mmol scale. After

full equilibration was obtained, the samples were re-

moved from the NMR tubes and slowly added to rapidly

stirred Et₂O (15 ml) which caused the precipitation of an

orange solid. The solvent was removed by ﬁlter cannula

and the solid dried in vacuo. Yield: 0.11 g. NMR

spectroscopic investigation of the orange powder re-

vealed the presence of FcCH₂NMe₂H⁺and

(FcCH₂)₂NMe₂⁺in an approximate ratio of 20:1.

3.9. Trapping experiment with NEt₃

FcCH₂NMe₂(0.39 g, 1.6 mmol) was dissolved in 25

ml of CH₂Cl₂and solid NaSbF₆(0.83 g, 0.32 mmol) and

NEt₃(2.50 g, 24.6 mmol, 15 equivalents) were added. The

mixture was stirred at room temperature for 3 days, and

the orange-red suspension ﬁltered over cannula. The

solvent and the amine were distilled off and the oily

residue chromatographed on neutral alumina with H₂O/

CH₃OH 1:15. An orange fraction was obtained which

was immediately followed by a second, darker orange

fraction. Both were dried over anhydrous MgSO₄,

ﬁltered and the solutions concentrated in vacuo. From

the ﬁrst fraction large orange needles soon formed. After

5 h the mother liquor was pipetted off and the crystalline

material dried in vacuo. The second fraction gave a

yellow oil which very slowly crystallized. Both samples

were found to contain (FcCH₂)₂NMe₂⁺and

FcCH₂NEt₃⁺, albeit in a somewhat different product

distribution. Combined yield: 0.385 g.

3.7. The reaction of FcCH₂NMe₂H⁺with

Me₂NCH₂NMe₂

N,N-(Dimethylaminomethyl)ferrocene hydrochloride

48 mg (0.17 mmol) was dissolved in CD₂Cl₂and added

to a NMR tube which was closed with a septum screw

cap. A total of eight 0.25 equivalent aliquots of the

aminal were added in portions via microliter syringe. The

sample was allowed to equilibrate for 20 min after each

consecutive addition and then NMR spectra were ac-

quired. They showed a continuous upﬁeld shift for the

signals associated with the substituted ferrocene as well

as a low ﬁeld shift for those of the aminal.

3.10. Reaction of FcCH₂NMe₂with acetyl chloride

FcCH₂NMe₂(0.698 g, 2.87 mmol) was suspended in

Et₂O and small portions of CH₃CN (ca. 4 ml total) were

added until a clear solution had formed. A solution of

CH₃COCl (100 ml, 1.43 mmol) in 8 ml of Et₂O was added

dropwise within 30 min. A bright orange powder imme-

216

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

Table 6

Experimental data for the X-ray structure determinations

Empirical formula

Temperature (K)

Radiation/wavelength (A)

Scan mode

Crystal system

Space group

C₁₃H₁₈ClFeN

173(2)

Mo–K_h/0.71073

V-Scans

Orthorhombic

Pna2₁

C₃₀H₂₈ClF₆Fe₂NSb

293(2)

C₂₄H₃₁ClFe₂NO_1.50

173(2)

˚

-Oscillation

Monoclinic

P2₁/n

V-Scans

Triclinic

(

P1

Cell dimensions

˚

a (A)

21.562(6)

5.8045(17)

10.472(4)

17.4776(14)

10.4790(5)

18.2368(13)

11.967(2)

12.044(2)

27.251(5)

˚

b (A)

˚

c (A)

h (°)

i (°)

94.839(14)

98.962(14)

110.282(7)

k (°)

V (A )

115.241(12)

3458.8(11)

3

˚

1310.6(7)

3132.9(4)

Z

4

6

D_calc(mg m⁻³

)

1.417

1.327

0.56×0.32×0.24

1.89–30.01

7531

3820 (R_int=0.0629)

Empirical (-scans)

—

1.665

1.911

0.60×0.44×0.28

2.99–26.03

43 459

6091 (R_int=0.0569)

Numerical

0.6167 and 0.3935

Stoe IPDS

SHELXS-97, SHELXL-97

1.454

1.392

Absorption coefﬁcient (mm⁻¹

Crystal size (mm)

Scan range (°)

Reﬂections collected

Independent reﬂections

Absorption correction

Max/min transmission

Diffractometer

Programs

Reﬁnement

Data/restraints/parameter

R (I\2|(I))

)

0.70×0.55×0.12

2.48–26.00

13 276

12 637 (R_int=0.0641)

Empirical (-scans)

0.865 and 0.548

Siemens P4

Siemens SHELXTL

Siemens P4

Siemens SHELXTL

Full matrix least-squares against F²

3820/1/151

6091/423/384

R₁=0.0542

12637/0/818

R₁=0.0529

R₁=0.0235

R_w(all data)

wR₂=0.0615

0.005(12)

wR₂=0.1490

—

wR₂=0.1379

—

Flack parameter

Weighting scheme

(P=(F²_o+2F²_c)/3)

w=1/[|²(F²_o)+(0.0236P)²

w=1/[|²(F²_o)+(0.0720P)²

w=1/[|²(F²_o)+(0.0572P)²

+0.0987P]

1.057

0.279 and −0.265

+0.1000P]

1.138

1.310 and −0.858

+6.3135P]

1.028

0.586 and −0.603

Goodness-of-ﬁt (all data)

Largest max and min (e A

−3

˚

)

diately precipitated from solution. After the addition was

complete, the solution was stirred for further 2 h and then

ﬁltered via a paper tipped cannula. The orange solid was

washed three times with 5 ml portions of Et₂O each and

then dried in vacuo to give pure (FcCH₂)₂NMe₂⁺Cl⁻.

Yield: 0.600 g, 88%.

(175), 468 (135), 360 (2500). Anal. found: C, 21.55; H,

2.46; N, 2.03. C₁₃H₁₈F₁₂FeNSb₂requires C, 21.82, H,

2.54; N, 1.97. IR: w (cation) 3420(s), 3125(m), 2963(m),

2730(m), 2724(m), 1475(m), 1419(m), 1261(s), 1162(w),

1104(s),1100(s) 1027(s), 1014(m), 952(w), 919(w), 863(m),

802(s), 486(w), 401(w), 277(vs).

3.11. Oxidation of FcCH₂NMe₂H⁺SbF⁻₆by NO⁺SbF⁻₆

FcCH₂NMe₂H⁺SbF₆⁻(0.042 g, 87.5 mmol) was dis-

3.12. Oxidation of (FcCH₂)₂NMe⁺₂Cl⁻with Ag⁺BF⁻₄

(FcCH₂)₂NMe₂⁺Cl⁻(1d) (0.12 g, 0.26 mmol) was

dissolved in CH₂Cl₂(20 ml). Upon addition of solid

AgBF₄(0.15 g, 0.78 mmol) the color of the solution

immediately changed to dark blue-green and a precipi-

tate formed (note that the potential of the Ag^0/+couple

is strongly solvent dependent [60] and that Ag⁺is a

strong enough oxidant to effect the conversion of

(FcCH₂)₂NMe₂⁺to its trication in CH₂Cl₂but not in

CH₃CN). The suspension was stirred for 2 h at room

temperature and then ﬁltered via a paper tipped can-

nula. The residue was dried in vacuo, extracted into

CH₃NO₂(2×5 ml) and ﬁltered by cannula. After

concentration to ca. 2 ml in vacuo, ether was added to

precipitate the product as a heavy dark blue oil which

solved in

1 ml of degassed CH₃CN and solid

NO⁺SbF₆⁻(0.023 g, 86 mmol) was added. The solution

rapidly turned intense green and was purged with Ar for

30 min. The product was then precipitated as a tar by

addition of Et₂O (3ml). After syringing off the mother

liquor and brieﬂy drying in vacuo, the material was

redissolved in the minimum amount of CH₃CN and this

solution very slowly added to 5 ml of cold, rapidly stirred

Et₂O. The mother liquor was again removed by a ﬁne

pipette and the residue dried in vacuo at elevated

temperatures. The product was obtained as a dark

blue-green, brittle solid. Yield: 0.047 g, 75%. UV–vis u

(nm) (m (M⁻¹cm⁻¹)) 672 (500), 580(sh) (280), 540(sh)

R.F. Winter, G. Wolmersha¨user / Journal of Organometallic Chemistry 570 (1998) 201–218

217

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469.

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601.

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104.

was dried in vacuo for several hours. The product was

obtained as a hard brittle intense colored solid. The

presence of both CH₃NO₂and CH₂Cl₂in this solid was

revealed by NMR-spectroscopy. Yield: 0.179 g, 81%.

Anal. found: C, 39.44; H, 3.98; N, 2.70.

C₂₄H₂₈B₃F₁₂Fe₂N×2/3CH₃NO₂×1/5CH₂Cl₂requires

C, 39.85, H, 4.07; N, 3.15. UV–vis u (nm) (m (M⁻¹

cm⁻¹)) 627 (670), 580(sh) (350), 535(sh) (280), 471

(270), 380(sh) (600). IR n (cm⁻¹) 3116(m), 2960(w),

1635(m), 1560(m), 1482(m), 1418(m), 1394(w), 1287(m),

1262(m), 1247(m), 1083(vs), 1031(vs), 909(m), 859(s),

763(m), 521(m).

3.13. X-ray structures

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1781.

Experimental data pertaining to the X-ray structures

have been summarized in Table 6. Hydrogen atoms

were positioned geometrically. A riding model was

assumed for reﬁnement of those atoms with isotropic

thermal parameters being 1.5 times (CH₃-groups) and

1.2 times (Cp–H, CH-v, CH₂-groups) the values of the

carrier carbon atoms.

For 1b the anion and the solvent molecules are

disordered. A ﬁxed geometry was applied for the latter.

In 1d, Cl(3) is statistically replaced by CN⁻(C(999),

N(4)). The cif-ﬁles have been deposited at the Cam-

bridge Structure Data Centre, University Chemical

Laboratory, Lensﬁeld Road, Cambridge, CB2 1EZ (de-

position number CCDC-101 238).

[12] (a) M.I. Bruce, P. Hinterding, P.J. Low, B.W. Skelton, A.H.

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White, J. Chem. Soc.; Chem. Comm. (1997) 715.

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Band C, 406, Gmelin-Verlag, Clausthal Zellerfeld, 1949; see also

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4. Supporting material

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Tables containing the fractional atomic coordinates

and isotropic displacement parameters for 2d, 1b and

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Acknowledgements

R.F.W. gratefully acknowledges ﬁnancial support of

this work by the Deutsche Forschungsgemeinschaft,

Professor Dr Wolfgang Kaim and the Institut fu¨r

Anorganische Chemie der Universita¨t Stuttgart. We

also wish to thank Birgit Brunner for her contributions

within an advanced laboratory course and Dr Frank

Baumann and Matthias Wanner for the recording of

the ESR spectra.

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Article Doi

The dichloromethane induced fragmentation of ferrocenylmethyldimethylamine. Mechanistic aspects and crystallographic and electrochemical investigation of the (FcCH2)2NMe2(+) and FcCH2NMe2H(+) ions

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