Structural Variety of Iron Carbonyl Clusters Featuring Ferrocenylphosphines

Full Papers

doi.org/10.1002/ejic.202100097

Structural Variety of Iron Carbonyl Clusters Featuring

Ferrocenylphosphines

[a]

[b]

[c]

Marcus Korb,* Xianming Liu, Sebastian Walz, Julia Mahrholdt, Alexey A. Popov, and

[b, d]

Heinrich Lang

Dedicated to Prof. Dr. Christoph Janiak on the occasion of his 60th birthday.

The reaction chemistry of Fe (CO) (10) with ferrocenenyl

dichlorophosphines of different substitution is discussed. Single

twisted by 35.31(9)° regarding their ferrocenyl axis. Usage of

2

9

1,2-(PCl ) functionalized 9 produced two isomers of a PÀ P

2

FcPCl , (5) as well as 1,1’- (6) and 1,2- (9) difunctionalized

connected dimer, which coordinates towards two independent

2

8

4

phosphines were used, of which 6 and 9, were prepared in a

novel straightforward synthetic process. Substrate 5 gave

butterfly-shaped Fe (CO) (μ -Cl)(μ -PFcCl) and Fe (CO) (μ -

Fe (CO) fragments in a novel μ,μ’,k or bis(μ,k ) fashion,

2 6

resulting in a meso isomer with a planar core, and a racem

mixture, possessing a pocket-type structure. The latter shows

the so far shortest observed P···P distance of 2.950(7) Å between

two ortho P atoms of a ferrocenyl backbone. The results confirm

that the geometric properties of ferrocenyls featuring 1,1’- and

1,2-substitution patterns are not comparable with phenyl-based

analogues. X-ray single crystal solid state structures, and DFT

calculations were carried out.

2

6

2

6

2

1

2

1

2

PFcR )(μ -PFcR ) (R , R =Cl, H). In addition, nido-Fe (CO) (μ -

2

3

10

3

PFc) and nido-Fe (CO) (μ -PFc) were obtained. 1,1’-Functional-

3

9

3

2

ized 6 bridges both ends of the Fe (CO) entity. Therein, the so

2

6

far smallest non-binding P···P distance (2.7674(12) Å) between

both 1,1’-substituents is observed. Additionally, an ‘organo-

metallic octabisvalene’, containing two [2]ferrocenophane enti-

ties was obtained. The eight-membered cyclic structure is

Introduction

monly used as chelating ligands for mono and multimetallic

[5,6,7,11]

metal carbonyl building blocks,

center towards the coordinated metal M in a k mode.

can interact with their iron

3

Phosphorus-bonded iron carbonyl clusters have intensively

been studied, due to, for example, their rich structural variety,

specific tuning of their electronic properties and their facile

cluster periphery functionalization.

genase biomimetics,

agents have been explored. It was in this respect, that 1,1’-

bisphosphino ferrocenes Fe(η -C H PR ) (R=alkyl, aryl), com-

[

1,2]

II

Especially, for M = Fe, Ni an inverse charge transfer from Fe to

[

3,4]

I

[4]

M occurs. Ferrocenyl groups are commonly used as redox-

active probes to investigate the conducting properties of

organic or organometallic conjugated linkers and their ability to

allow electronic communication in mixed-valent redox states of

[

5–7]

Their use as, e.g. hydro-

reduction catalysts and antibacterial

[5,6b,8]

[9]

[

10]

5

[12]

such molecules.

5

4

2 2

However, the so far chosen aryl and alkyl functionalities of

5

the Fe(η -C H PR ) starting materials limit the coordination

5

4

2 2

[

a] Dr. M. Korb

School of Molecular Sciences,

mode for each P donor towards the metal carbonyl fragments

to a k mode (Table S1). Hence, a direct incorporation of the

1

3

5 Stirling Highway, Crawley,

Perth, Western Australia

009, Australia

E-mail: marcus.korb@uwa.edu.au

phosphorus atom into the cluster core cannot be accessed. The

phenyl analogues instead, are known for their variety of

6

[1]

phosphinidene (=phosphanylidene) and phosphido clusters,

https://research-repository.uwa.edu.au/en/persons/marcus-korb

b] X. Liu, S. Walz, J. Mahrholdt, Prof. H. Lang

Technische Universität Chemnitz,

Faculty of Natural Sciences,

Institute of Chemistry,

where the required PhPCl educts are readily available. Attach-

2

ing ferrocenyl groups to phosphinidene or phosphide motifs

directly would require FcPCl as a starting material, which was

2

Inorganic Chemistry,

hitherto difficult to synthesize. Hence, the so far only reported

example of a cluster resulting from a reaction with FcPCl₂,

09107 Chemnitz, Germany

[

c] Dr. A. A. Popov

contained PFc and PFc functionalities, due to the difficulties

2

Leibniz Institute for Solid State and

Materials Research (IFW Dresden),

Helmholtzstrasse 20,

[

13]

within the purification process of the dichlorophosphine.

Thus, alternative strategies to link Fc substituents to P-

containing metal carbonyl fragments involved additional spacer

01069 Dresden, Germany

d] Prof. H. Lang

[14]

Center for Materials, Architectures and

Integration of Nanomembranes (MAIN),

Rosenbergstr. 6, 09126

groups, as found in e.g. Fe (CO) (μ -P(CH Fc)H) .

2 6 2 2 2

Recently a synthetic methodology was reported to obtain

[15]

FcPCl₂in analytical pure form from FcPH₂_,allowing us to

Chemnitz, Germany

investigate its reaction chemistry towards ^F^e⁽^C^O⁾9 and

Supporting information for this article is available on the WWW under

https://doi.org/10.1002/ejic.202100097

2

Co (CO) , respectively. Within these reactions nido phosphini-

2

8

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dene clusters Fe (CO) (μ -PFc) and Co (CO) (μ -PFc) were Results and Discussion

3

9

3

2

4

10

4

2

[16]

synthesized. For the sole preparation of edge-opened cluster

Fe (CO) (μ -PFc) a comparably long reaction time of 2 h at

Chlorophosphine Synthesis

3

9

3

2

5

0°C was required. It was, however, shown for phenyl-based

substrates that formation of such bipyramidal phosphinidene

clusters is a stepwise process, involving several intermediates

Iron carbonyl phosphide and phosphinidene clusters are

[

1]

accessible by reacting, for example, chlorophosphines (RPCl )

2

[1]

[14,28]

with different core geometries. These species will be accessed

herein for ferrocenyl derivatives.

or phosphines (RPH₂)

with an excess of Fe (CO) , of which

2 9

the latter procedure requires higher reaction temperatures and

The new protocol for the synthesis of FcPCl also enables a

longer reaction times, e.g. 90°C for 3 days, to enable the

2

[

14]

novel access to bis-PCl -functionalized ferrocenes, based on

formation of H .

The reaction with chlorophosphines pro-

2

[

17]

[18]

1

,1’- and 1,2-substitution pattern, which are so far synthe-

ceeds more rapidly at ambient temperature, whereby an excess

0

sized via the P(NEt ) /HCl route. The latter has only been

of Fe acts as the oxidant accompanied by the precipitation of

2

[18]

mentioned once in literature. The ferrocenyl core in both

type of compounds provides unique geometric properties that

cannot be achieved by condensed aromatics (Figure 1, Fig-

FeCl . Furthermore, structurally more divers products are

2

accessible, due to a kinetic product formation at lower reaction

[1]

temperatures.

[

19,20]

ure S1, Figure S2).

ity around the CpÀ Fe bond of the 1,1’-substituted sandwich

allows for the synthesis of di- and polymeric complexes

and the bending of the backbone for unique connectivity

Additionally, the conformational flexibil-

Hence, dichloroferrocenylphosphines 5, 6 and 9 were

synthesized from phosphonates 1, 2 and 7, which were reduced

to phosphines 3, 4 and 8 and quantitatively converted into

dichlorophosphines upon treatment with a toluene phosgene

[5,7,21,22]

[23]

[24]

[15]

modes.

The 1,2-substitution pattern (Figure 1) exhibits an

solution (Scheme 1, Experimental Part).

increased P···P distance and a wider opening angle compared

to 1,2 phenylenes, whereby a ferrocenyl annelation still occurs.

Such planar-chiral motifs are also known to introduce

Phosphonates 1 and 2 are accessible from ferrocene (FcH;

5

Fc = Fe(η -C H )(η -C H )) upon mono- and dilithiation, respec-

5

4

5

tively; the 1,2-substitution pattern was established upon ortho-

lithiation of 1. Compound 7 is the second of its type, following

[25]

chirality.

[

29]

Due to the limited accessibility of FcPCl₂its use as PFc

source within metal carbonyl cluster synthesis remained unex-

plored, except to our recent investigations on iron and cobalt

nido phosphinidene clusters Fe (CO) (μ -PFc) and Co (CO) (μ -

its iPr analogue.

Noteworthy, the so far only reported

5

example of 8 was based on reduction of Fe(η -C H -1,2-

(PCl ) )(η -C H ) (9), which in turn was obtained upon reaction

of P amidates with HCl.

5

3

5

2

5

III

[18]

However, the herein described

3

9

3

2

4

10

4

[

16]

PFc)₂. Hence, fundamental research needs to be carried out

to investigate the impact of the unique geometric and

electronic properties of the ferrocenyl unit within that field.

Herein, we discuss the reaction chemistry of Fe (CO) with

Fe(η -C H PCl )(η -C H ) (5), Fe(η -C H PCl ) (6) and Fe(η -C H -

,2-(PCl ) )(η -C H ) (9). The chemical and physical properties of

procedure does not require the synthesis of further chloro

phosphoramidates, which are highly sensitive towards acidic

conditions, and instead can be applied on commercially

available chloro phosphates.

2

9

5

4

2

5

4

2 2

5

3

5

1

2 2 5 5

the clusters synthesized were investigated by spectroscopic,

electrochemical, computational methods, as well as by single-

crystal X-ray diffraction analysis.

Cluster Synthesis

The dichlorophosphines 5, 6 and 9 were reacted with an excess

of Fe (CO) (10) in different ratios in toluene (see below and the

2

9

Experimental Section). The mixtures were placed in a 45–50 °C

pre-heated oil bath to control reaction time precisely. After-

wards, reaction mixtures were rapidly cooled to ambient

Figure 1. Unique geometrical properties of the ferrocenyl- compared to

phenyl-based motifs represented by their ypso (top) and P···P distance

4

Scheme 1. Synthesis of dichloroferrocenylphosphines 5, 6 and 9. i) Li[AlH ],

[

26]

(

bottom) in their non-bended/distorted shapes. (Values were calculated

based on reference and herein reported compounds).

ClSiMe

3

, THF, 45°C, 18 h; ii) COCl

2

(1.9 M in toluene), CH

2

Cl

2

, 25°C; iii) THF,

[

27]

[15]

BuLi, TMEDA, ClP(O)(OEt) .

2

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temperature and subsequently filtered through a pad of Celite.

influences the geometry and chirality of these intermediates

and reduced the reaction times to 0.5 hours (Scheme 2). There-

Purification was achieved by column chromatography with

silica, with the crude material pre-coated on silica. All obtained

clusters were eluted with hexane/toluene mixtures after

Fe (CO) .

1

2

in, Fe (CO) (μ -Cl)(μ -PFcCl) (11), Fe (CO) (μ -PFcR )(μ -PFcR )

2

6

2

6

2

1

2

1

2

(12a, R =R =Cl; 12b, R =Cl, R =H; 12c, R =R =H), nido-

Fe (CO) (μ -PFc) (13), and nido-Fe (CO) (μ -PFc) (14) were

3

12

3

10

3

9

3

2

Our recent findings showed that the reaction of 5 with a 7-

isolated.

It is known that by the reaction of Fe (CO) with RPCl (R=

fold excess of 10 gave the trimetallic phosphinidene cluster

nido-Fe (CO) (μ -PFc) (14) as the sole product (42% yield), as

2

9

2

e.g. Ph) at first mono-nuclear RCl P!Fe(CO) is formed, which

3

9

3

2

4

the thermodynamically most favored product within a 2 hour

on subsequent treatment with Fe (CO) produces Fe (CO) (μ -

2 9 2 6 2

[16]

[1]

reaction time. It is, however, known that cluster formation is a

multi-step process, including several mono- and bimetallic

Cl)(μ -PPhCl), isostructural to 11. It should be noted that PÀ C

2

[

30]

bond cleavage can occur, if halide substituents are absent.

[1a]

intermediates.

We were interested on how the ferrocenyl

During the course of the reaction, replacement of the μ -Cl

2

group, with its sterically and electronically modified backbone,

entity by FcPClx results in 12. That replacement of the bridging

[

1a,31]

chloride is preferred over PÀ Cl was shown recently.

Reaction of 11 with Fe (CO) probably also forms homotrinu-

2

9

clear nido-Fe (CO) (μ -PFc) (13) (Scheme 2). As shown, cluster

3

10

3

1

4 is the thermodynamically preferred product within this

reaction and most probably formed from all precursors.

Butterfly-type cluster 12 was obtained as a mixture of 3

species, in which the exo-Cl atoms have subsequently been

replaced by H atoms. Such an exchange has sparsely been

observed, but can be explained by a P-anion formation in the

0

[32]

presence of an excess of Fe .

Such a negatively charged

phosphide may act as an intermediate species, prior to its

subsequent coordination towards Fe (CO) .

2

x

The relative configuration of the PFcX entity towards the

butterfly core in dinuclear Fe (CO) (μ -Cl)(μ -PFcCl) (11) and

2

6

2

Fe (CO) (μ -PFcR) (12a–c) resulted in mixtures of diastereomers

2

6

2

Scheme 2. Reaction of 5 with Fe

2

(CO)

9

(10) giving compounds 11–14. (i)

(Scheme 2, Figure 2). For 11, the ratio of axial- and equatorial-Fc

Toluene, 0.5 h, 45°C, ratio of 5:10=1:6; a) the main isomer is shown; b)

31

1

[

16]

groups (a/e ratio) is approximated to ~3.3:1 by P{ H} NMR

t=2 h; c) ratio 5:10=1:1; a relative configuration is shown, for absolute

[

37]

configurations see Figure 2).

spectroscopy. According to the so far observed trend, an

3

1

31

1

2 6

Figure 2. P (top) and P{ H} NMR spectra (bottom) of mixtures of derivatives and isomers of 12. The dashed backbone represents the Fe (CO) unit as

observed within the crystal structure of a,a-12a (A) shown in Figure 3. (To avoid confusion caused by the different priority of H and Cl compared to a

ferrocenyl group, the expressions a (axial) and e (equatorial) refer to the Fc group; Cl-bonded P atoms are prioritized over H-bonded ones.).

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equatorial PÀ Cl bond, i.e. and axial alkyl/aryl group, results in a

diastereomers for 12a–c is given below. Single crystal X-ray

structures of phosphinidene clusters 13 and 14 confirm their

proposed structures (Figure 4).

1

13

31

high-field shifted set of signals for H, C and P nuclei. It is

furthermore known that the kinetically favored isomer bears

the aryl/alkyl groups in axial position, i.e. endo regarding the

butterfly core. That the a-isomer is the generally preferred

configuration was also shown for other PClR groups (R=alkyl,

Bis(dichlorophosphine) 6 was reacted with a 5-fold excess of

Fe (CO) under similar conditions (toluene, 45–50°C for 1 h;

2

9

5

Scheme 3). To the best of our knowledge, Fe(η -C H PCl ) (6)

5

4

2 2

[

28]

aryl) in μ -Cl and μ -SR iron carbonyl butterfly structures.

has not been used in reactions with either metal clusters or

metal carbonyl compounds to date. Column chromatographic

work-up gave clusters 15–18, which were all identified by NMR

spectroscopy and single crystal X-ray diffraction analysis (Fig-

ure 5 and Figure 6). Compounds 15–17 exhibit a butterfly-type

structure, similar to 12a–c, whereby solely one ferrocenyl

2

3

1

Compound 11 follows both trends. Based on P{ H} NMR

studies the signal of the major isomer was observed at

2

55.5 ppm (a-11) and the kinetically less-favoured e-11 isomer

[28]

at 263.9 ppm (Table 1, see below).

The ascribed ratio of

configurations is additionally supported by the results of single

crystal structure determinations of a-11 and a,a-12a (Figure 3).

Analysis of the ratio of isomers and absolute configurations of

4

fragment chelates to the Fe (CO) units in a μ’,k fashion. Cl-

2

6

substituted 17 was obtained as the main product (8%,

Scheme 3). Compounds 16 and 15 were obtained, in which one

and two chloride atoms were replaced by hydrogen (Figure S7),

respectively, similar to 12a–c.

3

1

Table 1. P{ H} NMR data (ppm) for 11–20 and multiplicity of the

3

1

In addition, compound 18 was identified possessing two [2]

respective P NMR signals for butterfly-type species 12a–c.

ferrocenophane fragments that act as bridging ligands for two

[a]

31

1

Compound

Isomer

P{ H}

^M^u^l^tⁱ^p^lⁱ^cⁱ3^t1^y

4

3

1

Fe (CO) P butterfly building blocks in a μ,μ’,k fashion.

P{ H}

P

2

6 2

Especially the PÀ P bond within the [2]ferrocenophane moiety is

FcPCl

2

an uncommon feature and is usually obtained upon reduction

1

a

e

a,a

a,e

225.5

263.9

247.4

255.0 (e)

s

[33a,34]

of a chlorophosphine with magnesium.

Given the stability

1

2a (Cl,Cl)

s

of PÀ Fe(CO) bonds, it is very unlikely that 15–16 re-open their

x

d

s

d

s

d

s

dd

butterfly structure, reassembling giving 18. Thus, it is more

likely that an open-butterfly 12-type structure has initially been

formed, followed by the PÀ P bond formation with an excess of

Fe (CO) acting as the reducing agent.

2

45.3 (a)

254.4

248.5 (P )

e,e

a,a

Cl

1

2b (Cl,H)

H

72.3 (P )

Cl

2

9

e,a

e,e

268.9 (P , e)

H

75.7 (P , a)

Changing the 6:Fe (CO) ratio from 1:5 to 1:14 slightly

2

9

1

2c (H,H)

3

4

,1’-(PCl ) -Fc

2 2

5 (H,H)

83.4

452.1

316.4

increases the yield of 17, whereby neither the formation of 15,

nor 16 was observed, and the yield of 18 remains similar. The

low overall yield might also be due to the formation of poorly

s

55.5

227.0 (P )

s

4

soluble polymers, based on μ,μ’,k coordination modes. In case

Cl

6 (H,Cl)

d

s

2

H

of dppf formation of linear chains based on a μ,k connectivity

52.9 (P )

[23]

1

7 (Cl,Cl)

8

,2-(PCl ) -Fc

2 2

9

216.0

139.1

have been reported. The nature of the PCl groups, however,

2

s

allows for further coordination modes, resulting in cross-linking

and hence insoluble species.

Cl

238.2 (P )

dd

d

P

118.7 (P )

The use of planar chiral 1,2-substituted ferrocenyl phos-

phines as ligands for metal carbonyls is not well developed.

They are so far limited to 1,2-(PPh ) derivatives coordinating to

Cl

2

0

277.1 (P )

P

169.9 (P )

d

2

[

a] a and e refers to the position of the Fc substituent with respect to a

5

[35]

Mo(CO) or Mn(η -C H )CO fragments, where a more complex

4

5

butterfly-type Fe

ferrocenes.

2 6

(CO) motif. Fc represents all types of substituted

coordination behavior of the P donor atoms is excluded,

similarly to dppf. Hence, the 1,2-(PCl ) -substituted ferrocene

2

5

Fe(η -C H -1,2-(PCl ) )(η -C H ) (9) was synthesized in order to

5

3

2 2

5

investigate how a change of the P···P geometry from 1,1’ to 1,2

(Figure 1) influences the resulting cluster geometry.

Compound 9 was reacted with 14 equiv. of Fe (CO) (10)

2

9

(Scheme 4). Neither for ferrocenes nor non-organometallic

substrates, the reaction of a 1,2-bis(dichlorophosphines) with

any homoleptic metal carbonyl has, to the best of our knowl-

edge, been investigated yet.

Compared to phosphines 5 and 6, where overall yields of

2

9% (11–14) and 13% (15–18) were obtained, the 1,2-

ferrocenyl substitution pattern produced less than 1% of a

mixture of 19 and 20 (Experimental Part). Due to an unsym-

metrical substitution pattern at the phosphorus atom planar

chirality is established in both compounds. Compound 19

2 9

Scheme 3. Reaction of 6 with Fe (CO) , resulting in the formation of clusters

1

5–18. (i) 6 (1 eqiv), 10 (5 equiv), toluene, 45–50°C, 1 h; a) 6:10 ratio of

:14.

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conformations of the involved structural motifs, particularly

with a higher amount of non-periplanar orientations for 20.

The analysis of compound 12 is more complex and requires

a more detailed discussion. It was initially obtained as a mixture

of six species, differing by the P-substitution pattern (a–c) as

well as the configuration at the P atoms (a/e) (Scheme 2,

Figure 2). Further chromatographic purification was compli-

cated by the small amount of the mixture, the similar color, and

behavior of the products. Nevertheless, further separation of

the a,a-12a and e,e-12a, and a,a-12b mixture was achieved by

column chromatography (Figure S6). Notably, monitoring via

TLC is less indicative. Due to the overall low yield of these

3

1

31

1

2 9

Scheme 4. Reaction of 9 with Fe (CO) to give 19 and 20. (i) toluene, 45–

fractions, identification is focused to P and P{ H} NMR

spectroscopy (Figure 2).

5

0°C, 1 h.

In similarity to 11, where a mixture of both a-/e-isomers was

observed, cluster 12a was identified in form of its isomers

a,a:a,e:e,e in the ratio of 2.9:1.67:1 per P atom (Table S3),

which reflects a similar preference towards the a-orientation

compared to 11. Each isomer was assigned following the above

described observation, where a-positioned groups R (herein,

assembles a racemic mixture of S - and R -configured ferrocen-

p

yls resulting in a meso-isomer. Contrary, the structure of 20

features only ferrocenyls possessing an equal configuration

(

S ,S ) or (R ,R ). Based on the low amount of product analysis of

p p p p

[37]

1

9 and 20 is limited to solid state structures obtained via single

R=Fc) show their signals at higher fields.

Isomers a,a

crystal X-ray diffraction, represented in Figure 7 and Figure 8,

respectively.

(247.4 ppm) and e,e (253.4 ppm) occurred as singlets; a,e-12a

2

with signals at 245.3 (a) and 255.0 ppm (e) each with a J

P,P

coupling constant of 109.1 Hz (Figure 2). Single Cl,H exchange

resulted in compound 12b, which was formed as a,a and e,a

isomers in a ratio of 8:1, based on integration of the PH signals

NMR and IR Analysis

3

1

in P NMR spectra. The formation of the e,e isomer has not

1

[28c]

Clusters 11–20 were identified by various NMR techniques ( H,

been observed since it could easily eliminate HCl

and react

13

1

31

1

C{ H}, P and P{ H}). Analysis via IR spectroscopy and

further to 14. All PCl based signals are accompanied with a

second set of signals, similar to 11, which is, however, not

present for the PH signals. In case of a,a-12b it was

unambiguously shown that these artifacts relate to the

compound (Table S3), most probably caused by different

orientations of the ferrocenyl group that solely impact PCl

moieties. It should be noted that the a,a/e,e isomerization

barrier for H-functionalized phosphido groups is comparably

high and inversion was found to be absent at 100°C for R=

elemental analysis was limited to 11, 13 and 14 that could be

isolated in a pure form and in substantial amounts. Compounds

1

2a–c and 15–17 were obtained as a mixtures of H- and Cl-

functionalized phosphides that could be hardly be separated

see the Experimental Section).

(

3

1

31

1

The P and P{ H} chemical shifts are the most indicative

parameter to identify the cluster core structures and P-

3

1

substitution pattern (Table 1). P{ H} signals of all herein

[36]

observed P-entities occur low-field-shifted in the order PÀ H

Ph. For sterically more crowded bis-(μ-PClFc) derivatives, the

obtained mixture is most probably kinetically controlled. The

identity of a,a-12a was additionally verified by single crystal X-

ray diffraction (Figure 3). Single crystals were obtained from the

a,a-12a, e,e-12a, and a,a-12b mixture in which it appeared as

the major product.

(

52–83 ppm)<PÀ P (119–170 ppm)<PÀ Cl (216–269 ppm)<

μ P) (Fe(CO) ) (14, 316 ppm)<(μ P)(Fe(CO) ) (13, 452 ppm).

3

2

3 3

3

3 3

For phosphinidenes 13 and 14, the increasing number of

electron withdrawing Fe(CO) fragments and the P/Fe(CO) ratio

affects the chemical shift.

3

The ‘closed’ butterfly structure in 15–17 causes a high-field

shift of the PÀ H and PÀ Cl resonances compared to ‘open’ 12a–

c, probably caused by an intramolecular transfer of electron

density from the ferrocenyl core of the more rigid 1,1’-

In addition to 12a and 12b, also 12c featuring two PH units

was formed and observed as the e,e-isomer exclusively. In

contrast to 12a, where the a,a-isomer is dominant (X=Cl), the

e,e-product in 12c is most probably preferred, due to its lower

[10]

[27]

substitution pattern. The endo-PÀ P entities in 18, 19 and 20

resonate at 119–170 ppm, which is significantly low-field shifted

compared to alkyl-substituted [2]ferrocenophanes, that are

steric demand in the axial position. The assignment as e,e is

3

1

in accordance with its P{ H} NMR resonance signal, which

appears as the most low-field shifted signal for PH fragments at

83.4 ppm compared to those where an a-configuration was

assigned 12b (a,a: 72.3; e,a: 75.7 ppm).

t

[34]

[33a]

observed at 21 ( Bu) and 42 ppm (NEt ) . Compounds 19

2

3

1

and 20 exhibit two signals in their P{ H} NMR spectra.

Resonances of 19 appear down-field shifted by 41 and 51 ppm

compared to 20. The former exhibits a dd distribution pattern

with large P,P coupling constants of 78 and 65 Hz. Instead, 20

solely couples as a doubled with J_P_,_P=21 Hz, indicating different

3

1

For H containing 12b,c, the P NMR data exhibit J_P_,_H

couplings of 404 Hz (e-PCl) and 387 Hz (a-PCl) for 12b and

319 Hz for e,e-12c. Interestingly, the anti-periplanar orientation

3

of the H atoms within e,e-12c results in a comparably high J

P,H

coupling of 85 Hz, whereas an equatorial positioning of an H

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Figure 3. ORTEP drawings of the molecular structures of a-11 (top, 30%

probability level) and a,a-12a (bottom, 50% probability level) with their

atom-numbering schemes. Hydrogen atoms are omitted for clarity. (Selected

bond properties are summarized in Table 3.) Symmetry operation to

generate equivalent atoms: (A) À x+2, y, À z+1/2.

Figure 4. ORTEP drawings of the molecular structures of 13 (top, 30%

probability level) and 14 (bottom, 50% probability level) with their atom-

numbering schemes. Hydrogen atoms are omitted for clarity. Symmetry

operation to generate equivalent atoms: (A) À x, y, z. (Selected bond

properties are summarized in Table 2).

atom (i.e. a-configuration) solely shows 23 (e,a-12b) and 8 Hz

(

a,a-12b).

1

An unusual effect occurs in the H NMR spectrum of 15 and

summarized in Tables 2 (phosphinidene clusters 13 and 14) and

3. Although the structure of 14 has recently been described by

31

the P NMR spectrum of e,e-12c, where an inverse ‘roof’-effect

[16]

for the PH hydrogen and phosphorous atoms can be observed

our group, it will briefly be discussed for comparison.

All herein described compounds crystallize in centrosym-

metric space groups; in triclinic P–1 (15–17, 19); monoclinic P2₁/

(

Figure S8).

1

3

1

The C{ H} NMR signals of the carbonyl ligands are less

indicative and are observed between 207.8 and 213.3 ppm.

The cluster cores can further be distinguished by IR

spectroscopy, where ν_C_Ostretching frequencies of terminal CO

c (a-11), P2 /n (13), C2/c (a,a-12a, 20); and orthorhombic Cmc2₁

1

(14). Compounds 17 and 19 contain two crystallographically

independent entities in their asymmetric units. Compounds a,a-

12a, 14, 19 and 20 contain symmetry elements and show only

half of molecule in the asymmetric unit.

À 1

ligands are observed between 2080 to 1960 cm . The bridging

carbonyl in compound 13 gave an additional band at

À 1

1

809 cm , similar to Fe (CO) (1828 cm ). For 11, the carbonyls

A C axis in a,a-12a intersects the FeÀ Fe bond perpendicu-

2

9

2

anti towards the electron-withdrawing Cl-bridge were found at

larly. Cluster 14 contains a mirror plane generated by the Fe₃

motif. Compound 19 possesses an inversion center in the

middle of the PÀ P bond, resulting in a meso-configuration

À 1 [37]

highest energy (2078 cm ).

(

R ,S ), whereas a C axis in 20 results in either a (S ,S )- or

p

2

p

Single-Crystal X-Ray Diffraction

(R ,R )-configuration.

p p

Compound 18 crystallizes in the non-centrosymmetric space

group P-4n2 and the absolute configuration was established

unambiguously (Flack x: 0.021(10) ). A mirror plane is con-

sequently absent. The tetragonal crystal system nevertheless

Single crystals of a-11, a,a-12a, and 13–20 were obtained upon

evaporation of dichloromethane solutions. Their ORTEP draw-

ings are depicted in Figures 3–8, selected bond properties are

[38]

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Figure 5. ORTEPs (50% probability level) of the molecular structures of 15 (left), 16 (middle) and 17 (right) with their atom numbering schemes. C-bonded

hydrogen atoms have been omitted for clarity. (Selected bond properties are summarized in Table 3).

Figure 6. ORTEP of the molecular structure of the organometallic octabisva-

lene 18. (A) y+1/2, xÀ 1/2, À z+1/2; (B) À x+2, À y+1, z; (C) 3/2À y, 3/2À x,

1

=

2

À z. (Selected bond properties are summarized in Table 3).

Figure 8. ORTEP (50% probability level) of the molecular structure of 20

shown in two different perspectives together with the atom numbering

schemes. H atoms have been omitted for clarity. Symmetry operation for

generating equivalent atoms: (A) À x, y, À z+3/2.

Figure 7. ORTEP (25% probability level) of the molecular structure of 19

showing the atom numbering scheme of one of the two molecules in the

asymmetric unit. H atoms have been omitted for clarity. Symmetry operation

for generating equivalent atoms: (A) À x+1, À y+1, À z.

structure is expanded by 3 C axis that all cross in center of the

2

P₄unit in a 90° angle. One intersects the Fe1À Fe1 bonds

perpendicularly (B-labelled in Figure 6). A second one directs

through both ferrocenyl’s iron atoms, generating the A- and D-

labelled parts. The third one proceeds perpendicularly with

results in a highly symmetrical structure of 18, showing only

one quarter of the molecule in the asymmetric unit. The

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to individual ligands. Hence, each of these ligands coordinates

Table 2. Selected bond properties of phosphinidene clusters 13 and 14

2

(

Å/°).

in a μ’,k fashion. The 1,1’-ferrocenediyl backbone in 15–17

4

instead, coordinates in a μ’,k motif, resulting in a ‘closed’

1

(μ

3

14

(μ

type

-PFc)(Fe(CO)

3

)

3

-PFc)

2

(Fe(CO)

3

)

3

butterfly.

Bond distances [Å]

The description of compound 18 is more complicated. The

P ligands within one Fe (CO) motif belong to different

CÀ P

1.759(4)

1.791(3)

2.6634(8)

2

6

Fe1À Fe2

Fe1À Fe3

Fe2À Fe3

PÀ Fe1

PÀ Fe2

PÀ Fe3

P···P*

2.7147(12)

2.6648(11)

2.6180(16)

2.1026(13)

2.1595(14)

2.2194(14)

2

ferrocenyls (2×μ’,k ). However, each sandwich fragment coor-

dinates to two butterfly entities (μ,μ’,k ), resulting in a macro-

²^.⁶⁶⁵⁷⁽⁸⁾[

a]

4

3.5864(8)

2.2095(8)

2.2643(9)

2.2282(9)

2.6027(14)

0.124(5)

1.641(6)

1.653(6)

cyclic assembly, known as organometallic octabisvalene, i.e. bis

(

hexacarbonyl-(μ -diaryldiphosphene)di-iron). Such structures

2

are rare and have solely been reported for two derivatives so

[

b]

[32,40]

P

o.o.p.···

C

5

H

4

0.166(8)

1.6403(9)

1.6464(9)

far, in which four methyl,

or two μ -bridging Fe(CO)₄

2

FeÀ Ct1

[2]

fragments replace the two ansa-ferrocenyls. One structural

feature of these diphosphenes is a PÀ P bond, which is

established between the 1,1’-substituents resulting in a 2,3-

diphospha[2]ferrocenophane motif. In compounds 19 and 20

the PÀ P bond is observed between two individual ferrocenyls,

since the increased P···P distance of the 1,2-substitution pattern

prevents an intramolecular PÀ P bond. The resulting tetraphos-

FeÀ Ct2

Angles and plane intersections [°]

176.17(10)

e)

Ct1À FeÀ Ct2

174.49(5)

[

c]

Fe

2

P···Fe

2

P (γ)

10.35(3)

[

a] Symmetry generated; [b] P shift out of the cyclopentadienyl plane; [c]

referring to the basal P Fe plane (Fe1 and Fe3).

2

8

phido ligand exhibits a μ,μ’,k coordination of the whole

4

regard to the P entity. The intersection of all three C axis also

fragment, or a bis(μ,k ) mode if the ligand is considered as a

4

2

acts as an inversion center.

dimer of two motifs. The latter formalism better represents the

symmetry within the solid state structures and allows for an

easier assignment via the k-nomenclature, resulting in a bis

Compounds 13 and 14 possess nido-Fe (CO) (μ -PFc) and

3

10

3

nido-Fe (CO) (μ -PFc) cluster cores, respectively. Structure 13

3

9

3

2

1

2’

2

1

2’

2

1

2’

(Figure 4) consists of a triangular Fe plane which is μ -bridged

(1k P ,P -2k P ,P ) coordination mode for 19 and bis(1k P ,P -

3

2

1

2

by a PFc phosphinidene fragment, similar to reported deriva-

2k P ,P ) for 20. Thus, the butterfly fragments in 19 are

exclusively connected by P atoms from different ferrocenes (μ),

whereas the ortho-P atoms in 20 chelate to one iron carbonyl

moiety (μ’). The different connectivity mode results in a rather

flat geometry for 19 and a pocket-type shape for 20. As a

further main difference between both structures, the conforma-

tion regarding the central PÀ P bond needs to be mentioned. In

case of 19, the inversion center, positioned in the PÀ P bond,

results in an ideal anti-periplanar orientation of bonds to

symmetry generated atoms. The smallest (synclinal) angles are

[39]

[14]

tives bearing alkyl or aryl groups at P. As expected, the

shortest PÀ Fe bond is observed towards Fe1 (2.1026(13) Å),

which is not involved in an additional μ -CO bridging

2

interaction. Hence, the interactions of P1 towards Fe2

(2.1595(14) Å) and Fe3 (2.2194(14) Å) are longer, but not sym-

metrical. The latter effect is compensated by a shift of the μ -CO

2

bridge towards Fe3 (C10À Fe3, 1.949(5) Å vs C10À Fe2,

2

.056(5) Å). A further compensation of the weaker PÀ Fe3

donation occurs by a significant shortening of the Fe3À Fe1

bond (2.6648(11) Å) compared to Fe2À Fe1 of 2.7147(12) Å.

Compound 14 is best described as a distorted square

pyramid, consisting of a tetragonal Fe P plane (rmsd=0.0589)

[41]

observed for the C7À P1À P1AÀ Fe2A torsion of 34.9(4)°. For 20,

the PÀ P bond intersects a perpendicular C axis, resulting in

2

torsion angles to equal atoms of 34.5(2) (C11), 114.12(5) (Fe2)

2

capped with a μ -Fe(CO) fragment in the axial position

and 157.09(5) (Fe1). The smallest torsion is observed for

4

3

2

(

Figure 4). The FeÀ Fe distances of 2.6634(8) and 2.6657(8) Å are

Fe1À P2AÀ P2À Fe2 of only 21.5(2)°, due to the μ’k coordination

,

comparable with the Fe1À Fe3 bond in 13. The P···P interaction

of the P entity towards a Fe (CO) fragment. The difference of

2

6

of 2.6027(14) Å was found to play a non-negligible role and

the syn-/anti-periplanar conformation is also reflected in the

[16]

31

1

even shortens upon reduction of the cluster. The non-binding

Fe1···Fe3 interaction is 3.5864(8) Å. Based on the geometry of

the core, the shortest PÀ Fe distances are found towards the

basal Fe atoms (2.2094(8)/2.2282(9) Å) and an increased value

towards Fe2 of 2.2643(9) Å.

Compounds a-11, a,a-12a, and 15–20 contain a Fe (CO) -

different coupling pattern of 19 (dd) and 20 (d) in the P{ H}

NMR spectra (see above).

The P-bonded ferrocenyl groups are predominantly found

in the axial (a-) positions regarding the butterfly motif, due to

structural requirements (15–17) or a kinetic preference (a-11

and a,a-12, see above). Equatorially (e-) positioned ferrocenyls

are only found in 18 and 19, containing PÀ P bonds as exo-

substituents.

[16]

2

6

based butterfly motif. It is generally coordinated by 2 PFc

ligands, except for a-11 and 20 in which one PFc moiety is

replaced by a μ -Cl and a P entity, respectively. Within the

For the ‘normal’ X Fe (CO) (X=P, Cl) butterfly structures a-

2

6

latter a ‘classic’ PFe (CO) and an ‘unusual’ P Fe(CO) fragment

11, a,a-12 and 15–19 a rather symmetrical coordination of the

P,X donors towards the iron atoms can be observed. The

highest deviation within a Fe -μ -X coordination entity is

2

6

2

4

are combined wherefore the structure cannot be described by

the classic butterfly parameters (see below and Figure S3,

Figure S4).

The butterfly entity in compounds a-11, a,a-12a can be

considered as ‘open’, meaning that the P donor atoms belong

2

observed for a,a-12a with 0.041 Å. FeÀ Cl bonds are with 2.30 Å

enlarged compared to FeÀ P bonds (~2.20 Å). Longer PÀ Fe

distances are only observed for the P Fe (CO) pattern in 20

2

6

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(

2.2957(10) and 2.3541(10) Å), in which the bridging P atoms

Both compounds feature coplanar C H planes (19, 0.0(7);

5 3

5

coordinate towards two trans-positioned Fe(CO) motifs instead

of one cis-Fe (CO) building block.

Although the PÀ Fe distances are constant throughout the

series of compounds (~2.21 Å), the FeÀ Fe distance of the

Fe (CO) motif spans from 2.55 to 2.77 Å (Table 3). A CSD search

20, 6.29(16)°) and {Fe(η -C H )} entities directing to opposite

3

5

directions. In case of 19, the distance between these planes is

2

6

1.23(10)/1.00(11) Å, which is compensated by o.o.p. shifts of the

P

P atoms by 0.445(17) and 0.34(2) Å for the central P , and

Cl

0.043(17)/0.008(18) Å for the outer P atoms. The different

2

6

revealed that an FeÀ Fe distance of ~2.62 Å (MEDIAN of 84 CSD

entries) is most common, which is close to the values observed

for closed 15–17. Increase of the opening angle as found in a,a-

o.o.p. shifts assemble the four P atoms in an ideal plane

(rmsd=0), which intersects the adjacent cyclopentadienyls by

17.7(5) and 16.0(4)°. The trans-directing Cl atoms are positioned

1

2 increases the FeÀ Fe bond length to 2.6955(8) Å, whereas a

reduced P···P distance decreased the bond length to

.6098(9) Å. It should however be noted that within the series

within the P plane (0.001(7)/0.054(7) Å).

4

Within the pocket-type structure of 20 (Figure 8 and

2

Figure 9) the C H entities of both ferrocenes are facing each

5

3

of 15–17 a steady reduction of the P···P distance is not reflected

in the accompanied FeÀ Fe bond distance. Hence, the nature

and electronic properties of the bridging ligands seem to be

decisive as found in a-11. Therein, replacement of one PFcCl by

a Cl group reduces the FeÀ Fe distance to 2.55 Å, due to the

longer FeÀ Cl interaction compared to FeÀ P. The significantly

smaller FeÀ Fe bond length in 18 is thus better explained by the

different electronic nature of the PÀ P entity compared to a PÀ Cl

or PÀ H functionality.

other, resulting in a strong intramolecular parallel displaced π-π

interaction between the C H rings of both organometallics of

5

3

3.327(2) Å with a slippage of ~1.2 Å (α_C₅_H₃_·_·_·_C₅_H₃=6.29(16)°). The

shortest distance can be found between C10 and the centroid

of the opposite C H plane (d=3.124(3) Å). This repulsion might

5

3

cause the large bending of both P atoms out of the C H

planarity by 0.261(6) (P ) and 0.361(6) Å (P ).

5

3

Cl

P

Another important parameter to particularly describe [2]

ferrocenophanes is τ (Table 3). It describes the torsion angles of

the PÀ P bond with regard to the ferrocenyl axis. For compar-

ison, τ does not exceed 3.34(3)° in 15–17. [2]Ferrocenophane

18 shows a slightly increased value of 8.98(4)°, which is the

The P···P distance between both phosphorous donor atoms

of ~2.78 Å herein (Table 3), is similar to clusters bearing other

bridging groups including flexible (e.g. alkyl), and rigid (e.g.

[33b,42]

[34]

1

,8-naphthalenyl) fragments.

The P···P interaction of ~2.8 Å

second lowest twist parameter (τ) reported so far. Usually,

[

33a]

seems to be ideal (Figure S4) since non-bridged butterfly

structures such as a-11 and a,a-12a adopt similar values

values of up to 43.2° are typical.

Herein, the system escapes

the tension with a reduced FeÀ Ct distance of solely 1.6285(1) Å.

(Table 3). Furthermore, the 1,8-C···C distance in rigid 1,8-

A further tilting occurs in the central P unit of 18. The distorted

4

naphthalenyl fragments, which should ideally be equal to the

P···P separation in the respective bisphosphine ligand, is

rectangle with distances of 2.2459(14) (PÀ P) and 2.7550(11) Å

(P···P) is twisted by 17.40(8)°. This also causes a torsion of both

Fe (CO) groups by 16.71(4)° towards each other. For the whole

[43]

[42]

increased from ~2.50 Å to 2.74 Å. Other rigid bisphosphinyl

2

6

[27]

motifs, such as biphenylene (C···C ~3.65 Å), xanthene (C···C

molecule a twist angle of 35.31(9)° can be observed.

[44]

[45]

~

4.3–4.8 Å) , and [2.2]paracyclophane (C···C 3.1–3.5 Å) have

The unusual Fe P coordination mode in 20, which is the

2

3

so far not been used in metal carbonyl cluster chemistry,

wherefore comparison is limited to the mentioned examples

above. Herein, the P···P distance reaches its maximum for a,a-

second example of an iron carbonyl butterfly structure involv-

[46]

ing three different donor atoms so far, does not exhibit the

typical butterfly structure, wherefore a plane intersection

between both wings cannot easily be defined. The description

is complicated by the fact that the central P Fe coordination

1

2a (2.8848(15) Å), most probably due to an electronic

repulsion of the π-systems of both ferrocenyls. The repulsion

2

also results in a bending of the C H plane out of an ideal axial

fragments are not planar (rmsd=0.1895, Figure 9). The tetragon

is of an irregular shape, not only due to the differences between

PÀ P (2.1853(18) Å) and FeÀ Fe (2.7775(7) Å) bonds, but also

varying FeÀ P coordination distances (Fe2À P2, 2.3541(10);

Fe1À P2 A, 2.2957(10) Å). The Fe···P distances towards the

5

4

orientation by 13.53(10)° (Table 3). Contrary, a-11 is only bent

by 2.13(13)°. Besides these differences compounds a-11 and

a,a-12a show structurally similar butterfly cores with Fe P···PFe

2

opening angles (γ) of 100.49(4)° and 111.66(3)°, respectively.

Both structures have been superimposed for a better visual-

ization of their geometrical differences/similarities (Figure S5).

For closed butterfly structures 15–17 and [2]ferrocenophane

1

8 the P···P distance (~2.8 Å) is below the size of the ferrocenyl

backbone (~3.3 Å). The shortening of the P···P distance is

interestingly not compensated by a decrease of the CtÀ FeÀ Ct

tilt angle δ of the ferrocenylene entity. Instead, the shift of the

P atom out of the adjacent C H plane increases via 0.003(7) (a-

5

4

1

1)<0.059(5) (a,a-12a)<0.081(5) (15)<0.092(13)/0.118(13)

(16)<0.132(6)/0.173(6) (17)<0.254(5) Å (18).

Due to the 1,2-substitution pattern in 19 and 20 their o.o.p.

shift depends on whether the respective P atom is located

Cl

P

outside (P entity) or the inside (P ) of the assembly, as well as

Figure 9. Ball-and-Stick representation of 19 (left) and 20 (right). The iron

carbonyl coordination spheres are highlighted for comparison.

of structural differences between 19 and 20.

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P

opposite corners of 3.4541(10) Å (Fe1···P2) and 3.2277(10) Å

Fe2···P2 A) should not be considered as binding interactions.

0.052 (19) and 0.080 Å (20) (Table 3) compared to those of CÀ P

(

bonds, which is also observed for 15–17 (see above).

However, they divide the tetragon into two possible sets of

P Fe and PFe triangles, whose plane intersections of 25.26(3)°

2

(

shorter, Fe2···P2A hypotenuse) and 27.24(3)° (longer, Fe1·· P2

(Spectro)Electro Chemistry

hypotenuse) give a better expression of the shape of this

fragment. Reconsidering the bend angle of the butterfly

structure, values of 81.79(3)°, including the ortho P atom, and

[16]

The electrochemical behavior of 11, 13, 14

investigated by cyclic voltammetry (CV) and square-wave

voltammetry (SWV) (Figure 10 and Figure S9). The electrochem-

and 17 were

9

8.67(3)° with P2 A are observed. Compound 19 exhibits plane

intersections of ~104.5°, which is similar to those of 15–17

ical measurements were performed in anhydrous dichloro-

n

(Table 3).

methane solutions under inert conditions containing [N Bu ][B-

4

À 1

The either flat (19) or pocket-type (20) geometry signifi-

(C F ) ] (0.1 molL ) as supporting electrolyte, which stabilizes

6

5 4

cantly affects the P···P distance between the ortho-positioned P

atoms. The former shows values of 3.594(4)/3.581(4) Å, which is

close to an ideal value of 3.513(3)–3.603(6) Å (Table S2). For

compound 20 the proximity between both ortho phosphorous

atoms is reduced to 2.9149(12) Å, which is below the smallest

highly charged species and minimizes ion pairing effects

[48–51]

(Experimental Part).

The redox potentials are summarized

in Table 4. Compounds 11, 14 and 17 show reversible one-

electron processes of which four are present well-separated for

14. Cluster 13 instead exhibits several irreversible processes,

indicating decomposition under the conditions applied (Fig-

ure S9). The only observable redox process for 11 (E°’=327 mV)

so far reported value of 2.950(7) Å for a NiCl complex

2

[47]

coordinated by two PPh groups. In 20 both CÀ P bonds are

2

similarly bended away from an ideal CÀ CÀ P angle of 126° to

is related to the ferrocenyl group, indicating that the

1

13.1(2)/115.1(2)°, due to a coordination towards the same Fe

{Fe (CO) (μ-Cl)P} fragment is redox inactive in the electro-

2

6

atom, requiring a closer proximity. For 19 instead, the ortho-P

atoms bind to Fe atoms (μ) of the two trans-positioned Fe (CO)

chemical window applied. Cluster 14 showed both ferrocenyl-

related redox processes at 295 and 465 mV as well-separated

processes with a redox separation of 170 mV. This separation is

based on electrostatic interactions, since IVCT bands were not

2

6

fragments (Figure 7 and Figure 9). The CÀ P distances follow the

Cl

trend where CÀ P distances are significantly shorter by at least

[16]

a

c

observed in the NIR region. Comparison of the E /E differ-

ence for 11 and 14 reveals a slightly broadened signal for the

former, which is most probably caused by the presence of a

mixture of a- and e-isomers. Compound 17 shows the most

cathodically-shifted redox process (650 mV), due to the highly

electron withdrawing effect of the Fe (CO) fragment. The

2

6

reduction of the latter could be observed at À 1883 mV as an

irreversible process. Nido cluster 13 also showed a less-

reversible redox behavior under cathodic conditions, contrary

to nido cluster 14, which underwent two well-separated

reduction processes (À 1605 and À 1755 mV), based on a

reduction of the Fe (CO) P core. Therein, a radical anion is

3

9 2

formed initially, which is equally distributed within the core,

À 1

[16]

Figure 10. CV of 14 in dichloromethane solutions (1.0 mmolL ) at 25°C

proven by in situ EPR measurements and DFT calculations.

measured with a glassy carbon working electrode. Supporting electrolyte

*

À

Further reduction of [14] formed the diamagnetic anionic

À 1

n

0

4 6 5 4

.1 molL of [N Bu ][B(C F ) ]).

2

À

cluster [14] .

The redox potentials of the cluster core reflect the electronic

[

52]

[a]

properties of the P-bonded groups, as shown recently.

Table 4. Cyclic voltammetry data (in mV) of 11, 13, 14, and 17.

Comparison with the values therein reveals that the ferrocenyl

group in 14 (À 1605 and À 1755 mV) possesses electron

donating properties similar to those of strongly electron-

[

b]

[c]

[d]

Compd.

E°’ (ΔE

p

)

ΔE°’

11

13

14

327 (85)

–

[e]

346

295 (62)

65 (63)

–

170

[

f]

donating p-OMe (À 1530 and À 1760 mV) and p-NMe (À 1630

2

4

and À 1790 mV) groups attached at the Ph-functionalized

À 1605 (68)

À 1755 (64)

650 (99)

150

[3]

Fe (CO) P cluster cores.

3

9 2

[16,53,54]

The reversible redox behavior of 14

under electro-

1

7

[g]

À 1883

chemical conditions allowed for further spectro-electrochemical

IR measurements, where the shift of the ν_C_Ostretching

frequencies should reflect the charge distribution upon oxida-

tion and reduction (Figure 11 and Table 5). Upon single and

+

À 1

[

a] Potentials vs FcH/FcH , scan rate 100 mVs at a glassy-carbon

À 1

electrode of 1.0 mmolL

solutions in anhydrous dichloromethane

À 1

n

containing 0.1 molL of [N Bu

4

][B(C

6

F

5

)

4

] as supporting electrolyte at

2

5°C. [b] Formal potential. [c] Difference between the cathodic and anodic

+

2+

double oxidation to [14] and [14] , respectively, a hypsochro-

peak potential. [d] Potential difference between the first and the second

redox processes. [e] Obtained from SWV measurements. [f] Derived from

reference 16. [g] Irreversible; cathodic peak potential.

À 1

mic shift of all bands by ~10 cm occurs. The band distribution

2

+

for 14 and [14] is similar, indicating that the overall geometry

Eur. J. Inorg. Chem. 2021, 1–18

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potential of 1700 mV is reached. This in turn shows that

oxidation of the ferrocenylene backbone causes only minor

changes within the symmetry of the compound and the energy

of the carbonyl stretching.

The reduction of 14 resulted in a bathochromic shift (Δv) of

À 1

À

the carbonyl stretching frequencies by ~50 cm towards [14]

(

Table 5), showing an increased impact of a single charge

À 1

+ +

2+

compared to a Δv of 10 cm for the 14/[14] and [14] /[14]

transitions upon oxidation. This verifies that reduction occurs

within the Fe (CO) P core, directly affecting the coordinating

2

9 2

carbonyls. However, the steady conditions within the used

OTTLE (=optically transparent thin layer electrochemical) cell

2

À

resulted in a rapid decomposition of [14] upon steady

[16]

exposure to the negative potentials.

À

Reduction of 17 and formation of [17] reduced the

intensity of three of the four stretching frequencies and gave

rise to two new bands at lower wavenumbers (Table 5). The

Figure 11. In situ IR spectra of 14 (left) and 17 (right) at 25°C in dichloro-

À 1

methane (2 mmolL ) at rising (top) and decreasing potentials (bottom) vs.

À 1

n

Ag/AgCl. Supporting electrolyte 0.1 molL of [N Bu

4 6 5 4

][B(C F ) ]; Pt working

electrode.

À 1

equal intensity of the stretching at 1987 cm indicates that

vanishing and growth of bands occurred simultaneously. The

three bands of lowest energy seem to correspond to each

other, due to their similar intensity distribution and separation.

Table 5. Selected IR data of the carbonyl regions of 14 and 17 upon

reduction and oxidation.

[a]

À 1

Thus, a bathochromic shift of ~55 cm occurs upon reduction,

À

+

2+

Δνred

[14]

14

[14]

Δvox

À 1

which is similar to 14 (~50 cm ). This confirms that reduction

–

2065

2035

2075

2046

2085

2056

2036

10/10

occurs at the Fe (CO) P fragment. The slightly larger shifts for

2

6 2

4

5

9

2

9

1986

the oxidation and reduction processes of 17 can be explained

2

035

2027

013

with the smaller number of Fe(CO) fragments compared to 14.

1971

1935

2013

3

2

2013

For the latter, negative and positive charges are distributed

1994

17

¹⁹⁹⁸+

[17]

2089

2053

À

over three Fe(CO) cores, contrary to 17 with just two metal

3

Δνred

[17]

Δvox

16

17

carbonyl fragments.

2073

5

6

5

1

0

8

1985

1955

1929

2036

2015

1987

Computational Methods

À 1

[

a] All values are given in cm .

Recent investigations of nido-cluster 14 showed that its

reversible redox processes in the anodic and cathodic region

can be explained with ferrocenyl-based HOMO and core-based

+

remains comparable. In case of [14] a mixed pattern is

observed, representing a less symmetrical species, based on

oxidation states, excluding communication in this mixed-valent

species. That electrostatic interactions of distant, non-conju-

gated redox-active groups can affect the value of the respective

CO stretching frequencies was recently shown for a Fe (CO) (μ -

[16]

LUMO orbitals.

A cobalt derivative instead revealed core-

based HOMO orbitals, resulting in non-reversible redox

[16]

processes. Similar differences are observed for μ -Cl-bridged

2

butterfly compound a-11 and the pyramidal nido-Fe (CO) (μ -

3

10

3

PFc) phosphinidene cluster 13. The former gave one reversible

2

6

3

[14]

+

PR)₂butterfly species (R=CH Fc).

The congested bridged

Fc/Fc -related redox process (Figure 10), whereas 13 showed

2

butterfly species 17, showing a reversible ferrocenyl- and an

irreversible core-based redox event, was investigated for

comparison (Figure 11, Table 5). Upon stepwise oxidation of 17

to [17] only minor changes of its IR spectra occurred in which

the intensity of all four bands decreased slightly and two weak

bands rose at higher wavenumbers. Assuming that they are

an irreversible behavior and SWV measurements were required

(Figure S9). Hence, DFT calculations were carried out for a-11

and 13 to prove if this behavior can be correlated with the

location of HOMO and LUMO orbitals (Figure 12). Indeed,

whereas the LUMO is localized at the metal carbonyl units for

both compounds, the location of the HOMO differs. In agree-

ment with the reversible redox behavior of 11 in CV experi-

ments, its HOMO with the energy of À 6.384 eV is found to be

ferrocenyl-based.

+

related to the intense adjacent vibrations, a shift Δv of 17 and

ox

À 1

1

6 cm occurs, which is similar to 14.

Although our measurement conditions did not allow for a

further increase of the potential it can be assumed that

At the same level of theory, the HOMO of the neat ferrocene

is predicted at À 5.855 eV. Stabilization of the Fc-based orbital

in 13 by 0.529 eV agrees with its considerably more positive

oxidation potential when compared to the unsubstituted FcH/

oxidation was close to completeness at 1700 mV (vs Ag/AgCl).

2

+

For comparison, formation of [14] was almost finished at

100 mV (Figure S10). Together with the redox potentials for

1

+

2+

+

[

14] /[14] (465 mV vs FcH/FcH ) and 17/[17] (650 mV), that

FcH redox pair (note that the measured redox potential also

differ by 185 mV, formation of 17 should be finished before a

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binding modes. The reaction of 9 with homoleptic metal

carbonyls resulted in two isomers consisting of

PÀ P

connected dimer, which coordinates towards two independent

a

8

4

Fe (CO) fragments in a novel μ,μ’,k or bis(μ,k ) fashion. Both

2

6

structures vary in their binding modes of the ortho P atoms

towards the Fe (CO) entities. Compound 19 reveals μ-inter-

2

6

actions towards iron atoms of different metal carbonyl frag-

ments exclusively. For 20 instead, μ,μ’ motifs as well as

coordination towards same iron atoms occur. The different

coordination modes cause a flat and a pocket-type shape,

respectively. The chelating coordination mode in 20 also

requires a bent of both ortho P atoms towards each other,

resulting in the shortest so far observed P···P distance of

2

.950(7) Å.

Electrochemical measurements revealed reversible Fc-re-

lated redox processes, except for 13. The latter possesses its

HOMO distributed over the Fe (CO) P cluster core rather than

3

10

Figure 12. DFT-calculated energies and isosurfaces of the HOMO and LUMO

orbitals of a-11 (left) and 13 (right). Theory level: ZORA-PBE0-D3BJ/def2-

TZVPP(SARC).

the ferrocenyl entity as shown by DFT calculations

Experimental Section

General. All reactions were performed under an atmosphere of

argon using standard Schlenk techniques. Reaction flasks (Schlenk

tubes) were heated at reduced pressure with a heat gun and

flushed with argon. This procedure was repeated thrice. If

necessary, solvents were deoxygenated by standard procedures.

For column chromatography silica with a particle size of 40–60 μm

includes contribution from solvation energy and hence should

not be equal to the difference of Fc-based MO energies).

The HOMO of 13 with the energy of À 6.467 eV is localized

on the metalcarbonyl cluster core, which explains the irrever-

sible redox behavior of 13 in the anodic range. The ferrocenyl-

based MO in 13 is the HOMO-2 with the energy of À 6.671 eV,

(230–400 mesh (ASTM)) was used. The assignment of a-(axial) and

e-(equatorial) for substituents at butterfly-type fragments refers to

the positioning of the Fc group, even if Cl substituents are present,

possessing a higher priority contrary to H. This simplifies the

discussion regarding the configuration of the ferrocenyl group at

each phosphorous atom.

0

.204 eV below the HOMO of 13 and 0.816 eV below the HOMO

of Fc.

Conclusion

Reagents. Tetrahydrofuran was purified by distillation from

sodium/benzophenone ketyl. Dichloromethane, hexane and

toluene were dried and purified with an MBraun SPS-800

purification system and stored over molecular sieve (4 Å). Com-

[15]

5

The reaction of the PCl -functionalized ferrocenes Fe(η -

2

5

C H PCl )(η -C H ) (5), Fe(η -C H PCl ) (6) and Fe(η -C H -1,2-

5

4

2

5

4

2 2

5

3

[55]

[56]

[15]

pounds Fe (CO) (4), FcP(O)(OEt) (1), FcPH (3), FcPCl (5),

5

2

9

2

(

PCl ) )(η -C H ) (9) with Fe (CO) is reported, resulting in the

n

[48,57]

2

5

2

9

and [N( Bu) ][B(C F ) ]

were synthesized according to literature

4

6 5 4

formation of various single- and double-ferrocenyl-functio-

nalized clusters. All dichlorophosphines were obtained upon

procedures reported elsewhere. Ferrocene, phosgene (1.9 M in

n

t

toluene), Li[AlH ] (600 mg pallets), BuLi ( : 2.5 M in hexane; : 1.9 M

4

reaction of their PH species with a toluene phosgene solution,

a new approach for the latter two substrates.

in hexane), ClP(O)(OEt) , and Fe(CO) , were purchased from

commercial suppliers and were used without further purification.

2

5

2

The main structural feature of the clusters obtained is a

Fe (CO) (μ -PFc) butterfly entity, whereas 5 gave open and 6

closed motifs, with the ferrocenediyl building block bridging

both P donor atoms. The open butterfly structures were

obtained with different configurations of the PFc groups with

Instruments. FT-IR spectra were recorded as KBr pallets in transition

mode. NMR spectra were recorded with a Bruker Avance III 500

2

1

13

spectrometer (500.3 MHz for H, 125.8 MHz for C and 202.5 MHz

3

1

for P) and are reported with chemical shifts in δ (ppm) units

downfield from tetramethylsilane with the solvent as the reference

1

13

1

signal (chloroform-d : H at 7.26 ppm and C{ H} at 77.16 ppm), or

1

regard to the V-shaped P Fe (CO) building block were

2

[58]

13

1

2

6

by the H solvent lock signal. Two decimal places for C{ H}

values are given to clarify the assignment of signals, which are in

close proximity to each other. The melting or decomposition points

were determined by using a Gallenkamp MFB 595 010 M melting

point apparatus. Elemental analyses were performed with a Thermo

FlashAE 1112 instrument.

observed, whereby an axial (a-) positioning was preferred in

both cases. Dichlorophosphine 5 additionally gave phosphini-

dene clusters of type nido-Fe (CO) (μ -PFc) (13) and bipyrami-

3

10

3

dal nido-Fe (CO) (μ -PFc) (14).

3

9

3

2

In addition to the closed butterfly structures in which the

4

Electrochemistry. Electrochemical measurements of the respective

1

,1’-ferrocenediyl backbone adopts a μ’,k -binding mode, a

À 1

n

compounds (1.0 mmol·L ) using 0.1 mol·L [N Bu ][B(C F ) ] as

4

6 5 4

further example of an organometallic octabisvalene was

the supporting electrolyte in anhydrous, oxygen-free dichloro-

formed. Therein, a direct PÀ P bond between both cyclo-

methane were performed in an argon purged cell at 25°C with a

pentadienyls results in a [2]ferrocenophane motif, coordinating

Radiometer Voltalab PGZ 100 electrochemical workstation inter-

4

towards two exo-directing iron carbonyl fragments in μ ,μ’,k

2

Eur. J. Inorg. Chem. 2021, 1–18

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[

57]

faced with a personal computer. For the voltammetric measure-

ments a three electrode cell containing a Pt auxiliary electrode, a

When 750 mg (2.61 mmol) of 5 and 950 mg (2.61 mmol) of 10 were

reacted in 30 mL of toluene under equal conditions a mixture of

compounds 12a–c could be eluted using a 4:1 hexane/ toluene

mixture (v/v) from a silica column. Subsequent purification (silica,

20×3.5 cm) with the same solvent mixture allowed for the

2

glassy carbon working electrode (surface area 0.031 cm ) and an

Ag/Ag (0.01 mmolL [AgNO ]) reference electrode fixed on a

Luggin capillary was used. The working electrode was pretreated

+

À 1

3

by polishing on a Buehler microcloth first with 1 μm and then with

separation of

a

3:1 mixture of a,a-12a/e,e-12a (6.3 mg,

1

a = μm diamond paste. The reference electrode was constructed

0.008 mmol, 0.6% based on 5), and compound a,a-12b. After

removal of all volatiles, all compounds were obtained as orange-

yellow solids. Single crystals were grown from slow evaporation of

dichloromethane mixtures of the respective compound at ambient

conditions.

4

À 1

from a silver wire inserted into a 0.01 mmolL solution of [AgNO₃]

and 0.1 molL of an [N Bu ][B(C F ) ] acetonitrile solution in a

À 1

n

4

6 5 4

Luggin capillary with a CoralPor tip. This Luggin capillary was

À 1

inserted in a second Luggin capillary containing a 0.1 molL

n

[

N Bu ][B(C F ) ] dichloromethane solution and a CoralPor tip.

4

6 5 4

Fe (CO) (μ -Cl)(μ -PClFc) (11): The compound was obtained as a

2

6

2

Experiments under the same conditions showed that all reduction

~

3.3:1 mixture of the a- (major) and the e-isomer (minor) of 11. (All

and oxidation potentials were reproducible within �5 mV. Exper-

+

H atoms are summed up to a total of 3.3·9+9 H=38.7 H. HSQC

imental potentials were referenced against an Ag/Ag reference

and HMBC data support the assignment.) Yield: 44 mg (0.04 mmol,

electrode, but the presented results are referenced against

[59]

4% based on 5). Red solid. IR data (KBr, v˜): 2078 (vs), 2044 (s), 2020

ferrocene as an internal standard as required by IUPAC.

To

À 1

(

s), 2014 (s), 1986 (vs), 1969 (s) cm . Anal. Calcd for C H Cl Fe O P

1

6

9

2

3

6

achieve this, each experiment was repeated in the presence of

À 1

(566.65 g/mol): C, 33.91; H, 1.60. Found: C, 35.63; H, 1.91 (toluene

1

mmolL of decamethylferrocene (Fc*). Data were processed on a

1

impurities). Mp: 120°C. H NMR (CDCl , δ): 4.37 (s, 21.5 H, a-,e-C H ),

3

5

Microsoft Excel worksheet to set the formal reduction potentials of

+

[60]

+

4.493–4.494 (m, 13.2H, a-C

5

H

4

), 4.62–4.63 (m, 2H, e-C H ), 4.62–4.63

5 4

the FcH/FcH couple to 0.0 V. Under our conditions the Fc*/Fc*

1

3

1

+

(m, 2H, e-C

(s, e-C

5

H

4

) ppm. C{ H} NMR (CDCl

3

, δ): 70.77 (s, a-C H ), 70.87

5 5

couple was at À 614 mV vs FcH/FcH , ΔE =60 mV, while the FcH/

p

+

5

H

5

), 71.9 (d, JC,P =9.1 Hz, a-C

H

5

), 72.5 (d, JC,P =8.9 Hz, e-C

4

H

5

),

4

FcH couple itself was at 220 mV vs Ag/Ag , ΔE =61 mV.

p

7

3.44 (d, J =14.18 Hz, e-C H ), 73.48 (d, J =13.29 Hz, a-C H ),

C,P

5

4

C,P

5

4

1

Spectroelectrochemistry. Spectroelectrochemical IR measurements

78.7 (d, J =8.5 Hz, a-CÀ P), 207.7 (br s, e-CO), 207.9 (br s, a-CO)

C,P

À 1

31

1

of 2.0 mmol·L solutions of 14 and 17 in anhydrous dichloro-

ppm. (The e-CÀ P signal could not be resolved.) P{ H} NMR (CDCl ,

3

À 1

n

methane containing 0.1 mol·L of [N Bu ][B(C F ) ] as the support-

δ): 225.5 (a-isomer), 263.9 (e-isomer) ppm.

4

6 5 4

ing electrolyte were performed in an OTTLE (=Optically Trans-

parent Thin-Layer Electrochemical) cell with CaF₂windows at a

Varian Cary 5000 spectrophotometer at 25°C.

À 1

Crystal Data for a-11: C H Cl Fe O P, M=566.65 gmol , intense

1

6

9

2

3

6

red plate, 0.2·0.2·0.1, monoclinic, P2 /c, λ=1.54178 Å, a=

2.8422(6) Å, b=20.1801(9) Å, c=7.7843(4) Å, β=93.608(3), V=

2013.36(17) Å , Z=4, 1 =1.869 Mgm , μ=20.588 mm , F

1

3

À 3

À 1

Single crystal X-ray diffraction analysis. Data were collected with

an Oxford Gemini S diffractometer (a,a-12a, and 14–20) and a

Venture D8 diffractometer (a-11, 13) with Cu K_αradiation (λ=

=

calcd

000

1120, T=298 K, θ range 3.448À 65.480°, 41144 reflections collected,

3429 independent reflections (R =0.0777), 253 parameters, 0

int

1.54184 Å; 13) and Mo K_αradiation (λ=0.71073 Å, a-11, a,a-12a,

restraints, GooF=1.030, R =0.0373, wR =0.0957 (I>2σ(I)).

1

2

1

4–20) at 125 K (a,a-12a, 14–20) and ambient conditions (a-11, 13).

a,a-Fe (CO) (μ -PClFc) (a,a-12a): Present with 75% in a mixture

2

6

2

Measurements with Cu K radiation at the D8 Venture device were

performed with a fine-focus source. The molecular structures were

solved by direct methods using SHELXS-13 and refined by full-

matrix least-squares procedures on F using SHELXL-13.

hydrogen atoms were refined anisotropically and a riding model

was employed in the treatment of the hydrogen atom positions,

except otherwise noted. Graphics of the molecular structures have

α

1

with e,e-12a. Orange solid. H NMR (CDCl , δ): 4.03–4.01 (m, 4H,

3

1

3

1

[

61]

C

5

H

4

), 4.22–4.20 (m, 4H, C

5

H

4

), 4.22 (s, 10H, C

), 71.0 (t, JC,P =5.3 Hz, C

5

H

5

) ppm. C{ H} NMR

), 75.6 (t, JC,P

2

[62,63]

(CDCl

3

, δ): 70.8 (s, C

H

5

H

5

4

=

All non-

1

3

8

.0 Hz, C H ), 86.4 (dd,

J

C,P

1

=9.5 Hz, J_C_,_P=7.8 Hz, CÀ P), 210.8 (t,

5

4

2

31

J_C_,_P=4.1 Hz, CO) ppm. P{ H} NMR (CDCl , δ): 247.3 (s) ppm.

P

3

NMR (CDCl , δ): 247.3 (s) ppm.

3

[

64]

À 1

been created by using ORTEP.

Crystal Data for a,a-12a: C H Cl Fe O P , M=782.64 gmol ,

2

6

18

2

4

6 2

orange block, 0.2·0.2·0.05, monoclinic, C2/c, λ=0.71073 Å, a=

Deposition Numbers 1999233 (a -11 ), 1999234 (13 ), 1935472 (14 ),

2

1

0.0095(11) Å, b=9.4911(4) Å, c=14.7351(7) Å, β=93.179(5)°, V=

1

999235 (a ,a -12a ), 1999236 (15 ), 1999237 (16 ), 1999238 (17 ),

999239 (18 ), 1999240 (19 ), and 1999241 (20 ) contain the

3

À 3

À 1

794.1(2) Å , Z=4,

1

=1.861 Mgm , μ=2.382 mm ,

F

=

000

calcd

560, T=125.5(6) K, θ range 3.347–25.000°, 7823 reflections

supplementary crystallographic data for this paper. These data are

provided free of charge by the joint Cambridge Crystallographic

Data Centre and Fachinformationszentrum Karlsruhe Access Struc-

tures service www.ccdc.cam.ac.uk/structures.

collected, 2459 independent reflections (R =0.0463), 181 parame-

int

ters, 0 restraints, GooF=1.019, R1=0.0321, wR2=0.0665 (I>2σ(I)).

e,e-Fe (CO) (μ -PClFc) (e,e-12a): Present with 25% in a mixture

2

6

2

1

with a,a-12a. Orange solid. H NMR (CDCl , δ): 4.36 (s, 10H, C H ),

4.61–4.50 (m, 4H, C

3

5

Computational methods. DFT calculations were performed with

1

3

1

[65]

5

H

4

), 4.79–4.81 (m, 4H, C H ) ppm. C{ H} NMR

5 4

the Orca 4.2.1 suite using ZORA scalar-relativistic correction.

(

7

CDCl , δ): 71.0 (s, C H ), 72.1 (t, J =4.7 Hz, C H ), 73.6 (t, J =

3

5

C,P

5

4

C,P

2

.3 Hz, C H ), 210.0 (t, J =4.3 Hz, CO) ppm (the signal of the ipso

5 4 C,P

31 1

carbon could not be resolved). P{ H} NMR (CDCl , δ): 254.4 (s)

ppm. P NMR (CDCl , δ): 254.4 (s) ppm.

3

Reaction of FcPCl (5) with Fe (CO) (10)

2

9

3

1

3

Phosphine 5 (500 mg, 1.75 mmol) and 10, (3.82 g, 10.5 mmol) were

reacted in 50 mL of toluene at 45–50°C for 30 min. All volatiles

a,e-Fe (CO) (μ -PClFc) (a,e-12a): Solely identified from initial

2

6

2

1

mixture of isomers of 12a–c (See Figure S6). H NMR (CDCl , δ):

3

were removed in vacuo. The residue was taken up in 30 mL of

dichloromethane, mixed with silica and evaporated to dryness. This

mixture was put on a column (silica, 20×3.5 cm) and hexane was

used to remove Fe (CO) as the first, intense green fraction.

1

3

1

could not be assigned from the mixture. C{ H} NMR (CDCl , δ):

3

7

0.88 (s, C H ), 70.89 (s, C H ), 71.9 (d, J =9.6 Hz, C H ), 75.9 (d,

5

2

C,P

5

4

J_C_,_P=15.7 Hz, C H ), 210.3 (t, J =4.2 Hz, CO) ppm. Further signals

could not unambiguously be assigned. P{ H}/ P NMR (CDCl , δ):

2

5

4

C,P

3

12

31

1

31

3

Changing the eluent to a 4:1 hexane/toluene mixture (v/v) eluted

1, 13 and 14 as red bands. After removal of all volatiles all

compounds were obtained as purple-red solids.

2

a

2

e

45.3 (d, J =109.2, P ), 255.0 (d, J =109.1 Hz, P ) ppm.

C,P C,P

1

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doi.org/10.1002/ejic.202100097

5

a,a-Fe (CO) (μ-PClFc)(μ-PHFc) (a,a-12b): Yield: 5 mg (0.007 mmol,

Fe (CO) (μ -[Fe(η -C H PH) ]) (15): Yield: 17 mg (0.032 mmol, 2%

2 6 2 5 4 2

1

2

6

1

0

3

4

.3% based on 5). Orange solid. H NMR (CDCl , δ): 3.98 (dd, J

=

based on 6). H NMR (CDCl , δ): 4.28 (t, J =1.9 Hz, 4H, C H ), 4.56

3 H,H 5 4

1 [66] 3

3

H,P

3

86.6 Hz, J =8.7 Hz, 1H, PH)*, 4.25 (s, 5H, C H ), 4.36 (s, 5H, C H ),

(pt, J_H_,_H=1.7 Hz, 4H, C H ), 5.48 (dd, J =294.5,

J_H_,_P=76.3 Hz,

P,P

5

4

H,P

3

1

.46–4.45 (m, 2H, C H ), 4.49–4.47 (m, 2H, C H ), 4.54–4.52 (m, 4H,

1H, PH) ppm. P{ H} NMR (CDCl , δ): 55.5 (s) ppm. No signals could

5

4

5

4

3

13

1

H

13

1

31

C H ) ppm. C{ H} NMR (CDCl , δ): 70.4 ( J =2.1 Hz, CÀ P ), 70.4 (s,

be detected in the C{ H} and P NMR, due to the small amount of

compound.

5

4

3

C,P

C H ), 70.9 (s, C H ), 71.5 (d, J =10.0 Hz, C H ), 71.9 (d, J =8.4 Hz,

5

C,P

5

4

C,P

C H ), 73.5 (dd, J =11.8, 2.6 Hz, C H ), 73.9 (d, J =11.8 Hz, C H ),

5

4

C,P

5

4

C,P

5

4

À 1

1

Cl

2

31

1

Crystal Data for 15: C16

H

10Fe

3

O

6

P

2

, M=527.73 gmol , yellow block,

8

2.5 ( J =21.7 Hz, CÀ P ), 211.6 (t, J =4.7 Hz, CO) ppm. P{ H}

C,P

2 H 2

0.2·0.2·0.1, triclinic, P–1, λ=0.71073 Å, a=7.5447(7) Å, b=

NMR (CDCl , δ): 72.3 (d, J =113.8 Hz, P ), 248.5 (d, J =113.9 Hz,

P ) ppm. P NMR (CDCl , δ): 72.3 (dd, ^JP,H =387.2 Hz, ^JP,P

3

P,P

Cl

31

1

2

11.2403(9) Å, c=11.9775(10) Å, α=64.246(8)°, β=80.782(8)°, γ=

=

3

À 3

H

2

3

Cl

83.940(7)°, V=902.30(15) Å , Z=2,

1

calcd =1.942 Mgm , μ=

113.8 Hz, P ), 248.5 (dd, J =113.8 Hz, J =8.4 Hz, P ) ppm. *The

P,P P,H

À 1

2

1

.588 mm , F =524, T=125.00(10) K, θ range 3.129–25.000°,

0

00

signal partially overlaps with one of the C H moieties.

5

1140 reflections collected, 3142 independent reflections (R

=

int

e,a-Fe (CO) (μ-PClFc)(μ-PHFc) (e,a-12b): The compound could

0.0331), 252 parameters, 0 restraints, GooF=1.034, R1=0.0293,

wR2=0.0724 (I>2σ(I)).

2

6

3

1

solely be identified from the initial mixture of isomers of 12a–c.

H} NMR (CDCl , δ): 75.7 (d, ^JP,P =148.3 Hz, P ), 268.9 (d, ^JP,P

48.4 Hz, P ) ppm. P NMR (CDCl , δ): 75.7 (dd, J =148.3, J

04.3 Hz, P ), 268.9 (dd, J =148.3, J =23.0 Hz, P ) ppm.

P

1

2

H

2

{

=

3

5

Cl

31

2

1

Fe

(CO)

2

6

(μ

2

-[Fe(η -C

H

5

4

PCl)(η -C

5

H

PH)])

4

(16):

3

Yield:

, δ): 4.31 (pt*, JH,H

.0 Hz, 2H, C H ), 4.38 (pt*, J =2.0 Hz, 2H, C H ), 4.61 (dd*, J=2.2,

2 mg

1

4

3

P,P

Cl

P,H

1

H

2

3

(0.004 mmol,<1% based on 6). H NMR (CDCl

=

P,P

P,H

2

5

4

H,H

5

4

1

e,e-Fe (CO) (μ -PHFc) (e,e-12c): The compound could solely be

2.0 Hz, 2H, C H ), 4.79 (dd*, J=2.2, 2.0 Hz, 2H, C H ), 5.67 (dd, J

5 4 5 4 H,P

3 13 1

=

2

6

2

3

1

identified from the initial mixture of isomers of 12a–c. P{ H} NMR

365.1 Hz, J =14.1 Hz, 1H, PH) ppm. C{ H} NMR (CDCl , δ): no

H,P 3

31

1

(

CDCl , δ): 83.4 (s) ppm. P NMR (CDCl , δ): 83.4 (dd, J =319.3,

signals could be detected, due to the small amount of compound.

3

P,H

3

1

2

J_P_,_H=85.3 Hz) ppm.

P{ H} NMR (CDCl , δ): 52.9 (d, J =142.9 Hz, PH), 227.0 (d, J =

3 P,P P,P

1

43.3 Hz, PÀ Cl) ppm. *Coupling constants were obtained from fitted

Fe (CO) (μ -PFc) (13): Yield: 84 mg (0.16 mmol, 8% based on

3

10

3

spectra (see ESI)

FcPCl ). Red solid. IR data (KBr, v˜): 2080 (m), 2006 (vs), 1987 (w),

2

À 1

1

974 (w), 1956 (s), 1809 (s) cm . Anal. Calcd for C H Fe O P·3/

Crystal Data for 16: C H ClFe O P , M=562.17 gmol , pale orange

16 9 3 6 2

20

9

4

10

2

C₆H₁₄(663.63·3/2 86.18 g/mol): C, 45.09; H, 3.07. Found: C, 44.62;

plate, 0.2·0.2·0.02, triclinic, P–1, λ=0.71073 Å, a=7.6655(8) Å, b=

1

H, 3.57. Mp: 132°C. H NMR (CDCl , δ): 4.45 (s, 5H, C H ), 4.90–4.92

9.9831(13) Å, c=13.5566(15) Å, α=70.130(11)°, β=84.563(9)°, γ=

3

5

13

1

3

À 3

(m, 2H, C H ), 5.03–5.05 (m, 2H, C H ) ppm. C{ H} NMR (CDCl , δ):

74.880(10)°, V=941.9(2) Å , Z=2,

1

=1.982 Mgm , μ=

5

4

5

4

3

calcd

À 1

7

2

1.3 (s, C H ), 73.6 (d, J =9.2 Hz, C H ), 75.4 (d, J =12.5 Hz, C H ),

2.623 mm , F =556, T=126(2) K, θ range 3.094–25.000°, 7819

5

C,P

5

4

C,P

5

4

000

12.6 (s, CO) ppm. (The signal of the CÀ P carbon atom was not

reflections collected, 3297 independent reflections (R =0.0570),

int

31

1

resolved.) P{ H} NMR (CDCl , δ): 452.4 ppm.

257 parameters, 357 restraints, GooF=1.058, R1=0.0676, wR2=

3

0.1598 (I>2σ(I)).

À 1

Crystal Data for 13: C H Fe O P, M=663.64 gmol , intense violet-

20

9

4

10

5

red plate, 0.2·0.1·0.05, monoclinic, P2 /n, λ=1.54184 Å, a=

Fe (CO) (μ -[Fe(η -C H PCl) ]) (17): Yield: 39 mg (0.065 mmol, 5%

2 6 2 5 4 2

1

2

1

3

1.342(2) Å, ₃b=9.035(5) Å, c=23.488(5) Å, β=102.535(5), V=

based on 6). IR data (KBr, v˜): 2068 (s), 2036 (s), 2031 (s), 2007 (s),

À 3

À 1

À 1 1

349.6(17) Å , Z=4, 1 =1.876 Mgm , μ=20.553 mm , F

=

1997 (s), 1979 (s), 1966 (s) cm . H NMR (CDCl , δ): 4.43 (dd, J

=

calcd

000

3

H,H

1

3

312, T=299 K, θ range 3.856–65.497°, 18017 reflections collected,

1.9 Hz, 4H, C H ), 4.76 (dt, J =3.31, 1.53 Hz, 4H, C H ) ppm. C{ H}

5

4

H,H

5

4

987 independent reflections (R =0.0510), 316 parameters, 0

NMR (CDCl , δ): 73.1 (t, J =4.3 Hz, C H ), 76.2 (t, J =5 Hz, C H ),

3 C,P 5 4 C,P 5 4

1 31 1

int

restraints, GooF=1.113, R =0.0414, wR =0.0811 (I>2σ(I)).

91.6 (dd, J =18.7, J_C_,_P=16.0 Hz, CÀ P), 210.7 (b, CO) ppm. P{ H}

1

2

C,P

NMR (CDCl , δ): 216.0 (s) ppm.

3

Fe (CO) (μ -PFc) (14): Yield: 220 mg (0.32 mmol, 16% based on

FcPCl ). IR data (KBr, v˜): 2065 (w), 2035 (vs), 2013 (s), 1994 (m) cm .

3

9

3

2

À 1

Crystal Data for 17: C H Cl Fe O P , M=596.61 gmol , orange

2

16

8

2

3

6 2

Red solid. Anal. Calcd for C H Fe O P (851.62 g/mol): C, 40.90; H,

block, 0.2·0.2·0.1, triclinic, P–1, λ=0.71073 Å, a=10.0385(4) Å, b=

29

18

5

9 2

1

2

1

{

.13. Found: C, 40.75; H, 2.52. Mp: 132°C. H NMR (CDCl , δ): 4.39 (s,

13.1875(4) Å, c=15.4752(4) Å, α=93.731(2)°, β=105.137(3)°, γ=

3

1

3

À 3

0H, C H ), 4.64–4.66 (m, 4H, C H ), 4.69–4.71 (m, 4H, C H ) ppm.

H} NMR (CDCl , δ): 70.8 (s, C H ), 72.8 (br, s, C H ), 73.9 (br, C H ),

C

97.128(3)°, V=1952.10(11) Å , Z=4,

1

calcd

=2.030 Mgm , μ=

5

4

5

4

5

4

1

À 1

2.670 mm , F =1176, T=125.9(8) K, θ range 2.977–24.999°,

3

5

4

5

4

000

31

1

2

13.3 (s, CO) ppm. P{ H} NMR (CDCl , δ): 316.2 ppm. Spectroscopic

25982 reflections collected, 6833 independent reflections (R =

int

3

data and a crystal structure of 14 have recently been published by

0.0389), 524 parameters, 0 restraints, GooF=1.052, R1=0.0403,

wR2=0.1024 (I>2σ(I)).

16

our group and can be obtained via CCDC number: 1935472.

Bis{Fe (CO) (μ -2,3-diphospha[2]ferrocenophanediyl)} (18): Yield:

2

6

4

5

14 mg (0.013 mmol, 2% based on 6). IR data (KBr, v˜): 2050 (m),

031 (s), 2014 (w), 1989 (s), 1980 (vw), 1958 (s), 1944 (vw),

Reaction of [Fe(η -C H PCl ) ] (6) with Fe (CO) (10)

5

4

2 2

2

9

2

À 1

1

Compound 6 (510 mg, 1.44 mmol) and 10, (2.77 g, 7.61 mmol) were

reacted in 150 mL of toluene at 45–50°C for 1 h. All volatiles were

1916 cm . H NMR (CDCl , δ): 4.24 (pt, J =1.7 Hz, 4H, C H ), 5.19

3 H,H 5 4

13 1

(pt, J =1.8 Hz, 4H, C H ) ppm. C{ H} NMR (CDCl , δ): 72.3* ppm.

H,H

5

4

3

1

removed in vacuo and the residue was purified using column

chromatography (silica). Using hexane removed Fe (CO) as the

P{ H} NMR (CDCl , δ): 139.1 (s) ppm. (*Solely observed as a singlet;

3

12

further signals were not resolved.)

Crystal Data for 18: C H Fe O P , M=1051.43 gmol , red block,

first, intense green fraction, followed by 15 (17 mg) and 16 (2 mg)

as pale green bands. Changing the eluent to a 4:1 hexane/toluene

mixture (v/v) gave 17 (39 mg) and 18 (14 mg) as pale yellow

fractions. After removal of all volatiles all compounds were

obtained as solids.

À 1

3

2

16

6

12 4

0

1

2

1

.2·0.2·0.1, tetragonal, P-4n2, λ=0.71073 Å, a=10.1230(3) Å, c=

3

À 3

7.2619(8) Å, V=1051.43(2) Å , Z=2, 1_c_a_l_c_d=1.974 Mgm , μ=

À 1

.640 mm , F =1040, T=125.2(2) K, θ range 3.081–24.993°,

0

00

2408 reflections collected, 1537 independent reflections (R

=

int

When 730 mg (2.07 mmol) of 6 and 10.53 g (28.94 mmol) of 10

were reacted in 250 mL of toluene solely 17 (100 mg, 0.17 mmol,

%) and 18 (6.4 mg, 0.006 mmol, <1%) were obtained.

0.0372), 123 parameters, 0 restraints, GooF=1.099, R1=0.0181,

wR2=0.0407 (I>2σ(I)), absolute structure parameter 0.021(10).

38

8

Eur. J. Inorg. Chem. 2021, 1–18

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Full Papers

doi.org/10.1002/ejic.202100097

5

Reaction of [Fe(η -C H -1,2-(PCl ) )(η -C H )] (9) with Fe (CO)

9

1985, 118, 4426–4432; g) H. Lang, G. Huttner, B. Sigwarth, I. Jibril, L.

Zszlo, O. Orama, J. Organomet. Chem. 1986, 304, 137–155; h) H. Lang, G.

Huttner, L. Zsolnai, G. Mohr, B. Sigwarth, U. Weber, O. Orama, I. Jibril, J.

Organomet. Chem. 1986, 304, 157–179.

5

3

2 2

5

2

(10)

Compound 9 (740 mg, 2.07 mmol) and 10 (10.57 g, 29.06 mmol)

were reacted in 150 mL of toluene at 45–50°C for 1 h. All volatiles

[

2] M. Scheer, M. Dargatz, K. Schenzel, P. G. Jones, J. Organomet. Chem.

1

992, 435,123–132.

3] S.-G. Kang, K. Ryu, S.-K. Jung, J. Kim, Inorg. Chim. Acta 1999, 294, 140–

52.

4] a) M. R. Ringenberg, F. Wittkamp, U.-P. Apfel, W. Kaim, Inorg. Chem.

were removed in vacuo and the residue was purified using column

chromatography (silica). Using hexane removed Fe (CO) as the

3

12

1

first, intense green fraction. The solvent was changed to a 4:1

hexane/toluene mixture (v/v), which eluted 20 and 19 as short

yellow fractions. After removal of all volatiles both compounds

were obtained as yellow solids.

2

017, 56, 7501–7511; b) F. Döttinger, M. R. Ringenberg, Organometallics

019, 38, 586–592; c) M. R. Ringenberg, M. Schwilk, F. Wittkamp, U.-P.

Apfel, W. Kaim, Chem. Eur. J. 2017, 23, 1770–1774; d) M. R. Ringenberg,

Chem. Eur. J. 2019, 25, 2396–2406.

2

1

2’

2

1

2’

(

R ,S )-Bis(Fe (CO) {μ -[Fe(C H )(1-PCl-2-P-C H )]}-1k P ,P -2k P ,P )

p p 2 6 4 5 5 5 3

1

[5] a) L.-C. Song, Z.-Y. Yang, H.-Z. Bian, Q.-M. Hu, Organometallics 2004, 23,

3082–3084; b) L.-C. Song, Z.-Y. Yang, H.-Z. Bian, Y. Liu, H.-T. Wang, X.-F.

Liu, Q.-M. Hu, Organometallics 2005, 24, 6126–6135.

[6] a) C.-G. Li, S.-L. Wang, J.-Y. Shang, J. Coord. Chem. 2016, 69, 2845–2854;

b) S. Ghosh, G. Hogarth, N. Hollingsworth, K. B. Holt, S. E. Kabir, B. E.

Sanchez, Chem. Commun. 2014, 50, 945–947; c) G.-R. Xu, L. Liu, H.-L.

Gao, J.-Y. Shang, C.-G. Li, J. Coord. Chem. 2017, 70, 2684–2694.

(

19): Yield: 6 mg (0.006 mmol, 0.3% based on 9). H NMR (CDCl , δ):

3

13

1

signals could not unambiguously be assigned. C{ H} NMR (CDCl ,

δ): 73.2 (C H ) ppm. P{ H} NMR (CDCl , δ): 118.7 (dd, J =77.1,

5.1 Hz, P ), 238.2 (dd, J =78.7, 64.6 Hz, P ) ppm.

3

31

1

5

3

P,P

À P

Cl

6

P,P

À 1

Crystal Data for 19: C H Cl Fe O P , M=1122.33 gmol , red

block, 0.05·0.05·0.05, triclinic, P–1, λ=0.71073 Å, a=10.605(2) Å,

32

16

2

6

12 4

[7] T.-J. Kim, S.-C. Kwon, Y.-H. Kim, N. H. Heo, J. Organomet. Chem. 1992,

426, 71–86.

b=10.707(3) Å, c=17.196(3) Å, α=81.279(18)°, β=73.367(17)°, γ=

3

À 3

[8] M. Kaiser, G. Knör, Eur. J. Inorg. Chem. 2015, 2015, 4199–4206.

[9] S. Enthaler, M. Haberberger, E. Irran, Chem. Asian J. 2011, 6, 1613–1623.

10] V. Tirkey, R. Boddhula, S. Mishra, S. M. Mobin, S. Chatterjee, J. Organo-

met. Chem. 2015, 794, 88–95.

11] T.-J. Kim, K.-H. Kwon, S.-C. Kwon, J.-O. Baeg, S.-C. Shim, D.-H. Lee, J.

Organomet. Chem. 1990, 389, 205–217.

8

2

1

0

6.628(19)°, V=1849.0(7) Å , Z=2,

1

calcd

=2.016 Mgm , μ=

À 1

.672 mm , F =1108, T=124.8(6) K, θ range 2.931–24.999°,

000

[

5214 reflections collected, 6486 independent reflections (R

=

int

.1426), 469 parameters, 675 restraints, GooF=0.891, R1=0.0833,

wR2=0.1235 (I>2σ(I)).

12] a) Y. Yu, A. D. Bond, P. W. Leonard, U. J. Lorenz, T. V. Timofeeva, K. P. C.

Vollhardt, G. D. Whitener, A. A. Yakovenko, Chem. Commun. 2006, 2572–

2

1

2’

(

2

S ,S /R ,R )-Bis(Fe (CO) {μ -[Fe(C H )(1-PCl-2-P-C H )]}-1k P ,P -

p

2

6

4

5

3

2

1

2

1

k P ,P ) (20): Yield: 3 mg (0.003 mmol, 0.1% based on 9). H NMR

CDCl , δ): 4.48 (s, 5H, C H ), 4.81 (br s, 1H, C H ), 4.94 (t, J =

2574; b) A. Hildebrandt, U. Pfaff, H. Lang, Rev. Inorg. Chem. 2011, 31,

(

111–141; c) A. Hildebrandt, T. Rüffer, E. Erasmus, J. C. Swarts, H. Lang,

Organometallics 2010, 29, 4900–4905; d) R. K. Al-Shewiki, M. Korb, A.

Hildebrandt, S. Zahn, S. Naumov, R. Buschbeck, T. Rüffer, H. Lang, Dalton

Trans. 2019, 48, 1578–1585; e) A. Hildebrandt, D. Schaarschmidt, R.

Claus, H. Lang, Inorg. Chem. 2011, 50, 10623–10632; f) U. Pfaff, A.

Hildebrandt, M. Korb, H. Lang, Polyhedron 2015, 68, 2–9; g) D. Miesel, A.

Hildebrandt, M. Korb, P. J. Low, H. Lang, Organometallics 2013, 32,

3

5

3

H,H

13

1

2

7

2

.5 Hz, 1H, C H ), 4.95 (br s, 1H, C H ) ppm. C{ H} NMR (CDCl , δ):

5 3 5 3 3

31 1

À P

3.0 (C H ) ppm. P{ H} NMR (CDCl , δ): 169.9 (d, J =21.3 Hz, P ),

5

3

P,P

Cl

78.8 (d, J_P_,_P=21.5 Hz, P ) ppm.

À 1

Crystal Data for 20: C H Cl Fe O P , M=1122.33 gmol , red

block, 0.2·0.2·0.1, monoclinic, C2/c, λ=0.71073 Å, a=

32

16

2

6

12 4

2993–3002; h) M. Korb, U. Pfaff, A. Hildebrandt, T. Rüffer, H. Lang, Eur. J.

1

3

2

9.7315(10) Å, b=16.4009(7) Å, c=11.3186(5) Å, β=91.195(4)°, V=

3

À 3

À 1

Inorg. Chem. 2014, 2014, 1051–1061; i) U. Pfaff, G. Filipczyk, A.

Hildebrandt, M. Korb, H. Lang, Dalton Trans. 2014, 43, 16310–16321;

j) U. Pfaff, A. Hildebrandt, M. Korb, D. Schaarschmidt, M. Rosenkranz, A.

Popov, H. Lang, Organometallics 2015, 34, 2826–2840; k) D. Miesel, A.

Hildebrandt, M. Korb, D. A. Wild, P. J. Low, H. Lang, Chem. Eur. J. 2015,

662.1(3) Å , Z=4,

1

=2.698 Mgm , μ=2.698 mm ,

F

=

000

calcd

216, T=125.1(2) K, θ range 3.231–24.999°, 7328 reflections

collected, 3222 independent reflections (R =0.0344), 253 parame-

int

ters, 0 restraints, GooF=1.028, R1=0.0348, wR2=0.0706 (I>2σ(I)).

21, 11545–11559; l) J. M. Speck, M. Korb, A. Schade, S. Spange, H. Lang,

Organometallics 2015, 34, 3788–3798; m) D. Miesel, A. Hildebrandt, M.

Korb, D. Schaarschmidt, H. Lang, Organometallics 2015, 34, 4293–4304.

13] a) S. Onaka, H. Muto, Y. Katsukawa, S. Takagi, J. Organomet. Chem. 1997,

[

Acknowledgements

5

43, 241–243; b) S. Onaka, Y. Katsukawa, H. Muto, J. Coord. Chem. 2000,

1, 33–44.

14] A. Rahaman, C. Gimbert-Suriñach, A. Ficks, G. E. Ball, M. Bhadbhade, M.

M. K. thanks the Forrest Research Foundation for a PostDoc

Fellowship and the Univ. of Western Australia for financial

Support.

Haukka, L. Higham, E. Nordlander, S. B. Colbran, Dalton Trans. 2017, 46,

3207–3222.

[15] B. A. Surgenor, L. J. Taylor, A. Nordheider, A. M. Z. Slawin, K. S. Athukor-

ala Arachchige, J. D. Woollins, P. Kilian, RSC Adv. 2016, 6, 5973–5976.

[

16] M. Korb, X. Liu, S. Walz, M. Rosenkranz, E. Dmitrieva, A. A. Popov, H.

Lang, Inorg. Chem. 2020, 59, 6147–6160.

Conflict of Interest

[17] a) S. Dey, D. Buzsáki, C. Bruhn, Z. Kelemen, R. Pietschnig, Dalton Trans.

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2

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The authors declare no conflict of interest.

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Keywords: Ferrocene · Phosphine · Iron Carbonyl · Cluster ·

Electrochemistry · Phosphinidene

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Manuscript received: February 3, 2021

Revised manuscript received: April 1, 2021

Accepted manuscript online: April 1, 2021

1

846–1855.

Eur. J. Inorg. Chem. 2021, 1–18

www.eurjic.org

17

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These are not the final page numbers!

FULL PAPERS

Dr. M. Korb*, X. Liu, S. Walz, J.

Mahrholdt, Dr. A. A. Popov, Prof. H.

Lang

1

– 18

Structural Variety of Iron Carbonyl

Clusters Featuring Ferrocenyl-

phosphines

The reaction of Fe (CO) with ferrocen-

PÀ P bonds gave organometallic octa-

2

9

8

yl(bis)dichlorophosphines is investi-

gated. The products contain butterfly

motifs, phosphinidene cluster cores in

dependence of the ferrocenyl’s substi-

tution pattern. Compounds including

bisvalene and novel μ,k -coordinating

motifs. Single crystal structures, NMR,

IR, EC and DFT calculations confirm

their identity and properties in various

charged states.

Article Doi

Structural Variety of Iron Carbonyl Clusters Featuring Ferrocenylphosphines

DOI: 10.1002/ejic.202100097

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Authors:

Article abstract of DOI:10.1002/ejic.202100097

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