Mono- and dinuclear tetraphosphabutadiene ferrate anions

Article abstract of DOI:10.1039/c7dt04641c

Reduction of [Cp^ArFe(μ-Br)]₂ (1, Cp^Ar = C₅(C₆H₄-4-Et)₅) by potassium napthalenide, followed by the addition of white phosphorus, affords [K(18-c-6){Cp^ArFe(η⁴-P₄)}] (2, 18-c-6 = [18]crown-6), which features a planar cyclo-P₄^2- ligand. The related diiron complex [Na₂(THF)₅(Cp^ArFe)₂(μ,η^4:4-P₄)] (3) was obtained by reducing 1 with sodium amalgam in the presence of P₄. Protonation of 3 affords [Na(THF)₃][(Cp^ArFe)₂(μ,η^4:4-P₄)(H)] (4), while the reaction of 3 with trimethylchlorosilane gives the nortricyclane compound P₇(SiMe₃)₃ as the main product.

Full text of DOI:10.1039/c7dt04641c

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: U. Chakraborty, J.
Leitl, B. Muehldorf, M. Bodensteiner, S. Pelties and R. Wolf, Dalton Trans., 2018, DOI:
10.1039/C7DT04641C.
This is an Accepted Manuscript, which has been through the
Volume 45 Number
1 7 January 2016 Pages 1–398
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
Accepted Manuscripts are published online shortly after
An international journal of inorganic chemistry
www.rsc.org/dalton
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

Please do not adjust margins
Page 1 of 6
Dalton Transactions
View Article Online
DOI: 10.1039/C7DT04641C
Dalton Transactions
COMMUNICATION
Mono- and dinuclear tetraphosphabutadiene ferrate anions†
Received 00th
January 20xx,
Uttam Chakraborty, Julia Leitl, Bernd Mühldorf, Michael Bodensteiner, Stefan Pelties and Robert
Wolf*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Reduction of [CpArFe(μ-Br)]2 (1, CpAr = C5(C6H4-4-Et)5) by potassium
napthalenide, followed by the addition of white phosphorus,
affords [K(18-c-6){CpArFe(η4-P4)}] (2, 18-c-6 = [18]crown-6), which
Scheer and co-workers (2017):
[Fe]
tBu
P
tBu
tBu
tBu
2-
tBu
tBu
P
features a planar cyclo-P4 ligand. The related diiron complex
P
P
[Na2(THF)5(CpArFe)2(μ,η4:4-P4)] (3) was obtained by reducing 1 with
sodium amalgam in the presence of P4. Protonation of 3 affords
[Na(THF)3][(CpArFe)2(μ,η4:4-P4)(H)] (4), while the reaction of 3 with
trimethylchlorosilane gives the nortricyclane compound
P7(SiMe3)3 as the main product.
P
[Fe]
[Fe]
Co
Fe
Fe
[Fe]
P
P
P
P
P
P
P
P
P
P
P
[Fe]
[Fe]
A
B
C
[Fe]
= Cp'Fe(CO)2
this work: (cyclo)tetraphosphido ferrate anions
While numerous transition metal polyphosphido complexes
are reported in the literature, pentaphosphaferrocenes play a
pivotal role as phosphorus analogues of the ubiquitous
ferrocene molecule and their chemistry has been investigated
Ar5
Ar5
=
_
Ar5
Et
Fe
O
O
extensively.1
Among
other
applications,
P
P
P
P
Fe
Et
Et
Na
O
Na
P
P
pentaphosphaferrocenes were used as constituents of 1D and
2D polymers and spherical fullerene-like supramolecules.2-6
Strikingly, anionic tetraphosphido complexes [CpRFe(η4-cy-
clo-P4)]−, which are isoelectronic with pentaphosphaferrocene,
O
O
P
P
Fe
3
[K(18-c-6)]+
Et
Et
Ar5
2
are elusive. Cesium and potassium salts of the 6π aromatic
Figure
1.
Selected neutral and anionic polyphosphide complexes,
(cyclo-P4)2- dianion were synthesized and characterized by
Korber.7 Early transition metal complexes [Cp*M(CO)2(cyclo-
P4)] (M = Nb, Ta) and [{(P2N2)Zr}2(cyclo-P4)] (P2N2 = PhP-
(CH2SiMe2NSiMe2CH2)2PPh) were reported by Fryzuk and
Scherer.8‒10 Driess, Scheer and our group synthesized dinuclear
Cp' = C5H2-1,2,4-tBu3, Ar = C6H4-4-Et, 18-c-6 = [18]crown-6.
described.18‒22 Complexes
A‒C (Figure 1) reported by Scheer in
2017 are particularly noteworthy, because they are very rare
examples of mononuclear complexes with cyclo-P42− units.23,24
In 2011, we reported that the reaction of P4 with an anionic
cobalt and iron complexes with
middledeck.11-17 Related dinuclear cyclopentadienyl iron
complexes of bridging tetraphosphabutadiene and
tetraphoshabicyclo[1.1.0]butane-1,3-diyl ligands were also
a
planar cyclo-P4
“Cp*Fe−” source [K(18-c-6){Cp*Fe(η4-napthalene)}] (Cp*
=
C5Me5; 18-c-6
= [18]crown-6) produces a mixture of
polyphosphide anions including [K2(18-c-6)2{Cp*Fe(η4-P7)}] and
[[K(18-c-6)(thf)x][(Cp*Fe)3(cyclo-P3)2] (x = 0 − 2) as major
products.25 Hoping that steric bulk might afford the targeted
[CpRFe(cyclo-P4)]− anion, we turned to the sterically more
demanding pentaarylcyclopentadienyl ligand C5(C6H4-4-Et)5
(CpAr).26‒28 As a result of these investigations, we have
obtained
a.University of Regensburg, Institute of Inorganic Chemistry, D-93040 Regensburg;
E-mail: robert.wolf@ur.de; http://www.uni-regensburg.de/chemistry-
pharmacy/inorganic-chemistry-wolf/index.html
† Dedicated to Philip P. Power on the occasion of his 65th birthday.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 6
COMMUNICATION
Journal Name
Figure S20 in the ESI). A shoulder at 405 nm (ε = 2800
View Article Online
DOI: 10.1039/C7DT04641C
L·mol−1·cm−1) and a
Scheme 1. Synthesis and molecular structure of
2 (C10H8 = naphthalene). The H
atoms and ethyl group on the aryl rings are omitted for clarity. Thermal ellipsoids are
drawn at the 35% probability level. Selected bond distances (Å) and bond angles (°):
Fe1–CpAr(centroid) 1.6751(7), Fe1–P4(centroid) 1.7532(4), Fe1–P1 2.3247(6), Fe1–P2
2.3315(6), Fe1–P3 2.3221(5), Fe1–P4 2.3303(5), P1–P2 2.1633(7), P2–P3 2.1722(6), P3–
P4 2.1656 (7), P1–P4 2.1558(6), K···P1 3.6742(5), K1···P2 3.5701(5), K1···P3 3.4490(5),
K1···P4 3.5431(5); CpAr(centroid)–Fe1–P4(centroid) 178.1(1); P1–P2–P3 89.77(2), P2–
P3–P4 89.81(3), P3–P4–P1 90.13(2), P4–P1–P2 90.29(3), P1–P2–P3–P4 torsion angle
0.45, angle between CpAr and the P4 plane 1.79(6).
Figure 2. Selected Kohn-Sham-MOs of [(C5Ph5)Fe(η4-cyclo-P4)]− (2').
weak absorption at 653 nm (ε = 550 L·mol−1·cm−1) were
observed in the UV-vis spectrum (THF, Figure S4, ESI).
According to TDDFT calculations, these bands can assigned to
transitions from the cyclo-P42−-based HOMO to Cp-based as
well as metal-based virtual orbitals.
Attempting to improve the synthesis of
reduction of with an excess of Na/Hg in the presence of P4.
However, this reaction affords the diiron compound
[Na2(THF)5{(CpArFe)2(μ,η4:4-P4)}]
Scheme 2) instead.
Crystalline is highly air sensitive and slowly decomposes to
[Na(THF)3{(CpArFe)2(μ,η4:4-P4)(H)}] (
, vide infra) and other
products in THF solution. can nonetheless be isolated as a
dark brown-red solid in moderate yield (up to 67%) by
‡
mono- and dinuclear tetraphosphabutadiene complexes. Here,
we describe the synthesis and characterization of
2
, we investigated the
[K(18-c-6){CpArFe(η4-cyclo-P4)}] ( ) and [Na2(THF)5][(CpArFe)2-
2
1
(μ,η4:4-P4)] (
reactivity study of
to [Na(THF)3][(CpArFe)2(μ,η4:4-P4)(H)] (
compound P7(SiMe3)3 ( ).
The reaction of [CpArFe(μ-Br)]2
3
). Moreover, we report the results of an initial
with Et3N·HCl and Me3SiCl, which has led
(
3
,
‡
3
3
4
) and the nortricyclane
4
5
28
‡
3
(1
)
with potassium
napthalenide (four equiv.) in THF, followed by the addition of
P4 (two equiv.), affords the desired [CpArFe(η4-cyclo-P4)}]−
anion as the main phosphorus-containing product as
evidenced by a 31P NMR singlet at 112.2 ppm observed in the
crystallization from THF/diethyl ether.
3 is likely formed in a
21
stepwise process via neutral [(CpArFe)2(μ,η4:4-P4)]
and the
putative monoanionic complex Na[(CpArFe)2(μ,η4:4-P4)].
Single-crystal XRD on a crystal obtained from THF/diethyl ether
revealed a centrosymmetric dimer, where two P2 dumbbells
are sandwiched between two CpArFe units (Scheme 2). P1–P2
(2.0782(17) Å) and P3–P4 (2.0778(17) Å) of the planar cisoid-P4
moiety are slightly shorter than in the known neutral analogue
[(CpArˈFe)2(μ,η4:4-P4)] (CpAr' = C5(C6H4-4-nBu)5, P1–P2 2.100(2) Å,
P3–P4 2.098(2) Å).22 The P2···P3 bond distance of 2.635(2) Å is
long, indicating a weak interaction between the P2 moieties
similar to the weak P···P bond in kite-like distorted
crude reaction mixture. Overreduction of
1H NMR spectrum (formation of CpArK). Nevertheless, olive
green [K(18-c-6){CpArFe(η4-P4)}] (
) can be isolated as a pure
crystalline solid in low yield (4%) when [18]crown-6 (two
equiv. referring to ) is added to the reaction(Scheme 1).
Crystals suitable of for single-crystal XRD were obtained from
1 is apparent in the
2
1
2
‡
DME. The molecular structure (Scheme 2) shows an
η4-coordinated P4 square. The P–P bond lengths (2.1558(6) ‒
2.1722(6) Å) suggest a delocalized structure similar to that in
23,24
A
‒
C
(Figure 1) and [K2([18]-crown-6)2(P4)] (P–P 2.160(2)‒
2.172 (2) Å).7b The 1H and 13C{1H} NMR spectra are in
agreement with the crystallographically determined structure,
displaying one set of signals for the CpAr ligand. A sharp 31P{1H}
NMR singlet is observed for
2 at 114.1 ppm in THF-d8, which
compares to chemical shift of 322.8 ppm for [K2([18]-crown-
6)2(cyclo-P4)] and 175.2 ppm for cobalt complex
[Cp'Co(η4-cyclo-P4)] ( , Figure 1).7,13
A
The molecular structure of
2 was reproduced by a DFT
optimization of the truncated model [(C5Ph5)Fe(η4-cy-
clo-P4)]− (2') at the B3LYP/def2-TZVP level.29,30 An analysis of
the frontier Kohn-Sham molecular orbitals suggests a d6
configuration for iron. The HOMO and HOMO−1 are P-
centered MOs, while the HOMO−2, HOMO−3 and HOMO−4
have large contributions from Fe d orbitals (Figure 2, see also
Scheme 2. Synthesis and molecular structure of 3. The H atoms and ethyl group on
the aryl rings are omitted for clarity. Thermal ellipsoids are drawn at the 35%
probability level. Selected bond distances (Å) and bond angles (°):Fe1–CpAr(centroid)
1.706(1), Fe1–P4(centroid) 1.641(1), Fe1···Fe1’ 3.281(1), Fe1–P1 2.3575(9), Fe1–P2
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Dalton Transactions
Please do not adjust margins
Journal Name
COMMUNICATION
Figure 3. Proton-coupled 31P NMR spectrum of 4 in THF-d8 at 300 K. The phosphorus-
2.3626(9), Fe1–P3 2.3463(9), Fe1–P4 2.3390(9), P1–P2 2.0782(17), P2–P3 2.5246(16),
P3–P4 2.0778(17), P1–P4 2.779(2), Na1–P1 4.073(2), Na1–P2 3.003(2), Na2–P3
2.931(2), Na2–P4 2.997(2); CpAr(centroid)–Fe1–P4(centroid) 176.1(1); P1–P2–P3–P4
torsion angle 0.
View Article Online
decoupled 1H{31P} NMR signal of the Fe-H unit is shown in the inset.
DOI: 10.1039/C7DT04641C
and 27 Hz.32 The phosphorus-decoupled 1H{31P} NMR spectrum
displays a singlet at −7.25 ppm (Figure S11, ESI), which shows
the typical high-field shift for a hydride ligand. A seven-line
multiplet forming the X-part of the A2M2X spin system is
observed in the phosphorus-coupled 1H NMR spectrum
(Figures 5 and S10, ESI).
Ar5
i)
[Na2(THF)5{(CpArFe)2(µ,η4:4-P4)}]
Fe
O
H
P
3
P
Na
O
P
P
O
ii)
Fe
4
The NMR spectra of
4 are highly temperature dependent,
indicating fluxional behaviour.
‡
Upon cooling to 193 K, the
Ar5
31P{1H} NMR signals decoalesce to four broad signals (ABCD
spin system, Figure S14, ESI). This indicates that the H atom
apparently is highly mobile.
P
SiMe3
Me3Si
P
P
P
P
P
+
P
(SiMe3)3
+
P
H(SiMe3)2
SiMe3
6
7
DFT calculations performed on the truncated model
[Na{CpFe}2(μ,η4:4-P4)(H)] 29,30 hint at a plausible mechanism for
this fluxional behaviour. Two simultaneous dynamic processes
may be involved: i) fluctuation of the hydrogen atom between
the P-atoms; ii) fluctuation of P-atoms similar to that observed
in the related neutral complexes [(CpRFe)2(μ,η4:4-P4)] reported
previously by Scherer and Scheer. 18‒22 DFT optimizations gave
two minimum structures 4A and 4B (Figure 4), which are in
agreement with the unsymmetric ABCD spin system observed
by 31P{1H} NMR at 193 K. In both isomers, the hydride ligand
bridges the Fe center and one P atom. 4A and 4B are
separated merely by 3 kcal mol‒1 and are connected by the
transition state 4TS (+4.6 kcal mol‒1 with respect to 4A). In the
structure of 4TS, the hydrogen atom is located at the midpoint
between the two P atoms and the Fe atom (Figure 4).
Optimizations of other conceivable isomers converged to
either 4A or 4B in all cases (Figure S22, ESI). The averaging of
the 31P NMR signals at room temperature is thus easily
explained by the migration of the H atom between the
phosphorus atoms (see Figure S23, ESI).34
P
5
5
6 7
: = 10 : 1 : 1
ratio
:
Scheme 3. Reactivity of 3 with electrophiles. Reagents and conditions: i) Et3N·HCl / -
NaCl, - NEt3, THF, r.t.; ii) exc. Me3SiCl / - 2 NaCl, - 2 “CpArFeCl”, THF, r.t..
[(Cp'Fe)2(μ-P4)] reported by Walter and co-workers.21 Unlike
neutral [(CpAr'Fe)2(μ,η4:4-P4)],
3
gives rise to a single 31P{1H}
NMR signal at ambient temperature. This signal is slightly
broad (Δυ1/2 = 12 Hz) at 300 K and broadens upon cooling to
193
[(CpAr'Fe)2(μ,η4:4-P4)],
observed.Protonation of
K
(Δυ1/2 = 123 Hz, Figure S8).§ Different from
decoalescence is not
with Et3N·HCl affords
a
3
[Na(THF)3{(CpArFe)2(μ,η4:4-P4)(H)}] (
4, Scheme 3) in 44% yield.‡
1H NMR spectra of the crude product show paramagnetically
1
shifted H NMR resonances of a by-product, presumably the
oxidized compound Na[(CpArFe)2(μ-P4)], in addition to the
signals of the major product
solubility, rendering their complete separation difficult.§§
also converts to by reaction with traces of water present in
the solvent, and [H(Et2O)]BArF (BArF = B[C6H3-3,5-(CF3)2]4).31
Crystals of gave low intensities in the single-crystal X-ray
diffraction experiment. Nevertheless, the atom connectivity
could be firmly established, and we could refine the disorder
of the non-solvent parts of the structure.
spectrum reveals an A2M2 spin system (pseudo-triplets,
P,P = 52 Hz, Figure S12, ESI) at room temperature in THF-d8.
4. Both species have a similar
3
4
The reaction of
3
6
with an excess of Me3SiCl gives P7(SiMe3)3
and PH(SiMe3)2 (7) in a 10 : 1 : 1 ratio
4
36
37
(5
),35 P(SiMe3)3 (
)
(Scheme 3). This presents a proof-of-principle that the
phosphorus fragment can be liberated by a suitable electrophile
The fate of the “CpArFe” moiety is unknown.
are
‡
The 31P{1H} NMR
.
5
‒ 7
commonly prepared by alkali metal reduction of white or red
J
phosphorus and subsequent addition of Me3SiCl.35−37
The two multiplets form the A2M2 part of an A2M2X spin
system in the proton-coupled 31P NMR spectrum (Figures 5
and S13, ESI). A simulation converged with JP,H coupling
constants of 32 Hz
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 6
COMMUNICATION
Journal Name
1
Reviews: (a) B. M. Cossairt, N. A. Piro and C. C. Cummins,
Chem. Rev. 2010, 110, 4164; (b) M. CDaOpoI:r1a0l.i1,0L3V.9ie/GwCo7AnDrtsiTca0lel4vO6in,4l1iAnCe.
Rossin and M. Peruzzini, Chem. Rev. 2010, 110, 4178; (c) J. S.
Figueroa and C. C. Cummins, Dalton Trans. 2006, 2161; (d)
M. Peruzzini, L. Gonsalvi and A. Romerosa, Chem. Soc. Rev.
2005, 34
, 1038; (e) M. Peruzzini, R. Abdreimova, Y.
Budnikova, A. Romerosa, O. J. Scherer and H. Sitzmann, J.
Organomet. Chem. 2004, 689, 4319.
O. J. Scherer and T. Brück, Angew. Chem. Int. Ed. Engl., 1987,
26, 59.
C. Heindl, E. V. Peresypkina, A. V. Virovets, W. Kremer and
M. Scheer, J. Am. Chem. Soc., 2015, 137, 10938 and
references therein.
M. Detzel, T. Mohr, O. J. Scherer and G. Wolmershäuser,
Angew. Chem. Int. Ed. Engl., 1994, 33, 1110.
2
3
4
5
6
J. Bai, A. V. Virovets and M. Scheer, Science, 2003, 300, 781.
(a) M. V. Butovskiy, G. Balázs, M. Bodensteiner, E. V.
Peresypkina, A. V. Virovets, J. Sutter and M. Scheer, Angew.
Chem. Int. Ed., 2013, 52, 2972; (b) T. Li, M. T. Gamer, M.
Scheer, S. N. Konchenko and P. W. Roesky, Chem. Commun.,
2013, 49, 2183.
Synthesis and characterization of M2(cyclo-P4) salts (M = K,
Cs) in liquid ammonia: F. Kraus, J. C. Aschenbrenner and N.
Korber, Angew. Chem. Int. Ed., 2003, 42, 4030; (b) F. Kraus,
T. Hanauer and N. Korber, Inorg. Chem., 2006, 45, 1117; (c)
T. Hanauer, F. Kraus, M. Reil, N. Korber, Monatsh. Chem.
2006, 137, 147.
Figure 4. Relative energies of the isomers 4A, 4B and the transition state 4TS.
7
In summary, P4 activation by an in-situ generated naphthalene
iron complex resulted in the tetraphosphacyclobutadiene
ferrate anion [K(18-c-6){CpArFe(η4-P4)}] (
2
) with a terminal,
2−
planar cyclo-P4 ligand. This complex is a rare mononuclear
ferrate anion obtained directly from P4. §§§ The high tendency
of such species to form dinuclear structures is evident from
8
9
O. J. Scherer, J. Vondung and G. Wolmershäuser, Angew.
Chem. Int. Ed. Engl., 1989, 28, 1355.
O. J. Scherer, R. Winter and G. Wolmershäuser, Z. Anorg.
Allg. Chem., 1993, 619, 827.
the synthesis of [Na2(THF)5][(CpArFe)2(μ,η4:4-P4)] (
3
), which was
obtained under modified reactions conditions and using
sodium amalgam. The P4 fragment in remains intact upon
10 W. W. Seidel, O. T. Summerscales, B. O. Patrick and M. D.
Fryzuk, Angew. Chem., 2009, 121, 121.
3
11 S. Dürr, D. Ertler and U. Radius, Inorg. Chem., 2012, 51
,
protonation, while the reaction with trimethylchlorosilane
leads to uncoordinated P7 and P1 species. The latter reaction
shows that the polyphosphido ligands can be released from
the metal center by suitable electrophiles, which may open up
new prospects for P4 functionalization using anionic metalates.
Further studies in this direction are underway.
3904–3909.
12 S. Yao, N. Lindenmaier, Y. Xiong, S. Inoue, T. Szilvási, M.
Adelhardt, J. Sutter, K. Meyer and M. Driess, Angew. Chem.,
2015, 54, 1250.
13 F. Dielmann, A. Timoshkin, M. Piesch, G. Balázs and M.
Scheer, Angew. Chem. Int. Ed., 2017, 56, 1671.
14 S. Pelties, T. Maier, D. Herrmann, B. de Bruin, C. Rebreyend,
S. Gärtner, I. G. Shenderovich and R. Wolf, Chem. Eur. J.,
2017, 23, 6094.
15 F. Spitzer, C. Graßl, G. Balázs, E. Mädl, M. Keilwerth, E. M.
Acknowledgements
We thank Nele Berg (University of Regensburg) for help with
Zolnhofer, K. Meyer and M. Scheer, Chem. Eur. J., 2017, 23
2716.
,
NMR
measurements.
Funding
by
the
Deutsche
16 S. Yao, T. Szilvási, N. Lindenmaier, Y. Xiong, S. Inoue, M.
Adelhardt, J. Sutter, K. Meyer and M. Driess, Chem.
Commun., 2015, 51, 6153.
17 F. Spitzer, C. Graßl, G. Balázs, E. M. Zolnhofer, K. Meyer and
M. Scheer, Angew. Chem. Int. Ed., 2016, 55, 4340–4344.
18 O. J. Scherer, T. Hilt and G. Wolmershäuser, Organometallics,
1998, 17, 4110.
Forschungsgemeinschaft (WO1496/7-1 to R.W.) is gratefully
acknowledged.
Notes and references
‡ See the electronic supplementary information for details on
19 O. J. Scherer, G. Schwarz and G. Wolmershäuser, Z. Anorg.
Allg. Chem., 1996, 622, 951.
the synthesis and characterization of 2‒7.
§The low temperature 31P{1H} NMR spectrum of
3 at 193 K
20 C. Eichhorn, O. J. Scherer, T. Sögding and G. Wolmershäuser,
Angew. Chem. Int. Ed., 2001, 40, 2859.
shows an additional minor resonance at −111.5 ppm slightly
upfield from the dominant resonance. This minor signal might
presumably arise from a bonding isomer of 3.38
21 M. D. Walter, J. Grunenberg and P. S. White, Chem. Sci.,
2011, 2, 2120.
22 S. Heinl, G. Balázs and M. Scheer, Phosphorus, Sulfur, Silicon
Relat. Elem., 2014, 189, 924.
§§ The isolated product
4 may still contain unknown by-
products, which include a paramagnetic complex that gives rise
1
23 F. Dielmann, A. Timoshkin, M. Piesch, G. Balázs and M.
Scheer, Angew. Chem. Int. Ed., 2017, 56, 1671.
to broad H NMR signals at 6.57 and 2.57 ppm. In this case, the
compound can be purified further by recrystallization from
THF/n-hexane and THF/diethyl ether.
§§§ While this manuscript was under review, Mézailles and co-
workers reported the preparation of a terminal cyclo-P4 iron
complex stabilised by a tridentate phosphane ligand.39
24 J. Müller, S. Heinl, C. Schwarzmaier, G. Balázs, M. Keilwerth,
K. Meyer and M. Scheer, Angew. Chem. Int. Ed., 2017, 56
,
7312.
25 E.-M. Schnöckelborg, J. J. Weigand and R. Wolf, Angew.
Chem. Int. Ed., 2011, 50, 6657.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Dalton Transactions
Please do not adjust margins
Journal Name
COMMUNICATION
26 (a) C. Janiak and H. Schumann, Adv. Organomet. Chem. 1991,
33, 291; (b) R. H. Lowack, K. P. C. Vollhardt, J. Organomet.
Chem. 1994, 476, 25.
View Article Online
DOI: 10.1039/C7DT04641C
27 S. Heinl, E. V. Peresypkina, A. Y. Timoshkin, P. Mastrorilli, V.
Gallo and M. Scheer, Angew. Chem. Int. Ed., 2013, 52, 10887.
28 U. Chakraborty, M. Modl, B. Mühldorf, M. Bodensteiner, S.
Demeshko, N. J. C. van Velzen, M. Scheer, S. Harder and R.
Wolf, Inorg. Chem., 2016, 55, 3065.
29 F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005,
7
,
3297.
30 A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97
,
2571.
31 M. Brookhart, B. Grant and A. F. Volpe, Organometallics,
1992, 11, 3920.
1
32 The H chemical shifts and the P−H coupling constants were
extracted by simulation using the following program:
Budzelaar, P. H. M. gNMR, 5.1; Cherwell Scientific Publishing,
1995–1997, Ivory Soft.
33 V. Pelmenschikov, Y. Guo, H. Wang, S. P. Cramer and D. A.
Case, Faraday Discuss., 2010, 148, 409.
34 Other examples where the hydrogen atom in
a
(poly)phosphorus compound shows fluxional behavior: (a) R.
Wolf, S. Gomez-Ruiz, J. Reinhold, W. Böhlmann and E. Hey-
Hawkins, Inorg. Chem., 2006, 45, 9107; b) R. Wolf, A. W.
Ehlers, J. C. Slootweg, M. Lutz, D. Gudat, M. Hunger, A. L.
Spek and K. Lammertsma, Angew. Chem. Int. Ed., 2008, 47
4584.
,
35 H. Schmidbaur and A. Bauer, Phosphorus, Sulfur, and Silicon
and the Related Elements, 1995, 102, 217.
36 (a) A. A. Prishchenko, M. V. Livantsov, O. P. Novikova, L. I.
Livantsova and V. S. Petrosyan, Heteroatom Chem., 2010, 21
,
441; (b) E. Niecke and H. Westermann, Synthesis, 1988, 330;
(c) G. Fritz and J. Härer, Z. Anorg. Allg. Chem., 1983, 500, 14.
37 (a) D. C. Gary and B. M. Cossairt, Chem. Mater., 2013, 25, 2463;
(b) H. Bürger and U. Goetze, J. Organomet. Chem., 1968, 12,
451.
38 M. Schmidt, A. E. Seitz, M. Eckhardt, G. Balázs, E. V.
Peresypkina, A. V. Virovets, F. Riedlberger, M. Bodensteiner,
E. M. Zolnhofer, K. Meyer and M. Scheer, J. Am. Chem. Soc.,
2017, 139, 13981.
39 A. Cavaillé, N. Saffon-Merceron, N. Nebra, M. Fustier-
Boutignon, N. Mézailles, Angew. Chem. Int. Ed. DOI:
10.1002/anie.201711130.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Dalton Transactions
Page 6 of 6
View Article Online
DOI: 10.1039/C7DT04641C
Anionic tetraphosphido complexes are accessible by reacting white phosphorus with low-valent
cyclopentadienyliron species prepared by alkali metal reduction (Ar = C6H4-4-Et, 18-c-6 =
[18]crown-6).