Electronic response of a (P,N)-based ligand on metal coordination

Article abstract of DOI:10.1039/b405680a

The reaction of [(THF)Li{Ph₂PC(H)Py}] with ZnCl₂ in the presence of ZnO yields the zinc complex [Zn₃{Ph ₂PC(H)-Py}₄O] (1). Deprotonation of the phosphane Ph ₂P(CH₂Py) with [Fe{N(SiMe₃)₂} ₂] gives the iron complexes [{Ph₂P(CH₂Py)} Fe{Ph₂PC(H)Py}₂] (2) and [Fe{Ph₂PC(H)Py} {N(SiMe₃)₂}]₂ (3), depending on the ratio of phosphane. The solid state structures of the metal complexes illustrate the coordination flexibility of the [Ph₂C(H)Py]^--anion. Depending on the electronic requirements of the coordinated metal the anion acts as a (P,N)-chelating amide or C-coordinating carbanion with the P- and N-heteroatoms as donor bases.

Full text of DOI:10.1039/b405680a

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F U L L P A P E R
Electronic response of a (P,N)-based ligand on metal
coordination†
Alexander Murso and Dietmar Stalke*
Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
E-mail: dstalke@chemie.uni-wuerzburg.de; Fax: +49 931 888 4619;
Tel: +49 931 888 4783
Received 16th April 2004, Accepted 18th June 2004
First published as an Advance Article on the web 19th July 2004
The reaction of [(THF)Li{Ph2PC(H)Py}] with ZnCl2 in the presence of ZnO yields the zinc complex [Zn3{Ph2PC(H)-
Py}4O] (1). Deprotonation of the phosphane Ph2P(CH2Py) with [Fe{N(SiMe3)2}2] gives the iron complexes
[{Ph2P(CH2Py)}Fe{Ph2PC(H)Py}2] (2) and [Fe{Ph2PC(H)Py}{N(SiMe3)2}]2 (3), depending on the ratio of phosphane. The
solid state structures of the metal complexes illustrate the coordination flexibility of the [Ph2C(H)Py]−-anion. Depending
on the electronic requirements of the coordinated metal the anion acts as a (P,N)-chelating amide or C-coordinating carb-
anion with the P- and N-heteroatoms as donor bases.
Introduction
An essential concept in ligand design is that of hemilability,
introduced by Jeffrey and Rauchfuss in 1979.1 There has been
an increasing interest in synthesis, characterisation and use of
hemilabile ligands, as the different features associated with each
donor atom confer unique reactivity to their metal complexes.2 For
example, many complexes integrate a particular combination of
structure and electronic properties, furnish them abbilities in the
application as molecular devices by specific redox behaviour or
optical properties.3 Also in the design of biomimetical complexes
hemilability plays an important role, as the compounds should
not only model the direct metal coordination sphere, but also the
remote functionalities.4 In addition, the catalytic properties of metal
complexes are highly dependent on the ligand environment. Typical
functions of the ligands are to inhibit oligomerisation reactions, to
stabilise the low valent form and/or the low oxidation state of the
metal centre and to model the shape of the complex periphery.
Scheme 1 Coordination flexibility of the [Py2P]−-anion.
Thus, the interplay between metal, ligands and reagents controls the
to the pyridylphosphanes Ph3−nPynP (n = 1–3).6 The phosphane
reactivity, selectivity, stability and lability in catalytical reactions.5
Ph2P(CH2Py) and some metal complexes were already reported
The combination of phosphorus and nitrogen atoms makes a
in the 70s.13 Recently, C-substituted derivatives of the type
distinguished family of hemilabile ligands. These ligands can
Ph2PC(H)(R)Py (R = H2COEt, C3H6Si(OMe)3, H2COMent) gained
display quite different coordination modes compared to the classical
increasing importance as neutral hemilabile ligands in catalytical
(P,P)- or (N,N)-chelates.6 Recently, attention has been focused on
transfer hydrogenations (Scheme 2).14
chiral (P,N)-ligands: they have been employed very successfully
in asymmetric catalytic reactions such as allylic substitution,7
hydrosilylation,8 hydroboration9 and hydrogen transfer reactions.10
In our group we are interested in the synthesis and coordination
behaviour of 2-pyridyl substituted sec-phosphanes and sec-phos-
phanides.11,12 The incorporation of pyridyl substituents at a soft
phosphorus centre in the place of commonly applied alkyl or phenyl
groups alters and augments the coordination flexibility of the ligand
and leads to multidentate hemilabile ligands. Free rotation about
the P–Cipso bond can easily bring the pyridyl nitrogen atoms into the
right position to coordinate metals of different radii. Pyridyl-sub-
stituted sec-phosphanes are easily deprotonated giving delocalised
anionic systems. Thus, apart from the geometrical flexibility, they
Scheme 2 Catalytical active pyridylphosphanes Ph2PC(H)(R)Py.
provide electronic adaptability as well (Scheme 1).11,12
To obtain greater geometrical adaptability it is of interest to
In the abovementioned complexes the C-substituted derivatives
introduce alkyl bridges between the phosphorus atom and the
of the phosphane Ph2P(CH2Py) were employed as neutral ligands.
heterocycle. Depending on the length of the bridge it is possible
However, the acidic hydrogen atoms at the methylene bridge also
to tune the bite of the chelates and therefore tune them to various
open the way to new mono- or dianionic phosphanide compounds.
metal fragments. Although known for a long time, pyridyl-phos-
The electropositive phosphorus centre should be able to stabilise the
phanes with the phosphorus centre separated from the pyridyl ring
negative charge at the C-position, but the electron deficient nature
by methylene links have not been studied extensively in contrast
of the pyridyl susbstituent may lead to delocalisation. Thus, apart
from the geometrical flexibility, given by the methylene bridge and
free rotation about the P–CH2 bond, these charged species should
have an enhanced electronical adabtility as well.
† Electronic supplementary information (ESI) available: Full crystallographic
data of 1–3. See http://www.rsc.org/suppdata/dt/b4/b405680a/
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9
2 5 6 3

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In this contribution we elucidate the coordination behaviuor
of the C-deprotonated [Ph2PC(H)Py]−-anion. This anion shows
a remarkable response on the electronic requirements of the
coordinated metal, manifested in completely different coordination
modes.
Results and discussion
Syntheses
The phosphane Ph2P(CH2Py) was synthesised according to the
procedure described by Alvarez et al.14a Deprotonation at the
C-position of the phosphane with n-BuLi yields the lithiated spe-
cies [(THF)2Li{Ph2PC(H)Py}]15 which was reacted with ZnCl2.
However, a 31P-NMR experiment from the reaction mixture after
48 hours showed various signals. The clear solution obtained after
filtration was stored at room temperature, yielding yellow blocks
suitable for a structure determination. It turned out that the ZnCl2
used in the reaction was contaminated with ZnO, because in the iso-
lated product [Zn3{Ph2PC(H)Py}4O] (1), a central oxygen dianion
is coordinated to three zinc atoms (Scheme 3). Diffusion of oxygen
into the reaction mixture can be excluded, because this process
rather leads to oxidation of the phosphorus(III) atoms than to forma-
tion of ZnO. Hydrolysis with water causes protonation of the ligand
and formation of the phosphanoxide Ph2P(O)CH2Py. Employment
of pure ZnCl2 gives the [Zn{Ph2PC(H)Py}2] complex, which struc-
ture could not be refined successfully yet.
Scheme 5 Synthesis of [Fe{Ph2PC(H)Py}{N(SiMe3)2}]2 (3).
Structure discussion
The structure refinement of the zinc complex [Zn3{Ph2PC(H)}4O]
(1), revealed various disordered residues in the solid state. They
were resolved and modeled using distance and similarity restraints,
giving reasonable estimated standard deviations (esds) and R values.
For the disordered residues the averaged bond lengths and angles
are given in Table 1, the esds are maximum values. For full bond
lengths and angles see the electronic supplementary information
(ESI).† Fig. 1 depicts the molecular structure of the zinc complex 1.
The non-coordinating ether molecule on a special position is omit-
ted for clarity. The solid state structure of 1 is comprised of three
zinc cations, a single oxygen O2−-dianion and four monoanionic
[Ph2PC(H)Py]−-fragments. Two of them are solely (P,N)-bidentate
chelates (A, B in Fig. 1). Another ligand features an additional
Zn–C contact besides the Zn–P and Zn–N contacts (C) and the last
[Ph2PC(H)Py]−-anion coordinates exclusively via the nitrogen atom
N3 and the carbon atom C13 (D) while the phosphorus atom P3 is
a pendent spectator ligand (Zn2P3 314.5 pm). Interestingly, the
lone pair at this phosphorus atom points away from the zinc cation
Zn2 (Fig. 1). As expected for the different coordination behaviour
of the ligands in 1, the structural parameters in the [Ph2PC(H)Py]−-
fragments differ significantly.
The two (P,N)-chelating ligands (A, B) adopt almost planar five
membered metallacycles. The cations Zn1 and Zn3 are displaced
by 11.2 pm and 0.2 pm, respectively, from the best plane of the
corresponding anion. The P1–C1 and P4–C19 bond lengths with
on average 174.2 pm and the C1–C2 and C19–C20 distances
(average 139.0 pm) are shorter than the corresponding contacts
observed in the other anions (C, D) in 1. They are ca. 10 pm
shorter than formal P–C (185 pm) and ca. 7 pm shorter than
C(sp2)–C(sp2) (146 pm) single bonds.17 Therefore, the C2/20–N1/4
bond lengths of on average 138.3 pm are longer than in the anions
C and D and the phosphane Ph2P(CH2Py) (133.97 pm). The angles
P1/4–C1/19–C2/20 at the deprotonated C-atoms (average 121.32°)
and the sum of the angles around these atoms of approximately
360° illustrate the sp2-hybridisation. These bonding parameters
are closely related to those found for the parent lithiated phos-
phanamide [(THF)2Li{Ph2PC(H)Py}] (P–CH: 175.9 pm; HC–CPy:
139.0 pm)15 and the lead amide [Pb{Ph2PC(H)Py} {N(SiMe3)2}]
(P–CH: 173.9 pm; HC–CPy: 139.4 pm).18 As in the latter two com-
plexes, the negative charge in these anions in 1 appears delocalised
over the [P–C(H)–Py]-unit and shifted towards the ring nitrogen
atoms N1 and N4, leading to an amidic character of these atoms.
The bite angles of the ligands A and B are 84.73(4)° for P1–Zn1–N1
and 86.10(5)° for P4–Zn3–N4.
Scheme 3 Synthesis of [Zn3{Ph2PC(H)Py}4O] (1), by reaction of
[(THF)2Li{Ph2PC(H)Py}] with ZnCl2 and ZnO.
Considering, the broad application of hemilabile coordinated
iron complexes in catalysis, it seems worth reacting the phosphane
Ph2P(CH2Py) with the iron(II) amide [Fe{N(SiMe3)2}2].16 The 2:1
reaction instantaneously causes a redox processes yielding multiple
products, which could not be characterised unequivocally. However,
it turned out, that the use of an excess of the phosphane in the reaction
stabilises the iron centre to give the iron(II) amide rac-[(Ph2PCH2Py)-
Fe{Ph2PC(H)Py}2] (2). Both of the two [N(SiMe3)2]−-anions of the
iron amide starting material remove a single proton at the C-position
in the phosphane. A third equivalent of Ph2P(CH2Py) is employed
as a neutral chelating donor ligand and stabilises the intermediate
14 VE iron complex, yielding the 18 VE complex (2) (Scheme 4).
The remaining two anions C and D each coordinate a zinc cation
via the C-atoms. The P2–C7 and P3–C13 bond lengths are on aver-
age 180.5 pm. They are ca. 6.3 pm longer than those in the above-
mentioned purely (P,N)-chelating anions in A and B (174.2 pm) and
only 4.5 pm shorter than a formal P–C single bond (185 pm).17 Also
the C7–C8 and C13–C14 distances, which are equal within their
esds, are with 147.5 pm substantially longer in comparison to the
corresponding contacts in the other two anions (average 139.0 pm
for A, B) and to the bond length found in [(THF)2Li{Ph2PC(H)Py}].
They are only 2.5 pm shorter than in the phosphane Ph2P(CH2Py)
and therefore in the range of formal C–C single bond distances.17
The C8–N2 and C14–N3 distances in the pyridyl substituents of
C and D, averaging at 135.7 pm, are significantly shorter than in
Scheme 4 Reaction of [Fe{N(SiMe3)2}2] with an excess of Ph2P(CH2Py)
to give [{Ph2P(CH2Py)}Fe{Ph2PC(H)Py}2] (2).
Remarkably, the reaction of the phosphane Ph2P(CH2Py) with
[Fe{N(SiMe3)2}2] in a 1:1 ratio gives the dinuclear, heteroleptic
14 VE organoiron(II) complex [Fe{Ph2PC(H)Py}{N(SiMe3)2}]2 (3).
One amide anion of [Fe{N(SiMe3)2}2] deprotonates one molecule
of the phosphane Ph2P(CH2Py). The second [N(SiMe3)2]−-anion
remains coordinated to the iron(II) centre. Recrystallisation from
hexane/Et2O (2:1) yields the organoiron complex 3 as red needles,
decomposing at 123 °C (Scheme 5).
2 5 6 4
D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9

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Fig. 1 Top: Solid state structure of [Zn3{Ph2PC(H)Py}4O] (1). The non-coordinating ether molecule is omitted for clarity. Bottom: Superposition plot of the
two (P,N)-chelating anions (A bold lines, B narrow lines), coordination mode of the (P,N,C)-tridentate ligand (C) and the (N,C)-coordinating anion (D).
Table 1 Selected bond lengths/pm and angles/° of [Zn3{Ph2PC(H)Py}4
O] (1)
The Zn2 cation is displaced by 77.6 pm from the best plane of
the anion.
In [Zn3{Ph2PC(H)Py}4O] (1), the three Zn–Pdistances are almost
equal and range from 239.28(5) for Zn2–P2 to 240.09(5) pm for
Zn1–P1. They are comparable to Zn←P donor bonds, like in [Zn-
{Ph2PNSiMe3}{N(SiMe3)2}]2 (240.54 pm)20 and [(Ph2MeP)2ZnI2]
(241.6 pm).21 The Zn–P bond lengths are invariant towards the dif-
ferent coordination behaviour of the [Ph2PC(H)Py]−-anions. This
is different to the Zn–NPy distances in 1, as they vary by ca. 10 pm
from 202.72(16) to 212.57(16) pm. The shortest Zn–NPy contact is
found for Zn3–N4 (202.72(16) pm), which is consistent with an
amidic character for N4. The Zn1–N1 distance of 206.66(15) pm is
ca. 4 pm longer than the comparable (in terms of amidic character of
the nitrogen atom) Zn3–N4 contact. The difference arises from the
coordination of Zn1 to the carbanionic C7 centre of another anion,
in contrast to the Zn3 atom, which features a more dative Zn3–N3
bond (210.33(15) pm) and has no additional carbanionic contact.
The Zn2–N2 bond length is 212.57(16) pm, hence ca. 2.25 pm
longer than the Zn3–N3 bond. This slight bond elongation can be
assigned to the interaction of Zn2 with the carbanionic C13 centre,
whereas the Zn3 cation is bound to the delocalised fragment con-
taining the amidic pyridyl nitrogen atom N4.
The Zn–C distances show remarkable differences although
the coordination number is four in any case. The Zn2–C13 bond
length is 204.7(6) pm and much shorter than the Zn1–C7 contact
of 214.67(18) pm. This elongation is due to the different electronic
environments of the two zinc cations. While Zn1 is additionally
coordinated to the more pronounced amidic nitrogen atom N1, Zn2
is only coordinated to the less-charged nitrogen atom N2.
The differences in Zn–N and Zn–C bond lengths are also reflected
in the Zn–O distances. The shortest contact is found for Zn3–O with
186.97(12) pm, in accordance with the observed additional amidic
N4 and the more dative N3 coordination of the cation, followed
by the Zn1–O distance (190.66(12) pm). The Zn1 atom is further
bound to the amidic atom N1 and the carbanionic C7 centre. The
longest Zn–O bond is observed for Zn2–O (192.80(12) pm). The
Zn2 atom is coordinated to the less negatively charged ring nitrogen
atom N2, but additionally shows the shortest Zn–C contact (C13).
The iron complex rac-[{(Ph2PCH2Py)}Fe{Ph2PC(H)Py}2] (2),
crystallises from the reaction solution at r.t. as a racemic mixture
with the two diastereomers arranged along the two fold axis in
helical strands. The solid state structure of 2 is shown in Fig. 2;
(P,N)-chelating A, B
(P,N,C)- or (N,C)-coordinating C, D
P1–C1
C1–C2
C2–N1
Average P1–CPh
P1–C1–C2
P4–C19
C19–C20
C20–N4
174.4(2)
138.8(3)
138.1(2)
183.42
120.97(15)
173.9(2)
139.1(3)
138.5(2)
182.96
P2–C7
C7–C8
C8–N2
Average P2–CPh
P2–C7–C8
P3–C13
C13–C14
C14–N3
180.33(18)
147.6(3)
136.0(2)
182.83
109.64(13)
180.7(7)
147.4(7)
135.3(2)
186.2
Average P4–CPh
P4–C19–C20
Average P3–CPh
P3–C13–C14
121.67(16)
109.5(6)
Zn–E; E–Zn–E (E = P, N, C, O)
Zn1–P1
Zn1–N1
Zn1–C7
Zn1–O
Zn2–P2
Zn2–N2
Zn2–C13
Zn2–O
240.09(5)
206.66(15)
214.67(18)
190.66(12)
239.28(5)
212.57(16)
204.7(6)
Zn3–P4
Zn3–N3
Zn3–N4
Zn3–O
P1–Zn1–N1
P2–Zn2–N2
P4–Zn3–N4
239.41(5)
210.33(15)
202.72(16)
186.97(12)
84.73(4)
79.85(4)
86.10(5)
192.80(12)
the exclusively (P,N)-chelating anions (A, B: CPy–NPy: average
138.3 pm) and only 1.7 pm longer than in the parent phosphane
(133.97) pm). The average angles P2–C7–C8 and P3–C13–C14 of
109.5°, respectively, illustrate the tetrahedral environment of the
metal coordinated C-atoms in the two anions C and D in contrast
to the planar coordination sphere observed for the corresponding
atoms C1 and C19 not interacting with any zinc cation. In both
anions C and D, the sp2-hybridised C-atom of the starting lithiated
complex [(THF)2Li{Ph2PC(H)Py}] rehybridises to sp3. This kind of
re-hybridisation from sp2 in the starting material to sp3 in the prod-
uct was observed earlier in the reaction of [(THF)2Li–{HC(Py2)}]
with ZnMe2, to give [MeZn{HC(Py2)}]2.19 Thus, in the anions of C
and D in Fig. 1 the negative charge is accumulated and they exhibit
carbanionic rather than amidic character. In contrast to the five
membered metallacycles of A and B, which are planar as described
above, the ring system comprised of the [Zn2–P2–C7–C8–N2]-unit
in C shows envelope conformation, due to the C7–Zn1 interaction.
D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9
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The Fe–P distances in 2 show remarkable differences. Whereas,
the distances of the iron cation to the phosphorus atoms in the an-
ionic ligands are almost identical, the Fe–P1 contact to the neutral
ligand is on average 3.5 pm shorter. In the C-deprotonated ligands
the electron density at the phosphorus centres is considerably influ-
enced by the negative charge in the [P–C(H)–Py]−-moiety, resulting
in weaker P–Fe interactions. The Fe–N distances in the iron com-
plex 2 are located at the lower end of the range generally observed
for Fe–NPy distances in iron(II) complexes.22
In the solid-state structure of [Fe{Ph2PC(H)Py}{N(SiMe3)2}]2
(3), the FeN(SiMe3)2-fragment containing Fe2 shows heavy disor-
dering. The three positions found for this residue were successfully
refined using distance and simularity restraints, giving reasonable R
values and standard deviations. The bond lengths and angles for this
residue, given in Table 3 are averages, the standard deviations are
maximum values. The solid state structure of 3 is shown in Fig. 3.
Fig. 2 Solid state structure of rac-[{Ph2P(CH2Py)}Fe{Ph2PC(H)Py}2] (2).
Only the Ph(Cipso) atoms are depicted for clarity.
Table 2 Selected bond lengths/pm and angles/° of rac-[{Ph2P(CH2Py)}-
Fe{Ph2PC(H)Py}2] (2)
Anionic ligands
P2–C19
C19–C20
C20–N2
Average P2–CPh
Fe–P2
Fe–N2
P2–C19–C20
P2–Fe–N2
P2–Fe–N3
174.7(2)
138.6(3)
138.6(2)
185.05
227.42(5)
203.69(15)
116.90(15)
83.83(5)
174.07(5)
P3–C37
C37–C38
C38–N3
Average P3–CPh
Fe–P3
Fe–N3
P3–C37–C38
P3–Fe–N3
P3–Fe–N1
175.7(2)
139.7(3)
138.3(2)
185.19
228.66(5)
207.44(16)
116.17(15)
82.84(5)
171.04(5)
Neutral ligand
P1–C1
C1–C2
C2–N1
Average P1–CPh
P1–C1–C2
181.3(2)
146.9(3)
135.9(2)
183.81
Fe–P1
Fe–N1
P1–Fe–N1
P1–Fe–N2
224.58(5)
208.74(16)
83.07(5)
Fig. 3 Solid state structure of [Fe{Ph2PC(H)Py}{N(SiMe3)2}]2 (3). Only
the Ph(Cipso) and the central silicon atoms are depicted for clarity.
171.16(5)
112.06(14)
In the structure the [Ph2PC(H)Py]−-anion (P,N)-chelates a single
iron cation, forming a five membered metallacycle. Two of these
building blocks dimerise in a head-to-tail fashion with both iron
atoms Fe1 and Fe2 coordinated to the deprotonated carbon atoms
C19 and C1, respectively, giving a dinuclear, heteroleptic complex.
Thus, the main structural feature is a [2.2.1.1] metallacycle. Each
of the two iron atoms shows a distorted tetrahedral coordination
sphere. The (P–Fe–N) bite angles of, on average, 76.97° are more
acute than in the iron complex 2. The P1–C1 and P2–C19 bond
lengths are similar and on average 180.0 pm long. They are 5.6 pm
shorter than in the starting material but comparable to those found
in the (P,N,C)- and (N,C)-coordinating anions in 1. However, in
comparison to the structural parameters of the exclusively (P,N)-
chelating anionic ligands in 1 and 2 they are approximately 5 pm
longer. Thus, in the organoiron complex 3, the negative charge
created by deprotonation at the C-position is not delocalised,
but accumulates predominantly at the C-atom. This is further il-
lustrated by the C2–N1 and C20–N2 distances which are only 1.73
pm longer than in the posphane Ph2P(CH2Py) and identical to the
C2–N1 distance found in the neutral donor ligand Ph2P(CH2Py) of
the iron complex 2. As expected from these bonding parameters
the angles at the carbon atom C1 and C19 are very close to 109.5°,
indicating sp3-hybridisation for these atoms in contrast to the more
sp2-hybridisised C-atoms of the purely (P,N)-chelating anionic
ligands in 1 and 2.
selected bond lengths and angles are summerised in Table 2. The
asymmetric unit of 2 contains a non-coordinating ether molecule,
which is omitted in the figure for clarity.
The two anionic [Ph2PC(H)Py]− ligands and the neutral
phosphane [Ph2PCH2Py] act as (P,N)-bidentate chelats to the
central iron(II) cation. The coordination polyhedron at the metal
is a nearly perfect octahedron. The bite angles of the three ligands
(P–Fe–N) are very similar and on average 83.25°. Thus, there is
no significant difference in the bite of the anionic and the neutral
ligands in 2.
The iron amide 2 is an ideal system to elucidate the bonding
in the phosphane Ph2P(CH2Py),15 the metal-coordinated neutral
phosphane and the related anion. In comparison to the parent
phosphane, the (P,N)-coordination of the neutral ligand in 2
results in shorter P1–C1 and C1–C2 bonds. The C1–C2 bond in 2
is ca. 3.0 pm shorter than in the phosphane. This bond contraction
is a result of the Fe–N1 contact, which influences the bonding
parameters in the electron deficient pyridyl substituent. The
electron density is shifted towards the ring and accumulates at the
nitrogen atom. As a consequence the C1–C2 bond gets contracted
and the C2–N2 bond gets elongated. The P–C1 distance in the
phosphane Ph2P(CH2Py) is 185.59(14) pm, in 2 the corresponding
P1–C1 bond is only 181.3(2) pm long. The Fe–P1 interaction,
observed in 2, results in a more pronounced electropositive
character of the phosphorus atom in comparison to the isolated
phosphane, because electron density is transferred to the metal ion.
Therefore, the P1–C1 bond of the more electropositive phosphorus
atom with the electronegative carbon atom gets contracted by
stronger electrostatic interaction.
Due to the displacement of the iron atoms from the best plane of
the corresponding anionic ligand (56 pm for Fe1 and 45 pm for Fe2)
and the additional coordination to the carbon atoms C1 and C19, the
Fe1–N1, Fe2–N2 and the Fe1–P1 and Fe2–P2 distances are much
longer than in the iron amide 2. For the Fe1–C19 and Fe2–C1 bond
lengths, 217.6(3) pm and 222.6(3) pm were determined, respec-
tively. Thus, they match the range generally observed in organoiron
complexes (202.1–231.0 pm).23
In the anionic ligands, the respective P–C and the C–C distances
are very similar. They almost match those of the purely (P,N)-
chelating ligands in 1.
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Table 3 Selected bond lengths/pm and angles/° of [Fe{Ph2PC(H)Py}-
{N(SiMe3)2}]2 (3)
Table 4 Selected structural parameters (in pm and °) of the [Ph2P(CHPy)]−-
anions in 1–3, in comparison to the parent phosphane and the metal
coordinated neutral phosphane in 2
P1–C1
C1–C2
C2–N1
Fe1–P1
Fe1–N1
Fe1–N3
Fe1–C19
P1–C1–C2
P1–Fe1–N1
181.0(3)
146.8(3)
135.6(3)
253.51(11)
215.2(2)
195.8(2)
217.6(3)
107.81(17)
76.05(7)
P2–C19
179.1(2)
147.4(3)
135.8(3)
242.2(8)
214.6(3)
195.9(4)
222.6(3)
110.43(17)
77.88(20)
C19–C20
C20–N2
Fe2–P2
Fe2–N2
Fe2–N4
Fe2–C1
P2–C19–C20
P2–Fe2–N2
P–CH
HC–CPy
Cipso–N
134.0
P–C(H)–C
112.1
Ph2P(CH2Py)15
185.6
150.0
(P,N)-coordination
1
174.2
175.2
181.3
139.0
139.2
146.9
138.3
138.5
135.9
121.3
116.5
112.1
2 (anionic ligand)
2 (neutral ligand)
(P,N,C), (N,C)-coordination
Average P–CPh 183.13
P–CH
180.3
180.0
HC–CPy
147.6
147.2
Cipso–N
135.7
135.7
P–C(H)–C
109.6
109.1
1
3
Structural comparison
In Table 4 selected structural parameters of the [Ph2PC(H)Py]−-an-
ions and the metal coordinated neutral phosphanes Ph2P(CH2Py)
in the metal complexes 1–3 are compared, taking the different
coordination modes into account. Additionally, the corresponding
distances in the parent phosphane Ph2P(CH2Py)15 are given. The
distances for similar coordinated anions in one complex are aver-
age values.
Deprotonation at the methylene bridge of the parent phosphane
and coordination of the metal cation only via the P- and N-centres
results in ca. 11 pm shorter P–C(H) and (H)C–CPy distances and ca.
2.3 pm longer Cipso–N distances, relative to the phosphane. These
structural parameters are consistent with a delocalisation of the
negative charge over the [P–C(H)–Py]-moiety and charge transfer
into the electron deficient pyridyl substituent. Thus, the short P–C1
and C1–C2 distances originate from high electrostatic contributions
and polarisation effects.24 The P–C(H)–C angles are close to 120°.
The anion is best described as a phosphanamide. If a metal cation is
coordinated to the C-atom, the P–C(H) and HC–CPy distances are
only ca. 5 pm and 2.5 pm shorter than in Ph2P(CH2Py), respectively.
The multiple bond character for these bonds is less pronounced.
The P–C–C angles are near 109.5°. The anion is rather a carbanion
than an amide.
Scheme 6
sensitive to the the charge concentration of the coordinated metal
and adapts the coordination mode to the electronic requirements of
the cation (electronic differentiation).
Experimental section
Preparation of 1–3
All manipulations were performed under inert gas atmosphere of
dry N2 with Schlenk techniques or in an argon glovebox. All sol-
vents were dried over Na/K alloy and distilled prior to use. NMR
spectra were recorded at room temperature on a Bruker DRX 300
spectrometer at 300.1 (1H) and 121.5 (31P) MHz. Chemical shifts
are  values relative to the solvent for 1H and to H3PO4 (85%) for
31P, respectively. Elemental analyses were performed by the Micro-
analytisches Labor der Universität Würzburg. The chemical shifts
were assigned according to Scheme 7.
Conclusion
The coordination behaviour of the [Ph2PC(H)Py]−-anion was
examined. The metal derivatives 2 and 3 were prepared by reac-
tion of Ph2P(CH2Py) with [Fe{N(SiMe3)2}2]. Transmetallation of
[(THF)2Li{Ph2C(H)Py}] with ZnCl2 in the presence of ZnO gives
the zinc complex 1.
In the characterised metal complexes, the [Ph2P(CHPy)]−-anion
features three different coordination modes:
(i) bidentate, (P,N)-chelating
(ii) tridentate, (P,N)-chelating, C-coordinating
(iii) (C,N)-coordinating
In homoleptic complexes the [Ph2P(CHPy)]−-anion prefers
(P,N)-, rather than [M]–C-coordination. However, in heteroleptic
complexes the [Ph2P(CHPy)]−-fragment can bind to a metal cation
via the P- and N-atoms and additionally coordinate a second cation
via the C-atom. In the zinc complex 1, one anion coordinates only
via the pyridyl N- and the C-atom to cations. Here, the phosphorus
centre is not involved in coordination. C-metal coordination causes
sp3-rehybridisation of the carbon atom, in contrast to the sp2-charac-
ter found for the exclusively (P,N)-coordinating anion.
Scheme 6 gives an overview of the different coordination modes,
observed for the [Ph2P(CHPy)]−-anion.
As a solely (P,N)-chelate, the negative charge is delocalised and
transferred towards the ring nitrogen atom. The metal complexes
show short [M]–NPy distances. Thus, the anion should be described
as an amide. The coordination of metal fragments at the C-position
results in a pronounced carbanionic character of the deprotonated
carbon atom. The [M]–NPy distances are in the range of [M]←N-
donor bonds. The negative charge is predominantly accumulated
at the C-atom. In conclusion, the phosphane Ph2P(CH2Py) is a
very versatile starting material for the preparation of highly flex-
ible, hemilabile, ambident ligands. This Janus head responds very
Scheme 7
[Zn3{Ph2PC(H)Py}4O] (1). A solution of 1.00 g (2.34 mmol)
[(THF)2Li{Ph2PC(H)Py}] in 30 ml Et2O was added to a suspension
of 0.18 g (1.30 mmol) ZnCl2, containing ZnO impurities, in 20 ml
Et2O at room temperature. The suspension was stirred for 48 h, then
it was filtered to remove the white precipitate (LiCl). The volume
of the orange solution was reduced by evaporation. Storage of the
solution at room temperature affords [Zn3{Ph2P(H)Py}4O] (1) as
yellow blocks. The elemental analysis showed, that the non-coor-
dinating ether molecule found in the solid state structure is removed
during drying the complex in vacuum. Yield 1.03 g (0.80 mmol,
34%); m.p. (DTA) 189 °C; 31P-NMR (benzene-d6)  = −35.6 and
−32.4 (s, P1,4), −29.8 (s, P-2), −27.5 (s, P-3); 1H,1H-COSY-NMR
(benzene-d6)  = 3.12 (d, 1H, H-31), 3.70 and 3.90 (d, 2H, H-11, H-
D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9
2 5 6 7

View Article Online
Table 5 Crystallographic data for compounds 1–3
Compound
1
2
3
Formula
CCDC no.
Mr/g mol−1
T/K
C72H60N4OP4Zn3 + 0.5Et2O
236265
1354.29
C54H46FeN3P3 + Et2O
236264
959.82
C48H66Fe2N4P2Si4
236263
985.05
173(2)
100(2)
293(2)
Crystal system
Space group
a/pm
b/pm
c/pm
/°
/°
Triclinic
P1
Monoclinic
P21/n
1223.28(4)
3424.87(12)
1233.96(4)
Triclinic
P1
1266.88(6)
1355.52(7)
2206.51(11)
102.5850(10)
92.7750(10)
116.3710(10)
3.2673(3), 2
1.377
1240.1(7)
1288.9(7)
1805.3(10)
83.784(10)
82.791(11)
71.046(10)
2.700(1), 2
1.211
115.3450(10)
/°
V/nm−3, Z
4.6722(3), 4
1.365
0.472

calcd/Mg m−3
/mm−1
1.239
0.719
F(000)
1398
2016
1040
Crystal size/mm
 range/°
Reflections collected
Unique reflections
R(int)
0.3 × 0.2 × 0.2
2.15 to 25.05
52698
11554
0.0226
0.3 × 0.2 × 0.2
1.92 to 26.40
69564
9566
0.0302
0.3 × 0.1 × 0.06
3.00 to 25.35
45059
9884
0.0233
Absorption correction
Max. and min. transmission
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I > 2(I)]
Empirical
Empirical
1.000 and 0.927
9566 / 121 / 662
1.131
R1 = 0.0400
wR2 = 0.0934
R1 = 0.0427
wR2 = 0.0948
628 and −246
0.0375 / 4.6727
Empirical
1.000 and 0.846
9865 / 535 / 757
1.024
R1 = 0.0385
wR2 = 0.1013
R1 = 0.0471
wR2 = 0.1074
1130 and −306
0.0565 / 1.4306
1.000 and 0.878
11549 / 1240 / 862
1.045
R1 = 0.0284
wR2 = 0.0735
R1 = 0.0324
wR2 = 0.0755
387 and −228
0.0426 / 1.3861
R indices (all data)
Largest diff. peak and hole/e nm−3
g1 / g2
41), 3.98 (d, 1H, H-21), 5.15 (dd, 1H, H-35), 5.41 (dd, 1H, H-25),
5.80 and 5.90 (m, 2H, H-15, H-45), 6.10 and 6.14 (m, 2H, H-13,
H-43), 6.35 (m, 1H, H-33), 6.45 (m, 1H, H-23), 6.51 (m, 1H, H-34),
6.55 (m, 1H, H-24), 6.60 and 6.62 (m, 2H, H-14, H-44), 6.60 (m,
1H, H-36) 6.83 (m, 1H, H-26), 7.15 and 7.4 (m, 2H, H-16, H-46);
CHN, found, (calcd.) [%] C 65.42 (65.26), H 4.42 (4.30), N 4.29
(4.35).
Filtration and drying the solid in vacuum yields 1.47 g (1.49 mmol,
83%). Mp (DTA) 98 °C; CHN, found, (calcd.) [%] C 58.42 (58.53),
H 6.71 (6.75), N 5.73 (5.69).
Structure determination of 1–3
Crystallographic data for 1–3 are listed in Table 5. Data of 1 and 2
were measured at low temperature,25 data of 3 at room temperature,
using graphite monochromated Mo K radiation ( = 71.073 pm)
on a Bruker D8 goniometer platform, equipped with a Smart Apex
CCD detector. Cell parameters were determined and refined using
the SMART software.26 Series of -scans were performed at several
φ-settings. Raw frame data were integrated using the SAINT pro-
gram.27 The structures were solved using direct methods and refined
by full-matrix least squares on F2 using SHELXL.28 Data were em-
pirically absorption corrected with SADABS.29 The phenyl groups
C31–C36 at P1 and C67–C72 at P4 in [Zn3{Ph2PC(H)Py}4O] (1),
are disorderd. The site occupation factors refined to 0.54 and 0.46
for C31–C36 and 0.58 and 0.42 for C67–C72. The [Ph2P]-residue
at C13 and C13 is also disorder. The site occupation factors for this
fragment refined to 0.82 and 0.18, respectively. The non-coordi-
nated ether molecule was removed from the special position. The
site occupation factor was fixed to 0.50. The positions of the hydro-
gen atoms H1, H7 and H19 were taken from the Fourier map and re-
fined freely. In rac-[OC-6-43]-[{Ph2P(CH2Py)}Fe{Ph2PC(H)Py}2]
(2), the positions of the hydrogen atoms H1A, H1B, H19 and H37
at the methylene bridges C1, C19 and C37, respectively were taken
from the difference Fourier map and refined freely. The non-coor-
dinating ether molecule is disordered. The site occupation factors
refined to 0.57 and 0.43. The positions of the hydrogen atoms H1
and H19 at C1 and C19 in [Fe{Ph2P–C(H)Py}{N(SiMe3)2}]2 (3),
respectively, were taken from the difference Fourier map and re-
fined freely. The fragment containing Fe2, N4 and the SiMe3 groups
at Si3 and Si4 is disordered. The site occupation factors refined to
0.53, 0.35 and 0.12. All other hydrogen atoms in 1–3 were refined
using a riding model. The Uiso values for the hydrogen atoms of a
CH3 group were set to 1.5, those of all other hydrogen atoms to 1.2
of the Ueq values of the corresponding C atoms. All non-hydrogen
atoms were refined anisotropically. The anisotropic displacement
rac-[OC-6-43]-[{Ph2P(CH2Py)}Fe{Ph2PC(H)Py}2] (2).
To
1.00 g (3.61 mmol) of solid Ph2P(CH2Py) 0.45 g (1.20 mmol) pure,
liquid [Fe{N(SiMe3)2}2] were added via a syringe in a drybox. The
suspension turned immediately dark red. It was stirred for 3 h at
room temperature, then Et2O was added until a clear solution was
obtained. After five days, dark red crystals of [{Ph2P(CH2Py)}Fe-
{Ph2PC(H)Py}2] (2), were obtained. The iron complex was isolated
by filtration and dried in vacuum, yielding 2.62 g (2.96 mmol, 82%)
of pure 2. The elemental analysis showed, that the non-coordinating
ether molecule found in the crystal structure was removed during
drying in vacuum. Mp (DTA) 212 °C; 31P-NMR (THF-d8)  = 36.01
2
2
2
(dd, JP2–P3 = 44.2 Hz, JP2–P1 = 41.7 Hz P-2), 39.77 (dd, JP2–P3
=
2
2
44.2 Hz, JP1–P3 = 32.2 Hz, P-3), 54.03 (dd, JP1–P2 = 41.7 Hz,
2JP1–P3 = 32.2 Hz, P-1), 1H-NMR (THF-d8)  = 3.56 (d, 2H, H-11),
3.62 (d, 1H, H-21), 3.70 (d, 1H, H-31), 4.84 (dd, 1H, H-25), 5.05
(dd, 1H, H-35), 5.96 (d, 1H, H-24), 6.05 (d, 1H, H-34), 6.25 (dd,
1H, H-15), 6.62 (dd, 2H, H-23, H-33), 6.83 (dd, 1H, H-14), 6.99
(1H, H-13), 7.43 (d, 2H, H-26, H-36), 7.98 (d, 1H, H-16), 7.04–7.39
(m, 30H, PhH); CHN, found, (calcd.) [%] C 73.25 (73.23), H 5.37
(5.23), N 4.73 (4.74).
[Fe{Ph2PC(H)Py}{N(SiMe3)2}]2 (3). To 0.5 g (1.80 mmol) of
solidPh2P(CH2Py)0.68g(1.80mmol)pure,liquid[Fe{N(SiMe3)2}2]
were added via a syringe in a drybox. The suspension turned imme-
diately red. It was stirred for 2 h at room temperature, then 10 ml
hexane were added. The red suspension was stirred for an addi-
tional hour. The solvent and formed HN(SiMe3)2 were evaporated in
vacuum. The resulting red solid was dissolved in 10 ml hexane and
5 ml Et2O. Storage of the solution at room temperature for seven
days affords red crystals of [Fe{Ph2PC(H)Py}{N(SiMe3)}2]2 (3).
2 5 6 8
D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9

View Article Online
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parameters (ADPs) in the supplementary material were drawn at
the 50% probability level.
CCDC reference numbers 236263–236265.
See http://www.rsc.org/suppdata/dt/b4/b405680a/ for crystallo-
graphic data in CIF or other electronic format.
12 L. Mahalakshmi and D. Stalke, Struct. Bonding, 2002, 103, 85.
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Acknowledgements
Continuous financial support of the DFG (grants no. Sta 334/8 and
the Graduiertenkolleg 690 Elektronendichte-Theorie und Experi-
ment) is kindly acknowledged.
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15 A. Murso, PhD Thesis, Universität Würzburg, Germany, 2004.
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D a l t o n T r a n s . , 2 0 0 4 , 2 5 6 3 – 2 5 6 9
2 5 6 9