Synthesis and Structural Characterization of Potassium Salts of Phosphane-Substituted (Cyclopentadienyl)iron Dicyanides, and Their Use as Bridging Ligands for Copper(I) Phosphane Derivatives

Article abstract of DOI:10.1002/ejic.200300304

Phosphane-substituted CpFe(CN)₂ anions have been synthesized by photochemical decarbonylation of KCpFe(CN)₂CO in the presence of various mono- and diphosphanes. The synthesis and characterization of uniquely bridged diphosphane deriv

Full text of DOI:10.1002/ejic.200300304

FULL PAPER
Synthesis and Structural Characterization of Potassium Salts of Phosphane-
Substituted (Cyclopentadienyl)iron Dicyanides, and Their Use as Bridging
Ligands for Copper( ) Phosphane Derivatives
I
Donald J. Darensbourg,*[a] M. Jason Adams,[a] Jason C. Yarbrough,[a] and
Andrea L. Phelps[a]
Dedicated to the memory of Professor Dieter Sellmann, a good friend and brilliant chemist
Keywords: Cyanides / Heterometallic complexes / Bridging ligands / Iron / Copper / Potassium
Phosphane-substituted CpFe(CN)2 anions have been synthe-
sized by photochemical decarbonylation of KCpFe(CN)2CO
in the presence of various mono- and diphosphanes. The syn-
thesis and characterization of uniquely bridged diphosphane
derivatives, [KCpFe(CN)2]2-µ-(Ph2P)2−(CH2)n (n = 2−4), are
particularly noteworthy. These phosphane-substituted
shows these derivatives to display two-dimensional dia-
mond-shaped structures with copper( of the form
I)
[Fe(CN)2Cu]2, where the CuI centers exhibit both trigonal
and tetrahedral geometries. Infrared data reveal that the
withdrawal of electron density from the iron centers in these
mixed metal cyanides via the cyanide ligands is enhanced
upon replacing CO in CpFe(CN)2CO− with phosphanes.
−
CpFe(CN)2 units have afforded stable mixed-metal com-
plexes upon reaction with CuI in the presence of tricyclohex- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ylphosphane in acetonitrile solution. X-ray crystallography
Germany, 2003)
Introduction
monocyanide derivatives is particularly beneficial at re-
stricting the bridging capacity of the complex, and thus un-
complicating the study of the cyanide ligand as an elec-
tronic linkage between two metal centers. The chelated
phosphane ligand serves to block any sites on the iron ion
that a more labile ligand might leave open for substitution.
Furthermore, the bulkiness of the phosphane ligand often
aids in crystallization of the resulting multinuclear metal
complexes. Indeed, this simple metallocyanide has allowed
Vahrenkamp to examine in detail the redox chemistry of
cyanide-bridged trimetallic complexes using cyclic voltam-
metry. One such study involved the effect of linear vs. bent
bridging motifs in the FeϪCNϪPtϪNCϪFe metallocyan-
ide unit on electronic communication between the metal
centers.[5,6]
The use of substitutionally inert organometallic cyanides
as ligands to other metal ions has received much interest
due to their ability to simplify studies utilizing cyanide as a
bridging group.[1] Although, metal hexacyanide salts have
long been known to complex other metal ions through
bridging cyanide ligands, the resulting derivatives are often
highly insoluble aggregates which are difficult to definitively
characterize.[2] Organometallic derivatives having the three
facial coordination sites occupied by an ancillary ligand,
e.g., the cyclopentadienyl moiety, have been used to limit
the degree of aggregation.[3] Substitution of the metal center
by an additional strongly bonded ligand, such as a tertiary
phosphane, further limits bridging in a multidimensional
fashion. In addition to promoting solubility, phosphane ad-
ducts of these organometallic cyanides provide a convenient
31P NMR probe for studying these complexes. Despite these
advantages, relatively few studies have involved these sim-
ple metallocyanides.[4]
A long standing focus in our research efforts involves the
design of homogeneous catalysts for the copolymerization
of epoxides and carbon dioxide to provide polycarbon-
ates.[7] Relevant to this subject double metal cyanide deriva-
tives, especially those of Fe( and ) or CoIII and ZnII,
have received attention as heterogeneous catalysts for this
process in the patent literature.[8] In our efforts to synthesize
novel mixed-metal cyanides as models for these catalysts, a
series of metal complex salts of the general formula
[K][CpFe(CN)2PR3] have been prepared and characterized
both in solution and in the solid state. In addition, the em-
ployment of traditionally chelating phosphane ligands have
extended the range of these salts to include diiron deriva-
Vahrenkamp and co-workers have investigated neutral
iron monocyanide complexes of the type CpFe(dppe)CN,
where dppe ϭ 1,2-bis(diphenylphosphanyl)ethane, as bridg-
ing ligands to other metal complexes.[5] The use of metal
[a]
Department of Chemistry, Texas A&M University,
College Station, Texas 77843, USA
Fax: (internat.) ϩ 1-979/845-0158
E-mail: djdarens@mail.chem.tamu.edu
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D. J. Darensbourg, M. J. Adams, J. C. Yarbrough, A. L. Phelps
FULL PAPER
tives of the type [K]2[CpFe(CN)2PR2(CH2)nPR2-
(CN)2FeCp], where n ϭ 2Ϫ4 and R ϭ Ph, thereby affording
unique bridging ligands with specific bite angles. Import-
antly, the electronic character of the cyanide ligands can be
tailored by choosing phosphanes of the appropriate ba-
sicity. Examples of the viability of these anionic metallocy-
anide derivatives of iron as ligands towards copper() are
demonstrated with the isolation and crystallographic
characterization
of
the
mixed-metal
complexes
[CpFe(PPh3)(µ-CN)2Cu(PCy3)]2 and Cu(PCy3)[CpFe(µ-
CN)2]2Cu(PCy3)2-µ-dppp [dppp ϭ 1,2-bis(diphenylphos-
phanyl)propane].
essential for complete conversion into product. This com-
plex has alternatively been prepared thermally from
CpFe(CO)(PPh3)I and KCN in refluxing ethanol by Re-
ger.[4] The product, KCpFe(CN)2PPh3 (1), exhibited ν(CN)
frequencies at 2055 vs, 2040 s, and 2028 sh cmϪ1 in meth-
anol, which are shifted to lower wavenumbers when com-
pared to the parent compound (see Table 1). This shift to
lower frequencies is expected as the result of replacing the
carbonyl ligand by primarily a donor phosphane ligand,
thereby allowing the cyanide groups to be involved in
greater π-backbonding with the iron center. The 31P NMR
spectrum of 1 displays a downfield chemical shift from that
of the free ligand to δ ϭ 86.9 ppm. The more basic methyl-
diphenylphosphane ligand was incorporated at the iron
center for comparison with the PPh3 analog, where the only
other variance arises from its slightly reduced cone angle of
136 vs. 145° for PPh3.[10Ϫ12] In this instance it was not
necessary to employ a mixed-solvent system for the photo-
lytic reaction since both the KCpFe(CN)2CO salt and
PPh2Me are soluble in methanol. As expected, the increased
basicity of the monomethylated phosphane causes the
ν(CN) vibrations in KCpFe(CN)2PPh2Me (2) to shift to
lower wavenumbers at 2050, 2034, and 2025 cmϪ1. The 31P
NMR chemical shift in complex 2 appears at δ ϭ 71.3 ppm.
Interestingly, in an attempt to improve reaction yields, pho-
tolysis of the carbonyl salt with a fourfold excess of PPh2Me
afforded the bis(phosphane) neutral complex CpFe(CN)-
(PPh2Me)2 (3).
Results and Discussion
A series of phosphane (ϭ L) substituted salts of
[K][CpFe(CN)2L] has been prepared through photolytic de-
carbonylation of the parent [K][CpFe(CN)2CO] compound
(Scheme 1). The impetus for these studies comes from our
desire to synthesize well-defined double-metal cyanide
(DMC) complexes to serve as soluble structural and reactiv-
ity models for those employed as heterogeneous catalysts
for the polymerization of epoxides to polyols or epoxides
and CO2 to polycarbonates/cyclic carbonates. Relevant to
these studies we have previously noted that upon treating
analogous
DMC
complexes
derived
from
the
CpFe(CN)2COϪ anion with excess PCy3, the reaction ac-
cording to Equation (1) occurred over an extended reaction
time. That is, the metal aggregate was disrupted to afford a
trigonal copper() center and PCy3 had displaced CO at the
iron center (A).[9] Hence, an obvious concern is whether di-
mer disruption is a necessary structural prerequisite upon
substitution of the CO ligand at the iron center with a steri-
cally demanding phosphane ligand.
Table 1. Infrared and 31P NMR spectroscopic data (all spectra were
determined in methanol solution except for those of compound 3
which were determined in THF)
Compound
ν(CN) [cmϪ1
]
δ [ppm]
Scheme 1
KCpFe(CN)2(CO)
2095, 2084
N/A
86.9
71.3
57.2
78.2
77.0
76.5
64.9
KCpFe(CN)2(PPh3) (1)
KCpFe(CN)2(PPh2Me) (2)
CpFe(CN)(PPh2Me)2 (3)
[KCpFe(CN)2]2 µ-dppe (4)
[KCpFe(CN)2]2 µ-dppp (5)
[KCpFe(CN)2]2 µ-dppb (6)
[KCpFe(CN)2]2 µ-dppa (7)
2055 vs, 2040 s, 2028 sh
2050 vs, 2034 s, 2025 sh
2069
2050, 2032, 2025 sh
2050, 2032, 2025 sh
2050 vs, 2034 s, 2026 sh
2057 s, 2050 vs, 2032 sh
[CpFe(CO)(µ-CN)2Cu(PCy3)2]2 ϩ 2 PCy3 Ǟ
(1)
2 CpFe(PCy3)(CN)(µ-CN)Cu(PCy3)2 ϩ 2 CO
In order to tailor the electronic and structural properties
of the ancillary metal center we have photochemically sub-
stituted the CO ligand in the KCpFe(CN)2CO salt with
various phosphane and diphosphane ligands. A mixture of
methanol and acetonitrile was utilized to solubilize both the
parent salt and in this instance PPh3, respectively. Solubility
of the reagents, especially the KCpFe(CN)2CO derivative, is
A number of bidentate phosphanes have been utilized as
bridging ligands between two CpFe(CN)2 anionic units.
These derivatives were synthesized by photolysis of the par-
ent salt KCpFe(CN)2CO in the presence of 0.5 equiv. of the
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Potassium Salts of Phosphane-Substituted (Cyclopentadienyl)iron Dicyanides
FULL PAPER
Figure 1. 31P NMR spectrum of the crude product from the synthesis of [KCpFe(CN)2]2-µ-dppe (4) with baseline omitted from 0
to 70 ppm
corresponding diphosphane in a 1:1 mixture of acetonitrile/ crystallized from THF/hexane at 10 °C, whereas single crys-
methanol. A small impurity of the singly bonded phos- tals of 3 were obtained by slow concentration of a hexane
phorus derivative, such as KCpFe(CN)2dppe, often ac- solution at room temperature. Selected bond lengths and
companies these syntheses. Figure 1 depicts the 31P NMR angles of compounds 1, 3, 4, and 6 are listed in Table 2.
spectrum of the crude product resulting from the reaction
of KCpFe(CN)2(CO) with 0.5 equiv. of dppe, where in ad-
˚
Table 2. Selected bond lengths [A] and angles [°] for compounds 1,
31
dition to the desired product 4 (δ ϭ 78.2 ppm) two weak
P
3, 4, and 6
31P signals at δ ϭ 79.7 and Ϫ10.8 ppm with 31P coupling
constants of 38.3 Hz are observed corresponding to bound
1
3
4
6
and free phosphane, respectively. Varying the number of
ϪCH2Ϫ units linking the phosphorus donors from 2 to 4
allows for control of the orientation of the cyanide ligands
with respect to one another (vide infra). As anticipated, the
ν(CN) vibrational modes in complexes 4, 5, and 6 are vir-
tually identical (see Table 1) since all of the bridging phos-
phane ligands are of similar basicity.
A more contrasting example of a bridging phosphane can
be seen in the bis(diphenylphosphanyl)acetylene case, com-
plex 7. This short-chain bridging phosphane is comprised
of a linear alkylene backbone, with diminished electron-do-
nating ability compared to its dppe counterpart, 4. The de-
crease in basicity is readily apparent in the ν(CN) values in
complex 7 which are on average 10 cmϪ1 higher than those
of complex 4. Furthermore, the linear nature of the phos-
phane prohibits the cyanide ligands of the bis(iron) complex
Fe(1)ϪC(6A)
Fe(1)ϪP(1)
1.880(8)
2.175(2)
1.166(8)
2.847(5)
1.889(3)
2.2025(8)
1.156(3)
1.871(12)
2.180(3)
1.178(13)
2.980(9)
3.086(10)
2.971(9)
2.828(9)
1.847(9)
2.183(2)
1.163(10)
2.982(8)
3.138(7)
C(6A)ϪN(1A)
N(1A)ϪK(1)
N(2A)ϪK(1)
N(2B)ϪK(2)
N(1B)ϪK(1)
N(2B)ϪK(1)
N(1B)ϪK(2)
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
2.781(9)
2.744(7)
2.999(9)
C(6A)ϪFe(1)ϪC(7A)
C(6A)ϪFe(1)ϪP(1)
C(6A)ϪN(1A)ϪK(1)
P(1)ϪFe(1)ϪP(2)
89.3(3)
93.9(2)
136.8(4)
Ϫ
Ϫ
91.7(5)
89.7(3)
87.5(7)
Ϫ
91.6(3)
88.8(3)
85.9(6)
Ϫ
87.73(8)
Ϫ
98.42(3)
The effect of replacing the carbonyl group with a phos-
from interacting at the same metal center. One might im- phane donor can be seen in the metric data for the iron
agine this bis(cyanometalate) behaving as a strut which cyanide unit. Specifically, the ironϪcarbon(cyanide) dis-
links metal centers to form chain-like structures.
tances in compounds 1, 4, and 6 are shorter than those seen
The solid-state structures of representative examples of in KCpFe(CN)2CO, where an average FeϪCN distance of
[13,14]
˚
these phosphane-substituted (cyclopentadienyl)iron dicyan- 1.911(8) A was observed.
This subtle yet statistically
ide salts have been examined by X-ray crystallography. Sin- relevant bond-length change is the result of replacing the
gle crystals of compounds 1 and 4 were grown from a con- good π-acceptor, CO, with a good donor ligand, phos-
centrated methanol solution by slow concentration over phane. Concomitantly, the increase in bond order to the
several weeks at ambient temperature. Compound 6 was FeϪCN bond causes a decrease in the CϪN triple-bond
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D. J. Darensbourg, M. J. Adams, J. C. Yarbrough, A. L. Phelps
FULL PAPER
character, where the C(6A)ϪN(1A) bond lengths in com-
pounds 1, 4, and 6 are all longer than that determined in
˚
the CO analog [1.143(10) A]. Although this is compelling
crystallographic evidence, the decrease in the cyanide triple-
bond order is more evident by observing the ν(CN) vi-
brational modes shift to lower frequencies as previously
noted. As expected, the FeϪP bond lengths in compounds
1, 4, and 6 are quite similar, spanning the narrow range
˚
from 2.175(2) in 1 to 2.183(2) A in 6. In the diphosphane
neutral derivative, 3, there is a slight lengthening of the
˚
FeϪP bond where a distance of 2.2025(8) A is observed.
Although it is tempting to attribute the bond lengthening
to an electronic effect, it might also be due to enhanced
steric congestion about the iron center. Support for this
latter explanation comes from the metric parameters
obtained for the chelated CpFe(CN)(dppe) derivative.
CpFe(CN)(dppe) was prepared by the method of Vahren-
kamp and co-workers[5] and its solid-state structure defined
by X-ray crystallography.[15] The average FeϪP bond length
Figure 3. Thermal ellipsoid drawing of CpFe(CN)(dppe); selected
˚
bond lengths [A] and angles [°]: Fe(1)ϪP(2) 2.1747(14), Fe(1)ϪP(1)
2.1828(15),
Fe(1)ϪC(1)
1.898(5),
N(1)ϪC(1)
1.154(6);
89.02(14),
P(2)ϪFe(1)ϪP(1)
84.76(6),
C(1)ϪFe(1)ϪP(2)
C(1)ϪFe(1)ϪP(1) 88.43(14)
shorter interaction distance between N(1A) and K(1) as
compared to that of N(2A)ϪK(1). In order to utilize these
latter anionic metallocyanides as ligands towards other me-
tal centers, the bridging diphosphane ligand must be flex-
ible. That is, the orientation of the iron centers with respect
to one another is controlled by the length of the chain be-
tween the Ph2PϪ units. As is readily seen in Figure 5 of
compound 4 the dppe bridge between the iron centers (n ϭ
2) is sufficiently short so as to render it impossible for the
four cyanide ligands on the two iron centers to become co-
planar. The coplanarity of these four cyanide ligands is a
requirement for providing mixed-metal diamond-shaped
structures (vide infra). Upon lengthening the chain from
n ϭ 2 to n ϭ 3 (5) or 4 (6) allows greater flexibility in the
phosphane bridge, thereby, permitting the cyanide ligands
to become coplanar in their chelation towards other metal
centers (vide infra).
˚
in this instance was found to be 2.1788(14) A, which is in-
distinguishable from those seen in the anionic compounds
1, 4, and 6. The thermal ellipsoid representations of these
closely related neutral iron monocyanide derivatives, 3 and
CpFe(CN)(dppe), are provided in Figure 2 and Figure 3.
These drawings clearly illustrate the difference observed in
the solid state of the orientation of the phenyl substituents
of the phosphane ligands in 3 as compared with their im-
posed, sterically less demanding orientation seen in
CpFe(CN)(dppe).
Figure 2. Thermal ellipsoid representation of CpFe(CN)-
(PPh2Me)2 (3)
As noted in the thermal ellipsoid drawings in Figure 4,
Figure 5 and Figure 6 of the salts, 1, 4, and 6, in all in-
stances the compounds pack in the crystal lattice so as to
orient in such a manner as to maximize the number of
cyanideϪpotassium interactions. These ϪCNϪK interac-
tions are either bridging or terminal in nature, with the two
not being mutually exclusive. An instance of terminal inter-
action can be seen in Figure 4 between N(1A) and K(1),
Figure 4. Thermal ellipsoid drawing of KCpFe(CN)2(PPh3) (1) with
solvent molecules and hydrogen atoms removed for clarity
˚
with an average distance of 2.847 A. Potassium ions that
bridge cyanide ligands on the same iron center, such as K(1)
seen in Figure 5, display a stronger interaction with one of
the cyanide nitrogen atoms. This is evidenced by a 0.1 A CpFe(CN)2 units with bound phosphanes as anionic li-
Presently, we report studies involving the use of the
˚
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Potassium Salts of Phosphane-Substituted (Cyclopentadienyl)iron Dicyanides
FULL PAPER
lent of PCy3 was added to the copper() reagent prior to its
addition to the iron dicyanide salt. This procedure led to
the formation of a soluble double-metal cyanide derivative,
complex 9. Following the removal of acetonitrile, complex
9 was separated from the by-product KBF4 salt by dissol-
ution in dichloromethane. As anticipated for bridging cyan-
ide ligands, the ν(CN) vibrational modes in complex 9 were
shifted to higher frequencies compared to the correspond-
ing values in the parent salt (see Table 1 and Table 3). Single
crystals of 9 suitable for X-ray diffraction were grown by
vapor diffusion of a CH2Cl2/hexane solution at 10 °C over
a period of one week. A thermal-ellipsoid drawing of com-
plex 9 is depicted in Figure 7, whereas selected bond lengths
and angles are provided in Table 4.
Figure 5. Thermal ellipsoid drawing of [KCpFe(CN)2]2-µ-dppe (4)
with solvent molecules and hydrogen atoms removed for clarity
Figure 7. Thermal ellipsoid representation of [CpFe(PPh3)(µ-
CN)2CuPCy3]2 (9) with hydrogen atoms removed for clarity
The solid-state structure of complex 9 is similar to that
seen for its CpFe(CN)2COϪ-derived analog, [η5-
C5H5Fe(CO)(µ-CN)2CuPCy3]2.[16] That is, complex 9 exhib-
its a diamond-shaped motif composed of two CpFe(PPh3)
fragments, two copper() centers, and four bridging CNϪ
Figure 6. Thermal ellipsoid drawing of [KCpFe(CN)2]2-µ-dppb (6)
with solvent molecules and hydrogen atoms removed for clarity
gands for the formation of double-metal cyanides. Specifi- ligands. The copper() centers display trigonal geometry as
cally, the reaction of KCpFe(CN)2PPh3 with defined by the phosphorus and nitrogen donor groups. The
Cu(CH3CN)4(BF4) was carried out in acetonitrile to yield iron-bound phosphane ligands lie on opposite sides of the
a fine yellow powder. This material was insoluble in all metallacycle plane of the four metal atoms. The inversion
common organic solvents, which is in sharp contrast to its center present in the structure of 9 demonstrates the metal-
carbonylated analog.[16] In an effort to provide a soluble lacycle’s high symmetry. Figure 8 illustrates the channels
complex, a similar reaction was performed where an equiva- formed by the packing of complex 9 in the solid state, which
Table 3. Infrared [ν(CN)] and 31P NMR spectral data for complexes 8Ϫ12
Complex
Solvent
ν(CN) [cmϪ1
]
δ [ppm]
[a]
[CpFe(PPh3)(µ-CN)2Cu(CH3CN)2]2 (8)
[CpFe(PPh3)(µ-CN)2Cu(PCy3)]2 (9)
pyridine
CH2Cl2
pyridine
CH2Cl2
CH2Cl2
2081, 2070
2085, 2078
2075, 2065
2089, 2083, 2077
2082, 2077
Ϫ
84.7, 11.5
Ϫ
74.2, 14.1, 11.2
74.3, 13.5, 10.7
[CpFe(µ-CN)2Cu(CH3CN)2]2-µ-dppp[a] (10)
Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppp (11)
Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppb (12)
[a] Complexes were only soluble in pyridine under which conditions the acetonitrile ligands on copper() are most likely displaced by pyri-
dine.
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D. J. Darensbourg, M. J. Adams, J. C. Yarbrough, A. L. Phelps
FULL PAPER
˚
Table 4. Selected bond lengths [A] and bond angles [°] in complexes 9 and 11
Complex 9
Fe(1)ϪC(1)
Fe(1)ϪC(2)
Fe(1)ϪP(1)
Cu(1)ϪN(1)
1.868(7)
1.865(8)
2.173(2)
1.917(6)
Cu(1)ϪN(2)
Cu(1)ϪP(2)
C(1)ϪN(1)
C(2)ϪN(2A)
1.949(7)
2.1865(19)
1.169(8)
1.168(8)
C(1)ϪFe(1)ϪP(1)
C(2)ϪFe(1)ϪP(1)
N(1)ϪC(1)ϪFe(1)
N(2A)ϪC(2)ϪFe(1)
92.4(2)
87.0(2)
178.6(6)
178.0(6)
C(1)ϪN(1)ϪCu(1)
153.6(6)
C(2)ϪN(2A)ϪCu(1A)
N(1A)ϪCu(1A)ϪN(2A)
P(2)ϪCu(1)ϪN(1)
171.8(6)
109.2(3)
133.0(2)
Complex 11
Fe(1)ϪC(1)
Fe(1)ϪC(2)
Fe(2)ϪC(3)
Fe(2)ϪC(4)
Fe(1)ϪP(1)
Fe(2)ϪP(2)
Cu(1)ϪN(1)
Cu(1)ϪN(3)
Cu(2)ϪN(2)
Cu(2)ϪN(4)
1.96(2)
1.87(2)
1.92(2)
2.03(2)
2.174(6)
2.177(7)
1.986(18)
2.062(19)
1.949(18)
1.901(17)
Cu(1)ϪP(3)
Cu(1)ϪP(4)
Cu(2)ϪP(5)
C(1)ϪN(1)
C(2)ϪN(2)
C(3)ϪN(3)
C(4)ϪN(4)
2.324(7)
2.287(7)
2.206(8)
1.18(2)
1.19(2)
1.13(2)
1.07(2)
C(1)ϪFe(1)ϪP(1)
N(1)ϪC(1)ϪFe(1)
N(2)ϪC(2)ϪFe(1)
N(3)ϪC(3)ϪFe(2)
N(4)ϪC(4)ϪFe(2)
C(1)ϪN(1)ϪCu(1)
C(2)ϪN(2)ϪCu(2)
90.9(6)
178(2)
173.9(18)
177(2)
177(2)
159.3(18)
163.9(16)
C(3)ϪN(3)ϪCu(1)
C(4)ϪN(4)ϪCu(2)
N(1)ϪCu(1)ϪN(3)
N(2)ϪCu(2)ϪN(4)
N(2)ϪCu(2)ϪP(5)
N(1)ϪCu(1)ϪP(3)
P(3)ϪCu(1)ϪP(4)
175.0(19)
164(2)
100.4(7)
105.0(8)
123.3(5)
100.8(5)
127.3(3)
with a second metal center as a result of the chelate effect.
In a similar manner to the procedure employed in the syn-
thesis of complex 9, the iron cyanide salts (complexes 5 and
6) were treated with Cu(CH3CN)4(BF4) in the presence of
2 equiv. of Cy3P. The resulting mixed-metal cyanides 11
(dppp) and 12 (dppb) are soluble in dichloromethane, and
as expected for bridging CN ligands, exhibit ν(CN) vi-
brational modes shifted to higher frequencies compared to
the parent salts (see Table 1 and Table 3). The 31P NMR
spectra of both 11 and 12 display two broadened PCy3
peaks indicative of two different phosphorus environments,
with a single sharp signal for the iron-bound phosphorus
atoms. The broadened phosphorus resonances for the PCy3
ligands bound to CuI result from quadrupolar broadening
i.e., for 63Cu and 65Cu, I ϭ 3/2. Hence, spectroscopic data
(IR and 13P NMR) suggest the derivatives have similar
structures.
Single crystals of 11 were grown by slow concentration
of a concentrated hexanes solution of 11 over several days
at ambient temperature, and were subjected to X-ray dif-
fraction analysis. A thermal ellipsoid representation of
complex 11 is shown in Figure 9, with selected bond lengths
Figure 8. Crystal packing diagram of [CpFe(PPh3)(µ-
CN)2CuPCy3]2 (9), where the dichloromethane molecule is dis-
ordered
results in the inclusion of dichloromethane solvent mol- and angles given in Table 4. The crystal structure of 11
ecules. shows the familiar diamond-shaped motif with the bound
Utilization of two anionic CpFe(CN)2 units bridged by phosphanes bridging the iron() centers. This phosphane-
diphosphanes containing three or four methylene linkers bridged form of the mixed-metal dimer forces both iron-
should afford particularly stable metallacycle derivatives bound phosphane ligands to be positioned on the same face
3644
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 3639Ϫ3648

Potassium Salts of Phosphane-Substituted (Cyclopentadienyl)iron Dicyanides
FULL PAPER
Figure 9. Thermal ellipsoid representation (drawn with 30% probability) of Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppp (11); insert illus-
trates a ball-and-stick drawing of 11 where the substituents on the phosphane ligands are removed for clarity
of the metallacycle, with the two FeϪP distances being stat-
˚
istically equivalent at 2.174(6) and 2.177(7) A. Interestingly,
the basket shaped complex 11 crystallized with two PCy3
ligands bonded to one CuI center, and one PCy3 ligand at-
tached to the other CuI center. This results in tetrahedral
and trigonal-planar coordination geometries for the two
copper centers, respectively. In addition to the differences
in coordination geometries, the CNϪCu distances are
shorter for Cu(2) as compared with Cu(1), i.e., the average
˚
CNϪCu(2) distance is 1.925(17)
A
vs. the average
˚
CNϪCu(1) distance of 2.024(18) A. This can be explained
based on the higher Lewis acidity of Cu(2) resulting from
fewer electron-donating PCy3 ligands occupying its coordi-
nation sphere. The same effect is noted in the shorter
Figure 10. Space-filling model of: (A) [CpFe(PPh3)(µ-
CN)2Cu(PCy3)]2 (9) and (B) Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-
µ-dppp (11)
˚
Cu(2)ϪP(5) bond of 2.206(8) A, as compared to the average
PPh2Ϫ(CH2)nϪPPh2Fe(CN)2Cp2Ϫ (n ϭ 2Ϫ4). These latter
anions were shown to act as pincers to encapsulate (phos-
phane)copper() complexes, thereby leading to very stable
diamond-shaped, two-dimensional [Fe2(CN)4Cu2], mixed-
metal derivatives. These bridged (phosphane)metal anions
˚
Cu(1)ϪP bond length of 2.306(7)A.
Unlike the [Fe2(CN)4Cu2] derivative containing a mono-
dentate phosphane ligand bound to iron(), as in complex
9, complex 11 possesses no void channels for encompassing
solvent molecules. This is best illustrated in their respective
space-filling models depicted in Figure 10.
ϩ
may also serve to bind a variety of MIIXϩ or MIIIX2 ions
in an analogous manner.[17]
Concluding Remarks
Experimental Section
In summary, we have reported the syntheses and struc-
tures of several phosphane-substituted CpFe(CN)2 salts
Methods and Materials: All manipulations were carried out using
standard Schlenk techniques under argon unless otherwise stated.
THF and hexane were dried by refluxing in the presence of sodium/
benzophenone and distillation prior to use. Methanol was dried by
distillation from magnesium turnings and iodine. Acetonitrile was
dried by successive distillation from CaH2 and P2O5. 1-Propanol
was dried with molecular sieves and degassed by argon purge prior
obtained
by
photochemical
decarbonylation
of
KCpFe(CN)2CO in methanol. The anions of these salts,
which offer the opportunity for variation in steric and elec-
tronic modifications, were shown to serve as uninegative
bridging ligands towards copper() centers. Unique among
these derivatives was the preparation and characterization
of the diphosphane-bridged iron species, CpFe(CN)2 to use. All phosphanes were purchased from Strem Chemicals, ex-
Eur. J. Inorg. Chem. 2003, 3639Ϫ3648
www.eurjic.org  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3645

D. J. Darensbourg, M. J. Adams, J. C. Yarbrough, A. L. Phelps
FULL PAPER
cept for triphenylphosphane, which was purchased from Aldrich.
Copper() oxide and nitrosyl tetrafluoroborate were obtained from
Aldrich and Lancaster, respectively. KCpFe(CN)2(CO) was pre-
crude product was dissolved in 1-propanol and filtered through a
frit containing Celite. Subsequent to removal of solvent, the prod-
uct was washed repeatedly with hexane and dried under vacuum.
pared by applying published procedures.[13,18] Unless otherwise Specifics of reactions: KCpFe(CN)2CO (4.2 mmol, 1.0 g) and dppe
stated, all photolysis reactions were performed using a mercury-arc
450-W UV immersion lamp purchased from Hanovia. The 200-
mL water-cooled photolysis vessel was purchased from Ace Glass.
CpFe(dppe)CN was synthesized according to the procedure de-
scribed by Vahrenkamp and co-workers.[5] Copper tetrafluorobo-
rate was prepared as described previously.[19]
(1.0 mmol, 0.40 g) provided 4 in an 85% yield (0.70 g). X-ray qual-
ity crystals were grown by slow concentration of a solution of 4 in
methanol at ambient temperature over several weeks.
C40H34Fe2K2N4P2·6CH3OH (1014.5): calcd. C 54.44, H 5.76;
found C 55.01, H 5.52. KCpFe(CN)2CO (4.6 mmol, 1.1 g) and
dppp (1.6 mmol, 0.64 g) provided 5 in an 81% yield (1.08 g). Single
crystals of
5 were grown as described for compound 4.
Physical Measurements: All vibrational studies were carried out
with a Mattson 6021 FTIR spectrometer, using a 0.1-mm CaF2
sealed cell. 1H and 31P NMR were recorded with a 300-MHz
Varian Unity Plus spectrometer (121.4 MHz, 31P), with methanol
as the solvent unless otherwise stated. Deuterated water was used
as the lock solvent, and all spectra were referenced to an 85% phos-
phoric acid solution.
C41H36Fe2K2N4P2·6CH3OH (1028.5): calcd. C 54.87, H 5.88, N
5.45; found C 55.10, H 5.55, N 5.70. KCpFe(CN)2(CO) (1.6 mmol,
0.40 g) and dppb (0.70 mmol, 0.30 g)provided 6 in a 61% yield
(0.36 g). Single crystals of 6 were grown by vapor diffusion of hex-
ane into a THF solution of 6 maintained at 10° for approximately
one week. C42H38Fe2K2N4P2·2THF·2H2O·CH3OH (1062.6): calcd.
C 58.51, H 5.97; found C 58.97, H 5.62. KCpFe(CN)2CO
(3.1 mmol, 0.75 g) and dppa (1.0 mmol, 0.41 g) provided 7 in an
82% yield (0.67 g).
Synthesis of KCpFe(CN)2(PPh3) (1): 100 mL of a 1:1 mixture of
acetonitrile/methanol was added to KCpFe(CN)2(CO) (4.2 mmol,
1.0 g) and PPh3 (4.2 mmol, 1.1 g) in a photolysis vessel. An argon
purge was bubbled through the reaction slurry and the mixture was
photolyzed for 2 h while monitoring the infrared spectra in the
ν(CN) region at 30-min intervals to ensure complete replacement
of CO. The crude orange product precipitated from the solution
and the solvent was removed under vacuum. The isolated product
was dissolved in 1-propanol and filtered through a frit containing
Celite. The solvent was once again removed under vacuum, and the
solid washed with pentane to give 1 in 88% yield (1.7 g). Single
crystals of 1 were obtained by slow concentration of a methanol
Synthesis of [CpFe(PPh3)(µ-CN)2Cu(CH3CN)2]2 (8): A solution of
Cu(CH3CN)4(BF4) (0.08 g, 0.25 mmol) in 15 mL of CH3CN was
transferred via cannula to
KCpFe(CN)2PPh3 (0.12 g, 0.25 mmol) in 10 mL of CH3CN. The
reaction mixture was stirred at ambient temperature for 1 h to af-
ford a yellow precipitate. Upon removal of the solvent under vac-
uum a fine yellow powder was isolated. Among common organic
solvents, only pyridine was found to solubilize the yellow solid
product.
a
Schlenk flask containing
solution of
1
at room temperature over several days.
Synthesis of [CpFe(PPh3)(µ-CN)2Cu(PCy3)]2 (9): Cu(CH3CN)4-
(BF4) (0.06 g, 0.19 mmol) in 15 mL of CH3CN was transferred via
cannula to a Schlenk flask containing 0.054 g (0.19 mmol) of PCy3
in 10 mL of CH3CN, and the solution was stirred at ambient tem-
C25H20FeKN2P·CH3CN (515.3): calcd. C 62.92, H 4.50, N 8.15;
found C 62.54, H 4.67, N 8.03.
Synthesis of KCpFe(CN)2(PPh2Me) (2): 100 mL of methanol was
added to KCpFe(CN)2(CO) (1.0 mmol, 0.25 g) and PPh2Me
(1.0 mmol, 0.21 g) in a photolysis vessel and the solution was pho-
tolyzed with IR monitoring as described for the preparation of 1.
The reaction solution was concentrated to dryness under vacuum
to yield an orange powder. The solid product was washed repeat-
edly with hexane and dried to provide 2 in a 70% yield (0.31 g).
C20H18FeKN2P·CH3OH (444.3): calcd. C 56.77, H 4.99, N 6.30;
found C 55.97, H 5.08, N 6.52.
perature for
1 h prior to adding 0.091 g (0.19 mmol) of
KCpFe(CN)2PPh3 in CH3CN. The reaction mixture was stirred for
an additional hour during which time a turbid yellow solution was
observed. The solvent was removed under vacuum and the product
was redissolved in dichloromethane, leaving behind a white precipi-
tate of KBF4 which was removed by filtration through a frit con-
taining Celite. Evaporation of the solvent from the filtrate yielded
a fine yellow powder in a yield of 62% (0.092 g). Single crystals of
9 were grown by vapor diffusion of CH2Cl2/hexane at 10 °C over
a period of one week. C86H106Cu2Fe2N4P4·CH2Cl2 (1651.1): calcd.
C 63.58, H 6.62, N 3.41; found C 62.98, H 6.54, N 3.29.
Synthesis
of
CpFe(CN)(PPh2Me)2
(3):
Photolysis
of
KCpFe(CN)2CO (1.8 mmol, 0.45 g) and PPh2Me (7.4 mmol, 1.5 g)
in 100 mL of methanol was carried out in a photolysis vessel under
argon. Upon reaction completion, ca. 30 min as revealed by infra-
red spectroscopy in the ν(CO) region, the solution was concen-
trated to dryness under vacuum and the product was dissolved in
hexane. The solution was filtered through a glass frit containing
Celite to remove any remaining impurities and the product, com-
plex 3, was isolated upon removing the solvent under vacuum in
a yield of 56% (0.52 g). Single crystals of 3 were grown by slow
concentration of a hexane solution at ambient temperature.
C32H31FeNP (516.4): calcd. C 70.21, H 5.71; found C 69.92, H
5.86.
Synthesis of [CpFe(µ-CN)2Cu(CH3CN)2]2-µ-dppp (10): A solution
of 0.1 g (0.32 mmol) of Cu(CH3CN)4(BF4) in 15 mL of CH3CN
was transferred via a cannula to a flask containing 0.133 g
(0.16 mmol) of [KCpFe(CN)2]2-µ-dppp in 10 mL of CH3CN. The
solution was stirred at room temperature for 1.5 h to yield a yellow
precipitate. The solvent was evaporated under vacuum to give a
fine yellow powder. Among common organic solvents, only pyri-
dine was found to solubilize the precipitate.
Synthesis of Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppp (11):
Cu(CH3CN)4(BF4) (0.03 g, 0.1 mmol) in acetonitrile (15 mL) was
added via cannula to a Schlenk flask containing PCy3 (0.054 g,
Synthesis of [KCpFe(CN)2]2-µ-[Ph2P؊(CH2)n؊PPh2] [n ؍ 2 (4),
n ؍ 3 (5), n ؍ 4 (6), CϵC instead (CH2)n (7)]: These four derivatives 0.2 mmol). The solution was stirred at room temperature for 1 h.
were prepared in
a
similar manner by photolysis of
The mixture was transferred via cannula to a second flask contain-
ing [KCpFe(CN)2]2-µ-dppp (0.04 g, 0.05 mmol) in CH3CN
(10 mL), and the reaction mixture was stirred at room temperature
for 1.5 h to afford a turbid yellow solution. The solvent was re-
moved under vacuum and the product dissolved in dichlorometh-
KCpFe(CN)2CO and the diphosphanes in a 1:1 mixture of aceto-
nitrile/methanol over a 60-min reaction period in a photolysis ves-
sel. After the photolysis, the reaction solution was concentrated to
dryness under vacuum to produce an orange solid product. The
3646
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3639Ϫ3648

Potassium Salts of Phosphane-Substituted (Cyclopentadienyl)iron Dicyanides
FULL PAPER
Table 5. X-ray crystallographic data for KCpFe(CN)2(PPh3) (1), CpFe(PPh2Me)2(CN) (3), [KCpFe(CN)2]2µ-dppe (4), [KCpFe(CN)2]2µ-
dppb (6), [CpFe(PPh3)(µ-CN)2Cu(PCy3)]2 (9), and Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppp (11)
1
3
4
6
9
11
Empirical formula
C25H20-
C32H31-
C40H34Fe2K2N4P2· C42H38Fe2K2N4P2· C86H106Cu2Fe2N4P4· C105H159Cu2-
FeKN2P·CH3CN FeNP2·H2O 6CH3OH
2THF·2H2O·
CH3OH
1061.88
monoclinic
P21/c
CH2Cl2
Fe2N4P5
Formula mass [g/mol] 515.40 563.37 1002.71
1643.4
monoclinic
P21/n
1870.99
triclinic
P1
Crystal system
Space group
Z·
triclinic
monoclinic triclinic
P21/c
4
¯
¯
¯
P1
P1
2
2
4
4
2
˚
a [A]
7.962(2)
9.180(2)
17.425(4)
92.230(4)
97.864(4)
113.721(4)
1148.8(5)
1.490
9.959(2)
14.458(3)
19.892(4)
90
102.344(4)
90
2798.0(10)
1.337
110(2)
0.71073
0.679
12.302(3)
13.550(3)
16.119(3)
92.873(4)
94.038(4)
115.227(4)
2415.0(9)
1.379
14.4418(9)
34.147(2)
10.2584(6)
90
94.7500(10)
90
5041.5(5)
1.399
110(2)
17.248(3)
12.686(2)
18.556(4)
90
96.929(4)
90
4030.7(14)
1.354
110(2)
0.71073
1.066
12.925(13)
17.871(18)
23.75(2)
98.23(2)
101.62(2)
104.79(2)
5086(9)
1.222
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
Volume [A ]
dcalcd, [g/cm3]
Temperature [K]
110(2)
0.71073
0.929
110(2)
0.71073
Ϫ
110(2)
0.71073
0.817
˚
Wavelength [A]
0.71073
0.854
Abs. coeff. [mmϪ1
]
Goodness of fit on F2 0.867
0.801
4.59
0.757
8.60
0.899
7.18
0.599
6.69
0.662
10.37
R[a] (%)
6.28
(%)
Rw (%)
[b]
16.46
10.01
19.25
18.47
18.66
50.41
[a]
[b]
2
2 2
2 2
R ϭ Σ|Fo| Ϫ |Fc|/Σ|Fo|. Rw ϭ {[Σw(Fo Ϫ Fc ) ]/[Σw(Fo ) ]}1/2
.
ane. The salt by-product was removed by filtration through Celite, using full-matrix least-squares techniques on all non-hydrogen
and the solvent evaporated to give a yellow powder of 11 in a yield atoms. All hydrogen atoms were placed in idealized positions based
of 54% (0.050 g). Crystals suitable for X-ray diffraction studies on hybridization, with isotropic thermal parameters fixed at 1.2 or
were obtained from hexanes by slow concentration at ambient tem- 1.5 times the value of the attached atom. All atom scattering fac-
perature over several days. C105H159Cu2Fe2N4P5 (1871.2): calcd. C tors were obtained from the International Tables for X-ray Crystal-
67.40, H 8.57, N 2.99; found C 66.92, H 8.43, N 3.05.
lography, vol. C. For all compounds, data collection and cell refine-
ment, SMART;[20] data reduction, SAINTPLUS (Bruker[21]); pro-
grams used to solve structures, SHELXS-86 (Sheldrick[22]); pro-
grams used to refine structures, SHELXL-97 (Sheldrick[23]);
molecular graphics and to prepare material for publication,
SHLXTL-Plus version 5.0 (Bruker[24]). CCDC-211280 (1), -211281
(3), -211282 (4), -211283 (6), -211284 (9), -211285 (11) and -213786
[CpFe(CN)dppe] contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
Synthesis of Cu(PCy3)[CpFe(µ-CN)2]2Cu(PCy3)2-µ-dppb (12):
Cu(CH3CN)4(BF4) (0.022 g, 0.07 mmol) in 15 mL of CH3CN was
transferred via cannula to a Schlenk flask containing PCy3 (0.04 g,
0.14 mmol) in 10 mL of CH3CN. The reaction mixture was stirred
at room temperature for 1 h and transferred to a second flask con-
taining 0.03 g (0.035 mmol) of [KCpFe(CN)2]2-µ-dppb in 10 mL of
CH3CN. The solution was stirred for 1.5 h to give a turbid yellow
solution. Upon removal of the CH3CN solvent under vacuum, the
product was redissolved in dichloromethane and filtered through
Celite to remove KBF4. A yellow product of 12 was obtained in a
yield of 39% (0.026 g) following the evaporation of solvent and
was recrystallized from hexanes by slow concentration at ambient
temperature. C106H161Cu2Fe2N4P5 (1885.2): calcd. C 67.54, H 8.61;
found C 68.05, H 8.48.
CB2 1EZ, UK; Fax: (internat.)
deposit@ccdc.cam.ac.uk].
ϩ 44-1223/336-033; E-mail:
Acknowledgments
X-ray Crystallography: Orange single crystals of compounds 1, 3,
4, 6, and CpFe(CN)(dppe), and yellow crystals of 9 and 11 were
coated with paratone and mounted on a glass fiber using apiezon
grease at ambient temperature. The crystals were placed on a
Bruker SMART 1000 diffractometer equipped with a CCD detec-
tor. The crystals were placed in a nitrogen cold stream maintained
at 110 K. More than a hemisphere of data was collected on each
crystal over three batches of exposures using Mo-Kα radiation (λ ϭ
Financial support from the National Science Foundation (CHE 99-
10342 and CHE 02-34860), and CHE 98-07975 for purchase of X-
ray equipment, the Robert A. Welch Foundation, and by the Texas
Advanced Research Technology Program (Grant No. 0390-1999) is
greatly appreciated.
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0.71073 A). A fourth set of data was measured and compared to
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found in Table 5. Systematic absences and intensity statistics were
used in space-group determination. All structures were solved by
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[2]
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3647

D. J. Darensbourg, M. J. Adams, J. C. Yarbrough, A. L. Phelps
FULL PAPER
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3
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G. N. Richardson, U. Brand, H. Vahrenkamp, Inorg. Chem.
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Crystal for CpFe(CN)(dppe)·CH2Cl2: C33H31C12FeNP2
(630.28), monoclinic, P21/n, a ϭ 12.842(2), b ϭ 8.8075(16), c ϭ
[15]
3648
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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