Synthesis, characterization, and reactivity of the heterometallic dinuclear μ-PH2 and μ-PPhH complexes FeMn(CO)8(μ-PH 2) and FeMn(CO)8(μ-PPhH)

Article abstract of DOI:10.1021/om100736m

Deprotonation of Fe(CO)₄PRH₂ and treatment with Mn(CO)₅Br afforded the dinuclear complexes FeMn(CO) ₈(μ-PRH) (1a, R = H; 1b, R = Ph), which contain the relatively rare μ-PH₂ and μ-PPhH functionalities

Full text of DOI:10.1021/om100736m

Organometallics 2010, 29, 4611–4618 4611
DOI: 10.1021/om100736m
Synthesis, Characterization, and Reactivity of the Heterometallic
Dinuclear μ-PH2 and μ-PPhH Complexes FeMn(CO)8(μ-PH2) and
FeMn(CO)8(μ-PPhH)‡
Adam C. Colson and Kenton H. Whitmire*
Department of Chemistry, Rice University, MS 60, 6100 Main Street, Houston, Texas 77005-1892,
United States
Received July 26, 2010
Deprotonation of Fe(CO)4PRH2 and treatment with Mn(CO)5Br afforded the dinuclear com-
plexes FeMn(CO)8(μ-PRH) (1a, R=H; 1b, R=Ph), which contain the relatively rare μ-PH2 and
μ-PPhH functionalities. The heterometallic nature of these complexes was confirmed by mass
spectrometry, and the molecular structures of 1a and 1b were determined by X-ray diffraction
experiments. Deprotonation of 1b and subsequent addition of Mn(CO)5Br or AuPPh3Cl yielded the
trinuclear complexes FeMn(CO)8[μ-PPh(Mn(CO)5)] (3a) and FeMn(CO)8[μ-PPh(AuPPh3)] (3b),
both of which were characterized structurally and spectroscopically. Deprotonation of 1a at room
temperature resulted in rapid coupling of the deprotonated product [2a]- with neutral 1a to form
Mþ[FeMn(CO)8(μ3-PH)Mn(CO)4(μ-PH2)Fe(CO)4]- (Mþ[4]-) (Mþ = Liþ, Naþ, Kþ), the formation
of which was observed using in situ infrared spectroscopy. Mþ[4]- was found to decompose upon
solvent removal, and the structure of [4]- was elucidated by examination of spectroscopic data. The
1H NMR spectrum of [4]- was characterized by first-order [ABMX] and [AMX] spin systems, and
ESI-MS data confirmed that [4]- was formed by direct coupling of [2a]- with 1a without concomitant
fragmentation or loss of CO ligands. Deprotonation of 1a at lower temperatures slowed the coupling
process, allowing for the metalation of the monomeric anion [2a]- by treatment with AuPPh3Cl, the
product of which was found to decompose gradually in solution and rapidly upon concentration.
Introduction
functionalities, and the bridging phosphide has been observed
to prevent fragmentation of the complex during reactions with
organic substrates.3-6 However, the majority of these studies
have focused on homometallic dinuclear complexes containing
the μ-PR2 (R = aryl, alkyl) group, with relatively few references
describing the structures and chemistry of dinuclear complexes
containing μ-PRH and μ-PH2 groups.7-11 Fewer still are
references to heterometallic dinuclear complexes exhibiting the
μ-PRH or μ-PH2 functionalities.12,13 In addition to serving as
precursors to advanced materials, complexes of this type are of
Organometallic complexes containing transition metals
and main group elements may be used as precursors to
advanced materials such as nanoparticles or thin films.1
We have been exploring the use of iron carbonyl-
phosphorus compounds for the production of binary FexP
(x = 1-3) phase nanomaterials.1 The known complex
FeMn(CO)8(μ-PPh2)2 was explored as a single-source precur-
sor to the mixed-metal phase FeMnP, but proved ineffective,
leading only to the formation of FexOy phases. In order to
overcome these difficulties, the syntheses of previously un-
known μ-PH2 and μ-PRH analogues were explored to deter-
mine if these might prove to be more effective precursors by
having lower barriers to decomposition. The conversion
of these complexes to solid phase materials will be reported
elsewhere. This paper reports the results of the synthetic
molecular studies of the μ-PH2 and μ-PRH single-source
precursor complexes.
(3) Manojlovic-Muir, L.; Mays, M. J.; Muir, K. W.; Woulfe, K. W.
J. Chem. Soc., Dalton Trans. 1992, 1531.
(4) Caffyn, A. J. M.; Mays, M. J.; Solan, G. A.; Braga, D.; Sabatino,
P.; Tiripicchio, A.; Tiripicchio-Camellini, M. Organometallics 1993, 12,
1876.
(5) Harley, A. D.; Guskey, G. J.; Geoffroy, G. L. Organometallics
1983, 2, 53.
(6) Horton, A. D.; Mays, M. J.; Raithby, P. R. J. Chem. Soc., Chem.
Commun. 1985, 247.
(7) Vogel, U.; Sekar, P.; Ahlrichs, R.; Huniar, U.; Scheer, M. Eur. J.
Extensive research has been conducted on transition
metal complexes exhibiting one or more bridging phosphido
Inorg. Chem. 2003, 2003, 1518.
(8) Arif, A. M.; Cowley, A. H.; Pakulski, M.; Hursthouse, M. B.;
Karauloz, A. Organometallics. 1985, 4, 2227.
(9) Davies, J. E.; Mays, M. J.; Raithby, P. R.; Shields, G. P.;
Tompkin, P. K. Chem. Commun. 1997, 361.
(10) Davies, J. E.; Mays, M. J.; Pook, E. J.; Raithby, P. R.; Tompkin,
P. K. J. Chem. Soc., Dalton Trans. 1997, 3283.
‡ Dedicated to Professor Dietmar Seyferth for his outstanding years as
founding editor of Organometallics.
*To whom correspondence should be addressed. E-mail: whitmir@
rice.edu.
(11) Vogel, U.; Scheer, M. Z. Anorg. Allg. Chem. 2003, 629, 1491.
(12) King, R. B.; Fu, W. K.; Holt, E. M. Inorg. Chem. 1985, 24, 3094.
(13) Herrmann, W. A.; Koumbouris, B.; Herdtweck, E.; Ziegler,
M. L.; Weber, P. Chem. Ber. 1987, 120, 931.
€
(1) Kelly, A. T.; Rusakova, I.; Ould-Ely, T.; Hofmann, C.; Luttge, A.;
Whitmire, K. H. Nano Lett. 2007, 7, 2920.
(2) Yasufuku, K.; Yamazaki, H. J. Organomet. Chem. 1971, 28, 415.
r
2010 American Chemical Society
Published on Web 09/24/2010
pubs.acs.org/Organometallics

4612 Organometallics, Vol. 29, No. 20, 2010
Colson and Whitmire
Scheme 1. Synthesis and Reactivity of FeMn(CO)8(μ-PH2) (1a) and FeMn(CO)8(μ-PPhH) (1b)
interest because the presence of a P-H bond can be a useful
synthetic scaffold for additional derivatization and tuning of
the complex. Additionally, the inherent electronic differences
between homometallic and heterometallic species may affect
catalytic cycles or reactive pathways.14-21
was isolated jointly with the desired product. Although
Fe(CO)4PH3 and Fe(CO)4PPhH2 are both extremely sensitive
to air and moisture, complexes 1a and 1b can be handled in the
air for short periods of time with no discernible decomposition.
Complexes 1a and 1b obey the EAN rule, and all metal centers
can be assigned 18 electrons.
Here we report the synthesis and structural characterizations
of two new heterobimetallic carbonyl complexes containing the
μ-PRH and μ-PH2 functionalities: FeMn(CO)8(μ-PH2) (1a)
and FeMn(CO)8(μ-PPhH) (1b) (Scheme 1). Derivatization of
1b was achieved to give FeMn(CO)8[μ-PPh(Mn(CO)5)] (3a)
and FeMn(CO)8[μ-PPh(AuPPh3)] (3b). Deprotonation of 1a at
room temperature, on the other hand, led to rapid coupling of the
deprotonated product [2a]- and neutral 1a to form Mþ[FeMn-
The 1H NMR spectra of 1a and 1b in C6D6 show doublets
centered at 3.00 and 5.28 ppm, respectively. The large
coupling constants, 364 Hz for 1a and 357 Hz for 1b, are
consistent with direct phosphorus-hydrogen coupling over
a single bond.22 The 31P NMR spectrum of 1a contains a
single phosphorus resonance centered at 2.91 ppm and
appears as a triplet in the proton-coupled experiment. The
proton-coupled 31P NMR spectrum of 1b shows a doublet at
100 ppm, the downfield shift being attributed to deshielding
of the phosphorus nucleus by the replacement of a hydrogen
atom by a more electronegative carbon atom.22-24 The
structures of 1a and 1b were confirmed by single-crystal
X-ray diffraction studies (vide infra).
The possibility of derivatizing 1b by reaction at the phos-
phorus atom was investigated. Complexes 3a and 3b were
prepared by addition of Mn(CO)5Br and AuPPh3Cl, respec-
tively, to a solution of [2b]-, which was prepared by treating
1b with one equivalent of n-butyllithium at -76 °C. The
reaction of [2b]- with AuPPh3Cl appeared to proceed rapidly
and cleanly when monitored by IR spectroscopy, and 3b was
isolated with a relatively good yield of 73%. By contrast, 3a
was isolated with a significantly lower yield of 17%. This
difference in isolated yields may be accounted for in several
ways. First, the pseudotetrahedral phosphorus atom of 2b is
already sterically crowded due to the presence of the phenyl
ring and the carbonyl ligands of the attached metal centers
(see Figure 8), and the reaction with the sterically encum-
bered Mn(CO)5Br fragment would be expected to be less
favorable than the reaction with AuPPh3Cl, which is more
accessible. Additionally, the reaction of 2b with Mn(CO)5Br
(CO)8(μ3-PH)Mn(CO)4(μ-PH2)Fe(CO)4]- (Mþ[4]-) (Mþ
=
Liþ, Naþ, Kþ).
Results and Discussion
Complexes 1a and 1b were both prepared by employing the
strategy described by Yasufuku and Yamazaki to prepare
the structurally analogous FeMn(CO)8(μ-PPh2) complex.2
The preparations of 1a and 1b are achieved through the
intermediacy of the highly air-, light-, and moisture-sensitive
complexes Fe(CO)4PH3 and Fe(CO)4PPhH2. Freshly prepared
samples of the former were treated with diethylamine and
Mn(CO)5Br in THF to yield 1a via a bridge-assisted displace-
ment reaction, the metal centers being brought sufficiently close
together for a metal-metal bond to form. Similarly, 1b was
prepared from Fe(CO)4PPhH2 and Mn(CO)5Br, with n-butyl-
lithium being used as the base. The preparation of 1b appears to
be more prone to redox side-reactions than 1a, as Mn2(CO)10
(14) Xiao, J.; Puddephatt, R. J. Coord. Chem. Rev. 1995, 143, 457.
(15) Dell’Anna, M. M.; Trepanier, S. J.; McDonald, R.; Cowie, M.
Organometallics. 2000, 20, 88.
(16) Hidai, M.; Fukuoka, A.; Koyasu, Y.; Uchida, Y. J. Mol. Catal.
1986, 35, 29.
(17) Shima, T.; Suzuki, H. Organometallics 2000, 19, 2420.
(18) Kalck, P. Polyhedron 1988, 7, 2441.
(19) Adams, R. D.; Barnard, T. S.; Li, Z.; Wu, W.; Yamamoto, J.
J. Am. Chem. Soc. 1994, 116, 9103.
(20) Adams, R. D.; Captain, B.; Smith, M. D. Angew. Chem., Int. Ed.
2006, 45, 1109.
€
(22) Kuhl, O. Phosphoros-31 NMR Spectroscopy; Springer: Berlin,
2008.
(23) Bartsch, R.; Hietkamp, S.; Morton, S.; Stelzer, O. J. Organomet.
Chem. 1981, 222, 263.
(21) Adams, R. D.; Barnard, T. S. Organometallics 1998, 17, 2885.
(24) Schaefer, H.; Leske, W. Z. Anorg. Allg. Chem. 1987, 552, 50.

Article
Organometallics, Vol. 29, No. 20, 2010 4613
Figure 2. Change in the absorbance of representative peaks of
1a and [4]- as a function of the amount of base added.
Figure 1. FTIR spectra of 1a before (A) and after (B) deproton-
ation to form [4]- in THF. The peaks marked with an asterisk (*)
were used as reference peaks for in situ IR studies.
is prone to redox side-reactions, as evidenced by the forma-
tion of Mn2(CO)10. Finally, 3b was observed to exhibit
thermal instability and decomposed slowly in solution and
in the solid state. Davies and co-workers have reported
similar instability during the preparation of Cp2Mo2(CO)4-
(μ-H)[μ-PH(Mn(CO)5)].10
The 31P NMR spectrum of 3a displays a singlet at 144 ppm
that exhibits considerable broadening due to coupling to two
quadrupolar Mn nuclei (I = 5/2). The 31P NMR spectrum of
3b contains a doublet centered at 43.0 ppm (PPh3) and
another doublet centered at 151 ppm (μ-PPh(AuPPh3)), the
Figure 3. Experimental (A) and simulated (B) 1H NMR (500 MHz)
spectrum of [4]- in THF-d8. The peaks indicated by (*) and (**)
arise from residual THF and tert-butanol, respectively. The large
1JHP coupling constants are indicated, while the 3JHP and 2JHH
coupling constants have been omitted for clarity.
2
large JPP value of ∼280 Hz indicating a nearly linear
P-Au-P bond angle, as confirmed by the X-ray structure
(vide infra). The downfield shifting of the phosphorus reso-
nances of 3a and 3b reflects the deshielding of the phos-
phorus nuclei by addition of metals with larger Pauling
electronegativities. The molecular structures of 3a and 3b
(Figures 8 and 9) derived from X-ray diffraction experiments
are consistent with the spectroscopic data.
been added. Conversely, the representative peak for [4]- at
1920 cm-1 displayed minimum absorbance before base
addition and increased linearly with base addition, attaining
a maximum absorbance at 0.50 equivalents of base. In both
cases, the absorbance reached one-half of the maximum
absorbance after 0.25 molar equiv of base had been added.
On the basis of these data and the reaction stoichiometry, we
began to suspect that deprotonated 1a underwent a coupling
reaction with its neutral parent compound.
Similar attempts at metalation using 1a were made using a
variety of reaction conditions. Deprotonation of 1a using
potassium tert-butoxide or sodium hydride at room tem-
perature or 0 °C gave rise to a product Mþ[4]- (Mþ=Kþ or
Naþ) that decomposed upon removal of solvent. The infra-
red spectrum of this product (Figure 1) in solution appeared
more complex than the shift toward lower wavenumbers that
one would expect from simple deprotonation of 1a. Further-
more, the complete consumption of 1a was observed even
when substoichiometric amounts of base were used.
In order to study this result in more detail, a careful
titration of 1a with potassium tert-butoxide was performed,
and the reaction was monitored using in situ infrared spec-
troscopy. The strong IR peak at 2039 cm-1 of 1a and the
peak at 1920 cm-1 of the unknown product [4]- were selected
as representative peaks to monitor the concentrations of
each species in solution. Figure 2 contains a plot depicting
the change in the absorbance values of the representative
peaks as a function of the amount of base added. According
to this plot, the representative peak for 1a at 2039 cm-1 had a
maximum absorbance when no base had been added, and the
absorbance decreased linearly with incremental base addi-
tion, reaching a minimum when 0.50 molar equiv of base had
31P and 1H NMR data support the hypothesis of a base-
induced coupling reaction. The proton-coupled 31P NMR
spectrum obtained after treating 1a with 0.50 equivalents of
potassium tert-butoxide in THF-d8 showed complete con-
sumption of 1a and two new phosphorus resonances at
-74.0 and 97.6 ppm. Unfortunately, coupling constants
and multiplicities could not be determined from these peaks
due to their considerable width, each peak having a full width
of ∼600 Hz at one-half of the maximum intensity due to
1
coupling to quadrupolar manganese nuclei. The H NMR
spectrum, however, provides much more insight into the struc-
ture of [4]-. This spectrum, shown in Figure 3, is characterized
by a first-order [ABMX] spin system and a first-order [AMX]
spin system. The [ABMX] system is manifested as a pair of
doublets of doublets of doublets (ddd) centered at 3.14 and 3.04
ppm arising from two geminal diastereotopic protons HA and
HB (2JHH = 6.25 Hz). The geminal protons HA and HB appear
to reside on a single common phosphorus atom, as evidenced by

4614 Organometallics, Vol. 29, No. 20, 2010
Colson and Whitmire
Figure 4. Proposed structure of complex Mþ[4]- (Mþ = Liþ,
Naþ, Kþ).
large 1JHP coupling constants of 295 and 292 Hz for HA and HB,
respectively. The coupling of HA and HB to a second phos-
phorus nucleus completes the observed ddd pattern, the cou-
pling constants being consistent with coupling over three bonds
(3JH P = 12.4 Hz, 3JH P = 13.8 Hz). The [AMX] spin system
Figure 5. FTIR spectra of (A) FeMn(CO)8[μ-PPh(AuPPh3)]
(3b) and (B) product of reaction of [2a]- with AuPPh3Cl in THF.
A
B
observed in Figure 3 appears as a doublet of doublets and arises
as a result of a single proton HC coupling to two phosphorus
atoms with coupling constants 1JHP =243Hzand3JHP = 19.6 Hz,
indicating that HC is directly bound to one phosphorus atom
but is additionally arranged so that it can couple to a second
phosphorus atom over three bonds.
of 1a was not observed until 1.0 molar equiv of n-butyllithium
had been added, suggesting that the previously observed
coupling was inhibited at lower temperatures, favoring com-
plete deprotonation to form the ion [2a]-. The IR spectrum of
the product displayed similar peak patterns and intensities to
1a, but was shifted to lower wavenumbers by approximately
40-50 units, as one would predict from the formation of an
anion by simple deprotonation and as is observed during the
formation of [2b]- (see Supporting Information). Continued
monitoring of the characteristic peaks of [2a]- at -40 °C
revealed that the intensities of the peaks diminished linearly
over time, becoming unobservable after 30 min and giving rise
to a product characterized by a broad distribution of peaks in
the range 1980-1830 cm-1 (see Supporting Information).
Although the latter material was not isolated, it was observed
that brief exposure to the atmosphere lead to rapid conversion
to [4]-, suggesting the possibility that [2a]- may first condense
to form a dianionic dimer that is readily protonated upon
contact with ambient moisture.
On the basis of the NMR and in situ IR data, we have
assigned Mþ[4]- (Mþ = Liþ, Naþ, Kþ) the structure shown
in Figure 4. Negative-ion electrospray mass spectrometry of
Mþ[4]- displays a base peak with m/z=734.63, which is twice
the mass of 1a less a proton, supporting the hypothesis that
1a undergoes base-induced coupling without loss of any CO
ligands. Thus, it is likely that the condensation reaction
results in the breaking of a Fe-Mn bond in order to satisfy
the EAN rule at all metal sites. The absence of peaks in the
region 1900 to 1700 cm-1 in the IR spectrum also indicates
that isomers containing bridging carbonyls are not present in
[4]-. We have rationalized the connectivity of [4]- based on
the EAN rule, the terminal Fe(CO)4 fragment being satisfied
by a two-electron dative bond from phosphorus, and man-
ganese assuming the common LMn(CO)4X motif, where
L = [FeMn(CO)8(μ-PH)]- and X = [Fe(CO)4PH2]-. Lindner
and Funk proposed a similar, albeit charge-neutral, bonding
arrangement upon treating FeMn(CO)8(μ-PPh2) with
trimethylphosphine.25 The alternative possibility in which addi-
tion occurs at the iron atom of 1a to produce a terminal
Mn(CO)4 group is less likely, as the EAN rule would not be
satisfied for at least one of the metal centers. Five-coordinate
Mn(CO)4L species are rare, and in order for the metal center to
achieve an 18-electron count, it would need to be the location of
a negative charge. This does not fit the chemistry of the system,
as the negative charge should reside on the phosphorus atom of
the [FeMn(CO)8(μ-PH)]- fragment to produce an anionic two-
electron donor that adds to the metal center of an adjacent
molecule of 1a. Additionally, one would expect a Mn(CO)4L-
complex to readily undergo protonation to produce an octahe-
dral HMn(CO)4L species. No reaction, however, is observed
when [4]- is treated with acid.
In an attempt to trap [2a]-, AuPPh3Cl was added to a
solution of 1a immediately after deprotonation with n-butyl-
lithium at -40 °C. IR spectroscopy indicated rapid consump-
tion (<10 s) of [2a]-. The product formed from this reaction
was observed to decompose gradually in solution and rapidly
decomposed as the solvent was removed. Although the product
of this reaction could not be isolated for complete analysis, the
infrared spectrum in THF is markedly similar to that of FeMn-
(CO)8[μ-PPh(AuPPh3)] (3b), indicating that the desired product
FeMn(CO)8[μ-PH(AuPPh3)] was likely formed (Figure 5). The
instability of [4]- and FeMn(CO)8[μ-PH(AuPPh3)] toward
concentration and solvent removal may be a result of the high
reactivity of the P-H bond of the triply bridging phosphide.
Structural Analysis. X-ray quality single crystals of 1a and
1b were grown by slow sublimation at 30 °C and approxi-
mately 10-7 Torr, and their molecular structures were de-
termined (Figure 6). Selected bond angles and distances for
1a, 1b, and the analogous diphenyl complex FeMn(CO)8-
( μ-PPh2) are given in Table 1. In all three cases, the bridging
phosphorus atom adopts a distorted tetrahedral geometry
with acute M-P-M bond angles of 78.887(30)° for 1a,
78.599(69)° for 1b, and 77.8(2)° for FeMn(CO)8(μ-PPh2).
In an effort to achieve deprotonation while avoiding cou-
pling, a solution of 1a in THF was cooled to -40 °C and treated
with n-butyllithium, and the reaction was monitored by in situ
IR spectroscopy. Under these conditions, complete consumption
˚
The M-M bond lengths of 1a (2.8374(8) A) and 1b
˚
(2.8361(16) A) are very similar, differing from the
˚
(25) Lindner, E.; Funk, T. Chem. Ber. 1991, 124, 1075.
M-M bond length of FeMn(CO)8(μ-PPh2) by only 0.02 A.

Article
Organometallics, Vol. 29, No. 20, 2010 4615
Figure 6. Molecular structure of 1a (left) and 1b (right). The thermal ellipsoids are shown at the 30% probability level with the
exception of the hydrogen atoms, which were refined isotropically. Optimal refinement was achieved by treating the occupancies of the
metal centers as a statistical mixture.
and is only slightly shorter than the M-M bond lengths in
1a and 1b.
The triply bridging phosphorus atom of 3b is less sterically
Table 1. Selected Bond Lengths and Angles for Complexes 1a, 1b,
and FeMn(CO)8(μ-PPh2) (1c)
1a
1b
1c28
crowded than the phosphorus atom of 3a due to the longer
P-Au-P distance separating the bulky triphenylphosphine
group from the rest of the molecule. Similar to 3a, the M-M
bond of 3b also remains intact upon metalation and is also
slightly shorter than the M-M bonds observed in 1a and 1b.
The P-Au-P bond angle (173.7(3)°) is slightly less than the
ideal angle of 180°. A similar deviation from the ideal 180°
P-Au-P bond angle was observed in the isoelectronic
homometallic complex Mn2(CO)8[μ-P(Cy)(AuPCy3)](μ-H),
which was reported to have a P-Au-P angle of 171.12(5)°.29
˚
Lengths (A)
Fe/Mn1-Fe/Mn2
Fe/Mn1-P1
Fe/Mn2-P1
P1-H
2.8374(8)
2.2328(9)
2.2334(10)
2.8361(16) 2.8182(8)
2.2521(21) 2.2498(1)
2.2255(22) 2.2457(11)
1.23(4), 1.35(3) 1.15(5)
1.8199(61) 1.8250(34),
1.8297(34)
P1-C
Angles (deg)
78.887(30)
R1-P1-R2 (R = H or C) 101(2)
Fe/Mn1-P1-Fe/Mn2
78.599(69) 77.641(64)
102(2)
100(2)
Conclusions
Complexes 1a and 1b represent rare examples of dinuclear
heterometallic complexes containing a μ-PH2 or μ-PRH
functionality. Although structurally similar, these two com-
plexes differ greatly in their reactivities. 1b can be deproton-
ated and metalated to yield the isolable complexes 3a and 3b,
which contain a triply bridging phosphorus atom. By con-
trast, deprotonation of 1a at room temperature leads to rapid
and complete coupling with the parent complex to form
complex Mþ[4]- (Mþ = Liþ, Naþ, Kþ), which decomposes
upon concentration. At lower temperatures, coupling of 1a
and [2a]- is arrested and metalation of [2a]- can be achieved
via addition of AuPPh3Cl. However, the product of this
metalation decomposes slowly in solution and rapidly de-
composes as the solvent is removed. Further investigation
will be necessary to determine how the reactivity of 1a can be
exploited in the preparation of higher nuclearity complexes.
Structural comparisons between 1a and 1b and isoelectronic
homometallic dinuclear complexes containing iron and manga-
nese can also be made. The Fe-Fe bond length in Cp2Fe2-
˚
(CO)2(μ-H)(μ-PHMes) is 2.6969(6) A, considerably shorter
than the M-M bonds of 1a and 1b.26 Conversely, the Mn-Mn
˚
distance (2.937(5) A) in Mn2(CO)8(μ-PPh2)(μ-H) is longer than
the M-M distance observed in 1a and 1b.27 Interestingly, the
M-M distance in 1a and 1b very nearly matches the
arithmetic mean of the M-M distances in Cp2Fe2(CO)2-
(μ-H)( μ-PHMes) and Mn2(CO)8(μ-PPh2)(μ-H). The major
differences between 1a and 1b are the torsion angles be-
tween complementary carbonyl ligands on opposite metal
centers, shown in Figure 7. The twisting observed in 1b
likely results from the minimization of steric interactions
between the phenyl ring and equatorial CO ligands. The
twisting observed in 1b is absent in FeMn(CO)8(μ-PPh2),
presumably because the steric interactions between phenyl
rings and equatorial CO ligands are equally distributed on
both faces of the molecule.
Experimental Section
General Considerations. All manipulations were carried out
under an argon atmosphere using standard Schlenk techniques
in order to exclude moisture and oxygen. Argon was prepurified
The molecular structures of 3a and 3b are presented in
Figures 8 and 9. The steric congestion around the triply
bridging phosphorus atom and the six-coordinate manganese
atom in 3a is readily apparent and may contribute to the low
yields obtained for 3a, as mentioned earlier. The M-M bond
of 3a remains intact after deprotonation and metalation of 1b
(28) Vahrenkamp, H. Z. Naturforsch., B: Anorg. Chem., Org. Chem.
1975, 30B, 814. The CIF file previously deposited with the Cambridge
Crystallographic Data Center (CCDC) does not include atomic coordinates.
Therefore, the bond lengths and angles reported in Table 1 are the results of
data collected and refined in our laboratory. A complete CIF file for this
complex can be found in the Supporting Information and has also been
deposited with the CCDC.
(26) Sugiura, J.; Kakizawa, T.; Hashimoto, H.; Tobita, H.; Ogino, H.
Organometallics 2005, 24, 1099.
(27) Doedens, R. J.; Robinson, W. T.; Ibers, J. A. J. Am. Chem. Soc.
€
(29) Florke, U.; Haupt, H. J. Acta Crystallogr., Sect. C: Cryst. Struct.
1967, 89, 4323.
Commun. 1995, 51, 573.

4616 Organometallics, Vol. 29, No. 20, 2010
Colson and Whitmire
Figure 7. Projections of 1a (left), 1b (center), and FeMn(CO)8(μ-PPh2)28 (right) down the metal-metal bond showing the differences in
torsion angles between complementary carbonyl ligands. Oxygen atoms have been omitted for clarity. Only the ipso carbons of the
phenyl rings have been shown.
tert-butoxide was purchased from Sigma-Aldrich and was sub-
limed prior to use. General infrared (FTIR) spectra were
obtained using a Thermo-Nicolet 670 FT-IR with a 0.1 mm
CaF2 cell. In situ FTIR data were collected on a Mettler Toledo
45m ReactIR system using an immersion probe with a silicon
sampling tip coupled to a silver halide fiber. 1H and 31P NMR
data were recorded on Bruker spectrometers operating at 400 MHz
(162 MHz for 31P) or 500 MHz (202 MHz for 31P).
Modified Synthesis of Fe(CO)4PH3. P(SiMe3)3 (2.50 mL,
8.61 mmol) and Fe(CO)5 (1.30 mL, 9.89 mmol) were added to
a standard Schlenk flask and dissolved in 100 mL of THF. The
flask was then irradiated with a 450 W mercury-vapor UV lamp
for 4 h. After irradiation, THF and unreacted Fe(CO)5 were
removed under reduced pressure, and the remaining residues
were redissolved in diethyl ether and cooled to 0 °C. Methanol
Figure 8. Molecular structure of 3a with thermal ellipsoids at
(2.10 mL, 51.9 mmol) was added dropwise, and the reaction
mixture was stirred at 0 °C for 20 min in the dark. Diethyl ether
and unreacted methanol were removed in vacuo at 0 °C, leaving
behind a brown solid residue. The Schlenk flask was then fitted
with a jacketed condenser and a stopcock, and the assembly was
placed in a horizontal position and connected to a vacuum line
(10-7 Torr). The jacketed condenser was filled with liquid
nitrogen, and pure Fe(CO)4PH3 was sublimed from the Schlenk
flask into the cooled condenser. The sublimation apparatus
was refilled with argon, and the pale yellow Fe(CO)4PH3
was transferred to a tared Schlenk flask under a vigorous flow
of argon (1.11 g, 64% yield based on phosphorus). Spectral
analysis of the solid was consistent with data reported
elsewhere.24
the 30% probability level. For clarity, only the ispo carbon
˚
(C141) of the phenyl ring is shown. Selected bond distances (A)
and angles (deg): Fe/Mn1A-Fe/Mn1B 2.7954(9), Fe/Mn1A-P1
2.3067(10), Fe/Mn1B-P1 2.2891(11), P1-Mn3A 2.4774(11);
Fe/Mn1A-P1-Fe/Mn1B 74.9(6).
FeMn(CO)8(μ-PH2) (1a). Freshly prepared Fe(CO)4PH3
(498 mg, 2.47 mmol) was added to a Schlenk flask and dissolved
in 50 mL of THF. The solution was cooled to 0 °C, and one
equivalent (255 μL, 2.47 mmol) of diethylamine was added. The
solution was stirred at 0 °C for five minutes, followed by the
addition of 679 mg (2.47 mmol) of Mn(CO)5Br. The reaction was
covered with a dark cloth and stirred at 0 °C for four hours. The
solvent was removed under reduced pressure, and the residue was
chromatographed on silica using hexane as the eluent. The hexane
was removed under reduced pressure, leaving red-orange crystals
that could be further purified by sublimation (467 mg, 51% yield).
Single crystals for X-ray diffraction studies were obtained by slow
sublimation in a Schlenk tube at 30°C and 10-7 Torr. IR (hexanes,
cm-1): νCO 2096 (w), 2042 (s), 2026 (w), 2017 (vs), 2007 (m), 1992
(w), 1971 (w), 1963 (m), 1942 (vw). 1H NMR (400 MHz, C6D6):
δ 3.00 (d, 1JHP = 364 Hz, 2H). 31P NMR (162 MHz, C6D6, H3PO4
Figure 9. Molecular structure of 3b with ellipsoids shown at
˚
30% probability. Selected bond distances (A) and angles (deg):
Fe/Mn1-Fe/Mn2 2.7894(7), Fe/Mn1-P1 2.2969(9), Fe/Mn2-P1
2.2785(9), Au1-P1 2.3126(8), Au1-P2 2.3009(8); Fe/Mn1-
P1-Fe/Mn2 75.1(6), P1-Au1-P2 173.7(3).
by passing through columns of BTS catalyst and molecular
sieves. All solvents were dried and distilled prior to use accord-
ing to standard procedures.30 P(SiMe3)3, Mn(CO)5Br, and
Fe(CO)4PPhH2 were prepared according to literature pro-
cedures.23,31,32 Fe(CO)4PH3 was prepared using a modified
literature procedure.24 AuPPh3Cl and Fe(CO)5 were purchased
from Strem and used without further purification. Potassium
1
standard): δ 2.91 (t, JPH = 365 Hz). MS(EI): m/z 367.8 (Mþ),
339.8 (Mþ - CO), 311.8 (Mþ - 2CO), 283.8 (Mþ - 3CO), 255.8
(Mþ - 4CO), 227.8 (Mþ - 5CO), 199.8 (Mþ - 6CO), 171.8 (Mþ -
7CO), 143.8 (Mþ - 8CO). Anal. Calcd for FeMnC8O8PH2: C,
26.12; H, 0.55. Found: C, 25.79; H, 0.74.
(31) Holz, J.; Zayas, O.; Jiao, H.; Baumann, W.; Spannenberg, A.;
€
Monsees, A.; Riermeier, T. H.; Almena, J.; Kadyrov, R.; Borner, A.
(30) Perrin, D. D.; Armarego, W. L. Purification of Laboratory
Chemicals; Pergamon Press: New York, 1993.
Chem.;Eur. J. 2006, 12, 5001.
(32) Reimer, K. J.; Shaver, A. Inorg. Synth. 1990, 28, 154.

Article
Organometallics, Vol. 29, No. 20, 2010 4617
Table 2. X-ray Collection and Refinement Parameters for Complexes 1a, 1b, 3a, and 3b
1a
1b
3a
3b
formula
fw
C8H2FeMnO8P
367.86
triclinic
P1
7.8647(8)
9.2226(10)
9.3681(10)
90.966(2)
91.141(2)
110.032(2)
638.06(12)
2
C14H6FeMnO8P
443.95
monoclinic
P21/c
10.242(4)
14.193(6)
11.935(5)
90.00
97.927(8)
90.00
1718.4(13)
4
1.716
C19H5FeMn2O13
637.93
triclinic
P1
12.325(2)
14.204(3)
14.926(3)
107.600(3)
106.384(3)
95.561(4)
2341.8(8)
4
1.809
0.71073
213(2)
28.420
1.808
23 216
P
C32H20AuFeMnO8P2
902.18
orthorhombic
Pbcn
18.4784(14)
12.6296(9)
28.196(2)
90.00
90.00
90.00
6580.3(8)
8
1.821
0.71073
213(2)
28.29
cryst syst
space group
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dcalc (g cm-3
λ(Mo KR) (A)
T (K)
)
1.915
3
˚
0.71073
223(2)
28.33
2.280
5030
0.71073
293(2)
28.370
1.710
20 831
θ
max (deg)
abs coeff (mm-1
rflns (coll)
)
5.407
76 896
rflns (unique)
params
F(000)
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF (on F2)
2066
181
360
0.0276
0.0591
0.795
4226
230
880
0.0775
0.1328
1.122
9627
649
1256
0.0310
0.0532
0.453
8102
407
3488
0.0249
0.0551
1.111
FeMn(CO)8(μ-PPhH) (1b).Fe(CO)4PPhH2 (285 mg, 1.02 mmol)
was added to a Schlenk flask and dissolved in 30 mL of THF.
The solution was cooled to -76 °C, and one equivalent
(1.02 mmol) of n-butyllithium was added dropwise, followed
by the addition of Mn(CO)5Br (282 mg, 1.02 mmol). The
solution was then transferred to a 0 °C bath and stirred for four
hours. The solvent was removed in vacuo, and the oily residue
was extracted with hexanes. The hexanes extract was concen-
trated and chromatographed on a silica column using hexanes as
eluent. 1b eluted jointly with Mn2(CO)10, which formed as a
byproduct of the reaction. The collected fractions were concen-
trated and cooled to -40 °C for several days, whereupon red
crystals of 1b and yellow crystals of Mn2(CO)10 formed and were
separated manually using a hand lens and were further purified
by sublimation (93 mg, 21% yield). Single crystals suitable for
X-ray diffraction studies were prepared by slow sublimation in a
Schlenk tube at 30 °C and 10-7 Torr. IR (hexanes, cm-1): νCO
2092 (w), 2075 (vw), 2039 (s), 2024 (m), 2015 (vs), 2002 (m), 1988
(w), 1967 (m), 1957 (m). 1H NMR (400 MHz, C6D6): δ 7.37 (m,
2H); 6.89 (m, 2H); 5.28 (d, 1JHP = 357 Hz, 1H). 31P NMR (162
MHz, C6D6, H3PO4 standard): δ 100 (d, 1JPH = 357 Hz). MS(EI):
m/z 443.8 (Mþ), 415.9 (Mþ - CO), 387.8 (Mþ - 2CO), 359.8
(Mþ - 3CO), 331.8 (Mþ - 4CO), 303.9 (Mþ - 5CO), 275.9 (Mþ -
6CO), 247.9 (Mþ - 7CO), 219.9 (Mþ - 8CO). Anal. Calcd for
FeMnC14O8PH6: C, 37.88; H, 1.36. Found: C, 37.32; H, 1.32.
FeMn(CO)8[μ-PPh(Mn(CO)5)] (3a). A solution of 1b (132 mg,
0.297 mmol) in 30 mL of THF was cooled to -78 °C and treated
with one equivalent (0.297 mmol) of n-butyllithium, whereupon
the color of the solution changed from bright red-orange to dark
red. Mn(CO)5Br (82.0 mg, 0.297 mmol) was then added, and the
solution was removed from the cold bath and allowed to warm
to room temperature. As the solution warmed, the color gradu-
ally became a lighter shade of red. The solution was stirred at
room temperature for two hours, after which the solvent was
removed under reduced pressure, leaving behind a viscous, oily
residue. The residue was extracted with a 3:1 hexanes/toluene
solution and filtered through diatomaceous earth. The filtrate
was chromatographed on silica using 3:1 hexanes/toluene as
eluent. The collected fractions that were not contaminated with
Mn2(CO)10 were dried in vacuo, redissolved in minimal pentane,
and cooled to -40 °C for several days, whereupon red crystals of
3a formed (32.2 mg, 17% yield). 3a exhibits considerable
thermal instability in solution and in the solid state, resulting
in larger-than-expected deviations in the observed C and H
elemental analyses. IR (hexanes, cm-1): νCO 2117 (w), 2078 (m),
2061 (vw), 2036 (vs), 2015 (m), 1998 (m), 1992 (m), 1979 (w),
1955 (w), 1942 (w). 1H NMR (400 MHz, C6D6): δ 7.70 (m, 1H);
7.45 (m, 1H); 6.83 (m, 3H). 31P NMR (162 MHz, C6D6, H3PO4
standard): δ144(s,br).MS(EI):m/z637.8 (Mþ), 609.8 (Mþ - CO),
553.8 (Mþ - 3CO), 525.8 (Mþ - 4CO), 497.8 (Mþ - 5CO), 469.8
(Mþ - 6CO), 441.8 (Mþ - 7CO), 413.8 (Mþ - 8CO), 385.8 (Mþ -
9CO), 357.8 (Mþ - 10CO), 329.8 (Mþ - 11CO), 301.8 (Mþ
-
12CO), 273.8 (Mþ - 13CO), 218.9 (Mþ - 13CO, - Mn). Anal.
Calcd for FeMn2C19O13PH5: C, 35.77; H, 0.79. Found: C, 35.07; H,
0.92.
FeMn(CO)8[μ-PPh(AuPPh3)] (3b). A solution of 1b (118 mg,
0.266 mmol) in 30 mL of THF was cooled to -78 °C and treated
with n-butyllithium (0.266 mmol), causing the bright red-orange
solution to darken. AuPPh3Cl (132 mg, 0.266 mmol) was then
added, and the reaction mixture was removed from the cold bath
and allowed to warm to room temperature. As the reaction
mixture warmed, the dark coloration dissipated and the solution
took on a bright orange-yellow color. The reaction mixture was
stirred at room temperature for two hours, after which the
solvent was removed in vacuo. The resulting residue was ex-
tracted with hexanes, passed through a short pad of silica gel,
and dried under reduced pressure. The slightly oily residue was
then dissolved in minimal CH2Cl2, layered with two volumes of
hexanes, and placed in a -40 °C freezer. Red-orange crystals of
3b formed after several days (176 mg, 73% yield). 3b displays
slight thermal instability in solution and in the solid state,
resulting in larger-than-expected deviations in the observed
C and H elemental analyses. The agreement between observed
and calculated values for the elemental analyses improved when
the shipping and holding times of the samples were reduced.
IR (hexanes, cm-1): νCO 2076 (m), 2047 (w), 2022 (vs), 2008 (s),
1995 (s), 1980 (s), 1969 (m), 1947 (m), 1935 (m). 1H NMR
(400 MHz, C6D6): δ 7.97 (m, 2H); 7.23 (m, 6H), 6.99-6.86 (m,
12H). 31P NMR (162 MHz, C6D6, H3PO4 standard): δ 151 (d,
2
2JPP = 281 Hz); 43 (d, JPP = 281 Hz). Anal. Calcd for FeMn-
C32O8P2H20Au: C, 42.60; H, 2.23. Found: C, 41.93; H, 2.25.
MS(EI) data for 3b showed no evidence of the Mþ ion or any
readily identifiable fragments, leading us to conclude that the
complex decomposed completely upon heating.
Deprotonation of 1a Using the Mettler Toledo 45m ReactIR
System. A solution of 1a (85.0 mg, 0.230 mmol) in 50 mL of THF
was titrated with successive 23.0 μmol portions of potassium
tert-butoxide until the presence of 1a could no longer be detected

4618 Organometallics, Vol. 29, No. 20, 2010
Colson and Whitmire
by in situ IR spectroscopy, which occurred after 0.115 mmol of
KOtBu had been added. After the addition of 0.115 mmol of
KOtBu, 1H and 31P NMR showed only peaks corresponding to
[4]- and tert-butanol. Attempts to isolate Kþ[4]- for elemental
and structural analysis resulted in decomposition, as evidenced
by the formation of an insoluble brown solid upon concentra-
tion. IR (THF, cm-1): νCO 2080 (w), 2054 (m), 2043 (w), 2026
(m, sh), 2018 (vs), 1997 (s), 1942 (s), 1920 (s), 1868 (w). 1H NMR
(500 MHz, THF-d8): δ 3.32 (d, 1JHP = 243 Hz, 3JHP = 19.6 Hz,
1H); 3.14 (ddd, 1JHP = 295 Hz, 3JHP = 12.4 Hz, 2JHH = 6.25 Hz,
1H); 3.04 (ddd, 1JHP = 292 Hz, 3JHP = 13.8 Hz, 2JHH = 6.25 Hz,
1H). 31P NMR (202 MHz, THF-d8, H3PO4 standard): δ 98.0
(s, br); -74.0 (s, br). HRMS (ESI-TOF; negative-ion mode):
calcd for [C16O16H3P2Mn2Fe2]- m/z 734.6356, found 734.6336
(M-).
frames were integrated with the Bruker SAINTPLUS software
package and corrected for absorption effects using empirical
methods (SADABS).33,34 Structures were solved using direct
methods and refined by full-matrix least-squares on F2 using the
SHELXTL software package.35,36 Optimum refinements were
achieved by treating the iron and manganese sites as a statistical
mixture of the two metal atoms. The hydrogen atoms bound to
phosphorus in 1a and 1b were refined isotropically, and all other
protons were assigned idealized locations. Anisotropic displace-
ment parameters were assigned to all non-hydrogen atoms.
All thermal ellipsoid plots were generated using the Diamond
software package.37 A summary of X-ray data collection and
refinement parameters for complexes 1a, 1b, 3a, and 3b is given
in Table 2. Crystallographic data in CIF format can be found in
the Supporting Information.
Crystal Structure Determinations of 1a, 1b, 3a, and 3b.
Diffraction data were collected on a Bruker SMART 1000
CCD diffractometer equipped with a Mo-target X-ray tube in
a hemisphere with exposure times of 10-50 s. The collected
Acknowledgment. The authors thank Rice University,
the National Science Foundation (CHE-0719369), and
the Robert A. Welch Foundation (C-0976) for funding.
The Mettler Toledo 45m ReactIR system was purchased
using funding from the National Science Foundation.
(33) SAINTPlus, v. 7.23a; Bruker AXS Inc.: Madison, WI, 2002.
€
(34) Sheldrick, G. M. SADABS, v. 5.1; University of Gottingen:
€
Gottingen, 1997.
(35) Sheldrick, G. M. SHELXTL; Univeristy of Gottingen: Gottingen,
2001.
€
€
Supporting Information Available: Additional data from in
situ IR spectroscopy studies, tables of X-ray data collection and
refinement parameters, and crystallographic data in CIF
format are available free of charge via the Internet at http://
pubs.acs.org.
(36) Sheldrick, G. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112.
(37) Brandenburg, K. Diamond, v. 3.2e; Crystal Impact GbR: Bonn,
Germany, 2010.