Synthesis of μ-phosphide diiron complexes having a P-H bond: Hydrophosphination of phenylacetylene and methyl acrylate with the cationic μ-phosphide diiron complex

Article abstract of DOI:10.1021/om049000o

Thermal reaction of Cp₂Fe₂(CO)₄ with PRH₂ (R = Ph, Mes (mesityl)) in refluxing toluene afforded phosphide- and hydrido-bridged diiron complexes Cp₂Fe₂(CO) ₂(μ-H)(μ-PHR) (1a, R = Ph; 1b, R = Mes). Treatment of 1a with HOTf under a CO atmosphere produced the phosphide- and carbonyl-bridged cationic complex [Cp₂Fe₂(CO)₂(μ-CO)(μ-PHPh)](OTf) (2) via hydride abstraction as hydrogen and CO coordination. Complex 2 reacted with phenyl-acetylene and methyl acrylate at room temperature to give [Cp ₂Fe₂(CO)₂(μ-CO)(μ-(E)-PPh-(CH=CHPh))] (OTf) (3a) and [Cp₂Fe₂(CO)₂(μ-CO)(μ- P(CH₂CH₂CO₂Me)Ph)](OTf) (3b) in 78% and 65% yield, respectively, in the absence of any additive, as a result of hydrophosphination of the unsaturated carbon-carbon bond of the substrates with the P-H bond of 2.

Full text of DOI:10.1021/om049000o

Organometallics 2005, 24, 1099-1104
1099
Synthesis of µ-Phosphido Diiron Complexes Having a
P-H Bond: Hydrophosphination of Phenylacetylene and
Methyl Acrylate with the Cationic µ-Phosphido Diiron
Complex
Junji Sugiura,† Taeko Kakizawa,† Hisako Hashimoto,*,† Hiromi Tobita,*,† and
Hiroshi Ogino§
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai
980-8578, Japan, and Miyagi Study Center, The University of the Air,
Sendai 980-8577, Japan
Received December 16, 2004
Thermal reaction of Cp2Fe2(CO)4 with PRH2 (R ) Ph, Mes (mesityl)) in refluxing toluene
afforded phosphido- and hydrido-bridged diiron complexes Cp2Fe2(CO)2(µ-H)(µ-PHR) (1a, R
) Ph; 1b, R ) Mes). Treatment of 1a with HOTf under a CO atmosphere produced the
phosphido- and carbonyl-bridged cationic complex [Cp2Fe2(CO)2(µ-CO)(µ-PHPh)](OTf) (2) via
hydride abstraction as hydrogen and CO coordination. Complex 2 reacted with phenyl-
acetylene and methyl acrylate at room temperature to give [Cp2Fe2(CO)2(µ-CO)(µ-(E)-PPh-
(CHdCHPh))](OTf) (3a) and [Cp2Fe2(CO)2(µ-CO)(µ-P(CH2CH2CO2Me)Ph)](OTf) (3b) in 78%
and 65% yield, respectively, in the absence of any additive, as a result of hydrophosphination
of the unsaturated carbon-carbon bond of the substrates with the P-H bond of 2.
Introduction
some additives such as radical initiator or base to
activate the E-H bond or to abstract the proton from
the E-H group, direct functionalization of the E-H
group without any additive would be preferable from
the viewpoint of atom economy. In relation to this, we
previously reported the synthesis and reactivity of
silylene- and germylene-bridged diiron complexes hav-
ing an E-H bond, Cp2Fe2(CO)2(µ-CO)(µ-EHR) (E ) Si,
Ge).5 The E-H bond in these complexes is highly
activated by the attachment of two iron atoms, and the
hydrogen is easily replaced with halogen by treatment
with organic halides such as CCl4 at room temperature.
With our continuing interest in the reactivity of such
dinuclear complexes having an E-H bond, we investi-
gated the isoelectronic phosphorus analogue of them,
i.e., cationic phosphido-bridged complexes having a P-H
bond, [Cp2Fe2(CO)2(µ-CO)(µ-PHR)]+. Although a number
of phosphido-bridged dinuclear complexes are already
known,6,7 complexes that have active P-H bonds are
relatively less common.6c,e,7 Nevertheless, this type of
Functionalization of an E-H group (E ) heteroatom
such as Si and P) in the organometallic or organo-
heteroatom ligands coordinated to transition-metal com-
plexes has attracted increasing interest as an important
method in synthetic organometallic chemistry.1-4 Al-
though the majority of the known such reactions need
* To whom correspondence should be addressed. Fax: +81-22-217-
6543.
E-mail:
hhashimoto@mail.tains.tohoku.ac.jp;
tobita@
mail.tains.tohoku.ac.jp.
† Tohoku University.
§ The University of the Air.
(1) For functionalization of a Si-H group, see: (a) Malisch, W.; Kuhn
M. Chem. Ber. 1974, 107, 2835. (b) Malisch, W.; Lankat, R.; Fey, O.;
Reising, J.; Schmitzer, S. J. Chem. Soc., Chem. Commun. 1995, 1917.
(c) Mo¨ller, S.; Fey, O.; Malisch, W.; Seelbach, W. J. Organomet. Chem.
1996, 506, 239. (d) Nikonov, G. I.; Kuzmina, L. G.; Vyboishchikov, S.
F.; Lemenovskii, D. A.; Howard, J. A. K. Chem. Eur. J. 1999, 5, 2947.
(e) Malisch, W.; Hofmann, M.; Kaupp, G.; Ka¨b, H.; Reising, J. Eur. J.
Inorg. Chem. 2002, 3235.
(2) For deprotonation of a P-H group, see: (a) Treichel, P. M.;
Douglas, W. M.; Dewn, W. K. Inorg. Chem. 1972, 11, 1615. (b) Seyferth,
D.; Wood, T. G.; Henderson, R. S. J. Organomet. Chem. 1987, 336, 163.
(c) Crisp, G. T.; Salem, G.; Wild, S. B. Organometallics 1989, 8, 2360.
(d) Bohle, D. S.; Clark, G. R.; Richard, C. E. F.; Roper, W. R. J.
Organomet. Chem. 1990, 393, 243. (e) Oudet, P.; Bonnet, G.; Moise,
C. Polyhedron 1995, 14, 2173. (f) Edwards, P. G.; Fleming, J. S.;
Liyanage, S. S. J. Chem. Soc., Dalton Trans. 1997, 193.
(3) For insertion of substrates into a P-H bond of metal-coordinated
phosphines, see: (a) Huttner, G.; Mu¨ller, H.-D.; Friedrich, P.; Ko¨lle,
U. Chem. Ber. 1977, 110, 1254. (b) Treichel, P. M.; Wong, W. K.;
Calabrese, J. C. J. Organomet. Chem. 1978, 159, C20. (c) Nagel, U.;
Rieger, B.; Bublewitz, A. J. Organomet. Chem. 1989, 370, 223. (d) Diel,
B. N.; Brandt, P. F.; Haltiwanger, R. C.; Hackeney, M. L. J.; Norman,
A. D. Inorg. Chem. 1989, 28, 2811. (e) Leoni, P.; Pasquali, M.;
Sommovigo, M.; Albinati, A.; Lianza, F.; Pregosin, P. S.; Ru¨egger, H.
Organometallics 1994, 13, 4017. (f) Leoni, P.; Vichi, E.; Lencioni, S.;
Pasquali, M.; Chiarentin, E.; Albinati, A. Organometallics 2000, 19,
3062. (g) Edwards, P. G.; Ingold, F.; Liyanage, S. S.; Newman, P. D.;
Wong, W.-K.; Chen, Y. Eur. J. Inorg. Chem. 2001, 2865. (h) Malisch,
W.; Klu¨pfel, B.; Schumacher, D. G.; Nieger, M. J. Organomet. Chem.
2002, 661, 95. (i) Malisch, W.; Hofmann, M.; Kaupp, G.; Ka¨b, H.;
Reising, J. Eur. J. Inorg. Chem. 2002, 3235.
(4) For insertion of substrates into a P-H bond of phosphido-bridged
complexes, see: (a) Seyferth, D.; Wood, T. G. Organometallics 1987,
6, 2563. (b) Seyferth, D.; Wood, T. G. Organometallics 1988, 7, 717.
(5) (a) Kawano, Y.; Tobita, H.; Ogino, H. Angew. Chem., Int. Ed.
Engl. 1991, 30, 843. (b) Kawano, Y.; Tobita, H.; Ogino, H. J. Orga-
nomet. Chem. 1992, 428, 125. (c) Kawano, Y.; Tobita, H.; Ogino, H. J.
Am. Chem. Soc. 1994, 116, 8575. (d) Fujita, J.; Kawano, Y.; Tobita,
H.; Ogino, H. Chem. Lett. 1994, 1353.
(6) See for example: (a) Roberts, D. A.; Geoffroy, G. L. In Compre-
hensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel,
E., Eds.; Pergmon Press: London, 1982; Chapter 40. (b) Iggo, J. A.;
Mays, M. J.; Raithby, P. R. Hendrick, K. J. Chem. Soc., Dalton Trans.
1983, 205. (c) Henrick, K.; McPartlin, M.; Horton, A. D.; Mays, M. J.
J. Chem. Soc., Dalton Trans. 1988, 1083. (d) Brunner, H.; Ro¨tzer, M.
J. Organomet. Chem. 1992, 425, 119. (e) Manojlovic-Muir, L.; Muir,
K. W.; Jennings, M. C.; Mays, M. J.; Solan, G. A.; Woulfe, K. W. J.
Organomet. Chem. 1995, 491, 255. (f) Mealli, C.; Ienco, A.; Galindo,
A.; Perez, E. C. Inorg. Chem. 1999, 38, 4620. (g) Garcia, M. E.; Riera,
V.; Ruiz, M. A.; Reuda, M. T.; Saez, D. Organometallics 2002, 21, 5515,
and references therein.
10.1021/om049000o CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/08/2005

1100 Organometallics, Vol. 24, No. 6, 2005
Sugiura et al.
Chart 1
µ-phosphido complexes are potentially useful as re-
agents for reactions such as hydrophosphination. In-
deed, Seyferth et al. have previously reported4 that the
P-H bond of a neutral phosphido-bridged complex Fe2-
7b,c
(CO)6(µ-PPhH)2
reacted with olefinic and acetylenic
R,â-unsaturated carbonyl compounds to afford hydro-
phosphination products such as Fe2(CO)6(µ-PPhH)[µ-
PPh(CH2CH2CO2CH3)] in the presence of base. How-
ever, such examples are still limited.
This paper describes the synthesis of new neutral
phosphido- and hydrido-bridged complexes having a
P-H bond, Cp2Fe2(CO)2(µ-H)(µ-PHR) [1a, R ) Ph; 1b,
R ) Mes (2,4,6-trimethylphenyl)], and the conversion
of 1a to the cationic phosphido- and carbonyl-bridged
complex [Cp2Fe2(CO)2(µ-CO)(µ-PHPh)](OTf) (2) by hy-
dride abstraction with acid under a CO atmosphere. The
cationic phosphido-bridged complex 2 reacted with
phenylacethylene and methyl acrylate at room temper-
ature to produce the hydrophosphination products [Cp2-
Fe2(CO)2(µ-CO)(µ-PPhR)(OTf) (3a, R ) CHdCHPh; 3b,
R ) CH2CH2CO2Me), in the absence of any additive. The
details of these reactions and the mechanistic studies
are also presented.
Figure 1. ORTEP diagram of trans-1b with thermal
ellipsoids drawn at the 50% probability level. Selected bond
distances (Å) and angles (deg): Fe(1)-Fe(2) 2.6969(6), Fe-
(1)-P 2.1897(9), Fe(2)-P 2.1829(3), Fe(1)-H(1) 1.58(5), Fe-
(2)-H(1) 1.66(5), P-H(2) 1.38(5); Fe(1)-P-Fe(2) 76.16(3).
yield in the case of 1a but were not in the case of 1b (eq
1, Chart 1). The 31P NMR spectra of trans-isomers of
1a and 1b show the µ-phosphido signals at moderately
low field (131.3 ppm for 1a; 103.6 ppm for 1b). Their
µ-hydrido signals appear at very high field (-19.00 ppm
for 1a; -18.80 ppm for 1b) as a doublet of doublets
coupled with a phosphorus atom and a proton on the
phosphorus. Their trans-structure is supported by the
appearance of only one CO band (1903 cm-1 for 1a; 1905
cm-1 for 1b) in each IR spectrum and two inequivalent
Results and Discussion
Synthesis of Neutral Phosphido-Bridged Com-
plexes 1a and 1b. Thermal reaction of Cp2Fe2(CO)4
with PRH2 in refluxing toluene produced phosphido- and
hydrido-bridged diiron complexes Cp2Fe2(CO)2(µ-H)(µ-
PHR) (1a, R ) Ph; 1b, R ) Mes) (eq 1) as red crystals.
Similar reactions have been used previously to prepare
1
Cp signals in each H NMR spectrum (4.25 and 4.27
ppm for 1a; 4.18 and 4.25 ppm for 1b). The structure of
trans-1b was further confirmed by X-ray crystallogra-
phy as shown in Figure 1. Two Cp rings are positioned
trans to each other with respect to the Fe(1)-Fe(2)-P
three-membered ring. The aromatic ring of the mesityl
group is oriented nearly parallel to the Cp rings to
minimize the steric hindrance among them. The Fe-
Fe and Fe-P bond lengths are within normal single-
bond lengths.
Synthesis of Cationic Phosphido-Bridged Com-
plex 2. Treatment of trans-1a with HOTf under a CO
atmosphere gave a cationic complex, [Cp2Fe2(CO)2(µ-
CO)(µ-PHPh)](OTf) (2), as dark red microcrystals in 75%
yield (eq 2). In this reaction, the bridging hydrido ligand
related µ-phosphido complexes, e.g., Cp2Mo2(CO)4(µ-H)-
(µ-PPhH).6c,7f Among the possible three geometrical
isomers (Chart 1), trans-isomers of 1a and 1b were
isolated in 46% and 45% yields, respectively, and were
fully characterized. A mixture of two complexes that
were assignable to cis-isomers were also obtained in 5%
(7) (a) Treichel, P. M.; Dean, W. K.; Douglas, W. M. J. Organomet.
Chem. 1972, 42, 145. (b) Treichel, P. M.; Dean, W. K.; Douglas, W. M.
Inorg. Chem. 1972, 12, 1609. (c) Bartsch, R.; Hietkamp, S.; Morton,
S.; Stelzer, O. J. Organomet. Chem. 1981, 222, 263. (d) Mu¨ller, M.;
Vahrenkamp, H. Chem. Ber. 1983, 116, 2311. (e) Arif, A. M.; Cowley,
A. H.; Pakulski, M.; Hursthouse, M. B.; Karauloz, A. Organometallics
1985, 4, 2227. (f) Woodward, S.; Curtis, M. D. J. Organomet. Chem.
1992, 439, 319. (g) Haupt, H.-J.; Schwefer, M.; Flo¨rke, U. Inorg. Chem.
1995, 34, 292. (h) Manojlobvic-Muir, L.; Muir, K. W.; Jennings, M. C.;
Mays, M. J.; Solan, G. A.; Woulfe, K. W. J. Organomet. Chem. 1995,
491, 255. (i) Oudet, P.; Bonnet, G.; Moise, C. Polyhedron 1995, 14, 2173.
(j) Davis, J. E.; Mays, M. J.; Raithby, P. R.; Shields, G. P.; Tompkin,
P. K. Chem. Commun. 1997, 361. (k) Davies, J. E.; Feeder, N.; Gray,
C. A.; Mays M. J.; Woods, A. D. J. Chem. Soc., Dalton Trans. 2000,
1695.
of 1 was selectively attacked by an acidic proton and

µ-Phosphido Diiron Complexes
Scheme 1
Organometallics, Vol. 24, No. 6, 2005 1101
removed as a hydrogen molecule. The resulting vacant
site was saturated by CO coordination to produce 2. The
addition of acid is a common method to prepare cationic
complexes, but the addition of acid that is followed by
hydrogen release is rare. For example, the addition of
HBF4 to M2(CO)4(µ-H)(µ-PtBu2)(µ-dppm) (M ) Fe, Ru)
affords a µ-dihydride complex [M2(CO)4(µ-H)2(µ-PtBu2)-
(µ-dppm)](BF4).8 Further, although some related com-
plexes formulated as [Cp2Fe2(CO)2(µ-CO)(µ-PPhR)](X)
(R ) Me, Ph, CH2SiMe3, etc.; X ) Cl, I, and BPh4) have
been prepared by photoirradiation of [Cp2Fe2(CO)4(µ-
PPhR)](X),9 the ones that have active P-H bonds have
not been prepared by this method. Our thermal method
is useful to prepare cationic phosphido-bridged com-
plexes having P-H bonds.
Complex 2 exclusively takes a cis-geometry, as evi-
denced by spectroscopic data. Thus, the 1H NMR
spectrum of 2 shows a single Cp signal at 5.68 ppm (10H
intensity), which indicates a symmetrical cis-structure.
The IR spectrum exhibits two terminal CO bands (2013
and 1986 cm-1) and a bridging CO band (1821 cm-1).
The intensity of the νCOsym band (2013 cm-1) is dis-
tinctly higher than that of the νCOasym band (1986
cm-1). On consideration of the steric repulsion among
two Cp rings and a phenyl group on the µ-phosphido
ligand, the cis (H) type geometry in Chart 1 is preferred
to the cis (Ph) type one. A similar cis-configuration is
also found in a closely related cationic complex [Cp2-
Fe2(CO)2(µ-CO)(µ-PHtBu)][FeCl3(THF)], reported by Fen-
ske et al.10 Apparently, by replacing the bridging
hydrido ligand in 1a with a bridging carbonyl ligand to
form 2, the geometry changed drastically from trans to
cis. This may be attributable to the much larger steric
requirement of the µ-CO in 2 compared to that of the
µ-H in 1a. The 31P NMR spectrum of 2 shows a signal
at 191.0 ppm in a lower field compared to that of neutral
complex trans-1a (131.3 ppm). The 1H NMR signal of a
PH group also appears at 9.19 ppm (d, 1JPH ) 406.6 Hz)
that is greatly downfield shifted compared to that of
trans-1a (5.95 ppm). These large downfield shifts can
be attributable to the cationic nature of 2. In addition,
the same treatment of trans-1b with HOTf afforded only
an unidentified product mixture.
Figure 2. ORTEP diagram of the cationic part of 3a with
thermal ellipsoids drawn at the 30% probability level.
Selected bond distances (Å) and angles (deg): Fe(1)-Fe(2)
2.6175(10), Fe(1)-P 2.1947(14), Fe(2)-P 2.1891(14), P-C(4)
1.805(5), P-C(10) 1.788(5); Fe(1)-P-Fe(2) 73.32(5), Fe-
(1)-C(1)-Fe(2) 84.4(2), P-C(10)-C(11) 125.8(4).
highly activated and smoothly underwent hydrophos-
phination under mild conditions. Thus, reaction of 2
with an excess of phenylacetylene at room temperature
afforded [Cp2Fe2(CO)2(µ-CO)(µ-(E)-PPh(CHdCHPh))]-
(OTf) (3a) in 78% yield (Scheme 1). Complex 3a was
structurally characterized by X-ray crystallography. The
ORTEP view of the cationic part is shown in Figure 2.
The iron centers are bridged by a CO ligand and a
modified phosphido ligand, P(E-CHdCHPh)Ph. The
trans addition of the P-H bond took place exclusively
to generate an E-styryl group on the phosphorus atom.
No Z-styryl isomer was observed. The cis-configuration
of two Cp ligands is retained, and they are also on the
same side of the styryl group with respect to the Fe2P
three-membered ring. The four-membered ring com-
posed of Fe(1), P, Fe(2), and C(1) is folded at the Fe-
Fe bond, and the dihedral angle between the two three-
membered rings, Fe(1)-Fe(2)-P and Fe(1)-Fe(2)-C(1),
is 164°. Similar folding of the dinuclear framework has
also been observed in a number of carbene-, silylene-,
and germylene-bridged diiron µ-carbonyl complexes
with cis-configurations.5
As mentioned in the Introduction, Seyferth et al.
reported4 the related hydrophosphination of olefinic and
acetylenic R,â-unsaturated carbonyl compounds with
neutral complex Fe2(CO)6(µ-PPhH)2. Although these
reactions need the addition of a secondary amine such
as piperidine, our hydrophosphination system does not
need any additive. It should also be mentioned that
some insertion reactions of alkynes and alkenes into the
P-H bonds of metal-coordinated secondary phosphines3
Reaction of 2 with Phenylacetylene. The P-H
bond of the bridging ligand of cationic complex 2 was
(8) Bottcher, H.-C.; Graf, M.; Merzweiler, K.; Wagner, C. J. Orga-
nomet. Chem. 2001, 628, 144.
(9) (a) Klasen, C.; Effinger, G.; Schmid, S.; Lorenz, I.-P. Naturforsh.
Z. 1993, 48b, 705. (b) Lorenz, I.-P.; Pohl, W.; No¨th, H.; Schmidt, M. J.
Organomet. Chem. 1994, 475, 211
(10) Fenske, D.; Schottmuller, H. Z. Anorg. Allg. Chem. 1998, 624,
443.

1102 Organometallics, Vol. 24, No. 6, 2005
Sugiura et al.
Scheme 2
Chart 2
facilitated by delocalization of the unpaired electron over
two iron atoms in this dinuclear system (Chart 2).
Conclusions. We synthesized new neutral phos-
phido- and hydrido-bridged complexes having a P-H
bond, Cp2Fe2(CO)2(µ-H)(µ-PHR) (1a, R ) Ph; 1b, R )
Mes) by the reaction of Cp2Fe2(CO)4 with primary
phosphine PRH2 (R ) Ph, Mes). Complex 1a was
converted to the cationic phosphido-bridged complex
[Cp2Fe2(CO)2(µ-CO)(µ-PHPh)](OTf) (2) by hydride ab-
straction with HOTf under a CO atmosphere. The P-H
bond of cationic phosphido-bridged complex 2 is highly
activated and smoothly reacted with phenylacethylene
and methyl acrylate at room temperature to afford the
hydrophosphination products in good yields without any
base or other additive. The hydrophosphination reac-
tions in this system are suggested to proceed through a
radical chain mechanism. Further investigations on the
reactivity of the cationic phosphido-bridged complexes
are in progress.
and a cluster having µ3-P-H ligands11 are reported.
Most of such reactions are assisted by base, and only a
few cases proceed without base. For example, Huttner
et al. reported that phenylacetylene inserted into the
P-H bond of CpMn(CO)2(PPhH2) without base, but it
took 10 days at 80 °C to be completed.3a Albinati et al.
also reported the insertion of ethylene into the P-H
bond of cationic complex [Pd2(µ-PCy2)(PCy2H)4](OTf).3e
Interestingly, this reaction proceeds at room tempera-
ture, but the mechanistic studies have not been re-
ported.
Experimental Section
General Procedures. All manipulations were carried out
under high vacuum or a dry nitrogen atmosphere. Toluene,
hexane, and ether were freshly distilled from sodium-ben-
zophenone ketyl. Dichloromethane was dried over calcium
hydride and distilled just before use. Benzene-d6, acetone-d6,
and dichloromethane-d2 were dried over molecular sieves 4 A.
Duroquinone14 and mesitylphosphine15 were prepared accord-
ing to the literature methods. All other compounds were used
as received. NMR spectra were recorded on a Bruker ARX-
300 Fourier transform spectrometer at room temperature. IR
spectra were measured on a HORIBA FT-200 or FT-730
spectorometer. Mass analyses were performed on a Hitachi
M-2500 or JMS-HX 110 or a Shimadzu QP5050 spectorometer
at the Instrumental Analysis Center for Chemistry, Tohoku
University. Elemental analyses were performed at the Instru-
mental Analysis Center for Chemistry, Tohoku University.
Synthesis of Cp2Fe2(CO)2(µ-H)(µ-PHR) (1a, R ) Ph; 1b,
R ) Mes). A solution of Cp2Fe2(CO)4 (0.75 g, 2.1 mmol) and
PPhH2 (0.24 g, 2.1 mmol) in dry toluene (30 mL) was refluxed
for 2 days. The resultant mixture was evaporated and chro-
matographed on a silica gel flash column. Elution with hexane/
ether (20:1) first gave a red solution. Removal of the solvent
afforded the trans-isomer of Cp2Fe2(CO)2(µ-H)(µ-PHPh) (1a)
as a dark red solid (0.40 g, 0.95 mmol, 46%). Further elution
gave the second red fraction, which contained a mixture of cis-
and trans-isomers of the known complex Cp2Fe2(CO)2(µ-
PHPh)27a in 19% yield (0.21 g, 0.41 mmol). Finally, the fraction
with yellow-brown color was collected and the solvent was
removed to give an isomeric mixture of two cis-1a (see Chart
1) in 5% total yield (42 mg, 0.10 mmol). The ratio of the major
isomer and the minor isomer of cis-1a is approximately 2:1 by
Reaction of 2 with Methyl Acrylate and the
Reaction Mechanism. Complex 2 also reacted with
methyl acrylate at room temperature to produce [Cp2-
Fe2(CO)2(µ-CO)(µ-P(CH2CH2CO2Me)Ph)](OTf) (3b) in
65% isolated yield. Complex 3b was also fully charac-
terized. The spectroscopic data supports its cis-config-
uration based on their similarity with those of 3a.
Importantly, this reaction was completed within a day
at room temperature, but took 5 days in the presence
of 1 molar equiv of duroquinone, a typical radical
scavenger. These observations suggest a radical chain
mechanism for the hydrophosphination with 2.12
A
possible radical chain mechanism is illustrated in
Scheme 2. The key steps of the mechanism consist of
(1) homolytic cleavage of the P-H bond to produce
radical intermediate A, (2) addition of A to the double
bond of alkene to produce radical intermediate B, and
(3) abstraction of a hydrogen radical from 2 with B to
produce A and 3b. It is likely that the reaction of 2 with
phenylacetylene also proceeds via a similar mechanism.
The easy occurrence of this radical reaction for 2 is in
contrast to that for organic hydrophosphines, which
requires photoirradiation or radical initiators to be
induced.13 Generation of the intermediate phosphorus-
centered radical from the cationic complex 2 would be
1
1
the H NMR spectrum. trans-1a. H NMR (300 MHz, C6D6):
2
3
δ -19.00 (dd, JPH ) 42.9 Hz, JHH ) 1.4 Hz, 1H, µ-H), 4.25
3
3
(11) Caryn, C. B.-B.; Bautista, M. T.; Aschauer, C. K.; White, P. S.
J. Am. Chem. Soc. 2000, 122, 3952.
(12) (a) Schroeder, N. C.; Angelici, R. J. J. Am. Chem. Soc. 1986,
108, 3688. (b) Gracey, B. P.; Knox, S. A. R.; Macpherson, K. A.; Orpen,
A. G.; Stobart, S. R. J. Chem. Soc., Dalton Trans. 1985, 1935.
(13) Smith, D. J. H. In Comprehensive Organic Chemistry; Suther-
land, I. O., Ed.; Pergamon Press: Oxford, 1979; Vol. 2, p 1121.
(d, JPH ) 1.1 Hz, 5H, Cp), 4.27 (d, JPH ) 1.6 Hz, 5H, Cp),
5.95 (dd, 1JPH ) 340.3 Hz, 3JHH ) 1.4 Hz, 1H, PH), 7.06-7.11,
(14) Smith, L. I. Organic Syntheses; Wiley: New York, 1943; Collect.
Vol. II, p 254.
(15) Oshikawa, T.; Yamashita, M. Chem. Ind. (London) 1985, 126.

µ-Phosphido Diiron Complexes
Organometallics, Vol. 24, No. 6, 2005 1103
7.72-7.80 (m, 5H, Ph). 31P NMR (36.3 MHz, C6D6): δ 131.3.
13C NMR (75.5 MHz, C6D6): δ 80.5, 81.1 (s, Cp), 128.5 (d, JPC
) 10.4 Hz, o-C6H5), 129.0 (d, JPC ) 3.4 Hz, p-C6H5), 132.6 (d,
JPC ) 9.0 Hz, m-C6H5), 141.9 (d, JPC ) 30.6 Hz, ipso-C6H5),
talline solid (46 mg, 0.067 mmol, 78%). 3a: 1H NMR (300 MHz,
acetone-d6): δ 5.74 (d, 3JPH ) 0.7 Hz, 10H, Cp), 6.64 (dd, 3JHH
3
3
) 16.5 Hz, JPH ) 22.4 Hz, 1H, PCHdCHPh), 7.79 (dd, JHH
) 16.5 Hz, 2JPH ) 30.7 Hz, 1H, PCHdCHPh), 7.40-7.43, 7.61-
7.68, 8.03-8.10 (m, 10H, Ph). 31P NMR (121.5 MHz, acetone-
d6): δ 237.6. 13C NMR (75.5 MHz, acetone-d6): δ 90.5 (s, Cp),
129.3 (d, JPC ) 1.4 Hz, o-C6H5CHdCH), 129.6 (d, JPC ) 11.0
Hz, o-PC6H5), 129.8 (s, m-C6H5CHdCH), 131.1 (s, p-C6H5CHd
CH), 132.6 (d, JPC ) 2.6 Hz, p-PC6H5), 134.6 (d, JPC ) 49.5
2
2
216.5 (d, JPC ) 20.8 Hz), 217.7 (d, JPC ) 19.7 Hz, CO). IR
(KBr, cm-1): 1903 (vs, νCO), 1420 (w, PPh). EI-MS (70 eV):
m/z 408 (26, M+), 380 (78, M+ - CO), 350 (100, M+ - CO -
2H). Anal. Calcd for C18H17Fe2O2P: C, 52.99; H, 4.20. Found:
C, 53.18; H, 4.11. Data for a mixture of two cis-1a: 1H NMR
(300 MHz, C6D6): major isomer, δ -19.97 (d, 2JPH ) 45.3 Hz,
1H, µ-H), 4.07 (d, 3JPH ) 1.3 Hz, 10H, Cp), 6.59 (d, 1JPH ) 321.1
Hz, 1H, PH), 7.01-7.88 (m, 5H, Ph), minor isomer, -19.38
1
Hz, ipso-PC6H5), 135.2 (d, JPC ) 40.9 Hz, CHdCHPh), 135.6
(d, JPC ) 49.5 Hz, ipso-C6H5CHdCH), 136.0 (d, JPC ) 8.8 Hz,
2
2
p-PC6H5), 146.1 (d, JPC ) 3.4 Hz, CHdCHPh), 208.7 (d, JPC
) 17.9 Hz, CO), 256.0 (d, 2JPC ) 3.3 Hz, µ-CO). IR (THF, cm-1):
2013 (vs), 1986 (s) (νCOterm), 1821 (vs, νCObrid), 1423 (m, PPh),
1273 (vs, νSO). FAB-MS (Xe, m-nitrobenzyl alcohol): m/z 435
(100, M+), 407 (14, M+ - CO), 379 (2, M+ - 2CO), 351 (27, M+
- 3CO). Anal. Calcd for C28H22F3Fe2O6PS: C, 49.00; H, 3.23.
Found: C, 48.65; H, 3.56.
2
3
(dd, JPH ) 43.4 Hz, JPH ) 1.7 Hz, 1H, µ-H), 4.13 (s, 10H,
Cp), 5.39 (dd, 1JPH ) 358.2 Hz, 3JPH ) 1.7 Hz, 1H, µ-H), 7.01-
7.88 (m, 5H, Ph). 31P NMR (121.5 MHz, C6D6): δ 134.0, 138.2.
IR (C6H6, cm-1): 2023 (w, νPH), 1954 (vs, νCO), 1915 (s, νCO),
1435 (w, νPPh).
Complex 1b was prepared by a similar procedure with use
of PMesH2 in 45% yield. No cis-isomers were detected in this
case. trans-1b: 1H NMR (300 MHz, C6D6): δ -18.80 (dd, 2JHP
Complex 3b was prepared by a similar method with use of
methyl acrylate (65%). 3b (dark red crystals): 1H NMR (300
3
3
2
) 40.1 Hz, JHH ) 1.4 Hz, 1H, µ-H), 2.13 (s, 3H, p-CH3), 2.86
MHz, acetone-d6): δ 2.89 (td, JHH ) 8.2 Hz, JPH ) 10.8 Hz,
(s, 6H, o-CH3), 4.18 (d, 2JHP ) 1.2 Hz, 5H, Cp), 4.25 (d, 2JHP
)
2H, PCH2CH2), 3.57 (s, 3H, CO2Me), 3.59 (td, JHH ) 8.2 Hz,
3
1
3
1.8 Hz, 5H, Cp), 5.70 (d, JHP ) 334.2 Hz, 1H, PH), 6.83 (s,
2H, ArH). 31P NMR (121.5 MHz, C6D6): δ 103.6. 13C NMR (75.5
MHz, C6D6): δ 21.2 (s, p-CH3), 24.2 (d, Jpc ) 7.6 Hz, o-CH3),
81.0, 82.0 (s, Cp), 129.9 (d, Jpc ) 8.3 Hz, o-C6H3Me3), 132.2 (d,
Jpc ) 27.9 Hz, ipso-C6H3Me3), 138.7 (d, Jpc ) 3.8 Hz, p-C6H3-
Me3), 142.2 (d, Jpc ) 6.0 Hz, m-C6H3Me3), 217.4 (d, 2Jpc ) 20.4
3JPH ) 8.2 Hz, 2H, PCH2CH2), 5.76 (d, JPH ) 0.9 Hz, 10H,
Cp), 7.50-7.53, 7.95-8.02 (m, 5H, Ph). 31P NMR (121.5 MHz,
acetone-d6): δ 258.5. 13C NMR (75.5 MHz, acetone-d6): δ 32.6
2
1
(d, JPC ) 5.2 Hz, PCH2CH2), 37.6 (d, JPC ) 19.3 Hz, PCH2-
CH2), 52.2 (s, CO2Me), 90.4 (s, Cp), 129.3 (d, JPC ) 10.5 Hz,
o-PC6H5), 132.2 (d, JPC ) 2.6 Hz, p-PC6H5), 135.0 (d, JPC ) 8.2
Hz, m-PC6H5), 137.3 (d, JPC ) 42.2 Hz, ipso-PC6H5), 172.2 (s,
CO2Me), 208.7 (d, 2JPC ) 17.9 Hz, CO). IR (THF, cm-1): 2019
(vs), 1992 (s) (νCOterm), 1828 (vs, νCObrid), 1741 (m, νCO), 1432
(m, PPh), 1255 (vs, νSO). FAB-MS (Xe, m-nitrobenzyl alco-
hol): m/z 521 (91, M+), 493 (100, M+ - CO), 465 (6, M+ - 2CO),
437 (35, M+ - 3CO). Anal. Calcd for C24H22F3Fe2O8PS: C,
43.01; H, 3.31. Found: C, 42.63; H, 3.39.
2
Hz), 218.3 (d, Jpc ) 19.6 Hz, CO). IR (KBr, cm-1): 1905 (vs,
νCO), 1450 (w, PMes). EI-MS (70 eV): m/z 450 (16, M+), 422
(54, M+ - CO), 394 (3.9, M+ - 2CO), 390 (100, M+ - 2CO -
4H). Anal. Calcd for C21H23Fe2O2P: C, 56.04; H, 5.15. Found:
C, 56.15; H, 5.59
Reaction of trans-1a with HOTf: Synthesis of cis-
[Cp2Fe2(CO)2(µ-CO)(µ-PHPh)](OTf) (2). Under a CO atmo-
sphere (1 atm), HOTf (0.20 g, 1.3 mmol) was added to a CH2Cl2
(50 mL) solution of trans-1a (0.50 g, 1.2 mmol) at -48 °C. After
stirring for 4 h at room temperature, the solution was filtered
and evaporated under high vacuum. Recrystallization of the
resulting solid from dichloromethane layered with ether
provided cis-[Cp2Fe2(CO)2(µ-CO)(µ-PPhH)](OTf) (2) as a dark
red microcrystalline solid (0.53 g, 0.90 mmol, 75%). Data for
NMR Monitoring of the Reaction of 2 with Methyl
Acrylate. A Pyrex NMR tube equipped with a high-vacuum
stopcock was loaded with 2 (8.0 mg, 0.014 mmol), methyl
acrylate (0.014 mL, 0.15 mmol), and CD2Cl2 (0.4 mL). The
sample was flame-sealed under high vacuum. The reaction was
allowed to proceed at room temperature and was monitored
by 1H NMR spectroscopy. After 24 h, 2 was completely
3
1
2: 1H NMR (300 MHz, acetone-d6): δ 5.68 (d, JPH ) 1.4 Hz,
consumed and the H NMR spectrum revealed the formation
1
10H, Cp), 7.54-7.67, 7.85-7.91 (m, 5H, Ph), 9.19 (d, JPH
)
of 3b.
406.6 Hz, 1H, PH). 31P NMR (121.5 MHz, CDCl3): δ 191.0.
13C NMR (75.5 MHz, acetone-d6): δ 88.7 (s, Cp), 129.6 (d, JPC
) 12.8 Hz, o-C6H5), 132.7 (d, JPC ) 4.8 Hz, p-C6H5), 132.7 (d,
JPC ) 10.3 Hz, m-C6H5), 135.0 (d, JPC ) 47.8 Hz, ipso-C6H5),
NMR Monitoring of the Reaction of 2 with Methyl
Acrylate in the Presence of Duroquinone. A solution of 2
(8.0 mg, 0.014 mmol), methyl acrylate (0.010 mL, 0.11 mmol),
and duroquinone (0.2 mg, 0.014 mmol) in CD2Cl2 (0.4 mL) in
a sealed NMR tube was kept at room temperature and
monitored by 1H NMR spectroscopy. After 5 days, 2 was
completely consumed to produce 3b.
2
2
207.8 (d, JPC ) 18.1 Hz, CO), 253.7 (d, JPC ) 3.8 Hz, µ-CO).
IR (KBr, cm-1): 2013 (vs), 1986 (s) (νCOterm), 1821 (vs, νCObrid),
1423 (m, PPh), 1273 (vs, νSO). FAB-MS (Xe, m-nitrobenzyl
alcohol): m/z 435 (100, M+), 407 (14, M+ - CO), 379 (2, M+
-
X-ray Crystal Structure Determination of trans-1b
and 3b. The crystals of trans-1b and 3a suitable for X-ray
crystal structure determination were mounted on a glass fiber.
The intensity data for trans-1b were collected on a RIGAKU
RAXIS-RAPID imaging plate diffractometer with graphite-
monochromated Mo KR radiation to a maximum 2θ value of
55.0 at 150 K. A total of 44 images, corresponding to 220.0°
oscillation angles, were collected with two different goniometer
settings. Exposure time was 1.30 min/deg. Readout was
performed in the 0.100 mm pixel mode. Numerical absorption
collections were applied on the crystal shape. The intensity
data for 3a were collected by a Rigaku AFC-6A four-circle
diffractometer with graphite-monochromated Mo KR radiation
at 18 °C. Diffraction data were collected in the ω-2θ scan
mode. The structure of trans-1b was solved by Patterson and
Fourier transform methods. All non-hydrogen atoms were
refined by full-matrix least-squares techniques with anisotro-
pic displacement parameters based on F2 with all reflections.
The positions of two hydrogen atoms directly attached to
phosphorus and iron atoms were found on the difference
2CO), 351 (27, M+ - 3CO). Anal. Calcd for C20H16F3Fe2O6PS:
C, 41.18; H, 2.93. Found: C, 41.13; H, 2.76.
Reaction of trans-1b with HOTf. Complex trans-1b was
treated with HOTf in a method similar to that described for
the reaction of trans-1a with HOTf. After workup, a red oil
was obtained. The 31P NMR spectrum of the oil shows several
signals around -50 ppm, but the signal assignable for the
analogous complex of 2 was not observed.
Synthesis of [Cp2Fe2(CO)2(µ-CO)(µ-PPhR)](OTf) (3a, R
) CHdCHPh; 3b, R ) CH2CH2CO2Me). A Pyrex glass tube
(10 mm o.d.) was charged with 2 (50 mg, 0.086 mg). Dichloro-
methane (5 mL) and phenylacetylene (47 µL, 0.43 mmol) were
transferred to the tube by trap-to-trap distillation and flame-
sealed under high vacuum. The sample was allowed to stand
at room temperature. After 10 days, the reaction mixture was
filtered and evaporated under reduced pressure. The residue
was washed with 8 mL of dichloromethane/hexane (3:5) and
then recrystallized from a mixture of dichloromethane, hexane,
and ether (4:5:5, 7 mL) to afford 3a as a dark red microcrys-

1104 Organometallics, Vol. 24, No. 6, 2005
Sugiura et al.
Fourier synthesis and refined with isotropic thermal param-
eters. All other hydrogen atoms were placed at their geo-
metrically calculated positions and added to the structure
factor calculations without refinement. The final residue R and
the weighted Rw for total reflections (4341) were R ) 0.073
and Rw ) 0.153 and the R1 for reflections (3634) with I > 2σ-
(I) was R1 ) 0.046. All calculations were performed using the
teXsan crystal structure analysis package.16The structure of
3a was solved by the heavy-atom method and refined by the
block-diagonal least-squares method with individual aniso-
tropic thermal parameters for non-hydrogen atoms. The posi-
tions of all hydrogen atoms were found by difference Fourier
syntheses and refined with isotropic thermal parameters. The
final residue R1 and the weighted wR2 for reflections (3417)
with I > 2σ(I) was R1 ) 0.0545 and wR2 ) 0.1168. All
calculations were performed using the SHELEX 86 program
for crystal structure analysis package.17 Crystallographic
information has been deposited with the Cambridge Crystal-
lographic Data Centre (CCDC Nos. 232043 (trans-1b), 232044
(3a)).
Acknowledgment. This work was supported by the
Ministry of Education, Culture, Sports, Science and
Technology of Japan [Grants-in-Aid for Scientific Re-
search Nos. 14204065, 14078202, and 14044010].
Supporting Information Available: Crystallographic
data for trans-1b and 3a, including tables of atomic coordi-
nates, anisotropic thermal parameters, bond distances and
angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM049000O
(16) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corporation, 1985 & 1999.
(17) Sheldrich, G. M. SHELX 86, Program for Crystal Structure
Determination; University of Go¨ettingen: Germany, 1986.