P-C and C-H Bond Cleavages in the Photochemical Reactions of [Fe 2(η5-C5H5)2(CO) 4] with Bis(diphenylphosphino)methane

Article abstract of DOI:10.1021/om034091v

The photochemical reactions of [Fe₂Cp₂(CO) ₄] (Cp = η⁵-C₅H₅) and the bidentate ligand Ph₂PCH₂PPh₂ give a complex mixture of products. These include the known complexes [Fe₂-Cp ₂(μ-CO)₂(μ-Ph₂PCH₂PPh ₂)] and cis-[Fe₂Cp₂(μ-PPh₂) ₂(CO)₂], as well as the new species [Fe ₂Cp(μ-η⁵:κ¹-C₅H ₄CH₂PPh₂)(μ-CO) ₂(CO)],cis-[Fe₂Cp₂(μ-H)(μ-PPh ₂)(CO)₂], [Fe₂Cp(μ-η ⁵:κ¹-C₅H₄-CH ₂PPh₂)(μ-H)(μ-PPh₂)(CO)], trans-[Fe ₂Cp₂(μ-H)(μ-PPh₂)(CO)(PMePh ₂)], and [Fe₂Cp₂(μ-PPh₂) ₂(μ-CO)]. An intermediate species, trans-[Fe₂Cp ₂(μ-CO)₂(CO)(κ¹-Ph₂PCH ₂PPh₂)], having an intact diphosphine ligand coordinated through one of the P atoms, can be detected at the early stages of the reaction. Separate experiments indicate that the latter species is the precursor of the unique diphosphine-bridged complex, but of none of the other products. The above results indicate that different P-C (diphosphine) and C-H (cyclopentadienyl) bond cleavage processes are operative under the conditions examined, as well as novel C-C bond formations. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR ( ¹H, ³¹P, and ¹³C) data, as well as a single-crystal X-ray study on the (diphenylphosphinomethyl)cyclopentadienyl complex [Fe₂Cp(μ-η⁵:κ¹-C ⁵H⁵CH²PPh²)-(μ-CO) ₂(CO)]. A reassessment of the ³¹ P chemical shifts for cis- and trans[Fe₂Cp₂(μ-PPh₂)2-(CO) ₂ ] is also made.

Full text of DOI:10.1021/om034091v

5504
Organometallics 2003, 22, 5504-5512
P -C a n d C-H Bon d Clea va ges in th e P h otoch em ica l
Rea ction s of [F e2(η5-C5H5)2(CO)4] w ith
Bis(d ip h en ylp h osp h in o)m eth a n e
Celedonio M. Alvarez, Bele´n Gala´n, M. Esther Garc´ıa, V´ıctor Riera, and
Miguel A. Ruiz*
Departamento de Quı´mica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
E-33071, Oviedo, Spain
J acqueline Vaissermann
Laboratoire de Chimie Inorganique et Mate´riaux Moleculaires, Universite´ P. et M. Curie,
75252, Paris, Cedex 05, France
Received August 5, 2003
The photochemical reactions of [Fe2Cp2(CO)4] (Cp ) η5-C5H5) and the bidentate ligand
Ph2PCH2PPh2 give a complex mixture of products. These include the known complexes [Fe2-
Cp2(µ-CO)2(µ-Ph2PCH2PPh2)] and cis-[Fe2Cp2(µ-PPh2)2(CO)2], as well as the new species [Fe2-
Cp(µ-η5:κ1-C5H4CH2PPh2)(µ-CO)2(CO)], cis-[Fe2Cp2(µ-H)(µ-PPh2)(CO)2], [Fe2Cp(µ-η5:κ1-C5H4-
CH2PPh2)(µ-H)(µ-PPh2)(CO)], trans-[Fe2Cp2(µ-H)(µ-PPh2)(CO)(PMePh2)], and [Fe2Cp2(µ-
PPh2)2(µ-CO)]. An intermediate species, trans-[Fe2Cp2(µ-CO)2(CO)(κ1-Ph2PCH2PPh2)], having
an intact diphosphine ligand coordinated through one of the P atoms, can be detected at the
early stages of the reaction. Separate experiments indicate that the latter species is the
precursor of the unique diphosphine-bridged complex, but of none of the other products.
The above results indicate that different P-C (diphosphine) and C-H (cyclopentadienyl)
bond cleavage processes are operative under the conditions examined, as well as novel C-C
bond formations. The structures of the new complexes are analyzed on the basis of the
corresponding IR and NMR (1H, 31P, and 13C) data, as well as a single-crystal X-ray study
on the (diphenylphosphinomethyl)cyclopentadienyl complex [Fe2Cp(µ-η5:κ1-C5H4CH2PPh2)-
(µ-CO)2(CO)]. A reassessment of the 31P chemical shifts for cis- and trans-[Fe2Cp2(µ-PPh2)2-
(CO)2] is also made.
In tr od u ction
the bidentate phosphorus ligands (P-O or P-C bonds)
are processes in competition with the oxidative addition
of C-H bonds of the cyclopentadienyl ligands. However,
we noticed that P-C bond cleavage of the diphosphine
ligands required higher thermal activation than P-O
bond cleavages in the diphosphite, so that the former
could be suppressed at low temperatures, thus allowing
the C-H bond cleavages to occur as a dominant process.
As far as the above trends would hold at diiron centers,
we could then make the hypothesis that chances to
observe cyclopentadienyl C-H bond cleavages during
decarbonylation reactions would be higher in the pres-
ence of diphosphines rather than diphosphites. We thus
decided to study the reaction between [Fe2Cp2(CO)4] and
dppm.
We have recently reported our studies on the thermal
and photochemical reactions of the metal-metal bonded
dimer [Fe2Cp2(CO)4] (1; Cp ) η5-C5H5) and the bidentate
phosphite (EtO)2POP(OEt)2 (tedip).1 From these studies
we concluded that these reactions seem to proceed
mainly through the radical intermediates [FeCp(CO)2]
and [FeCp(CO)(κ1-tedip)], which then evolve in different
ways, always implying either C-O (ethoxy) or P-O
(backbone) bond cleavages of the diphosphite ligand, but
never involving activation of the C-H bonds in the
cyclopentadienyl ligands. These results are in contrast
with our studies on the thermal or photochemical
reactions of the binuclear Mo and W compounds [M2-
Cp2(CO)4(µ-A2PXPA2)] [A2PXPA2 ) Ph2PCH2PPh2 (dppm)
or Me2PCH2PMe2 (dmpm); M2 ) W2,2 Mo2.3 or MoW;4
First, we examined the thermal reaction of [Fe2Cp2-
(CO)4] with dppm, studied originally by Haines et al.,6
but we found no evidence of any ligand bond cleavage
5
A2PXPA2 ) (EtO)2POP(OEt)2; M2 ) Mo2 or W2 ]. In the
latter we found that bond cleavages of the backbone of
(3) (a) Garcia, G.; Garcia, M. E.; Melon, S.; Riera, V.; Ruiz, M. A.;
Villafan˜e, F. Organometallics 1997, 16, 624-631. (b) Riera, V.; Ruiz,
M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J . Organomet. Chem. 1989,
375, C23-C26.
(4) Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organometallics
1997, 16, 1378-1383.
* To whom correspondence should be addressed. E-mail: mara@
sauron.quimica.uniovi.es
(1) Alvarez, C. M.; Gala´n, B.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.;
Bois, C. Organometallics 2003, 22, 3039-3048.
(2) (a) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello,
L.; Bois, C. Organometallics 1997, 16, 354-364. (b) Alvarez, M. A.;
Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L.; Bois, C.; J eannin, Y.
J . Am. Chem. Soc. 1993, 115, 3786-3787.
(5) Alvarez, M. A.; Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Bois, C. Organometallics 1997, 16, 2581-2589.
(6) Haines, R. J .; Du Preez, A. L. J . Organomet. Chem. 1970, 21,
181-196.
10.1021/om034091v CCC: $25.00 © 2003 American Chemical Society
Publication on Web 11/15/2003

Photochemical Reactions of [Fe2(η5-C5H5)2(CO)4]
Organometallics, Vol. 22, No. 26, 2003 5505
Ch a r t 1
in the pathway to the final product [Fe2Cp2(µ-CO)2(µ-
dppm)] (2). Then we turned to the photochemical
reactions, and the results thus obtained are the focus
of the present paper. The photochemical reactions of
[Fe2L2(CO)4] complexes (L ) cyclopentadienyl or related
ligands) have been extensively studied,7,8 but none of
the reactive intermediates thus generated appear to
have been recognized as being involved in the activation
of ligands. We note, however, that Shade et al. have
reported a cyclopentadienyl C-H activation during the
photolysis of the dppm-bridged complex 2 in chloroform
solutions to yield [Fe2Cp{C5H4(CHO)}(µ-CO)2(µ-dppm)].9
Surprisingly, no new products could be isolated during
the photolysis of 2 in benzene solutions. A photoinduced
electron transfer to the solvent has been proposed to
explain the above observations. We also note that
related work on [Ru2Cp2(CO)4] has shown the involve-
ment of C-H (Cp) bond cleavage steps under photo-
chemical conditions.10 There is also at least one prece-
dent of a C-H bond cleavage of an iron-bound cyclo-
pentadienyl ligand under “dark” conditions, this occur-
ring in the reaction between [NbCp2H] and [FeCp(Me)-
(CO)2] to give [NbCp2H(µ-η1:η5-C5H4)Fe(CO)2] after
extrusion of methane.11 As we will next discuss, the
photochemical reactions of 1 with dppm are rather
complex, and not only C-H (Cp) or P-C (dppm) bond
cleavages have been detected, but also unexpected
reductive C-C couplings between the fragments gener-
ated after the initial bond cleavage steps.
having stoichiometric amounts of 1 and dppm leads to
a complex mixture of different species, with seven of
them having been fully identified or characterized.
These are the reported product of the thermal reaction,
compound 2,6 and the new species [Fe2Cp(µ-η5:κ1-C5H4-
CH2PPh2)(µ-CO)2(CO)] (3), cis-[Fe2Cp2(µ-H)(µ-PPh2)-
(CO)2] (4), [Fe2Cp(µ-η5:κ1-C5H4CH2PPh2)(µ-H)(µ-PPh2)-
(CO)] (5), trans-[Fe2Cp2(µ-H)(µ-PPh2)(CO)(PMePh2)] (6),
cis-[Fe2Cp2(µ-PPh2)2(CO)2] (7), and [Fe2Cp2(µ-PPh2)2(µ-
CO)] (8) (Chart 1). Compound 7 was first described by
Hayter12 and has been prepared also by other au-
thors.13,14 In fact, it is a minor product in our photo-
chemical reaction that cannot be completely separated
from other minor and unidentified products present in
the reaction mixture. However, several aspects of its
spectroscopic characterization have to be revised, as will
be discussed later on.
The ratio among the above products in the final
mixture is dependent on the reaction conditions (solvent,
temperature, irradiation time, and glassware used). For
example, we have found that the amount of 2 in the final
mixture is increased when the photolysis experiment
is carried out at room temperature, while compounds 5
and 6 are somewhat favored upon increasing the reac-
tion time. On the other hand, formation of the dppm
compound 2 is also favored when using Pyrex rather
than quartz vessels, this indicating that UV light favors
the bond cleavage processes required to form compounds
3-8. The highest relative amounts of the new complexes
3-8 are obtained when the reaction is carried out at
low temperatures (-25 °C) and using THF as solvent.
In any case, we could not find experimental conditions
to make more selective the photochemical reaction
between 1 and dppm. In addition, spectroscopic moni-
toring of the photolytic experiments allowed us to detect
the new complex trans-[Fe2Cp2(µ-CO)2(CO)(κ1-dppm)]
(9) as an intermediate species, which transforms into
the dppm-bridged 2 at longer reaction times. Finally,
as would be expected, the carbonyl-bridged compound
8 can be selectively prepared from dicarbonyl 7 under
similar conditions, as shown by a separate experi-
ment.
Resu lts a n d Discu ssion
P h otoch em ica l Rea ction s of Com p ou n d 1 w ith
Dp p m . Irradiation with UV-visible light of solutions
(7) Bitterwolf, T. E. Coord. Chem. Rev. 2000, 206-207, 419-450.
(8) (a) Wrighton, M. Chem. Rev. 1974, 74, 401-430. (b) Hooker, R.
H.; Mamound, K. A.; Rest, A. J . J . Chem. Soc., Chem. Commun. 1983,
1022. (c) Zhang, S.; Brown, T. L. J . Am. Chem. Soc. 1992, 114, 2723-
2725. (d) Zhang, S.; Brown, T. L. Organometallics 1992, 11, 4166-
4173. (e) Dixon, A. J . George, M. W.; Hughes, C.; Poliakoff, M.; Turner,
J . J . J . Am. Chem. Soc. 1992, 114, 1719-1729. (f) Zhang, S.; Brown,
T. L. J . Am. Chem. Soc. 1993, 115, 1779-1789. (g) Vitale, K. K.; Lee,
C. F.; Hille, R.; Gustafson, T. L.; Bursten, B. E. J . Am. Chem. Soc.
1995, 117, 2286-2296.
(9) Shade, J . E.; Pearson, W. H.; Brown, J . E.; Bitterwolf, T. E.
Organometallics 1995, 14, 157-161.
(10) Feasey, N. D.; Forrow, N. J .; Hogarth, G.; Knox, S. A. R.;
Macpherson, K. A.; Morris, M. J .; Orpen, A. G. J . Organomet. Chem.
1984, 267, C41-C44.
(12) Hayter, R. G. J . Am. Chem. Soc. 1963, 85, 3120-3124.
(13) Treichel, P. M.; Dean, W. K.; Douglas, W. M. J . Organomet.
Chem. 1972, 42, 145-158.
(14) Spencer, J . T.; Spencer, J . A.; J acobson, R. A.; Verkade, J . G.
New J . Chem. 1989, 13, 275-291.
(11) Pasynskii, A. A.; Skripkin, Y. V.; Kalinnikov, J . T.; Poraikoshits,
M. A.; Antsyshkina, A. S.; Sadikov, G. G.; Ostrikova, V. N. J .
Organomet. Chem. 1980, 201, 269-281.

5506 Organometallics, Vol. 22, No. 26, 2003
Alvarez et al.
metal-coordinated Cp and alkyl ligands; (b) complex 3
seems to be the first example structurally characterized
where the phosphinomethylcyclopentadienyl ligand
bridges two metal atoms that are also connected by a
metal-metal bond. The presence of this metal-metal
interaction, however, has little influence on the struc-
tural parameters in the ligand; thus the C4-P1-Fe1
and C5-C4-P1 angles (ca. 110°, Table 1) are similar
to those in previous C5H4CH2PPh2 complexes.15 The
reverse is not true, and the presence of this bridging
ligand seems to have a genuine shortening effect on the
intermetallic separation. In fact, compound 3 can be
considered a “linked” cyclopentadienyl derivative of the
general family of phosphine complexes of the type [Fe2-
Cp2(µ-CO)2(CO)(PR3)] first reported by Haynes et al. (R
) alkyl, aryl, alkoxy, etc.).18 However, the intermetallic
distances in these complexes are significantly longer
than the value of 2.504(1) Å found for 3: for example,
the complexes [Fe2Cp2(µ-CO)2(CO){P(OPh)3}]19a and
[Fe2Cp2(µ-CO)2(CO){PPh2(CH2Ph)}]19b exhibit interme-
tallic bond lengths of 2.545(2) and 2.540(2) Å, respec-
tively. This shortening effect on the iron-iron distance
is observed when other bridging ligands are present. For
example, the diphosphine- or diphosphite-bridged com-
pounds [Fe2Cp2(µ-CO)2(µ-L2)] (L2 ) tedip,1 dppe9) dis-
play similar short Fe-Fe distances (ca. 2.51 Å).
F igu r e 1. CAMERON view of the molecular structure of
[Fe2Cp(µ-η5:κ1-C5H4CH2PPh2)(µ-CO)2(CO)] (3). Ellipsoids
represent 30% probability.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3
d (Å)
θ (deg)
Spectroscopic data in solution for 3 are in agreement
with the structure observed in the solid state. The IR
spectrum of 3 (Table 2) exhibits two bands (weak and
strong, in order of decreasing frequency) in the region
of the C-O stretches of bridging carbonyls, as expected
for two CO ligands defining almost a 180° relative
angle.20 There is also a strong band at 1939 cm-1
corresponding to the terminal carbonyl. Its frequency
is characteristic of trans-[Fe2Cp2(µ-CO)2(CO)(PR3)] ge-
ometries. For example, the trans-complex having PEt-
Fe(1)-Fe(2)
Fe(1)-P(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(2)-C(1)
Fe(2)-C(2)
Fe(2)-C(3)
P(1)-C(4)
P(1)-C(21)
P(1)-C(31)
C(5)-C(4)
2.504(1)
2.190(2)
1.888(5)
1.883(5)
1.923(5)
1.943(5)
1.737(7)
1.851(5)
1.829(4)
1.830(5)
1.500(8)
Fe(2)-Fe(1)-P(1)
Fe(1)-Fe(2)-C(3)
Fe(1)-C(1)-Fe(2)
Fe(1)-C(2)-Fe(2)
C(5)-C(4)-P(1)
C(4)-C(5)-C(6)
C(4)-C(5)-C(9)
C(4)-P(1)-Fe(1)
C(21)-P(1)-C(31)
C(4)-P(1)-C(21)
C(4)-P(1)-C(31)
90.02(5)
99.1(2)
82.1(2)
81.7(2)
111.2(4)
126.6(6)
124.9(6)
113.8(2)
102.7(2)
102.9(3)
102.3(3)
Ph2 exhibits a terminal stretch at 1940 cm-1 18
The
.
Cr ysta l a n d Solu tion Str u ctu r e of Com p ou n d 3.
The structure of 3 has been determined through an
X-ray study. There are two independent but almost
identical molecules in the unit cell. Only one of them is
depicted in Figure 1, while Table 1 lists the most
relevant bond distances and angles. The molecule
displays two iron cyclopentadienyl fragments bridged
by a new seven-electron (diphenylphosphinomethyl)-
cyclopentadienyl ligand (C5H4CH2PPh2) and two carbo-
nyl ligands. A third carbonyl ligand is terminally bound
to one of the iron atoms, thus completing the pseudot-
etrahedral coordination around the metal atoms (Cp
assumed to occupy a single coordination position).
Although different complexes containing the above
phosphinomethylcyclopentadienyl bridging group have
been previously described,15 the presence of this ligand
in 3 has two novel aspects: (a) previous complexes have
been typically obtained through reactions that used a
precursor already containing this ligand, such as [FeCp-
(µ-η5:κ1-C5H4CH2PPh2)]16 or [TiCl2(µ-η5:κ1-C5H4CH2-
PPh2)2],17 and not through a C-C coupling reaction from
31P{1H} NMR spectrum of 3 exhibits just one signal at
114.2 ppm (Table 2) in the usual region of phosphine
ligands coordinated to iron centers. For example, the
diphosphine-bridged compound 2 displays a 31P reso-
nance at 86.56 ppm.9 The 1H NMR spectrum of 3
exhibits a singlet for the cyclopentadienyl protons and
two multiplets for the hydrogen atoms of the second ring
ligand, as expected for monosubstituted cyclopentadi-
enyls in general,21 and also observed for previous C5H4-
CH2PPh2 complexes.15 The presence of a mirror plane
defined by the C5, C4, and P1 atoms makes the
methylene protons equivalent, thus explaining their
appearance as a doublet at 2.02 ppm (J PH ) 8 Hz).
Str u ctu r a l Ch a r a cter iza tion of Com p ou n d 4. The
structure of compound 4 can be deduced unambiguously
from the corresponding spectroscopic data. The 31P{1H}
NMR spectrum of 4 exhibits just one signal at 187.3
ppm in the range expected for diarylphosphide ligands
(17) Graham, T. W.; Llamazares, A.; McDonald, R.; Cowie, M.
Organometallics 1999, 18, 3490-3501.
(18) Haines, R. J .; Du Preez, A. L. Inorg. Chem. 1969, 8, 1459-
(15) For recent work on the subjet, see for example: (a) Barranco,
E. M.; Crespo, O.; Gimeno, M. C.; Laguna, A. Inorg. Chem. 2000, 39,
680-687. (b) Ma, J . F.; Yamamoto, Y. Inorg. Chim. Acta 2000, 299,
164-171. (c) Graham, T. W.; Llamazares, A.; McDonald, R.; Cowie,
M. Organometallics 1999, 18, 3502-3510. (d) Goodwin, N. J .; Hend-
erson, W.; Nicholson, B. K.; Fawcet, J .; Russell, D. R. J . Chem. Soc.,
Dalton Trans. 1999, 1785-1795.
1464.
(19) (a) Cotton, F. A.; Frenz, B. A.; White, A. J . Inorg. Chem. 1974,
13, 1407-1411. (b) Klasen, C.; Lorenz, I. P.; Schmid, S.; Beuter, G. J .
Organomet. Chem. 1992, 428, 363-378.
(20) (a) Braterman, P. S. Metal Carbonyl Spectra; Academic Press
Inc.: London, 1975. (b) Bellamy, L. J . The Infrared Spectra of Complex
Molecules; Wiley: New York, 1975.
(16) Yamamoto, Y.; Tanase, T.; Mori, I.; Nakamura, Y. J . Chem. Soc.,
Dalton Trans. 1994, 3191-3192.
(21) Coville, N. J .; Plooy, K. E.; Pickl, W. Coord. Chem. Rev. 1992,
116, 3-267.

Photochemical Reactions of [Fe2(η5-C5H5)2(CO)4]
Organometallics, Vol. 22, No. 26, 2003 5507
Ta ble 2. IR a n d NMR Da ta for Com p ou n d s 3-8
c
compound
νst(CO)a
δ(P)b
J PP
[Fe2Cp(µ-η5:κ1-C5H4CH2PPh2)(µ-CO)2(CO)] (3)
cis-[Fe2Cp2(µ-H)(µ-PPh2)(CO)2] (4)
1939(s), 1771(w), 1727(vs)
1950(vs)
1898(vs)
1898(vs)
1951(vs)
114.2
187.3d
[Fe2Cp(µ-η5:κ1-C5H4CH2PPh2)(µ-H)(µ-PPh2)(CO)] (5)
trans-[Fe2Cp2(µ-H)(µ-PPh2)(CO)(PMePh2)] (6)
cis-[Fe2Cp2(µ-PPh2)2(CO)2] (7)
193.3, 89.4
180.3, 61.9
-8.1
29
37
[Fe2Cp2(µ-PPh2)2(µ-CO)] (8)
1747(s)
1929(s), 1725(vs)
116.9d
trans-[Fe2Cp2(µ-CO)2(CO)(κ1-dppm)] (9)
65.4, -23.7e
29
a
b
Recorded in CH2Cl2 solution, unless otherwise stated, ν in cm-1
.
Recorded in C6D6 solution at 290 K and 81.01 MHz, unless otherwise
stated; δ in ppm relative to external 85% aqueous H3PO4. c Coupling constants in hertz. Recorded in CD2Cl2 and 121.49 MHz. e Recorded
at 121.49 MHz.
d
bridging two iron atoms connected by a metal-metal
and related hydrocarbon chains).25 Under these condi-
tions, a mixture of cis- and trans-[Fe2Cp2(µ-H)(µ-PR2)-
(CO)2] could be prepared in moderate to good yields. Our
photochemical preparation of 4, although quite unsat-
isfactory from a synthetic point of view, gives specifically
the cis isomer of the diphenylphosphide-hydride deriva-
tive, thus allowing its full spectroscopic characterization.
As will be seen, the formation of 4 in our photochemical
reaction also explains the presence of compound 6 in
the reaction mixture.
1
bond.22 Its H NMR spectrum indicates the equivalence
of both cyclopentadienyl ligands (just a resonance at
4.60 ppm) and the presence of a hydride ligand (-19.24
ppm). The chemical shift of the latter signal, much lower
than the usual values for terminal hydride ligands, and
the P-H coupling to the phosphide group (J HP ) 43 Hz)
are consistent with a bridging coordination of the
hydride ligand. These spectroscopic parameters are
comparable to those measured for the diphenylphos-
phide-hydride [Fe2Cp2(µ-H)(µ-PPh2)(µ-dppm)], a com-
plex isolated from the reaction of [FeCl2(dppm)] with
activated Mg and C5H6,23 which exhibits δ (µ-P) ) 172.3
ppm, δ (µ-H) ) -22.00 ppm, and J PH ) 42.2 Hz. The IR
spectrum of 4 displays one band in the region of the
terminal C-O stretches. Its frequency (1950 cm-1 in
Str u ctu r a l Ch a r a cter iza tion of Com p ou n d s 5
a n d 6. Compound 5 combines the structural elements
present in complexes 3 (diphenylphosphinomethyl-
cyclopentadienyl) and 4 (diphenylphosphide and hydride
ligands). Thus, the spectroscopic data for 5 are very
similar to those previously discussed for compounds 3
and 4 (Table 2 and Experimental Section). For example,
the 31P{1H} NMR spectrum exhibits two signals at 193.3
and 89.4 ppm in the usual range for iron-bonded
diarylphosphide (187.3 ppm for 4)22,25 or phosphine
ligands (114.2 ppm for 3), respectively. The 1H NMR
spectrum of 5 exhibits as most relevant features a triplet
hydride resonance at -18.70 ppm (J PH ) 37 Hz),
indicative of a bridging hydride defining similar H-Fe-P
angles with the phosphide and phosphine P atoms. As
a result, the symmetry plane bisecting the phosphinom-
ethylcyclopentadienyl ligand in 3 is no longer present
in 5, thus yielding all the C5H4 and methylene protons
to be unequivalent. This asymmetry is also evident from
the 13C{1H} NMR spectrum of 5, which exhibits inde-
pendent resonances for the four phenyl groups or the
C5H4 ring atoms.
CH2Cl2) falls in the range observed (1963-1943 cm-1
)
for isoelectronic and isostructural dicarbonyl complexes
having a cis-disposition of the carbonyl ligands, cis-[Ru2-
Cp2(µ-H)(µ-PPh2)(CO)2]24 and cis-[Fe2Cp2(µ-H)(µ-PR2)-
(CO)2] (R ) menthyl and related hydrocarbon chains).25
The presence of just one band rather than the expected
strong and weak bands in the CO stretching region is
not attributed to a low intensity (perfect parallelism
between the CO ligands) of the asymmetric stretch,20
but to an almost identical frequency (small value of the
interaction constant). The cis relative position of the
carbonyl ligands in 4 is confirmed by its 13C{1H} NMR
spectrum, which exhibits two different sets of signals
for the phenyl groups. This is an indication of different
environments at both sides of the approximate plane
defined by the iron and phosphorus atoms, which is
caused by the presence of both carbonyls ligands at the
same side of that plane (Chart 1). We should note that
a compound with the same formulation as 4 was
reported by Hayter to be formed in very low yield (5%)
from the thermal reaction of [Fe2Cp2(CO)4] with Ph2P-
PPh2,12 but this product was not fully characterized at
the time. In the same paper the complex [Fe2Cp2(µ-H)-
(µ-PMe2)(CO)2] was also described, but, surprisingly, the
only related phosphide hydride diiron complexes de-
scribed in the literature since Hayter’s original report
have been prepared by Brunner et al. from the thermal
reaction of secondary phosphines HPR2 (R2 ) menthyl
The structure of complex 6 is shown in Chart 1. It is
formally derived from 4 after replacement of a CO
ligand by methyldiphenylphosphine. In fact, we have
shown through a separate experiment that 4 reacts with
PMePh2 under the usual photochemical conditions to
give 6 as the major product. The spectroscopic data for
6 (Table 2) totally support that structure. The presence
of diphenylphosphide and hydride ligands similar to
those in 4 is indicated by the appearance of resonances
at δ (µ-P) ) 180.3 ppm and δ (µ-H) ) -21.38 ppm. On
the other hand, the incorporation of a PMePh2 phos-
phine to the iron center is clearly revealed by the
appearance of a 31P resonance at 61.9 ppm and a 1H
doublet resonance at 0.67 ppm (J HP ) 7 Hz) assigned
to the methyl group of the phosphine. The coupling
between P atoms (J PP ) 37 Hz) is similar to that found
for 5 (J PP ) 29 Hz), as expected from their similar
relative positions. The same applies to the hydride
resonance, which exhibits H-P couplings of 33 and 48
Hz, in the range found for 5 (J HP ) 37 Hz). Finally, the
(22) Carty, A. J .; McLaughlin, S. A.; Nucciarone, D. Phosphorus-31
NMR Spectroscopy in Stereochemical Analysis; Verkade, J . G., Quin,
L. D., Eds.; VCH: Florida, 1987; Chapter 16.
(23) Raubenheimer, H. G.; Scott, F.; Cronje, S.; Van Rooyen, P. H.
J . Chem. Soc., Dalton Trans. 1992, 1859-1863.
(24) Caffyn, A. J . M.; Mays, M. J .; Raithby, P. R. J . Chem. Soc.,
Dalton Trans. 1991, 2349-2356.
(25) (a) Brunner, H.; Peter, H. J . Organomet. Chem. 1990, 393, 411-
422. (b) Brunner, H.; Rotzer, M. J . Organomet. Chem. 1992, 425, 119-
124.

5508 Organometallics, Vol. 22, No. 26, 2003
Alvarez et al.
exact coincidence of the C-O stretching frequencies
exhibited by 5 and 6 proves that the CO and the
phosphine ligands in the latter lie on opposite sides of
the plane defined by the bridging groups (trans isomer),
as it necessarily happens in the case of 5.
ligands, while the four phenyl rings are related pairwise,
in agreement with a (CpFe)2 moiety bridged sym-
metrically by two diphenylphosphide groups and one
carbonyl ligand (Chart 1). The chemical shift of the
phosphide P atoms (δ ) 116.9 ppm) can be considered
as somewhat low, when compared to the shifts of ca.
190 ppm for other metal-metal bonded complexes in
this work. Although we are not sure about the origin of
this low shift, we suspect that this could be an indication
of strain in the Fe2P cycle or steric congestion around
the dimetal unit, all of which could have definite effects
on the Fe2P or PC2 angles.22 In fact, compound 8 is not
very stable, and prolonged manipulation of its solution
causes its progressive decomposition. In line with this
idea we note that, to our surprise, no other carbonyl-
bridged phosphide complex of type [Fe2Cp2(µ-PX2)2(µ-
CO)] appears to have been reported in the literature.
Interestingly, Bitterwolf et al. have recently reported
the detection of similar thiolate-bridged complexes
[Fe2Cp2(µ-SR)2(µ-CO)] as transient intermediates in the
photolytic isomerization between cis and trans dicar-
bonyls [Fe2Cp2(µ-SR)2(CO)2], both in solution and in
frozen matrix supports.27
Once the structure of 8 was firmly established, it
could be anticipated that 8 was very likely to be a
photoproduct derived from dicarbonyl 7. Indeed, when
a mixture of cis and trans isomers of 7 (as directly
obtained by Hayter’s method) is photolyzed in THF
solution at - 25 °C, it slowly but cleanly transforms into
the monocarbonyl compound 8. No other side products
were formed in significant amounts, as verified by
recording a 31P NMR spectrum of the reaction mixture.
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of
Com p ou n d 9. As we have stated above, complex 9 is
detected by IR and 31P NMR during the photolysis of 1
in the presence of dppm, but it gradually disappears
from the reaction mixture. To prepare this compound
selectively, we considered the same strategy used before
to obtain the isostructural complex [Fe2Cp2(µ-CO)2(CO)-
(κ1-tedip)],1 based on the fact that the acetonitrile ligand
in [Fe2Cp2(CO)3(NCMe)]28 is easily displaced by two-
electron donor ligands. As expected, [Fe2Cp2(CO)3-
(NCMe)] reacts rapidly with dppm in toluene even at 0
°C to give 9 in very good yield. The presence of a
unidentate dppm ligand in 9 is clearly shown in its 31P-
{1H} NMR spectrum, which exhibits two coupled reso-
nances. The doublet at 65.4 ppm (Table 2) has a
chemical shift in the region observed for arylphosphines
bonded to iron complexes, while the signal at -23.7 ppm
has a chemical shift very close to that for the free dppm
ligand (-23.2 ppm in C6D6). Compound 9 is then
another member of the large family of phosphine
derivatives of compound 1 having the general formula
[Fe2Cp2(µ-CO)2(CO)(PR3)].18 For these compounds, cis
and trans isomers are possible, as defined by the relative
positions of the terminal ligands with respect to the
average Fe2(µ-C)2 plane. When both isomers of the same
compound are known, it is always found that the cis
isomers exhibit ν(CO) stretching frequencies around 20
cm-1 higher than the trans isomers. Therefore, by
recalling that trans-[Fe2Cp2(µ-CO)2(CO)(PEtPh2)] ex-
Id en tifica tion a n d NMR P r op er ties of Com -
p ou n d 7. In our photochemical reaction, compound 7
is just a minor compound that is formed in very low
yield and is difficult to purify even after laborious
chromatographic work. However, its presence in the
reaction mixture is relevant in order to understand the
reaction pathways under operation. Complex 7 has been
identified as the cis isomer of the phosphide complex
[Fe2Cp2(µ-PPh2)2(CO)2], first reported by Hayter,12 and
structurally characterized through an X-ray study.26
Although only the IR and 1H NMR spectra for this
product were originally recorded, thus precluding a
more complete comparison with our data, we have
independently prepared compound 7 as well as its trans
isomer by the Hayter’s route (thermal reaction of 1 with
Ph2P-PPh2). In our hands, the ν(CO) stretching fre-
quencies for cis and trans isomers of [Fe2Cp2(µ-PPh2)2-
(CO)2] are respectively 1949 and 1927 cm-1, both in
CH2Cl2 solution. These figures compare well with the
values 1961 and 1917 cm-1 reported in CS2 solution.12
1
The H NMR spectrum of 7 in C6D6 solution exhibits
the expected phenyl resonances and a singlet cyclopen-
tadienyl resonance at 3.93 ppm, in agreement with the
symmetry of the complex and the reported shift of 3.99
ppm in CS2.12 The 31P{1H} NMR spectrum of 7 exhibits
a resonance at -8.1 ppm in C6D6. This chemical shift
must be viewed as normal by considering that there is
no metal-metal bond in this molecule. Usually, the
absence of metal-metal bonds causes a strong shielding
of the 31P resonances of diphenylphosphide ligands.22
Indeed, this is also the case of the trans isomer of 7.
For this trans isomer we have measured a 31P chemical
shift of -11.6 ppm in C6D6 solution, to be compared with
shifts of ca. 190 ppm for the metal-metal bonded
phosphide compounds 4-6. There is, however, a conflict
involving the 31P shifts of these compounds. As part of
a general study on the spectroscopic properties of cis
and trans diiron complexes of general formula [Fe2Cp2-
(µ-PX2)2(CO)2], with X being electronegative substitu-
ents of type OR, SR, or NR2, Verkade and co-workers
reported 31P chemical shifts of 206.6 and 212.0 ppm for
the cis and trans isomers of compound [Fe2Cp2(µ-PPh2)2-
(CO)2], respectively.14 Those values are in radical dis-
agreement with our own data for the same compounds
(-8.1 and -11.6 ppm, respectively), but we cannot
explain this strong discrepancy in these NMR data.
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of
Com p ou n d 8. The IR spectrum of compound 8 displays
a single band at 1747 cm-1 in CH2Cl2 solution, thus
clearly indicating its bridging character. This is cor-
roborated by the appearance of a highly deshielded
resonance at 276.4 ppm in the 13C{1H} NMR spectrum.
The latter resonance appears as a triplet (J PC ) 21 Hz)
due to coupling with two equivalent phosphorus atoms.
1
Other features in the 13C{1H} and H NMR spectra (see
Experimental Section) are indicative of a rather sym-
metric molecule having equivalent phosphorus and Cp
(27) Bitterwolf, T. E.; Scallorn, W. B.; Li, B. Organometallics 2000,
19, 3280-3287.
(26) Ginsburg, R. E.; Rothrock, R. K.; Finke, R. G.; Collman, J . P.;
Dahl, L. F. J . Am. Chem. Soc. 1979, 101, 6550-6562.
(28) Labinger, J . A.; Madhaven, S. J . Organomet. Chem. 1977, 134,
381-389.

Photochemical Reactions of [Fe2(η5-C5H5)2(CO)4]
Organometallics, Vol. 22, No. 26, 2003 5509
Sch em e 1. In itia l Rea ction P a th w a ys P r op osed to
Occu r in th e P h otoch em ica l Rea ction of 1 w ith
Dp p m
Sch em e 2. Oxid a tive Ad d ition s a n d C-C
Red u ctive Cou p lin g P r op osed to Occu r d u r in g th e
P h otoch em ica l F or m a tion of Com p ou n d 5
hibits a terminal C-O stretch at 1940 cm-1 (cyclohexane
solution)18 and that the terminal C-O band of 9 appears
at 1929 cm-1 (CH2Cl2 solution), we can safely assign a
trans structure to the latter complex (Chart 1).
When toluene or tetrahydrofuran solutions of com-
pound 9 were exposed to UV light at -25 °C for 1 h, a
clean transformation into the dppm-bridged 2 occurred.
No other P-containing species were present in the crude
reaction mixture, a result that is of relevance when
analyzing the pathways under operation in these pho-
tochemical experiments, as we will next discuss.
Rea ction P a th w a ys of Dp p m a t Diir on Cen ter s.
As it can be deduced from the results discussed above,
the photochemical reaction between 1 and the diphos-
phine ligand dppm cannot be a simple process. This is
readily apparent by just considering the large number
and structural variety of the complexes formed. Al-
though the detailed reaction pathways in operation
cannot be revealed from our synthetic work, we have
enough information to propose rational steps that could
explain some of the processes likely to be responsible
for the formation of compounds 2-9 (Schemes 1-3).
These necessarily involve different P-C and C-H bond
cleavages, as well as some C-C couplings, in order to
explain the nature of the compounds isolated.
The photochemical reaction between 1 and dppm
would be mainly initiated by the homolytic cleavage of
the Fe-Fe bond to give the [FeCp(CO)2] radical A7,8
(Scheme 1), which is well known to experience easy
substitution of CO by ligands.8d,e,29 In our case, A would
thus easily give the 17-electron dppm derivative [FeCp-
(CO)(κ1-dppm)], B. At this point, three radical recom-
binations can occur: A-A, A-B, or B-B. The first one
affords the starting complex 1, which obviously must
be in equilibrium with radical A under photolytic
conditions. Reaction A + B would give compound 9, and
this is surely the main reaction pathway leading to 2.
Indeed, pure compound 9 transforms cleanly into 2
under similar photolytic conditions, as we have dis-
cussed above. However, this also means that compound
9 is not a precursor of compounds 3-8. Finally, the
dimerization process B + B could happen as well, but
this is expected to be slow, as shown for other phos-
phine-substituted radicals of type [FeCp(CO)L]. As a
result, further evolution of the radicals A and B,
different from simple recombination, must be involved
in order to justify the formation of compounds 3-8.
As we have proposed for the photolytic reactions of 1
in the presence of diphosphite tedip,1 it is likely that
either radical A or B could experience further decarbo-
nylation to give 15-electron radicals (Scheme 1).8f In our
case, this would lead to radicals C and D, the combina-
tion of which (A + D or B + C) would give the
monocarbonyl intermediate E, isoelectronic to compound
[Fe2Cp2(µ-η1,η2-CO)(CO)2]8b,30 and also having probably
a µ-η1:η2 bridging CO ligand. This intermediate could
lead to the formation of complex 5 by stepwise intramo-
lecular oxidative additions of a P-C bond of the dppm
ligand and a C-H bond of the cyclopentadienyl ligand,
via intermediates F or G, followed by a C-C coupling
(reductive elimination) that would generate the (diphe-
nylphosphinomethyl)cyclopentadienyl ligand (Scheme
2). Both types of oxidative additions have been previ-
ously observed for related binuclear complexes such as
[Fe2(CO)5(µ-dppm)2] (thermal P-C cleavage)31 or [M2-
Cp2(CO)4(µ-dppm)] (M ) Mo, W; thermal P-C and
photochemical C-H cleavages).2-4 We note, however,
that previous examples of P-C cleavages are always
(30) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Unpublished
results.
(31) Dohery, N. M.; Hogarth, G.; Knox, S. A. R.; Macpherson, K. A.;
Melchior, F.; Morton, D. A. V.; Orpen, A. G. Inorg. Chim. Acta 1992,
198, 257-270.
(29) Sun, S.; Sweigart, D. W. Adv. Organomet. Chem. 1996, 40, 171-
214.

5510 Organometallics, Vol. 22, No. 26, 2003
Alvarez et al.
Sch em e 3. P r op osed Rea ction P a th w a ys in th e
P h otoch em ica l F or m a tion of th e
Dip h en ylp h osp h id e Der iva tives 4, 6, 7, a n d 8
(F e ) F eCp )
yield methyldiphenylphosphine, which under photolytic
conditions does react with 4 to give 6, as we have shown
through separate experiments. The key step to explain
the formation of compounds 4, 6, 7, and 8 then is the
P-C cleavage of the backbone of the dppm ligand at
the mononuclear radical [FeCp(CO)(κ1-dppm)], B. Un-
fortunately, we have not been able to find previous
reports of P-C bond cleavages occurring at paramag-
netic iron phosphine complexes that would provide
further support to our hypothesis. In any case, we
should stress that the influence of the reaction time on
the relative amounts of compounds 4, 6, 7, and 8 is in
full agreement with the above proposal. It is experi-
mentally observed that on prolonged photolysis the yield
of 6 is somewhat increased, and that of 8 is decreased
while the yields of 4 or 7 are almost reduced to zero.
This is in agreement with our proposal, which implies
the generation of stoichometric amounts of PMePh2
relative to the overall J + 7, that is, 4 + 6 + 7 + 8.
Moreover, the fact that the yields in 7 and 8 are reduced
upon extended photolysis suggests that the dimerization
from intermediate I is a reversible step.
In any case the results just discussed indicate that
the intermediates generated during the photolysis of
mixtures of 1 and dppm are much more reactive than
the unsaturated species generated through decarbony-
lation of the Mo and W complexes [Mo2Cp2(CO)4(µ-L2)].
This is deduced from the observation that the P-C bond
cleavage of the dppm ligand at the iron centers cannot
be suppressed even at -25 °C under photolytic condi-
tions.
Con clu d in g Rem a r k s
The photochemical reactions between [Fe2Cp2(CO)4]
and the diphosphine ligand Ph2PCH2PPh2 seem to
proceed through the radical intermediates [FeCp(CO)2]
and [FeCp(CO)(κ1-dppm)], which then evolve and expe-
rience C-H (cyclopentadienyl) or P-C (backbone of
dppm) bond cleavages even at -25 °C. These bond
cleavages are responsible for the appearance of di-
phenylphosphide and methyldiphenylphosphine ligands
in the reaction products and may be followed by reduc-
tive C-C coupling involving cyclopentadienylidene in-
termediates, thus leading to products with a seven-
electron-donor (diphenylphosphinomethyl)cyclopentadienyl
bridging ligand.
induced thermally, not photochemically. On the other
hand, we should stress that precedents for related
reductive C-C couplings are extremely scarce. In fact,
we have been able to find just one example of a related
coupling involving cyclopentadienyl and phosphine
ligands. Thus, refluxing xylene solutions of 1 and PPh3
to yield [Fe4Cp4(CO)4] has been reported to give the C-C
coupling product [Fe4Cp3(C5H4Ph)(CO)4] in 3% yield.32
On the other hand, it is also likely that similar bond
cleavage and forming processes are involved in the
buildup of tricarbonyl 3, although the sequence of events
is more unclear to us at the moment.
Intermediate B could alternatively evolve through the
homolytic cleavage of a C-P bond in the unidentate
dppm ligand to give the diphenylphosphide intermediate
I and the phosphinomethyl radical CH2PPh2 (Scheme
3). The dimerization of I then would lead to the
formation of complexes 7 and 8, while the combination
of this intermediate with radical C would form the
paramagnetic dicarbonyl J . The latter is a 33-electron
radical isoelectronic with [Mo2Cp2(µ-PPh2)(CO)4] and
therefore is expected to abstract easily an H atom either
from the solvent or from traces of water present in the
reaction mixture.33 In this way the formation of the
hydride complex 4 can be explained. A similar H atom
abstraction from the phosphinomethyl radical would
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations and reactions were
carried out using standard Schlenk techniques under an
atmosphere of dry, oxygen-free nitrogen. Solvents were puri-
fied according to standard literature procedures34 and distilled
under nitrogen prior to use. Petroleum ether refers to the
fraction distilling in the range 60-65 °C. The compounds
dppm35 and [Fe2Cp2(CO)3(NCMe)]28 were prepared as described
previously. Compound [Fe2Cp2(CO)4] was obtained from the
usual commercial suppliers and used without further purifica-
tion. Photochemical experiments were preformed using jack-
eted Pyrex or quartz Schlenk tubes, refrigerated by a closed
2-propanol circuit kept at the desired temperature with a
cryostat or by tap water. A 400 W mercury lamp (Applied
(32) Westmeyer, M. D.; Massa, M. A.; Rauchfuss, T. B.; Wilson, S.
R. J . Am. Chem. Soc. 1998, 120, 114-123.
(33) Garc´ıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Lanfranchi,
M.; Tiripicchio, A. J . Am. Chem. Soc. 1999, 121, 4060-4061.
(34) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
(35) Aguiar, A. M.; Beisler, J . J . Org. Chem. 1964, 29, 1660-1662.

Photochemical Reactions of [Fe2(η5-C5H5)2(CO)4]
Organometallics, Vol. 22, No. 26, 2003 5511
Ta ble 3. Cr ysta l Da ta for Com p ou n d 3
Photophysics), placed ca. 1 cm away from the Schlenk tube,
was used for these experiments. Low-temperature chromato-
graphic separations were carried out analogously using jack-
eted columns. Commercial aluminum oxide (alumina, Aldrich,
activity I, 150 mesh) was degassed under vacuum prior to use.
The latter was mixed afterward under nitrogen with the
appropriate amount of water to reach the activity desired.
NMR spectra were recorded at 300.13 (1H), 81.01 (31P{1H}),
or 50.32 MHz (13C{1H}), at room temperature unless otherwise
stated. Chemical shifts (δ) are given in ppm, relative to
internal TMS (1H, 13C) or external 85% H3PO4 aqueous solution
(31P), with positive values for frequencies higher than that of
the reference. Coupling constants (J ) are given in hertz. 13C-
{1H} NMR spectra were routinely recorded on solutions
containing a small amount of tris(acetylacetonate) chromium-
(III) as a relaxation reagent.
P h otoch em ica l Rea ction of [F e2Cp 2(CO)4] (1) w ith
Dp p m . A tetrahydrofuran solution (20 mL) of 1 (0.250 g, 0.707
mmol) and dppm (0.275 g, 0.716 mmol) was placed in a
refrigerated quartz Schlenk tube. This solution was photolyzed
at -25 °C for 5 h while bubbling N2 (99.9995%) through the
solution to give a brown solution. Solvent was then removed
under vacuum and the residue dissolved in a minimum of
petroleum ether/CH2Cl2 (2/1). This solution was chromato-
graphed at -15 °C on an alumina column (activity III, 50 × 3
cm) prepared in petroleum ether. After washing the column
with petroleum ether, elution with a petroleum ether/CH2Cl2
(5/1) mixture gave an orange fraction containing a small
amount of compound 7 and some other unidentified species,
which was discarded. Elution with a petroleum ether/CH2Cl2
(4/1) mixture gave two light brown fractions containing
complexes 4 and 8, respectively, followed by a third dark brown
fraction containing complex 6. Elution with petroleum ether/
CH2Cl2 (3/1) gave a red fraction containing compound 5, and
elution with petroleum ether/CH2Cl2 (1/1) gave a light green
fraction containing compound 3. Finally, a dark green fraction
of 2 was collected when a petroleum ether/CH2Cl2 (1/4) mixture
was used as eluant. Removal of solvents under vacuum from
the above fractions gave respectively compounds 4 (red-brown,
0.051 g, 15%), 8 (yellow-orange, 0.066 g, 14%), 6 (brown, 0.014
g, 3%), 5 (brown, 0.018 g, 4%), 3 (green, 0.063 g, 17%), and 2
(green, 0.066 g, 15%) as microcrystalline powders. The crystals
used in the X-ray diffraction study of compound 3 were grown
by slow diffusion of petroleum ether into a solution of this
complex in CH2Cl2 at -20 °C. The use of longer reaction times
causes a significant change in the relative amounts of the
above complexes. For example, using a photolysis time of 8 h
increases the amount of compounds 5 and 6, while the yields
of compounds 3 and 8 are lower and compounds 4 and 7
disappear from the final reaction mixture. The yield of complex
2 remains roughly unchanged.
mol formula
mol wt
C26H21Fe2O3P
524.12
cryst syst
orthorhombic
space group
cryst color
P21cn
dark green
radiation (λ, Å)
a, Å
Mo KR (λ ) 0.71069 Å)
8.510(2)
b, Å
13.070(4)
c, Å
39.411(19)
4383(3)
V, Å3
Z
8
1.59
calcd density, g cm-3
µ(Mo KR), cm-1
diffractometer
temperature, K
scan type
θ limits, deg
scan width
total no. of data
no. of total unique data
no. of unique data used
Ra
14.21
CAD4 Enraf-Nonius
295
ω/2θ
1-30
0.8 + 0.345 tan θ
7131
6766
3850 [(Fo)2 > 3σ(Fo)2]
0.0394
0.0487
0.94
b
Rw
GOF
octants collected
decay %
extinction param
no. of variables
∆Fmin (e/Å3)
∆Fmax (e/Å3)
0,11; 0,18; 0,55
< 5
855
580
-0.46
0.38
R ) ∑||Fo| - |Fc||/∑|Fo|. bRw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
;
a
2
w ) w′[1 - (||Fo| - |Fc||/6σFo)2]2, with w′ ) 1/∑rArTr(X) with 3
coefficients 8.29, -0.232, and 6.65 for a Chebyshev series, for
which X is Fc/Fc(max).
29, µ-PPh2), 89.4 (d, J PP ) 29, µ-CH2PPh2). 13C{1H} NMR (CD2-
Cl2): δ 219.5 (d, J CP ) 16, CO), 148.7 [d, J CP ) 28, 1C(Ph)],
1
1
147.5 [d, J CP ) 18, C(Ph)], 144.6 [d, J CP ) 28, C(Ph)], 142.2
[d, J CP ) 25, 1C(Ph)], 135-126 (Ph), 97.2 (d, J CP ) 4, C5H4),
82.3 (s, C5H4), 82.1 (s, C5H4), 77.1 (s, Cp), 71.2 (s, C5H4), 28.7
(d, J CP ) 23, CH2).
Da ta for Com p ou n d 6. Anal. Calcd for C36H34OP2Fe2: C,
65.88; H, 5.22. Found: C, 65.53; H, 5.45. 1H NMR (200.13
MHz, C6D6): δ 8.30-6.80 (m, 20H, Ph), 4.35, 3.91 (2 × s, 2 ×
5H, Cp), 0.67 (d, J HP ) 7, 3H, Me), -21.38 (dd, J HP ) 48, 33,
1H, µ-H). 31P{1H} NMR (C6D6): δ 180.3 (d, J PP ) 37, µ-PPh2),
61.9 (d, J PP ) 37, PPh2Me).
P r ep a r a tion of [F e2Cp 2(µ-P P h 2)2(µ-CO)] (8). A mixture
of cis and trans isomers of compound 7, obtained as described
in ref 12 (0.050 g, 0.08 mmol), was dissolved in tetrahydrofuran
(15 mL) and photolyzed at -25 °C for 2 h in a quartz Schlenk
tube while keeping a strong bubbling of N2 through the
solution. The resulting dark brown solution was filtered and
the solvent removed from the filtrate under vacuum. Washing
of the residue with petroleum ether (3 × 5 mL) gave compound
Da ta for Com p ou n d 3. Anal. Calcd for C26H21O3PFe2: C,
1
59.58; H, 4.04. Found: C, 59.12; H, 3.95. H NMR (C6D6): δ
7.80-6.80 (m, 20H, Ph), 4.76 (t, AA′XX′, J AX + J AX′ ) 4, 2H,
C5H4), 4.40 (s, br, 2H, C5H4), 4.24 (s, 5H, Cp), 2.02 (d, J HP ) 8,
2H, CH2). 31P{1H} NMR (C6D6): δ 114.2 (s, CH2PPh2).
Da ta for Com p ou n d 4. Anal. Calcd for C24H21O2PFe2: C,
59.55; H, 4.37. Found: C, 59.46; H, 4.31. 1H NMR (CD2Cl2): δ
8 as a brown powder (0.041 g, 80%). Anal. Calcd for C35H30
-
OP2Fe2: C, 65.66; H, 4.72. Found: C, 65.38; H, 4.49. 1H NMR
(400.13 MHz, C6D6): δ 7.30-6.70 (m, 20H, Ph), 4.54 (s, 10H,
Cp). 31P{1H} NMR (121.49 MHz, CD2Cl2): δ 116.9 (s). 13C{1H}
NMR (75.47 MHz, CD2Cl2): δ 276.4 (t, J CP ) 21, µ-CO), 149.9
[false t, J CP + J CP′ ) 32, 1C(Ph)], 135.0 [m, 2C(Ph)], 134.6 [false
7.80-7.15 (m, 10H, Ph), 4.60 (s, 10H, Cp), -19.24 (d, J HP
)
43, 1H, µ-H). 31P{1H} NMR (121.49 MHz, CD2Cl2): δ 187.3 (s,
µ-PPh2). 13C{1H} NMR (75.47 MHz, CD2Cl2): δ 215.8 (d, J CP
1
2
t, J CP + J CP′ ) 34, C(Ph)], 131.9 [m, C(Ph)], 129.2, 128.3 [2
4
3
× s, C(Ph)], 127.7, 127.4 [2 × m, C(Ph)], 86.0 (s, Cp).
P r ep a r a tion of tr a n s-[F e2Cp 2(µ-CO)2(CO)(K1-d p p m )]
(9). A cold (0 °C) toluene solution (20 mL) of dppm (0.100 g,
0.26 mmol) was transferred over [Fe2Cp2(CO)3(NCMe)]28 (0.095
g, 0.26 mmol), previously placed in a refrigerated flask at 0
°C, and the mixture was stirred at this temperature for 15
min to yield a green solution. Solvent was then removed under
vacuum, and the residue was dissolved in CH2Cl2/petroleum
ether (1/2) and chromatographed at -15 °C on an alumina
column (activity 3.5, 12 × 1.5 cm) prepared in petroleum ether.
Elution with the same solvent mixture gave a red fraction,
1
1
) 20, CO), 147.8 [d, J CP ) 12, C(Ph)], 140.8 [d, J CP ) 39, C-
(Ph)], 135.8 [d, J CP ) 9, 2C(Ph)], 132.3 [d, J CP ) 9, 2C(Ph)],
128.9 [s, C(Ph)], 128.2 [d, J CP ) 9, C(Ph)], 128.1 [s, C(Ph)],
4
3
4
3
127.8 [d, J CP ) 9, C(Ph)], 80.6 (s, Cp).
Da ta for Com p ou n d 5. Anal. Calcd for C36H32OP2Fe2: C,
1
66.09; H, 4.93. Found: C, 66.18; H, 4.95. H NMR (C6D6): δ
8.20-6.90 (m, 20H, Ph), 4.99, 4.72, 4.61 (3 × s, 3 × 1H, C5H4),
4.13 (s, 5H, Cp), 4.02 (s, br, 1H, C5H4), 1.87 (t, J HH ) J HP
)
13, 1H, CH2), 1.00 (dd, J HH ) 13, J HP ) 5, 1H, CH2), -18.70
(t, J HP ) 37, 1H, µ-H). 31P{1H} NMR (C6D6): δ 193.3 (d, J PP
)

5512 Organometallics, Vol. 22, No. 26, 2003
Alvarez et al.
containing 1, followed by a green fraction that contains
complex 9. Removal of solvents from the latter fraction yielded
compound 9 (0.162 g, 88%) as a microcrystalline green solid.
Anal. Calcd for C38H32O3P2Fe2: C, 64.26; H, 4.54. Found: C,
(SHELXS),38 completed by Fourier techniques, and refined by
full-matrix least-squares. All non hydrogen atoms were aniso-
tropically refined. Hydrogen atoms were introduced in calcu-
lated positions in the last least-squares refinements; they were
allocated an overall isotropic thermal parameter. Two inde-
pendent molecules are present in the asymmetric unit, having
no significant differences in their structural parameters. The
main bond lengths and bond angles are summarized in Table
1. Figure 1 contains a CAMERON39 view of one of the
molecules.
1
64.95; H, 5.10. H NMR (200.13 MHz, C6D6): δ 7.90 (m, 4H,
Ph), 7.22-6.88 (m, 16H, Ph), 4.43, 4.13 (2 × s, 2 × 5H, Cp),
2.57 (br, 2H, CH2). 31P{1H} NMR (121.49 MHz, C6D6): δ 65.4
(d, J PP ) 29, P-Fe), -23.7 (d, J PP ) 29, P).
X-r a y Str u ctu r e Deter m in a tion for Com p ou n d 3. The
selected crystal was stuck on a glass fiber and mounted on a
Enraf-Nonius CAD4 automatic diffractometer. Accurate cell
dimensions and orientation matrix were obtained by least-
squares refinements of 25 accurately centered reflections. No
significant variations were observed in the intensities of two
checked reflections during data collection. Complete crystal-
lographic data and collection parameters are listed in Table
3. The data were corrected for Lorentz and polarization effects.
Computations were performed by using the PC version of
CRYSTALS.36 Scattering factors and corrections for anomalous
absorption were taken from the International Tables for
Crystallography.37 The structure was solved by direct methods
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog´ıa of Spain for financial support
(Projects BQU2000-0220 and BQU2000-0944) and the
Universidad de Oviedo for a grant to C.M.A.
Su p p or tin g In for m a tion Ava ila ble: Tables of fractional
atomic coordinates, anisotropic thermal parameters, and bond
lengths and angles for compound 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM034091V
(36) Watkin, D. J .; Prout, C. K.; Carruthers, J . R.; Betteridge, P.
W. Crystals Issue 10; Chemical Crystallography Laboratory, University
of Oxford: Oxford, UK, 1996.
(37) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. IV.
(38) Sheldrick, G. M. SHELXS 86, Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, 1986.
(39) Pearce, L. J .; Watkin, D. J . CAMERON; Chemical Crystal-
lography Laboratory: Oxford, U.K., 1989.