Formation of Iron-Fluorophosphorane Complexes (η5-C5H5)(CO)LFe{P(OPh)nF 4-n} (L = CO, P(OPh)3; n = 0, 1) and (η5-C5H5)(CO)2Fe{P(OC 6H4NMe)F2}. Nucleophilic Attack of F- toward a Trivalent Phosphorus Atom Coordinated to a Transition Metal

Article abstract of DOI:10.1021/om990564f

The reaction of a phosphite complex, [Cp(CO)₂Fe{P(OPh)₃}]PF₆, with Et₄NF in CH₂CI₂ at room temperature yielded a mixture of metallafluorophosphoranes, Cp(CO)₂Fe(PF₄) (1) and Cp(CO)₂Fe{P(OPh)F₃} (2). Similar phosphite complexes [Cp(CO)Fe{P(OPh)₃}₂]PF₆ and [Cp(CO)₂Fe(P(OC₆H₄NMe)(OC₆H ₄NMeH)}]PF₆ also reacted with F^- to form CpCCO){P(OPh)₃}- Fe(PF₄) (3) and Cp(CO)₂Fe{P(Oc₆H₄NMe)F₂} (4), respectively. The ³¹P and ¹⁹F NMR studies of these metallafluorophosphoranes revealed that pseudorotation around the hypervalent phosphorus center takes place readily in 1 and 3, whereas it marginally occurs at room temperature in 4, but not in 2 even at elevated temperature. The difference in the energy barrier of the rotation process was interpreted in terms of the apicophilicity of the substituents on the phosphorane phosphorus.

Full text of DOI:10.1021/om990564f

Organometallics 1999, 18, 4311-4316
4311
F or m a tion of Ir on -F lu or op h osp h or a n e Com p lexes
(η5-C5H5)(CO)LF e{P (OP h )n F 4-n } (L ) CO, P (OP h )3; n ) 0,
1) a n d (η5-C5H5)(CO)2F e{P (OC6H4NMe)F 2}. Nu cleop h ilic
Atta ck of F - tow a r d a Tr iva len t P h osp h or u s Atom
Coor d in a ted to a Tr a n sition Meta l
Kazuyuki Kubo, Kumiko Bansho, Hiroshi Nakazawa,* and Katsuhiko Miyoshi*
Department of Chemistry, Graduate School of Science, Hiroshima University,
Higashi-Hiroshima 739-8526, J apan
Received J uly 19, 1999
The reaction of a phosphite complex, [Cp(CO)2Fe{P(OPh)3}]PF6, with Et4NF in CH2Cl2 at
room temperature yielded a mixture of metallafluorophosphoranes, Cp(CO)2Fe(PF4) (1) and
Cp(CO)2Fe{P(OPh)F3} (2). Similar phosphite complexes [Cp(CO)Fe{P(OPh)3}2]PF6 and
[Cp(CO)2Fe{P(OC6H4NMe)(OC6H4NMeH)}]PF6 also reacted with F- to form Cp(CO){P(OPh)3}-
Fe(PF4) (3) and Cp(CO)2Fe{P(OC6H4NMe)F2} (4), respectively. The 31P and 19F NMR studies
of these metallafluorophosphoranes revealed that pseudorotation around the hypervalent
phosphorus center takes place readily in 1 and 3, whereas it marginally occurs at room
temperature in 4, but not in 2 even at elevated temperature. The difference in the energy
barrier of the rotation process was interpreted in terms of the apicophilicity of the
substituents on the phosphorane phosphorus.
In tr od u ction
nate phosphorus ligand such as a phosphide or a
phosphite ligand, coordinated to a transition metal, into
a pentacoordinate phosphorus species by oxidative or
nucleophilic addition of some inorganic or organic re-
agents to the phosphorus atom. For example, Ebsworth
et al. reported the oxidative addition of halogens (Cl2
or XeF2) to a phosphide phosphorus coordinated to an
iridium center (eq 1),9 and we recently reported a new
synthetic method for metallaphosphoranes, in which a
trivalent phosphorus compound coordinated to a cationic
transition-metal center is nucleophilically attacked by
organic Lewis bases to expand its formal valence (eq
2).10
During the past few decades, much attention has been
focused on the syntheses, structures, and properties of
pentacoordinate phosphorus compounds, phosphoranes,
partly because they have many attractive properties
arising from their unusual valency.1 However, studies
on the transition-metal derivatives have been started
in relatively recent years, and a few synthetic ap-
proaches to metallaphosphoranes have been reported
to date.2 They are based roughly on two strategies. One
is based on reactions of a transition-metal complex with
an organic phosphorane or a phosphoranide (a tetra-
coordinate anionic phosphorus compound).3-8 Most of
metallaphosphoranes reported so far have been pre-
pared with recourse to this simple strategy. The other
approach involves valence expansion of a lower-coordi-
As an extension of our above-mentioned preparative
method, we herein report the synthesis of metallafluo-
(6) (a) Khasnis, D. V.; Lattman, M.; Siriwardane, U. Inorg. Chem.
1989, 28, 681. (b) Khasnis, D. V.; Lattman, M.; Siriwardane, U. Inorg.
Chem. 1989, 28, 2594. (c) Khasnis, D. V.; Lattman, M.; Siriwardane,
U. J . Chem. Soc., Chem. Commun. 1989, 1538. (d) Khasnis, D. V.;
Lattman, M.; Siriwardane, U.; Chopra, S. K. J . Am. Chem. Soc. 1989,
111, 3103. (e) Khasnis, D. V.; Lattman, M.; Siriwardane, U. Organo-
metallics 1991, 10, 1326. (f) Khasnis, D. V.; Lattman, M.; Siriwardane,
U.; Zhang, H. Organometallics 1992, 11, 2074.
(1) For review articles, see: Holmes, R. R. Pentacoordinated Phos-
phorus; ACS Monographs No. 175 and 176; American Chemical
Society: Washington, DC, 1980; Vols. I and II.
(2) For review articles, see: (a) Montgomery, C. D. Phosphorus,
Sulfur, Silicon 1993, 84, 23. (b) Dillon, K. B. Chem. Rev. 1994, 94,
1441.
(3) (a) Lattman, M.; Chopra, S. K.; Cowley, A. H.; Arif, A. M.
Organometallics 1986, 5, 677. (b) Lattman, M.; Burns, E. G.; Chopra,
S. K.; Cowley, A. H.; Arif, A. M. Inorg. Chem. 1987, 26, 1926.
(4) Brunus, E. G.; Chu, S. S. C.; Meester, P.; Lattman, M. Organo-
metallics 1986, 5, 2383.
(5) (a) Wachter, J .; Mentzen, B. F.; Reiss, J . G. Angew. Chem., Int.
Ed. Engl. 1981, 20, 284. (b) Vierling, P.; Riess, J . G. J . Am. Chem.
Soc. 1981, 103, 2466. (c) J eanneaux, F.; Grand, A.; G.Riess, J . J . Am.
Chem. Soc. 1981, 103, 4272. (d) Dupart, J . M.; Grand, A.; Pace, S.;
Riess, J . G. J . Am. Chem. Soc. 1982, 104, 2316. (e) Vierling, P.; Riess,
J . G. J . Am. Chem. Soc. 1984, 106, 2432. (f) Dupart, J . M.; Grand, A.;
Riess, J . G. J . Am. Chem. Soc. 1986, 108, 1167. (g) Vierling, P.; Riess,
J . G. Organometallics 1986, 5, 2543. (h) Vierling, P.; Riess, J . G.;
Grand, A. Inorg. Chem. 1986, 25, 4144. (i) Khasnis, D. V.; Burton, J .
M.; Zhang, H.; Lattman, M. Organometallics 1992, 11, 3745.
(7) (a) Lattman, M.; Anand, B. N.; Grrett, D. R.; Whitener, M. A.
Inorg. Chim. Acta 1983, 76, L139. (b) Lattman, M.; Morse, S. A.;
Cowley, A. H.; Lasch, J . G.; Norman, N. C. Inorg. Chem. 1985, 24,
1364. (c) Anand, B. N.; Bains, R.; Usha, K. J . Chem. Soc., Dalton Trans.
1990, 2315.
(8) (a) Chopra, S. K.; Martin, J . C. Heteroatom Chem. 1991, 2, 71.
(b) Faw, R.; Montgomery, C. D.; Rettig, S. J .; Shurmer, B. Inorg. Chem.
1998, 37, 4136.
(9) (a) Ebsworth, E. A. V.; McManus, N. T.; Pilkington, N. J .; Rankin,
D. W. H. J . Chem. Soc., Chem. Commun. 1983, 484. (b) Ebsworth, E.
A. V.; Holloway, J . H.; Pilkington, N. J .; Rankin, D. W. H. Angew.
Chem., Int. Ed. Engl. 1984, 23, 630.
(10) (a) Nakazawa, H.; Kubo, K.; Miyoshi, K. J . Am. Chem. Soc.
1993, 115, 5863. (b) Kubo, K.; Nakazawa, H.; Mizuta, T.; Miyoshi, K.
Organometallics 1998, 17, 3522.
10.1021/om990564f CCC: $18.00 © 1999 American Chemical Society
Publication on Web 09/18/1999

4312 Organometallics, Vol. 18, No. 21, 1999
Kubo et al.
products in the reaction were two iron-phosphorane
complexes, Cp(CO)2Fe(PF4) (1) and Cp(CO)2Fe{P(OPh)-
F3} (2) (eq 3).
(1)
(2)
rophosphoranes by the reactions of cationic iron com-
plexes having a phosphite ligand with a fluoride anion
as a nucleophile. Also reported is dynamic behavior of
the resulting metallaphosphoranes, i.e., pseudorotation
around the hypervalent phosphorus.
(3)
Resu lts a n d Discu ssion
The 31P NMR spectrum of the reaction mixture
exhibits three main signals; a septet at -142.87 ppm
(J ) 710 Hz), a quintet at 45.26 ppm (J ) 1127 Hz),
and a doublet of triplets at 31.23 ppm (J ) 1168 and
1032 Hz) (Figure 1). The septet is unambiguously
assigned to PF6-. The chemical shifts of the quintet and
the doublet of triplets are at a higher field by ca. 120
ppm than that of the starting complex, indicating that
the valence of the phosphorus atoms is expanded. The
large coupling constants (greater than 1000 Hz) indicate
that these products have direct P-F bond(s). These
observations suggest that the quintet arises from com-
plex 1 if a pseudorotation process around the penta-
coordinate phosphorus is taking place fast on the NMR
time scale and that the doublet of triplets arises from
complex 2 if the corresponding pseudorotation does not
occur or is very slow on the NMR time scale.
Rea ction of [Cp (CO)LF e{P (OP h )3}]P F 6 (L ) CO,
P (OP h )3) w ith F -. In any case, products obtained were
extremely moisture-sensitive, and several attempts to
isolate them were unsuccessful (vide infra). The IR data
of the products were somewhat unreliable because of
their high instability. Therefore, the products were
characterized by the NMR measurements of the reaction
mixture alone. Their 31P NMR and 19F NMR data are
given in Table 1.
A cationic iron complex with a triphenyl phosphite
ligand [Cp(CO)2Fe{P(OPh)3}]PF6 (Cp stands for η5-
C5H5) was treated with 5 equiv of Et4NF in CH2Cl2 at
room temperature. The 31P NMR monitoring of the
mixture revealed that the signal assignable to the
starting complex disappeared in a few minutes, and new
signals appeared around 35 ppm. On the basis of the
following discussions, we concluded that the main
Ta ble 1. 31P a n d 19F NMR Da ta a
a
b
In CH2Cl2. At room temperature. c At -80 °C.

Formation of Iron-Phosphorane Complexes
Organometallics, Vol. 18, No. 21, 1999 4313
signals, a doublet of triplets at -34.01 ppm (J ) 1173
and 92 Hz) and a doublet of doublets at 76.44 ppm (J )
1033 and 92 Hz), can be thought to arise from 2, in
which a pseudorotation does not take place. Considering
the great equatophilicity of an OPh and a Cp(CO)2Fe
group (vide infra), it is reasonably concluded that the
doublet of triplets is due to the equatorial F which
couples with P with a coupling constant of 1173 Hz,
corresponding to 1168 Hz observed in the 31P NMR
spectrum, and also with the two apical F’s with a
coupling constant of 92 Hz, and the doublet of doublets
is due to the two apical F’s which couple with P with a
coupling constant of 1033 Hz, corresponding to 1032 Hz
observed in the 31P NMR spectrum, and also with the
equatorial F with a coupling constant of 92 Hz.
On the basis of the 31P and 19F NMR spectra exam-
ined above, it is reasonably proposed that 1 and 2 have
PF4 and P(OPh)F3 fragments, respectively. However, it
is still not clear whether they have a Cp(CO)2Fe
1
fragment or not. Thus, 13C NMR and H NMR spectra
of [Cp(CO)2Fe{P(OPh)3}]PF6 treated with Et4NF in CD2-
Cl2 in a sealed NMR tube were measured. The 13C NMR
spectrum showed two broad doublets at 210.19 ppm
(J CP ) 50.9 Hz) and 211.27 ppm (J CP ) 52.2 Hz). They
are assignable to the terminal carbonyl carbons in the
Cp(CO)2Fe fragment in 1 and 2, respectively, which
couple with a P atom (and probably with F atoms as
well). These P-C coupling constants strongly suggest
that the phosphorus atom is directly bonded to the Cp-
(CO)2Fe fragment both in 1 and in 2. In addition, the
13C NMR spectrum exhibited two signals at 86.30 and
86.17 ppm due to Cp carbons for 1 and 2, respectively.
F igu r e 1. 31P NMR spectrum of the reaction mixture of
[Cp(CO)2Fe{P(OPh)3}]PF6 with 5 equiv of Et4NF in CH2-
Cl2 at room temperature.
1
The H NMR spectrum also showed two intense signals
in a Cp-proton region at 5.24 and 5.20 ppm, which are
assignable to 1 and 2, respectively, together with a few
1
small signals. However, in the 13C NMR and H NMR
spectra, the signals due to the OPh group in 2 were not
assignable because of overlap with the signals due to
free PhO-.
The metallafluorophosphoranes thus formed decom-
pose slowly even under a nitrogen atmosphere at room
temperature, and they are extremely moisture-sensitive.
During the continued stirring of the solution for several
days, the color changed from pale yellow to reddish
yellow, and the Cp-proton signal assignable to a reduced
1
iron complex, [Cp(CO)2Fe]2, appeared in the H NMR
spectrum of the reaction mixture. When the reaction
mixture was exposed to air, the signals due to 1 and 2
disappeared rapidly, while small signals around 115
ppm, which had been also observed before exposure to
air, increased in intensity in the 31P NMR spectrum,
indicating the hydrolysis of the products occurring.
Unfortunately, any effort to isolate the metallafluoro-
phosphoranes from the mixture was in vain. Therefore,
we attempted to estimate the yields of the products
directly from the integrated intensity of the signals in
the NMR spectra. The reaction mixture was homoge-
neous and seemed to have no insoluble material.
However, the signals in the 1H NMR spectrum were not
well resolved, and we could not estimate the exact
yields. Thus, the yields were obtained roughly from the
31P NMR and 13C NMR spectra. The 31P NMR spectrum
revealed that 1 and 2 were generated approximately in
86% total yield, and their formation ratio was about 2:7.
F igu r e 2. 19F NMR spectrum of the reaction mixture of
[Cp(CO)2Fe{P(OPh)3}]PF6 with 5 equiv of Et4NF in CH2-
Cl2. A doublet assignable to PF6- is omitted for simplicity.
(a) At room temperature. (b) At -50 °C.
The 19F NMR spectrum of the reaction mixture shown
in Figure 2a exhibits three main signals, together with
some other weak ones. For the doublet at 20.71 ppm,
the coupling constant (1128 Hz) is the same as that
(1127 Hz) of a quintet at 45.26 ppm in the 31P NMR
spectrum within experimental error. The doublet is thus
assigned to 1, in which a facile pseudorotation around
the phosphorus is taking place. The other two strong

4314 Organometallics, Vol. 18, No. 21, 1999
Kubo et al.
Similarly, the Cp-carbon signals in the 13C NMR
spectrum suggested ca. 80% total yield for them on the
basis of all Cp-containing species. These observations
suggest that 1 and 2 had formed quantitatively with
the accompanying decomposition of the products.
Complexes 1 and 2 were formed from [Cp(CO)2Fe-
{P(OPh)3}]PF6 and F- presumably by several cycles of
nucleophilic attack of F- at the P atom coordinated to
Fe and a sequential elimination of OPh- from the P.
Complex 2 can be thought as an intermediate complex
formed during the course of the formation of 1. Indeed,
the treatment of [Cp(CO)2Fe{P(OPh)3}]PF6 with a greater
excess amount of Et4NF and a longer reaction time led
to almost exclusive formation of 1. It should be noted
that complex 2 is the first example of a phosphorane
with three different monodentate substituents including
a metal fragment.
Recently, Verkade et al. reported fluoride-catalyzed
reduction of Pd(II) to Pd(0)-phosphine complexes, in
which a phosphine ligand coordinated to the Pd center
is oxidized to R3PF2, which is finally converted to Od
PR3.11 In this reaction, a metallafluorophosphorane
intermediate was proposed, although it has not been
detected. Our present results seem to be consistent with
their proposal.
Next we attempted the reaction of [Cp(CO)2Fe-
{P(OMe)3}]PF6, having P(OMe)3 in place of P(OPh)3,
with F- (eq 5). In this reaction, the formation of a
(5)
phosphonate complex, Cp(CO)2Fe{P(O)(OMe)2}, was
confirmed by comparison of its spectroscopic data with
those of the authentic sample, and there was no
evidence that the phosphorus atom was directly at-
tacked by F- to give a pentacoordinate phosphorus
species. In general, a transition-metal complex LnMX
(X ) halogen) reacts with trialkyl phosphite P(OR)3 to
give a cationic phosphite complex, [LnM{P(OR)3}]X, as
an intermediate. Then, X- readily attacks an R-carbon
in the OR group on the phosphorus atom to form a
phosphonate complex LnM{P(O)(OR)2} and RX (the
Arbuzov-like dealkylation reaction).12 Therefore, in the
reaction of [Cp(CO)2Fe{P(OMe)3}]PF6 with F-, F- at-
tacks not a phosphorus atom of the P(OMe)3 ligand but
its methyl carbon, yielding the phosphonate complex.
This reaction seems in general to be an energetically
more favorable process because of greater stability of
the resulting phosphonate complex. However, in the
reaction of [Cp(CO)2Fe{P(OPh)3}]PF6, the formation of
Cp(CO)2Fe{P(O)(OPh)2} is kinetically prevented by a
reluctance of the sp2 ipso-carbon in the Ph group to be
nucleophilically attacked by F-. Instead, F- directly
attacks the phosphorus center to form a pentavalent
species.
The reaction with Et4NF of [Cp(CO)Fe{P(OPh)3}2]PF6
having two phosphite ligands on the iron center was also
examined under conditions similar to those in the
reaction of [Cp(CO)2Fe{P(OPh)3}]PF6 (eq 4). Although
(4)
Rea ction of [Cp (CO)2F e{P (OC6H4NMe)(OC6H4N-
MeH)}]P F 6 w ith F -. We recently reported the synthe-
ses of metallaphosphoranes with two chelate substitu-
ents on the phosphorane phosphorus (eq 2). In contrast,
metallaphosphoranes discussed above have only mono-
dentate substituents on the phosphorus. Then, we
attempted to obtain a metallaphosphorane having one
chelate and two monodentate substituents in addition
to a transition-metal fragment on the phosphorus
center. For this purpose, a readily available phosphite
the reaction mixture contained a considerable amount
of the starting materials even after overnight stirring,
the formation of Cp(CO){P(OPh)3}Fe(PF4) (3) was veri-
fied by the following observations (ca. 30% yield): The
31P NMR spectrum displayed a doublet at 170.02 ppm
(J PP ) 190 Hz) assignable to a P(OPh)3 ligand and a
quintet of doublets at 49.07 ppm (J PF ) 1108 Hz, J PP
)
191 Hz) assignable to a PF4 ligand. The coupling
constant of J PP ) 191 Hz strongly suggests that P(OPh)3
and PF4 ligands are coordinated to the same iron center.
Namely, one of the two P(OPh)3 ligands was converted
into the PF4 group, while the other remained intact.
This observation can be rationally explained as fol-
lows: The nucleophilic substitution of an F atom for an
OPh group may be promoted on a phosphorus atom, if
it has been already substituted by F because of the
accompanying increase in positive charge on the phos-
phorus. Therefore, the subsequent substitution may be
more incident to that phosphorus atom on which the
first nucleophilic attack of the F- had occurred, eventu-
ally to form 3. However, F- may not be so nucleophilic
to attack the remaining P(OPh)3 phosphorus in electri-
cally neutral 3. When the reaction mixture was sub-
jected to prolonged stirring, a decomposition reaction
proceeded with some starting materials remaining.
complex, [Cp(CO)2Fe{P(OC6H4NMe)(OC6H4NMeH)}]-
PF6, which has one O-N chelate on the phosphorus
atom, was chosen as a starting material and treated
with F- (eq 6). The reaction mixture at room tempera-
ture displayed broad signals in the NMR spectra, which
sharpened at low temperature, because of dynamic
behavior of the product (vide infra). Therefore, the NMR
data were collected at -80 °C. The 31P NMR spectrum
of the mixture showed a doublet of doublets at 39.98
ppm (J PF ) 1205, 1010 Hz) as a unique product. Signals
-
due to the inert PF6 were also observed. In the 13C
NMR spectrum, a broad doublet at 212.56 ppm (J CP
)
50.4 Hz) and a broad multiplet at 211.61 ppm were
observed, both of which are assignable to diastereotopic
carbonyl carbons in the Cp(CO)2Fe fragment. The
signals assignable to the carbons in NMe (32.73 ppm,
d, J CP ) 14.3 Hz), Cp (85.96 ppm, s) and aromatic ring
(11) (a) Mason, M. R.; Verkade, J . G. Organometallics 1992, 11,
2212. (b) McLaughlin, P. A.; Verkade, J . G. Organometallics 1999, 17,
5937.
(12) (a) Brill, T. B.; Landon, S. J . Chem. Rev. 1984, 84, 577, and
references therein. (b) Nakazawa, H.; Fujita, T.; Kubo, K.; Miyoshi,
K. J . Organomet. Chem. 1994, 473, 243, and references therein.

Formation of Iron-Phosphorane Complexes
Organometallics, Vol. 18, No. 21, 1999 4315
Sch em e 1. Ber r y’s P seu d or ota tion Mech a n ism
metal fragment in 3 a stronger π donor than in 1.
Recently, we have reported that greater π donacity of a
transition-metal fragment gives a lower magnetic field
shift to a phosphorane phosphorus in the 31P NMR
spectrum.10b The chemical shift of the PF4 group in 3
is, as expected, in a lower magnetic field than that of 1,
suggesting that this trend is general for metallaphos-
phoranes.
(6)
P seu d or ota tion P r ocess a n d Ap icop h ilicity. Re-
arrangement of substituents around the central atom
is one of the unique properties exhibited by pentacoor-
dinate hypervalent compounds. It is widely accepted
that this process proceeds via the Berry’s pseudorotation
mechanism (Scheme 1).14 For complex 1, a very fast
pseudorotation is observed at room temperature, and
thus four F atoms look equivalent on the 31P and 19F
NMR time scale. When a CH2Cl2 solution of 1 is cooled
to -50 °C, broadening of its signal is observed in the
19F NMR spectrum, indicating that the rotation becomes
slower (Figure 2b). For 2, in contrast, the rearrangement
does not take place or is very slow on the NMR time
scale at room temperature. When a toluene solution of
2 was heated to 100 °C, slight broadening of its signals
was observed in both the 31P and 19F NMR spectra with
some decrease in their intensity due to the accompany-
ing decomposition of 2. Thus, a quantitative estimate
of the energy barrier for the pseudorotation could not
be performed. Previous NMR studies on the MePF4 and
Me2PF3 have revealed that the fast rotation takes place
for MePF4, whereas no evidence for such a rotation is
obtained for Me2PF3.15 Such contrasting dynamic be-
havior has been examined theoretically by Wasada et
al. and has been interpreted in terms of site preference
of the substituents on the pentacoordinate phosphorus
as follows:16e an electronegative group prefers an apical
position (apicophilicity), and a less electronegative
group, a group forming a strong covalent bond to
phosphorus, and/or a good π donor group prefer an
equatorial position.16 In the pseudorotation process of
Me2PF3, at least one relatively equatophilic Me group
has to occupy an apical position, which would lead to
the phosphorane to a high-energy state. Therefore, its
rotation process may be hindered. In contrast, a low-
energy barrier is expected for MePF4 because the Me
group can keep a pivotal position during the pseudoro-
tation process and apical and equatorial F atoms can
(107.46 ppm, s; 108.66 ppm, d, J CP ) 9.4 Hz; 119.02
ppm, s; 119.43 ppm, s; 134.65 ppm, d, J CP ) 18.1 Hz;
149.52 ppm, d, J CP ) 11.8 Hz) were also observed. In
1
the H NMR spectrum, a signal assignable to protons
in Cp (5.08 ppm, s) was also observed, although the
signals due to aromatic ring and NMe protons could not
be identified because of overlap with free [OC6H4NHMe]-
and intense NEt4+ signals, respectively. In the 19F NMR
spectrum, two doublets of doublets at -21.20 ppm
(J PF ) 1205 Hz, J FF ) 107 Hz) and at 63.13 ppm (J PF
)
1009 Hz, J FF ) 105 Hz) were observed in equal
-
intensity, together with a doublet assignable to PF6
.
We assigned the former to an equatorial F atom and
the latter to an apical F atom on the basis of the
similarity in chemical shifts to those of 2. In this way,
the formation of the metallaphosphorane Cp(CO)2Fe-
{P(OC6H4NMe)F2} (4) is indicated in which one F atom
is in an apical position and the other F atom is in an
equatorial position. The yield of 4 was estimated as 97%
from the 31P NMR spectrum.
Tr en d s for th e Meta lla flu or op h osp h or a n es in
31P NMR Sp ectr a . The 31P NMR chemical shifts of the
metallafluorophosphoranes reported here are reason-
able when compared with those of the reported metal-
laphosphoranes having a Cp(CO)LFe fragment (L ) CO,
P(OPh)3, P(OMe)3, PMe3).8,10 In 2 and 4, an apical P-F
bond displays a smaller coupling constant than an
equatorial P-F bond. The same trend is also observed
in non-transition-metalated fluorophosphoranes and can
be explained by the intrinsic difference in bond nature
between apical and equatorial bonds. It has been well-
known that the apical bond in a trigonal bipyramidal
structure is weaker and longer than an equatorial bond.
This reflects the difference in the overlap populations
between the two, which has been ascribed to the smaller
3s orbital character in the apical bond than that in the
equatorial bond.13 Therefore, this smaller s character
in the apical bond should give rise to a smaller P-F
coupling constant in the NMR spectra. In this way, the
electronic structure of the transition-metalated phos-
phoranes is understood similarly to that of organic ones.
In complex 3, the iron center has a P(OPh)3 ligand,
which is a more efficient electron donor than CO.
Therefore, 3 should have a greater electron density on
the iron center than 1, which renders the transition-
(14) Berry, R. S. J . Chem. Phys. 1960, 32, 933.
(15) Muetterties, E. L.; Mahler, W.; Schmutzler, R. Irorg. Chem.
1963, 2, 613.
(16) For recent theoretical considerations on apicophilicity and
equatophilicity or equatoriphilicity, see: (a) Deiters, J . A.; Holmes, R.
R.; Holmes, J . M. J . Am. Chem. Soc. 1988, 110, 7672. (b) Mathiew, S.;
Morokuma, K.; Dorigo, A. E. The 1989 International Chemical Congress
of Pacific Basin Societies; Chemical Society of J apan: Tokyo, 1989;
Phys590. (c) Mathiew, S.; Morokuma, K. Annu. Rev. Inst. Mol. Sci.
1990, 18. (d) Wang, P.; Zhang, Y.; Glaser, R.; Reed, A. E.; Schleyer, P.
v. R.; Streitwieser, A. J . Am. Chem. Soc. 1991, 113, 55. (e) Wasada,
H.; Hirao, K. J . Am. Chem. Soc. 1992, 114, 16. (f) Wang, P.; Zhang,
Y.; Glaser, R.; Streitwieser, A.; Schleyer, P. v. R. J . Comput. Chem.
1993, 14, 522.
(13) Strich, A.; Veillard, A. J . Am. Chem. Soc. 1973, 95, 5574, and
references therein.

4316 Organometallics, Vol. 18, No. 21, 1999
Kubo et al.
tube. CH2Cl2 was purified by distillation from P2O5, and
toluene was distilled from sodium benzophenone ketyl, and
they were stored under a nitrogen atmosphere. Et4NF was
obtained from a common commercial source and dried by
azeotropic distillation with CHCl3 three times before use. [Cp-
(CO)2Fe(THF)]PF6,19 [Cp(CO)2Fe{P(OPh)3}]PF6,10a [Cp(CO)2-
exchange their positions readily. The same argument
could be applied to the difference in rotation energy
barriers between 1 and 2. That is, a transition-metal
fragment acts as a good π donor toward a hypervalent
phosphorus center and thus prefers an equatorial posi-
tion, as Martin8a and we10b have revealed. In addition,
Akiba et al. found the high pseudorotation barrier in
some hypervalent antimony species, which was at-
tributed to the great electron donacity and bulkiness of
transition-metal substituents.17 Thus, both Cp(CO)2Fe
and OPh groups, which are more equatophilic groups
than an F atom, are expected to keep equatorial posi-
tions, leading to a high rotation energy barrier in 2. To
date, the pseudorotation process of metalated hyperva-
lent compounds has been examined only for the species
bearing chelate substituents.2a,10b,17 The chelate would
introduce some steric rigidity around the phosphorus
center and make the rotation energy barrier higher.
Therefore, metallaphosphoranes having no chelate sub-
stituent on the phosphorus center could be better probes
to estimate the relative apicophilicity of substituents.
Additional information about the pseudorotation pro-
cess was derived from the NMR study of the metalla-
phosphorane 4. A five-memberd ring generally prefers
to occupy an apical-equatorial position rather than an
equatorial-equatorial position on steric grounds.18 There-
fore, the o-OC6H4NMe chelate preferentially takes an
apical-equatorial position, in which a more equatophilic
nitrogen atom may occupy an equatorial position. The
strong π donor Cp(CO)2Fe group then should be in an
equatorial site. 4 is thus expected to have a high
rotational energy barrier because the two equatophilic
substituents are in equatorial positions as in 2. How-
ever, a CH2Cl2 solution of 4 at room temperature
displays a broad doublet of doublets in the 31P NMR
spectrum, which sharpens at -80 °C. This observation
indicates that the pseudorotation is almost beginning
even at room temperature. The reason for a relatively
low energy barrier for 4 could arise from the F atom
being in an equatorial position; although an F atom is
generally highly apicophilic, one F atom has to take an
equatorial position in 4 because the o-OC6H4NMe che-
late occupies an apical-equatorial position on steric
demand. This electronically unfavorable situation prob-
ably makes the energy barrier lower.
Fe{P(OMe)3}]PF6,20 and [Cp(CO)2Fe{P(OC6H4NMe)(OC6H4-
10b
NMeH)}]PF6 were prepared according to the literature.
A J EOL LA-300 spectrometer was used to obtain 1H NMR,
1
13C NMR, 31P NMR, and 19F NMR spectra. H NMR and 13C
NMR data were referred to SiMe4, as an internal standard.
31P NMR and 19F NMR data were referred to 85% H3PO4 and
CFCl3, respectively, as external standards.
P r epar ation of [Cp(CO)Fe{P (OP h )3}2]P F6. P(OPh)3 (0.60
mL, 2.3 mmol) was added to a solution of [Cp(CO)2Fe(THF)]-
PF6 (450 mg, 1.14 mmol) in CH2Cl2 (6 mL), and the mixture
was refluxed for 14 h. After the volatile components were
removed under reduced pressure, the resulting residue was
dissolved in a small amount of CH2Cl2. Then the CH2Cl2
solution was loaded on a silica gel column and eluted with CH2-
Cl2 and then with acetone. A pale yellow band, which contained
Cp2Fe, was first eluted with CH2Cl2. The second yellow band
that eluted with CH2Cl2/acetone (1:1) was collected, and the
effluent was concentrated to ca. 0.5 mL in vacuo. Addition of
ether resulted in the formation of a pale yellow precipitate,
which was washed with ether several times and dried under
reduced pressure to give a pale yellow powder of [Cp(CO)Fe-
{P(OPh)3}2]PF6 (767 mg, 0.84 mmol, 73% yield). Anal. Calcd
for C42H35F6FeO7P3: C, 55.16; H, 3.86. Found: C, 54.92; H,
3.85. IR (νCO, in CH2Cl2): 2016. 31P NMR (δ, in acetone-d6):
1
158.55. H NMR (δ, in acetone-d6): 4.91 (s, 5H, C5H5), 7.32-
7.50 (m, 30H, OPh). 13C NMR (δ, in acetone-d6): 86.51 (s,
C5H5), 122.36 (s, OPh), 127.63 (s, OPh), 131.80 (s, OPh), 152.15
(t, J CP ) 5.58 Hz, OPh), 212.65 (t, J CP ) 37.54 Hz, CO).
Rea ction s of Ir on -P h osp h ite Com p lexes w ith NEt4F .
Since reactions of iron-phosphite cationic complexes with F-
are basically similar in all cases, the reaction of [Cp(CO)2Fe-
{P(OPh)3}]PF6 with NEt4F is shown as a typical example. A
CH2Cl2 solution (0.83 mL) containing [Cp(CO)2Fe{P(OPh)3}]-
PF6 (106 mg, 0.17 mmol) and NEt4F (124 mg, 0.83 mmol) was
stirred at room temperature for a few minutes. Then, the
resulting reaction mixture was subjected to 31P and 19F NMR
measurements at room temperature and at -50 °C. After
removal of volatile components under reduced pressure from
the CH2Cl2 solution, the products were extracted with toluene
and the toluene solution was subjected to NMR measurements
at 100 °C.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research (Nos. 10440195 and
11740371) and a Grant-in-Aid on Priority Area of
Interelement Chemistry (No. 11120235) from the Min-
istry of Education, Science, Sports and Culture of J apan.
Exp er im en ta l Section
All reactions were carried out under an atmosphere of dry
nitrogen by using Schlenk tube techniques or in a sealed NMR
OM990564F
(17) Yamamoto, Y.; Okazaki, M.; Wakisaka, Y.; Akiba, K. Organo-
metallics 1995, 14, 3364.
(18) Deiters, J . A.; Holmes, R. R. Organometallics 1996, 15, 3944,
and references therein.
(19) Catheline, D.; Astruc, D. Organometallics 1984, 3, 1094.
(20) Nakazawa, H.; Kubo, K.; Tanisaki, K.; Kawamura, K.; Miyoshi,
K. Inorg. Chim. Acta 1994, 222, 123.