Ring opening of (spiro[2.4]hepta-4,6-diene)tricarbonyliron: A revisit

Article abstract of DOI:10.1021/om970703y

(Spiro[2.4]hepta-4,6-diene)tricarbonyliron (2) self-converts to the tethered acyl complex (CO)₂FeC(O)CH₂CH₂(η⁵-C ₅H₄) (3) when refluxed for 1 h in common organic solvents. The reaction of 2 with an external electrophile (CPh₃⁺, H⁺) opens the three-membered ring, resulting in the cation (η⁵-C₅H₄CH₂CH ₂R)Fe(CO)₃⁺ whose structure was determined by spectroscopic methods and confirmed by X-ray analysis of the PPh₃ derivative (η⁵-C₅H₄CH₂CH ₃)Fe(CO)₂(PPh₃)⁺. The reaction of 3 with a strong electrophile (CPh₃⁺, Me⁺) affords the rotationally restricted Fe-(alkoxy)carbene cation (CO)₂Fe=C(OR)CH₂CH₂(η⁵-C ₅H₄)⁺, which can be converted to the Fe-(anilino)carbene cation (CO)₂Fe=C(NHPh)CH₂CH₂(η⁵-C ₅H₄)⁺.

Full text of DOI:10.1021/om970703y

Organometallics 1998, 17, 221-226
221
Rin g Op en in g of
(Sp ir o[2.4]h ep ta -4,6-d ien e)tr ica r bon ylir on : A Revisit
Yuan-Te Fu,† Pei-Chi Chao,† and Ling-Kang Liu*,†,‡
Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China, and
Department of Chemistry, National Taiwan University, Taipei,
Taiwan 10767, Republic of China
Received August 11, 1997X
(Spiro[2.4]hepta-4,6-diene)tricarbonyliron (2) self-converts to the tethered acyl complex
(CO)2FeC(O)CH2CH2(η5-C5H4) (3) when refluxed for 1 h in common organic solvents. The
reaction of 2 with an external electrophile (CPh3+, H+) opens the three-membered ring,
+
resulting in the cation (η5-C5H4CH2CH2R)Fe(CO)3 whose structure was determined by
spectroscopic methods and confirmed by X-ray analysis of the PPh3 derivative (η5-C5H4CH2-
CH3)Fe(CO)2(PPh3)+. The reaction of 3 with a strong electrophile (CPh3+, Me+) affords the
rotationally restricted Fe-(alkoxy)carbene cation (CO)2FedC(OR)CH2CH2(η5-C5H4)+, which
can be converted to the Fe-(anilino)carbene cation (CO)2FedC(NHPh)CH2CH2(η5-C5H4)+.
In tr od u ction
Resu lts a n d Discu ssion
In 1958, Hallam and Pauson1 reported that spiro[2.4]-
hepta-4,6-diene (1) formed only ring-opened dinuclear
complexes upon reaction with Fe(CO)5 at 140 °C, no
mononuclear iron complexes being isolated. In 1968,
Depuy, Kobal, and Gibson2 reported that 1 reacted with
Fe2(CO)9 at room temperature in Et2O to give, in 38%
yield, a compound formulated as the iron tricarbonyl
complex of spiro[2.4]hepta-4,6-diene (2). In 1976, how-
ever, Eilbracht3 revealed that the reported complex (2)
was in actuality the tethered acyl complex (CO)2FeC-
(O)CH2CH2(η5-C5H4) (3). Mechanistically, the existence
of 2 was assumed to be an intermediate in the formation
of 3.
Gen er a tion of 2 by Rea ction of 1 w ith 4. Com-
pound 4 exhibits ν(CO) stretching bands at 2044 (m)
and 1966 (vs) cm-1 in n-hexane at -40 °C.4 When the
solution was warmed to room temperature, these char-
acteristic bands disappeared due to decomposition. An
equimolar mixture of 1 and 4 in n-hexane, after gradual
warming from -60°C to room temperature, shows final
ν(CO) stretching bands at 2047 (s), 1983 (s), 1961 (s)
cm-1, implying a successful transfer of Fe(CO)3 and the
formation of the iron tricarbonyl complex of spiro[2.4]-
hepta-4,6-diene (2) (cf. (η4-C5H6)Fe(CO)3,7 IR(n-hexane)
ν(CO) 2048, 1981, 1974 cm-1).
Self-Con ver sion of 2 to 3. At room temperature
under N2 atmosphere, compound 2 in THF gradually
shows a decrease in the ν(CO) absorption at 2040 cm-1
with an increase at 2020 and 1663 cm-1 (Figure 1).
When an equimolar mixture of 1 and 4 in THF under
N2 atmosphere is warmed from -60°C to room temper-
ature, only 2 is present in solution, as characterized by
the IR ν(CO) bands in Figure 1a. After 13 h, the ν(CO)
bands of 3 are just discernible, Figure 1b. After 112 h,
ν(CO) absorptions due to 3 at 2020, 1964, and 1663 cm-1
are clearly seen, Figure 1c. Comparison of the ν(CO)
intensities in Figures 1a and 1c suggests that the loss
of 2 after 112 h is about 10-20%. Among the solvents
studied, the conversion of 2 to 3 in n-hexane is much
slower than that in CH2Cl2, Et2O, or THF. Compound
2 is soluble in common organic solvents but it is difficult
to purify due to the conversion to 3 and the interference
of cis-C8H14, which is a high boiling impurity (bp 145-
146 °C) originating from 4. If brought to reflux for 1 h,
compound 2 in solution is fully converted to 3, whose
IR ν(CO) stretching bands are shown in Figure 1d.
Compound 3 is not soluble in n-hexane or Et2O but is
soluble in THF and chlorinated solvents.
In 1984, Flecker, Grevels, and Hess4 reported a much
more facile Fe(CO)3 transfer reagent (η2-cis-C8H14)2Fe-
(CO)3 (4), which was demonstrated to transfer a Fe(CO)3
unit effectively to a variety of bidentate ligands in
common organic solvents at or above -35°C. A number
of successful preparations of dieneiron tricarbonyl com-
plexes employing 4 followed in the literature, for
example, the preparation of (2-stannylated butadiene)-
tricarbonyliron5 and (substituted cyclohexadiene)tricar-
bonyliron.6 In order to see if the intermediate 2 could
be detected, the reaction of 1 with the mild Fe(CO)3
transfer reagent 4 was examined; the results are
presented herein.
† Academia Sinica.
‡ National Taiwan University.
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) Hallam, B. F.; Pauson, P. L. J . Chem. Soc. 1958, 646.
(2) DePuy, C. H.; Kobal, V. M.; Gibson, D. H. J . Organomet. Chem.
1968, 13, 266.
(3) (a) Eilbracht, P.; Mayser, U. J . Organomet. Chem. 1977, 135,
C26. (b) Eilbracht, P.; Mayser, U. Chem. Ber. 1980, 113, 2211.
(4) Fleckner, H.; Grevels, F.-W.; Hess, D. J . Am. Chem. Soc. 1984,
106, 2027.
(5) Colson, P.-J .; Franck-Neumann, M.; Sedrati, M. Tetrahedron
Lett. 1989, 30, 2393.
(6) (a) Eilbracht, P.; Hittinger, C.; Kufferath, K. Chem. Ber. 1990,
123, 1071. (b) Eilbracht, P.; Hittinger, C.; Kufferath, K.; Henkel, G.
Chem. Ber. 1990, 123, 1079. (c) Eilbracht, P.; Hittinger, C.; Kufferath,
K.; Schmitz, A.; Gilsing, H.-D. Chem. Ber. 1990, 123, 1089.
Rea ction s of 2 w ith Lew is a n d P r otic Acid s.
Scheme 1 shows a proposed, intramolecular, ionic rear-
(7) Kochhar, R. K.; Pettit, R. J . Organomet. Chem. 1966, 6, 272.
S0276-7333(97)00703-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/19/1998

222 Organometallics, Vol. 17, No. 2, 1998
Fu et al.
F igu r e 2. Molecular plot of 9‚BF4. The thermal ellipsoids
for non-H atoms are plotted at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å): Fe-C1 2.116(4), Fe-C2 2.090(4), Fe-C3
2.074(4), Fe-C4 2.098(4), Fe-C5 2.104(4), Fe-C6 1.777-
(5), Fe-C7 1.774(5), Fe-P 2.2380(15), C1-C8 1.496(7),
C8-C9 1.505(8), C6-O1 1.139(6), C7-O2 1.146(6), P-C11
1.817(4), P-C21 1.839(4), P-C31 1.831(4). Selected bond
angles (deg): P-Fe-C6 91.74(15), P-Fe-C7 94.00(15),
C6-Fe-C7 95.43(21), Fe-C1-C8 129.5(3), C1-C8-C9
110.4(5), Fe-C6-O1 178.5(4), Fe-C7-O2 177.9(4), Fe-
P-C11 110.87(13), Fe-P-C21 115.65(14), Fe-P-C31
117.19(15).
in agreement with the structure of 5 (see Experimental
Section).
The reaction of 2 in CH2Cl2 with electrophilic methyl-
ating reagents, [Me3O+][BF4-], MeSO3CF3, MeI, or
[(MeO)2CH+][PF6-] (from 1:1 [Ph3C+][PF6-]/(MeO)3-
CH),9 produces acyl 3 in part, which is expected in view
of the conversion of 2 to 3, but no [(η5-C5H4CH2CH2-
Me)Fe(CO)3+] [X-] (6‚X, X ) BF4, SO3CF3, I, or PF6) is
formed. With [Me3O+][BF4-], [(η5-C5H4CH2CH3)Fe-
(CO)3+][BF4-] (7‚BF4) is formed,10 and with [Ph3C+]-
[PF6-]/(MeO)3CH, 5‚PF6 is the product.
The reaction of 2 in CH2Cl2 with excess HBF4‚OEt2
yields 7‚BF4 with IR (CH2Cl2) ν(CO) stretching bands
at 2122, 2077, and 2067 cm-1. Cation 7 has a blue shift
of ca. 80 cm-1 from those of 2 in the IR ν(CO) stretching
bands. The 1H NMR data of cation 7 are also consistent
with the structure: the two Cp resonances at δ 5.82 and
5.67 and the tethered ethyl signals at δ 2.52 (q) and
1.28 (t).
F igu r e 1. IR ν(CO) bands of 2 in THF as a function of
time: (a) at 0 h, (b) at 13 h, (c) at 112 h. The IR ν(CO)
bands of 3 are shown in d.
rangement pathway for the conversion of 2 to 3, where
one ring is opened and another joined. The carbonyl
carbon atom plays the role of an electrophile in this
mechanism.8 The ionic pathway is preferred to the also-
plausible homolytic pathway. If indeed ionic, this
intramolecular electrophilic ring-opening process at the
three-membered ring should be in competition with an
intermolecular one by external strong electrophiles.
Compounds 5‚PF6 and 7‚BF4 were collected as pre-
cipitates from the reaction of the respective electrophiles
with 2 prepared in situ in CH2Cl2. To eliminate cis-
C8H14 contamination, compounds 5‚PF6 and 7‚BF4 were
chemically derivatized by stirring equimolar 5‚PF6 (or
7‚BF4) and PPh3; initiation with a drop of Et3N produced
The reaction of 2 in CH2Cl2 with [Ph3C+][PF6-],
included in Scheme 1, produces [(η5-C5H4CH2CH2CPh3)-
Fe(CO)3+][PF6-] (5‚PF6). The Ph3C+ addition opens the
three-membered ring, which in turn effectively changes
the bonding mode of η4-Fe to η5-Fe and the oxidation
96% [Fe(CO)2(PPh3)(η5-C5H4CH2CH2CPh3)+][PF6-] (8‚
-
PF6; or 98% [Fe(CO)2(PPh3)(η5-C5H4CH2CH3)+][BF4
]
(9‚BF4)). A single-crystal X-ray diffraction study of 9‚
BF4 confirms a three-legged piano-stool structure with
an ethyl tether arm on the Cp ring (see Figure 2). With
1
state of Fe from 0 to +2. The H NMR and IR data are
(8) (a) Wong, A.; Pawlick, R. V.; Thomas, C. G.; Leon, D. R.; Liu,
L.-K. Organometallics 1991, 10, 530. (b) Liu, L.-K.; Sun, C.-H.; Yang,
C.-Z.; Wen, Y.-S.; Wu, C.-F.; Shih, S.-Y.; Lin, K.-S. Organometallics
1992, 11, 972. (c) Liu, L.-K.; Eke, U. B.; Mesubi, M. A. Organometallics
1995, 14, 3958.
(9) Bodnar, T. W.; Cutler, A. R. Synth. React. Inorg. Met.-Org.
Chem. 1985, 15, 31.
(10) Me3O+ was noted as a proton source rather than a methylating
source in H2O, see: Webb, M. J .; Stewart, R. P.; Graham, W. A. G. J .
Organomet. Chem. 1973, 59, C21.

(Spiro[2.4]hepta-4,6-diene)tricarbonyliron
Organometallics, Vol. 17, No. 2, 1998 223
Sch em e 1
Et3N initiation, the PPh3 replacement for CO in cations
5 and 7 takes a few seconds to reach completion, due to
an electron-transfer-chain catalytic process.11 Without
Et3N initiation, the PPh3 substitution takes overnight
and the yield is much lower.
CH2(η5-C5H4)+ (12) upon reaction with NH2Ph, in anal-
ogy to the known preparation of Fp-(amino)carbenes
from Fp-(methoxy)carbenes, Fp ) (η5-C5H5)Fe(CO)2.15
In such a transformation, the IR ν(CO) bands are red-
shifted, the shifts being from 2072 and 2028 cm-1 in 11
to 2054 and 2011 cm-1 in 12, giving evidence for more
back-bonding from Fe to the CO ligands in 12. As a
consequence, a cationic Fe-(anilino)carbene is more
stable than a cationic Fe-(methoxy)carbene.16 Crystals
of 12‚PF6 suitable for X-ray diffraction analysis were
grown from MeOH/THF by slow evaporation. A dif-
fraction study confirms the structure of 12‚PF6 (Figure
3). In the reaction of 11 with NHEt2 as detailed
elsewhere,17 the cationic Fe-(diethylamino)carbene
[(CO)2FedC(NEt2)CH2CH2(η5-C5H4)+][BF4-] is obtained.
The IR spectrum of 3 does not change when compound
3 is mixed with 1 equiv of HBF4‚OEt2, suggesting that
there is little Fe-(hydroxy)carbene cation formation.
Interestingly anionic (CO)2ReC(O)CH2CH2(η5-C5H4)-,
the isolobal Re analog of neutral 3, reacts with HBF4‚
OEt2 to give rise to the corresponding neutral Re-
(hydroxy)carbene (CO)2RedC(OH)CH2CH2(η5-C5H4) that
is in equilibrium with the Re-hydride (CO)2(H)-
ReC(O)CH2CH2(η5-C5H4).18 When 3 was added to neat
CF3CO2H, transient IR ν(CO) bands were seen at 2129,
2081, 2042, and 2011cm-1, but the latter two disap-
X-r a y Str u ctu r e of 9‚BF 4. An ORTEP molecular
plot of 9‚BF4 with relevant bond lengths and angles is
given in Figure 2. The cation has a three-legged piano-
stool geometry, as found with [(η5-C5H5)Fe(CO)2(PPh3)+]-
[X-] (X ) C3(CN)5,12 Cl13). The ethyl arm in 9‚BF4
points away from Fe, as indicated by the torsion angle
Fe-C1-C8-C9 of 178.8(6)°, whereby C8 is displaced
by 0.097(9) Å from the Cp plane in the direction opposite
to Fe and C9 is located 1.538(11) Å from the Cp plane.
Rea ction s of 3 w ith Lew is a n d P r otic Acid s. The
reaction of 3 with [Ph3C+][PF6-] in CH2Cl2 yields partial
conversion to the carbene [(CO)2FedC(OCPh3)CH2CH2-
(η5-C5H4)+] [PF6-] (10‚PF6), as judged from the new IR
ν(CO) bands at 2068 and 2024 cm-1. Treatment of 3
with [(MeO)2CH+][PF6-] in CH2Cl2 results in the car-
bene [(CO)2FedC(OMe)CH2CH2(η5-C5H4)+][PF6-] (11‚
PF6); reaction of 3 with [Me3O+] [BF4-] gives the same
-
carbene with a BF4 anion, 11‚BF4 (Scheme 1). It is
reported that the reaction of (η5-C5H5)Fe(CO)2C(O)Me
with a methylating reagent gives rise to the carbene
[(η5-C5H5)Fe(CO)2dC(OMe)Me+][PF6-] (IR (CH2Cl2) ν-
(CO) 2060, 2014 cm-1).14 Compound 3 does not react
with MeI to produce a carbene. Also shown in Scheme
1, the Fe-(methoxy)carbene cation 11 proceeds smoothly
to a Fe-(anilino)carbene cation (CO)2FedC(NHPh)CH2-
(14) (a) Bodnar, T.; LaCrose, S. J .; Cutler, A. R. J . Am. Chem. Soc.
1980, 102, 3292. (b) Bodnar, T.; Cutler, A. R. J . Organomet. Chem.
1981, 213, C31. (c) Brookhart, M.; Tucker, J . R.; Husk, G. R. J . Am.
Chem. Soc. 1981, 103, 979. (d) Casey, C. P.; Miles, W. H.; Tukada, H.;
O’Connor, J . M. J . Am. Chem. Soc. 1982, 104, 3761.
(15) Rueck-Braun, K.; Kuehn, J .; Schollmeyer, D. Chem. Ber. 1996,
129, 937.
(11) Pevear, K. A.; Banaszak Holl, M. M.; Carpenter, G. B.; Rieger,
A. L.; Rieger, P. H.; Sweigart, D. A. Organometallics 1995, 14, 512
and references within.
(16) Petz, W. Iron-Carbene Complexes; Springer-Verlag: Berlin,
Germany, 1993.
(12) Sim, G. A.; Woodhouse, D. I.; Knox, G. R. J . Chem. Soc., Dalton
Trans. 1979, 629.
(13) Riley, P. E.; Davis, R. E. Organometallics 1983, 2, 286.
(17) Fu, Y.-T.; Liu, L.-K. Bull. Inst. Chem., Acad. Sin. 1997, 44, 7.
(18) Casey, C. P.; Czerwinski, C. J .; Hayashi, R. K. J . Am. Chem.
Soc. 1995, 117, 4189.

224 Organometallics, Vol. 17, No. 2, 1998
Fu et al.
Sch em e 2
tionally restricted Re-(methoxy)carbene (CO)2RedC-
(OMe)CH2CH2(η5-C5H4) also shows a bending of the
alkyl tether toward the Re by 9° and a decrease of the
angle between Cp(centroid), the Re atom, and the
carbene C atom (111.8°).18
1
Rota tion a l Isom er s of 12‚P F 6. The H NMR spec-
trum of 12‚PF6 in acetone-d6 indicates the presence of
F igu r e 3. Molecular plot of 12‚PF6. The thermal ellipsoids
for non-H atoms are plotted at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å): Fe-C1 1.769(5), Fe-C2 1.770(5), Fe-C3
1.933(5), Fe-C11 2.084(4), Fe-C12 2.090(4), Fe-C13
2.112(5), Fe-C14 2.108(5), Fe-C15 2.093(5), N-C3 1.296-
(6), N-C21 1.436(5), C1-O1 1.139(6), C2-O2 1.143(6),
C3-C4 1.522(6), C4-C5 1.519(7), C5-C11 1.497(7). Se-
lected bond angles (deg): C1-Fe-C2 94.18(23), C1-Fe-
C3 95.61(20), C2-Fe-C3 96.92(20), C3-N-C21 1278.0(4),
Fe-C1-O1 176.8(4), Fe-C2-O2 176.2(5), Fe-C3-N 131.4-
(3), Fe-C3-C4 115.3(3), N-C3-C4 113.3(4), C3-C4-C5
110.5(4), C11-C5-C4 106.9(4), Fe-C11-C5 114.6(3).
1
two isomers at room temperature. One isomer has H
peaks for the Cp ring protons and the methylene protons
at δ 5.85, 5.44, 3.87, and 2.61 (C3,4, C2,5, CR, Câ), while
the other isomer has peaks at δ 5.79, 5.35, 4.10 and 2.64,
with an integration ratio of 54:46 between the two,
respectively. The numerical atom numbering is applied
to the Cp ring, whereas the Greek letters refer to
positions relative to the carbene C atom. The two
isomers were not assigned to a specific Z- or E-config-
uration (Scheme 2). The FedC bond in resonance with
the planar N atom results in a relatively strong C-N
bond. Due to the restricted rotation around the C-N
bond, (η5-C5H5)(CO)2Fe-(amino)carbene complexes can
usually be obtained as a mixture of rotational isomers
provided that the amino substituents are unsymmetri-
cal; (η5-C5H5)(CO)2FedC(i-Pr)NHPh+ was reported to
have a C-N bond rotational barrier of 77 ( 2 kJ /mol.19
peared within minutes. Attempts to isolate and char-
acterize the protonated 3 species were unsuccessful.
X-r a y Str u ctu r e of 12‚P F 6. Figure 3 shows the
ORTEP plot of 12‚PF6 with relevant bond lengths and
angles. The X-ray structure shows that ring closure
produces a moderately strained system in comparison
with rotationally unrestricted (η5-C5H5)Fe(CO)2 carbene
complexes. The alkyl tether of the Cp ring of 12‚PF6 is
bent down ca. 10° toward Fe (Cp(centroid)-C1-C8 )
170.1(4)°), while in untethered systems, an alkyl arm
on the ring is normally positioned away from the metal
center. The carbene C atom has sp2 bonding, indicated
by the fact that the sum of angles around C10 is 360°.
The interplanar angle between the carbene C and the
neighboring atoms and the planar anilino N and the
neighboring atoms is only 1.1(2)°, indicative of a reso-
nance, indeed, between the carbene C atom and the
attached anilino N atom. The resonance does not
extend to the phenyl group, however. The phenyl group
is positioned far from coplanarity with the carbene plane
or the anilino N plane, the respective interplanar angles
with the phenyl group being ca. 76.9(2)° and 77.0(2)°.
A vertical molecular mirror plane as defined by Fe, Cp-
(centroid), Cipso of the Cp ring, and the midpoint of two
carbonyl C atoms is only 13.3(2)° with the carbene
plane, placing the carbene plane in an approximately
upright position. The C-N bond of 1.296(6) Å suggests
a partial double-bond character. In this regard, the
X-ray structure of 12‚PF6 is in a Z-configuration, the
torsion angle Fe-C10-N-C11 being 2.2(2)°. Ring
strain also narrows the angle between Cp(centroid), the
Fe atom, and the carbene C atom to 117.1(1)°, as
compared to 121.2(2)-124.3(2)° angles in the three-
legged piano-stool (η5-C5H5)FeL3 systems. The rota-
Con clu sion
The iron tricarbonyl complex of spiro[2.4]hepta-4,6-
diene, 2, converts to the tethered acyl 3. Compounds 2
and 3 act differently toward Lewis and protic acids.
Opening of the three-membered ring occurs in the
reaction of 2 with Lewis and protic acids, resulting in
+
compounds with a (η5-C5H4R)Fe(CO)3 fragment. In
contrast, 3 reacts with Lewis and protic acids to form
Fe-carbene compounds.
Exp er im en ta l Section
Gen er a l. All manipulations were performed under an
atmosphere of prepurified nitrogen with standard Schlenk
techniques, and all solvents were distilled from an appropriate
drying agent.20 IR spectra were recorded in CH2Cl2 on a
Perkin-Elmer 882 spectrophotometer. The 1H and 13C NMR
spectra were obtained on Bruker AC200/AC300 spectrometers,
with chemical shifts reported in δ values relative to the
residual solvent resonance of CDCl3 (1H, 7.24 ppm; 13C, 77.0
ppm). FAB mass spectra were obtained on a VG system, model
70-250S spectrometer. Microanalytical data were obtained
with the use of a Perkin-Elmer 240C elemental analyzer
independently operated by the Institute of Chemistry, Aca-
demia Sinica. The melting points were measured on a Yanaco
(19) Fehlhammer, W. P.; Hirschmann, P.; Mayr, A. J . Organomet.
Chem. 1982, 224, 153.
(20) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals; Pergamon Press: Oxford, U.K., 1981.

(Spiro[2.4]hepta-4,6-diene)tricarbonyliron
Organometallics, Vol. 17, No. 2, 1998 225
micro melting point apparatus. Compounds 1 and 4 were
synthesized according to procedures in the literature.4,21 All
reagents including [Me3O+][BF4-], MeSO3CF3, [Ph3C+][PF6-],
and (MeO)3CH were obtained from commercial sources and
used without further purification.
(d ) With [(MeO)2CH+][P F 6-]. A solution of 2 (0.46 g, 2.0
mmol) in CH2Cl2 (10 mL), prepared in situ, was added to a
solution of [(MeO)2CH+][PF6-] in CH2Cl2 (40 mL), prepared
in situ by mixing in CH2Cl2 [Ph3C+][PF6-] (0.78 g, 2.0 mmol)
and (MeO)3CH (0.27 mL, 2.5 mmol). After the mixture was
stirred overnight, the reaction mixture was concentrated to
about 50 mL and diluted with Et2O (150 mL) to obtain a
precipitate, which was washed with sufficient CHCl3. After
recrystallization from CH2Cl2/Et2O, the yellow solid was found
to be 5‚PF6 (0.38 g, 0.62 mmol, 31%) by the following spectro-
scopic data. IR (CH2Cl2) ν(CO): 2122 (s), 2079 (s), 2069 (s)
(η4-Sp ir o[2.4]h ep ta -4,6-d ien e)F e(CO)3 (2). Compound 1
(0.18 g, 2.0 mmol) in THF (10 mL) was slowly added to a
stirred solution of 4 (0.72 g, 2.0 mmol) in THF (100 mL) at
-60 °C. After the mixture was stirred for 2 h at -60 °C, the
solution was gradually warmed to room temperature, giving
2, quantitatively, in solution, which was ready for use in
further reactions. IR (THF) ν(CO): 2039 (s), 1966 (s, br) cm-1
.
cm-1 1H NMR (CD2Cl2): δ 7.35-7.09 (m, 15H), 5.68 (s, 2H),
.
Similar solutions of 2 were prepared in n-hexane and CH2Cl2.
IR (n-hexane) ν(CO): 2047 (s), 1983 (s), 1961 (s) cm-1. IR (CH2-
Cl2) ν(CO): 2040 (s), 1971 (s, br) cm-1. Using CD2Cl2 as the
solvent, the 1H NMR spectrum of 2 was obtained. 1H NMR
(CD2Cl2): δ 5.73 (b, 2H), 2.90 (b, 2H), 0.90 (t, J ) 7.8 Hz, 2H),
0.32 (t, J ) 7.8 Hz, 2H).
5.41 (s, 2H), 2.89 (t, J ) 7.6 Hz, 2H), 2.28 (t, J ) 7.8 Hz, 2H).
[F e(CO)3(η5-C5H4CH2CH3)+][BF 4-] (7‚BF 4). To a solution
of 2 (2.0 mmol) in CH2Cl2 (100 mL), prepared in situ, was
slowly added HBF4‚OEt2 (0.53 g, 6.0 mmol). After the mixture
was stirred overnight, the reaction mixture was concentrated
to about 50 mL and diluted with Et2O (300 mL) to precipitate
7‚BF4, which was recrystallized from MeOH/Et2O as a yellow
solid (0.17 g, 0.52 mmol, 26%). Mp: 203 °C (dec). IR (CH2-
Self-Con ver sion of 2 to (CO)2F eC(O)CH2CH2(η5-C5H4)
(3). A solution of 2 (2.0 mmol) in THF (100 mL), prepared in
situ as described previously, was refluxed for 1 h before the
solvent was removed under vacuum. The dark brown residue
was purified by SiO2 column chromatography, eluting with
ethyl acetate/n-hexane (1:5) to give 3 (0.25 g, 1.1 mmol, 55%)
as a yellow solid after the eluate was dried. IR (CH2Cl2) ν-
Cl2) ν(CO): 2122 (s), 2077 (s), 2067 (s) cm-1 1H NMR (CD2-
.
Cl2): δ 5.82 (s, 2H), 5.67 (s, 2H), 2.52 (q, J ) 7.4 Hz, 2H), 1.28
(t, J ) 7.4 Hz, 3H). 13C{1H} NMR (CD2Cl2): δ 202.2 (CO),
119.0 (Cp, Cipso), 89.2 (Cp), 88.0 (Cp), 21.1 (CH2), 14.1 (Me).
MS: m/ z 233 (cation). Anal. Calcd for C10H9BF4FeO3: C,
37.55; H, 2.84. Found: C, 37.24; H, 2.66.
(CO): 2024 (s), 1966 (s), 1645 (m) cm-1 1H NMR (CDCl3): δ
.
[F e(CO)2(P P h 3)(η5-C5H4CH2CH2CP h 3)+][P F 6-] (8‚P F 6).
A solution of 5‚PF6 (0.28 g, 0.45 mmol) and PPh3 (0.12 g, 0.45
mmol) in CH3CN (30 mL) was treated with a drop of NEt3.
An IR measurement indicated that the transformation was
complete after a few seconds. The solvent was then removed,
and the residue was re-dissolved in a minimum amount of CH2-
Cl2 and diluted with Et2O to precipitate 8‚PF6 (0.37 g, 0.43
mmol, 96%) as a yellow solid. Mp: 203-206 °C (dec). IR (CH3-
5.06 (b, 2H), 4.72 (b, 2H), 3.44 (t, J ) 7.6 Hz, 2H), 2.15 (t, J )
7.6 Hz, 2H); 1H NMR (acetone-d6): δ 5.37 (t, J ) 1.8 Hz, 2H),
4.91 (t, J ) 1.8 Hz, 2H), 3.40 (t, J ) 7.6 Hz, 2H), 2.18 (t, J )
7.6 Hz, 2H) (lit.22 IR (KBr) ν(CO) 2000, 1960, 1940, 1915, 1640,
1620 cm-1 1H NMR (C6D6) δ 5.08 (t, J ) 2 Hz, 2H), 4.72 (t, J
.
) 2 Hz, 2H), 3.46 (t, J ) 7.5 Hz, 2H), 2.17 (t, J ) 7.5 Hz, 2H)).
Anal. Calcd for C10H8FeO3: C, 51.77; H, 3.98. Found: C,
51.68; H, 3.51.
[F e(CO)3(η5-C5H4CH2CH2CP h 3)+][P F 6-] (5‚P F 6). To a
solution of 2 (2.0 mmol) in CH2Cl2 (100 mL), prepared in situ,
was slowly added Ph3C+PF6- (2.33 g, 6.0 mmol) in CH2Cl2 (50
mL). After the mixture was stirred overnight, the reaction
mixture was concentrated to about 50 mL and diluted with
Et2O (300 mL) to precipitate 5‚PF6, that was then recrystal-
lized from CH2Cl2/Et2O as a yellow solid (0.58 g, 0.94 mmol,
47%). Mp: 188 °C (dec). IR (CH2Cl2) ν(CO): 2122 (s), 2079
CN) ν(CO): 2051 (s), 2008 (s) cm-1 31P{1H} NMR (CDCl3): δ
.
61.9. 1H NMR (CDCl3): δ 7.53-7.43 (m), 7.35-7.01 (m), 5.01
(b, 2H), 4.97 (b, 2H), 2.78 (t, J ) 7.9 Hz, 2H), 2.09 (t, J ) 7.9
Hz, 2H). 13C{1H} NMR (CDCl3): δ 209.6 (d, J P-C ) 23.6 Hz,
CO), 146.0 (Cipso, CPh), 132.8 (d, J P-C ) 9.7 Hz, o-C, PPh), 132.3
(p-C, PPh), 130.8 (d, J P-C ) 51.6 Hz, Cipso, PPh), 129.9 (d, J P-C
) 10.4 Hz, m-C, PPh), 129.0 (o-C, CPh), 128.2 (m-C, CPh),
126.3 (p-C, CPh), 111.4 (Cipso, Cp), 89.8 (Cp), 86.9 (Cp),
56.7(CPh), 40.9 (CpCH2CH2), 24.0 (CpCH2CH2). MS: m/ z 710
(cation). Anal. Calcd for C46H38F6FeO2P2: C, 64.65; H, 4.48.
Found: C, 64.94; H, 4.86.
(s), 2069 (s) cm-1 1H NMR (CD2Cl2): δ 7.35-7.09 (m, 15H),
.
5.69 (b, 2H), 5.41 (b, 2H), 2.89 (t, J ) 7.1 Hz, 2H), 2.28 (t, J )
7.1 Hz, 2H). MS: m/ z 475 (cation). Anal. Calcd for
[F e(CO)2(P P h 3)(η5-C5H4CH2CH3)+][BF 4-] (9‚BF 4). A so-
lution of 7‚BF4 (0.26 g, 0.81 mmol) and PPh3 (0.21 g, 0.81
mmol) in CH3CN (50 mL) was treated with a drop of NEt3.
An IR measurement indicated that the conversion was com-
plete after a few minutes; the solvent was then removed, and
the residue was re-dissolved in a minimum amount of MeOH
and diluted with Et2O to precipitate 9‚BF4 (0.44 g, 0.79 mmol,
98%) as a yellow solid. Mp: 186-188 °C. IR (CH3CN) ν(CO):
C
29H23F6FeO3P: C, 56.15; H, 3.74. Found: C, 55.29; H, 3.81.
Rea ction s of 2 w ith Meth yla tin g Rea gen ts. (a ) With
[Me3O+][BF 4-]. To a slurry of [Me3O+][BF4-] (0.89 g, 6.0
mmol) in CH2Cl2 (50 mL) was added a solution of 2 (2.0 mmol)
in CH2Cl2 (100 mL), prepared in situ. After the mixture was
stirred overnight, the reaction mixture was concentrated to
about 10 mL and diluted with Et2O (100 mL) to obtain a
precipitate, which was washed with CHCl3. After recrystal-
lization from MeOH/Et2O as a yellow solid, the compound was
identified to be 7‚BF4 (0.07 g, 0.22 mmol, 11%) based on the
following spectroscopic data. IR (CH2Cl2) ν(CO): 2122 (s), 2077
2052 (s), 2008 (s) cm-1
.
31P{1H} NMR (CDCl3): δ 62.1. 1H
NMR (CDCl3): δ 7.57-7.55 (m, 9H), 7.39-7.31 (m, 6H), 5.26
(b, 2H), 5.03 (b, 2H), 2.42 (q, J ) 7.4 Hz, 2H), 1.18 (t, J ) 7.5
Hz, 3H). 13C{1H} NMR (CDCl3): δ 209.8 (d, J P-C ) 23.6 Hz,
CO), 132.7 (d, J P-C ) 10.3 Hz, o-C, Ph), 132.1 (p-C, Ph), 131.0
(d, J P-C ) 51.5 Hz, Cipso, Ph), 129.7 (d, J P-C ) 10.8 Hz, m-C,
Ph), 113.4 (Cipso, Cp), 89.2 (Cp), 86.0 (Cp), 20.4 (CH2), 13.9 (Me).
MS: m/ z 467 (cation). Anal. Calcd for C27H24BF4FeO2P: C,
58.53; H, 4.37. Found: C, 58.30; H, 4.26. The crystals suitable
for X-ray diffraction analysis were grown from CH2Cl2/n-
hexane by a slow evaporation method.
(s), 2067 (s) cm-1 1H NMR (CD2Cl2): δ 5.82 (s, 2H), 5.67 (s,
.
2H), 2.52 (q, J ) 7.4 Hz, 2H), 1.28 (t, J ) 7.4 Hz, 3H).
(b) With MeI. To a solution of 2 (2.0 mmol) in CH2Cl2 (100
mL), prepared in situ, was added MeI (0.84g, 6.0 mmol). The
mixture was monitored with IR, revealing only a gradual
growth of ν(CO) bands at 2024, 1966, 1645 cm-1 and a
concurrent decrease of bands at 2041 and 1970 cm-1, indicative
of self-conversion of 2 to 3 only.
(c) With MeSO3CF 3. To a solution of 2 (2.0 mmol) in CH2-
Cl2 (100 mL), prepared in situ, was added MeSO3CF3 (0.98 g,
6.0 mmol). The IR ν(CO) bands immediately changed to 2024
(s), 1966 (s), 1645 (m) cm-1, indicative the formation of 3.
Rea ction of 3 a n d P h 3C+P F 6-. To a solution of 3 (0.46 g,
2.0 mmol) in CH2Cl2 (50 mL) was added dropwise a solution
of Ph3C+PF6 (1.55 g, 4.0 mmol) in CH2Cl2 (40 mL). The
-
mixture was stirred for 2 h and was constantly monitored by
IR, revealing the following ν(CO) bands: 2123 (m), 2068 (s),
2024 (s), 1968 (s), 1649 (m) cm-1. The ν(CO) bands at 2068
(s) and 2024 (s) were assigned to [(CO)2FedC(OCPh3)CH2CH2-
(21) (a) Alder, K.; Ache, H.-J .; Flock, F. H. Chem. Ber. 1960, 93,
1888. (b) Wilcox, C. F.; Craig, R. R. J . Am. Chem. Soc. 1961, 83, 3866.
(22) Eilbracht, P. Chem. Ber. 1976, 109, 1429.

226 Organometallics, Vol. 17, No. 2, 1998
Fu et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Refin em en t
(0.78 g, 2.0 mmol) in 50 mL of CH2Cl2. The reaction mixture
was stirred for 1 h and then diluted with Et2O (300 mL) to
yield [(CO)2FedC(NHPh)CH2CH2(η5-C5H4)+][PF6-] (12‚PF6) as
a yellow solid (0.85 g, 1.88 mmol, 94%). Mp: 209-212 °C. IR
-
Deta ils for [F e(CO)2(P P h 3)(η5-C5H4CH2CH3)+][BF 4
]
(9‚BF 4) a n d [(CO)2F edC(NHP h )CH2CH2(η5-C5H4)+]-
[P F 6-] (12‚P F 6)
(CH2Cl2) ν(CO): 2054 (s), 2011 (s) cm-1
.
1H NMR (acetone-
9‚BF4
12‚PF6
d6): δ 7.60-7.34 (m, 10H), 5.85 (t, J ) 1.8 Hz, 2H), 5.79 (t, J
) 1.9 Hz, 2H), 5.44 (t, J ) 1.9 Hz, 2H), 5.35 (t, J ) 1.9 Hz,
2H), 4.10 (t, J ) 7.5 Hz, 2H), 3.87 (t, J ) 7.5 Hz, 2H), 2.64 (t,
J ) 7.5 Hz, 2H), 2.61 (t, J ) 7.5 Hz, 2H). 13C{1H} NMR
(acetone-d6): δ 264.9, 264.1(FedC), 211.4, 211.3 (CO), 141.5,
138.5, 130.3, 130.2, 129.8, 129.7, 126.9, 125.4, 86.8 (Cp), 83.9
(Cp), 83.5 (Cp), 68.1, 63.0, 23.6, 22.5. MS: m/ z 308 (cation).
Anal. Calcd for C16H14F6FeNO2P: C, 42.41; H, 3.11, N 3.09.
Found: C, 42.52; H, 3.13; N, 2.99. The crystals of 12‚PF6
suitable for X-ray diffraction analysis were grown from MeOH/
THF by a slow evaporation method.
X-r a y Str u ctu r e An a lysis. A summary of crystal data and
refinement details for 9‚BF4 and 12‚PF6 is given in Table 1.
Diffraction intensities were measured with background counts
made for one-half the total scan time on each side of the peak.
Three standard reflections, measured after every hour, showed
no significant decrease in intensity during data collection. Data
were corrected for Lorentz-polarization and absorption (em-
pirical ψ corrections). The structures were solved by direct
methods, MULTAN.23 Calculations and full-matrix least-
squares refinements were performed utilizing the NRCVAX
program package.24 All non-H atoms were refined with
anisotropic thermal parameters with all hydrogen atoms fixed
(C-H ) 1.00 Å, N-H ) 0.85 Å) at the anisotropic convergence
stage. Scattering factor curves of Fe, P, F, O, N, C, and H
were taken from ref 25.25
formula
fw
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
C27H24BF4FeO2P
554.10
P21/c
11.0297(24)
17.5912(15)
13.774(7)
70.62(3)
2521.1(14)
4
1135.85
1.460
298
7.1
0.710 69
C16H14F6FeNO2P
453.10
P21/n
10.819(10)
15.769(5)
10.965(4)
70.83(5)
1767.0(18)
4
911.86
1.703
298
10.1
F(000)
D
calc (g cm-3
)
temp (K)
µ (cm-1
)
λ (Mo KR) (Å)
cryst dimens (mm)
2θ (max)
0.710 69
0.44 × 0.22 × 0.09 0.25 × 0.38 × 0.75
50.0
50.0
Nonius CAD-4
θ/2θ
-12 < h < 12,
0 < k < 18,
0 < l < 13
3097
diffractometer
scan mode
data range
Nonius CAD-4
θ/2θ
-12 < h < 13,
0 < k < 20,
0 < l < 16
4432
2673, Io > 2.5σ(Io) 2709, Io > 2.5σ(Io)
yes
0.914-1.000
60
no. of unique reflns
no. of obs
abs corr
transmission factors
total no. of atoms
no. of params
weights
weight modifier
R
yes
0.914-1.000
41
245
326
counting-statistics counting-statistics
0.01
0.040
0.044
1.69
0.01
0.056
0.080
5.20
0.005
10(1)
Ack n ow led gm en t. The authors thank Academia
Sinica and the National Science Council, ROC, for
financial support. Thanks are due to Mr. Yuh-Sheng
Wen for the collection of X-ray diffraction data.
Rw
goodness of fit
max ∆/σ
0.019
γ (2nd ext coeff × 104) 0.3(2)
D-map
highest peak (e Å-3
)
)
0.520
-0.310
1.090
-0.710
deepest hole (e Å-3
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data and refinement details, positional and aniso-
tropic thermal parameters, bond distances and angles, and
torsion angles for 9‚BF4 and 12‚PF6 (15 pages). Ordering
information is given on any current masthead page.
(η5-C5H4)+][PF6-], 10‚PF6. The attempted work-up failed to
yield the desired carbene, only 3 was recovered.
[(CO)2F edC(OMe)CH2CH2(η5-C5H4)+][P F 6-] (11‚P F 6). A
solution of 3 (0.46 g, 2.0 mmol) in CH2Cl2 (10 mL) was added
to a solution of [(MeO)2CH+][PF6-] in CH2Cl2 (40 mL), prepared
in situ according to the procedure described for the attempted
preparation of 6‚PF6. The reaction mixture was stirred for 2
h and then diluted with Et2O (300 mL) to precipitate 11‚PF6
as a yellow solid (0.71 g, 1.81 mmol, 91%). Mp: 119-121 °C.
OM970703Y
(23) Main, P. In Crystallographic Computing 3: Data Collection,
Structure Determination, Proteins and Database; Sheldrick, G. M.,
Krueger, C., Goddard, R., Eds.; Clarendon: Oxford, U.K., 1985; pp
206-215.
(24) Gabe, E. J .; Le Page, Y.; Lee, F. L. In Crystallographic
Computing 3: Data Collection, Structure Determination, Proteins and
Database; Sheldrick, G. M., Krueger, C., Goddard, R., Eds.; Claren-
don: Oxford, U.K., 1985; pp 167-174.
(25) International Tables for X-ray Crystallography; Ibers, J . A.,
Hamilton, W. C., Eds.; Kynoch: Birmingham, U.K. (current distributor
D. Reidel, Dordrecht, The Neitherlands), 1974; Vol. 4, Tables 2.2A and
2.3.1D.
IR (CH2Cl2) ν(CO): 2072 (s), 2028 (s) cm-1
.
1H NMR (CD2-
Cl2): δ 5.67 (2H), 5.26 (2H), 4.55 (3H), 4.06 (2H), 2.71 (2H).
MS: m/ z 247 (cation). Anal. Calcd for C11H11F6FeO3P: C,
33.70; H, 2.83. Found: C,33.13; H, 2.72.
[(CO)2F edC(NHP h )CH2CH2(η5-C5H4)+][P F 6-] (12‚P F 6).
NH2Ph (0.19 g, 2.0 mmol) was added to a solution of 11‚PF6