Photochemical C-C coupling reaction of an iron acetylide complex [Fe(η5-C5Me5)(CO)2(C≡CPh)] with alk-1-ynes (RC≡CH) leading to cyclic compounds including paramagnetic iron(I) cyclopentadienone complexes [Fe(η5-C5Me 5)(η4-2-Ph-5-R-C5H2O)]

Article abstract of DOI:10.1039/a606836g

Photolysis of [Fe(η⁵-C₅Me₅)(CO)₂(C≡CPh)] with methyl propynoate which bears a coordinating substituent (CO₂Me) affords a metallabicyclic compound incorporating two molecules of the alkyne, whereas the reaction with alk-1-ynes (RC≡CH) bearing a non-coordinating substituent (R = alkyl, Ph, SiMe₃) produces paramagnetic 17e iron(I)-cyclopentadienone complexes [Fe(η⁵-C₅Me₅)(η ⁴-2-Ph-5-R-C₅H₂O)].

Full text of DOI:10.1039/a606836g

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Photochemical C–C coupling reaction of an iron acetylide complex
[Fe(h5-C5Me5)(CO)2(C·CPh)] with alk-1-ynes (RC·CH) leading to cyclic
compounds including paramagnetic iron(i) cyclopentadienone complexes
[Fe(h5-C5Me5)(h4-2-Ph-5-R-C5H2O)]
Munetaka Akita,* Masako Terada and Yoshihiko Moro-oka*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan
Photolysis of [Fe(h5-C5Me5)(CO)2(C·CPh)] with methyl
propynoate which bears a coordinating substituent (CO2Me)
affords a metallabicyclic compound incorporating two
molecules of the alkyne, whereas the reaction with alk-
1-ynes (RC·CH) bearing a non-coordinating substituent
(R = alkyl, Ph, SiMe3) produces paramagnetic 17e iron(I)-
cyclopentadienone complexes [Fe(h5-C5Me5)(h4-2-Ph-
5-R-C5H2O)].
substituent (R) afforded air-stable orange products 3
(R = CH2Ph a, SiMe3 b, Ph c, Bu d, But e) after separation by
alumina column chromatography. The striking features of 3 are
(i) paramagnetism, (ii) loss of the n(C·O) absorption, and (iii)
the appearance of an IR absorption around 1550 cm21 (KBr)
which is assignable to a n(CNO) vibration. Complex 3 has been
characterized as a 17e iron(i) cyclopentadienone complex,
4
[Fe(h-C5Me5)(h -2-Ph-5-R-C5H2O), on the basis of the results
of X-ray crystallography of the SiMe3 and Ph derivatives 3b,c.§
A view of 3c is shown in Fig. 2. The Fe–C(1) distance [2.22(1)
Å] is substantially longer than the Fe–C(2)–(5) distances
[2.090(9), 2.029(9), 2.028(9), 2.075(9) Å; suggesting that the
cyclopentadienone ring C(1)–(5) is coordinated to the Fe centre
C–C coupling reactions of alkynes have been realized by the
action of a transition-metal species.1 One versatile trans-
formation is insertion into an M–C bond leading to oligomeric
or polymeric conjugated systems.2 In a previous paper, we
reported the photochemical dimerization of iron acetylides
[Fe(h-C5Me5)(CO)2(C·CR)] (R = H, Ph), giving dinuclear
complexes with an enyne ligand.3 The study reveals that, when
a C·C group is introduced into the coordination sphere of the
acetylide complex, insertion takes place quite readily. Herein
we disclose photochemical reactions of the phenylacetylide
complex with alk-1-ynes leading to cyclic products including
iron(i) cyclopentadienone complexes.4
4
essentially in an h -mode (3A) [C(1)–C(2) 1.43(1), C(1)–C(5)
1.48(1), C(2)–C(3) 1.42(1), C(3)–C(4) 1.50(1), C(4)–C(5)
4
1.42(1) Å], like an h -diene ligand. However, the considerably
elongated C(1)–O bond [1.26(1) Å] and the lowered wave-
number of the n(CNO) vibration (Scheme 1) are indicative of a
5
minor contribution of the iron(ii) h -cyclopentadienoxyl struc-
ture (3B), where the unpaired electron is localized on the
oxygen atom and the Fe centre attains an 18e configuration. The
cyclopentadienone ring is located virtually parallel to the
C5Me5 ring [Fe–C(C5Me5) 2.06–2.10(1) Å], and the two Ph
groups at the 2 and 5 positions are arranged almost coplanar
with the central five-membered ring to extend the conjugated p
system.
Irradiation of
a benzene solution of [Fe(h-C5Me5)-
(CO)2(C·CPh)] 15 with a high-pressure mercury lamp in the
presence of methyl propynoate (5 equiv.) afforded a red–brown
complex 2 in 31% yield (Scheme 1). The NMR spectrum of the
mononuclear complex 2† showed two MeO signals [dH(CDCl3)
3.74, 3.80] and revealed the incorporation of two molecules of
the alkyne. The bicyclic structure of 2 has been determined by
X-ray crystallography (Fig. 1)‡ and the contribution of a
carbene structure 2B in addition to the dominant resonance
structure 2A is evident as indicated by the structural parameters
as well as the spectroscopic data {dC(C2) 280.7 (s),
n[C(23)NO(3)] 1600 cm21}.
A possible formation mechanism of 2 and 3 is summarized in
Scheme 2. Initial photodecarbonylation followed by coordi-
2
nation of the alk-1-yne gives an h -alkyne intermediate 4.
Subsequent insertion of the C·C moiety into the Fe–C· bond
with the orientation of the substituent directing toward the metal
centre gives an ynenyl species 5. In the case of the reaction with
methyl propynoate, a sequence of (i) further insertion of the
acetylene substrate 6, (ii) insertion of the terminal PhC·C part
into the Fe–C(sp2) bond, and (iii) coordination of the ester CNO
moiety would give 2. On the other hand, the reaction of
In contrast to the reaction with alk-1-yne bearing a coordinat-
ing substituent (CO2R) mentioned above, the photochemical
reaction with alk-1-ynes (RC·CH) bearing a non-coordinating
H
H
Ph
Ph
CO2Me
CO2Me
HC≡CCO2Me
hν / benzene
[Fe(η-C5Me5)(CO)2(C≡CPh)]
(η-C5Me5)Fe
(η-C5Me5)Fe
1
H
H
(CO)
(CO)
O
O
HC≡CR
OMe
2A
OMe
hν / benzene
2B
2 (31%)
H
H
Ph
Ph
O•
H
H
O
R
R
R
Yield (%) ν(C=O) / cm–1
FeI
FeII
3a CH2Ph
3b SiMe3
3c Ph
28
23
60
32
38
1545
1547
1550
1551
1553
3d Bu
3e But
3A
3B
3
Scheme 1
Chem. Commun., 1997
265

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alk-1-yne with a non-coordinating substituent follows CO
insertion of the ynenyl moiety to form the acyl intermediate 7.
Successive ring closure via C·C insertion and H abstraction
from the reaction medium gives the cyclopentadienone complex
3. The reaction pathways may depend on the nucleophilicity of
the a-carbon atom of the ynenyl group in 5 as well as the
coordinating ability of the alk-1-yne substituent (R).
O(1)
C(13)
In summary, a C·C functional group incorporated in a metal
coordination sphere readily inserts into the M–C· bond to form
a conjugated system via C–C coupling. The obtained 17e
species 3, which can be viewed as a dehydrogenated form of the
classical hydroxyferrocene or a paramagnetic counterpart of
well known cyclopentadienone complexes,4 belongs to a rare
class of iron(i) compounds.6 Despite the paramagnetic charac-
ter, 3 is air stable and passes through an alumina column. A
study on the physical properties and reactivity of 3 is now under
way.
C(11)
C(22)
C(14)
C(12)
C(21)
C(2)
O(3)
O(2)
C(1)
Fe
C(23)
O(4)
C(24)
Footnotes
Fig. 1 Molecular structure of 2 with thermal ellipsoids drawn at the 30%
probability level. Selected bond distances (Å): Fe–C(2) 1.922(4), Fe–O(3)
1.995(3), C(2)–C(1) 1.406(6), C(1)–C(11) 1.435(6), C(1)–C(22) 1.451(6),
C(11)–C(12) 1.379(6), C(12)–C(21) 1.428(6), C(21)–C(22) 1.365(6),
C(22)–C(23) 1.427(6), C(23)–O(3) 1.234(5), C(13)–O(1) 1.197(6).
† Selected spectroscopic data for 2: NMR data for the ring: dH(CDCl3) 6.62,
7.64 [d 3 2, J 2 Hz, C(11 H) and C(21 H)]. dC(CDCl3) 280.7 [s, C(2)], 174.1
[s, C(23)], 166.6 [s, C(13)], 155.7 [t, J 7 Hz, C(12)], 148.9 [q, J 4 Hz, C(1)],
131.4, 118.3 [d 3 2, J 164 Hz, C(11) and C(21)], 116.4 [d, J 9 Hz, C(22)].
IR (KBr) n(C·O) 1927, n(CNO) 1703, 1600 cm21
.
‡ Crystallographic data: 2: C27H28FeO5, M = 488.4, triclinic, space group
–
P1, a = 11.190(2), b = 12.181(3), c = 8.812(2) Å, a = 97.60(2),
b = 96.42(2), g = 90.21(2)°, U = 1182.9(5) Å3, Z = 2, Dc = 1.37 g cm23
,
C(4)
C(5)
R(Rw) = 0.046 (0.049) for 2474 unique data with I > 3s(I) and 298
C(3)
variables.
3c:
=
C
26H27FeO,
M
=
=
423.4, monoclinic, space group P21/n,
C(2)
C(1)
Fe
a
11.901(5), b
9.235(6), c = 19.77(1) Å, b = 94.94(4)°,
O
U = 2165(2) Å3, Z = 4, Dc = 1.30 g cm23 R(Rw) = 0.064 (0.065) for 1711
unique data with I > 3s(I) and 262 variables.
3b: C24H31OSiFe,
12.003(3), b
M
=
419.4, monoclinic, space group P21/n,
a
=
=
12.186(3), c 16.258(3) Å, b 104.90(3)°,
=
=
U = 2298(2) Å3, Z = 4, Dc = 1.21 g cm23, R(Rw) = 0.078 (0.081) for 1994
unique data with I > 3s(I) and 186 variables. Atomic coordinates, bond
lengths and angles, and thermal parameters have been deposited at the
Cambridge Crystallographic Data Centre (CCDC). See Information for
Authors, Issue No. 1. Any request to the CCDC for this material should
quote the full literature citation and the reference number 182/320.
§ Slippage of the cyclopentadienone ring is more evident for the SiMe3
derivative 3b [Fe–C(1) 2.29(1), Fe–C(2) 2.09(1), Fe–C(3) 2.014(9), Fe–
C(4) 1.996(9), Fe–C(5) 2.10(1) Å]; however, the relative arrangement of the
ring with respect to the C5Me5 ligand can not be determined satisfactorily
because of the severe disorder of the C5Me5 ligand, which was refined by
using rigid models.
Fig. 2 An overview of 3c with thermal ellipsoids drawn at the 30%
probability level
RC CH
i
References
1
(η-C5Me5)Fe
C CPh
(CO)
1 For leading references, see: Comprehensive Organometallic Chemistry
II, ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford,
1995, vol. 12, ch. 7; J. P. Collman, L. S. Hegedus, J. R. Norton and
R. G. Finke, Principles and Applications of Organotransition Metal
Chemistry, 2nd edn., University Science Book, California, 1987;
G. W. Parshall and S. D. Ittel, Homogeneous Catalysis, 2nd edn., Wiley-
International, New York, 1992.
4
ii
R
H
C
C
(η-C5Me5)Fe
C
2 For polymerization, see C. I. Simionescu and V. Percec, Prog. Polym.
Sci., 1982, 8, 133; T. Masuda and T. Higashimura, Adv. Polym. Sci.,
1986, 81, 121.
(CO)
C
Ph
5
3 M. Akita, S. Sugimoto, M. Terada and Y. Moro-oka, J. Organomet.
Chem., 1993, 447, 103.
v
iii
4 For related hydroxyferrocenes and diamagnetic cyclopentadienone
complexes, see: D. P. Dawson, W. Yongskulrote, J. M. Bramlett,
J. B. Wirht, B. Durham and N. T. Allison, Organometallics, 1994, 13,
3873; C. Slugovc, K. Mauthner, K. Mereiter, R. Schmid and K. Kirchner,
Organometallics, 1996, 15, 2954; K. Mauthner, K. Mereiter, R. Schmid
and K. Kirchner, Organometallics, 1994, 13, 5054 and references
therein.
5 M. Akita, M. Terada, S. Oyama and Y. Moro-oka, Organometallics,
1990, 9, 816. See also: M. Akita and Y. Moro-oka, Bull. Chem. Soc. Jpn.,
1995, 68, 420.
O
C
H
C
Ph
C
C
C
R
H
(η-C5Me5)Fe
C
C
(η-C5Me5)Fe
C
CO2Me
(CO)
C
iv
C
C
MeO2C
H
Ph
6
2
7
vi
3
6 For 19e iron(i) species, see: D. Astruc, Chem. Rev., 1988, 88, 1189. For
organometallic 17e species, see: M. C. Baird, Chem. Rev., 1988, 88,
1217.
Scheme 2 i, Photodecarbonylation and coordination of RC·CH; ii, insertion
of alk-1-yne; iii, insertion of a second molecule of alk-1-yne; iv, insertion of
the PhC·C part and coordination of the ester CNO group; v, CO insertion;
vi, PhC·C insertion and H abstraction
Received, 7th October 1996; Com. 6/06836G
266
Chem. Commun., 1997