Photolytic reaction of substituted (ethynyl)benzaldehyde and Fe(CO) 5: Formation of indenone and chelated iron complexes

Article abstract of DOI:10.1016/j.jorganchem.2012.02.032

At 0 °C, photolysis of a hexane solution containing Fe(CO)₅ and 2-(phenylethynyl)benzaldehyde (1) affords a mixture of mononuclear (tricarbonyliron-2-phenylindenone, (2) and binuclear acetylene coupled iron carbonyl complexes [Fe(CO)₃{η⁴-2,4-(C ₆H₄CHO)₂-3,5-(C₆H₅) ₂C₄}Fe(CO)₃], 3, [Fe(CO)₃{ η⁴-2-(η¹-C₆H₄CHO)-4-(C ₆H₄CHO)-3,5-(C₆H₅)₂C ₄}Fe(CO)₂], 4 and [Fe(CO)₃{ η⁴-4-(η¹-2-C₆H₄CHO)-2- (C₆H₄CHO)-3,5-(C₆H₅)₂ C₄}Fe(CO)₂], 5. In compounds 4 and 5, the exocyclic iron atom is η⁴-bonded with the ferracyclopentadiene unit, and it bears two terminal carbonyls. Its 18 electron count is completed by virtue of the aldehydic oxygen atom coordinating to the iron atom. Photolysis of 2-(ferrocenylethynyl)benzaldehyde (6) under similar condition leads to the formation of tricarbonyliron-2-ferrocenylindenone (7) and tetracarbonyl(2- ferrocenyl-3-(2-formylphenyl)maleoyl)iron (8) predominantly.

Full text of DOI:10.1016/j.jorganchem.2012.02.032

Journal of Organometallic Chemistry 712 (2012) 7e14
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Photolytic reaction of substituted (ethynyl)benzaldehyde and Fe(CO)5: Formation
of indenone and chelated iron complexes
,
b,
c
,
a
a
a
b
Pradeep Mathur a
, Badrinath Jha , Abhinav Raghuvanshi , Raj Kumar Joshi , Shaikh M. Mobin
*
a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
b National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
c School of Basic Sciences, Indian Institute of Technology Indore, Khandwa Road, Indore 452017, India
a r t i c l e i n f o
a b s t r a c t
At 0 ꢀC, photolysis of a hexane solution containing Fe(CO)5 and 2-(phenylethynyl)benzaldehyde
(1) affords mixture of mononuclear (tricarbonyliron-2-phenylindenone, (2) and binuclear
acetylene coupled iron carbonyl complexes [Fe(CO)3{
4-2,4e(C6H4CHO)2e3,5-(C6H5)2C4}Fe(CO)3],
3, [Fe(CO)3{ and [Fe(CO)3{
4-2-(h1eC6H4CHO)e4e(C6H4CHO)e3,5-(C6H5)2C4}Fe(CO)2], 4-4-
1-2eC6H4CHO)e2e(C6H4CHO)e3,5-(C6H5)2 C4}Fe(CO)2], 5. In compounds 4 and 5, the exocy-
clic iron atom is
4-bonded with the ferracyclopentadiene unit, and it bears two terminal
carbonyls. Its 18 electron count is completed by virtue of the aldehydic oxygen atom coordi-
nating to the iron atom. Photolysis of 2-(ferrocenylethynyl)benzaldehyde (6) under similar
condition leads to the formation of tricarbonyliron-2-ferrocenylindenone (7) and tetra-
carbonyl(2-ferrocenyl-3-(2-formylphenyl)maleoyl)iron (8) predominantly.
Article history:
Received 8 December 2011
Received in revised form
28 February 2012
a
h
h
4
h
Accepted 28 February 2012
(
h
h
Keywords:
Iron pentacarbonyl
Photolysis
Ferracyclopentadiene
Indenone
Ó 2012 Elsevier B.V. All rights reserved.
Demetallation
1. Introduction
[30]), or a d6 CpML2 fragment (CpFeþ(CO)2 [31,32]). Some excep-
tions occur for the d6 ML5 [Os(NH3)5]2þ fragment, the coordination
Activation of acetylene on transition metal complexes is of
considerable importance [1e3]. Reactions of iron pentacarbonyl
with mono or diacetylenes result in the formation of mononuclear
and/or dinuclear ironcarbonyl complexes along with some acety-
lene coupled and CO inserted organic products [4e12]. In our
previous reports, we have shown the formation of quinones from
the photochemical reaction of different acetylenes using iron
pentacarbonyl [4,5,13,14]. Recently, we have reported the role of
is
coordination is
in the case of CpRe(CO)2 [38]. In such complexes, the two forms can
coexist with a h2 h1 ratio depending on the substituents [39].
h
2 [33,34] and, in the case of the d6 CpReþNO(PR3) fragment, the
h
1 for ketones [35] and 2 for aldehydes [36,37] as
h
/
There are several reports on the method of synthesis of indenone
[40e48]. However, to the best of our knowledge there is no report of
their synthesis using ironpentacarbonyl. Indenones are useful
intermediates [41] in the synthesis of a variety of molecules,
including the C-nor D-homosteroid ring system [49], photochromic
indenone oxides [50], 2,4- and 3,4-disubstituted-1-naphthols [51],
gibberellines [52], indanones [53] and indanes [54], a building block
of many natural products [55]. Use of substituted indenone for the
complex formation with Fe3(CO)12 was first reported by Braye and
Hübel in 1965 [56]. In this communication we report a reaction of 2-
(phenylethynyl)benzaldehyde and 2-(ferrocenylethynyl)benzalde-
hyde with iron pentacarbonyl under photochemical conditions to
form Fe(CO)3 coordinated indenone which underwent oxidative
demetallation to yield the free indenone and demonstrated activa-
tion of acetylene using simple metal carbonyl under facile condition.
iron pentacarbonyl in the formation of
a,b-vinylesters and alkoxy
substituted -lactones under photochemical condition [15]. We
g
have extended our investigation on the effect of formyl group in
ortho phenylethynylbenzaldehyde towards the complex formation
by iron pentacarbonyl. It has been observed that h
2 form of bonding
of the formyl group is preferred when the metallic part [M] is a d10
ML2 fragment (Pt(PR3)2 [16,17], Pd(PR3)2 [18], Ni(PR3)2 [19e21]) or
a C2v d8 ML4 fragment (Os(CO)2(PR3)2 [22], Ru(CO)2(PR3)2 [23,24],
Fe(CO)2(PR3)2 [25]) while the h
1 form is preferred when [M] is a d8
ML3 fragment ( PtCl2(pyridine) [26,27], PtþCH3(PR3)2 [28]), an
octahedral d6 ML5 fragment (RuCOCl(PR3)2, SnCl3 [29], Mn2(CO)9
2. Results and discussion
* Corresponding author. Department of Chemistry, Indian Institute of Technology
Bombay, Powai, Mumbai 400076, India. Tel.: þ91 22 25767180; fax: þ91 22
25767152.
When hexane solution containing 2-(phenylethynyl)benzalde-
E-mail addresses: mathur@iitb.ac.in, mathur@chem.iitb.ac.in (P. Mathur).
hyde (1) and Fe(CO)5 was photolysed under continuous bubbling of
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.032

8
P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
argon at 0 ꢀC for 30 min, formation of compounds 2e5 was
observed (Scheme 1). These compounds were found to be stable in
solid state and characterized by IR and NMR spectroscopy. Suitable
single crystals of 2e5 were grown from hexane/dichloromethane
solvent mixture and their structures were established
crystallographically.
hydrogen atoms (H11 and H9) of another molecule in the
vicinity; the distances O1 to H11, 2.369 Å and O1 to H9, 2.559 Å are
less than the sum of Vander Waals radii of two atoms.
Compounds 3,
tricarbonylferraindene)-
4
and
5
belong to the class of (1,1,1-
complexes [56]. In
p-carbonyliron
compound 3 (Fig. 2), a ferracyclopentadiene ring is formed by the
coupling of two units of 2-(phenylethynyl)benzaldehyde and
insertion of ironcarbonyl. The ring is substituted with formylphenyl
group at 1 and 3ꢁcarbon positions and with phenyl group at 2 and
4ꢁcarbon positions. The ferracyclopentadiene ring is bonded to
another Fe(CO)3 unit in an h4 fashion which is reflected by almost
similar bond distances for C14ꢁC15 ¼1.423(7), C15ꢁC29 ¼ 1.435(7)
and C29ꢁC30 ¼ 1.410(7) in the ring plane. This Fe(CO)3 unit is in
turn bonded to the cyclic Fe through an FeꢁFe bond. One carbonyl
group semi-bridges between Fe1 and Fe2, where Fe1eC1eO1 bond
angle is 159.9(7)ꢀ.
IR spectra of compounds 2e5 show the presence of terminal
carbonyls. In compound 2 the n(C]O) aldehyde peak is shifted from
1691 to 1625 cmꢁ1, which is also observed in tricarbonylcyclo-
pentadienoneiron complexes, indicative of an increased polarity of
the ketonic group.
The molecular structure of compound 2 (Fig. 1) consists of a 2-
phenylindenone ring. The five-membered ring is coordinated to
a Fe(CO)3 unit in an h
4- fashion. A compound similar to 2, has been
synthesised by Braye and Hübel by the thermal reaction of bis(p-
chlorophenyl)acetylene with Fe3(CO)12 [56], however, its crystal
structure was not established. It is suggested that the phenyl ring of
the indenone retains its aromaticity as the tricarbonylironindenone
does not participate in DielseAlder cycloaddition reaction. Unequal
CeC bond lengths of the phenyl ring of the indenone unit of 2
ORTEP diagrams of compound 4 and 5 as have shown in Figs. 3
and 4 respectively show them to be chelated iron complexes and
isomers. The infrared spectra of these compounds show an addi-
tional n
(C]O) peak at 1729 and 1720 cmꢁ1 respectively. The fer-
(C5eC10
¼
1.422(2), C5eC6
¼
1.424(2), C6eC7
¼
1.342(3),
racyclopentadiene ring is bonded to two formylphenyl groups at 2
and 4ꢁcarbon positions and to two phenyl groups at 3 and
5ꢁcarbon positions. This ferracyclopentadiene ring is coordinated
in h4 fashion to another Fe(CO)2 unit. In both compounds, the
oxygen atom of one of the formylphenyl unit coordinates to the
C7eC8 ¼ 1.429(3), C8eC9 ¼ 1.348(3), C9eC10 ¼ 1.424(2) Å) indi-
cates a partial localization of p-electron density in phenyl ring. Also,
the CO of indenone is found 7.5ꢀ above the plane of indenone ring.
This is probably due to weak interaction of oxygen (O1) with CeH
Scheme 1. Photolysis of 2-(phenylethynyl)benzaldehyde with Fe(CO)5.

P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
9
Fig. 1. ORTEP diagram of compound 2 with 50% probability ellipsoids. Selected bond
lengths (Å) and bond angles (deg): C1eC5
¼
1.477(2), C1eC12
1.342(3), C7eC8
¼
1.482(2),
1.429(3),
C5eC10 1.422(2), C5eC6 1.424(2), C6eC7
¼
¼
¼
¼
C8eC9 ¼ 1.348(3), C9eC10 ¼ 1.424(2), C10eC11 ¼ 1.425(2), C11eC12 ¼ 1.439(2),;
O2eC2eFe1
¼
177.85(19), O3eC3eFe1
¼
178.01(18), O4eC4eFe1
¼
178.6(2),
C5eC10eC11 ¼ 108.03(15), C10eC11eC12 ¼ 108.79(15), C11eC12eC1 ¼ 107.96(15),
C5eC1eC12 ¼ 103.89(14), C10eC5eC1 ¼ 109.09(15).
Fig. 3. ORTEP diagram of compound 4 with 50% probability ellipsoids. Selected bond
exocyclic iron atom whereas in 4 the coordinated formylphenyl
substituent in the ferracyclopentadiene unit is adjacent to the iron
atom in the ring, in 5, it is at position 4. It is known that the mode of
bonding of the aldehydic group as h1 or h2 depends on electronic
lengths (Å) and bond angles (deg): Fe1eC3
¼
1.764(4), Fe1eC2
¼
1.784(4),
Fe1eO1 ¼ 1.991(2), Fe1eC13 ¼ 2.066(3), Fe1eC14 ¼ 2.119(3), Fe1eC28 ¼ 2.162(3),
Fe1eC29 ¼ 2.067(3), Fe1eFe2 ¼ 2.4916(7), Fe2eC13 ¼ 1.952(3), Fe2eC29 ¼ 1.972(3),
O1eC1 ¼ 1.234(4), O7eC21 ¼ 1.209(4), C13eC14 ¼ 1.445(4), C14eC28 ¼ 1.429(5),
C28eC29 ¼ 1.423(5), C1eC7 ¼ 1.429(6), C7eC12 ¼ 1.408(5), C12eC13 ¼ 1.467(5);
environment around the metal atom; h
1 being preferred when the
C1eO1eFe1
O2eC2eFe1
O5eC5eFe2
C14eC13eFe2
¼
¼
¼
130.1(2), O1eC1eC7
176.3(4), O3eC3eFe1
177.8(4), O6eC6eFe2
¼
128.6(3), O7eC21eC22
169.4(3), O4eC4eFe2
175.6(3), C13eFe2eC29
¼
¼
124.9(4),
175.6(3),
80.26(13),
metal fragment to which it is bonded has electron withdrawing
capabilities [57]. The CO bonded iron centre is sufficiently electron
withdrawing in nature favouring h1 coordination of aldehydic
group and this is also supported by the crystal structure where
there is no significant difference between the bond lengths of free
and the coordinated aldehydic CeO bond.
¼
¼
¼
¼
116.9(2), C28eC14eC13
¼
111.9(3), C29eC28eC14
¼
113.1(3),
C28eC29eFe2 ¼ 116.1(2), Fe2eFe1eO1 ¼ 124.2(8).
not a
p acceptor like carbonyl, electron density is more on the
In compound 3, the formyl group is not coordinated to the
exocyclic iron and one of the carbonyl groups semi-bridges
exocyclic iron which in turn increases the electron density on the
endocyclic iron atom. Therefore, the semibridging character is less
between two iron atoms. Since aldehydic oxygen is a
s donor and
Fig. 4. ORTEP diagram of compound 5 with 30% probability ellipsoids. Solvent mole-
cule is removed for clarity. Selected bond lengths (Å) and bond angles (deg):
Fe1eO1 ¼ 2.002(5), Fe1eC2 ¼ 1.770(8), Fe1eC3 ¼ 1.768(7), Fe1eC13 ¼ 2.118(5),
Fe1eC14 ¼ 2.110(6), Fe1eC28 ¼ 2.080(6), Fe1eC29 ¼ 2.123(5), Fe1eFe2 ¼ 2.5063(12),
Fe2eC14 ¼ 1.939(5), Fe2eC28 ¼ 1.988(6), O1eC1 ¼ 1.230(8), O7eC21 ¼ 1.195(7),
Fig. 2. ORTEP diagram of compound 3 with 30% probability ellipsoids. Solvent mole-
cule is removed for clarity. Selected bond lengths (Å) and bond angles (deg):
Fe1eC1 ¼ 1.780(6), Fe1eC29 ¼ 2.162(5), Fe1eC30 ¼ 2.100(5), Fe1eC14 ¼ 2.119(5),
Fe1eC15 ¼ 2.154(5), Fe1eFe2 ¼ 2.4902(12), Fe2eC1 ¼ 2.357(7), Fe2eC14 ¼ 1.985(6),
Fe2eC30 ¼ 1.967(5), C14eC15 ¼ 1.423(7), C15eC29 ¼ 1.435(7), C29eC30 ¼ 1.410(7);
C13eC14
¼
1.393(7),
C13eC29
¼
1.428(8),
C28eC29
¼
1.454(7);
124.1(4),
173.5(6),
177.2(6),
112.5(5),
O1eC1eFe1
O3eC3eFe1
O6eC6eFe2
C30eFe2eC14
¼
¼
¼
159.9(7), O1eC1eFe2
176.2(6), O4eC4eFe2
178.9(8), C1eFe1eFe2
80.2(2), C15eC14eFe2
¼
¼
¼
127.6(6), O2eC2eFe1
175.1(8), O5eC5eFe2
64.5(2), C1eFe2eFe1
¼
¼
176.7(6),
178.8(8),
C1eO1eFe1
¼
133.1(5),
87.39(19),O2eC2eFe1
177.5(7), O5eC5eFe2
C12eC13eFe1
¼
O1eFe1eC13
O4eC4eFe2
C14eC13eC29
¼
¼
¼
175.7(7), O3eC3eFe1
176.0(7), O6eC6eFe2
117.4(4), C13eC29eC28
¼
¼
42.96(16),
¼
¼
¼
¼
117.0(4), C14eC15eC29
¼
111.1(5),
¼
114.0(5), C13eC14eFe2
¼
¼
C30eC29eC15 ¼ 115.0(4), C29eC30eFe2 ¼ 115.7(4).
C29eC28eFe2 ¼ 114.0(5), C14eFe2eC28 ¼ 81.1(2), Fe2eFe1eO1 ¼ 145.4(15).

10
P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
Scheme 2. Photochemical formation of [Fe(CO)3{ h h h
4-2-(h1eC6H4CHO)e4e(C6H4CHO)e3,5-(C6H5)2C4}Fe(CO)2], 4 and [Fe(CO)3{ 4-4-( 1-2eC6H4CHO)e2e(C6H4CHO)e3,5-(C6H5)2
C4}Fe(CO)2], 5 from [Fe(CO)3{ h
4-2,4e(C6H4CHO)2e3,5-(C6H5)2C4}Fe(CO)3], 3.
Scheme 3. Photolysis of 2-(ferrocenylethynyl)benzaldehyde with Fe(CO)5.
Scheme 4. Demetallation of irontricarbonylindenones to respective indenones.
in compounds 4 and 5. Further, in compound 4, Fe2eFe1eO1 bond
angle is 124.2(8)ꢀ whereas in compound 5, Fe2eFe1eO1 bond
angle is 145.4(1)ꢀ. In compound 5, the aldehydic oxygen is more
trans to endocyclic iron compared to compound 4, and therefore,
the carbonyl group (C3eO3) in 5 has more terminal character
(Fe1eC3eO3 ¼ 173.5(6)ꢀ) compared to compound 4 (bond angle
Fe1eC3eO3 ¼ 169.4(3)ꢀ).
along with two other minor products, formed in insufficient
amounts to enable characterization. (Scheme 2).
Photolysis of 2-(ferrocenylethynyl)benzaldehyde (6) and
Fe(CO)5 under similar condition results in a mixture of two prod-
ucts, (tricarbonyl(2-ferrocenylindenone)iron)
7
and (tetra-
carbonyl(3-ferrocenyl-4-(2-formylphenyl)maleoyl)iron) 8, a ferrole
derivative (Scheme 3). Usually, it has been observed that ferrole
derivative forms when any acetylene containing compound is
photolysed in presence of ironpentacarbonyl in hexane solution
[5,58]. ORTEP diagram of compounds 7 and 8 are shown in Figs. 5
and 6 respectively.
Compounds
4 and 5 are considered to be formed from
compound 3 by loss of one carbonyl group from Fe2(CO)6 unit. To
confirm this, we photolyzed hexane solution of compound 3 in
inert atmosphere, which gives a mixture of compounds 4 and 5,

Table 1
Crystal data and structure refinement parameters for compounds 2, 3, 4, 5, 7 and 8.
Compound
2
3.CH2Cl2
4
5.CH2Cl2
7
8
Empirical formula
Formula wt.
Crystal system
Spacegroup
a, Å
C
18H10FeO4
C37H20Cl2Fe2O8
775.13
Monoclinic
P 21/c
9.2635(6)
14.6879(9)
25.803(2)
90
92.373(6)
90
3507.8(4)
4
1.468
1.030
1568
C35H20Fe2O7
664.21
Orthorhombic
P 21 21 21
8.2853(2)
16.2348(5)
21.1882(6)
90
C36H22Cl2Fe2O7
749.14
Triclinic
C22H14Fe2O4
454.03
Triclinic
P-1
6.3970(2)
6.8058(4)
20.5310(8)
91.002(4)
95.004(3)
93.280(4)
C25H14Fe2O7
538.06
Monoclinic
P 21/n
9.1172(3)
24.5770(6)
9.6731(2)
90
96.344(2)
90
2168.39(10)
4
1.648
1.384
1088
346.11
Monoclinic
P 21/c
6.5965(2)
12.3155(3)
18.3500(5)
90
94.747(2)
P-1
11.5919(10)
11.7133(14)
12.6860(16)
105.575(11)
90.579(9)
99.400(9)
1634.3(3)
2
b, Å
c, Å
a
, deg
, deg
, deg
b
90
90
g
90
Volume, Å3
Z
1485.63(7)
4
1.547
1.032
2850.03(14)
4
1.548
1.070
888.76(7)
2
1.697
1.659
Dcalcd, Mg/m3
Abs coeff, mmꢁ1
F(000)
1.522
1.100
760
704
1352
460
Crystal size, mm
0.28 ꢂ 0.23 ꢂ 0.18
3.31 to 25.00
ꢁ7<¼h<¼7, ꢁ14<¼
k<¼14, ꢁ21<¼n<¼21
10626/2611 [R(int) ¼
0.0198]
0.33 ꢂ 0.28 ꢂ 0.23
3.45 to 25.00
ꢁ11<¼h<¼10, ꢁ17<¼
k<¼17, ꢁ30<¼l<¼29
28184/6155 [R(int) ¼
0.0527]
0.33 ꢂ 0.28 ꢂ 0.23
3.36 to 25.00
ꢁ9<¼h<¼9, ꢁ19<¼
k<¼19, ꢁ24<¼l<¼25
23481/5003 [R(int) ¼
0.0634]
0.23 ꢂ 0.18 ꢂ 0.13
3.34 to 25.00
ꢁ13<¼h<¼13, ꢁ13<¼
k<¼13, ꢁ15<¼l<¼10
11279/5612 [R(int) ¼
0.0527]
0.33 ꢂ 0.29 ꢂ 0.26
3.27 to 25.00
ꢁ7<¼h<¼6, ꢁ7<¼
k<¼8, ꢁ23<¼l<¼24
6143/3129 [R(int) ¼
0.0271]
0.31 ꢂ 0.28 ꢂ 0.23
3.27 to 25.00
ꢁ9<¼h<¼10, ꢁ28<¼
k<¼29, ꢁ11<¼l<¼11
17199/3810 [R(int) ¼
0.0514]
q
range, deg
Index ranges
Reflections collected/unique
Completeness to
q
¼ 25
99.8%
2611/0/208
1.063
99.7%
6155/0/442
1.071
99.6%
5003/0/397
0.982
97.7%
5612/0/424
0.852
99.8%
3129/0/253
1.100
99.8%
3810/0/307
0.966
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole
s
(I)]
R1 ¼ 0.0243, wR2 ¼ 0.0674
R1 ¼ 0.0305, wR2 ¼ 0.0687
0.241 and ꢁ0.152 e.Aꢁ3
R1 ¼ 0.0748, wR2 ¼ 0.2267
R1 ¼ 0.1033, wR2 ¼ 0.2386
0.737 and ꢁ0.446 e.Aꢁ3
R1 ¼ 0.0349, wR2 ¼ 0.0790
R1 ¼ 0.0427, wR2 ¼ 0.0807
0.599 and ꢁ0.229 e.Aꢁ3
R1 ¼ 0.0633, wR2 ¼ 0.1551
R1 ¼ 0.1320, wR2 ¼ 0.1727
0.683 and ꢁ0.693 e.Aꢁ3
R1 ¼ 0.0719, wR2 ¼ 0.2162
R1 ¼ 0.0770, wR2 ¼ 0.2196
2.902 and ꢁ0.632e.Aꢁ3
R1 ¼ 0.0335, wR2 ¼ 0.0664
R1 ¼ 0.0535, wR2 ¼ 0.0697
0.409 and ꢁ0.277 e.Aꢁ3

12
P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
At room temperature, stirring of compounds 2 and 7 in
dichloromethane in presence of diiodine (1 h) results in quantita-
tive formation of the previously reported indenone compound 9
[59] and new ferrocenyl derivative, 10 respectively (Scheme 4). The
demetallated product was confirmed by IR and 1H NMR spectros-
copy. The IR spectra of these compounds (9 and 10) show absence
of metal carbonyl peaks as well as large shift in cyclic n(CO).
3. Conclusion
In conclusion, we have demonstrated a one step photochemical
synthesis of phenyl and ferrocenyl substituted tricarbonylir-
onindenone complexes and their clean conversion to respective
indenones. We have seen that ferrocenyl substituted ortho ethy-
nylbenzaldehyde gives higher yield of indenoneironcarbonyl
compared to phenyl substituted one. In case of phenyl substituted
ortho ethynylbenzaldehyde intermolecular coupling is preferred
over intramolecular coupling.
Fig. 5. ORTEP diagram of compound 7 with 50% probability ellipsoids. Selected bond
lengths (Å) and bond angles (deg): Fe1eC6
¼
2.049(5), Fe1eC7
¼
2.121(5),
Fe1eC5 ¼ 2.147(4), Fe1eC12 ¼ 2.178(5), Fe1eC1 ¼ 2.399(5), C1eC12 ¼ 1.471(7),
C1eC5
C7eC8
C11eC12
¼
¼
1.490(6), C5eC6
1.437(7), C8eC9
¼
1.443(7), C6eC7
1.364(7), C9eC10
¼
¼
1.417(7), C7eC12
1.432(7), C10eC11 ¼ 1.341(7),
¼
1.435(7),
¼
4. Experimental
¼
1.433(7); C4eFe1eC2
102.0(2), O2eC2eFe1
178.9(5), C12eC1eC5
¼
97.7(2), C4eFe1eC3
178.4(5), O3eC3eFe1
104.1(4), C6eC5eC1
¼
¼
¼
91.6(2),
178.1(5),
107.8(4),
C2eFe1eC3
O4eC4eFe1
¼
¼
¼
¼
4.1. General procedures
C7eC6eC5 ¼ 108.9(4), C6eC7eC12 ¼ 108.2(4), C7eC12eC1 ¼ 108.8(4).
All reactions and manipulations were performed using standard
Schlenk line techniques under an inert atmosphere of pre-purified
nitrogen or argon. Solvents were purified, dried and distilled under
argon or nitrogen atmosphere prior to use. Infrared spectra were
recorded on Nicolet 380 FTIR spectrometer. NMR spectra were
recorded on Varian VXR-300S and Bruker AVANCEIII/400 spec-
trometer with TMS as internal standard. Ferrocenylacetylene was
prepared by established procedure [60]. Iron pentacarbonyl, phenyl
acetylene and 2-bromobenzaldehyde were purchased from Fluka,
Aldrich and Spectrochem, respectively, and were used without
further purification. Photochemical reactions were carried out in
a water cooled double-walled quartz vessel having a 125 W
mercury lamp manufactured by SAIC. TLC plates were purchased
from Merck (20 ꢂ 20 cm, silica gel 60 F254). 2-(phenylethynyl)
benzaldehyde and 2-(ferrocenylethynyl)benzaldehyde were
prepared by cuprous iodide free Sonogashira coupling [61,62].
4.2. Crystal structure determination
Suitable X-ray quality crystals of compounds 2 to 5, 7 and 8 were
grown by slow evaporation of n-hexane and dichloromethane
solution at 0 ꢀCe5 ꢀC, and X-ray crystallographic data were
collected. Oxford Diffraction X caliber-S, CCD system equipped with
area detector was used for the cell determination and intensity data
collection for compounds. Monochromatic Mo
(0.71359 Å) was used for the measurements. Absorption correc-
tions using multi -scans were applied. Structures were solved by
direct methods (SHELXS) and refined by full-matrix least squares
against Fo2 using SHELXL-97 software [63]. Non-hydrogen atoms
were refined with anisotropic thermal parameters. All hydrogen
atoms were geometrically fixed and allowed to refine using a riding
model. The crystal and refinement data are summarized in Table 1.
Ka radiation
Fig. 6. ORTEP diagram of compound 8 with 50% probability ellipsoids: Selected bond
lengths (Å) and bond angles (deg): Fe1eC1 2.015(3), Fe1eC2 2.015(3),
j
¼
¼
C1eC15 ¼ 1.511(4), C2eC14 ¼ 1.506(4), C14eC15 ¼ 1.336(4), C1eFe1eC2 ¼ 82.31(11),
C15eC1eFe1
C14eC2eFe1
O5eC5eFe1 ¼ 177.1(3), O6eC6eFe1 ¼ 177.4(3).
¼
¼
113.4(2), C14eC15eC1
112.43(19), O3eC3eFe1
¼
114.8(2), C15eC14eC2
175.2(3), O4eC4eFe1
¼
¼
116.8(2),
178.3(3),
¼
The yield of tricarbonyl(2-ferrocenylindenone)iron 7 (22%) is
much higher than its phenyl analogue (9%). Possibly the steric
crowding due to ferrocene prevents two molecules to come
together and hence prevent the formation of ferracyclopentadiene
ring, as we have observed in the case of phenyl substituted prod-
ucts. Thus ferrocenyl substituted reactant prefers intramolecular
CeC bond formation while in phenyl substituted reactant inter-
molecular CeC bond formation competes with the intramolecular
CeC bond formation.
4.3. General procedure for photolysis of ironpentacarbonyl and 2-
(phenylethynyl)benzaldehyde and 2-(ferrocenylethynyl)
benzaldehyde
4.3.1. Photolysis of 2-(phenylethynyl)benzaldehyde with Fe(CO)5
To
a solution of 2-(phenylethynyl)benzaldehyde (410 mg,
2.04 mmol), in dry hexane (60 mL), Fe(CO)5 (0.4 mL, 2.92 mmol) was
added and the mixture was photolysed at 0 ꢀC for 30 min. The solvent
was removed under reduced pressure, and the residuewas subjected to

P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
13
a chromatographic workup on silica gel TLC plates using dichloro-
121.17e136.19
(aromatic),
143.35(C¼CPh),
144.95(C¼CPh),
methane/hexane solvent mixtures as eluent, which afforded 105 mg of
unreacted 2-(phenylethynyl)benzaldehyde along with compound 2
(45 mg, 9%), 3 (97 mg, 20%), 4 (74 mg, 16%), 5 (52 mg, 11%).
198.81(CO); mþ1/z ¼ 207.14; % C ¼ 88.09, % H ¼ 5.21.
Compound 10: Green solid; IR (
NMR (
n
C ¼ O in KBr, cmꢁ1): 1712 (s); 1H
d
in ppm, CDCl3): 4.1e4.8 (m, 9H, C5H5 and C5H4), 6.9e7.5 (m,
3H, aromatic), 7.6(s, 1H, C]CH), 7.81(d, 1H, o-H to C]O); 13C NMR
(d, CDCl3): 67.7e77.5(C5H5 and C5H4), 121e137.7 (6C, aromatic
4.3.2. Photolysis of 2-(ferrocenylethynyl)benzaldehyde with
Fe(CO)5
carbon), 138.2 (C¼CFc), 145.5(C¼CFc), 196.7 (CO); mþ1/z ¼ 315.06;
To a solution of 2-(ferrocenylethynyl)benzaldehyde (240 mg,
0.76 mmol), in dry hexane (60 mL), Fe(CO)5 (0.2 mL,1.46 mmol) was
added and the mixture was photolysed at 0 ꢀC for 30 min. The
solvent was removed under reduced pressure, and the residue was
subjected to a chromatographic workup on silica gel TLC plates by
using dichloromethane/hexane solvent mixtures as eluent, which
afforded 38 mg of unreacted 2-(ferrocenylethynyl)benzaldehyde
along with compound 7(62 mg, 22%) and 8(24 mg, 7%).
% C ¼ 72.11, % H ¼ 4.78.
Acknowledgments
P.M. and R.K.J (DST-Fast Track Young scientist) are grateful to the
DST, Government of India for research Grant. B.J. is grateful to UGC,
Government of India and A.R. is grateful to CSIR, Government of
India for research fellowships.
4.3.3. General procedure for demetallation of 2-(phenylethynyl)
benzaldehyde and 2-(ferrocenylethynyl)benzaldehyde
Appendix A. Supplementary material
0.1 mmol of compound was taken in 20 mL dichloromethane. To
this solution 0.2 mmol of diiodine was introduced and stirred for
60 min. Reaction mixture was worked up using sodium thio-
sulphate solution in water to remove excess diiodine. Product was
collected in dichloromethane, dried over sodium sulphate. The
solvent was removed under reduced pressure. (Yield of 9 is 19 mg,
91% and yield of 10 is 29 mg, 94%.)
CCDC 825969(2), 825970(3), 825971(4), 825972(5), 825968(7),
and 825973(8) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre. CCDC
nos. 825969, 825970, 825971, 825972, 825968, and 825973 for
compounds 2, 3, 4, 5, 7 and 8 respectively. Copies of this informa-
tion may be obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 IEZ, UK (Fax: þ44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
5. Analytical data
Compound 2:Orange solid; IR (
n
C ¼ O in hexane, cmꢁ1) 2050 (s),
1992 (m), 1974 (s), 1625 (s); 1H NMR (
d in ppm, CDCl3): 6.52, 7.22 to
8.01; 13C NMR (
d
in ppm, CDCl3): 67.5 (CH-Cph), 91.2 (CPh),
References
102.7(C¼CeC¼O), 123.0 to 132.5 (aromatic carbons), 167.2 (cyclic
C]O), 209.4(FeeCO); % C ¼ 62.94, % H ¼ 3.01.
[1] I. Cano, E. Álvarez, M.C. Nicasio, P.J. Pérez, J. Am. Chem. Soc. 133 (2011)
191e193.
Compound 3: Maroon solid; IR (
n
C ¼ O in hexane, cmꢁ1): 2069
(s), 2023 (s), 1997 (s), 1911 (m), 1689 (s); 1H NMR (
d in ppm, CDCl3):
[2] M. Lin, F. Li, L. Jiao, Z.-X. Yu, J. Am. Chem. Soc. 133 (2011) 1690e1693.
[3] V. Cadierno, J. Francos, J. Gimeno, Organometallics 30 (2011) 852e862.
[4] P. Mathur, V.D. Avasare, S.M. Mobin, Tetrahedron 64 (2008) 8943e8946.
[5] P. Mathur, A.K. Bhunia, S.M. Mobin, V.K. Singh, C. Srinivasu, Organometallics
23 (2004) 3694e3700.
[6] A.J. Carty, G. Hogarth, G. Enright, G. Frapper, A.J. Carty, G. Hogarth, Chem.
Comm. (1997) 1883e1884.
[7] P. Blenkiron, G.D. Enright, A.J. Carty, Chem. Comm. (1997) 483e484.
[8] Y. Chi, A.J. Carty, P. Blenkiron, E. Delgado, G.D. Enright, W. Wang, S.-M. Peng,
G.-H. Lee, Organometallics 15 (1996) 5269e5271.
[9] M. Akita, S. Sugimoto, M. Terada, Y. Moro-oka, J. Organomet. Chem. 447 (1993)
103e106.
[10] E. Delgado, Y. Chi, W. Wang, G. Hogarth, P.J. Low, G.D. Enright, S.-M. Peng, G.-
H. Lee, A.J. Carty, Organometallics 17 (1998) 2936e2938.
[11] C.-H. Wu, Y. Chi, S.-M. Peng, G.-H. Lee, J. Chem. Soc. Dalton Trans. (1990)
3025e3031.
[12] P. Mathur, M.O. Ahmed, J.H. Kaldis, M.J. McGlinchey, J. Chem. Soc. Dalton
Trans. (2002) 619e629.
[13] P. Mathur, A.K. Singh, V.K. Singh, P. Singh, R. Rahul, S.M. Mobin, C. Thöne,
Organometallics 243 (2005) 4793e4798.
[14] P. Mathur, V.K. Singh, A.K. Singh, S.M. Mobin, C. Thöne, J. Organomet. Chem.
691 (2006) 3336e3342.
[15] P. Mathur, R.K. Joshi, B. Jha, A.K. Singh, S.M. Mobin, J. Organomet. Chem. 695
(2010) 2687e2694.
[16] B. Carke, M. Green, R.B.L. Osborn, F.G.A. Stone, J. Chem. Soc. A (1968) 167e169.
[17] R.A. Head, J. Chem. Soc. Dalton Trans. (1982) 1637e1639.
[18] H.D. Empsall, M. Green, F.G.A. Stone, J. Chem. Soc. Dalton Trans. (1972)
96e101.
[19] R. Countryman, B.R. Penfold, J. Cryst. Mol. Struct. 2 (1972) 281e290.
[20] T.T. Tsou, J.C. Huffman, J.K. Kochi, Inorg. Chem. 18 (1979) 2311e2317.
[21] J. Kaiser, J. Sieler, D. Walther, E. Dinjus, L. Golic, Acta Crystallogr. B38 (1982)
1584e1586.
[22] G.R. Clark, C.E.L. Headford, K. Marsden, W.R. Roper, J. Organomet. Chem. 231
(1982) 335e360.
[23] M. Cooke, M. Green, J. Chem. Soc. A (1969) 651e655.
[24] R. Burt, M. Cooke, M. Green, J. Chem. Soc. A (1970) 2975e2981.
[25] H. Berke, G. Huttner, G. Weiler, L. Zsolnai, J. Organomet. Chem. 219 (1981)
353e362.
7.0e8.0 (m, aromatic), 10.0 (CHO); 13C NMR (
d in ppm, CDCl3): 68.3,
71.9, 127.8e136.4 (aromatic), 193.4 (PhCHO), 215.2 (FeeCO); %
C ¼ 62.90, % H ¼ 2.93.
Compound 4: Maroon solid; IR (
n
C ¼ O in hexane, cmꢁ1): 2048,
d in ppm, CDCl3): 6.6e7.9 (m,
1982, 1913, 1729, 1697; 1H NMR (
aromatic), 8.9 (HCOeFe), 10.2 (CHO); 13C NMR (
d in ppm, CDCl3):
68.3 and 71.9 (C]C), 125.4e136.0 (aromatic), 190.9 (PhCHO), 199.5
(HCOeFe), 205.8 to 220.3 (FeeCO); % C ¼ 63.51, % H ¼ 3.62.
Compound 5: Maroon solid; IR (
n
C ¼ O in hexane, cmꢁ1): 2050,
1986, 1927, 1720 1691; 1H NMR (
d in ppm, CDCl3): 6.7e7.7
(aromatic), 8.9 (HCOeFe), 9.9 (CHO); 13C NMR (
d in ppm, CDCl3):
68.3 and 71.9 (C]C), 126.3e136.9 (aromatic), 190.5 (PhCHO), 199.7
(HCOeFe), 206.2 to 219.9 (FeeCO); % C ¼ 58.21, % H ¼ 3.11.
Compound 7: Maroon solid; IR (
n
C ¼ O in KBr, cmꢁ1): 2051,1994,
1978, 1629; 1H NMR (
d in ppm, CDCl3): 4.0e4.3 (m, 9H, C5H5 and
C5H4), 5.9 (CH ¼ Cfc), 7.1e7.7 (m, 4H, aromatic); 13C NMR (
d in ppm,
CDCl3): 67.4 (CH ¼ Cfc), 68.8e70.4 (C5H5 and C5H4), 90.6 (CH ¼ Cfc),
101.4(C¼CeC¼O), 123.2 to 131.9 (aromatic), 166.3 (cyclic CO), 209.7
(FeeCO); % C ¼ 58.38, % H ¼ 3.59.
Compound 8: Blue solid; IR (
n
C ¼ O in hexane, cmꢁ1): 2113 (s),
2065 (s), 2042 (s), 2023 (s), 1699 (s), 1648 cmꢁ1(s); 1H NMR (
d in
ppm, CDCl3): 4.1e4.8 (m, 9H, C5H5 and C5H4), 6.9e8.0 (m, 4H,
aromatic), 9.9 (CHO); 13C NMR (
d
in ppm, CDCl3): 69e73.5 (ferro-
cene), 129.2e136.7 (aromatic), 165.5 (¼Cfc) 169 (¼CPh), 191.44
(eCHO), 199.2, 199.3 (cyclic CO), 202.3, 202.9 (FeeCO); % C ¼ 62.01,
% H ¼ 3.78.
Compound 9: Orange solid; IR (
NMR (
n
C ¼ O in KBr, cmꢁ1): 1725 (s); 1H
d
in ppm, CDCl3): 7.1e7.56 (m, 8H, aromatic), 7.59 (s, 1H, C]
CH), 7.88 (d, 1H, o-H to C]O); 13C NMR (
d
in ppm, CDCl3):
[26] P. Courtot, R. Pichon, J.Y. Salaun, J. Organomet. Chem. 286 (1985) c17ec21.

14
P. Mathur et al. / Journal of Organometallic Chemistry 712 (2012) 7e14
[27] J. Auffret, P. Courtot, R. Pichon, J.Y. Salaun, J. Chem. Soc. Dalton Trans. (1987)
1687e1692.
[28] A.G. Thayer, N.C. Payne, Acta Crystallogr. C42 (1986) 1302e1305.
[29] R.O. Gould, W.J. Sime, T.A. Stephenson, J. Chem. Soc. Dalton Trans. (1978)
76e79.
[30] R.M. Bullock, B.J. Rappoli, E.G. Samsel, A.L. Rheingold, J. Chem. Soc. Chem.
Comm. (1989) 261e263.
[31] W.E. Williams, F.J. Lalor, J. Chem. Soc. Dalton Trans. (1973) 1329e1332.
[32] B.M. Foxman, P.T. Klemarczyk, R.E. Liptrot, M. Rosenblum, J. Organomet.
Chem. 187 (1980) 253e265.
[44] H.O. House, R.G. Carlson, J. Org. Chem. 29 (1964) 74e78.
[45] H.O. House, W.C. McDaniel, J. Org. Chem. 42 (1977) 2155e2160.
[46] M. Zengin, A. Das¸ tan, M. Balci, Syn. Comm. 31 (2001) 1993e1999.
[47] H.H. Szmant, R. Nanjundiah, J. Org. Chem. 43 (1978) 1835e1837.
[48] R. Leardini, D. Nanni, A. Tundo, G. Zanardi, Tetrahedron Lett. 39 (1998)
2441e2442.
[49] A. Chatterjee, S. Banerjee, Tetrahedron 26 (1970) 2599e2608.
[50] E.F. Ullman Jr., W.A. Henderson, J. Am. Chem. Soc. 88 (1966) 4942e4960.
[51] K. Buggle, U.N. Ghogain, D. O’Sullivan, J. Chem. Soc. Perkin Trans. 1 (1983)
2075e2076.
[33] W.D. Harman, D.P. Fairlie, H. Taube, J. Am. Chem. Soc. 108 (1986) 8223e8227.
[34] W.D. Harman, M. Sekine, H. Taube, J. Am. Chem. Soc. 110 (1988) 2439e2445.
[35] D.M. Dalton, J.M. Fernandez, K. Emerson, R.D. Larsen, A.M. Arif, J.A. Gladysz,
J. Am. Chem. Soc. 112 (1990) 9198e9212.
[52] H.O. House, J.K. Larson, J. Org. Chem. 33 (1968) 448e451.
[53] H.E. Zimmerman, J. Am. Chem. Soc. 78 (1956) 1168e1173.
[54] E.N. Alesso, D.G. Tombari, A.F. Ibanez, G.Y.M. Iglesias, J.M. Aguirre, Can. J.
Chem. 69 (1991) 1166e1170.
[36] C.M. Garner, N. Quiros Mendez, J.J. Kowalczyk, J.M. Fernandez, K. Emerson,
R.D. Larsen, J.A. Gladysz, J. Am. Chem. Soc. 112 (1990) 5146e5160.
[37] W.E. Buhro, S. Georgiou, J.M. Fernandez, A.T. Patton, C.E. Strouse, J.A. Gladysz,
Organometallics 5 (1986) 956e965.
[38] H. Berke, R. Birk, G. Huttner, L. Zsolnai, Naturforsch 39B (1984) 1380e1388.
[39] M.N. Quiros, A.M. Arif, J.A. Gladysz, Angew. Chem. Int. Ed. Engl. 29 (1990)
1473e1475.
[40] R.C. Larock, M.J. Doty, S. Cacchi, J. Org. Chem. 58 (1993) 4579e4583.
[41] H. Martens, G. Hoornaert, Tetrahedron 30 (1974) 3641e3645.
[42] M.B. Floyd, G.R. Allen Jr., J. Org. Chem. 35 (1970) 2647e2653.
[43] H.O. House, V. Paragamian, R.S. Ro, D.J. Wluka, J. Am. Chem. Soc. 82 (1960)
1452e1457.
[55] Y. Endo, T. Ohta, S. Nozoe, Tetrahedron Lett. 33 (1992) 353e356.
[56] E.H. Braye, W. Hübel, J. Organomet. Chem. 3 (1965) 38e42.
[57] F. Delbecq, P. Sautet, J. Am. Chem. Soc. 114 (1992) 2446e2455.
[58] P. Mathur, V.D. Avasare, S.M. Mobin, J. Clust. Sci. 20 (2009) 399e415.
[59] K. Katsumoto, C. Kitamura, T. Kawase, Eur. J. Org. Chem. (2011) 4885e4891
(and references there in).
[60] G. Doisneau, G. Balavoine, T.F. Khan, J. Organomet. Chem. 425 (1992) 113e117.
[61] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 44 (1975)
4467e4470.
[62] A. Chandra, B. Singh, S. Upadhyay, R.M. Singh, Tetrahedron 64 (2008)
11680e11685.
[63] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112e122.