Photolysis of dicarbonyl(cyclopentadiene)rhodium complexes with a pendent alkyne unit

Article abstract of DOI:10.1016/j.jorganchem.2007.06.053

The syntheses of dicarbonyl[1-(5,5-dimethylhex-3-inyl)-3-phenylcyclopentadienyl]rhodium (7) and its congeners 8 and 9 are reported. Photolysis of 8 and 9 leads to a replacement of one CO ligand by the tethered alkyne unit, yielding 16, and to the dirhodiu

Full text of DOI:10.1016/j.jorganchem.2007.06.053

Journal of Organometallic Chemistry 692 (2007) 4281–4286
www.elsevier.com/locate/jorganchem
Photolysis of dicarbonyl(cyclopentadiene)rhodium complexes
with a pendent alkyne unit
*
Carsten Schaefer, Rolf Gleiter , Frank Rominger
Organisch-Chemisches Institut, Universita¨t Heidelberg, INF 270, 69120 Heidelberg, Germany
Received 19 March 2007; received in revised form 23 June 2007; accepted 28 June 2007
Available online 4 July 2007
Abstract
The syntheses of dicarbonyl[1-(5,5-dimethylhex-3-inyl)-3-phenylcyclopentadienyl]rhodium (7) and its congeners 8 and 9 are reported.
Photolysis of 8 and 9 leads to a replacement of one CO ligand by the tethered alkyne unit, yielding 16, and to the dirhodium complexes 17
and 18. The structural assignment of 17 and 18 is based on X-ray studies. The photolysis of 9 leads to 19 and 20.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Rhodiumdicarbonyl complexes; Alkynes; Dirhodium carbon clusters; Photolysis
1. Introduction
metal complexes no discrete products with more than one
metal center could be isolated [2–4]. In this paper we report
photochemical experiments of the [phenylcyclopentadie-
nyl]rhodium dicarbonyl complexes 7–9 (Chart 1).
Endohedral metal complexes of cyclophanes, D, are usu-
ally prepared either from an uncomplexed cyclophane, A,
by reaction with a metal or metal ion, or by adding tethers
to a metallocene, B, (Scheme 1) [1]. Recently, we proposed
a third path by using an intramolecular ring closure of a
metal-p-complex, C, containing two or more pendent
alkyne units and a metal template MLn [2–4]. The latter
protocol enabled us to synthesize new endohedral cobalt
and rhodium complexes. In the cases of two pendent
alkyne groups and cobalt dicarbonyl as metal fragment
we generated cyclophanes with cyclobutadiene (1 and 2)
or cyclopentadienone (3 and 4) as second ring. When the
metal fragment was rhodium dicarbonyl, only cyclopenta-
dienone rings were built from the alkyne units (5 and 6)
(Fig. 1). The yields of these intramolecular template reac-
tions turned out to be low, especially when heavier transi-
tion metals than cobalt were employed [3,4]. This reflects
the increased tendency of the heavier metal centers to form
bimetallic or cluster compounds [5]. Nevertheless, we have
previously found that when Cp ligands with two pendent
alkyne groups were involved apart from the endohedral
2. Results and discussion
2.1. Synthesis
In order to decrease the reaction possibilities of the
substituted Cp ligand and to facilitate the formation of
higher molecular products we synthesized Cp rhodium
dicarbonyl complexes with only one pendent alkyne group.
The synthesis of the corresponding cyclopentadiene ligands
13–15 started with the addition of phenyllithium to the
monosubstituted cyclopentenones 10–12 [4] followed by
acidic work-up to generate the cyclopentadiene ligands
13–15. These ligands were deprotonated by butyllithium
and treated with [RhCl(CO)2]2 to yield the corresponding
rhodium dicarbonyl complexes 7–9 (Scheme 2).
The obtained dicarbonyl complexes 7–9 were then
reacted by irradiating a hexane solution with UV light.
We regarded these reaction conditions to be milder than
the pyrolytic reaction conditions used for the synthesis of
the previously described endohedral complexes and there-
fore more likely to yield complexes with more than one
*
Corresponding author. Tel.: +49 6221 548400; fax: +49 6221 544205.
E-mail address: Rolf.Gleiter@oci.uni-heidelberg.de (R. Gleiter).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.053

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C. Schaefer et al. / Journal of Organometallic Chemistry 692 (2007) 4281–4286
π
Ph
n
Rh
π
OC
CO
A
7
8
9
(n = 2)
(n = 3)
(n = 4)
π
π
π
M
π
Chart 1.
2
M
+
MLn
π
O
B
D
C
Ph
a, b
n
Scheme 1. Possible approaches to generate endohedral cyclophanes.
13- (n = 2)
n
14- (n = 3)
15- (n = 4)
metal center. In the case of the photolytic reaction of 7 we
could only observe decomposition. However, in the cases
of 8 and 9 we were able to isolate defined products
(Schemes 3 and 4).
10 (n = 2)
11 (n = 3)
12 (n = 4)
c
The irradiation of 8 yielded a mono-alkyne complex 16
and two dirhodium complexes, 17 and 18 (Scheme 3).
Complex 16 was obtained in a 6% yield as a very air sen-
sitive solid. It was identified by mass spectrometry and
shows a strong IR band at 1963 cmꢀ1. Similar intermedi-
ates with an alkyne unit bound to a CpM(CO)n fragment
are reported in the literature for M = Co, n = 1 [6,7],
and M = Mn, n = 2 [8,9]. Also complexes of the type
Ph
n
Rh
OC
CO
(n = 2)
(n = 3)
(n = 4)
7
8
9
Scheme 2. Synthesis of CpRh(CO)2 complexes 7–9. (a) PhLi, THF,
ꢀ78ꢁC to r.t.; HCl (aq). (b) n-BuLi, THF, ꢀ78ꢁC to r.t. (c) [RhCl(CO)2]2 ,
THF, r.t.
(CH2)m
Co
(CH2)n
Co
(CH2)m
(CH2)n
R
R
R
Ph
Ph
hν
Rh
Rh
OC
CO
OC
R
t
-Bu
1
2
8
16
Ph
(CH2)n
R
(CH2)n
t
-Bu
O
Co
Co
Rh
Rh
17
R
R
(CH2)m
t
-Bu
t
-Bu
(CH2)m
Rh
Rh
+
+
Ph
R
t
-Bu
O
O
Ph
4
3
Ph
18
Scheme 3. Photolysis of 8 to generate 16–18.
(CH2)n
R
Rh
Rh
ArCr(CO)2(alkyne) have been reported [8,10–12]. How-
ever, most of them proved to be rather unstable [13]
whereas the species 17 and 18 were dark red colored air-
stable solids. The assigned structures are based on their
analytical data and their structures in the solid state.
Photolysis of 9 yielded an air-sensitive yellow oil to
which we assign the structure of 19 based on its strong
IR band at 1967 cmꢀ1. Besides, we isolated a dark red
R
R
R
(CH2)m
(CH2)n
(CH2)m
O
O
5
6
Fig. 1. Endohedral cyclophanes obtained by intramolecular reaction of
alkyne units with Co and Rh as metal.

C. Schaefer et al. / Journal of Organometallic Chemistry 692 (2007) 4281–4286
4283
Ph
Ph
h
ν
C42H50Rh2
+
Rh
Rh
OC
CO
OC
t
-Bu
9
19
20
Scheme 4. Photolysis of 9 to generate 19 and 20.
solid, 20 (26%), whose high resolution mass spectrum gave
a formula of C42H50Rh2. This suggests a structure analo-
gous to 17 with tetramethylene bridges (Scheme 4). Thus,
loss of the first CO ligand leads to a coordination of the
alkyne bond whereas on loss of the second CO ligand a
dimerization to 17, 18, and 20 occurs. Probably the syn
configuration of the Cp-rings in 18 requires an additional
group or atom between the sp2 centers for steric reasons.
The presence of the oxygen atom in 18 we attribute to
traces of oxygen in the reaction vessel.
O
R
R
Me
Me
CF3
CF3
R
R
Rh
Rh
Rh
Rh
21 R = Phf
22
23
R = CF3
Fig. 3. Binuclear rhodium complexes found in the literature.
The structures of 17 and 18 reveal a Rh-Rh single bond
with a length of 2.562 A (17) and 2.617 A (18). The dis-
tances between the carbon atoms of the former triple bonds
amount to 1.41 A (17) and 1.42 A (18). Both show double
bond character as indicated in the respective formulae in
Scheme 3.
˚
˚
2.2. Structural investigations
˚
˚
We were able to isolate singe crystals of 17 and 18 which
allowed X-ray diffraction studies. Both molecular struc-
tures are shown in Fig. 2.
Binuclear complexes from reaction of cyclopentadienyl
rhodium dicarbonyl complexes with alkynes have been
described in the literature (Fig. 3). The structures of com-
plexes 21 and 22 can be described as a rhodacyclopentadi-
ene ring p bonded to a CpRh unit [14–16]. A coordination
similar to that found in 17 and 18 can be found in complex
23, however in this complex a CO unit is inserted between
the two coordinated double bonds [17]. More examples
˚
with a (CpRh)2 unit with Rh–Rh distances around 2.6 A
and alkyne units coordinated to the metal centers can be
found in the literature [18].
3. Conclusion
In this paper we report the synthesis and photochemical
reactions of the cyclopentadienyl rhodium dicarbonyl com-
plexes 7–9. The photolysis of 7 did not yield any isolable
products, possibly due to the short dimethylene tether.
However, complexes 8 and 9 bearing trimethylene and
tetramethylene tethers respectively, yielded the mono-
alkyne complexes 16 and 19 and the dirhodium complexes
17, 18 and 20. We were able to investigate species 17 and 18
by X-ray diffraction methods revealing Rh–Rh bonds in
both cases.
4. Experimental
4.1. General remarks
All melting points are uncorrected. Elemental analyses
were carried out by the Mikroanalytisches Laboratorium
Fig. 2. ORTEP drawing for 17 (top) and 18 (bottom) (50% probability
ellipsoids). Hydrogen atoms are omitted for clarity.

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C. Schaefer et al. / Journal of Organometallic Chemistry 692 (2007) 4281–4286
Table 1
der Universita¨t Heidelberg. UV/Vis absorption data were
recorded using a Hewlett Packard HP 8452A Diode
Array-spectrometer. IR spectra were recorded with a Bru-
ker Vector 22 FT-IR-spectrometer. The NMR spectra were
measured with a Bruker WH 300 or Avance 500 spectrom-
eter (1H NMR at 300 or 500 MHz and 13C NMR at 75 or
125 MHz) using the solvent as internal standard (d). FAB
and FD mass spectra refer to data from a Jeol JMS-700
instrument. All reactions were carried out in dried glass-
ware under argon atmospheres using dried and oxygen-free
solvents. The investigated crystals were obtained by evapo-
rating solvent from the respective column chromatography
fractions. X-ray diffraction data were collected on a Bruker
Smart CCD-diffractometer at 200 K. Relevant crystal and
data collection parameters are given in Table 1. The struc-
tures were solved by direct methods and refined against F2
with a full-matrix least-square algorithm by using the SHEL-
XTL [19] package. In both cases an empirical absorption
correction was applied by using SADABS [20], based on the
Laue symmetry of the reciprocal space.
Crystal data and structural refinement for 17 and 18
17
18
Empirical formula
Molecular weight
Wavelength (A)
Crystal system
Space group
C40H46Rh2
732.59
0.71073
Monoclinic
C2/c
C40H46ORh2
748.59
0.71073
Orthorhombic
P212121
200
˚
Temperature (K)
200
8
Z
a
b
c
4
34.4254(5)
11.9626(1)
16.4381(2)
102.540(1)
6608.00(14)
1.473
10.5933(2)
15.5095(2)
20.0712(3)
90
3297.63(9)
1.508
b
3
˚
V (A )
Dcalcd (g/cm3)
Absorption coefficient l [mmꢀ1
Maximum and minimum
transmission
]
1.025
0.87 and 0.71
1.031
0.94 and 0.77
Crystal shape
Polyhedron
0.36 · 0.18 · 0.14 0.27 · 0.11 · 0.06
Polyhedron
Crystal size (mm3)
h Range for data coll [deg]
Index ranges
1.81 to 27.49
ꢀ44 6 h 6 44
ꢀ15 6 k 6 15
ꢀ21 6 l 6 21
33883
7592 (0.0438)
6045 [I > 2r(I)]
7592 / 0 / 385
1.02
1.7 to 26.4
ꢀ12 6 h 6 13
ꢀ19 6 k 6 19
ꢀ24 6 l 6 25
31769
6749 (0.0540)
5963 [I > 2r(I)]
6749 / 0 / 394
1.03
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 638944 for compound 17 and CCDC
No. 638945 for compound 18.
Reflections collected
Independent reflections [R(int)]
Observed reflections
Data/restraints/parameters
Goodness-of-fit on F2
R(F)
4.2. General procedure for the preparation of CpRh
complexes 7–9
0.025
0.085
0.87 and ꢀ0.50
0.027
0.049
0.28 and ꢀ0.41
RW(F2)
(Dq)max, (Dq)min (e A
ꢀ3
˚
)
The corresponding cyclopentenones 10–12, respectively,
were dissolved in THF and cooled to ꢀ78 ꢁC. Then the
phenyllithium solution was added via syringe and the
resulting mixture was stirred for one hour keeping the
solution at ꢀ78 ꢁC. After warming up to room tempera-
ture the mixture was poured on ice. The mixture was acid-
ified by addition of aqueous HCl and extracted with
diethylether. The elimination to the cyclopentadiene was
monitored by TLC. Then the organic phase was washed
with aqueous NaHCO3 and brine, solvent removed by
rotary evaporation and the residue was purified by flash
column chromatography on alox III (neutral) using pen-
tanes as eluent.
The purified ligand was immediately subjected to the
next reaction step: n-butyllithium was added to a solution
of the cyclopentadiene ligand in THF at ꢀ78 ꢁC. After
warming up to room temperature the solution was added
to a solution of dicarbonylchlororhodium(I)dimer in
THF and stirred for 24 h. The solvents were removed
under vacuum and the products purified by flash column
chromatography on silica gel using pentanes as eluent.
2.68 ml, 4.29 mmol), dicarbonylchlororhodium(I)dimer
(500 mg, 1.29 mmol) in THF (100 ml). Yield 708 mg
(67%) of 7 as an orange oil. H NMR (500 MHz, CDCl3):
1
d 1.24 (s, 9H, CH3), 2.40 (m, 2H, CH2), 2.54 (s, 2H, CH2),
5.55 (ps, 1H, CH), 5.77 (ps, 1H, CH), 5.97 (ps, 1H, CH),
7.20–7.46 (m, 5H, CH). 13C NMR (125 MHz, CDCl3): d
22.5 (CH2), 27.4 (C), 28.2 (CH2), 31.4 (CH3), 77.55 (C),
83.4 (CH, JRh,C = 3.4 Hz), 86.5 (CH, JRh,C = 3.4 Hz),
88.0 (CH, JRh,C = 3.8 Hz), 90.2 (C), 109.4 (C,
JRh,C = 3.3 Hz), 111.2 (C, JRh,C = 3.8 Hz), 125.8 (CH),
127.4 (CH), 128.7 (CH), 133.5 (C), 191.4 (CO, JRh,
~
C = 83.9 Hz). IR (Film) m ¼ 2968, 2865, 2034, 1968,
1476, 1452, 1362, 1267 cmꢀ1. UV/Vis (CH2Cl2) (log e)
k
max = 256 (4.01), 314 (3.83), 420 (2.51) nm. MS (positive
FAB): m/z = 380 ([MꢀCO]+), 352 ([Mꢀ2CO]+). HRMS
(positive FAB) calcd. for C20H21ORh ([MꢀCO]+),
380.0647; 380.0629 found, (ꢀ1.8 mmu).
4.2.2. Dicarbonyl-g5-[1-(6,6-dimethylhept-4-ynyl)-3-
phenylcyclopentadienyl]rhodium(I) (8)
4.2.1. Dicarbonyl-g5-[1-(5,5-dimethylhex-3-ynyl)-3-
phenylcyclopentadienyl]rhodium(I) (7)
Reaction mixture in the first reaction step: Cyclopente-
none 10 (816 mg, 4.86 mmol) in THF (10 ml), phenylli-
thium (20% in n-Bu2O, 2.00 g, 4.76 mmol). Reaction
mixture in the second reaction step: Cyclopentadiene 13
in THF (25 ml), n-butyllithium (1.6 M in hexanes,
Reaction mixture in the first reaction step: Cyclopente-
none 11 (1.05 g, 5.14 mmol) in THF (10 ml), phenyllithium
(20% in n-Bu2O, 2.40 g, 5.71 mmol). Reaction mixture in
the second reaction step: Cyclopentadiene 14 in THF
(25 ml), n-butyllithium (1.6 M in hexanes, 3.21 ml,
5.14 mmol), dicarbonylchlororhodium(I)dimer (600 mg,

C. Schaefer et al. / Journal of Organometallic Chemistry 692 (2007) 4281–4286
4285
1.54 mmol) in THF (100 ml). Yield 621 mg (48%) of 8 as an
orange oil. H NMR (500 MHz, CDCl3): d 1.21 (s, 9 H,
4.3.1. Irradiation of dicarbonyl-g5-[1-(6,6-dimethylhept-4-
ynyl)-3-phenylcyclopentadienyl] rhodium(I) (8)
Reaction mixture: CpRh complex (485 mg,
1
CH3), 1.50 (m, 2 H, CH2), 2.05 (m, 2H, CH2), 2.16 (m,
2H, CH2), 5.02 (ps, 1H, CH), 5.33 (ps, 1H, CH), 5.48 (ps,
1H, CH), 6.96–7.21 (m, 5H, CH). 13C NMR (125 MHz,
CDCl3): d 18.8 (CH2), 27.5 (CH2), 27.7 (C), 31.7 (CH3),
32.0 (CH2), 78.2 (C), 83.6 (CH, JRh,C = 3.5 Hz), 86.6
(CH, JRh,C = 3.0 Hz), 88.1 (CH, JRh, C = 3.8 Hz), 90.0
(C), 109.7 (C), 112.0 (C, JRh,C = 3.8 Hz), 126.2 (CH),
127.5 (CH), 128.9 (CH), 133.9 (C), 192.4 (CO,
8
1.15 mmol), hexane (250 ml). First complex 16 was eluted
from the column as a light orange fraction, then a dark
red fraction containing complex 17 and finally a light red
fraction containing complex 18 was obtained. Yields:
25 mg (6%) of 16, 64 mg (15%) of 17 and 38 mg (9%) of 18.
16: Yellow oil, very sensitive to air, therefore we were
only able to get reliable data from IR and mass spectra.
IR (Film) m = 1963 cmꢀ1. MS (positive FD): m/z = 394
([M]+).
~
JRh,C = 84.0 Hz). IR (Film) m ¼ 3064, 2968, 2865, 2033,
1969, 1603, 1475, 1453, 1362, 1329, 1265, 1205 cmꢀ1. UV/
Vis (CH2Cl2) (loge) kmax = 242 (4.14), 258 (4.10), 312
(3.88), 378 (2.60), 410 (2.50) nm. MS (positive FAB):
m/z = 394 ([MꢀCO]+), 366 ([Mꢀ2CO]+). HRMS (positive
FAB) calcd. for C21H23ORh ([MꢀCO]+), 394.0804;
394.0805 found, (+0.1 mmu). C22H23O2Rh Æ 1/6 C6H6
(422.32): calcd. C 63.46, H 5.56, found C 63.69, H 5.58.
17: Dark red solid, m.p. 170 ꢁC (dec.). 1H NMR
(500 MHz, CDCl3): d 1.16 (s, 18 H, CH3), 1.55 (m, 4H,
CH2), 2.23 (m, 8H, CH2), 5.27 (ps, 2H, CH), 5.32 (ps,
2H, CH), 5.51 (ps, 2H, CH), 7.11–7.33 (m, 10H, CH).
13C NMR (125 MHz, CDCl3): d 1.2 (CH3), 25.3 (CH2),
30.5 (CH2), 31.5 (CH2), 37.4 (C), 77.5 (CH), 79.3 (C),
85.6 (CH), 87.1 (CH), 100.0 (C), 104.1 (C), 123.3 (CH),
4.2.3. Dicarbonyl-g5-[1-(7,7-dimethyloct-5-ynyl)-3-
phenylcyclopentadienyl]rhodium(I) (9)
125.3 (CH), 128.8 (CH), 135.4 (C). IR (Film) m ¼ 2993,
~
2947, 2913, 2847, 1600, 1517, 1477, 1450, 1436, 1383,
1356, 1190 cmꢀ1. UV/Vis (CH2Cl2) (log e) kmax = 236
(4.47), 314 (4.28), 336 (4.28), 456 (3.33), 522 (3.31). MS
(positive FAB): m/z = 732 ([M]+). HRMS (positive FAB)
calcd. for C40H46Rh2 ([M]+), 732.1709, 732.1694 found,
(ꢀ1.5 mmu). C40H46Rh2 (732.60): calcd. C 65.58, H 6.33,
found C 65.54, H 6.33.
Reaction mixture in the first reaction step: Cyclopente-
none 12 (936 mg, 4.29 mmol) in THF (10 ml), phenylli-
thium (20% in n-Bu2O, 2.00 g, 4.76 mmol). Reaction
mixture in the second reaction step: Cyclopentadiene 15
in THF (25 ml), n-butyllithium (1.6 M in hexanes,
2.68 ml, 4.29 mmol), dicarbonylchlororhodium(I)dimer
(500 mg, 1.29 mmol) in THF (100 ml). Yield 732 mg
(65%) of 9 as an orange solid, m.p. 47 ꢁC. 1H NMR
(500 MHz, CDCl3): d 1.23 (s, 9 H, CH3), 1.59 (m, 2H,
CH2), 1.66 (m, 2H, CH2), 2.20 (m, 2H, CH2), 2.38 (m,
2H, CH2), 5.50 (ps, 1H, CH), 5.76 (ps, 1H, CH), 5.90
(ps, 1H, CH), 7.21–7.46 (m, 5H, CH). 13C NMR
(125 MHz, CDCl3): d 18.5 (CH2), 27.0 (C), 27.9 (CH2),
28.8 (CH2), 31.5 (CH3), 78.0 (C), 83.2 (CH,
JRh,C = 3.6 Hz), 86.5 (CH, JRh,C = 3.5 Hz), 88.0 (CH,
JRh,C = 3.8 Hz), 89.5 (C), 109.2 (C, JRh,C = 3.4 Hz), 112.3
(C, JRh,C = 3.6 Hz), 125.9 (CH), 127.4 (CH), 128.7 (CH),
133.5 (C), 191.5 (CO, JRh,C = 84.0 Hz). IR (Film)
18: Dark red solid, m.p. 155 ꢁC (dec.). 1H NMR
(300 MHz, CDCl3): d 0.74 (s, 9 H, CH3), 0.84–0.89 (m,
2H, CH2), 1.16 (s, 9H, CH3), 1.44–2.32 (m, 10H, CH),
5.10 (ps, 1H, CH), 5.36 (ps, 1H, CH), 5.42 (ps, 1H, CH),
5.45 (ps, 1H, CH), 5.70 (ps, 1H, CH), 5.96 (ps, 1H, CH),
7.06–7.26 (m, 10H, CH). 13C NMR (75 MHz, CDCl3): d
19.6 (C), 22.7 (C), 25.2 (CH2), 26.0 (CH2), 30.6 (CH2),
30.9 (CH2), 31.0 (CH3), 33.7 (CH2), 33.8 (CH2), 37.3 (C),
38.3 (C), 76.2 (CH, JRh,C = 4.2 Hz), 79.1 (CH,
JRh,C = 5.5 Hz), 82.7 (CH, JRh,C = 6.2 Hz), 85. 3 (CH,
JRh, C = 2.1 Hz), 86.2 (CH, JRh,C = 6.9 Hz), 87.9 (CH,
JRh,C = 3.5 Hz), 98.5 (C, JRh,C = 5.5 Hz), 99.8 (C,
JRh,C = 4.9 Hz), 104.6 (C, JRh, C = 2.1 Hz), 107.2 (C,
JRh,C = 2.8 Hz), 123.4 (CH), 125.1 (CH), 125.6 (CH),
126.0 (CH), 128.6 (CH), 128.7 (CH), 135.5 (C), 135.6 (C).
~
m ¼ 2967, 2930, 2862, 2035, 1970, 1603, 1475, 1452, 1361,
1265, 1205 cmꢀ1. UV/Vis (CH2Cl2) (log e) kmax = 242
(3.98), 302 (3.94), 314 (3.93), 424 (2.54) nm. MS (positive
FAB): m/z = 408 ([M-CO]+), 380 ([M-2CO]+). HRMS
(positive FAB) calcd. for C22H25ORh ([M-CO]+),
408.0960; 408.0965 found, (+0.5 mmu).
IR (KBr) m ¼ 2924, 2855, 1636 cmꢀ1. UV/Vis (CH2Cl2)
~
(log e) kmax = 242 (4.45), 264 (4.40), 300 (4.28), 348
(4.19), 458 (3.49), 526 (3.24), 574 (2.88). MS (positive
FAB): m/z = 748 ([M]+), 732 ([M-O]+). HRMS (positive
FAB) calcd. for C40H46ORh2 ([M]+), 748.1659, 748.1641
found, (ꢀ1.8 mmu).
4.3. General procedure for the irradiation of CpRh
complexes 7–9
A deoxygenated solution of 7–9 in hexanes under argon
atmosphere was irradiated with UV light (HPK 125 W
high pressure mercury vapour lamp in a reactor fitted with
a water cooled jacket). The reaction was monitored by IR.
The colour of the reaction mixture turned from light
orange to dark brownish red. The solvent was removed
in vacuo and the residue was chromatographed on alox
III (neutral) using pentanes as eluent.
4.3.2. Irradiation of Dicarbonyl-g5-[1-(7,7-dimethyloct-5-
ynyl)-3-phenylcyclopenta- dienyl]rhodium(I) (9)
Reaction mixture: CpRh complex
9
(250 mg,
0.573 mmol), hexane (250 ml). First complex 19 was eluted
from the column as a light orange fraction, then a purple
fraction containing complex 20 was obtained. Yields:
76 mg (32%) of 19, 57 mg (26%) of 20.
ꢀ1
~
19: Yellow oil. IR (Film) m ¼ 1967cm
.

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C. Schaefer et al. / Journal of Organometallic Chemistry 692 (2007) 4281–4286
[6] (a) C. Benisch, J. Chavez, R. Gleiter, B. Nuber, H. Irngartinger,
~
20: Dark red solid, m.p. 82 ꢁC. IR (KBr) m ¼ 3060, 2962,
2920, 2857, 2033, 1969, 1876, 1599, 1477, 1446, 1032 cmꢀ1
.
T. Oeser, H. Pritzkow, F. Rominger, Eur. J. Inorg. Chem.
(1998) 629;
UV/Vis (CH2Cl2) (log e) kmax = 276 (4.33), 332 (4.11), 516
(3.67). MS (positive FD): m/z = 760 ([M]+). HRMS (posi-
tive FAB) calcd. for C42H50Rh2 ([M]+), 760.2022, 760.2006
found, (ꢀ1.8 mmu).
(b) C. Benisch, R. Gleiter, T.H. Staeb, B. Nuber, T. Oeser, H.
Pritzkow, F. Rominger, J. Organomet. Chem. 641 (2002) 102.
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Acknowledgement
We are grateful to the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie for finan-
cial support.
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