Synthesis of 9-anthrylmethyl-functionalised cyclopentadienyl derivatives of rhodium(I) and iridium(I) and study of their luminescence properties

Article abstract of DOI:10.1016/S0022-328X(99)00415-5

The compound 9-anthrylmethylcyclopentadiene 1 was prepared by reacting 9-bromomethylanthracene with cyclopentadienylsodium and transformed into its thallium(I) derivative on reaction with thallium ethoxide 3. The 9-anthrylmethylcyclopentadienyl (AnCH₂C₅H₄) derivatives of rhodium(I) and iridium(I) of formula [M(η⁵-AnCH₂C₅H₄)L₂] (M=Rh or Ir; L=C₂H₄, CO, PPh₃, C₈H₁₄; L₂=C₇H₈, 1,5-C₈H₁₂) 4-6 and 9-11 were obtained in good yields by reacting the corresponding rhodium(I) and iridium(I) chlorides with 3. Both [Rh(η⁵-AnCH₂C₅H₄)(η²-C₂H₄)₂] (4) and [Rh(η⁵-AnCH₂C₅H₄)(CO)₂] (5) react with triphenylphosphine, at 130°C to give [Rh(η⁵-AnCH₂C₅H₄)(η²-C₂H₄)(PPh₃)] (7) and [Rh(η⁵-AnCH₂C₅H₄)(CO)(PPh₃)] (8). All complexes were characterised by elemental analysis, mass spectrometry, ¹H-NMR and FTIR. The structures of two of them, i.e. [Rh(η⁵-AnCH₂C₅H₄)(η²-C₂H₄)₂] (4) and [Rh(η⁵-AnCH₂C₅H₄)(CO)₂] (5), were elucidated by single crystal X-ray diffraction. Compound 4 crystallises in the triclinic space group P1? with a=11.112(1), b=12.065(1), c=15.982(2) A?; α=99.83(1), β=107.86(1), γ=107.22(1)°. V=1865.6(3) A?³. Z=4, D_calc=1.475 g cm^-1, R₁=0.0414 [I>2σ(I)], wR₂=0.0953. Compound 5 crystallises in the triclinic space group P1? with a=12.232(1), b=13.463(1), c=13.488(1) A?; α=61.25(1), β=68.51(1), γ=67.45(1)°. V=1752.5(2) A?³. Z=4, D_calc=1.570 g cm^-1, R₁=0.0313 [I>2σ(I)], wR₂=0.0795. The UV-vis spectra (280-700 nm) of 1 and of complexes 4-11 were recorded. The spectra of 4-11 are indicative of important interactions between the anthrylic chromophore and the cyclopentadienyl-metal moiety. When excited at 365 nm, 1 results to be an efficient light-emitting molecule, while its derivatives 4-11 are poorly luminescent compounds. Indeed, all complexes exhibit similar fluorescence spectra which are typical of the anthrylic fluorophore but have extremely low intensity (the one observed for 9-methylanthracene was below 5% and taken as the reference compound). The mechanism of fluorescence quenching in the complexes 4-11 is discussed.

Full text of DOI:10.1016/S0022-328X(99)00415-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 251–266
Synthesis of 9-anthrylmethyl-functionalised cyclopentadienyl
derivatives of rhodium(I) and iridium(I) and study of their
luminescence properties
Francesca Cicogna a, Massimo Colonna a, Julien L. Houben b, Giovanni Ingrosso a,*,
Fabio Marchetti c
a Dipartimento di Chimica e Chimica Industriale, Uni6ersita` di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
b Istituto di Chimica Quantistica ed Energetica Molecolare del CNR, Via Risorgimento 35, I-56126 Pisa, Italy
c Dipartimento di Ingegneria Chimica, dei Materiali, delle Materie Prime e Metallurgia, Uni6ersita` ‘La Sapienza’ di Roma,
Via del Castro Laurenziano, 7, Box 15 Roma 62, I-00185 Rome, Italy
Received 5 June 1999; accepted 12 July 1999
Dedicated to Professor F. Calderazzo on his 70th birthday.
Abstract
The compound 9-anthrylmethylcyclopentadiene 1 was prepared by reacting 9-bromomethylanthracene with cyclopentadienyl-
sodium and transformed into its thallium(I) derivative on reaction with thallium ethoxide 3. The 9-anthrylmethylcyclopentadienyl
(AnCH2C5H4) derivatives of rhodium(I) and iridium(I) of formula [M(h5-AnCH2C5H4)L2] (M=Rh or Ir; L=C2H4, CO, PPh3,
C8H14; L2=C7H8, 1,5-C8H12) 4–6 and 9–11 were obtained in good yields by reacting the corresponding rhodium(I) and
iridium(I) chlorides with 3. Both [Rh(h5-AnCH2C5H4)(h2-C2H4)2] (4) and [Rh(h5-AnCH2C5H4)(CO)2] (5) react with
triphenylphosphine, at 130°C to give [Rh(h5-AnCH2C5H4)(h2-C2H4)(PPh3)] (7) and [Rh(h5-AnCH2C5H4)(CO)(PPh3)] (8). All
1
complexes were characterised by elemental analysis, mass spectrometry, H-NMR and FTIR. The structures of two of them, i.e.
[Rh(h5-AnCH2C5H4)(h2-C2H4)2] (4) and [Rh(h5-AnCH2C5H4)(CO)2] (5), were elucidated by single crystal X-ray diffraction.
(
,
Compound 4 crystallises in the triclinic space group P1 with a=11.112(1), b=12.065(1), c=15.982(2) A; h=99.83(1),
3
i=107.86(1), k=107.22(1)°. V=1865.6(3) A . Z=4, Dcalc=1.475 g cm−1, R1=0.0414 [I\2|(I)], wR2=0.0953. Compound 5
,
(
,
crystallises in the triclinic space group P1 with a=12.232(1), b=13.463(1), c=13.488(1) A; h=61.25(1), i=68.51(1),
k=67.45(1)°. V=1752.5(2) A . Z=4, Dcalc=1.570 g cm−1, R1=0.0313 [I\2|(I)], wR2=0.0795. The UV–vis spectra (280–700
3
,
nm) of 1 and of complexes 4–11 were recorded. The spectra of 4–11 are indicative of important interactions between the anthrylic
chromophore and the cyclopentadienyl–metal moiety. When excited at 365 nm, 1 results to be an efficient light-emitting molecule,
while its derivatives 4–11 are poorly luminescent compounds. Indeed, all complexes exhibit similar fluorescence spectra which are
typical of the anthrylic fluorophore but have extremely low intensity (the one observed for 9-methylanthracene was below 5% and
taken as the reference compound). The mechanism of fluorescence quenching in the complexes 4–11 is discussed. © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Rhodium complexes; Iridium complexes; Electron transfer; Energy transfer; Fluorescence
design new transition metal-containing building blocks
which may be used to form assemblies having multiple
1. Introduction
electron transfer properties or cooperative magnetic
Increasing attention is devoted to the synthesis of
behaviour. Such compounds are designed to undergo
transition metal compounds which have interesting
intramolecular electron transfer so that their chemical
electronic, magnetic or photochemical properties so to
and physical behaviour can be controlled through their
redox properties. The interest of this research is funda-
* Corresponding author. Fax: +39-50-918410 or +39-50-918260.
mental: to gain a deeper understanding of electron
E-mail address: vanni@dcci.unipi.it (G. Ingrosso)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00415-5

252
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
transfer behaviour in metal-containing compounds, and
it is also highly relevant to applications in the general
field of molecular electronics (optoelectronics, molecu-
lar wires, switches, and molecular magnets) [1].
The transition-metal–cyclopentadienyl system can
undergo one-electron-reduction or one-electron oxida-
tion, easily, thus giving rise to relatively stable radical
species [2]:
thrylmethylcyclopentadienyl ligand and to study their
photophysical properties. Part of this work is reported
in this paper which deals with several derivatives of
rhodium(I) and iridium(I).
2. Results and discussion
2.1. Preparation of 9-anthrylmethyl-functionalised
cyclopentadienyl deri6ati6es of rhodium(I) and
iridium(I)
The unpaired electron spin delocalisation varies
markedly within these radicals and may be ligand- or
metal-centred or may interest the whole complex, de-
pending upon various structural parameters [3]. Thus,
owing to its electron donor-acceptor properties, the
cyclopentadienyl–metal moiety appears interesting for
projecting new two-component supramolecular devices
in which it is connected to a luminescent fragment
behaving as an ‘antenna’. It is expected that the cy-
clopentadienyl–metal system can behave as a control
unit capable of modifying the physical properties char-
acteristic of the antenna (light emitting properties,
charge transfer, redox properties, etc.). Therefore, the
idea of synthesising new transition-metal cyclopentadi-
enyl derivatives in which the C5 ring is linked to a
fluorophore through a spacer appeared attractive:
The synthesis of 9-anthrylmethylcyclopentadiene 1
was performed according to the reactions outlined in
Scheme 1: commercial 9-hydroxymethylanthracene was
converted into the corresponding bromide 2 on reaction
with Br2 in the presence of PPh3 [5], and the subsequent
reaction of 2 with cyclopentadienylsodium [6] furnished
1 in satisfactory yields (75%).Three isomeric structures
are possible for 1, namely 1a–1c:
Indeed, GC–MS analysis of 1, after its isolation from
the reaction mixture by column chromatography on
silica gel (see Section 4), revealed the presence of three
peaks, each having m/z=256. Accordingly, its 1H-
NMR spectrum is quite complex. Indeed, apart from
the aromatic protons, which give rise to the expected
pattern for a 9-anthryl group, the vinylic and allylic
protons of the cyclopentadiene ring give rise to two sets
of broad signals, respectively, owing to the presence of
isomers (Table 1). Six signals of the same intensity are
observed for the vinylic protons between l 6.54 and
5.60 ppm, while the three signals, at l 3.17, 3.11, and
3.01 ppm, are due to the allylic protons. Since the
low-field signal (3.17 ppm) can be associated with the
tertiary allylic proton of the isomer 1a and the other
two with the secondary allylic protons of isomers 1b
and 1c (Table 1), the integrated area of the three signals
allows one to conclude that 1a–1c are present in a 1:1:1
ratio. Finally, the broad split signal, centred at l 4.70
ppm, is attributed to the methylene group which con-
Compounds of this type should allow one to test how
the active sites, i.e. the cyclopentadienyl–metal system
and the fluorophore, communicate under those condi-
tions (chemical, photochemical, and electrochemical)
which can induce the intramolecular transmission of
electronic effects.
Although a variety of ligands carrying a fluorophore
as well as their metal derivatives have been reported in
the literature [4], to our knowledge no cyclopentadiene
derivative carrying an efficient light-emitting fragment
has been so far reported in the literature. We were then
attracted by the idea to synthesise an anthryl-substi-
tuted cyclopentadiene derivative in which the anthryl
group and the cyclopentadiene ring are separated by a
methylene group and we have now succeeded in the
synthesis of 9-anthrylmethylcyclopentadiene 1.
We have then started a research aimed to synthesise
various transition metal derivatives carrying the 9-an-
Scheme 1.

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
253
Table 1
Both 4 and 5 undergo ligand exchange reaction on
reaction with triphenylphosphine in p-xylene, at 130°C,
1H-NMR data for 9-anthrylmethylcyclopentadiene 1 *
thus
giving
rise
to
[Rh(h5-AnCH2C5H4)(h2-
C2H4)(PPh3)] (7) and [Rh(h5-AnCH2C5H4)(CO)(PPh3)]
(8), respectively.
Finally, by reacting 3 with the following rhodium(I)
and
iridium(I)
derivatives:
[Rh2Cl2(h4-C7H8)2],
Protons
l (ppm), J (Hz)
[Rh2Cl2(h2-C8H14)4], [Ir2Cl2(h2-C8H14)4], [Rh2Cl2(h4-
C8H12)2] and [Ir2Cl2(h4-C8H12)2], the corresponding 9-
anthrylmethylcyclopentadienyl derivatives 9, 10a, 10b,
11a, and 11b were obtained in good yields.
H1, H8
8.24, 2H, d, J 9
8.00, 2H, d, J 9
8.39, 1H, s
7.47, 4H, m
4.70, 2H, broad split signal
6.54, bs; 6.40, bs; 6.32, bs; 6.21, bs; 5.97, bs;
5.60, bs
H4, H5
H9
H2, H3, H6, H7
H10
Hv
Ha
3.17, 1H, bs; 3.11, 2H, bs; 3.01, 2H, bs
* Spectra recorded in CDCl3; s, singlet; m, multiplet; d, doublet; bs,
broad signal.
nects the anthrylic moiety with the C5 ring: these pro-
tons should give rise to a doublet in the case of isomer
1a, and to two singlets in the case of 1b and 1c (Table
1).
A suspension of 1 in absolute ethanol reacted with
thallium ethoxide, at room temperature (r.t.), to form
9-anthrylmethylcyclopentadienylthallium(I) 3, which is
a yellow–ochre solid that can be stored under dinitro-
gen at r.t. for long periods of time without apparent
decomposition.
Complexes 4–11 are quite thermally stable at the
solid state and can be stored under dinitrogen at −
20°C for long periods of time without apparent decom-
position. They were characterised by elemental analysis,
1
mass spectrometry (EI MS), H-NMR, and, where ap-
propriate, also by FTIR. For two of them, i.e. 4 and 5,
the molecular and crystal structure was elucidated by
single-crystal X-ray diffraction (see Section 2.2). In all
1
The reaction of 3 with [Rh2Cl2L4] (L=C2H4 or CO)
produced [Rh(h5-AnCH2C5H4)(h2-C2H4)2] (4) and
[Rh(h5-AnCH2C5H4)(CO)2] (5) (AnCH2=9-anthryl-
methyl) in good yields. Analogously, [Rh(h5-
AnCH2C5H4)(PPh3)2] (6) was prepared by reacting
[RhCl(PPh3)3] with 3.
cases, well resolved H-NMR were obtained in C6D6
(Table 2) which were consistent with the proposed
structures and in agreement with the spectral pattern
observed for many rhodium(I) complexes of mono-sub-
stituted h5-C5H4X rings [7].
The resonances of the cyclopentadienyl ring as well
as those of the olefinic protons of the complexes re-
ported in this paper are generally observed at a slightly
higher field when compared with the corresponding
h5-C5H5 derivatives. Furthermore, by examining the
resonances of the cyclopentadienylic and olefinic pro-
tons exhibited by the complexes 10 and 11, a high-field

Table 2
1H-NMR data for complexes 4–11 a
/
Complex
l (ppm), J (Hz)
[Rh(h5-AnCH2C5H4)
(h2-C2H4)2] (4)
8.34 (2H, d, JHH 9, H1 and H8), 8.13 (1H, s, H9), 7.80 (2H, d, JHH 9, H4 and H5), 7.37–7.18 (4H, m, H2, H3, H6, and H7), 4.66 (2H, d, JHH 6, H12 and H13),
4.56 (2H, d, JHH 6, H11 and H14), 4.48 (2H, s, H10), 2.65 (4H, bs, C2H4), 1.10 (4H, bs, C2H4)
[Rh(h5-AnCH2C5H4)
(CO)2] (5)
8.12 (2H, d, JHH 9, H1 and H8), 8.14 (1H, s, H9), 7.81 (2H, d, JHH 9, H4 and H5), 7.38–7.21 (4H, m, H2, H3, H6, and H7), 4.86 (2H, d, JHH 6, H12 and H13),
4.68 (2H, d, JHH 6, H11 and H14), 4.30 (2H, s, H10
)
[Rh(h5-AnCH2C5H4)
(PPh3)2] (6)
8.50 (2H, d, JHH 9, H1 and H8), 8.15 (1H, s, H9), 7.86–7.75 (12H, m, PPh3), 7.09–6.92 (18H, m, PPh3), 7.89 (2H, d, JHH 9, H4 and H5), 7.41–7.29 (4H, m, H2,
H3, H6, and H7), 4.94 (2H, d, JHH 6, H12 and H13), 4.71 (2H, d, JHH 6, H11 and H14), 4.47 (2H, s, H10), 2.65 (4H, bs, C2H4), 1.10 (4H, bs, C2H4)
8.54 (2H, d, JHH 9, H1 and H8), 8.27 (1H, s, H9), 7.92 (2H, d, JHH 9, H4 and H5), 7.68–7.58 (6H, m, PPh3), 7.08–7.02 (9H, m, PPh3), 7.42–7.30 (4H, m, H2, H3,
H6, and H7), 5.03 (2H, d, JHH 6, H12 and H13), 4.76 (2H, d, JHH 6, H11 and H14), 4.56 (2H, s, H10), 2.83 (2H, bs, C2H4), 1.76 (2H, bs, C2H4)
[Rh(h5-AnCH2C5H4)
(h2-C2H4)
(PPh3)] (7)
59393
[Rh(h5-AnCH2C5H4)
(CO)
8.49 (2H, d, JHH 9, H1 and H8), 8.21 (1H, s, H9), 7.90 (2H, d, JHH 9, H4 and H5), 7.68–7.52 (6H, m, PPh3), 7.04–6.98 (9H, m, PPh3), 7.41–7.29 (4H, m, H2, H3,
H6, and H7), 5.05 (2H, d, JHH 6, H12 and H13), 4.81 (2H, d, JHH 6, H11 and H14), 4.65 (2H, s, H10
)
59494
(PPh3)] (8)
(2000)2000)
[Rh(h5-AnCH2C5H4)
(h4-C7H8)] (9)
8.40 (2H, d, JHH 9, H1 and H8), 8.16 (1H, s, H9), 7.84 (2H, d, JHH 9, H4 and H5), 7.38–7.21 (4H, m, H2, H3, H6, and H7), 4.88–4.90 (4H, m, H11ꢀH14), 4.50
(2H, s, H10), 3.02 (2H, m, C7H8), 2.86 (4H, m, C7H8), 0.96 (2H, m, C7H8)
[Rh(h5-AnCH2C5H4)
(h2-C8H14)2] (10a)
[Ir(h5-AnCH2C5H4)
(h2-C8H14)2] (10b)
[Rh(h5-AnCH2C5H4)
(h4-C8H12)] (11a)
[Ir(h5-AnCH2C5H4)
(h4-C8H12)] (11b)
8.58 (2H, d, JHH 9, H1 and H8), 8.19 (1H, s, H9), 7.88 (2H, d, JHH 9, H4 and H5), 7.43–7.25 (4H, m, H2, H3, H6, and H7), 4.74 (4H, m, H11–H14), 4.21 (2H, s,
25151
H10), 2.29–2.06 (4H, m, C8H14), 1.88–1.20 (24H, m, C8H14
)
8.48 (2H, d, JHH 9, H1 and H8), 8.18 (1H, s, H9), 7.83 (2H, d, JHH 9, H4 and H5), 7.40–7.22 (4H, m, H2, H3, H6, and H7), 4.67 (4H, m, H11–H14), 4.32 (2H, s,
H10), 2.18–2.00 (4H, m, C8H14), 1.78–1.12 (24H, m, C8H14
8.42 (2H, d, JHH 9, H1 and H8), 8.19 (1H, s, H9), 7.86 (2H, d, JHH 9, H4 and H5), 7.40–7.24 (4H, m, H2, H3, H6, and H7), 4.82 (2H, d, JHH 6, H11 and H14),
4.71 (2H, d, JHH 6, H11 and H14), 4.43 (2H, s, H10), 3.89–3.80 (4H, m, C8H12), 2.31–1.90 (8H, m, C8H12
8.31 (2H, d, JHH 9, H1 and H8), 8.12 (1H, s, H9), 7.80 (2H, d, JHH 9, H4 and H5), 7.38–7.20 (4H, m, H2, H3, H6, and H7), 4.74 (2H, d, JHH 6, H11 and H14),
4.60 (2H, d, JHH 6, H11 and H14), 4.40 (2H, s, H10), 3.78–3.69 (4H, m, C8H12), 2.28–1.88 (8H, m, C8H12
26666
)
)
)
a Spectra recorded in C6D6; s, singlet; m, multiplet; d, doublet; bs, broad signal.

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
255
Table 3
Table 4
,
Comparison of the CꢀO IR stretching frequencies of complexes 5 and
8 with those of the corresponding cyclopentadienyl derivatives
Selected bond lengths (A) and angles (°) for complex 4
Rh(1)ꢀC(1A)
Rh(1)ꢀC(2A)
Rh(1)ꢀC(3A)
Rh(1)ꢀC(4A)
Rh(1)ꢀEth1A
Rh(1)ꢀEth2A
Rh(1)ꢀCpA
C(1A)ꢀC(2A)
C(3A)ꢀC(4A)
C(5A)ꢀC(6A)
C(5A)ꢀC(9A)
C(6A)ꢀC(7A)
C(7A)ꢀC(8A)
C(8A)ꢀC(9A)
C(9A)ꢀC(10A)
C(10A)ꢀC(11A)
2.088(9) Rh(2)ꢀC(1B)
2.100(9) Rh(2)ꢀC(2B)
2.112(9) Rh(2)ꢀC(3B)
2.106(10) Rh(2)ꢀC(4B)
1.978(10) Rh(2)ꢀEth1B
1.994(11) Rh(2)ꢀEth2B
1.897(6) Rh(2)ꢀCpB
1.377(15) C(1B)ꢀC(2B)
1.372(16) C(3B)ꢀC(4B)
1.400(11) C(5B)ꢀC(6B)
1.408(10) C(5B)ꢀC(9B)
1.400(12) C(6B)ꢀC(7B)
1.425(11) C(7B)ꢀC(8B)
1.400(10) C(8B)ꢀC(9B)
1.516(10) C(9B)ꢀC(10B)
1.529(9) C(10B)ꢀC(11B)
2.100(9)
2.088(9)
Complex
w CꢀO (cm−1
)
2.128(11)
2.109(9)
1.978(11)
1.997(10)
1.891(9)
1.375(15)
1.414(17)
1.413(11)
1.420(10)
1.418(11)
1.393(10)
1.417(10)
1.512(10)
1.514(10)
[Rh(h5-AnCH2C5H4)(CO)2] (5)
[Rh(h5-C5H5)(CO)2]
2042; 1979
2051; 1987
1951
[Rh(h5-AnCH2C5H4)(PPh3)(CO)] (8)
[Rh(h5-C5H5)(PPh3)(CO)]
1942
shift is observed, as expected [8], on passing from
rhodium to iridium derivatives.
Finally, it is interesting to note that the CꢀO IR
stretching frequencies of complexes 5 and 8 result to be
slightly lower than those exhibited by [Rh(h5-
C5H5)(CO)2] [9] and [Rh(h5-C5H5)(PPh3)(CO)] [10]
(Table 3), thus showing a moderately higher electron-
donating power for the h5-9-anthrylmethylcyclopenta-
dienyl ligand.
Eth1AꢀRh(1)ꢀEth2A
Eth1AꢀRh(1)ꢀCpA
Eth2AꢀRh(1)ꢀCpA
C(6A)ꢀC(5A)ꢀC(9A)
C(5A)ꢀC(6A)ꢀC(7A)
C(6A)ꢀC(7A)ꢀC(8A)
C(7A)ꢀC(8A)ꢀC(9A)
C(5A)ꢀC(9A)ꢀC(8A)
94.9(5) Eth1BꢀRh(2)ꢀEth2B
132.4(4) Eth1BꢀRh(2)ꢀCpB
132.8(4) Eth2BꢀRh(2)ꢀCpB
109.2(7) C(6B)ꢀC(5B)ꢀC(9B)
107.4(7) C(5B)ꢀC(6B)ꢀC(7B)
108.2(7) C(6B)ꢀC(7B)ꢀC(8B)
107.8(7) C(7B)ꢀC(8B)ꢀC(9B)
107.3(6) C(5B)ꢀC(9B)ꢀC(8B)
94.9(5)
132.5(4)
132.6(4)
107.5(7)
108.7(7)
107.2(7)
109.5(7)
107.1(6)
2.2. X-ray crystallographic studies
The asymmetric unit in the crystal structure of (h5-9-
anthrylmethylcyclopentadienyl)bis(h2-ethylene) rhod-
ium(I) (4) consists of two independent molecules ar-
ranged as shown in Fig. 1. The main bond distances
and angles are listed in Table 4.
C(8A)ꢀC(9A)ꢀC(10A) 126.2(7) C(8B)ꢀC(9B)ꢀC(10B) 127.1(7)
C(5A)ꢀC(9A)ꢀC(10A) 126.3(7) C(5B)ꢀC(9B)ꢀC(10B) 125.4(7)
C(9A)ꢀC(10A)ꢀC(11A) 112.6(5) C(9B)ꢀC(10B)ꢀC(11B) 113.0(6)
The coordination geometry of the metal may be
described as trigonal planar referring to the centroids of
cp and ethylene ligands (thereafter, we will use the
symbols Cp and Eth to indicate these centroids). The
larger steric demand by the cyclopentadienyl ligand, if
compared with ethylene, makes the angles among the
ligands to be very different. In fact, while the
Eth(1)ꢀRhꢀEth(2) angle is 94.9°, the mean value of
CpꢀRhꢀEth angle is 132.6°. Such an effect has been
already observed in analogous derivatives of formula
[Rh(h5-RC5H4)(h2-C2H4)2], where R is an aryl or an
alkyl group [11]. In both the independent molecules one
of the ethylene ligands, C(3)ꢀC(4), is on the same side
of the C(9) atom of the cyclopentadienyl ring, i.e. the
carbon atom carrying the bulky 9-anthrylmethyl group.
Interestingly, the eclipsed position does not weaken the
,
RhꢀEth(2) bond, this showing a mean length (1.994 A)
which is not much longer than the RhꢀEth(1) one
,
(1.978 A). A and B show different rotation angles of
the
9-anthrylmethyl-substituted
cyclopentadienyl
groups with respect to the coordination planes as
defined above. In fact, while the atom C(3A) is almost
eclipsed by the atom C(9A) (dihedral angle,
C(3A)ꢀRh(1)ꢀCpAꢀC(9A)= −3.5°) in molecule A, the
corresponding atoms are staggered (dihedral angle
C(3B)ꢀRh(2)ꢀCpBꢀC(9B)=34.3°) in molecule B.
Moreover, the torsion angles C(8)ꢀC(9)ꢀC(10)ꢀC(11),
which define the orientation of the 9-antryl group with
respect to the rest of the molecule, result to be very
different in the two molecules A and B, i.e. 95.7 and
65.7°, respectively.
A very similar situation is found in (h5-9-an-
thrylmethylcyclopentadienyl)dicarbonylrhodium(I) (5),
whose molecular structure is shown in Fig. 2. Bond
Fig. 1. Drawing of the molecular structure of complex 4. Thermal
ellipsoids are at the 50% probability.

256
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
Table 5
distances and angles are listed in Table 5. Also in this
case, the asymmetric unit consists of two independent
molecules showing rather different conformations. In
both the molecules the centroids of the cyclopentadi-
enyl ring and the two coordinated carbonyls define an
irregular triangle around the rhodium atom. As already
pointed out in discussing the structure of 4, the pres-
ence of the bulky 9-anthrylmethyl group on Cp ring
does not weaken the nearest RhꢀCO bond that shows
the same length as the other one, in both molecules A
and B. These structural features have also been ob-
served in closely related rhodium(I) complexes of for-
mula [Rh(h5-RC5H4)(CO)2], where R is an aryl or an
alkyl group [7a,12].
Finally, in the case of 5, the molecules A and B differ
in their conformation much more than the two inde-
pendent molecules do in 4. In fact, while the torsion
angle C(1A)ꢀRh(1)ꢀCpAꢀC(7A) is 17.6°, the corre-
sponding C(1B)ꢀRh(2)ꢀCpBꢀC(7B) is 56.4°. More-
over, the torsion angles C(6)ꢀC(7)ꢀC(8)ꢀC(9), de-
fining the orientation of the anthryl group, are
134.3 and −155.2°, respectively for the molecules A
and B.
,
Selected bond lengths (A) and angles (°) for complex 5
Rh(1)ꢀC(1A)
Rh(1)ꢀC(2A)
Rh(1)ꢀCpA
1.845(5) Rh(2)ꢀC(1B)
1.842(5) Rh(2)ꢀC(2B)
1.911(5) Rh(2)ꢀCpB
1.135(5) C(1B)ꢀO(1B)
1.142(6) C(2B)ꢀO(2B)
1.404(5) C(3B)ꢀC(4B)
1.406(5) C(3B)ꢀC(7B)
1.418(6) C(4B)ꢀC(5B)
1.391(5) C(5B)ꢀC(6B)
1.444(5) C(6B)ꢀC(7B)
1.524(5) C(7B)ꢀC(8B)
1.517(5) C(8B)ꢀC(9B)
1.847(5)
1.835(5)
1.916(5)
1.127(6)
1.147(6)
1.424(6)
1.405(5)
1.405(6)
1.408(5)
1.436(5)
1.504(5)
1.516(5)
C(1A)ꢀO(1A)
C(2A)ꢀO(2A)
C(3A)ꢀC(4A)
C(3A)ꢀC(7A)
C(4A)ꢀC(5A)
C(5A)ꢀC(6A)
C(6A)ꢀC(7A)
C(7A)ꢀC(8A)
C(8A)ꢀC(9A)
C(1A)ꢀRh(1)ꢀC(2A)
C(1A)ꢀRh(1)ꢀCpA
C(2A)ꢀRh(1)ꢀCpA
C(4A)ꢀC(3A)ꢀC(7A)
C(3A)ꢀC(4A)ꢀC(5A)
C(4A)ꢀC(5A)ꢀC(6A)
C(5A)ꢀC(6A)ꢀC(7A)
C(3A)ꢀC(7A)ꢀC(6A)
C(3A)ꢀC(7A)ꢀC(8A)
C(6A)ꢀC(7A)ꢀC(8A)
C(7A)ꢀC(8A)ꢀC(9A)
91.4(2) C(2B)ꢀRh(2)ꢀC(1B)
135.3(2) C(1B)ꢀRh(2)ꢀCpB
133.3(2) C(2B)ꢀRh(2)ꢀCpB
107.6(4) C(4B)ꢀC(3B)ꢀC(7B)
108.9(3) C(3B)ꢀC(4B)ꢀC(5B)
107.9(4) C(4B)ꢀC(5B)ꢀC(6B)
107.8(3) C(5B)ꢀC(6B)ꢀC(7B)
107.6(3) C(3B)ꢀC(7B)ꢀC(6B)
126.2(3) C(3B)ꢀC(7B)ꢀC(8B)
125.8(3) C(6B)ꢀC(7B)ꢀC(8B)
112.6(3) C(7B)ꢀC(8B)ꢀC(9B)
89.5(2)
134.9(2)
135.6(3)
108.3(3)
109.1(3)
106.4(3)
109.7(3)
106.3(3)
126.1(3)
127.4(3)
115.1(3)
2.3. Spectroscopic studies
(PPh3)2], are shown in Fig. 5, which illustrates clearly
that only the [(h5-C5H5)Rh(PPh3)2] still absorbs in the
visible while the other two have relatively small absorp-
tion coefficients in the near UV.
The UV–vis spectra (280–700 nm) of complexes
4–11, along with those of 9-methylanthracene (9-
MeAn) and 9-anthrylmethylcyclopentadiene 3, are
shown in Figs. 3 and 4 and the corresponding parame-
ters are given in Table 6. Moreover, the UV–vis spectra
of three reference complexes, i.e. [Rh(h5-C5H5)(h2-
C2H4)2], [(h5-C5H5)Rh(CO)2], and [(h5-C5H5)Rh-
The comparison of the spectrum of 9-methylan-
thracene (9-MeAn) with those of 9-anthrylmethylcy-
clopentadiene 3 and complexes 4–11 points out clearly
that the substitution of a methylic hydrogen atom of
9-methylanthracene with the cyclopentadiene ring or
with a cyclopentadienyl–metal moiety causes rather
little effect on the main parameters of the spectra. In
fact, molar absorption coefficients, positions of the
maxima, and vibrational structures (Table 6) are all
typical of 9-methylanthracene, apart from relatively
small displacement of the maxima. Furthermore, the
molar absorption coefficients of the metal derivatives
are generally lower than those of 9-MeAn and 9-an-
thrylmethylcyclopentadiene 3. Analogously, the spectral
resolution, as measured by the ratio between the molar
absorption coefficients of the maximum at ca. 390 nm
and of the following minimum (m1/mmin), decreases on
going from 9-methylanthracene to the metal derivatives
4–11 (Table 6). As expected, also the ratio (m1max/m2max
)
between the molar coefficients of the maxima at ca. 390
and ca. 370 nm, which depends on the changes in
geometry between the ground and the excited state,
results were influenced by the structural changes. These
data, which are summarised below, suggest that signifi-
cant interactions occur between the anthrylic sub-unit
and the cyclopentadienyl–metal moiety:
Fig. 2. Drawing of the molecular structure of complex 5. Thermal
ellipsoids are at the 50% probability.

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
257
Fig. 3. Absorption spectra (m vs. u, nm) of 9-methylanthracene (MeAn), 9-anthrylmethylcyclopentadiene 3, and of complexes [Rh(h5-
AnCH2C5H4)(h2-C2H4)2] (4), [Rh(h5-AnCH2C5H4)(CO)2] (5), [Rh(h5-AnCH2C5H4)(PPh3)2] (6), [Rh(h5-AnCH2C5H4)(PPh3)(h2-C2H4)] (7),
Rh(h5-AnCH2C5H4)(PPh3)(CO)] (8) and [Rh(h5-AnCH2C5H4)(h4-C7H8)] (9), in 5×10−5–10−4 M benzene solution.
m1max/mmin: 6B7=8B11aB9B4B10aB5B3
sorption tail above 450 nm. This also happens in the
case of [Rh(h5-AnCH2C5H4)(PPh3)2] (6), [Rh(h5-An-
CH2C5H4)(PPh3)(h2-C2H4)] (7), and [Rh(h5-AnCH2-
C5H4)(PPh3)(CO)] (8) (Fig. 3). Nevertheless, the absor-
ption spectra of all complexes 4–11 extend above 400
nm (Figs. 3 and 4). The presence of such tails is another
indication that important interactions effectively occur
between the anthrylic chromophore and the metal-con-
taining moiety. Between 410 and 450 nm, the molar
absorption coefficients increase as indicated below:
B9-MeAn
m1max/m2max: 8B9B9-MeAnB11aB10aB4B5B3
B6B7
A close look at the spectra of cyclopentadienylic
derivatives of rhodium(I) (Fig. 5) shows that only the
triphenylphosphine-modified complex, i.e. [Rh(h5-
C5H5)(PPh3)2], exhibits a long but non-structured ab-

258
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
Fig. 4. Absorption spectra (m vs. u, nm) of [Rh(h5-AnCH2C5H4)(h2-C8H14)2] (10a), [Ir(h5-AnCH2C5H4)(h2-C8H14)2] (10b), [Rh(h5-
AnCH2C5H4)(h4-1,5-C8H12)] (11a) and [Ir(h5-AnCH2C5H4)(h4-1,5-C8H12)] (11b), in 5×10−5–10−4 M benzene solution.
u=410 nm: 5B11aB8B10aB9B4B7B6
u=420 nm: 5B11aB9B10aB4B8B7B6
u=430 nm: 5B4B11aB9B10aB8B7B6
u=450 nm: 5B4B11aB9B10aB8B7B6
again can be accounted for only by invoking an interac-
tion between the anthrylic and cyclopentadienyl–metal
moieties. Similarly, in complexes 6, 7, and 8, which
contain at least one triphenylphosphine in the coordi-
nation sphere of the rhodium(I) centre, the interactions
appear to increase in the order: 6B7B8. A further
indication of a rather strong interaction is given by the
fact that to the quite long and intense tail of the model
compound, i.e. [Rh(h5-C5H5)(PPh3)2], corresponds a re-
duction of the molar absorption coefficient in the 330–
390 nm region and a large reduction of the spectral
resolution as measured by m1max/mmin ratio. The interac-
tion strength as suggested by these data can be sum-
marised as follows:
Since these data suggest the presence of a CT absorp-
tion band, a more detailed analysis of the absorption
spectra is necessary. In Figs. 6–8, the spectra complexes
[Rh(h5-AnCH2C5H4)(h2-C2H4)2] (4), [Rh(h5-AnCH2-
C5H4)(CO)2] (5), and [Rh(h5-AnCH2C5H4)(PPh3)2] (6),
respectively, are compared with those of 9-methylan-
thracene, which was necessarily adjusted, the corre-
sponding non anthrylmethyl-substituted cyclopenta-
dienyl complex, and with the sum of the latter spectra.
In the cases of the complexes 4 and 5 (Figs. 6 and 7) the
molar absorption coefficients in the tail appear to be
related to the difference in the energies of the anthrylic
and the cyclopentadienyl–metal moieties, such a differ-
ence being higher in 5 than in 4.
Indeed, both the corresponding non anthrylmethyl-
substituted complexes, i.e. [Rh(h5-C5H5)(h2-C2H4)2]
and [Rh(h5-C5H5)(CO)2], show a negligible absorption
above 370 nm. Furthermore, the m1max/mmin ratios sug-
gest that a stronger interaction between the subunits
occurs in 4 rather than 5. The tails are rather short
because, at 450 nm, the molar extinction coefficients are
quite negligible, for both complexes. The m1max/m2max
ratios (Table 6) have rather similar values in all cases.
5B4B8B7B6
Again, these absorption data support the existence of
CT states.
Table 7 reports the fluorescence emission spectra
data for complexes 4–11, 9-anthrylmethylcyclopentadi-
ene 3, and 9-methylanthracene which is taken as a
reference compound. A rapid examination of the tabu-
lated figures shows first that 9-anthrylmethylcyclopen-
tadiene
3 results were an efficient light-emitting
molecule, when excited at 365 nm, while its derivatives,
i.e. the complexes 4–11, are poorly luminescent com-
pounds. Indeed, all complexes exhibit similar fluores-
cence spectra which are typical of the anthrylic
fluorophore but have extremely low intensity: a few
percent or less the one observed for 9-methylanthracene
(Table 7). In some cases, the fluorescence intensity
results were rather high (about 10 to 15%), if the
samples were purified by the routine procedure de-
However, these data, when compared with the m1max
m2max ratio found for 9-methylanthracene, indicate a
clear change in the Franck–Condon factor, which
/

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
259
Table 6
UV–vis absorption spectra parameters for 9-methylanthracene (MeAn), 9-anthrylmethylcyclopentadiene (AnMeCPD) 1, and for complexes 4–11 a
Compound
u1max
m1max
u2max
m2max
umin
mmin
m1max/mmin
m1max/m2max
MeAn
AnMeCPD 1
4
5
6
7
8
9
10a
10b
11a
11b
390
392
393
392
392
392
392
393
392
396
392
392
9313
11 960
9000
9720
7300
7650
6800
9200
8550
8500
7200
7000
370
372
372
372
372
372
372
372
372
375
372
372
10 000
12 200
9500
10 000
7350
7700
7900
10 000
9000
8600
380
380
382
380
384
380
380
382
380
384
380
382
2351
3800
4100
3320
6150
4800
4300
5000
4100
3750
4100
3400
3.96
3.14
2.19
2.93
1.19
1.60
1.58
1.84
2.08
2.27
1.76
2.06
0.93
0.98
0.95
0.97
0.99
0.99
0.86
0.92
0.95
0.99
0.95
0.97
7600
7200
a All spectra were recorded in 5×10−5–10−4 M benzene solution; wavelength is given in nm.
scribed in Section 4. As discussed in detail in Section 4,
a rapid estimate of the lifetime suggested the presence
of small amounts of a fluorescent impurity, which was
identified with 9-anthrylmethylcyclopentadiene, by thin
layer chromatography. Indeed, further purification of
the samples caused a drastic reduction in the fluores-
cence emission. Thus, in all cases the fluorescence inten-
sity is below 5% in the one observed for
9-methylanthracene, the only apparent exception con-
cerning [Rh(h5-AnCH2C5H4)(PPh3)(h2-C2H4)2] (7),
whose further purification resulted to be less efficient
than in the other cases. For this reason 7 has not been
further considered in the following discussion.
the involved groups occur. When compared with the
qualitative evaluation of the strength of the interaction
between the anthrylic and the cyclopentadienyl–metal
moieties, as obtained from the above absorption data,
the fluorescence quenching data appear to be more or
less in a reverse order:
interaction strength form absorption:
5B4B8B6
fluorescence quenching:
4\5\6\8
With the aim to gain more insight on the role played by
the electron donating and accepting properties of the
various components of the supramolecules described in
this paper, the influence exerted by the nature of the
transition metal centre was explored, at a preliminary
stage, by comparing the spectroscopic behaviour of the
The intensity of fluorescence emission, although be-
ing very low in all cases, increases in the following
order:
rhodium(I)
derivatives
[Rh(h5-AnCH2C5H4)(h2-
4B5B10aB6B11aB8B9
C8H14)2] (10a) and [Rh(h5-AnCH2C5H4)(h4-1,5-C8H12)]
(11b) with that exhibited by the isostructural iridium(I)
complexes [Ir(h5-AnCH2C5H4)(h2-C8H14)2] (10b) and
[Ir(h5-AnCH2C5H4)(h4-1,5-C8H12)] (11b).
However, since it is likely than traces of fluorescent
impurities contribute to the spectra of all compounds, a
main conclusion is that fluorescence quenching is highly
efficient in all cases. The fluorescence quenching is
expected to be higher when strong interactions between
Just looking at the m1max/mmin and m1max/m2max ratios for
the complexes 10a, 10b, 11a, and 11b (Table 6), one can
Fig. 5. Absorption spectra (m vs. u, nm) of [Rh(h5-C5H5)(h2-C2H4)2], [(h5-C5H5)Rh(CO)2] and [(h5-C5H5)Rh(PPh3)2], in 5×10−5–10−4
benzene solution.
M

260
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
conclude that: (i) the resolution of the absorption spec-
trum is higher when cyclooctene is present in the coor-
dination sphere of the metal centre as ancillary ligand
and (ii) under the same structural conditions, the ab-
sorption spectra of the iridium derivatives are more
resolved than those of the rhodium ones. Thus, accord-
ing to the above discussion, the interaction between the
anthrylic and the cyclopentadienyl–metal subunits is
higher in the rhodium(I) derivatives than it is in the
case of the isostructural iridium(I) complexes and when
the cyclooctene, instead of 1,5-cyclooctadiene, com-
pletes the coordination sphere of the metal centre.
When compared with the qualitative evaluation of the
strength of the interaction between the anthrylic and
the cyclopentadienyl–metal moieties, as obtained from
the absorption data, the fluorescence quenching data
obtained for the complexes 10 and 11 appear to be in
the following order:
ment and the cyclopentadienyl–metal moiety is a more
likely candidate. The occurrence of such an electron
transfer is fully justified on a thermodynamic ground-
ing. In fact, on the base of a study of the electrochem-
ical behaviour of some of the complexes 4–11 [13]1, it
was possible to estimate the free energy change associ-
ated with the intramolecular transfer of one electron
from the metal–cyclopentadienyl moiety to the pho-
toexcited anthryl group (Scheme 2). Such a free energy
change, calculated for the complexes [Rh(h5-AnCH2C5-
H4)(h2-C2H4)2] (4) and [Rh(h5-AnCH2C5H4)(CO)2] (5)
through the combination of photophysical and electro-
chemical quantities, results to have a marked negative
value, at 25°C, in both cases (DG°= −0.24 eV, for
complex 4; DG°= −0.73 eV, for complex 5), thus
indicating that the process outlined in Scheme 2 is
thermodynamically favourable [13b].
interaction strength form absorption:
11a\11b\10a\10b
fluorescence quenching:
11b\11a\10a\10b
3. Conclusions
Various 9-anthrylmethylcyclopentadienylic deriva-
tives of rhodium(I) and iridium(I) of general formula
[M(h5-AnCH2C5H4)L2] can be prepared in good yields
by reacting 9-anthrylmethylcyclopentadienylthallium(I)
1
with the corresponding metal chlorides. H-NMR and
IR data of the complexes 4–11 indicates that 9-anthryl-
methylcyclopentadienyl is a better electron-donor than
cyclopentadienyl.
Fig. 6. Comparison of the sum (bold solid line) of the UV–vis spectra
of 9-methylanthracene (dots and dashes) and [Rh(h5-C5H5)(h2-
C2H4)2] (crosses) with the spectrum of [Rh(h5-AnCH2C5H4)(h2-
C2H4)2] (4) (solid line); (diamonds) amplification (×10) of the tail of
the spectrum of 4.
The absorption and fluorescence spectra suggest
some preliminary conclusions: (i) the presence of the
methylene group as a spacer between the anthryl group
and the cyclopentadienyl–metal moieties makes them
to interact, the strength of such an interaction depend-
ing upon the nature of the ancillary ligands bound to
the transition metal centre and (ii) while 9-anthryl-
methylcyclopentadiene is an efficient light-emitting
molecule, the fluorescence of anthryl group is strongly
quenched in all rhodium and iridium complexes. As far
as this last point is concerned, it must be underlined
that since rhodium and iridium cause similar effects on
the fluorescence quenching, an energy transfer mecha-
nism, implicating either the reabsorption of the an-
thracene emission by the metal centre or a dipolar
interaction, should not be the fundamental quenching
process involved. Moreover, the absence of a clear
correlation between the absorption tail and the fluores-
cence quenching suggests that intramolecular energy
transfer should not be an important parameter. Conse-
quently, the electron transfer between the anthryl frag-
1 Free energy changes were calculated through the equation:
0−0%
(An)
DG°= −E
+e (E°(RhCpL2+/RhCpL2)−E°(An/Anꢀ))−DGS
0−0%
(An)
where E
=3.2 eV is the absorption energy of the anthryl group as
determined through the UV spectra of the complexes 4 and 5;
E° and E° are the standard reduction poten-
(RhCpL2+/RhCpL2)
(An/Anꢀ)
tials for the rhodium(I) moiety and the anthryl group, respectively, as
they were determined through the voltammetric study of 4 and 5 in
THF, and have the following figures:
E°(RhCpL2+/RhCpL2)= +0.85 V and E°
(An/Anꢀ)=
−1.89 V, in the case of 4
E°(RhCpL2+/RhCpL2)= +1.00 V and E°
(An/Anꢀ)=1.94 V, in the case of 5
finally, DGS is a corrective term which accounts for the electrostatic
free energy change occurring as a consequence of the electron transfer
as well as for the passage from THF, solvent in which the electrocto-
chemical measurements were performed, to benzene, solvent in which
were carried out the photophysical measurements.

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
261
Table 7
Fluorescence emission spectra data for 9-methylanthracene (MeAn),
9-anthrylmtehylcyclopentadiene (AnMeCPD) 1, and complexes 4–
11 a
b
Compound
umax
Imax/I365
Irel
Q (%) c
MeAn
AnMeCPD 1
4
5
392
392
392
390
394
392
393
393
392
392
394
393
12.14
11.55
0.05
0.12
0.31
1.06
0.40
0.61
0.29
0.63
0.34
0.15
100.0
93.1
0.4
1.0
2.5
8.7
3.3
5.0
2.4
5.2
2.8
1.2
0.0
6.9
99.6
99.0
97.5
91.3
96.7
95.0
97.6
94.8
97.2
98.8
6
7 c
8
9
10a
10b
11a
11b
Fig. 7. Comparison of the sum (bold solid line) of the UV–vis spectra
of 9-methylanthracene (dots and dashes) and [Rh(h5-C5H5)(CO)2]
(crosses) with the spectrum of [Rh(h5-AnCH2C5H4)(CO)2] (5) (solid
line); (diamonds) amplification (×10) of the tail of the spectrum of 5.
a Wavelength is given in nm.
b The emission intensity of 9-methylanthracene (MeAn) was taken
as reference, i.e. 100.
Furthermore, work is still in progress with the aim to
clarify further the complex phenomenology associated
with the photophysical properties of the metal deriva-
tives reported in this paper.
c The sample contained a few percent of 9-anthrylmethylcyclopen-
tadiene 1.
tained by a FTIR Perkin–Elmer 1750 spectrometer.
Electron ionisation mass spectra (EI MS) were obtained
with a VG Analytical 7070E apparatus.
4. Experimental details
9-bromomethylanthracene [14], cyclopentadienyl-
sodium [7], di-m-chlorotetrakis(carbonyl)dirhodium(I)
[15], di-m-chlorotetrakis(h2-ethylene)dirhodium(I) [16],
chlorotris(triphenylphosphine)rhodium(I) [17], di-m-
chloro-tetrakis(h2-cyclooctene)dirhodium(I) [18], di-m-
4.1. General
The reactions and manipulations of organometallics
were carried out under dinitrogen or argon using stan-
dard techniques. All solvents were dried and distilled
prior to use following standard procedures. Micro-
analyses were performed by the Laboratorio di Mi-
croanalisi, Facolta` di Farmacia, Universita` di Pisa.
Melting or decomposition points were determined by a
MEL-TEMP II (Aldrich) apparatus and are not cor-
chlorobis(h4-cycloocta-1,5-diene)dirhodium(I)
[19],
di-m-chlorobis(h4-norbornadiene)dirhodium(I) [20], di-
m-chlorotetrakis(h2-cyclooctene)diiridium(I) [21], and
di-m-chlorobis(h4-cycloocta-1,5-diene)diiridium(I) [19],
(h5-cyclopentadienyl)bis(h2-ethylene)rhodium(I)
[22]
and (h5-cyclopentadienyl)dicarbonylrhodium(I) [9] were
1
prepared as reported. Thallium(I) ethoxide (Aldrich),
rected. H-NMR spectra were run at 200 MHz on a
Varian Gemini 200 instrument. IR spectra were ob-
Fig. 8. Comparison of the sum (bold solid line) of the UV–vis spectra
of 9-methylanthracene (dots and dashes) and [Rh(h5-C5H5)(PPh3)2]
(crosses) with the spectrum of [Rh(h5-AnCH2C5H4)(PPh3)2] (6) (solid
line).
Scheme 2.

262
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
Table 8
triphenylphosphine
(Aldrich),
9-methylanthracene
Crystal data and structure refinement for complexes 4 and 5
(Aldrich), 1,5-cyclooctadiene (Aldrich), cyclooctene
(Aldrich), ethylene (Matheson Gas Products), carbon
monoxide (Matheson Gas Products) and 9-
chloromethylanthracene (Aldrich) were used as re-
ceived. Dicyclopentadiene (Fluka) was cracked
immediately prior to use.
Compound
4
5
Empirical formula
Formula weight
Temperature (K)
C24H23Rh
414.33
293(2)
0.71073
Triclinic
C22H15O2Rh
414.25
293(2)
0.71073
Triclinic
,
Wavelength (A)
Crystal system
Space group
(
(
P1
P1
4.2. X-ray diffraction analysis
Unit cell dimensions
,
a (A)
11.112(1)
12.065(1)
15.982(2)
99.83(1)
107.86(1)
107.22(1)
1865.6(3)
4
12.232(1)
13.463(1)
13.488(1)
61.25(1)
68.51(1)
67.45(1)
1752.5(2)
4
Single crystals of [Rh(h5-AnCH2C5H4)(h2-C2H4)2] (4)
suitable for X-ray analysis were obtained by slowly
cooling a saturated toluene/pentane solution of such a
compound. The crystals were great red–orange prisms.
A splinter, obtained by cutting one of them in air, was
sealed in a capillary under dinitrogen atmosphere. The
measurements were done on a Siemens P4 four circles
diffractometer, equipped with graphite monochroma-
tised Mo–Ka radiation. The crystal parameters are
listed in Table 8.
Data collection was performed by following the con-
ditions displayed in Table 8 and the redundant set of
data was corrected for Lorentz, polarisation and ab-
sorption effects by using the c-scan method [23], then it
was merged. The structure solution was obtained by
means of the standard direct methods contained in the
TREF procedure of the SHELXTL program [24] and was
completed by the usual Fourier transform method. The
hydrogen atoms were in part found in the difference
Fourier maps and in part introduced in calculated
positions. Those of ethylene ligands were kept fixed in
the found positions during the next refinement. Some
statistical parameters obtained in the final refinement
cycles are listed in Table 8.
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
Dcalc (Mg m−3
Absorption
)
1.475
0.918
1.570
0.985
coefficient (mm−1
)
F(000)
848
832
Crystal size (mm3)
q Range for data
collection (°)
0.64×0.12×0.12
2.01–21.24
0.48×0.38×0.26
2.02–25.00
Index ranges
−15h511,
−115k511,
−165l515
−15h514,
−135k514,
−155l516
6862
5942
[Rint=0.0132]
96.5
Reflections collected 4910
Independent
reflections
Completeness to
q=21.24° (%)
Refinement method Full-matrix least-
4098
[Rint=0.0286]
98.8
Full-matrix least-
squares on F2
5942/0/451
squares on F2
4098/0/451
Data/restraints/
parameters
Goodness-of-fit a
on F2
1.002
1.015
Final R indices a
[I\2|(I)]
R1=0.0414,
wR2=0.0953
R1=0.0343,
wR2=0.0795
R1=0.0487,
wR2=0.0862
0.0460, 0.60
0.564 and −0.438
Single crystals of [Rh(h5-AnCH2C5H4)(CO)2] (5) suit-
able for X-ray analysis were obtained by slowly cooling
a saturated toluene/pentane solution of such a com-
pound. The crystals were well shaped yellow prisms.
One of them was selected in air and sealed in a capillary
under dinitrogen atmosphere. The measurements were
done on a Siemens P4 four circles diffractometer,
equipped with graphite monochromatised Mo–Ka radi-
ation. The lattice parameters are listed in the third
column of Table 8. Data collection was performed by
following the conditions displayed in the same column
and the redundant set of data was corrected for
Lorentz, polarisation and absorption effects by using
the c-scan method [23], then it was merged. The struc-
ture solution was obtained by means of the standard
direct methods contained in the TREF procedure of the
SHELXTL program [24] and was completed by the usual
Fourier transform method. The hydrogen atoms were
in part found in the difference Fourier maps and in part
introduced in calculated positions. Some statistical
parameters obtained in the final refinement cycles are
listed in Table 8.
R indices a (all data) R1=0.0727,
wR2=0.1113
A, B (w) a
0.0645, 0.00
1.151 and −0.904
Largest difference
peak and hole
(e A
−3
,
)
a Goodness-of-fit=[S[w(Fo2−Fc2)2]/(N−P)]1/2, where N, P are the
numbers of observations and parameters, respectively, R1=SꢀꢀFoꢀ−
ꢀFcꢀꢀ/SꢀFoꢀ;
wR2=[S[w(F2o−F2c)2]/S[w(Fo2)2]]1/2
;
w=1/[|2(F2o)+
(AQ)2+BQ] where Q=[max(Fo2, 0)+2Fc2]/3.
4.3. Spectroscopic measurements
The absorption spectra were measured at r.t. in ben-
zene solutions using a Cary 14 spectrophotometer with
a resolution of 1 nm. The fluorescence properties at r.t.
were measured on an ISS-GREG 200 multi-phase
fluorimeter with resolution of 2–4 nm in dinitrogen-sat-
urated solutions at an absorbance of 0.1 at the excita-
tion wavelength, i.e. ca. 365 nm. The emission spectra
were not corrected for the instrumental response since

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
263
they were all similar. The relative values of the fluores-
cence quantum yields were therefore obtained by com-
resulting mixture was stirred at this temperature for 1.5
h and then filtered. A yellow solution was obtained
which was kept to dryness under reduced pressure, at
0°C. The residue was subdivided into 0.5 g portions and
each portion was purified by column (internal diameter,
10 mm; length, 300 mm) chromatography on silica gel
60 (230–400 mesh) (Merck), using a 1/1 (v/v) chloro-
form/hexane mixture as eluant. The first dark yellow
band which eluted was collected and kept to dryness
under vacuum. The overall yield was: 11 g of 9-anthryl-
methylcyclopentadiene (75%) as a dark yellow micro-
crystalline solid. Found: C, 93.68; H, 6.20. Anal. Calc.
for C20H16: C, 93.75; H, 6.25%. EI MS, m/z (relative
intensity %): 256 [M]+ (31), 215 (10), 191 (100), 165
(19), 83 (50), 47 (22).
parison
with
the
emission
intensity
of
9-methylanthracene which has a quantum yield of 0.35
and a lifetime 4.6 ns in cyclohexane [25]. The solvent
Rayleigh scattering was used as an internal reference.
All data have been normalised to the same absorbance
at the excitation wavelength. The relative fluorescence
quantum yields observed in most samples (0.01–0.05)
indicate fluorescence lifetimes of about 40–200 ps
which can be obtained with a minimum of accuracy
only if molecular rotation is accounted for, i.e. by the
use of a polariser which implies some intensity loss.
Consequently, this imposes extremely long measure-
ment periods and the resulting measurements are of
limited precision. In the case of too high fluorescence
yields (typically of the order of 10%), the fundamental
problem is to discriminate between the presence of
fluorescent impurities and a high intrinsic emission
intensity so that fluorescence lifetime estimate can be
sufficient. Preliminary measurements were thus carried
out at 40 MHz. In all cases, the lifetime values, ob-
tained by phase and modulation, turned out to be a few
ns. Such a long lifetime suggests the presence of a
fluorescent impurity which, together with a non negligi-
ble scattering component, can yield such an apparent
lifetime. Indeed, high resolution TLC analysis of com-
plexes 4–11, performed on Aluminium Oxide 60
(Merck) by using a benzene–pentane mixture (3/7, v/v)
as eluant, revealed the presence of very small amounts
of 9-anthrylmethylcyclopentadiene 3. On this basis, fur-
ther purification of the metallorganic compounds was
successfully performed only by extracting the samples
with absolute ethanol. Compound 3 being more soluble
in such a solvent than complexes 4–11 were; the treat-
ment allowed a marked reduction of the impurity con-
tent. Consequently, the fluorescence quenching, which
in some cases had resulted in relatively lower values,
became drastically higher after the purification of the
sample by ethanol extraction. The following examples
illustrates the observed effects:
4.5. Preparation of
9-anthrylmethylcyclopentadienylthallium(I) (3)
A mixture of 9-anthrylmethylcyclopentadiene (2.6 g,
10.1 mmol), thallium(I) ethoxide (975 ml, 13.7 mmol),
and absolute ethanol (180 ml) was stirred for 3 h, at r.t.
An ochre–yellow solid precipitated which was sepa-
rated by decanting off the surnatant solution, washed
with absolute ethanol (2×60 ml), then with dry diethyl
ether (2×60 ml) and with pentane (2×60 ml), and,
finally dried under vacuum. A 2.54 g sample of the title
compound (54% yield) as a ochre–yellow microcrys-
talline solid, was obtained. Found: C, 52.00; H, 3.38.
Anal. Calc. for C20H15Tl: C, 52.13; H, 3.47%.
4.6. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)bis(p2-ethylene) rhodium(I) (4)
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.75 g, 1.63 mmol), di-m-chlorotetrakis(h2-
ethylene)dirhodium(I) (0.32 g, 0.81 mmol), and
anhydrous benzene (60 ml) was stirred for 100 min, at
r.t., and then filtered. An orange solution was obtained
which was kept to dryness under reduced pressure. The
residue was dissolved in benzene (2 ml) and the result-
ing solution was passed through a column (internal
diameter, 10 mm; length, 30 mm) of alumina (Alu-
minium oxide 90, 70–230 mesh, Merck), using benzene
as eluant. From the first orange–yellow band which
eluted, 0.5 g of the title compound (74% yield), as a
yellow microcrystalline solid, was obtained. Found: C,
69.50; H, 5.50. Anal. Calc. for C24H23Rh: C, 69.56; H,
5.56%. EI MS, m/z (relative intensity %): 414 [M]+
(11), 386 [M−C2H4]+ (17), 358 [M−2 C2H4]+ (100),
253 (15).
Complex Before purification by
ethanol
After purification by
ethanol
Fluorescence Quenching Fluorescence Quenching
4
2.9
97.1
89.9
0.4
1.2
99.6
98.8
11b
10.1
4.4. Preparation of 9-anthrylmethylcyclopentadiene 1
4.7. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)dicarbonyl-rhodium(I) (5)
9-Bromomethylanthracene (14.3 g, 53 mmol) was
added to a solution of cyclopentadienylsodium (6.08 g,
69.1 mmol) in tetrahydrofuran (180 ml) at 0°C. The
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.71 g, 1.54 mmol), di-m-chlorotetrakis(car-

264
F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
bonyl)dirhodium(I) (0.30 g, 0.77 mmol), and benzene
(60 ml) was stirred at r.t. for 2 h and then filtered. The
solution was kept to dryness under reduced pressure.
The residue was dissolved in benzene (2 ml) and
purified by column (internal diameter, 10 mm; length,
30 mm) chromatography on alumina (Aluminium oxide
90, 70–230 mesh, Merck), using benzene as eluant.
From the first orange–yellow band which eluted, 0.57 g
of the title compound (89% yield), as an orange–yellow
microcrystalline solid, was obtained. Found: C, 63.70;
H, 3.57. Anal. Calc. for C22H15O2Rh: C, 63.77; H,
3.62%. EI MS, m/z (relative intensity %): 414 [M]+
(17), 386 [M−CO]+ (36), 358 [M−2 CO]+ (100), 253
(21), 191 (53), 103 (11). IR (Nujol, cm−1): 2953(s),
2919(s), 2854(s), 2042(s), 1979(s), 1461(s), 1377(s),
722(w).
triphenylphosphine (0.06 g, 0.24 mmol), and benzene
(16 ml) was refluxed for 5 h, filtered and then kept to
dryness under reduced pressure. The residue was dis-
solved in benzene (2 ml) and purified by column (inter-
nal diameter, 10 mm; length, 30 mm) chromatography
on alumina (Aluminium oxide 90, 70–230 mesh,
Merck), using a 1/1 (v/v) benzene/hexane mixture as
eluant. From the first orange band which eluted, 0.12 g
of the title compound (74% yield) was obtained as an
orange–red microcrystalline solid. Found: C, 72.18; H,
4.59. Anal. Calc. for C39H30OPRh: C, 72.22; H, 4.63%.
IR (Nujol, cm−1): 2953(s), 2921(s), 2855(vw), 1951(m),
1461(s), 1377(s), 723(w).
4.11. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)(p4-norborna-diene)rhodium(I) (9)
4.8. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)bis(triphenyl phosphine)rhodium(I) (6)
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.16 g, 0.34 mmol), di-m-chlorobis(h4-norborna-
diene)dirhodium(I) (0.08 g, 0.17 mmol), and benzene
(30 ml) was stirred at r.t. for 3 h, filtered, and then kept
to dryness under reduced pressure. A yellow residue
was obtained which was dissolved in benzene (2 ml)
and purified by column (internal diameter, 10 mm;
length, 30 mm) chromatography on alumina (Alu-
minium oxide 90, 70–230 mesh, Merck), using benzene
as eluant. From the first orange band which eluted, 0.12
g of the title compound (76% yield) was obtained as a
yellow microcrystalline solid. Found: C, 69.70; H, 5.06.
Anal. Calc. for C27H23Rh: C, 72.00; H, 5.11%. EI MS,
m/z (relative intensity %): 450 [M]+ (45), 358 [M−
C7H8]+ (100), 252 (23), 191 (16), 103 (13), 78 (34).
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.11 g, 0.24 mmol), chlorotris(triphenylphos-
phine)rhodium(I) (0.22 g, 0.24 mmol), and benzene (20
ml) was stirred at r.t. for 5 h. Afterwards, the mixture
was filtered and the resulting solution was kept to
dryness under reduced pressure. The residue was dis-
solved in benzene (2 ml) and purified by column (inter-
nal diameter, 10 mm; length, 30 mm) chromatography
on alumina (Aluminium oxide 90, 70–230 mesh,
Merck), using benzene as eluant. From the first orange
band which eluted, 0.16 g of the title compound (77%
yield) was obtained as a red–brown microcrystalline
solid. Found: C, 76.00; H, 4.98. Anal. Calc. for
C56H45P2Rh: C, 76.19; H, 5.10%.
4.12. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)bis(p2-cyclo-octene)rhodium(I) (10a)
4.9. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)(p2-ethylene) (triphenylphosphine)rhodium(I) (7)
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.35 g, 0.76 mmol), di-m-chlorotetrakis(h2-cy-
clooctene)dirhodium(I) (0.27 g, 0.38 mmol), and
benzene (40 ml) was stirred at r.t. for 2.5 h, filtered, and
then kept to dryness under reduced pressure. A yellow
residue was obtained which was dissolved in benzene (2
ml) and purified by column (internal diameter, 10 mm;
length, 30 mm) chromatography on alumina (Alu-
minium oxide 90, 70–230 mesh, Merck), using benzene
as eluant. From the first orange band which eluted, 0.34
g of the title compound (78% yield) was obtained as an
orange microcrystalline solid. Found: C, 74.70; H, 7.40.
Anal. Calc. for C36H43Rh: C, 74.74; H, 7.44%. EI MS,
m/z (relative intensity %): 578 [M]+ (6), 503 (20), 429
(28), 192 (11), 110 (100).
A mixture of (h5-9-anthrylmethylcyclopentadienyl)-
bis(h2-ethylene)rhodium(I) (0.11 g, 0.27 mmol),
triphenylphosphine (0.07 g, 0.27 mmol) and p-xylene (5
ml) was stirred at 130°C for 3.5 h and then filtered. The
solution was kept to dryness under reduced pressure.
The residue was dissolved in benzene (2 ml) and
purified by column (internal diameter, 10 mm; length,
30 mm) chromatography on alumina (Aluminium oxide
90, 70–230 mesh, Merck), using benzene as eluant.
From the first orange band which eluted, 0.14 g of the
title compound (80% yield) was obtained as a red–
brown microcrystalline solid. Found: C, 74.00; H, 5.18.
Anal. Calc. for C40H34PRh: C, 74.07; H, 5.25%.
4.10. Preparation of (p5-9-anthrylmethylcyclopenta-
dienyl)(carbonyl) (triphenylphosphine)rhodium(I) (8)
4.13. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)bis(p2-cyclo-octene)iridium(I) (10b)
A
mixture of (h5-9-anthrylmethylcyclopentadi-
enyl)dicarbonyl-rhodium(I) (0.1 g, 0.24 mmol),
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.35 g, 0.77 mmol), di-m-chlorotetrakis(h2-cy-

F. Cicogna et al. / Journal of Organometallic Chemistry 593–594 (2000) 251–266
265
clooctene)diiridium(I) (0.35 g, 0.38 mmol), and benzene
5. Supplementary material
(30 ml) was stirred at r.t. for 2 h, filtered, and then kept
to dryness under reduced pressure. A yellow residue
was obtained which was dissolved in benzene (2 ml)
and purified by column (internal diameter, 10 mm;
length, 30 mm) chromatography on alumina (Alu-
minium oxide 90, 70–230 mesh, Merck), using benzene
as eluant. From the first orange band which eluted, 0.35
g of the title compound (68% yield) was obtained as an
orange–red microcrystalline solid. Found: C, 64.71; H,
6.40. Anal. Calc. for C36H43Ir: C, 64.75; H, 6.44%. EI
MS, m/z (relative intensity %): 668 [M]+ (26), 558
[M−C8H14]+ (52), 448 [M−2C8H14]+ (100), 367 (40),
191 (39), 67 (93).
A full list of atomic parameters and details about
the data collection and structure refinement in the
form of CIF file have been deposited with the Cam-
bridge Crystallographic Data Centre, CCDC Nos.
124876 and 124877.
Acknowledgements
We are grateful to Professor S. Roffia, Dr. F.
Paolucci, Dr. L. Mottier, and Dr. M. Carano (Diparti-
mento di Chimica ‘G. Ciamician’, Universita` di
Bologna, Italy) for the study of the electrochemical
behaviour of some rhodium(I) complexes described in
this paper. Furthermore, we thank Dr. S. Pucci (Centro
per lo Studio delle Macromolecole Stereordinate ed
Otticamente Attive, CNR, Pisa, Italy) for the measure-
ment of the mass spectra. Finally, financial support
from the MURST (Rome) is gratefully acknowledged.
4.14. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)(p4-cycloocta-1,5-diene)rhodium(I) (11a)
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.25 g, 0.55 mmol), di-m-chlorobis(h4-cy-
cloocta-1,5-diene)diirhodium(I) (0.14 g, 0.27 mmol),
and benzene (30 ml) was stirred at r.t. for 2.5 h,
filtered, and then kept to dryness under reduced pres-
sure. A yellow residue was obtained which was dis-
solved in benzene (2 ml) and purified by column
(internal diameter, 10 mm; length, 30 mm) chro-
matography on alumina (Aluminium oxide 90, 70–
230 mesh, Merck), using benzene as eluant. From the
first orange band which eluted, 0.22 g of the title
compound (85% yield) was obtained as an orange–
red microcrystalline solid. Found: C, 72.06; H, 5.72.
Anal. Calc. for C28H27Rh: C, 72.10; H, 5.79%. EI
MS, m/z (relative intensity %): 466 [M]+ (58), 358
[M−C8H12]+ (100), 253 (10), 191 (12), 78 (86), 51
(15).
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4.15. Preparation of (p5-9-anthrylmethylcyclopentadi-
enyl)(p4-cycloocta-1,5-diene)iridium(I) (11b)
A mixture of 9-anthrylmethylcyclopentadienylthalli-
um(I) (0.17 g, 0.36 mmol), di-m-chlorobis(h4-cy-
cloocta-1,5-diene)diiridium(I) (0.12 g, 0.18 mmol), and
benzene (40 ml) was stirred at r.t. for 2.5 h, filtered,
and then kept to dryness under reduced pressure. A
yellow residue was obtained which was dissolved in
benzene (2 ml) and purified by column (internal di-
ameter, 10 mm; length, 30 mm) chromatography on
alumina (Aluminium oxide 90, 70–230 mesh, Merck),
using benzene as eluant. From the first orange band
which eluted, 0.13 g of the title compound (64%
yield) was obtained as an orange–red microcrystalline
solid. Found: C, 60.50; H, 4.78. Anal. Calc. for
C28H27Ir: C, 60.52; H, 4.85%. EI MS, m/z (relative
intensity %): 556 [M]+ (100), 448 [M−C8H12]+ (26),
363 (13), 84 (12).
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