Group 8 and 10 metal acetylide naphthalimide dyads

Article abstract of DOI:10.1016/j.ica.2004.12.013

[M]-C≡C-naphthalimide derivatives {[M] = CpNi(PPh₃), CpFe(dppe), CpRu(dppe) and Cp*Ru(dppe)} have been prepared and their X-ray structures determined. The structures show significant non-linearity of the acetylide link, with concomitant ν_C≡C at low energy and high intensity. Other properties confirm the strong-donor/strong-naphthalimide acceptor nature of the compounds. All the compounds exhibit an intense MLCT band in the visible spectrum that resolves into two bands in non-polar solvents. Spectroelectrochemistry of the CpFe species shows that the MLCT band disappears upon oxidation, and the appearance of a LMCT band at lower energy.

Full text of DOI:10.1016/j.ica.2004.12.013

Inorganica Chimica Acta 358 (2005) 1673–1682
www.elsevier.com/locate/ica
Group 8 and 10 metal acetylide naphthalimide dyads
a,
b
a
a
C. John McAdam *, Anthony R. Manning , Brian H. Robinson , Jim Simpson
a
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
b
Department of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
Dedicated to Professor F.G.A. Stone
Abstract
[M]–C„C–naphthalimide derivatives {[M] = CpNi(PPh3), CpFe(dppe), CpRu(dppe) and Cp*Ru(dppe)} have been prepared
and their X-ray structures determined. The structures show significant non-linearity of the acetylide link, with concomitant mC„C
at low energy and high intensity. Other properties confirm the strong-donor/strong-naphthalimide acceptor nature of the com-
pounds. All the compounds exhibit an intense MLCT band in the visible spectrum that resolves into two bands in non-polar sol-
vents. Spectroelectrochemistry of the CpFe species shows that the MLCT band disappears upon oxidation, and the appearance of a
LMCT band at lower energy.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Metal-acetylide; X-ray structure; Donor–acceptor; MLCT; Naphthalimide; Spectroelectrochemistry
1. Introduction
thalimide-acceptor arrays can be extended to organome-
tallic/naphthalimide dyads [7].
Organometallic architectures incorporating metal
atoms in organic p networks have been receiving exten-
sive interest due to their potential use in molecular-scaled
electronics [1,2]. The attraction of having an organome-
tallic component in these systems is the capacity for a
range of accessible oxidation states and the tunability
of properties by variation of the ligand environment.
Our recent work has focussed on the effect of incorpora-
tion of ferrocenyl substituents on the absorption and
emission characteristics of known fluorophores [3–6].
The chemistry of 1,8-naphthalimides has proved particu-
larly fertile. We have synthesised ferrocenyl derivatives
of these that retain significant fluorescence and shown
that charge transfer properties in organic-donor/naph-
Incorporation of the metal into the plane of the p-sys-
tem should enhance its communication with the naph-
thalimide, and to this end, one group of compounds
that appear particularly attractive are the Group 8 and
10 metal half-sandwich r-acetylide complexes. The –
C„C–linkage in these provides facile electronic commu-
nication between the electron-rich metal donor and an
acceptor moiety. Both mononuclear and multiple
metal-centred compounds have been extensively studied
[8–17] particularly with potential NLO properties in
mind. IR spectroscopy has been used to investigate the
bonding within the M–C„C unit particularly the bal-
ance between acetylenic and cumulenic character in
D–A assemblies [18–20].
This paper reports a series of 18-electron metal acet-
ylide systems with a common naphthalimide acceptor
terminus and metal donor functionality based on CpNi,
CpFe, CpRu and Cp*Ru metal hubs.
*
Corresponding author.
E-mail address: mcadamj@alkali.otago.ac.nz (C.J. McAdam).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.013

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C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
2. Experimental
2.1. General remarks
2.3. CpFe(dppe)–C„C–naphthalimide (2)
CpFe(dppe)I (97 mg, 0.15 mmol), NH4PF6 (29 mg,
0.18 mmol) and 4-ethynyl-N-methyl-naphthalimide (44
mg, 0.19 mmol) were heated at 40 ꢁC in N2 degassed
MeOH (6 ml) 8 h. The MeOH was removed under vac-
uum and the brown vinylidene solid (2v) obtained con-
verted to 2 by flash chromatography on (Al2O3/
CH2Cl2). Crystallization from CH2Cl2/EtOH gave pur-
ple black crystals of 2 (12 mg, 10%). Anal. Calc. for
C46H37FeNO2P2: C, 73.32; H, 4.95; N, 1.86; P, 8.22.
Found: C, 72.92; H, 5.14; N, 1.95; P, 8.48%. MS: m/e
754 (MH+). 1H NMR (d): 2.35, 2.64 [2 · (m, 2H,
C2H4)], 3.49 (s, 3H, N–Me), 4.39 (s, 5H, –C5H5), 6.56
[d (J = 8 Hz), naphth. H3], 7.15 [dd (J = 8, 7 Hz),
naphth. H6], 7.3–7.4 (m, 16H, phenyl-H), 7.70 [dd
(J = 8, 1 Hz), naphth. H5], 7.90 (m, 4H, phenyl-H),
8.16 [d (J = 8 Hz), naphth. H2], 8.38 [dd (J = 7, 1 Hz),
naphth. H7]. 31P NMR (d): 106.5. IR (KBr): mC„C
2037 (sh), 2025, mCO 1692, 1649 cmꢁ1. UV–Vis (CH2Cl2):
kmax (e) 339 (12800), 544 (14200). Eꢁ 0.31 V, Ic/Ia = 1.0
(CH2Cl2 versus Fc* = 0.0 V).
Solvents were dried and distilled by standard proce-
dures, and all reactions were performed under nitrogen.
4-ethynyl-N-methyl-1,8-naphthalimide [7], CpNi(PPh3)
Br [21], CpFe(dppe)I [22], CpRu(dppe)Cl [23] and
Cp*Ru(dppe)Cl [24] were prepared by literature meth-
ods. Microanalyses were carried out by the Campbell
Microanalytical Laboratory, University of Otago. Mass
spectra were recorded on a Shimadzu LCMS-QP8000a.
IR spectra were recorded on a Perkin–Elmer Spectrum
BX FT-IR spectrometer, H and 13C NMR spectra on
1
Varian Unity Inova 300 MHz and 500 MHz spectrome-
ters in CDCl3 (7.26 ppm) at 25 ꢁC; electronic spectra
were recorded on a Varian Cary 500 UV–Vis. Band
maxima were obtained from convoluted spectra. Cyclic
and square wave voltammetry in CH2Cl2 were per-
formed using a three-electrode cell with a polished Pt
1 mm disk working electrode; solutions were ꢀ10ꢁ3
M
in electroactive material and 0.10 M in supporting elec-
trolyte (recrystallised TBAPF6). Data was recorded on a
Powerlab/4sp computer-controlled potentiostat. Scan
rates of 0.05–1 V sꢁ1 were typically employed for cyclic
voltammetry and for square-wave voltammetry, square-
wave step heights of 5 mV, a square amplitude of 25 mV
with a frequency of 15 Hz. All potentials are referenced
to decamethylferrocene; E1/2 for sublimed ferrocene was
0.55 V. UV–Vis OTTLE data were obtained from a
standard cell with a platinum grid electrode.
2.4. CpRu(dppe)–C„C–naphthalimide (3)
CpRu(dppe)Cl (300 mg, 0.5 mmol), NH4PF6 (212
mg, 1.3 mmol) and 4-ethynyl-N-methyl-naphthalimide
(294 mg, 1.25 mmol) were refluxed in MeOH (20 ml)
for 2 h. The MeOH was removed under vacuum and
the solid obtained redissolved in CH2Cl2 and filtered.
Column chromatography (SiO2) with CH2Cl2 eluent re-
moved unreacted parent acetylene; the product eluted
with CH2Cl2:EtOAc (10%). Crystallization from EtOH
gave red crystals of 3 (72 mg, 18%). Anal. Calc. for
C46H37NO2P2Ru: C, 69.17; H, 4.67; N, 1.75; P, 7.76.
Found: C, 69.20; H, 4.68; N, 1.76; P, 7.99%. MS: m/e
800 (MH+). 1H NMR (d): 2.4, 2.7 [2 (br m, 2H,
C2H4)], 3.48 (s, 3H, N–Me), 4.90 (s, 5H, –C5H5), 6.56
[d (J = 8 Hz), naphth. H3], 7.16 [dd (J = 8, 7 Hz),
naphth. H6], 7.2–7.4 (m, 16H, phenyl-H), 7.61 [dd
(J = 8, 1 Hz), naphth. H5], 7.93 (m, 4H, phenyl-H),
8.12 [d (J = 8 Hz), naphth. H2], 8.36 [dd (J = 7, 1 Hz),
naphth. H7]. 31P NMR (d): 87.0. IR (KBr): mC„C
2046, 2037 (sh), mCO 1687, 1647 cmꢁ1. UV–Vis (CH2Cl2):
kmax (e) 310 (13200), 493 (16800). Eꢁ 0.65 V, Ic/Ia = 0.7
(CH2Cl2 versus Fc* = 0.0 V).
2.2. CpNi(PPh3)–C„C–naphthalimide (1)
CpNi(PPh3)Br (287 mg, 0.62 mmol) and 4-ethynyl-N-
methyl-naphthalimide (145 mg, 0.62 mmol) were stirred
16 hours in N2 degassed Et3N (20 ml) with CuI (2.5
mol%). The dark precipitate obtained was dissolved in
CH2Cl2 and filtered. Column chromatography (Al2O3/
CH2Cl2) followed by crystallization from CH2Cl2/EtOH
gave dark brown crystals of 2 (150 mg, 40%). Anal. Calc.
for C38H28NNiO2P: C, 73.58; H, 4.55; N, 2.26; P, 4.99.
Found: C, 73.35; H, 4.58; N, 2.19; P, 4.71%. MS: m/e
1
620 (M+). H NMR (d): 3.48 (s, 3H, N–Me), 5.32 (s,
5H, –C5H5), 7.11 [d (J = 8 Hz), naphth. H3], 7.21 [dd
(J = 8, 7 Hz), naphth. H6], 7.4 (m, 9H, phenyl-H), 7.8
[(m, 6H, phenyl-H) + naphth. H5], 8.25 [d (J = 8 Hz),
naphth. H2], 8.39 [dd (J = 7, 1 Hz), naphth. H7]. 13C
NMR (d): 93.2 (–C5H5), 108.9 [d (J = 46 Hz), Ni–
C„C], 118.4 (Ni–C„C). 31P NMR (d): 42.7. IR
(KBr): mC„C 2074, mCO 1692, 1648 cmꢁ1; (CH2Cl2):
2.5. Cp*Ru(dppe)–C„C–naphthalimide (4)
Cp*Ru(dppe)Cl (273 mg, 0.41 mmol), NH4PF6 (82
mg, 0.5 mmol) and 4-ethynyl-N-methyl-naphthalimide
(118 mg, 0.5 mmol) were refluxed in MeOH (60 ml) 2
h. Solvent was removed under vacuum and the solid ob-
tained was loaded dry onto a deactivated neutral alu-
mina column. The column was flushed with toluene
m
C„C 2079, mCO 1693, 1654 cmꢁ1; (cyclohex/benz): mC„C
2084, mCO 1700, 1663 cmꢁ1. UV–Vis (CH2Cl2): kmax (e)
304 (18800), 409 (10700), 484 (14400). Epa 0.93 V, Ic/
Ia = 0.7 (CH2Cl2 versus Fc* = 0.0 V).

C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
1675
and then the product eluted with EtOAc. Crystallization
from Et2O/pentane gave dark red crystals of 4 (114 mg,
32%). Anal. Calc. for C51H47NO2P2Ru: C, 70.49; H,
5.45; N, 1.61; P, 7.13. Found: C, 70.55; H, 5.60; N,
1.60; P, 7.19%. MS: m/e 871 (MH+). 1H NMR (d):
1.61 [t (J = 2 Hz), 15H, –C5Me5), 2.2, 2.7 [2 · (br m,
2H, C2H4)], 3.52 (s, 3H, N–Me), 6.80 [d (J = 8 Hz),
naphth. H3], 7.17 [dd (J = 8, 7 Hz), naphth. H6], 7.2–
7.4 (m, 16H, phenyl-H), 7.77 [dd (J = 8, 1 Hz), naphth.
H5], 7.93 (m, 4H, phenyl-H), 8.23 [d (J = 8 Hz), naphth.
H2], 8.41 [dd (J = 7, 1 Hz), naphth. H7]. 31P NMR (d):
[26] and refined by full-matrix least squares on F2 using
TITAN2000 [27] and SHELXL-97 [28]. Non-hydrogen
atoms were assigned anisotropic temperature factors,
with hydrogen atoms included in calculated positions.
A difference Fourier synthesis following location of all
non-hydrogen atoms for 2 revealed a number of addi-
tional high peaks which could be assigned to positional
disorder in the naphthalene fragment of the naphthali-
mide unit. The disorder can be described in terms of
two, discrete orientations of the naphthalene rings,
approximately related through rotation by 180ꢁ and a
81.7. IR (KBr): mC„C 2035, 2024, mCO 1688, 1651 cmꢁ1
.
translation of approximately 1 A in the naphthalimide
˚
UV–Vis (CH2Cl2): kmax (e) 344 (15000), 543 (16800). Eꢁ
0.50 V, Ic/Ia = 1.0 (CH2Cl2 versus Fc* = 0.0 V).
ring plane, such that the discrete naphthalene fragments
shared two common C atoms C3 and C5. The disorder
was resolved by refining two unique positions for the
remaining C atoms of the naphthalene moieties with
their occupancy factors f and f0 refined such that
f0 = 1 ꢁ f. The final value of f refined to 0.531(5). Fol-
lowing the resolution of the positional disorder, a fur-
ther high peak remained in the difference Fourier map.
This was assigned to the O atom of a water molecule
and refinement of the occupancy factor for the atom
converged at 0.5. In the final refinement cycles, this
occupancy factor was fixed at 0.5 and the atom was re-
fined anisotropically resulting in a significant improve-
ment in R1. No attempt was made to locate the H
atoms of the water solvate.
2.6. X-ray data collection, reduction and structure
solutions
Crystal data for 1–4 are given in Table 1. Crystals of
1 and 2 were obtained from CH2Cl2/hexane and
CH2Cl2/pentane. Those of the ruthenium based com-
pounds 3 and 4 were grown from ethyl acetate/pentane
and Et2O/pentane, respectively. Data were collected at
low temperatures on a Bruker SMART CCD diffrac-
tometer, processed using SAINT, with empirical absorp-
tion corrections applied using SADABS [25]. The
structures were solved by direct methods using SHELXS
Table 1
Crystal data and structure refinement for 1–4
1
2
3
4
Empirical formula
Formula weight
Crystal system
C
620.29
38H28NO2PNi
C46H38NO2.5P2Fe
761.56
triclinic
C46H37NO2P2Ru
798.78
C51H47NO2P2Ru
868.91
monoclinic
C2/c
monoclinic
P21/n
monoclinic
P21/n
ꢀ
Space group
Unit cell dimensions
P1
˚
a (A)
21.946(1)
11.825(5)
23.43(1)
90
11.7881(12)
13.4064(14)
13.7534(14)
116.561(1)
107.461(1)
90.515(1)
1828.3(3)
2
10.8093(19)
31.018(5)
11.9809(19)
90
8.7254(6)
22.5474(17)
21.5817(16)
90
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
105.324
90
112.054(2)
90
90.470(1)
90
3
˚
V (A
)
5865(4)
8
1.405
3723.1(11)
4
1.425
4245.7(5)
4
1.359
Z
Dcalc (Mg mꢁ3
)
1.383
˚
Wavelength (A)
l(Mo Ka) (mmꢁ1
F(000)
0.71073
0.753
2576
0.71073
0.543
792
0.71073
0.548
1640
0.71073
0.486
1800
)
Temperature (K)
Crystal size (mm)3
h Range (ꢁ)
168(2)
163(2)
164(2)
173(2)
0.35 · 0.20 · 0.15
1.92–26.40
37052
0.45 · 0.26 · 0.15
1.76–26.48
23680
0.24 · 0.19 · 0.01
1.95–26.49
45968
0.85 · 0.39 · 0.30
1.81–26.44
53998
Total reflections
Independent reflections
Rint
5991
7435
0.0214
7547
0.3417
8654
0.0226
0.0880
359
0.956
Number of parameters
Goodness-of-fit (F2)
R1[I > 2r(I)]
552
1.071
470
0.989
520
1.032
0.0656
0.1799
1.555 and ꢁ0.708
0.0463
0.1214
0.0944
0.1805
0.0377
0.1058
wR2 (all data) ꢁ3
˚
Residuals (e A
)
0.792 and ꢁ0.740
1.252 and ꢁ0.463
1.959 and ꢁ0.463

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C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
O
N
O
H
C
C
Naphth
Ni C
Ph3P
C
Naphth
Naphth =
Ni Br
Ph3P
Me
CuI, Et3N
1
Scheme 1.
3. Results and discussion
of all the acetylides show the expected ordering and
splitting patterns of a 4-(donor) substituted naphthali-
mide and confirm the stoichiometry of the compounds.
The naphthalimide H3 of 1–4 shows significant shielding
when compared to alkyne naphthalimides previously re-
ported [7]. This shielding effect has been previously
noted for ortho protons of CpFe phenyl acetylides with
increasing acceptor strength and is attributed to p-back
donation between the metal orbitals and C„C acetylide
group [33]. Cyclopentadienyl 1H and 13C resonances for
1 fall into the narrow range typical of CpNi(PPh3)-C2-
aryl compounds [13,16,34,35]. The 31P NMR of the
phosphine and alkyne C(2) are likewise unremarkable.
The carbon shift of the alkyne C(1) varies significantly
1 was prepared in good yield by reaction of 4-ethynyl-
N-Me-naphthalimide and CpNi(PPh3)Br in Et3N at
ambient temperature with a CuI catalyst following the
methodology of Bruce et al. [29] (Scheme 1). The acety-
lide formed precipitates out of the Et3N solvent, and un-
like the parent nickel bromide proved stable to
chromatographic work-up. Solutions of 1 were a rich
red-orange in contrast to most simple aryl acetylides
which are a pale green-yellow [30].
The general preparative route to Group 8 CpML2 (=
[M]) alkynes is via the vinylidene salt generated from the
reaction of H–C„C–R with [M]–X and NH4PF6 in
MeOH. The vinylidene salt is converted to the alkyne
by deprotonation, either on alumina [31], with KOBut
in THF [10], with NaOMe or proton sponge [32]. Thus
reaction of CpFe(dppe)I with 4-ethynyl-N-Me-naph-
thalimide in the presence of NH4PF6 produced the
brown vinylidene salt 2v in high yield (Scheme 2). An in-
tense purple solution of 2 was prepared by flash chroma-
with acceptor properties of the alkyne substituent. For
13
1,
benchmark p-nitrophenyl nickel acetylide C(1) of 103.5
C
occurs at 108.9 ppm and compares with the
(1)
13
ppm [13].
3
C
exhibits the typical coupling to phos-
(1)
phorus, JPC = 46 Hz. For the Group 8 [M]–C„C–
naphthalimides, H and 13C NMR of Cp and Cp* rings
1
and 31P NMR resonances, although differing between 2,
3 and 4 fall within the narrow ranges reported for other
[M] acetylides [12,32,33]. The potentially most interest-
ing resonances, the alkyne C(1) carbons, of inherently
low intensity and further reduced in height by phospho-
rus coupling, could not be located. Similarly the alkyne
C(2) which generally do not show the P–C coupling and
occur in a much narrower range [10] could not be
assigned.
i
tography of 2v on Pr2NH deactivated Al2O3 with
EtOAc eluent. Although the initial yield of crude mate-
rial was high, significant losses occurred on the column,
in solution and during recrystallisation attempts, partic-
ularly in chlorinated solvents, which resulted in low
yields of pure product. Dark red and purple [Ru] deriv-
atives 3 and 4 were prepared similarly by reaction of
CpRu(dppe)Cl and Cp*Ru(dppe)Cl with 4-ethynyl-N-
Me-naphthalimide in the presence of NH4PF6. As with
2, there were problems attaining pure crystalline samples
due to instability of the compounds during chromatog-
raphy and recrystallisation.
m
C„C energies of 1–4 in CH2Cl2 solution are included
in Table 2. In all cases the vibration occurs at lower en-
ergy than the equivalent p-NO2-phenyl analogue indi-
cating a weaker C„C bond, and consistent with
substantial electron delocalisation. This, and the shift
to lower energy with increasing solvent polarity, suggest
Products 1–4 were characterised by microanalysis,
NMR and spectroscopic techniques. Proton resonances
Scheme 2.

C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
1677
Table 2
3.1. Crystal structure 1–4
IR (mC„C
(CH2Cl2 solution)
) of R–C„C–naphthalimides and related compounds
The X-ray structures of 1–4 were determined and are
shown in Figs. 2–5. These representations define the
atom numbering schemes used in the following discus-
sion. Selected bond length and angle data are given in
Table 3. The naphthalimide fragment in each case is
unremarkable. Of more interest is the geometry at the
respective metal centre. The Ni atom of 1 has a distorted
square pyramidal coordination sphere with the alkyne–
naphthalimide residue and the phosphine ligand cis to
one another. C(15)–Ni(1)–P(1) at 90.21(17)ꢁ and dis-
tances and angles within the cyclopentadienyl ring and
phosphine fragment fall into the expected ranges. The
CpFe and CpRu derivatives 2, 3 and Cp*Ru acetylide
4 are sufficiently similar to be discussed together. A
familial resemblance and similarity to CpNi(PPh3)–
C„C–naphthalimide is clear from Figs. 3–5. However,
the Fe Group metallocenes 2–4 each require an addi-
tional pair of electrons in comparison to the Ni complex.
These are provided by the additional phosphorus atoms
of the bidentate, chelate dppe ligands giving a distorted
octahedral coordination geometry at the Fe and Ru
atoms with the ligated alkyne C atom and both P atoms
of the diphosphine mutually cis. As with 1, the bond
length and angle data within the naphthalimide ring sys-
tems of 2–4 are unremarkable although disorder in the
naphthalimide rings of 2 means that data for this system
should be treated with caution.
mC„C
e
(cmꢁ1
)
(molꢁ1 cmꢁ1 L)
Fc–C„C–naphth [7]
H–C„C–naphth [7]
2200
2101
2079
2091
400
6
CpNi(PPh3)–C„C–naphth (1)
CpNi(PPh3)–C„C–C6H4–NO2 [13]
CpFe(dppe)–C„C–naphth (2)
CpFe(dppe)–C„C–C6H4–NO2 [12]
Cp*Fe(dppe)–C„C–C6H4–NO2 [10]
CpRu(dppe)–C„C–naphth (3)
1100
2037, 2023
2044
900
2036, 2008
2047,
1900
2032(sh)
2056
2039, 2028
CpRu(dppe)–C„C–C6H4–NO2 [12]
Cp*Ru(dppe)–C„C–naphth (4)
2000
O
O
N
O
Me
N
O
Me
+
[M]
C
C
[M]
C
C
↔
-
Fig. 1. Acetylide and cumulene configurations.
a contribution of a cumulene form to the ground state
structure (Fig. 1). Of note are the twin peaks recorded
for 2–4. The splitting also occurs in the solid state
(KBr) spectra and is attributed to Fermi coupling. Sim-
ilar behaviour has been reported for Cp*Fe acetylides in
the IR [10] and Raman [20] spectra. Extinction coeffi-
cients were calculated for the alkyne stretching vibration
and are also shown in Table 2. The high values for com-
pounds 1–4 reflect a large change in dipole moment
associated with the vibration and are not simply a func-
tion of oscillator mass [30].
Acetylides 1–4 all show an extended C(14)–C(4) dis-
tance in comparison with other [M]–C„C–aryl com-
pounds. This probably reflects the greater steric
Fig. 2. Perspective view of 1 showing the atom numbering scheme.

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C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
Fig. 3. Perspective view of 2 showing the atom numbering scheme. Only one set of atoms of the disordered naphthalimide unit (occupancy 0.53, see
Section 2) are shown.
Fig. 4. Perspective view of 3 showing the atom numbering scheme.
demands of the naphthalimide system. The Ni(1)–C(15)
˚
with electron withdrawing acetylide substituents [33]. 3
˚
shows Ru(1)–C(15) distance at 2.055(9) A and C(15)–
bond is short, 1.834(5) A and C(14)„C(15) relatively
˚
long, 1.220(7) as was observed for CpNi(PPh3)–C„C–
CHO [16] and CpNi(PPh3)–C„C–p-NO2-phenyl [15].
For 2, Fe(1)–C(15) and C(15)–C(14) at 1.888(3) and
C(14) at 1.085(12) A similar to the [Ru]–C„C–p-NO2-
phenyl analogue [12] and Cp*RuL2–C„C–phenyl
[L2 = dppe, (PPh3)2] [36,37]. In contrast the Ru(1)–
C(15) bond in 4 is significantly shorter and the corre-
˚
1.208(4) A are similar to other CpFe(dppe) compounds

C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
1679
Fig. 5. Perspective view of 4 showing the atom numbering scheme. In all figures for clarity only the first two C atoms of the consecutively numbered
cyclopentadiene and phenyl rings and the methyl substituents on the pentamethyl cyclopentadiene ring have been labelled.
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) for 1–4
1
2
3
4
M(1)–C(15)
C(15)–C(14)
C(14)–C(4)
1.834(5)
1.220(7)
1.532(8)
1.888(3)
1.208(4)
1.488(7), 1.533(8)a
2.055(9)
1.085(12)
1.496(14)
1.992(3)
1.208(4)
1.427(4)
M(1)–P(1)
M(1)–P(2)
M(1)–C(21)
M(1)–C(22)
M(1)–C(23)
M(1)–C(24)
M(1)–C(25)
2.1362(16)
–
2.1827(8)
2.1734(8)
2.098(3)
2.107(3)
2.105(3)
2.090(3)
2.101(3)
2.285(3)
2.282(3)
2.249(10)
2.258(10)
2.262(9)
2.230(11)
2.205(10)
2.2636(7)
2.2786(7)
2.251(3)
2.230(3)
2.266(3)
2.277(3)
2.262(3)
2.144(5)
2.134(5)
2.107(5)
2.125(5)
2.079(5)
M(1)–C(15)–C(14)
C(15)–C(14)–C(4)
171.7(5)
167.6(6)
177.2(3)
162.6(5), 158.9(5)a
166.0(10)
162.4(13)
173.3(3)
176.5(4)
C(15)–M(1)–P(1)
C(15)–M(1)–P(2)
P(1)–M(1)–P(2)
a
90.21(17)
85.09(9)
88.69(8)
86.50(3)
87.9(2)
80.8(3)
84.54(9)
85.40(8)
86.08(9)
83.02(3)
–
–
Crystal contains disordered naphthalimide.
sponding C(15)–C(14) vector is longer than in these
comparable molecules.
The Group 8 [M]–C„C–naphthalimides 2–4 exhibit
similar variations. The M–C„C and C„C–C angles
for 4 at 173.3(3) and 176.5(4)ꢁ are comparable with
the other Cp*Ru compounds reported by Bruce et al.
[36,37]. However, the deviations shown by 2 and 3 are
remarkably different from their [M]–C„C–p-NO2-phe-
nyl analogues. Thus for 2, while Fe(1)–C(15)–C(14) at
177.2(3)ꢁ is of similar magnitude to the Fe–C„C angle
of 178.7(8)ꢁ for CpFe(dppe)–C„C–p-NO2-phenyl [33],
A common feature of all four alkynenaphthalimide
systems is the significant deviation from linearity of
the acetylide links between the metals and the naphthal-
imide units. Thus 1 shows significantly greater non-line-
arity than the eleven previously reported CpNi(PPh3)
acetylides [14–16,34,35] with Ni(1)–C(15)–C(14) at
171.7(5)ꢁ and C(15)–C(14)–C(4) at 167.6(6)ꢁ.

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C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
the C(15)–C(14)–C(4) angles of 162.6(5)ꢁ and 158.9(5)ꢁ
of the disordered naphthalimide are significantly lower
than those for the nitrophenyl compound, 173.2(9)ꢁ.
For 3, Ru(1)–C(15)–C(14) and C(15)–C(14)–C(4) angles
of 166(1)ꢁ and 162.4(13)ꢁ compare with 177.4(3) and
176.7(3) for CpRu(dppe)–C„C–p-NO2-phenyl [12].
A common feature of the solid state chemistry of naph-
thalimide derivatives is the occurrence of offset p-stacking
interactions involving the naphthalimide rings [7,38].
There is good evidence for comparable p-stacking inter-
actions for both 1 and 2, with interplanar separations in
344
.8
.6
.4
562
560
496
.2
0
˚
˚
300
400
500
600
700
800
the range 3.44–3.48 A for 1 and 3.37–3.41 A for 2 [39]
and displacement angles in the range 18.8–20.2ꢁ for 1
and 25.4–31.4ꢁ for 2 [40]. In sharp contrast, there is no
evidence for any degree of stabilisation of the solid state
structures of 3 or 4 by way of p-stacking interactions, de-
spite the structural similarities between them. Indeed the
only intermolecular contacts of note in these structures
are weak non-classical H-bonding interactions involving
the O atoms of the naphthalimide units.
λ / nanometers
Fig. 6. Electronic spectra of 2, (–) hexane, (Æ Æ Æ) ethanol.
a naphthalimide p–p* transition. More significantly
the group 8 [M]-acetylides exhibit another strong but
lower energy band at ca. 500 nm (e ꢀ 15000). This is
close to the intensity of, but slightly lower in energy than
the charge transfer band reported for enamine-donor
naphthalimide-acceptor compounds [7]. The absorption,
broad in ethanol solution, resolves into two kmax in less
polar solvents. The accompanying blue shift fits with an
assignment to a MLCT transition. Why there should be
two transitions is uncertain. The related Cp*Fe- and
CpFe-p-nitrophenyl acetylides [10,33] are only reported
as having one band, albeit broad, in the 400–800 nm re-
gion. The energy of the MLCT bands for 2–4 are the
lowest reported for Group 8 [M] arylacetylides and
diminish in the order 3 > 4 > 2, a trend that matches
the observed [M]II/III oxidation potential. Spectra of
the CpNi acetylide 1 show evidence of two CT bands
in CH2Cl2 at 409 (e = 11000) and 484 nm (e = 14000).
Unlike the Group 8 metal compounds these remain
clearly resolved in ethanol. These are the lowest energy
transitions reported for a CpNi acetylide.
3.2. Spectroelectrochemistry
1 undergoes a partially reversible one-electron oxida-
tion process in CH2Cl2 associated with the NiII/NiIII
couple with Ic/Ia ꢀ 0.7. In acetonitrile, the nickel oxida-
tion step becomes completely irreversible; the explana-
tion for this is discussed in detail elsewhere [30]. Epa
0.93 V (Fc* = 0.0 V) is consistent with a strongly elec-
tron withdrawing substituent on the CpNi alkyne
[13,30]. The naphthalimide moiety undergoes an irre-
versible reduction ca. ꢁ1.0 V. The Group 8 metal acet-
ylides 2–4 undergo a similar one-electron oxidation in
CH2Cl2 associated with the MII/III couple; the ruthe-
nium compounds 3 and 4 show an irreversible second
anodic process at Epa ꢀ 1.3 V. Ease of oxidation de-
creases on replacing Fe with Ru, but predictably be-
comes easier again for the methylated Cp derivative 4.
The [M]–C„C–naphthalimides are consistently 0.16 V
more difficult to oxidise than [M] phenylacetylides, but
on a par with the stronger acceptor nitrophenylacety-
lides. The Ic/Ia ratios resemble those reported for other
[M] acetylides [12,32,33].
The electronic absorption of the oxidised CpFe acet-
ylide 2 was obtained by performing an oxidation in an
OTTLE cell. The resultant spectra (Fig. 7) showed clean
isosbestic points and reversal of the cell potential regen-
.7
.6
UV–Visible data for 1–4 are given in Table 4 and a
representative spectrum, that of 2 shown in Fig. 6. All
show a high intensity band between 300 and 350 nm
(e ꢀ 13000) with vibrational structure characteristic of
.5
405
544
.4
.3
Table 4
Electronic spectra (charge transfer bands) for 1–4
.2
CT bands (nm)
800
.1
Hexane
Ethanol
1
2
3
4
400, 465
496, 560
460, 491
482, 518
415, 489
562
501
0
300
400
500
600
700
800
900
λ /nanometers
545
Fig. 7. OTTLE spectra of 2 (0–0.3 V, CH2Cl2, 0.1 M TBAPF6).

C.J. McAdam et al. / Inorganica Chimica Acta 358 (2005) 1673–1682
1681
erated the starting spectrum. Upon oxidation of FeII to
FeIII the MLCT transition/s at ꢀ550 nm disappears, re-
placed by a band s at 405 nm and weak broad band in
the NIR at 800 nm. This type of NIR absorption is char-
acteristic of dyads where a Fc+–C„C or Fc+–C@C
group is linked to a p donor [41], including naphthali-
mide [7] and is ascribed to a Fc+ p-donor LMCT.
The oxidised dyad 2+ provides the first example of a sim-
ilar LMCT NIR bands for a [M]–C„C complex with
the naphthalimide acting as the p-donor in the excited
state. The energy of the LMCT for 2+ of 12500 cmꢁ1
is high compared to polyaromatic donors such as
anthracene (8900 cmꢁ1) but identical to that in Fc–
C„C–naphthalimide [7]. A detailed analysis of the
NIR LMCT are given elsewhere [42].
[10] R. Denis, L. Toupet, F. Paul, C. Lapinte, Organometallics 19
(2000) 4240.
[11] M.I. Bruce, Coord. Chem. Rev. 166 (1997) 91.
[12] C.E. Powell, M.P. Cifuentes, A.M. McDonagh, S.K. Hurst, N.T.
Lucas, C.D. Delfs, R. Stranger, M.G. Humphrey, S. Houbrechts,
I. Asselberghs, A. Persoons, D.C.R. Hockless, Inorg. Chim. Acta
352 (2003) 9.
[13] I.R. Whittall, M.P. Cifuentes, M.G. Humphrey, B. Luther-
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´
Bogsanyi, Organometallics 16 (1997) 2631.
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51 (1998) 219.
[16] J.F. Gallagher, P. Butler, R.D.A. Hudson, A.R. Manning,
J. Chem. Soc., Dalton Trans. (2002) 75.
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4. Conclusions
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Peruzzini, P. Zanello, F. Zanobini, J. Am. Chem. Soc. 115 (1993)
2723.
Compounds 1–4 provide further examples of donor–
acceptor arrays in which the metal half-sandwich moiety
is acting as the donor. In the dyads the naphthalimide is
a strong acceptor on a par with the previously reported
[M]–C„C–p-NO2-phenyl compounds. The latter pos-
sess interesting NLO properties and it is expected that
this will also be the case for 1–4. The intense mC„C at
low energy and significant non-linearity in the X-ray
structures indicate some cumulene or vinylidene charac-
ter to the acetylide link. All neutral dyads show an in-
tense band in the visible spectrum due to a MLCT
transition, and upon oxidation, the interesting NIR
band due to a naphthalimide (p) ! C„C–[M] LMCT
in the excited state. Absorption of NIR radiation is of
technological significance [43] and it should be possible
to tune the energy and intensity of the absorption in
these acetylide dyads by appropriate substitution
around the metal centre or naphthalimide component.
[20] F. Paul, J.-Y. Mevellec, C. Lapinte, J. Chem. Soc., Dalton Trans.
(2002) 1783.
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[23] G.S. Ashby, M.I. Bruce, I.B. Tomkins, R.C. Wallis, Aust.
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[24] F. Morandini, A. Dondana, I. Munari, G. Pilloni, G. Consiglio,
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