Organometallic complexes for nonlinear optics: Part 20. Syntheses and molecular quadratic hyperpolarizabilities of alkynyl complexes derived from (E)-4,4′-HCCC6H4N=NC6H4NO 2

Article abstract of DOI:10.1016/S0022-328X(00)00312-0

The syntheses of the alkyne (E)-4,4′-HCCC₆H₄N=NC₆H₄NO ₂ (1) and alkynyl complexes L_nM{(E)-4,4′-CCC₆H₄N=NC₆H ₄NO₂} [L_nM=trans-[RuCl(dppm)₂] (2), Ru(PPh₃)₂(η-C₅H₅) (3), Au(PPh₃) (4)] are reported. A structural study of 2 reveals E stereochemistry about the azo-linkage. Electrochemical data for the ruthenium complexes reveal that the azo-linkage in complexes 2 and 3 perturbs the metal-centred oxidation potential compared to all other alkynyl complexes of similar composition. Quadratic optical nonlinearities by hyper-Rayleigh scattering (HRS) at 1064 nm are very large for 2 and 3, but resonance-enhanced. Comparison of HRS data for 4 with those of Au{(E)-4,4′-CCC₆H₄X=CHC₆H ₄NO₂}(PPh₃) (X=CH, N) reveals that complex 4 has a significantly larger quadratic nonlinearity than its ene- or imino-linked analogues.

Full text of DOI:10.1016/S0022-328X(00)00312-0

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 205 (2000) 193–201
Organometallic complexes for nonlinear opticsꢀ
Part 19. Syntheses and molecular quadratic hyperpolarizabilities of
indoanilino–alkynyl–ruthenium complexes
Andrew M. McDonagh a, Marie P. Cifuentes a, Nigel T. Lucas a,
Mark G. Humphrey a,*, Stephan Houbrechts b, Andre´ Persoons b
a Department of Chemistry, Australian National Uni6ersity, Canberra, ACT 0200, Australia
b Laboratory for Chemical and Biological Dynamics, Uni6ersity of Leu6en, Celestijnenlaan 200D, B-3001 Leu6en, Belgium
Received 19 April 2000; accepted 18 May 2000
Abstract
¸¹¹¹¹¹¹¹¹¹¹¹¹º
The terminal alkyne 4-HCꢀCC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH (1) and ruthenium complex derivatives trans-[Ru(CꢀC-4-
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
¸¹¹¹¹¹¹¹¹¹¹¹¹º
C6H4NꢁCCH=CtBuC(O)CtBuꢁCH}Cl(dppm)2] (2) and [Ru{CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH}(PPh3)2(h-C5H5)] (3)
have been synthesized. An X-ray structural study of 3 reveals the expected equivalent CꢂC bond lengths of the phenyl and
alternating CꢂC and CꢁC bond lengths of the quinonal ring in the indoanilino–alkynyl ligand; there is a dihedral angle of 47.59°
between the phenyl and quinonal rings, probably a result of ortho-hydrogen repulsion. Metal-centred oxidation potentials of 2 and
3 are similar to those of ‘extended chain’ 4-nitroaryl–alkynyl complex analogues. Irreversible quinonal ring-centred reductions
occur at significantly more negative potentials than the quasi-reversible reductions in their nitro-containing analogues. Quadratic
optical nonlinearities by hyper-Rayleigh scattering at 1064 nm for 2 (417×10−30 esu) and 3 (658×10−30 esu) are both large, but
resonance enhanced. Two-level-corrected nonlinearities for these complexes (124×10−30, 159×10−30 esu, respectively) are also
large, despite the presence of electron-donating tert-butyl groups reducing the efficiency of the (formally) electron-accepting
quinonal ring in these donor-bridge-acceptor complexes. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium; X-ray structure; Electrochemistry; Quadratic hyperpolarizabilities; Alkynyl; Nonlinear optics
rich ligated metal donor to the nitro acceptor affords
robust metal complexes, it is not necessarily the most
1. Introduction
effective bridge for maximizing NLO merit. This can be
The quadratic and cubic nonlinear optical (NLO)
understood by considering the perturbation theory-
properties of organometallic complexes have come un-
derived expression for NLO responses, in which a
der intense scrutiny recently [2–6]. The most successful
charge-separated excited state is mixed into the ground
class of compounds for quadratic NLO merit are those
state of the molecule. For complexes such as trans-
coupling an electron-rich donor to an electron-poor
acceptor by means of a p-delocalizable bridging unit.
[Ru(CꢀCC6H4NO2-4)Cl(dppm)2], the charge-separated
excited state is energetically disfavoured by the loss of
Aryl–alkynyl complexes with a donor-bridge-acceptor
aromatic stabilization energy in proceeding from the
composition
such
as
trans-[Ru(CꢀCC6H4NO2-
aromatic ground state to the quinonal-like charge sepa-
rated excited state (Fig. 1(a)); the excited state conse-
quently mixes less with the ground state, resulting in a
less-efficient NLO material than would otherwise be
achievable.
This problem has been addressed with organic
molecules. In the search for efficient organic NLO
materials, attention has turned to indoanilines [8,9], in
4)Cl(dppm)2] are amongst the most efficient
organometallic quadratic NLO materials [7]. However,
although the aryl–alkynyl p-bridge linking the electron-
ꢀ For Part 18, see Ref. [1].
* Corresponding author. Tel.: +61-2-62492927; fax: +61-2-
62490760.
E-mail address: mark.humphrey@anu.edu.au (M.G. Humphrey).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00312-0

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A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
2. Results and discussion
2.1. Synthesis and characterization of
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
4-HCꢀCC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH (1)
The preparation of the new alkyne (1) follows the
procedure outlined in Scheme 1(a). The iodide 4-
IC6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH was obtained in
good yield by employing two modifications to the liter-
ature procedure for preparing indoanilines [10]: (i) an
excess of 4-iodoaniline was used to ensure the complete
reaction of 2,6-di-tert-butylbenzoquinone and to sim-
plify the purification of the product (the product is
difficult to separate from 2,6-di-tert-butylbenzoquinone
Fig. 1. (a) Ground and CT excited states of donor(D)-acceptor aryl
compounds. (b) Ground and CT excited states of indoaniline com-
pounds.
by column chromatography, but is readily separated
from the excess 4-iodoaniline), and (ii) the boron trifl-
uoride catalyst was replenished periodically over the
course of the reaction (without this periodic addition,
the reaction will not proceed further). Sonogashira
coupling [11] was then employed to obtain the terminal
alkyne 1 in moderate yield. No advantage in purity or
yield of the final product was gained by isolating the
intermediate trimethylsilyl-protected alkyne prior to the
deprotection step. An alternative synthesis involving the
coupling of trimethylsilylethyne to 4-iodoaniline fol-
lowed by reaction of the resulting 4-trimethylsi-
lylethynylaniline with 2,6-di-tert-butylbenzoquinone
(Scheme 1(b)) afforded a lower yield of 1, along with
several unidentified by-products.
which an arylene group is connected to a quinonal
group via a nitrogen atom. In the ground state, there is
one aromatic ring and one quinonal ring. Upon excita-
tion, this system compensates for the loss in aromaticity
of the aromatic ring by the gain of aromaticity of the
quinonal ring (Fig. 1(b)). As a consequence, organic
compounds with this composition are efficient NLO
materials.
No transition metal complexes bearing this type of
substituent have thus far been reported. This paper
reports the preparation of the new alkyne 4-
1
The H-NMR spectra of the new indoaniline com-
pounds are particularly informative. The 1H-NMR
HCꢀCC6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH, its use in the
preparation of indoanilino–alkynyl–ruthenium com-
plexes, an X-ray structural study of a representative
complex, electrochemical data and quadratic NLO data
for the new compounds, and comparison of their effi-
ciency with previously reported aryl–alkynyl
complexes.
spectrum¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
of the iodo-containing intermediate, 4-
IC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH, contains a charac-
teristic AA%BB% pattern centred on 7.16 ppm and
assigned to the protons on the aromatic ring. Restricted
rotation about the CꢁN bond results in inequivalent
quinone ring protons (doublet signals at 7.01 and 6.74
ppm) and inequivalent tert-butyl groups (singlet signals
¸¹¹¹¹¹¹¹¹¹¹¹¹º
Scheme 1. Alternate routes for the preparation of 4-HCꢀCC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH) (1).

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
195
¸¹¹¹¹¹¹¹¹¹¹¹º
Scheme 2. Preparation of trans-[Ru(CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH)Cl(dppm)2] (2).
¸¹¹¹¹¹¹¹¹¹¹¹¹º
Scheme 3. Preparation of [Ru(CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH)(PPh3)2(h-C5H5)] (3).
1
C5H5)] with the terminal alkyne in refluxing methanol
at 1.30 and 1.18 ppm). The H-NMR spectrum of the
new alkyne 1 is similar to that of its precursor (quinone
ring protons at 7.00 and 6.72 ppm, and tert-butyl
protons at 1.31 and 1.17 ppm), and contains a charac-
teristic signal assigned to the terminal alkyne proton at
3.10 ppm.
afforded the vinylidene complex [Ru{CꢁCH-4-
C6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH}(PPh3)2(h-C5H5)]+;
unlike the chlorobis(dppm)ruthenium–vinylidene com-
plex above, the cyclopentadienylbis(triphenylphos-
phine)ruthenium analogue does not require the
presence of large counter-ions (such as hexafluorophos-
phate) for stability, the displaced chloride presumably
being sufficient. This vinylidene complex was similarly
deprotonated in situ to afford 3 in 32% yield.
2.2. Synthesis and characterization of
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
LnM{CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH}
[LnM=trans-[RuCl(dppm)2] (2), Ru(PPh3)2(p-C5H5)
(3)]
The new alkynyl complexes were characterized by
FAB mass spectrometry, UV–vis, IR, 1H-, 31P- and
13C-NMR spectroscopy. The FAB mass spectra of 2
and 3 contain molecular ions, with fragmentation of the
former proceeding by competitive loss of chloro and
alkynyl ligands to afford the base peak corresponding
to [Ru(dppm)2]+, and fragmentation of the latter pro-
ceeding by competitive loss of phosphine and alkynyl
ligand to afford the base peak corresponding to
[Ru(PPh3)(h-C5H5)]+. The IR spectra contain charac-
teristic bands assigned to w(CꢀC) at 2067 (2) and 2061
(3) cm−1. The 31P-NMR spectra contain singlet reso-
nances at −6.1 (2) and 50.7 (3) ppm, with that of the
former confirming the mutually trans stereochemistry of
We have previously reported studies of quadratic
NLO efficiencies of donor-p-bridge acceptor alkynyl–
metal complexes with a range of ligated metal centres
[7,12–15]; ruthenium-containing complexes are signifi-
cantly more efficient than their nickel- or gold-contain-
ing analogues. It is sensible to employ the most efficient
donor when evaluating acceptor groups. We have con-
sequently prepared alkynyl–ruthenium derivatives of 1
with ligand sets shown to afford highly efficient
quadratic NLO materials in our earlier work.
The syntheses of alkynyl complexes 2 (Scheme 2) and
3 (Scheme 3) follow the literature procedures of
Dixneuf [16] and Bruce [17], respectively, for the prepa-
ration of the phenyl–alkynyl complex analogues. Reac-
tion of cis-[RuCl2(dppm)2], sodium hexafluoro-
phosphate and the terminal alkyne in dichloromethane
at room temperature (r.t.) afforded trans-[Ru{CꢁCH-4-
1
the chloro and alkynyl ligands. The H-NMR spectra
contain the above-mentioned characteristic signals from
the quinonal rings. The 13C-NMR spectra contain
downfield resonances at 187.8 (2) and 187.9 (3) ppm
corresponding to the quinonal carbon atoms. Com-
plexes 2 and 3 both show a small positive solvatochro-
matic response with their electronic absorption spectra
C6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH}Cl(dppm)2]PF6.
This product was not isolated, but instead deproto-
nated with base in situ (using either sodium methoxide
or triethylamine) to afford the desired alkynyl complex
2 in good yield (65%). Reaction of [RuCl(PPh3)2(h-
maxima in proceeding from solvent cyclohexane (umax
2
637, 3 613 nm) to solvent methanol (umax 2 640, 3 619
nm).

196
A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
Table 1
Selected
RuꢂP and RuꢂC(Cp) distances and intraphosphine
and intracyclopentadienyl bond lengths and angles are
unexceptional [18]. The RuꢂC(alkynyl) and CꢀC dis-
tances are also similar to literature precedents, with the
deviation from linearity of the RuꢂCꢀC and CꢀCꢂC
linkages presumably due to packing effects. The bond
distances within the indoanilino phenyl and quinonal
rings are those expected for the ground-state structure,
namely a bond-equalized phenyl group and bond-alter-
nated quinonal moiety. The phenyl and quinonal rings
are significantly removed from coplanarity (dihedral
angle 47.59°) consistent with previous work with or-
ganic indoanilines by Marder et al. [8] where steric
interactions between o-hydrogens were proposed to
preclude coplanar indoaniline rings.
structural
data
for
[Ru(CꢀC-4-C6H4Nꢁ
¸¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH)(PPh3)2(h-C5H5)] (3)
Ru(1)ꢂP(1)
Ru(1)ꢂP(2)
Ru(1)ꢂC(1)
C(1)ꢂC(2)
C(2)ꢂC(3)
C(3)ꢂC(4)
C(3)ꢂC(8)
C(4)ꢂC(5)
C(7)ꢂC(8)
C(5)ꢂC(6)
C(6)ꢂC(7)
C(6)ꢂN(1)
N(1)ꢂC(9)
C(9)ꢂC(10)
C(9)ꢂC(14)
C(10)ꢂC(11)
C(13)ꢂC(14)
C(11)ꢂC(12)
C(12)ꢂC(13)
C(12)ꢂO(1)
2.309(2)
2.292(2)
2.010(7)
1.200(9)
1.43(1)
1.41(1)
1.41(1)
1.38(1)
1.38(1)
1.40(1)
1.40(1)
1.40(1)
1.28(1)
1.47(1)
1.46(1)
1.33(1)
1.34(1)
1.50(1)
1.49(1)
1.21(1)
2.4. Electrochemical studies
The results of cyclic voltammetric studies on the
alkynyl complexes 2 and 3 are summarized in Table 2,
together with previously reported data for related
complexes.
Ru(1)ꢂC(1)ꢂC(2)
C(1)ꢂC(2)ꢂC(3)
C(6)ꢂN(1)ꢂC(9)
175.4(6)
168.8(8)
122.2(8)
We have previously noted that (i) ruthenium is oxi-
dized at potentials 0.2 V higher upon replacement of
CꢀCPh by 4-CꢀCC6H4NO2 (proceeding from 8 or 9 to
4 or 5, respectively), and that (ii) a significant decrease
in potential of the RuII/III couple (0.16–0.18 V) is
observed on ‘chain-lengthening’ the acetylide ligand
from 4-CꢀCC6H4NO2 to 4-CꢀCC6H4-(E)-CHꢁCH-4-
C6H4NO2 in proceeding from 4 or 5 to 6 or 7, respec-
tively [14]. In this work substitution of the 4-NO2
2.3. X-ray structural study of
[Ru(CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH)(PPh3)2-
(p-C5H5)] (3)
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
We have completed an X-ray diffraction study of 3 to
confirm the molecular composition. Important bond
lengths and angles are given in Table 1 and an ORTEP
plot is displayed in Fig. 2.
moiety by the 4-Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH group re-
sults in a decrease of 0.19 V (proceeding from 5 to 3) or
0.23 V (from 4 to 2). Thus, the indoanilinoalkynyl
¸¹¹¹¹¹¹¹¹¹¹¹¹º
Fig. 2. Molecular structure and atomic labeling scheme for [Ru(CꢀC-4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH)(PPh3)2(h-C5H5)] (3) with 20%
anisotropic displacement ellipsoids.

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
197
Table 2
Cyclic voltammetric, linear optical and quadratic nonlinear optical response parameters for indoanilino–alkynyl–ruthenium complexes and related
compounds
Compound
E0Ru
[ipc/ipa
(V)
EA0
[ipa/ipc
(V)
0/−I
umax (nm)
i (10−30 esu) a
i0
(10−30 esu) b
Ref.
II/III
]
]
[m (104 M−1 cm−1)]
b
4-HCꢀCC6H4Nꢁ
448 (0.5)
This work
¸¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH (1)
4-HCꢀCC6H4NO2
4-HCꢀCC6H4-(E)-CHꢁCH-4-C6H4NO2
288 (1.5)
358 (3.3)
645 (0.8)
14 c
9 d
[13]
[13]
This work
55 c
27 d
124 d
trans-[Ru{CꢀC-4-C6H4Nꢁ
0.49 (1.0)
−1.15 h
417 c
¸¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH}Cl(dppm)2]
(2)
trans-[Ru(CꢀCPh)Cl(dppm)2] (8)
trans-[Ru(CꢀC-4-C6H4NO2)Cl(dppm)2]
(4)
trans-[Ru{CꢀC-4-C6H4-(E)-CHꢁ
CH-4-C6H4NO2}Cl(dppm)2] (6)
0.55 (1.0)
0.72 (0.9)
308 (1.7)
473 (1.8)
20 c
12 d
[7]
[7]
−1.08 (0.7)
−0.87 (0.4)
−1.23 h
767 c
129 d
0.56 (1.0)
0.54 (1.0)
490 (2.6)
622 (1.6)
1964 c
658 c
235 d
159 d
[7]
[Ru{CꢀC-4-C6H4Nꢁ
This work
¸¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH}-
(PPh3)2(h-C5H5)] (3)
[Ru(CꢀCPh)(PPh3)2(h-C5H5)] (9)
[Ru(CꢀC-4-C6H4NO2)(PPh3)2-
(h-C5H5)] (5)
0.55 (0.7)
0.73 (1.0)
310 (2.0)
460 (1.1)
16 c
10 d
96 d
[14]
[12,14,19]
−1.08 (1.0)
−0.92 (0.3)
468 c
[Ru{CꢀC-4-C6H4-(E)-CHꢁCH-4-
0.55 (0.9)
476 (2.6)
1455 c
232 d
[12,14,19]
C6H4NO2}(PPh3)2(h-C5H5)] (7)
¸¹¹¹¹¹¹¹¹¹¹º
e
590
190 f
78 f
116 f
106 g
47 g
77 g
[8]
[9]
[9]
4-Me2NC6H4NꢁCCHꢁCHC(O)CHꢁCH
¸¹¹¹¹¹¹¹¹¹¹¹º
558 e
512 e
4-2NC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH
4-Me2NC6H4-(E)-CHꢁCH-4-C6H4Nꢁ
¸¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH
a All compounds are optically transparent at the fundamental frequencies.
b Response too low to measure.
c HRS at 1064 nm; values 910%, using p-nitroaniline (i=21.4×10−30 esu) as a reference.
d Data corrected for resonance enhancement at 532 nm using the two-level model with i0=i[1−(2umax/1064)2][1−(umax/1064)2]; damping
factors not included.
e Molar absorptivity not reported.
f First hyperpolarizability measured by EFISH at 1.91 mm.
g Data corrected for resonance enhancement at 0.96 mm using the two-level model with i0=i[1−(2umax/1910)2][1−(umax/1910)2].
h Epc A
(V).
0/−I
ligand has the same effect upon metal-centred oxidation
potential as ‘chain-lengthening’ nitro-substituted aryl–
alkynyl ligands. Unlike the nitro-centred reductions in
4–7 which are quasi-reversible, the reductions of the
quinonal group in 2 and 3 are irreversible using a scan
rate of 100 mV s−1, with evidence of return peaks
(Epa−Epc=0.9 V) observed at higher scan rates (400–
1000 mV s−1). The oxidations are correlated with a
metal-centred HOMO and the reductions with a
quinonal-localized LUMO. Proceeding from 4-nitro-
phenyl–alkynyl complexes 4 and 5 to 4-indoanilino–
alkynyl complexes 2 and 3, respectively, results in a
decrease in the energy difference between HOMO and
LUMO, manifested in both an increase in umax and a
decrease in E0RuII/III −EA0 0/−I; a similar result has been
observed in proceeding from 4-nitrophenyl–alkynyl
complexes 4 and 5 to 4,4%-(E)-nitrostilbenylalkynyl
complexes 6 and 7 [14].
2.5. Nonlinear optical studies
Quadratic optical nonlinearities of the new com-
pounds were determined using the hyper-Rayleigh scat-
tering technique at 1064 nm. The results of these studies
are given in Table 2, together with linear optical ab-
sorption data, and results for related ruthenium com-
plexes and organic indoanilines for comparison.
The two-level model, which was developed to explain
the quadratic NLO merit of simple donor-bridge-accep-
tor organics, assumes that the dominant contribution to
i is associated with the charge-transfer transition along
the molecular dipole axis. The iCT (i in the direction of
the charge-transfer axis) is then given by:
v2eg(ve−vg)ꢀ2eg
(ꢀe2g−ꢀ2)(ꢀ2eg−4ꢀ2)
iCT
h

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A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
where ꢀeg is the ground to excited state transition
energy (which can be obtained from umax in the elec-
tronic absorption spectrum), veg is the transition dipole
moment (obtained from integration of the absorption
band in the UV–vis spectrum), and vg and ve are the
ground state and the excited state dipole moments. The
applicability of this model to donor-bridge-acceptor
organometallics is questionable (it is likely more than
one transition may be important for i in complex
molecules). This model suggests that the quadratic
NLO coefficient should be increased upon red-shifting
the optical absorption band, and upon increasing the
intensity of this transition. The optical absorption max-
imum for the indoanilino–alkynyl–ruthenium com-
plexes prepared in the current study are significantly
red-shifted compared to those of related nitroaryl–
alkynyl complexes [18,20]; whereas the latter complexes
are red in colour, the former complexes are blue. How-
ever, the intensity of this MLCT transition is signifi-
cantly weaker for the indoanilino–alkynyl–ruthenium
complexes.
The optical nonlinearities of the new complexes are
resonance enhanced due to the proximity of the optical
absorption frequency to the second-harmonic fre-
quency. Assuming that the dominant contribution to
resonance enhancement arises from the charge-transfer
transition (as in the present complexes), it is possible to
apply a two-level correction to the experimental data to
afford approximated zero-frequency nonlinearities i0.
The shortcomings of this approach when applied to
organometallics have been discussed elsewhere [5], but
this procedure arguably provides a useful way to com-
pare resonance-enhanced data and afford qualitative
insights. To facilitate comparisons of quadratic NLO
merit in the present study, two-level-corrected nonlin-
earities are also presented.
have a similar chromophore chain length, reveals that
the latter possess much larger iexp and i0 coefficients.
The 4,4%-(E)-nitrostilbenylalkynyl complexes 6 and 7
have some of the largest quadratic optical nonlinearities
observed thus far for organometallic complexes. The
presence of the indoanilinoalkynyl ligands in 2 and 3
might have been expected to afford complexes with
similarly large nonlinearities. The lower-than-expected
i values recorded for 2 and 3 may be due to both steric
and electronic factors. The structural study above confi-
rms that steric repulsion between the ortho-hydrogens
of the indoanilino–alkynyl ligand phenyl and quinonal
rings results in a lack of coplanarity which will disfa-
vour extensive p-delocalization. The presence of elec-
tron-rich tert-butyl groups may reduce the electron
acceptor properties of the quinone ring. The electronic
factor has been noted previously with organic com-
pounds [9]. Quadratic nonlinearity i was reduced by a
factor of two or more on proceeding from
4,4%-Me2NC6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH to the
di-tert-butylated
compound
4,4%-Me2NC6H4Nꢁ
¸¹¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH. Although synthetic consid-
erations have so far necessitated the inclusion of the
tert-butyl groups in our organometallic complexes,
these observations in the organic system suggest that a
similar ligand without tert-butyl groups should afford
complexes with very large two-level-corrected
nonlinearities.
3. Experimental
3.1. General
All reactions were performed under a nitrogen atmo-
sphere with the use of Schlenk techniques unless other-
wise stated. Dichloromethane was dried by distilling
over CaH2, methanol was dried by distilling over Mg–
I2, and tetrahydrofuran was dried by distilling over
sodium–benzophenone; other solvents were used as
received. ‘Pet. spirit’ refers to a fraction of petroleum
ether of boiling range 60–80°C. Chromatography was
on silica gel (230–400 mesh ASTM) or ungraded basic
alumina.
[RuCl(PPh3)2(h-C5H5)] [21] and cis-[RuCl2(dppm)2]
[22] were prepared by the literature procedures.
Sodium methoxide solutions were prepared by reacting
sodium with dry methanol. Bis(triphenylphosphine)-
palladium(II) chloride was prepared by stirring two
equivalents of triphenylphosphine with palladium(II)
chloride in dimethylformamide at reflux for 2 h. The
resulting precipitate was collected and recrystallized
from chloroform. Sodium hexafluorophosphate
(Aldrich) was recrystallized from acetonitrile before
use. 2,6-Di-tert-butyl-1,4-benzoquinone (Aldrich), 4-
The quadratic nonlinearity of the new organic alkyne
was too low to measure. In contrast, experimental i
values of the indoanilino–alkynyl–ruthenium com-
plexes 2 and 3 are both large. As with the related
complexes bearing 4-nitrophenylalkynyl (4, 5) or 4,4%-
(E)-nitrostilbenylalkynyl ligands (6, 7) (Table 2), com-
plexes 2 and 3 can be viewed as (conceptual) derivatives
of their phenylalkynyl analogues (8, 9). Introduction of
acceptor substituent in proceeding from phenyl–
alkynyl complex (8, 9) to indoanilino–alkynyl analogue
(2, 3) results in significant increases in both experimen-
tally obtained and two-level-corrected nonlinearities
(Table 2). Complex 3 has larger iexp and i0 values than
its 4-nitrophenylalkynyl analogue 5. However, the op-
posite trend is observed for iexp for 2 and its 4-nitro-
phenylalkynyl analogue 4, and i0 for these complexes
are equivalent within experimental error; from the per-
spective of i normalized for chromophore chain length,
the complexes with the 4-nitrophenylalkynyl ligand are
the more efficient. Comparison of 2 and 3 with their
4,4%-(E)-nitrostilbenylalkynyl analogues (6, 7), which

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
199
1
iodoaniline (Aldrich), boron trifluoride etherate
(Aldrich), trimethylsilylethyne (Aldrich), copper(I) io-
dide (Unilab), tetrabutylammonium fluoride (1 M solu-
tion in tetrahydrofuran) (Aldrich), sulfuric acid (98%)
(Univar), and anhydrous magnesium sulfate (Aldrich)
were used as received.
421.0903, found 421.0906. H-NMR (l): 1.18 (s, 9H,
Mea), 1.30 (s, 9H, Meb), 6.63 (d, JHH=8 Hz, 2H, H5),
6.74 (d, JHH=3 Hz, 1H) 7.01 (d, JHH=3 Hz, 1H, H10,
H14), 7.69 (d, JHH=8 Hz, 2H, H4).
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
3.2.2. 4-HCꢀCC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH (1)
EI (electron impact) mass spectra (both unit resolu-
tion and high resolution (HR)) were recorded using a
VG Autospec instrument (70 eV electron energy, 8 kV
accelerating potential) and secondary ion mass spectra
were recorded using a VG ZAB 2SEQ instrument (30
kV Cs+ ions, current 1 mA, accelerating potential 8 kV,
3-nitrobenzyl alcohol matrix) at the Research School of
Chemistry, Australian National University; peaks are
reported as m/z (assignment, relative intensity). Micro-
analyses were carried out at the Research School of
Chemistry, Australian National University. IR spectra
were recorded as dichloromethane solutions using a
Perkin–Elmer System 2000 FTIR. UV–vis spectra re-
ported below and in Table 2 were recorded using either
a Cary 4 or Cary 5 spectrophotometer of solutions in
THF in 1 cm cells (additional spectra for solva-
tochromic studies summarized in Section 2 were ob-
tained under similar conditions in cyclohexane and
methanol). 1H- (300 MHz), 13C- (75 MHz) and 31P-
(121 MHz) NMR spectra were recorded using a Varian
Gemini-300 FT NMR spectrometer in CDCl3 and are
referenced to residual solvent (1H, 13C) or external 85%
H3PO4 (31P). The assignments follow the numbering
schemes shown in Fig. 3. Electrochemical measure-
ments were recorded using a MacLab 400 interface and
MacLab potentiostat from ADInstruments. The sup-
porting electrolyte was 0.1 M [NnBu4] [PF6] in distilled,
deoxygenated CH2Cl2. Solutions containing ca. 1×
10−3 M complex were maintained under nitrogen.
Measurements were carried out using a platinum disc
working, Pt auxiliary and Ag–AgCl reference electrode,
such that the ferrocene–ferrocenium redox couple was
A mixture of 4-IC6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH
(300 mg, 0.71 mmol), trimethylsilylethyne (0.40 ml, 2.8
mmol), bis(triphenylphosphine)palladium(II) chloride
(5 mg, 0.007 mmol) and copper(I) iodide (5 mg, 0.03
mmol) was stirred in triethylamine (10 ml, deoxy-
genated) for 1 h. The solvent was removed in vacuo
and the residue was dissolved in dichloromethane and
passed through a plug of silica. The volume was re-
duced to around 20 ml, and a solution of tetrabutylam-
monium fluoride (1 ml,
1
M
solution in
tetrahydrofuran) was added with stirring. After 5 min,
the solvent was removed and the residue purified by
silica column chromatography. Concentration of sol-
vent volume on a rotary evaporator afforded the
product as an orange powder (85 mg, 37%). EI MS: 319
([M]+, 100), 304 ([M−Me]+, 25). Anal. Calc. for
C22H25NO: C, 82.72; H, 7.89; N, 4.38. Found: C, 82.48;
H, 7.79; N, 3.89%. UV–vis (umax, nm [m, M−1 cm−1]):
448 [4700], 256 [28 000], 254 [15 000]. IR: w(CꢁO) 1633
cm−1. 1H-NMR: l 1.17 (s, 9H), 1.31 (s, 9H, Mea, Meb),
3.10 (s, 1H, HCꢀC), 6.72 (d, JHH=3 Hz, 1H), 7.00 (d,
J
HH=3 Hz, 1H, H10, H14), 6.82 (d, JHH=8 Hz, 2H,
H4), 7.50 (d, JHH=8 Hz, 2H, H5). 13C-NMR: l 29.4
(Mea, Meb), 35.4 (C16), 35.8 (C15), 77.5 (C1), 83.4 (C2),
118.9 (C3), 120.8 (C5), 132.8 (C4), 121.3, 134.3 (C10,
C14), 150.0 (C6), 153.4, 154.2, 158.8 (C9, C11, C13), 187.5
(C12).
3.3. Syntheses of metal acetylide complexes
located at 0.56 V. Scan rates were 100 mV s−1
.
3.3.1. Trans-[Ru(CꢀC-4-C6H4Nꢁ
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH)Cl(dppm)2] (2)
3.2. Syntheses of indoanilines
Cis-[RuCl2(dppm)2] (140 mg, 0.16 mmol), 4-HCꢀ
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
¸¹¹¹¹¹¹¹¹¹¹¹¹º
3.2.1. 4-IC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH
CC6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH (75 mg, 0.24
mmol) and sodium hexafluorophosphate (55 mg, 0.33
mmol) were stirred in dichloromethane (5 ml) for 5 h at
r.t. Triethylamine (1 ml) was added with stirring and
the solvent removed in vacuo after 1 min. The residue
was adsorbed onto basic alumina and placed atop
an alumina column. Elution with 1:3 dichloro-
methane–pet. spirit removed unreacted alkyne. The
product was eluted with 4:1 dichloromethane–pet.
A mixture of 2,6-di-tert-butyl-1,4-benzoquinone (500
mg, 2.27 mmol), 4-iodoaniline (1.40 g, 6.39 mmol) and
boron trifluoride etherate (30 ml, 0.16 mmol) was stirred
in tetrahydrofuran (30 ml) at reflux for 7 h with a
further six aliquots of boron trifluoride etherate (30 ml)
being added at hourly intervals. The mixture was then
allowed to cool to r.t. and the solvent removed in
vacuo. The residue was purified by silica column chro-
matography, the product being eluted with 3:5
dichloromethane–pet. spirit. Reduction of solvent vol-
ume on a rotary evaporator afforded the product as an
orange powder (800 mg, 84% based on di-tert-butyl-
benzoquinone). HR MS (EI) C20H24INO: Anal. Calc.
spirit. Evaporation of the solvent on
a rotary
evaporator yielded 123 mg (65%) of a deep blue
powder. FAB MS: 1223 ([M]+, 50), 1188 ([M−Cl]+,
15), 905 ([RuCl(dppm)2]+, 20), 869 ([Ru(dppm)2]+,
100). Anal. Calc. for C72H68ClNOP4Ru: C, 70.67; H,

200
A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
5.60; N, 1.14. Found: C, 70.30; H, 5.93; N, 0.92%.
UV–vis (umax nm [m, M−1 cm−1]): 645 [8020], 319 [sh,
18 100], 273 [29 600], 268 [29 400]: IR: w(CꢀC) 2067
in transmission factors ranging from 0.888–0.986. Data
were corrected for Lorentz and polarization effects. The
structure was solved by direct methods (SIR-92), and
expanded using difference Fourier techniques. The non-
hydrogen atoms were refined with anisotropic displace-
cm−1 1H-NMR: l 1.27 (s, 9H), 1.31 (s, 9H) (Mea,
.
Meb), 4.91 (m, 4H, CH2), 6.04 (d, 2H, JHH=8 Hz, H4),
6.53 (d, 2H, JHH=8 Hz, H5), 6.94 (d, 1H, JHH=3 Hz,
H10 or H14), 7.02–7.43 (m, 50H, phenyl and H14 or
H10). 31P-NMR: l −6.1 (PPh2). 13C-NMR: l 29.4
(Mea, Meb), 35.3, 35.7 (C15, C16), 50.3 (CH2), 114.2
ment
by
minimising
Sw(ꢀFoꢀ−ꢀFcꢀ)2
where
w=[|c2(Fo)+(p2/4)Fo2]−1, except for those in the sol-
vent molecule which were modelled isotropically. Hy-
drogen atoms were included in calculated positions but
not refined. No hydrogens were included with the hep-
tane solvent molecule. The final cycle of full-matrix
least-squares refinement was based on 7320 observed
reflections [I\3|(I)] and 641 variable parameters. The
(C2), 122.0 (C5), 127.5 (Cp), 128.5 (C3), 129.2 (d, JCP
=
23 Hz, Cm), 133.5 (d, JCP=23 Hz, Co), 134.5 (m, Ci),
130.5 (C4), 122.2, 135.0 (C10, C14), 144.5 (C6), 151.8,
152.1, 156.5 (C9, C11, C13), 187.8 (C12).
maximum and minimum peaks in the final difference
−3
,
3.3.2. [Ru(CꢀC-4-C6H4Nꢁ
Fourier map corresponded to 1.02 and −0.67 e A
,
¸¹¹¹¹¹¹¹¹¹¹¹¹¹º
CCHꢁCtBuC(O)CtBuꢁCH)(PPh3)2(p-C5H5)] (3)
respectively, and were found in the region of the disor-
dered heptane molecule (0.5 occupancy). All calcula-
tions were performed using the crystallographic
software package MAXUS [23] and TEXSAN [24].
[RuCl(PPh3)2(h-C5H5)] (90 mg, 0.12 mmol) and 4-
HCꢀCC6H4Nꢁ¸C¹C¹H¹ꢁC¹t¹B¹u¹C¹(O¹)¹C¹tB¹u¹ꢁCºH (50 mg, 0.16
mmol) were stirred in methanol (10 ml) at reflux for 45
min. The mixture was then cooled to r.t. and sodium
methoxide solution (1 ml, 0.2 M solution in methanol)
was added with stirring. The solvent was removed and
the residue purified by column chromatography on
silica. The product was then recrystallized from
dichloromethane–pet. spirit to afford 40 mg (32%) of
dark blue microcrystals. FAB MS: 1009 ([M]+, 25), 746
([M+H−PPh3]+, 30), 691 ([Ru(PPh3)2(h-C5H5)+, 25),
429 ([Ru(PPh3)(h-C5H5)]+, 100). Anal. Calc. for
C63H59NOP2Ru: C, 74.98; H, 5.89; N, 1.39. Found: C,
75.92; H, 5.97; N, 1.12%. UV–vis (umax, nm [m, M−1
cm−1]): 625 [15 500], 317 [29 800], 239 [34 400]. IR:
3.4.1. Crystal data for C66.5H59NOP2Ru
Mf=1051.22, monoclinic, space group P21/a, a=
17.0623(5) A, b=18.8222(6) A, c=20.4641(7)) A, i=
106.482(2)°, V=6302.0(3) A , Z=4, Dcalc=1.108 g
,
,
,
3
,
cm−3
,
v(Mo–Ka)=3.37 cm−1
.
R=S(ꢀFoꢀ−ꢀFcꢀ)/
S(ꢀFoꢀ)=0.075, Rw[{Sw(ꢀFoꢀ−ꢀFcꢀ)2}/SwFo2]1/2=0.093,
GOF=2.22.
3.5. Hyper–Rayleigh scattering measurements
An injection-seeded Nd:YAG laser (Q-switched
Nd:YAG Quanta Ray GCR5, 1064 nm, 8 ns pulses, 10
Hz) was focussed into a cylindrical cell (7 ml) contain-
ing the sample. The intensity of the incident beam was
varied by rotation of a half-wave plate placed between
crossed polarizers. Part of the laser pulse was sampled
by a photodiode to measure the vertically polarized
incident light intensity. The frequency doubled light
1
n(CꢀC) 2061 cm−1. H-NMR: l 1.24 (s, 9H), 1.32 (s,
9H, Mea, Meb), 4.32 (s, 5H, C5H5), 6.77 (d, 2H, JHH=8
Hz, H4), 7.01–7.48 (m, 34H, Ph). 31P-NMR: l 50.7
(PPh3). 13C-NMR: l 29.5 (Mea, Meb), 35.3, 35.7 (C15,
C16), 85.3 (C5H5), 115.6 (C2), 122.5 (C5), 127.2 (t,
JCP=5 Hz, Cm), 128.4 (Cp), 129.1 (C3), 131.0 (C4),
133.8 (t, JCP=5 Hz, Co), 122.1, 135.0 (C10, C14), 138.7
(m, Ci), 145.2 (C6), 151.9, 152.5, 156.9 (C9, C11, C13),
187.9 (C12).
3.4. X-ray structural study
A purple plate (0.30×0.30×0.04 mm3) grown by
diffusion of n-heptane into a chloroform solution of 3
was mounted on a glass fiber with oil. Data were
collected on a Nonius KappaCCD diffractometer using
graphite-monochromated Mo–Ka radiation. A set of
ten images were collected and used to determine the cell
constants. Data were collected (200 K) as 334 frames
via ꢀ-rotation (Dꢀ=0.7°) with 52 s exposure times.
The intensities of 217 072 reflections were collected to
2qmax=55.0°; equivalent reflections were merged to
yield 14 433 unique reflections (Rint=0.087). An ana-
lytical absorption correction was applied which resulted
Fig. 3. NMR labeling schemes.

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 193–201
201
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and linear scattering were distinguished by appropriate
filters; gated integrators were used to obtain intensities
of the incident and harmonic scattered light. The ab-
sence of luminescence contribution to the harmonic
signal was confirmed by using interference filters of
different wavelengths near 532 nm. All measurements
were performed in tetrahydrofuran using p-nitroaniline
(i=21.4×10−30 esu) [25] as a reference. Solutions
were sufficiently dilute that absorption of scattered
second-harmonic light was negligible. Further details of
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Crystallographic data for the structure reported in
the paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 141947 for
compound 3. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
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Acknowledgements
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Synth. 21 (1982) 78.
We thank the Fund for Scientific Research-Flanders
(G.0338.98, G.0407.98) (A.P.), the Belgian Government
(IUAP-IV/11) (A.P.), the K.U. Leuven (GOA/2000/03)
(A.P.), and the Australian Research Council (M.G.H.)
for financial support, and Johnson-Matthey Technol-
ogy Centre for the loan of ruthenium salts (M.G.H.).
S.H. is a postdoctoral researcher of the Fund for Scien-
tific Research-Flanders, M.G.H. is an ARC Australian
Senior Research Fellow, N.T.L. holds and A.M.M.
held an Australian Postgraduate Award.
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