Organometallic complexes for nonlinear optics: Part 19. Syntheses and molecular quadratic hyperpolarizabilities of indoanilino-alkynyl-ruthenium complexes

Article abstract of DOI:10.1016/S0022-328X(00)00311-9

The terminal alkyne 4-HCCC₆H₄N=CCH=C^tBuC(O)C^tBu=CH (1) and ruthenium complex derivatives trans-[Ru(CC-4-C₆H₄N=CCH=C^tBuC(O)C ^tBu=CH}Cl(dppm)₂] (2) and [Ru{CC-4-C₆H₄N=CCH=C^tBuC(O)C ^tBu=CH}(PPh₃)₂(η-C₅H ₅)] (3) have been synthesized. An X-ray structural study of 3 reveals the expected equivalent C-C bond lengths of the phenyl and alternating C-C and C=C 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.

Full text of DOI:10.1016/S0022-328X(00)00311-9

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Journal of Organometallic Chemistry 605 (2000) 184–192
Organometallic complexes for nonlinear opticsꢀ
Part 20. Syntheses and molecular quadratic hyperpolarizabilities of
alkynyl complexes derived from (E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2
Andrew M. McDonagh a, Nigel T. Lucas a, Marie P. Cifuentes 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 18 April 2000; accepted 18 May 2000
Abstract
The syntheses of the alkyne (E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 (1) and alkynyl complexes LnM{(E)-4,4%-
CꢀCC6H4NꢁNC6H4NO2} [LnM=trans-[RuCl(dppm)2] (2), Ru(PPh3)2(h-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%-CꢀCC6H4XꢁCHC6H4NO2}(PPh3) (X=CH,
N) reveals that complex 4 has a significantly larger quadratic nonlinearity than its ene- or imino-linked analogues. © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Ruthenium; Gold; Cyclic voltammetry; X-ray structure; Quadratic hyperpolarizabilities; Alkynyl; Nonlinear optics
One possible change to this efficient molecular com-
position is to modify the ethenyl linkages by introduc-
1. Introduction
tion of heteroatoms. Replacing the trans-CHꢁCH
Organic compounds with a donor-p-bridge-acceptor
linkage in 4-N,N-dimethylamino-4%-nitrostilbene by a
composition can have significant nonlinear optical
trans-NꢁCH group, to afford the corresponding ben-
(NLO) properties, and have a potential for use in a
zylideneaniline, results in a 25% decrease in both exper-
variety of technologically important processes [1]. For
imentally-obtained [by EFISH (electric field-induced
this reason, studies have been promulgated to uncover
second harmonic generation) at 1.36 mm] molecular
molecular structure–NLO activity relationships. One
quadratic nonlinearity i and two-level-corrected non-
molecular modification, which has significant impact on
quadratic NLO merit, is the variation of the length and
linearity i0 [8]. While the current work was in progress,
this system was reinvestigated, together with the imino-
linked and azo-linked analogues which result from re-
composition of the p-system. In particular, extending a
p-system by incorporating arylethenyl groups into the
placing the trans-CHꢁCH linkage by a trans-CH=N
bridge is an efficient way to increase the quadratic NLO
group or trans-NꢁN group, respectively [9]. i0 data
coefficient [2–7].
(EFISH at 1.91 mm) revealed that the first hyperpolariz-
abilities of trans-CHꢁCH and NꢁN bridged donor–ac-
ꢀ Part 19: A.M. McDonagh, M.P. Cifuentes, N.T. Lucas, M.G.
Humphrey, S. Houbrechts, A. Persoons, J. Organomet. Chem. (in
press).
* Corresponding author. Tel.: +61-2-62492927; fax: +61-2-
62490760.
E-mail address: mark.humphrey@anu.edu.au (M.G. Humphrey).
ceptor compounds are of comparable magnitude, but
that substitution of one carbon by a nitrogen atom (in
proceeding from ene-linked to imino-linked compound)
results in a significant reduction of second-order NLO
activity, confirming the findings of the earlier study.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00311-9

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
185
2. Results and discussion
Very recently, zinc complexes bearing 4,4%-bis(dialkyl-
aminophenylazo)-2,2%-bipyridine, 4,4%-bis(dialkylamino-
2.1. Synthesis and characterization of
(E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 (1)
phenylimino)-2,2%-bipyridine
and
4,4%-bis(dialkyl-
aminophenylalkenyl)-2,2-bipyridine ligands have been
examined by EFISH [10]. A small increase in nonlinear-
ity was observed on replacing CH by N, but this was
largely ascribed to resonance enhancement.
The preparation of (E)-4,4%-HCꢀCC6H4NꢁNC6-
H4NO2 (1) is outlined in Scheme 1; diazotization of
commercially available (E)-4,4%-H2NCꢀCC6H4NꢁNC6-
H4NO2 followed by reaction with iodide [23] affords the
aryl iodide (E)-4,4%-IC6H4NꢁNC6H4NO2 (37%) which is
then reacted in the standard manner [24] to give the
terminal alkyne 1 (45%). Isolation of the trimethylsilyl-
protected alkyne intermediate offered no advantage in
terms of yield or purity.
Organometallics can also be prepared with a donor–
p-bridge-acceptor composition, but have additional de-
sign flexibility compared to organics. The metal,
co-ligands, coordination geometry and oxidation state
can all be varied, which may impact favourably on NLO
merit. Not surprisingly, the quadratic and cubic NLO
properties of organometallic complexes have come un-
der intense scrutiny [11–15]. We have shown previously
that alkynyl complexes with a ligated metal as donor
group are amongst the most efficient organometallics
for their quadratic NLO response [16–22], with nonlin-
earities comparable in magnitude to the best organics.
Similar to the above studies with alkenes and imines, we
have shown (by HRS at 1.06 mm) that complexes
The UV–vis spectra of (E)-4,4%-IC6H4NꢁNC6H4NO2
and 1 contain absorption bands at 28 300 and 28 400
cm−1, respectively, assigned to a p“p* transition, and
much weaker bands at 21 400 and at 21 700 cm−1
,
respectively, assigned to a n“p* transition. Character-
istic symmetric and asymmetric NꢁO stretches are ob-
served in the IR spectrum of (E)-4,4%-IC6H4Nꢁ
NC6H4NO2 at 1347 and 1527 cm−1, respectively, and in
the IR spectrum of 1 at 1346 and 1527 cm−1, respec-
LnM{(E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2}
{Ln=
1
tively. The H-NMR spectrum of 1 contains a signal at
Ru(PPh3)2(h-C5H5), Au(PPh3), Ni(PPh3)(h-C5H5)} are
significantly more efficient than LnM{(E)-4,4%-
CꢀCC6H4NꢁCHC6H4NO2}. Computational studies uti-
lizing ZINDO confirmed these observations, but also
suggested that the azo-linked analogue should be twice
as efficient as the ene-linked example [16]. However, no
complexes with this alkynyl ligand were prepared, as the
corresponding alkyne (E)-4,4%-HCꢀCC6H4NꢁNC6-
H4NO2 was unknown. We now report the synthesis of
this alkyne and some alkynyl metal derivatives, a struc-
tural study of a representative complex, electrochemical
and quadratic NLO data for these new compounds, and
comparison with previously reported data for the
cognate ene- and imino-linked analogues.
3.27 ppm assigned to the proton of the terminal alkyne.
2.2. Synthesis and characterization of
LnM{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}
[LnM=trans-RuCl(dppm)2 (2), Ru(PPh3)2(p-C5H5) (3),
Au(PPh3) (4)]
The preparation of the new alkynyl complexes 2 [25],
3 [26], and 4 [17] followed published procedures for the
preparation of phenyl- or 4-nitrophenyl-alkynyl ana-
logues, and are shown in Schemes 2–4. Reaction of
cis-[RuCl2(dppm)2], sodium hexafluorophosphate and
the terminal alkyne in dichloromethane at room temper-
ature (r.t.) afforded trans-[Ru{(E)-4,4%-CꢁCHC6-
Scheme 1. Preparation of (E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 (1).
Scheme 2. Preparation of trans-[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}Cl(dppm)2] (2).

186
A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
Scheme 3. Preparation of [Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)2(h-C5H5)] (3).
Scheme 4. Preparation of [Au{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)] (4).
H4NꢁNC6H4NO2}Cl(dppm)2]PF6. Subsequent deproto-
gles are listed in Table 1, and an ORTEP diagram
showing the molecular structure and atomic labeling
scheme is displayed in Fig. 1.
nation with base in situ afforded the desired alkynyl
complex
2
in good yield (62%). Reaction of
[RuCl(PPh3)2(h-C5H5)] with terminal alkyne in reflux-
ing methanol afforded the vinylidene complex [Ru-
{(E)-4,4%-CꢁCHC6H4NꢁNC6H4NO2}(PPh3)2(h-C5H5)]+
which, unlike its bis(dppm) analogue above, does not
require the presence of large counterions (such as hex-
afluorophosphate) for stability, the displaced chloride
presumably being sufficient. The vinylidene complex
was deprotonated with base in situ to afford 3 in 51%
yield. A mixture of (triphenylphosphine)gold chloride,
(E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 and sodium meth-
oxide solution was stirred in dichloromethane for 18 h
to give [Au{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)]
(4) in 71% yield.
The new alkynyl complexes were characterized by
FABMS, satisfactory microanalyses, UV–vis and IR
spectroscopy, 1H-, 31P- and 13C-NMR spectroscopy.
The FAB mass spectrum of 2 and 3 contain molecular
ions, with fragmentation of the former proceeding by
loss of chloro and alkynyl ligands to afford a peak
corresponding to [Ru(dppm)2]+, and fragmentation of
the latter proceeding by successive loss of alkynyl and
phosphine ligand to afford a peak corresponding to
[Ru(PPh3)(h-C5H5)]+. The FAB mass spectrum of 4
does not contain a molecular ion, but rather signals
corresponding to [Au(PPh3)x]+ (x=1, 2). The IR spec-
tra contain characteristic bands assigned to w(CꢀC) at
2061 (2), 2054 (3) and 2113 (4) cm−1. The 31P-NMR
spectra contain singlet resonances at −6.3 (2), 50.7 (3)
and 42.6 (4) ppm, with that of the first-mentioned
confirming the trans stereochemistry of the chloro and
alkynyl ligands.
The structural study confirms the octahedral geome-
try at ruthenium and the trans-disposed chloride and
alkynyl ligands, and reveals the E stereochemistry
about the azo-linkage. Bond distances and angles in-
volving the diphosphine ligands are unexceptional. Im-
portant bond lengths about the metal center are similar
to those of the related donor-bridge-acceptor complexes
trans-[Ru(4-CꢀCC6H4NO2)Cl(dppm)2] (5) [37] and
trans-[Ru(4,4%-CꢀCC6H4C6H4NO2)Cl(dppm)2] (6) [27]
(Table 1). We have shown previously by semi-empirical
Table 1
,
Selected bond lengths (A) and angles (°) for trans-[Ru{(E)-4,4%-
CꢀCC6H4NꢁNC6H4NO2}Cl(dppm)2] (2), trans-[Ru(4-CꢀCC6H4-
NO2)Cl(dppm)2]
Cl(dppm)2] (6)
(5)
and
trans-[Ru(4,4%-CꢀCC6H4C6H4NO2)-
4
5
6
Bond lengths
RuꢂCl
RuꢂP(1)
RuꢂP(2)
RuꢂP(3)
RuꢂP(4)
RuꢂC(1)
C(1)ꢂC(2)
C(2)ꢂC(3)
N(1)ꢂN(2)
C(12)ꢂN(3)
N(3)ꢂO(1)
N(3)ꢂO(2)
2.508(2)
2.322(2)
2.352(2)
2.349(2)
2.355(2)
1.974(7)
1.224(9)
1.406(9)
1.263(9)
1.47(1)
2.483(2)
2.332(2)
2.332(2)
2.358(2)
2.379(2)
1.998(7)
1.190(8)
1.428(8)
2.499(1)
2.330(1)
2.358(1)
2.350(1)
2.361(1)
1.994(4)
1.198(6)
1.439(7)
1.467(9)
1.220(8)
1.207(8)
1.481(6)
1.237(7)
1.226(7)
1.22(1)
1.18(1)
Bond angles
P(1)ꢂRuꢂP(2)
P(3)ꢂRuꢂP(4)
ClꢂRuꢂC(1)
RuꢂC(1)ꢂC(2)
C(1)ꢂC(2)ꢂC(3)
C(6)ꢂN(1)ꢂN(2)
N(1)ꢂN(2)ꢂC(9)
O(1)ꢂN(3)ꢂO(2)
72.20(7)
71.47(7)
173.1(2)
175.2(6)
179.8(9)
112.9(8)
111.5(8)
124(1)
70.98(6)
70.18(6)
177.7(2)
176.8(5)
168.4(7)
71.85(5)
71.63(5)
175.2(1)
177.9(4)
179.1(5)
2.3. X-ray structural study of trans-[Ru{(E)-4,4%-
CꢀCC6H4NꢁNC6H4NO2}Cl(dppm)2] (2)
The identity of 2 was confirmed by a single-crystal
X-ray diffraction study. Selected bond lengths and an-

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
187
Fig. 1. Molecular geometry and atomic labelling scheme for trans-[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}Cl(dppm)2] (2). Non-hydrogen atoms are
,
depicted with 30% thermal ellipsoids; hydrogen atoms are placed in calculated positions with arbitrary bond lengths of 0.95 A.
across
CꢀCC6H4CꢀC6H4NO2,
the
series
4,4%-CꢀC6H4C6H4NO2,
4,4%-
ZINDO that short RuꢂC distances lead to large
quadratic nonlinearities [28]; significantly, the RuꢂC(1)
distances in these complexes are amongst the shortest
for alkynyl–ruthenium complexes. The ClꢂRuꢂC(1)
and RuꢂC(1)ꢂC(2) angles deviate slightly from the ide-
alized 180°, presumably a result of packing effects.
Lack of co-planarity in adjacent phenyl rings may lead
to a diminution in quadratic NLO merit from that
expected for a co-planar disposition; we have previ-
ously reported that the rotation from co-planarity of
adjacent phenyl groups in 6 reduces computationally-
derived molecular NLO activity [27]. For 2, the two
phenylene units of the acetylide ligand are not co-pla-
nar, with the angle between the two planes being 16.9°.
The centrosymmetric space group suggests that no bulk
NLO response would be observed; the molecules have
packed pair-wise with dipoles aligned antiparallel.
(E)-4,4-CꢀC6H4NꢁCHC6H4-
NO2, (E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2) did not af-
fect the RuII/III couple significantly [18]. Extending the
comparison to the new azo-linked complexes reveals
that oxidation potentials increase as E0: 8, 9 (extended
chain nitrophenylalkynyl complexes)B2, 3 (azo-linked
complexes)B5, 7 (4-nitrophenyl–alkynyl complexes);
thus, the azo-linkage produces a perturbation of the
oxidation potential of the RuII/III couple compared to
other extended chain acetylides. Anodic scans to −1.6
V show that, in contrast to the single nitro-centred
reduction observed in cyclic voltammograms of the
nitroaryl–alkynyl–ruthenium complexes, the azo-
linked 2 and 3 each have two reduction waves, the
second process presumably due to a reduction process
involving the azo-linkage.
2.4. Electrochemical studies
2.5. Nonlinear optical studies
In order to gain insight into the electronic environ-
ment of the metal atom in the new alkynyl complexes,
the redox properties of 2 and 3 were examined by cyclic
voltammetry; the results are summarized in Table 2,
together with data for some related complexes for
comparison.
Cyclic voltammetric scans of complexes 2 and 3 using
potentials of 0–1.0 V each show an electrochemically
reversible wave with similar potentials (0.62 for 2, 0.66
V for 3), attributed to the metal-centered RuII/III oxida-
tion process. We have previously reported that pro-
gressing from the 4-nitrophenyl–alkynyl complexes
trans-[Ru(4-CꢀCC6H4NO2)Cl(dppm)2] (5) and Ru(4-
CꢀCC6H4NO2)(PPh3)2(h-C5H5) (7) to trans-[Ru{(E)-
4,4%-CꢀCC6H4CHꢁCHC6H4NO2}Cl(dppm)2] (8) and
Ru{(E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2}(PPh3)2(h-C5-
H5) (9) leads to a decrease of 0.16–0.18 V in oxidation
potential [18,22]. More subtle variations (changing the
bridging unit in the extended chain acetylide complexes
Quadratic optical nonlinearities of the new com-
pounds were determined using the hyper-Rayleigh scat-
tering (HRS) technique at 1064 nm. The results of these
studies are given in Table 2, together with linear optical
absorption data, two-level-corrected quadratic nonlin-
earities, results for related ruthenium and gold com-
plexes, and data for the relevant alkynes for
comparison. We have previously noted that quadratic
nonlinearities for gold and ruthenium–alkynyl com-
plexes are larger than those for the parent organic
alkynes [30]. A similar result is observed with the new
compounds; progression from 1 to 2–4 leads to signifi-
cant increases in both observed and two-level corrected
nonlinearities. Data for the new alkynyl complexes 2–4
are much larger than those for the phenylalkynyl (10–
12) or nitrophenylalkynyl (5, 7, 13) analogues. This
may not be surprising given that proceeding from 10–
12 to complexes 2–4 involves the introduction of an
acceptor substituent and proceeding from 5, 7, 13 to

188
A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
2–4 involves chromophore chain-lengthening, i.e. two
structural modifications which are known to enhance
quadratic NLO merit. Comparison of the azo-linked
complexes 2–4 with the ene-linked (8, 9, 14) and imino-
linked (15, 16) analogues reveals that the nonlinearity
increases on proceeding from the imino-linked com-
plexes to the ene-linked and azo-linked complex ana-
logues. Comparison between ene-linked and azo-linked
ruthenium complexes is difficult given the proximity of
the linear optical absorption maxima to the second-har-
monic wavelength (532 nm); resonance enhancement
and damping render such comparisons very difficult. In
contrast, the gold-containing complexes 4, 14 and 16
have absorption maxima far removed from the second
harmonic, permitting comment on the effect of bridging
unit variation. Data for both experimentally obtained
and two-level-corrected nonlinearities follow the trend:
imino-linked (16)Bene-linked (14)Bazo-linked (4)
complex.
3. Conclusions
Synthetic routes into the terminal alkyne (E)-4,4%-
HCꢀCC6H4NꢁNC6H4NO2 and derivative metal alkynyl
complexes have been developed. An X-ray structural
study of trans-[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}-
Cl(dppm)2] (2) confirms the E stereochemistry of the
azo-linkage. Electrochemical data reveals that the
metal-centered oxidation is sensitive to bridging atom
variation. NLO measurements using the HRS technique
show that the new ruthenium complexes bearing the
Table 2
Cyclic voltammetric data, experimental linear optical spectroscopic and quadratic nonlinear optical response parameters
b,c
d
Compound
E°
(V) a E° 0/−1 (V) a
umax (nm) b
i
i0
Reference
II/III
Ru
A
[ipc/ipa
]
[ipa/ipc
]
[m (104 M−1
(10−30 esu)
(10−30 esu)
cm−1)]
(E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 (1)
trans-[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}-
Cl(dppm)2] (2)
381 (2.7)
583 (2.7)
59
1649
29
232
This work
This work
0.62 (1.0)
0.66 (1.0)
−0.63 (1.0)
−1.03 (0.5)
−0.74 (1.0)
[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)2-
(h-C5H5)] (3)
565 (2.9)
1627
149
This work
−0.97 (0.5)
[Au{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)] (4)
(E)-4,4%-HCꢀCC6H4CHꢁCHC6H4NO2
trans-[Ru{(E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2}- 0.56 (1.0)
Cl(dppm)2] (8)
398 (3.3)
358 (3.3)
490 (2.6)
180
55
1964
68
27
235
This work
[17]
[22]
−0.87 (0.4)
−0.92 (0.3)
[Ru{(E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2}(PPh3)2- 0.55 (0.9)
476 (2.6)
386 (3.8)
1455
120
232
49
[16,18,29]
[17]
(h-C5H5)] (9)
[Au{(E)-4,4%-CꢀCC6H4CHꢁCHC6H4NO2}(PPh3)]
(14)
4-HCꢀCC6H4NO2
288 (1.5)
473 (1.8)
460 (1.1)
338 (2.5)
355 (1.4)
496 (1.3)
14
767
468
22
36
840
9
129
96
12
18
[17]
[22]
[16,18,29]
[17]
[16,18,29]
[16]
trans-[Ru(4-CꢀCC6H4NO2)Cl(dppm)2] (5)
[Ru(4-CꢀCC6H4NO2)(PPh3)2(h-C5H5)] (7)
[Au(4-CꢀCC6H4NO2)(PPh3)] (13)
(E)-4,4%-HCꢀCC6H4NꢁCHC6H4NO2
[Ru{(E)-4,4%-CꢀCC6H4NꢁCHC6H4NO2}(PPh3)2- 0.57 (1.0)
0.72 (0.9)
0.73 (1.0)
−1.08 (0.7)
−1.08 (1.0)
−0.79 (0.5)
86
(h-C5H5)] (15)
[Au{(E)-4,4%-CꢀCC6H4NꢁCHC6H4NO2}(PPh3)]
(16)
392 (2.1)
85
34
[17]
trans-[Ru(CꢀCPh)Cl(dppm)2] (10)
[Ru(4-CꢀCPh)(PPh3)2(h-C5H5)] (11)
[Au(CꢀCPh)](PPh3) (12)
0.55 (1.0)
0.55 (0.7)
308 (1.7)
310 (2.0)
296 (1.3)
20
16
6
12
10
4
[22]
[18]
[17]
a Ag/AgCl reference; CH2Cl2 solvent.
b THF solvent.
c All compounds are optically transparent at the fundamental frequency. 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 are not included.

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
189
pared 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 hex-
afluorophosphate (Aldrich) was recrystallized from ace-
tonitrile before use. Trimethylsilylethyne (Aldrich),
copper(I) iodide (Unilab), tetra-n-butylammonium
fluoride (1 M solution in tetrahydrofuran) (Aldrich),
sulfuric acid (98%) (Univar), (E)-4,4%-H2NC6H4Nꢁ
NC6H4NO2 (Disperse Orange 3, 95%) (Aldrich),
sodium nitrite (M & B), potassium iodide (M & B) and
anhydrous magnesium sulfate (Aldrich) were used as
received.
Fig. 2. NMR numbering scheme.
azo-linked alkynyl ligand have very large second-order
molecular nonlinearities. The gold complex 4 is opti-
cally transparent at both the fundamental and second-
harmonic wavelengths, permitting a comparison of the
effect of ligand variation to be made. Complex 4 has
significantly larger quadratic nonlinearity than its ene-
linked or imino-linked analogues.
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. Infrared
spectra were recorded as dichloromethane solutions
using a Perkin–Elmer System 2000 FTIR. 1H- (300
MHz), 13C- (75 MHz) and 31P- (121 MHz) NMR
spectra were recorded using a Varian Gemini-300 FT
NMR spectrometer and are referenced to residual sol-
vent (1H, 13C) or external 85% H3PO4 (31P). The assign-
ments follow the numbering schemes shown in Fig. 2.
UV-vis spectra were recorded using either a Cary 4 or
Cary 5 spectrophotometer of solutions in THF in 1 cm
cells. Electrochemical measurements were recorded us-
ing a MacLab 400 interface and MacLab potentiostat
from ADInstruments. The supporting electrolyte was
0.1 M [NBun4][PF6] in distilled, deoxygenated CH2Cl2.
Solutions containing ca. 1×10−3 M complex were
maintained under nitrogen. Measurements were carried
out using Pt disc working-, Pt auxiliary- and Ag–AgCl
reference-electrodes, such that the ferrocene–ferroce-
nium redox couple was located at 0.56 V. Scan rates
We have recently investigated another possibility for
enhancing quadratic NLO merit by modification of the
alkynyl ligand, namely utilizing indoanilinoalkynyl lig-
ands [1]. R¸ep¹la¹c¹in¹g¹t¹he¹i¹n¹do¹a¹n¹ilºinoalkynyl ligand CꢀC-
4-C6H4NꢁCCHꢁCtBuC(O)CtBuꢁCH by the azo-linked
alkynyl ligand results in
a dramatic increase in
quadratic nonlinearity for both the chlorobis-
(dppm)ruthenium system (417×10−30 esu cf 1649×
10−30 esu) and (cyclopentadienyl)bis(triphenylphos-
phine)ruthenium system (658×10−30 esu cf 1627×
10−30 esu). Significantly, the optical absorption max-
ima are two to three times more intense for the
azo-linked complexes 2 and 3 in the present study than
their indoanilino–alkynyl complex analogues. Modifi-
cation of the arylalkynyl ligand by incorporation of an
azo bridging unit is an effective way to enhance nonlin-
earity. Oligomeric and polymeric compounds for non-
linear optics are frequently constructed using yne- or
ene-linkages; the current studies suggest that attention
should also be focussed on azo-linkages for construct-
ing efficient NLO materials.
4. Experimental
4.1. General conditions, reagents and instruments
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.
The following were prepared by literature proce-
dures: [RuCl(PPh3)2(h-C5H5)] [31], cis-[RuCl2(dppm)2]
[38], [AuCl(PPh3)] [32]. Sodium methoxide solutions
were prepared by reacting sodium with dry methanol.
Dichlorobis(triphenylphosphine)palladium(II) was pre-
were 100 mV s−1
.
4.2. Synthesis of (E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2
(1)
4.2.1. (E)-4,4%-IC6H4NꢁNC6H4NO2
No attempt to exclude air was made during this
procedure. Concentrated sulfuric acid (2 ml) was added
to water (250 ml) in a 500 ml round-bottomed flask.
(E)-4,4-H2NC6H4NꢁNC6H4NO2 (2.0 g, 8.3 mmol) was
added and the mixture stirred until a fine suspension
was formed (ca. 10 min). Sodium nitrite (800 mg, 11.6
mmol) was added and the mixture stirred at r.t. for 1 h.
The mixture was filtered through a plug of Celite and

190
A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
an aqueous solution of potassium iodide (2.5 g, 15
mmol in 50 ml of water) was added to the filtrate with
stirring, whereupon a precipitate formed. The mixture
was extracted with dichloromethane, the organic phase
separated and dried with magnesium sulfate, and the
solvent removed on a rotary evaporator. The residue
was then purified by column chromatography on silica.
Yield was 1.02 g (37%) of an orange–brown powder.
HR MS (EI) C12H8IN3O2: Calc. 352.9661, Found
352.9665. UV–vis (umax, nm [m, M−1 cm−1]): 461
[1500], 353 [28 300]. IR (cm−1): 1527 (m) was(NꢁO),
1347 (w) ws(NꢁO). 1H-NMR: l 7.68 (d, JHH=9 Hz, 2H,
H4), 7.90 (d, JHH=9 Hz, 2H, H5), 8.02 (d, JHH=9 Hz,
2H, H10), 8.37 (d, JHH=9 Hz, 2H, H11).
moved on a rotary evaporator. The residue was recrys-
tallized from dichloromethane–methanol to yield 75
mg (62%) of dark purple microcrystals identified as 2.
A crystal suitable for X-ray diffraction studies was
grown by the slow diffusion of methanol into a
dichloromethane solution. FABMS: 1155 ([M]+, 40),
869 ([Ru(dppm)2]+, 20). Anal. Calc. for C64H52ClN3-
O2P4Ru: C, 66.52; H, 4.54; N, 3.64. Found: C, 66.60;
H, 4.24; N, 3.72%. UV–vis (umax, nm [m, M−1 cm−1]):
585 [27 200], 366 [14 000], 267 [41000]. IR (cm−1): 2061
1
(w) w(CꢀC), 1341 (m) w(NꢁO). H-NMR: l 4.93 (m,
4H, CH2), 6.06 (d, 2H, JHH=9 Hz, H4), 7.06–7.42 (m,
40H, Ph), 7.53 (d, 2H, JHH=9 Hz, H5), 7.92 (d, 2H,
J
HH=9 Hz, H10), 8.33 (d, 2H, JHH=9 Hz, H11). 31P-
NMR: l −6.3 (PPh2). 13C-NMR: l 50.2 (CH2), 117.5
(C2), 122.7, 123.0, 124.7 (C5, C10, C11), 127.6 (Cp),
129.2, 129.4 (Cm), 130.7 (C4), 133.2, 133.4 (Co), 134.3
(m, partially obscured by Co, Ci) 136.0 (C3), 147.6 (C6),
148.0 (C12), 156.6 (C9).
4.2.2. (E)-4,4%-HCꢀCC6H4NꢁNC6H4NO2 (1)
(E)-4,4%-IC6H4NꢁNC6H4NO2 (250 mg, 0.71 mmol)
and trimethylsilylethyne (0.4 ml, 2.8 mmol) were dis-
solved in tetrahydrofuran (5 ml) with stirring. Triethy-
lamine (2 ml) was added followed by dichlorobis-
(triphenylphosphine)palladium(II) (50 mg, 0.071 mmol)
and copper(I) iodide (20 mg, 0.11 mmol), and the
resultant mixture was stirred for 1 h. The mixture was
4.3.2. [Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}-
(PPh3)2(p-C5H5)] (3)
[RuCl(PPh3)2(h-C5H5)] (170 mg, 0.23 mmol) and 1
(70 mg, 0.28 mmol) were stirred in methanol (10 ml) at
reflux for 30 min. The mixture was then cooled to r.t.
and sodium methoxide solution (2 ml, 0.2 M solution in
methanol) was added with stirring. The solvent was
removed and the residue passed through a silica column
eluting first with 3:5 dichloromethane–pet. spirit to
remove excess alkyne, and then with 1:20 acetone–
dichloromethane. The solvent was removed from the
second fraction and the residue purified by thin-layer
chromatography to yield 112 mg (51%) of dark purple
microcrystals. FABMS: 941 ([M]+, 55), 691
([Ru(PPh3)2(h-C5H5)]+, 40), 429 ([Ru(PPh3)(h-C5H5)]+
, 70). Anal. Calc. for C55H43N3O2P2Ru: C, 70.20; H,
4.61; N, 4.47. Found: C, 69.37; H, 4.60; N, 4.62%.
UV–vis (umax, nm [m, M−1 cm−1]): 565 [28 600], 347 [17
300], 291 [16 800], 251 [24 500]. IR (cm−1): 2054 (m)
w(CꢀC), 1342 (m) w(NꢁO). 1H-NMR: l 4.36 (s, 5H,
C5H5), 7.07–7.47 (m, 32H, Ph), 7.80 (d, 2H, JHH=8
Hz, H5), 7.96 (d, 2H, JHH=9 Hz, H10), 8.34 (d, 2H,
then passed through
a silica plug eluting with
dichloromethane. The volume was reduced to ca. 40 ml
on a rotary evaporator and a solution of tetra-n-buty-
lammonium fluoride (1 ml, 1 M solution in tetrahydro-
furan) was added without the exclusion of air. The
mixture was stirred for 5 min and then the solvent was
removed on a rotary evaporator. The residue was
purified by column chromatography on silica eluting
with 1:1 dichloromethane–pet. spirit. The yield was 89
mg (45%) of an orange powder. EI MS: 251 ([M]+, 45),
150 ([N2C6H4NO2]+, 5), 129 ([HCꢀCC6H4N2]+, 35),
101 ([HCꢀCC6H4]+, 100). Anal. Calc. for C14H9N3O2:
C, 66.93; H, 3.61; N, 16.73. Found: C, 66.03; H, 3.48;
N, 16.04%. UV–vis (umax, nm [m, M−1 cm−1]): 461
[860], 352 [27 200]. IR (cm−1): 1527 (m) was(NꢁO), 1346
1
(m) ws(NꢁO). H-NMR: l 3.27 (s, 1H, HCꢀC), 7.65 (d,
2H, JHH=9 Hz, H4), 7.92 (d, 2H, JHH=9 Hz, H5),
8.02 (d, 2H, JHH=9 Hz, H10), 8.38 (d, 2H, JHH=9 Hz,
H11). 13C-NMR: l 80.4 (C1), 83.0 (C2), 123.4, 123.6,
124.8 (C5, C10, C11), 126.2 (C3), 133.1 (C4), 148.8 (C12),
151.8 (C6), 155.5 (C9).
J
HH=9 Hz, H11). 31P-NMR: l 50.7 (PPh3). 13C-NMR:
l 85.6 (C5H5), 118.7 (C2), 122.9, 123.8, 124.7 (C5, C10,
C11), 127.3 (t, JCP=5 Hz, Cm), 128.6 (Cp), 131.2 (C4),
133.7 (t, JCP=5 Hz, CO), 135.7 (C3), 138.5 (m, Ci),
147.7 (C6), 148.5 (C12), 156.5 (C9).
4.3. Syntheses of metal alkynyl complexes
4.3.1. Trans-[Ru{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}-
Cl(dppm)2] (2)
4.3.3. [Au{(E)-4,4%-CꢀCC6H4NꢁNC6H4NO2}(PPh3)]
(4)
Cis-[RuCl2(dppm)2] (90 mg, 0.096 mmol) (1) (30 mg,
0.12 mmol) and sodium hexafluorophosphate (40 mg,
0.24 mmol) were stirred in dichloromethane (10 ml) for
4 h at r.t. A solution of sodium methoxide (1 ml, 0.3 M
solution in methanol) was added with stirring. The
mixture was passed through a plug of alumina, eluting
with dichloromethane, and the solvent was then re-
[AuCl(PPh3)] (167 mg, 0.34 mmol), 1 (85 mg, 0.34
mmol) and sodium methoxide solution (1 ml, 0.5 M
solution in methanol) were stirred in dichloromethane
(5 ml) for 18 h. Methanol (10 ml) was then added and
the volume reduced to ca. 10 ml whereupon the product
precipitated. After filtration in air and washing with

A.M. McDonagh et al. / Journal of Organometallic Chemistry 605 (2000) 184–192
191
methanol (2×5 ml), 170 mg (71%) of orange–brown
microcrystals were collected. FABMS: 721
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
was collected by an efficient condenser system and
detected by a photomultiplier. The harmonic scattering
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 a luminescence contribution to the harmonic
signal was confirmed by using interference filters at
different wavelengths near 532 nm. All measurements
were performed in tetrahydrofuran using p-nitroaniline
(i=21.4×10−30 esu) [34] as a reference. Solutions
were sufficiently dilute that absorption of scattered light
was negligible. Further details of the experimental pro-
cedure have been reported in the literature [35,36].
([Au(PPh3)2]+, 15), 459 ([Au(PPh3)]+, 95). Anal. Calc.
for C32H23AuN3O2P: C, 54.17; H, 3.27; N, 5.92. Found:
C, 54.07; H, 3.18; N, 6.12%. UV–vis (umax, nm [m, M−1
cm−1]: 398 [32 800], 288 [14 000], 268 [17 400], 241 [32
000]. IR (cm−1): 2113 (w) w(CꢀC), 1345 (s) ws(NꢁO).
1H-NMR: l 7.42–7.57 (m, 15H, Ph), 7.64 (d, 2H,
JHH=8 Hz, H4), 7.87 (d, 2H, JHH=8 Hz, H5), 7.98 (d,
2H, JHH=9 Hz, H10), 8.35 (d, 2H, JHH=9 Hz, H11).
31P-NMR: l 42.6 (PPh3). 13C-NMR: l 123.3, 124.7
(two of C5, C10, C11), 129.2 (d, JCP=6 Hz, Cm), 131.6
(Cp), 133.2 (C4), 134.2 (d, JCP=14 Hz, Co), 148.4 (C12),
150.6 (C6), 155.8 (C9).
4.4. X-ray structure determination
A purple needle (0.40×0.10×0.05 mm) grown by
diffusion of methanol into a dichloromethane solution
of 2 was mounted on a glass fiber. Data were collected
on a Rigaku AFC6R diffractometer using graphite
5. Supplementary material
,
monochromated Cu–Ka radiation (u=1.54178 A) at
296(1) K. The intensities of 9692 reflections were col-
lected to 2qmax=120.1°; equivalent reflections were
merged to yield 9120 unique reflections (Rint=0.049).
The intensities of three representative standards were
measured after every 150 reflections to monitor stability
and orientation. No decay correction was applied. An
analytical absorption correction was applied which re-
sulted in transmission factors ranging from 0.42 to 0.81.
Data were corrected for Lorentz and polarization ef-
Crystallographic data for the structure reported in
the paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC No. 139410 for
compound 2. 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).
fects. The structure was solved by direct methods (SIR
-
92), and expanded using difference Fourier synthesis.
The non-hydrogen atoms were refined with anisotropic
displacement parameters, by minimizing Sw(ꢀFoꢀ−ꢀFcꢀ)2
where w=[|c2(Fo)+(p2/4)F2o]−1. Hydrogen atoms were
included in calculated positions but were not refined.
The final cycle of full-matrix least-squares refinement
was based on 5803 observed reflections (I\2|(I)) and
703 variable parameters. The maximum and minimum
peaks in the final difference Fourier map corresponded
Acknowledgements
We thank the Fund for Scientific Research-Flanders
(G.0338.98, G.0407.98) (A.P.), the Belgian Government
(IUAP-IV/11) (AP), 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, A.M.M. held and N.T.L.
holds an Australian Postgraduate Award.
to 0.98 and −0.89 e A−3, respectively. All calculations
,
were performed using the TEXSAN [33] crystallographic
software package.
Crystal data for C64H52ClN3O2P4Ru·CH2Cl2. Mf=
1240.48, monoclinic, space group, P21/n, a=10.242(4)
,
,
,
A, b=32.063(6) A, c=18.310(4) A, i=95.24(2)°, V=
3
5987(3) A , Z=4, Dcalc=1.376 g cm−3, v(Cu–Ka)=
,
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