Organometallic complexes for nonlinear optics. 41: Syntheses and quadratic NLO properties of 4-{4-(4-nitrophenyl)diazophenyl}ethynylphenylethynyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2007.11.004

The syntheses of [Au(C{triple bond, long}C-4-C₆H₄C{triple bond, long}C-4-C₆H₄N{double bond, long}N-4-C₆H₄NO₂)(PPh₃)] (3), trans-[Ru(C{triple bond, long}C-4-C₆H₄-C{triple bond, long}C-4-C₆H₄N{double bond, long}N-4-C₆H₄NO₂)Cl(dppm)₂] (4), [Ru(C{triple bond, long}C-4-C₆H₄C{triple bond, long}C-4-C₆H₄N{double bond, long}N-4-C₆H₄NO₂)(dppe)(η-C₅Me₅)] (5), and [Ni(C{triple bond, long}C-4-C₆H₄N{double bond, long}N-4-C₆H₄NO₂)(PPh₃)(η-C₅H₅)] (6) are reported, together with a single-crystal X-ray diffraction study of 4. Quadratic nonlinearities for 3-6 and [Ru(C{triple bond, long}C-4-C₆H₄NO₂)(dppe)(η-C₅Me₅)] (7) have been determined at 1.064 μm and 1.300 μm by the hyper-Rayleigh scattering (HRS) technique, comparison to related complexes revealing that β values increase on introduction of azo group and π-system lengthening.

Full text of DOI:10.1016/j.jorganchem.2007.11.004

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1605–1613
www.elsevier.com/locate/jorganchem
Organometallic complexes for nonlinear optics. 41: Syntheses
and quadratic NLO properties of
4-{4-(4-nitrophenyl)diazophenyl}ethynylphenylethynyl complexes
Timothy N. Fondum a, Katy A. Green a, Michael D. Randles a, Marie P. Cifuentes a,
Anthony C. Willis b, Ayele Teshome c, Inge Asselberghs c, Koen Clays c,
Mark G. Humphrey a,*
a Department of Chemistry, Australian National University, Canberra, ACT 0200, Australia
b Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
c Department of Chemistry, University of Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
Received 13 October 2007; accepted 5 November 2007
Available online 13 November 2007
Vale Professor F. Albert Cotton, who bestrode the inorganic chemistry world like a colossus.
Abstract
The syntheses of [Au(C„C-4-C6H4C„C-4-C6H4N@N-4-C6H4NO2)(PPh3)] (3), trans-[Ru(C„C-4-C6H4-C„C-4-C6H4N@N-4-
C6H4NO2)Cl(dppm)2] (4), [Ru(C„C-4-C6H4C„C-4-C6H4N@N-4-C6H4NO2)(dppe)(g-C5Me5)] (5), and [Ni(C„C-4-C6H4N@N-4-
C6H4NO2)(PPh3)(g-C5H5)] (6) are reported, together with a single-crystal X-ray diffraction study of 4. Quadratic nonlinearities for
3–6 and [Ru(C„C-4-C6H4NO2)(dppe)(g-C5Me5)] (7) have been determined at 1.064 lm and 1.300 lm by the hyper-Rayleigh scattering
(HRS) technique, comparison to related complexes revealing that b values increase on introduction of azo group and p-system
lengthening.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Crystal structure; Ruthenium; Alkynyl; Non-linear optics
1. Introduction
C6H4NO2}Cl(dppm)2] (n = 0–2) [9], for which quadratic
nonlinearity increased slightly on proceeding from n = 0
to n = 1, but significantly on further progression to n = 2.
We have also described bridge modifications in the series
The nonlinear optical (NLO) properties of organometal-
lic complexes have been studied intensively over the past
years [1–6], with the majority of studies focusing on qua-
dratic nonlinearities of complexes with a donor-bridge-
acceptor composition. After metallocenyl complexes, alky-
nyl complexes have probably attracted most attention [7,8].
One area of interest is the effect of p-bridge lengthening on
molecular nonlinearities. We have previously reported the
series of complexes trans-[Ru{C„C(-4-C6H4C„C)n-4-
[M(C„C-4-C6H4XY-4-C6H4NO2)Ln]
[MLn = trans-
RuCl(dppm)2, Ru(PPh3)2(g-C5H5), Au(PPh3); XY = Z
and E CH@CH, N@N, N@CH, C„C, nothing (i.e.
biphenylene)] [10–14], for which quadratic nonlinearity
peaked at the azo-linked examples. These observations
prompted us to examine longer p-bridge alkynyl ligands
incorporating an azo linkage. We report herein the synthe-
sis of 4-O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CH and
gold and ruthenium alkynyl complex derivatives, together
*
with
a
nickel alkynyl complex derived from 4-
Corresponding author. Tel.: +61 2 6125 2927; fax: +61 2 6125 0760.
E-mail address: Mark.Humphrey@anu.edu.au (M.G. Humphrey).
O2NC6H4N@N-4-C6H4C„CH, and their quadratic non-
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.004

1606
T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
linearities bzzz from hyper-Rayleigh scattering studies at
1.064 and 1.300 lm.
dissolved in triethylamine (30 mL) and dichloromethane
(20 mL). 1-Ethynyl-4-(triisopropylsilylethynyl)benzene
(648 mg, 2.29 mmol) was added and the mixture refluxed
under N2 for 15 h. The solvent was removed on a rotary
evaporator and the residue was passed through a 7 cm
pad of silica with CH2Cl2 (200 mL). The solvent was
removed and the residue was washed well with petrol
(4 ꢁ 10 mL). The product was obtained as an orange pow-
der (456 mg, 63%). Anal. Calc. for C31H33N3O2Si: C,
73.34; H, 6.55; N, 8.28. Found: C, 73.38; H, 6.72; N,
8.17%. UV–Vis (kmax, nm [e, Mꢂ1 cmꢂ1]): 382 [18100]. IR
2. Experimental
2.1. General experimental conditions and starting materials
All reactions were carried out under a nitrogen atmo-
sphere using standard Schlenk techniques. Dichlorometh-
ane was dried by distilling over CaH2, and methanol was
dried by distilling over Mg/I2; other solvents were used as
received. The term ‘‘petrol” refers to a fraction of petro-
leum ether with a boiling range of 60–80 °C. Column chro-
matography was performed using either Merck silica gel 60
(0.063–0.200 mm) or Sigma–Aldrich aluminium oxide,
activated, basic, Brockmann 1, standard grade ꢀ150 mesh,
1
(cmꢂ1): m(NO2), 1347 (s), 1527 (s); v(C„C) 2154 (m). H
NMR: d 8.38, 8.03 (AB system, 4H, C6H4NO2), 7.96 and
7.68 (AB system, 4H, C6H4), 7.47 (s, 4H, C2C6H4C2),
1.15–1.11 (m, 21H, SiPri3). 13C NMR: d 11.3 (SiC), 18.7
(Me), 90.7, 92.7 (C9, C10), 93.4 (C1), 106.5 (C2), 122.5,
124.0, 127.3 (C3, C6, C11), 123.6 (C4, C5), 124.8 (C12),
131.5, 132.1, 132.6 (C13, C18, C19), 148.8, 151.7, 155.7
(C14, C17, C20). EI MS: 507 ([M]+, 35), 464 ([MꢂPri]+,
100). HR EI MS: Calculated C31H33N3O2Si: 507.2342,
Found: 507.2353.
˚
58 A. Thin layer preparative chromatography was per-
formed using Fluka silica gel GF254. NaOMe was prepared
as needed from metallic sodium and dry methanol. The fol-
lowing were prepared by the literature procedures:
[AuCl(PPh3)] [15], [NiCl(PPh3)(g-C5H5)] [16], [RuCl(dp-
pe)(g-C5Me5)] [17], cis-[RuCl2(dppm)2] [18], [Ru(C„C-4-
C6H4NO2)(dppe)(g-C5Me5)] [19] 1-ethynyl-4-(triisopropyl-
silylethynyl)benzene [20], 4-iodo-40-nitroazobenzene [14], 4-
ethynyl-40-nitroazobenzene [14], 1-ethynyl-4-nitrobenzene
[21]. Tetra-n-butylammonium fluoride (1 M solution in
tetrahydrofuran) (Aldrich), sodium hexafluorophosphate
(Aldrich), and tetrakis(triphenylphosphine)palladium(0)
(Aldrich) were used as received.
2.4. Synthesis of 4-O2NC6H4N@N-4-C6H4C„C-4-
C6H4C„CH (2)
4-O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CSiPri3 (399
mg, 0.79 mmol) was dissolved in CH2Cl2 (50 mL). Tetra-
n-butylammonium fluoride in tetrahydrofuran (1 M,
1 mL, 1 mmol) was added to the orange solution to afford
an immediate colour change to black. The reaction mixture
was stirred for a further 1 h. The solvent was removed on a
rotary evaporator and the residue was passed through a
7 cm pad of silica with CH2Cl2 (200 mL). The solvent
was removed and the residue was washed with petrol
(2 ꢁ 10 mL). The product was obtained as an orange pow-
der (202 mg, 73%). Anal. Calc. for C22H13N3O2: C, 75.20;
H, 3.73; N, 11.96. Found: C, 75.89; H, 4.17; N, 11.29%.
UV–Vis (kmax, nm [e, Mꢂ1 cmꢂ1]): 379 [17100]. IR
2.2. Instrumentation
Electrospray ionization (ESI) mass spectra were
recorded using a Micromass/Water’s LC-ZMD single
quadrupole liquid chromatograph–MS, high resolution
ESI mass spectra were carried out utilizing a Bruker Apex
4.7T FTICR-MS instrument and EI mass spectra were
recorded using a VG Quattro II triple quadrupole MS;
all mass spectrometry peaks are reported as m/z (assign-
ment, relative intensity). Microanalyses were carried out
at the Research School of Chemistry, Australian National
University. Infrared spectra were recorded using a Perkin–
Elmer System 2000 FT-IR spectrometer as CH2Cl2 solu-
tions using CaF2 cells. UV–Vis spectra were recorded on
a Cary 5 spectrometer as THF solutions in 1 cm cells.
1H, 13C and 31P NMR spectra were recorded using a Var-
ian Gemini-300 FT NMR spectrometer (300, 75 and
121 MHz, respectively) and referenced to residual CHCl3
(7.24 ppm), solvent CDCl3 (77.0 ppm) and external
H3PO4 (0.0 ppm), respectively.
1
(cmꢂ1): m(NO2) 1346 (s); m(C„C) 2203 (w). H NMR: d
8.40, 8.05 (AB system, 4H, C6H4NO2), 7.98, 7.70 (AB sys-
tem, 4H, C6H4), 7.50 (s, 4H, C2C6H4C2), 3.19 (s, 1H,
HC„C). 13C NMR: d 79.3 (C1), 83.1 (C2), 92.3 (C),
103.6 (C), 123.5, 124.8, 131.6, 132.2, 132.6 (CH ꢁ 5),
92.3, 103.6, 122.4, 123.1, 127.1, 155.6. ESI MS: 352
([M+H]+, 20).
2.5. Synthesis of [Au(C„C-4-C6H4C„C-4-C6H4N@N-4-
C6H4NO2)(PPh3)] (3)
[AuCl(PPh3)]
(55
mg,
0.11 mmol)
and
4-
O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CH
(40 mg,
2.3. Synthesis of 4-O2NC6H4N@N-4-C6H4C„C-4-
C6H4C„CSiPri3 (1)
0.11 mmol) were dissolved in CH2Cl2 (15 mL) to form an
orange solution. Addition of 1 mL of sodium methoxide
in methanol solution (ca. 0.5 M) caused the solution to rap-
idly change colour to brown. The mixture was stirred for
15 h. The volume was reduced to ca. 10 mL under reduced
pressure and 20 mL of methanol added. A precipitate
4-Iodo-40-nitroazobenzene (502 mg, 1.42 mmol), cop-
per(I) iodide (17 mg, 0.089 mmol) and tetrakis(triphenyl-
phosphine)palladium(0) (32 mg, 0.028 mmol)
were

T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
1607
formed and was collected by filtration and washed with
iced MeOH (3 ꢁ 5 mL) to yield a red-brown powder
(40 mg, 45%). Anal. Calc. for C40H27N3O2PAu: C, 59.34;
H, 3.36; N, 5.19. Found: C, 59.36; H, 3.51; N, 5.12%.
UV–Vis (kmax, nm [e, Mꢂ1 cmꢂ1]): 392 [40000], 378
[41000], 313 [48000], 278 [178000], 234 [257000]. IR
change to black and the mixture stirred for 10 min. The
reaction mixture was passed through a short pad of alu-
mina eluting with CH2Cl2. The solvent was removed from
the eluant to yield a black powder that was further purified
by passing through an alumina column with CH2Cl2. The
solvent was removed from the eluent to yield a fine dark
purple powder, which was recrystallised by slow diffusion
of methanol into a dichloromethane solution (41 mg,
34%). Anal. Calc. for C58H51N3O2P2Ru ꢃ CH3OH: C,
69.67; H, 5.45; N, 4.13. Found: C, 68.85; H, 5.78; N,
4.22%. UV–Vis (kmax, nm [e, Mꢂ1 cmꢂ1]): 522 [8600], 387
[31000], 237 [27000]. IR (cmꢂ1) m(NO2) 1346 (s), 1589 (s);
m(C„C) 2056 (s); m(C„C) 2203 (w). 1H NMR: d 8.39,
8.03 (AB system, 4H, C6H4NO2), 7.94, 7.63 (AB system,
4H, C6H4N2), 7.74, 7.35–7.21, 6.97 (m, 22H, PPh2, H5),
6.72 (d, 2H, H4, JHH = 8 Hz), 3.49 (s, 3H, CH3OH), 2.67
(m, 2H, CH2/dppe), 2.06 (m, 2H, CH2/dppe), 1.57 (s, 15H,
1
(cmꢂ1) v(NO2) 1346 (s); m(C„C) 2211 (m), 2112 (w). H
NMR: d 8.40, 8.04 (AB system, 4H, C6H4NO2), 7.96,
7.68 (AB system, 4H, C6H4N2), 7.51–7.42 (m, 19H,
PPh3 + C2C6H4C2). 31P NMR: d 42.8 (PPh3). 13C NMR:
d 90.1, 93.3, 104.0, 120.8, 127.7, 130.0 (C2, C3, C6, C7,
C8, C9), 123.5, 124.8, (C16, C17), 129.2 (d, Cm,
JCP = 12 Hz), 131.4 (Cp), 131.59, 131.62 (C4, C5), 132.4,
132.5 (C10, C11), 134.4 (d, Co, JCP = 14 Hz), 148.7 (C18),
151.4 (C12), 155.7 (C15). ESI MS: 832 ([M + Na]+, 10),
810 ([M+H]+, 8), 721 ([Au(PPh3)2]+, 100), 459
([Au(PPh3)]+, 80).
C5(CH3)5). 31P NMR: d 81.3 (dppe). 13C NMR: d 10.0
(C5Me5), 30.0 (m, PCH2), 89.1 (C), 92.7 (C5Me5), 95.2,
111.4, 115.5 (C), 123.5 (d, PPh2, JCP = 7 Hz), 124.7,
130.1, 131.1, 132.1 (4 of C4, C5, C10, C11, C16, C17), 125.5
(PPh2), 127.3 (d of t, PPh2, JCP = 4 Hz, JCP = 17 Hz),
128.2, 128.5 (C), 128.9 (d, PPh2, JCP = 6 Hz), 131.7 (C),
133.3 (d of t, PPh2, JCP = 5 Hz, JCP = 33 Hz), 135.7,
136.3, 137.0, 138.6 (C), 148.6 (CN), 151.0 (CN), 155.7
(CN). HR ESI MS: Calculated C58H52N3O2P2Ru
[M+H]+: 986.2573, Found: 986.2502.
2.6. Synthesis of trans-[Ru(C„C-4-C6H4-C„C-4-
C6H4N@N-4-C6H4NO2)Cl(dppm)2] (4)
cis-[RuCl2(dppm)2] (108 mg, 0.111 mmol) and NaPF6
(158 mg, 0.940 mmol) were dissolved in CH2Cl2 (15 mL)
and 4-O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CH (40
mg, 0.11 mmol) was added. The orange/red mixture was
stirred at reflux for 4 h. The addition of sodium methoxide
in methanol solution (0.5 M, 0.3 mL, 0.015 mmol) caused
an instant colour change to purple-black. The reaction
mixture was passed through a short pad of alumina eluting
with CH2Cl2. The solvent was removed from the eluate on
a rotary evaporator to yield the dark purple product
(81 mg, 59%). Anal. Calc. for C72H56N3O2P4ClRu: C,
68.87; H, 4.49; N, 3.35. Found: C, 68.52; H, 4.50; N,
3.77%. UV–Vis (kmax, nm [e, Mꢂ1 cmꢂ1]): 510 [5000], 380
[19000]. IR (cmꢂ1) m(NO2) 1346 (s); v(C„C) 2072 (m);
m(C„C) 2199 (w). 1H NMR: d 8.38, 8.03 (AB system,
4H, C6H4NO2), 7.94, 7.62 (AB system, 4H, C6H4), 7.41–
7.03 (m, 42 H, PPh2, H5), 5.98 (d, 2H, H4, JHH = 9 Hz),
4.90 (m, 4H, PCH2). 31P NMR: d ꢂ6.0 (dppm). 13C
NMR: d 50.3 (CH2), 89.2, 95.1, 113.6, 115.2 (C2, C3, C7,
C8), 123.4, 123.5, 124.8 (C5, C10, C11), 127.6 (Cp), 128.4
(C), 129.1, 129.3 (Cm), 130.1, 130.5, 132.1 (C4, C16, C17),
131.8 (C), 133.3, 133.7 (Co), 134.0 (Ci), 134.9 (t, C1,
JCP = 12 Hz), 147.7, 148.8 (C12, C15), 155.7 (C18). ESI
MS: 1256 ([M+H]+, 50), 1220 ([MꢂCl]+, 83), 905
([RuCl(dppm)2]+, 20), 869 ([Ru(dppm)2ꢂH]+, 25). HR
ESI MS: Calculated C74H59N4O2P4Ru [MꢂCl+MeCN]:
1261.2632, Found: 1261.2530.
2.8. Synthesis of [Ni(C„C-4-C6H4N@N-4-
C6H4NO2)(PPh3)(g-C5H5)] (6)
[NiCl(PPh3)(g-C5H5)]
(58 mg,
0.15 mmol),
4-
HC„CC6H4N@N-4-C6H4NO2 (41 mg, 0.16 mmol) and
CuI (6 mg, 0.03 mmol) were stirred in triethylamine
(20 mL) for 18 h. The solvent was removed under reduced
pressure, and the residue extracted with CH2Cl2 (50 mL)
and filtered through a short pad of silica. Removal of the
solvent afforded a black residue, which was washed with
methanol (2 ꢁ 5 mL) to isolate the product, a fine black
powder (40 mg, 42%). Anal. Calc. for C37H28N3O2PNi:
C, 69.84; H, 4.44; N, 6.60. Found: C, 68.87; H, 4.71; N,
6.56%. UV–Vis (kmax, nm [e, Mꢂ1cmꢂ1]): 519 [9000], 396
[17000], 309 [19000], 259 [25000]. IR (cmꢂ1) m(NO2) 1345
1
(s); m(C„C) 2088 (m). H NMR: d 8.32, 7.91 (AB system,
4H, C6H4NO2), 7.72 (m, 6H, Ho), 7.59, 6.73 (AB system,
4H, C6H4), 7.41 (m, 9H, Hm, Hp), 5.28 (s, 5H, C5H5). 31P
NMR: d 42.0 (PPh3).13C NMR: d 92.9 (C5H5), 94.4 (C1),
123.0, 124.7, 129.7 (C5, C10, C11), 128.4 (d, Cm,
JCP = 10 Hz), 130.4 (Cp), 131.6 (C4), 133.9 (d, Co,
JCP = 11 Hz), 134.1 (d, Ci, JCP = 4 Hz), 134.4 (C3), 156.0
(C9). ESI MS: 647 ([Ni(PPh3)2(C5H5)]+, 15), 385
([Ni(PPh3)(C5H5)]+, 65).
2.7. Synthesis of [Ru(C„C-4-C6H4C„C-4-C6H4N@N-4-
C6H4NO2)(dppe)(g-C5Me5)] (5)
[RuCl(dppe)(g-C5Me5)] (81 mg, 0.12 mmol), NaPF6
(195 mg, 1.2 mmol) and 4-O2NC6H4N@N-4-C6H4C„C-
4-C6H4C„CH (43 mg, 0.12 mmol) were dissolved in
CH2Cl2 (20 mL) and the reaction was stirred for 48 h. Tri-
ethylamine (5 mL) was added, resulting in a rapid colour
2.9. Structure determination
A suitable crystal of 4 was obtained by slow diffusion of
petrol into a dichloromethane solution. A single crystal

1608
T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
was mounted on a fine glass capillary, and data were col-
lected at 200 K on a Nonius KappaCCD diffractometer
using graphite-monochromated Mo Ka radiation
For studies at 1.300 lm, a Tsunami-pumped OPAL
(model Spectra-Physics) was used. With a high repetition
rate of the laser, high frequency demodulation of fluores-
cence contributions can be effected, a full description being
given in ref. [27]. All measurements were performed in tetra-
hydrofuran using disperse red 1 (DR1, b = 54 ꢁ 10ꢂ30 esu in
chloroform) as a reference. Experiments utilized low chro-
mophore concentrations, the linearity of the HRS signal as
a function of the chromophore concentration confirming
that no significant self-absorption of the SHG signal
occurred.
˚
(k = 0.71073 A). The unit cell parameters were obtained
by least-squares refinement [22] of 163428 reflections with
2.6 6 h 6 25.0°. The reduced data [22] were corrected for
absorption using numerical methods [23] implemented
from within MAXUS [24]; equivalent reflections were merged.
The structure was solved by direct methods and expanded
using Fourier techniques [25], and refined using the soft-
ware package CRYSTALS [26].
Crystal/refinement
data:
C73.5H59Cl4N3O2P4Ru,
M = 1383.07. Monoclinic, C2/c, a = 44.5509(8), b =
3. Results and discussion
˚
11.3619(2), c = 28.0643(5) A, b = 92.2274(6)°, V =
3
14194.9(4)
A .
Dc
specimen:
(Z = 8) = 1.294 g cmꢂ3
0.45 ꢁ 0.28 ꢁ 0.11 mm;
.
3.1. Synthesis and characterization
˚
l
Tmin/max
Mo = 0.51 mmꢂ1
;
=
0.891/0.986. 2hmax = 50.0°; Ntotal = 98760
(CCD diffractometer, monochromatic Mo Ka radiation,
k = 0.71073 A; T 200 K) merging to N = 12520 unique
The new acetylenes that were required for alkynyl com-
plex synthesis were prepared by standard organic synthetic
procedures: a Sonogashira coupling of 4-iodo-40-nitroazo-
benzene with 1-ethynyl-4-(triisopropylsilylethynyl)benzene
afforded 4-O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CSi-
Pri3 (1), subsequent desilylation with tetra-n-butylammo-
nium fluoride giving 4-O2NC6H4N@N-4-C6H4C„C-4-
C6H4C„CH (2) (Scheme 1). Compounds 1 and 2 were
˚
(Rint = 0.08),
No = 12499
(I > 3r(I))
refining
to
R = 0.0470, Rw = 0.0509.
The crystallographic asymmetric unit consists of one mol-
ecule of 4 and one and a half molecules of dichloromethane.
The second dichloromethane site lies close to an inversion
centre and, as a result, close intermolecular contacts arise
with itself. It was thus set to have half occupancy. Due to
the length of the alkynyl ligand, the atoms at the end of the
alkynyl ligand remote from the metal atom were too disor-
dered to be solved anisotropically, and so were made isotro-
pic. Restraints on the bond lengths and angles of the end of
the chain were thus also made so as to help resolve this disor-
der. All other non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included in the refinement at
idealized positions, riding on the atoms to which they were
bonded and frequently recalculated.
characterized by a combination of H and 13C NMR, IR,
and UV–Vis spectroscopy.
1
The preparation of the new alkynyl complexes 3 and 4
(Scheme 1) proceeded by adaptation of the published proce-
dures for the preparation of the 4-nitrophenylethynyl com-
plex analogues [11,13]. The synthesis of the gold complex 3
was achieved by coupling [AuCl(PPh3)] to 2 in methanol in
the presence of sodium methoxide, its identity being con-
firmed by 1H, 13C and 31P NMR spectroscopy and ESI mass
spectrometry. The ESI spectrum displays a signal at 810
mass units assigned to [M+H]+ and a fragment at 721 mass
units assigned to [Au(PPh3)2]+, the latter typical for (triphen-
ylphosphine)gold alkynyl complexes [11]. The synthesis of 4
proceeded by way of a vinylidene intermediate that was not
isolated, deprotonation in situ affording the alkynyl complex
4which was characterized by 1H, 13C and 31P NMR spectros-
copy and ESI mass spectrometry. The ESI spectrum shows a
protonated molecular ion at 1256 mass units, as well as frag-
ments corresponding to the loss of chlorine and alkynyl
ligands at 1220 ([MꢂCl]+) and 905 mass units
([RuCl(dppm)2]+), respectively. A high resolution ESI mass
spectrum obtained using acetonitrile as a solvent revealed a
peak corresponding to the replacement of chloride by aceto-
nitrile, mirroring solution chemistry of RuClX(L2)2 (X = Cl,
C2R) complexes [28,29]. Complex 5, which incorporates a
very electron-rich metal centre, was similarly prepared by
adaptation of the published procedure for the 4-nitropheny-
lethynyl analogue 7 [19] and characterized by the usual spec-
troscopic techniques complemented by a high-resolution
ESI mass spectrum of the protonated molecular ion.
2.10. Hyper-Rayleigh scattering measurements
For studies at 1.064 lm, an injection-seeded Nd:YAG
laser (Q-switched Nd:YAG Quanta Ray GCR5,
1.064 lm, 8 ns pulses, 10 Hz) was focused into a cylindrical
cell (7 mL) containing the sample. The intensity of the inci-
dent 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 fil-
ters; gated integrators were used to obtain intensities of the
incident and harmonic scattered light. The absence of a
luminescence contribution to the harmonic signal was con-
firmed by using interference filters at different wavelengths
near 532 nm. All measurements were performed in tetrahy-
drofuran using 4-nitroaniline (b = 21.4 ꢁ 10ꢂ30 esu) as a
reference. Solutions were sufficiently dilute that absorption
of scattered light was negligible.
The preparation of 6 (Scheme 2) proceeded by adapta-
tion of the published procedure for the 4-nitrophenylethy-
nyl complex analogue [30]. Its identity was confirmed by

T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
1609
Scheme 1. Preparation of 1–5.
Scheme 2. Synthesis of 6.
1H, 13C and 31P NMR spectroscopy, with the ESI mass
spectrum showing peaks corresponding to the fragment
ion [Ni(PPh3)(g-C5H5)]+ and the ion–molecule product
[Ni(PPh3)2(g-C5H5)]+.
an angle of 4.3° and 17.8° separating it from the C(11)–
C(16) and C(3)–C(8) rings, respectively. The reduction in
coplanar character of adjacent phenyl rings has been previ-
ously demonstrated to reduce computationally-derived
quadratic NLO merit [32].
3.2. X-ray structural study of 4
Fig. 2 shows cell-packing diagrams for 4 and 8. Both
complexes pack pair-wise in the lattice with dipoles aligned
antiparallel, arrangements that would result in zero NLO
bulk susceptibility.
A single-crystal X-ray diffraction study of 4 was under-
taken.
A comparison of selected interatomic bond
distances and angles of 4 with those from the previously-
determined structural study of the related complex trans-
[Ru(C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm)2] (8) [14]
is given in Table 1. Fig. 1 contains ORTEP depictions of
the molecular geometries of 4 and 8.
The bond lengths and angles around the Cl–Ru–C(1)–
C(2)–C(3) chain in 4 are comparable to those in 8, with
Cl–Ru–C(1) and Ru–C(1)–C(2) angles close to the ideal-
ized 180° and a short Ru–C distance, the latter having been
shown semi-empirically to lead to large quadratic nonlin-
earities [31]. The bond distances and angles involving the
diphosphine ligands are unexceptional. Phenyl rings
C(3)–C(8) and C(11)–C(16) are not co-planar, the angle
between them being 21.9°. Phenyl ring C(1701)–C(2201)
lies in a plane between those of the other two rings, with
3.3. HRS studies
Quadratic optical nonlinearities of compounds 3–7 were
determined by the hyper-Rayleigh scattering (HRS) tech-
nique at 1.064 lm employing ns pulses and at 1.300 lm
employing fs pulses. Table 2 includes these results together
with important linear optical absorption data, and relevant
data from related compounds. For complexes of this type,
the NLO properties are dominated by the energy of the
lowest-lying charge-transfer state, and frequency-indepen-
dent nonlinearities calculated using the two-level model
would be expected to have some applicability. The data
obtained at two wavelengths provides a test of the applica-
bility – if the two-level model is appropriate, b0(1.064) and

1610
T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
Table 1
Important bond lengths and angles for 4 and trans-[Ru(C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm)2] (8)
4a
8b
4a
8b
Ru–Cl
2.507(14)
2.354(16)
2.360(16)
2.329(15)
2.364(16)
2.001(7)
2.508(2)
2.322(2)
2.352(2)
2.349(2)
2.355(2)
1.974(7)
C(1)–C(2)
C(2)–C(3)
N(1)–N(2)
C(20/12)–N(3)
N(3)–O(1)
N(3)–O(2)
1.187(8)
1.435(8)
1.227(12)
1.509(14)
1.263(16)
1.176 (13)
1.224(9)
1.406(9)
1.263(9)
1.47(1)
1.22(1)
1.18(1)
Ru–P(1)
Ru–P(2)
Ru–P(3)
Ru–P(4)
Ru–C(1)
P(1)–Ru–P(2)
P(3)–Ru–P(4)
Cl–Ru–C(1)
71.78(5)
72.04(5)
175.1(17)
177.7(5)
72.20(7)
71.47(7)
173.1(2)
175.2(6)
C(1)–C(2)–C(3)
178.1(7)
118.5(10)
111.4(9)
127.9(13)
179.8(9)
112.9(8)
111.5(8)
124(1)
C(14/6)–N(1)–N(2)
N(1)–N(2)–C(17/9)
O(1)–N(3)–O(2)
Ru–C(1)–C(2)
a
This work.
Ref. [14].
b
Fig. 1. Molecular geometry and labelling schemes for 4 and trans-[Ru(C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm)2] (8) [14]. Non-hydrogen atoms have
˚
been depicted with 30% thermal ellipsoids; for 8, hydrogen atoms have been placed in calculated positions with arbitrary bond lengths of 0.95 A.
b0(1.300) should be identical, but this is not the case, so the
b0 data should be treated with caution.
tion of an azo-linkage in 6 compared to earlier nickel alky-
nyl complexes for which p-bridge lengthening was achieved
by ene or yne linkages. Compounds 5 and 7 both have an
[Ru(alkynyl)(dppe)(g-C5Me5)] centre and display large b,
though values are marginally lower than those of their ana-
logues with a [Ru(alkynyl)Cl(dppm)2] composition.
The complexes in Table 2 have been grouped by metal
and by co-ligand set (for ruthenium). Compounds 3 and
6 have the largest quadratic nonlinearities reported for gold
and nickel alkynyl complexes thus far, a result that can be
attributed to the longer p-system in 3 than previously
reported gold complexes (see below), and to the introduc-
We have previously noted the difficulty in developing
structure–NLO activity relationships for nickel and ruthe-

T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
1611
Fig. 2. Molecular packing of 4 and trans-[Ru(C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm)2] 8.
nium complexes with these ligand sets, due to the proximity
4. Conclusion
of optical absorptions to the second-harmonic wavelength
corresponding to the fundamental frequency of the laser.
In contrast, (triphenylphosphine)gold complexes with alky-
nyl ligands of this type are transparent at 532 nm, permit-
ting assessment of the effect of structural change on NLO
merit. [Our earlier studies contrasted these specific ligated
metal units, permitting us to derive ‘‘figures of merit” for
the efficiency of the various metal–ligand combinations
[30]; the (phosphine)gold unit was shown to be a weaker
donor, but the lack of resonance enhancement in data from
its alkynyl complexes is very useful in developing struc-
ture–property relationships for alkynyl ligand modifica-
The present studies have afforded several examples of
complexes incorporating the new alkyne 4-
O2NC6H4N@N-4-C6H4C„C-4-C6H4C„CH as an alky-
nyl ligand. The new complexes have significant qua-
dratic nonlinearities, and the enhanced magnitude of
these data compared to those of previously reported
related complexes can be ascribed to a combination of
p-system lengthening and incorporation of the azo
group. We have previously reported molecular NLO
switching by protic and electrochemical means [9]. The
azo group itself is a photoisomerizable unit whose
incorporation potentially affords the possibility of
switching nonlinearity – this will be the subject of a
future report.
tion.] Inspection of the data in Table
2 reveals
progressively increasing b1.064 and b0(1.064) values on p-
bridge lengthening (proceeding from [Au(C„C-4-
C6H4NO2)(PPh3)] to [Au(C„C-4-C6H4-E-CH@CH-4-
C6H4NO2)(PPh3)] and from [Au(C„C-4-C6H4N@N-4-
C6H4NO2)(PPh3)] to 3) and replacement of ene-linkage
by azo linkage (proceeding from [Au(C„C-4-C6H4-E-
CH@CH-4-C6H4NO2)(PPh3)] to [Au(C„C-4-C6H4N@N-
4-C6H4NO2)(PPh3)]). Proceeding from gold to nickel, and
then to ruthenium centres for the present series of com-
plexes results in red-shifted optical absorption maxima,
and larger b1.064 values, but with progressively increasing
resonance enhancement for which the two-level model is
increasingly inappropriate at accommodating. The b1.300
values similarly increase in proceeding from gold, to nickel,
and then ruthenium complex.
Acknowledgements
We thank the Australian Research Council (M.G.H.),
the Fund for Scientific Research-Flanders (FWO-Vla-
anderen; FWO0297.04) (K.C.), and the Katholieke Uni-
versiteit Leuven (GOA/2006/03) (K.C.) for support of
this work and Johnson-Matthey Technology Centre for
the generous loan of ruthenium salts (M.G.H.).
M.G.H. is an ARC Australian Professorial Fellow,
M.P.C. held an ARC Australian Research Fellowship,
K.A.G. is an Australian Postgraduate Awardee, and
I.A. is a Postdoctoral Fellow of FWO-Vlaanderen.

Table 2
Quadratic nonlinearities for compounds 3–7 and related compounds
k
max(nm) [e(104 Mꢂ1 cmꢂ1)]
HRS, 1.064 lm
bzzz (10ꢂ30 esu)
HRS, 1.300 lm
bzzz (10ꢂ30 esu)
Reference
ba0 (10ꢂ30 esu)
bb0 (10ꢂ30 esu)
Au complexes
[Au(C„C-4-C6H4NO2)(PPh3)]
[Au(C„C-4-C6H4-E-CH@CH-4-C6H4NO2)(PPh3)]
[Au(C„C-4-C6H4N@N-4-C6H4NO2)(PPh3)]
[Au(C„C-4-C6H4C„C-4-C6H4N@N-4-C6H4NO2)(PPh3)] (3)
338 (2.5)
368 (3.8)
398 (3.3)
392 (4.0)
22
120
180
213 20
12
49
68
[11]
[11]
[14]
This work
91
9
6
83
98
51
34
Ni complexes
[Ni(C„C-4-C6H4NO2)(PPh3)(g-C5H5)]
[Ni(C„C-4-C6H4-E-CH@CH-4-C6H4 NO2)(PPh3)(g-C5H5)]
[Ni(C„C-4-C6H4N@N-4-C6H4NO2)(PPh3)(g-C5H5)] (6)
439 (0.9)
437 (2.8)
519 (0.9)
221
445
605 72
59
120
46
[33]
[30]
This work
trans-[Ru(alkynyl)Cl(dppm)2] complexes
trans-[Ru(C„C-4-C6H4NO2)Cl(dppm2)]
trans-[Ru(C„C-4-C6H4-E-CH@CH-4-C6H4NO2)Cl(dppm2)]
trans-[Ru(C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm2)]
trans-[Ru(C„C-4-C6H4C„C-4-C6H4C„C-4-C6H4NO2)Cl(dppm)2]
trans-[Ru(C„C-4-C6H4C„C-4-C6H4N@N-4-C6H4NO2)Cl(dppm)2]
(4)
473 (1.8)
490 (2.6)
583 (2.7)
439 (2.0)
510 (0.5)
767
1964
1649
1379
129
235
232
365
51
[13]
[13]
[14]
[9]
1215 146
6
225
70
This work
[Ru(alkynyl)(L)2(g-C5R5)] complexes
[Ru(C„C-4-C6H4NO2)(PPh3)2(g-C5H5)]
[Ru(C„C-4-C6H4N@N-4-C6H4NO2)(PPh3)2(g-C5H5)]
[Ru(C„C-4-C6H4NO2)(dppe)(g-C5Me5)] (7)
[Ru(C„C-4-C6H4C„C-4-C6H4N@N-4-C6H4NO2)(dppe)(g-C5Me5)]
(5)
460 (8.5)
565 (2.9)
479 (1.7)
522 (0.9)
468
1627
544 133
1136 150
96
149
82 20
c
[10]
[14]
This work
This work
50
220
19
60
Errors 15% unless otherwise indicated.
a
b0 = b[1 ꢂ (2kmax/1064)2][1 ꢂ (kmax/1064)2].
b
b0 = b[1 ꢂ (2kmax/1300)2] [1 ꢂ (kmax/1300)2].
c
Not applicable: the two-level model diverges when the SHG wavelength becomes identical to kmax
.

T.N. Fondum et al. / Journal of Organometallic Chemistry 693 (2008) 1605–1613
1613
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(1989) 324.
Appendix A. Supplementary material
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CCDC 662443 contains the supplementary crystallo-
graphic data for compound 4. These data can be obtained
free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
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