Large second-order nonlinear optical properties of novel organometallic (σ-aryl-enynyl)ruthenium complexes

Article abstract of DOI:10.1021/om960556o

Novel homo- and heterobimetallic complexes have been synthesized, and their nonlinear optical properties were evaluated. The effects upon the hyper-polarizability of chain length, configuration of the metal donor group, and kind of metal acceptor group ar

Full text of DOI:10.1021/om960556o

5266
Organometallics 1996, 15, 5266-5268
La r ge Secon d -Or d er Non lin ea r Op tica l P r op er ties of
Novel Or ga n om eta llic (σ-Ar yl-en yn yl)r u th en iu m
Com p lexes
Stephan Houbrechts,† Koen Clays,† Andre´ Persoons,*,†,‡ Victorio Cadierno,§
M. Pilar Gamasa,§ and J ose´ Gimeno§
Laboratory of Chemical and Biological Dynamics, Center for Research on Molecular
Electronics and Photonics, University of Leuven, 3001 Leuven, Belgium, Optical Sciences
Center, University of Arizona, Tucson, Arizona 85721, and Departamento de Qu´ımica
Orga´nica e Inorga´nica, Instituto de Quı´mica Organometa´lica “Enrique Moles”,
Universidad de Oviedo, 33071 Oviedo, Spain
Received J uly 8, 1996X
Summary: Novel homo- and heterobimetallic complexes
have been synthesized, and their nonlinear optical
properties were evaluated. The effects upon the hyper-
polarizability of chain length, configuration of the metal
donor group, and kind of metal acceptor group are
reported.
ruthenium(II)-ruthenium(III) and ruthenium(II)-chro-
mium(0) or tungsten(0) bimetallic complexes in which
a donor indenyl-ruthenium(II) moiety and an acceptor
metal fragment are bridged by enynyl N-functionalized
systems.
Synthesis of the novel complexes is shown in Scheme
1. Treating a THF solution of alkynyl-phosphonio
complex 3 with 1 equiv of nBuLi at -20 °C,15 subse-
quently adding unsaturated aldehydes OdC(H)-
(CHdCH)n-p-C6H4A (A ) NO2, CN), and allowing the
mixture to reach room temperature resulted in the
formation of enynyl complexes 7a ,b and 8. These
compounds were obtained as a mixture of the E and Z
stereoisomers in 70-90% yield. In a similar way enynyl
complexes 4 and 6 were obtained from the reaction with
the corresponding aldehyde or ketone, respectively. The
spectroscopic properties of 4, 6, 7a ,b, and 8 are consis-
tent with the proposed structures, in particular the νCtC
IR absorption (2027-2041 cm-1) and the typical triplet
resonance in the 13C{1H} NMR for the RusCt carbon
nucleus at δ 132.47-141.39 (2J C-P ) 22.3-25.1 Hz). The
presence of an uncoordinated pyridine ring or a cyano
group in complexes 4 and 7b, respectively, was used for
preparing mixed-valence complexes by the reaction with
[M(CO)5(THF)] (M ) Cr, W) and [Ru(NH3)5(OSO2-
The search for suitable nonlinear optical (NLO) active
materials has been focused mainly on organic
products,1-4 though in recent years the interest in
organometallic complexes has increased drastically.5-14
It is expected that electron-rich metal moieties such as
half-sandwich transition-metal phosphine derivatives
may enable the electronic delocalization in appropriate
π-conjugated systems attached to the metal. Moreover,
the incorporation of the metal into the plane of the
conjugated system and the potential introduction of
metal-carbon multiple-bond character has been sug-
gested to enhance the NLO response.12,14
Here we report novel donor-acceptor complexes
which display large quadratic hyperpolarizabilities (â).
We have investigated compounds of the following
types: (i) alkynyl, enynyl, and polyenynyl indenyl-
ruthenium(II) complexes with nitro or cyano substitu-
ents at the end of the hydrocarbon chain and (ii) enynyl
CF3)]2+
. Workup gave the novel bimetallic enynyl
* To whom correspondence should be addressed at the University
of Leuven. E-mail: andre@lcbdiris.fys.kuleuven.ac.be.
† University of Leuven.
complexes 5a ,b, 9a ,b, and 10 in 53-82% yield. The IR
spectra showed the expected νCtC and νCdO absorptions,
and the 13C{1H} NMR spectra exhibited the RusCt
triplet resonances (δ 138.51 (2J C-P ) 24.4 Hz), 5a ; δ
141.67 (2J C-P ) 24.5 Hz), 5b). Complexes 2, 12a ,b, and
13 with potential NLO properties were also prepared
(70-85% yield) through conventional procedures.16
All hyperpolarizabilities were determined using hy-
per-Rayleigh scattering,17,18 which made it possible to
investigate also the ionic species in solution (Table 1).
‡ University of Arizona.
§ Universidad de Oviedo.
X Abstract published in Advance ACS Abstracts, October 1, 1996.
(1) Cheng, L.-T.; Tam, W.; Stevenson, S. H.; Meredith, G. R.; Rikken,
G.; Marder, S. R. J . Phys. Chem. 1991, 95, 10631-10643.
(2) Cheng, L.-T.; Tam, W.; Marder, S. R.; Stiegman, A. E.; Rikken,
G.; Spangler, C. W. J . Phys. Chem. 1991, 95, 10643-10652.
(3) Williams, D. J . Angew. Chem., Int. Ed. Engl. 1984, 23, 690.
(4) Prasad, P. N.; Williams, D. J . Introduction to Nonlinear Optical
Effects in Molecules and Polymers; Wiley-Interscience: New York,
1991.
(5) Nalwa, H. S. Appl. Organomet. Chem 1991, 5, 349-377.
(6) Marder, S. R. In Inorganic Materials; Bruce, D. W., O’Hare, D.,
Eds.; Wiley-Interscience: Chichester, U.K., 1992; pp 115-164.
(7) Laidlaw, W. M.; Denning, R. G.; Verbiest, T.; Chauchard, E.;
Persoons, A. Nature 1993, 363, 58-59.
(8) Zyss, J .; Dhenaut, C.; Chauvan, T.; Ledoux, I. Chem. Phys. Lett.
1993, 206, 409.
(9) Long, N. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 21-38.
(10) Coe, B. J .; Hamor, T. A.; J ones, C. J .; McCleverty, J . A.; Bloor,
D.; Cross, G. H.; Axon, T. L. J . Chem. Soc., Dalton Trans. 1995, 673-
684.
(11) Dhenaut, C.; Ledoux, I.; Samuel, I. D. W.; Zyss, J .; Bourgault,
M.; Le Bozec, H. Nature 1995, 374, 339-342.
(12) Di Bella, S.; Fragala`, I.; Ledoux, I.; Marks, T. J . J . Am. Chem.
Soc. 1995, 117, 9481.
(13) Whittall, I. R.; Humphrey, M.; Hockless, D. C. R.; Skelton, B.
W.; White, A. H. Organometallics 1995, 14, 3970-3979.
(14) Whittal, I. R.; Humphrey, M. G.; Persoons, A.; Houbrechts, S.
Organometallics 1996, 15, 1935-1941.
(15) Complex 3 can be obtained in a one-pot synthesis as previously
described for the analogous complex [Ru{CtCCH(Ph)(PMe3}-
(PPh3)2(η5-C9H7)][PF6]: Cadierno, V.; Gamasa, M. P.; Gimeno, J .;
Borge, J .; Garc´ıa-Granda, S. J . Chem. Soc., Chem. Commun. 1994,
2495. Both alkynyl-phosphonio complexes are excellent substrates
for Wittig reactions leading to the formation of new double carbon-
carbon bonds.
(16) The alkynyl complex 2 was prepared in 79% yield by the
deprotonation of the corresponding vinylidene complex 1, which is
easily formed from the reaction of [RuCl(PPh3)2(η5-C9H7)] with (p-
nitrophenyl)acetylene. Complexes 12a ,b and 13 were prepared as
described for the analogous bimetallic complexes 9a ,b and 10.
(17) Clays, K.; Persoons, A. Rev. Sci. Instrum. 1992, 63, 3285-3289.
(18) Hendrickx, E.; Dehu, C.; Clays, K.; Bre´das, J . L.; Persoons, A.
In Polymers for Second-Order Nonlinear Optics; ACS Symposium
Series 601; Lindsay, G. A., Singer, K. D., Eds.; American Chemical
Society: Washington, DC, 1995; pp 82-94.
S0276-7333(96)00556-0 CCC: $12.00 © 1996 American Chemical Society

Communications
Organometallics, Vol. 15, No. 25, 1996 5267
Sch em e 1a
a
Reagents and conditions: (i) NaPF6, HCtC-p-C6H4NO2, MeOH, reflux; (ii) Al2O3, CH2Cl2, room temperature; (iii) NaPF6,
HCtCCH2OH, PPh3, MeOH, room temperature; (iv) LinBu, OdC(H)-p-C5H4N, THF, -20 °C; (v) [M(CO)5(THF)], THF, room
temperature; (vi) LinBu, OdC(m-C6H4NO2)2, THF, -20 °C; (vii) LinBu, OdC(H)(CHdCH)n-p-C6H4A, THF, -20 °C; (viii) n ) 0, A
) CN, [M(CO)5(THF)], THF, room temperature or n ) 0, A ) CN, [Ru(NH3)5(OSO2CF3)][CF3SO3]2, acetone, room temperature;
(ix) KCN, MeOH, reflux; (x) [M(CO)5(THF)], THF, room temperature or [Ru(NH3)5(OSO2CF3)][CF3SO3]2, acetone, room temperature.
Ta ble 1. Wa velen gth of Ma xim u m Absor p tion sa
contributor to â. Only for these compounds for which
λmax approaches the harmonic frequency does this
simple model lead to an underestimation of â0, probably
due to neglect of damping (e.g. as for 7a and 8).
a n d F ir st Hyp er p ola r iza bilitiesb for Com p lexes
1-13
λmax
â
â0
λmax
â
â0
Although a triple carbon-carbon bond is known to
be less effective as a π-conjugated bridge for NLO
materials,2 the determined hyperpolarizability of 2 is
far greater than that of its 4-nitro-â-(dimethylamino)-
styrene analogue (â1900 nm ) 35 × 10-30 esu), in which
the donor is separated from the benzene system through
a double bond. This also holds for 7a , 8, and their N,N-
dimethylnitrostilbene analogues.2 The high effective-
ness of the half-sandwich [Ru]sCtC donor moiety,
especially compared to metallocene derivatives,22 is
probably due to the in-plane metal-to-ligand charge-
transfer (MLCT) transition, opposite to the out-of-plane
MLCT transition for metallocenes. The results (com-
pare 2, 7a , and 8) show a large increase in hyperpolar-
izability on going from the benzene (2) to the stilbene
form (7a ). However, the addition of an extra double
bond (8) has little influence. The decreased hyper-
polarizability of 1 compared to 2 emanates most likely
from the net positive charge on the ruthenium center,
which leads to a decrease of the electron donor ability
of the [Ru]+dCdC metal fragment as compared to
[Ru]sCtC. Furthermore, the rather low â value for 6
compared to that for 2 indicates that the increased
π-system is insufficient to account for the loss in
hyperpolarizability as the para acceptor is replaced with
the meta one. Substitution of the nitro group by a cyano
acceptor (7a for 7b) changes â, as generally expected
from the difference in acceptor strengths.1
1
2
4
5a
5b
6
7a
7b
379
476
399
451
462
398
507
427
116
746
100
260
535
177
1257
238
50
119
37
60
71
67
89
71
8
9a
523
442
456
442
396
392
392
621
1320
465
700
315
13
25
40
108
34
119
150
80
5
10
9b
10c
11
12a
12b
13c
15
26
a
b
In nm. Hyper-Rayleigh scattering measurements; the hy-
perpolarizabilities â (10% error) and the calculated â0 values are
given in 10-30 esu. The hyperpolarizabilities are reported in cgs
units (esu). They can be converted into SI units (C3 m3 J -2) by
dividing by a factor of 2.693 × 1020
. p-Nitroaniline was used as
an external reference.27 All measurements have been performed
in dichloromethane. c Acetone solutions.
The external reference method was used, and all
molecules were checked for fluorescence that can inter-
fere with the second-harmonic signal.18,19 In contrast
to recent theoretical studies,13,20 the measured hyper-
polarizabilities were among the highest values reported
for organometallic materials.5,6,9
The corrections for resonance enhancement were
made using the two-level model21 with the absorption
band closest to the harmonic frequency. Since the
molecules exhibit weaker absorption bands at lower
wavelengths, the calculated value will only be an
estimate of the static hyperpolarizability (â0). However,
the good correlation1 found between â0 and the wave-
length of maximal absorption (λmax) seems to justify this
procedure. In other words, the optical transition cor-
responding to the given λmax seems to be the main
Three series of bimetallic complexes have been in-
vestigated (5a ,b , 9-10, and 12-13) and the hyper-
polarizabilities compared with the monometallic precur-
sor complexes (4, 7b, and 11, respectively). In general,
an increase of â and λmax is observed upon addition of
(19) Morrison, I. D.; Denning, R. G.; Laidlaw, W. M.; Stammers, M.
A. Rev. Sci. Instrum. 1996, 67, 1445-1453.
(20) Kanis, D. R.; Lacroix, P. G.; Ratner, M. A.; Marks, T. J . J . Am.
Chem. Soc. 1994, 116, 10089-10102.
(21) Huijts, R. A.; Hesselink, G. L. J . Chem. Phys. Lett. 1989, 156,
209.
(22) Calabrese, J . C.; Cheng, L.-T.; Green, J . C.; Marder, S. R.; Tam,
W. J . Am. Chem. Soc. 1991, 113, 7227-7232.

5268 Organometallics, Vol. 15, No. 25, 1996
Communications
the metal group. Previous ZINDO-SOS calculations on
(pyridine)metal pentacarbonyl compounds (analogous to
5a ,b) suggested that the pyridine ring remains the
effective molecular acceptor; the role of the metal group
is that of an inductive acceptor of the pyridine lone pair
that induces a positive charge on the pyridine ring,
which lowers the energy of the pyridine-centered
LUMO.20,23 By assumption that this mechanism also
holds for the analogous cyano complexes (9-13), the
differences in the determined hyperpolarizabilities can
be explained by the different σ-acceptor effectiveness of
the metal atoms attached to the cyano (pyridine for
5a ,b) group. Comparison of the chromium and tungsten
complexes (5a ,b, 9a ,b, and 12a ,b) shows that the
compounds containing W, which is more capable than
Cr of reducing its electron density by π back-donation
to CO,24 indeed display larger hyperpolarizabilities.
Similar results have been reported for group 6 metal
Fischer type carbene complexes.25 The differences in
hyperpolarizability between the RuII-RuIII complexes
(10 and 13) and the corresponding chromium and
tungsten derivatives (9a ,b and 12a ,b, respectively) show
an inverse order in both series (9-10 and 12-13). It
is apparent that an explanation for his behavior may
require theoretical calculations that should reveal which
effect, either the higher intrinsic electronegativity of the
Ru(III) center with respect to W(0) and Cr(0) or the
presence of the donor NH3 ligands as compared to the
π-acceptor CO ligands, will finally have the largest
influence on the LUMO.
to date for bimetallic compounds.19,26 That the larger
values are determined for the metal-cyanobenzene
compounds (9a ,b and 10) is not unexpected, since the
precursor cyanobenzene complex 7b is a stronger ac-
ceptor than the pyridine complex 4.
In conclusion, a series of novel ruthenium σ-acceptor
aryl-enynyl complexes, including homo- and heterobi-
metallic complexes, have been synthesized. The deter-
mined values of the quadratic hyperpolarizabilities,
which are significantly larger than those of the more
commonly studied metallocene and related derivatives,
can be explained by the molecular design. Further work
in this direction is in progress.
Ack n ow led gm en t. V.C. thanks the Fundacio´n para
la Investigacio´n Cient´ıfica y Te´cnica de Asturias
(FICYT) J .G. gratefully acknowledges financial support
from the Spanish DGICYT (Grant No. PB93-0325) and
European Community (Human and Capital Mobility
Programme: Contract No. ERBCHRXCT 940501). S.H.
is a Research Assistant and K.C. a Senior Research
Associate of the Belgian National Fund for Scientific
Research.
Su p p or tin g In for m a tion Ava ila ble: Text giving IR and
31P{1H}, 1H, and 13C{1H} nuclear magnetic resonance spec-
troscopic data and elemental analytical data for 1-13 (9
pages). Ordering information is given on any current mast-
head page.
OM960556O
It is noteworthy to mention that the bimetallic
complexes described in the present work show hyper-
polarizabilities surpassing the largest values reported
(26) Laidlaw, W. M.; Denning, R. G.; Verbiest, T.; Chauchard, E.;
Persoons, A. Proc. SPIE-Int. Soc. Opt. Eng. 1994, 2143, 14. In both
ref 19 and this paper the hyperpolarizabilities reported previously by
Laidlaw et al.7 are revisited and the value found for [Ru(η5-C5H5)-
(PPh3)2(µ-CN)Ru(NH3)5]3+ (â ) 157 × 10-30 esu) compares well to that
of the analogous complex 13.
(23) Kanis, D. R.; Ratner, M. A.; Marks, T. J . Chem. Rev. 1994, 94,
195-242.
(24) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; Wiley-Interscience: New York, 1994.
(25) Maiorana, S.; Papagni, A.; Licandro, E.; Persoons, A.; Clays,
K.; Houbrechts, S. Gazz. Chim. Ital. 1995, 125, 377.
(27) Sta¨helin, M.; Burland, D. M.; Rice, J . E. Chem. Phys. Lett. 1992,
191, 245.