Synthesis and luminescence properties of a series of tris(4-styrylphenyl)phosphorus-(III) and -(V) compounds and of a [Cu(PR3)4]BF4 complex

Article abstract of DOI:10.1039/b309735h

The series of compounds PR₃, O=PR₃, MeR₃PI, Cl₂PR₃ and [Cu(PR₃)₄] BF₄ (R = (E)-4-(4-tert-butylstyryl)phenyl) has been prepared and optical properties explored by absor

Full text of DOI:10.1039/b309735h

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Synthesis and luminescence properties of a series of
tris(4-styrylphenyl)phosphorus-(III) and -(V) compounds and
of a [Cu(PR3)4]BF4 complex†
Rhett C. Smith and John D. Protasiewicz*
Department of Chemistry, Case Western Reserve University, Cleveland, USA.
E-mail: jdp5@po.cwru.edu
Received 18th August 2003, Accepted 4th October 2003
First published as an Advance Article on the web 28th October 2003
The series of compounds PR , O᎐PR , MeR PI, Cl PR and [Cu(PR ) ]BF (R = (E)-4-(4-tert-butylstyryl)phenyl) has
᎐
3
3
3
2
3
3
4
4
been prepared and optical properties explored by absorption and fluorescence spectroscopy. The effect of geometry
and coordination number on luminescence intensity is presented.
or polymeric materials based on such a morphology may be
Introduction
thought of as hybrids between poly(diphenylphosphine) (a
phosphorus analogue of polyaniline that has been reported
recently)7 and short sections of poly(phenylenevinylene) (PPV).
Both PPV and polyaniline are technologically important π con-
jugated and conducting polymers, and research aimed at vary-
ing the functionality in these materials is an area of extensive
current interest.8
Materials incorporating extended π-conjugation have attracted
a great deal of attention recently. Such materials display a
diverse set of electronic properties, spanning the range from
insulating to conducting, while maintaining the facile process-
ability typical of other organic polymers.1 This unique property
set has led to their use in applications ranging from OLEDs
and use in display devices,2 to molecular sensors,3 wires, and
switches for molecular electronics.1,4 Such extended π conju-
gation is also a common feature of non-linear optical (NLO)
materials, and ligands with π conjugated units tethered to their
framework have recently found application in quadrupolar
NLO-active metal complexes (two examples, Chart 1).5
Previous reports describe amines and phosphines with NLO
and/or LED applications.9 These reports serve as a starting
point for designing the system employed in the current study,
since they feature the general structural features of interest.
Recently, a systematic investigation of absorption and lumines-
cence properties with respect to coordination number and
geometry has been carried out on trianthrylphosphorus com-
pounds.10 At the start of our investigation, we were surprised to
find that no tris(styrylphenyl)phosphines were known. While
this manuscript was in preparation a report appeared des-
cribing synthesis of and study of energy transfer in a tris(4-(4-
styrylstyryl))phenyl)phosphine.11 This study was limited to the
triarylphosphine, and not extended to other organophosphorus
compounds where one could induce other possible geometries
and coordination numbers, however. Furthermore, to our
knowledge, none of the previously reported related systems
have been used as ligands for metal complexes. We herein pres-
ent the systematic investigation of the absorption and lumines-
cence behavior exhibited by a series of tris(4-styrylphenyl)-
phosphorus compounds in a variety of geometries and by
a representative metal complex. The availability of various
geometries and oxidation states/coordination numbers at the
phosphorus center allows some flexibility in the proximity and
orientation of bound chromophores (and their associated
dipoles) to one another, and may thus allow for switching or
tuning of optical properties in these materials.
Experimental
General considerations
All syntheses were carried out either in a glove box or using
modified Schlenk line techniques, under an atmosphere of dry
N2. Diethyl ether, THF, hexanes, benzene, and toluene were
distilled from benzophenone–Na ketyl under N2 before use.
Acetonitrile was refluxed under N2 over CaH2 for 6 h and
distilled. Absolute ethanol was dried by stirring over freshly
activated powdered 3Å molecular sieves prior to use. Phos-
phorus trichloride was purified by vacuum transfer. Anhydrous
CH2Cl2 and p-bromobenzaldehyde (Acros) were used as
received. Fluorescence measurements were carried out on a
SPEX Fluorolog FL3–12 in degassed HPLC grade CHCl3 on
solutions with absorbance of approximately 0.10 with an excit-
ation wavelength of 310 nm. Absorption spectra were carried
Chart 1
Our ongoing interest in incorporating phosphorus centers
into materials with novel opto-electronic properties6 led us to
explore the possibility of creating triphenylphosphine-based
ligands having an extended π conjugated system. Such materials
could be utilized as fundamental building blocks in extended
systems (oligomers, polymers or dendrimers) or as ligands for
novel metal complexes with possible NLO activity. Oligomeric
† Electronic supplementary information (ESI) available: 1H, 13C and 31
NMR spectra. See http://www.rsc.org/suppdata/dt/b3/b309735h/
P
D a l t o n T r a n s . , 2 0 0 3 , 4 7 3 8 – 4 7 4 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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out in the same solvent on a Lambda 25 spectrophotometer.
NMR spectra were recorded on a Varian Gemini instrument
operating at 300 MHz (1H), 75.5 MHz (13C) and 121.5 MHz
(31P). Proton, carbon and phosphorus spectra are referenced to
residual solvent signals, CDCl3, and 85% phosphoric acid,
respectively.
for 4 h. After cooling to room temperature, the product was
filtered off, rinsed with n-pentane, and dried in vacuo to afford
1
the phosphonium salt as a white powder (0.308 g, 86.2%): H
NMR (CDCl3) δ 1.33 (s, 27H), 3.16 (d, 3H, JHP = 13 Hz),
7.08 (d, 3H, J = 16 Hz), 7.30 (d, 3H, J = 16 Hz), 7.41 (d, 6H,
J = 8 Hz), 7.49 (d, 6H, J = 8 Hz), 7.73–7.77 (m, 12H); 31P{1H}
NMR (CDCl3) δ 20.0. HRMS (FAB, m/z, (M Ϫ I)ϩ): Calc. for
C55H60P, 751.4433; found, 751.4434. UV-vis: λmax 343 nm
(ε = 87800 MϪ1 cmϪ1).
(E )-4-Bromo-4Ј-tert-butylstilbene (TbsBr)
A 0.36 M solution of LiOEt was prepared by placing 0.25 g
(36 mmol) of freshly-cut Li metal in 100 mL of anhydrous
ethanol and stirring until reaction was complete. To this solution
was added a solution of (p-tert-butylbenzyl)triphenylphosphon-
ium bromide12 (15.9 g, 32.4 mmol) and p-bromobenzaldehyde
(6.00 g, 32.4 mmol) in 75 mL ethanol over a 30 min period. The
resultant yellow suspension was stirred at room temperature for
6 h, filtered off, and the off-white solid rinsed with cold ethanol
and dried to give the product as a mixture of (E) and (Z) isomers
Cl2PTbs3 (4)
A solution of 0.300 g (0.407 mmol) PTbs3 and 0.106 g
(0.448 mmol) hexachloroethane in 25 mL anhydrous benzene
was refluxed for 3 h. After cooling to room temperature, all
volatiles were removed in vacuo and the crude solid was rinsed
with anhydrous n-pentane, and dried in vacuo to afford 0.293 g
(89.1%) of the product as an off-white powder: 1H NMR
(CDCl3) δ 1.31 (s, 27H), 7.06 (d, 3H, J = 16 Hz), 7.17 (d, 3H,
J = 16 Hz), 7.30 (br d, 6H, J = 8 Hz), 7.41 (br d, 6H, J = 8 Hz),
7.48 (br, 6H), 7.68 (br, 6H). 31P NMR (CDCl3) δ 30.2. HRMS
(FAB, m/z, (M Ϫ 2Cl ϩ Na)ϩ): Calc. for C54H57PNa, 759.4096;
found, 759.4081. UV-vis: λmax 329 nm (ε = 103000 MϪ1 cmϪ1).
1
as ascertained by H NMR spectroscopy. Transformation to the
all-(E) form was accomplished by refluxing the material for 3 h in
50 mL toluene in the presence of a crystal of iodine. The solution
was then cooled to room temperature, washed with 5% Na2SO3.
The organic layer was collected and all volatiles removed under
reduced pressure to give 7.28 g (71.2%) of the product as an off-
white powder: mp 153–155 ЊC; 1H NMR (CDCl3) δ 1.33 (s, 9H),
6.99 (d, 1H, JHH = 16 Hz), 7.09 (d, 1H, JHH = 16 Hz), 7.35–7.40
(m, 4H), 7.43–7.48 (m, 4H); 13C{1H} NMR (CDCl3) δ 151.0,
136.4, 134.1, 131.7, 129.2, 127.8, 126.5, 126.3, 125.6, 121.0, 34.6,
31.2. Calc. for C18H19Br: C, 68.58; H, 6.07. Found: C, 68.50, H,
6.04%.
[Cu(PTbs3)4]BF4 (5)
To a 50 mL round-bottom flask containing 20 mL dry CH2Cl2
was added 53 mg (0.17 mmol) [Cu(NCMe)4]BF4 13 and 500 mg
(0.68 mmol) PTbs3 with rapid stirring. After 1 h of stirring at
room temperature all volatiles were removed in vacuo to afford 5
1
(500 mg, 95%) as a fine off-white powder. H NMR (CDCl3)
δ 1.35 (s, 108H), 7.04 (d, 12H, JHH = 16 Hz), 7.12 (d, 12H,
JHH = 16 Hz), 7.33–7.42 (m, 96H); 13C{1H} NMR (CDCl3)
δ 151.0, 138.7, 134.4 (d, JPC = 16 Hz), 134.1, 132.0 (d,
JPC = 26 Hz), 129.8, 127.1, 126.5, 126.4 (d, JPC = 11 Hz), 125.6,
34.6, 31.3; 31P NMR (CDCl3) δ 5.2. UV-vis: λmax 332 nm
(ε = 395,000 MϪ1 cmϪ1).
PTbs3 (1)
To a solution of (E)-4-bromo-4Ј-tert-butylstilbene (5.00 g,
15.9 mmol) in 25 mL THF at Ϫ78 ЊC was added 6.7 mL n-BuLi
(2.5 M in hexanes, 17 mmol) via cannula, and the resultant
mixture stirred for 1 h. PCl3 (0.28 mL, 3.2 mmol) was then
added to the cold solution via syringe and the mixture was
allowed to slowly warm to room temperature. All volatiles were
removed in vacuo and the resultant orange residue was sequen-
tially rinsed with hexanes, acetonitrile and diethyl ether to
afford 1 as a white powder (2.34 g, 77.4%): mp 284–286 ЊC; 1H
NMR (300 MHz, CDCl3) δ 1.33 (s, 27H), 7.05 (d, 3H, JHH = 16
Hz), 7.14 (d, 3H, JHH = 16 Hz), 7.30–7.40 (m, 12H), 7.44–7.50
(m, 12H); 13C{1H} NMR (CDCl3) δ 151.0, 138.0, 136.2 (d,
JPC = 11 Hz), 134.4, 134.0 (d, JPC = 20 Hz), 129.3, 127.3, 126.5
(d, JPC = 7 Hz), 126.3, 125.6, 34.6, 31.3; 31P{1H} NMR (CDCl3)
δ Ϫ6.1; HRMS (FAB, m/z): calc. for C54H57P, 737.4276; found,
737.4269. UV-vis: λmax 336 nm (ε = 112000 MϪ1 cmϪ1). Calc. for
C54H57P: C, 88.00; H, 7.80. Found: C, 88.18, H, 7.84%.
Results and discussion
Synthesis
Tris(4-(4-tert-butylstyryl)phenyl)phosphine (PTbs3), was pre-
pared in 77.4% yield by the reaction of trichlorophosphine with
the organolithium formed from TbsBr. The 31P{1H} NMR shift
of δ Ϫ6.1 for 1 in solution differs by only about 1 ppm from that
reported for PPh3.14 Compound 1 served as a convenient pre-
cursor to 2–5 by established methodologies (Scheme 1). Triaryl-
phosphine oxide 2 was formed by reaction with hydrogen per-
oxide, phosphonium salt 3 by refluxing with MeI, and Cl2PTbs3
4 by reaction with hexachloroethane.15 The dendrimeric metal
complex 5 was readily formed upon mixing of four equivalents
O᎐PTbs (2)
᎐
3
13
of phosphine with [Cu(NCMe)4]BF4 in dichloromethane at
A suspension of PTbs3 (100 mg, 0.136 mmol) in 10 mL 15%
H2O2 in 1 : 1 EtOH–H2O was stirred overnight. Excess peroxide
was quenched by addition of 5% aqueous Na2SO3, and the
organics extracted in chloroform. Removal of volatiles under
reduced pressure affords the product as a fine white powder
room temperature. Successful formation of compounds was
readily confirmed by high resolution mass spectroscopy. Multi-
nuclear NMR spectroscopy (1H, 13C and 31P) indicates the pres-
ence of a single species in all cases. The high resolution mass
spectrum of 5, however, did not show the Mϩ peak corre-
sponding to the proposed structure. Instead, the highest mass
peak observed corresponds to a formulation of [Cu(PTbs3)3]-
BF4. Confidence in the assigned stoichiometry is thus derived
from a number of additional checks. First, the reaction is nearly
quantitative when the Cu salt and phosphine are mixed in a 1 : 4
ratio to produce a single species with new 1H, 13C and 31P NMR
resonances. Spiking an NMR sample of the complex with
additional 1 leads to the appearance of additional resonances
attributable to the free 1. Finally, comparison of 1H NMR peak
integrations of 5 to those of an internal standard (1,4-di-
methoxybenzene) also confirms the assigned ratio. Attempts to
acquire accurate elemental analysis of 5 were unsuccessful, pre-
sumably due to the very hygroscopic nature of the material.
1
(89 mg, 87%): mp 290–292 ЊC; H NMR (CDCl3) δ 1.34 (s,
27H), 7.08 (d, 3H, JHH = 16 Hz), 7.20 (d, 3H, JHH = 16 Hz), 7.40
(d, 6H, JHH = 8 Hz), 7.47 (d, 6H, JHH = 8 Hz), 7.57–7.70 (m,
12H); 13C{1H} NMR (CDCl3) δ 151.5, 141.1, 133.9, 132.5 (d,
JPC = 10 Hz), 131.5 (d, JPC = 31 Hz), 131.1, 126.7, 126.5, 126.3
(d, JPC = 13 Hz), 125.7, 34.7, 31.2; 31P{1H} NMR (CDCl3)
δ 29.4; HRMS (FAB, m/z): calc. for C54H57PO, 753.4225; found,
753.4246. UV-vis: λmax 335 nm (ε = 142000 MϪ1 cmϪ1). Calc. for
C54H57OP: C, 86.13; H, 7.63. Found: C, 86.05, H, 7.48%.
MeTbs3PI (3)
A solution of 0.300 g (0.407 mmol) of PTbs3 and 0.116 g
(0.814 mmol) MeI in 20 mL of anhydrous toluene was refluxed
D a l t o n T r a n s . , 2 0 0 3 , 4 7 3 8 – 4 7 4 1
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Scheme 1
Initial questions concerning the ability of the Cu center to
accommodate four of the somewhat bulky phosphine ligands
were also addressed by calculations to determine the optimized
geometry of the complex (vide infra).
drive the formation of such a conformation. This geometry
may be further stabilized by π–π stacking between adjacent
stilbene units in each strand. Such a supermolecular tetra-
hedron places three terminal tert-butyl groups at each corner
with the metal charge isolated in the center, creating an
arrangement of dipoles appropriate for the type of quadru-
polar NLO properties that are of current interest.5 From
a structural standpoint, the ability to distribute 12 dipolar
units in such a way is anticipated to lead to more striking
effects than those exhibited by other tetrahedral systems such
as A (Chart 1, four dipolar units). Such properties could
conceivably be further enhanced by replacement of tert-butyl
groups with more strongly donating groups to create a stronger
set of dipoles. Current work is underway to construct such
systems.
Structure
In addition to simply confirming the ability of the metal center
in [Cu(PTbs3)4]BF4 to accommodate four of the phosphine lig-
ands, acquiring structural information for the complex would
also help assess the viability of the material for practical appli-
cations. For example, the geometric arrangement of dipolar
components is a critical factor in determining the utility of a
material in NLO applications. Unfortunately, repeated efforts
to grow X-ray quality crystals of [Cu(PTbs3)4]BF4 have thus far
been unsuccessful. Calculations at the PM3 level of theory
(MacSpartan Plus, version 1.2.1), however, predict a fascinating
“supermolecular tetrahedron” (Fig. 1). Such an arrangement
is formed as three stilbene moieties, one from each phosphine
on a face of a CuP4 tetrahedral dendrimer core, are intertwined
to form each of the four protrusions. Steric clashes between
the stilbene moieties about adjacent phosphines appear to
Spectroscopy
Fig. 2 shows the absorption (top) and fluorescence (bottom)
spectra for the series of compounds 1–5. The absorptivity and
fluorescence intensity have been normalized to intensity per
mole of stilbenyl units to facilitate direct comparison. The
spectra for the model compound (E)-4-methyl-4Ј-tert-butyl-
stilbene (6) are also shown for comparison. This material was
chosen because it represents a single chromophore hydrocarbon
with approximately the same morphology as the stilbenyl
subunits of which 1–5 are composed. As such, this model is
expected to approximate the properties that would be exhibited
by 1–5 in the absence of heavy atom or lone pair effects, or
intramolecular chromophore–chromophore interactions, all of
which may impact photophysical properties.
The absorptivity per stilbenyl is fairly constant for the entire
series, with all compounds having an absorptivity slightly lower
than that of 6. The absorption maxima (λπ–π*) for 1–5 are all
slightly red shifted with respect to 6, indicating that some
degree of conjugation with or across the phosphorus center
may be taking place. The extent of conjugation is less dramatic
than that observed for the interaction of nitrogen with aromatic
systems (the “amino conjugation effect”).16 The diminished
interaction with phosphorus is to be anticipated, as a conju-
gative interaction requires phosphorus to acquire a planar con-
formation and formal sp2 hybridization, a much less favorable
process for heavier main group elements.17
Fig. 1 Calculated structure of [Cu(PTbs3)4]BF4.
D a l t o n T r a n s . , 2 0 0 3 , 4 7 3 8 – 4 7 4 1
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as a dendrimeric Cu() complex, have been prepared. While
absorption spectra show no striking changes with geometry or
coordination number, fluorescence intensities vary. The
observed fluctuation in fluorescence seems to indicate that the
phosphorus lone pair contributes to fluorescence quench-
ing. Calculations indicate that the Cu() complex displays an
interesting “supermolecular tetrahedron” geometry with an
arrangement of dipoles appropriate for nonlinear optical sys-
tems. Current efforts are underway to confirm this geometry
and to apply the initial findings presented herein to the rational
design of related systems with specific optical and structural
properties.
Acknowledgements
The authors thank Prof. Christoph Weder and Prof. Malcolm
E. Kenney for use of instrumentation and the National Science
Foundation (CHE-0202040) for support.
References
1 (a) H. Shirakawa, Angew. Chem., Int. Ed., 2001, 40, 2574; (b) A. G.
MacDiarmid, Angew. Chem., Int. Ed., 2001, 40, 2581; (c) A. J.
Heeger, Angew. Chem., Int. Ed., 2001, 40, 2591; (d ) Handbook of
Conductive Materials and Polymers, ed. H. S. Nalwa, Wiley,
New York, 1997; (e) Handbook of Conducting Polymers, ed. T. A.
Skotheim, R. L. Elsenbaumer and J. R. Reynolds, Dekker,
New York, 2nd edn., 1998.
2 J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. MacKay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature,
1990, 347, 539.
3 D. T. McQuaid, A. E. Pullen and T. M. Swager, Chem. Rev., 2000,
100, 2537, and references therein.
Fig.
2
Absorption (top) and fluorescence (bottom) spectra for
compounds 1–6 (CHCl3, per mole of stilbenyl moiety).
4 (a) N. Robertson and C. A. McGowan, Chem. Soc. Rev., 2003, 32,
96; (b) J. M. Tour, Acc. Chem. Res., 2000, 33, 791; (c) J. Roncali, Acc.
Chem. Res., 2000, 33, 147; (d ) F. Paul and C. Lapinte, Coord. Chem.
Rev., 1998, 178–180, 431.
5 (a) T. Renouard, H. Le Bozec, S. Brasselet, I. Ledoux and J. Zyss,
Chem. Commun., 1999, 871; (b) K. Senechal, O. Maury, H. Le
Bozec, I. Ledoux and J. Zyss, J. Am. Chem. Soc., 2002, 124, 4560; (c)
J. Zyss and I. Ledoux, Chem. Rev., 1994, 94, 77.
6 (a) S. Shah, T. Concolino, A. L. Rheingold and J. D. Protasiewicz,
Inorg. Chem., 2000, 39, 3860; (b) C. Dutan, S. Shah, R. C. Smith,
S. Choua, T. Berclaz, M. Geoffroy and J. D. Protasiewicz,
Inorg. Chem., 2003, 42, 6241; (c) R. C. Smith, X. Chen and
J. D. Protasiewicz, Inorg. Chem., 2003, 42, 5468.
7 J. Zhou and B. L. Lucht, J. Organomet. Chem., 2002, 653,
167.
8 A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem.,
Int. Ed., 1998, 37, 402, and references therein.
9 (a) R. Sander, V. Stumpflen, J. H. Wenderhoff and A. Greiner,
Macromolecules, 1996, 29, 7750; (b) C. Lambert, E. Schmalzlin,
K. Meerholz and C. Brauchle, Chem. Eur. J., 1998, 3, 512.
10 S. Yamaguchi, S. Akiyama and K. Tamao, J. Organomet. Chem.,
2002, 646, 277.
11 Y. Wang, M. I. Ranasinghe and T. Goodson, III, J. Am. Chem. Soc.,
2003, 125, 9562.
12 H. Kagechika, T. Himi, K. Namikawa, E. Kawachi, Y. Hashimoto
and K. Shudo, J. Med. Chem., 1989, 32, 1098.
In contrast to absorptivity, the fluorescence intensity per
stilbenyl unit varies greatly across the series. The variation of
fluorescence intensity with coordination number or geometry in
trianthryl phosphorus compounds revealed that the extent to
which adjacent fluorophores interact most influences the
luminescence.10 Close contact of adjacent fluorophores may
allow nonradiative internal quenching by exiton transfer, for
example. Such interactions were anticipated to be reduced here,
as the stilbenyl fluorophores employed have considerably less
lateral extension than anthryl groups. Indeed, the trend seen in
Fig. 2 (bottom) suggests that the phosphorus lone pair may be
responsible for fluorescence quenching in the current case. The
involvement of the phosphorus lone pair in nonradiative decay
pathways has previously been presented as an explanation for
diminished fluorescence.18 This conclusion is supported by
the observation that the fluorescence intensity of Cl2PTbs3,
[Cu(PTbs ) ]BF and O᎐PTbs are all significantly enhanced vs.
᎐
3
4
4
3
PTbs3 in which the lone pair is unbound. The notably lower
fluorescence in MeTbs3PI may indicate that the iodide counter-
ion, a well documented fluorescence quencher, decreases lumin-
escence. It should also be noted that although the proposed
geometry of [Cu(PTbs3)4]BF4 (Fig. 1) places adjacent stilbenyl
fluorophores in close proximity to one another, the relative
fluorescence is not significantly diminished. In fact, the fluor-
escence intensity of 5 is only slightly less per stilbenyl moiety
than that of Cl2PTbs3, in which the stilbenyl units are maxi-
mally disposed. This may be at least partially attributed to the
utility of bulky tert-butyl groups that prevent close face-to-face
interactions of adjacent π systems.
13 B. J. Hathaway, D. G. Holah and J. D. Postlethwaite, J. Chem. Soc.,
1961, 3215.
14 N. Muller, P. C. Laterbur and J. Goldenson, J. Am. Chem. Soc.,
1956, 78, 3557.
15 S.-Z. Dong, H. Fu and Y.-F. Zhao, Synth. Commun., 2001, 31,
2067.
16 (a) L.-H. Ma, Z.-B. Chen and Y.-B. Jiang, Chem. Phys. Lett., 2003,
372, 104; (b) J. Yang, S.-Y. Chiou and K.-L. Liau, J. Am. Chem. Soc.,
2002, 124, 2518.
17 (a) E. Magnusson, J. Am. Chem. Soc., 1984, 106, 1177;
(b) W. Kutzelnigg, Angew. Chem., Int. Ed., 1984, 23, 272; (c) D. C.
Gilheany, Chem. Rev., 1994, 94, 1339.
18 M. E. R. Marcondes, V. G. Toscano and R. G. Weiss, J. Photochem.,
1979, 10, 425.
Conclusion
In conclusion, a series of new phosphorus-() and -() com-
pounds featuring stilbenyl ligands in various geometries, as well
D a l t o n T r a n s . , 2 0 0 3 , 4 7 3 8 – 4 7 4 1
4741