The preparation of novel ruthenium complexes for use in Langmuir-Blodgett films

Article abstract of DOI:10.1016/0022-328X(91)86206-6

A range of cationic cyclopentadienyl bisphosphine ruthenium nitrile complexes <(η⁵-C5H5)L2RuNC-Aryl>⁺ (L = phosphine or phosphite) have been prepared and characterised for use with the Langmuir-Blodgett deposition technique.

Full text of DOI:10.1016/0022-328X(91)86206-6

181
Journal of Organometallic Chemistry, 401 (1991) 181-186
Elsevier Sequoia S.A., Lausanne
JOM 21271
The preparation of novel ruthenium complexes for use
in Langmuir-Blodgett films
Stephen G. Davies *, Andrew J. Smallridge
The Dyson PerrinsLaboratory, South Parks Road, Oxford OXI 3QY (UK)
Richard Colbrook, Tim Richardson and Gareth G. Roberts
The Department of Engineering Science, Unioersity of Oxford, Oxford OXI 3PJ (UK)
(Received June 18th, 1990)
Abstract
A range of cationic cyclopentadienyl bisphosphine ruthenium nitrile complexes [(~s-CsHs)L2RuNC-
Aryl] + (L = phosphine or phosphite) have been prepared and characterised for use with the Langmuir-
Bkxlgett deposition technique.
Introduction
The Langmuir-Blodgett (LB) deposition technique has evoked considerable
interest in recent years due to the possibility of developing novel electronic and
optical devices [1,2]. Substituted benzonitriles are liquid crystal materials which
often possess the chemical and electronic properties necessary for the preparation of
LB films. Unfortunately the preparation of multilayer LB films from these com-
pounds is often impossible. We have previously reported that complexing molecules
of this type to cyclopentadienyl bistriphenylphosphine ruthenium dramatically
increases their film forming ability [3,4] and can lead to materials with potentially
useful pyroelectric coefficients or non linear optical properties [5]. We now wish to
report the synthesis of a variety of complexes containing the cyclopentadienyl
bisphosphine ruthenium unit which are currently undergoing studies on their
suitability for use with the LB technique.
Results and discussion
Acetonitrile [6,7] and benzonitrile derivatives [8] readily react with 015-
CsHs)(PR3)2RuC1 in the presence of non-chelating anions to form complexes of the
type [(~5-CsHs)(PR3)2RuNCR']+X- which we considered ideal candidates for LB
film work [3]. The ready substitution of the phosphine ligands bound to the
ruthenium [9] allows the complexes to be tailored for a wide range of electronic and
steric properties.
0022-328X/91/$03.50
© 1991 - Elsevier Sequoia S.A.

182
Table 1
Selected analytical data for the cationic ruthenium complexes
No.
Analysis (found (calcd.) (%))
Yield
(%)
94
lH NMR (ppm)
(*/5-C5H5)
C
H
N
I
65.12
6.20
0.92
4.54
4.74
4.68
4.81
5.10
4.57
4.36
4.78
4.48
4.62
4.59
4.77
4.80
(65.18)
50.90
(50.61)
59.47
(59.26)
61.82
(61.88)
45.35
(45.23)
68.82
(68.56)
77.80
(78.09)
54.65
(54.66)
64.45
(64.62)
65.38
(65.51)
65.73
(65.78)
61.28
(61.24)
48.28
(6.15)
7.62
(7.49)
6.82
(6.70)
6.07
(5.87)
6.94
(6.70)
6.70
(6.47)
7.10
(6.85)
6.90
(6.88)
6.91
(6.60)
6.13
(5.97)
6.31
(6.14)
4.35
(4.19)
6.23
(1.19)
1.60
(1.73)
1.27
(1.41)
1.19
(1.34)
1.34
(1.55)
1.52
(1.25)
0.92
(1.04)
1.53
(1.59)
1.34
(1.25)
3.62
(3.27)
3.99
(4.32)
3.92
(3.97)
7.04
2
3
4
5
6
7
$
9
24
75
53
22
23
86
85
74
79
54
86
81
10b
1Ib
12b
13b
(48.18)
(6.19)
(7.02)
A methanol solution of (,/5-CsHs)(PPh3)2RuC1 , 4-hexadecyloxybenzonitrile and
N H 4 P F6 was heated under reflux for 2 hours to give the cationic complex 1 in near
quantitative yield as a yellow crystalline solid. Analogous complexes 2-5 with a
variety of phosphine or phosphite ligands were prepared from the appropriate
ruthenium chloride complexes [10,11]. The analytical data and the chemical shift of
the cyclopentadienyl moiety for all the compounds prepared in this study are given
in T a b l e 1. The mechanism of this reaction is believed to involve ionisation of the
R u - C l bond in methanol followed by trapping of the thus formed [(,/5-C5H5 )L2Ru] ÷
by the nitrile. This ionisation is particularly favoured by electron donating phos-
phine ligands but not by phosphite ligands. Thus in the preparation of 5 significant
amounts of starting material, (~/5-CsHs)(P(OMe)3)2RuCI , remained even after 24
hours at reflux. The cationic complex 5 was separated from the neutral ruthenium
chloride complex with difficulty in low yield as a pale yellow crystalline solid.
Furthermore, no product was formed when (,/5-CsHs)(PPh3)(CO)RuC1 , containing
the electron withdrawing ligand CO, was treated with 4-hexadecyloxybenzonitrile.
The bistrimethyl phosphine derivative 2 is relatively unstable towards chromatogra-
phy, hence its low yield. Complexes with counterions other than PF6- (6,7) were
obtained by carrying out the reaction in the presence of N a B P h4 or AgBF4.

183
(i), (ii)
CI
~
-- OC16H33
(iii)
x'l
I
L
L
1 - 7
No.
1
L
L'
X
PPh~
PPh3
PMe3
PMe3
PF6
PF6
PF6
PF6
PF6
BF4
BPh4
2
3
4
S
6
7
PMe3
PPh3
dI 3e
P(OMe)3 P(OMe):~
PPh3
PPh3
PPh3
PPh3
Scheme 1. Reagents: (i)
NCC6H4OC16H33. (ii) NH4PF6. NaBPh4 or AgBF4 (iii) MeOH.
Complexes 8 and 9 were prepared in high yield from OIs-CsHs)(PPh3)2RuCI and
the approximate nitrile using the standard complexation conditions. The complexes
1-9 were all obtained as yellow solids.
~ , ~ , , P P h 3 / ~
J
+
e
PPh3
PF6"] u'--NC
PPh3
~
-'~ ~ - ~ O C 1 4 H 2 9
PF6]Ru-NCClsH37
PPh3
8
9
Materials with a strong absorbance near 500 nm were required for nonlinear
optics applications. Therefore, several highly conjugated azo compounds were
prepared using standard diazotisation procedures [12]. Complexation of these com-
pounds using a similar procedure to that described above gave the novel cationic
ruthenium complexes 8-11 as intensely coloured crystalline solids in good yield.
Values of hmax and ¢0 for both the complexed and uncomplexed azo compounds
are given in Table 2.
L'
C1
(i), (ii)
,, ,,,
u-NC ~ ' - N.
~ "Rd"-
~'~R ,L'
]
L
N C
N .
N
L
O OR
"-L2
13b
1 0 a
-
1 3 a
10b
-
No
10
11
12
13
L
L
R
PPh3
PPh3
PPh3
PMo~
PPh3
PPh3
PPh3
PMe~
OC16H33
N(Me)CI6H33
OH
N(Me)C7H15
Scheme 2. Reagents: (i) NH4PF6, (ii) MeOH.

184
Table 2
Values of Areax and ~0 for the complexed and uncomplexed azo compounds
No.
Colour
Amax
(nm)
e0
(×103 mo1-1 lcm -1)
10a
10b
11a
11b
12a
12b
13a
13b
pale strange
bright red
orange
bright red
orange
dark orange
dark red
dark red
362
383
456
486
367
382
462
490
17.0
17.2
25.2
32.4
22.1
23.2
24.7
28.9
Conclusion
Materials suitable for use with the LB deposition technique need to form fluid
monolayers; in addition ideally they should possess a large dipole and for nonlinear
optics purposes absorb light around 500 nm. Complexing nitriles to (75-
CsHs)(PPh3)2RuCI enhances the film forming ability of the nitrile, increases its
dipole and shifts the absorbance of the material to higher wavelengths as has been
demonstrated for the azo compounds.
Experimental
General
N-Heptyl-N-methylaniline [13], 4-[(4'-cyanophenyl)azo]phenol (12a) [14] and 4-
[[4'-(N-methyl)phenyl]azo]benzonitrile [15] were prepared using literature proce-
dures. Octadecylnitrile and 4-cyanophenyl-4'-(tridecyloxy)phenylacetylene were
kindly provided by Dr. D. Lacey (Hull University, UK). 1H N M R spectra were
recorded at 200 MHz on a Varian Gemini 200 instrument.
4-Hexadecyloxybenzonitrile.
An ethanol solution of 4-cyanophenol (1.19 g, 10
mmol), KOH (1 g, 18 mmol) and hexadecylbromide (3.05 g, 10 mmol) was heated at
reflux for 8 h. After cooling the product was filtered off and recrystallised from
methanol. Yield 2.8 g (82%). M.p. 52-53°C. 1H N M R (CDC13): 0.88 (t, J = 6.4 Hz,
3H, CH3), 1.26 (m, 26H), 1.60 (m, 2H, CH2CH20), 4.00 (t, J = 6.5 Hz, 2H, CH20 ),
6.96 (d, J = 8.9 Hz, 2H, H2 H6), 7.58 (d, J = 8.9 Hz, 2H, H3 H5).
4-[{4'-(Hexadecyloxy)phenyl}azo]benzonitrile (lOa). An ethanol solution of 4-
[(4'-cyanophenyl)azo]phenol (223 mg,
1 mmol), KOH (0.1 g, 1.8 mmol) and
hexadecylbromide (400 mg, 1.3 mmol) was heated at reflux for 20 h. After cooling
the precipitate was filtered off to give the product as a pale orange solid. Yield 328
mg (73%). M.p. 98-100°C. 1H N M R (CDCI3): 0.89 (t, J = 6.3 Hz, 3H, CH3), 1.27
(m, 26H), 1.6 (m, 2H, CH2CH20), 4.07 (t, J = 6.4 Hz, 2H, CH20 ), 7.04 (d, J = 9.0
Hz, H2 H6), 7.81 (d, J = 8.4 Hz, 2H, H3" H 5 ' ) , 7.96 (d, J = 8.6 Hz, 4H, H2' H6'
H3 H5).
4-[{4'-(N-hexadecyl-N-methyl)phenyl}azo]benzonitrile (11a). Sodium hydride (50
mg, 2.1 mmol) was added to a THF solution of 4-[{4'-( N-methyl)phenyl} azo]benzo-
nitrile (455 mg, 1.92 mmol). After stirring at room temperature for 1 h, hexade-

185
cylbromide (588 mg, 1.3 mmol) was added and the resulting solution heated at
reflux for 20 h. Water (20 ml) was added and the solution extracted with dichloro-
methane (3 × 20 ml). Removal of the solvent under reduced pressure gave the
product as an orange solid. Yield 854 mg (96%). M.p. 82-84 oC. 1H N MR (CDCI3):
0.88 (t, J = 6.2 Hz, 3H, CH3), 1.27 (m, 26H), 1.6 (m, 2H, CH2CH2N), 3.09 (s, 3H,
NMe), 3.44 (t, J = 7 . 8 Hz, 2H, CH2N), 6.74 (d, J = 9 . 2 Hz, H2 H6), 7.75 (d,
J = 8.3 Hz, 2H, H3' H5'), 7.89 (d, J = 8.5 Hz, 4H, H2' H6' H3 H5).
4-[{4'-(N-heptyl-N-methyl)phenyl}azo]benzonitrile (13a). Using a procedure sim-
ilar to that described by Hartman and Dickey [16], 4-cyanoaniline was dissolved in
aq. hydrochloric acid (18%, 10 ml) and cooled to 0°C. With stirring a solution of
sodium nitrite (0.7 g) in water (10 ml) was added dropwise over 30 rain. Addition at
0 °C of N-heptyl-N-methyl aniline (2.0 g) and aq. sodium hydroxide (10%, 10 ml)
gave during 30 min stirring the product 13a as a red precipitate. Filtration,
dissolution in chloroform, drying (Na2SO4) and chromatography (A1203, grade V,
CHC13) gave after evaporation 13a as a bright red solid. Yield 1.1 g (33%). M.p.
78-79° C. 1H NMR (CDCI3) 0.90 (t, J = 6.7 Hz, 3H, CH3) , 1.32 (m, 26H), 1.65 (m,
2H, CH2CH2N), 3.09 (s, 3H, NMe), 3.44 (t, J---7.5 Hz, 2H, CH2N), 6.61 (d,
J = 9.2 Hz, H2 H6), 7.75 (d, J = 8.7 Hz, 2H, H3' H5'), 7.89 (d, J = 8.6 Hz, 4H, H2'
H6' H3 H5).
N-[Ruthenium ( ~5-cyclopentadienyl)(bistriphenylphosphine)]-4.hexadecyloxybenzo-
nitrile hexafluorophosphate (1). A solution of (~15-cyclopentadienyl)(bistriphenyl-
phosphine)ruthenium chloride [17] (95 mg, 1.3 mmol) 4-hexadecyloxybenzonitrile
(46 mg, 1.3 mmol) and ammonium hexafluorophosphate (50 mg, 3 mmol) in
methanol was heated under reflux for 2 h. After removal of the methanol under
reduced pressure dichloromethane was added and the solution filtered. Column
chromatography (Flash silica, eluent: 5% Et20:CH2C12) gave the product. Yield
145 mg (94%). M.p. 68-70°C. 1H NMR (CDCI3) 0.88 (t, J = 6 . 4 Hz, 3H, CH3),
1.27 (m, 26H, (CH2)13), 1.77 (m, 2H, CH2CH20), 3.99 (t, J = 6.4 Hz, 2H, CH20),
4.54 (s, 5H, Cp), 6.88 (d, J = 8.9 Hz, H2 H6), 7.1-7.8 (m, 32H, Ar).
A similar procedure was used for the preparation of complexes 2-13.
2: m.p. 95°C. 1H NMR (CDC13): 0.88 (t, J = 6 . 8 Hz, 3H, CH3), 1.26 (m, 26H,
(CH2)13), 1.58 (m, 18H, PMe3), 1.78 (m, 2H, CH2CH20), 4.00 (t, J = 6.4 Hz, 2H,
CH20 ), 4.74 (s, 5H, Cp). 6.98 (d, J = 8.9 Hz, H2 H6), 7.55 (d, J = 8.9 Hz, H3 H5).
3: m.p. 61-62°C. 1H NMR (CDCI3): 0.88 (t, J = 6.5 Hz, 3H, CH3), 1.27 (m,
26H, (CH2)13), 1.35 (d, J = 9.2 Hz, 6H, PMe3), 1.77 (m, 2H, CH2CH20), 3.99 (t,
J -- 6.5 Hz, 2H, CH20, 4.68 (s, 5H, Cp), 6.90 (d, J = 8.9 Hz, 2H, H2 H6), 7.2-7.5
(m, 17H, Ar).
4: m.p. 71-72°C. 1H NMR (CDCI3): 0.88 (t, J = 6.4 Hz, 3H, CH3), 1.27 (m,
26H, (CH2)13), 1.72 (m, 2H, CH2CH20), 2.6 (m, 4H, PCH2CH2P), 3.90 (t, J = 6.5
Hz, 2H, CH20), 4.81 (s, 5H, Cp), 6.45 (d, J = 8.8 Hz, Ar), 6.67 (d, J = 8.9 Hz, Ar)
7.2-7.9 (m, 30H, Ar).
5: m.p. 46-47°C. 1H NMR (CDC13): 0.88 (t, J = 6.6 Hz, 3H, CH3), 1.27 (m,
26H, (CH2)13), 1.74 (m, 2H, CH2CH20), 3.68 (m, 18H, P(OMe)3), 4.00 (t, J = 6.4
Hz, 2H, CH20), 5.10 (s, 5H, Cp), 6.99 (d, J = 8.9 Hz, 2H, H2 H6), 7.58 (d, J = 8.9
Hz, H3 H5).
6: m.p. 67°C. 1H NMR (CDCI3): 0.89 (t, J = 6.3 Hz, 3H, CH3) , 1.27 (m, 26H,
(CH2)13), 1.78 (m, 2H, CH2CH20), 4.00 (t, J = 6.5 Hz, 2H, CH20), 4.57 (s, 5H,
Cp), 6.90 (d, J = 8.9 Hz, 2H, H2 H6), 7.1-7.4 (m, 32H, Ar).

186
7: m.p. 7 4 ° C . 1H N M R (CDCI3): 0.89 (t, J = 6.4 Hz, 3H, CH3), 1.27 (m, 26H,
(CH2)13), 1.77 (m, 2H, C H 2 C H 2 0), 3.86 (t, J = 6.4 Hz, 2H, C H 2 0 ) , 4.36 (s, 5H,
Cp), 6.7-7.1 (m, 54H, Ar).
8: m.p. 108°C. 1H N M R (CDC13): 0.88 (t, J = 6.4 Hz, 3H, CH3), 1.27 (m, 26H,
(CH2)13), 1.58 (m, 18H, PMe3), 1.77 (m, 2H, C H 2 C H 2 0), 3.98 (t, J = 6.5 Hz, 2H,
C H 2 0 ) , 4.78 (s, 5H, Cp), 6.89 (d, J = 8,6 Hz, 2H, H3 H5), 7.47 (d, J = 8.7 Hz, 2H,
H3' H 5 ' ) , 7.59 (s, 4H, H2 H2' H6 H 6 ' ) .
9: m.p. 7 3 ° C . 1H N M R (CDCI3): 0.88 (t, J = 6.7 Hz, 3H, CH3), 1.27 (m, 32H,
(CH2)16), 2.67 (t, J = 6.8 Hz, 2H, CH2CN), 4.48 (s, 5H, Cp), 7.0-7.5 (m, 34H, Ar).
10b: m.p. 9 0 ° C . IH N M R (CDCI3): 0.89 (t, J = 6.1 Hz, 3H, CH3), 1.27 (m,
26H, (CH2)13), 1.35 (m, 2H, CH2CH20), 4.07 (t, J = 6.7 Hz, CH20 ), 4.62 (s, 5H,
Cp), 7.02 (d, J = 9.0 Hz, 2H, H2 H6), 7.1-7.5 (m, 32H, Ph), 7.86 (d, J = 8.6 Hz,
2H, H3' H 5 ' ) , 7.93 (d, J = 9.0 Hz, 4H, H3 H5 H2' H 6 ' ) .
lib: m.p. 9 1 ° C . 1H N M R (CDC13): 0.88 (t, J---6.1 Hz, CH3), 1.26 (m, 26H),
1.62 (m, 2H, C H 2 C H 2 0), 3.09 (s, 3H, NMe), 3.44 (t, J = 7.4 Hz, 2H, CH2N ), 4.59
(s, 5H, Cp), 6.73 (d, J = 9.3 Hz, 2H, H2 H6), 7.0-7.5 (m, 32H), 7.79 (d, J = 8.6 Hz,
2H, H3' H 5 ' ) , 7.87 (d, J = 9.2 Hz, 4H, H3 H5 H2' H 6 ' ) .
12b: m.p. 1 4 7 ° C . 1H N M R (acetone-d6): 4.77 (s, 5H, Cp), 7.05 (d, J = 8.8 Hz,
2H, H2 H6), 7.2-7.5 (m, 32H, Ar), 7.58 (d, J = 8.6 Hz, 2H, H3' H 5 ' ) , 7.90 (d,
J = 8.6 Hz, 2H, Ar), 7.93 (d, J = 8.3 Hz, 2H, Ar).
13b: m.p. 113°C. 1H N M R (CDCI3): 0.89 (t, J = 6.4 Hz, 3H, CH3), 1.30 (m,
10H, (CH2)13), 1.61 (m, 18H, PMe3), 3.10 (s, 3H, NMe), 3.45 (t, J = 7.1 Hz, 2H,
CH2N ), 4.80 (s, 5H, Cp), 6.73 (d, J = 9.1 Hz, 2H, H2 H6), 7.67 (d, J = 8.1 Hz, 2H,
H3' H 5 ' ) , 7.88 (d, J = 7.1 Hz, 2H, Ar), 7.92 (d, J = 8.0 Hz, 2H, Ar).
Acknowledgements
We thank the SERC for support (to AJS). This work is supported by T h o r n EMI
through the LINK initiative scheme.
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