Novel pyridyl-stabilised rigid-rod organometallic polymers and their monomeric precursors

Article abstract of DOI:10.1039/a706586h

Reaction of trans-[Pt(NC₅H₄CHBuⁿ₂) ₂Cl₂] 1 with an excess of HC≡CR (R = Ph, C₆H₄Me, C₆H₄NO₂) affords the monomeric complex trans-[Pt(N

Full text of DOI:10.1039/a706586h

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Novel pyridyl-stabilised rigid-rod organometallic polymers and their
monomeric precursors
Christopher J. Adams, Stuart L. James and Paul R. Raithby*
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
Reaction of trans-[Pt(NC5H4CHBun ) Cl2] 1 with an excess
selected bond parameters. The Pt atom sits on a crystallographic
2 2
of HC·CR (R = Ph, C6H4Me, C6H4NO2) affords the
centre of symmetry, which imposes exact planarity at the metal
centre, and requires the two alkynyl groups and the two
substituted pyridine ligands to occupy mutually trans positions,
respectively. The Pt–C(21)–C(22) alkynyl unit is essentially
linear. The geometry is similar to that found in a number of
trans-bis(phosphine) stabilised platinum bis(alkynyl) com-
plexes,8 and the Pt–C(21) distance lies within the range
1.98(1)–2.06(1) Å found in the other complexes.
monomeric complex trans-[Pt(NC5H4CHBun ) (C·CR)2]
2 2
(R = Ph 2a, C6H4Me 2b, C6H4NO2 2c), the trans arrange-
ment of the alkynyl ligands being confirmed from spectro-
scopic data and by an X-ray analysis of 2c; when 1 is treated
with 1 equiv. of HC·CC6H2(Me)2C·CH the polymer
[Pt(NC5H4CHBun ) C·CC6H2Me2C·C]n is formed, which
2 2
is soluble in a range of organic solvents.
The reaction of 1 with 1 equiv. of HC·CC6H2Me2C·CH,
There is considerable current interest in s-alkynyl transition-
metal complexes and in the polymers formed from them
because of their potential for use as non-linear optical, low-
dimensional conducting, luminescent or liquid-crystalline ma-
terials.1 Within this group the ‘rigid-rod’ trans-bis(s-alkynyl)
systems with the general formula [MLx–C·C–R–C·C]n
(M = Fe, Ru, Os, Ni, Pd, Pt; L = phosphine, arsine, n = 2,4;
R = C6H4, C6H2Me2, C6H2F2, C4H4S, C14H8)2 have been
shown to exhibit a variety of novel electronic properties.3 The
ancillary ligands, L, in these metal-containing polymers are
almost always phosphines, and this derives from the over-
whelming proportion of monomeric platinum-group alkynyl
precursor complexes which are stabilised by phosphines.4 Imine
donors are expected to impart different properties to both
monomeric and polymeric systems, particularly with regard to
their optical and redox behaviour.5 We have, therefore,
embarked on the development of platinum-group alkynyl
chemistry with nitrogen donor ligands, and have recently
reported the preparation of the cis-diimine stabilised complexes
[(Me2bipy)Pt(C·CC6H4R-4)2] (bipy = bipyridyl; R = H, Me,
NO2).6 We now report the synthesis of the first diimine
under the same reaction conditions as described above,
afforded,
after
purification,
the
polymer
trans-
[Pt(NC5H4CHBun ) C·CC6H2Me2C·C]n 3 as a brown solid in
2 2
moderate yield (Scheme 1). The polymer was characterised by
spectroscopic techniques,† and the presence of the s-alkynyl
confirmed by the presence of the n(C·C) stretching vibration in
N
Pt
N
R
C
C
C C R
R = Ph 2a, C6H4Me 2b, C6H4NO2 2c
stabilised
trans-bis(s-alkynyl)
platinum
= Ph 2a, C6H4Me 2b,
complex
i
[Pt(NC5H4CHBun ) (C·CR)2] (R
2 2
N
Pt
N
C6H4NO2 2c) and the formation of the novel polymer
2 2
[Pt(NC5H4CHBun ) C·CC6H2Me2C·C]n 3.
Cl
Cl
A frequent problem in the synthesis of s-alkynyl complexes
and the subsequent formation of the polymers is their in-
solubility in common organic solvents. In order to reduce this
ii
problem trans-[Pt(NC5H4CHBun ) Cl2] 1, prepared by an
2 2
adaption of the literature method,7 was used as the starting
material; the long hydrocarbon chains attached to the 4-position
of the pyridine group greatly enhance the solubility. The
reaction of 1 with 3 equiv. of HC·CR (R = Ph, C6H4Me,
C6H4NO2), in the presence of catalytic amounts of CuI, in
1
CH2Cl2
solution
containing
Pri2NH,
Ph 2a, C6H4Me 2b,
afforded
[Pt(NC5H4CHBun ) (C·CR)2] (R
=
2 2
N
C6H4NO2 2c) in high yield, after stirring for 1 h (Scheme 1).
The products were isolated as crystalline solids after purifica-
tion by column chromatography on alumina using CH2Cl2–
hexane (1:1) as eluent. The products were characterised
Pt
N
C
C
C C
initially by IR, H and 13C NMR spectroscopy, and by mass
1
spectrometry.† The single n(C·C) stretching frequency in the
range 2102–2098 cm21 in the IR spectrum confirmed the
presence of the s-alkynyl ligands, consistent with the trans
geometry.
In order to confirm the trans geometry of the products a
single-crystal X-ray analysis of 2c was undertaken. The
molecular structure‡ is illustrated in Fig. 1 which includes
n
3
Scheme 1 i, 3 equiv. HC·CR (R = Ph 2a, C6H4Me 2b, C6H4NO2 2c),
catalytic amount of CuI in Pri2NH, CH2Cl2, stirred at room temp. for 1 h; ii,
1 equiv. HC·CC6H2Me2C·CH, catalytic amount of CuI in Pri2NH, CH2Cl2,
stirred at room temp. for 1 h
Chem. Commun., 1997
2155

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Hz), 6.98 (d, 2 H, J 8 Hz), 2.50 (qnt, 1 H), 2.27 (s, 3 H), 1.2 (m, 18 H); 13
C
NMR (CDCl3) d 157.92 (py), 155.5 (py), 135.14 (toluene), 131.5 (toluene),
128.6 (toluene), 124.8 (toluene), 124.5 (py), 118.2 (C·C), 100.0 (C·C), 45.7
(nonyl), 35.6 (nonyl), 29.5 (nonyl, 22.6 (nonyl), 21.3 (nonyl), 13.9 (nonyl).
2c: IR n(C·C)/cm21 (CH2Cl2) 2098; m/z 898.5 (M+); 1H NMR (CDCl3) d
9.16 (d, 2 H, J 6.75 Hz), 7.36 (d, 2 H, J 5. Hz), 7.11 (d, 2 H, J 7 Hz), 3.05
(d, 2 H, J 5.Hz), 2.56 (qnt, 1 H), 1.25 (m, 18 H); 13C NMR (CDCl3) d 158.9
(py), 154.9 (py), 145.0 (arene), 132.0 (arene), 127.9 (arene), 124.9 (py),
123.4 (arene), 100.12 (C·C), 82.3 (C·C), 45.76 (nonyl), 35.6 (nonyl), 22.6
(nonyl), 13.9 (nonyl). 3: IR n(C·C)/cm21 (CH2Cl2) 2097; 1H NMR
(CDCl3) d 9.29 (d, 2 H, J 6.98 Hz), 7.01 (s, 2 H), 6.98 (d, 2 H, J 6.8 Hz),
2.49 (qnt, 1 H), 2.16 (s, 6 H), 1.10 (m, 18 H); 13C NMR (CDCl3) d 157.6
(py), 155.43 (py), 135.97 (arene), 132.3 (arene), 124.51 (py), 124.3 (arene),
45.65 (nonyl), 35.64 (nonyl), 29.5 (nonyl), 22.61 (nonyl), 20.4 (arene),
13.88 (nonyl). Satisfactory microanalyses were obtained on all the
complexes.
‡ Crystal data for 2c: C44H54N4O4Pt, Mr = 898.00, monoclinic, space
group P21/c, a = 7.693(2), b = 22.908(5), c = 11.738(2) Å, b = 94.35(3)°,
U = 2062.6(8) Å3, Z = 2, Dc = 1.446 g cm23, m = 3.447 mm21 for Mo-
Ka radiation (l = 0.71073 Å), F(000) = 912, T = 153(2) K. 3471
Refelctions measured on a Rigaku AFC7R diffractometer, 2696 unique
absorption corrected (Rint = 0.082) used for structure solution (Patterson)
and refinement (full-matrix least squares on F2, anisotropic displacement
parameters for non-H atoms, riding isotropic H-atoms); R1 = 0.053 for
1670 reflections with I > 2s(I) and wR2 = 0.172 for all data, goodness of
fit = 1.079 for all F2 values, 243 parameters; final difference map showed
only ripples in the vicinity of the Pt atom. Programs: TeXsan, SHELXTL-
PLUS and SHELXL 93. CCDC 182/614.
C(8)
C(7)
C(10)
C(6)
C(12)
C(9)
C(11)
C(13)
C(14)
C(3)
C(2)
C(1)
C(4)
C(5)
O(1)
N(2)
C(25)
N(1)
C(24)
C(23)
C(26)
C(22)
C(28a)
C(22a)
C(27)
O(2a)
O(2)
C(27a)
N(2a)
C(21)
Pt
N(1a)
C(21a)
C(28)
C(26a)
C(23a)
C(25a)
C(24a)
O(1a)
C(5a)
C(4a)
C(1a)
C(2a)
C(3a)
C(11a)
C(12a)
C(14a)
C(9a)
C(6a)
C(10a)
C(13a)
C(8a)
C(7a)
Fig. 1 Molecular structure of 2c showing the atom numbering scheme.
Selected bond lengths (Å) and angles (°): Pt–N(1) 2.001(10), Pt–C(21)
2.02(2), C(21)–C(22) 1.21(2), C(22)–C(23) 1.42(2), C(26)–N(2) 1.49(2),
N(2)–O(1) 1.22(2), N(2)–O(2) 1.22(2); N(1)–Pt–C(21) 88.2(4), N(1)–Pt–
C(21A) 91.8(4), Pt–C(21)–C(22) 174.8(11), C(21)–C(22)–C(23) 174(2),
O(1)–N(2)–C(26) 118.2(13), O(2)–N(2)–C(26) 116.1(14), O(1)–N(2)–O(2)
125.6(14).
1 N. J. Long, Angew. Chem., Int. Ed. Engl., 1995, 34, 21; I. Manners,
Angew. Chem., Int. Ed. Engl., 1996, 35, 1602; A. Harriman and
R. Ziessel, Chem. Commun., 1996, 1707.
the IR spectrum. As in other s-alkynyl polymers9 this n(C·C)
stretch does not show a significant shift from the position in the
precursor complex. The 13C NMR spectrum confirmed the
presence of both the arene spacer group and the substituted
pyridine ligands, but in common with other ‘rigid-rod’
polymers chemical shifts corresponding to the s-alkynyl
carbons were not observed.2,3
2 S. J. Davies, B. F. G. Johnson, M. S. Khan and J. Lewis, J. Chem. Soc.,
Chem. Commun., 1991, 187; B. F. G. Johnson, A. K. Kakkar,
M. S. Khan and J. Lewis, J. Organomet. Chem., 1991, 409, C12;
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B. Spencer, F. Wittman and R. H. Friend, J. Organomet. Chem., 1994,
472, 247.
3 J. Lewis, M. S. Khan, A. K. Kakkar, B. F. G. Johnson, T. B. Marder,
H. B. Fyfe, F. Wittmann and R. H. Friend, J. Organomet. Chem., 1992,
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Chem., 1994, 4, 1227; A. E. Dray, F. Wittmann, R. H. Friend,
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1991, 41–43, 871; C. W. Faulkner, S. L. Ingham, M. S. Khan, J. Lewis,
N. J. Long and P. R. Raithby, J. Organomet. Chem., 1994, 482, 139;
A. Ko¨hler, H. F. Wittmann, R. H. Friend, M. S. Khan and J. Lewis,
Synth. Met., 1994, 67, 245; D. Beljonne, F. H. Wittmann, A. Ko¨hler,
S. Graham, M. Younus, J. Lewis, P. R. Raithby, M. S. Khan,
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J. L. Bre´das, Synth. Met., 1996, 81, 179.
Unlike many of the phosphine-stabilised ‘rigid-rod’ poly-
mers 3 is soluble in a range of organic solvents. Therefore, it has
been possible to run a series of electronic spectra to observe the
shift in the absorption consistent with the greater delocalisation
of electron density through the extended p-system along the
polymer chain. In the free ligand, HC·CC6H2Me2C·CH, two
strong absorptions are observed at lmax = 263.8 nm (e = 1.9 3
104 dm3 mol21 cm21) and lmax = 273.3 (2.31 3 104) in the UV
region.
For
the
precursor
complex
trans-
[Pt(NC5H4CHBun ) Cl2] 1 one broad absorption is observed at
2 2
lmax = 252.5 nm (e = 9.39 3 103 dm3 mol21 cm21), while in
2 2
the alkynyl-substituted monomer [Pt(NC5H4CHBun ) -
(C·CPh)2] 2a the absorption is slightly shifted to lmax = 281.0
nm (e = 3.53 3 104 dm3 mol21 cm21). In contrast, for the
polymer there is a considerable shift in absorption to
lmax = 342.2 nm (e = 2.92 3 104 dm3 mol21 cm21), again a
very broad band being observed. This shift in the position of the
absorption is consistent with the greater delocalisation along the
polymer chain. Similar shifts in the absorption spectra have
been observed previously for related systems.10
4 R. Nast, Coord. Chem. Rev., 1982, 47, 89; J. Manna, K. D. John and
M. D. Hopkins, Adv. Organomet. Chem., 1995, 38, 79.
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L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1996, 329;
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1996, 2393.
6 S. L. James, J. Lewis, P. R. Raithby and M. Younus, J. Organomet.
Chem., in the press.
We thank the EPSRC for support (to C. J. A. and S. L. J.), and
Dr J. E. Davies for assistance with X-ray data collection.
7 P.-C. Kong and F. D. Rochon, Can. J. Chem., 1978, 56, 441.
8 R. A. Mariezcurrena and S. E. Rasmussen, Acta Chem. Scand., 1973, 27,
2678; A. Sebald, C. Strader and B. Wrackmeyer, J. Organomet. Chem.,
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R. J. Puddephatt, Organometallics, 1989, 8, 2055.
9 A. J. Hodge, S. L. Ingham, A. K. Kakkar, M. S. Khan, J. Lewis,
N. J. Long, D. G. Parker and P. R. Raithby, J. Organomet. Chem., 1995,
488, 205.
Footnotes and References
* E-mail: prr1@cam.ac.uk
† 2a: IR n(C·C)/cm21 (CH2Cl2) 2102; m/z 807.8 (M+); 1H NMR (CDCl3)
d 9.31 (d, 2 H, J 6.73 Hz), 7.23 (m, 5 H), 7.03 (d, 2 H, J 6.79 Hz), 2.50 (qnt,
1 H), 1.2 (m, 18 H); 13C NMR (CDCl3) d 158.05 (py), 155.44 (py), 131.67
(arene), 127.8 (arene), 125.46 (arene), 124.6 (py), 119.2 (C·C), 100.13
(C·C), 45.73 (nonyl), 35.64 (nonyl), 29.59 (nonyl), 22.67 (nonyl), 13.9
(nonyl). 2b: IR n(C·C)/cm21 (CH2Cl2) 2102; m/z 835.7 (M+); 1H NMR
(CDCl3) d 9.32 (d, 2 H, J 6.72 Hz), 7.22 (d, 2 H, J 8 Hz), 7.01 (d, 2 H, J 6.8
10 W. Blau, H. J. Byrne, D. J. Cardin and A. P. Davey, J. Mater. Chem.,
1991, 1 245.
Received in Basel, Switzerland, 9th September 1997; 7/06586H
2156
Chem. Commun., 1997