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Extremely Long-Wavelength Charge-Transfer Absorptions of Binuclear Complexes with Azo-Modified 2 2-Bipyridyl Ligands.

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[I] W. Klaui, A. Muller, M. Scotti, J . Organomef. Chem. 253 (1983) 45.
[2] W. Klaui, J. Okuda, M. Scotti, M. Valderrama, J . Organomet. Chem. 280
(1985) C26.
[3] W. Klaui, A. Muller, unpublished results.
[4] Experimental procedure: 2a: A solution containing NaL (131 mg, 0.28
mmol) in 5 m L of chloroform was added to a suspension of
[IRh(C0)2CIl?](35 mg, 0.09 mmol) in 25 mL of chloroform. The reaction
mixture was stirred for 24 h at 25°C and then evaporated in vacuum,
and the residue was washed several times with distilled water. After drying in high vacuum, the product was recrystallized from dichloromethane. Yield 66 mg (61%) yellow, air-stable crystals.-'H-NMR (100
MHz, CDCI3j: 6=3.75, (virt. q, 18H, OCH,), 5.07 (s, 5 H , CSH5).--IR
(KBr): 1838 ( s , v(CO)j, II15 c m - ' ( s , v(P=O)).--M, ( o m . CH,CI,),
I184 (calcd. 1192).-Correct
C,H analysis.-2b:
Prepared from
[(Rh(CO),CIJ,] (78 mg, 0.20 mmol) a n d NaL (246 mg, 0.44 mmol) in 30
m L of hexane and worked-up as described above. Yield 214 mg (78%)
yellow, air-stable crystals.-'H-NMR (100 MHz, CDCI?): 6 = 1.26 (t,
I8H, CH,), 4.10 (m, 12H, OCHI), 5.00 (s, 5H, C5H5).-IR(KBr): 1835
(s, v(COj), 1120 c m - ' ( s , v(P=O)).-M,
( o m . CH,CI,) 1342 (calcd.
1360).-Correct C,H analysis.
[5] 0. S. Mills, J . P. Nice, J . Organomet. Chem. I0 (1967) 337.
[6] F. A. Cotton, Chem. SOC.Rev. 4 (1975) 27.
[7] J. G. Norman, Jr., H. G. Kolari, J. Am. Chem. SOC.100 (1978) 791.
[8] R. Hill, S. A. R. Knox, J. Chem. Soc. Dalton Trans. 197s. 2622.
191 1. Fischer, K. Hildenbrand, E. Koerner von Gustorf, Angew. Chem. 87
(1975) 35; Angew. Chem. I n ( . Ed. Engl. 14 (1975) 54.
[ l o ] S:I. Murahashi, T. Mizoguchi, T. Hosokawa, 1. Moritani, Y. Kai, M.
Kohara, N. Yasuoka, N. Kasai, J. Chem. Sue. Chem. Commun. 1974,
[ I I] H. G. Schuster-Woldan, F. Basolo, J . Am. Chem. Soc. 88 (1966) 1657.
[I21 See, for example, F. Basolo, R. G. Pearson: Mechanismen in der anorganischen Chemie, Thieme, Stuttgart 1973, chapter 7. I : F. Basolo, Inorg.
Chim. Acta 50 (1981) 65; J. A. S. Howell, P. M. Burkinshaw, Chem. Reu.
83 (1983) 557, section X.
1. la-d
2. 2a. d
Table I. Long-wavelrngth absorption maxima A [nm] and reduction potentials Ercd[V vs. SCE] [a] of the ligands 1 and 2 and their binuclear d h metal
- 0.07
- 0.06
- 0.03 [dl
- 0.96
+ 0.27 [d]
[a] Measurements in dimethylformamide/O. 1 M BuaN'ClO?, cyclovoltammetry at a glassy carbon electrode. [b] Irreversible step. [c] Measurements not
possible because of insolubility. [d] Measurements in acetonitrile/O.l M
B u ~ N " C I O ~[el
. Absorption maximum at 952 nm in isooctane.
The long-wavelength absorption maxima, which, for the
ligands, are already in the visible region due to n-n* transitions and lie between 550 and 700 nm for the mononuclear complexes,@' reach the NIR region in the binuclear
complexes (Fig. 1, Table I).
Extremely Long-Wavelength Charge-Transfer
Absorptions of Binuclear Complexes with
Azo-Modified 2,2'-Bipyridyl Ligands**
By Stephan Kohlmann, Sylvia Emst, and
Wolfgang Kaim*
The controlled synthesis of complexes with very longwavelength charge-transfer absorptions is of interest owing
to their potential applications in the chemical use of solar
energy, since a major fraction of the solar radiation that
reaches the earth's surface is in the near-infrared (NIR).'']
In view of the advantageous photophysical properties of
complexes containing a-diimines of the 2,2'-bipyridine
(bpy) type,''] we have modified this system by introducing
coordinatively bifunctional n-acceptor moieties, which
should allow coordination of more than one n-electronrich metal fragment and thus produce particularly strong
We chose the bridging bis(che1ate) ligands 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine 1L41 and azo-2,2'-bipyridine 2,15'
which incorporate the n-electron-deficient azo function
-N=N-,l6] and report here the binuclear complexes l a - d
and 2a, d containing low-spin d6 metal-complex fragments"] (see Table I).
Priv.-Doz. Dr. W. Kaim, Dip].-Chem. S. Ernst,
Dip1.-Chem. S. Kohlmann
Institut fur Anorganische Chemie der Universitlt
Niederurseler Hang, D-6000 Frankfurt am Main 50 (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, the Hermann-Willkomm-Stiftung, the
Flughafen Frdnkfurt/Main AG, the BASF AG, the Degussa AG, and
the Karl-Winnacker Stiftung of the Hoechst AG. We thank Dip1:Chem.
D. Ventur and Prof. Dr. K . Wieghardt (Bochum) for absorption measurements in the near-IR.
0 VCH Verlogsgesrllschaft mbH, 0-6940 Wrinheim, 1985
Fig. I . Absorption spectra of the ligand 2 ( . - . ) , the mononuclear complex
[ 2 Mo(CO),] (---), and the binuclear complex [Z{MO(CO),)~]
2a (-)
in toluene (arbitrary intensity units). Solutions of the mononuclear complex are
deep blue, solutions of 2a have a faint green color because of the absorption
gap in the visible (band tails from the NIR and UV regions).
Both the extinction coefficients ( E = 104-105 M - ' cm-')
and the characteristic solvent dependence (negative solvat o c h r ~ r n i s m ~indicate
metal-to-ligand charge-transfer
(MLCT) transitions; ESR studies of reduced species'lol
confirm the n* character of the lowest unoccupied molecular orbital (LUMO) for the complexes l a , d .
The extremely low energy levels of the complex LUMOs
are illustrated by electrochemical data (Table 1). The binuclear complexes l a , b , d, and 2a are reduced at ca. 0 V relative to the saturated calomel electrode, and the binuclear
ruthenium(i1) complex 2d is an even stronger acceptor
than tetracyanoethylene (TCNE, Ered= 0.24 V" 'I) and
thus clearly superior to all known polyazine ruthenium(I1)
The redox potentials suggest how to obtain further complexes with even smaller energy differences between the
frontier orbitals and correspondingly longer-wavelength
charge-transfer absorptions. On the one hand, the ligands
must be easily reducible, while, on the other hand, the oc-
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Angew. Chem. Int. Ed. Engl. 24 (1985) No. 8
cupied metal d levels should be energetically destabilized
by the loss of ligands capable of back-bonding. In the
complexes 1 and 2, this strong charge-transfer interaction
is possible through coordination to the azo nitrogen centers; chelate coordination via the basic but less strongly
back-bonding 2-pyridyl substituents stabilizes the complex
toward dissociation.
The steric crowding in the coordination-induced trans
conformation of the ligand 2 has several interesting consequences. Thus, mononuclear[81but no binuclear complexes
of this ligand could be obtained containing tetracarbonyltungsten or bromo(tricarbony1)manganese; examination of
models as well as the marked low-field 'H-NMR shift for
the pyridyl protons H-3 in 2aL7Iindicate non-bonded interactions between these protons and the equatorial substituents L in binuclear complexes with coplanar conformation of the ligand 2.
Also remarkable is the similarity of the complexes l a
and 2a and the fact that the n-acceptor level of 2d is lower
than that of I d even though the ligand 1 is more easily reduced than 2 (Table 1). One reason is that the smaller system 2 exhibits a stronger reaction upon N-c~ordination;''~'
on the other hand, it is also important to note the relative
proximity of the two metal centers in binuclear complexes
of 2. Application of the model of Richardson and Taz~be"~'
to this case yields an even smaller metal-metal distance
(ca. 460 pm) than for N,-bridged binuclear systems
(d,-r4 = 500 pm[''?l).
Received: April 16, 1985 [ Z 1268 IE]
German version: Angew. Chem. 97 (1985) 698
CAS Registry numbers:
la, 97374-20-4: lb, 97374-21-5; lc, 97374-22-6; Id, 97374-24-8; 2a, 9737425-9; 2d, 97374-27-1; [(thf)W(CO)j], 36477-75-5; BrMn(CO)I, 14516-54-2;
crs-[Ru(bpy),C12], 19542-80-4; tetracarbonyl(norbornadiene)molybdenum,
I ? 146-37-1.
from 1 and 2 , respectively, and czs-[Ru(bpy),C12].2 H 2 0 in refluxing water/ethanol (2 : I). The products were precipitated as the tetrakis(hexafluorophosphates) and purified by column chromatography (AlZO1,
CH,CN). The analytically pure complexes Id and 2d were obtained as
the tetrahydrates in 23 and 5% yield, respectively.
Mononuclear complexes of 1 and 2 were obtained by corresponding
reactions of the starting materials in a 1 : 1 ratio: S. Kohlrnann, Diplomarbeit. Universitat Frankfurt 1985.
Cf. H. tom Dieck, 1. W. Renk, Chem. 5er. I04 (1971) 110; D. M. Manuta, A. J. Lees, Inorg. Chem. 22 (1983) 3825.
W. Kaim, S. Ernst, S. Kohlmann, Chem. Phys. Lett.. in press; Polyhedron. in press.
M. E. Peover, Trans. Faraday SOC.58 (1962) 2370.
Cf. E. A. Seddon, K. R. Seddon: The Chemistry of Ruthenium. Elsevier,
Amsterdam 1984, p. 414f. and 1173f.
Cf. Hiickel MO perturbation calculations: W. Kaim, S. Kohlmann, unpublished results.
D. E. Richardson, H. Taube, J. A m . Chem. Sue. 105 (1983) 40;
=200 pm.
Three-Phase Synthesis of Oligonucleotides**
By Hartrnut Seliger* and Kailash Chand Gupta
In the synthesis of oligonucleotides via phosphite triesters"] using the solid-phase method,[*]the nucleoside N , Ndimethylpho~phoramidites~~~
activated by tetrazole have
proved particularly useful as highly reactive intermediates.
However, since they are relatively unstable, we have investigated polymeric reagents of the nucleoside phosphoramidite type. We describe here their preparation and their application to the synthesis of oligonucleotides.
The polystyrene 3,substituted with N-ethylaminomethyl
groups, was prepared from the commercially available
CHzCl + HZP\C2H5
@- I l O H + (H3CO)3Si(CH2)3N-NH
111 I. R. Bolton, Science 202 (1978) 705: Inorganic Chemistry: Toward the
27sf Cenfury, ACS Symp. Ser. 211 (1983) 3.
121 a) V. Balzani, F. Bolletta, M. T. Gandolfi, M. Maestri, Top. Curr. Chem.
76 (1978) 1: b) K. Kalyanasundaram, Coord. Chem. Reu. 46 (1982) 159.
131 a) D. P. Rillema, R. W. Callahan, K. B. Mack, Inorg. Chem. 21 (1982)
2589, 3849; b) mononuclear Ru" complexes absorbing at long wavelengths: P. Belser, A. von Zelewsky, Helu. Chim. Act0 63 (1980) 1675: R.
A. Krause, K. Krause, Inorg. Chem. 23 (1984) 2195.
[41 a) Synthesis of the ligand: F. Dallacker, Monatsh. Chem. 91 (1960) 294;
b) metal halide complexes of the ligand: K. Gustav, C. J. Schmitt, 2.
Chem. 9 (1969) 32: c) pentacarbonyl metal(o) complexes of unsubstituted 1.2,4,S-tetrazine: M. Herberhold, M. Suss-Fink, 2. Naturforsch.
5 3 1 (1976) 1489.
151 a) Synthesis of the ligand: A. Kirpal, L. Reiter, Ber. Drsch. Chem. Ges. 60
(1927) 664; b) metal halide complexes of the ligand: A. Baldwin, A. B.
P. Lever, R. V. Parish, Inorg. Chem. 8 (1969) 107; P. J. Beadle, R. Grzeskowiak, J. Chem. Soc. A 1970, 305.
"4 For the use of the azo group in classical complex formation, see F. Umland: Theorie und prakfische Anwendung oon Komplexbildnern, Akademische Verlagsgesellschaft, Frankfurt am Main 1971.
171 l a and 2a were prepared by reaction of excess tetracarbonyl(norbornadiene)molybdenum with 1 and 2, respectively, in toluene. After removal
or the solvent, olefin, and olefin complex in vacuum (and purification of
2a by column chromatography on florid), the products were recrystallized from toluene/hexane. Yields: 76% ( l a ) and 5% (2a), dark crystals,
correct elemental analysis. IR (THF; v(C0) [cm-'1): l a : 1995, 1940 (br),
1875: ?a: 1985, 1945, 1908, 1872. 'H-NMR (CDCI,, 270 MHz): l a :
6=7.62 (dd, H-5), 8.08 (dd, H-4), 8.81 (d, H-3), 9.06 (d, H-6); 'J,.,=8
Hz, 'J,i=7 Hz, *J,.,=5 Hz: 2a:S=7.53 (dd, H-5), 7.98(ddd, H-4),9.04
(dd, H-6). 9.17 (d, H-3); *J3,4=8.6 Hz, 'Jq.s=7.3 Hz, ' J 5 6 = 5 . 5 Hz,
'J4.,,= 1.5 Hz.- l b was prepared from photochemically generated
[(thf)W(CO),] and 1 at 0°C in tetrahydrofuran. The unstable complex
was purified as for l a ; yield 3%; dark crystals. IR (THF; v(C0) [cm- 'I):
1979, 1935 (br), 1872.- l c was prepared from BrMn(CO)S and 1 in toluene and purified by column chromatography on f l o r i d ; yield 35%,
dark crystals, correct elemental analysis. 1R (CH,C12; v(C0) [cm- 'I):
2022, 1965, 1945. 'H-NMR (CDCI,, 270 MHz): S=7.78 (H-5), 8.20 (H4), 8.84 (H-3), 9.14 (H-6), all signals broad.- Id and 2d were prepared
Angew. Chem I n t . Ed. Engl. 24 (198s) No. 8
Scheme I. 1'= Merrilield resin, P'=silica gel; DMTr=dimethoxytrityl. a.
B=Nh-Benzoyladenin-9-yl; b, B=N4-benzoylcytosin-I-yl: c , B= N2-isobutyrylguanin-9-yl; d , B = thymin-1-yl.
[*I Prof. Dr. H. Seliger, Dr. K. C. Gupta
Sektion Polymere der Universitat
Oberer Eselsberg, D-7900 Ulm (FRG)
[**I Carrier Syntheses, Part 1 I . This work was supported by the Deutsche
Forschungsgemeinschaft. K . C . G . thanks the Deutscher Akademischer
Austauschdienst for a fellowship.-Part 10: [16].
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binucleata, extremely, azo, long, transfer, modified, bipyridyl, complexes, absorption, ligand, wavelength, charge
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