Bis(β-diketonate) ligands for the synthesis of bimetallic complexes of TiIII, VIII, MnIII and FeIII with a triple-helix structure

Article abstract of DOI:10.1039/a702971c

Addition of the bis(β-diketone) ligand L [L = 1,3-bis(3-phenyl-3-oxopropanoyl)benzene] to a suitable source of M^III ions (M = Ti, V, Mn, Fe) in a L:M = 3:2 ratio gives the dinuclear products [M₂L₃], which have a triple-helical structure.

Full text of DOI:10.1039/a702971c

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Bis(b-diketonate) ligands for the synthesis of bimetallic complexes of TiIII, VIII,
MnIII and FeIII with a triple-helix structure
Vincent A. Grillo, Elisa J. Seddon, Craig M. Grant, Guillem Arom´ı, John C. Bollinger, Kirsten Folting and
George Christou*
Department of Chemistry and the Molecular Structure Center, Indiana University, Bloomington, IN 47405-4001, USA
Addition of the bis(b-diketone) ligand L [L = 1,3-bis(3-
phenyl-3-oxopropanoyl)benzene] to a suitable source of MIII
ions (M = Ti, V, Mn, Fe) in a L:M = 3:2 ratio gives the
dinuclear products [M2L3], which have a triple-helical
structure.
7.224(2) 2, 7.350(2) 3, 7.262(4) Å 4] and the molecules are in
a triple-helix conformation, as emphasized by the view along
the M···M vector (Fig. 2). The average ligand twist angles
(defined as the angles between the two M–M–C(methine)
planes for each ligand) are 42.8 1, 44.0 2, 47.4 3 and 40.8° 4.
The structural parameters show only the small differences
expected from varying the MIII ion and the presence in 3 of a
Jahn–Teller axial elongation along the O(3)–Mn(1)–O(35) and
O(8)–Mn(2)–O(40) axes. The metal geometries are essentially
octahedral. The series could undoubtedly be extended to other
MIII ions (e.g., CrIII, CoIII) and this is currently being explored.
The triple-helix structures of 1–4 with the ligand L22 are new
additions to the relatively small but growing family of dinuclear
metal complexes with a triple-helix structure, hitherto with
ligands other than b-diketonates.2,3,6,9,15–17
The use of oligopyridyl, oligo-2,2A-bipyridyl and related ligands
in transition-metal chemistry has been receiving a great deal of
attention in recent years.1–7 Their products with mononuclear
metal ions have displayed a variety of fascinating structures
such as double1,2,4,8 or triple helices,1,2,3,6,9 and ‘cylindrical’,10
‘capped’11 or ‘circular’12 architectures. As such, these ligands
have been amongst the central players in the supramolecular
chemistry field.
Bis(b-diketonate) ligands offer similar potential for the
preparation of supramolecular assemblies, and we herein report
the initial use of the ligand L for the synthesis of bimetallic
complexes of formula [M2L3] (M = TiIII, VIII, MnIII, FeIII) with
a triple-helix structure. Ligand L† was prepared from a Claisen
condensation employing dimethyl isophthalate and acetophe-
none in the presence of NaH, a method related to that in the early
literature of bis(b-diketonates).13 Addition of L to a convenient
source of MIII [MCl3(thf)314 (M = Ti, V), Mn(O2CMe)2·4H2O/
O
O
O
O
L
Detailed characterisation of 1–4 by a variety of spectroscopic
and physical methods is in progress. Preliminary electro-
chemical studies by cyclic voltammetry in dmf confirm that the
two MIII ions are interacting. The ‘richest’ CV scans belong to
1 and 2 which show very similar electrochemical behaviour
(Fig. 3). Both exhibit two pairs of closely spaced reversible
reductions: 21.076, 21.212 V (DE = 0.136 V) and 21.720,
NBun MnO4, Fe(ClO4)2·6H2O/air] in dmf or CH2Cl2 gave dark
4
coloured solutions from which could be isolated crystalline
[M2L3] (M = Ti 1, V 2, Mn 3, Fe 4) in 30–70% yields, followed
by recrystallisation from dmf–MeOH (1–3) or thf–Me2CO (4).‡
Complexes 1–4 are isostructural§ (Fig. 1) and consist of two
six-coordinate MIII ions chelated and bridged by three L22
groups. The M···M separations are very similar [7.222(2) 1,
O(12)
O(40)
O(68)
Mn(2)
O(31)
O(12)
O(36)
O(36)
O(7)
O(64)
O(8)
O(35)
O(8)
O(40)
O(59)
O(3)
O(35)
O(7)
O(63)
O(68)
O(64)
O(63)
Mn(1)
O(3)
O(59)
O(31)
Fig. 2 A view down the Mn···Mn vector of 3 emphasizing the triple-helical
Fig. 1 The structure of [Mn2L3] 3; complexes 1, 2 and 4 are isostructural
conformation of the molecule
Chem. Commun., 1997
1561

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C72H48O12V2·0.72 MeOH, Mr = 1207.06 (excl. solv), monoclinic, space
group C2/c, a = 22.982(4), b = 17.906(3), c = 18.057(3) Å, b =
127.09(1)°, U = 5945.7 Å3, Z = 4, T = 106 K, m = 3.829 cm21, 3038
reflections with F > 3s(F), R(F) = 0.0481, Rw(F) = 0.0510. 3·CH2Cl2:
C73H50O12Cl2Mn2, Mr = 1300.0, triclinic, space group P1, a = 15.682(3),
b = 16.850(4), c = 13.843(3) Å, a = 105.63(1), b = 102.92(1), g =
113.93(1)°, U = 2980.5 Å3, Z = 2, T = 102 K, m = 5.806 cm21, 8025
200.0
150.0
100.0
50.0
¯
reflections with F > 3s(F), R(F)
= 0.0657, Rw(F) = 0.0589. 4·thf:
¯
C76H56O13Fe2, Mr = 1293.00, triclinic, space group P1, a = 16.151(5), b
= 16.982(6), c = 11.817(4) Å, a = 108.50(2), b = 103.54(2), g =
87.24(2)°, U = 2987.0 Å3, Z = 2, T = 103 K, m = 5.561 cm21, 4128
00.0
i
reflections with F > 3s(F), R(F)
182/522.
= 0.0911, Rw(F) = 0.0835. CCDC
–50.0
–100.0
–150.0
–200.0
1 J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995.
2 C. Piguet, G. Bernardinelli, B. Bocquet, A. Quattropani and A. F.
Williams, J. Am. Chem. Soc., 1992, 114, 7440; C. Piguet, J.-C. G.
Bu¨nzli, G. Bernardinelli, G. Hopfgartner and A. F. Williams, J. Am.
Chem. Soc., 1993, 115, 8197; C. Piguet, G. Bernardinelli, B. Bocquet,
O. Schaad and A. F. Williams, Inorg. Chem., 1994, 33, 4112.
3 M.-T. Youinou, R. Ziessel and J.-M. Lehn, Inorg. Chem., 1991, 30,
2144.
4 T. M. Garrett, U. Koert, J.-M. Lehn, A. Rigault, D. Meyer and J. Fischer,
J. Chem. Soc., Chem. Commun., 1990, 557; J.-M. Lehn, A. Rigault, J.
Siegal, J. Harrowfield, B. Chevrier and D. Moras, Proc. Natl. Acad. Sci.
USA, 1987, 84, 2565; W. Zarges, J. Hall, J.-M. Lehn and C. Bolm, Helv.
Chim. Acta, 1991, 74, 1843.
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1985, 107, 6540.
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Chem., 1988, 27, 4499; S. Ferrere and C. M. Elliot, Inorg. Chem., 1995,
34, 5818.
7 K. T. Potts, K. A. Gheysen Raiford and M. Keshavarz-K, J. Am. Chem.
Soc., 1993, 115, 2793.
8 R. Chotalia, E. C. Constable, M. Neuburger, D. R. Smith and M.
Zehnder, J. Chem. Soc., Dalton Trans., 1996, 4207; C. Piguet, G.
Hopfgartner, B. Bocquet, O. Schaad and A. F. Williams, J. Am. Chem.
Soc., 1994, 116, 9092.
1.50
0.50
–0.50
E / V
–1.50
–2.50
–2.00
1.00
0.00
–1.00
Fig. 3 Cyclic voltammogram at 100 mV s21 for complex 2 in dmf at a glassy
carbon electrode and with NBun4PF6 as supporting electrolyte
21.900 V (DE = 0.180 V) for 1 and 21.104, 21.240 V (DE
= 0.136 V) and 21.840, 22.000 V (DE = 0.160 V) for 2 vs.
SCE. In addition, for both complexes, there is a less well
resolved pair of oxidation processes: +0.016, +0.092 V for 1
(DE = 0.076 V) and +0.808, +0.884 V for 2 (DE = 0.080 V).
The large DE values are indicative of intramolecular inter-
actions between the two MIII ions. Complex 4 shows only a
single pair of reversible reductions, at 20.460 and 20.584 V.
Complex 3 shows a broad, quasi-reversible reduction process at
20.018 V (Epc 2 Epa = 0.520 V), with an additional
irreversible oxidation at approximately +1.238 V. For all four
species, additional reductions are observed at < 22.0 V. The
redox behaviour of 1–4 is related to that of the corresponding
mononuclear M(dbm)3 (dbm = anion of dibenzoylmethane),
which exhibit single redox processes at similar processes to 1–4.
Variable-temperature magnetic susceptibility studies on 1–4 are
currently in progress to quantitate the strength of intramolecular
interactions within these molecules.
9 R. Kra¨mer, J.-M. Lehn, A. De Cian and J. Fischer, Angew. Chem., Int.
Ed. Engl., 1993, 32, 703.
10 P. Baxter, J.-M. Lehn, A. De Cian and J. Fischer, Angew. Chem., Int. Ed.
Engl., 1993, 32, 69.
11 E. Leize, A. Van Dorsselaer, R. Kra¨mer and J.-M. Lehn, J. Chem. Soc.,
Chem. Commun., 1993, 990; M. Albrecht, S. J. Franklin and K. N.
Raymond, Inorg. Chem., 1994, 33, 5785.
This work was supported by the National Science Founda-
tion.
12 B. Hasenknopf, J.-M. Lehn, B. O. Kneisel, G. Baum and D. Fenske,
Angew. Chem., Int. Ed. Engl., 1996, 35, 1838.
13 D. F. Martin, M. Shamma and W. C. Fernelius, J. Am. Chem. Soc., 1958,
80, 4891.
Footnotes and References
14 L. E. Manzer, Inorg. Synth., 1982, 21, 138.
* E-mail: christou@indiana.edu
15 T. B. Karpishin, T. D. P. Stack and K. N. Raymond, J. Am. Chem. Soc.,
1993, 115, 6115; B. Kersting, M. Meyer, R. E. Powers and K. N.
Raymond, J. Am. Chem. Soc., 1996, 118, 7221.
16 E. J. Enemark and T. D. P. Stack, Angew. Chem., Int. Ed. Engl., 1995,
34, 996.
17 M. Albrecht and S. Kotila, Angew. Chem., Int. Ed. Engl., 1995, 34,
2134; M. Albrecht and S. Kotila, Chem. Commun., 1996, 2309; M.
Albrecht, H. Rottele and P. Burger, Chem. Eur. J., 1996, 2, 1264.
† Selected spectroscopic data for L: 1H NMR (CD2Cl2, 500 MHz): d 6.98
(s, 2 H), 7.53 (t, J 8 Hz, 4 H), 7.61 (t, J 8 Hz, 2 H), 7.66 (t, J 8 Hz, 1 H), 8.04
(d, J 8 Hz, 4 H), 8.19 (d, J 8 Hz, 2 H), 8.60 (s, 1 H); EI-MS (M+) 370.1
(C24H18O4 requires 370.1).
‡ The complexes analysed satisfactorily.
§ Crystal data 1: C72H48O12Ti2, Mr = 1200.90, monoclinic, space group
C2/c, a = 22.924(3), b = 17.721(2), c = 18.870(2) Å, b = 129.60(1)°, U
= 5906.7 Å3, Z = 4, T = 106 K, m = 3.293 cm21, 1689 reflections with
F > 4s(F), R(F)
=
0.0645, Rw(F2)
=
0.1030. 2·0.72 MeOH:
Received in Cambridge, UK, 1st May 1997; 7/02971C
1562
Chem. Commun., 1997