Bimetallic reactivity. Preparations, properties and structures of complexes formed by unsymmetrical binucleating ligands bearing 4- and 6-coordinate sites supported by alkoxide bridges

Article abstract of DOI:10.1039/b103164n

Four binucleating ligands which potentially could provide bimetallic complexes bearing 5- and 6-coordinate sites have been prepared. These ligands, which have alkoxide bridging groups, can be regarded as more elaborate versions of binucleating ligands which have tridentate chelates on each side of the alkoxy bridge. Unlike these previous, less complex ligands, the present series of binucleating ligands have a strong tendency to form oligomers. This has been demonstrated with a series of crystal structures of copper(II) complexes of these ligands. It is probable that oligomers are formed because of the high flexibility of the present ligands. The work serves to illustrate the limits of binuclear ligand design and suggests that, with alkoxide ligand bridges, rigidity is necessary in order to obtain bimetallic complexes with extended multidentate binucleating ligands. One of the ligands gives a mixed valence Mn(II)-Mn(IV) complex after O₂ oxidation of a di-Mn(II) precursor.

Full text of DOI:10.1039/b103164n

View Article Online / Journal Homepage / Table of Contents for this issue
Bimetallic reactivity. Preparations, properties and structures of
complexes formed by unsymmetrical binucleating ligands bearing
4- and 6-coordinate sites supported by alkoxide bridges
Christopher Incarvito,a Matthew Lam,a Brian Rhatigan,a Arnold L. Rheingold,*a C. Jin Qin,b
Anna L. Gavrilovab and B. Bosnich*b
a Department of Chemistry and Biochemistry, University of Delaware, Newark,
Delaware 19716, USA
b Department of Chemistry, The University of Chicago 5735 South Ellis Avenue, Chicago,
Illinois 60637, USA
Received 4th April 2001, Accepted 5th September 2001
First published as an Advance Article on the web 14th November 2001
Four binucleating ligands which potentially could provide bimetallic complexes bearing 5- and 6-coordinate sites
have been prepared. These ligands, which have alkoxide bridging groups, can be regarded as more elaborate versions
of binucleating ligands which have tridentate chelates on each side of the alkoxy bridge. Unlike these previous, less
complex ligands, the present series of binucleating ligands have a strong tendency to form oligomers. This has been
demonstrated with a series of crystal structures of copper() complexes of these ligands. It is probable that oligomers
are formed because of the high flexibility of the present ligands. The work serves to illustrate the limits of binuclear
ligand design and suggests that, with alkoxide ligand bridges, rigidity is necessary in order to obtain bimetallic
complexes with extended multidentate binucleating ligands. One of the ligands gives a mixed valence
Mn()–Mn() complex after O2 oxidation of a di-Mn() precursor.
whereas either site of, 4, can support Co3ϩ, when one site is
oxidized, the other becomes deactivated to oxidation. The
major source of deactivation appears to be mechanical coup-
ling, a conformational effect which causes one site to be
Introduction
The respiratory protein, hemerythrin,1 has as its active site two
contiguous Fe2ϩ ions bridged by a hydroxide and two carboxyl-
ates, one iron is 5-coordinate, the other is 6-coordinate. The
remaining ligands are imidazoles, 1. Dioxygen adds to the
deactivated because of conformational rearrangements which
ensue as a consequence of metal oxidation in the other site. We
5-coordinate Fe2ϩ ion and is converted to hydroperoxide after
have shown that mechanical coupling can amount to 18 kcal
two electrons, one from each of the iron atoms, are transferred
molϪ1 in certain cases.3 Thus the design of binucleating ligands
and the OH proton is delivered to the peroxide, 2.2 The proton-
coupled electron transfer process, 1
one-site addition two-metal oxidation reaction which, as far as
we are aware, has not been reproduced in a synthetic system.
which attempt to reproduce the function of hemerythrin must
2, is an example of a
minimize mechanical coupling between sites. It is probable that
mechanical coupling is particularly acute in macrocyclic sys-
tems such as 3 and 4 because the degrees of freedom are
reduced compared to open binucleating ligands.
Our previous work on the two bimetallic complex types, 3
and 4, has revealed certain deactivating factors, peculiar to
bimetallic complexes, which control the accessibility of the
higher oxidation states.3 The two monometallic parts of, 3,
namely the 6-coordinate and 5-coordinate sites, readily support
the Co3ϩ state but when these two sites are incorporated into the
bimetallic complex, 3, the complex is inert to oxidizing agents
which would oxidize the metals in the monometallic parts. This
result is independent of chelate ring sizes shown by loops A and
B, 3. The complex, 4, is somewhat more reactive, in this case the
Co2ϩ ion in the 6-coordinate site is readily oxidized but, once
this oxidation is achieved, the Co2ϩ in the 5-coordinate site is
not readily oxidized even in the presence of added ligands.
Similarly, when the Co2ϩ in the 5-coordinate site is oxidized, the
6-coordinate Co2ϩ ion becomes inert to oxidation. Thus,
The other feature of hemerythrin is the presence of 6- and
5-coordinate sites. Thus in order to reproduce the binding site
and to direct the substrate to the 5-coordinate site, binucleating
ligands should incorporate this feature. Finally, an exogenous
OH bridge would provide a proton for stabilizing the peroxide
group. As yet, no such binucleating ligands incorporating these
features have been reported.
Binucleating ligands which provide an alkoxide bridge
flanked by multidentate ligands have been the subject of exten-
sive study.4–15 These ligands are usually symmetrical systems of
3478
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103164n

View Article Online
the type, I, where the two metals are coordinated on each side
of the alkoxide bridge, and the coordination number is satisfied
by exogenous bridging ligands such as acetate, hydroxide, azide
or halides. Given this known chemistry, it seemed attractive to
prepare unsymmetrical alkoxide bearing binucleating ligands
which, upon coordination and the addition of an exogenous
bridging ligand, would provide 6- and 4-coordinate metal sites.
The preparation of four such ligands, II, III, IV, V, is
described here. They were expected to form the generic com-
plexes of the type, 5. It will be noted that three variations of
these ligands are introduced according to the number of methyl-
ene groups linking the alcohol bearing carbon atom and the
nearest flanking nitrogen atom. Molecular models suggest that
the most stable combination is when there are two pairs of
methylene groups in these positions, II and III. Such ligands
were expected to bind in the manner illustrated in, 5, strain-
lessly. The other ligands, IV and V, were expected to introduce
strain in the topology, 5, but simpler versions of these two lig-
ands were found to form stable complexes.4–14 The benzyl group
serves no structural purpose, its presence makes the syntheses
easier. These ligands provided unexpectedly complex metal
compounds. We report on these here.
Experimental
General procedures and methods
All reagents were obtained from commercial suppliers and were
used without further purification. NMR spectra were taken on
Bruker DRX400 or Bruker DMX500 spectrometers. Conduct-
ance measurements were made at 25 ЊC with a YSI Model 35
conductance meter on 1 mM solutions of the complexes, using
dry solvents. The UV/VIS solution spectra were obtained on a
Perkin-Elmer Lambda 6 spectrophotometer using spectral
grade solvents. Infrared spectra were recorded on a Nicolet
20SXB FTIR spectrometer using Nujol mulls on NaCl discs.
Magnetic susceptibilities were measured on powdered solid
samples using a Johnson–Mathey–Evans magnetic suscepti-
bility balance. Elemental analyses were performed by Desert
Analytics, Arizona. Melting points are uncorrected. Ethanol
refers to absolute ethanol. Acetonitrile was dried over CaH2,
THF was dried over potassium–benzophenone ketyl and ethyl
ether was dried over sodium–benzophenone ketyl. TLC was
carried out on precoated silica gel (Whatman, PE SIL G/UV)
or aluminium oxide (J. T. Baker, aluminium oxide IB-F). Silica
gel 60 Å (Merck, 230–400 mesh) or aluminium oxide 58 Å
(Aldrich, activated, basic, 150 mesh) were used for flash
chromatography.
Bis-pyridin-2-ylmethylamine (VII). The imine VI (27.4 g,
138 mmol) was dissolved in CH3CN (250 mL) and was cooled
to Ϫ5 ЊC. Glacial acetic acid (8 mL, 138 mmol) was added in
one portion. To the resulting clear yellow solution was added a
suspension of sodium borohydride (10.7 g, 276 mmol) in abso-
lute ethanol (300 mL) over a period of 1 h at Ϫ5 ЊC. Vigorous
bubbling occurred during the addition, accompanied by the
precipitation of a white solid. The color of the solution
changed from yellow to bright red by the end of addition. After
stirring for 18 h at room temperature, the reaction mixture was
quenched with 12 M HCl (160 mL, 1.9 mol), and was heated at
60 ЊC for 2 h, until no more gas was evolved. The white precipi-
tate was filtered, the filtrate was concentrated in vacuo, and then
redissolved in water (70 mL). The resulting yellow aqueous
solution was basified by addition of solid NaOH pellets (64 g,
1.6 mol) with efficient cooling. A red oil separated immediately.
It was extracted with ether (3 × 400 mL). The ether extracts
were dried over solid NaOH. Evaporation of the solvent
Ligand synthesis
Pyridin-2-ylmethylpyridin-2-ylmethyleneamine (VI). To
a
suspension of anhydrous MgSO4 (82 g, 683 mmol) in CH2Cl2
(160 mL) was added 2-pyridinecarboxaldehyde (15 g, 138 mmol),
followed by 2-(aminomethyl)pyridine (14.8 g, 138 mmol). The
mixture became warm and the color changed to yellow. After
being stirred for 3 h at room temperature, the suspension
was filtered, washed with CH2Cl2 (200 mL), and the solvent was
removed under vacuum. A yellow oil (27.4 g, 100%) was
1
obtained. H NMR (400 MHz, C6D6): δ 8.59 (s, 1H), 8.47
(m, 2H), 8.11 (d, 1H, J = 7.9 Hz), 7.16 (d, 1H, J = 10.1 Hz),
7.09–6.99 (m, 2H), 6.61 (m, 2H), 4.89 (s, 2H).
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
3479

View Article Online
yielded 30 g of a red oil. Upon distillation, the pure product was
obtained as a yellow oil (20 g, 73%). Bp 130–135 ЊC (0.1 Torr).
Lit. 148–149 ЊC (1.05 Torr).16 1H NMR (500 MHz, C6D6):
δ 8.46 (d, J = 7.5 Hz, 2H), 7.07 (m, 4H), 6.62 (m, 2H), 3.90
(s, 4H), 2.52 (s, br, 1H).
the white suspension was brought to room temperature, and
was stirred for 18 h. Then 12 M HCl (50 mL) was added, and
the mixture was stirred for 30 min at 50 ЊC. The white granular
precipitate was filtered off, washed with water, and the filtrate
was evaporated in vacuo. The white residue was dissolved in
15% NaOH (330 mL). A yellow oil separated. It was extracted
with CH2Cl2 (5 × 200 mL), dried over anhydrous Na2SO4,
filtered, and evaporated in vacuo to yield the product (12.62 g,
91%) as a yellow oil. 1H NMR (500 MHz, C6D6): δ 8.45 (d, 2H,
J = 4.0 Hz), 7.33 (m, 4H), 7.20–7.06 (m, 5H), 6.60 (m, 2H), 3.85
(s, 4H), 3.56 (s, 2H), 2.67–2.57 (dt, 4H, J = 37.5 Hz, J = 5.8 Hz).
2-[2-(Bis-pyridin-2-ylmethyl-amino)ethyl]phthalimide (VIII).
This compound was prepared using a modified literature pro-
cedure.17 Anhydrous K2CO3 (42 g, 304 mmol) and KI (1.5 g,
0.1 mmol) were suspended in fresh CH3CN (350 mL). The
amine, VII (18.3 g, 92 mmol) was added to this suspension,
followed by bromoethylphthalimide (25.6 g, 101 mmol). The
mixture was refluxed for 24 h, filtered and concentrated under
vacuum to yield a red oil. This red oil was dissolved in CH2Cl2
(200 mL), and was washed with saturated NaHCO3 solution
(3 × 200 mL) and with water (2 × 200 mL). Then the solvent
was evaporated in vacuo, and to the resulting dark oil was added
2 M HCl (140 mL). The aqueous solution was washed with
CH2Cl2 (5 × 60 mL), and then it was carefully basified with
solid sodium bicarbonate (60 g). An orange solid precipitated.
It was extracted into CH2Cl2 (4 × 100 mL), and concentrated
under vacuum to yield dark brown crystals. These were chrom-
atographed on 50 g of silica-gel (5% CH2Cl2 in ethyl acetate as
N-(4-Butenyl)phthalimide (XII). Was prepared as described
in the literature.18 The product was obtained as white crystals
1
in 85% yield. H NMR (400 MHz, CDCl3): δ 7.84 (dd, 2H,
J = 3.1 Hz, J = 5.4 Hz), 7.71 (dd, 2H, J = 3.0 Hz, J = 5.5 Hz),
5.85–5.75 (m, 1H), 5.09–5.01 (m, 2H), 3.78 (t, 2H, J = 9.2 Hz),
2.45 (m, 2H).
N-(3,4-Epoxybutyl)phthalimide (XIII). The olefin, XII (6.12 g,
31.7 mmol) was dissolved in chloroform (90 mL). m-Chloro-
perbenzoic acid (10.56 g, 57%, 34.9 mmol) was added to the
olefin solution. The reaction mixture was stirred for 18 h at
room temperature and was refluxed for 1 h. The solution was
cooled to room temperature and was washed successively with
5% Na2CO3 solution (100 mL), water (100 mL), 5% Na2SO3
solution (100 mL), 5% Na2CO3 solution (50 mL), and water
(50 mL). The chloroform fraction was dried over anhydrous
MgSO4, and was evaporated under vacuum to yield the pure
product as a white crystalline solid (6.46 g, 94%). Mp 84–85 ЊC.
Lit. mp 84–85 ЊC.19 1H NMR (500 MHz, CDCl3): δ 7.86
(dd, 2H, J = 2.8 Hz, J = 6.0 Hz), 7.72 (dd, 2H, J = 3.1 Hz, J =
5.5 Hz), 3.95–3.84 (m, 2H), 3.02–2.99 (m, 1H), 2.72 (t, 1H,
J = 4.5 Hz), 2.45 (dd, 1H, J = 2.5 Hz, J = 4.9 Hz), 2.03–1.97
(m, 1 H), 1.89–1.82 (m, 1H). 13C NMR (125 MHz, CDCl3):
δ 168.27, 133.98, 123.28, 50.14, 46.38, 35.13, 31.62.
1
eluant). A tan solid (23.19 g, 68%) was obtained. H NMR
(400 MHz, C6D6): δ 8.36 (d, 2H, J = 4.8 Hz,), 7.44 (dd, 2H,
J = 3.1 Hz, J = 5.4 Hz), 7.33 (d, 2H, J = 7.9 Hz), 6.96 (td, 2H,
J = 1.8 Hz, J = 7.6 Hz), 6.88 (dd, 2H, J = 3.0 Hz, J = 5.4 Hz),
6.53 (dd, 2H, J = 4.9 Hz, J = 7.3 Hz), 3.59 (t, 2H, J = 5.8), 2.75
(t, 2H, J = 5.8 Hz)
N,N-Bis(2-pyridylmethyl)ethane-1,2-diamine (IX). The pro-
tected amine VIII (23.19 g, 62.3 mmol) was dissolved in abso-
lute ethanol (80 mL), and was added to a solution of hydrazine
monohydrate (3.11 g, 62.3 mmol) in ethanol (60 mL). The sol-
ution was diluted with 110 mL of ethanol and was refluxed for
3 h. After 1 h of reflux, a white solid precipitated. The mixture
was concentrated under vacuum, and 2 M HCl (200 mL), fol-
lowed by 12 M HCl (8.5 mL) was added. A white solid separ-
ated immediately. The suspension was stirred for 2 h at 50 ЊC,
followed by 24 h at room temperature. Then it was filtered,
concentrated under vacuum, and dissolved in water (70 mL).
To this aqueous solution was added 15% aqueous NaOH
(200 mL). A red oil separated. It was extracted with CH2Cl2
(3 × 100 mL). The combined extracts were dried over Na2SO4,
filtered, and then were concentrated under vacuum to yield a
brown oil (15.2 g). Upon distillation, the product was obtained
as a pale-yellow oil (10.18 g, 68%). Bp 165–170 ЊC (0.1 Torr). 1H
NMR (400 MHz, C6D6): δ 8.47 (d, 2H, J = 4.6 Hz), 7.34 (d, 2H,
J = 7.6 Hz), 7.10 (m, 2H), 6.62 (m, 2H), 3.84 (s, 4H), 2.57 (t, 2H,
J = 5.9 Hz), 2.46 (t, 2H, J = 5.9 Hz). 13C NMR (125 MHz,
C6D6): δ 160.55, 149.36, 135.78, 122.89, 121.71, 60.77, 57.76,
40.22.
2-(4-{Benzyl[2-(bis-pyridin-2-ylmethylamino)ethyl]amino}-3-
hydroxybutyl)phthalimide (XIV). A mixture of the amine XI
(4.58 g, 13.8 mmol) and the epoxide XIII (3 g, 13.8 mmol) in n-
butanol (14 mL) was stirred at 100 ЊC for 8 h. Then the solvent
was removed in vacuo azeotropically with cyclohexane. The
resulting black oil was chromatographed on 140 g of silica-gel
with 5% triethylamine in CH2Cl2 as an eluant. The product was
1
obtained as a brown oil (6.2 g, 82%). H NMR (500 MHz,
C6D6): δ 8.48 (d, 2H, J = 5.0 Hz), 7.46 (m, 4H), 7.25 (td, 2H, J =
1.7 Hz, J = 7.8 Hz), 7.13 (m, 2H), 7.06–6.99 (m, 3H), 6.85 (dd,
2H, J = 3.0 J = 5.5 Hz), 6.65 (dd, 2H, J = 5.0 Hz, J = 7.0 Hz),
4.87 (s, 1H, br), 4.04 (m, 1H), 3.84–3.50 (m, 6H), 3.49 (d, 1H,
J = 13.5 Hz), 3.09 (s, 1H, J = 13.5 Hz), 2.68 (m, 2H), 2.38 (m,
1H), 2.25 (m, 2H), 2.08 (dd, 1H, J = 2.7 Hz, J = 12.7 Hz), 1.77
(m, 1H), 1.60 (m, 1H). 13C NMR (125 MHz, C6D6): δ 168.13,
159.76, 149.25, 139.46, 136.1, 133.28, 132.84, 129.37, 128.50,
128.36, 127.16, 123.66, 122.84, 121.90, 66.42, 60.24, 59.89,
51.90, 51 43, 35.87, 33.93.
NЈ-Benzylidene-N,N-bis-pyridin-2-ylmethyl-ethane-1,2-di-
amine (X). Anhydrous magnesium sulfate (60 g, 500 mmol)
was suspended in CH2Cl2 (135 mL) with the amine IX (10.18 g,
42 mmol) and benzaldehyde (4.46 g, 42 mmol). The mixture
was stirred for 3 h at room temperature, filtered, and was con-
centrated under vacuum to yield a yellow oil (13.8 g, 100%).
1H NMR (400 MHz, C6D6): δ 8.46 (d, 2H, J = 4.5 Hz), 7.91
(s, 1H), 7.72 (d, 2H, J = 7.9 Hz), 7.48 (d, 2H, J = 7.8 Hz), 7.10
(m, 5H), 6.59 (dd, 2H, J = 7.2 Hz, J = 5.0 Hz), 4.00 (s, 4H), 3.62
(t, 2H, J = 6.6 Hz), 2.92 (t, 2H, J = 6.3 Hz).
4-Amino-1-{benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]-
amino}butan-2-ol (XV). A solution of the protected amine XIV
(6.2 g, 11.3 mmol) in 15 mL of absolute ethanol was added
to a solution of hydrazine monohydrate (0.56 g, 11.3 mmol)
in 10 mL of ethanol. It was diluted with ethanol (15 mL), and
refluxed for 3 h. A white precipitate formed after 1 h. The
mixture was cooled, and the solvent evaporated in vacuo, to
yield a brown residue. To this residue was added 2 M HCl
(56 mL, 112 mmol), followed by 12 M HCl (5 mL, 60 mmol).
The mixture was refluxed for 1.5 h, and was stirred at room
temperature for 18 h. A granular white precipitate formed. It
was filtered, the filtrate was concentrated in vacuo to yield a
brown oil. It was dissolved in 60 mL of methanol, and stirred
for 1 h with 250 mL of Amberlite-401 ion-exchange resin in the
NЈ-Benzyl-N,N-bis-pyridin-2-ylmethyl-ethane-1,2-diamine
(XI). Imine, X (13.8 g, 42 mmol) was dissolved in acetonitrile
(75 mL), and was cooled to Ϫ5 ЊC. Glacial acetic acid (2.2 mL,
42 mmol) was added to this solution, followed by a suspension
of sodium borohydride (3.18 g, 84 mmol) in absolute ethanol
(70 mL) with continuous cooling. When the bubbling subsided,
3480
J. Chem. Soc., Dalton Trans., 2001, 3478–3488

View Article Online
OHϪ form. The suspension was filtered, concentrated under
vacuum, redissolved in benzene, and dried over anhydrous
MgSO4. After filtration, and evaporation of the solvent, the
NMR (500 MHz, C6D6): δ 8.47 (d, 2H, J = 4.6 Hz), 7.34 (d, 2H,
J = 7.8 Hz), 7.18–7.06 (m, 7H), 6.64 (dd, 2H, J = 6.9 Hz, J = 5.0
Hz), 3.85 (s, 4H), 3.68 (d, 2H, J = 5.0 Hz), 3.23 (s, 2H), 2.62 (t,
2H, J = 6.7 Hz), 2.51 (t, 2H, J = 6.9 Hz), 2.45 (t, 2H, J = 6.7 Hz),
2.00 (t, 2H, J = 6.9 Hz), 1.44 (s, 9H).
1
product was obtained as a brown oil (4.01 g, 85% yield). H
NMR (500 MHz, C6D6): δ 8.47 (d, 2H, J = 5.0 Hz), 7.45 (d, 2H,
J = 8.1 Hz), 7.20–7.05 (m, 7H), 6.62 (dd, 2H, J = 7.5 Hz, J =
5.0 Hz), 3.90–3.76 (m, 5H), 3.52 (d, 1H, J = 13.5 Hz), 3.27 (d,
1H, J = 13.5 Hz), 2.77–2.68 (m, 4H), 2.51 (m, 1H), 2.44–2.37
(m, 2H), 2.19 (dd, 1H, J = 3.8 Hz, J = 12.8 Hz), 1.33 (m, 2H).
1-Amino-4-{benzyl-[2-(bis-pyridin-2-ylmethyl-amino)ethyl]-
amino}butan-2-ol (XIX). To a stirred solution of ketone XVIII
(5.23 g, 9.5 mmol) in methanol (20 mL) cooled to 0 ЊC was
added sodium borohydride (1.1 g, 28.5 mmol). The pale yellow
solution was stirred for 3 h at 5 ЊC, and was quenched with 4 M
HCl (40 mL). The mixture was stirred for 18 h at room temper-
ature, by which time it turned brown. The acidic solution was
washed with ethyl acetate (50 mL). The volume of the aqueous
solution was reduced in vacuo. The residue was basified with
saturated sodium bicarbonate solution (100 mL), and was
washed with ethyl acetate (50 mL). The aqueous layer was con-
centrated to dryness in vacuo, and was extracted into hot ethyl
acetate (150 mL) with sonication. After filtration, the solvent
was removed in vacuo to afford pure product as a yellow oil
2-(4-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-3-
hydroxybutylimino)methyl]phenol (IV(H)2). A solution of XV
(500 mg, 1.2 mmol) in benzene (1.7 mL) was added to the sus-
pension of anhydrous MgSO4 (2 g) in benzene (3 mL). Then
salicylaldehyde (145 mg, 1.2 mmol) was added. The bright
yellow mixture was stirred at room temperature for 20 h, and
was filtered. The filtrate was evaporated in vacuo to yield the
1
product (90% purity) as a yellow oil (570 mg, 91%). H NMR
(500 MHz, C6D6): δ 13.86 (s, 1H), 8.47 (dd, 2H, J = 1.6 Hz, J =
4.9 Hz), 7.87 (s, 1H), 7.41 (d, 2H, J = 7.6 Hz), 7.11 (m, 8H), 6.89
(dd, 2H, J = 1.5 Hz, J = 7.5 Hz), 6.67 (m, 3H), 4.57 (s, 1H, br),
3.92–3.68 (m, 5H), 3.50 (m, 3H), 3.16 (d, 1H, J = 13.5 Hz), 2.73
(m, 2H), 2.50 (m, 1H), 2.32 (m, 2H), 2.13 (dd, 1H, J = 2.5 Hz,
J = 12.5 Hz), 1.49 (m, 2H). 13C NMR (125 MHz, C6D6):
δ 165.35, 132.08, 159.71, 149.29, 149.27, 136.01, 132.22, 131.46,
129.38, 128.44, 127.26, 123.58, 121.93, 119.41, 118.42, 117.41,
65.53, 60.63, 60.23, 59.79, 56.58, 52.00 51.83, 36.31.
1
(3.0 g, 75%). H NMR (400 MHz, C6D6): δ 8.46 (d, 2H, J =
7.5 Hz), 7.44 (d, 2H, J = 7.9 Hz), 7.23 (d, 2H, J = 8.5 Hz), 7.18–
7.04 (m, 5H), 6.62 (dd, 2H, J = 7.5 Hz, J = 4.6 Hz), 3.84 (s, 4H),
3.55 (m, 1H), 3.48 (d, 1H, J = 13.3 Hz), 3.08 (d, 1H, J =
13.3 Hz), 2.72–2.64 (m, 3H), 2.52 (d, 2H, J = 5.7 Hz), 2.39–2.33
(m, 3H), 1.52 (m, 1H), 1.19 (m, 1H).
2-[(4-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-
2-hydroxybutylimino)methyl]phenol (V(H)2). A solution of the
amine XIX (250 mg, 0.59 mmol) and salicylaldehyde (72 mg,
0.59 mmol) in benzene (1 mL) was stirred at 40 ЊC for 1 h. The
solution was concentrated 4 times under reduced pressure, each
time with addition of fresh benzene (15 mL total). The repeated
benzene evaporation procedure serves to remove the water
formed in the reaction. The product was obtained as a yellow
oil (308 mg, 100%). 1H NMR (500 MHz, C6D6): δ 13.93 (s, 1H),
8.44 (d, 2H, J = 6.2 Hz), 7.93 (s, 1H), 7.40 (d, 2H, J = 7.9 Hz),
7.19–7.02 (m, 9H), 6.92 (dd, 1H, J = 1.5 Hz, J = 7.6Hz), 6.67 (t,
1H, J = 7.6 Hz), 6.62 (dd, 2H, J = 7.3 Hz, J = 4.9 Hz), 3.88 (m,
1H), 3.80 (dd, 4H, J = 16.7 Hz, J = 14.3 Hz), 3.43 (d, 1H, J =
13.2 Hz), 3.34 (d, 2H, J = 5.7 Hz), 3.03 (d, 2H, J = 13.3 Hz), 2.64
(m, 3H), 2.38–2.27 (m, 3H), 1.54 (m, 1H), 1.32 (m, 1H).
N-ꢀ-tert-Butoxycarbonyl glycine N-methyl-N-methoxyamide
(XVI). To a stirred solution of t-BOC-glycine (14 g, 80 mmol)
in dry THF (85 mL) cooled to 0 ЊC was added carbonyldi-
imidazole (12.95 g, 80 mmol) in small portions. After 2 h of
stirring at room temperature methoxymethylamine hydro-
chloride (7.8 g, 80 mmol) was added to the clear solution. A
white suspension formed, and was stirred for 3 h. Triethylamine
(13 mL, 93 mmol) was added, and the suspension was stirred
for 20 h. It was filtered and washed with THF (50 mL). The
filtrate was concentrated under reduced pressure to afford white
crystals. They were recrystallized from ethyl acetate–hexane to
yield the pure product (16 g, 92%). Mp 99–100 ЊC. Lit. mp 100–
101 ЊC.20 1H NMR (500 MHz, CDCl3): δ 5.27 (s, 1H, br), 4.08
(s, 2H, br), 3.72 (s, 3H), 3.21 (s, 3H), 1.46 (s, 9H).
(2-Oxo-but-3-enyl)carbamic acid tert-butyl ester (XVII). This
compound was prepared using a modified literature pro-
cedure.21 To a stirred suspension of the Weinreb amide XVI (5
g, 23 mmol) in dry ether (60 mL) with cooling to Ϫ20 ЊC was
added vinylmagnesium bromide (1 M solution in THF, 92 mL)
dropwise. The suspension was warmed to 0 ЊC and was stirred
at this temperature for 2 h. It was poured into an ice-cold mix-
ture of 2 M HCl (240 mL) and ether (100 mL), and the product
was extracted into ether. The organic extracts were washed with
saturated sodium bicarbonate solution, and were dried over
anhydrous sodium sulfate. The solvent was removed in vacuo at
25 ЊC. The product was obtained as a pale-yellow oil with a
pungent smell (3.0 g, 70%). The product is unstable, and was
used in the next step immediately after its isolation. Higher
temperatures than mentioned above, and long exposure to HCl
solutions significantly lower the yield of this reaction. 1H NMR
(500 MHz, CDCl3): δ 6.38 (m, 2H), 5.94 (dd, 1H, J = 1.2 Hz, J =
10.1 Hz), 5.37 (s, 1H, br), 4.26 (d, 2H, J = 3.2 Hz), 1.46 (s, 9H).
N-ꢀ-tert-Butoxycarbonyl ꢁ-alanine N-methyl-N-methoxy-
amide (XX). To a stirred solution of N-t-BOC-β-alanine
(14.19 g, 75 mmol) in dry THF (100 mL) under N2 was carefully
added solid 1,1Ј-carbonyldiimidazole (13.38 g, 82.5 mmol). The
solution bubbled. It was stirred at room temperature for 4 h.
In a separate flask was added a suspension of N,O-dimethyl-
hydroxylamine hydrochloride (8.21 g, 82.5 mmol) in dry THF
(45 mL) and triethylamine (23 mL, 165 mmol). The mixture was
stirred at room temperature for 2 h to give a white turbid sol-
ution. The first solution was slowly added to the second under
N2. The white suspension was stirred at room temperature for
20 h. The white solid was filtered, and was washed with THF.
The filtrate was evaporated in vacuo to yield a yellow liquid
(30.1 g). The liquid was dissolved in CH2Cl2 (100 mL), was
washed with 0.1 M HCl (150 mL), and water (150 mL). It
was dried over anhydrous Na2SO4. The solvent was evaporated
1
in vacuo to afford pure product (17.49 g, 100%). H NMR
(400 MHz, CDCl3): δ 5.23 (s, 1H, br), 3.68 (s, 3H), 3.42 (t, 2H,
J = 9.2 Hz), 2.64 (s, 2H, br), 1.43 (s, 9H).
(4-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-2-
oxo-butyl)carbamic acid tert-butyl ester (XVIII). To a stirred
solution of amine XI (3.15 g, 9.5 mmol) in methanol (5 mL)
was added a solution of the Michael acceptor XVII (2.73 g,
14.7 mmol) in methanol (15 mL). The reaction is complete after
18 h of stirring at room temperature. The solution was concen-
trated under reduced pressure to yield a yellow oil (6 g, 100%)
which was used in the next step without further purification. 1H
(2-Oxo-but-3-enyl)carbamic acid tert-butyl ester (XXI). To a
solution of XX (13.94 g, 60 mmol) in dry ether (150 mL) cooled
to 0 ЊC was added vinylmagnesium bromide (180 mL of 1 M
THF solution) over a period of 10 min. The orange mixture
was stirred at 0 ЊC for 70 min. Cold 2 M HCl (150 mL) was
added to it in one portion to yield a yellow–orange solution.
The product was extracted into ether (450 mL). The ether layer
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
3481

View Article Online
was washed with saturated sodium bicarbonate solution, and
was dried over anhydrous sodium carbonate. After evaporation
of the solvent in vacuo the product was isolated as an orange oil
(11.14 g, 93%). H NMR (500 MHz, CDCl3): δ 6.31 (m, 2H),
5.90 (d, 1H, J = 10.0 Hz), 5.05 (s, 1H, br.), 3.43 (m, 2H), 2.84
salicylaldehyde (0.76 mL, 7 mmol). The intense yellow solution
was stirred at room temperature for 30 min. It was evaporated
in vacuo at 50 ЊC 4 times, with the addition of fresh benzene
each time (45 mL total). The benzene solution was evaporated
in vacuo to yield the product as a yellow oil (3.74 g, 95% pure,
1
1
(t, 2H, J = 11.1 Hz), 1.43 (s, 9H).
94% yield). H NMR (400 MHz, CDCl3): δ 13.65 (s, 1H, br),
8.50 (d, 2H, J = 4.1 Hz), 8.36 (s, 1H), 7.61 (td, 2H, J = 1.7 Hz,
J = 7.7 Hz), 7.44 (d, 2H, J = 7.8 Hz), 7.20 (m, 9H), 6.95 (d, 1H,
J = 8.2 Hz), 6.86 (t, 1H, J = 7.5 Hz), 5.95 (s, 1H, br), 3.76 (s,
4H), 3.68 (m, 3H), 3.29 (d, 2H, J = 13.2 Hz), 2.74 (m, 3H), 2.64
(m, 2H), 2.50 (m, 1H), 1.69 (m, 3H), 1.49 (m, 1H). 13C NMR
(400 MHz, CDCl3): δ 169.85, 164.68, 161.12, 158.87, 148.53,
137.48, 136.06, 131.66, 130.81, 128.81, 128.11, 126.98, 122.66,
121.68, 118.46, 117.97, 116.63, 71.22, 69.60, 60.14, 58.49, 55.37,
52.66, 50.90, 50.77, 38.02, 32.37.
(5-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-3-
oxo-pentyl)carbamic acid tert-butyl ester (XXII). To a stirred
solution of amine XI (16.04 g, 48.25 mmol) in dry methanol
(50 mL) was added a solution of XXI (10.97 g, 50.66 mmol) in
methanol (100 mL). The clear orange solution was stirred
under N2 atmosphere at room temperature for 24 h. Then
more of XI was added (2.17 g, 11 mmol) and the solution was
stirred at room temperature for a further 20 h. The solution
was concentrated under reduced pressure to afford a yellow
oil, which was chromatographed on silica-gel with ethyl acet-
ate as an eluant. The pure product was obtained as a yellow
oil (24.89 g, 97%). 1H NMR (500 MHz, CDCl3): δ 8.52 (d, 2H,
J = 7.2 Hz), 7.62 (td, 2H, J = 1.8 Hz, J = 5.3 Hz), 7.46 (d, 2H,
J = 7.8 Hz), 7.19 (m, 7H), 5.04 (s, 1H, br), 3.81 (s, 4H), 3.49 (s,
2H), 3.28 (m, 2H), 2.67 (m, 6H), 2.48 (m, 4H), 1.42 (s, 9H).
13C NMR (125 MHz, CDCl3): δ 209.40, 159.56, 155.71, 148.84,
138.93, 136.20, 128.63, 128.04, 127.97, 122.75, 121.77, 78.95,
60.65, 58.79, 51.70, 51.50, 48.81, 42.51, 40.82, 34.96, 28.26.
Synthesis of the complexes
[Cu2(IV)(ꢂ-OAc)]PF6 (6). To a stirred solution of IV(H)2
(200 mg, 0.38 mmol) in methanol (0.5 mL) was added a suspen-
sion of copper acetate monohydrate (168 mg, 0.84 mmol) in
methanol (5.2 mL). The resulting dark-green solution was
stirred for 15 min. When all of the starting materials dissolved,
a solution of triethylamine (77 mg, 0.76 mmol) in methanol
(0.3 mL) was added. The dark-green solution was stirred for
2 h. A solution of ammonium hexafluorophosphate (250 mg,
1.5 mmol) in methanol (3 mL) was added. A dark-green pre-
cipitate formed within 5 min. The suspension was brought to
boiling and the volume of methanol was reduced to 6 mL. The
suspension was kept at 5 ЊC for 24 h. The dark-green precipitate
(272 mg, 84%) was collected, was washed with methanol, then
ether, and was dried in air. It was recrystallized by vapor
diffusion of ether into an acetonitrile solution. [Cu(IV)-
(µ-OAc)]PF6 was obtained as dark-green needles (192 mg, 62%).
ΛM (CH3CN) = 119 ΩϪ1 molϪ1 cm2. UV [λmax/nm, (ε/L molϪ1
cmϪ1)]: 639 (178). Selected IR bands (Nujol mull, cmϪ1): 769,
839, 1377, 1454, 1564, 1577, 1627. µeff (20 ЊC) = 2.52 µB. Anal.
calc. for C34H38N5O4PF6Cu2: C, 47.88; H, 4.49; N, 8.21. Found:
C, 48.01; H, 4.62; N, 8.34%.
1-Amino-5-{benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]-
amino}pentan-3-ol (XXIII). To a stirred solution of XXII
(22.36 g, 42.14 mmol) in methanol (180 mL) cooled to 0 ЊC was
carefully added solid sodium borohydride (4.78 g, 126.4 mmol)
in portions. The pale-yellow solution bubbled, was stirred at
room temperature for 3 h, and was quenched with 4 M HCl
(100 mL) at 0 ЊC. After stirring for 20 h at room temperature a
brownish solution formed. It was concentrated in vacuo, was
triturated with ethanol (50 mL), and was filtered. The filtrate
was evaporated in vacuo to afford a brown oil. The oil was
washed with ethyl acetate (100 mL), basified with saturated
sodium bicarbonate solution (150 mL) and was washed again
with ethyl acetate (300 mL). The aqueous solution was evapor-
ated to dryness under reduced pressure, was extracted into ethyl
acetate (300 mL), and was dried over anhydrous Na2SO4. After
concentration in vacuo an orange oil was obtained (20.86 g).
Chromatography on neutral alumina with ethyl acetate yielded
pure product as an orange oil. (17.74 g, 97%). 1H NMR
(500 MHz, CDCl3): δ 8.46 (d, 2H, J = 4.5 Hz), 7.57 (td, 2H, J =
1.5 Hz, J = 7.8 Hz), 7.41 (d, 2H, J = 8.0 Hz), 7.17 (m, 5H), 7.08
(t, 2H, J = 6.0 Hz), 3.75 (s, 4H), 3.64 (d, 1H, J = 13.5 Hz), 3.27
(d, 1H, J = 13.5 Hz), 2.84–2.44 (m, 9H), 1.59 (m, 1H), 1.44 (m,
3H). 13C NMR (125 MHz, CDCl3): δ 159.13, 148.69, 137.96,
136.18, 128.83, 128.05, 126.87, 122.80, 121.74, 71.25, 60.36,
58.60, 52.68, 51.17, 50.91, 39.59, 39.11, 32.92.
[Cu4(V)2(ꢂ-OAc)](PF6)3ؒH2O (7). To a stirred solution of the
ligand V(H)2 (308 mg, 0.57 mmol) in methanol (10 mL) was
added solid copper acetate monohydrate (252 mg, 1.26 mmol).
The solution was warmed up to 40 ЊC, and was filtered. To
the clear green filtrate was added triethylamine (116 mg,
1.15 mmol), and the solution was stirred for 15 min at 40 ЊC. A
solution of NH4PF6 (373 mg, 2.29 mmol) in methanol (2 mL)
was added. A light-Lgreen precipitate formed immediately. The
mixture was brought to boiling, and was refluxed for 10 min. It
was then cooled to 5 ЊC. The green precipitate was collected,
washed with cold methanol (3 mL) and ether (5 mL) and was
dried in air (325 mg, 67%). It was recrystallized by vapor
diffusion of ether into an acetonitrile solution. Green needles
suitable for X-ray crystallography formed (215 mg, 44%). ΛM
(CH3CN) = 378 ΩϪ1 molϪ1 cm2. UV [λmax/nm, (ε/L molϪ1 cmϪ1)]:
665 (703). Selected IR bands (Nujol mull, cmϪ1): 769, 839, 1377,
1454, 1564, 1577, 1627. µeff (20 ЊC) = 3.10 µB. Anal. calc. for
C66H75N10O7P3F18Cu4: C, 43.81; H, 4.18; N, 7.74. Found: C,
43.94; H, 4.00; N, 7.51%.
1-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-5-
[(3-methyl-3H-imidazol-4-ylmethylene)amino]pentan-3-ol
(III(H)). To a stirred solution of XXIII (2.68 g, 6.2 mmol)
in benzene (15 mL) was added 1-methyl-2-imidazole carbox-
aldehyde (0.68 g, 6.2 mmol). The light-orange solution was
stirred at room temperature for 30 min. It was evaporated in
vacuo at 50 ЊC 4 times, with the addition of fresh benzene each
time (30 mL total). The benzene solution was filtered and was
evaporated in vacuo to yield the product as an orange oil
[Cu4(III)2(ꢂ-OAc)2](PF6)4 (8). To a stirred solution of the
ligand III(H) (0.14 g, 0.27 mmol) in methanol (3 mL) was
added a solution of copper acetate monohydrate (107 mg,
0.53 mmol) in methanol (2 mL). A dark-blue solution formed
at once. Triethylamine (37.1 µL, 0.27 mmol) was added, and
the solution was refluxed for 30 min. A solution of NH4PF6
(0.174g, 1.07 mmol) in methanol (2 mL) was added dropwise
to the hot reaction mixture, which was refluxed for 20 min.
Ethanol (3 mL) was added to the hot solution to induce pre-
cipitation. The mixture was refluxed for 30 min. It was cooled
1
(3.12 g, 96%). H NMR (400 MHz, CDCl3): δ 8.50 (d, 2H,
J = 4.3 Hz), 8.32 (s, 1H), 7.62 (td, 2H, J = 1.7 Hz, J = 7.6 Hz),
7.46 (d, 2H, J = 7.8 Hz), 7.21 (m, 5H), 7.13 (m, 3H), 6.92
(s, 1H), 3.92 (s, 2H), 3.79 (m, 5H), 3.67 (m, 2H), 3.31 (d, 1H,
J = 13.2 Hz), 2.77–2.50 (m, 8 H), 1.71 (m, 3H), 1.54 (m, 1H).
2-[(5-{Benzyl[2-(bis-pyridin-2-ylmethyl-amino)ethyl]amino}-
3-hydroxypentylimino)methyl]phenol (II(H)2). To a stirred sol-
ution of XXIII (3.04 g, 7 mmol) in benzene (30 mL) was added
3482
J. Chem. Soc., Dalton Trans., 2001, 3478–3488

View Article Online
and was kept at 5 ЊC for 20 h. The pale-blue solid was collected,
washed with cold ethanol (2 mL), ether (20 mL), and was dried
in air (170 mg, 64%). It was recrystallized by slow diffusion
of ether into acetonitrile solution. Bluish-green needles suitable
for X-ray crystallography were collected (170 mg, 64%). ΛM
(CH3CN) = 450 ΩϪ1 molϪ1 cm2. UV [λmax/nm, (ε/L molϪ1 cmϪ1)]:
661 (517). Selected IR bands (Nujol mull, cmϪ1): 737, 770,
841, 1022, 1091, 1294, 1339, 1406, 1496, 1599, 1601, 2722,
3148, 3161. µeff (20 ЊC) = 2.83 µB. Anal. calc. for C66H82-
N14O6P4F24Cu4: C, 39.61; H, 4.13; N, 9.80. Found: C, 39.20; H,
4.00; N, 9.68%.
Fourier syntheses and refined by full-matrix least-squares pro-
cedures. Structures 9 and 10 co-crystallized with two molecules
of ethanol. Structures 8 and 9 reside on crystallographic inver-
sion centers. Structure 7 co-crystallized with one molecule
of water for which the protons could not be located from the
electron difference map. Due to the poorly diffracting nature
of 7 and 10, only select atoms were refined with anisotropic
displacement coefficients. The two phenyl rings in 7 were
constrained to rigid planar hexagons (C–C = 1.39 Å). The
asymmetric unit of 6 contains chemically equivalent but
crystallographically independent molecules. All non-hydrogen
atoms, with the exception of those noted, were refined with
anisotropic displacement coefficients and hydrogen atoms were
treated as idealized contributions.
[Cu4(II)2(ꢂ-OAc)2](PF6)2ؒ2EtOH (9). To a stirred solution
of the ligand II(H)2 (0.27 g, 0.5 mmol) in ethanol (3 mL)
was added a solution of copper acetate monohydrate (200 mg,
1 mmol) in ethanol (5 mL). A dark-green solution formed
immediately. After the solution was stirred for 10 min at room
temperature, triethylamine (139 µL, 1 mmol) was added. After
1.5 h of stirring, a solution of NH4PF6 (0.33 g, 2 mmol) in
ethanol (3 mL) was added dropwise to the reaction mixture. A
pale-green precipitate formed immediately. The mixture was
stirred at 80 ЊC for 30 min, was slowly cooled to room temper-
ature, and was kept at Ϫ15 ЊC for 18 h. The pale-green pre-
cipitate was collected, washed with cold ethanol (3 mL), ether
(15 mL), and was dried under vacuum (320 mg, 74%). It was
recrystallized by slow diffusion of ether into acetonitrile–
ethanol solution. Dark-green blocks suitable for X-ray crystal-
lography were collected, washed with ether, and were dried
under vacuum (0.27 g, 62%). ΛM (CH3CN) = 231 ΩϪ1 molϪ1
cm2. UV [λmax/nm, (ε/L molϪ1 cmϪ1)]: 641 (491), 822 (456).
Selected IR bands (Nujol mull, cmϪ1): 764, 844, 1326, 1617,
The structures of 7 and 10 were both restricted in quality due
Ϫ
to the presence of spherically disordered PF6 anions. Add-
itionally, there is alkyl group disorder in the EtOH solvent
molecules in 10. These factors contributed to the high residuals
obtained, but have not seriously compromised the chemical
information concerning the cations.
All software and sources of the scattering factors are
contained in the SHELXTL (5.1) program library (G. M.
Sheldrick, Siemens XRD, Madison, WI, 1998).
CCDC reference numbers 170793–170797.
See http://www.rsc.org/suppdata/dt/b1/b103164n/ for crystal-
lographic data in CIF or other electronic format.
Results
1
Ligand synthesis
The common element, excluding the Schiff base, in the ligands,
II, III, IV and V, is the fragment, XI, which was prepared by the
methods outlined in Scheme 1. The methods follow con-
ventional procedures which provide high yields for each step.
Magnesium sulfate suspended in CH2Cl2 was used to form the
imines. It serves to absorb the water and is a mild Lewis-acid
catalyst. The method proved to be simple and effective because
we found that other methods gave poor yields and impure
products. Ligand, IV, was efficiently prepared by the methods
outlined in Scheme 2.
Reaction of potassium phthalimide with homoallylic bro-
mide in CH3CN solution gave XII which was epoxidized with
meta-chloroperbenzoic acid (m-CPBA) to give XIII. Reaction
of XI with XIII in n-butanol at 100 ЊC for 8 hours gave XIV.
The presence of the benzyl group in XI is necessary, for without
it, the primary amine IX undergoes multiple additions to the
epoxide. The other steps follow conventional procedures.
The preparative procedures for II(H)2, III(H) and V(H)2 are
similar and are outlined in Scheme 3.
The t-BOC protected amino acids were first activated with
carbonyldiimidazole and were then reacted with Weinreb’s
amine to give the amides, XVI, XX. These, in turn, were reacted
with vinyl Grignard to give the vinyl ketones, XVII, XXI. They
are very sensitive compounds with a tendency to polymerize.
These were used immediately for the next step, the Michael
addition of XI to give XVIII and XXII. As in the case of the
reaction of XI with the epoxide in Scheme 2, the absence of the
benzyl group led to multiple addition products. Sodium boro-
hydride reduced the ketones and HCl removed the t-BOC group
to give the amino alcohols, XIX and XXIII. Schiff base form-
ation in benzene solution gave II(H)2, III(H) or V(H)2 in
nearly quantitative yield.
2334, 2359. µeff (20 ЊC)
= 2.62 µB. Anal. calc. for
C74H92N10O10P2F12Cu4: C, 48.68; H, 5.08; N, 7.67. Found: C,
48.84; H, 5.02; N, 8.39%.
[Mn2(II)(OEt)(ꢂ-OAc)(ꢂ-OEt)](PF6)ؒ2EtOH (10). Ligand
II(H)2 (0.16 g, 0.3 mmol) and manganese() acetate tetra-
hydrate (0.15 g, 0.6 mmol) were dissolved in deaerated ethanol
(5 mL) under nitrogen to give a yellow–orange solution. After
stirring for 30 min, triethylamine (84 µL, 0.6 mmol) was added.
The resulting orange solution was stirred at room temperature
for 1.5 h, then it was warmed up to 60 ЊC, and a solution of
NH4PF6 (0.2 g, 1.2 mmol) in ethanol (4 mL) was added. The
resulting suspension was heated at 80 ЊC for 1 h. The pale
orange–brown suspension was cooled down to room temper-
ature, and then was kept at Ϫ15 ЊC for 18 h. The solid was
collected under nitrogen. The filtrate was exposed to air. Brown
X-ray quality crystals deposited from the filtrate. They were
collected, and were dried in air (110 mg, 39%). They lose solv-
ent of crystallization when dry; for X-ray purposes the crystals
were kept in their mother liqor. ΛM (CH3CN) = 140 ΩϪ1 molϪ1
cm2. UV [λmax/nm, (ε/L molϪ1 cmϪ1)]: 376 (4000), 520 sh (420).
Selected IR bands (Nujol mull, cmϪ1): 842, 1293, 1376, 1539,
1616, 1652, 1700, 2334, 2361, 3744, 3854. µeff (20 ЊC) = 7.31 µB.
Anal. calc. for C39H50N5O6PF6Mn2: C, 49.85; H, 5.36; N, 7.46.
Found: C, 49.58; H, 4.90; N, 7.57%.
Crystallographic structural determination
Crystal, data collection, and refinement parameters are given in
Table 1. Suitable crystals for data collection were selected and
mounted with epoxy cement on the tips of fine glass fibers. All
data were collected with a Siemens P4/CCD diffractometer with
graphite-monochromated Mo-Kα X-radiation (λ = 0.71073 Å).
No symmetry higher than triclinic was observed in the dif-
fraction data of 7–10. For each structure the centrosymmetric
space group option, P1, was chosen based on E-statistics. The
systematic absences in the diffraction data for 6 are uniquely
consistent with the reported space group. All structures were
solved using direct methods, completed by subsequent difference
2
Complexes
Described here are five complexes which include all four lig-
ands, II, III, IV and V. Four complexes are of Cu2ϩ, one each
for the four ligands, and a di-manganese complex of ligand, II,
is described. The synthesis, properties and structure of each is
described separately.
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
3483

View Article Online
Table 1 Crystallographic data for [Mn2(II)(OEt)(µ-OAc)(µ-OEt)](PF6)ؒ2EtOH (10), [Cu4(II)2(µ-OAc)2](PF6)2ؒ2EtOH (9), [Cu4(III)2(µ-OAc)2](PF6)4
(8), [Cu4(V)2(µ-OAc)](PF6)3ؒH2O (7), and [Cu2(IV)(µ-OAc)]PF6 (6)
10
9
8
7
6
Formula
Formula weight
Space group
C43H62F6Mn2N5O8P
1031.82
P1
C74H92Cu4F12N10O10P2 C66H82Cu4F24N14O6P4
C66H75Cu4F18N10O7P3
1809.43
P1
C34H38Cu2F6N5O4P
852.74
P21/c
1825.68
P1
2001.49
P1
a/Å
b/Å
c/Å
α/Њ
12.1741(2)
13.5908(2)
16.5007(2)
79.2919(8)
68.9785(3)
79.8058(8)
2485.88(3)
2, 1
10.3158(2)
12.0891(2)
17.6124(2)
74.0125(2)
81.8911(5)
71.7472(7)
2001.61(5)
1, 1/2
11.5418(6)
13.7097(7)
14.0734(8)
69.5232(11)
83.0061(13)
77.5450(11)
2034.5(3)
1, 1/2
11.7811(2)
16.6703(3)
19.1074(2)
96.1665(2)
96.5247(6)
96.2454(5)
3678.78(12)
2, 1
18.0761(2)
21.1395(2)
19.3919(2)
—
97.9872(2)
—
β/Њ
γ/Њ
V/Å3
7338.14(3)
8, 2
Z, Z
Crystal color, habit
Dcalc/g cmϪ3
µ(Mo-Kα)/cmϪ1
T /K
Brown, plate
1.378
6.16
223(2)
9.55
Green, plate
1.515
11.78
173(2)
6.37
Blue, needle
1.633
12.23
223(2)
7.27
Green, plate
1.633
13.11
173(2)
10.70
Green, rod
1.544
12.78
173(2)
4.67
R(F) (%)a
R(wF2) (%)a
31.49
19.22
17.51
27.43
15.49
1
2
–
a Quantity minimized = R(wF2) = Σ[w(Fo Ϫ Fc ) ]/Σ[(wFo ) ] ; R = Σ∆/Σ(Fo), ∆ = |(Fo Ϫ Fc)|, w = 1/[σ (Fo ) ϩ (aP) ϩ bP], P = [2Fc2 ϩ Max(Fo, 0)]/3.
2
2
2
2
2
2
2
2
Scheme 1
Scheme 2
[Cu2(IV)(ꢂ-OAc)]PF6 (6). When IV(H)2 is allowed to react
with copper acetate in methanol solution, a green solution is
formed after the addition of triethylamine. Dark green crystals
are formed upon the addition of NH4PF6, and deep green
needles are obtained by ether diffusion into an acetonitrile sol-
ution. The product is a 1 : 1 electrolyte in acetonitrile solution
and its solid state magnetic moment at 25 ЊC is 2.52 µB based on
the formula above.
3484
J. Chem. Soc., Dalton Trans., 2001, 3478–3488

View Article Online
Scheme 3
Table 2 Selected bond lengths (Å) and angles (Њ) for [Cu2(IV)-
(µ-OAc)]PF6 (6)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–N(1)
Cu(1)–O(4)
Cu(1)–N(5)
1.903(3)
1.932(3)
1.992(3)
2.139(3)
2.260(3)
Cu(2)–O(2)
Cu(2)–O(3)
Cu(2)–N(4)
Cu(2)–N(3)
Cu(2)–N(2)
1.949(2)
1.964(2)
2.006(3)
2.089(3)
2.400(3)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–N(1)
O(2)–Cu(1)–N(1)
O(1)–Cu(1)–O(4)
O(2)–Cu(1)–O(4)
N(1)–Cu(1)–O(4)
O(1)–Cu(1)–N(5)
O(2)–Cu(1)–N(5)
N(1)–Cu(1)–N(5)
O(4)–Cu(1)–N(5)
174.68(11)
93.64(12)
89.68(12)
91.66(12)
89.81(10)
125.22(12)
85.69(12)
89.10(11)
140.16(12)
94.60(11)
O(2)–Cu(2)–O(3)
O(2)–Cu(2)–N(4)
O(3)–Cu(2)–N(4)
O(2)–Cu(2)–N(3)
O(3)–Cu(2)–N(3)
N(4)–Cu(2)–N(3)
O(2)–Cu(2)–N(2)
O(3)–Cu(2)–N(2)
N(4)–Cu(2)–N(2)
N(3)–Cu(2)–N(2)
93.82(10)
161.87(12)
92.58(12)
89.60(11)
174.34(12)
82.85(12)
77.26(11)
103.03(12)
117.67(12)
82.13(13)
Fig. 2 Structure of [Cu4(V)2(µ-OAc)](PF6)3ؒH2O (7). Hydrogen atoms,
counter-ions, and lattice solvent are omitted for clarity.
Metal–metal distance
Cu(1)–Cu(2)
3.128(5)
The Cu2ϩ ions (Cu(1), Cu(2)) are bridged by the alkoxide
oxygen atom (O(2)) and by an acetate ion. Each Cu2ϩ ion is
5-coordinate, (Cu(1)) is in a distorted trigonal bipyramidal
geometry and the other (Cu(2)) is a distorted square pyramid
with an elongated axial (Cu(2)–N(2)) bond length. The pyridine
ligand bearing N(5) is bonded to Cu(1) rather than to Cu(2) in
which case Cu(2) would have become 6-coordinate, a coordin-
ation number disfavored by Cu2ϩ. The Cu(1)–N(5) bond length
is longer than the others which surround Cu(1). To some extent,
this structure probably reflects the inability of Cu2ϩ to form
stable 6-coordinate complexes.
[Cu4(V)2(ꢂ-OAc)](PF6)3 (7). This complex was prepared in a
similar manner to that described for the previous complex. The
complex forms crystals which are green needles, it has a solid
state magnetic moment at room temperature of 3.10 µB and is a
3 : 1 electrolyte in acetonitrile solutions.
Fig. 1 ORTEP25 structure of [Cu2(IV)(µ-OAc)]PF6 (6). Thermal
Table 1 contains the crystallographic data. Table 3 lists
selected bond lengths and angles and the structure is shown in
Fig. 2.
ellipsoids are at 30% probability, counter-ion omitted for clarity.
The solid state structure was determined by X-ray diffrac-
tion. Table 1 contains diffraction data, Table 2 contains selected
bond length and angle data and the structure is shown in Fig. 1.
The structure consists of two different di-Cu2ϩ-ligand units, a
unit consisting of Cu(1) and Cu(2) and the other is Cu(3) and
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
3485

View Article Online
Table 3 Selected bond lengths (Å) and angles (Њ) for [Cu4(V)2-
(µ-OAc)](PF6)3ؒH2O (7)
Cu(1)–O(2)
Cu(1)–N(3)
Cu(1)–N(5)
Cu(1)–N(2)
Cu(1)–N(4)
Cu(2)–N(1)
Cu(2)–O(3)
Cu(2)–O(1)
Cu(2)–O(2)
Cu(3)–N(6)
1.927(11)
2.023(14)
2.068(11)
2.138(13)
2.144(9)
1.891(11)
1.941(9)
1.957(11)
2.001(11)
1.906(15)
Cu(3)–O(5)
Cu(3)–O(4)
Cu(3)–O(6)
Cu(3)–O(1)
Cu(4)–O(6)
Cu(4)–N(10)
Cu(4)–N(8)
Cu(4)–N(9)
Cu(4)–N(7)
1.918(12)
1.923(11)
1.988(12)
2.382(8)
1.932(10)
2.058(13)
2.089(14)
2.116(12)
2.138(15)
O(2)–Cu(1)–N(3)
O(2)–Cu(1)–N(5)
N(3)–Cu(1)–N(5)
O(2)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
N(5)–Cu(1)–N(2)
O(2)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)
N(5)–Cu(1)–N(4)
N(2)–Cu(1)–N(4)
N(1)–Cu(2)–O(3)
N(1)–Cu(2)–O(1)
O(3)–Cu(2)–O(1)
N(1)–Cu(2)–O(2)
O(3)–Cu(2)–O(2)
O(1)–Cu(2)–O(2)
N(6)–Cu(3)–O(5)
N(6)–Cu(3)–O(4)
177.7(5)
101.1(5)
80.8(5)
93.6(5)
84.2(5)
132.8(4)
100.7(4)
79.4(5)
119.8(5)
100.8(4)
169.2(4)
92.1(5)
89.6(4)
86.3(5)
91.2(4)
175.7(3)
91.7(6)
174.4(4)
O(5)–Cu(3)–O(4)
N(6)–Cu(3)–O(6)
O(5)–Cu(3)–O(6)
O(4)–Cu(3)–O(6)
N(6)–Cu(3)–O(1)
O(5)–Cu(3)–O(1)
O(4)–Cu(3)–O(1)
O(6)–Cu(3)–O(1)
O(6)–Cu(4)–N(10)
O(6)–Cu(4)–N(8)
N(10)–Cu(4)–N(8)
O(6)–Cu(4)–N(9)
N(10)–Cu(4)–N(9)
N(8)–Cu(4)–N(9)
O(6)–Cu(4)–N(7)
N(10)–Cu(4)–N(7)
N(8)–Cu(4)–N(7)
N(9)–Cu(4)–N(7)
90.1(5)
84.7(6)
164.6(4)
92.1(5)
96.4(4)
92.3(3)
88.8(3)
102.9(4)
98.2(5)
177.7(5)
83.2(5)
98.7(4)
122.5(5)
79.0(5)
95.3(5)
129.2(5)
85.2(6)
103.2(5)
Fig. 3 ORTEP structure of [Cu4(III)2(µ-OAc)2](PF6)4 (8). Thermal
ellipsoids are at 30% probability and counter-ions are omitted for
clarity.
Metal–metal distances
Cu(1)–Cu(2)
Cu(2)–Cu(3)
3.482(5)
3.045(3)
3.398(5)
Cu(3)–Cu(4)
a room temperature, solid state magnetic moment of 2.83 µB,
and is a 4 : 1 electrolyte in acetonitrile solutions. The crystallo-
graphic data is collected in Table 1, selected bond lengths and
angles are listed in Table 4 and the structure is shown in Fig. 3.
The molecule lies on a center of inversion. The central two
Cu2ϩions are bridged by the alkoxide groups of the two ligands
and the terminal Cu2ϩ ions are bridged to the two central ions
by acetate ligands. All Cu2ϩ ions are 5-coordinate, the central
two Cu2ϩ ions are distorted square pyramids with an elongated
Cu–O acetate bond whereas the terminal Cu2ϩ ions are in a
distorted trigonal bipyramidal geometry.
Table 4 Selected bond lengths (Å) and angles (Њ) for [Cu4(III)2-
(µ-OAc)2](PF6)4 (8)
Cu(1)–O(3)
Cu(1)–N(5)
Cu(1)–N(6)
Cu(1)–N(7)
Cu(1)–N(4)
1.914(5)
2.045(5)
2.079(5)
2.079(6)
2.187(5)
Cu(2)–O(1)#1
Cu(2)–O(1)
Cu(2)–N(3)
Cu(2)–N(1)
Cu(2)–O(2)
1.924(4)
1.933(4)
2.011(5)
2.019(5)
2.243(5)
O(3)–Cu(1)–N(5)
O(3)–Cu(1)–N(6)
N(5)–Cu(1)–N(6)
O(3)–Cu(1)–N(7)
N(5)–Cu(1)–N(7)
N(6)–Cu(1)–N(7)
O(3)–Cu(1)–N(4)
N(5)–Cu(1)–N(4)
N(6)–Cu(1)–N(4)
N(7)–Cu(1)–N(4)
168.7(2)
107.0(2)
81.0(2)
87.8(2)
81.4(2)
116.9(2)
96.9(2)
84.3(2)
125.3(2)
112.4(2)
O(1)#1–Cu(2)–O(1)
O(1)#1–Cu(2)–N(3)
O(1)–Cu(2)–N(3)
O(1)#1–Cu(2)–N(1)
O(1)–Cu(2)–N(1)
N(3)–Cu(2)–N(1)
O(1)#1–Cu(2)–O(2)
O(1)–Cu(2)–O(2)
N(3)–Cu(2)–O(2)
N(1)–Cu(2)–O(2)
77.16(18)
170.3(2)
104.46(18)
93.55(19)
163.0(2)
82.4(2)
94.82(18)
107.87(19)
93.7(2)
[Cu4(II)2(ꢂ-OAc)2](PF6)2ؒ2EtOH (9). By similar methods to
those above, this complex was isolated as dark green blocks, it
has a solid state magnetic moment at room temperature of 2.62
µB and is a 2 : 1 electrolyte in acetonitrile solutions. Crystallo-
graphic data is provided in Table 1, selected bond lengths and
angles are collected in Table 5 and the structure is illustrated in
Fig. 4.
86.9(2)
As for the previous structure, the present molecule has a cen-
ter of inversion and generally resembles the tetramer formed by
III. The major difference is associated with the acetate ligands
which, in this case, are terminally bonded to the outer Cu2ϩ
ions. As a consequence, the inner two Cu2ϩ ions are square
planar and are bridged to each other by the alkoxide groups
of the two ligands. The terminal Cu2ϩ ions are in a distorted
trigonal bipyramidal geometry.
Metal–metal distances
Cu(2)–Cu(2A)
3.0154(14)
a Symmetry transformation used: #1 Ϫx ϩ 1, Ϫy ϩ 1, Ϫz ϩ 1.
Cu(4). These two units are bridged by an acetate ligand joining
Cu(2) and Cu(3) and a phenolate oxygen atom O(1). The pairs
of Cu2ϩ ions of each unit are bridged by alkoxide oxygen atoms,
namely, Cu(1)–O(2)–Cu(2) and Cu(3)–O(6)–Cu(4). The two
Cu2ϩ ions, Cu(1) and Cu(4) are in a distorted trigonal bipyram-
idal geometry, whereas Cu(2) is square-planar and Cu(3) is
square pyramidal. In the last, the axial bond Cu(3)–O(1) is
elongated. The other bond lengths vary but are within the range
expected for the individual Cu2ϩ geometries. As in the previous
structure, this structure adopts favorable Cu2ϩ geometries.
[Mn2(II)(OEt)(ꢂ-OAc)(ꢂ-OEt)](PF6)ؒ2EtOH (10). The lig-
and, II(H)2, was reacted with Mn(OAc)2ؒ4H2O in ethanol under
an inert atmosphere to give a yellow-orange solution which
turned orange upon the addition of one equivalent of tri-
ethylamine. Heating this solution and the addition of NH4PF6
led to the formation of a brown suspension. After filtration, the
filtrate was exposed to air. Orange-brown crystals of [Mn2(II)-
(OEt)(µ-OAc)(µ-OEt)](PF6)ؒ2EtOH slowly formed which
effloresce when the solvent is removed. The material has a
room temperature magnetic moment of 7.31 µB and is a 1 : 1
electrolyte in acetonitrile solutions. Thus the complex could
[Cu4(III)2(ꢂ-OAc)2](PF6)4 (8). This compound was prepared
in a manner similar to that for the two previous compounds. It
crystallizes from acetonitrile–ether as blue-green needles, it has
3486
J. Chem. Soc., Dalton Trans., 2001, 3478–3488

View Article Online
Table 6 Selected bond lengths (Å) and angles (Њ) for [Mn2(II)(OEt)-
(µ-OAc)(µ-OEt)](PF6)ؒ2EtOH (10)
Table 5 Selected bond lengths (Å) and angles (Њ) for [Cu4(II)2-
(µ-OAc)2](PF6)2ؒ2EtOH (9)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–O(2)#1
Cu(1)–N(1)
Cu(2)–O(3)
1.898(4)
1.925(3)
1.956(3)
1.977(4)
1.956(4)
Cu(2)–N(3)
Cu(2)–N(5)
Cu(2)–N(4)
Cu(2)–N(2)
2.063(4)
2.086(4)
2.133(4)
2.154(4)
Mn(1)–O(1)
Mn(1)–O(3)
Mn(1)–O(2)
Mn(1)–N(1)
Mn(1)–O(4)
Mn(1)–O(6)
1.896(7)
1.901(6)
1.912(6)
2.010(8)
2.220(6)
2.326(6)
Mn(2)–O(5)
Mn(2)–O(3)
Mn(2)–O(2)
Mn(2)–N(4)
Mn(2)–N(3)
Mn(2)–N(2)
2.117(5)
2.130(7)
2.136(6)
2.270(9)
2.333(5)
2.354(9)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–O(2)#1
O(2)–Cu(1)–O(2)#1
O(1)–Cu(1)–N(1)
O(2)–Cu(1)–N(1)
O(2)#1–Cu(1)–N(1)
O(3)–Cu(2)–N(3)
O(3)–Cu(2)–N(5)
166.48(15)
91.77(14)
75.56(15)
95.38(16)
97.72(16)
170.83(15)
170.43(17)
90.15(17)
N(3)–Cu(2)–N(5)
O(3)–Cu(2)–N(4)
N(3)–Cu(2)–N(4)
N(5)–Cu(2)–N(4)
O(3)–Cu(2)–N(2)
N(3)–Cu(2)–N(2)
N(5)–Cu(2)–N(2)
N(4)–Cu(2)–N(2)
80.85(18)
100.42(16)
81.01(16)
117.05(15)
102.90(16)
85.29(15)
127.46(15)
110.25(14)
O(1)–Mn(1)–O(3)
O(1)–Mn(1)–O(2)
O(3)–Mn(1)–O(2)
O(1)–Mn(1)–N(1)
O(3)–Mn(1)–N(1)
O(2)–Mn(1)–N(1)
O(1)–Mn(1)–O(4)
O(3)–Mn(1)–O(4)
O(2)–Mn(1)–O(4)
N(1)–Mn(1)–O(4)
O(1)–Mn(1)–O(6)
O(3)–Mn(1)–O(6)
O(2)–Mn(1)–O(6)
N(1)–Mn(1)–O(6)
O(4)–Mn(1)–O(6)
93.2(3)
176.6(2)
83.8(3)
88.8(3)
174.4(2)
94.1(3)
93.1(3)
93.7(3)
88.6(2)
91.4(3)
85.8(3)
85.6(3)
92.4(2)
89.3(3)
178.7(3)
O(5)–Mn(2)–O(3)
O(5)–Mn(2)–O(2)
O(3)–Mn(2)–O(2)
O(5)–Mn(2)–N(4)
O(3)–Mn(2)–N(4)
O(2)–Mn(2)–N(4)
O(5)–Mn(2)–N(3)
O(3)–Mn(2)–N(3)
O(2)–Mn(2)–N(3)
N(4)–Mn(2)–N(3)
O(5)–Mn(2)–N(2)
O(3)–Mn(2)–N(2)
O(2)–Mn(2)–N(2)
N(4)–Mn(2)–Mn(1)
N(3)–Mn(2)–Mn(1)
96.8(2)
93.0(2)
73.3(3)
93.9(2)
91.7(3)
164.1(3)
163.8(3)
93.5(2)
101.8(2)
73.4(2)
95.2(3)
161.9(3)
92.5(3)
128.4(2)
112.2(2)
Metal–metal distance
Cu(1)–Cu(1A)
a Symmetry transformation used: #1 Ϫx ϩ 1, Ϫy ϩ 1, Ϫz ϩ 1.
3.067(5)
Metal–metal distance
Mn(1)–Mn(2)
3.0367(19)
Fig. 5 Structure of [Mn2(II)(OEt)(µ–OAc)(µ-OEt)](PF6)ؒ2EtOH (10).
Hydrogen atoms, counter-ion, and lattice solvent omitted for clarity.
Mn(1)) and (O(4)–Mn(1)) bond lengths are longer than the
bond lengths in the Mn(1) plane. The axial bond lengths of
Mn(1) are comparable to the bond lengths found for Mn(2).
The crystal structure contains two ethanol molecules which are
oriented and positioned for hydrogen bonding with O(6) and
O(4). If this is so, the elongation of the axial bonds may be
caused by hydrogen bonding. The two ethanols of crystalliz-
ation are omitted from Fig. 5 for clarity. It is perhaps significant
that the bridge bonds are of different lengths, that is, the
Mn(1)–O(3) and Mn(1)–O(2) bond lengths are much shorter
than the analogous bonds, Mn(2)–O(3) and Mn(2)–O(2). This
asymmetry and the average bond lengths of the two metals
suggest that Mn(1) is in the Mn4ϩ oxidation state and that
Mn(2) is in the Mn2ϩ level. Consistent with this mixed valence
assignment is the presence of four negative oxygen ligands
coordinated to the Mn4ϩ ion. The ability of O2 to oxidize Mn2ϩ
to Mn4ϩ probably depends on the presence of these oxygen
donors. It will be noted that one of the pyridine ligands of the
binucleating ligand is not coordinated.
Fig. 4 ORTEP structure of [Cu4(II)2(µ-OAc)2](PF6)2ؒ2EtOH (9).
Thermal ellipsoids are at 30% probability and hydrogen atoms, counter-
ions, and lattice solvent are omitted for clarity.
be a Mn3ϩMn3ϩ or Mn2ϩMn4ϩ complex where, in either case,
the metals are antiferromagnetically coupled which decreases
the moment from the spin-only value of 8.9 µB. One, poorly
resolved, d–d electronic absorption band is observed at 520 nm
(ε, 420 L molϪ1 cmϪ1). The crystal structure of this complex
suggests that it is a mixed valence Mn2ϩMn4ϩ compound. Crys-
tallographic data is provided in Table 1, selected bond lengths
and angles are given in Table 6 and the structure is shown in
Fig. 5.
In the structure, the two manganese ions are bridged by the
alkoxide group of the ligand, by an exogenous ethoxide ion and
by an acetate ligand. Both manganese ions are 6-coordinate
with Mn(1) bonded to a terminal ethoxide ligand. Of the two
molecules of ethanol of crystallization, one appears to be
hydrogen bonded to the oxygen atom of the terminal ethoxide
ligand and the other seems to be bonded to one of the oxygen
atoms of the acetate bridge. The bond lengths of Mn(1) are
generally shorter than those of Mn(2) although the axial (O(6)–
Discussion
This series of crystal structures indicates that the present set of
ligands does not readily form the desired bimetallic complexes,
J. Chem. Soc., Dalton Trans., 2001, 3478–3488
3487

View Article Online
8277; (b) E. I. Solomon and T. C. Brunold, J. Am. Chem. Soc., 1999,
121, 8288.
5. Rather oligomeric complexes or otherwise unexpected struc-
tures are formed when the structure is not oligomeric. It is not
clear that the structures reported, particularly for the oligo-
meric Cu2ϩ complexes, are not a consequence of solubility
where the least soluble solution species crystallizes. If this were
the case for some of the complexes, the structure would depend
on the solvent and the counter-ion. It could be argued that the
Cu2ϩ oligomers form in part because of the instability of the
octahedral geometry and that oligomerization leads to stable 4-
and 5-coordination numbers as observed. This may be a factor
for the copper complexes but it is probably not the only factor.
Attempts to prepare Co2ϩ, Ni2ϩ and Mn2ϩ complexes with these
ligands led to the formation of ill-defined species which
appeared to be oligomeric. Since these metals were expected to
accommodate 6-coordination, the formation of oligomers sug-
gests that the ligands carry an inherent proclivity to oligomer-
ize. The tendency of this set of ligands to form oligomers is
perhaps surprising, given the observations reported on ligands
of type I. Binucleating ligands of this type, whether possessing
a phenolate bridge22–24 or an alkoxide bridge4–15 are reported to
form binuclear complexes with nearly all first row transition
metals, including a number of di-Cu2ϩ complexes.4–8 There are
examples where tetrametallic complexes are formed when two
bimetallic complexes are joined by exogenous bridges, but in
these cases the ligand in each bimetallic unit binds in the
expected way.15 In this respect the present ligands are unique in
not forming the expected bimetallic structures, 5. The binuclear
complexes formed by type I ligands represent a part of the
structure, 5, and it might be anticipated that the final extension
of the type I complexes to 5 would not represent a com-
plication. This, of course, was the assumption, which provided
the impetus for the present work. The tendency for the for-
mation of oligomers with ligands, II, III, IV and V, is probably
connected with the flexibility of these ligands. The traditional
ligands of type I have fewer degrees of freedom to form oligo-
mers than do the present ligands. The possibility that alkoxides
are poor bridging ligands and thus allow for oligomerization
is unlikely because the present oligomeric complexes display
extensive dimetal alkoxide bridging. It thus appears that the
major reason for oligomerization is the flexibility of the ligands.
The present work serves to illustrate the limits of binucleating
ligand design.
3 (a) C. Fraser, L. Johnston, A. L. Rheingold, B. S. Haggerty, C. K.
Williams, J. Whelan and B. Bosnich, Inorg. Chem., 1992, 31, 1835;
(b) C. Fraser, R. Ostrander, A. L. Rheingold, C. White and B.
Bosnich, Inorg. Chem., 1994, 33, 324; (c) C. Fraser and B. Bosnich,
Inorg. Chem., 1994, 33, 338; (d ) D. G. McCollum, L. Hall, C. White,
R. Ostrander, A. L. Rheingold, J. Whelan and B. Bosnich, Inorg.
Chem., 1994, 33, 924; (e) D. G. McCollum, C. Fraser, R. Ostrander,
A. L. Rheingold and B. Bosnich, Inorg. Chem., 1994, 33, 2383; ( f )
D. G. McCollum, G. P. A. Yap, A. L. Rheingold and B. Bosnich,
J. Am. Chem. Soc., 1996, 118, 1365; (g) D. G. McCollum, G. P. A.
Yap, L. Liable-Sands, A. L. Rheingold and B. Bosnich, Inorg.
Chem., 1997, 36, 2230; (h) B. Bosnich, Inorg. Chem., 1999, 38,
2554.
4 V. McKee, J. V. Dagdigian, R. Bau and C. A. Reed, J. Am. Chem.
Soc., 1981, 103, 7000.
5 Y. Nishida and S. Kida, J. Chem. Soc., Dalton Trans., 1986, 2633.
6 S. S. Tandon, L. K. Thompson, J. N. Bridson, V. McKee and A. J.
Downard, Inorg. Chem., 1992, 31, 4635.
7 T. Kayatani, Y. Hayashi, M. Suzuki, K. Inomata and A. Uehara,
Bull. Chem. Soc. Jpn., 1996, 69, 389.
8 H. Nie, S. M. J. Aubin, M. S. Mashuta, R. A. Porter, J. F.
Richardson, D. N. Hendrickson and R. M. Buchanan, Inorg. Chem.,
1996, 35, 3325.
9 Y. Hayashi, T. Kayatani, H. Sugimoto, M. Suzuki, K. Inomata,
A. Uehara, Y. Mizutani, T. Kitagawa and Y. Maeda, J. Am. Chem.
Soc., 1995, 117, 11220.
10 J. H. Satcher, Jr., A. L. Balch, M. M. Olmstead and M. W. Droege,
Inorg. Chem., 1996, 35, 1749.
11 B. Eulering, M. Schmidt, U. Pinkernell, U. Karst and B. Krebs,
Angew. Chem., Int. Ed. Engl., 1996, 35, 1973.
12 T. Tanase, Y. Yamada, K. Tanaka, T. Miyazu, M. Kato, K. Lee,
Y. Sugihara, W. Mori, A. Ichimura, I. Kinoshita, Y. Yamamoto,
M. Haga, Y. Sasaki and S. Yano, Inorg. Chem., 1996, 35, 6230.
13 K. Yamaguchi, S. Koshino, F. Akagi, M. Suzuki, A. Uehara and
S. Suzuki, J. Am. Chem. Soc., 1997, 119, 5752.
14 S. J. Brudenell, L. Spiccia, D. C. R. Hockless and E. R. T. Tiekink,
J. Chem. Soc., Dalton Trans., 1999, 1475.
15 J. H. Satcher, Jr., M. M. Olmstead, M. W. Droege, S. R. Parkin, B. C.
Noll, L. May and A. L. Balch, Inorg. Chem., 1998, 37, 6751.
16 J. K. Romary, J. D. Barger and J. E. Bunds, Inorg. Chem., 1968, 7,
1142.
17 O. Horner, E. Anxolabehere-Mallart, M.-F. Charlot, L. Chertanov,
J. Guilhem, T. A. Mattioli, A. Boussac and J.-J. Girerd, Inorg.
Chem., 1999, 38, 1222.
18 K. E. Harding and D. Nam, Tetrahedron Lett., 1988, 29, 3793.
19 J. R. Piper, L. M. Rose and T. P. Johnston, J. Med. Chem., 1979, 22,
631.
20 P. Brown, D. T. Davies, P. J. O’Hanlon and J. M. Wilson, J. Med.
Chem., 1996, 39, 446.
21 D. T. Davies and P. J. O’Hanlon, Synth. Commun., 1988, 18, 2273.
22 M. S. Mashuta, R. J. Webb, J. K. McCusker, E. A. Schmitt, K. J.
Oberhausen, J. F. Richardson, R. M. Buchanan and D. N.
Hendrickson, J. Am. Chem. Soc., 1992, 114, 3815.
23 M. Suzuki, A. Uehara, H. Oshio, K. Endo, M. Yanaga, S. Kida and
K. Saito, Bull. Chem. Soc. Jpn., 1987, 60, 3547.
Acknowledgements
This work was supported by grants from the NSF, NIH and
PRF.
24 P. Dapporto, M. Formica, V. Fusi, M. Micheloni, P. Paoli,
R. Pontellini and P. Rossi, Inorg. Chem., 2000, 39, 4663.
25 C. K. Johnson, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
References
1 R. E. Stenkamp, Chem. Rev., 1994, 94, 715 and references therein.
2 (a) E. I. Solomon and T. C. Brunold, J. Am. Chem. Soc., 1999, 121,
3488
J. Chem. Soc., Dalton Trans., 2001, 3478–3488