Coordinative flexibility in an acyclic bis(sulfonamide) ligand

Article abstract of DOI:10.1039/b912617a

The new acyclic and potentially heptadentate dinucleating ligand, 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp ^-) contains two tertiary sulfonamide groups. The sulfonamide donors permit a greater degree of control ove

Full text of DOI:10.1039/b912617a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Coordinative flexibility in an acyclic bis(sulfonamide) ligand†
Sune Veltze´, Rune Kirk Egdal, Frank B. Johansson, Andrew D. Bond and Christine J. McKenzie*
Received 26th June 2009, Accepted 25th September 2009
First published as an Advance Article on the web 19th October 2009
DOI: 10.1039/b912617a
The new acyclic and potentially heptadentate dinucleating ligand, 2,6-bis(N,N-bis-(2-pyridylmethyl)-
sulfonamido)-4-methylphenolato (bpsmp-) contains two tertiary sulfonamide groups. The sulfonamide
donors permit a greater degree of control over the accessibility of mono versus dinuclear complexes
compared to their closely related amine-containing counterparts, on account of their relatively weaker
donor properties. A series of air-stable dinuclear complexes of CoII, MnII and CuII containing two
auxiliary acetate ligands have been prepared. The absence of acetate in reaction mixtures containing
CoII and MnII led to mononuclear complexes, with water ligands completing the coordination spheres
of the metal ions, even in the presence of large excess of the metal ions. Thus, bridging acetate ligands
appear to stabilise the dinuclear structures for the relatively labile CoII and MnII ions. A mononuclear
complex of VIV O was isolated even in the presence of acetate, possibly because the oxyl groups on
=
each VIV prevent formation of a bis-acetato-bridged complex. Reaction of one equivalent of CuCl2 with
bpsmpH led to isolation of two different mononuclear complexes, dependent on the identity of the
solvent. The phenol group is coordinated in only one of these complexes. A dinuclear CuII complex was
isolated when two equivalents of the metal salt were used in the reaction.
nolate (bpbp-),2 except that it contains two tertiary sulfonamide
Introduction
groups ortho to the central phenol group, instead of tertiary amine
groups (Scheme 1). This paper describes the coordination chem-
istry of bpsmp- with copper, manganese, cobalt and vanadium,
and compares this to the chemistry that has previously been
described for bpmp- and bpbp-.
A major impetus for the preparation of dimetallic complexes
lies in the anticipation of cooperativity between metal ions.
This cooperativity might reveal itself in altered electronic, mag-
netic, chemical or catalytic properties which are not additive
compared to two equivalents of analogous mononuclear com-
pounds. Biology has taken advantage of this phenomenon for
a large range of enzymatic processes including reversible dioxy-
gen binding, catalysis of non-redox hydrolysis, and catalysis
of multi-electron redox reactions involving important inorganic
substrates like O2, N2, H2 and H2O. A common approach to
construct complexes that can furnish dimetallic “active sites”
for coordination of ancillary ligands or substrates is to employ
open-ended acyclic dinucleating ligands. In this case, the ligand
field strength, stereochemistry and coordinative flexibility of the
dinucleating ligand combine to influence the reactivity of the
dimetallic active sites towards binding and activation of substrate
molecules. In an effort towards discovery of new dimetallic
systems that may exhibit enhanced reactivity, we have pre-
pared the new acyclic phenolato-hinged dinucleating ligand 2,6-
bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolate,
(bpsmp-). This ligand is closely related to 2,6-bis(N,N-bis(2-
pyridylmethyl)aminomethyl)-4-methyl-phenolate (bpmp-)1 and
2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphe-
Scheme 1 Acyclic dinucleating pro-ligands based on hinging phenolate
groups containing two amine or two tertiary sulfonamide groups.
There are few known metal complexes of ligands containing
tertiary sulfonamide donors.3-6 The weaker M–N bond fur-
nished by the sulfonamide N donor relative to comparable
amine N donors is clearly demonstrated by comparison of the
structures of the matched pair of complexes [LNi(CH3CN)3]2+,
where L is either bis(1-methylbenzimidazolyl-2-methyl)amine
or its 10-camphorsulfonamide derivative:3 the Ni–Namine bond
Department of Physics and Chemistry, University of Southern Denmark,
Campusvej 55, 5230, Odense M, Denmark. E-mail: chk@ifk.sdu.dk;
Fax: +45 6615 8780; Tel: +45 6550 2518
† Electronic supplementary information (ESI) available: S1, Figure and
discussion of the structure of 2-hydroxy-3-(N,N-bis(2-pyridylmethyl)-
sulfonamido)-5-methylbenzenesulfonic acid (hpsmsH). CIF files for all
structures. S2, A table containing data concerning the geometries around
the sulfonamide N atoms. CCDC reference numbers 737969–737978. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/b912617a
˚
in the first complex is 2.160(3) A while the Ni–Nsulfonamide
˚
bond in the second complex is 2.377(8) or 2.405(10) A (in
two crystallographically independent complexes). The availabil-
ity of stronger potential auxilary ligands in reactions con-
taining the nickel complexes of bis(1-methylbenzimidazolyl-
2-methyl)-10-camphorsulfonamide appears to override the
chelate effect so that decoordination of sulfonamide ensues.
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For example, reaction of [LNi(CH3CN)3]2+, where L is the
tridentate bis(1-methylbenzimidazolyl-2-methyl)-10-camphorsul-
fonamide, with acetate or chloride results in decoordination of the
sulfonamide group so that the ligand becomes bidentate and is
bound only through the two N atoms of the benzamidazole units.3
The coordination sphere of Ni2+ is completed by two acetato or
two chlorido ligands, resulting in six- or four-coordination in the
acetato and chlorido products, respectively. By contrast, decoor-
dination of the amine group does not occur for the Ni2+ com-
plexes of the parent bis(1-methylbenzimidazolyl-2-methyl)amine
if the acetonitrile complex is treated with acetate or chloride.3
Nickel(II) complexes of the macrocyclic ligands 1,4,8,11-tetra-
azacyclotetradecane (cyclam)7 and its mono-N-tosylated counter-
part are also known. Decoordination of the sulfonamide does not
occur so readily for these complexes,6 although the Ni–Nsulfonamide
˚
bond is also at least 0.25 A longer than the Ni–Namine bonds.
The additional stability afforded by a macrocyclic tetradentate
versus linear tridentate ligand can account for this difference.
Metal complexes of secondary sulfonamides, predominantly N-
coordinated in their basic deprotonated forms, are considerably
more common than those of tertiary sulfonamides. For example
there are numerous examples of these where the deprotonated
sulfonamide is a tosylate group.8 Deprotonation will compensate
for the analogous weak donor properties of the protonated
secondary sulfonamides. Clearly, this mechanism for enhancing
the ligand field is not possible for a tertiary sulfonamide ligand.
The complexes of deprotonated secondary sulfonamides typically
have planar conformations around the N atom and short N–S
distances consistent with delocalisation of the electrons over the
–NS(O)2– unit.
Scheme 2 Preparation of the protonated bpsmpH and hpsmsH from
commercial starting materials.
methylpyridylamine (1.00 mL, 5.56 mmol) and pyridine (2.00 mL,
24.8 mmol). The solution turned dark red and was allowed to
stand one day with stirring. Methanol (10 mL) was then added
and the mixture was cooled to -18 ◦C causing precipitation of
a yellow-white product. The product was filtered off, washed
with ice-cold methanol and recrystallized from methanol. Yield
0.979 g (62%). M.p. 141 ◦C. Anal. calcd. for C31H30N6O5S2: C,
59.03; H, 4.79; N, 13.32; S, 10.17. Found: C, 59.20; H, 4.49;
N, 13.17; S, 10.09%. 1H NMR (CDCl3): d = 2.30 (s, 3 H,
CH3C), 4.68 (s, 8 H, NCH2C), 7.13 (m, 4 H, J = 1.2 Hz, J =
1.5 Hz, J = 2.7, pyridine NCHCHCH), 7.36 (dd, 4 H, J =
1.2 Hz, J = 0.9 Hz, pyridine CHCHC), 7.61 (multiplet, 4 H, J =
1.8 Hz, J = 3 Hz, J = 1.5 Hz, pyridine CHCHCH), 7.92 (s, 2 H,
CCHC), 8.46 (multiplet, 4 H, J = 0.9 Hz, J = 2.1 Hz, pyridine
NCHCH). 13C NMR (CDCl3): d = 20.41 (CH3C), 52.66 (NCH2C),
122.86 (pyridine NCHCHCH), 122.90 (pyridine CHCHC), 128.57
(CHCSC), 131.08 ((CH)2CCH3), 136.21 (pyridine CHCHCHC),
137.43 (CCHC), 148.87 (pyridine NCHCH), 153.06 (C2COH),
155.91 (pyridine CHCN). MS (MALDI): m/z (%, assignment):
675 (72, [2Na(bpsmp - H)]+), 631 (2, [bpsmpH]+), 438 (42),
220 (100). IR (KBr): n/cm-1 = 1592(m), 1572(m), 1476(m),
1438(m), 1328(vs), 1143(vs), 1091(w), 1056(w), 929(m), 816(s),
769(s), 712(w), 617(m), 571(s).
Experimental section
Solvents and starting materials were used as supplied from
commercial sources and reactions were carried out in air un-
less otherwise specified. 2,6-Dichlorosulfone-4-methylphenol9 was
1
prepared using literature methods, Scheme 2. H and 13C NMR
spectra were recorded on a 300 MHz Varian Gemini 2000
instrument, using TMS as an internal reference. Electrospray
Ionization Mass Spectra (ESI MS) were obtained using a Finnigan
TSQ 700 triple quadrapole or Qstar instrument equipped with a
Finnigan API source in the nanoelectrospray mode. Acetonitrile
was used to dissolve the complexes. IR spectra were measured
as KBr discs using a Hitachi 270–30 IR spectrophotometer.
UV-visible absorption spectra were recorded on a Shimadzu
UV-3100 spectrophotometer. Elemental analyses were per-
formed at the Chemistry Department II, Copenhagen Univer-
sity, Denmark and Atlantic Microlab, Inc., Norcross, Georgia,
USA.
CAUTION! Although we encountered no problems during
preparation of the perchlorate salts, care should be exercised when
handling these potentially explosive compounds.
2-Hydroxy-3-(N,N-bis-(2-pyridylmethyl)-sulfonamido)-5-
methylbenzenesulfonic acid (hpsmsH)
The reaction and crystallisation was carried out under dinitro-
gen. 2,6-Dichlorosulfone-4-methylphenol (0.21 g, 0675 mmol)
was added to bis-2-methylpyridylamine (0.25 mL, 1.39 mmol)
dissolved in chloroform (4 mL) over a period of 20 min under
N2. The mixture turned red and crystals of the product deposited
after about 2 days. The crystals decompose rapidly when removed
2,6-Bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenol,
(bpsmpH)
The reaction was carried out under dinitrogen. 2,6-
Dichlorosulfone-4-methylphenol (0.766 g, 2.51 mmol) was added
over a period of fifteen minutes to a mixture of bis-2-
10496 | Dalton Trans., 2009, 10495–10504
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from the mother liquor, and no yield has been recorded. For
X-ray crystallographic work (see ESI†), the crystals were trans-
ferred directly from their mother liquor to polyfluoroether oil
then moved rapidly into the N2 stream of the cryostat, operating
at 180 K. Once mounted in the N2 stream, the crystals were stable
for the duration of the data collection.
(10, [Cu(bpsmp)(Cl)Na]+); 692.1 (100, [Cu(bpsmp)]+). IR (KBr):
n/cm-1 = 1610 (m), 1475 (vs), 1330 (m) (asym. SO), 1141 (vs)
(sym. SO).
[Cu(Hbpsmp)Cl2]·2CH3CN (5)
A solution of Hbpsmp (0.0246 g, 0.039 mmol) in methanol
(4 mL) was mixed with CuCl2·2H2O (0.0067 g, 0.039 mmol) in
methanol (0.5 mL) to give a dark green solution. The solution was
evaporated to dryness and the residue redissolved in acetonitrile.
After approximately two hours, the solution had turned dark
red, and red crystals precipitated overnight. Yield 10.7 mg
(36%). Anal calcd. for C31H30Cl2CuN6O5S2 ([Cu(bpsmpH)Cl2]):
C, 48.66; H: 3.95; N, 10.98. Found: C, 48.02; H, 4.00; N, 10.58%.
ESIMS, m/z (%, assignment): 728.1 (18, [Cu(Hbpsmp)Cl]+); 692.1
(100, [Cu(bpsmp)]+); 631.2 (4, H2bpsmp+); 431.0 (75); 346.6 (25,
[Cu(Hbpsmp)]2+).
[VO(bpsmpH)](ClO4)2·1.7CH3OH·1.6H2O (1)10
Solutions of bpsmpH (0.0507 g, 0.0809 mmol) in methanol
(2 mL) and VO(ClO4)2 (0.2 mL, 0.8 M) in a 0.5 M aque-
ous HClO4 were mixed. The solution turned blue, then pur-
ple, and crystals of the product formed within a few hours.
Yield 45 mg (75%). Anal. calcd. for C32H36Cl2N6O16S2V
([VO(bpsmpH)](ClO4)2·CH3OH·H2O): C, 40.60; H, 3.83; N,
8.88. Found: C, 40.42; H, 3.43; N, 9.01%. ESIMS, m/z
(%, assignment): 736.1 (23, [NaVO(bpsmp)(OH)]+), 714.2 (11,
[VO(bpsmp)(H2O)]+), 696.1 (100, [VO(bpsmp)]+). IR (KBr)
n/cm-1: 1612 (m), 1465 (s), 1341 (m) (asym. SO), 1150 (vs)
(sym. SO).
[Cu2(bpsmp)Cl2]2CuCl4 (6)
A solution of bpsmpH (0.0619 g, 0.0982 mmol) in methanol (4 mL)
was mixed with CuCl2·2H2O (0.0519 g, 0.3045 mmol) dissolved in
methanol (2 mL). The resultant grass green precipitate was filtered
off and washed with methanol (3 ¥ 1.5 mL). Yield 67 mg (72%).
Anal. calcd. for C62H58Cl8 Cu5N12O12S4 ([Cu2(bpsmp)Cl2]2CuCl4):
C, 39.34; H, 3.09; N, 8.88. Found: C, 38.99, 38.90; H, 3.04,
3.17; N, 8.51, 8.55%. ESIMS, m/z (%, assignment): 825.0
(100, [Cu2(bpsmp)Cl2]+); 395.0 (75, [Cu2(bpsmp)Cl]2+). IR (KBr):
n/cm-1 = 1611(m), 1485 (s), 1341 (m) (asym. SO), 1149(vs)
(sym. SO).
1
2
[Mn(bpsmp)(H2O)2]ClO4·11 CH3CN· H2O (2)
2
BpsmpH (0.0577 g, 0.0918 mmol) and Mn(ClO4)2·6H2O (0.1625 g,
0.6403 mmol) were mixed in methanol (5 mL) to give a slightly
yellow solution. Reduction of the solution volume on standing
in an open vessel overnight resulted in the formation of white
crystals. Yield 71.0 mg (95%). Anal. calcd. for C31H33ClMnN6O11S2
([Mn(bpsmp)(H2O)2]ClO4): C, 45,40; H, 4,06; N, 10,25. Found:
C, 44.57; H, 3.86; N, 9.96%. ESIMS, m/z (%, assignment):
784.1 (3, [Mn(bpsmpH)ClO4]+); 720.1 (63, [Mn(bpsmp)(H2O)]+);
684.1 (100, [Mn(bpsmp)]+); 653.2 (4, [Na(bpsmpH)]+); 631.2 (89,
[bpsmpH2]+). IR (KBr): n/cm-1: 1606 (s), 1417 (s), 1336 (m)
(asym. SO), 1150 (vs) (sym. SO).
[Mn2(bpsmp)(CH3CO2)2]ClO4·CH3CN (7)
A solution of bpsmpH (0.0686 g, 0.1088 mmol) in acetonitrile
(4 mL), Mn(ClO4)2·6H2O (0.0608 g, 0.2395 mmol) in water
(1 mL) and sodium acetate (0.0268 g, 0.3265 mmol) in wa-
ter (1 mL) were mixed. This was followed by addition of
NaClO4·H2O (15.3 mg, 0.1088 mmol) in acetonitrile (0.5 mL).
Slow evaporation afforded colourless crystals after 1 day. The
crystals were separated, and washed with water. Yield 57 mg
(54%). Anal. calcd. for C37H38N7S2O13Mn2Cl ([Mn2(bpsmp)-
(CH3CO2)2]ClO4.CH3CN): C, 44.52; H, 3.84; N, 9.82. Found: C,
46.02; H, 3.79; N, 9.96%. ESIMS, m/z (%, assignment): 857.0
(70, [Mn2(bpsmp)(OOCCH3)2]+); 684.1 (100, [Mn(bpsmp)]+). IR
(KBr): n/cm-1: 1594(vs) (asym. CO2), 1471 (s), 1438 (vs) (sym.
CO2), 1338 (m) (asym. SO), 1151 (vs) (sym. SO).
[Co(bpsmpH)(H2O)2](ClO4)2·CH3CH2OH·H2O (3)
A solution of bpsmpH (0.0790 g, 0.1252 mmol) in methanol
(3.5 mL) was added to a solution of Co(ClO4)2·6H2O (0.2410 g,
0.6586 mmol) in water (2mL) to give a pink solution which
yielded red needles of the product after approx. two hours.
Yield 103 mg (83%). Anal. calcd. for C31H36Cl2CoN6S2O16
([Co(bpsmpH)(H2O)2](ClO4)2·H2O): C, 39.49; H, 3.85; N, 8.92.
Found: 39.59 H, 3.72; N, 8.80%. ESIMS, m/z (%, assignment):
788.0 (44, [Co(bpsmpH)ClO4]+); 724.1 (14, [Co(bpsmp)(H2O)2]+);
688.1 (73, [Co(bpsmp)]+); 631.2 (55, [(bpsmpH)]+); 491.0 (100);
344.6 (43, [Co(bpsmpH)]2+). IR (KBr) n/cm-1: 1610 (m), 1472 (s),
1333 (m) (asym. SO), 1145 (vs) (sym. SO).
[Co2(bpsmp)(CH3CO2)2]ClO4·CH3OH·2H2O (8)
[Cu(bpsmp)Cl]·4H2O (4)
BpsmpH (0.050 g, 0.0798 mmol) and Co(CH3CO2)2·4H2O
(0.0397 g, 0.1596 mmol) were mixed in methanol (15 mL). The
solution was heated for a few minutes during which time the
colour changed from pink to purple. NaClO4·H2O (0.022 g,
0.16 mmol) was added and the solution was cooled. Pink crystals
were deposited overnight. Yield 60 mg (78%). Anal. calcd.
for C35H39ClCo2N6O15S2. ([Co2(bpsmp)(CH3CO2)2]ClO4·2H2O):
C, 42,00; H, 3,93; N, 8,40. Found: C, 41.96. H, 3.71; N, 8.29%. ES-
IMS, m/z (%, assignment): 865.4 (100, [Co2(bpsmp)(CH3CO2)2]+);
837.3 (22, [Co2(bpsmp)(HCO2)2]+). IR (KBr) n/cm-1: 1608 (vs)
A solution of bpsmpH (0.080 g, 0.1269 mmol) in methanol (6 mL)
was mixed with CuCl2·2H2O (0.0206 g, 0.1208 mmol) dissolved in
methanol (1 mL). The solution first turned brown, then finally
became dark green. The solution was evaporated to dryness
then redissolved in a mixture of methanol (1 mL) and water
(2 mL). Dark green crystals of the product were deposited on
standing. Yield 43 mg (49%). Anal. calcd. For C31H35ClCuN6O8S2
([Cu(bpsmp)Cl]·3H2O): C, 47.57; H: 4.51; N, 10.74. Found: C,
47.60; H, 4.28; N, 10.55%. ESIMS, m/z (%, assignment): 750.1
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(asym. CO2), 1435 (s) (sym. CO2), 1341 (m) (asym. SO), 1154 (vs)
(sym. SO).
[CuII(bpsmp)(CH3CO2)Na]+,); 755.1 (100; [CuI2(bpsmp)]+);
692.13 (74; [Cu(bpsmp)]+). IR (KBr): n/cm-1 1611 (s), 1574 (m),
1466 (m), 1438 (s), 1331 (m), 1151(s), 1121 (s), 1108 (s).
[Cu2(bpsmp)(CH3CO2)2](ClO4) (9)
Single-crystal X-ray diffraction
Hbpsmp (0.1066 g, 0.1692 mmol) and NaCH3CO2·3H2O
(0.0921 g, 0.6766 mmol) were dissolved in methanol (4 mL).
Cu(ClO4)2·6H2O (0.1379 g, 0.3722 mmol) in methanol (2 mL)
was added, turning the solution dark green. After few hours
of standing, a light-green solid formed, which was isolated
and washed with small amounts of methanol. Yield: 104.6 mg
(65%). Anal. calcd. for C35H35ClCu2N6O13S2: C: 43.14; H: 3.62;
N: 8.63. Found C: 43.00; H: 33.67; N: 8.87. ESIMS, m/z (%,
assignment): 913.03 (10; [CuII2(bpsmp)(CH3CO2)ClO4]+),
889.0 (7; [CuII2(bpsmp)(H2O)(OH)ClO4]+); 873.06 (32;
[CuII2(bpsmp)(CH3CO2)2]+); 859.1 (17; [CuII2(bpsmp)(CH3CO2)-
(HCO2)]+); 814.1 (7; [CuIICuI(bpsmp)(CH3CO2]+); 774.2 (31,
Diffraction data were collected at 180(2) K on a Bruker–Nonius
X8 APEX-II instrument (MoKa radiation). Structure solution
and refinement was carried out using SHELXTL.11 Selected
crystallographic data are presented in Table 1. Complex 1 exhibits
disorder between coordinated H2O and MeOH molecules: in the
refined model, MeOH is considered to be present in 70% of
the complexes while H2O is present in the other 30%. Where
H2O is present, an associated H-bonded lattice H2O molecule
is also present. Thus, the structure is most clearly represented
as 70% [VO(bpsmpH)(MeOH)](ClO4)2·2MeOH·H2O and 30%
[VO(bpsmpH)(H2O)](ClO4)2·2MeOH·2H2O. In most cases, H
Table 1 Selected crystallographic details for bpsmpH, hpsmsH and complexes 1–8
bpsmpH
hpsmsH
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
C31H30N6O5S2
630.73
monoclinic
P21/n
8.8121(2)
99.746(2)
33.1686(7)
90
94.344(1)
90
2907.05(11)
4
C20H20Cl3N3O6S2
568.86
triclinic
P-1
8.1135(9)
11.9046(17)
13.1532(19)
72.956(5)
87.292(6)
89.602(4)
1213.3(3)
2
C33.7H44Cl2N6O18.3S2V
1011.93
monoclinic
P21/n
13.9275(11)
25.6124(17)
14.0430(10)
90
119.576(3)
90
4356.7(6)
4
C68H77Cl2Mn2N15O23S4
1781.47
triclinic
P-1
13.1117(7)
16.4295(7)
19.0495(12)
77.147(2)
86.282(2)
80.932(1)
3948.9(4)
2
C33H42Cl2CoN6O17S2
988.68
monoclinic
P21/c
12.8054(10)
21.2676(14)
15.8384(11)
90
96.797(3)
90
4283.1(5)
4
1.533
0.701
67973
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g/◦
3
˚
V/A
Z
D
calc/g cm-3
1.441
0.237
32567
1.557
0.593
8967
1.543
0.528
86785
1.498
0.577
91586
m(Mo Ka)
Total data
Unique data
Rint
5903
0.036
4384
0.037
0.096
1.05
-0.34, 0.30
4856
0.045
2748
0.094
0.286
1.05
-0.90, 0.99
8891
0.068
6006
0.050
0.144
1.07
-0.50, 0.89
16090
0.039
12128
0.045
0.129
1.07
-1.37, 1.40
8080
0.054
5569
0.088
0.279
1.02
-0.90, 2.32
Observed data [I > 2s(I)]
R1 [I > 2s(I)]
wR2 (all data)
Goodness of fit, S
-3
˚
r
min, rmax/e A
4
5
6
7
8
Empirical formula
Formula weight
Crystal system
Space group
C31H37ClCuN6O9S2
800.78
C35H36Cl2CuN8O5S2
847.28
monoclinic
P21/c
C62H58Cl8Cu5N12O10S4
C37H38ClMn2N7O13S2
998.19
monoclinic
P21/c
C36H43ClCo2N6O16S2
1033.19
monoclinic
C2/c
1860.74
orthorhombic
Pbcn
28.033(2)
15.1201(11)
17.8190(13)
90
90
90
7552.8(9)
4
1.636
1.841
58312
6692
0.096
4948
0.124
0.305
1.12
-1.73, 2.56
triclinic
P-1
˚
a/A
12.3780(9)
12.6820(9)
12.7179(7)
114.347(2)
104.098(2)
92.327(2)
1741.5(2)
2
1.527
0.886
27383
6012
0.063
3657
0.052
0.134
1.02
-0.59, 0.40
17.2665(16)
23.398(3)
9.6361(11)
90
106.029(4)
90
3741.6(7)
4
1.504
0.892
59920
6629
0.087
10.3700(4)
13.7747(6)
28.8164(12)
90
92.712(2)
90
4111.6(3)
4
1.613
0.855
29239
7244
0.043
32.4899(9)
17.0596(5)
18.0011(5)
90
119.150(1)
90
8713.7(4)
8
1.575
0.995
79861
8879
0.043
˚
b/A
˚
c/A
a/◦
b/◦
g/◦
3
˚
V/A
Z
D
calc/g cm-3
m(Mo Ka)
Total data
Unique data
Rint
Observed data [I > 2s(I)]
R1 [I > 2s(I)]
wR2 (all data)
Goodness of fit, S
4884
0.041
0.091
1.02
5470
0.043
0.122
1.01
7092
0.047
0.137
1.04
-3
˚
r
min, rmax/e A
-0.56, 0.29
-0.51, 0.73
-1.45, 1.08
10498 | Dalton Trans., 2009, 10495–10504
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atoms associated with N and O atoms could be located in
difference Fourier maps, but were included as riding on their
parent atoms for subsequent refinement. Where the H atoms could
not be located, they were included so as to form a reasonable
H-bond network (see CIFs in the ESI for complete details†). The
monoclinic lattice of 5 approximates orthorhombic-C and the
crystal was pseudo-merohedrally twinned according to the twin
law [1 0 1/0–1 0/0 0–1] (refined batch scale factor 0.1453(6)).
The structure of 6 is of relatively low quality, but was the best
that could be obtained from several batches. Modelling of the
2-
disordered CuCl4 counter anion seems to be only a moderate
source of difficulty. Although the largest peaks in the difference
density lie in this area, application of a continuous solvent-area
model (using SQUEEZE in PLATON12) to account for this anion
improves wR2 to only about 25%. Solvent-accessible voids of
3
˚
ca 80 A remain in the final refined structure, but no further
Fig. 1 X-ray crystal structure of bpsmpH with displacement ellipsoids
drawn at 50% probability (H atoms omitted).
atomic sites could be resolved and application of SQUEEZE
to the final model again gave no significant improvement. In
all structures containing perchlorate anions, the geometry of
-
Synthesis and X-ray crystal structures of the metal complexes
ClO4 was restrained to be tetrahedral, by restraining all Cl–O
distances to a single refined value and all O ◊ ◊ ◊ O distances to be
Mononuclear VIVO, MnII, CoII, CuII, and dinuclear MnII2, CoII
2
1.633 times that value. In cases with apparent rotational disorder,
and CuII2 complexes of bpsmpH have been prepared (Scheme 3). In
contrast to our experience with the phenolate-hinged dinucleating
ligands, bpmp- and bpbp-, it is apparent that a much greater degree
of control is possible over the formation of mono versus dinuclear
complexes using bpsmp-. This is not controlled by reaction
stoichiometry, rather it is by the nature of the potential ancillary
ligands and the specific metal ions provided in reactions. For
example, reaction of more than two equivalents of the perchorate
salts of MII (M = Mn or Co) with one equivalent of bpsmpH
leads to isolation of the mononuclear aqua MII complexes in high
yields. By contrast, reaction under similar conditions of bpbpH
with more than two equivalents of the perchorate salts of MII
(M = Mn, Co or Cu) gives dinuclear CoIII2, MnII2, MnIIIMnII and
-
the ClO4 anions are modelled either in two orientations and/or
with distorted anisotropic displacement ellipsoids.
Results and discussion
Ligand synthesis and X-ray crystal structures
Reaction of 2,6-dichlorosulfone-4-methylphenol with two equiv-
alents of bis-(2-methylpyridyl)amine gives 2,6-bis(N,N-bis-(2-
pyridylmethyl)-sulfonamido)-4-methylphenol, (bpsmpH) in good
yield when the reaction is carried out in pyridine, Scheme 2.
Initial attempts to carry out the reaction in chloroform resulted
only in mono-substitution of the dichlorosulfonic acid by bis-2-
methylpyridylamine, while the second chlorosulfonic acid group
was hydrolysed to give 2-hydroxy-3-(N,N-bis-(2-pyridylmethyl)-
sulfonamido)-5-methylbenzenesulfonic acid (see ESI for crystal-
lographic details†).
The X-ray crystal structure of bpsmpH (Fig. 1) suggests that
its deprotonated form is appropriate for the provision of two
metal binding cavities. All four sulfone O atoms are located
on one side of the plane defined by the phenol group so that
the potential metal binding cavities are located on the opposite
side of the plane. One of the pyridine groups forms an H-bond
CuII complexes containing combinations of water- or methanol-
2
derived ligands and/or perchlorate auxiliary ligands.13-17 Given
similarities of these ligand systems and product complexes with
respect to charge and topology this observation is thus not likely
to be due to solubility effects, rather it attests to the relatively
weaker ligand field provided by the second binding site once
the first is occupied by a metal ion in cases where relatively
weakly coordinating auxiliary ligands are provided. When the
geometrically suitable bridging, negatively charged acetate ligand
is introduced to reaction mixtures, high yields of the dinuclear
complexes are attained, even in the presence of stoichiometric
amounts of the metal ions.
˚
to the phenol group (N ◊ ◊ ◊ O distance 2.4819(19) A), with the
H
atom apparently disordered between N ◊ ◊ ◊ H–O and
N+–H ◊ ◊ ◊ O- arrangements. Each sulfonamide N atom is located
˚
approximately 0.3 A from the plane formed by the two C atoms
Mononuclear complexes
and one S atom to which it is connected, and the N–S distance is
˚
shorter by around 0.1 A compared to the corresponding distance
Reaction of bpsmpH with vanadyl(IV), manganese(II) and
cobalt(II) perchlorate gave the mononuclear complexes, 1, 2 and
3 (Scheme 3), while reaction of bpsmpH with copper(II) chloride
led to three different compounds depending on the solvent and
reaction stoichiometry. Mononuclear complexes 4 and 5 were
formed with one equivalent of CuCl2. Complex 4 was isolated
from methanol/water, while 5 was isolated from acetonitrile. The
dinuclear complex 6 was obtained by adding more than two
equivalents of CuCl2 to the reaction.
in the metal complexes (vide infra). Thus, there must be significant
electron delocalisation in the sulfonamide unit with the N atoms
close to sp2 hybridised, similar to that observed in complexes of
deprotonated secondary sulfonamides. Inspection of the X-ray
structures of the metal complexes of bpsmp- (vide infra) indicates
that the electron density is redistributed on coordination, and a
more pyramidal geometry is approached around the sulfonamide
N atoms.
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Scheme 3 Structurally-characterised complexes 1–8 (charges are not depicted).
+
The X-ray crystal structures of 1–5 are shown in Figs. 2–6.
In complexes 1–3, the metal ions show an octahedral geom-
etry coordinated by the phenolate O atom and one bis-(2-
methylpyridyl)sulfonamide group in a fac coordination mode.
Two water ligands complete the coordination sphere in the MnII
and CoII complexes, while the VIVO complex has an oxido
ligand and either a methanol or water ligand (disordered in
the crystal structure). In this case, the oxido group lies trans
to the sulfonamide N-donor (Fig. 2). In 1, the two pyridine
rings in the non-coordinated bis-(2-methylpyridyl)sulfonamide
group adopt an approximately coplanar arrangement (akin to
the mer coordination mode in complexes 4–6), and the proton
associated with the bpsmpH ligand links the two rings through an
˚
N –H ◊ ◊ ◊ N hydrogen bond (N ◊ ◊ ◊ N distance 2.740(4) A). Complex
2 contains two complexes in its crystallographic asymmetric unit,
˚
with closely comparable geometries (rms deviation 0.18 A for
least-squares overlay of 47 non-H atoms). Both pyridine rings
of the non-coordinated bis-(2-methylpyridyl)sulfonamide group
accept H-bonds from coordinated water molecules in an adjacent
complex, and phenolate and sulfonate O atoms also accept
H-bonds from one of these water molecules. In this way, the crys-
tallographically distinct complexes are associated into H-bonded
pairs having approximate (non-crystallographic) C2 symmetry
(Fig. 3(b)). In the structure of 3, the non-coordinated pyridine
rings adopt an approximately coplanar arrangement similar to
that in 1, forming an N+–H ◊ ◊ ◊ N hydrogen bond (N ◊ ◊ ◊ N distance
˚
2.705(8) A).
In 4, the Cu2+ ion adopts 5+1 octahedral coordination, bound by
the phenolate O atom and the bis-(2-methylpyridyl)sulfonamide
group in a mer coordination mode. One chloride ligand with a
˚
Cu–Cl distance of 2.2485(12) A lies approximately in the same
plane as the three N donors of the bis-(2-methylpyridyl)sulfo-
namide group, while a second chloride from an adjacent complex
is associated with the copper ion trans to the phenolate group,
˚
with Cu–Cl = 3.410(2) A. Thus, the [Cu(bpsmp)Cl] complexes
are associated into centrosymmetric dimeric units through typical
rhomboid-type Cu(m-Cl)2Cu bridges. The non-coordinated bis-
(2-methylpyridyl)sulfonamide group forms a “pincer” type con-
formation in which the two pyridine rings come into approximate
face-to-face contact, and the N atoms of both rings are involved
in an H-bonded network through the lattice water molecules. One
pyridine ring is apparently disordered and is modelled in two
orientations. In one orientation, the N atom accepts an H-bond
from a lattice water molecule, while in the other orientation it is
involved in a C–H ◊ ◊ ◊ N contact with an adjacent pyridine ring
Fig. 2 Cation in 1 with displacement ellipsoids drawn at 50% probability.
H atoms are omitted, except for that involved in the intra-complex
N+–H ◊ ◊ ◊ N hydrogen bond (dotted line). The coordinated methanol
molecule is disordered; alternatively, a water molecule occupies this
coordination site.
˚
(H ◊ ◊ ◊ N = 2.49 A).
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Fig. 5 Two complexes in 4 with displacement ellipsoids drawn at 50%
probability (H atoms omitted). The dimeric unit is formed across a
crystallographic centre of inversion.
Fig. 6 Complex 5 with displacement ellipsoids drawn at 50% probability.
H atoms are omitted, except for that involved in the intra-complex
N+–H ◊ ◊ ◊ O hydrogen bond (dotted line).
accepts an intra-complex H-bond from one protonated pyridine
ring in the non-coordinated bis-(2-methylpyridyl)sulfonamide
Fig. 3 (a) One of the two crystallographically distinct cations in 2 with
displacement ellipsoids drawn at 50% probability (H atoms omitted).
(b) Pair of complexes in 2 associated through O–H ◊ ◊ ◊ N and O–H ◊ ◊ ◊ O
hydrogen bonds, projected along the approximate C2 symmetry axis.
˚
group (N ◊ ◊ ◊ O distance 2.529(4) A). The N atom of the other non-
coordinated pyridine ring does not form any H-bond interaction
or any other obviously significant intermolecular interaction in
the crystal structure.
In all of the mononuclear complexes 1–5, most of the non-
coordinated N-donors are either protonated or involved in
H-bonding interactions (the exceptions being one N-donor in 5
and the N atom in one component of the disordered pyridine
ring in 4). Thus, after complexation of the first metal ion, the
second potential metal binding does not appear to out-compete
protonation and/or H-bonding interactions with polar protic
solvents. Attempts to prepare dinuclear complexes simply by
increasing the pH were unsuccessful, showing that protonation
state alone is not sufficient to control formation of mononuclear
versus dinuclear complexes.
Fig. 4 Cation in 3 with displacement ellipsoids drawn at 50% probability.
H atoms are omitted, except for that involved in the intra-complex
N+–H ◊ ◊ ◊ N hydrogen bond (dotted line).
Dinuclear complexes
The X-ray crystal structure of the dinuclear Cu2+ complex 6
is shown in Fig. 7. Both Cu2+ ions are coordinated by a
bis-(2-methylpyridyl)sulfonamide group and the bridging phe-
nolato O atom. The mer coordination mode of the bis-(2-
methylpyridyl)sulfonamide group is consistent with that observed
in the mononuclear Cu2+ complexes (4 and 5). The sulfonamide
N atoms lie on opposite sides of the plane of the phenol ring, in
In the structure of 5, the Cu2+ ion is bound by one bis-(2-
methylpyridyl)sulfonamide group in a mer coordination mode and
by two chlorides, giving a geometry between square-pyramidal and
trigonal-bipyramidal (Addison parameter, t = 0.27).18 The com-
plex is unique amongst those described herein in that the phenolate
O atom is not involved in metal coordination. Instead, the O atom
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as [M(bpsmp]+ are also present. This is not the case for the ESI
mass spectra of analogous [M2(bpbp)(CH3CO2)2]+/2+ complexes.14
Thus, it is apparent again that the affinity of bpsmp- for binding
a second metal ion is less than that for binding the first.
In the crystalline state, the structures of complexes 7 and 8
˚
are closely comparable (rms deviation 0.44 A for least-squares
overlay of 54 non-H atoms). The structure of 8 is shown in Fig. 8.
The complexes exhibit approximate (non-crystallographic) C2
symmetry, with the pseudo-rotation axis lying along the C–Ophenolate
bond. The bis-(2-methylpyridyl)sulfonamide groups adopt a fac
coordination mode and the M2+ ions adopt distorted octahedral
coordination geometries. In both complexes, the M–Nsulfonamide
bonds are significantly longer than the M–Npyridine bonds: 2.443(3)
˚
˚
and 2.481(3) A in 7 cf Mn–Npyridine ave 2.276 A; 2.263(3) and
˚
˚
2.312(3) A in 8 cf Co–Npyridine ave 2.123 A. The M–Oacetato distances
are slightly more asymmetric in 7 compared to 8, with the
Mn–Oacetato bond trans to the sulfonamide N donor being slightly
longer than the Mn–Oacetato bond trans to the pyridine N donor
˚
(2.122(2) and 2.103(2) cf 2.054(2) and 2.068(2) A).
Fig. 7 (a) Complex 7 with displacement ellipsoids drawn at 50%
probability (H atoms are omitted). (b) Coordination polymer formed
through Cu(m-Cl)2Cu bridges.
contrast to the conformation observed in the crystal structure
of the free bpsmpH ligand. The geometry around the Cu2+
ions is 5+1 octahedral. In addition to the donor O and N
atoms derived from bpsmp-, two chlorides complete the Cu2+
Fig. 8 Complex 8 with displacement ellipsoids drawn at 50% probability
(H atoms are omitted).
˚
coordination sphere, with one short (Cu–Cl av. 2.25 A) and
one long (Cu ◊ ◊ ◊ Cl av. 3.32 A) distance. The longer Cu ◊ ◊ ◊ Cl
To date, crystals of the dinuclear CuII complex 9 suitable for
structural analysis have not been obtained. Two possibilities are
conceivable for its structure: both acetato ligands could bridge
the Cu2+ ions in a conformation comparable to 7 and 8, or each
acetato ligand could be coordinated to only one Cu2+ ion in a
monodentate manner to give a structure more similar to that of
6 (Scheme 3) The first proposal gives six-coordinated Cu2+ with a
fac coordination mode for the bis-(2-methylpyridyl)sulfonamide
groups, while five-coordinated Cu2+ and a mer coordination
˚
contacts associate the complexes into dimeric units through Cu(m-
Cl)2Cu bridges comparable to those in 4, thereby constructing a
1D coordination polymer (Fig. 7(b)). The stoichiometry of the
reaction that produced 6 was approximately 1:3 bpsmpH:CuCl2
2-
and the excess CuCl2 is found in the CuCl4 counter anion.
When reactions of bpsmpH with two equivalents of copper(II)
manganese(II) or cobalt(II) perchlorate are carried out in the
presence of acetate ions, the products are the dinuclear complexes
7–9 (Scheme 3). A similar reaction using VO(ClO4)2 resulted
only in isolation of the mononuclear complex 1; apparently,
the possibility for VIVO to coordinate only one bridging acetato
ligand is not sufficient to yield dinuclear vanadyl complexes. The
dinuclear complexes of bpsmp- are isolated in lower oxidation
states under aerobic conditions compared to their bpmp- and
bpbp- counterparts, for which CoIICoIII, CoIIICoIII, and MnIIMnIII
dominate.14,16,19 This resistance to aerobic oxidation is consistent
with the presence of electron-withdrawing sulfonamide groups.
ESI mass spectra show all of the relevant cations as the dominant
species, but daughter ions assignable to mononuclear species such
mode are most commonly seen in CuII complexes of bpbp-
2
and bpmp-.17,20 Furthermore the ESI mass spectra of the 9
shows a different pattern of ions compared to 7 and 8. Ions
containing two metal ions and either one or two acetates along
with ions containing one metal ion and an acetate. By contrast
the Co and Mn systems gave ESIMS spectra showing either the
molecular cation containing two metal ions and two acetates or
mononuclear ions with no acetate. Taken together these results
point to 9 containing non-bridging auxiliary acetato ligands. The
most probable structure of 9 is therefore given by the second
proposal. Mono-coordinated acetate has previously been observed
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in the mono- and di-nuclear pentacoordinated CuII complexes of
bis(2-pyridylmethyl)aniline.21,22
greater than the sum of the standard covalent radii for the Mn and
23
˚
N atoms concerned (1.35 + 0.68 = 2.03 A) and might therefore
be regarded as a non-bonding contact. Thus, the structures of
complexes 1–8 demonstrate a significant degree of topological
and coordinative flexibility for the bpsmp- ligand. Although the
tertiary sulfonamide N atom may be ostensibly non-bonded, it
is unable to move too far from the metal ion since it connects
three donor atoms in three chelating rings. This contrasts to the
situation in the Ni2+ complexes of bis(1-methylbenzimidazolyl-
2-methyl)-10-camphorsulfonamide (L),3 where only two donor
atoms in two chelating rings are connected by the sulfonamide.
On decoordination in those cases, the sulfonamide can move away
Discussion of the structural chemistry
Comparison of the N–S bond distances and angles around the
sulfonamide N atoms of coordinated versus non-coordinated
groups (in bpsmpH and its mono-substituted analogue†) reveals
that the N–S distances in the non-coordinated groups are shorter
˚
by about 0.1 A and that there is a near planar conformation around
the N atom of an uncoordinated tertiary sulfonamide (for full
details, see Table in ESI†). This confirms significant contribution
from the canonical forms containing an N S double bond in the
resonance structures shown in Scheme 4. Although involvement
of the N lone pair in coordination bonding should reduce the
=
from the metal centre, resulting in M ◊ ◊ ◊ Nsulfonamide distances greater
2+
˚
than 3.65 A in the octahedral [LNi(CH3CO2)2] and tetrahedral
LNiCl2 complexes, and a loss of integrity in the overall structure
of the complex through coordination of additional compensating
ligands. In bpsmp-, the sulfonamide group cannot be lost to
the complex on decoordination, but rather is forced to remain
in close proximity to the metal ions so that the integrity of the
dinuclear complexes is retained. This feature permits speculation
about feasible processes of pseudo-decoordination of the tertiary
sulfonamide group(s) in bpsmp- complexes, for the purpose of
stabilising various metal geometries needed for electrochemical
or catalytic events involving coordination expansion or reduction
(Scheme 5).
=
contribution of the N S forms, inductive effects are still expected
to decrease significantly the strength of the M–N bond. Thus, a
tertiary sulfonamide N atom is a poorer electron donor than the
N atom of a tertiary amine.
Scheme 4 Resonance structures for the tertiary sulfonamide group.
Conclusions
The two halves of the bpsmp- ligand are chemically equivalent
until the first metal ion is bound. After coordination of the first
metal ion, the donor strength of the bridging phenolate group
is apparently reduced to such an extent that a second metal ion
cannot be coordinated without the stabilising effect of auxiliary
ligands, at least in polar and hydroxylic solvents. This effect
is clearly not as strong for the bpbp- system. Apparently, two
bridging acetate ligands are required to form dinuclear complexes
for Mn2+ and Co2+. For the vanadyl complexes, the presence
The ability to control the outcome of reactions of bpsmp- with
metal ions, in terms of whether mononuclear or dinuclear com-
plexes are isolated, stands in sharp contrast to the coordination
chemistry observed for the counterpart acyclic dinucleating lig-
ands containing tertiary amine groups in the same position (bpmp-
and bpbp-). One determining factor favouring the formation of
dinuclear complexes is the availability of bridging acetate ligands.
For example, reactions using Mn2+ or Co2+ carried out in the
absence of acetate yielded only mononuclear complexes, even in
the presence of excess metal ions (greater than 2 equivalents per
bpsmp-). The addition of acetate yielded dinuclear complexes from
similar reaction mixtures, even without the presence of excess
metal ions. The propensity for 5 or 5+1 coordination means
that Cu2+ complexes behave differently from the other metal ions
described here, and dinuclear complexes could be synthesised
without supporting acetate bridges. By contrast, under similar
reaction conditions dinuclear copper,17 manganese,13 cobalt17
and vanadium24 complexes containing exclusively dioxygen-,
=
of V O prohibits more than one bridging acetate ligand and
dinuclear complexes with bpsmp- have not been observed. For
Cu2+, the propensity for 5 or 5+1 coordination means that the
dinuclear complex 6 could be synthesised without supporting
acetate bridges, although some stabilisation must also be provided
by formation of the coordination polymer in the solid state.
The M–Nsulfonamide distances in the eight crystal structures
described herein show a relatively large range, from 2.114(11)
˚
˚
in 6 to 2.481(3) A in 7. The latter distance is more than 0.4 A
Scheme 5 Proposal for coordination flexibility of the tertiary sulfonamide groups bpsmp- in accordance with metal geometry changes during addition
and elimination reactions involving both metal centres.
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water- or methanol-derived auxiliary ligands have been isolated
using bpbp-. The formation of mononuclear complexes of bpsmp-
can be ascribed to the fact that the sulfonamide groups of bpsmp-
are weaker donors compared to, for example, the corresponding
amine groups of bpmp- and bpbp-. The controllable accessibility
in high yield of a range of mononuclear bpsmp- complexes might
find use in stepwise preparations of mixed-metal complexes.
In addition to the control over metal nucleation a comparatively
extensive range of structural types were observed via the coordi-
nation/decoordination of the pyridine, sulfonamide and phenol
donors of bpsmp- compared to the structural topologies of the
metal complexes of related heptadentate phenolato-hinged dinu-
cleating ligands. The coordinative flexibility of bpsmp- evidenced
here suggests potential for bpsmp- to be used for construction of
complexes which might furnish a coordinatively flexible dimetallic
active site for addition and elimination reactions, with the con-
current assistance of M–Nsulfonamide coordination/decoordination.
Thus, the ditopic site could potentially support two metal ions
in various and different geometries. Future work will focus on a
search for reactions which might be promoted or catalysed by such
a geometrically and redox-flexible dimetallic site.
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10504 | Dalton Trans., 2009, 10495–10504
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