Reductive nitrosylation and proton-assisted bridge splitting of a (μ-oxo)dimanganese(III) complex derived from a polypyridine ligand with one carboxamide group

Article abstract of DOI:10.1021/ic0503535

Aerobic oxidation of the Mn(II) complex [Mn(Papy₃)(H ₂O)](ClO₄) (1, PaPy₃^- is the anion of the designed ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2- carboxamide) in acetonitrile affords the (μ-oxo)dimanganese-(III) complex [(Mn(PaPy₃))₂(μ-O)](ClO₄)₂ (3) in high yield, The unsupported single oxo bridge between the two high-spin Mn(III) centers in 3 is readily cleaved upon addition of proton sources such as phenol, acetic acid, and benzole acid, and complexes of the type [Mn(PaPy ₃)(L)](ClO₄) (5, L = PhO^-; 6, L = AcO ^-; 7, L = BzO^-) are formed. The basicity of the bridge is evident by the fact that simple addition of methanol to a solution of 3 in acetonitrile affords the methoxide complex [Mn(PaPy₃)(OMe)](CLO ₄) (4). The structures of 3-5 and 7 have been determined. Passage of NO through a solution of 3 in acetonitrile produces the {Mn-NO}⁶ nitrosyl [Mn(PaPy₃)-(NO)](CLO₄) (2) via reductive nitrosylation. Complexes 4-7 also afford the {Mn-NO}⁶ nitrosyl 2 upon reaction with NO. In the latter case, the anionic O-based ligands (such as MeO^- and PhO^-) act as built-in bases and promote reductive nitrosylation of the Mn(III) complexes.

Full text of DOI:10.1021/ic0503535

Inorg. Chem. 2005, 44, 8469−8475
Reductive Nitrosylation and Proton-Assisted Bridge Splitting of a
-Oxo)dimanganese(III) Complex Derived from a Polypyridine Ligand
with One Carboxamide Group
(
µ
Kaushik Ghosh,† Aura A. Eroy-Reveles,† Marilyn M. Olmstead,‡ and Pradip K. Mascharak*,†
Department of Chemistry and Biochemistry, UniVersity of California,
Santa Cruz, California 95064, and Department of Chemistry, UniVersity of California,
DaVis, California 95616
Received March 7, 2005
-
Aerobic oxidation of the Mn(II) complex [Mn(Papy3)(H2O)](ClO4) (1, PaPy3 is the anion of the designed ligand
N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) in acetonitrile affords the (
(III) complex [(Mn(PaPy3))2( -O)](ClO4)2 (3) in high yield. The unsupported single oxo bridge between the two
high-spin Mn(III) centers in 3 is readily cleaved upon addition of proton sources such as phenol, acetic acid, and
benzoic acid, and complexes of the type [Mn(PaPy3)(L)](ClO4) (5, L
PhO-; 6, L AcO-; 7, L BzO-) are
formed. The basicity of the bridge is evident by the fact that simple addition of methanol to a solution of 3 in
acetonitrile affords the methoxide complex [Mn(PaPy3)(OMe)](ClO4) (4). The structures of 3 5 and 7 have been
µ-oxo)dimanganese-
µ
)
)
)
−
6
determined. Passage of NO through a solution of 3 in acetonitrile produces the
{
Mn
}
−NO
}
nitrosyl [Mn(PaPy3)-
6
(NO)](ClO4) (2) via reductive nitrosylation. Complexes 4 7 also afford the Mn NO
−
{
−
nitrosyl 2 upon reaction with
NO. In the latter case, the anionic O-based ligands (such as MeO- and PhO-) act as built-in bases and promote
reductive nitrosylation of the Mn(III) complexes.
Introduction
plexes of manganese are numerous, a much smaller number
of binuclear complexes in which two manganese ions are
bridged by a single oxo group have been reported.3a
It has recently been recognized that coordination of
deprotonated carboxamido nitrogen(s) provides additional
stabilization to metal ions in higher oxidation states.4 Indeed,
complexes of Mn(III),5 Mn(IV),6 and Mn(V)7 with coordi-
nated carboxamido nitrogen(s) have been isolated and
structurally characterized. Recently, we have reported the
Manganese (Mn) is widely distributed in nature, and
among the first-row transition elements, it is second to iron
in terms of its natural abundance.1 In biological systems,
manganese not only acts as a Lewis acid like magnesium,
zinc, or calcium but also plays important roles in oxidation
catalysis like iron and copper, cycling among the oxidation
states of +2, +3, and +4. The chemistry of oxo-bridged
polynuclear manganese complexes has been investigated in
detail because of their potential relevance to Mn-containing
catalase and the oxygen-evolving complex (OEC) of pho-
tosystem II.2,3 Although examples of binuclear bis(µ-oxo),
bis(µ-carboxylato), and mixed µ-oxo µ-carboxylato com-
(3) (a) Mukhopadhyay, S.; Mandal, S. K.; Bhaduri, S.; Armstrong, W.
H. Chem. ReV. 2004, 104, 3981. (b) Wu, A. J.; Penner-Hahn, J. E.;
Pecoraro, V. L. Chem. ReV. 2004, 104, 903. (c) Renger, G. Angew.
Chem., Int. Ed. Engl. 1987, 26, 643.
(4) (a) Marlin, D. S.; Mascharak, P. K. Chem. Soc. ReV. 2000, 29, 69. (b)
Marlin, D. S.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem. 1999,
38, 3258.
(5) (a) Lin, J.; Tu, C.; Lin, H.; Jiang, P.; Ding, J.; Guo, Z. Inorg. Chem.
Commun. 2003, 6, 262. (b) Moreira, R. F.; When, P. M.; Sames, D.
Angew. Chem., Int. Ed. 2000, 39, 1618. (c) Che, C.-M.; Cheng, W.-
K. J. Chem. Soc., Chem. Commun. 1986, 1443.
(6) (a) Chandra, S. K.; Chakravorty, A. Inorg. Chem. 1992, 31, 474. (b)
Chandra, S. K.; Choudhury, S. B.; Ray, D.; Chakravorty, A. J. Chem.
Soc., Chem. Commun. 1990, 474.
* To whom correspondence should be addressed. E-mail:
pradip@chemistry.ucsc.edu.
† University of California, Santa Cruz.
‡ University of California, Davis.
(1) (a) Frausto da Silva, J. J. R.; Williams, R. J. P. The Biological
Chemistry of Elements. The Inorganic Chemistry of Life; Clarendon
Press: Oxford, England, 1991. (b) Cotton, F. A.; Wilkinson, G.
AdVanced Inorganic Chemistry; John Wiley & Sons: New York, 1988.
(2) (a) Manganese Redox Enzymes; Pecoraro, V. L., Ed.; VCH: New
York, 1992. (b) Babcock, G. T. In New ComprehensiVe Biochemis-
try: Photosynthesis; Amesz, J., Ed.; Elsevier: Amsterdam, 1987; pp
125-158.
(7) (a) MacDonnell, F. M.; Fackler, N. L. P.; Stern, C.; O’Halloran, T.
V. J. Am. Chem. Soc. 1994, 116, 7431. (b) Collins, T. J.; Powell, R.
D.; Slebodnick, C.; Uffelman, E. S. J. Am. Chem. Soc. 1990, 112,
899.
10.1021/ic0503535 CCC: $30.25
Published on Web 10/13/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 23, 2005 8469

Ghosh et al.
syntheses of Mn(II) and Mn(III) complexes of a pentadentate
ligand (PaPy3H, H is dissociable proton) in which the metal
centers are coordinated to one deprotonated carboxamido
nitrogen, three pyridyl nitrogens, and a tert-amine nitrogen.8
Studies on the reactivity of these manganese complexes with
NO revealed that the Mn(II) complex [Mn(PaPy3)(H2O)]-
(ClO4) (1) readily reacts with NO to afford the diamagnetic
{Mn-NO}6 nitrosyl [Mn(PaPy3)(NO)](ClO4) (2).9 This Mn-
nitrosyl releases NO when exposed to visible light.8 Interest-
ingly, the Mn(III) complexes [Mn(PaPy3)Cl](ClO4) and
[Mn(PaPy3)(MeCN)](ClO4)2 do not react with NO.
the reported formation of {Mn-NO}5 nitrosyls in the
reactions of non-porphyrin Mn(III) complexes with NO.12
Experimental Section
2-(Aminomethyl)pyridine, N-(2-bromoethyl)phthalimide, picolin-
ic acid, hydrazine monohydrate, and Mn(ClO4)2‚6H2O were pur-
chased from Aldrich Chemical Co. and used without further
purification. NO gas, procured from Johnson Matthey Chemical
Co., was purified by passage through a KOH column. All solvents
were distilled from the appropriate drying agents prior to use as
follows: DMF from BaO; MeCN and CH2Cl2 from CaH2; MeOH
from Mg(OMe)2; Et2O from Na.
Selected manipulations were carried out using standard Schlenk
techniques to avoid exposure to dioxygen.
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Only small quantities of these
compounds should be prepared and handled with proper protection.
Synthesis of the Compounds. The ligand N,N-bis(2-pyridyl-
methyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy3H),13 [Mn-
(DMF)6](ClO4)3,14 [Mn(PaPy3)(H2O)](ClO4) (1),8 and [Mn(PaPy3)-
(NO)](ClO4) (2)8 were synthesized by following the published
procedures.
Coordination of the carboxamido nitrogen to the Mn(II)
center in [Mn(PaPy3)(H2O)](ClO4) (1) also makes it highly
susceptible to oxidation. The beige complex rapidly turns
dark brown upon exposure to air. We have now investigated
the oxidation reaction, and in this paper we report the spectral
and structural characterization of the oxidized product [(Mn-
(PaPy3))2(µ-O)](ClO4)2 (3), a binuclear Mn(III) species with
a single unsupported oxo bridge. This (µ-oxo)dimanganese-
(III) complex is an excellent precursor for the synthesis of
mononuclear Mn(III) complexes of the type [Mn(PaPy3)-
(L)]+ with various LH ligands (H ) dissociable proton). The
syntheses, structures, and properties of four such complexes
namely, [Mn(PaPy3)(OMe)](ClO4) (4), [Mn(PaPy3)(OPh)]-
(ClO4) (5), [Mn(PaPy3)(OAc)](ClO4) (6), and [Mn(PaPy3)-
(OBz)](ClO4) (7), are reported herein.
Recent studies on the interactions of NO with the OEC of
photosystem II and the Mn-containing catalase have revealed
that the oxo-bridged Mn(III,III) units are reduced by NO to
Mn(II,III) moieties (and NO+).10 Quite in contrast, the present
(µ-oxo)dimanganese(III) complex 3 undergoes a novel
reductive nitrosylation to afford the previously reported
{Mn-NO}6 nitrosyl 2. Although mononuclear iron nitrosyls
have been synthesized from oxo-bridged iron porphyrin
complexes,11 to our knowledge, this is the first example of
a {Mn-NO}6 nitrosyl synthesized from a (µ-oxo)dimanga-
nese(III) species. We further report that the mononuclear Mn-
(III) complexes 3-7 also form the {Mn-NO}6 nitrosyl 2
via reductive nitrosylation. This behavior is in contrast to
[(Mn(PaPy3))2(µ-O)](ClO4)2 (3). A batch of 200 mg of [Mn-
(PaPy3)(H2O)](ClO4) (1) was suspended in 10 mL of acetonitrile
(MeCN) and stirred for 6 h in the presence of air when a clear
deep brown solution was obtained. The solvent was then removed
under vacuum, and the resulting brown solid was redissolved in 5
mL of a mixture of dichloromethane (CH2Cl2) and MeCN (97:3).
Next, hexane (5 mL) was layered on the top of this solution and
the mixture was stored at room temperature. Brown crystals were
obtained in 55% yield within 2 days. Anal. Calcd for [(Mn(PaPy3))2-
(µ-O)](ClO4)2‚2.7CH2Cl2‚0.5CH3CN (3‚2.7CH2Cl2‚0.5CH3CN,
C
43.70H48.40Cl7.40Mn2N10.50O11): C, 41.36; H, 3.84; N, 11.59.
Found: C, 41.82; H, 3.95; N, 11.71. Selected IR frequencies (cm-1
,
KBr disk): 3585 (m), 3419 (m), 1627 (s, νCO), 1601 (s), 1480 (m),
1444 (m), 1395 (m), 1293 (m), 1091(s), 1019 (m), 817 (s, µ-O),
759 (m), 689 (m), 623 (m). Electronic absorption spectrum in
MeCN, λmax (nm) (ꢀ, M-1 cm-1): 715 (260), 547 (475), 260 (28
100).
[Mn(PaPy3)(OMe)](ClO4) (4). Method A. A batch of 100 mg
of 1 was suspended in a mixture of 10 mL of MeCN and 2 mL of
methanol (MeOH), and the mixture was stirred vigorously for 8 h.
The reaction mixture gradually became homogeneous during this
period. Diffusion of diethyl ether (Et2O) into the red-brown solution
afforded dark red crystals in 80% yield. Anal. Calcd for [Mn-
(PaPy3)(OMe)](ClO4) (4, C21H23ClMnN5O6): C, 47.43; H, 4.36;
N, 13.17. Found: C, 47.54; H, 4.39; N, 13.25. Selected IR
frequencies (cm-1, KBr disk): 3436 (w), 2802 (w), 1633 (s, νCO),
1603 (s), 1445 (m), 1389 (m), 1293 (m), 1085 (s), 1023 (m), 765
(m), 690 (m), 623 (m), 558 (m). Electronic absorption spectrum in
MeCN, λmax (nm) (ꢀ, M-1 cm-1): 710 (115), 540 (185), 260 (12
800). Value of µeff (298 K, polycryst): 4.54 µB.
(8) Ghosh, K.; Eroy-Reveles, A. A.; Avila, B.; Holman, T. H.; Olmstead,
M. M., Mascharak, P. K. Inorg. Chem. 2004, 43, 2988.
(9) The {M-NO}n notation used in this paper is that of Feltham and
Enemark. See: Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV.
1974, 13, 339.
(10) (a) Schansker, G.; Goussias, C.; Petrouleas, V.; Rutherford, A. W.
Biochemistry, 2002, 41, 3057. (b) Ioannidis, N.; Schansker, G.;
Barynin, V. V.; Petrouleas, V. J. Biol. Inorg. Chem. 2000, 5, 354. (c)
Sarrou, J.; Ioannidis, N.; Deligiannakis, Y.; Petrouleas, V. Biochemistry
1998, 37, 3581.
Method B. A batch of 200 mg (0.58 mmol) of PaPy3H was
dissolved in 10 mL of degassed MeOH, and the solution was stirred
with 123 mg (1.2 mmol) of Et3N for 1 h. Next, a solution of 460
mg (0.58 mmol) of [Mn(DMF)6](ClO4)3 in 4 mL of MeOH was
added to it, and the reaction mixture was stirred for another 2 h
(12) Coleman, W. M.; Taylor, L. T. J. Am. Chem. Soc. 1978, 100, 1705.
(13) Rowland, J. M.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
2001, 40, 2810.
(11) (a) Ellison, M. K.; Schulz, C. E.; Scheidt, W. R. Inorg. Chem. 1999,
38, 100. (b) Settin, M. F.; Fanning, J. C. Inorg. Chem. 1988, 27, 1431.
(14) Prabhakaran, C. P.; Patel, C. C. J. Inorg. Nucl. Chem. 1968, 30, 867.
8470 Inorganic Chemistry, Vol. 44, No. 23, 2005

A (µ-Oxo)dimanganese(III) Complex
when a red-brown color developed. A batch of 5 mL of Et2O was
then added to it, and the mixture was stored at -20 °C for 24 h.
The red-brown microcrystalline product 4 was isolated by filtration,
washed with Et2O, and dried in vacuo (yield: 55%).
Method C. A batch of 100 mg of 3 was suspended in a mixture
of 10 mL of MeOH, and the mixture was stirred vigorously for 8
h. The reaction mixture gradually became homogeneous during this
period. Diffusion of Et2O into the red-brown solution afforded dark
red crystals in 70% yield.
[Mn(PaPy3)(OPh)](ClO4) (5). Method A. A solution of 30 mg
(0.32 mmol) of phenol in 2 mL of MeCN was slowly added to a
solution of 200 mg (0.16 mmol) of 3 in 15 mL of MeCN, and the
mixture was stirred for 30 min. The initial brown color changed to
deep reddish brown during this time. The solvent was then removed
and the red-brown solid was recrystallized form CH2Cl2/toluene
mixture (yield: 80%). Anal. Calcd for [Mn(PaPy3)(OPh)](ClO4)
(5, C26H25N5ClO6Mn): C, 52.58; H, 4.24; N, 11.79. Found: C,
52.63; H, 4.28; N, 11.73. Selected IR frequencies (cm-1, KBr
disk): 1634 (s, νCO), 1603 (s), 1482 (m), 1382 (m), 1256 (m), 1085
(s), 1020 (m), 780 (m), 688 (w), 623 (m). Electronic absorption
spectrum in MeCN, λmax (nm) (ꢀ, M-1 cm-1): 460 sh (1 270), 370
sh (3 100), 320 sh (3 850), 260 (14 520). Value of µeff (298 K,
polycryst): 4.92 µB.
Cl2, C28H27Cl3MnN5O7): C, 47.58; H, 3.85; N, 9.90. Found: C,
47.79; H, 3.87; N, 9.94. Selected IR frequencies (cm-1, KBr disk):
1709 (m, νCO of OBz), 1643 (s, νCO), 1604 (s), 1444 (m), 1365
(m), 1320 (s) 1300 (s), 1089 (s), 1021 (m), 723 (m), 623 (m).
Electronic absorption spectrum in MeCN, λmax (nm) (ꢀ, M-1 cm-1):
855 (105), 590 (160), 315 (5 700), 260 (19 200). Value of µeff
(298 K, polycryst): 4.90 µB.
Method B. A solution of 17 mg (0.69 mmol) of NaH in 2 mL
of MeCN was added to a solution of 200 mg (0.58 mmol) of PaPy3H
in 10 mL of MeCN under dinitrogen. The yellow mixture was
stirred for 1 h, and a batch of 460 mg (0.58 mmol) of [Mn(DMF)6]-
(ClO4)3 was added to it. Following additional stirring for 2 h, a
solution of 92 mg (0.64 mmol) of sodium benzoate (NaOBz) in 3
mL of MeCN was added to the reaction mixture. The deep green
solution thus obtained was evaporated to dryness, and the green
solid was recrystallized from CH2Cl2 (yield: 50%).
In this work, complex [Mn(PaPy3)(NO)](ClO4) (2) was synthe-
sized by a new procedure. A batch of 200 mg of 3 was dissolved
in 15 mL of degassed MeCN, and purified NO gas was passed
through the solution for 20 min. The solution was then kept under
NO in dark for 24 h. Addition of Et2O to the dark green solution
thus obtained afforded dark green crystals of 2 in 70% yield.
Physical Measurements. Electronic absorption spectra were
recorded on a Perkin-Elmer Lambda 9 spectrophotometer. Infrared
spectra were obtained with a Perkin-Elmer 1600 or Spectrum 1
FTIR spectrophotometer. 1H NMR spectra were recorded at 298 K
on a Varian Unity Plus 500 spectrometer running Solaris 2.6/VNMR
6.1B. A Johnson-Matthey magnetic susceptibility balance was used
to determine the room-temperature magnetic susceptibility of 4, 5,
and 7‚CH2Cl2. Dc magnetic susceptibility data for ground [(Mn-
(PaPy3))2(µ-O)](ClO4)2‚2.7CH2Cl2‚0.5CH3CN were collected using
a Quantum Design MPMS-XL SQUID magnetometer at temper-
ature ranging from 2 to 300 K under an applied magnetic field of
1000 G. Data were corrected for diamagnetic contributions using
Pascal’s constants.
Method B. A solution of 17 mg (0.69 mmol) of NaH in 2 mL
MeCN was slowly added to a solution of 200 mg (0.58 mmol) of
PaPy3H in 10 mL of MeCN under dinitrogen. The yellow mixture
was stirred for 1 h and then a batch of 460 mg (0.58 mmol) of
[Mn(DMF)6](ClO4)3 was added to it. After additional stirring for 2
h, a solution of 73 mg (0.63 mmol) of sodium phenoxide (NaOPh)
in 3 mL of MeCN was added to the greenish-brown reaction
mixture. This changed the color rapidly to reddish brown. Next,
the solvent (MeCN) was removed and the solid was redissolved in
5 mL of CH2Cl2. Slow evaporation of the CH2Cl2 solution afforded
crystalline product in 65% yield.
[Mn(PaPy3)(OAc)](ClO4) (6). Method A. A solution of 22 mg
(0.35 mmol) of glacial acetic acid in 2 mL of MeCN was slowly
added to a solution of 200 mg (0.16 mmol) of 3 in 10 mL of MeCN
when the color rapidly changed from brown to green. Removal of
solvent afforded a green microcrystalline solid which was recrystal-
lized from CH2Cl2 (yield: 75%). Anal. Calcd for [Mn(PaPy3)(OAc)]-
(ClO4) (6, C22H23N5MnClO7): C, 47.20; H, 4.14; N, 12.51.
Gas Chromatographic Analyses. Gas chromatography was
performed on a Hewlett-Packard 5890 Series II instrument equipped
with a thermal conductivity (TC) detector and a 10 ft Haysep packed
column. The column flow rate of He carrier gas was 25 mL/min at
35 °C. Under these conditions, the retention times (min) for various
gases were determined as N2 (0.59), NO (0.69), and NO2 (2.56).
The reaction of 3 with NO was performed in a 20 mL Schlenk
flask. A solution of 35 mg of the µ-oxo dimer 3 in 10 mL of MeCN
was first degassed thoroughly, and then 4 equiv of purified NO
gas was delivered into the flask via a gastight syringe. The solution
was then stirred for 16 h. During this time, the color of the solution
changed from brown to green. Next, 50 µL of the gas from the
headspace was taken out and analyzed by GC.
Found: C, 47.31; H, 4.19; N, 12.44. Selected IR frequencies (cm-1
,
KBr disk): 1644 (s, νCO), 1604 (s), 1445 (m), 1367 (s), 1276 (s),
1144 (m), 1085 (s), 795 (m), 761 (m), 677 (m), 625 (m). Electronic
absorption spectrum in MeCN, λmax (nm) (ꢀ, M-1cm-1): 840 (100),
570 (155), 310 (4 760), 260 (17 000).
Method B. A solution of 17 mg (0.69 mmol) of NaH in 2 mL
of MeCN was slowly added to a solution of 200 mg (0.58 mmol)
of PaPy3H in 10 mL of MeCN under dinitrogen. The resulting
yellow solution was stirred for 1 h, and then a batch of 460 mg
(0.58 mmol) of [Mn(DMF)6](ClO4)3 was added to it. Following
additional stirring for 2 h, a solution of 52 mg (0.63 mmol) of
sodium acetate (NaOAc) in 3 mL of MeCN was added to the
greenish brown mixture. The color slowly turned to deep green.
Next, the solvent was removed and the green solid was recrystal-
lized from CH2Cl2 (yield: 55%).
[Mn(PaPy3)(OBz)](ClO4) (7). Method A. A solution of 40 mg
(0.33 mmol) benzoic acid (HOBz) in 2 mL of MeCN was slowly
added to a solution of 200 mg (0.16 mmol) of 3 in 15 mL of MeCN.
The color of the reaction mixture changed from brown to green
within 15 min. Removal of solvent and recrystallization of the green
solid from CH2Cl2/toluene mixture afforded the complex in yield
80%. Anal. Calcd for [Mn(PaPy3)(OBz)](ClO4)‚CH2Cl2 (7‚CH2-
X-ray Crystal Structure Analysis. Deep purple crystals of
[(Mn(PaPy3))2(µ-O)](ClO4)2‚2.7CH2Cl2‚0.5CH3CN (3‚2.7CH2Cl2‚
0.5CH3CN) were grown by layering hexane over a solution of the
complex in CH2Cl2/MeCN (97:3). Reddish crystals of [Mn(PaPy3)-
(OMe)](ClO4) (4) were grown via ether diffusion into a solution
of 4 in MeCN at -20 °C. Red crystals of [Mn(PaPy3)(OPh)](ClO4)-
(5) and green crystals of [Mn(PaPy3)(OBz)](ClO4)‚CH2Cl2 (7‚CH2-
Cl2) were grown by slow evaporation of solutions of the complexes
in CH2Cl2/toluene (60:40). Diffraction data for 3-5 were collected
at 90 K on a Bruker SMART 1000 diffractometer while data for 7
were collected at 90 K on a Bruker Apex CCD diffractometer. Mo
KR (0.710 73 Å) radiation was used, and an absorption correction
was applied in each case. The structures were solved by direct
methods (SHELXS-97). The intensities of twostandard reflections
Inorganic Chemistry, Vol. 44, No. 23, 2005 8471

Ghosh et al.
Table 1. Summary of Crystal Data and Intensity Collection and
Structural Refinement Parameters for [(Mn(PaPy3))2(µ-O)](ClO4)2‚
2.7CH2Cl2‚0.5CH3CN (3‚2.7CH2Cl2‚0.5CH3CN),
[Mn(PaPy3)(OMe)](ClO4) (4), [Mn(PaPy3)(OPh)](ClO4) (5), and
[Mn(PaPy3)(OBz)](ClO4)‚CH2Cl2 (7‚CH2Cl2)
Results and Discussion
-
Syntheses. The deprotonated ligand PaPy3 serves as a
pentadentate ligand in all complexes reported in this account
and employs three pyridine nitrogens, one tert-amine nitro-
gen, and one deprotonated carboxamido nitrogen to bind
param
formula
3
4
5
7
C
43.70H48.40Cl7.40
Mn2N10.50O11
-
C
21H23ClMn-
N5O6
C
26H25ClMn-
N5O6
C
28H27Cl3-
MnN5O7
-
manganese. Among the manganese complexes of PaPy3 ,
mol wt
cryst color,
habit
1268.94
purple plate
531.83
593.90
706.84
the mononuclear Mn(II) species [Mn(PaPy3)(H2O)](ClO4) (1)
reported previously by this group is sensitive to oxidation
in solution.8 Isolation of this complex under anaerobic
condition has been possible because of its insolubility in
common solvents such as MeOH and MeCN. When a
suspension of 1 in MeCN is exposed to air, the beige
insoluble compound gradually goes into the solution and the
brown (µ-oxo)dimanganese(III) complex [(Mn(PaPy3))2(µ-
O)](ClO4)2 (3) is formed. Complex 3 is stable in aprotic
solvents and exhibits no tendency of disproportionation into
Mn(II) and/or Mn(IV) species. However, when a few drops
of MeOH are added to a solution of 3 in MeCN, it is rapidly
converted into the mononuclear Mn(III) complex [Mn-
(PaPy3)(OMe)](ClO4) (4). Complex 4 can also be prepared
directly by reacting [Mn(DMF)6](ClO4)3 and PaPy3H in the
presence of 2 equiv of Et3N in MeOH. This reaction
presumably proceeds via in situ formation of [Mn(PaPy3)-
(MeOH)]2+ which is further deprotonated (by Et3N) to form
4 in high (55%) yield.
brown needle dark red block green plate
T, K
90(2)
90(2)
90(2)
123(2)
cryst syst
monoclinic
orthorhombic orthorhombic triclinic
space group C2/c
P212121
8.4315(6)
11.0777(8)
24.0524(18) 26.6159(17)
90
90
90
2246.5(3)
4
1.572
0.756
P212121
8.5126(6)
11.2530(7)
P1h
a, Å
17.112(3)
11.2904(9)
17.3599(13)
17.8750(13)
110.209(4)
105.526(2)
102.543(3)
2976.3(4)
4
b, Å
c, Å
13.682(3)
22.511(5)
90
106.344(9)
90
R, deg
â, deg
γ, deg
V, Å3
Z
90
90
90
2549.6(3)
4
5057.5(18)
4
d
calcd, g cm-3 1.667
1.547
0.675
1.577
0.769
abs coeff, µ, 0.961
mm-1
GOFa on F2 1.065
1.021
3.14
6.97
1.026
2.84
6.84
0.995
5.24
12.50
R1,b %
6.15
15.60
wR2,c %
2
2
a GOF ) [Σw(Fo - Fc )2]/(M - N)]1/2 (M ) number of reflections; N
) number of parameters refined). b R1 ) Σ||Fo| - |Fc||/Σ|Fo|. c wR2 )
2
2
[Σ[w(Fo - Fc )2]/Σ[w(Fo)2]]1/2
.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for
[(Mn(PaPy3))2(µ-O)](ClO4)2‚2.7CH2Cl2‚0.5CH3CN
(3‚2.7CH2Cl2‚0.5CH3CN), [Mn(PaPy3)(OMe)](ClO4) (4),
[Mn(PaPy3)(OPh)](ClO4) (5), and [Mn(PaPy3)(OBz)](ClO4)‚CH2Cl2
(7‚CH2Cl2)
Treatment of the (µ-oxo)dimanganese(III) species 3 with
phenol, acetic acid, or benzoic acid affords the mononuclear
Mn(III) species [Mn(PaPy3)(OPh)]ClO4 (5), [Mn(PaPy3)-
(OAc)]ClO4 (6), and [Mn(PaPy3)(OBz)]ClO4 (7), respec-
tively. These complexes can be independently synthesized
from the mononuclear Mn(III) precursor [Mn(PaPy3)-
param
Mn-N(1)
3
4
5
7
2.130(4)
1.969(4)
2.213(4)
2.206(4)
2.200(4)
2.1192(19) 2.1147(13) 2.127(2)
1.9488(19) 1.9315(13) 1.925(2)
2.245(2)
2.128(2)
Mn-N(2)
Mn-N(3)
Mn-N(4)
Mn-N(5)
Mn-O(2)
O(1)-C(6)
N(2)-C(6)
N(3)-C(15)
O(2)-C(21)
O(3)-C(21)
Mn-Mn
2.2093(13) 2.207(2)
2.1821(13) 2.141(2)
-
(MeCN)]2+, generated from reaction of deprotonated PaPy3
2.1844(19) 2.2183(13) 2.170(2)
(with NaH) and [Mn(DMF)6](ClO4)3 in MeCN. Although all
attempts to isolate the intermediate species [Mn(PaPy3)-
(MeCN)]2+ have failed so far, addition of NaOPh, NaOAc,
or NaOBz to this species (formed in situ) has resulted in the
formation of complexes 5-7, respectively.
1.7886(8) 1.8256(16) 1.8513(11) 1.8987(19)
1.244(6)
1.327(7)
1.486(7)
1.240(3)
1.332(3)
1.480(3)
1.403(3)
1.2384(19) 1.229(3)
1.3444(19) 1.341(4)
1.4812(19) 1.485(3)
1.3538(19) 1.302(3)
1.227(3)
3.5636(8)
Structure and Properties. [(Mn(PaPy3))2(µ-O)](ClO4)2‚
2.7CH2Cl2‚0.5CH3CN (3‚2.7CH2Cl2‚0.5CH3CN). The struc-
ture of [(Mn(PaPy3))2(µ-O)]2+ (the cation of 3) is shown in
Figure 1, and selected bond distances and bond angles are
listed in Table 2. In 3, the coordination of the pentadentate
PaPy3- ligand is similar to that observed in the mononuclear
Mn(III) complex [Mn(PaPy3)(Cl)](ClO4) reported previously
by this group.8 The tert-amine and three pyridine nitrogens
of the ligand comprise the equatorial plane while the
carboxamido nitrogen occupies a position trans to the
bridging oxide. Both Mn(III) centers exist in distorted
octahedral geometry represented by the trans angles of
156.83(15)° for N(1)-Mn-N(3) and 152.16(16)° for N(4)-
Mn-N(5). The equatorial plane of each Mn center is almost
parallel to the other resulting in the nearly linear Mn-O-
Mn angle of 173.0(3)°. All structurally characterized (µ-oxo)-
dimanganese(III) complexes contain linear or nearly linear
Mn-O-Mn units.3a The two Mn centers are equivalent with
the halves of the dimer related by a 2-fold axis through the
bridging oxygen atom. Comparison of the metric parameters
N(1)-Mn-N(2)
N(1)-Mn-N(3)
N(1)-Mn-N(4)
N(1)-Mn-N(5)
N(1)-Mn-O(2)
N(2)-Mn-N(3)
N(2)-Mn-N(4)
N(2)-Mn-N(5)
N(2)-Mn-O(2)
N(3)-Mn-N(4)
N(3)-Mn-N(5)
N(3)-Mn-O(2)
N(4)-Mn-N(5)
N(4)-Mn-O(2)
N(5)-Mn-O(2)
Mn-O(2)-C(21)
O(2)-C(21)-O(3)
Mn(1)-O(2)-Mn(1) 173.0(3)
77.76(17) 78.35(8)
156.83(15) 157.04(8) 159.86(5) 160.53(9)
98.55(16) 109.58(8) 105.91(5) 100.44(9)
106.50(16) 96.73(8)
101.43(15) 99.77(8)
80.19(16) 80.49(7)
91.35(16) 85.36(8)
82.43(16) 94.35(8)
177.23(16) 172.03(8) 173.52(5) 170.93(9)
74.87(16) 77.28(7)
77.33(15) 76.06(7)
100.93(14) 102.39(8) 102.60(5) 93.02(8)
152.16(16) 153.00(7) 151.99(5) 154.07(9)
91.39(14) 88.02(7)
95.32(18) 93.56(7)
78.91(5)
79.00(9)
101.78(5) 105.31(9)
97.32(5)
81.52(5)
86.52(5)
94.78(5)
106.31(8)
81.53(9)
86.47(9)
95.40(9)
77.41(5)
75.13(4)
78.44(9)
76.29(9)
89.49(5)
91.13(5)
85.33(9)
90.30(9)
129.81(16) 131.75(10) 127.20(19)
124.1(3)
showed no significant decay during the course of data collection.
Machine parameters, crystal data, and data collection parameters
are summarized in Table 1, while selected bond distances and angles
are listed in Table 2.
8472 Inorganic Chemistry, Vol. 44, No. 23, 2005

A (µ-Oxo)dimanganese(III) Complex
Figure 1. Thermal ellipsoid plot (50% probability level) of the cation of
[(Mn(PaPy3))2(µ-O)]2+ (cation of 3) with the atom-numbering scheme. The
hydrogen atoms are omitted for the sake of clarity.
Figure 2. Plot of the product of magnetic susceptibility/mol by temperature
(øMT) vs temperature (T) for 3‚2.7CH2Cl2‚0.5CH3CN. The solid line was
generated by the best-fit parameters given in the text.
of [(Mn(PaPy3))2(µ-O)]2+ (Table 2) and [Mn(PaPy3)(Cl)]+
reveal that the metal-ligand distances of both Mn(III)
complexes are relatively similar. For example, the average
Mn-N bond distance in the equatorial plane of 3 is 2.187
(4) Å while the same average for [Mn(PaPy3)(Cl)](ClO4) (a
high-spin complex)8 is 2.1710 (11) Å. This similarity strongly
suggests that the Mn(III) centers in 3 are high-spin. In 3,
the strong trans-influence of the bridging oxo group is clearly
reflected in the longer Mn-Namido (Mn-N(2)) bond distance
of 1.969(4) Å; in [Mn(PaPy3)(Cl)](ClO4) and the following
three structures, this distance is considerably shorter (1.9133-
1.9488 Å). The Mn-N(2) bond distance of 3 is also longer
than the two Mn-Namido bonds in [Mn(bpb)(H2O)Cl] (1.922-
(4) and 1.945(3) Å).4a The trans effect of the carboxamido
moiety results in a slightly longer Mn-O distance of 1.7886-
(8) Å in 3 when compared to other structurally characterized
complexes containing the Mn(III)-O-Mn(III) core (1.72-
1.77 Å).3a The Mn-Mn distance (3.5636 Å) of 3 (calculated
from the Mn-O bond distance and the Mn-O-Mn angle)
is also longer than all other Mn-O-Mn dimers reported
(3.42-3.54 Å), even when compared to complexes with
strong field ligands such as CN-, Pc (phthalocyanate), and
TPP (tetraphenylporphyrin).3a To our knowledge, this is the
first structurally characterized (µ-oxo)dimanganese(III) com-
plex with carboxamido nitrogen coordination. Interestingly,
the Mn-Namido (Mn-N(2)) bond of 3 is shorter than the Fe-
been measured as a function of the temperature T (2-300
K). The results are shown in Figure 2 in the form of a øMT
versus T plot. The øMT value decreases from 0.792 cm3 mol-1
K at 300 K to 0.188 cm3 K mol-1 at 40 K, which is
characteristic of a strong antiferromagnetic coupling between
the two S ) 2 high-spin Mn(III) centers. Below 40 K, the
øMT values exhibit a small maximum around 10 K (0.03 cm3
K mol-1) due to paramagnetic Mn(II) impurities. The data
above 40 K were fitted with the aid of the program MAGFIT
3.117 and an exchange Hamiltonian of the form Hˆ ) - 2J(Sˆ1‚
Sˆ2), where S1 ) S2 ) 2, to give g ) 2.010 and J ) -115.8
cm-1. The magnitude and sign of J for 3 compare well with
those of [Mn2O(5-NO2-saldien)2] (J ) -120.0 cm-1)18 and
[Mn2O(bpmsed)2](ClO4)2 (J ) -108.0 cm-1),19 two Mn(III)
Schiff base complexes containing a similar linear Mn(III)-
O-Mn(III) core.
Mononuclear Mn(III) Complexes. The structures of the
cations of [Mn(PaPy3)(OMe)]ClO4 (4), [Mn(PaPy3)(OPh)]-
ClO4 (5), and [Mn(PaPy3)(OBz)]ClO4 (7) are shown in
Figures 3-5, respectively. In these complexes, the mode of
coordination of the pentadentate PaPy3- ligand is similar to
that observed in 3. The carboxamido nitrogen in each
complex is trans to the sixth ligand: MeO- for 4; PhO- for
5; BzO- for 7. Each anionic sixth ligand is coordinated in a
monodentate fashion. The metric parameters of the three
complexes are comparable to each other (Table 2) and are
consistent with the high-spin nature of the Mn(III) centers.8
Interestingly, the average Mn-Namide distances in the present
complexes 4, 5, and 7 are comparable to the Mn-Namide
distances of 1.922(4) and 1.945(3) Å noted for the dicar-
boxamido complex [Mn(bpb)(H2O)Cl].5a However, the Mn-
N
amido distance of 2.064(4) Å in the high-spin (µ-oxo)diiron-
(III) complex [(Fe(PaPy3))2(µ-O)]ClO4)2.15
Coordination of the carboxamido nitrogen to Mn(III) in 3
is indicated by the red shift in νCO frequency from 1666 cm-1
in free PaPy3H to 1627 cm-1 in 3. This value is close to that
displayed by mononuclear Mn(III) species presented here
with the same pentadentate ligand (1644-1633 cm-1). The
µ-oxo bridge displays a strong IR band at 817 cm-1.16 The
molar magnetic susceptibility (øM) of 3 (ground crystals) has
Npy distance observed in [Mn(bpb)(H2O)Cl] (2.061(3) Å) is
noticeably shorter than the same distance in 4, 5, or 7. The
Mn-O(OMe) bond distance in 3 (1.8256(16) Å) is similar
(17) Schmitt, E. A. Ph.D. Thesis, University of Illinois at Urbana-
Champaign, 1995.
(15) Patra, A. K.; Afshar, R. K.; Rowland, J. M.; Olmstead, M. M.;
Mascharak, P. K. Angew. Chem., Int. Ed. 2003, 42, 4517.
(16) (a) Ziolo, R. F.; Stanford, R. H.; Rossman, G. R.; Gray, H. B. J. Am.
Chem. Soc. 1974, 96, 7910. (b) Schardt, B. C.; Hollander, F. J.; Hill,
C. L. J. Am. Chem. Soc. 1982, 104, 3964.
(18) Kipke, C. A.; Scott, M. J.; Gohdes, J. W.; Armstrong, W. H. Inorg.
Chem. 1990, 29, 2193.
(19) Horner, O.; Anxolabe´he`re-Mallart, E.; Charlot, M.-F.; Tchertanov, L.;
Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem.
1999, 38, 1222.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8473

Ghosh et al.
Scheme 1
(III) complexes of Schiff base ligands that incorporate
phenolate groups such as [Mn(sal-N-1,5,8,12)](ClO4) and
[Mn(salpn)H2DCBI(DMF)] (Mn-O(OPh) distance: 1.869(4)
and 1.877(2) Å, respectively).21
Figure 3. Thermal ellipsoid plot (50% probability level) of cation of [Mn-
(PaPy3)(OMe)]+ (cation of 4) with the atom-numbering scheme. The
hydrogen atoms are omitted for the sake of clarity.
In 7, the benzoate ligand is monodentate. To our knowl-
edge, this mode of coordination of benzoate to Mn(III) is
unique. The Mn-O(OBz) bond length of 1.8987(19) Å in 7
is shorter than the Mn-O(OBz) distance of 2.083(3) Å
observed in [Mn(piap)(OBz)2], a Mn(II) complex containing
two monodentate benzoate ligands.22 It is interesting to note
that the Mn-O(OBz) bond distance of 7 is quite comparable
to the Mn-O distance (1.903(3) Å) of the Mn(III) complex
(Et4N)[MnCl2(pic)2] that contains the chelating pyridine-2-
carboxylate (pic) ligand.23
Reactivity of [(Mn(PaPy3))2(µ-O)](ClO4)2 (3). Aerobic
oxidation of the Mn(II) starting complex [Mn(PaPy3)-
(H2O)](ClO4) (1) in MeCN readily affords 3, a Mn(III)
dimer with a single unsupported oxo bridge. The single µ-oxo
bridge in 3 is not stable toward proton donors. Protona-
tion of the µ-oxo bridge results in splitting of the dimer and
allows the corresponding anion to bind at the sixth site
(trans to the carboxamido N). For example, simple addition
of a few drops of MeOH to a solution of 3 in MeCN re-
sults in the formation of the monomeric methoxide com-
plex 4. Similar reactivity is observed with other proton
donors such as benzoic acid, acetic acid, and phenol. These
reactions can be followed visually since treatment of 1 equiv
of the dark brown 3 with 2 equiv of acetic or benzoic acid
affords the green acetate complex 6 (λmax ) 570 nm) or the
green benzoate complex 7 (λmax ) 590 nm). Addition of
Figure 4. Thermal ellipsoid plot (50% probability level) of cation of [Mn-
(PaPy3)(OPh)]+ (cation of 5) with the atom-numbering scheme. The
hydrogen atoms are omitted for the sake of clarity.
phenol affords the deep red phenolate complex 5 (λmax
)
460 nm). Interestingly, addition of NaOAc or NaOPh to a
solution of 3 in MeCN does not result in a color change.
This clearly demonstrates that protons are required for the
bridge-splitting reaction. A working hypothesis is provided
in Scheme 1.
(20) Hubin, T. J.; McCormick, J. M.; Alcock, N. W.; Busch, D. H. Inorg.
Chem. 2001, 40, 435.
(21) (a) Rajendiran, T. M.; Caudle, M. T.; Kirk, M. L.; Setyawati, I.; Kampf,
J. W.; Pecoraro, V. L. J. Biol. Inorg. Chem. 2003, 8, 283. (b) Panja,
A.; Shaikh, N.; Gupta, S.; Butcher, R. J.; Banerjee, P. Eur. J. Inorg.
Chem. 2003, 1540.
(22) Warzeska, S. T.; Micciche, F.; Mimmi, M. C.; Bouwman, E.;
Kooijman, H.; Spek, A. L.; Reedijk, J. J. Chem. Soc., Dalton Trans.
2001, 3507.
(23) Huang, D.; Wang, W.; Zhang, X.; Chen, C.; Chen, F.; Liu, Q.; Liao,
D.; Li, L.; Sun, L. Eur. J. Inorg. Chem. 2004, 1454.
Figure 5. Thermal ellipsoid plot (50% probability level) of cation of [Mn-
(PaPy3)(OBz)]+ (cation of 7) with the atom-numbering scheme. The
hydrogen atoms are omitted for the sake of clarity.
to that reported for other Mn(III) complexes such as [Mn-
(L)(OMe)2]PF6 (L is a tetraazamacrocycle, Mn-O dis-
tance: 1.838(2) Å).20 Likewise, the Mn-O(OPh) bond length
of 5 (1.8513(11) Å) is comparable to that reported for Mn-
8474 Inorganic Chemistry, Vol. 44, No. 23, 2005

A (µ-Oxo)dimanganese(III) Complex
Scheme 2
provides an additional synthetic route to the photosensitive
{Mn-NO}6 nitrosyl 2.
Metal nitrosyls have been synthesized by reductive ni-
trosylation in MeOH in the presence of a base (metal:base
ratio ) 1:1).24 In the present case, the basic ligands (like
OMe and OAc) in 4-7 serve as the in-situ base to promote
the reductive nitrosylation reaction. The mechanism of this
base-initiated reductive nitrosylation has recently been
reviewed by Ford and co-workers.25
In addition, facile ligand substitution reactions can take
place at the labile sixth site in these complexes. For example,
simple dissolution of 7 in MeOH results in conversion of 7
into 4. The reverse reaction takes place when benzoic acid
is added to a solution of 4 in MeCN. These reactions are
summarized in Scheme 2.
In general, non-porphyrin Mn(III) complexes react with
NO to afford EPR-active {Mn-NO}5 species. For example,
Mn(III) complexes of the type [Mn(Z-SALDPT)(NCS)] (Z-
SALDPT ) pentadentate Schiff base ligands derived from
various salicylaldehydes and triamines) react with NO to
yield EPR-active species arising from the transfer of the
radical electron from NO to the manganese center.12 The
formation of the non-porphyrin {Mn-NO}6 nitrosyl 2 from
the various Mn(III) precursors reported here (eqs 1 and 2)
is therefore quite unprecedented. In porphyrin chemistry, only
a handful of {Mn-NO}6 species of the type [(NO)Mn(TPP)-
(B)] (TPP ) tetraphenylporphyrinato ligand, B ) piperidine,
4-methylpiperidine, N-methylimidazole) has been derived
from the Mn(III) starting complex [ClMn(TPP)].26,27
In conclusion, [(Mn(PaPy3))2(µ-O)](ClO4)2 (3), a diman-
ganese(III) complex with a single unsupported oxo bridge,
has been synthesized and characterized by crystallography.
This complex serves as an excellent precursor for mono-
nuclear Mn(III) complexes of the type [Mn(PaPy3)(L)](ClO4),
where L is typical anionic O-based ligands such as MeO-
and AcO-. These mononuclear Mn(III) complexes as well
as 3 undergo reductive nitrosylation to afford the photosensi-
tive {Mn-NO}6 nitrosyl [Mn(PaPy3)NO](ClO4) (2).
Reductive Nitrosylation. In a previous account, we have
reported that the Mn(II) center of 1 with bound carboxamido
N readily forms the {Mn-NO}6 nitrosyl 2 in the presence
of NO.8 Since passage of NO through a solution of the
mononuclear Mn(III) complex [Mn(PaPy3)(MeCN)](ClO4)2
or [Mn(PaPy3)(Cl)](ClO4) did not afford a nitrosyl complex,
we suggested that NO only reacts with Mn(II) center in the
presence of coordinated carboxamido group(s).8 Interestingly,
in this work, we have discovered that passage of NO through
a degassed solution of the (µ-oxo)dimanganese(III) complex
3 in MeCN affords 2 (Scheme 2). It appears that reduction
of the Mn(III) centers and concomitant coordination by NO
gives rise to the {Mn-NO}6 species 2 in such reaction. This
reactivity presumably arises from the instability of the single
unsupported oxo bridge in 3. Loss of the bridging oxide from
3 as O atom upon reaction with NO (and formation of NO2)
is the reason for the observed Mn(III) f Mn(II) reduction
(eq 1). This mechanism is supported by the fact that when
3 is completely converted into 2 in the presence of NO (as
followed by the absorption spectrum of the reaction mixture),
one detects 1 equiv of NO2 in the headspace by GC analysis.
Acknowledgment. Experimental assistance from Prof.
Jeffrey Long and Dr. Hye Jin Choi is gratefully acknowl-
edged. A.A.E.-R. was supported by the NIH ISMD Grant
GM58903.
[(PaPy3)Mn-O-Mn(PaPy3)]2+ (3) 3NO8
2[Mn(PaPy3)(NO)]+ (2) + NO2 (1)
Supporting Information Available: X-ray crystallographic files
in CIF format for [(Mn(PaPy3))2(µ-O)](ClO4)2‚2.7CH2Cl2‚0.5CH3-
CN (3‚2.7CH2Cl2‚0.5CH3CN), [Mn(PaPy3)(OMe)](ClO4) (4), [Mn-
(PaPy3)(OPh)](ClO4) (5), and [Mn(PaPy3)(OBz)](ClO4)‚CH2Cl2
(7‚CH2Cl2). This material is available free of charge via the Internet
at http://pubs.acs.org.
Another aspect of the reductive nitrosylation reaction must
be mentioned here. We have previously shown that NO does
not react with the Mn(III) center of either [Mn(PaPy3)-
(MeCN)](ClO4) or [Mn(PaPy3)(Cl)](ClO4).8 However, when
a strongly basic ligand like (dimethylamino)pyridine (DMAP)
or MeO- is present at the site trans to the coordinated
carboxamido nitrogen, NO reacts with such species in MeCN
and causes reduction (and binding). In fact, all the mono-
nuclear complexes reported here afford the {Mn-NO}6
complex 2 by reductive nitrosylation (eq 2). This reaction
IC0503535
(24) Gwost, D.; Caulton, K. G. Inorg. Chem. 1973, 12, 2095.
(25) Ford, P. C.; Fernandez, B. O.; Lim, M. D. Chem. ReV. 2005, 105,
2439.
(26) (a) Piciulo, P. L. Rupprecht, G.; Scheidt, W. R. J. Am. Chem. Soc.
1974, 96, 5293. (b) Piciulo, P. L.; Scheidt, W. R. Inorg. Nucl. Chem.
Lett. 1975, 11, 309.
(27) Zahran, Z. N.; Lee, J.; Alguindigue, S.; Khan, M. A.; Richter-Addo,
G. B. J. Chem. Soc., Dalton Trans. 2004, 44.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8475