[(CO)3(dppe)Mn(OH2)]BF4 (1). A synthetically versatile compound and its use as a probe for determining the preferred site of coordination on ambident ligands

Article abstract of DOI:10.1016/j.poly.2005.08.032

Previous work in this laboratory has shown that the Mn(I) octahedral complex, [(CO)₃(dppe)Mn(OH₂)]BF₄ (1), may be used for the synthesis of many related complexes by the ready replacement of the aqua ligand by neutral and anionic ligands, leading to new complexes having a variety of functional groups sigma (η¹) bonded to the Mn atom. This procedure has now been extended to ligands possessing phenolic and carboxylic acid groups, including amino acids. Compound 1 is used as a probe to compare the relative coordinating ability of different heteroatoms on ambident ligands. The ¹H NMR spectra of the resulting complexes show two signals at room temperature for the four protons (each 2H m) of the dppe-Mn metallacyle whose position depends on the specific atom of the ligand that is attached to the metal. The spectrum of 1, however, shows only one signal (4H m). On cooling to -53°C this signal is split in two (both 2H, m) owing to a slowing of the rapid reversible dissociation of the aqua ligand.

Full text of DOI:10.1016/j.poly.2005.08.032

Polyhedron 25 (2006) 1147–1156
www.elsevier.com/locate/poly
[(CO)3(dppe)Mn(OH2)]BF4 (1). A synthetically versatile compound
and its use as a probe for determining the preferred site of
coordination on ambident ligands
*
Padmanabha R. Ettireddy, Milton Orchin
Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172, United States
Received 3 August 2005; accepted 16 August 2005
Available online 28 September 2005
Abstract
Previous work in this laboratory has shown that the Mn(I) octahedral complex, [(CO)3(dppe)Mn(OH2)]BF4 (1), may be used for the
synthesis of many related complexes by the ready replacement of the aqua ligand by neutral and anionic ligands, leading to new com-
plexes having a variety of functional groups sigma (g1) bonded to the Mn atom. This procedure has now been extended to ligands pos-
sessing phenolic and carboxylic acid groups, including amino acids. Compound 1 is used as a probe to compare the relative coordinating
1
ability of different heteroatoms on ambident ligands. The H NMR spectra of the resulting complexes show two signals at room tem-
perature for the four protons (each 2H m) of the dppe-Mn metallacyle whose position depends on the specific atom of the ligand that
is attached to the metal. The spectrum of 1, however, shows only one signal (4H m). On cooling to ꢀ53 °C this signal is split in two (both
2H, m) owing to a slowing of the rapid reversible dissociation of the aqua ligand.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Manganese complexes; Ambident ligands; Competitive coordination; Infrared and NMR spectra; Metallacycles
1. Introduction
moles of 1, dinuclear Mn complexes are formed, and tricar-
boxylic acids give K1, K1, K1 (O, O, O) complexes. Polymeric
sodium poylacrylate (av. mol. wt. 2100) reacts to give a no-
vel polymer in which a manganese atom is attached to
each unit of the polymer. When a ligand possesses two
non-equivalent coordination sites (ambident ligands) 1 is
used to evaluate their relative ligating ability. Differential
coordination at the bonding sites of ambident ligands has
important implications for the design of chelating catalysts.
Compound 1 may also be used for screening potential imag-
ing agents related to its widely used congener 99mTc [5].
Table 1 shows the various compounds that we have used
as ligands and identifies the atoms attached to the Mn
atom in their complexes.
Although the ionic octahedral Mn(I) aqua complex,
[(CO)3(dppe)Mn(OH2)]BF4 (1) is an air-stable crystalline
[1,3] complex, which is thermally stable to about 150 °C
[2], the aqua ligand of the complex is extremely labile in solu-
tion; it exchanges rapidly with D2O [3], and is readily re-
placed by a large variety of other neutral or anionic
ligands [4]. The preparation of 1 [2,3] involves the synthesis
of the hydride, (CO)3(dppe)MnH, followed by its reaction
with HBF4. Although weak acids such as carboxylic acids
and phenols do not react with the hydride, they do react
as anions in water or aqueous NaOH, to give neutral
K1(O) complexes. When a ligand possessing two equivalent
coordinating sites, such as dibasic acids, reacts with two
2. Experimental
*
Corresponding author. Tel.: +1 513 556 9253/281 5857; fax: +1 513
All reactions were conducted under an argon
atmosphere in a 50-mL round-bottom flask fitted with
556 9239.
E-mail address: Milton.Orchin@uc.edu (M. Orchin).
0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.08.032

1148
P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
Table 1
orated. The resulting yellow to brown solids are thor-
oughly washed with hexane, dried in vacuo, collected
and weighed. The yield of recovered product is 80–
90%; the loss of material is incurred in handling the very
small quantities involved. Only deviations form the gen-
eral procedure are included in the experimental details.
Our characterization of the new complexes, after ascer-
taining purity by TLC, relies very heavily on three tech-
niques: high-resolution mass spectra (identification of the
exact mass of the molecular ion and some significant
daughter ions); close inspection of infrared spectra (car-
bonyl and nitrile stretching frequencies); and 1H NMR
spectra (particularly the chemical shifts of the dppe
methylene protons). High-resolution mass spectra were
obtained using a Kratos MS-25 high performance mass
spectrometer fitted with an electrospray ionization (ESI)
attachment. IR spectra were recorded on a P-E spectrum
One FT-IR employing a 5-mm CaF2 liquid cell. 1H
NMR data were obtained with CDCl3 solutions using
a Bruker AC-400 MHz spectrometer with the chemical
shifts recorded relative to TMS [Si(CH3)4]. Ultimate
analyses were not routinely determined, because, in addi-
tion to being less definitive for the characterization of
pure compounds than exact mass spectra, such analyses
are frequently unreliable and are further complicated
by the tendency of many of these types of complexes
to crystallize with non-integral molecules of solvent,
which resist efforts to remove, and whose reported con-
tent must be adjusted in order to conform with results
of ultimate analysis.
Ligands substituted for H2O in (CO)3(dppe)Mn(OH2) (* indicates atom(s)
attached to Mn)
A. Monodentate ligands
-
-
O
*
*
*
C(O)O
H3C C(O)O
2
N
O
N*
+
*
-
*
H2C CH C(O)O
Br
3
4
11
12
13
B. Polydentate ligands
-
-
*
-
-
-
-
H2C C(O)O
C(O)O *
*
*
*
*
H2C C(O)O
HO C(O)O
H2C C(O)O
-
*
H2C C(O)O
H
C
C
OH
H
-
C
HO
C
C(O)OH
5
-
*
HO
H2C C(O)O
H2C C(O)O
-
C(O)O *
O(O)C
H
*
C
C
H
-
7
8
9
C(O)O
*
6
-
C(O)O *
H3C
H3C
CH3
H3C
H3C
CH3
N* CH2CH2
N
N* CH2CH2 N*
CH3CH2
n
CH3
CH3
10
32
33
C. Ambident ligands
-
*
-
C(O)O
C(O)O
*
CN*
CN*
N*
N
N
N*
+
H
14
15
16
17
-
*
-
*
CN*
O
O
CN
CN*
N
N*
-
-
OH
*
*
O
O
18
19
20
21
22
-
-
-
*
*
*
C(O)O
C(O)O
C(O)O
C(O)OH
C(O)O
2.1. Reaction of 1 with monocarboxylic acids
-
*
OH
23
O
CN*
CN
26
2.1.1. Acetic acid complex, [(CO)3(dppe)MnOC(O)CH3]
(2)
24
25
-
*
CH2 CH C(O)O
-
Data 2: m.p.: softens at about 172 °C and decomposes
*
-
NH3
*
CH2 C(O)O
above 178 °C; IR (cmꢀ1, CHCl3): m(CO) 2026, 1959 and
+
NH3
1
+
N
1910; H NMR (d, CDCl3): 7.8–7.3 (m, 20H, Ph), 2.92
H
(m, 2H) and 2.74 (m, 2H) both from dppe, 2.18 (s, 3H,
CH3); High-resolution MS (m/z): 597.084, calc.
for [(CO)3(dppe)MnOC(O)CH3 + H]+, C31H28O5P2Mn,
597.079; 537.060, calc. for [(CO)3(dppe)Mn]+, C29H24O3-
P2Mn, 537.058.
CN*
27
28
29
Ph
CH3
Ph
Ph
CH3
P*
CH
CH2
N
N*
P* CH2CH2
2
Ph
CH3
CH3
30
31
The reversibility of the reaction was demonstrated by
the following experiment. One drop of HBF4 was added
to the acetic acid complex 2, dissolved in CHCl3 and then
stirred for 1 min. The IR of the solution showed the spec-
trum characteristic of the aqua complex 1.
a magnetic stirrer and all involved the simple replace-
ment of the aqua ligand of 1 by a new ligand. If the
new ligand is neutral, it is used as a solution in CHCl3,
and if acidic, it is dissolved either in a few milliliters of
water or in aqueous alkali. The general procedure was as
follows: To a CHCl3 solution of about 40–100 mg of 1 in
about 20 mL CHCl3, a solution of an equimolar quantity
of the new ligand is added drop-wise. The order of addi-
tion is reversed when ambident ligands are used. After
addition, stirring is continued for 10–20 min, the CHCl3
solution is separated, washed with water, dried and evap-
2.1.2. Acrylic acid complex,
[(CO)3(dppe)MnOC(O)CH@CH2] (3)
Data 3: m.p.: the color of the solid product changes
from pale yellow at room temperature to white at 276–
280 °C and decomposes at 372–378 °C; IR (cmꢀ1, CHCl3):
1
m(CO) 2026, 1960 and 1911; H NMR (d, CDCl3): 7.9–7.2
(m, 20H, Ph), 5.65 (t, 1H, CH), 4.97 (d, 2H, CH2 attached
to double bond), 2.91 (m, 2H), and 2.82 (m, 2H) both from

P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
1149
dppe; High-resolution MS (m/z): 609.0764, calc. for
2.3. Reaction of 1 with polycarboxylic acids
[(CO)3(dppe)MnOC(O)CH@CH2 + H]+, C32H28O5P2Mn,
609.0792, 537.0335, calc. for [(CO)3(dppe)Mn]+, C29H24-
O3P2Mn, 537.058.
2.3.1. Preparation of citric acid complex,
K1(O),K1(O)[(CO)3(dppe)MnOC(O)CH2–C(OH)-
(COOH)CH2C(O)OMn(dppe)(CO)3] (8)
8.2 mg (0.039 mM) of citric acid (99%, Aldrich) was sus-
pended in a solution of 1 (75 mg, 0.117 mM) in 25 mL
CHCl3. After stirring for approximately 45 min, the solvent
was removed by rotary evaporator. The residue was chro-
matographed on a column of neutral alumina gel with hex-
ane and ethyl acetate as gradient eluents to give 8 as a
yellow solid.
2.1.3. p-Bromobenzoic acid complex,
[(CO)3(dppe)MnOC(O)C6H4Br] (4)
The reaction was carried out using an aqueous solution
of p-bromobenzoic acid.
Data 4: m.p.: softens at about 192 °C and decomposes at
above 225 °C; IR (cmꢀ1, CHCl3): m(CO) 2027, 1959 and
1
1913; H NMR (d, CDCl3): 7.9–7.2 (m, 24H, Ph), 2.99
Data 8: m.p.: softens at 205 °C and decomposes above
(m, 2H) and 2.89 (m, 2H) both from dppe; High-resolution
MS (m/z): 772.9814, calc. for [(CO)3(dppe)Mn–
OC(O)C6H4Br-p + Cl]ꢀ, C36H28O5P2BrClMn, 772.9646
(Clꢀ originated from the chloroform solvent used in the
electrospray).
1
220 °C; IR (cmꢀ1, CHCl3) m(CO) 2027, 1959 and 1916; H
NMR (d, CDCl3): 7.9–7.2 (m, 40H, Ph), 2.92 (m, 4H, from
dppe), 2.72 (m, 4H, from dppe), 2.51 (s, 4H, CH2); High-
resolution MS (m/z): 1265.1896, calc. for [(CO)3(dppe)MnO-
C(O)CH2C(OH)(COOH)CH2C(O)OMn(dppe)(CO)3 + H]+,
C64H55O13P4Mn2, 1265.19. Anal. Calc. for C64H54O13-
P4Mn2 Æ 2H2O Æ C6H14: C, 60.61; H, 5.23. Found: C, 59.34;
H, 5.28% (NMR showed both water and hexane; the
stoichiometry of the associated solvents is adjusted to
conform with the hydrogen analysis). It is assumed that
the manganese coordinates at the terminal carboxylic
groups.
2.2. Reaction of 1 with dicarboxylic acids
Unless otherwise noted, aqueous solutions of the so-
dium salts of the acids were used.
2.2.1. Succinic acid complex, [(CO)3(dppe)MnOC(O)-
CH2CH2C(O)OMn(dppe)(CO)3] (5)
Data 5: m.p.: softens at about 268 °C and decomposes
2.3.2. Preparation of citric acid complex, K1(O),K1(O),
K1(O)[(CO)3(dppe)Mn–OC(O)CH2C(OH)C(O)
OMn(CO)3(dppe)CH2C(O)OMn(dppe)(CO)3] (9)
A solution of 1 (75 mg, 0.117 mM) in 25 mL of CHCl3
was added drop-wise to 3.9 mL of an aqueous solution
containing 8.2 mg of citric acid (0.039 mM) and 4.68 mg
of NaOH (0.117 mM). After stirring the mixture for
approximately 75 min, the product was isolated in the
usual manner.
above 298 °C; IR (cmꢀ1, CHCl3): m(CO) 2025, 1958 and
1
1907; H NMR (d, CDCl3): 7.9–7.2 (m, 40H, Ph), 2.86
(m, 4H, from dppe), 2.68 (m, 4H, from dppe), 2.52 (m,
2H, from succinic acid), 2.27 (m, 2H, from succinic acid);
High-resolution MS (m/z): 1191.1299, calc. for [(CO)3(dp-
pe)Mn–OC(O)CH2CH2C(O)O–Mn(dppe)(CO)3 + H]+, C62-
H53O10P4Mn2, 1191.135.
2.2.2. Fumaric acid complex, [(CO)3(dppe)MnOC(O)-
CH@CHC(O)OMn(dppe)(CO)3] (6)
Data 9: m.p.: softens at 176 °C and decomposes above
200 °C; IR (cmꢀ1, CHCl3) m(CO) 2026, 1955 and 1909;
1H NMR (d, CDCl3): 7.9–7.2 (m, 40H, Ph), 2.96 (m, 6H,
from dppe), 2.71 (m, 6H, from dppe), 2.51 (s, 4H, CH2);
High-resolution MS (m/z): 1802.2294 calc. for [(CO)3(dp-
pe)MnOC(O)CH2C(OH)C(O)OMn(CO)3(dppe)CH2C(O)
OMn(dppe)(CO)3 + H]+, C93H78O16P6Mn3, 1802.19.
Data 6: m.p.: softens at about 145 °C and decomposes
above 160 °C; IR (cmꢀ1, CHCl3) m(CO) 2027, 1959 and
1
1914; H NMR (d, CDCl3): 7.9–7.2 (m, 40H, Ph), 6.5 (s,
2H, from two CHs of fumaric acid moiety), 3.05 (m, 4H,
from dppe), 2.84 (m, 4H, from dppe); High-resolution
MS (m/z): 1189.200, calc. for [(CO)3(dppe)MnOC(O)
CH@CHC(O)OMn(dppe)(CO)3 + H]+, C62H51O10P2Mn2,
1189.1188.
2.3.3. Na-polyacrlyate polymer complex, –[–CH2–CH–
[C(O)OMn(CO)3(dppe)]]n– (10)
A solution of the aqua complex, 1 (67.2 mg, 0.105 mM)
in 25 mL of MeOH was placed in a round-bottom flask. A
solution of sodium polyacrylate (10 mg, 0.005 mM) in
10 mL water was added drop-wise to the solution of 1
and the resulting solution was stirred for 2 h. During this
time, the original clear solution became turbid. Stirring
was continued overnight. The reaction mixture was evapo-
rated to dryness with a rotary evaporator. The resulting so-
lid was washed with 20 mL of CHCl3 and 10 mL of
CH3OH leaving an orange solid, which was dried in vac-
uum. Yield 67%.
2.2.3. D-Tartaric acid complex,
[(CO)3(dppe)MnOC(O)(CHOH)2C(O)OMn(dppe)-
(CO)3] (7)
Data 7: m.p.: softens at about 131 °C and decomposes
above 154 °C; IR (cmꢀ1, CHCl3) m(CO) 2029, 1962 and
1
1916; H NMR (d, CDCl3): 7.9–7.2 (m, 40H, Ph), 2.95
(m, 4H, from dppe), 2.84 (m, 4H, from dppe); High-resolu-
tion MS (m/z): 1223.1241, calc. for [(CO)3(dppe)Mn–OC
(O)(CHOH)2C(O)O–Mn(dppe)(CO)3 + H]+, C62H53O12-
P2Mn2, 1223.1248.

1150
P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
Data 10: m.p.: decomposes without melting at about
OC6H5 + H]+, C35H30O4P2Mn, 630.20; 537.028, calc. for
[Mn(CO)3-(dppe)]+, C29H24O3P2Mn, 537.058.
350 °C; IR (cmꢀ1, KBr): m(CO) 2025, 1953 and 1910;
Anal. Calc. for one unit of polymer, C31H27O5P2Mn: C,
62.42; H, 4.56; P, 10.38. Found: C, 60.25; H, 5.12; P,
9.86%. The calculated atomic C/P for one unit of poly-
mer is 15.8; Found: 16.0, indicating that approximately
each unit of the polyacrylate polymer is bonded to an
Mn atom.
2.6. Reaction of 1 with ambident ligands
2.6.1. Derivatives of pyridine
2.6.1.1. K1(O) complex with pyridine-3-carboxylic acid,
(nicotinic acid), [(CO)3(dppe)MnOC(O)C5H4N] (14).
Data 14: m.p.: softens at about 108 °C and decomposes
above 135 °C; IR (cmꢀ1, CHCl3): m(CO) 2027, 1960 and
2.4. Reaction of 1 with pyridine and pyridine-N-oxide
1
1914; H NMR (d, CDCl3): 7.9–7.2 (m, 24H, Ph), 3.02
2.4.1. Pyridine complex,
K1(N)[(CO)3(dppe)MnNC5H5]þBF 4 (11)
(m, 2H) and 2.87 (m, 2H) both from dppe; High-resolution
MS (m/z): 660.105, calc. for [(CO)3(dppe)MnNC5H4-
C(O)OH]+, C35H29NO5P2Mn, 660.112.
ꢀ
Data 11: m.p.: softens at about 103 °C and decomposes
above 116 °C; IR (cmꢀ1, CHCl3): m(CO) 2030, 1957 and
1
1944; H NMR (d, CDCl3): 7.90–6.65 (m, 20H, from Ph,
2.6.1.2. K1(N),K1(O) dinuclear Mn complex with pyridine-
5H, from pyridine), 3.65 (m, 2H) and 3.25 (m, 2H) both
3-carboxylic acid, (nicotinic acid), [(CO)3(dppe)MnN-
1
C5H4C(O)OMn(dppe)(CO)3]þBF 4 (15). Pure 15 was
ꢀ
from dppe; Low temperature (ꢀ53 °C) H NMR gave the
same two signals with the same intensity. High-resolution
MS (m/z): 616.0856, calc. for [(CO)3(dppe)MnNC5H5]+,
C34H29NO3P2Mn, 616.0921.
obtained by column chromatography on neutral alumina
using hexane and ethyl acetate as gradient eluents.
Data 15: m.p.: softens at 110 °C and decomposes above
150 °C; IR (cmꢀ1, CHCl3): m(CO) 2027 (broad), 1960
(broad) and 1939 (shoulder) and 1913; 1H NMR (d,
CDCl3): 8.73 (m), 8.35 (m, H) and 7.98 (m, H) all from nic-
otinic acid moiety, 7.9–7.2 (m, 40H, from Ph) 6.97 (m, H,
from nicotinic acid), 3.63 (m, 2H, from dppe bonded to
the Mn attached to N), 3.20 (m, 2H, from dppe bonded
to the Mn attached to N), 3.01 (m, 2H, from dppe bonded
to the Mn attached to the acid group), 2.85 (m, 2H, from
dppe bonded to the Mn attached to the acid group);
High-resolution MS (m/z): 1196.1440, calc. for [(CO)3-
(dppe)Mn–NC5H4C(O)O–Mn(dppe)(CO)3] C64H52NO8-
P4Mn2, 1196.1404; 537.0581, calc. for [Mn(dppe)(CO)3],
C29H24O3P2Mn, 537.0581. This complex was also prepared
by adding 2 molar equivalents of aqua complex to 1 mol of
nicotinic acid.
2.4.2. Pyridine-N-oxide complex,
K1(O)[(CO)3(dppe)MnONC5H4]þBF 4 (12)
ꢀ
Data 12: m.p.: softens at about 82 °C and decomposes
above 90 °C; IR (cmꢀ1, CHCl3): m(CO) 2025, 1950 and
1
1925; H NMR (d, CDCl3): 7.8–6.8 (m, 20H, from dppe
Ph, 5H, from pyridine-N-oxide), 3.41 (m, 2H), 2.88
(m, 2H) both from dppe CH2; High-resolution MS
(m/z): 632.0970, calc. for [(CO)3(dppe)MnONC5H5]+,
C34H29NO4P2Mn, 632.0952, 537.0581, calc. for [Mn-
(dppe)(CO)3], C29H24O3P2Mn, 537.0581.
2.4.3. Reaction of 1 with 1:1 mixture of pyridine and
pyridine-N-oxide
Data: 1H NMR (d, CDCl3): 7.8–6.8 (m, 40H, from
dppe Ph, 5H, from pyridine and 5H, from py-N-oxide),
3.62 (m, 2H, from pyridine complex), 3.41 (m, 2H, from
pyridine-N-oxide complex), 3.25 (m, 2H, from pyridine
complex), 2.89 (m, 2H, from pyridine-N-oxide complex)
These data (Table 2) for the dppe CH2 indicate that both
ligand complexes were present; from the relative intensi-
ties it was estimated that they were present in approxi-
mately equal quantities.
2.6.1.3. K1(NC) complexꢀwith 4-cyanopyridine, [(CO)3-
(dppe)MnNCC5H4N]þBF 4 (16). The product was chro-
matographed on a column of neutral alumina with hexane
and ethyl acetate as gradient eluents to give pure 16.
Data 16: m.p.: softens at about 85 °C and decomposes
above 108 °C; IR (cmꢀ1, CHCl3): m(CO) 2039, 1971 and
1
1961: H NMR (d, CDCl3): 7.8–6.8 (m, 20H, from dppe
Ph, 4H, from 4-cyanopyridine), 3.48 (m, 2H), 3.05 (m,
2H) both from dppe CH2; High-resolution MS (m/z):
641.0930, calc. for [(CO)3(dppe)MnNCC5H4N]+, C35H28-
N2O3P2Mn, 641.0956, 537.0316, calc. for [Mn(dppe)(CO)3],
C29H24O3P2Mn, 537.0581.
2.5. Reaction of 1 with phenolate anion
2.5.1. Preparation of phenol complex,
[(CO)3(dppe)MnOC6H5] (13)
The reaction was carried out either by using pure phe-
nol, or more rapidly, by adding complex 1 in CHCl3 to
an aqueous NaOH solution of phenol.
2.6.1.4. Preparation of K1(NC),K1(N) dinuclear Mn
complex with 4-cyanopyridine, [(CO)3(dppe)MnNCC5H4-
N–Mn(dppe)(CO)3]2þ2BF 4 (17). The crude product was
ꢀ
Data 13: m.p.: softens at about 128 °C and decomposes
above 142 °C; IR (cmꢀ1, CHCl3): m(CO) 2017, 1942 and
chromatographed on neutral alumina with hexane and
ethyl acetate as gradient eluents to give pure 17.
1
1906; H NMR (d, CDCl3): 7.8–7.1 (m, 25H, Ph), 2.97
(m, 2H) and 2.83 (m, 2H) both from dppe; High-resolution
MS (m/z): 630.19, calc. for [(CO)3(dppe)Mn–
Data 17: m.p.: softens at about 105 °C and decomposes
above 128 °C; IR (cmꢀ1, CHCl3): m(CO) 2039, 2027

P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
1151
CN
Table 2
Chemical shift of dppe CH2 protons (ppm) and IR spectra (cmꢀ1, in CHCl3) of (CO)3(dppe)MnZ
Complex No.
Attached to Mn
DPPE methylene protons (d)
ppm
Stretching frequencies
CO
a
b
Z
Atom of Z
CH2
CH2
Diff.
A0
A00
A0
1
1
2
3
4
5
6
7
8
H2O (ꢀ53 °C)
H2O (25 °C)
Acetic acid
Acrylic acid
O
O
O
O
3.04
2.97
2.92
2.91
2.99
2.86d
3.05d
2.95d
2.92d
2.96e
2.65
2.97
2.74
2.82
2.89
2.68d
2.84d
2.84d
2.72d
2.71e
0.39
0.00
0.18
0.09
0.10
0.18
0.21
0.11
0.20
0.15
2035
2026
2026
2027
2025
2027
2029
2027
2026
2025
2030
1965
1959
1960
1959
1958
1959
1962
1959
1955
1953
1957
1934
1910
1911
1913
1907
1914
1916
1916
1909
1910
1944
p-Bromobenzoic acid
Succinic acidc
Fumaric acidc
D-Tartaric Acidc
Citric acidc
O
O, O
O, O
O, O
O, O
O, O, O
9
Citric acidc
10
11
11
12g
13
14
15
15
16
17
Na-Polyacrylatec,f
Pyridine (25 °C)
Pyridine (ꢀ50 °C)
Pyridine-N-oxide
Phenol
N
N
O
O
O
N
O
CN
N
CN
O
O
N
N
O
N
O
C(O)O
C(O)O, O
N
O
N
O
O
O
P
3.65
3.53
3.41
2.97
3.02
3.63
3.01
3.48
3.50
3.50
3.07
3.05
3.59
3.39
2.99
3.36
3.01
3.00
3.03d
3.27
3.00
3.26
3.00
3.03
3.15
3.34
3.34
2.97
3.05
3.05
2.7
3.25
3.20
2.88
2.83
2.87
3.20
2.85
3.05
3.11
3.11
2.92
2.89
3.23
3.04
2.83
3.04
2.85
2.85
2.85d
2.86
2.83
2.86
2.74
2.87
2.95
3.09
3.09
2.80
2.87
2.87
2.58
2.23
2.80
0.40
0.33
0.53
0.14
0.15
0.43
0.16
0.43
0.39
0.39
0.15
0.16
0.36
0.35
0.16
0.32
0.16
0.15
0.18
0.41
0.17
0.40
0.16
0.16
0.20
0.25
0.25
0.17
0.18
0.18
0.12
0.28
0.17
2025
2017
2027
2027
2027
2039
2027
2039
2025
2028
2028
2038
2019
2038
2021
2027
2027
2038
2028
2038
2027
2026
2026
2027
1931
1931
2025
2025
2015
1995
2034
1950
1942
1960
1960
1960
1971
1961
1971
1948
1955
1955
1971
1945
1971
1947
1960
1959
1969
1961
1969
1960
1953
1955
1958
1957
1957
1952
1951
1919
1915
1968
1925
1906
1914
1939
1913
1961
1939
1961
1922
1918
1940
1959
1911
1958
1912
1911
1916
1960
1914
1960
1916
1908
1910
1917
1916
1934
1908
1906
1895
1910
1925
Nicotinic acid
Nicotinic acid
Nicotinic acid
4-Cyanopyridine
4-Cyanopyridine (2)
2259
2240
2259
18
19
3-Hydroxypyridine
3-Hydroxypyridine (2)
20
21
22
3-Cyanophenol
3-Cyanophenol
3-Cyanophenol (2)
2257
2223
2257
23
24
25
26
27
3-Hydroxybenzoic acid
3-Hydroxybenzoic acidc
3-Cyanobenzoic acid
3-Cyanobenzoic acid
3-Cyanobenzoic acid (2)
2259
2231
2259
28
29
30
31
Glycine
Tryptophan
Ph2PCH2CH2N(CH3)2
Ph2PCH2CH2N(CH3)2 (2)
P
N
N
N, N
N
H
O
32
33
34h
35
36
a
(CH3)2NCH2CH2N(CH3)2
(CH3)2NCH2CH2N(CH3)2
(CH3)2NCH2CH2N(CH3)2
Hydride (at 25 and 100 °C)
Nitrato (at 25 and 100 °C)
c
2.51
2.97
Assumed to be ‘‘trans’’ to apical CO.
b
c
d
e
f
Assumed to be ‘‘cis’’ to apical CO.
CO stretching frequencies essentially the same for each set of carbonyls.
Integrates for four protons for each signal.
Integrates for six protons for each signal.
IR spectra of Na-polyacrylate complex was taken by using Kbr pellet.
This complex is excluded from the generalizations discussed below.
K2(N) complex.
g
h
(shoulder) 1971, 1961 (broad) and 1939 shoulder; 1H NMR
(d, CDCl3): 7.8–6.8 (m, 40H, from dppe Ph, 4H, from 4-
cyanopyridine), 3.50 (broad, m, 4H), 3.11 (broad, m, 4H)
both from dppe CH2; High-resolution MS (m/z):
complex was also prepared by adding one mole of 1 to a
solution of 17.
2.6.1.5. Preparation of K1(O) complex with 3-hydroxypyri-
dine, [(CO)3(dppe)Mn–OC5H4N] (18). A solution of 1
was added drop-wise to a solution containing an equimolar
1178.1601,
calc.
for
[(CO)3(dppe)MnNCC5H4N–
Mn(dppe)(CO)3]2+, C64H62N2O6P4Mn2, 1178.1537. This

1152
P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
quantity of 3-hydroxypyridine dissolved in aqueous
NaOH.
sence of alkali but in the presence of water, 20, and an al-
most equal quantity of 21 were formed.
Data 18: m.p.: softens at about 75 °C and decomposes
above 88 °C; IR (cmꢀ1, CHCl3): m(CO) 2025, 1948 and
2.6.2.3. Preparation of K1(N),K1(O) dinuclear Mn complex
1
1922: H NMR (d, CDCl3): 7.8–6.8 (m, 20H, from dppe
with 3-cyanophenol, [(CO)3(dppe)MnNCC6H4OMn(dpp)-
(CO)3]þBF 4 (22). A CHCl3 solution of two molar equiv-
ꢀ
Ph, 4H, from 3-hydroxypyridine), 3.07 (m, 2H), 2.92 (m,
2H) both from dppe CH2; High-resolution MS (m/z):
632.1005, calc. for [(CO)3(dppe)MnOC5H4N + H]+,
alents of 1 is added to an aqueous NaOH solution of one
molar equivalent of 3-cyanophenol. Compound 22 was
also prepared by adding molar equivalents of 1 to either
20 or 21.
C34H29NO4P2Mn,
632.0952,
537.0556,
calc.
for
[Mn(dppe)(CO)3], C29H24O3P2Mn, 537.0581.
Data 22: m.p.: softens at about 162 °C and decomposes
above 178 °C; IR (cmꢀ1, CHCl3): m(CO) 2038, 2021, 1971,
broad 1957 (1959 due to CN, and 1956 due to OH merged)
and 1912; 1H NMR (d, CDCl3): 7.8–6.2 (m, 40H, from dppe
Ph, 4H, from 3-cyanophenol), 3.36 (m, 2H), 3.04 (m, 2 H)
both from dppe CH2 Mn attached to N; 3.01 (m, 2H), 2.85
(m, 2H) both from dppe CH2 of Mn attached to O; High-res-
olution MS (m/z): 1192.1501, calc. for [(CO)3(dppe)MnNC-
C6H4OMn(dppe)(CO)3]+, C65H52O5P2Mn2, 1192.1454,
656.0961, calc. for [(CO)3(dppe)MnNCC6H4OH]+,
C36H29NO4P2Mn, 656.0952; 537.0461, calc. for [Mn(dppe)-
(CO)3], C29H24O3P2Mn, 537.0581.
2.6.1.6. K1(O),K1(N) dinuclear Mn complex with
3-hydroxypyridine,
(CO)3]þBF 4ꢀ(19). The reaction was carried out in CHCl3
using an equimolar solution of 1 and 18.
[(CO)3(dppe)MnOC5H4NMn(dppe)-
Data 19: m.p.: softens at about 89 °C and decomposes
above 112 °C; IR (cmꢀ1, CHCl3): m(CO) 2028 (broad),
1955 (broad), 1940 (shoulder) and 1918; 1H NMR (d,
CDCl3): 7.8–6.8 (m, 40H, from dppe Ph, 4H, from 3-
hydroxypyridine), 3.59 (m, 2H, from dppe bonded to the
Mn attached to N), 3.23 (m, 2H, from dppe bonded to
the Mn attached to N), 3.05 (m, 2H, from dppe bonded
to the Mn attached to O), 2.89 (m, 2H, from dppe bonded
to the Mn attached to O); High-resolution MS (m/z):
1168.1505, calc. for [(CO)3(dppe)MnOC5H4N–Mn(dppe)-
(CO)3]+, C63H62NO7P4Mn2, 1168.1454, 537.0567, calc.
for [Mn(dppe)(CO)3], C29H24O3P2Mn, 537.0581. This com-
plex was also prepared by using 2 molar equivalents of 1 to
one of 3-hydroxypyridine.
2.6.3. Derivatives of benzoic acid
2.6.3.1. Preparation of K1(OCO) complex with 3-hydroxy-
benzoic acid, [(CO)3(dppe)Mn–OC(O)C6H4OH] (23).
The reaction was carried out by adding a CHCl3 solution
of 1 to an equimolar quantity of 3-hydroxybenzoic acid
in aqueous NaHCO3.
Data 23: m.p.: softens at about 114 °C and decomposes
at above 124 °C; IR (cmꢀ1, CHCl3): m(CO) 2027, 1960 and
2.6.2. Derivatives of phenol
1
1911; H NMR (d, CDCl3): 7.9–6.8 (m, 20H, from dppe
2.6.2.1. Preparation of K1(N) compleꢀx with 3-cyanophenol,
[(CO)3(dppe)Mn–NCC6H4OH]þBF 4 (20). The reaction
was carried out in CHCl3 using equimolar amounts of 1
and ligand.
Ph, 4H, from 3-hydroxybenzoic acid), 3.00 (m, 2H) and
2.85 (m, 2H) both from dppe CH2; High-resolution MS
(m/z): 673.0842, calc. for [(CO)3(dppe)Mn–OC6H4-
COOH + H], C37H30O6P2Mn, 674.0820.
Data 20: m.p.: softens at about 155 °C and decomposes
above 163 °C; IR (cmꢀ1, CHCl3): m(CO) 2038, 1971 and
2.6.3.2. Preparation of K1(OCO),K1(O) complex of
3-hydroxybenzoic acid, [(CO)3(dppe)Mn–OC(O)C6H4-
O–Mn(dppe)(CO)3] (24). A CHCl3 solution of two
molar equivalents of 1 is added to one molar equivalent
of an aqueous NaOH solution of 3-hydroxybenzoic acid.
Data 24: m.p.: softens at about 118 °C and decomposes
above 133 °C; IR (cmꢀ1, CHCl3): m(CO) 2027, 1959 and
1
1959: H NMR (d, CDCl3): 7.8–6.2 (m, 20H, from dppe
Ph, 5H, from 3-cyanophenol), 3.39 (m, 2H), 3.04 (m, 2H)
both from dppe CH2; High-resolution MS (m/z):
656.0961, calc. for [(CO)3(dppe)MnNCC6H4OH]+,
C36H29NO4P2Mn, 656.0952, 537.0461, calc. for [Mn(dppe)
(CO)3], C29H24O3P2Mn, 537.0581.
1
1916; H NMR (d, CDCl3): 7.9–7.2 (m, 40H, from dppe
2.6.2.2. Preparation of K1(O) complex with 3-cyanophenol,
[(CO)3(dppe)MnOC6H4CN] (21). The reaction was car-
ried out using a CHCl3 solution of 1 and a molar equiva-
lent of 3-cyanophenol in aqueous NaOH.
Ph, 4H, from 3-hydroxybenzoic acid), 3.03 (broad, m,
4H) and 2.85 (broad, m, 4H) both from dppe CH2; High-
resolution MS (m/z): 1211.1406, calc. for [(CO)3(dppe)-
Mn–OC(O)C6H4O–Mn(dppe)(CO)3 + H]+, C65H53O9P4Mn2,
1211.1401.
Data 21: m.p.: softens at about 167 °C and decomposes
above 181 °C; IR (cmꢀ1, CHCl3): m(CO) 2019, 1945 and
1
2.6.3.3. Preparation of K1(N) complex with 3-cꢀyanobenzoic
acid, [(CO)3(dppe)MnꢀNCC6H4COOH]þBF 4 (25). The
reaction is carried out in carefully dried MeOH. The yel-
low solid consisted of two complexes, which were sepa-
rated by chromatography on a neutral alumina column.
Based on spectroscopic data, the composition of the
1911; H NMR (d, CDCl3): 7.8–6.2 (m, 20H, from dppe
Ph, 5H, from 3-cyanophenol), 2.99 (m, 2H), 2.83 (m, 2H)
both from dppe CH2; High-resolution MS (m/z):
656.0991, calc. for [(CO)3(dppe)MnOC6H4CN + H],
C36H29-NO4P2Mn, 656.0952, 537.0603, calc. for
[Mn(dppe)(CO)3], C29H24O3P2Mn, 537.0581. In the ab-

P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
1153
1
mixture was estimated to consist of about 85% of 25 and
15% of 26.
1910; H NMR (d, CDCl3): 7.9–7.2 (m, 20H, from dppe,
4H, from 3-cyanobenzoic acid), 5.1 (broad peak due to
NH3 zwitter ion), 3.15 (m, 2H), and 2.95 (m, 2H) both
from dppe; 2.5 (m, 2H) from CH2 of tryptophan, 2.25 (t,
H) from CH of tryptophan; High-resolution MS (m/z):
726.138, calc. for [(CO)3(dppe)Mn–OC(O)CHCH2(NH2)-
C8H5N + H]+, C40H35O5P2NMn, 726.1372.
þ
Data 25: m.p.: softens at about 106 °C and decomposes
at above 112 °C; IR (cmꢀ1, CHCl3): m(CO) 2038, 1969 and
1
1960; H NMR (d, CDCl3): 7.9–7.2 (m, 20H, from dppe
Ph, 4H, from 3-cyanobenzoic acid), 3.27 (m, 2H) and
2.86 (m, 2H) both from dppe; High-resolution MS (m/z):
684.0953, calc. for [(CO)3(dppe)Mn–NCC6H4COOH]+,
C37H29O5P2NMn: 684.0901.
2.6.5. Reaction of 1 with Ph2PCH2CH2N(CH3)2(pn)
2.6.5.1. Preparation of K1(P)[(CO)3(dppe)MnP(Ph)2-
2.6.3.4. Preparation of K1(O) complex with 3-cyanobenzoic
acid, [(CO)3(dppe)Mn–O(O)CC6H4CN] (26). A CHCl3
solution of 1 is added to an equimolar quantity of 3-cyano-
benzoic acid in aqueous NaOH.
CH2CH2N(CH3)2]þBF 4 (30). The reaction is carried
ꢀ
out by adding a CHCl3 solution of 1 to a CHCl3 solution
of half the molar equivalent of pn.
Data 30: m.p.: softens at about 87 °C, decomposes
above 104 °C; IR (cmꢀ1, CHCl3): m(CO) 2027, 1958 and
Data 26: m.p.: softens at about 112 °C and decomposes
at above 120 °C; IR (cmꢀ1, CHCl3): m(CO) 2028, 1961 and
1
1917; H NMR (d, CDCl3): 8.0–7.0 (m, 30H, Ph), 3.34
1
1914; H NMR (d, CDCl3): 7.9–7.2 (m, 20H, from dppe,
(m, 2H), 3.09 (m, 2H), 3.02 (m, 2H attached to P of pn),
2.72 (2H, CH2 attached to N), 2.27 (s, 6H, CH3 attached
to N); High-resolution MS (m/z): 794.1915, calc. for
[(CO)3Mn(dppe)P(Ph)2CH2CH2 N(CH3)2], C45H44NO3-
P3Mn, 794.1910; 537.023, calc. for [(CO)3Mn(dppe)],
C29H24O3P2Mn, 537.058.
4H, from 3-cyanobenzoic acid), 3.00 (m, 2H) and 2.83
(m, 2H) both from dppe; High-resolution MS (m/z):
684.0961, calc. for [(CO)3(dppe)Mn–O(O)CC6H4CN +
H]+, C37H29O5P2NMn, 684.0901.
2.6.3.5. Preparation of K1(O),K1(N) dinuclear Mn complex
with
3-cyanobenzoic
acid,
[(CO)3(dppe)Mn–OðOÞ-
2.6.5.2. K1(P); K1(N)[(dppe)ꢀ(CO)3MnP(Ph)2(CH2)2N-
(CH3)Mn(CO)3(dppe)]2þ2BF 4 (31). A CHCl3 solution
of equimolar quantities of 1 and 30 was used.
CC6H4CN–Mn(dppe)(CO)3]þBF 4 (27). A CHCl3 solu-
tion of two molar equivalents of 1 is added to one molar
equivalent of 3-cyanobenzoic acid in aqueous NaOH
solution.
ꢀ
Data 31: m.p.: softens at 144 °C, decomposes above
210 °C;IR(cmꢀ1, CHCl3):m(CO)2031(broad), 1957(broad),
1913 (broad) and 1916; 1H NMR (d, CDCl3): 8.00–7.00 (m,
50H, Ph), 3.39 (m, 2H, from dppe bonded to the Mn attached
to N), 3.10 (m, 2H, from dppe, bonded to the Mn attached to
P of pn), 3.01 (m, 4H, CH2 attached to P of pn), 2.97 (m, 2H,
from dppe bonded to the Mn attached to N), 2.80 (m, 2H,
from dppe bonded to the Mn attached to N), 2.79 (m, 2H,
CH2 attached to N), 2.60 (s, 6H, 2CH3 attached to N); High-
resolution MS (m/z): 1418.2647, calc. for ½ðdppeÞðCOÞ3Mn–
PðPhÞ ðCH2Þ NðCH3Þ –MnðCOÞ ðdppeÞꢁ2þBF4ꢀ, 1418.2530;
Data 27: m.p.: softens at about 118 °C and decomposes
above 124 °C; IR (cmꢀ1, CHCl3): m(CO) 2038, 2027 and
1969, cyanobenzoic acid, 3.26 (m, 2H), 2.86 (m, 2H) both
from dppe CH2 Mn attached to N; 3.00 (m, 2H), 2.74
(m, 2H) both from dppe CH2 Mn attached to O; High-res-
olution MS (m/z): 3.36 (m, 2H), 3.04 (m, 2H); 3.01 (m, 2H),
2.85 (m, 2H) both from dppe CH2 of Mn attached to O;
High-resolution MS (m/z): 1220.1394, calc. for [(CO)3(dp-
pe)Mn-OC(O)C6H4CN–Mn(dppe)(CO)3]+, C65H62O8P4-
NMn2, 1220.140.
2
2
2
3
822.2166, calc. for ½ðdppeÞðCOÞ3Mn–PðPhÞ2ðCH2Þ2N-
ðCH3Þ Hꢁ2þBF4, 882.2029, 794.1882, calc. for [(CO)3-
2
2.6.4. Reaction of 1 with amino acids
2.6.4.1. Preparation of K1(O) complex with glycine,
[(CO)3(dppe)MnOC(O)CH2NH2] (28). A CHCl3 solu-
tion of 1 is added to an equimolar aqueous solution of
glycine.
Mn(dppe)P(Ph)2CH2CH2N(CH3)2],
C45H44NO3P3Mn,
794.1915, 537.047, calc. for [(CO)3Mn(dppe)], C29H24O3-
P2Mn, 537.058.
Data 28: m.p.: softens at about 130 °C and decomposes
2.7. Reaction of 1 with (CH3)2NCH2CH2N(CH3)2 (TMED)
above 138 °C; IR (cmꢀ1, CHCl3): m(CO) 2026, 1953.7 and
1
1908; H NMR (d, CDCl3): 7.9–7.2 (m, 20H, from dppe,
2.7.1. K1(N)[ꢀ(CO)3(dppe)Mn–N(CH3)2CH2CH2N-
4H, from 3-cyanobenzoic acid), 3.03 (m, 2H) and 2.87
(m, 2H) both from dppe; High-resolution MS (m/z):
612.0921, calc. for [(CO)3(dppe)Mn–OC(O)CH2NH2 +
H]+, C31H29O5P2NMn, 6121.0903.
(CH3)2]þBF 4 (32)
A CHCl3 solution of 1 is added drop-wise to a half mo-
lar equivalent of TMED in CHCl3.
Data 32: m.p.: softened at 107 °C, decomposes at above
116 °C; IR (cmꢀ1, CHCl3): m(CO) 2025, 1952 and 1908. 1H
NMR (d, CDCl3): 7.80–7.20 (m, 20H, Ph), 3.05 (m, 2H,
CH2) and 2.87 (m, 2H, CH2) both from dppe, 2.78 (s,
3H, CH3 attached to quaternary N), 2.75 (s, 3H, CH3 at-
tached to quaternary N), 2.52 (m, 2H, CH2 attached to
quaternary N), 2.39 (m, 2H, CH2 attached to tertiary N),
2.6.4.2. K1(O) complex with tryptophan, [(CO)3(dppe)-
Mn–OC(O)CHCH2(NH2)C8H5N], (29). The reaction is
carried out in MeOH.
Data 29: m.p: softens at about 138 °C and decomposes
above 160 °C; IR (cmꢀ1, CHCl3): m(CO) 2026, 1955 and

1154
P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
2.24 (s, 6H, CH3 attached to tertiary N); High-resolution
MS (m/z): 643.234, calc. for [(CO)3(dppe)Mn–N(CH3)2
CH2CH2N(CH3)2], C35H38N2O3P2Mn, 643.268, 537.042,
calc. for [(CO)3Mn(dppe)], C29H24O3P2Mn, 537.058.
Z = PhCN, CH3CN, CH2@CHCN, m-xylylNC, PPh3 and
CO [7].
We have reported [2], that the hydride, (CO)3(dppe)-
MnH, precursor to the corresponding aqua complex, reacts
not only with HBF4 but also with a variety of other strong
acids. These reactions result in the liberation of dihydrogen
and the direct formation of the neutral complex containing
the anion of the acid as a new ligand. However, weaker
acids such as acetic acid and phenol do not react in this
fashion. We now report that such weaker acids do react
with the aqua complex resulting in the replacement of the
aqua ligand by the anion (conjugate base) of the weak acid
thus making available a new route to the corresponding
neutral complexes. Water-soluble carboxylic acids can be
used in a two-phase system without added alkali, but
others require the presence of base to speed the reaction.
Amino acid ligands in methanol solution react in their
zwitter ion form. Complexes have been prepared from both
aliphatic and aromatic carboxylic acids, as well as from
phenol. The reaction with succinic and fumaric acids leads
to complexes containing two Mn atoms. The reaction with
citric acid gives either the 2:1 complex, presumably involv-
ing the two terminal carboxyl groups, or when alkali is
present, a 3:1 complex. Stirring an excess of the aqua com-
plex with sodium acrylate polymer (Aldrich, av. mol wt.
2100) gives a product that is insoluble in all common
solvents and thus resists conventional methods of charac-
terization. The ultimate analysis of the polymer and the
calculated C/P ratio from that analysis, (see supra) indi-
2.7.2. K1(N), K1(N)[(CO)3(dppe)MnN(CH3)2-
CH2CH2N(CH3)2Mn(CO)3(dppe)]2þ2BF 4 (33)
ꢀ
A CHCl3 solution of TMED is added to an equimolar
CHCl3 solution of 1 and the product recrystallized from
CHCl3/hexane.
Data 33: m.p.: softens at about 120 °C and decomposes
above 142 °C; IR (cmꢀ1, CHCl3): m(CO) 2025, 1951 and
1
1906; H NMR (d, CDCl3): 8.00–7.00 (m, 40H, Ph), 3.07
(m, 4H, from dppe), 2.91 (m, 4H, from dppe) 2.79 (s, 6H,
2CH3 attached to N), 2.73 (s, 6H, 2CH3 attached to N),
2.52 (m, 2H, attached to N), 2.51 (s, 2H, attached to N);
High-resolution MS (m/z): 1277.1953; calc. for ½ðCOÞ3
ðdppeÞMnNðCH3Þ CH2CH2NðCH3Þ MnðCOÞ ðdppeÞꢁþ
2
2
3
BF4ꢀ, C64H64N2O6P4Mn2BF4, 1277.2505, 1191.1655, calc.
for [(CO)3(dppe)Mn–N(CH3)2CH2CH2N(CH3)2–Mn(CO)3
(dppe) + H]+, C64H65N2O6P4Mn2, 1191.2554.
2.7.3. [K2(N,N-TMED)]Mn(CO)3Br (34)
To a solution of Mn(CO)5Br [6] (0.274 g, 1.0 mmol), in
20 mL of toluene in a round-bottom flask equipped with
a condenser, 0.150 mL (1.0 mmol) of TMED dissolved in
20 mL of toluene is added drop-wise. The solution is re-
fluxed for 3 h and the toluene is removed via rotary evap-
orator to give a brown solid, which is dissolved in
benzene, stirred for 5 min and filtered. The filtrate is evap-
orated via rotary evaporator. The brown solid is recrystal-
lized from 1:1 CH2Cl2/hexane, giving orange crystals of 34.
Yield 75%.
cates that almost every –½–CH2–CH–ðCOꢀÞ–ꢁ– unit of
2
the acrylate polymer is attached to a separate Mn atom,
giving a new polymer, 10, of the approximate formula:
–½–CH2–CH–½CðOÞOMnðCOÞ3ðdppeÞꢁꢁnꢀ. This appears to
be a unique type of polymer, one highly loaded with a tran-
sition metal, and it merits further investigation. Attempts
to prepare a similar polymer by initiating polymerization of
[(CO)3(dppe)Mn(NCCH@CH2)]BF4 with benzoyl peroxide
or AIBN were unsuccessful.
Data 34: m.p.: 154–158 °C, IR (cmꢀ1, CH2Cl2): m(CO)
2015, 1919, 1893 and 1895 as a doublet; 1H NMR (d,
CDCl3): 2.98 (s, 6H, CH3), 2.92 (s, 6H, CH3), 2.7 (m, 2H),
2.58 (m, 2H); High-resolution MS (m/z): 333.9628, calc.
for Mn(CO)3(TMED)Br, 334.0189; 249.9882, calc. for
[Mn(TMED)Br], 249.9877; 171.07, calc. for [Mn(TMED)],
171.0694. Anal. Calc. for [Mn(CO)3(TMED)Br]: C, 32.26:
H, 4.81. Found: C, 32.6; H, 4.85%.
1
3.1. H NMR studies
3.1.1. Aqua complex 1
3. Results and discussion
The signals associated with the protons of the dppe-Mn
metallacycle are of particular interest. Unlike the other re-
lated dppe complexes, which all show two signals, 1 in
CDCl3 at room temperature shows a single signal (d 2.95,
m, 4H) for these four protons. The crystal structure [3] of
1 shows a puckered metallacycle, similar to that of other
dppe complexes. Apparently the rapid reversible dissocia-
tion of the aqua ligand of 1, which may involve a concom-
itant rearrangement to an intermediate 5-coordinate
trigonal bipyramidal structure, results in all the protons
appearing equivalent on the NMR timescale. However, at
ꢀ53 °C, this signal is split into two distinct methylene sig-
nals (m, d 2.67, 2H; m, d 3.1, 2H) owing to the slowing of
dissociation of the aqua ligand at low temperature.
However, even at this low temperature it appears that
The octahedral Mn(I) complex fac-½ðCOÞ3ðdppeÞ-
MnOH2ꢁþBF (1) central to this study, is easily prepared
ꢀ
4
in high yield by a two-step process from readily available
starting materials [2,3]. Replacement of the aqua ligand is
achieved by simply stirring a solution of 1 with the desired
ligand, Z. Thus derivatives of 1 have been reported, where
Z represents the following anions: CN; OMe; NO3; OC(O)-
CH3; OTf; N3 [4]; and F [6]. (In the case of the azide,
further reaction of the coordinated N3 by 1,3-dipolar addi-
tion, either to acetylenic compounds or to nitriles, gave
new manganese-bonded triazoles and tetrazoles, respec-
tively [3]). With neutral ligands [4], the corresponding ionic
complexes [(CO)3(dppe)MnZ]BF4 were prepared, where

P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
1155
axial–equatorial interconversions of the puckered structure
continue, leading, on average, to an essentially planar,
5-membered ring (see Graphical Abstract). Such a planar
Cs structure results in a pair of equivalent protons on adja-
cent carbon cis to the apical CO and a pair that is trans to
this CO, giving rise to the two signals characteristic of the
1H NMR of the dppe-metallacyle.
We were able to assign symmetry species A0, A00, and A0 in
decreasing order of frequency, to the three carbonyl
stretches in each of these related Cs complexes. The partial
positive charge on the carbon atom of coordinated CO is
the most important factor affecting the frequency; the more
positive this charge, the larger the force constant and the
higher the frequency. Data for the new complexes are
shown in Table 2. These 29 complexes may be grouped into
four categories (Table 3) depending on the nature of the
ligand atom that is bonded to the Mn, namely cyano-
nitrogen, pyridine-nitrogen, carboxyl-oxygen and phenolic-
oxygen. This order is the descending order of frequencies
(with one minor exception) for all three A0, A00, and A0
bonding modes. The largest difference in frequencies be-
tween the four categories of bonding types occurs with
the lower A0 mode, which involves the equatorial COs
moving in phase with respect to each other and out of
phase with respect to the axial CO. The group of complexes
with the highest frequencies of the four groups is the cate-
gory in which a nitrile nitrogen atom is bonded to the Mn.
The six complexes having such coordination have the rele-
vant A0 stretching frequencies in the narrow range 1957–
1961 cmꢀ1 (noticeably shifted, as expected, from the values
observed with ligands having free nitrile groups). The ni-
trile groupꢀs p* orbitals probably compete with the car-
bonyl p* orbitals in accepting back-donation from the
Mn d-electrons, thus increasing the partial positive charge
on the carbonyl carbon atoms with the net effect of increas-
ing the carbonyl frequencies as compared to those with
pyridine or oxygen-bonded ligands.
3.1.2. Hydrido and nitrato derivatives of 1
In an attempt to obtain evidence for ligand dissociation,
1
the H NMR of the hydrido (the smallest ligand) and nit-
rato (with a long Mn–O bond) complexes [2,4] was exam-
ined in the temperature range 100 to 120 °C. However,
the chemical shifts remained unchanged (m, 2H, 2.51 and
m, 2H, 2.23 for hydrido, m, 2.97, 2H and m, 2.80, 2H for
nitrato) indicating no dissociation under these conditions.
3.1.3. The dppe-Mn metallacycle
The chemical shifts of the methylene protons provide
valuable evidence for the preferred site of mono-coordi-
1
nated ambident ligands. One of the most instructive H
NMR studies [8] of this system involved the dppe complex,
6-exophenylcyclohexadienylmanganese(I), [PhC6H6(dppe)-
Mn(NO)]PF6. At 25 °C, this complex showed the CH2
protons of the dppe as two signals (d 3.53 and 3.02) as
expected. However at ꢀ75 °C four different signals were
observed, which the authors ascribe to two non-equivalent
axial and two non-equivalent equatorial protons, in accor-
dance with a stable puckered C1 structure. We examined
1
the H NMR of our pyridine complex, 11, at ꢀ50 °C, but
the two signals observed at room temperature remained
essentially unchanged at the lower temperature.
3.3. Competition for coordination sites on ambident ligands
The chemical shift data (Table 2) of the methylene pro-
tons on the dppe ligand, provide valuable diagnostic infor-
mation as to the site (Table 1) of mono-coordination of
ambident ligands. These data show a consistent pattern,
particularly, with respect to the difference between the
chemical shifts of the two sets of protons. For the 21 re-
lated complexes in which the Mn is coordinated to an oxy-
gen atom, this difference ranges from 0.09 to 0.19 ppm or
an average of 0.14 ppm. For the 10 complexes in which
the Mn is attached to a nitrogen atom, either that of a pyr-
idine or a nitrile nitrogen, this difference ranges from 0.32
to 0.43 ppm or an average of 0.39 ppm.
Previous evaluations of the relative coordinating ability
of some monodentate ligands have relied on the determina-
tion of equilibrium studies of substitution reactions, e.g.,
(amine)W(CO)5 + L ¢ LW(CO)5 + amine [10]. The deter-
mination of the equilibrium constants by such studies is,
however, rather limited and have to be carefully chosen be-
cause of analytical difficulties. The interest in unsymmetri-
cal chelation in ambident ligands stems from their potential
use in transition metal-catalyzed homogeneous reactions.
The K2 chelation of such ligands affords stability, but if
one of the donor atoms is more easily dissociated than
the other, the resulting vacated site on the K1 complex
may then be occupied by a substrate molecule, followed
by a desired insertion reaction and a subsequent reconstitu-
tion of the original K2 complex. One of the most frequently
used ligand for such reactions is the bidentate P,N ligand,
3.2. Infrared studies
In a previous paper [9], we analyzed the carbonyl
stretching frequencies of 38 [(CO)3(dppe)MnZ] complexes.
Table 3
CO stretching frequencies from Table 2 of (various) [(CO)3(dppe)MnZ] complexes arranged according to Mn–Z bond
Cyano ‘‘N’’ (6)
Pyridine ‘‘N’’ (4)
Carboxyl ‘‘O’’ (15)
Phenolic ‘‘O’’ (3)
Range
Median
Range
Median
Range
Median
Range
Median
A0
A00
A0
2038–2039
1969–1971
1958–1961
2038
1970
1960
2027–2030
1955–1961
1939–1944
2026
1959
1940
2025–2029
1953–1962
1907–1916
2027
1959
1913
2017–2021
1942–1947
1906–1912
2019
1945
1911

1156
P.R. Ettireddy, M. Orchin / Polyhedron 25 (2006) 1147–1156
(CH3)2NCH2CH2PPh2, (pn). It has been found, for exam-
ple [11] that the rhodium-catalyzed hydroformylation of
styrene gives a substantially better yield of aldehydes when
pn rather than dppe is used as a chelating ligand and a sim-
ilar result was found [12,13] in the case of the carbonyl-
ation of a Pt-K2(N,P) pn complex. Studies of Ni [14], Ru
[15], and heteronuclear Pt complexes [16] containing the
pn ligand in its K2(N,P) form have shown that the nitrogen
site is more easily dissociated from the metal than the phos-
phorous atom.
Most studies involving mixed bidentate ligands, such as
the ones cited above, have been devoted to investigating
selective dissociation of the chelated K2-complex to a corre-
sponding K1-complex. The results of such studies are gen-
erally consistent with hard-acid, soft-base (HASB)
theory, with the central cationic metal acting as the hard
acid, and the ligand, with two competing heteroatoms of
differing hardness/softness, as the base [17]. In the case of
a the K2(N,P) pn complexes, the metal–N bond, as ex-
pected, and as the cited references show, dissociates prefer-
entially. Although it may be reasonable to assume that
preferred coordination is the reverse of preferred dissocia-
tion, it was nevertheless thought to be instructive to ascer-
tain the preferred coordination site in the case of pn by
reacting it with one mole of 1.
3-hydroxybenzoic acid exclusively at the carboxyl group,
23, while with NaOH both functional groups are coordi-
nated, 24. The synthesis of 16 from 4-cyanopyridine indi-
cates coordination at nitrile nitrogen in preference to
pyridine nitrogen. In the absence of alkali or water, the ni-
trile group coordinates more rapidly than carboxyl of 3-
hydroxybenzoic acid (25) or the hydroxyl of 3-cyanophenol
(20). It would appear that a useful ambident chelating li-
gand for certain catalytic reactions might consist of a pyr-
idine derivative having a suitably situated nitrile group, or
one containing CN and N(CH3)2 groups. We have no plans
to pursue this area of research.
Acknowledgments
We thank Prof. A. Pinhas and Dr. J.K. Bauer for valu-
able discussions and Drs. Tom Becker and K. Jayasimhulu
for help with experimental work.
References
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1
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