Syntheses of tris(pyrazolyl)methane ligands and {[tris(pyrazolyl)methane]Mn(CO)3} SO3CF3 complexes: Comparison of ligand donor properties

Article abstract of DOI:10.1016/S0022-328X(00)00290-4

The known ligands HC(pz)₃, HC(3,5-Me₂pz)₃, HC(3-Phpz)₃, and HC(3-^tBupz)₃ and the new ligand HC(3-ⁱPrpz)₃ (pz = pyrazolyl ring) are prepared in CHCl₃-H₂

Full text of DOI:10.1016/S0022-328X(00)00290-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 607 (2000) 120–128
Syntheses of tris(pyrazolyl)methane ligands and
{[tris(pyrazolyl)methane]Mn(CO)3}SO3CF3 complexes: comparison
of ligand donor properties
Daniel L. Reger a,*, T. Christian Grattan a, Kenneth J. Brown a, Christine A. Little a,
Jaydeep J.S. Lamba a, Arnold L. Rheingold b, Roger D. Sommer b
a Department of Chemistry and Biochemistry, Uni6ersity of South Carolina, Columbia, SC 29208, USA
b Department of Chemistry and Biochemistry, Uni6ersity of Delaware, Newark, DE 19716, USA
Received 3 April 2000; received in revised form 4 May 2000
Dedicated to Professor Martin A. Bennett on the occasion of his 65th birthday.
Abstract
The known ligands HC(pz)3, HC(3,5-Me2pz)3, HC(3-Phpz)3, and HC(3-tBupz)3 and the new ligand HC(3-iPrpz)3 (pz=pyrazolyl
ring) are prepared in CHCl3–H2O using the appropriate pyrazole, an excess of Na2CO3, and tetra-n-butylammonium bromide as
the phase transfer catalyst. Using these conditions, good yields of the ligands are consistently obtained. The new ligand
PhC(pz)2py (py=pyridyl ring) is prepared in the CoCl2 catalyzed condensation reaction of (pz)2SꢀO and Ph(py)CꢀO. The
reaction of HC(pz)3, KOtBu and para-formaldehyde followed by quenching with water yields HOCH2C(pz)3. All of these ligands,
except HC(3-tBupz)3, react with [Mn(CO)5]SO3CF3, prepared in situ from Mn(CO)5Br and Ag(SO3CF3), to yield the respective
[(ligand)Mn(CO)3]SO3CF3 complex. The carbonyl stretching frequencies and 13C-NMR trends of these complexes indicate that the
donor abilities of all of the ligands are fairly similar. The solid state structure of {[HC(3-iPrpz)3]Mn(CO)3}+ shows the
HC(3-iPrpz)3 ligand is tridentate with the iso-propyl groups rotated away from the Mn(CO)3 core of the cation relieving any
possible steric congestion. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Tris(pyrazolyl)methane ligands; Manganese carbonyl complexes; Second generation ligands
1. Introduction
Metal complexes of the tris(pyrazolyl)borate ligand
system, first prepared in the late 60’s by Trofimenko,
are one of the most extensively studied classes of coor-
dination compounds in inorganic chemistry [1]. An
important impetus in this chemistry was the introduc-
tion, again by Trofimenko, of ‘second generation’ lig-
ands in which the pyrazolyl rings contain bulky
The isoelectronic tris(pyrazolyl)methane ligands have
substituents, especially at the three-position [2].
received less attention [3]. These neutral ligands are
formally derived from tris(pyrazolyl)borate ligands by
replacing the central boron anion with a carbon atom.
Trofimenko reported the syntheses of several tris(pyra-
zolyl)methane ligands and demonstrated that these neu-
tral ligands bind both early (Cr, Mo, W and Mn) and
late transition metals (Co, Ni, and Pd) [4]. Later,
Elguero et al. developed an improved procedure for the
* Corresponding author. Tel.: +1-803-7772587; fax: +1-803-
7779521.
E-mail address: reger@psc.sc.edu (D.L. Reger).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00290-4

D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
121
syntheses of these ligands [5]. Despite these early re-
ports, syntheses of ‘second generation’ tris(pyra-
zolyl)methane ligands with bulky substituents at the
three-position have only recently been reported [6]. One
reason for the diminished activity in this area is that the
syntheses of the tris(pyrazolyl)methane ligands, with the
exception of HC(pz)3 (pz=pyrazolyl ring), are more
difficult than the tris(pyrazolyl)borate analogs. In gen-
eral, yields are only 25–45% and the isolation proce-
dures require several steps, generally including a
chromatography. Even the HC(3,5-Me2pz)3 ligand was
not extensively used until recently, with Enemark pub-
lishing the first solid-state structures of complexes con-
taining this ligand in 1995 [3r].
As part of our program to synthesize metal complexes
of tris(pyrazolyl)methane and related ligands [6a,b, 7],
we have carefully investigated the preparative proce-
dures of the ligands. Reported here are improved prepa-
rations of HC(pz)3, HC(3,5-Me2pz)3, HC(3-Phpz)3 and
HC(3-tBupz)3, and the first report of the syntheses of
HC(3-iPrpz)3, PhC(pz)2py (py=pyridyl ring) and
HOCH2C(pz)3. We are also interested in how substitu-
tion on the pyrazolyl rings influences the donor proper-
ties of the ligands. To that end, we have prepared the
[(ligand)Mn(CO)3]SO3CF3 complex of each (except with
HC(3-tBupz)3) and report ligand donor trends based on
the carbonyl stretching frequencies and positions of the
13C-NMR resonances.
equipped with a reflux condenser. This mixture was
heated at gentle reflux for 3 days over which time it
became a pale yellow emulsion. The mixture was al-
lowed to cool to r.t. and filtered through a Bu¨chner
funnel to remove the excess base. To the filtrate was
added diethyl ether (500 ml) and H2O (300 ml). The
organic layer was separated and the aqueous layer
extracted with diethyl ether (3×200 ml). The combined
organic layers were then washed with saturated brine
solution (200 ml). The organic layer was treated with
decolorizing charcoal and dried over sodium sulfate.
The mixture was filtered and the solvent removed by
rotary evaporation. The resulting pale yellow solid (12.6
g, 63%) was then dried under vacuum. M.p. 100–102°C,
1
([6c] 102–104°C). H-NMR (acetone-d6): l 8.73 (s, 1H,
HC), 7.86 (d, 3H, JHH=2.6, 3-H (pz)), 7.62 (d, 3H,
J
HH=1.7, 5-H (pz)), 6.40 (d of d, 3-H, JHH=1.7, 2.6,
4-H (pz)).
2.3. Tris(3,5-dimethyl-1-pyrazoyl)methane (2)
Distilled water (700 ml) was added to a 2 l flask
containing a mixture of 3,5-dimethyl pyrazole (68.1 g,
707 mmol) and tetra-n-butylammonium bromide (11.4
g, 35 mmol). With vigorous stirring, sodium carbonate
(586 g, 4.2 mol) was added gradually to the reaction
mixture1. After cooling to near r.t., chloroform (350 ml)
was added and the flask was equipped with a reflux
condenser. This mixture was heated at gentle reflux for
3 days over which time it became an orange–red emul-
sion. The mixture was allowed to cool to r.t., filtered
through a Bu¨chner funnel to remove the excess base,
and the organic layer separated from the aqueous layer.
The organic layer was washed with distilled water (3×
50 ml) and dried over sodium sulfate. The drying agent
was removed by filtration and the solvent was removed
by rotary evaporation. Unreacted pyrazole was removed
from the resulting brown solid by sublimation (80°C in
oil bath at 0.2 mmHg). The remaining solid was then
dissolved in methylene chloride (50 ml) and flushed
through a plug of silica with methylene chloride (2×
250 ml). The solvent was removed by rotary evapora-
tion to afford a yellow–white solid (19.8 g, 65%). M.p.
2. Experimental
2.1. General
All manipulations were carried out under a nitrogen
atmosphere using standard Schlenk techniques or in a
Vacuum Atmospheres HE-493 dry box unless otherwise
noted. All solvents were dried and distilled prior to use
according to standard methods. 1H- and 13C-NMR
chemical shifts are reported in ppm versus TMS. All
reagents were purchased from Aldrich. The pyrazoles
not purchased were synthesized according to published
procedures; 3-PhpzH [8], 3-tBupzH [8], and 3-iPrpzH [9].
1
154–155°C, ([4] 153–154°C). H-NMR (acetone-d6): l
2.2. Tris(1-pyrazoyl)methane (1)
8.20 (s, 1H, HC), 5.92 (s, 3H, 4-H (pz)), 2.09, 2.03 (s, s,
9H, 9H, 3,5-Me).
Distilled water (294 ml) was added to a 500 ml round
bottom flask containing a mixture of pyrazole (20.0 g,
294 mmol) and tetra-n-butylammonium bromide (4.7 g,
14.7 mmol). With vigorous stirring, sodium carbonate
(187 g, 1.8 mol) was added gradually to the reaction
mixture; constant stirring increases the efficiency of the
reaction1. After cooling to near room temperature (r.t.),
chloroform (147 ml) was added and the flask was
2.4. Tris(3-phenylpyrazoyl)methane (3)
Distilled water (40 ml) was added to a 100 ml flask
containing a mixture of 3-phenylpyrazole (2.88 g, 0.020
mol) and tetra-n-butylammonium bromide (0.32 g, 0.99
mmol). With vigorous stirring, sodium carbonate (12.7
g, 120 mmol) was added gradually to the reaction
mixture1. After cooling to near r.t., chloroform (10 ml)
was added and the flask was equipped with a reflux
1 Caution: this addition is exothermic.

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D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
condenser. This mixture was heated at gentle reflux for
3 days over which time it became a dark yellow emul-
sion. The mixture was allowed to cool to r.t. and the
organic layer separated from the aqueous layer. The
aqueous layer was extracted with diethyl ether (1×15
ml). The combined organic layers were washed with
distilled water (2×10 ml) and dried over sodium sul-
fate. The solution was filtered and the solvent was
removed by rotary evaporation. The resulting off-white
solid was then dissolved in toluene (50 ml) and added
to a 100 ml flask containing a catalytic amount of
pre-dried p-toluenesulfonic acid (0.050 g, 0.27 mmol).
The golden solution was heated at reflux for 1 day.
After it had cooled to r.t., the solution was neutralized
with a 5% aqueous Na2CO3 solution (50 ml) and
washed with distilled water (3×15 ml). The dark yel-
low solution was dried over sodium sulfate. The drying
agent was removed by filtration and the solvent was
removed by rotary evaporation resulting in a dark
yellow solid. The solid was dissolved in methylene
chloride (20 ml) and chromatographed on a silica gel
column (23×4 cm) that was packed and flushed with a
1:1 methylene chloride–toluene solution. When moni-
tored by UV light, the product has a Rf=0.3, while the
starting material, 3-PhpzH, has a Rf=0.1. The frac-
tions that contained the desired product were combined
and the solvent was removed by rotary evaporation to
yield an off-white solid (1.98 g, 67%). M.p. 174–175°C,
with a 5% aqueous Na2CO3 solution (100 ml) and
washed with distilled water (3×100 ml). The organic
layer was then dried over sodium sulfate, the drying
agent removed by filtration and the solvent removed by
rotary evaporation resulting in brown oil. An impurity
of 3-i-propylpyrazole was removed by vacuum distilla-
tion at 170°C. The remaining brown oil was dissolved
in a 1:1 solution of hexane–toluene (20 ml) and flushed
through a plug of silica with 1:1 hexane–toluene (350
ml). The solvent was removed by rotary evaporation to
afford a yellow oil (5.04 g, 35%). The oil contains a 5:1
mixture of the desired isomer and an isomer with two
pyrazole rings having the iso-propyl group at the three-
position and the other one with the iso-propyl group at
1
the five-position. H-NMR (acetone-d6): l 8.39 (s, 1H,
HC), l 7.65 (d, 3H, JHH=2.5 Hz, 5-H (pz)), 6.22 (dd,
3H, 4-H (pz)), 2.96 (septet, 3H, CH(CH3)2), 1.21 (d,
18H, JHH=7.0, CH(CH3)2). 13C-NMR (acetone-d6): l
161.1 (5-C (pz)), 129.5 (3C (pz)), 103.8 (4C (pz)), 83.2
(HC), 27.8 (CH(CH3)2), 22.6 (CH(CH3)2). FAB+ MS:
m/z Anal. Calc. 340.2375, Found: 340.2369 [M]+.
2.6. Tris(3-t-butylpyrazoyl)methane (5)
Distilled water (20 ml) was added to a 100 ml flask
containing a mixture of 3-t-butylpyrazole (2.48 g, 0.020
mol) and tetra-n-butylammonium bromide (0.32 g, 1.0
mmol). With vigorous stirring, sodium carbonate (12.7
g, 0.12 mol) was added gradually to the reaction
mixture1. After cooling the mixture to near r.t., chloro-
form (10 ml) was added and the flask was equipped
with a reflux condenser. This mixture was heated at
gentle reflux for 3 days over which time it became a
dark yellow emulsion. The mixture was allowed to cool
to r.t., filtered through a Bu¨chner funnel to remove the
excess base, and the organic layer separated from the
aqueous layer. The aqueous layer was then extracted
with diethyl ether (3×15 ml). The combined organic
fractions were washed with distilled water (2×10 ml)
and dried over sodium sulfate. The drying agent was
removed by filtration and the solvent was removed by
rotary evaporation. The resulting yellow oil was dis-
solved in toluene (50 ml) and added to a 100 ml flask
containing a catalytic amount of pre-dried p-toluenesul-
fonic acid (0.050 g, 0.27 mmol). The golden solution
was heated at reflux for 1 day. The solution was cooled
to r.t. and neutralized with a 5% aqueous Na2CO3
solution (50 ml) and washed with distilled water (3×15
ml). The organic layer was then dried over sodium
sulfate, the drying agent removed by filtration and the
solvent removed by rotary evaporation resulting in a
dark, yellow oil. The oil was dissolved in a 1:1 solution
of hexane–toluene (15 ml) and chromatographed on a
silica gel column (15×4 cm) that was packed and
flushed with a 1:1 hexane–toluene solution. Due to the
poor UV visibility of the product, a small aliquot from
1
([6d] 177–178°C). H-NMR (acetone-d6): l 8.86 (s, 1H,
HC), 8.10 (d, 3H, 5-H (pz)), 7.90 (d, 6H, JHH=2.6 Hz,
o-H (Ph)), 7.42 (dd, 6H, m-H (Ph)), 7.35 (d, 3H, p-H
(Ph)), 6.90 (d, 3, JHH=2.6 Hz, 4-H (pz)).
2.5. Tris(3-i-propylpyrazoyl)methane (4)
Distilled water (125 ml) was added to a 250 ml flask
containing a mixture of 3-i-propylpyrazole (14.1 g, 0.13
mol) and tetra-n-butylammonium bromide (2.42 g, 8.0
mmol). With vigorous stirring, sodium carbonate (63.6
g, 0.60 mol) was added gradually to the reaction
mixture1. After cooling the mixture to near r.t., chloro-
form (75 ml) was added and the flask was equipped
with a reflux condenser. This mixture was heated at
gentle reflux for 3 days over which time it became a
dark red–orange emulsion. The mixture was allowed to
cool to r.t., filtered through a Bu¨chner funnel to remove
the excess base, and the organic layer separated from
the aqueous layer. The organic fraction was washed
with brine (3×30 ml) and dried over sodium sulfate.
The drying agent was removed by filtration and the
solvent was removed by rotary evaporation. The result-
ing red oil was dissolved in toluene (100 ml) and added
to a 250 ml flask containing a catalytic amount of
predried p-toluenesulfonic acid (0.086 g, 0.47 mmol).
The red solution was heated at reflux for 1 day. After it
had cooled to r.t., the toluene solution was neutralized

D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
123
each fraction was evaporated and checked by NMR.
The fractions that contained the desired product were
combined and the solvent volume was again reduced by
rotary evaporation giving yellow oil (1.11 g, 43.7%).
Most of the oil crystallized neat after several days. The
remaining oil was decanted from the crystals by tipping
the flask, the crystals washed with cold pentane, the
pentane and remaining oil removed to a second flask
and crystallized in a low temperature freezer to yield a
yellow solid. 1H-NMR (acetone-d6): l 8.38 (s, 1H, HC),
7.63 (d, 3H, JHH=2.5 Hz, 5H (pz)), 6.28 (d, 3H,
Hz, 4-H (py)), 7.58 (d, 3H, JHH=1.2 Hz, 5-H (pz)),
7.44 (d, 3H, JHH=2.7 Hz, 3-H (pz)), 7.33–7.38 (m, 4H,
5-H (py), p-H (Ph), o-H (Ph)), 7.15–7.16 (m, 3H, m-H
(Ph), 3-H (py)), 6.33 (dd, 3-H, JHH=2.4, 1.7 Hz, 4-H
(pz)). 13C-NMR (acetone-d6): l 158.5 (2-C (py)), 148.0
(6-C (py)), 140.1 (CC(pz)2(py), 139.6 (5-C (pz)), 136.4
(4-C (py)), 132.0 (3C (pz)), 129.3 (m-C (Ph)), 128.5 (p-C
(Ph)), 127.3 (o-C (Ph)), 124.4 (3C (py)), 123.4 (5C (py)),
105.2 (4-C (pz)), 87.0 (PhC(pz)2(py)). These assign-
ments were confirmed by standard Varian gradient
enhanced HMQC and HMBC pulse sequences.
JHH=2.5 Hz, 4-H (pz)) 1.26 (s, 27H, C(CH3)3).
2.9. Tris(1-pyrazoyl)methanetricarbonylmanganese
triflate (8)
2.7. Tris-2,2,2-(1-pyrazoyl)ethanol (6)
In a 250 ml Schlenk flask, tris(1-pyrazoyl)methane
(1.5 g, 7.0 mmol), potassium tert-butoxide (2.0 g, 18
mmol) and para-formaldehyde (0.53 g, 18 mmol) were
dissolved in THF (100 ml) and stirred at r.t. overnight.
Water (100 ml) was added and the mixture was ex-
tracted with diethyl ether (3×50 ml). The organic
extracts were combined and dried over sodium sulfate
and filtered. The solvent was removed in vacuo result-
ing in a pale yellow solid (1.3 g, 76%). M.p. 113–115°C.
1H-NMR (acetone-d6): l 7.65 (d, 3H, JHH=1.3 Hz,
5-H (pz)), 7.30 (d, 3H, JHH=2.6 Hz, 3-H (pz)), 6.39
(dd, 3H, JHH=2.2, 2.2 Hz, 4-H (pz)), 5.04–5.09 (s, 2H,
CH2). 13C-NMR (acetone-d6): l 140.8 (3-C (pz)), 130.3
(5-C (pz)), 106.1 (4-C (pz)), 89.6 (HC), 66.8 (CH2).
In a 100 ml Schlenk flask wrapped in foil,
Mn(CO)5Br (0.10 g, 0.36 mmol) and AgSO3CF3 (0.093
g, 0.36 mmol) were combined under a nitrogen atmo-
sphere. These reagents were diluted with 30 ml of dry
acetone and stirred at reflux for 45 min. The yellow
solution was filtered using a cannula to remove the
precipitated AgBr and added to a 100 ml Schlenk flask
containing HC(pz)3 (0.077 g, 0.36 mmol). This mixture
was then heated at reflux for 1 h and then cooled and
stirred an additional 15 h at r.t. The solvent was then
removed in vacuo to yield a pale yellow solid. This
solid was washed with 10 ml of dry diethyl ether and
then filtered to yield a light yellow solid (0.18 g, 85%).
1
M.p. 221–223°C. H-NMR (acetone-d6): l 9.85 (s, 1H,
HC), 8.62 (d, 6H, 5-H, 3-H (pz)), 6.75 (s, 3H, 4-H (pz)).
13C-NMR (acetone-d6): l 220.5 (CO), 148.8 (3-C (pz)),
129.2 (5C (pz)), 109.5 (4-C (pz)), 59.1 (HC). FAB+ MS:
m/z Anal. Calc. 353.0195, Found: 353.0209 [M]+. IR
(CH2Cl2): 2051 (s), 1956 cm−1(m).
2.8. h,h,h-Bis(1-pyrazoyl)(2-pyridyl)toluene (7)
In a 500 ml Schlenk flask, NaH (4.8 g, 0.20 mol) was
mixed in dry THF (200 ml) and stirred at 0°C. Pyrazole
(13.6 g, 0.20 mol) were added gradually to the mixture
over 15 min and the stirring was continued for 30 min
at 0°C resulting in a pale yellow solution. Thionyl
chloride (7.3 ml, 0.10 mol) was added drop-wise to this
mixture via syringe at 0°C. After stirring for an addi-
tional 45 min, benzoyl pyridine (9.2 g, 50 mmol) and a
catalytic amount of cobalt (II) chloride (2.5 mmol, 5
mol%) were added and the reaction mixture was heated
at reflux overnight. The reaction mixture was allowed
to cool to r.t. and then diethyl ether (100 ml) and water
(200 ml) were added. The bi-phase solution was then
stirred for 30–45 min to quench the cobalt catalyst.
The layers were separated and the aqueous phase ex-
tracted with diethyl ether (2×100 ml). The combined
organic layers were washed with distilled water (50 ml),
dried over sodium sulfate and filtered. The solvent was
then removed in vacuo and the resulting solid was
re-dissolved in methylene chloride and flushed through
a plug of silica gel with methylene chloride (2×150
ml). A yellow–brown solid resulted (14.0 g, 93%). M.p.
123–125°C. 1H-NMR (acetone-d6): l 8.61 (d, 1H,
2.10. Tris(3,5-dimethyl-1-pyrazoyl)-
methanetricarbonylmanganese triflate (9)
The same procedure was followed as with the parent
ligand using HC(3,5-Me2pz)3 (0.11 g, 0.36 mmol) yield-
ing the desired product {[HC(3,5-Me2pz)3]Mn(CO)3}-
SO3CF3 (0.18 g, 85%). M.p. 357–359°C. 1H-NMR
(acetone-d6): l 8.15 (s, 1H, HC), 6.39 (s, 3H, 4-H (pz)),
2.76, 2.61 (s, s, 9H, 9H, CH3, CH3). 13C-NMR (ace-
tone-d6): l 221.3 (CO), 157.1 (3-C (pz)), 145.3 (5-C
(pz)), 109.8 (4-C (pz)), 68.1 (HC), 14.7 (3-Me), 11.0
(5-Me). FAB+ MS: m/z Anal. Calc. 437.1154, Found:
437.1134 [M]+. IR (CH2Cl2): 2044 (s), 1949 cm−1(m).
2.11. Tris(3-phenyl-1-pyrazoyl)methanetricarbonyl-
manganese triflate (10)
The same procedure was followed as with the parent
ligand using HC(3-Phpz)3 (0.16g, 0.36 mmol) yielding
the desired product {[HC(3-Phpz)3]Mn(CO)3}SO3CF3
1
JHH=2.3 Hz, 6-H (py)), 7.80 (dd, 1H, JHH=6.1, 6.1
(0.19 g, 72%). mp 276–278°C. H-NMR (acetone-d6): l

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D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
9.87 (s, 1H, HC), 8.75 (d, 3H, 5-H (pz)), 7.41–7.57 (m,
15H, C6H5), 6.76 (d, 3H, 4-H (pz)). 13C-NMR (acetone-
d6): l 219.5 (CO), 162.4 (3-C (pz)), 136.5 (5-C (pz)),
131.7 (pz-C (C6H5)), 130.8 (o-H (C6H5)), 130.7 (p-H
(C6H5)), 129.0 (m-H (C6H5)), 110.8 (4-C (pz)), 76.1
(HC). FAB+ MS: m/z Anal. Calc. 581.1134, Found:
581.1137 [M]+. IR (CH2Cl2): 2048 (s), 1956 cm−1 (m).
23.1 (CH(CH3)2). FAB+ MS: m/z Anal. Calc.
479.1603, Found: 479.1602 [M]+. IR (CH2Cl2): 2045
(s), 1949 cm−1(m).
2.13. Tris-2,2,2-(1-pyrazoyl)ethanoltri-
carbonylmanganese triflate (12)
The same procedure was followed as with the parent
ligand using HOCH2C(pz)3 (0.11 g, 0.36 mmol) yielding
the desired product {[HOCH2C(pz)3]Mn(CO)3}SO3CF3
2.12. Tris(3-isopropyl-1-pyrazoyl)-
methanetricarbonylmanganese triflate (11)
1
(0.11 g, 78%). M.p. 214–216°C. H-NMR (acetone-d6):
The same procedure was followed as with the parent
ligand using HC(3-iPrpz)3 (0.15 g, 0.44 mmol) yielding
the desired product {[HC(3-iPrpz)3]Mn(CO)3}SO3CF3
(0.13 g, 75%, based on Mn). M.p. 233–235°C. 1H-
NMR (acetone-d6): l 9.56 (s, 1H, HC), 8.50 (s, 3H, 5H
(pz)), 6.72 (s, 3H, 4H (pz)), 2.90–3.00 (m, 3H,
CH(CH3)2), 1.23 (d, 18H, CH(CH3)2). 13C-NMR (ace-
tone-d6): l 221.6 (CO), 168.4 (3-C (pz)), 136.4 (5-C
(pz)), 106.2 (4-C (pz)), 75.3 (HC), 29.4 (CH(CH3)2),
l 8.74 (d, 3H, 3-H (pz)), 8.61 (s, 3H, 5-H (pz)), 6.75
(dd, 3H, 4-H (pz)) 5.93 (s, 2H, CH2). 13C-NMR (ace-
tone-d6): l 220.2 (CO), 148.4 (3-C (pz)), 136.4 (5-C
(pz)), 109.2 (4-C (pz)), 84.5 (C(pz)3) 60.7 (CH2). FAB+
MS: m/z Anal. Calc. 383.0296, Found: 383.0300 [M]+.
IR (CH2Cl2): 2051 (s), 1958 cm−1(m).
2.14. h,h,h-Bis(1-pyrazoyl)(2-pyridyl)-
toluenetricarbonylmanganese triflate (13)
Table 1
The same procedure was followed as with the parent
ligand using PhC(pz)2py (0.11 g, 0.36 mmol) yielding
the desired product {[PhC(pz)2py]Mn(CO)3}SO3CF3
Crystal data and structure refinement for {[HC(3-iPrpz)3]Mn-
(CO)3}SO3CF3 (11)
1
(0.17 g, 80%). M.p. 207–209°C. H-NMR (acetone-d6):
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C23H28F3MnN6O6S
628.51
173(2)
l 9.49 (d, 1H, 6-H (py)), 8.73 (d, 2H, 3-H (pz)), 8.29
(m, 3H, 5-H (pz), 4-H (py)), 8.08 (dd, 1H, 5-H (py)),
7.817.89 (m, 7H, Ph, 3-H (py), 6.72 (dd, 2H, 4-H (pz)).
13C-NMR (acetone-d6): l 221.0 (CO), 220.1 (CO),
157.3 (6-C (py)), 156.1 (2-C (py)), 149.4 (3-C (pz)),
141.9 (4-C (py)), 137.8 (5-C (pz)), 133.3 (3-C (py)),
132.7 (m-C Ph), 130.7 (o-C Ph), 129.8 (CC(pz)2(py)),
127.9 (5-C (py)), 126.7 (p-C Ph), 109.7 (4-C (pz)), 83.6
(PhC(pz)2(py). FAB+ MS: m/z Anal. Calc. 440.0555,
Found: 440.0569 [M]+. IR (CH2Cl2): 2049 (s), 1956
cm−1(m).
,
0.71073
Orthorhombic
Pbca
Unit cell dimensions
,
a (A)
17.564(3)
17.700(3)
18.439(3)
90
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
90
90
3
,
Volume (A )
Z
5732.4(17)
8
Dcalc (g cm−3
)
1.457
2.15. Crystallographic studies
Absorption coefficient (mm−1
F(000)
)
0.600
2592
0.08×0.06×0.06
1.97–22.00
Crystal size (mm3)
Crystal, data collection, and refinement parameters
are given in Table 1. Compound 11 crystallized in the
orthorhombic space group Pbca. The structure was
solved using direct methods and was completed by
subsequent difference Fourier syntheses and refined by
full-matrix least-squares procedures. Empirical absorp-
tion corrections were applied. All non-hydrogen atoms
were refined with anisotropic displacement coefficients.
Hydrogen atoms were refined as isotropic contributions
and with thermal parameters set to 1.2 or 1.5 times that
of the parent atom. The large thermal parameters for
the atoms in the triflate ion suggest the presence of
end-for-end disorder about its center. The high R value
for this structure can be attributed to diffuse diffraction
from the sample, and the likelihood of disorder associ-
ated with the triflate ion.
Theta range for data collection
(°)
Index ranges
−175h518, −185k518,
−175l519
14 006
3448 [Rint=0.1161]
98.2%
Reflections collected
Independent reflections
Completeness to theta=22.00°
Absorption correction
Max/min transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
Empirical from SADABS
0.9649, 0.9536
Full-matrix least-squares on F2
3448/0/362
1.063
R1=0.1039, wR2=0.2002
R1=0.1347, wR2=0.2202
0.0047(6)
Extinction coefficient
Largest difference peak and hole 0.635 and −0.778
−3
,
(e A
)

D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
125
3. Results and discussion
HC(pz)3+KOtBuꢁTꢁHꢁFꢁꢂHOCH2C(pz)3
(2)
2)CH O
2
3)H O
(6)
2
This new ligand allows for an increase in the hy-
drophilic nature of the system. In other studies, we
have modified this ligand to prepare new ligands with
solubility properties that allow dissolution either in
water or typical organic solvents, depending on the
modification [11]. Analogous deprotonation chemistry
is successful for the other 3-substituted ligands de-
scribed here, but not with HC(3,5-Me2pz)3 [11].
The syntheses of unsymmetrical ligands related to
tris(pyrazolyl)methane ligands, such as HC(pz)2py, has
been developed by Canty [12]. The reaction used is a
metal catalyzed condensation of (pz)2CꢀO, prepared
from the reaction of pyrazolate and phosgene, with
aldehydes to yield the desired ligand and CO2. We have
shown that this condensation chemistry is also success-
ful with ketones, but have found that using (pz)2SꢀO,
[13] derived from thionyl chloride, provides a more
efficient route and avoids the use of phosgene, Eq. (3).
3.1. Syntheses of ligands
Although the original preparations of HC(pz)3 and
HC(3,5-Me2pz)3 were from the direct reaction of the
appropriate pyrazolate and CHCl3 [4,12c] and liquid–
liquid phase transfer conditions were used in one case
[10], most recent preparations use a solid–liquid phase-
transfer procedure [5,6c,d]. We have determined that
standard CHCl3–H2O phase transfer conditions cou-
pled with replacing the K2CO3, used as the base in the
earlier preparations, with a large excess of Na2CO3
leads to higher yields and substantially less darkening
of the reaction solutions over the 3 days at reflux
needed for these reactions to go to completion, Eq. (1).
(1)
Using these conditions, we consistently observe yields
over 60% for both HC(pz)3 and HC(3,5-Me2pz)3, a
major improvement especially for the latter ligand. The
modified literature preparation reported a yield of 42%
for HC(3,5-Me2pz)3 using the solid–liquid phase-trans-
fer procedure [5], but in our hands consistently gave
yields of ca. 25%. In addition, because the reaction
proceeds with substantially less discoloration, our
purification procedure involves washing the product
through a plug of silica rather than a full chromatogra-
phy. Yields ranging from 17 to 42% have been reported
using the original Trofimenko preparation that involves
a sublimation step to purify the product [3w,4,6e].
As observed previously in the preparation of HC(3-
Phpz)3 [6c], with this pyrazole reaction 1 yields a num-
ber of regioisomers that isomerize to the desired
3-isomer in the presence of anhydrous p-toluenesulfonic
acid in toluene [6c]. The same result is observed in the
synthesis of the new ligand HC(3-iPrpz)3, except in this
case the isomerization reaction yields a 5:1 mixture of
the desired HC(3-iPrpz)3 and an isomer with a 2:1 ratio
of pyrazolyl-rings, presumably HC(5-iPrpz)(3-iPrpz)2.
As reported previously [6d], HC(3-tBupz)3 is hard to
crystallize. In the preparation reported here, the oil
formed after removal of the solvent from the purified
product largely crystallizes over several days.
(3)
Unfortunately, similar chemistry using substituted
pyrazolyl rings is unsuccessful.
3.2. Syntheses of metal complexes
Reaction of these ligands with Mn(CO)5SO3CF3, pre-
pared in situ from Mn(CO)5Br and AgSO3CF3, results
in the preparation of the respective [(ligand)Mn-
(CO)3]SO3CF3, Eq. (4). The complex {[HC(pz)3]Mn-
(CO)3}PF6 has been reported previously [4]. As ex-
pected, the reaction was unsuccessful with the bulky
‘tetrahedral enforcer’ HC(3-tBupz)3 ligand. The reac-
tion using the HC(3-iPrpz)3–HC(5-iPrpz)(3-iPrpz)2 lig-
and mixture was carried out with a slight excess of
HC(3-iPrpz)3 and yielded only the desired {[HC(3-
iPrpz)3]Mn(CO)3}SO3CF3 (11) product.
(4)
The complexes are air stable and soluble in acetone
and CH2Cl2.
The IR stretching frequencies and the location of the
13C-NMR carbonyl resonances for these complexes are
provided in Table 2.
The methine hydrogen of the HC(pz)3 ligand is acidic
and can be removed [3o,14]. Once deprotonated, we
have shown that an alcohol functional group may be
introduced using para-formaldehyde and water, Eq. (2).

126
D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
Table 2
Given the variation in the substitution on the pyra-
zolyl rings, the changes in the carbonyl stretching fre-
quencies are surprisingly small. Although the spread is
only ca. 7 cm−1, the values fall into two groups, with
the alkyl-substituted ligands in one group showing
lower values and all the other ligands in the other
group. The alkyl-substituted ligands are slightly more
basic; the increased electron density at the metal in-
creases the backbonding to the carbonyl ligands. Sur-
prisingly, the PhC(pz)2py ligand, containing the more
basic pyridyl ring, falls in the latter group. The varia-
tions in the carbonyl 13C-NMR resonances are also
small but the values fall into the same two groups. The
slightly more basic alkyl-substituted ligands have the
higher values, again indicating more backbonding [15].
For {[PhC(pz)2py]Mn(CO)3}SO3CF3, the carbonyl res-
onance for the CO ligands trans to the pz groups fall
into the lower group and the resonance for the CO
trans to the py into the higher group. Both the IR and
13C-NMR trends indicate that the alkyl-substituted lig-
ands donate slightly more electron density to the metal,
but the differences are small.
IR and 13C-NMR data on [(Ligand)Mn(CO)3]SO3CF3
Ligand
IR (w CO) cm−1
13C (CO) ppm
1
2
3
4
5
6
HC(pz)3
1956, 2051
1949, 2044
1956, 2048
1949, 2045
1958, 2051
1956, 2049
220.5
221.3
219.5
221.6
220.2
220.1(2), 221.0(1)
HC(3,5-Me2pz)3
HC(3-Phpz)3
HC(3-Pripz)3
HOCH2C(pz)3
PhC(pz)2py
4. X-ray structure of {[HC(3-Pripz)3]Mn(CO)3}SO3CF3
(11)
Fig. 1. ORTEP diagram of {[HC(3-iPrpz)3]Mn(CO)3}+
.
Crystals of {[HC(3-iPrpz)3]Mn(CO)3}SO3CF3 were
grown by layering hexane over an acetone solution of
the complex. Fig. 1 shows an ORTEP diagram and
selected bond distances and angles are collected in
Table 3. The manganese is surrounded by three nitro-
gen atoms from the HC(3-iPrpz)3 ligand and three
carbonyl ligands in a nearly octahedral arrangement.
The chelate rings of the HC(3-iPrpz)3 ligand restrict the
NꢁMnꢁN angles to an average of 85°. The CꢁMnꢁC
angles of the carbonyl groups are nearly 90°.
Table 3
i
,
Selected bond distances (A) and angles (°) for {[HC(3- Prpz)3]Mn-
(CO)3}+
Bond distances
MnꢁN(1)
MnꢁN(3)
MnꢁN(5)
MnꢁC(20)
MnꢁC(21)
MnꢁC(22)
C(1)ꢁN(2)
C(1)ꢁN(4)
C(1)ꢁN(6)
2.054(8)
2.079(8)
2.083(7)
1.808(11)
1.789(11)
1.791(12)
1.428(12)
1.433(12)
1.463(11)
This first structural characterization of this new lig-
and demonstrates that despite the substitution of the
bulky iso-propyl substituents the ligand is tridentate
with no distortions caused by steric interaction. The
iso-propyl substituents are oriented away from the
Mn(CO)3 center of the cation reducing steric strain.
This same arrangement is observed in the 6-coordinate
structure of [HB(3-iPrpz)3]MoO2(OMe) [16] and related
molecules [17], but not in 4-coordinate structures of this
ligand such as [HB(3-iPrpz)3]Co(NCS) [9]. The MnꢁN
Bond angles
N(1)ꢁMnꢁN(3)
N(1)ꢁMnꢁN(5)
N(3)ꢁMnꢁN(5)
C(20)ꢁMnꢁC(21)
C(20)ꢁMnꢁC(22)
C(21)ꢁMnꢁC(22)
N(1)ꢁMnꢁC(21)
N(1)ꢁMnꢁC(22)
N(3)ꢁMnꢁC(20)
N(3)ꢁMnꢁC(22)
N(5)ꢁMnꢁC(20)
N(5)ꢁMnꢁC(21)
N(1)ꢁMnꢁC(20)
N(3)ꢁMnꢁC(21)
N(5)ꢁMnꢁC(22)
N(2)ꢁC(1)ꢁN(4)
N(2)ꢁC(1)ꢁN(6)
N(4)ꢁC(1)ꢁN(6)
85.3(3)
85.8(3)
83.9(3)
89.0(5)
89.8(5)
90.1(4)
93.2(4)
91.1(4)
92.5(4)
93.0(4)
93.2(4)
93.0(4)
177.7(4)
176.6(4)
175.7(4)
111.1(8)
110.5(8)
109.6(7)
,
bond distances average 2.07 A, exactly the distance
observed in the structure of the neutral tris(pyra-
zolyl)borate complex [HB(3,5-Me2pz)3]Mn(CO)3 [18],
indicating that there is no large steric strain causing
elongation of these bonds. Overall, this tris(pyra-
zolyl)borate structure is very similar to that reported
here for 11, except the BꢁN distance is longer (average
,
1.53 A) than the analogous CꢁN distance (average 1.44
,
A) due to the larger size of boron.

D.L. Reger et al. / Journal of Organometallic Chemistry 607 (2000) 120–128
127
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5. Conclusions
The synthetic methodology reported here represents
a
significant improvement in the preparation of
tris(pyrazolyl)methane ligands, especially HC(3,5-
Me2pz)3. The main changes are the use of standard
phase transfer reaction conditions and the replacement
of K2CO3 as the base with a large excess of Na2CO3.
These methods have been used to prepare the new
ligand HC(3-iPrpz)3. We have shown that tris(pyra-
zolyl)methane ligands without 5-substituents can be
derivatized at the methine carbon atom to form the
ligand HOCH2C(pz)3. We have also shown that the
metal catalyzed condensation of (pz)2CꢀO with alde-
hydes is successful with ketones, but the reaction is
more successful using (pz)2SꢀO in place of (pz)2CꢀO.
All of these ligands form [(ligand)Mn(CO)3]SO3CF3
complexes, with the exception of HC(3-tBupz)3. The
carbonyl stretching frequencies and locations of the
carbonyl resonances in the 13C-NMR spectra indicate a
very small variation in the basicity of the various
ligands. The structure of {[HC(3-iPrpz)3]Mn(CO)3}+
shows this ligand is tridentate with no unusual steric
congestion caused by the iso-propyl substituents.
6. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge crystallographic
Centre, CCDC no. 142413 for compound 11. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336-033; e-mail: de-
posit@ccdc.cam.ac.uk, or www: http://www.ccdc.
cam.ac.uk).
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Acknowledgements
We thank the National Science Foundation (CHE-
9727325) for support. The NSF (Grants CHE-8904942
and CHE-9601723) and NIH (Grant RR-02425) have
supplied funds to support NMR equipment and the
NIH (Grant RR-02849) has supplied funds to support
mass spectrometry equipment at the University of
South Carolina.
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