Bitopic phenylene-linked bis(pyrazolyl)methane ligands: Preparation and supramolecular structures of hetero- And homobimetallic complexes incorporating organoplatinum(II) and tricarbonylrhenium(I) centers

Article abstract of DOI:10.1021/om049112f

The new fixed-geometry, phenylene-linked bis(pyrazolyl)methane ligands α,α,α′,α′-tetra-(1-pyrazolyl)-m-xylene (m-[CH(pz)₂]₂C₆H₄, L_m), α,α,α′,α′-tetra(1-pyrazolyl)-p-xylene (p-[CH(pz)₂]₂C₆H₄, L_p), and α,α,α′,α′-tetrakis(4-benzylpyrazol-1-yl) -p-xylene (p-[CH(^4Bnpz)₂]₂C₆H ₄, ^4BnL_p) have been synthesized in order to prepare hetero- and homobimetallic complexes incorporating tricarbonylrhenium(I) and bis(p-tolyl)platinum(II) fragments. Coordination of one rhenium center to L_m was achieved to yield the monometallic rhenium complex {m-[CH(pz)₂]₂C₆H₄}Re(CO) ₃Br, which then incorporated a second metal center to give the heterobimetallic complex {μ-m-[CH(pz)₂]₂C ₆H₄}[Re(CO)₃Br][Pt(p-tolyl)₂]. The homobimetallic rhenium complexes of each ligand, {μ-m-[CH(pz) ₂]₂C₆H₄}[Re(CO)₃Br] ₂, {μ-p-[CH(pz)₂]₂C₆H ₄}[Re(CO)₃Br]₂, and {μ-p-[CH( ^4Bnpz)₂]₂C₆H₄}[Re(CO) ₃Br]₂, were also prepared. The crystalline structure of each complex shows extensive noncovalent interactions, including weak hydrogen bonds and π...π and CH...π interactions, that organize the molecules into complex supramolecular structures.

Full text of DOI:10.1021/om049112f

1544
Organometallics 2005, 24, 1544-1555
Bitopic Phenylene-Linked Bis(pyrazolyl)methane
Ligands: Preparation and Supramolecular Structures of
Hetero- and Homobimetallic Complexes Incorporating
Organoplatinum(II) and Tricarbonylrhenium(I) Centers
Daniel L. Reger,* Russell P. Watson, Mark D. Smith, and Perry J. Pellechia
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina 29208
Received November 16, 2004
The new fixed-geometry, phenylene-linked bis(pyrazolyl)methane ligands R,R,R′,R′-tetra-
(1-pyrazolyl)-m-xylene (m-[CH(pz)2]2C6H4, Lm), R,R,R′,R′-tetra(1-pyrazolyl)-p-xylene (p-[CH-
(pz)2]2C6H4, Lp), and R,R,R′,R′-tetrakis(4-benzylpyrazol-1-yl)-p-xylene (p-[CH(4Bnpz)2]2C6H4,
4BnLp) have been synthesized in order to prepare hetero- and homobimetallic complexes
incorporating tricarbonylrhenium(I) and bis(p-tolyl)platinum(II) fragments. Coordination of
one rhenium center to Lm was achieved to yield the monometallic rhenium complex {m-
[CH(pz)2]2C6H4}Re(CO)3Br, which then incorporated a second metal center to give the hetero-
bimetallic complex {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-tolyl)2]. The homobimetallic rhe-
nium complexes of each ligand, {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2, {µ-p-[CH(pz)2]2C6H4}-
[Re(CO)3Br]2, and {µ-p-[CH(4Bnpz)2]2C6H4}[Re(CO)3Br]2, were also prepared. The crystalline
structure of each complex shows extensive noncovalent interactions, including weak hydrogen
bonds and π‚‚‚π and CH‚‚‚π interactions, that organize the molecules into complex supra-
molecular structures.
Introduction
ligands, but the syntheses of heterometallic complexes
of such ligands are more challenging than those of
homometallic complexes because of the need to initially
prepare selectively a monometallic intermediate.5 Other
paths to heterometallic complexes do exist, such as the
coupling of two monometallic complexes or the coupling
of a monometallic complex with a ligand followed by
introduction of the second metal,6 but the preparation
from the bitopic ligand is often difficult if not unfeasible.
We are actively developing synthetic routes to homo-
and heterometallic complexes using multitopic ligands
based on linking multiple poly(pyrazolyl)methane donor
units in a single molecule. We have prepared multitopic
ligands in which poly(pyrazolyl)methane fragments are
linked by flexible,7 semirigid,8 and rigid9 organic spac-
ers. For example, we recently reported the structures
and supramolecular organizations of cyclic silver(I)
bimetallic complexes using the flexible alkylidene-linked
Homo- and heteromultimetallic complexes have been
intensely studied in search of reactivity not observed
for their monometallic counterparts.1 For example, some
catalytic processes employing bi- or multimetallic com-
plexes have been found to proceed with efficiencies
greater than those catalyzed by the corresponding
monometallic species.2,3 Heterobimetallic catalysts also
offer the possibility of tandem catalytic processes as in
recent examples of olefin polymerization in which one
site produces a specific type of polymer that is im-
mediately incorporated into another type of polymer
produced by the other proximate metal center.4 One
method to prepare such complexes is the use of bitopic
* To whom correspondence should be addressed. E-mail: reger@
mail.chem.sc.edu.
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Organometallics 2000, 19, 602. (c) Fukuoka, A.; Fukagawa, S.; Hirano,
M.; Koga, N.; Komiya, S. Organometallics 2001, 20, 2065. (d) Fabre,
S.; Findeis, B.; Tro¨sch, D. J. M.; Gade, L. H.; Scowen, I. J.; McPartlin,
M. Chem. Commun. 1999, 577. (e) Schubart, M.; Mitchell, G.; Gade,
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Organometallics 2004, 23, 5112. (b) Abramo, G. P.; Li, L.; Marks, T.
J. J. Am. Chem. Soc. 2002, 124, 13966.
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Chem. Rev. 1996, 96, 759. (b) Chong, S. H.-F.; Lam, S. C.-F.; Yam, V.
W.-W.; Zhu, N.; Cheung, K.-K.; Fathallah, S.; Costuas, K.; Halet, J.-
F. Organometallics 2004, 23, 4924. (c) Masllorens, J.; Roglans, A.;
Moreno-Man˜as, M.; Parella, T. Organometallics 2004, 23, 2533.
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Inorg. Chem. 2003, 955. (b) Bo¨rje, A.; Ko¨the, O.; Juris, A. J. Chem.
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Inorg. Chem. 2004, 43, 6609. (b) Reger, D. L.; Gardinier, J. R.;
Semeniuc, R. F.; Smith, M. D. J. Chem. Soc., Dalton Trans. 2003, 1712.
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10.1021/om049112f CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/22/2005

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1545
procedures. All other chemicals were purchased from Aldrich
or Fisher Scientific. Pyrazole was purified by sublimation prior
to use. Thionyl chloride was distilled prior to use. All other
purchased chemicals were used as received. Reported melting
points are uncorrected. IR spectra were obtained on a Nicolet
5DXBO FTIR spectrometer. 1H and 13C NMR spectra were
recorded on a Mercury/VX 300, Mercury/VX 400, or INOVA
500 spectrometer. All chemical shifts are in ppm and are
secondary referenced using the solvent signals. Mass spectro-
metric measurements were obtained on a MicroMass QTOF
spectrometer or on a VG 70S instrument. Elemental analyses
were performed on vacuum-dried samples by Robertson Mi-
crolit Laboratories (Madison, NJ).
r,r,r′,r′-Tetra(1-pyrazolyl)-m-xylene, m-[CH(pz)2]2C6H4
(Lm). CO(pz)2 Method. Isophthalaldehyde (1.57 g, 11.7
mmol), 1,1′-carbonyldipyrazole (4.817 g, 29.7 mmol), and
anhydrous cobalt chloride (0.32 g, 2.5 mmol) were dissolved
in 100 mL of anhydrous THF and heated at reflux for 24 h.
After cooling to room temperature, 50 mL of distilled water
was added, and the solution was stirred for 30 min and
extracted with CH2Cl2 (3 × 50 mL). The combined organic
extracts were washed with concentrated NaCl solution and
dried over MgSO4. The solution was then concentrated and
chromatographed (silica gel, Et2O) to afford 2.55 g (59% yield)
of a white solid. Mp: 129-130 °C. Anal. Calcd for C20H18N8:
C, 64.86; H, 4.90; N, 30.25. Found: C, 64.53; H, 4.95; N, 30.41.
IR (KBr, cm-1): 3138, 3113, 3101, 2999, 2942, 2897, 2823,
2692, 2656, 2623, 1736, 1601, 1516. 1H NMR (300 MHz,
acetone-d6): δ 7.93 (s, 2 H, CH(pz)2), 7.76 (dd, J ) 2.4, 0.6 Hz,
4 H, 5-H pz), 7.53 (dd, J ) 2.0, 0.6 Hz, 4 H, 3-H pz), 7.40 (t, J
) 8.0 Hz, 1 H, 5-H C6H4), 7.08 (d, J ) 7.8 Hz, 2 H, 4,6-H C6H4),
6.80 (s, 1 H, 2-H C6H4), 6.31 (dd, J ) 2.6, 2.0 Hz, 4 H, 4-H pz).
13C NMR (75.5 MHz, acetone-d6): δ 140.3, 138.2, 130.2, 129.0,
127.8, 126.1, 106.4, 77.1. HRMS: calcd for C20H18N8, 370.1654;
found, 370.1662. Direct Probe MS m/z (rel int %) [assgn]: 370
(5) [M]+, 302 (100) [M - Hpz]+, 235 (95) [M - Hpz - pz ]+.
SO(pz)2 Method. A flask containing sodium hydride (3.90
g, 0.163 mol) suspended in anhydrous THF was cooled in an
ice-water bath for 30 min. Pyrazole (11.3 g, 0.163 mol) was
added over 15 min, and the resulting solution was allowed to
stir at 0 °C for 30 min. Thionyl chloride (5.94 mL, 81.4 mmol)
was added dropwise over 10 min. Once the addition was
complete, the ice-water bath was removed, and the resulting
suspension was allowed to warm to room temperature with
stirring over 40 min, after which time isophthalaldehyde (2.73
g, 20.4 mmol) and anhydrous cobalt chloride (0.26 g, 2.0 mmol)
were added at once, and the system was heated at reflux for
24 h. After cooling to room temperature, 160 mL of water was
added and the resulting solution was stirred at room temper-
ature for 30 min. The organic and aqueous layers were
separated, and the aqueous layer was extracted with CH2Cl2
(2 × 100 mL). The combined organic extracts were washed
with water (100 mL) and dried over MgSO4. Removal of the
solvent left a brown solid that was recrystallized from absolute
ethanol to yield 5.06 g (67%) of Lm that was pure by melting
point (129-130 °C) and by NMR.
r,r,r′,r′-Tetra(1-pyrazolyl)-p-xylene, p-[CH(pz)2]2C6H4
(Lp). CO(pz)2 Method. Terephthaldicarboxaldehyde (0.50 g,
3.73 mmol), 1,1′-carbonyldipyrazole (1.21 g, 7.46 mmol), and
anhydrous cobalt chloride (0.10 g, 0.77 mmol) were dissolved
in 50 mL of anhydrous THF and heated at reflux for 21 h.
After cooling to room temperature, 25 mL of distilled water
was added, and the solution was stirred for 30 min and
extracted with CH2Cl2 (3 × 25 mL). The combined organic
extracts were washed with water (75 mL), concentrated NaCl
solution (35 mL), and water (40 mL) and then dried over
bis(pyrazolyl)methane ligands CH(pz)2(CH2)nCH(pz)2
(pz ) 1-pyrazolyl; n ) 1, 2, 3).7 We have also extensively
developed the chemistry of the semirigid multitopic tris-
(pyrazolyl)methane ligands C6H6-n[CH2OCH2C(pz)3]n,
where n ) 2, 3 4, and 6.10 Our studies thus far have
revealed that in the solid state poly(pyrazolyl)methane
compounds often support important noncovalent inter-
actions such as weak hydrogen bonds, π‚‚‚π stacking,
and C-H‚‚‚π interactions.11 In particular we have
identified an important structural feature in which two
pairs of adjacent pyrazolyl rings are noncovalently
associated through cooperative CH‚‚‚π and π‚‚‚π inter-
actions. We have found that these interactions are
common not only in our compounds but in a large
number of known poly(pyrazolyl)borate and -methane
compounds, and we have termed this supramolecular
motif the “quadruple pyrazolyl embrace”.7b We are
interested in contrasting the molecular and supramo-
lecular structures of complexes of rigid ligands with the
more flexible counterparts studied earlier. Our previous
efforts in preparing complexes of rigid ligands contain-
ing tridentate tris(pyrazolyl)methane units, however,
have been limited by solubility problems.9
Herein we describe the synthesis of three rigidly
linked bitopic bis(pyrazolyl)methane ligands, m-C6H4-
[CH(pz)2]2 (Lm), p-C6H4[CH(pz)2]2 (Lp), and p-C6H4-
[CH(4Bnpz)2]2 (4BnLp; 4Bnpz ) 4-benzyl-1-pyrazolyl), and
the use of these ligands to prepare the homobimetallic
complexes {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2 (3), {µ-p-
[CH(pz)2]2C6H4}[Re(CO)3Br]2 (4), and {µ-p-[CH(4Bn
-
pz)2]2C6H4}[Re(CO)3Br]2 (5). We also report the first
heterobimetallic complex of a linked bis(pyrazolyl)-
methane ligand, {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt-
(p-tolyl)2] (2), prepared from monometallic {m-[CH-
(pz)2]2C6H4}Re(CO)3Br (1). In the solid state, each
complex shows extensive noncovalent interactions that
organize the molecules into complex supramolecular
structures.
Experimental Section
General Considerations. Air-sensitive materials were
handled under a nitrogen atmosphere using standard Schlenk
techniques or in a Vacuum Atmospheres HE-493 drybox. All
solvents were dried and distilled by conventional methods prior
to use. Re(CO)5Br,12 [Pt(SEt2)(p-tolyl)2]2,13 1,1′-carbonyldipyra-
zole,14 and 4-benzylpyrazole7c were prepared following reported
(10) (a) Reger, D. L.; Semeniuc, R. F.; Rassolov, V.; Smith, M. D.
Inorg Chem. 2004, 43, 537. (b) Reger, D. L.; Semeniuc, R. F.; Silaghi-
Dumitrescu, I.; Smith, M. D. Inorg Chem. 2003, 42, 3751. (c) Reger,
D. L.; Semeniuc, R. F.; Smith, M. D. J. Chem. Soc., Dalton Trans. 2003,
285. (d) Reger, D. L.; Brown, K. J.; Smith, M. D. J. Organomet. Chem.
2002, 658, 50. (e) Reger, D. L.; Semeniuc, R. F.; Smith, M. D. J. Chem.
Soc., Dalton Trans. 2002, 476. (f) Reger, D. L.; Semeniuc, R. F.; Smith,
M. D. Inorg. Chem. 2001, 40, 6545.
(11) (a) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.; Lemen-
ovskii, D. A.; Majouga, G.; Zyk, N. V.; Schroder, M. Coord. Chem. Rev.
2001, 222, 155. (b) Se´ne`que, O.; Giorgi, M.; Reinaud, O. Chem.
Commun. 2001, 984. (c) Weiss, H.-C.; Blaser, D.; Boese, R.; Doughan,
B. M.; Haley, M. M. Chem. Commun. 1997, 1703. (d) Madhavi, N. N.
L.; Katz, A. K.; Carrell, H. L.; Nangia, A.; Desiraju, G. R. Chem.
Commun. 1997, 1953. (e) Jennings, W. B.; Farrell, B. M.; Malone, J.
F. Acc. Chem. Res. 2001, 34, 885. (f) Calhorda, M. J. Chem. Commun.
2000, 801. (g) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441. (h)
Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga, D. Organo-
metallics 1998, 17, 296. (i) Weiss, H.-C.; Boese, R.; Smith, H. L.; Haley,
M. M. Chem. Commun. 1997, 2403. (j) Hunter, C. A.; Sanders, J. K.
M. J. Am. Chem. Soc. 1990, 112, 5525. (k) Janiak, C. J. Chem. Soc.,
Dalton Trans. 2000, 3885.
(13) Casado Lacabra, M. A.; Canty, A. J.; Lutz, M.; Patel, J.; Spek,
A. L.; Sun, H.; van Koten, G. Inorg. Chim. Acta 2002, 327, 15.
(14) Byers, P. K.; Canty, A. J.; Honeyman, R. T. Inorg. Synth. 2004,
34, 30.
(12) Schmidt, S. P.; Trogler, W. C.; Basolo, F. Inorg. Synth. 1990,
28, 160.

1546 Organometallics, Vol. 24, No. 7, 2005
Reger et al.
MgSO4. The solution was then concentrated and chromato-
graphed (silica gel, acetone/hexanes, 1:1) to afford 0.920 g (67%
yield) of a white solid. Mp: 165-166 °C. Anal. Calcd: C, 64.86;
H, 4.90; N, 30.25. Found: C, 64.69; H, 4.76; N, 30.11. IR (KBr,
cm-1): 3130, 3109, 3011, 2942, 1516, 1434, 1413, 825, 792. 1H
NMR (300 MHz, CDCl3): δ 7.71 (s, 2 H, CH(pz)2), 7.62 (d, J )
1.2 Hz, 4 H, 5-H pz), 7.54 (d, J ) 2.4 Hz, 4 H, 3-H pz), 7.02 (s,
4 H, C6H4), 6.33 (dd, J ) 0.6, 2.0 Hz, 4 H, 4-H pz). 13C NMR
(100.6 MHz, acetone-d6): δ 141.1, 139.1, 131.0, 128.2, 107.2,
77.8. HRMS: calcd for C20H18N8, 370.1654; found 370.1644.
Direct Probe MS m/z (rel int %) [assgn]: 370 (45) [M]+, 303
(100) [M - pz]+, 235 (30) [M - pz - Hpz]+.
SO(pz)2 Method. Sodium hydride (4.29 g, 0.179 mol) was
suspended in 200 mL of THF and cooled in an ice-water bath
for 30 min. Pyrazole (12.2 g, 0.179 mol) was added over 15
min, and the resulting solution was stirred at 0 °C for 30 min.
Thionyl chloride (6.53 mL, 89.4 mmol) was added dropwise
over 10 min at 0 °C, and the resulting pale yellow suspension
was allowed to reach room temperature while stirring for 40
min. Terephthaldicarboxaldehyde (3.00 g, 22.4 mmol) and
anhydrous cobalt chloride (0.29 g, 2.24 mmol) were added to
this suspension at once, and the system was heated at reflux
for 24 h. After cooling to room temperature, 160 mL of water
was added and the system stirred for 30 min. The organic and
aqueous layers were separated, and the aqueous layer was
extracted with CH2Cl2 (2 × 100 mL). The combined organic
extracts were washed with water (100 mL), dried over MgSO4,
and stripped, leaving a pale yellow solid that was recrystallized
from absolute ethanol to afford 7.33 g (89%) of Lp that was
pure by melting point (166-168 °C) and by NMR.
acetone. Crystals of pure 1 were grown by vapor diffusion of
Et2O into 1 mL solutions of the crude solid. Yield ) 0.235 g
(33%). Mp: 254-255 °C. Anal. Calcd for C23H18BrN8O3Re: C,
38.34; H, 2.52; N, 15.55. Found: C, 38.66; H, 2.29; N, 15.41.
1
IR, νC≡O (KBr, cm-1): 2018, 1916, 1887. H NMR (400 MHz,
acetone-d6): δ 8.54 (s, 1 H, CH(pz)2[Re]), 8.42 (dd, J ) 2.6, 0.6
Hz, 2 H, 5-H pz[Re]), 8.10 (dd, J ) 2.4, 0.8 Hz, 2 H, 3-H pz-
[Re]), 7.86 (s, 1 H, CH(pz)2), 7.73 (dd, J ) 2.4, 0.8 Hz, 2 H,
5-H pz), 7.52 (dd, J ) 2.0, 0.8 Hz, 2 H, 3-H pz), 7.42 (t, J ) 7.8
Hz, 1 H, 5-H C6H4), 7.05 (d, J ) 8.8 Hz, 1 H, 4-H C6H4), 6.69
(dd, J ) 2.4, 2.4 Hz, 2 H, 4-H pz[Re]), 6.44 (d, J ) 8.0 Hz, 1 H,
6-H C6H4), 6.32 (dd, J ) 2.4, 1.8 Hz, 2 H, 4-H pz), 5.68 (s, 1 H,
2-H C6H4). HRMS: calcd for C23H18BrN8O3Re, 720.0226; found
720.0213. Direct Probe MS m/z (rel int %) [assgn]: 720 (5)
[M]+, 370 (3) [Lm]+, 302 (100) [Lm - Hpz]+, 235 (93) [Lm
-
Hpz - pz ]+.
{µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-tolyl)2] (2). {µ-
m-[CH(pz)2]2C6H4}Re(CO)3Br (1) (0.10 g, 0.14 mmol) and [Pt-
(p-tolyl)2(SEt2)]2 (0.080 g, 0.086 mmol) were combined in a
flask, and CH2Cl2 (15 mL) was added. Soon after stirring was
begun, a precipitate formed. After stirring for 48 h at room
temperature, the precipitate was isolated by filtration and
dried under vacuum. Yield ) 0.073 g (48%). Mp: 280 °C dec.
Anal. Calcd for C37H32BrN8O3PtRe: C, 40.48; H, 2.94; N, 10.21.
Found: C, 40.44; H, 2.63; N, 10.21. IR νC≡O (KBr, cm-1): 2020,
1893. 1H NMR (500 MHz, acetone-d6): δ 8.47 (s, 1 H, CH(pz)2-
[Re]), 8.39 (dd, J ) 0.4, 2.6 Hz, 2 H, 5-H pz[Pt], 8.26 (s, 1 H,
CH(pz)2[Pt]), 8.16 (d, J ) 2.6 Hz, 2 H, 5-H pz[Re]), 8.05 (d, J
) 2.3 Hz, 2 H, 3-H pz[Re]), 7.54 (t, J ) 8.0 Hz, 1 H, 5-H C6H4),
7.38 (d, J ) 2.2 Hz, 2 H, 3-H pz[Pt]), 6.92 (d, J ) 7.9 Hz, JPtH
) 69 Hz, 4 H, 2,6-H Pt(C6H4CH3)), 6.78 (d, J ) 7.7 Hz, 1 H,
4-H C6H4), 6.66 (d, J ) 8.3 Hz, 1 H, 6-H C6H4), 6.62 (d, J )
7.7 Hz, 4 H, 3,5-H Pt(C6H4CH3)), 6.57 (t, J ) 2.6 Hz, 2 H, 4-H
pz[Re]), 6.50 (d, J ) 2.5 Hz, 2 H, 4-H pz[Pt]), 4.97 (s, 1 H, 2-H
C6H4), 2.10 (s, 6 H, Pt(C6H4CH3)). ESI(+) HRMS: calcd for
[C37H32BrKN8O3PtRe]+, 1133.0603; found 1133.0574. MS ESI
(+) m/z (rel int %) [assgn]: 1097 (5) [M - H]+, 1007 (20) [M -
C7H7]+, 721 (20) [M - Pt(C7H7)2]+, 641 (30) [M - Pt(C7H7)2 -
CO - H]+, 303 (100) [Lm - pz]+.
{µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2 (3). Toluene Method.
Re(CO)5Br (0.900 g, 2.22 mmol) and m-[CH(pz)2]2C6H4 (Lm)
(0.400 g, 1.08 mmol) were combined in a flask to which 50 mL
of toluene was then added. Upon heating, the solids dissolved,
and the solution was heated at reflux for 21 h, during which
time a white precipitate formed. After cooling, the solvent was
removed in vacuo, leaving an off-white solid that was chro-
matographed (silica gel, 1:9 to 3:7 acetone/Et2O) to yield 0.58
g (50%) of pure 3. Mp: 275 °C dec. Anal. Calcd for C26H18-
Br2N8O6Re2: C, 29.17; H, 1.69; N, 10.47. Found: C, 29.27; H,
1.52; N, 10.02. IR νC≡O (KBr, cm-1): 2026, 1904. 1H NMR (300
MHz, acetone-d6): δ 8.55 (s, 2 H, CH(pz)2), 8.41 (d, J ) 2.4
Hz, 4 H, 5-H pz), 8.12 (d, J ) 2.4 Hz, 4 H, 3-H pz), 7.47 (t, J
) 8.0 Hz, 1 H, 2-H C6H4), 6.75 (t, J ) 2.8 Hz, 4 H, 4-H pz),
6.67 (d, J ) 8.8 Hz, 2 H, 4,6-H C6H4), 4.92 (s, 1 H, 2-H C6H4).
Direct Probe MS m/z (rel int %) [assgn]: 1070 (1) [M]+, 990
(1) [M - Br]+, 962 (1) [M - Br - CO]+, 934 (1) [M - Br -
2CO]+, 906 (1) [M - Br - 3CO]+, 720 (15) [M - Re(CO)3Br]+,
302 (100) [Lm - Hpz]+, 235 (99) [Lm - Hpz - pz]+.
r,r,r′,r′-Tetrakis(4-benzylpyrazol-1-yl)-p-xylene, p-[CH-
(
4Bnpz)2]2C6H4 (4BnLp). Sodium hydride (0.607 g, 25.3 mmol)
was suspended in 100 mL of THF and cooled in an ice-water
bath. A 30 mL THF solution of 4-benzylpyrazole (4.00 g, 25.3
mmol) was added over 15 min, and the resulting solution was
stirred at 0 °C for 30 min. Thionyl chloride (0.92 mL, 12.6
mmol) was added dropwise over 10 min at 0 °C, and the
resulting pale yellow suspension was allowed to warm to room
temperature while stirring for 40 min. Terephthaldicarboxal-
dehyde (0.424 g, 3.16 mmol) and CoCl2 (0.082 g, 0.63 mmol)
were added to this suspension at once, and the system was
heated at reflux for 24 h. After cooling to room temperature,
100 mL of water was added and the system stirred for 45 min.
The resulting solution was extracted with CH2Cl2 (1 × 100
mL, 2 × 70 mL), and the combined extracts were washed with
water (100 mL) and dried over MgSO4. Removal of the solvent
afforded a red-brown oil that was taken up in CH2Cl2 and
chromatographed (silica gel, Et2O/CH2Cl2, 1:1) to yield 1.47 g
(64%) of an off-white solid. Mp: 124-125 °C. Anal. Calcd for
C48H42N8: C, 78.88; H, 5.79; N, 15.33. Found: C, 78.66; H,
5.69; N, 15.24. IR (KBr, cm-1): 3142, 3101, 3085, 3019, 2938,
2913, 1597, 1512, 1495, 1446, 768, 814, 694. 1H NMR (400
MHz, acetone-d6): δ 7.76 (s, 2 H, CH(4Bnpz)2), 7.60 (d, J ) 0.8
Hz, 4 H, 5-H 4Bnpz), 7.38 (s, 4 H, 3-H 4Bnpz), 7.26-7.14 (m, 20
1
H, CH2C6H5), 7.04 (s, 4 H, C6H4), 3.80 (s, 8 H, CH2C6H5). H
NMR (400 MHz, DMSO-d6): δ 7.89 (s, 2 H, CH(4Bnpz)2), 7.62
(s, 4 H, 5-H 4Bnpz), 7.40 (s, 4 H, 3-H 4Bnpz), 7.27-7.14 (m, 20
H, CH2C6H5), 7.02 (s, 4 H, C6H4), 3.74 (s, 8 H, CH2C6H5) 13C
NMR (75.5 MHz, acetone-d6): δ 142.2, 141.0, 139.1, 129.4,
129.35, 129.31, 128.1, 126.9, 122.5, 77.9, 30.98. HRMS: calcd
for C48H42N8, 730.3582; found 730.3517. Direct Probe MS m/z
(rel int %) [assgn]: 730 (15) [M]+, 573 (75) [M - 4Bnpz]+, 415
(30) [M - 4Bnpz-H4Bnpz]+, 158 (100) [H4Bnpz]+.
Acetone Method. Re(CO)5Br (0.450 g, 1.11 mmol) and
m-[CH(pz)2]2C6H4 (Lm) (0.200 g, 0.540 mmol) were dissolved
in acetone, and the solution was heated at reflux for 2 days.
Removal of the solvent after cooling yielded 0.50 g (87%) of 3,
1
whose H NMR spectra suggested slight contamination with
the monometallic complex.
{m-[CH(pz)2]2C6H4}Re(CO)3Br (1). Re(CO)5Br (0.400 g,
0.985 mmol) was dissolved in hot toluene (ca. 70 °C) and added
gradually by cannula to a refluxing toluene solution of excess
m-[CH(pz)2]2C6H4 (Lm) (1.00 g, 0.270 mmol). A precipitate was
soon noticeable. After the addition was complete, the system
was stirred at reflux for an additional 5 h. After cooling, the
solvent was removed in vacuo to leave a discolored solid that
was washed with CH2Cl2 (5 mL) and dissolved in ca. 4 mL of
{µ-p-[CH(pz)2]2C6H4}[Re(CO)3Br]2 (4). Toluene Method.
Re(CO)5Br (0.22 g, 0.54 mmol) and p-[CH(pz)2]2C6H4 (Lp) (0.10
g, 0.27 mmol) were combined in a flask to which 40 mL of
toluene was then added. Upon heating, the solids dissolved,
and the solution was heated at reflux for 6 h. The precipitate
that had formed was filtered and washed with 10 mL of
toluene to yield 0.220 g (76% yield) of a white solid. Mp: 250

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1547
Table 1. Crystal Data and Refinement Details for {m-[CH(pz)2]2C6H4}Re(CO)3Br (1),
{µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-tolyl)2]‚Et2O (2‚Et2O), {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚CH3CN
(3‚CH3CN), {µ-p-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚3C3H6O (4‚3C3H6O), and
{µ-p-[CH(4Bnpz)2]2C6H4}[Re(CO)3Br]2‚Et2O‚4DMSO (5‚Et2O‚4DMSO)
1
2‚Et2O
3‚CH3CN
4‚3C3H6O
5‚Et2O‚4DMSO
empirical formula
fw
C
23H18BrN8O3Re
C41H42BrN8O4PtRe
1172.03
C28H21Br2N9O6Re2
1111.76
C
35H36Br2N8O9Re2
C
66H76Br2N8O11Re2S4
720.56
1244.94
150(1)
1817.81
T (K)
293(1)
monoclinic
P21/n
8.1445(4)
20.6300(11)
15.6330(8)
90
104.5000(10)
90
2543.0(2)
4
1.882
6.391
150(1)
200(1)
150(1)
cryst syst
space group
a, Å
monoclinic
P21/c
15.5427(7)
15.3800(7)
18.8150(9)
90
112.0780(10)
90
4167.9(3)
4
triclinic
P1h
monoclinic
C2/c
18.5053(11)
14.6677(9)
15.6163(10)
90
92.034(2)
90
4236.1(5)
4
triclinic
P1h
11.3267(18)
13.334(2)
14.442(2)
108.914(3)
93.987(3)
108.683(3)
1917.8(5)
2
11.9047(6)
12.4073(7)
13.0787(7)
92.3880(10)
90.2820(10)
112.0980(10)
1787.89(17)
1
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
D(calc), Mg‚m-3
abs coeff, mm-1
cryst size, mm3
final R indices
[I > 2σ(I)]
R1
1.868
7.264
0.14 × 0.10 × 0.08
1.925
8.437
0.38 × 0.18 × 0.14
1.952
7.656
0.16 × 0.08 × 0.06
1.688
4.679
0.40 × 0.28 × 0.14
0.28 × 0.20 × 0.16
0.0267
0.0642
0.0313
0.0697
0.0366
0.0851
0.0469
0.1065
0.0243
0.0617
wR2
°C dec. Anal. Calcd for C26H18Br2N8O6Re2: C, 29.17; H, 1.69;
N, 10.47. Found: C, 28.75; H, 1.75; N, 10.41. IR νC≡O (KBr,
cm-1): 2018, 1900. 1H NMR (300 MHz, acetone-d6): δ 8.59 (s,
2 H, CH(pz)2), 8.45 (dd, J ) 2.7, 0.6 Hz, 4 H, 5-H pz), 8.16 (d,
J ) 1.8 Hz, 4 H, 3-H pz), 6.74 (t, J ) 2.6 Hz, 4 H, 4-H pz),
6.43 (s, 4 H, C6H4). ESI(+) HRMS calcd for C26H18Br2KN8O6-
Re2, 1108.8429; found 1108.8461. MS ESI(+) m/z (rel int %)
[assgn]: 1109 (40) [M + K]+, 991 (100) [M - Br]+, 720 (5) [M
- Re(CO)3Br]+, 641 (5) [M - Re(CO)3Br - Br]+, 614 (10) [M -
Re(CO)3Br - Br - CO]+.
Acetone Method. Re(CO)5Br (0.450 g, 1.11 mmol) and
p-[CH(pz)2]2C6H4 (Lp) (0.200 g, 0.540 mmol) were dissolved in
acetone, and the solution was heated at reflux for 70 h, by
which time a white precipitate had formed. After cooling to
room temperature, the precipitate was isolated by cannula
filtration, washed with acetone (2 × 20 mL), and dried in
vacuo. The precipitate was found to be pure 4. Yield ) 0.164
g (57%).
data showed negligible crystal decay during data collection.
An empirical absorption correction was applied with SAD-
ABS.15 Patterson (for 1) or direct (for 2-5) methods structure
solution, difference Fourier calculations, and full-matrix least-
squares refinement against F 2 were performed with SHELX-
TL.16 Hydrogen atoms for all species were placed in geometri-
cally idealized positions and included as riding atoms. Details
of the data collections are given in Table 1 while further notes
regarding the solution and refinement for 1-5 follow.
Systematic absences in the intensity data for compound 1
confirmed the space group P21/n. The asymmetric unit consists
of a complete molecule of the monometallic complex.
For compound 2, systematic absences in the intensity data
were consistent with the space group P21/c. All non-hydrogen
atoms of the metal complex were refined with anisotropic
displacement parameters. The metal complex crystallizes with
one badly disordered diethyl ether molecule per complex. The
Et2O was modeled as being statistically disordered over three
independent sites in the asymmetric unit and was refined with
the aid of 22 distance restraints. Each disorder component was
assigned a common isotropic displacement parameter.
Compound 3 crystallizes in the triclinic system. The space
group P1h was assumed and confirmed by successful solution
and refinement of the data. Location and anisotropic refine-
ment of the Re complex proceeded without incident. Another
region of electron density in the near vicinity of the Re complex
was successfully modeled as an acetonitrile molecule of
crystallization disordered over three positions. Atoms of the
acetonitrile were refined isotropically subject to a total of six
distance restraints. The acetonitrile nitrogen atom occupies a
site common to all three disorder components. Another region
of electron density assumed to be severely disordered solvent
species was also observed in channels running parallel to the
crystallographic a-axis. This could not be modeled successfully
and was treated with the SQUEEZE routine in PLATON.17
The program calculated a solvent-accessible void volume
of 276.2 Å3, corresponding to 64 e-/cell. The contribution of
these diffusely scattering species was removed from subse-
quent structure factor calculations. The final reported F(000),
MW, and calculated density reflect the identified species
only.
{µ-p-[CH(pz4Bn)2]2C6H4}[Re(CO)3Br]2 (5). Re(CO)5Br (0.23
g, 0.57 mmol) and p-[CH(pz4Bn)2]2C6H4 (4BnLp) (7) (0.20 g, 0.27
mmol) were combined in a flask to which 50 mL of toluene
was added, and the system was heated at reflux for 5 h, during
which time a white precipitate formed. After cooling to room
temperature, the solid was isolated by cannula filtration,
washed with acetone (5 mL), and dried in vacuo to yield 0.285
g (71%) of a white solid. Mp: 296 °C dec. Anal. Calcd for C54H42-
Br2N8O6Re2: C, 45.32; H, 2.96; N, 7.83. Found: C, 45.61; H,
2.99; N, 7.52. IR νC≡O (KBr, cm-1): 2022, 1912, 1896. 1H NMR
(400 MHz, DMSO-d6): δ 8.49, (s, 2 H, CH(4-Bnpz)2), 8.16 (s, 4
H, 5-H 4-Bnpz), 7.97 (s, 4 H, 3-H 4-Bnpz), 7.34-7.21 (m, 20
H, CH2C6H5), 6.21 (s, 4 H, C6H4), 3.91 (dd, J ) 20, 16 Hz, 8 H,
CH2C6H5).
Crystal Structure Determinations. X-ray intensity data
from colorless blocks of 1, 2, and 5, a colorless prism of 3, and
an irregular colorless crystal of 4 were measured at 150(1) K
for 2, 4, and 5, at 293(1) K for 1, and at 200(1) K for 3 on a
Bruker SMART APEX CCD-based diffractometer (Mo KR
radiation, λ ) 0.71073 Å).15 All crystals were taken directly
from the crystallizing container. Raw data frame integration
and Lp corrections were performed with SAINT+.15 Final unit
cell parameters were determined by least-squares refinement
of 6699, 7111, 7862, 5660, and 8246 reflections from the data
sets of 1-5, respectively, each with I > 5σ(I). Analysis of the
(16) Sheldrick, G. M. SHELXTL Version 6.1; Bruker Analytical
X-ray Systems, Inc.: Madison, WI, 2000.
(15) SMART Version 5.625, SAINT+ Version 6.22, and SADABS
Version 2.05; Bruker Analytical X-ray Systems, Inc.: Madison, WI,
2001.
(17) PLATON: (a) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46,
C34. (b) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2002.

1548 Organometallics, Vol. 24, No. 7, 2005
Reger et al.
Scheme 1
significant amounts of the bimetallic rhenium complex
{µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2 (3). The separation
of the two species by column or preparative thin-layer
chromatography was impractical on a useful scale.
Instead, the most reliable method of obtaining the
monometallic species analytically pure was by selec-
tively crystallizing it through vapor diffusion of diethyl
ether into acetone solutions of the mixture. Interest-
ingly, although the two species possessed almost identi-
cal Rf values in the solvent systems tested, their
solubility in acetone/ether was distinct such that 1 was
the only species to crystallize within 1-2 weeks. Nev-
ertheless, when starting from equimolar amounts of the
reactants, the final yield of 1 was extremely low because
of the significant amounts of the bimetallic species
concomitantly formed. A modified procedure, therefore,
was developed in which the formation of the unwanted
species was minimized (Scheme 2). Thus, slow addition
of a hot toluene solution of Re(CO)5Br to a refluxing
solution of excess Lm reduced the level of 3 formed
Systematic absences in the intensity data of compound 4
were consistent with either of the space groups C2/c or Cc;
the former was eventually confirmed. The asymmetric unit
consists of half of the [(ReBr(CO)3)2(µ-C20H18N8)] complex on
a center of symmetry along with one complete acetone and
half of another acetone located on a C2 axis.
Compound 5 crystallizes in the triclinic system. The space
group P1h was assumed and confirmed by the successful
solution and refinement of the data. The asymmetric unit
consists of half a [((CO)3ReBr)2(µ-C48H42N8)] complex located
on an inversion center, half an Et2O molecule of crystallization
that is disordered about an inversion center, and two inde-
pendent DMSO molecules of crystallization. One of the DMSO
molecules (S2) is disordered, and a restrained model employing
two orientations in the ratio 0.75 (S2A):0.25 (S2B) was refined.
The geometry of the disordered DMSO was restrained to be
similar to that of the ordered DMSO (12 restraints, SHELX
SAME). All non-hydrogen atoms were refined with anisotropic
displacement parameters except the carbon and oxygen atoms
of the disordered DMSO (isotropic).
1
almost to the limit of detection by H NMR.
It is worth noting that a similar route was also
attempted in which Re(CO)3(THF)2Br was prepared by
heating Re(CO)5Br in THF at reflux according to a
report by Storhoff and Lewis.20 Unfortunately, after
several trials, the reaction of this adduct failed to yield
the desired complex.
The corresponding monometallic rhenium complex of
Lp could not be prepared. The solubilities of the com-
plexes of the p-phenylene-linked ligands used in this
work were relatively low, likely preventing the isolation
of the monometallic complex.
Results and Discussion
A suspension of 1 in CH2Cl2 at room temperature
slowly reacted with dissolved [Pt(SEt2)(p-tolyl)2]2 to
yield the heterobimetallic complex {µ-m-[CH(pz)2]2C6H4}-
[Re(CO)3Br][Pt(p-tolyl)2], 2 (Scheme 2). We chose the
organometallic Pt(II) unit [Pt(p-tolyl)2] because of the
ease with which it could be introduced into the complex
Syntheses. The ligands m- and p-C6H4[CH(pz)2]2 (Lm
and Lp, respectively) were prepared as shown in Scheme
1 by the cobalt-catalyzed condensation reaction, first
reported by Peterson,18 between the respective dicar-
boxaldehyde and EO(pz)2 (E ) C or S). Although the
reagent CO(pz)2 is sometimes preferred in this reaction
because of greater reactivity,18b we have found that SO-
(pz)2, prepared in situ from sodium pyrazolate and
thionyl chloride, gives higher yields and requires sim-
pler workup procedures with many of our systems.19 The
additional advantage of avoiding the use of phosgene,
from which CO(pz)2 is prepared,14 is clear. The CO(pz)2
route, therefore, was ultimately abandoned, and the
ligand p-C6H4[CH(4Bnpz)2]2 (4BnLp; 4Bnpz ) 4-benzyl-1-
pyrazolyl) was synthesized only by using SO(4Bnpz)2.
Each ligand is air stable and freely soluble in halo-
genated solvents, acetone, and toluene but only mod-
erately soluble in diethyl ether and acetonitrile. When
using the SO(pz)2 route, they may be obtained analyti-
cally pure after workup by recrystallization of the crude
solid from boiling absolute ethanol.
13
via the dimer [Pt(SEt2)(p-tolyl)2]2 and because of the
known unusual photochemical properties of related
complexes.21 Complex 2 was insoluble in CH2Cl2 and
could be isolated analytically pure by filtration. The
complex could be redissolved in acetone.
The bimetallic rhenium complex of Lm, {µ-m-[CH-
(pz)2]2C6H4}[Re(CO)3Br]2 (3), as mentioned above, was
formed in significant amounts in the equimolar reaction
of Re(CO)5Br and Lm. The complex was formed exclu-
sively when 2 equiv of Re(CO)5Br was used in the
reaction. The corresponding complex of Lp, {µ-p-[CH-
(pz)2]2C6H4}[Re(CO)3Br]2 (4), was prepared by the same
route (Scheme 3). The reactions could be carried out in
toluene or in acetone. Re(CO)5Br is insoluble in toluene
at room temperature but does dissolve at higher tem-
peratures. Shortly after its complete dissolution in the
presence of ligand, a precipitate formed, and after
several hours, the homobimetallic complexes were iso-
lated by filtration from the supernatant, in which they
were completely insoluble. Alternatively, either ligand
and Re(CO)5Br could be dissolved in acetone at room
The monometallic rhenium complex of Lm, {m-[CH-
(pz)2]2C6H4}Re(CO)3Br (1), could be prepared by react-
ing equimolar amounts of the ligand and Re(CO)5Br in
either toluene or acetone, but the product also contained
(18) (a) The´, K. I.; Peterson, L. K. Can. J. Chem. 1973, 51, 422. (b)
The´, K. I.; Peterson, L. K.; Kiehlman, E. Can. J. Chem. 1973, 51, 2448.
(c) Peterson, L. K.; Kiehlman, E.; Sanger, A. R.; The´, K. I. Can. J.
Chem. 1974, 52, 2367.
(19) Reger, D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba,
J. J. S.; Rheingold, A. L.; Sommer, R. D. J. Organomet. Chem. 2000,
607, 120.
(20) Storhoff, B. N.; Lewis, H. C. Synth. React. Inorg. Metal-Org.
Chem. 1974, 4, 467.
(21) (a) Wadas, T. J.; Lachicotte, R. J.; Eisenberg, R. Inorg. Chem.
2003, 42, 3772. (b) Hissler, M.; McGarrah, J. E.; Connick, W. B.; Geiger,
D. K.; Cummings, S. D.; Eisenberg, R. Coord. Chem. Rev. 2000, 208,
115.

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1549
Scheme 2
Scheme 3
uncoordinated site compared with 7.93, 7.76, and 7.53
ppm for the free ligand, but the corresponding reso-
nances of the coordinated site are at 8.54, 8.42, and 8.10
ppm. Similarly, each homobimetallic complex yielded
symmetric spectra where the pyrazolyl ring resonances
were shifted downfield from those of the respective free
ligands.
1
The H NMR spectrum of the heterobimetallic com-
plex 2 could not be readily assigned because the
resonances of the pyrazolyl groups for the rhenium and
platinum ends of the molecule overlapped. A combina-
tion of correlation and NOE difference spectroscopy was
used to make the assignments shown in Figure 1. The
downfield region, which excludes the aryl proton HN at
4.97 ppm and the tolyl methyl protons at 2.10 ppm, is
shown. The signals from the pyrazolyl groups bound to
Re are in the same regions as they are in the other Re
complexes. The 5- and 3-pyrazolyl protons of the groups
bound to Pt, however, are widely separated (8.40 and
7.37 ppm, respectively). In fact, the 5-pyrazolyl protons
associated with the Pt center, HB, are perturbed to such
an extent that they resonate at a lower field than does
the respective methine proton (8.27 ppm), a feature
unique among the complexes described in this work.
Furthermore, the 3-pyrazolyl protons, HG, display a
rather drastic shift upfield compared to the other
complexes. The latter observation may be explained by
the fact that these protons are likely within the shield-
ing regions of the tolyl groups bound to Pt, a contention
that is supported by the solid-state structure discussed
below. The 195Pt-1H coupling satellites are located
about the aryl doublet (HH) at 6.92 ppm.
Another interesting feature of the spectrum of each
complex is the dramatic upfield shift of the phenylene
protons closest to the pyrazolyl rings. In the meta-
phenylene-linked complexes, the most dramatic effects
are observed with the proton that is ortho to both
substituted carbon atoms of the central linker, e.g., HN
in the structure inset of Figure 1. For the para-
phenylene-linked complexes, the aromatic protons on
the central ring are all equivalent and ortho to one
substituted ring carbon atom. Table 2 compares the
chemical shifts of these protons in the complexes with
those in the free ligands. The shielding effects are
greatest for the single 2-hydrogen atom in Lm and are
larger for the bimetallic complexes 2 and 3 than for the
monometallic 1. Less dramatic shielding effects in the
complexes of Lm of ca. 0.3 ppm are observed with the 4-
and 6-hydrogen atoms that are adjacent to only one
substituent. The upfield shifts are likely caused by the
temperature and heated at reflux for 3 days to yield the
respective complex. Despite the longer reaction time, the
latter method was preferred because it was easier to
monitor by NMR. Complex 3 did not precipitate from
acetone, but some precipitate of 4 was observed. The
addition of more acetone redissolved the product.
The reaction of 2 equiv of Re(CO)5Br with p-C6H4-
[CH(4Bnpz)2]2 (4BnLp) in refluxing toluene yielded {µ-p-
[CH(pz4Bn)2]2C6H4}[Re(CO)3Br]2 (5) (Scheme 3). Al-
though pendent benzyl groups might have improved
solubility through increased interactions with solvents,
5 was considerably less soluble than the corresponding
underivatized compound and could be dissolved only in
dimethyl sulfoxide. It was also insufficiently volatile to
yield useful mass spectral characterization. As shown
below, the pendent benzyl group introduced new types
of noncovalent intermolecular forces to the supramo-
lecular structure.
IR, NMR, and Mass Spectral Characterization.
The IR spectrum of each complex displays the charac-
teristic ν(CtO) absorbances at ca. 2000 (sharp) and
1900 (broad) cm-1, which are indicative of local C3v
symmetry and consistent with facial coordination of the
CO ligands. The 1H NMR spectra of the homobimetallic
complexes 3-5 each show equivalent pyrazolyl rings
indicating free rotation at room temperature of the bis-
(pyrazolyl)methane group about the bond joining it to
the linking phenylene ring. The 1H NMR spectrum of 1
shows the nonequivalence of the coordinated and un-
coordinated bis(pyrazolyl)methane units of the ligand,
as expected. The uncoordinated bis(pyrazolyl)methane
site in 1 has resonances nearly identical to those of the
free ligand, whereas the resonances of the coordinated
site are all shifted significantly downfield. For example,
the methine, 5-pyrazolyl, and 3-pyrazolyl protons reso-
nate at 7.86, 7.73, and 7.52 ppm, respectively, at the

1550 Organometallics, Vol. 24, No. 7, 2005
Reger et al.
Figure 1. Downfield region of 1H NMR spectrum of {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-tolyl)2] (2) (500 MHz, acetone-
d6) showing peak assignments.
Table 2. 1H NMR Data (ppm) for Lm, Lp, and 1-5
compound
phenylene 2-Ha
phenylene 4-, 6-H
Lm
6.80
5.68
4.97
4.92
7.08
6.43
7.04
6.21
7.08
1
7.05, 6.44
6.78, 6.66
6.67
2
3
Lp
4
4BnLp
5
a In the meta-phenylene-linked compounds, the proton ortho to
both substituted aromatic carbons atoms. In the para-phenylene-
linked compounds, all phenylene protons are equivalent.
positions of the protons in the shielding regions of
coordinated pyrazolyl rings (vide infra).
Figure 2. ORTEP drawing of {m-[CH(pz)2]2C6H4}Re(CO)3-
Br (1). Displacement ellipsoids are drawn at 30% prob-
ability.
The mass spectrum of the monometallic complex 1
includes a weak peak corresponding to the molecular
ion as well as fragmentation peaks. The spectrum of the
heterobimetallic complex 2 shows loss of a tolyl sub-
stituent at platinum as well as loss of the [Pt(p-tolyl)2]
unit itself. Spectra of the homobimetallic complexes 3
and 4 are somewhat more detailed and contain fragment
peaks indicating sequential loss of Br and CO as well
as [Re(CO)3Br]. As mentioned above, the benzyl-
substituted derivative 5 was insufficiently volatile for
mass spectrometric analysis.
tions with C(8)-H(8)‚‚‚Ct (Ct ) centroid) angles of
approximately 120° support the assumption made ear-
lier that the shielding of H(8) noticed in the NMR
spectrum is due to its proximity to the π clouds of these
pyrazolyl rings. Similarly, the upfield shifts of the 4-
and 6-protons (H(4) and H(6), respectively) on the
linking phenylene ring can be explained by noting the
ca. 3.0 Å interactions between these protons and the
pyrazolyl rings containing N(21) and N(31). In contrast
to H(8), H(4) and H(6) are each exposed to only one
shielding pyrazolyl region and are at greater distances
from these regions, thus explaining the smaller mag-
nitude of the shielding.
The extended structure of 1 consists of sheets in the
bc-plane that stack along the a-axis with no appreciable
interactions between the planes. The planes are com-
posed of chains of molecules along the b-axis (Figure 3,
top) held together by pyrazolyl embrace interactions in
which the CH‚‚‚Ct interactions are edge-to-face in
orientation. The two protons interacting with the C(41)-
containing pyrazolyl ring are H(21), at a distance of 3.04
Å and C(21)-H(21)‚‚‚Ct angle of 128°, and H(22), at a
distance of 3.37 Å and C(22)-H(22)‚‚‚Ct angle of 113°.
Similarly, H(32) is 3.74 Å from the C(11)-containing
pyrazolyl ring with a C(32)-H(32)‚‚‚Ct angle of 114°,
and H(33) is 3.81 Å from the same ring with a C(33)-
Solid-State Structures. The details of the crystal-
lographic analysis of the ligand m-[CH(pz)2]2C6H4}, Lm,
including a description of its supramolecular structure,
are given in the Supporting Information.
An ORTEP diagram of {m-[CH(pz)2]2C6H4}Re(CO)3-
Br (1) is shown in Figure 2, and selected bond distances
and angles are given in Table 3. In contrast to the other
complexes in this study, the two bis(pyrazolyl)methane
sites of 1 are both oriented on the same side of the
connecting phenylene ring. One of the carbonyl ligands
attached to the Re center is positioned directly over the
central phenylene ring and is participating in π‚‚‚π
interactions. This feature is found in each of the
complexes of this study, and its implications are dis-
cussed below.
Another important feature is an intramolecular CH‚
‚‚π interaction between H(8) and the nearby pyrazolyl
rings containing C(11) and C(41). These 2.77 Å interac-

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1551
Figure 4. ORTEP drawing of the heterobimetallic mol-
ecule of {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-tolyl)2]‚
Et2O (2‚Et2O). Displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms are omitted.
a perpendicular distance of 3.56 Å (slip angle â )
23.12°). A recent survey of pyrazolyl embrace param-
eters for known bis(pyrazolyl)methane complexes7b
revealed an average CH‚‚‚centroid distance of 2.76 Å,
an average corresponding angle of 142°, and an average
centroid-centroid distance of 3.71 Å. Thus, the CH‚‚‚
Ct parameters for complex 1 indicate a relatively weak
pyrazolyl embrace.
Figure 3. Views of 1 showing the pyrazolyl embrace (top)
and sheets in the bc-plane (bottom). Pyrazolyl embrace
interactions are shown in red; other CH‚‚‚π interactions
are in blue.
Table 3. Selected Bond Distances (Å) and Angles
Each chain along the b-axis is bound to two adjacent
chains by an interaction between H(23), at the 3-pyra-
zolyl position of the coordinated bis(pyrazolyl)methane
site, and the π cloud of the meta-phenylene linker, thus
completing the sheets in the bc-plane (Figure 3, bottom).
An ORTEP diagram showing the heterobimetallic
molecule of {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br][Pt(p-
tolyl)2]‚Et2O (2‚Et2O) is shown in Figure 4. Selected
bond distances and angles are given in Table 3. As
observed in all of the bimetallic complexes prepared
here, the metal units are oriented on opposite sides of
the linking phenylene group, with one carbonyl ligand
attached to the Re center positioned over the central
phenylene ring. There are two noncovalent intramo-
lecular interactions of note. First, the CH‚‚‚π interac-
tions between H(4) and the pyrazolyl rings containing
C(21) and C(41) explain the shielding of this proton in
the NMR spectrum. Second, another intramolecular CH‚
‚‚π interaction between H(43) and the C(51)-containing
tolyl ring bound to platinum explains the analogous
shielding of H(43) in the NMR spectrum.
Significant noncovalent interactions extend the solid-
state structure of 2‚Et2O into all three dimensions. The
basic unit is a dimer held together by reciprocal CH‚‚‚π
interactions, which include a 2.98 Å interaction between
the methine hydrogen atom H(1) associated with the
Re center and the tolyl ring containing C(51) (Figure 5,
red dashed lines) and a 2.97 Å interaction between the
5-pz proton H(11) associated with Re and the same tolyl
group (not pictured). The other 5-pz hydrogen atom of
the Re side is weakly bound to the other tolyl group of
the same Pt atom at a distance of 2.85 Å (Figure 5, red
dashed lines). Each dimeric unit is interacting with two
adjacent dimers along the b-axis via 2.77 Å CH‚‚‚π
(deg) for 1, 2‚Et2O, and 3‚CH3CN
1
2‚Et2O
3‚CH3CN
Re(1)-N(11)
2.171(3)
2.177(3)
2.184(4)
2.183(4)
2.173(5)
2.174(5)
2.184(6)
2.167(5)
2.6330(8)
2.6313(8)
1.904(8)
1.912(8)
1.889(7)
Re(1)-N(21)
Re(2)-N(31)
Re(2)-N(41)
Re(1)-Br(1)
2.6208(5)
2.6201(6)
Re(2)-Br(2)
Re(1)-C(51)
1.898(4)
1.907(4)
1.896(4)
Re(1)-C(52)
Re(1)-C(53)
Re(1)-C(71)
1.910(7)
1.909(6)
1.912(6)
2.098(4)
2.115(4)
1.994(5)
1.991(5)
Re(1)-C(72)
Re(1)-C(73)
Pt(1)-N(31)
Pt(1)-N(41)
Pt(1)-C(51)
Pt(1)-C(61)
N(11)-Re(1)-N(21)
N(11)-Re(1)-Br(1)
C(51)-Re(1)-N(11)
C(53)-Re(1)-N(11)
C(51)-Re(1)-Br(1)
N(31)-Re(2)-N(41)
N(31)-Re(2)-Br(2)
C(61)-Re(2)-N(31)
C(63)-Re(2)-N(31)
C(61)-Re(2)-Br(2)
C(61)-Pt(1)-C(51)
C(51)-Pt(1)-N(31)
C(61)-Pt(1)-N(31)
C(61)-Pt(1)-N(41)
C(51)-Pt(1)-N(41)
N(31)-Pt(1)-N(41)
C(72)-Re(1)-C(71)
C(71)-Re(1)-C(73)
83.78(10)
82.99(8)
97.43(13)
91.73(17)
179.38(11)
84.06(19)
83.92(13)
174.9(2)
97.4(2)
92.5(2)
84.66(19)
84.90(13)
174.1(3)
96.3(3)
90.3(2)
93.1(2)
173.7(2)
91.62(19)
174.9(2)
88.34(18)
87.34(16)
89.6(3)
87.7(2)
H(33)‚‚‚Ct angle of 113°. The centroids of the pyrazolyl
rings containing C(21) and C(31) are 3.88 Å apart with

1552 Organometallics, Vol. 24, No. 7, 2005
Reger et al.
Table 4. Selected Bond Distances (Å) and Angles
(deg) for 4‚3C3H6O and 5‚Et2O‚4DMSO
4‚3C3H6O
5‚Et2O‚4DMSO
Re(1)-N(11)
2.164(7)
2.184(6)
1.869(11)
1.908(9)
1.923(9)
2.6363(9)
1.178(11)
1.147(10)
1.140(9)
87.7(4)
2.186(2)
2.178(2)
1.912(3)
1.912(3)
1.913(3)
2.6428(3)
1.153(4)
1.154(4)
1.136(4)
89.13(12)
88.67(12)
89.49(12)
173.44(10)
95.30(10)
96.12(10)
91.78(10)
173.41(10)
97.09(11)
83.69(8)
90.37(9)
88.37(9)
177.81(9)
84.54(6)
85.05(6)
110.6(2)
Re(1)-N(21)
Re(1)- C(31)
Re(1)-C(33)
Re(1)-C(32)
Re(1)-Br(1)
C(31)-O(31)
C(32)-O(32)
C(33)-O(33)
C(31)-Re(1)-C(33)
C(31)-Re(1)-C(32)
C(32)-Re(1)-C(33)
C(31)-Re(1)-N(11)
C(32)-Re(1)-N(11)
C(33)-Re(1)-N(11)
C(31)-Re(1)-N(21)
C(32)-Re(1)-N(21)
C(33)-Re(1)-N(21)
N(11)-Re(1)-N(21)
C(31)-Re(1)-Br(1)
C(32)-Re(1)-Br(1)
C(33)-Re(1)-Br(1)
N(11)-Re(1)-Br(1)
N(21)-Re(1)-Br(1)
N(12)-C(1)-N(22)
88.4(4)
88.4(4)
176.4(3)
93.5(3)
95.4(3)
93.3(3)
173.0(3)
98.4(3)
84.5(2)
Figure 5. View of 2‚Et2O showing sheets in the ab-plane
formed from CH‚‚‚π (red and blue dashed lines) and CH‚
‚‚Br (green dashed lines) noncovalent interactions. Solvent
molecules are omitted.
93.5(3)
89.9(3)
177.9(3)
83.40(18)
83.23(16)
109.9(6)
bonds from the 4-pz hydrogen on the Pt side to an
adjacent tolyl ring containing C(61) (Figure 5, blue
dashed lines). These chains along the b-axis are ex-
tended into sheets by CH‚‚‚Br hydrogen bonds between
both the methine and 5-pz hydrogens on the Pt side and
Br atoms on adjacent dimers in the ab-plane (Figure 5,
green dashed lines). Finally, these sheets stack on one
another along the c-axis by weak CH‚‚‚O bonds between
a 4-pz hydrogen atom on the Re side and a CO ligand
in a molecule belonging to an adjacent sheet, thus
completing the three-dimensional supramolecular struc-
ture of 2‚Et2O.
Figure 6 shows the ORTEP diagrams of the bimetallic
molecules of {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚CH3CN
(3‚CH3CN) and {µ-p-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚
3C3H6O (4‚3C3H6O). Selected bond distances and angles
for 3 and 4 are given in Tables 3 and 4, respectively. In
both structures the two bis(pyrazolyl)methane sites are
on opposite sides of the central phenylene ring. The
Figure 6. Orthogonal views of the bimetallic molecules of {µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚CH3CN (3‚CH3CN) (left)
and {µ-p-[CH(pz)2]2C6H4}[Re(CO)3Br]2‚3C3H6O (4‚3C3H6O) (right). Ellipsoids are drawn at the 40% (3) and 50% (4)
probability levels. Hydrogen atoms are omitted.

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1553
Figure 7. View of 3‚CH3CN showing distinct CH‚‚‚Br
hydrogen bonds as well as π‚‚‚π interactions.
carbonyl groups in the crystal structure of the para-
derivative are positioned directly over the centroid of
the phenylene spacer, whereas the same groups in the
meta-derivative are offset from the centroid such that
edge-centered rather than face-centered interactions
exist.
As with the other meta-phenylene-linked complexes,
intramolecular CH‚‚‚π interactions between the ortho
hydrogen atom H(8) and the nearby N(21)- and N(41)-
containing pyrazolyl rings in 3 are present and explain
the upfield shift of this proton in solution. In addition,
the 4- and 6-protons on the phenylene linker (H(4) and
H(6)) show CH‚‚‚π interactions with the nearby N(31)-
and N(11)-containing pyrazolyl rings, respectively. The
phenylene protons in the para-phenylene-linked com-
plex 4 are equivalent in solution and are shielded to an
extent comparable to the 4- and 6-protons of the meta-
phenylene-linked derivatives. This shielding can also be
explained by the ca. 2.8 Å CH‚‚‚π interactions between
H(3) and H(4), which are crystallographically non-
equivalent, and the nearby pyrazolyl rings containing
N(11) and N(21), respectively.
Figure 8. Views of 4‚3C3H6O showing (a) the pyrazolyl
embrace (only the π‚‚‚π stacking of the embrace is indi-
cated, red dashed lines) and supporting CH‚‚‚Br interac-
tions (green dashed lines) forming chains in the ab-plane
and (b) two molecules bridged by an acetone (blue dashed
lines) leading to chains along the c-axis.
The supramolecular structure of 3‚CH3CN is domi-
nated by CH‚‚‚Br hydrogen bonds. The two bis(pyra-
zolyl)methane units in each molecule are crystallograph-
ically nonequivalent, and each unit forms distinct
hydrogen bonds. One unit is oriented toward its identi-
cal site on an adjacent molecule such that weak π‚‚‚π
stacking between the appropriate pyrazolyl rings occurs
along with reciprocal CH‚‚‚Br interactions between the
Br and methine hydrogen atoms (Figure 7, red dashed
lines). A shorter CH‚‚‚Br interaction exists between the
bromine atom of the other bis(pyrazolyl)methane unit
and an adjacent 3-pyrazolyl hydrogen atom. This inter-
action is again reciprocal (Figure 7, blue dashed lines).
The combination of these two hydrogen bonds results
in the formation of chains. These chains are joined into
two-dimensional sheets by the short CH‚‚‚Br bonds
between the latter bromine atoms mentioned above and
3-pyrazolyl hydrogen atoms on adjacent chains (Figure
7, green dashed lines). Finally, the sheets stack upon
one another along the b-axis by CH‚‚‚O interactions
between CO ligands and a 5-pyrazolyl hydrogen atom
on adjacent sheets (not pictured), thus completing the
three-dimensional structure.
are long at 3.44 Å (C(22)H(22)‚‚‚Ct angle 147°). Sup-
porting the embrace is a CH‚‚‚Br hydrogen bond involv-
ing the 5-pz hydrogen atom H(21) (green dashed lines).
There are two distinct chains of molecules formed from
the embrace, both in the ab-plane.
In contrast to the previous complexes discussed, the
three-dimensional supramolecular structure of 4‚3C3H6O
is organized by solvent-complex interactions. One of
the three crystallographic types of acetone molecules in
the structure bridges two adjacent molecules through
CH‚‚‚O interactions between the acetone oxygen atom
O(42) and the aryl proton H(3) on two symmetry-
equivalent phenylene linkers (Figure 8b). This bridging
interaction results in chains along the c-axis that are
orthogonal to the pyrazolyl embrace chains. The chains
formed from the pyrazolyl embrace, which exist in the
ab-plane, alternate direction of propagation. That is, as
one pyrazolyl embrace chain runs diagonally from top
right to left bottom in the view shown in Figure 9 (red
dashed lines), the next chain runs above and below it
along the c-axis, running from top left to right bottom.
The bridging hydrogen bonds involving acetone mol-
ecules are shown by the blue dashed lines and connect
the pyrazolyl embrace chains along the c-axis. The
combination of the pyrazolyl embrace and the CH‚‚‚O
hydrogen bonds involving the solvent results in a three-
dimensional network that contains columnar voids that
The extended structure of 4‚3C3H6O exhibits a pyra-
zolyl embrace, as illustrated in Figure 8a, with distances
in the upper range of those previously encountered.7b
The centroid‚‚‚centroid distance of 3.81 Å is within the
usual ranges (red dashed line), but the CH‚‚‚π bonds

1554 Organometallics, Vol. 24, No. 7, 2005
Reger et al.
Figure 11. View of bimetallic molecules of 5‚Et2O‚4DMSO
showing π‚‚‚π and CH‚‚‚π interactions. Solvent molecules
are excluded.
phenylene ring with a carbonyl ligand from each in a
π‚‚‚π stacking position. An intramolecular interaction
exists between C(4)-H(4) and the pyrazolyl ring con-
taining C(11) (CH‚‚‚Ct distance ) 2.75 Å, CH‚‚‚Ct angle
) 126°) and again explains the upfield shift of the proton
resonances in the NMR spectrum. Although H(3) does
not show similar bonding in the crystal, C(4) and C(3)
are equivalent in solution.
Figure 9. View of 4‚3C3H6O down the c-axis emphasizing
columnar arrangement of the bimetallic molecules formed
by the combination of the pyrazolyl embrace (red dashed
lines) and bridging acetone molecules (blue dashed lines).
The poor solubility of 5‚Et2O‚4DMSO is explained by
the extensive π‚‚‚π stacking present in the solid state.
The structure comprises chains of molecules along the
b-axis held together by pyrazolyl-pyrazolyl (pz-pz) and
phenyl-pyrazolyl (Ph-pz) π‚‚‚π stacking between ad-
jacent molecules (Figure 11). The rings involved in pz-
pz interactions, which are between adjacent molecules
through the respective rings containing C(11), are
perfectly parallel, but the stacking is offset significantly
(slip angle ) 36°) such that the closest interactions are
between the C(11)-C(12) edges with an edge to edge
distance of 3.56 Å and perpendicular distance of 3.49
Å. There are two Ph-pz interactions for each of the pz‚
‚‚pz interactions. They are related by an inversion center
and involve the pz ring containing C(21) and the Ph ring
containing C(15). Again the rings are nearly perfectly
parallel but offset by 35°. The edge containing C(15) and
C(16) is 3.90 Å from the pz ring centroid.
In this structure there are also CH‚‚‚π interactions
between the benzyl protons and phenyl groups of
adjacent molecules. These interactions re-enforce the π‚
‚‚π interactions along the b-axis (Figure 11). In the
crystal the chains of molecules along the b-axis are
joined together by intercalated DMSO (ordered and
disordered) and diethyl ether molecules. The solvent
molecules interact with the phenyl rings from the benzyl
substituents. The remaining three-dimensional ex-
tended structure, therefore, is dominated by solvent
interactions.
Figure 10. ORTEP drawing showing the bimetallic mol-
ecule of {µ-p-[CH(4Bnpz)2]2C6H4}[Re(CO)3Br]2‚Et2O‚4DMSO
(5‚Et2O‚4DMSO). Displacement ellipsoids are drawn at the
50% probability level.
extend down the c-axis, in the same direction in which
the solvent-bridged chains propagate (Figure 9). The
columnar voids are filled by the remaining two types of
acetone molecules (not pictured). Of these two types, the
one containing O(41) is also involved in a CH‚‚‚O
hydrogen bond with the methine proton H(1), but this
interaction does not result in extended structure.
An ORTEP diagram of the bimetallic molecule of {µ-
p-[CH(4Bnpz)2]2C6H4}[Re(CO)3Br]2‚Et2O‚4DMSO (5‚Et2O‚
4DMSO) is shown in Figure 10, and selected distances
and angles are given in Table 4. The ether molecule and
one of the DMSO molecules of solvation are disordered.
As observed in the other bimetallic structures the metal
units are oriented on opposite sides of the linking
A remarkable feature of the compounds 1-5 pre-
sented above is that only one isomer of each respective
complex was formed during the syntheses. During
characterization of the bulk products, which represented
the only isolable metal complex products of the reac-
tions, the lack of proton resonances corresponding to
isomeric products in the NMR spectra and the simplicity

Bitopic Bis(pyrazolyl)methane Ligands
Organometallics, Vol. 24, No. 7, 2005 1555
Table 5. Distances for CtO‚‚‚Ph π‚‚‚π Interactions
monometallic complex {m-[CH(pz)2]2C6H4}Re(CO)3Br
(1) was isolated in low but synthetically useful yield.
The use of bidentate poly(pyrazolyl)methane units in
our rigid bitopic ligands, especially when oriented in the
meta position, has led to much more soluble complexes
than in our previous work with analogous rigid bitopic
tridentate ligands,9 for which we were unable to isolate
a monometallic complex, presumably because solubility
problems prevented useful separation procedures.
The monometallic complex 1 was readily converted
to the heterobimetallic complex {µ-m-[CH(pz)2]2C6H4}-
[Re(CO)3Br][Pt(p-tolyl)2] (2) in good yield, the first such
complex that we have been able to prepare with any of
our multitopic poly(pyrazolyl)methane ligands. We also
prepared fixed-geometry homobimetallic rhenium com-
plexes of Lm ({µ-m-[CH(pz)2]2C6H4}[Re(CO)3Br]2, 3) and
p-C6H4[CH(pz)2]2, Lp ({µ-p-[CH(pz)2]2C6H4}[Re(CO)3-
Br]2, 4), as well as of the 4-benzylpyrazolyl derivative
p-C6H4[CH(4Bnpz)2]2, 4BnLp ({µ-p-[CH4Bn(pz)2]2C6H4}-
[Re(CO)3Br]2, 5).
The crystal structures of these complexes formed from
fixed-geometry bitopic ligands exhibit significant non-
covalent interactions that result in extended supramo-
lecular structures, in much the same way as observed
previously with flexible and semirigid ligands.7,8 The
pyrazolyl embrace interaction dominates the structures
of 1 and 4, whereas CH‚‚‚X (X ) O, Br) hydrogen bonds
are more important for compounds 2 and 3. Finally,
introduction of the benzyl substituent on the pyrazolyl
rings of the ligand in compound 5 leads to strong π‚‚‚π
interactions dominating the supramolecular structure,
demonstrating that we can substantially influence the
supramolecular structures by simple substitutions on
the pyrazolyl rings. These additional noncovalent in-
teractions manifest themselves in this compound’s poor
solubility in most common organic solvents.
in Rhenium Complexes
centroid
centroid
CtO‚‚‚centroid
Ph distance/Å
CtO‚‚‚Ph plane
perpendicular
distance/Å
compound
1
3.16
3.10
2‚Et2O
3.11
3.05
3‚CH3CN
4‚3C3H6O
5‚Et2O‚4DMSO
3.37, 3.60
3.24
3.53
3.08, 3.12
3.19
3.20
of the carbonyl absorption regions in the infrared
confirmed their isomeric purities. The facial arrange-
ment of the CO ligands about rhenium is consistent with
what is expected from the trans effect in the Re(CO)5Br
starting material. For this facial arrangement, two
isomers may be formed upon coordination by the bis-
(pyrazolyl)methane donor. The only one observed for any
of these complexes is the isomer in which the bromine
atom attached to rhenium is oriented cis to the methine
proton in the boat or twist boat conformation of the six-
membered metallacycle. This isomer can orient one of
the CO ligands on rhenium in a position to participate
in π‚‚‚π interactions with the central phenylene ring;
the other isomer would place the bromine in this
position. Table 5 gives for each complex the distance
from the phenylene ring centroid to the center of the
proximate C-O bond as well as the perpendicular
distance from the phenyl plane to the center of the C-O
bond. Since the perpendicular distances of strong π‚‚‚π
stacking interactions average 3.3-3.6 Å,22 the com-
plexes presented here exhibit rather strong π‚‚‚π inter-
actions between the CO ligands and the linking phe-
nylene ring. The greater the CO ligands are offset from
the center of the phenylene ring, as in the structures of
3 and 5, the greater the difference between the centroid-
(CO)‚‚‚centroid(Ph) distance and the centroid(CO)‚‚‚
plane perpendicular distance.
In previous work with rhenium complexes of bis-
(pyrazolyl)methane ligands,23 we proposed that weak
intramolecular CH‚‚‚Br interactions in the transition
state of the reacting [Re(CO)3Br] unit and the ligands
directed the formation of a single geometrical isomer
analogous to those found in this work. It is reasonable
to assume that the same directing force is responsible
for the isomeric purity of the current complexes and that
additional stabilizing π‚‚‚π interactions are also present
between the CO ligands and the phenylene linkers, a
feature absent from the previous work.
The rigid phenylene-linked ligands introduced here
show promise toward the goal of preparing heterome-
tallic complexes, and additionally, they provide ample
comparisons to their more flexible counterparts con-
cerning their supramolecular chemistry.
Acknowledgment. We thank Dr. Radu Semeniuc
for helpful discussion, Dr. James Gardinier for a sample
of 4-benzylpyrazole, and the National Science Founda-
tion (CHE-0414239) for financial support. We also thank
the Alfred P. Sloan Foundation and the EPSCoR
program of the state of South Carolina for support of
R.P.W. The Bruker CCD single crystal diffractometer
was purchased using funds provided by the NSF In-
strumentation for Materials Research Program through
Grant DMR:9975623.
Conclusions
We have demonstrated a direct route to the first
heterobimetallic bis(pyrazolyl)methane complex by us-
ing the ligand m-C6H4[CH(pz)2]2 (Lm), in which the two
bidentate donor sites are linked by a rigid phenylene
spacer. In this chemistry, the tricarbonylrhenium(I)
Supporting Information Available: X-ray crystallo-
graphic files in CIF format for all structures reported, includ-
ing that of m-[CH(pz)2]2C6H4. Written and graphical descrip-
tions of the structure of m-[CH(pz)2]2C6H4 in text format. This
information is available free of charge via the Internet at
http://pubs.acs.org.
(22) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885.
(23) Reger, D. L.; Gardinier, J. R.; Pellechia, P. J.; Smith, M. D.;
Brown, K. J. Inorg. Chem. 2003, 42, 7635.
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