Multitopic third generation tris(pyrazolyl)methane ligands built on alkyne structural scaffolding: First preparation of mixed tris(pyrazolyl)methane/ tris(pyrazolyl)borate ligands

Article abstract of DOI:10.1039/b414770g

A series of new multitopic ligands with rigid linear geometry are formed by joining tris(pyrazolyl)methane and tris(pyrazolyl)borate units with arenyl and alkynyl linkers using Sonogashira and related alkynyl coupling reactions. These ligands are new examples of "third generation" poly(pyrazolyl)borate and poly(pyrazolyl)methane ligands, ligands functionalized at the non-coordinating "back" positions of either the boron or central carbon atoms. The reaction of Na[OCH₂C(pz)₃] with propargyl bromide yields HC₂CH₂OCH₂C(pz) ₃ (2) and homocoupling of this alkyne yields [-C₂CH ₂OCH₂C(pz)₃]₂. The reaction of Na[OCH₂C(pz)₃] with 3,5-(BrCH₂) ₂C₆H₃I yields 3,5-[(pz)₃CCH ₂OCH₂]₂C₆H₃I (4), which can be converted to 3,5-[(pz)₃CCH₂OCH₂] ₂C₆H₃(C₂H) (6) by reaction with HC₂SiMe₃ followed by removal of the SiMe₃ group. Compounds 4 and 6 can be combined to form {3,3′,5,5′-[(pz) ₃CCH₂OCH₂]₄(1,1′-C ₆H₃C₂C₆H₃) (7) and 6 homocoupled to form {3,5-[(pz)₃CCH₂OCH₂] ₂C₆H₃C₂-}₂. Compound 6 reacts with p-I₂C₆H₄ to produce 3,3′,5,5′-[(pz)₃CCH₂OCH₂] ₄[p-(1,1′-C₆H₃C₂) ₂C₆H₄], which can also be formed by the reaction of 4 with bis(ethynyl)benzene. The reaction of 2 with Fe[(p-IC ₆H₄)B(pz)₃]₂ yields the bitopic, metalloligand Fe[(pz)₃CCH₂OCH₂-C ₂-C₆H₄B(κ³-N,N′, N″-pz)₃]₂ (10) and a similar reaction with 6 yields the tetratopic metalloligand Fe[{3,5-[(pz)₃CCH₂OCH ₂]₂C₆H₃C₂}C ₆H₄B(κ³-N,N′,N″-pz) ₃]₂. The molecular structures of 2, 4, 7, and 10-4CH ₂Cl₂ are reported and their supramolecular structures, organized by a series of CH...I and CH π interactions, are detailed. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.

Full text of DOI:10.1039/b414770g

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P A P E R
Multitopic third generation tris(pyrazolyl)methane ligands built on
alkyne structural scaffolding: first preparation of mixed
tris(pyrazolyl)methane/tris(pyrazolyl)borate ligands
Daniel L. Reger,* James R. Gardinier, Selma Bakbak,w Radu F. Semeniuc,
Uwe H. F. Bunzw and Mark D. Smith
Department of Chemistry and Biochemistry, University of South Carolina, Columbia,
SC 29208, USA. E-mail: Reger@mail.chem.sc.edu
Received (in St Louis, USA) 27th September 2004, Accepted 8th April 2005
First published as an Advance Article on the web 25th May 2005
A series of new multitopic ligands with rigid linear geometry are formed by joining tris(pyrazolyl)methane
and tris(pyrazolyl)borate units with arenyl and alkynyl linkers using Sonogashira and related alkynyl
coupling reactions. These ligands are new examples of ‘‘third generation’’ poly(pyrazolyl)borate and
poly(pyrazolyl)methane ligands, ligands functionalized at the non-coordinating ‘‘back’’ positions of either the
boron or central carbon atoms. The reaction of Na[OCH2C(pz)3] with propargyl bromide yields
HC2CH2OCH2C(pz)3 (2) and homocoupling of this alkyne yields [-C2CH2OCH2C(pz)3]2. The reaction of
Na[OCH2C(pz)3] with 3,5-(BrCH2)2C6H3I yields 3,5-[(pz)3CCH2OCH2]2C6H3I (4), which can be converted to
3,5-[(pz)3CCH2OCH2]2C6H3(C2H) (6) by reaction with HC2SiMe3 followed by removal of the SiMe3 group.
Compounds 4 and 6 can be combined to form {3,30,5,50-[(pz)3CCH2OCH2]4(1,10-C6H3C2C6H3) (7) and 6
homocoupled to form {3,5-[(pz)3CCH2OCH2]2C6H3C2-}2. Compound 6 reacts with p-I2C6H4 to produce
3,30,5,50-[(pz)3CCH2OCH2]4[p-(1,10-C6H3C2)2C6H4], which can also be formed by the reaction of 4 with
bis(ethynyl)benzene. The reaction of 2 with Fe[(p-IC6H4)B(pz)3]2 yields the bitopic, metalloligand
Fe[(pz)3CCH2OCH2-C2-C6H4B(k3-N,N0,N00-pz)3]2 (10) and a similar reaction with 6 yields the tetratopic
metalloligand Fe[{3,5-[(pz)3CCH2OCH2]2C6H3C2}C6H4B(k3-N,N0,N00-pz)3]2. The molecular structures of
2, 4, 7, and 10 ꢀ 4CH2Cl2 are reported and their supramolecular structures, organized by a series of CHꢀ ꢀ ꢀI
and CH–p interactions, are detailed.
pyrazolyl groups as well as on the ethereal arms have resulted
Introduction
in a variety of structurally magnificent compounds organized
by non-covalent interactions. In order to develop more sophis-
ticated architectures based on intermolecular interactions it is
necessary to introduce new functionalities into the ligand
backbones. Alkynes are very attractive functional groups to
build into these types of ligands because they have a fixed,
linear geometry, they can become involved in p-stacking inter-
actions, and they are good ligands to a variety of metals.
We now report the synthesis of a new family of semi-rigid
linked tris(pyrazolyl)methane ligands that take advantage of
Sonogashira coupling reactions4 to give phenylalkynyl based
systems. These compounds represent a new class of ‘‘third
generation’’ poly(pyrazolyl)borate and poly(pyrazolyl)-
methane ligands,5 ligands specifically functionalized at the
non-coordinating ‘‘back’’ position of the scorpionate.5 In
poly(pyrazolyl)methane chemistry, the derivatization of the
central carbon in HC(pz)3 to the alcohol HOCH2C(pz)33j then
to the linked ligands of the type C6H6ꢁn[CH2OCH2C(pz)3]n
was our first development of ‘‘third generation’’ tris(pyrazolyl)
methane compounds.3 The use of Sonogashira coupling reac-
tions with Fe[(p-IC2C6H4)B(3-Mepz)3]2 to produce compounds
of the formula Fe[(p-RC2C6H4)B(3-Mepz)3]2 (R ¼ H, Me3Si,
Ph) was our first development of ‘‘third generation’’ poly(pyr-
azolyl)borate ligands.5 By utilizing this alkyne coupling meth-
odology, we report here the preparation of the first compounds
containing both a tris(pyrazolyl)methane and a tris(pyrazolyl)
borate ligating unit that can be considered ‘‘third generation’’
at each site. Future studies will be directed at exploring the
coordination chemistry of these ligands.
The design of solids with specific architectures is a current topic
of research that has potential applications in diverse areas from
catalysis to separations to gas storage. One approach to
developing such materials is to take advantage of the coordi-
nation chemistry of metals with carefully designed multitopic
ligands. The construction of robust and fairly predictable
architectures can be achieved by synthetically tailoring the
length between and geometric disposition of the ligating units
in rigidly linked organic frameworks.1 Studies using more
flexible ligand architectures are less numerous but are poten-
tially more attractive in the sense that one can envision shape-
adaptable architectures whose final structure could be envir-
onmentally dependent, similar to proteins, for example.2
Our group has been developing the chemistry of semi-rigid,
multitopic tris(pyrazolyl)methane ligands initially of the type
C6H6ꢁn[CH2OCH2C(pz)3]n (n ¼ 2, 3, 4, 6; pz ¼ pyrazolyl
ring).3 These ligands, when bound to metals, are structurally
adaptive in that their final molecular and supramolecular
structures depend on the nature of the metal, the anion, and
included solvent, among other factors.3a The multiple coordi-
nation modes of the C(pz)3 unit and inherent functionalities
such as the p-systems, the acidic hydrogens of the arene and
w Current address: School of Chemistry and Biochemistry, Georgia
Institute of Technology, 770 State Street, Atlanta, GA 30332, USA.
Fax: (þ1) 404-385-1795.
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 0 3 5 – 1 0 4 3
1035

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the crude yellow solid by column chromatography on silica gel
with Et2O as the eluent (Rf ¼ 0.6) afforded 0.502 g (84%) pure
3 as a colorless solid. Mp 143–145 1C. Anal. Calcd (Obs) for
C28H26N12O2: C, 59.78 (59.39); H, 4.66 (4.89); N, 29.88
(29.53%). 1H NMR (300 MHz, CDCl3): d7.67 (d, J ¼ 1.6
Hz, 6H, H3-pz), 7.39 (d, J ¼ 2.5 Hz, 6H, H5-pz), 6.35 (dd, 6H,
J ¼ 2,1 Hz, H4-pz), 5.19 [s, 4H, OCH2C(pz)3], 4.24 (s, 4H,
OCH2CC); 13C NMR (75.4 MHz, CDCl3): d 141.4 (C3-pz),
130.7 (C5-pz), 106.6 (C4-pz), 89.5 (Ca), 74.9, 73.4 (CRC),
71.4 (CH2), 60.0 (CH2); Accurate ESI(þ) MS Calculated for
[M þ H] [C28H27N12O2], 563.2380, found 563.2387.
Experimental
General considerations
All operations were carried out under a nitrogen atmosphere
by using either standard Schlenk techniques or in a Vacuum
Atmospheres HE-493 inert atmosphere dry box, unless other-
wise specified. Solvents for synthetic procedures and spectro-
scopic studies were dried by conventional methods and distilled
under N2 atmosphere immediately prior to use. All chemicals
were purchased from Aldrich Chemicals. The compounds
HOCH2C(pz)3 (1),3j 3,5-di(bromomethyl)iodobenzene,6 4-
ethynylphenyl-terpyridine,7 and Fe[(IC6H4)B(pz)3]2,8 were pre-
pared by literature procedures. Robertson Microlit Labora-
tories performed all elemental analyses. Melting point
determinations were made on samples contained in glass
capillaries by using an Electrothermal 9100 apparatus and
are uncorrected. Mass spectrometric measurements recorded
in ESI(ꢂ) mode were obtained on a Micromass Q-Tof spectro-
meter whereas those performed by using direct probe analyses
were made on a VG 70S instrument. NMR spectra were
recorded by using either a Varian Gemini 300 or a Varian
Mercury 400 instrument, as noted within the text. Chemical
shifts were referenced to solvent resonances at dH 7.27 and dC
77.23 for CDCl3; and dH 2.05 and dC 29.15 for acetone-d6.
3,5-[(pz)3CCH2OCH2]2C6H3I (4). A solution of 0.463 g (1.19
mmol) 3,5-(BrCH2)2C6H3I in 20 mL THF was added via
cannula to a 40 mL THF solution containing 2.38 mmol
NaOCH2C(pz)3 [generated in situ from 0.580 g (2.38 mmol)
HOCH2C(pz)3 and an excess of NaH (0.067 g, 2.79 mmol)].
The resulting mixture was stirred and heated at reflux for 12 h.
Water was carefully added, followed by 100 mL of methylene
chloride. The aqueous and organic fractions were separated;
the aqueous fraction was extracted with three 100 mL portions
of CH2Cl2. The combined organic portions were washed with
100 mL,
6 wt% NaHCO3 [to remove any unreacted
HOCH2C(pz)3], then with 100 mL H2O. The organics were
dried over MgSO4, filtered and solvent was removed by rotary
evaporation to leave a pale yellow oil. The oil was adsorbed
onto a pad of silica and loaded on a short pad of fresh silica.
The plug was first flushed with CH2Cl2 to remove an unidenti-
fied impurity (TLC Rf ¼ 0.75), and then with Et2O to elute the
desired product (TLC Rf ¼ 0.75). Removing diethyl ether by
rotary evaporation left a colorless oil that was triturated with
5 mL hexanes to give a colorless solid. The hexane solution was
decanted, and the remaining solid was dried under vacuum to
give 0.768 g (90%) of pure 4 as a colorless solid. Crystals
suitable for X-ray diffraction were grown by dissolving a
portion in Et2O and adding an equal volume of hexanes and
allowing the solution to evaporate slowly. Mp 124–127 1C.
Anal. Calcd. (Obs.) for C30H29N12O2I: C, 50.29 (50.34); H,
4.08 (4.26); N 23.46 (23.28%). 1H NMR (300 MHz, CDCl3): d
7.67 (d, J ¼ 1 Hz, 6H, H3-pz), 7.41 (d, J ¼ 3 Hz, 6H, H5-pz),
7.38 (m, 2H, C6H3I), 6.92 (s, 1H, C6H3I), 6.36 (dd, 6H, J ¼ 3,1
Hz, H4-pz), 5.11 (s, 4H, OCH2C(pz)3), 4.43 (s, 4H, OCH2CC);
13C NMR (75.4 MHz, CDCl3): d 141.6 (C3-pz), 139.7 (aryl),
136.2 (aryl), 131.1 (C5-pz), 126.1 (C4-aryl), 106.8 (C4-pz), 94.7
(Ci-I), 89.7 (Ca), 73.9 (CH2), 73.3 (CH2). Accurate ESI(þ) MS
Calculated for [M þ H] [C30H30N12O2I] 717.1659, found
717.1653.
Syntheses
HC2CH2OCH2C(pz)3 (2). Tris-2,2,2-(1-pyrazolyl) ethanol,
HOCH2C(pz)3 (5.67 g, 23.2 mmol) was dissolved in 150 mL
dry THF and was added dropwise over 30 min via cannula to a
suspension of 0.930 g NaH (23.1 mmol) in 50 mL dry THF.
The mixture was stirred and heated at reflux for 2 h, then
propargyl bromide, HCCCH2Br (2.76 g, 23.2 mmol), was
injected via syringe. After the mixture was heated at reflux
for 24 h, 100 mL H2O was carefully added. The organic and
aqueous portions were separated, the aqueous portion was
extracted with two 100 mL portions of CH2Cl2, then the
combined organic extracts were washed with 100 mL saturated
NaHCO3 solution and water (3 ꢃ 100 mL). After separation,
the organics were dried over anhydrous Na2SO4, filtered, and
the solvent was removed by rotary evaporation to give a brown
solid residue. After chromatography on silica gel with hexane :
ethyl acetate (1 : 1) as eluent 3.35 g (52%) of 2 was obtained as
a colorless solid. Mp 75–76 1C. Anal. Calcd (Obs) for
C14H14N6O: C, 48.00 (48.32); H, 4.03 (3.89); N, 23.99
1
(24.26%). H NMR (300 MHz, CDCl3): d 7.67 (d, J ¼ 1 Hz,
3H, H3-pz), 7.42 (d, J ¼ 2 Hz, 3H, H5-pz), 6.38 (d of d, 3H, J ¼
2,1 Hz, H4-pz), 5.00 (s, 2H, OCH2C (pz)3), 4.20 (d, 2H, J ¼ 2.5
Hz, OCH2CC), 2.43 (m, 1H, CCH); 13C NMR (75.4 MHz,
CDCl3): d 141.6 (C3-pz), 131.0 (C5-pz), 106.8 (C4-pz), 89.5
(Ca), 78.7, 76.0 (CRC), 73.0 (CH2), 59.4 (CH2). 1H NMR
(300 MHz, acetone-d6): d 7.61 (d, J ¼ 1 Hz, 3H, H3-pz), 7.47
(d, J ¼ 2 Hz, 3H, H5-pz), 6.36 (d of d, 3H, J ¼ 2,1 Hz, H4-pz),
5.17 [s, 2H, OCH2C(pz)3], 4.23 (d, 2H, J ¼ 2.4 Hz, OCH2CC),
3.10 (m, 1H, CCH); 13C NMR (75.4 MHz, acetone-d6): d 141.2
(C3-pz), 131.3 (C5-pz), 106.6 (C4-pz), 90.0 (Ca), 79.3, 76.8
((CRC),), 72.9 (CH2), 59.0 (CH2); High Res ESI(þ) MS
Calculated for [M þ Na] [C14H14N6ONa], 305.1127, found
305.1134.
3,5-[(pz)3CCH2OCH2]2C6H3(C2SiMe3) (5). A Schlenk tube
containing 1.83 g (2.55 mmol) of 3,5-[(pz)3CCH2OCH2]2-
C6H3I, 90 mg (0.13 mmol, 6 mol%) Pd(PPh3)2Cl2, and 24
mg (0.13 mmol, 6 mol%) CuI was evacuated and backfilled
with nitrogen three times. Dry THF (10 mL) and piperidine (5
mL) were added by syringe through a septum secured by
copper-wire, the resulting mixture was frozen (ꢁ196 1C),
evacuated, and backfilled with N2. Next, 1.0 mL (7.2 mmol
HC2SiMe3) was added to the frozen mixture under a N2
blanket by syringe. The mixture was placed in an external
60 1C water bath (the stopcock was momentarily opened to the
nitrogen line bubbler to relieve excess pressure) and was stirred
at 60 1C for 8 h, then at room temperature overnight. The
mixture was poured into 100 mL H2O and the aqueous phase
was extracted with three 100 mL portions of CH2Cl2 followed
by one 100 mL portion of Et2O. The combined organics were
dried over MgSO4, filtered and solvent was removed to give a
brown oil. The oil was subject to chromatography on SiO2, the
column was first eluted with methylene chloride to remove fast-
moving impurities then with Et2O where the desired product
elutes near the solvent front. A second chromatographic
[–C2CH2OCH2C(pz)3]2 (3). A mixture of 0.600 g (2.13
mmol) HC2CH2OCH2C(pz)3 and 3.86 g (21.0 mmol) anhy-
drous Cu(OAc)2 in 30 mL acetonitrile was stirred at 70 1C for
6 h. The mixture was then partitioned between 150 mL each of
CH2Cl2 and water, the organic fraction was collected and the
aqueous fraction was extracted with three 50 mL portions of
CH2Cl2. The combined organics were dried over Na2SO4,
filtered and solvent was removed under vacuum to leave
0.540 g (90%) crude 3 as a pale yellow solid. Purification of
1036
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 0 3 5 – 1 0 4 3

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separation on basic Al2O3 with CH2Cl2 as the eluent (Rf 0.8)
affords the desired compound as a colorless semi-solid (1.4 g
82%). Anal. Calcd. (Obs.) for C35H38N12O2Si: C, 61.20
MgSO4, filtered, and solvent was removed to leave a yellow oil.
The yellow oil was adsorbed onto silica and then was added to
a plug of fresh silica. The plug was fist eluted with Et2O to
remove unidentified impurity, and then with THF to give the
desired compound that moved with the solvent front. Solvent
was removed by rotary evaporation and the residue was
triturated with 10–20 mL Et2O to precipitate the product that
was collected by filtration. The Et2O insoluble solid was
washed with 5 mL hexanes, and dried under vacuum to leave
0.650 g (86%) of pure 8 as a colorless solid. Mp 180–182 1C.
Anal. Calcd (Obs) for C64H58N24O4: C, 62.63 (62.38); H, 4.76
(4.69); N, 27.39 (27.15%). 1H NMR (300 MHz, CDCl3): d 7.68
(d, J ¼ 1 Hz, 12H, H3-pz), 7.43 (d, J ¼ 3 Hz, 12H, H5-pz), 7.23
(s, 4H, C6H3), 6.97 (s, 2H, C6H3), 6.36 (dd, J ¼ 3, 1 Hz, 12H, 4-
H pz), 5.13 (s, 8H, OCH2C(pz)3), 4.47 (s, 8H, OCH2CC); 13C
NMR (75.4 MHz, CDCl3): d 141.6 (C3-pz), 138.1 (aryl), 131.2
(aryl), 131.1 (C5-pz), 127.8 (Ci-aryl), 122.3 (Ci-aryl), 106.8 (C4-
pz), 90.0 (Ca), 81.4, 74.3 (CRC), 73.9 (CH2); 73.6 (CH2);
ESI(þ) MS Calculated for [M þ H] [C64H39N24O4], 1227.5151,
found 1227.5150.
1
(60.71); H, 5.58 (5.84%). H NMR (CDCl3): d 7.67 (d, J ¼ 1
Hz, 6H, H3-pz), 7.42 (d, J ¼ 2 Hz, 6H, H5-pz), 7.17 (br s, 2H,
C6H3I), 6.92 (s, 1H, C6H3I), 6.34 (dd, 6H, J ¼ 2, 1 Hz, H4-pz),
5.11 (s, 4H, OCH2C(pz)3), 4.44 (s, 4H, OCH2CC), 0.27 (s, 9H,
SiCH3); 13C NMR (75.4 MHz, CDCl3): d 141.6 (C3-pz), 137.7
(aryl), 131.1 (C5-pz), 130.9 (aryl), 127.1(C4-aryl), 123.7 (Ci-Si),
106.8 (C4-pz), 104.7, 94.9 (CRC), 90.0 (Ca), 73.8 (CH2),
73.7 (CH2), 0.15 (SiCH3). Accurate ESI(þ) MS Calculated
for [M þ H] [C35H39N12O2Si], 687.3088, found 687.3080.
3,5-[(pz)3CCH2OCH2]2C6H3(C2H) (6). A 4.4 mL (4.4 mmol)
aliquot of a 1.0 M NBu4F solution in THF was added to a
solution of 5 (3.00 g, 4.40 mmol) in 5 mL THF. After the
mixture had stirred for 30 min, it was partitioned between 50
mL CH2Cl2 and 100 mL H2O. The organic and aqueous phases
were separated and the aqueous phase was extracted with three
50 mL portions of CH2Cl2. The combined organics were dried
over Na2SO4, filtered and solvent was removed by rotary
evaporation to leave 2.65 g (88%) 6 as a nearly colorless, pale
yellow solid. Mp 102–103 1C. Anal. Calcd. (Obs.) for
C32H30N12O2: C, 62.53 (62.22); H, 4.92 (4.91); N, 27.34
3,30,5,50-[(pz)3CCH2OCH2]4[p-(1,10-C6H3C2)2C6H4] (9)
Method A. A mixture of 0.555 g (0.903 mmol) 3,5-
[(pz)3CCH2OCH2]2C6H3(C2H) (6), 0.136 g (0.412 mmol) p-
I2C6H4, 0.023 g (0.033 mmol) Pd(PPh3)2Cl2, 20 mL THF, and
10 mL piperidine was subject to two freeze–pump–thaw cycles
and was frozen once more. Then, 2 mg (0.01 mmol) CuI was
added under a nitrogen blanket, the vessel (sealed with a
copper wire reinforced septum) was evacuated and the mixture
was subject to two more freeze–pump–thaw cycles, then the
flask was back filled with nitrogen. The mixture was heated to
60 1C with an external water bath, the stopcock was momen-
tarily opened to the nitrogen line to relieve excess pressure, and
the mixture was allowed to heat at 60 1C 12 h with stirring. The
resulting yellow solution was added to 10 g of silica gel and
solvents were removed by rotary evaporation. The dry silica gel
was loaded onto a fresh pad of silica and eluted first with
hexanes then Et2O to remove any unwanted impurities. Flush-
ing the plug with with 2 : 1 (v : v) THF : hexanes elutes the
desired compound in a pale yellow band (TLC Rf ¼ 0.8; bright
blue luminescence when irradiated with either 254 nm or 365
nm light). Evaporation of solvent, triturating the residue with
hexanes, filtering and drying under vacuum afforded 0.529 g
(95%) 9 ꢀ 2H2O as a hygroscopic and solvophilic pale yellow
solid. Mp 70 1C glass transition 95–100 1C (liq). Anal. Calcd
(Obs) for C70H66N24O6: C, 62.77 (63.26); H, 4.97 (4.88); N,
25.10 (24.32%). 1H NMR (300 MHz, CDCl3): d 7.68 (d, J ¼ 1
Hz, 12H, H3-pz), 7.53 (s, 4H, C6H4), 7.44 (d, J ¼ 3 Hz, 12H,
H5-pz), 7.26 (s, 4H, C6H3), 6.96 (s, 2H, C6H3), 6.36 (dd, J ¼ 3,
1 Hz, 12H, 4-H pz), 5.15 (s, 8H, OCH2C(pz)3), 4.49 (s, 8H,
OCH2CC), 1.66 (br s, 4H, H2O); 13C NMR (75.4 MHz,
CDCl3): d 141.6 (C3-pz), 138.0 (C6H3), 131.8 (C6H3), 131.1
1
(27.27%). H NMR (300 MHz, CDCl3): d 7.67 (d, J ¼ 1 Hz,
6H, H3-pz), 7.43 (d, J ¼ 2 Hz, 6H, H5-pz), 7.20 (br s, 2H,
C6H3), 6.95 (br s, 1H, C6H3), 6.35 (dd, 6H, J ¼ 2, 1 Hz, 6H, 4-
H pz), 5.13 (s, 4H, OCH2C(pz)3), 4.46 (s, 4H, OCH2CC), 3.08
(s, 1H, CCH); 13C NMR (CDCl3): d 141.6 (C3-pz), 137.9 (aryl),
131.1 (C5-pz), 130.9 (aryl), 127.4 (aryl), 122.6 (aryl), 106.8 (C4-
pz), 90.0 (Ca), 83.3 (CRC), 77.7 (CRC), 73.8 (CH2), 73.6
(CH2); Accurate ESI(þ) MS: Calcd. for [M
þ
H]
[C32H31N12O2], 615.2693, found 615.2684.
{3,30,5,50-[(pz)3CCH2OCH2]4(1,10-C6H3C2C6H3) (7). A mix-
ture of 5.00 g (7.00 mmol) 4 and 4.30 g (7.0 mmol) 6 was
dissolved in THF (5 mL) and purged with N2. Under a
nitrogen blanket Pd(PPh3)2Cl2 (100 mg, 2 mol%), CuI (67
mg, 5 mol%), and piperidine (5 mL) were each added to the
mixture. The flask was flushed for 15 min with a slow stream of
nitrogen then an additional 5 mL of THF was added. The
mixture was stirred overnight in a 60 1C water bath, then 100
mL methylene chloride was added. After aqueous work up
(washing with H2O and brine), crude 7 was obtained as a light
yellow solid (8.85 g 74%). Purification was achieved by ad-
sorbing crude 7 onto a pad of silica, loading the silica onto a
pad of fresh silica, eluting with Et2O to remove any impurities,
then with THF to give the desired product that moves with the
solvent front. Removing solvent by rotary evaporation, tritur-
ating with Et2O, filtering, and drying the colorless Et2O
insoluble solid under vacuum afforded 7 ꢀ H2O. Mp 207–209 1C
(decomp.). Anal. Calcd (Obs) for C62H60N24O5: C, 60.97
(60.51); H, 4.86 (4.75); N, 27.52 (27.13%). 1H NMR (300
MHz, CDCl3): d 7.67 (d, J ¼ 1 Hz, 12H, H3-pz), 7.43 (d, J ¼
2 Hz, 12H, H5-pz), 7.25 (s, 4H, C6H3), 6.96 (s, 2H, C6H3), 6.35
(dd, J ¼ 2, 1 Hz, 12H, H4-pz), 5.14 [s, 8H, OCH2C(pz)3], 4.48
(s, 8H, OCH2CC), 1.62 (br s, 2H, H2O); 13C NMR (75.4 MHz,
CDCl3): d 141.6 (C3-pz), 138.0 (aryl), 131.1 (C5-pz), 130.5
(aryl), 127.1 (aryl), 123.6 (aryl), 106.8 (C4-pz), 90.0 (Ca), 89.4
(CRC), 73.84 (CH2), 73.79 (CH2); Accurate ESI(þ) MS
Calculated for [7 þ H], [C62H59N24O4], 1203.5151, found
1203.5127.
(C5-pz), 130.5 (C2,3,5,6-C6H4), 127.1 (Ci-C6H4), 123.6 (C4/i
-
C6H3), 123.3 (C4/i-C6H3), 106.8 (C4-pz), 91.1 (CRC), 90.0
(Ca), 89.6 (CRC), 73.8 (CH2); 73.7 (CH2). Accurate ESI(þ)
MS Calculated for [9 þ H] [C70H63N24O4], 1304.5464, found
1304.5437;
Method B. A 2.0 mL THF solution of 0.040 g (0.15 mmol)
bis(trimethylsilylethynyl)benzene and 0.14 mL of a 1.0 M
NBu4F in THF (0.14 mmol) was stirred for 30 min. The
product mixture was partitioned between 50 mL each CH2Cl2
and H2O, the organic phase is separated and the aqueous is
extracted with an additional 50 mL CH2Cl2. The combined
organics were dried over Na2SO4, filtered, and solvent was
removed under vacuum, the residue (1,4-diethynylbenzene)
was taken up in 10 mL THF and was transferred under
nitrogen to a 4 mL nitrogen-purged solution of THF : piper-
idine (1 : 1) containing 0.20 g (0.28 mmol) 4, and 5 mol% each
Pd(PPh3)2Cl2 and CuI. After the mixture had been stirred for
{3,5-[(pz)3CCH2OCH2]2C6H3C2-}2 (8). 2.47 g (12.4 mmol)
Cu(OAc)2 ꢀ H2O was added to a solution of 0.760 g (1.24
mmol) 6 in 50 mL CH3CN. The resulting heterogeneous
mixture was stirred at 70 1C for 5 hours, then was added to
150 mL H2O. The aqueous phase was extracted with three 100
mL portions CH2Cl2. The combined organics were dried over
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 0 3 5 – 1 0 4 3 1037

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12 h at room temperature, it was worked up as described above
to leave 0.10 g (0.074 mmol, 53% based on NBu4F) of 9 ꢀ 2H2O
as a yellow solid. The characterization data were identical to
those found described under Method A.
pink-orange solid by using 0.158
g
(0.178 mmol)
Fe[IC6H4B(pz)3]2, 0.243 g (0.395 mmol) 1-(HC2)C6H3[3,5-
CH2OCH2C(pz)3]2, 25 mg (5 mol%) Pd(PPh3)2Cl2, 6 mg (9
mol%) CuI, 10 mL THF and 5 mL piperidine. Mp 310 1C
(decomp.). Anal. Calcd. (Obs.) for C94H84N36O4B2Fe: C, 60.72
(60.32); H, 4.55 (4.59); N, 27.12 (26.28%). 1H NMR (300
MHz, CDCl3) d 8.92 (br s), 8.06 (br s), 7.72 (s, 12H, H3-pz-
C), 7.67 (s), 7.49 (s, 12 H, H5-pz-C), 7.41 (m, overlapping), 7.02
(s), 6.40 (H4-pz-C), 6.36 (br, s, H4-pz-B), 5.20 (s, 8H,
OCH2Cpz3) , 4.56 (s, 8 H, OCH2CC). ESI(þ) MS: Calcd.
For Md1: 1859, Found: 1859.
General procedure for alkyne coupling reactions involving iron
borate compounds
A Schlenk flask is charged with the desired iron(II)(iodo-
phenyl)tris(pyrazolyl)borate, Pd(PPh3)2Cl2, terminal alkyne
(XC2H), THF and piperidine (ca. 20 mL, between 4 : 1 to 2 :
1 v/v). The reaction vessel is then subjected to three freeze–
pump–thaw cycles. The reaction mixture is frozen once more,
the vessel is backfilled with N2, CuI is added under a N2
blanket. After the reaction flask is sealed with a septum
reinforced by copper wire, it is frozen, evacuated, backfilled
with nitrogen once more and then placed in a 60 1C bath
overnight. Then, the product mixture is adsorbed onto alumi-
na, solvent is evaporated, and the alumina is added to a pad of
fresh alumina. Eluting with hexanes eliminates any excess
alkyne and homocoupled alkynyl impurities. Then, elution
with CH2Cl2 affords the desired alkynylphenyl borate complex,
Fe[(X-C2C6H4)B(pz)3]2, in a fast moving purple band.
Attempted preparation of Fe[4-[40-(4- C2C6H4)(2,20:6,200-ter-
py)]C6H4B(j3-N,N0,N00-pz)3]2 (12). A mixture of 0.297 g (0.335
mol) Fe[IC6H4B(pz)3]2, 0.233 g (0.699 mmol) 40-(4-HC2C6H4)-
2,20:6,200-terpy, 12 mg (8 mol%) Pd(PPh3)2Cl2, 2 mg (5 mol%)
CuI, 3 mL THF and 3 mL piperidine was heated for 8 h at
70 1C followed by 12 h at room temperature. The resulting
purple solid was collected by filtration, washed with three
10 mL portions of MeOH, three 10 mL portions of Et2O and
was air dried to afford 0.298 g of a very insoluble (trace
solubility in either refluxing tetrachloroethane or refluxing
DMF) purple solid mixture of the mono- and disubstituted
compounds as identified by High Res. ESI(þ) TOF MS.
Calcd (obs) for Fe[IC6H4B(pz)3][(terpy)C6H4C2C6H4B(pz)3]:
1091.2190 (1091.2190) and for Fe[(terpy)C6H4C2C6H4B(pz)3]2
1296.4338 (1296.4326).
Fe[{3,5-[(pz)3CCH2OCH2]2C6H3C2}C6H4B(j3-N,N0,N00-pz)3]2
.
(10 CH2Cl2). This compound was prepared in quantitative
yield (312 mg) as a pink solid by using 0.231 g (0.261 mmol)
Fe[IC6H4B(pz)3]2, 0.162 g (0.574 mmol) HC2CH2OCH2C(pz)3,
15 mg (8 mol%) Pd(PPh3)2Cl2, 4 mg (8 mol%) CuI, 40 mL
THF and 10 mL piperidine. An additional heating period of
8 h at 80 1C was used in this case. Recrystallization by allowing
a layer of MeOH to slowly diffuse into a CH2Cl2 solution at
ꢁ20 1C afforded pink-purple needles of 10 ꢀ CH2Cl2. The
needles lose the solvent of crystallization when collected, and
this solid was used for the characterization. Mp 220 1C
(decomp.), 255 1C liquefies. Anal. Calcd. (Obs.) For
C58H52N24O2B2Fe: C, 58.31 (57.71); H, 4.39 (4.12); N, 28.14
(27.84%). 1H NMR (300 MHz, CDCl3) d 8.17 (part of
AA0BB0, J ¼ 8 Hz, 4 H), 7.86 (d, J ¼ 1 Hz, 6 H, H3-pz-C),
7.71 (br s, 6 H, H5-pz-B), 7.69 (part of AA0BB0, 4 H), 7.51 (d,
J ¼ 2 Hz, 6 H, H5-pz-C), 7.02 (br s, 6 H, H3-pz-B), 6.39 (dd,
J ¼ 2,1 Hz, 6 H, H4-pz-C), 6.26 (br s, 6H, H4-pz-B), 5.35 (s, 4
H, OCH2Cpz3), 4.49 (s, 4 H, OCH2CC). 13C NMR (75.4 MHz,
CDCl3) d 149.9, 141.6, 138.7, 135.1, 131.5, 131.1, 122.1, 106.8,
89.9, 87.7, 73.1, 60.3, 46.9. Accurate ESI(þ) MS: Calcd. For
M1: 1194.4260, Found: 1194.4302.
Crystallography
A
colorless chunk sectioned from a larger crystal of
HC2CH2OCH2C(pz)3 (2), an irregular colorless block sec-
tioned from a larger crystalline mass of 4, a colorless plate of
7, and a purple plate of 10 ꢀ 4CH2Cl2 were each mounted onto
the end of thin glass fibers using inert oil. X-Ray intensity data
covering the full sphere of reciprocal space were measured at
150(1) K (2, 4, 7) or 100(1) K (10 ꢀ 4CH2Cl2) on a Bruker
SMART APEX CCD-based diffractometer (Mo Ka radiation,
l ¼ 0.710 73 A).9 The raw data frames were integrated with
SAINTþ,9 which also applied corrections for Lorentz and
polarization effects. The final unit cell parameters for 2, 4, 7,
and 10 ꢀ 4CH2Cl2 are based on the least-squares refinement of
4515, 5607, 6918, and 9926 reflections, respectively, each with
I 4 5s(I) from the appropriate data set. Analyses of the data
showed negligible crystal decay during data collection. Struc-
tures were solved by a combination of either direct methods for
10
2, 7, and 10 ꢀ 4CH2Cl2 or Patterson methods
for 4, and
subsequent difference Fourier syntheses, and refined by full-
matrix least-squares against F2, using SHELXTL.11 Except
where noted in the refinement of 10 ꢀ 4CH2Cl2, all non-hydro-
Fe[{3,5-[(pz)3CCH2OCH2]2C6H3C2}C6H4B(j3-N,N0,N00-pz)3]2,
(11). This compound was prepared in 91% yield (301 mg) as a
Table 1 Summary of crystallographic data for 2, 4, 7, and 10 ꢀ 4CH2Cl2
2
4
7
10 ꢀ 4CH2Cl2
Empirical formula
Formula weight
C14H14N6O
282.31
150(1)
C30H29IN12O2
716.55
150.0(2)
C62H58N24O4
1203.32
150.0(2)
Monoclinic
P21/c
C62H60B2Cl8FeN24O2
1534.41
100(1)
T/K
Crystal system
Monoclinic
Cc
Triclinic
ꢀ
P1
Triclinic
ꢀ
P1
Space group
a/A
13.2954(8)
12.4529(8)
8.5445(5)
90
8.7819(6)
8.1473(5)
34.148(2)
11.3257(7)
90
8.5941(4)
13.4373(7)
16.3188(8)
b/A
c/A
12.1248(8)
15.3073(10)
96.8400(10)
99.5630(10)
105.9950(10)
1521.48(18)
2
a/1
b/1
103.9530(10)
98.3300(10)
106.9990(10)
97.9170(10)
90
109.1850(10)
90
g/1
V/A3
1401.20(15)
4
1.338
2976.0(3)
2
1.343
1701.26(15)
1
Z
r(calcd.)/Mg mꢁ3
1.564
1.103
1.498
0.600
m/mmꢁ1
0.091
0.0294, 0.0625
0.0314, 0.0630
0.091
0.0639, 0.1656
0.0815, 0.1752
Final R indices [I > 2s(I)] R1, wR2
R indices (all data) R1, wR2
0.0318, 0.0796
0.0340, 0.0812
0.0728, 0.2133
0.0816, 0.2232
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gen atoms were refined with anisotropic displacement para-
meters while hydrogen atoms were placed in geometrically
idealized positions and included as riding atoms. Crystallo-
graphic data are collected in Table 1 and further details of the
structure solutions and refinement are noted for each below.
Systematic absences in the intensity data of 2 were consistent
with the space groups C2/c and Cc; intensity statistics indicated
acentricity. The space group Cc was verified by examination of
the structure and checked with ADDSYM/PLATON.12 Due to
the lack of heavy atoms in the structure, Friedel opposites were
merged during data processing and the absolute structure was
not determined.
Compound 4 crystallizes in the triclinic crystal system. The
ꢀ
space group P1 was assumed and confirmed by the successful
solution and refinement of the structure.
Systematic absences in the intensity data from 7 determined
the space group P21/c. The molecule resides on a crystallo-
graphic inversion center. One of the pyrazolyl rings (N21–C23)
is rotationally disordered about the N–Cmethine bond in equal
proportions.
tions and was accounted for with the SQUEEZE program after
several unsuccessful attempts at modeling the disorder. (61
electrons and 208.5 A3 solvent-accessible volume per unit cell.)
The contribution of the disordered solvent was subtracted from
the structure factors but was included in the final formula weight
and calculated density. During the refinement a large residual
electron density peak (2.88 e A3) persistently appeared near the
midpoint of the C77–C78 triple bond, ca. 0.7 A from each atom.
The origin of this peak is unknown, but is responsible for the
anisotropy of the displacement ellipsoids of atoms C77 and C78
as well as an unreasonably short (B1 A) C–C bond. To correct
for this, the atomic parameters for C77 and C78 were fixed at
reasonable Uij values and a C–C bond length of 1.15 A. This
peak as well as the disorder in the crystal is the reason for the
low quality of this refinement and the high final residuals.
CCDC reference numbers 270421–270424.
See http://www.rsc.org/suppdata/nj/b4/b414770g/ for crys-
tallographic data in CIF or other electronic format.
Results and discussion
Compound 10ꢀ 4CH2Cl2 crystallizes in the triclinic system.
Syntheses of tris(pyrazolyl)methane ligands
ꢀ
The space group P1 was assumed and eventually confirmed.
Half of the iron cation located on an inversion center and two
CH2Cl2 molecules of crystallization could be identified in the
asymmetric unit. One CH2Cl2 is disordered over several orienta-
A summary of the routes to the new alkynyl-containing
tris(pyrazolyl)methane ligands is given in Scheme 1. The reac-
tion between the sodium alkoxide, Na[OCH2C(pz)3] [prepared
Scheme 1 Preparation of alkynyl-containing tris(pyrazolyl)methane ligands.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 0 3 5 – 1 0 4 3
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Fig. 1 Molecular structures of alkynyl-containing tris(pyrazolyl)methane ligands.
in situ from NaH and the parent alcohol HOCH2C(pz)3 (1)],
and either propargyl bromide or di(bromomethyl)–iodoben-
zene afforded the monotopic terminal alkyne 2 and ditopic
iodophenyl derivative 4, respectively, in high yields. The iodo-
phenyl derivative 4, was converted to the terminal alkynyl
derivative 6, by standard protocol (Sonogashira coupling with
trimethylsilylacetylene followed by deprotection with tetrabu-
tylammonium fluoride). Both terminal alkynes were subject to
a number of coupling reactions. Thus, 2 and 6 were homo-
coupled with an excess of copper(II) acetate to give the ditopic
derivative 3 and the tetratopic derivative 8. Sonogashira cou-
pling of 4 with 6 provided the tetratopic diphenylethynylene
derivative 7. The bright blue luminescent tetratopic derivative 9
was prepared in quantitative yield by coupling 6 with diiodo-
benzene or in modest yield by coupling 4 with diethynylben-
zene. The identity of compounds 2–9 was established by a
combination of elemental analyses, NMR spectroscopic meth-
ods, mass spectral data, and in the case of 2, 4, and 7 by single
crystal X-ray diffraction.
tional in these three compounds, the ability of the alkynyl and
pyrazolyl groups to participate in non-covalent interactions is
evident in the supramolecular structures.
In the case of 2, the three-dimensional supramolecular
structure is comprised of two sets of CH–p interactions. As
shown by red lines on the left side of Fig. 2, CH–p interactions
between a pyrazolyl hydrogen donor [H(21)] and the p-cloud of
the pyrazolyl ring containing N(12) organize the molecules of 2
into chains that run along the c axis. The geometry of the
interaction, CH(21)–Ct[N(12)] 2.93 A, 137.81 (Ct ¼ ring
centroid), is within expected values13,14. These chains are
shown rotated 901 into the a, b plane in the center of Fig. 2.
The right side of the figure, also in the a, b plane, shows that
the chains are organized into a three-dimensional structure
by CH–p interactions (green lines) with the alkynyl hydro-
gens [H(5)] interacting with the pyrazolyl groups that contain
N(31). The geometry of this type of interaction {CH(5)–Ct[N(31)]
3.12 A, 166.81} is also within accepted values.15
The supramolecular structure of 4 (Fig. 3) is that of sheets
organized by CH–p and CHꢀ ꢀ ꢀI interactions in the crystal. A
set of prototypical CH–p interactions (red lines, Fig. 3) be-
tween H(33) on a pyrazolyl ring and the p-cloud of the
pyrazolyl ring containing N(61) {CH(33)–Ct[N(61)] 2.93 A,
165.21} organizes neighboring molecules of 4 into dimers
Structures of tris(pyrazolyl)methane ligands
ORTEP diagrams of 2, 4, and 7 are found in Fig. 1. While the
intramolecular bond lengths and angles are rather unexcep-
Fig. 2 Three-dimensional supramolecular structure of HC2CCH2OCH2C(pz)3 (2) held together via pyrazolyl CH–p (pyrazolyl) interactions (red
lines) and alkynyl CH–p (pyrazolyl) interactions (green lines).
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Fig. 3 Two-dimensional sheet structure of IC6H4[CH2OCH2C(pz)3]2 (4) comprised of CH–p interactions (red and pink lines) and CHꢀ ꢀ ꢀI
interactions (green lines).
(Fig. 3, left). These dimers are further organized into chains
that run along the crystallographic [111] direction by another
set of CH–p interactions (pink lines, Fig. 3, middle) that occur
between H(71a) from a methylene group and the p-cloud of the
pyrazolyl ring containing N(21), CH(71a)–Ct[N(21)] 3.09 A,
148.11. These chains are organized into sheets by a set of
CHꢀ ꢀ ꢀI interactions (green lines, Fig. 3, right) along the c axis
involving the acidic hydrogen at the 3-position of a pyrazolyl
ring, H(23). The geometry of the interaction [CH(23)ꢀ ꢀ ꢀI, 3.08
A, 162.91] is similar to that seen in other systems.16
Interestingly, it has not yet been possible to crystallize the
related complex 1,3-C6H4[CH2OCH2C(pz)3]2 (where a hydro-
gen replaces the iodine) which exists as an oil.3d This fact
underscores the importance of introducing groups that can
participate in non-covalent interactions (as in the case of the
iodine group and allowing CHꢀ ꢀ ꢀI interactions) for the ulti-
mate purpose of learning to control the crystal packing beha-
vior of molecular solids. Another intriguing feature in the
current system and its phenyl analogue, in terms of the future
of ‘crystal engineering’ is that it remains unclear what role the
orientation of the ethereal arms have on the crystal packing
behavior or vice versa. Thus, 4 has the ether sidearms located
above and below the plane of the central arene ring but the
arms in the metal complex {1,3-C6H4[CH2OCH2C(pz)3]2(Mn
3d,f
(CO)3]2}(BF4)2
the same side of the arene ring.
have the opposite orientation with both on
The supramolecular structure of 7 (Fig. 4) is three-dimen-
sional, mainly as a result of CH–p interactions (Table 2),
including some that involve the central alkynyl spacer as
originally intended at the outset of this research. The building
blocks are held in chains by CH–p interactions, which occur
between the acidic hydrogen H(53) at the three positon of a
pyrazolyl ring and the p-cloud of the alkyne fragment. The
geometrical parameters for this interaction [CH(53)–C(80)
distance of 2.74 A, C–H–C angle of 149.91] are in line with
other CH–p alkyne interactions.15 Given the fact that the
molecule is centrosymmetric, this interaction links the mole-
cular building blocks into chains positioned in the bc plane and
running along the c axis of the unit cell. One chain, built up
from three molecules, is shown at the top of Fig. 4, where the
red lines represent the CH–p (alkyne) interactions. These
chains are connected into a 3D network (bottom of Fig. 4)
as a result of two sets of CH–p interactions. In contrast to the
previous CH–p interaction where the acceptor p-cloud was
located on the alkyne moiety, here in both cases the hydrogen
atom acceptors are pyrazolyl rings. For the first set of interac-
Table 2 Summary of intermolecular non-covalent interactions for 7
Donor(D)–Hꢀ ꢀ ꢀAcceptor(A)
Chain formation
D–Hꢀ ꢀ ꢀA/A
D–Hꢀ ꢀ ꢀA/1
C(53)–H(53)ꢀ ꢀ ꢀC(80)
3D network
2.74
149.9
C(12)–H(12)ꢀ ꢀ ꢀCt[N(41)]
C(78)–H(78a)ꢀ ꢀ ꢀCt[N(51)]
C(21b)–H(21b)ꢀ ꢀ ꢀN(11)
2.80
3.07
2.56
158.0
145.4
161.1
Fig.
4
Supramolecular structure of 3,30,5,50-[(pz)3CCH2OCH2]4
(C6H3C2C6H3) (7). Top: View emphasizing one chain created by
CH(pz)–p (alkyne) interactions (red lines). Bottom: 3D network of 7.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 0 3 5 – 1 0 4 3
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Scheme 2 Preparation of mixed tris(pyrazolyl)methane–tris(pyrazolyl)borate ligands.
tions the hydrogen donor is the pyrazolyl ring containing the
C(12) ring {C–H(12)ꢀ ꢀ ꢀCt[N(41)] distance ¼ 2.80 A and
C–Hꢀ ꢀ ꢀCt angle ¼ 158.01}. For the second set, the hydrogen
donor involves an ethereal methylene group located on one of
the side arms of the compound {CH(78a)–Ct[N(51)], 3.07 A,
145.41}. It is worth mentioning that this arrangement is sup-
ported by CH–N interactions that occur between H(21b) of the
rotationally disordered pyrazolyl ring and N(11) of a neighbor-
ing well-behaved pyrazolyl ring. The combination of these
interactions build up the 3D network of 7.
the NMR spectra showed the expected resonances with che-
mical shifts in typical ranges 1–10 ppm.
The solid state structure of 10 ꢀ 4CH2Cl2 has been deter-
mined crystallographically, Fig. 5. While disorder problems
precluded a high accuracy structure, the Fe–N average bond
distance of 1.96 is typical of low spin iron(II), as expected from
the color and NMR spectra. Disorder problems in the struc-
ture prevent further analysis of the crystal packing.
It was found that a similar Sonogashira coupling reaction
between HC2C6H4-terpy and Fe[(p-IC6H4)B(pz)3]2 afforded a
highly insoluble solid mixture that showed signals in the
Mixed tris(pyrazolyl)borate/tris(pyrazolyl)methane
metallo-ligands
The chemistry used to build organic ligands in Scheme 1 can be
extended to properly functionalized metal complexes. We have
previously reported the syntheses of Fe[(p-IC6H4)B(3-Rpz)3]2
(R ¼ H, Me) compounds with interesting spin-crossover
properties (for R ¼ Me).8 The compound Fe[(p-IC6H4)B(pz)3]2
was smoothly converted to the dialkynlated bitopic Fe[(pz)3C-
CH2OCH2–C2–C6H4B(k3-N,N0,N00-pz)3]2 (10) by reaction with
2 and a similar reaction with 6 yields the tetratopic metalloli-
gand Fe[{3,5-[(pz)3CCH2OCH2]2C6H3C2}C6H4B(k3-N,N0,N00-
pz)3]2 (11) (Scheme 2) by using Sonogashira coupling reactions.
These iron-containing unsubstituted pyrazolyl derivatives are
purple, low spin diamagnetic species at room temperature, and
Scheme 3 Iron-containing products obtained from attempted Sono-
gashira coupling reactions between Fe[IC6H4B(pz)3]2 and HC2C6H4-
terpy.
Fig. 5 Molecular structure and atom labelling scheme of Fe[(pz)3CCH2OCH2C2C6H4B(k3-N,N0,N00-pz)3]2.
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ESI(þ) mass spectra that could be attributed to the mono- and
dialkynyl coupled products (Scheme 3). Considering the ease of
the previous reactions, it is evident that the low solubility of the
mono- and disubstituted (alkynylphenyl)terpy derivatives in
every solvent hampered the completion of the reaction in
addition to inhibiting the potential for product separation
and characterization.
Chem., 2004, 69, 2910; (c) M. Fujita, S. Nagao and K. Ogura,
J. Am. Chem. Soc., 1995, 117, 1649.
3
(a) D. L. Reger, R. F. Semeniuc, V. Rassolov and M. D. Smith,
Inorg. Chem., 2004, 43, 537; (b) D. L. Reger, R. F. Semeniuc and
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Reger, R. F. Semeniuc and M. D. Smith, J. Chem. Soc., Dalton
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Reger, T. D. Wright, R. F. Semeniuc, T. C. Grattan and M. D.
Smith, Inorg. Chem., 2001, 40, 6212; (j) D. L. Reger, T. C.
Grattan, K. J. Brown, C. A. Little, J. J. S. Lamba, A. L.
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K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett.,
1975, 4467.
D. L. Reger, J. R. Gardinier, W. R. Gemmill, M. D. Smith, A. M.
Shahin, G. L. Long, L. Rebbouh and F. Grandjean, J. Am. Chem.
Soc., in press.
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Conclusion
We have prepared a new family of semi-rigid, multitopic
ligands based on linking tris(pyrazolyl)methane units via cen-
tral alkynyl spacers. Sonogashira coupling reactions were used
to prepare phenylalkynyl based compounds while Glaser oxi-
dative homocoupling reactions have been used to prepare
butadiynyl based compounds. The main architectural feature
of the new linked ligands is their overall rigid linear geometry,
but with semi-rigid ending groups. The flexibility of these end
groups is important to future chemistry as they provide
solubility and structural adaptivity to metal complexes. In
addition, we have shown that these compounds exhibit rich
supramolecular (structural) chemistry that is a function of the
added substituents along the ligand periphery—the addition of
iodide allows for CHꢀ ꢀ ꢀI interactions whereas the addition of
alkynyl moieties allows for extended structures based on CH–p
interactions involving this electron rich group. While we have
centred our chemistry on symmetrical multitopic ligands based
on tris(pyrazolyl)methane units, the chemistry outlined here is
applicable for other ligand systems; the syntheses of unsymme-
trical analogs are in progress.
Importantly, we were able to use this chemistry to prepare
new examples of ‘‘third generation’’ poly(pyrazolyl)borate and
poly(pyrazolyl)methane ligands. First generation poly(pyrazo-
lyl)borate ligands, initially introduced by Trofimenko,17 are the
simple [HB(Rpz)3]ꢁ type ligands with non-bulky substituents
at the 3-position. Second generation ligands, also introduced
by Trofimenko,18 are those with bulky substituents at the 3-
position. Third generation ligands are designed to be those
specifically functionalized at the non-coordinating, ‘‘back’’
position of the ligands, either at boron or carbon and a number
of examples have been reported previously.3,14,19 In this chem-
istry we have prepared the first third generation compound
containing both the tris(pyrazolyl)methane and tris(pyrazolyl)-
borate ligating units where the borate end was bound to
iron(II). This chemistry opens up the door for further explora-
tion into incorporating methyl-substituted pyrazolyls (which
undergo spin transitions in iron(II) chemistry) or even other
metal systems with the purpose of putting electro- and/or
photoactive centers into highly organized coordination net-
work solids.
4
5
6
7
8
9
D. L. Reger, J. R. Gardinier, M. D. Smith, A. M. Shahin, G. J.
Long, L. Rebbouh and F. Grandjean, Inorg. Chem., 2005, 44,
1852.
SMART Version 5.625 and SAINTþ Version 6.02a, Bruker Ana-
lytical X-ray Systems, Inc., Madison, WI, 1998.
10 P. T. Beurskens, G. Beurskens, R. de Gelder, S. Garcia-Granda,
R. Israel, R. O. Gould and J. M. M. Smits, The DIRDIF99
program system, Crystallography Laboratory, University of
Nijmegen, The Netherlands, 1999.
11 G. M. Sheldrick, SHELXTL (Version 5.1), Bruker Analytical
X-ray Systems, Inc., Madison, WI, 1997.
12 A. L. Spek, PLATON, A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 1998.
13 C. Janiak, J. Chem. Soc., Dalton Trans., 2000, 3885.
14 D. L. Reger, J. R. Gardinier, R. F. Semeniuc and M. D. Smith,
Dalton Trans., 2003, 1712.
15 (a) W. Lu, M. C. W. Chan, N. Zhu, C.-M. Che, Z. He and K.-Y.,
Chem. Eur. J., 2003, 9, 6155; (b) T. Steiner and M. Tamm,
J. Organomet. Chem., 1998, 570, 235.
16 (a) F. Ugozzoli, A. Arduini, C. Massera, A. Pochini and A. Secchi,
New J. Chem., 2002, 26, 1718; (b) M. Freytag, P. G. Jones, B.
Ahrens and A. K. Fischer, New J. Chem., 1999, 12, 1137.
17 S. Trofimenko, Scorpionates - The Coordination Chemistry of
Polypyrazolylborate Ligands, Imperial College Press, London,
1999.
18 S. Trofimenko, J. C. Calabrese and J. S. Thompson, Inorg. Chem.,
1987, 28, 1507.
Acknowledgements
19 (a) D. White and J. W. Faller, J. Am. Chem. Soc., 1982, 104, 1548;
(b) C. P. Brock, M. K. Das, R. P. Minton and K. Niedenzu, J. Am.
Chem. Soc., 1988, 110, 817; (c) C. Janiak, L. Braun and F.
Girgsdies, J. Chem. Soc., Dalton Trans., 1999, 3133; (d) J. L.
Kisko, T. Hascall, C. Kimblin and G. Parkin, J. Chem. Soc.,
Dalton Trans., 1999, 1929; (e) N. C. Hardin, J. C. Jeffery, J. A.
McCleverty, L. H. Rees and M. A. Ward, New J. Chem., 1998,
661; (f) K. Niedenzu and S. Trofimenko, Inorg. Chem., 1985, 24,
We thank the National Science Foundation (CHE-0414239)
and the University of South Carolina for support. The Bruker
CCD Single Crystal Diffractometer was purchased using funds
provided by the NSF Instrumentation for Materials Research
Program through Grant DMR: 9975623.
4222; (g) F. Jakle, K. Polborn and M. Wagner, Chem. Ber., 1996,
¨
129, 603; (h) F. Fabrizi de Biani, F. Jakle, M. Spiegler, M. Wagner
¨
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