Synthesis, structural characterization, and properties of heavier alkaline earth complexes containing bis(pyrazolyl)borate or bis(3,5-diisopropylpyrazolyl) borate ligands

Article abstract of DOI:10.1016/j.poly.2011.02.026

Treatment of a solid mixture of KBH₄ with six equivalents of 3,5-diisopropylpyrazole (iPr₂pzH) at 180 °C afforded KTp ^iPr2(iPr₂PzH)₃ in 53% yield. KBp^iPr2 was synthesized in 56% yield by treatment of a 1:2 M ratio of KBH₄ and iPr₂PzH in refluxing dimethylacetamide. Treatment of MI₂ (M = Ca, Sr, Ba) with two equivalents of KBp or KBp^iPr2 in tetrahydrofuran afforded MBp₂(THF)₂ (M = Ca, 64%, M = Sr, 81%), BaBp ₂(THF)₄ (32%), and M(Bp^iPr2) ₂(THF)₂ (M = Ca, 63%; M = Sr, 61%, M = Ba, 48%) as colorless crystalline solids upon workup. These complexes were characterized by spectral and analytical techniques and by X-ray crystal structure determinations of all complexes except KBp^iPr2. KTp^{i Pr2}(iPr₂PzH)₃ contains one κ³- N,N,N-Tp^iPr2 ligand and three κ¹-iPr ₂pzH ligands, with overall distorted octahedral geometry about the K ion. The iPr₂PzH nitrogen-hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen atoms of the Tp ^iPr2 ligand. The solid state structures of MBp ₂(THF)₂, BaBp₂(THF)₄, and M(Bp ^iPr2)₂(THF)₂ contain κ³-N,N,H Bp and Bp^iPr2 ligands, which form through metal-nitrogen bond formation to the 2-nitrogen atoms of the pyrazolyl fragments and metal-hydrogen bond formation to one boron-bound hydrogen atom per Bp ligand. SrBp₂(THF)₂has the shortest metal-hydrogen interactions among the series. A combination of preparative sublimations, solid state decomposition temperatures, and thermogravimetric analysis demonstrated that MBp₂(THF)₂, BaBp ₂(THF)₄, and M(Bp^iPr2) ₂(THF)₂ undergo solid state decomposition at moderate temperatures.

Full text of DOI:10.1016/j.poly.2011.02.026

Polyhedron 30 (2011) 1330–1338
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structural characterization, and properties of heavier
alkaline earth complexes containing bis(pyrazolyl)borate or
bis(3,5-diisopropylpyrazolyl)borate ligands
⇑
Mark J. Saly, Mary Jane Heeg, Charles H. Winter
Department of Chemistry, Wayne State University, Detroit, MI 48202, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Treatment of a solid mixture of KBH4 with six equivalents of 3,5-diisopropylpyrazole (iPr2pzH) at 180 °C
afforded KTpiPr2(iPr2PzH)3 in 53% yield. KBpiPr2 was synthesized in 56% yield by treatment of a 1:2 M ratio
of KBH4 and iPr2PzH in refluxing dimethylacetamide. Treatment of MI2 (M = Ca, Sr, Ba) with two equiv-
alents of KBp or KBpiPr2 in tetrahydrofuran afforded MBp2(THF)2 (M = Ca, 64%, M = Sr, 81%), BaBp2(THF)4
(32%), and M(BpiPr2)2(THF)2 (M = Ca, 63%; M = Sr, 61%, M = Ba, 48%) as colorless crystalline solids upon
workup. These complexes were characterized by spectral and analytical techniques and by X-ray crystal
Received 29 January 2011
Accepted 15 February 2011
Available online 26 February 2011
Keywords:
Group 2 elements
Calcium
Strontium
Barium
structure determinations of all complexes except KBpiPr2. KTpiPr2(iPr2PzH)3 contains one
j
3-N,N,N-TpiPr2
ligand and three
j
1-iPr2pzH ligands, with overall distorted octahedral geometry about the K ion. The
iPr2PzH nitrogen–hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen
atoms of the TpiPr2 ligand. The solid state structures of MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2
Potassium
Bis(pyrazolyl)borate ligands
contain
j
3-N,N,H Bp and BpiPr2 ligands, which form through metal–nitrogen bond formation to the
2-nitrogen atoms of the pyrazolyl fragments and metal–hydrogen bond formation to one boron-bound
hydrogen atom per Bp ligand. SrBp2(THF)2has the shortest metal–hydrogen interactions among the
series. A combination of preparative sublimations, solid state decomposition temperatures, and thermo-
gravimetric analysis demonstrated that MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2 undergo solid
state decomposition at moderate temperatures.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
group 2 precursors containing Tp-based ligands is their low vapor
pressures; temperatures of P200 °C at 0.05 Torr are required to ef-
We recently reported the synthesis, structure, and thermal
stability of a series of calcium, strontium, and barium complexes
containing tris(pyrazolyl)borate (Tp) ligands and 3,5-dialkyl-
substituted analogs [1], and also described the use of BaTp2Et2
(TpEt2 = tris(3,5-diethylpyrazolyl)borate) and CaTp2 as precursors
for the atomic layer deposition (ALD) growth of BaB2O4 and CaB2O4
films, respectively, with water as the oxygen source [2]. Significant
findings from these reports included documentation of the very
high thermal stabilities of the complexes (decomposition temper-
atures >400 °C for optimized calcium and strontium complexes,
ꢀ380 °C for optimized barium complexes), the first reports of
metal borate film growth by ALD, and demonstration that the 2:1
boron to metal stoichiometries in BaTpE2t2 and CaTp2 are main-
fect sublimation and vapor transport in an ALD reactor [1,2]. ALD
precursors must be thermally stable at the film growth tempera-
ture, to avoid loss of the self-limited growth mechanism through
precursor decomposition [3]. To reduce molecular weight, increase
volatility, and hopefully retain high thermal stability observed in
the Tp-based precursors, we sought to explore the synthesis and
thermal stabilities of group 2 complexes containing bis(pyrazol-
yl)borate (Bp) ligands and 3,5-disubstituted analogs (BpR2). There
have been few reports of group 2 complexes that contain Bp-based
ligands. Examples include MBpM2 e2(THF) (BpMe2 = bis(3,5-
dimethylpyrazolyl)borate, M = Ca, Sr, Ba), MBpt2Bu(THF) (Bpt Bu
=
bis(3-tert-butylpyrazolyl)borate, M = Ca, Sr, Ba), and BaTpMe2BpMe2
(TpMe2 = tris(3,5-dimethylpyrazoly)borate) [4]. Sohrin carried out
ion extraction studies of the group 2 ions using Bp ligands, and
found that significant extraction did not occur for Ca2+, Sr2+, or
tained in the MB2O4 films. A drawback of BaTpEt2, CaTp2, and other
2
Ba2+ [5]. The solid state structures of MgBp(THF)(
l-Cl)2MgBp-
(THF)2, MgBp2(THF), and MgBp2(THF)2 have been described [6].
⇑
We have recently reported the synthesis, structure, and
Corresponding author. Tel.: +1 313 577 5224; fax: +1 313 577 8289.
E-mail address: chw@chem.wayne.edu (C.H. Winter).
properties of M(BptBu2
)
(M = Ca, Sr, Ba) and Ba(BptBu2)2(THF)
2
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.02.026

M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
1331
(BptBu2 = bis(3,5-di-tert-butylpyrazolyl)borate, and noted that ex-
R
R
THF, 18 h
treme distortions of the BptBu2 ligands are present within the coor-
dination spheres due to intraligand and interligand tert-butyl steric
crowding [7].
23 oC, -2 KI
N
N
R
R
MI2
2
+
N
N
K
H
R
B
H
Herein, we report the synthesis, structure, and properties of a
series of calcium, strontium, and barium complexes containing
Bp and BpiPr2 ligands. These complexes also incorporate
tetrahydrofuran ligands. In addition, attempted synthesis of the
key starting material KBpiPr2 by a literature method instead
R
O
R
N
x
N
R
R
H
B
H
N
N
M
N
N
B
H
ð3Þ
afforded the structurally novel complex KTpiPr2(iPr2pzH)3 (TpiPr2
=
R
H
N
N
tris(3,5-diisopropylpyrazolyl)borate; iPr2pzH = 3,5-diisopropylpy-
razole). An alternate procedure for the synthesis of KBpiPr2 is
reported.
R
R
3, M = Ca, R = H, x = 2, 64%
4
, M = Sr, R = H, x = 2, 81%
5, M = Ba, R = H, x = 4, 32%
6, M = Ca, R = iPr, x = 2, 63%
2. Results and discussion
7
, M = Sr, R = iPr, x = 2, 61%
8, M = Ba, R = iPr, x = 2, 48%
2.1. Synthetic aspects
KBp was prepared in 72% yield using a literature procedure,
which entailed thermolysis of a 1:2 M ratio mixture of solid
KBH4 and pyrazole at 120 °C [8]. A previously reported synthesis
of KBpiPr2 (1) relied upon heating a solid mixture of KBH4 and
iPr2PzH in a 1:2 stoichiometry at 120 °C, followed by crystalliza-
tion from hexane [9]. However, multiple attempts to reproduce
this synthesis instead afforded KTpiPr2(iPr2PzH)3 (2). Optimiza-
tion involved conducting the thermolysis at 180 °C with a 1:6
stoichiometry of KBH4 and iPr2PzH, which afforded colorless
crystals of 2 in 53% yield (Eq. (1)). For comparison, KTpiPr2 was
previously synthesized by heating a 1:3 M ratio of solid KBH4
and iPr2PzH at 260 °C, followed by crystallization from pentane
[10]. In the present work, 1 was synthesized in 56% yield by
treatment of a 1:2 M ratio of KBH4 and iPr2PzH in refluxing
dimethylacetamide (DMAC), as described in Section 4 (Eq. (2)).
Complexes 1 and 2 are very soluble in tetrahydrofuran and
toluene.
The compositions of 1–8 were assessed by spectral and analyt-
ical data, and by X-ray crystal structure determinations for 2–8. In
the 1H NMR spectra of 1 and 6–8, the 4-H atoms of the iPr2pz
groups were observed at d 5.78 and 5.76, respectively. Additional
resonances belonging to the magnetically inequivalent isopropyl
groups were observed. The 1H NMR spectra for 6–8 also contained
resonances corresponding to two tetrahyrofuran ligands centered
at d 3.61 and 1.79, respectively. Similar to 1 and 6–8, the 1H
NMR spectra for 2 showed the 4-H atom resonance of the TpiPr2 li-
gand at d 5.70, as well as the resonances from the magnetically
inequivalent isopropyl groups. The three iPr2pzH ligands in 2
showed the 4-H atom resonance at d 5.84 and the methine and
methyl resonances of the isopropyl groups at d 2.60 and 1.21,
respectively. A broad N-bound H atom resonance appeared at d
9.98. Broad B-bound H atom resonances for 1 and 2 were centered
at d 3.45 and 4.90, respectively. The B-bound H atom resonances
were not clearly observed in the 1H NMR spectra of 6–8, because
the signals were too broad and overlapped with the downfield iso-
propyl methine and tetrahydrofuran 2-H atom resonances. The 1H
NMR spectra for 3–5 contained three resonances belonging to the
three different protons from the pyrazolyl ring of the Bp ligand,
with the 4-H atom resonance observed at about d 6.0. All of the ex-
pected C atom resonances were observed in the 13C{1H} NMR spec-
tra for 1–5, 7, and 8. However, the 13C{1H} NMR spectrum for 6
only showed one C atom resonance at 25.79 ppm corresponding
to the isopropyl methyl groups, instead of the expected two reso-
nances. The methyl C atom resonances appear to overlap, which
is supported by the inequivalent methyl proton resonances ob-
served in the 1H NMR spectrum of 6. In the infrared spectra of 1
and 3–8, the B–H stretches are observed in the range of 2248–
2448 cmꢁ1. The C–N stretching frequencies are observed between
1492–1502 cmꢁ1 and 1527–1532 cmꢁ1 for 3–5 and 1 and 6–8,
respectively. The shift to higher wavenumbers for the C–N
stretches in 1 and 6–8 appears to arise from the isopropyl substit-
uents on the pyrazolyl groups, compared to H atoms in 3–5. The
infrared spectrum of 2 showed a B–H stretch at 2469 cmꢁ1, which
is consistent with one B–H bond. Two C–N stretches in 2 were ob-
served at 1529 and 1565 cmꢁ1, and correspond to the B-bound
iPr2pz moieties and the iPr2pzH ligands in 2. Furthermore, two
N–H stretches at 3261 and 3358 cmꢁ1 were observed, which arise
from the iPr2pzH ligands.
180 o
C
-3 H2
iPr
iPr
KBH4
+
6
N
N
iPr
H
N
iPr
iPr
iPr
HN
N
iPr
N
iPr
ð1Þ
H
N
N
iPr
K
N
N
B
H
N
N
iPr
iPr
NH iPr
iPr
N
iPr
2, 53%
DMAC, 120 o
C
-2 H2
iPr
iPr
KBH4
+
2
N
N
H
iPr
iPr
iPr
ð2Þ
N
N
iPr
K
N
N
H
B
H
1, 56%
Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of KBp or
1 yielded 3–8 as colorless crystalline solids upon workup (Eq. (3)).
Complexes 3 and 4 are very soluble in tetrahydrofuran and diethyl
ether and are moderately soluble in hexane. By contrast, 5 is insol-
uble in hexane and diethyl ether, but is soluble in tetrahydrofuran.
Complexes 6–8 are soluble in hexane, and their solubilities
increase in the order 6 < 7 < 8.
2.2. Structural aspects
The X-ray crystal structures of 2–8 were determined to estab-
lish the geometry about the metal centers and the bonding modes
of the Bp and BpiPr2 ligands. Experimental crystallographic data are

1332
M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
Table 2
summarized in Table 1, selected bond lengths and angles are given
in Tables 2–5, and perspective views are presented in Figs. 1–5.
Complexes 7 and 8 are isostructural with 6, and are not discussed
specifically herein, but have been deposited with the Cambridge
Crystallographic Structural Database.
Selected atomic distances (Å) and angles (°) for 2.
K–N(1)
K–N(3)
K–N(5)
K–N(7)
K–N(8)
K–N(9)
K–N(10)
K–N(11)
2.795(2)
2.823(2)
2.913(2)
3.466(3)
2.780(3)
2.833(2)
3.396(2)
3.453(3)
2.781(3)
2.48(3)
A perspective view of 2 is shown in Fig. 1. The complex contains
one j j
3-N,N,NTpiPr2 ligand and three 1-iPr2pzH ligands, with over-
all distorted octahedral geometry about the K ion. The K–N bond
distances associated with the TpiPr2 ligand are 2.795(2), 2.823(2),
and 2.913(2) Å, compared to very similar values of 2.782(3),
2.784(3), and 2.832(3) Å for the iPr2pzH ligands. The average K–N
bond distance found in 2 (2.82(5) Å) is similar to the related values
K–N(12)
N(1)–H(N7)
N(3)–H(N10)
N(5)–H(N11)
K–N(1)–N(2)
K–N(3)–N(4)
K–N(5)–N(6)
B–N(2)–N(1)
B–N(4)–N(3)
B–N(6)–N(5)
N(2)–B–N(4)
N(2)–B–N(6)
N(4)–B–N(6)
2.17(4)
2.26(3)
in KTptBu2 (K–Navg = 2.73(2) Å) [11a], KTpPic,Me(H2O)2 (Pic = 5-
a-
115.89(16)
114.80(15)
111.51(15)
121.1(2)
121.7(2)
121.5(2)
111.0(2)
110.3(2)
109.2(2)
picolyl, K–Navg = 2.9(1) Å) [12], KTp3Py,Me(H2O) (3Py = 3-pyridyl,
K–Navg = 2.90(8) Å) [12], and KTpR,H (R = 2-methoxy-1,1-dimethyl-
ethyl, K–Navg = 2.692(2) Å) [13]. The N-bound H atom of each
iPr2pzH ligand is directed toward the 2-N atoms of the TpiPr2 li-
gand, suggesting the presence of weak intramolecular N–Hꢂ ꢂ ꢂN
hydrogen bonds. The pyrazolyl 2-Nꢂ ꢂ ꢂH distances are 2.48(3) (to
N(1)), 2.17(4) (to N(3)), and 2.26(3) Å (to N(5)). The sum of the
van der Waals radii for N and H atoms is 2.75 Å [14], so these inter-
actions are consistent with hydrogen bonds. Further evidence of
hydrogen bonding comes from broad N–H bond stretches in the
infrared spectrum of 2 at 3261 and 3358 cmꢁ1. A sharp band at
3374 cmꢁ1 was previously reported to arise from a non-hydrogen
bonded N–H stretch in a iPr2pzH adduct [12]. The structure of 2
is similar to that of [PbTpMe2(Me2pzH)3]Cl, which contains one
Table 3
Selected atomic distances (Å) and angles (°) for 3 and 4.
3
4
M–O(1)
M–O(2)
M–N(1)
2.381(2)
2.394(2)
2.451(2)
2.567(4)
2.560(4)
2.624(5)
2.641(5)
2.634(5)
2.676(5)
111.7(4)
110.8(4)
109.6(4)
108.7(4)
120.2(5)
120.2(5)
119.8(5)
120.1(6)
108.9(5)
109.4(6)
81.51(14)
j
3-TpMe2 ligand and three Me2pzH ligands arrayed in a distorted
M–N(3)
M–N(5)
M–N(7)
2.491(2)
2.443(2)
2.477(2)
114.76(14)
114.38(15)
118.64(15)
117.47(15)
119.26(19)
118.82(19)
119.3(2)
octahedral geometry [15]. Unlike the hydrogen bonding in 2, the
three N-bound H atoms of the Me2pzH ligands in [PbTpMe2(-
Me2pzH)3]Cl form hydrogen bonds to the chloride counterion,
M–N(1)–N(2)
M–N(3)–N(4)
M–N(5)–N(6)
M–N(7)–N(8)
B(1)–N(2)–N(1)
B(1)–N(4)–N(3)
B(2)–N(6)–N(5)
B(2)–N(8)–N(7)
N(2)–B(1)–N(4)
N(6)–B(2)–N(8)
O(1)–M–O(2)
apparently due to its higher basicity compared to the TpMe2
N
atoms that are bonded to the Pb2+ ion. In 2, the 2-N atoms of the
TpiPr2 ligand are the most basic within the molecule, and it is not
surprising that these N atoms act as hydrogen bond acceptors.
The molecular structures of 3–5 are similar and their perspec-
tive views are shown in Figs. 2–4. Complexes 3 and 4 crystallize
as monomeric complexes containing two Bp and two tetrahydrofu-
ran ligands, with a coordination number of eight. By contrast, 5
contains two Bp and four tetrahydrofuran ligands, affording a coor-
119.4(2)
109.2(2)
109.2(2)
79.34(6)
dination number of ten. In 3–5, the Bp ligands adopt the j
3-N,N,H
coordination mode, through M–N bond formation to the 2-N atoms
3–5 have Mꢂ ꢂ ꢂH–B distances of 2.77(2) and 3.01(3) Å, 2.59(6) and
2.73(4) Å, and 3.23(3) and 3.33(2) Å, respectively. The sum of van
der Waals radii for Ca + H, Sr + H, and Ba + H are 3.51, 3.69, and
of the pyrazolyl fragments and M–H bond formation to one
B-bound H atom per Bp ligand. j
3-N,N,H coordination of Bp ligands
is commonly observed in many metal complexes [16]. Complexes
Table 1
Crystal data and data collection parameters for 2–6.
2
3
4
5
6
7
8
Formula
Formula weight
Space group
C
54H94BKN12
C20H32B2CaN8O2
478.24
P21/c
C20H32B2N8O2Sr
525.78
P21/n
C28H48B2BaN8O4
719.70
P21/c
C44H80B2CaN8O2
814.86
P2/c
C44H80B2N8O2Sr
862.40
P2/c
C44H80BaB2N8O2
912.12
P2/c
961.32
P1
ꢀ
a (Å)
b (Å)
c (Å)
a
13.4823(4)
14.4362(4)
15.0315(4)
89.916(2)
88.740(2)
88.405(2)
2923.79(14)
2
8.1820(3)
32.1359(13)
9.6550(4)
11.5239(11)
14.3932(14)
16.1877(17)
10.0475(3)
18.4400(5)
18.6347(5)
9.0091(6)
12.5037(7)
22.2896(14)
9.0253(4)
12.5252(6)
22.6409(10)
8.9791(5)
12.5148(7)
22.8178(13)
b
c
97.639(2)
108.581(7)
99.0340(10)
99.030(4)
99.414(3)
97.585(3)
V (Å3)
Z
2516.42(17)
4
2545.0(4)
4
3409.73(17)
4
2479.7(3)
2
2524.9(2)
2
2541.6(2)
2
T (K)
k (Å)
100(2)
0.71073
1.092
0.135
9.02
100(2)
0.71073
1.262
0.282
5.89
100(2)
0.71073
1.372
2.151
9.02
100(2)
0.71073
1.402
1.209
2.85
100(2)
0.71073
1.091
0.168
6.64
100(2)
0.71073
1.134
1.108
6.94
100(2)
0.71073
1.192
0.822
4.83
qcalc (g cmꢁ3
)
l
(mmꢁ1
R (F) (%)
Rw (F) (%)
)
20.36
13.22
14.86
6.85
12.22
13.15
11.55
w(Fo ꢁ Fc2)2/
R r(I).
w(Fo2)2]1/2 for I > 2
2
R (F) =
R
||Fo| ꢁ |Fc||/
R
|Fo|; Rw (F) = [
R

M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
1333
Table 4
Selected atomic distances (Å) and angles (°) for 5.
Ba–O(1)
2.791(1)
Ba–O(2)
Ba–O(3)
Ba–O(4)
Ba–N(1)
Ba–N(3)
Ba–N(5)
Ba–N(7)
Ba–N(1)–N(2)
Ba–N(3)–N(4)
Ba–N(5)–N(6)
Ba–N(7)–N(8)
B(1)–N(2)–N(1)
B(1)–N(4)–N(3)
B(2)–N(6)–N(5)
B(2)–N(8)–N(7)
N(2)–B(1)–N(4)
N(6)–B(2)–N(8)
O(1)–Ba–O(2)
O(1)–Ba–O(3)
O(1)–Ba–O(4)
O(2)–Ba–O(3)
O(2)–Ba–O(4)
O(3)–Ba–O(4)
2.788(1)
2.824(1)
2.919(1)
2.902(2)
2.852(2)
2.886(2)
2.862(2)
118.34(1)
120.82(1)
115.86(1)
115.64(1)
121.16(2)
120.66(2)
121.77(2)
121.45(2)
109.91(2)
110.68(2)
139.28(4)
142.61(4)
72.77(4)
72.94(4)
147.42(4)
80.34(4)
Fig. 2. Perspective view of 3 with thermal ellipsoids at the 50% probability level.
Table 5
Selected atomic distances (Å) and angles (°) for 6.
3.88 Å, respectively [14]. As such, strong M–H interactions are
present in 3–5. The average Ca–N bond distance in 3 is 2.47(2) Å,
which is similar to those in CaTp2 (avg = 2.44(2) Å) [4], CaTp2Me2
(avg = 2.454(2) Å) [4], and CaTpE2t2 (avg = 2.459(6) Å) [1]. The aver-
age Sr–N distance in 4 (2.64(2) Å) is slightly longer than those in
SrTp2 (avg = 2.593(19) Å) and SrTpE2t2 (avg = 2.606(9) Å) [1]. The
average Ba–N distance in 5 is 2.88(2) Å, which again is longer than
those in Tp-based complexes such as BaTpM2 e2 (avg = 2.754(3) Å,
2.760(1) Å) [4,17] and BaTp2Et2 (avg = 2.78(2) Å) [1]. The slightly
longer M–N distances in 3–5, compared to related Tp complexes,
is likely related to the higher coordination numbers in the former,
which arise through tetrahydrofuran coordination and M–H bond
formation. The M–O distances in 3 and 4 are 2.387(7) and
2.564(4) Å, respectively. The Ba–O bond lengths in 5 range from
2.788(1) to 2.919(1) Å, with an average of 2.83(6) Å. The average
N–B–N bond angles in 3–5 are 109.2(2)°, 109.2(3)°, and
110.3(4)°, respectively, indicating tetrahedral geometry about the
boron atoms.
Ca–O(1)
2.431(2)
Ca–N(1)
2.478(2)
Ca–N(3)
2.562(2)
Ca–N(1)–N(2)
Ca–N(3)–N(4)
B–N(2)–N(1)
B–N(4)–N(3)
N(2)–B–N(4)
O(1)–Ca–O(1)0
118.22(13)
110.48(12)
117.55(18)
119.25(17)
110.9(2)
149.28(8)
A perspective view of 6 is shown in Fig. 5. Complex 6 is eight
coordinate, and contains two j
3-N,N,H-BpiPr2 and two tetrahydro-
furan ligands. The Ca–H distance in 6 (2.95(2) Å) is similar to the
values in 3 (2.77(2), 3.01(3) Å), but is considerably longer than
the related distances in CaTpt2Bu (2.47(2) Å) [18] and Ca(C5H2(Si-
Me3)3)(HBEt3)(THF)2 (2.21(4) Å) [19]. The Ca–H interactions in 3,
6, and previously reported borohydride complexes are electro-
static, and the Ca–H distances appear to be determined by steric
interactions about the Ca ion. In 3 and 6, the coordination spheres
are crowded with tetrahydrofuran ligands, which do not permit
enough space for shorter Ca–H bonds. The Ca–N distances in 6
are 2.478(2) and 2.562(2) Å, respectively, with a Ca–O distance of
2.431(2) Å and a N–B–N bond angle of 110.9(2)°. The longer Ca–
N distances in 6 versus 3 are likely related to the larger steric pro-
file of the BpiPr2 ligand compared to the Bp ligand. The B–N–N–Ca
torsion angles in 6 are 4.4(2) (B–N(2)–N(1)–Ca) and 31.8(2)°
(B–N(4)–N(3)–Ca), which are larger than those of 3 due to the
higher steric congestion about the Ca ion arising from the isopropyl
groups in 6.
In 3 and 5, the two M–H interactions are anti with respect to
each other within each molecule, whereas 4 contains syn Sr–H
units within each molecule. Such an arrangement in 4 also requires
Fig. 1. Perspective view of 2 with thermal ellipsoids at the 50% probability level.
The isopropyl groups have been removed for clarity.

1334
M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
Fig. 3. Perspective view of 4 with thermal ellipsoids at the 50% probability level.
Fig. 4. Perspective view of 5 with thermal ellipsoids at the 50% probability level.
cis-coordination of the tetrahydrofuran ligands. A Cambridge Crys-
tallographic Database search of compounds containing Bp-based
ligands revealed no previous examples of syn M–H units such as
those found in 4. The most common orientation for Bp-based li-
gands is with the Mꢂ ꢂ ꢂH–B and pyrazolyl moieties anti to each
other [6,20–23]. Divalent transition metal Bp complexes of the
formula MBp2 contain j
3-N,N,H Bp ligands where the coordinated
H atoms are 90° from one another in the equatorial plane [24,25].
Complexes 3, 5–8, MgBp2(THF) [6], MBptBu2 (M = Sr, Ba) [7],
2
MBpt2Bu2(THF) [7], Y(Bp)3 [21], and U(BpMe2
) [22] all contain anti
3
Bp and BpMe2 ligand conformations within the metal coordination
spheres, further illustrating the structural novelty of 4.

M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
1335
Fig. 5. Perspective view of 6 with thermal ellipsoids at the 50% probability level.
Table 6 contains structural data for 3–5, MgBp2(THF) [6],
122
120
118
116
114
112
110
108
MBp2tBu2 (M = Sr, Ba) [7], and BaBpt2Bu2(THF) [7] associated with
the Mꢂ ꢂ ꢂH–B interactions. To allow direct comparison of the
Mꢂ ꢂ ꢂH–B interactions, the M–H bond lengths were normalized to
the ionic size of Ca2+ by subtracting or adding the difference be-
tween the M2+ and Ca2+ ionic radii to the Mꢂ ꢂ ꢂH–B distance of
the other group 2 ions. The data reveal that the Srꢂ ꢂ ꢂH–B interac-
tions in 4 are the shortest among 3–5, with Srꢂ ꢂ ꢂH0–B distances
of 2.59(6) and 2.73(4) Å. Stabilization of the syn conformation of
4 is probably a result of the ionic size, tetrahydrofuran ligand
arrangement, and formation of stronger Srꢂ ꢂ ꢂH–B interactions off-
setting the slight increase in energy upon eclipsing the pyrazolyl
moieties. The six membered B–(NN)2–M chelate rings in 3–8 form
boat conformations, due to the M–H bond formation. Depending
on the strength of the Mꢂ ꢂ ꢂH–B interaction, the boat can be shallow
or deep. A plot of the Mꢂ ꢂ ꢂH0–B distances versus the average B–N–N
and M–N–N angles is shown in Fig. 6. The plot indicates that the B–
N–N angles vary little as a function of the Mꢂ ꢂ ꢂH0–B distances,
whereas the M–N–N bond angles change significantly with respect
y = 0.916x + 117.4
y = 16.09x + 70.49
B-N-N(avg) angle
M-N-N(avg) angle
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
M
H'-B Distance (Å)
Fig. 6. Plot of Mꢂ ꢂ ꢂH0–B distances (Å) versus average B–N–N and M–N–N angles (°).
to the Mꢂ ꢂ ꢂH0–B distance. Hence, the M–N bonds act as hinges for
the M–H interactions, and thus the extent of the M–H interactions
and depth of the boat are directly related to the M–N–N angles.
Such flexibility of the M–N–N angles is facilitated by the non-
directional, ionic M–N bonds.
Table 6
Selected metrical data for 3–5 and MgBp2(THF).
Complex
Mꢂ ꢂ ꢂH–B
Mꢂ ꢂ ꢂH0–Ba
B–N–Navg
(°)
M–N–Navg
(°)
(Å)
(Å)
The present study allows us to compare the structural distor-
tions of the Bp and BpiPr2 ligands in 3–6 with those that occur in
MBp2tBu2 (M = Sr, Ba) and BaBpt2Bu2(THF) [7]. In our previous paper
describing Sr and Ba complexes containing BptBu2 ligands [7], the
B–N–N–M torsion angles ranged from 20.0° to 60.9°, which are lar-
ger than the corresponding values found in MgBp2(THF) [6], Y(Bp)3
MgBp2(THF) [6]
2.69
2.97
118.6
115.80(7)
114.91
Sr(BptBu2
)
[7]
2.56(1)
2.59(1)
2.66(2)
2.71(2)
2.83(2)
2.89(2)
2.77(2)
3.01(3)
2.73(4)
2.59(6)
3.33(2)
3.23(3)
2.39(1)
2.41(1)
2.31(2)
2.36(2)
2.48(2)
2.54(2)
2.77(2)
3.01(3)
2.55(4)
2.41(6)
2.98(2)
2.88(3)
2
Ba(BptBu2
)
[7]
116.28(12)
115.9(2)
2
Ba(BptBu2)2(THF)
[7]
3
[21], and U(BpMe2
) [22]. The B–N–N–M torsion angles in 3 (0.72–
3
119.0(2)
119.35(5)
120.2(0)
120.0(2)
120.9(3)
121.6(2)
114.6(2)
118.1(6)
111.3(5)
109.2(5)
120(1)
8.62°) and 4 (2.39–7.37°) imply low steric congestion about the
metal ions. The corresponding values in 5 are larger (0.20–
20.02°) and suggest more steric congestion, consistent with the
higher coordination number in 5 compared to 3 and 4. The B–N–
4
5
115.8(1)
N–Ca torsion angles in
6 are 4.4(2) (B–N(2)–N(1)–Ca) and
a
Values are normalized to the ionic size of Ca2+ by subtracting or adding the
31.8(2)° (B–N(4)–N(3)–Ca), which are larger than those of 3–5
due to the higher steric congestion about the Ca ion arising from
difference between the M2+ and Ca2+ ionic radii to the Mꢂ ꢂ ꢂH–B distance.

1336
M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
the isopropyl groups in 6. The B–N–N–M torsion angles found in 3–
6 (0.2–31.8°) are in the same range as those found in TlBptBu2 (20.8,
from sodium benzophenone ketyl. Hexane was distilled from P2O5.
KBp [8]7 and iPr2pzH [10] were synthesized according to literature
procedures. All other starting materials were purchased from Acros
or Aldrich Chemical Company and were used as received.
1H and 13C{1H} NMR spectra were obtained at 400, 300, 125, or
75 MHz in methylene chloride-d2, benzene-d6, or acetone-d6. Infra-
red spectra were obtained using Nujol as the medium. Elemental
analyses were performed by Midwest Microlab, Indianapolis,
Indiana. Melting points were obtained on an Electrothermal Model
9200 melting point apparatus and are uncorrected. TGA was con-
ducted on a Perkin–Elmer Pyris 1 TGA system between 50 and
550 °C, using nitrogen as the flow gas with a heating rate of
10 °C/min.
23.7°) [11b], and U(BpMe2
) (17.6–21.3°) [23], and are much smal-
3
ler than the values found in MBpt2Bu2 (M = Sr, Ba) and BaBp2tBu2(THF)
[7]. Accordingly, the increased steric congestion upon coordination
of tetrahydrofuran in 3–6 does not lead to large distortions of the
Bp or BpiPr2 ligand bonding to the metal ions. B–N–N–M torsion an-
gles have been proposed as a measure of the sterically-induced
twisting of the pyrazoyl moieties in Tp-based ligands [7,11]. The
B–N–N–K torsion angles in 2 range from 40.7(3)° to 44.4(3)°
(avg = 42(2)°), which are nearly double the corresponding torsion
angles found in KTptBu2(C6H6) (avg = 23.4°), TlBptBu2 (avg = 22.8°),
and CsTptBu2 (avg = 24.4°) [11a]. The larger torsion angles in 2,
compared to complexes containing the TptBu2 ligand, are caused
by the extreme steric crowding that arises upon coordinating one
TpiPr2 and three iPr2pzH ligands to the K ion.
4.2. Preparation of KBpiPr2 (1)
A
100-mL round-bottomed flask was charged with KBH4
(0.794 g, 14.72 mmol), iPr2pzH (5.000 g, 32.42 mmol), anhydrous
DMAC (50 mL), and a stir bar. The mixture was slowly heated in
an oil bath to 120 °C, while carefully monitoring hydrogen evolu-
tion. Once gas evolution ceased (ꢀ670 mL), the oil bath was re-
moved and the reaction mixture was allowed to cool to ambient
temperature. The DMAC was then removed under reduced pres-
sure. The resulting crude mixture was then heated to ꢀ130 °C
and the excess iPr2pzH was distilled at 0.05 Torr. The product
was washed with cold hexane (30 mL) and was isolated by vacuum
filtration. To remove any unreacted KBH4, the solid was further dis-
solved in methylene chloride (25 mL) and the solution was filtered
through a medium glass filter frit. The methylene chloride was re-
moved under reduced pressure to afford 1 as a white powder
(2.913 g, 56%). The analytical sample was obtained by crystalliza-
tion of 0.250 g of 1 from toluene (20 mL) at ꢁ23 °C: mp 168–
2.3. Evaluation of thermal stability and volatility
Complexes 3–8 were studied by preparative sublimations and
solid state decomposition temperature determinations to assess
their volatilities and thermal stabilities. Preparative sublimations
of 3–8 between 160 and 220 °C at 0.05 Torr led to the vapor trans-
port of complex mixtures of compounds, among which pyrazole
(from 3 to 5) or 3,5-diisopropylpyrazole (from 6 to 8) were identi-
fied by 1H NMR spectroscopy. The yields of sublimed materials
were low, suggesting extensive decomposition prior to sublimation
upon heating in the sublimation tube. The melting points for 3, 4,
and 6–8 are 116, 121, 113, 168, and 167 °C, respectively. Upon
melting, the liquid compounds exhibited gas evolution, which
most likely corresponds to loss of the tetrahydrofuran ligands.
After melting, 3, 4, and 6–8 remained colorless liquids until reach-
ing temperatures between 330 and 360 °C, over which range the
clear melts underwent rapid darkening (3, 360 °C; 4, 330 °C; 6,
340 °C; 7, 350 °C; 8, 348 °C). Complex 5 melts at a higher temper-
ature than the others (281 °C), and likewise shows gas evolution
upon reaching the liquid state. The clear, colorless melt of 5 turned
black rapidly at 330 °C, indicating thermal decomposition.
169 °C; IR (Nujol, cmꢁ1 C–N = 1526; 1H NMR
) mB–H = 2248–2438, m
(CD2Cl2, 23 °C, d) 5.78 (s, 2H, 4-CH), 3.45 (broad s, 2H, BH2,), 3.21
(septet, J = 6.8 Hz, 2H, CH(CH3)2), 2.80 (septet, J = 6.8 Hz, 2H,
CH(CH3)2), 1.11 (d, J = 6.6 Hz, 12H, CH(CH3)2), 1.07 (d, J = 6.9 Hz,
12H, CH(CH3)2); 13C{1H} NMR (CD2Cl2, 23 °C, ppm) 158.95 (s, Cq),
155.97 (s, Cq), 96.96 (s, 4-CH), 28.32 (s, CH(CH3)2), 26.42 (s,
CH(CH3)2), 23.61 (s, CH(CH3)2), 23.48 (s, CH(CH3)2); (Anal. Calc.
for C18H32BKN4 requires: C, 61.01; H, 9.10; N, 15.81. Found: C,
61.02; H, 8.97; N, 15.53%).
3. Conclusions
We have prepared the novel potassium complex 2 upon treat-
ment of KBH4 with six equivalents of iPr2pzH. The solid state struc-
ture of 2 exhibits large distortions of the TpiPr2 ligand due to
accommodation of the sterically demanding isopropyl groups
within the coordination sphere. An improved synthesis of 1 was
also developed. Treatment of KBp or 1 with MI2 (M = Ca, Sr, Ba)
in tetrahydrofuran afforded 3–8. The crystal structures of 3–8
4.3. Preparation of KTpiPr2(HPziPr2
) (2)
3
A 50-mL round-bottomed flask was charged with KBH4 (0.112 g,
2.080 mmol), iPr2pzH (2.000 g, 13.137 mmol), and a stir bar. The
flask was then heated at 180 °C in an oil bath for 18 h, at which
point gas evolution had ceased and the melt was a clear viscous li-
quid. The reaction mixture was cooled to room temperature, the
resultant solid was dissolved in hexane (20 mL), and the solution
was filtered through a 2-cm pad of Celite on a medium glass frit.
The clear filtrate was set aside in an Erlenmeyer flask and slow
evaporation at room temperature afforded colorless crystals of 2
showed j
3-N,N,H-coordination of the Bp and BpiPr2 ligands as well
as coordination of two (2–4, 6–8) or four (5) tetrahydrofuran li-
gands. Examination of the B–N–N–M torsion angles demonstrated
that distortions of the Bp and BpiPr2 ligand bonding to the metal
ions are smaller than those observed in the previously reported
complexes MBpt2Bu2 (M = Sr, Ba) and BaBpt2Bu2(THF) [7], thus indicat-
ing that tetrahydrofuran coordination does not drastically increase
the steric crowding in the coordination spheres of these com-
plexes. Complexes 3–6 decompose in the solid state upon heating
to afford complex mixtures of products, and are not volatile.
(1.068 g, 53%): mp 147–149 °C; IR (Nujol, cmꢁ1
) mN–H = 3261,
3358, B–H = 2469,
m
m
C–N = 1565, 1529; 1H NMR (CD2Cl2, 23 °C, d)
9.98 (b, 3H, NH), 5.84 (s, 3H, CH), 5.79 (s, 3H, 4-CH), 4.90 (broad
s, 1H, BH), 3.19 (septet, J = 6.9 Hz, 3H, CH(CH3)2), 2.87 (septet,
J = 6.9 Hz, 6H, CH(CH3)2), 2.60 (septet, J = 6.8 Hz, 3H, CH(CH3)2),
1.21 (d, J = 6.4 Hz, 36H, CH(CH3)2), 1.03 (d, J = 6.4 Hz, 18H,
CH(CH3)2), 0.99 (d, J = 7.2 Hz, 18H, CH(CH3)2); 13C{1H} NMR (tolu-
ene-d8, 23 °C, ppm) 159.33 (s, Cq), 155.66 (s, Cq), 154.40 (broad s,
2Cq), 97.87 (s, 4-CH), 97.02 (s, 4-CH), 27.93 (s, CH(CH3)2), 27.30
(broad s, CH(CH3)2), 26.71 (s, CH(CH3)2), 23.67 (s, CH(CH3)2),
23.43 (s, CH(CH3)2), 23.02 (s, CH(CH3)2); (Anal. Calc. for
4. Experimental
4.1. General considerations
All reactions were performed under argon using either standard
glovebox or Schlenk line techniques. Tetrahydrofuran was distilled
C
54H94B2KN12 requires: C, 67.46; H, 9.78; N, 17.49. Found: C,
67.64; H, 9.81; N, 17.76%).

M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
1337
4.4. Preparation of CaBp2(THF)2 (3)
100-mL Schlenk flask was charged with CaI2 (0.200 g,
cmꢁ1
)
mB–H = 2285–2432,
m
C–N = 1527; 1H NMR (CD2Cl2, 23 °C, d),
5.76 (s, 4H, 4-CH), 3.63 (m, 8H, CH2CH2O), 3.38 (septet, J = 6.8 Hz,
8H, CH(CH3)2), 2.42 (septet, J = 6.8 Hz, 8H, CH(CH3)2), 1.79 (m,
8H, CH2CH2O), 1.18 (d, J = 6.6 Hz, 24H, CH(CH3)2), 0.94 (d,
J = 7.5 Hz, 24H, CH(CH3)2); 13C{1H} NMR (CD2Cl2, 23 °C, ppm)
159.76 (s, Cq), 155.99 (s, Cq), 96.68 (s, 4-CH), 68.62 (s, CH2CH2O),
27.62 (s, CH(CH3)2), 26.42 (s, CH(CH3)2), 25.79 (s, CH2CH2O),
23.54 (s, 2 overlapping CH(CH3)2); (Anal. Calc. for C44H80B2CaN8O2
requires: C, 64.85; H, 9.90; N, 13.75. Found: C, 64.46; H, 9.93; N,
13.96%).
A
0.680 mmol), KBp (0.253 g, 1.360 mmol), and a stir bar. Tetrahy-
drofuran (30 mL) was added, resulting in the immediate formation
of a white precipitate of KI. The reaction mixture was stirred for
18 h, at which point the volatile components were removed under
reduced pressure to afford a white residue. Hexane (30 mL) was
added to extract the product. The resulting solution was filtered
through a 3-cm pad of Celite on a medium glass frit to yield a clear
filtrate, which was placed in a ꢁ23 °C freezer for 24 h. Decanting of
the solvent with a fine cannula, followed by vacuum drying at
ambient temperature for 1 h, afforded colorless crystals of 3
4.8. Preparation of SrBpi2Pr2(THF)2 (7)
(0.804 g, 64%): mp 115–116 °C; IR (Nujol, cmꢁ1
)
m
B–H = 2263–
In a fashion similar to the preparation of 4, treatment of SrI2
(0.201 g, 0.589 mmol) with KBpiPr2 (0.415 g, 1.17 mmol) afforded
7 as a white solid (0.310 g, 61%). The analytical sample and single
crystals for the X-ray crystallographic analysis were obtained by
crystallization from hexane at ꢁ23 °C: mp 167–168 °C; IR (Nujol,
2415,
m
C–N = 1500; 1H NMR (CD2Cl2, 23 °C, d) 7.59 (d, J = 1.8 Hz,
4H, CH), 7.41 (d, J = 1.8 Hz, 4H, CH), 6.13 (t, J = 1.8 Hz, 4H, CH),
3.71 (b, 4H, BH2), 3.69 (m, 8H, CH2CH2O), 1.80 (m, 8H, CH2CH2O);
13C{1H} NMR (CD2Cl2, 23 °C, ppm) 139.82 (s, CH), 135.54 (s, CH),
104.29 (s, 4-CH), 69.03 (s, CH2CH2O), 25.69 (s, CH2CH2O); (Anal.
Calc. for C20H32B2CaN8O2 requires: C, 50.23; H, 6.74; N, 23.43.
Found: C, 50.58; H, 6.69; N, 23.67%).
cmꢁ1 C–N = 1532; 1H NMR (CD2Cl2, 23 °C, d),
) mB–H = 2279–2429, m
5.76 (s, 4H, 4-CH), 3.57 (m, 8H, CH2CH2O), 3.38 (septet, J = 6.9 Hz,
8H, CH(CH3)2), 3.38 (septet, J = 7.0 Hz, 8H, CH(CH3)2), 1.78 (m,
8H, CH2CH2O), 1.16 (d, J = 6.4 Hz, 24H, CH(CH3)2), 1.03 (d,
J = 7.2 Hz, 24H, CH(CH3)2); 13C{1H} NMR (CD2Cl2, 23 °C, ppm)
159.44 (s, Cq), 156.02 (s, Cq), 96.33 (s, 4-CH), 68.51 (s, CH2CH2O),
28.15 (s, CH(CH3)2), 26.40 (s, CH(CH3)2), 25.75 (s, CH2CH2O),
23.75 (s, CH(CH3)2), 23.57 (s, CH(CH3)2); (Anal. Calc. for
4.5. Preparation of SrBp2(THF)2 (4)
In a fashion similar to the preparation of 3, treatment of SrI2
(0.207 g, 0.606 mmol) with KBp (0.218 g, 1.172 mmol) afforded 4
as a white powder (0.250 g, 81%). The analytical sample and single
crystals for the X-ray crystallographic analysis were obtained by
crystallization from hexane at ꢁ23 °C: mp 118–121 °C; IR (Nujol,
C44H80B2N8O2Sr requires: C, 61.28; H, 9.35; N, 12.99. Found: C,
61.30; H, 9.36; N, 12.95%).
cmꢁ1
)
mB–H = 2264–2416,
m
C–N = 1502; 1H NMR (CD2Cl2, 23 °C, d)
4.9. Preparation of BaBpi2Pr2(THF)2 (8)
7.57 (d, J = 2.4 Hz, 4H, CH), 7.46 (d, J = 1.8 Hz, 4H, CH), 6.14 (t,
J = 1.8 Hz, 4H, 4-CH), 3.69 (m, 8H, CH2CH2O), 3.61 (broad s, 2H,
BH2), 1.78 (m, 8H, CH2CH2O); 13C{1H} NMR (CD2Cl2, 23 °C, ppm)
139.62 (s, CH), 135.44 (s, CH), 104.30 (s, 4-CH), 68.83 (s, CH2CH2O),
25.66 (s, CH2CH2O); (Anal. Calc. for C20H32B2N8O2Sr requires: C,
45.68; H, 6.13; N, 21.32. Found: C, 45.84; H, 6.09; N, 21.49%).
In a fashion similar to the preparation of 4, treatment of BaI2
(0.204 g, 0.522 mmol) with KBpiPr2 (0.363 g, 1.02 mmol) afforded
8 as a white solid (0.205 g, 48%). The analytical sample and single
crystals for the X-ray crystallographic analysis were obtained by
crystallization from hexane at ꢁ23 °C: mp 165–167 °C; IR (Nujol,
cmꢁ1 C–N = 1530; 1H NMR (CD2Cl2, 23 °C, d),
) mB–H = 2274–2426, m
4.6. Preparation of BaBp2(THF)4 (5)
5.76 (s, 4H, 4-CH), 3.61 (m, 8H, CH2CH2O), 3.36 (septet, J = 6.6 Hz,
8H, CH(CH3)2), 2.66 (septet, J = 6.6 Hz, 8H, CH(CH3)2), 1.79 (m,
8H, CH2CH2O), 1.15 (d, J = 6.6 Hz, 24H, CH(CH3)2), 1.03 (d,
J = 6.6 Hz, 24H, CH(CH3)2); 13C{1H} NMR (CD2Cl2, 23 °C, ppm)
159.28 (s, Cq), 156.12 (s, Cq), 96.48 (s, 4-CH), 68.32 (s, CH2CH2O),
28.14 (s, CH(CH3)2), 26.31 (s, CH(CH3)2), 25.78 (s, CH2CH2O),
23.83 (s, CH(CH3)2), 23.58 (s, CH(CH3)2); (Anal. Calc. for
A
100-mL Schlenk flask was charged with BaI2 (0.257 g,
0.657 mmol), KBp (0.245 g, 1.317 mmol), and a stir bar. Tetrahy-
drofuran (30 mL) was added, resulting in the immediate formation
of a white precipitate of KI. The reaction mixture was stirred for
18 h, then the resulting mixture was filtered through a 3-cm pad
of Celite on a medium glass frit to yield a clear filtrate. The filtrate
was reduced in volume to about 10 mL, and the solution was place
in a ꢁ23 °C freezer for 24 h. Decanting of the solvent with a fine
cannula, followed by vacuum drying at ambient temperature for
1 h, afforded colorless crystals of 5 (0.150 g, 32%): mp 280–
C44H80B2BaN8O2 requires: C, 57.94; H, 8.84; N, 12.29. Found: C,
58.09; H, 8.61; N, 12.40%).
4.10. X-ray crystallographic structure determinations of 2–8
282 °C; IR (Nujol, cmꢁ1
)
m
B–H = 2253–2448,
m
C–N = 1492; 1H NMR
Diffraction data were measured on a Bruker X8 APEX-II kappa
geometry diffractometer with Mo radiation and a graphite mono-
chromator. Frames were collected at 100 K with the detector at
40 mm and 0.3° between each frame, and were recorded for 10 s
(acetone-d6, 23 °C, d) 7.44 (d, J = 1.6 Hz, 8H, CH), 7.28 (d,
J = 1.6 Hz, 8H, CH), 5.95 (t, J = 2.0 Hz, 4H, 4-CH), 4.07 (broad s,
J = 4H, BH2), 3.61 (m, 16H, CH2CH2O), 1.78 (m, 16H, CH2CH2O);
13C{1H} NMR (acetone-d6, 23 °C, ppm) 139.24 (s, CH), 134.82 (s,
CH), 103.36 (s, 4-CH), 68.03 (s, CH2CH2–O), 26.12 (s, CH2CH2–O);
(0.5 equivalents of tetrahydrofuran was lost due to its lability at
room temperature. Anal. Calc. for C26H44B2BaN8O3.5 requires: C,
45.65; H, 6.49; N, 16.40. Found: C, 45.73; H, 6.39; N, 16.58%).
unless otherwise noted. APEX-II [26] and SHELX [27] software were
used in the collection and refinement of the models. Crystals of 2
appeared as colorless thin fragments. About 97116 reflections were
measured, yielding 17717 unique data (Rint = 0.121). Hydrogen
atoms were placed in observed or calculated positions. Three sets
of pendant isopropyl groups were described with positional disor-
der at C35, C36, C41, C42, and C54 and were refined using partial
occupancy sites and held isotropic. Complex 3 crystallized as color-
less rods. 48358 hkl data points were harvested, which averaged to
6392 data (Rint = 0.079). Hydrogen atoms were calculated or ob-
served. The C–C bonds in the two disordered tetrahydrofuran li-
gands were held fixed at 1.54 Å and partial occupancies were
assigned for C14, C15, C18, C19, and C20, which were kept isotropic
4.7. Preparation of CaBpi2Pr2(THF)2 (6)
In a fashion similar to the preparation of 4, treatment of CaI2
(0.205 g, 0.698 mmol) with KBpiPr2 (0.483 g, 1.362 mmol) afforded
6 as a white solid (0.352 g, 63%). The analytical sample and single
crystals for the X-ray crystallographic analysis were obtained by
crystallization from hexane at ꢁ23 °C: mp 112–113 °C; IR (Nujol,

1338
M.J. Saly et al. / Polyhedron 30 (2011) 1330–1338
during refinement. Crystals of 4 were obtained as colorless plates.
68843 reflections were counted, which averaged to 12155 inde-
pendent data (Rint = 0.22). Hydrogen atoms were placed at calcu-
lated or observed positions. Statistically, this is a poor structure
due to crystal quality, but certainly the overall connectivity of
the complex is correct. Crystals of 5 were colorless fragments.
89094 total data were measured, averaging to 9799 unique data
(Rint = 0.043). Hydrogen atoms were placed in observed or calcu-
lated positions. One of the tetrahydrofuran ligands was disordered
in a 55/45 ratio at one carbon (C22). Complex 6 crystallized as col-
orless plates and yielded 72788 total data, of which 6198 were
independent (Rint = 0.064). Hydrogen atom positions were either
calculated or observed. The central Ca ion occupies a 2-fold rota-
tion axis. Complex 7 produced crystalline colorless triangular
plates. 56905 data were recorded to merge into 6299 data
(Rint = 0.134). Hydrogen atoms were placed in calculated or ob-
served positions. The crystal diffracted poorly, which required a
48 h collection time (30 s frames). There are typical large thermal
parameters for parts of the isopropyl groups and the tetrahydrofu-
ran ligands. The Sr ion occupies a crystallographic 2-fold rotation
axis. Complex 8 is isostructural with 6 (vide supra). Crystals were
colorless flat rods. 88165 data were integrated to net 9664 inde-
pendent data. Hydrogen atoms were placed in calculated and ob-
served positions. There was significant disorder and partial
occupancies were assigned for atoms C4, C5, C6, C13, C14, C15,
C19, C22, and O1. These atoms were held isotropic during refine-
ment. The Ba ion occupies a crystallographic 2-fold rotation axis.
Lowering the space group symmetry did not resolve the disorder.
References
[1] M.J. Saly, M.J. Heeg, C.H. Winter, Inorg. Chem. 48 (2009) 5303.
[2] (a) M.J. Saly, F. Munnik, R.J. Baird, C.H. Winter, Chem. Mater. 21 (2009) 3742;
(b) M.J. Saly, F. Munnik, C.H. Winter, J. Mater. Chem. 20 (2010) 9995.
[3] (a) M. Leskelä, M. Ritala, Angew. Chem., Int. Ed. 42 (2003) 5548;
(b) L. Niinistö, J. Päiväsaari, J. Niinistö, M. Putkonen, M. Nieminen, Phys. Stat.
Sol. A 201 (2004) 1443;
(c) M. Putkonen, L. Niinistö, Top. Organomet. Chem. 9 (2005) 125;
(d) R.L. Puurunen, J. Appl. Phys. 97 (2005) 121301;
(e) S.M. George, Chem. Rev. 110 (2010) 111.
[4] T.R. Belderraín, L. Contreras, M. Paneque, E. Carmona, A. Monge, C. Ruiz,
Polyhedron 15 (1996) 3453.
[5] (a) H. Kokusen, Y. Sohrin, S. Kihara, M. Matsui, Anal. Sci. 7 (1991) 7;
(b) N. Yasuda, H. Kokusen, Y. Sohrin, S. Kihara, M. Matsui, Bull. Chem. Soc. Jpn.
65 (1992) 781;
(c) Y. Sohrin, H. Kokusen, S. Kihara, M. Matsui, Y. Kushi, M. Shiro, J. Am. Chem.
Soc. 115 (1993) 4128.
[6] D.J. Loroño-Gonzalez, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 64
(2008) m229.
[7] M.J. Saly, C.H. Winter, Organometallics 29 (2010) 5472.
[8] S. Trofimenko, J. Am. Chem. Soc. 89 (1967) 3170.
[9] L. Maria, Â. Domingos, I. Santos, Inorg. Chem. Commun. 6 (2003) 58.
[10] N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Moro-oka, S. Hashimoto, T. Kitagawa,
K. Toriumi, K. Tatsumi, A. Nakamura, J. Am. Chem. Soc. 114 (1992)
1277.
[11] (a) C.M. Dowling, D. Leslie, M.H. Chisholm, G. Parkin, Main Group Chem. 1
(1995) 29;
(b) C. Dowling, P. Ghosh, G. Parkin, Polyhedron 16 (1997) 3469.
[12] K. Weis, H. Vahrenkamp, Inorg. Chem. 36 (1997) 5589.
[13] (a) M.H. Chisholm, J.C. Gallucci, G. Yaman, Chem. Commun. (2006) 1872;
(b) M.H. Chisholm, J.C. Gallucci, G. Yaman, Inorg. Chem. 46 (2007) 8676.
[14] (a) A. Bondi, J. Phys. Chem. 68 (1964) 441;
(b) M. Mantina, A.C. Chamberlin, S. Valero, C.J. Cramer, D.G. Truhlar, J. Phys.
Chem. A 113 (2009) 5806.
[15] D.L. Reger, Y. Ding, A.L. Rheingold, R.L. Ostrander, Inorg. Chem. 33 (1994)
4226.
[16] (a) S. Trofimenko, Chem. Rev. 93 (1993) 943;
(b) S. Trofimenko, Scorpionates
–
The Coordination Chemistry of
Acknowledgement
Polypyrazolylborate Ligands, Imperial College Press, London, 1999.
[17] S.G. Dutremez, D.B. Leslie, W.E. Streib, M.H. Chisolm, K.G. Caulton, J.
Organomet. Chem. 462 (1993) C1.
[18] S. Harder, J. Brettar, Angew. Chem., Int. Ed. 45 (2006) 3474.
[19] M.J. Harvey, T.P. Hanusa, M. Pink, Chem. Commun. (2000) 489.
[20] P. Capporto, F. Mani, C. Mealli, Inorg. Chem. 17 (1978) 1232.
[21] D.L. Reger, J.A. Lindeman, L. Lebioda, Inorg. Chem. 27 (1988) 1890.
[22] A. Carvalho, Â. Domingos, P. Gaspar, N. Marques, A. Pires De Matos, I. Santos,
Polyhedron 11 (1992) 1481.
[23] L. Maria, Â. Domingos, I. Santos, Inorg. Chem. 42 (2003) 3323.
[24] H.V.R. Dias, J.D. Gordan, Inorg. Chem. 35 (1996) 318.
[25] (a) L.J. Guggenberger, C.T. Prewitt, P. Meakin, S. Trofimenko, J.P. Jesson, Inorg.
Chem. 12 (1973) 508;
We thank the Army Research Office (grant no. W911NF-07-01-
0489) for generous support of this research.
Appendix A. Supplementary data
CCDC 783233, 783234, 783235, 783236, 783237, 783238, and
783239 contains the supplementary crystallographic data for
2–8. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
(b) D.L. Reger, T.D. Wright, M.D. Smith, A.L. Rheingold, B. Rhagitan, J. Chem.
Crystallogr. 30 (2000) 665.
[26] APEX II Collection and Processing Programs are Distributed by the Manufacturer,
Bruker AXS Inc., Madison WI, USA, 2009.
[27] G.M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 64 (2008) 112.