Lewis acid catalyzed synthesis of poly(pyrazolyl)borate ligands

Article abstract of DOI:10.1021/om100590x

Lewis acids catalyze the reaction of Li[MeBH₃] and Na[BH ₄] with pyrazoles to yield poly(pyrazolyl)borates under mild conditions. The reaction of Li[MeBH₃] with 2 equiv of 3-mesitylpyrazole (Hpz^Ms) at 23 °C (2 d

Full text of DOI:10.1021/om100590x

Organometallics 2010, 29, 3679–3682 3679
DOI: 10.1021/om100590x
Lewis Acid Catalyzed Synthesis of Poly(pyrazolyl)borate Ligands
Changle Chen and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois, 60637
Received June 16, 2010
Scheme 1a
Summary: Lewis acids catalyze the reaction of Li[MeBH3]
and Na[BH4] with pyrazoles to yield poly(pyrazolyl)borates
under mild conditions. The reaction of Li[MeBH3] with 2 equiv
of 3-mesitylpyrazole (HpzMs) at 23 °C (2 days) affords Li-
[MeB(3-mesityl-pz)2H] (Li[MeBpMs]) and Li[MeB(3-mesityl-
pz)(5-mesityl-pz)H] (Li[MeBpMs*]) in 88% yield (3:1 isomer
ratio) in the presence of MeB(OiPr)2 (5 mol % vs HpzMs) but
only 28% yield without this additive. Similar enhancements in
the yield of Li[MeBpR] products are observed in the reaction of
Li[MeBH3] with 3-tBu-pyrazole, 3,5-Me2-pyrazole (Hpz*),
and 3,5-tBu2-pyrazole. The reaction of Li[MeBH3] with 3
equiv of HpzMs (THF, 60 °C, 2 days) in the presence of
3 mol % MeB(OiPr)2 affords Li[MeB(3-Ms-pz)3] (75%),
but only Li[MeBpMs] and Li[MeBpMs*] without this additive.
Similar results were observed for the reaction of Li[MeBH3]
with 3-CF3-pyrazole. The reaction of Na[BH4] and 3 equiv of
Hpz* (THF, 60 °C, 4 h) yields Na[B(3,5-Me2-pz)2H2] in 93%
yield in the presence of BF3 Et2O (5 mol % vs Hpz*) but only
3
a Ms = mesityl.
5% without this additive. Coordination of the pyrazole to the
Lewis acid is expected to decrease the pKa of the pyrazole and
increase the rate of B-H bond protonolysis.
pyrazole derivatives.3 Here we report that Lewis acids cata-
lyze the reaction in eq 1, which enables poly(pyrazolyl)-
borates to be prepared under mild conditions.
Results and Discussion
Introduction
MeB(OiPr)2-Catalyzed Synthesis of Methyl-bis(pyrazolyl)-
borates. In the course of studying group 4 metal poly-
(pyrazolyl)borate chemistry, we prepared the methyl-
Poly(pyrazolyl)borate ligands have found wide applica-
tion in coordination chemistry.1 The most general route to
these ligands, developed by Trofimenko, is the hydrogen
elimination reaction of pyrazoles (Hpzx) with BH4- (eq 1).2
This reaction can be controlled to yield mono-, bis-, tris-, and
tetrakis(pyrazolyl)borates.
bis(pyrazolyl)borate salts Li[MeBpMs] and Li[MeBpMs*
]
([MeBpMs]-=MeB(3-mesityl-pz)2H-, [MeBpMs*]-=MeB-
(3-mesityl-pz)(5-mesityl-pz)H-) by the reaction of Li[MeBH3]
with 2 equiv of 3-mesitylpyrazole (HpzMs), as shown in
Scheme 1.4 Surprisingly, we observed that the yield of Li-
[MeBpMs] and Li[MeBpMs*] varied significantly between
experiments. Careful studies showed that the variation in
yield was due to the presence or absence of MeB(OiPr)2, a
contaminant from the synthesis of Li[MeBH3] (Scheme 1).
NMR monitoring experiments showed that the reaction of
Li[MeBH3] with HpzMs to generate a 2:1 mixture of Li[MeB-
(3-Ms-pz)H2] and Li[MeB(5-Ms-pz)H2] (Ms = mesityl) is
complete within 4 h at 23 °C in THF. The subsequent
reaction of these species with the second equivalent of HpzMs
-
-
BH4 þ nHpzx f H4 - nBðpzxÞn þ nH2
ð1Þ
n ¼ 1 - 4
For the synthesis of bis-, tris-, and tetrakis(pyrazolyl)-
borates, the Trofimenko synthesis often requires an excess
of the pyrazole as well as elevated temperatures that necessi-
tate the use of high boiling solvents. In some cases, the
isolation of the product is difficult due to the need to remove
the excess pyrazole and solvent. Furthermore, the high
reaction temperatures preclude the use of thermally sensitive
to generate a 2.3:1 mixture of Li[MeBpMs] and Li[MeBpMs*
]
at 23 °C is accelerated by the presence of MeB(OiPr)2.5 For
example, addition of 5 mol % (vs HpzMs) of MeB(OiPr)2
increases the rate of this step by a factor of ca. 5.6 The
reaction of Li[MeBH3] with 2 equiv of HpzMs on a gram scale
*To whom correspondence should be addressed. E-mail: rfjordan@
uchicago.edu.
(1) (a) Trofimenko, S. Polyhedron 2004, 23, 197. (b) Trofimenko, S.
Scorpionates: The Coordination Chemistry of Polypyrazolylborate Li-
gands; Imperial College Press: London, 1999. (c) Pettinari, C. Scorpionates
II: Chelating Borate Ligands; Imperial College Press: London, 2008.
(2) (a) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288. (b) Trofimenko,
S. Inorg. Chem. 1970, 11, 2493. (c) Trofimenko, S.; Calabrese, J. C.;
Thompson, J. S. Inorg. Chem. 1987, 26, 1507.
(3) (a) Janiak, C.; Esser, L. Z. Naturforsch., B 1993, 48, 394. (b) Janiak,
C.; Scharmann, T. G.; Guenther, W.; Girgsdies, F.; Hemling, H.; Hinrichs, W.;
Lentz, D. Chem.-Eur. J. 1995, 9, 637.
(4) (a) Chen, C.; Lee, H.; Jordan, R. F. Organometallics 2010, ASAP
(DOI: 10.1021/om1004034). (b) The formation and interconversion of
isomers in Scheme 1 is due to 1,2-borotropic shifts, which are common in
these systems, as discussed in ref 1.
(5) The isomer ratio varies with temperature but is not influenced by
the presence of MeB(OiPr)2 or other Lewis acids.
r
2010 American Chemical Society
Published on Web 07/22/2010
pubs.acs.org/Organometallics

3680 Organometallics, Vol. 29, No. 16, 2010
Chen and Jordan
Table 1. Influence of MeB(OiPr)2 (5 mol %, vs pyrazole) on the
Generation of Li[MeBpx] by the Reaction of Li[MeBH3] with
2 equiv of 3-R-pyrazole or 3,5-R2-pyrazole at 23 °C in THF
(2 days)a
Table 3. Influence of Lewis Acids (5 mol % vs Hpz*) on the
Generation of Na[Bp*] by the Reaction of Na[BH4] and 3 equiv of
Hpz* (eq 3) at 60 °C in THF (4 h)a
conversion to
Na[Bp*] (%)
conversion to Li[MeBpx]
in the presence of 5 mol %
MeB(OiPr)2 (%)
conversion to Li[MeBpx]
in the absence of
Lewis acid
none
ZnCl2
5
5
pyrazole
MeB(OiPr)2 (%)
HpzMs
HpztBu
Hpz*
88
95
80
82b
28
50
16
20b
MgCl2
5
MeB(OiPr)2
Cu(CF3SO3)2
B(C6F5)3
19
52
55
93b
HpztBu2
BF3 Et2O
3
a [pyrazole]initial = 0.51 M. b Reaction performed at 60 °C.
a [Hpz*]initial = 0.51 M. b 5% of Na[Tp*] is also formed.
and 3 equiv of HpzMs for 2 days.7
Table 2. Influence of MeB(OiPr)2 (3 mol % vs pyrazole) on the
Generation of Li[MeTpx] by the Reaction of Li[MeBH3] and
3 equiv of 3-R-pyrazole at 60 °C in THF (2 days)a
Li½MeBH3ꢀ þ 3Hpzx f Li½MeTpxꢀ þ 3H2
Lewis Acid Catalyzed Formation of Na[Bp*] ([Bp*]-
ð2Þ
conversion to Li[MeTpx]
in the presence of 3 mol %
MeB(OiPr)2 (%)
conversion to Li[MeTpx]
in the absence of
=
3-R-pyrazole
MeB(OiPr)2 (%)
H2B(3,5-dimethylpyrazolyl)2-). The reaction of Na[BH4]
with Hpz* (3,5-Me2-pyrazole) at 60 °C in THF to generate
Na[Bp*] was used as a test reaction to explore the effective-
ness of other Lewis acids as catalysts for the formation of
bis(pyrazolyl)borates (eq 3). As summarized in Table 3, a
variety of Lewis acids catalyze this reaction. BF3 is the most
effective catalyst among those tested and improves the yield
of Na[Bp*] from 5% (uncatalyzed) to 93%. No Na[Tp*]
([Tp*]- = HB(3,5-dimethylpyrazolyl)3-) or other bypro-
ducts were observed in these reactions except for the case of
HpzMs
75
67
0b
0c
HpzCF3
a [pyrazole]initial = 0.76 M. b The product is predominantly Li[MeBpMs
and Li[MeBpMs*]. c The product is predominantly Li[MeBpCF3] and
Li[MeBpCF3*] ([MeBpCF3 - = MeB(3-CF3-pz)2H-, [MeBpCF3* -
MeB(3-CF3-pz)(5-CF3-pz)H-).
]
]
] =
in THF at 23 °C for 3 days with 3 mol % of MeB(OiPr)2
followed by reaction with TlOAc affords Tl[MeBpMs] in
76% isolated yield. For comparison, we synthesized Tl-
[MeBpMs] in 73% yield by the same reaction at 60 °C
(3 days) in the absence of a Lewis acid.4a
BF3 Et2O, in which case a small amount (5%) of Na[Tp*] is
3
formed. ZnCl2 and MgCl2 are ineffective as catalysts under
these conditions, probably due to their insolubility in the
reaction medium. For comparison, K[Bp*] was previously
prepared by refluxing a mixture of K[BH4] with Hpz*
(3 equiv) in dimethylacetamide (bp 165 °C).2a
The catalytic effect of MeB(OiPr)2 on the reaction of
Li[MeBH3] with pyrazoles (2 equiv) to generate Li[MeBpx]
compounds is general (Table 1). For the reaction of Li-
[MeBH3] with 2 equiv of the 3-subsituted pyrazoles HpzMs
and 3-tBu-pyrazole (HpztBu), the conversion to Li[MeBpx] is
increased by 2-3 times in the presence of 5 mol % MeB-
(OiPr)2. For the 3,5-disubstituted pyrazoles 3,5-Me2-pyra-
zole (Hpz*) and 3,5-tBu2-pyrazole (HpztBu2), the conversion
to Li[MeBpx] is increased by 4-5 times by 5 mol % MeB-
(OiPr)2.
MeB(OiPr)2-Catalyzed Synthesis of Methyl-tris(pyrazolyl)-
borates. MeB(OiPr)2 also catalyzes the formation of methyl-
tris(pyrazolyl)borates (MeTpx) (eq 2, Table 2). The reaction
of Li[MeBH3] with 3 equiv of HpzMs or 3-CF3-pyrazole
(HpzCF3) in THF at 60 °C for 2 days in the presence of
MeB(OiPr)2 (3 mol % vs pyrazole) affords the corresponding
Li[MeTpx] products with good conversion. In contrast, in
the absence of MeB(OiPr)2, only Li[MeBpx] products are
formed under these conditions. The reaction of Li[MeBH3]
with 3 equiv of HpzMs on a gram scale in THF at 60 °C for
3 days with 3 mol % of MeB(OiPr)2 followed by reaction
with TlOAc affords Tl[MeTpMs] in 89% isolated yield. For
comparison, Dias synthesized Tl[MeTpMs] in 75% yield by
refluxing a mesitylene solution (bp =165 °C) of Li[MeBH3]
Lewis Acid Catalyzed Formation of Li[MeTpMs] ([Me-
TpMs - = MeB(3-mesitylpyrazolyl)3-). The reaction of Li-
]
[MeBH3] with 3 equiv of HpzMs at 60 °C in THF to generate
Li[MeTpMs] was used as a test reaction to explore the
effectiveness of other Lewis acids in catalyzing the formation
of tris(pyrazolyl)borates (Scheme 1). In the absence of Lewis
acid, no Li[MeTpMs] is formed under these conditions; after
3 days only Li[MeBpMs] and Li[MeBpMs*] (3:1 mixture,
100%)5 along with 1 equiv of unreacted HpzMs were ob-
served. In contrast, in the presence of MeB(OiPr)2 (3 mol %
vs HpzMs), Li[MeTpMs] is formed in 93% yield after 3 days.
The use of stronger boron Lewis acids results in lower yields
of Li[MeTpMs]. The reaction with 3 mol % of B(C6F5)3 for
3 days generates a mixture of Li[MeTpMs] (35%) and Li-
[MeBpMs]/Li[MeBpMs*] (57%, 3:1 ratio). The 1H NMR
spectrum of the reaction mixture showed that unreacted
HpzMs was present. The 19F NMR spectrum contained
resonances for two new two -C6F5 species, but only trace
resonance for free B(C6F5)3. No further reactionwas observed
at longer times, presumably because the B(C6F5)3 is either
sequestered by coordination by the products or consumed by
some other side reaction. The reaction with 3 mol % of
(6) The kinetics of the MeB(OiPr)2-catalyzed and uncatalyzed reac-
tion of Li[MeB(3-Ms-pz)H2]/Li[MeB(5-Ms-pz)H2] with HpzMs were
compared assuming that Li[MeB(3-Ms-pz)H2] and Li[MeB(5-Ms-pz)
H2] react at the same rate. (The 2:1 ratio of these species remained
approximately constant during the reaction.) The rate law under this
assumption is Rate = k[HPzMs]{[Li[MeB(3-Ms-pz)H2]] + [Li[MeB(5-
Ms-pz)H2]]}. The estimated second-order rate constants are kcatalyzed
s
See the Supporting Information for details.
=
1.0 ꢁ 10-4 M-1 -1
; kuncatalyzed = 2.1 ꢁ 10-5 M-1 s-1 at 23 °C in THF.
(7) Dias, H. V. R.; Wang, X. Y. Polyhedron 2004, 23, 2533.
BF3 Et2O generates a 30%yieldof Li[MeBpMs]/Li[MeBpMs*
]
3

Note
Organometallics, Vol. 29, No. 16, 2010 3681
Table 4. Influence of Lewis Acids (3 mol % vs HpzMs) on the
purified N2 atmosphere. Nitrogen was purified by passage
through activated molecular sieves and Q-5 oxygen scavenger.
THF was distilled from sodium benzophenone ketyl. Na[BH4],
Generation of Li[MeTpMs] by the Reaction of Li[MeBH3] with
3 equiv of HpzMs at 60 °C in THFa
Cu(CF3SO3)2, BF3 Et2O, Hpz* (3,5-Me2-pyrazole), and HpzCF3
3
conversion to Li[MeTpMs
after 3 h (%)
]
conversion to Li[MeTpMs
after 3 days (%)
]
(3-CF3-pyrazole) were purchased from Aldrich and used as
received. B(C6F5)3 was obtained from Boulder Scientific and
sublimed twice before use. MeB(OiPr)2,15 Li[MeBH3],16 HpzMs
(3-mesitylpyrazole), HpztBu (3-tBu-pyrazole),17 and HpztBu2
(3,5-tBu2-pyrazole)18 were prepared by literature procedures.
NMR spectra were recorded on Bruker DMX-500 or DMX-400
spectrometers in Teflon-valved NMR tubes. 1H and 13C chemi-
cal shifts are reported versus SiMe4 and were determined by
reference to the solvent peaks. 11B chemical shifts are reported
Lewis acid
none
0b
16
30
30
0c
93
35
30
MeB(OiPr)2
B(C6F5)3
BF3 Et2O
3
a [HpzMs
]
initial = 0.76 M. b The product is Li[MeBpMs] and Li[MeBpMs*
]
(3:1 mixture, 90%) and Li[MeB(3-Ms-pz)H2] and Li[MeB(5-Ms-pz)H2] (3:1
mixture, 10%). c The product is Li[MeBpMs] and Li[MeBpMs*] (3:1 mixture,
100%).
relative to external BF3 Et2O. 19F chemical shifts are reported
3
relative to external CFCl3. Coupling constants are reported in
hertz.
(3:1 mixture) after 3 h, but no additional product is formed
after longer reaction times. NMR analysis showed that a
complex mixture of species is present.8 Thus the weak Lewis
acid MeB(OiPr)2 is the best catalyst for Scheme 1 among those
studied.
1H NMR Monitoring of Poly(pyrazolyl)borate Synthesis
Reactions. The following procedure for monitoring the genera-
tion of Li[MeBpMs] and Li[MeBpMs*] with 5 mol % MeB(OiPr)2
as catalyst is representative. An NMR tube was charged with Li
[MeBH3] (5.4 mg, 0.15 mmol), HpzMs (55.8 mg, 0.30 mmol), and
MeB(OiPr)2 (2.7 μL, 0.015 mmol). THF-d8 (0.5 mL) was added
by vacuum transfer at -78 °C. The NMR tube was agitated at
23 °C and monitored periodically by 1H NMR. The B-Me
resonances of the starting Li[MeBH3] and poly(pyrazolyl)bo-
rate products were monitored. For the generation of Na[Bp*],
the 4-pz 1H NMR resonances were monitored.
Reaction Mechanism. These results are consistent with a
mechanism involving Lewis acid catalyzed protonolysis of
B-H bonds, as shown for the formation of Li[MeBpMs] in
eq 4 (LA = Lewis acid). Coordination of the pyrazole to the
Lewis acid is expected to decrease the pKa of the pyrazole and
thus increase the rate of B-H protonolysis.9 MeB(OiPr)2 is
an effective catalyst because it does not bind strongly to the
(pyrazolyl)borate products and does not undergo side reac-
tions, at least for the cases studied here. Coordination of
Hpzx to MeB(OiPr)2 was not detected by NMR under the
synthetic conditions studied here. However, the coordina-
tion of Hpz* to BF3 to form the known (Hpz*)BF3 adduct
NMR and ESI-MS Data for Li[poly(pyrazolyl)borate] Salts
(THF-d8). Tl[MeTpMs],7 Tl[MeTptBu],7 and Li[MeTpCF3 19
] have
1
been characterized previously. H and 11B NMR and ESI-MS
data for the Li+ pyrazolylborate species studied here are listed
below. Broad B-H resonances in the region δ 4-6 are observed
for these species and are not listed here. Li[MeB(3-Ms-pz)H2]:
1H NMR: δ 7.25 (d, J = 2, 1H, pz), 6.75 (s, 2H, Ms), 5.76 (d, J =
2, 1H, pz), 2.09 (s, 3H, Me), 1.96 (s, 6H, Me), -0.52 (t, J = 8, 3H,
BCH3). 11B NMR: δ -14.4 (br). Li[MeB(5-Ms-pz)H2]: δ 7.43 (d,
J = 2, 1H, pz), 6.82 (s, 2H, Ms), 5.86 (d, J = 2, 1H, pz), 2.25 (s,
3H, Me), 2.04 (s, 6H, Me), -0.05 (t, J = 8, 3H, BCH3). 11B
1
under the conditions of eq 3 was confirmed by H and 19F
NMR.10,11
-
NMR: δ -9.1 (br). ESI-MS: Li[MeB(3-Ms-pz)H2]2 and Li
-
[MeB(5-Ms-pz)H2]2 calcd m/z = 433.3, found 433.2. Li
[MeBpMs]: δ 7.58 (d, J = 2, 2H, pz), 6.79 (s, 4H, Ms), 5.85 (d,
J = 2, 2H, pz), 2.22 (s, 6H, Me), 1.98 (s, 12H, Me), 0.46 (d, J = 5,
3H, BCH3). 11B NMR: δ -5.7 (br). Li[MeBpMs*]: δ 7.46 (d, J =
2, 1H, pz), 7.38 (d, J = 2, 1H, pz), 6.89 (s, 2H, Ms) 6.85 (s, 1H,
Ms), 6.83 (s, 1H, Ms), 5.85 (d, J = 2, 1H, pz), 5.83 (d, J = 2, 1H,
pz), 2.30 (s, 3H, Me), 2.28 (s, 3H, Me), 2.27 (s, 3H, Me), 2.07 (s,
3H, Me), 1.97 (s, 3H, Me), 1.82 (s, 3H, Me), -0.03 (d, J = 5, 3H,
BCH3). 11B NMR: δ -2.2 (br). ESI-MS: MeBpMs- and
MeBpMs*- calcd m/z = 397.3, found 397.2. Li[MeTpMs]: δ
7.80 (d, J = 2.1, 3H, pz), 6.76 (s, 6H, Ms), 5.91 (d, J = 2.1,
3H, pz), 2.20 (s, 9H, Me), 1.90 (s, 18H, Me), 1.14 (s, 3H, BCH3).
11B NMR: δ 0.6 (br). Li[MeB(3-tBu-pz)H2]: δ 7.33 (d, J = 2.0,
1H, pz), 6.00 (d, J = 2.0, 1H, pz), 1.28 (s, 9H, Me), -0.09 (t, J =
5.8, 3H, BCH3). Li[MeBptBu]: δ 7.32 (d, J = 2.0, 2H, pz), 5.86 (d,
J = 2.0, 2H, pz), 1.27 (s, 18H, Me), 0.27 (d, J = 5.0, 3H, BCH3).
11B NMR: δ -5.4 (br). Li[MeB(3,5-Me2-pz)H2]: δ 5.69 (s, 1H,
pz), 2.19 (s, 3H, Me), 2.11 (s, 3H, Me), -0.26 (t, J = 5.8, 3H,
BCH3). Li[MeBp*]: δ 5.52 (s, 2H, pz), 2.24 (s, 6H, Me), 2.09 (s,
6H, Me), -0.14 (d, J = 5.4, 3H, BCH3). Li[MeB(3,5-tBu2-pz)
Conclusion
Lewis acids catalyze the reaction of Li[MeBH3] and Na
[BH4] with pyrazoles to yield poly(pyrazolyl)borates under
mild conditions. This approach may be a useful complement
to the classic Trofimenko synthesis of poly(pyrazolyl)bo-
rates and other scorpionate ligands.12-14
Experimental Section
General Procedures. All manipulations were performed using
standard vacuum line, Schlenk, or glovebox techniques under a
(8) Li[MeBH3] reacts with BF3 rapidly under these conditions to
produce a mixture of species.
(9) (a) Johnson, C. R.; Henderson, W. W.; Shepherd, R. E. Inorg.
Chem. 1984, 23, 2754. (b) Evans, C. A.; Rabenstein, D. L.; Geier, G.; Erni,
I. W. J. Am. Chem. Soc. 1977, 99, 8106. (c) Johnson, C. R.; Shepherd, R. E.;
Marr, B.; Donnell, S. O.; Dressick, W. J. Am. Chem. Soc. 1980, 102, 6227.
(d) Hoq, M. F.; Shepherd, R. E. Inorg. Chem. 1984, 23, 1851. (e) Evans, E. J.
Chem. Educ. 2004, 81, 1191.
(15) Rheingold, A. L.; White, C. B.; Trofimenko, S. Inorg. Chem.
1993, 32, 3471.
(10) Komorowski, L.; Maringgele, W.; Meller, A.; Niedenzu, A.;
(16) Li[MeBH3] was synthesized by the procedure reported in Sin-
garam, B.; Cole, T. E.; Brown, H. C. Organometallics 1984, 3, 774, except
that the product was further purified by washing with CH2Cl2 and dried under
vacuum for at least 12 h. The extended vacuum drying ensures the removal of
MeB(OiPr2)2.
(17) Trofimenko, S. J.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem.
1987, 26, 1507.
Serwatowski, J. Inorg. Chem. 1990, 29, 3845.
(11) HOiPr has no effect on the formation of bis- and tris(pyrazolyl)
borate products in these reactions.
(12) Smith, J. M. Comments Inorg. Chem. 2008, 29, 189.
(13) Reglinski, J.; Spicer, M. D. Eur. J. Inorg. Chem. 2009, 12, 1553.
(14) Jernigan, F. E.; Sieracki, N. A.; Taylor, M. T.; Jenkins, A. S.;
ꢀ
Engel, S. E.; Rowe, B. W.; Jove, F. A.; Yap, G. P. A.; Papish, E. T.;
(18) Wang, Z. X.; Qin, H. L. Green Chem. 2004, 2, 90.
(19) Dias, H. V. R.; Wang, X. Dalton Trans. 2005, 2985.
Ferrence, G. M. Inorg. Chem. 2007, 46, 360.

3682 Organometallics, Vol. 29, No. 16, 2010
Chen and Jordan
H2]: δ 5.80 (s, 1H, pz), 1.49 (s, 9H, Me), 1.29 (s, 9H, Me), 0.01 (t,
J = 5.2, 3H, BCH3). Li[MeBptBu2]: δ 5.68 (s, 2H, pz), 1.38 (s,
18H, Me), 1.24 (s, 18H, Me), -0.20 (d, J = 5.5, 3H, BCH3). Li
[MeBpCF3]: δ 7.67 (br s, 2H, pz), 6.44 (d, J = 2, 2H, pz), 0.14 (d,
J = 5, 3H, BCH3). Li[MeBpCF3*]: δ 7.49 (br s, 1H, pz), 7.42 (br s,
1H, pz), 6.43 (d, J = 2, 1H, pz), 6.34 (d, J = 2, 1H, pz), 0.01 (d,
J = 5, 3H, BCH3). Li[MeTpCF3]: δ 7.71 (m, 3H, pz), 6.55 (m,
3H, pz), 0.97 (s, 3H, BCH3).
scopically identical to and behaves identically in the synthesis of
group 4 metal MeBpMs compounds as Tl[MeBpMs] made in the
absence of MeB(OiPr)2.
Tl[MeTpMs]. A mixture of Li[MeBH3] (0.37 g, 0.010 mol),
HpzMs (5.7 g, 0.031 mol), and MeB(OiPr)2 (0.18 mL, 0.0010 mol,
3 mol % vs HpzMs) in THF (50 mL) was stirred at 60 °C for 3
days. The mixture was allowed to cool to 23 °C. Tl(OAc) (2.7 g,
0.010 mmol) was added, and the mixture was stirred overnight at
23 °C. The mixture was filtered through Celite, and the colorless
filtrate was dried under vacuum to give a white solid. The solid
was washed with hexanes (3 ꢁ 10 mL) and dried under vacuum
to yield a white solid (7.22 g, 89%). This material is spectro-
scopically identical to Tl[MeTpMs] made in the absence of
MeB(OiPr)2.
Tl[MeBpMs]. A mixture of Li[MeBH3] (0.87 g, 0.024 mol),
HpzMs (9.0 g, 0.048 mol), and MeB(OiPr)2 (0.25 mL, 0.0014 mol,
3 mol % vs HpzMs) in THF (50 mL) was stirred at 23 °C for
3 days. The mixture was allowed to cool to 23 °C. Tl(OAc) (6.5 g,
0.024 mmol) was added, and the mixture was stirred for 3 days at
23 °C. The mixture was filtered through Celite, and the colorless
filtrate was dried under vacuum to give a white solid. The solid
was washed with hexanes (3 ꢁ 30 mL) and dried under vacuum
to yield a white solid (11.1 g, 76%). This material is spectro-
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.