Magnitudes of electron-withdrawing effects of the trifluoromethyl ligand in organometallic complexes of copper and nickel

Article abstract of DOI:10.1021/om901122z

A variety of nickel and copper complexes bearing the trifluoromethyl ligand have been prepared in order to quantify by electrochemical methods the redox potentials relative to their chloro and methyl counterparts. The effects of coordination number and geometry, as well as the oxidation state of the metal, on the relative ease with which trifluoromethyl complexes can be oxidized have for the first time been identified. In the d¹⁰ system [(NHC)Cu(X)] (NHC = N-heterocyclic carbene, X = methyl or trifluoromethyl), a single substitution of methyl for trifluoromethyl raised the oxidation potential of the organometallic complex by approximately +0.6 V versus the ferrocene/ferrocenium (Fc/Fc⁺) couple, a testament to the extreme electron-withdrawing properties of the trifluoromethyl ligand. The ΔE_ox (methyl vs trifluoromethyl) for d⁸ nickel complexes were of similar magnitude; however the absolute oxidation potentials were dramatically dependent on the ligand (dippe = 1,2-bis(diisopropylphosphino)ethane vs BOXAM = bis(4-isopropyl-4,5-dihydrooxazol-2-yl)phenyl)amine).

Full text of DOI:10.1021/om901122z

Organometallics 2010, 29, 1451–1456 1451
DOI: 10.1021/om901122z
Magnitudes of Electron-Withdrawing Effects of the Trifluoromethyl
Ligand in Organometallic Complexes of Copper and Nickel
†
Iris Kieltsch, Galyna G. Dubinina, Claudia Hamacher, Andre Kaiser,
†
‡
‡
ꢀ
Jorge Torres-Nieto,† John M. Hutchison,† Axel Klein,‡ Yulia Budnikova,§ and
David A. Vicic*,†
†Department of Chemistry, University of Hawaii, 2545 McCarthy Mall, Honolulu, Hawaii 96822,
‡
€
Institut fu€r Anorganische Chemie, Universitat zu Koln, Greinstrasse 6, D-50939 Koln, Germany, and
€
€
§A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian Academy of
Sciences, 8 Arbuzov Street, 420088 Kazan, Russian Federation
Received December 25, 2009
A variety of nickel and copper complexes bearing the trifluoromethyl ligand have been prepared in
order to quantify by electrochemical methods the redox potentials relative to their chloro and methyl
counterparts. The effects of coordination number and geometry, as well as the oxidation state of the
metal, on the relative ease with which trifluoromethyl complexes can be oxidized have for the first
time been identified. In the d10 system [(NHC)Cu(X)] (NHC=N-heterocyclic carbene, X=methyl
or trifluoromethyl), a single substitution of methyl for trifluoromethyl raised the oxidation potential
of the organometallic complex by approximately þ0.6 V versus the ferrocene/ferrocenium (Fc/Fcþ)
couple, a testament to the extreme electron-withdrawing properties of the trifluoromethyl ligand. The
ΔEox (methyl vs trifluoromethyl) for d8 nickel complexes were of similar magnitude; however the
absolute oxidation potentials were dramatically dependent on the ligand (dippe=1,2-bis(diiso-
propylphosphino)ethane vs BOXAM = bis(4-isopropyl-4,5-dihydrooxazol-2-yl)phenyl)amine).
Introduction
trifluoromethylations of aryl halides using copper;9-15 how-
ever the first example of a process catalytic in copper to
couple the trifluoromethyl group with aryl iodides was only
recently reported in 2009.16 The promise of nickel is related
to its recent widespread success in the ability to catalytically
cross-couple nonfluorinated alkyl substrates.17-23 Consider-
ing the fact that alkyl groups and perfluoroalkyl groups such
The introduction of fluorine into an organic molecule can
bring about many changes in physical properties such as inc-
reased chemical and metabolic stability, enhanced lipophili-
city, conformational changes, and changes in polarity.1,2
Fluorination can also serve as a diagnostic tool, enabling
such techniques as 19F NMR spectroscopy or positron
emission tomography.1 The trifluoromethyl group, the simp-
lest perfluoroalkyl, is a chemical functionality with growing
importance in the agrichemical, pharmaceutical, and mate-
rials industries.3-6 This small, fluorinated analogue of a
simple methyl group has also gained notoriety in the syn-
thetic community because catalytic methods to incorporate
the trifluoromethyl group into aryl bromides and chlorides
have yet to be developed.7,8
(9) Dubinina, G. G.; Furutachi, H.; Vicic, D. A. J. Am. Chem. Soc.
2008, 130, 8600–8601.
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catalyzing the introduction of a trifluoromethyl group into
an organic halide. There is a rich history of stoichiometric
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Pulay, P.; Vicic, D. A. J. Am. Chem. Soc. 2006, 128, 13175–13183.
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*Corresponding author. E-mail: vicic@hawaii.edu.
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r
2010 American Chemical Society
Published on Web 02/15/2010
pubs.acs.org/Organometallics

1452 Organometallics, Vol. 29, No. 6, 2010
Kieltsch et al.
as trifluoromethyl are all sp3-hybridized, it is not unreason-
able to predict that nickel may also be a suitable metal to
catalyze the coupling of the trifluoromethyl group. Stoichio-
metric studies with well-defined [(dippe)Ni(Aryl)(CF3)]
(dippe=1,2-bis(diisopropylphosphino)ethane) complexes sug-
gest, however, that the reactivity of nickel-alkyl and nickel-
perfluoroalkyl complexes are drastically different24 and that
more fundamental studies are needed to rationally control
perfluoroalkyl manipulations at a metal center.
Chart 1. First Oxidation Potential for Selected Metal
Complexesa
In the context of improving perfluoroalkyl cross-coup-
lings, one must consider the fact that first-row transition
metals often react with organic halides via radical-based
mechanisms involving one-electron changes in metal oxida-
tion states.18,25-31 It is therefore important to understand the
degree to which the trifluoromethyl ligand may affect such
one-electron redox shuttles so that strategies may be deve-
loped to better direct reactivity of potential perfluoroalkyl
organometallic intermediates of a catalytic cycle, especially
considering the fact that trifluoromethyl ligands often stabi-
lize higher oxidation states of metals.32,33 Electrochemical
studies of well-defined metal-perfluoroalkyl complexes may
aid in this regard; however we were surprised to discover that
there is not a single report on the electrochemical properties
of nickel- or copper-trifluoromethyl complexes. To begin to
fill this gap in knowledge, we report herein a comparison of
the redox properties of nickel and copper organometallic and
perfluoro-organometallic complexes.
Results and Discussion
The redox properties of NHC-copper complexes (NHC=
N-heterocyclic carbenes) were first established, as [(NHC)-
Cu(CF3)] complexes have recently been reported to be active
stoichiometric trifluoromethylation agents.9,10 The one-
electron oxidations were all irreversible, which limits largely
the meaning of the measured potentials. However, by apply-
ing reasonably similar conditions (concentration, solvent,
temperature, electrode) to all complexes we are confident
that at least a qualitative comparison is feasible. The results,
shown in Chart 1, demonstrate that the potential required to
oxidize these copper complexes follows the order [(SIPr)Cu-
(CH3)] (1)<[(SIPr)CuCl] (2)<[(SIPr)Cu(CF3)] (3) (SIPr=
N,N0-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene)
with relative magnitudes of 0.65, 1.04, and 1.24 V, respectively.34
Thus, it is extremely difficult to oxidize the [(SIPr)Cu(CF3)]
a All values measured as the peak potential relative to Fc/Fcþ.
complex 3. In fact, there are few practical chemical oxidants
capable of oxidizing 3 by an outer-sphere electron transfer
mechanism.35 It is important to clarify here that the intrinsic
difficulty in oxidizing [(NHC)Cu(CF3)] at the anode does not
mean that these copper complexes are chemically unreactive;
in fact solutions of [(NHC)Cu(CF3)] complexes are extre-
mely air-sensitive.9 The data may imply, however, that the
mechanism for aryl halide activation by [(NHC)Cu(CF3)] is
likely similar to that recently suggested for [LCu(NR2)] (L=
chelating ligands such as 1,10-phenanthroline), involving
either an inner-sphere electron transfer event or η2-arene
intermediates.36
(24) Dubinina, G. G.; Brennessel, W. W.; Miller, J. L.; Vicic, D. A.
Organometallics 2008, 27, 3933–3938.
The oxidation potentials of the two-coordinate copper
complexes are perhaps the best measure of the inductive
nature of the trifluoromethyl ligand since electron-withdraw-
ing effects can be reasonably separated out from changes in
orbital energies caused by molecular deformations that might
be seen in higher-coordinate, more sterically encumbered
species. Steric effects can be considerable for metal-trifluoro-
methyl complexes because the CF3 ligand has a calculated
cone angle of 133°,37 much larger than a methyl (90°) and near
the reported value of a tert-butyl ligand (126°).38 Indeed,
(25) Phapale, V. B.; Bunuel, E.; Garcia-Iglesias, M.; Cardenas, D. J.
Angew. Chem., Int. Ed. 2007, 46, 8790–8795.
(26) Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979, 101, 6319–
6332.
(27) Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979, 101, 7547–
7560.
(28) Ohmiya, H.; Yorimitsu, H.; Oshima, K. Org. Lett. 2006, 8, 3093–
3096.
(29) Ohmiya, H.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2006,
128, 1886–1889.
(30) Bedford, R. B.; Betham, M.; Bruce, D. W.; Davis, S. A.; Frost,
R. M.; Hird, M. Chem. Commun. 2006, 1398–1400.
(31) Dongol, K. G.; Koh, H.; Sau, M.; Chai, C. L. L. Adv. Synth.
Catal. 2007, 349, 1015–1018.
(32) Naumann, D.; Tyrra, W.; Trinius, F.; Wessel, W.; Roy, T.
J. Fluor. Chem. 2000, 101, 131–135.
(33) Naumann, D.; Roy, T.; Tebbe, K. F.; Crump, W. Angew. Chem.
1993, 105, 1555–1556.
(34) Complexes 2 and 3 were insoluble in THF; therefore CH2Cl2 was
used as solvent. Complex 1 decomposed in CH2Cl2, so a different solvent
(THF) had to be used.
(35) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877–910.
(36) Strieter, E. R.; Bhayana, B.; Buchwald, S. L. J. Am. Chem. Soc.
2009, 131, 78–88.
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T. E.; Lam, K.-C.; Incarvito, C.; Rheingold, A. L. Dalton 2000, 873–879.
(38) McMahon, C. N.; Obrey, S. J.; Keys, A.; Bott, S. G.; Barron,
A. R. Dalton 2000, 2151–2161.

Article
Organometallics, Vol. 29, No. 6, 2010 1453
crystal structures of [(dippe)Ni(CH3)2] (4, dippe = 1,2-bis-
(diisopropylphosphino)ethane) and [(dippe)Ni(CF3)2] (7) do
show substantial differences in bond angles for only minor
changes in chemical composition.24 The copper complexes
reported herein maintain a linear two-coordinate form, even
for the chloride complex 2.39
Scheme 1. Preparation of New BOXAM Nickel Complexes
The nickel complexes 4-6 (Chart 1) all display one
irreversible oxidation (see Supporting Information) with
the trend in redox potentials mirroring that seen with
copper.40 Thus, [(dippe)Ni(CH3)2)] is much easier to oxidize
than [(dippe)Ni(CF3)2] (-0.17 vs 1.00 V, respectively).41 The
[(dippe)Ni(aryl)(CF3)] derivative 5, a reasonable model for
an intermediate in an aryl-CF3 cross-coupling reaction,24
displays a large positive oxidation potential (0.61 V) in
between the values for 4 and 6. These values for the nickel
derivatives offer insight into our previous efforts to oxida-
tively induce reductive eliminations of trifluoroarenes from
NiII with chemical oxidants (eq 1).24 The electrochemical
data in Chart 1 suggest that this approach is feasible,
although very powerful oxidants are required to oxidize
Ni(Ar)CF3 complexes such as 5.35
The electrochemical data in Chart 1 for compounds 1-6
provide a glimpse into the extreme electron-withdrawing
properties of the trifluoromethyl ligand, which raises the
oxidation potentials relative to the methyl complexes by at
least 500 mV. This large ΔEox presents daunting challenges
for doing any further oxidative chemistry at trifluoromethyl
complexes of CuI or NiII. In order to circumvent the large
barriers associated with oxidizing a late transition-metal
complex bearing a trifluoromethyl ligand, we explored the
use of tridentate nitrogen-donor ligands to bring the oxidation
potential to a more reasonable window. A bis(4-isopropyl-
4,5-dihydrooxazol-2-yl)phenyl)amine (BOXAM) ligand (7)42
was chosen as our model tridentate ligand, since oxidations of
nickel complexes bearing similar amido-pincer ligands such as
BOXAM ligand to [(TMEDA)Ni(Ph)Cl],45 loss of benzene
occurred with formation of the convenient precursor [(BOXAM)-
NiCl] (10) in 96% yield. Complex 10 can then be transmeta-
lated with methyllithium to afford [(BOXAM)Ni(CH3)] (11),
a combination of TMS-CF3 and CsF to afford [(BOXAM)-
Ni(CF3)] (12), and PhMgCl to afford [(BOXAM)Ni(Ph)] (13)
(Scheme 1). Compounds 11-13 have all been structurally
characterized, and ORTEP plots of their molecular structure
are shown in Figures 1-3. Each of the three organometallic
compounds has a structure that is C2 symmetric, with the
nickelcenters all adoptingsquare-planararrangements. While
the nickel-carbon bond lengths for [(BOXAM)Ni(CH3)] and
43 and 944 have Eox values much lower than those seen for 4-6.
˚
[(BOXAM)Ni(CF3)] are comparable (2.077(4) and 2.040(4) A,
8
respectively), the [(BOXAM)Ni(Ph)] was relatively shorter at
˚
1.910(2) A.
The redox behavior of the BOXAM nickel complexes
10-12 strongly depends on the co-ligand Cl, CF3, or CH3,
and they display the same trends in oxidation potentials
observed for the phosphine complexes 4-6 in the sense that
the [(BOXAM)Ni(CF3)] complex was much more difficult to
oxidize than the [(BOXAM)Ni(CH3)] complex (-0.17 vs
þ0.42 V). The cyclic voltammograms of 10-12 are shown
in Figure 4 for comparison. First of all we can note that while
the one-electron oxidation of the CH3 complex 11 is com-
pletely irreversible (also at lower temperature and higher
scan rates), the CF3 and Cl derivatives exhibit a certain
degree of reversibility. When measuring 11, the first irrever-
sible oxidation wave is followed by a reversible wave at
higher potential. This wave was also obtained when a solu-
tion of the methyl complex was treated with oxygen prior to
measurement. Following the idea that the CH3 co-ligand
might cleave after one-electron oxidation, we prepared the
complex [(BOXAM)Ni(THF)]þ (14) by abstraction of Cl-
from the precursor complex [(BOXAM)NiCl] (10) using
The preparation of a series of BOXAM nickel complexes
proceeded as described in Scheme 1. Upon addition of free
(39) Diez-Gonzalez, S.; Stevens, E. D.; Nolan, S. P. Chem. Commun.
2008, 4747–4749.
(40) Again, complex 4 reacts with CH2Cl2, so a different solvent had
to be used. Complex 6 was insoluble in THF.
(41) The oxidation potential for [(dippe)NiCl2] in CH2Cl2 was mea-
sured to be 1.3 V. However this value is very close to that for free chloride
ion oxidation, so no discussion of this value will be made.
(42) Lu, S.-F.; Du, D.-M.; Zhang, S.-W.; Xu, J. Tetrahedron: Asym-
metry 2004, 15, 3433–3441.
(43) Adhikari, D.;Mossin, S.;Basuli, F.;Huffman, J. C.;Szilagyi, R. K.;
Meyer, K.; Mindiola, D. J. J. Am. Chem. Soc. 2008, 130, 3676–3682.
(44) Vechorkin, O.; Proust, V.; Hu, X. J. Am. Chem. Soc. 2009, 131,
9756–9766.
(45) Marshall, W. J.; Grushin, V. V. Can. J. Chem. 2005, 83, 640–645.

1454 Organometallics, Vol. 29, No. 6, 2010
Kieltsch et al.
Figure 1. ORTEP diagram of 11. All hydrogen atoms ex-
cept those on methyl have been omitted for clarity. Selected
bond lengths (A): Ni(1)-N(2) 1.894(3), Ni(1)-N(3) 1.898(3),
Ni(1)-N(1) 1.933(3), Ni(1)-C(1) 2.077(4). Selected bond
angles (deg): N(2)-Ni(1)-N(3) 175.63(15), N(2)-Ni(1)-
N(1) 88.19(14), N(3)-Ni(1)-N(1) 89.47(13), N(2)-Ni(1)-
C(1) 90.07(15), N(3)-Ni(1)-C(1) 92.32(14), N(1)-Ni(1)-
C(1) 178.06(14).
Figure 3. ORTEP diagram of 13. All hydrogen atoms except
those on phenyl have been omitted for clarity. Selected bond
lengths (A): Ni(1)-N(3) 1.891(2), Ni(1)-N(1) 1.8961(19), Ni(1)-
C(1) 1.910(2), Ni(1)-N(2) 1.9385(19). Selected bond angles (deg):
N(3)-Ni(1)-N(1), 172.46(9), N(3)-Ni(1)-C(1) 88.60(9), N(1)-
Ni(1)-C(1) 91.62(9), N(3)-Ni(1)-N(2) 89.80(8), N(1)-
Ni(1)-N(2) 90.97(8), C(1)-Ni(1)-N(2) 172.15(10).
˚
˚
Figure 4. Cyclic voltammograms of (BOXAM)Ni complexes
10-12 (each about 10 mM) in THF/[nBu4N][PF6] (100 mM), at
100 mV/s scan rate and 298 K. Potentials referenced vs Fc/Fcþ.
The reversible wave marked * is assigned to the solvent complex
[(BOXAM)Ni(THF)]þ/2þ (see text).
Figure 2. ORTEP diagram of 12. Hydrogen atoms are omitted
˚
for clarity. Selected bond lengths (A): Ni(1)-N(2) 1.909(3),
Ni(1)-N(1) 1.921(3), Ni(1)-N(3) 1.923(3), Ni(1)-C(1) 2.040(4).
Selected bond angles (deg): N(2)-Ni(1)-N(1) 87.03(12), N(2)-
Ni(1)-N(3) 171.46(13), N(1)-Ni(1)-N(3) 89.85(12), N(2)-
Ni(1)-C(1) 92.37(14), N(1)-Ni(1)-C(1) 172.99(15), N(3)-
Ni(1)-C(1) 91.68(14).
active methylating species.46 Interestingly, the trifluoro-
methyl derivative 12 also appears to lose CF3 from the
complex when treated with O2 (bubbling at atmospheric
pressure). However the rate of conversion to 14 is far slower
from 12, and total conversion is only achieved within 24 h,
while the complete disappearance of 11 occurs within one
minute. Therefore we assume that within the time scale of the
CV experiment the CF3 co-ligand remains on the nickel
atom. Furthermore, the similarity of the oxidation potentials
for the two nickel complexes 10 and 12, in contrast to the
marked difference for 5 and 6, suggests that the redox
chemistry is occurring on the common BOXAM ligand,
while the redox chemistry of the methyl derivative 11 resem-
bles far more that of the phosphine complex 4 and might
be more centered on the nickel atom. Investigations pro-
viding more evidence for such assignments using EPR
spectroscopy and UV-vis spectroelectrochemistry are
under way.
thallium acetate (see Experimental Section) and measured its
cyclic voltammogram and UV-vis absorption spectrum (for
details see Supporting Information). Thus, we provide evi-
dence that the [(BOXAM)Ni(CH3)] complex undergoes
rapid splitting of the methyl co-ligand upon oxidation (at
the anode or by oxygen) and forms 14, supporting our
assumption that one-electron oxidation induces labilization
of the Ni-CH3 bond (eq 1). This reactivity is in line with
what is observed for the methyl coenzyme M reductase
(MCR), where CH3-NiIIIF430M is considered to be the
(46) Jaun, B.; Thauer, R. K. In Metal Ions in Life Sciences; Sigel, A.;
Sigel, H.; Sigel, R. K. O., Eds.; John Wiley & Sons, Ltd.: Chichester, UK,
2009; Vol. 6, pp 115-132.

Article
Organometallics, Vol. 29, No. 6, 2010 1455
Experimental Section
-30 °C, and passed again through a syringe filter (0.20 μm).
Slow evaporation of pentane at atmospheric pressure yielded
1
dark red crystals of 11 (229 mg, 0.493 mmol, 62%). H NMR
General Considerations. All manipulations were performed
using standard Schlenk and high-vacuum techniques47 or in a
nitrogen-filled drybox, unless otherwise noted. Solvents were
distilled from Na/benzophenone or CaH2. All reagents were
used as received from commercial vendors unless otherwise
noted. Celite was dried at 200 °C under vacuum for two days
prior to use. 1H NMR spectra were recorded at ambient
temperature (unless otherwise noted) on a Varian Oxford 300
MHz spectrometer and referenced to residual proton solvent
peaks. 19F spectra were recorded on the Varian Oxford spectro-
meter operating at 282 MHz and were referenced to CFCl3 set to
zero. A Rigaku SCXMini diffractometer was used for X-ray
structure determinations. Cyclic voltammetry was carried out at
100 mV/s scan rate in 0.1 M [nBu4N][PF6] solutions using a
three-electrode configuration (glassy carbon electrode, Pt coun-
ter electrode, Ag/AgCl reference) and an Autolab PG STAT 30
potentiostat and function generator. The ferrocene/ferrocenium
(Fc/Fcþ) couple served as internal standard. UV-vis absorp-
tion spectra were recorded in 1 cm quartz cells using a Varian
Cary50 Scan photospectrometer. Complexes 1,48 2,39 and 4-624
were prepared according to literature procedures.
(300 MHz, THF-d8): δ -0.99 (s, 3H), 0.84 (d, J = 6.9 Hz, 6H)
0.88 (d, J=6.9 Hz, 6H), 2.35-2.42 (m, 2H), 3.89-3.93 (m, 2H),
4.21-4.23 (m, 4H), 6.48-6-53 (m, 2H), 6.95-6.98 (m, 4H),
7.48 (dd, J=7.8 Hz, 1.8 Hz, 2H). 13C NMR (75 MHz, THF-d8):
δ -14.9, 15.5, 18.6, 33.1, 68.3, 116.2, 116.4, 122.8, 130.0, 132.5,
155.6, 161.3. HRMS (FABþ): calcd (m/z) for C25H31N3NiO2
463.1770; obsd 463.1889.
Preparation of [(BOXAM)Ni(CF3)] (12). TMSCF3 (237 μL,
1.5 mmol, 6 equiv) was added dropwise to a solution of 10
(121 mg, 0.25 mmol) and CsF (272 mg, 1.5 mmol, 6 equiv) in dry
DMF (10 mL) and stirred at rt under nitrogen. After 15 h the
volatiles were evaporated using a high-vacuum line. The residue
was resolved in pentane, and the solution was passed through a
syringe filter (0.45 μm, cellulose acetate). The blood red solution
was concentrated and crystallized from pentane to yield dark
1
red crystals of 12 (106 mg, 0.205 mmol, 82%). H NMR (300
MHz, THF-d8): δ 0.88 (d, J =6.9 Hz, 6H) 0.94 (d, J =6.9 Hz,
6H), 2.21-2.29 (m, 2H), 3.93-3.95 (m, 2H), 4.32-4.36 (m, 4H),
6.66 (t, J=7.8 Hz, 2H), 6.87 (d, J=78.4 Hz, 2H), 7.08 (td, J=
8.4 Hz, 1.5 Hz, 2H), 7.57 (td, J=7.8 Hz, 1.5 Hz, 2H). 13C NMR
(75 MHz, THF-d8): δ 16.2, 17.9, 33.5, 70.5, 70.5 (q, 4J(C,F) =
3.2 Hz), 116.9, 117.7, 123.0, 126.7 (q, 1J(C,F)=371.2 Hz), 130.2,
133.5, 153.7, 163.0. 19F NMR (188 MHz, THF-d8): δ -29.9 (s).
HRMS (FABþ) calcd (m/z) for C25H28F3N3NiO2 517.1487;
obsd 517.2883.
Preparation of [(BOXAM)Ni(Ph)] (13). A solution of 10
(100 mg, 0.206 mmol) in THF (10 mL) was cooled to -30 °C,
and a solution of PhMgCl in hexane (2 M, 0.125 mL 0.25 mmol,
1.2 equiv) was added dropwise. The reaction mixture immedi-
ately turned red, and it was stirred 12 h at rt. 1,4-Dioxane (43 μL,
0.5 mmol) was added, the mixture was stirred for another hour,
and then the volatiles were evaporated using a high-vacuum line.
The residue was resolved in pentane (30 mL), the solution was
passed through a syringe filter (0.45 μm, cellulose acetate), and
the filter was rinsed with pentane. The blood red solution was
concentrated to half of its volume, cooled 1 h at -30 °C, and
passed again through a syringe filter (0.20 μm). Slow evapora-
tion of pentane at atmospheric pressure yielded dark red crystals
of 13 (87 mg, 0.165 mmol, 80%). 1H NMR (300 MHz, THF-d8):
δ 0.40 (d, J=6.9 Hz, 6H) 0.55 (d, J=6.9 Hz, 6H), 2.23-2.28 (m,
2H), 2.66-2.70 (m, 2H), 3.89-4.02 (m, 4H), 6.46-6.50 (m, 2H),
6.58-6.62 (m, 1H), 6.70 (m, 2H), 6.91-6.95 (m, 4H), 7.46 (d, J=
7.5 Hz, 2H), 7.54 (d, J=7.5 Hz, 2H). 13C NMR (75 MHz, THF-
d8): δ 14.8, 18.6, 32.4, 70.5, 115.5, 117.0, 122.8, 123.21, 126.0,
130.1, 132.7, 138.4, 155.5, 159.4, 162.0. HRMS (FABþ): calcd
(m/z) for C30H33N3NiO2 525.1926; obsd 525.2120.
Preparation of [(BOXAM)Ni(THF)](OAc) (14). To a solution
of 10 (100 mg, 0.206 mmol) in THF (10 mL) was added thallium
acetate (65 mg, 0.247 mmol, 1.2 equiv). The reaction mixture
immediately turned blue-green, and it was stirred 1 h at rt. The
white precipitate of thallium chloride was removed by filtration.
Evaporation of THF at low pressure yielded blue-green micro-
crystalline materials of 14 (87 mg, 0.165 mmol, 80%). 1H NMR
(300 MHz, CD2Cl2-d2): δ 0.88 (m, 12H), 1.27 (s, 3H), 1.82 (t, J=
6.6 Hz, 4H), 2.68 (m, 2H), 3.42 (m, 2H), 3.68 (t, J=6.8 Hz, 4H),
4.24 (m, 2H), 4.38 (t, J=9.3 Hz, 2H), 6.71 (t, J =7.1 Hz, 2H),
6.96 (d, J=8.3 Hz, 2H), 7.06 (t, J=7.0 Hz, 2H), 7.61 (d, J=7.6
Hz, 2H). 13C NMR (75 MHz, CD2Cl2-d2): δ 15.2, 18.9, 22.3,
26.1, 31.9, 67.0, 68.3, 69.5, 116.4, 118.3, 125.3, 129.3, 132.4,
153.8, 162.1, 176.2. Anal. Calcd (found) for C30H39N3NiO5
(579.22): C, 62.09 (61.89, 0.32%); H, 6.77 (6.74, 0.42%); N,
7.24 (7.20, 0.51%).
Preparation of [(SIPr)Cu(CF3)] (3). [(SIPr)CuCl] (979 mg,
2 mmol) and tBuOK (224 mg, 2 mmol) were dissolved in 7 mL
of DMF and stirred 2 h at room temperature. The solution was
then filtered through a pad of Celite and washed two times with
1 mL of DMF. CF3Si(CH3)3 (588 uL, 4 mmol) was then added
to the filtrate, and the resulting solution was stirred 16 h at room
temperature. The product precipitated as a white solid and was
filtered, washed with 1 mL of DMF then 3 mL of pentane, and
1
dried under vacuum. Yield: 94%. H NMR (CD2Cl2): δ 1.33
(d, J=6.7 Hz, 12H), 1.35 (d, J=6.7 Hz, 12H), 3.08 (hept., J=
6.7 Hz, 4H), 4.03 (s, 4H), 7.29 (d, J = 7.8 Hz, 4H), 7.45 (t, J =
7.8 Hz, 2H). 13C NMR (75 MHz, CD2Cl2): δ 204.5, 147.4, 134.7,
130.3, 125.0, 124.9, 29.4, 25.6, 24.1. (Note: the resonance for the
carbon atom of the trifluoromethyl group was not observed.)
19F{1H} NMR (CD2Cl2): δ -32.2 (s, 3F, CF3).
Preparation of [(BOXAM)NiCl] (10). A solution of 8 (1.089 g
2.78 mmol, 1 equiv) in THF (10 mL) was added under a nitrogen
atmosphere to a suspension of [(tmeda)Ni(Ph)Cl] (800 mg, 2.78
mmol) in THF (40 mL) at room temperature and stirred over-
night, during which time the orange solution turned dark green.
The reaction mixture was filtered, concentrated in volume, and
layered with pentane. Cooling to -30 °C afforded dark green
1
crystals of 10 (1.29 g, 2.67 mmol, 96%). H NMR (300 MHz,
THF-d8): δ 0.94 (d, J = 6.6 Hz, 6H) 0.95 (d, J = 6.6 Hz, 6H),
2.63-2.68 (m, 2H), 4.21-4.34 (m, 6H), 6.69 (t, J=7.8 Hz, 2H),
6.93 (d, J = 8.4 Hz, 2H), 7.04 (t, J = 8.4 Hz, 2H), 7.56 (d, J =
7.8 Hz, 2H). 13C NMR (75 MHz, THF-d8): δ 15.8, 18.5, 32.4,
67.6, 69.8, 117.5, 118.5, 125.1, 129.6, 132.9, 154.1, 161.1. HRMS
(FABþ): calcd (m/z) for C24H28ClN3NiO2 483.1224; obsd
483.1166.
Preparation of [(BOXAM)Ni(CH3)] (11). A solution of 10
(388 mg, 0.8 mmol) in THF (30 mL) was cooled to -30 °C, and a
solution of MeLi in hexane (1.6 M, 0.6 mL 0.96 mmol, 1.2 equiv)
was added dropwise. The reaction mixture immediately turned
red, and it was stirred 12 h at rt. 1,4-Dioxane (86 μL, 1 mmol)
was added, the mixture was stirred for another hour, and then
the volatiles were evaporated using a high-vacuum line. The
residue was resolved in pentane, the solution was cooled 1 h at
-30 °C and passed through a syringe filter (0.45 μm, cellulose
acetate), and the filter was rinsed with pentane. The blood red
solution was concentrated to half of its volume, cooled 1 h at
(47) Vicic, D. A.; Jones, G. D. In Comprehensive Organometallic
Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: 2006; Vol. 1.
(48) Goj, L. A.; Blue, E. D.; Delp, S. A.; Gunnoe, T. B.; Cundari,
T. R.; Pierpont, A. W.; Petersen, J. L.; Boyle, P. D. Inorg. Chem. 2006,
45, 9032–9045.
Acknowledgment. D.A.V. thanks the Office of Basic
Energy Sciences of the U.S. Department of Energy (DE-
FG02-07ER15885) and the National Science Foundation

1456 Organometallics, Vol. 29, No. 6, 2010
Kieltsch et al.
(CHE-0822523) for support of this work. C.H., A.K., and
A.K. are grateful for support by the DFG (DFG KL
1194/4-1 and 5-1). We also wish to thank Bill Geiger and
Michael Stewart at the University of Vermont for assis-
tance with the cyclic voltammograms of 1, 2, and 6.
Supporting Information Available: NMR spectra of all new
compounds, cyclic voltammograms of 1-7 and 10-13, crystallo-
graphic data for 11-13, and UV-vis absorption spectra of
complexes 10, 11, 12, and 14. This material is available free of
charge via the Internet at http://pubs.acs.org.