Copper(I) and -(II) complexes of neutral and deprotonated N-(2,6-diisopropylphenyl)-3-[bis(2-pyridylmethyl)amino]propanamide

Article abstract of DOI:10.1021/ic0505697

As part of a study of atom-transfer radical polymerization (ATRP) catalysts, four new copper(I) and -(II) compounds of a new monoanionic, tripodal tetradentate ligand, N-(2,6-diisopropylphenyl)-3-[bis(2-pyridylmethyl)amino] propanamide (DIPMAP), were prepared. Ligand synthesis followed from the addition-elimination reaction of 2,6-diisopropylaniline with acryloyl chloride and then a Lewis acid catalyzed Michael addition of bis(2-pyridylmethyl)amine to this product. The ligand was complexed to CuCl to yield monomeric Cu(DIPMAP)Cl featuring an intramolecular hydrogen bond between the free amide hydrogen and the coordinated chloride ligand. Deprotonation of the amide hydrogen in Cu(DIPMAP)Cl using n-BuLi led to the incorporation of LiCl in the resulting product, Li₂Cu₂(DIPMAP)₂Cl₂. This complex exhibited an unusual dimeric structure, with the amine nitrogens of one ligand coordinated to a lithium ion, the amide oxygen of the same ligand bridging between the lithium ions, and the amidate nitrogen of that ligand coordinated to a CuCl unit that has a structure analogous to dihalocuprate ions. Deprotonation of Cu(DIPMAP)Cl using KO^tBu yielded an alkali-metal chloride free product, Cu₂(DIPMAP)₂, that also exhibited a dimeric structure in which the three amine nitrogens of one ligand were coordinated to one Cu^I ion and the amidate nitrogen of the same ligand was coordinated to the other Cu^I ion. Cu₂(DIPMAP) ₂ was effective in abstracting halogen atoms from organic halides, but in the attempted ATRP of tert-butyl acrylate, molecular weight versus conversion behavior reminiscent of a redox-initiated polymerization was observed. DIPMAP was coordinated to CuBr₂ to yield [Cu(DIPMAP)Br]Br with a square-pyramidal structure. The amide hydrogen in this complex could be deprotonated using KO^tBu to form complex [DIPMAP]CuBr (6). Spectral characterization of complex 6 confirmed deprotonation of the ligand and that it most likely had an axially distorted trigonal-bipyramidal structure, although crystals suitable for X-ray analysis could not be obtained. Solution oxidation of Cu₂(DIPMAP)₂ using CBr₄ yielded a product, complex 4, whose spectral signatures did not match those of complex 6. The dimeric structure of Cu₂(DIPMAP)₂ might be a significant contributing factor to the slow rate of deactivation observed in atom-transfer reactions using Cu₂(DIPMAP)₂ as the catalyst.

Full text of DOI:10.1021/ic0505697

Inorg. Chem. 2005, 44, 9197−9206
Copper(I) and -(II) Complexes of Neutral and Deprotonated
N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridylmethyl)amino]propanamide
Timothy E. Patten,* Christina Troeltzsch, and Marilyn M. Olmstead
Department of Chemistry, UniVersity of California at DaVis, One Shields AVenue,
DaVis, California 95616-5292
Received April 12, 2005
As part of a study of atom-transfer radical polymerization (ATRP) catalysts, four new copper(I) and -(II) compounds
of a new monoanionic, tripodal tetradentate ligand, N-(2,6-diisopropylphenyl)-3-[bis(2-pyridylmethyl)amino]propanamide
(DIPMAP), were prepared. Ligand synthesis followed from the addition−elimination reaction of 2,6-diisopropylaniline
with acryloyl chloride and then a Lewis acid catalyzed Michael addition of bis(2-pyridylmethyl)amine to this product.
The ligand was complexed to CuCl to yield monomeric Cu(DIPMAP)Cl featuring an intramolecular hydrogen bond
between the free amide hydrogen and the coordinated chloride ligand. Deprotonation of the amide hydrogen in
Cu(DIPMAP)Cl using n-BuLi led to the incorporation of LiCl in the resulting product, Li2Cu2(DIPMAP)2Cl2. This
complex exhibited an unusual dimeric structure, with the amine nitrogens of one ligand coordinated to a lithium ion,
the amide oxygen of the same ligand bridging between the lithium ions, and the amidate nitrogen of that ligand
coordinated to a CuCl unit that has a structure analogous to dihalocuprate ions. Deprotonation of Cu(DIPMAP)Cl
using KOtBu yielded an alkali-metal chloride free product, Cu2(DIPMAP)2, that also exhibited a dimeric structure in
which the three amine nitrogens of one ligand were coordinated to one CuI ion and the amidate nitrogen of the
same ligand was coordinated to the other CuI ion. Cu2(DIPMAP)2 was effective in abstracting halogen atoms from
organic halides, but in the attempted ATRP of tert-butyl acrylate, molecular weight versus conversion behavior
reminiscent of a redox-initiated polymerization was observed. DIPMAP was coordinated to CuBr2 to yield
[Cu(DIPMAP)Br]Br with a square-pyramidal structure. The amide hydrogen in this complex could be deprotonated
using KOtBu to form complex [DIPMAP]CuBr (6). Spectral characterization of complex 6 confirmed deprotonation
of the ligand and that it most likely had an axially distorted trigonal-bipyramidal structure, although crystals suitable
for X-ray analysis could not be obtained. Solution oxidation of Cu2(DIPMAP)2 using CBr4 yielded a product, complex
4, whose spectral signatures did not match those of complex 6. The dimeric structure of Cu2(DIPMAP)2 might be
a significant contributing factor to the slow rate of deactivation observed in atom-transfer reactions using Cu2(DIPMAP)2
as the catalyst.
Introduction
to a transition-metal complex to generate and deactivate
intermediate radicals that can undergo further addition
reactions. The radical formed after the addition step is less
stable than the initially formed radical, so after halogen atom
abstraction from the higher oxidation state deactivator
complex, the organic halide that is formed cannot react
further with the metal catalyst. Atom transfer radical
polymerization (ATRP)8-12 is similar to ATRA but utilizes
Copper (I) complexes have gained importance as catalysts
for polymerizations and transformations that involve halogen
atom-transfer chemistry. Atom-transfer radical addition
(ATRA)1-7 employs atom transfer from an organic halide
* To whom correspondence should be addressed. E-mail: patten@
chem.ucdavis.edu.
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10.1021/ic0505697 CCC: $30.25
Published on Web 11/16/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 25, 2005 9197

Patten et al.
organic halide polymer end groups that have similar reactivity
before and after monomer addition, thus facilitating multiple
addition processes and the growth of a polymer chain. The
controlled nature of ATRA and ATRP (i.e., little or no
radical-radical coupling or disproportionation) is derived
from the persistent radical effect,13-16 and with ATRP,
polymers can be prepared with a high degree of synthetic
control over the final molecular weight, molecular weight
distributions, and end group structures.17-20 When the higher
oxidation state deactivator complex cannot react with the
intermediate radical to form the dormant halide polymer
chain end (or if the rate of such a reaction is too slow relative
to the rate of radical propagation), the polymerization
becomes a simple redox-initiated polymerization. Redox-
initiated polymerizations display molecular weight behavior
akin to free-radical polymerizations, and the mechanism of
metal complex promoted radical formation can involve
processes other than halogen atom transfer.21
about the structure, solution dynamics, and chemistry of the
copper centers involved in the atom-transfer step.
The first barrier to developing ATRP catalyst systems that
could be studied in solution was to reduce or eliminate the
dynamic behavior observed for many of the ligand/copper(I)
salt catalyst mixtures. Processes such as ligand dissociation,
displacement, and exchange have all been observed and can
be attributed to the d10 electronic structure of the copper(I)
ion. Monoanionic, tripodal tetradentate ligand designs have
been shown to be effective for preparing ATRP catalyst
systems that exhibit simple solution structures that mirror
their solid-state structures.31 The stability of such complexes
was achieved by maximizing the chelate effect and adding
electrostatic attraction between the ligand and metal center.
Additionally, the halide ligand is substituted by the anionic
donor in the coordination sphere of the copper(I) center; thus,
the complication of halide exchange between the alkyl halide
and metal center is eliminated. In a prior example, the
ligand’s anionic donor was a sulfonamide group, so we
sought to explore the different types of anionic donors, such
as the amidato group32-34 in this study, that might be
applicable to the monoanionic, tripodal tetradentate ligand
design.35-38
Whether a given metal complex can promote ATRP versus
a redox-initiated polymerization and the relative reactivity
of the catalyst in ATRP depends very strongly on the nature
of the ligands.22 There are many combinations of polydentate
amine-based ligands with copper(I) salts that are effective
catalysts for ATRP and a few that promote only redox-
initiated polymerization.23,24 Changes in the ligand-sphere
affect the polymerization kinetics and molecular weight
control in ways that are often unexpected.25-30 Thus, a better
understanding of the inorganic chemistry side of copper(I)
polymerization catalysts can be gained through knowledge
Experimental Section
Materials. Tetrahydrofuran (THF) was distilled from sodium
benzophenone just prior to use. Chloroform, methylene chloride-
d2, and acetonitrile were stirred over P2O5, distilled, and degassed.
Ethyl 2-bromopropionate was distilled from CaH2 just prior to use.
tert-Butyl acrylate, p-xylene, and triethylamine were stirred over
CaH2, distilled, and degassed. Methylene chloride was distilled from
P2O5 just prior to use. Bis(2-methylpyridyl)amine was prepared by
the condensation of (2-aminomethyl)pyridine and pyridine-2-
carboxaldehyde over MgSO4 followed by reduction of the imine
intermediate using NaBH4. Alumina gel for column chromatography
was Acros aluminum oxide, activated and neutral (50-200 µm).
Analytical thin-layer chromatography (TLC) was performed on
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5615.
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7573.
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molecules 1995, 28, 1721-1723.
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1996, 29, 1070-1072.
(13) Fischer, H. J. Am. Chem. Soc. 1986, 108, 3925-3927.
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(15) Daikh, B. E.; Finke, R. G. J. Am. Chem. Soc. 1992, 114, 2938-2943.
(16) Matyjaszewski, K.; Patten, T. E.; Xia, J. H. J. Am. Chem. Soc. 1997,
119, 674-680.
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903.
commercial EM Science plates coated with aluminum oxide 60 F254
,
neutral (0.2 mm thick). Unless stated otherwise, all materials were
purchased from commercial sources and used without further
purification. Reagents were handled under a nitrogen atmosphere
using standard drybox and Schlenk techniques.
Characterization. 1H NMR (400 MHz) and 13C NMR (100
MHz) spectra were recorded on a Varian Inova 400 instrument.
Chemical shifts, δ (ppm), were referenced to the residual proton
signal or 13C signal of the specified solvent. Number-averaged
molecular weights (Mn), weight-averaged molecular weights (Mw),
and molecular weight distributions (Mw/Mn) were determined using
(20) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. ReV. 2001, 101, 3689-
3745.
(21) Odian, G. Principles of Polymerization; John Wiley and Sons:
Hoboken, NJ, 2004.
(22) Qiu, J.; Matyjaszewski, K. Acta Polym. 1997, 48, 169-180.
(23) Haddleton, D. M.; Jasieczek, C. B.; Hannon, M. J.; Shooter, A. J.
Macromolecules 1997, 30, 2190-2193.
(24) Xia, J. H.; Matyjaszewski, K. Macromolecules 1997, 30, 7697-7700.
(25) Haddleton, D. M.; Clark, A. J.; Crossman, M. C.; Duncalf, D. J.;
Heming, A. M.; Morsley, S. R.; Shooter, A. J. J. Chem. Soc., Chem.
Commun. 1997, 1173-1174.
(31) Goodwin, J. M.; Olmstead, M. M.; Patten, T. E. J. Am. Chem. Soc.
2004, 126, 14352-14353.
(32) Ishikawa, Y.; Ito, S.; Nishino, S.; Ohba, S.; Nishida, Y. Z. Naturforsch.,
C: J. Biosci. 1998, 53, 378-382.
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T.; Nishida, Y. Inorg. Chem. Commun. 2000, 3, 145-148.
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68, 2741-2747.
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(36) Inoue, Y.; Matyjaszewski, K. Macromolecules 2004, 37, 4014-4021.
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357 (2), 619-624.
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E59, m502-m503.
(26) Haddleton, D. M.; Heming, A. M.; Kukulj, D.; Duncalf, D. J.; Shooter,
A. J. Macromolecules 1998, 31, 2016-2018.
(27) Matyjaszewski, K.; Nakagawa, Y.; Jasieczek, C. B. Macromolecules
1998, 31, 1535-1541.
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Soc., Chem. Commun. 1999, 1817-1818.
9198 Inorganic Chemistry, Vol. 44, No. 25, 2005

Copper(I) and -(II) Complexes of DIPMAP
Table 1. X-ray Refinement Data for DIPMAP Complexes
complex 1:
complex 2:
complex 3:
complex 5:
(DIPMAP)CuICl‚n-BuCN
[Li(DIPMAP)CuICl]2‚2CH3CN
[(DIPMAP)CuI]2
[(DIPMAP)CuIIBr]Br‚0.175H2O
formula
fw
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
T, K
C31H41ClCuN5O
598.68
P1
C58H72Cl2Cu2Li2N10O2
1153.12
P21/n
10.3087(8)
22.191(2)
12.8290(9)
90
100.160(7)
90
2888.69(18)
91(2)
C54H66Cu2N8O2
986.23
C2/c
18.948(3)
16.282(3)
17.272(3)
90
112.815(4)
90
C27H34.45Br2CuN4O1.17
657.2
P21/n
22.460(3)
8.8356(10)
29.944(3)
90
111.318(2)
90
8.5385(6)
9.6593(6)
9.8370(7)
103.197(1)
106.646(1)
94.001(1)
748.80(9)
90(2)
4911.7(15)
92(2)
5535.9(11)
91(2)
Z
F
1
2
4
8
calc, Mg cm-3
1.328
0.851
0.797-0.876
0.0728
1.326
0.879
0.844-0.917
0.0982
1.334
0.916
0.746-0.906
0.1014
1.577
3.704
0.555-0.836
0.1026
µ(Mo KR), mm-1
range of transm factors
wR2a (all data)
R1b (obsd data)
0.0269
0.0391
0.0366
0.0493
a wR2 ) [∑[w(Fo - Fc )2]/∑[(wFo )2]]1/2; w ) 1/[σ2(Fo ) + (aP)2 + bP], where P ) (Fo + 2Fc )/3. b R1 ) ∑||Fo| - |Fc||/∑|Fo|.
2
2
2
2
2
2
1
gel permeation chromatography (GPC) in THF at 30 °C. Three
Polymer Standard Services columns (100 Å, 1000 Å, and linear)
were connected in series to a Thermoseparation Products P-1000
isocratic pump, autosampler, column oven, and Knauer refractive
index detector. Calibration was performed using polystyrene
samples (Polymer Standard Services; Mp ) 400-1 000 000; Mw/
Mn < 1.10). Monomer conversion was determined using a Shimadzu
GC 14-A gas chromatograph equipped with a J&W Scientific 30
M DB WAS Megabore column. Injector and detector temperatures
were kept constant at 200 °C. The column temperature was held at
80 °C for the initial 2 min of the run followed by an increase to
150 °C with a heating rate of 10 °C/min. Compound elutions are
reported in retention times, Rt (min), for these specific conditions.
An internal standard, p-xylene, was used to quantify the amount
of monomer present. UV-vis spectra were recorded on a Cary 17
with an Olis Conversion. Gas chromatography-mass spectrometry
(GC-MS) experiments were reported on a Varian 3400 gas
chromatograph with a Finnigan Mat ion trap detector. Elemental
analyses were performed by Midwest Microlabs. Electron para-
magnetic resonance (EPR) spectra were recorded at 100-kHz
modulation and 10-G modulation amplitude on a Bruker ECS 106
spectrometer; unless otherwise noted, 0.80-mW incident power was
used and resonance conditions were typically 9.69 GHz at 10 K.
X-ray Structure Determinations. Diffraction data were col-
lected with a Bruker SMART 1000 diffractometer, graphite-
monochromated Mo KR radiation, and a nitrogen cold stream
provided by a CRYO Industries apparatus. Corrections for absorp-
tion were applied using the program SADABS 2.03.39 The structures
were solved by direct methods (SHELXS-97)40 and refined by full-
matrix least-squares on F 2 (SHELXL-97).40 All non-hydrogen
atoms were refined with anisotropic thermal parameters. Hydrogen
atoms on water molecules were located on a difference map and
refined using distance restraints. Other hydrogen atoms were added
by geometry and refined using a riding model. The maximum and
minimum peaks in the final difference Fourier map for each
structure can be found in the data tables located in the Supporting
Information. Crystal data and refinement details for the complexes
are shown in Table 1. For complex 5, the structure contains two
nearly identical molecules related by translation along the a
direction. However, in the smaller unit cell (a′ ) /2a), thermal
ellipsoids are unreasonable. Because of the superlattice, intensity
statistics appear to be worse than normal. There is a disordered
atom, presumed to be from water, that is weakly coordinated to
Cu1; no such atom is located near Cu2. The O1W atom occupancy
refined to 0.32(2) and was fixed at 0.35 for future runs. No hydrogen
was located for this water. Additional experimental information,
including atomic positional parameters, is supplied in CIF format
as described in the Supporting Information.
Synthesis of N-(2,6-Diisopropylphenyl)propenamide. A solu-
tion of 6.00 mL (31.8 mmol) of 2,6-diisopropylaniline and 4.50
mL (31.8 mmol) of triethylamine in 40 mL of dry CH2Cl2 was
added dropwise to 2.64 mL (31.8 mmol) of acryloyl chloride in 40
mL of dry CH2Cl2 stirred in an ice bath. The reaction was stirred
overnight. The solution was then washed with NaHCO3 (50 mL),
H2O (50 mL), dilute HCl (50 mL), and H2O (50 mL). The CH2Cl2
layer was dried over anhydrous Na2SO4, filtered, and concentrated.
The resulting white powder was recrystallized from toluene, yielding
6.81 g (93%). Mp: 182-184 °C. 1H NMR (300 MHz, DMSO-d6):
δ (ppm) 7.2 (m, 3H), 6.5 (dd, J ) 10.2 Hz, 1H), 6.2 (d, J ) 15.3
Hz, 1H), 5.7 (d, J ) 8.1 Hz, 1H), 3.0 (p, J ) 6.9 Hz, 2H), 1.1 (d,
J ) 6.3 Hz, 12H). 13C NMR (75 MHz, DMSO-d6): δ (ppm) 164.0,
154.7, 154.5, 145.7, 132.0, 121.0, 127.5, 126.0, 123.0, 28.1, 23.7,
23.3. IR (CH2Cl2): ν (cm-1) 3415 (br), 3238 (br), 3052, 2966, 2870,
1662, 1625, 1525.
Synthesis of N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamide (DIPMAP). To 50 mL of degassed
toluene was added 3.17 g (13.7 mmol) of N-(2,6-diisopropylphenyl)-
propenamide. Then 2.65 g (13.3 mmol) of bis(2-pyridylmethyl)-
amide was added, along with 0.94 mL (7.32 mol) of BF3‚Et2O.
The reaction was stirred at reflux for 5 days. The solution was then
extracted with 3 × 50 mL of 10% HCl. The acidic layers were
combined, and the pH was adjusted to >9 with 10% NaOH. The
resulting solution was then extracted with 4 × 100 mL of CH2Cl2.
The organic layers were combined, dried over anhydrous Na2SO4,
filtered, and concentrated. The crude product was purified using
alumina column chromatography, eluted with 5% Et3N in EtOAc.
The fractions containing product (determined by TLC, Rf ) 0.603)
were combined and concentrated, and volatile materials were
removed under vacuum, yielding 4.33 g (76%) of an orange gel.
MS: m/z 430. 1H NMR (400 MHz, CD3CN): δ (ppm) 9.2 (s, 1H),
8.3 (d, J ) 3.9 Hz, 2H), 7.7 (t, J ) 6 Hz, 2H), 7.4 (d, J ) 7.8 Hz,
2H), 7.2 (m, 6H), 3.9 (s, 4H), 3.1 (p, J ) 6.9 Hz, 2H), 3.0 (t, J )
(39) Sheldrick, G. M. In SADABS, 2.03 ed.; Sheldrick, G. M., Ed.;
Unviersity of Go¨ttingen: Go¨ttingen, Germany, 2000.
(40) Sheldrick, G. M. In SHELXTL, 5.10 ed.; Sheldrick, G. M., Ed.; Bruker
Analytical X-ray Instuments, Inc.: Madison, WI, 1997.
Inorganic Chemistry, Vol. 44, No. 25, 2005 9199

Patten et al.
6.3 Hz, 2H), 2.6 (t, J ) 6.3 Hz, 2H), 1.1 (d, J ) 6.9 Hz, 12H). 13
C
Synthesis of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamide]copper(II) Bromide ([DIPMAP]-
CuIIBr2, 5). A solution of 0.987 g (2.30 mmol) of DIPMAP in 20
mL of dry CH3CN was cannulated onto 0.533 g (2.38 mmol) of
CuBr2. The reaction was heated at reflux and then cooled. Volatile
materials were removed by rotary evaporation, and the resulting
blue-green solid was recrystallized from THF, yielding 0.934 g
NMR (100 MHz, DMSO-d6): δ (ppm) 171, 159, 149, 146, 137,
133, 127, 123, 60, 51, 34, 29, 24.5, 24.0; IR (CH2Cl2): ν (cm-1
)
3239, 3187, 2964, 2868, 1670, 1590, 1526.
Synthesis of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamide]copper(I) Chloride ([DIPMAP]-
CuICl, 1). A solution of 1.09 g (2.54 mmol) of DIPMAP in 25 mL
of dry CH2CN was cannulated onto 0.252 g (2.55 mol) of CuCl.
The mixture was stirred at reflux for 10 min and then allowed to
cool slowly to 0 °C when yellow crystals formed. The solution
was filtered, and all volatile materials were removed under vacuum,
yielding 1.11 g (83%) of product. Crystals suitable for X-ray
crystallography were grown by diffusion of hexane into a butyro-
(62%) of crystals suitable for X-ray analysis. IR (CH2Cl2): ν (cm-1
)
3156, 2962, 2927, 2867, 1671, 1639, 1608, 1523. UV-vis: λmax
) 816 nm, ꢀ ) 425 M-1 cm-1. Anal. Calcd for C27H34N4OCuBr2:
C, 49.59; H, 5.24; N, 8.57. Found: C, 47.1; H, 5.2; N, 8.0.
Synthesis of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamidate]copper(II) Bromide ([DIPMAP]-
CuBr, 6). A solution of 0.540 g (0.826 mmol) of [DIPMAP]CuBr2
in 30 mL of dry CH3CN was cannulated onto 0.101 g (0.902 mmol)
of KOtBu. The reaction was stirred for 2 days and then filtered.
Volatile materials were removed under vacuum. The resulting solid
was recrystallized from dry THF, yielding 0.230 g (42%) of a green
solid. IR (CH3CN): ν (cm-1) 2962, 2927, 2867, 1603, 1564. UV-
1
nitrile solution. Mp: 169-171°C. H NMR (400 MHz, CD3CN):
δ (ppm) 8.7 (s, 1H), 8.5 (d, J ) 3.6 Hz, 2H), 7.8 (d, J ) 7.5 Hz,
2H), 7.4 (d, J ) 5.6 Hz, 2H), 7.2 (t, J ) 7.2 Hz, 2H), 7.1 (t, J )
6.8 Hz, 3H), 3.8 (s, 4H), 3.1 (d, J ) 7.2 Hz, 2H), 7.1 (t, J ) 6.8
Hz, 3H), 3.8 (s, 4H), 3.1 (d, J ) 7.2 Hz, 2H), 3.0 (t, J ) 6.6 Hz,
2H), 2.8 (d, J ) 7.2 Hz, 2H), 1.0 (d, J ) 6.9 Hz, 12H). 13C NMR
(150 MHz, CD2Cl2): δ (ppm) 172.5, 156.4, 149.8, 146.8, 137.2,
132.2, 127.9, 124.3, 123.9, 123.2, 59.9, 51.2, 38.0, 28.5, 23.9, 23.1;
IR (CH2Cl2): ν (cm-1) 3239, 3179, 2962, 2868, 1676, 1599, 1526.
Anal. Calcd for C31H41N5OCuCl: C, 62.19; H, 6.90; N, 11.70.
Found: C, 61.7; H, 7.0; N, 11.2.
vis: λmax ) 786 nm, ꢀ ) 80 M-1 cm-1
.
Oxidation of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamidate]copper(I) Using CBr4, 4. To
2.0 mL of a 5.6 × 10-4 M solution of [DIPMAP]Cu in dry
CH3CN was added 3.7 mg (1.12 × 10-2 mmol) of CBr4. The
solution was stirred until the color turned green and the UV-vis
spectrum showed no CuI present. IR (CH3CN): ν (cm-1) 2962,
2927, 2867, 1603, 1564. UV-vis: λmax ) 786 nm, ꢀ ) 80 M-1
Synthesis of Lithium [N-(2,6-Diisopropylphenyl)-3-[bis(2-
pyridylmethyl)amino]propanamidate]copper(I) Chloride (2). A
solution of 0.600 g (1.13 mmol) of [DIPMAP]CuCl in 40 mL of
dry THF was stirred at 0 °C while 0.810 mL (1.13 mmol) of n-BuLi
was added dropwise. The solution was stirred overnight at room
temperature. The resulting mixture was then filtered, and the filtrate
was concentrated. The residue was recrystallized from dry CH3CN,
yielding 0.512 g (86%) of white crystals suitable for X-ray analysis.
1H NMR (400 MHz, CD3CN): δ (ppm) 9.14 (d, 2H), 8.36 (d, J )
4.5 Hz, 2H), 8.25 (s, 2H), 7.65 (t, J ) 6.5 Hz, 4H), 7.2-6.8 (m,
12H), 4.49 (d, J ) 15 Hz, 2H), 3.94 (d, J ) 3.9 Hz, 4H), 3.82 (d,
J ) 15.5 Hz, 2H), 3.63 (d, J ) 15.5 Hz, 2H), 2.95 (m, 2H), 2.85
(t, J ) 6.5 Hz, 2H), 2.76 (d, J ) 5.5 Hz, 2H), 2.60 (d, J ) 4.0 Hz,
2H), 2.00 (d, J ) 4.0 Hz, 2H), 1.87 (s, 4H), 1.03 (d, J ) 7.0 Hz,
2H), 0.94-0.80 (m, 24H). 13C NMR (150 MHz, CD2Cl2): δ (ppm)
177.5, 161.5, 160.6, 152.0, 151.7, 145.1, 145.0, 144.1, 140.3, 139.7,
126.8, 125.3, 124.2, 123.1, 63.4, 60.7, 54.5, 53.6, 38.1, 31.3, 30.1,
29.9, 25.9, 25.8, 25.6, 24.8. IR (CH2Cl2): ν (cm-1) 2962, 2876,
1591, 1565.
cm-1
.
Reaction of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamidate]copper(I) with Benzyl Bromide
in the Presence of TEMPO. A 4.0-mL sample of a 1.23 × 10-2
M solution of [DIPMAP]Cu in dry CH3CN was diluted with 0.9
mL of dry CH3CN. Then, 0.09 mL of a 1.09 M solution of TEMPO
in dry CH3CN was added, followed by the addition of 0.05 mL of
benzyl bromide. At time intervals, 0.1-mL samples were taken and
diluted with 1:100 bromobenzene/CH2Cl2 and injected into the GC-
MS (benzyl bromide, Rt ) 5.02; TEMPO, Rt ) 5.30; benzyl-
TEMPO derivative, Rt ) 7.33).
Polymerization of tert-Butyl Acrylate. A 25-mL Schlenk flask
was charged with an amount of Cu[DIPMAP] (see Table 3) and
dry p-xylene. Dry tert-butyl acrylate and ethyl 2-bromopropionate
were then added, and the flask was immersed in either a room-
temperature water bath (T ) 25 °C) or an ice bath (T ) 0 °C).
At time intervals, 0.5-mL samples were taken and added to 5 mL
of THF. Concentrations were measured using GC, and mo-
lecular weights were determined by GPC. All GPC samples were
passed through a short alumina column to remove copper from the
samples.
Synthesis of [N-(2,6-Diisopropylphenyl)-3-[bis(2-pyridyl-
methyl)amino]propanamidate]copper ([DIPMAP]Cu, 3). A so-
lution of 0.401 g (0.758 mmol) of [DIPMAP]CuCl in ∼50 mL of
dry CH3CN was heated and then cannulated while hot onto 0.104
g (0.923 mmol) of potassium tert-butoxide (KOtBu). The reaction
was stirred for 2 days and then hot filtered. The supernatant was
cooled, and orange crystals that were suitable for X-ray analysis
formed over several days. The solution was filtered, and the
remaining volatile materials were removed under vacuum, yielding
0.320 g (81%) of product. 1H NMR (400 MHz, CD3CN): δ (ppm)
8.5 (d, J ) 4.4 Hz, 1H), 8.4 (s, 2H), 7.8-7.0 (m, 29H), 5.3 (s,
5H), 4.0 (s, 6H), 3.5 (q, J ) 6.4 Hz, 4H), 3.3 (q, J ) 7.2 Hz, 4H),
3.1 (s, 3H), 3.0 (t, J ) 7.2 Hz, 4H), 2.8 (d, J ) 8.4 Hz, 1H), 2.6
(s, 2H), 1.2-0.7 (m, 36H). 13C NMR (150 MHz, CD2Cl2): δ (ppm)
172.5, 156.4, 150.4, 149.2, 146.6, 137.7, 136.6, 132.2, 128.4, 127.4,
124.8, 124.5, 123.8, 123.4, 122.7, 60.8, 59.9, 59.0, 51.2, 38.0, 28.9,
28.0, 24.3, 23.5, 22.6. IR (CH2Cl2): ν (cm-1) 2961, 2876, 1591,
1565. UV-vis: λmax ) 360 nm, ꢀ ) 996 M-1 cm-1. Anal. Calcd
for C54H66N8O2Cu2: C, 65.76; H, 6.75; N, 11.36. Found: C, 65.6;
H, 6.8; N, 11.2.
Results and Discussion
The ligand in this study was N-(2,6-diisopropylphenyl)-
3-[bis(2-pyridylmethyl)amino]propanamide (DIPMAP), which
contained the basic structure of neutral tripodal tetradentate
ligands that have been explored in ATRP studies and could
be deprotonated to become monoanionic. DIPMAP was
prepared in two steps. First, N-(2,6-diisopropylphenyl)-
propenamide was prepared by the addition-elimination
reaction of 2,6-diisopropylaniline with acryloyl chloride.
Then, bis(2-pyridylmethyl)amine was added to the
product via a Lewis acid catalyzed Michael addition
(Scheme 1).
9200 Inorganic Chemistry, Vol. 44, No. 25, 2005

Copper(I) and -(II) Complexes of DIPMAP
Scheme 1. Synthetic Route for the Preparation of DIPMAP
Figure 1. Molecular structure of complex 1.
Table 2. Bond Lengths for DIPMAP Complexes
complex complex complex
complex
bond
1
2
3
5
amide C-N
amide C-O
3° amine-Cu
1.357(2) 1.321(2) 1.336(3)
1.232(2) 1.269(2) 1.252(2)
1.365(8),a 1.336(8)
1.242(7),a 1.248(7)
2.064(5),a 2.051(5)
2.265(2)
2.234(2)
pyridyl N-Cu 2.017(2)
pyridyl N-Cu 2.087(2)
Cu-amide N
2.063(2)) 1.999(5),a 1.995(4)
2.141(2)
1.875(2) 1.954(2)
2.008(5),a 1.993(5)
2.260(4),a 2.213(4)
2.54,a 2.54
Cu-amide O
The complexation of DIPMAP with CuCl was accom-
plished when a CH3CN solution of 1 equiv each of DIPMAP
and CuCl was heated at reflux (eq 1). A yellow-orange
H‚‚‚Cl1
H‚‚‚Br2
Cu-Cl
2.41
2.252(2) 2.103(1)
a Values for the complex with an additional coordinated water molecule.
(111°, 120°, and 130°). The two bond angles containing the
central nitrogen donor atom, the copper center, and a pyridyl
donor nitrogen atom are both 80°, while the bond angle
containing the pyridyl donor nitrogen atoms and the copper
center is 118°. All of these angles reflect the fact that the
short methylene bridge between the central nitrogen atom
and the pyridyl rings constrains the bite angle of the N1, N2
and N1, N3 pairs. The pyridyl C-C and C-N bond lengths
as well as the N-Cu distances are within the range found
for other pyridyl rings coordinated to copper(I) centers.41-43
The X-ray structure also revealed a weak intramolecular
hydrogen bond [N4‚‚‚Cl1 distance of 3.2648(16) Å] between
the amide proton and the chloride ligand bound to the copper
center.44
solution formed, and upon slow cooling, yellow crystals grew
in 83% yield, complex 1. Elemental analysis confirmed that
the empirical formula of complex 1 was Cu[DIPMAP]Cl.
The next step was to deprotonate the amide group in
complex 1 and coordinate the anionic donor to the copper
center via an intramolecular halogen metathesis reaction. A
stoichiometric amount of n-butyllithium was added to a THF
solution of complex 1 (eq 2). Colorless crystals were ob-
tained, complex 2, which was unexpected because pyridine/
copper(I) complexes are colored as a result of metal-to-ligand
charge-transfer absorptions, and the anticipated product
would have this ligand set. Deprotonation of the amide group
was confirmed by the absence of an amide proton signal at
1
Differences in the H NMR chemical shifts of the pyridyl
ring protons (8.5, 7.8, and 7.4 ppm) and the bridging
methylene protons (3.1 and 2.9 ppm) in the product versus
those of the free ligand (8.2, 7.7, and 7.4 ppm for the pyridyl
ring protons and 2.8 and 2.6 ppm for the bridging methylene
protons) also confirmed complex formation.
Crystals suitable for X-ray crystallography were grown
from a butyronitrile/hexane solvent system. The molecular
structure for complex 1 is shown in Figure 1, and the crystal
data are contained in Table 1. The complex crystallized in
the space group P1 with one molecule of butyronitrile. The
geometry about the copper center is approximately tetrahedral
with distortions due to the geometrical constraints of the
ligand, and Table 2 shows key bond angle and distance data
for the complex. The three bond angles containing a nitrogen
atom, Cu1, and Cl1 are all greater than the ideal of 109.5°
1
8.7 ppm in the H NMR spectrum and the absence of an
N-H stretch at 3200 cm-1 in the IR spectrum.
(41) Levy, A. T.; Olmstead, M. M.; Patten, T. E. Inorg. Chem. 2000, 39,
1628-1634.
(42) Munakata, M.; Kitagawa, S.; Ashara, A.; Masuda, H. Bull. Chem. Soc.
Jpn. 1987, 1987, 1927-1929.
(43) Dobson, J. F.; Green, B. E.; Healy, P. C.; Kennard, C. H. L.;
Pakawatchai, C.; White, A. H. Aust. J. Chem. 1984, 37, 649-659.
(44) Emsley, J. Chem. Soc. ReV. 1980, 9, 91-124.
Inorganic Chemistry, Vol. 44, No. 25, 2005 9201

Patten et al.
Figure 2. Molecular structure of complex 2.
solvents such as THF or CH3CN. A stoichiometric amount
of KOtBu was added to [DPPMAP]CuICl in CH3CN, and
the solution was stirred (eq 3). After removal of a precipitate
Crystals suitable for X-ray crystallography were obtained
from CH3CN. The molecular structure for complex 2 is
shown in Figure 2, and the crystal data are contained in Table
1. The structure of complex 2 is that of a centrosymmetric
dimer of Li[DIPMAP]CuCl consisting of a central ring of
two lithium and two oxygen atoms flanked by two ap-
proximately linear N-Cu-Cl units. The asymmetric unit also
contains a cocrystallized molecule of CH3CN. The presence
of four cations (two Li+ and two Cu+) and only two anions
(two Cl-) indicates that the amide group in complex 2 must
be deprotonated in order to maintain overall charge neutrality.
The lithium ions are five coordinate and are complexed to
the three nitrogen donor atoms and the amidate oxygen atom
of one ligand plus the amidate oxygen atom of the other
ligand. A comparison of the amidate C-O [1.268(2) Å] and
C-N [1.321(2) Å] bond distances in complex 2 (Table 2)
with those of the amide in complex 1 [C-O ) 1.230(2) Å
and C-N ) 1.357(2) Å] indicates a shorter C-N distance
and a longer C-O distance in complex 2 relative to complex
1. This is consistent with delocalization of the amidate
negative charge onto both the nitrogen and oxygen atoms in
complex 2, as shown in eq 2. The presence of a negative
charge on the amidate nitrogen makes it possible to form
the linearly coordinated N1-Cu1-Cl1 cuprate structure. The
Cu1-Cl1 distance of 2.1034(5) Å is consistent with those
by filtration, the filtrate was set aside and orange crystals
formed, complex 3. Elemental analysis indicated that com-
plex 3 had the empirical formula Cu(DIPMAP). The IR
spectrum of this complex did not show a broad signal at
3200 cm-1 expected for amides, and the signal for the CdO
stretch at 1676 cm-1 seen for complex 1 was replaced by a
signal at 1565 cm-1, consistent O-C-N stretching frequen-
cies for metal-coordinated amidates.46 The 1H NMR spectrum
of complex 1 exhibited two sets of signals, and it appeared
as if the spectrum were doubled, consistent with two similar
complexes or a monomer/dimer equilibrium mixture.
The crystals formed from the filtrate were suitable for
X-ray analysis. The molecular structure of complex 3 is
shown in Figure 3, and the crystal data are contained in Table
1. The structure is a centrosymmetric dimer with each half
unit consisting of the pyridyl and central amine donor of
one ligand coordinated to one copper center with the amidate
nitrogen of the same ligand coordinated to the second copper
center. The geometry of the copper centers is distorted
tetrahedral. The N-Cu-N angles from the central donor
atom, N2, are 79.61(7)°, 80.99(7)°, and 140.04(7)° (Table
-
found in CuCl2 ions (2.107 Å)45 and is shorter than the
Cu1-Cl1 distance found in complex 1 [2.2517(4) Å]. The
N1-Cu1-C11 angle is 171.35(5)°, and the structure is bent
away from the core of lithium and oxygen atoms. No specific
interactions between the nearest lithium atom and the copper
center at a distance of 3.260 Å away can be inferred because
dihalocuprate ions are known to bend away from linear 180°
coordination geometries depending upon the steric forces of
crystal packing. The dihalocuprate-like structure of the
copper(I) ion in complex 2 is also consistent with the
observation that its crystals were colorless because the
analogous CuCl2- ion is also colorless (CuBr2- is typically
a very pale lilac or green color).45
The unwanted incorporation of LiCl into the product was
most likely a consequence of its solubility in THF. Thus,
KOtBu was used as the base in place of n-BuLi, because
KCl is insoluble in relatively nonpolar and aprotic organic
(45) Nilsson, M. Acta Chem. Scand. B 1982, 36, 125-126.
(46) Patterson, R. E.; Gordon-Wylie, S. W.; Woomer, C. G.; Norman, R.
G.; Weintraub, S. T.; Horwitz, C. P.; Collins, T. J. Inorg. Chem. 1998,
37, 4748-4750.
9202 Inorganic Chemistry, Vol. 44, No. 25, 2005

Copper(I) and -(II) Complexes of DIPMAP
Table 3. Data for the Polymerization of tert-Butyl Acrylate in
p-Xylene with a [DIPMAP]CuI Catalyst System
[M] [M]/ [I]/
%
Mw/ temp time
(M) [I]
[Cu] yield
Mn
Mn(theor) Mn (°C) (min)
5.15 91
3.65 85 1.8 × 10-4 9.9 × 10-3 2.05 25
4.26 50 1.8 × 10-4 5.4 × 10-3 1.39 25
10
91
108
3.38 88 11.05 46 5.4 × 10-4 5.2 × 10-3 1.42 25
2.55 84
a 10-fold excess of TEMPO and an equimolar amount of
benzyl bromide were added (eq 4). Over time, the com-
ponents of the solution were monitored using GC-MS,
and the benzyl bromide (Rt ) 5.02) was converted to the
benzyl-TEMPO adduct (Rt ) 7.33). This transformation
demonstrated that complex 3 was capable of abstracting
halogen atoms from certain organic halides to generate
radicals.
Figure 3. Molecular structure of complex 3.
2), indicating that the bite angles between the pyridyl nitrogen
atoms and the central nitrogen atom are too small to
accommodate tetrahedral 109.5° geometry. Dimer formation
is most likely driven by steric strain that would be present
in the hypothetical monomeric complex: the three-carbon
bridge between the central donor nitrogen and the amidate
nitrogen is too short to accommodate the 140° corresponding
N-Cu-N angle observed in the dimer. The monomeric
species most likely adopts a severely distorted tetrahedral
geometry. Inspection of the coordination geometry and bite
angles available to DIPMAP indicates that the copper atom
in such a monomeric complex would be very close to the
tetrahedral face of the three pendant donor atoms, N1, N3,
and N4. Formation of a dimer, as in complex 3, would
effectively release this strain. A solution equilibrium between
the monomer and dimer would be consistent with the
Complex 3 was then examined as a potential ATRP
catalyst (eq 5 and Table 3). A polymerization of tert-butyl
acrylate initiated using ethyl 2-bromopropionate was at-
tempted using an initiator to complex 3 ratio of 4:1 and a
monomer to initiator ratio of 90:1. The resulting polymeri-
zation was extremely rapid, reaching 85% conversion after
just 10 min, and the molecular weight control was poor, as
shown by the molecular weight distribution (Mw/Mn) of 2.05.
The molecular weight versus conversion plot deviated from
the linear correspondence normally observed for controlled/
living polymerizations. Reducing the polymerization tem-
perature to 0 °C slowed the rate of polymerization such that
minimal conversion was observed over the course of a few
hours. Increasing the ratio of initiator to complex 3 from
4:1 to 11:1 while holding the monomer to initiator ratio
constant, produced a more narrow molecular weight distribu-
tion. Reducing the monomer concentration by half while
holding the monomer to initiator ratio and the initiator to
complex 3 ratio constant led to the best molecular weight
distribution, but the molecular weight versus conversion plots
still did not show a linear correlation and the molecular
weights were too high by factors ranging from 2 to 9. This
polymerization behavior strongly indicated that the deactiva-
tion of the organic radical, by reabstraction of a halogen atom
from the copper(II) complex, was too slow relative to the
rate of propagation. The polymerization displayed more
characteristics of a redox initiated polymerization than a
controlled polymerization. The polymerization of styrene was
attempted, but at the temperatures necessary for this reaction,
complex 3 underwent decomposition to an insoluble brown
solid.
1
doubling of signals in the H NMR spectrum. Complex 3,
the dimer, may have preferentially crystallized from the
solution. The pyridyl C-C and C-N bond lengths as well
as the N-Cu distances are within the range found for other
pyridyl rings coordinated to copper(I) centers.41-43 A com-
parison of the bond lengths of C15-N4 [1.337(3) Å] and
C15-O1 [1.252(3) Å] with those of complexes 1 and 2
shows that these distances are between those found for
complexes 1 and 2. Thus, it is reasonable to conclude that
while the negative charge of the amidate group is delocalized,
more of the charge is localized on the nitrogen atom next to
the positively charged copper center.
The reaction of complex 3 with benzyl bromide was
studied to see if the compound would promote halogen atom
transfer. Complex 3 was dissolved in dry CH3CN, and then
To gain a better understanding about the radical deactiva-
tion process for this ATRP system, we attempted to isolate
and identify the copper(II) complex formed after atom
Inorganic Chemistry, Vol. 44, No. 25, 2005 9203

Patten et al.
Figure 4. Overlay of UV-vis spectra at different times of the reaction
between complex 3 and CBr4 plus registered plot of the expanded region
of the long-wavelength portion of the spectra.
transfer. Carbon tetrabromide, an efficient halogen atom-
transfer oxidizing agent, was added to a solution of complex
3 (eq 6), and the reaction was monitored using UV-vis
spectroscopy (Figure 4). A decrease in the intensity of the
ligand-to-metal charge-transfer band at 360 nm was observed
along with the growth of a d-d transition band of a new
copper(II) species, complex 4, at 786 nm (ꢀ ) 80 L mol-1
cm-1). An isosbestic point was observed in overlay spectra,
indicating that complex 3 was converted directly into
complex 4. Unfortunately, it was not possible to isolate
complex 4 cleanly upon repeated attempts.
Hence, we tried to prepare and characterize a copper(II)
complex from deprotonated DIPMAP and CuBr2 and then
match its spectroscopic signatures to those of complex 4.
One equivalent of DIPMAP was added to CuBr2 in CH3CN,
and the solution was heated at reflux (eq 7). Blue-green
Figure 5. Molecular structure of complex 5 showing (A) the molecule
with a coordinated water and (B) the molecule with a vacant sixth
coordination site.
were recovered and recrystallized from THF, complex 5.
Crystals suitable for X-ray analysis were obtained from this
process. Crystal data are contained in Table 1. There are
two complexes in the asymmetric unit, shown as A and B
in Figure 5. In molecule A, the pyridyl nitrogens, the amine
nitrogen (N2), and Br1 are in the square plane, and the amide
oxygen (O1) is in the axial position. An additional disordered
water oxygen (O1W) is at 0.35 occupancy and is trans to
the axial amide oxygen; it exhibits a long Cu-O distance
of 2.695(12) Å (Table 2). Molecule B has no atom in the
sixth coordination site. There are minor, yet significant,
differences between the two molecules. The C-O and C-N
bond distances in the amide group are consistent with those
found in complex 1. About the copper centers, the N-Cu-N
bond angles range from 81.2° to 82.8°, which reflects the
chelate bite angle of the ligand. Correspondingly, the
N-Cu-Br bond angles are a bit greater than 90°: 96.1-
98.3°. The copper centers are displaced outward from the
square plane, which is reflected in the O-Cu-N and
O-Cu-Br bond angles being slightly greater than 90°:
91.8-101.5°. The copper-pyridine N bond lengths range
from 1.993(5) to 2.008(5) Å, and the copper-tertiary amine
crystals formed almost immediately in good yield, which
9204 Inorganic Chemistry, Vol. 44, No. 25, 2005

Copper(I) and -(II) Complexes of DIPMAP
of the two complexes were noticeably different in appear-
ance. The spectrum for complex 6 exhibited hyperfine
coupling to the Cu nucleus with A| ) 150 G, similar to other
examples of axially distorted trigonal-bipyramidal N4Br-
CuII complexes.31 The spectrum for complex 4 appears quite
different from that of complex 6, and barring further
characterization, we can only tentatively postulate that the
structure of complex 4 is not distorted trigonal-bipyramidal.
The structure of complex 3 is dimeric, so it is reasonable to
assume that after atom transfer the resulting complex would
be a mixed CuI-CuII dimeric species or quite possibly that
significant ligand-sphere reorganization occurs to yield
separate copper(I) and (II) complexes. Both possibilities
could account for the slow rate of deactivation observed in
the ATRP of acrylates using complex 3.
Conclusions
A new monoanionic, tripodal tetradentate ligand, N-(2,6-
diisopropylphenyl)-3-[bis(2-pyridylmethyl)amino]propan-
amide (DIPMAP), was prepared by the addition-elimination
reaction of 2,6-diisopropylaniline with acryloyl chloride and
then a Lewis acid catalyzed Michael addition of bis(2-
pyridylmethyl)amine to this product. The ligand was com-
plexed to CuCl to yield a monomeric complex with a N3Cl
donor set, complex 1, featuring an intramolecular hydrogen
bond between the free amide hydrogen and the coordinated
chloride ligand. Deprotonation of the amide hydrogen in
complex 1 using n-BuLi led to the incorporation of LiCl in
the resulting product, complex 2. Complex 2 exhibited an
unusual dimeric structure with the amine nitrogens of one
ligand coordinated to a lithium ion, the amide oxygen
bridging between the lithium ions, and the amide nitrogen
coordinated to a CuCl unit with a structure analogous to
dihalocuprate ions. Deprotonation of complex 1 using KOtBu
yielded an alkali-metal chloride free product, complex 3, that
also exhibited a dimeric structure in which the three amine
nitrogens of one ligand were coordinated to one CuI ion and
the amidate nitrogen of the same ligand was coordinated to
the other CuI ion. Complex 3 was effective in abstracting
halogen atoms from organic halides, but in the attempted
ATRP of tert-butyl acrylate, the complex only showed
polymerization behavior reminiscent of a redox-initiated
polymerization. DIPMAP was coordinated to CuBr2 to yield
a N3OBr donor set with a square-pyramidal structure,
complex 5. The amide hydrogen in complex 5 could be
deprotonated using KOtBu to form complex 6. Spectral
characterization of complex 6 indicated that deprotonation
had occurred and that it most likely had an axially distorted
trigonal-bipyramidal structure, although crystals suitable for
X-ray analysis could not be obtained so confirmation of this
conclusion was not possible. Solution oxidation of com-
plex 3 using CBr4 yielded a product, complex 4, whose
spectral signatures did not match those of complex 6,
Figure 6. EPR spectra of complexes 4 (top) and 6 (bottom).
N bond lengths are 2.064(5) and 2.051(5) Å, which are
consistent with the values found in complexes similar to those
of CuII. The Cu-Br bond distances are also similar to those
found in CuII complexes. The copper-amide oxygen bond
distances show some variation, depending upon the presence
of the additional water ligand: Cu2-O2, 2.213(4) Å, in the
water-free complex was slightly shorter than Cu1-O1,
2.260(4) Å, in the complex with the coordinated water. This
small difference is most likely due to the trans influence of
the water ligand. The free bromide anion is hydrogen bonded
to the amide hydrogen, with N-Br distances of 3.390(5)
(N4-Br3) and 3.328(5) Å (N8-Br4).
A stoichiometric amount of KOtBu was added to complex
5 in CH3CN (eq 8). After removal of a precipitate by
filtration, the resulting solid was recrystallized from THF,
complex 6. Repeated attempts to grow crystals of this
complex failed to yield crystals suitable for X-ray analysis.
Deprotonation of the amide hydrogen was confirmed by the
absence of a signal at 3200 cm-1 in the IR spectrum. The
UV-vis spectrum of complex 6 showed a d-d transition at
786 nm (ꢀ ) 80 L mol-1 cm-1). Considering the similarities
of the UV-vis spectra, we then compared the EPR spectra
of complexes 4 and 6. As seen in Figure 6, both complexes
had similar g values (g| ) 2.2 and g ) 2.0), analogous to
those of other copper(II) complexes with comparable,
noncentrosymmetric ligand spheres.47,48 However, the spectra
(48) Kurosaki, H.; Hayashi, K.; Ishikawa, Y.; Goto, M.; Inada, K.;
Taniguchi, I.; Shionoya, M.; Kimura, E. Inorg. Chem. 1999, 38, 2824-
2832.
(47) Peisach, J.; Mims, W. B. Chem. Phys. Lett. 1976, 37, 307-310.
Inorganic Chemistry, Vol. 44, No. 25, 2005 9205

Patten et al.
indicating that the dimeric structure of complex 3 might
be a significant factor in the slow rate of deactivation
observed in atom-transfer reactions using complex 3 as the
catalyst.
also thank the research group of Dr. David Britt (UCD) for
their assistance with EPR.
Supporting Information Available: Crystallographic data for
complexes 1-3 and 5. This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. We thank the ACS Petroleum Re-
search Fund (35150-AC7) for support of this research. We
IC0505697
9206 Inorganic Chemistry, Vol. 44, No. 25, 2005