Structural comparison of copper(I) and copper(II) complexes with tris(2-pyridylmethyl)amine ligand

Article abstract of DOI:10.1021/ic1016142

Copper(I) complexes with the tris(2-pyridylmethyl)amine (TPMA) ligand were synthesized and characterized to examine the effect of counteranions (Br ^-, ClO₄^-, and BPh₄^-), as well as auxiliary ligands (

Full text of DOI:10.1021/ic1016142

Inorg. Chem. 2010, 49, 10617–10626 10617
DOI: 10.1021/ic1016142
Structural Comparison of Copper(I) and Copper(II) Complexes with
Tris(2-pyridylmethyl)amine Ligand
William T. Eckenhoff and Tomislav Pintauer*
Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, 308 Mellon Hall,
Pittsburgh, Pennsylvania 15282, United States
Received August 9, 2010
Copper(I) complexes with the tris(2-pyridylmethyl)amine (TPMA) ligand were synthesized and characterized to
examine the effect of counteranions (Br-, ClO4-, and BPh4 ), as well as auxiliary ligands (CH3CN, 4,40-dipyridyl, and
-
PPh3) on the molecular structures in both solid state and solution. Partial dissociation of one of the pyridyl arms in
TPMA was not observed when small auxiliary ligands such as CH3CN or Br- were coordinated to copper(I), but was
found to occur with larger ones such as PPh3 or 4,40-dipyridyl. All complexes were found to adopt a distorted
tetrahedral geometry, with the exception of [CuI(TPMA)][BPh4], which was found to be trigonal pyramidal because of
˚
stabilization via a long cuprophilic interaction with a bond length of 2.8323(12) A. Copper(II) complexes with the
general formula [CuII(TPMA)X][Y] (X = Cl-, Br- and Y = ClO4-, BPh4-) were also synthesized to examine the effect
of different counterions on the geometry of [CuII(TPMA)X]þ cation, and were found to be isostructural with previously
reported [CuII(TPMA)X][X] (X = Cl- or Br-) complexes.
Introduction and Background
mimic certain metalloenzymes of relevance to oxygen
activation.6-14 Also, on the other hand, it is complexes with
copper that have been shown to be among the most active in
atom transfer radical addition (ATRA)15-17 and polymeri-
zation (ATRP).18,19 Both processes originated from well-
known Kharasch addition in which polyhalogenated com-
pounds were added to alkenes via free-radical means.20-22
Recent studies have also indicated that TPMA is a superior
Tris(2-pyridylmethyl)amine (TPMA) is a widely used
neutral tripodal nitrogen based ligand that has been com-
plexed to a wide variety of transition metals. Currently, the
Cambridge Crystallographic Database contains over 350
structures with metals spanning from group 1 to 13 of the
periodic table, including many cases from the lanthanide and
actinide series. TPMA is an excellent chelator that typically
coordinates to a metal in a tetradentate fashion. However, in
some cases, tridentate coordination achieved by pyridyl
nitrogen arm dissociation has also been observed. Some
representative structures of copper(I and II),1,2 iron(II),3
ruthenium(II),4 and europium(III)5 complexes with TPMA
ligand are shown in Figure 1.
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*To whom correspondence should be addressed. E-mail: pintauert@
duq.edu. Phone: 412-396-1626. Fax: 412-396-5683.
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r
2010 American Chemical Society
Published on Web 10/12/2010
pubs.acs.org/IC

10618 Inorganic Chemistry, Vol. 49, No. 22, 2010
Eckenhoff and Pintauer
Figure 1. Examples of different transition metal complexes containing coordinated TPMA ligand; (a) CuI(TPMA)Br,1 (b) [CuII(TPMA)Br][Br],1
(c) FeII(TPMA)Cl2,2 (d) [RuII(TPMA)2][PF6]2,3 and (e) EuIII(TPMA)Cl3.4.
complexing ligand in ATRA1,2,16,17,23-32 and ATRP26,33-36
that utilize reducing agents. The role of a reducing agent in both
Scheme 1. Proposed Mechanism for Copper Catalyzed ATRA in the
Presence of Radicals Generated by Thermal Decomposition of AIBN
systems is to continuously regenerate the activator species
(copper(I) complex) from the corresponding deactivator
(copper(II) complex). The latter one accumulates in the system
as a result of unavoidable and often diffusion controlled
radical-radical termination reactions. This is schematically
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illustrated in Scheme 1 in the case of simple ATRA addition.
ATRP is a mechanistically similar process with the exception
that the structure of the starting alkyl halide and alkene (or
monomer) are modified in such a way that multiple activation/
deactivation cycles can occur. As a result, these synthetically
useful reactions for the syntheses of small organic molecules
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Despite a significant effort devoted to the use of copper(I)
and copper(II) complexes with TPMA ligand in synthetic
aspects of ATRA and ATRP, structural and mechanistic
studies of this active catalytic system still need further

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10619
Scheme 2. Proposed Equilibria for CuI(TPMA)Br Involving Bromide
Anion and Pyridine Nitrogen Association/Dissociation
on the linear correlation of E1/2 values with the equilibrium
constant for atom transfer (KATRA).18,27,43-46 Clearly, the
counterion in the copper(I) state, which was previously
thought to be merely a spectator ion, plays an important role
in the reaction mechanism.
In this article, copper(I and II) complexes with TPMA
ligand were synthesized, and counterion and coordinating
ligand effects on the catalyst structure in the solid state and
solution examined.
investigation. Recently, the molecular structures of CuI-
(TPMA)Cl and CuI(TPMA)Br were elucidated and surpris-
ingly, taking into account the tetradentate nature of TPMA
ligand, the copper(I) centers were found to contain coordinated
halide anions (Figure 1a).1,2 While these complexes can be seen
as pseudo-pentacoordinated, they were formally described as
distorted tetrahedral because of the elongated Cu-N axial
bond. It was further hypothesized that the high activity of CuI-
(TPMA)X and the corresponding [CuII(TPMA)X][X] (X =
Br- or Cl-) complexes in ATRA can be explained by the fact
that minimum entropic rearrangement was required upon
oxidation and reduction. However, the presence of coordinated
halide anions raised further questions regarding the catalytic
mechanism of ATRA, which was conventionally described as
an inner sphere electron transfer (ISET).18,37-40 The outer
sphere electron transfer (OSET) mechanism,18,37,38,40 while
theoretically feasible, was recently probed by extensive ab initio
calculations, which concluded that OSET was approximately
12 orders of magnitude slower than the ISET, clearly making
this an unlikely scenario. Therefore, the ISET process for
copper(I) halide complexes with TPMA ligand would require
an open coordination site, and is most likely preceded by either
dissociation of the halide anion or one arm of TPMA, as
indicated in Scheme 2.
Experimental Section
General Procedures. All chemicals were purchased from
commercial sources and used as received. Tris(2-pyridyl-
methyl)amine (TPMA)47 and [CuI(CH3CN)4][ClO4]48 were
synthesized according to literature procedures. Caution!
Although we have experienced no problems, perchlorate metal
salts are potentially explosive and should be handled with care. All
manipulations involving copper(I) complexes were performed
under argon atmosphere in the drybox (<1.0 ppm O2 and <0.5
ppm H2O), or using standard Schlenk line techniques. Solvents
(pentane, acetonitrile, acetone, and diethyl ether) were degassed
and deoxygenated using an Innovative Technology solvent
purifier. Methanol was vacuum distilled and deoxygenated by
bubbling argon for 30 min prior to use. Synthesis of copper(II)
complexes were performed in ambient conditions and solvents
1
were used as received. H NMR spectra were obtained using
Bruker Avance 400 and 500 MHz spectrometers and chemical
shifts are given in ppm relative to residual solvent peaks (CDCl3
δ7.26 ppm; (CD3)2CO δ2.05 ppm; CD3CN δ1.96 ppm). 31P
NMR was referenced externally with 85% H3PO4 in D2O at δ0.
iNMR software and Kaleidagraph were used to generate images
of NMR spectra. Temperature calibrations were performed
using a pure methanol sample. IR spectra were recorded in the
solid state using a Nicolet Smart Orbit 380 FT-IR spectrometer
(Thermo Electron Corporation). Elemental analyses for C, H,
and N were obtained from Midwest Microlabs, LLC.
Dynamic behavior of CuI(TPMA)X(X =Br- and Cl-) was
1
further probed by H NMR spectroscopy, which confirmed
that the most probable structure in solution was in fact a
monomer with chemically equivalent pyridyl arms.1,41 Coordi-
nation of a solvent molecule, such as acetone, could theoreti-
cally also produce a symmetrical monomeric structure, but no
evidence was found to suggest this. Hence, bromide anion was
assumed to be the coordinating auxiliary ligand. Isolation of a
dimeric complex, [CuI(TPMA)]2[ClO4]2,42 was achieved in the
absence of a coordinating solvent or ligand, and the variable
X-ray Crystal Structure Determination. The X-ray intensity
data were collected at 150 K using graphite-monochromated
˚
Mo-K radiation (0.71073 A) with a Bruker Smart Apex II CCD
diffractometer. Data reduction included absorption corrections by
the multiscan method using SADABS.49 Structures were solved by
direct methods and refined by full matrix least-squares using
SHELXTL 6.1 bundled software package.50 The H-atoms were
positioned geometrically (aromatic C-H 0.93, methylene C-H
0.97, and methyl C-H 0.96) and treated as riding atoms during sub-
sequent refinement, with Uiso(H)=1.2Ueq(C) or 1.5Ueq(methyl C).
The methyl groups were allowed to rotate about their local 3-fold
axes. ORTEP-3 for windows51 and Crystal Maker 7.2 were used to
generate molecular graphics.
1
temperature H NMR showed, as expected, all three pyridyl
arms as chemically distinct. This also suggested that the
bromide anion was bound to copper in solution in the case of
CuI(TPMA)Br, thus preventing dimer formation. Similar con-
clusions were also drawn for CuI(TPMA)Cl complex.
To further investigate the role of the anion, copper(I and II)
complexes were synthesized with a variety of counterions such
as perchlorate (ClO4-), hexafluorophosphate (PF6-), and
tetraphenylborate (BPh4-). However, complexes with these
“non-coordinating” anions were found to be less reducing by
approximately 300 mV, when compared to their halide ana-
logues.1 These results also indicated that such complexes
should be substantially less active in ATRA systems based
[CuI(TPMA)(CH3CN)][BPh4] (1). TPMA (89.0 mg, 0.306
mmol) was dissolved in 2 mL of methanol followed by addition of
[CuI(CH3CN)4][ClO4] (100 mg, 0.306 mmol), resulting in a yellow
(43) Matyjaszewski, K.; Gobelt, B.; Paik, H.-j.; Horwitz, C. P. Macro-
molecules 2001, 34, 430–440.
(44) Qiu, J.; Matyjaszewski, K.; Thounin, L.; Amatore, C. Macromol.
Chem. Phys. 2000, 201, 1625–1631.
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M. L.; Matyjaszewski, K. J. Am. Chem. Soc. 2008, 130, 10702–10713.
(46) Tang, W.; Tsarevsky, N. V.; Matyjaszewski, K. J. Am. Chem. Soc.
2006, 128, 1598–1604.
(47) Britovsek, G.; England, J.; White, A. Inorg. Chem. 2005, 44, 8125–
8134.
(37) Kochi, J. K. Free Radicals; John Wiley & Sons: New York, 1973; Vol. 1.
(38) Lin, C. Y.; Coote, M. L.; Gennaro, A.; Matyjaszewski, K. J. Am.
Chem. Soc. 2008, 130, 12762–12774.
(39) Matyjaszewski, K. Macromolecules 1998, 31, 4710–4717.
(40) Tsarevsky, N. V.; Braunecker, W. A.; Matyjaszewski, K. J. Organo-
met. Chem. 2007, 692, 3212–3222.
(48) Munakata, M.; Kitagawa, S.; Asahara, A.; Masuda, H. Bull. Chem.
Soc. Jpn. 1987, 60, 1927–1929.
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(49) Sheldrick, G. M. SADABS, Version 2.03; University of Gottingen:
(41) Hsu, S. C.; Chien, S. S.; Chen, H. H.; Chiang, M. Y. Chin. Chem. Soc.
2007, 54, 685–692.
(42) Eckenhoff, W. T.; Manor, B. C.; Pintauer, T. Polym. Prepr. (Am.
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Gottingen, Germany, 2002.
(50) Sheldrick, G. M. SHELXTL,Crystallographic Computing System,
6.1; Bruker Analytical X-Ray System: Madison, WI, 2000.
(51) Faruggia, L. J. J. Appl. Crystallogr. 1997, 30(5, Pt. 1), 565.

10620 Inorganic Chemistry, Vol. 49, No. 22, 2010
Eckenhoff and Pintauer
solution. NaBPh4 (105 mg, 0.306 mmol) was then added to the
reaction mixture, which resulted in immediate precipitation of a
yellow powder. The crude product was filtered, thoroughly washed
with methanol, and redissolved in acetonitrile, resulting in a red
solution. [CuI(TPMA)(CH3CN)][BPh4] was precipitated as an
orange powder by slow addition of diethyl ether (yield = 137
mg, 62%). X-ray quality crystals were obtained by crystallization
in acetonitrile via slow diffusion of diethyl ether. 1H NMR
((CD3)2CO, 400 MHz, 180 K): δ9.17 (d, J = 4.7 Hz, 3H), δ7.77
(td, J = 7.6, 1.5 Hz, 3H), δ7.39 (d, J=7.8 Hz, 4H), δ7.30 (m, 4H),
δ7.10 (m, 3H), δ6.92 (t, J = 7.3 Hz, 4H), δ6.76 (t, J = 7.2 Hz, 2H),
δ4.03 (s, 6H), δ 3.54 (s, 3H). FT-IR (solid): ν (cm-1) = 3058 (m),
1599 (m), 1573 (w), 1475 (m), 1434 (m), 1367 (w), 1269 (w), 1153
(w), 1051 (w), 974 (w), 841 (w), 764 (m), 746 (m), 733 (s), 704 (s),
611 (s). Anal. Calcd. for C44H41N5CuB (714.17): C, 74.00; H, 5.79;
N, 9.81. Found C, 73.89; H, 6.01; N, 9.67.
[CuI(TPMA)][BPh4] (2). TPMA (89.0 mg, 0.306 mmol) was
dissolved in 2 mL of methanol followed by addition of [CuI-
(CH3CN)4][ClO4] (100 mg, 0.306 mmol), resulting in a yellow solu-
tion. NaBPh4 (105 mg, 0.306 mmol) was then added to the reaction
mixture which resulted in immediate precipitation of a yellow
powder. The crude product was washed thoroughly with methanol
to yield 156 mg (76%) of [CuI(TPMA)][BPh4]. Crystals suitable for
X-ray diffraction were obtained in acetone via slow diffusion of
diethyl ether. 1HNMR((CD3)2CO, 400 MHz, 298 K): δ8.67(s, 3H),
δ7.82 (td, J = 7.7, 1.3 Hz, 3H), δ7.43 (d, J = 7.8 Hz, 3H), δ7.38-
7.33 (m, 12H), δ6.92 (t, J=7.4 Hz, 7H), δ6.77 (t, J=7.2 Hz, 4H),
δ4.15 (bs, 6H). FT-IR (solid): ν(cm-1) =3053(w), 2982(w),
1601(m), 1475(m), 1427(m), 1269(w), 1134(w), 1101(w), 762(m),
733(s), 702(s), 611(m), 501(w). Anal. Calcd. for C42H38N4CuB
(673.14): C, 74.94; H, 5.69; N, 8.32. Found: C, 74.63; H, 5.66; N, 8.13.
[(CuI(TPMA))2-μ-Br][BPh4] (3). CuI(TPMA)Br (100 mg,
0.231 mmol), previously synthesized according to published
procedures,1 was dissolved in 5 mL of methanol followed by
addition of half an equivalent of NaBPh4 (39.4 mg, 0.115 mmol).
Although the precipitation of yellow powder occurred immediately,
it quickly dissolved back into the reaction mixture, resulting in the
formation of an orange solution. Upon slow addition of diethyl
ether or tetrahydrofuran (THF), [(CuI(TPMA))2-μ-Br][BPh4] pre-
cipitated as a red-orange powder (yield =81.0 mg, 32%). X-ray
quality crystals were obtained in acetone via slow diffusion of diethyl
ether. 1H NMR ((CD3)2CO, 400 MHz, 180 K): δ9.17 (d, J = 3.8
Hz, 6H), δ7.78 (t, J = 7.4 Hz, 6H), δ7.40 (d, J = 7.7 Hz, 6H), δ7.31
(m, 8H), δ 7.08 (m, 6H), δ6.92 (m, 8H), δ6.76 (m, 4H), δ4.03
(bs, 12H). FT-IR (solid): ν (cm-1)=3051(w), 2982(w), 2885(w),
2843(w), 1597(m), 1566(w), 1473(m), 1427(m), 1365(w), 1315(w),
1150(m), 1049(m), 975(w), 894(w), 758(s), 725(s), 706(s), 613(m),
501(m). Anal. Calcd. for C60H56N8Cu2BrB (1106.95): C, 65.10;
H, 5.10; N, 10.12. Found: C, 65.00; H, 5.19; N, 10.15.
[CuI(TPMA)]2[ClO4]2*CH3OH (4). [CuI(CH3CN)4][ClO4]
(50.0 mg, 0.153 mmol) and TPMA (44.4 mg, 0.153 mmol) were
dissolved in 1.0 mL of methanol. The vial was then sealed and
placed in the freezer for 2 days, after which yellow crystals suitable
for X-ray analysis were obtained (yield =48.0 mg, 35%). 1H NMR
((CD3)2CO, 400 MHz, 185 K): δ8.54 (d, J=4.4 Hz, 2H), δ8.26 (d,
J=4.4 Hz, 2H), δ8.06 (m, 4 H), δ7.81 (t, J=7.2, 2H), δ7.73 (d, J =
5.2, 2H), δ7.54 (pt, J=7.6, 4H), δ7.24 (pt, J=2.6, 4H), δ7.11 (t,
J=6.0, 2H), δ6.95 (t, J=6.0, 2H), δ4.82 (d, J= 11.6, 2H), δ4.69 (d,
J = 14.4, 2H), δ4.57 (m, J = 14.0, 4H), δ4.17 (dd, J = 23.1, 16.2
Hz, 4H). FT-IR (solid): ν (cm-1) = 3068 (w), 2881 (w), 2359 (w),
2159 (w), 1600 (m), 1547 (w), 1477 (m), 1435 (m), 1082 (s), 724 (m),
620 (m). Anal. Calcd. for C36H36N8Cu2Cl2O8 (906.72): C, 47.69; H,
4.00; N, 12.36. Found: C, 47.72; H, 4.29; N, 12.27.
[(CuI(TPMA))2(4,40-dipy)][BPh4]2 (5) and [CuI(TPMA)(4,40-
dipy)][BPh4] (6). [CuI(TPMA)][BPh4] (135 mg, 0.201 mmol) was
dissolved in 10.0 mL of acetone followed by addition of 5 equiv
of 4,40-dipyridyl (156 mg, 1.00 mmol), which resulted in a
dark red solution. Crystals of X-ray quality were obtained in
acetone by slow diffusion of diethyl ether, and contained
both [(CuI(TPMA))2(4,40-dipy)][BPh4]2 and [CuI(TPMA)(4,40-
dipy)][BPh4] in the asymmetric unit.
[CuI(TPMA)(PPh3)][BPh4] (7). [CuI(TPMA)][BPh4] (100 mg,
0.149 mmol) was dissolved in 3.0 mL of acetone, and PPh3 (39.0
mg, 0.149 mmol) was added, which resulted in a light yellow
solution. Crystallization occurred immediately, producing colorless
1
crystals suitable for X-ray analysis (yield = 109 mg, 78%). H
NMR ((CD3)2CO, 400 MHz, 180 K): δ8.46 (d, J = 4.4 Hz, 3H),
δ7.88 (td, J = 7.7, 1.6 Hz, 3H), δ7.54 (m, 10H), δ7.39 (m, 11H),
δ7.30 (m, 8H), δ6.92 (t, J = 7.4 Hz, 8H), δ6.76 (t, J = 7.1 Hz, 4H),
δ4.17 (bs, 6H). 31P NMR ((CD3)2CO, 162 MHz, 220 K): δ 2.88.
FT-IR (solid): ν (cm-1) = 3051(w), 2997(w), 1581(w), 1477(m),
1434(m), 1265(w), 1095(w), 841(w), 733(s), 702(s), 609(m), 498(m).
Anal. Calcd. for C60H53BCuN4P (935.42): C, 77.04; H, 5.71; N,
5.99. Found: C, 76.69; H, 5.70; N, 5.92.
[CuII(TPMA)Cl][ClO4] (8). [CuII(TPMA)Cl][Cl] (50.0 mg,
0.118 mmol), synthesized by previously reported methods,2 was
dissolved in 5.0 mL of methylene chloride and NaClO4 (14.4 mg,
0.118 mmol) added. After stirring overnight, NaCl was filtered
from the solution and blue powder precipitated by slow addition of
pentane. [CuII(TPMA)Cl][ClO4] was collected by filtration and
dried under vacuum (yield = 34.0 mg, 59%). Crystals suitable for
X-ray analysis were obtained in acetonitrile by slow diffusion of
diethyl ether. FT-IR (solid): ν (cm-1) = 3066(w), 2935(w),
1608(m), 1574(w), 1477(m), 1435(m), 1308(w), 1265(w), 1076(s),
764(m), 621(s). Anal. Calcd. for C18H18N4CuCl2O4 (488.81): C,
44.23; H, 3.71; N, 11.46. Found: C, 44.25; H, 3.76; N, 11.41.
[CuII(TPMA)Cl][BPh4]*CH3CN (9). [CuII(TPMA)Cl][Cl]
(50.0 mg, 0.118 mmol), synthesized by previously reported
methods,2 was dissolved in 3.0 mL of methanol followed by the
addition of NaBPh4 (40.3 mg, 0.118 mmol). Precipitation of a green
powder occurred immediately. The crude product was washed with
methanol, collected by filtration, and dried under vacuum to yield
64.5 mg (77%) of [CuII(TPMA)Cl][BPh4]. Crystals of [CuII(TP-
MA)Cl][BPh4]*CH3CN suitable for X-ray analysis were obtained
in acetonitrile by slow diffusion of diethyl ether. FT-IR (solid):
ν(cm-1) = 3054(w), 2989(w), 2931(w), 1605(m), 1574(w), 1477(m),
1427(m), 1261(m), 1022(m), 737(s), 710(s), 613(m), 505(w). Anal.
Calcd. for C44H41N5CuClB (749.64): C, 70.50; H, 5.51; N, 9.34.
Found: C, 70.35; H, 5.63; N, 9.36.
[CuII(TPMA)Br][ClO4] (10). [CuII(TPMA)Br][Br] (100 mg,
0.195 mmol), synthesized by previously reported methods,1 was
dissolved in 5.0 mL of methylene chloride and NaClO4 (23.9 mg,
0.195 mmol) added. After stirring overnight, NaBr was removed
from the reaction mixture by filtration and blue powder precipitated
by slow addition of pentane. [CuII(TPMA)Br][ClO4] was collected
by filtration and dried under vacuum (yield = 50.0 mg, 47%).
Crystals suitable for X-ray analysis were obtained in acetonitrile by
slow diffusion of diethyl ether. FT-IR (solid) ν (cm-1) = 3066(w),
1608(w), 1477(m), 1308(m), 1265(w), 1080(s), 652(m), 621(s),
505(m). Anal. Calcd. for C18H18N4CuClBrO4 (533.26): C, 40.54;
H, 3.40; N, 10.51. Found: C, 40.54; H, 3.39; N, 10.45.
[CuII(TPMA)Br][BPh4]*CH3CN (11). [CuII(TPMA)Br][Br]
(100 mg, 0.193 mmol), synthesized by previously reported
methods,1 was dissolved in 3.0 mL of methanol and NaBPh4 (66.0
mg, 0.193 mmol) added. Green powder which precipitated immedi-
ately was washed with methanol, collected by filtration, and dried
under vacuum to yield 95.0 mg (65%) of [CuII(TPMA)Br][BPh4].
Crystalsof[CuII(TPMA)Br][BPh4]*CH3CN suitable for X-ray anal-
ysis were obtained in acetonitrile by slow diffusion of diethyl ether.
FT-IR (solid): ν (cm-1) = 3055(w), 2997(w), 2931(w), 1605(m),
1574(m), 1477(m), 1427 (m), 1261(m), 1022(m), 733(s), 706(s),
613(m), 505(m). Anal. Calcd. for C44H41N5CuBBr (794.09): C,
66.55; H, 5.20; N, 8.82. Found: C, 66.47; H, 5.16; N, 8.79.
Results and Discussion
Solid State Structural Studies of Copper(I) Complexes.
Following the structural elucidation of CuI(TPMA)Cl

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10621
be acute as a result, ranging from 74.04(4)° to 76.08(3)°.
The larger bond angles between the copper atom and
pyridine/acetonitrile nitrogen atoms (Npy-Cu-Npy and
Npy-Cu-N5) were between 103.19(4)° and 115.97(4)°.
The coordinated acetonitrile molecule was nearly linear
(C-N-C bond angle = 178.68(6)°) and bent by 11.79(6)°
from the Cu-N5 bond toward the N4 pyridine ring. With
this exception, [CuI(TPMA)(CH3CN)]þ cation had near
perfect (non-crystallographic) C3 symmetry. In the unit
cell, the absence of available heteroatoms resulted in only
weak C- - -H-C interactions between TPMA ligands,
˚
which ranged between 2.823(6) and 2.898(6) A (see Sup-
porting Information).
Because of the axial elongation observed in 1, the
nature of the auxiliary ligand can therefore be ruled out
as causing Cu-Nam elongation that was previously ob-
served in copper(I) halide complexes with TPMA ligand.
Although the preferred geometry for copper(I) is tetra-
hedral, the rigid structure of TPMA restricts such an
arrangement. The elongation of the Cu-Nam bond and
the long distance of copper to the LSP derived from
nitrogen atoms in pyridine rings is likely the result of a
distorted-tetrahedral geometry comprising of three nitro-
gen atoms from TPMA and the auxiliary ligand coordi-
nated in the fourth site.
Figure 2. Molecular structure of [CuI(TPMA)CH3CN][BPh4] (1) at
150 K, shown with 50% probability displacement ellipsoids. H-atoms and
˚
counteranion have been omitted for clarity. Selected distances [A] and angles
[deg]: Cu1-N1 2.4109(10), Cu1-N2 2.1031(10), Cu1-N3 2.1114(11),
Cu-N4 2.0624(10), Cu1-N5 1.9914(11), N1-Cu1-N2 74.47(4), N1-
Cu1-N3 74.04(4), N1-Cu1-N4 76.08(3), N1-Cu1-N5 175.94(4), N2-
Cu1-N3 109.44(4), N2-Cu1-N4 115.97(4), N2-Cu1-N5 104.02(5),
N3-Cu1-N4 114.92(4), N3-Cu1-N5 103.19(5), N4-Cu1-N5
107.90(5).
and CuI(TPMA)Br, it was immediately observed that
these complexes were pseudo-pentacoordinated in the solid
state because of the coordination of halide anions to the
copper(I) centers.1,2 These results were not expected, particu-
larly taking into account the strong preference for copper(I)
complexes to adopt tetrahedral geometry and the tetradentate
nature of TPMA ligand. However, after careful examination,
it was observed that the copper-amine (Cu-Nam) bond
length in both complexes was slightly elongated at approxi-
When the synthesis of 1 was repeated in methanol, which
does not readily coordinate to copper, [CuI(TPMA)][BPh4]
(2) was isolated. Complex 2 was surprisingly found to have a
slightly distorted trigonal pyramidal geometry stabilized by a
˚
weak cuprophilic interaction at 2.8323(12) A (Figure 3). The
˚
axial Cu-Nam bond (2.211(3) A) was found to be shorter
than in the previous examples of copper(I) TPMA complexes
(Table 1), and the three equatorial Cu-Npy bonds were
statistically equivalent with lengths of 2.042(4), 2.037(4), and
˚
mately 2.4 A, when compared to a typical Cu-N bond
˚
(2.0-2.1 A). Additionally, the copper atom in each complex
was positioned below the least-squares-plane (LSP) derived
˚
2.036(4) A. In conjunction with the shorter Cu-Nam
bond length, the copper atom in 2 was displaced to a lesser
˚
from three pyridyl nitrogen atoms by approximately 0.53 A.
˚
extent (0.304 A) from the LSP derived from nitrogen atoms
in pyridine rings. The two [CuI(TPMA)]þ cations stabilized
by a cuprophilic interaction were arranged in such a way that
the pyridyl rings were staggered to achieve minimal steric
interference. Weak intermolecular C-H- - -C interactions
were also observed in the crystal lattice ranging from 2.74
Therefore, copper(I) halide complexes containing TPMA
ligand can be best described as formally being distorted
tetrahedral in geometry, as a result of this elongation.
It was initially hypothesized that the elongation was the
result of the large halide anion coordinated to copper on the
opposing axial site.42 To test this, [CuI(TPMA)CH3CN]-
[BPh4] (1) was synthesized via salt metathesis of CuI-
(TPMA)Br with NaBPh4 in acetonitrile (Figure 2). The axial
Cu1-Nam bond in 1 was found to be elongated with a bond
˚
to 2.99(6) A (see Supporting Information).
The salt metathesis of CuI(TPMA)Br with half equiva-
lent of NaBPh4 formed [(CuI(TPMA)2-μ-Br][BPh4] (3)
(Figure 4). The formation of 3 was also observed in the
synthesis of 2, unless the byproduct NaBr was rapidly
removed from the reaction mixture. Complex 3 exhibited
a highly unusual structure where two [CuI(TPMA)]þ
cations were bridged by a single bromide anion, creating
two pseudo-pentacoordinated moieties each with a dis-
torted tetrahedral geometry. The remaining charge was
˚
length of 2.4109(10) A, and the Cu-Npy bonds ranged from
˚
2.0624(10) to 2.1114(11) A. These results are in good agree-
ment with previously characterized CuI(TPMA)Cl and CuI-
(TPMA)Br complexes.1,2 Also, on the other hand, the
copper(I) center was positioned below the LSP derived from
˚
N2, N3, and N4 toward the acetonitrile by 0.545(6) A. The
same distances in CuI(TPMA)Cl and CuI(TPMA)Br were
-
balanced by a non-coordinating BPh4 anion. The two
found to be 0.534(6) A and 0.538(6) A, respectively.1,2 The
discussed Cu-N bond lengths in 1 also compare very well
with previously reported complexes of similar structure
(Table 1).12-14,52,53
˚
˚
sides of the large cation were quite similar, and the pyridyl
rings of TPMA were arranged in a pseudo staggered
conformation to minimize steric hindrance partially im-
posed by the Cu1-Br-Cu2 angle (117.46(1)°). The aver-
In complex 1, the Cu1-N5 bond was the shortest bond
in the coordination sphere with a bond distance of
˚
age Cu1-Nam bond in 3 was determined to be 2.424(2) A,
which was in good agreement with previously isolated
CuI(TPMA)Cl2 and CuI(TPMA)Br1 complexes. Simi-
larly, the average Cu1-Npy bonds ranged from 2.062(2)
˚
1.9914(11) A. The Nam-Cu1-Npy angles were found to
(52) Lim, B. S.; Holm, R. H. Inorg. Chem. 1988, 37, 4898–4908.
(53) Xu, X.; Maresca, K. J.; Das, D.; Zahn, S.; Zubieta, J.; Canary, J. W.
Chem.;Eur. J. 2002, 8, 5679–5683.
˚
to 2.112(2) A. The Cu-Br bond lengths in 3 (2.5228(4)
˚
and 2.5564(4) A) were slightly longer when compared to

10622 Inorganic Chemistry, Vol. 49, No. 22, 2010
Eckenhoff and Pintauer
Table 1. Structural Comparison of Copper(I) Complexes with TPMA Containing Halide Anions or Monodentate R-CtN Ligandsa
complexb
Cu-Nam
Cu-Npy
Cu-NAN
Nam-Cu-NAN
Cu-LSPN,py
ref.
c
d
[CuI(L)(AN)][BPh4]
[CuI(L)(AN)][ClO4]
[CuI(L0)(AN)][PF6]
CuI(L)Cl
2.4109(10)
2.43(1)
2.439(8)
2.4366(11)
2.4397(14)
2.0923(18)
2.09(2)
2.110(11)
2.0808(19)
2.0825(26)
1.9914(11)
1.99(1)
1.999(9)
175.94(4)
179.5(5)
174.9(2)
0.545(6)
0.545(6)
0.569(6)
0.534(6)
0.538(6)
this work
52
14
2, 41
1
CuI(L)Br
a
b
Bond lengths are given in angstroms (A) and angles in degrees (deg). L = TPMA, L0 = methyl-6-((bis(2-pyridinylmethyl)amino) methyl)pyridine-
3-carboxylate, AN = CH3CN. c Average Cu-N(pyridine) bond length. d Distance between copper(I) atom and LSP derived from nitrogen atoms in
pyridine rings.
˚
Figure 5. Molecular structure of [CuI(TPMA)]2[ClO4]2*CH3OH (4) at
150 K, shown with 50% probability displacement ellipsoids. H-atoms,
Figure 3. Molecular structure of [CuI(TPMA)][BPh4] (2) at 150 K, shown
with 50% probability displacement ellipsoids. H-atoms and counteranion
counteranions, and solvent molecules have been omitted for clarity.
˚
˚
have been omitted for clarity. Selected distances [A] and angles [deg]: Cu1-
N1 2.211(3), Cu1-N2 2.042(4), Cu1-N3 2.037(4), Cu1-N4 2.036(4),
Cu1-Cu2 2.8323(12), N1-Cu1-N2 80.73(13), N1-Cu1-N3 82.08(14),
N1-Cu1-N4 81.39(14), N2-Cu1-N3 117.83(15), N2-Cu1-N4
117.49(14), N3-Cu1-N4 118.10(15), Cu1-Cu2-N5 177.73(10), [sym-
metry codes: (i) -xþ2, -yþ2, -zþ1].
Selected distances [A] and angles [deg]: Cu1-N1 2.2590(13), Cu1-N2
1.9909(12), Cu1-N3 2.2213(16), Cu1-N4 1.9593(13), N1-Cu1-N2
81.87(5), N1-Cu1-N3 75.63(5), N1-Cu1-N4 123.01(5), N2-Cu1-N3
95.25(5), N2-Cu1-N4 150.49(6), N3-Cu1-N4 105.68(6), [symmetry
codes: (i) -xþ1, y, -zþ1/2].
˚
nitrogen atoms (0.537(6) and 0.499(6) A, respectively).
Lastly, the crystal structure of 3 was stabilized by a series
˚
of weak C-H- - -C (2.814(6)-2.887(6) A) and dipole
˚
N- - -H-C (2.643(6) A) interactions (see Supporting In-
formation).
A very different structure was observed when [CuI(CH3-
CN)4][ClO4] was reacted with 1 equiv of TPMA in methanol.
Instead of a long cuprophilic interaction between two mon-
omeric [CuI(TPMA)]þ cations, the dimer [CuI(TPMA)]2-
[ClO4]2*CH3OH (4) was isolated in the solid state. Presum-
ably, copper(I)/TPMA complex rearranged into a dimer via
pyridyl arm dissociation and coordination to a second
copper(I) center, and vice versa (Figure 5). On the basis of
a Cambridge Crystallographic Database search, only one
other complex with a structurally similar 6-Ph-TPMA (1-(6-
phenylpyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methana-
-
mine) ligand and PF6 counterion has been reported.54
Each copper(I) center in 4 was coordinated to four nitro-
gen atoms with bond lengths of 2.2590(13), 1.9909(12),
˚
2.2213(16), and 1.9593(13) A, respectively. The bond
Figure 4. Molecular structure of [(CuI(TPMA))2-μ-Br][BPh4]2 (3) at
150 K, shown with 50% probability displacement ellipsoids. H-atoms and
˚
counteranion have been omitted for clarity. Selected distances [A] and angles
[deg]: Cu1-N1 2.429(2), Cu1-N2 2.067(2), Cu1-N3 2.131(2), Cu1-N4
2.065(2), Cu1-Br1 2.5228(4), N1-Cu1-N2 76.00(7), N1-Cu1-N3
74.08(7), N1-Cu1-N4 75.28(8), N2-Cu1-N3 107.70(8), N4-Cu1-N2
111.32(8), N4-Cu1-N3 121.61(8), Cu1-Br1-Cu2 117.456(13).
angles between the copper(I) center and N2, N3, and N4
atoms (75.63(5)°, 81.87(5)°, and 95.25(5)°, respectively)
indicated distortions from ideal tetrahedral geometry.
Furthermore, the larger angles in this complex were asso-
ciated with the bridging pyridine N4 atom (N3-Cu1-N4
105.68(6)°, N1-Cu1-N4 123.01(5)°, and N2-Cu1-N4
I
˚
[Cu (TPMA)Br] (2.5088(3) A), which was presumably a
result of the bridging of two CuI centers. Distorted
tetrahedral geometry of Cu1 and Cu2 atoms in [(CuI-
(TPMA)2-μ-Br]þ cation was further evident by relatively
large displacement from the LSP derived from pyridine
(54) Jensen, M. P.; Que, E. L.; Shan, X.; Rybak-Akimova, E.; Que, L. J.
J. Chem. Soc., Dalton Trans. 2006, 29, 3523–3527.

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10623
Figure 7. Molecular structure of [CuI(TPMA)(4,40-dipy)][BPh4] (6) at
150 K, shown with 50% probability displacement ellipsoids. H-atoms and
Figure 6. Molecular structure of [(CuI(TPMA))2(4,40-dipy)][BPh4]2 (5)
at 150 K, shown with 50% probability displacement ellipsoids. H-atoms
˚
counteranions have been omitted for clarity. Selected distances [A] and
˚
and counteranions have been omitted for clarity. Selected distances [A]
angles [deg]: Cu2-N6 2.248(2), Cu2-N7 2.065(2), Cu2-N8 2.043(2),
Cu2-N10 1.970(2), N6-Cu2-N7 78.60(9), N6-Cu2-N8 80.75(9),
N6-Cu2-N10 141.14(9), N7-Cu2-N8 116.98(9), N7-Cu2-N10
118.09(9), N8-Cu2-N10 115.09(9).
and angles [deg]: Cu1-N1 2.325(3), Cu1-N2 2.052(3), Cu1-N3
2.085(2), Cu1---N4 2.523(6), Cu1-N5 1.998(2), N1-Cu1-N2 78.59(9),
N1-Cu1-N3 77.53(9), N1-Cu1-N5 157.08(9), N2-Cu1-N3
102.06(9), N2-Cu1-N5 118.82(9), N3-Cu1-N5 110.33(9), [symmetry
codes: (i) -xþ1, -yþ2, -z, (ii) -xþ1, -yþ1, -z].
complex 6 (141.14(9)°) which resulted in displacement
of N9 pyridyl nitrogen atom further away from copper(I)
150.49(6)°). The molecular structure of [CuI(TPMA)]2-
[ClO4]2*CH3OH was stabilized by weak C-H-- -C con-
tacts between TPMA ligands with distances ranging from
˚
center (Cu1-N9 = 4.360(6) A), in contrast to complex 5
(157.08(9)°) where the ousted nitrogen atom appeared to be
˚
˚
2.806(6) to 2.994(6) A. Additionally, weak Cl-O-- -H-
weakly interacting with copper (Cu1-N4 = 2.523(6) A). In
addition, the alkyl amine-copper bond was also shorter in 6
C and Cl-O-- -H-O interactions were detected bet-
ween the ClO4- counterion and TPMA ligand (2.562(6)-
˚
˚
(Cu2-N6 = 2.248(2) A) than in 5 (Cu1-N1 = 2.325(3) A).
In both complexes, the remaining copper-pyridyl nitrogen
bonds from TPMA ligand were relatively unchanged
-
˚
2.627(6) A), and ClO4 and CH3OH solvate (2.403(6)-
2.678(6) A) (see Supporting Information).
˚
˚
˚
While changing the anion in copper(I) complexes with
TPMA ligand has produced a wide variety of molecular
structures with different degrees of steric hindrance
around the copper(I) center, preliminary studies have indi-
cated that such variations had small effect on the reaction
rate in ATRA containing free radical diazo initiators
as reducing agents. Recent kinetic studies of this process
revealed that the rate of alkene consumption was dependent
on the concentration and rate of decomposition of the radical
initiator, but independent of the concentration of the copper
catalyst.23,32,55 Therefore, more precise kinetic data could be
provided by careful measurements of the activation (CuI þ
RX f CuIIX þ R•) and deactivation (CuIIX þ R• f CuI þ
RX) rate constants, which are currently being conducted in
our laboratories. If the activation in ATRA catalyzed by
copper(I)/TPMA complexes is proceeding via an inner
sphere electron transfer and does not increase in the presence
of non-coordinating anions, then it is possible that arm
dissociation from TPMA could create an open coordination
site necessary for the homolytic cleavage of the carbon-halide
bond. By coordinating ligands of different steric bulk to
[CuI(TPMA)][BPh4] (2), this possibility could be structurally
examined. The bidentate bridging ligand 4,40-dipyridyl (4,40-
dipy) was added to complex 2 as a slightly larger alternative
to acetonitrile. Several equivalents of the ligand were used to
obtain X-ray quality crystals, and two complexes were
identified in the unit cell, the bridged [(CuI(TPMA)2(4,40-
dipy)][BPh4] (5) (Figure 6) and [CuI(TPMA)(4,40-dipy)]-
[BPh4] (6) (Figure 7). The coordination of 4,40-dipyridyl
sterically forced dissociation of one arm of TPMA ligand
in both cases, resulting in a distorted tetrahedral geometry.
(2.052(3) and 2.085(2) A for 5; 2.065(2) and 2.043(2) A for
6), and the distance to 4,40-dipyridyl was also similar
(1.998(2) and 1.970(2) A, respectively). Furthermore, coor-
˚
dinated 4,40-dipyridyl was found to be planar in complex 5,
and slightly twisted in 6with a torsion angle of 24.76(6)°. The
free 4,40-dipyridyl molecule found in the structure served to
stabilize the crystal packing via weak N- - -H-C dipole
˚
interactions at 2.707(6) A (see Supporting Information).
Additionally, the non-coordinating N11 in 6 was found to
weakly interact with the copper atom of adjacent mole-
˚
cule at the distance of 3.438(6) A, which could explain the
non-planarity of 4,40-dipyridyl discussed above. It is also
interesting to note that both 5 and 6 appear to be much more
air stable than the corresponding copper(I) complexes with
halide anions and/or acetonitrile.
To study the outcome of larger monodentate ligand
complexation to [CuI(TPMA)][BPh4], triphenylphosphine
(PPh3) was used to synthesize [CuI(TPMA)(PPh3)][BPh4]
(7). The coordination of PPh3 had even larger effect on arm
dissociation of TPMA ligand than 4,40-dipyridyl, displacing
˚
the N4 pyridyl atom by 3.258(6) A (Figure 8). As a result,
complex 7 was distorted tetrahedral in geometry, and the
complexation to copper(I) center occurred through the ali-
˚
phatic (Cu1-N1=2.2089(14) A) and two pyridine (Cu1-
˚
˚
N2=2.0661(14) A and Cu1-N3=2.1083(15) A) nitrogen
atoms of TPMA, and phosphorus atom from PPh3 (Cu1-
˚
P1=2.1852(5) A). The structural features of 7were similar to
[CuI(TPMA)(PPh3)][PF6], with the exception that in the
latter complex the nitrogen atom from the displaced arm in
TPMA was pointing away from copper (Cu-N = 6.530(2)
A).14 This could be attributed to a much smaller N1-Cu1-
˚
0
The Nam-Cu1-N4,4 -dipy bond angle was more skewed in
P1 bond angle (127.8°) when compared to 7 (141.78(4)°).
˚
Nevertheless, the Cu-N4 bond distance in 7 (3.258(6) A)
was longer than the sum of van der Waals radii (2.95 A), indi-
cating negligible interactions between the displaced pyridyl
˚
(55) Balili, M. N. C.; Pintauer, T. Polym. Prepr. (Am. Chem. Soc., Div.
Polym. Chem.) 2008, 49(2), 161–162.

10624 Inorganic Chemistry, Vol. 49, No. 22, 2010
Eckenhoff and Pintauer
Figure 9. 1H NMR spectra (400 MHz, (CD3)2CO) of [CuI(TPMA)Br]
at 180 K (a), [CuI(TPMA)][ClO4] at 298 K (b), and [CuI(TPMA)]2[ClO4]2
at 185 K (c).
Figure 8. Molecular structure of [CuI(TPMA)PPh3][BPh4] (7) at 150 K,
shown with 50% probability displacement ellipsoids. H-atoms and
˚
counteranions have been omitted for clarity. Selected distances [A] and
angles [deg]: Cu1-N1 2.2089(14), Cu1-N2 2.0661(14), Cu1-N3
2.1083(15), Cu1-P1 2.1852(5), N1-Cu1-N2 81.08(5), N1-Cu1-N3
78.86(5), N2-Cu1-N3117.66(6), N1-Cu1-P1 141.78(4), P1-Cu1-N2
119.17(4), P1-Cu1-N3 112.65(4).
(cone angle = 141.72°) in complex 7, in which the same dis-
tance was determined to be 4.217 A. Although there appears
˚
to be no direct correlation between the cone angle and
pyridine ring displacement from the copper(I) center, it is
apparent that the latter does to some extend depend on the
steric bulk of the auxiliary ligand. Studies on the effect of
these monodentate ligands on catalytic activity in ATRA are
currently underway in our laboratories.
Table 2. Structural Comparison of Complexes 1, 5, 6, and 7 with the General
Formula [CuI(TPMA)(L)][BPh4] (L= CH3CN, 4,40-dipyridyl, or PPh3)a
complex
Laux
Cu-Nam
1
5
6
7
CH3CN
2.4109(10)
2.1031(10)
2.1114(11)
2.0624(10)
1.9914(11)
175.94(4)
3.481
4,4-dipy
2.325(3)
2.052(3)
2.085(2)
2.523(6)
1.998(2)
157.08(9)
3.824
4,40-dipy
2.248(2)
2.065(2)
2.053(2)
4.360(5)
1.970(2)
141.14(9)
4.305
PPh3
Solution Studies of Copper(I) Complexes. Variable
temperature H NMR spectroscopy was used to probe
2.2089(14)
2.0661(14)
2.1083(15)
3.258(6)
2.1852(5)
141.78(4)
4.217
1
Cu-Npy,1
Cu-Npy,2
Cu-Npy,3
Cu-Laux
structures of copper(I) complexes with TPMA ligand in
solution. This technique was previously shown to be useful
in examining the structure of CuI(TPMA)Br,1 which was
found to be highly symmetrical and monomeric in solution,
as indicated by chemically equivalent pyridine rings (Figure
9A). A very similar 1H NMR spectrum was also observed for
[CuI(TPMA)(CH3CN)][BPh4] (1) (see Supporting Informa-
tion). In 1, a singlet for acetonitrile was shifted downfield by
approximately 1.6 ppm in acetone-d6 upon cooling from 298
to 180 K, indicating a deshielding effect as a result of coordi-
nation. On the other hand, [CuI(TPMA)]2[ClO4]*CH3OH
(4), exhibited four broad resonances at room temperature
similar to CuI(TPMA)Br, suggesting the structure was also
monomeric (Figure 9B). Interestingly, upon cooling to 185 K,
evidence for dimer formation consistent with the solid
state structure was clearly observed by the emergence of
three sets of unequal peaks between 8.54 and 6.95 ppm for
the pyridyl and 4.82 and 4.17 ppm for the methylene protons
(Figure 9C). When the same complex was dissolved in
acetonitrile-d3, only peaks corresponding to the monomer
were observed, indicating the formation of [CuI(TPMA)-
(CD3CN)][ClO4]. Similarly, at room temperature [CuI(TP-
MA)][BPh4] (2) also exhibited a monomeric structure
resembling 1. However, upon cooling to 180 K, the peaks
associated with the dimer formation clearly emerged in re-
latively equal proportions relative to the monomer. There-
fore, it is likely that an equilibrium between the monomer and
dimer exists in solution for complex 2 as shown in Scheme 3.
The 1H NMR spectrum for [(CuI(TPMA)2-μ-Br][BPh4]
(3) showed five peaks for TPMA at 9.17, 7.78, 7.40, 7.08,
and 4.03 ppm (see Supporting Information). This sug-
gested that the complex had highly symmetrical structure
in solution, which was inconsistent with the solid state in
Nam-Cu-Laux
c
Cu-Pycentroid
cone angleb
37.8
86.5
87.4
141.72
a
˚
Selected bond lengthsare given in angstroms (A) and the cone angles
in degrees (deg). b Cone angle was calculated for the auxiliary ligand
using Mercury 3.2 software. c Distance between the copper(I) atom and
centroid point derived from nitrogen and carbon atoms in the pyridine
ring furthest away from copper.
nitrogen atom and copper. Intermolecular interactions ob-
served in the unit cell included only weak C-H- - -C contacts
ranging from 2.809 to 2.850(6) A (see Supporting In-
formation).
˚
The auxiliary ligands used in the above-discussed com-
plexes (acetonitrile, 4,40-dipyridyl, and triphenylphosphine)
are all strong σ-donors, but vary drastically in terms of steric
bulk. Therefore, these monodentate ligands should have
different effects on TPMA coordination in copper(I) com-
plexes. To quantitatively assess the steric bulk of each ligand,
cone angles56 were calculated from the molecular structures
using a previously reported method.57 As indicated in Table 2,
acetonitrile in complex 1 was found to have a cone angle of
37.80°, which did not result in arm dissociation of TPMA
ligand. However, the larger 4,40dipyridyl, with a cone angle of
86.46° in 5 and 87.26° in 6, displaced one of the pyridine rings
˚
in TPMA by 3.824 and 4.305 A, respectively (the distance
was calculated between the copper(I) atom and centroid
point derived from nitrogen and carbon atoms in the pyridine
ring). The effect was also observed for triphenylphosphine
(56) Tolman, C. A. Chem. Rev. 1977, 77, 313–348.
(57) Muller, T.; Mingos, M. P. Trans. Met. Chem. 1995, 20, 533–539.

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10625
Table 3. Structural Comparison of [CuII(TPMA)Cl[A] (A = Cl-, ClO4- (8) and
BPh4 (9)) Complexesa
-
parameter
[CuII(TPMA)Cl][Cl]b
8c
9c
Cu1-N1ax
Cu1-N2eq
Cu1-N3eq
Cu1-N4eq
Cu1-Neq,av.
Cu1-Cl1
N1-Cu1-N2
N1-Cu1-N3
N1-Cu1-N4
N2-Cu1-N3
N3-Cu1-N4
N4-Cu1-N2
Cl1-Cu1-N2
Cl1-Cu1-N3
Cl1-Cu1-N4
Cl1-Cu1-N1
2.0481(14)
2.0759(8)
2.0759(8)
2.0759(8)
2.0759(8)
2.2369(4)
80.71(2)
80.71(2)
80.71(2)
117.447(12)
117.447(12)
117.447(12)
99.29(2)
2.0413(15)
2.1115(16)
2.0567(16)
2.0292(16)
2.0658(28)
2.2390(5)
81.05(7)
80.63(6)
81.97(6)
108.44(6)
126.20(6)
118.43(6)
99.23(5)
2.0555(8)
2.0304(10)
2.0876(9)
2.0505(9)
2.0562(18)
2.2341(3)
81.60(4)
80.83(4)
82.36(3)
115.65(4)
110.49(4)
127.52(4)
98.49(3)
d
Figure 10. 1H NMR (400 MHz, 180 K, (CD3)2CO) spectrum of
[CuI(TPMA)PPh3][BPh4].
Scheme 3. Proposed Equilibrium between Monomeric [CuI(TPMA)]-
[BPh4] and Dimeric [CuI(TPMA)]2[BPh4]2 in the Absence of a Coordi-
nating Solvent
99.29(2)
99.29(2)
180.000(19)
99.88(5)
97.33(5)
179.29(5)
99.47(3)
97.28(3)
179.60(3)
a
˚
Bond lengths are given in angstroms (A) and angles in degrees (deg).
b ref 2. c This work, values for complex 8 are averaged from two molecules in
the asymmetric unit. d Average Cu-N equatorial bond length.
which two [CuI(TPMA)]þ cations were bridged by bro-
mide anion at an angle of 117.46(1)°. We ruled out the
possibility for dissociation because it would have resulted
in the formation of CuI(TPMA)Br, [CuI(TPMA)][BPh4],
and [CuI(TPMA)]2[BPh4]2, which was not observed ex-
1
perimentally using low temperature H NMR studies.
Similarly to 1 and 3, [CuI(TPMA)(PPh3)][BPh4] (7) also
showed five resonances for TPMA ligand, indicating that
in solution all three pyridyl arms were symmetrically
coordinated to the copper(I) center (Figure 10). However,
the chemical shift of the proton in closest proximity to the
pyridyl nitrogen showed a significant upfield shift (8.46
ppm), in contrast to 1 (8.65 ppm) or CuI(TPMA)Br (9.10
ppm), which was presumably the result of σ-donation
from the coordinated triphenylphosphine. This was also
confirmed by 31P{1H} NMR which showed a downfield
shift of 8.9 ppm relative to free phosphine.
Figure 11. Molecular structure of [CuII(TPMA)Cl][ClO4] (8) at 150 K,
shown with 50% probability displacement ellipsoids. H-atoms and
counteranion have been omitted for clarity.
˚
chloride complex (2.2369(4) A). Furthermore, the copper(II)
atom in complexes 8 and 9 was displaced from the LSP
derived from nitrogen atoms in pyridine rings by 0.317(6)
˚
(averaged) and 0.299(6) A respectively, which also compared
II
well with [Cu (TPMA)Cl][Cl] (0.335(6) A). Complexes 8
˚
and 9 lacked perfect crystallographic 3-fold symmetry with
respect to Cu-Cl or Cu-Nam vector observed in [CuII(TP-
MA)Cl][Cl], which was presumably due to the presence of
Solid-State Structural Studies of Copper(II) Complexes.
ATRA is commonly performed starting with the copper(II)
complex or deactivator because of its oxidative stability.
When such complex is reduced in the presence of radicals
generated by the decomposition of initiator such as AIBN,
the copper(I) or activator is formed which starts the catalytic
cycle by homolytically cleaving an alkyl halide bond. To in-
vestigate the counterion effect on the structure of copper(II)
complexes with TPMA ligand [CuII(TPMA)Cl][ClO4] (8),
[CuII(TPMA)Cl][BPh4] (9), [CuII(TPMA)Br][ClO4] (10),
and [CuII(TPMA)Br][BPh4] (11) where synthesized by
salt methathesis of previously reported [CuII(TPMA)X][X]
(X = Br- or Cl-) complexes.1,2 Although 8 and 9 were crys-
tallographically quite different from [CuII(TPMA)Cl][Cl],
[CuII(TPMA)Cl]þ cations were nearly identical in both cases
(Table 3). Each copper(II) cation in 8 and 9 was distorted
trigonal bipyramidal in geometry, as a result of coordination
of four nitrogen atoms from TPMA ligand and one chlorine
-
-
more bulky ClO4 and BPh4 counterions. However, the
cations in each case had nearly perfect (non-crystallographic)
C3 symmetry. The intermolecular interactions in 8 consisted
mostly of O- - -H-C dipole interactions between the per-
chlorate counterion and TPMA ligand, which ranged from
˚
2.396(6) to 2.694(6) A. Weak Cl- - -H-C attractions between
the coordinated chloride and TPMA ligand in the adjacent
molecule were also observed ranging from 2.793(6) to
˚
2.860(6) A (see Supporting Information). On the other hand,
the crystal structure of complex 9 was stabilized by weak
C-H- - -C contacts involving the anion, TPMA, and a
solvent acetonitrile with distances ranging from 2.669(6) to
˚
2.884(6) A. Lastly, two Cl- - -H-C interactions were also
detected between the chlorine atom and TPMA with dis-
˚
tances of 2.857(6) and 2.840(6) A, respectively (see Support-
ing Information).
The corresponding bromide complexes, [CuII(TPMA)Br]-
[ClO4] (10) and [CuII(TPMA)Br][BPh4] (11), were found
to be structurally similar to the chlorides 8, 9, and
II
˚
atom. (Figure 11). The Cu -Cl bonds in 8 (2.2390(5) A)
and 9 (2.2341(3) A) were very similar to the corresponding
˚

10626 Inorganic Chemistry, Vol. 49, No. 22, 2010
Eckenhoff and Pintauer
van der Waals C-H- - -C interaction between co-
ordinated TPMA ligands was found to exist at 2.875(6)
˚
A (see Supporting Information). In the crystal structure
of 11, weak C-H- - -C contacts ranging from 2.703(6) to
˚
2.892(6) A, as well as weak C-H- - -Br dipole interac-
tions at 2.951(6) and 2.921(6) were observed A (see
Supporting Information).
˚
In solution, 8, 9, 10, and 11 were found to have similar
UV-vis spectra (λmax ≈ 960 nm, εmax ≈ 190 L mol-1 cm-1),
indicating negligible interactions of anions with the
copper(II) centers, consistent with the solid state studies
discussed above.
Figure 12. Molecular structure of [CuII(TPMA)Br][ClO4] (10) at 150 K,
shown with 50% probability displacement ellipsoids. H-atoms and
counteranion have been omitted for clarity.
Conclusions
-
In conclusion, the effects of counterions (Cl-, Br-, ClO4
,
and BPh4 ) and auxiliary ligands (Cl-, Br-, CH3CN, 4,40-
dipyridyl, and PPh3) on the structures of copper(I) and copper-
(II) complexes with TPMA ligand were investigated. Copper-
(I)/TPMA complexes with Br- and CH3CN were found to be
distorted tetrahedral in geometry, and each copper(I) center
was coordinated by an auxiliary monodentate ligand and three
nitrogen atoms from pyridyl rings. In these complexes, the axial
-
II
˚
Table 4. Selected Bond Lengths [A] and Angles [deg] for [Cu (TPMA)Br][A]
(A = Br-, ClO4- (10) and BPh4 (11)) Complexes
-
parameter
[CuII(TPMA)Br][Br]a
10b
11b
Cu1-N1ax
Cu1-N2eq
Cu1-N3eq
Cu1-N4eq
Cu1-Neq,av.
Cu1-Br1
N1-Cu1-N2
N1-Cu1-N3
N1-Cu1-N4
N2-Cu1-N3
N3-Cu1-N4
N4-Cu1-N2
Br1-Cu1-N2
Br1-Cu1-N3
Br1-Cu1-N4
Br1-Cu1-N1
2.040(3)
2.073(2)
2.073(2)
2.073(2)
2.073(2)
2.3836(6)
80.86(5)
80.86(5)
80.86(5)
117.53(3)
117.53(3)
117.53(3)
99.14(5)
99.14(5)
99.14(5)
180.00(5)
2.0387(17)
2.0642(18)
2.0515(17)
2.1163(18)
2.0773(31)
2.3765(3)
80.36 (7)
81.44(7)
2.0534(11)
2.0545(12)
2.0328(12)
2.0909(12)
2.0594(21)
2.3711(2)
82.32(5)
81.55(5)
80.98(5)
128.21(5)
115.28(5)
110.17(5)
97.55(3)
elongation of CuI-Nam bond (∼2.4 A) was observed, indicat-
˚
c
ing not only the rigidity of TPMA ligand, but also the strong
preference for copper(I) to adopt four coordinated geometry.
In the absence of monodentate ligand, two structures were
observed. A monomeric trigonal pyramidal [CuI(TPMA)]-
[BPh4] complex was characterized in the solid state, which
81.03(7)
124.95(7)
117.89(7)
109.80(7)
100.44(5)
97.76(5)
˚
was stabilized by a weak cuprophilic interaction (2.8323(12) A).
On the other hand, [CuI(TPMA)]2[ClO4]2 was found to be
dimeric in which dissociated pyridyl arms of TPMA ligand
bridged two copper(I) centers. In copper(I) complexes contain-
ing larger auxiliary ligands such as 4,40-dipyridyl or PPh3, a
pyridyl arm of TPMA ligand was found to partially or totally
dissociate. These complexes were all monomeric in the solid
state, with the exception of [(CuI(TPMA))2(4,40-dipy)][BPh4]2
in which 4,40-dipyridyl ligand bridged two [CuI(TPMA)]þ
cations.
98.68(3)
98.89(4)
179.77(3)
99.03(5)
179.11(5)
a ref 1. b This work, values forcomplex10 are averaged for two molecules
in the asymmetric unit. c Average Cu-N equatorial bond length.
[CuII(TPMA)Cl][Cl] discussed above (Figure 12). The
cations lacked perfect crystallographic 3-fold symmetry
observed in [CuII(TPMA)Br][Br],1 but pyridine rings in
coordinated TPMA ligand were nearly symmetrical with
respect to C3 rotation. From the point of view of TPMA
coordination, these complexes were also comparable to
previously discussed 8 and 9. While the typical CuII-Cl
Copper(II) complexes with the general formula [CuII(TP-
MA)X][Y] (X=Cl-, Br- and Y=ClO4-, BPh4-) were synthe-
sized and characterized in the solid state to investigate the
counterion effect on the structure of [CuII(TPMA)X]þ. In each
complex, the copper(II) atom was found to be distorted trigonal
bipyramidal in geometry with nearly perfect C3 symmetry for
coordinated TPMA ligand. The average CuII-N bond dis-
II
˚
bond length in 8and 9was close to 2.23 A, theCu -Br bond
distance in 10 and 11 was found to be longer as a result of
the larger atomic radii of bromine atom (2.3765(3) and
˚
2.3711(2) A, respectively). The copper(II) atom was dis-
placed from the LSP by 0.330(6) (averaged) in complex 10
˚
and 0.299(6) A in 11, which compared well with the bromide
˚
tances were found to range between 2.03 and 2.12 A, consistent
with previous studies.
˚
complex (0.329(6) A) (Table 4). No other significant differ-
ences in the structures were observed.
Acknowledgment. Financial support from National
Science Foundation Career Award (CHE-0844131) is
gratefully acknowledged
Additionally, intermolecular interactions in 10 and 11
were found to closely resemble 8 and 9. The crystal
structure of 10 was stabilized by predominately strong
C-H- - -O dipole forces at distances ranging from
1
Supporting Information Available: Crystal tables, H NMR
spectra, infrared spectra, full crystal structures, and crystal
packing diagrams. This material is available free of charge via
the Internet at http://pubs.acs.org.
˚
2.429(6) to 2.620(6) A, and two weaker C-H- - -Br dipole
˚
contacts (2.963(6)-2.987(6)) A. Furthermore, one