Copper(I) complexes of tripodal tris(imidazolyl) ligands: Potential mimics of the Cu(A) site of hydroxylase enzymes

Article abstract of DOI:10.1021/ic061985+

Copper(I) complexes of tripodal tris(N-methyl-4,5-diphenyl-imidazolyl) methane ligands, N₃CR (1a-c, R = OH, OMe, H), have been prepared as models for the Cu(A) site of copper hydroxylase enzymes. In the absence of additional donors, the ligands 1 react with [Cu(CH₃CN) ₄]PF₆ (2) to produce dinuclear complexes [(N ₃CR)₂Cu₂](PF₆)₂ (3) in which the tripodal ligands bridge two trigonal Cu centers; the structures of 3b and 3c are established by X-ray diffraction. Mononuclear adducts [(N ₃CR)CuL]Z are produced with L = acetonitrile (4), carbon monoxide (5), and t-BuNC (6, 7). The carbonyl complexes 5 are in dynamic equilibrium with the dimeric complexes 3, but 5c (R = H) can be isolated. The structures of the isocyanide derivatives depend critically on the tripod methane substituent, R. Thus, the X-ray structures of 6 (R = OMe) and 7 (R = H) show trigonal and tetrahedral geometries, respectively, with bi- or tridentate coordination of the tripod. A trinuclear complex [Cu₃(N₃COH) ₂(t-BuNC)₂](PF₆)₃ (8) is formed from N₃COH (1a) which features both three-coordinate and two-coordinate Cu atoms and bidentate tripod coordination. Reactions of dioxygen with dinuclear 3c or mononuclear [(N₃CR)CuL]Z are sluggish, producing from the latter in acetone [(N₃CH)Cu^II(L)(L′)](PF ₆)₂ (9, L = acetone, L′ = H₂O).

Full text of DOI:10.1021/ic061985+

Inorg. Chem. 2007, 46, 2316−2321
Copper(I) Complexes of Tripodal Tris(imidazolyl) Ligands: Potential
Mimics of the Cu(A) Site of Hydroxylase Enzymes
Lei Zhou, Douglas Powell, and Kenneth M. Nicholas*
Department of Chemistry and Biochemistry, UniVersity of Oklahoma, Norman, Oklahoma 73019
Received October 16, 2006
Copper(I) complexes of tripodal tris(N-methyl-4,5-diphenyl-imidazolyl)methane ligands, N3CR (1a−c, R ) OH, OMe,
H), have been prepared as models for the Cu(A) site of copper hydroxylase enzymes. In the absence of additional
donors, the ligands 1 react with [Cu(CH3CN)4]PF6 (2) to produce dinuclear complexes [(N3CR)2Cu2](PF6)2 (3) in
which the tripodal ligands bridge two trigonal Cu centers; the structures of 3b and 3c are established by X-ray
diffraction. Mononuclear adducts [(N3CR)CuL]Z are produced with L
t-BuNC (6, 7). The carbonyl complexes 5 are in dynamic equilibrium with the dimeric complexes 3, but 5c (R
H) can be isolated. The structures of the isocyanide derivatives depend critically on the tripod methane substituent,
R. Thus, the X-ray structures of 6 (R OMe) and 7 (R H) show trigonal and tetrahedral geometries, respectively,
) acetonitrile (4), carbon monoxide (5), and
)
)
)
with bi- or tridentate coordination of the tripod. A trinuclear complex [Cu3(N3COH)2(t-BuNC)2](PF6)3 (8) is formed
from N3COH (1a) which features both three-coordinate and two-coordinate Cu atoms and bidentate tripod coordination.
Reactions of dioxygen with dinuclear 3c or mononuclear [(N3CR)CuL]Z are sluggish, producing from the latter in
acetone [(N3CH)CuII(L)(L
′)](PF6)2 (9, L ) acetone, L′ ) H2O).
Introduction
incorporated the biologically most relevant bis/tris(imidazole)
donors,5 which have significantly different donor/acceptor
properties.6
The copper hydroxylase enzymes, dopamine â-hydroxy-
lase (DâM) and peptidylglycine R-hydroxylating monooxy-
genase (PHM), catalyze the regio- and enantioselective
hydroxylation of mildly activated C-H bonds by O2.1 These
enzymes appear to have very similar active-site structures,
featuring two Cu centers separated by ca. 12 Å, with the
Cu(A) site ligated by three histidine-derived imidazoles and
the Cu(B) site by two histidines and a methionine residue.2
Evidence derived from studies of the enzymes suggests that
the N3-Cu(A) site is an electron-transfer relay for the N2S-
Cu(B) site, at which dioxygen and the substrate associate
and are transformed.3 Although many synthetic model
complexes for these and other poly(imid)-Cu enzymes have
been prepared with a variety of polydentate saturated amine,
pyridine, and pyrazolylborate-based ligands,4 rather few have
We recently described rare bis(imidazole)thioether N2S-
ligands and derived Cu(I) complexes that share close
structural, electronic, and reactivity features with the Cu(B)
(4) (a) Shinobu, I.; Shunichi, F. Bull. Chem. Soc. Jpn. 2002, 75, 2081-
2095. (b) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. ReV.
2004, 104, 1013-1045. (c) Lewis, E. A.; Tolman, W. B. Chem. ReV.
2004, 104, 1047-1076. (d) Hatcher, L. Q.; Karlin, K. D. J. Biol. Inorg.
Chem. 2004, 9, 669-683. (e) Fujisawa, K.; Tanaka, M.; Moro-oka,
Y.; Kitajima, N. J. Am. Chem. Soc. 1994, 116, 12079-12080. (f)
Aboelella, N. W.; Kryatov, S. V.; Gherman, B. F.; Brennessel, W.
W.; Young, V. G.; Sarangi, R.; Rybak-Akimova, E. V.; Hodgson, K.
O.; Hedman, B.; Solomon, E. I.; Cramer, C. J.; Tolman, W. B. J. Am.
Chem. Soc. 2004, 126, 16896-16911.
(5) (a) Sorrell, T. N.; Borovik, A. S. J. Am. Chem. Soc. 1987, 109, 4255-
4260. (b) Tang, C. C.; Davalian, D.; Huang, P.; Breslow, R. J. Am.
Chem. Soc. 1978, 100, 3918-3922. (c) Breslow, R.; Hunt, J. T.;
Smiley, R.; Tarnowski, T. J. Am. Chem. Soc. 1983, 105, 5337-5342.
(d) Sorrell, T. N.; Allen, W. E.; and White, P. S. Inorg. Chem. 1995,
34, 952-960. (e) Tran, K. C.; Battioni, J. P.; Zimmermann, J. L.;
Bois, C.; Koolhaas, G. J. A. A.; Leduc, P.; Mulliez, E.; Boumchita,
H.; Reedijk, J.; Chottard, J. C. Inorg. Chem. 1994, 33, 2808-2814.
(f) Blain, I.; Giorgi, M.; De Riggi, I.; Reglier, M. Eur. J. Inorg. Chem.
2000, 2, 393-398.
* To whom correspondence should be addressed. E-mail: knicholas@
ou.edu.
(1) Klinman, J. P. Chem. ReV. 1996, 96, 2541-2562.
(2) Prigge, S. T.; Mains, R. E.; Amzel, L. M. Science 1997, 278, 1300-
1305.
(3) (a) Prigge, S. T.; Mains, R. E.; Eipper, B. A.; Amzel, L. M. Cell.
Mol. Life Sci. 2000, 57, 1236-1259. (b) Prigge, S. T.; Kolhekar, A.
S.; Eipper, B. A.; Mains, R. E.; Amzel, L. M. Nat. Struct. Biol. 1999,
6, 976-983. (c) Evans, J. P.; Ahn, K.; Klinman, J. P. J. Biol. Chem.
2003, 278, 49691-49698. (d) Chen, P.; Solomon, E. I. J. Am. Chem.
Soc. 2004, 126, 4991-5000.
(6) (a) Bruice, P. Y. Organic Chemistry, 4th ed.; Prentice Hall: Upper
Saddle River, NJ, 2004; pp A8 and A9. (b) Marques, H. M.; Munrro,
O. Q.; Munro, T.; Wet, M. D.; Vashi, P. R. Inorg. Chem. 1999, 38,
2312-2319. (c) Johnson, C. R.; Henderson, W. W.; Shepherd, R. E.
Inorg. Chem. 1984, 23, 2754-2763. (d) Peters, L.; Hubner, E.;
Burzlaff, N. J. Organomet. Chem. 2005, 690, 2009-2016.
2316 Inorganic Chemistry, Vol. 46, No. 6, 2007
10.1021/ic061985+ CCC: $37.00
© 2007 American Chemical Society
Published on Web 02/13/2007

Copper(I) Complexes of Tripodal Tris(imidazolyl) Ligands
Scheme 1
site.7 Regarding the Cu(A) site of the hydroxylases, few CuI
or CuII complexes with polydentate imidazole ligands have
been reported.8 Sorrell and co-workers prepared copper(I)
complexes from tris(N-methyl-2-imidazolyl)carbinol5a and
substituted tris(2-imidazolyl)phosphines.5d From the former
ligand either dinuclear [(tripod)2Cu2]Z2 or monometallic
[(tripod)CuL]Z complexes were produced, depending on the
coordinating ability of L. Tris[2-(1,4-diisopropylimidazolyl)]-
phosphine forms a cationic copper(I) complex that reacts with
dioxygen at low temperature to produce a reactive peroxo-
dicopper(II) adduct, but the corresponding complex of the
tert-butyl-substituted ligand does not react with dioxygen,
demonstrating that steric effects are important in defining
CuI-O2 interactions in these systems.5d We report here the
preparation of new, sterically encumbered tripodal tris-
(imidazole) ligands, characterization of the corresponding
Cu(I) complexes, and their novel reactivity with isocyanides,
CO, and O2.
solution presumed to be the corresponding carbocation;
addition of solid NaBH4 gave methane derivative 1c in good
yield.
Ligands 1a-c react with [Cu(CH3CN)4]PF6 (2) in CH2-
Cl2 to form dinuclear complexes 3a-c of composition [(N3-
CR)2Cu2](PF6)2 on the basis of ESI-MS and NMR analysis.
1
The H NMR spectrum of 3b shows two singlets (3H, 6H)
for the N-methyl resonances, indicating two inequivalent
N-methyl groups, whereas the spectrum of 3c indicated that
all methyl groups are equivalent on the NMR time scale at
room temperature. Crystals of 3b and 3c were analyzed by
X-ray diffraction, and the structure of the latter is shown in
Figure 1. In both structures the two tripodal ligands bridge
between nearly trigonal planar Cu(I) atoms (sum of N-Cu-N
angles ) 358.8° for 3b and 358.4° for 3c), each coordinated
via three imidazole nitrogens, two from one tripod and one
from the second. These structures are similar to that reported
for the copper(I) complex of the non-arylated N-methylimi-
dazolyl carbinol ligand.5a Both 3b (in SI) and 3c have
Results and Discussion
The tripodal tris(4,5-diphenyl-N-methylimidazolyl)-based
ligands (1) were targeted since they offer a sterically
hindered, hydrophobic Cu-binding pocket which could
disfavor the formation of bridging, binuclear complexes. The
hydroxy-substituted ligand 1a8b provided a convenient source
of the new -methoxy (1b) and -methine (1c) derivatives via
O-alkylation or reductive substitution, respectively, as out-
lined in Scheme 1. Several reported methods for the reductive
substitution of the hydroxyl group were ineffective5c,9,10 for
the conversion of 1a to 1c. However, treatment of 1a with
trifluoroacetic anhydride in CH2Cl2 produces an intense blue
(7) Zhou, L.; Powell, D.; Nicholas, K. N. Inorg. Chem. 2006, 45, 3840-
3842.
(8) (a) Kujime, M.; Fujii, H. Tetrahedron Lett. 2005, 46, 2809-2812.
(b) Higgs, T. C.; Helliwell, M.; McInnes, E. J. L.; Mabbs, F. E.;
Harding, C. J.; Garner, C. D. J. Chem. Soc., Dalton Trans. 1997, 927-
933.
(9) Nicholas, K. M.; Siegel, J. J. Am. Chem. Soc. 1985, 107, 4999-5001.
(10) Rathore, R.; Burns, C. L.; Guzei, I. A. J. Org. Chem. 2004, 69, 1524-
1530.
Figure 1. X-ray structure of the dication of 3c. Selected bond lengths
(Å) and angles (deg): Cu(1)-N(14) 1.950(3), Cu(1)-N(2) 2.008(3), Cu-
(1)-N(8) 2.034(3); N(14)-Cu(1)-N(2) 132.56(14), N(14)-Cu(1)-N(8)
133.34(14), N(2)-Cu(1)-N(8) 92.50(14).
Inorganic Chemistry, Vol. 46, No. 6, 2007 2317

Zhou et al.
inversion symmetry so that two N-methyl groups in each
tripod are equivalent but inequivalent to the third one. The
differing solution-state NMR behaviors of 3b and 3c suggest
that the latter undergoes a dynamic process that averages
the imidazole environments.
In the presence of suitable coordinating molecules, L,
mononuclear [(N3CR)CuL]Z complexes are produced, start-
ing either from [Cu(CH3CN)4]Z (2), the tripodal ligands, and
L or from the addition of L to the dimers 3, indicative of an
L- and tripod-dependent mono/dimer equilibrium. 1H NMR
and ESI mass spectra of solutions of 3c in donor solvents,
e.g., CH3CN and acetone, indicated the presence of a new
species [(N3CR)Cu(solv)]PF6 (4). Reactions between 2 and
tripods 1a and 1b in CH2Cl2 under CO (1 atm) produced
labile CO adducts detected by IR (5a, 2115 cm-1; 5b, 2100
cm-1). Ether addition to these solutions precipitated only the
dimers 3a and 3b, respectively. However, the adduct from
3c, [(N3CH)Cu(CO)]PF6 (5c), was isolable as a solid and
exhibited appropriate IR spectroscopic data (2092 cm-1).
Inspection of computer-generated models suggests that the
apparently greater stability of the tripod complex 5c (R )
H) relative to the -OH and -OMe derivatives (5a, 5b) may
be the result of steric crowding between the N-Me groups
and the larger methine substituents on the backside of the
tripod caused by tridentate Cu coordination. It is noteworthy
that the ν(CO) values of these complexes are ca. 40 cm-1
higher than those reported for some tris(His)Cu(CO) en-
zymes,11 suggesting a less-electron-rich Cu in 5. This
difference may reflect a lower donicity of the 2-substituted
Figure 2. X-ray structure of the cation of 6. Selected bond lengths (Å)
and angles (deg): Cu(1)-C(58) 1.824(2), Cu(1)-N(5) 1.9739(17), Cu-
(1)-N(11) 1.9855(19), C(58)-Cu(1)-N(5) 134.91(9), C(58)-Cu(1)-N(11)
129.51(9), N(5)-Cu(1)-N(11) 93.65(7).
imidazoles of 5 relative to 4-substituted His-imidazoles,5c
a
lower denticity of the tripod in [(N3CR)Cu(CO)], coordina-
tion geometry differences, or medium/secondary sphere
effects in the protein.
More stable mononuclear adducts [(N3CR)CuL]PF6 were
formed with L ) t-BuNC, the structures of which were
remarkably dependent on the tripod substituent R. Thus,
reaction of ligand 1b (R ) OMe) and 2 with 1 equiv of
t-BuNC (CH2Cl2, at room temperature (rt)) produced a
monometallic isocyanide derivative 6 (νCN 2189 cm-1) on
Figure 3. X-ray structure of the cation of 7. Selected bond lengths (Å)
and angles (deg): Cu(1A)-C(56A) 1.897(2), Cu(1A)-N(8A) 2.098(6), Cu-
(1A)-N(2A) 2.118(6), Cu(1A)-N(14A) 2.135(6), C(56A)-N(57A) 1.101-
(3); C(56A)-Cu(1A)-N(8A) 129.0(3), N(8A)-Cu(1A)-N(2A) 86.1(3),
N(2A)-Cu(1A)-N(14A) 91.5(3).
the basis of NMR and ES-MS analysis. Both the 1H and 13
C
NMR spectra of 6 at rt exhibit a single peak for the three
N-methyl groups; this peak sharpened at 40 °C in the H NMR
spectrum, suggesting a dynamically averaged, nearly sym-
metrical structure in solution. Surprisingly, the X-ray crystal
structure of 6 (Figure 2) revealed the presence of a trigonal
Cu(I) atom ligated by isocyanide and the tripod ligand in a
bidentate mode with one imidazole group uncoordinated. The
observed NMR spectra of 6 could be explained by a rapid
associative/dissociative exchange of the imidazole groups in
solution.
(Figure 3) showed a four-coordinate pyramidal Cu(I) center
bound to the isocyanide and all three imidazole units of the
tripod ligand, consistent with the solution-state NMR spec-
trum. We suggest that the contrasting solid-state structures
of 6 and 7 are the result of a delicate energetic balance
between the stereoelectronic characteristics of the tripod’s
donor atom set, similar stabilities of the three- and four-
coordinate copper(I) geometries, and steric crowding on the
tripod backside between the methine substituent R and the
imidazole N-methyl groups.
The ligand 1c (R ) H) reacted with Cu(I) and t-BuNC
analogously to form a [(N3CH)CuL]PF6 derivative 7 (νNC
The reaction of 2 with tripod 1a (R ) OH) and 1 equiv
of t-BuNC (CH2Cl2, rt) afforded yet a different type of
complex 8, again illustrating the subtle effects of the tripod
capping group on the reaction product. The ES mass
spectrum of 8 shows only a monomeric [Cu(tripod)(t-
1
2186 cm-1). The H NMR spectrum of 7 shows a sharp
singlet for the three N-methyl groups, indicating symmetric
structure in solution. The X-ray structure (solid state) of 7
(11) (a) Jaron, S.; Blackburn, N. J. Biochemistry 1999, 38, 15086-15096.
(b) Blackburn, N. J.; Pettingill, T. M.; Seagraves, K. S.; Shigeta, R.
T. J. Biol. Chem. 1990, 265, 15383-15386.
1
BuNC)]+ peak, whereas its H NMR spectrum shows a 1:1
tripod/t-BuNC ratio and a single somewhat broadened peak
2318 Inorganic Chemistry, Vol. 46, No. 6, 2007

Copper(I) Complexes of Tripodal Tris(imidazolyl) Ligands
and water ligands, and the anion/Cu ratio indicates that the
Cu has been oxidized by O2. Whether the water ligand of 9
is derived from dioxygen reduction or from water present
in the solvent has not been determined.
A number of factors may contribute to the relatively low
dioxygen reactivity of the [(imidazolyl)3CR]Cu+ complexes.
Their positive charge probably renders them less electron
rich (and less oxidizable) than corresponding Cu(I) deriva-
tives with anionic ligands, e.g., tris(pyrazolyl)borate,4e
diketiminato,4f and those with more basic aliphatic poly-
amines.5 The basis for the lower reactivity of the present
poly(aryl-imidazole) complexes vis a vis Sorrell’s cationic
Cu[P(imid-i-Pr)3]+ complex is less apparent but could derive
from a combination of steric inhibition by the aryl groups
and a stereoelectronic effect from the more acute chelate bite
angles of the (imid)3CR vs the (imid)3P ligands. It is
noteworthy that dinuclear µ-oxo or hydroxo type complexes,
e.g., [(N3CR)Cu[µ-O(H)]2Cu(N3CR)]2+, often derived from
LnCu(I) reactions with dioxygen,12,13 were not observed in
the present system. Molecular models suggest that the
formation of such species would be inhibited by the
imidazole aryl substituents. It is also significant that no ligand
oxygenation was observed, in contrast to findings in a
number of other polyamine model complexes.5f Nonetheless,
the cationic Cu-tris(imid) and bis(imid)(thioether)7 coordina-
tion of the systems that we have investigated are the most
accurate structural models presently available for the Cu(A)
and Cu(B) sites of the hydroxylase enzymes. The lower
reactivity toward dioxygen of the present N3-Cu(I) com-
plexes relative to the corresponding N2S-tripod-Cu(I)
complexes7 is consistent with the relative reactivity of the
Cu(A) and Cu(B) enzyme sites.3
Figure 4. X-ray structure of the trication of 8. Selected bond lengths (Å)
and angles (deg): Cu(1A)-C(50A) 1.846(6), Cu(1A)-N(3A) 1.973(4), Cu-
(1A)-N(1A) 2.018(4), Cu(2A)-N(5B) 1.901(4), Cu(2A)-N(5A) 1.909-
(4), C(50A)-Cu(1A)-N(3A) 138.3(2), C(50A)-Cu(1A)-N(1A) 128.2(2),
N(3A)-Cu(1A)-N(1A) 92.04(17), N(5B)-Cu(2A)-N(5A) 169.40(17).
Figure 5. X-ray structure of the dication of 9. Selected bond lengths (Å)
and angles (deg): Cu(1)-O(56) 1.977(3), Cu(1)-O(57) 1.982(2), Cu(1)-
N(8) 1.988(3), Cu(1)-N(2) 2.015(3), Cu(1)-N(14) 2.249(3), O(56)-Cu-
(1)-O(57) 84.93(11), O(57)-Cu(1)-N(8) 95.74(11), O(56)-Cu(1)-N(2)
89.71(11), N(8)-Cu(1)-N(2) 87.48(11).
In summary, the Cu complexes of tripodal tris(imidazolyl)
ligands reported here provide rare examples of well-
characterized tris(imidazole) Cu(I) and Cu(II) complexes of
the type found in several metalloenzymes. The Cu(I)
derivatives can form either mononuclear or polynuclear
complexes, the latter with the tripod bridging, depending
upon the presence (or absence) of suitable auxiliary ligands.
Copper(I) derivatives of the tris(imidazolyl) ligands exhibit
modest dioxygen reactivity in which the Cu center is oxidized
without the formation of oxygen-bridged products or ap-
preciable ligand oxidation. Efforts are underway to provide
new, more accurate structural and functional mimics of the
Cu hydroxylase enzymes and to explore their catalytic and
redox activity.
for the three N-methyl groups. An X-ray structure determi-
nation of 8 revealed it to be more complex, containing three
Cu(I) atoms, two tripod ligands, and two isocyanides, [(t-
BuNC)2Cu3(N3-COH)2](PF6)3 (Figure 4). The structure con-
sists of two flanking (tripod) Cu units, each having a trigonal,
nearly planar Cu(I) atom bound to an isocyanide and to the
tripod in a bidentate mode, with the third imidazole from
each unit bridged to the central copper in a nearly linear
geometry (N-Cu-N angle, 169°); secondary bonding
interactions of the central copper with the tripod hydroxyl
groups are suggested by the relatively short Cu-O distances
(Cu-OH, 2.5-2.6 Å).
The dinuclear complexes 3b,c are remarkably unreactive
toward dioxygen, both largely unchanged after exposure to
1 atm of O2 (CH2Cl2, rt) after 20 h, perhaps the result of a
very stable trigonal Cu geometry reinforced by steric
shielding of the Cu atoms by the polyaryl imidazole ligands.
However, when an acetone solution of 2 and 1c (R ) H),
which forms [(N3CH)Cu(acetone)]PF6, was stirred under 1
atm of O2 at rt (24 h), it gradually turned greenish brown.
Ether diffusion into the reaction solution induced crystal-
lization of [(N3CH)CuII(acetone)(H2O)](PF6)2 (9), which was
identified by X-ray diffraction (Figure 5). The five-coordinate
structure of 9 is defined by the tridentate tripod, acetone,
Experimental Section
Materials and Methods. All operations were carried out under
nitrogen or argon by means of standard Schlenk and vacuum-line
techniques. Organic solvents were dried by standard procedures
and distilled under N2 before use. Glassware was oven-dried at 150
°C overnight. A Vacuum Atmospheres glovebox was used in the
handling of air-sensitive solids. IR spectra were recorded in either
CH2Cl2 solution or KBr pellets with a Perkin-Elmer 283-B infrared
(12) Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. ReV. 2004,
104, 1013-1046.
(13) Lewis, E. A.; Tolman, W. B. Chem. ReV. 2004, 104, 1047-1076.
Inorganic Chemistry, Vol. 46, No. 6, 2007 2319

Zhou et al.
Table 1. X-ray Crystal Data for Compounds 3c, 6, 7, 8, 9
compound
empirical formula
3c
108H104Cl4Cu2F12-
N12O2P2
2160.85
triclinic
P1h
6
7
8
9
C
C63H71CuF6N7-
O3P
1182.78
triclinic
P1h
C60H64CuF6N7-
C118H123Cl4Cu3-
F18N14O4.5P3
2576.63
triclinic
P1h
C56H58CuF12N6-
O3P2
1216.56
monoclinic
P21/n
O1.5P
fw
1115.69
monoclinic
P21/n
crystal syst
space group
unit cell dimens
a, Å
b, Å
c, Å
14.2688(18)
14.3040(18)
14.8469(19)
65.390(2)
65.275(2)
74.127(2)
2484.3(5)
1, 0.5
13.420(2)
15.024(2)
16.470(3)
89.324(5)
69.714(5)
68.746(5)
2878.1(8)
2, 1
15.141(5)
19.367(7)
40.820(15)
90
92.987(15)
90
11954(7)
8, 2
1.240
18.605(4)
23.695(6)
29.271(7)
73.480(8)
81.182(8)
89.827(8)
12214(5)
4, 2
15.328(4)
24.336(5)
15.890(4)
90
100.667(8)
90
5825(2)
4, 1
1.387
R, deg
â, deg
γ, deg
V, Å3
Z, Z′
D, Mg/m3
wavelength, Å
T, K
1.444
0.71073
100(2)
1.365
0.71073
100(2)
1.401
0.71073
100(2)
0.71073
100(2)
0.71073
100(2)
F(000)
1116
0.649
semiemp from
equiv
1240
0.480
semiemp from
equiv
4664
0.456
semiemp from
equiv
5308
0.729
semiemp from
equiv
2508
0.516
semiemp from
equiv
abs coeff, mm-1
abs correction
max, min trans
θ range, deg
reflns collected
independ reflns
0.9321, 0.7860
1.58-26.00
19 371
9635 [R(int) )
0.0282]
0.9581, 0.8616
1.47-26.00
22 933
11 196 [R(int) )
0.0231]
0.9820, 0.8211
2.07-18.85
41 918
9396 [R(int) )
0.0947]
0.9048, 0.7896
1.82-25.00
103 751
41 983 [R(int) )
0.0314]
0.9648, 0.9038
1.70-26.00
42 480
11 431 [R(int) )
0.0377]
data/restraints/param
Rw(F2 all data)
9635/0/577
0.2652
11196/138/680
0.1261
9396/6238/1370
0.2648
41983/4043/3351
0.2452
11431/105/682
0.1917
R(F obsd data)
0.0823
1.046
0.0437
1.035
0.1005
1.047
0.0813
1.024
0.0612
1.005
GOF on F2
obs data [I > 2σ(I)]
largest, mean shift, s.u.
largest diff peak, hole, e/Å3
6717
0.001, 0.000
1.063, -1.336
8967
0.001, 0.000
0.830, -0.435
6594
0.000, 0.000
0.912, -0.595
33113
0.010, 0.000
1.823, -1.461
8257
0.001, 0.000
1.155, -0.841
spectrophotometer (resolution 4 cm-1). The 1H and 13C NMR
spectra were recorded on a Varian Mercury-300 spectrometer. Mass
spectra were acquired on a Finnigan TSQ 700 spectrometer in
methanol or acetonitrile solution by ESI. Elemental analyses were
performed by Midwest Microlab, LLC. 4,5-Diphenylimidazole,14
N-methyl-4,5-diphenylimidazole,15 and tris(1-methyl-4,5-diphen-
ylimidazol-2-yl)methanol8b (1a) were prepared according to reported
procedures.
acetic anhydride (0.21 mL, 5 equiv) dropwise under Ar at 0 °C to
form a dark blue solution immediately. The resulting mixture was
stirred for 30 min, another portion of NaBH4 (114 mg, 10 equiv)
was added slowly to the blue solution, and the suspension was
stirred for 1 h during which H2 was given off and the solution
became light green gradually. The mixture was quenched with
water, extracted with CH2Cl2, and dried over MgSO4. After
evaporative removal of the CH2Cl2, a white solid was obtained.
Recrystallization of the solid from CH2Cl2 and petroleum ether gave
Tris(1-methyl-4,5-diphenylimidazol-2-yl)methyl Methyl Ether
(1b). Sodium hydride (48 mg, 60% mineral oil suspension, 1.2
mmol) was suspended in dry THF (10 mL) under N2. Compound
1a (0.73 g, 1.0 mmol) was dissolved in dry THF (10 mL) and was
added dropwise to the NaH suspension over 2 min, and the resulting
mixture was stirred for 2 h at room temperature until no bubbles
(H2) appeared. Methyl iodide (75 µL, 1.2 mmol) was added
dropwise, and then the reaction mixture was stirred for 20 h. Then
the reaction was quenched with 80 mL of deionized water, the
mixture was extracted twice with 50 mL portions of dichlo-
romethane, and the organic phase was dried over MgSO4. Rotary
evaporation of the dichloromethane gave 0.53 g of 1b as a light
yellow solid (73%) (recrystallization from CH2Cl2/petroleum ether,
1
pure 1c as a white solid (126 mg, 64.3%). H NMR (300 MHz,
CD2Cl2): δ 3.48 (s, 9H); 6.24 (s, 1H); 7.11-7.50 (m, 30H). 13C
NMR (75 MHz, CD2Cl2): δ 143.7, 136.9, 135.5, 131.6, 131.2,
129.5, 129.2, 128.5, 127.1, 126.6, 32.4, 30.3. HRMS (ESI): m/z
713.3392 (M + 1); calcd for C
49H41N6 713.3393. IR (KBr, cm-1):
3058, 2927, 1603, 1508, 1445, 1392, 1072, 1025, 966, 775, 696.
[(N3COH)Cu]2(PF6)2 (3a). To 1a (72 mg, 0.10 mmol) and [Cu-
(CH3CN)4]PF6 (38 mg, 0.10 mmol) was added dry CH2Cl2 (5 mL),
and the resulting light yellow solution was stirred at room
temperature for 2 h under argon. After removal of CH2Cl2, a white
solid was obtained that was recrystallized from CH2Cl2 and diethyl
1
ether to give 20 mg of 3a as a white solid (20%). H NMR (400
1
mp 180-181 °C). H NMR (300 MHz, CD2Cl2): δ 3.43 (s, 9H,
MHz, CD2Cl2): δ 3.22 (s, 9H), 5.89 (s, 1H), 7.21-7.48 (m, 30H).
NCH3), 3.85 (s, 3H, OCH3), 7.13-7.51 (m, 30H). 13C NMR (75
MHz, CD2Cl2): δ 144.3, 135.5, 135.0, 131.5, 131.1, 129.0, 128.7,
128.0, 126.5, 126.1, 79.6, 54.9, 32.7. HRMS (ESI): m/z 743.3499
(M + 1); calcd for C50H43N6O 743.3516. IR (KBr, cm-1): 3100,
2927, 1603, 1444, 1388, 1073, 777, 696.
13C NMR (100 MHz, CD2Cl2): δ 132.8, 131.5, 130.4, 130.1, 129.9,
129.5, 129.3, 128.5, 69.7, 33.9. LRMS (ESI): m/z 791.2, 792.2
+
(100%, 26%) for C98H8063Cu2N12O22+ and C98H8063Cu65CuN12O22
,
respectively. IR (KBr, cm-1): 3110, 2927, 1487, 1446, 842, 776,
699, 558.
Tris(1-methyl-4,5-diphenylimidazol-2-yl)methane (1c). To a
colorless suspension of 1a (0.218 g, 0.30 mmol) and NaBH4 (114
mg, 3.0 mmol, 10 equiv) in CH2Cl2 (20 mL) was added trifluoro-
[(N3COMe)Cu]2(PF6)2 (3b). To 1b (0.074 g, 0.10 mmol) and
[Cu(CH3CN)4]PF6 (0.038 g, 0.10 mmol) was added dry CH2Cl2 (8
mL), and the resulting light yellow solution was stirred at room
temperature for 2 h under argon. After removal of CH2Cl2, a white
solid was give and then recrystallized from DMF and diethyl ether
(14) Kang, P.; Foote, C. S. J. Am. Chem. Soc. 2002, 124, 9629-38.
(15) LaRonde, F. J.; Brook, M. A. Inorg. Chim. Acta 1999, 296, 208-
221.
1
to give 50 mg of 3b as colorless crystals (50%). H NMR (300
2320 Inorganic Chemistry, Vol. 46, No. 6, 2007

Copper(I) Complexes of Tripodal Tris(imidazolyl) Ligands
MHz, CD2Cl2): δ 3.33 (s, 3H), 3.79 (s, 6H), 4.23 (s, 3H), 6.31-
7.48 (m, 30H). 13C NMR (75 MHz, CD2Cl2): δ 142.8, 139.0, 137.1,
134.5, 132.5, 131.2, 131.0, 130.9, 130.1, 129.8, 129.6, 129.1, 128.9,
128.0, 127.8, 127.4, 127.3, 127.1, 126.8, 110.0, 80.7, 36.8, 34.5.
LRMS (ESI): m/z 805.3, 807.3 (54%, 27%) for C100H84-
solution was stirred at room temperature for 2 h. Colorless crystals
were obtained overnight by slow diffusion of ether into the reaction
solution (50%). 1H NMR (300 MHz, CD2Cl2): δ 1.02 (s, 9H), 3.21
(br s, 9H), 6.00 (s, 1H), 7.22-7.48 (m, 30H). 13C NMR (75 MHz,
CD2Cl2): δ 138.3, 134.1, 132.4, 131.0, 130.9, 130.0, 129.9, 129.6,
129.1, 128.9, 128.7, 128.2, 128.0, 69.2, 33.5, 29.5. LRMS (ESI)
m/z 874.3, 876.3 (100%, 27%) for C54H4963CuN7O+ and C54H49-
65CuN7O+, respectively. IR (KBr, cm-1): 3110, 2927, 2189, 1446,
840, 700, 558. See Supporting Information for crystallographic data
on 8.
2+
63Cu2N12O2 and C100H8465Cu2N12O22+, respectively. IR (KBr,
cm-1): 3110, 2927, 1478, 1444, 1075, 840, 700, 558. See
Supporting Information for crystallographic data on 3b.
[(N3CH)Cu]2(PF6)2 (3c). To 1c (71 mg, 0.10 mmol) and [Cu-
(CH3CN)4]PF6 (38 mg, 0.10 mmol, 1:1 equiv) was added dry CH2-
Cl2 (8 mL), and the resulting light yellow solution was stirred at
room temperature for 2 h under argon. After removal of CH2Cl2, a
white solid was obtained and then was recrystallized from CH2Cl2
and diethyl ether to give 40 mg of 3c as colorless crystals (40%).
1H NMR (300 MHz, CD2Cl2): δ 4.03 (s, 9H), 6.40-7.38 (m, 31H).
13C NMR (75 MHz, CD2Cl2): δ 140.7, 138.5, 132.1, 130.9, 130.3,
130.0, 129.2, 129.0, 128.8, 128.6, 128.0, 127.0, 33.3, 32.7. LRMS
Reaction of [(N3COH)Cu]2(PF6)2 with CO. To solid 1a (72
mg, 0.10 mmol) and [Cu(CH3CN)4]PF6 (38 mg, 0.10 mmol) was
added dry CH2Cl2 (5 mL). The resulting light yellow solution was
stirred at room temperature for 1 h under argon. Carbon monoxide
was then bubbled into the solution at room temperature for 2 h.
An IR spectrum of the reaction solution showed a strong absorption
(νCO) at 2115 cm-1 (5a). A white solid precipitated overnight by
diffusion of ether vapor into the reaction solution and was found
2+
(ESI): m/z 775.2, 777.3 (65%, 26%) for C98H8063Cu2N12 and
C98H8065Cu2N122+, respectively. IR (KBr, cm-1): 3110, 2927, 1487,
1446, 841, 790, 699, 558. See Supporting Information for crystal-
lographic data on 3c.
1
to be dimer 3a from its H NMR spectrum in CD2Cl2.
Reaction of [(N3COMe)Cu]2(PF6)2 with CO (5b). To solid 1b
(74 mg, 0.10 mmol) and [Cu(CH3CN)4]PF6 (38 mg, 0.10 mmol)
was added dry CH2Cl2 (5 mL). The resulting light yellow solution
was stirred at room temperature for 1 h under argon. Carbon
monoxide was bubbled into the solution at room temperature for 2
h. An IR spectrum of the reaction solution showed a strong
absorption (νCO) at 2100 cm-1 (5b). Colorless crystals, found to
be dimer 3b, were obtained overnight by slow diffusion of ether
vapor into the reaction solution.
Formation of [(N3CH)Cu(CH3CN)]PF6 (4c) from Dimer 3c.
Dimer 3c (5 mg) was dissolved in 1 mL of CD3CN. The 1H NMR
spectrum of the resulting solution showed disappearance of the
dimer and the formation of a new species assigned to [(N3CH)Cu-
(CH3CN)]PF6. 1H NMR (300 MHz, CD3CN): δ 3.71 (s, 9H), 6.00
(s, 1H), 7.26-7.53 (m, 30H). LRMS (ESI in CH3CN): m/z 816.3,
+
818.3 (100%, 30%) for C51H4363CuN7 and C51H4365CuN7+, re-
spectively.
[(N3CH)CuCO]PF6 (5c). To compound 1c (30 mg, 42 µmol)
and [Cu(CH3CN)4]PF6 (16 mg, 42 µmol) was added dry CH2Cl2
(5 mL). The resulting light yellow solution was stirred at room
temperature for 1 h under argon. Carbon monoxide was bubbled
into the solution at room temperature for 2 h. Colorless needles
were obtained overnight by slow diffusion of ether vapor into the
reaction solution (50%). 1H NMR (300 MHz, CD2Cl2): δ 3.85 (s,
9H), 6.27 (s, 1H), 7.29-7.48 (m, 30H). 13C NMR (75 MHz, CD2-
Cl2): δ 142.9, 138.3, 132.9, 131.4, 130.1, 129.7, 128.9, 128.6, 32.8,
31.7. LRMS (ESI): m/z 803.3, 805.3 (100%, 31%) for C50H40-
63CuN6O+ and C50H4065CuN6O+, respectively. IR (KBr, cm-1):
3059, 2927, 2087, 1509, 840, 699, 558.
[(N3CH)CuII(CH3COCH3)(H2O)](PF6)2 (9). To compound 1c
(71.2 mg, 0.10 mmol) and [Cu(CH3CN)4]PF6 (38 mg, 0.10 mmol)
was added acetone (5 mL), and the resulting light greenish solution
was stirred at room temperature for 0.5 h under argon. Then the
solution was stirred under an O2 atmosphere (balloon) at room
temperature for 24 h to give a cloudy greenish solution. A white
solid separated from the solution, which proved to be dimer 3c
(50%). Yellow crystals of 9 were obtained by slow diffusion of
ether into the green solution (10%). LRMS(ESI): m/z 416.7, 417.6
(2.5%, 1.4%) for C52H4663CuN6O2+ and C52H4665CuN6O2+, respec-
tively. IR (KBr, cm-1): 3059, 2927, 1654, 1511, 1446, 1026, 841,
793, 700, 558. See Supporting Information for crystallographic data
on 9.
[(N3COMe)CuCNBut]PF6 (6). To ligand 1b (74 mg, 0.10 mmol)
and [Cu(CH3CN)4]PF6 (38 mg, 0.10 mmol) was added dry CH2Cl2
(5 mL). The resulting light yellow solution was stirred at room
temperature for 2 h under argon. tert-Butyl isocyanide (11 µL, 0.10
mmol) was added dropwise, and the resulting yellow solution was
stirred at room temperature for 2 h. Colorless crystals were obtained
overnight by slow diffusion of ether vapor into the reaction solution
(85%). 1H NMR (300 MHz, CD2Cl2): δ 1.06 (s, 9H), 3.44 (s, 4H),
3.58 (br s, 8H), 7.20-7.50 (m, 30H). 13C NMR (75 MHz, CD2-
Cl2): δ 131.4, 130.2, 129.7, 128.7, 66.2, 30.1, 15.7. LRMS (ESI):
m/z 888.3, 890.3 (100%, 32%) for C55H5163CuN7O+ and C55H51-
65CuN7O+, respectively. IR (KBr, cm-1): 3059, 2927, 2186, 1446,
837, 700, 557. See Supporting Information for crystallographic data
on 6.
[(N3CH)CuCNBut]PF6 (7). To compound 1c (15 mg, 21 µmol)
and [Cu(CH3CN)4]PF6 (8 mg, 21 µmol) was added dry CH2Cl2 (5
mL). The resulting light yellow solution was stirred at room
temperature for 1 h under argon. tert-Butyl isocyanide (2.5 µL, 21
mmol) was added dropwise, and the resulting yellow solution was
stirred at room temperature for 2 h. Colorless needles were obtained
overnight by slow diffusion of ether vapor into the reaction solution
(45%). 1H NMR (300 MHz, CD2Cl2): δ 1.53 (s, 9H), 3.81 (s, 9H),
6.16 (s, 1H), 7.24-7.52 (m, 30H). 13C NMR (75 MHz, CD2Cl2):
δ 143.4, 133.3, 131.5, 130.8, 129.8, 129.5, 128.5, 127.8, 32.5, 30.4.
LRMS (ESI): m/z 858.2, 860.2 (100%, 29%) for C54H4963CuN7
+
Acknowledgment. We are grateful for the (partial)
support of this work provided by the Petroleum Research
Fund of the American Chemical Society.
and C54H4965CuN7+, respectively. IR (KBr, cm-1): 3059, 2927,
2178, 1509, 842, 697, 558. See Supporting Information for
crystallographic data on 7.
[(N3COH)CuCNBut]PF6 (8). To compound 1a (146 mg, 0.20
mmol) and [Cu(CH3CN)4]PF6 (80.0 mg, 0.20 mmol) was added
dry CH2Cl2 (5 mL). The resulting light yellow solution was stirred
at room temperature for 2 h under argon. tert-Butyl isocyanide (22
µL, 0.20 mmol) was added dropwise, and the resulting yellow
Supporting Information Available: X-ray diffraction data and
tables for 3b, 3c, 6, 7, 8, and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC061985+
Inorganic Chemistry, Vol. 46, No. 6, 2007 2321