Modular syntheses of multidentate ligands with variable N-donors: Applications to tri- and tetracopper(i) complexes

Article abstract of DOI:10.1039/b705806c

A general method for the preparation of multidentate ligands comprised of a multi-imine platform derived from 1,1,1-tris(aminomethyl)ethane or tris(aminoethyl)amine connected to bi- and tridentate N-donor chelates has been developed. The feasibility of the method has been demonstrated through the synthesis and characterization of a large set of these ligand types. Complexation to Cu(i) was accomplished for several cases, yielding tri- and tetracopper(i) complexes that have been characterized in solution by NMR spectroscopy and conductivity, and in the solid state by elemental analysis, mass spectrometry, and/or X-ray crystallography. These complexes are potentially useful for modeling multicopper protein active sites. The Royal Society of Chemistry.

Full text of DOI:10.1039/b705806c

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PAPER
www.rsc.org/dalton | Dalton Transactions
Modular syntheses of multidentate ligands with variable N-donors:
applications to tri- and tetracopper(I) complexes†‡
Eric C. Brown,a Brandon Johnson,a Sara Palavicini,b Benjamin E. Kucera,a Luigi Casellab and
William B. Tolman*a
Received 17th April 2007, Accepted 14th May 2007
First published as an Advance Article on the web 8th June 2007
DOI: 10.1039/b705806c
A general method for the preparation of multidentate ligands comprised of a multi-imine platform
derived from 1,1,1-tris(aminomethyl)ethane or tris(aminoethyl)amine connected to bi- and tridentate
N-donor chelates has been developed. The feasibility of the method has been demonstrated through the
synthesis and characterization of a large set of these ligand types. Complexation to Cu(I) was
accomplished for several cases, yielding tri- and tetracopper(I) complexes that have been characterized
in solution by NMR spectroscopy and conductivity, and in the solid state by elemental analysis, mass
spectrometry, and/or X-ray crystallography. These complexes are potentially useful for modeling
multicopper protein active sites.
Introduction
Among the diverse range of copper protein active sites found
in biology, those comprising histidine-rich tri- and tetracopper
clusters have attracted special interest as a result of their struc-
tural novelty and functional/mechanistic features.1 Illustrative
examples are the [(His)8Cu3] and [(His)7Cu4(l-S)] clusters in the
multicopper blue oxidases1,2 and nitrous oxide reductase (N2OR),3
respectively, for which intriguing mechanistic hypotheses have
been proposed involving intermediates such as those derived from
theory shown in Fig. 1.4,5 Important aspects of the fundamental
chemistry underlying the properties and catalytic behavior of such
clusters, as well as related ones with different metal ions (e.g.
Zn),6,7 may be obtained through studies of synthetic analogs.8
Fig. 1 Intermediates proposed on the basis of theory for (left) O2
One strategy for constructing these analogs is to use appropriately
designed multinucleating ligands to position the copper ions in
the targeted arrangement. Some success in applying this strategy
has been reported, mostly aimed at modeling the multicopper blue
oxidases.9 While several different ligand platforms have been used
in these studies, they are typically designed to bind three copper
ions and feature N-donor ligand sets of narrow scope (typically
one type). In view of the absence of any reports of [Cu4(l-S)]
models of the N2OR active site and the demonstrated effects of
reduction by a multicopper oxidase (green, Cu; red, O), and (right) N2O
reduction by nitrous oxide reductase. Reproduced with permission from
ꢀ
C
ref. 4 and 5b. 2003 and 2007 American Chemical Society.
demonstrate its utility by preparing multiple ligand examples with
variable N-donors and characterizing several potentially useful
CuI3 and CuI4 complexes.
10
Experimental
supporting ligand structural variation on the course of Cu/O2
and Cu/S11 reactivity, it would be advantageous to develop a more
general ligand synthesis protocol that would enable incorporation
of a variety of N-donor types for generating structurally diverse
3- and 4-copper clusters. Herein we report such a method, and
General considerations
All solvents and reagents were obtained from commercial sources
and used as received unless noted otherwise. The solvents toluene,
tetrahydrofuran (THF), diethyl ether (Et2O), and CH2Cl2 were
passed through solvent purification columns (Glass Contour,
Laguna, CA) prior to use. CH3CN was dried over CaH2 and
distilled prior to use. All metal complexes were prepared and stored
in a Vacuum Atmospheres inert atmosphere glove box under a dry
nitrogen atmosphere or were manipulated using standard Schlenk
line techniques. N-Isopropyl-N-(2-methylpyridine) was prepared
according to a previously reported procedure.9h The syntheses of
the ligands used in this study are shown in Scheme 1 and Scheme 2,
and the derived copper(I) compounds are presented in Scheme 3.
aDepartment of Chemistry and Center for Metals in Biocatalysis, University
of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA. E-mail:
tolman@chem.umn.edu; Fax: +01-612-624-7029; Tel: +01-612-625-4061
bDipartimento di Chimica Generale, University of Pavia, Via Taramelli 12,
27100, Pavia, Italy
† CCDC reference numbers 644162–644164. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b705806c
‡ Electronic supplementary information (ESI) available: Drawing of the
X-ray structure of 19 and some representative 1H NMR spectra. See DOI:
10.1039/b705806c
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Scheme 3 Copper(I) compounds prepared in this work. Asterisks indicate
those complexes characterized by X-ray diffraction.
Scheme 1
spectra were obtained at −196 ◦C using a backscattering geometry;
samples were frozen onto a cold-plated copper coldfinger in
thermal contact with a Dewar flask containing liquid nitrogen.
Raman shifts were externally referenced to liquid indene. High-
resolution mass spectra were obtained on a Bruker BioTOF II
ESI-TOF/MS spectrometer. Elemental analyses were performed
by Robertson Microlit (Madison, NJ).
X-Ray crystallography. In each case, a crystal was placed onto
the tip of a 0.1 mm diameter glass capillary and mounted on a
Bruker SMART Platform CCD diffractometer for a data collec-
tion at 173(2) K. Data collections were carried out using MoKa
radiation (graphite monochromator) with a detector distance of
∼4.9 cm. A randomly oriented region of reciprocal space was
Scheme 2
˚
surveyed to the extent of one sphere and to a resolution of 0.84 A.
Four major sections of frames were collected with 0.30◦ steps in
x at four different φ settings and a detector position of −28◦ in
2h. The intensity data were corrected for absorption and decay
(SADABS).12 Final cell constants were calculated from the xyz
centroids of strong reflections from the actual data collection after
integration (SAINT).13 See ESI† for full crystal and refinement
details in the form of CIFs.
Physical methods
NMR spectra were recorded on a Varian VI-300 or VXR-300
spectrometer. Chemical shifts (d) for 1H or 13C NMR spectra
were referenced to residual protium in the deuterated solvent.
UV-vis spectra were recorded on a HP8453 (190–1100 nm)
diode array spectrophotometer. Low temperature spectra were
acquired through the use of a Unisoko low temperature UV-vis cell
holder. When necessary, UV-vis spectra were corrected for drifting
baselines due to minimal frosting of the UV cells caused by the low-
temperature device. This was achieved by subtracting the average
of a region with no absorbance (i.e., baseline, typically 950–
1000 nm) from the entire spectrum. Resonance Raman spectra
were recorded on an Acton 506 spectrometer using a Princeton
Instruments LN/CCD-11100-PB/UVAR detector and ST-1385
controller interfaced with Winspec software. A Spectra-Physics
Beamlok 2065-7S Ar Laser provided excitation at 568.2 nm. The
Conductivity measurements. Electrical conductivity measure-
ments were carried out in acetonitrile using a Fischer Scientific
Accumet Portable AP65 model conductivity bridge with a cell
having a cell constant of 1.0 cm−1. The equivalent conductance, Ke,
was calculated from the conductance measurements and plotted
against the square root of the concentration for each sample.
Extrapolation of the linear portion to zero concentration resulted
in the determination of the equivalent conductance at infinite
dilution, Ko. A plot of (Ko − Ke) versus the square root of the
3036 | Dalton Trans., 2007, 3035–3042
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concentration gave Onsager plots14 with straight lines that enabled
1 : 1, 2 : 1,15 3 : 1, and 4 : 1 electrolytes to be distinguished.
2,2-Dimethyl-3-((methyl)(pyridin-2-ylmethyl)amino)-propanal
(A, L = PyN(Me)). Method 1 (32%), distilled at 0.05 Torr and
65 ◦C. 1H NMR (300 MHz, CDCl3): d 1.01 (s, 6H), 2.18 (s, 3H),
2.63 (s, 2H), 3.65 (s, 2H), 7.10 (m, 1H), 7.39 (m, 1H), 7.61 (m, 1H),
8.46 (m, 1H), 9.47 (s, 1H). 13C NMR (75 MHz, CDCl3): d 20.3,
44.4, 47.8, 64.7, 65.5, 121.9, 122.7, 136.3, 148.7, 159.5, 206.2. IR
(KBr): 2967, 2844, 2701, 1725, 1589, 1570, 1473, 1434, 1362, 1259,
1045, 995, 882, 863, 762 cm−1. HRMS (ESI, Pos) calculated for
[C12H18N2O + Na]+: 229.1312, found 229.1313. HRMS (ESI, Pos)
calculated for [C12H18N2O + H]+: 207.1492, found 207.1477.
1,1,1-Tris(aminomethyl)ethane (tame). This compound was
prepared by a modification of a literature procedure.16 Sodium
azide (10.8 g, 166.4 mmol) was added to a mixture containing
tris(benzenesulfonyloxymethyl)ethane (15.0 g, 27.8 mmol) and
diethylene glycol (350 mL). The mixture was heated to 135 ◦C for
24 h under an atmosphere of dry nitrogen. The resulting brown
solution was allowed to cool to room temperature and 300 mL
of water was added. The mixture was stirred for 15 min, then
extracted with CH2Cl2 (3 × 100 mL). Triphenylphosphine (36.4 g,
139 mmol) was then added to the organic phase and stirred for
3.5 h. The mixture was hydrolyzed by adding NaOH (3.3 g) in
10 mL of water. The mixture was stirred for 48 h, evaporated to
a white semisolid and distilled at 100 ◦C (50 mTorr) to yield a
colorless liquid. The colorless liquid was then added to a 200 mL
flask equipped with a magnetic stirring bar and a Dean–Stark
condenser. Dry toluene (100 mL) was added and the solution
heated to reflux. Toluene (90 mL) was distilled and removed before
the mixture was concentrated to give the product as a colorless oil
(2.0 g, 17.1 mmol, 62%).
3-((2-(Dimethylamino)ethyl)(methyl)amino)-2,2-dimethyl-pro-
panal (A, L = Me3eda). M◦ethod 1 (35%), Method 2 (80%),
1
distilled at 0.05 Torr and 38 C. H NMR (300 MHz, CDCl3):
d 1.01 (s, 6H), 2.17 (s, 6H), 2.18 (s, 3H), 2.30 (m, 2H), 2.45 (m,
2H), 2.49 (s, 2H), 9.51 (s, 1H). 13C NMR (75 MHz, CDCl3): d
20.4, 44.5, 45.8, 47.5, 57.5, 57.7, 65.5, 206.5. IR (KBr): 2966,
2816, 2771, 1725, 1464, 1261, 1118, 1038, 880 cm−1. HRMS (ESI,
Pos) calculated for [C10H22N2O + Na]+: 209.1625, found 209.1615.
3-((3-(Dimethylamino)propyl)(methyl)amino)-2,2-dimethylpro-
panal (A, L = Me3pda). Method 1 (34%), Method 2 (54%),
◦
1
distilled at 0.05 Torr and 51 C. H NMR (300 MHz, CDCl3):
d 1.01 (s, 6H), 1.53 (dt, J = 7.2, 7.5 Hz, 2H), 2.14 (s, 3H), 2.16
(s, 6H), 2.19 (t, J = 7.2 Hz, 2H), 2.32 (t, J = 7.5 Hz, 2H), 2.45
(s, 2H), 9.50 (s, 1H). 13C NMR (75 MHz, CDCl3): d 20.4, 25.7,
44.0, 45.4, 47.5, 57.4, 57.5, 65.2, 206.5. IR (KBr): 2951, 2813,
2781, 1726, 1461, 1098, 1042 cm−1. HRMS (ESI, Pos) calculated
for [C11H24N2O + Na]+: 223.1781, found 223.1787. HRMS (ESI,
Pos) calculated for [C11H24N2O + H]+: 201.1961, found 201.1958.
General procedure for synthesis of aldehydes A. The aldehydes
can be synthesized by two methods. Method 1. Concentrated
HCl (6.60 mL) was added dropwise to the appropriate diamine
(typically 40.0 mmol) in CH3CN or ethanol (60 mL) at 0 ◦C. The
solution was stirred at room temperature for 15 min before
paraformaldehyde (1.47 g, 49.0 mmol) and isobutyraldehyde
(3.10 g, 43.0 mmol) were added and refluxed for 1.5 h. After cool-
ing to room temperature, additional paraformaldehyde (1.47 g,
49.0 mmol) was added and the solution refluxed for another
1.5 h. To this solution, was added 200 mL of water which was
extracted with diethyl ether (2 × 125 mL) to remove unreacted
paraformaldehyde and isobutyraldehyde. The aqueous solution
was made strongly alkaline with 10% NaOH and added to 250 mL
of diethyl ether. The organic layer was separated, dried with
MgSO4 and the solvent removed under reduced pressure. The
resulting clear liquid was purified by distillation. Method 2. The
appropriate diamine or triamine (typically 50.0 mmol) was added
to 50 mL of dry methanol at 0 ◦C. HCl gas was bubbled through the
solution for 5 min, causing the formation of a white precipitate.
The cold solution was filtered, washed with diethyl ether (2 ×
75 mL) and dried under reduced pressure for 3 h. The resulting
dihydrochloride or trihydrochloride of the appropriate diamine
or triamine (45 mmol) was added to paraformaldehyde (1.58 g,
52.5 mmol) in CH3CN (150 mL) and heated to reflux for 15 min.
After cooling to room temperature, isobutyraldehyde (3.60 g,
50 mmol) was added and the solution was refluxed for 1 h. Upon
cooling to ambient temperature, additional paraformaldehyde
(1.58 g, 52.5 mmol) was added and the solution refluxed for
1.5 h. To this solution, was added 200 mL of water which was
extracted with diethyl ether (2 × 125 mL) to remove unreacted
paraformaldehyde and isobutyraldehyde. The aqueous solution
was made strongly alkaline with 10% NaOH and added to 250 mL
of diethyl ether. The organic layer was separated, dried with
MgSO4 and the solvent removed under reduced pressure. The
resulting clear liquid was purified by distillation.
2,2-Dimethyl-3-(4-methyl-piperazin-1-yl)propanal (A, L = Mepip).
Method 1 (27%), Method 2 (47%), distilled at 0.05 Torr and 50 ◦C.
1H NMR (300 MHz, CDCl3): d 0.99 (s, 6H), 2.19 (m, 4H), 2.31 (s,
3H), 2.40 (s, 2H), 2.43 (m, 4H), 9.49 (s, 1H). 13C NMR (75 MHz,
CDCl3): d 20.3, 45.8, 47.4, 54.6, 55.0, 64.9, 206.4. IR (ATR): 2934,
2792, 1667, 1456, 1373, 1280, 1163, 1123, 1016, 822 cm−1. HRMS
(ESI, Pos) calculated for [C10H20N2O + Na]+: 207.1457, found
207.1468.
3-((Isopropyl)(pyridin-2-ylmethyl)amino)-2,2-dimethyl-propanal
(A, L = PyN(iPr)). Method 1 (18%), distilled at 0.05 Torr and
95 ◦C. 1H NMR (300 MHz, CDCl3): d 0.96 (s, 6H), 0.96 (d, J =
6.6 Hz, 6H), 2.63 (s, 2H), 2.64 (m, J = 6.6 Hz, 1H), 3.68 (s, 2H),
7.08 (m, 1H), 7.46 (m, 1H), 7.61 (m, 1H), 8.42 (m, 1H), 9.37 (s,
1H). 13C NMR (75 MHz, CDCl3): d 17.8, 20.3, 47.6, 51.6, 57.2,
58.1, 121.6, 122.4, 136.4, 148.5, 161.0, 206.3. IR (KBr): 2965,
2870, 2834, 2701, 1724, 1590, 1469, 1433, 1365 cm−1. HRMS
(ESI, Pos) calculated for [C14H22N2O + Na]+: 257.1625, found
257.1616.
Bis(3-((methyl)(pyridine-2-ylmethyl)amino)-2,2-dimethyl-pro-
panal (A, L = Py2N). Method 2 (52%); purification by distillation
was not required. 1H NMR (300 MHz, CDCl3): d 1.02 (s, 6H), 2.94
(s, 2H), 3.81 (s, 4H), 7.20 (m, 2H), 7.47 (d, J = 7.8 Hz, 2H), 7.70
(m, 2H), 8.56 (d, J = 4.8 Hz, 2H), 9.28 (s, 3H). 13C NMR (75 MHz,
CDCl3): d 20.1, 48.1, 61.1, 61.6, 122.1, 123.3, 136.5, 148.8, 159.0,
206.1. IR (ATR): 2965, 2931, 2825, 1723, 1589, 1569, 1473, 1434,
1361, 1120, 1085, 1047, 995, 881, 766, 614 cm−1. HRMS (ESI, Pos)
calculated for [C17H21N3O + H]+: 284.1757, found 284.1765.
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General procedure for synthesis of ligands 1–13. To a 100 mL
roundbottom flask equipped with a Dean–Stark condenser, 1,1,1-
tris(aminomethyl)ethane (1–6) or tris(2-aminoethyl)amine (7–9)
(1 equiv) was added to the appropriate aldehyde A (3.3 equiv)
in 80 mL of dry toluene. The solution was heated to reflux and
75 mL of toluene was distilled and removed. The remaining solvent
was removed under reduced pressure and unreacted aldehyde was
removed by distillation (see below for conditions) leaving the
product as a yellow oil.
3.75 (s, 6H), 7.10 (m, 3H), 7.47 (m, 3H), 7.60 (s, 3H), 7.62 (m, 3H),
8.46 (m, 3H). 13C NMR (75 MHz, CDCl3): d 17.86, 19.38, 20.23,
23.84, 39.98, 41.04, 51.44, 58.87, 66.66, 121.4, 122.2, 136.2, 148.5,
161.8, 171.5. IR (ATR): 2963, 2869, 2829, 1667, 1589, 1463, 1432,
1387, 1364, 1165, 1045, 781, 752. HRMS (ESI, Pos) calculated for
[C47H75N9 + Na]+: 788.6038, found 788.6054. HRMS (ESI, Pos)
calculated for [C47H75N9 + H]+: 766.6218, found 766.6242.
Compound 6. Unreacted aldehyde A (L = Py2N) was removed
by distillation (160 ◦C at 0.05 Torr). Yield from 160 mg of 1,1,1-
tris(aminomethyl)ethane: 0.99 g (1.08 mmol, 79%). 1H NMR
(300 MHz, CDCl3): d 0.73 (s, 3H), 0.92 (s, 18H), 2.73 (s, 6H), 3.04
(s, 6H), 3.75(s, 12H), 7.20 (m, 6H), 7.37(s, 3H), 7.51(d, J = 8.0 Hz,
6H), 7.71(m, 6H), 8.49 (d, J = 5.0 Hz, 6H). 13C NMR (75 MHz,
CDCl3): d 20.29, 23.83, 40.22, 41.63, 61.24, 62.04, 63.49, 121.8,
123.2, 136.3, 148.9, 159.9, 171.2. IR (KBr): 2957, 2939, 2828, 1666,
1589, 1472, 1433, 1361, 1047 cm−1. HRMS (ESI, Pos) calculated
for [C56H72N12 + Na]+: 935.5895, found 935.5927.
Compound 1. Unreacted aldehyde A (L = PyN(Me)) was
removed by distillation (80 ◦C at 0.05 Torr). Yield from 186 mg of
1,1,1-tris(aminomethyl)ethane: 0.87 g (1.3 mmol, 80%). 1H NMR
(300 MHz, CDCl3): d 0.823 (s, 3H), 1.03 (s, 18H), 2.20 (s, 9H), 2.51
(s, 6H), 3.23 (s, 6H), 3.68 (s, 6H), 7.10 (m, 3H), 7.48 (m, 3H), 7.50
(s, 3H), 7.61 (m, 3H), 8.47 (m, 3H). 13C NMR (75 MHz, CDCl3): d
20.40, 23.86, 40.25, 41.57, 44.98, 66.05, 66.82, 67.16, 121.8, 122.7,
136.3, 148.8, 160.4, 171.5. IR (ATR): 2957, 2924, 2838, 2812, 1667,
1589, 1456, 1433, 1360, 1044 cm−1. HRMS (ESI, Pos) calculated
for [C41H63N9 + Na]+: 704.5099, found 704.5088.
Compound 7. Unreacted aldehyde A (L = Me3eda) was
removed by distillation (160 ◦C at 0.05 Torr). Yield from 337 mg
of tris(2-aminoethyl)amine: 1.212 g (1.86 mmol, 82%). 1H NMR
(300 MHz, CDCl3): d 0.996 (s, 18H), 2.18 (s, 18H), 2.20 (s, 9H),
2.29 (t, J = 5.9 Hz, 6H), 2.33 (s, 6H), 2.47 (t, J = 5.9, 6H), 2.67 (t,
J = 7.5 Hz, 6H), 3.40 (t, J = 7.1 Hz, 6H), 7.53 (s, 3H). 13C NMR
(75 MHz, CDCl3): d 23.78, 41.05, 45.24, 46.01, 55.54, 57.75, 58.22,
59.87, 67.93, 172.7. IR (KBr): 2948, 2814, 2765, 1665, 1463, 1119,
1036 cm−1. Anal. Calcd for C36H78N10: C, 66.41; H, 12.08; N, 21.51.
Found: C, 66.22; H, 12.18; N, 21.90.
Compound 2. Unreacted aldehyde A (L = Me3eda) was
removed by distillation (55 ◦C at 0.05 Torr). Yield from 207 mg of
1,1,1-tris(aminomethyl)ethane: 0.88 g (1.4 mmol, 80%). 1H NMR
(300 MHz, CDCl3): d 0.898 (s, 3H), 1.06 (s, 18H), 2.24 (s, 18H),
2.26 (s, 9H), 2.35 (m, 6H), 2.40 (s, 6H), 2.52 (m, 6H), 3.30 (s, 6H),
7.55 (s, 3H). 13C NMR (75 MHz, CDCl3): d 20.31, 23.81, 40.13,
41.20, 45.19, 45.88, 57.65, 58.17, 66.79, 67.70, 171.6. IR (KBr):
2953, 2815, 2765, 1669, 1465, 1118, 1035 cm−1. HRMS (ESI, Pos)
calculated for [C35H75N9 + Na]+: 644.6038, found 644.6023.
Compound 8. Unreacted aldehyde A (L = Me3pda) was
Compound 3. Unreacted aldehyde A (L = Me3pda) was
removed by distillation (100 ◦C at 0.05 Torr). Yield from 411 mg of
1,1,1-tris(aminomethyl)ethane: 1.40 g (2.1 mmol, 60%). 1H NMR
(300 MHz, CDCl3): d 0.842 (s, 3H), 1.02 (s, 18H), 1.56 (m, 6H),
2.18 (s, 9H), 2.19 (s, 18H), 2.23 (m, 6H), 2.32 (s, 6H), 2.35 (m, 6H),
3.25 (s, 6H), 7.51 (s, 3H). 13C NMR (75 MHz, CDCl3): d 20.45,
23.94, 26.03, 40.28, 41.27, 44.77, 45.57, 57.79, 58.18, 66.88, 67.44,
171.83. IR (ATR): 2949, 2812, 2763, 1667, 1458, 1383, 1042 cm−1.
HRMS (ESI, Pos) calculated for [C38H81N9 + Na]+: 686.6507,
found 686.6503. HRMS (ESI, Pos) calculated for [C38H81N9 +
H]+: 664.6688, found 664.6673.
removed by distillation (165 ◦C at 0.05 Torr). Yield from 262 mg
1
of tris(2-aminoethyl)amine: 1.19 g (1.7 mmol, 96%). H NMR
(300 MHz, CDCl3): d 1.00 (s, 18H), 1.55 (q, J = 7.1, 6H), 2.17
(s, 18H), 2.21 (t, J = 7.0 Hz, 6H), 2.30 (t, J = 7.0, 6H), 2.68 (t,
J = 7.4 Hz, 6H), 3.42 (t, J = 6.8 Hz, 6H), 7.53 (s, 3H). 13C NMR
(75 MHz, CDCl3): d 23.79, 26.03, 41.02, 44.75, 45.60, 55.55, 57.78,
58.14, 59.87, 67.53, 172.8. IR (KBr): 2948, 2812, 1666, 1459, 1153,
1041 cm−1. Anal. Calcd for C39H84N10: C, 67.58; H, 12.21; N, 20.21.
Found: C, 67.43; H, 11.99; N, 20.45.
Compound 9. Unreacted aldehyde A (L = Py2N) was removed
by distillation (125 ◦C at 0.05 Torr). Yield from 230 mg of tris(2-
aminoethyl)amine: 0.95 g (1.01 mmol, 64%). 1H NMR (300 MHz,
CDCl3): d 0.92 (s, 18H), 2.44 (t, J = 7.7 Hz, 6H), 2.73 (s, 6H), 3.16
(t, J = 7.4 Hz, 6H), 3.75 (s, 12H), 7.21 (m, 6H), 7.40 (s, 3H), 7.52 (d,
J = 8.1 Hz, 6H), 7.72 (m, 6H), 8.49 (d, J = 4.2 Hz, 6H). 13C NMR
(75 MHz, CDCl3): d 23.66, 41.56, 55.41, 59.72, 62.19, 63.66, 122.1,
123.4, 136.4, 149.0, 159.8, 172.8. IR (KBr): 2957, 2939, 2828, 1666,
1589, 1472, 1433, 1361, 1047, cm−1. HRMS (ESI, Pos) calculated
for [C57H75N13 + Na]+: 964.6161, found 964.6201.
Compound 4. Unreacted aldehyde A (L = Mepip) was removed
◦
by distillation (125 C at 0.05 Torr). Yield from 64 mg of 1,1,1-
tris(aminomethyl)ethane: 0.29 g (1.43 mmol, 89%). 1H NMR
(300 MHz, CDCl3): d 0.853 (s, 3H), 1.02 (s, 18H), 2.22 (s, 9H),
2.32 (m, 12H), 2.33 (s, 6H), 2.47 (m, 12H), 3.25 (s, 6H), 7.51 (s,
3H). 13C NMR (75 MHz, CDCl3): d 20.44, 23.82, 40.33, 41.32,
46.10, 55.23, 55.44, 66.96, 67.13, 171.7. IR (ATR): 2935, 2792,
1667, 1456, 1373, 1280, 1163, 1123, 1016, 822 cm−1. HRMS (ESI,
Pos) calculated for [C35H69N9 + Na]+: 638.5568, found 638.5574.
HRMS (ESI, Pos) calculated for [C35H69N9 + H]+: 616.5749, found
616.5745.
Compound 10. Unreacted aldehyde was removed by distil-
lation (80 ◦C at 0.05 Torr). Yield from 133 mg of 1,1,1-
1
tris(aminomethyl)ethane: 0.240 g (0.75 mmol, 66%). H NMR
Compound 5. Unreacted aldehyde A (L = PyN(iPr)) was
(300 MHz, CDCl3): d 0.86 (s, 3H), 1.06 (s, 27H), 3.22 (s, 6H),
7.52 (s, 3H). 13C NMR (75 MHz, CDCl3): d 20.21, 23.74, 36.31,
40.17, 55.10, 172.3. IR (KBr): 2962, 2832, 1675, 1465, 1362, 1065,
954 cm−1. HRMS (ESI, Pos) calculated for [C20H39N3 + H]+:
322.3217, found 322.3222.
removed by distillation (125 ◦C at 0.05 Torr). Yield from 255 mg of
1
1,1,1-tris(aminomethyl)ethane: 1.4 g (1.8 mmol, 84%). H NMR
(300 MHz, CDCl3): d 0.795 (s, 3H), 0.968 (d, 18H, J = 6.6 Hz),
0.995 (s, 18H), 2.50 (s, 6H), 2.73 (m, 3H, J = 6.6 Hz), 3.14 (s, 6H),
3038 | Dalton Trans., 2007, 3035–3042
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Compound 11. Unreacted aldehyde was removed by distil-
lation (80 ◦C at 0.05 Torr). Yield from 467 mg of tris(2-
aminoethyl)amine: 0.91 g (2.94 mmol, 92%). 1H NMR (300 MHz,
CDCl3): d 1.05 (d, 18H), 2.35 (m, J = 6.7 Hz, 3H), 2.68 (t, J =
1106, 1038, 949, 840, 558 cm−1. HRMS (ESI, Pos) calculated for
[C35H75N9Cu3Cl]2+: 880.3405, found 880.3741.
Compound 16. Yield from 459 mg of 3: 742 mg (0.58 mmol,
83%). Drying under vacuum resulted in the loss of coordinated
7.2 Hz, 6H), 3.37 (t, J = 7.0 Hz, 6H), 7.57 (d, J = 4.9 Hz, 2H). 13
C
1
CH3CN. H NMR (300 MHz, CD3CN): d 1.19 (s, 3H), 1.23 (s,
NMR (75 MHz, CDCl3): d 19.23, 33.91, 55.41, 59.48, 170.5. IR
(KBr): 2962, 2833, 1671, 1465, 1364, 1067, 953 cm−1. HRMS (ESI,
Pos) calculated for [C18H36N4 + Na]+: 331.2832, found 331.2839.
18H), 2.37 (s, 18H), 2.42 (m, 6H), 2.50 (s, 9H), 2.57 (s, 6H), 2.61 (m,
6H), 2.78 (m, 6H), 3.53 (s, 6H), 7.70 (s, 3H). IR (KBr): 2969, 2874,
1634, 1468, 1389, 1026, 1004, 839, 751, 559 cm−1. HRMS (ESI,
Pos) calculated for [C38H81N9Cu3]3+: 284.8158, found 284.8071.
Compound 12. Unreacted aldehyde was removed by dis-
tillation (80 ◦C at 0.05 Torr). Yield from 1.01 g of tris(2-
aminoethyl)amine: 2.19 g (6.25 mmol, 90.6%) 1H NMR (300 MHz,
CDCl3): d 1.05 (s, 27H), 2.73 (t, J = 7.3 Hz, 6H), 3.42 (t, J =
7.0 Hz, 6H), 7.52 (s, 3H). 13C NMR (75 MHz, CDCl3): d 26.90,
36.00, 55.63, 59.75, 172.8. IR (KBr): 2956, 2930, 2814, 1667, 1475,
1362, 1071, 919 cm−1. HRMS (ESI, Pos) calculated for [C21H42N4 +
H]+: 351.3482, found 351.3491.
Compound 17. Yield from 72 mg of 6: 120.4 mg (0.078 mmol,
98%). Drying under vacuum resulted in the loss of coordinated
1
CH3CN. H NMR (300 MHz, CD3CN): d 1.18 (s, 18H), 1.59 (s,
3H), 2.95 (s, 6H), 3.68 (s, 6H), 4.00 (s, 12H), 7.32 (m, 12H), 7.68
(s, 3H), 7.85 (t, J = 7.7 Hz, 6H), 8.52 (d, J = 5.1 Hz, 6H). IR
(KBr): 2967, 2926, 2871, 1669, 1604, 1479, 1442, 1097, 1054, 840,
763, 558 cm−1. HRMS (ESI, Pos) calculated for [C56H72N12Cu3]3+:
367.1291, found 367.1206.
Compound 13. Unreacted aldehyde was removed by distil-
lation (80 ◦C at 0.05 Torr). Yield from 538 mg of tris(2-
aminoethyl)amine: 1.16 g (2.83 mmol, 77%). 1H NMR (300 MHz,
CDCl3): d 2.94 (t, J = 6.5 Hz, 6H), 3.70 (t, J = 5.85 Hz, 6H),
7.38 (m, 9H), 7.52 (d, J = 6.6 Hz, 6H), 8.10 (s, 3H). 13C NMR
(75 MHz, CDCl3): d 55.78, 60.20, 128.1, 128.6, 130.5, 136.3, 161.9.
IR (KBr): 2952, 2848, 2795, 1647, 1064, 1034 cm−1. HRMS (ESI,
Pos) calculated for [C27H30N4 + Na]+: 433.2363, found 433.2382.
Compound 18. Yield from 123 mg of 10: 191 mg (0.36 mmol,
87%). 1H NMR (300 MHz, CD3CN): d 0.76 (s, 3H), 1.16 (s, 27H),
3.39 (s, 6H), 7.58 (s, 3H). IR (KBr): 2693, 2929, 2391, 1654, 1476,
1054, 927, 738, 555 cm−1. Anal. Calcd for C20H39N3CuPF6: C,
45.32; H, 7.42; N, 7.93. Found: C, 45.01; H, 7.38; N, 8.21.
Compound 19. Yield from 127 mg of 11: 200 mg (0.39 mmol,
87%). 1H NMR (300 MHz, CD3CN): d 1.10 (s, 18H), 2.54 (m, J =
6.6 Hz, 3H), 2.87 (t, J = 5.9 Hz, 6H), 3.48 (t, J = 5.2 Hz, 6H),
7.56 (d, J = 0.6 Hz, 2H). IR (KBr): 2975, 2915, 2342 1665, 1409,
1235, 1065, 958, 763, 556 cm−1. HRMS (ESI, Pos) calculated for
[C18H36N4Cu]+: 371.2230, found 371.3155.
General procedure for the preparation of Cu(I) complexes. To
a slurry of [Cu(CH3CN)4]PF6 (1.0, 3.0, or 4.0 equiv, depending
on the ligand used) or, for the case of 15b, CuCl (6.0 equiv), in
CH3CN (3 mL), was added a 5 mL solution of the appropriate
ligand (1.0 equiv) in CH3CN. The solution was stirred for 15 min
and the volume reduced to 2 mL under reduced pressure. Addition
of diethyl ether (7 mL) resulted in the formation of a white-yellow
solid which was collected, washed with diethyl ether (3 × 5 mL)
and dried under reduced pressure.
Compound 20. Yield from 96.5 mg of 12: 136.8 mg
1
(0.245 mmol, 89%). H NMR (300 MHz, CD3CN): d 1.18 (s,
27H), 2.84 (dt, J = 5.0 Hz, 6H), 3.47 (dt, J = 5.4 Hz, 6H), 7.77
(s, 3H). IR (KBr): cm−1: 2966, 2929, 2348, 1670, 1405, 1210, 1071,
930, 773, 559. Anal. Calcd for C21H42N4CuPF6: C, 45.11; H, 7.57;
N, 10.02. Found: C, 44.70; H, 7.40; N, 10.01.
Compound 14. Yield from 101 mg of 1: 169 mg (0.13 mmol,
87%). Drying under vacuum resulted in the loss of coordinated
CH3CN. H NMR (300 MHz, CD3CN): d 1.30 (s, 18H), 1.36 (s,
Compound 21. Yield from 22 mg of 13: 29.3 mg (0.05 mmol,
83%). 1H NMR (300 MHz, CD3CN): d 3.15 (t, J = 5.6 Hz, 6H),
3.87 (t, J = 5.1 Hz, 6H), 6.93 (t, J = 7.8 Hz, 6H), 7.42 (t, J =
7.4, 3H), 8.08 (d, J = 7.8, 6H), 8.52 (s, 3H). IR (KBr): 2976, 2918,
2342 1665, 1403, 1230, 1065, 956, 763, 559 cm−1. HRMS (ESI,
Pos) calculated for [C27H30N4Cu]+: 473.1761, found 473.1978.
1
3H), 2.38 (s, 9H), 2.71 (s, 6H), 3.65 (s, 6H), 3.72 (s, 6H), 7.35 (m,
6H), 7.71 (s, 3H), 7.83 (t, J = 8.1 Hz, 3H), 8.44 (d, J = 4.8 Hz,
3H). 13C NMR (75 MHz, CD3CN): d 20.2, 24.2, 38.8, 39.8, 46.5,
65.4, 65.8, 69.9, 123.7, 124.2, 138.0, 148.6, 156.8, 178.1. IR (KBr):
2966, 2871, 1667, 1630, 1608, 1463, 1446, 1381, 1307, 1159, 1108,
1033, 840, 764, 738, 558 cm−1. Anal. Calcd for C41H63N9Cu3P3F18:
C, 37.66; H, 4.86; N, 9.64. Found: C, 37.25; H, 4.67; N, 9.68.
Compound 22. Yield from 63 mg of 7: 144 mg (0.0873 mmol,
91%). Drying under vacuum resulted in the loss of coordinated
1
CH3CN. H NMR (300 MHz, CD3CN): d 1.25 (s, 18H), 2.46
Compound 15. (a) Yield from 154 mg of 2: 285 mg (0.23 mmol,
(s, 18H), 2.49 (m, 6H), 2.51 (s, 9H), 2.58 (s, 6H), 2.64 (m, 6H),
2.88 (m, 6H), 3.53 (m, 6H), 7.74 (s, 3H). IR (KBr): 2695, 2873,
1629, 1469, 1285, 1036, 945, 836, 555 cm−1. Anal. Calcd for
C44H90N14Cu4P4F24: C, 32.04; H, 5.50; N, 11.89. Found: C, 31.92;
H, 5.25; N, 11.48.
92%). Drying under vacuum resulted in the loss of coordinated
1
CH3CN. H NMR (300 MHz, CD3CN): d 1.28 (s, 18H), 1.39 (s,
3H), 2.43 (s, 18H), 2.50 (m, 6H), 2.52 (s, 9H), 2.56 (s, 6H), 2.62 (m,
6H), 3.55 (s, 6H), 7.75 (s, 3H). IR (KBr): 2969, 2875, 1633, 1470,
1288, 1038, 949, 840, 558 cm−1. Anal. Calcd for C35H75N9Cu3P3
F18: C, 33.70: H, 6.06; N, 10.10. Found: C, 33.66; H, 5.52; N,
10.58. (b) Yield from 68.6 mg of 2: 130 mg (0.109 mmol, 94%).
Drying under vacuum resulted in the loss of coordinated CH3CN.
1H NMR (300 MHz, CD3CN): d 1.19 (s, 3H), 1.26 (s, 18H), 2.39
(s, 18H), 2.45 (m, 6H), 2.48 (s, 9H), 2.53 (s, 6H), 2.58 (m, 6H),
3.63 (s, 6H), 7.78 (s, 3H). (KBr): 2969, 2875, 1633, 1470, 1288,
Compound 23. Yield from 60 mg of 8: 129 mg (0.0763 mmol,
88%). Drying under vacuum resulted in the loss of coordinated
1
CH3CN. H NMR (300 MHz, CD3CN): d 1.20 (s, 18H), 1.60
(quintet, J = 6.7 Hz, 6H), 2.22 (s, 18H), 2.24 (m, 6H), 2.26 (s, 9H),
2.45 (s, 6H), 2.49 (m, 6H), 2.85 (t, J = 6.0 Hz, 6H), 3.55 (t, J =
6.0 Hz, 6H), 7.80 (s, 3H). IR (KBr): 2965, 2875, 1629, 1465, 1283,
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1036, 940, 834, 557. Anal. Calcd for C47H96N14Cu4P4F24: C, 33.38;
H, 5.72; N, 11.59. Found: C, 33.05; H, 5.55; N, 11.59.
(1–6) and the other from tris(2-aminoethyl)amine (7–9) to provide
tri- and tetradentate ligation, respectively, to the metal ion
envisioned to reside in the unique, basal “platform” position.
Mononucleating ligands 10–13 (Scheme 2) were prepared as
models of the platform portions of 1–9, in order to test the ability
of these fragments to coordinate a Cu(I) ion.
Compound 24. Yield from 96.5 mg of 9: 176.7 mg (0.091 mmol,
89%, assuming a molecular weight that included CH3CN coli-
1
gands). H NMR (300 MHz, CD3CN): d 1.15 (s, 18H), 2.94 (s,
6H), 3.08 (m, 6H), 3.56 (m, 6H), 4.00 (s, 12H), 7.30 (m, 12H),
7.64 (s, 3H), 7.79 (m, 6H), 8.59 (d, J = 4.5 Hz, 6H). IR (KBr):
2965, 1658, 1604, 1479, 1443, 1095, 840, 766, 558 cm−1. While high
quality elemental analysis or HRMS data for this compound was
not obtained, its identity is supported by the full characterization
of its isocyanide derivative (25, see below).
The syntheses of 1–9 involved condensation of the platform
polyamine with amino-2,2-dimethylpropanals (A), which were
prepared from the appropriate secondary amine L–H, isobu-
tyraldehyde, and formaldehyde (Scheme 1). The products were
obtained after distillation and obtained in purity suitable for
complex preparation without the need for chromatography. The
general utility of this relatively straightforward and high-yielding
protocol is illustrated by its application toward ligands with
a range of potentially bi- and tridentate N-donors L (1–9);
further derivatives may be readily envisioned. In principle, the
synthetic schemes could also be applied to obtain ligands with
higher denticity, and complexes with higher nuclearity. Similar
condensations with simpler aldehydes were used to prepare 10–13.
Compound 25. A 3 mL solution of xylyl isocyanide (4.0 equiv)
in CH3CN was added to 24 (47.2 mg, 0.027 mmol) in 2 mL of
CH3CN. The solution was stirred for 20 min, filtered through
Celite and the volume reduced to 2 mL under reduced pressure.
Diethyl ether (7 mL) was added, causing the formation of a white-
yellow solid. The solid was collected, washed with diethyl ether
(2 × 4 mL) and dried under vacuum. Yield: 35.5 mg (0.015 mmol,
63%). 1H NMR (300 MHz, CD3CN): d 1.30 (s, 18H), 2.31 (s, 24H),
2.71 (m, 6H), 3.09 (s, 6H), 3.43 (m, 6H), 3.92 (s, 12H), 7.13 (d,
J = 7.3 Hz, 8H), 7.27 (t, J = 6.6 Hz, 4H), 7.38 (d, J = 6.6 Hz,
6H), 7.47 (t, J = 7.9 Hz, 6H), 7.86 (m, 9H), 8.70 (d, J = 4.6 Hz,
6H). IR (KBr): 2967, 1650, 1471, 1387, 1105, 840, 558 cm−1. Anal.
Calcd for C93H111N17Cu4P4F24: C, 48.54; H, 4.86; N, 10.35. Found:
C, 48.53; H, 5.07; N, 10.08.
1
All of the ligands were fully characterized by H and 13C NMR
and IR spectroscopy and either CHN analysis or high resolution
mass spectrometry (HRMS). A particularly diagnostic property of
the ligands is a single peak at ∼7.5 ppm in the 1H NMR spectrum
due to the presence of 3 equivalent imine groups (C3-symmetry).
Synthesis and characterization of Cu(I) complexes
Compound 26. A 3 mL solution of triphenylphosphine
(4.0 equiv) in CH3CN was added to 22 (37.9 mg, 0.015 mmol)
in 2 mL of CH3CN. The solution was stirred for 20 min, filtered
through Celite and the volume reduced to 2 mL under reduced
pressure. Diethyl ether (7 mL) was added, causing the formation
of a white solid. The solid was collected, washed with diethyl ether
(2 × 4 mL) and dried under vacuum. Yield: 52.0 mg (0.023 mmol,
90%). Anal. Calcd for C108H138N10Cu4P8F24: C, 51.18; H, 5.49; N,
5.53; P, 9.78. Found: C, 51.15; H, 5.33; N, 5.53; P, 9.72 (for P: ICP
emission).
Treatment of ligands 1–3 or 6 in CH3CN with 3 or more equivalents
of [Cu(CH3CN)4]PF6 or, in one case, CuCl (preparation of 15b)
yielded trinuclear complexes 14–17 (Scheme 3). The anticipated
binding of a fourth Cu(I) ion was not observed, as indicated
by CHN analysis, HRMS, and/or X-ray crystallography (15b).
Coordination of Cu(I) to the imine portion of the ligands was
evident from a downfield shift of ∼0.2 ppm of the imine proton
peak. Most of the signals of the other protons of the ligands
undergo downfield shifts to variable extent upon Cu(I) binding.
The NMR data indicated C3-symmetry in the complexes in
solution.
The X-ray crystal structure of the tris-acetonitrile adduct of 15b
is shown in Fig. 2. The close similarities between the spectroscopic
properties for 15b and those for 14, 15a, 16, and 17, for which
X-ray diffraction data are not available, implicate analogous
structures for the set. Complex 15b is comprised of a trication
with three [CuCl2]− counteranions (not shown). Each Cu(I) ion
in the tricationic portion shown is coordinated by a bidentate
Me3eda fragment, an imine N-donor, and an acetonitrile solvent
molecule in a distorted tetrahedral geometry. The Cu–N bond
Low temperature reaction of 24 with O2. Solutions of 24 in
propionitrile were cooled to −78 ◦C and exposed to dry O2,
causing a color change from yellow to intense purple. A sample for
resonance Raman (15 mM) was prepared by removing an aliquot
of the purple solution in propionitrile by frozen pipet. Solutions
of the purple species decomposed at −78 ◦C in propionitrile to
yield a green colored solution. Counterion metathesis with 4 equiv
NaB(3,5-(CF3)2C6H3)4 (4.2 mg, 0.0047 mmol) in THF (4 mL) and
oxygenation at −78 ◦C produced a more stable purple species
(no decomposition after 2 h at −78 ◦C). UV-vis (propionitrile)
[kmax/nm]: 535, 610; resonance Raman (kex 568.2 nm, 77 K,
propionitrile): 832 (18O2 786), 544 (18O2 516) cm−1.
˚
distances to the imine and CH3CN donors (Cu–N ∼ 1.9–2.0 A)
are shorter than those to the Me3eda amine N-atoms (Cu–N ∼
˚
2.1–2.2 A). Most significantly, instead of the three imine N-donors
acting as a tridentate platform to bind a fourth Cu(I) ion, they act
independently to complete the coordination sphere of each of the
three metal ions. That this platform can coordinate a single Cu(I)
ion was shown by the successful synthesis and characterization of
18 (Scheme 3), in which the 1,1,1-tris(iminomethyl)ethane portion
of the ligands 1–6 is capped by tert-butyl groups. Evidently,
particular thermodynamic stability is conferred by the tridentate
binding with two fused chelate rings of three Cu(I) ions observed
in 14–17.
Results and discussion
Design and synthesis of ligands
We designed two types of multidentate ligands with the initial
aim of preparing tetranuclear complexes, the specific goal being to
bind one metal ion to a tris-imine platform and another three to
tethered bi- or tridentate N-donor chelates “L” (1–9, Scheme 1).
One ligand set was derived from 1,1,1-tris(aminomethyl)ethane
3040 | Dalton Trans., 2007, 3035–3042
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on the basis of NMR spectroscopy (for representative data, see
ESI‡), conductivity measurements (see below), and, for 22 and 23,
CHN analysis data. Crystals suitable for X-ray crystallography
have yet to be obtained. Although analytical purity was not
established for 24, its tris(xylyl-isocyanide) adduct 25 was fully
characterized. In addition, a tris(triphenyl-phosphine) adduct of
22 was isolated and characterized by elemental analysis (26,
Scheme 3).
Conductivity data was useful for assaying the nature of the
various Cu(I) complexes in solution and verifying their metal
ion content. Onsager plots14 were determined for a subset of the
compounds prepared in this work, as well as an example of a 2 : 1
electrolyte reported previously15 (Fig. 4). Good linear fits to the
data were obtained, and each class of electrolyte (anion : cation
ratio) is readily distinguished. Importantly, the clear separation of
the lines for 22–24 from those for the 3 : 1 electrolytes 14, 15a, and
16 provide strong support for the tetracopper(I) (4 : 1) formulations
for 22–24.
Fig. 2 Representation of the tricationic portion of the X-ray crystal
structure of 15b as its tris-acetonitrile adduct, showing all nonhydrogen
◦
˚
atoms as 50% thermal ellipsoids. Selected bond distances (A) and angles ( )
are as follows: Cu1–N4, 1.931(4); Cu1–N1, 1.990(4); Cu1–N3, 2.163(4);
Cu1–N2, 2.214(4); Cu2–N8, 1.930(4); Cu2–N5, 1.977(4); Cu2–N7,
2.155(4); Cu2–N6, 2.197(4); Cu3–N12, 1.925(4); Cu3–N9, 1.972(4); Cu3–
N11, 2.161(4); Cu3–N10, 2.224(4); N4–Cu1–N1, 133.47(16); N4–Cu1–N3,
102.56(17); N1–Cu1–N3, 116.41(16); N4–Cu1–N2, 112.26(15); N1–Cu1–
N2, 95.82(14); N3–Cu1–N2, 85.57(14); N8–Cu2–N5, 135.71(16); N8–
Cu2–N7, 106.54(18); N5–Cu2–N7, 112.81(16); N8–Cu2–N6, 106.91(18);
N5–Cu2–N6, 95.56(15); N7–Cu2–N6, 85.96(16); N12–Cu3–N9,
137.82(17); N12–Cu3–N11, 105.89(17); N9–Cu3–N11, 111.81(15); N12–
Cu3–N10, 106.09(17); N9–Cu3–N10, 95.78(15); N11–Cu3–N10,
84.60(16).
To offset this undesired propensity, we examined the Cu(I)
complexes of ligands 7–9 and the model fragments 11–13, which
contain an additional N-donor in the basal platform. Treatment
of 11–13 with [Cu(CH3CN)4]PF6 yielded 19–21, respectively, of
which the complexes with iPr (19) and Ph (21) substituents were
defined structurally by X-ray crystallography (Fig. 3 and Fig. S1‡).
These structures resemble others reported for related tetradentate
tripodal ligands17 and demonstrate the capability of the tris(2-
iminoethyl)amine moiety to bind a single Cu(I) ion.
Fig. 4 Onsager conductivity plot (c = concentration) with the various
electrolytes grouped by color (labeled on right as anion : cation ratios).
Each data set corresponds to the compounds listed in the legend, where
“2 : 1” in the legend refers to a dicopper(I) complex (2 : 1 electrolyte)
reported in ref. 15.
Dioxygen reactivity of 24
Fig. 3 Representation of the cationic portion of the X-ray crystal
structure of 21, showing all nonhydrogen atoms as 50% thermal el-
With the viable synthetic procedures in hand for the aforemen-
tioned multicopper(I) clusters supported by variable N-donor
ligands, reactivity studies can begin. In preliminary studies, we
examined the reaction of 24 with O2 at low temperature. These
studies were motivated by literature reports of the O2 reactiv-
ity of [bis(pyridylmethyl)amine]Cu(I) complexes, which yield l-
◦
˚
lipsoids. Selected bond distances (A) and angles ( ) are as follows:
Cu1–N1, 1.9746(18); Cu1–N3, 2.0027(17); Cu1–N2, 2.0097(18); Cu1–N4,
2.2231(17); N1–Cu1–N3, 128.64(7); N1–Cu1–N2, 120.37(8); N3–Cu1–N2,
108.47(7); N1–Cu1–N4, 85.85(7); N3–Cu1–N4, 83.71(7); N2–Cu1–N4,
84.58(7).
2
2
g :g -peroxo and/or bis(l-oxo)dicopper complexes.18 In contrast,
bubbling O2 through solutions of 24 in propionitrile at −78 ◦C
resulted in the formation of a deep purple species readily identified
Reaction of 7–9 with 4 equivalents of [Cu(CH3CN)4]PF6 re-
sulted in the formation of 22–24 (Scheme 3), which were identified
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as a trans-1,2-peroxo species through comparison of UV-vis and
resonance Raman spectroscopic data to those of known examples.
In particular, absorption features with kmax values at 535 and
610 nm and a resonance enhanced peak at 832 cm−1 that shifted by
46 cm−1 with 18O2 in the Raman spectrum (kex = 568.2 nm) were
observed, and these closely match data reported previously for
(trans-1,2-peroxo)dicopper(II) complexes (see Table 5 in ref. 19).
Multiple structures are possible for this species derived from 24,
including intramolecular and intermolecular (oligomeric) adducts,
but we are unable to unambiguously identify it with the data
currently available.
Zumft and A. J. Thomson, Biochemistry, 2000, 39, 12753; T. Haltia,
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Conclusions
A versatile synthetic method for preparing multidentate ligands
with variable N-donor sets has been developed, and Cu(I)
complexes of a subset of these ligands have been prepared
and characterized by spectroscopic, analytical, and, in several
cases, X-ray crystallographic and conductivity measurements. The
ligands derived from 1,1,1-tris(aminomethyl)ethane (1–6) bind
three copper ions, each of which is coordinated to one of the imines
in the lower platform of the ligand (cf. Fig. 4). Incorporation
of an additional N-donor into the lower platform (ligands 7–9
derived from tris(aminoethyl)amine) results instead in the binding
of four Cu(I) ions. Future explorations of reactivity relevant to
multicopper enzyme active site chemistry are now enabled, with
feasibility being supported by the finding of trans-1,2-peroxo
species in preliminary studies of the oxygenation of 24.
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Acknowledgements
We thank the NIH (grant GM47365 to W. B. T. and grant NSRA-
GM68307 to E. C. B.) and the University of Pavia (through
FAR to L. C. and a grant to S. P.) for financial support of this
research. We also thank Dr Victor G. Young, Jr., for assistance with
X-ray structural data collection and refinement, and Professor
Lawrence Que, Jr., for the use of resonance Raman spectroscopy
instrumentation.
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3042 | Dalton Trans., 2007, 3035–3042
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