Three-coordinate copper(II)-phenolate complexes

Article abstract of DOI:10.1021/ic010615c

The reactions of LCuCl (L = 2,4-bis((2,6-diisopropylphenyl)imido)pentane (L^iPr), 2,4-bis((2,6-diisopropylphenyl)-imido)-3-chloropentane (L^CliPr)) with the phenolates T1OAr (Ar = C₆H₃Me₂, C₆H₄Me, C₆H₄tBu) and NaOC₆H₃(tBu)₂ were explored. Novel three-coordinate CU(II) -phenolates, LCuOAr, were isolated from the reactions with the thallium phenolates and were characterized by X-ray crystallography and spectroscopy (UV-vis, EPR). The complexes feature short Cu-O(phenolate) distances (average Cu-O = 1.81 A) and, with one exception, irregular N-Cu-O(phenolate) angles that differ within each compound (15° < Δ < 28°, where Δ = ∠N₁-Cu-O-∠N₂-Cu-O). The exception is L^iPrCu(OC₆H₄tBu), for which X-ray structures at -100 and 25 °C differed due to an unusual reversible phase change with nonmerohedral twinning (2:1 ratio) in the low-temperature form. The high-temperature form has local C_2ν symmetry (Δ = 0°), and upon cooling below the phase transition temperature (-8 ± 5 °C) lateral movement of the phenolate ligand (Δ = 17.6°) and rotation of the phenolate plane by 10.7° occurs. Resonance Raman spectroscopic data acquired for L^iPrCu(OC₆H₄tBu) corroborated assignment of phenolate → Cu(II) LMCT character in the UV-vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu₄PF₆) revealed negative E_1/2 values for the Cu(II)/Cu(I) couples relative to NHE, consistent with enhanced stabilization of the Cu(II) state by both the strongly electron donating β-diketiminate ligand and the phenolates. Although thermally stable, the Cu(II)-phenolates are unusually reactive with dioxygen, albeit to give product(s) that have yet to be identified. In the reaction of L^iPrCuCl with NaOC₆H₃(tBu)₂ no Cu(II)-phenolate was observed. Instead, a Cu(I) complex was generated quantitatively by trapping with added isocyanide, [L^iPrCuNC(C₆H₃Me₂)], along with 3,3′,5,5′-tetra-tert-butyl-4,4′-dibenzoquinone and 2,6-di-tert-butylphenol in 27 ± 3% and 46 ± 6% yields, respectively, corresponding to the overall reaction 4L^iPrCu¹¹Cl + 4NaOAr → 4L^iPrCu(I) + 4NaCl + dibenzoquinone + 2(phenol).

Full text of DOI:10.1021/ic010615c

Inorg. Chem. 2001, 40, 6097-6107
6097
Three-Coordinate Copper(II)-Phenolate Complexes
Brian A. Jazdzewski, Patrick L. Holland, Maren Pink, Victor G. Young, Jr.,
Douglas J. E. Spencer, and William B. Tolman*
Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota,
207 Pleasant Street SE, Minneapolis, Minnesota 55455
ReceiVed June 11, 2001
The reactions of LCuCl (L ) 2,4-bis((2,6-diisopropylphenyl)imido)pentane (LiPr), 2,4-bis((2,6-diisopropylphenyl)-
imido)-3-chloropentane (LCliPr)) with the phenolates TlOAr (Ar ) C6H3Me2, C6H4OMe, C6H4tBu) and NaOC6H3-
(tBu)2 were explored. Novel three-coordinate Cu(II)-phenolates, LCuOAr, were isolated from the reactions with
the thallium phenolates and were characterized by X-ray crystallography and spectroscopy (UV-vis, EPR). The
complexes feature short Cu-O(phenolate) distances (average Cu-O ) 1.81 Å) and, with one exception, irregular
N-Cu-O(phenolate) angles that differ within each compound (15° < ∆ < 28°, where ∆ ) N1-Cu-O -
N2-Cu-O). The exception is LiPrCu(OC6H4tBu), for which X-ray structures at -100 and 25 °C differed due
to an unusual reversible phase change with nonmerohedral twinning (2:1 ratio) in the low-temperature form. The
high-temperature form has local C2V symmetry (∆ ) 0°), and upon cooling below the phase transition temperature
(-8 ( 5 °C) lateral movement of the phenolate ligand (∆ ) 17.6°) and rotation of the phenolate plane by 10.7°
occurs. Resonance Raman spectroscopic data acquired for LiPrCu(OC6H4tBu) corroborated assignment of phenolate
f Cu(II) LMCT character in the UV-vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu4PF6) revealed
negative E1/2 values for the Cu(II)/Cu(I) couples relative to NHE, consistent with enhanced stabilization of the
Cu(II) state by both the strongly electron donating â-diketiminate ligand and the phenolates. Although thermally
stable, the Cu(II)-phenolates are unusually reactive with dioxygen, albeit to give product(s) that have yet to be
identified. In the reaction of LiPrCuCl with NaOC6H3(tBu)2 no Cu(II)-phenolate was observed. Instead, a Cu(I)
complex was generated quantitatively by trapping with added isocyanide, [LiPrCuNC(C6H3Me2)], along with
3,3′,5,5′-tetra-tert-butyl-4,4′-dibenzoquinone and 2,6-di-tert-butylphenol in 27 ( 3% and 46 ( 6% yields,
respectively, corresponding to the overall reaction 4LiPrCuIICl + 4NaOAr f 4LiPrCu(I) + 4NaCl + dibenzoquinone
+ 2(phenol).
Introduction
typical for the coordination chemistry of Cu(II). In addition,
the phenolates in most of these compounds usually are
Considerable recent emphasis has been placed on the detailed
study of the properties of Cu(II)-phenolate complexes because
of their postulated involvement in a range of biological and
catalytic processes. Thus, Cu(II)-phenolate units have been
proposed as intermediates in the catalytic cycles of metallo-
enzymes (e.g., galactose oxidase,1 tyrosinase2), in the biogenesis
of novel metalloenzyme cofactors (e.g., topaquinone in amine
oxidases3), and in synthetic catalysis (e.g., alcohol oxidation,4
phenol polymerization5).6 The known Cu(II)-phenolate com-
plexes exhibit coordination numbers ranging from 4 to 6, as is
incorporated as part of multidentate ligand systems;6 complexes
with simple, exogenous phenolate ligands are less common.7
Of particular note are the recently reported series of four-
coordinate complexes TpiPr2Cu(OAr) (Ar ) C6H4-4-F, C6H3-
2,6-Me2, C6H3-2,6-tBu) that exhibit unusual thermal and air
sensitivity attributed to the contribution of Cu(I)-phenoxyl
radical resonance forms to their ground-state structures.8
We recently discovered9 the first example of a three-
coordinate Cu(II) complex, LiPrCuCl (LiPr ) 2,4-bis(2,6-
diisopropylphenylimido)pentane),10 and showed that it may be
converted by metathesis reactions to three- and four-coordinate
Cu(II)-thiolate complexes that model various type 1 metallo-
protein active sites.9,11,12 Here we report results of further
explorations of the chemistry of three-coordinate Cu(II) ions
in which we have examined the reactions of phenolates with
LiPrCuCl and with a new derivative that contains an electron-
withdrawing chlorine substituent, LCliPrCuCl (Scheme 1). Key
findings include the isolation and spectroscopic, electrochemical,
and X-ray crystallographic characterization of a new class of
Cu(II)-phenolate compounds that exhibit three-coordination and
* To whom correspondence should be addressed. Fax: 612-624-7029.
E-mail: tolman@chem.umn.edu.
(1) (a) Whittaker, J. W. In Metalloenzymes InVolVing Amino Acid Residue
and Related Radicals; Sigel, H., Sigel, A., Eds.; Marcel Dekker: New
York, 1994; Vol. 30, pp 315-360. (b) Knowles, P. F.; Ito, N. In
PerspectiVes in Bio-inorganic Chemistry; Jai Press: London, 1994;
Vol. 2, pp 207-244. (c) Whittaker, J. W.; Whittaker, M. M. Pure
Appl. Chem. 1998, 70, 903-910.
(2) Solomon, E. I.; Sundaram, U. M.; Machonkin, T. E. Chem. ReV. 1996,
96, 2563-2605.
(3) (a) Dooley, D. M. J. Biol. Inorg. Chem. 1999, 4, 1-11. (b) Williams,
N. K.; Klinman, J. P. J. Mol. Catal. B: Enzym. 1999, 8, 95-101.
(4) (a) Wang, Y.; DuBois, J. L.; Hedman, B.; Hodgson, K. O.; Stack, T.
D. P. Science 1998, 279, 537-540. (b) Chaudhuri, P.; Hess, M.; Flo¨rke,
U.; Wieghardt, K. Angew. Chem., Int. Ed. Engl. 1998, 37, 2217-
2220. (c) Chaudhuri, P.; Hess, M.; Weyhermu¨ller, T.; Wieghardt, K.
Angew. Chem., Int. Ed. 1999, 38, 1095-1098. (d) Chaudhuri, P.; Hess,
M.; Mu¨ller, J.; Hildenbrand, K.; Bill, E.; Weyhermu¨ller, T.; Wieghardt,
K. J. Am. Chem. Soc. 1999, 121, 9599-9610.
(5) (a) Hay, A. S. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 505-
517. (b) Higashimura, H.; Kubota, M.; Shiga, A.; Fujisawa, K.; Moro-
oka, Y.; Uyama, H.; Kobayashi, S. Macromolecules 2000, 33, 1986-
1995 and references therein.
(6) Jazdzewski, B. A.; Tolman, W. B. Coord. Chem. ReV. 2000, 200-
202, 633-685.
10.1021/ic010615c CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/13/2001

6098 Inorganic Chemistry, Vol. 40, No. 24, 2001
Jazdzewski et al.
Scheme 1
(LCliPr)‚Et2O with CuCl2‚0.8THF13 yielded LCuCl (L ) LiPr,
LCliPr) (Scheme 1). Characterization by X-ray crystallography
and spectroscopy (previously described9 for L ) LiPr) confirmed
analogous three-coordinate Cu(II) structures for these chloride
complexes, which serve as convenient starting materials for the
construction of other derivatives via metathesis reactions.
Attempts to prepare Cu(II)-phenolate complexes via metathesis
of LCuCl (L ) LiPr, LCliPr) with sodium salts of several
phenolates generally were unsuccessful, however, usually lead-
ing to intractable mixtures because of incomplete conversions
to products. This problem was obviated by using thallium
phenolates TlOAr (Ar ) C6H3Me2, C6H4OMe, C6H4tBu) that
were prepared by reaction of the phenols HOAr with TlOEt.14
Treatment of LCuCl with TlOAr resulted in rapid precipitation
of TlCl and generation of the series of dark green compounds
LCuOAr (Scheme 1), each of which was characterized by
spectroscopic, X-ray crystallographic, and analytical methods.
The complexes are stable at room temperature under an N2
atmosphere as solids or in solution for long periods (months).
The stability of LiPrCuOC6H3Me2 in particular is noteworthy,
because the four-coordinate complex of the same phenolate,
TpiPr2CuOC6H3Me2, was observed to decay upon warming above
-50 °C under Ar to form 3,3′,5,5′-tetramethyldibenzoquinone
(albeit in 12% yield).8
A different course was followed in the reaction of LiPrCuCl
with 1 equiv of sodium 2,6-di-tert-butylphenoxide in THF;
instead of yielding a dark green solution indicative of copper-
(II)-phenoxide complex formation, a yellow-brown color
developed immediately upon mixing of the reagents. Removal
of the solvent under reduced pressure led to product decomposi-
tion, as indicated by the formation of a muddy green-brown
solution and the deposition of a large amount of insoluble
material. The absence of discernible features in the visible region
of the optical absorption spectrum of the original reaction
mixture led us to suspect that an unstable Cu(I) product was
formed by reduction of the Cu(II) starting material (or a species
derived therefrom) by the hindered phenoxide. To test this
hypothesis, the reaction was repeated, but with 2,6-dimeth-
ylphenyl isocyanide added as a Cu(I) trap (Scheme 2). Careful
that are thermally stable, yet are dioxygen-sensitive. These
results shed new light on the possible nature of intermediates
involved in the processing of phenolic species by Cu(II) sites
in biology and catalysis.
Results and Discussion
Syntheses. The crystalline ligand Li(LCliPr)‚Et2O was prepared
by chlorination of the previously reported Li(LiPr)10 with CF3-
SO2Cl followed by deprotonation with nBuLi in Et2O (Scheme
1). The presence of the Et2O solvate in Li(LCliPr)‚Et2O was
confirmed by NMR spectroscopy, elemental analysis, and an
X-ray crystal structure (see below). Reaction of Li(LiPr) or Li-
(7) A search of the Cambridge Crystallographic Database (v. 5.20, October
2000) revealed the following reports of examples of structurally defined
Cu(II) complexes of exogenous phenolates: (a) Bullock, J. I.; Hobson,
R. J.; Povey, D. C. J. Chem. Soc., Dalton Trans. 1974, 2037. (b) Wong,
R. Y.; Palmer, K. J.; Tomimatsu, Y. Acta Crystallogr., Sect. B 1976,
32, 567. (c) Yablokov, Y. V.; Simonov, Y. A.; Yampol’skaya, M. A.;
Dvorkin, A. A.; Matuzenko, G. S.; Voronkova, V. K.; Mosina, L. V.
Zh. Neorg. Khim. 1980, 25, 2468. (d) Ladd, M. F. C.; Perrins, D. H.
G. Acta Crystallogr., Sect. B 1980, 36, 2260. (e) Yampol’skaya, M.
A.; Dvorkin, A. A.; Simonov, Y. A.; Voronkova, V. K.; Mosina, L.
V.; Yablokov, Y. V.; Turte, K. I.; Ablov, A. V.; Malinovskii, T. I.
Zh. Neorg. Khim. 1980, 25, 174. (f) Calderazzo, F.; Marchetti, F.;
Dell’Amico, G.; Pelizzi, G.; Colligiani, A. J. Chem. Soc., Dalton Trans.
1980, 1419. (g) Dvorkin, A. A.; Matuzenko, G. S.; Simonov, Y. A.;
Yampol’skaya, M. A.; Gerbeleu, N. V.; Malinovskii, T. I. Zh. Neorg.
Khim. 1982, 27, 365. (h) Marengo-Rullan, J. R.; Willet, R. D. Acta
Crystallogr., Sect. C 1986, 42, 1487. (i) Kwik, W.-L. J. Coord. Chem.
1988, 19, 279. (j) Whittaker, M.; Chuang, Y.; Whittaker, J. J. Am.
Chem. Soc. 1993, 115, 10029-10035. (k) Ji, B.; Zhou, Z.; Ding, K.;
Li, Y. Polyhedron 1998, 17, 4327. (l) Gokagac, G.; Tatar, L.;
Kisakurek, D.; Ulku, D. Acta Crystallogr., Sect. B 1999, 55, 1413.
(m) Tatar, L.; Gokagac, G. Acta Crystallogr., Sect. C 2000, 56, 668.
(8) Fujisawa, K.; Iwata, Y.; Kitajima, N.; Higashimura, H.; Kubota, M.;
Miyashita, Y.; Yamada, Y.; Okamoto, K.; Moro-oka, Y. Chem. Lett.
1999, 739-740.
1
analysis of the reaction by H NMR spectroscopy revealed
quantitative formation of LiPrCu(CNC6H3Me2) based on the
amount of the starting complex LiPrCuCl. Crystalline LiPrCu-
(CNC6H3Me2) was isolated from the reaction mixture in 49%
yield and was identified by spectral, analytical, and X-ray
diffraction methods. In addition, 3,3′,5,5′-tetra-tert-butyl-4,4′-
dibenzoquinone and 2,6-di-tert-butylphenol were identified by
1H NMR spectroscopy as coproducts in 27 ( 3% and 46 ( 6%
yields, respectively, based on the amount of 2,6-di-tert-
butylphenoxide used. These yields match those expected for
the stoichiometry indicated by reaction 1 to within experimental
error (25% and 50%).
4LiPrCuIICl + 4NaOAr f
4LiPrCuI + 4NaCl + dibenzoquinone + 2(phenol) (1)
The observation of reaction 1 contrasts with the reactivity
described previously for the system supported by TpiPr2.8 Thus,
the complex TpiPr2Cu(OC6H3tBu2) was reported to be isolable
at low temperature and to decay under Ar to yield dibenzo-
(9) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270-
7271.
(10) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514-1516.
(11) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2000, 122, 6331-
6332.
(12) Randall, D. W.; DeBeer, S.; Holland, P. L.; Hedman, B.; Hodgson,
K. O.; Tolman, W. B.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122,
11632-11648.
(13) So, J.-H.; Boudjouk, P. Inorg. Chem. 1990, 29, 1592-1593.
(14) After this work was completed but prior to submission of this paper,
an alternative preparation of TlOC3H3Me3 and its X-ray crystal
structure were reported: Zechmann, C. A.; Boyle, T. J.; Pedrotty, D.
M.; Alam, T. M.; Lang, D. P.; Scott, B. L. Inorg. Chem. 2001, 40,
2177-2184.

Three-Coordinate Copper(II)-Phenolate Complexes
Inorganic Chemistry, Vol. 40, No. 24, 2001 6099
Scheme 2
X-ray Structures. X-ray crystal structures were solved for
Li(LCliPr)‚Et2O (Figure 1a), LCliPrCuCl (Figure 1b), each of the
phenolate complexes (Figure 1c and Figure S1 in the Supporting
Information), and LiPrCu(CNC6H3Me2) (Figure 1d). Selected
crystallographic data and interatomic distances and angles are
listed in Tables 1 and 2, respectively. Analysis of the N2OLi
core in Li(LCliPr)‚Et2O (Figure 1a) reveals a pattern of divergent
bond angles about the Li+ ion; the â-diketiminate ligand “bite”
angle N1-Li1-N2 is 95.04(13)°, while the other two O-Li-N
angles are larger (O1-Li1-N1 ) 132.27(15)° and O1-Li1-
N2 ) 132.65(15)°). The lithium ion resides 0.209 Å above the
N2O plane. The structure of LCliPrCuCl (Figure 1b) is closely
analogous to that previously reported for LiPrCuCl,9 with both
characterized by trigonal-planar, approximately C2V symmetric,
three-coordinate geometries and short Cu-N (1.87 ( 0.01 Å)
and Cu-Cl (2.13 ( 0.01 Å) distances consistent with their low
coordination numbers and Cu(II) oxidation states.
Similar monomeric, three-coordinate formulations were con-
firmed for each of the Cu(II)-phenolate complexes, with the
structure of one, LiPrCu(OC6H4OMe), illustrated in Figure 1c
(the others are supplied in Figure S1). Short Cu-O(phenolate)
distances are a notable general feature (average Cu-O ) 1.81
Å, range 1.79-1.82 Å), with a shorter Cu(II)-O(phenolate)
(exogenous) distance having been reported only once previously
(1.731(3) Å in TpiPr2Cu(OC6H4-4-F)).8 The Cu(II) ions are only
slightly displaced from the plane of the ligand N2O donors
(average Cu-N2O ) 0.06 Å, range 0.03-0.10 Å), with the
absence of apparent contacts of the metal ion with additional
donor atoms being indicative of three-coordination in these
compounds. Interestingly, with only one exception, the Cu(II)
geometries are irregular, with N-Cu-O(phenolate) angles that
differ within each complex so that structures distorted from local
quinone only in 32% yield; no formation of phenol coproduct
was cited. While no mechanistic data are available, we speculate
that dibenzoquinone formation in both systems involves a similar
first step: C-C bond formation between species with phenoxyl
radical character (Scheme 3, step 1) as previously suggested8,15
or, alternatively, between free phenoxyl radicals generated by
one-electron reduction of Cu(II) species. Trapping of the Cu(I)
coproduct by isocyanide and further oxidation of the dihydro-
dibenzoquinone would then ensue. In our system the starting
LCuIICl complex or the (unobserved) LCuIIOAr species acts as
the oxidant (Scheme 3, step 2), yielding the dibenzoquinone
and 2 equiv more of Cu(I) species and phenol. This oxidation
step must be fast relative to the C-C coupling in order to
rationalize the observed yield of phenol coproduct, a rate
disparity that may be lessened or reversed in the TpiPr2 system,
where no phenol was reported.8
C
2V symmetry are adopted (15° < ∆ < 28°, where ∆ ) N1-
Cu-O - N2-Cu-O). This distortion, which is absent in other
three-coordinate complexes LCuX (L ) LiPr, LCliPr, X ) Cl,
SCPh3, SC(Ph)2CH2OCH3, SC6H3Me2),9,11,12 is accompanied by
a translation of the phenolate aryl ring to one side of the axis
defined by the Cu-O bond.
Scheme 3

6100 Inorganic Chemistry, Vol. 40, No. 24, 2001
Jazdzewski et al.
Figure 1. X-ray crystal structure representations of (a) Li(LCliPr)‚Et2O, (b) LCliPrCuCl‚CH2Cl2, (c) LiPrCu(OC6H4OMe), and (d) LiPrCu(CNC6H3-
Me2). All structures are shown as 50% thermal ellipsoids with only heteroatoms labeled and hydrogen atoms and solvent molecules omitted for
clarity.
Table 1. Summary of X-ray Crystallographic Dataa
Li(LCliPr)‚
Et2O
LCliPrCuCl‚ LiPrCu(OC6H4- LiPrCu(OC6H3- LiPrCu(OC6H4- LiPrCu(OC6H4-
CH2Cl2 OMe) Me2) tBu)
tBu)b
LCliPrCu(O-
C6H4tBu)
LiPrCu(CN-
C6H3Me2)
empirical
formula
fwt
cryst syst
space group
a (Å)
C33H50ClLiN2O C30H42Cl4CuN2 C36H48CuN2O2 C37H50CuN2O C39H54CuN2O C39H54CuN2O C39H53ClCuN2O C38H50CuN3
533.14
triclinic
P1h
636.00
604.30
602.33
monoclinic
P21/n
9.0263(5)
20.1213(12)
18.9777(12)
90
92.9610(10)
90
630.38
monoclinic
P21/n
8.241(1)
21.411(2)
20.185(2)
90
92.920(2)
90
3556.9(12)
4
630.38
664.82
612.35
triclinic
P1h
orthorhombic monoclinic
Pbca
17.189(3)
18.347(4)
20.988(4)
90
90
90
6619(2)
8
orthorhombic monoclinic
C2/c
Pnma
21.620(2)
20.252(2)
8.3555(6)
90
90
90
C2/c
11.001(2)
11.486(2)
14.182(3)
90.25(3)
98.44(3)
116.42(3)
1582.7(5)
2
40.420(2)
8.4524(5)
19.7553(11)
90
99.3350(10)
90
25.6875(18)
20.0203(13)
17.5872(11)
90
125.0890(10)
90
8.6687(17)
12.150(2)
17.406(4)
70.98(3)
79.67(3)
82.73(3)
1700.5(6)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
6660.0(7)
8
3442.1(4)
4
3658.4(5)
4
7400.8(8)
8
d
calcd (g cm-3
)
1.119
1.276
1.205
1.162
1.048
1.145
1.193
1.196
cryst dimens 0.40 × 0.25 × 0.35 × 0.25 × 0.20 × 0.18 × 0.30 × 0.25 × 0.18 × 0.18 × 0.18 × 0.18 × 0.30 × 0.25 × 0.40 × 0.30 ×
(mm)
0.15
0.25
1.89-27.49
1.004
0.10
2.04-27.55
0.688
0.10
1.48-27.53
0.663
0.15
1.39-27.50
0.645
0.15
1.39-27.50
0.627
0.05
1.40-27.51
0.693
0.20
1.25-27.49
0.671
θ range (deg) 1.46-27.56
abs coeff
0.147
(mm-1
)
no. of rflns
collected
no. of unique 7077
rflns
16 263
40 235
7583
344
32 517
7608
381
21 079
7835
374
31 489
8156
402
19 450
3343
211
22 937
8430
402
11 970
7319
383
no. of params 363
R1, wR2 (I > 0.0432, 0.1282 0.0436, 0.1029 0.0557, 0.1216 0.0389, 0.0958 0.0598, 0.1415 0.0444, 0.1152 0.0474, 0.0998 0.0409, 0.1036
2σ(I))c
goodness of fit 0.946
1.026
1.240
0.924
1.048
1.035
0.945
1.037
largest peak, 0.266, -0.232 0.528, -0.437 0.536, -0.720 0.402, -0.378 0.622, -0.679 0.366, -0.270 0.402, -0.418 0.411, -0.413
hole (e/Å3)
a All structures determined at T ) -100 °C, except the indicated structure of LiPrCu(OC6H4tBu). b Determined at 25 °C. c R1 ) ∑||Fo| - |Fc|/
|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2, where w ) 1/[σ2(Fo + (aP)2 + bP], P ) (Fo + 2Fc2)/3, and a and b are constants given in the
2
2
2
2
Supporting Information.

Three-Coordinate Copper(II)-Phenolate Complexes
Inorganic Chemistry, Vol. 40, No. 24, 2001 6101
Table 2. Selected Bond Distances (Å) and Angles (deg)
Li(LCliPr)‚Et2O
Li1-N1
Li1-O1
1.909(3)
1.916(3)
Li1-N2
1.913(3)
N1-Li1-O1
N1-Li1-N2
132.27(15)
95.04(13)
LCliPrCuCl‚CH2Cl2
1.869(2)
N2-Li1-O1 132.65(13)
Cu1-N1
Cu1-Cl1
Cu1-N2
1.864(2)
2.1228(8)
N1-Cu1-Cl1
N1-Cu1-N2
131.85(7)
96.09(9)
N2-Cu1-Cl1 132.00(7)
LiPrCu(OC6H4OMe)
Cu1-N1
Cu1-O1
1.864(2)
1.806(2)
Cu1-N2
1.888(2)
N1-Cu1-O1
Cu1-O1-C30
N1-Cu1-N2
140.87(12)
128.5(2)
96.66(12)
LiPrCu(OC6H3Me2)
1.8825(17)
1.8096(15)
N2-Cu1-O1 122.13(12)
b
∆
18.74
Figure 2. Overlay of the X-ray structures of LiPrCu(OC6H4tBu)
determined at 25 and -100 °C, with maximal overlap of the Cu and
â-diketiminate backbone N and C atoms to emphasize the differences
in the phenolate conformations in the two structures.
Cu1-N1
Cu1-O1
Cu1-N2
1.8946(17)
N1-Cu1-O1
Cu1-O1-C30
N1-Cu1-N2
138.76(7)
134.94(15)
96.31(8)
N2-Cu1-O1 123.98(7)
b
∆
14.78
LiPrCu(OC6H4tBu)c (-100/25 °C)
1.869(3)/1.880(2) Cu1-N2/N1A 1.896(3)/
1.817(2)/1.794(3) 1.880(2)
Cu1-N1
Cu1-O1
N1-Cu1-O1
Cu1-O1-C30/
C16
140.4(1)/131.39(6) N2/N1A-Cu1 122.8(1)/
117.4(2)/118.1(3) -O1 131.39(6)
17.60/0
b
∆
N1-Cu1-N2/NA 96.26(9)/97.10(13)
LCliPrCu(OC6H4tBu)
1.858(2)
Cu1-N1
Cu1-O1
Cu1-N2
1.8959(17)
1.8080(17)
N1-Cu1-O1
Cu1-O1-C30
N1-Cu1-N2
145.72(8)
123.94(16)
96.26(9)
LiPrCu(CNC6H3Me2)
1.9284(17)
N2-Cu1-O1 117.77(8)
b
∆
27.95
Cu1-N1
Cu1-C30
Cu1-N2
1.9616(17)
1.817(2)
N1-Cu1-C30
Cu1-C30-N3
N1-Cu1-N2
141.76(8)
173.64(19)
98.20(7)
N2-Cu1-C30 119.96(9)
d
∆
21.80
a Estimated standard deviations in parentheses. b ∆ ) (N1-Cu1-
O1) - (N2/N1A-Cu1-O1). c At -100 °C. d ∆ ) (N1-Cu1-C30)
- (N2-Cu1-C30).
The exception is LiPrCu(OC6H4tBu), for which X-ray struc-
tures determined at 25 and -100 °C differed significantly due
to an unusual reversible (nondestructive) phase change ac-
companied by conversion to a nonmerohedral twin. This phase
change is signaled by a change in cell setting (orthorhombic to
monoclinic), space group (Pnma to P21/n), and overall structure
of the complex upon cooling. Careful analysis of cell parameters
obtained for a single crystal examined over a range of temper-
atures showed that the phase change is fully reversible and
occurs at -8 ( 5 °C. The low-temperature phase comprises a
nonmerohedral twin (2:1 ratio) that may be visualized by
comparing two zone images (a* based on the high-temperature
orthorhombic cell) from X-ray data collections of sample frames
showing the same region of reciprocal space at low and high
temperatures (Figure S2). Only the major twin component in
the low-temperature structure was integrated and solved, with
a correction applied for the minor component using ROTWIN.16
Figure 3. Similarly oriented packing diagrams of the X-ray structures
of LiPrCu(OC6H4tBu) determined at (a) 25 °C and (b) -100 °C.
The structures of the complex in the high- and low-
temperature phases are compared by an overlay in Figure 2 and
by packing diagrams in Figure 3. The low-temperature structure
is similar to those of the other phenolate complexes described
above, with an asymmetric N2OCu core characterized by ∆ )
17.5°. In contrast, such an angle distortion is absent (∆ ) 0°)
at high temperature due to the crystallographic mirror plane that
bisects the Cu-O(phenolate) bond axis, yielding a C2V-sym-
(16) Young, V. G., Jr.; Pink, M. ROTWIN: Software for the Creation of
HKLF 5 Data from the Twin Law, Metric Tensor, and an Algorithm
for Reflection Overlaps; University of Minnesota, 2001 (unpublished).
(15) Kitajima, N.; Koda, T.; Iwata, Y.; Moro-oka, Y. J. Am. Chem. Soc.
1990, 112, 8833.

6102 Inorganic Chemistry, Vol. 40, No. 24, 2001
Jazdzewski et al.
metric structure. This lateral movement of the phenolate ligand
in the phase change is accompanied by a 10.7° shift of the
phenolate plane (best seen in Figure 3), a change in the Cu-O
bond distance (by 0.03 Å), and small changes in the isopropyl
substituents of the â-diketiminate ligand.
The observed retention of crystalline order during the phase
change that involves reversible onset of nonmerohedral twinning
is unusual, with only a few cases of similar phenomena having
been reported previously.17 Here, the associated geometric
changes in the complex suggest an interestingly low thermo-
dynamic preference for a particular direction of the Cu-
O(phenolate) bond. In other words, the potential energy surface
for lateral movement of the phenolate ligand in the three-
coordinate Cu(II) complex appears to be fairly flat. This
movement is transmitted over long range in the crystal, resulting
in the phase change, with twinning probably resulting because
it may occur in either of two directions relative to the mirror
plane in the C2V-symmetric form. Perhaps most intriguing is
the fact that these relatively large conformational changes in
different crystalline domains occur reversibly without any
apparent overall damage to the crystal.
Finally, in the X-ray structure of LiPrCu(CNC6H3Me2) (Figure
1d), the first copper(I) complex of LiPr to be characterized (but
see Note Added in Proof), the average Cu-N bond distance of
1.945 Å is longer than even the longest Cu-N distance observed
in the copper(II) complexes described above (Cu1-N2 )
1.897(3) Å in the low-temperature structure of LiPrCu(OC6H4-
tBu)). This expansion is consistent with the lower formal
oxidation state for the central metal ion. The coordination
geometry is distorted from trigonal planar (∆ ) 21.80°), which
is not uncommon for Cu(I), and the Cu(I) ion resides slightly
above the N2C plane (by 0.0295(11) Å).
Figure 4. X-band EPR spectra of LCliPrCuCl (a) observed at 20 K in
1:1 CH2Cl2/toluene and (b) simulated and of LiPrCu(OC6H4OMe) (c)
observed at 20 K in toluene and (d) simulated.
Spectroscopic Properties. The diamagnetic species Li(LCliPr)‚
Et2O and LiPrCu(CNC6H3Me2) exhibited sharp 1H NMR spectra
with diastereotopic peaks for the methyl groups on the 2,6-iPr
substituents of the aryl rings of the â-diketiminate ligands. These
data are consistent with solution structures like those seen in
the crystalline state. The Cu(I)-isocyanide complex is colorless,
and the optical absorption spectrum has only one feature, an
intense band with λmax ) 347 nm (ꢀ ) 28 300 M-1cm-1). We
attribute this band to a â-diketiminate π f π* transition by
analogy to assignments reported previously for some Cu(II)
complexes of the same ligand that were based on combined
absorption, MCD, and Raman spectroscopic data.12 In further
support of this assignment, a similar band is exhibited by LiLiPr
that contains the spectroscopically innocent Li+ ion.
The X-band EPR spectrum of LCliPrCuCl in 1:1 CH2Cl2/
toluene (20 K) contains an axial signal with the parameters g|
) 2.20, A|(Cu) ) 129 G, g ) 2.05, and A (N) ) 18 G as
determined by spectral simulation (Figure 4a,b). The signal
closely resembles that measured previously for LiPrCuCl,9,12
indicating that the Cl substituent on the â-diketiminate backbone
does not significantly alter the electronic structure of the
complex. Importantly, the large g|, small A|(Cu), and large
nitrogen superhyperfine A (N) values distinguish these three-
coordinate Cu(II) complexes from more typical tetragonal
species and corroborate the previously described high degree
of covalency in the bonding between the â-diketiminate ligand
and the Cu(II) ion.12 In further support for the similar electronic
Figure 5. UV-vis absorption spectra of solutions of (a) LiPrCuCl in
CH2Cl2 (dotted line), (b) LCliPrCuCl in CH2Cl2 (solid line), and (c)
LiPrCu(OC6H4tBu) in THF (dashed line).
structures of the Cu(II)-chloride complexes supported by LiPr
and LCliPr, their electronic absorption spectra are almost identical
(Figure 5a,b). Multiple intense absorptions between 400 and
1000 nm are seen that are due to overlapping CT and d-d
transitions.12,18 The absence of any significant shift in these
features upon chlorine substitution in the â-diketiminate back-
bone is a clear sign that the electron-withdrawing effect at the
metal ion of such backbone substitution is minor at best.
The copper(II)-phenolate complex LiPrCu(OC6H4OMe) dis-
plays an EPR spectrum similar to those of the copper(II)-
chloride complexes described above, although adequate simu-
lation required distinct g values (rhombicity) and a reduction
in the already low copper-hyperfine splitting value relative to
the chloride precursor: gz ) 2.22, Az ) 90 G, gy ) 2.07, gx )
2.02 (Figure 4c,d). In contrast, the spectra observed for the other
phenolate complexes are broadened and more complicated (cf.
(17) (a) Colombo, D.; Young, V. G., Jr.; Gladfelter, W. L. Inorg. Chem.
2000, 39, 4621-4624. (b) Reger, D. L.; Little, C. A.; Young, V. G.,
Jr.,; Pink, M. Inorg. Chem. 2001, 40, 2870-2874. (c) Choe, W.;
Pecharsky, V. K.; Pecharsky, A. O.; Gschneidner, K. A., Jr.; Young,
V. G., Jr.; Miller, G. J. Phys. ReV. Lett. 2000, 84, 4617-4620.
(18) Randall, D. W.; Holland, P. L.; Tolman, W. B.; Solomon, E. I.
Unpublished results.

Three-Coordinate Copper(II)-Phenolate Complexes
Inorganic Chemistry, Vol. 40, No. 24, 2001 6103
Figure S3 (Supporting Information) for the spectrum of LiPr-
Cu(OC6H4tBu) in toluene at 20 K). Variation of solvent (pentane
or toluene) and data collection temperature (20 or 77 K) did
not perturb the spectra significantly. These data suggest the
presence of multiple copper-containing species in the EPR
samples, although we note that the complexes used in these
experiments were determined to be pure by X-ray crystal-
lographic and analytical methods and integration of the observed
signals vs that of an external standard revealed the correct spin
quantitation in all cases. One possible rationale for these EPR
spectral results would be the existence in solution of phenoxide-
bridged dimers of four-coordinate centers, but this appears
unlikely on the basis of comparison of the spectral features to
those exhibited by other bona fide dimeric complexes of less
sterically encumbered â-diketiminates that indicate magnetic
coupling interactions.19 Solvent binding to yield four-coordinate
complexes also seems unlikely in view of the poor coordinating
abilities of the solvents used, toluene or pentane. Perhaps the
most appealing explanation of the EPR data is to invoke the
presence of multiple copper(II)-phenolate conformations in
solution akin to those seen in the X-ray structures, but further
experiments are necessary to confirm this notion (e.g., combined
single-crystal EPR/X-ray diffraction analysis).
Figure 6. Resonance Raman spectrum of LiPrCu(OC6H4tBu) in CH2-
Cl2 (77 K, λex ) 632.8 nm). Peaks marked “s” are derived from the
solvent.
UV-vis spectra with intense (ꢀ ≈ 1000-3000 M-1 cm-1
)
absorption features with λmax ≈ 450, 625 (sh), and 700 nm were
measured for the dark green â-diketiminate-containing copper-
(II)-phenolate complexes; a representative spectrum for LiPr-
Cu(OC6H4tBu) in THF is shown in Figure 5c. On the basis of
preliminary resonance Raman experiments (see below) and
comparison to other copper(II)-phenolate complexes, we sug-
gest that these absorptions possess at least partial phenolate f
copper(II) LMCT character. Additional overlapping contribu-
tions from d-d transitions also are likely, by analogy to the
results of previous studies of other â-diketiminate-Cu(II)
complexes.12 Comparison of the λmax values for LiPrCu(OC6H4-
OMe) and LiPrCu(OC6H4tBu), which differ only with respect
to the nature of the para phenolate substituent, shows that
increasing the electron-donating ability of the phenolate results
in a ∼20 nm red shift in the most intense low-energy transition,
consistent with predominant phenolate f copper(II) LMCT
character for this feature. As was observed in the copper(II)-
chloride complexes described above, analysis of the UV-vis
spectra for LiPrCu(OC6H4tBu) and LCliPrCu(OC6H4tBu) revealed
no significant difference in the observed λmax values, again
suggesting that introduction of the Cl substituent in the
â-diketiminate backbone does not significantly affect the overall
electronic structure of these complexes.
Figure 7. Cyclic voltammograms of LiPrCu(OC6H4tBu) (see text for
conditions).
ring C-C stretching vibrations for the coordinated phenolate
ligand. Importantly, the strong enhancement of these bands upon
excitation at 632.8 nm supports significant contribution of
phenolate f copper(II) LMCT to the longest wavelength feature
in the absorption spectrum.
Electrochemistry. Cyclic voltammetry experiments were
performed for LiPrCuOAr (OAr ) OC6H4tBu, OC6H4OMe) at
room temperature in THF solution with 0.5 M NBu4PF6 as
supporting electrolyte. Both complexes exhibit a reversible wave
when scanned initially to reductive potential, with ia ≈ ic and
an Epa - Epc value of 80 mV that is invariant at scan rates
between 100 and 300 mV s-1 (Figure 7). We attribute this wave
to the Cu(II)/Cu(I) redox couple. When initial scans were taken
to oxidative potentials irreversible oxidations were observed at
+1.30 V and +1.17 V vs NHE for the complexes with OAr )
OC6H4tBu, OC6H4OMe, respectively, and the Cu(II)/Cu(I)
couple became irreversible. We hypothesize that a rearrangement
or decomposition reaction occurs upon oxidation at positive
potential (perhaps due to phenolate ligand oxidation) and that
this is the cause of the loss of reversibility of the Cu(II)/Cu(I)
couple. Of particular note is the finding of high potentials for
the irreversible oxidation reactions, which appears to belie the
air sensitivity of the compounds that is discussed below.
In one instance, LiPrCu(OC6H4tBu), resonance Raman spectral
data were obtained in order to lend support to the UV-vis
spectral assignments. The Raman spectrum of a CH2Cl2 solution
measured using 632.8 nm laser excitation is shown in Figure
6. The set of multiple features between 1100 and 1600 cm-1
are typical of metal-phenolate complexes and metal-tyrosinate
sites in proteins,20 with those at 1174, 1270, 1500, and 1598
cm-1 being diagnostic for coordinated phenolates that have a
substituent at the 4-position.21 On the basis of comparison to
previously reported data,20,21 the bands at 1174 and 1270 cm-1
are assigned as C-H bending and C-O stretching modes,
respectively, and those at 1500 and 1598 cm-1 are attributed to
The E1/2 values for the Cu(II)/Cu(I) couples of the phenolate
complexes are compared in Table 3 to values reported previously
(under similar conditions) for other three-coordinate Cu(II)
complexes of the same LiPr ligand.9,11 The negative potentials
are consistent with the expected effect of the strongly electron-
donating â-diketiminate ligand, which preferentially stabilizes
the oxidized metal center.12 Coordination of a phenolate further
destabilizes the Cu(I) form compared to the compounds with
(19) Holland, P. L.; Toia, C.; Jazdzewski, B. A.; Reynolds, A.; Bowen,
L.; Tolman, W. B. Unpublished results.
(20) Que, L., Jr. In Biological Applications of Raman Spectroscopy;
Wiley: New York, 1988; Vol. 3, pp 491-521.
(21) Pyrz, J. W.; Roe, A. L.; Stern, L. J.; Que, L., Jr. J. Am. Chem. Soc.
1985, 107, 614-620.

6104 Inorganic Chemistry, Vol. 40, No. 24, 2001
Table 3. Values of E1/2 for Cu(II) Complexes of LiPr a
Jazdzewski et al.
complexes so far. In an effort to examine the fate of the ligands
in the oxygenation/decomposition process, a THF solution of
the decomposition product solution was treated with aqueous
HCl (6 M) to remove the copper ions and then was extracted
with CH2Cl2. Analysis of these extracts by GC/MS revealed
the presence of 4-methoxyphenol, multiple organic species in
small amounts, none of which could be conclusively identified,
and (LiPr)H that was identified in nearly quantitative yield. These
findings indicate that significant â-diketiminate ligand degrada-
tion does not occur and that any functionalization of the
phenolate occurs to a minor extent to yield a mixture of
unidentified products. Although we remain puzzled about the
course of the oxygenation reaction, it is clear that the Cu(II)-
phenolate unit does react with O2, thus supporting the notion
that such units are competent intermediates in oxidation
processes.
complex
E1/2 (V)
ref
LiPrCuCl
-0.08
-0.12
-0.18
-0.20
-0.26
-0.28
9
11
9
11
this work
this work
LiPrCuS(Ph2)CH2OMe
LiPrCuSCPh3
LiPrCuS(Ph2)CH2SMe
LiPrCuOC6H4tBu
LiPrCuOC6H4OMe
a All values reported vs NHE, by adding 800 mV to the value
measured vs Fc/Fc+ in THF with Bu4NPF6 as electrolyte (Connelly,
N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910).
Summary and Conclusion
By using a straightforward metathesis protocol with selected
thallium-phenolates a series of novel three-coordinate Cu(II)-
phenolate complexes were prepared and structurally character-
ized by X-ray crystallography. In one instance, structural
differences were observed as a function of temperature due to
an unusual reversible phase change accompanied by the onset
of nonmerohedral twinning. The formulations of the complexes
are corroborated by UV-vis absorption, EPR, and resonance
Raman spectroscopic data. Cyclic voltammetry experiments
revealed potentials for the Cu(II)/Cu(I) couple that are negative
relative to NHE and that are more negative than analogues with
chloride or thiolate ligands, consistent with enhanced stabiliza-
tion of the Cu(II) state by both the strongly electron donating
â-diketiminate ligand and the phenolate. Spectral data further
show that attachment of a chlorine substituent to the â-diketimi-
nate backbone does not appreciably influence the electronic
structure of the Cu(II)-phenolate unit. The Cu(II)-phenolates
are unusually air-sensitive, although we have been unable to
characterize the oxygenation product(s). Both the low coordina-
tion number and the electron-rich nature of the Cu(II) ion in
the complexes may be considered as rationales for this reactivity,
the finding of which implicates the possible direct involvement
of similar Cu(II)-phenolate units in biological and/or catalytic
oxidations. Finally, a copper complex of the highly hindered
2,6-di-tert-butylphenoxide was not observed; instead, oxidative
coupling occurred to yield a Cu(I) complex (trapped with an
isocyanide and fully characterized), dibenzoquinone, and phenol
(eq 1). While the C-C coupling step of this reaction is similar
to that seen in the four-coordinate TpiPrCuOAr complexes
reported previously,8 the stoichiometry we observe differs, in
particular with respect to the yield of phenol, and suggests
mechanistic differences between the two systems.
Figure 8. UV-vis absorption spectroscopic changes that occur upon
oxygenation of LiPrCu(OC6H4OMe) in THF.
chloride or thiolate ligands, as expected from simple hard/soft
acid/base considerations, with a modest additional perturbation
caused by the different para substituents (20 mV shift to more
negative potential by the more electron-donating OMe group).
The redox instability of the Cu(I) form in the entire series of
compounds is noteworthy, as one might expect three-coordina-
tion to be more favorable for Cu(I) than Cu(II). Instead, ligand
charge effects are dominant, and there is little inherent problem
with the atypical three-coordinate topology for Cu(II) when
supported by the hindered â-diketiminate system.
Dioxygen Reactivity. Unlike most Cu(II)-phenolate com-
plexes, solutions of the compounds LCuOAr are quite air
sensitive, as indicated by rapid bleaching of their diagnostic
deep green color and associated optical absorption spectral
features upon exposure to air or pure O2. We have not been
able to definitively identify the oxygenation product(s), however,
despite repeated efforts to characterize the Cu-containing species
formed or the organic species remaining after removal of the
copper ions. As a case in point, we present results for the
oxygenation of LiPrCu(OC6H4OMe); similar data were obtained
for LiPrCu(OC6H4tBu).22 Absorption spectral changes associated
with the reaction of LiPrCu(OC6H4OMe) in THF (0.6 mM) with
excess O2 (1 atm, constant bubbling) at 20 °C are shown in
Figure 8. The decay of the starting phenolate features follows
Experimental Section
pseudo-first-order kinetics under these conditions, with kobs
)
[1.0(2)] × 10-2 s-1 (t1/2 ) 70 s). Similar data were obtained at
lower temperatures but at slower rates. The light green product
solution is EPR silent at 77 K. This product was found to
decompose within 24 h at ambient temperature, as indicated
by the formation of a light brown solution that lacks the ∼400
nm absorption present in the light green precursor. Attempts to
isolate the copper-containing light green intermediate or brown
decomposition product have failed to yield discrete copper
General Considerations. All solvents and reagents were obtained
from commercial sources and used as received unless noted otherwise.
The solvents THF, Et2O, pentane, benzene, and toluene were distilled
from Na/benzophenone under nitrogen; CH2Cl2 and hexamethyldisi-
loxane (HMDSO) were distilled from CaH2 under nitrogen. The
concentration of n-butyllithium was determined by titration with
diphenylacetic acid in THF prior to use. CuCl2‚0.8THF was prepared
according to published procedures.13 Thallium ethoxide was purchased
from Aldrich, filtered through a pad of Celite to remove a small amount
of black insoluble material, and stored in the glovebox. Sodium 2,6-
di-tert-butylphenoxide was prepared by reaction of 2,6-di-tert-butyl-
phenol with sodium bis(trimethylsilyl)amide in toluene. 3,3′,5,5′-Tetra-
tert-butyl-4,4′-benzoquinone was prepared according to a literature
(22) Resonance Raman data were acquired for solutions of LiPrCu(OC6H4-
tBu) that had been treated with 16O2 or 18O2 (Figure S4, Supporting
Information). While new features at 960 and 1557 cm-1 were observed,
neither shifted upon oxygen isotope substitution.

Three-Coordinate Copper(II)-Phenolate Complexes
Inorganic Chemistry, Vol. 40, No. 24, 2001 6105
procedure.23 The complex LiPrCuCl was prepared as described previ-
ously.9 All transition-metal complexes were synthesized and stored in
a Vacuum Atmospheres inert-atmosphere glovebox under a dry N2
atmosphere or by using standard Schlenk and vacuum line techniques.
Physical Methods. NMR spectra were recorded on Varian VI-300,
VXR-300, VXR-500, VAC-200, and VAC-300 spectrometers. Chemical
shifts (δ) for 1H and 13C NMR spectra are reported vs tetramethylsilane
and referenced to residual protium in the deuterated solvent. IR spectra
were recorded on either a Mattson Polaris FTIR or an Avatar 320 FTIR
spectrometer. IR samples were prepared as KBr pellets. Routine GC/
MS experiments were performed on a Hewlett-Packard 1800A GCD
system equipped with a 30 m × 0.25 µm HP-5 column (5% cross-
linked PhMe-silicone), 1 mL/min He flow, an initial solvent delay of
2 min at 50 °C, and a ramp rate of 20 °C/min to a final temperature of
250 °C. Quantitation of (LiPr)H was accomplished similarly, but with
an initial solvent delay of 2 min at 130 °C followed by a ramp rate of
20 °C/min to a final temperature of 250 °C. Elemental analyses were
performed by Atlantic Microlabs of Norcross, GA. UV-vis spectra
were recorded on a Hewlett-Packard HP8452A (190-820 nm) or
HP8453 (190-1100 nm) diode array spectrophotometer. Low-temper-
ature spectra were acquired using a custom-manufactured vacuum
Dewar equipped with quartz windows, with low temperatures achieved
using a Neslab circulating bath. The cuvette assembly consisted of either
a 1 cm or 2 mm quartz cuvet fused to one end of a glass tube while
the other end was attached to a high-vacuum stopcock and 14/20 ground
glass joint. X-Band EPR spectra were recorded on either a Bruker
ESP300 spectrometer fitted with a liquid nitrogen finger Dewar (77
K, approximately 9.44 GHz) or a Bruker E-500 spectrometer, with an
Oxford Instruments EPR-10 liquid helium cryostat (20 K, approximately
9.61 GHz). Quantitation of EPR signal intensity for copper complexes
was accomplished by comparing the double integration of the derivative
spectrum to that of LtBu4Cu‚MeOH24 or crystalline LiPrCuCl9 in 1:1 CH2-
Cl2/toluene. Where appropriate, EPR spectra were simulated using
QPOW.25 Resonance Raman spectra were collected on an Acton 506
spectrometer using a Princeton Instruments LN/CCD-1100-PB/UVAR
detector and ST-1385 controller interfaced with Winspec software. A
Spectra-Physics 2030-15 argon ion laser with a power of roughly 40
mW at the sample was employed to give the excitation at 457.9 nm.
This argon laser also was used to pump a 375B CW dye (Rhodamine
6G) laser for excitation at 632.8 nm. The spectra were obtained at 77
K using a backscattering geometry; samples were frozen onto a gold-
plated copper coldfinger in thermal contact with a Dewar containing
liquid nitrogen. Raman shifts were externally referenced to liquid
indene. Cyclic voltammetry was performed using Pt working and
auxiliary electrodes, a Ag-wire reference electrode, and a BAS Epsilon
potentiostat linked to a cell mounted in a Vacuum Atmospheres inert-
atmosphere glovebox.
1.95 (s, 6H), 1.12 (dd, J ) 6.9 Hz, 24H) ppm. 13C{1H} NMR (C6D6,
75 MHz): δ 161.6, 143.1, 140.9, 126.6, 124.1, 29.0, 24.7, 23.4, 20.1
ppm; UV-vis (THF; λmax, nm (ꢀ, M-1cm-1)): 337 (16 500). FTIR
(KBr; cm-1): 3063, 2967, 2926, 2867, 1671, 1660, 1605, 1538, 1462,
1437, 1383, 1365, 1325, 1271, 1255, 1239, 1190, 1161, 1102, 1058,
1044, 1017, 1001, 934, 848, 822, 790, 759, 707, 687, 528, 518, 492,
446, 435, 420. LRCIMS: m/z 453.4 ([M + H]+). Anal. Calcd for
C29H41N2Cl: C, 76.87; H, 9.12; N, 6.18. Found: C, 77.41; H, 9.35; N,
6.19.
Li(LCliPr)‚Et2O. A solution of (LCliPr)H (1.35 g, 2.98 mmol) in Et2O
(20 mL) was cautiously treated with 1.22 mL of n-butyllithium (2.56
M in hexanes) at room temperature. After the resulting orange solution
was stirred for 30 min, the solvent volume was decreased to 15 mL
under reduced pressure and the solution was stored at -20 °C overnight.
Colorless crystals deposited, which were washed with cold Et2O (2 ×
2 mL) and dried in vacuo. Further concentration of the supernatant
and storage at -20 °C led to the isolation of a second batch (total
yield 1.25 g, 79%). 1H NMR (C6D6, 300 MHz): δ 7.01-7.11 (m, 6H),
3.24 (heptet, J ) 6.6 Hz, 4H), 2.57 (q, J ) 7.2 Hz, 4H), 2.30 (s, 6H),
1.14 (dd, J ) 6.6 Hz, 24H), 0.36 (t, J ) 7.2 Hz, 6H) ppm. 13C{1H}
NMR (C6D6, 75 MHz): δ 163.6, 149.4, 141.2, 124.0, 123.8, 63.3, 28.5,
24.5, 24.2, 23.4, 13.7 ppm. UV-vis (THF; λmax, nm (ꢀ, M-1cm-1)):
317 (8800). Anal. Calcd for C33H50N2ClLiO: C, 74.35; H, 9.45; N,
5.25. Found: C, 73.86; H, 9.33; N, 5.40.
LCliPrCuCl. To a solution of Li(LCliPr)‚Et2O (0.400, 0.750 mmol) in
THF (25 mL) was added CuCl2‚0.8THF (0.144 g, 0.750 mmol) as a
solid, causing the development of a dark purple color. The reaction
mixture was stirred for 90 min at ambient temperature, and the solvent
was removed in vacuo. The purple residue was extracted with CH2Cl2
(15 mL) and filtered through a pad of Celite, and the filtrate was
evaporated to dryness. HMDSO (10 mL) and CH2Cl2 (2 mL) were then
added, and the resulting purple solution was stored at -20 °C overnight,
yielding purple crystalline material. The volume of the mother liquor
was reduced and the solution cooled to give a second crop (total yield
0.217 g, 53%). EPR (1:1 CH2Cl2/toluene, 20 K, 9.614 GHz): g| )
2.20, A|(Cu) ) 129 G, A|(N) ) 3 G, g ) 2.05, A (N) ) 18 G, A (Cl)
) 3 G. UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1cm-1)): 284 (9500), 327
(17 000), 363 (24 500), 505 (3600), 838 (1200). Anal. Calcd for
C29H40N2CuCl2: C, 63.20; H, 7.32; N, 5.08. Found: C, 63.09; H, 7.32;
N, 5.07.
General Method for the Preparation of Thallium Phenoxides
TlOAr. The appropriate phenol (typically 0.15 g) was dissolved in
pentane (5 mL) and the minimum amount of THF (if necessary). The
colorless solution was treated with a solution of thallium ethoxide (1
equiv) in pentane (5 mL), causing the immediate precipitation of a
colorless solid. The mixture was stirred for 2 h and filtered and the
filter cake washed with cold pentane (15 mL). The colorless solid was
dried in vacuo to yield pure product in the yields noted.
Thallium 4-Methoxyphenoxide (Tl[OC6H4OMe]; 96%). 1H NMR
(300 MHz, d6-DMSO): δ 6.70 (d, J ) 8.7 Hz, 2H), 6.60 (d, J ) 8.7
Hz, 2H), 3.61 (s, 3H) ppm. 13C{1H} NMR (d6-DMSO, 75 MHz): δ
159.3, 149.4, 117.8, 114.8, 55.5 ppm. Anal. Calcd for C7H7OTl: C,
25.67; H, 2.15. Found: C, 25.79; H, 2.11.
Thallium 2,6-Dimethylphenoxide (Tl[OC6H3Me2]; 79%). 1H NMR
(300 MHz, d6-DMSO): δ 6.79 (d, J ) 7.2 Hz, 2H), 6.12 (t, J ) 7.2
Hz, 1H), 2.38 (s, 6H) ppm. 13C{1H} NMR (d6-DMSO, 75 MHz): δ
164.6, 127.4, 126.2, 112.3, 19.2 ppm. Anal. Calcd for C8H9OTl: C,
29.52; H, 2.79. Found: C, 29.85; H, 2.82. For an alternate preparation
and a description of the X-ray structure of this compound, see ref 14.
2-((2,6-Diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)-
imino)-3-chloro-2-pentene ((LCliPr)H). Under a N2 atmosphere, tri-
fluoromethanesulfonyl chloride (0.70 mL, 6.43 mmol) was added to a
10
cold (-78 °C) solution of Li(LiPr
)
(2.60 g, 6.12 mmol) in THF (40
mL), causing bleaching of the solution. The reaction mixture was slowly
warmed to ambient temperature with stirring for 1 h. Water (2 mL)
and saturated aqueous Na2CO3 (15 mL) were then added, causing the
deposition of a small amount of white precipitate. An additional 10
mL of H2O was added, and the solution was extracted with pentane (3
× 75 mL). The organic fractions were combined and dried over MgSO4
and the volatiles removed under reduced pressure to yield a light yellow
solid. This solid was dissolved in a minimum amount of warm pentane
and slowly cooled to induce the deposition of colorless crystals.
Concentration of the supernatant and storage at -20 °C yielded an
Thallium 4-tert-Butylphenoxide (Tl[OC6H4tBu]; 95%). No NMR
data were available, due to lack of solubility. Anal. Calcd for C10H13-
OTl: C, 33.97; H, 3.71. Found: C, 33.92; H, 3.53.
1
additional crop (total yield 1.40 g, 50%). H NMR (C6D6, 300 MHz):
δ 13.21 (br s, 1H), 7.09-7.18 (m, 6H), 3.20 (heptet, J ) 6.9 Hz, 4H),
General Method for the Preparation of the Complexes LCuOAr
(L ) LiPr, LCliPr). A solution of LCuCl (typically 0.15 g) in THF (10
mL) was treated with the appropriate thallium phenoxide salt (1.05
equiv) as a solid, causing the development of a dark green color and
formation of a white precipitate. After the mixture was stirred for 1 h,
the filtrate was evaporated to dryness and the residue redissolved in a
minimum amount of pentane. The dark green solution was then filtered
through a pad of Celite, and the solvent was removed under reduced
(23) Nishino, H.; Itoh, N.; Magashima, M.; Kurosawa, K. Bull. Chem. Soc.
Jpn. 1992, 65, 620-622.
(24) Halfen, J. A.; Jazdzewski, B. A.; Mahapatra, S.; Berreau, L. M.;
Wilkinson, E. C.; Que, L., Jr.; Tolman, W. B. J. Am. Chem. Soc. 1997,
119, 8217-8227.
(25) (a) Nigles, M. J. Ph.D. Thesis, University of Illinois, Urbana, IL, 1979.
(b) Maurice, A. M. Ph.D. Thesis, University of Illinois, Urbana, IL,
1980.

6106 Inorganic Chemistry, Vol. 40, No. 24, 2001
Jazdzewski et al.
pressure. Recrystallization from pentane at -20 °C gave crystalline
solids in the yields noted.
unless stated otherwise. The data were corrected for Lorentz and
polarization effects, but no correction for crystal decay was applied.
Structure solutions were performed with either SHELXS28 or SIR92.29
Structure refinements were performed using the programs SHELXTL-
Plus V5.0 or SHELXTL V5.1 on a Pentium PC computer. All structure
refinements were performed on F2. Pertinent details for each structure
are noted below; see the Supporting Information for full information
in the form of CIF files.
LiPrCu(OC6H4OMe) (51%). EPR (toluene, 20 K, 9.62 GHz): gz )
2.22, Az ) 90 G, gy ) 2.07, gx ) 2.02. UV-vis (THF; λmax, nm (ꢀ,
M-1 cm-1)): 329 (20 600), 346 (22 400), 450 (2000), 630 (sh, 1800),
717 (2900). Anal. Calcd for C36H48N2O2Cu: C, 71.55; H, 8.01; N, 4.64.
Found: C, 71.43; H, 8.01; N, 4.62.
LiPrCu(OC6H3Me2) (50%). UV-vis (THF; λmax, nm (ꢀ, M-1 cm-1)):
280 (6500), 344 (21 000), 460 (2100), 643 (sh, 1400), 723 (1800). Anal.
Calcd for C37H50N2OCu: C, 73.78; H, 8.37; N, 4.65. Found: C, 73.14;
H, 8.29; N, 4.68.
LiPrCu(OC6H4tBu) (66%). UV-vis (THF; λmax, nm (ꢀ, M-1 cm-1)):
283 (5700), 345 (20 300), 456 (2100), 584 (sh, 1900), 697 (2700). Anal.
Calcd for C39H54N2OCu: C, 74.31; H, 8.63; N, 4.44. Found: C, 74.33;
H, 8.59; N, 4.45.
LCliPrCu(OC6H4tBu) (30%). UV-vis (THF; λmax, nm (ꢀ, M-1
cm-1)): 282 (9000), 326 (15 000), 361 (23 500), 458 (1900), 581 (sh,
1800), 699 (2900).
Li(LCliPr)‚Et2O. Crystals suitable for X-ray crystallographic analysis
were grown from Et2O at -20 °C. Partial disorder was found in the
coordinated Et2O molecule. One of the two ethyl arms was rotationally
disordered over two positions, with 50% occupancy for each conforma-
tion.
LCliPrCuCl‚CH2Cl2. Crystals suitable for X-ray crystallographic
analysis were grown from a mixture of HMDSO and CH2Cl2 (ap-
proximately 5:1) at -20 °C. One molecule of CH2Cl2 was found in
the asymmetric unit. The solvate molecule does not interact with the
complex.
LiPrCu(OC6H4OMe). Crystals suitable for X-ray crystallographic
analysis were grown from pentane at -20 °C.
LiPrCu(CNC6H3Me2). A solution of 2,6-di-tert-butylphenol (0.022
g, 0.106 mmol) in THF (2 mL) was treated with NaH (0.009 g, 0.106
mmol) and the mixture stirred under N2 for 30 min. The reaction mixture
was then filtered through a pad of Celite, and the filtrate was treated
with a solution of LiPrCuCl (0.050 g, 0.097 mmol) in THF (5 mL).
The reaction mixture immediately became light orange. After this
mixture was stirred for 0.5 h, a solution of 2,6-dimethylphenyl
1-isocyanide (0.013 g, 0.097 mmol) in THF (1 mL) was added and the
reaction mixture was stirred at ambient temperature overnight. The
solvent was removed under reduced pressure to yield a orange solid,
which was extracted with pentane (20 mL) and filtered through a pad
of Celite. The filtrate was then evaporated to dryness, and the residue
was dissolved in HMDSO (3 mL) and stored at -20 °C overnight.
Pale yellow crystals formed over 3 days (0.029 g, 49%). 1H NMR
(C6D6, 300 MHz): δ 7.06-7.17 (m, 6H), 6.55 (t, J ) 7.5 Hz, 1H),
6.35 (d, J ) 7.5 Hz, 2H), 5.03 (s, 1H), 3.57 (heptet, J ) 6.9 Hz, 4H),
1.83 (s, 6H), 1.61 (s, 6H), 1.42 (d, J ) 6.9 Hz, 12H), 1.26 (d, J ) 6.9
Hz, 12H) ppm. 13C{1H} NMR (C6D6, 75 MHz): δ 163.8, 150.4, 140.9,
135.4, 128.8, 128.0, 124.3, 123.7, 94.7, 28.6, 25.2, 23.8, 23.7, 18.6
ppm. UV-vis (THF; λmax, nm (ꢀ, M-1 cm-1)): 347 (28 300). FTIR
(KBr, cm-1): 3054, 2958, 2922, 2866, 2126 (νCN), 1545, 1518, 1463,
1439, 1404, 1313, 1254, 1230, 1172, 1102, 1055, 1019, 934, 791, 782,
758, 743, 720, 511, 444. Anal. Calcd for C38H50N3Cu: C, 74.53; H,
8.23; N, 6.86. Found: C, 74.56; H, 8.29; N, 6.94.
NMR Quantification of LiPrCu(CNC6H3Me2), 2,6-Di-tert-but-
ylphenol, and 3,3′,5,5′-Tetra-tert-butyl-4,4′-dibenzoquinone. A solu-
tion of LiPrCuCl (0.010 g, 0.019 mmol) in THF (2 mL) was treated
with 2,6-dimethylphenyl 1-isocyanide (0.0025 g, 0.019 mmol) and a
solution of sodium 2,6-di-tert-butylphenoxide in THF (2 mL), causing
the formation of a light brown solution. The reaction mixture was stirred
for 10 min, and the solvent was removed under reduced pressure to
yield a light orange solid. This solid was dissolved entirely in 1.0 mL
of a 15.3 mM solution of 1,3,5-trimethoxybenzene in C6D6, and the
sample was analyzed by 1H NMR spectroscopy (delay time 30 s).
Chemical shifts for LiPrCu(CNC6H3Me2), 2,6-di-tert-butylphenol, and
3,3′,5,5′-tetra-tert-butyl-4,4′-dibenzoquinone were determined from data
acquired on independently prepared materials. Integration vs the 1,3,5-
trimethoxybenzene standard for selected resonances from each com-
pound was then performed, giving yields of 97 ( 5% for LiPrCu-
(CNC6H3Me2), 46 ( 6% for 2,6-di-tert-butylphenol, and 27 ( 3% for
3,3′,5,5′-tetra-tert-butyl-4,4′-dibenzoquinone.
LiPrCu(OC6H3Me2). Crystals suitable for X-ray crystallographic
analysis were grown from HMDSO at -20 °C. Preliminary crystal-
lographic experiments indicated that the compound not only had a phase
transition below room temperature but also formed a nonmerohedral
twin. The specimen used for final data collection for both phases was
glued to a glass fiber with epoxy and transferred to the diffractometer,
and an initial data collection was completed at 25 °C without the use
of the cryostat. Upon completion of the data collection (1 hemisphere)
the cryostat was set at -100 °C and the data collection process was
repeated on the same specimen; 1.5 hemispheres of data were collected
on the twinned low-temperature polymorph by extending the number
of frames collected in each set. Both twin components of the
nonmerohedral twin were indexed with GEMINI30 using reflections
gleaned from 3 sets of 30 frames obtained at orthogonal ω settings.
The major twin component was indexed with a random set of 73
reflections to cell constants a ) 8.263(6) Å, b ) 21.429(15) Å, c )
20.187(14) Å, and â ) 93.02(2)°. The minor twin component was
indexed with 39 of the remaining 41 reflections to the cell constants a
) 8.257(8) Å, b ) 21.424(19) Å, c ) 20.170(18) Å, and â )
92.94(4)°. Reflections that were common to both cells were ignored in
the initial determination of cell constants. The twin law (by rows) is
[100, 0,-1,0, -0.25,0,-1], which corresponds to 180° rotations about
[100] and (100) in reciprocal and direct space, respectively. The
difference between the masses of the twin components mandated the
integration of only the major twin and applying a correction for the
minor twin component with ROTWIN.16 Of the 8156 total reflections,
2038 had contributions from both twin components. The overall effect
was that every h ) 4n reflection, where n ) -2, -1, 0, 1, 2, had exact
overlaps with the other twin component. No partial overlaps were
considered when producing the final SHELX HKLF 5 reflection file.
A series of a* zone images on the diffractometer (based on the
orthorhombic cell) confirmed that the phase transition occurred at -8
( 5 °C (see Figure S2 in the Supporting Information).
LCliPrCu(OC6H4tBu). Crystals suitable for X-ray crystallographic
analysis were grown from pentane at -20 °C. Initial attempts to mount
the crystals at 25 °C were unsuccessful due to crystal dissolution upon
warming of the mother liquor. To avoid this problem, the crystals were
mounted at -80 °C. The isopropyl group containing atoms C24-C26
was found to be slightly disordered. Attempts to model this disorder
did not lead to significant improvement in the refinement and were
not pursued further.
X-ray Crystallography. Crystal data and collection parameters are
listed in Table 1. With one exception (see below), a crystal of the
appropriate size was mounted on a glass fiber using hydrocarbon or
perfluorinated oil, transferred to a Siemens SMART diffractometer/
CCD area detector, and kept at -100 °C. The crystal was then centered
in the X-ray beam (Mo KR radiation; λ ) 0.710 73 Å, graphite
monochromator) for data collection. Initial cell constants and an
orientation matrix were determined by collection of 60 10 s frames,
followed by spot integration and least-squares refinement. A minimum
of 1.3 hemispheres of data were collected using 0.3° $ scans. The
raw data were integrated, and final unit cell constants were calculated
using SAINT.26 Absorption corrections were applied using SADABS27
(26) SMART V. 5.1, Software for the Integration of Area Detector Data;
Bruker-AXS, Madison, WI.
(27) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. Sheldrick, G.
SADABS V2.03: Program for the Application of Absorption Cor-
rections to Bruker-AXS CCD Single-Crystal Diffraction Data, 2000.
(28) SHELXTL V5.0 and V5.1, Software for the Solution and Refinement
of Crystal Structures; Bruker-AXS, Inc.: Madison, WI.
(29) Altomare, A.; Cascarno, G.; Giacovazzo, C.; Gualardi, A. J. Appl.
Crystallogr. 1993, 26, 343-350.
(30) GEMINI: Software for Indexing and Correcting Data Affected by
Nonmerohedral Twinning; Bruker-AXS, Madison, WI, 1999.

Three-Coordinate Copper(II)-Phenolate Complexes
Inorganic Chemistry, Vol. 40, No. 24, 2001 6107
LiPrCu(CNC6H3Me2). Crystals suitable for X-ray crystallographic
analysis were grown from HMDSO at -20 °C.
Supporting Information Available: X-ray crystal structure rep-
resentations (50% thermal ellipsoids) of LCliPrCu(OC6H4tBu), LiPrCu-
(OC6H3Me2), and LiPrCu(OC6H4tBu) at 25 °C and -100 °C (Figure
S1), zone images from X-ray data collections of LiPrCu(OC6H4tBu) at
25 and -51 °C surveying identical regions of reciprocal space (Figure
S2), an X-band EPR spectrum of LiPrCu(OC6H4tBu) (Figure S3), UV-
vis and Raman spectra of oxygenated LiPrCu(OC6H4tBu) (Figure S4),
and X-ray crystallographic files, in CIF format, for the structure
determinations listed in Table 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. We thank Dr. Raymond Ho and Professor
Lawrence Que, Jr., for providing access to the resonance Raman
facility, Professor John Lipscomb for access to his EPR
spectrometer, Nermeen Aboellela for help with the electro-
chemical measurements, and the NIH for funding (Grant No.
GM47365).
Note Added in Proof. Cu(I) complexes of some â-diketimi-
nate ligands recently have been reported: Yokota, S.; Tachi,
Y.; Nishiwaki, N.; Ariga, M.; Itoh, S. Inorg. Chem. 2001, 40,
5316. Dai, X.; Warren, T. H. Chem. Commun. 2001, 1998.
IC010615C