Carbonylation of a Tetrameric Aryloxocopper(I) Cluster

Article abstract of DOI:10.1021/ic961287x

Carbonylation of 2,6-diphenylphenoxocopper(I). tetrameric [(CuOC₆H₃Ph₂)₄] (1, Ph = C₆,H₅), has been shown to result in a [{Cu(OC₆H₃Ph₂)(CO)}₂] di

Full text of DOI:10.1021/ic961287x

3232
Inorg. Chem. 1997, 36, 3232-3236
Carbonylation of a Tetrameric Aryloxocopper(I) Cluster
Cesar Lopes, Mikael Håkansson, and Susan Jagner*
Department of Inorganic Chemistry, Chalmers University of Technology, S-412 96 Go¨teborg, Sweden
ReceiVed October 24, 1996X
Carbonylation of 2,6-diphenylphenoxocopper(I), tetrameric [(CuOC6H3Ph2)4] (1, Ph ) C6H5), has been shown to
result in a [{Cu(OC6H3Ph2)(CO)}2] dimer (2). The parent aryl oxide, [(CuOC6H3Ph2)4], which has been prepared
from mesitylcopper(I) and 2,6-diphenylphenol, has an approximately planar Cu4O4 core, in which copper(I) is
two-coordinated and Cu-O bonds range from 1.834(7) to 1.865(7) Å. Its carbonylation product 2 is a µ2-phenoxo-
bridged dimer, containing three-coordinated copper(I), with longer Cu-O bonds, Viz. 1.953(7)-1.995(7) Å. Cu-C
bond lengths in [{Cu(OC6H3Ph2)(CO)}2] are 1.78(1) and 1.79(1) Å, respectively, with both carbonyl C-O distances
equal to 1.12(1) Å, and Cu-C-O angles of 174(1) and 179(1)°, respectively. Carbonyl stretching frequencies
in the infrared are 2099, 2103, and 2112 cm-1 for the solid and 2102 cm-1 in toluene solution, and the 13C NMR
signal (toluene solution) is at 168 ppm. From comparison with other carbonyl complexes of copper(I), the Cu-C
bond is judged to be predominantly of σ character, with minimal metal f ligand π* contribution. Both [(CuOC6H3-
Ph2)4] and [{Cu(OC6H3Ph2)(CO)}2] retain their aggregation states on dissolution in nonpolar solvents, as ascertained
by cryoscopic molecular weight determinations of the compounds in benzene. Crystal data: 1, triclinic, space
group P1h (No. 2), a ) 12.738(9), b ) 22.426(5), and c ) 9.984(3) Å, R ) 101.62(2), â ) 91.02(4), and γ )
85.93(3)°, Z ) 2, R ) 0.052 (Rw ) 0.058) for 721 parameters and 3843 reflections; 2, triclinic, space group P1h
(No. 2), a ) 10.67(3), b ) 15.72(1), and c ) 10.05(1) Å, R ) 96.99(8), â ) 104.66(16), and γ ) 101.46(12)°,
Z ) 2, R ) 0.049 (Rw ) 0.054) for 397 parameters and 2152 reflections.
Introduction
Experimental Section
General. All operations were carried out under nitrogen or argon
using standard Schlenk techniques. Solvents [hexane (after addition
of a small amount of tetraglyme) and toluene] were distilled under
nitrogen from sodium/benzophenone shortly prior to use. Copper(I)
chloride was purified according to literature methods.11 Mesitylcopper-
(I) was prepared from copper(I) chloride, 2-bromomesitylene, and
magnesium according to methods described previously.12
Preparation of [(CuOC6H3Ph2)4]. Mesitylcopper(I) (12.7 mmol,
2.33 g) was dissolved in toluene (15 mL), and the resulting yellow
solution was centrifuged and transferred to a Schlenk tube containing
2,6-diphenylphenol (10.6 mmol, 2.61 g). After stirring of the mixture
for 20 min, 2,6-diphenylphenol had dissolved. Stirring was continued,
and, after 2 days, white microcrystalline [(CuOC6H3Ph2)4] had pre-
cipitated from a pale yellow solution. The mixture was centrifuged,
the solvent removed, and the precipitate washed four times with 5 mL
portions of hexane and dried under reduced pressure. The pale yellow
solution was evaporated to half its volume, 10 mL of hexane was added,
and the solution was stirred overnight, resulting in a second crop of
microcrystalline [(CuOC6H3Ph2)4], which was washed and dried as
above. Yield: 2.6 g (79%). The compound decomposes rapidly on
exposure to the atmosphere at ambient temperature.
For the preparation of single crystals suitable for X-ray diffraction
work, 0.5 mmol (0.1 g) of mesitylcopper(I), dissolved in a mixture of
toluene (1 mL) and hexane (3 mL), was allowed to react, as above,
with 0.5 mmol (0.13 g) of 2,6-diphenylphenol. The mixture was stirred
until 2,6-diphenylphenol dissolved, and the solution was allowed to
stand, colorless plates of [(CuOC6H3Ph2)4] being deposited after 1-2
days.
Preparation of [{Cu(OC6H3Ph2)(CO)}2]. Microcrystalline
[(CuOC6H3Ph2)4] was prepared, washed, and dried as above. Toluene
(5 mL) was added to 2,6-diphenylphenoxocopper(I) (1.6 mmol, 0.5
Copper(I) carbonyl complexes and, more specifically, the
nature of the copper(I)-carbonyl bond and reversible binding
of carbon monoxide by copper continue to be subjects of much
interest.1-8 Although carbonylation of [(CuOtBu)4], which is
tetrameric in the solid state,2 yields a remarkably stable [(Cu-
(OtBu)(CO))4] compound retaining the tetrameric aggregation
state of the parent alkoxide, both in the solid and on dissolution,3
carbonyl derivatives of aryl oxides have, hitherto, defied solid
state isolation.1a In connection with our current investigations
into aryl oxides of copper(I),9,10 we therefore considered it of
interest to attempt to isolate and characterize both the parent
aryl oxides and their carbonylation products. We here report
the preparation and characterization of 2,6-diphenylphenoxo-
copper(I), [(CuOC6H3Ph2)4] (Ph ) C6H5), and its carbonylated
derivative, [{Cu(OC6H3Ph2)(CO)}2].
X Abstract published in AdVance ACS Abstracts, July 1, 1997.
(1) See, for example: (a) Fiaschi, P.; Floriani, C.; Pasquali, M.; Chiesi-
Villa, A.; Guastini, C. Inorg. Chem. 1986, 25, 462. (b) Pasquali, M.;
Floriani, C.; Venturi, G.; Gaetani-Manfredotti, A.; Chiesi-Villa, A. J.
Am. Chem. Soc. 1982, 104, 4092. (c) Pasquali, M.; Floriani, C.;
Gaetani-Manfredotti, A. Inorg. Chem. 1981, 20, 3382. (d) Floriani,
C.; Fiaschi, P.; Chiesi-Villa, A.; Guastini, C.; Zanazzi, P. F. J. Chem.
Soc., Dalton Trans. 1988, 1607 and references therein. (e) Solari, E.;
Latronico, M.; Blech, P.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Inorg. Chem. 1996, 35, 4526.
(2) Greiser, T.; Weiss, E. Chem. Ber. 1976, 109, 3142.
(3) Geerts, R. L.; Huffman, J. C.; Folting, K.; Lemmen, T. H.; Caulton,
K. G. J. Am. Chem. Soc. 1983, 105, 3503.
(4) Håkansson, M. Inorg. Synth., in press.
(5) Håkansson, M.; Jagner, S. Inorg. Chem. 1990, 29, 5241.
(6) Håkansson, M.; Jagner, S.; Kettle, S. F. A. Spectrochim. Acta 1992,
48A, 1149.
(7) Rack, J. J.; Webb, J. D.; Strauss, S. H. Inorg. Chem. 1996, 35, 277
and references therein.
(8) See, for example: Karlin, K. D.; Tyeklar, Z.; Farooq, A.; Haka, M.
S.; Ghosh, P.; Cruse, R. W.; Gultneh, Y.; Hayes, J. C.; Toscano, P.
J.; Zubieta, J. Inorg. Chem. 1992, 31, 1436 and references therein.
(9) Lopes, C.; Håkansson, M.; Jagner, S. Inorg. Chim. Acta 1997, 254,
361.
(11) Keller, R. N.; Wycoff, H. D. Inorg. Synth. 1946, 2, 1.
(12) (a) Tsuda, T.; Yazawa, T.; Watanabe, K.; Fujii, T.; Saegusa, T. J.
Org. Chem. 1981, 46, 192. (b) Tsuda, T.; Watanabe, K.; Miyata, K.;
Yamamoto, H.; Saegusa, T. Inorg. Chem. 1981, 20, 2728. (c)
Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Chem.
Soc., Chem. Commun. 1983, 1156. (d) Meyer, E. M.; Gambarotta, S.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics 1989, 8,
1067.
(10) Lopes, C.; Håkansson, M.; Jagner, S. Manuscript in preparation.
S0020-1669(96)01287-6 CCC: $14.00 © 1997 American Chemical Society

Carbonylation of 2,6-Diphenylphenoxocopper(I)
Inorganic Chemistry, Vol. 36, No. 15, 1997 3233
Table 1. Crystallographic Data for [(CuOC6H3Ph2)4] (1) and
[{Cu(OC6H3Ph2)(CO)}2] (2)
Table 2. Selected Interatomic Distances (Å) and Angles (deg) for
[(CuOC6H3Ph2)4] (1)
1
2
Cu(1)-O(1)
Cu(1)-O(4)
Cu(3)-O(2)
Cu(3)-O(3)
O(1)-C(1)
O(3)-C(37)
Cu(1)‚‚‚Cu(2)
Cu(1)‚‚‚Cu(4)
1.865(7)
1.861(7)
1.834(7)
1.857(8)
1.35(1)
1.36(1)
2.933(3)
2.798(2)
Cu(2)-O(1)
Cu(2)-O(2)
Cu(4)-O(3)
Cu(4)-O(4)
O(2)-C(19)
O(4)-C(55)
Cu(2)‚‚‚Cu(3)
Cu(3)‚‚‚Cu(4)
1.859(6)
1.861(7)
1.855(7)
1.837(7)
1.36(1)
1.34(1)
2.926(2)
2.962(3)
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
C72H52Cu4O4
1235.4
C38H26Cu2O4
673.7
triclinic
P1h (No. 2)
12.738(9)
22.426(5)
9.984(3)
101.62(2)
91.02(4)
85.93(3)
2784(2)
2
triclinic
P1h (No. 2)
10.67(3)
15.72(1)
10.05(1)
96.99(8)
104.66(16)
101.46(12)
1573(5)
2
R, deg
â, deg
γ, deg
V, Å3
Z
O(1)-Cu(1)-O(4)
O(2)-Cu(3)-O(3)
Cu(1)-O(1)-Cu(2)
Cu(3)-O(3)-Cu(4)
Cu(1)-O(1)-C(1)
Cu(2)-O(1)-C(1)
Cu(2)-O(2)-C(19)
Cu(3)-O(2)-C(19)
173.4(3) O(1)-Cu(2)-O(2)
166.7(3) O(3)-Cu(4)-O(4)
103.9(3) Cu(2)-O(2)-Cu(3)
105.9(4) Cu(1)-O(4)-Cu(4)
118.0(6) Cu(3)-O(3)-C(37)
137.4(6) Cu(4)-O(3)-C(37)
123.3(7) Cu(1)-O(4)-C(55)
131.3(7) Cu(4)-O(4)-C(55)
160.0(3)
165.1(3)
104.7(3)
98.4(3)
128.2(7)
125.6(7)
126.1(7)
134.9(7)
d
calc, g/cm3
1.47
1.42
radiation (λ)
µ, cm-1
T, °C
Mo KR (0.71073 Å)
Mo KR (0.71073 Å)
15.6
-120
0.052
13.9
-120
0.049
Cu(4)‚‚‚Cu(1)‚‚‚Cu(2) 95.17(7) Cu(2)‚‚‚Cu(3)‚‚‚Cu(4) 91.91(6)
Cu(3)‚‚‚Cu(2)‚‚‚Cu(1) 85.54(7) Cu(1)‚‚‚Cu(4)‚‚‚Cu(3) 87.33(6)
Ra
Rw
a
0.058
0.054
2
a R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [(∑w(|Fo| - |Fc| )2/∑wFo )]1/2
.
(λ ) 0.71073 Å) radiation from an RU200 rotating anode source
operated at 9 kW (50 kV, 180 mA). The ω/2θ scan mode was
employed, and stationary background counts were recorded on each
side of the reflection, the ratio of peak counting time vs background
counting time being 2:1. Data were measured for 5 < 2θ < 50°
(+h,(k,(l) for a pale yellow plate of 1, with approximate dimensions
0.25 mm × 0.20 mm × 0.10 mm, using an ω scan rate of 8 deg/min
and a scan width of (1.21 + 0.30 tan θ)°. For 2, a colorless rod with
approximate dimensions 0.20 mm × 0.05 mm × 0.05 mm was used
under identical experimental conditions. In both cases, weak reflections
(I < 10.0σ(I)) were rescanned up to three times and counts accumulated
to improve counting statistics. The intensities of three reflections
monitored regularly after measurement of 150 reflections indicated
crystal stability during data collection. For 1, correction was made
for Lorentz and polarization effects; an empirical correction based on
azimuthal scans for several reflections was made for the effects of
absorption (minimum/maximum transmission factors ) 0.61/1.00). For
2, correction was made for Lorentz and polarization effects but not for
the effects of absorption. Of the 9782 unique reflections measured
for 1, 3843 had I > 3.0σ(I) and were considered observed. Cell
constants for 1 were obtained by least-squares refinement from the
setting angles of 20 reflections in the range 14.1 < 2θ < 18.9°. Of
the 5528 unique reflections measured for 2, 2152 had I > 3.0σ(I) and
were considered observed. Cell constants for 2 were obtained by least-
squares refinement from the setting angles of eight reflections in the
range 14.4 < 2θ < 26.9°.
g), and the slurry was stirred under carbon monoxide for 30 min, during
which time the white precipitate dissolved, giving a yellow solution.
The solution was evaporated almost to dryness, 3 mL of hexane was
added, and the resulting white microcrystalline [{Cu(OC6H3Ph2)(CO)}2]
was isolated. Yield: 0.52 g (96%). [{Cu(OC6H3Ph2)(CO)}2] decom-
poses rapidly on exposure to the atmosphere at ambient temperature.
The compound can also be prepared in a way analogous to the
preparation of [(CuOC6H3Ph2)4], under an atmosphere of carbon
monoxide instead of argon. In order to obtain single crystals suitable
for X-ray diffraction work, 0.4 mmol (0.08 g) of mesitylcopper(I) was
dissolved in a mixture of toluene (0.6 mL) and hexane (3.5 mL). The
solution was added to 0.4 mmol (0.10 g) of 2,6-diphenylphenol, and
the mixture was stirred under an atmosphere of carbon monoxide. After
prolonged stirring (for 3 h), excess [{Cu(OC6H3Ph2)(CO)}2] was
deposited as a white precipitate. This was removed by centrifuging
the mixture, and the colorless solution was allowed to stand at -18 °C
for approximately 1 week, after which time colorless rods of [{Cu-
(OC6H3Ph2)(CO)}2] had formed.
Cryoscopy. [(CuOC6H3Ph2)4] dissolves slowly in toluene and is
also soluble in benzene. Cryoscopic determination of the molecular
weight of the compound in benzene solution yielded a value of 1176
g mol-1 (calculated for [(CuOC6H3Ph2)4], 1235 g mol-1). Cryoscopic
measurement on the solution obtained by carbonylation of 1 in
benzene: experimental, 655 g mol-1; calculated for [{Cu(OC6H3Ph2)-
(CO)}2], 674 g mol-1. Similarly, [(CuOC6H3Ph2)4] was carbonylated
in toluene prior to investigation of 2 by 1H and 13C NMR spectroscopy.
NMR and Infrared Spectroscopy. 1H NMR spectra (400 MHz)
for 1, 2, and 2,6-diphenylphenol in toluene, and a 13C NMR spectrum
(100 MHz) for 2 in toluene, were recorded at 20 °C on a Varian XL
400 spectrometer using toluene-d8 and the most upfield signal from
toluene as an internal standard (s ) singlet, d ) doublet, t ) triplet, m
) multiplet, b ) broad).
Both structures were solved by direct methods (MITHRIL13). Full-
matrix least-squares refinement, including anisotropic thermal param-
eters for the non-hydrogen atoms, and with the hydrogen atoms as a
fixed contribution (C-H ) 0.95 Å, B ) 1.2Beq of the carrying carbon
atom), gave final residuals of R ) 0.052 (Rw ) 0.058) for 721
parameters and 3843 observed reflections for 1 and R ) 0.049 (Rw
)
0.054) for 397 parameters and 2152 observed reflections for 2. The
maximum and minimum values in the final difference map were 0.88
and -0.74 e/Å3 for 1 and 0.54 and -0.58 e/Å3 for 2, respectively.
1H NMR (ppm): For 2,6-diphenylphenol, δ 5.07 (s, 1H, -OH), 6.85
(t, 1H), 7.04-7.17 (m, 8H), 7.37 (s, 2H), 7.39 (d, 2H). For 1, δ 6.76-
7.44 (m). For 2, δ 6.88 (t, 1H), 7.00 (t, 2H), 7.18 (t, 4H), 7.27 (d,
2H), 7.60 (d, 4H). No trace of uncarbonylated 1 was observed in the
spectrum.
13C NMR (ppm): For 2, δ(CO) 168.2 (s, b) (∆ν1/2 ) 10 Hz). No
coupling with the quadrupolar copper nucleus was observed.
Carbonyl stretching frequencies for 2 were recorded on a Mattson
Reflections were weighted according to w ) [σ2(Fo)]-1
.
All calculations were carried out with the TEXSAN14 program
package. Atomic scattering factors and anomalous dispersion correction
factors were taken from ref 15. Selected interatomic distances and
angles are given in Tables 2 and 3.
Results and Discussion
Polaris FTIR spectrometer with a resolution of 2 cm-1
.
IR: for [{Cu(OC6H3Ph2)(CO)}2] (s) (2, Nujol mull, CaF2 windows,
cm-1), νCO 2099 s, 2103 s, 2112 m (13CO, 2052 w, 2058 w). Crystals
of 2 dissolved in toluene (CaF2 cell, cm-1), νCO 2102. 1 carbonylated
in toluene (CaF2 cell, cm-1), νCO 2102.
X-ray Crystallography. Crystal and experimental data are sum-
marized in Table 1. Crystals were mounted using low-temperature
methods.4 Diffracted intensities were measured at -120 °C using a
Rigaku AFC6R diffractometer and graphite-monochromated Mo KR
The reaction between methylcopper(I) and phenols or alcohols
has been demonstrated to be an effective preparatory method
(13) Gilmore, C. J. J. Appl. Crystallogr. 1984, 17, 42.
(14) TEXSANsTEXRAY Structure Analysis Package. Molecular Structure
Corp., The Woodlands, TX, 1989.
(15) International Tables for X-Ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV.

3234 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lopes et al.
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for
[{Cu(OC6H3Ph2)(CO)}2] (2)
Cu(1)-C(1)
C(1)-O(1)
Cu(1)-O(3)
Cu(1)-O(4)
O(3)-C(3)
Cu(1)‚‚‚Cu(2)
1.78(1)
1.12(1)
1.953(7)
1.995(7)
1.36(1)
3.012(3)
Cu(2)-C(2)
C(2)-O(2)
Cu(2)-O(3)
Cu(2)-O(4)
O(4)-C(21)
1.79(1)
1.12(1)
1.965(7)
1.966(7)
1.34(1)
Cu(1)-C(1)-O(1)
O(3)-Cu(1)-O(4)
O(3)-Cu(1)-C(1)
O(4)-Cu(1)-C(1)
174(1)
Cu(2)-C(2)-O(2)
179(1)
79.6(3) O(3)-Cu(2)-O(4)
148.5(4) O(3)-Cu(2)-C(2)
130.9(4) O(4)-Cu(2)-C(2)
80.0(3)
139.4(4)
140.4(4)
99.0(3)
Cu(1)-O(3)-Cu(2) 100.5(3) Cu(1)-O(4)-Cu(2)
Cu(1)-O(3)-C(3)
Cu(2)-O(3)-C(3)
132.3(6) Cu(1)-O(4)-C(21) 126.9(6)
127.2(6) Cu(2)-O(4)-C(21) 133.4(6)
for copper(I) alkoxides and aryl oxides.16 Mesitylcopper(I) has
been used analogously to prepare copper(I) amides from the
relevant amines12b and copper(I) silyl oxides from the corre-
sponding silanols.17 We have shown recently that this general
approach can be utilized successfully for the preparation of
o-allylphenoxocopper(I) and methylbutenoxocopper(I) from
mesitylcopper(I) and o-allylphenol and 2-methyl-3-buten-2-ol,
respectively.10 A further example is provided by the present
preparation of 2,6-diphenylphenoxocopper(I), which is tet-
rameric both in solution and in the solid state.
Figure 1. ZORTEP drawing of [(CuOC6H3Ph2)4] (1), showing the
crystallographic numbering. The Cu4 square in the Cu4O4 core is
emphasized by means of dashed lines.
Whereas [(CuOtBu)4] retains its tetrameric aggregation state,
albeit with a different type of Cu4O4 core, on carbonylation to
[(Cu(OtBu)(CO))4],3 we have found that carbonylation of the
2,6-diphenylphenoxo analogue, tetrameric [(CuOC6H3Ph2)4],
results in a [{Cu(OC6H3Ph2)(CO)}2] dimer (2) and that prepara-
tion from mesitylcopper(I) and 2,6-diphenylphenol under carbon
monoxide also yields 2. As for [(Cu(OtBu)(CO))4], which is
tetrameric both in solution and in the solid state,3 the degree of
aggregation of 2 in the solid state, here dimeric, would appear
to persist in solution.
The parent aryl oxide, [(CuOC6H3Ph2)4], provides a unique
example of a homoleptic copper(I) aryl oxide without the
presence of stabilizing ancillary ligands or functions. The
compound has an approximately planar Cu4O4 core, in which
copper(I) is two-coordinated, with Cu-O bonds ranging from
1.834(7) to 1.865(7) Å and O-Cu-O angles close to 180° (cf.
Figures 1 and 2 and Table 2). As can be seen from Figure 2,
the Cu4O4 core in 1 is approximately planar, with a mean atomic
deviation from the best plane through these eight atoms of 0.05
Å. (Alternatively, the core could be described in terms of a
planar, to within 0.005Å, O4 unit, with the copper(I) atoms
deviating between 0.02 and 0.10 Å from this plane). The four
copper atoms form an approximate square, less regular than that
in [(CuOtBu)4],2 in which the copper(I)‚‚‚copper(I) separations
are somewhat shorter, ranging from 2.646(2) to 2.771(3) Å. The
irregularity of the “square” Cu4 core and the long Cu‚‚‚Cu
separations, 2.798(2)-2.962(3) Å, provide perhaps the most
significant difference between tetrameric copper(I) aryl oxides
and tetrameric copper(I) aryls, Cu‚‚‚Cu distances in the latter
being of the order of 2.4 Å or less,18 due to the presence of
three-center two-electron Cu-C-Cu bonds.
Figure 2. PLUTON drawing of [(CuOC6H3Ph2)4] (1) with the Cu4O4
core viewed side-on. Cu, “globe” pattern; O, crossed pattern; and C,
filled.
[(CuOC6H3Ph2)4], as can be seen from Figure 2. The phenoxo
phenyl rings situated diametrically opposite one another with
respect to the core of 1 (cf. Figure 1) are approximately
perpendicular to one another, i.e., mutually inclined at angles
of 78.7 and 87.1°, respectively. Within each C6H3Ph2 fragment,
the outer rings are also appreciably inclined, the dihedral angles
between these pairs of outer phenyl rings within the four C6H3-
Ph2 groups being 74.2, 53.0, 66.5, and 74.1°, respectively. There
are a few Cu‚‚‚C(arene) distances less than 3 Å, Viz. Cu(1)‚‚‚C-
(13) ) 2.80(1), Cu(1)‚‚‚C(66) ) 2.90(1), Cu(2)‚‚‚C(12) ) 2.62-
(1), Cu(2)‚‚‚C(25) ) 2.81(1), Cu(2)‚‚‚C(26) ) 2.76(1), Cu-
(3)‚‚‚C(32) ) 2.80(1), Cu(4)‚‚‚C(49) ) 2.90(1), and Cu(4)‚‚‚C(54)
) 2.88(1) Å.
Carbonylation of [(CuOC6H3Ph2)4] yields dimeric [{Cu(OC6H3-
Ph2)(CO)}2] (2, Figures 3 and 4), containing three-coordinated
copper(I), with, as expected, longer Cu-O bonds than those in
[(CuOC6H3Ph2)4], Viz. 1.953(7)-1.995(7) Å (cf. Table 3). Cu-
(1) and Cu(2) are displaced by 0.099 and 0.047 Å, respectively,
from the trigonal planes through the relevant ligand atoms. The
Cu2O2 core is planar to within 0.07 Å, the dihedral angle
between the planes through Cu(1), O(3), and O(4) and Cu(2),
O(3), and O(4) being 171°. As can be seen from Figure 4, this
slight folding is accompanied by bending of the carbonyl groups
In [(CuOtBu)4],2,19 the tBu substituents are all bent in the same
direction away from the Cu4O4 core. This is not the case in
(16) Whitesides, G. M.; Sadowski, J. S.; Lilburn, J. J. Am. Chem. Soc.
1974, 96, 2829.
(17) McGeary, M. J.; Wedlich, R. C.; Coan, P. S.; Folting, K.; Caulton,
K. G. Polyhedron 1992, 11, 2459.
(18) Nobel, D.; van Koten, G.; Spek, A. L. Angew. Chem., Int. Ed. Engl.
1989, 28, 208. Håkansson, M.; Eriksson, H.; O¨ rtendahl, M. Organo-
metallics 1996, 15, 4823. Håkansson, M.; Eriksson, H. Manuscript in
preparation.
(19) Caulton, K. G.; Goeden, G. V.; Lemmen, T. H.; Rhodes, L. F.;
Huffman, J. C. In Biological and Inorganic Copper Chemistry; Karlin,
K. D., Zubieta, J., Eds.; Adenine Press: New York, 1985.

Carbonylation of 2,6-Diphenylphenoxocopper(I)
Inorganic Chemistry, Vol. 36, No. 15, 1997 3235
namely the out-of-phase coupling of the two individual CO
stretchings. However, we also have to consider that, in this
case, the CO bond vectors make a non-zero angle, the deviation
from linearity being of the order of 27°, also causing the in-
phase combination to be IR-active, although with a lower
intensity.20 Furthermore, intermolecular interactions may be of
importance, since the O‚‚‚O separation of carbonyl groups of
the nearest neighboring dimer is only 3.76(2) Å [i.e., O(1)‚‚‚O-
(1i), where i ) -x, -y, 2 - z], and intermolecular CO couplings
could lead to further splittings according to the correlation field
approximation.21 A complete, unambiguous assignment would,
however, require more detailed investigations beyond the scope
of the present report.
[{Cu(OC6H3Ph2)(CO)}2] loses carbon monoxide somewhat
more slowly than [Cu(CO)Cl],5 from which carbon monoxide
is released extremely rapidly. That [(Cu(OtBu)(CO))4] is
resistant to decarbonylation has been attributed to its “kinetic
stability”, i.e., the unfavorable pyramidal coordination geometry
for copper(I) which would occur in the initial decarbonylation
product.3 Similar reasoning has also been exploited to account
for the formation of a copper(I) carbonyl complex stabilized
by a tris-chelating oxygen donor ligand.22 Such reasoning might
also be used to rationalize the more rapid decarbonylation of
[Cu(CO)Cl] as compared to that of 2, since, in the former
compound, the proximity of chloride ligands to an initially
pyramidal decarbonylated copper(I) center provides ready access
to tetrahedral coordination,5 whereas loss of a carbonyl group
from [{Cu(OC6H3Ph2)(CO)}2] would result initially in a two-
coordinated copper(I) center with nonlinear coordination ge-
ometry.
Figure 3. ZORTEP drawing of [{Cu(OC6H3Ph2)(CO)}2] (2), showing
the crystallographic numbering.
As in [(Cu(OtBu)(CO))4],3 the 13CO shift of CO bonded to
copper(I) in [{Cu(OC6H3Ph2)(CO)}2] (168 ppm) is upfield of
that of free CO (184 ppm)23 and slightly lower than the 173
ppm observed for [(Cu(OtBu)(CO))4].3 The values for both
[(Cu(OtBu)(CO))4] and [{Cu(OC6H3Ph2)(CO)}2] lie in the range
of 13C chemical shifts exhibited by transition metal carbonyls,
in which the OCfM interaction is considered to be predomi-
nantly of σ character.24
Similar conclusions concerning bonding within the Cu-C-O
unit in copper(I) carbonyls have been drawn from infrared
stretching frequencies, νCO, in these complexes invariably being
high, approaching and sometimes even exceeding25 (see below)
the value of 2143 cm-1 observed for the gaseous molecule.26
The observed carbonyl stretching frequencies for 2, Viz. 2099,
2103, and 2112 cm-1 (solid) and 2102 cm-1 (toluene solution)
are in good agreement with values determined1 for carbonyl
ligands terminally bonded to copper(I) and are intermediate
between those found for [(Cu(OtBu)(CO))4] (in toluene)3 and
[(Cu(CO)Cl] (s),5,6 i.e., 2063 and 2127 cm-1, respectively. This
trend is matched by the Cu-C bond lengths in the three
compounds, which are shortest (1.767(6) and 1.783(9) Å) in
[(Cu(OtBu)(CO))4],3 slightly, if not significantly, longer in [{Cu-
(OC6H3Ph2)(CO)}2], i.e., 1.78(1) and 1.79(1) Å, and longest,
1.856(16) Å, in [Cu(CO)Cl].5 Owing to the low precision
Figure 4. PLUTON drawing of [{Cu(OC6H3Ph2)(CO)}2] (2) with the
Cu2O2 core viewed side-on. Cu, “globe” pattern; O, crossed pattern;
and C, filled.
toward one another. We estimate the angle between the O(1)-
C(1) and O(2)-C(2) bond vectors to be approximately 153°.
The phenoxo phenyl rings of the aryloxo ligands situated
diametrically opposite to one another with respect to the Cu2O2
core are mutually perpendicular, with a dihedral angle of 94.2°.
Likewise, the outer rings within each C6H3Ph2 fragment are also
approximately perpendicular to one another and exhibit dihedral
angles of 90.3 and 83.8°, respectively. The closest Cu‚‚‚C-
(arene) distances are of the order of 3 Å, Viz. Cu(1)‚‚‚C(14) )
3.14(1), Cu(2)‚‚‚C(15) ) 3.08(1), Cu(2)‚‚‚C(20) ) 3.03(1), and
Cu(2)‚‚‚C(28) ) 3.10(1) Å.
It is noteworthy that it is the aryloxo rather than the carbonyl
ligands which bridge the copper(I) centers. This is in ac-
cordance with the previous findings of Floriani et al.1a Further
attempts to isolate carbonylated phenoxocopper(I) derivatives
with bulky substituents adjacent to the oxo ligand have resulted
in dimeric species essentially similar to [{Cu(OC6H3Ph2)-
(CO)}2], with bridging aryloxo and terminal carbonyl ligands.10
In the solid state, three carbonyl stretching frequencies have
(20) Kettle, S. F. A. Physical Inorganic Chemistry; Spektrum Academic
Publishers: Oxford, England, 1996; p 274.
(21) Cotton, F. A. Chemical Applications of Group Theory, 3rd ed.;
Wiley: New York, 1990; p 344.
(22) Kla¨ui, W.; Lenders, B.; Hessner, B.; Evertz, K. Organometallics 1988,
7, 1357.
(23) Heaton, B. T.; Jonas, J.; Eguchi, T.; Hoffman, G. A. J. Chem. Soc.,
Chem. Commun. 1981, 331.
(24) Aubke, F.; Wang, C. Coord. Chem. ReV. 1994, 137, 483.
(25) Plitt, H. S.; Ba¨r, M. R.; Ahlrichs, R.; Schno¨ckel, H. Inorg. Chem.
1992, 31, 463.
(26) Nakamoto, K. Infrared Spectra of Inorganic Compounds and Coor-
dination Compounds; Wiley: New York, 1963; p 72.
been observed for 2, Viz. 2099 (s), 2103 (s), and 2112 (m) cm-1
.
Corresponding weak 13C peaks were found at 2052 and 2058
cm-1, in good agreement with the isotope effect predicted by
the diatomic harmonic oscillator for a 2100 cm-1 vibration, 47
cm-1. As a first approximation, one would expect a single
vibration in this region for a planar OC-Cu2O2-CO unit,

3236 Inorganic Chemistry, Vol. 36, No. 15, 1997
Lopes et al.
associated with the determination of C-O distances, it is not
possible to detect any differences or trends in these distances
between the three compounds.
stretching frequencies, 2164-2178 cm-1, have been isolated,
providing further evidence for the importance of nonclassical
OCfCu(I) bonding, predominantly of σ type.7 In any event,
it may be concluded that the copper(I)-carbonyl interaction is
weak and that carbonyl derivatives of, e.g., aryl oxides and
alkoxides (cf. ref 3) can probably be isolated only when the
structure is such that initial decarbonylation of a copper(I) center
would result in an unfavorable coordination geometry for this
center.
Furthermore, as has been pointed out in a recent review,27
copper(I) and CO may be considered to be poorly matched
reaction partners, in that CO relies heavily on back-bonding
for the strength of the M-C bond, whereas copper(I) is reluctant
to participate strongly in back-bonding. Thus, the Cu-C bond
is considered to be primarily a dative bond, with negligible
multiple bond character.27 This has later been supported by an
investigation of matrix-isolated monomeric Cu(CO)Cl, exhibit-
ing νCO of 2157 cm-1, in which the Cu-C bond is predomi-
nantly a σ-bond and π* back-donation is considered to play a
minor role.25 Ab initio calculations on the Cl-Cu-CO species
now, however, suggest that π* back-donation is not negligible.28
Moreover, the presence of π back-bonding, in addition to the
stronger σ-donor interaction in the Cu(I)-CO interaction, as
compared with that involving Zn(II), has been demonstrated to
be crucial for enhancement of methanol formation from CO by
Cu(I)-promoted ZnO catalysts.29 Very recently, solid cationic
[Cu(CO)n]+ (n ) 1, 2, 3) complexes with very high ν(CO)
Acknowledgment. We thank Dr. Lars O¨ hrstro¨m for valuable
discussions concerning the carbonyl stretching frequencies of
2 and Dr. O¨ jvind Davidsson and Dr. Go¨ran Hilmersson for
assistance with the NMR studies. Financial support from the
Swedish Natural Science Research Council is gratefully ac-
knowledged.
Supporting Information Available: Tables giving crystal data and
details of the structure determinations, fractional coordinates and
equivalent isotropic thermal parameters for the non-hydrogen atoms,
anisotropic thermal parameters, atomic coordinates for the hydrogen
atoms and bond distances and angles involving the non-hydrogen atoms
for 1 and 2 (25 pages). Ordering information is given on any current
masthead page.
IC961287X
(27) Caulton, K. G.; Davies, G.; Holt, E. M. Polyhedron 1990, 9, 2319.
(28) Antes, I.; Dapprich, S.; Frenking, G.; Schwerdtfeger, G. Inorg. Chem.
1996, 35, 2089.
(29) Solomon, E. I.; Jones, P. M.; May, J. A. Chem. ReV. 1993, 93, 2623.