σ-Carbon versus π-arene interactions in the solid-state structures of trimeric and dimeric copper aryls (CuAr)n (n = 3, Ar = 2,6-Ph2C6H3; n = 2, Ar = 2,6-Mes2C6H3)

Article abstract of DOI:10.1021/om980446c

Reaction of LiC₆H₃Ph₂-2,6 or LiC₆H₃Mes₂-2,6 with CuOt-Bu in pentane or toluene yields the unsolvated copper aryls (CuC₆H₃Ph₂-2,6)₃ (2) and (CuC₆H₃Mes₂-2,6)₂ (3). Addition of another equivalent of lithium aryl to 3 affords the lithium cuprate LiCu(C₆H₃Mes₂-2,6)₂ (4). The new compounds 2-4 were characterized by ¹H NMR, ¹³C NMR, IR spectroscopy, mass spectrometry, and X-ray crystallography. The X-ray structure shows 2 to be trimeric in the solid state. The bridging terphenyl ligands exhibit two different coordination modes. Two of them connect two copper atoms via their ipso C₆H₃ carbons, while the third bridges two copper centers by either a σ-C (ipso C₆H₃) or a π-arene (ipso/ortho phenyl) interaction. A dimeric unit is observed in the solid-state structure of 3, in which the two aryl groups are linked by two bridging coppers. The copper atoms mainly interact with the ipso carbons of the C₆H₃ group. The quasi-linear coordination is completed by two ipso and ortho carbons of a mesityl group. Molecular weight determinations of the copper aryls 2 and 3 by cryoscopy in benzene solution show an equilibrium between monomers and dimers. Compound 4 is the first example of a structurally characterized, monomeric, nonsolvated lithium cuprate. It crystallizes with two independent molecules, showing C-Cu-C angles of 171.1° and 173.8°, respectively. The lithium ions are accommodated between two adjacent mesityl groups of the terphenyl ligands.

Full text of DOI:10.1021/om980446c

Organometallics 1998, 17, 4649-4656
4649
σ-Ca r bon ver su s π-Ar en e In ter a ction s in th e Solid -Sta te
Str u ctu r es of Tr im er ic a n d Dim er ic Cop p er Ar yls
(Cu Ar )n (n ) 3, Ar ) 2,6-P h 2C6H3; n ) 2, Ar )
2,6-Mes2C6H3)
Mark Niemeyer
Institut fu¨r Anorganische Chemie der Universita¨t Stuttgart,
Pfaffenwaldring 55, D-70569 Stuttgart, Germany
Received J une 1, 1998
Reaction of LiC6H3Ph2-2,6 or LiC6H3Mes2-2,6 with CuOt-Bu in pentane or toluene yields
the unsolvated copper aryls (CuC6H3Ph2-2,6)3 (2) and (CuC6H3Mes2-2,6)2 (3). Addition of
another equivalent of lithium aryl to 3 affords the lithium cuprate LiCu(C6H3Mes2-2,6)2 (4).
1
The new compounds 2-4 were characterized by H NMR, 13C NMR, IR spectroscopy, mass
spectrometry, and X-ray crystallography. The X-ray structure shows 2 to be trimeric in the
solid state. The bridging terphenyl ligands exhibit two different coordination modes. Two
of them connect two copper atoms via their ipso C6H3 carbons, while the third bridges two
copper centers by either a σ-C (ipso C6H3) or a π-arene (ipso/ortho phenyl) interaction. A
dimeric unit is observed in the solid-state structure of 3, in which the two aryl groups are
linked by two bridging coppers. The copper atoms mainly interact with the ipso carbons of
the C6H3 group. The quasi-linear coordination is completed by two ipso and ortho carbons
of a mesityl group. Molecular weight determinations of the copper aryls 2 and 3 by cryoscopy
in benzene solution show an equilibrium between monomers and dimers. Compound 4 is
the first example of a structurally characterized, monomeric, nonsolvated lithium cuprate.
It crystallizes with two independent molecules, showing C-Cu-C angles of 171.1° and 173.8°,
respectively. The lithium ions are accommodated between two adjacent mesityl groups of
the terphenyl ligands.
In tr od u ction
trinuclear5b,9 compounds, have been obtained only by
using chelating heteroatom-containing ligands and/or
coordinating solvents. In this paper, the synthesis and
structural characterization of aryl copper derivatives of
the bulky terphenyl ligands 2,6-Ph2C6H3 and 2,6-
Organocopper reagents are of major importance for
the carbon-carbon bond formation in organic synthe-
sis.1 This is part of the reason why their solution and
solid-state structures2 have attracted considerable in-
terest for the last two or three decades. Most of the
attention has been given to the structural characteriza-
tion of the synthetically important lithium diorganocu-
prates3 and higher order cuprates.4 A lot of interest has
been focused also on alkyl or aryl copper complexes
stabilized by either heteroatom donor substituents in
the ortho position5 or coordination to donor solvents such
as dimethyl sulfide (DMS) or tetrahydrothiophene
(THT).6 However, structural reports on simple homo-
leptic alkyl or aryl copper compounds are relatively rare
and currently limited to tetra- and pentameric species.7,8
Smaller aggregates, namely, mono-,6d,e di-,5d,g,6d and
(3) Examples for neutral contact-ion-paired compounds: (a)
Li2Cu2(C6H4CH2NMe2-2)4: van Koten, G.; J astrzebski, J . T. B. H.;
Muller, F.; Stam, C. H. J . Am. Chem. Soc. 1985, 107, 697. (b) Li2Cu2-
Ph4(OEt2)2: Lorenzen, N. P.; Weiss, E. Angew. Chem. 1990, 102, 322;
Angew. Chem., Int. Ed. Engl. 1990, 29, 300. (c) Li2Cu2Ph4(DMS)3:
Olmstead, M. M.; Power, P. P. J . Am. Chem. Soc. 1990, 112, 8008.
Examples for solvent-separated species: (d) [Cu(dppe)2][CuMes2] (dppe
) bis(diphenylphosphino)ethane): Leoni, P.; Pasquali, M.; Ghilardi.
C. A. J . Chem. Soc., Chem. Commun. 1983, 240. (e) [Li(thf)4][Cu-
(CH2SiMe3)2]: Eaborn, C.; Hitchcock, P. B.; Smith, J . D.; Sullivan, A.
C. J . Organomet. Chem. 1984, 263, C23. (f) [Li(12-crown-4)2][CuMe2]
or [CuPh2]: Hope, H.; Olmstead, M. M.; Power, P. P.; Sandell, J .; Xu,
X. J . Am. Chem. Soc. 1985, 107, 4337.
(4) (a) Li3(CuPh2)(CuPh3)(DMS)4 and Li5(CuPh2)3(CuPh3)(DMS)4:
see ref 3c. (b) Li6(OEt2)3Cu4(CCPh)10: Olbrich, F.; Kopf, J .; Weiss, E.
Angew. Chem. 1993, 105, 1136; Angew. Chem., Int. Ed. Engl. 1993,
32, 1077.
(5) (a) (CuC6H3CH2NMe2-2-Me-5)4: Guss, J M.; Mason, R.; Søtofte,
I.; van Koten, G.; Noltes, J . G. J . Chem. Soc., Chem. Commun. 1972,
446. (b) {CuCH(PPh2)2}3: Camus. A.; Marsich, N.; Nardin, G.; Ran-
daccio, L. J . Organomet. Chem. 1973, 60, C39. (c) (CuC6H4OMe-2)8:
Camus. A.; Marsich, N.; Nardin, G.; Randaccio, L. J . Organomet. Chem.
1979, 174, 121. (d) {CuC(SiMe3)2C5H4N-2}2: Papasergio, R. I.; Raston,
C. L.; White, A. H. J . Chem. Soc., Chem. Commun. 1983, 1419. (e)
(CuCHSiMe3C5H4N-2)4: Papasergio, R. I.; Raston, C. L.; White, A. H.
J . Chem. Soc., Dalton Trans. 1987, 3085. (f) (CuC10H6NMe2-8)4:
Wehman, E. van Koten, G.; Knotter, M.; Spelten, H.; Heijdenrijk, D.;
Mak, A. N. S.; Stam, C. H. J . Organomet. Chem. 1987, 325, 293. (g)
(CuOxl)2 (Oxl ) 2-(4,4-dimethyl-2-oxazolinyl)-5-methylphenyl): Weh-
man, E.; van Koten, G.; J astrzebski, J . T. B. H.; Rotteveel, M. A.; Stam,
C. H. Organometallics 1988, 7, 1477. (h) (CuC6H4CH2NMe2-2)4: cited
in ref 2d.
(1) (a) Ba¨hr, G.; Burba, P. Houben-Weyl Methoden der Organischen
Chemie; Mu¨ller, E., Ed.; Georg Thieme: Stuttgart, 1970; Vol. 13/1, pp
735-761. (b) Posner, G. H. An Introduction to Synthesis Using
Organocopper Reagents; Wiley: New York, 1980. (c) Taylor, R. J . K.,
Ed. Organocopper Reagents: A Practical Approach; Oxford University
Press: Oxford, 1994. (d) Lipshutz, B. H. In Comprehensive Organo-
metallic Chemistry; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon Press: Oxford, 1995; Vol. 12, Chapter 3.2.
(2) (a) van Koten, G. J . Organomet. Chem. 1990, 400, 283. (b) Power,
P. P. Progr. Inorg. Chem. 1991, 39, 75. (c) Holloway, C. E.; Melnik, M.
Rev. Inorg. Chem. 1995, 15, 147. (d) van Koten, G.; J ames, S. L.;
J astrzebski, J . T. B. H. In Comprehensive Organometallic Chemistry;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, 1995; Vol. 3, Chapter 2.
S0276-7333(98)00446-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/17/1998

4650 Organometallics, Vol. 17, No. 21, 1998
Niemeyer
182 and 185 °C. 1H NMR (C6D6): δ 6.85-7.17 (m, aryl-H).
13C NMR (C6D6): δ 124.3 (p-Ph), 126.2 (m-C6H3), 126.8 (o-Ph),
128.3 (p-C6H3), 128.8 (m-Ph), 147.6 (i-C6H3), 149.0 (i-Ph), 155.6
(o-C6H3). IR (Nujol, cm-1): 1949 w 1867 vw, 1798 vw, 1593
m, 1568 m, 1544 m, 1304 w, 1275 w, 1233 w, 1171 m, 1153 m,
1093 w, 1070 ms, 1025 ms, 974 w 963 w, 914 m, 841 m, 833
m, 804 s, 749 vs, 730 vs, 719 sh, 699 vs, 629 w, 612 s, 557 m,
533 m, 525 ms, 517 m, 483 w, 465 ms, 421 w, 394 ms, 363 w,
344 w, 331 w. MS (70 eV): m/z (%) 686.2 (1) [C54H38+], 458.2
(51) [C36H26+], 230.1 (100) [C18H14+], no Cu-containing fragment
detected. Anal. Calcd for C18H13Cu: C, 73.83; H, 4.47; Cu,
21.70. Found: C, 74.18; H, 4.76. Molar mass (cryoscopically
in C6H6, c ) 61.4 mmol/L, crystals of 2‚C6D6, obtained by
crystallization from benzene, were used) calcd for monomer
292.8; found 560.
(Cu C6H3Mes2-2,6)2 (3). A solution of LiC6H3Mes2-2,6 (0.96
g, 3.0 mmol) in 30 mL of pentane was added at ambient
temperature to CuOt-Bu (0.41 g, 3.0 mmol) in 10 mL of
n-pentane, and the mixture was stirred for 1 h. The formed
off-white precipitate was isolated by filtration over a glass filter
frit. Cooling of the filtrate to 0 °C afforded a small amount of
4 as colorless plates (0.08 g, 4%). The remaining solid was
extracted into toluene, and the resulting amber solution was
concentrated under reduced pressure. After cooling in a -25
°C freezer colorless crystals (0.62 g, 55%) of 3 were obtained.
Mp: crystals change color to orange at ca. 140 °C and
decompose to a brown liquid at 185 °C. 1H NMR (C6D6): δ
2.01 (o-CH3), 2.19 (p-CH3), 6.70 (m-Mes), 6.80 (d, m-C6H3), 7.12
(t, p-C6H3). 13C NMR (C6D6): δ 21.1 (o-CH3), 21.8 (p-CH3),
124.6 (m-C6H3), 126.6 (p-C6H3), 127.2 (m-Mes), 134.2 (o-Mes),
134.8 (p-Mes), 143.5 (i-Mes), 152.3 (o-C6H3), 159.6 (i-C6H3). IR
(Nujol, cm-1): 1723 vw, 1606 sh, 1579 m br, 1304 w, 1232 m,
1168 m, 1097 w, 1077 m, 1027 m, 1010 w, 887 w, 852 sh, 848
s, 794 s, 7735 w, 740 sh, 726 vs, 588 w, 571 m, 556 w, 545 w,
458 w, 329 m. MS (70 eV): m/z (%) 752.2 (95) [M+ (dimer)
with 63Cu], 377.1 (100) [M+/2+H with 63Cu], 376.1(54) [M+/2
(monomer) with 63Cu]. Anal. Calcd for C24H25Cu: C, 76.46;
H, 6.68; Cu, 16.86. Found: C, 75.87; H, 6.77; Cu, 16.50. Molar
mass (cryoscopically in C6H6, c ) 38.2 mmol/L) calcd for
monomer 377.0; found 440.
Mes2C6H3 is reported. Especially the latter has been
used successfully in the past few years for the stabiliza-
tion of low coordination numbers,10 compounds free of
Lewis donors,11 and new multiple-bond systems.12 It
is shown that the presence of these sterically encum-
bered ligands enables the isolation of previously un-
characterized types of lowly aggregated copper com-
pounds.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were performed by
using modified Schlenk techniques under an inert atmosphere
of purified argon. Solvents were freshly distilled under argon
from Na wire or LiAlH4. The compounds 2,6-Ph2C6H3I (1),13
14
(2,6-Mes2C6H3Li)2,11a and (CuOt-Bu)4 were synthesized by
known literature procedures. NMR spectra were recorded on
Bruker AM 200 and AC 250 spectrometers and referenced to
solvent resonances. IR spectra (Nujol mull, CsBr plates) were
obtained in the range 4000-200 cm-1 with a Perkin-Elmer
Paragon 1000 PC spectrometer.
(Cu C6H3P h 2-2,6)3 (2). CuOt-Bu (0.62 g, 4.53 mmol) was
added at ambient temperature to a solution of LiC6H3Ph2-2,6
in 60 mL of toluene, freshly prepared from n-BuLi (1.81 mL
hexane solution, 4.53 mmol) and 2,6-Ph2C6H3I (1.61 g, 4.53
mmol). The reaction was allowed to stir overnight, whereupon
the solvent was removed under reduced pressure. The re-
maining solid was extracted with ca. 20 mL of a n-hexane/
toluene (1:1) mixture. Cooling of the filtered solution in a -25
°C freezer afforded 2 as pale yellow polycrystalline material.
It was dried overnight by pumping at ca. 10-3 Torr to remove
cocrystallized toluene. Yield: 0.82 g (62%). Mp: crystals turn
gray at ca. 130 °C and decompose to a black liquid between
(6) (a) (CuMes)4(THT)2: Meyer, E. M.; Gambarotta, S.; Floriani, C.;
Chiesi-Villa, A.; Guastini, C. Organometallics 1989, 8, 1067. (b)
(CuPh)4(DMS)2: in ref 3c. (c) (CuC6H4Me-2)4(DMS)2: Lenders, B.;
Grove, D. M.; Smeets, W. J . J .; van der Sluis; P.; Spek, A. L.; van Koten;
G. Organometallics 1991, 10, 786. (d) (CuC6H2Ph3-2,4,6)2(DMS)2 and
(CuC6H2tBu3-2,4,6)(DMS): He, X.; Olmstead, M. M.; Power, P. P. J .
Am. Chem. Soc. 1992, 114, 9668. (e) (CuC6H3Trip2-2,6)(DMS) (Trip )
C6H2-i-Pr3-2,4,6): Schiemenz, B.; Power, P. P. Organometallics 1996,
15, 958.
(7) (a) (CuCH2SiMe3)4: J arvis, J . A. J .; Pearce, R.; Lappert, M. F.
J . Chem. Soc., Dalton Trans. 1977, 999. (b) (CuMes)5: see refs 6a and
7e. (c) (CuC6H2-i-Pr3-2,4,6)4: Nobel, D.; van Koten, G.; Spek, A. L.
Angew. Chem. 1989, 101, 211; Angew. Chem., Int. Ed. Engl. 1989, 28,
208. (d) (CuC6H4CHdCH2-2)4: Eriksson, H.; O¨ rtendahl, M.; Ha˚kans-
son, M. Organometallics 1996, 15, 4823. (e) (CuMes)4: Eriksson, H.;
Ha˚kansson, M. Organometallics 1997, 16, 4243. (f) (CuC6Me5)4: Eriks-
son, H.; Ha˚kansson, M. Inorg. Chim. Acta 1998, 277, 233.
LiCu (C6H3Mes2-2,6)2 (4). CuOt-Bu (0.28 g, 2.05 mmol) was
added at ambient temperature via a solids-addition tube to a
solution of LiC6H3Mes2-2,6 (1.31 g, 4.1 mmol) in 60 mL of
n-pentane. The mixture was allowed to stir overnight, where-
upon the volume was reduced to ca. 30 mL. The white
precipitate was separated by filtration over a glass filter frit
and washed two times with small portions of cold n-pentane.
Yield: 1.04 g (73%). Mp: crystals change color from yellow
to gray between 145 and 215 °C and decompose to a dark red
liquid between 215 and 220 °C. 1H NMR (C6D6): δ 1.92 (o-
CH3), 2.15 (p-CH3), 6.80 (m-Mes), 6.84 (d, m-C6H3), 7.17 (t,
p-C6H3). 13C NMR (C6D6): δ 21.1 (p-CH3), 22.0 (o-CH3), 124.6
(m-C6H3), 125.6 (p-C6H3), 128.5 (m-Mes), 135.1 (p-Mes), 136.5
(o-Mes), 146.5 (i-Mes), 151.1 (o-C6H3), 165.9 (i-C6H3); 7Li NMR
(C6D6): δ -8.3. IR (Nujol, cm-1): 1610 m, 1569 w, 1540 w,
1231 m, 1206 sh, 1168 w, 1094 w, 1075 m, 1029 m, 1010 m,
960 w, 866 m, 848 vs, 797 ms, 779 w, 755 w, 731 s, 715 ms,
576 m, 560 m, 547 m, 463 w. MS (70 eV): m/z (%) 752.3 (1.7)
(8) The copper compound CuC6H2Ph3-2,4,6 was reported to be
monomeric in the solid state: Lingnau, R.; Stra¨hle, J . Angew. Chem.
1988, 100, 409; Angew. Chem., Int. Ed. Engl. 1988, 27, 436. However,
this result has been contested, as the crystal used for the X-ray
structure determination seems to have contained
a considerable
amount of cocrystallized BrC6H2Ph3-2,4,6: Haaland, A.; Rypdal, K.;
Verne, H. P.; Scherer, W.; Thiel, W. R. Angew. Chem. 1994, 106, 2515;
Angew. Chem., Int. Ed. Engl. 1994, 33, 2443.
(9) Trinuclear heteroleptic copper complexes: (a) Cu3(Mes)(O2-
CC6H5)2: Aalten, H. L.; van Koten, G.; Goubitz, K.; Stam, C. H. J .
Chem. Soc., Chem. Commun. 1985, 1252. (b) Cu3(Mes)(SC6H4CH2-
NMe2-2-Cl-3)2(PPh3): Knotter, D. M.; Grove, D. M.; Smeets, W. J . J .;
Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 1992, 114, 3400. (c) Cu3-
Br(C6H4CH2N(Me)CH2CH2NMe2-2)2: cited in ref 2d.
(10) (a) Ellison, J . J .; Ruhlandt-Senge, K.; Hope, H.; Power, P. P.
Inorg. Chem. 1995, 34, 49. (b) Simons, R. S.; Pu, L.; Olmstead, M. M.;
Power, P. P. Organometallics 1997, 16, 1920. (c) Niemeyer, M.; Power,
P. P. Inorg. Chem. 1997, 36, 4688.
(11) (a) Ruhlandt-Senge, K.; Ellison, J . J .; Wehmschulte, R. J .;
Pauer, F.; Power, P. P. J . Am. Chem. Soc. 1993, 115, 11353. (b)
Niemeyer, M.; Power, P. P. Inorg. Chem. 1996, 35, 7264. (c) Niemeyer,
M.; Power, P. P. Organometallics 1997, 16, 3258.
7
[(CuAr)2+ with 63Cu], 696.3 (0.3) [M+ with 63Cu and Li], 689.3
(1.1) [CuAr2 with 63Cu], 314.1(100) [Ar+]. Anal. Calcd for
+
C
48H50CuLi: C, 82.66; H, 7.22; Cu, 9.11; Li, 0.99. Found: C,
82.80; H, 7.32.
Rea ction of 3 a n d 4 w ith Oxygen . A solution of 3 in
toluene was stirred at ambient temperature for ca. 4 h under
an atmosphere of dry oxygen. The solvent was removed under
reduced pressure, and the dark brown residue was treated
with a mixture of 5% hydrochloric acid and diethyl ether. The
organic layer was separated, dried over K2CO3, and filtered,
whereupon the solvent was removed in vacuum. The re-
maining material was shown by NMR spectroscopy to consist
of HOC6H3Mes2-2,6 (68%) and C6H4Mes2-1,3 (32%).11c In a
(12) (a) Li, X.-W.; Pennington, W. T.; Robinson, G. H. J . Am. Chem.
Soc. 1995, 117, 7578. (b) Simons, R. S.; Power, P. P. J . Am. Chem.
Soc. 1996, 118, 11966. (c) Olmstead, M. M.; Pu, L.; Simons, R. S.;
Power, P. P. Chem. Commun. 1997, 1595. (d) Olmstead, M. M.; Simons,
R. S.; Power, P. P. J . Am. Chem. Soc. 1997, 119, 11705.
(13) Saednya, A.; Hart, H. Synthesis 1996, 1455.

σ-Carbon versus π-Arene Interactions
Organometallics, Vol. 17, No. 21, 1998 4651
Ta ble 1. Selected Cr ysta llogr a p h ic Da ta for Com p ou n d s 1-4a
1
2‚C6D6
3
4b
formula
fw
C18H13
356.2
I
C60H39Cu3D6
962.7
C48H50Cu2
754.0
C96H100Cu2.09Li1.91
1400.0
color, habit
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
colorless, plate
0.50 × 0.50 × 0.08
monoclinic
P21/c
9.472(4)
7.178(3)
pale yellow, block
0.60 × 0.35 × 0.25
monoclinic
P21/c
23.211(4)
10.475(2)
colorless, plate
0.45 × 0.22 × 0.05
triclinic
P1h
10.009(3)
11.328(4)
17.650(6)
103.34(3)
99.34(3)
97.08(3)
1894(1)
2
1.322
11.55
3-50
6672
4528
511
0.0591
0.1423
colorless, plate
1.00 × 0.60 × 0.10
monoclinic
P21/c
10.701(2)
37.010(7)
21.966(6)
19.862(5)
19.474(4)
95.06(3)
111.96(2)
94.20(3)
1487.6(9)
4
1.590
21.36
3-54
3168
2617
221
0.0372
0.0958
1.193
0.88/-0.84
4479(2)
4
1.419
14.52
3-54
9188
6137
772
0.0450
0.1096
1.010
0.56/-0.46
7692(3)
4
1.209
6.25
2-48
12 090
7224
Z
d
calc (g/cm3)
µ (cm-1
)
2θ range (deg)
unique data
data with I >2σ(I) (No)
no. of params (Np)
R1 (I > 2σ(I))c
wR2 (all data)d
GOFe
1024
0.0643
0.1368
1.198
0.54/-0.38
1.135
0.83/-0.52
resd dens (e/Å3)
a
b
All data were collected at 173 K using Mo KR (λ ) 0.710 73 Å) radiation. Two independent molecules; for Cu/Li disorder see
experimental part. c R1 ) ∑(||Fo| - |(Fc||)/∑(|Fo|. wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
e GOF ) {∑[w(Fo - Fc2)2]/(No - Np)}1/2
.
d
2
2
Sch em e 1. Syn th esis of Com p ou n d s 2-4
similiar experiment the oxidation of 4 yielded a mixture of 55%
ROH and 45% RH. NMR data for HOC6H3Mes2-2,6: 1H NMR
(C6D6) δ 2.11 (o-CH3), 2.17 (p-CH3), 6.84 (m-Mes), 6.93 (d,
m-C6H3), 6.93 (t, p-C6H3). 13C NMR (C6D6) δ 20.5 (o-CH3), 21.1
(p-CH3), 121.0 (p-C6H3), 128.8 (m-Mes), 129.9 (m-C6H3), 133.9
(i-Mes), 137.1 (o-Mes), 137.2 (p-Mes), 150.3 (i-C6H3).
X-r a y Cr ysta llogr a p h y. X-ray-quality crystals were ob-
tained as described in the Experimental Section. Crystals
were removed from Schlenk tubes and immediately covered
with a layer of viscous hydrocarbon oil (Paratone N, Exxon).
A suitable crystal was selected, attached to a glass fiber, and
instantly placed in a low-temperature N2-stream.15 All data
were collected at 173 K using either a Syntex P21 (1, 3, 4) or
a Siemens P4 (2) diffractometer. Crystal data are given in
Table 1. Calculations were carried out with the SHELXTL
PC 5.0316a and SHELXL-9716b program systems installed on
a local PC. The structures were solved by direct methods and
groups. Their isotropic thermal parameters were either al-
lowed to refine or constrained to 1.2 (aryl H) or 1.5 (methyl
groups) times Ueq of the bonded carbon. Final R values are
listed in Table 1. Important bond distances and angles are
given in Table 2. Further details are provided in the Sup-
porting Information.
Resu lts a n d Discu ssion
Syn th esis. The preparation of organocopper com-
pounds of the type RCu usually involves the reaction of
a copper(I) halide with an organolithium or -magnesium
reagent in donor solvents such as Et2O, THF, or DMS.
A commonly encountered problem of this method is the
contamination of the desired copper compounds with
lithium or magnesium halides and the formation of
stable mixed organocopper copper halide aggregates.2d
Therefore, it seemed advantageous to us to use copper
tert-butoxide as a halide-free starting material.18 The
good solubility of this complex permitted the reaction
with lithium aryls in nonpolar solvents such as n-
pentane or toluene according to Scheme 1. Thus, the
pale yellow CuC6H3Ph2-2,6 (2) and the colorless complex
CuC6H3Mes2-2,6 (3) were obtained in moderate yields
of 62 and 55%, respectively. They show considerable
thermal stability with decomposition points in the range
130-185 °C. The lithium cuprate LiCu(C6H3Mes2-2,6)2
(4) was synthesized in good yield of 73% by the reaction
of CuOt-Bu with 2 equiv of LiC6H3Mes2-2,6. Com-
pounds 2-4 are air sensitive and possess good solubility
2
refined on Fo by full-matrix least-squares refinement. An
absorption correction was applied by using semiempirical
ψ-scans (2, 3) or the program XABS217 (1, 4). Anisotropic
thermal parameters were included for all non-hydrogen atoms.
The C atoms of the solvate benzene in 2 showed rotational
disorder (occupancy 0.5/0.5) and were constrained to a regular
hexagon. The copper atom Cu(3) in 2 is disordered and was
sucessfully modeled with two split positions (occupancy 0.93/
0.07). The preliminary refinement of 4 revealed a substantial
residue electron density (2.3 e/Å3) in one of the two indepen-
dent molecules. This Fourier peak was assigned to a partially
occupied (0.092) copper atom of a cocrystallizing copper cuprate
moiety. The corresponding lithium atom Li(2) was refined
with a site occupation factor of 0.908. Positions and isotropic
thermal parameters for most H atoms in 1 and 2 were allowed
to refine. All other H atoms were placed geometrically and
refined using a riding model, including free rotation of methyl
(14) (a) Tsuda, T.; Hashimoto, T.; Saegusa, T. J . Am. Chem. Soc.
1972, 94, 658. (b) Brussaard, Y.; Olbrich, F.; Behrens, U. J . Organomet.
Chem. 1996, 519, 115.
(15) Hope, H. Progr. Inorg. Chem. 1995, 41, 1.
(16) (a) SHELXTL PC 5.03; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1994. (b) Sheldrick, G. M. SHELXL-97, Program
for Crystal Structure Solution and Refinement; University of Go¨ttin-
gen, Germany, 1997.
(18) The use of metal tert-butoxides for the preparation of alkyl or
aryl compounds of the heavier alkali metals is well-known: Lochmann,
L.; Posp´ısˇil, J .; L´ım, D. Tetrahedron Lett. 1966, 257.
(17) Parkin, S. R.; Moezzi, B.; Hope, H. J . Appl. Crystallogr. 1995,
28, 53.

4652 Organometallics, Vol. 17, No. 21, 1998
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Com p ou n d s 1-4
Niemeyer
Compound 1
I-C(1)
2.122(4)
1.393(5)
1.404(5)
1.399(6)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.379(6)
1.391(6)
1.398(6)
C(1)-C(2)
C(1)-C(6)
C(2)-C(3)
C(2)-C(1)-C(6)
C(2)-C(1)-I
122.5(3)
118.9(3)
C(6)-C(1)-I
118.6(3)
Compound 2‚C6D6
Cu(1)-C(1)
Cu(1)-C(19)
Cu(2)-C(19)
Cu(2)-C(37)
Cu(3)-C(1)
Cu(3)-C(43)
Cu(3)-C(44)
Cu(1)‚‚‚Cu(2)
Cu(1)‚‚‚Cu(3)
Cu(2)‚‚‚Cu(3)
C(1)-C(2)
2.047(3)
1.989(3)
2.085(3)
1.924(3)
1.989(4)
2.158(3)
2.232(4)
2.3758(7)
2.4224(10)
2.9136(11)
1.428(5)
1.421(5)
1.393(5)
1.381(6)
1.374(6)
1.405(5)
1.392(5)
1.403(5)
1.395(6)
1.401(6)
C(19)-C(20)
C(19)-C(24)
C(20)-C(21)
C(21)-C(22)
C(22)-C(23)
C(23)-C(24)
C(25)-C(26)
C(25)-C(30)
C(31)-C(32)
C(31)-C(36)
C(37)-C(38)
C(37)-C(42)
C(38)-C(39)
C(39)-C(40)
C(40)-C(41)
C(41)-C(42)
C(43)-C(48)
C(43)-C(44)
C(49)-C(54)
C(49)-C(50)
1.418(5)
1.421(5)
1.404(5)
1.380(6)
1.386(6)
1.408(5)
1.395(5)
1.401(5)
1.399(5)
1.398(5)
1.425(5)
1.426(5)
1.403(5)
1.383(6)
1.376(6)
1.399(5)
1.408(5)
1.416(5)
1.396(5)
1.401(6)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(7)-C(8)
C(7)-C(12)
C(13)-C(18)
C(13)-C(14)
C(19)-Cu(1)-C(1)
C(19)-Cu(2)-C(37)
C(1)-Cu(3)-C(43)
C(1)-Cu(3)-C(44)
C(1)-Cu(3)‚‚‚X
Cu(3)-C(1)-Cu(1)
Cu(1)-C(19)-Cu(2)
C(6)-C(1)-C(2)
C(6)-C(1)-Cu(3)
C(2)-C(1)-Cu(3)
C(6)-C(1)-Cu(1)
C(2)-C(1)-Cu(1)
C(1)-C(2)-C(7)
170.83(14)
171.32(14)
162.96(14)
159.4(2)
177.5
73.77(12)
71.30(11)
117.2(3)
130.2(3)
111.6(2)
90.7(2)
C(1)-C(6)-C(13)
121.0(3)
121.7(3)
121.0(3)
116.6(3)
130.1(3)
111.6(2)
96.1(2)
118.3(2)
115.4(3)
125.9(3)
117.8(2)
121.7(3)
119.9(3)
C(19)-C(20)-C(25
C(19)-C(24)-C(31)
C(20)-C(19)-C(24)
C(20)-C(19)-Cu(1)
C(24)-C(19)-Cu(1)
C(20)-C(19)-Cu(2)
C(24)-C(19)-Cu(2)
C(38)-C(37)-C(42)
C(38)-C(37)-Cu(2)
C(42)-C(37)-Cu(2)
C(37)-C(38)-C(43)
C(37)-C(42)-C(49)
118.9(2)
120.6(3)
Compound 3
Cu(1)-C(1)
Cu(1)-C(31)
Cu(1)-C(32)
Cu(2)-C(25)
Cu(2)-C(7)
Cu(2)-C(8)
Cu(1)‚‚‚Cu(2)
C(1)-C(2)
1.927(5)
2.295(4)
2.123(4)
1.921(4)
2.220(4)
2.160(4)
2.5953(12)
1.398(6)
1.406(7)
1.391(6)
1.384(7)
1.385(7)
1.395(7)
1.420(7)
C(7)-C(8)
1.430(6)
1.394(7)
1.411(6)
1.398(6)
1.420(6)
1.389(7)
1.392(7)
1.379(7)
1.385(7)
1.417(7)
1.421(7)
1.398(7)
1.403(7)
C(16)-C(21)
C(16)-C(17)
C(25)-C(30)
C(25)-C(26)
C(26)-C(27)
C(27)-C(28)
C(28)-C(29)
C(29)-C(30)
C(31)-C(32)
C(31)-C(36)
C(40)-C(41)
C(40)-C(45)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(7)-C(12)
C(1)-Cu(1)-C(31)
C(1)-Cu(1)-C(32)
C(1)-Cu(1)-X1
C(25)-Cu(2)-C(7)
C(25)-Cu(2)-C(8)
C(25)-Cu(2)-X2
168.1(2)
154.7(2)
174.0
170.6(2)
151.2(2)
170.5
C(2)-C(1)-C(6)
116.6(4)
123.3(4)
119.9(3)
116.3(4)
122.7(3)
121.0(3)
C(2)-C(1)-Cu(1)
C(6)-C(1)-Cu(1)
C(30)-C(25)-C(26)
C(26)-C(25)-Cu(2)
C(30)-C(25)-Cu(2)
Compound 4
Molecule 1
Li(1)-C(7)
Li(1)-C(8)
Li(1)-C(9)
Li(1)-C(10)
Li(1)-C(11)
Li(1)-C(12)
2.462(10)
2.468(11)
2.521(11)
2.600(9)
2.550(11)
2.495(11)
Li(1)-C(25)
Li(1)-C(26)
Li(1)-C(31)
Cu(1)-C(1)
Cu(1)-C(25)
Li(1)‚‚‚Cu(1)
2.312(10)
2.704(10)
2.780(12)
1.922(5)
1.957(5)
2.400(8)
C(1)-Cu(1)-C(25)
C(2)-C(1)-C(6)
C(26)-C(25)-C(30)
C(2)-C(1)-Cu(1)
171.1(2)
115.3(4)
114.9(4)
116.2(3)
C(6)-C(1)-Cu(1)
C(26)-C(25)-Cu(1)
C(30)-C(25)-Cu(1)
128.4(3)
126.3(4)
118.1(3)

σ-Carbon versus π-Arene Interactions
Organometallics, Vol. 17, No. 21, 1998 4653
Ta ble 2 (Con tin u ed )
Compound 4
Molecule 2
Li(2)-C(55)
Li(2)-C(56)
Li(2)-C(57)
Li(2)-C(58)
Li(2)-C(59)
Li(2)-C(60)
2.529(11)
2.519(12)
2.528(12)
2.574(12)
2.552(14)
2.557(14)
Li(2)-C(73)
2.447(12)
2.569(14)
2.515(14)
1.925(5)
1.945(5)
2.429(11)
Li(2)-C(79)
Li(2)-C(80)
Cu(2)-C(49)
Cu(2)-C(73)
Li(2)‚‚‚Cu(2)
C(49)-Cu(2)-C(73)
C(54)-C(49)-C(50)
C(74)-C(73)-C(78)
C(50)-C(49)-Cu(2)
173.8(2)
115.2(5)
114.8(4)
116.6(4)
C(54)-C(49)-Cu(2)
C(74)-C(73)-Cu(2)
C(78)-C(73)-Cu(2)
128.1(4)
122.6(4)
120.4(4)
Copper cuprate
Cu(3)-C(60)
Cu(3)-C(59)
2.065(8)
2.244(8)
Cu(3)-C(73)
Cu(2)‚‚‚Cu(3)
2.250(8)
2.260(7)
C(60)-Cu(3)-C(73)
C(59)-Cu(3)-C(73)
151.8(4)
169.9(4)
X-Cu(3)-C(73)
171.6
in aromatic solvents such as benzene or toluene, but are
almost insoluble in aliphatic hydrocarbons. The reac-
tion of organocopper compounds with molecular oxygen
has been studied before19 to give biaryls, arenes, and
diaryl ethers as main products. Similarly, oxidation of
mesitylcopper(I) has resulted in the isolation of the
intermediate Cu10O2Mes6.20 In contrast, the reaction
between toluene solutions of compound 3 or 4 and dry
oxygen affords the hitherto unknown phenol HOC6H3-
Mes2-2,6 in a NMR yield of 68 or 55%.
Solid -Sta te Str u ctu r es. The new compounds 2-4
and the starting material IC6H3Ph2-2,6 (1) were char-
acterized by X-ray crystallography. The structure of 1
reveals no unusual features. The C-I bond length of
2.122(4) Å is very similiar to the values found for other
aryl iodides.21 Dihedral angles of 81.8° and 84.5° are
observed between the ortho phenyl substituents and the
central C6H3 ring.
F igu r e 1. Molecular structure of 2, showing 30% thermal
ellipsoids and the numbering scheme. Hydrogen atoms
have been omitted for clarity.
Pale yellow crystals of 2‚C6D6, suitable for X-ray
crystallographic studies, were grown from a saturated
C6D6 solution at ambient temperature. The molecular
structure consists of trimeric units with a central Cu3
core (Figure 1). The trimers possess no crystallographi-
cally imposed symmetry, and there are no close interac-
tions with the cocrystallized C6D6 molecule. The copper
atoms are bridged by the terphenyl ligands in two
different coordination modes. Two of the ligands coor-
dinate via their ipso C6H3 carbon atoms C(1) and C(19)
to the copper atoms Cu(1), Cu(3) and Cu(1), Cu(2),
respectively. The third terphenyl group acts as a
bidentate bridging unit between two copper atoms. It
binds to Cu(2) by the ipso C6H3 carbon C(37), while the
bridging to Cu(3) is accomplished by a η2-π-arene
interaction to the ipso and ortho phenyl carbons C(43)
and C(44). The different coordination is reflected by the
dihedral angles of the C(1), C(19), and C(37) C6H3 rings
to the central Cu3 plane with values of 84.2°, 66.2°, and
34.1°, respectively. The displacements of the coordinat-
ing atoms C(1) (0.809 Å), C(19) (-0.493 Å), C(37) (0.555
Å), C(43) (-0.273 Å), and C(44) (-1.566 Å) show an
alternating arrangement below and above the Cu(1)-
Cu(2)Cu(3) plane (Figure 2). Some important bond
parameters together with a view perpendicular to the
F igu r e 2. View of 2 along the central Cu3 plane. Five ortho
phenyl groups and hydrogen atoms have been omitted for
clarity.
Cu3 plane are depicted in Figure 3. The copper atoms
are almost linearly coordinated (C(1)-Cu(1)-C(19) )
170.8(1)°, C(19)-Cu(2)-C(37)
) 171.3(1)°, C(1)-
Cu(3)-X ) 177.5°, where X ) midpoint of C(43)-C(44)).
With values of 1.924(3)-2.085(3) the Cu-Cipso bond
lengths fall in the range of those reported for other aryl
copper compounds.2d Shorter Cu(3)-C(1) and Cu(1)-
C(19) distances and larger Cu(3)-C(1)-C(4) and Cu-
(1)-C(19)-C(22) angles alternate with larger and smaller
values for Cu(1)-C(1), Cu(2)-C(19), and Cu(1)-C(1)-
(19) Camus, A.; Marsich, N. J . Organomet. Chem. 1972, 46, 385.
(20) Ha˚kansson, M.; O¨ rtendahl, M.; J agner, S.; Sigalas, M. P.;
Eisenstein, O. Inorg. Chem. 1993, 32, 2018.
(21) Recherche in Cambridge Structural Database: Allen, F. H.;
Kennard, O. Chem. Des. Autom. News 1993, 8, 31.

4654 Organometallics, Vol. 17, No. 21, 1998
Niemeyer
F igu r e 3. View of 2 perpendicular to the central Cu3 plane
showing important bond distances (Å) and angles (deg).
Four ortho phenyl groups and hydrogen atoms have been
omitted for clarity.
F igu r e 4. Molecular structure of 3, showing 30% thermal
ellipsoids and the numbering scheme. Hydrogen atoms
have been omitted for clarity.
the dimeric product (CuC6H3Mes2-2,6)2, as depicted in
Figure 4. The planes of the central C6H3 rings show a
dihedral angle of 60.0°. Both aryl groups act as biden-
tate ligands, with the bridging performed by an ipso aryl
carbon and two ipso or ortho carbon atoms of an
adjacent mesityl group. With Cipso-Cu-X angles of
174.0° and 170.5°, respectively, where X defines the
midpoint of the C(31)-C(32) or C(7)-C(8) bonds, the
coordination of the copper atoms is pseudolinear. The
Cu(1)-C(1) and Cu(2)-C(25) distances of 1.927(5) and
1.921(4) Å are almost identical to the Cu(2)-C(37) bond
length observed in 2. In addition, the η2-copper-arene
interactions of 2.123(4)-2.295(4) Å (av 2.200 Å) are very
similar to those in 2. The different Cu-Cipso-Cortho
angles of 119.9°/123.3° and 122.7°/121.0° and the
Cu(1)‚‚‚Cu(2) distance of 2.5953(12) can be interpreted
in terms of a relatively stronger η2-copper-arene coor-
dination compared to the weaker copper‚‚‚copper inter-
action.25 Presumably, the alternative of a η1-copper-
C(4), Cu(2)-C(19)-C(22), respectively (Figure 3). There-
fore, the bonding situation can be interpreted as an
alternating 2e-2c Cipso-Cu and π-type Cipso-Cu interac-
tion. This kind of coordination has been noted before
in (CuC6H2-i-Pr3-2,4,6)4,7c whereas a more symmetrical
2e-3c Cipso-Cu bonding was observed in (CuMes)5,7b
(CuMes)4,7e and (CuC6H4CHdCH2-2)4.7d The slightly
longer Cu(3)-C(43) (2.158(3) Å) and Cu(3)-C(44) (2.232-
(4) Å) η2-arene interactions are unique in aryl copper
chemistry.22 However, a similiar CdC π-coordination
with Cu-C distances of 2.03-2.24 Å has been observed
in the anionic cuprates [Cu5(C6H4CHdCH2-2)2Br4]- and
[Cu5(C6H4CHdCH2-2)4Br2]-,7d in the phenoxide Cu4-
(OC6H4CH2CHdCH2-2)4,23 in the alkoxide Cu6(OCMe2-
CHdCH2)6,23 and in olefin and diene complexes of
copper(I) halides.24 It is noteworthy that tetrameric
o-vinylphenylcopper7d shows no π-coordination in the
solid state and in THF solution. The good quality of
the structure determination allows a comparison be-
tween the length of the coordinated C(43)-C(44) bond
(1.416(5) Å) and the uncomplexed C(ipso phenyl)-
C(ortho phenyl) distances (average 1.398 Å). With
values of 2.3758(7), 2.4224(10), and 2.9136(11) Å, re-
spectively, the rather different copper‚‚‚copper interac-
tions25 in 2 are of the same magnitude as previously
observed in other aryl copper compounds.2d
C
ipso(arene) coordination, which should result in a
shorter Cu-Cu distance, seems to be less advantageous.
Colorless plates of the lithium cuprate 4, suitable for
X-ray crystallographic studies, were grown from a
saturated n-pentane solution at 5 °C. It crystallizes as
contact ion paired monomers with two independent
molecules in the asymmetric unit, as shown in Figure
5 for molecule 1. Compound 4 is the first example of a
neutral monomeric cuprate with simple LiCuR2 stoi-
chiometry. Earlier reports of lithium diaryl cuprates
are limited to dimeric complexes3a-c or monomeric
solvent separated anionic species.3d,f Significant differ-
ences in the coordination of the lithium cation and the
arrangement of the aryl ligands justify a separate view
of both independent molecules. Interplanar angles of
77.3° (molecule 1) and 85.0° (molecule 2) are observed
between the central C6H3 rings of the aryl substituents.
The coordination of Li(1) can be described as η1, η6 with
the lithium atom interacting most strongly with one ipso
C6H3 terphenyl carbon (Li(1)-C(25) 2.312(10) Å) and
Colorless, X-ray-quality crystals of 3 were obtained
from toluene at 0 °C. Increasing the size of the aryl
substituent from 2,6-Ph2C6H3 to 2,6-Mes2C6H3 leads to
(22) Arene-copper(I) interactions as in (C6H6)CuAlCl4 have been
known for a long time, however: Turner, R. W.; Amma, E. L. J . Am.
Chem. Soc. 1966, 88, 1877.
(23) Ha˚kansson, M.; Lopes, C.; J agner, S. Organometallics 1998,
17, 210.
(24) See for example: (a) Ha˚kansson, M.; J agner, S. J . Organomet.
Chem. 1990, 397, 383. (b) Ha˚kansson, M.; Wettstro¨m, K.; J agner, S.
J . Organomet. Chem. 1991, 421, 347. (c) Ha˚kansson, M.; J agner, S.;
Walther, D. Organometallics 1991, 10, 1317; and the examples cited
in: Camus, A.; Marsich, N.; Nardin, G.; Randaccio, L. Inorg. Chim.
Acta 1977, 23, 131.
(25) Pyykko¨, P. Chem. Rev. 1997, 97, 597.

σ-Carbon versus π-Arene Interactions
Organometallics, Vol. 17, No. 21, 1998 4655
F igu r e 5. Molecular structure of molecule 1 in 4, showing
30% thermal ellipsoids and the numbering scheme. Hy-
drogen atoms have been omitted for clarity.
F igu r e 6. Molecular structure of the cocrystallized copper
cuprate moiety in molecule 2 of compound 4, showing 30%
thermal ellipsoids and the numbering scheme. Hydrogen
atoms have been omitted for clarity. The side occupation
factor for Cu(3) is 0.092. The lithium atom Li(2) of the main
LiCuR2 component is not shown.
with six mesityl carbon atoms of the second aryl group
(2.462(10)-2.600(9) Å, av 2.516 Å). Additional weaker
contacts of 2.704(10) and 2.780(12) Å are observed to
the ortho C6H3 carbon C(26) and the ipso mesityl carbon
C(31). In the case of molecule 2 the lithium atom Li(2)
is bonded in a η3, η6 fashion. It is coordinated to the
ipso C6H3 carbon C(73) (2.447(12) Å), the ipso and ortho
mesityl carbons C(79) and C(80) (2.569(14) and 2.515-
(14) Å), and to six mesityl carbon atoms of the adjacent
terphenyl ligand (2.519(12)-2.574(12) Å, av 2.543 Å).
η6-π-interactions of Li ions to arene rings are known26,27
and usually cover a range of 2.31-2.46 Å, but may be
as large as 2.57 Å.11b The relatively large values in 4
can be explained by steric crowding and the higher
coordination of the lithium atoms taking into account
the additional relatively short Li‚‚‚Cu contacts of 2.400-
(8) and 2.429(11) Å, respectively. The copper-carbon
distances of 1.922(5), 1.957(5) (molecule 1) and 1.925-
(5), 1.945(5) Å (molecule 2) are close to the values found
for other lithium diaryl cuprates.2b The longer bonds
to the carbon atoms C(25) and C(73) are consistent with
the interactions of those atoms to the lithium centers.
A notable feature of the structure of 4 is the presence
of cocrystallized CuC6H3Mes2-2,6, as already mentioned
in the Experimental Section. This is in accordance with
NMR spectroscopic data for solutions of crystalline
material, which always show signals for the copper aryl
3 in a ratio of less than 5%. In contrast to the dimeric
structure observed for 3, the cocrystallized CuC6H3Mes2-
2,6 species in the crystal structure of 4 can be best
described as a copper cuprate moiety Cu[CuR2] (Figure
6). The formally cationic Cu(3) is coordinated in a η1,
η2 fashion with the copper atom interacting almost
equally with the ipso C6H3 aryl carbon (Cu(3)-C(73)
2.250(8) Å) and with an ortho and meta carbon of an
opposite mesityl group. The copper-arene interactions
of 2.065(8) and 2.244(8) Å are comparable to those in 2
and 3. With an Cipso-Cu-X angle of 171.6, where X
defines the midpoint of the C(59)-C(60) bond, the
coordination of the copper atom is pseudolinear.
Ta ble 3. Selected In ter - a n d In tr a m olecu la r
Con ta cts (Å) for Com p ou n d s 2-4a ,b
Compound 2
C(4)‚‚‚C(44)′
C(5)‚‚‚C(29)′
C(11)‚‚‚C(51)′′
C(15)‚‚‚C(28)′′′
3.637
3.632
3.584
3.499
X(31-36)‚‚‚H(47a)′′′′
X(13-18)‚‚‚H(26a)
X(25-30)‚‚‚H(44a)
2.68
2.81
2.78
Compound 3
C(3)‚‚‚C(44)′
C(9)‚‚‚C(32)′′
3.636
3.605
C(9)‚‚‚C(33)′′
C(29)‚‚‚C(29)′′′
3.404
3.642
Compound 4
C(4)‚‚‚C(42)′
C(18)‚‚‚C(85)′′
3.590
3.513
C(19)‚‚‚C(85)′′
C(23)‚‚‚C(95)′′′
3.503
3.592
a
Atoms marked by primes are generated by the following
symmetry operations. (′): x, 1+y, z. (′′): 1-x, 0.5+y, 0.5-z. (′′′):
-x, -y, -z. (′′′′): x, 0.5-y, 0.5+z for 2. (′): -x, 2-y, 1-z. (′′): 1+x,
y, z. (′′′): -x, 1-y, 2-z for 3. (′): 1+x, y, z. (′′): x, y, -1+z. (′′′):
b
-1+x, 0.5-y, +z for 4. X(nn-mm) defines the centroid of the C(nn)-
C(mm) plane.
To verify the low degree of aggregation in compounds
2-4, a few intermolecular contacts are stated in Table
3. No intermolecular distances shorter than 4.5 Å
between copper or lithium centers and carbon atoms are
observed. An interesting feature in compound 2 is the
presence of a relatively short C-H π-contact28 of 2.68
Å, which involves the midpoint of the aromatic C(31)-
C(36) plane and an adjacent H(47a)′ hydrogen atom
generated by the symmetry operation (x, 0.5-y, 0.5+z).
In addition, slightly longer intramolecular C-H π-dis-
tances of 2.78 and 2.81 Å are found between the
hydrogen atoms H(44a) or H(26a) and the centers of the
C(25)-C(30) and C(13)-C(18) planes, respectively.
Cr yoscop y a n d Sp ectr oscop y. The good solubility
of compounds 2 and 3 allowed the cryoscopic determi-
nation of the molecular mass in benzene. A value of
560 g mol-1 was obtained for CuC6H3Ph2-2,6 (calculated
for monomer, 293 g mol-1). This can be interpreted in
terms of either a dimeric association or an equilibrium
of mono-, di-, and trimeric species in solution. The
molecular mass determination for CuC6H3Mes2-2,6
yielded a value of 440 g mol-1, whereas M ) 377 g mol-1
would be expected for monomeric 3. This is consistent
(26) (a) Pilz, M.; Allwohn, J .; Willershausen, P.; Massa, W.; Berndt,
A. Angew. Chem. 1990, 102, 1085; Angew. Chem., Int. Ed. Engl. 1990,
29, 1032. (b) Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M.
M.; Power, P. P. Inorg. Chem. 1991, 30, 2487. (c) Kurz, S.; Hey-
Hawkins, E. Organometallics 1992, 11, 2729. (d) Schiemenz, B.; Power,
P. P. Angew. Chem. 1996, 108, 2288; Angew. Chem., Int. Ed. Engl.
1996, 35, 2150. See also ref 11a.
(28) Braga, D.; Grepioni, F.; Tedesco, E. Organometallics 1998, 17,
(27) Tacke, M. Eur. J . Inorg. Chem. 1998, 537.
2669.

4656 Organometallics, Vol. 17, No. 21, 1998
Niemeyer
with an association of ca. 1.2 and the presence of
monomers and dimers in benzene. In the mass spectrum
of 3 intense signals of monomeric (basis peak) and
dimeric units (rel intensity of 95%) are observed. This
may be contrasted with the mass spectra of products 2
and 4, which showed either no copper-containing frag-
ments or a molecular mass peak of low intensity.
is very close to that found for lithium cyclopentadien-
ide.29 This high-field shift is consistent with a well-
shielded lithium ion caused by the aromatic ring current
of the η6-coordinated arene.
Ack n ow led gm en t. The author wishes to thank
Prof. Gerd Becker for generous support and Mrs. J a
Young Lee for the help in preparing compound 2.
1
Compounds 2-4 were also characterized by H and
13C NMR spectroscopy. No dynamic character was
observed for 2 and 3 in the range from -70 to 80 °C in
toluene-d8 solution. This is in agreement with the fast
conversion of different mono-, di-, and trimeric species
even at low temperatures. Relatively sharp resonances
of 147.6 (2) and 159.6 ppm (3) were observed in the 13C
NMR for the ipso C6H3 carbons. A chemical shift of
165.9 ppm was found for the corresponding carbon in
the cuprate 4. This lies somewhere in the middle of the
values reported for the lithium aryl LiC6H3Mes2-2,6
(173.5 ppm)11a and the copper aryl 3. The 7Li NMR
chemical shift of -8.3 ppm differs greatly from the value
observed for the parent lithium aryl (+2.58 ppm)11a but
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, data collection, solution, and refinement parameters,
atomic coordinates, bond distances and angles, anisotropic
displacement coefficients, hydrogen atom coordinates, and
additional structure plots (48 pages). Ordering information
is given on any current masthead page.
OM980446C
(29) The chemical shift of LiCp in THF solution is observed at -8.37
ppm: Gu¨nther H. High Resolution 6,7Li NMR of Organometallic
Compounds. In Advanced Applications of NMR to Organometallic
Chemistry; Gielen, M., Willem, R., Wrackmeyer, B., Eds.; J ohn Wiley:
Chichester, 1996; Chapter 9.