Novel copper(I) complexes containing 1,1′-bis(diphenylphosphino)ferrocene (dppf) as a chelate and bridging ligand: Synthesis of tetrabridged dicopper(I) complexes [Cu2(μ-η1-C≡R)2(μ-dppf) 2] and X-ray crystal structure

Article abstract of DOI:10.1021/om980592i

Binuclear copper(I) complexes [Cu(κ²-P,P-dppf)(CH₃CN)₂][BF₄] (1), [Cu(κ²-P,P-dppf)(bipy)]-[BF₄] (2) containing the chelating dppf ligand (dppf = 1,1′-bis(diphenylphosphino)ferrocene) have been prepared by substitution reactions of the acetonitrile ligands from the complexes [Cu(CH₃CN)₄][BF₄] and (1) with dppf and bipy, respectively. Similarly, the treatment of the complex [Cu₂(μ-dppm)₂(CH₃CN)₂][BF ₄]₂ with dppf in CH₂Cl₂ at room temperature gives the tetranuclear complex [Cu₂(μ-dppm)₂(κ²-P,P-dppf) ₂][BF₄]₂ (3). The analogous bridging chloride tetranuclear complex [Cu₂(μ-Cl)₂(κ²-P,P-dppf)₂] (4) has been also prepared by the addition of dppf to a solution in THF containing an equimolar mixture of CuCl and tetramethylethylenediamine. Complex 4 has been used as a precursor for μ-η¹-alkynyl bridging dicopper(I) complexes containing the framework [Cu₂(μ-dppf)₂]. Complexes [Cu₂(μ-η¹-C≡CR)₂(μ-dppf) ₂] (R = C₆H₄CH₃-4 (5), C₆H₅ (6), CH₂OCH₃ (7), CH₂CH₂CH₃ (8), (η⁵-C₅H₄)Fe(η⁵-C ₅H₅) (9)) are obtained by the treatment of complex 4 with an excess of LiC≡CR hi THF. Complexes 5-9 can also be prepared from the reaction of an equimolar mixture of [Cu(C≡CR)]_n and dppf in toluene at room temperature. The crystal structure of complex 5 has been determined by X-ray diffraction. The crystallographic asymmetric unit consists of three molecules of 5, all with related stereochemistries at their centers. The complex consists of two copper atoms linked by two bridging dppf ligands and two bridging alkynyl groups in a μ-η¹ bonding arrangement with an almost planar [Cu₂(μ-η¹-C≡CR)₂] framework. The arylethynyl groups are nearly linear (C≡C-C angles 174(2)-175(2)°), and the C≡C distances (1.20(2)-1.21(2) A?) are typical for cases of metal-acetylide σ-bonding. Both bridging dppf ligands are twisted from the eclipsed conformation (mean value 77(2)°) and also show a relatively large value of the angle (mean value 56.8(6)°) formed by the projection of the Cp?Cp axis of dppf onto the Cu?Cu axis. This seems to indicate that the molecular core [Cu₂(μ-η¹-C≡CC₆H ₄CH₃-4)₂] is a sterically demanding system that forces the dppf ligand to adopt a relatively strained conformation.

Full text of DOI:10.1021/om980592i

662
Organometallics 1999, 18, 662-669
Novel Cop p er (I) Com p lexes Con ta in in g
1,1′-Bis(d ip h en ylp h osp h in o)fer r ocen e (d p p f) a s a Ch ela te
a n d Br id gin g Liga n d : Syn th esis of Tetr a br id ged
Dicop p er (I) Com p lexes [Cu 2(µ-η1-CtR)2(µ-d p p f)2] a n d
X-r a y Cr ysta l Str u ctu r e of
[Cu 2(µ-η1-CtCC6H4CH3-4)2(µ-d p p f)2]
J osefina D´ıez,† M. Pilar Gamasa,† J ose´ Gimeno,*,† Angel Aguirre,‡ and
Santiago Garc´ıa-Granda‡
Departamento de Quı´mica Orga´nica e Inorga´nica and Departamento de Qu´ımica Fı´sica y
Analı´tica, Instituto Universitario de Quı´mica Organometa´lica “Enrique Moles”
(Unidad Asociada al C.S.I.C.), Universidad de Oviedo, E-33071 Oviedo, Spain
J ana Holubova
Department of General and Inorganic Chemistry, Faculty of Chemical Technology,
University of Pardubice, Pardubice, Czech Republic
Larry R. Falvello
Departamento de Quı´mica Inorga´nica, Facultad de Qu´ımica, Universidad de Zaragoza,
Zaragoza, Spain
Received J uly 13, 1998
Binuclear copper(I) complexes [Cu(κ2-P,P-dppf)(CH3CN)2][BF4] (1), [Cu(κ2-P,P-dppf)(bipy)]-
[BF4] (2) containing the chelating dppf ligand (dppf ) 1,1′-bis(diphenylphosphino)ferrocene)
have been prepared by substitution reactions of the acetonitrile ligands from the complexes
[Cu(CH3CN)4][BF4] and (1) with dppf and bipy, respectively. Similarly, the treatment of the
complex [Cu2(µ-dppm)2(CH3CN)2][BF4]2 with dppf in CH2Cl2 at room temperature gives the
tetranuclear complex [Cu2(µ-dppm)2(κ2-P,P-dppf)2][BF4]2 (3). The analogous bridging chloride
tetranuclear complex [Cu2(µ-Cl)2(κ2-P,P-dppf)2] (4) has been also prepared by the addition
of dppf to a solution in THF containing an equimolar mixture of CuCl and tetramethyleth-
ylenediamine. Complex 4 has been used as a precursor for µ-η1-alkynyl bridging dicopper(I)
complexes containing the framework [Cu2(µ-dppf)2]. Complexes [Cu2(µ-η1-CtCR)2(µ-dppf)2]
(R ) C6H4CH3-4 (5), C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (η5-C5H4)Fe(η5-C5H5) (9)) are
obtained by the treatment of complex 4 with an excess of LiCtCR in THF. Complexes 5-9
can also be prepared from the reaction of an equimolar mixture of [Cu(CtCR)]n and dppf in
toluene at room temperature. The crystal structure of complex 5 has been determined by
X-ray diffraction. The crystallographic asymmetric unit consists of three molecules of 5, all
with related stereochemistries at their centers. The complex consists of two copper atoms
linked by two bridging dppf ligands and two bridging alkynyl groups in a µ-η1 bonding
arrangement with an almost planar [Cu2(µ-η1-CtCR)2] framework. The arylethynyl groups
are nearly linear (CtC-C angles 174(2)-175(2)°), and the CtC distances (1.20(2)-1.21(2)
Å) are typical for cases of metal-acetylide σ-bonding. Both bridging dppf ligands are twisted
from the eclipsed conformation (mean value 77(2)°) and also show a relatively large value of
the angle (mean value 56.8(6)°) formed by the projection of the Cp‚‚‚Cp axis of dppf onto the
Cu‚‚‚Cu axis. This seems to indicate that the molecular core [Cu2(µ-η1-CtCC6H4CH3-4)2] is
a sterically demanding system that forces the dppf ligand to adopt a relatively strained
conformation.
In tr od u ction
[Cu3(CtCR)n(µ-dppm)3][BF4]3-n (n ) 1, 2) containing a
triangular Cu3 arrangement stabilized by three bridging
bis(diphenylphosphino)methane (dppm) ligands (A).1b
This metal framework appears to be an appropriate
support for the µ3-η1-acetylide group (B)1c,d and bis-
(µ3-η1-acetylide) groups (C)1c as well as for the mixed
bridging systems (µ3-η1-acetylide)-(µ2-η1-isocyanide) (D)2
We have recently reported1a the systematic synthe-
sis and structural characterization of a series of cat-
ionic trinuclear copper(I) alkynyl complexes of the type
† Departamento de Qu´ımica Orga´nica e Inorga´nica.
‡ Departamento de Qu´ımica F´ısica y Anal´ıtica.
10.1021/om980592i CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/29/1999

Synthesis of Tetrabridged Dicopper(I) Complexes
Organometallics, Vol. 18, No. 4, 1999 663
Ch a r t 1
and (µ3-η1-alkoxy)-(µ3-η1-chloride) (E)3 (Chart 1). The
remarkable ability of the bridging dppm ligand to
stabilize triangular metallic frameworks M3(µ-dppm)3
is evidenced by the isolation of the structurally and
electronically related clusters with M ) Ni, Pd, Pt,
which are also able to support triply bridging carbonyl
or isocyanide ligands.4
It is well-known that the bidentate ligand 1,1′-bis-
(diphenylphosphino)ferrocene (dppf) shows a versatile
coordination ability adapting its steric bite angle to the
geometric requirement of the metal through the ap-
propriate ring twisting or tilting. Although the chelating
coordination mode is the predominant character of dppf
in most metal centers to which it is attached,5 homo-
and heteropolinuclear complexes containing bridging
dppf are also known.6-13 As part of our ongoing work
on the chemistry of alkynyl copper(I) complexes, we
have investigated the ability of dppf to act as a stabiliz-
ing ligand for polynuclear copper(I) systems. Our inter-
est in this stems from the possibility of using these
complexes as alternative frameworks for the stabiliza-
tion of bridging alkynyl groups in a manner similar to
that shown by dppm in the aforementioned trinuclear
[Cu3(µ-dppm)3] systems.
Here we report the synthesis and characterization of
novel copper(I) dppf-containing complexes of the follow-
ing types: (a) with chelating dppf in binuclear com-
plexes [Cu(κ2-P,P- dppf)(CH3CN)2][BF4] (1), [Cu(κ2-P,P-
dppf)(bipy)][BF4] (2) and tetranuclear complexes [Cu2-
(µ-dppm)2(κ2-P,P-dppf)2][BF4]2 (3) and [Cu2(µ-Cl)2(κ2-
P,P-dppf)2] (4); (b) tetranuclear complexes with bridging
dppf [Cu2(µ-η1-CtCR)2(µ-dppf)2] (R ) C6H4CH3-4 (5),
C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (η5-C5H4)-
Fe(η5-C5H5) (9)) in which the metal centers are also
linked by bridging alkynyl groups, forming an unusual
mixed tetrabridged system consisting of two µ-η1-
alkynyl groups and two µ-dppf ligands. The bridging
coordination mode of the ligands has been confirmed by
an X-ray diffraction study of complex 5.
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K. Inorg. Chim. Acta 1995, 233, 1.
Resu lts a n d Discu ssion
Syn t h esis of Ch ela t in g d p p f Com p lexes (1-4).
We have previously reported14,15 that the reaction of
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3684
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(4) (a) Ferguson, G.; J ennings, M. C.; Mirza, H. A.; Puddephatt, P.
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(5) Hor, T. S. A.; Neo, P. S.; Tan, C. S.; Mak, T. C. W.; Leung, K. W.
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Organic Synthesis and Materials Science; Togni, A., Hayashi, T., Eds.;
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T. C. W. J . Organomet. Chem. 1994, 464, 113. (c) Neo, S.P.; Zhou, Z.-
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Organomet. Chem. 1994, 469, 253, and references therein. (b) Canales,
F.; Gimeno, M.C.; Laguna, A.; J ones, P. G. J . Am. Chem. Soc. 1996,
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(8) Cu: (a) Pilloni, G.; Graziani. R.; Longato, B.; Corain, B. Inorg.
Chim. Acta 1991, 190, 165. (b) Caselato, U.; Graziani, R.; Pilloni, G.
J . Crystallogr. Spectrosc. Res. 1993, 23, 571. (c) Aw, B. H.; Looh, K.
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J . Organomet. Chem. 1992, 435, 9. Pt-W: (b) Phang, L. T.; Au-Yeung,
S. C. F.; Hor, T. S. A.; Khoo, S. B.; Zhou, Z. Y.; Mak, W. T. C. J . Chem.
Soc., Dalton Trans. 1993, 165. M-M (M ) Cr, Mo): (c) Hor, T. S. A.;
Phang, L. T.; Liu, L.-K.; Wen, Y.-S. J . Organomet. Chem. 1990, 397,
29. (M ) Rh): (d) Kalck, P.; Randrianalimanana, C.; Ridmy, M.;
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Organomet. Chem. 1994, 481, 183.

664 Organometallics, Vol. 18, No. 4, 1999
Ta ble 1. IR, 31P {1H}, a n d 1H NMRa Da ta for th e Com p lexes 1-9
D´ıez et al.
complex
υ(NtC) or υ(CtC)
31P{1H}
1H
[Cu(CH3CN)2(κ2-P,P-dppf)] [BF4] (1)
2303 w, 2276 w
-12.7
2.22 (s,6H,CH3CN), 4.11 (s,4H,C5H4), 4.31
(s,4H,C5H4), 7.3-7.6 (m,20H,Ph)
4.49 (s,4H,C5H4), 4.75 (s,4H,C5H4), 8.80-7.75
(m,28H,Ph,bipy)
[Cu(bipy)(κ2-P,P-dppf)] [BF4] (2)
[Cu2(µ-dppm)2(κ2-P,P-dppf)2] [BF4]2 (3)
[Cu2(µ-Cl)2(κ2-P,P-dppf)2] (4)
-8.9
-5.90,-6.7 3.45 (m,4H,CH2P2), 4.10 (s,8H,C5H4), 4.33
(s,8H,C5H4), 7.45-6.80 (m,80H, Ph)
4.12 (s,8H,C5H4), 4.30 (s,8H,C5H4),
8.10-6.90 (m,40H,Ph)
2.3 (s,6H,C6H4CH3), 3.53 (s,4H,C5H4), 3.58
(s,4H,C5H4), 3.87 (s,4H,C5H4), 6.6-8.0
(m,52H,Ph,C5H4)
3.61 (s,4H,C5H4), 3.66 (s,4H,C5H4), 3.95
(s,4H,C5H4), 6.7-8.1 (m,54H,Ph,C5H4)
3.27 (s,6H,CH3O), 3.84 (s,4H,CH2O), 3.58
(s,4H,C5H4), 3.76 (s,4H,C5H4), 3.99
(s,4H,C5H4), 6.6-8.0 (m,44H,Ph,C5H4)
0.96 (t,6H,CH3), 1.46 (m,4H,CH2), 2.12
(m,4H,CCH2), 3.58 (s,4H,C5H4), 3.66
(s,4H,C5H4), 3.93 (s,4H,C5H4),
-19.7
[Cu2(µ-η1-CtCC6H4CH3-4)2(µ-dppf)2] (5)
2036 w
-11.04
[Cu2(µ-η1-CtCC6H5)2(µ-dppf)2] (6)
2030 w
2044 w
-10.31
-11.99
[Cu2(µ-η1-CtCCH2OCH3)2(µ-dppf)2] (7)
[Cu2(µ-η1-CtCCH2CH2CH3)2(µ-dppf)2] (8)
2046 w
2033 w
-12.10
-12.79
6.6-8.0 (m,44H,Ph,C5H4)
[Cu2{(µ-η1-CtC(η5-C5H4)Fe(η5-C5H5)}2(µ-dppf)2] (9)
4.14 (s,4H,C5H4), 3.99 (s,14H,C5H5,C5H4),
3.95 (s,4H,C5H4), 3.75 (s,4H,C5H4), 3.60
(s,4H,C5H4), 6.6-8.05 (m,44H,PPh,C5H4)
a
Spectra recorded in CDCl3; δ in ppm.
[Cu(CH3CN)4][BF4] and dppm affords in high yield the
binuclear copper(I) complex [Cu2(µ-dppm)2(CH3CN)2]-
[BF4]2 (I). This complex proved to be an efficient
precursor for a large series of novel triply bridged
binuclear copper(I) complexes containing the moieties
[Cu2(µ-dppm)2(µ-L-L)] and [Cu2(µ-dppm)(µ-L-L)2]. (L-L
) 6-methypyridin-2-olate, 3,5-dimethylpyrazolate, 1,3-
di-p-tolyltriazenide, acetate).15 Accordingly, we set out
to explore similar reactions with dppf hoping to get a
good entry point for the preparation of bridging dppf
copper(I) complexes. However, the reaction of an equimo-
lar mixture of [Cu(CH3CN)4][BF4] and dppf in CH2Cl2
or in CH3CN, in contrast to the synthesis of complex I,
leads16 to the formation of the chelate complex [Cu-
(κ2-P,P-dppf)(CH3CN)2][BF4] (1), which is isolated, after
addition of Et2O to a concentrated solution, as a yellow
solid (80% yield). As expected the remaining coordinated
acetonitrile molecules are easily displaced; thus, the
reaction of complex 1 with 2,2′-bipyridine (bipy) in
Me2CO leads to a solution from which the complex [Cu-
(κ2-P,P-dppf)(bipy)][BF4] (2) was obtained as an in-
soluble orange solid (80%yield).
In a similar way, the acetonitrile ligands of [Cu2-
(µ-dppm)2(CH3CN)2][BF4]2 are also easily substituted by
dppf in dichloromethane, leading to the formation of the
cationic tetranuclear complex [Cu2(µ-dppm)2(κ2-P,P-
dppf)2][BF4]2 (3) isolated as a yellow solid (75% yield)
after addition of Et2O to the concentrated solution of
the reaction mixture. The analogous bridging chloride
complex [Cu2(µ-Cl)2(κ2-P,P-dppf)2] (4) has also been
prepared by the addition of dppf to a THF solution
containing an equimolar mixture of CuCl and tetra-
methylethylenediamine (tmeda). Complex 4 is isolated
from the reaction mixture as an insoluble yellow solid
(72%yield)17a,b (eq 1).
characterized by elemental analyses, conductance mea-
surements, and IR and NMR (1H, and 31P{1H}) spec-
troscopy. Selected spectroscopic data are given in Table
1. Conductivity data (in Me2CO) show that complexes
1 and 2 are 1:1 electrolytes and complex 3 is a 1:2
electrolyte. IR spectra (KBr) exhibit the expected ab-
sorptions for the tetrafluoroborate anion as well as those
characteristic for dppf and the rest of the ligands (see
Experimental Section). In particular, the presence of the
coordinated MeCN molecules is evidenced by the ap-
pearance of two weak ν(CtN) absorption bands at 2303
and 2276 cm-1 and is confirmed by the 1H NMR
spectrum, which shows a single methyl resonance at δ
2.22 ppm. The NMR spectra (1H and 31P{1H}) of
complexes 1-4 reveal the presence of dppf, although no
conclusive information can be obtained regarding its
coordination mode. Thus, 31P{1H} NMR spectra in CDCl3
show a single resonance (δ -12.7 (1), -8.9 (2), and
-19.7(4) ppm) for dppf, while that of complex 3 appears
as two very broad signals (δ -5.9 and -6.7 ppm)
probably as a consequence of overlap with the corre-
sponding resonances of the bridging dppm ligands.
Although we have not carried out variable-temperature
experiments, chemical exchange of dppf and dppm
cannot be discarded given the ability of dppf to act as a
bridging ligand (see below) and the dissociation pro-
cesses of dppm shown by the solutions of complex I in
dichloromethane.14 An analogous chemical exchange of
bridging and chelating dppf has also been described for
the complex [Cu2(µ-dppf)(κ2-P,P-dppf)2] [BF4]2.8a The 1H
NMR (CDCl3) spectra of complexes 1-4 exhibit, in
(14) D´ıez, J .; Gamasa, M. P.; Gimeno, J .; Tiripicchio, A.; Tiripicchio
Camellini, M. J . Chem. Soc., Dalton Trans. 1987, 1275.
(15) D´ıez, J .; Gamasa, M. P.; Gimeno, J .; Lanfranchi, M.; Tiripicchio,
A. J . Chem. Soc., Dalton Trans. 1990, 1027.
(16) It has been reported previously that the reaction of [Cu-
(CH3CN)4][BF4] with dppf in a molar ratio of 1:2 leads to the formation
of the complex [Cu2(µ-dppf)(κ2-P,P-dppf)2][BF4]2. See ref 8a.
(17) (a) The X-ray crystal structure determination confirms the
dinuclear nature of this complex: Tiripicchio, A.; Lanfranchi, M.;
Unpublished results. (b) The structure is isotypic with that described
for [Cu2(κ2-P,P-dppf)2(µ-I)2]: Neo, S. P.; Zhou, Z.-Y.; Mak, T. C. W.;
Hor, T. S. A. J . Chem. Soc., Dalton Trans. 1994, 3451.
CuCl + tmeda + dppf f
[Cu2(µ-Cl)2(κ2-P,P-dppf)2] + tmeda (1)
All of the complexes are air stable in the solid state
and soluble in chlorinated solvents. They have been

Synthesis of Tetrabridged Dicopper(I) Complexes
Organometallics, Vol. 18, No. 4, 1999 665
Ta ble 2. Cr ysta llogr a p h ic Da ta for Com p lex 5
addition to the aromatic and methylene resonances of
the ligands, the typical pair of unresolved multiplets at
δ 4.10-4.49 and 4.30-4.75 ppm expected for the A2B2
spin system of the η5-C5H4 ring, in accord with the
proposed formulations. The structure of complex 4 has
been confirmed by an X-ray diffraction study.17
empirical formula
fw
C86 H70 Cu2 Fe2 P4
1466.08
temp
293(2) K
wavelength
cryst syst, space group
unit cell dimens
0.710 73 Å
monoclinic, C2
a ) 46.713(9) Å, R ) 90°
b ) 22.586(5) Å, â ) 90.55(3)°
c ) 19.961(4) Å, γ ) 90°
21 059(7) Å3
Syn th esis of Br id gin g d p p f Com p lexes (5-9). We
have previously shown that complex I reacts with LiCt
CR to give the complexes [Cu3(µ3-η1-CtCR)(µ-dppm)3]-
[BF4]2 and [Cu3(µ3-η1-CtCR)2(µ-dppm)3][BF4]. The struc-
tures of these complexes show that the alkynyl groups
are able to form electron-deficient bonding systems con-
taining the triply bridging moieties Cu3(µ3-η1-CtCR)x
(x ) 1, 2) stabilized by the triangular framework Cu3-
(µ-dppm)3. This efficient synthetic approach involves the
transformation of a dinuclear species into a trinuclear
one, likely promoted by the dissociation of dppm in the
starting complex I. Since the ability of dppf ligands to
bridge a wide range of metallic systems may provoke
the assembly of similar systems, we have investigated
the reactivity of complex 4 with alkynyl groups. Thus,
the treatment of a solution of complex 4 in THF with
an excess of LiCtCR (prepared in situ from the reaction
of equimolar amounts of HCtCR and LinBu 1.6 M in
THF at -20 °C) gives, after workup, complexes 5-9 in
good yields (70-80%) (eq 2).
volume
Z, calcd density
abs coeff
12, 1.387 Mg/m3
1.140 mm-1
F(000)
9072
cryst size
θ range for data collection
index ranges
0.30 × 0.26 × 0.26 mm
0.87-24.98°
-55 e h e 49, 0 e k e 23,
0 e le 21
no. of reflns collected/unique
completeness to 2θ
14759/14291 [R(int) ) 0.0429]
24.98, 37.5%
refinement method
full-matrix least-squares on F2
14291/65/1238
1.043
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
abs structure param
R1 ) 0.0715, wR2 ) 0.1790
R1 ) 0.2073, wR2 ) 0.2246
0.55(7)
largest diff peak and hole
0.734 and -0.650 e Å-3
dppf ligands and to obtain information on the dppf
conformation, provided that a bridging mode is adopted,
the structure of complex 5 has been analyzed by X-ray
crystallography.
Solid Sta te Str u ctu r e of [Cu 2(µ-η1-CtCC6H4CH3-
4)2(µ-d p p f)2] (5). The crystallographic asymmetric unit
consists of two molecules at general positions, plus two
crystallographically independent half-molecules related
to their respective other halves by crystallographic
2-fold axes. All of the molecules are chiral, because of
twisting of the dppf ligands (described below). The two
complete molecules in the asymmetric unit have op-
posite hands, as do the two molecules that sit astride
crystallographic 2-fold axes. A more detailed description
of the asymmetric unit is given in the Experimental
Section and in the Supporting Information, as this
aspect of the structure is relevant to the correct choice
of space group. For now, we will limit the discussion to
chemically relevant features of the structure. Although
there are conformational differences among the mol-
ecules of the asymmetric unit, the chemically important
derived parameters, especially the bond distances and
angles, are very similar in all four molecules; so the
distances and angles of just one of them will be used
for the present discussion. General crystallographic
parameters are given in Table 2. A view of the molecular
structure is shown in Figure 1. Selected bond distances
and bond angles are listed in Table 3. The molecule
consists of two copper atoms linked by two bridging dppf
ligands and two bridging alkynyl groups in a µ-η1
bonding arrangement. Each copper atom, which dis-
plays a distorted tetrahedral geometry (internal angles
in the range 99.6(6)-118.9(3)°), is bonded to two phos-
phorus atoms of the dppf ligands and to the two carbon
atoms of the alknyl groups. The Cu-P distances, in the
range 2.284(7)-2.317(7) Å, are slightly longer than
those shown by other polynuclear copper(I) complexes
with dppm1c and dppf8b,d bridging ligands. The two
alkynyl ligands, which are C-bonded to the two copper
atoms, form an almost planar Cu2(µ-η1-CtCR)2 frame-
work, with Cu-C distances varying over the range
2.136(2)-2.03(2) Å. The arylethynyl groups which are
[Cu2(µ-Cl)2(κ2-P,P-dppf)2] + 2LiCtCR f
[Cu2(µ-η1-CtCR)2(µ-dppf)2] + 2LiCl (2)
(R
) C6H4CH3-4 (5), C6H5 (6), CH2OCH3 (7),
CH2CH2CH3 (8), (η5-C5H4)Fe(η5-C5H5) (9).)
Alternatively, these complexes can also be prepared
in similar yields from the reaction of an equimolar
mixture of [Cu(CtCR)]n and dppf in toluene at room
temperature. All the alkynyl complexes are air stable
in the solid state and soluble in chlorinated solvents and
THF. They have been characterized by elemental analy-
sis and IR and NMR (1H and 31P{1H}) spectroscopy
(details are given in the Experimental Section and Table
1). All the spectroscopic data are in accord with the
proposed formulations, but these are not relevant to the
question of the coordination modesbridging or terminals
of the ligands. Thus, although the presence of the
alkynyl group is confirmed by the appearance in the IR
spectra (KBr) of a weak ν(CtC) absorption18 in the
range 2046-2030 cm-1 and 31P{1H} NMR spectra show
a single signal (δ from -11.04 to -12.79 ppm) consistent
with the chemical equivalence of the phosphorus atoms,
these data do not allow an unambiguous elucidation of
1
the structure. The H NMR spectra of complexes 5-9
show only three signals (ca. δ 3.55, 3.70, and 3.90 ppm),
attributed to the protons of the cyclopentadienyl rings
on the dppf ligand. Apparently the remaining signal
undergoes the largest shifting to lower field and is
masked by the phenyl resonances. This large range of
1
the chemical shifts has been observed in the H NMR
spectra of a series of related complexes [Re2(µ-OR)2-
(µ-dppf)(CO)6], and it is attributed to ring current effects
from the phenyl groups of the bridging dppf ligand.19
To ascertain the coordination modes of the alkynyl and
(18) Manna, J .; J ohn, K. D.; Hopkins, M. D. Adv. Organomet. Chem.
1995, 38, 79.
(19) See ref 11d and references therein.

666 Organometallics, Vol. 18, No. 4, 1999
D´ıez et al.
Ta ble 3. Selected Bon d a n d In ter a tom ic Dista n ces
(Å) a n d Bon d An gles (d eg) for
[Cu 2(µ-η1-CtCC6H4CH3-4)2(µ-d p p f)2] (5)
Distances
Cu(1)-Cu(2)
Cu(1)-P(2)
Cu(2)-P(4)
Cu(1)-C(10)
Cu(2)-C(10)
C(10)-C(11)
2.447(4)
2.284(7)
2.315(6)
2.11(2)
2.03(2)
1.21(2)
Cu(1)-P(1)
Cu(2)-P(3)
Cu(1)-C(1)
Cu(2)-C(1)
C(1)-C(2)
2.310(6)
2.317(7)
2.136(2)
2.06(2)
1.20(2)
Angles
C(10)-Cu(1)-C(1)
C(1)-Cu(1)-P(2)
C(1)-Cu(1)-P(1)
C(10)-Cu(1)-Cu(2)
P(2)-Cu(1)-Cu(2)
C(10)-Cu(2)-C(1)
C(1)-Cu(2)-P(4)
C(1)-Cu(2)-P(3)
C(10)-Cu(2)-Cu(1)
P(4)-Cu(2)-Cu(1)
C(2)-C(1)-Cu(1)
Cu(2)-C(1)-Cu(1)
104.9(8)
116.6(6)
100.0(6)
52.1(6)
120.2(2)
111.1(8)
98.6(6)
116.1(6)
55.4(6)
122.3(2)
151(2)
C(10)-Cu(1)-P(2)
C(10)-Cu(1)-P(1)
P(2)-Cu(1)-P(1)
C(1)-Cu(1)-Cu(2)
P(1)-Cu(1)-Cu(2)
C(10)-Cu(2)-P(4)
C(10)-Cu(2)-P(3)
P(4)-Cu(2)-P(3)
C(10)-Cu(1)-Cu(2)
P(3)-Cu(2)-Cu(1)
C(2)-C(1)-Cu(2)
C(1)-C(2)-C(3)
99.6(6)
116.7(6)
118.9(3)
52.8(6)
120.9(2)
117.0(6)
100.8(6)
114.0(3)
55.7(6)
123.7(2)
136.6(19)
175(2)
71.5(7)
C(11)-C(10)-Cu(2) 149.7(19) C(11)-C(10)-Cu(1) 137.4(19)
Cu(2)-C(10)-Cu(1)
C(34)-P(4)-Cu(2)
C(45)-P(1)-Cu(1)
72.4(7)
118.2(7)
117.0(7)
C(10)-C(11)-C(12) 174(2)
C(24)-P(3)-Cu(2)
C(29)-P(2)-C8(1)
113.7(8)
119.2(7)
and metallic copper (2.556 Å).20 On the whole, the Cu-
Cu distances found for 5 are comparable to those found
in other polynuclear complexes containing organyl µ-η1
bridging groups.27
The structure of complex 5 also shows the ability of
the dppf ligand to adapt its conformation to the steric
demands of the dicopper(I) fragment to which it is
bonded. It is apparent that the skeletal flexibility of dppf
is also able to stabilize the planar system [Cu2(µ-η1-
CtCC6H4CH3-4)2]. In this respect the following struc-
tural features are significant (see Figure 2): (a) the
angle φ formed by the projection of the Cp‚‚‚Cp axis of
dppf onto the Cu‚‚‚Cu vector (mean value 56.8(6)°); (b)
the angle ω by which the two Cp rings of a given dppf
are twisted from the eclipsed position (mean value 77-
(2)°); (c) the angle R Cipso(Cp)-P-Cu of 117.55(8)° (aver-
age). Structural data of analogous dinuclear rhenium
(20) Naldini, L.; Demartin, F.; Manassero, M.; Sansoni, M.; Rasau,
G.; Zoroddu, A. J . Organomet. Chem. 1985, 279, C42.
(21) Gamasa, M. P.; Gimeno, J .; Lastra, E.; Solans, X. J . Organomet.
Chem. 1988, 346, 277.
(22) Corfield, P. W. R.; Shearer, H. M. N. Acta Crystallogr. 1966,
21, 957.
(23) ten Hoedt, R. W.; Noltes, J . G.; van Koten, G.; Spek, A. L. J .
Chem. Soc., Dalton Trans. 1978, 1800.
(24) Edwards, A. J .; Paver, M. A.; Raithby, P. R.; Rennie, M.-A.;
Russell, G. A.; Wright, D. S. Organometallics 1994, 13, 4967.
(25) Olbrich, F.; Behreus, U.; Weiss, E. J . Organomet. Chem. 1994,
472, 365.
F igu r e 1. ORTEP views of the structure of the complex
[Cu2(µ-η1-CtCC6H4CH3-4)2(µ-dppf)2] (5).
almost linear (CtC-C angles 174(2)-175(2)°), and the
CtC distances (1.20(2)-1.21(2) Å) (Table 3), are con-
sistent with the presence of metal-acetylide σ-bonding.
Table 4 collects structural data of several alkynyl
polynuclear copper(I) complexes including for compari-
son other dinuclear copper(I) complexes bearing bridg-
ing dppf ligands. The Cu2-C bond lengths in 5 (average
2.08(2) Å) are comparable to those of other µ-η1-bonded
alkynyl groups (see Table 4) and significantly shorter
than those found in the µ3-η1-coordination modes, i.e.,
(26) Yam, V. W.-W.; Lee, W.-K.; Cheung, K. K.; Lee, H.-K.; Leung,
W.-P. J . Chem. Soc., Dalton Trans. 1996, 2335.
(27) (a) For aryl groups, see for instance: [Cu3(µ-η1-C6H2(CH3)3-
2,4,6)(m-O2CC6H5)2], Cu-Cu 2.421(2) Å; Cu-C 1.957(6) Å. Aalten, H.
L.; van Koten, G.; Goubitz, K.; Stam, C. H. Organometallics 1989, 10,
2293. (b) [Cu(µ-η1-C6H2(CH3)3-2,4,6)]5, Cu-Cu 2.437(8)-2.469(9) Å;
Cu-C 1.96(2)-2.06(2) Å. Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. J . Chem. Soc., Chem. Commun. 1983, 1156. (c) [Cu4(µ-
η1-C6H2(CH3)3-2,4,6)4(µ-SAr)2(MgSAr)2], Cu-Cu 2.431(1) and 2.464-
(1) Å; Cu-C 1.981(8)-2.064(8) Å. Knotter, D. M.; Smeets, W. J . J .;
Spek, A. L.; van Kotten, G. J . Am. Chem. Soc. 1990, 112, 5895. Knotter,
D. M.; Grove, D. M.; Smeets, W. J . J .; Spek, A. L.; van Kotten, G. J .
Am. Chem. Soc. 1992, 114, 3400. (d) For alkyl groups, see for
instance: [Cu(CH2Si(CH3)3)]4 Cu-Cu 2.417 Å; Cu-C 2.02 Å. J arvis,
J . A. J .; Pearce, R.; Lappert, M. F. J . J . Chem. Soc., Dalton Trans.
1977, 999. (e) For a recent discussion on metal-metal interactions in
copper(I) complexes [Cu3(2-(3(5)-pz)py)3]2‚2py, Cu-Cu 2.905(3) Å.
Singh, K.; Long, J . R.; Stavropoulos, P. J . Am. Chem. Soc. 1997, 119,
2942.
[Cu(µ3-η1-CtCC6H5){P(C6H5)3}]4 and [Cu(µ3-η1-Ct
20
21
CC6H5)(κ-P-(C6H5)2Ppy)]4 (2.185(4) and 2.1708(8) Å,
respectively). The Cu-Cu distance, 2.447(4) Å, may be
compared to that found in analogous dicopper(I) µ-η1-
alkynyl-bridged derivatives (see Table 4), and it is
significantly shorter than those found in trinuclear
complexes containing the moiety [Cu3(µ3-η1-CtCR)x] (x
) 1, 2) (distances in the range 2.523(1)-3.274(3) Å)1c

Synthesis of Tetrabridged Dicopper(I) Complexes
Organometallics, Vol. 18, No. 4, 1999 667
Ta ble 4. Selected Atom ic a n d Bon d Dista n ces (Å) of Sever a l Releva n t Alk yn yl Cop p er (I) a n d Rela ted
Com p lexes
complex
Cu-P
Cu‚‚‚Cu
Cu-C
ref
[Cu(µ3-η1-CtCC6H5){(κ-P)-(C6H5)2Ppy}]4
[Cu(µ3-η1-CtCC6H5){P(C6H5)3}]4
2.230(2)
2.227(1)
2.240(5)
2.605(1)
2.599(1)
2.450(3)a
2.474(4)
2.3892 (14)
2.386(1)
2.454(1)
2.447(4)
2.528(2)
2.199(8)
2.226(4)
2.090(17)a
2.057(6)
2.101(19)
2.018(3)
2.011(3)
2.08(2)
21
20
22
23
24
25
26
b
8d
8b
1c
1c
1c
[Cu4(µ-η1-CtCC6H5)2(µ3-η2-CtCC6H5)2{P(CH3)3}4]
[Cu6(µ-η1-CtCC6H4CH3-4)2{C6H4N(CH3)2-2}4]
[Cu2(µ-η1-CtCtBu)2{P(C6H5)3}2{P(C6H11)3}]
[Cu(µ-η1-CtCC6H5)(tmtch)]2
2.253(3)
[Cu2(µ-η1-CtCC6H5)2{P(C6H5)2CH3}4]
[Cu2(µ-η1-CtCC6H4CH3-4)2(µ-dppf)2]
2.2816(1)
2.313(7)
2.23(4)
2.264(5)
2.277(6)
2.266(5)
2.267(4)
[Cu2 Ru4 (µ3-H)2(µ-dppf)(CO)12
[Cu2 (µ-dppf)(dppf)2](ClO4)2
]
[Cu3(µ3-η1-CtCC6H5)2(µ-dppm)3][BF4]
[Cu3(µ3-η1-CtCC6H5)(µ3-Cl) (µ-dppm)3][BF4]
[Cu3(µ3-η1-CtCC6H5)(µ-dppm)3][BF4]2
2.594(3)
2.820(3)
2.997(3)
2.202(2)
2.344(2)
1.906(1)
a
b
µ3-η1 bridge. This paper.
spectra were recorded (4000-200 cm-1) on a Perkin-Elmer
1720-X FT spectrometer using KBr pellets. The C and H
analyses were carried out with a Perkin-Elmer 240-B mi-
croanalyzer. Conductivities of acetone solutions in ca. 5 × 10-4
mol dm-3 were measured with a J enway PCM3 conductimeter.
NMR spectra were recorded on a Bruker AC300 at 300 MHz
(1H) and 121.5 MHz (31P) using SiMe4 or 85% H3PO4 as
standards. The complexes of [Cu(NCCH3)4][BF4]28 and [Cu2-
F igu r e 2.
14
(µ-dppm)2(NCCH3)4][BF4]2 were prepared as previously de-
scribed. Infrared and NMR spectral data for all the new
complexes are collected in Table 1.
and silver complexes with bridging dppf are listed in
Table 5 for comparison. It is interesting to note that
while the angles ω and R in complex 5 can be compared
to those of the other complexes, the value of the angle
φ for 5 is the largest of the set. This seems to indicate
that the [Cu2(µ-η1-CtCC6H4CH3-4)2] core in 5 is the
most sterically demanding of the systems listed, forcing
the dppf ligand to adopt a relatively strained conforma-
tion.
Syn th esis of [Cu (CH3CN)2(K2-P ,P -d p p f)][BF 4] (1). dppf
(0.554 g, 1 mmol) was added to a solution of [Cu(NCCH3)4]-
[BF4] (0.314 g, 1 mmol) in CH3CN (30 mL), at room temper-
ature. The mixture was stirred at room temperature for 8 h.
The addition of diethyl ether (30 mL) to the concentrated
solution led to the precipitation of a yellow solid, which was
recrystallized from CH3CN/diethyl ether. Yield: 80%. Con-
ductivity, ∆M (Ω-1 cm2 mol-1): 138. IR spectra (KBr), ν(B-F)
(cm-1): 1060. Anal. Calcd for C38N2H44BCuF4P2Fe: C, 58.03;
N, 3.56; H, 4.32. Found: C, 56.33; N, 2.42; H, 4.32.
F in a l Rem a r k s
In this work we report novel copper(I) complexes
containing dppf of two types: (a) mono- and dicopper
complexes [Cu(κ2-P,P-dppf)L2][BF4] (L ) CH3CN (1),
bipy (2)), [Cu2(µ-X)2(κ2-P,P-dppf)2] (X ) P,P-dppm (3),
Cl (4)) with dppf chelating ligands, and (b) unprec-
edented tetrabridged dicopper complexes [Cu2(µ-η1-
CtCR)2(µ-dppf)2] (R ) C6H4CH3-4 (5), C6H5 (6),
CH2OCH3 (7), CH2CH2CH3 (8), (η5-C5H4)Fe(η5-C5H5)
(9)) containing two three-center two-electron systems
(3c-2e) of two µ-η1-alkynyl groups forming a typical
electron deficient system of 3c-2e. It is interesting to
note that the bridging alkynyl complexes are formed
through reactions that proceed via transformation of the
dppf coordination mode from chelating in the precursor
[Cu2(µ-Cl)2(κ2-P,P-dppf)2] (4) to bridging in the resulting
novel products [Cu2(µ-η1-CtCR)2(µ2-dppf)2] (5-9). This
change seems to indicate the ability of the ligand dppf
to adapt to the electronic and/or steric requirements of
the dicopper(I) fragment Cu2(µ2-η1-CtCR)2. In this
regard the complexes described here show the capacity
of dppf ligands to stabilize, for the first time, the doubly
bridged system M2(µ-η1-CtCR)2. This represents one
further example of the well-known bonding and struc-
tural analogies between metal acetylide and carbonyl
complexes.
Syn th esis of [Cu (bip y)(K2-P ,P -d p p f)][BF 4]. (2). bipy
(0.037 g, 0.25 mmol) was added at room temperature to a
solution of [Cu(CH3CN)2(dppf)][BF4] (0.175 g, 0.25 mmol) in
acetone (30 mL). The mixture was stirred at room tempera-
ture for 8 h. After 2 h the orange precipitate was filtered
and washed with diethyl ether (3 × 10 mL) and vacuum-
dried. Yield: 80%. Conductivity, ∆M (Ω-1 cm2 mol-1): 136.
IR spectra (KBr), ν(B-F) (cm-1): 1060. Anal. Calcd for
C
38N2H36BCuF4P2Fe: C, 61.37; N, 3.25; H, 4.18. Found: C,
61.21; N, 3.12; H, 3.94.
Syn th esis of [Cu 2(µ-d p p m )2(K2-P ,P -d p p f)2][BF 4]2 (3).
[Cu2(µ-dppm)2(CH3CN)4][BF4]2 (0.0864 g, 0.07 mmol) was
added at room temperature to a solution of dppf (0.08 g, 0.14
mmol) in CH2Cl2 (30 mL). The mixture was stirred at room
temperature for 6 h. The addition of diethyl ether (30 mL) to
the concentrated solution led to the precipitation of a yellow
solid, which was filtered, washed with diethyl ether (3 × 10
mL), and vacuum-dried. Yield: 75%. Conductivity, ∆M (Ω-1
cm2 mol-1): 207. IR spectra (KBr), ν(B-F) (cm-1): 1066. Anal.
Calcd for C118H100B2Cu2F8P4Fe2: C, 65.05; H, 4.59. Found: C,
64.11; H, 4.59.
Syn th esis of [Cu 2(µ-Cl)2(K2-P ,P -d p p f)2] (4). dppf (0.5 g,
0.9 mmol) was added at room temperature to a mixture of CuCl
(0.089 g, 0.9 mmol) and tmeda (0.136 mL, 0.9 mmol) in THF
(30 mL) after 10 min. The solution was stirred at room
temperature for 6 h. The yellow precipitate was filtered and
washed with diethyl ether (3 × 10 mL) and vacuum-dried.
Yield: 72%. Anal. Calcd for C68H56Cu2P4Fe2Cl2: C, 62.50; H,
4.32. Found: C, 61.91; H, 4.46.
Exp er im en ta l Section
Syn th esis of [Cu 2(µ-η1-CtCR)2(µ-d p p f)2], R d C6H4-
CH3-4 (5), C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (η5-
The reactions were carried out under dry nitrogen using
Schlenk techniques. All solvents were dried by standard
methods and distilled under nitrogen before use. Infrared
(28) Kubas, G. J . Inorg. Synth. 1979, 119, 90.

668 Organometallics, Vol. 18, No. 4, 1999
D´ıez et al.
Ta ble 5. Selected Str u ctu r a l P a r a m eter s of Sever a l Releva n t Com p lexes Con ta in in g th e F r a m ew or k
[M2(µ-X)2(µ-d p p f)n ] (n ) 1 or 2)
complexes
θa (deg)
ω (deg)
φ (deg)
R (deg)
ref
[Re2(µ-OH)2(µ-dppf)(CO)6]
29.7
30.7
26.3
0.1
86.1
85.9
84.0
77.2
89.6
88.8
46.1
53.5
50.8
56.8(6)
42.3
120.5
122.6
123.7
117.55(8)
117.85
112.85
11d
11d
11d
b
5
5
[Re2(µ-OCH3)2(µ-dppf)(CO)6]
[Re2(µ-OCH2CH3)2(µ-dppf)(CO)6]
[Cu2(µ-η1-CtCC6H4CH3-4)2(µ-dppf)2]
[Ag2(µ-ONO2)2(µ-dppf)2]
[Ag2(CH3CO2)2(µ-dppf)2]
42.64
a
b
θ is the fold angle of the {Re2O2} and {Cu2O2} cores. This paper.
C5H 4)F e(η5-C5H 5) (9). Gen er a l P r oced u r e. [Cu2(µ-Cl)2-
(dppf)2] (0.1 g, 0.08 mmol) was added at room temperature to
a solution of 0.46 mmol of LiCtCR in THF (40 mL) (prepared
“in situ” by treating the corresponding alkyne with 1.60 M Lin-
Bu at -20 °C). The mixture was stirred at room temperature
for 2 h and evaporated to dryness to give a solid residue, which
was extracted with dichloromethane (30 mL). The addition of
hexane (30 mL) to the concentrated solution led to the
precipitation of cream solids, which were washed with hexane
(3 × 10 mL) and vacuum-dried. Analytically pure samples were
obtained by recrystallization from dichloromethane/hexane.
Yields: 60-70%. Anal. Calcd for C86H70Cu2P4Fe2 (5): C, 70.49;
H, 4.78. Found: C, 69.37; H, 4.81. Calcd for C84H66Cu2P4Fe2
(6): C, 70.16; H, 4.63. Found: C, 69.21; H, 4.90. Calcd for
because of the size of the calculation. Hydrogen atoms were
placed at idealized positions and refined as riding atoms with
a common isotropic thermal parameter. Several rings were
held to ideal stereochemistries, either by restraints to planarity
or by restraints to ideal bond distances, or both. The structure
was refined on F2, and all data were used in the final
refinement, which gave the residuals listed in Table 2. In all,
1238 parameters were refined to 14 291 data, for a data-to-
parameter ratio of 11.5. The maximum shift to esd ratio in
the last, full-matrix least-squares cycle was 0.076. The final
difference Fourier map showed no features of chemical inter-
est. As will be discussed below, the Flack parameter refined
to a value of 0.55(7).31 Atomic scattering factors were taken
from International Tables for X-ray Crystallography.32 Geo-
metrical calculations were made with PARST.33 The figure
showing the coordination and the atom-numbering scheme was
drawn using the EUCLID package.34 All calculations at the
University of Oviedo were done at the Scientific Computer
Center and on X-ray Group DEC/AXP computers.
C
76H76Cu2O2P4Fe2 (7): C, 66.34; H, 4.98. Found: C, 66.04; H,
4.87. Calcd for C78H70Cu2P4Fe2 (8): C, 68.38; H, 5.15. Found:
C, 67.00; H, 5.00. Calcd for C92H74Cu2P4Fe4 (9): C, 66.81; H,
4.51. Found: C, 68.30; H, 4.58.
Dir ect Syn th esis of 6. A mixture of dppf (0.443 g, 0.8
mmol) and [CuCtCC6H5]n (0.13 g, 0.8 mmol) in toluene (40
mL) was stirred at room temperature for 3 h and filtered. The
resulting solution was evaporated to dryness, giving a solid
residue, which was extracted with CH2Cl2 (15 mL). The
addition of hexane to the partially evaporated solution gave
by precipitation the corresponding complex as a cream solid.
Yield: 70%. Anal. Calcd for C84H66Cu2P4Fe2 (6): C, 70.16; H,
4.63. Found: C, 69.70; H, 4.57.
The structure of compound 5 possesses some uncommon
features that require further comment. The crystallographic
asymmetric unit consists of a total of three molecules of the
complex: two whole molecules on general equivalent positions
and two independent half-molecules sitting alongside crystal-
lographic 2-fold axes which complete the molecules. We report
this structure in space group C2, and there are 12 molecules
in the unit cell. In the following, we shall refer to the two whole
molecules as molecule 1 (containing Cu(1), Cu(2), Fe(1), and
Fe(2)) and molecule 2 (which has Cu(3), Cu(4), Fe(3), and Fe-
(4)). The two molecules sitting on crystallographic 2-fold axes
will be referred to as molecule 3 (Cu(5) and Fe(5)) and molecule
4 (Cu(6) and Fe(6)). Each molecule of 5 is chiral, as the two
dppf ligands are twisted in the same sense. Molecules 1 and 2
are of opposite handedness, as are molecules 3 and 4. Because
of the suggestive aspects of this structure, Z′ ) 3, an acentric
group with the same systematic absences as a centric group
(C2/m), and a monoclinic cell with â near 90°, we comment
briefly here, and in full detail in the Supporting Information,
on the choice of crystal system and space group.
X-r a y Diffr a ction Stu d y of 5. Data collection, crystal, and
refinement parameters are collected in Table 2. Data were
taken from a red crystal of 5 using a Nonius CAD-4 single-
crystal diffractometer. The lattice parameters were verified
by normal-beam oscillation photography. Accurate values for
the unit-cell dimensions were determined from the angular
settings of 25 reflections with θ between 10° and 15°. Intensity
data were measured using the ω-2θ scan technique and a
variable scan rate with a maximum scan time of 60 s per
reflection. The final drift correction factors were between 0.99
and 1.07. Profile analysis was performed for all reflections.29
Redundant data were averaged (Rint ) ∑(I - I )/∑I ) 0.043),
giving a total of 14 291 unique reflections of which 7022 had
I > 2σ(I). The structure solution began with the successful
location of some copper, iron, and phosphorus atoms by direct
methods.30 The remaining atoms were found and refined in
the usual alternating sequence of least-squares refinements
and difference Fourier maps. Isotropic least-squares refine-
ment using SHELXL-9331 converged to R1 ) 0.087. In the final
stages of refinement, anisotropic displacement parameters
were used only for the copper, phosphorus, and iron atoms;
the remaining non-hydrogen atoms were treated isotropically,
Systematic absences limit the choice of space groups in the
monoclinic system to three, namely, C2, Cm, and C2/m. Note:
there is no systematic absence for a c-glide. The successful
refinement in space group C2 and the absence of important
features in the final difference Fourier map mean that the
structural model is correct in its general aspects, although the
choice of space group could still be erroneous. But specifically,
the refinement establishes that each of the molecules in the
cell, taken individually, is chiral and cannot possess a crys-
tallographically imposed mirror plane. Considering molecule
(29) Lehman, M. S.; Larsen, F. K. Acta Crystallogr. 1974, A30, 580.
Grant, D. F.; Gabe, E. J . J . Appl. Crystallogr. 1978, 11, 114.
(30) (a) Calculations for the initial solution of the structure were
performed on a Hewlett-Packard 9000 model 715/50 (HP-UX V9.05)
and on an AlphaStation 200 4/166 (OpenVMS/Alpha V6.2). (b) Sheld-
rick, G. M. SHELXS-86: FORTRAN program for crystal structure
solution; Go¨ttingen University, 1986. (c) Beurskens, P. T.; Admiraall,
G.; Beurskens, G.; Bosman, W. P.; Garc´ıa-Granda, S.; Gould, R. O.;
Smits, J . M. M.; Smykalla, C. DIRDIF Users’s Guide; Technical report;
Crystallography Laboratory, University of Nijmegen: The Nether-
lands, 1992.
(31) (a) Sheldrick, G. M. SHELXL93, Program for crystal structure
determination; University of Go¨ttingen, 1993. (b) Flack parameter:
Flack, H. D. Acta Crystallogr. 1983, A39, 876-881. (c) Flack param-
eter: Bernardinelli, G.; Flack, H. D. Acta Crystallogr. 1985, A41, 500-
511.
(32) International Tables for X-ray Crystallography; Kynoch Press:
Byrmingham (Present distributor Kluwer Academic Publishers: Dor-
drecht), 1974; Vol. IV.
(33) Nardelli, M. Comput. Chem. 1983, 7, 95.
(34) Spek, A. L. The Euclid Package. In Computational Crystal-
lography; Sayre, D., Ed.; Clarendon Press: Oxford, 1982; p 528.

Synthesis of Tetrabridged Dicopper(I) Complexes
Organometallics, Vol. 18, No. 4, 1999 669
3, it and one symmetry relative of the same hand are present
in the unit cell. If the space group were Cm, which has four
operators, then molecule 3 would have to sit astride a mirror
plane in order to give rise to just two molecules in the cell.
The same consideration applies to molecule 4. But since
molecules 3 and 4 cannot possess mirror symmetry, space
group Cm is ruled out. Similarly for C2/m, molecules 3 and 4
would have to sit on positions of symmetry 2/m in order for
there to be just two of each in the cell. So space group C2/m is
ruled out.
Since on the whole this structure is racemic, with equal
numbers of molecules of each enantiomer, the enantiomorph
determination gives the expected result that the Flack pa-
rameter refines to a value of about one-half. The C2 structure
is thus indistinguishable from its enantiomorph and further
indistinguishable from a racemic twin.
A fuller description of all of the possible space groups,
including the orthorhombic system, along with further twin-
ning possibilities and alternative refinements, is given in the
Supporting Information.
Ack n ow led gm en t. This work was supported by the
Direccio´n General de Investigacio´n Cient´ıfica y Te´cnica
(Projects PB93-0325 and PB95-0792).
Su p p or tin g In for m a tion Ava ila ble: Tables giving all
bond lengths and angles, positional and thermal parameters,
torsion angles, and least-squares planes for 5, along with a
detailed description of the choice of space group, tests for
twinning, and alternative refinements (48 pages). Ordering
information is given on any current masthead page.
OM980592I