Synthesis, crystal structure and DFT calculations on 2,6-diisopropylphenylcopper; its use in the preparation of dichloro-2,6-diisopropylphenylphosphine

Article abstract of DOI:10.1016/j.jorganchem.2006.09.004

The homoleptic aryl copper reagent [Cu₄Dipp₄] (Dipp = 2,6-diisopropylphenyl) has been prepared and structurally characterized by a single-crystal X-ray diffraction study. Its tetrameric structure differs in significant details from t

Full text of DOI:10.1016/j.jorganchem.2006.09.004

Journal of Organometallic Chemistry 691 (2006) 5585–5591
www.elsevier.com/locate/jorganchem
Synthesis, crystal structure and DFT calculations on
2,6-diisopropylphenylcopper; its use in the preparation of
dichloro-2,6-diisopropylphenylphosphine
1
*
´
´
Rene T. Boere , Jason D. Masuda , Peter Tran
Department of Chemistry and Biochemistry, The University of Lethbridge, Lethbridge, AB, Canada T1K 3M4
Received 10 July 2006; received in revised form 5 September 2006; accepted 5 September 2006
Available online 19 September 2006
Abstract
The homoleptic aryl copper reagent [Cu4Dipp4] (Dipp = 2,6-diisopropylphenyl) has been prepared and structurally characterized by a
single-crystal X-ray diffraction study. Its tetrameric structure differs in significant details from that of the previously reported [Cu4Tripp4]
(Tripp = 2,4,6-triisopropylphenyl). The electronic structure of the cluster has been probed through B3LYP/6311G(2d,p)//B3LYP/6-31G
calculations on [Cu4Ph4] constrained to D2d symmetry. The utility of the new copper reagent is demonstrated by the preparation of pure
DippPCl2, for which the crystal structure is also reported.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Organocopper; Dichlorophosphine; X-ray Crystallography; NMR
1. Introduction
can be used in non-coordinating solvents. There are still
relatively few structural characterizations of the homolep-
tic, Lewis base-free, reagents. Structures have been
reported for [Cu5Mes5] [7], [Cu4Tripp4] [8], [Cu4(CH2-
SiMe3)4] [9], [Cu4(C6F5)4] [10], [Cu4(C6Me5)4] [11],
[Cu4(C6H4{CH@CH2}-2)4] [12], [Cu3(C6H3Ph2-2,6)3] [13]
and [Cu2(C6H3Mes2-2,6)2] [13], suggesting in general a
decreasing cluster nuclearity with increasing steric bulk of
the organic group. The monomeric structure of the terphe-
nyl derivative [CuC6H2Ph3-2,4,6] [14] has been questioned
[15]. However, the structure determination of [Cu4Mes4]
[16] and solution studies [7] suggest that the nuclearity of
aryl copper(I) reagents is variable depending on the med-
ium, leading many researchers to describe them by the gen-
eric formula (RCu)x. Herein we report the synthesis and
X-ray crystal structure of a new aryl copper reagent based
on the 2,6-diisopropylphenyl (Dipp) substituent, which we
have been exploiting as a new bulky group in phosphorus
chemistry [17], [Cu4Dipp4], and its use in the preparation
of DippPCl2.
Organocopper(I) reagents find extensive use in organic
synthesis, where they generally impart greater selectivity
than conventional Grignard and organolithium reagents
[1]. The most popular copper(I) synthetic reagents are ter-
nary lithium diorganocuprates [R2Cu]Li [2] and ‘‘higher
order’’ cuprates [3], especially those containing the cyanide
ligand, and in general these are utilized only in coordinat-
ing solvents such as THF or CH3SCH3. Homoleptic
organocopper reagents are used less often and correspond-
ingly less is known about them. However, they are of great
utility in main group organometallic chemistry [4], and
more recently have found application in supramolecular
cluster synthesis [5,6]. Like organolithium reagents, they
*
Corresponding author. Tel.: +1 403 329 2045; fax: +1 403 329 2057.
´
E-mail address: boere@uleth.ca (R.T. Boere).
Present address: Department of Chemistry, University of California,
1
Riverside, CA, USA.
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.09.004

5586
R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
2. Experimental
2.1. General methods
175.0674 (within 0.5 ppm calc. C11H12P+, 25%), 161.1324
(within 4 ppm calc. C12Hþ17, 19%), 149.0521 (within
0.5 ppm of C9H10P+, 25%). Previously prepared only as a
mixture of DippPCl2 along with DippPBrCl and DippPBr2
[19].
DippBr was prepared as previously reported [18]. Anhy-
drous CuCl, 1,2-dibromoethane and PCl3 (Aldrich) were
used as received. THF was distilled from sodium benzophe-
none immediately before use. Hexanes and heptane were
distilled from LiAlH4; toluene and 1,4-dioxane from
sodium under N2. All reactions were performed in an
atmosphere of dry N2 in oven-dried glassware (>4 h at
>160 ꢁC) unless otherwise noted. NMR spectra (250 or
300 MHz) were referenced to the solvent (1H and 13C) or
to external H3PO4 (31P).
3.2. Crystallography
The data were corrected for Lorentz and polarization
effects and for absorption using Bruker SADABS [20]. The
structures were solved by direct methods and expanded
using Fourier techniques [21]. Crystal, solution and refine-
ment details for both structures are found in Table 1.
Selected interatomic distances and angles for Dipp4Cu4
are presented in Table 2, and for DippPCl2 in Table 3.
The structure of Dipp4Cu4 is overwhelmingly successful,
but the huge model with 969 refined parameters resulted
in less than ideal anisotropic thermal parameters for C43
(and hence for the attached H atom). A careful analysis
of the structure shows that all the para and meta phenyl
ring carbon atoms show similar, though less severe, flatten-
ing as in C43. This effect can be attributed to a rocking
motion of whole Dipp groups perpendicular to the Cu4
planes, which is an entirely plausible molecular vibration
in the crystal lattice.
3. Synthesis of (DippCu)x
1.76 g (72.5 mmol) of activated Mg turnings were sus-
pended in 60 mL THF, 0.15 mL (0.33 g, 1.8 mmol) 1,2-dib-
romoethane was added, and refluxed for 30 m. 15.0 g
(62.2 mmol) DippBr in 195 mL THF was added dropwise
at RT, and the mixture was then refluxed overnight.
6.16 g (62.2 mmol) of CuCl was added at RT and the mix-
ture then refluxed for 30 m. Next 37.5 mL of 1,4-dioxane
was added at RT, the mixture filtered and the solvent
removed. An off-white residue was redissolved in 150 mL
warm toluene, filtered and evaporated to yield 11.3 g
(50.3 mmol, 81% based on DippBr) of moisture- and
light-sensitive off-white (DipCu)x. Single crystals obtained
by slow cooling of heptane solutions under N2, mp
150 ꢁC (dec) were pure by NMR (C6D6): 1H d 7.25 (t,
8 Hz, 1H, p-CH), 7.05 (d, 8 Hz, 2H, m-CH), 3.86 (sept,
7 Hz, 2H, CH(CH3)2), 1.26 (d, 7 Hz, 12H, CH(CH3)2);
13C d 167.3 (o-C), 139.2 (i-C), 132.5 (p-C), 123.0 (m-C),
42.2 (CH(CH3)2), 27.7 (CH(CH3)2). MS(70 eV): m/z (calcu-
3.3. Computational study
Hybrid HF/DFT calculations were performed on key
model systems at the B3LYP/6-311G(2d,p)//B3LYP/6-
31G level of theory using GAUSSIAN-98 [22]. The Dipp
groups are modeled by Ph groups, and symmetry was
imposed at the D2d level.
lated
on
63Cu)
896
ðDipp4Cuþ; 2%Þ,
735
4. Results and discussion
4
(Dipp3Cuþ; 100%, exact mass: 735.115, calc. 735.117),
4
162 (DippPH+, 17%), 147 ([DippH–CH3]+, 50%), 119
([DippH–CH(CH3)2]+, 20%).
4.1. Synthesis of (DippCu)x and DippPCl2
In a typical procedure, the Grignard reagent is prepared
from DippBr using activated magnesium chips in THF. To
the solution of this reagent is added anhydrous copper(I)
chloride. Filtration of the resulting suspension and removal
of the solvent affords an off-white powder of DippCu that
is synthetically useful.
Ja¨kle and Manners have shown the utility of, specifi-
cally, (MesCu)x for the synthesis of a variety of main group
mesityl derivatives [4]. Thus with (MesCu)x and excess
PCl3, MesPCl2 can be produced in 95% yield based on
the organocopper reagent (NMR evidence). According to
Xie and Neilson, MesPCl2 can also be produced on a large
scale by the reaction of MesMgBr with PCl3, but no details
of the procedure are given [23]. In our experience, the reac-
tion of DippMgBr with PCl3 in many trials leads exclu-
sively to a mixture of all three halides, DippPBr2,
DippPBrCl and DippPCl2 in distributions that imply that
all the bromide originally introduced from the Grignard
3.1. Synthesis of pure DippPCl2
(DippCu)x (7.8 g. 35 mmol) was suspended in 100 mL of
THF, and PCl3 (4.8 g, 35 mmol) in 10 mL THF was added
dropwise at 0 ꢁC. After stirring at room temperature for
14 h, filtering off the precipitate, extracting in hexanes, fil-
tering again, the solvent was removed in vacuo. Distillation
of the residue (bp 91 ꢁC at 0.1 Torr) yielded 4.5 g (50%) of
1
a colourless liquid which was pure by NMR in CDCl3: H
d 7.45 (t, 8 Hz, 1H, p-CH), 7.25 (d of d, 8 and 3 Hz, 2H, m-
CH), 4.12 (sept. of d., 7 and 5 Hz, 2H, CH(CH3)2), 1.31 (d,
7 Hz, 12H, CH(CH3)2); 13C d 154.6 (d, 23 Hz, o-C), 134.7
(d, 69 Hz, i-C), 133.4 (p-C), 125.0 (m-C), 30.9 (d, 31 Hz,
CH(CH3)2), 24.9 (CH(CH3)2); 31P d +165.3. MS(70 eV)
(calculated on 35Cl): m/z 262.0436 (within 4 ppm calc.
DippPClþ2 , 37%), 227.0751 (within 2 ppm calc. DippPCl+,
100%), 191.0988 (within 1 ppm calc. C12H16P+, 59%),

R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
5587
Table 1
Crystal data and structure refinement for the compounds
Compound
DippCu
DippPCl2
Crystal colour and habit
Crystal size (mm)
Colourless prism
0.28 · 0.52 · 0.62
Colourless parallelepiped
0.26 · 0.23 · 0.22
C12H17Cl2P
7.843(3)
9.838(3)
Chemical formula
C48H68Cu4
˚
a (A)
12.5923(8)
16.2213(10)
21.9435(14)
90.7850(10)
98.6040(10)
91.3950(10)
0.71073
˚
b (A)
˚
c (A)
17.429(6)
a (ꢁ)
b (ꢁ)
c (ꢁ)
˚
Wavelength (A)
0.71073
Temperature (K)
Crystal system
Space group
193(2)
Triclinic
173(2)
Orthorhombic
P212121
ꢀ
P1
Z
4
4
Diffractometer
Data collection
Reflections collected
Bruker Smart
x and u scans
21279
Bruker APEX II
x and u scans
15886
Independent reflections (Rint
Completeness to h
)
17776 (0.0234)
26.40ꢁ, 97.8%
1.925
3312 (0.0202)
27.95ꢁ, 99.6%
0.569
Absorption coefficient (mmꢀ1
Absorption correction
)
SADABS
SADABS
Maximum and minimum transmission
Data/restraints/parameters
Final R indices [I > 2r(I)]
R indices (all data)
0.518 and 0.409
17776/0/969
R1 = 0.0292, wR2 = 0.0745
R1 = 0.0415, wR2 = 0.0783
0.966
0.885 and 0.866
3312/0/140
R1 = 0.0258, wR2 = 0.0650
R1 = 0.0310, wR2 = 0.0677
1.049
Goodness-of-fit on F2
Hydrogen atoms
Largest difference in peak and hole (e/A
Riding model
0.494 and ꢀ0.433
Riding model
0.306 and ꢀ0.131
ꢀ3
˚
)
reagent ends up on phosphorus, a remarkable testimony to
the greater nucleophilicity of bromide relative to chloride
(31P NMR and mass spectroscopic evidence) [19]. Similar
halide-scrambling reactions have been reported by others,
e.g. in the synthesis of Mes2P(Br,Cl) [24]. While there are
undoubtedly many situations in which the preparation of
such mixed halides is of no consequence, a reliable and
convenient way to prepare the pure chloride is worth hav-
ing, and the copper reagents provide one such route. Thus
the reaction of one equivalent of (DippCu)x with PCl3 leads
to the production of pure DippPCl2.
Table 2
˚
Selected interatomic distances (A) and angles (ꢁ) for [Cu4Dipp4]
Molecule 1
Cu(1)–Cu(2)
Cu(1)–Cu(4)
Cu(2)–Cu(3)
Cu(3)–Cu(4)
Cu(1)–C(1)
Cu(1)–C(37)
Cu(2)–C(1)
Cu(2)–C(13)
Cu(3)–C(25)
Cu(3)–C(13)
Cu(4)–C(25)
Cu(4)–C(37)
2.4161(3)
2.4175(3)
2.4071(3)
2.4045(4)
2.027(2)
2.028(2)
2.0183(19)
2.024(2)
2.030(2)
2.033(2)
2.024(2)
2.026(2)
Cu(2)–Cu(1)–Cu(4)
Cu(3)–Cu(2)–Cu(1)
Cu(4)–Cu(3)–Cu(2)
Cu(3)–Cu(4)–Cu(1)
C(1)–Cu(2)–Cu(3)
C(1)–Cu(1)–Cu(4)
C(13)–Cu(2)–Cu(1)
C(13)–Cu(3)–Cu(4)
C(25)–Cu(3)–Cu(2)
C(25)–Cu(4)–Cu(1)
C(37)–Cu(1)–Cu(2)
C(37)–Cu(4)–Cu(3)
97.326(13)
82.361(12)
97.924(12)
82.388(12)
132.02(6)
145.24(6)
132.16(6)
145.99(6)
145.82(6)
132.12(6)
145.13(6)
131.66(6)
4.2. Structure of (DippCu)x
The crystal structure of (DippCu)x (Tables 1 and 2,
Fig. 1) consists of two highly similar independent molecules
in the asymmetric unit of the triclinic unit cell, which are,
Table 3
˚
Selected interatomic distances (A) and angles (ꢁ) for DippPCl2
Molecule 2
Cu(5)–Cu(6)
Cu(5)–Cu(8)
Cu(6)–Cu(7)
Cu(7)–Cu(8)
Cu(5)–C(49)
Cu(5)–C(85)
Cu(6)–C(49)
Cu(6)–C(61)
Cu(7)–C(61)
Cu(7)–C(73)
Cu(8)–C(73)
Cu(8)–C(85)
2.4150(4)
2.4140(4)
2.4217(4)
2.4053(4)
2.040(2)
2.028(2)
2.025(2)
2.021(2)
2.026(2)
2.033(2)
2.028(2)
2.034(2)
Cu(8)–Vu(5)–Cu(5)
Cu(5)–Cu(6)–Cu(7)
Cu(8)–Cu(7)–Cu(6)
Cu(7)–Cu(8)–Cu(5)
C(49)–Cu(5)–Cu(8)
C(85)–Cu(5)–Cu(6)
C(61)–Cu(6)–Cu(5)
C(49)–Cu(6)–Cu(7)
C(61)–Cu(7)–Cu(8)
C(73)–Cu(7)–Cu(6)
C(85)–Cu(8)–Cu(7)
C(73)–Cu(8)–Cu(5)
98.206(13)
81.581(12)
98.261(13)
81.937(12)
144.73(6)
147.03(6)
130.38(7)
130.90(6)
145.58(6)
146.04(6)
131.63(6)
131.93(6)
P(1)–C(1)
P(1)–Cl(1)
P(1)–Cl(2)
C(1)–C(6)
C(1)–C(2)
C(2)–C(3)
C(2)–C(7)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(10)
1.8262(14)
2.0681(8)
2.0707(8)
1.4165(19)
1.4258(18)
1.3890(19)
1.5265(18)
1.384(2)
C(1)–P(1)–Cl(1)
C(1)–P(1)–Cl(2)
Cl(1)–P(1)–Cl(2)
C(6)–C(1)–C(2)
C(6)–C(1)–P(1)
C(2)–C(1)–P(1)
C(3)–C(2)–C(1)
C(3)–C(2)–C(7)
C(4)–C(3)–C(2)
C(5)–C(4)–C(3)
C(4)–C(5)–C(6)
C(5)–C(6)–C(1)
102.73(6)
102.55(5)
101.07(3)
120.27(12)
114.00(10)
125.73(10)
118.04(12)
117.32(12)
121.71(13)
120.14(13)
121.11(14)
118.74(13)
1.377(2)
1.3948(19)
1.529(2)

5588
R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
˚
The average of the 8 Cu–Cu distances is 2.413(6) A [25],
and the angles at copper fall into acute (Cu2,4,6,8 average
82.1(4)ꢁ) and obtuse (Cu1,3,5,7 average 97.9(4)ꢁ) groups
indicating considerable distortion in the trapezoidal direc-
tion. The deviation of the ipso carbon atoms from the mean
˚
copper planes is also quite uniform at 0.58(2) A. Unlike the
structure of [Cu4Tripp4] in which the Cu–Cipso distances are
considerably skewed towards one of the two bridged cop-
per atoms, [Cu4Dipp4] has very regular bridging distances
˚
that average to 2.028(5) A. In conjunction with the trape-
zoidal distortion at copper, each Dipp group is tilted from
the vertical by a small amount; despite the opposing ‘up’
and ‘down’ Cu2Cipso envelope configurations, all four Dipp
groups in a cluster tilt in the same direction, imparting a
slight helicity to each cluster. The average tilt angles
between planes defined by the Cu4 group and the six car-
bon atoms of each Dipp group fall into two groups, seven
of the rings having fairly uniform tilt angles of 83(1)ꢁ, while
the eighth (C85,86,90,91,92,93) has a tilt of 79.6ꢁ; this tilting
seems to be dictated by the steric interference between
the isopropyl groups on adjacent aryl rings. In general,
the structure of [Cu4Dipp4] is quite similar to that of the
isosteric [Cu4Tripp4], but the geometry of its Cu–C–Cu
bridges are much more regular. We note that the latter
crystallizes in a high symmetry space group with crystallo-
graphically imposed fourfold rotation symmetry, whereas
our structure has no imposed symmetry and likely reflects
a more natural structural arrangement for the molecule.
Indeed, these results along with that of the completely reg-
ular structure of [Cu4(C6Me5)4] [11] which has crystallo-
graphically imposed square, orthogonal and Cu–Cipso
coplanar geometry, suggests that the solid-state geometries
of homoleptic aryl copper complexes are extremely suscep-
tible to crystal packing effects. Thus the previously invoked
bonding arguments for [Cu4Tripp4] on the basis of its dis-
torted structure are most likely over interpreted [8].
Fig. 1. Structures of DippCu in the crystal at ꢀ80 ꢁC (two independent
molecules in unit cell) viewed perpendicular to the Cu4 plane: (a) molecule
1; (b) molecule 2. Thermal ellipsoids are drawn at the 50% probability
level.
however, statistically distinct (e.s.d. of refinement). Each
molecule consists of a trapezoidal plane of copper atoms
bridged along each Cu–Cu contact by an approximately
perpendicular aryl group. The ispo carbon atoms are not
coplanar with the copper atoms (though such coplanarity
has been observed previously [11,16]), and are displaced
to different sides of the copper plane in an opposed manner
to give a ‘‘gull wing’’ structure that has also been observed
before [8].
4.3. NMR spectroscopic studies
The NMR spectra in solution are extremely similar to
those reported for [Cu4Tripp4] at RT, but with no evidence
of line-broadening in d6-benzene [8]. There has been con-
siderable discussion in the literature on the possibility of
having various stoichiometries in solution for the homolep-
tic copper aryls [7], and just as reported for [Cu5Mes5] dis-
solved in aromatic solvents, we observed small additional
peaks in both d6-benzene and d8-toluene solutions made
up from pure crystalline [Cu4Dipp4]. In both solvents, there
were two sets of signals quite similar to those of the main
peaks (see Section 2); the isopropyl CH3 doublets are at
slightly lower frequency, while the methine CH septets
are at slightly higher frequency. Finally, we note that only
the tetramer is observed in the low-resolution mass spec-
trum (the observed fragments are [Cu4Dipp4]+ and [Cu4
Dipp3]+). Thus the form of DippCu that crystallizes from
petroleum solvents is a tetrameric molecule of considerable
Dipp
Cu
Cu
Dipp
Dipp
Cu
Cu
Dipp

R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
5589
thermal stability, which can be ionized intact via electron
impact mass spectrometry. However, in solution in aro-
matic solvents slow equilibration leads to species which
are likely to differ in nuclearity from the crystallized
tetramer.
the two Cl atoms are found on opposite sides of the central
aryl ring, in contrast to DippPCl2, the group is significantly
twisted, an effect that is correlated to the twisting of the
2,6-(4-tert-butylphenyl) aryl rings. The PCl2 unit in this
structure is distorted from the trigonal angle by about 8ꢁ,
but here this is accompanied by being pushed out of the
˚
plane of the central benzene ring by 0.42 A, an effect that
4.4. Electronic structure
is also correlated with the twist of the flanking groups.
˚
The C–P distance in the terphenyl at 1.8355 A is also longer
In order to gain further insights into the electronic struc-
ture of homoleptic copper aryl reagents we have performed
hybrid DFT calculations on a model compound where phe-
nyl groups replace Dipp. An optimized geometry was
obtained for this [Cu4Ph4] molecule restrained to D2d
symmetry at the B3LYP/6-31G level of theory, and this
structure is presented in Fig. 3. The significant frontier
Kohn–Sham orbitals and their energies are obtained from
a B3LYP/6-311G(2d,p) calculation, namely the LUMO,
the HOMO and the doubly degenerate HOMO ꢀ 1. Main
group organometallic compounds are most often utilized as
carbanion sources, and thus we expect to find energetic
filled orbitals with considerable electron density – in this
instance – on the ipso carbon atoms of the aryl ligands.
To a certain extent, we do find this, because the degenerate
set of orbitals of symmetry e that lie at ꢀ5.87 eV have con-
siderable Cipso rLP character, in conjunction with metal
dx2ꢀy2 acceptor orbitals. However, the HOMO of the cluster
at ꢀ5.44 eV is an orbital of b2 symmetry that is effectively
non-bonding and is largely composed of copper dxy orbi-
tals, with no contribution from ipso carbon orbitals. In this
sense, these homoleptic Cu(I) aryl complexes are less
‘‘reduced’’ at carbon than complexes of the more electro-
positive metals, and it is this character that is responsible
for the milder, more selective, reactions that they undergo
compared to Grignard or organolithium reagents.
˚
than the 1.826 A found in DippPCl2. Another aryl PCl2
compound is 1,8-bis(dichlorophosphino)naphthalene, but
its structure is distorted by interactions between the two
PCl2 units on the adjacent side of the naphthalene back-
bone, making comparisons less valid [27]. Here the C–P
˚
bond distances are also longer at 1.8303 A (average of 4
values). By contrast, when a PCl2 group is bonded to
five-membered rings such as furan [28] or ferrocene [29],
the C–P bond distances are noticeably shorter at 1.776,
˚
1.788 or 1.789 A. None of these structures has any steric
congestion from flanking groups, but the values are consid-
erably shorter than the average C–P distances in triaryl-
˚
phosphines at 1.836 0.010 A determined from 102
examples in the CCDC database [40]. The P–Cl distances
˚
in all of these examples range from 2.046 to 2.072 A, rather
˚
longer than the average value of 2.008 0.035 A from the
database [40]. Within this range, DippPCl2 is normal.
4.6. NMR spectra of DippPCl2
The 31P chemical shift in DippPCl2 of +165.3 ppm is
unremarkable for an ArylPCl2 species. In the 1H spectrum,
there is clear indication of 31P coupling to the isopropyl CH
(5 Hz) and the meta CH (4 Hz) atoms. Similarly, the
{1H}–13C spectrum displays 1:1 doublets from 31P coupling
to the ipso and ortho benzene ring carbon atoms and the
isopropyl CH atoms. In addition, the signal from the ben-
zene ring meta carbon atoms is line-broadened from unre-
solved coupling to phosphorus.
4.5. Structure of DippPCl2
The crystal structure of DippPCl2 (Tables 1 and 3) with
atom numbering scheme is shown in Fig. 2. The compound
is quite flat, with both the CH atoms of the isopropyl and
the P atoms co-planar with the benzene ring. The Cl–P–Cl
angle is bisected by the aryl plane almost perfectly (within
1ꢁ). In response to steric pressure from the C7–9 isopropyl
group, the PCl2 group is distorted from the ideal trigonal
angle at C1 by about 6ꢁ towards C6 but with the P atom
remaining in the aryl ring plane. Since there are no signif-
icant intermolecular contacts within the unit cell, the
observed structural distortions may be attributed to intra-
molecular forces.
There are still relatively few published crystal structures
for dichlorophosphines, particularly for aryl phosphines
[26–39]. The terphenyl compound (2,6-bis(4-tert-butylphe-
nyl)phenyl)dichlorophosphine is perhaps the closest valid
structure for comparison with that of DippPCl2 [26], as it
possesses flanking 2,6-aryl substituents playing much the
same role as the isopropyl groups in our structure. While
Fig. 2. Structure of DippPCl2 in the crystal at ꢀ100 ꢁC. Thermal
ellipsoids are drawn at the 50% probability level. There are no significant
intermolecular contacts less than the sums of van der Waals radii.

5590
R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
Fig. 3. Geometry optimized structure of [Cu4Dipp4] at the B3LYP/6-31G level of theory under D2d symmetry, and surface diagrams of the LUMO,
HOMO and HOMO ꢀ 1 (e symmetry set) Kohn–Sham orbitals. Orbitals and their energies are from a B3LYP/6-311G(2d,p) calculation.
Acknowledgments
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2006.09.004.
We thank the Natural Sciences and Engineering Re-
search Council (Canada) and the University of Lethbridge
for financial support and for the purchase of the X-ray dif-
fractometers and NMR spectrometers employed in this
study. R. Macdonald (University of Alberta) is thanked
for obtaining X-ray data on [Cu4Dipp4].
References
[1] Abbreviations used in this paper. Mes: 2,4,6-trimethyphenyl. Dipp:
2,6-diisopropylphenyl. Tripp: 2,4,6-triisopropylphenyl. RT: room
temperature, 22 ꢁC unless otherwise specified. EI: electron impact.
DMS: dimethyl sulphide. Ph: phenyl. Me: methyl. Et: ethyl. dppe:
bis(diphenylphosphino)ethane. THF: tetrahydrofuran.
Appendix A. Supplementary material
[2] (a) [Cu(dppe)2][CuMes2] P. Leoni, M. Pasquali, C.A. Ghilardi, J.
Chem. Soc., Chem. Commun. (1983) 240;
CCDC 614243 and 614244 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
(b) [Li(THF)4][Cu-(CH2SiMe3)2] C. Eaborn, P.B. Hitchcock, J.D.
Smith, A.C. Sullivan, J. Organomet. Chem. 263 (1984) C23;
(c) [Li(12-crown-4)2][CuMe2] or [CuPh2] H. Hope, M.M. Olmstead,
P.P. Power, J. Sandell, X. Xu, J. Am. Chem. Soc. 107 (1985)
4337;
(d) Li2Cu2(C6H4CH2NMe2-2)4 G. van Koten, J.T.B.H. Jastrzebski,
F. Muller, C.H. Stam, J. Am. Chem. Soc. 107 (1985) 697;

R.T. Boere´ et al. / Journal of Organometallic Chemistry 691 (2006) 5585–5591
5591
(e) Li2Cu2-Ph4(OEt2)2 N.P. Lorenzen, E. Weiss, Angew. Chem. 102
(1990) 322;
(f) Li2Cu2-Ph4(OEt2)2 N.P. Lorenzen, E. Weiss, Angew. Chem., Int.
Ed. Engl. 29 (1990) 300;
(g) Li2Cu2Ph4(DMS)3 M.M. Olmstead, P.P. Power, J. Am. Chem.
Soc. 112 (1990) 8008.
[20] Bruker SMART v 5.631, Bruker AXS Inc., 2003.
[21] G.M. Sheldrick, SHELXTL, Version 6.14, Bruker AXS Inc., Madison,
WI, 2003.
[22] M.J. Frisch et al., GAUSSIAN-98, Revision A.9, Gaussian Inc., Pitts-
burgh, PA, 1998.
[23] Z.-M. Xie, R.H. Neilson, Organometallics 2 (1983) 921.
[24] (a) J.B. Lambert, J.-H. So, J. Org. Chem. 56 (1991) 5960;
(b) D.J. Brauer, F. Bitterer, F. Do¨rrenbach, G. Heßler, O. Stelzer,
[3] (a) Li6(OEt2)3Cu4(CCPh)10 F. Olbrich, J. Kopf, E. Weiss, Angew.
Chem. 105 (1993) 1136;
(b) Li6(OEt2)3Cu4(CCPh)10 F. Olbrich, J. Kopf, E. Weiss, Angew.
Chem., Int. Ed. Engl. 32 (1993) 1077;
C. Kruger, F. Lutz, Z. Naturforsch. B 51 (1996) 1183.
¨
[25] Errors in averaged derived parameters refer to standard deviations of
the values from the mean; we note that in most cases these deviations
are larger than the e.s.d.’s from the refinement.
[26] R.J. Wehmschulte, M.A. Khan, S.I. Hossain, Inorg. Chem. 40 (2001)
2756.
[27] P. Kilian, A.M.Z. Slawin, J.D. Woollins, Chem.-Eur. J. 9 (2003) 215.
[28] S.A. Reiter, S.D. Nogai, H. Schmidbaur, Dalton Trans. (2005) 247.
[29] E. Niecke, M. Nieger, R. Pietschnig, Phosphorus Sulfur Silicon
Relat. Elem. 147 (1999) 325.
[30] P. Kilian, H.L. Milton, A.M.Z. Slawin, J.D. Woollins, Inorg. Chem.
43 (2004) 2252.
[31] G.P. Matveicheva, T.L. Krasnova, G.M. Apal’kova, A.I. Gusev,
V.A. Sharapov, E.F. Bugerenko, E.A. Chernyshev, Zh. Obshch.
Khim. (Russ.) (Russ. J. Gen. Chem.) 55 (1985) 1433.
[32] H. Schumann, F.H. Gorlitz, M. Schafers, Acta Crystallogr., Sect. C
49 (1993) 688.
(c) Li3(CuPh2)(CuPh3)(DMS)4 and Li5(CuPh2)3(CuPh3)(DMS)4
M.M. Olmstead, P.P. Power, J. Am. Chem. Soc. 112 (1990) 8008;
(d) For detailed reviews of the field see: J.T.B.H. Jastrzebski, G. van
Koten, in: N. Krause (Ed.), Modern Organocopper Chemistry,
Wiley–VCH, Weinheim, 2002, p. 1;
(e) E. Nakamura, S. Mori, Angew. Chem., Int. Ed. 39 (2000) 3750.
[4] F. Ja¨kle, I. Manners, Organometallics 18 (1999) 2628.
[5] A.L. Keen, M. Doster, H. Han, S.A. Johnson, Chem. Commun.
(2006) 1221.
[6] A. Sundararaman, L.N. Zakharov, A.L. Rheingold, F. Ja¨kle, Chem.
Commun. (2005) 1708.
[7] E.M. Meyer, S. Gambarotta, C. Floriani, A. Chiesi-Villa, C.
Guastini, Organometallics 8 (1989) 1067.
[8] D. Nobel, G. van Koten, A.L. Spek, Angew. Chem. 101 (1989) 211;
Angew. Chem., Int. Ed. 28 (1989) 208.
[9] J.A.J. Jarvis, R. Pearce, M.F. Lappert, J. Chem. Soc., Dalton Trans.
(1977) 999.
[33] R.K. Bansal, N. Gupta, S. Singh, K. Karaghiosoff, P. Mayer, M.
Vogt, Tetrahedron Lett. 45 (2004) 7771.
[10] A. Sundararaman, R.A. Lalancette, L.N. Zakharov, A.L. Rheingold,
F. Ja¨kle, Organometallics 22 (2003) 3526.
[34] T.R. van den Ancker, P.C. Andrews, S.J. King, J.E. McGrady, C.L.
Raston, B.A. Roberts, B.W. Skelton, A.H. White, J. Organomet.
Chem. 607 (2000) 213.
˚
[11] H. Eriksson, M. Hakansson, S. Jagner, Inorg. Chim. Acta 277 (1988)
233.
[35] S.S. Al-Juaid, S.M. Dhaher, C. Eaborn, P.B. Hitchcock, C.A.
McGeary, J.D. Smith, J. Organomet. Chem. 366 (1989) 39.
[36] Y. Ehleiter, G. Wolmershauser, H. Sitzmann, R. Boese, Z. Anorg.
Allg. Chem. 622 (1996) 923.
[37] C. Jones, P.C. Junk, A.F. Richards, M. Waugh, New J. Chem.
(Nouv. J. Chim.) 26 (2002) 1209.
[12] H. Eriksson, M. Ortendahl, M. Hakansson, Organometallics 15
(1996) 4823.
[13] M. Niemeyer, Organometallics 17 (1998) 4649.
[14] R. Lingnau, J. Stra¨hle, Angew. Chem., Int. Ed. 27 (1988) 436.
[15] A. Haaland, K. Rypdal, H.P. Verne, W. Scherer, W.R. Thiel, Angew.
Chem., Int. Ed. 33 (1994) 2443.
[38] A. Schmidpeter, H. Noth, G. Jochem, H.-P. Schrodel, K. Karagh-
iosoff, Chem. Ber. 128 (1995) 379.
˚
[16] H. Eriksson, M. Hakansson, Organometallics 16 (1997) 4243.
´
[17] R.T. Boere, Y.K. Zhang, J. Organomet. Chem. 690 (2005) 2651.
[39] V. Plack, J.R. Goerlich, A. Fischer, H. Thonnessen, P.G. Jones, R.
Schmutzler, Z. Anorg. Allg. Chem. 621 (1995) 1080.
[40] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen,
R. Taylor, J. Chem. Soc., Perkin Trans. II (1987) S1.
[18] R.R. Schrock, M. Wesolek, A.H. Liu, K.C. Wallance, J.C. Dewan,
Inorg. Chem. 27 (1988) 2050.
´
[19] R.T. Boere, J.D. Masuda, Can. J. Chem. 80 (2002) 1607.