Synthesis, crystal structures and dynamic NMR studies of novel trinuclear copper(I) halide complexes with 2,5-bis[(diphenylphosphino)-methyl]thiophene

Article abstract of DOI:10.1039/a803440k

Novel trinuclear copper(I) halide complexes with 2,5-bis[(diphenylphosphino)methyl]thiophene (dpmt), [Cu₃(μ₃-X)(μ-X)₂(μ-dpmt)₂] (X = 11, Br 2 or Cl 3), have been synthesized and structurally characterised. They

Full text of DOI:10.1039/a803440k

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Synthesis, crystal structures and dynamic NMR studies of novel
trinuclear copper(I) halide complexes with 2,5-bis[(diphenylphosphino)-
methyl]thiophene
Bang-Lin Chen, Kum-Fun Mok*,† and Siu-Choon Ng*
Department of Chemistry, National University of Singapore, Kent Ridge, 119260, Singapore
Novel trinuclear copper() halide complexes with 2,5-bis[(diphenylphosphino)methyl]thiophene (dpmt),
[Cu3(µ3-X)(µ-X)2(µ-dpmt)2] (X = I 1, Br 2 or Cl 3), have been synthesized and structurally characterised. They
have unusual three-runged ladder structures with one triple-bridging and two double-bridging halide atoms. Two
of the CuI are tetrahedrally co-ordinated and one, in the middle of the structure unit, has trigonal co-ordination
geometry. The trinuclear Cu3(µ3-X)(µ-X)2 framework shows some changes with halide anion X due to the size
effect and intramolecular non-bonding Cu ؒ ؒ ؒ Cu and X ؒ ؒ ؒ X interactions. The NMR studies showed that the
trinuclear framework is retained in solution for 1 (X = I), is in equilibrium with Cu3(µ-X)3 for 2 (X = Br) and
changes to Cu3(µ-Cl)3 for 3 (X = Cl), an effect attributable to the decrease of halide size from iodide to chloride.
The frameworks in the solutions of 2 and 3 exhibit fluxional behaviour involving bromine and chlorine mobility
respectively.
Copper()–phosphine complexes have attracted increasing
attention over the past decade due to their structural,1–12 photo-
chemical6,10,12,13 and antitumor properties.14 These complexes
are of diverse structural architecture which is mainly influenced
by the preparation conditions, steric properties such as the
chain length, spatial arrangements and bulkiness of phosphine
ligands and the co-ordinating ability and properties of the
counter-ions. Thus copper() complexes with monodentate
and 2,5-bis[3-(diphenylphosphino)propyl]thiophene. In 2,5-bis-
[2-(diphenylphosphino)ethyl]thiophene complexes with Mo0,
CoI and RhI, the thiophene is η1 (S) co-ordinated, while in 2,5-
bis[3-(diphenylphosphino)propyl]thiophene complexes with
RhI the η2, η3 and η7 co-ordination modes have been estab-
lished. The different behaviour indicates that the chain length
between the phosphorus atom and the thiophene ring in the
above two ligands affects the co-ordination properties of thio-
phene sulfur. In an attempt to study the co-ordination proper-
ties of thiophene derivatives in more detail, we have synthesized
another novel ligand, 2,5-bis[(diphenylphosphino)methyl]thio-
phene (dpmt). With suitable bridging length and spatial
arrangement, its complexes with copper() halides displayed
unusual trinuclear Cu3 frameworks with a three-runged ladder
structure. Here we report the synthesis of dpmt and its
novel trinuclear copper() halide complexes [Cu3(µ3-X)(µ-X)2-
(µ-dpmt)2] (X = I 1, Br 2 or Cl 3). Crystal structure and dynamic
NMR studies show that there are no direct copper()–thiophene
sulfur interactions in the solid as well as in solution in the
trinuclear copper() halide complexes.
2
phosphine ligands exist as mononuclear [Cu(PPh3)4]ClO4 and
[Cu(PPh3)3Cl],3 binuclear [{Cu[P(totp)3](µ-X)}2]4 (totp = tri-o-
tolylphosphine, X = Br or Cl) and [Cu2(PPh3)3(µ-X)2]5 (X = I,
Br or Cl) and tetranuclear [{Cu(PPh3)X}4] with pseudo-
‘cubane’6 (X = I, Br or Cl) and open ‘step’7 (X = I or Br) struc-
tures. The dppm [bis(diphenylphosphino)methane] ligand has
been reported to support mono- and bi-capping triangular-Cu3
frameworks which are further stabilised by anions in [Cu3-
(µ3-Cl)2(dppm)3]Cl,8a [Cu3(µ3-I)2(µ-I)(dppm)2],8b [Cu3(dppm)3-
1
8d
(µ3-OH)][BF4]2,8c [Cu (µ -η -C᎐CR)(µ-dppm) ]X
(R = Ph,
᎐
᎐
3
3
3
2
t
1
᎐
X = BF ; R = Bu , X = PF ), [Cu (µ -η -C᎐CR)(µ -Cl)(dppm) ]-
᎐
4
6
3
3
3
3
X8e (R = Ph, X = BF4; R = But, X = PF6) and [(dppm)3Cu3-
8h
᎐
᎐
(µ -C᎐CC H C᎐C-p-µ )Cu (dppm) ]. It can also stabilise the
᎐
᎐
3
6
4
3
3
3
open ‘step’ tetrameric [{(CuX)2(dppm)}2]9 (X = I, Br or Cl) and
10
᎐
planar [Cu4(dppm)4(µ4-E)][BF4]2 (E = C᎐C, S or Se) com-
᎐
plexes. As 1,2-bis(diphenylphosphino)ethane (dppe) can co-
ordinate as a bidentate bridging and chelating ligand, binuclear
complexes are common in its copper() complexes [{CuX-
(dppe)}2(µ-dppe)]11 (where X is a monoanionic ligand such as
N3, Cl, OPh, PhCO2, etc.). Among the above diverse mono-, bi-,
tri- and tetra-nuclear arrangements, trinuclear Cu3 frameworks
are comparatively few and found only in copper() complexes
with dppm8 and bis(diphenylphosphino)-alkyl/-arylamine
(PNP)12 ligands with triangular Cu3 frameworks which are
further bridged and stabilised by anions.
Meanwhile, the co-ordination chemistry of thiophene deriv-
atives has been less developed.15,16 The thiophene sulfur shows
weak co-ordination ability and thiophene rings usually act as
spacing units in the co-ordination compounds of Schiff bases
derived from thiophene-2-carbaldehyde or thiophene-2,5-
dicarbaldehyde.16 Mathieu et al.17 examined the co-ordination
properties of 2,5-bis[2-(diphenylphosphino)ethyl]thiophene
Results and Discussion
The ligand was synthesized by reaction of freshly distilled 2,5-
bis(chloromethyl)thiophene with LiPPh2 and characterised by
MS, NMR and elemental analysis. It is stable in the solid state
and unstable in CH2Cl2 and CHCl3 solutions, being easily
oxidised to form 2,5-bis(diphenylphosphorylmethyl)thiophene.
Reaction of [Cu(MeCN)4]PF6 with dpmt in the molar ratio of
3:2 in acetonitrile, followed by additions of methanolic potas-
sium halide or aqueous sodium chloride, gave the trinuclear
complexes 1 (X = I), 2 (X = Br) and 3 (X = Cl) as colourless
solids. These can also be synthesized by treating CuX with
dpmt in dichloromethane followed by addition of methanol.
Recrystallisation from dichloromethane–methanol gave single
† E-Mail: chmmokkf@nus.edu.sg
J. Chem. Soc., Dalton Trans., 1998, Pages 2861–2866
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Table 1 Selected bond and contact distances (Å), angles (Њ) and some
structural parameters for complexes for 1–3
2ؒ2CH2Cl2
(X = Br)
3ؒ1.25CH2Cl2
(X = Cl)
1 (X = I)
Cu(1)᎐X(1)
Cu(1)᎐X(2)
Cu(1)᎐X(3)
Cu(2)᎐X(1)
Cu(2)᎐X(2)
Cu(3)᎐X(1)
Cu(3)᎐X(3)
Cu(2)᎐P(1)
Cu(2)᎐P(4)
Cu(3)᎐P(2)
Cu(3)᎐P(3)
2.542(2)
2.545(2)
2.577(2)
2.862(2)
2.678(2)
2.744(2)
2.724(2)
2.273(2)
2.273(2)
2.255(3)
2.264(3)
2.438(2)
2.419(2)
2.379(2)
2.563(1)
2.577(1)
2.791(1)
2.482(1)
2.254(2)
2.245(2)
2.250(2)
2.249(2)
2.377(2)
2.275(2)
2.237(2)
2.435(2)
2.456(2)
2.757(2)
2.340(2)
2.253(2)
2.242(2)
2.248(2)
2.241(2)
Fig.
1
Perspective view of the structure of [Cu3(µ3-Cl)(µ-Cl)2-
(µ-dpmt)2] 3 with atomic numbering scheme
X(1)᎐Cu(1)᎐X(2)
X(1)᎐Cu(1)᎐X(3)
X(2)᎐Cu(1)᎐X(3)
P(1)᎐Cu(2)᎐P(4)
P(1)᎐Cu(2)᎐X(2)
P(4)᎐Cu(2)᎐X(2)
P(1)᎐Cu(2)᎐X(1)
P(4)᎐Cu(2)᎐X(1)
X(2)᎐Cu(2)᎐X(1)
P(2)᎐Cu(3)᎐P(3)
P(2)᎐Cu(3)᎐X(3)
P(3)᎐Cu(3)᎐X(3)
P(2)᎐Cu(3)᎐X(1)
P(3)᎐Cu(3)᎐X(1)
X(3)᎐Cu(3)᎐X(1)
Cu(1)᎐X(1)᎐Cu(3)
Cu(1)᎐X(1)᎐Cu(2)
Cu(3)᎐X(1)᎐Cu(2)
Cu(1)᎐X(2)᎐Cu(2)
Cu(1)᎐X(3)᎐Cu(3)
120.02(6)
120.65(6)
119.17(6)
131.33(9)
104.99(6)
102.17(6)
105.35(7)
105.32(7)
105.33(4)
124.30(10)
103.09(8)
103.69(8)
106.78(8)
109.21(8)
108.86(4)
65.32(4)
113.01(5)
119.88(5)
120.08(5)
123.65(6)
102.41(5)
101.57(5)
110.27(5)
112.08(5)
104.01(3)
126.58(6)
105.34(5)
109.29(5)
99.35(5)
109.65(5)
104.35(3)
64.85(3)
70.40(3)
132.77(3)
70.45(3)
107.87(7)
116.61(8)
127.40(8)
122.20(7)
102.53(7)
101.86(7)
112.19(6)
113.58(6)
100.51(6)
126.30(7)
105.57(7)
111.91(7)
100.56(6)
108.60(6)
100.45(6)
66.47(5)
framework constructed of one triple-bridging, atom X(1), two
double-bridging X atoms X(2) and X(3), two tetrahedrally co-
ordinated copper atoms Cu(2) and Cu(3) and one trigonally co-
ordinated atom Cu(1), in the middle of the trinuclear structure
unit. Atoms Cu(2) and Cu(3) are each co-ordinated to the
phosphorus donor of two bridging dpmt molecules, one bridg-
ing halide and one µ3-bridging halide. The two thiophene rings
are syn sandwiching the Cu3(µ3-X)(µ-X)2 plane. Structures
involving a mixed copper() stereochemistry of tetrahedral and
trigonal chromophores and both triple- and double-bridging X
have been found in the tetranuclear open ‘step’ [{Cu(PPh3)-
X}4]7 and [{(CuX)2(dppm)}2]9 (X = I, Br or Cl). The structures
of complexes 1–3 have some similarities with these open ‘step’
molecules, but differ from them by the virtual planarity of the
trinuclear Cu3(µ3-X)(µ-X)2 frame. Obviously the dpmt ligands
with a suitable bridging length and spatial arrangement play
important roles in stabilising the planar trinuclear Cu3(µ3-X)-
(µ-X)2 framework. Such a ‘three-runged ladder’ structure is
comparatively uncommon and has so far been found only in
65.84(4)
131.15(4)
68.70(4)
73.84(5)
137.94(7)
75.24(6)
65.16(4)
70.87(4)
76.41(7)
Cu(1) ؒ ؒ ؒ Cu(2)
Cu(1) ؒ ؒ ؒ Cu(3)
Cu(2) ؒ ؒ ؒ Cu(3)
X(1) ؒ ؒ ؒ X(2)
X(1) ؒ ؒ ؒ X(3)
Cu(1) ؒ ؒ ؒ S(1)
Cu(1) ؒ ؒ ؒ S(2)
2.949(2)
2.857(2)
5.104(3)
4.406(2)
4.448(2)
2.971(2)
3.134(2)
2.885(2)
2.819(2)
4.907(3)
4.051(2)
4.189(2)
2.659(2)
3.339(2)
2.891(2)
2.832(2)
4.648(3)
3.761(3)
3.926(3)
2.645(2)
3.341(2)
18a
trinuclear rhodium() complexes [Rh3(µ-dpmp)2(CO)3I2]BPh4
and [Rh3(µ-dpmp)2(CO)I4]BPh4 18b {dpmp = bis[(diphenylphos-
phino)methyl]phenylphosphine} in which the planar trinuclear
Rh3(µ3-I)(µ-I)(µ-CO) or Rh3(µ3-I)(µ-I)2 planes are bridged by
two dpmp ligands.
S(1) ؒ ؒ ؒ Cu(1) ؒ ؒ ؒ S(2)
175.99(8)
0.008
172.26(5)
0.164
168.76(7)
0.146
Mean deviation of
Cu3X(1) plane/Å
As previously noted,5,7,9 the Cu᎐X bond distances for tetra-
hedrally co-ordinated Cu(2) and Cu(3) are longer than those
for trigonally co-ordinated Cu(1) and decrease with the halide
anions from iodide to chloride. The longest Cu᎐X bond dis-
tance is 2.862(2) Å in 1, 2.791(1) Å in 2 and 2.757(2) Å in 3.
Such long distances suggest that the above three bond inter-
actions are comparatively weak. As the size of the bridging
halogen atoms decreases along the sequence I > Br > Cl the
X(2)᎐Cu(2)᎐X(1) and X(3)᎐Cu(3)᎐X(1) angles decrease and
Cu(3)᎐X(1)᎐Cu(2), Cu(1)᎐X(2)᎐Cu(2) and Cu(1)᎐X(3)᎐Cu(3)
angles increase. The X᎐Cu(1)᎐X angles are all within 1Њ of an
ideal 120Њ for trigonal planar co-ordinated copper() in 1, but
deviate increasingly from the ideal value from 2 [X = Br,
Mean deviation of
Cu(1)X3 plane/Å
0.023
0.019
0.140
0.159
0.142
0.156
Mean deviation of
Cu3X3 plane/Å
Deviation of Cu(1)
from Cu3X3 plane/Å
0.046
0.349
0.341
crystals suitable for structure determinations. Complexes 1–3
were found stable in solution as well as in the solid state, but
single crystals turned opaque on standing in air.
113.01(5), 119.88(5), 120.08(5)Њ] to
3 [X = Cl, 107.87(7),
116.61(8), 127.40(8)Њ]. The mean deviation of Cu(1) from the
corresponding Cu3X3 mean plane is 0.046 Å in 1, 0.349 Å in 2
and 0.341 Å in 3, all towards S(1), so that the Cu(1) ؒ ؒ ؒ S(1)
distance decreases with halide anions in the above three tri-
nuclear complexes: 2.971(2) Å in 1, 2.659(2) Å in 2 and 2.645(2)
Å in 3.
The stereochemical changes with the halide anions in the
above three structures, to some extent, are due to the size effects
of the different halide anions on the trinuclear Cu3(µ3-X)(µ-X)2
frameworks and intramolecular non-bonding Cu ؒ ؒ ؒ Cu and
X ؒ ؒ ؒ X interactions. Size effects of halide anions on structural
changes have been found in trinuclear [Rh3(µ-dpmp)2(CO)3X2]-
Structures of complexes 1–3
In order to investigate any systematic structural changes with
the halide anions, complexes 1–3 were structurally character-
ised. They displayed a similar ‘three-runged ladder’ structure
where the Cu3(µ3-X)(µ-X)2 units were bridged by two dpmt
ligands above and below the trinuclear plane. Fig. 1 shows a
representative perspective drawing of complex 3. Selected bond
distances and angles are listed in Table 1. To the best of our
knowledge, complexes 1–3 are the first examples of trinuclear
copper() complexes with a ‘three-runged ladder’ structural
18a,c
18a,c
BPh4
(X = I, Br or Cl). In [Rh3(µ-dpmp)2(CO)3I2]BPh4
2862
J. Chem. Soc., Dalton Trans., 1998, Pages 2861–2866

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and [Rh3(µ-dpmp)2(CO)I4]BPh4,18b which have similar struc-
tural features to our reported complexes, only iodide anions can
bridge the planar Rh3(µ3-I)(µ-I)(µ-CO) or Rh3(µ3-I)(µ-I)2, while
the bromide and chloride anions are not large enough to act as
18a,c
µ3 planar ligands. Thus [Rh3(µ-dpmp)2(CO)3X2]BPh4
(X =
Br or Cl) have slightly different structural features [the two tri-
dentate bridging dpmp ligands determine the Rh3(µ3-I)(µ-I)-
(µ-CO) or Rh3(µ3-I)(µ-I)2 planes]. Teo and Calabrese19 have
systematically studied the structures of (R3Y)4M4X4-type
complexes (R = Ph or Et; Y = P or As; M = Cu or Ag; X = Cl,
Br or I) and made an unequivocal conclusion that their
stereochemistries are to a significant extent dictated by intra-
molecular non-bonded van der Waals interactions which are
a function of the size of the metal, the bridging X and the
terminal ligands. In our three trinuclear [Cu3(µ3-X)(µ-X)2-
(µ-dpmt)2] complexes the Cu(2) ؒ ؒ ؒ Cu(3) separation decreases
with the halide anion from iodide [1, 5.104(3) Å] to bromide [2,
4.907(3) Å] and to chloride [3, 4.648(3) Å] due to the decreasing
atom size. Distortion of the planar Cu3(µ3-X)(µ-X)2 framework
in 2 and 3, to some extent, can minimise the repulsions between
Cu ؒ ؒ ؒ Cu and X ؒ ؒ ؒ X as shown in the X ؒ ؒ ؒ X distances
[Cl ؒ ؒ ؒ Cl 3.761(3) and 3.926(3); Br ؒ ؒ ؒ Br 4.051(2) and 4.189(2);
I ؒ ؒ ؒ I 4.406(2) and 4.448(2) Å]. These distances are all greater
than or close to normal van der Waals contacts (viz. Cl ؒ ؒ ؒ Cl
3.60; Br ؒ ؒ ؒ Br 3.90; I ؒ ؒ ؒ I 4.30 Å)20 suggesting that these
halogen–halogen interactions are strongly repulsive. The
CuI ؒ ؒ ؒ S contact distances in the range 2.89–3.44 Å were found
in other systems containing thiophene units16 and were con-
sidered to be weak or non-bonding interactions. Copper()–
sulfur bond distances are in the range 2.23–2.48 Å for co-
ordinated sulfurs.1 Co-ordination of thiophene sulfur has
Fig. 2 Comparison of some triangular CuI3 frameworks. (i) Ref. 8,
(ii) ref. 25, (iii) this work, (iv) ref. 26. See text for detailed discussion
by the spatial arrangements and bridging length of the ligands
and the electronic properties of the bridging anions. The
Cu ؒ ؒ ؒ Cu distances in some of the trinuclear Cu3 complexes are
listed in Table 2. Besides the triangular Cu3 frameworks shown
in Fig. 2, equilateral triangular Cu3 geometry linked by Cu᎐
H᎐B and Cu᎐Cu interactions was found in [Cu3(µ-H)3-
{C2B9H9[C5H4N(CO2CH3)-4]}]28a with
a
relatively short
copper–copper distance of 2.519(2) Å. G. van Koten and co-
workers28c reported two triangular organocopper() complexes
bridged by aryl and O2CPh in [Cu3(C6H2Me3-2,4,6)(O2CPh)2],
aryl and Br in [Cu3Br{C6H4(CH2MeCH2CH2NMe2)-2}2].
been established in [M(sttp)Cl]21 (M = Fe2ϩ, Ni2ϩ or Cu2ϩ
,
Hsttp = 5,10,15,20-tetraphenyl-21-thiaporphyrin) with M᎐S
bond distances of 2.388 (M = FeII), 2.296(1) (M = NiII) and
2.335(2) Å (M = CuII), fac-[Mo(CO)3L]17a [Mo0᎐S 2.569(1) Å]
and [Rh(CO)L][ClO4]17a [RhI᎐S, 2.318(1) Å] {L = 2,5-bis-
[2-(diphenylphosphino)ethyl]thiophene}. The fact that the
Cu(1) ؒ ؒ ؒ S(1) distances in the range 2.645(2)–2.971(2) Å are
longer than the sum of the covalent radii (2.21 Å),22 whilst the
S(1)᎐C(14), S(1)᎐C(17), S(2)᎐C(44) and S(2)᎐C(47) bond dis-
tances are comparable with 1.714(2) Å in free thiophene,23
together with corroborating solution NMR studies, suggest
that there are no direct bonded interactions between CuI and
thiophene sulfur in our complexes. The copper–copper dis-
tances are in the range 2.819(2)–2.949(2) Å in 1–3, shorter than
those found in ‘cubane’ [Cu4X4(PPh3)4]6 (X = I, Br or Cl)
[2.874(5)–3.164(4) Å] and ‘step’ [Cu4X4(PPh3)4]7 (X = I or Br)
[2.835(3)–3.448(3) Å], and comparable with those found in
‘step’ [{(CuX)2(dppm)}2]9 (X = I, Br or Cl) [2.682(7)–3.180(2)
Å], indicating that there are no direct Cu ؒ ؒ ؒ Cu interactions.
Trinuclear copper() complexes though comparatively rare
can be found in some reduced forms of ascorbate oxidase.24
Some spatial Cu3 arrangements together with the tricopper()
site of ascorbate oxidase are shown in Fig. 2. The ligand dppm
is the appropriate supporter in Cu3 framework (i)8 which are
further mono- or bi-capped by acetylide, alkynyl, halide, iso-
cyanide and WS4 anions. In Cu3 framework (ii)25 S-donor edge-
bridging ligands such as ethane-1,2-dithiolate, S4, S6, Me3PS
and (PhO)2P(S)NC(S)NEt2 are needed to stabilise the structure
framework. N-Donor ligands have recently been developed to
support the triangular Cu3 framework (iv)26 as models of the
active site of ascorbate oxidase; as no co-ordinated anions are
involved in bridging, Cu ؒ ؒ ؒ Cu distances in structure frame-
work (iv) are comparatively long. In our reported Cu3 frame-
work (iii) the new ligand dpmt with suitable bridging length and
spatial arrangement stabilises the Cu3(µ3-X)(µ-X)2 framework,
the triangular Cu3 core is approximately isosceles with one edge
distance much longer than the other two as shown in Table 1.
As no obvious direct Cu ؒ ؒ ؒ Cu bonding interactions27 exist in
these systems the Cu ؒ ؒ ؒ Cu distances were mainly determined
Solution studies
The electronic absorption spectrum of complexes 1–3 show
bands at about 226 and 256 nm in dichloromethane, attribut-
able to the intraligand transition of dpmt, since the unco-
ordinated dpmt also absorbs strongly in this region. The
low-energy absorptions at about 320 nm of 1 and 300 nm of
2 are likely to arise from a ligand-to-metal charge transfer
1
(LMCT) transition. The room-temperature 31P-{1H} and H
NMR spectra of 1 show a singlet 31P resonance at δ Ϫ16.9 and
singlet thiophene proton resonances at δ 5.61 respectively,
which means the surroundings of the two dpmt ligands around
the trinuclear Cu3(µ3-I)(µ-I)2 plane are identical. The existence
of two sets of doublet methylene proton resonances at δ 4.12
(J = 14.0) and 3.61 (J = 14.0 Hz) indicates that the two geminal
methylene protons are non-equivalent and are coupled to each
other, so that rotation of bridging ligands around the trinuclear
Cu3(µ3-I)(µ-I)2 framework is blocked. The non-equivalence of
the two methylene protons in the 1H NMR spectrum arises on
account of the different orientations of the two protons to the
trinuclear Cu3(µ3-I)(µ-I)2 framework, with one equatorial and
the other axial which is also established in the solid structure of
1. The 31P-{1H} and 1H NMR spectra of 2 at room temperature
(300 K) are similar to those of 1 in CDCl3 solution, exhibiting
a singlet 31P resonance at δ Ϫ10.3, singlet thiophene proton
resonances at δ 5.44 and two sets of doublets at δ 4.04 and 3.48,
again indicating that the two ligands are symmetrically oriented
with respect to the trinuclear Cu3(µ3-Br)(µ-Br)2 framework.
Additional weak resonances at δ 1.2 and Ϫ8.0 in 31P-{1H}
NMR and δ 5.73 in 1H NMR suggest that there is also a minor
amount of another isomer in solution. Variable-temperature
1
31P-{1H} and H NMR spectra of 2 are unchanged over the
range 218 to 320 K. Those of the minor isomer exhibit some
changes as evident in thiophene protons at δ 5.68 (320 K) to
5.85 and 5.79 (218 K) and several methylene proton resonances
J. Chem. Soc., Dalton Trans., 1998, Pages 2861–2866
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Table 2 Comparison of Cu ؒ ؒ ؒ Cu distances (Å) in some of the triangular Cu3 frameworks
Complex
Cu ؒ ؒ ؒ Cu
Ref
[Cu3(µ3-I)(µ-I)2(µ-dpmt)2]
2.857(2)
2.819(2)
2.832(2)
2.546(3)
3.175(4)
3.120(2)
2.497(2)
2.813(2)
2.570(3)
2.785(3)
2.749(1)
2.769(1)
2.421(2)
2.403(1)
2.915
2.949(2)
2.885(2)
2.891(2)
2.916(4)
3.175(4)
3.127(2)
2.800(2)
2.904(3)
2.598(3)
2.803(3)
2.751(1)
2.773(1)
2.421(2)
2.409(1)
3.500
5.104(3)
4.907(3)
4.648(3)
3.142(4)
3.281(3)
3.322(2)
3.294(2)
3.274(3)
2.615(3)
2.871(3)
2.846(1)
2.816(1)
2.888(2)
3.299(1)
3.614
a
a
a
[Cu3(µ3-Br)(µ-Br)2(µ-dpmt)2]ؒ2CH2Cl2
[Cu3(µ3-Cl)(µ-Cl)2(µ-dpmt)2]ؒ1.25CH2Cl2
[Cu3(µ3-I)2(µ-I)(µ-dppm)3]
8(b)
8(a)
8(c)
8(i)b
8(d)
8(d)
8(d)
25(d)
25(e)
28(b)
28(c)
26(b)
26(a)
24
[Cu3(µ3-Cl)2(µ-dppm)2]Cl
[Cu3(µ3-OH)(µ-dppm)3][BF4]2
1
1
᎐
᎐
[Cu3(µ3-η -C᎐CR)(µ-η -C᎐CNR)(µ-dppm)3][BF4]
᎐
᎐
1
᎐
[Cu3(µ3-η -C᎐CPh)(µ-dppm)3][BF4]2
᎐
1
᎐
[Cu3(µ3-η -C᎐CPh)2(µ-dppm)3][BF4]
᎐
1
᎐
[Cu3(µ3-η -C᎐CPh)(µ3-Cl)(µ-dppm)3][BF4]
᎐
Na[Me3NCH2Ph]2[Cu3(S2C2H4)3]ؒMeOH
[{Cu[(PhO)2P(S)NC(S)NEt2]}3]
[Cu3(C6H2Me3-2,4,6)(O2CPh)2]
[Cu3Br{C6H4(CH2MeCH2CH2NMe2)-2}2]
[Cu3L1 ][PF6]c
2
[Cu(µ-L2)2{Cu(cnge)(MeCN)}2][BF4]3ؒMeCNd
Tricopper() site of ascorbate oxidase
3.624(16)
4.1
3.634(15)
4.4
5.011(15)
5.1
a This work. b R = 4-MeC6H4. c L1 = Hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate. d L2 = 3,6-Bis(3-tert-butylpyrazolyl)pyridazine, cnge = 2-cyano-
guanidine.
at 218 K, suggesting fluxional behaviour in solution. It is of
interest that the relative concentration of the two isomers is
dependent on the temperature. The minor:major concentration
ratio is 0.08, 0.10, 0.18, 0.21 and 0.75:1 at 218, 233, 273, 300
and 320 K respectively, indicating that the higher the temper-
ature the higher is the concentration of the minor isomer, and
transformation of the major to the minor isomer is an endo-
thermic reaction. The solid structure of 2 shows that the
Cu(3)᎐Br(1) interaction is comparatively weak with a long
bond distance of 2.79(1) Å, so there is a possible equilibrium (1)
Fig. 3 Variable-temperature 31P-{1H} (a) and 1H (b) NMR spectra of
complex 3 in CDCl3; the signals at δ ca. 5.30 in (b) are from CH2Cl2
in CDCl3 solution with ∆H‡ ca. 6.5 kJ molϪ1 obtained from the
from that in the solid phase. The molecular structure of 3 indi-
Van’t Hoff equation.29
cates that the Cu(3)᎐Cl(1) bond distance [2.757(2) Å] is very
long and interaction between Cu(3) and Cl(1) is comparatively
weak. The above NMR behaviour in solution suggests that 3 is
undergoing the fluxional process shown in equation (2).
1
Room-temperature 31P-{1H} and H NMR spectra of com-
plex 3 in CDCl3 solution, however, are quite different from
those of 1 and 2, and show two sets of singlet 31P resonances at
δ Ϫ2.5 and Ϫ7.4, one set of thiophene proton resonances at
δ 5.70 and one set of methylene proton resonances at δ 3.71.
Variable-temperature NMR spectroscopy was used to probe the
dynamic behaviour of 3 in CDCl3 solution as shown in Fig. 3.
At ambient and sub-ambient temperatures, the 31P-{1H} NMR
spectrum shows two singlet resonances. On increasing the
temperature the two sets of singlet 31P resonances gradually
coalesce to a broad 31P resonance at δ Ϫ2.9 with a coalescence
1
temperature of 323 K. Likewise, at low temperatures, the H
NMR spectrum has two sets of singlet at δ 5.84 and 5.77 (218
K), which gradually coalesce to a singlet for thiophene protons
at δ 5.70 (300 K) with a coalescence temperature of 286 K. At
218 K the 1H NMR shows four sets of doublet methylene
protons at δ 4.28 (2J = 13.5), 3.70 (2J = 13.7), 3.52 (2J = 13.5)
and 3.46 (2J = 13.7 Hz). Irradiation of the protons at δ 3.70
removes the doublet coupling at δ 3.46, indicating they are
coupled to each other; similarly, the protons at δ 4.28 are
coupled with those at δ 3.52. The two sets of singlet 31P reson-
ances have an integration ratio of 1:0.92 at 218 K. The different
NMR behaviour of 3, compared with those of 1 and 2 in solu-
tion, possibly indicates that its structure in solution is different
At high temperature, rapid equilibration leads to equivalence
of four phosphorus atoms and only one set of 31P-{1H} signals
can be resolved. Fluxional processes involving chlorine mobil-
ity have been established in NMR studies of some trinuclear
complexes such as [Rh3(CO)3(µ-Cl)Cl(µ-dpmp)2]BPh4,18a,c [Ir3-
(µ-CO)2(CO)2(µ-Cl)Cl(µ-dpma)2]BPh4, [Ir2Rh(µ-CO)2(CO)3-
(µ-Cl)(µ-dpma)2]BPh4 and [Rh2Pd(µ-Cl)(CO)2Cl2(µ-dpma)2]-
BPh4 30 {dpma = bis[(diphenylphosphino)methyl]phenylarsine}.
The activation energy ∆G‡ for process (2) calculated by the
Eyring equation31 is ca. 57 kJ molϪ1 from VT 31P-{1H} NMR
2864
J. Chem. Soc., Dalton Trans., 1998, Pages 2861–2866

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Table 3 Crystal data and refinement details for complexes 1, 2ؒ2CH2Cl2 and 3ؒ1.25CH2Cl2
1
2ؒ2CH2Cl2
3ؒ1.25CH2Cl2
Formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
C60H52Cu3I3P4S2
1532.34
C62H56Br3Cl4Cu3P4S2
1561.22
C61.25H54.5Cl5.5Cu3P4S2
1364.14
Monoclinic
P21/c (no. 14)
29.207(4)
9.929(2)
22.083(4)
110.78(1)
5987(2)
Monoclinic
C2/c (no. 15)
58.950(6)
10.390(2)
21.589(3)
104.33(2)
12 812(3)
8
Monoclinic
C2/c (no. 15)
58.830(1)
10.219(1)
21.663(1)
104.00(1)
12 636(1)
8
β/Њ
U/Å3
Z
4
Dc/mg cmϪ3
µ/mmϪ1
F(000)
1.700
2.816
3000
1.619
3.229
6240
1.434
1.438
5556
Crystal size/mm
hkl Index ranges
0.33 × 0.25 × 0.23
Ϫ35 to 29,
Ϫ9 to 11,
Ϫ21 to 26
10 820
649
2.34, Ϫ1.70
0.0713
0.30 × 0.20 × 0.13
Ϫ57 to 71,
Ϫ12 to 11,
Ϫ24 to 26
11 775
703
2.69, Ϫ2.36
0.0536
0.50 × 0.38 × 0.25
Ϫ47 to 73,
Ϫ12 to 11,
Ϫ27 to 26
12 811
703
1.62, Ϫ1.41
0.0685
Independent reflections
No. parameters refined
Largest difference peak and hole/e ÅϪ3
R1a [I > 2σ(I)]
wR2b
0.1844
1.031
0.1449
1.047
0.1956
0.966
Goodness of fit on F2
¹
4
a R1 = Σw|Fo Ϫ Fc|/Σ(Fo). b wR2 = [Σw(Fo2 Ϫ Fc2)2/ΣwFo ]².
spectra (Tc = 323 K, ∆ν = 2171 Hz), agreeing well with a value
δ(31P) Ϫ11.2 (s); δ(1H) 7.60–7.34 (m, 20 H, phenyl ring), 6.36
(s, 2 H, thiophene ring) and 3.48 (s, 4 H, methylene). EI MS:
m/z 480 (Mϩ) (Found: C, 74.85; H, 5.38; S, 6.46. Calc. for
C30H26P2S: C, 74.96; H, 5.45; S, 6.67%).
1
of ca. 60 kJ molϪ1 derived from VT H NMR spectra for the
coalescence of thiophene protons (Tc = 286 K, ∆ν = 34.3 Hz).
Variable-temperature 31P-{1H} and 1H NMR spectra of the
minor isomer of 2 are similar to those of 3 in solution, indicat-
ing that the minor isomer of 2 also shows similar fluxional
behaviour to that of 3. The different NMR behaviours of com-
plexes 1–3, to some extent, are attributed to a size effect of the
halide anions. The small size of chlorine (X = Cl) is not large
enough for Cl(1) to make contact with all three copper centres,
so that the Cu(2)᎐Cl(1) or Cu(3)᎐Cl(1) bond is readily broken
in solution.
2,5-Bis(diphenylphosphorylmethyl)thiophene.
A
dichloro-
methane solution (20 cm3) of dpmt (1 mmol, 0.48 g) was gently
heated for 5 min. After removing the solvent in vacuo, crystal-
lisation of the residue from dichloromethane–acetonitrile gave
0.38 g (75%) of colourless crystals. δ(31P) 28.4 (s); δ(1H) 7.69–
3
7.40 (m, 20 H), 6.57 (d, 2 H) and 3.72 [d, 4 H, J(PH) = 12.4
Hz]. EI MS: m/z 512 (Mϩ) (Found: C, 70.20; H, 5.01; S, 6.18.
Calc. for C30H26O2P2S: C, 70.28; H, 5.11; S, 6.25%).
Experimental
Materials and methods
[Cu3(ì3-X)(ì-X)2(ì-dpmt)2] (X ؍ I 1 or Br 2). The compound
dpmt (0.30 mmol) was added to a stirred solution of [Cu-
(MeCN)4]PF6 (0.45 mmol) in acetonitrile (15 cm3). After 2 h,
methanol (10 cm3) containing KX (0.90 mmol) was added and
stirred for 1 h. The precipitated white powder was collected and
recrystallised from CH2Cl2–MeOH in 45–58% yield. Com-
pound 1: δ(31P) (CDCl3, 298 K) Ϫ16.9 (s); δ(1H) (CDCl3, 298
All solvents were dried and degassed prior to use and all reac-
tions were carried out under a nitrogen atmosphere. Elemental
analyses were carried out by the Microanalytical Laboratory
of the Department of Chemistry, National University of
Singapore. Electron impact mass spectra were recorded on a
Micromass VG 7035 mass spectrometer at 70 eV (ca.
1.12 × 10Ϫ17 J), UV/VIS spectra at room temperature on a
Shimadzu UV-240 spectrophotometer in CH2Cl2 solution and
NMR spectra on a Bruker AC500 at 500.14 (1H) or 202.46 MHz
(31P) using SiMe4 or 85% H3PO4 as standards. The compounds
2,5-bis(chloromethyl)thiophene,32 PPh2H33 and [Cu(MeCN)4]-
2
K) 8.61–6.90 (m, 20 H), 5.61 (s, 2 H), 4.12 [d, 2 H, J(HH) =
2
14.0] and 3.61 [d, 2 H, J(HH) = 14.0 Hz]; UV/VIS λmax/nm
(ε/Ϫ1 cmϪ1) 226 (88 200), 256 (sh, 54 100) and 320 (sh,
12 200) (Found: C, 47.15; H, 3.46; Cu, 11.86; S, 4.32. Calc. for
C60H52Cu3I3P4S2: C, 47.02; H, 3.42; Cu, 12.44; S, 4.18%). Com-
pound 2: δ(31P) (CDCl3, 300 K) Ϫ10.3 (s); δ(1H) (CDCl3, 300
K) 7.72–6.87 (m, 20 H), 5.44 (s, 2 H), 4.04 [d, 2 H,
34
PF6 were prepared according to the published methods.
2
2J(HH) = 13.6] and 3.48 [d, 2 H, J(HH) = 13.4 Hz]; UV/VIS
Other reagents were used as received.
λmax/nm (ε/Ϫ1 cmϪ1) 226 (89 300), 256 (sh, 61 200) and 300
(sh, 24 500) (Found: C, 51.49; H, 3.58; Cu, 13.14; S, 4.25. Calc.
for C60H52Br3Cu3P4S2: C, 51.78; H, 3.77; Cu, 13.71; S, 4.61%).
Preparations
2,5-Bis[(diphenylphosphino)methyl]thiophene. A solution of
LiPPh2 (45.0 mmol) in thf (150 cm3) was prepared from PPh2H
(7.9 cm3, 45.0 mmol) and LiBun in hexane (1.6 , 28.1 cm3, 45.0
mmol) and cooled to 0 ЊC. To this solution was slowly added
freshly distilled 2,5-bis(chloromethyl)thiophene (22.5 mmol,
4.08 g) dissolved in thf (150 cm3). The solution was stirred for
3 h at room temperature, after which the thf was removed under
vacuum. The residue was dissolved in dichloromethane
(150 cm3), and the solution washed with water (3 × 150 cm3).
After removing the solvent, crystallisation of the residue from
methanol gave 4.76 g (44%) of dpmt as pale yellow crystals.
[Cu3(ì3-Cl)(ì-Cl)2(ì-dpmt)2] 3. Compound dpmt (0.30 mmol)
was added to a stirred solution of [Cu(MeCN)4]PF6 (0.45
mmol) in acetonitrile (15 cm3). After 2 h an aqueous solution
(10 cm3) containing NaCl (0.90 mmol) was added and stirred
for 1 h. After the acetonitrile was removed in vacuo, CH2Cl2 (30
cm3), was added to the residue. The CH2Cl2 phase was washed
twice with water (20 cm3) and evaporated to give crude complex
3. This was purified by washing with small amounts of meth-
anol and recrystallisation from CH2Cl2–MeOH to get 3 in
35% yield. δ(31P) (CDCl3, 300 K) Ϫ2.5 (s) and Ϫ7.4 (s); δ(1H)
J. Chem. Soc., Dalton Trans., 1998, Pages 2861–2866
2865

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Dalton Trans., 1972, 1938; P. Fiaschi, C. Floriani, M. Pasquali,
(CDCl3, 300 K) 7.37 and 7.17 (br, 20 H), 5.70 (s, 2 H) and 3.71
(s, 4 H). UV/VIS: λmax/nm (ε/Ϫ1 cmϪ1) 226 (88 300) and 256
(sh, 53 600) (Found: C, 56.93; H, 4.46; Cu, 14.68; S, 4.85. Calc.
for C60H52Cl3Cu3P4S2: C, 57.27; H, 4.17; Cu, 15.16; S, 5.10%).
A. Chiesi-Villa and C. Guastini, Inorg. Chem., 1986, 25, 462; E. W.
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13 See, for example, (a) D. Li, H. K. Yip, C. M. Che, Z. Y. Zhou,
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Crystallography
A single crystal of complex 1 was mounted on a glass fiber and
covered with a film of an inert oil, while crystals of 2 and 3 were
sealed into glass capillaries with the mother-liquor. Crystal data
and a summary of the crystallographic analyses are given in
Table 3. The data were collected at 295 K on a Siemens CCD dif-
fractometer using graphite-monochromated Mo-Kα radiation
(λ = 0.710 73 Å). All the structures were solved by direct
methods and some non-hydrogen atoms located from Fourier-
difference maps. All non-hydrogen atoms were refined anisotrop-
ically. Refinement was by full-matrix least squares based on F 2
using SHELXL 93.35 Hydrogen atoms were placed in assigned
positions and with their isotropic thermal parameters riding on
the parent carbon atoms. The largest residual peaks and holes
were found above and below the Cu3(µ3-X)(µ-X)2 plane.
CCDC reference number 186/1066.
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Acknowledgements
We thank the National University of Singapore for the research
scholarship to B.-L. Chen and Dr. P. H. Leung and Ms. S.-Y.
Wong for their discussion of the NMR studies.
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Received 7th May 1998; Paper 8/03440K
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