Copper(I) halide chelates of the wide bite angle diphosphane xantphos: Crystal structures of [CuBr(xantphos)(dmpymtH)] and [CuI(xantphos)(imdtH2)] · CH3CN

Article abstract of DOI:10.1016/j.ica.2006.02.046

Copper(I) halide complexes containing the diphosphane xantphos (4,5-bis(diphenylphosphano)-9,9-dimethyl-xanthene) and some heterocyclic thione ligands have been synthesized and characterized by ¹H NMR, IR spectroscopy, elemental analyses and melting point determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in acetonitrile/methanol solution. The molecular structures of [CuBr(xantphos)(dmpymtH)] and [CuI(xantphos)(imdtH₂)] · CH₃CN have been established by single-crystal X-ray diffraction. Each of these structures features a tetrahedral copper(I) center with two phosphorus atoms from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. Rapid decomposition of the mixed-ligand complexes via ligand dissociation occurs upon standing of their acetonitrile solutions at room temperature for several days. The resulting colored crystals, which not only on elemental analysis but also on the basis of their NMR and IR spectra, are found to be phosphane-free coordination polymers of composition [CuX(thione)].

Full text of DOI:10.1016/j.ica.2006.02.046

Inorganica Chimica Acta 359 (2006) 3183–3190
www.elsevier.com/locate/ica
Copper(I) halide chelates of the wide bite angle diphosphane
xantphos: Crystal structures of [CuBr(xantphos)(dmpymtH)] and
[CuI(xantphos)(imdtH2)] Æ CH3CN
a
b
c,
*
P.J. Cox , A. Kaltzoglou , P. Aslanidis
a
School of Pharmacy, The Robert Gordon University, Schoolhill, Aberdeen AB10 1FR, Scotland, United Kingdom
b
Department Chemie, Technische Universita¨t Mu¨nchen, Lichtenbergstr. 4, D-85747 Garching, Germany
Aristotle University of Thessaloniki, Faculty of Chemistry, Inorganic Chemistry Laboratory, P.O. Box 135, GR-541 24 Thessaloniki, Greece
c
Received 24 November 2005; received in revised form 17 February 2006; accepted 23 February 2006
Available online 8 March 2006
Abstract
Copper(I) halide complexes containing the diphosphane xantphos (4,5-bis(diphenylphosphano)-9,9-dimethyl-xanthene) and some
heterocyclic thione ligands have been synthesized and characterized by 1H NMR, IR spectroscopy, elemental analyses and melting point
determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in acetonitrile/
methanol solution. The molecular structures of [CuBr(xantphos)(dmpymtH)] and [CuI(xantphos)(imdtH2)] Æ CH3CN have been estab-
lished by single-crystal X-ray diffraction. Each of these structures features a tetrahedral copper(I) center with two phosphorus atoms
from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. Rapid decompo-
sition of the mixed-ligand complexes via ligand dissociation occurs upon standing of their acetonitrile solutions at room temperature for
several days. The resulting colored crystals, which not only on elemental analysis but also on the basis of their NMR and IR spectra, are
found to be phosphane-free coordination polymers of composition [CuX(thione)].
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Copper(I) halide complexes; Heterocyclic thiones; Xantphos; Crystal structures
1. Introduction
efforts within this field of research involved the incorpora-
tion of tertiary arylphosphanes as a strong r-donor/p-
acceptor co-ligand. The aim was to investigate the interplay
between electronic and/or steric parameters of each ligand
in determining the overall molecular topology of the com-
pound being formed. The structural variety observed
within the quite large number of thione/phosphane
mixed-ligand copper(I) halide complexes obtained seemed
to be mainly produced by the choice of the halide ligand.
Thus, divergence from the common mononuclear four-
coordinate complexes [4] was virtually limited to pseudo-
tetrahedrally coordinated symmetrical doubly bridged
dicopper species [5]. Interestingly, there was no clear evi-
dence of steric requirements on the part of the neutral het-
erocyclic thiones applied in somehow affecting the
structural features of the complexes formed, but in a few
The interaction of heterocyclic thioamide derivatives
with many transition metals has been an intense area of
study for the last three decades, as certain of these ligands
are found to be present in the active sites of many metallo-
proteins [1], or have shown interesting biochemical proper-
ties [2]. Specific attention has been given to the employment
of simple thiolato ligands such as pyridine-2-thione or
pyrimidine-2-thione, in complexes of closed-shell d10 metal
ions, mainly CuI and AgI, that result in an extraordinary
variety of molecular structures [3]. Our long standing
*
Corresponding author.
E-mail addresses: p.j.cox@rgu.ac.uk (P.J. Cox), aslanidi@chem.
auth.gr (P. Aslanidis).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.02.046

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P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
cases, a decrease of the coordination number from four to
three could be achieved for the sterically demanding tri-o-
tolylphosphane [6].
sured in open tubes with a STUART scientific instrument
and are uncorrected. Molar conductivities, magnetic sus-
ceptibility measurements and elemental analyses for car-
bon, nitrogen and hydrogen were performed as described
previously [4b].
Having recognized the preference for a given geometry
within this class of complexes to be related to the steric
requirements on the part of the phosphane ligand only,
we turned our attention to multidentate phosphanes as a
further option for inducing and controlling structural var-
iation. Starting with symmetric oligomethylene-backboned
diphosphanes of the type Ph2P(CH2)nPPh2, we observed
chelation with formation of six-membered rings only in
the case of 1,3-bis(diphenylphosphano) propane (dppp)
[7]. However, macrocyclic dimers in which the two cop-
per(I) centers are linked together by two bidentate phos-
2.2. Crystal structure determination
Single crystals suitable for crystal structure analysis were
obtained by slow evaporation of acetonitrile/methanol
solutions of the complexes at room temperature.
X-ray diffraction data were collected on an Enraf-Non-
ius Kappa CCD area-detector diffractometer. The pro-
grams DENZO [11] and COLLECT [12] were used in data
collection and cell refinement. Details of crystal and struc-
ture refinement are shown in Table 1. The structures were
solved using program SIR97 [13] and refined with program
SHELX-97 [14]. Molecular plots were obtained with program
ORTEP-3 [15].
phane ligands have been obtained when
a longer
methylene chain connects the two P atoms, and this also
occurs with 1,2-bis(diphenylphosphano)ethane (dppe) [8].
Meanwhile, the above subfamily of diphosphanes has been
explored almost completely with respect to the effect of
chain length on the coordination behaviour (chelating or
bridging mode) towards monovalent coinage metals [9],
but such systematic studies on analogous compounds bear-
ing diphosphanes constructed on the basis of a rigid back-
bone are still lacking. Recently, we reported on thione
ligated tetrahedrally coordinated copper(I) halide com-
plexes bearing chelating cis-1,2-bis(diphenylphosp-
hano)ethene or 1,2-bis(diphenylphosphano)benzene with
very interesting structural features [10]. Continuing our
investigations in this area, we now wish to study the behav-
iour of new bidentate ligands based on rigid heterocyclic
xanthene-like aromatic backbones. In this paper, we report
on derivatives resulting from the reactions of copper(I)
halides with 4,5-bis(diphenylphosphano)-9,9-dimethylx-
anthene (xantphos) and some heterocyclic thiones.
2.3. General synthesis of complexes 1–9
To a suspension of 0.5 mmol of copper(I) halide
(49.5 mg for CuCl, 71.7 mg for CuBr, 95.2 mg for CuI) in
30 cm3 of dry acetonitrile, 289.3 mg (0.5 mmol) of 9,9-
dimethyl-4,5-bis(diphenylphosphano) xanthene was added
and the mixture was stirred for 2 h at 50 ꢁC during which
time a white precipitate was formed. To this was added a
solution of the appropriate thione (0.5 mmol) in a small
amount (ꢁ20 cm3) of methanol and the new reaction mix-
ture was heated under reflux for 2 h whereupon the precip-
itate gradually disappeared. The resulting clear solution
was filtered off and left to evaporate at ambient tempera-
ture. The microcrystalline solid, which was deposited upon
standing for several days, was filtered off and dried in
vacuo.
2. Experimental
2.1. Materials and instrumentation
2.3.1. [CuCl(xantphos)(imdtH2)] (1)
White crystals (343 mg, 88%), m.p. 211 ꢁC. Anal. Calc.
for C42H38ClCuN2OP2S: C, 64.69; H, 4.91, N: 3.59.
Found: C, 64.47; H, 4.81; N, 3.47%. IR (cmꢀ1): 3430m,
3049w, 2970w, 1585m, 1532vs, 1500s, 1480vs, 1434vs,
1317s, 1229s, 1186s, 1095s, 916m, 792m, 747vs, 695vs,
511vs, 463s. UV–Vis [kmax (nm), log e], (CHCl3): 250
Commercially available copper(I) halides and 9,9-
dimethyl-4,5-bis(diphenylphosphano) xanthene were used
as received while the thiones (Merck or Aldrich) were re-
crystallized from hot ethanol prior to their use. All the sol-
vents were purified by respective suitable methods and
allowed to stand over molecular sieves. Infra-red spectra
in the region of 4000–250 cmꢀ1 were obtained in KBr discs
with a Perkin–Elmer FT-IR Spectrum One spectrophotom-
eter, while a Perkin–Elmer–Hitachi 200 spectrophotometer
1
(4.10), 286 (3.83). H NMR (CDCl3, d ppm): 14.33 (br,
2H, NHimdtH2), 7.42 (m, 8H, PPh), 7.20 (m, 12H, PPh),
7.31 (d, 2H, H6xantphos), 7.04 (t, 2H, Hx7antphos), 6.60 (d, 2H,
H8xantphos), 3.59 (s, 4H, CHimdtH2), 1.63 (s, 6H, H3Cxantphos).
1
was used to obtain the electronic absorption spectra. H
NMR spectra were recorded on a Brucker AM 300 spec-
trometer at 298 K with positive chemical shifts given down-
field from TMS. TGA were performed under dry N2 using
a SETSYS-1200 machine with DTG facility with a heating
rate of 10ꢁ/min in the temperature range 298–1253 K. Sam-
ple sizes were in the range 8–10 mg and open Pt crucibles
were used. For the photolyses, an Osram high pressure
HBO 200 W/4 lamp was used. Melting points were mea-
2.3.2. [CuBr(xantphos)(imdtH2)] (2)
White crystals (383 mg, 93%), m.p. 272 ꢁC. Anal. Calc.
for C42H38BrCuN2OP2S: C, 61.20; H, 4.65; N, 3.40%.
Found: C, 61.11; H, 4.61; N, 3.51%. IR (cmꢀ1): 3438m,
3051w, 2969w, 1586m, 1527vs, 1500s, 1480s, 1456vs,
1434s, 1404vs, 1317m, 1228s, 1186m, 1095m, 916m,
793m, 747vs, 695vs, 534m, 511vs, 504vs, 463m. UV–Vis
[kmax (nm), log e], (CHCl3): 250 (3.98), 275 (3.77).

P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
3185
Table 1
Crystal data and structure refinements for [CuI(xantphos)(imdtH2)] Æ CH3CN (3) and [CuBr(xantphos)(dmpymtH)] (5)
3
5
Molecular formula
Formula weight
Temperature (K)
C42H38CuIN2OP2S Æ C2H3N
912.24
120(2)
0.71073
C45H40BrCuN2OP2S
862.24
120(2)
˚
Wavelength (A)
0.71073
Crystal system
Space group
a (A)
monoclinic
P21/c
17.4799 (3)
10.7989 (2)
21.9151 (5)
90
92.5540 (10)
90
4132.67 (14)
4
1.466
1.441
monoclinic
P21/n
10.8927 (2)
12.7487 (3)
31.5240 (8)
90
98.6950 (10)
90
4327.35 (17)
4
˚
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Density (calculated) (Mg mꢀ3
Absorption coefficient (mmꢀ1
F(000)
)
)
1.323
1.585
1768
1848
Crystal size (mm)
H range for data collection (ꢁ)
Index ranges
0.42 · 0.38 · 0.16
2.93–27.47
0.26 · 0.16 · 0.12
2.92–27.47
ꢀ22 6 h 6 22; ꢀ13 6 k 6 13; ꢀ28 6 l 6 28
ꢀ14 6 h 6 14; ꢀ16 6 k 6 16; ꢀ40 6 l 6 40
Reflections collected
43152
40981
Independent reflections [Rint
]
9399 [0.0420]
9660 [0.0454]
Completeness, % (h, ꢁ)
Data/restraints/parameters
99.2 (27.47)
9399/0/481
97.4 (27.48)
9660/0/482
Maximum and minimum transmission
Refinement method
Goodness-of-fit on F2
0.8022 and 0.5829
full-matrix least-square on F2
1.048
0.8326 and 0.6834
full-matrix least-square on F2
1.082
Final R indices [I > 2r(I)]
R indices (all data)
Final weighting scheme
R1 = 0.0363, wR2 = 0.0808
R1 = 0.0607, wR2 = 0.0894
R1 = 0.0358, wR2 = 0.0791
R1 = 0.0597, wR2 = 0.0840
2
2
Calc w ¼ 1=½r2ðF o2Þ þ ð0:0356PÞ þ 3:6035Pꢂ
Calc w ¼ 1=½r2ðF 2oÞ þ ð0:0356PÞ ꢂ
where P ¼ ðF 2o þ 2F c2Þ=3
where P ¼ ðF 2o þ 2F c2Þ=3
0.445 and ꢀ0.389
ꢀ3
˚
Largest difference in peak and hole (e A
)
1.188 (close to iodine) and ꢀ1.244
1
1H NMR (CDCl3, d ppm): 7.43 (m, 8H, PPh), 7.21 (m,
12H, PPh), 7.31 (d, 1H, H6xantphos), 7.04 (t, 1H, Hx7antphos),
6.60 (d, 1H, H8xantphos), 3.59 (s, 4H, CHimdtH2), 1.63 (s,
6H, H3Cxantphos).
(4.25), 407 (3.29). H NMR (CDCl3, d ppm): 14.75 (br,
1H, NHdmpymtH), 7.47 (m, 8H, PPh), 7.13 (m, 12H, PPh),
7.19 (d, 1H, H6xantphos), 7.03 (t, 1H, Hx7antphos), 6.71 (d, 1H,
H8xantphos), 2.23 (s, 6H, CHdmpymtH), 1.62 (s, 6H,
H3Cxantphos).
2.3.3. [CuI(xantphos)(imdtH2)] (3)
White crystals (413 mg, 95%), m.p. 254 ꢁC. Anal. Calc.
for C42H38CuIN2OP2S: C, 57.90; H, 4.40; N, 3.22. Found:
C, 57.82; H, 4.46; N, 3.26%. IR (cmꢀ1): 3435m, 3049w,
2961w, 1616s, 1523vs, 1480s, 1434vs, 1406vs, 1231vs,
1186m, 1094m, 997m, 915m, 745vs, 695vs, 512vs, 460s.
UV–Vis [kmax (nm), log e], (CHCl3): 245 (4.02), 290
(3.61). 1H NMR (CDCl3, d ppm): 7.42 (m, 8H, PPh),
7.22 (m, 12H, PPh), 7.30 (d, 1H, H6xantphos), 7.04 (t, 1H,
H7xantphos), 6.60 (d, 1H, Hx8antphos), 3.59 (s, 4H, CHimdtH2),
1.62 (s, 6H H3Cxantphos).
2.3.5. [CuBr(xantphos)(dmpymtH)] (5)
Yellow crystals (411 mg, 91%), m.p. 271 ꢁC. Anal. Calc.
for C45H40BrCuN2OP2S Æ CH3CN: C, 62.49; H, 4.79; N,
4.65. Found: C, 62.36; H, 4.82; N, 4.54%. IR (cmꢀ1):
3468m, 3048m, 2970w, 1625vs, 1563vs, 1481s, 1435vs,
1405vs, 1228vs, 1188s, 1095m, 983m, 879m, 743vs, 695vs,
511vs, 504s, 461m. UV–Vis [kmax (nm), log e], (CHCl3):
244 (4.12), 278 (3.96), 384 (3.04). 1H NMR (CDCl3, d
ppm): 13.85 (br, 1H, NHdmpymtH), 7.47 (m, 8H, PPh),
7.14 (m, 12H, PPh), 7.20 (d, 1H, H6xantphos), 7.05 (t, 1H,
H7xantphos), 6.72 (d, 1H, H8xantphos), 2.30 (s, 6H, CHdmpymtH),
1.63 (s, 6H, H3Cxantphos).
2.3.4. [CuCl(xantphos)(dmpymtH)] (4 )
Yellow crystals (376 mg, 92%), m.p. 240 ꢁC. Anal. Calc.
for C45H40ClCuN2OP2S: C, 66.09; H, 4.93; N, 3.43.
Found: C, 65.80; H, 5.08; N, 3.37%. IR (cmꢀ1): 3468m,
3047w, 2925w, 1616s, 1567vs, 1480m, 1434vs, 1404vs,
1231vs, 1192m, 1095m, 982s, 878m, 743vs, 695vs, 511vs,
461s. UV–Vis [kmax (nm), log e], (CHCl3): 246 (4.24), 287
2.3.6. [CuI(xantphos)(dmpymtH)] (6)
Yellow crystals (386 mg, 85%), m.p. 254 ꢁC. Anal. Calc.
for C45H40CuIN2OP2S: C, 59.44; H, 4.43; N, 3.08. Found:
C, 59.14; H, 4.40; N, 2.94%. IR (cmꢀ1): 3447m, 3048w,
2959m, 1611s, 1559vs, 1480m, 1435s, 1405vs, 1225vs,

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P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
1184m, 1095m, 981m, 875m, 747s, 695vs, 511vs, 503s,
bis(diphenylphosphano) benzene (dppbz), have been
already utilized in the course of our previous attempts to
chelate thione-ligated copper(I), both of them leading to
the formation of stable five-membered chelate rings,
despite their small bite angles [10]. Thus, attempting to
explain the coordination behaviour of these two diphos
ligands in terms of bite angle effects, one should consider,
apart from their strong chelating power, a significant
degree of versatility on the part of the metal ion to hold
responsibility for the formation of constrained P–M–P
angles having values far away from the ideal tetrahedral
one.
While a flexible diphosphane can adopt virtually any
bite angle required by the geometry of the coordination
polyhedron being formed, within limits determined by its
backbone length only, rigid diphosphanes are in this
respect less adaptable, and variations of their bite angles
as a consequence of coordination are expected to be quite
small. In this context, considering further rigid diphos-
phanes as potential chelating agents for CuI in a tetrahe-
dral coordination environment, the xantphos family of
diphos ligands, providing natural bite angles between
108ꢁ and 114ꢁ, may be expected to express strong prefer-
ence for chelation. Indeed, the diphosphane used in the
present study, on grounds of its calculated bite angle of
111ꢁ [16], proved to be best designed to span tetrahedral
sites which require P–M–P angles (about) of 109ꢁ. Note
that, as far as we are aware, no copper(I) derivatives of this
diphosphane are currently known, although xantphos has
already found extensive utilisation both as a cis- and
trans-chelating ligand in square planar or octahedral com-
plexes of diverse metal centres [17].
The new compounds can be properly prepared following
the one-top two-step synthetic procedure that has already
produced a number of mixed-ligand copper(I) halide com-
plexes. In particular, treatment of a suspension of copper(I)
halide in dry acetonitrile with the equimolar quantity of
4,5-bis(diphenylphosphano)-9,9-dimethylxanthene (xant-
phos) affords the intermediate [CuX(xantphos)] as a white
precipitate. Subsequent dropwise addition of methanolic
solution of one equivalent of the appropriate thione (L)
[L = tetrahydropyrimidine-2-thione, imidazolidine-2-thi-
one and 4,6-dimethyl-pyrimidine-2-thione] (Fig. 1) and
heating the mixture at reflux causes complete disappear-
ance of the precipitate. Slow evaporation of these solutions
gave the pure mixed-ligand complexes as air stable diamag-
netic microcrystalline solids. Their composition has been
confirmed by elemental analysis.
464m. UV–Vis [kmax (nm), log e], (CHCl3): 247 (3.78),
1
285 (3.69), 410 (2.63). H NMR (CDCl3, d ppm): 13.30
(br, 1H, NHdmpymtH), 7.48 (m, 8H, PPh), 7.17 (m, 12H,
PPh), 7.25 (d, 1H, H6xantphos), 7.02 (t, 1H, H7xantphos), 6.75
(d, 1H, H8xantphos), 2.32 (s, 6H, CHdmpymtH), 1.64 (s, 6H,
H3Cxantphos).
2.3.7. [CuCl(xantphos)(tHpymtH)] (7)
Colorless crystals (329 mg, 83%), m.p. 251 ꢁC. Anal.
Calc. for C43H40ClCuN2OP2S: C, 65.06; H, 5.08; N, 3.53.
Found: C, 64.88; H, 5.19; N, 3.48%. IR (cmꢀ1): 3423w,
3050m, 2966m, 1563s, 1543s, 1480m, 1434vs, 1405vs,
1228vs, 1203m, 1095m, 876m, 745vs, 695vs, 512s, 463m.
UV–Vis [kmax (nm), log e], (CHCl3): 249 (4.31), 287
(4.09). 1H NMR (CDCl3,
d ppm): 7.54 (br, 1H,
NHtHpymtH), 7.44 (m, 8H, PPh), 7.22 (m, 12H, PPh), 7.41
(d, 1H, H6xantphos), 7.03 (t, 1H, Hx7antphos), 6.58 (dd, 1H,
H8xantphos), 3.18 (m, 4H, H3tHpymtH), 1.78 (m, 2H, Ht4HpymtH),
1.63 (s, 3H, H3Cxantphos), 1.57 (s, 3H, H3Cxantphos).
2.3.8. [CuBr(xantphos)(tHpymtH)] (8)
Colorless crystals (377 mg, 90%), m.p. 287 ꢁC. Anal.
Calc. for C43H40BrCuN2OP2S: C, 61.83; H, 4.81; N, 3.34.
Found: C, 61.72; H, 4.76; N, 3.22%. IR (cmꢀ1): 3429w,
3050w, 2965m, 1563s, 1480m, 1434s, 1405vs, 1228s,
1203s, 1095m, 876m, 744vs, 695vs, 513vs, 503s, 462m.
UV–Vis [kmax (nm), log e], (CHCl3): 248 (4.15), 292
(3.81). 1H NMR (CDCl3,
d ppm): 7.70 (br, 1H,
NHtHpymtH), 7.43 (m, 8H, PPh), 7.21 (m, 12H, PPh), 7.41
(d, 1H, H6xantphos), 7.06 (t, 1H, H7xantphos), 6.57 (d, 1H,
H8xantphos), 3.07 (m, 4H, H3tHpymtH), 1.98 (m, 2H, Ht4HpymtH),
1.65 (s, 6H, H3Cxantphos).
2.3.9. [CuI(xantphos)(tHpymtH)] (9)
Colorless crystals (376 mg, 85%), m.p. 275 ꢁC. Anal.
Calc. for C43H40CuIN2OP2S: C, 58.34; H, 4.55; N: 3.16.
Found: C, 58.66; H, 4.41; N, 3.23%. IR (cmꢀ1): 3460w,
3048w, 2965m, 1559s, 1479m, 1434s, 1405vs, 1230vs,
1190s, 1093m, 877m, 745s, 695s, 511s, 464m. UV–Vis [kmax
(nm), log e], (CHCl3): 255 (4.15), 285 (4.11). 1H NMR
(CDCl3, d ppm): 7.70 (br, 1H, NHtHpymtH), 7.47 (m, 8H,
PPh), 7.17 (m, 12H, PPh), 7.31 (d, 1H, H6xantphos), 7.03 (t,
1H, H7xantphos), 6.62 (dd, 1H, H8xantphos), 3.07 (m, 4H,
H3tHpymtH), 1.98 (m, 2H, H4tHpymtH), 1.65 (s, 6H, H3Cxantphos).
3. Results and discussion
3.1. General considerations – synthesis
All prepared compounds are moderately soluble in ace-
tonitrile and only slightly soluble in non-polar solvents
such as chloroform or acetone. Their solutions in common
organic solvents are non-conducting. As far as possible, we
characterized all of the compounds by elemental analysis
and IR, UV–Vis and 1H NMR spectra. The molecular
structures of [CuI(xantphos)(imdtH2)] Æ CH3CN and
[CuBr(xantphos)(dmpymtH)] were determined by X-ray
crystallographic analyses.
For a bidentate phosphane, the concept of the ‘‘bite
angle’’, defined as the donor-atom–metal–donor-atom
angle, provides a measure especially useful for predicting
and discussing its ligating properties, since it displays the
‘‘natural’’ preference of the ligand for a certain coordina-
tion mode (chelating or bridging). The rigid diphosphanes,
cis-1,2-bis(diphenylphosphano) ethene (cis-dppen) and 1,2-

P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
3187
CH3
NH
N
HN
NH
N
H
S
O
N
H
S
H3C
S
PPh2
PPh2
tHpymtH
dmpymtH
imdtH2
xantphos
Fig. 1. The diphosphane and the heterocyclic thiones used as ligands with their abbreviations.
3.2. Spectroscopy
istic four ‘‘thioamide bands’’ required by the presence of
the heterocyclic thione ligands, with shifts due to coordina-
tion indicative of an exclusive S-coordination mode, as well
as a broad band in the 3430–3460 cmꢀ1 region assigned to
the m(NH) stretching vibration.
1
The room temperature H NMR spectra of the com-
plexes under investigation, recorded in deuterated chloro-
form, are dominated by the presence of a typical set of
multiplets in the region of d = 7.40–7.20 ppm attributed
to the phenyl resonances of the xantphos ligand. Upon
coordination, the complex multiplet assigned to the PPh2
units undergoes splitting due to the upfield shift of the
ortho-positioned protons by ca. 0.25 ppm. The correspond-
ing shifts of the backbone protons, as well as of the methyl-
protons (see Fig. 1), are in the same direction but of clearly
smaller magnitude (less than 0.1 ppm). Values of the chem-
ical shifts attributed to the thione protons are as expected.
The electronic absorption spectra of the complexes 1–9,
recorded in chloroform at room temperature, show two
intense broad bands with maxima in the 243–255 and 285–
310 nm regions, respectively. With reference to the absorp-
tion bands of the uncoordinated xantphos, the first one
can be attributed to intraligand p ! p* transitions on the
phenyl groups of the phosphane ligand, whereby the lower
energy band, which lies in the region where the free thiones
absorb, expressing a small red shift as a consequence of
the coordination to CuI, should be considered as a thione-
originating intraligand transition which possesses some
MLCT character [18]. The presence of 4,6-dimethyl-pyrim-
idine-2-thione in 3, 4 and 5 is further associated with absorp-
tions at 407, 384 and 410 nm, respectively.
3.3. Photochemical and thermal decomposition studies
While there is no evidence of decomposition of com-
plexes 1–9 in the solid state, these were found to be light
sensitive in solution. In particular, upon standing of their
acetonitrile solutions over the course of a couple of weeks,
separation of a colored solid accompanied by a gradual dis-
coloration of the solution was obtained. Exposure to sun-
light clearly accelerated the decomposition, and the
insoluble powder that was released quantitatively could
be spectroscopically defined as a phosphane-free adduct
of composition [CuX(thione)], most likely of polymeric
nature. No other copper-containing species could be iden-
tified in the solution, but for the free xantphos; thus a
decomposition of these compounds according to Scheme
1 can be proposed.
The photochemical nature of this decomposition process
was confirmed by photolytic experiments on degassed chlo-
roform solutions of the mixed-ligand complexes. Thus, UV
irradiation of such solutions at k = 250–300 nm was found
to cause complete decomposition of the compounds within
60 s, resulting in the deposition of the corresponding phos-
phane-free polymer, while xantphos remained in solution
as the only soluble photoproduct.
The infrared spectra of compounds 1–9, recorded in the
range 4000–250 cmꢀ1, show distinct strong vibrational
phosphane bands, which remain practically unshifted upon
coordination. Moreover, the spectra contain the character-
We also examined the thermal behavior of the new com-
pounds using simultaneous differential thermoanalysis
HN
Cu
HN
O
X
S
S
S
S
X
h.ν
2n
Ph2P
PPh2
+ 2n xantphos
Cu
Cu
Cu
CHCl3
X
X
Cu
X
S
NH
NH
NH
n
Scheme 1. Photochemical decomposition of compounds 1–9.

3188
P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
Fig. 2. TG and DTA curves for compound 2.
Table 2
(DTA) and thermogravimetry (TG) in a nitrogen atmo-
sphere. Against their photochemical instability, complexes
1–9 proved to be thermally stable to at least 285 ꢁC. On
further heating in the course of a DTA/TG experiment,
they expressed similar decomposition patterns, generally
consisting of two main stages. From the experimental mass
loss percentages, as a general behavior, the thione ligand
was released first, followed by loss of the phosphane, which
apparently forms more stable bonds with the metal cation.
For all the compounds further heating caused gradual sub-
limation of the residual CuBr, which was completely
removed at the temperature of 980 ꢁC.
TG and DTA curves obtained for [CuBr(xant-
phos)(imdtH2)] (2) are exemplarily shown in Fig. 2. The
low temperature initial stage of the decomposition proce-
dure, which is observed in the TG curve at about 280–
350 ꢁC and produces two endothermic events in the DTA
curve, involves overall weight loss (12%) indicative of grad-
ual thermal breakdown of the thione ligand (calculated
value = 12.38%).
˚
Selected bond lengths (A) and bond angles (ꢁ) for 3
Cu(1)–I(1)
Cu(1)–P(1)
Cu(1)–P(2)
2.6859(4)
2.2656(8)
2.2803(8)
Cu(1)–S(1)
S(1)–C(28)
2.3294(8)
1.690(3)
P(1)–Cu(1)–P(2)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(1)–Cu(1)–I(1)
116.76(3)
103.87(3)
111.50(3)
106.83(2)
P(2)–Cu(1)–I(1)
S(1)–Cu(1)–I(1)
C(28)–S(1)–Cu(1)
102.10(2)
116.21(3)
106.0(1)
Hydrogen bridges
N(2)–H(2)
NH(2)ꢃ ꢃ ꢃI(1)
N(1)–H(1)
NH(1)ꢃ ꢃ ꢃN(3)a
a
0.88
2.99
0.88
2.14
N(2)ꢃ ꢃ ꢃI(1)
3.825(3)
158.3
2.990(5)
163.0
I(1)ꢃ ꢃ ꢃH(2)–N(2)
N(1)ꢃ ꢃ ꢃN(3)a
I(1)ꢃ ꢃ ꢃH(2)–N(2)
Coordinates transposed by x, ꢀy ꢀ 0.5, z + 0.5.
Table 3
Selected bond lengths (A) and bond angles (ꢁ) for 5
˚
Cu(1)–Br(1)
Cu(1)–P(1)
Cu(1)–P(2)
2.5006(3)
2.2771(7)
2.2994(6)
Cu(1)–S(1)
S(1)–C(28)
2.3345(6)
1.692(2)
Removal of the phosphane ligand is noticed in a contin-
uous step at elevated temperatures in the 420–480 ꢁC range,
accompanied by two strong endothermic effects. The corre-
sponding relative mass loss (70%) is consistent with com-
plete burning of the diphosphane ligand (calculated
value = 70.22%).
P(1)–Cu(1)–P(2)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(1)–Cu(1)–Br(1)
113.22(2)
104.72(2)
106.72(2)
108.435(2)
P(2)–Cu(1)–Br(1)
S(1)–Cu(1)–Br(1)
C(28)–S(1)–Cu(1)
112.435(2)
111.04(2)
113.17(8)
Hydrogen bridge
N(1)–H(1)
NH(1)–Br(1)
0.8800
2.3000
Br(1)ꢃ ꢃ ꢃN(1)
3.2758(2)
170
Br(1)ꢃ ꢃ ꢃH(1)–N(1)
3.4. X-ray structural investigations
The X-ray crystal structures of [CuI(xantphos)(imdtH2)]
(3) and [CuBr(xantphos)(dmpymtH)] (5) (details of crystal
and structure refinement are shown in Table 1) corroborate
the spectroscopic results discussed above. Tables 2 and 3
list selected distances and angles of these complexes. Note
that the X-ray crystal structure determinations of these two
complexes are the first to be carried out on copper(I) com-
pounds bearing xantphos.
Colorless single crystals of 3 and yellow crystals of 5
were grown from their acetonitrile/methanol mother

P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
3189
liquids upon slow evaporation during several days. Com-
plexes 3 and 5 crystallize in the monoclinic space group
P21/c and P21/n, respectively, both with four formula units
in the unit cell, as well as four lattice CH3CN molecules in
the case of compound 3. Each of these later solvent mole-
cules is linked to a thione-nitrogen-bound hydrogen atom
of the imdtH2 ligand (see Table 2).
As shown in Figs. 3 and 4, the crystal structures of the
two mixed-ligand compounds are very similar having the
tetrahedral coordination of the copper(I) center in com-
mon, which is surrounded by the S donor of the thione
ligand, two P atoms of the chelating xantphos unit, as well
as the corresponding halogen atom.
thus the tetrahedral environment of the copper atom can
be considered as remarkably regular when compared with
several reported, four coordinated, copper(I) halide com-
plexes bearing a heterocyclic thione and two monodentate
arylphosphanes or a chelating short bite angle diphosphane
[10]. In fact, the P(1)–Cu(1)–P(2) angle, with a value of
116.76(3)ꢁ and 113.22(2)ꢁ in 3 and 5, respectively, is not
far from the ligands calculated ‘‘natural’’ bite angle of
111ꢁ [16]. Thus, one can suggest the diphenylphosphane
moieties of xantphos to be nearly perfect oriented to act
as a chelate. Nevertheless, it is obvious that chelation
requires some adjustment on the part of the diphos ligand,
to keep constraints within the tetrahedron at a minimum.
As it can be seen from its crystal structure [16a], there is
a folding of the xanthene unit along the axis through the
oxygen atom and the xanthene carbon atom C9 forming a
dihedral angle of 156.58ꢁ between the planes of the two ben-
zenoid rings. Apparently, chelation enforces further folding
within the xanthene unit, as indicated by the corresponding
values of 149.3(1)ꢁ and 137.7(8)ꢁ for 3 and 5, respectively.
As a consequence, the remarkably short Pꢃ ꢃ ꢃP distance of
In both complexes described here, angular deviations
from the ideal tetrahedral value of 109.4ꢁ are quite small;
˚
4.045(1) A of the xanthene unit appears further shortened
˚
upon chelation to values of 3.8710(10) and 3.8213(9) A in
3 and 5, respectively.
In both structures, the two individual Cu–P distances
are within the limits of the range expected for tetrahedrally
coordinated copper(I). Likewise, the Cu–S and Cu–Br
bond lengths are comparable to those reported for other
tetrahedrally coordinated copper(I) complexes with termi-
nal bromine and thione-sulfur donors.
The most outstanding structural feature within molecule
3 is the inclination of the five-membered imidazolidine-ring
to the C(31)–C(36) phenyl ring, the dihedral angle between
mean planes through these two rings being 26.0(1)ꢁ. As a
˚
Fig. 3. A view of compound 3 with atom labels. Displacement ellipsoids
are shown in the 50% probability level.
consequence, there is a 3.949(2) A separation between ring
centroids arising from a weak p-stacking interaction. This
quite small interligand interaction, together with the hydro-
gen bonds may be considered to significantly contribute to
the alignment of the molecules in the crystalline state.
4. Conclusion
The aim of this work was the study of the coordination
capability of the diphos ligand 4,5-bis(diphenylphosp-
hano)-9,9-dimethylxanthene (xantphos) toward copper(I)
halides. We have found that xantphos readily forms com-
pounds of composition [CuX(diphos)], probably of mono-
meric nature, that proves to be a good precursor for the
preparation of other derivatives; in the course of the pres-
ent study these are chosen for the synthesis of monomeric
complexes which contain, besides the chelating diphos unit,
a heterocyclic thioamide bonded to the metal via the thi-
one-S atom. These complexes are light sensitive and
undergo rapid decomposition when exposed to daylight
or intense UV irradiation. According to the overall geom-
etries of the two structures presented, the xantphos ligand
applied can be considered as best tailored for chelation of
Fig. 4. A view of compound 5 with atom labels. Displacement ellipsoids
are shown in the 50% probability level.

3190
P.J. Cox et al. / Inorganica Chimica Acta 359 (2006) 3183–3190
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Dartmann, Inorg. Chim. Acta 156 (1989) 47;
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dination, to significantly modify its natural bite angle, and
at the same time chelation does not requires any accommo-
dation on the part of the metal center.
(b) S.K. Hadjikakou, P. Aslanidis, P. Karagiannidis, A. Hountas, A.
Terzis, Inorg. Chim. Acta 184 (1991) 161;
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5. Supplementary material
CCDC-289082 (3) and CCDC-289083 (5) contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge at www.ccdc.cam.
ac.uk/conts/retrieving.html or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: (intrnat.) +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk).
[8] P.J. Cox, P. Aslanidis, P. Karagiannidis, Polyhedron 19 (2000) 1615.
[9] Effendy, C. Di Nicola, M. Fianchini, C. Pettinari, B.W. Skelton,
A.H. White, Inorg. Chim. Acta 358 (2005) 735.
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Acknowledgment
(b) A. Kaltzoglou, P.J. Cox, P. Aslanidis, Inorg. Chim. Acta 358
(2005) 3048.
We thank the EPSRC X-ray crystallography service at
the University of Southampton for collecting the X-ray
data.
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CarterJr., R.M. Sweet (Eds.), Macromolecular Crystallography, Part
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