A copper(I)-catalysed template synthesis of solvatochromic aryl-arsonium and -stibonium systems and a synchrotron structural study of a tetraarylstibonium di-iodocuprate

Article abstract of DOI:10.1039/a805759a

A route to solvatochromic tetraaryl-arsonium and -stibonium phenolate betaines is described, together with a synchrotron structural study of a precursor arylstibonium di-iodocuprate salt in which both cation and anion have unusual geometries.

Full text of DOI:10.1039/a805759a

View Article Online / Journal Homepage / Table of Contents for this issue
A copper(I)-catalysed template synthesis of solvatochromic aryl-arsonium and
-stibonium systems and a synchrotron structural study of a tetraarylstibonium
di-iodocuprate
David W. Allen,*a Joanne P. L. Mifflina and Simon Colesb†
a Division of Chemistry, Sheffield Hallam University, Sheffield, UK S1 1WB
b Department of Chemistry, University of Wales, Cardiff, Cardiff, UK CF1 3TB
A route to solvatochromic tetraaryl-arsonium and -stibon-
ium phenolate betaines is described, together with a
synchrotron structural study of a precursor arylstibonium
di-iodocuprate salt in which both cation and anion have
unusual geometries.
phosphonium salts using copper( ) iodide as catalyst in
I
acetonitrile were unsuccessful. Clearly, the group 15 ligand
must influence crucial stages of the reaction, for which the
mechanism is uncertain. A kinetic study of related nickel(II)-
catalysed reactions of phosphines with template aryl halides
supported a mechanism in which oxidative insertion of an
intermediate phosphine–nickel complex into the carbon–halo-
gen bond was the key step, followed by reductive elimination of
the arylphosphonium salt and regeneration of the effective
catalyst.5 It is likely that a similar mechanism applies in the
Methods for the synthesis of aryl-arsonium or -stibonium salts
from tertiary arsines or stibines and aryl halides are limited, the
usual route being the reaction of the tertiary arsine or stibine,
commonly the triphenyl derivative, and an aryl halide, in the
presence of aluminium chloride at > 200 °C.1 We have shown
that tertiary phosphines react with aryl halides bearing appro-
priate donor atoms in the ortho position to the halogen in the
above reactions, perhaps involving a copper( )–copper(III)
I
redox cycle, in which the triaryl-arsine and -stibine ligands are
able to stabilise intermediate organometallic species more
effectively than the related triarylphosphines.
presence of catalytic quantities of nickel(II) or copper(II
)
compounds under mild conditions in refluxing ethanol,2 and
were interested in exploring similar template-assisted reactions
of triaryl-arsines and -stibines. As triaryl-arsines and -stibines
X
X
Z
X
Z
X
coordinate readily to copper(
are labile in solution,3 we have investigated their reactions with
a series of template aryl halides in the presence of copper(
I) halides to form complexes which
CH
Br
N
CH N
I)
iodide, in acetonitrile, and wish to report the formation of
tetraaryl-arsonium and -stibonium systems in high yield under
these remarkably mild conditions. We have also applied this
procedure in the synthesis of the first solvatochromic tetraaryl-
arsonium and -stibonium iminophenolate betaines, the proper-
ties of which are compared with those of the related phosphon-
EAr3 Y–
+
1
2
S
S
ium system.
A synchrotron structural study of one
N
N
tetraarylstibonium salt is also reported, which reveals a
significant intramolecular coordinative interaction between the
onium centre and the donor atom in the ortho position of the
+
Br
SbAr3 Y–
template system, and also the presence of a di-iodocuprate( )
I
3
4
anion which interacts with a second di-iodocuprate anion via a
short copper–copper interaction to give a dinuclear anion.
The reaction of the aryl halides 1 (X = H, Z = OMe; X = Cl,
A structural study‡ has been made of the stibonium salt 2 (E
= Sb; Ar = Ph; X = Br; Z = OH, Y = CuI2). Routine
investigations, using a rotating anode X-ray source, failed to
provide data of sufficient intensity to produce a fully refinable
structure. Data were therefore collected, upon a crystal of
dimensions 200 3 20 3 20 mm, using station 9.8 of the
Daresbury SRS.6 The cation of the observed structure is
displayed in Fig. 1 (together with selected bond lengths and
angles for both cation and anion). Significant points of interest
are the close intramolecular approach of the imino nitrogen to
the stibonium centre, the antimony–nitrogen distance (2.65 Å),
lying well within the sum of the van der Waals’ radii (3.75 Å),7
and the consequent distortion of the bond angles at antimony
from the idealised tetrahedral angle towards a five-coordinate
arrangement, consistent with an intramolecular coordinative
interaction from nitrogen to antimony to form a five-membered
ring. Tetraarylstibonium halides also show considerable distor-
tion from idealised tetrahedral geometry as a result of weak
interactions of the stibonium centre with the halide ion,
resulting in essentially trigonal bipyramidal structures in which
the antimony–halogen bond is unusually long.8,9 The structure
co-crystallises with a 50% occupied CH2Cl2 solvent and the
Br, or Ph, Z = OH) with triphenylarsine and copper( ) iodide in
I
acetonitrile under reflux for several hours gave, after pouring
into aqueous potassium iodide solution and solvent extraction
into dichloromethane, the tetraarylarsonium salts 2 (E = As, Y
1
= I or CuI2) as yellow-brown crystalline solids. H and 13C
NMR spectra were consistent with the proposed structures.
Under FABMS conditions, the arsonium salts gave a character-
istic molecular ion for the cation present. The structure of the
salt 2 (X = H, Z = OMe, E = As, Ar = Ph, Y = I) was also
confirmed by a full X-ray crystallographic study.4 Similarly,
treatment of the aryl halides 1 (X = H, Z = OMe; X = Cl, Br,
or Ph, Z = OH) and 3 with triphenyl- or tri-p-tolyl-stibine and
copper( ) iodide in acetonitrile under reflux gave the related
I
arylstibonium salts 2 (E = Sb; Ar = Ph or p-tolyl, Y = CuI2)
and 4 (Ar = Ph or p-tolyl, Y = CuI2). Again, 1H and 13C NMR
spectra were consistent with the proposed structures, and under
FABMS conditions, each stibonium salt gave a characteristic
molecular ion for the cation present. The nature of the anion
present was confirmed by negative ion mass spectrometry. The
stibonium salts formed more quickly than the related arsonium
salts under the same conditions. Attempts to prepare the related
counter-ion, which was found to be di-iodocuprate(
I
). The CuI2
Chem. Commun., 1998
2115

View Article Online
methane to 576 nm in THF. The solvatochromic behaviour of
the arsonium and stibonium betaines is almost identical to that
of the related phosphonium betaines 5 (E = P, Ar = Ph; X =
Cl, Br, or Ph) which we reported recently.15 There is currently
growing interest in the optical properties of organic derivatives
of the main group 15 elements.16,17
We thank the EPSRC National Mass Spectrometry Service
Centre, University of Wales, Swansea, for high resolution
FABMS determinations, and also Neotronics Scientific Ltd for
financial support.
Notes and References
† Author to whom crystallographic enquiries should be addressed.
‡ Crystal data: C31.5H23NOClSbBr2·CuI2, Mr = 1065.87, monoclinic,
space group P21/n, a = 9.259(5), b = 24.785(11), c = 15.100(7) Å, b =
98.998(2)°, U = 3422.6(3) Å3, Z = 4, Dc = 2.069 g cm23, m = 5.653
mm21, F(000) = 2000, crystal size 0.2 3 0.02 3 0.02 mm. Data were
collected at 160 K, with a wavelength of 0.6875 Å, on a Bruker (formerly
Siemens) SMART CCD area detector diffractometer, equipped with a
silicon(111) crystal monochromator and a palladium coated focussing
mirror on station 9.8 of the Daresbury SRS. w scans, with a frame increment
Fig. 1 Structure of the tetraarylstibonium cation with selected bond lengths
(Å) and angles (°) for cation and di-iodocuprate anion: Sb–N1 2.65(4), Sb–
C1 2.09(2), Sb–C7 2.13(2), Sb–C13 2.13(2), Sb–C19 2.114(14), C25–N1
1.28(2), Cu1–I1 2.508(2), Cu1–I2 2.576(2), Cu–Cu 2.732(4); C1–Sb–C7
106.7(7), C1–Sb–C13 119.2(6), C1–Sb–C19 113.6(6), C7–Sb–C13
102.0(7), C7–Sb–C19 101.4(6), C13–Sb–C19 115.9(6), C19–C24–C25
121.2(14), N1–C25–C24 118.9(13), N1–Sb–C1 83.9(7).
of 0.3°, were used to cover a hemisphere of reciprocal space, giving qmin
=
1.54° and qmax = 20.00° (index ranges 211 @ h @ 12, 226 @ k @ 32, 218
@ l @ 19). Corrections were applied to account for incident beam decay and
absorption effects. A solution was obtained via direct methods and refined
by full-matrix least-squares on F2. 3520 unique data were produced from
moiety shows a considerable distortion from the expected linear
arrangement as a result of a very short copper–copper
interaction (2.73 Å) with a second di-iodocuprate anion in the
11707 measured reflections (Rint = 0.0882). 389 parameters refined to R1
=
0.0573 and wR2 = 0.1253 [I > 2s(I)] with s = 1.057 and residual electron
densities of 0.967 and 21.124 e Å23. CCDC 182/984.
lattice. The stabilisation of poly[dihalocuprate( )] anions by
I
large phosphonium cations has been documented,10,11 but the
only stibonium salt involving a related anion is that of the
copper(II) complex, (SbPh4)2·Cu2Cl6.12 However the Cu–Cu
separation in this structure is much greater (3.394 Å) than that
1 J. Chatt and F. G. Mann, J. Chem. Soc., 1940, 1192; G. Doak and L. D.
Freedman, Organometallic Compounds of Arsenic, Antimony, and
Bismuth, Wiley Interscience, 1970, and references therein.
2 D. W. Allen, P. E. Cropper, P. G. Smithurst, P. R. Ashton and B. F.
Taylor, J. Chem. Soc., Perkin Trans. 1, 1986, 1989; D. W. Allen, I. W.
Nowell, L. A. March and B. F. Taylor, J. Chem. Soc., Perkin Trans. 1,
1984, 2523; D. W. Allen and P. E. Cropper, Polyhedron, 1990, 9,
129.
3 N. R. Champness and W. Levason, Coord. Chem. Rev., 1994, 133, 115;
G. A. Bowmaker, R. D. Hart, E. N. de Silva, B. W. Skelton and A. H.
White, Aust. J. Chem., 1997, 50, 553; G. A. Bowmaker, R. D. Hart and
A. H. White, Aust. J. Chem., 1997, 50, 567.
in the di-iodocuprate(
with other di-iodocuprate(
I
) counter-ion discussed here. Comparison
I
) anions crystallizing in the same
manner shows the Cu–Cu separation to be somewhat greater
than in our example (average = 2.95 Å).13,14
Treatment of the salts 2 (E = As or Sb; Ar = Ph; X = Cl, Br,
or Ph), dissolved in dichloromethane, with aqueous sodium
hydroxide solution, resulted in a marked colour change from
yellow to red-purple with formation of the related betaines 5,
4 D. W. Allen, J. P. L. Mifflin, M. B. Hursthouse and K. M. A. Malik, to
be published.
5 D. W. Allen and P. E. Cropper, J. Organomet. Chem., 1992, 435,
203.
X
O–
6 R. J. Cernik, W. Clegg, C. R. A. Catlow, G. Bushnell-Wye, J. V.
Flaherty, G. N. Greaves, I. D. Burrows, D. J. Taylor, S. J. Teat and M.
Hamichi, J. Synchrotron Rad., 1997, 4, 279.
CH
N
X
7 A. Bondi, J. Phys. Chem., 1964, 68, 441.
8 G. Ferguson, C. Glidewell, D. Lloyd and S. Metcalfe, J. Chem. Soc.,
Perkin Trans. 2, 1988, 731.
+
EAr3
5
9 L-J. Baker, C. E. F. Rickard and M. J. Taylor, J. Chem. Soc., Dalton
Trans., 1995, 2895.
10 S. Andersson, M. Hakansson and S. Jagner, Inorg. Chim. Acta, 1993,
209, 195.
11 A. Pfitzner and D. Schmitz, Z. Anorg. Allg. Chem., 1997, 623, 1555.
12 A. Bencini, D. Gatteschi and C. Zanchini, Inorg. Chem., 1985, 24,
704.
13 H. Hartl, I. Brudgam and F. Mahdjour-Hassan-Abadi, Z. Naturforsch.,
Teil B, 1985, 40, 1032.
14 M. Hofer and H. Hartl, Z. Anorg. Allg. Chem., 1992, 45, 612.
15 D. W. Allen and X. Li, J. Chem. Soc., Perkin Trans. 2, 1997, 1099
16 C. Lambert, S. Stadler, G. Bourhill and C. Brauchle, Angew. Chem., Int.
Ed. Engl., 1996, 35, 644.
17 C. Lambert, E. Schmalzlin, K. Meerholz and C. Brauchle, Chem. Eur.
J., 1998, 4, 512.
which were subsequently isolated and purified by trituration
with diethyl ether. Again, 1H and 13C NMR spectra were
consistent with the proposed structures, showing some sig-
nificant chemical shift changes compared to the parent salts.
Under FABMS conditions, cationic molecular ions were again
observed. Conversion to the betaines resulted in a significant
shift of the visible absorption maximum to longer wavelength.
Thus, e.g. lmax for the salt 2 (E = Sb; Ar = Ph; X = Cl, Y =
CuI2) in dichloromethane was observed at 358 nm, whereas for
the related betaine 5 in the same solvent, lmax = 536 nm.
Significantly, in view of the potential link with non-linear
optical properties, the betaines exhibited negative solvatochro-
mism, the visible absorption maximum moving to longer
wavelength on moving to a solvent of lower polarity. In the case
of the above betaine, lmax moved from 536 nm in dichloro-
Received in Cambridge, UK, 23rd July 1998; 8/05759A
2116
Chem. Commun., 1998