Preparation and properties of sterically demanding and chiral distibine ligands

Article abstract of DOI:10.1039/b808493a

A series of new rigid distibines, 1,8-bis(R₂Sb)naphthalene (R = Me: (1); R = Ph: (2)), and chiral distibines, 2,2′-bis(R ₂Sb)-1,1′-binaphthyl (R = Me: (3); R = Ph: (4) obtained as racemic mixtures) and the discrete enantiomers of 4,5-bis((R₂Sb) methyl)-2,2-dimethyl-1,3-D/L-dioxolane (R = Me: (5) (l), (7) (d); R = Ph: (6) (l), (8) (d)) have been obtained in high yields, using either electrophilic halostibine reagents with di-lithium reagents ((1)-(4)) or nucleophilic stibide reagents with dibromo-derivatives ((5)-(8)). The distorted octahedral complexes [Mo(CO)₄(L)], L = (1)-(8), planar [PtCl₂(L)], L = (1), (2), (3), (5), and neutral, five-coordinate [RhCl(cod)(L)], L = (2), (4), (6), are reported and trends in the spectroscopic data are discussed in terms of the ligand donor properties. Crystal structures of (3) and [Mo(CO)₄(3)] reveal significant structural changes occur upon coordination, and these are also reflected in the solution NMR spectroscopic parameters. Changes in the C-Sb-C angles and C-Sb bond distances upon coordination of (3) are discussed in term of increased s/p orbital mixing. Air oxidation of (1) forms a very unusual stibine oxide, the structure of which shows a distorted Sb₄O ₄ cubane core (bridging O atoms) with two orthogonal naphthalene units.

Full text of DOI:10.1039/b808493a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Preparation and properties of sterically demanding and
chiral distibine ligands†
Marek Jura, William Levason, Gillian Reid and Michael Webster
Received 20th May 2008, Accepted 8th July 2008
First published as an Advance Article on the web 11th September 2008
DOI: 10.1039/b808493a
A series of new rigid distibines, 1,8-bis(R2Sb)naphthalene (R = Me: (1); R = Ph: (2)), and chiral
distibines, 2,2¢-bis(R2Sb)-1,1¢-binaphthyl (R = Me: (3); R = Ph: (4) obtained as racemic mixtures) and
the discrete enantiomers of 4,5-bis((R2Sb)methyl)-2,2-dimethyl-1,3-D/L-dioxolane (R = Me: (5) (L),
(7) (D); R = Ph: (6) (L), (8) (D)) have been obtained in high yields, using either electrophilic halostibine
reagents with di-lithium reagents ((1)–(4)) or nucleophilic stibide reagents with dibromo-derivatives
((5)–(8)). The distorted octahedral complexes [Mo(CO)4(L)], L = (1)–(8), planar [PtCl2(L)], L = (1),
(2), (3), (5), and neutral, five-coordinate [RhCl(cod)(L)], L = (2), (4), (6), are reported and trends in the
spectroscopic data are discussed in terms of the ligand donor properties. Crystal structures of (3) and
[Mo(CO)4(3)] reveal significant structural changes occur upon coordination, and these are also reflected
in the solution NMR spectroscopic parameters. Changes in the C–Sb–C angles and C–Sb bond
distances upon coordination of (3) are discussed in term of increased s/p orbital mixing. Air oxidation
of (1) forms a very unusual stibine oxide, the structure of which shows a distorted Sb4O4 cubane core
(bridging O atoms) with two orthogonal naphthalene units.
The reduced s-donor properties of stibines has been used to good
Introduction
effect in the catalytic polymerisation of styrene10 and norbornene
insertion polymerisation11 by SbPh3 complexes of nickel, in which
the rapid and reversible Ni–SbPh3 coordination is thought to be
key.
The development of routes to stibine ligands (SbR3) has been
hampered by a number of factors, the most important un-
doubtedly being (i) the reactivity of the Sb–C bonds which can
lead to significant scrambling of R groups and (ii) the lack of
readily available organoantimony precursors (for antimony(III)
only SbPh3 and SbX3, X = Cl, Br or I, are routinely available
commercially).1–3 However, work from Werner and co-workers4–6
and ourselves3,7–9 has revealed important differences in the chem-
istry of stibines compared to phosphines and arsines. For example,
rhodium carbene complexes of SbiPr3 have provided the first
cases of bridging neutral Group 15 ligands. Considering the
vast number of documented phosphine and (to a lesser extent)
arsine complexes, none of which feature bridging ER3 (E =
P or As) groups, this clearly demonstrates that very different
electronic properties are manifested by the stibine. Furthermore,
entry into the corresponding PR3 and AsR3 bridged species
requires initial preparation of the bridged stibine species and
then substitution of SbR3 by ER3. The organometallic chemistry
of platinum metal stibine complexes has also revealed that the
stibines promote different reaction pathways, reflected in different
products being generated compared to those obtained using
analogous phosphines. Work on Rh(I) distibines also reveals
important differences compared to their diphosphine analogues,
e.g. reaction of [Rh(CO){Ph2Sb(CH2)3SbPh2}2]+ with HCl gas
leads to both oxidative addition and cleavage of Ph groups from
the stibine (the latter producing chelating PhClSb(CH2)3SbClPh
on Rh(III)—a very rare example of a coordinated halostibine).8
The preparations of the distibines R2Sb(CH2)nSbR2 (R = Ph or
Me; n = 1, 3, 4, 5; n π 2) were reported in the 1970s, via reaction
of the stibide R2Sb- with appropriate a,w-dihaloalkanes.1,2 Our
attempts to develop this route towards other distibines such
as o/m/p-C6H4(CH2SbR2)2 led to low yields of the desired
compounds. However, very much higher yields (>80%) could
be achieved by reacting electrophilic halostibines (R2SbCl) with
di-Grignards such as o/m/p-C6H4(CH2MgCl)2.12 This approach
has led to new rigid, semi-rigid and wide-angle distibines, adding
significantly to the range of ligand architectures available in this
area of chemistry.9,12 The recent reports of catalytic activity for
transition metal stibine complexes have prompted us to try to
develop effective synthetic methods for new sterically demanding
distibines and optically active distibines containing either Me or
Ph terminal substituents on Sb to modulate the donor properties
towards metal fragments. We report our findings here, including
studies of the relative donor properties of the new ligands
towards selected transition metal species. The Ph- and p-tolyl
substituted ligands 2,2¢-bis(diphenylstibino)-1,1¢-binaphthyl (2)
and 2,2¢-bis(di(p-tolyl)stibino)-1,1¢-binaphthyl have been reported
previously; the Pd(II) complex of the latter catalyses asymmetric
allylic alkylation and Rh(I) complexes of both have been shown to
catalyse asymmetric hydrosilylation of ketones.13
Results and discussion
School of Chemistry, University of Southampton, Southampton, UK SO17
1BJ. E-mail: gr@soton.ac.uk
The methods employed for the preparations of the new distib-
ines are illustrated in Scheme 1. In view of the much higher
† CCDC reference numbers 688589–688591. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b808493a
5774 | Dalton Trans., 2008, 5774–5782
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uncertain structures.14 The crystal structure of the oxidised form of
(1) shows (Fig. 1) an unusual arrangement involving two molecules
of (1) linked via m3-bridging O atoms to produce a pseudo-cubane
Sb4O4 core, with the naphthalene linkages mutually orthogonal.
One naphthalene unit lies on a crystallographic mirror plane,
while the second bisects the plane. The structure solution revealed
one well-defined naphthalene unit associated with the Sb4O4 core,
while the second naphthalene is disordered (see Experimental).
However, the structure confirms unambiguously the presence of
the SbMe2 groups in the 1,8-positions of the naphthalene ring. The
Sb1 ◊ ◊ ◊ Sb2 distance (i.e. within the well defined naphthalene unit)
˚
for these formally Sb(V) centres is 3.227(1) A, and with C1 ◊ ◊ ◊ C9 of
˚
2.521 A it is clear from the structure that the Cipso–Sb bonds are not
mutually parallel, but lie with an angle of 19◦ between them. The
˚
Sb4O4 residue has Sb–O distances in the range 2.105(5)–2.127(5) A
and O–Sb–O 75.3(2)–78.7(3)◦ with approximate Td symmetry. For
comparison Ph3SbO is a centrosymmetric dimer d(Sb–O) = 1.928,
◦
˚
2.075 A; mean values for the Sb–O–Sb angles 102.5 and for
O–Sb–O 77.5◦.15
Scheme 1 Preparative routes for compounds (1)–(8).
Fig. 1 View of the structure of the oxidised form of (1) with num-
bering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity. The disordered naph-
thyl residue (C13a–C22a) has anisotropic C atoms each with a sof
of 0.5. The other component of the disorder model is not shown
but is related by the mirror symmetry operation i. Symmetry oper-
yields obtained for distibines with aromatic backbones using
electrophilic Sb reagents in our earlier work,12 we adopted the
same approach for the rigid distibines (1) to (4) in this work.
Thus, reaction of 1,8-dibromonaphthalene with elemental lithium
in Et2O, followed by the addition of two mol. equivs. of Me2SbCl
in toluene (itself obtained by bubbling HCl gas through a toluene
solution of Me2PhSb12) or Ph2SbCl in diethyl ether at 0 ◦C gives the
naphthalene-based compounds in good yields as an air-sensitive
colourless oil (1) or an air-stable white solid (2) respectively. The
ready incorporation of the large and bulky SbR2 substituents in the
1- and 8-positions of the naphthalene framework was somewhat
◦
1
˚
ation: i = x,
- y, z. Selected bond lengths (A) and angles ( ):
2
Sb1–C1 2.155(10); Sb2–C9 2.143(11); Sb1 ◊ ◊ ◊ Sb2 3.2270(9); Sb1–C11
2.125(7); Sb2–C12 2.114(9); Sb1–O1 2.125(5); Sb1–O3 2.111(7); Sb2–O1
2.105(5); Sb2–O2 2.108(7); C1–Sb1–C11 97.9(3); C11–Sb1–C11i 93.9(4);
O3–Sb1–O1 75.6(2); Sb1–O1–Sb2 99.4(2).
1
1H and 13C{ H} NMR spectroscopic studies on the solution
1
unexpected. However, the disubstitution was confirmed from H
from which the crystal was obtained showed that oxidation was
incomplete, and we were unable to achieve complete conversion
to the oxide even after prolonged stirring in dry air. Oxidation
was therefore also attempted by passing ozonised oxygen through
a solution of (1) in CH2Cl2. NMR spectroscopic data on the
off-white product indicated essentially complete oxidation, with
the Me resonances on Sb(V) occurring at significantly higher
1
and 13C{ H} NMR spectroscopy, the SbMe2 resonances of (1)
being particularly characteristic (dH = 1.05; dC = 2.37), EIMS
which shows [parent - Me]+ and [parent - Ph]+ respectively
as the highest m/z peaks, with further fragmentation of the
compound also evident. Microanalyses were also consistent with
the successful formation of the naphthalene-based distibines.
Several attempts were made to obtain crystals of these ligands.
Some single crystals were obtained from a CHCl3 solution of (1)
after several weeks. However, the structure analysis showed that in
fact the compound had undergone oxidation at antimony. Unlike
frequency compared to those in (1) (SbVMe: dH = 1.45, dC
=
22.9).
Distibines bearing binaphthyl backbones, (3) and (4), may be
obtained as racemic mixtures by treatment of 2,2¢-dibromo-1,1¢-
phosphine oxides which form terminal P O units, stibine oxides
binaphthyl with BuLi in diethyl ether at -70 ◦C, to give the
t
=
form Sb–O–Sb bridges, often giving polymeric materials with
corresponding di-lithiated reagent. Addition of two mol. equivs.
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of R2SbCl, followed by workup allowed (3) and (4) each to be
obtained in ~70% isolated yield, the former as a colourless air-
sensitive solid, the latter an air-stable solid. EIMS shows [parent -
R]+ to be the highest m/z cluster in each case. Both the 1H
in each case. The inequivalence of the two Me groups on each
Sb atom observed by the solution NMR spectroscopic studies is
also obvious from the structure determination, with C22 and C23
in Fig. 2 lying adjacent to aromatic rings. The distance between
C23 and the centroid of the closest aromatic ring (defined by
1
and 13C{ H} NMR spectra of (3) reveal two d(Me) resonances
˚
at chemical shifts typical of SbMe units dH = 0.36, 0.81; dC
=
C1,2,3,4,9,10) is 4.145 A, while that between C22 and the centroid
˚
-1.42, -1.23, consistent with two different Me environments in
the racemic mixture. The inequivalence arises from the presence
of the bulky binaphthyl backbone, leading to one Me group on
each Sb pointing towards an aryl group and the other pointing
away. No coalescence was observed by 1H NMR spectroscopy in
d6-DMSO solution up to 150 ◦C.
of its closest ring (defined by C11,12,13,14,19,20) is 4.212 A.
˚
The Sb ◊ ◊ ◊ Sb distance is 4.063(1) A, and the CCCC torsion
angle linking the Sb atoms (associated with the twist about the
two planar naphthalene units) is 79.5(6)◦. The bond distances and
angles are discussed further below.
The saturated DIOP-based distibines (5)–(8) were each obtained
in the enantiopure form by treatment of the appropriate D- or
L-form of 4,5-bis(bromomethyl)-2,2-dimethyl-1,3-dioxolane (ob-
tained by bromination of the corresponding ditosylate precursor
using LiBr) with two mol. equivs. of NaSbR2. Use of the
nucleophilic R2Sb- reagents in these reactions led to moderate
yields of the products. As expected the enantiomeric pairs (5)/(7)
and (6)/(8) are indistinguishable spectroscopically, however, the
optical rotations of ligands (6) and (8) were measured as -14.8◦ and
+14.6◦ respectively in CHCl3. Given the air sensitivity of these Me-
substituted compounds, we prepared the air stable distibonium
salt of (5), [(5)Me2]I2, for characterisation purposes. This was
achieved by reaction of the ligand with excess MeI in acetone,
Confirmation of the identity of (3) and the Me group inequiv-
alences follow also from a crystal structure determination. The
structure of (3) clearly shows (Fig. 2, Table 1) one of the Me
groups on each Sb atom pointing towards one of the naphthalene
ring fragments while the other is directed away from the backbone
1
giving the product as a stable white solid whose 1H and 13C{ H}
NMR spectra are fully consistent with the formulation, with the
SbMe3 groups shifted to higher frequency (dH = 2.01; dC = 6.7).
The electrospray MS (MeCN) shows the highest m/z cluster of
peaks corresponding to [(5) + Me]+.
In order to probe the relative donor properties of the new
distibines, the ligands were reacted with selected transition metal
species and characterised spectroscopically and where possible
by crystallography. Treatment of [Mo(CO)4(nbd)] with one mol.
equiv. of L–L in anhydrous EtOH–CH2Cl2 gives [Mo(CO)4(L–
L)] as beige through to brown solids in good yields. Selected
spectroscopic data are presented in Table 2. As expected the IR
spectra mostly show four terminal n(CO) vibrations, consistent
with cis-disubstitution and hence chelation of the stibine (in
some cases the a1 and b1 modes ~1900 cm-1 are overlapping and
only three bands are evident). The IR data show that n(CO)
for the Me-substituted ligands are around 10 cm-1 or more to
low frequency of the Ph-substituted analogues, consistent with
the former transferring more electron density to the Mo(CO)4
Fig. 2 View of the structure of (3) with numbering scheme adopted.
Ellipsoids are drawn at the 50% probability level and H atoms are omitted
for clarity.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for (3)
Sb1–C22
Sb1–C2
Sb2–C24
C22–Sb1–C21
C21–Sb1–C2
C23–Sb2–C12
2.152(4)
2.169(4)
2.158(4)
93.7(2)
96.12(18)
95.42(18)
Sb1–C21
Sb2–C23
Sb2–C12
C22–Sb1–C2
C23–Sb2–C24
C24–Sb2–C12
2.154(5)
2.155(5)
2.174(4)
96.39(17)
94.1(2)
1
fragment and hence likely stronger donors. The 13C{ H} NMR
96.59(17)
spectra each show two CO resonances as expected, with d(CO) to
Table 2 Selected spectroscopic data for [Mo(CO)4(L–L)]
L–L
n(CO) CH2Cl2/cm-1
d(CO)
d(95Mo)
Ref.
Ph2Sb(CH2)3SbPh2
2021,1927,1912, 1892
2014, 1903, 1880
211.0, 215.6
213.0, 218.4
210.9, 215.5
213.8, 218.5
210.7, 215.8
210.6, 216.9
211.3, 216.4
211.7, 216.6
209.2, 213.6
-1849
-1843
-1798
-1782
n.o.b
19
19
12
Me2Sb(CH2)3SbMe2
o-C6H4(CH2SbMe2)2
1,8-C10H6(SbMe2)2 (1)
1,8-C10H6(SbPh2)2 (2)
2,2¢-C20H12(SbMe2)2 (3)
2,2¢-C20H12(SbPh2)2 (4)
C7H12O2(SbMe2)2 (5, 7)
C7H12O2(SbPh2)2 (6, 8)
2017, 1935, 1901, 1867a
2020, 1946, 1912, 1886
2009, 1936, 1873
This work
This work
This work
This work
This work
This work
2014, 1908, 1877
2027, 1936, 1882
2019, 1945, 1914, 1885(sh)
2023, 1940(sh), 1913, 1880(sh)
-1747
n.o.b
-1841
n.o.b
a Nujol mull. b n.o. = not observed.
5776 | Dalton Trans., 2008, 5774–5782
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higher frequency for the Me-substituted distibines, also consistent
with increased electron density on CO in these complexes.16 In
˚
2.735(1)–2.756(1) A. The chelate angles, Sb1–Mo1–Sb2 =
84.61(4) and Sb3–Mo2–Sb4
84.13(4)◦, are remarkably
acute for seven-membered chelate ring—undoubtedly
=
both the H and 13C{ H} NMR spectra the d(Me) resonances
for [Mo(CO)4(L–L)] (L–L = (1), (5) and (7)) are shifted to
high frequency upon coordination. However, for [Mo(CO)4(3)]
we observe one d(Me) shifted to high frequency and the other to
low frequency upon coordination. This suggests that the already
inequivalent Me groups on each of the Sb atoms, which are clearly
very sensitive to the proximity of the binaphthyl backbone, are
also affected significantly by the presence of the metal fragment.
Confirmation of the coordination environment in [Mo(CO)4(3)]
follows from a crystal structure determination (Fig. 3, Table 3)
which shows two crystallographically independent molecules
in the asymmetric unit, each with the Mo atom in a distorted
octahedral environment through four CO ligands and two Sb
donor atoms from a chelating molecule of (3), with d(Mo–Sb) =
1
1
a
a
consequence of the steric constraints imposed by the bulky
and rather rigid binaphthyl backbone. These compare with for
example <Sb–Pt–Sb of 97.58(2)◦ in the planar cis-[PtCl2{o-
C6H4(CH2SbMe2)2}],17 <Sb–Pt–Sb of 95.25(1)◦ in the distorted
octahedral [PtMe3I{o-C6H4(CH2SbMe2)2}] (both complexe◦s
contain seven-membered chelate rings),7 <Sb–Rh–Sb of 87.86(6)
in trans-[RhCl2{Ph2Sb(CH2)3SbPh2}2]+18 and <Sb–Pt–Sb
of 89.63(3)◦ in [PtMe3I{Me2Sb(CH2)3SbMe2}] (six-membered
chelate rings).7 The Sb ◊ ◊ ◊ Sb distances in the two independent
˚
[Mo(CO)4(3)] molecules are 3.696(1) A (molecule containing
˚
˚
Mo1) and 3.679(1) A (molecule containing Mo2)—some 0.3 A
shorter than in the uncomplexed (3) above. This reduction in
d(Sb ◊ ◊ ◊ Sb) is accompanied by a reduction of ca. 3◦ in the
CCCC torsion angles between the two Sb atoms in the chelate, to
-76.8(1.5) and +76.4(1.5)◦ (for Mo1 and Mo2 respectively).
It is also clear from the crystal structure that the distances
between the centroids of the closest aromatic rings and C22/C23
in the Mo1 molecule (or C50/C52 in the Mo2 molecule) are
˚
considerably shorter (by ca. 0.5 A) in [Mo(CO)4(3)] compared
to the structure of (3) itself (vide supra) (the relevant distances
are: between C23 and the centroid of the ring defined by
˚
C1,2,3,4,9,10 = 3.588 A; C22 and the centroid of the ring defined
˚
by C11,12,13,14,19,20 = 3.466 A; C52 and the centroid of the ring
˚
defined by C29,30,31,32,37,38 = 3.649 A; C50 and the centroid of
˚
the ring defined by C39,40,41,42,47,48 = 3.536 A). This structural
change upon coordination is consistent with the shifts observed
for the Me resonances in the NMR spectra on complexation.
The Mo–C distances in [Mo(CO)4(3)] fall into two distinct sets,
those trans to Sb being significantly shorter than those occupying
axial (mutually trans) positions reflecting the modest s-donor/p-
acceptor properties of the stibine compared to CO.
Comparison of the C–Sb–C angles in uncomplexed (3) (range
93.7(2) to 96.6(2)◦) and in the complex [Mo(CO)4(3)] (range
97.0(5) to 104.1(5)◦) also reveals evidence for some rehybridisation
of the s and p orbitals at Sb upon complexation. Thus the
angles in the former are closer to the idealised 90◦ anticipated
for a system which is mainly p-orbital in character, whereas the
C–Sb–C angles in the coordinated ligand are closer to tetrahedral,
suggesting greater s/p mixing (sp3 hybridisation). This is in line
with observations drawn from crystallographic studies on ‘free’
SbPh3 and Ph2SbCH2SbPh2 and their complexes.3
Molybdenum-95 NMR spectra were recorded for the Me-
substituted ligand complexes, each showing a single resonance
around -1750 to -1850 ppm, in line with related complexes,19,20
revealing a quite significant dependence of the 95Mo chemical shift
on the linking group between the Sb donor atoms.
The distorted square planar complexes [PtCl2(L–L)] (L–L =
(1), (2), (3), (5), (7)) were obtained as yellow solids from reaction
of [PtCl2(MeCN)2] with L–L in MeCN–CH2Cl2 solution. IR
spectroscopy shows two clear peaks in the far IR, assigned
as n(PtCl) and hence indicative of a cis-dichloro arrangement
with chelating L–L (Table 4). Platinum-195 NMR spectra were
recorded for these compounds, although the very low solubility
of the complexes involving the Ph-substituted ligands meant that
no resonances were observed. However, for the Me-substituted
ligand complexes the 195Pt NMR spectra (Table 4) are singlets in
Fig. 3 View of one of the two crystallographically independent molecules
of [Mo(CO)4(3)] with numbering scheme adopted. Ellipsoids are drawn at
the 50% probability level and H atoms are omitted for clarity. The other
molecule is essentially identical.
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for [Mo(CO)4(3)]
Mo1–C25
Mo1–C26
Mo1–C27
Mo1–C28
Mo1–Sb1
Mo1–Sb2
O1–C25
O2–C26
1.969(14)
2.012(14)
2.036(14)
2.048(14)
2.7562(14)
2.7351(14)
1.170(15)
1.134(16)
1.131(15)
1.146(15)
89.4(5)
90.1(5)
92.0(6)
90.2(5)
94.2(6)
173.8(6)
94.0(4)
176.5(4)
86.9(4)
86.9(4)
178.3(4)
92.1(4)
Mo2–C53
Mo2–C54
Mo2–C55
Mo2–C56
Mo2–Sb3
Mo2–Sb4
O5–C53
O6–C54
1.967(13)
1.954(13)
2.045(16)
2.045(13)
2.7385(13)
2.7527(14)
1.160(15)
1.164(14)
1.163(16)
1.138(14)
91.0(5)
90.6(5)
92.8(5)
90.2(6)
91.1(5)
176.0(5)
92.6(4)
176.2(4)
88.4(3)
87.6(4)
176.2(4)
92.3(4)
O3–C27
O4–C28
O7–C55
O8–C56
C25–Mo1–C26
C25–Mo1–C27
C26–Mo1–C27
C25–Mo1–C28
C26–Mo1–C28
C27–Mo1–C28
C25–Mo1–Sb2
C26–Mo1–Sb2
C27–Mo1–Sb2
C28–Mo1–Sb2
C25–Mo1–Sb1
C26–Mo1–Sb1
C27–Mo1–Sb1
C28–Mo1–Sb1
Sb2–Mo1–Sb1
C54–Mo2–C53
C54–Mo2–C56
C53–Mo2–C56
C54–Mo2–C55
C53–Mo2–C55
C56–Mo2–C55
C54–Mo2–Sb3
C53–Mo2–Sb3
C56–Mo2–Sb3
C55–Mo2–Sb3
C54–Mo2–Sb4
C53–Mo2–Sb4
C56–Mo2–Sb4
C55–Mo2–Sb4
Sb3–Mo2–Sb4
90.8(3)
88.8(3)
84.61(4)
87.3(3)
91.7(4)
84.13(4)
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Table 4 Selected spectroscopic data for [PtCl2(L–L)]
Solvents were dried by standard procedures prior to use and all
preparations were undertaken using standard Schlenk techniques
under a N2 atmosphere. The stibine ligands were stored and
handled in a glove box under N2.
L–L
n(Pt–Cl)/cm-1
d(195Pt)
Ref.
Ph2Sb(CH2)3SbPh2
Me2Sb(CH2)3SbMe2
{CH2(o-C6H4CH2SbMe2)}2
1,8-C10H6(SbMe2)2 (1)
2,2¢-C20H12(SbMe2)2 (3)
C7H12O2(SbMe2)2 (5, 7)
283, 305
273, 295
307, 316
273, 309
296, 316
281, 316
-4556
-4553
-4960
-4602
-4403
-4522
21
22
9
Ligands
This work
This work
This work
1,8-Bis(dimethylstibino)naphthalene (1). 1,8-Dibromonaph-
thalene (2.00 g, 7.00 mmol) was added dropwise as a diethyl ether
solution (40 mL) to a 3-neck flask charged with lithium (freshly
pressed into a thin foil) (0.35 g, 0.05 mol) in Et2O (50 mL) at
0 ◦C under a flow of nitrogen. The reaction was left to stir at this
temperature for 2 h, followed by a further 2 h at room temperature,
the solution was then filtered into a Schlenk tube using a filter
cannula. Dimethylchlorostibine (15.4 mmol) was produced in
situ by bubbling HCl(g) through a toluene solution (40 mL) of
dimethylphenylstibine (3.50 g, 15.4 mmol) for 15 min, followed by
purging the solution with N2 for 20 min. The SbMe2Cl solution
was added dropwise to the solution of the dilithio reagent over a
period of 2 h at 0 ◦C. The final few drops of the SbMe2Cl solution
discharged the deep red colour of the solution. The reaction
mixture was left to stir at room temperature overnight, after
which the mixture was hydrolysed with degassed water (50 mL).
The organics were separated and dried over MgSO4, filtered and
reduced to dryness under reduced pressure yielding a colourless
the region -4400 to -4600 ppm, consistent with a planar Sb2Cl2
donor set at Pt(II).9,21,22
We have also prepared Rh(I)–cod complexes of some of
the new distibines. Our previous work has shown that the
ligand Ph2Sb(CH2)3SbPh2 forms relatively stable complexes with
organometallic Rh(I) species, whereas Me-based distibines such
as Me2Sb(CH2)3SbMe2 and o-C6H4(CH2SbMe2)2 give much less
stable complexes, hence we have focused on the Ph-based distibines
in this work.8 Ligands (2), (4) and (6) were successfully reacted
with 0.5 mol. equivs. of [RhCl(cod)]2 in EtOH–CH2Cl2 at room
temperature to afford products of composition [Rh(cod)(L–L)Cl]
as orange solids in ca. 60% yield. The 1H NMR spectra suggest that
these compounds are five-coordinate with the cod resonances split
into four distinct environments. Conductivity measurements in
CH2Cl2 solution also show that the products are non-electrolytes,
consistent with the neutral, five-coordinate geometries proposed.
1
oil (1.6 g, 53%). H NMR (CDCl3): d = 1.05 (s) SbCH3 [12H],
1
7.35 (t) [2H], 7.72 (d) [2H], 7.84 (d) [2H] aromatic CH. 13C{ H}
NMR (CDCl3): d = 2.4 CH3Sb, 125.3, 125.8, 129.9, 135.6, 139.8
aromatic C. EIMS: m/z = 415 [(1)–CH3]+. Anal. found: C, 38.8; H,
4.5%. Calc. for C14H18Sb2: C, 39.1; H, 4.2%.
Conclusions
Distibines (1)–(8) have been isolated in good to very good yields
using either Sb-containing nucleophiles (R2Sb-) or electrophiles
(R2SbCl). The new ligands extend considerably the range of avail-
able distibines and offer significantly different steric and electronic
properties from the more widely studied distibinoalkanes. Four
chiral distibines have been prepared as single enantiomers. Spec-
troscopic data on these and their complexes with tetracarbonyl-
molybdenum and dichloro-platinum(II) are described in terms
of the steric/electronic properties of the ligands. Selected ex-
amples of five coordinate chloro-rhodium(I)-diene complexes are
also described. Some unexpected structural consequences of the
binaphthyl-based ligands are discussed along with a rare example
of a stibine oxide containing a pseudo-cubane Sb4O4 core.
1,8-Bis(diphenylstibino)naphthalene (2). 1,8-Dibromonaph-
thalene (2.00 g, 7.00 mmol) was added dropwise as a diethyl
ether solution (40 mL) to a 3-neck flask charged with lithium
(freshly pressed into a thin foil) (0.35 g, 0.05 mol) in Et2O (50 mL)
at 0 ◦C under a flow of nitrogen. The reaction was left to stir
at this temperature for 2 h, followed by a further 2 h at room
temperature, the solution was then filtered into a Schlenk tube
using a filter cannula. Diphenylchlorostibine (4.40 g, 14.0 mmol)
in diethyl ether (100 mL) was added dropwise to the solution of
the dilithio reagent over a period of 2 h at 0 ◦C. The final few drops
of the SbPh2Cl solution discharged the deep red colour of the
lithium salt solution. The reaction mixture was left to stir at room
temperature overnight, after which the mixture was hydrolysed
with degassed water (50 mL). The organics were separated and
dried over MgSO4, filtered and reduced to dryness under reduced
pressure yielding a white solid which was recrystallised from
Experimental
Infrared spectra were recorded as Nujol nulls between CsI discs
or in CH2Cl2 solution using a Perkin-Elmer 983G spectrometer
1
hexane–CH2Cl2 to give a white solid (2.40 g, 50%). H NMR
1
(CDCl3): d = 6.81–7.91 (m) aromatic H. 13C{ H} NMR (CDCl3):
1
over the range 4000–200 cm-1. 1H and 13C{ H} NMR spectra were
d = 127.6, 127.9, 128.4, 128.6, 128.9, 129.1, 134.1, 134.4, 136.0.
136.2 aromatic C. EIMS: m/z = 601 [(2) - Ph]+, 524 [(2) -
2Ph]+ 401 [(2) - SbPh2]+. Anal. found: C, 58.5; H, 4.2. Calc. for
recorded using a Bruker AV300 spectrometer and are referenced to
TMS. 95Mo and 195Pt NMR spectra were recorded using a Bruker
DPX400 spectrometer operating at 26.1 or 85.6 MHz respectively
and are referenced to external aqueous Na2[MoO4] and 1 mol dm-3
Na2[PtCl6] respectively. Mass spectra were run by electron impact
on a VG-70-SE Normal geometry double focusing spectrome-
ter or by positive ion electrospray (MeCN solution) or APCI
using a VG Biotech platform. Microanalyses were undertaken
either by the University of Strathclyde microanalytical service or
Medac Ltd.
1
3
C34H26Sb2· CH2Cl2: C, 58.4; H, 3.8%.
2,2¢-Bis(dimethylstibino)-1,1¢-binaphthyl (3). 2,2¢-Dibromo-
1,1¢-binaphthyl (1.00 g, 2.43 mmol) was added as a diethyl ether
solution (30 mL) to tert-butyllithium (10.69 mmol) in a diethyl
ether solution (30 mL) at -70 ◦C over 30 min. The red/orange
solution was left to stir at the lowered temperature for 1 h.
SbMe2Cl (5.35 mmol), prepared by bubbling HCl(g) through a
5778 | Dalton Trans., 2008, 5774–5782
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toluene solution of SbMe2Ph (1.23 g), was added to the lithium
salt solution at -70 C over 30 min. The reaction was left to stir
for 15 min. The solution was allowed to stir for a further 20 min
and was then purged with N2 for 30 min. The toluene solution
was added to a solution of sodium (0.53 g, 22.90 mmol) in liquid
ammonia (200 mL) maintained at -78 ◦C (acetone/CO2 slush).
Within 1 h the colour of the reaction mixture had changed from
dark-blue to dark-red. Stirring was continued for a further 2 h,
followed by the dropwise addition of 4,5-bis(bromomethyl)-2,2-
dimethyl-1,3-L-dioxolane (1.50 g, 5.21 mmol) as a thf solution
(50 mL). The reaction mixture was stirred overnight to allow
evaporation of the ammonia. The solution was hydrolysed with
degassed H2O (100 mL) and the organic layer separated. The
aqueous layer was washed with diethyl ether (2 ¥ 100 mL), and the
combined organics were dried over MgSO4. Following filtration
the volatiles were removed under reduced pressure yielding the title
◦
for 12 h and was then quenched with degassed water (30 mL).
The aqueous phase was washed with diethyl ether (2 ¥ 30 mL)
and the combined organic phases were dried over MgSO4. The
solution was filtered and the volatiles were removed under reduced
pressure, yielding a viscous, colourless oil which crystallised over
time (0.90 g, 67%). 1H NMR (CDCl3): d = 0.36 (s) SbCH3 [6H],
3
3
0.81 (s) SbCH3 [6H], 6.92 (d, J = 7.3 Hz) [2H], 7.04 (t, J =
3
3
8.0 Hz) [2H], 7.25 (t, J = 7.3 Hz) [2H], 7.62 (d, J = 8.4 Hz)
[2H], 7.72 (d, 3J = 8.4 Hz) [2H], 7.78 (d, 3J = 8.4 Hz) [2H]
aromatic CH. 13C{ H} NMR (CDCl3): d = -1.42, -1.23 SbCH3,
1
125.3, 126.0, 126.2, 126.7, 128.0, 128.2, 129.0, 133.2, 138.0, 146.5
aromatic C. EIMS: m/z = 540 [(3) - Me], 405 [(3) - SbMe2], 389
[(3) - (SbMe2 + Me)], 273 [(3) - (SbMe2 + 2Me)]. Anal. found: C,
52.1; H, 3.8. Calc. for C24H24Sb2: C, 51.9; H, 4.4%.
1
product as a pale yellow air sensitive oil (0.8 g, 36%). H NMR
(CDCl3): d = 0.78 (s) SbCH3 [12H], 1.37 (s) [6H] CCH3, 1.60–1.80
1
(m) [4H] CH2, 3.85 (m) [2H] CH. 13C{ H} NMR (CDCl3): d =
2,2¢-Bis(diphenylstibino)-1,1¢-binaphthyl (4). 2,2¢-Dibromo-
1,1¢-binaphthyl (1.00 g, 2.43 mmol) was added as a diethyl ether
solution (30 mL) to tert-butyllithium (10.69 mmol) in a diethyl
ether solution (30 mL) at -70 ◦C over 30 min. The red/orange
solution was left to stir at the lowered temperature for 1 h.
SbPh2Cl (1.51 g, 4.86 mmol) was added to the lithium salt
solution at -70 ◦C over 30 min. The reaction was left to stir
for 12 h and was then quenched with degassed water (30 mL).
The aqueous phase was washed with diethyl ether (2 ¥ 30 mL)
and the combined organic phases were dried over MgSO4. The
solution was filtered and the volatiles were removed under reduced
pressure, yielding a yellow/orange solid which was recrystallised
-3.9 (s), SbCH3, 19.7 CH2, 27.4 CCH3, 82.2 CH, 108.5 Cq. EIMS:
m/z = 417 [(5) - Me]+. Anal. found: C, 29.6; H, 4.9. Calc. for
C11H24O2Sb2: C, 30.6; H, 5.6%.
Dimethiodide of (5). An aliquot of compound 5 was dissolved
in dry acetone (50 mL) and treated with an excess of methyl iodide.
The reaction was left to stir for 30 min and the air-stable white
solid was filtered, washed with acetone and dried under reduced
1
pressure. H NMR (CDCl3): d = 1.42 (s) [6H] CCH3, 2.01 (s)
[18H] SbCH3, 3.17 (t, 3J = 11.7 Hz) [2H] CH, 3.47 (d, 3J = 11.7
3
1
Hz) [2H] CH2, 4.43 (d, J = 11.7 Hz) [2H] CH2. 13C{ H} NMR
(CDCl3): d = 6.7 SbCH3, 26.9 CCH3, 30.9 CH2, 78.4 CH, 108.5
Cq. ESMS (MeCN): m/z = 447 [(5) + Me]+.
1
from CH2Cl2 (1.45 g, 74%). H NMR (CDCl3): d = 6.80–8.15
1
(m) aromatic CH. 13C{ H} NMR (CDCl3): d = 125.3, 125.8,
126.6, 127.8, 127.9, 128.2, 128.6, 128.9, 129.0, 133.5, 133.8, 136.3,
136.5, 138.5 aromatic C. EIMS: m/z = 727 [(4) - Ph], 527 [(4) -
SbPh2], 450 [(4) - (SbPh2 + Ph)], 373 [(4) - (SbPh2 + 2Ph)], 252
[(4) - 2SbPh2]. Anal. found: C, 64.6; H, 4.5. Calc. for C44H32Sb2:
C, 65.7; H, 4.1% (NMR spectra show small amounts of residual
CH2Cl2).
4,5-Bis((diphenylstibino)methyl)-2,2-dimethyl-1,3-L-dioxolane
(6). Diphenylchlorostibine (3.42 g, 10.42 mmol) was added as
a toluene solution to a solution of sodium (0.53 g, 22.90 mmol)
in liquid ammonia (200 mL) maintained at -78 ◦C (acetone/CO2
slush). Within 1 h the colour of the reaction mixture had changed
from dark-blue to dark-red. Stirring was continued for a further
2 h, followed by the dropwise addition of 4,5-bis(bromomethyl)-
2,2-dimethyl-1,3-L-dioxolane (1.50 g, 5.21 mmol) as a thf solution
(50 mL). The reaction mixture was stirred overnight to allow
evaporation of the ammonia. The solution was hydrolysed with
degassed H2O (100 mL) and the organic layer separated. The
aqueous layer was washed with diethyl ether (2 ¥ 100 mL), and the
combined organics were dried over MgSO4. Following filtration
the volatiles were removed under reduced pressure yielding the title
product as a thick yellow oil (0.91 g, 46%). 1H NMR (CDCl3): d =
1.30 (s) CCH3 [6H], 2.05 (m) CH2 [4H], 3.94 (m) CH [2H], 7.10–
4,5-Bis(bromomethyl)-2,2-dimethyl-1,3-L-dioxolane. 1,4-Di-
O-tosyl-2,3-O-isopropylidene-L-threitol (5.00 g, 10.0 mmol) was
dissolved in DMSO (30 mL) in a round bottomed flask fitted with
a dinitrogen inlet. LiBr (3.20 g, 36.8 mmol) was added over a period
over 30 mins. The reaction was left to stir for 18 h at 60 ◦C. The
solution was then poured over ice, the organic phase was separated
and washed with water (2 ¥ 50 mL), and dried over MgSO4. The
volatiles were removed under reduced pressure and the product
was purified by Kugelro¨hr distillation (110 ◦C/5 mmHg) to yield
1
a colourless oil (1.80 g, 63%). H NMR (CDCl3): d = 1.42 (s)
1
7.42 (m) aromatic CH [18H]. 13C{ H} NMR (CDCl3): d = 23.6
1
CCH3 [6H], 3.48 (m) CH2 [4H], 4.11 (m) CH [2H]. 13C{ H} NMR
CH2, 27.4 CCH3, 81.5 CH, 107.9 Cq, 128.6, 128.8, 133.8, 135.8
aromatic C. EIMS: m/z = 603 [(6) - Ph]+, 403 [(6) - SbPh2]. Anal.
found: C, 54.7; H, 4.6. Calc. for C31H32O2Sb2: C, 54.8; H, 4.7%.
[a]2D5= -14.8◦ (0.5, CHCl3).
(CDCl3): d = 27.4 CH3, 32.5 CH2, 79.1 CH, 110.5 Cq. [a]2D5= -3.6◦
(0.5, CHCl3).
4,5-Bis(bromomethyl)-2,2-dimethyl-1,3-D-dioxolane. Synthe-
sis as above using 1,4-Di-O-tosyl-2,3-O-isopropylidene-D-threitol.
1H NMR (CDCl3): d = 1.42 (s) CCH3 [6H], 3.48 (m) CH2 [4H],
4,5-Bis((dimethylstibino)methyl)-2,2-dimethyl-1,3-D-dioxolane
(7). Method followed as for the L-isomer (5) giving identical
spectroscopic and analytical data.
1
4.11 (m) CH [2H]. 13C{ H} NMR (CDCl3): d = 27.4 CH3, 32.5
CH2, 79.1 CH, 110.5 Cq. [a]2D5= +3.6◦ (0.5, CHCl3).
4,5-Bis((dimethylstibino)methyl)-2,2-dimethyl-1,3-L-dioxolane
(5). Hydrogen chloride gas was bubbled through a solution of
dimethylphenylstibine (2.38 g, 10.41 mmol) in toluene (50 mL)
4,5-Bis((diphenylstibino)methyl)-2,2-dimethyl-1,3-D-dioxolane
(8). Method followed as for the L-isomer (6) giving identical
spectroscopic and analytical data. [a]2D5= +14.6◦ (0.5, CHCl3).
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Complexes
n = 2027(m), 1936(s), 1882(m) (CO). Anal. found: C, 57.3; H, 3.6.
Calc. for C48H32MoO4Sb2: C, 57.0; H, 3.2%.
[Mo(CO)4(1)]. [Mo(CO)4(nbd)] (0.081 g, 0.27 mmol) was
dissolved in ethanol (30 mL) the ligand (0.015 g, 0.27 mmol)
was added dropwise as a CH2Cl2 solution and the reaction was
left to stir until the carbonyl stretches associated with the starting
material were no longer observed in the solution IR spectrum.
The solvent was removed under reduced pressure and the crude
solid was washed with hexane and filtered. The resulting beige
[Mo(CO)4(5)]. [Mo(CO)4(nbd)] (0.050 g, 0.17 mmol) was
dissolved in ethanol (30 mL) the ligand (0.072 g, 0.17 mmol) was
added dropwise as a CH2Cl2 solution and the reaction was left to
stir for 4 h. The solvent was removed under reduced pressure and
the crude solid was washed with hexane and filtered. The resulting
1
beige solid was dried under reduced pressure (0.050 g, 46%). H
1
solid was dried in vacuo. (0.105 g, 58%). H NMR (CDCl3): d =
NMR (CDCl3): d = 0.98 (s) SbCH3 [6H], 1.23 (s) [12H] SbCH3
1.45 (s) SbCH3 [12H], 7.36 (t, 3J = 7.5 Hz) [2H], 7.55 (d, 3J = 8.3
1
and CCH3, 1.64–1.85 (m) [4H] CH2, 4.05 (m) CH [2H]. 13C{ H}
1
Hz) [2H], 7.94 (d, 3J = 7.5 Hz) [2H] aromatic CH. 13C{ H} NMR
NMR (CDCl3): d = -3.7 SbCH3, 20.2 CH2, 27.5 CH3, 82.5 CH,
108.1 Cq, 211.7, 216.6 CO. 95Mo NMR (CH2Cl2–CDCl3): d =
-1841. IR (cm-1/CH2Cl2): n = 2019(m), 1945(s), 1914(m) (CO).
Anal. found: C, 28.4; H, 3.8. Calc. for C15H24MoO6Sb2: C, 28.2;
H, 3.8%.
(CH2Cl2–CDCl3): d = 1.2 (SbCH3), 125.8, 126.6, 128.8, 129.9,
136.5, 138.1 aromatic C, 213.8, 218.5 CO. 95Mo NMR (CH2Cl2–
CDCl3): d = -1782. Anal. found: C, 38.3; H, 4.2%. Calc. for
3
C18H18MoO4Sb2· C6H14: C, 38.4; H, 4.1%. IR (cm-1/CH2Cl2): n =
4
2020(s), 1946(sh), 1912(vs), 1886(m) (CO). IR (cm-1/Nujol): n =
[Mo(CO)4(6)]. [Mo(CO)4(nbd)] (0.081 g, 0.27 mmol) was
dissolved in ethanol (30 mL) the ligand (0.185 g, 0.27 mmol) was
added dropwise as a CH2Cl2 solution and the reaction was left to
stir for 4 h. The solvent was removed under reduced pressure and
the crude solid was washed with hexane and filtered. The resulting
2012, 1944, 1914, 1880 (CO).
[Mo(CO)4(2)]. [Mo(CO)4(nbd)] (0.100 g, 0.33 mmol) was
dissolved in ethanol (40 mL) the ligand (0.226 g, 0.33 mmol) was
added dropwise as a CH2Cl2 solution and the reaction was left to
stir for 2 h. The solvent was removed under reduced pressure and
the crude solid was washed with hexane and filtered. The resulting
orange solid was dried in vacuo. (0.135 g, 46%). 1H NMR (CDCl3):
1
brown solid was dried under reduced pressure (0.11 g, 46%). H
NMR (CDCl3): d = 1.25 (s) CCH3 [6H], 2.10 (m) CH2 [4H], 3.65
1
(m) CH [2H], 6.95–7.45 (m) aromatic CH [18H]. 13C{ H} NMR
1
d = 6.73–7.97 (m) aromatic H. 13C{ H} NMR (CH2Cl2–CDCl3):
(CDCl3): d = 25.5 CCH3, 29.2 CH2, 108.4 Cq, 127.7, 128.3, 134.0,
137.3 aromatic C, 209.2, 213.6 CO. IR (cm-1/Nujol): n = 2023,
1945(sh), 1911, 1890(sh) (CO). IR (cm-1/CH2Cl2): n = 2023(m),
1940(sh), 1913(s), 1880(sh) (CO). Anal. found: C, 48.2: H, 3.7.
Calc. for C35H32MoO6Sb2: C, 47.3, H, 3.6%.
d = 127.5, 129.3, 129.4, 129.8, 130.0, 130.6, 131.0, 135.5, 136.5,
137.4 (aromatic C), 210.7, 215.8 (CO). 95Mo NMR (CH2Cl2–
CDCl3): not observed. Anal. found: C, 51.9, H, 3.6. Calc. for
C38H26MoO4Sb2: C, 51.5; H, 3.0%. IR (cm-1/CH2Cl2): n = 2009(s),
1936(br,s), 1873(m) (CO).
[Mo(CO)4(7)]. Method followed as for the L-isomer
[Mo(CO)4(5)] giving identical spectroscopic and analytical data.
[Mo(CO)4(3)]. [Mo(CO)4(nbd)] (0.081 g, 0.27 mmol) was
dissolved in ethanol (30 mL) the ligand (0.150 g, 0.27 mmol) was
added dropwise as a CH2Cl2 solution and the reaction was left to
stir until no carbonyl stretches associated with the starting material
were observed in the IR spectrum. The solvent was removed under
reduced pressure and the crude solid was washed with hexane
and filtered. The resulting beige solid was dried under reduced
pressure (0.100 g, 58%). 1H NMR (CDCl3): d = -0.02 [6H], 1.37
[Mo(CO)4(8)]. Method followed as for the L-isomer
[Mo(CO)4(6)] giving identical spectroscopic and analytical data.
[PtCl2(1)]. PtCl2 (0.100 g, 0.36 mmol) was suspended in
acetonitrile and heated to 70 ◦C until a clear yellow solution was
produced. The solution was allowed to reach room temperature
and the ligand (0.155 g, 0.36 mmol) was added dropwise as a
CH2Cl2 solution (10 mL). The reaction was left to stir for 12 h,
initially turning orange in colour then back to yellow. The reaction
mixture was reduced in volume by half and the solid which
precipitated was filtered off and washed with hexane to give a
yellow solid (0.09 g, 36%). 1H NMR (CDCl3): d = 1.60 (s) SbCH3
[12H], 7.40–8.05 (m) aromatic CH [6H] (and residual MeCN
3
[6H] SbCH3 (s), 7.04 CH (d, J = 8.4 Hz) [2H], 7.26 CH (t,
3
3J = 7.2 Hz) [2H], 7.49 CH (t, J = 7.2 Hz) [2H], 7.66 CH (d,
3
3J = 8.4 Hz) [2H], 7.93 CH (d, J = 8.4 Hz) [2H], 7.99 CH (d,
1
3J = 8.4 Hz) [2H] aromatic CH. 13C{ H} NMR (CH2Cl2–CDCl3):
d = -3.14, -0.13 (SbCH3), 125.8, 126.1, 126.8, 127.6, 128.0, 128.5,
133.3, 134.5, 135.5, 142.4 aromatic C, 210.6, 216.9 CO. 95Mo NMR
(CH2Cl2–CDCl3): d = -1747. Anal. found: C, 43.8; H, 3.1. Calc.
for C28H24MoO4Sb2: C, 44.0; H, 3.2%. IR (cm-1/CH2Cl2): n =
2014, 1908, 1877 (CO). IR (cm-1/Nujol): n = 2009(m), 1913(s),
1875(m), 1857(m) (CO).
resonances). 195Pt NMR (CH2Cl2–CDCl3): d = -4602 (w1 = 450
2
Hz). IR (cm-1/Nujol): n = 273, 309 (Pt–Cl). Anal. found: C, 26.8;
H, 2.7; N, 1.8. Calc. for C14H18Cl2PtSb2·MeCN: C, 26.1; H, 2.9;
N, 1.9%.
[Mo(CO)4(4)]. [Mo(CO)4(nbd)] (0.081 g, 0.27 mmol) was
dissolved in ethanol (30 mL) the ligand (0.220 g, 0.27 mmol) was
added dropwise as a CH2Cl2 solution and the reaction was left to
stir for 4 h. The solvent was removed under reduced pressure and
the crude solid was washed with hexane and filtered. The resulting
brown solid was dried under reduced pressure (0.100 g, 48%). 1H
[PtCl2(2)]. PtCl2 (0.100 g, 0.36 mmol) was suspended in
acetonitrile and heated to 70 ◦C until a clear yellow solution was
produced. The solution was allowed to reach room temperature
and the ligand (0.244 g, 0.36 mmol) was added dropwise as a
CH2Cl2 solution (10 mL). The reaction was left to stir for 6 h,
and then the mixture was reduced in volume giving a yellow
precipitate which was filtered and washed with hexane yielding
the title compound (0.130 g, 38%). 1H NMR (CDCl3): d = 6.95–
7.84. IR (cm-1/Nujol): n = 279, 314 (Pt–Cl). Anal. found: C, 43.7;
1
NMR (CDCl3): d = 6.80–8.15 (m) aromatic CH. 13C{ H} NMR
(CH2Cl2–CDCl3): d = 125.2, 125.6, 125.8, 127.7, 128.0, 128.4,
128.8, 132.6, 133.4, 135.1, 137.7, 138.2 aromatic C, 211.3, 216.4
CO. 95Mo NMR (CH2Cl2–CDCl3): d = -1770. IR (cm-1/CH2Cl2):
5780 | Dalton Trans., 2008, 5774–5782
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1
H, 3.1; N, 1.5. Calc. for C34H26Cl2PtSb2·MeCN: C, 43.9; H, 3.0;
give the title compound (0.105 g, 57%). H NMR (CDCl3): d =
1.30 (s) CCH3 [6H], 1.82–2.08 (m) CH2 [8H], 2.41 (br) cod CH2
[4H], 4.07–4.25 (m) CH [6H], 7.10–7.42 (m) aromatic CH [18H].
Anal. found: C, 51.2; H, 4.9. Calc. for C39H44ClO2RhSb2: C, 50.6;
H, 4.7%. Conductivity KM (1 ¥ 10-3 mol dm-3 in CH2Cl2): 0.15
X-1 cm2 mol-1.
N, 1.4%.
[PtCl2(3)]. PtCl2 (0.096 g, 0.36 mmol) was suspended in
acetonitrile and heated to 70 ◦C until a clear yellow solution was
produced. The solution was allowed to reach room temperature
and the ligand (3) (0.20 g, 0.36 mmol) was added dropwise as a
CH2Cl2 solution (10 mL). The reaction was left to stir for 12 h,
initially turning orange in colour then back to yellow. The reaction
mixture was reduced in volume by half and the solid was filtered
X-Ray crystallography
Details of the crystallographic data collection and refinement
parameters are given in Table 5. Colourless crystals of the oxide
of (1) were obtained by slow evaporation from a solution of (1) in
CHCl3, while crystals of (3) and [Mo(CO)4(3)] were obtained by
diffusion of diethyl ether into a CH2Cl2 solution of the compound.
Data collection used a Nonius Kappa CCD diffractometer (T =
120 K) and with monochromated (graphite or confocal mirrors)
1
and washed with hexane to give a yellow solid (0.13 g, 44%). H
NMR (CDCl3): d = 0.23 (s) SbCH3 [6H], 1.71 (s) SbCH3 [6H],
6.99 (d, 3J = 8.4 Hz) [2H], 7.32 (t, 3J = 8.0 Hz) [2H], 7.57 (t, 3J =
8.0 Hz) [2H], 7.69 (d, 3J = 8.0 Hz) [2H], 8.00 (d, 3J = 8.0 Hz) [2H],
1
8.08 (d, 3J = 8.0 Hz) [2H] aromatic CH. 13C{ H} NMR (CDCl3):
d = -4.18, -3.20 SbCH3, 126.0, 127.9, 128.0, 128.6, 128.7, 129.7,
134.0, 134.4 aromatic C. 195Pt NMR (CH2Cl2–CDCl3): d = -4403
(w12 = 1200 Hz). IR (cm-1/Nujol): n = 296, 316 (Pt–Cl). Anal.
found: C, 36.1; H, 3.2; N, 1.6. Calc. for C24H24Cl2PtSb2·MeCN: C,
36.2; H, 3.2%; N, 1.6%.
˚
Mo-Ka X-radiation (l = 0.71073 A). Structure solution and
refinement for (3) and [Mo(CO)4(3)] were routine.23,24 with H
atoms added to the model in calculated positions and using the
default C–H distance. However, for the oxide of (1) the systematic
absences indicated space groups Pna21 (33) and Pnma (62) (in
the standard settings). In the centrosymmetric Pnma a solution
readily emerged showing an Sb4O4 cubane-like fragment with two
of the Sb atoms linked 1,8 to a naphthalene residue. The other
two Sb atoms (symmetry related in this space group) showed the
two Me groups, and a third Sb–C to the ipso-C (see Fig. 1).
The peaks in the difference electron-density map based on the
model with just the Me C atoms included showed very distorted
C6 rings and far too many peaks to simply complete the second
naphthalene skeleton. Ten peaks were selected which seemed
closest to the expected naphthyl residue and introduced into the
model as isotropic C atoms with a fixed sof of 0.5 and DFIX
commands used to restrain the C–C bond distances. Refinement
converged well and anisotropic refinement of these C atoms gave
slightly elongated ellipsoids which seemed not unreasonable in
view of the disorder. The disorder problem might indicate the lower
[PtCl2(5)]. PtCl2 (0.062 g, 0.23 mmol) was suspended in
acetonitrile (30 mL) and heated to 70 ◦C until a clear yellow
solution was produced. The solution was allowed to reach room
temperature and the ligand (5) (0.10 g, 0.23 mmol) was added
dropwise as a CH2Cl2 solution (10 mL). The reaction was left to
stir for 2 h, initially turning orange in colour then back to yellow.
The reaction mixture was reduced to low volume and the solid was
filtered and washed with hexane to give a yellow solid (0.085 g,
52%). IR (cm-1/Nujol): n = 281, 316 (Pt–Cl). 195Pt NMR (CH2Cl2–
CDCl3): d = -4522 (w1 = 500 Hz). Anal. found: C, 22.1; H, 3.1;
2
3
2
N, 2.5. Calc. for C11H24Cl2O2PtSb2· MeCN: C, 22.1; H, 3.8; N,
2.8%.
[Rh(cod)(2)Cl]. Ligand (2) (0.138 g, 0.20 mmol) was added
dropwise as a CH2Cl2 solution to [Rh2Cl2(cod)2] (0.049 g,
0.10 mmol) in ethanol (40 mL). The orange solution was stirred for
6 h and reduced in volume under vacuum. An orange precipitate
was formed, filtered and washed with diethyl ether (10 mL) to
Table 5 Crystallographic parametersa
1
give the title compound (0.120 g, 65%). H NMR (CDCl3): d =
(1)2O4
(3)
[Mo(CO)4(3)]
1.81 (br) cod CH2 [4H], 2.43 (br) cod CH2 [4H], 4.20 (br) cod CH
[4H], 6.73–7.97 (m) aromatic H [26H]. Anal. found: C, 54.5; H,
4.2. Calc. for C42H38ClRhSb2: C, 54.6; H, 4.0%. Conductivity KM
(1 ¥ 10-3 mol dm-3 in CH2Cl2): 0.29 X-1 cm2 mol-1.
Formula
M
C28H36O4Sb4
923.57
C24H24Sb2
555.93
Orthorhombic Triclinic
C28H24MoO4Sb2
763.91
Crystal system
Space group (no.)
Triclinic
¯
¯
Pnma (62)
20.032(2)
13.1268(10)
10.7375(10)
90
90
90
2823.5(4)
4
3.819
P1 (2)
8.352(2)
11.212(3)
11.969(3)
96.433(12)
101.872(12) 82.036(9)
103.953(12) 80.998(8)
1048.9(5)
2
2.580
11174
4392
0.042
235
P1 (2)
˚
a/A
12.7993(15)
15.073(3)
16.058(2)
64.903(8)
[Rh(cod)(4)Cl]. Ligand (4) (0.163 g, 0.20 mmol) was added
dropwise as a CH2Cl2 solution to [Rh2Cl2(cod)2] (0.049 g,
0.10 mmol) in ethanol (40 mL). The orange solution was stirred for
6 h and reduced in volume under vacuum. An orange precipitate
was formed, filtered and washed with hexane (10 mL) to give the
title compound (0.135 g, 64%). 1H NMR (CDCl3): d = 1.75 (br)
cod CH2 [4H], 2.42 (br) cod CH2 [4H], 4.20 (br) cod CH [4H],
6.52–8.46 (m) aromatic CH [32H]. Anal. found: C, 60.0; H, 4.3.
Calc. for C52H44ClRhSb2: C, 59.5; H, 4.1%. Conductivity KM (1 ¥
10-3 mol dm-3 in CH2Cl2): 0.05 X-1 cm2 mol-1.
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
U/A
2761.9(7)
4
2.420
50073
11362
0.106
631
Z
m(Mo-Ka)/mm-1
No. of data collected 23985
No. of unique data
Rint
No. of parameters
R1, wR2 (I > 2s(I))b
R1, wR2 (all data)
3358
0.033
233
0.049, 0.104
0.054, 0.105
0.036, 0.074 0.082, 0.129
0.055, 0.081 0.148, 0.153
[Rh(cod)(6)Cl]. Ligand (6) (0.138 g, 0.20 mmol) was added
dropwise as a CH2Cl2 solution to [Rh2Cl2(cod)2] (0.049 g,
0.10 mmol) in ethanol (40 mL). The orange solution was stirred for
4 h and reduced in volume under vacuum. An orange precipitate
was formed, filtered and washed with diethyl ether (10 mL) to
a
˚
Common items: temperature = 120 K; wavelength (Mo-Ka) = 0.71073 A;
ꢀ
ꢀ
q(max) = 27.5◦ (26.5◦ for [Mo(CO)4(3)]). b R1 = ꢀFo| - |Fcꢀ/ |Fo|;
ꢀ
ꢀ
2
4 1/2
wR2 = [ w(Fo - Fc2)2/ wFo
] .
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The Royal Society of Chemistry 2008
Dalton Trans., 2008, 5774–5782 | 5781
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symmetry space group Pna21 but attempted solution here gave the
same problem, requiring the TWIN command and with the least-
squares refinement failing to converge. The model reported is thus
in the centrosymmetric higher symmetry system with modelling
of the disorder and clearly confirms the identity of compound (1).
Selected bond lengths and angles are given in Tables 1 and 3.
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Acknowledgements
We thank the EPSRC (EP/D003148/1) for support and Johnson-
Matthey plc for generous loans of precious metal salts. We also
thank the crystallographic referee for suggesting a useful strategy
for dealing with the disorder in one of the naphthyl residues in the
oxidised form of (1).
14 D. B. Sowerby, in Chemistry of Organic Arsenic, Antimony and Bismuth
Compounds, ed. S. Patai, Wiley, NY, 1994, pp. 25–28.
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5782 | Dalton Trans., 2008, 5774–5782
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The Royal Society of Chemistry 2008
©