Preparation and coordinating properties of {CH2(o-C 6H4CH2SbMe2)}2, a novel wide-angle cis-chelating distibine

Article abstract of DOI:10.1039/b610808c

The unique wide-angle distibine, {CH₂(o-C₆H ₄CH₂SbMe₂)}₂, 1, has been prepared indirectly by reaction of Me₂SbCl with the di-Grignard formed unexpectedly by coupling of o-C₆H₄(CH₂MgCl) ₂ in concentrated thf solution, and directly by treatment of the {CH₂(o-C₆H₄CH₂MgCl)}₂ with Me₂SbCl. The very oxygen-sensitive distibine 1 has been characterised by ¹H and ¹³C{¹H} NMR spectroscopy and high-resolution EIMS. Oxidation of 1 with Br₂ gives the air-stable tetrabromide {CH₂(o-C₆H₄CH ₂SbMe₂Br₂)}₂. Surprisingly, 1 shows a very strong tendency to function as a cis-chelate, e.g. to Pt(iv) in the complex [PtMe₃I(1)], forming an 11-membered ring and providing a stable Pt(iv) stibine complex, the crystal structure of which shows the Sb-Pt-Sb angle to be 95.96(1)°. The yellow Pt(ii) complex [PtCl₂(1)] is obtained from reaction of [PtCl₂(MeCN)₂] with 1 and IR spectroscopic data and a crystal structure determination confirm the Cl ligands are mutually cis in this species. Reaction of [W(CO)₄(piperidine) ₂] with 1 in refluxing EtOH gives [W(CO)₄(1)], the IR spectrum of which shows four ν(CO) bands, also consistent with cis-Sb ₂ coordination. The cis-chelation is also confirmed by single-crystal X-ray structure determinations of two polymorphs of [W(CO)₄(1)]. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b610808c

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PAPER
www.rsc.org/dalton | Dalton Transactions
Preparation and coordinating properties of {CH2(o-C6H4CH2SbMe2)}2, a
novel wide-angle cis-chelating distibine
Michael D. Brown, William Levason, Gillian Reid* and Michael Webster
Received 27th July 2006, Accepted 3rd October 2006
First published as an Advance Article on the web 16th October 2006
DOI: 10.1039/b610808c
The unique wide-angle distibine, {CH2(o-C6H4CH2SbMe2)}2, 1, has been prepared indirectly by
reaction of Me2SbCl with the di-Grignard formed unexpectedly by coupling of o-C6H4(CH2MgCl)2 in
concentrated thf solution, and directly by treatment of the {CH2(o-C6H4CH2MgCl)}2 with Me2SbCl.
1
The very oxygen-sensitive distibine 1 has been characterised by 1H and 13C{ H} NMR spectroscopy
and high-resolution EIMS. Oxidation of 1 with Br2 gives the air-stable tetrabromide
{CH2(o-C6H4CH2SbMe2Br2)}2. Surprisingly, 1 shows a very strong tendency to function as a
cis-chelate, e.g. to Pt(IV) in the complex [PtMe3I(1)], forming an 11-membered ring and providing a
stable Pt(IV) stibine complex, the crystal structure of which shows the Sb–Pt–Sb angle to be 95.96(1)◦.
The yellow Pt(II) complex [PtCl2(1)] is obtained from reaction of [PtCl2(MeCN)2] with 1 and IR
spectroscopic data and a crystal structure determination confirm the Cl ligands are mutually cis in this
species. Reaction of [W(CO)4(piperidine)2] with 1 in refluxing EtOH gives [W(CO)4(1)], the IR spectrum
of which shows four m(CO) bands, also consistent with cis-Sb2 coordination. The cis-chelation is also
confirmed by single-crystal X-ray structure determinations of two polymorphs of [W(CO)4(1)].
despite the length of the linking group between the Sb atoms.
Crystal structures of [PtMe3I(1)], [PtCl2(1)] and two polymorphs
In recent years the very elegant work of Werner et al. has
of [W(CO)4(1)] are described.
Introduction
provided a clear demonstration that the donor properties of stibine
ligands are quite distinct from those of phosphine and arsine
congeners in organometallic systems, both in promoting different
product distributions and providing unprecedented examples of
Results and discussion
SbR3 ligands bridging between rhodium centres.1,2 Further, within
transition metal stibine complexes there is an increased tendency
for higher coordination numbers and less M–ER3 dissociation
when E = Sb.3,4 Despite these observations there are very few
examples of polystibine compounds involving linkages other
than saturated, flexible polymethylene units. One of the major
constraints in the development of new organostibine ligands is
the relative fragility of the C–Sb bonds, the result of which
is that fragmentation of these linkages can occur both during
the formation of the stibine compounds themselves and upon
reaction with certain metal reagents, resulting in substantial
decomposition. Furthermore, very little work has been done to
probe the effect of the backbone architecture in determining the
coordinating properties of distibines.
In our recent work we have used electrophilic reactions of
R2SbCl (R = Me or Ph) with di-Grignard compounds to obtain
a series of new distibine ligands incorporating phenylene and
xylylene linkages in very good yields, including the o-xylyl com-
pound, o-C6H4(CH2SbMe2)2.5,6 Here we describe the formation
and characterisation of the unprecedented wide-angle distibine,
1, initially obtained as a by-product during such a preparation,
and demonstrate its unexpectedly strong tendency to function as a
bidentate cis-chelate only, to Pt(II) and (IV) and to the W(CO)4 unit,
During the course of our work on the chemistry of o-
C6H4(CH2SbMe2)2 we have found that this compound may be
obtained in very high yield (88%), without the need to distill.
However, depending upon the precise conditions employed, the
yield is sometimes much lower and its preparation is accompanied
by formation of other Sb-containing compounds, including a
substantial quantity of Me4Sb2, consistent with a deficit of o-
C6H4(CH2MgCl)2. In an effort to probe the identity of the
by-products from a lower yielding reaction further, we have
investigated the less volatile species obtained by further distillation
after fractional distillation of o-C6H4(CH2SbMe◦2)2 in vacuo from
the reaction mixture. At high temperature (225 C, 0.5 mm Hg),
1
we obtained a colourless, viscous oil. The H NMR spectrum
of this shows peaks at similar chemical shifts to the o-xylyl
distibine, although the CH2 singlet at 2.96 ppm integrates as 1 :
1 with the o-C6H4 protons and the aromatic protons and SbMe
protons (0.80 ppm) integrate as 2 : 3 (rather than the 1 : 3 ratio
expected for o-C6H4(CH2SbMe2)2). The accidental coincidence
of the SbCH2 and CH2CH2 resonances in this compound was
1
unexpected and initially misleading. However, the 13C{ H} NMR
spectrum shows the expected o-C6H4 resonances, and the CH2CH2
resonances appear as a singlet at 34.9 ppm, while the SbCH2
and SbMe2 groups occur at 20.9 and −2.3 ppm respectively—the
low frequency resonance arising from the proximity of the heavy
Sb atoms. The EIMS shows no evidence for o-C6H4(CH2SbMe2)2
(which we have shown previously appears as [parent − Me], m/z =
393), but rather the major cluster of peaks is centred at m/z = 497,
School of Chemistry, University of Southampton, Highfield, Southampton,
UK SO17 1BJ. E-mail: gr@soton.ac.uk; Fax: 023 80593781; Tel: 023
80593609
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that the coupling reaction takes place during formation of the
di-Grignard when the concentration of the solution is higher than
the ‘critical concentration’ of 0.075 mol dm−3 identified by Lappert
et al.8 As long as the concentration of the solution is maintained
below this, the preparation of o-C6H4(CH2SbMe2)2 is clean and
the yield is very high (routinely >80%).
consistent with loss of Me from the coupled compound {CH2(o-
C6H4CH2SbMe2)}2 (1). A minor [parent + H]+ ion is also evident
at m/z = 513. The simulated isotope patterns are fully consistent
with these assignments and high resolution EIMS confirms the
formulation.
Noltes and coworkers have shown previously that the com-
pounds Me2Sb(CH2)nSbMe2 (n = 3–6) undergo redistribution re-
actions at temperatures in excess of 200 ◦C to eliminate Me3Sb and
give either polymeric species (n = 3, 6) or 1-methylstibacycloalkane
(n = 4, 5).7 However, we did not see any evidence for formation
of 1 when a sample of o-C6H4(CH2SbMe2)2 was heated on the
MS probe. Furthermore, no change was observed in the 1H NMR
spectrum of a pure sample of o-C6H4(CH2SbMe2)2 after heating
to 250 ◦C for 1 h under static vacuum. These results suggest that
1 does not form via thermolysis in the fractional distillation.
On this basis we concluded that the formation of 1 occurs
through partial coupling of the o-C6H4(CH2MgCl)2 di-Grignard
in concentrated thf solution. The sensitivity of this di-Grignard to
concentration has been noted, and it has been shown to undergo
C–C coupling above a critical concentration, also producing
bibenzyl species.8,9 In order to establish whether this is indeed
the source of 1, o-C6H4(CH2Cl)2 was treated with Mg powder in
thf solution and the solution was concentrated in vacuo to ca.
0.16 mol dm−3 and left to stand overnight. D2O was then added
to quench the Grignard, and the organics extracted with Et2O,
dried (MgSO4) and the solvent removed in vacuo to leave a light
The new distibine 1 was also prepared directly from {CH2(o-
C6H4CH2Cl)}2 (Scheme 2), itself obtained by slight modifica-
tions of the literature procedure.10 Specifically, the conversion
of the dialdehyde {CH2(o-C6H4CHO)}2 to the diol {CH2(o-
C6H4CH2OH)}2 was achieved in >90% yield using LiAlH4 in
Et2O, and the conversion of {CH2(o-C6H4CH2OH)}2 to {CH2(o-
C6H4CH2Cl)}2 using SOCl2 required much longer (17 h) re-
flux to achieve complete conversion. To obtain 1, the {CH2(o-
C6H4CH2Cl)}2 was then treated overnight with Mg powder and
0.1 mol equiv. of anthracene in thf solution to give the di-Grignard
{CH2(o-C6H4CH2MgCl)}2. Addition of 2 mol equiv. of Me2SbCl
in toluene and subsequent stirring overnight gave 1 as a yellow,
air-sensitive oil after work-up. The yield of 1 from this direct
synthesis is much higher (68%) than that from the indirect coupling
described above. 1 produced by this method was also characterised
1
by 1H and 13C{ H} NMR spectroscopy and EIMS and shown to
be identical to that obtained as described earlier.
Treatment of 1 with Br2 gives the tetrabromide of 1 as an air-
stable light yellow powder in good yield. The SbCH2 (d1H: 4.30;
d13C: 46.33) and SbMe protons (d1H: 2.50; d13C: 25.69) which are
now bonded directly to the formally Sb(V) centres are significantly
shifted to high frequency cf . 1, whereas, as expected, the bibenzyl
CH2 groups are much less affected (d1H: 3.20; d13C: 34.11).
The coordination of long chain diphosphine ligands of the form
R2P(CH2)nPR2 (n = 6–16) to transition metals has been studied in
detail and shown to give ligand bridged dimers or polymers and
occasionally trans chelates, but rarely are cis-chelates produced
1
brown oil (Scheme 1). The H NMR spectrum of this product
showed a singlet for the CH2CH2 of the coupled ligand backbone
at 2.85 ppm and a broad singlet at 2.20 ppm corresponding to
(CH2D). The presence of the CH2D groups of o-C6H4(CH2D)2
at 2.14 ppm was also evident. EIMS also showed the only
significant species to be [{CH2(o-C6H4CH2D)}2]+ (m/z = 212) and
o-C6H4(CH2D)2 (m/z = 108). This result provides strong evidence
Scheme 1 Formation of 1 via coupling of o-C6H4(CH2MgCl)2 in concentrated thf solution.
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Fig. 1 View of the structure of [PtMe3I(1)] with numbering scheme
adopted. Note that there is disorder in the C21–Pt1–I1 region (see
Experimental section), the molecule shown is the major component.
Ellipsoids are drawn at the 50% probability level and H atoms are omitted
for clarity.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for [PtMe3I(1)]
Pt1–Sb1
Pt1–Sb2
Pt1–I1
Sb1–C3
Sb–C(Me)
2.6329(4)
2.6279(4)
2.7573(5)a
2.173(4)
Pt1–C22
Pt1–C23
Pt1–C21
Sb2–C18
2.103(5)
2.108(5)
2.377(3)a
2.182(4)
3.908(1)
2.122(5)–2.128(5) Sb1 · · · Sb2
Sb1–Pt1–Sb2
Sb1–Pt1–C22
Sb1–Pt1–C23
Sb1–Pt1–I1
Pt1–Sb1–C3
Sb1–C3–C4
Pt1–Sb–C(Me)
95.957(12)
175.09(15)
88.34(15)
87.96(1)a
118.97(13)
114.1(3)
Sb2–Pt1–C22
Sb2–Pt1–C23
Sb2–Pt1–I1
C22–Pt1–C23
Pt1–Sb2–C18
Sb2–C18–C17
88.71(15)
174.63(15)
90.83(1)a
87.1(2)
116.53(13)
112.4(3)
Scheme 2 Direct synthesis of 1.
cleanly from such systems.11 However, wide-angle cis-chelating
phosphines are of considerable current interest owing to the very
favourable catalytic properties displayed by their metal complexes,
and this has led to major industrial usage.12 The presence of
the two o-xylyl substituted units in the backbone of the new
distibine 1 led us to speculate on whether 1 has the potential
to behave as a wide-angle chelate to metal centres. In order to
probe the ligating properties of 1, one mol equiv. of [PtMe3I] was
reacted with 1 in refluxing CHCl3 solution under N2. Following
workup, the product [PtMe3I(1)] was isolated as a light yellow
solid. Electrospray MS (MeCN) shows clusters of peaks with
isotope patterns corresponding to [Pt(1)]+ (m/z = 706), [PtMe(1)]+
112.9(1)–121.6(1) C9–C10–C11–C12
176.1(4)
a The I1(C21A)–Pt1–C21(I1A) form a disordered group with chemically
unreliable bond lengths (see text). The data given are for the major
component.
compound and the cis-Sb2 coordination. The structure (Fig. 1,
Table 1) shows 1 occupying mutually cis coordination sites at a
distorted octahedral Pt(IV) centre, with three facial Me ligands
and the iodine completing the coordination environment. The
˚
Pt–Sb distances are 2.6279(4) and 2.6329(4) A, slightly longer
1
1
13
(721) and [PtMe(1)(MeCN)]+ (762). The H and 13C{ H} NMR
than in [PtMe3I{o-C6H4(CH2SbMe2)2}] (2.6052(4), 2.6204(5) A)
˚
spectra confirm the presence of three fac Me ligands on Pt, one at
and substantially longer than in the Pt(II) distibines,6 e.g.
very low frequency trans to I (d13C: −7.8) giving JPtC = 614 Hz
[PtCl2{o-C6H4(CH2SbMe2)2}] (2.4860(7), 2.4931(8) A) and [Pt{o-
1
˚
1
C6H4(CH2SbMe2)2}2]2+ (2.5690(8) to 2.5802(8) A)—although, of
˚
and two trans to the Sb atoms (6.2 ppm) giving JPtC = 563 Hz.
These data are in accord with the other trimethyl-Pt(IV) stibine
course the higher coordination number in the Pt(IV) species and
the strong trans influence of the Me groups will both have a
significant effect on d(Pt–Sb). We also note that the Sb2–Pt1–
Sb1 angle in [PtMe3I(1)] is 95.96(1)◦, whereas the corresponding
Sb–Pt–Sb angle [PtMe3I{o-C6H4(CH2SbMe2)2}] is 95.25(1)◦ and
within the more common six-membered chelate rings is < 90◦.13
The Pt(II) complex [PtCl2(1)] was obtained in good yield
as a yellow solid from reaction of [PtCl2(MeCN)2] with 1 in
MeCN–CH2Cl2 solution. The IR spectrum confirms the presence
of mutually cis Cl atoms, revealing two m(PtCl) bands at 316
and 307 cm−1. Platinum-195 NMR spectroscopy shows a single
resonance at −4960 ppm, indicative of an Sb2Cl2 donor set
complexes which we have recently reported.13 Two singlet 13C{ H}
1
resonances for the SbMe groups in the coordinated ligand 1 are
evident, consistent with the absence of axial symmetry in the
[PtMe3I(1)] complex. The 195Pt NMR spectrum of this complex
shows a single resonance at −4440 ppm. This too is in accord with
other related stibine complexes of Pt(IV).13 These data provide
strong support for 1 unexpectedly behaving as a wide-angle cis-
bidentate on Pt(IV), giving the stable [PtMe3I(1)], containing a very
large 11-membered ring.
A single-crystal structure determination on [PtMe3I(1)] provides
unambiguous confirmation of the identity of the coupled distibine
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at Pt(II).14 The crystal structure of the yellow [PtCl2(1)] shows
(Fig. 2(a) and (b), Table 2) the distibine coordinated to Pt(II)
with two mutually cis Cl ligands completing the distorted square-
section, and the discussion refers to the major (91%) component.
˚
These compare with d(Pt–Sb) = 2.4860(7) and 2.4931(8) A, d(Pt–
◦
˚
Cl) = 2.368(3), 2.376(3) A and angle Sb–Pt–Sb = 97.58(2) in
the related species [PtCl2{o-C6H4(CH2SbMe2)2}].6 The [PtCl2(1)]
molecules are distributed across a centre of symmetry such that
the planes lie face to face, giving a weakly associated dimer
˚
planar geometry, d(Pt–Sb) = 2.4998(9) and 2.5163 A, d(Pt–
˚
Cl) = 2.338(2) and 2.350(3) A. The chelate angle Sb1–Pt1–Sb2 =
94.91(3)◦. There is some disorder at the Pt atom – see Experimental
˚
with d(Pt1 · · · Pt1a) = 3.176(1) A. This is within the range
observed for other weakly associated Pt(II) dimers and chains,
15
˚
e.g. [PtCl2(H2NCH2CH2NH2)] d(Pt · · · Pt) = 3.381(3) A.
Refluxing a 1 : 1 molar solution of [W(CO)4(piperidine)2]
and 1 in EtOH gave a light fawn coloured powder following
work-up. The Nujol mull IR spectrum of this product shows
strong bands in the CO stretching region at 2011, 1898 and a
shoulder at 1868 cm−1, indicative of formation of cis-[W(CO)4(1)].
These compare with 2012, 1935, 1901 and 1863 cm−1 for cis-
[W(CO)4{o-C6H4(CH2SbMe2)2}] and 2011, 1896 and 1870 for cis-
[W(CO)4{Me2Sb(CH2)3SbMe2}].5,16 The APCI MS of this product
shows the only significant species is [W(CO)4(1) + H]+ (m/z =
809) and microanalyses are also consistent with the formulation.
Even under prolonged reflux (overnight) in EtOH solution cis-
[W(CO)4(1)] remains the only significant species. Single crystals of
two distinct polymorphs of this compound were obtained from
slow evaporation from CH2Cl2–Et2O solutions. The structures
show that in each molecule the W(CO)4 fragment is coordinated
to two mutually cis Sb atoms of 1 to give a cis-chelated distorted
octahedral complex. In one of the polymorphs (Fig. 3(a), Table 3)
there are two molecules of [W(CO)4(1)] in the asymmetric unit. In
one of the two independent molecules the two aromatic rings of
the ligand backbone are in the same plane, however, in the second
molecule there is some disorder in the backbone of 1, arising
from the presence of two slightly different conformations. The
second polymorph shows (Fig. 3(b), Table 3) a very similar species
with similar bond length and angle distributions. The W–Sb bond
˚
distances lie in the range 2.758–2.774 A, towards the long end of
the range for other stibine complexes with tungsten carbonyl.17
The Sb–W–Sb chelate angles are in the range 90.34(1)–93.26(1)◦.
The W–C distances are also sensitive to the trans ligand, being
significantly longer for d(W–Ctrans CO) cf . d(W–Ctrans Sb), reflecting
the modest r-donor/p-acceptor properties of the stibine compared
to CO.
Fig. 2 (a) View of the structure of [PtCl2(1)] with numbering scheme
adopted. Note that only the major component of the disorder is shown (see
Experimental section). Ellipsoids are drawn at the 45% probability level
and H atoms are omitted for clarity. (b) View of the weakly associated,
centrosymmetric dimer formed by [PtCl2(1)] (a: 1 − x, −y, 2 − z).
Conclusions
The new, very air-sensitive distibine, 1, has been obtained
both indirectly and (in high yield) directly from reaction of
{CH2(o-C6H4CH2MgCl)}2 with Me2SbCl. Incorporation of two
o-substituted xylylene groups within the backbone of 1 plays a
very important role in determining its ligating properties. All
of our evidence points to 1 functioning as a cis-chelate only,
giving high yields of the transition metal complexes. Prior to this
work, the distibine complexes involving the largest chelate rings
were based upon o-C6H4(CH2SbMe2)2 (seven-membered ring),
however, long chain diphosphine ligands with aliphatic linkages,
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for [PtCl2(1)]
Pt1–Cl1
Pt1–Sb1
Pt1 · · · Pt1a
Sb1–C2
Sb2–C20
Sb2–C18
2.338(2)
Pt1–Cl2
Pt1–Sb2
Sb1–C1
Sb1–C3
Sb2–C19
2.350(3)
2.4998(9)
3.1761(12)
2.119(10)
2.104(10)
2.169(11)
2.5163(11)
2.095(10)
2.162(10)
2.138(10)
t
e.g. Bu2P(CH2)nPtBu2 (n = 8–10, 12) and Ph2P(CH2)nPPh2 (n =
Cl1–Pt1–Cl2
Cl2–Pt1–Sb1
Cl2–Pt1–Sb2
90.48(9)
87.13(7)
171.45(7)
Cl1–Pt1–Sb1
Cl1–Pt1–Sb2
Sb1–Pt1–Sb2
173.75(7)
86.63(7)
94.91(3)
6–16), have been known for many years. These usually pro-
duce polymeric, bridged dimeric or occasionally trans chelating
systems.11 The surprising tendency for cis-chelation observed in
these complexes of 1 may be due to the cis-directing properties
a 1 − x, −y, 2 − z.
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atmosphere. [PtMe3I] and [W(CO)4(piperidine)2] were obtained
via the literature methods.18,19
Preparation of 1
Method A. o-C6H4(CH2MgCl)2 was prepared from Mg pow-
der (3.26 g, 134.3 mmol) in thf (150 mL) and o-C6H4(CH2Cl)2
(5.7 g, 32.75 mmol) in thf (50 mL) added dropwise over 1 h giving
a 0.16 mol dm−3 solution. Me2SbCl (PhSbMe2 (15 g, 65.5 mmol)
and HCl gas)5 in toluene (50 mL) was added dropwise over 30 min,
and the reaction was left to stir overnight. The mixture was
then hydrolysed (100 mL of 1 mol dm−3 aqueous NH4Cl), the
organics separated, the aqueous layer extracted with Et2O (2 ×
50 mL). After drying (MgSO4), filtering and removing the solvent
by distillation at atmospheric pressure, and fractionation of the
◦
o-C6H4(CH2SbMe2)2 (200 C, 0.5 mm Hg), 1 was obtained as a
clear oil by Kugelro¨hr distillation (225 ◦C, 0.5 mm Hg) (yield 1.2 g,
14%). 1H NMR (CDCl3): d 7.1–7.3 (m, 8H, o-C6H4), 2.96 (s, 8H,
1
SbCH2, CH2CH2), 0.80 (s, 12H, SbMe). 13C{ H} NMR (CDCl3):
d 139.9, 138.8, 129.6, 128.5, 126.9, 125.5 (o-C6H4), 34.9 (CH2CH2),
20.9 (SbCH2), −2.3 (SbMe). EIMS: m/z 497 [parent − Me]+, 513
[parent + H]+. High-resolution MS: calc. for [parent − Me] m/z =
497.00367; found: m/z = 496.9697.
Method B. {CH2(o-C6H4CH2MgCl)}2 was prepared by
adding {CH2(o-C6H4CH2Cl)}2 (1.6 g, 5.73 mmol) in thf (170 mL)
dropwise over 2 h to a flask containing magnesium powder (0.42 g,
17.3 mmol) and anthracene (0.31 g, 1.73 mmol) (which was
activated with 1,2-dibromoethane (0.1 mL) in thf (5 mL), and
stirred for 5 min). The mixture was stirred at RT overnight,
then a solution of Me2SbCl (prepared from PhSbMe2 (2.62 g,
11.46 mmol) and HCl gas)5 in toluene (50 mL) was added dropwise
over 2 h, and the resulting mixture stirred at RT overnight.
The reaction was hydrolysed with a solution of NH4Cl (50 mL,
1 mol dm−3 in H2O). The organics were separated and the aqueous
layer washed with Et2O (2 × 50 mL). The combined organics were
then dried over MgSO4, filtered and then reduced to dryness. The
residues were dissolved in Et2O (20 mL), the anthracene filtered
off, and the pale yellow solution reduced to dryness in vacuo.
Fig. 3 (a) View of the structure of one of the two crystallographically
independent molecules of the first polymorph of [W(CO)4(1)] (P21/n) with
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity. There is some disorder in
the ligand backbone in the second molecule—see Experimental section.
(b) View of the structure of the second polymorph of [W(CO)4(1)] (Cc) with
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity.
1
Yellow oil (yield 2.0 g, 68%). H NMR (CDCl3): d 7.2–7.0 (m,
conferred by the two o-substituted aromatic units in the inter-
donor linkage.
8H, o-C6H4), 2.86 (s, 8H, CH2Sb, CH2CH2), 0.80 (s, 12H, SbMe).
1
13C{ H} NMR (CDCl3): d 139.9, 138.7, 129.6, 128.8, 127.0, 125.5
(o-C6H4), 34.9 (CH2CH2), 20.9 (CH2Sb), −2.3 (SbMe2). The NMR
spectra also show evidence for traces of residual anthracene in the
compound. EIMS: m/z 497 [parent − Me]+, 513 [parent + H]+.
Experimental
Infrared spectra were recorded as Nujol mulls between CsI plates
using a Perkin-Elmer 983G spectrometer over the range 4000–
200 cm−1. Mass spectra were run by electron impact on a VG-
70-SE Normal geometry double focusing spectrometer or by
positive ion electrospray or APCI (MeCN solution) using a VG
{CH2(o-C6H4CH2SbMe2Br2)}2. 1 (0.05 g, 0.098 mmol) was
dissolved in dry CH2Cl2 (5 mL) and a solution of Br2 (0.5 mL)
and CH2Cl2 (10 mL) was added dropwise until a yellow colour
was observed. The reaction was then stirred for 2 h, reduced
in volume to ca. 2 mL and then hexane (5 mL) was added to
precipitate a solid. The light yellow solid was isolated by filtration
and dried in vacuo (yield 61%). Required for C20H28Br4Sb2: C, 28.9;
H, 3.4. Found: C, 30.1; H, 3.4% (note that the NMR spectra of
this compound and of 1 itself show traces of anthracene from
the original direct synthesis of 1 which remain despite repeated
washing, hence the poorer than normal fit for the analytical data).
1H NMR (CDCl3): d 7.2–7.4 (m, 8H, o-C6H4), 4.30 (s, 4H, CH2Sb),
1
Biotech platform. 1H NMR and 13C{ H} NMR spectra were
recorded using a Bruker AV300 or DPX400 spectrometer (for
1
13C{ H} operating at 75.5 or 100.6 MHz respectively) and were
referenced to TMS. 195Pt NMR spectra used a Bruker DPX400
spectrometer operating at 85.72 MHz and are referenced to
external 1 mol dm−3 Na2[PtCl6] in H2O. Microanalyses were
undertaken by the University of Strathclyde microanalytical
service. Solvents were dried prior to use and all preparations
were undertaken using standard Schlenk techniques under a N2
1
3.20 (s, 4H, CH2CH2), 2.50 (s, 12H, Me). 13C{ H} NMR (CDCl3):
5652 | Dalton Trans., 2006, 5648–5654
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◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for [W(CO)4(1)]
Polymorph in P21/n
W1–Sb1
W1–Sb2
W1–C21
W1–C22
W1–C23
W1–C24
Sb1–C3
2.7736(4)
2.7590(4)
2.025(5)
1.968(5)
1.975(5)
2.019(5)
2.188(4)
3.978(1)
W2–Sb3
W2–Sb4
W2–C45
W2–C46
W2–C47
W2–C48
Sb2–C18
Sb3 · · · Sb4
2.7734(4)
2.7589(4)
2.029(5)
1.977(5)
1.980(5)
2.036(5)
2.175(4)
4.022(1)
Sb1 · · · Sb2
Sb1–W1–Sb2
C21–W1–Sb1
C22–W1–Sb1
C23–W1–Sb1
C24–W1–Sb1
C–W1–C (ca. 90◦)
W1–Sb1–C3
91.947(12)
88.46(11)
174.34(13)
94.31(14)
92.08(12)
85.4(2)–91.2(2)
121.25(11)
113.0(3)
Sb3–W2–Sb4
C21–W1–Sb2
C22–W1–Sb2
C23–W1–Sb2
C24–W1–Sb2
C24–W1–C21
W1–Sb2–C18
Sb2–C18–C17
93.265(12)
89.70(12)
82.45(13)
172.35(14)
98.80(13)
171.45(18)
127.20(11)
110.3(3)
Sb1–C3–C4
C9–C10–C11–C12
174.3(4)
Polymorph in Cc
W1–C23
W1–C21
W1–Sb2
Sb1 · · · Sb2
1.966(5)
2.021(5)
2.7580(4)
3.918(1)
W1–C24
W1–C22
W1–Sb1
1.968(5)
2.041(6)
2.7661(4)
C23–W1–Sb2
C21–W1–Sb2
C23–W1–Sb1
C21–W1–Sb1
Sb2–W1–Sb1
W1–Sb1–C3
174.31(13)
87.78(14)
85.04(14)
88.80(13)
90.339(14)
110.85(14)
C24–W1–Sb2
C22–W1–Sb2
C24–W1–Sb1
C22–W1–Sb1
C–W1–C (ca. 90◦)
W1–Sb2–C18
89.66(15)
95.50(15)
177.23(16)
96.50(15)
88.3(2)−94.8(1)
112.45(13)
d 130.3, 129.5, 129.2, 127.9, 125.7 (o-C6H4), 46.3 (CH2Sb), 34.1
(CH2CH2), 25.7 (Me).
8H, o-C6H4), 3.36 (s, 4H, CH2Sb), 2.93 (s, 4H, CH2CH2), 1.25 (s,
1
12H, Me). 195Pt{ H} NMR (CH2Cl2–CDCl3): d −4960. IR (Nujol
mull): m = 316, 307 (m(PtCl)) cm−1.
[PtMe3I(1)]. [PtMe3I] (0.075 g, 0.2 mmol) and 1 (0.102 g,
0.2 mmol) were dissolved in dry CHCl3 (20 mL) under N2 and
refluxed under N2 for 4 h. The light yellow solution was then
pumped to dryness in vacuo to give a waxy solid which was
triturated with hexane to produce a light yellow powder (yield
60%). Required for C23H37IPtSb2·CHCl3: C, 28.9; H, 3.8. Found:
C, 28.2; H, 3.8%. Electrospray MS (MeCN): found m/z = 761,
720, 705; calc. for [PtMe(1)(MeCN)]+ 762, [PtMe(1)]+ 721, [Pt(1)]+
706. 1H NMR (CDCl3): d 0.65 (s, 6H, SbMe), 0.89 (s, 3H, Me trans
I (2JPtH = 71 Hz)), 1.16 (s, 6H, SbMe), 1.52 (s, 6H, Me trans Sb
(2JPtH = 66 Hz)), 3.10 (s, 4H, CH2CH2), 3.28 (m, 4H, SbCH2),
[W(CO)4(1)]. [W(CO)4(piperidine)2] (0.18 g, 0.39 mmol) and
1 (0.20 g, 0.39 mmol) were refluxed in EtOH (20 mL) for 2 h,
cooled to RT and the reaction mixture was filtered. The EtOH was
removed in vacuo and the residues were dissolved in a minimum
of CH2Cl2. Hexane (10 mL) was added to precipitate a solid, and
the light brown powder was isolated and dried in vacuo (yield
40%). Required for C24H28O4Sb2W: C, 35.7; H, 3.5. Found: C,
1
35.7; H, 3.5%. H NMR (CDCl3): d 7.1–7.4 (m, 8H, o-C6H4),
3.25 (s, 4H, CH2Sb), 2.74 (s, 4H, CH2CH2), 1.08 (s, 12H, Me). IR
(Nujol mull): m = 2011s, 1898vs, 1868sh (m(CO)) cm−1. APCI MS
(MeCN): m/z = 809; calc. for [W(CO)4(1 + H)]+ 809.
1
7.0–7.3 (m, 4H, o-C6H4). 13C{ H} NMR (CDCl3): d −8.5 (2C,
SbMe), −7.8 (1C, Me trans I (1JPtC = 614 Hz)), −5.1 (2C, SbMe),
6.2 (2C, Me trans Sb (1JPtC = 563 Hz)), 20.5 (2C, SbCH2), 34.9
(2C, CH2CH2), 138.9–124.7 (o-C6H4). 195Pt NMR: d −4440.
X-Ray crystallography
[PtCl2(1)]. PtCl2 (0.052 g, 0.195 mmol) was suspended in dry
acetonitrile (20 mL) and refluxed for 1 h until all the solid was
dissolved and a light yellow solution was obtained. This was then
cooled to room temperature, and 1 (0.10 g, 0.195 mmol) in CH2Cl2
(5 mL) was added slowly. The reaction mixture was stirred for
2 h at room temperature, until an orange solution was obtained.
The solvent was then removed in vacuo and the residues were
dissolved in a minimum of CH2Cl2 and hexane (10 mL) was added
to precipitate a solid. The yellow solid was isolated and dried in
vacuo (yield 55%). Required for C20H28Cl2PtSb2·CH2Cl2: C, 29.2;
H, 3.5. Found: C, 29.0; H, 3.9%. 1H NMR (CDCl3): d 7.0–7.3 (m,
Details of the crystallographic data collection and refinement pa-
rameters are given in Table 4. Yellow single crystals of [PtMe3I(1)],
[PtCl2(1)] and two polymorphs of [W(CO)4(1)] were obtained by
diffusion of hexane into a CH2Cl2 solution, by diffusion of Et2O
into a solution of the complex in CH2Cl2 or by slow evaporation
from a solution of the complex in CH2Cl2–Et2O, respectively. Data
collection used a Nonius Kappa CCD diffractometer (T = 120 K)
and with graphite-monochromated Mo-Ka X-radiation (k =
20–22
˚
0.71073 A). Structure solution and refinement were routine,
except for some disorder between the I and C atoms within the
trans-I–Pt–Me unit in [PtMe3I(1)]. This was modelled using partial
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Table 4 Crystallographic data and refinement detailsa
Complex
[PtMe3I(1)]
[PtCl2(1)]
[W(CO)4(1)] (a)
[W(CO)4(1)] (b)
Formula
M
C23H37IPtSb2
879.02
C20H28Cl2PtSb2
777.91
C24H28O4Sb2W
807.81
C24H28O4Sb2W
807.81
Crystal system
Space group
Monoclinic
P21/n (no. 14)
12.2870(15)
12.7061(10)
16.623(2)
91.307(6)
2594.5(5)
4
8.64
0.034
29152
5928
Monoclinic
P21/c (no. 14)
14.243(5)
13.068(3)
12.380(4)
90.302(12)
2304.1(12)
4
8.62
0.148
25377
5290
Monoclinic
P21/n (no. 14)
12.9641(15)
23.323(3)
17.0599(15)
96.210(5)
5128.0(9)
8
6.59
0.048
58518
11741
Monoclinic
Cc (no. 9)
17.705(3)
11.6869(15)
12.4991(10)
94.506(10)
2578.2(5)
4
6.56
0.025
17199
5633
˚
a/A
˚
b/A
˚
c/A
b/◦
U/A
Z
3
˚
l(Mo-Ka)/mm−1
Rint
Total no. of obsns.
Unique obsns.
No. parameters
R1 [Io > 2r(Io)]
R1 (all data)
wR2 [Io > 2r(Io)]
wR2 (all data)
245
0.029
0.036
0.062
240
0.057
0.147
0.090
605
0.028
0.046
0.054
281
0.024
0.025
0.049
0.064
0.109
0.059
0.049
ꢀ
ꢀ
ꢀ
ꢀ
Details in common: T = 120 K; k(Mo-Ka) = 0.71073 A; hmax = 27.5◦. R1 = ꢀFo| − |Fcꢀ/ |Fo|; wR2 = [ w(Fo − Fc2)2/ wFo
]
a
2
4 1/2
˚
atom positions, with the sum of the occupancies of the two I and
two C components each being one. Distinct partial C atom and
partial I atoms could not be identified, hence these units were
refined with identical atomic coordinates and atom displacement
parameters. Consequently the Pt–I and Pt–C distances in the
trans-I–Pt–C unit are weighted averages, and should not be
used in comparative studies. The H atoms associated with the
disordered Me groups were not included in the final structure
factor calculation. The structure of [PtCl2(1)] shows some disorder
in the position of the PtCl2 fragment. This was evident from a
residual unassigned peak in the difference map which based upon
the thermal ellipsoids, coordination environment, the distances
and angles relative to the Sb2PtCl2 plane could not be assigned
to a light atom. The disorder model presented gave a very
satisfactory refinement for two alternative positions for the Pt
atom with relative occupancies of 91 and 9%. This leads to two
Sb2PtCl2 planes with different orientations, and examination of
the centrosymmetric dimer shows that the Cl atoms associated
with the minor Pt component and those on the symmetry related
Pt1a are common. The discussion and the geometric parameters
in Table 2 refer to the major component.
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Acknowledgements
We thank the EPSRC for support (M. D. B.) and Johnson Matthey
plc for loans of platinum metal salts. We also thank Ms Julie
Herniman for assistance with the mass spectrometry experiments.
21 G. M. Sheldrick, SHELXL-97, program for crystal structure refinement,
University of Go¨ttingen, Germany, 1997.
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5654 | Dalton Trans., 2006, 5648–5654
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