Halostibines SbMeX2 and SbMe2X: Lewis acids or Lewis bases?

Article abstract of DOI:10.1021/om2010996

Alkylhalostibines have been shown to behave either as Lewis acids toward appropriate neutral ligands or as Lewis bases to low-valent metal fragments. The boundaries of their Lewis acid and Lewis base behavior have been determined, and the structural and spectroscopic consequences of the different behaviors probed. [SbMeX₂(L-L)] (L-L = 2,2′-bipyridyl, 1,10-phenanthroline) and [SbMeX₂(L)₂] (L = OPMe ₃, OPPh₃) are five-coordinate, distorted square-pyramidal monomers with the Me group axial, with the bond distances little affected by coordination. Significant changes in the bonding within the group 6 carbonyl complexes [M(CO)₅(L′)] are evident, with L′→M σ-donation decreasing across the series L′ = SbMe₃ → SbMe₂Br → SbMeBr₂, and an increase in M→L′ π-acceptance within the same series. Intermolecular interactions are a major feature within these systems, ranging from weak, MCO···Sb interactions in [M(CO)₅(SbMe ₂Br)] and [M(CO)₅(SbMeBr₂)] to remarkably strong O···Sb hypervalent bonds in [Mn(CO) ₅(SbMe₂Br)][CF₃SO₃] and [Mn(CO) ₃(SbMe₂Br)₃][CF₃SO₃], the latter involving the triflate anions. These lead to large changes in the geometry at Sb and represent very rare examples in which the antimony exhibits significant Lewis acid and Lewis base behavior simultaneously. The coordinated alkylhalostibines are alkylated cleanly with MeLi or ⁿBuLi.

Full text of DOI:10.1021/om2010996

Article
pubs.acs.org/Organometallics
Halostibines SbMeX2 and SbMe2X: Lewis Acids or Lewis Bases?
Sophie L. Benjamin, William Levason, Gillian Reid,* and Robert P. Warr
School of Chemistry, University of Southampton, Southampton, U.K. SO17 1BJ
S
* Supporting Information
ABSTRACT: Alkylhalostibines have been shown to behave
either as Lewis acids toward appropriate neutral ligands or as
Lewis bases to low-valent metal fragments. The boundaries of
their Lewis acid and Lewis base behavior have been
determined, and the structural and spectroscopic consequences
of the different behaviors probed. [SbMeX2(L−L)] (L−L =
2,2′-bipyridyl, 1,10-phenanthroline) and [SbMeX2(L)2] (L =
OPMe3, OPPh3) are five-coordinate, distorted square-
pyramidal monomers with the Me group axial, with the
bond distances little affected by coordination. Significant
changes in the bonding within the group 6 carbonyl complexes
[M(CO)5(L′)] are evident, with L′→M σ-donation decreasing
across the series L′ = SbMe3 → SbMe2Br → SbMeBr2, and an
increase in M→L′ π-acceptance within the same series. Intermolecular interactions are a major feature within these systems,
ranging from weak, MCO···Sb interactions in [M(CO)5(SbMe2Br)] and [M(CO)5(SbMeBr2)] to remarkably strong O···Sb
hypervalent bonds in [Mn(CO)5(SbMe2Br)][CF3SO3] and [Mn(CO)3(SbMe2Br)3][CF3SO3], the latter involving the triflate
anions. These lead to large changes in the geometry at Sb and represent very rare examples in which the antimony exhibits
significant Lewis acid and Lewis base behavior simultaneously. The coordinated alkylhalostibines are alkylated cleanly with MeLi
n
or BuLi.
results in scrambling to SbR3−nXn (n = 1 or 2),11,12 but at least
INTRODUCTION
Stibines, SbR3, and derivatives thereof have gained increasing
■
one (unstable) adduct, [Sb2I6(SbMe3)2(thf)2], is known.13
The major objective of the present work was to establish the
importance in recent years for a number of reasons, most of
boundaries of the Lewis acid to Lewis base behavior of the
which concern the realization that their chemistry is
mixed alkylhalostibines, SbMe2Br and SbMeBr2, through
significantly different from that of the lighter group 15
phosphine and arsine analogues.1,2 Triorganostibines utilize
detailed spectroscopic and structural measurements. This has
allowed us to probe the consequences of the different behavior
the antimony-based lone pair to function as modest Lewis bases
on the antimony center, especially the nature of their bonding
toward a wide range of d- and p-block acceptors in medium or
toward either neutral donor ligands or transition metal centers.
low oxidation states. Toward electron-rich d-block metals in
low oxidation states they also exhibit weak π-acceptor ability
Few examples are available for compounds of this type. Lewis acid
adducts include [SbMeCl2(2,2′bipy)],14 [SbPhX2(2,2′-bipy)],
(M(dπ)→Sb−C(σ*)).1 Arguably the most important recent
[SbPhX2(py)n] (n = 1 or 2), and [SbPh2X(2,2′-bipy)].15 Lewis
contribution to stibine chemistry has come from Werner and
co-workers, who prepared the first examples of bridging ER3
base behavior is found in [Cr(CO)5(SbMeCl2)],16 in [W(CO)5-
(SbPh2X)] (X = Cl, Br, or I),17 and in the unique example of a
bidentate halostibine in [Rh{Ph2Sb(CH2)3SbPh2}{PhClSb-
(CH2)3SbClPh}Cl2]Cl.18
(E = P, As, Sb) ligands with SbiPr3 (akin to bridging CO) and
who showed that metathesis with PR3 or AsR3 also led to
examples of these as bridging ligands, although the latter
complexes cannot be obtained directly.3 Theoretical studies
have been used to probe the bonding in the bridging ER3
ligands.4 Although little studied, SbY3 and SbR3−nYn (Y = GeR3,
SnR3, NR2, OR, SR, etc.), where the organic R groups are
partially or wholly replaced by other substituents from groups
14−16, are also weak Lewis bases toward transition metal
carbonyls and low-valent organometallics.5 In marked contrast,
while they retain the antimony-based lone pair, antimony(III)
halides, SbX3 (X = F, Cl, Br, or I), behave as moderately strong
Lewis acids6 toward a wide range of neutral N-,7 P- or As-,8 O-,9
S-, or Se10-donor ligands, as well as forming a range of
haloanions with X−.6 The reaction of SbR3 with SbX3 usually
A further important phenomenon in organo-antimony
chemistry that clearly distinguishes it from organo-phosphorus
chemistry is the occurrence of hypervalency. For example, SbR3
(and BiR3) compounds can form significant interactions with
adjacent electron donor groups (amines, ethers, etc.).19 The
extent of these interactions can lead to unexpected and
potentially useful differences in reactivity, e.g., increasing the
efficiencies and rates of Pd-catalyzed cross-coupling reactions.20
In our recent work we have developed a range of new,
Received: November 9, 2011
Published: January 13, 2012
© 2012 American Chemical Society
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Article
potentially tridentate, Sb2E (and Bi2E)-donor ligands (E = O, S,
NMe) and shown that varying degrees of hypervalent E→
Sb(Bi) contacts occur both in the ligands themselves and also
within their transition metal complexes.21 We also anticipated
that hypervalency might be evident in the chemistry of
alkylhalostibines, and this would contribute to our under-
standing of this important and currently very active area of
heavy p-block chemistry (vide infra). Finally, metal-coordinated
alkylhalostibines may provide templates for the construction of
polydentate and macrocyclic stibine ligands, very few examples
of which are known.1,22
RESULTS AND DISCUSSION
■
Figure 2. View of the structure of [SbMeBr2(OPMe3)2] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg): Sb1−C1 = 2.120(7), Sb1−O1 = 2.235(4), Sb1−O2 =
2.203(4), Sb1−Br1 = 2.8370(9), Sb1−Br2 = 2.8344(8), Sb2−C2 =
2.128(7), Sb2−O3 = 2.261(5), Sb2−O4 = 2.244(5), Sb2−Br3 =
2.8072(9), Sb2−Br4 = 2.8133(8), P1−O1 = 1.524(5), P2−O2 =
1.527(5), P3−O3 = 1.524(5), P4−O4 = 1.524(5); C1−Sb1−O1 =
86.8(2), C1−Sb1−O2 = 88.1(2), O1−Sb1−O2 = 83.1(2), C1−Sb1−
Br2 = 84.7(2), O1−Sb1−Br2 = 167.72(12), O2−Sb1−Br2 =
87.71(12), C1−Sb1−Br1 = 85.6(2), O1−Sb1−Br1 = 91.25(12), O2−
Sb1−Br1 = 171.79(12), Br1−Sb1−Br2 = 96.97(3), C2−Sb2−O3 =
85.2(2), C2−Sb2−O4 = 87.7(2), O3−Sb2−O4 = 83.9(2), C2−Sb2−
Br3 = 85.8(2), O4−Sb2−Br3 = 172.88(12), O3−Sb2−Br3 = 92.52(12),
C2−Sb2−Br4 = 85.3(2), O3−Sb2−Br4 = 167.72(12), O4−Sb2−Br4 =
87.90(12).
Halostibines as Lewis Acids. Complexes with phosphine
oxides (OPR3, R = Me or Ph) and the N-heterocycles 2,2′-
bipyridyl and 1,10-phenantholine were examined, the ligands
being chosen since there are comparator data on SbX3
adducts available.7,9 Reaction of the methyldihalostibine
SbMeBr2 with OPPh3 or OPMe3 in anhydrous MeCN
resulted in formation of the 1:2 complexes [SbMe-
Br2(OPPh3)2] and [SbMeBr2(OPMe3)2] as white, powdered
solids. Refrigeration of the filtrates gave the complexes as
colorless crystals. Attempts to form analogous complexes
with the dimethylhalostibines SbMe2X were unsuccessful;
the in situ 1H NMR spectrum of a mixture of OPMe3 and the
SbMe2Br showed no evidence of interaction. Slow crystal-
lization from a mixture of SbMe2Cl and OPPh3 in acetoni-
trile deposited crystals identified as [SbMeCl2(OPPh3)2] (in 46%
isolated yield), formed by disproportionation (see below). The
structures of SbMeCl2 and SbMeBr216 are both polymeric, based
upon a pyramidal (SbCX2) core, linked into very distorted square
pyramids with apical Me groups, by two further long Sb−X bonds
in the basal plane, although the chain structure differs between the
two compounds. In the phosphine oxide complexes the two OPR3
ligands are disposed cis and replace the longer Sb−X bonds
(Figure 1−3). In both [SbMeX2(OPPh3)2] species the axial Me
Figure 3. View of the structure of [SbMeCl2(OPPh3)2] with atom-
numbering scheme. Ellipsoids are shown at the 30% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = −x, y,
1/2−z. Note that the Me substituent on Sb1 is disordered over two
sites (related by the crystallographic 2-fold axis); hence only one can
be present in a given molecule. The alternative position is shown by
the dotted bonds. Selected bond lengths (Å) and angles (deg): Sb1−
C1 = 1.941(6), Sb1−O1 = 2.507(2), Sb1−Cl1 = 2.5167(9), P1−O1 =
1.503(2); C1−Sb1−O1a = 91.4(2), C1−Sb1−O1 = 87.3(2), O1−
Sb1−O1a = 84.74(10), C1−Sb1−Cl1a = 92.2(2), C1−Sb1−Cl1 =
89.0(2), O1−Sb1−Cl1 = 174.32(6), O1−Sb1−Cl1a = 91.05(6), P1−
O1−Sb1 = 141.27(12), C1−Sb1−Cl1 = 92.17(18).
Figure 1. View of the structure of [SbMeBr2(OPPh3)2] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = 1−x, y,
1/2−z. Note that the Me substituent on Sb1 is disordered over two
sites; hence only one can be present in a given molecule. The
alternative position is shown by the dotted bonds. Selected bond
lengths (Å) and angles (deg): Sb1−C1 = 1.947(7), Sb1−O1 =
2.440(2), Sb1−Br1 = 2.6675(5), P1−O1 = 1.508(2); C1−Sb1−O1a =
86.2(2), C1−Sb1−O1 = 94.1(2), O1−Sb1−O1a = 85.33(11), C1−
Sb1−Br1a = 89.8(2), O1−Sb1−Br1a = 174.31(6), C1−Sb1−Br1 =
89.9(2), O1−Sb1−Br1 = 90.80(6), Br1−Sb1−Br1a = 93.35(2).
group is disordered over two sites, and this disorder results in
an unreasonably short Sb−C distance in each, accompanying
elongated Sb ellipsoids along the C−Sb−C axis. [SbMe-
Br2(OPMe3)2] has two molecules in the asymmetric unit, each
of which shows the Sb atom displaced below the plane by an
average of 0.170 Å in the direction opposite of the axial C.
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The Sb−X distances in the OPR3 adducts are longer than the
corresponding distances in the parent SbMeX2 (Sb−Cl =
16
́
́
2.392(2)−2.442(3) Å; Sb−Br = 2.564(3), 2.583(3) Å),
suggesting a rather stronger interaction with the trans
phosphine oxide than in the secondary bonding to bridging
́
halides in SbMeX2. The Sb−CH3 in SbMeX2 (2.129(7) Å,
́
X = Cl; 2.301(9) Å, X = Br) compare with 2.120(7) and
́
2.128(7) Å in [SbMeBr2(OPMe3)2]. Comparison of the
angles at antimony with those in the parent SbMeX2 show
16
that while ∠X−Sb−X are little changed, ∠C−Sb−X become
more acute on formation of the phosphine oxide adducts,
in the OPMe3 complex by ∼7°, and by much less than in the
OPPh3 analogues. Square-pyramidal coordination with cis
basal OPPh3 groups is also present in [SbCl3(OPPh3)2]23
Figure 4. View of the structure of [SbMeCl2(1,10-phen)] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = x, 3/2 −
y, z. Selected bond lengths (Å) and angles (deg): Sb1−C1 = 2.133(8),
Sb1−N1 = 2.376(4), Sb1−Cl1 = 2.6534(14); C1−Sb1−N1 = 86.9(2),
N1−Sb1−N1a = 69.9(2), C1−Sb1−Cl1 = 84.64(13), N1−Sb1−Cl1 =
87.40(12), N1−Sb1−Cl1a = 156.20(11), Cl1−Sb1−Cl1a = 113.83(6).
́
(Sb−Cl = 2.211(2), 2.466(1) Å). The Sb−O(P) distances
are [SbMeBr2(OPPh3)2] 2.440(2), [SbMeCl2(OPPh3)2]
2.507(2), [SbCl3(OPPh3)2]23 2.455(2), and [SbMe-
́
Br2(OPMe3)2] 2.203(4)−2.261(5) Å. The IR spectra show
modest low-frequency shifts in ν(PO) on complexation,
similar to those found in SbX3 (X = F, Cl, Br) adducts.9
The solution spectroscopic data show small high-frequency
1
shifts in the H, 13C{1H}, and 31P{1H} NMR resonances of
the OPMe3 groups on coordination, again similar to the
corresponding SbX3 adducts,9 and since these complexes are
expected to be labile and undergoing fast dissociative ligand
exchange in solution at ambient temperatures, detailed numerical
comparisons are not appropriate. In contrast, the 1H resonances of
the SbMe groups are little changed from those in SbMeX2.11
Three complexes with N-donor chelates [SbMeX2(1,10-
phenanthroline)] (X = Cl or Br) and [SbMeBr2(2,2′-bipyridyl)]
were prepared as yellow powders from reaction of the
constituents in dry acetonitrile solution. Refrigeration of the
filtrates from the syntheses gave crystalline samples used for the
structure determinations. [SbMeCl2(2,2′-bipyridyl)] has been
described previously by Althaus et al.,14 and its structure
determined. The reaction of SbMe2Br with 1,10-phenanthroline
in MeCN gave an intensely orange solution, which over the
course of ∼30 min paled and deposited a yellow precipitate.
The precipitate was identified as [SbMeBr2(1,10-phenanthro-
line)] by spectroscopic comparison with a genuine sample.
Attempts to isolate the first, deeply colored product by working
up the reaction immediately after mixing or by using low
temperatures were unsuccessful, producing mixtures of starting
materials, [SbMeBr2(1,10-phenanthroline)], and an unstable
orange-red solid. The last is assumed to be [SbMe2Br(1,10-
phenanthroline)], which is too unstable to separate and
disproportionates into the yellow [SbMeBr2(1,10-phenanthro-
line)] and SbMe3. The SbMe3 was identified in situ by its
Figure 5. View of the structure of [SbMeBr2(2,2′-bipy)] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = x, 1/2−
y, z. Selected bond lengths (Å) and angles (deg): Sb1−C1 = 2.117(8),
Sb1−N1 = 2.365(5), Sb1−Br1 2.7999(7), C1−Sb1−N1 = 85.2(2),
N1−Sb1−N1a = 69.2(2), C1−Sb1−Br1 = 84.56(2), N1−Sb1−Br1 =
91.44(12), N1−Sb1−Br1a = 158.82(12), Br1−Sb1−Br1a = 106.01(3).
1
characteristic H NMR resonance.
The structures of the four [SbMeX2(diimine)] complexes are
similar (Figures 4−6), discrete square-pyramidal molecules
with no contacts to neighboring molecules within the sum of
the van der Waals radii. In each, the antimony lies slightly
below the base plane and the strong σ-donor Me group is axial.
Compared to SbMeX2 both the Sb−C and Sb−X bond lengths
have increased, probably reflecting the increase in coordination
number to five, from a pyramidal three-coordinate core with
two weaker secondary Sb−X bonds to neighboring molecules
in SbMeX2. The small chelate bite angles of the diimines result
in an acute ∠N−Sb−N of ∼70°, but correspondingly the ∠X−
Sb−X have opened up by 10−15° compared to SbMeX2. The
symmetrical Sb−N coordination contrasts with the often
disparate Sb−N bond lengths found in structures of these
Figure 6. View of the structure of [SbMeBr2(1,10-phen)] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = x, −y, z.
Selected bond lengths (Å) and angles (deg): Sb1−C1 = 2.120(4),
Sb1−N1 = 2.377(3), Sb1−Br1 = 2.8138(5), C1−Sb1−N1 =
86.76(12), N1−Sb1−N1a = 70.23(12), C1−Sb1−Br1 = 84.91(7),
N1−Sb1−Br1a = 88.46(6), N1−Sb1−Br1 = 157.52(6), C1−Sb1−
Br1a = 84.90(7), Br1−Sb1−Br1a = 111.48(2).
two ligands with SbX3 acceptors,7,24 which seem to have no
simple rationalization.
Halostibines as Lewis Bases. Both methyldihalo- and
dimethylhalo-stibines function as Lewis bases toward group 6
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Table 1. Selected Spectroscopic and Structural Data
ν(CO)/cm−1
ν(CO)/cm−1
complex
(CH2Cl2 solution)
Nujol mull
δ(CO) 13C{1H} NMR
d(M−Sb)/Å
2.6969(6)
[W(CO)5(SbMeBr2)]
[W(CO)5(SbMe2Br)
[W(CO)5(SbMe3)]
[Cr(CO)5(SbMeBr2)]
[Cr(CO)5(SbMe2Br)]
2085, 2005, 1966
2078, 1996, 1951
2084, 1978, 1965, 1934
2077, 1993, 1962, 1953
194.5, 196.6
195.6, 198.3
2.7186(4) to 2.7309(4)
a
b
a
b
2068, 1972, 1940
2068, 1938, 1909
197.1, 199.7
2.759(1)
c
not reported
2076, 1982, 1964
2069, 1991, 1966, 1952
2069, 1940
not reported
215.9, 221.8
218.3, 223.6
2.556(1)
2.574(2)
2.611(1)
2068, 1996, 1951
not reported
b
[Cr(CO)5(SbMe3)]
a
b
c
This work. Data from ref 25. Data from ref 16.
carbonyl residues, affording [M(CO)5L] complexes. However,
attempted reaction of SbBr3 with [W(CO)5(thf)] failed, only
decomposition products being observed. The precursors
[M(CO)5(thf)] (M = Cr, W), generated by photolysis of
M(CO)6 in thf, react with SbMe2Br to give the air-stable
complexes [M(CO)5(SbMe2Br)]. Similarly, treatment of [W-
(CO)5(thf)] with SbMeBr2 results in formation of [W-
(CO)5(SbMeBr2)]. The analogous chromium complex [Cr-
(CO)5(SbMeBr2)] has been reported previously.16 In chlo-
rocarbon solutions these complexes show three carbonyl
stretching vibrations in the IR spectra, as expected for a C4v
fragment (theory 2a1 + e) (the asymmetry of alkylhalostibine
ligands does not lead to observable splitting). Data are listed in
Table 1 along with literature data on related complexes of SbMe3.
In the solid state several of the complexes show splitting of the
carbonyl vibrations due to intermolecular interactions, discussed
below when the crystal structures are described.
The 1H and 13C{1H} NMR data show significant high-
frequency shifts in the δ(Me) resonances on coordination to
metal carbonyl residues, which contrasts with their behavior as
Lewis acids (above), where no appreciable changes occurred.
Considering the IR data, it is clear that ν(CO) generally fall
along the series [M(CO)5(SbMeBr2)] → [M(CO)5(SbMe2Br)]
→ [M(CO)5(SbMe3)], consistent with higher electron density in
the CO π* orbitals along the series, which corresponds to higher
electron density on the metal center in the same order. This could
result either from greater σ-donation or reduced π-acceptance (or
a combination of the two). The 13C{1H} NMR data show the
two resonances typical of a C4v pentacarbonyl unit, and the
shift to high frequency [M(CO)5(SbMeBr2)] → [M(CO)5-
(SbMe2Br)] → [M(CO)5(SbMe3)] leads to the same conclu-
sions as drawn from the IR spectroscopic data.26
The X-ray structures of [W(CO)5(SbMeBr2)], [Cr-
(CO)5(SbMe2Br)], and [W(CO)5(SbMe2Br)] are shown in
Figures 7−9; the structure of [Cr(CO)5(SbMeBr2)] has been
reported by Breunig.16 It is well established that on
coordination of a triorganostibine to a metal center, the ∠C−
Sb−C widen significantly, as the essentially Sb p3 character in
the Sb−C bonds in the stibine changes toward sp3 in the metal
complex, which improves the directional properties and
strength of the Sb−M bond.1,27,28 Similar effects are not
generally found in P−M bonds in metal phosphine complexes
and have their origin in the greater s−p orbital energy separa-
tions at antimony. SbMe2Br is an oil at ambient temperatures,
and no structural data are available. However, when SbMeBr2,
which has ∠C−Sb−Br = 91.2(2)°, 92.6(2)° and ∠Br−Sb−Br =
97.6(1)°, coordinates in [W(CO)5(SbMeBr2)], the angles open
to ∠C−Sb−Br = 96.9(2)°, 96.5(2)° and ∠Br−Sb−Br = 98.9(1)°,
and similar trends are seen in [Cr(CO)5(SbMeBr2)].16 This
widening of the angles at Sb is thus similar to that in tri-
organostibines, but contrasts with the contraction found in the
Figure 7. (a) View of the structure of [Cr(CO)5(SbMe2Br)] with
atom-numbering scheme. Ellipsoids are shown at the 50% probability
level, and H atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Cr1−C3 = 1.882(9), Cr1−C4 = 1.899(9), Cr1−C5 =
1.907(9), Cr1−C6 = 1.905(9), Cr1−C7 = 1.864(9), Cr1−Sb1 =
2.5736(15), Sb1−Br1 = 2.5239(13); Br1−Sb1−Cr1, 108.42(5). (b)
View of the packing in [Cr(CO)5(SbMe2Br)] showing the
intermolecular (C)O···Sb interactions
Lewis acid adducts (above), the latter reflecting the increase in
coordination number at Sb as well as electronic effects. Within
the essentially square-pyramidal M(CO)5 units, the M−
C(O)transSb are typically shorter than M−C(O)transC, but the
major feature of interest is the trend in M−Sb bonds (Table 1).
Along the two series of tungsten and chromium complexes
there is a clear lengthening of the M−Sb bond as CH3 re-
places Br in the ligands. Combining this observation with the
IR and 13C{1H} NMR spectroscopic data discussed above
leads to the conclusion that the key component must be an
increase in π-acceptance by Sb as the number of Br substituents
is increased, which shortens the M−Sb bond, but also leads
to reduced electron density at M and in the carbonyl π*
orbitals.
Examination of the packing of the [W(CO)5(SbMe2Br)]
molecules shows three intermolecular Sb···O contacts (3.367−
3.426 Å) between the SbMe2Br and carbonyl groups within the
sum of the van der Waals radii (3.52 Å) that lead to a “double-
chain” arrangement in the crystal lattice (Figure 8).29 Similar
Sb···O contacts are present between adjacent molecules in the
structures of [Cr(CO)5(SbMe2Br)], [W(CO)5(SbMeBr2)],
and [Cr(CO)5(SbMeBr2)], although in these compounds
these lead to infinite “single-chain” polymers (Figure 7b and
Supporting Information) and although clearly weak, they are
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sufficient to account for the complex IR spectra in the solid
state. Similar behavior has been noted in [W(CO)5(SbPh2X)]
complexes.17
The reaction of SbMe2Br and [Mn(CO)5(CF3SO3)] in anhy-
drous CH2Cl2 produced yellow crystals of [Mn(CO)5-
(SbMe2Br)][CF3SO3]. The only comparable triorganostibine
cation is [Mn(CO)5(SbPh3)]+,30,31 but the IR and NMR data
(including the observation that the 55Mn quadrupole causes
1
serious line broadening in the H and 13C{1H} NMR spectra)
are much as expected, although very detailed comparisons as
drawn in group 6 are not possible here due to insufficient
literature examples.
The structure (Figure 10) shows the expected square-
pyramidal Mn(CO)5 residue with the sixth site occupied by
Figure 8. (a) View of the structure of [W(CO)5(SbMe2Br)] with
atom-numbering scheme. Ellipsoids are shown at the 50% probability
level, and H atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): W1−Sb1 = 2.7280(4), W2−Sb2 = 2.7186(4), W3−
Sb3 = 2.7247(4), W4−Sb4 = 2.7309(4), Sb1−Br1 = 2.5089(6), Sb2−
Br2 = 2.5121(7), Sb3−Br3 = 2.5144(7), Sb4−Br4 = 2.5148(6); Br1−
Sb1−W1 = 112.49(2), Br2−Sb2−W2 = 111.24(2), Br3−Sb3−W3 =
111.12(2), Br4−Sb4−W4 = 111.41(2). (b) View of the structure of
[W(CO)5(SbMe2Br)] showing the “double-chain” arrangement
formed through intermolecular (C)O···Sb interactions.
Figure 10. View of the structure of [Mn(CO)5(SbMeBr2)][CF3SO3]
with atom-numbering scheme, showing the long contact to Sb1 via
O8a of an adjacent [CF3SO3]− anion. Ellipsoids are shown at the 50%
probability level, and H atoms are omitted for clarity. Only one of the
disordered CF3SO3− anions is shown (the position of O8a is common
to both). Symmetry operation: a = x, 1/2−y, −1/2+z. Selected bond
lengths (Å) and angles (deg): Mn1−C1 = 1.849(8), Mn1−C2 =
1.870(8), Mn1−C3 = 1.894(8), Mn1−C4 = 1.887(7), Mn1−C5 =
1.870(8), Mn1−Sb1 = 2.5847(12), Sb1−Br1 = 2.4933(11), Sb1···O8a =
2.696(5); C6−Sb1−C7 = 109.1(4), C6−Sb1−Br1 = 94.6(2), C7−
Sb1−Br1 = 94.8(2).
SbMe2Br (Mn−Sb = 2.5847(12) Å), which compares with
2.596(3) Å in [Mn(CO)5(SbPh3)]+.31 Most unusually, one of
the O atoms of the triflate anion forms a strong hypervalent
interaction with the coordinated Sb center (O···Sb = 2.70 Å),
compared with the sum of the van der Waals radii of 3.52 Å.29
The effect of this interaction is to severely distort the geometry
at antimony, as evidenced by the ∠Mn1−Sb1−Br1 angle of
102.4°, compared to 125.9° and 120.0° for ∠Mn1−Sb1−C6
and ∠Mn1−Sb1−C7, respectively, and the wide ∠C6−Sb1−
C7 = 109.1(4)°.
[Mn(CO)3(Me2CO)3][CF3SO3] in acetone solution reacted
with SbMe2Br to give the 3:1 complex [Mn(CO)3(SbMe2Br)3]-
[CF3SO3], the first example of a transition metal coordinating
three halostibine ligands; the key to the successful reaction is
the lability of the weak donor acetone ligands. However, several
attempts to prepare [Mn(CO)3(SbMeBr2)3][CF3SO3] were
unsuccessful. The solution IR spectrum of [Mn(CO)3(SbMe2Br)3]-
[CF3SO3] shows one sharp and one broad ν(CO) band (a1 + e),
Figure 9. View of the structure of [W(CO)5(SbMeBr2)] with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Note that the intermolecular
(C)O···Sb contacts give rise to a chain structure (see Supporting
Information). Selected bond lengths (Å) and angles (deg): W1−C2 =
2.032(6), W1−C3 = 2.049(6), W1−C4 = 2.071(6), W1−C5 =
2.044(6), W1−C6 = 2.002(6), W1−Sb1 = 2.6969(6), Sb1−C1 =
2.116(6), Sb1−Br1 = 2.5031(8), Sb1−Br2 = 2.5012(8); C1−Sb1−
Br1 = 96.5(2), C1−Sb1−Br2 = 96.9(2), Br1−Sb1−Br2 = 98.78(3).
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but again the IR spectrum obtained from a Nujol mull is more
complicated due to intermolecular interactions (see below). The
crystal structure (Figure 11) shows a pseudo-octahedral Mn center
For example [W(CO)5(SbMe2Br)] is air-stable both as a solid
and in solution, whereas SbMe2Br is extremely air-sensitive and
the neat oil disproportionates over time even in an inert
atmosphere. Another possible advantage would be to use the
central transition metal as a template to produce chelating
polydentate (or macrocyclic) antimony ligands selectively. As
proof-of-concept, [W(CO)5(SbMe2Br)] was treated with a
n
stoichiometric amount of either MeLi in thf or BuLi in Et2O.
This resulted in formation of [W(CO)5(SbMe3)]25 and
n
[W(CO)5(SbMe2 Bu)] in good yield, spectroscopically pure
by IR and NMR, indicating clean substitution of the halide at
the Sb center.
EXPERIMENTAL SECTION
■
Infrared spectra were recorded as Nujol mulls between CsI plates
using a Perkin-Elmer Spectrum 100 spectrometer over the range
4000−200 cm−1. 1H NMR spectra were recorded in CDCl3 or CD2Cl2
unless otherwise stated, using a Bruker AV300 spectrometer. 13C{1H},
31P{1H}, and 55Mn NMR spectra were recorded using a Bruker
DPX400 spectrometer and are referenced to the solvent resonance
(13C), external 85% H3PO4 (31P), and aqueous KMnO4 (55Mn).
Microanalyses were undertaken by Medac Ltd. The CH2Cl2 and
acetonitrile were dried by distillation over CaH2, while the toluene,
benzene, THF, and n-hexane were dried over Na/benzophenone ketyl.
SbMe2X and SbMeX2 (X = Cl or Br) were made as described.32
Antimony trihalides and all other reagents were obtained from Aldrich.
The OPR3, 2,2′-bipy, and 1,10-phen were dried by heating in vacuo
before use. All preparations were performed under an atmosphere of
dry N2 using Schlenk techniques, and spectroscopic samples were
prepared in a dry N2-purged glovebox. SbMePh2, SbMe2Ph,32
[M(CO)5(thf)] (M = Cr or W),33 [Mn(CO)5(CF3SO3)],30 and
[Mn(CO)3(Me2CO)3][CF3SO3]30 were prepared via the literature
methods.
Figure 11. View of the structure of the [Mn(CO)3(SbMe2Br)3]+
cation with atom-numbering scheme. Ellipsoids are shown at the 50%
probability level, and H atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Mn1−C9 = 1.814(3), Mn1−C8 =
1.825(3), Mn1−C7 = 1.835(3), Mn1−Sb1 = 2.5706(5), Mn1−Sb2 =
2.5852(5), Mn1−Sb3 = 2.5932(4), Sb1−Br1 = 2.5398(4), Sb2−Br2 =
2.5322(4), Sb3−Br3 = 2.5418(4), Sb1···O6 = 2.799(2), Sb2···O6 =
2.874(2), Sb3···O4a = 2.798(2); Sb1−Mn1−Sb2 = 93.646(15), Sb1−
Mn1−Sb3 = 92.699(14), Sb2−Mn1−Sb3 = 93.863(15), Br1−Sb1−
Mn1 = 107.191(14), Br2−Sb2−Mn1 = 107.956(14), Br3−Sb3−
Mn1 = 105.471(13). (b) View of the packing within [Mn(CO)3-
(SbMe2Br)3][CF3SO3] showing the hypervalent contacts between
the O atoms of the [CF3SO3]− anions and the Sb atoms of the cation.
SbMeBr2. SbMePh2 (2.00 g, 6.87 mmol) was dissolved in toluene
(80 mL), and HBr was bubbled through the solution for 15 min. The
reaction vessel was sealed, and the reaction mixture was stirred for
30 min. Residual HBr was removed by passing a slow stream of nitrogen
through the solution overnight. The solvent was removed in vacuo,
yielding an off-white solid. Yield: 1.75 g, 86%. 1H NMR (CDCl3): 2.23
(s, Me); lit.12 2.2. 13C{1H} NMR (CDCl3): 21.9 (Me).
SbMeCl2. SbMePh2 (2.00 g, 6.87 mmol) was dissolved in toluene
(80 mL), and HCl was bubbled through the solution for 15 min. The
reaction vessel was sealed, and the reaction mixture was stirred for
30 min. Residual HCl was removed by passing a slow stream of nitrogen
through the solution overnight. The solvent was removed in vacuo,
in the cation. The Mn−Sb, Sb−Br, and Sb−C bond lengths are very
similar to those in [Mn(CO)5(SbMe2Br)][CF3SO3] and contain
hypervalent contacts from the triflate anions to the antimony,
producing very distorted geometries. In this case, O6 from the
triflate has short contacts with both Sb1 (2.80 Å) and Sb2 (2.87 Å),
forming a puckered four-membered ring, while Sb3 interacts with
O4 from the anion of the next unit (Sb···O4 = 2.80 Å), producing a
polymeric chain structure as seen in Figure 11b. O5 from each
anion has no interactions. These hypervalent Sb···O distances are
significantly shorter, and the distortions in the antimony environ-
ment are greater than those we observed in metal carbonyl
complexes of distibine ether ligands (which show intramolecular
O→Sb hypervalency involving the ether function),21 suggesting that
the halostibines are much stronger acceptors toward the triflate
oxygen donors than are triorganostibines toward ether oxygen.
Finally, species in which one or more halostibines are
complexed to a transition metal could potentially be of use as
reagents in the synthesis of more complex antimony ligands, by
exploiting the reactivity of the antimony halide link with
organolithium or Grignard reagents. As precursors, these com-
plexes are far more stable than noncoordinated halostibines.
1
yielding an off-white solid. Yield: 1.00 g, 70%. H NMR (CDCl3):
1.88, (s, Me); lit.12 1.9. 13C{1H} NMR (CDCl3): 27.5 (Me).
SbMe2Br. SbMe2Ph (2.1 g, 9.2 mmol) was dissolved in benzene
(100 mL), and HBr was bubbled through the solution for 15 min. The
reaction vessel was sealed, and the reaction mixture was stirred for
30 min. Residual HBr was removed by passing a slow stream of nitrogen
through the solution overnight. The solution was filtered, and the
solvent was removed in vacuo, yielding a pale yellow oil. Yield: 1.2 g,
1
56%. H NMR (CDCl3): 1.49, (s, Me). 13C{1H} NMR (CDCl3):
8.9 (Me).
Halostibines As Lewis Acids. [SbMeBr2(OPPh3)2]. SbMeBr2
(0.14 g, 0.47 mmol) was added to a solution of OPPh3 (0.26 g,
0.94 mmol) in acetonitrile (12 mL). The reaction was stirred for 1 h,
yielding a clear solution and white precipitate. The solid was isolated
by filtration and dried in vacuo. Refrigeration of the filtrate (∼16 h)
gave colorless crystals, from which the X-ray data set was collected.
Yield: 0.21 g, 52%. Anal. Calcd for C37H33Br2O2P2Sb (853.2): C, 52.1;
1
H, 3.9. Found: C, 51.9; H, 3.8. IR (Nujol/cm−1): 1133 (PO). H
NMR (CDCl3): 2.18 (s, [3H], MeSb), 7.4−7.7 (m, [30H], aromatics).
31P{1H} NMR (CDCl3): 30.5.
[SbMeBr2(OPMe3)2]. SbMeBr2 (0.25 g, 0.85 mmol) was added to a
solution of OPMe3 (0.17 g, 1.9 mmol) in acetonitrile (12 mL). The
reaction was stirred for 1 h, resulting in a clear, colorless solution,
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which was reduced in vacuo to ∼5 mL, causing precipitation of a white
solid, which was isolated by filtration and dried in vacuo. Refrigeration of
the filtrate (∼16 h) gave colorless crystals, from which the X-ray data set
was collected. Yield: 0.23 g, 52%. Anal. Calcd for C7H21Br2O2P2Sb
(480.6): C, 17.5; H, 4.4. Found: C, 18.4; H, 4.5. IR (Nujol/cm−1):
1100(sh), 1085 (PO). H NMR (CDCl3): 1.64 (d, J = 13.2 Hz,
[18H], MeP), 2.03 (s, [3H], MeSb). 13C{1H} NMR (CDCl3): 18.4 (d,
1J = 74 Hz, MeP), 29.8 (MeSb). 31P{1H} NMR (CDCl3): 50.5.
[W(CO)5(SbMeBr2)]. A solution of W(CO)6 (0.24 g, 0.67 mmol)
in thf (40 mL) was photolyzed for 1.25 h. The resulting solution was
added to a solution of SbMeBr2 (0.20 g, 0.67 mmol) in thf (10 mL).
The mixture was stirred for 1 h, after which the volatiles were removed
in vacuo to yield a bright yellow solid. n-Hexane (40 mL) was added,
the resultant yellow-orange solution stirred for 30 min and filtered, and
the filtrate reduced in vacuo to ∼10 mL. The orange solid precipitate was
isolated by filtration and dried in vacuo. Orange crystals grew from the
filtrate at −18 °C and were used for the X-ray structure determination.
Yield: 0.28 g, 64%. Anal. Calcd for C6H3Br2O5SbW (620.5): C, 11.6; H,
1
2
[SbMeCl2(OPPh3)2] from the Reaction of SbMe2Cl with
OPPh3. SbMe2Cl (0.17 g, 0.90 mmol) was added to a solution of
OPPh3 (0.50 g, 1.80 mmol) in acetonitrile (15 mL). The reaction was
stirred for 1 h, resulting in a clear, colorless solution. The volume was
reduced in vacuo to ∼5 mL, and the solution refrigerated to yield
colorless crystals identified by their X-ray structure. Yield: 0.15 g, 46%
−1
0.5. Found: C, 11.9; H, 1.2. IR (CH2Cl2/cm ): 2085m, 2005w, 1966s,
−1
1
br; (Nujol/cm ): 2084m, 1978sh, 1965sh, 1934m. H NMR (CDCl3):
2.73 (s, SbMe). 13C{1H} NMR (CDCl3): 27.3 (SbMe), 194.5 (1JWC
=
123 Hz, CO), 196.6 (1JWC ≈ 164 Hz, CO).
1
(based upon antimony). IR (Nujol/cm−1): 1136 (PO). H NMR
Reaction of [W(CO)5(SbMe2Br)] with MeLi. [W(CO)5(SbMe2Br)]
(0.12 g, 0.22 mmol) was dissolved in thf (30 mL) and cooled to
−78 °C. MeLi (1.6 M in Et2O, 0.135 mL, 0.22 mmol) was added
dropwise, and the mixture was stirred at −78 °C for 45 min, then
allowed to warm very slowly to room temperature and stirred for 1 h.
The volatiles were removed in vacuo to yield a yellow solid, identified
as [W(CO)5(SbMe3)]. IR (Nujol/cm−1): 2067m, 1941s, 1903s. (lit.25
(CDCl3): 1.84 (s, [3H], MeSb), 7.4−7.7 (m, [30H], aromatics).
13C{1H} NMR (CDCl3): 30.0 (MeSb), 129.3, 129.4, 132.8, 132.9,
133.0, and 133.1 (aromatics). 31P{1H} NMR (CDCl3): 32.0.
[SbMeBr2(2,2′-bipyridyl)]. SbMeBr2 (0.25 g, 0.84 mmol) was
added to a solution of 2,2′-bipyridyl (0.13 g, 0.84 mmol) in acetonitrile
(10 mL). The reaction mixture was stirred for 1 h, resulting in a pale
yellow solution and a yellow precipitate. The solid was isolated by
filtration and dried in vacuo. Refrigeration of the filtrate (∼16 h) gave
yellow crystals, from which the X-ray data were collected. Yield: 0.23 g,
60%. Anal. Calcd for C11H11Br2N2Sb (542.8): C, 29.2; H, 2.5; N, 6.2.
1
2068, 1938, 1901). IR (CH2Cl2/cm−1): 2068m, 1972w, 1935vs. H
NMR (C6D6): 0.56 (s, Me) (lit.21 0.56). 13C{1H} NMR (C6D6): 2.8
(Me), 197.1 (CO), 199.7 (CO) (lit.25 2.8, 197.1, 199.7).
Reaction of [W(CO)5(SbMe2Br)] with nBuLi. [W-
(CO)5(SbMe2Br)] (0.15 g, 0.3 mmol) was dissolved in diethyl ether
1
Found: C, 28.9, H, 2.7; N, 4.9. H NMR (CD2Cl2): 1.86 (s, [3H],
n
(30 mL), and the resultant yellow solution cooled to −78 °C. BuLi
MeSb), 7.86 (t, [2H]), 8.19 (t, [2H]), 8.32 (d, [2H]), and 9.54 (d, [2H])
(aromatics).
(0.19 mL of 1.6 M solution, 0.3 mmol) was added dropwise, and the
reaction mixture was stirred for 45 min, then warmed to room
temperature and stirred for 1 h. The resultant cloudy yellow solution
was filtered over Celite to remove LiBr, then concentrated in vacuo to
∼10 mL. Hexane (15 mL) was added, precipitating a pale yellow solid,
which was isolated by filtration. IR (CH2Cl2/cm−1): 2068w, 1970sh,
1936s; (Nujol/cm−1): 2068w, 1939s. 1H NMR (CDCl3): 0.96 (t,
[3H], Me), 1.24 (s, [6H], SbMe), 1.39 (m, [2H], CH2), 1.58 (m,
[2H], CH2), 1.83 (m, [2H], CH2). 13C{1H} NMR (CDCl3): −2.9
(SbMe), 13.9, 17.2, 25.9, and 28.9 (SbnBu), 197.2 and 200.0 (CO).
[Mn(CO)5(SbMe2Br)][CF3SO3]. [Mn(CO)5Br] (0.15 g, 0.54
mmol) and Ag[CF3SO3] (0.21 g, 0.81 mmol) were dissolved in
CH2Cl2 (20 mL). The reaction was stirred for 2 h in the absence of
light, forming a yellow solution and an off-white solid, which was
removed by filtration. The filtrate was added to a solution of SbMe2Br
(0.25 g, 1.1 mmol) in CH2Cl2 (5 mL) and stirred (∼48 h), yielding a
yellow solution, which was filtered to remove some solid impurities
and reduced in vacuo to ∼10 mL. Then n-hexane (10 mL) was added.
This caused precipitation of a yellow solid, which was isolated by
filtration and dried in vacuo. Refrigeration of the filtrate (∼16 h)
yielded yellow crystals, used for X-ray data collection. Yield: 0.2 g,
71%. Anal. Calcd for C8H6BrF3MnO8SSb (575.8): C, 16.7; H, 1.1.
Found: C, 17.3; H, 1.2. IR (Nujol/cm−1): 2145 m, 2054s,br; (CH2Cl2/
[SbMeBr2(1,10-phenanthroline)]. SbMeBr2 (0.25 g, 0.84 mmol)
was added to a solution of 1,10-phenanthroline (0.15 g, 0.84 mmol) in
acetonitrile (10 mL). The reaction was stirred for 1 h, resulting in a
yellow solution and yellow precipitate. The solid was isolated by
filtration and dried in vacuo. Refrigeration of the filtrate (∼16 h) gave
yellow crystals. Yield: 0.27 g, 67%. Anal. Calcd for C13H11Br2N21Sb
(476.8): C, 32.8; H, 2.3; N, 5.9. Found: C, 32.8; H, 2.3; N, 5.6. H
NMR (CD2Cl2): 1.96 (s, [3H], MeSb), 8.00 (m, [2H]), 8.11 (s,
[2H]), 8.70 (d, [2H]), and 9.93 (d, [2H]) (aromatics).
[SbMeCl2(1,10-phenanthroline)]. SbMeCl2 (0.25 g, 1.2 mmol)
was added to a solution of 1,10-phenanthroline (0.22 g, 1.2 mmol) in
acetonitrile (12 mL). The reaction was stirred for 2 h, resulting in a
yellow precipitate. The solid was isolated by filtration and dried in
vacuo. Refrigeration of the filtrate (∼16 h) gave yellow crystals. Yield:
0.38 g, 82%. Anal. Calcd for C13H11Cl2N2Sb (387.9): C, 40.3; H, 2.9;
1
N, 7.2. Found: C, 39.9; H, 3.1; N, 6.5. H NMR (CD2Cl2): 1.78 (s,
[3H], MeSb), 7.99 (m, [2H]), 8.09 (s, [2H]), 8.63 (d, [2H]), and 9.82
(d, [2H]) (aromatics).
Halostibines As Lewis Bases. [W(CO)5(SbMe2Br)]. A solution of
W(CO)6 (0.30 g, 0.86 mmol) in thf (50 mL) was photolyzed for 1.25 h.
The resulting yellow solution was added to a solution of SbMe2Br
(0.20 g, 0.86 mmol) in thf (10 mL). The mixture was stirred for 3 h, after
which the volatiles were removed in vacuo to yield a bright yellow solid.
n-Hexane (40 mL) was added, and the resultant pale yellow solution
stirred for 0.5 h, then filtered to remove some undissolved solids. The
filtrate was reduced in volume to ∼10 mL, causing precipitation of a pale
yellow solid, which was isolated by filtration. Crystals grew from the
filtrate at −18 °C, and these were used for the X-ray data collection.
Yield: 0.19 g, 40%. Anal. Calcd for C7H6BrO5SbW (555.6): C, 15.1; H,
1.1. Found: C, 14.7; H, 1.5. IR (CH2Cl2/cm−1): 2078m, 1996w, 1951vs,
1
cm−1): 2138m, 2056s, 2042(sh). H NMR (CDCl3): 2.57 (s, Me).
13C{1H} NMR (CDCl3): 17.3 (Me), 205 (br, CO). 55Mn NMR
(CH2Cl2): −1672 (w1/2 = 1400 Hz).
[Mn(CO)3(SbMe2Br)3][CF3SO3]. [Mn(CO)5Br] (0.2 g, 0.73
mmol) and Ag[CF3SO3] (0.19 g, 0.73 mmol) were dissolved in
acetone (30 mL), and the mixture was refluxed for 1 h, resulting in a
yellow solution and a white solid, which was removed by filtration.
The solvent from the filtrate was removed in vacuo, leaving a yellow
oil, which was redissolved in CH2Cl2 (20 mL), forming a yellow
solution. A solution of SbMe2Br (2.18 mmol) in toluene (40 mL) was
added, and the mixture stirred for 16 h. The volume was reduced
in vacuo until a yellow precipitate formed, which was isolated by
filtration and dried in vacuo. Refrigeration of the filtrate (3 d) gave
small yellow crystals and a small amount of insoluble white
decomposition product. Anal. Calcd for C10H18Br3F3MnO6SSb3
(983.2): C, 12.2; H, 1.9. Found: C 12.3, H 1.3. IR (Nujol/cm−1):
−1
1
br; (Nujol/cm ): 2077s, 1993w, 1962sh, 1953s. H NMR (CDCl3):
2.06 (s, SbMe). 13C{1H} NMR (CDCl3): 12.3 (SbMe), 195.6 (1JWC
=
118 Hz, CO), 198.3 (1JWC = 162 Hz, CO).
[Cr(CO)5(SbMe2Br)]. The preparation was similar to that for
[W(CO)5(SbMe2Br)], from Cr(CO)6 (0.19 g, 0.86 mmol) and
SbMe2Br (0.20 g, 0.86 mmol). Yellow crystals grew from the filtrate.
Yield: 0.12 g, 33%. Anal. Calcd for C7H6BrCrO5Sb (423.8): C, 19.8;
H, 1.4. Found: C, 20.4; H, 1.5. IR (CH2Cl2/cm−1): 2068m, 1996w,
1
1
1951vs, br; (Nujol/cm−1): 2069s, 1991m, 1966m, 1952s. H NMR
2039s, 1984m, 1973s, 1969sh; (CH2Cl2/cm−1): 2040s, 1974s, br. H
(CDCl3): 1.97 (s, SbMe). 13C{1H} NMR (CDCl3): 12.1 (SbMe),
215.9 (CO), 221.8 (CO).
NMR (CDCl3): 2.37 (s, Me). 13C{1H} NMR (CDCl3): 15.0 (Me),
224.7 (CO). 55Mn NMR (CH2Cl2): −1381 (w1/2 = 450 Hz).
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a
Table 2. Crystal Data and Structure Refinement Details
[SbMeCl2-
(1,10-phen)]
[SbMeBr2-
(1,10-phen)]
[SbMeBr2-
(2,2′-bipy)]
[SbMeBr2(OPPh3)2] [SbMeBr2(OPMe3)2] [SbMeCl2(OPPh3)2]
formula
C37H33Br2O2P2Sb
853.14
C7H21Br2O2P2Sb
480.75
C37H30Cl2O2P2Sb
761.20
C13H11Cl2N2Sb
387.89
C13H11Br2N2Sb
476.81
monoclinic
Cm (no. 8)
7.7806(15)
16.546(3)
5.5726(10)
90
C11H11Br2N2Sb
452.79
M
cryst syst
space group
a [Å]
monoclinic
C2/c (no. 15)
17.128(4)
12.347(2)
16.956(4)
90
monoclinic
P21/c (no. 14)
20.039(3)
9.235(2)
19.831(4)
90
monoclinic
C2/c (no. 15)
17.307(3)
12.339(3)
17.099(4)
90
monoclinic
P21/m (no. 11)
5.4428(5)
15.996(3)
7.7092(15)
90
monoclinic
P21/m (no. 11)
5.7015(10)
16.459(3)
7.0828(10)
90
b [Å]
c [Å]
α [deg]
β [deg]
104.979(10)
90
117.145(10)
90
104.664(15)
90
96.317(10)
90
98.455(10)
90
95.639(10)
90
γ [deg]
U [Å3]
3464.1(12)
4
3265.8(11)
8
3532.6(13)
4
667.12(19)
2
709.6(2)
2
661.46(18)
2
Z
μ(Mo Kα) [mm−1]
total no. reflns
unique reflns
Rint
3.227
6.761
1.054
2.450
7.558
8.101
19 016
37 437
25 941
8803
4534
11 179
3986
7450
4054
1565
1545
1574
0.060
0.056
0.040
0.035
0.028
0.046
no. of params, restraints
205, 0
253, 0
204, 0
90, 4
91, 5
81, 4
b
R1 [Io > 2σ(Io)]
0.040
0.049
0.042
0.045
0.018
0.043
R1 [all data]
0.050
0.059
0.054
0.046
0.018
0.047
b
wR2 [Io > 2σ(Io)]
0.094
0.101
0.103
0.107
0.041
0.105
wR2 [all data]
0.099
0.104
0.111
0.107
0.041
0.107
[Mn(CO)5(SbMe2Br)]
[CF3SO3]
[Mn(CO)3(SbMe2Br)3]
[CF3SO3]·C6H5Me
[Cr(CO)5(SbMe2Br)] [W(CO)5(SbMe2Br)] [W(CO)5(SbMeBr2)]
formula
M
C8H6BrF3MnO8SSb
575.79
C17H26Br3F3MnO6SSb3
1075.36
C7H6BrCrO5Sb
423.78
C7H6BrO5SbW
555.63
C6H3Br2O5SbW
620.50
cryst syst
space group
a [Å]
monoclinic
P21/c (no. 14)
13.023(2)
7.6958(14)
16.455(3)
90
monoclinic
P21/n (no. 14)
14.4226(5)
14.6672(10)
14.5421(10)
90
monoclinic
P21/c (no. 14)
16.261(5)
6.488(5)
12.287(5)
90
triclinic
orthorhombic
Pbca (no 61)
6.5876(10)
12.473(3)
31.209(6)
90
P1 (no. 2)
̅
6.6070(5)
17.0844(15)
24.302(2)
105.828(4)
96.329(4)
97.999(5)
2581.7(4)
8
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
U [Å3]
93.553(7)
90
102.658(3)
90
107.735(5)
90
90
90
1646.0(5)
4
3001.5(3)
4
1234.7(11)
4
2564.4(8)
8
Z
μ(Mo Kα) [mm−1]
total no. reflns
unique reflns
Rint
5.026
7.193
6.300
14.089
17.300
18 193
44 598
14 744
42 746
18 132
3727
6850
2377
11 817
2951
0.034
0.039
0.060
0.039
0.043
no. of params,
restraints
235, 0
308, 0
136, 0
541, 0
137, 0
b
R1 [Io > 2σ(Io)]
0.061
0.0667
0.154
0.158
0.023
0.025
0.051
0.053
0.065
0.066
0.180
0.028
0.033
0.065
0.069
0.028
0.036
0.056
0.060
R1 [all data]
b
wR2 [Io > 2σ(Io)]
wR2 [all data]
0.182
a
b
Common items: temperature = 120 K; wavelength (Mo Kα) = 0.71073 Å; θ(max) = 27.5°. R1 = ∑∥Fo| − |Fc∥/∑|Fo|. wR2 = [∑w(Fo2 − Fc2)2/
4
∑wFo ]1/2
.
X-ray Crystallography. Details of the crystallographic data
collection and refinement parameters are given in Table 2. Crystals
were obtained as described above. Data collection used a Nonius Kappa
CCD diffractometer fitted with monochromated (confocal mirrors) Mo
Kα X-radiation (λ = 0.71073 Å). Crystals were held at 120 K in a
nitrogen gas stream. Structure solution and refinement were generally
routine34,35 except as described below, with hydrogen atoms on C were
added to the model in calculated positions and using the default C−H
distance. The structures of [SbMeX2(OPPh3)2] (X = Cl or Br) revealed
the Me group to be disordered over two sites related by the
crystallographic 2-fold axis, although this was modeled satisfactorily.
For [SbMeX2(2,2′-bipyridyl)] (X = Cl, Br) the H atoms on the Me
group were placed using AFIX 137. The Z value of 8 (Z′ = 4) for
[W(CO)5(Me2BrSb)] was unexpected, but appears to be genuine,
probably resulting from the long Sb···O intermolecular contacts (vide
supra). The anion in [Mn(CO)5(SbMe2Br)][CF3SO3] is disordered
and was modeled well as two overlapping half-occupancy triflates.
CCDC reference numbers 850439 to 850449 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
CONCLUSIONS
■
This work has established that halostibines can behave as both
Lewis acids and Lewis bases to appropriate neutral ligands and
1032
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Organometallics
Article
Schoneboom, J.; Werner, H. Organometallics 1999, 18, 952.
̈
to metal fragments, respectively. The boundaries of their Lewis
acid and Lewis base behavior have been determined, and the
structural consequences of the different behaviors probed.
Spectroscopic and structural studies show that where they
behave as Lewis acids, only small differences from the parent
halostibine are observed, whereas their Lewis base behavior
results in significant changes in the geometric parameters at Sb.
The studies reveal that the bonding between the halostibine
and transition metal carbonyl fragments varies significantly
across the series SbR3, SbR2X, SbRX2, showing that the
anticipated decrease in σ-donation is accompanied by an
unexpectedly large increase in π-acceptance as the number of X
groups increases. Typically, π-acceptance in SbR3 systems is
only ever modest (considerably less important than in PR3) due
to the large orbital size and low electronegativity of the Sb
atom.
Intermolecular interactions are clearly evident in the new
metal carbonyl complexes, including both M−CO···Sb contacts
(producing extended chain structures in the solid state) in the
Group 6 pentacarbonyl complexes and surprisingly strong
triflate O···Sb bonds evident in the manganese complexes. The
bond distances in the latter are approaching those of normal
covalent bonds and lead to very significant distortions at the Sb
atoms. This results in the antimony center functioning as an
electron pair donor and acceptor (both Lewis acid and Lewis
base) simultaneously, and such behavior may have important
implications in the reaction chemistry of halostibine complexes.
The first example of three halostibines on a single metal
center is reported and taken together with the clean alkylation
of [W(CO)5(SbMe2Br)] to [W(CO)5(SbMe2R)] (R = Me or
nBu) using MeLi or nBuLi, respectively, suggests that this
chemistry may have potential for metal-templated routes to
polystibines.
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ASSOCIATED CONTENT
* Supporting Information
Cif files for the crystal structures described, together with
packing diagrams showing the Sb···O intermolecular contacts in
[W(CO)5(SbMeBr2)] and [Cr(CO)5(SbMeBr2)]. This materi-
al is available free of charge via the Internet at http://pubs.acs.
org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: G.Reid@soton.ac.uk.
■
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ACKNOWLEDGMENTS
■
We thank the EPSRC for support (EP/F038763/1) and for a
studentship (S.L.B.). We also thank Dr. M. Webster for
assistance with the X-ray crystallographic studies.
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