Synthesis, structural characterization and reactivities of hexaosmium carbonyl clusters with six-membered cyclic thioether and thioxane ligands

Article abstract of DOI:10.1039/a900808j

Cluster complexes [Os₆(CO)₁₅{S(CH₂)₄CH₂} {μ-S(CH₂)₄CH₂}] 1 and [Os₅(CO)₁₅{S(CH₂)₄CH₂}] 2 were isolated from the reaction of [Os₆(CO)₁₆(MeCN)₂] with S(CH₂)₄CH₂ (L¹) in 24 and 22% yields respectively. Cluster degradation from 1 to 2 can be achieved by addition of a stoichiometric quantity of L¹ in CHCl₃ under reflux. Monosubstituted cluster complex [Os₆(CO)₁₆{μ-S(CH₂)₃SCH ₂}] 3 containing a S(CH₂)₃SCH₂ (L²) ligand bridging across an Os-Os edge via one of the sulfur atoms was isolated in good yield from a similar reaction. However, similar reaction between [Os₆(CO)₁₆(MeCN)₂] and S(CH₂)₂SCH₂CH₂ (L³) gave [Os₆(CO)₁₆{S(CH₂)₂SCH ₂CH₂}₂] 4 as the major product instead. The two thio ligands are found to co-ordinate in terminal fashion to two different vertices of the Os₆ core. Interaction of tridentate sulfur donor ligand SCH₂SCH₂SCH₂ (L⁴) with [Os₆(CO)₁₆(MeCN)₂] afforded [Os₆(CO)₁₄-(μ-CO)(SCH₂SCH ₂SCH₂)] 5 in which the ligand L⁴ was found to cap over a triangular face of the Os₆ skeleton. Treatment of mixed-donor ligand S(CH₂)₂OCH₂CH₂ (L⁵) yielded a pair of isomeric complexes [Os₆(CO)₁₅-{(S(CH₂)₂OCH ₂CH₂} {μ-S(CH₂)₂OCH₂CH₂}] 6 and [Os₆(CO)₁₅{O(CH₂)₂SCH ₂CH₂) {μ-S(CH₂)₂OCH₂CH₂}] 7. Carboxylation of 6 gave [Os₆(CO)₁₆{μ-S(CH₂)₂OCH ₂CH₂}] 8 and [Os₆(CO)₁₈]. Hydrogenation of 6 led to the formation of dihydrido cluster [Os₆(CQ)₁₅(μ-H)₂{S(CH₂) ₂OCH₂CH₂} {μ-S(CH₂)₂OCH₂CH₂}] 9. The metal skeleton of 9 can be described as two fused tetrahedra sharing a common edge. All new compounds were fully characterized by spectroscopic and analytical techniques. In addition the structures of 1, 2, 3, 4, 5, 6, 8 and 9 were established by X-ray crystallography.

Full text of DOI:10.1039/a900808j

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Synthesis, structural characterization and reactivities of
hexaosmium carbonyl clusters with six-membered cyclic thioether
and thioxane ligands
Kelvin Sze-Yin Leung and Wing-Tak Wong*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong,
P. R. China
Received 29th January 1999, Accepted 30th April 1999
Cluster complexes [Os6(CO)15{S(CH2)4CH2}{µ-S(CH2)4CH2}] 1 and [Os5(CO)15{S(CH2)4CH2}] 2 were isolated from
the reaction of [Os6(CO)16(MeCN)2] with S(CH2)4CH2 (L1) in 24 and 22% yields respectively. Cluster degradation
from 1 to 2 can be achieved by addition of a stoichiometric quantity of L1 in CHCl3 under reflux. Monosubstituted
cluster complex [Os6(CO)16{µ-S(CH2)3SCH2}] 3 containing a S(CH2)3SCH2 (L2) ligand bridging across an Os–Os
edge via one of the sulfur atoms was isolated in good yield from a similar reaction. However, similar reaction between
[Os6(CO)16(MeCN)2] and S(CH2)2SCH2CH2 (L3) gave [Os6(CO)16{S(CH2)2SCH2CH2}2] 4 as the major product
instead. The two thio ligands are found to co-ordinate in terminal fashion to two different vertices of the Os6 core.
Interaction of tridentate sulfur donor ligand SCH2SCH2SCH2 (L4) with [Os6(CO)16(MeCN)2] afforded [Os6(CO)14-
(µ-CO)(SCH2SCH2SCH2)] 5 in which the ligand L4 was found to cap over a triangular face of the Os6 skeleton.
Treatment of mixed-donor ligand S(CH2)2OCH2CH2 (L5) yielded a pair of isomeric complexes [Os6(CO)15-
{S(CH2)2OCH2CH2}{µ-S(CH2)2OCH2CH2}] 6 and [Os6(CO)15{O(CH2)2SCH2CH2}{µ-S(CH2)2OCH2CH2}] 7.
Carboxylation of 6 gave [Os6(CO)16{µ-S(CH2)2OCH2CH2}] 8 and [Os6(CO)18]. Hydrogenation of 6 led to the
formation of dihydrido cluster [Os6(CO)15(µ-H)2{S(CH2)2OCH2CH2}{µ-S(CH2)2OCH2CH2}] 9. The metal skeleton
of 9 can be described as two fused tetrahedra sharing a common edge. All new compounds were fully characterized
by spectroscopic and analytical techniques. In addition the structures of 1, 2, 3, 4, 5, 6, 8 and 9 were established by
X-ray crystallography.
S
S
Introduction
Following the industrial applications of hydrodesulfurization in
fossil fuel purification,1 much interest has been shown in cluster
compounds bearing sulfur heteroatoms. A new class of cluster
derivatives containing sulfido ligands has been extensively
studied and reported in tri-,2 tetra-,3 and penta-4 osmium
systems by Adams and co-workers over the past decades.
These have been widely used in the systematic build-up of high
nuclearity clusters5 as exemplified by the thermally activated
coupling of [Os4(CO)13(µ3-S)2] and [Os3(CO)10(MeCN)2] to
yield the heptanuclear cluster compound [Os7(CO)20(µ4-S)2].6
The ring-opening oligomerization of thiirane7 and thietane8
have been shown to be catalysed by [Os6(CO)16(MeCN)2] and
S
S
S
L2
L3
L1
S
S
S
S
O
L4
L5
MeCN ligand to yield mono- and di-substituted cluster
derivatives has previously been reported in the triosmium
system.11,12 Cluster 1 consists of an identical metal-core archi-
tecture to that in the parent cluster [Os6(CO)18]. A perspective
drawing of cluster 1 with the atomic numbering scheme is
shown in Fig. 1. Selected bond parameters are presented in
Table 1. The metal–metal bond distances are comparable to the
corresponding values in [Os6(CO)18].13 However, the Os(1)–
Os(4) vector [2.931 Å] is significantly longer than Os(1)–Os(3)
[2.823 Å], leading to a ‘distorted’ bicapped tetrahedron. The
observed bond elongation may be attributed to steric influence
between the bulky L1 and equatorial CO on Os(4). The Os(2)–
Os(5) bond distance is the shortest M–M bond length [2.679 Å]
which might be due to the ‘clamping’ effect of the bridging
ligand. Two ligands L1 are co-ordinated to the Os6 core in a
terminal and a bridging mode respectively. According to the
eighteen electron rule, the vertices Os(1) and Os(6) are electron
deficient and hence susceptible to nucleophilic attack.14,15
Similar edge bridging of heteroatoms across a central tetra-
[Os4(CO)11(SCH2CH2CH2)(µ-H)4] respectively. Recently we
have also reported some triosmium alkylidyne clusters contain-
ing cyclic thioether ligands that undergo facile isomerization.9
However, further explorations on these cyclic sulfur donor lig-
ands in larger cluster systems are relatively rare. Herein we
report the syntheses, spectroscopic studies and reactivities
of a series of cyclic sulfur-containing hexaosmium carbonyl
clusters.
Results and discussion
The reaction (Scheme 1) of preformed labile cluster [Os6(CO)16-
(MeCN)2] with L1 yielded the hexanuclear [Os6(CO)15-
{S(CH2)4CH2}{µ-S(CH2)4CH2}] 1 and pentanuclear [Os5(CO)15-
{S(CH2)4CH2}] 2 species together with small amount of the
known cluster [Os3(CO)12].10 Facile replacement of the labile
J. Chem. Soc., Dalton Trans., 1999, 2077–2086
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L1
Refluxing CHCl3
Os
Os
Os
Os
Os
Os
Os
S
+
S
Os
Os
S
S
Os
S
S
Os
Os
Os
Os
4
Os
Os
L3
Os
S
2
1
S
S
S
L1
O
L4
Os
Os
Os
[Os6(CO)16(MeCN)2]
S
Os
Os
Os
Os
L5
H
H2
Os
Os
L2
5
Refluxing CHCl3
Os
S
O
Os
H
Os
S
O
S
S
9
O
Os
Os
Os
Os
Os
S
Os
Os
Os
Os
S
Os
Os
Os
+
[Os6(CO)18]
O
Os
Os
Os
Os
6
CO
+
3
Os
Refluxing CHCl3
Os
7
8
[Os6(CO)15{O(CH2)2SCH2CH2}{m-S(CH2)2OCH2CH2}]
Scheme 1
Table 1 Selected bond distances (Å) and angles (Њ) for cluster 1
Table 2 Selected bond distances (Å) and angles (Њ) for cluster 2
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
2.740(1)
2.823(1)
2.931(1)
2.859(1)
2.753(1)
2.679(1)
2.766(1)
2.845(1)
2.838(1)
Os(4)–Os(5)
Os(4)–Os(6)
Os(5)–Os(6)
Os(1)–S(1)
Os(2)–S(2)
Os(5)–S(2)
2.795(1)
2.848(1)
2.714(1)
2.368(5)
2.269(4)
2.276(5)
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
2.893(1)
2.765(1)
2.776(1)
2.832(1)
2.828(1)
2.833(1)
2.790(1)
Os(3)–Os(5)
Os(4)–Os(5)
Os(2)–S(1)
2.773(1)
2.813(1)
2.430(4)
2.49(1)
Os(4) ؒ ؒ ؒ C(4)
Os(2)–C(4)–O(4)
158(1)
Os(2)–S(2)–Os(5)
Os(5)–Os(2)–S(2)
S(2)–Os(5)–Os(2)
72.2(1)
54.0(1)
53.8(1)
Fig. 2 Molecular structure of cluster 2.
SCH2CMe2CH2Cl)],18 respectively. Both ligands are in the
stable chair conformation.
Fig. 1 Molecular structure of cluster 1 showing the atom-labelling
scheme for non-hydrogen atoms.
Cluster 2 was found to be a pentanuclear osmium compound
having a trigonal bipyramidal metal core arrangement with fif-
teen terminally bonded carbonyl ligands (Fig. 2). Selected bond
parameters are in Table. 2. The Os(2) atom, which has four
terminally bonded ligands, is considerably electron-rich and all
Os–Os vectors involving Os(2) are significantly longer than
other metal–metal bonds in the structure. This phenomenon is
hedron is also observed in [Os6(CO)16(µ-H)(µ-C8H11)].16
However, the Os(2)–S(2) and Os(5)–S(2) distances [2.269(4)
and 2.276(5) Å, respectively] are considerably shorter than
those found in other thietane and thiolate bridging analogues
[Os3(CO)10(µ-SCH2CMe2CH2)]17
and
[Os3(CO)10(µ-H)(µ-
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Fig. 4 Molecular structure of cluster 4.
Fig. 3 Molecular structure of cluster 3.
generally in line with those observed in other Os5(CO)15(L)
20
[L = CO,19 PMe3 or P(OMe)3 21] analogues. Besides, this kind
of electronic imbalance within a metal core leads to the form-
ation of ‘semibridging’ carbonyl ligands. Cotton22 has sug-
gested that this type of interaction could alleviate the polar
nature of donor–acceptor metal–metal bonds. Cluster 2 also
manifests this effect in C(4)–O(4) [Os(2)–C(4)–O(4) 158Њ;
Os(4) ؒ ؒ ؒ C(4) 2.49 Å]. On the electronic grounds, as in the
rationalization of site preference in cluster 1, nucleophilic
attack would be expected on the apical atoms which are
relatively electron deficient. However, the solid state structure
of compound 2 revealed the co-ordination of L1 in the equa-
torial plane of the metal core. This observation can be attrib-
uted to the better σ-donating ability of L1, together with three
carbonyl ligands, stabilizing the dative metal–metal bonds
originated from electron rich Os(2).23
Fig. 5 Molecular structure of cluster 5.
four groups of well defined multiplets in close proximity due to
two individual ligands in the same magnetic environment. The
molecular structure of cluster 4 established by X-ray analysis is
depicted in Fig. 4 and some important bond parameters are
given in Table 5. The Os6 metal skeleton contains a more sym-
metrical ligand deposition with a non-crystallographic twofold
axis passing through the midpoints of Os(3)–Os(4) and Os(2)–
Os(5). Two ligands are terminally bonded to the two vertices of
the polyhedron. Both S(2) and S(4) are unco-ordinated and
might be able to act as donor groups for further cluster build-
up. However, cluster 4 does not react with labile clusters such as
[Os6(CO)16(MeCN)2] and [Os3(CO)10(MeCN)2]24 to give linked
clusters. Attempts to generate a pentanuclear species as in com-
pound 1 using an excess of ligand at elevated reaction temper-
ature only led to cluster decomposition. It is also noteworthy
that no C–S bond cleavages were observed under forcing
thermolytic conditions which contrasts to those findings in
triosmium analogues.25
Using an excess of ligand in the reaction leads to higher
yields of compounds 1 and 2 and also the disappearance of the
known cluster [Os3(CO)12]. However, a number of additional
products in relatively low yields are also observed and are
proposed to be multi-substituted hexaosmium species based on
the spectroscopic and elemental analyses. Treatment of 1 with a
stoichiometric quantity of L1 in refluxing CHCl3 leads to the
formation of 2. Therefore, we believe 1 is likely to be an inter-
mediate for the formation of 2. Unfortunately, we are not able
to isolate and characterize the mononuclear osmium fragment
formed in this conversion.
Under similar reaction conditions, both 1,3-dithiane (L2)
and 1,4-dithiane (L3) reacted with [Os6(CO)16(MeCN)2]. How-
ever, the major products isolated from these reactions are rather
different from that with L1. Clusters 3 and 4 were isolated in
moderate yields. Positive FAB MS of 3 revealed an intense
molecular envelope centre at m/z 1709 (Table 3), which along
Treatment of ligand L4 with an equivalent of [Os6(CO)16-
(MeCN)2] gave a moderate yield of cluster 5 as the major
product isolated upon TLC purification. The molecular
structure of 5 is shown in Fig. 5 and selected bond lengths
and angles are summarized in Table 6. The tridentate ligand
asymmetrically caps the triangular face defined by Os(1)–
Os(2)–Os(4) forming a cage and slightly tilted towards Os(1)–
Os(2) edge as is evident from the non-orthogonal bond
angles S(1)–Os(1)–Os(4), S(2)–Os(2)–Os(4) and S(3)–Os(4)–
C(9). Facial cappings by this type of ligand have also
1
with the H NMR spectroscopy suggested that it consists of a
monosubstituted ligand in a Os6 core. Its molecular structure
was ascertained by a single crystal X-ray analysis. A perspective
drawing of it with atomic numbering scheme is shown in Fig. 3
and important bond parameters are summarized in Table 4. Its
metal core arrangement is similar to that of 1, comprising six
osmium atoms in a bicapped tetrahedral mode. The Os–Os
bond lengths in the structure span a range [2.713 to 2.867 Å]
which is commonly observed for Os–Os single bonds except for
the one bridged by the thio ligand [Os(2)–Os(5) 2.662 Å].
The 1H NMR spectra can be interpreted with reference to the
solid state structure of compound 4. The spectrum of 4 exhibits
been observed in [Ru3(CO)9(SCH2SCH2SCH2)],26 [Rh4(CO)9-
(SCH2SCH2SCH2)]27 and [Ir4(CO)9(SCH2SCH2SCH2)].28 The
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Table 3 Spectroscopic data for clusters 1 to 9
Complex
IR, ν(CO)a/cmϪ1
1H NMR, δ(J/Hz)b
Mass, m/zc
2073s, 2018s,
2005s, 1983m
3.07–3.12 (m, 4 H, Ha, Hb)
2.76–2.83 (m, 4 H, HaЈ or HbЈ)
1.41 (m, 1 H, HeЈ or HfЈ)
1.35 (m, 1 H, He or Hf)
1.11 (m, 2 H, HcЈ or HdЈ)
0.96 (m, 2 H, Hc or Hd)
0.87 (m, 2 H, Hc or HdЈ)
0.77 (m, 2 H, Hc or Hd)
0.57 (m, 1 H, HeЈ or HfЈ)
0.35 (m, 1 H, He or Hf)
1765
(1765)
2089w, 2068m,
2055s, 2032vs,
2010m, 1979w
2.86 (m, 2 H, Ha or Hb)
2.47 (m, 2 H, Ha or Hb)
1.35 (m, 1 H, He or Hf)
0.96 (m, 2 H, Hc or Hd)
0.77 (m, 2 H, Hc or Hd)
0.35 (m, 1 H, He or Hf)
1473
(1473)
2080w, 2068w,
2024 (br)
4.34 (m, 2 H, Ha, HaЈ)
3.57 (m, 2 H, Hb, HbЈ)
2.05 (m, 2 H, Hd, HdЈ)
1.96 (m, 2 H, Hc, HcЈ)
1709
(1709)
2080
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Table 3 (Contd.)
Complex
IR, ν(CO)a/cmϪ1
1H NMR, δ(J/Hz)b
Mass, m/zc
2093w, 2080w,
2064s, 2032s,
2024vs, 2001s,
1941w
3.78–3.80 (m, 4 H, Ha, HaЈ or Hb, HbЈ)
2.86–2.92 (m, 4 H, Hb, HbЈ or Ha, HaЈ),
1.92–2.02 (m, 4 H, Hc, Hd or HcЈ, HdЈ)
1.67–1.71 (m, 4 H, HcЈ, HdЈ or Hc, Hd)
1829
(1829)
2084s, 2039s,
2020vs, 1999m,
1968w
2.86–2.92 (m, 2 H, Ha, Hb)
1.92–2.02 (m, 2 H, He, Hf)
1.67–1.71 (m, 2 H, Hc, Hd)
1699
(1699)
2078s, 2020vs,
2006vs, 1985 (br)
3.34–3.43 (m, 4 H, Ha, Hb, HaЈ, HbЈ)
2.45–2.51 (m, 4 H, Hc, Hd, HcЈ, HdЈ)
1769
(1769)
2081s, 2019vs,
2005vs, 1983 (br)
4.67–4.78 (m, 2 H, HaЈ or HbЈ)
4.41–4.44 (m, 2 H, HcЈ or HdЈ)
3.38–3.41 (m, 2 H, Ha or Hb)
2.62–2.78 (m, 2 H, Hc or Hd)
1769
(1769)
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Table 3 (Contd.)
Complex
IR, ν(CO)a/cmϪ1
1H NMR, δ(J/Hz)b
Mass, m/zc
2064s, 2037m,
2024s
3.91–3.94 (m, 2 H, Ha or Hb)
2.67–2.69 (m, 2 H, Hc or Hd)
1693
(1693)
2084m, 2033m,
2020s, 2006vs,
1979w
3.68–3.75 (m, 4 H, Ha, Hb, HaЈ, HbЈ)
2.76–2.85 (m, 4 H, Hc, Hd, HcЈ, HdЈ)
Ϫ11.98 (s, 1 H, OsH)
1770
(1770)
Ϫ15.98 (s, 1 H, OsH)
a In CH2Cl2. b In C6D6. c Simulated values given in parentheses.
Table 4 Selected bond distances (Å) and angles (Њ) for cluster 3
Table 5 Selected bond distances (Å) for cluster 4
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
2.713(2)
2.861(2)
2.836(2)
2.865(2)
2.771(3)
2.662(2)
2.755(2)
2.852(2)
2.849(2)
Os(4)–Os(5)
Os(4)–Os(6)
Os(5)–Os(6)
Os(2)–S(1)
Os(5)–S(1)
2.759(2)
2.867(2)
2.714(2)
2.27(1)
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
2.869(2)
2.829(2)
2.808(2)
2.794(2)
2.779(2)
2.756(2)
2.787(2)
2.786(2)
Os(3)–Os(6)
Os(4)–Os(5)
Os(4)–Os(6)
Os(5)–Os(6)
2.797(2)
2.799(2)
2.828(2)
2.876(2)
2.26(1)
Os(1)–S(1)
Os(6)–S(3)
2.36(1)
2.39(1)
Os(2)–S(1)–Os(5)
Os(5)–Os(2)–S(1)
S(1)–Os(5)–Os(2)
71.9(3)
53.9(3)
54.3(3)
metal–metal bond lengths in the triangle lie in the range of
2.793 to 2.836 Å which are comparable to the corresponding
Os–Os vectors in [Os6(CO)18].13 All the carbonyl ligands are
terminally bonded except the one bridging the polyhedral edge
Os(2)–Os(5) which leads to the shortest metal–metal bond dis-
tance in the structure. Cluster 5 is rather stable and does not
react with molecular hydrogen or carbon monoxide even under
forcing conditions (in refluxing CHCl3 for 24 h). The strong and
rigid ligand chelation of ligand L4 may account for the relative
inertness of the complex towards hydrogenation and carboxyl-
ation.
the reactions with 1,4-thioxane (L5) containing hetero-donor
atoms S and O. The molecular structure of 6 is illustrated in
Fig. 6 and pertinent bond parameters are given in Table 7. The
bonding architecture of cluster 6 is similar to that of 1 with all
their bonding parameters comparable. All attempts to obtain
suitable single crystals of 7 were not successful owing to its
instability in solution, however it is thought to be of similar
1
structure to 6 according to FAB MS and H NMR spectro-
scopies. In fact, the high resemblances between the IR patterns
of 6 and 7, along with their identical molecular ion envelopes
exhibited in mass spectra, imply that both structures have simi-
lar carbonyl ligand depositions with disubstituted ligand L5.
Compounds 6 and 7 were isolated as a pair of isomers from
2082
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Table 6 Selected bond distances (Å) and angles (Њ) for cluster 5
Table 9 Selected bond distances (Å) and angles (Њ) for cluster 9
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
Os(4)–Os(5)
Os(4)–Os(6)
2.793(3)
2.740(2)
2.836(2)
2.845(3)
2.824(3)
2.663(3)
2.733(3)
2.791(3)
2.863(3)
2.835(3)
2.812(3)
Os(5)–Os(6)
Os(1)–S(1)
Os(2)–S(2)
Os(4)–S(3)
2.704(3)
2.38(1)
2.42(1)
2.43(1)
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
Os(4)–Os(5)
2.896(1)
2.808(1)
2.869(2)
2.888(1)
2.841(2)
2.771(2)
2.879(2)
2.872(2)
2.826(1)
Os(4)–Os(6)
Os(5)–Os(6)
Os(1)–S(1)
Os(2)–S(2)
Os(5)–S(2)
2.778(2)
2.857(2)
2.380(7)
2.321(7)
2.278(6)
S(1)–Os(1)–Os(4)
S(1)–Os(1)–Os(2)
S(2)–Os(2)–Os(1)
S(2)–Os(2)–Os(4)
S(3)–Os(4)–Os(2)
S(3)–Os(4)–Os(1)
94.6(3)
95.0(3)
92.3(3)
95.9(3)
89.7(3)
90.1(3)
Os(2)–S(2)–Os(5)
S(2)–Os(5)–Os(3)
Os(5)–Os(3)–Os(2)
Os(3)–Os(2)–S(2)
99.1(2)
88.8(2)
74.7(4)
87.7(2)
Table 7 Selected bond distances (Å) and angles (Њ) for cluster 6
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
2.733(1)
2.843(1)
2.924(1)
2.850(1)
2.764(1)
2.679(1)
2.754(1)
2.855(1)
2.848(1)
Os(4)–Os(5)
Os(4)–Os(6)
Os(5)–Os(6)
Os(1)–S(1)
Os(2)–S(2)
Os(5)–S(2)
2.795(1)
2.837(1)
2.731(1)
2.385(4)
2.272(4)
2.284(4)
Os(2)–S(2)–Os(5)
Os(5)–Os(2)–S(2)
S(2)–Os(5)–Os(2)
72.0(1)
54.2(1)
53.8(1)
Table 8 Selected bond distances (Å) and angles (Њ) for cluster 8
Os(1)–Os(2)
Os(1)–Os(3)
Os(1)–Os(4)
Os(2)–Os(3)
Os(2)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(3)–Os(5)
Os(3)–Os(6)
2.708(1)
2.880(1)
2.857(1)
2.788(1)
2.865(1)
2.666(1)
2.769(1)
2.757(1)
2.884(1)
Os(4)–Os(5)
Os(4)–Os(6)
Os(5)–Os(6)
Os(2)–S(1)
Os(5)–S(1)
2.878(1)
2.841(1)
2.726(1)
2.281(5)
2.263(5)
Os(2)–S(1)–Os(5)
Os(5)–Os(2)–S(1)
S(1)–Os(5)–Os(2)
71.8(2)
53.8(1)
54.4(1)
Fig. 7 Molecular structure of cluster 8.
CO ligand from the metal framework afforded compound 8.
Complete conversion into the parent cluster, [Os6(CO)18], could
be achieved upon further refluxing of compound 6 in CHCl3
under a stream of CO for 48 h. Indeed, the metal–ligand archi-
tecture of 8 can be obtained in a similar reaction with L2, as
discussed previously. A perspective view of 8 is illustrated in
Fig. 7 with selected bond parameters in Table 8. As in 3, all
sixteen carbonyl ligands are terminally bonded in cluster 8 with
a thioxane ligand L5 bridging the edge Os(2)–Os(5) of the
central tetrahedron. The bonding parameters of both struc-
tures are in good agreement, except for the Os(3)–Os(6) vector
in cluster 8 which is slightly elongated, leading to a distorted
bicapped tetrahedron.
Hydrogenation of compound 6 induced bond cleavage along
the Os(2)–Os(5) edge and gave a new cluster 9. Its molecular
structure is presented in Fig. 8. Important bond parameters are
summarized in Table 9. The metal core consists of six osmium
atoms that are arranged in the form of two fused tetrahedra
sharing a common edge. This kind of metal skeleton arrange-
ment is rather rare in hexaosmium systems and a similar core
is reported for [Os6(CO)12(µ-CNMe2)2(µ3-SMe)2(µ-H)2].32 The
cleavage of the Os(2)–Os(5) bond not only gives a relatively
long non-bonding Os ؒ ؒ ؒ Os distance [3.50 vs. 2.679 Å in 6] but
also results in longer average Os–S distances [2.300 vs. 2.273 in
1 and 2.278 Å in 6 respectively]. Both 1H NMR and a potential-
energy calculation33 suggested the presence of a pair of bridg-
ing hydrides across the Os(1)–Os(5) and Os(5)–Os(6) edges so
as to complete the co-ordination sphere by 86 CVE which the
edge-fused bi-tetrahedron should attain.34
Fig. 6 Molecular structure of cluster 6.
1
The only difference lies in their H NMR spectra, with a con-
siderably downfield shift shown by two groups of multiplets.
1
With reference to the H NMR spectrum of cluster 6, this is
unambiguously assigned to the terminally bonded ligand L5.
We believe the co-ordination of Os(1) via O atom in L5 results in
such changes in chemical shift. In the literature, the occurrence
of terminally co-ordinated O-donors is not uncommon and
there are many alkoxytriosmium clusters such as [Os3(CO)10-
n
(µ-H)(µ-OR)], R = H,29 Me30 or Bu.31 However, the difference
in chemical reactivities between 1 and 6 towards neutral mole-
cules such as CO and H2 can be attributed to the presence of the
reactive oxygen atom in L5, which conferred higher reactivities
to 6. Facile displacement of a terminally bonded atom S(1) by a
Experimental
All reactions and manipulations were carried out in an
J. Chem. Soc., Dalton Trans., 1999, 2077–2086
2083

View Article Online
mmol) in CH2Cl2 (35 cm3) under ambient conditions over a
period of 24 h afforded a deep brown reaction mixture. Purifi-
cation by TLC using hexane–CH2Cl2 (10:10 v/v) gave the
brown cluster 3 (Rf 0.45, 30 mg, 0.018 mmol, 29%) together
with several uncharacterized, low-yield products (Found: C,
14.1; H, 0.5; S, 1.8. Calc. for C10H4O8Os3S: C, 14.3; H, 0.5; S,
1.9%).
[Os6(CO)16{S(CH2)2SCH2CH2}2] 4. To a solution of [Os6-
(CO)16(MeCN)2] (92 mg, 0.055 mmol) in CH2Cl2 (30 cm3) was
added L3 (13 mg, 0.108 mmol). The reaction mixture was stirred
at room temperature for 6 h during which time it darkened.
Excess of solvent was then removed under reduced pressure,
yielding a deep brown residue. This was then dissolved in
CH2Cl2 (5 cm3) and subjected to preparative TLC on silica
using hexane–CH2Cl2 (10:30, v/v) as eluent. The brown cluster
4 was isolated as the major product (Rf 0.78, 32 mg, 0.017
mmol, 32%) (Found: C, 15.9; H, 0.9; S, 6.9. Calc. for C12H8O8-
Os3S2: C, 15.7; H, 0.9; S, 7.0%).
[Os6(CO)14(ì-CO)(SCH2SCH2SCH2)] 5. A solution of [Os6-
(CO)16(MeCN)2] (75 mg, 0.045 mmol) was stirred with L4 (5.4
mg, 0.045 mmol) in CH2Cl2 (30 cm3) at ambient temperature for
3 h. After reduction in solvent volume, the filtrate was separated
by preparative TLC on silica, with an eluent of hexane–CH2Cl2
(10:30 v/v). Compound 5 was isolated as the major product (Rf
0.35, 24 mg, 0.014 mmol, 31%) (Found: C, 12.5; H, 0.3; S, 5.5.
Calc. for C6H2O5Os2S: C, 12.7; H, 0.4; S, 5.7%).
Fig. 8 Molecular structure of cluster 9.
atmosphere of dry argon using standard Schlenk techniques.
All solvents were purified and dried by standard methods prior
to use.35 Chemicals were purchased from Aldrich chemicals and
used as received. The compound [Os6(CO)18]36 was obtained
from vacuum pyrolysis of [Os3(CO)12] and the activated cluster
[Os6(CO)16(MeCN)2] was prepared by the literature method.37
Infrared spectra were recorded on a Bio-Rad FTS-7 spec-
trometer, using 0.5 mm thick calcium fluoride solution cells,
proton NMR spectra on a Bruker DPX 300 spectrometer using
C6D6 with reference to SiMe4 (δ = 0) and mass spectra on a
Finnigan MAT 95 instrument by the fast atom bombardment
technique, using m-nitrobenzyl alcohol or α-thioglycerol as
the matrix solvent. Elemental analyses were conducted by
Butterworth Laboratories, UK. Routine separation of products
in air was performed by thin-layer chromatography (TLC) on
[Os6(CO)15{S(CH2)2OCH2CH2}{ì-S(CH2)2OCH2CH2}]
6
and [Os6(CO)15{O(CH2)2SCH2CH2}{ì-S(CH2)2OCH2CH2}] 7.
To a CH2Cl2 solution (40 cm3) of [Os6(CO)16(MeCN)2] (100 mg,
0.060 mmol), a dilute solution of an equivalent of L5 (0.56 cm3
diluted in 10 cm3 CH2Cl2) was added dropwise with stirring for
24 h under ambient conditions. After reduction of solvent to ca.
5 cm3, the residue was subjected to preparative TLC for purifi-
cation using hexane–CH2Cl2 as eluent (10:10 v/v). Two con-
secutive bands of nearly equal abundance were then eluted:
compound 6 (Rf 0.65, 20 mg, 0.011 mmol, 19%) and 7 (Rf 0.55,
18 mg, 0.010 mmol, 17%) (Found for 6: C, 15.8; H, 0.8; S, 3.7.
Calc. for C23H16O17Os6S2: C, 15.6; H, 0.9; S, 3.6%).
plates coated with Merck Kieselgel 60 GF254
.
Syntheses
Carboxylation of compound 6. Compound 6 (30 mg, 0.017
mmol) was dissolved in CHCl3 (10 cm3) to give a pale brown
solution. It was purged by a stream of carbon monoxide at 1
atm continuously for 3 h and the reaction monitored by spot
TLC and IR spectroscopy. Following evaporation of most of
the solvent, the residue was purified by preparative TLC using
hexane–CH2Cl2 (10:10 v/v) as eluent. Two brown bands were
eluted, namely [Os6(CO)18] (Rf 0.85, 6 mg, 0.004 mmol, 22%)
and cluster 8 (Rf 0.55, 8 mg, 0.005 mmol, 28%) (Found for 8: C,
14.5; H, 0.4; S, 1.9. Calc. for C20H8O17Os6S: C, 14.2; H, 0.5; S,
1.9%).
[Os6(CO)15{S(CH2)4CH2}{ì-S(CH2)4CH2}] 1 and [Os5(CO)15-
{S(CH2)4CH2}] 2. The complex [Os6(CO)16(MeCN)2] (112 mg,
0.067 mmol) was dissolved in CH2Cl2 (40 cm3) and stirred with
dropwise addition of one equivalent of L1 (0.70 cm3 diluted in
10 cm3 CH2Cl2) under ambient conditions. After the reaction
had proceeded for 4 h, the mixture gradually changed from
blackish brown to turbid brown. It was then filtered and the
volume reduced to 5 cm3 in vacuo. The residue was subsequently
purified by TLC using hexane–CH2Cl2 (20:10 v/v) as eluent.
The first yellow band was found to be [Os3(CO)12] (<5%, as
confirmed by IR spectroscopy). Two major bands of brown
cluster 1 (Rf 0.70, 28 mg, 0.016 mmol, 24%) and red cluster 2
(Rf 0.65, 22 mg, 0.015 mmol, 22%) were then eluted consecu-
tively (Found for 1: C, 16.9; H, 1.0; S, 3.6. Calc. for C25H20-
O15Os6S2 C, 17.0; H, 1.1; S, 3.6. Found for 2: C, 14.4; H, 0.7; S,
2.1. Calc. for C20H10O15Os5S: C, 14.5; H, 0.7; S, 2.2%).
Hydrogenation of compound 6. The procedure described
above was followed but using hydrogen instead of carbon mon-
oxide. Compound 9 (Rf 0.40, 8 mg, 0.005 mmol, 27%) was isol-
ated as the only major product along with traces of unchanged
6 (Found for 9: C, 15.8; H, 0.9; S, 3.7. Calc. for C23H18O17Os6S2:
C, 15.6; H, 1.0; S, 3.6%).
Conversion of compound 1 into 2. A deep brown solution of
compound 1 (40 mg, 0.02 mmol) in refluxing CHCl3 was added
to an equivalent of L1 (0.23 cm3 diluted in 5 cm3 CH2Cl2). Two
bands were eluted [hexane–CH2Cl2 (10:10 v/v)] which were
identified by solution IR as 2 (Rf 0.60, 18 mg, 0.012 mmol, 54%)
and unchanged 1 (Rf 0.45, 10 mg, 0.006 mmol, 24%).
Crystallography
Single crystals suitable for X-ray crystallographic analyses for
clusters 1–6, 8 and 9 were mounted on a glass fibre (except for 4
and 5) or a Lindermann glass capillary (4 and 5) using epoxy
resin. All samples except for 5 were obtained by slow evapor-
ation of a saturated toluene–CHCl3 solution at room temper-
ature for several days. Brown crystals of cluster 5 were obtained
[Os6(CO)16{ì-S(CH2)3SCH2}] 3. Treatment of equimolar L2
(7.2 mg, 0.06 mmol) with [Os6(CO)16(MeCN)2] (100 mg, 0.06
2084
J. Chem. Soc., Dalton Trans., 1999, 2077–2086

Table 10 Summary of crystal data and data collection parameters for clusters 1–6, 8 and 9
1
2
3
4ؒ0.5C7H8
5ؒ0.5C7H8
6
8
9
Empirical formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
C25H20O15Os6S2
1765.74
Orthorhombic
Pbca (no. 61)
20.998(1)
15.341(2)
21.779(2)
—
—
—
7015.7(9)
8
218.18
59908
C20H10O15Os5S
1473.35
Monoclinic
P21/c (no. 14)
9.062(1)
16.484(2)
18.892(2)
—
94.76(1)
—
2812.3(5)
4
C20H8O16Os6S2
1709.59
C27.5H20O16Os6S4
1875.89
Monoclinic
P21/n (no. 14)
9.181(1)
28.787(1)
16.533(1)
—
102.38(1)
—
4268.0(6)
4
C21.5H10O15Os6S3
1745.69
Orthorhombic
P212121 (no. 19)
10.120(1)
11.170(1)
29.792(3)
—
—
—
3367.7(5)
4
227.84
21402
C23H16O17Os6S2
1769.69
C20H8O17Os6S
1693.53
Monoclinic
P21/c (no. 14)
15.251(1)
12.358(2)
16.422(2)
—
102.29(1)
—
3024.1(5)
4
C23H18O17Os6S2
1769.69
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
11.976(3)
13.059(4)
9.823(2)
90.43(2)
90.44(2)
87.36(2)
1534.6(6)
2
10.314(1)
12.160(2)
14.420(2)
108.01(2)
92.80(1)
102.84(2)
1663.4(5)
2
8.992(1)
10.348(2)
18.637(2)
99.00(2)
94.67(1)
104.25(1)
1647.0(5)
2
β/Њ
γ/Њ
U/Å3
Z
µ(Mo-Kα)/cmϪ1
226.37
23912
249.32
4245
180.38
17557
230.10
14561
252.38
20502
232.39
10408
No. reflections collected
No. unique reflections
R
7090
0.050
5330
0.045
4013
0.067
6612
0.065
2904
0.062
5736
0.048
5863
0.053
5630
0.061
RЈ
0.051
25
0.134
0.053
25
0.079
0.067
25
0.064
0.070
25
0.115
0.050
25
0.100
0.062
25
0.077
0.063
25
0.089
0.065
25
0.080
T of data collection/ЊC
R(int)

View Article Online
5 (a) R. D. Adams, J. E. Babin and H.-S. Kim, Inorg. Chem., 1986, 25,
1122; (b) R. D. Adams, I. T. Horvath and P. Mathur, Organo-
metallics, 1984, 3, 623; (c) R. D. Adams and J.-G. Wang, Polyhedron,
1989, 8, 1437; (d) R. D. Adams, I. T. Horvath and L.-W. Yang,
J. Am. Chem. Soc., 1983, 105, 1533; (e) R. D. Adams, Z. Dawoodi,
D. F. Foust and B. E. Segmuller, J. Am. Chem. Soc., 1983, 105, 831.
6 R. D. Adams, I. T. Horvath, P. Mathur, B. E. Segmuller and
L.-W. Yang, Organometallics, 1983, 2, 1078.
7 R. D. Adams, G. Chen, S. Sun and Thomas A. Wolfe, J. Am. Chem.
Soc., 1990, 112, 868.
8 R. D. Adams and S. B. Falloon, Organometallics, 1995, 14, 4594.
9 W. Y. Wong and W. T. Wong, J. Chem. Soc., Dalton Trans., 1995,
2735.
10 M. R. Churchill and B. G. DeBoer, Inorg. Chem., 1977, 16, 878.
11 R. D. Adams, J. E. Cortopassi, J. H. Yamamoto and W. Wu,
Organometallics, 1993, 12, 4955.
12 A. J. Deeming, S. Donovan-Mtunzi, S. E. Kabir and P. J. Manning,
J. Chem. Soc., Dalton Trans, 1985, 1037.
13 R. Mason, K. M. Thomas and D. M. P. Mingos, J. Am. Chem. Soc.,
1973, 95, 3802.
14 B. F. G. Johnson and J. Lewis, Adv. Inorg. Radiochem., 1980, 24, 225.
15 C. Coutoure, D. H. Farrar, M. P. Gomez-Sal, B. F. G. Johnson,
R. A. Kamarudin, J. Lewis and P. R. Raithby, Acta Crystallogr.,
Sect. C, 1986, 42, 163.
as a solvate of stoichiometry 5ؒ0.5C6H5Me at Ϫ10 ЊC for 2 d.
Diffraction data were collected at room temperature on a
Rigaku AFC7R diffractometer (for cluster 3) using graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) and ω–2θ
scan technique. Unit-cell parameters were determined from 25
accurately centred reflections. The stability of the crystal was
monitored at regular intervals using three standard reflections
and no significant decay was observed. For clusters 1, 2, 4–6, 8
and 9, data were collected on a MAR research image plate
scanner using graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) and the ω scan technique. A summary of the
crystallographic data and structure refinement is listed in Table
10. All diffracted intensities were corrected for Lorentz-
polarization effects. Absorption correction by the ψ-scan
method was applied for structure 3. An approximate absorp-
tion correction by interimage scaling was applied for 1, 2, 4–6, 8
and 9. Space groups of all the crystals were determined from a
combination of Laue symmetry check, and their systematic
absences were confirmed by successful refinement of the struc-
tures. The structures were solved by a combination of direct
methods: SIR 8838 for 9, SIR 9239 for 1–6 and 8 along with
Fourier-difference techniques. Structure refinements were made
on F by full-matrix least-squares analysis. The hydrogen atoms
of the organic moieties were generated in their idealized posi-
tions whereas all metal hydrides were estimated by potential-
energy calculations.33 All calculations were performed on a
Silicon-Graphics computer using the program package
TEXSAN.40
16 C. Coutoure and D. H. Farrar, J. Chem. Soc., Dalton Trans., 1987,
2253.
17 R. D. Adams and M. P. Pompeo, J. Am. Chem. Soc., 1991, 113,
1619.
18 R. D. Adams, J. A. Belinski and M. P. Pompeo, Organometallics,
1991, 10, 2539.
19 C. R. Eady, B. F. G. Johnson, J. Lewis, B. R. Reichert and G. M.
Sheldrick, J. Chem. Soc., Chem. Commun., 1976, 271.
20 W. Wang, R. J. Batchelor, F. W. B. Einstein, C.-Y. Lu and R. K.
Pomeroy, Organometallics, 1993, 12, 3598.
21 R. Khattar, B. F. G. Johnson, J. Lewis, P. R. Raithby and M. J.
Rosales, J. Chem. Soc., Dalton Trans., 1990, 2167.
22 F. A. Cotton, Prog. Inorg. Chem., 1976, 21, 1.
CCDC reference number 186/1449.
See http://www.rsc.org/suppdata/dt/1999/2077/ for crystallo-
graphic files in .cif format.
23 G. R. John, B. F. G. Johnson and J. Lewis, J. Organomet. Chem.,
1979, 181, 143.
24 J. N. Nicholls and M. D. Vargas, Inorg. Synth., 1989, 26, 989.
25 R. D. Adams, L. Chen and J. H. Yamamoto, Inorg. Chim. Acta,
1995, 229, 47.
26 S. Rossi, K. Kallinen, J. Pursianinen, T. T. Pakkanen and T. A.
Pakkanen, J. Organomet. Chem., 1992, 440, 367.
27 R. J. Crowte, J. Evans and M. Webster, J. Chem. Soc., Chem.
Commun., 1984, 1344.
Acknowledgements
We gratefully acknowledge financial support from the Hong
Kong Research Grants Council and the University of Hong
Kong. K. S.-Y. L acknowledges the receipt of a postgraduate
studentship and a scholarship, administered by the University
of Hong Kong and the Epson Foundation respectively.
28 G. Suardi, A. Strawczynski, R. Ros, R. Roulet, F. Grepioni and
D. Braga, Helv. Chim. Acta, 1990, 73, 154.
29 M. G. Karpov, S. P. Tunik, V. R. Denisov, G. L. Starova, A. B.
Nikol’skii, F. M. Dolgushin, A. I. Yanovsky and Yu. T. Struchkov,
J. Organomet. Chem., 1995, 219, 485.
30 M. R. Churchill and H. J. Wasserman, Inorg. Chem., 1980, 19, 2391.
31 W. T. Wong, unpublished results.
32 R. D. Adams and J. E. Babin, Inorg. Chem., 1987, 26, 980.
33 A. G. Orpen, J. Chem. Soc., Dalton Trans., 1980, 2509.
34 M. McPartlin and D. M. P. Mingos, Polyhedron, 1984, 3, 1321.
35 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory
Chemicals, 3rd edn., Pergamon, Oxford, 1988.
36 C. R. Eady, B. F. G. Johnson and J. Lewis, J. Chem. Soc., Dalton
Trans., 1975, 2606.
37 B. F. G. Johnson, R. A. Kamarudin, F. J. Lahoz, J. Lewis and
P. R. Raithby, J. Chem. Soc., Dalton Trans., 1988, 1205.
38 SIR 88, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo,
G. Polidor, R. Spagna and D. Viterbo, J. Appl. Crystallogr., 1989,
22, 389.
39 SIR 92, A. Altomare, M.C. Burla, M. Camalli, M. Cascarano,
C. Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr,
1994, 27, 435.
40 TEXSAN, Crystal Structure Analysis Package, Molecular Structure
Corporation, Houston, TX, 1985 and 1992.
References
1 R. J. Angelici, Acc. Chem. Res., 1988, 21, 387; C. M. Friend and
J. T. Roberts, Acc. Chem. Res., 1988, 21, 394; E. J. Markel, G. L.
Schrader, N. N. Sauer and R. J. Angelici, J. Catal., 1989, 116, 11;
N. N. Sauer, E. J. Markel, G. L. Schrader and R. J. Angelici,
J. Catal., 1989, 117, 295; W. R. Moser, G. A. Rossetti, J. T. Gleaves
and J. R. Ebner, J. Catal., 1991, 127, 190.
2 R. D. Adams, H.-S. Kim and S. Wang, J. Am. Chem. Soc., 1985,
107, 6107; R. D. Adams, T. S. A. Hor and I. T. Horvath, Inorg.
Chem., 1984, 23, 4733; R. D. Adams, J. E. Babin, H.-S. Kim, J. T.
Tanner and T. A. Wolfe, J. Am. Chem. Soc., 1990, 112, 3426; R. D.
Adams and J. E. Babin, New J. Chem., 1988, 12, 641; R. D. Adams,
I. T. Horvath and H.-S. Kim, Organometallics, 1984, 3, 548; R. D.
Adams, X. Qu and W. Wu, Organometallics, 1993, 12, 4117.
3 R. D. Adams, I. T. Horvath and K. Natarajan, Organometallics,
1984, 3, 1540; R. D. Adams and L.-W. Yang, J. Am. Chem. Soc.,
1983, 105, 235; R. D. Adams, G. Chen, S. Sun, J. T. Tanner and
T. A. Wolfe, Organometallics, 1990, 9, 251; R. D. Adams and W. Wu,
Inorg. Chem., 1991, 30, 3605.
4 R. D. Adams, I. T. Horvath and L.-W. Yang, Organometallics, 1983,
2, 1257; R. D. Adams, J. E. Babin, R. Mathab and S. Wang, Inorg.
Chem., 1986, 21, 1623; R. D. Adams, J. E. Babin and K. Natarajan,
J. Am. Chem. Soc., 1986, 108, 3518; R. D. Adams, J. E. Babin,
M. Tasi and J.-G. Wang, Inorg. Chem., 1987, 26, 3708.
Paper 9/00808J
2086
J. Chem. Soc., Dalton Trans., 1999, 2077–2086