Cluster expansion reactions of group 6 and 8 metallaboranes using transition metal carbonyl compounds of groups 7-9

Article abstract of DOI:10.1021/ic200802c

The reinvestigation of an early synthesis of heterometallic cubane-type clusters has led to the isolation of a number of new clusters which have been characterized by spectroscopic and crystallographic techniques. The thermolysis of [(Cp*Mo)₂B₄H₄E₂] (1: E = S; 2: E = Se; Cp* = η⁵-C₅Me₅) in presence of [Fe₂(CO)₉] yielded cubane-type clusters [(Cp*Mo)₂(μ₃-E)₂B₂H(μ-H) {Fe(CO)₂}₂Fe(CO)₃], 4 and 5 (4: E = S; 5: E = Se) together with fused clusters [(Cp*Mo)₂B₄H ₄E₂Fe(CO)₂Fe(CO)₃] (8: E = S; 9: E = Se). In a similar fashion, reaction of [(Cp*RuCO)₂B ₂H₆], 3, with [Fe₂(CO)₉] yielded [(Cp*Ru)₂(μ₃-CO)₂B₂H(μ- H){Fe(CO)₂}₂Fe(CO)₃], 6, and an incomplete cubane cluster [(μ₃-BH)₃(Cp*Ru) ₂{Fe(CO)₃}₂], 7. Clusters 4-6 can be described as heterometallic cubane clusters containing a Fe(CO)₃ moiety exo-bonded to the cubane, while 7 has an incomplete cubane [Ru ₂Fe₂B₃] core. The geometry of both compounds 8 and 9 consist of a bicapped octahedron [Mo₂Fe₂B ₃E] and a trigonal bipyramidal [Mo₂B₂E] core, fused through a common three vertex [Mo₂B] triangular face. In addition, thermolysis of 3 with [Mn₂(CO)₁₀] permits the isolation of arachno-[(Cp*RuCO)₂B₃H₇], 10. Cluster 10 constitutes a diruthenaborane analogue of 8-sep pentaborane(11) and has a structural isomeric relationship to 1,2-[{Cp*Ru} ₂(CO)₂B₃H₇].

Full text of DOI:10.1021/ic200802c

ARTICLE
pubs.acs.org/IC
Cluster Expansion Reactions of Group 6 and 8 Metallaboranes Using
Transition Metal Carbonyl Compounds of Groups 7ꢀ9
K. Geetharani,† Shubhankar Kumar Bose,† Satyanarayan Sahoo,† Babu Varghese,‡ Shaikh M. Mobin,§ and
Sundargopal Ghosh*,†
†Department of Chemistry and ‡Sophisticated Analytical Instruments Facility, Indian Institute of Technology Madras,
Chennai 600 036, India
§National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology Bombay, Mumbai 400 076, India
S Supporting Information
b
ABSTRACT: The reinvestigation of an early synthesis of heterometallic cubane-type
clusters has led to the isolation of a number of new clusters which have been
characterized by spectroscopic and crystallographic techniques. The thermolysis
of [(Cp*Mo)2B4H4E2] (1: E = S; 2: E = Se; Cp* = η5-C5Me5) in presence of
[Fe2(CO)9] yielded cubane-type clusters [(Cp*Mo)2(μ3-E)2B2H(μ-H){Fe(CO)2}2-
Fe(CO)3], 4 and 5 (4: E = S; 5: E = Se) together with fused clusters
[(Cp*Mo)2B4H4E2Fe(CO)2Fe(CO)3] (8: E = S; 9: E = Se). In a similar fashion,
reaction of [(Cp*RuCO)2B2H6], 3, with [Fe2(CO)9] yielded [(Cp*Ru)2(μ3-CO)2-
B2H(μ-H){Fe(CO)2}2Fe(CO)3], 6, and an incomplete cubane cluster [(μ3-BH)3-
(Cp*Ru)2{Fe(CO)3}2], 7. Clusters 4ꢀ6 can be described as heterometallic cubane
clusters containing a Fe(CO)3 moiety exo-bonded to the cubane, while 7 has an
incomplete cubane [Ru2Fe2B3] core. The geometry of both compounds 8 and 9
consist of a bicapped octahedron [Mo2Fe2B3E] and a trigonal bipyramidal [Mo2B2E]
core, fused through a common three vertex [Mo2B] triangular face. In addition, thermolysis of 3 with [Mn2(CO)10] permits the
isolation of arachno-[(Cp*RuCO)2B3H7], 10. Cluster 10 constitutes a diruthenaborane analogue of 8-sep pentaborane(11) and has
a structural isomeric relationship to 1,2-[{Cp*Ru}2(CO)2B3H7].
’ INTRODUCTION
(8: E = S; 9: E = Se) from 1 and 2, respectively. Preliminary
results have already been communicated earlier.14 Further,
the chemistry of 3 has been elaborated with [Mn2(CO)10] and
[Re2(CO)10], which led to the isolation of arachno-[(Cp*RuCO)2-
B3H7], 10 and hydrido carbonyl complex [Cp*Ru(CO)-
(μ-H)]2, 11.
Over time, and in the shadow of organometallic chemistry, a
systematic structural chemistry for Polyboronꢀmetal com-
pounds developed. The development of metallaborane chemis-
try blossomed with the discovery of both cluster electron
counting rules and the isolobal principle, that provide a solid
foundation for understanding the interrelationships between
structure and composition.1 In cluster chemistry, several ap-
proaches to the construction of clusters have received much
attention.2,3 For example, (i) condensation involving monobor-
ane reagents,4 (ii) insertion or fragmentation involving borane or
metal carbonyl fragments,5 and (iii) intercluster fusion with two
or more atoms held in common between the constituent
subclusters.6 In each case the reaction often leads to the forma-
tion of a wide range of products with different metal-to-boron
ratios.7ꢀ11
’ RESULTS AND DISCUSSION
As shown in Scheme 1, reaction of a reddish brown solution of
1 in toluene with excess of [Fe2(CO)9] resulted in the formation
of 4 and 8. Similarly, compound 2 on reaction with [Fe2(CO)9]
yielded 5 and 9. Reaction of a yellow solution of 3 in presence
of [Fe2(CO)9] generated compounds 6 and 7. Details of
spectroscopic and structural characterization of 4ꢀ9 using IR,
1H, 11B, 13C NMR, mass spectrometry, and X-ray diffraction
studies follow.
Cubane Clusters 4ꢀ7. The constitution of 5 was ascertained
by an X-ray diffraction study on a suitable single crystal
(Figure 1). The compound crystallizes in the monoclinic space
group P21/c and displays the existence of a novel “capped
cubane” cluster core. Although X-ray quality crystals of 4 have
not been obtained yet, its identity is inferred by comparison to
Compounds 1ꢀ312,13 were found to be useful precursors
for the formation of cubane clusters. Thus, the chemistry
was elaborated by means of cluster expansion reaction with
[Fe2(CO)9], which led to the isolation of cubane-type clusters
[(Cp*M)2(μ3-E)2B2H(μ-H){Fe(CO)2}2Fe(CO)3], 4ꢀ6 (4:
M = Mo, E = S; 5: M = Mo, E = Se; 6: M = Ru, E = CO). In
addition to the cubane clusters, we have isolated an incomplete
cubane-type cluster [(μ3-BH)3(Cp*Ru)2{Fe(CO)3}2], 7, from
3 and fused clusters [(Cp*Mo)2B4H4E2Fe(CO)2Fe(CO)3]
Received: April 19, 2011
Published: May 25, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
Scheme 1. (a) Synthesis of 4, 5, 8, and 9; (b) Synthesis of 6, 7, 10, and Triply Bridged Heterometallic Borylene Complexes
ARTICLE
the selenium analogue 5. The overall structure of 5 is interest-
ing and can be viewed as a cubane shape made of two Mo, two
Fe, two Se, and two B atoms and its “cap”, a third iron atom, is
attached to one of the BꢀFeꢀFe faces of the cube.
distance is 2.5220(4) Å, which is 0.2 Å shorter than those
observed in single and double-cubane clusters; while the mean
MoꢀFe distances of 2.792 Å is not unusual.19 Exo-bonded to the
cubane at the B2ꢀFe1ꢀFe3 face is the third iron atom (Fe2)
with a long FeꢀFe distance of 2.632 Å and the short FeꢀBboride
bond distance of 2.026(3) Å. The average MoꢀSe distance of 5
(2.439 Å) is significantly shorter than that of diselenamolybda-
boranes 2 (2.585 Å).
The spectroscopic data of 5 are fully in accord with the solid-
state structure, and no evidence of fluxional behavior is observed.
The 11B NMR of 4 and 5 rationalize the presence of two boron
resonances in the ratio of 1:1. The 11B resonances at δ 143.4 and
144.1 ppm of 4 and 5, respectively, lie in the range typical of a
metal rich boride cluster.20 In addition to the resonances of the
BH proton, the 1H NMR spectrum also reveals two equivalents
of Cp* ligands, indicating two different Mo environments. The
13C NMR spectra contain signals attributable to the two types of
Cp* ligands and the Fe(CO)3 fragment. The 77Se NMR spectra
of 5 displayed single resonance at δ 995 ppm for the bridged
μ3-Se atoms. The parent ion of 4 and 5 in the mass spectrum
fragments by the sequential loss of seven CO molecules, and the
molecular mass corresponds to Cp*2Mo2B2H2S2Fe3(CO)7 and
The cubane-type sulfido clusters have been extensively in-
vestigated in the chemistry of metal sulfido clusters;15 in contrast
the corresponding selenido derivatives have received little inter-
est, the only structurally characterized examples being the Mo,
Sn, and Pd derivatives with [M3M0Se4] single cube structure.16
Compound 5 is the first heterobimetallic selenido cuboidal
cluster containing a boride unit (B2) as one of the vertices.
The boron atom (B2) lies within an open MoFe3 skeleton which
can be described as an open butterfly framework. In 5, the unique
boron atom (B2) lies 0.318 Å above the MowingꢀFewing (i.e.,
Mo(2)ꢀFe(2)) axis. The internal dihedral angle of the MoFe3
butterfly is 114°, which corresponds well with the value observed
for [HFe4(CO)12BH2] (114°)17 and for a four-atom butterfly
cluster (109°) derived from an octahedron.18
The Mo1ꢀMo2 bond length of 2.9216(3) Å is in the range
observed for a bond order of one but slightly (0.08 Å) longer than
the corresponding distances in [Mo3CuSe4Cl4(dmpe)3]PF6
(dmpe = 1,2-bis(dimethylphosphino)ethane).16c The Fe1ꢀFe3
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Figure 1. Molecular structure and labeling diagram for 5. Thermal
ellipsoids are shown at the 40% probability level. Selected bond lengths
(Å) and angles (deg): Mo1ꢀMo2 2.9216(3), Mo1ꢀB1 2.115(3),
Mo2ꢀB2 2.061(3), Fe1ꢀB1 2.128(3), Fe1ꢀB2 2.056(3), Fe3ꢀB1
2.119(3), Fe3ꢀB2 2.056(3), Mo1ꢀSe2 2.4253(3), Mo2ꢀSe2 2.4544(3),
Fe1ꢀSe1 2.4064(4), Fe3ꢀSe2 2.4027(4), Fe1ꢀFe3 2.5220(4), Fe1ꢀFe2
Figure 2. Molecular structure and labeling diagram for 6. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths
(Å) and angles (deg): Ru1ꢀRu2 2.7167(4), Ru1ꢀFe3 2.6663(6),
Ru1ꢀFe1 2.6573(5), Fe2ꢀFe3 2.6800(7), Fe1ꢀFe2 2.6735(8),
Fe1ꢀFe3 2.4838(8), Ru2ꢀFe3 2.64996, Ru2ꢀFe1 2.6354(6), Ru1ꢀB2
1.985(4), Fe1ꢀB2 2.029(4); B2ꢀRu1ꢀFe1 49.27(12), Fe1ꢀRu1ꢀFe3
55.623(17), Fe1ꢀRu1ꢀRu2 58.721(13), B2ꢀFe1ꢀB1 105.53(18),
B1ꢀFe1ꢀFe3 53.41(13), B2ꢀFe1ꢀRu2 98.10(12), Ru2ꢀFe1ꢀRu1
61.764(13).
2.6294(4),
Fe3ꢀFe2
2.6360(5);
B1ꢀMo1ꢀSe1
101.06(7),
Se1ꢀMo1ꢀSe2 105.829(10), B1ꢀMo1ꢀFe1 49.13(7), Mo2ꢀFe1ꢀMo1
63.228(9), Mo1ꢀSe1ꢀMo2 73.575(8), Fe1ꢀMo2ꢀFe3 53.582(10).
Cp*2Mo2B2H2Se2Fe3(CO)7 respectively. The IR spectrum of
compounds 4 and 5 also supports the presence of terminal
carbonyl ligands that appeared at 2029, 1978 and 2022,
1976 cmꢀ1 respectively.
packing of the unit cell of 6 shows an intermolecular CH--O
distance of 2.482 Å, which is shorter than the normal van der
Waals H O separation of 2.6 Å. This may possibly reflect weak
3 3 3
Mild thermolysis of 3 with [Fe2(CO)9] generated 6, in
parallel with the formation of the incomplete cubane cluster
[(μ3-BH)3(Cp*Ru)2{Fe(CO)3}2], 7, and the triply bridged
borylene complex [{(μ3-BH)(Cp*Ru)Fe(CO)3}2(μ-CO)].13
The mass spectrum of 6 shows a molecular ion at m/z = 915
corroborating the composition of C29H32B2Fe3Ru2O9. The
11B{1H} NMR spectrum displayed two resonances with equal
intensities. The peak at δ 128.5 ppm has been assigned to the
borylene boron atom, and the significantly deshielded resonance
at δ 158.5 ppm has been assigned to the boride boron which
hydrogen bonding between the methyl hydrogen of Cp* and the
terminal carbonyl oxygen.21
The metalꢀmetal distances, 2.7167(4) Å (RuꢀRu), 2.657(9)
Å (RuꢀFe), and 2.4838(8) Å (FeꢀFe), are all consistent with
single bonds between the metal atoms. All MꢀMꢀM angles in a
regular tetrahedron are 60°, and the observed angles in 6 are very
close to this ideal value. The deviations are a consequence of the
shorter FeꢀFe and RuꢀFe distances relative to the RuꢀRu
distance. The average triply bridging MꢀCO (M = Ru, Fe) bond
length of 2.088 Å compares favorably with the average value
of 2.059 Å observed for the similar triply bridging carbonyl
ligand in [(Cp*Ru)3(μ3-CO)Co(CO)2B3H3].22 In contrast, the
FeꢀCO distances for the terminal carbonyl ligands in 6 has an
average value of 1.779 Å. This latter value emphasizes that
a significant MꢀCO bond lengthening of approximately
0.25ꢀ0.30 Å occurs when a terminal carbonyl ligand bonded
to only one metal atom formally transmutes into a ligand
symmetrically coordinated to three metal atoms.
Primarily the overall shape of the cubane cluster remains
unchanged while the MꢀM distances reflect changes in cluster
electronic structure accompanying the addition and loss of
electrons.23 Earlier, Kennedy in his review24 described
[(CpNi)4B4H4]25 and [(CpCo)4B4H4]26 as 68 and 64-electron
clusters, with two and four metalꢀmetal bonds. Further, he
suggested that the putative [(CpFe)4B4H4] cluster with 60
electrons should exhibit a cubane structure with six FeꢀFe
bonds and a fully bonded metal tetrahedron. The metallaborane
that connects these clusters is 60 cluster valence electrons (cve)
1
implies a greater degree of boronꢀmetal interaction. The H
NMR spectra showed one broad signal at lowest field for the
terminal BH proton, two sets of distinct chemical shifts for the
two Cp* ligands at δ 2.17 and 1.84 ppm, and a singlet at higher
field for the FeꢀHꢀB proton at δ ꢀ8.48 ppm. The infrared
spectrum of 6 shows two strong bands at 2029 and 1978 cmꢀ1
,
assigned to the CO stretching modes of the Fe(CO) group and a
band at 1730 cmꢀ1 for the bridging carbonyl stretching frequency.
A single crystal suitable for an X-ray diffraction study could be
obtained from a solution of 6 in hexane by slow evaporation of
the solvent. The molecular structure and relevant bond lengths
and angles are displayed in Figure 2. The structure of 6 adopts
cubane-type geometry with four metal atoms at the corners of a
tetrahedron with two CO, one BH, and one boride unit capping
each face of the tetrahedron. In addition, one of the Fe2B faces of
the cubane is capped by a Fe(CO)3 fragment. The coordination
sphere of the Ru atoms is completed by Cp* ligands, and each
iron atom has terminally bonded CO ligands. Furthermore, the
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Inorganic Chemistry
ARTICLE
Figure 4. Molecular structure and labeling diagram for 9. Thermal
ellipsoids are shown at the 30% probability level. Terminal carbonyl ligands
are excluded for clarity. Selected bond lengths (Å) and angles (deg):
Mo1ꢀMo2 2.7437(16), Mo1ꢀSe1 2.5391(16), Mo1ꢀB1 2.426(16),
Fe1ꢀSe2 2.296(2), Fe1ꢀB4 2.085(16), Fe2ꢀB3 2.149(16), Fe1ꢀFe2
2.634(3), B1ꢀB2 1.71(2), B2ꢀB4 1.79(2), B1ꢀSe1 2.02(2);
Mo1ꢀSe1ꢀMo2 65.46(5), Mo1ꢀB1ꢀMo2 69.0(4), Mo1ꢀFe1ꢀMo2
58.43(5).
Figure 3. Molecular structure and labeling diagram for 7. Thermal
ellipsoids are shown at the 30% probability level. Terminal carbonyl
ligands are excluded for clarity. Selected bond lengths (Å) and angles
(deg): Ru1ꢀRu2 2.7477(3), Ru1ꢀFe1 2.6088(4), Ru1ꢀFe2
2.6687(4), Fe1ꢀFe2 2.6204(5), Ru2ꢀFe1 2.6155(4), Ru2ꢀFe2
2.6232(4), Ru2ꢀB1 2.022(3), Fe1ꢀB1 2.078(3), Fe2ꢀB1 2.096(3);
Ru2ꢀB1ꢀFe1 79.27(10), Ru1ꢀFe1ꢀFe2 61.375(12), Ru2ꢀFe1ꢀFe2
60.132(12), Fe1ꢀFe2ꢀRu2 59.842(12).
[(Cp*Ru)3(μ3-CO)Co(CO)2B3H3], a cubane geometry with six
MꢀM bonds.22 Compounds 4ꢀ6, presented in this report, are
also 60 cve tetrametal metallaboranes, which can be compared to
those discussed above. In fact, the first member (and parent) of
this particular class of cubane-like molecules, that is, [Cp4Fe4-
(μ3-CO)4], also represents a 60 cve cluster with six MꢀM bonds.
Compound 7 was isolated in 5% yield as a red brown solid.
The atom connectivity within the compounds was persuasively
determined by performing a single-crystal X-ray diffraction study
of 7 (Figure 3). The Ru2Fe2B3 core in 7 appears to be the
incomplete cubane-type;28 it consists of a metalꢀmetal bonded
Ru2Fe2 tetrahedron, in which each Ru atoms bound to a
Cp* ligand and Fe atoms bound to carbonyl ligands. The
three triangular faces Ru1ꢀRu2ꢀFe1, Ru1ꢀRu2ꢀFe2, and
Ru2ꢀFe1ꢀFe2 are capped by a borylene ligand (BH) in a μ3
fashion; thereby generating a overall tricapped tetrahedron
structure 7. A formal electron count1 for 7 is in agreement with
the metallaborane, [(Cp*Re)2B4H8],29 that is, six skeletal elec-
tron pair (sep) appropriate for tetrahedral geometry.
CO molecules, and the molecular mass corresponds to
Cp*2Ru2Fe2(CO)6B3H3. The IR spectrum shows two terminal
carbonyl frequencies at 2009 and 1969 cmꢀ1, and the band at
2489 cmꢀ1 is due to the terminal BꢀH stretches.
Fused Clusters 8 and 9. Compounds 8 and 9 were isolated in
11% and 22% yield as green solids. Unfortunately, all of our
efforts to grow single crystals of 8 resulted in weakly diffracting
material, and no data sets of sufficient quality for resolution of the
molecule were obtained. However, the structure of 8 was
confirmed by comparing its spectroscopic data with that of the
selenium analogue 9. Single crystals suitable for X-ray diffraction
analysis of 9 were obtained from a hexane solution at ꢀ10 °C,
thus allowing for the structural characterization of cluster 9.
Compound 9 crystallizes in the triclinic system with a space
group P1. It contains six independent molecules in the asym-
metric unit. A solid-state structure of one of the six independent
molecules of 9 is shown in Figure 4. The sides a and b are nearly
equal, and the γ angle is 119°. Although it was felt that the crystal
suffered from some pseudomerohedral twinning, the exact twin
relationship can not be found. The higher residual factor
(0.1280) and the unaccountable difference electron density
might have been caused by twinning.
The interatomic Ru1ꢀRu2 distance of 2.7477(3) Å indicates
the existence of a single bond between the ruthenium atoms;
however, it is slightly longer than observed in 6. The average
BꢀRu distance of 2.054 Å lies in the range of those reported for
the transition metal borylene complexes.30 In 7, one of the
carbonyl groups covalently linked to iron (Fe1) interacts with the
ruthenium (Ru1) center in a semi bridged fashion (RuꢀFeꢀ
CO 66.6°).13 The average dihedral angle between the plane of
B2ꢀFe1ꢀFe2ꢀB3 atoms relative to the Cp* ligands is 146.1°,
whereas the tilt of the plane of two Cp* ligands is 112.2°.
The observed geometry of 9 can be viewed as a fused cluster, in
which a bicapped octahedron {Mo2Fe2B3Se} unit fused with a
trigonal bipyramidal {Mo2B2Se} unit with three atoms held
common between the two subclusters. An alternative interpreta-
tion of the structure of 9 as a tricapped octahedron, with Mo1,
Mo2, B2, B3, B4, and Fe1 occupying the vertices of the core
octahedron, in which the faces Mo1ꢀMo2ꢀFe1, B3ꢀB4ꢀFe1,
and Mo1ꢀMo2ꢀB2 are capped by Se2, Fe2, and B1, respec-
tively. The resulting Mo1ꢀMo2ꢀB1 face in turn is capped by the
Se1 atom; thus, cluster 9 may be considered as a tetracapped
octahedron. On the basis of the capping principle, the skeletal
electron count is determined by the central polyhedron, that is,
the Mo2Fe1B3 octahedron, and is seven sep. Formally, the μ3-E
(E = S and Se) group contributes four electrons; hence for 8 and
9, eight sep are available and the observed structures do not obey
1
The H and 11B NMR spectra are consistent with the solid-
state X-ray structure of 7, which rationalizes the presence of two
boron environments in ratio of 2:1 at δ 126.2 and 92.9 ppm.
Furthermore, the 1H NMR spectrum reveals the presence of two
Cp* resonances and two terminal BꢀH protons in the ratio of
2:1. The 13C NMR spectrum indicates the presence of carbonyl
ligands that appeared at δ 212.5 and 210.9 ppm. The parent ion
of 7 in the mass spectrum fragments by the sequential loss of six
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ARTICLE
the counting rules.1 Although the bicapped octahedral geometry
is well-known in metallaborane chemistry,31 clusters 8 and 9
provide the unique example of a tetracapped octahedral core.
The MoꢀMo bond length of 9 (2.7437(16) Å) is somewhat
longer than that found in 2 (2.665(2) Å). The MoꢀFe distances
(2.8400(19) and 2.781(2) Å) are consistent with the presence
of a single bond and markedly shorter than [(Cp*Mo)2-
B5H9Fe(CO)3].31a The FeꢀFe bond distance is within the
expected range (2.634 Å). The MoꢀB bond lengths show
variation within the cluster. Of the direct MoꢀB linkages, those
to B1 are somewhat longer (2.426(16) and 2.420(17) Å), reflec-
ting a weaker MoꢀB interaction. Although the crystal structure
of 9 does not display the BH hydrogens, which are assigned using
1H{11B} NMR spectroscopy.
The spectroscopic data for 9 in solution also support the solid
state structure. Mass spectrometry analysis of 8 and 9 is consistent
with a compound of the formulation Cp*2Mo2B4H4S2Fe2(CO)5
and Cp*2Mo2B4H4Se2Fe2(CO)5, respectively, and the parent
ion shows the sequential loss of five CO molecules. The 11B
NMR spectrum of 8 and 9 shows three types of boron environ-
ments in the ratio of 2:1:1. The low field 11B chemical shifts of δ
75.1 (8) and 74.2 ppm (9) may be assigned to the boron that is
bonded to three metals. The high field 11B resonances at δ 5.2
(8) and 11.6 ppm (9) can be assigned to boron bonded to the
sulfur and selenium atom, respectively. Furthermore, the 1H and
13C NMR spectra imply one Cp* ligand, and three distinct BH
terminal groups (2:1:1). Terminal BH and CO stretching
frequencies are observed in the IR spectrum, and the presence
of the latter is confirmed by the 13C NMR spectrum. The 77Se
NMR spectra of 9 displayed two resonances at δ 894 and 578
ppm for the bridged μ3-Se atoms.
Figure 5. Molecular structure and labeling diagram for 10. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths
(Å) and angles (deg): Ru1ꢀRu2 2.9386(8), Ru1ꢀB2 2.302(9), Ru2ꢀB3
2.118(9), B1ꢀB3 1.758(13), B2ꢀB3 1.761(13); B2ꢀRu1ꢀRu2 84.6(2),
B3ꢀRu2ꢀB1 46.8(4), B1ꢀRu2ꢀRu1 85.5(3), B3ꢀRu2ꢀRu1 46.4(2).
Chart 1. Structural Comparison of 10 and
[{Cp*Ru}2(CO)2B3H7], I
Reactivity of 3 toward Group 7 and 9 Metal Carbonyls. In
an ongoing effort to access higher order clusters, the reactivity
of 3 with other metal fragment sources have been examined.
The reactions of 3 with [Cp*Re(CO)3] and [Co2(CO)8] led
to decomposition of the starting material, whereas [Mn2(CO)10]
was found accompanied of a compound identified spectro-
scopically as arachno-[(Cp*RuCO)2B3H7], 10, along with
the formation of a bridged borylene complex [(μ3-BH)-
(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}].13 Mild thermolysis
of 3 with [Re2(CO)10], on the other hand, produces only the
nonboron-containing bridged hydride complex [Cp*Ru(CO)-
(μ-H)]2, 11.
cluster. In terms of structure, consider the ancillary ligands
first; the Cp* ligands and the carbonyl groups are arranged in a
transoid fashion. As shown in Figure 5, opening a basal-
apical edge of a nido square pyramidal cluster generates the
observed geometry. Arachno-10 is a structural isomer of
[{Cp*Ru}2(CO)2B3H7],32 I, reported earlier by Fehlner
(Chart 1). The bridging hydrogen along the Ru1ꢀRu2 edge
has not been positioned by X-ray diffraction studies; however, its
connectivity with Ru1 and Ru2 has been assertively determined
by 1H NMR.
In cluster 10 the interatomic distance between Ru1 and Ru2
(2.9386(8) Å) is near the longer limit of reported RuꢀRu single
bond distances. This difference is consistent with the presence
of a bridging hydrogen atom at the Ru1ꢀRu2 edge, resulting in a
longer RuꢀRu interaction. The average bond length of Ru2
and the boron atom at the bridging position, B3 (2.124 Å), is
substantially shorter than that Ru2ꢀB1 (2.293(10) Å) and
Ru1ꢀB2 (2.302(9) Å). The dihedral angle between the three-
membered rings of Ru2ꢀRu1ꢀB3 and B3ꢀRu2ꢀB1 is 138.3°.
This value is slightly wider than the corresponding angle in
arachno-B4H10 (125.5° by electron diffraction;33 117.4° by
electron diffraction and microwave spectroscopy) and reported
arachno-dimetallaboranes.34
The FAB mass analysis of 10 gives a molecular ion peak
corresponding to [{Cp*Ru}2(CO)2B3H7], and the presence of
terminal metal-bound CO ligands is evident in the IR spectrum.
The 11B spectrum exhibits two signals of area 1:2 (δ = 54.5
and ꢀ9.7 ppm). A peak at the lower field was assigned to the
boron atom that bridges the two ruthenium metals. In addition to
1
the resonances due to the BH proton, the H NMR spectrum
reveals a signal at δ 1.81 ppm for the Cp* protons, indicating
identical Ru environments and the presence of BꢀHꢀB and
RuꢀHꢀRu protons, each appearing at δ ꢀ1.54 and ꢀ18.19
ppm of intensity 2:1. Consistent with this observation, the 13C
NMR spectrum also shows one Cp* signal and the signal due to
1
carbonyl groups. The variable-temperature H and 13C NMR
experiments demonstrated that compound 10 is not fluxional.
After recrystallization in hexane, 10 was isolated as air- and
moisture-sensitive yellow crystals. The molecular structure of 10,
shown in Figure 5, is determined by single-crystal X-ray diffrac-
tion studies. The framework structure of 10 is predicted by the
electron counting rules to be an eight sep, five-vertex arachno
The number of metal, boron, and hydrogen atoms in 10 and I
remains the same, and considering the close similarity of the
chemical shifts indicates that the structures of 10 and I are closely
related. I is shown to convert into a second isomeric form of
similar stability. Although 10 and I have the same metalꢀmetal,
5828
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Inorganic Chemistry
ARTICLE
boronꢀboron, and metalꢀboron connectivities, there are some
significant differences in the arrangement of hydrogen atoms and
the structural metrics. Selected comparisons are given in Chart 1.
For instance, the major differences between 10 and I can be
appreciated by looking at the RuꢀRu bond distance and the
atoms in the MꢀMꢀB plane as shown in Chart 1. In going from
10 to I, the metalꢀmetal and metalꢀboron distances shorten
and the MꢀMꢀB angles open. Furthermore, the environments
of the boron atoms are slightly changed from those in I, and the
difference is the metal to which the BH2 group is attached and
their hydrogen atoms. In the case of I the low-field 11B resonance
is coupled to the high-field BꢀHꢀRu proton and one terminal
proton. In contrast, the low field 11B resonance of 10 coupled to
the high-field BꢀHꢀB protons only.
The pathway for the formation of 10 from 3 is of interest. A
plausible reaction stochiometry is shown in eq 1. As loss of BH3
and H2 is a common feature of borane, as well as metallaborane
cluster chemistries,35 the formation of 10 is most simply viewed
as a metallaborane combination followed by [HMn(CO)5] loss.
2½ðCpꢁRuCOÞ B2H6ꢂ þ ½Mn2ðCOÞ ꢂ
2
10
ꢁ
ꢁ
Δ
f½ðCp RuCOÞ2B3H7ꢂ þ½ðCp RuCOÞ2BH2fMnðCOÞ4gꢂ
10
þ ½HMnðCOÞ5ꢂ þ CO þ H2
ð1Þ
Although the objective of the thermolysis of 3 with [Re2(CO)10]
was to generate an analogue of the bridged borylene complex
[(μ3-BH)(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}], it led to the
isolation of nonboron compound 11. Compound 11 has been
isolated and spectroscopically characterized by Forrow and
Knox;36 however, no detailed structural insights were available.
In this report we describe the isolation (under different reaction
conditions) and structural characterization of 11. From the mass
1
spectral analysis combined with the H NMR spectrum, 11 is
formulated as [Cp*Ru(CO)(H)]2. A single-crystal X-ray diffrac-
tion study has been carried out on 11 with the results shown in
Figure 6. The osmium analogue of 11 had been synthesized and
structurally characterized previously.37 The structure of 11
consists of a diruthenium unit bridged by a pair of μ-H atoms.
In addition, each Ru atom has a Cp* ligand and a terminally
bound carbonyl group attached to it. The terminal carbonyl
groups and Cp* ligands have an anti orientation with respect to
Figure 6. Molecular structure and labeling diagram for 11. Thermal
ellipsoids are shown at the 40% probability level. Selected bond lengths
(Å) and angles (deg): Ru1ꢀRu1_1 2.6920(3), Ru1ꢀH1 1.806(19);
O1ꢀC11ꢀRu1 173.75(16), C11ꢀRu1ꢀH195.2(6), C11ꢀRu1ꢀRu1_1
94.52(5).
Table 1. Crystallographic Data and Structure Refinement Information for 5ꢀ7 and 9ꢀ11
5
6
7
9
10
11
empirical formula
formula weight
crystal system
space group
a (Å)
C27H32B2Fe3Mo2O7Se2 C29H32B2Fe3Ru2O9 C26H33B3Fe2Ru2O6 C63H76B8Fe4Mo4O11Se4 C22H37B3O2Ru2 C22H30O2Ru2
1007.50
monoclinic
P21/c
915.86
787.79
2018.72
568.09
528.60
triclinic
monoclinic
P21
triclinic
monoclinic
P21/n
monoclinic
P21/n
P1
P1
12.2619(4)
13.3712(3)
21.2481(6)
90
10.3081(4)
10.8988(5)
16.0185(7)
74.054(4)
81.082(3)
67.255(4)
1593.39(12)
2
9.3791(8)
14.9670(14)
10.9142(9)
90.00
18.0715(9)
18.3109(9)
41.907(2)
92.939(3)
97.194(2)
119.025(2)
11929.4(11)
6
8.3363(4)
36.354(2)
9.1085(4)
90
7.2377(3)
15.2598(6)
10.1424(4)
90
b (Å)
c (Å)
R (deg)
β (deg)
106.675(3)
90
106.910(4)
90.00
116.469(6)
90
107.4460(10)
90
γ (deg)
V (Å3)
3337.26(16)
4
1465.9(2)
2
2471.1(2)
4
1068.66(7)
2
Z
Dcalc (g/cm3)
2.005
1.909
1.785
1.686
1.527
1.643
F (000)
1960
908
784
5940
1152
532
μ (mmꢀ1
)
4.226
2.311
2.019
3.198
1.237
1.425
θ range (deg)
3.37- 25.00
25265
3.32ꢀ25.00
10911
2.27ꢀ24.99
27674
0.99ꢀ25.00
135275
3.36ꢀ25.00
16928
2.49ꢀ28.49
7722
no. of refins collected
no. of unique refins [I > 2σ(I)] 5867
5578
5135
135275
4335
2651
goodness-of-fit on F2
1.027
1.045
1.036
1.098
1.350
1.262
final R indices [I > 2θ(I)]
R1 = 0.0172
wR2 = 0.0416
R1 = 0.0205
wR2 = 0.0423
R1 = 0.0257
wR2 = 0.0750
R1 = 0.0310
wR2 = 0.0763
R1 = 0.0136
wR2 = 0.0341
R1 = 0.0140
wR2 = 0.0343
R1 = 0.1280
wR2 = 0.3117
R1 = 0.1839
wR2 = 0.3417
R1 = 0.0675
wR2 = 0.1057
R1 = 0.0779
wR2 = 0.1083
R1 = 0.0182
wR2 = 0.0499
R1 = 0.0217
wR2 = 0.0520
R indices (all data)
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Inorganic Chemistry
ARTICLE
the RuꢀRu bond. The RuꢀRu distance of 2.6920(3) Å in 11 is
much shorter than observed in 3 (2.9258(10) Å) and longer than
the hydrido carbonyl complex [(Cp*Ru(μ-H)2(μ-CO)RuCp*]
(2.444(1) Å).38 The RuꢀRu distance in 11 is considerably
longer than the RudRu distance of 2.26ꢀ2.29 Å, observed in
tetracarboxylate ruthenium(II) dimers and other related
species.39 The terminal CO ligands are almost linear, with a
RuꢀCꢀO angle of 173.7°. The Ru(μ-H)2Ru core of 11 is planar,
and the dihedral angle between the plane of the central core
relative to the Cp* ligand is 127.2°.
5: 11B NMR (25 °C, 128 MHz, CDCl3): δ 144.1 (br, 1B), 108.1
ppm (br, 1B). 1H NMR (25 °C, 400 MHz, CDCl3): δ 9.98 (pcq, 1BHt),
1.73 (s, 15H, 1Cp*), 1.66 (s, 15H, 1Cp*), ꢀ7.78 ppm (s, 1H,
FeꢀHꢀB). 13C NMR (25 °C, 100 MHz, CDCl3): δ 216.2, 203.8
(s, CO), 112.9, 104.7 (s, C5Me5), 12.8, 12.3 ppm (s, C5Me5). 77Se NMR
(25 °C, 95 MHz, CDCl3): δ 995 ppm (s, 2Se). IR (hexane) ν/cmꢀ1
:
2449w (BHt), 2022, 1976 cmꢀ1 (CO). MS (FAB) Pþ(max): m/z (%)
1007. Elem anal. Calcd for C27H32B2Fe3Mo2O7Se2: C, 32.19; H, 3.20.
Found: C, 33.02; H, 3.36.
6: 11B NMR (25 °C, 128 MHz, CDCl3): δ 158.5 (br, 1B), 128.5
ppm (br, 1B). 1H NMR (25 °C, 400 MHz, CDCl3): δ 8.48 (pcq, 1BHt),
2.17 (s, 15H, 1Cp*), 1.84 (s, 15H, 1Cp*), ꢀ8.48 ppm (s, 1H,
FeꢀHꢀB). 13C NMR (25 °C, 100 MHz, CDCl3): δ 215.5, 209.4
(s, CO), 120.3, 119.9 (s, C5Me5), 13.1, 9.0 ppm (s, C5Me5). IR (hexane)
ν/cmꢀ1: 2465w (BHt), 2029, 1978 (CO), 1730 cmꢀ1 (μ3-CO). MS
(FAB) Pþ(max): m/z (%) 915. Elem anal. Calcd for C29H32B2Fe3R-
u2O9: C, 38.03; H, 3.52. Found: C, 39.28; H, 3.72.
’ CONCLUSION
From the results described in this article, it can be concluded
that reaction of group 6 or 8 metallaboranes or their derivatives
with metal carbonyl fragments constitute a useful route to
heterometallaborane clusters. Compounds 8 and 9 represent a
novel class of hybrid clusters, in which a [Mo2B2Se] trigonal
bipyramid has been fused to a [Mo2Fe2B3Se] bicapped octahe-
dron subcluster. Further, as demonstrated in this article, the
difference in reactivity pattern of the different metal carbonyls
with [(Cp*RuCO)2B2H6], 3, is also reflected in the observed
product distribution.
7: 11B NMR (25 °C, 128 MHz, CDCl3): δ 126.2 (br, 2B), 92.9
ppm (br, 1B). 1H NMR (25 °C, 400 MHz, CDCl3): δ 8.48 (pcq, 2BHt),
8.15 (pcq, 1BHt) 1.84 (s, 15H, 1Cp*), 1.76 (s, 15H, 1Cp*). 13C NMR
(25 °C, 100 MHz, CDCl3): δ 212.5, 210.9 (s, CO), 113.2, 104.1
(s, C5Me5), 14.4, 9.7 ppm (s, C5Me5). IR (hexane) ν/cmꢀ1: 2489w
(BHt), 2009 m, 1969 m (CO) cmꢀ1. MS (FAB) Pþ(max): m/z (%) 787.
Elem anal. Calcd for C26H33B3Fe2Ru2O6: C, 39.63; H, 4.22. Found: C,
38.18; H, 3.92.
’ EXPERIMENTAL SECTION
8: 11B NMR (25 °C, 128 MHz, CDCl3): δ 75.1 (br, 2B), 61.4 (s, 1B),
5.2 (s, br, 1B). 1H NMR (25 °C, 400 MHz, CDCl3): δ 6.05 (pcq, 2BHt),
1.94 (s, 30H, 2Cp*), ꢀ0.26 (pcq, 1BHt), ꢀ0.63 (pcq, 1BHt). 13C NMR
(25 °C, 100 MHz, CDCl3): δ 217.1, 211.2 (CO), 108.4 (s; C5Me5), 12.8
(s; C5Me5). IR (hexane) ν/cmꢀ1: 2485w (BHt), 2038 m, 1983 m (CO).
MS (FAB) Pþ(max): m/z (%) 825. Elem anal. Calcd for C25H34B4Fe2-
Mo2O5S2: C, 36.37; H, 4.15. Found: C, 36.32; H, 4.12.
General Procedures and Instrumentation. All the operations
were conducted under an Ar/N2 atmosphere using standard Schlenk
techniques or glovebox. Solvents were distilled prior to use under Argon.
[Co2(CO)8], [Mn2(CO)10], [Re2(CO)10], [Fe2(CO)9] (Aldrich) and
[Cp*Re(CO)3] (Strem) were used as received. Compounds 1ꢀ3 were
prepared according to literature methods.12,13 The external reference
[Bu4N(B3H8)] for the 11B NMR was synthesized with the literature
method.40 Thin layer chromatography was carried on 250 mm dia
aluminum supported silica gel TLC plates (MERCK TLC Plates). NMR
spectra were recorded on a 400 and 500 MHz Bruker FT-NMR
spectrometer. Residual solvent protons were used as reference
(δ, ppm, CDCl3, 7.26), while a sealed tube containing [Bu4N(B3H8)]
in [D6]benzene (δB, ppm, ꢀ30.07) was used as an external reference for
the 11B NMR. Infrared spectra were recorded on a Nicolet 6700 FT
spectrometer. Microanalyses for C, H, and N were performed on Perkin
Elmer Instruments series II model 2400. Mass spectra were obtained on
a Jeol SX 102/Da-600 mass spectrometer with argon/xenon (6kv,
10 mÅ) as FAB gas.
9: 11B NMR (25 °C, 128 MHz, CDCl3): δ 74.2 (br, 2B), 58.5 (s, 1B),
1
11.6 (s, br, 1B). H NMR (25 °C, 400 MHz, CDCl3): δ 6.26 (pcq,
2BHt), 1.93 (s, 30H, 2Cp*), 0.62 (pcq, 1BHt), ꢀ0.63 (pcq, 1BHt). 13
C
NMR (25 °C, 100 MHz, CDCl3): δ 218.4, 211.1 (CO), 107.2
(s; C5Me5), 13.5 (s; C5Me5). 77Se NMR (25 °C, 95 MHz, CDCl3): δ
894 and 578 ppm (s, 2Se). IR (hexane) ν/cmꢀ1: 2474w (BHt), 2039 m,
1981 m (CO). MS (FAB) Pþ(max): m/z (%) 919. Elem anal. Calcd for
C25H34B4Fe2Mo2O5Se2: C, 32.66; H, 3.72. Found: C, 32.60; H, 3.71.
Synthesis of 10 and 11. A yellow solution of compound 3 (0.075
g, 0.13 mmol) in toluene (15 mL) was stirred at 85 °C in the presence of
3 equiv of [Mn2(CO)10] (0.154 g, 0.39 mmol) for 12 h. All volatiles were
removed in vacuo, the residue was extracted into hexane, and passed
through Celite. The mother liquor was concentrated, and the residue
was chromatographed on silica gel TLC plates. Elution with hexane/
CH2Cl2 (8:2 v/v) yielded yellow 10 (0.011 g, 14%) and reddish brown
bridged borylene [(μ3-BH)(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}]
(0.023 g, 24%). Under similar reaction conditions, [Re2(CO)10]
(0.254 g, 0.39 mmol) yielded red 11 (0.03 g, 42%).
Synthesis of 4ꢀ9. In a typical reaction, compound 1 (0.07 g,
0.12 mmol) in toluene (15 mL) was stirred with 4 equiv of [Fe2(CO)9]
(0.17 g, 0.48 mmol) for 12 h at 85 °C. The solvent was removed in vacuo,
the residue was extracted in hexane, and passed through Celite. The
filtrate was concentrated and kept at ꢀ40 °C to remove [Fe3(CO)12].
The mother liquor was concentrated, and the residue was chromato-
graphed on silica gel TLC plates. Elution with a hexane/CH2Cl2 (9:1)
mixture yielded 4 (0.005 g, 4%) and 8 (0.011 g, 11%). The isolated yield
of the Se analogue 5 and 9 from 2 were 16% (0.017 g) and 22%
(0.021 g), respectively. Further, in a similar fashion, reaction of 3 (0.075
g, 0.13 mmol) in hexane at 65 °C provided 6 (0.02 g, 16%), along with
the formation of 7 (0.005 g, 5%) and [{(μ3-BH)(Cp*Ru)Fe(CO)3}2-
(μ-CO)] (0.03 g, 27%).
Compound 11 has been characterized by comparison of its spectro-
scopic data with those reported by Knox et al.36
10: 11B NMR (25 °C, 128 MHz, CDCl3): δ 54.5 (br, 1B), ꢀ9.7
ppm (br, 2B). 1H NMR (25 °C, 400 MHz, CDCl3): δ 2.76 (pcq, 4BHt),
1.81 (s, 30H, 2Cp*), ꢀ1.54 ppm (br, 2H, BꢀHꢀB), ꢀ18.19 ppm
(s, 1H, RuꢀHꢀRu). 13C NMR (25 °C, 100 MHz, CDCl3): δ 210.4
(s, CO), 112.4 (s, C5Me5), 10.1 ppm (s, C5Me5). IR (hexane) ν/cmꢀ1
:
2469w (BHt), 1934 (CO). MS (FAB) Pþ(max): m/z (%) 568. Elem
anal. Calcd for C22H37B3Ru2O2: C, 46.51; H, 6.56. Found: C, 45.29;
H, 5.91.
4: 11B NMR (25 °C, 128 MHz, CDCl3,): δ 143.4 (br, 1B), 107.2
1
ppm (br, 1B). H NMR (25 °C, 400 MHz, CDCl3): δ 9.95 (partially
collapsed quartet (pcq), 1BHt), 1.74 (s, 15H, 1Cp*), 1.68 (s,
15H, 1Cp*), ꢀ7.86 ppm (s, 1H, FeꢀHꢀB). 13C NMR (25 °C,
100 MHz, CDCl3): δ 215.5, 203.4 (s, CO), 108.6, 105.9 (s, C5Me5),
13.1, 12.8 ppm (s, C5Me5). IR (hexane) ν/cmꢀ1: 2496w (BHt), 2029,
1978 cmꢀ1 (CO). MS (FAB) Pþ(max): m/z (%) 913.
X-ray Structure Determination. Crystallographic informations
for 5ꢀ7, and 9ꢀ11 are listed in Table 1. Crystal data for 5, 6, and 10
were collected and integrated using Oxford Diffraction Xalibur-S CCD
system equipped with graphite-monochromated Mo KR radiation
5830
dx.doi.org/10.1021/ic200802c |Inorg. Chem. 2011, 50, 5824–5832

Inorganic Chemistry
ARTICLE
(λ = 0.71073 Å) radiation at 150 K. The crystal data for 7, 9, and 11 were
collected and integrated using a Bruker Axs kappa apex2 CCD diffract-
ometer, with graphite monochromated MoꢀKR (λ = 0.71073 Å)
radiation at 293, 273, and 173 K respectively. The structures
were solved by heavy atom methods using SHELXS-97 or SIR9241
and refined using SHELXL-97 (Sheldrick, G. M., University of
G€ottingen).42,43
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’ ASSOCIATED CONTENT
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9ꢀ11. This material is available free of charge via the Internet
at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sghosh@iitm.ac.in.
(18) Fehlner, T. P.; Housecroft, C. E.; Scheidt, W. R.; Wong, K. S.
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’ ACKNOWLEDGMENT
Generous support of the Department of Science and Tech-
nology, DST (Project No. SR/S1/IC-19/2006), New Delhi, is
gratefully acknowledged. K.G. and S.K.B. thank the Council of
Scientific and Industrial Research (CSIR) and University Grants
Commission (UGC), India, respectively for Research Fellow-
ships. We would also like to thank Mass lab, SAIF, CDRI,
Lucknow 226001, India, for FAB mass analysis and SAIF, IIT
Madras, for variable temperature NMR facilities.
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