Metallaheteroboranes containing group 16 elements: An experimental and theoretical study

Article abstract of DOI:10.1016/j.jorganchem.2019.01.007

Thermolysis of diphenyl dichalcogenides, Ph₂E₂ (E = S, Se and Te) with an insitu generated intermediate, obtained from the reaction of [Cp*WCl₄] (Cp* = η⁵-C₅Me₅) with [LiBH₄·THF]

Full text of DOI:10.1016/j.jorganchem.2019.01.007

Accepted Manuscript
Metallaheteroboranes containing group 16 elements: An experimental and theoretical
study
Moulika Bhattacharyya, Rini Prakash, R. Jagan, Sundargopal Ghosh
PII:
S0022-328X(19)30013-0
DOI:
https://doi.org/10.1016/j.jorganchem.2019.01.007
JOM 20685
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 19 November 2018
Revised Date: 9 January 2019
Accepted Date: 11 January 2019
Please cite this article as: M. Bhattacharyya, R. Prakash, R. Jagan, S. Ghosh, Metallaheteroboranes
containing group 16 elements: An experimental and theoretical study, Journal of Organometallic
Chemistry (2019), doi: https://doi.org/10.1016/j.jorganchem.2019.01.007.
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ACCEPTED MANUSCRIPT
Metallaheteroboranes containing group 16 elements:
An experimental and theoretical study
Moulika Bhattacharyya, Rini Prakash, R. Jagan and Sundargopal Ghosh*
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India
E-mail: sghosh@iitm.ac.in, Fax: (+91) 44 2257 4202; Tel: (+91) 44 2257 4230
Keywords: oblatoarachno, metallaheteroboranes, tungsten, diphenyl dichalcogenide
Abstract:
Thermolysis of diphenyl dichalcogenides, Ph2E2 (E = S, Se and Te) with an insitu generated
intermediate, obtained from the reaction of [Cp*WCl4] (Cp*= η5-C5Me5) with [LiBH4·THF], yielded
new tungstaheteroboranes, [(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)], 1 and 2 (1: E = S; 2: E = Se),
and [(Cp*W)2(µ-TePh)B5H5(µ-H)3], 4. Formation of compounds 1 and 2 substantiate the evidence of
[(Cp*W)2B4H10], which supports our previous studies. Compound 4 has a capped octahedral
geometry that is unique due to the presence of three W-H-B bridging hydrogens in a closo cluster.
Alternatively, the shape of cluster 4 can be defined as oblatoarachno that can be derived from a
1
heptagonal bipyramid. All the compounds have been characterized by mass spectrometry, H,
13
11B{1H}, IR and C{1H} NMR spectroscopy in solution and the structural architectures of 1 and 4
were unequivocally established by X-ray crystallographic analysis. The density functional theory
calculations also yielded geometries in close agreement with the observed structures.
1. Introduction
Heteroborane chemistry is one of the robust branches of polyhedral borane chemistry, mainly
due to the wide development of carboranes and their derivatives.1-3 In parallel to the expansion of the
carboranes, the chemistry of heteroboranes and heterometallaboranes containing group 16 elements
have grown in numbers albeit in a slower rate, especially thiaboranes and thiametallaboranes.4-6
1

There is always an urge to synthesize the heavier chalcogen containing heterometallaborane and
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there has been a few success in this area.7-8 From the earlier time, the strategies and reagents used for
this purpose are varied and explored to make interesting cluster geometries.9-10 Apart from this
geometrical importance, many applications are also registered such as active homogeneous catalyst
precursors in the hydrogenation and isomerization of alkenes.11-12 Current investigations in our
laboratory are focused on the development of new methods for the synthesis of di-
metallaheteroboranes through the activation of diorganyl-dichalcogenide ligands13-14 or chalcogen
powders,15 which have been shown to be one of the effective routes for the preparation of
dimetallaheteroboranes.
In a recent study, we have described the direct evidence for the existence of saturated
molybdaborane/tungstaborane compound, [(Cp*M)2B4H10]16 which was hypothesized earlier as
[(Cp*M)2B4H8].17 Therefore, there remains
a
possibility of similar analogues in
metallaheteroboranes, which can substantiate this result further. Hence, in order to put some insight
into this problem, we have reinvestigated the synthesis of group 6 heterometallaborane especially
tungstaheteroborane where only a very few structurally characterized compounds are known.18 The
reaction led to the isolation of [(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)] (E= S and Se) which
supports the existence of a saturated tungstaborane compound [(Cp*W)2B4H10] as the intermediate.
After perceiving success with S and Se, an investigation to isolate the Te analogues led to the
formation of an unexpected [(Cp*W)2(µ-TePh)B5H5(µ-H)3], a new entry into the rare class of
oblatoarachno geometry containing a bridging TePh ligand. Along with the other tools, density
functional theory (DFT) calculations have been used to provide some insight into the nature of the
bonding of these new molecules.
2. Results and discussion
2.1. Synthesis and characterizations of ditungstaheteroboranes, 1-4
As shown in Scheme 1, treatment of an insitu generated intermediate obtained from the
reaction of Cp*WCl4 with [LiBH4·THF] at -78°C, with Ph2E2 [E= S, Se and Te] at 85°C led to the
2

isolation of tungstaheteroborane clusters [(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)], 1 and 2 (1: E =
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S; 2: E = Se) and [(Cp*W)2(µ-TePh)B5H5(µ-H)3], 4 along with known [(Cp*W)2B5H9], 3.19 Detailed
characterizations of these molecules are described below.
(Scheme 1 near here)
2.1.1.[(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)], 1 and 2 (1: E=S; 2: E=Se):
Compound 1 was isolated as brown sticky semi solid in low yield. The mass spectral analysis
of 1 shows the molecular ion peak at m/z 924.1886 corresponding to [M]+. The formation of new
boron-containing species, 1 was indicated by the presence of three 11B{1H} signals in 1:1:1 ratio at δ
= 91.8, 73.3 and -12.2 ppm indicating the presence of different boron environments. The 11B
chemical shift at δ = -12.2 ppm can be assigned to the boron attached with the chalcogen atom which
is a part of the cluster core. The 1H and 13C{1H} NMR spectra imply two equivalents of Cp* ligands.
1
Further analysis of H NMR spectrum shows the presence of a single W-H-B proton at δ = -7.81
ppm. The characteristics bands for B-Ht proton stretching frequency is observed at 2498 cm-1. These
spectroscopic data were not adequate to envisage the identity of 1. A clear explanation eluded us
until the solid-state X-ray structure analysis of 1 was carried out.
(Fig. 1 near here)
The solid-state X-ray structure of 1, shown in Fig. 1, is fully consistent with the spectroscopic
data. The molecular structure of 1 consists of a planar unit of one sulphur and three boron atoms
perpendicular to the W1-W2 bond and nearly parallel to the two Cp* planes. In another way, the
core structure can be considered as a bicapped tetrahedron similar to [(Cp*ReH2)2B4H4]20 proposed
by Fehlner et al. In compound 1, two {W2B} triangular faces are capped by one boron (B3) and
sulphur (S3) atom in a {W2B2} tetrahedron and the W-W edge is further bridged by a sulfido ligand
(S1), which led to a short W-W bond of 2.6930(3) Å as compared to usual W-W single bond.19 It is
in between the double and single bond distance and very much comparable to that of [(Cp*W)2(µ-
S)2(µ-η2-S2CH2)].18c The shape of 1 can also be visualized as an oblatoarachno with the removal of
3

two equatorial vertices from oblatocloso hexagonal bipyramid with 2n (12 e) Wadean21 skeletal
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electrons (6 skeletal electron pairs). One of the interesting features of 1 is the presence of three
different types of S- ligands, i) µ3- S, ii) µ2-SPh, iii) SPh. The µ3-S ligand is connected to the boron
atom and the observed B(1)-S(3) bond length of 1.845(6) Å is comparable to that of other sulphur
containing metalla-thiaborane compounds.7-8 The µ2-SPh ligand bridge between two tungsten centres
symmetrically with an average metal-sulfur bond length of 2.493 Å. This is comparable to the
symmetric coordination of the disulfide bridges in [(Cp*W)2(µ-S)2(µ-η2-S2CH2)].18c
As listed in Table 1, there are many iso-structural metallaboranes and metallaheteroboranes
known to that of 1, where a planar opened ring connected with two linear metal centers. One of the
earlier examples is unsaturated chromaborane, [(Cp*Cr)2B4H8].22 Later various metallaboranes were
synthesized and structurally characterized such as [(Cp*Ta)2B4H10],23a [(Cp*ReH2)2B4H4]20 with the
same structure but different sep (skeletal electron pair) count. Other than the pure metallaboranes, a
series of group 9 heterometallaboranes, [(Cp*M)2B2E2H2]24-25 (M= Co, Rh, Ir; E = S, Se) are also
reported with the similar core. The analogues structurally characterized tungsten and molydaborane
compounds shown in Table 1 (entries 4-9) are iso-structural and iso-electronic to 1. Compound 1
indeed is a mediator in the transition between [(Cp*WCO)2B4H6], from which one and two boron
atoms are replaced by sulphur atoms to form 1 and [(Cp*W)2(µ-S)(µ-η4:η4-S2B2H2)] respectively.
Even though there is not much deviation in the distance between two boron atoms (B1 and B2) in the
M2B2 tetrahedron core of bicapped tetrahedral geometry, the M-M bond distance is considerably
shortened in case of chalcogen substituted complexes, mostly when bridging chalcogen present
across the M-M bond. All the molybdenum and tungsten complexes, shown in Table 1, demonstrate
the direct evidence for the formation of saturated molybda and tungstaborane compounds i.e
[(Cp*M)2B4H10] (6 sep) as one of the possible intermediates.
(Table 1 near here)
4

In an attempt to extend this chemistry to heavier group-16 elements under similar reaction
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conditions, we have carried out the reaction of tungsten intermediate with Ph2Se2 that led us to
isolate the Se analogue of 1, that is [(Cp*W)2(µ-SePh)(µ3-Se)(µ-H)(B3H2SePh)], 2. Several attempts
to grow X-ray quality crystals of 2 were not achieved, however complete characterization of 2 was
done based on the spectroscopic data. Compound 2 shows three resonances at δ = 108.3, 77.2 and
11
1
1.3 ppm in 1:1:1 ratio in B{1H} NMR, whereas H NMR shows presence of two equivalents of
Cp* ligand and one equivalent of bridging W-H-B proton. The mass spectrometry of compound 2
shows a molecular ion peak at m/z 1106.9778 corresponds to the molecular formula of
C32H43B3KSe3W2.
Theoretical calculations on molecule 1' (Cp analogue of 1) reveal a satisfactory agreement
11
between the density functional theory optimized and crystallographic structure (Table S1). The B
chemical shifts of 1' and 2', calculated using the gauge including atomic orbital (GIAO) and B3LYP
functional, agreed well with the experimental chemical shifts, listed in Table S2, hence confirming
the structural assignments. Calculated natural charges (from natural bond orbital analysis (NBO),
Table S4) complemented well with the 11B chemical shifts which indeed show three dissimilar boron
environments. The highest occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) energies as well as the HOMO−LUMO gap for the clusters 1' and 2' are
listed in Supporting Information, Table S3. The computed substantial HOMO-LUMO gap of 1' is
around 3.25 eV, while it has reduced slightly in case of 2' to 3.20 eV, that indicates the viability of
these clusters. The HOMO-LUMO gap for 1' and 2' is in between [(Cp*WCO)2B4H6]16 (1.99 eV)
and [(Cp*W)2(µ-S)(µ-η4:η4-S2B2H2)]18c (3.50 eV) that indicates the increased stability upon the
replacement of boron by chalcogen atom. The HOMO for both 1' and 2' is predominantly localized
on metals and metal-boron bonds, whereas LUMO orbitals are oriented on metals and boron-boron
bonds.
5

The nature of W-W bonding has been evaluated by the DFT calculations. The Wiberg bond
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index of 0.77 and 0.76 indicates a strong M-M interaction in 1' and 2' respectively. Following the
same trend as HOMO-LUMO energy gap, the WBI values of M-M bond also increased from
(Cp*WCO)2B4H6 (0.52) <1' <2' < (Cp*W)2(µ-S)(µ-η4:η4-S2B2H2) (0.97) indicating the strengthening
of cross cluster M-M bonding. The NBO (natural bond orbital) analysis shows the localized
molecular orbital corresponding to M-M bond by the overlap of dz2 orbitals to form a σ-bond (Fig.
2(a)). Further, a strong σ bonding interaction has been observed between B1-S3 (WBI = 0.93) and
B1-Se3 (WBI = 0.89) (Fig. S14(b) and Fig. S15(c)). There was no orbital overlap between the boron
atoms, instead a 3c-2e bond between B1-B2-W2 in 1' (Fig. S14(a)) and two 3c-2e bonds between
B1-B2-W2 bond and B2-B3-W2 observed for 2' (Fig. S15(a) and (b)). The nature of S-B, B-B and
M-M interactions are also probed by QTAIM analysis. Fig.2(b) and (c) show the contour map of the
Laplacian electron density ∆2ρ(r) along the S3-B1-B2-B3 plane of 1' and Se3-B1-B2-B3 plane in 2'.
There is a strong bonding interaction present among the atoms in the corresponding plane in 2',
whereas there is a slight charge depletion between B2-B3 in the plane of 1' which can be attributed
to the positive natural valence population of B3 (Table S4).
(Fig. 2 near here)
2.1.2. [(Cp*W)2(µ-TePh)B5H5(µ-H)3], 4
In an effort to synthesize the Te analogue of 1-2, we have carried out the reaction of
[Cp*WCl4] with [LiBH4·THF] at -78°C followed by thermolysis with Ph2Te2. In contrast, extension
of this approach to the diphenyl ditelluride resulted in the formation of [(Cp*W)2(µ-TePh)B5H5(µ-
H)3], 4. Compound 4 has been isolated by thin layer chromatography (TLC) in low yield and the
composition of 4 was recognized from the mass spectral analysis together with multinuclear NMR
spectroscopy. The mass spectrum of the compound showed single molecular ion peak corresponding
to C26H43B5TeW2Na, which is consistent with the formula containing five B, two W, and one Te
11
atoms. The B{1H} NMR spectrum shows four distinct boron environments appeared at δ = 64.9,
6

52.7, 9.4, and -14.1 ppm. The 1H NMR spectrum of 4 suggests the presence of single Cp* resonance
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at δ = 2.04 ppm. In addition, the 1H spectrum reveals the presence of two kinds of W-H-B protons.
(Fig. 3 near here)
In order to confirm the spectroscopic assignments and to determine the solid state X-ray
structure of 4, the X-ray structure analysis was undertaken. Single crystals suitable for X-ray
diffraction analysis of 4 were obtained from a mixture of hexane/CH2Cl2 solution at -4° C, thus
allowing the structural characterization of [(Cp*W)2(µ-TePh)B5H5(µ-H)3] and confirm the structural
inferences made on the basis of spectroscopic results. As shown in Fig.3(b), the structure of 4 can be
described as a capped octahedron in which {W2B4} occupies the core vertices and capped by one
BH3 unit over the M2B face, similar to the geometry found in [(Cp*M)3B4H4]26 (M = Co, Rh and Ir).
One of the interesting features of 4 is the presence of three bridging hydrogens, which cannot be
seen in other pileo-capped octahedrons. The terminal hydrogen at the capping boron atom (B5)
1
could not be located by X-Ray crystallography, however it has been confirmed by H NMR. In
addition, the crystal structure of 4 does not display the W-H-B hydrogens, the position of the
bridging W-H-B hydrides are assigned by comparing with those of the bicapped octahedron,
[(Cp*W)2B6H10].27 The bridging hydrogens at δ = -7.37 and -12.97 ppm of intensity ratio 1:2 are
assigned to B1 and B5 borons respectively. The bridging hydrogen at δ = -7.37 ppm might be
fluxional between W1 and W2, that makes both the metal centres symmetric. Hence, it displays
single resonance for Cp* and four resonances for boron in which the peak at δ = 64.9 ppm
corresponds to equivalent B2 and B3 borons. Interestingly, the core geometry of 4 is first of its kind
with M2B5 unit, different from the earlier reported geometries, which are i) oblatonido geometry
derived from the one vertex removal of hexagonal bipyramid observed in the case of
[(Cp*Ta)2B5H11],23a [(Cp*M)2B5H9]28 (M = Mo and W) and [(Cp*ReH)2B5Cl5]29 ii) oblatoarachno
structure with the example of [{(η5-C5Me5)TaCl}2B5H11].23b
7

The W-W bond length of 2.848 Å in 4 is somewhat shorter as compared to [(Cp*W)2B6H10]27
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but longer than [(Cp*W)2B5H9]28 and 1. The W-B bond lengths have shown variation within the
cluster. The hydrogen-bridged linkages are of comparable length to those found in [(Cp*W)2B5H9]
(average 2.24 Å). Likewise, the W-B bond, B-B distances are also of different ranges from 1.63-1.85
Å, among which the shortest bond is found between B2-B3 and longest between B4-B5 atoms. On
the other hand, the µ-Te ligands which is bridged between two tungsten centres are symmetric with
an average bond length of 2.711 Å.
(Fig. 4 near here)
On the basis of capping principle that predicts capped-closo geometry for n-vertex polyhedra
having n skeletal electron pairs is validated in case of 4 with 7 sep. Although the observed capped
octahedral closo-cluster geometry is well documented, such clusters with three edge-bridging W-H-
B hydrogens are rare. Hence in a close inspection, we found that it is slightly distorted than normal
capped octahedron which make one of its face open to some extent. So, in an alternative way the
geometry of 4 can be explained as oblatoarachno geometry derived from heptagonal bipyramid with
two diamond-square-diamond (DSD) rearrangements and removal of two vertices (Fig. 4). The
electron count satisfies with this finding by having oblatoarachno polyhedron with n vertices have
(2(n+2)-4) = 2n (14 e or 7 ep) Wadean skeletal electrons.30 The core reported for [{(η5-
C5Me5)TaCl}2B5H11]23b is a structural isomer of the geometry reported for 4. The electron count for
4 can also be validated using Mingos’s fusion formalism. According to Mingos’s approach,
condensation process occurs by vertex, edge or face sharing.31 The total electron count in such
condensed clusters is equal to the sum of the electron count of the parent polyhedra minus the
electron count of the shared units (atom, pair of atoms etc.). The total cluster valence electrons (cve)
available for 4 is 48 [2Cp*W (2×11 = 22) + 5B (5×3 = 15) + 8H (8×1 = 8) + µ-TePh (3) = 48]. The
geometry of 4 can be considered as a fused cluster in which an octahedron and a tetrahedron cluster
got fused via a triangular W2B face. Thus, if one applies Mingos’s fusion formalism for this cluster,
8

this would give 48 electrons (octahedron [W2B4] (46 e) + tetrahedron [W2B2] (40 e) - triangle [W2B]
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(38 e) = 48 e).
Quantum chemical calculations at the B3LYP/6-31G* level for the structure of 4' (Cp analogue
of 4) yielded optimized geometries in good agreement with the crystallographically determined
structure (Table S1). Likewise, the GIAO calculated chemical shifts and resonance assignments are
listed in Table S2, which are in accord with the experimental values obtained from the NMR studies.
The molecular orbital analysis shows the HOMO-LUMO gap of 2.25 eV that indicates its high
stability. The WBI values of 0.64 further supports a strong M-M bond which is slightly weaker than
1'. A very strong bonding interaction has also been found between W-Te (WBI = 0.83 and 0.87).
Natural bond order analysis shows the bonding orbitals between W-W with the occupancy of 1.71 by
the overlap of dz2 orbitals (Fig S16). Interestingly there is a 3c-2e bond present between B1-B2-B3
and B4-B3-B2 (Fig. 5). The topology analysis shows a high charge concentrated area around B1-B2-
B3 plane forming a triangular ring (Fig. 5(b)). The strong covalent character of boron-boron bond is
indicated by higher values of electron density (ρ(r),) and a negative value of energy density (H(r)) at
bond critical point (bcp) (Table S5). Natural charge and valence population analysis shows a high
electron donating nature of Te atom (Table S4).
(Fig. 5 near here)
3. Conclusion
The results described herein demonstrate the synthesis and structural characterization of a series of
di-tungstaheteroborane molecules. Compounds 1 and 2 are the derivatives of nido-[(Cp*M)2B4H10],
in which one of the vertices is substituted by S and Se respectively. We have also isolated and
structurally characterized one ditungstaheteroborane cluster 4 with capped octahedron geometry.
Although the structural type of 4 is well known, the presence of three W-H-B bridging hydrogens is
9

exceptional for a closo cluster. The experimental results have also been complemented and
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rationalized by means of DFT studies.
4. Experimental details
4.1. General procedures and instrumentation
All the syntheses were carried out under argon atmosphere with standard Schlenk and glove
box techniques. Solvents were dried by common methods and distilled under N2 before use.
[Cp*WCl4]32 were prepared according to literature method while other chemicals, LiBH4·THF and
Ph2E2 (E=S, Se, Te) are purchased from Aldrich chemicals and used as received. The external
reference for the 11B NMR, [Bu4N(B3H8)] was synthesized according to literature method.33 Thin
layer chromatography was carried on 250-mm diameter aluminium supported silica gel TLC plates
(MERCK TLC Plates). NMR spectra were recorded on 400 and 500 MHz Bruker FT-NMR
spectrometers. The residual solvent protons were used as reference (δ, ppm, d6-benzene, 7.16,
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. Mass spectra were recorded with a Bruker
MicroTOF-II mass spectrometer in ESI ionization mode. Infrared spectra were recorded with a
JASCO FT/IR-4100 spectrometer. Due to low yields, oily nature and higher sensitivity of these
compounds, the elemental as well as melting point analysis could not been carried out. Thus, the
combustion analysis and melting point data are not reported.
4.2. Synthesis of 1-4
In a Flame-dried Schlenk tube, [Cp*WCl4], (0.5 g, 1.08 mmol) was suspended in toluene (20 mL)
and cooled to -780C. LiBH4·THF (2.16 mL, 4.32 mmol) was added via syringe, and the reaction
mixture was warmed slowly over 20 min to room temperature and left stirring for an additional hour.
The solvent was evaporated under vacuum, and the residue extracted into hexane. The brownish
green hexane extract was thermolyzed at 850C with excess of diphenyl disulfide, PhS-SPh (0.9 g,
4.32 mmol) for 18h. The solvent was removed in vacuo, and the residue was extracted into hexane.
10

After removal of solvent from the filtrate, the residue was subjected to chromatographic work up
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using silica gel TLC plates. Elution with hexane/CH2Cl2 (95:05 v/v) yielded brown oily solid
[(Cp*W)2(µ-SPh)(µ3-S)(µ-H)(B3H2SPh)], 1 (0.06 g, 6%). Under the similar reaction conditions,
diphenyl diselenide, PhSe-SePh (1.34 g, 4.32 mmol) yielded brown oily solid [(Cp*W)2(µ-SePh)(µ3-
Se)(µ-H)(B3H2SePh)], 2 (0.04 g, 3%), whereas diphenyl ditelluride, Ph2Te2 (1.76 g, 4.32 mmol)
produced [(Cp*W)2(µ-TePh)B5H5(µ-H)3], 4 (0.05 g, 5%), as a red oily solid.
Note that compounds 1, 2 and 4 have been isolated along with the yellow solid metallaborane,
[(Cp*W)2B5H9],19 3, in ~10-12% yield.
+
11
1: MS (ESI+): m/z calcd for C32H43B3S3W2 : 924.1825 [M]+, found: 924.1886 [M]+; B{1H} NMR
1
(160 MHz. CDCl3, 22 °C): δ = 91.8 (s, 1B), 73.3 (s, 1B), -12.2 (s, 1B) ppm; H NMR (500 MHz,
CDCl3, 22 °C): δ = 7.52 - 6.99 (m, C6H5), 8.63 (pcq, 1H, BHt), -2.06 (br, 1B-Ht), 2.28 (s, 15H, Cp*)
1.83 (s, 15H, Cp*), -7.81 (s, 1H, M-H-B) ppm; 13C{1H} NMR (125 MHz, CDCl3, 22 °C): δ =
134.03- 127.33 (s, C6H5), 104.76 (s, C5Me5), 104.51 (s, C5Me5), 12.80 (s, C5Me5), 12.46 (s, C5Me5);
IR (hexane, cm-1): 2498w (BHt).
+
2: HRMS (ESI+): m/z calcd for C32H43B3KSe3W2 : 1106.9796 [M+K]+, found: 1106.9778 [M+K]+;
11B{1H} NMR (160 MHz. CDCl3, 22 °C): δ = 108.3 (s, 1B), 77.2 (s, 1B), 1.3 (s, 1B) ppm; 1H NMR
(500 MHz, CDCl3, 22 °C): δ = 7.52 - 7.05 (m, C6H5), 9.28 (pcq, 1H, BHt), -0.73 (br, 1B-Ht), 2.19 (s,
13
15H, Cp*), 2.13 (s, 15H, Cp*), -8.72 (s, 1H, M-H-B) ppm; C{1H} NMR (125 MHz, CDCl3, 22
°C): δ = 133.43- 127.57 (s, C6H5), 104.38 (s, C5Me5), 104.23 (s, C5Me5), 13.28 (s, C5Me5), 12.95 (s,
C5Me5); IR (hexane, cm-1): 2495w (BHt).
+
4: HRMS (ESI+): m/z calcd for C26H43B5NaTeW2 : 931.1809 [M+Na]+, found: 931.1825 [M+Na]+;
11B{1H} NMR (160 MHz. CDCl3, 22 °C): δ = 64.9 (s, 2B), 52.7 (s, 1B), 9.4 (s, 1B), -14.1(s, 1B)
1
ppm; H NMR (500 MHz, CDCl3, 22 °C): δ = 7.40 -7.10 (m, C6H5), 8.46 (br, 1H, B-Ht), 8.07 (br,
1H, B-Ht), 4.42(br, 2H, B-Ht), -0.90 (pcq, 1H, B-Ht), 2.04 (s, 30H, Cp*), -7.37 (s, 1H, M-H-B), -
11

12.97 (s, 2H, M-H-B) ppm; 13C{1H} NMR (125 MHz, CDCl3, 22 °C): δ = 130.06 - 127.58 (s, C6H5),
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100.85 (s, C5Me5), 13.00 (s, C5Me5); IR (hexane, cm-1): 2412w, 2502w (B-Ht).
4.3. Computational details.
The Quantum chemical calculations were performed on the simplified model compounds 1', 2', and
4' (Cp analogues of 1, 2, and 4) using the Gaussian 09 program package.34 Geometry optimization
were conducted in the gaseous state (no solvent effect) without any symmetry constraints using the
BP8635 functional paired with a mixed basis set: Stuttgart/Dresden double−ζ(SDD) effective core
potentials (ECPs)36 for W; 6−31g* basis set for the other atoms. The optimized geometries were
characterized as true minima by using analytical frequency calculations. The gauge including atomic
orbital (GIAO)37 method has been employed to compute the NMR chemical shifts with hybrid
Becke–Lee–Yang– Parr (B3LYP) functional38 with the BP86/6−31g*, SDD optimized geometries.
The 11B NMR chemical shifts were calculated relative to B2H6 (B3LYP/6−31g* B shielding
constant, 93.5 ppm) and converted to the usual [BF3·OEt2] scale by using the experimental δ(11B)
1
value of B2H6 (δ = 16.6 ppm).39 TMS (SiMe4) was used as the internal standard for the H NMR
1
chemical shift calculations. The H chemical shifts were referenced to TMS. Wiberg bond indices
(WBIs)40 were obtained from a natural bond orbital (NBO)41 analysis. All the optimized structures
and orbital graphics were generated by using the Chemcraft.42 The two dimensions of the electron
density and the Laplacian electronic distribution plots were generated using the Multiwfn package.43
4.4. X-ray crystal structure determinations
Crystallographic information for 1 and 4 are shown in Table 2. The crystal data for 1 and 4 were
collected and integrated using a Bruker kappa apex2 CCD diffractometer, with graphite-
monochromated MoKα (λ = 0.71073 Å) radiation at 273 K. The structures were solved by heavy
atom methods using SHELXS-2016 and refined by using SHELXL-2016 (Sheldrick, G.M.,
University of Göttingen) 44
(Table 2 near here)
12

Conflict of interest
ACCEPTED MANUSCRIPT
The authors declare no competing financial interest.
Acknowledgements
This project was supported by the Council of Scientific and Industrial Research (CSIR; No.
01(2837)/15/EMR-II), New Delhi, India. DST-FIST, India, is gratefully acknoweldged for the
HRMS facility. M.B and R. P are grateful to IIT Madras for fellowship. The computational facility
of IIT Madras is gratefully acknowledged. We thank Mr. C. Ghosh for X−ray data collection.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org
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18

Table of Content
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New tugstaheteroboranes, [(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)], an analogue of [(Cp*W)2
B4H10] (right) and [(Cp*W)2(µ-TePh)B5H5(µ-H)3], a capped octahedron having three W-H-B
bridging hydrogens (left).
Scheme 1
Fig. 1
Synthesis of dimetallaheteroborane clusters 1-4
Molecular structure and labeling diagram of 1. Selected bond lengths (Å) and bond
angles (ο): W1-W2 2.6930(3), B1-B2 1.691(9), B1-S3 1.845(6), B1-W2 2.332(7), B2-
W1 2.244(6), S1-W1 2.5244(14), W2-S3 2.4119(16); B2-B1-S3 123.1(4), S3-B1-W1
69.3(2), W1-B1-W2 70.86(19), W2-S1-W1 65.36(3), B3-W1-W2 49.63(17), B1-S3-
W2 64.9(2).
Table 1
Fig. 2
Skeletal electron pair (sep) count, structural parameters and chemical shift of M2B4
core or its derivatives
(a) σ bonding orbital of W1-W2 from NBO analysis of 1' (contour value: ±0.05
[e/bohr3]1/2), (b) and (c) showing the contour line diagrams of the Laplacian of the
electron density, ∇2ρ(r) of S3-B1-B2-B3 plane in 1' and Se3-B1-B2-B3 plane in 2'
that generated using the Multiwfn program package at the B3LYP/SDD, 6-31g* level
of theory. Dashed red lines indicate areas of charge concentration (∇2ρ(r)<0) while
19

dotted black lines show areas of charge depletion (∇2ρ(r)>0). Black dots indicate
ACCEPTED MANUSCRIPT
BCPs. Solid brown lines connecting the atomic nuclei are the bond paths. Blue, and
orange dots indicate BCPs and RCPs.
Fig.3
Molecular structure and labeling diagram of 4 ((a) and (b) two different view of 4).
Selected bond lengths (Å) and bond angles (ο): W1-W2 2.848, B2-B3 1.63(4), B4-B3
1.76(4), B5-B4 1.85(4), W1-B5 2.30(4), W2-B4 2.32(3), W1-Te1 2.748(2); W1-Te1-
W2 63.37(5), B3-B2-W2 106.1(13), B1-B2-B4 98.0(18), W1-B5-W2 76.4(12).
Fig.4
Sequence of diamond-square-diamond (DSD) process converting the heptagonal
bipyramid into the oblatoarachno deltahedron 4.
Fig. 5
(a) showing 3c-2e bonding orbital of B1-B2-B3 from NBO analysis of 4' (contour
value: ±0.05 [e/bohr3]1/2), (b) showing the contour line diagrams of the Laplacian of
the electron density, ∇2ρ(r) of B1-B2-B3 plane in 4' that generated using the
Multiwfn program package at the B3LYP/SDD, 6-31g* level of theory. Dashed red
lines indicate areas of charge concentration (∇2ρ(r)<0) while dotted black lines show
areas of charge depletion (∇2ρ(r)>0). Black dots indicate BCPs. Solid brown lines
connecting the atomic nuclei are the bond paths. Blue, and orange dots indicate BCPs
and RCPs.
Table 2.
Crystallographic data and structure refinement information for compounds 1 and 4
20

Scheme 1
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Fig. 1
21

Table 1
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Sl
No
1
Compounds
sep
d[M-M] d[B-B]a 11B NMR
Ref.
[Å]
[Å]
[(Cp*Ta)2B4H10]
5
5
6
6
6
6
6
6
6
6
6
8
8
8
2.89
1.93
0.3, 16.6
34.3, 126.5
1.30, 68.7
63.7, 15.8
60.4, 7.6
84.4, 49.8, 30.4
78.8, 54.0, 19.2
18.8
23a
22
20
16
16
7a
7a
7a
18c
*
2
[(Cp*Cr)2B4H8]
2.87
2.81
2.92
--
1.75
1.94
1.61
--
3
[(Cp*ReH2)2B4H4]
[(Cp*MoCO)2B4H6]
[(Cp*WCO)2B4H6]
[(Cp*Mo)2B2H5(BER)2(µ-η1-ER)]b
[(Cp*Mo)2B2H5(BER)2(µ-η1-ER)]c
[(Cp*Mo)2B2S2H2(µ-η1-S)]
[(Cp*W)2(µ-S)(µ-η4:η4-S2B2H2)]
1
4
5
6
2.69
2.71
2.63
2.65
2.69
--
1.63
1.65
1.69
1.66
1.69
--
7
8
9
3.52
10
11
91.8, 73.3, -12.2
108.3, 77.2, 1.3
22.7
*
2
12 [(Cp*Co)2B2S2H2]
13 [(Cp*Rh)2B2Se2H2]
14 [(Cp*Ir)2B2Se2H2]
3.07
3.42
3.46
1.73
1.74
1.75
25b
24
24
23.9
7.3
aDistance between two boron atoms (B1 and B2) in the M2B2 tetrahedron core of bicapped
tetrahedral geometry. bE = S, R = 2,6-(tBu)2C6H2OH. cE = Se, R = Ph. *This work
22

Fig. 2
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Fig.3
Fig.4
23

Fig.5
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Table 2
1
4
empirical formula
CCDC NO
formula weight
crystal system
space group
a (Å)
C32H43B3S3W2
C26H39B5TeW2
1878746
923.97
Orthorombic
F 2 -2d
18.003(2)
46.906(5)
15.5706(17)
90
1878747
900.92
triclinic
P -1
11.202(2)
14.438(3)
18.750(4)
88.407(5)
81.888(4)
80.168(5)
2958.1(11)
4
b (Å)
c (Å)
α (°)
β (°)
90
γ (°)
90
V(Å3)
13149(2)
16
Z
Dcalc(g/cm3)
F (000)
1.867
2.023
7136
1680
µ (mm-1)
θ Range (°)
no. of total refins collected
7.205
8.751
1.737-28.32
53195
1.05-28.5
55441
no. of unique refins [I> 2σ(I)]
7201
55441
24

max and min transmission
goodness-of-fit on F2
0.411 and 0.327
0.354 and 0.274
1.081
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1.010
final R indices [I> 2σ(I)]
R1 = 0.0231
wR2 = 0.0337
R1 = 0.0271
wR2 = 0.0345
R1 = 0.0846
wR2= 0.2557
R1 = 0.1032
wR2 = 0.2694
R indices (all data)
25

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Research Highlights:
•
•
Explored the synthesis of tungstaheteroboranes employing diphenyl dichalcogenides.
Formation of [(Cp*W)2(µ-EPh)(µ3-E)(µ-H)(B3H2EPh)] (E= S and Se) supports the
existence of saturated tungstaborane compound [(Cp*W)2B4H10] as the intermediate.
[(Cp*W)2(µ-TePh)B5H5(µ-H)3], with capped octahedron geometry is exceptional due
to the presence of three W-H-B bridging hydrogens.
•