Unusual cationic rhodathiaboranes: Synthesis and characterization of [8,8,8-(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H 10]+ and [1,3-μ-(H)-1,1-(PR3) 2-3-(Py)-isonido-1,2-RhSB9H8]+

Article abstract of DOI:10.1039/c3dt52018h

The treatment of the hydridorhodathiaboranes, [8,8,8-(H)(PR ₃)₂-9-(Py)-nido-8,7-RhSB₉H₉], where PR₃ = PPh₃ (2), PMePh₂ (3), PPh₃ and PMe₂Ph (4), or PMe₃ and PPh₃ (5), and [8,8,8-(H)(PMePh₂)₂-9-(PMePh₂)-nido-8,7- RhSB₉H₉] (6), with TfOH affords [8,8,8-(H)(PR ₃)₂-9-(Py)-nido-8,7-RhSB₉H₁₀] ⁺ cations, where PR₃ = PPh₃ (12), PMePh ₂ (13), PPh₃ and PMe₂Ph (14), or PMe ₃ and PPh₃ (15), and [8,8,8-(H)(PMePh₂) ₂-9-(PMePh₂)-nido-8,7-RhSB₉H₁₀] ⁺ (16). Compounds 13 and 14 lose H₂ to give [1,3-μ-(H)-1,1-(PR₃)₂-3-(Py)-isonido-1,2-RhSB ₉H₈]⁺, where PR₃ = PMe₂Ph (18), PPh₃ and PMe₂Ph (21), or PMePh₂ (22). Similarly, the 11-vertex rhodathiaboranes, [1,1-(PR₃) ₂-3-(Py)-1,2-RhSB₉H₈], where PR₃ = PPh₃ (7), PMe₂Ph (8), PMe₃ (9), or PPh ₃ and PMe₃ (10), react with TfOH to give the corresponding cations, [1,3-μ-(H)-1,1-(PR₃)₂-3-(Py)-isonido-1,2- RhSB₉H₈]⁺, where PR₃ = PPh ₃ (17), PMe₂Ph (18), PMe₃ (19), or PPh ₃ and PMe₃ (20). Four conformers of 20 are studied by X-ray diffraction methods and DFT-calculations, identifying packing motifs that stabilize different metal-thiaborane linkages, and energy variations that are involved in these conformational changes. It is demonstrated that the proton induces nonrigidity on these clusters as well as an enhancement of their Lewis acidity.

Full text of DOI:10.1039/c3dt52018h

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Unusual cationic rhodathiaboranes: synthesis and
characterization of [8,8,8-(H)(PR3)2-9-(Py)-nido-
8,7-RhSB9H10]+ and [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-
isonido-1,2-RhSB9H8]+†
Cite this: Dalton Trans., 2014, 43,
5121
Beatriz Calvo, Ramón Macías,* Maria Jose Artigas, Fernando J. Lahoz and
Luis A. Oro
The treatment of the hydridorhodathiaboranes, [8,8,8-(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H9], where PR3
=
PPh3 (2), PMePh2 (3), PPh3 and PMe2Ph (4), or PMe3 and PPh3 (5), and [8,8,8-(H)(PMePh2)2-9-(PMePh2)-
+
nido-8,7-RhSB9H9] (6), with TfOH affords [8,8,8-(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H10
]
cations, where
PR3 = PPh3 (12), PMePh2 (13), PPh3 and PMe2Ph (14), or PMe3 and PPh3 (15), and [8,8,8-(H)(PMePh2)2-9-
+
(PMePh2)-nido-8,7-RhSB9H10
]
(16). Compounds 13 and 14 lose H2 to give [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-
isonido-1,2-RhSB9H8]+, where PR3 = PMe2Ph (18), PPh3 and PMe2Ph (21), or PMePh2 (22). Similarly, the
11-vertex rhodathiaboranes, [1,1-(PR3)2-3-(Py)-1,2-RhSB9H8], where PR3 = PPh3 (7), PMe2Ph (8), PMe3 (9),
or PPh3 and PMe3 (10), react with TfOH to give the corresponding cations, [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-
isonido-1,2-RhSB9H8]+, where PR3 = PPh3 (17), PMe2Ph (18), PMe3 (19), or PPh3 and PMe3 (20). Four con-
formers of 20 are studied by X-ray diffraction methods and DFT-calculations, identifying packing motifs
that stabilize different metal–thiaborane linkages, and energy variations that are involved in these confor-
mational changes. It is demonstrated that the proton induces nonrigidity on these clusters as well as an
enhancement of their Lewis acidity.
Received 24th July 2013,
Accepted 24th September 2013
DOI: 10.1039/c3dt52018h
www.rsc.org/dalton
The deltahedral structures of polyhedral boron clusters are
supported by a highly delocalized three-dimensional bonding
Introduction
Polyhedral boron-containing compounds exhibit unique elec- that leads to cluster aromaticity.3,4 The resulting three-dimen-
tronic properties, geometries, and extraordinary versatility that sional geometries of these molecules provide precise direc-
are of interest for a variety of applications, including medicine, tional control at their vertices, which can be functionalized
health and nutrition, boron neutron capture therapy, optoelec- with a vast variety of organic substituents. In addition, hetero-
tronics, energy storage and nanomaterial.1,2 This is best illus- boranes can accommodate in their structures metal elements
trated by the icosahedral carboranes, which have been from almost all of the periodic table, leading to the synthesis
intensively studied over the years, mainly due to their commer- of a huge number of metallaheteroboranes, in which, many
cial availability.
times, the heteroborane fragment can be regarded as a subro-
Carboranes are boron-based clusters with triangular facets gate of well-known organic ligands.5–14
that incorporate carbon atoms into their structures, being, by
Bearing in mind that tunable ligands for transition metals
far, the most ubiquitous members of polyhedral hetero- constitute a broad field that centers on the idea that one can
boranes: cages that incorporate elements of the p-block of the engender novel reactivity, the flexibility of heteroboranes as
periodic table.
face-bound ligands affords interesting possibilities for the
design of new systems with potential in the activation of
unreactive bonds and ultimately in catalysis.2,15 In addition,
heteroboranes can act as substituents changing the steric and/
or electronic properties of classical ligands.16–20
Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis
Homogénea-ISQCH, Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, 50009
Zaragoza, Spain. E-mail: rmacias@unizar.es
†Electronic supplementary information (ESI) available: Additional NMR spectra,
It is clear, therefore, that heteroboranes have a huge poten-
tial for creating catalysts tailored to specific needs. In this
regard, the use of carboranes as ligands of transition metal
complexes has been extensively explored with very interesting
results.2,16,21–23 Of special interest to our work is the intensely
and DFT-calculated details and coordinates. CCDC 907304 for 20a and 937675
for 20b. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt52018h
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5121

View Article Online
Paper
Dalton Transactions
Scheme 1 Proton assisted hydrogen activation.
studied
hydridorhodathiaborane,
[3,3,3-(H)(PPh3)2-3,1,2- L = PPh3 (7), PMe2Ph (8), PMe3 (9), PPh3 and PMe3 (10), or
RhC2B9H11],24 which undergoes rapid and reversible closo– PPh3 and PMe2Ph (11).
nido tautomerism that is the key to its catalytic activity in, for
As yields are generally good, these 11 vertex nido- and
example, the hydrogenation and isomerization of olefins. This isonido-rhodathiaboranes constitute subjects for further reac-
illustrates an interesting dichotomy when dealing with tion chemistry. Most recently, treatment of 2, 7, 9 and 10 with
polyhedral boron-containing compounds: clusters such as icosa- Brønsted acids has been found to yield polyhedral cations that
hedral carboranes and boranes are among the most thermo- exhibit remarkable reactivity, including a significant case of
dynamically stable molecules known, but the incorporation of proton-assisted hydrogen activation via metal–thiaborane
a transition metal centre in the cage can lead to non-rigid cooperation
by
closo–nido
cluster
transformations
systems that can generate interesting chemistry.25,26
(Scheme 1).35,36
It is interesting to note that although protonation of tran-
Although the possibility of utilizing the structural flexibility
of metallaboranes in catalytic reactions has been investi- sition metal complexes is fundamental chemistry that induces
gated,24,27 polyhedral boron-containing compounds show a an enhancement of the Lewis acidity of the metal centres,37–39
marked lack of examples in which the stereochemical non- and it is relevant to many catalytic processes, to our knowl-
rigidity of the cluster leads to bond activation and ultimately edge, there are few examples of cationic metallaheteroboranes
to catalysis, the most studied system being the commented formed upon treatment with Brønsted acids.40 In fact, the
hydridorhodathiaborane reported by Hawthorne and co- large majority of cationic metallaheteroboranes are based on
workers.24,28,29 Therefore, an interesting goal in metallahetero- charge-compensated heteroborane fragments, which act as
borane chemistry is to develop systems that combine the oxi- face-bound ligands and which are somewhat different in
dative and coordinative flexibility of transition metal centres nature from the polyhedral cations we describe in the present
with the capability of boron clusters to exhibit oxidative/reduc- work.41–46
tive flexibility in their classical closo–nido–arachno structural
transformation.
Herein, we build upon protonation reactions of the above-
presented series of 11-vertex rhodathiaboranes, reporting a
In our recent work dealing with the reaction chemistry of unique set of polyhedral cations that represent some of the
the unsaturated 11-vertex rhodathiaborane, [8,8,8-(PPh3)2-nido- few examples of cationic boron-based clusters of any type.
8,7-RhSB9H10] (1), we have demonstrated that the nido–closo
Given the unique properties of polyhedral boron-containing
structural and redox flexibility of pyridine-bound rhodathia- compounds, commented in the Introduction, and our recent
boranes, [8,8,8-(H)(PPh3)2-9-(Py)-nido-8,7-RhSB9H9] (2) and discovery that protonation of rhodathiaboranes leads to
[1,1-(PPh3)2-3-(Py)-isonido-1,2-RhSB9H8], is the key in the an enhancement of non-rigidity in the metal–thiaborane
heterolytic H–H bond splitting and subsequent catalytic hydro- linkage,35 this series of cationic rhodathiaboranes represents a
genation of olefins, as well as in the oxidative addition of potentially rich source of polyhedral Lewis acids that can lead
sp-C–H bonds to the clusters.30–32
to new opportunities for bond activation via cooperation
In an attempt to modify the reactivity of these clusters, we between the metal and the thiaborane cage ligand.
have already carried out substitution of the exo-polyhedral
PPh3 ligands in 1 and 2 with the more basic (less bulky) mono-
dentate phosphines, PMe3, PMe2Ph and PPh2Me. This sub-
Results and discussion
stitutional chemistry has provided
a
series of new
The treatment of 2–6 with triflic acid (TfOH) leads to protona-
tion of the nido-cage to give the corresponding polyhedral
cations, [8,8,8-(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H10]+, where PR3
= PPh3 (12),36 PMePh2 (13), PPh3 and PMe2Ph (14), PPh3
and PMe3 (15), and [8,8,8-(H)(PMePh2)2-9-(PMePh2)-nido-8,7-
RhSB9H10]+ (16) (Scheme 2).
hydridorhodathiaboranes of the general formulation, [8,8,8-
(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H9], where PR3 = PPh3 (2),31
PMePh2 (3),33 PPh3 and PMe2Ph (4),33 or PPh3 and PMe3 (5).33
The PMePh2-substituted analogue, [8,8,8-(H)(PMePh2)2-9-
(PMePh2)-nido-8,7-RhSB9H9] (6),34 is available from the reac-
tion of 1 with PMePh2.34 The thermal dehydrogenation of 2–5
affords isonido-derivatives, [1,1-(L)2-3-(Py)-1,2-RhSB9H8], where
These polyhedral nido-cations have been characterized by
multinuclear NMR spectroscopy, mass spectrometry,
5122 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Scheme 2 Protonation of 11-vertex nido-rhodathiaboranes.
Fig. 1 Diagram that represents the chemical shifts in the 11B NMR
spectra. Hatched lines connect equivalent positions. Assignments were
made based on 1H–{11B(sel)} experiments and DFT calculations.
combined with DFT calculations. Table 1 shows 11B and 1H
NMR data of compounds 12, 15 and 16. Additional 1H and
31P–{1H} NMR data, assigned to exo-polyhedral ligands, can be
found in the Experimental section.
The 11B{1H} NMR spectra of the nido-cations, 12–16, show spectra with respect to the neutral counterparts depends on
peaks in the interval δ(11B) 16 to −26 ppm. Some signals the nature of the PR3 ligands (see ESI, Fig. S1 and S2†); thus,
exhibit relative intensities too, and these correspond to acci- the methyl-containing phosphines, PMe2Ph and PMe3, suffer a
dentally coincident resonances, which were indirectly resolved high frequency shift of ∼14 ppm in compounds 14 and 15,
1
by H–{11B} decoupling experiments that identified two sepa- whereas the PPh3 resonances are slightly shielded (∼2 ppm).
rate proton resonances and also established nine cage 11B–1H These significant changes are also suggestive of a strong influ-
(terminal) related pairs for the cluster B–H(exo) units. These ence of the proton on the exo-polyhedral ligands.
data reveal that the 11-vertex cationic nido-rhodathiaboranes
In the negative region of the 1H–{11B} NMR spectra, the
maintain an asymmetric structure in solution, which is nido-cations exhibit three signals (Fig. 2). The lowest frequency
in agreement with the presence of two 31P resonances in the multiplet, which is not affected by broad-band boron decou-
31P–{1H} spectra of these compounds.
pling, can be safely assigned to the Rh–H hydride ligand. In
The main difference that can be noted in the 11B NMR contrast, the singlet at the highest frequency and the doublet
spectra of the cationic nido-clusters versus their neutral parent at intermediate frequencies broaden when the boron broad-
counterparts is an overall deshielding of the boron resonances. band decoupling is turned off, indicating that these reson-
This is particularly so for the resonances that are assigned to ances are due to boron-bound protons and, therefore, they
the boron atoms at positions 2 and 5 in the cluster (Fig. 1), may be assigned to B–H–B (high frequency) and Rh–H–B
suggesting that there has been an important change in (intermediate frequency) bridging hydrogen atoms. Together,
the {Rh(H)(L)2}–{η4-SB9H9(Py)} bonding interaction upon pro- the NMR data demonstrate that the nido-hydridorhodathia-
tonation of the cluster (vide infra). The effect in the 13P–{1H} boranes are protonated on the pentagonal faces.
+
+
Table 1 11B and 1H NMR data for [8,8,8-(H)(PPh3)2-9-(Py)-nido-8,7-RhSB9H10
] (12) and [8,8,8-(H)(PMe3)(PPh3)-9-(Py)-nido-8,7-RhSB9H10] (15),
+
and [8,8,8-(H)(PMePh2)2-9-(PMePh2)-nido-8,7-RhSB9H10
]
(16) in CD2Cl2 compared to the corresponding DFT/GIAO-calculated 11B-nuclear shield-
ing values [in brackets]
12
15
16
Assign.a
δ(11B)
δ(1H)
δ(11B)
δ(1H)
3.89
δ(11B)
δ(1H)
3.62
5
3
9
4
2
11
6
10
15.7 [16.7]
8.9 [11.9]
[5.7]
−8.2 [−2.3]
−10.1 [−7.1]
−11.5 [−9.8]
−12.4 [−12.7]
−20.3 [−19.3]
−22.2 [−22.1]
3.79
3.14
—
15.3 [16.5]
7.9 [11.3]
[4.8]
−11.5 [−9.4]
[−8.2]
−15.4 [−9.6]
−21.9 [−13.9]
−23.3 [−20.6]
−25.9 [−22.7]
14.8 [14.5]
7.8 [9.6]
2.87
2.78
—
−8.5 [−8.5]
−7.1 [−2.1]
−5.9 [−1.5]
−9.8 [−9.0]
−13.2 [−12.3]
−21.9 [−22.4]
−20.9 [−22.1]
—
1.65
2.61
2.12
2.47
1.43
1.53
−4.32
−7.9b
−9.84e
1.42
2.67
1.49
2.34
0.35
0.61
−4.41
−7.13c
−10.28f
2.77
2.92
2.62
2.51
1.75
1.65
−4.19
−8.70d
−10.98g
1
μ(11, 10)
μ(9, 8)
Rh(8)–H
a Assignments based on 1H–{11B} selective experiments and DFT calculations. b Broad doublet: 60 Hz. c Broad doublet: 57 Hz. d Broad doublet:
58 Hz. e Apparent quartet: 1J(103Rh–1H) + 2J(31PA–1H) + 2J(31PB–1H) ≈ 15 Hz, 1J(103Rh–1H) = 16.3 Hz. f Apparent quartet: 1J(103Rh–1H) + 2J(31PA–1H)
+ 2J(31PB–1H) ≈ 19 Hz, 1J(103Rh–1H) = 20.2 Hz. g Apparent quartet: 1J(103Rh–1H) + 2J(31PA–1H) + 2J(31PB–1H) ≈ 18 Hz, 1J(103Rh–1H) = 17.1 Hz.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5123

View Article Online
Paper
Dalton Transactions
Scheme 3 Protonation of isonido-rhodathiaboranes to give isonido-
cations.
always formed in a mixture with its bis-(PMe2Ph)-ligated counter-
part, [1,1-(PMe2Ph)2-3-(Py)-isonido-1,2-RhSB9H8] (8), complicating,
therefore, the isolation of these compounds and of their
protonated derivatives, [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-isonido-1,2-
RhSB9H8]+, where PR3 = PPh3 and PMe2Ph (21) or PMe2Ph (18)
(Scheme 3). This can be inferred from Fig. 2 where is shown
the negative region of a 1H–{11B} NMR spectrum that was
measured a few minutes after the addition of TfOH to a solu-
tion of 4: the second trace from the top. This spectrum shows
the formation of a mixture of cationic bis-(PPh3)(PMe2Ph)-
ligated nido-conformers, 14a (red triangles) and 14b (blue tri-
angles), together with the isonido-polyhedral cations, 21 (red
ellipsoid) and 18 (blue ellipsoid).
Fig. 2 Negative region of 1H–{11B} spectra. From top to bottom: 12, 14,
15 and 16. The third trace from the bottom shows a mixture of proto-
nated nido-conformers, 14a and 14b, together with the cationic
isonido-clusters, 18 and 21 (vide infra), a result of protonation and
dehydrogenation.
However, the bis-(PMe2Ph)-ligated rhodathiaborane, 8, can
be synthesized selectively by treatment of the mixed (PMe2Ph)-
(PPh3)-ligated nido-parent compound, 4, with excess of
PMe2Ph. This reaction entails that the cationic cluster, 18, is
available by direct protonation of its parent neutral compound,
8, leading to its quantitative formation and subsequent charac-
terization as a single product. In contrast, its bis-(PPh3)-
(PMe2Ph)-ligated counterpart, 21, was characterized by multi-
nuclear NMR spectroscopy in mixtures such as those illus-
trated in Fig. 2.
The bis-(PMePh2)-ligated isonido-rhodathiaborane, an
analogue of 7–9, is not available from the thermal treatment
of [8,8,8-(H)(PMePh2)2-9-(Py)-nido-8,7-RhSB9H9] (3), precluding
the formation of the isonido-cation, [1,3-μ-(H)-1,1-(PMePh2)2-3-
(Py)-1,2-RhSB9H8]+ (22), by direct protonation of its hypotheti-
cal conjugate base, [1,1-(PMePh2)2-3-(Py)-isonido-1,2-RhSB9H8].
However, treatment of 3 with TfOH affords selectively the
product of protonation and H2 lost, compound 22 (see Fig. S3
included in the ESI† for this paper).
Fig. 3 DFT-optimized structures at the B3LYP/6-31G*/LANL2DZ level
+
for (left) [8,8,8-(H)(PMe3)(PPh3)-9-(Py)-nido-8,7-RhSB9H10
]
(15) and
(right) [8,8,8-(H)(PMePh2)2-9-(PMePh2)-nido-8,7-RhSB9H10
]
+ (16).
The final configuration of the B–H–B bridging hydrogen
atoms is ambiguous, because the initial hydrogen atom along
the B(9)–B(10) edge in the neutral hydridorhodathiaboranes
could shift to the adjacent B(10)–B(11) edge. Thus, we carried
out DFT-optimizations starting from nido-clusters that exhibi-
ted two contiguous bridging hydrogen atoms along the B(9)–
B(10) and Rh(8)–B(9) edges. In all cases, the optimization
ended with the bridging hydrogen atoms along the B(10)–B(11)
and Rh(8)–B(9) edges (Fig. 3). The calculated 11B chemical
shifts, presented in Table 1 for 12, 15 and 16, agree well with
the experimental data, supporting that this energetically favor-
able configuration of bridging hydrogen atoms is reasonable.
We have recently reported that the 11-vertex isonido-
rhodathiaboranes, [1,1-(PR3)2-3-(Py)-1,2-RhSB9H8], where PR3 =
PPh3 (7), PMe3 (9), or PPh3 and PMe3 (10), react with TfOH to
give 11-vertex cations of the formulation [1,3-μ-(H)-1,1-(PR3)2-
3-(Py)-isonido-1,2-RhSB9H8]+, where PR3 = PPh3 (17), PMe3 (19),
or PPh3 and PMe3 (20) (Scheme 3).35 From [8,8,8-(H)(PMe2Ph)-
(PPh3)-9-(Py)-nido-8,7-RhSB9H9] (4), the corresponding neutral
isonido-cluster, [1,1-(PMe2Ph)(PPh3)-3-(Py)-1,2-RhSB9H8] (11), is
The 11B and 1H NMR data of the cluster atoms for the
isonido-cations, 18, 19, 20 and 22, are listed in Table 2 together
with GIAO calculated nuclear magnetic chemical shieldings
for some of them. Overall the pattern of 11B spectra of the pro-
tonated isonido-cluster suffers a slight deshielding with respect
to the neutral parent isonido-compounds, but maintaining a
clear resemblance. Characteristic of this family of neutral and
cationic 11-vertex isonido-rhodathiaboranes is the presence
5124 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 2 11B and 1H NMR data for [1,3-μ-(H)-1,1-(PMe2Ph)2-3-(Py)-isonido-1,2-RhSB9H8]+ (18), [1,3-μ-(H)-1,1-(PMe3)2-3-(Py)-isonido-1,2-RhSB9H8]+
(19), [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-isonido-1,2-RhSB9H8]+ (20), and [1,3-μ-(H)-1,1-(PMePh2)2-3-(Py)-isonido-1,2-RhSB9H8]+ (22) in CD2Cl2 com-
pared to the corresponding DFT/GIAO-calculated 11B-nuclear shielding values [in brackets]
18
19
20
22
Assign.a
δ(11B)
δ(1H)
δ(11B)
δ(1H)
δ(11B)
δ(1H)
δ(11B)
δ(1H)
3
9
5
4
8
7
11
6
58.1
30.0
9.6
—
4.71
2.95
58.3 [60.9]
29.7 [31.1]
9.0 [17.2]
—
4.70
2.87
57.9 [60.1]
29.6 [29.4]
10.8 [16.9]
—
58.3
29.8
10.9
—
4.67
2.79
4.65
0.97
2.87
1.32
0.90
0.82
−0.13
0.58
−5.45d
[15.0]
8.9 [14.9]
−13.1
2.43
−13.2 [−13.6]
1.46
−13.6 [−13.8]
−23.8 [−15.3]
−21.8 [−15.2]
−19.9 [−14.4]
−26.2 [−21.2]
−12.9
0.80
[−14.2]
[−15.9]
−23.4
−24.3
0.35
0.74
−23.6 [−20.7]
−24.9 [−21.5]
0.40
0.75
−21.8
−22.5
0.21
2.27
10
1,3-μ-(H)
−6.40b
−6.70c
−5.28e
a Assignments based on 1H{11B} selective experiments and DFT calculations. b dt, 1J(103Rh–1H) = 25 Hz, 2J(31P–1H) = 16 Hz. c dt, 1J(103Rh–1H) =
25 Hz, 2J(31P–1H) = 16 Hz. d ddd, 1J(103Rh–1H) = 12 Hz, 2J(31P–1H) = 11 Hz. e dt, 1J(103Rh–1H) = 25 Hz, 2J(31P–1H) = 16 Hz.
of a high-frequency resonance of relative intensity 1 around
δ(11B) 60 ppm, which is assigned to the pyridine-substituted
B(3) vertex. This signal is well separated from the rest of the
peaks, which are in the range δ(11B) 30 to −28 ppm. The
31P–{1H} spectra demonstrate the presence of the exo-poly-
hedral ligands in each of the cationic isonido-clusters
(Fig. S4†). It is interesting to note that upon protonation the
Me-containing phosphine ligands, PMe3 and PMe2Ph, suffer a
shift to higher frequencies whereas the PPh3 ligand shifts
towards lower frequencies. As commented above, the same
effect is observed for the protonated nido-clusters versus their
neutral conjugated nido-bases.
1
1
The H–{11B} and H NMR spectra provide decisive data for
the characterization of the proton site on the clusters. Thus,
all the isonido-cations exhibit a multiplet in the range δ(1H)
−5.0 to −7.0 ppm, which broadens when the boron broad-
band decoupling is turned off (Fig. 4). 1H–{11B(sel)} experi-
ments that relate δ(1H) to corresponding directly bound δ(11B) Fig. 4 1H–{11B} NMR spectra showing the low-frequency resonance
assigned to the Rh(1)–H–B(3) bridging hydrogen atom. From top to
bottom: 17 (at −50 °C), 22, 20, 18 and 19.
demonstrated that these protons bind the pyridine-substituted
boron atom at the 3-position. This fact together with the multi-
plicity of the peaks demonstrate clearly that protonation takes
place along the Rh(1)–B(3) edge. Therefore, the presence of
1
these low-frequency multiplets in the H–{11B} NMR spectra is
obtained from CH2Cl2–hexane, 20a, showed an uncommon
case of conformational isomerism.47 This feature was com-
diagnostic of the formation of the isonido-cations. The chemi-
cal shift of this resonance moves towards low frequencies as
mented in a previous publication,35 and herein we give a
the phenyl rings on the PR3 ligands are substituted by methyl
groups (Fig. 4). This effect could be related to an increase in
the basicity of the phosphine ligands, to anisotropic effects of
the aromatic rings or to a combination of these and other
factors. It should be noted that the Rh–H–B resonance in the
bis-PPh3 species, 17, is only seen at low temperatures.35
rationale based on the intermolecular interactions in the
lattice. The results are compared with new structural data from
the crystal grown in Me2CO–hexane, 20b. This crystallographic
analysis is combined with DFT-calculations to estimate energy
variations driven by {Rh(PR3)2}–{ηn-SB9H8(Py)} conformational
changes.
The X-ray diffraction analysis of crystals 20a and 20b has
given rise to four [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-1,2-
RhSB9H8]+ structural isomers: three in the unit cell of 20a,
labeled as isonido-20a1, isonido-20a2 and nido-20a3 and one in
crystal 20b, labeled isonido-20b (Fig. 5). Of special relevance
are the distances that define the rhodium–thiaborane inter-
action in these conformational isomers. The interatomic-
X-ray diffraction analysis of [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-
1,2-RhSB9H8]+ (20)
Two crystals of this cationic rhodathiaborane were grown by
slow diffusion of hexane into TfOH acidified solutions of
the neutral parent compound, [1,1-(PMe3)(PPh3)-3-(Py)-1,2-
RhSB9H8] (10), in dichloromethane and in acetone. The crystal
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5125

View Article Online
Paper
Dalton Transactions
length pattern of this linkage is illustrated in Fig. 6 for: (a) the would be of the order of 2.4 to 2.5 Å; therefore in these cationic
cationic cluster, isonido-20b, (b) its DFT-optimized structure, conformational isomers, the Rh–B length can be viewed as
(c) the conformer, nido-20a3, (d) compound 10, (e) cluster 7, non-bonding, rendering a quadrilateral open face.
and ( f ) the parent rhodathiaborane, 1. Table
3
shows
This structural motif can be formed by a simple diamond-
additional Rh–B distances and angles for these compounds.
square process in a canonical closo-structure based on an octa-
The first noticeable difference of the protonated clusters dodecahedron, giving a more open structure that is usually
versus the neutral counterparts is an elongation of the classified as isonido.48–54
distances that involve the {Rh(PMe3)(PPh3)–{SB9H8(Py)}
In the neutral cluster [Fig. 6(d)], the Rh–B lengths of boron
interaction as well as the exo-polyhedral Rh–P lengths. In par- vertices, 4 and 5, flanking the sulfur atom, lie just on the
ticular, the conformers isonido-20a1, isonido-20a2 and isonido- upper part of the bonding limit that leads to the generation of
20b exhibit long Rh(1)–B(5) distances at 2.617(9), 2.7171(11) a triangular closo-face. However, the bis-PPh3-ligated analogue,
and 2.607(5) Å, respectively: the second being significantly [1,1-(PPh3)2-3-(Py)-1,2-RhSB9H8] (7) [Fig. 6(e)], exhibits a Rh(1)–
longer than the other two. A bonding Rh(1)–B(5) distance B(5) distance at 2.562 Å that falls just outside of what may be
considered as bonding. Thus previously reported by us as a
closo, this rhodathiaborane is perhaps better described as
isonido.
In marked contrast, the third conformer in crystal 20a,
nido-20a3, shows a {Rh(1)S(2)B(3)B(4)B(7)} pentagonal face
[Rh(1)–B(5) 3.5187(9) Å] distinctive of an 11-vertex polyhedral
boron-containing compound with a nido structure. This struc-
tural feature is clear from the comparison of the conformer
nido-20a3 with crystallographically determined [8,8-(PPh3)2-
nido-8,7-RhSB9H10] (1) [Fig. 6(c) and ( f ), respectively].
These structural changes found in the cationic conformers
with respect to the neutral counterparts indicate that the
metal–thiaborane linkage is non-rigid and that conformational
changes can be produced at a low energy cost in this system.
In order to evaluate this fact, we carried out DFT-optimizations
starting from the X-ray determined structure of isonido-20b,
adding a hydrogen atom along the Rh(1)–B(3) edge (closo/
Fig. 5 ORTEP-type drawing of [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-
isonido-labeling) as inferred by the spectroscopic NMR charac-
isonido-1,2-RhSB9H8]+ in crystal 20b. Only the ipso-carbon atoms on
terization. The initial structure of the isonido-cluster exhibited
the phenyl rings of the PPh3 ligand are included to aid clarity. Ellipsoids
a hydrogen atom in a bridging position at 1.698 Å from the
are shown at the 50% probability level.
Fig. 6 Details of [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-1,2-RhSB9H8]+: (a) crystallographically determined, cationic isonido-20b, (b) DFT-calculated
cationic isonido-20b, and (c) crystallographically determined, cationic nido-20a3. (d) Neutral [1,1-(PMe3)(PPh3)-3-isonido-(Py)-1,2-RhSB9H8] (10), (e)
neutral [1,1-(PPh3)2-3-(Py)-isonido-1,2-RhSB9H8] (7) and (f) neutral [8,8-(PPh3)2-nido-8,7-RhSB9H10] (1).
5126 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 3 Selected lengths [Å] and angles [°] of crystallographically determined neutral parent compounds [1,1-(PPh3)2-3-(Py)-isonido-1,2-RhSB9H8]
(7) and [1,1-(PMe3)(PPh3)2-3-(Py)-isonido-1,2-RhSB9H8] (10), together with the crystallographically determined [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-
1,2-RhSB9H8]+, isonido-20b, and DFT-calculated [1,3-μ-(H)-1,1-(PPh3)2-3-(Py)-1,2-RhSB9H8]+ (7a)a
7
7a
10
isonido-20b
Rh(1)–P(1)
Rh(1)–P(2)
Rh(1)–S(2)
Rh(1)–B(3)
2.3012(12)
2.3278(13)
2.3997(14)
2.085(6)
2.4852
2.5081
2.4685
2.092
2.2889(10) [2.3529]
2.2710(9) [2.36203]
2.3841(9) [2.4895]
2.087(4) [2.096]
2.3228(11) [2.4107]
2.3505(10) [2.4662]
2.3761(11) [2.4622]
2.098(4) [2.103]
Rh(1)–B(4)
Rh(1)–B(5)
2.400(6)
2.562(6)
2.592
2.850
2.401(4) [2.504]
2.471(4) [2.628]
2.475(5) [2.581]
2.607(5) [2.813]
Rh(1)–B(6)
Rh(1)–B(7)
2.387(6)
2.344(6)
2.473
2.415
2.380(4) [2.438]
2.354(4) [2.393]
2.445(5) [2.501]
2.374(4) [2.398]
P(1)–Rh(1)–P(2)
P(1)–Rh(1)–S(2)
P(2)–Rh(1)–S(2)
P(1)–Rh(1)–B(3)
P(2)–Rh(1)–B(3)
B(3)–Rh(1)–S(2)
96.97(4)
99.81
95.34
102.50
120.74
122.51
111.38
96.68(4) [97.55]
96.28(4) [98.14]
98.21(4) [97.30]
98.53(4) [96.67]
122.33(13) [125.11]
119.58(13) [121.80]
116.97(14) [111.97]
110.83(5)
102.32(5)
112.42(16)
112.65(17)
119.02(16)
103.17(4) [103.60]
110.92(3) [107.05]
114.79(11) [116.81]
108.42(11) [114.00]
120.32(11) [115.77]
a DFT-calculated values in brackets.
Rh(1)–B(3) edge. This structural change and the observed
anion/cation packing motifs commented below are clear proof
of the presence of a Rh(1)–H–B(3) bridging hydrogen atom in
the crystalline structures of compound 20.
Interestingly, the optimization of nido-20a3, starting with a
hydrogen atom along the Rh(8)–H–B(9) edge, ended with a
nido-structure that shows a bridging hydrogen atom along the
B(9)–B(10) edge on the pentagonal face, resembling the struc-
ture of the crystallographically determined [8,8-(PPh3)2-8,7-
RhSB9H10] [Fig. 6( f )], which is isoelectronic with the cationic
pyridine adduct. This suggests that in the solid state the nido-
conformer, 20a3, could exhibit the hydrogen atom, arising
from protonation, at the B(9)–B(10) edge rather than along the
Rh(8)–B(9) edge, as suggested by the isonido-configuration
(Fig. 7).
Fig. 7 DFT-calculated energies and structures, computed at the B3LYP/
6-31G*/LANL2DZ level for B–H–B containing nido- and Rh–H ligated
isonido-isomers, [(PMe3)(PPh3)(Py)RhSB9H9]+.
In any event, the DFT-calculated energy difference between
the optimized nido-structure and the isonido-cation is 2.5 kcal
mol−1 (Fig. 7). To put this energy into perspective, we should
bear in mind that the barrier to rotation about the single bond
of ethane is about 2.8 kcal mol−1, that hydrogen bond
strengths are generally estimated to be in the range 1 to
10 kcal mol−1, and that the differences in lattice energy among
different polymorphic forms is expected to be in the range 1 to
Rh(1) center and at 1.330 Å from the B(3) vertex, which after
optimization at the B3LYP/6-31G*/LANL2DZ level ended as a
hydride ligand trans to the sulphur vertex, with a distance of
2.094 Å to B(3) [Fig. 6(b) and Fig. 7].
2 kcal mol−1 47
Therefore, the DFT-calculated nido- and
.
isonido-energy minima for the polyhedral cation [(PMe3)(PPh3)-
RhSB9H9(Py)]+ demonstrate that these conformers are thermo-
dynamically accessible, providing a rationale for this signifi-
cant case of conformational isomorphism in crystal 20a
(different conformers in the same crystal), nicely comple-
mented by the existence of a different isonido-conformer in
crystal 20b.
To analyze possible packing motifs leading to crystal
environments that may favor the predominance of one confor-
mation versus another, we need to discuss in more detail the
crystal structures of 20a and 20b. Both structures are based on
a matrix of rhodathiaborane cations and triflate anions, which
assimilates solvent molecules. In the extended structure of
Note that in the calculated structures the Rh(1)–B(4) and
Rh(1)–B(5) lengths are substantially elongated with respect to
the experimental values (Fig. 6 and Table 3), suggesting that
there is an important withdrawal of skeletal electronic density
from the B(4)S(3)B(5) side to the B(6)B(3)B(7) side where the
cluster is protonated. This supports the commented experi-
mental data, giving a further indication that the Rh(1)–H–B(3)
bridging-bound hydrogen atom, fully characterized in solu-
tion, exerts a strong influence on the rhodium–thiaborane
bonding interaction. In this regard, it is also important to note
that the P(1)–Rh(1)–S(2) and P(2)–Rh(1)–S(2) angles decrease
significantly upon protonation (Table 3), proving the strong
effect brought about by the presence of a proton along the
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5127

View Article Online
Paper
Dalton Transactions
Fig. 10 Details of the intermolecular SPE involving the PPh3 ligands of
two isonido-conformers in 20a.
Fig. 8 Dimer of nido-conformers, 20a3, stabilized by pyridine π–π
interactions.
Fig. 11 Crystal packing of 20b along the c axis, showing the zigzag
ribbon-like structure running along the b axis.
Fig. 9 Crystal packing of 20a along the a axis: in red the layer of nido-
conformers, 20a3; in blue and green the isonido-conformers, 20a1 and
20a2.
leading to relatively short cage contacts (4.136 Å the shortest)
that are reminiscent of the interdigitated protruding teeth of a
zip fastener. The overall effect is the formation of zigzag
ribbon-like layers in the ab plane: two of these layers sandwich
a layer of nido-cages (Fig. 9).
Similarly, the isonido-clusters found in the crystal 20b
exhibit attractive interactions of the phenyl groups of adjacent
clusters forming dimers. This basic supramolecular motif
packs in the same fashion as their isonido-congeners above,
leading to a zigzag ribbon-like structure that runs along the b
axis. This packing forms large rhombohedral channels that are
filled with the triflate anions as well as co-crystallized solvent
molecules of hexane and acetone (Fig. 11).
It is interesting to note that in both crystals, 20a and 20b,
the triflate anions lie close to the pyridine rings of the poly-
hedral cations (shortest N⋯O length at 3.278 Å). As illustrated
in Fig. 12, the anion/cation packing motif involving the
isonido-clusters is virtually the same, being, as expected,
different for the nido-isomer. These packing motifs agree well
with the fact that there is a region of net positive charge
along the Rh(1)–B(3) edge of the polyhedral cations, where,
as demonstrated by NMR spectroscopy, the neutral isonido-
rhodathiaboranes are protonated.
crystal 20a, the nido-cations, 20a3, form dimers via π–π inter-
actions between the pyridine rings. The configuration of the
pyridine rings in the dimer falls into the category of parallel-
displaced,55 and an inversion centre relates both pyridine-sub-
stituted clusters (Fig. 8). These dimers pack along the crystallo-
graphic a direction forming ribbons that are repeated down
the b direction leading to the formation of a layer of cationic
nido-clusters (Fig. 9). There is one crystallographically indepen-
dent triflate anion at 3.780 Å from the pyridine rings, following
the nido-rhodathiaborane cations along the a axis.
Alternatively, both isonido-conformers, 20a1 and 20a2,
associate in pairs through sextuple phenyl embrace (SPE) inter-
actions (Fig. 10). The P⋯P separation and the Rh–P⋯P–Rh
colinearity are 6.9 Å and 173°, respectively, and fall in the
range reported for this attractive edge-to-face interaction
(Fig. 10).56 The resulting rhodathiaborane dimers pack along
the a-axis, forming two crystallographically independent
ribbons (blue and green in Fig. 9). Each dimer interleaves
between two {RhSB9}-heads of dimers on adjacent ribbons,
5128 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
The herein reported reactions with TfOH together with pre-
vious results with HCl36,64 give an overall view of the reactivity
of this family of rhodathiaboranes with Brønsted acid
(Scheme 4).
The reactions start by protonation of the cages along Rh–B
edges. The proton induces an enhancement of the Lewis
acidity of the clusters, which undergo further transformations
depending on the nature of the exo-polyhedral ligands and on
the anion: Cl− versus TfO−. Thus, upon protonation with HCl,
the putative cationic species suffer an attack of the chlorine
anion, leading to the formal incorporation of HCl into the
cluster framework, which in the case of the isonido-clusters
results in the opening of the structure to nido-species with
pentagonal faces; in addition, for the PPh3-ligated species,
phosphine release is also found (Scheme 4). In a similar
fashion, the neutral nido-reagents undergo formal HCl
addition and H2 liberation, followed, in some cases, by PPh3
extrusion (Scheme 4). The reactions with TfOH involve the
same protonated intermediates, which are more stable in
the presence of weakly coordinating triflate anions than in
the presence of strong coordinating chlorine anions.
However, upon protonation with TfOH, some of the nido-
clusters undergo H2 lost and nido → isonido transforma-
tions; but more spectacular is the lability of the bis-PPh3-
ligated isonido-rhodathiaborane, 7, that with TfOH leads to
an equilibrium between cationic and neutral OTf-ligated
species.35
The herein reported crystallographic and DFT studies
demonstrate that the high degree of flexibility associated with
the metal–thiaborane linkage upon protonation enables the
formation of different structural isomers that in the case
of the cation, [1,3-μ-(H)-1,1-(PMe3)(PPh3)-3-(Py)-isonido-1,2-
RhSB9H8]+, are stabilized in the solid state by common inter-
molecular interactions. This proton-induced cluster non-rigid-
ity can lead to new ways of reactivity by polyhedral boron-
containing compounds, which may be useful in the activation
of unreactive bonds.
Fig. 12 View of isonido-cation/triflate packing motifs in crystals 20a
and 20b, and the nido-cation/triflate packing recognition.
After this analysis, it is clear that there are two packing
motifs that play an important role in the stabilization of
different conformers in the unit cell of crystal 20a. Thus, π–π
pyridine dimer formation brings about a distortion of the 11
vertex rhodathiaborane cage to give a nido-structure with a
pentagonal face, whereas attractive edge-to-face interactions of
phenyl groups favor a closer isonido-conformation with a
pseudo-Cs symmetry. We should bear in mind that π–π pyri-
dine binding energies have been calculated to be in the range
2.2 to 3.8 kcal mol−1 55
action of a phenyl ring within a SPE is estimated to be 2.4 kcal
mol−1 to 3.3 kcal mol−1 56 It is clear that given the proximity of
,
and that an edge-to-face attractive inter-
.
cluster conformational energies between the nido- and isonido-
rhodathiaborane cations, these intermolecular forces are
sufficient to stabilize both isomers. Thus, the creation of
different crystal environments within the lattice leads to the
formation of different conformers in the same unit cell.
We are currently developing these and other aspects,
dealing with the reaction chemistry of these unique
rhodathiaboranes.
General considerations and
conclusions
Experimental section
General
11-Vertex nido- and isonido-rhodathiaboranes are easily proto- All reactions were carried out under an argon atmosphere
nated by TfOH to afford nido- and isonido-cations. Since the using standard Schlenk-line techniques. Solvents were
yields of these neutral 11-vertex rhodathiaboranes are generally obtained from an Innovative Technology Solvent Purification
good, this is a convenient entry into the area of polyhedral System. All commercial reagents were used as received without
boron-containing cations which is scarcely explored with further purification. The rhodathiaboranes [8,8,8-(H)(PR3)2-9-
only a small number of reported cationic boranes and (Py)-nido-8,7-RhSB9H9], where PR3 = PPh3 (2), PMePh2 (3), PPh3
metallaheteroboranes.39–46,57–63 It is important to recall and PMe2Ph (4), PPh3 and PMe3 (5); [8,8,8-(H)(PMePh2)2-9-
that the majority of reported cationic metallaheteroboranes (PMePh2)-nido-8,7-RhSB9H9] (6), and [1,1-(PR3)2-3-(Py)-1,2-
generally contain charge-compensating ligands;41–46 and the RhSB9H8] where PR3 = PPh3 (7), PMe2Ph (8), PMe3 (9), PPh3
number of cationic polyhedral boron clusters formed by and PMe3 (10), or PPh3 and PMe2Ph (11), were prepared by
simple protonation is very small indeed.39,40
published methods.30,33,34 The synthesis and characterization
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5129

View Article Online
Paper
Dalton Transactions
Scheme 4 Stepwise reactions of 11-vertex rhodathiaboranes with HCl and TfOH.
of the cationic rhodathiaboranes, [8,8,8-(H)(PPh3)2-9-(Py)-nido- head. Data collection was performed using a Bruker Kappa
8,7-RhSB9H10]+ (12) and [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-isonido-1,2- APEX DUO CCD area detector diffractometer with monochro-
RhSB9H9]+, where PR3 = PPh3 (17), PMe3 (19), PPh3 and PMe3 matic radiation λ(MoΚα) = 0.7107073 Å, using narrow frames
(20), were reported previously.35,36
(0.3° in ω). The data were reduced (SAINT)66 and corrected for
NMR spectra were recorded on Bruker Avance 300 MHz and absorption effects by multiscan methods (SADABS).67 The
AV 400 MHz spectrometers, using 11B, 11B–{1H}, 1H, 1H{11B}, structure was solved using the SHELXS-86 program,68 and
1H{11B(selective)} and 31P–{1H} techniques. H chemical shifts refined against all F2 data by full-matrix least-squares tech-
1
were measured relative to partially deuterated solvent peaks niques (SHELXL-97).69 All non-hydrogen atoms were refined
but are reported in ppm relative to tetramethylsilane. 11B with anisotropic displacement parameters. Hydrogen atoms
chemical shifts were measured relative to [BF3(OEt)2)]. 31P were included in calculated positions and refined with a posi-
(121.48 MHz) chemical shifts were measured relative to H3PO4 tional and thermal riding model.
(85%). Mass spectrometry data were recorded using a VG Auto-
spec double focusing mass spectrometer, a microflex MALDI- plementary crystallography data for this paper.
TOF, and a ESQUIRE 3000+ API-TRAP, operating in either posi-
[8,8,8-(H)(PMePh2)2-9-(Py)-nido-8,7-RhSB9H10]+ (13). In
CCDC 907304 (20a) and 937675 (20b) contains the sup-
a
tive or negative mode. In each case there was excellent corres- 5 mm NMR tube, a solution of [8,8,8-(H)(PMePh2)2-9-(Py)-nido-
pondence between the calculated and measured isotopomer 8,7-RhSB9H9] (3) (0.0054 mg, 0.0075 mmol) in CD2Cl2 (0.3 mL)
envelopes. A well-matched isotope pattern may be taken as a under argon was treated with triflic acid (0.66 mL,
good criterion of identity.65
0.075 mmol). The resulting light orange sample was studied by
NMR spectroscopy. The data revealed the formation of a
mixture formed by the nido-cluster, 13, and its dehydrogena-
tion isonido-product, 22 (see below), in a 1 : 0.5 ratio. As time
passes, this mixture of compounds changes to give 22 as a
single product. This reactivity precluded the isolation of 13,
and its characterization was carried out in situ in samples that
contained mixtures of this cationic hydridorhodathiaborane
(two conformers, see Fig. S3 ESI†) and its isonido-derivative.
NMR data: the A label corresponds to the major conformer
and B to the minor. 11B (128 MHz; CD2Cl2; 298 K): δ 15.6, 12.8,
X-ray structure analysis of crystals 20a and 20b
Crystal 20a was grown by slow diffusion of hexane into a
dichloromethane solution, and its structure has been pre-
viously reported (CCDC 907304). Crystal 20b was obtained by
slow diffusion of hexane into an acetone solution (CCDC
937675). In both cases, the studied crystals, 20a and 20b, were
coated with perfluoropolyether, mounted on a glass fiber and
fixed in a cold nitrogen stream (T = 100(2) K) to the goniometer
5130 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
1
6.8, 4.5, −11.2, −14.9, −21.0, −23.6. NMR H–{11B} (400 MHz, 9-(PMePh2)-nido-8,7-RhSB9H10] (6) (45.6 mg; 0.054 mmol) was
3
CD2Cl2, 300 K): δ 10.64 (2H, d, JHH = 4.8 Hz, HoA-NC5H5), added 5 μL (0.054 mmol) of triflic acid (HOTf). After 30 min of
3
3
10.36 (1H, t, JHH = 8.1 Hz, HpA-NC5H5), 10.19 (2H, d, JHH
=
stirring at −30 °C under an argon atmosphere, the solvent was
3
5.2 Hz, HoB-NC5H5), 10.02 (1H, t, JHH = 7.9 Hz, HpB-NC5H5), removed under vacuum and the residue was washed three
3
9.66 (2H, t, JHH = 6.7 Hz, HmA-NC5H5), 9.50 (2H, m, HmB
-
times with hexane to afford 41.7 mg of compound 16
NC5H5), 9.6 to 8.7 (40H, m, PMePh2), 3.88 (1H, s, BH), 2.58 (0.072 mmol, 78%). NMR 1H–{11B} (500 MHz, CD2Cl2, 300 K): δ
2
2
(1H, s, BH), 2.36 (1H, s, BH), 2.29 (3H, d, JHP = 10.9 Hz, 7.80 to 6.65 (30H, m, PMePh2), 2.24 (3H, d, JHP = 13.2 Hz,
PMeAPh2), 2.16 (3H, d, JHP = 10.9 Hz, PMeBPh2), 1.90 (3H, d, PMePh2), 2.11 (3H, d, 2JHP = 11.2 Hz, PMePh2), 2.07 (3H, d, 2JHP
2
2JHP = 9.6 Hz, PMeBPh2), 1.81 (3H, d, JHP = 10.9 Hz, PMeAPh2), = 10.0 Hz, PMePh2). NMR 31P–{1H} (202 MHz; CD2Cl2; 298 K):
2
1
1
1.62 (1H, s, BH), 1.12 (1H, s, BH), −4.28 (1H, s, BHAB), −4.54 δ 28.8 (1P, d, JPRh = 121 Hz, PMePh2), 10.0 (1P, dd, JPRh
=
2
(1H, s, B–HB–B), −5.18 (1H, m, Rh–HB–B), −7.49 (1H, d br, 99.5 Hz, JPP = 28 Hz, PMePh2), 2.6 (1P, q, B-PMePh2).
1JHRh 2JPH = 60 Hz, Rh–HA–B), −10.16 (1H, apparent q, LRMS (MALDI+/DIT): m/z calcl. for C39H50B9P3RhS: 843
≈
1JHRh ≈ JHP = 20.5 Hz, Rh–HA), −10.64 (1H, m, Rh–HB). NMR [M]+; found 843, the isotope envelope matches that calculated
2
31P–{1H} (162 MHz; CD2Cl2; 298 K):
δ 30.5 (1P, dd, from the known isotopic abundances of the constituent
1JPRh = 121 Hz, JPP = 25 Hz, PAMePh2), 27.7 (1P, dd, JPRh
=
=
elements.
2
1
2
1
136 Hz, JPP = 22 Hz, PBMePh2), 15.7 (1P, d-br, JPRh
117 Hz, PAMePh2), 12.5 (1P, dd, JPRh = 100 Hz, JPP = 25 Hz, To 0.3 mL of a CD2Cl2 solution of neutral [1,1-(PMe2Ph)2-3-
PAMePh2). (Py)-isonido-1,2-RhSB9H8] (8) (3.8 mg; 0.064 mmol) in a 5 mm
[1,3-μ-(H)-1,1-(PMe2Ph)2-3-(Py)-isonido-1,2-RhSB9H8]+
(18).
1
2
[8,8,8-(H)(PMe2Ph)(PPh3)-9-(Py)-nido-8,7-RhSB9H9]+ (14). A NMR tube was added 0.57 μL of TfOH. The initial red colour of
5 mm NMR tube was charged with 5.4 mg (0.0075 mmol) of the solution turned into yellow upon addition of the strong
[8,8,8-(H)(PMe2Ph)(PPh3)-9-(Py)-nido-8,7-RhSB9H9] (4), 0.3 mL acid. The reaction was studied by multinuclear NMR spec-
of CD2Cl2 and 0.66 μL (0.075 mmol) of TfOH. The resulting troscopy, showing a quantitative protonation of 8 to give 18.
orange solution was studied by NMR spectroscopy. The data Spectral data of 18: NMR H–{11B} (300 MHz; CD2Cl2; 298 K):
1
3
3
demonstrated the formation of a mixture of protonated 14, δ 9.23 (2H, d, JHH = 5.4 Hz, Ho-NC5H5), 8.58 (1H, t, JHH
=
[1,3-μ-(H)-1,1-(PMe2Ph)(PPh3)-3-(Py)-isonido-1,2-RhSB9H8]+ (21) 7.8 Hz, Hp-NC5H5), 8.14 (2H, t, JHH = 7.8 Hz, Hm-NC5H5), 1.55
3
and [1,3-μ-(H)-1,1-(PMe2Ph)2-3-(Py)-closo-1,2-RhSB9H8]+ (18) in (6H, [AX3]2 spin system, N = JHP
+
4JHP = 10.5 Hz, PMe2Ph),
2
2
a
1 : 1 : 0.5 ratio, respectively. After several hours, the 1.48 (6H, [AX3]2 spin system, N = JHP
+
4JHP = 10.2 Hz,
system evolves to give a mixture that contains the isonido- PMe2Ph). 31P NMR (121 MHz; CD2Cl2; 298 K): δ 0.51 (2P, d,
derivatives, 21 and 18, in a 1 : 0.3 ratio. 14: 1H–{11B} NMR 1JPRh = 100 Hz, PMe2Ph). NMR 19F–{1H} (282 MHz; CD2Cl2;
2
(400 MHz, CD2Cl2, 300 K): δ 2.25 (6H, overlapped t, JHP
=
=
300 K): δ −78.8 (3F, s, OTf). LRMS (MALDI+/DIT): m/z calcl.
1
13.6 Hz, PMe2Ph), −4.42 (1H, s, B–H–B), −7.38 (1H, d, JHRh
for C21H36B9NP2RhS: 597 [M]+; found 597. Calcl. for
56.6 Hz, B–H–Rh), −10.1 (1H, q, JHRh ≈ JPP = 22 Hz, Rh–H). C13H25B9NPRhS: 458 [M − PMe2Ph]+; found 521. Isotope envel-
1
2
1
31P–{1H} NMR (162 MHz; CDCl3; 298 K): δ 32.9 (1P, dd, JPRh
=
opes match those calculated from the known isotopic abun-
2
1
97 Hz, JPP = 22 Hz, PPh3), 14.4 (1P, d br, JPRh = 116 Hz, dances of the constituent elements.
PMe2Ph).
[1,3-μ-(H)-1,1-(PMe2Ph)(PPh3)-3-(Py)-isonido-1,2-RhSB9H8]+
[8,8,8-(H)(PMe3)(PPh3)-9-(Py)-nido-8,7-RhSB9H10]+
(15). A (21). Obtained in the reaction of 14 with TfOH as described
Schlenk tube, immersed in an isopropanol/dry ice bath at above, it was characterized in situ. 1H–{11B} NMR (400 MHz,
2
−15 °C, was charged (under an atmosphere of argon) with CD2Cl2, 300 K): δ 1.59 (3H, d, JHP = 10.5 Hz, PMe2Ph),
2
1
20 mg (0.030 mmol) of [8,8,8-(H)(PMe3)(PPh3)-9-(Py)-nido-8,7- 1.39 (3H, d, JHP = 10.6 Hz, PMe2Ph), −5.51 (1H, ddd, JHRh
=
RhSB9H9] (5), 10 mL of CD2Cl2 and 2.69 μL (0.030 mmol) 23 Hz, JHP = 14 Hz, JHP = 17 Hz, B–H–Rh). 31P–{1H} NMR
2
2
of TfOH. The reaction mixture was stirred for 15 minutes. (162 MHz; CD2Cl2; 298 K): δ 35.9 (1P, dd, 1JPRh = 110 Hz, 2JPP
=
1
2
The solvent was then removed in vacuo and the residue was 20 Hz, PPh3), −1.5 (1P, dd, JPRh = 100 Hz, JPP = 20 Hz,
washed three times with hexane to yield 16.0 mg of PMe2Ph).
15 (0.019 mmol, 66%). 1H–{11B} NMR (400 MHz, CD2Cl2,
[1,3-μ-(H)-1,1-(PMePh2)2-3-(Py)-isonido-1,2-RhSB9H8]+ (22). A
300 K): δ 8.86 (2H, d, 2JHH = 5.5 Hz, Ho-NC5H5), 8.32 (1H, t, Hp- 14.6 mg (0.02 mmol) amount of [8,8,8-(H)(PMePh2)2-9-(Py)-
NC5H5), 7.85 (2H, t, Hm-NC5H5), 7.62 and 7.20 (15H, m, PPh3), nido-8,7-RhSB9H9] (3) was dissolved in 10 mL of dichloro-
2
1.42 (6H, d, JHP = 11.1 Hz, PMe3). 31P–{1H} NMR (162 MHz; methane in a Schlenk tube immersed in a dry-ice bath at
1
2
CDCl3; 298 K): δ 33.9 (1P, dd, JPRh = 110 Hz, JPP = 22 Hz, −25 °C. Then TfOH (1.8 μL, 0.020 mmol) was added, and the
1
2
PPh3), 6.3 (1P, dd, JPRh = 104 Hz, JPP = 22 Hz, PMe3). NMR reaction mixture was stirred for 1 h at −25 °C. The solvent was
19F–{1H} (282 MHz; CD2Cl2; 300 K): δ −78.2 (3F, s, OTf). then removed in vacuo and the residue was washed three times
LRMS (MALDI+/DIT): m/z calcl. for C26H40B9NP2RhS: 659 with hexane to yield 11.0 mg of 22 (0.013 mmol, 63%). NMR
[M − 2H]+; found 659. Calcl. for C23H29B9NPRhS: 583 [M − (2H + 1H–{11B} (500 MHz, CD2Cl2, 298 K): δ 9.05 (2H, d, JHH
=
2
PMe3)]+; found 58. Isotope envelopes match those calculated 5.6 Hz, Ho-NC5H5), 8.61 (1H, t, Hp-NC5H5), 8.14 (2H, t, Hm-
from the known isotopic abundances of the constituent elements. NC5H5), 7.83 a 6.89 (20H, m, PMePh2), 1.84 (6H, [AX3]2 spin
2
[8,8,8-(H)(PMePh2)2-9-(PMePh2)-nido-8,7-RhSB9H10]+
(16). system, N = JHP
+
4JHP = 8.6 Hz n, 2PMePh2). NMR 31P–{1H}
1
To 7 mL of a dichloromethane solution of [8,8,8-(H)(PMePh2)2- (202 MHz, CD2Cl2, 298 K): δ 12.3 (2P, d, JPRh = 141 Hz,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5131

View Article Online
Paper
Dalton Transactions
PMePh2). NMR 19F–{1H} (282 MHz, CD2Cl2, 300 K): 20 A. M. Spokoyny, M. G. Reuter, C. L. Stern, M. A. Ratner,
δ −78.5 (3F, s, OTf). LRMS (MALDI+/DIT): m/z calcl. for
C31H40B9NP2RhS: 721 found 721. Calcl.
[M]+;
T. Seideman and C. A. Mirkin, J. Am. Chem. Soc., 2009, 131,
9482–9483.
for C18H27B9NPRhS: 521 [M − PMePh2]+; found 521. Isotope 21 S. Liu, Y.-F. Han and G.-X. Jin, Chem. Soc. Rev., 2007, 36,
envelopes match those calculated from the known isotopic
1543–1560.
abundances of the constituent elements.
22 X. Wang, S. Liu, L.-H. Weng and G.-X. Jin, Chem.–Eur. J.,
2007, 13, 188–195.
23 N. P. E. Barry and P. J. Sadler, Chem. Soc. Rev., 2012, 41,
3264–3279.
24 J. A. Belmont, J. Soto, R. E. King, A. J. Donaldson,
J. D. Hewes and M. F. Hawthorne, J. Am. Chem. Soc., 1989,
111, 7475–7486.
25 J. D. Kennedy and B. Stíbr, in Current Topics in the
Chemistry of Boron, ed. G. Kabalka, The Royal Society of
Chemistry, Cambridge, 1994, pp. 285–292.
26 J. D. Kennedy, in The Borane, Carborane, Carbocation
Continuum, ed. J. Casanova, Wiley, New York, 1998, pp.
85–116.
Notes and references
1 Boron Science: New Technologies and Applications, ed.
N. S. Hosmane, CRC Press, Boca Raton, FL, 2012.
2 R. N. Grimes, Carboranes, Academic Press, Elsevier Inc.,
Amsterdam, 2011.
3 R. B. King, J. Math. Chem., 1990, 4, 69–85.
4 J. Aihara, J. Am. Chem. Soc., 1978, 100, 3339–3342.
5 L. Wesemann, in Comprehensive Organometallic Chemistry,
ed. D. M. P. Mingos and R. H. Crabtree, Elsevier, Oxford, 27 C. W. Jung and M. F. Hawthorne, J. Am. Chem. Soc., 1980,
2007, vol. 3, pp. 113–131. 102, 3024–3032.
6 N. S. Hosmane and J. A. Maguire, in Comprehensive 28 P. E. Behnken, D. C. Busby, M. S. Delaney, R. E. King,
Organometallic Chemistry, ed. R. H. Crabtree and D. M. P.
Mingos, Elsevier, Oxford, 2007, vol. 3, ch. 3.05, pp.
175–264.
C. W. Kreimendahl, T. B. Marder, J. J. Wilczynski and
M. F. Hawthorne, J. Am. Chem. Soc., 1984, 106, 7444–
7450.
7 T. Onak, in Comprehensive Organometallic Chemistry, ed. 29 P. E. Behnken, J. A. Belmont, D. C. Busby, M. S. Delaney,
E. W. Abel, F. G. A. Stone and G. Wilkinson, Elsevier
Science Ltd, Oxford, 1995, vol. 1, pp. 217–255.
8 R. N. Grimes, in Comprehensive Organometallic Chemistry II,
R. E. King, C. W. Kreimendahl, T. B. Marder,
J. J. Wilczynski and M. F. Hawthorne, J. Am. Chem. Soc.,
1984, 106, 3011–3025.
ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, 30 Á. Álvarez, R. Macías, J. Bould, C. Cunchillos, F. J. Lahoz
Oxford, 1995, vol. 1, pp. 373–430. and L. A. Oro, Chem.–Eur. J., 2009, 15, 5428–5431.
9 L. T. Todd, in Comprehensive Organometallic Chemistry, ed. 31 Á. Álvarez, R. Macías, M. J. Fabra, F. J. Lahoz and L. A. Oro,
G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon
Press Ltd, Oxford, 1982, vol. 1, pp. 534–553.
10 T. Onak, in Comprehensive Organometallic Chemistry, ed.
J. Am. Chem. Soc., 2008, 130, 2148–2149.
32 Á. Álvarez, R. Macías, J. Bould, M. J. Fabra, F. J. Lahoz and
L. A. Oro, J. Am. Chem. Soc., 2008, 130, 11455–11466.
G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon 33 B. Calvo, Á. Álvarez, R. Macías, P. García-Orduña,
Press, Ltd, Oxford, 1982, vol. 1, pp. 411–457.
F. J. Lahoz and L. A. Oro, Organometallics, 2012, 31, 2986–
11 R. N. Grimes, in Comprehensive Organometallic Chemistry,
2995.
ed. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon 34 B. Calvo, M. Kess, R. Macias, C. Cunchillos, F. J. Lahoz,
Press Ltd, Oxford, 1982, vol. 1, pp. 459–542.
12 Z. Xie, Acc. Chem. Res., 2003, 36(1), 9.
J. D. Kennedy and L. A. Oro, Dalton Trans., 2011, 40, 6555–
6564.
13 Z. Xie, Coord. Chem. Rev., 2002, 231, 23–46.
14 J. Zhang and Z. W. Xie, Pure Appl. Chem., 2013, 85, 661–
670.
15 S. Hao and X. Zuowei, in Boron Science, ed. N. S. Hosmane,
CRC Press, 2011, pp. 517–528.
35 B. Calvo, R. Macías, M. J. Artigas, F. J. Lahoz and L. A. Oro,
Chem.–Eur. J., 2013, 19, 3905–3912.
36 B. Calvo, R. Macías, C. Cunchillos, F. J. Lahoz and
L. A. Oro, Organometallics, 2012, 31, 2526–2529.
37 G. J. Kubas, Metal Dihydrogen and s-Bond Complexes: Struc-
ture, Theory and Reactivity, Kluwer Academic/Plenum,
New York, 2001.
16 S. Bauer and E. Hey-Hawkins, in Boron Science, ed.
N. S. Hosmane, CRC Press, 2011, pp. 529–578.
17 A. M. Spokoyny, C. W. Machan, D. J. Clingerman, 38 E. T. Papish, M. P. Magee and J. R. Norton, in Recent
M. S. Rosen, M. J. Wiester, R. D. Kennedy, C. L. Stern,
A. A. Sarjeant and C. A. Mirkin, Nat. Chem., 2011, 3, 590–
596.
Advances in Hydride Chemistry, ed. M. Peruzzini and R. Poli,
Elsevier, London, 2001, ch. 2, pp. 39–74.
39 O. Bondarev, Y. V. Sevryugina, S. S. Jalisatgi and
M. F. Hawthorne, Inorg. Chem., 2012, 51, 9935–
9942.
40 W. C. Kalb, Z. Demidowicz, D. M. Speckman, C. Knobler,
R. G. Teller and M. F. Hawthorne, Inorg. Chem., 1982, 21,
4027–4036.
18 A. M. Spokoyny, C. D. Lewis, G. Teverovskiy and
S. L. Buchwald, Organometallics, 2012, 31, 8478–
8481.
19 M. E. El-Zaria, H. Arii and H. Nakamura, Inorg. Chem.,
2011, 50, 4149–4161.
5132 | Dalton Trans., 2014, 43, 5121–5133
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
41 A. R. Kudinov, P. Zanello, R. H. Herber, D. A. Loginov, 54 J. Bould, C. Cunchillos, F. J. Lahoz, L. A. Oro,
M. M. Vinogradov, A. V. Vologzhanina, Z. A. Starikova,
M. Corsini, G. Giorgi and I. Nowik, Organometallics, 2010,
29, 2260–2271.
J. D. Kennedy and R. Macías, Inorg. Chem., 2010, 49, 7353–
7361.
55 Q. A. Smith, M. S. Gordon and L. V. Slipchenko, J. Phys.
Chem. A, 2011, 115, 4598–4609.
42 G. Ferguson, J. Pollock, P. A. McEneaney, D. P. Oconnell,
T. R. Spalding, J. F. Gallagher, R. Macías and J. D. Kennedy, 56 I. Dance and M. Scudder, J. Chem. Soc., Chem. Commun.,
Chem. Commun., 1996, 679–681. 1995, 1039–1040.
43 D. D. Ellis, P. A. Jelliss and F. G. A. Stone, Dalton Trans., 57 J. J. Solomon and R. F. Porter, J. Am. Chem. Soc., 1972, 94,
2000, 2113–2122. 1443–1450.
44 R. Núñez, O. Tutusaus, F. Teixidor, C. Viñas, R. Sillanpää 58 E. L. Muetterties, Pure Appl. Chem., 1965, 10, 53.
and R. Kivekäs, Chem.–Eur. J., 2005, 11, 5637–5647.
45 J. G. Planas, C. Viñas, F. Teixidor, M. E. Light,
59 P. Brint, E. F. Healy, T. R. Spalding and T. Whelan, J. Chem.
Soc., Dalton Trans., 1981, 2515–2522.
M. B. Hursthouse and H. R. Ogilvie, Eur. J. Inorg. Chem., 60 E. J. M. Hamilton, H. T. Leung, R. G. Kultyshev, X. Chen,
2005, 2005, 4193–4205.
E. A. Meyers and S. G. Shore, Inorg. Chem., 2012, 51, 2374–
46 J. P. Sheehan, T. R. Spalding, G. Ferguson, J. F. Gallagher,
2380.
B. Kaitner and J. D. Kennedy, J. Chem. Soc., Dalton Trans., 61 M. Kameda, M. Shimoi and G. Kodama, Inorg. Chem., 1984,
1993, 35–42. 23, 3705–3709.
47 J. Bernstein, Polymorphism in Molecular Crystals, Oxford 62 M. Kameda and G. Kodama, Inorg. Chem., 1985, 24, 2712–
University Press, Oxford, 2002. 2714.
48 K. Nestor, X. L. R. Fontaine, N. N. Greenwood, 63 M. Kameda and G. Kodama, J. Am. Chem. Soc., 1980, 102,
J. D. Kennedy, J. Plešek, B. Štíbr and M. Thornton-Pett,
Inorg. Chem., 1989, 28, 2219–2221.
3647–3649.
64 B. Calvo, R. Macías, M. J. Artigas, F. J. Lahoz and L. A. Oro,
Inorg. Chem., 2012, 52, 211–221.
65 W. Henderson and J. S. McIndoe, Mass Spectrometry of
Inorganic and Organometallic Compounds, John Wiley &
Sons Ltd, 2005.
66 Z. Otwinowski and W. Minor, in Methods in Enzymology, ed.
J. R. M. S. C. W. Carter, Academic Press, New York, 1997,
vol. 276, pp. 307–326.
67 R. H. Blessing, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 1995, 51, 33.
49 M. Bown, X. L. R. Fontaine, N. N. Greenwood, J. D. Kennedy
and M. Thornton-Pett, Organometallics, 1987, 6, 2254–2255.
50 M. Bown, X. L. R. Fontaine, N. N. Greenwood,
J. D. Kennedy and M. Thornton-Pett, J. Chem. Soc., Dalton
Trans., 1990, 3039–3049.
51 K. Nestor, X. L. R. Fontaine, N. N. Greenwood,
J. D. Kennedy and M. Thornton-Pett, J. Chem. Soc., Chem.
Commun., 1989, 455–456.
52 J. Bould, N. P. Rath and L. Barton, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1997, 53, 416–419.
68 G. M. Sheldrick, Acta Crystallogr., 1990, A46, 467–473.
53 O. Volkov, R. Macias, N. P. Rath and L. Barton, J. Organo- 69 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
met. Chem., 2002, 657, 40–47.
logr., 2008, 64, 112–122.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 5121–5133 | 5133