Facile formation of exo-nido→closo-rearrangement products upon the replacement of PPh3 ligands with bis(diphenylphosphino)alkanes in "three-bridge" ruthenacarborane 5,6,10-[RuCl(PPh3) 2]-5,6,10-(μ-H)3-10-H-exo-n

Article abstract of DOI:10.1007/s11172-006-0151-0

The replacement of the PPh₃ ligands in "three-bridge" exo-nido-ruthenacarborane 5,6,10-[RuCl(PPh₃)₂]-5,6,10- (μ-H)₃-10-H-exo-nido-7,8-C₂B₉H₈ with diphosphines, viz., 1,3-bis(diph

Full text of DOI:10.1007/s11172-006-0151-0

Russian Chemical Bulletin, International Edition, Vol. 54, No. 11, pp. 2535—2539, November, 2005
2535
Facile formation of exoꢀnido→closoꢀrearrangement products
upon the replacement of PPh3 ligands with bis(diphenylphosphino)alkanes
in "threeꢀbridge" ruthenacarborane
5,6,10ꢀ[RuCl(PPh3)2]ꢀ5,6,10ꢀ(µꢀH)3ꢀ10ꢀHꢀexoꢀnidoꢀ7,8ꢀC2B9H8
D. N. Cheredilin, E. V. Balagurova, I. A. Godovikov, S. P. Solodovnikov, and I. T. Chizhevskyꢀ
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5085. Eꢀmail: chizbor@ineos.ac.ru
The replacement of the PPh3 ligands in "threeꢀbridge" exoꢀnidoꢀruthenacarborane
5,6,10ꢀ[RuCl(PPh3)2]ꢀ5,6,10ꢀ(µꢀH)3ꢀ10ꢀHꢀexoꢀnidoꢀ7,8ꢀC2B9H8 with diphosphines, viz.,
1,3ꢀbis(diphenylphosphino)propane (dppp) or 1,4ꢀbis(diphenylphosphino)butane (dppb) draꢀ
matically decreases the barrier to the thermal exoꢀnido→closo rearrangement affording the
chelate closoꢀcomplexes 3,3ꢀ[Ph2P(CH2)nPPh2]ꢀ3ꢀHꢀ3ꢀClꢀclosoꢀ3,1,2ꢀRuC2B9H11 (n = 3 or 4)
under mild conditions. In the reaction with dppp, the rearrangement is accompanied by the
formation of 17ꢀelectron paramagnetic closoꢀruthenacarborane 3,3ꢀ[Ph2P(CH2)3PPh2]ꢀ3ꢀClꢀ
closoꢀ3,1,2ꢀRuC2B9H11, which could be isolated as the main product when the reaction was
carried out at 80 °C.
Key words: synthesis, diphosphine exoꢀnidoꢀ and closoꢀruthenacarboranes,
exoꢀnido→closo rearrangement, paramagnetic closoꢀruthenacarborane.
The chemistry of exoꢀnidoꢀmetallacarboranes, in
which the metal atom is coordinated by the nidoꢀcarborane
ligand through a multiple twoꢀelectron threeꢀcenter
(B—H)n...M bonds (n = 2 or 3), is of interest because
these clusters can easily be transformed into new monoꢀ
nuclear closoꢀ1,2 or dinuclear exoꢀclosoꢀmetallacarboꢀ
ranes.3—5 A detailed study of the exoꢀnido→closo rearꢀ
rangement of metallacarboranes has been primarily perꢀ
formed for 16ꢀelectron "twoꢀbridge" bis(triphenylphosꢀ
phine)ꢀexoꢀnidoꢀrhodacarboranes.6 It has been found that
isomeric exoꢀnidoꢀ and closoꢀrhodacarboranes exist in soꢀ
lution as an equilibrium mixture, and for complexes conꢀ
taining the sterically more hindered carborane ligand, this
equilibrium is normally shifted to exoꢀnido structures.6 In
the case of stronger coordination of the transition metal
atom by the nidoꢀcarborane ligand via three twoꢀelectron
threeꢀcenter (B—H)3...M bonding interactions, only
18ꢀelectron chlorobis(triphenylphosphine)ꢀexoꢀnidoꢀ
metallacarboranes containing unsubstituted carborane can
be rearranged into isomeric closoꢀcomplexes. If M = Ru,
heating is required for such a rearrangement,1 whereas
compounds with M = Os undergo the rearrangement at
room temperature.2
[Ph2P(CH2)nPPh2] (n = 3 or 4) decreases the barrier to
the thermal exoꢀnido→closo rearrangement, with the reꢀ
sult that it proceeds in benzene at 22 °C.
Results and Discussion
The reaction of exoꢀnidoꢀruthenacarborane 1 with
a 10% excess of 1,4ꢀbis(diphenylphosphino)butane
(2, dppb) in benzene at 22 °C for 48 h afforded
the closoꢀcomplex 3,3ꢀ(dppb)ꢀ3ꢀHꢀ3ꢀClꢀclosoꢀ3,1,2ꢀ
RuC2B9H11 (3) (Scheme 1). After column chromatoꢀ
graphy of the reaction mixture (silica gel; C6H6—nꢀhexꢀ
ane, 1 : 1, as the eluent), product 3 was isolated as airꢀ
stable yellow crystals in 78% yield. Complex 3 is moderꢀ
ately soluble in C6H6, CH2Cl2, and acetone and is virtuꢀ
ally insoluble in hydrocarbons. Upon recrystallization
from a CH2Cl2—nꢀhexane mixture, complex 3 formed a
stable solvate with CH2Cl2.
The composition and structure of closoꢀcomplex 3 were
determined by elemental analysis and 31P{1H}, 1H,
1H{31P}, 13C{1H}, 11B, and 11B{1H} NMR spectroscopy.
The 31P{1H} NMR spectrum of complex 3 in CD2Cl2
exhibited two closely spaced singlet resonances with equal
intensities at δ 37.5 and 37.45 (the spectrum of 3 in C6D6
consists of only one collapsed resonance), which indiꢀ
cates that complex 3 contains the chelate dppb ligand
coordinated to the metal atom. It should be noted that the
In the present study, we found that the replacement of
the PPh3 ligands in "threeꢀbridge" exoꢀnidoꢀruthenaꢀ
carborane 5,6,10ꢀ[RuCl(PPh3)2]ꢀ5,6,10ꢀ(µꢀH)3ꢀ10ꢀ
Hꢀexoꢀnidoꢀ7,8ꢀC2B9H8 (1) with diphosphines
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2455—2459, November, 2005.
1066ꢀ5285/05/5411ꢀ2535 © 2005 Springer Science+Business Media, Inc.

2536
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005
Cheredilin et al.
Scheme 1
Although complex 3 was isolated under the aboveꢀ
mentioned conditions as the only product, TLC monitorꢀ
ing of the reaction provided evidence for the formation of
an apparent intermediate. The intermediate complex was
isolated as a mixture with complex 3 when the reaction
was terminated immediately after the disappearance of
the starting reagent 1 from the reaction mixture, i.e., after
approximately ~2 h. This complex was further identified
as 5,6,10ꢀ[RuCl(dppb)]ꢀ5,6,10ꢀ(µꢀH)3ꢀ10ꢀHꢀexoꢀnidoꢀ
7,8ꢀC2B9H8 (4). In spite of the fact that complex 4 was
observed on a silica gel column as an individual band,
whose Rf differs substantially from that of the final prodꢀ
uct (3, Rf = 0.75; 4, Rf = 0.35), this complex appeared to
be kinetically unstable since, upon storage in a benzene
solution, it is readily transformed into compound 3. This
fact was unambiguously confirmed by monitoring of the
1H NMR spectrum of this solution.
That is why the structure of exoꢀnidoꢀcomplex 4 was
i. C6H6, 22 °C, 48 h.
1
studied only by H and 31P{1H} NMR spectroscopy of a
~1 : 1 mixture of 4 with complex 3 (Fig. 1). The upfield
region of the 1H NMR spectrum from 0 to –20 ppm,
where the hydride resonances of the exopolyhedral
B—H...Ru bonds and the resonances of the Hextra atom
are observed, is proved to be most informative. Analysis
of the NMR data demonstrated that complex 4, like its
precursor 1, exists as a mixture of geometric isomers havꢀ
ing symmetric (s) and asymmetric (as) structures (see
Fig. 1). We assigned the signals of these isomers by analꢀ
ogy with the Ru 7 and Os 9 exoꢀnidoꢀcomplexes described
spectrum of the starting complex 1, which exists as a
mixture of symmetrical and asymmetrical isomeric speꢀ
cies, shows resonances of the PPh3 ligands at substantially
lower field (at δ 50—55) as a singlet and two doublets,
respectively.7 In the 1H NMR spectrum of complex 3, the
signals of the aliphatic moiety of the coordinated diꢀ
phosphine ligand are observed as four multiplets, the inꢀ
tensity of each multiplet being 2H. The resonances of the
methylene groups of the dppb ligand in 3 were assigned
based on the 1H{31P} NMR spectrum, in which the multiꢀ
plicities of the signals of the CH2 groups directly bound to
the phosphorus atoms differ substantially from those obꢀ
served in the 1H NMR spectrum, which allowed us to
estimate the coupling constant for the pairs of the
nonequivalent geminal protons HA and HB of these groups
(JA,B ≈ 14.5 Hz). The assignment was confirmed by the
{1H—1H} COSY correlation spectrum, which shows the
corresponding crossꢀpeaks between the signals for HA and
HB of each CH2 group. It should also be noted that the
1H NMR spectrum of complex 3 revealed a highꢀfield
resonance at δ –8.16 as a doublet of triplets with the
coupling constants J1 = 27.5 Hz and J2 = 6.0 Hz characꢀ
teristic of a metal hydride. In the 1H{31P} NMR specꢀ
trum, this signal is collapsed to a doublet with J2 = 6.0 Hz.
Hence, the coupling constants J1 and J2 in the initially
H3(Ru)
a
Hasꢀ4(6)
H
sꢀ4(5,6)
Hasꢀ4(10)
(s+as)ꢀ4
Hsꢀ4(10)
Hextra
H
asꢀ4(5)
–4
–8
–12
δ
P3
b
Psꢀ4
2
observed doublet of triplets can be assigned to JH,P and
3JH,H, respectively. The constant 3JH,H is associated with
either the longꢀrange spinꢀspin coupling H(Ru)...H(B)
through the metal atom or the specific throughꢀspace
coupling interaction between the metal hydride and
the hydrogen atom of the BH group, which has been
observed earlier for the structurally similar rutheꢀ
nium complexes closoꢀ3,3ꢀ(PPh3)2ꢀ3ꢀHꢀ3ꢀClꢀ3,1,2ꢀ
RuC2B9H11 (see Ref. 1) and 1,1ꢀ(PPh3)2ꢀ1ꢀHꢀ1ꢀClꢀclosoꢀ
1,2,3ꢀRuC2B4H6 (see Ref. 8).
P
asꢀ4(1)
Pasꢀ4(2)
56
52
48
44
40
δ
Fig. 1. 1H NMR (a) and 31P{1H} NMR (b) spectra of a mixture
of the s and as isomers of complexes 3 and 4 in CD2Cl2.

[Bis(phosphino)alkane]ꢀclosoꢀruthenacarboranes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005 2537
Scheme 2
earlier. The presence of two isomers in a solution of 4 was
confirmed also by the 31P{1H} NMR spectrum of 4 in
CD2Cl2, which showed two sets of resonances, a singlet at
δ 51.8 (s isomer) and two doublets of equal intensities at
δ 55.5 and 50.3 with 2JP,P = 35 Hz (the as isomer).
* Trace amounts.
plates using a 1 : 1 benzene—hexane mixture as the eluꢀ
ent. The 1H and 31P{1H} NMR spectroscopic data for
diamagnetic complex 8 agree well with its postulated strucꢀ
We thus established that the replacement of the
triphenylphosphine ligands in complex 1 with dppb iniꢀ
tially affords exoꢀnidoꢀcomplex 4, which is readily rearꢀ
ranged into the final closoꢀcomplex 3 at room temperature.
Taking into account this reaction pathway, we turned
our attention to the exoꢀnidoꢀcomplex with 1,3ꢀbis(diꢀ
phosphino)propane (5, dppp) as a chelating diphosphine
ligand, viz., 5,6,10ꢀ[RuCl(dppp)]ꢀ5,6,10ꢀ(µꢀH)3ꢀ10ꢀHꢀ
exoꢀnidoꢀ7,8ꢀC2B9H8 (6), which has been studied earꢀ
lier.10 The conditions of the exoꢀnido→closo rearrangeꢀ
ment of complex 6 remained unknown. In spite of the fact
that exoꢀnidoꢀcomplex 6 is rather stable in the solid state,
in a benzene solution the B—H...Ru coordination bonds
in this complex are readily cleaved in the presence of free
dppp ligands to produce the 16ꢀelectron cationic species
[RuCl(dppp)2]+[nidoꢀ7,8ꢀC2B9H12]– (7). Because of this,
the synthesis of 6 by the replacement of the PPh3 ligands
in 1 with dppp always gives rise to a mixture consisting of
complexes 6 and 7.10
1
ture. The H NMR spectrum of complex 9, which has a
number of broad unassignable peaks in the region from
—14 to + 12 ppm, is characteristic of paramagnetic
ruthenacarborane complexes.11 Pure 17ꢀelectron comꢀ
plex 9 can be prepared in 44% yield by refluxing a mixture
of complexes 8 and 9 in benzene for 3.5 h. The composiꢀ
tion of complex 9 was confirmed by elemental analysis,
and its paramagnetic structure was supported by the ESR
spectrum (Fig. 2). It should be noted that paramagnetic
closoꢀruthenacarborane complexes of this type have been
prepared for the first time only recently.11 Therefore, the
direct synthesis of new 17ꢀelectron complex 9 is of obviꢀ
ous interest. It should also be noted that exoꢀnidoꢀrutheꢀ
nacarborane 4 under analogous thermal conditions (benꢀ
zene, 80 °C) does not give a paramagnetic complex strucꢀ
turally similar to 9.
In the present study, we found that exoꢀnidoꢀcomplex
6, like complex 4, can be rearranged under mild conditions
into closoꢀ3,3ꢀ(dppp)ꢀ3ꢀHꢀ3ꢀClꢀ3,1,2ꢀRuC2B9H11 (8).
However, this reaction in benzene at 22 °C proceeds very
slowly, and 60 h are required to achieve 100% conversion.
The exoꢀnido→closo rearrangement is accompanied by
the formation of the 17ꢀelectron paramagnetic complex
closoꢀ3,3ꢀ(dppp)ꢀ3ꢀClꢀ3,1,2ꢀRuC2B9H11 (9) as a byꢀ
product (Scheme 2).
gstand
g1
g2
g3
Complexes 8 and 9 were isolated as a mixture in a total
yield of 86%. We succeeded in separating these comꢀ
plexes into individual compounds only by TLC on Silufol
Fig. 2. ESR spectrum of 17ꢀelectron complex 9: g1 = 2.39,
g2 = 2.08, g3 = 1.96.

2538
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005
Cheredilin et al.
(CD2Cl2), δ: –21.8 (d, 2 B, J = 135.0 Hz); –19.9 (br.d, 1 B);
–8.1 (d, 5 B, J = 138.0 Hz); 5.5 (d, 1 B, J = 142.5 Hz).
A mixture of chlorodiphenylphosphinobutaneꢀexoꢀnidoꢀ
[10ꢀhydroorthocarboraneꢀ5,6,10ꢀtris(hydro)]ruthenium (4) and
complex 3. A solution of complex 1 (0.06 g, 0.08 mmol) and
diphosphine 2 (0.04 g, 0.09 mmol) in benzene (10 mL) was
stirred at 22 °C until the starting complex 1 was completely
consumed (~2 h, TLC control). The solvent was removed in
vacuo. The residue was chromatographed on a silica gel column
under a low pressure of an inert gas, a colored band with Rf = 0.75
being eluted with benzene (the first fraction) followed by elution
of the band with Rf = 0.35 (the second fraction). After removal
of the solvent in vacuo, pure complex 3 was isolated from the
first fraction in 4% yield, and a mixture of complexes 3 and 4 in
an approximate ratio of 1 : 1 was isolated from the second
(major) fraction. The total yield of complexes 3 and 4 isolated
from the second fraction was 89%.
Complex 4 (s : as = 2.5 : 1). 1H NMR* (CD2Cl2), δ: –17.12
(m, s); –15.69 (m, as); –6.10 (m, as); –4.70 — –3.10 (m, as + s);
–1.32 (m, Hextra, s + as); 2.25 (br.s, CcarbH, s); 2.20 and 2.30
(both br.s, CcarbH, as); 2.01, 2.41, 3.43, and 3.57 (all br.m,
PCH2CH2CH2P, s + as); 7.31—7.84 (m, Ph, s + as).
31P{1H} NMR, δ: 50.3 and 55.5 (both d, as, JP,P = 35 Hz);
51.8 (c, s).
A mixture of 3ꢀchloroꢀ3,3ꢀ(1,3ꢀdiphenylphosphinopropane)ꢀ
3ꢀhydroꢀ3,1,2ꢀclosoꢀdicarbollylruthenium (8) and 3ꢀchloroꢀ3,3ꢀ
(1,3ꢀdiphenylphosphinopropane)ꢀ3,1,2ꢀclosoꢀdicarbollylrutheꢀ
nium (9). A solution of complex 6 (0.035 g, 0.05 mmol), which
was prepared according to a procedure described earlier,10 in
benzene (10 mL) was stirred at 22 °C for ~60 h until the starting
complex 6 was completely consumed. The solvent was removed
in vacuo. The residue was chromatographed on a silica gel colꢀ
umn, a mixture of complexes 8 and 9 being eluted with benzene.
The yield of the mixture was 86%. To identify the complexes by
NMR and ESR spectroscopy, the mixture of 8 and 9 (0.008 g)
was separated into individual compounds by TLC on Silufol
plates with the use of a 1 : 1 benzene—hexane mixture as the
eluent.
Based on the results of the present study and earlier
data,10,11 it can be concluded that exoꢀnidoꢀruthenaꢀ
carborane complex 1 is a convenient and readily available
reagent for the synthesis of closoꢀruthenacarboranes with
various chelate diphosphines, including the synthesis of
particular paramagnetic complexes of type 9 in moderate
yields. In this process, the formation of closo products
occurs through the exoꢀnido→closo rearrangement of
diphosphine exoꢀnidoꢀcomplexes.
Experimental
All reactions were carried out under argon with the use of
anhydrous solvents, which were prepared according to standard
procedures. The reaction products were isolated and purified by
column chromatography with the use of silica gel (Merck,
230—400 mesh). Diphosphines dppb and dppp were purchased
from Strem Chemicals. The NMR spectra were recorded on
Bruker AMXꢀ400 (400.13 MHz for 1H, 161.98 MHz for 31P, and
128.3 MHz for 11B) and Bruker AvanceTM300 (300.13 MHz
for 1H) spectrometers. The ESR spectrum of complex 9 was
measured on a Varian Eꢀ12A radiospectrometer. Elemental
analysis was carried out in the Laboratory of Microanalysis of
the A. N. Nesmeyanov Institute of Organoelement Compounds
of the Russian Academy of Sciences.
3ꢀChloroꢀ3,3ꢀ(1,4ꢀdiphenylphosphinobutane)ꢀ3ꢀhydroꢀ3,1,2ꢀ
closoꢀdicarbollylruthenium (3). A. Complex 1 (0.03 g, 0.04 mmol)
was added to a solution of diphosphine 2 (0.02 g, 0.05 mmol)
in benzene (12 mL), and the reaction mixture was stirred at
22 °C for 48 h. The solvent was removed in vacuo. The residue
was chromatographed on a silica gel column, complex 3 being
eluted with a 1 : 1 benzene—hexane mixture. The orange crysꢀ
talline product was recrystallized from an nꢀhexane—CH2Cl2
mixture, and analytically pure complex 3 was isolated in 77%
yield.
B. exoꢀnidoꢀRuthenacarborane 1 (0.1 g, 0.13 mmol) was
added to a solution of diphosphine 2 (0.06 g, 0.14 mmol) in
benzene (15 mL). The reaction mixture was stirred under gentle
reflux for 1 h. The solvent was evaporated in vacuo. The residue
was chromatographed on a short silica gel column, complex 3
being eluted with a 1 : 1 benzene—hexane mixture. The yield
of 3 was 73%.
Complex 8. 1H NMR (CDCl3), δ: –8.75 (dt, 1 H, RuH,
JH...H—B = 14.0 Hz, JH,P = 25.0 Hz); 1.94 (br.m, 1 H,
(PCH2)2CHAHB); 2.38 (br.m, 1 H, (PCH2)2CHAHB); 2.58 (m,
2 H, (PCHAHB)2CH2); 3.44 (dt, 2 H, (PCHAHB)2CH2, J1
=
13.5 Hz, J2 = 3.0 Hz); 3.59 (br.s, 2 H, CcarbH); 7.23—7.66 (m,
20 H, Ph). 31P{1H} NMR (CDCl3), δ: 28.5 (s).
Paramagnetic complex 9. A solution of a mixture of comꢀ
plexes 8 and 9 (0.02 g, 0.03 mmol) in benzene (7 mL) was
refluxed for 3 h. The solvent was evaporated in vacuo. The resiꢀ
due was chromatographed on a silica gel column, complex 9
being eluted with benzene. The yield of 9 was 44%. Found (%):
C, 51.12; H, 5.44; B, 14.29. C29H37B9ClP2Ru. Calculated (%):
C, 50.68; H, 5.10; B, 14.23. ESR (CH2Cl2, gstand = 2.0023, T =
77 K): g1 = 2.3933; g2 = 2.0796; g3 = 1.9594.
Found (%): C, 50.63; H, 5.65; P, 8.64.
C30H40B9ClP2Ru•0.25CH2Cl2. Calculated (%): C, 50.52; H,
5.85; P, 8.66. 1H NMR (CDCl3), δ: –8.22 (dt, 1 H, RuH,
JH...H—B = 6.0 Hz, JH,P = 27.5 Hz); 1.52 (br.m, 2 H,
(PCH2CHAHB)2); 1.72 (br.m, 2 H, (PCH2CHAHB)2); 2.50
(br.m, 2 H, (PCHAHB)2(CH2)2); 3.28 (br.s, 2 H, CcarbH); 3.45
(br.m, 2 H, (PCHAHB)2(CH2)2); 7.93—7.21 (2 t + m, 20 H,
Ph). 1H{31P} NMR (CDCl3), δ: –8.22 (d, 1 H, RuH, JH...H—B
=
6.0 Hz); 1.52 (br.m, 2 H, (PCH2CHAHB)2); 1.72 (br.m, 2 H,
(PCH2CHAHB)2); 2.50 (br.dt, 2 H, (PCHAHB)2(CH2)2, J =
3.5 Hz, JA,B = 14.5 Hz); 3.28 (br.s, 2 H, CcarbH); 3.45 (ddd, 2 H,
(PCHAHB)2(CH2)2, J1 = 3.5 Hz, J2 = 9.0 Hz, JA,B = 14.5 Hz);
7.93—7.21 (2 d + m, 20 H, Ph). 13C{1H} NMR (CDCl3), δ:
21.56 (2 C), 25.81, 26.26 (P(CH2)4P); 63.39 (Ccarb); 127.35,
128.68, 130.20, 131.14, 133.14, 134.32 (Ph). 31P{1H} NMR
(CD2Cl2), δ: 37.4 and 37.5 (both s, 1 P + 1 P). 11B NMR
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 03ꢀ03ꢀ
32651).
* Only hydride resonances of isomers sꢀ4 and asꢀ4 with their
assignment are given.

[Bis(phosphino)alkane]ꢀclosoꢀruthenacarboranes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005 2539
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Received September 26, 2005