Facile method for the synthesis of ruthenacarboranes, diamagnetic 3,3-[Ph2P(CH2)nPPh2]-3-H-3-Cl-closo- 3,1,2-RuC2B9H11 (n = 3 or 4) and paramagnetic 3,3-[Ph2P(CH2)nPPh2]-3-Cl-closo-3,1, 2-RuC2B9H11 (n = 2 or 3), as efficient initiators of ...

Article abstract of DOI:10.1007/s11172-006-0394-9

Title full: Facile method for the synthesis of ruthenacarboranes, diamagnetic 3,3-[Ph₂P(CH₂)_nPPh₂]-3-H-3-Cl-closo- 3,1,2-RuC₂B₉H₁₁ (n = 3 or 4) and paramagnetic 3,3-[Ph₂P(CH₂)_nPPh₂]-3-Cl-closo-3,1, 2-RuC₂B₉H₁₁ (n = 2 or 3), as efficient initiators of controlled radical polymerization of vinyl monomers. A facile preparative procedure was developed for the synthesis of 17-and 18-electron closo-(diphosphine)ruthenacarborane complexes. This method is based on the replacement of PPh₃ ligands with bis(diphenylphosphino)alkanes Ph₂P(CH₂)_nPPh₂ (n = 2-4) in ruthenacarborane 3,3-(PPh₃)₂-3-Cl-3-H-closo-3,1,2-RuC ₂B₉H₁₁. The resulting complexes exhibit high activity in controlled radical polymerization of vinyl monomers. Springer Science+Business Media, Inc. 2006.

Full text of DOI:10.1007/s11172-006-0394-9

Russian Chemical Bulletin, International Edition, Vol. 55, No. 7, pp. 1163—1170, July, 2006
1163
Facile method for the synthesis of ruthenacarboranes, diamagnetic
3,3ꢀ[Ph2P(CH2)nPPh2]ꢀ3ꢀHꢀ3ꢀClꢀclosoꢀ3,1,2ꢀRuC2B9H11 (n = 3 or 4)
and paramagnetic 3,3ꢀ[Ph2P(CH2)nPPh2]ꢀ3ꢀClꢀclosoꢀ3,1,2ꢀRuC2B9H11
(n = 2 or 3), as efficient initiators of controlled
radical polymerization of vinyl monomers
D. N. Cheredilin,a F. M. Dolgushin,a I. D. Grishin,b E. V. Kolyakina,b A. S. Nikiforov,a S. P. Solodovnikov,a
b
M. M. Il´in,a V. A. Davankov,a I. T. Chizhevsky,a and D. F. Grishin
ꢀ
ꢀ
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 6549. Eꢀmail: chizbor@ineos.ac.ru
bNizhny Novgorod N. I. Lobachevsky State University,
23 prosp. Gagarina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831) 265 8162. Eꢀmail: grishin@ichem.unn.runnet.ru
A facile preparative procedure was developed for the synthesis of 17ꢀ and 18ꢀelectron
closoꢀ(diphosphine)ruthenacarborane complexes. This method is based on the replacement
of PPh3 ligands with bis(diphenylphosphino)alkanes Ph2P(CH2)nPPh2 (n = 2—4) in ruthenaꢀ
carborane 3,3ꢀ(PPh3)2ꢀ3ꢀClꢀ3ꢀHꢀclosoꢀ3,1,2ꢀRuC2B9H11. The resulting complexes exhibit high
activity in controlled radical polymerization of vinyl monomers.
Key words: bis(diphenylphosphino)alkanes, ruthenium carborane complexes, synthesis,
controlled radical polymerization, vinyl monomers.
Recently,1—3 we have demonstrated that the replaceꢀ
ment of PPh3 ligands in threeꢀbridge exoꢀnidoꢀruthenaꢀ
carboranes 5,6,10ꢀ{Cl(Ph3P)2Ru}ꢀ[5,6,10ꢀ(µꢀH)3ꢀ10ꢀHꢀ
7,8ꢀR2ꢀexoꢀnidoꢀ7,8ꢀC2B9H8] (R = H (1) or Me (2))
with chelating diphosphine ligands affords either diamagꢀ
netic (18ꢀelectron) or paramagnetic (17ꢀelectron) chelate
closoꢀ(diphosphine)ruthenacarboranes depending on the
reaction conditions. This method proved to be rather effiꢀ
cient for the synthesis of certain closoꢀruthenacarboranes,
for example, with 1,4ꢀbis(diphenylphosphino)butane
(dppb) (see Ref. 2) or chiral (–)ꢀ2,4ꢀbis(diphenylphosphiꢀ
no)pentane (bdpp).1,3 The synthesis of chelate closo comꢀ
plexes with the use of diphosphinoalkanes having a shorter
unbranched aliphatic chain according to this scheme
is complicated by the formation of the byꢀproducts
[RuCl(Ph2P(CH2)nPPh2)2]+[7,8ꢀR2ꢀ7,8ꢀnidoꢀC2B9H10]–
(see Ref. 4) via the cleavage of B—H...Ru coordination
bonds in exoꢀnidoꢀ(diphosphine)ruthenacarboranes that
are generated in the first step in the presence of an excess
of diphosphine (Scheme 1).
Diamagnetic and paramagnetic closoꢀ(diphosphine)ruꢀ
thenacarboranes are of interest not only for the chemistry
of metallacarboranes but also for the synthesis of narrowꢀ
disperse macromolecules based on vinyl monomers. In
Scheme 1
i. Ph2P(CH2)nPPh2, C6H6; ii. Ph2P(CH2)nPPh2.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1120—1127, July, 2006.
1066ꢀ5285/06/5507ꢀ1163 © 2006 Springer Science+Business Media, Inc.

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Cheredilin et al.
Table 1. Selected geometric parameters of molecule 3
polymerization of the latter, such ruthenacarboranes serve
as initiators and regulators5 of atom transfer radical polyꢀ
merization (ATRP).6,7 In this connection, it was imporꢀ
tant to develop a more versatile procedure for the syntheꢀ
sis of diphosphine closo complexes, which is not compliꢀ
cated by the formation of byꢀproducts.
Bond
d/Å Bond angle
ω/deg
Ru(3)—P(1)
Ru(3)—P(2)
2.3756(5) P(1)—Ru(3)—P(2) 103.665(19)
2.3757(5) P(1)—Ru(3)—Cl(1) 84.871(18)
Ru(3)—Cl(1) 2.4284(5) P(2)—Ru(3)—Cl(1) 87.729(19)
In the present study, we examined the direct ligand
exchange in the reaction of the closo complex 3,3ꢀ(PPh3)2ꢀ
3ꢀClꢀ3ꢀHꢀclosoꢀ3,1,2ꢀRuC2B9H11 (3) with bis(diphenylꢀ
phosphino)alkanes Ph2P(CH2)nPPh3 (n = 2—4). As a reꢀ
sult, we succeeded not only in extending a series of known
17ꢀ and 18ꢀelectron closoꢀ(diphosphine)ruthenacarboꢀ
ranes but also in developing a new efficient initiator of
controlled radical polymerization of methyl methacrylate
(MMA) and styrene.
Ru(3)—H(3M)
Ru(3)—C(1)
Ru(3)—C(2)
Ru(3)—B(4)
Ru(3)—B(7)
Ru(3)—B(8)
P(1)—C(13)
P(1)—C(19)
P(1)—C(25)
P(2)—C(31)
P(2)—C(37)
P(2)—C(43)
C(1)—C(2)
1.40(3) P(1)—Ru(3)—H(3M) 73.4(11)
2.257(2) P(2)—Ru(3)—H(3M) 69.9(11)
2.226(2) Cl(1)—Ru(3)—H(3M) 143.5(11)
2.316(2) C(13)—P(1)—C(19) 104.24(10)
2.242(2) C(13)—P(1)—C(25) 100.15(10)
2.281(2) C(25)—P(1)—C(19) 103.63(10)
1.835(2) C(13)—P(1)—Ru(3)
1.847(2) C(19)—P(1)—Ru(3)
1.838(2) C(25)—P(1)—Ru(3)
1.841(2) C(37)—P(2)—C(31)
119.09(7)
110.89(7)
116.94(7)
97.32(10)
1.837(2) C(43)—P(2)—C(31) 104.84(10)
1.826(2) C(43)—P(2)—C(37) 104.43(10)
Results and Discussion
1.624(3) C(31)—P(2)—Ru(3)
C(37)—P(2)—Ru(3)
123.57(7)
117.11(7)
107.53(7)
The starting closo complex 3 has been synthesized earꢀ
lier by two methods: (1) according to a scheme8 involving
the reaction of the [NHMe3]+[nidoꢀ7,8ꢀC2B9H12]– salt
with the (PPh3)3RuHCl•PhMe complex to form diꢀ
hydride metallacarborane 3,3ꢀ(PPh3)2ꢀ3,3ꢀ(H)2ꢀclosoꢀ
3,1,2ꢀRuC2B9H11, whose treatment with gaseous HCl afꢀ
forded complex 3 in 40% yield and (2) by the thermal
exoꢀnido → closo rearrangement of complex 1,9 which,
in turn, was prepared by the reaction of 16ꢀelectron
(PPh3)3RuCl2 (4) with the nidoꢀdicarbaundecaborate salt
[K]+[nidoꢀ7,8ꢀC2B9H10]– (5) in an Et2O—THF mixture10
or benzene at 22 °C.5 In the present study, we substanꢀ
tially modified the latter method by using the oneꢀpot
thermal reaction of complex 4 with an insignificant excess
of salt 5 in benzene to prepare closo complex 3 (Scheme 2).
This reaction under argon gave the target product 3 (after
purification on a silica gel column and crystallization) in
51% yield. The structure of complex 3 was confirmed by
IR and 1H, 31P{1H}, and 11B/11B{1H} NMR spectra, which
were completely identical to the spectroscopic data for
the authentic sample.9
C(43)—P(2)—Ru(3)
In addition, we performed repeated singleꢀcrystal
Xꢀray diffraction study of closo complex 3, because the
principal Xꢀray diffraction data published in the brief comꢀ
munication9 were lost and are missing from the Camꢀ
bridge Structural Database. In the present study, we
performed Xꢀray diffraction analysis of monosolvate
3•CH2Cl2. The molecular structure of this complex is
shown in Fig. 1. Selected bond lengths and bond angles
of 3 are given in Table 1.
The positions of all hydrogen atoms, including the
hydride ligand at the metal atom (Ru—H, 1.40(3) Å), in
complex 3 were located. The metal atom is almost
symmetrically coordinated to the open C2B3 face of
nidoꢀcarborane so that the Ru—C (2.257(2) and
2.226(2) Å) and Ru—B (2.242(2)—2.316(2) Å) distances
vary only slightly, the shift of the metal atom from the
center of the plane toward the boron or carbon atoms
being virtually absent. The Ru...C2B3 distance is 1.721 Å.
The bond lengths between the Ru atom and the other
ligands (Ru—P(1), 2.3756(5) Å; Ru—P(2), 2.3757(5) Å)
and the Ru—Cl bond length (2.4284(5) Å) are similar to
the corresponding parameters in structurally related
closoꢀruthenacarboranes, for example, in the neutral
complex 1,1ꢀ(PPh3)2ꢀ1ꢀClꢀ1ꢀHꢀclosoꢀ1,2,3ꢀRuC2B4H6
(Ru—P, 2.3653 and 2.3773 Å; Ru—Cl, 2.4311 Å)11 and
the anionic complex [3,3ꢀ(PPh3)2ꢀ3ꢀClꢀclosoꢀ3,1,2,ꢀ
RuC2B9H11]–[Et4N]+ (Ru—P, 2.346 and 2.344 Å;
Ru—Cl, 2.452 Å).12 The conformation of the rutheniumꢀ
containing group RuHCl(PPh3)2 relative to the pentagoꢀ
nal C2B3 plane of the nidoꢀcarborane ligand is of interest.
The Ru—H bond exactly projects onto the B(8)—H bond
(P(3)—Ru—B(8)—H(8) torsion angle is 15°), the
B(8)—H(8)...H—Ru distance being very short (2.02 Å),
which might result from the unique throughꢀspace interꢀ
Scheme 2

Ruthenacarboraneꢀcatalyzed polymerization
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 7, July, 2006
1165
C(34)
C(16)
C(15)
C(33)
C(17)
C(35)
C(36)
C(18)
C(14)
C(32)
C(27)
C(13)
C(26)
C(31)
C(28)
C(29)
C(37)
C(25)
C(30)
C(38)
C(44)
P(1)
P(2)
C(39)
C(19)
C(24)
C(20)
C(21)
C(45)
C(43)
Cl(1)
C(46)
C(47)
C(40)
C(41)
C(22)
Ru(3)
H(3M)
C(42)
C(23)
C(48)
B(8)
H(8)
B(7)
C(1)
C(2)
B(4)
B(9)
B(11)
B(6)
B(12)
B(5)
B(10)
Fig. 1. Molecular structure of complex 3.
Scheme 3
action between these two hydrogen atoms. As a conseꢀ
quence, the spinꢀspin coupling constant 3J(HRu,H8) =
10.3 Hz in the 1H NMR spectrum of this complex is
unusually large.9
From the chemical standpoint, closoꢀruthenacarborane
complex 3 proved to be a rather convenient and active
reagent. It was found that the reaction of 3 with a 10%
excess of 1,4ꢀbis(diphenylphosphino)butane (dppb) or
1,3ꢀbis(diphenylphosphino)propane (dppp) in benzene is
accomplished by the replacement of the PPh3 ligands by
diphosphines already at room temperature. However, unꢀ
der these conditions the formation of the target products
in both reactions occurs very slowly (in the reaction with
dppb, the 100% conversion of 3 is attained within 3 days;
in the reaction with dppp, within 6 days). In the former
case, the replacement affords exclusively the 18ꢀelectron
complex 3,3ꢀ(Ph2P(CH2)4PPh2)ꢀ3ꢀHꢀ3ꢀClꢀclosoꢀ3,1,2ꢀ
RuC2B9H11 (6) in 86% yield. In the latter case, the reacꢀ
tion produces a mixture of the 18ꢀ and 17ꢀelectron comꢀ
plexes 3,3ꢀ(Ph2P(CH2)3PPh2)ꢀ3ꢀHꢀ3ꢀClꢀclosoꢀ3,1,2ꢀ
RuC2B9H11 (7) and 3,3ꢀ(Ph2P(CH2)3PPh2)ꢀ3ꢀClꢀclosoꢀ
3,1,2ꢀRuC2B9H11 (8) in a ratio of 6.7 : 1 in a total yield of
~90% (Scheme 3). Earlier, we have synthesized2 an analoꢀ
gous mixture of complexes 7 and 8 by the reaction of
Reagents and conditions: i. Ph2P(CH2)4PPh2, C6H6, 80 °C, 1 h;
ii. Ph2P(CH2)3PPh2, C6H6, 80 °C, 2 h.

1166
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Cheredilin et al.
exoꢀnido complex 1 with dppp, and this mixture has been
separated into individual compounds by TLC. The strucꢀ
tures of these complexes were established by 1H and
31P{1H} NMR or ESR spectroscopy.
produces the 17ꢀelectron paramagnetic complex
3,3ꢀ(PPh2CH2CH2PPh2)ꢀ3ꢀClꢀclosoꢀ3,1,2ꢀRuC2B9H11
(9) in 35% yield (Scheme 4) both on heating in benzene
(2 h) and at room temperature (54 h). However, the forꢀ
mation of target product 9 in both reactions was accomꢀ
panied by the formation of an insignificant amount of the
yellow diamagnetic carboraneꢀcontaining ruthenium
complex (10). We failed to establish the exact structure of
It was found that heating of complex 3 with dppb or
dppp in benzene substantially accelerates the replacement
of the PPh3 ligands by diphosphines (reactions were comꢀ
pleted within 1 and 2 h, respectively). However, the reacꢀ
tion of 3 with dppb at high temperature produces diamagꢀ
netic complex 6 in a somewhat lower yield (70%). The
reaction of 3 with dppp affords a mixture of compounds 7
and 8 with paramagnetic complex 8 predominating.
A separate experiment demonstrated that refluxing of a
mixture of approximately equal amounts of 7 and 8 in
benzene for 6 h afforded predominantly paramagnetic
complex 8 (according to HPLC data, the 8 : 7 ratio was
98 : 2). In the case of the favorable formation of one
product, chromatographic (TLC) monitoring of this reꢀ
action presents substantial difficulty because of the close
values of Rf for complexes 7 and 8 (0.35 and 0.31, respecꢀ
tively). It is also impossible to perform 1H or 31P{1H} NMR
monitoring in the case of a predominance of paramagꢀ
netic complex 8 in the reaction mixture. Hence, we moniꢀ
tored the reaction of 3 with dppp by HPLC on a silica gel
column with the use of a 4 : 1 nꢀhexane—CH2Cl2 mixture
as the eluent. The clear separation of the chromatographic
peaks corresponding to complexes 7 and 8 (Fig. 2) alꢀ
lowed us to rather precisely determine the ratio of prodꢀ
ucts 7 and 8 in the final mixture (see above) and estimate
the purity of paramagnetic complex 8.
1
the latter complex in spite of the H and 31P{1H} NMR
spectroscopic data (see the Experimental section).
Scheme 4
Note: 10 is diamagnetic ruthenacarborane with unknown
structure.
Paramagnetic complex 9 can also be synthesized startꢀ
ing from the ionic complex [RuCl(dppe)2]+[7,8ꢀnidoꢀ
C2B9H12]– (11), which has been prepared earlier4 as the
only product by replacing the PPh3 ligands in exoꢀnidoꢀruꢀ
thenacarborane 1 by dppe. In a dilute CH2Cl2 solution,
one of the dppe ligands in complex 11 undergoes slow
dissociation with the concomitant formation of closo comꢀ
plex 9. After 7 days, the latter was isolated by silica gel
column chromatography in 24% yield (Scheme 5).
It was found that the reaction of closoꢀcomplex 3
with a 10% excess of bis(diphenylphosphino)ethane (dppе)
8
7
a
b
Scheme 5
c
2.000
2.667
3.333
4.000
4.667
τ/min
Fig. 2. Chromatographic (HPLC) separation of complexes 7
and 8 on a Separon SGX column (150×3 mm) packed with silica
gel 5 µ with the use of a 4 : 1 nꢀhexane—CH2Cl2 mixture as the
eluent: (a) a mixture of complexes 7 and 8 (41 : 59) prepared by
the reaction of 3 with dppp at 80 °C for 2 h and isolated by silica
gel column chromatography; (b) thermolysis products of a mixꢀ
ture of complexes 7 and 8 (starting ratio was 41 : 59) after
refluxing in benzene for 2 h; (c) the final thermolysis products of
a mixture of complexes 7 and 8 (2 : 98) after refluxing in benzene
for 6 h.
Reagents and conditions: i. CH2Cl2, 7 days.
The structures of diamagnetic and paramagnetic comꢀ
plexes 3 and 6—8 synthesized in the present study
were confirmed by comparing their 1H, 31P{1H}, and
11B/11B{1H} NMR and ESR spectra with the spectra of
the samples prepared earlier. The composition and strucꢀ
ture of new paramagnetic complex 9 was established by
elemental analysis, ESR spectroscopy (Fig. 3), and Xꢀray

Ruthenacarboraneꢀcatalyzed polymerization
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 7, July, 2006
1167
C(19)
C(20)
C(14)
C(13)
C(18)
C(28)
C(29)
C(15)
C(22)
C(27)
Cl(1)
C(23)
P(1)
P(2)
C(17)
C(30)
C(34)
C(33)
C(21)
C(26)
C(31)
C(32)
C(16)
C(25)
C(24)
C(35)
C(38)
C(37)
Ru(3)
C(36)
C(1)
B(4)
B(7)
B(8)
B(12)
C(2)
B(9)
B(5)
B(11)
B(6)
B(10)
Fig. 3. ESR spectrum of complex 9.
Table 2. Selected geometric parameters of molecule 9
diffraction (Fig. 4). The ESR spectrum of lowꢀspin
d5 complex 9 has a rhombic nature with three distinct
g factors, g1 = 2.253, g2 = 2.108, and g3 = 1.998.
Bond
d/Å
Bond angle
ω/deg
The molecular structure of complex 9 established by
Xꢀray diffraction is shown in Fig. 4. Selected geometric
parameters are given in Table 2. The Ru atom has a
pseudooctahedral configuration and is bound to two phosꢀ
phorus atoms of the dppe ligand (Ru—P, 2.345(1) and
2.325(1) Å), the chlorine ligand (Ru—Cl, 2.381(1) Å),
and the nidoꢀcarborane ligand (Ru—C, 2.237(4) and
2.261(4) Å; Ru—B(4), Ru—B(7), and Ru—B(8),
2.235(5)—2.256(5) Å). Taking into account that the
carborane ligand in molecule 9 is doubly charged (2–),
whereas the chlorine ligand is singly charged (1–), the
formal oxidation state of the Ru atom is +3 and this atom
Ru(3)—P(1)
Ru(3)—P(2)
2.3448(11) P(2)—Ru(3)—P(1)
2.3249(11) P(2)—Ru(3)—Cl(1)
82.02(4)
86.61(4)
88.49(4)
Ru(3)—Cl(1) 2.3809(11) P(1)—Ru(3)—Cl(1)
Ru(3)—C(1)
Ru(3)—C(2)
Ru(3)—B(4)
Ru(3)—B(7)
Ru(3)—B(8)
P(1)—C(13)
P(1)—C(15)
P(1)—C(21)
P(2)—C(14)
P(2)—C(27)
P(2)—C(33)
C(1)—C(2)
C(13)—C(14)
2.237(4) C(15)—P(1)—C(13) 108.25(19)
2.261(4) C(15)—P(1)—C(21) 102.54(18)
2.235(5) C(21)—P(1)—C(13) 101.81(19)
2.243(5) C(13)—P(1)—Ru(3) 111.29(13)
2.256(5) C(15)—P(1)—Ru(3) 107.65(13)
1.863(4) C(21)—P(1)—Ru(3) 124.23(14)
1.831(4) C(27)—P(2)—C(14) 102.93(19)
1.833(4) C(33)—P(2)—C(14) 107.49(19)
1.842(4) C(33)—P(2)—C(27) 101.69(19)
1.831(4) C(14)—P(2)—Ru(3) 108.41(13)
1.829(4) C(27)—P(2)—Ru(3) 118.21(14)
1.611(6) C(33)—P(2)—Ru(3) 116.85(13)
gstand = 2.0028
1.536(6) C(14)—C(13)—P(1)
C(13)—C(14)—P(2)
112.5(3)
112.2(3)
has 17 electrons, which is confirmed by the ESR specꢀ
trum. It should be noted that, as in other known
17ꢀelectron closoꢀruthenacarboranes,1,3,5 the general tenꢀ
dency toward a shortening of the Ru—Cl bond by ~0.1 Å
compared to 18ꢀelectron analogs is retained in complex 9.
In continuation of studies on catalytic activity of
diamagnetic and paramagnetic phosphineꢀsubstituted
closoꢀ and exoꢀnidoꢀruthenacarboranes,5 we tested new
paramagnetic complex 9 as a catalyst for the controlled
radical polymerization of methyl methacrylate (MMA)
gx = 2.253
20 T
gy = 2.108
gz = 1.998
Fig. 4. Molecular structure of complex 9.

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Cheredilin et al.
and styrene according to the ATRP 6 and reverse ATRP 7
mechanisms.
Mw/Mn is 1.37,5 indicates that binding of phosphine
ligands by methylene bridges is the most substantial
factor responsible for the formation of narrowꢀdisperse
macromolecules in polymerization processes. Apparently,
the electronic configuration of the metal atom in this
series of compounds has no noticeable effect on the moꢀ
lecularꢀweight characteristics of the resulting macromolꢀ
ecules.
Our experiments demonstrated that ruthenium
carborane complex 9 is an efficient coꢀinitiator of the
controlled synthesis of macromolecules. For example, in
the presence of CCl4 and complex 9, the conversion of
styrene into polystyrene at 90 °C was higher than 91%
(after 69 h). The average molecular weight (Mn) is 19630,
and the polydispersity of the resulting macromolecules
(Mw/Mn) is 1.56. The polydispersity is somewhat larger
than the analogous parameters for the ideal living polyꢀ
merization6,7 but is substantially lower than those obꢀ
tained in the synthesis of polystyrene under conditions of
classical radical polymerization (Mw/Mn > 2).
Complex 9 is more active compared to analogous
cyclopentadienyl derivatives of ruthenium, for example,
[RuCl(Cp*)(PPh3)2] or [RuCl(η5ꢀC9H7)(PPh3)2], which
have been proposed13—15 for the controlled synthesis of
macromolecules in the living polymer chain mode. These
ruthenium complexes are efficient only in combination
with additives of coꢀcatalysts, in particular, of aluminum
alkoxides, the polymerization rate in the presence of these
compounds being very low and the deep conversion
(~90%) being attained only within 400—600 h. In addiꢀ
tion, taking into account the weight, the yield, and the
polydispersity coefficient of polystyrene, complex 9 is
nowadays the most efficient catalyst precursor among
metallacarboranes tested in the controlled radical polyꢀ
merization of styrene.16,17
Experimental
The phosphine/diphosphine replacement reactions of comꢀ
plex 3 were carried out under argon in anhydrous solvents, which
were prepared according to standard procedures. A new oneꢀpot
method was developed for the synthesis of complex 3. The reacꢀ
tion products were isolated by column chromatography with the
use of silica gel (Merck, 230—400 mesh). Commercial phosꢀ
phines were used (Strem Chemicals and AldrichꢀChemie). 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
spectra of complexes 8 and 9 were measured on a Varian Eꢀ12A
radiospectrometer. The mixture of complexes 7 and 8 was anaꢀ
lyzed on a Separon SGX column (150×3 mm, silica gel 5 µ)
equipped with an UV detector (254 nm). Elemental analysis was
carried out in out in the Laboratory of Microanalysis of the
A. N. Nesmeyanov Institute of Organoelement Compounds of
the Russian Academy of Sciences.
Synthesis of 3,3ꢀbis(triphenylphosphine)ꢀ3ꢀchloroꢀ3ꢀhydridoꢀ
3,1,2ꢀclosoꢀdicarbollylruthenium (3). A mixture of complex 4
(0.5 g, 0.52 mmol) and the potassium salt of nidoꢀ7,8ꢀdicarbaꢀ
undecaborate 5 (0.11 g, 0.63 mmol) in anhydrous benzene
(120 mL) was heated for 3 h with magnetic stirring at 75—78 °C
(mixture was prevented from boiling) and argon was bubbled
directly through the solution. Then the reaction temperature
was raised with stirring to the boiling point of the solvent, the
major portion of the latter being distilled off under argon
to ~8—10 mL. After cooling, the residue was purified by a silica
gel column chromatography, the product being eluted under a
pressure of argon with a 5 : 1 benzene—nꢀhexane mixture. The
first green fraction consisting of a mixture of PPh3 and comꢀ
plex 3 was collected separately. After repeated chromatography
of this fraction under the same conditions, complex 3 was obꢀ
tained in a yield of 0.03 g. The major amount of complex 3 as
darkꢀyellow crystals (0.18 g) was obtained from the second fracꢀ
tion, which was diluted (after elution from the column) with an
equal volume of nꢀhexane and crystallized at 0—2 °C for 15 h.
The total yield of complex 3 was 0.21 g (51%). Elution from the
chromatographic column with benzene afforded the third orꢀ
ange fraction containing 0.02 g of exoꢀnido complex 1.
The polydispersity coefficients in polymerization of
MMA according to the ATRP mechanism in the presence
of complex 9 and CCl4 as the coꢀinitiator are much lower
(Mw/Mn is at most 1.23) than those observed in the synꢀ
thesis of polystyrene under analogous conditions.
Polymerization in the presence of metal complex cataꢀ
lysts with the use of azoisobutyronitrile (AIBN) instead of
CCl4 as the coꢀinitiator occurs according to the reverse
ATRP mechanism. In this case, the average molecuꢀ
lar weight of poly(methyl methacrylate) (PMMA)
(Mn = 45870) and the polydispersity (Mw/Mn = 1.43) of
samples are substantially larger. The observed deterioraꢀ
tion of the molecularꢀweight characteristics in the presꢀ
ence of AIBN is undoubtedly associated with thermal
decomposition of the latter and related noncontrolled radiꢀ
cal polymerization occurring in parallel with the synthesis
of macromolecules in the living polymer chain mode.
A comparison of the polydispersity coefficients
of PMMA samples synthesized according to the
ATRP mechanism with the use of ruthenacarborane 9
(Mw/Mn = 1.23) and diamagnetic ruthenium comꢀ
plexes 3 and 6 (Mw/Mn are 1.62 and 1.25, respecꢀ
tively5) and the paramagnetic oꢀcycloboronated anaꢀ
log of these complexes, [3ꢀClꢀ3,3ꢀPh2PMe3PPhꢀ
Synthesis of 3ꢀchloroꢀ3,3ꢀ(1,4ꢀdiphenylphosphinobutane)ꢀ3ꢀ
hydridoꢀ3,1,2ꢀclosoꢀdicarbollylruthenium (6). A. A solution of
complex 3 (0.04 g, 0.05 mmol) and dppb (0.025 g, 0.06 mmol) in
benzene (12 mL) was stirred at room temperature for 72 h. The
solvent was evaporated in vacuo. The residue was chromatoꢀ
graphed on a silica gel column, and yellowꢀorange closo comꢀ
plex 6 was eluted with a 1 : 1 benzene—nꢀhexane mixture. After
recrystallization from an nꢀhexane—CH2Cl2 mixture, the yield
of complex 6 was 0.03 g (86%). The 1H and 31P{1H} NMR
оꢀC6H4}ꢀ1,2ꢀMe2ꢀclosoꢀ3,1,2ꢀRuC2B9H10], for which

Ruthenacarboraneꢀcatalyzed polymerization
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 7, July, 2006
1169
spectroscopic data for complex 6 were completely identical to
the spectroscopic data of the sample prepared earlier.2
(0.02 g) was the next elution product. The structure of the latꢀ
ter was not established in the present study. Complex 10.
1H NMR (C6D6), δ: 7.70, 7.60, 7.38, 7.11, 6.98, and 6.78 (all m,
20 H, Ph); 2.63, 2.25, 2.14, and 2.01 (all m, 1 H each, CH2CH2);
2.59 and 1.31 (both br.s, 1 H each, CH carb.). 31P{1H} NMR
(C6D6), δ: 62.8 (d, 2 P, JP,P = 31.5 Hz); 35.9 (m, 1 P); 10.75 (d,
1 P, JP,P = 31.5 Hz). 11B{1H} NMR (C6D6), δ: –3.0 and –6.2
(both br, 1 B); –12.2 (v.br, 5 B); –24.6 (v.br, 2 B).
B. A solution of complex 3 (0.045 g, 0.056 mmol) and dppe
(0.025 g, 0.056 mmol) in benzene (10 mL) was stirred at room
temperature for 2.5 days. The reaction mixture was worked up
analogously to method A. The yield of complex 9 was 0.015 g
(35%). The amount of complex 10 generated under these condiꢀ
tions was insignificant (<0.005 g).
C. Complex 11 (0.2 g, 0.19 mmol) was placed in a flask filled
with argon, and anhydrous CH2Cl2 (75 mL) was added. The
darkꢀred solution was stirred for 7 days until the starting comꢀ
plex completely disappeared. The course of the reaction was
monitored by TLC using a 3 : 1 CH2Cl2—nꢀhexane mixture as
the eluent. The mixture was concentrated in vacuo to 5—7 mL
and chromatographed on a silica gel column, complex 9 being
eluted with a 3 : 1 CH2Cl2—nꢀhexane mixture. After evapoꢀ
ration and recrystallization, the yield of compound 9 was
0.03 g (24%). The ESR spectroscopic data for complex 9 are
identical to those of the sample prepared according to the
method A.
Xꢀray diffraction study of complexes 3 and 9. Crystallographic
data and details of the structure refinement for compounds 3
and 9 are given in Table 3. Experimental data sets were collected
on a Bruker SMART 1000 diffractometer equipped with an area
detector (graphite monochromator, λ(MoꢀKα) = 0.71073 Å,
B. A solution of complex 1 (0.05 g, 0.06 mmol) and
diphosphine 3 (0.03 g, 0.07 mmol) in benzene (12 mL) was
stirred at 80 °C for 1 h. The mixture was concentrated in vacuo.
The residue was chromatographed on a silica gel column, comꢀ
plex 6 being eluted with a 1 : 1 benzene—nꢀhexane mixture.
Then the mixture was concentrated. After recrystallization from
a CH2Cl2—nꢀhexane mixture, complex 6 was obtained in a yield
of 0.03 g (70%). The 1H and 31P{1H} NMR spectroscopic data
for complex 6 were completely identical to those for the sample
prepared earlier.2
Synthesis of the complexes 3ꢀchloroꢀ3,3ꢀ(1,3ꢀdiphenylꢀ
phosphinopropane)ꢀ3ꢀhydridoꢀ3,1,2ꢀclosoꢀdicarbollylruthenium
(7) and 3ꢀchloroꢀ3,3ꢀ(1,3ꢀdiphenylphosphinopropane)ꢀ3,1,2ꢀ
closoꢀdicarbollylruthenium (8). A. A solution of complex 1 (0.05 g,
0.06 mmol) and dppp (0.03 g, 0.07 mmol) in benzene (8 mL)
was stirred at room temperature for 144 h. The solvent was
evaporated in vacuo. The residue was chromatographed on a
silica gel column, the orange band consisting of complexes 7
and 8 being eluted with a 1 : 1 benzene—nꢀhexane mixture. The
resulting fraction was concentrated, after which a mixture of
complexes 7 and 8 was obtained in a yield of 0.04 g (90%).
A comparison of Rf for complexes 7 (Rf = 0.31) and 8 (Rf = 0.35)
with Rf for the samples prepared earlier2 provided evidence for
the identity of these compounds. The percentage of the products
in the mixture determined by HPLC were as follows: 87% of
complex 7 and 13% of complex 8.
B. A solution of complex 3 (0.04 g, 0.050 mmol) and dppp
(0.021 g, 0.050 mmol) in benzene (10 mL) was refluxed with
stirring for 3 h until diamagnetic complex 7 disappeared from
the reaction mixture. The course of the reaction was monitored
by HPLC. The solvent was evaporated in vacuo. The residue was
chromatographed on a silica gel column, complex 8 being eluted
with a 1 : 1 benzene—nꢀhexane mixture. The yield of paramagꢀ
netic complex 8 was 0.017 g (49%).
Table 3. Crystallographic data and details of structure refineꢀ
ment for compounds 3 and 9
Parameter*
3
9
C. A mixture of complexes 7 and 8 (0.02 g, ~0.029 mmol;
which was prepared in a ratio of ~1 : 1 by heating complex 3 with
dppp in benzene for 1.5 h) was dissolved in benzene (10 mL),
and the mixture was refluxed with stirring for 6 h. The course of
the reaction was monitored by HPLC, and heating was termiꢀ
nated when diamagnetic complex 7 was completely consumed.
The solvent was evaporated in vacuo. The residue was chromatoꢀ
graphed on a silica gel column, complex 8 being eluted with
benzene. After evaporation of the solvent and crystallization
from a 3 : 1 CH2Cl2—nꢀhexane mixture, the yield of 8 was 0.013 g
(66%). The ESR spectroscopic data (CH2Cl2, gstand = 2.003,
T = 77 K) for complex 8 are identical to those for the sample of
complex 8 synthesized earlier.2
Synthesis of 3ꢀchloroꢀ3,3ꢀ(1,2ꢀdiphenylphosphinoethane)ꢀ
3,1,2ꢀclosoꢀdicarbollylruthenium (9) and complex 10. A. A soluꢀ
tion of complex 3 (0.17 g, 0.214 mmol) and dppe (0.085 g,
0.214 mmol) in benzene (20 mL) was refluxed with stirring
for 2 h. The solvent was evaporated in vacuo. The residue was
chromatographed on a silica gel column, orange complex 9 beꢀ
ing eluted with a 2 : 1 benzene—nꢀhexane mixture. After recrysꢀ
tallization from a 3 : 1 CH2Cl2—nꢀhexane mixture, the yield of
complex 9 was 0.05 g (35%). Complex 9. Found (%): C, 49.70;
H, 5.01; B, 14.15. C28H35B9ClP2Ru. Calculated (%): C, 50.40;
H, 5.25; B, 14.58. ESR (CH2Cl2, gstand = 2.003, T = 77K):
g1 = 2.253; g2 = 2.108; g3 = 1.998). Diamagnetic complex 10
Molecular weight
Space group
Т/К
a/Å
b/Å
c/Å
α/deg
β/deg
879.39
P21/n
293(2)
12.8963(2)
22.6214(3)
14.8518(2)
667.31
P–1
120(2)
10.170(2)
11.517(2)
15.452(3)
70.383(3)
75.303(3)
64.880(3)
1530.4(5)
2
1.448
7.24
54
6633
105.573(1)
γ/deg
V/Å3
4173.7(1)
4
1.399
6.74
Z
dcalc/g cm–3
µ/cm–1
2θmax/deg
Number of independent reflections
Rint
58
11048
0.0349
0.0351
(7779)
0.0820
518
0.0384
0.0553
(5476)
0.1327
370
R1 (based on F for reflections
with I > 2σ(I ))
wR2 (based on F 2 for all reflections)
Number of parameters im refinement
GOOF
0.992
0.991
* The molecular formulas are C38H42B9ClP2Ru•CH2Cl2 (3) and
28H35B9ClP2Ru (9).
C

1170
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 7, July, 2006
Cheredilin et al.
ωꢀscanning technique). The structures were solved by
References
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method against F 2
with anisotropic displacement paramꢀ
hkl
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(AIBN) was used as the initiator of polymerization according to
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This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 05ꢀ03ꢀ32668
and 06ꢀ03ꢀ32172) and the Council on Grants of the Presiꢀ
dent of the Russian Federation (Program for State Supꢀ
port of Leading Scientific Schools of the Russian Federaꢀ
tion, Grant NShꢀ1153.2006.3).
Received July 6, 2006