Base-mediated transformation of the agostic (π-allyl)-closo- rhodacarboranes into complexes with an open (1-5-η5)-pentadienyl ligand

Article abstract of DOI:10.1039/c3dt52838c

The reactions of agostic (CH₃...Rh) complexes [3-{(1-3-η³)-1,1,2-trimethylallyl}-1-R-2-R′-closo-3,1, 2-RhC₂B₉H₉] [1: R = R′ = Me; 2: R,R′ = μ-(ortho-xylylene); 3: R = Ph, R′ = Me] in a cooled (+5 °C) toluene solution with the strong non-nucleophilic base N,N,N′,N′-tetramethylnaphthalene-1,8-diamine (tmnd) formally involve a linear coupling of the π-allyl ligand of one molecule of the complex to the π-allyl ligand of the second molecule of the complex, ultimately forming the structurally novel mononuclear species [3-{(1-5-η⁵)-2,3- dimethyl-5-(3-methylbuten-2-yl)pentadienyl}-1-R-2-R′-closo-3,1,2-RhC ₂B₉H₉] (4, 5) and (6a,b, a mixture of diastereomers). Complexes 5 and 6a,b were also prepared using weaker bases such as PPh₃ or even EtOH instead of tmnd. All new complexes 4-6 were characterized by a combination of analytical and multinuclear NMR data, as well as by single-crystal X-ray diffraction studies of two selected species 5 and the major diastereomer of 6, which revealed an open η⁵-pentadienyl coordination mode of the hydrocarbon ligands in these complexes.

Full text of DOI:10.1039/c3dt52838c

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Base-mediated transformation of the agostic
(π-allyl)-closo-rhodacarboranes into complexes
Cite this: DOI: 10.1039/c3dt52838c
with an open (1-5-η5)-pentadienyl ligand†
K. I. Galkin, F. M. Dolgushin, A. F. Smol’yakov, E. A. Sergeeva, I. A. Godovikov and
I. T. Chizhevsky*
The reactions of agostic (CH3⋯Rh) complexes [3-{(1-3-η3)-1,1,2-trimethylallyl}-1-R-2-R’-closo-3,1,2-
RhC2B9H9] [1: R = R’ = Me; 2: R,R’ = μ-(ortho-xylylene); 3: R = Ph, R’ = Me] in a cooled (+5 °C) toluene
solution with the strong non-nucleophilic base N,N,N’,N’-tetramethylnaphthalene-1,8-diamine (tmnd)
formally involve a linear coupling of the π-allyl ligand of one molecule of the complex to the π-allyl ligand
of the second molecule of the complex, ultimately forming the structurally novel mononuclear species
[3-{(1-5-η5)-2,3-dimethyl-5-(3-methylbuten-2-yl)pentadienyl}-1-R-2-R’-closo-3,1,2-RhC2B9H9] (4, 5)
and (6a,b, a mixture of diastereomers). Complexes 5 and 6a,b were also prepared using weaker bases
such as PPh3 or even EtOH instead of tmnd. All new complexes 4–6 were characterized by a combination
of analytical and multinuclear NMR data, as well as by single-crystal X-ray diffraction studies of two
selected species 5 and the major diastereomer of 6, which revealed an open η5-pentadienyl coordination
mode of the hydrocarbon ligands in these complexes.
Received 9th October 2013,
Accepted 4th December 2013
DOI: 10.1039/c3dt52838c
www.rsc.org/dalton
presence of cyclic dienes such as dcp, cod, chd, nbd, and
Introduction
C5Me5H was shown to afford a series of neutral (η4-diene)-
Acyclic (π-allyl)-closo-metallacarborane complexes of transition closo-nickelacarboranes of the general formula [2-(η4-diene)-
metals constitute an important class of compounds which are closo-2,1,7-NiC2B9H11].3 Relevant to these studies4 are investi-
widely used in stoichiometric reactions in metallacarborane gations on the hydrogen activation by (π-allyl)-closo-rhoda-
chemistry. Thus, much success has been achieved by Stone carborane [3-{(1-3-η3)-C3H5}-3-PPh3-closo-3,1,2-RhC2B9H11] that
and co-workers by employing the anionic molybdenum and quantitatively produces either the known dimeric compound
5
tungsten (π-allyl)-closo-metallacarboranes1 and later on related [3-PPh3-3,1,2-RhC2B9H11]2 or, in the presence of PPh3, the
complexes of other transition metals2 in the development of a catalytically active hydrido complex [3,3-(PPh3)2-3-H-closo-3,1,2-
highly efficient synthetic route to a variety of neutral carbo- RhC2B9H11].6
rane-containing complexes of different compositions and
structures. In particular, Stone’s method relies on the displace-
ment of the π-allyl ligand in the anionic 1,2-dicarborane-
Results and discussion
Synthesis of pentadienyl-type complexes 4–6
(π-allyl)–metal complexes with different donor molecules, such
as t-BuNC, CO, and PPh3, by treating the latter complexes with
strong acids.1,2 Closely related to the above stoichiometric reac-
tions are the transformations of (π-allyl) nickel complexes
[NEt4][2-{(1-3-η3)-C3H4R)}-closo-2,1,7-NiC2B9H11] (R = H, Ph)
derived from the “carbons apart” {nido-7,9-C2B9}-carborane
ligand; the treatment of these species with HBF4 Et2O in the
Recently, we have reported a convenient one-pot synthesis of a
series of acyclic (π-allyl)-closo-rhodacarboranes of the general
formula [3-{π-(R″-allyl)}-1-R-2-R′-closo-3,1,2-RhC2B9H9] (where
R″ is an aliphatic substituent), a new family of neutral metalla-
carborane complexes containing
a relatively rare agostic
(CH3⋯Rh) bonding system.7,8 The facile and efficient synthesis
of these π-allyl compounds allowed us to undertake the sys-
tematic exploration of their reactivity and catalytic properties.7
Thus, in the present work we found that the treatment of
[3-{(1-3-η3)-1,1,2-trimethylallyl}-1-R-2-R′-closo-3,1,2-RhC2B9H9]
[1: R = R′ = Me;7 2: R,R′ = μ-(ortho-xylylene);7 3: R = Ph, R′ =
Me8] in a cooled (+5 °C) toluene solution with 2.5 equiv. of the
A. N. Nesmeyanov Institute of Organoelement Compounds of the RAS, 28 Vavilov
Street, 119991, Russian Federation. E-mail: chizbor@ineos.ac.ru; http://www.ineos.
ac.ru/en/131-lmctm.html; Fax: +7 499 135 0176; Tel: +7 499 135 9334
†Electronic supplementary information (ESI) available: Crystallographic data of
5 and 6a, and 2D [1H–1H]-COSY spectra of 4. CCDC 965360 and 965361. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3dt52838c
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Scheme 1 Synthesis of closo-rhodacarborane complexes with an open (1-5-η5)-pentadienyl-type ligands in the presence of tmnd.
N,N,N′,N′-tetramethylnaphthalene-1,8-diamine (tmnd is the
non-nucleophilic base frequently used as the proton sponge)
for 12 h afforded air-stable crystalline products [3-{(1-5-η5)-2,3-
dimethyl-5-(3-methylbuten-2-yl)-pentadienyl}-1-R-2-R′-closo-
3,1,2-RhC2B9H9] (4–6), respectively (Scheme 1). Each of these
complexes was isolated from the reactions as the only metalla-
carborane product in reasonable to good yields based on one-
half of reacted complexes 1–3. They are air-stable in the solid
state and in solutions of aromatic or chlorinated hydrocar-
bons, and their purification can be accomplished by column
chromatography on silica gel. Based on the single-crystal X-ray
diffraction data for 5 and the major diastereomer of 6 (vide
infra) and on the multinuclear NMR data, all complexes 4–6
were assigned as having conventional 12-vertex closo geometry.
However, a particularly noteworthy structural feature of mole-
cules 4–6 is an open (1-5-η5)-pentadienyl-type hydrocarbon
ligand newly formed at their rhodium vertices.
Within the family of acyclic 18-electron (π-allyl)-closo-metal-
lacarborane complexes of transition metals, several quite
stable triphenylphosphine-containing rhodium species, such
as [3-{(1-3-η3)-C3H4R}-3-PPh3-closo-3,1,2-RhC2B9H11] (R = H,
Me) and [2-PPh3-2-{(1-3-η3)-C3H5}-closo-2,1,7-RhC2B9H11], have
been previously described.9 It seemed probable, therefore, that
similar non-agostic 18-electron complexes of the general
formula [3-{(1-3-η3)-1,1,2-trimethylallyl}-3-PPh3-1-R-2-R′-closo-
3,1,2-RhC2B9H9] might also be expected to be formed via
simple treatment of agostic complexes 1–3 with the PPh3
reagent. However, this turned out not to be the case. It was
found that in the reaction of either 2 or 3 with PPh3 the latter
reagent serves as a non-nucleophilic base, again, giving rise to
complexes 5 and 6, respectively. Moreover, complexes 5 and 6
can also be prepared by the treatment of a solution of 2 and 3,
respectively, in toluene with a much weaker base (EtOH). Com-
pared with the relatively short reaction time when using tmnd as a
base, the duration of both these reactions of 2 or 3 with PPh3 and/
or EtOH is greatly increased from 12 h to two days and one week,
respectively, as can be seen from Table 1. Taking this into account
and the fact that the reaction of 1 to form 4 failed to proceed in the
presence of a base weaker than tmnd, the former route for prepar-
ing complexes 4–6 can be considered to be the most synthetically
useful. A likely explanation for such a behavior of 1 is that the
acidity of the agostic hydrogen atom in this complex is weaker com-
pared to those in complexes 2 and 3, although we have no definite
proof for this suggestion other than the above experimental fact.
Table 1 Reaction conditions and yields of compounds 4–6
Base
tmnd (2.5 eq.)
PPh3 (2.5 eq.)
EtOH (>50 eq.)
Base-mediated
formation of 4–6
Reaction time/yield of 4–6 (%)
1 → 4
2 → 5
3 → 6a,b
(diastereomeric
mixture)
12 h/49
12 h/75
12 h/78
No reaction
2 days/56
2 days/62
No reaction
1 week/14
1 week/15
Although at this point there is insufficient experimental evi-
dence for the exact pathway of this coupling reaction, we can
suggest a possible mechanism by which pentadienyl-type com-
plexes 4–6 are formed (Scheme 2). Since the agostic hydrogen
atom in 1–3 possesses an acidic character, the likely pathway
for the first stage of the reaction may involve the agostic hydro-
gen abstraction either from complexes 1–3 or their diene-
hydride isomers [3,3-(η4-diene)-3-hydrido-1-R-2-R′-closo-3,1,2-
RhC2B9H9] (not shown in Scheme 2). Under base-mediated
conditions, both these species may yield the reactive anionic
Rh(I) species A with the 1,3-diene ligand at the rhodium
vertex,10 which may slowly transform in solution to give the
σ-allylic complex B having a potential electrophilic reactivity.
This complex B may further get alkylated at the rhodium
center by the nucleophilic anion A to give the allylic π,σ-binuc-
lear complex C, which may become agostic in nature after the
migration of the Rh-bound moiety to the diene ligand. Again,
the doubly agostic complex D, through complex E, can ulti-
mately convert to products 4–6 via the diene-hydride mechan-
ism and through the migration of the β-hydrogen to the
nearest allylic function. The latter route should be
accompanied by the loss of one of the Rh carborane moieties,
presumably in the form of [R,R′C2B9H9RhH(base)n] (n = 1 or
2), as proposed in Scheme 2.
Single-crystal X-ray diffraction study of 5 and 6a (the major
diastereomer)
The rather unusual result obtained in the reactions of 1–3 that
produce a short series of η5-pentadienyl-type complexes 4–6
was confirmed by a single-crystal X-ray diffraction study of
species 5 and the major diastereomer of 6, complex 6a. Single
crystals of both 5 and 6a suitable for X-ray diffraction were
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Scheme 2 Possible mechanism of the formation of (1-5-η5)-pentadienyl-type complexes 4–6 under base-mediated conditions.
grown from dichloromethane–n-hexane mixtures at room metallacarborane species with a pseudooctahedral 18-electron
temperature. The molecular structures of both complexes are configuration of the Rh(III) center. The rhodium atoms in both
shown in Fig. 1. Selected geometric parameters (bond dis- species are η5-coordinated in a symmetric fashion by C,C′-di-
tances and bond angles) are listed in Table 2. Although numer- substituted nido-carborane cage ligands with the Rh–C(1,2)
ous examples of transition metal complexes with (1-5-η5)- and Rh–B(4,7,8) distances averaging for 5 at 2.258 and 2.181 Å
pentadienyl ligands are known and structurally characterized and for 6a at 2.249 and 2.182 Å, respectively, and are rather
in organometallic chemistry,11 we are aware of only several asymmetrically bound to the same type η5-pentadienyl ligand
structurally studied smaller-cage metallacarborane mixed- terminally substituted by the isopenten-2-yl function. Indeed,
sandwich dimeric complexes reported by Hosmane and co- the Rh–C(01) separation of 2.122(5) and 2.148(2) Å in 5 and 6a,
workers, such as [(1-5-η5)-2,4-(Me)2C5H5)(η5-2-R-3-(Me3Si)-2,3- respectively, proved to be considerably shorter than the other
C2B4H4)M]2 [M = lanthanides (Y, Dy, Gd, Tb, Ho, Er, Tm, Lu); four Rh–C(02⋯05) distances, which range from 2.213(3) to
R = Me3Si or Me],12 in which the 2,4-pentadienyl ligands are 2.447(2) Å in 5 and from 2.221(4) to 2.372(5) Å in 6a. Interest-
coordinated symmetrically by lanthanide metals.
ingly, despite the U-shaped η5-pentadienyl ligand in 5 and 6a,
The overall geometry of 5 and 6a clearly confirmed that the carbon atoms C(01⋯05) are not all coplanar. In molecule
these complexes can be considered as neutral closo- 6a, the carbon atom C(05) is 0.22 Å above the plane defined by
Fig. 1 ORTEP drawings of the molecular structures of compounds 5 (left) and 6a (right) with thermal ellipsoids drawn at the 50% probability level;
hydrogen atoms are omitted for clarity.
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known 2,4-pentadienyl-type rhenium complex [(η5-C5Me5)ReCl
{η5-(3,4-diphenylhexa-2,4-diene-6-yl)}],13 where the η5-co-
ordinated pentadienyl skeleton composed of five carbon atoms
is not planar.
Table 2 Selected interatomic distances (Å) and angles (°) of complexes
5 and 6a
Complexes
5
6a
Rh(3)–C(1)
Rh(3)–C(2)
Rh(3)–B(4)
Rh(3)–B(7)
Rh(3)–B(8)
Rh(3)–C(01)
Rh(3)–C(02)
Rh(3)–C(03)
Rh(3)–C(04)
Rh(3)–C(05)
C(1)–C(2)
C(01)–C(02)
C(02)–C(03)
C(02)–C(09)
C(03)–C(04)
C(03)–C(010)
C(04)–C(05)
C(05)–C(06)
C(06)–C(07)
C(06)–C(011)
C(07)–C(08)
C(07)–C(012)
2.253(5)
2.262(5)
2.159(5)
2.179(6)
2.206(5)
2.122(5)
2.221(4)
2.286(4)
2.226(5)
2.372(5)
1.593(7)
1.426(7)
1.424(6)
1.501(6)
1.431(7)
1.514(6)
1.385(7)
1.473(7)
1.353(7)
1.507(6)
1.499(7)
1.495(7)
2.227(2)
2.271(2)
2.164(3)
2.170(3)
2.213(3)
2.148(2)
2.230(2)
2.251(3)
2.243(3)
2.447(2)
1.624(3)
1.425(3)
1.417(3)
1.518(4)
1.455(4)
1.510(3)
1.375(3)
1.476(3)
1.351(3)
1.516(4)
1.502(4)
1.509(4)
Multinuclear NMR spectroscopic characterization of
compounds 4–6
The detailed examination of the room-temperature 1H and
13C{1H} NMR spectra of 4–6 reveals their solution structures.
Standard homo- and heteronuclear 2D correlation techniques
were successfully used to assign the proton and carbon reson-
ances in their 1H and 13C{1H} NMR spectra. Two correlation
spectra of 4: 2D [1H–1H]-COSY and [13C–1H]-HMBC are given
as ESI.†
The 1H NMR spectra of all η5-pentadienyl rhodacarborane
complexes are somewhat similar in that they all display a set of
two pairs of characteristic proton resonances in the range from
2.3 to 5.5 ppm along with five upfield methyl resonances and
resonances corresponding to arene and methyl substituents at
the carborane cage ligand. Of these sets of resonances, the
first two for complexes 4 and 5, a sharp doublet at ca. 4.0 ppm
with Jgem ∼ 3.9 Hz and a broad triplet-like signal at ca.
2.5 ppm, share a cross-peak in the 2D [1H–1H]-COSY spectra.
In the 2D [13C–1H]-HSQC spectra of 4 and 5 (see, for example,
Fig. 2) both these resonances are also connected by a cross-
peak to the single carbon resonance at ca. 58.0 ppm originat-
ing from the terminal CH2 groups of the pentadienyl ligands.
The fact that the resonances of this pair observed at higher
field split into triplets can reasonably be explained by an
additional coupling arising from J(103Rh–1H) = 2.6 Hz. Based
on this observation, the resonances at ca. 2.5 ppm in the
spectra of 4 and 5 can be assigned to the protons H(1-anti),
and the other resonances at ca. 4.0 ppm can be assigned to
H(1-syn). Both proton resonances in the lower field region of
C(03)–C(02)–C(01)
C(03)–C(02)–C(09)
C(01)–C(02)–C(09)
C(02)–C(03)–C(04)
C(02)–C(03)–C(010)
C(04)–C(03)–C(010)
C(05)–C(04)–C(03)
C(04)–C(05)–C(06)
C(07)–C(06)–C(05)
C(07)–C(06)–C(011)
C(05)–C(06)–C(011)
C(06)–C(07)–C(08)
C(06)–C(07)–C(012)
C(08)–C(07)–C(012)
120.9(4)
122.2(4)
116.8(4)
123.6(4)
119.8(4)
116.3(4)
127.1(5)
124.5(4)
118.8(4)
122.6(4)
118.6(4)
124.5(5)
121.8(4)
113.7(4)
121.3(2)
120.5(2)
117.9(2)
123.2(2)
121.5(2)
115.2(2)
129.6(2)
123.1(2)
120.1(2)
121.0(2)
118.6(2)
123.3(2)
123.0(2)
113.7(2)
1
the C(01⋯C04) atoms, whereas C(04) is only 0.003 Å above it.
The carbon atoms C(04) and C(05) in 5 do not lie in the plane
of the C(01)–C(02)–C03) atoms, the deviations from this plane
toward and away from the rhodium atom being 0.11 and
0.08 Å, respectively. Moreover, the C–C bond lengths in the η5-
coordinated pentadienyl moiety of the ligand are highly
different; the C(03)–C(04) distances in both complexes are
longer (1.431(7) Å for 5 and 1.455(4) Å for 6a), whereas C(04)–
C(05) are shorter (1.385(7) Å for 5 and 1.375(3) Å for 6a) than
the other two carbon–carbon bonds in this part of the ligand.
Note that the latter distances are similar to the C(05)–C(06)
and C(06)–C(07) bond lengths in the uncoordinated isopenten-
2-yl substituent, which have average values of 1.4745 and
1.352 Å for complexes 5 and 6a, respectively. The X-ray diffrac-
tion data suggest some contribution of the η3,2-allylolefinic
form into the total pentadienyl structure of the hydrocarbon
ligand in these complexes where the carbon atoms C(01⋯03)
define the allyl moiety and the C(04⋯05) atoms define the
olefin moiety of the ligands. In fact, this description may be
applied at least to 5, where the deviation of the pentadienyl
ligand from planarity is more pronounced. Note that more
or less the same structural pattern is observed in the
the H NMR spectra of 4 and 5 exhibit doublet structures due
to the transoid couplings of J(H,H) = 12.9 Hz; the higher-field
doublet is somewhat broadened again due to the additional
coupling J(103Rh–1H), which is, however, smaller than 1.0 Hz
in this case. These doublet resonances at 5.32 and 4.68 ppm
(in the case of 4) and at 4.96 and 4.45 ppm (in the case of 5)
share a cross-peak between themselves in the 2D [1H–1H]-
COSY spectra of 4 and 5, whereas these doublets in the 2D
[13C–1H]-HSQC spectra are connected by cross-peaks to
different carbon resonances (see, for instance, Fig. 2). Based
on these spectroscopic data, the above doublet resonances
were assigned to the protons H(4) and H(5) of the 2,3-
dimethylpentadienyl moiety of the ligand in 4 and 5. Taking
all these facts into account and based on the observed cross-
peaks between other signals in the 2D [13C–1H]-HSQC, 2D
[13C–1H]-HMBC, as well as 2D [1H–1H]-COSY spectra of 4 and
5, we made the remaining assignments in their 1H and 13C
NMR spectra as shown in the Experimental section.
By analogy with 4 and 5, we also assigned the resonances in
1
the H and 13C{1H} NMR spectra of diastereomeric complexes
6a,b, in which double sets of all principal proton and carbon
resonances of both the pentadienyl and carborane ligands are
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Fig. 2 The 2D [13C–1H]-HSQC spectrum of 5 in CD2Cl2 at 20 °C showing the assignment of the proton and some carbon resonances.
clearly observed (see the Experimental section). Based on the
integration of the resonances associated with the pentadienyl
ligand, such as well-resolved signals originating from the term-
Experimental
Materials and methods
inal CH2 groups, the relative ratio of diastereomers 6a and 6b All reactions were carried out under an atmosphere of dry
was estimated as ca. 2 : 1.
argon using standard Schlenk techniques. Solvents including
The examination of the 11B/11B{1H} NMR spectra of com- those used for the column chromatography were distilled from
pounds 4–6 provided additional confirmation of their struc- appropriate drying agents under argon prior to use. Chromato-
tures. These spectra of 4 and 5 revealed a set of resonances graphy columns (ca. 12–15 cm in length and 1.8 cm in dia-
corresponding to nine cage boron atoms of these molecules, meter) were packed with silica gel (Acros, 230–400 Mesh).
all of which are observed in the expected integral ratio. The 11
B
NMR spectra were recorded in CD2Cl2 (5.32 ppm vs. Me4Si)
{1H} NMR spectrum of the diastereomeric mixture 6a,b with a Bruker AMX-400 spectrometer at the following frequen-
proved, however, to be more complicated. Thus, it displays, cies: 400.13 MHz (1H), 100.61 MHz (13C) and 128.33 MHz
along with resonances of the major diastereomer 6a, a set of (11B). Proton and boron chemical shifts were referenced to
more weak boron signals consistent with the presence of the residual protons in CD2Cl2 or to external BF3·Et2O, respect-
minor isomeric product which, due to overlapping, were only ively, with downfield shifts taken as positive. IR spectra in KBr
partly presented in the Experimental section.
were obtained using a Nicolet Magna-750 spectrometer.
Elemental analyses were performed by the Analytical Labora-
tory of the Institute of Organoelement Compounds of the RAS.
Starting rhodium allylic complexes (1–3)7,8 were prepared
according to the literature methods. All other reagents were
supplied commercially.
Conclusions
The unusual base-mediated linear coupling reactions of the
agostic (CH3⋯Rh) (π-allyl)rhodacarborane complexes have
been described. The products of these reactions (compounds
Synthetic procedures
General method for the synthesis of {(1-5-η5)-2,3-dimethyl-5-
4, 5 and 6a,b, a mixture of diastereomers) were characterized (3-methylbutene-2-yl)pentadienyl}rhodacarborane complexes
by a combination of analytical and multinuclear NMR data, as (4–6). To a solution of complexes 1–3 (0.2 mmol) in 8 ml of
well as by single-crystal X-ray diffraction studies of two selected degassed toluene was added either tmnd (0.6 mmol) or PPh3
species 5 and 6a. A particularly noteworthy structural feature (0.6 mmol) or EtOH (ca. 2 ml). The resulting mixture was then
of molecules 4–6 is an open η5-pentadienyl-type hydrocarbon stirred at 5 °C overnight, 2 days or 1 week, respectively. After
ligand newly formed at their rhodium vertices.
the reactions were completed (TLC control using the CH2Cl2–
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n-hexane (1 : 4) mixture as an eluent), the resulting dark sus- 136 Hz), −13.3 (m, 2B). Anal. calcd for C22H36B9Rh: C 52.77;
pension was treated by column chromatography eluting a H 7.25; B 19.43%; found: C 52.76; H 7.35; B 19.58%.
colored fraction with CH2Cl2–n-hexane (1 : 2). The solvent was
{(1-5-η5)-2,3-Dimethyl-5-(3-methylbutene-2-yl)pentadienyl}-1-
evaporated under reduced pressure, and the residue was CH3-2-Ph-closo-3,1,2-RhC2B9H9] (6a,b). The general method
treated with n-hexane to afford 4–6a,b as crystalline solids. described above was employed: 3 (80 mg, 0.2 mmol), degassed
Recrystallization of crude solids from a dichloromethane– toluene (6 ml), tmnd (112 mg, 0.6 mmol; reaction time, 12 h),
n-hexane mixture resulted in analytically pure complexes 4–6a,b.
PPh3 (154 mg, 0.6 mmol; reaction time, 48 h) or EtOH (1.5 ml;
[3-{(1-5-η5)-2,3-Dimethyl-5-(3-methylbuten-2-yl)pentadienyl}- reaction time, one week). Yield of 6a,b (deep-red microcrys-
1,2-(CH3)2-closo-3,1,2-RhC2B9H9] (4). The general method tals): 38 mg (78%) (in the presence of tmnd), 30 mg (62%) (in
described above was employed: 1 (100 mg, 0.29 mmol), tmnd the presence of PPh3), 7 mg (15%) (in the presence of EtOH).
(161 mg, 0.87 mmol), degassed toluene (8 ml), reaction time, IR spectrum (KBr, cm−1): 2547 (νBH). H NMR (CD2Cl2, *major
1
12 h. Yield of 4 (orange microcrystals) after recrystallization diastereomer): δ 7.22–7.21 (10H, H-aryl*, H-aryl), 5.38 (d, 2H,
from a mixture of CH2Cl2–n-hexane: 30 mg (49%). IR spectrum 3JHH = 14.0 Hz, H5*, H5), 4.83 (d, 2H, 3JHH = 14.0 Hz, H4*, H4),
2
2
(KBr, cm−1): 2549 (νBH). 1H NMR (CD2Cl2): δ 5.33 (d, 1H, 3JHH
=
4.13 [d, 1H, JHH = 3.9 Hz, H(1-anti)*], 4.08 [d, 1H, JHH = 4.0
3
2
12.9 Hz, H4), 4.68 (br.d, 1H, JHH = 12.9 Hz, H5), 4.09 [d, 1H, Hz, H(1-anti)], 2.97 [d, 1H, JHH = 3.9 Hz, H(1-syn)*], 2.80 [d,
2JHH = 3.9 Hz, H(1-syn)], 2.45 [br.t, 2JHH = 3.9 Hz, JRhH = 2.6 Hz, 1H, JHH = 3.6 Hz, H(1-syn)], 2.23 (s, 3H, CH3-carb*), 2.13 (s,
2
1H, H(1-anti)], 2.12 [s, 3H, 3-CH3], 2.01 (s, 3H, CH3-carb), 2.00 3H, CH3-carb), 1.86 (s, 3H, 2-CH3*), 1.83 (s, 3H, 2-CH3), 1.81
(s, 3H, CH3-carb), 1.95 (s, 3H, 2-CH3), 1.84, 1.81 (s, 2 × 3H, (s, 3H, 3-CH3), 1.77 (s, 3H, 3-CH3*), 1.75 (s, 3H, 7-CH3), 1.74 (s,
7-CH3), 1.75 (s, 3H, 6-CH3). 13C{1H} NMR (CD2Cl2): δ 143.4 6H, 7-CH3*, 7-CH3), 1.69 (s, 3H, 7-CH3*), 1.51 (s, 3H, 6-CH3*),
(C7), 127.1 (C6), 112.3 (d, JRhC = 3.7 Hz, C2), 111.0 (d, JRhC
=
1.27 (s, 3H, 6-CH3). 13C{1H} NMR (CD2Cl2): δ 145.3 (C3*), 145.0
3.0 Hz, C3), 104.0 (d, JRhC = 3.7 Hz, C4), 100.3 (d, JRhC = 5.3 Hz, (C3), 142.2 (Cipso*), 142.0 (Cipso), 128.8, 128.5, 128.3, 128.1,
C5), 72.2 (m, C-carb), 69.5 (m, C-carb), 58.0 (d, JRhC = 14.0 Hz, 128.1, 128.1, 127.9 (C-aryl*, C-aryl), 127.6 (C6*), 127.3 (C6),
C1), 29.8 (s, 3H, CH3-carb), 27.6 (s, 3H, CH3-carb), 23.6, 22.8 119.6 (C5*, C5), 114.6 (d, JRhC = 3.7 Hz, C3), 114.1 (d, JRhC = 4.4
(7-CH3), 21.4 (2-CH3), 20.1 (3-CH3), 14.8 (6-CH3). 11B NMR Hz, C2*, C2), 106.3 (d, JRhC = 4.2 Hz, C3*), 105.3 (d, JRhC = 12.5
(CD2Cl2, J = JBH): δ 5.7 (d, 1B, J = 143 Hz), 3.2 (d, 1B, J = Hz, C4*, C4), 84.6, 78.5 (C-carb*), 79.0 (C-carb), 58.6 (d, JRhC
=
154 Hz), 0.2 (d, 1B, J = 146 Hz), −2.9 (d, 1B, J = 146 Hz), −7.3 12.5 Hz, C1*), 58.2 (d, JRhC = 12.9 Hz, C1), 32.1 (CH3-carb, CH3-
(d, 2B, J = 136 Hz), −11.7 (d, 2B, J = 156 Hz), −13.9 (d, 1B, J = carb*), 23.8 (7-CH3*), 23.7 (7-CH3), 22.9 (7-CH3*, 7-CH3), 22.2
151 Hz). Anal. calcd for C16H34B9Rh: C 45.04; H 8.03; B (2-CH3*, 2-CH3), 20.2 (3-CH3), 19.4 (3-CH3)*, 14.8 (6-CH3*),
22.81%; found: C 45.25; H 8.29; B 22.88%.
14.0 (6-CH3). 11B NMR (CD2Cl2, J = JBH): δ 7.2 (d, J = 143 Hz),
{(1-5-η5)-2,3-Dimethyl-5-(3-methylbutene-2-yl)pentadienyl}- 6.2 (d, J = 114 Hz), 3.3 (d, J = 142 Hz), 1.8 (d, J = 225 Hz), 1.5 (d,
1,2-μ-(1′,2′-xylylene)-closo-3,1,2-RhC2B9H9] (5). The general J = 150 Hz), 0.3 (d, J = 162 Hz), −2.3 (d, J = 139 Hz), −5.2 (d, J =
method described above was employed:
2
(100 mg, 125 Hz), −6.2 (d, J = 131 Hz), −7.3 (d, J = 136 Hz), −8.4 (d, J =
0.24 mmol), degassed toluene (8 ml), tmnd (133 mg, 143 Hz), −10.2 (d, J = 160 Hz), −11.5 (d, J = 162 Hz), −12.7 (d,
0.72 mmol; reaction time, 12 h), PPh3 (189 mg, 0.72 mmol; J = 165 Hz), −13.1 – −15.9 (m). Anal. calcd for C21H36B9Rh:
reaction time, 48 h) or EtOH (2 ml; reaction time, one week). C 51.61; H 7.42; B 19.91%; found: C 50.89; H 7.15; B 19.86%.
Yield of 5 (yellow microcrystals) after recrystallization from a
X-Ray diffraction studies
mixture of CH2Cl2–n-hexane: 45 mg (75%) (in the presence of
tmnd); 33 mg (56%) (in the presence of PPh3); 8 mg (14%) (in Crystals of 5 and 6a suitable for X-ray diffraction study were
the presence of EtOH). IR spectrum (KBr, cm−1): 2549 (νBH). obtained by recrystallization of purified complexes from a
1H NMR (CD2Cl2): δ 7.28–7.19 (m, 2H, H-aryl), 7.09 (br. d, 1H, methylenechloride–n-hexane mixture at ambient temperature.
3
H-aryl), 7.05 (br. d, 1H, H-aryl), 4.96 (d, 1H, JHH = 12.8 Hz, Single-crystal X-ray diffraction studies were carried out using a
3
2
H4), 4.45 (d, 1H, JHH = 12.8 Hz, H5), 4.08 [d, 1H, JHH
=
Bruker SMART APEX II diffractometer (graphite monochro-
3.8 Hz, H(1-syn)], 3.98 (d, 1H, JAB = 19.2 Hz, CHH-aryl), 3.81 (d, mated Mo-Kα radiation, λ = 0.71073 Å, ω-scan technique, T =
1H, JAB = 18.7 Hz, CHH-aryl), 3.59 (d, 1H, JAB = 18.7 Hz, CHH- 100 K). The APEX II software14 was used for collecting frames
2
aryl), 3.49 (d, 1H, JAB = 19.2 Hz, CHH-aryl), 2.34 [br. t, JHH
=
of data, indexing reflections, determination of lattice con-
3.8 Hz, JRhH = 2.7 Hz, 1H, H(1-anti)], 1.89 (s, 3H, 7-CH3), 1.86 stants, integration of intensities of reflections, scaling and
(s, 3H, 2-CH3), 1.82 (s, 3H, 7-CH3), 1.78 (s, 3H, 6-CH3), 1.06 (s, absorption correction, and SHELXTL15 for space group and
3H, 3-CH3). 13C{1H} NMR (CD2Cl2): δ 143.9 (C7), 131.2, 131.2 structure determination, refinements, graphics, and structure
(Cipso), 130.5, 129.3, 127.8, 127.6 (C-aryl), 126.5 (C6), 115.4 (d, reporting. The structures were solved by direct methods and
JRhC = 2.1 Hz, C2), 111.0 (d, JRhC = 3.5 Hz, C3), 101.6 (d, JRhC
=
refined by the full-matrix least-squares technique against F2
3.6 Hz, C4), 98.3 (br. s, C5), 70.9 (m, C-carb), 65.9 (m, C-carb), with the anisotropic thermal parameters for all non-hydrogen
58.0 (d, JRhC = 14.4 Hz, C1), 43.6 (CH2-carb), 42.2 (CH2-carb), atoms. The hydrogen atoms at the cage boron atoms as well as
23.7, 23.0 (7-CH3), 21.1 (2-CH3), 19.6 (3-CH3), 15.1 (6-CH3). 11B at the C(01), C(04), C(05) atoms of the pentadienyl ligands
NMR (CD2Cl2, J = JBH): δ 7.7 (d, 1B, J = 135 Hz), 4.2 (d, 1B, J = were located from difference Fourier maps and refined isotro-
139 Hz), 1.1 (d, 1B, J = 144 Hz), −4.2 (d, 1B, J = 153 Hz), −7.0 pically without restraints; the rest of the hydrogen atoms were
(d, 1B, J = 138 Hz), −8.0 (d, 1B, J = 132 Hz), −10.7 (d, 1B, J = placed in the geometrically calculated positions and included
Dalton Trans.
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Dalton Transactions
Paper
2 (a) N. Carr, D. F. Mullica, E. L. Sappenfield and
F. G. A. Stone, Inorg. Chem., 1994, 33, 1666; (b) K. A. Fallis,
D. F. Mullica, E. L. Sappenfield and F. G. A. Stone, Inorg.
Chem., 1994, 33, 4927.
Table 3 Crystal data, data collection and structure refinement para-
meters for 5 and 6a
Compound
5
6a
Molecular formula
C
22H36B9Rh
C21H36B9Rh
488.70
0.27 × 0.10 × 0.07
Orthorhombic
P212121
9.575(5)
15.128(9)
16.401(9)
90
90
90
2376(2)
4
1.366
3 B. E. Hodson, T. D. McGrath and F. G. A. Stone, Inorg.
Chem., 2004, 43, 3090.
4 (a) J. A. Walker, L. Zheng, C. B. Knobler, J. Soto and
M. F. Hawthorne, Inorg. Chem., 1987, 26, 1608;
(b) R. E. King III, D. C. Busby and M. F. Hawthorne, J. Orga-
nomet. Chem., 1985, 279, 103.
5 P. E. Behnken, T. B. Marder, R. T. Baker, C. B. Knobler,
M. R. Thompson and M. F. Hawthorne, J. Am. Chem. Soc.,
1985, 107, 932 and references therein.
6 J. A. Belmont, J. Soto, R. E. King III, A. J. Donaldson,
J. D. Hewes and M. F. Hawthorne, J. Am. Chem. Soc., 1989,
111, 7475 and references therein.
Formula weight
500.71
0.16 × 0.11 × 0.08
Monoclinic
P21/n
9.3802(7)
17.295(1)
14.8261)
90
93.867(2)
90
2399.6(3)
4
Dimension, mm3
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalc (g cm−3
2θmax (°)
)
1.386
56
7.21
60
7.26
Linear absorption (μ) (cm−1
)
7 K. I. Galkin, S. E. Lubimov, I. A. Godovikov,
F. M. Dolgushin, A. F. Smol’yakov, E. A. Sergeeva,
V. A. Davankov and I. T. Chizhevsky, Organometallics, 2012,
31, 6080.
8 K. I. Galkin, F. M. Dolgushin, A. F. Smol’yakov,
I. A. Godovikov, E. A. Sergeeva and I. T. Chizhevsky, Mende-
leev Commun., 2013, 23, 193.
No. unique refl. (Rint
)
5771 (0.1174)
3489
346
0.0511
0.1268
0.995
6881 (0.0400)
6505
337
0.0284
0.0649
1.002
No. observed refl. (I > 2σ(I))
No. parameters
R1 (on F for observed refl.)a
wR2 (on F2 for all refl.)b
GOOF
a R1 = ∑||Fo| − |Fc||/∑|Fo|. b wR2 = {∑[w(Fo2 − Fc2)2]/∑w(Fo2)2}1/2
.
9 J. A. Walker, L. Zheng, C. B. Knobler, J. Soto and
M. F. Hawthorne, Inorg. Chem., 1987, 26, 1608.
10 The 1H NMR monitoring of the reaction of 1 with 2.5 eq. of
tmnd in C6D6 for 4 h revealed a set of new resonances con-
sisting of two separate 2H broad singlet resonances at 5.04
and 4.92 ppm with Jgem < 0.5 Hz as well as an additional
methyl resonance in the area between 2.44 and 2.08 ppm.
These sets of resonances were tentatively attributed to an
anionic η4-diene complex A which is proposed to be a key
intermediate in the formation of complexes 4–6
(Scheme 2).
11 (a) P. Powell, in Advances in Organometallic Chemistry, ed.
R. West, F. G. A. Stone, Academic, New York, 1986, vol. 26,
p. 125; (b) R. D. Ernst, Chem. Rev., 1988, 88, 1255.
12 (a) A. Li, J. Wang, C. Zheng, J. A. Maguire and
N. S. Hosmane, Organometallics, 2004, 23, 3091;
(b) J. Wang, C. Zheng, G. Canseco-Melchor, D. J. Hilby,
J. A. Maguire and N. S. Hosmane, Organometallics, 2007,
26, 577.
in the structure factor calculations in the riding motion
approximation. The Flack parameter value 0.46 (2) found for
6a shows a racemic mixture in this case. The principal experi-
mental and crystallographic parameters are presented in
Table 3.
Acknowledgements
This work was supported by grant no. 12-0300102 from the
Russian Foundation for Basic Research. The authors are also
grateful to Dr M. G. Ezernitskaya for recording the IR spectra
of compounds 4–6.
Notes and references
1 See for instance: (a) S. J. Dossett, S. Li and F. G. A. Stone,
J. Chem. Soc., Dalton Trans., 1993, 1585; (b) S. Li and
F. G. A. Stone, Polyhedron, 1993, 12, 1689; (c) S. J. Dossett,
D. F. Mullica, E. L. Sappenfield and F. G. A. Stone, J. Chem.
Soc., Dalton Trans., 1993, 3551; (d) D. F. Mullica,
E. L. Sappenfield, F. G. A. Stone and S. F. Woolam, Organo-
metallics, 1994, 13, 157.
13 W. A. Hermann, R. A. Fischer and E. Herdweck, Organo-
metallics, 1989, 8, 2821.
14 APEX II software package, Bruker AXS Inc., 5465, East Cheryl
Parkway, Madison, WI, 2005, 5317.
15 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 2008, 64, 112.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.