Activation of dichloromethane by (phosphane)nrhodium(I) Complexes - X-ray structure of [{(PEt3)2RhCl}2(μ-Cl) 2(μ-CH2)]

Article abstract of DOI:10.1002/(SICI)1099-0682(199803)1998:3<349::AID-EJIC349>3.0.CO;2-5

Dichloromethane reacts with dinuclear rhodium complexes [{(PR₃)₂Rh}₂(μ-Cl)₂] to give the bridging-methylene complexes [{(PR₃)₂(μ-Cl)₂(μ-CH₂)] (PR₃ = PEt

Full text of DOI:10.1002/(SICI)1099-0682(199803)1998:3<349::AID-EJIC349>3.0.CO;2-5

FULL PAPER
Activation of Dichloromethane by (Phosphane)nrhodium(I) Complexes ؊
X-ray Structure of [{(PEt3)2RhCl}2(µ-Cl)2(µ-CH2)]
Jean-Jacques Brunet*, Xavier Couillens, Jean-Claude Daran, Ousmane Diallo, Christine Lepetit, and Denis Neibecker
Laboratoire de Chimie de Coordination du CNRS, UPR 8241,
205 route de Narbonne, F-31077 Toulouse Cedex 4, France
Fax: (internat.) ϩ33 (0) 561 553 003
E-mail: brunet@lcctoul.lcc-toulouse.fr
Received November 11, 1997
Keywords: Rhodium / Phosphanes / Ligand redistribution / Dichloromethane activation / Oxidative addition
Dichloromethane reacts with dinuclear rhodium complexes
[{(PR3)2Rh}2(µ-Cl)2] to give the bridging-methylene comple- [{(C8H14)2Rh}2(µ-Cl)2] with monophosphanes have been
xes [{(PR3)2RhCl}2(µ-Cl)2(µ-CH2)] (PR3 = PEt3, PPh2Me). The
monitored by 31P NMR, evidencing chloride bridges cle-
diffraction study. The early stages of the reaction of
structure of the PEt3 complex has been established by X-ray avage and phosphane redistribution processes.
Activation of dihalomethanes by low oxidation state volved in the reaction of monophosphanes with the chloro-
transition metal complexes has attracted a great deal of bridged dimer [{(C8H14)2Rh}2(µ-Cl)2], 1 (C8H14 ϭ cyclooc-
interest as a means of generating haloalkyl transition metal tene).
derivatives which are versatile precursors for a wide range
As part of our work on the synthesis of amidorhodium
of useful compounds[1]. Oxidative addition of diiodo and
complexes, we have been led to prepare the dimer
[{(PEt3)2Rh}2(µ-Cl)2], 2[12][13]. Compound 2 is prepared in
dibromomethane is well documented, and, although less
common, the case of dichloromethane is now well recog-
nized.
Several examples of simple oxidative addition of di-
chloromethane (CH2Cl2) to electron-rich RhI complexes of
mono or polydentate phosphorus[2][3], nitrogen[4][5][6], sul-
fur[7], and phosphorus/nitrogen[8][9] ligands have been re-
ported. They usually afford chloromethylrhodium(III) com-
plexes.
pure form [31P{1H} NMR, δ (THF) ϭ 44.3, JP-Rh ϭ 194
Hz] by treating 4 equivalents of PEt3 with 1 in THF. It can
also be prepared in CH2Cl2 by reacting the starting materi-
als for 10 min, followed by immediate evaporation of the
solvent. Incidentally, we observed that if the reaction time
in CH2Cl2 is longer than 10 min, a second complex is
formed [31P{1H} NMR, δ (CH2Cl2) ϭ 31.1, JP-Rh ϭ 147
Hz] which becomes the only reaction product after 2 h. This
new complex was isolated by precipitation with THF. Apart
from the expected signals for the triethylphosphane ligands,
However, we found only two examples of double oxidat-
ive addition of CH2Cl2 on binuclear RhI complexes[10][11]
.
1
The chloride-bridged rhodium(I) dimer [{(dppe)Rh}2(µ-
Cl)2] [dppe ϭ 1,2-bis(diphenylphosphanyl)ethane] has been
reported to react with CH2Cl2 to generate a bridging-meth-
the H-NMR spectrum exhibits a broad signal at δ ϭ 3.7,
which becomes sharper on phosphorus decoupling, and the
13C{1H,31P} NMR spectrum shows a triplet at δ ϭ 38.9
(JC-Rh ϭ 22 Hz, see Experimental Section). These signals
could correspond to the methylene bridge of a dinuclear
RhIII complex, as suggested by the relatively small JP-Rh
coupling constant. This complex was definitely identified as
ylene rhodium(III) complex (eq. 1)[10]
.
the
methylene-bridged
dinuclear
complex
[{(PEt3)2RhCl}2(µ-Cl)2(µ-CH2)] 3 by single crystal X-ray
diffraction analysis.
The other example concerns the oxidative addition of
The molecular structure, which has a 2-fold symmetry, is
gem-dichlorocarbons on the binuclear basic complex shown in Figure 1. The binuclear structure is built up by
[{Rh(µ-pz)(CNtBu)2}2] (pz ϭ pyrazolate) to give [{Rh(µ- two rhodium centers joined by two chloride ligands and a
pz)Cl(CNtBu)2}2(µ-CHR)][11]
.
bridging methylene unit the carbon of which is located on
In this paper, we report that activation of CH2Cl2 to gen- the 2-fold axis. This structure is very similar to that of the
erate methylene-bridged dimers is not limited to dinuclear recently reported [{(dppe)RhCl}2(µ-Cl)2(µ-CH2)] com-
RhI complexes and to RhI complexes bearing chelating di- plex[10]. As in the dppe compound, each rhodium center
phosphanes, and can be obtained from both mononuclear has a symmetrical, quasi-octahedral environment and for-
and dinuclear monophosphane rhodium(I) complexes. Fur- mally can be considered as RhIII. A comparison of import-
thermore, some insight is given on the intermediates in- ant bond distances and bond angles within the
Eur. J. Inorg. Chem. 1998, 349Ϫ353
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349

J. J. Brunet, X. Couillens, J.-C. Daran, O. Diallo, C. Lepetit, D. Neibecker
FULL PAPER
Figure 1. Molecular structure and numbering scheme for [{(PEt3)2RhCl}2(µ-Cl)2(µ-CH2)].
Rh2Cl4P4CH2 framework for the two complexes is given in
Table 1.
This results (eq. 2) shows that the activation of CH2Cl2
by a chloride-bridged rhodium(I) dimer discovered by Fry-
zuk et al. (eq. 1) is not limited to the case of rhodium(I)
˚
Table 1. Comparison of interatomic distances [A] and bond angles
complexes with chelating diphosphanes[10]
.
[°] within the Rh2Cl4P4CH2 framework of [{L2RhCl}2(µ-Cl)2(µ-
CH2)]. E.s.d.s. in parentheses refers to the last significant digit
L ϭ PEt3
L ϭ dppe
Rh(1)ϪCl(1)
Rh(1)ϪCl(1Ј)
Rh(1)ϪCl(2)
Rh(1)ϪP(1)
Rh(1)ϪP(2)
Rh(1)ϪC(1)
2.4458(4)
2.4618(4)
2.5310(4)
2.2851(4)
2.2605(4)
2.060(2)
2.4532(7)
2.4700(8)
2.5071(7)
2.2587(8)
2.2394(8)
2.057(3)
More surprisingly, the same methylene-bridged dinuclear
rhodium complex 3 is formed as the major product by reac-
tion of the mononuclear complex [(Et3P)3RhCl] with
CH2Cl2 for 24 h at room temperature. On the basis of 31P-
NMR analysis, some others unidentified (phosphane)rho-
dium complexes are also formed in small amounts.
Cl(1)ϪRh(1)ϪCl(1Ј)
Cl(1)ϪRh(1)ϪCl(2)
Cl(1Ј)ϪRh(1)ϪCl(2)
Cl(1)ϪRh(1)ϪP(1)
Cl(1Ј)ϪRh(1)ϪP(1)
Cl(2)ϪRh(1)ϪP(1)
Cl(1)ϪRh(1)ϪP(2)
Cl(1Ј)ϪRh(1)ϪP(2)
Cl(2)ϪRh(1)ϪP(2)
P(1)ϪRh(1)ϪP(2)
Cl(1)ϪRh(1)ϪC(1)
Cl(1Ј)ϪRh(1)ϪC(1)
Cl(2)ϪRh(1)ϪC(1)
P(1)ϪRh(1)ϪC(1)
P(2)ϪRh(1)ϪC(1)
Rh(1)ϪCl(1)ϪRh(1Ј)
Rh(1)ϪC(1) ϪRh(1Ј)
81.64(2)
89.69(1)
87.41(1)
174.87(2)
93.28(1)
89.40(1)
89.61(1)
169.97(1)
97.49(1)
95.51(2)
81.95(4)
81.55(4)
166.99(5)
98.04(4)
92.42(3)
75.58(1)
93.7(1)
82.35(3)
94.15(3)
93.07(3)
176.65(3)
99.23(3)
88.72(3)
93.74(3)
175.99(3)
86.30(3)
84.72(3)
80.70(7)
80.29(7)
172.0(1)
96.62(8)
100.02(7)
76.20(2)
95.2(2)
This result (eq. 3) is somewhat surprising in view of the
reaction described by Milstein et al. in the case of PMe3
(eq. 4)[2]
.
The main differences are observed for the angles around
the metal atom. They are certainly related to the larger
strain resulting from the chelating coordination of the dppe
ligand, as is clearly shown by the P(1)ϪRh(1)ϪP(2) angle
which varies from 95.51° in the triethylphosphane complex
to 84.72° in the dppe one.
350
Eur. J. Inorg. Chem. 1998, 349Ϫ353

Activation of Dichloromethane by (Phosphane)nrhodium(I) Complexes
FULL PAPER
Indeed PEt3 and PMe3 have similar electronic properties bridged [{(PPh2Me)2RhCl}2(µ-Cl)2(µ-CH2)] (4) which can
(pKa 8.69 vs 8.65) and differ by their cone angles, only (132° be readily isolated. This CH2Cl2 activation appears to be
vs 118°)[14]. Nevertheless, this reaction may occur via dis- slower than in the case of [{(PEt3)2Rh}2(µ-Cl)2], probably
placement of an equilibrium between [(PEt3)3RhCl] and as a consequence of the lower electron-donating ability of
[14]
[{(PEt3)2Rh}2(µ-Cl)2], a well-known process in the case of PPh2Me (pKa ϭ 4.57) as compared to that of PEt3
[(PPh3)3RhCl][15]
The different behaviour of
[(PMe3)3RhCl] may be merely ascribed to the unfavorable treated with 4 equivalents of PR3 (either PEt3 or PPh2Me),
dissociation of the smaller phosphane. cleavage of chloride bridges occurs, followed by phosphane
.
.
It is thus clear that when [{(C8H14)2Rh}2(µ-Cl)2] 1 is
In the course of our study of the reaction of PEt3 (4 redistribution, affording the dinuclear complexes
equiv.) with [{(C8H14)2Rh}2(µ-Cl)2] 1, we made another [{(PR3)2Rh}2(µ-Cl)2]. In both cases, these complexes acti-
interesting observation. Indeed, according to literature vate CH2Cl2 to give the methylene-bridged complexes
data[16][17][18], e.g. in the case of Ph2PMe[18], this reaction [{(PR3)2RhCl}2(µ-Cl)2(µ-CH2)].
was believed to occur by stepwise replacement of the cyclo-
As a complement, we also studied the reaction of 1 with
octene ligands, without cleavage of the chloride bridges, to only 2 equivalents of either PEt3 or PPh2Me, again by 31P-
ultimately yield [{(PEt3)2Rh}2(µ-Cl)2] (2). We surprisingly NMR monitoring at the early stage of the reaction at room
observed that, after a few min at room temp. in dichloro- temperature. Indeed, the authors who previously reported
methane, the very major phosphane complex is on the reaction with PPh2Me indicated that the NMR spec-
[(PEt3)3RhCl]. The reaction rapidly evolves to generate the tra were recorded several hours after mixing the reac-
chloride-bridged dimer 2, together with the bridging-meth- tants[18]
ylene one 3 which is the only product after 1 h. The obser- In both cases, after 5Ϫ10 min mixing the reactants in
.
vation of [(PEt3)3RhCl] as the only phosphane complex (no THF at room temperature, the tetrasubstituted [{(PR3)2-
free PEt3) at the early stage of the reaction implies the pres- Rh}2(µ-Cl)2] and the disubstituted [{(C8H14)(PR3)Rh}2(µ-
ence of unreacted 1 and suggests a subsequent redistri- Cl)2] complexes are present as the two major products. In
bution of the phosphane ligands. This was demonstrated the case of PPh2Me, three others complexes are also observ-
independently by reacting [(PEt3)3RhCl] (4 equiv.) with 1 able, two of them giving rise to doublets (31P NMR: δ ϭ
(1 equiv.) in THF, affording quantitatively [{(PEt3)2Rh}2(µ- 40.0, JP-Rh ϭ 187 Hz and δ ϭ 33.2, JP-Rh ϭ 195 Hz) and
Cl)2] (31P NMR) (eq. 5).
the third one (minor) giving a spin figure corresponding to
a tris(phosphane)rhodium complex, as previouly observed
with 4 equivalents of PPh2Me (vide supra). After 2 h, only
the
doublet
corresponding
to
the
expected
[{(C8H14)(PR3)Rh}2(µ-Cl)2] is present.
Thus, although the cleavage of the chloride bridges could
not be clearly evidenced in the case of two equivalents of
The above results led us to reinvestigate the previously phosphane, these results indicate that reaction of mono-
reported reaction of PPh2Me (4 equiv.) with 1[18] by 31P- phosphanes with [{(C8H14)2Rh}2(µ-Cl)2] always involves
NMR monitoring at the early stage of the reaction at room substitution of the four cyclooctene ligands, followed by re-
temperature. In THF, the reaction is very fast. Within 5 min distribution of the phosphane with unreacted starting com-
the main reaction product is [{(PPh2Me)2Rh}2(µ-Cl)2] and plex.
only traces of other complexes {among which
[(PPh2Me)3RhCl]} are observable. In CH2Cl2, however, a
It must be noted that a related ligand redistribution pro-
cess has been recently evidenced by NMR in the special
mixture of 5 complexes is observed after 5Ϫ10 min. The
case of terdentate nitrogen ligands[5]
.
major product is [(PPh2Me)3RhCl] (31P NMR: δ ϭ 31.8,
dt, JP-Rh ϭ 187 Hz, JP-P ϭ 42 Hz and δ ϭ 16.5, dd,
JP-Rh ϭ 139 Hz, J
ϭ 42 Hz). Among the four others
P-P
complexes, only two could be identified. On the basis of
literature data[18], one is [{(PPh2Me)(C8H14)Rh}2(µ-Cl)2]
(31P NMR δ ϭ 40.4, JP-Rh ϭ 187 Hz) while the other is the
expected [{(PPh2Me)2Rh}2(µ-Cl)2] (31P NMR: δ ϭ 34.0,
JP-Rh ϭ 196 Hz). Among the two other minor complexes,
one gives a broad doublet (31P NMR: δ ϭ 32.8, JP-Rh
ϭ
194.5 Hz) and the second a spin figure which resembles that
of a tris(phosphane)rhodium(I) complex (31P NMR: δ ϭ
22.8, dt, JP-Rh ϭ 150 Hz, JP-P ϭ 24 Hz anf δ ϭ 10.6, dd,
JP-Rh ϭ 96 Hz, J
ϭ 24 Hz). After 20 min, all the above
P-P
signals have evolved to leave those of the dinuclear complex
[{(PPh2Me)2Rh}2(µ-Cl)2], exclusively. Then this signal pro-
gressively vanishes to cleanly leave a doublet (31P NMR:
The resulting complex has also been shown to react with
δ ϭ 17.7, JP-Rh ϭ 148 Hz) attributed to the methylene- CD2Cl2 at 298 K to yield the corresponding chloro-
Eur. J. Inorg. Chem. 1998, 349Ϫ353
351

J. J. Brunet, X. Couillens, J.-C. Daran, O. Diallo, C. Lepetit, D. Neibecker
FULL PAPER
difference Fouriers maps, but they were introduced in calculation in
idealized positions [d(CH) ϭ 0.96 A] and their atomic coordinates
methyl complex [RhCl2(CD2Cl)({2,6-C(Me)ϭN-p-anisyl}2
˚
C5H3N)][5]
.
were recalculated after each cycle. They were given isotropic ther-
mal parameters 20% higher than those of the carbon to which they
are attached. Only the H atoms attached to the C methylene carbon
were refined with an isotropic thermal parameter. Least-squares
refinements were carried out by minimizing the function Σw(͉Fo͉ Ϫ
͉Fc͉)2, where Fo and Fc are the observed and calculated structure
factors. The weighting scheme used in the last refinement cycles
This research was supported by the Centre National de la Recher-
´
´ ´
che Scientifique and by the Region Midi-Pyrenees (France) which
are gratefully acknowledged. The authors also wish to thank B.
Donnadieu for collection of the X-ray data and F. Lacassin for
NMR experiments.
n
was w ϭ wЈ{1 Ϫ [∆F/6σ(Fo)]2}2 where wЈ ϭ 1/Σ1 ArTr(x) with 3
Experimental Section
coefficients Ar for the Chebyshev polynomial ArTr(x) where x was
Fc/Fc(max)[21]. Models reached convergence with Rϭ Σ(ʈFo͉ Ϫ ͉Fcʈ)/
Σ(͉Fo͉) and Rwϭ [Σw(͉Fo͉ Ϫ ͉Fc͉)2/Σw(Fo)2]1/2, having values listed
in Table 1. Criteria for a satisfactory complete analysis were the
ratios of rms shift to standard deviation less than 0.1 and no sig-
nificant features in final difference maps. Details of data collection
and refinement are given in Table 2.
General: All reactions were performed under argon using stand-
ard Schlenk techniques. [{(C8H14)2Rh}2(µ-Cl)2] 1 was prepared ac-
cording to the literature procedure[19]. Ϫ C, H analyses: Perkin-
Elmer 2400 apparatus. Ϫ NMR: Bruker AC 200 (monitoring of
reactions), AMX 400 (isolated complexes) (400.1, 162.0, 100.6, and
12.6 MHz, for 1H, 31P, 13C, and 103Rh, respectively). For 1H NMR,
CD2Cl2 as solvent, δH ϭ 5.33; for 31P NMR, H3PO4 as external
standard; for 13C NMR, CD2Cl2 as solvent, δC ϭ 52.9; for 103Rh
NMR, CD2Cl2 as solvent, rhodium metal as external standard.
Table 2. Crystal and collection data for compound 3·2 CH2Cl2
[{(PEt3)2RhCl}2(µ-Cl)2(µ-CH2)] (3): Triethylphosphane (0.37
ml, 2.51 mmol) was added to a solution of [{(C8H14)2Rh}2(µ-Cl)2]
(0.450 g, 0.63 mmol) in CH2Cl2 (20 ml). After 2 h stirring at room
temp., the solvent was evaporated under reduced pressure. The re-
sulting powder was washed with THF (20 ml) and dried in vacuo
Crystal Parameters
formula
C25H62Cl4P4Rh2 ·2 CH2Cl2
1004.15
box (yellow)
0.50 ϫ 0.40 ϫ 0.30
orthorhombic
Pnan
fw [g]
shape (color)
size [mm]
crystal system
space group
1
(0.401 g, 77%). Ϫ H NMR: δ ϭ 1.25 (m, 36 H, CH3CH2P), 2.00
˚
(m, 12 H, CH3CH2P), 2.15 (m, 12 H, CH3CH2P), 3.69 (bs, 2 H,
a [A]
13.1328(9)
17.479(2)
18.734(2)
4300.5(6)
4
˚
CH2).Ϫ31P{1H} NMR:
δ ϭ 34.4, d, JP-Rh ϭ 147 Hz. Ϫ
b [A]
˚
13C{1H,31P} NMR: δ ϭ 8.12 (s, CH3CH2), 18.20 (s, CH3CH2),
38.88 (t, JC-Rh ϭ 22 Hz, CH2). Ϫ 103Rh{1H} NMR: δ ϭ 1696 (t).
Ϫ C25H62Cl4P4Rh2 (834.3): calcd. C 35.99, H 7.49; found C 35.32,
H 7.43.
c [A]
V [A3]
˚
Z
F(000)
2052
ρ (calcd) [g·cmϪ3
]
]
1.551
µ (Mo-Kα) [cmϪ1
14.238
[{(PPh2Me)2RhCl}2(µ-Cl)2(µ-CH2)] (4): The same procedure
as above was followed using PPh2Me (41 µl; 0.217 mmol) and
[{(C8H14)2Rh}2(µ-Cl)2] (0.039 g; 0.054 mmol) in CH2Cl2 (0.7 ml)
Data collection
Diffractometer
monochromator
radiation
IPDS Stoe
graphite
1
Mo-Kα (λ ϭ 0.71073)
and 6 h stirring at room temp. (0.045 g; 71%). Ϫ H NMR: δ ϭ
detector distance [mm]
Scan mode
80
1.53 (A3XMXЈAЈ3 spin system with a broad line symmetrically
flanked by two sharp lines separated by 10.8 Hz, 12 H, CH3P), 4.25
(bs, 2 H, CH2), 6.9Ϫ7.6 (m, 40 H, aromatic H). Ϫ 31P{1H} NMR:
δ ϭ 20.31, d, JP-Rh ϭ 148.7 Hz. Ϫ 13C{31P} NMR: δ ϭ 14.90 (q,
JC-H ϭ 133 Hz, CH3P), 56.78 (tt, JC-H ϭ 143 Hz, JC-Rh ϭ 18 Hz,
CH2), 127Ϫ133 (aromatic C). Ϫ 103Rh{1H} NMR: δ ϭ 1847 (t).
Ϫ C53H54Cl4P4Rh2 (1162.5): calcd. C 54.76, H 4.68; found C 54.25,
H 4.49.
φ range [°]
φ incr. [°]
0 < φ < 149.5
1.3
2
exposure time [min]
2θ range [°]
4.9 < 2θ < 47.9
19755
no. of rflns collected
no. of unique rflns
merging factor R(int)
reflections used [I>2σ(I)]
3308
0.0353
2737
Refinement
R
X-ray Crystallographic Analysis of [{(PEt3)2RhCl}2(µ-Cl)2(µ-
CH2] (3): X-ray quality crystals were obtained by slow diffusion
of THF vapors into a concentrated CH2Cl2 solution of the com-
plex. The data were collected on a Stoe Imaging Plate Diffraction
System (IPDS) equipped with an Oxford Cryosystems cooler de-
vice. The crystal-to-detector distance was 80 mm. 115 exposures (2
min per exposure) were obtained with 0 < φ < 149.5° and with the
crystals rotated through 2° in φ. Coverage of the unique set was
over 99% complete to at least 24°. Crystal decay was monitored by
measuring 200 reflexions per image. The Final unit cell parameters
were obtained by the least-squares refinement of 5000 reflections.
Only statistical fluctuations were observed in the intensity monitors
over the course of the data collection.
0.0186
Rw
0.0213
Weighting scheme
Coefficient .Ar
(∆/s)max
∆rmax
∆rmin
GOF
Chebyshev
1.39, Ϫ0.222, 1.22
0.009
0.39
Ϫ0.35
1.102
The calculations were carried out with the CRYSTALS package
programs[22] running on a PC. The drawing of the molecule was
realized with the help of CAMERON[23]. The atomic scattering
factors were taken from International Tables for X-ray Crystal-
lography[24]. Crystallographic data (excluding structure factors) for
the structure reported in this paper have been deposited at the
The structure was solved by direct methods (SIR92)[20] and re-
fined by least-squares procedures on Fo. One of the methyl of an Cambridge Crystallographic Data Centre as supplementary publi-
ethyl group attached to P(1) is distributed statistically over two po- cation no. CCDC-100808. Copies of the data can be obtained
sitions. The coordinates for these disordered carbon atoms were
free of charge on application to CCDC, 12 Union Road, Cam-
refined applying geometrical restraints to maintain reasonable bridge CB2 1EZ, UK [Fax: int. code ϩ 44(1223)336-033; E-mail:
CϪC distances and CϪCϪC bond angles. H atoms were located on
deposit@ccdc.cam.ac.uk].
352
Eur. J. Inorg. Chem. 1998, 349Ϫ353

Activation of Dichloromethane by (Phosphane)nrhodium(I) Complexes
FULL PAPER
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