Oxidative addition of chlorinated solvents (e.g. CH2Cl2 and CHCl3) with rhodium(I) complexes; crystal structure of mer-[Rh(py)3(CH2Cl)Cl2]

Article abstract of DOI:10.1039/a809652j

Common chlorinated solvents (e.g. CH₂Cl₂ and CHCl₃) readily reacted with [Rh₂(C₈H₁₄)₄(μ-Cl)₂] (C₈H₁₄ = cyclooctene), in the presence of a monodentate, nitrogen donor ligand (L = py or 4-Bu^tpy), to give the oxidative addition product [RhL₃RCl₂] (R = CH₂Cl, CHCl₂ or CH₂Ph) which for R = CH₂Cl and CH₂Ph has been shown by X-ray analysis to adopt the mer configuration. NMR Spectroscopic measurements (¹³C and ¹⁵N) in solution were consistent with this configuration, although these NMR data cannot unambiguously distinguish between the mer and fac isomers.

Full text of DOI:10.1039/a809652j

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Oxidative addition of chlorinated solvents (e.g. CH2Cl2 and
CHCl3) with rhodium(I) complexes; crystal structure of
mer-[Rh(py)3(CH2Cl)Cl2]
Kerry J. Bradd, Brian T. Heaton,* Chacko Jacob, Jeyagowry T. Sampanthar and
Alexander Steiner
Chemistry Department, University of Liverpool, Liverpool, UK L69 7ZD.
E-mail: amf@liverpool.ac.uk
Received 10th December 1998, Accepted 9th February 1999
Common chlorinated solvents (e.g. CH2Cl2 and CHCl3) readily reacted with [Rh2(C8H14)4(µ-Cl)2] (C8H14
=
cyclooctene), in the presence of a monodentate, nitrogen donor ligand (L = py or 4-Butpy), to give the oxidative
addition product [RhL3RCl2] (R = CH2Cl, CHCl2 or CH2Ph) which for R = CH2Cl and CH2Ph has been shown
by X-ray analysis to adopt the mer configuration. NMR Spectroscopic measurements (13C and 15N) in solution
were consistent with this configuration, although these NMR data cannot unambiguously distinguish between
the mer and fac isomers.
The oxidative addition reaction of aliphatic compounds con-
taining a C–X bond (X = Cl, Br or I) by low-valent transition
metal complexes is of interest because many catalytic processes
involve this reaction as the key step. There are many examples
of oxidative addition reactions involving molecules of the type
CH3X (X = I or Br) and numerous reports with CH2I2, CH2Br2
and CH2ICl. Early reports of analogous reactions with the
common solvents CH2Cl2 and CHCl3 suggested that thermal1
or photochemical2–4 initiation was necessary. However, several
reactions involving the reaction of CH2Cl2 with transition
metal complexes under mild conditions have been documented
over recent years and the group derived from CH2Cl2 in the
resulting product can be either (i) CH2Cl, (ii) µ-CH2 or (iii) a
metal carbene species.
Examples of simple oxidative addition of CH2Cl2 to form
chloromethyl complexes have been reported for electron-rich
transition metal complexes containing mono-5–7 or poly-
dentate phosphine ligands,8,9 bi- or tri-dentate nitrogen
ligands,10–12 sulfur macrocycles13 and phosphorus–nitrogen
hybrid ligands.14–16
[Rh2(C8H14)4(µ-Cl)2]
6L
L = py, 4-Butpy
L
L
Rh Cl
L
CH2Cl2
L
PhCH2Cl
CHCl3
L
Cl
L
CH2Cl
Cl
CH2Ph
Cl
L
Rh
L
Rh
Cl
L
CHCl2
Cl
Rh
Cl
L
L
L
1
3
a L = 4-Butpy
a L = 4-Butpy
b L = py
2
a L = 4-Butpy
b L = py
Double oxidative addition reactions to two metal centres
have been observed with the highly basic rhodium complexes
[Rh2(dppe)2(µ-Cl)2],17 [Rh2(PR3)4(µ-Cl)2]18 (PR3 = PEt3 or
PPh2Me) and [Rh2(CNBut)4 (µ-pz)2] (pz = pyrazolate).19
The third type of oxidative addition reaction of CH2Cl2 to
form a metal–carbene species has been reported to occur with
the ruthenium complex [RuH2(H2)2L2] [L = P(C6H11)3] to form
[RuCl2(CH2)L2].20 This is the only known example of this type
of reaction and involves the double oxidative addition of
CH2Cl2 to a single metal centre.
Scheme 1
[RhL3Cl], by carrying out spectroscopic measurements at low
temperature in the absence of RCl were unsuccessful and there
is no NMR spectroscopic evidence for other complexes of RhI
or RhIII containing co-ordinated cyclooctene. However, NMR
measurements (13C and 15N) show that oxidative addition of
RCl occurs to give [RhL3RCl2] but it proved impossible to
distinguish between isomers A and B from spectroscopic
measurements. However, in the case of [Rh(py)3(CH2Cl)Cl2]
1b† it was possible to isolate crystals for X-ray diffraction
which establishes the geometry shown in Scheme 1.
Some of the above work has recently been reviewed.21
In this paper we report the facile oxidative addition of
CH2Cl2, CHCl3 and PhCH2Cl to the rhodium() complex
[Rh2(C8H14)4(µ-Cl)2] in the presence of monodentate nitrogen
ligands (e.g. py, 4-Butpy) to form the rhodium() product
[RhL3RCl2] (L = py or 4-Butpy; R = CH2Cl, CHCl2 or CH2Ph)
(see Scheme 1). This is the first example of this type of reaction
involving complexes containing only monodentate nitrogen-
donor ligands.
L
L
L
Cl
R
L
L
Cl
R
Rh
Rh
Cl
L
Cl
A
B
† Crystals of [Rh(4-Butpy)3(CH2Ph)Cl2] 3a have also been isolated but
refinement of the X-ray data only resulted in a value of R = 0.135.
Nevertheless, the refinement again indicated a mer arrangement of
pyridine ligands.
Results and discussion
The reactions shown in Scheme 1 occur readily at room tem-
perature but attempts to identify the presumed intermediate,
J. Chem. Soc., Dalton Trans., 1999, 1109–1112
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Table 1 Selected bond lengths (Å) and angles (Њ) for complex 1b
Rh–C(1)
Rh–N(1)
Rh–N(2)
Rh–N(3)
Rh–Cl(2)
Rh–Cl(3)
C(1)–Cl(1)
2.045(10)
2.083(9)
2.041(9)
2.210(9)
2.340(3)
2.345(3)
1.773(12)
Rh–C(1)–Cl(3)
C(1)–Rh–N(1)
C(1)–Rh–N(3)
C(1)–Rh–N(2)
C(1)–Rh–Cl(2)
C(1)–Rh–Cl(3)
118.1(6)
88.5(4)
177.7(4)
91.2(4)
89.0(3)
92.8(3)
Fig. 2 The NMR spectra of mer-[Rh(4-Butpy)3(CH2Cl)Cl2] 1a in
D8-THF at Ϫ30 ЊC, (a) 13C-{1H}, (b) 13C and (c) 15N-{1H} INEPTRD.
Fig. 1 Crystal structure of mer-[Rh(py)3(CH2Cl)Cl2] 1b.
INEPT measurements but the 15N resonance for 1a at δ Ϫ114.9
X-Ray measurements
1
[Fig. 2(c)] is both less intense and has a lower value of J(Rh–
1
N) (7.2 Hz) than the other resonance [δ(N) Ϫ162.0; J(Rh–N)
The crystal structure of mer-[Rh(py)3(CH2Cl)Cl2] 1b has been
determined (see Fig. 1) and found to adopt an octahedral
geometry with the py ligands arranged in a mer environment.
Selected bond lengths and angles for 1b are given in Table 1.
Comparison of d(Rh–CH2Cl) in complex 1b with other
rhodium() chloromethyl complexes show that the value of
2.045(10) Å for 1b is similar to that observed for the chloro-
methyl complex [RhCl(CH2Cl)(edmp)2]ϩ [2.050(7) Å; edmp =
(2-aminoethyl)dimethylphosphine]14 and should be compared
with the longest value which was found for [RhCl(CH2Cl)-
(dmpe)2]ClؒCH2Cl2 [2.161(2) Å].5 The different Rh–N bond
lengths within 1b reflect the influence of the trans ligand. Thus,
d[Rh–N(1)] and d[Rh–N(2)] [2.083(9) and 2.041(9) Å respect-
ively] are significantly shorter than d[Rh–N(3)] [2.210(9) Å],
as a result of the strong trans influence of the CH2Cl group.
The values of d[Rh–N(1)] and d[Rh–N(2)] in 1b are also similar
to the Rh–N distances found in mer-[Rh(py)3Cl3]22 which
are shorter than those observed in other mer-[M(py)3Cl3]
analogues. For [M(py)3Cl3] (M = Ti,23 Fe,24 Os25 or Rh22) there
is little variation in the values of d(M–Cl). The Rh–C–Cl bond
angle [118.1(6)Њ] for 1b falls within the range observed for other
rhodium() chloromethyl complexes [115.3(4) and 119.9(7)Њ].
17.7 Hz] and is consistent with 4-Butpy being trans to the
CH2Cl group. However all the above NMR data, together with
the observed 2:1 relative intensity of all the pyridine 13C reson-
ances (see Experimental section), do not readily allow the two
possible isomers, A and B, to be distinguished, see above.
Furthermore, there is little variation in either the values of δ(N)
and 1J(Rh–N) for pyridine trans to pyridine or trans to chloride
as shown by measurements on fac- and mer-[RhL3Cl3] (L = py
or 4-Butpy) (see Table 3). As a result, NMR measurements can-
not distinguish A from B but, since only one isomer is formed,
we feel that the structures adopted by 1a in solution and the
solid state are the same and the other rhodium() complexes
shown in Scheme 1 probably adopt the same geometry.
The NMR data for all the rhodium() complexes shown in
Scheme 1 are summarised in Table 2 and in the Experimental
section and are entirely consistent with the proposed formu-
lations. It should be noted that, because of the high trans
effect of the R group, the 15N resonance due to L trans to R
disappears at room temperature probably because of rapid
interexchange with the solvent (THF), whereas the 15N reson-
ance due to the trans-pyridines remains unchanged. Addition
of >1 mol of CH2Cl2 or CHCl3 per Rh atom (L = py) results in
the exclusive formation of mer-[Rh(py)3Cl3]. It should be noted
that 15N NMR measurements on the product resulting from
the preparation of [RhL3Cl3] (L = 4-Butpy) always show the
presence of fac- and mer-[RhL3Cl3] but refluxing in toluene
(111 ЊC) results in the exclusive isomerisation of the fac to the
more thermodynamically stable mer isomer.
NMR measurements
The 13C NMR measurements on the rhodium() complexes
shown in Scheme 1 clearly establish that the predominant
reaction involves oxidative addition of all these halogenated
solvents, although it should be noted that a minor amount of
mer-[RhL3Cl3] is formed when L = Butpy on reaction with the
stoichometric amount of CHCl3; this does not occur with either
CH2Cl2 or PhCH2Cl. Thus, for [Rh(4-Butpy)3(CH2Cl)Cl2] 1a
both the 13C-{1H} [Fig. 2(a)] and 13C spectra [Fig. 2(b)] show
Conclusion
This study has shown that facile oxidative addition of common
solvents (e.g. CH2Cl2, CHCl3 and PhCH2Cl) occurs to give
stable rhodium() adducts. The structure of mer-[Rh(py)3-
(CH2Cl)Cl2] has been determined by X-ray crystallography and
NMR measurements are consistent with this configuration in
solution. A possible mechanism for this reaction could involve
the initial formation of [RhL3Cl] but attempts to spectro-
1
the presence of the RhCH2Cl group [δ(C) 45.0, J(C–H) 152.9
Hz] and the different 13C resonances associated with the pyrid-
ines (see Experimental section) all occur in the expected region
with a relative intensity of 2:1. 15N INEPT measurements on
1a also show the presence of two resonances [Fig. 2(c)]. How-
ever, it is impossible to obtain accurate relative intensities from
1110
J. Chem. Soc., Dalton Trans., 1999, 1109–1112

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Table 2 The NMR data for [RhL3RCl2] (L = py or 4-Butpy; R = CH2Cl, CHCl2 or CH2Ph) at 243 K (see Scheme 1)
Complex
δ(C)a
1J(Rh–C)a/Hz
δ(Na)b
δ(Nb)c
1J(Rh–Na)b/Hz
1J(Rh–Nb)c/Hz
1a mer-[Rh(4-Butpy)3(CH2Cl)Cl2]
1b mer-[Rh(py)3(CH2Cl)Cl2]
45.0
45.0
73.6
71.7
25.0
25.5
26.0
34.0
32.7
19.0
Ϫ162.0
Ϫ157.4
Ϫ163.5
Ϫ160.7
Ϫ161.4
Ϫ114.9
Ϫ110.9
Ϫ124.7
Ϫ119.8
Ϫ109.5
17.7
17.7
17.9
18.0
17.9
7.2
7.7
8.7
8.5
7.2
2a mer-[Rh(4-Butpy)3(CHCl2)Cl2]
2b mer-[Rh(py)3(CHCl2)Cl2]
3a mer-[Rh(4-Butpy)3(CH2Ph)Cl2]
a Data for the RhCRЈ group (RЈ = H2Cl, HCl2 or H2Ph). b Na is trans to N-donor, L (L = py or 4-Butpy). c Nb is trans to R (R = CH2Cl, CHCl2 or
CH2Ph).
Table 3 15N NMR data for [RhL3Cl3] (L = py or 4-Butpy)
Complex
δ(Na)a
Ϫ171.8
Ϫ158.7
δ(Nb)b
1J(Rh–Na)a/ Hz
1J(Rh–Nb)b/ Hz
mer-[Rh(4-Butpy)3Cl3]
fac-[Rh(4-Butpy)3Cl3]
mer-[Rh(py)3Cl3]
Ϫ163.7
Ϫ168.3
Ϫ148.5
16.6
17.7
17.3
16.2
19.5
a Na is trans to the donor, L (L = py or 4-Butpy). b Nb is trans to Cl.
scopically identify this complex failed. This highly nucleophilic
intermediate activates common solvents at room temperature
towards oxidative addition to give the mer-rhodium() product
but with an excess of RCl [RhL3Cl3] is formed.
[Rh(4-Butpy)3(CHCl2)Cl2] 2a. Chloroform (78.1 µl, 0.98
mmol) and 4-Butpy (432.5 µl, 2.94 mmol) were added to a sus-
pension of [Rh2(C8H14)4(µ-Cl)2] (350 mg, 0.49 mmol) in THF
(1 cm3) to give a very deep red solution. The solution was con-
centrated to give a yellow-orange solid. This solid was then
dissolved in D8-THF (2 cm3) to give a red solution and the
species present were characterised by NMR spectroscopy.
13C-{1H} NMR (D8-THF) with relative intensities of the
4-Butpy ligands in parentheses: δ(C) 164.5 (1) and 163.8 (2)
(p-C), 157.0 (2) and 154.3 (1) (o-C), 123.7 (1) and 123.0 (2)
(m-C), 36.8 (1) and 36.7 (2) (ipso-C), 31.8 (1) and 31.7 (2) (CH3).
Experimental
The NMR measurements were carried out on a Bruker
AMX200 or AMX400 spectrometer using commercial probes.
15N-{1H} NMR spectra were obtained on the AMX400 spec-
trometer using the INEPTRD (insensitive nuclei enhanced
by polarisation transfer refocussed and decoupled) pulse
sequence.26 All spectra were recorded at Ϫ30 ЊC unless other-
wise stated. Chemical shifts are quoted relative to internal
SiMe4 (13C) and external MeNO2 (15N). All reactions were
carried out under a nitrogen atmosphere using standard
Schlenk-line techniques. Solvents were distilled under N2 after
reflux over CaH2 (CH2Cl2, CHCl3, PhCH2Cl) or sodium–
benzophenone (THF). Deuteriated solvents were dried over
molecular sieves and stored under nitrogen. Pyridine and 4-tert-
butylpyridine were used as received from Aldrich and [Rh2-
(C8H14)4(µ-Cl)2] was prepared using the literature method.27
[Rh(py)3(CHCl2)Cl2] 2b. Pyridine (236.7 µl, 2.93 mmol) was
added to a suspension of [Rh2(C8H14)4(µ-Cl)2] (350 mg, 0.49
mmol) in CHCl3–CD2Cl2 (3:1; 2 cm3) to give a very deep red
solution. The species present in solution were characterised by
NMR spectrosopy. 13C NMR (CHCl3–CD2Cl2) with relative
intensities of the py ligands in parentheses: δ(C) 156.3 (2) and
152.7 (1) (o-C), 139.0 (1) and 138.8 (2) (p-C), 125.6 (1) and
125.0 (2) (m-C).
[Rh(4-Butpy)3(CH2Ph)Cl2] 3a. Benzyl chloride (112.3 µl, 0.98
mmol) and 4-Butpy (432.5 µl, 2.94 mmol) were added to a sus-
pension of [Rh2(C8H14)4(µ-Cl)2] (350 mg, 0.49 mmol) in THF
(1 cm3) to give a red solution. The solution was concentrated to
give a yellow-orange solid (538 mg, 82%). This solid dissolved
in D8-THF (2 cm3) to give a red solution and the species
formed was characterised by NMR spectroscopy (Found: C,
60.7; H, 7.05; N, 6.0. C34H46Cl2N3Rh requires C, 60.9; H, 6.9;
N, 6.3%). 13C-{1H} NMR (D8-THF) with relative intensities of
the 4-Butpy ligands in parentheses: δ(C) 163.1 (1) and 162.4 (2)
(p-C), 156.8 (2) and 153.7 (1) (o-C), 154.4 (ipso-C, PhCH2),
131.8 (o-C, PhCH2), 129.5 (m-C, PhCH2), 124.8 (p-C, PhCH2),
123.8 (1) and 122.6 (2) (m-C), 37.0 (1) and 36.8 (2) (ipso-C), 32.2
(1) and 32.1 (2) (CH3).
Preparation of the complexes
[Rh(4-Butpy)3(CH2Cl)Cl2] 1a. Dichloromethane (62.5 µl, 0.98
mmol) and 4-Butpy (432.5 µl, 2.94 mmol) were added to a sus-
pension of [Rh2(C8H14)4(µ-Cl)2] (350 mg, 0.49 mmol) in THF
(1 cm3) to give a red solution. The solution was concentrated to
give a yellow-orange solid (475 mg, 77%). This solid dissolved
in D8-THF (2 cm3) to give a red solution and the species present
was characterised by NMR spectroscopy (Found: C, 53.05; H,
6.6; N, 6.1. C28H41Cl3N3Rh requires C, 53.5; H, 6.6; N, 6.7%).
13C-{1H} NMR (D8-THF) with relative intensities of the
4-Butpy ligands in parentheses: δ(C) 163.6 (1) and 163.3 (2)
(p-C), 156.7 (2) and 153.7 (1) (o-C), 123.7 (1) and 123.0 (2)
(m-C), 36.8 (2) and 36.7 (1) (ipso-C), 31.8 (1) and 31.7 (2) (CH3).
Crystallography
[Rh(py)3(CH2Cl)Cl2] 1b. Pyridine (236.7 µl, 2.93 mmol) was
added to a suspension of [Rh2(C8H14)4(µ-Cl)2] (350 mg, 0.49
mmol) in CH2Cl2–CD2Cl2 (3:1; 2 cm3) to give a red solution of
complex 1b which was characterised by NMR spectroscopy.
The formation of 1b was immediate as evidenced by measuring
the 13C NMR spectrum at 243 K immediately after addition
of reactants at room temperature. Yellow-orange crystals were
obtained by layering this solution with light petroleum (bp 40–
60 ЊC). 13C NMR (CH2Cl2–CD2Cl2) with relative intensities of
the py ligands in parentheses: δ(C) 155.4 (2) and 152.2 (1) (o-C),
138.7 (1) and 138.2 (2) (p-C), 125.5 (1) and 124.7 (2) (m-C).
Crystal data, data collection and processing details are given in
Table 4. All data were recorded on a Rigaku AFC6S diffract-
ometer at Ϫ120 ЊC using graphite-monochromatised Mo-Kα
radiation, λ = 0.710 73 Å, 2θ–ω scans, 2θmax = 50Њ. An empirical
absorption correction using ψ scans was applied by the TEX-
SAN system.
Structure analysis. The structure was refined by full-matrix
least-square procedures on F 2.28 All non-hydrogen atoms were
treated as anisotropic and hydrogen atoms placed in geometric
ideal positions and assigned isotropic thermal parameters 20%
J. Chem. Soc., Dalton Trans., 1999, 1109–1112
1111

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Table 4 Crystal structure analysis, crystal data and experimental
details for complex 1b
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Formula
M
Appearance
Space group
Crystal system
a/Å
b/Å
c/Å
C16H17Cl3N3Rh
460.59
Yellow prism
P21/c
Monoclinic
13.103(6)
8.238(4)
16.808(5)
100.21(4)
1785.6(13)
4
1.713
920
14.06
0.25 × 0.25 × 0.20
3194
β/Њ
U/Å3
Z
Dc/g cmϪ3
F(000)
µ(Mo-Kα)/cmϪ1
Crystal dimensions/mm
Reflections measured
Unique reflections
Tmax, Tmin
3051
1.00, 0.872
0.068
0.190
1.38, Ϫ1.35
R [I > 2σ(I)]
wR2 (all data)
Final difference electron density
(maximum, minimum)/e ÅϪ3
17 G. E. Ball, W. R. Cullen, M. D. Fryzuk, B. R. James and S. J. Rettig,
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235.
greater than the B equivalent value of the atom to which they
were bonded.
CCDC reference number 186/1349.
See http://www.rsc.org/suppdata/dt/1999/1109/ for crystallo-
graphic files in .cif format.
22 K. R. Acharya, S. S. Tavale and T. N. Guru Row, Acta Crystallogr.,
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Acknowledgements
We thank EPSRC for a studentship (to K. J. B.) and the
Leverhulme Trust for the award of a Research Fellowship (to
B. T. H.).
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J. Chem. Soc., Dalton Trans., 1999, 1109–1112