A new structural type of dinuclear rhodium(II) compounds: Synthesis by serendipity and design; catalytic behaviour in carbene transfer reactions

Article abstract of DOI:10.1039/a903811f

The compound [Rh₂(μ-O₂CCH₃)₃(O ₂CCH₃)[η²-(o-CH₃OC ₆H₄)P(C₆H₅)₂] 1, having one phosphine acting as a chelating, equatorial (P)-axial(O), ligand has been structurally characterized. A new family of structurally related dirhodium(II) compounds of general formula [Rh₂(μ-O₂CR)₂(X)₂{η ²-(o-YC₆H₄)P(C₆H₅) ₂}₂] (R = CH₃, X = CH₃CO₂, Y = CH₃O 2; R = CF₃, X = CF₃CO₂, Y = CH₃O 3; R = CH₃, X = Cl 4 or R = CH₃, X = Cl, Y = CH₃O 5) has been synthesized. All these compounds are structurally related; they have two orthofunctionalized phosphines acting as equatorial (P) and axial (Cl, O) donor ligands and two bridging carboxylates. The two remaining equatorial sites around the rhodium atoms are occupied by two monodentate carboxylates (2, 3) or two chlorine atoms (4, 5). Compounds 4 and 5 have been structurally characterized by X-ray methods. Compound 4, initially obtained in low yield by serendipity, was also prepared in moderate yield from rhodium acetate and P(o-ClC₆H₄)(C₆H₅)₂ in the presence of a stoichiometric amount of Me₃SiCl. Compounds 2 and 3 were prepared by treating the corresponding rhodium tetracarboxylate with two moles of P(o-CH₃OC₆H₄)(C₆H₅) ₂ and 5, obtained by serendipity, was best synthesized from the reaction of 2 and two moles of Me₃SiCl. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a903811f

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A new structural type of dinuclear rhodium(II) compounds:
synthesis by serendipity and design; catalytic behaviour in
carbene transfer reactions†
Francisco Estevan,a Abel García-Bernabé,a Santiago García-Granda,c Pascual Lahuerta,*a
Eduardo Moreno,a Julia Pérez-Prieto,b Mercedes Sanaúa and M. Angeles Ubeda*a
a Department de Química Inorgànica, Facultat de Química, Universitat de Valencia,
Dr. Moliner, 50. 46100-Burjassot-Valencia, Spain
b Departament de Química Orgànica, Facultat de Farmacia, Universitat de Valencia,
Av. Vicent A. Estelles, s/n, 46100 Burjassot-Valencia, Spain
c Departamento de Química Física y Analítica, Universidad de Oviedo, Julian Clavería s/n,
33006 Oviedo, Spain
Received 12th May 1999, Accepted 15th July 1999
The compound [Rh2(µ-O2CCH3)3(O2CCH3)[η2-(o-CH3OC6H4)P(C6H5)2] 1, having one phosphine acting as a
chelating, equatorial (P)–axial(O), ligand has been structurally characterized. A new family of structurally related
dirhodium() compounds of general formula [Rh2(µ-O2CR)2(X)2{η2-(o-YC6H4)P(C6H5)2}2] (R = CH3, X = CH3CO2,
Y = CH3O 2; R = CF3, X = CF3CO2, Y = CH3O 3; R = CH3, X = Cl 4 or R = CH3, X = Cl, Y = CH3O 5) has been
synthesized. All these compounds are structurally related; they have two orthofunctionalized phosphines acting as
equatorial (P) and axial (Cl, O) donor ligands and two bridging carboxylates. The two remaining equatorial sites
around the rhodium atoms are occupied by two monodentate carboxylates (2, 3) or two chlorine atoms (4, 5).
Compounds 4 and 5 have been structurally characterized by X-ray methods. Compound 4, initially obtained in low
yield by serendipity, was also prepared in moderate yield from rhodium acetate and P(o-ClC6H4)(C6H5)2 in the
presence of a stoichiometric amount of Me3SiCl. Compounds 2 and 3 were prepared by treating the corresponding
rhodium tetracarboxylate with two moles of P(o-CH3OC6H4)(C6H5)2 and 5, obtained by serendipity, was best
synthesized from the reaction of 2 and two moles of Me3SiCl.
When orthofunctionalized phosphines were used in this reac-
Introduction
tion different intermediates could be isolated and structurally
characterized.2 In these studies the orthofunctionalized phos-
phines of formula P(o-YC6H4)(C6H5)2, Y = Cl (PCCl) or CH3O
(PCOMe), have been particularly useful, due to their ability to
act as bidentate P,Cl or P, O donors, allowing the isolation of
reaction intermediates of type B and C (Chart 1).3
We describe in this paper the synthesis and characterization
of new rhodium compounds with a new type of structure D.
They contain two orthofunctionalized phosphines, PCCl or
PCOMe, in an equatorial–axial chelating mode and they
have the formula [Rh2(µ-O2CR)2(X)2{η2-(o-YC6H4)P(C6H5)2}2,
(R = CH3, X = CH3CO2, Y = CH3O; R = CF3, X = CF3CO2,
Y = CH3O, R = CH3, X = Y = Cl or R = CH3, X = Cl,
Y = CH3O. The catalytic behaviour of these compounds in
cyclopropanation reactions is also described.
The reaction of rhodium acetate and triphenylphosphine to
form a bis-cyclometallated compound of formula [Rh2(µ-O2-
CCH3)2{µ-(C6H4)P(C6H5)2}2]ؒ2HO2CCH3 (Chart 1, A) was first
reported by Cotton and co-workers1 in 1985. Dinuclear com-
pounds with bridging metallated phosphines were rare at that
time and this reaction represented a synthetic method of gen-
eral application for the preparation of metallated rhodium()
compounds.
Results
Synthesis of dinuclear rhodium(II) compounds, [Rh2(ꢀ-O2CR)2-
(X)2(ꢁ2-PCOMe)2] (R ؍ CH3, X ؍ CH3CO2 2; R ؍ CF3,
X ؍ CF3CO2 3
Earlier work showed that Rh2(O2CCH3)4 and PCOMe react, in
a 1:1 molar ratio, to form the adduct Rh2(O2CCH3)4ؒPCOMe
that, under UV irradiation, readily rearranged to form the
compound [Rh2(µ-O2CCH3)3(η-O2CCH3)(η2-PCOMe)], 1, in
quantitative yield.4 We report here a single crystal X-ray study
that confirms the structure B for this compound (Chart 1). This
was the first time that a compound with this structure was
†Supplementary data available: rotatable 3-D crystal structure diagram
in CHIME format. See http://www.rsc.org/suppdata/dt/1999/3493/
Chart 1
J. Chem. Soc., Dalton Trans., 1999, 3493–3498
This journal is © The Royal Society of Chemistry 1999
3493

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Table 1 31P-{1H} NMR Data.a
Table 2 Selected bond distances (Å) and angles (Њ) for compound 4
Compound
δ(P)b
1JRh-P
2JRh-P
3JP-P
1JRh-Rh
Rh(1)–Rh(2)
Rh(1)–P(33)
Rh(1)–Cl(52)
Rh(1)–Cl(4)
Rh(1)–O(7)
Rh(1)–O(12)
2.5692(14)
2.2474(15)
2.5870(18)
2.3243(18)
2.049(3)
Rh(2)–P(13)
Rh(2)–Cl(32)
Rh(2)–Cl(3)
Rh(2)–O(11)
Rh(2)–O(8)
2.2466(16)
2.5916(15)
2.3154(14)
2.050(3)
1
38.2
32.7
33.0
33.7
29.7
37.6
45.8
46.2
161
165
158
153
158
152
177
181
4
Ϫ5
Ϫ5
Ϫ5
Ϫ5
2
0
0
0
0
Ϫ20
2.112(3)
3
Ϫ21
Ϫ23
Ϫ21
2.102(3)
4
5
Cl(52)–Rh(1)–Rh(2) 164.94(3)
P(33)–Rh(1)–O(7) 92.38(10)
P(33)–Rh(1)–O(12) 169.37(10)
Cl(4)–Rh(1)–O(7) 172.24(10)
Rh(1)–Rh(2)–Cl(32) 165.22(3)
P(13)–Rh(2)–O(11)
P(13)–Rh(2)–O(8)
6
7c
8d
4
91.10(10)
169.33(9)
Cl(3)–Rh(2)–O(11) 173.64(9)
a Chemical shifts in ppm; coupling constants in Hz. b Equatorial phos-
phine. c For metallated phosphine: δ(P) 13.2, JRh-P 153, JRh-P 8 Hz.
1
2
d For metallated phosphine: δ(P) 10.8, 1JRh-P 148, 2JRh-P 8 Hz.
formed by direct reaction of rhodium carboxylate and the
phosphine ligand. A structurally analogous compound with
bipyridine has been prepared by direct reaction of rhodium
carboxylate and bipyridine.5 The synthesis of a similar com-
pound with PCCl was reported2e by a different route: electro-
philic Rh–C bond cleavage in the corresponding mono-
metallated compound.
We also observed, that irradiation of compound 1 in the
presence of an equimolar amount of PCOMe gave a new com-
pound [Rh2(µ-O2CCH3)2(η-O2CCH3)2(η2-PCOMe)2], 2, that has
two chelating PCOMe phosphines and structure D (Chart 1).
The direct photochemical reaction of Rh2(O2CCH3)4 and two
moles of PCOMe was not a convenient route for the prepar-
ation of 2, as other products of type C were also formed. The
characterization of 2 was based on spectroscopic data. The 31
P
Fig.
1
Molecular view of [Rh2(µ-O2CCH3)2(Cl)2{η2-(o-ClC6H4)-
P(C6H5)2}2] 4.
NMR spectrum (Table 1) showed a second order signal cen-
tered at δ 32.7, that corresponds to the AAЈ part of a AAЈXXЈ
system. This high value of the chemical shift is characteristic of
The 31P NMR spectra for compounds 2–5 were very similar,
giving good evidence of all having the same structure D.
We have obtained compounds 4 and 5 in higher yields using
properly designed synthetic methods. It is known9 that ClSiMe3
is an excellent reagent for the substitution of carboxylates by
chloride in rhodium(). Thus, the reaction of rhodium acetate
with ClSiMe3 (2 moles) at 50 ЊC for 30 min followed by addi-
tion of PCCl (2 moles) and further stirring of the mixture for 12
h at room temperature gave 4 in high yield (75%). Heating must
be avoided in the last reaction step to prevent the formation of
cylometallated products.
We also tried the analogous reaction of rhodium acetate with
ClSiMe3 and PCOMe in order to prepare compound 5. This
reaction was slow and only gave the desired compound in
30% yield after 2 h of irradiation. Compound 5 was obtained
in 60% yield from 2 and ClSiMe3 in stoichiometric amounts
at 50 ЊC.
1
phosphines in equatorial co-ordination.2a,3,4b The H and 13C
NMR spectra indicated the presence of two different acetates,
but only one environment for the PCOMe phosphine. No
evidence of metallated carbon was observed in the 13C NMR
spectrum.6 All these spectroscopic data suggested for 2 one
structure of type D, with two chelating phosphines partially
displacing two carboxylates in the rhodium acetate.
The compound PCOMe also reacted with Rh2(O2CCF3)4 to
form [Rh2(O2CCF3)2(η-O2CCF3)2(η2-PCOMe)2], 3, that accord-
ing to the NMR data has the same structure as 2. Photo-
chemical irradiation was not required in this case and the
reaction was completed after stirring for two hours at room
temperature. This higher reactivity of rhodium trifluoroacetate
compared to rhodium acetate was observed in reactions with
other arylphosphines.7,8
Synthesis of dinuclear rhodium(II) compounds, [Rh2(ꢀ-
O2CCH3)2(Cl)2{ꢁ2-(o-YC6H4)P(C6H5)2}2] (Y ؍ Cl 4 or CH3O 5)
Structural results
In order to explore the utility of this synthetic method we tried
the reaction of PCCl and [Rh2(O2CCH3)4(CH3OH)2] (1:1
molar ratio), under thermal or photochemical conditions. The
major products were species resulting from the cyclometallation
of the PCCl phosphine, identified by 31P NMR spectroscopy.
However in the spectrum there was one multiplet signal of
minor intensity, centered at δ 33.7, that could not be structur-
ally assigned. Careful manipulation of the sample allowed the
isolation of small amounts of a crystalline yellow-orange com-
pound, that was characterized by single crystal X-ray methods
as [Rh2(µ-O2CCH3)2(Cl)2(η2-PCCl)2], 4. This compound
The crystal structures for compounds 1, 4 and 5 have been
determined by X-ray procedures. A perspective drawing of
compound 4 is shown in Fig. 1, and important bond distances
and angles are listed in Table 2. The overall structure is based
on that of the rhodium acetate dimer where two cisoid acetate
bridges have been replaced by two phosphines and two chlorine
atoms. Each PCCl phosphine is acting as a chelating ligand, at
one equatorial (P) and one axial (Cl) site of the dirhodium. As
expected, the average equatorial Rh–Cl bond distance (2.319
Å) is considerably shorter than the axial one (2.5893 Å). This
co-ordination mode was observed in other rhodium() com-
pounds with this and other orthofunctionalized phos-
phines.2e,3,4 The Rh–Rh distance, 2.5692(14) Å, is longer than
that of rhodium acetate and reflects the presence of only two
bridging ligands in the dinuclear unit.
showed a second order 31P NMR spectrum (Table 1) that was
1
fitted to the AAЈ part of a AAЈXXЈ system (δ 33.72, JRh-P
=
153, 2JRh-P = Ϫ5, 3JP-P = 0 and 1JRh-Rh = Ϫ23 Hz).
Analogous reaction with PCOMe gave small amounts of a
similar product of formula [Rh2(µ-O2CCH3)2(Cl)2{η2-(o-CH3-
OC6H4)P(C6H5)2}2], 5, also characterized by X-ray crystal-
lography.
A perspective drawing of compound 5 is shown in Fig. 2 and
important bond distances and angles are listed in Table 3. The
overall structure is similar to that described for compound 4,
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Table 3 Selected bond distances (Å) and angles (Њ) for compound 5
Table 4 Selected bond distances (Å) and angles (Њ) for compound 1
Rh(1)–Rh(2)
Rh(1)–Cl(1)
Rh(1)–P(1)
Rh(1)–O(1)
Rh(1)–O(4)
Rh(1)–O(5)
2.5605(11)
2.322(3)
2.234(3)
2.111(7)
2.061(6)
2.342(7)
Rh(2)–Cl(2)
Rh(2)–O(3)
Rh(2)–P(2)
Rh(2)–O(6)
Rh(2)–O(2)
2.318(3)
2.094(7)
2.247(3)
2.298(7)
2.058(7)
Rh(1)–Rh(2)
Rh(1)–O(2)
Rh(1)–O(7)
Rh(1)–O(4)
Rh(1)–O(9)
Rh(1)–O(5)
2.439(3)
Rh(2)–O(1)
Rh(2)–O(6)
Rh(2)–O(3)
Rh(2)–P(1)
Rh(2)–O(111)
2.071(14)
2.089(12)
2.063(12)
2.235(10)
2.353(10)
2.019(11)
2.037(11)
2.058(14)
2.248(12)
2.015(12)
O(5)–Rh(1)–Rh(2)
O(4)–Rh(1)–P(1)
O(4)–Rh(1)–Cl(1)
O(5)–Rh(1)–Cl(1)
170.3(2)
90.6(2)
171.6(2)
86.2(2)
O(6)–Rh(2)–Rh(1)
O(2)–Rh(2)–P(2)
O(2)–Rh(2)–Cl(2)
O(6)–Rh(2)–Cl(2)
165.5(2)
94.5(2)
172.8(2)
90.7(2)
O(5)–Rh(1)–Rh(2)
O(4)–Rh(1)–O(9)
O(5)–Rh(1)–O(7)
O(2)–Rh(1)–O(4)
87.1(4)
91.5(6)
178.0(4)
174.1(5)
P(1)–Rh(2)–Rh(1)
O(6)–Rh(2)–P(1)
O(1)–Rh(2)–P(1)
O(1)–Rh(2)–O(111)
106.47(11)
167.3(3)
89.0(3)
89.3(5)
quality of the crystal was not very good and consequently the
data collected were poor. However the refinement was suf-
ficiently good (R = 10%) unambiguously to establish the relative
situation of the ligands around the dinuclear unit. The overall
structure is based on that of the rhodium acetate dimer where
one acetate group has been partially replaced by one PCOMe
phosphine. The phosphine co-ordinates in a chelating mode
acting as an equatorial (P) and axial(O) ligand. The Rh–Rh
distance is 2.439(3)Å, considerably shorter than in 4 or 5.
Discussion
It is remarkable that in the reaction of Rh2(O2CCF3)4
and PCOMe the intermediate [Rh2(µ-O2CCF3)3(O2CCF3)-
(η2-PCOMe)] 6, structurally analogous to 1, was not observed
and, independently of the Rh:P ratio used, 1:1 or 1:2, 3 was
the only species detectable by 31P NMR spectroscopy in the
reaction mixture. We observed that 6 was formed on treating
[Rh2(O2CCH3)3{(C6H4)P(o-CH3OC6H4)(C6H5)}]4b with CF3-
CO2H; this reaction involves simultaneous exchange of acetates
by trifluoroacetate groups and electrophilic Rh–C bond
cleavage. We confirmed that 6 readily reacts with PCOMe to
form 3.
Fig.
2
Molecular view of [Rh2(µ-O2CCH3)2(Cl)2{η2-(o-OCH3C6-
H4)P(C6H5)2}2] 5.
The fact that compounds 2 and 3 are isolable and do not
readily undergo cyclometallation, might be attributed to the
ability of PCOMe to exhibit intramolecular (P,O) co-ordination
that makes the metallation reaction less favorable. However,
when 2 was heated in toluene solution at 90 ЊC for 24 h only one
of the equatorial phosphines was metallated yielding [Rh2-
(µ-O2CCH3)2(O2CCH3)[(C6H4)(o-CH3OC6H4)P(C6H5)](η2-
PCOMe)] 7 as the only reaction product (Scheme 1). The 31P
NMR spectrum of this compound is consistent with the exist-
ence of one bridging (metallated) and one chelating (non-metal-
lated) phosphine (Table 1). The 1H NMR spectrum also shows
two resonances, δ 3.93 and 4.26, due to the two different meth-
oxy groups of the phosphines.
Compound 3 is also stable in solution at moderate temperat-
ures (< 50 ЊC). The cyclometallation reaction was only com-
pleted after heating at 90 ЊC for 24 h or after stirring in
CF3CO2H for 9 d. The resulting product was formulated as
[Rh2(µ-O2CCF3)2(O2CCF3)[(C6H4)(o-CH3OC6H4)P(C6H5)](η2-
PCOMe)], 8. The spectroscopic data indicate that in solution 8
exists as two species in equilibrium. Their ratio changes with the
amount of CF3CO2H in solution, suggesting that they differ in
Fig. 3 Molecular view of [Rh2(µ-O2CCH3)3(O2CCH3){η2-(o-CH3-
OC6H4)P(C6H5)2}] 1. Atom O(9) corresponds to a water molecule.
as is the Rh–Rh bond distance 2.5605(11) Å. The phosphines
co-ordinate in the same chelating mode observed in 4 for PCCl.
The equatorial Rh–O bond distances (2.1 Å) are also shorter
than the axial ones (2.3 Å).
Ϫ
the mode of co-ordination of the CF3CO2 group, as mono-
There are in the literature some dinuclear rhodium () com-
pounds with chlorine ligands in axial9,10 or bridging9b,11 dis-
position but rhodium() compounds with equatorial chlorides
are rare.10b,c,11 In most cases the chloride ligand arises from
Me3SiCl, HCl or LiCl used in the reaction. It seems very likely
that in the reactions yielding compounds 4 and 5 by serendipity
the chlorines were extracted from the CHCl3 used as reaction
solvent, as in the absence of it, these compounds were not
formed at all.
dentate (equatorial) or chelating (equatorial–axial). Examples
of these two co-ordination modes have been found2,3 for similar
rhodium() species.
In contrast to the ability shown by PCOMe to stabilize
compounds with structure D, all the efforts to prepare bis-
equatorial compounds with PCCl in high yield failed. Appar-
ently, in this case, the axial rhodium–chlorine interaction is
weak and does not prevent cyclometallation of this ligand.
Thus, Rh(O2CCH3)4 (or Rh2(O2CCF3)4) reacted with PCCl, at
room temperature, to give a complex mixture of cyclo-
metallated compounds of type C.
A perspective drawing of compound 1 is shown in Fig. 3 and
important bond distances and angles are listed in Table 4. The
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Scheme 1 X = H, (i) 1 mol of PCOMe; (ii) hν (ref. 4); (iii) 1 mol of PCOMe, hν; (iv) 2 mol of Me3SiCl, 50 ЊC; (v) 2 mol Me3SiCl, 50 ЊC, 2 mol
PCCl, RT; (viii) 90 ЊC, 24 h. X = F, (vi) 2 mol PCOMe; (vii) 2 h, RT; (viii) 90 ЊC, 24 h.
Table 5 Catalytic results from cyclopropanation reactions
Catalysis
Compound 2 completely transformed the α-diazo ketone I
(Scheme 2) upon heating the reaction mixture for 1 h; a 56%
Diazo I
recovered (%)
Yield of
II (%)
Catalyst
t/h
2
3
4
5
1
1
3
3
<2
20
>99
>99
56
28
—
—
Varian-300 and Varian-400 spectrophotometers; chemical
shifts being relative to TMS (1H, 13C), 85% H3PO4 (31P) or
CFCl3(19F).
Scheme 2
yield of the cyclopropanation product II was observed (Table
5). In the case of 3 20% of diazo compound was recovered
unchanged under these conditions and ketone II was only
obtained in 28% yield. However, 4 and 5 did not react after
heating for 3 h. These results indicate that at high temperature
there is cleavage of the axial Rh–O bonds in 2 and 3, allowing
the diazo compound to reach the catalytic center. The order
of reactivity observed for compounds 2 and 3 is opposite to
the general observation (compounds with acetate groups are
usually less active than the analogues with trifluoroacetates).
This observation suggests that the total substitution of acetates
by more electron withdrawing groups such as trifluoroacetates
strengthens the axial Rh–OCH3 bond in 3, reducing the activity
of this catalyst. Exchanging the monodentate acetates by
chlorides, apparently has even a more pronounced effect and
makes the products 4 and 5 even less reactive.
Synthesis of compounds
[Rh2(ꢀ-O2CCH3)2(O2CCH3)2(ꢁ2PCOMe)2] 2. Compound 14
(100 mg, 0.14 mmol) was dissolved in 100 ml of CHCl3 and 40
mg (0.14 mmol) of PCOMe were added. The solution was
stirred for 30 min. After irradiation for 1 h with an Hg-vapour
lamp (OSRAM-125) the solution became green-yellow. The
solvent was removed under vacuum, the residue extracted with
5 mL of 1:1 CH2Cl2–hexane and the extract transferred to a
column (2 × 30 cm, silica gel, hexane). Elution with CH2Cl2–
hexane–acetone (10:10:2) separated a minor green band that
was discarded. Further elution with hexane–acetone (1:1) gave
a green-yellow band. The solution was evaporated to dryness
and the residue dissolved in 3 mL of CH2Cl2; slow addition
of hexane gave 106 mg (76% yield ) of compound 2. NMR:
1
2
31P-{1H}, AAЈXXЈ system, δ 32.65, JRh-P = 165, JRh-P = Ϫ5,
3JP-P = 0 and 1JRh-Rh = Ϫ20 Hz; 1H, δ 1.02 (s, CH3, 6 H), 1.28 (s,
CH3, 6 H), 4.27 (s, CH3, 6 H) and 6.5–7.5 (aromatics, m, 28 H);
13C, δ 22.66 (s, CH3), 23.06 (s, CH3), 57.81 (s, OCH3), 112.39
(s, aromatics), 122.02 (m, aromatics), 127–135 (m, aromatics),
163.96 (s, aromatic, C bonded to OCH3) and 180.16 (s, OCO).
Found: C, 52.30; H, 4.70. C46H46O10P2Rh2ؒH2O requires C,
52.89; H, 4.63%.
Experimental
General comments
Compounds Rh2(O2CCF3)4,3a,12 [Rh2(µ-O2CCH3)3(O2CCH3)-
(η2-PCOMe)]4 [Rh2(O2CCH3)3[(C6H4)P(o-CH3OC6H4)(C6H5)]4
and PCCl13 were prepared according to literature methods.
Comercially available [Rh(O2CCH3)4(CH3OH)2] (Pressure
Chemical Co.), PCOMe (Strem Chemicals), CF3CO2H
(Fluorochem) and CH3CO2H were used as purchased. All
solvents were of analytical grade. Chloroform and toluene were
dried and degassed before use; acetic acid was only degassed.
The NMR spectra were recorded in CDCl3 on Bruker AC-200,
[Rh2(ꢀ-O2CCF3)2(O2CCF3)2(ꢁ2-PCOMe)2] 3. (a) A mixture
of 100 mg (0.14 mmol) of Rh2(O2CCF3)4 and 89 mg (0.30
mmol) of PCOMe in CHCl3 was stirred for two hours. The
resulting green-yellow solution was evaporated under reduced
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pressure and the crude oil obtained dissolved in 5 ml of 1:1
CH2Cl2–hexane and chromatographed on a column (2 × 30 cm,
silica–gel, hexane). After elution with CH2Cl2–hexane (1:1) a
green-yellow band was collected from which 140 mg (78%
(2 × 30 cm, silica gel, hexane). After elution with CH2Cl2–
hexane–acetone (10:10:1) a minor orange band separated. The
orange solution was evaporated under reduced pressure to give
an orange solid that after crystallization from CH2Cl2–hexane
gave compound 5 (8 mg, yield 2%). NMR: 31P-{1H}, AAЈXXЈ
yield) of compound
3
were obtained. NMR: 31P-{1H},
AAЈXXЈ system, δ 32.98, 1JRh-P = 158, 2JRh-P = Ϫ5, 3JP-P = 0 and
1JRh-Rh = Ϫ21 Hz; 1H, δ 4.23 (s, CH3, 6 H), 6.77 (t, J = 9,
aromatics, 2 H), 6.97 (t, J = 8 Hz, aromatics, 2 H), 7.15–7.36
(m, aromatics, 14 H) and 7.44–7.58 (m, aromatics, 10 H); 13C,
δ 57.98 (s, CH3O, 2C), 112.04 (aromatics, d, J = 6, 2 C), 112.61
(CF3, q, J = 291, 4 C), 119.43 (aromatic C bonded to P, d,
J = 54, 2 C), 122.34 (aromatics, d, J = 8, 2 C), 126.31 (aromatic
C bonded to P, d, J = 59, 2 C), 127.06 (C aromatic bonded to P,
d, J = 57, 2 C), 128.42 (aromatics, d, J = 12, 4 C), 128.66 (aro-
matics, d, J = 11, 4 H), 131.00 (aromatics, d, J = 3, 2 C), 131.26
(aromatics, d, J = 2, 2C), 132.86 (aromatics, d, J = 10, 4 C),
134.02 (aromatics, s, 2 C), 134.24 (aromatics, s, 2 C), 134.51
(aromatics, d, J = 10, 4 C), 161.80 (C aromatic bonded to
CH3O, d, J = 8, 2C), 163.40 (OCO, q, J = 37, 2C) and 171.91
(OCO, q, J = 42 Hz, 2 C); 19F, δ Ϫ74.74 (s) and Ϫ75.04 (s).
Found: C, 44.17; H, 2.81. C23H17O5F6PRh requires C, 44.47; H,
2.76%.
system, δ 29.74, 1JRh-P = 158, 2JRh-P = Ϫ5, 3JP-P = 0 and 1JRh-Rh
Ϫ21 Hz).
=
(b) Compound 2 (100 mg, 0.097 mmol) was dissolved in 100
ml of CHCl3 and 21 mg of Me3SiCl (0.184) were added. The
mixture was stirred for 30 min at 50 ЊC. The yellow solution
obtained was evaporated to dryness. Following procedure (a)
compound 5 was isolated in 60% yield.
[Rh2(ꢀ-O2CCF3)3(O2CCF3){ꢁ2-(o-CH3OC6H4)P(C6H5)2}] 6.
The compound [Rh2(O2CCH3)3[(C6H4)P(o-CH3OC6H4)(C6H5)]
(100 mg, 0.15 mmol) was dissolved in CF3CO2H and was
stirred for two days at room temperature. The green solution
obtained was evaporated to dryness and the residue dissolved in
5 mL of 1:1 CH2Cl2–hexane and chromatographed on a
column (2 × 30 cm, silica gel, hexane). After elution with
CH2Cl2–hexane–acetone (20:20:1) a green band separated.
Removal of the solvent gave a crude oil which was recrystallized
from CH2Cl2–hexane yielding 110 mg of compound 6 (78%
Compound 6 (b) (100 mg, 0.10 mmol) dissolved in 100 ml of
CHCl3 was stirred with 30 mg ( 0.10 mmol) of PCOMe for 30
min. After further irradiation for 30 min with an Hg-vapour
lamp (OSRAM-125) the resulting green-yellow solution was
manipulated as described to obtain 100 mg (73% yield) of 3.
1
1
yield). NMR: 31P-{1H}, δ 37.6, JRh-P= 152; H, δ 4.60 (1 CH3,
3 H) and 6.80–7.80 (aromatics, 14 H); 19F NMR, δ Ϫ74.2 (3F),
Ϫ74.65 (3F) and Ϫ75.0 (6F). Found: C, 33.24; H, 2.05.
C27H17O9F12PRh2ؒH2O requires C, 33.50%; H, 1.98%.
[Rh2(ꢀ-O2CCH3)2(Cl)2{ꢁ2-(o-ClC6H4)P(C6.H5)2}2] 4. (a) By
serendipity. To 40 mL of 10:4 toluene–CH3CO2H 600 mg of
[Rh2(O2CCH3)4(CH3OH)2] (1.19 mmol) were added. The mix-
ture was refluxed under an argon an atmosphere until complete
dissolution and 348 mg of PCCl (1.19 mmol), dissolved in 20
mL of 1:3 CHCl3–toluene, were added. The solution immedi-
ately changed from blue to brown-red. It was refluxed for 30
min and changed to blue. The solvent was removed under
vacuum, the resulting crude oil dissolved in 5 mL of 1:1
CH2Cl2–hexane and the resulting solution chromatographed
on a column (2 × 30 cm, silica gel, hexane). After elution with
CH2Cl2–hexane (1:1) a minor yellow band separated that
was discarded. Increasing polarity (CH2Cl2–hexane–acetone,
10:10:1) gave an orange band . Other products obtained with
more polar solvents were not characterized. The eluted orange
solution was evaporated under reduced pressure to give a yel-
low residue that after crystallization from CH2Cl2–hexane gave
compound 4 as a yellow-brown solid (49 mg, yield 10%). NMR:
X-Ray crystallography
An Enraf-Nonius CAD 4 diffractometer was employed for data
collection on 1 and 4. The structure of 1 was solved by direct
methods using the program SHELXS 86 and refined by means
of full-matrix least squares procedures using SHELXL 93.14
The structure of 4 was also solved by direct methods using
SHELXS 97 and refined by full-matrix least squares methods
on F 2 with SHELXL 97.15 For data collection on crystals of
compound 5 a Siemens SMART CCD diffractometer was used.
The structure was solved by direct methods and refined on F 2
for all reflections using SHELXTL V 5.05.16 In all cases the
positions of non-hydrogen atoms were deduced from Fourier-
difference maps and refined anisotropically. Hydrogen atoms
were placed in geometrically generated positions and refined
riding on the carbon atom to which they are attached.
Complex 1. Crystal data. C27H31O10PRh2, M = 752.31, mono-
clinic, space group P21/c, a = 10.751(6), b = 16.282(6),
c = 17.22(2) Å, β = 105.20(6)Њ, V = 2908(3) Å3, T = 293 K, Z = 4,
µ(Mo-Kα) = 1.244 mmϪ1. Final conventional R = 0.1078 for
4998 ‘observed’ reflections and 365 variables.
Owing to the poor quality of the crystals we could not refine
the structure further (based on F and 2σ(I) cut-off). On
the other hand no crystal deterioration was observed
during data collection nor strong disorder in the presence
of solvents. Nevertheless the molecular structure is well
established. Multiple attempts to make better crystals were
unsuccessful.
1
2
31P-{1H}, AAЈXXЈ system, δ 33.7, JRh-P = 153, JRh-P = Ϫ5,
1
1
3JP-P = 0 and JRh-Rh = Ϫ23); H, δ 1.60 (s, CH3, 6 H), 6.63 (t,
J = 8, aromatics, 2 H), 7.16 (m, aromatics, 8 H), 7.45 (s, aromat-
ics, 10 H) and 7.68 (m, aromatics, 8 H); 13C, δ 22.5 (s, CH3),
125.0–138.0 (m, aromatics) and 186.5 (s, OCO).
(b) A mixture of 100 mg (0.198 mmol) of [Rh2(O2C-
CH3)4(CH3OH)2] and 42.25 mg of Me3SiCl (0.376 mmol) was
stirred for one hour at 50 ЊC; 123 mg of PCCl (0.436) were
added to the resulting brown-green solution and the mixture
was stirred at room temperature for 12 h. The solvent was
removed under vacuum, the resulting crude oil dissolved in 5
mL of 1:1 CH2Cl2–hexane and chromatographed on a column
(2 × 30 cm, silica gel, hexane). The column was washed with
CH2Cl2. Further elution with CH2Cl2–acetone (4:1) gave an
orange band from which compound 4 was isolated in 75% yield.
Complex 4. Crystal data. C42H36Cl10O4P2Rh2, M = 1226.97,
triclinic, space group P1, a = 13.398(6), b = 13.623(5), c =
14.538(5) Å, α = 77.40(5), β = 84.25(5), γ = 69.69(4)Њ, V =
2427.7(17) Å3, T = 293 K, Z = 2, µ(Mo-Kα) = 1.336 mmϪ1, 8941
reflections measured, 8538 unique (Rint; = 0.0182) which were
used in all calculations. The final R was 0.0352.
¯
[Rh2(ꢀ-O2CCH3)2(Cl)2{ꢁ2-(o-CH3OC6H4)P(C6H5)2}2] 5. (a)
By serendipity. To 70 mL of degassed toluene–CH3CO2H (5:2)
200 mg of [Rh2(O2CCH3)4(CH3OH)2] (0.39 mmol) were added.
The mixture was refluxed until complete dissolution and 231 mg
of PCCl (0.79 mmol) dissolved in 10 mL of CHCl3 were added.
After refluxing for 90 min the solution changed from red-brown
to blue. After evaporation in vacuum, the residue was extracted
with 5 mL of 1:1 CH2Cl2–hexane and transferred to a column
Complex 5. Crystal data. C43.50H43Cl5O6P2Rh2, M = 1106.79,
monoclinic, space group P21/n, a = 17.9125(10), b = 13.0427(8),
c = 19.6074(12) Å, β = 94.8900(10)Њ, V = 4564.2(5) Å3, T = 293
K, Z = 4, µ(Mo-Kα) = 1.132 mmϪ1, 16640 reflections measured,
6475 unique (Rint = 0.0553) which were used in all calculations.
The final R was 0.076.
J. Chem. Soc., Dalton Trans., 1999, 3493–3498
3497

View Article Online
4 (a) C. J. Alarcón, P. Lahuerta, E. Peris, M. A. Ubeda, A. Aguirre,
CCDC reference number 186/1576.
See http://www.rsc.org/suppdata/dt/1999/3493/ for crystallo-
graphic files in .cif format.
S. García-Granda and F. Gómez-Beltrán, Inorg. Chim. Acta, 1997,
254, 177; (b) C. J. Alarcón, F. Estevan, P. Lahuerta, M. A. Ubeda,
G. González, M. Martínez and S. E. Stiriba, Inorg. Chim. Acta,
1998, 278, 61.
5 S. P. Perlepes, J. C. Huffman, J. Matonic, K. R. Dunbar and
G. Chistou, J. Am. Chem. Soc., 1991, 113, 2770.
6 F. Estevan, unpublished work.
7 P. Lahuerta, M. A. Ubeda, J. Payá, S. García-Granda and F. Gómez-
Beltrán, Inorg. Chim. Acta, 1993, 205, 91.
8 F. Estevan, P. Lahuerta, E. Peris, M. A. Ubeda, S. García-Granda,
F. Gómez-Beltrán, E. Pérez-Carreño, G. González and M.
Martínez, Inorg. Chim. Acta, 1994, 218, 189.
9 (a) F. A. Cotton, K. R. Dunbar and M. G. Verbruggen, J. Am.
Chem. Soc., 1987, 109, 5498; (b) F. A. Cotton, K. R. Dunbar and
C. T. Eagle, Inorg. Chem., 1987, 26, 4127.
Catalytic experiments
All the catalytic reactions were performed by addition of the
corresponding rhodium() complex (1 mol%) in 1 ml of CH2Cl2
to an anhydrous dichloromethane solution containing the diazo
compound. The mixture was stirred at 100 ЊC in a sealed tube.
After cooling, the reaction mixture was filtered through a short
plug of silica gel to remove the catalyst and the solvent removed
1
under reduced pressure. The residue was analysed by H and
13C NMR spectroscopy.
10 (a) J. L. Bear, C. L. Yao, R. S. Lifsey, J. D. Korp and K. M. Kadish,
Inorg. Chem., 1991, 30, 336; (b) Y. Fuchita, Y. Ohta, K. Hiraki,
M. Kawatani and N. Nishiyama, J. Chem. Soc., Dalton Trans., 1990,
3767; (c) J. A. Jenkins, J. P. Ennet and M. Cowie, Organometallics,
1988, 7, 1845; (d) V. M. Miskowski, R. F. Dallinger, G. G. Chistoph,
D. E. Morris, G. H. Spies and W. H. Woodruff, Inorg. Chem., 1987,
26, 2127; (e) F. A. Cotton and M. Matusz, Inorg. Chim. Acta, 1988,
143, 45; ( f ) T. Glowiak, H. Pasternak and F. Pruchnik, Acta.
Crystallogr., Sect. C., 1987, 43, 1036; (g) F. A. Cotton and K. R.
Dunbar, J. Am. Chem. Soc., 1987, 109, 3142; (h) F. A. Cotton and
T. R. Felhouse, Inorg. Chem., 1980, 19, 320.
11 A. T. Baker, W. R. Tikkanen, W. C. Kaska and P. C. Ford, Inorg.
Chem., 1984, 23, 3254.
12 S. A. Johnson, H. R. Hunt and H. M. Neumann, Inorg. Chem.,
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13 E. A. Hart, J. Chem. Soc., 1960, 3324.
Acknowledgements
We thank the Dirección General de Investigación Científica y
Tecnica (Project PB94-988) and the EC (Project TMR Network
ERBFMRXCT 60091) for financial support.
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Paper 9/03811F
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J. Chem. Soc., Dalton Trans., 1999, 3493–3498