Rhodium(III)-mediated cycloaddition of alkynes: Reactivity of [Cp*Rh(η2-NO3)(OTf)] bearing two labile ligands

Article abstract of DOI:10.1016/S0022-328X(03)00451-0

[Cp*Rh(η²-NO₃)(OTf)] (1) mediated cyclodimerization or cyclotrimerization of alkynes and alkynyl esters. In addition, compound 1 reacted with propargyl halides to give triply halide-bridged dinuclear compounds, [Cp*Rh(μ₂-X

Full text of DOI:10.1016/S0022-328X(03)00451-0

Journal of Organometallic Chemistry 678 (2003) 102Á107
/
www.elsevier.com/locate/jorganchem
Rhodium(III)-mediated cycloaddition of alkynes: reactivity of
[Cp*Rh(h2-NO3)(OTf)] bearing two labile ligands
Won Seok Han, Soon W. Lee *
Department of Chemistry (BK21), Institute of Basic Science, Sungkyunkwan University, Natural Science Campus, Suwon 440-746, South Korea
Received 24 February 2003; received in revised form 12 May 2003; accepted 14 May 2003
Abstract
[Cp*Rh(h2-NO3)(OTf)] (1) mediated cyclodimerization or cyclotrimerization of alkynes and alkynyl esters. In addition,
compound 1 reacted with propargyl halides to give triply halide-bridged dinuclear compounds, [Cp*Rh(m2-X)3RhCp*](OTf) (Xꢀ
/Cl
or Br).
# 2003 Elsevier B.V. All rights reserved.
Keywords: Cyclodimerization; Cyclotrimerization; Alkynes; Alkynyl esters
1. Introduction
terminal with various substituents. In this paper, we
report the results of the reactivity of 1 toward several
alkynes.
Metal-mediated cycloaddition of alkynes has received
widespread attractions [1], and cyclobutadieneÁmetal
/
compounds are particularly interesting due to their
applications as reagents or intermediates in organic
synthesis [2]. Many synthetic strategies employ a de-
signed metal precursor to modify and control its
reactivity toward alkynes [3]. In this context, extensive
2. Experimental
Unless otherwise stated, all reactions have been
performed with standard Schlenk line and cannula
techniques under argon. Air-sensitive solids were ma-
nipulated in a glove box filled with argon. Glassware
was soaked in KOH-saturated 2-propanol for about 24
h and washed with distilled water and acetone before
use. Glassware was either flame- or oven-dried. Hydro-
carbon solvents were stirred over concentrated H2SO4
for about 48 h, neutralized with K2CO3, stirred over
sodium metal, and distilled by vacuum transfer. Diethyl
ether was stirred over sodium metal and dichloro-
methane over CaH2. Acetone, methyl alcohol, and ethyl
alcohol were distilled and stored under argon. NMR
solvent (CDCl3) was degassed by freeze-pump-thaw
cycles before use and stored over molecular sieves under
argon. Rhodium(III) chloride hydrate, 1,2,3,4,5-penta-
methylcyclopentadiene (Cp*), silver nitrate (AgNO3),
silver trifluoromethanesulfonate (AgOTf), diphenylace-
studies on alkyneÁ
metric, have demonstrated a high chemo-, regio-, or
stereoselectivity [1Á4]. For example, Caffyn et al.
recently reported the reaction of (h5-phospholyl)cobalt
dicarbonyl with alkynes to give an (h4-cyclobutadiene)Á
/cobalt reactions, catalytic or stoichio-
/
/
cobalt compound and free arenes [4a]. However, corre-
sponding studies on rhodium counterparts have been
relatively unexplored, and most reactions have been
carried out with rhodium(I) compounds although a few
rhodium(III) compounds have been investigated [1Á3,5].
/
Very recently, we reported the synthesis and structure
of [Cp*Rh(h2-NO3)(OTf)] (1), which contains two labile
ligands, nitrato (NO3ꢁ) and trifluoromethanesulfonato
(OTfꢁ) [6]. As a continuation of our work, we examined
the reactivity of 1 toward alkynes, which are internal or
tylene (PhCÅ
nyltoluene
(HCÅCCH2Cl), 3-bromo-1-propyne (HCÅ
/
CPh), phenylacetylene (HCÅ
(HCÅCC6H4CH3), 3-chloro-1-propyne
CCH2Br), di-
/
CPh), 4-ethy-
* Corresponding author. Tel.: ꢂ
7075.
E-mail address: swlee@chem.skku.ac.kr (S.W. Lee).
/
82-31-290-7066; fax: ꢂ82-31-290-
/
/
/
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00451-0

W.S. Han, S.W. Lee / Journal of Organometallic Chemistry 678 (2003) 102Á
/107
103
methyl acetylenedicarboxylate (MeO2CCÅ
/
CCO2Me),
2.4. Preparation of [Cp*Rh(m-X)3RhCp*](OTf) (4a:
XꢀCl; 4b: XꢀBr)
and diethyl acetylenedicarboxylate (EtO2CCÅ
/
CCO2Et)
were purchased. [Cp*Rh(h2-NO3)(OTf)] (1) was pre-
pared by the literature method [6].
/
/
A solution of 1 (100 mg, 0.22 mmol) and 3-chloro-1-
propyne (0.051 ml, 0.66 mmol) in acetone (30 ml) was
stirred for 3 h, and then the solvent was removed under
vacuum. The resulting solids were washed with diethyl
1H- and 13C{1H}-NMR spectra were recorded with a
Bruker AMX 500 MHz spectrometer. IR spectra were
recorded with a Nicolet Avatar 320 FTIR spectro-
photometer. Elemental analyses were performed by the
Korea Basic Science Institute.
ether (20 mlꢃ
/
2) and hexane (20 mlꢃ2), and then dried
/
under vacuum to give an orange solid of [Cp*Rh(m-
Cl)3RhCp*](OTf) (4a) (58 mg, 0.080 mmol, 72%). This
product was recrystallized from CH2Cl2Á
NMR (CDCl3): d 1.69 (s, 15H, C5(CH3)5). 13C{1H}-
NMR (CDCl3): d 9.9 (s, C5(CH3)5), 96.5 (d, JRhÃC
16.3 Hz, C5(CH3)5). Anal. Calc. for
C21H30F3O3SCl3Rh2: C, 34.47; H, 4.13; S, 4.38%.
Found: C, 33.95; H, 4.02; S, 4.46%. M.p. (dec.)ꢀ
300 8C. IR (KBr): 2915, 1632, 1470, 1376, 1265, 1173,
1034, 646 cmꢁ1
/
hexane. 1H-
2.1. Preparation of [Cp*Rh(h4-C4Ph4)] (2)
ꢀ
/
A solution of 1 (100 mg, 0.22 mmol) and diphenyla-
cetylene (79 mg, 0.44 mmol) in EtOH (30 ml) was
refluxed for 3 h, and then the solvent was removed
under vacuum. The resulting solids were washed with
/
EtOH (20 ml) and diethyl ether (20 mlꢃ
dried under vacuum to give yellow solid of
[Cp*Rh(h4-C4Ph4)] (2) (98 mg, 0.16 mmol, 74%). This
product was recrystallized from CH2Cl2Á
MeOH. 1H-
NMR (CDCl3): d 1.55 (s, 15H, C5(CH3)5), 7.26Á7.12
(m, 20H, C6H5). 13C{1H}-NMR (CDCl3): d 9.30 (s,
C5(CH3)5), 93.9 (d, JRhÃC 6.7 Hz, C5(CH3)5). Anal.
Calc. for C38H35Rh: C, 76.76; H, 5.93%. Found: C,
76.59; H, 6.07%. M.p. (dec.): 273Á275 8C. IR (KBr):
3058, 2965, 1635, 1601 (CÄC), 1499, 1097, 1070, 1027,
804, 743, 701, 648 cmꢁ1
/
2), and then
.
a
Compound 4b was similarly prepared (76 mg, 0.088
mmol, 79%). 1H-NMR (CDCl3): d 1.76 (s, 15H,
/
C5(CH3)5). 13C{1H}-NMR (CDCl3):
d 10.4 (s,
15.2 Hz, C5(CH3)5). Anal.
/
C5(CH3)5), 97.3 (d, JRhÃC
Calc. for C21H30F3O3SBr3Rh2: C, 29.16; H, 3.50; S,
ꢀ
/
ꢀ
/
3.71%. Found: C, 30.02; H, 3.46; S, 3.67%. M.p.
300 8C. IR (KBr): 2920, 1629, 1470, 1376,
(dec.)ꢀ
/
/
1271, 1146, 1026, 640 cmꢁ1
.
/
.
2.5. X-ray structure determination
2.2. Preparation of [Cp*Rh{(h4-C4)HAr2(CÅ
(3a: ArꢀPh; 3b: Arꢀp-tolyl)
/CAr)}]
All X-ray data were collected with the use of a
Siemens P4 diffractometer equipped with a Mo X-ray
tube. Details on crystal and intensity data are given in
Table 1. The orientation matrix and unit-cell parameters
were determined by the least-squares analyses of the
setting angles of 23 reflections for both 2 and 4a in the
/
/
A solution of 1 (100 mg, 0.22 mmol) and phenylace-
tylene (0.024 ml, 0.22 mmol) in acetone (30 ml) was
stirred for 3 h, and then the solvent was removed under
vacuum. The resulting solids were washed with MeOH
(20 ml), and then dried under vacuum to give a yellow
solid of 3a (28 mg, 0.052 mmol, 23%).
Compound 3b was similarly prepared (29 mg, 0.050
mmol, 22%). Compounds 3a and 3b were identified by
the comparison with literature data [7].
range of 15.08B
/
2u B25.08. Intensity data were empiri-
/
cally corrected for absorption with c-scan data. All
calculations were carried out with the use of SHELXTL
programs [9].
All crystal structures were solved by direct methods.
All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were generated in ideal positions
and refined in a riding model. Details on crystal data
and refinement details are given in Table 1. Selected
bond lengths and bond angles are given in Table 2.
2.3. Reactions of 1 with dimethyl acetylenedicarboxylate
and diethyl acetylenedicarboxylate
A solution of 1 (100 mg, 0.22 mmol) and dimethyl
acetylenedicarboxylate (0.059 ml, 0.66 mmol) in acetone
(30 ml) was stirred for 3 h, and then the solvent was
removed under vacuum. The resulting solids were
3. Results and discussion
extracted with diethyl ether (20 mlꢃ
/
2), and then dried
3.1. Reactivity toward alkynes
under vacuum to give a mixture of 1,2,4- and 1,3,5-
C6H3(CO2Me)3 (38 mg, 0.15 mmol, 68%).
Refluxing 1 with a stoichiometric amount of an
The reaction of 1 with diethyl acetylenedicarboxylate
similarly proceeded (41 mg, 0.14 mmol, 62%). The
spectral data for these trimers are exactly the same as
those for the genuine compounds in the literature [8].
internal alkyne PhCÅ
/
CPh in ethanol for 3 h gives an
(h4-cyclobutadiene)Á
/
rhodium(I) compound (2) in 74%
yield (Scheme 1). The same reaction in methanol in place
of ethanol also proceeds, although with a lower yield

104
W.S. Han, S.W. Lee / Journal of Organometallic Chemistry 678 (2003) 102Á107
/
Table 1
X-ray data collection and structure refinement
2
4a
Empirical formula
Fw
C
38H35Rh C21H30F3O3SCl3Rh2
594.57
293(2)
monoclinic triclinic
731.68
293(2)
Temperature (K)
Crystal system
Space group
¯
P1
P21/n
/
Unit cell dimensions
˚
a (A)
˚
13.720(2)
14.046(2)
16.556(3)
14.913(3)
15.401(4)
15.630(3)
96.27(1)
113.25(1)
115.86(2)
2791(1)
4
b (A)
˚
c (A)
a (8)
b (8)
g (8)
112.38(1)
3
˚
V (A )
2950.2(7)
4
Z
Dcalc (g cmꢁ3
)
1.339
0.603
1232
1.741
1.585
m (mmꢁ1
F(0 0 0)
Tmin
)
Scheme 1.
1456
0.4143
0.8023
0.3714
0.7807
Tmax
of rhodium from ꢂ
/
3 to ꢂ1 during the reaction suggests
/
2u Range (8)
Scan type
3.5Á
v
variable
/
50
3.5Á50
v
variable
/
that ethanol might also act as a reducing agent although
we did not isolate acetaldehyde, the oxidation product
of ethanol. The reducing ability of ethanol in this type
was also observed in the Pd-mediated cyclotrimerization
of phenylethyne to fulvene [10]. However, solvent effects
cannot be fully understood only in terms of the acidity
of alcohols, because methanol is a little bit more acidic
than ethanol. Some other factors such as solubility seem
to operate in our reactions.
One possible mechanism for the formation of com-
pound 2 is proposed in Scheme 2. This mechanism
adopts the most common process that goes via a
metallacyclopentadiene intermediate [2]. The first step
Scan speed
Number of reflections measured
Number of reflections unique
5358
5136
9686
9263
Number of reflections with I ꢀ
2s(I)
Number of parameters refined
/
4709
4452
353
0.261
595
1.629
ꢁ3
˚
Max in Dr (e A
)
ꢁ3
˚
Min in Dr (e A
)
ꢁ
/
0.370
ꢁ0.678
/
Goodness-of-fit on F2
1.052
0.0307
0.0760
1.010
0.0698
0.1462
R
a
wR2
a
wR2ꢀ
/
S[w(Fo2ꢁF2c)2]/S[w(Fo2)2]1/2
.
/
(21%). However, the reaction in acetone does not occur
at all. These results suggest that the solvent ethanol
might act as a proton donor to the two labile ligands
(NO3ꢁ and OTfꢁ) to facilitate their leaving from the
rhodium coordination sphere. In addition, the reduction
is the formation of the intermediate bis(alkyne)Árho-
/
dium, which accompanies the removal of the two labile
ligands in their protonated forms. In this step, the
solvent ethanol is likely to have acted as a proton donor.
The next step is the oxidative coupling of the two
Table 2
˚
Selected bond lengths (A) and bond angles (8)
Compound 2
Bond lengths
Rh1Ã
Rh1Ã
C23Ã
C35Ã
/
C35
2.120(3)
2.117(3)
1.462(4)
1.474(4)
Rh1Ã
C11Ã
C29Ã
C36Ã
/
C36
2.113(3)
1.461(4)
1.468(4)
1.464(4)
Rh1Ã
C17Ã
C35Ã
C37Ã
/
C37
2.120(2)
1.471(4)
1.467(4)
1.465(4)
/C38
/
C35
C38
C37
/
C36
C36
C38
/
C37
C38
/
/
/
/
/
Bond angles
C36Ã
C37Ã
/
C35Ã
C38Ã
/
C38
89.2(2)
90.4(2)
C36Ã
/
C37Ã
/
C38
89.7(2)
C37Ã
/
C36Ã/C35
90.7(2)
/
/C35
Compound 4a
Bond lengths
Rh1Ã
Rh2Ã
/
Cl1
2.477(4)
2.475(4)
Rh1Ã
Rh2Ã
/
Cl2
Cl2
2.451(4)
2.451(4)
Rh1Ã
Rh2Ã
/
Cl3
2.456(4)
2.444(4)
/Cl1
/
/Cl3
Bond angles
Rh1ÃCl1ÃRh2
/
/
81.3(1)
Rh1Ã
/
Cl2Ã/Rh2
82.3(1)
Rh1Ã
/
Cl3Ã/Rh2
82.3(1)

W.S. Han, S.W. Lee / Journal of Organometallic Chemistry 678 (2003) 102Á
/107
105
Scheme 2.
Fig. 1. ORTEP drawing of 2, showing the atom-labeling scheme and
50% probability thermal ellipsoids.
coordinated alkyne ligands to give the intermediate
metallacyclopentadiene, which undergoes reductive
elimination to form the cyclobutadiene compound 2.
A related cycloaddition reaction of dimethyl acetyle-
base, and therefore the reactivity of 1 seems to be
comparable to that of [Cp*Rh(L-alaninate)Cl]. The
structures of 3a and 3b were confirmed by comparing
their spectral and crystallographic data with those for
the genuine compounds [7]. Compound 1 also readily
nedicarboxylate (MeO2CCÅ
H2 was reported for the tetrahaptobenzeneÁ
compound [Cp*Rh{h4-C6(CO2Me)6}] [11]. Unfortu-
nately, the reactions of 1 with MeO2CCÅCCO2Me,
PhCÅCÃCÅCÃPh, or Me3SiÃCÅCÃCÅCÃSiMe3 in
/CCO2Me) in the presence of
/rhodium
reacts with other terminal alkynes (HCÅ
CÃSiMe3, HCÅCÃ(CH2)3CH3, HCÅCÃ
CÃ(CH2)2OH, HCÅCÃCH(OH)ÃCH3, and HCÅ
/
CÃ
CH2OH, HCÅ
CÃ
/
CMe3, HCÅ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
EtOH gave a mixture of several species, and we failed
to separate them. In acetone, however, we do not
observe any sign of reactions of 1 with internal alkynes
CH2OCH3), but these reactions give intractable mix-
tures and we failed to separate them.
Although the present results do not give any detailed
information about how compound 3 has been formed,
one of the possible mechanisms is shown in Scheme 3,
on the basis of the previous reports on alkyne cyclo-
trimerization. We speculate that the aryl alkyne proto-
nates the triflate and nitrato ligands to give an
intermediate A. Because we have used acetone as a
solvent in place of ethanol, the acidic terminal alkyne
hydrogen is likely to act as a proton source. In this
reaction, the variable haptacity of the nitrato ligand is
expected to play an important role to retain coordina-
tive saturation of the intermediates. Compounds related
to the intermediate A were previously reported by
Maitlis’s group ([Cp*Rh(C2Ph)2(NCMe)], [5]), Lamata’s
or alkynyl esters (PhCÅ
EtCÅCEt, EtCÅCMe, MeCÅ
CÅCÃPh, Me3SiÃCÅCÃCÅ
CCO2Me, and EtO2CCÅCCO2Et). To our best knowl-
edge, cyclodimerization reactions of internal alkynes
have not been investigated for Cp*Rh(III) compounds,
and most of those reactions have been carried out for
Cp*Rh(I) compounds [12].
Compound 2 was fully characterized by spectroscopy,
elemental analysis, and X-ray diffraction. It has a two-
legged pseudo-piano-stool structure, with the tetraphe-
nylcyclobutadiene ring being regarded as the two legs
/
CPh, PhCÅ
C(CH2)2CH3, PhÃ
CÃSiMe3, MeO2CCÅ
/
CMe, PhCÅ
/
CEt,
/
/
/
/
CÅ
/
CÃ
/
/
/
/
/
/
/
/
/
/
(Fig. 1). The RhÃ
/
Ct1 (Ct1: a centroid of C35Ã
Ct2 (Ct2: a centroid of C1ÃC5; 1.866
A) distances and the Ct1ÃRhÃCt2 angle (178.568) are
/
C38;
˚
1.846 A) and RhÃ
/
/
group ([Cp*Rh(
group ([Cp*Rh(C2Ph)2(PEt3)], [13]). The intermediate
A binds one alkyne, which inserts into the RhÃalkynyl
bond, followed by the CÃC coupling to give the
L-prolinate)(C2Ph)], [7]), and Ara’s
˚
/
/
very close to those of the cyclopentadienyl (Cp) analo-
/
gue [CpRh(h4-C4Ph4)] [12a].
/
Compound 1 undergoes cyclotrimerization with term-
inal aryl alkynes. It reacts with a stoichiometric amount
metallacyclopentadiene. This metallacycle intermediate
undergoes reductive elimination to give the ultimate
product, compound 3.
We examined the reactivity of 1 toward propargyl
halides, terminal alkynes with a halide at the propargyl
of HCÅ
give
[Cp*Rh{(h4-C4)HAr2(CÅ
Arꢀ
recently prepared the identical compounds (3a and 3b)
by treating [Cp*Rh( -alaninate)Cl] with phenylethyne
/
CAr in acetone at room temperature for 3 h to
(h4-cyclobutadiene)Á
CAr)}] {Arꢀ
/
rhodium(I)
compounds
/
/Ph (3a), 23%;
/
p-tolyl (3b), 22%} (Scheme 1). Lamata et al.
position. Treatment of 1 with three equivalents of HCÅ
/
CCH2X in acetone at room temperature for 12 h gives
triply halide-bridged dinuclear compounds [Cp*Rh(m-
L
in the presence of a base (NEt3) for 20 h [7]. We could
prepare them relatively fast even in the absence of a
X)3RhCp*](OTf) {Xꢀ
/
Cl (4a), 72%; XꢀBr (4b), 79%}
/
(Scheme 1). This reaction can be interpreted as the

106
W.S. Han, S.W. Lee / Journal of Organometallic Chemistry 678 (2003) 102Á
/107
Scheme 3.
replacement of weakly coordinating ligands (NO3ꢁ and
OTfꢁ) by strong donor ligands (Clꢁ or Brꢁ). Similar
triply halide-bridged rhodium salts are known:
[Cp*Rh(m-Cl)3RhCp*](BPh4), [Cp*Rh(m-Cl)3RhCp*]-
(PF6), and [Cp*Rh(m-I)3RhCp*](BF4) [14]. The mole-
cular structure of 4a is given in Fig. 2. There are two
crystallographically independent molecules in an asym-
metric unit, which are chemically equal and have either
eclipsed or staggered Cp* rings.
cleavage does not occur. We examined the possibility of
a catalytic cyclotrimerization by treating a catalytic
amount of
[Rh]:[ester]ꢀ
1
1:100), and we obtained a mixture of
with HCÅ
/
CCO2Me (mole ratio:
/
1,2,4- and 1,3,5-C6H3(CO2Me)3 in 42% yield with the
mole ratio of 1:6 (1H-NMR). The spectral data for these
trimers are exactly the same as those for the genuine
compounds in the literature [8].
ð1Þ
3.2. Reactivity toward alkynyl esters
Treating terminal alkynyl esters with 1 produces free
arenes instead of (h4-cyclobutadiene)Á
/
rhodium com-
pounds. The reaction of 1 (100 mg) with three equiva-
lents of HCÅCCO2R in acetone at room temperature
for 24 gives mixture of 1,2,4- and 1,3,5-
C6H3(CO2R)3 (RꢀMe, 68%; RꢀEt, 62%), together
with 1 (63 mg) (Eq. (1)). On the contrary to the cases for
the formation of 3a and 3b, the terminal CÃH bond
In summary, [Cp*Rh(h2-NO3)(OTf)] (1) mediated the
cycloaddition of alkynes and alkynyl esters. On the
other hand, the reaction of 1 with propargyl halides gave
triply halide-bridged dinuclear compounds. These re-
sults indicate that the reactivity of 1 depends basically
on the substituent on the alkyne. We observed a
possibility of 1 as a catalyst for the cyclotrimerization
of alkynyl esters to benzene derivatives. We do believe
that the interesting reactivity of 1 is attributed to the two
labile ligands, nitrato and trifluoromethanesulfonato.
/
h
a
/
/
/
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Center: CCDC No. 201654 for compound 2 and 201655
for compound 4a. Copies of this information may be
obtained free of charge from The director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: ꢂ44-
/
1223-336033; email: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Fig. 2. ORTEP drawing of 4a.

W.S. Han, S.W. Lee / Journal of Organometallic Chemistry 678 (2003) 102Á
/107
107
[7] M.P. Lamata, E.S. Jose´, D. Carmona, F.J. Lahoz, R. Atencio,
L.A. Oro, Organometallics 15 (1996) 4852.
Acknowledgements
[8] (a) M. Herberhold, H. Yan, W. Milius, B. Wrackmeyer,
Organometallics 19 (2000) 4289;
This work is based on research sponsored by the
Korea Research Foundation Grant (KRF-2002-015-
DP0262).
(b) H. Yan, A.M. Beatty, T.P. Fehlner, Angew. Chem. Int. Ed. 40
(2001) 4498.
[9] R. Bruker, SHELXTL, Structure Determination Software Pro-
grams, Bruker Analytical X-ray Instruments Inc, Madison,
Wisconsin, USA, 1997.
References
[10] H.-J. Kim, N.-S. Choi, S.W. Lee, J. Organomet. Chem. 616 (2000)
67.
[1] (a) D.B. Grotjahn, in: E.W. Abel, F.G.A. Stone, G. Wilkinson
(Eds.), Comprehensive Organometallic Chemistry, vol. 12, Perga-
[11] J.W. Kang, R.F. Childs, P.M. Maitlis, J. Am. Chem. Soc. 92
(1970) 720.
mon Press, Oxford, 1995, pp. 741Á
/
751;
(b) N.E. Schore, Chem. Rev. 88 (1988) 1081;
[12] (a) G.G. Cash, J.F. Helling, M. Mathew, G.J. Palenik, J.
Organomet. Chem. 50 (1973) 277;
(c) S. Saito, Y. Yamamoto, Chem. Rev. 100 (2000) 2901;
(d) K.P.C. Vollhardt, Acc. Chem. Res. 10 (1977) 1.
[2] A. Efraty, Chem. Rev. 77 (1977) 691.
(b) R.S. Dickson, G.S. Evans, G.D. Fallon, J. Organomet. Chem.
236 (1982) C49;
(c) R.P. Hughes, A.S. Kowalski, B.T. Donovan, J. Organomet.
Chem. 472 (1994) C18 (and references therein).
[13] I. Ara, J.R. Berenguer, E. Eguiza´bal, J. Fornie´s, E. Lalinde, A.
Mart´ın, F. Mart´ınez, Organometallics 17 (1998) 4578.
[14] (a) J.W. Kang, P.M. Maitlis, J. Organomet. Chem. 30 (1971) 127;
(b) U. Koelle, J. Electroanal. Chem. 292 (1990) 217;
[3] M. Lautens, W. Klute, W. Tam, Chem. Rev. 96 (1996) 49.
[4] (a) A.J.M. Caffyn, D. Carmichael, F. Mathey, L. Ricard,
Organometallics 16 (1997) 2049 (and references therein);
(b) L. Yong, H. Butenschon, Chem. Commun. (2002) 2852.
¨
[5] J. Moreto, K.-I. Maruya, P.M. Bailey, P.M. Maitlis, J. Chem.
Soc. Dalton Trans. (1982) 1341.
[6] W.S. Han, S.W. Lee, Inorg. Chim. Acta 348 (2003) 15.
(c) I.I.R. Salas, M.A.P. Sandoval, H. Noth, Organometallics 21
¨
(2002) 4696.