Reactions of [Cp*RuCl(PP)] (PP = dppm, dppe) with NaBAr′4: Structural characterization of [{Cp*Ru}2(μ-Cl)(μ-dppm)2] [BAr′4] and of [Cp*Ru(N2)(Dppm)][BAr′4] (Ar′ = 3,5-C6H3</

Article abstract of DOI:10.1021/om020880l

The reaction of [Cp*RuCl(dppm)] with NaBAr′₄ in fluorobenzene under argon generates the binuclear complex [{Cp*Ru}₂(μ-Cl)(μ-dppm)₂] [BAr′₄], which has been structurally characterized. No complex was isolated fro

Full text of DOI:10.1021/om020880l

Organometallics 2003, 22, 1779-1782
1779
Rea ction s of [Cp *Ru Cl(P P )] (P P ) d p p m , d p p e) w ith
Na BAr ′4: Str u ctu r a l Ch a r a cter iza tion of
[{Cp *Ru }2(µ-Cl)(µ-d p p m )2][BAr ′4] a n d of
[Cp *Ru (N2)(d p p m )][BAr ′4] (Ar ′ ) 3,5-C6H3(CF 3)2)
Halikhedkar Aneetha, Manuel J ime´nez-Tenorio, M. Carmen Puerta, and
Pedro Valerga*
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Quı´mica Inorga´nica,
Facultad de Ciencias, Universidad de Ca´diz, 11510 Puerto Real, Ca´diz, Spain
Kurt Mereiter
Institute of Chemical Technologies and Analytics, Vienna University of Technology,
Getreidemarkt 9, A-1060 Vienna, Austria
Received October 22, 2002
Summary: The reaction of [Cp*RuCl(dppm)] with Na-
BAr′4 in fluorobenzene under argon generates the bi-
nuclear complex [{Cp*Ru}2(µ-Cl)(µ-dppm)2][BAr′4], which
has been structurally characterized. No complex was
isolated from the reaction of [Cp*RuCl(dppe)] with
NaBAr′4 under argon, but halide abstraction from
[Cp*RuCl(PP)] (PP ) dppm, dppe) under dinitrogen
using NaBAr′4 yielded the corresponding cationic ter-
minal dinitrogen complexes [Cp*Ru(N2)(PP)][BAr′4].
known systems, namely [Cp*RuCl(dppm)] and [Cp*RuCl-
(dppe)], toward NaBAr′4 in fluorobenzene both under
argon and under dinitrogen. Despite the fact that the
moieties {[Cp*Ru(dppm)]+} and {[Cp*Ru(dppe)]+} can
be generated in situ and constitute binding sites for a
range of small molecules such as dihydrogen,3 dioxy-
gen,4,5 and dinitrogen,6 no cationic 16-electron species
could be isolated. In this note we describe the outcome
of these experiments, which complete our works on this
subject.1,2
In tr od u ction
Exp er im en ta l Section
The introduction of the noncoordinating anion [BAr′4]-
(BAr′4 ) tetrakis(3,5-bis(trifluoromethyl)phenyl)borate)
as halide scavenger has recently allowed the isolation
of a series of coordinatively unsaturated cationic com-
plexes of the type [Cp*Ru(PP)][BAr′4] (PP ) 1,2-bis-
(diisopropylphosphino)ethane (dippe), (PMeiPr2)2, (PEt3)2,
(PPhiPr2)2, (PPh3)2).1 Whereas some of these compounds
have been subjected to X-ray structure analysis, others
decomposed readily to a variety of final products, most
often to species containing η6-arene moieties. In an
attempt to synthesize the Cp counterparts of these
complexes, we carried out the reaction of [CpRuCl(PP)]
(PP ) dippe, (PMeiPr2)2, (PEt3)2) with NaBAr′4 under
Ar. However, in these cases, the 16-electron species were
too reactive to be detected, as they react with traces of
N2 present in the argon, furnishing the dinitrogen-
bridged complexes [{CpRu(PP)}2(µ-N2)][BAr′4]2. Only
the reaction of [CpRuCl(PMeiPr2)(PPh3)] with NaBAr′4
under Ar yielded a cationic compound of formula [CpRu-
(PMeiPr2)(PPh3)][BAr′4], which however turned out to
be an 18-electron complex containing a rare η3-PPh3
ligand.2 To finish the survey of the range of phosphine
ligands capable of stabilizing cationic 16-electron spe-
cies, we have now examined the reactivity of two well-
All synthetic operations were performed under a dry dini-
trogen or argon atmosphere by following conventional Schlenk
techniques. Tetrahydrofuran, diethyl ether, and petroleum
ether (boiling point range 40-60 °C) were distilled from the
appropriate drying agents. Solvents were deoxygenated by
three freeze/pump/thaw cycles and stored under argon. Na-
[BAr′4],7 [Cp*RuCl(dppm)],8 and [Cp*RuCl(dppe)]4a were pre-
pared according to reported procedures. IR spectra were
recorded in Nujol mulls on a Perkin-Elmer FTIR Spectrum
1000 spectrophotometer. NMR spectra were obtained on
Varian Unity 400 MHz or Varian Gemini 200 MHz equipment.
Chemical shifts are given in parts per million from SiMe4 (1H)
or 85% H3PO4 (31P{1H}). Microanalysis was performed by the
Serveis Cient´ıfico-Te`cnics, Universitat de Barcelona.
[{Cp *Ru }2(µ-Cl)(µ-d p p m )2][BAr ′4] (1). To a solution of
[Cp*RuCl(dppm)] (0.33 g, 0.5 mmol) in fluorobenzene (15 mL)
under argon was added solid NaBAr′4 (0.44 g, 0.5 mmol). The
mixture was stirred for 15 min at room temperature. The
initial yellow-orange solution was converted to a red suspen-
sion. Sodium chloride was removed by filtration through Celite.
The resulting solution was layered with petroleum ether and
(3) (a) J ia, G.; Lough, A. J .; Morris, R. H. Organometallics 1992,
11, 161. (b) Klooster, W. T.; Koetzle, T. F.; J ia, G.; Fong, T. P.; Morris,
R. H.; Albinati, A. J . Am. Chem. Soc. 1994, 116, 7677.
(4) (a) Mauthner, K.; Mereiter, K.; Schmid, R.; Kirchner, K. Inorg.
Chim. Acta 1995, 236, 95. (b) Kirchner, K.; Mauthner, K.; Mereiter,
K.; Schmid, R. J . Chem. Soc., Chem. Commun. 1993, 892.
(5) J ia, G.; Ng, W. S.; Chu, H. S.; Wong, W.-T.; Yu, N.-T.; Williams,
I. D. Organometallics 1999, 18, 3597.
(6) Hembre, R. T.; McQueen, S. J . Am. Chem. Soc. 1994, 116, 2141.
(7) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920.
(8) Lin, W.; Wilson, S. R.; Girolami, G. S. Organometallics 1997,
16, 2987.
* To whom correspondence should be addressed. E-mail:
pedro.valerga@uca.es.
(1) (a) J ime´nez-Tenorio, M.; Mereiter, K.; Puerta, M. C.; Valerga,
P. J . Am. Chem. Soc. 2000, 122, 11230. (b) Aneetha, H.; J ime´nez-
Tenorio, M.; Puerta, M. C.; Valerga, P.; Sapunov, V. N.; Schmid, R.;
Kirchner, K.; Mereiter, K. Organometallics 2002, 21, 5334.
(2) Aneetha, H.; J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.;
Mereiter, K. Organometallics 2002, 21, 628.
10.1021/om020880l CCC: $25.00 © 2003 American Chemical Society
Publication on Web 03/14/2003

1780 Organometallics, Vol. 22, No. 8, 2003
Notes
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for
Com p ou n d s 1 a n d 2
1‚solva
2
formula
C
106H86BCl-
C67H49BF24
N2P2Ru
1511.90
223(2)
-
F
24P4Ru2
fw
T (K)
2188.03
297(2)
cryst size (mm)
0.40 × 0.22 ×
0.75 × 0.65 ×
0.18
0.50
cryst syst
space group
cell params
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
monoclinic
P21/n (No. 14) P1h (No. 2)
triclinic
16.575(8)
31.380(14)
19.692(9)
12.579(3)
14.410(3)
20.033(3)
80.36(1)
71.77(1)
83.21(1)
3392(1)
2
90.61(1)
10242(8)
4
1.419
4.73
4432
Z
Fcalcd (g cm-3
)
1.480
3.86
1520
µ(Mo KR) (cm-1
F(000)
)
max. min transmissn factors
θ range for data collecn (deg)
no. of rflns collected
1.000, 0.897
1.60-25.00
103 542
17 893 (Rint
0.048)
1.000, 0.935
1.44-30.00
60 455
19 292 (Rint
0.019)
F igu r e 1. ORTEP drawing (30% thermal ellipsoids) of the
cation [{Cp*Ru}2(µ-Cl)(µ-dppm)2]+ in complex 1. Hydrogen
atoms have been omitted. Selected bond lengths (Å) and
angles (deg) with estimated standard deviations in paren-
theses: Ru(1)-Cl ) 2.466(1); Ru(1)-C(1) ) 2.242(5); Ru-
(1)-C(2) ) 2.275(5); Ru(1)-C(3) ) 2.250(5); Ru(1)-C(4) )
2.248(5); Ru(1)-C(5) ) 2.273(5); Ru(1)-P(1) ) 2.319(1); Ru-
(1)-P(4) ) 2.331(1); Ru(2)-Cl ) 2.454(1); Ru(2)-C(11) )
2.226(5); Ru(2)-C(12) ) 2.268(5); Ru(2)-C(13) ) 2.263-
(5); Ru(2)-C(14) ) 2.246(5); Ru(2)-C(15) ) 2.255(5); Ru-
(2)-P(2) ) 2.335(1); Ru(2)-P(3) ) 2.325(1); Ru(1)-Cl-
Ru(2) ) 134.49(5); P(1)-Ru(1)-P(4) ) 91.50(4); P(2)-
Ru(2)-P(3) ) 94.79(4); P(1)-C(21)-P(2) ) 126.8(2); P(3)-
C(46)-P(4) ) 125.8(2).
no. of unique rflns
)
)
no. of obsd rflns (I > 2σI)
no. of params
final R1, wR2 values (I > 2σI)
final R1, wR2 values (all data) 0.0710, 0.1535 0.0564, 0.1270
14 290
1243
16 472
942
0.0535, 0.1350 0.0471, 0.1174
residual electron density
+0.94, -0.71
+0.93, -0.51
peaks (e Å-3
)
a
Contains petroleum ether with four solvent peaks per asym-
metric unit, which have been included as carbon atoms in chemical
formula and derived quantities.
left standing undisturbed at room temperature. Well-formed
red crystals were obtained by slow diffusion of the petroleum
ether into the fluorobenzene solution. These crystals were
isolated by cannulating off the supernatant liquor, washed
with petroleum ether, and dried under an argon stream.
Yield: 0.32 g, 60%. Anal. Calcd for C102H86BClF24P4Ru2: C,
applied. All structures were solved by direct methods using
the program SHELXS97.9 Structure refinement on F2 was
carried out with the program SHELXL97.9 ORTEP10 was used
for plotting.
1
57.2; H, 4.02. Found: C, 57.5; H, 3.90. H NMR (CD2Cl2): δ
1.25 s (C5(CH3)5); 2.78, 2.82 (m, PCH2); 6.80, 7.09, 7.19, 7.30,
7.47 (m, PC6H5). 31P{1H} NMR (CD2Cl2): δ 39.04 s.
Resu lts a n d Discu ssion
[Cp *Ru (N2)(d p p m )][BAr ′4] (2). Yellow crystals of this
compound were obtained in a fashion analogous to that for 1,
starting from [Cp*RuCl(dppm)] (0.33 g, 0.5 mmol) and NaBAr′4
(0.44 g, 0.5 mmol) in fluorobenzene (15 mL), under a dinitrogen
atmosphere instead of argon. Yield: 0.49 g, 66%. Anal. Calcd
for C67H49BF24N2P2Ru: C, 53.2; H, 3.24; N, 1.85. Found: C,
The reaction of [Cp*RuCl(dppm)][BAr′4] with NaBAr′4
in fluorobenzene under argon yielded a dark red solu-
tion, at variance with other [Cp*RuCl(PP)] (PP ) dippe,
(PEt3)2, (PPh3)2) complexes, for which deep blue solu-
tions are generated under similar conditions.1 The blue
color in these systems is indicative of the generation of
stable cationic 16-electron species, something that ap-
parently does occur in the dppm system. Workup of the
reaction mixture afforded red crystals which were
subjected to X-ray structure analysis, turning out to be
the dinuclear complex [{Cp*Ru}2(µ-Cl)(µ-dppm)2][BAr′4]
(1). Figure 1 shows an ORTEP view of the dinuclear
complex cation. There are one chloride and two dppm
ligands acting as bridges between the two ruthenium
atoms. The Ru(1)-Ru(2) separation of 4.537(1) Å sug-
gests that there is no metal-metal bonding interaction,
at variance with the RuIII-RuIII dinuclear complex
53.0; H, 3.12; N, 1.5. IR: ν(N2) 2166 cm-1. H NMR (CD2Cl2):
1
δ 1.64 s (C5(CH3)5); 4.58, 5.28 (m, PCH2); 7.37, 7.44, 7.54 (m,
PC6H5). 31P{1H} NMR (CD2Cl2): δ 3.98 s.
[Cp *Ru (N2)(d p p e)][BAr ′4] (3). This compound was ob-
tained in a fashion analogous to that for 2, starting from
[Cp*RuCl(dppe)] (0.33 g, 0.5 mmol) and NaBAr′4 (0.44 g, 0.5
mmol) in fluorobenzene (15 mL). Yield: 0.52 g, 68%. Anal.
Calcd for
C69H53BF24N2P2Ru: C, 53.8; H, 3.44; N, 1.82.
Found: C, 53.6; H, 3.40; N 1.5. IR: ν(N2) 2159 cm-1. H NMR
(CD2Cl2): δ 1.52 s (C5(CH3)5); 2.52, 2.64 (m, PCH2); 6.98, 7.41,
7.59 (m, PC6H5). 31P{1H} NMR (CD2Cl2): δ 71.8 s.
1
X-r a y Str u ctu r e Deter m in a tion s. Crystals of 1 (in the
form of 1‚solv) and 2 were obtained by slow diffusion of
petroleum ether into fluorobenzene solutions at -20 °C.
Crystal data and experimental details are given in Table 1.
X-ray data were collected on a Bruker Smart CCD area
detector diffractometer (graphite-monochromated Mo KR ra-
diation, λ ) 0.710 73 Å, 0.3° ω-scan frames covering complete
spheres of the reciprocal space). Corrections for Lorentz and
polarization effects, for crystal decay, and for absorption were
(9) (a) SHELXS97, Program for Crystal Structure Solution; Uni-
versity of Go¨ttingen, Go¨ttingen, Germany, 1997. (b) SHELXL97,
Program for Crystal Structure Refinement; University of Go¨ttingen,
Go¨ttingen, Germany, 1997.
(10) J ohnson, C. K. ORTEP, A Thermal Ellipsoid Plotting Program;
Oak Ridge National Laboratory, Oak Ridge, TN, 1965.

Notes
Organometallics, Vol. 22, No. 8, 2003 1781
Sch em e 1. P r op osed Rea ction Sequ en ce for th e F or m a tion of 1 a t th e Exp en se of [Cp *Ru Cl(d p p m )]
[{Cp*Ru}2(µ-Cl)2(µ-dppm)][CF3SO3]2, which contains
one Ru-Ru bond with a separation of 2.921(1) Å.11 The
bond lengths and angles of the bridging chloride and
dppm ligands compare well with data in the literature
for other dppm-bridged Cp*Ru complexes. It is not clear
how the dinuclear complex cation 1 is generated. Its
formation could be easily explained if we assume that
the starting material [Cp*RuCl(dppm)] had a dimeric
nature, i.e., [{Cp*RuCl}2(µ-dppm)2], as has been found
for the related complex [{Cp*RuCl}2(µ-dmpm)2] (dmpm
) Me2PCH2PMe2).8 It has been found that the standard
procedure for the preparation of [Cp*RuCl(PP)] com-
plexes, namely the addition of phosphine to [{Cp*RuCl}4]
in a suitable solvent, yields in the case of dppm the
dinuclear species [{Cp*Ru}2(µ-Cl)2(µ-dppm)] irrespective
of the phosphine-to-metal ratio, if the solvent is Et2O
or THF,8 or even CH2Cl2 if the dppm is added over a 2
h period in order to minimize the formation of mono-
meric [Cp*RuCl(dppm)].11 Girolami and co-workers have
shown that pure [Cp*RuCl(dppm)] can be obtained
using MeCN as solvent, presumably due to the inter-
mediacy of [Cp*Ru(MeCN)3]+.8 In our case, we checked
carefully by NMR the starting material to ensure that
it was monomeric [Cp*RuCl(dppm)]. Therefore, 1 is
actually formed at the expense of [Cp*RuCl(dppm)]. We
can tentatively postulate the reaction sequence shown
in Scheme 1 to account for the formation of 1. Given
the strong tendency of dppm to adopt η1 or a bridging
coordination mode,8,11,12 a fast ring-opening equilibrium
between the chelate [Cp*RuCl(η2-dppm)] and the pen-
dant-arm 16-electron species [Cp*RuCl(η1-dppm)] should
be possible. The reaction of the latter with [Cp*Ru-
(dppm)]+ generated in situ upon chloride abstraction
would yield the dppm-bridged species [{Cp*Ru(dppm)}-
(µ-dppm){Cp*RuCl}]+. A rearrangement within this
species would lead to 1. In a variant of this reaction
sequence, once the chloride is removed, the resulting
16-electron cation might react with the chloride ligand
of [Cp*RuCl(dppm)], giving [{Cp*Ru(dppm)}2(µ-Cl)]+ as
intermediate, which upon rearrangement would yield
1. As has been mentioned, these are just tentative
proposals. Other alternative explanations cannot be
disregarded. No pure product was obtained from the
reaction of [Cp*RuCl(dppe)] with NaBAr′4 in fluoroben-
zene under argon. When the reagents were mixed, the
mixture took on a brown color, with no trace of blue or
red. Workup of the reaction mixture only yielded dark
brown oily substances, which were not characterized.
The reaction of both [Cp*RuCl(dppm)] and [Cp*RuCl-
(dppe)] with NaBAr′4 under dinitrogen is more straight-
forward and leads to the corresponding terminal dini-
trogen complexes [Cp*Ru(N2)(dppm)][BAr′4] (2) and
[Cp*Ru(N2)(dppe)][BAr′4] (3). These compounds are
yellow materials, which exhibit one strong ν(N2) band
in their IR spectra at 2166 cm-1 for 2 and 2159 cm-1
for 3. These compounds add to the series of end-on and
bridging half-sandwich ruthenium dinitrogen complexes
(12) Orth, S. D.; Terry, M. R.; Abboud, K. A.; Dodson, B.; McElwee-
White, L. Inorg. Chem. 1996, 35, 916. Ko¨lle, U.; Ho¨rnig, A.; Englert,
U. J . Organomet. Chem. 1992, 438, 309. Albers, M. O.; Liles, D. C.;
Robinson, D. J .; Singleton, E. Organometallics 1987, 6, 2179.
(11) Mauthner, K.; Kalt, D.; Slugovc, C.; Mereiter, K.; Schmid, R.;
Kirchner, K. Monatsh. Chem. 1997, 128, 533.

1782 Organometallics, Vol. 22, No. 8, 2003
Notes
dinitrogen molecule, whereas the Ru-N(1) separation
of 1.975(2) Å compares well with the value of 1.961(3)
Å found in [CpRu(N2)(dippe)][BAr′4],2 being in the range
observed for other terminal Ru-N2 complexes.14 The
reason the bond distance in the dinitrogen molecule in
these complexes does not change to a great extent upon
coordination to a metal center has been interpreted
elsewhere in terms of EHMO calculations.14b
Summing up, halide abstraction from either [Cp*RuCl-
(dppm)] or [Cp*RuCl(dppe)] using NaBAr′4 under argon
does not lead to isolable cationic 16-electron compounds,
whereas both systems are capable of stabilizing the
Ru-N2 bond. From a total of 10 different phosphine
ligands studied in systems of the types [Cp*RuCl(PP)]
(PP ) dippe, (PEt3)2, (PPh3)2, (PMe3)2, dppe, dppm) and
[Cp*RuCl(P)] + P (P ) PMeiPr2, PPhiPr2, PiPr3, PCy3),
only in five cases were cationic 16-electron [Cp*Ru(PP)]+
detected, and in three cases they were crystallized.1 No
genuine 16-electron species were isolated or detected
using Cp instead of Cp* as coligand.2 Several monoden-
tate phosphine ligands which keep a fine balance
between donor abilities and steric hindrance are capable
of stabilizing cationic half-sandwich 16-electron species.
However, this is only accomplished in the case of
bidentate phosphine ligands by using the bulky, strongly
electron releasing phosphine dippe. It remains to be
seen whether bulkier bidentate ligands of the type
F igu r e 2. ORTEP drawing (30% thermal ellipsoids) of the
cation [Cp*Ru(N2)(dppm)]+ in complex 2. Hydrogen atoms
have been omitted. Selected bond lengths (Å) and angles
(deg) with estimated standard deviations in parentheses:
Ru-N(1) ) 1.975(2); Ru-C(1) ) 2.239(3); Ru-C(2) ) 2.224-
(3); Ru-C(3) ) 2.244(2); Ru-C(4) ) 2.233(2); Ru-C(5) )
2.235(2); Ru-P(1) ) 2.3311(7); Ru-P(2) ) 2.3309(6); N(1)-
N(2) ) 1.083(4); Ru-N(1)-N(2) ) 175.7(3); P(1)-Ru-P(2)
) 71.44(2); P(1)-C(35)-P(2) ) 94.7(1).
t
already reported by our research group.2,13 It must be
mentioned that [Cp*Ru(N2)(dppm)]+ was detected in the
course of the reaction of the monohydride [Cp*RuH-
(dppm)] with the hydride acceptor N-methylacridinium
hexafluorophosphate under dinitrogen, in an attempt
to model the reactivity of the hydrogenase enzyme with
the dihydrogen complex [Cp*Ru(H2)(dppm)]+.6 The value
of 2169 cm-1 reported for ν(N2) in [Cp*Ru(N2)(dppm)]-
[PF6]6 is consistent with ours for 2. However, J ia and
co-workers did not observe [Cp*Ru(N2)(dppm)]+ in their
studies of the interaction of [Cp*RuCl(dppm)] with
aerial oxygen.5 The X-ray crystal structure of 2 has been
determined. An ORTEP view of the dinitrogen complex
cation is shown in Figure 2. The cation has a typical
three-legged piano-stool structure, with the dinitrogen
ligand bound in an end-on manner, with a Ru-N(1)-
N(2) angle of 175.7(3)°. The N(1)-N(2) bond distance
of 1.083(4) Å is essentially identical with that of the free
R2P(CH2)nPR2 (R ) Bu, Cy, n ) 2, 3) can effectively
contribute to the stabilization of such unsaturated
complexes.
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog´ıa (DGICYT, Project BQU2001-4046)
and the Ministerio de Asuntos Exteriores of Spain
(Accion Integrada HU2001-0020) for financial support
and J ohnson Matthey plc for generous loans of ruthe-
nium trichloride.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
structural data, including data collection parameters, posi-
tional and thermal parameters, and bond distances and angles
for complexes 1 and 2. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM020880L
(14) (a) J ime´nez-Tenorio, M. A.; J ime´nez-Tenorio, M.; Puerta, M.
C.; Valerga, P. J . Chem. Soc., Dalton Trans. 1998, 3601. (b) Gemel,
C.; Wiede, P.; Mereiter, K.; Sapunov, V. N.; Schmid, R.; Kirchner, K.
J . Chem. Soc., Dalton Trans. 1996, 4071. (c) Schlaf, M.; Lough, A. J .;
Morris, R. H. Organometallics 1997, 16, 1253. (d) J ia, G.; Meek, D.
W.; Gallucci, J . C. Inorg. Chem. 1991, 30, 403.
(13) J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J . Organomet.
Chem. 2000, 609, 161. de los R´ıos, I.; J ime´nez-Tenorio, M.; Padilla, J .;
Puerta, M. C.; Valerga, P. Organometallics 1996, 15, 4565.