Cyclopalladated complexes with functionalized diphosphines via activation of chelated 1,1-bis(diphenylphosphino) ethene

Article abstract of DOI:10.1021/om0106884

The reaction of 1 with 1,1-bis(diphenylphosphino)ethene (vdpp) gave the mononuclear cyclometalated compound 2. The withdrawing effect of the cyclopalladated moiety suffices to polarize the C=CH₂ double bond to afford the addition products 3-8,

Full text of DOI:10.1021/om0106884

1304
Organometallics 2002, 21, 1304-1307
Cyclop a lla d a ted Com p lexes w ith F u n ction a lized
Dip h osp h in es via Activa tion of Ch ela ted
1,1-Bis(d ip h en ylp h osp h in o)eth en e
Berta Teijido,† Alberto A. Ferna´ndez,† Margarita Lo´pez-Torres,† Antonio Sua´rez,†
J ose´ M. Vila,*,‡ Roberto Mosteiro,† and J esu´s J . Ferna´ndez*,†
Departamento de Quı´mica Fundamental, Universidad de A Corun˜a, 15071 A Corun˜a, Spain,
and Departamento de Quı´mica Inorga´nica, Universidad de Santiago de Compostela,
15782 Santiago de Compostela, Spain
Received J uly 31, 2001
Summary: The reaction of 1 with 1,1-bis(diphenylphos-
phino)ethene (vdpp) gave the mononuclear cyclometa-
lated compound 2. The withdrawing effect of the cyclo-
palladated moiety suffices to polarize the CdCH2 double
bond to afford the addition products 3-8, by treatment
of complex 2 with primary aliphatic and aromatic
amines. The molecular structures of 2, 4, and 8 have
been determined by X-ray crystallography, showing that
the C-C distance in 4 and 8 has the expected single-
bond length upon addition.
Pd, Pt; X ) Me, AcO, Cl, I),9,10 and RuCl2,11 or even
complexes with an A-frame structure,12 activates the
double bond toward conjugate or Michael addition, due
to the additional polarizing effect of the metal center,
of a variety of nucleophiles (amines, hydrazines, acetyl-
ide anions, among others). To the best of our knowledge,
only one example of previous work on the attempted
activation of vdpp bonded to a cyclopalladated moiety,
in an 8-methylquinoline derivative, has been reported.13
In this paper we report that in complexes of the type
[(C-N)Pd(vdpp-P,P)]+X- nucleophilic addition to the
vinylidene double bond was made possible, and the
present work constitutes the synthesis and isolation of
the first pure addition products of cyclometalated
complexes with functionalized phosphines, which is
difficult to achieve through other procedures.
In tr od u ction
Tertiary mono- and polydentate phosphine ligands
play an important role in coordination and in organo-
metallic chemistry, owing to their ability to stabilize a
great variety of metal complexes in different oxidation
states as well as to their application in homogeneous
catalysis.1,2
Exp er im en ta l Section
Gen er a l Com m en ts. Solvents were dried prior to use
according to the standard methods.14 Ph2PC(dCH2)PPh2 (vdpp)
was prepared following to procedures described elsewhere.6
Chemicals were used as supplied from commercial sources.
Elemental analyses were carried out by the Servicios Gen-
erales de la Universidad de A Corun˜a using a Carlo-Erba
elemental analyzer (Model 1108). IR spectra were recorded as
Nujol mulls or polythene disks on a Perkin-Elmer 1330
spectrophotometer. NMR spectra were obtained as CDCl3
solutions and referenced to SiMe4 (1H) or 85% H3PO4 (31P{1H})
and were recorded on a Bruker AC 20005 spectrometer (200
The design and availability of new types of phosphines
may be accomplished in the absence of a metal, and the
new phosphine may then be integrated into the metal
coordination sphere, but it may also be convenient to
develop new ligands once the phosphine precursor has
been coordinated to the metal center(s). Typical ex-
amples of the latter case are the C-H acidity of the CH2
bridge in bis(diphenylphosphino)methane (dppm)3-5 or
the activated CdC group of 1,1-bis(diphenylphosphino)-
ethene (vdpp).
1
MHz for H, 81 MHz for 31P{1H}). Conductivity measurements
were made on a CRISON GLP 32 conductivimeter using 10-3
mol dm-3 solutions in dry acetonitrile. The synthesis of [Pd-
{3,4-[O(CH2)2O]C6H2C(H)dN(C6H11)-C6,N}(µ-CH3CO2)]2 was
reported in a recent paper from this laboratory.15
It has been reported that, although the vinylidene
double bond in uncoordinated vdpp is not susceptible
to nucleophilic attack,6 complexation to different metal
fragments, e.g. M(CO)4 (M ) Cr, Mo, W),7,8 MX2 (M )
[P d {3,4-[O(CH2)2O]C6H2C(H)dN(C6H11)-C6,N}{(P h 2P )2-
CHCH2(4-MeNC5H9)-P ,P ’}](P F 6) (3). To a solution of 2 (100
† Universidad de A Corun˜a.
‡ Universidad de Santiago de Compostela.
(9) Higgins, S. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1989,
1527 and references therein.
(10) (a) King, G.; Higgins, S. J .; Hopton, A. J . Chem. Soc., Dalton
Trans. 1992, 3403. (b) Keiter, R. L.; Benson, J . W.; Keiter, E. A.; Lin,
W.; J ia, Z.; Olson, D. M.; Brandt, D. E.; Wheeler, J . L. Organometallics
1998, 17, 4291.
(11) Barkley, J . V.; Higgins, S. J .; McCart, M. K.; Pounds, T. J . Inorg.
Chem. 1997, 36, 6188.
(12) Schmidbaur, H.; Herr, R.; Mu¨ller, G.; Riede, J . Organometallics
1985, 4, 1208.
(1) Cotton, F. A.; Hong, B. Prog. Inorg. Chem. 1992, 40, 179.
(2) Pignolet, L. H. Homogeneous Catalysis with Metal Phosphine
Complexes; Plenum Press: New York, 1983.
(3) Al-J ibori, S.; Shaw, B. L. Inorg. Chim. Acta 1982, 65, L123.
(4) Al-J ibori, S.; Hall, M.; Hutton, A. T.; Shaw, B. L. J . Chem. Soc.,
Dalton Trans. 1984, 863.
(5) (a) Ruiz, J .; Riera, V.; Vivanco, M.; Lanfranchi, M.; Tiripicchio,
A. Organometallics 1998, 17, 3835. (b) Ruiz, J .; Riera, V.; Vivanco,
M.; Garc´ıa-Granda, S.; D´ıaz, M. R. Organometallics. 1998, 17, 4562.
(6) Colquhoun, I. J .; McFarlane, W. J . Chem. Soc., Dalton Trans.
1982, 1915.
(13) Herring, A. M.; Higgins, S. J .; J acobsen, G. B.; Shaw, B. L. J .
Chem. Soc., Chem. Commun. 1986, 882.
(7) (a) Herring, A. M.; Koskimies, S. H.; Shaw, B. L. J . Organomet.
Chem. 1988, 338, 13. (b) Hassan, F. S. M.; Shaw, B. L.; Thornton-
Pett, M. J . Chem. Soc., Dalton Trans. 1988, 89.
(8) Bookham, J . L.; McFarlane, W.; Colquhoun, I. J . J . Chem. Soc.,
Dalton Trans. 1988, 503.
(14) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. L. Purification of
Laboratory Chemicals, 3rd ed.; Pergamon: London, 1988.
(15) Teijido, B.; Ferna´ndez, A.; Lo´pez-Torres, M.; Castro-J uiz, S.;
Ortigueira, J . M.; Vila, J . M.; Ferna´ndez, J . J . J . Organomet. Chem.
2000, 598, 71.
10.1021/om0106884 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/16/2002

Notes
Organometallics, Vol. 21, No. 6, 2002 1305
mg, 0.112 mmol) in benzene (5 mL) was added 4-methylpip-
eridine (12 mg, 0.120 mmol). After the mixture was stirred
for 2 h under argon, the solid formed was filtered off, washed
with cold benzene, and dried in vacuo. The final product was
isolated as pale yellow needles by recrystallization from
dichloromethane/n-hexane (89.1%). Anal. Found: C, 57.0; H,
5.4; N, 2.8. Calcd for C47H53O2PdN2P3F6: C, 56.8; H, 5.6; N,
2.9. IR: ν(CdN) 1610 s cm-1. NMR: δH (CDCl3) 8.06 (1H, d,
J (PH) ) 7.8 Hz, Hi), 6.94 (1H, d, J (PH) ) 3.9 Hz, H2), 6.00
(1H, dd, J (PH) ) 9.8, 7.4 Hz, H5), 4.95 (1H, m, PCHP), 4.11
(4H, br, OCH2CH2O), 0.80 (3H, d, J (HH) ) 6.4 Hz, Me); δP
(CDCl3) 11.84 (1P, d, J (PP) ) 54.0 Hz, Ptrans-N), -9.16 (1P, d,
Sch em e 1
P
trans-C), -146.9 (1P, h, J (PF) ) 713.0 Hz, PF6-). Specific molar
conductivity, Λm: 131.5 Ω-1 cm2 mol-1
.
A similar method was used for the addition products 4-8.
Cr ysta l Str u ctu r e Deter m in a tion . For complexes 2, 4,
and 8 three-dimensional X-ray data were collected on a
Siemens Smart CCD diffractometer by the ω-scan method (at
room temperature for 2 and 4 and at 173 K for 8). All the
reflections measured were corrected for Lorentz and polariza-
tion effects (and for absorption by semiempirical methods
based on symmetry-equivalent and repeated reflections). The
structures were solved by direct methods and refined by full-
matrix least squares on F2 with allowance for thermal aniso-
tropy of all non-hydrogen atoms. Hydrogen atoms were
included in calculated positions and refined in the riding mode.
-
In complex 4 the PF6 ion was found to be disordered,
occupying two positions with one of the components showing
less than ideal geometry and large Uij values. The occupancies
of each component were approximately 50%. In complex 8 the
disordered C(9), C(10), and C(11) atoms were refined by taking
into account the minor components with approximately 65%
and 35% occupancies. The largest residual peaks were adjacent
to the palladium atoms, except for complex 4, which showed a
reflections): R1 ) 0.1037, wR2 ) 0.1659. GOF ) 1.043. The
residual electron density is between -0.946 and 1.061 e/Å3.
Resu lts a n d Discu ssion
For the convenience of the reader the compounds and
reactions are shown in Scheme 1. We have reported the
synthesis of the dinuclear acetate-bridged complex a ,15
which when treated with an aqueous solution of sodium
chloride gave the chloride-bridged complex 1. Coordina-
tion of the metal to the imine nitrogen atom was
evidenced by the shift of the ν(CdN) stretching vibration
toward lower wavenumbers by ca. 30 cm-1 in the IR
spectrum and by the upfield shift of the HCdN proton
large peak (1.571 e/Å3) in the vicinity of the disordered PF6
-
ion. The structure solution and refinement were carried out
using the program package SHELX-97.16
Cr ysta l Da ta a n d Deta ils on Da ta Collection a n d
Refin em en t. (a ) Com p ou n d 2:
C41H40F6NO2P3Pd, fw )
892.05, monoclinic, C2/c, a ) 25.507(3) Å, b ) 12.977(1) Å, c
) 24.061(4) Å, â ) 95.59(1)°, V ) 7926.4(17) Å3, Z ) 8; 21 598
reflections measured; 9777 unique reflections (Rint ) 0.021).
The θ range was 1.60-28.30° with hkl indices -33 to +33,
-17 to +12, and -32 to +31. An absorption correction was
applied (µ ) 0.654 mm-1, 0.76-0.96 transmission). R values
(I >2σ(I)): R1 ) 0.0388, wR2 ) 0.0997. R values (all reflec-
tions): R1 ) 0.0520, wR2 ) 0.1083. GOF ) 1.039. The residual
electron density is between -0.607 and 1.018 e/Å3.
1
signal in the H NMR spectrum by ca. 0.4 ppm.17,18 The
IR spectra showed two ν(Pd-Cl) bands, consistent with
an asymmetric Pd2Cl2 bridging unit.19
Reaction of 1 with vdpp in a 1:2 molar ratio and of
ammonium hexafluorophosphate in acetone at room
temperature gave the mononuclear cyclometalated pal-
ladium(II) complex 2. The molecular structure of 2 is
depicted in Figure 1, and selected bond lengths and
angles are given in the figure caption.
Com p ou n d 4: C46H51F6N2O2P3Pd, fw ) 977.20, triclinic,
P1h, a ) 11.239(1) Å, b ) 14.599(1) Å, c ) 17.885(1) Å, R )
74.885(1)°, â ) 83.533(1)°, γ ) 82.472(1)°, V ) 2799.2(1) Å3, Z
) 2, F ) 1.159 Mg/m3; 16 333 reflections measured; 9702
unique reflections (Rint ) 0.034). The θ range was 1.18-25.00°,
with hkl indices -13 to +13, -17 to +17, and -21 to +15. An
absorption correction was applied (µ ) 0.469 mm-1, 0.77-0.82
transmission). R values (I >2σ(I)): R1 ) 0.0778, wR2 ) 0.2239.
R values (all reflections): R1 ) 0.1059, wR2 ) 0.2508. GOF )
0.994. The residual electron density is between -1.052 and
1.571 e/Å3.
Treatment of a benzene solution of 2 at room tem-
perature under argon with ca. 1 mol equiv of 4-methyl-
piperidine for 2 h afforded in high yield (>80%) the
addition derivative 3, as an air-stable solid (Scheme 1).
The 1H NMR spectrum showed the absence of the
vinylidene proton resonance of 2 and a multiplet ca. 4.80
ppm assignable to the P2CH proton. The 31P{1H} NMR
spectrum showed two doublets assigned to the two
inequivalent phosphorus atoms with a coupling constant
very differenct from that observed for the starting
Com p ou n d 8: C48H50Cl2F6N5O3P3Pd, fw ) 1129.14, mono-
clinic, C2/c, a ) 12.042(2) Å, b ) 17.688(1) Å, c ) 23.011(1) Å,
â ) 91.699(1)°, V ) 4898.9(1) Å3, Z ) 4, F ) 1.531 Mg/m3;
35 801 reflections measured; 12 110 unique reflections (Rint
)
2
material. Surprisingly, the J (PP) value in 2 is smaller
0.049). The θ range was 1.45-28.32° with hkl indices -15 to
+16, -20 to +23, and -20 to +30. An absorption correction
was applied (µ ) 0.656 mm-1, 0.73-0.88 transmission). R
values (I > 2σ(I)): R1 ) 0.0603, wR2 ) 0.1418. R values (all
that in 3 (14.8 vs 54 Hz), despite the fact that the
P-C-P carbon atom in 2 shows sp2 hybridization, as
(17) Onoue, H.; Moritani, I. J . Organomet. Chem. 1972, 43, 431.
(18) Ustynyuk, Y.; Chertov, V. A.; Barinov, J . V. J . Organomet.
Chem. 1971, 29, C53.
(19) Pereira, M. T.; Vila, J . M.; Gayoso, E.; Gayoso, M.; Hiller, W.;
Stra¨hle, J . J . Coord. Chem. 1988, 18, 245.
(16) Sheldrick, G. M. SHELX-97: An Integrated System for Solving
and Refining Crystal Structures from Diffraction Data; University of
Gottingen, Gottingen, Germany, 1997.

1306 Organometallics, Vol. 21, No. 6, 2002
Notes
F igu r e 2. ORTEP view of the cation for complex 4 with
thermal ellipsoids at 30% probability. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Pd(1)-C(1), 2.052(6); Pd(1)-N(1), 2.112-
(5); C(7)-N(1), 1.259(9); Pd(1)-P(2), 2.2726(18); Pd(1)-
P(1), 2.3622(16); C(16)-C(41), 1.509(9); C(1)-Pd(1)-N(1),
81.8(2); C(1)-Pd(1)-P(2), 99.4(2); N(1)-Pd(1)-P(1), 106.52-
(15); P(2)-Pd(1)-P(1), 72.93(6); P(1)-C(16)-P(2), 95.2(3).
F igu r e 1. ORTEP view of the cation for complex 2 with
thermal ellipsoids at 30% probability. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Pd(1)-C(1), 2.035(3); Pd(1)-N(1), 2.121-
(2); C(7)-N(1), 1.280(4); Pd(1)-P(1), 2.2492(7); Pd(1)-P(2),
2.4182(7); C(40)-C(41), 1.315(4); C(1)-Pd(1)-N(1), 81.02-
(10); C(1)-Pd(1)-P(1), 96.56(8); N(1)-Pd(1)-P(2), 110.40-
(7); P(1)-Pd(1)-P(2), 72.25(3); P(1)-C(40)-P(2), 98.03(13).
opposed to the sp3 hybridization of the same carbon in
3. We believe this may be due to the greater contribution
of 2J (PP) across the metal center (normally of negative
sign) in the addition products than in 2, thus lowering
the absolute value of the coupling constant; the reverse
trend has been observed in complexes of the group 6
metals.20,21 Reaction of 2 with piperidine and 2-meth-
ylpiperidine gave the adducts 4 and 5, respectively, as
air-stable solids (Scheme 1). The conductivity data for
complexes 2-5 (125-150 Ω-1 cm2 mol-1 in 10-3 mol
dm-3 solutions in dry acetonitrile) show they are 1:1
1
electrolytes.22 In complexes 2-5, the H NMR spectra
showed that the HCdN resonance (doublet) was only
coupled to the trans phosphorus nucleus (4J (PHi) ) ca.
7.8 Hz). The H5 resonance appeared as a doublet of
doublets due to coupling to both phosphorus nuclei
(4J (Ptrans-NH5) ) ca. 9.8 Hz, 4J (Ptrans-CH5) ) ca. 7.4 Hz),
while the signal assigned to the H2 nucleus appeared
as a doublet (5J (PH2) ) ca. 3.4 Hz) by coupling to only
the phosphorus atom trans to carbon. These data
support the presence of the cyclometalated ring.23 Of
particular interest is the addition compound 5, the
2-methylpiperidine derivative, in which the 31P{1H}
NMR spectrum showed two pairs of doublets, suggesting
the presence of isomers probably due to the presence of
two chiral carbon atoms, the CR atom with respect to
both phosphorus atoms and the C-Me atom of the
piperidine ring. The molecular structure of 4 is depicted
F igu r e 3. ORTEP view of the cation for complex 8 with
thermal ellipsoids at 30% probability. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å)
and angles (deg): Pd(1)-C(1), 2.036(4); Pd(1)-N(1), 2.091-
(4); C(7)-N(1), 1.271(6); Pd(1)-P(1), 2.2432(11); Pd(1)-
P(2), 2.3965(11); C(16)-C(17), 1.516(6); C(1)-Pd(1)-N(1),
81.38(16); C(1)-Pd(1)-P(1), 97.49(12); N(1)-Pd(1)-P(2),
108.95(12); P(1)-Pd(1)-P(2), 72.25(4); P(1)-C(16)-P(2),
95.08(19).
in Figure 2, and selected bond lengths and angles are
given in the figure caption.
The addition products 6-8 could be obtained by
stirring the reaction mixture in benzene for 6 h and
conveniently isolated and characterized. The molecular
structure of 8 is depicted in Figure 3, and selected bond
lengths and angles are given in the figure caption. Thus,
under the mild conditions used here the withdrawing
effect of the cyclopalladated moiety suffices to polarize
(20) Vila, J . M.;; Shaw, B. L. Unpublished results.
(21) Vila, J . M.; Gayoso, M.; Ferna´ndez, A.; Ferna´ndez, J . J .; Sua´rez,
A. 29th International Conference on Coordination Chemistry: Lau-
sanne, Switzerland, J uly 1992.
(22) Geary, W. J . Coord. Chem. Rev. 1971, 7, 81.
(23) Vila, J . M.; Gayoso, M.; Lo´pez-Torres, M.; Ferna´ndez, J . J .;
Ferna´ndez, A.; Ortigueira, J . M.; Bailey, N. A.; Adams, H. J . Orga-
nomet. Chem. 1996, 511, 129.

Notes
Organometallics, Vol. 21, No. 6, 2002 1307
the CdCH2 double bond and to afford the addition
product.
The palladium-nitrogen bond lengths, 2.121(2) Å (2),
2.112(5) Å (4), and 2.091(4) Å (8), are shorter than
expected, reflecting the trans influence of the phospho-
rus atom.23 In contrast with this, the palladium-carbon
bond lengths, 2.035(3) Å (2), 2.052(6) Å (4), and 2.036-
(4) Å (8), are shorter than the theoretical value, in
agreement with the proposed partial multiple-bond
character of the Pd-C bond.26,27
The differing trans influences of the phenyl carbon
and imine nitrogen atoms is reflected in the palladium-
phosphorus distance trans to carbon, relative to that
trans to nitrogen. Thus, we have Pd(1)-P(1) ) 2.2492-
(7) Å vs Pd(1)-P(2) ) 2.4182(7) Å in complex 2, Pd(1)-
P(2) ) 2.2726(18) Å vs Pd(1)-P(1) ) 2.3622(16) Å in
complex 4, and Pd(1)-P(1) ) 2.2432(11) Å vs Pd(1)-
P(2) ) 2.3965(11) Å in complex 8.23,28
The C(40)-C(41) bond length in complex 2, 1.315(4)
Å, is shorter than in compounds 4 and 8, 1.509(9) and
1.516(6) Å, respectively, consequent upon addition. For
complex 8 the purine moiety is essentially planar, and
it is tilted with respect to the cyclometalated ring at ca.
108°, but the packing arrangement shows that it is
parallel to a phenyl ring of the phosphorus atom trans
to nitrogen (the angle between these planes is 9.3°, and
the mean distance is 3.50 Å).
Treatment of 2 with 2,2,6,6-tetramethylpiperidine did
not give the addition product, and no change in the
starting complex was observed, regardless of the reac-
tion conditions used, even when a large excess of the
amine was added. This suggests that the presence of
the two methyl substituents in the R-position of the
piperidine ring does not allow addition to the CdCH2
double bond of the coordinated diphosphine, presumably
due to steric hindrance by the phenyl rings of the
diphosphine ligand, as opposed to less sterically de-
manding 2-methylpiperidine.
Molecu la r Str u ctu r es of Com p lexes 2, 4, a n d 8.
Suitable crystals were grown by slowly evaporating
dichloromethane solutions of complexes 2, 4, and 8. The
labeling schemes for the complexes are shown in Figures
1-3. The crystals consist of discrete molecules, sepa-
rated by normal van der Waals distances. Crystal-
lographic data are given in the Experimental Section
and the Supporting Information, and selected inter-
atomic distances and angles are listed in the figure
captions.
Each palladium atom is in a slightly distorted square-
planar environment. The coordination sphere around
each palladium atom consists of a nitrogen atom of the
imine group, an ortho carbon of the phenyl ring, and
two phosphorus atoms from a chelating diphospine
ligand (see Figures 1-3). The sums of angles about
palladium are 360.23° (2), 360.25° (4), and 360.07° (8),
with the more noticeable distortions in the somewhat
reduced “bite” angles consequent upon chelation, which
are C(1)-Pd(1)-N(1) ) 81.02(10)° (2), 81.8(2)° (4), and
81.38(16)° (8) and P(1)-Pd(1)-P(2) ) 72.25(3)° (2),
72.93(6)° (4), and 72.25(4)° (8), respectively. The re-
quirements of the four-membered chelate rings force the
Ack n ow led gm en t. We thank the DGES (Proyecto
PB98-0638-C02-01/02) for financial support. R.M. ac-
knowledges a fellowship from the Ministerio de Ciencia
y Tecnolog´ıa of Spain.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails for the synthesis and characterization of 1, 2, and 4-8
and tables giving atomic coordinates, displacement param-
eters, and bond distances and angles for 2, 4, and 8. This
material is available free of charge via the Internet at
http://pubs.acs.org.
2
OM0106884
bond angles P(1)-C(40)sp -P(2) to 98.03(13)° (2), P(1)-
3
3
C(16)sp -P(2) to 95.2(3)° (4), and P(1)-C(16)sp -P(2) to
95.08(19)° (8), which are smaller than the value in free
vdpp, 118.4°,24 and rather low values for sp2 and sp3
bond angles, although some four-membered chelate
rings involving coordinated phosphines with a even
smaller P-C-P angle have been reported.25
(25) (a) Steffen, W. L.; Palenik, G. J . Inorg. Chem. 1976, 15, 2432.
(b) Lee, C. L.; Yang, Y. P.; Rettig, S.; J ames, B. R., Nelson, D. A.; Lilga,
M. A. Organometallics 1986, 5, 2220.
(26) Suarez, A.; Vila, J . M.; Gayoso, E.; Gayoso, M.; Hiller, W.;
Castin˜eiras, A.; Stra¨hle, J . Z. Inorg. Allg. Chem. 1986, 535, 213.
(27) Lousame, M.; Ferna´ndez, A.; Lo´pez-Torres, M.; Va´zquez-Garc´ıa,
D.; Vila, J . M.; Sua´rez, A.; Ortigueira, J . M.; Ferna´ndez, J . J . Eur. J .
Inorg. Chem. 2000, 2055.
(28) Bosque, R.; Lo´pez, C.; Solans, X.; Font-Bardia´, M. Organome-
tallics 1999, 18, 1267.
(24) Schmidbaur, H.; Herr, R.; Riede, J . Chem. Ber. 1984, 117, 2372.