Coupling reactions of terminal acetylenes with a cyclometalated aryl ligand

Article abstract of DOI:10.1021/om960800b

Reaction of RuCl₂(PPh₃)₃ with 1,3-(PPh₂-CH₂)₂C₆H₄ in refluxing 2-propanol produced RuCl(PPh₃)(PCP) (PCP = 2,6-(PPh₂CH₂)₂C₆H₃). Reaction of RuCl(PPh₃)(PCP) with PhC≡CH gave the unusual coupling product RuCl(PPh₃){η⁴-CHPh=C-2,6-(PPh₂CH ₂)₂C₆H₃}, which has been characterized by X-ray diffraction. Coupling also occurred between RuCl-(PPh₃)(PCP) and HC≡CC(OH)(Ph)CH₃ to give RuCl-(PPh₃){η⁴-CH₂=CPhCH=C-2,6-(PPh ₂CH₂)₂C₆H₃}.

Full text of DOI:10.1021/om960800b

Organometallics 1996, 15, 5453-5455
5453
Cou p lin g Rea ction s of Ter m in a l Acetylen es w ith a
Cyclom eta la ted Ar yl Liga n d
Guochen J ia,* Hon Man Lee, Hai Ping Xia, and Ian D. Williams
Department of Chemistry, The Hong Kong University of Science & Technology,
Clear Water Bay, Kowloon, Hong Kong
Received September 19, 1996X
Sch em e 1
Summary: Reaction of RuCl2(PPh3)3 with 1,3-(PPh2-
CH2)2C6H4 in refluxing 2-propanol produced
RuCl(PPh3)(PCP) (PCP ) 2,6-(PPh2CH2)2C6H3). Reac-
tion of RuCl(PPh3)(PCP) with PhCtCH gave the un-
usual coupling product RuCl(PPh3){η4-CHPhdC-2,6-
(PPh2CH2)2C6H3}, which has been characterized by
X-ray diffraction. Coupling also occurred between RuCl-
(PPh3)(PCP) and HCtCC(OH)(Ph)CH3 to give RuCl-
(PPh3){η4-CH2dCPhCHdC-2,6-(PPh2CH2)2C6H3}.
The chemistry of vinylidene and allenylidene com-
plexes has attracted considerable attention because of
its relevance to catalysis and organic and organometallic
synthesis.1 One of the most common routes to prepare
vinylidene and allenylidene complexes is to react ter-
minal acetylenes HCtCR and HCtCC(OH)RR′ with
coordinatively unsaturated or labile transition-metal
complexes. In our attempts to prepare neutral vi-
nylidene- or allenylidene-ruthenium complexes, we have
studied the reactions of the coordinatively unsaturated
complex RuCl(PPh3)(PCP) (PCP ) 2,6-(Ph2PCH2)2C6H3,
a cyclometalated tridentate ligand) with terminal acety-
lenes such as PhCtCH and HCtCC(OH)(Ph)CH3. To
our surprise, these reactions did not lead to the expected
vinylidene or allenylidene complexes but to unusual
coupling products. The formation of the coupling prod-
ucts can be best explained by the pathway of migratory
insertion of the aryl group of the PCP ligand to R-carbon
atoms of vinylidene ligands. These interesting reactions
provide rare examples of metal-assisted CsC bond
formation between vinylidene and aryl ligands.2 Carbon-
carbon coupling reactions involving vinylidenes are
interesting, especially in view of the fact that vinylidene
intermediates have been postulated in various CsC
bond formation processes.1 In this regard, several
examples of CsC bond formation between vinylidene
ligands and alkyls,2-4 vinyls,2,5 and alkynyls6 have been
reported recently.
methylene protons, indicating that the two PPh2 groups
are trans to each other.10 The 31P NMR spectrum in
CDCl3 showed a doublet at 32.5 ppm for the PPh2 group
and a triplet at 79.4 ppm (J (PP) ) 27.7 Hz) for the PPh3
ligand. Thus, the PPh3 ligand is significantly deshielded
compared to the PPh2 groups. Such a 31P NMR pattern
has been observed for several similar square-pyramidal
ruthenium dichloro complexes with apical phosphines,
such as RuCl2(PR3)3 (PR3 ) PPh3, PEtPh2) and RuCl2-
(PPh3)(L2) (L2 ) dppb, dppp).11 For example, the
resonance for the apical PPh3 appeared at 75.0 ppm and
(6) See for example: (a) Bianchini, C.; Innocenti, P.; Peruzzini, M.;
Romerosa, A.; Zanobini, F. Organometallics 1996, 15, 272 and refer-
ences therein. (b) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.;
Zanobini, F. Organometallics 1994, 13, 4616. (c) Bianchini, C.; Bo-
hanna, C.; Esteruelas, M. A.; Frediani, P.; Meli, A.; Oro, L. A.;
Peruzzini, M. Organometallics 1992, 11, 3837. (d) Bianchini, C.;
Peruzzini, M.; Zanobini, F.; Frediani, P.; Albinati, A. J . Am. Chem.
Soc. 1991, 113, 5453. (e) Wakatsuki, Y.; Koga, N.; Yamazaki, H.;
Morokuma, K. J . Am. Chem. Soc. 1994, 116, 8105 and references
therein. (f) Field, L. D.; George, A. V.; Purches, G. R.; Slip, I. H.
Organometallics 1992, 11, 3019. (g) Wakatsuki, Y.; Yamazaki, H.;
Kumegawa, N.; Satoh, T.; Satoh, J . Y. J . Am. Chem. Soc. 1991, 113,
9604. (h) Heeres, H. J .; Nijhoff, J .; Teuben, J . H. Organometallics 1993,
12, 2609. (i) Albertin, D.; Amendola, P.; Antoniutti, S.; Ianelli, S.;
Pelizzi, G.; Bordignon, E. Organometallics 1991, 10, 2876. (j) McMullen,
A.; Selegue, J . P.; Wang, J . G. Organometallics 1991, 10, 3421. (k)
Santos, A.; Lopez, J .; Matas, L.; Ros, J .; Galan, A.; Echavarren, A. M.
Organometallics 1993, 12, 4215.
The coordinatively unsaturated compound RuCl(PPh3)-
(PCP) (3) was obtained as a green solid by refluxing a
mixture of RuCl2(PPh3)3 (1)8 and the ligand 27 in
2-propanol (see Scheme 1). The analytical and spec-
troscopic data9 of 3 are consistent with a square-
pyramidal complex with a meridional PCP ligand and
a PPh3 ligand occupying the apical position. The 1H
NMR spectrum (in CDCl3) showed a virtual doublet of
triplets signal at 3.47 ppm assignable to two of the
(7) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259, C6.
(8) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.
(9) Preparation of 3: a mixture of 0.13 g of 1,3-(Ph2PCH2)2C6H4 (0.27
mmol) and 0.24 g of RuCl2(PPh3)3 (0.25 mmol) in 2-propanol was
refluxed until a deep green solid separated from the solution. The solid
was collected on a filter frit, washed with ether, and dried under
vacuum overnight. Yield: 0.16 g, 82%. Anal. Calcd for C50H42ClP3Ru:
C, 68.84; H, 4.85. Found: C, 68.43; H, 5.12. 31P{1H} NMR (161.70 MHz,
CDCl3): δ 32.5 (d, J (PP) ) 27.7 Hz), 79.4 (t, J (PP) ) 27.7 Hz). 1H NMR
(400 MHz, CDCl3): δ 2.42 (d, J ) 16.6 Hz, 2 H, CHH(C6H3)CHH), 3.47
(dt, J ) 16.1, 5.9 Hz, 2 H, CHH(C6H3)CHH), 6.78-7.86 (m, 38 H, PPh3,
PPh2, C6H3).
X Abstract published in Advance ACS Abstracts, November 15, 1996.
(1) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197. (b) Bruce, M. I.;
Swincer, A. G. Adv. Organomet. Chem. 1983, 22, 59.
(2) Wiedemann, R.; Steinert, P.; Schafer, M.; Werner, H. J . Am.
Chem. Soc. 1993, 115, 9864.
(3) Fryzuk, M. D.; Huang, L.; McManus, N. T.; Paglia, P.; Rettig, S.
J .; White, G. S. Organometallics 1992, 11, 2979.
(4) Wiedemann, R.; Wolf, J .; Werner, H. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1244.
(10) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; Wiley: New York, 1994; Chapter 10, p 236.
(5) Selnau, H. E.; Merola, J . S. J . Am. Chem. Soc. 1991, 113, 4008.
S0276-7333(96)00800-X CCC: $12.00 © 1996 American Chemical Society

5454 Organometallics, Vol. 15, No. 26, 1996
Communications
the basal PPh3 at 23.3 ppm in RuCl2(PPh3)3. The
related square-pyramidal complex RuCl(PPh3)(NCN)
(NCN ) (Me2NCH2)2C6H3) has been recently character-
ized by X-ray diffraction.12 Metal complexes with PCP
and related cyclometalated bisphosphine ligands have
been reported for Ni, Pd, Pt, Rh, and Ir.13-15
In the hopes of preparing the vinylidene complex
RuCl(PPh3)(PCP)(CdCHPh), the reaction of RuCl(PCP)-
(PPh3) with phenylacetylene was carried out. RuCl-
(PPh3)(PCP) reacted with phenylacetylene to give a pale
green compound. Analytical data of the product indi-
cate that one molecule of PhCtCH has been incorpo-
1
rated into RuCl(PCP)(PPh3). In the H NMR spectrum
(in CDCl3), a vinyl proton signal was observed as a
singlet at 4.98 ppm. In the 13C{1H} NMR spectrum, the
signal of the methylene carbons of the PCP ligand
appeared as a virtual triplet at 37.8 ppm, indicating that
the PCP ligand is meridionally bound to ruthenium.16
The signals for the carbon atoms (both are quaternary,
as confirmed by 13C DEPT and 1H-13C-HETCOR 2D
experiments) attached on ruthenium were observed at
164.1 (td, J (PC) ) 12.8, 5.1 Hz) and 113.2 ppm (t, J (PC)
) 6.7 Hz). The other carbon signals were observed in
the region of 124.0-139.1 ppm. The absence of 13C
signals above 200 ppm implies that the product is not
a simple vinylidene complex.1 On the basis of the
spectroscopic data,17 the structure for the isolated
product could not be assigned with confidence.
F igu r e 1. Molecular structure of 4. Selected bond lengths
(Å) and angles (deg) are as follows: Ru-Cl, 2.497(2); Ru-
P(1), 2.440(2); Ru-P(2), 2.412(2); Ru-P(3), 2.243(2); Ru-
C(8), 2.007(5); Ru-C(16); 2.437(6); Ru-C(11), 3.079(7);
Ru-C(15), 3.080(7); C(7)-C(8), 1.341(8); C(8)-C(16),
1.468(9); C(11)-C(12), 1.367(11); C(12)-C(13), 1.372(11);
C(13)-C(14), 1.401(11); C(14)-C(15), 1.371(10); C(15)-
C(16), 1.421(9); C(16)-C(11), 1.413(9); P(1)-Ru-Cl,
96.43(5); P(1)-Ru-P(2), 159.17(6); P(1)-Ru-P(3),
96.72(6); P(1)-Ru-C(8), 79.7(2); P(1)-Ru-C(16), 79.5(2);
P(2)-Ru-Cl, 97.17(5); P(2)-Ru-P(3), 95.87(6); P(2)-Ru-
C(8), 81.0(2); P(2)-Ru-C(16), 80.4(2); P(3)-Ru-Cl,
101.70(6); P(3)-Ru-C(8), 105.1(2); P(3)-Ru-C(16),
142.1(2); C(8)-Ru-Cl, 153.2(2); C(8)-Ru-C(16), 37.0(2);
C(16)-Ru-Cl, 116.2(2); C(1)-C(7)-C(8), 131.1(6); C(7)-
C(8)-C(16), 129.5(6); C(7)-C(8)-Ru, 142.8(5); C(16)-C(8)-
Ru, 87.6(3); C(8)-C(16)-Ru, 55.4(3); C(8)-C(16)-C(11),
121.1(6); C(8)-C(16)-C(15), 120.2(6); Ru-C(16)-C(11),
102.9(4); Ru-C(16)-C(15), 102.8(4).
An X-ray diffraction study18 on the product reveals
that the isolated product is actually RuCl(PPh3){η4-
CHPhdC-2,6-(PPh2CH2)2C6H3} (4). Thus, one molecule
(11) (a) J ung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G.
Inorg. Chem. 1984, 23, 726. (b) Armit, P. W.; Boyd, A. S. F.;
Stephenson, T. A. J . Chem. Soc., Dalton Trans. 1975, 1663.
(12) Sutter, J . P.; J ames, S. L.; Steenwinkel, P.; Karlen, T.; Grove,
D. M.; Veldman, N.; Smeets, W. J . J .; Spek, A. L.; van Koten, G.
Organometallics 1996, 15, 941.
(13) (a) Liou, S. Y.; Gozin, M.; Milstein, D. J . Chem. Soc., Chem.
Commun. 1995, 1965 and references therein. (b) Liou, S. Y.; Gozin,
M.; Milstein, D. J . Am. Chem. Soc. 1995, 117, 9774.
(14) (a) Kaska, W. C.; Nemeh, S.; Shirazi, A.; Potuznik, S. Organo-
metallics 1988, 7, 13. (b) Nemeh, S.; J ensen, C.; Binamira-Soriaga,
E.; Kaska, W. C. Organometallics 1983, 2, 1442. (c) Cross, R. J .;
Kennedy, A. R.; Manojlovic-Muir, L.; Muir, K. W. J . Organomet. Chem.
1995, 493, 243. (d) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton
Trans. 1976, 1020.
(15) (a) Gorla, F.; Venanzi, L. M.; Albinati, A. Organometallics 1994,
13, 43. (b) Gorla, F.; Togni, A.; Venanzi, L. M.; Albinati, A.; Lianza, F.
Organometallics 1994, 13, 1607.
of PhCtCH is incorporated into the central aromatic
ring of the bisphosphine ligand in the form of the vinyl
substituent CdCHPh. The C-C bond formation reaction
is unexpected, especially in view of the fact that C-C
bond cleavage reactions13 were observed in the reactions
of related bisphosphine ligands with rhodium com-
plexes. For example, 1,3,5-Me3-2,6-(PPh2CH2)2C6H re-
acted with RhH(PPh3)3 under H2 pressure to give
Rh(PPh3)(3,5-Me2-2,6-(PPh2CH2)2C6H) and CH4.
Figure 1 shows the molecular structure of compound
4. The CdCHPh vinyl group is bonded to both ruthe-
nium and the central aromatic ring of the bisphosphine
ligand with Ru-C(8) ) 2.007(5) Å and C(8)-C(16) )
1.468(9) Å. The most unusual feature of the structure
is that the ruthenium center is also close to C(16).
Although the Ru-C(16) distance (2.437(6) Å) is quite
long compared to normal Ru-Ar bonds, it is close to the
Ru-C distances observed for some Ru-(ηn-hydrocarbon)
complexes. For example, the RusCH2 and RusC(OMe)
bond distances in the diene complex [Cp*Ru(η4-CH2dC-
(OMe)C(OMe)dCH2)Br2]CF3SO3 were observed at 2.180-
(7) and 2.428(7) Å, respectively.19 The distances be-
tween ruthenium and other carbons (C(11) to C(15)) of
(16) Wilkes, L. M.; Nelson, J . H.; McCusker, L. B.; Seff, K.; Mathey,
F. Inorg. Chem. 1983, 22, 2746 and references therein.
(17) Preparation of 4: a mixture of 0.16 g of RuCl(PPh3)(PCP) (0.18
mmol) and 0.10 mL of phenylacetylene (0.91 mmol) in dichloromethane
was stirred for 2 h to give a dark green solution. The solvent was
pumped away under vacuum. A pale green solid was obtained when
diethyl ether was added. The solid was collected on a filter frit, washed
with hexane, and dried under vacuum overnight. Yield: 0.16 g, 82%.
Anal. Calcd for C59H50Cl3P3Ru (4‚CH2Cl2): C, 71.49; H, 4.97. Found:
C, 71.32; H, 4.91. 31P{1H} NMR (161.70 MHz, CDCl3): δ -7.4 (d, J (PP)
) 33.3 Hz), 69.3 (t, J (PP) ) 33.3 Hz). 1H NMR (400 MHz, CDCl3): δ
2.67 (dt, J ) 13.7, 4.2 Hz, 2 H, CHH(C6H3)CHH), 3.90 (dt, J ) 13.5,
4.9 Hz, 2 H, CHH(C6H3)CHH), 4.98 (s, 1 H, CdCHPh), 6.60-8.24 (m,
43 H, PPh3, PPh2, C6H3, Ph). 13C{1H} NMR (75.49 MHz, CDCl3):
δ
37.8 (t, J ) 12.8 Hz, CH2), 113.2 (t, J (PC) ) 6.7 Hz, Ru-C(aryl), 164.1
(td, J (PC) ) 12.8, 5.1 Hz, Ru-C(vinyl)), 124.0-139.1 (m, other aromatic
and olefinic carbons). IR (KBr, cm-1): 3050 (m), 1619 (w), 1590 (m),
1567 (sh), 1481 (m), 1433 (s), 1401 (w), 1190 (m), 1092 (m), 745 (s),
698 (s), 535 (s), 506 (s), 434 (m).
(18) Crystallographic data for 4‚CH2Cl2: monoclinic, space group
P21/n (No. 14), a ) 13.400(1) Å, b ) 19.207(1) Å, c ) 19.902(3) Å, â )
103.91(1)°, V ) 4972.07(2) Å3, Z ) 4, Dcalcd ) 1.415 g cm-3. Cu KR
radiation, λ ) 1.541 84 Å, µ ) 53.5 cm-1, crystal size 0.05 × 0.10 ×
0.30 mm3. Of 9147 reflections collected (Enraf-Nonius CAD4 diffrac-
tometer, 296 K), 8747 were unique and 5540 were observed with Fo2
>
3σ(Fo2). The structure was solved by the Patterson method.
Hydrogen atoms are included as fixed contributions to the structure
(19) Gemel, C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organome-
tallics 1996, 15, 532.
factors. The R and Rw values were 0.054 and 0.071, respectively.

Communications
Organometallics, Vol. 15, No. 26, 1996 5455
the central aromatic ring are over 3 Å. Interaction of
both C(8) and C(16) with ruthenium is also reflected by
the angle of Ru-C(8)-C(16) (87.6(3)°), which is much
smaller than the value expected for an sp2 carbon
environment. Further evidence for the interaction is
from the 13C NMR spectrum, which showed signals at
164.1 ppm (td, J (PPh2-C) ) 12.8 Hz, J (PPh3-C ) 5.1
Hz) assignable to C(8) and 113.2 ppm (t, J (PPh2-C) )
6.7 Hz, coupling to PPh3 is not resolved) assignable to
C(16).
The short distance for Ru-C(16) could be attributed
to the geometry of the chelating ligand. Due to the
ligand geometry, the ruthenium has no choice but to be
close to C(16). Alternatively, there may be a real
bonding interaction between the ruthenium and the
central aromatic ring. Three electrons may formally be
donated from the arylvinyl ligand CArdCHPh to the
ruthenium center, which then satisfies the 18e rule. One
electron comes from the σ-bond to C(8) and the other
two by π-donation from the aromatic ring. In this
regard, it is noted that several η2- or ηn-benzyl com-
plexes of early transition metals (e.g. Cp2Zr(η2-CH2Ph)-
(CH3CN)]BPh4 and Cp*Mo(NO)(CH2SiMe3)(η2-CH2Ph))
and actinides (e.g. Cp*3Th(ηn-CH2Ph)3) have been re-
ported,20 in which the CH2Ph group also functions as a
3e donor.
Complex 4 is likely formed from the vinylidene
complex RuCl(PPh3)(PCP)(CdCHPh). Migratory inser-
tion of the aryl group of the PCP ligand at the R-carbon
atom of the vinylidene ligand would produce the prod-
uct. Unfortunately, we have not been able to observe
the vinylidene intermediates. Only starting material
3 and complex 4 were observed, when the reaction was
monitored by 31P{1H} NMR in the temperature range
220-298 K. Although we have not been able to isolate
the vinylidene complex yet, reactions of terminal acety-
lenes RCtCH with coordinatively unsaturated or labile
transition-metal complexes to give vinylidene complexes
are now well-established.1 A precedent for CsC bond
formation between vinylidene and aryl ligands comes
from the recent report by Werner and co-workers, in
which reaction of RhPh(P(i-Pr3))2dCdCHR with CO
gives Rh(CO)(P(i-Pr3))2CPhdCHR (R ) Ph, t-Bu).2
To test whether the coupling reaction would also occur
with other terminal acetylenes, reaction of HCtCC-
(OH)(Ph)CH3 with RuCl(PPh3)(PCP) was carried out.
This reaction leads to the formation of the analogous
coupling product RuCl(PPh3){η4-CH2dCPhCHdC-2,6-
(PPh2CH2)2C6H3} (5), which was characterized by el-
emental analysis and NMR spectroscopy.21 The pres-
ence of the CdCHCPhdCH2 unit is indicated by three
1
vinyl proton signals in the H NMR spectrum. Forma-
tion of the coupling product is supported by 13C NMR,
which displayed the signals for the carbons attached to
ruthenium at 112.5 (t, J (PC) ) 7.6 Hz, Ru-C(aryl)) and
166.9 ppm (dt, J (PC) ) 12.8, 5.7 Hz, RusC(vinyl)). As
reactions of HCtCC(OH)RR′ with ruthenium(II) com-
plexes can lead to hydroxyvinylidene22 or vinyl-
vinylidene23 complexes, the hydroxyvinylidene complex
RuCl(PPh3)(PCP)(CdCH-C(OH)(Ph)CH3 or the vinyl-
vinylidene complex RuCl(PPh3)(PCP)(CdCHCPhdCH2)
and possible intermediates for the formation of complex
5.
In summation, we have observed interesting coupling
reactions of PhCtCH and HCtCC(OH)(Ph)CH3 with
a cyclometalated aryl ligand to give unusual products.
We are now in the process of investigating the mecha-
nism and scope of the reactions.
Ack n ow led gm en t. We acknowledge financial sup-
port from the Hong Kong Research Grants Council and
Croucher Foundation.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic details, bond distances and angles, atomic coordi-
nates and equivalent isotropic displacement coefficients, aniso-
tropic displacement coefficients, and positional and thermal
parameters for hydrogen for 4 (9 pages). Ordering information
is given on any current masthead page.
OM960800B
(21) Preparation of 5: the procedure was similar to that described
for 4. The starting materials were RuCl(PPh3)(PCP) (0.20 g, 0.23 mmol)
and 2-phenyl-3-butyn-2-ol (0.34 g, 2.3 mmol). The product is a pale
green solid. Yield: 0.17 g, 74%. Anal. Calcd for C60H50ClP3Ru: C, 72.03;
H, 5.04. Found: C, 72.17; H, 5.10. 31P{1H} NMR (121.50 MHz,
CDCl3): δ -7.3 (J (PP) ) 31.8 Hz), 68.8 (t, J (PP) ) 31.8 Hz). 1H NMR
(300 MHz, CDCl3): δ 2.71 (dt, J ) 13.8, 4.4 Hz, 2 H, CHH(C6H3)CHH),
3.96 (dt, J ) 11.7, 4.8 Hz, 2 H, CHH(C6H3)CHH), 4.51 (s, 1 H, dCH),
4.92 (s, 1 H, dCH), 5.17 (s, 1 H, dH), 6.70-8.21 (m, 43 H, PPh3, PPh2,
C6H3, Ph). 13C{1H} NMR (75.49 MHz, CDCl3): δ 38.1 (t, J ) 12.7 Hz,
PCH2), 107.5 (s, dCH2), 112.5 (t, J (PC) ) 7.6 Hz, RusC(aryl)), 166.9
(dt, J (PC) ) 12.8, 5.7 Hz, Ru-C(vinyl), 126.7-144.8 (m, other aromatic
and olefinic carbons).
(22) See for example: (a) Le Lagadec, R.; Roman, E.; Toupet, L.;
Muller, U.; Dixneuf, P. H. Organometallics 1994, 13, 5030. (b) Werner,
H.; Rappart, T.; Wiedemann, W.; Wolf, J .; Mahr, N. Organometallics
1994, 13, 2721 and references therein.
(23) See for example: (a) Selegue, J . P.; Young, B. A.; Logan, S. L.
Organometallics, 1991, 10, 1972. (b) Cadierno, V.; Gamasa, M. P.;
Gimeno, J .; Gonzalez-Cueva, M.; Lastra, E.; Borge, J .; Garcia-Granda,
S.; Perez-Carreno, E. Organometallics 1996, 15, 2137.
(20) (a) Legzdins, P.; J ones, R. H.; Phillips, E. C.; Yee, V. C.; Trotter,
J .; Einstein, F. W. B. Organometallics 1991, 10, 986. (b) Dryden, N.
H.; Legzdins, P.; Phillips, E. C.; Trotter, J .; Yee, V. C.Organometallics
1990, 9, 883. (c) Dryden, N. H.; Legzdins, P.; Trotter, J .; Yee, V. C.
Organometallics 1991, 10, 2857. (d) J ordan, R. F.; LaPointe, R. E.;
Baenziger, N.; Hinch, G. D. Organometallics 1990, 9, 1539. (e) Latesky,
S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P. Organometallics
1985, 4, 902. (f) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols,
S. F.; Willett, R. J . Am. Chem. Soc. 1987, 109, 4111. (g) Mintz, E. A.;
Moloy, K. G.; Marks, T. J . J . Am. Chem. Soc. 1982, 104, 4692.