Phosphine substitution in indenyl- and cyclopentadienylruthenium complexes. Effect of the η5 ligand in a dissociative pathway

Article abstract of DOI:10.1021/om950428k

The indenyl complex [RuCl(η⁵-C₉H₇)(PPh₃) ₂] (1) reacts with monodentate (L: PMePh₂, PMe₂Ph, PMe₃) or bidentate [L-L: Ph₂PCH₂PPh₂ (dppm), Ph₂P(CH₂)₂PPh₂ (dppe)] phosphines to give monosubstituted [RuCl(η⁵-C₉H₇)(PPh₃)(L)], bisubstituted [RuCl(η⁵-C₉H₇)(L)₂], or chelated complexes [RuCl(η⁵-C₉H₇)(L-L)] in toluene or tetrahydrofuran. The corresponding cyclopentadienyl complex [RuCl(η⁵-C₅H₅)(PPh₃) ₂] (2) reacts similarly, at higher temperatures or longer reaction times. In refluxing toluene, PMe₃ and dppm give ionic products [Ru(η⁵-C₉H⁷)(L)₃]Cl. The kinetics of PPh₃ substitution by PMePh₂ and PMe₂Ph in tetrahydrofuran yield first-order rate constants that are independent of the concentration or the nature of phosphine. Rate decrease in the presence of added PPh₃ or saturation behavior at high [PPh₃] indicates that the reaction proceeds by a dissociative mechanism, in which extrusion of PPh₃ is rate determining. Kinetics for the reaction with PMePh₂ in the temperature range 12-40°C for the indenyl and 20-50°C for the cyclopentadienyl complex give the following activation parameters: ΔH^? = 26 ± 1 kcal mol^-1 and ΔS^? = 11 ± 2 cal mol^-1 K^-1 for 1 and ΔH^? = 29 ± 1 kcal mol^-1 and ΔS^? = 17 ± 2 cal mol^-1 K^-1 for 2. Complex 1 is 1 order of magnitude more reactive than 2, indicating more efficient stabilization of 16-electron intermediates RuCl(η⁵-ligand)(PPh₃) by the indenyl group. Cyclic voltammetry measurements for [RuCl(η⁵-ligand)(L)₂] in dichloromethane indicate that indenyl or pentamethylcyclopentadienyl complexes are oxidized at lower potentials than cyclopentadienyl complexes. Kinetics and electrochemistry suggest that indenyl is electron donating toward the metal fragment, with respect to cyclopentadienyl.

Full text of DOI:10.1021/om950428k

302
Organometallics 1996, 15, 302-308
P h osp h in e Su bstitu tion in In d en yl- a n d
Cyclop en ta d ien ylr u th en iu m Com p lexes. Effect of th e η5
Liga n d in a Dissocia tive P a th w a y
M. Pilar Gamasa, J ose´ Gimeno,* Covadonga Gonzalez-Bernardo, and
Blanca M. Mart´ın-Vaca
Instituto de Quı´mica Organometa´lica “Enrique Moles”, Departamento de Qu´ımica Orga´nica e
Inorga´nica, Facultad de Quı´mica, Universidad de Oviedo, 33071 Oviedo, Spain
Donato Monti and Mauro Bassetti*
Centro C.N.R. di Studio sui Meccanismi di Reazione, c/ o Dipartimento di Chimica,
Universita’ “La Sapienza”, 00185 Roma, Italy
Received J une 6, 1995X
The indenyl complex [RuCl(η5-C9H7)(PPh3)2] (1) reacts with monodentate (L: PMePh2,
PMe2Ph, PMe3) or bidentate [L-L: Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe)] phos-
phines to give monosubstituted [RuCl(η5-C9H7)(PPh3)(L)], bisubstituted [RuCl(η5-C9H7)(L)2],
or chelated complexes [RuCl(η5-C9H7)(L-L)] in toluene or tetrahydrofuran. The correspond-
ing cyclopentadienyl complex [RuCl(η5-C5H5)(PPh3)2] (2) reacts similarly, at higher temper-
atures or longer reaction times. In refluxing toluene, PMe3 and dppm give ionic products
[Ru(η5-C9H7)(L)3]Cl. The kinetics of PPh3 substitution by PMePh2 and PMe2Ph in tetrahy-
drofuran yield first-order rate constants that are independent of the concentration or the
nature of phosphine. Rate decrease in the presence of added PPh3 or saturation behavior
at high [PPh3] indicates that the reaction proceeds by a dissociative mechanism, in which
extrusion of PPh3 is rate determining. Kinetics for the reaction with PMePh2 in the
temperature range 12-40 °C for the indenyl and 20-50 °C for the cyclopentadienyl complex
give the following activation parameters: ∆Hq ) 26 ( 1 kcal mol-1 and ∆Sq ) 11 ( 2 cal
mol-1 K-1 for 1 and ∆Hq ) 29 ( 1 kcal mol-1 and ∆Sq ) 17 ( 2 cal mol-1 K-1 for 2. Complex
1 is 1 order of magnitude more reactive than 2, indicating more efficient stabilization of
16-electron intermediates RuCl(η5-ligand)(PPh3) by the indenyl group. Cyclic voltammetry
measurements for [RuCl(η5-ligand)(L)2] in dichloromethane indicate that indenyl or pen-
tamethylcyclopentadienyl complexes are oxidized at lower potentials than cyclopentadienyl
complexes. Kinetics and electrochemistry suggest that indenyl is electron donating toward
the metal fragment, with respect to cyclopentadienyl.
In tr od u ction
of indenyl complexes for a large number of transition
metals. The chemistry of bis(phosphine)ruthenium
auxiliaries η5 bonded to ligands of the cyclopentadienyl
family is an area of current active research.3 We have
recently reported on the preparation and reactivity of
novel indenylruthenium complexes, mainly with respect
to the chemistry of alkynyl, vinylidene, and carbene
derivatives.4 The synthetic features of metal-carbon
unsaturated moieties are also displayed in the reactions
of pentamethylcyclopentadienylruthenium (Cp*, C5Me5)
complexes.5 Moreover, the complex [RuCl(η5-Ind)-
(PPh3)2] has shown enhanced catalytic activity in redox
isomerizations of allylic alcohols.6
Indenyl (Ind, C9H7) transition metal complexes are
often characterized by greater reactivity with respect
to their cyclopentadienyl (Cp, C5H5) analogues, either
in stoichiometric1 or in catalytic processes.2 This evi-
dence has prompted widespread interest regarding both
the synthetic applications and the mechanistic features
X Abstract published in Advance ACS Abstracts, November 15, 1995.
(1) For recent leading references, see for instance: Frankcom, T.
M.; Green, J . C.; Nagy, A.; Kakkar, A. K.; Marder, T. B. Organome-
tallics 1993, 12, 3688.
(2) (a) Caddy, P.; Green, M.; Smart, L. E.; White, N. J . Chem. Soc.,
Chem. Commun. 1978, 839. (b) Cioni, P.; Diversi, P.; Ingrosso, G.;
Lucherini, A.; Ronca, P. J . Mol. Catal. 1987, 40, 337. (c) Marder, T.
B.; Roe, D. C.; Milstein, D. Organometallics 1988, 7, 1451. (d) Brunner,
H.; Fisch, K. Angew. Chem., Int. Ed. Engl. 1990, 1131. (e) Ceccon, A.;
Gambaro, A.; Santi, S.; Venzo, A. J . Mol. Catal. 1991, 69, 337. (f)
Halterman, R. L. Chem. Rev. 1992, 92, 965. (g) Trost, B. M.; Kulawiec,
R. J . J . Am. Chem. Soc. 1992, 114, 5579.
(3) (a) Halcrow, M. A.; Urbanos, F.; Chaudret, B. Organometallics
1993, 12, 955. (b) Trost, B. M.; Martinez, J . A.; Kulawiec, R. J .;
Indolese, A. F. J . Am. Chem. Soc. 1993, 115, 10402. (c) Mitsudo, T.;
Kokuryo, K.; Shinsugi, T.; Nakagawa, Y.; Watanabe, Y.; Takegami,
Y. Angew. Chem., Int. Ed. Engl. 1994, 33, 580. (d) Lindner, E.;
Haustein, M.; Fawzi, R.; Steimann, M.; Wegner, P. Organometallics
1994, 13, 5021. (e) Pertici, P.; Ballantini, V.; Salvadori, P.; Bennett,
We intend to explore the properties of [RuCl(η5-Ind)-
(4) (a) Gamasa, M. P.; Gimeno, J .; Mart`ın-Vaca, B. M.; Borge, J .;
Garc`ıa-Granda, S.; Perez-Carreno, E. Organometallics 1994, 13, 4045.
(b) Cadierno, V.; Gamasa, M. P.; Gimeno, J .; Lastra, E.; Borge, J .;
Garc`ıa-Granda, S. Organometallics 1994, 13, 745. (c) Cadierno, V.;
Gamasa, M. P.; Gimeno, J .; Lastra, E. J . Organomet. Chem. 1994, 474,
C27. (d) Cadierno, V.; Gamasa, M. P.; Gimeno, J .; Borge, J .; Garc`ıa-
Granda, S. J . Chem. Soc., Chem. Commun. 1994, 2495. (e) Gamasa,
M. P.; Gimeno, J .; Godefroy, I.; Lastra, E.; Mart`ın-Vaca, B. M.; Garc`ıa-
Granda, S.; Gutierrez-Rodriguez, A. J . Chem. Soc., Dalton Trans. 1995,
1901.
M. A. Organometallics 1995, 14, 2565. (f) For
Butenshon, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 636. (g) Davies,
S. G.; McNally, J . P.; Smallridge, J . Adv. Organomet. Chem. 1991, 30,
1.
a
summary, see
(5) (a) Le Lagadec, R.; Roman, E.; Toupet, L.; Muller, U.; Dixneuf,
P. H. Organometallics 1994, 13, 5030 and references cited therein. (b)
Touchard, D.; Haquette, P.; Daridor, A.; Toupet, L.; Dixneuf, P. H. J .
Am. Chem. Soc. 1994, 116, 11157.
0276-7333/96/2315-0302$12.00/0 © 1996 American Chemical Society

Ru Indenyl and Cyclopentadienyl Complexes
Organometallics, Vol. 15, No. 1, 1996 303
(PPh3)2] in basic reactions to understand the nature of
the intimate steps occurring at the metal center and to
describe in parallel the behavior of the corresponding
cyclopentadienyl complex. The chemistry of [RuCl(η5-
Cp)(PPh3)2] is characterized by facile displacement of
either chloride or one or both triphenylphosphine ligands,
affording cationic or neutral compounds, respectively,
depending on solvent and reaction conditions.7 The
synthesis of [RuCl(η5-Ind)(PPh3)2] and the formation of
ionic complexes have been reported.8 Pentamethylcy-
clopentadienyl complexes [RuX(η5-C5Me5)(phosphine)2]
have been described with regard to the kinetics for
trimethylphosphine exchange9 and with regard to the
relative binding energies of sterically demanding phos-
phines.10 The extrusion of a phosphine ligand to create
coordinative unsaturation at the metal center and the
effect of the spectator ligand on reactive 16-electron
intermediates obviously are of central relevance.
In this paper, we report on the exchange of PPh3 in
[RuCl(η5-Ind)(PPh3)2] and [RuCl(η5-Cp)(PPh3)2] by alkyl-
arylphosphines and on the kinetics and mechanisms of
some of these reactions.
Exp er im en ta l Section
Gen er a l Com m en ts. The reactions were carried out under
dry nitrogen using Schlenk techniques. All solvents were dried
by standard methods and distilled under nitrogen before use.
The complex [RuCl(η5-C9H7)(PPh3)2] and the phosphines Ph2-
PCH2PPh2 (dppm) and Ph2PCH2CH2PPh2 (dppe) were pre-
pared by literature methods. The phosphines PMePh2, PMe2Ph,
and PMe3 were available commercially. PMe2Ph used in the
kinetic experiments was distilled over sodium under argon.
Cyclic voltammetry measurements (25 °C) were carried out
with a three-electrode system. The working electrode was a
platinum disk electrode, the counter electrode was a platinum
spiral, and the reference electrode was an aqueous saturated
calomel electrode (SCE) separated from the solution by a
porous septum. Current and voltage parameters were con-
trolled by using a PAR system M273. In a typical experiment,
10-2 mmol of complex was dissolved under a nitrogen atmo-
sphere in 20 mL of recently distilled and deoxygenated
dichloromethane containing 0.77 g of pure NBu4PF6 (0.2 mol)
as electrolyte. The conductivities were measured at room
temperature, in ca. 10-3 mol dm-3 acetone solutions, with a
J enway PCM3 conductimeter. NMR spectra were recorded on
a Bruker AC300 instrument at 300 (1H), 121.5 (31P), or 75.4
MHz (13C) using SiMe4 and 85% H3PO4 as standards. The
following atom labels are used for the 1H and 13C{1H} NMR
spectroscopic data.
Ligand substitution reactions in indenyl transition
metal complexes proceed at faster rates than in the
corresponding cyclopentadienyl analogues. The higher
reactivity has been explained as the result of facile
metal ring slippage from η5 to η3 coordination of indenyl
and the consequent creation of a vacant coordination
site to host the entering ligand.11a,b In fact, the reactions
generally proceed by associative pathways for complexes
of the metals rhodium,2e,11b,c iridium,12 rhenium,13 and
manganese.14 On the other hand, carbonyl substi-
tutions in [MoX(η5-Ind)(CO)3] (X ) Cl, Br, I)11a and
[WCl(η5-Ind)(CO)3]15 proceed by mixed associative and
dissociative mechanisms and are still orders of magni-
tude faster than those of the Cp complexes. In the iron
triad, the carbonyl substitution reaction of [FeI(η5-Ind)-
(CO)2] by phosphorus donors is characterized by rate-
determining carbonyl dissociation and is independent
of the incoming ligand.16 The same reaction in the 19-
electron radical [Fe(η5-Ind)(CO)3] is also dissociative,
The parameter ∆δ(C-3a,7a) is defined as the difference be-
tween δ(C-3a,7a) of the indenyl complex and δ(C-3a,7a) of
sodium indenyl (δ ) 130.70 ppm).21 The term “Ind-6” in the
NMR data is used for the undefined signals of carbon and
hydrogen atoms at the 4, 5, 6 and 7 positions of the benzoid
ring.
although slower than that of [Fe(η5-Cp)(CO)3] by 103 s-1
,
displaying an “inverse indenyl effect”.17 With regard
to cyclopentadienyl complexes, although Co(I) and Rh-
(I) prefer associative routes,18 the majority of 18-electron
metal complexes undergo ligand substitution by dis-
sociative pathways.19 For instance, substitution in [Co-
(η5-Cp)(PPh3)2] proceeds by rate-determining loss of
PPh3.20
Syn th esis of In d en yl Com p lexes. (a ) P r ep a r a tion of
[Ru Cl(η5-C9H7)(P P h 3)L] [L ) P MeP h 2 (3a ), P Me2P h (3b),
a n d P Me3 (3c). Gen er a l P r oced u r e. A solution of the
complex [RuCl(η5-C9H7)(PPh3)2] (1) (776 mg, 1 mmol) and the
corresponding phosphine (1 mmol) in toluene (80 mL) was
heated until complete substitution of one triphenylphosphine
ligand was achieved, as monitored by 31P NMR. The toluene
was then evaporated under vacuum and the solid residue was
purified by column chromatography on silica, collecting the
band eluted with dichlomethane. Yield (%), temperature of
reaction (°C), reaction time, color, and electrochemical [1/2(Ep,a
+ Ep,c) in volts], analytical, and NMR spectroscopic data are
as follows. L ) PMePh2 (3a ): 65, 45, 3.5 h, orange, 0.43. Anal.
Calcd for RuC40H35P2Cl: C, 67.27; H, 4.94. Found: C, 66.91;
H, 4.85. 31P{1H} NMR (CDCl3) δ: 42.48 (d, J PP ) 41.5 Hz,
PMePh2), 45.61 (d, J PP ) 41.5 Hz, PPh3). 1H NMR (CDCl3) δ:
1.13 (d, 3H, J HP ) 10.0 Hz, PMePh2), 3.21 and 4.69 (br s, 1H
each, H-1 and H-3), 4.85 (m, 1H, H-2), 6.43 (m, 1H, Ind-6),
6.8-8.0 (m, 28H, PPh3, PMePh2 and Ind-6). 13C{1H} NMR
(CDCl3) δ: 11.90 (d, J CP ) 29.3 Hz, PPh2CH3), 68.88 and 69.11
(C-1 and C-3), 89.49 (C-2), 109.13 and 111.73 (C-3a and C-7a),
(6) Trost, B. M.; Kulawiec, R. J . J . Am. Chem. Soc. 1993, 115, 2027.
(7) (a) Ashby, G. S.; Bruce, M. I.; Tomkins, I. B.; Wallis, R. C. Austr.
J . Chem. 1979, 32, 1003. (b) Blackmore, T.; Bruce, M. I.; Stone, F. G.
A. J . Chem. Soc. A 1971, 2376.
(8) Oro, L. A.; Ciriano, M. A.; Campo, M.; Foces-Foces, C.; Cano, F.
H. J . Organomet. Chem. 1985, 289, 117.
(9) Bryndza, H. E.; Paciello, R. A.; Domaille, P. J .; Bercaw, J . E.
Organometallics 1989, 8, 379.
(10) Luo, L.; Nolan, S. P. Organometallics 1994, 13, 4781.
(11) (a) Hart-Davis, A. J .; White, C.; Mawby, R. J . Inorg. Chim. Acta
1970, 4, 441. (b) Rerek, M. E.; Basolo, F. J . Am. Chem. Soc. 1984, 106,
5908. (c) Kakkar, A. K.; Taylor, N. J .; Marder, T. B.; Shen, J . K.;
Hallinan, N.; Basolo, F. Inorg. Chim. Acta 1992, 198-200, 219.
(12) Habib, A.; Tanke, R. S.; Holt, E. M.; Crabtree, R. H. Organo-
metallics 1989, 8, 1225.
(13) (a) Bang, H.; Lynch, T. J .; Basolo, F. Organometallics 1992,
11, 40. (b) Casey, C. P.; O’Connor, J . M. Organometallics 1985, 4, 384.
(14) J i, L.-N.; Rerek, M. E.; Basolo, F. Organometallics 1984, 3, 740.
(15) Turaki, N. N.; Huggins, J . M.; Lebioda, L. Inorg. Chem. 1988,
27, 424.
(16) J ones, D. J .; Mawby, R. J . Inorg. Chim. Acta 1972, 6, 157.
(17) Pevear, K. A.; Banaszak Holl, M. M.; Carpenter, G. B.; Rieger,
A. L.; Rieger, P. H.; Sweigart, D. A. Organometallics 1995, 14, 512.
(18) (a) Wojcicki, A.; Basolo, F. J . Inorg. Nucl. Chem. 1961, 17, 77.
(b) Schuster-Woldan, H. G.; Basolo, F. J . Am. Chem. Soc. 1966, 88,
1657. (c) Weiller, B. H.; Wasserman, E. P.; Bradley Moore, C.;
Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 4326.
(19) (a) Basolo, F. Polyhedron 1990, 9, 1503. (b) Basolo, F. Coord.
Chem. Rev. 1982, 43, 7. (c) Chen, L.; Poe¨, A. J . Inorg. Chem. 1989, 28,
3641.
(20) J anowicz, A. H.; Bryndza, H. E.; Bergman, R. G. J . Am. Chem.
Soc. 1981, 103, 1516.
(21) Baker, R. T.; Tulip, T. H. Organometallics 1986, 5, 839.

304 Organometallics, Vol. 15, No. 1, 1996
Gamasa et al.
123.36 and 124.70 (Ind-6), 126.99-136.53 (m, Ph and Ind-6).
∆δ(C-3a,7a) ) -20.27 (av.). L ) PMe2Ph (3b): 60, 50, 2 h,
orange, 0.39; elemental analyses were unsatisfactory. 31P{1H}
NMR (CDCl3) δ: 25.72 (d, J PP ) 42.0 Hz, PMe2Ph), 47.56 (d,
triphenylphosphine ligand was achieved. The toluene was
then evaporated under vacuum and the solid residue was
purified by column chromatography over silica, collecting the
yellow band eluted with dichloromethane. Yield (%), temper-
ature of reaction (°C), reaction time, and electrochemical
[1/2(Ep,a + Ep,c) in volts], analytical, and NMR spectroscopic
data are as follows. L ) PMePh2 (5a ) (improvement of
published method): 65, 45, 4.5 h, 0.54. 1H NMR is in
agreement with published data. Additional data: 31P{1H}
NMR (CDCl3) δ: 33.09 (d, J PP ) 42.0 Hz, PPh2Me), 47.07 (d,
J PP ) 42.0 Hz, PPh3). L ) PMe2Ph (5b): 55, 50, 3 h, 0.50.
Anal. Calcd for RuC31H31P2Cl: C, 61.79; H, 5.15. Found: C,
61.51; H, 5.24. 31P{1H} NMR (CDCl3) δ: 12.54 (d, J PP ) 44.9
Hz, PPhMe2), 46.61 (d, J PP ) 44.9 Hz, PPh3). 1H NMR (CDCl3)
δ: 1.39 (d, 3H, J HP ) 8.8 Hz, PMeaMebPh), 1.48 (d, 9.0 Hz,
J HP ) 8.8 Hz, PMeaMebPh), 4.12 (br s, 5H, Cp), 7.28-7.51 (m,
24H, Ph).
(b) P r ep a r a tion of [Ru Cl(η5-C5H5)L2] [L ) P MeP h 2 (6a )
a n d P Me2P h (6b)]. Im p r ovem en t of P u blish ed Meth od .
A solution of the complex [RuCl(η5-C5H5)(PPh3)2] (2) (726 mg,
1 mmol) and the corresponding phosphine (2 mmol) in toluene
(80 mL) was refluxed until complete substitution of tri-
phenylphosphine was achieved. Toluene was then evaporated
under vacuum and the solid residue was purified by column
chromatography over silica, collecting the band eluted with
diethyl ether. Yield (%) and time of reaction are as follows
(analytical and NMR spectroscopic data are in agreement with
published values). L ) PMePh2 (6a ): 65, 2.5 h. L ) PMe2Ph
(6b): 45, 1.5 h.
Syn th esis of Ca tion ic Der iva tives. (a ) P r ep a r a tion of
[Ru (η5-C9H7)(P P h 3)(d p p m )]Cl. A solution of [RuCl(η5-C9H7)-
(PPh3)2] (776 mg, 1 mmol) and bis(diphenylphosphine)methane
(1 mmol) in toluene was refluxed for 15 min. A yellow
precipitate appeared. The solution was decanted and the solid
was washed with hexane (3 × 20 mL) and dried under vacuum.
Yield (%), conductivity (acetone, 20 °C, Ω-1 cm2 mol-1), and
analytical and NMR spectroscopic data are as follows: 70, 115.
Anal. Calcd for RuC52H44P3Cl: C, 69.52; H, 4.93. Found: C,
69.34; H, 4.63. 31P{1H} NMR (CDCl3) δ: 3.70 (d, J PP ) 28.9
Hz, dppm), 45.55 (d, J PP ) 28.9 Hz, PPh3). 1H NMR (CDCl3)
δ: 4.17 (dt, 1H, J HH ) 14.6 Hz, J HP ) 10.7 Hz, PCHaHbP), 4.9
(br s, 2H, H-1,3), 5.07 (dt, 1H, J HH ) 14.6 Hz, J HP ) 10.7 Hz,
PCHaHbP), 5.23 (br s, 1H, H-2), 6.15-7.34 (m, 39H, PPh2,
PPh3, and Ind-6).
(b) P r ep a r a tion of [Ru (η5-C9H7)(P Me3)3]Cl. A solution
of [RuCl(η5-C9H7)(PPh3)2] (776 mg, 1 mmol) and trimeth-
ylphosphine (3 mmol) in toluene was refluxed for 15 min. A
yellow precipitate appeared. The solution was decanted and
the solid was washed with hexane (3 × 20 mL) and dried under
vacuum. Yield (%), conductivity (acetone, 20 °C, Ω-1 cm2
mol-1), and analytical and NMR spectroscopic data are as
follows: 85, 127. Anal. Calcd for RuC18H34P3Cl: C, 45.05; H,
7.14. Found: C, 45.33; H, 7.09. 31P{1H} NMR (CDCl3) δ: 7.01
(PMe3). 1H NMR (CDCl3) δ: 1.46 (m, 18H, PMe3), 5.20 (d, 2H,
J HH ) 2.7 Hz, H-1,3), 5.35 (d, 2H, J HH ) 2.7 Hz, H-2), 7.23
and 7.48 (m, 2H each, H-4,7 and H-6,7).
J PP ) 42.0 Hz, PPh3). 1H NMR (CDCl3) δ: 1.18 (d, 3H, J HP
)
10.0 Hz, PMeaMebPh), 1.49 (d, 3H, J HP ) 10.0 Hz, PMeaMeb-
Ph), 3.15 and 4.47 (2 s, 1H each, H-1 and H-3), 4.58 (m, 1H,
H-2), 6.49 and 6.68 (m, 1H each, Ind-6), 7.10-7.62 (m, 22H,
PPh3, PMe2Ph, and Ind-6). 13C{1H} NMR (CDCl3) δ: 16.15 (d,
J CP ) 30.2 Hz, PMeaMebPh), 17.05 (d, J CP ) 30.8 Hz, PMeaMeb-
Ph), 66.22 and 66.38 (C-1 and C-3), 88.65 (C-2), 107.64 and
111.94 (C-3a and C-7a), 124.0, 124.32, and 126.51 (Ind-6),
126.51-137.15 (m, Ph, Ind-6). ∆δ(C-3a,7a) ) -20.91 (av.). L
) PMe3 (3c): 80, 30, 0.5 h, orange, 0.36. Anal. Calcd for
RuC30H31P2Cl: C, 61.07; H, 5.30. Found: C, 61.25; H, 5.28.
31P{1H} NMR (CDCl3) δ: 16.30 (d, J PP ) 44.8 Hz, PMe3), 50.10
(d, J PP ) 44.8 Hz, PPh3). 1H NMR (CDCl3) δ: 1.15 (d, 9H, J HP
) 9.8 Hz, PMe3), 3.47 and 4.91 (s, 1H each, H-1 and H-3), 5.19
(m, 1H, H-2), 6.74 and 7.01 (m, 1H each, Ind-6), 7.10-7.43
(m, 17H, PPh3, Ind-6). 13C{1H} NMR (CDCl3) δ: 19.05 (d, J CP
) 20.6 Hz, PMe3), 63.75 and 63.98 (C-1 and C-3), 87.99 (C-2),
107.84 and 111.56 (C-3a and C-7a), 123.84, 124.09, 126.24, and
127.15 (C-4,5,6,7), 127.38-135.57 (m, PPh3). ∆δ(C-3a,7a) )
-22.86 (av.).
(b) P r ep a r a tion of com p lexes [Ru Cl(η5-C9H7)L2] [L )
P MeP h 2 (4a ), P Me2P h (4b), d p p m (4c), d p p e (4d )]. Gen -
er a l P r oced u r e. A solution of the complex [RuCl(η5-C9H7)-
(PPh3)2] (1) (776 mg, 1 mmol) and the corresponding phosphine
(2 mmol of monodentate L, 1 mmol of bidentate L) in toluene
(80 mL) was refluxed until complete substitution of tri-
phenylphosphine was achieved (31P NMR). The toluene was
then evaporated under vacuum, and the solid residue was
purified by column chromatography over silica, collecting the
band eluted with diethyl ether for complexes 4a and 4b and
that with dichloromethane for complexes 4c and 4d . Yield
(%), reaction time, color, and electrochemical [1/2(Ep,a + Ep,c
)
in volts], analytical, and NMR spectroscopic data are as
follows. L ) PMePh2 (4a ): 80, 2 h, orange, 0.39. Anal. Calcd
for RuC35H33P2Cl: C, 64.46; H, 5.10. Found: C, 64.70; H, 5.38.
31P{1H} NMR (CDCl3) δ: 36.02 (PMePh2). 1H NMR (CDCl3)
δ: 1.36 (vt, J ) 9.1 Hz, 6H, PMePh2), 4.39 (br s, 2H, H-1,3),
4.60 (br s, 1H, H-2), 6.98 and 7.09 (m, 2H each, H-4,7 and
H-5,6), 7.14-7.41 (m, 20H, PMePh2). 13C{1H} NMR (CDCl3)
δ: 13.50 (vt, J ) 30.3 Hz, PMePh2), 64.14 (C-1,3), 89.20 (C-2),
109.80 (C-3a,7a), 123.91 and 126.83 (C-4,7 and C-5,6), 127.61-
132.37 (m, Ph). ∆δ(C-3a,7a) ) -20.90. L ) PMe2Ph (4b): 80,
1.5 h, orange, 0.31. Anal. Calcd for RuC25H29P2Cl: C, 56.87;
H, 5.54. Found: C, 57.10; H, 5.55. 31P{1H} NMR (CDCl3) δ:
21.71 (PMe2Ph). 1H NMR (CDCl3) δ: 1.37 (vt, J ) 9.4 Hz,
6H, PMeaMebPh), 1.55 (vt, J ) 8.7 Hz, 6H, PMeaMebPh), 4.41
(br s, 2H, H-1,3), 4.48 (br s, 1H, H-2), 7.12 and 7.26 (m, 2H
each, H-4,7 and H-5,6), 7.33-7.46 (m, 10H, PMe2Ph). 13C{1H}
NMR (CDCl3) δ: 15.93 (vt, J ) 30.3 Hz, PMeaMebPh), 18.42
(vt, J ) 29.6 Hz, PMeaMebPh), 61.99 (C-1,3), 87.06 (C-2), 109.62
(C-3a,7a), 124.02 and 126.07 (C-4,7 and C-5,6), 127.95-129.99
(m, Ph). ∆δ(C-3a,7a) ) -21.08. L2 ) dppm (4c): 80, 2 h, red,
0.39. Anal. Calcd for RuC34H29P2Cl: C, 64.14; H, 4.56.
Found: C, 63.89; H, 4.80; 31P{1H} NMR (CDCl3) δ: 15.37
Kin etic Mea su r em en ts. Manipulations were carried out
under argon, and tetrahydrofuran was distilled over potas-
sium/benzophenone. Kinetic experiments were carried out
under pseudo-first-order conditions, using a large excess of
phosphine, by UV-visible spectroscopy. The phosphines were
added as neat liquids by syringe to solutions of the ruthenium
complex in 1-cm quartz cells. Solutions of triphenylphosphine
were mixed with solutions of the complex. Several kinetic runs
were performed simultaneously in the instrument. The de-
crease in absorbance associated with the reaction was followed
with time. Pseudo-first-order rate constants (kobs) were ob-
tained by fitting the exponential dependence of absorbance vs
time data using a nonlinear least-squares regression program,
which provides kobs and A∞. Values of A∞ generally were well-
defined in the experiments and in agreement with calculated
ones. Fittings of kobs to eq 2, to give the parameters k1 and
(dppm). 1H NMR (CDCl3) δ: 4.25 (dt, J HH ) 14.2 Hz, J HP
11.4 Hz, PCHaHbP), 4.84 (br s, 3H, H-1,2,3), 4.96 (dt, J HH
)
)
14.2 Hz, J HP ) 10.2 Hz, PCHaHbP), 7.10-7.38 (m, 22H, PPh2,
Ind-6), 7.58 (m, 2H, Ind). 13C{1H} NMR (CDCl3) δ: 48.23 (t,
J CP ) 20.8 Hz, PCH2P), 62.79 (t, J CP ) 3 Hz, C-1,3), 85.50 (C-
2), 109.30 (t, J CP ) 2.5 Hz, C-3a,7a), 124.38 and 125.34 (C-4,7
and C-5,6), 127.82-138.15 (m, PPh2). ∆δ(C-3a,7a) ) -21.4.
L2 ) dppe (4d ): 80, 1.5 h, orange, 0.43. 31P{1H} NMR (CDCl3)
δ: 83.45 (dppe).
Syn th esis of Cyclop en ta d ien yl Com p lexes. (a ) P r ep a -
r a tion of [Ru Cl(η5-C5H5)(P P h 3)L] [L ) P MeP h 2 (5a ) a n d
P Me2P h (5b)]. A solution of [RuCl(η5-C5H5)(PPh3)2] (2) (726
mg, 1 mmol) and the corresponding phosphine (1 mmol) in
toluene (80 mL) was heated until complete substitution of one

Ru Indenyl and Cyclopentadienyl Complexes
Organometallics, Vol. 15, No. 1, 1996 305
(k2/k-1), were obtained with nonlinear least-squares calcula-
tions carried out by the program Kaleidagraph. Duplications
of single kinetic runs were reproducible to within 6%. Activa-
tion parameters for the reaction with PPh3 were obtained by
linear least-squares analysis of the dependence of ln(k2/T) on
1/T. Blank experiments on solutions of the ruthenium complex
(10-4 M) in the absence of phosphine showed no significant
decomposition during the time required for the kinetic runs
both in the dark and under irradiation.
Resu lts
F igu r e 1. UV-vis spectral changes in the reaction of
[RuCl(η5-C9H7)(PPh3)2] (1) with PMe2Ph in tetrahydrofuran
at 22 °C (cycle time, 30 min).
Rea ction s. The complex [RuCl(η5-C9H7)(PPh3)2] (1)
reacts with phosphines [L ) PMePh2, PMe2Ph, PMe3;
L-L ) Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe)]
to give the products of mono- or disubstitution of PPh3,
depending on the reaction conditions, in either tetrahy-
drofuran or toluene (eq 1). A similar reaction pattern
is displayed by the analogous cyclopentadienyl complex
[RuCl(η5-C5H5)(PPh3)2] (2), which, however, requires
more vigorous conditions than 1.
Ta ble 1. Rea ction of [Ru Cl(η5-C9H7)(P P h 3)2] (1)
w ith P MeP h 2 a n d P Me2P h
tetrahydrofuran
toluene
time conversionb
time conversionc
La
T (°C) (h)
(%)
T (°C) (h)
(%)
PMePh2
18
18
15
20
18
24
90
100
80
22
3
ca. 50:40:10
PMe2Ph
+L
f
-PPh3
+L
f
-PPh3
RuCl(η5-C9H7)(PPh3)L
L ) PMePh2 (3a )
L ) PMe2Ph (3b)
L ) PMe3 (3c)
RuCl(η5-C9H7)(PPh3)2
100
a
b
[L] ) 0.1-0.01 M. With respect to the starting material.
c 1/3a (monosubstituted)/4a (disubstituted).
Ta ble 2. Rea ction of [Ru Cl(η5-C5H5)(P P h 3)2]
(2) w ith P MeP h 2 a n d P Me2P h in
Tetr a h yd r ofu r a n (Con -
ver sion to Mon osu bstitu ted P r od u cts 5a or 5b)
RuCl(η5-C9H7)L2 (1)
L ) PMePh2 (4a )
L ) PMe2Ph (4b)
L2 ) dppm (4c)
La
T (°C)
time (h)
conversionb (%)
PMe2Ph
PMePh2
PMe2Ph or PMePh2
22
22
35-40
24
24
3
ca. 1
no reaction
ca. 50
70
L2 ) dppe (4d )
5
The complexes [RuCl(η5-C9H7)(PPh3)(L)] (3a , L )
PMePh2; 3b, L ) PMe2Ph; 3c, L ) PMe3) are obtained
selectively with respect to further substitution upon
reacting complex 1 with the appropriate phosphine in
a 1:1 molar ratio, in toluene just above room tempera-
ture. The disubstituted complexes [RuCl(η5-C9H7)(L)2]
(4a , L ) PMePh2; 4b, L ) PMe2Ph) are prepared in
refluxing toluene (2 h) using a 2-fold molar ratio of L.
Under the same reaction conditions, the two molecules
of PPh3 in 1 undergo substitution by either bis(di-
phenylphosphino)methane (dppm) or bis(diphenylphos-
phino)ethane (dppe) to give the chelated complexes
[RuCl(η5-C9H7)(L-L)] (4c, L-L ) dppm; 4d , L-L )
dppe). Instead, reaction of 1 with PMe3 or with the
chelating phosphine dppm proceeds to the formation of
cationic trisubstituted complexes [Ru(η5-C9H7)(PMe3)3]-
Cl or [Ru(η5-C9H7)(dppm)(PPh3)]Cl as insoluble ionic
species after heating under reflux for 15 min, even in
the presence of a 2-fold excess of PMe3. When the
mixture is heated for a longer time (2 h), complex [Ru-
(η5-C9H7)(dppm)(PPh3)]Cl yields the neutral species 4c.
The complexes [RuCl(η5-C5H5)(PPh3)(L)] (5a , L )
PMePh2; 5b, L ) PMe2Ph) and [RuCl(η5-C5H5)(L)2] (6a ,
L ) PMePh2; 6b, L ) PMe2Ph) have been prepared by
heating compound 2 in the presence of phosphine either
at 50 °C (monosubstituted) or at reflux (disubstituted)
in toluene. Complexes 4d , 5a , 6a , and 6b have been
previously described;22,23 we report here an improved
preparation or additional characterization.
7
80-90
a
b
[L] ) 0.01 M. With respect to the starting material.
The progress of the reaction and consecutive forma-
tion of mono- and disubstitution products have been
monitored conveniently by 31P NMR. By choosing the
appropriate temperature, it is possible to selectively
obtain monosubstitution (also in the presence of excess
phosphine). The conditions under which monosubsti-
tuted complexes are formed from [RuCl(η5-C9H7)(PPh3)2]
(1) or from [RuCl(η5-C5H5)(PPh3)2] (2) are reported in
Tables 1 and 2, respectively. Although reactions proceed
similarly in tetrahydrofuran and in toluene, monosub-
stitution occurs more selectively at room temperature
in the former solvent. Tetrahydrofuran therefore has
been the solvent of choice to study the kinetics of
triphenylphosphine exchange by PMePh2 or PMe2Ph in
complexes 1 and 2 to yield 3a or 3b and 5a or 5b.
Kin etics. Both 31P NMR and UV-vis spectroscopy
have been used to follow the first step in eq 1. In the
presence of at least a 10-fold excess of phosphine, the
increase in the NMR signal of 3a ,b or the decrease in
the absorbance of 1, in the range 400-550 nm, exhibits
first-order behavior when plotted vs time and gives
similar values of half-life times (∼4 h, 20 °C). For
convenience, UV-vis spectroscopy has been used to
obtain most experimental data. The spectral changes
observed in the reaction of 1 (8.5 × 10-4 M) with PMe2-
Ph (0.066 M) in tetrahydrofuran (22 °C) are shown in
Figure 1. Absorbance increases between 360 and 400
nm and decreases at higher wavelengths clearly define
an isosbestic point at 400 nm. Values (A) taken at 426
(22) Lomprey, J . R.; Selegue, J . P. J . Am. Chem. Soc. 1992, 111,
5518.
(23) Treichel, P. M.; Komar, D. A.; Vincenti, P. J . Synth. React. Inorg.
Met.-Org. Chem. 1984, 14, 383.
and 520 nm vs time yield observed rate constants (kobs
)

306 Organometallics, Vol. 15, No. 1, 1996
Gamasa et al.
Ta ble 3. Obser ved Ra te Con sta n ts (kobs) for th e
Rea ction of Ru Cl(η5-C9H7)(P P h 3)2 (1) w ith P MeP h 2
a t Differ en t Tem p er a tu r es in Tetr a h yd r ofu r a n
T (°C)
11.9
[PMePh2] (M)
[PPh3] (M)
kobs (s-1
)
0.0663
0.131
0.256
0.0111
0.0267
0.0663
0.131
0.256
0.375
0.0663
0.131
0.256
0.0663
0.131
0.0132
0.0267
0.0663
0.131
0.192
0.256
0.131
0.131
0.131
0.131
0.131
0.131
1.31 × 10-5
1.28 × 10-5
1.25 × 10-5
4.13 × 10-5
3.95 × 10-5
4.34 × 10-5
4.61 × 10-5
4.43 × 10-5
4.30 × 10-5
2.04 × 10-4
2.10 × 10-4
2.05 × 10-4
8.65 × 10-4
8.28 × 10-4
1.39 × 10-5
2.38 × 10-5
4.72 × 10-5
7.43 × 10-5
9.08 × 10-5
10.3 × 10-5
1.91 × 10-4
1.73 × 10-4
1.45 × 10-4
1.15 × 10-4
9.4 × 10-5
20.0
30.0
F igu r e 2. Observed rate constants (kobs) for the reaction
of [RuCl(η5-C9H7)(PPh3)2] (1) with PMePh2 (a) and with
PMePh2 (b) in the presence of PPh3 (0.51 M) in tetrahy-
drofuran at 30 °C.
39.9
30.0
0.51
0.51
0.51
0.51
0.51
0.51
0.011
0.046
0.128
0.249
0.366
0.567
30.0
6.97 × 10-5
Ta ble 4. Obser ved Ra te Con sta n ts (kobs) for th e
Rea ction of [Ru Cl(η5-C5H5)(P P h 3)2] (2) w ith
P MeP h 2 a t Differ en t Tem p er a tu r es in
Tetr a h yd r ofu r a n
T (°C)
20.6
[PMePh2] (M)
[PPh3] (M)
kobs (s-1
)
0.066
0.131
0.256
0.375
0.027
0.066
0.131
0.256
0.375
0.066
0.192
0.0663
0.131
0.256
0.375
0.247
0.247
0.247
0.247
0.247
0.247
4.5 × 10-6
5.6 × 10-6
4.7 × 10-6
5.5 × 10-6
3.0 × 10-5
2.8 × 10-5
2.8 × 10-5
3.0 × 10-5
2.8 × 10-5
1.30 × 10-4
1.37 × 10-4
5.75 × 10-4
5.67 × 10-4
5.93 × 10-4
6.03 × 10-4
1.22 × 10-4
1.09 × 10-4
9.72 × 10-5
8.10 × 10-5
6.98 × 10-5
5.13 × 10-5
F igu r e 3. Observed rate constants (kobs) for the reaction
of [RuCl(η5-C5H5)(PPh3)2] (2) with PMePh2 (0.131 M) at
increasing concentrations of PPh3 in tetrahydrofuran at 40
°C.
30.0
Ta ble 5. Obser ved Ra te Con sta n ts (kobs) for th e
Rea ction of [Ru Cl(η5-C9H7)(P P h 3)2] (1)a a n d
[Ru Cl(η5-C5H5)(P P h 3)2] (2)b w ith P Me2P h in
Tetr a h yd r ofu r a n
40.1
50.6
Ind
Cp
[PMe2Ph] (M) kobs (s-1 × 105) [PMe2Ph] (M) kobs (s-1 × 105)
0.0024
0.0048
0.0091
0.0175
0.0523
0.138
4.33
4.43
4.35
4.07
4.33
4.52
4.68
4.60
0.035
0.104
0.205
0.335
0.490
2.72
2.35
2.67
2.38
2.37
40.1
0.015
0.050
0.133
0.226
0.341
0.545
0.270
0.490
of 4.9 × 10-5 and 4.8 × 10-5 s-1, respectively, whereas
data at 366 nm, where absorbance increases, do not give
a clean first-order fit. Most experiments therefore have
been carried out in the range 420-430 nm. Very similar
spectral changes are displayed in the presence of
PMePh2.
a
b
T ) 20.0 °C. T ) 30.0 °C.
[PPh3] is shown graphically in Figure 3. Reaction rates
appear to be independent of either the concentration or
the nature of the reacting phosphine.
Observed rate constants from measurements at dif-
ferent concentrations of phosphine and temperatures
are reported in Table 3 for the reaction of 1 and in Table
4 for the reaction of 2 with PMePh2. Data for the
reactions of both 1 and 2 with PMe2Ph are reported in
Table 5. The effect of PPh3 in large excess has been
observed at increasing concentrations of PMePh2 at 30
°C (Figure 2). Experiments have also been carried out
for the reaction with PMePh2 at different concentrations
of PPh3. The rate reduction that occurs upon increasing
Electr och em istr y. Different complexes [RuCl(η5-
ligand)L2] have been studied in CH2Cl2 solutions (25 °C)
by cyclic voltammetry. Table 6 lists oxidation potential
data for the novel indenyl mono- and disubstituted
complexes, along with those of analogous cyclopentadi-
enyl and pentamethylcyclopentadienyl5a,23 complexes.
The compounds undergo one-electron oxidation, which
is chemically reversible under the experimental condi-
tions.

Ru Indenyl and Cyclopentadienyl Complexes
Organometallics, Vol. 15, No. 1, 1996 307
Ta ble 6. Electr och em ica l P oten tia ls for Red ox
Cou p lesa
Ta ble 7. Rea ction P a r a m eter s for P P h 3
Su bstitu tion in [Ru Cl(η5-C9H7)(P P h 3)2] (1) a n d
[Ru Cl(η5-C5H5)(P P h 3)2] (2) in Tetr a h yd r ofu r a n
[RuCl(η5-ligand)(L2)] h [RuCl(η5-ligand)(L2)]+ + e
T
k1 (×105)
∆Hq
∆Sq
ligand (°C)
L
(s-1
)
k2/k-1 (kcal mol-1) (cal mol-1 K-1
)
Ind 12.1 PMePh2 1.3 ( 0.1
20.0 PMePh2 4.2 ( 0.2
30.0 PMePh2 21 ( 1
26 ( 1
29 ( 1
11 ( 2
1/2(Ep,a + Ep,c
(V, vs SCE)
)
Ep,a + Ep,c
compound
(mV)
2.0
1.6
[RuCl(η5-C9H7)(PPh3)2] (1)
0.45
0.43
0.39
0.36
0.39
0.31
0.39
0.43
0.56
0.54
0.50
0.52
0.44
0.49
0.51
0.43
0.30
0.33
66
68
64
64
64
39.9 PMePh2 85 ( 3
[RuCl(η5-C9H7)(PPh3)(PMePh2)] (3a )
[RuCl(η5-C9H7)(PPh3)(PMe2Ph)] (3b)
[RuCl(η5-C9H7)(PPh3)(PMe3)] (3c)
[RuCl(η5-C9H7)(PPh2Me)2] (4a )
[RuCl(η5-C9H7)(PMe2Ph)2] (4b)
[RuCl(η5-C9H7)(dppm)] (4c)
20.0 PMe2Ph 4.4 ( 0.2
Cp 20.6 PMePh2 0.50 ( 0.05
30.0 PMePh2 2.9 ( 0.2
40.1 PMePh2 13.5 ( 1
50.6 PMePh2 58 ( 2
17 ( 2
70
62
30.0 PMe2Ph 2.5 ( 0.2
[RuCl(η5-C9H7)(dppe)] (4d )
64
[RuCl(η5-C5H5)(PPh3)2] (2)
360b
72
When k2[L] is larger than k-1[PPh3], then the expression
reduces to kobs ) k1. This is infact the condition shown
by the kinetic measurements which exhibit a first order
dependence on 1 and 2, and no dependence on L (Figure
2, Tables 3, 4, 5). The constant k1 represents the rate
of thermal ligand dissociation from RuCl(η5-ligand)-
(PPh3)2 to yield an intermediate species of empirical
formula RuCl(η5-ligand)(PPh3), including solvation ef-
fects on the two species.
When the concentration of PMePh2 is kept constant
in different runs, the reaction rate is retarded by added
PPh3 (Figure 3), which competes with PMePh2 for the
intermediate RuCl(η5-ligand)(PPh3). A plot of 1/kobs vs
[PPh3] is linear, as predicted by eq 3. The ordinate
[RuCl(η5-C5H5)(PPh3)(PMePh2)] (5a )
[RuCl(η5-C5H5)(PPh3)(PMe2Ph)] (5b)
[RuCl(η5-C5H5)(PMePh2)2] (6a )
[RuCl(η5-C5H5)(PMe2Ph)2] (6b)
[RuCl(η5-C5H5)(dppm)] (6c)
70
110b
340b
340b
110b
240b
70c
270b
[RuCl(η5-C5H5)(dppe)] (6d )
[RuCl(η5-C5Me5)(PPh3)2] (7)
[RuCl(η5-C5Me5)(PMe2Ph)2] (7b)
[RuCl(η5-C5Me5)(dppe)] (7d )
Cyclic voltammetry in CH2Cl2. Reference 23. c Reference 5a.
a
b
Sch em e 1
k-1[PPh3]
1
kobs
1
k1
)
+
(3)
k1k2[PMePh2]
intercept yields the k1 value 2.04 × 10-4 s-1 for complex
1, in good agreement with the directly observed rate
constants obtained at 30 °C (kobs ) k1, Table 3). In
experiments at increasing [PMePh2] and a high constant
concentration of PPh3, a saturation effect is observed
(Figure 2), as expected for a situation in which k-1[PPh3]
= k2[L], so that eq 2 holds in its extended form. Fitting
of the experimental points with the equation also gives
a ratio of rate constants (k2/k-1) ) 2 at 30 °C, in
agreement with a faster attack of PMePh2 than PPh3
on the intermediate RuCl(η5-Ind)(PPh3). The positive
values of entropy of activation are consistent with the
proposal that PPh3 dissociation is rate limiting (k1). The
overall reaction parameters are listed in Table 7.
All of the experimental evidence therefore is in
harmony with the dissociative mechanism depicted in
Scheme 1. An alternative mechanism implying the
formation of ring-slipped η3 intermediates, which is very
common in the reactions of indenyl complexes,11-14 may
be involved in the case of rate-determining solvent (S)
coordination in 1 to give (S)RuCl(η3-Ind)(PPh3)2, fol-
lowed by PPh3 extrusion. This would also exhibit zero-
order dependence on L, although a strong solvent effect
(tetrahydrofuran vs toluene) should be expected, which
is not the case in these reactions.
Discu ssion
The driving force in the reactions of eq 1 is either
stabilization of the product by chelation or formation
of less congested complexes. There are in fact many
examples showing that phosphine extrusion is governed
by the steric bulk of the dissociating molecule.10,24 For
instance, loss of PMe3 in [RuX(η5-C5Me5)(PMe3)2] is
achieved only at temperatures around 100 °C.9 The
triphenylphosphine molecule in [RuCl(η5-ligand)(PPh3)-
(L)] is bound more tightly than in 1, and displacement
of chloride can effectively compete with PPh3 dissocia-
tion in the presence of a chelating ligand. The electro-
chemical data [1/2(Ep,a + Ep,c)] reported in Table 6 for
the redox couples [RuCl(η5-ligand)L2]/[RuCl(η5-ligand)-
L2]+ indicate that 17-electron complexes are formed at
lower potential from indenyl and pentamethylcyclopen-
tadienyl species than from the cyclopentadienyl ana-
logues. With respect to PPh3-substituted complexes,
coordination by chelating or by σ-donor alkylarylphos-
phines also reduces the oxidation potential.
The lack of rate dependence on the concentration or
the nature of phosphine for the substitution of PPh3 by
PMePh2 or PMe2Ph (L) in [RuCl(η5-Ind)(PPh3)2] and
[RuCl(η5-Cp)(PPh3)2] suggests that the reactions proceed
by a dissociative mechanism, as indicated in Scheme 1
for complex 1. This is described by the rate law shown
in eq 2:
Group 9 metal-carbonyl complexes of the type M(η5-
ligand)(CO)2 (M ) Co, Rh) have been known for years
to undergo carbonyl substitution by an associative
mechanism via the formation of ring-slipped η3 inter-
mediates or SN2 type transition states. In the case of
M ) Rh, direct rate measurements of CO substitution
by PPh3 exhibited a tremendous difference in reactivity
(108 M-1 s-1) for the second-order rate constant between
indenyl and cyclopentadienyl complexes, which has
k1k2[L]
kobs
)
(2)
k-1[PPh3] + k2[L]
(24) Darensbourg, D. J . Adv. Organomet. Chem. 1982, 21, 113.

308 Organometallics, Vol. 15, No. 1, 1996
Gamasa et al.
become known as the indenyl ligand effect.11b On the
other hand, when the ligand is a weaker and sterically
bulky triphenylphosphine instead of carbonyl, as in [Co-
(η5-Cp)(PPh3)2], substitution of PPh3 by PMe3 proceeds
by a clean dissociative mechanism (toluene, -60 °C),
in a pattern very similar to that observed in the present
study.20 Competition between PMe3 and PPh3 for Co-
(η5-Cp)(PPh3) gave a ratio of rate constants (k2/k-1) )
4, which can be compared with the value (k2/k-1) ) 2
for competition between PMePh2 and PPh3 in the
indenylruthenium system, although at a different tem-
perature.
In metals of group 8, a direct comparison for the
reactivity of indenyl and cyclopentadienyl compounds
is available from the measurements of carbonyl substi-
tution by phosphites in the complexes Fe(η5-ligand)-
(CO)2I (ligand ) Cp, indenyl, and tetrahydroindenyl).16
Although substitution involved strongly bound carbonyl
ligands, the mechanism was found to be dissociative,
and the indenyl complex was estimated to react 600
times faster than the cyclopentadienyl analogue. Such
an effect in a dissociative mechanism was explained as
the result of a favorable electronic interaction between
the aromatic six-membered ring of indenyl and the
metal to compensate for weakening of the metal-CO
bond in the transition state. It has now been reported
that the 19-electron radicals Fe(η5-ligand)(CO)3 ex-
change CO with P and As donors via a strictly dissocia-
tive mechanism, that ring slippage phenomena are not
involved, and that the rate constant for the cyclopen-
tadienyl species is 103 s-1 greater than that of indenyl,
giving an inverse indenyl effect.17
corresponding cyclopentadienyl derivative to form tran-
sient 16-electron species RuCl(η5-ligand)(PPh3) through
a mechanism that excludes the occurrence of η3 inter-
mediates. The small effect thus depends on different
intrinsic properties of the indenyl group. The possibility
of rate enhancements due to a less stable ground state
in indenyl than in Cp complexes has been suggested.25
It is also feasible that indenyl, acting as an electron
reservoir toward the metal fragment RuCl(PPh3)2 in 1
or RuCl(PPh3) in the transient, favors ruthenium-
phosphorus bond rupture or stabilizes the 16-electron
intermediate. The results of cyclic voltammetry are in
agreement with this intepretation, since the easier
oxidation of the indenyl complexes suggests higher
electron density at the metal. Indenyl has already been
described as a stronger donor than cyclopentadienyl
from photoelectron spectroscopy studies of rhodium(I)
complexes Rh(η5-ligand)(L)2 (L ) ethylene, CO)1 and
from infrared data of iron(II) complexes Fe(η5-ligand)-
(CO)2R.26 From this work and from the literature, it is
clear that the higher reactivity of indenyl complexes not
only depends on ring slippage isomerizations but that
more involved phenomena come into play.
Ack n ow led gm en t. Financial support from DGICYT
(Project PB93-325), a fellowship from FICYT de As-
turias (B.M.M.-V.), and a travel award from NATO
(Collaborative Research Grant 950794) are gratefully
acknowledged.
OM950428K
(25) Kubas, G. J .; Kiss, G.; Hoff, C. D. Organometallics 1991, 10,
2870.
(26) Ambrosi, L.; Bassetti, M.; Buttiglieri, P.; Mannina, L.; Monti,
D.; Bocelli, G. J . Organomet. Chem. 1993, 455, 167.
In the present study, an indenylruthenium complex
dissociates PPh3 an order of magnitude faster than the