A facile route to 1-trifluoromethyl-2,3,4,5-tetramethylcyclopentadienyl ruthenium half- and mixed-sandwich compounds

Article abstract of DOI:10.1021/om010863g

A series of half- and mixed-sandwich (Cp^? = 1-trifluoromethyl-2,3,4,5-tetramethylcyclopentadienide) ruthenium compounds have been synthesized from a new Cp^?Ru synthon, [Cp^?Ru(NCCH₃)₃](PF₆). [Cp^?Ru-(NCCH₃)₃J(PF₆) is efficiently generated by photolysis of [Cp^?RuBz](PF₆) in acetonitrile with a quantum yield of approximately 0.34. The methods described here should be useful for the synthesis of other compounds that contain the Cp^?Ru group.

Full text of DOI:10.1021/om010863g

Organometallics 2002, 21, 993-996
993
A F a cile Rou te to
1-Tr iflu or om eth yl-2,3,4,5-tetr a m eth ylcyclop en ta d ien yl
Ru th en iu m Ha lf- a n d Mixed -Sa n d w ich Com p ou n d s
J on K. Evju and Kent R. Mann*
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431
Received October 2, 2001
Summary: A series of half- and mixed-sandwich (Cpq )
1-trifluoromethyl-2,3,4,5-tetra methylcyclopenta dien-
ide) ruthenium compounds have been synthesized from
a new CpqRu synthon, [CpqRu(NCCH3)3](PF6). [CpqRu-
(NCCH3)3](PF6) is efficiently generated by photolysis of
[CpqRuBz](PF6) in acetonitrile with a quantum yield of
approximately 0.34. The methods described here should
be useful for the synthesis of other compounds that
contain the CpqRu group.
cyclopentadienide (Cpq), that is electronically similar to
Cp,18,19 but sterically similar to Cp*.19 So far, only a few
CpqRu compounds have been studied.20-22 CpqRu(CO)2I
has allowed new CpqRu half-sandwich compounds to be
prepared, but the possibilities are limited to complexes
with at least one carbonyl ligand.20 More recently, [Cpq-
RuCl2]2, the Cpq analogue of [Cp*RuCl2]2, was re-
ported,21 but its synthetic utility is somewhat limited22
and the procedures involve multistep syntheses. The
synthesis of more useful Cpq analogues of the Cp**Ru
and CpRu synthons has been hampered by the instabil-
ity of simple salts containing the Cpq anion.19 It was
clear that a new CpqRu synthon was required to produce
a wider range of complexes for comparison with existing
CpRu and Cp*Ru complexes. We chose as a target [Cpq-
Ru(NCCH3)3]+, an analogue of [CpRu(NCCH3)3]+ 23-25
with high versatility for preparing sandwich and half-
sandwich compounds under very mild reaction condi-
tions. Other analogues of this reactant ([Cp*Ru-
(NCCH3)3]+ 25-28 and [CpOs(NCCH3)3]+ 29,30) have previ-
ously been developed. The synthesis of [CpqRu(NCCH3)3]+
and its initial development as a synthon for half-
sandwich CpqRu complexes is reported herein.
In tr od u ction
Ruthenium half-sandwich complexes with the auxil-
iary η5-cyclopentadienide (Cp), η5-pentamethylcyclopen-
tadienide (Cp*), or other substituted η5-cyclopentadien-
ide ligands have been of interest because they give
stable compounds with a wide range of ligands in the
remaining three coordination sites.1-14 Many of the
CpRu and Cp*Ru compounds are catalytically active,15
and they frequently have interesting electrochemical
and spectroscopic properties.4,6,7,10,16 It has also been
observed that the differences in the Cp and Cp* ligands
produce complexes with unique reactivity and properties
through a combination of steric and electronic effects
at the metal center.17
Exp er im en ta l Section
In 1992, Gassman, Mickelson, and Sowa introduced
a new ligand, 1-trifluoromethyl-2,3,4,5-tetramethyl-
Gen er a l Con sid er a tion s. All reactions were carried out
using standard Schlenk line techniques under a nitrogen or
argon atmosphere. Solvents were supplied by Fisher Scientific
* To whom correspondence should be addressed.
(1) Pigge, F. C.; Coniglio, J . J . Curr. Org. Chem. 2001, 5, 757.
(2) Bleeke, J . R.; Hinkle, P. V.; Rath, N. P. Organometallics 2001,
20, 1939.
(3) Slugovc, C.; Ru¨ba, E.; Schmid, R.; Kirchner, K.; Mereiter, K.
Monatsh. Chem. 2000, 131, 1241.
(4) Weinberger, D. A.; Higgins, T. B.; Mirkin, C. A.; Stern, C. L.;
Liable-Sands, L. M.; Rheingold, A. L. J . Am. Chem. Soc. 2001, 123,
2503.
(5) Buntem, R.; Gallagher, J . F.; Lewis, J .; Raithby, P. R.; Rennie,
M.-A.; Shields, G. P. J . Chem. Soc., Dalton Trans. 2000, 23, 4297.
(6) Dysard, J . M.; Tilley, T. D. Organometallics 2000, 19, 4726.
(7) Contakes, S. M.; Beatty, S. T.; Dailey, K. K.; Rauchfuss, T. B.;
Fenske, D. Organometallics 2000, 19, 4767.
(8) Simanko, W.; Tesch, W.; Sapunov, V. N.; Mereiter, K.; Schmid,
R.; Kirchner, K.; Coddington, J .; Wherland, S. Organometallics 1998,
17, 5674.
(9) Lewis, J .; Morewood, C. A.; Raithby, P. R.; De Arellano, Ramirez,
C. M. J . Chem. Soc., Dalton Trans. 1997, 18, 3335.
(10) Graf, D. D.; Mann, K. R. Inorg. Chem. 1997, 36, 141.
(11) Glatzhofer, D. T.; Liang, Y.; Khan, M. A. Organometallics 1993,
12, 624.
(12) Luginbuehl, W.; Zbinden, P.; Pittet, P. A.; Armbruster, T.;
Buergi, H. B.; Merbach, A. E.; Ludi, A. Inorg. Chem. 1991, 30, 2350.
(13) Fish, R. H.; Kim, H. S.; Fong, R. H. Organometallics 1991, 10,
770.
(14) Miller, D. C.; Angelici, R. J . Organometallics 1991, 10, 79.
(15) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001,
101, 2067.
(18) Gassman, P. G.; Sowa, J . R., J r.; Hill, M. G.; Mann, K. R.
Organometallics 1995, 14, 4879.
(19) Gassman, P. G.; Mickelson, J . W.; Sowa, J . R., J r. J . Am. Chem.
Soc. 1992, 114, 6942.
(20) Barthel-Rosa, L. P.; Sowa, J . R.; Gassman, P. G.; Fischer, J .
McCarty, B. M.; Goldsmith, S. G.; Gibson, M. T.; Nelson, J . T.
Organometallics 1997, 16, 1595.
(21) (a) Gusev, O. G.; Ievlev, M. A.; Peganova, R. A.; Peterleitner,
M. G.; Petrovskii, P. V.; Oprurenko, Y. F. and Ustunyuk, N. A. J .
Organomet. Chem. 1998, 551, 93. (b) Gusev, O. G.; Ievlev, M. A.;
Lyssenko, K. A.; Petrovskii, P. V.; Ustunyuk, N. A.; Maitilis, P. M.
Inorg. Chim. Acta 1998, 280, 249.
(22) Ru¨ba, E.; Simanko, W.; Mauthner, K.; Soldouzi, K. M.; Slogovc,
C.; Mereiter, K.; Schmid, R. and Kirchner, K. Organometallics 1999,
18, 3843.
(23) Gill, U. S.; Moriarty, R. M.; Ku, Y. Y.; Butler, I. R. J . Organomet.
Chem. 1991, 417, 313.
(24) Gill, T. P.; Mann, K. R. Organometallics 1982, 1, 485.
(25) McNair, A. M.; Boyd, D. C.; Mann, K. R. Organometallics 1986,
5, 303.
(26) (a) Fagan, P. J .; Ward, M. D.; Caspar, J . V.; Calabrese, J . C.;
Krusic, P. J . J . Am. Chem. Soc. 1988, 110, 2981. (b) Fagan, P. J .; Ward,
M. D.; Calabrese, J . C. J . Am. Chem. Soc. 1989, 119, 1698. (c) Fagan,
P. J .; Mahoney, W. S.; Caspar, J . C.; Calabrese, J . C.; Williams, I. D.
Organometallics 1990, 9, 1843.
(27) Schrenk, J . L.; McNair, A. M.; McCormick, F. B.; Mann, K. R.
Inorg. Chem. 1986, 25, 3501.
(28) McNair, A. M. Schrenk, J . L.; Mann, K. R. Inorg. Chem. 1984,
23, 2633.
(16) Mann, K. R.; Blough, A. M.; Schrenk, J . L.; Koefod, R. S.;
Freedman, D. A.; Matachek, J . R. Pure Appl. Chem. 1995, 67, 95.
(17) Butenscho¨n, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 636.
10.1021/om010863g CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/01/2002

994 Organometallics, Vol. 21, No. 5, 2002
Notes
or Mallinckrodt. Acetonitrile and dichloromethane were dried
over P2O5 and distilled under nitrogen, hexanes and heptane
were dried over 4 Å molecular sieves, and anhydrous diethyl
ether and methanol were used as received. Ruthenium trichlo-
ride hydrate was supplied by J ohnson Matthey, anhydrous
ammonium hexafluorophosphate was supplied by Aldrich and
was used as received, and 1-trifluoromethyl-2,3,4,5-tetra-
methylcyclopentadiene (HCpq) was prepared by the literature
method.31 Triphenylphosphine was supplied by Aldrich and
sublimed before use. Elemental analyses were carried out by
MHW Laboratories, Phoenix, AZ. NMR spectra were obtained
with Varian VI 300, VXR 300 (19F and 31P), or VI 500
spectrometers. 1H spectra are referenced to the residual
protons of the solvent which are referenced to TMS, 19F spectra
are referenced to CFCl3 internal standard, and 31P spectra are
referenced to 80% phosphoric acid external standard. UV-
vis absorption spectra were recorded with a Cary 17 or Tracor
Northern 6500 system as noted. FT-IR spectra were obtained
on a Nicolet Magna 550 with an attenuated total reflectance
(ATR) cell; samples were deposited on the ATR ZnSe crystal
from dichloromethane solution.
Calcd for [CpqRuBz](PF6): C, 37.44; H, 3.53; F, 33.31. Found:
C, 37.31; H, 3.63; F, 33.18.
[Cp qRu (NCCH3)3](P F 6). A solution of [CpqRu(Bz)](PF6)
(1.35 g, 2.63 mmol) in 350 mL of freshly distilled acetonitrile
was placed in a quartz photochemical reaction well. The clear
solution was purged with nitrogen for 20 min prior to and
during the photolysis. Light for the photolysis was provided
by a 400 W medium-pressure mercury lamp (converted Syl-
vania type H33 street lamp). After 2 h of photolysis at 10 ( 5
1
°C, the reaction was determined to be complete by H NMR.
The solvent was removed from the amber solution in vacuo to
give 1.25 g (2.23 mmol, 85% yield) of the bright orange “tris”
complex. 1H NMR (CD2Cl2) (shift (ppm), multiplicity, J HH, J HF
,
integration): 2.40, s, 9H; 1.72, q, J HF 0.9 Hz, 6H; 1.68, s, 6H.
19F NMR (CD2Cl2) (shift (ppm), multiplicity, J HF, integration):
-52.92, q, CF3, J HF 0.8 Hz; -73.13, PF6, d, J PF 710 Hz. Anal.
Calcd for [CpqRu(NCCH3)3](PF6): C, 34.42; H, 3.79; N, 7.53;
F, 30.62. Found: C, 34.14; H, 3.94; N, 7.40; F, 30.48.
[Cp qRu (C10H8)](P F 6). Solid [CpqRu(NCCH3)3](PF6) (78 mg,
0.14 mmol) and naphthalene (29.7 mg, 0.23 mmol) were placed
in a 50 mL round-bottom flask. The flask was evacuated and
backfilled with Ar three times. The flask was protected from
light with aluminum foil, and 7 mL of freshly distilled
dichloromethane was added under positive pressure of argon.
The resulting solution was allowed to stir for 36 h, at which
time it was determined to be complete by 1H NMR. To
precipitate the product, 40 mL (dried over sieves) of degassed
hexanes was added to the reaction mixture. The product was
filtered and washed with a 12 mL of a 5:1 mixture of hexanes
and dichloromethane. The microcrystalline cream-colored
product was dried in vacuo to give 59 mg (0.10 mmol, 69%
Ma ter ia ls. [Cp qRu Bz]Cl‚1.25 H2O. η5-1-Trifluoromethyl-
2,3,4,5-tetramethylcyclopentadienyl-η6-benzene ruthenium chlo-
ride was synthesized through a multiple-step reaction, similar
to Chaudret’s method used for the analogous [Cp*Ru(arene)]+
complexes.32 A flask was charged with RuCl3‚xH2O (2.62 g, 10.0
mmol) and 200 mL of nitrogen-saturated methanol and was
brought to reflux under a nitrogen atmosphere. A neat aliquot
of HCpq (2.3 mL, 13 mmol) was added to the reddish orange
mixture, which became more brown in color. This mixture was
refluxed for 48 h and cooled, and granulated zinc metal (297
mg, 4.54 mmol) was added. Heating was reinitiated, and the
reaction mixture turned purple. After 2 h, 50 mL of benzene
was added and the mixture was allowed to reflux for an
additional 36 h. The dark reddish brown reaction mixture was
cooled, 50 mL of charcoal was added with stirring (15 min),
and the mixture was filtered through Celite, to give a clear
reddish orange filtrate. The filtrate was rotoevaporated to
dryness, and the residue was triturated (3 × 100 mL of H2O)
and rotoevaporated to dryness again. The resulting residue
was redissolved in 12 mL of acetonitrile and placed on a 2 ×
20 cm column of neutral alumina. A green band moved with
the solvent front and was discarded. Subsequently, a very pale
yellow clear solution containing the product was eluted. A total
of 5 L of acetonitrile was used to elute the product. The clear
acetonitrile solution was rotoevaporated in an aluminum foil-
covered flask to give 1.45 g (3.45 mmol) of pale yellow crude
product (35% yield based on ruthenium). The crude product
was recrystallized from wet acetonitrile and ether to give 1.42
g (99% recovery) of a hygroscopic white precipitate. A water
peak observed in the 1H NMR is consistent with the hygro-
scopic behavior observed in the combustion analysis. 1H NMR
(CDCl3) (shift (ppm), multiplicity, J HH, J HF, integration): 6.29,
s, 6H; 2.21, s, 6H; 2.18, q, J HF ) 0.9 Hz, 6H. 19F NMR (CDCl3):
-55.79, s. Anal. Calcd for [CpqRuBz]Cl‚1.25 H2O: C, 45.07;
H, 4.85; F, 13.39. Found: C, 45.09; H, 4.72; F, 13.40.
yield). 1H NMR (CD2Cl2) (shift (ppm), multiplicity, J HH
,
integration): 7.81 (dd, 2.0 H), J HH 6.9 Hz, J HH 3.3 Hz; 7.59
(dd, 2.0H) J HH 6.9 Hz, J HH 3.3 Hz; 7.59 (dd, 2.0H) J HH 6.9 Hz,
J HH 3.3 Hz; 6.69 (dd, 2.0H) J HH 4.5 Hz, J HH 2.4 Hz; 6.18 (dd,
2.0H) J HH 4.5 Hz, J HH 2.4 Hz; 1.75 (q, 6.0H) J HF 1.2 Hz; 1.72
(s, 6.0H) J HF 1.2 Hz. 19F NMR (CD2Cl2): -54.79 (unresolved
m), CF3; -72.68, PF6, (d), J PF 711 Hz. Anal. Calcd for [CpqRu-
(C10H8)](PF6): C, 42.64; H, 3.58.; F, 30.35. Found: C, 42.47;
H, 3.79; F, 30.13.
[Cp qRu (NCCH3)2(P P h 3)](P F 6). Solid [CpqRu(NCCH3)3]-
(PF6) (46 mg, 0.082 mmol) and triphenylphosphine (93 mg, 0.36
mmol) were placed in a 50 mL round-bottom flask. The flask
was evacuated and backfilled with Ar three times. To dissolve
the reactants, 7 mL of freshly distilled dichloromethane was
added under positive pressure of argon. The resulting solution
was allowed to stir for 12 h, after which it was determined to
be complete by proton NMR. Addition of 20 mL of hexanes
produced a yellow oil, which clung to the sides of the flask
from which the solvent was decanted. Redissolving the yellow
film in 2 mL of dichloromethane and adding 25 mL of hexanes
precipitated the product as a pale yellow powder (58 mg). The
product was recrystallized one additional time from dichlo-
romethane and hexanes to give microcrystalline material,
which was dried in vacuo to give 39.2 mg (0.050 mmol, 62%
yield). 1H NMR (CD2Cl2) (shift (ppm), multiplicity, J HH
,
[Cp qRu Bz](P F 6).21a A solution of NH4(PF6) (1.50 g, 9.20
mmol) in 2 mL of H2O was added to a solution of [ CpqRuBz]-
Cl (1.19 g, 2.95 mmol) in a minimal amount (<5 mL) of H2O
filtered through Celite. The resulting white precipitate of [Cpq-
integration): 7.5 (m, 15.0 H)*; 2.35 (d, 6.0H) J HP 1.5 Hz; 1.66
(dq, 6.0H) J HP 1.2 Hz, J HF 1.2 Hz;1.36 (d, 6.0H) J HP 1.2 Hz.
19F NMR (CD2Cl2): -51.6 (d of unresolved m)*, CF3, J FP 4.5
Hz; -71.5 (d), PF6, J PF 708 Hz. 31P NMR (CD2Cl2): 47.17
(unresolved m), PF6; -142.75 (septet), J PF 708 Hz. Anal. Calcd
for [CpqRu(NCCH3)2(PPh3)](PF6): C, 49.30; H, 4.27; N, 3.59.
Found: C, 49.40; H, 4.37; N, 3.42.
1
RuBz](PF6) (1.45 g, 2.82 mmol) was collected (96% yield). H
NMR (CD2Cl2) (shift (ppm), multiplicity, J HH, J HF, integra-
tion): 6.02, s, 6H; 2.15, q, J HF ) 1.2 Hz, 6H; 2.09, s, 6H. Anal.
[Cp qR u (NCCH 3)2(CO)](P F 6). Freshly distilled dichlo-
romethane (7 mL) was added to a 50 mL round-bottom flask
containing [CpqRu(NCCH3)3](PF6) (253 mg, 0.453 mmol) to
produce an orange solution. This solution was purged with
carbon monoxide for 50 min, resulting in a more yellow
solution. Upon layering with hexanes, the product crystallized
as yellow needles that were filtered and dried in vacuo to give
48 mg (0.088 mmol, 70% yield). Several preparations of this
(29) Freedman, D. A.; Gill, T. P.; Blough, A. M.; Koefod, R. S.; Mann,
K. R. Inorg. Chem. 1997, 36, 95.
(30) Freedman, D. A.; Matachek, J . R.; Mann, K. R. Inorg. Chem.
1993, 32, 1078.
(31) Gassman, P. G.; Mickelson, J . W.; Sowa, J . R., J r. Inorg. Synth.
1997, 31, 232.
(32) (a) Chaudret, B.; J alo´n, F. A. Chem. Commun. 1988, 711. (b)
Chaudret, B.; J alo´n, F. A.; Pere´z-Manrique; Lahoz, F.; Plou, F. J .;
Sa´nchez-Delgado, R. New J . Chem. 1990, 14, 331.

Notes
Organometallics, Vol. 21, No. 5, 2002 995
Sch em e 1. Syn th esis of [Cp qRu (Bz)]Cl
compound gave consistently low fluorine analyses. 1H NMR
(CD2Cl2) (shift (ppm), multiplicity, J HH, integration): 2.48 (s,
6.0H); 1.96 (q, 6.0H) J HF 1.2 Hz; 1.86 (s, 6.0 H). 19F NMR (CD2-
Cl2): -54.2 (unresolved m); -73.1 (d), J PF 711 Hz. IR: ν(CO),
2012 cm-1. Anal. Calcd for [CpqRu(NCCH3)2(CO)](PF6): C,
33.04; H, 3.33; F, 31.35. Found: C, 33.15; H, 3.19; F, 29.88.
Cp Cp qRu . Freshly distilled acetonitrile (5 mL) was added
to a 50 mL round-bottom flask containing [CpqRu(NCCH3)3]-
(PF6) (253 mg, 0.453 mmol) to produce an orange solution. A
solution of LiCp (110 mg, 1.53 mmol) in 20 mL of CH3CN was
added by cannula, and the orange solution became slightly
lighter in color. After 4 h, the reaction was determined to be
complete and the solvent was removed under vacuum. The
residue was triturated with 3 × 25 mL of diethyl ether. The
triturate was filtered through 1 cm activated alumina and
rotoevaporated to dryness, yielding 141 mg (0.397 mmol, 88%
yield) of the pale yellow microcrystalline mixed ruthenocene
F igu r e 1. UV-vis absorbance changes during the pho-
tolysis of a 9.69 × 10-4 M solution of [CpqRu(Bz)](PF6) in
acetonitrile with the unfiltered output of a 75 W xenon
lamp (Osram XBO 75/2). The spectra were collected with
a Tracor Northern 6500 diode array UV-vis spectrom-
eter: (a), t ) 0; (b) t ) 2.5 min; (c) t ) 7.5 min; (d) t ) 12.5
min; (e) t ) 20 min; (f) t ) 65 min.
Sch em e 2. Syn th esis of [Cp qRu (NCCH3)3]+ a n d a
F ew Rea ction s Dem on str a tin g Its Syn th etic Utility
product. 1H NMR (CD2Cl2) (shift (ppm), multiplicity, J HH
,
integration): 4.18 (s, 5.0 H); 2.03 (q, 6.0H) J HF 1.2 Hz; 1.98 (s,
6.0H). Anal. Calcd for CpCpqRu: C, 50.70; H, 4.82; F, 16.04.
Found: C, 50.55; H, 5.01; F, 15.89.
Th er m a l Liga n d Exch a n ge of [Cp qRu Bz]+. No exchange
of the coordinated benzene ring with acetonitrile was observed
in the absence of light during the purification processes of [Cpq-
RuBz]Cl and [CpqRuBz](PF6) at temperatures that ranged
between 25 and 50 °C. In separate experiments, specifically
designed to investigate thermal arene replacement, a solution
of [CpqRuBz](PF6) in acetonitrile was stored at room temper-
ature in the dark for 12 days. No decomposition of [CpqRuBz]-
(PF6) or formation of [CpqRu(NCCH3)3](PF6) was observed. A
room-temperature solution of [CpqRuBz](PF6) and toluene in
CD2Cl2 showed no arene exchange after 3 days.
Deter m in a tion of Rela tive Qu a n tu m Yield s. The rela-
tive quantum yield for the formation of [CpqRu(NCCD3)3](PF6)
from [CpqRuBz](PF6) in acetonitrile-d3 solution was estimated
by comparing the percent conversion with time for this reaction
and the analogous reactions with [CpRuBz](PF6) and [Cp*RuBz]-
(PF6) by 1H NMR. A solution of [CpqRuBz](PF6) (0.0751 M, 13.5
mg, 0.0263 mmol, in 0.35 mL of CD3CN), a solution of
[CpRuBz](PF6) (0.0747 M, 10.2 mg, 0.0262 mmol, in 0.35 mL
of CD3CN), and a solution of [Cp*RuBz](PF6) (0.0759 M, 12.2
mg, 0.0266 mmol, in 0.35 mL of CD3CN) were prepared and
photolyzed in 4 mm quartz NMR tubes with the unfiltered
output of a 100 W Hg lamp (USHIO 2D). The reactions were
monitored by comparing the integration of the free benzene
resonance (7.2 ppm) with the bound η6-benzene peak at ∼6
ppm. Between acquisitions of 1H NMR spectra, the NMR tubes
were protected from adventitious light.
zinc metal. We observe that the zinc reduction in
Scheme 1 produces a blue air-sensitive intermediate,
characteristic of mixed valence Ru(III)-Ru(II) com-
pounds18 and eventually the tetramer, [CpqRuCl]4, the
analogue of [Cp*RuCl]4.26 Addition of benzene to this
mixture in step 3 leads to the formation of [CpqRuBz]-
Cl, which was readily isolated and separated from side
products. Metathesis to the PF6- salt in water gives the
mixed-sandwich complex as a water-insoluble white
powder that may be recrystallized from dichloromethane/
hexane.
[CpqRuBz](PF6) is inert to thermal arene bond cleav-
age as previously observed for [Cp*RuBz](PF6) and
[CpRuBz](PF6). No arene exchange or replacement was
observed in thermal control reactions; however, the
photolysis of [CpqRuBz](PF6) in acetonitrile to give the
tris(acetonitrile) complex (step 1, Scheme 2) is facile and
convenient. Figure 1 shows the progression of the
photolysis monitored by UV-vis absorption spectros-
copy. Clean conversion of the benzene complex to the
tris(acetonitrile) complex, without the formation of an
intermediate species, is indicated by the isosbestic
Resu lts a n d Discu ssion
When we started this work, no synthesis of [Cpq-
RuBz]+ was available, so we fashioned one (Scheme 1)
after Chaudret’s [Cp*Ru(arene)]+ synthesis32 that uses
the [Cp*RuCl2]2 dimer. During the course of our work,
a synthesis of the [CpqRuBz]+ precursor from isolated
[CpqRuCl2]2 was published.21 In our hands, the isolation
and purification of [CpqRuCl2]2 was problematic, so we
generated and then reduced this compound in situ with

996 Organometallics, Vol. 21, No. 5, 2002
Notes
Ta ble 1. Room -Tem p er a tu r e Electr on ic Sp ectr a a of
[Cp xRu (NCCH3)3](P F 6) a n d [Cp xRu Bz](P F 6)
Com p lexes in Aceton itr ile
(NCCH3)3]+,22-25 [Cp*Ru(NCCH3)3]+,25-28 and [CpOs-
(NCCH3)3]+ 29,30 reactions under similar conditions, but
generally the CpqRu compounds have higher solubilities
than the Cp or Cp* analogues. [CpqRu(NCCH3)3]+
cleanly substitutes one acetonitrile ligand to form the
bis(acetonitrile) monocarbonyl compound in dichlo-
romethane solutions bubbled with carbon monoxide at
atmospheric pressure and ambient temperature. Reac-
tion with triphenyl phosphine in dichloromethane at
room temperature yields the mono(triphenylphosphine)
bis(acetonitrile) complex exclusively. Reaction of the
tris(acetonitrile) compound with LiCp or with naphtha-
lene in acetonitrile solution yields the neutral mixed
ring ruthenocene and the η6-naphthalene complex,
respectively. All of the products reported here were
compound
λ(nm) ((ꢀ(M-1 cm-1))
[CpRuBz](PF6)
320(136)
[CpqRuBz](PF6)
321(190)b
[Cp*RuBz](PF6)
321(221)c
[CpRu(NCCH3)3](PF6)
[CpqRu(NCCH3)3](PF6)
[Cp*Ru(NCCH3)3](PF6)
309(860); 365(1071)
310(784); 364(1074)b
317(870); 370(1287)c
Recorded on a Cary 17 UV-vis spectrophotometer. b Reference
a
24. c Reference 27.
changes in the UV-vis absorption spectrum. The
colorless solution gradually turns orange as [CpqRu-
(NCCH3)3]+ is formed. The UV absorption peak (λmax at
321 nm) decreases in intensity, while peaks at 364 and
310 nm increase as the orange product is formed. The
conversion is quantitative in dry acetonitrile under a
dry nitrogen atmosphere. Removal of the solvent in
vacuo leaves essentially pure [CpqRu(NCCH3)3](PF6),
which may be purified further by column chromatog-
raphy. Scale-up of this general photolysis procedure to
gram quantities results in excellent isolated yields.
UV-vis spectral data for [CpqRuBz](PF6) and [Cpq-
Ru(NCCH3)3](PF6) are compared in Table 1 with data
for the Cp and Cp* analogues. The close agreement of
the values for the respective analogues is striking and
is in agreement with the previously reported similarity
in the electronic influence of Cpq and Cp in other
ruthenium complexes.18
Another comparison that is of synthetic importance
is the quantum yield for the production of [CpqRu-
(NCCH3)3](PF6) relative to the Cp and Cp* analogues.
The photolyses of nearly equimolar solutions (vide
supra) of [CpRuBz](PF6), [CpqRuBz](PF6), and [Cp*RuBz]-
(PF6) were followed by 1H NMR. The data collected gave
percent conversion vs time plots shown in the Support-
ing Information. The relative percentage of conversion
at a given time indicates that the quantum yield, Φ, is
similar for the CpRu (Φ ) 0.34)24,28 and CpqRu ana-
logues, which are larger than the Cp*Ru complex (Φ )
0.19).27 The curvature in the plots is due to the large
inner-filter effect that has been noted previously.24,29
Again the Cpq result is in close agreement with the Cp
result, in line with the electronic, rather than steric
control of the photochemical arene ring displacement.24-28
The synthetic utility of [CpqRu(NCCH3)3]+ as a new
CpqRu synthon is demonstrated by the synthesis of a
few new half- and mixed-sandwich compounds under
very mild conditions (Scheme 2). The products were
similar to those formed from the analogous [CpRu-
1
characterized by H and 19F NMR, satisfactory elemen-
tal analyses, and, when appropriate, FT-IR spectroscopy
1
and 31P NMR spectrosopy. The salient feature of the H
NMR spectra of these compounds is the observation of
two signals for the Cpq resonance, a singlet and a
quartet; each peak integrated for six protons. The
quartet is assigned to the methyl protons in the 2
position next to the CF3 group with a J HF coupling
constant in the range 0.8-1.2 Hz for all the compounds
investigated.
Con clu sion s
We have synthesized a new compound, [CpqRu-
(NCCH3)3](PF6), that functions as an effective synthon
for the CpqRu moiety. [CpqRu(NCCH3)3](PF6) is ef-
ficiently generated by photolysis of [CpqRuBz](PF6) in
acetonitrile with a quantum yield similar to one ob-
tained previously for the Cp analogue. The utility of the
new synthon is illustrated by the synthesis of several
new open-face and mixed-sandwich ruthenium com-
pounds under very mild conditions (room temperature/
atmospheric pressure). The methods described here
should be useful for the further development of synthetic
chemistry designed to incorporate the CpqRu group into
other molecules of interest.
Ack n ow led gm en t. This work was supported by the
National Science Foundation, most recently under
Grant No. CHE-9307837.
Su p p or tin g In for m a tion Ava ila ble: Plots of percent
conversion vs time for the photolysis of [CpRuBz](PF6), [Cpq-
RuBz](PF6), and [Cp*RuBz](PF6). This material is available
free of charge via the Internet at http://pubs.acs.org.
OM010863G