Synthesis and reactivity of ruthenium allyl carbene complexes. C-H activation/dehydrogenation of a cyclohexyl substituent in PCy3

Article abstract of DOI:10.1021/om9905409

The complexes [RuCp(PR₃)(CH₃CN)₂]PF₆ (R = Me, Ph, Cy) react with 1,6-heptadiyne and HC≡CR′ (R′ = Ph, C₆H₉, n-Bu, H), most likely via a ruthenacy-clopentatriene intermediate, to give the ruthenium allyl carbene complexes [CpRu(=CH-η³-C(CH₂)₃CCHPR ₃)]PF₆ and [CpRu(=C(R′)-η³-CHC(R′)CHPMe₃)]PF ₆, respectively. In the case of R = Cy, the allyl carbene complex rearranges to afford the complex [CpRu(η³-CH₂C(CH₂)₃-CCH ₂PCy₂(η²-C₆H ₉)]PF₆, featuring an η²-coordinated cyclohexenyl ligand. This reaction involves dehydrogenation of one cyclohexyl substituent of the phosphine ligand.

Full text of DOI:10.1021/om9905409

Organometallics 1999, 18, 4681-4683
4681
Syn th esis a n d Rea ctivity of Ru th en iu m Allyl Ca r ben e
Com p lexes. C-H Activa tion /Deh yd r ogen a tion of a
Cycloh exyl Su bstitu en t in P Cy3
Klaus Mauthner,† Kamran M. Soldouzi,† Kurt Mereiter,‡ Roland Schmid,† and
Karl Kirchner*,†
Institute of Inorganic Chemistry and Institute of Mineralogy, Crystallography, and Structural
Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Received J uly 12, 1999
Sch em e 1
Summary: The complexes [RuCp(PR3)(CH3CN)2]PF6 (R
) Me, Ph, Cy) react with 1,6-heptadiyne and HCtCR′
(R′ ) Ph, C6H9, n-Bu, H), most likely via a ruthenacy-
clopentatriene intermediate, to give the ruthenium allyl
carbene complexes [CpRu(dCH-η3-C(CH2)3CCHPR3)]PF6
and [CpRu(dC(R′)-η3-CHC(R′)CHPMe3)]PF6, respec-
tively. In the case of R ) Cy, the allyl carbene complex
rearranges to afford the complex [CpRu(η3-CH2C(CH2)3-
CCH2PCy2(η2-C6H9)]PF6, featuring an η2-coordinated
cyclohexenyl ligand. This reaction involves dehydroge-
nation of one cyclohexyl substituent of the phosphine
ligand.
Transition-metal complexes having a vacant coordi-
nation site or bearing weakly coordinating ligands are
known to have a rich chemistry with alkynes to give,
for instance, vinylidene complexes,1 metallacyclopenta-
dienes,2 and in some cases metallacyclopentatrienes.3
All these species are of considerable interest, because
of being reactive intermediates in organic and organo-
metallic synthesis as well as in catalytic processes, e.g.,
the polymerization and cyclization of alkynes. We have
recently described the synthesis of the labile complexes
[RuCp(PR3)(CH3CN)2]PF6 (R ) Me (1a ), Ph (1b), Cy
(1c))4 which serve as synthetic equivalents for the 14-
electron fragment [RuCp(PR3)]+. In this communication
we report that the reaction of 1a -c with 1,6-heptadiyne
and HCtCR′ (R ) Ph, C6H9, n-Bu, H) results in the
formation of ruthenium allyl carbene complexes rather
than ruthenacyclopentadiene or ruthenacyclopentatriene
complexes. We further demonstrate that ruthenium
allyl carbene complexes are acting as pseudo-16e spe-
cies, reacting with both nucleophiles and electrophiles
and being able to dehydrogenate alkyl groups of bulky
phosphine ligands.
Treatment of 1a -c with 1 equiv of 1,6-heptadiyne
results in the formation of the dark red allyl carbene
complexes [CpRu(dCH-η3-C(CH2)3CCHPR3)]PF6 (2a -
c) in essentially quantitative yields, as monitored by 1H
NMR spectroscopy (Scheme 1). Unfortunately, no in-
termediate could be detected. Preliminary stopped-flow
studies revealed that the rate-determining step is the
dissociation of the first acetonitrile ligand in 1. The CH3-
CN self-exchange in 1 has been recently studied by
NMR spectroscopy.4 The identity of 2a -c was estab-
1
lished by H, 13C{1H}, and 31P{1H} NMR spectroscopy
and, in the case of 2a and 2b, also by elemental
1
analysis.5 The H NMR spectrum of 2a exhibits a low-
field resonance of the carbene hydrogen atom H1 at
12.27 ppm and a signal for the allyl proton H4 at 5.27
ppm (d, 2J HP ) 8.4 Hz). The most characteristic features
in the 13C{1H} NMR spectrum are a low-field resonance
* To whom correspondence should be addressed. E-mail: kkirch@
mail.zserv.tuwien.ac.at.
† Institute of Inorganic Chemistry.
‡ Institute of Mineralogy, Crystallography, and Structural Chem-
istry.
(5) Preparation and data for 2a : A solution of 1a (145 mg, 0.309
mmol) in acetone (5 mL) was treated with 1,6-heptadiyne (36 µL, 0.309
mmol) and was stirred for 45 min, whereupon the solution turned red.
After the volume of the solution was reduced to about 1 mL, Et2O (20
mL) was slowly added and a red microcrystalline precipitate was
formed. The supernatant was decanted, and the solid was washed twice
with Et2O and dried under vacuum. Yield: 126 mg (85%). Anal. Calcd
for C15H22F6P2Ru: C, 37.58; H, 4.63. Found: C, 37.34; H, 4.51. 1H NMR
(δ, CD3NO2, 20 °C): 12.27 (s, 1H, H1), 5.27 (d, J PH ) 8.4 Hz, 1H, H4),
5.19 (s, 5H), 2.90 (m, 2H, CH2), 2.01 (m, 2H, CH2) 1.43 (m, 2H, CH2),
1.37 (d, J PH ) 13.9 Hz, 9H, Me). 13C{1H} NMR (δ, acetone-d6, 20 °C):
236.5 (d, J CP ) 6.2 Hz, 1C, C1), 115.2 (d, J CP ) 3.5 Hz, 1C, C3), 83.1 (s,
5C, Cp), 70.4 (s, 1C, C2), 36.5 (d, J CP ) 4.9 Hz, 1C, CH2), 31.9 (d, J CP
(1) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197. (b) Bruneau, C.;
Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.
(2) Yi, C. S.; Torres-Lubian, J . R.; Liu, N.; Rheingold, A. L.; Guzei,
I. A. Organometallics 1998, 17, 1257 and references therein.
(3) For metallacyclopentatriene complexes see: (a) Albers, M. O.;
deWaal, P. J . A.; Liles, D. C.; Robinson, D. J .; Singleton, E.; Wiege, M.
B. J . Chem. Soc., Chem. Commun. 1986, 1680. (b) Gemel, C.; LaPanse´e,
A.; Mauthner, K.; Mereiter, K.; Schmid, R.; Kirchner, K. Monatsh.
Chem. 1997, 128, 1189. (c) Pu, L.; Hasegawa, T.; Parkin, S.; Taube,
H. J . Am. Chem. Soc. 1992, 114, 2712. (d) Hirpo, W.; Curtis, M. D. J .
Am. Chem. Soc. 1988, 110, 5218. (e) Kerschner, J . L.; Fanwick, P. E.;
Rothwell, I. P. J . Am. Chem. Soc. 1988, 110, 8235.
(4) Ru¨ba, E.; Simanko, W.; Mauthner, K.; Soldouzi, K. M.; Slugovc,
C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics 1999, 18,
3843.
) 75.6 Hz, 1C, C4), 29.1 (s, 1C, CH2), 25.1 (s, 1C, CH2), 10.7 (d, J CP
)
58.9 Hz, 3C, Me). 31P{1H} NMR (δ, acetone-d6, 20 °C): 31.7 (PMe3),
-142.7(PF6). Complexes 2b-g have been prepared analagously.
However, 2c is not stable and rearranges to give 5.
10.1021/om9905409 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/16/1999

4682 Organometallics, Vol. 18, No. 23, 1999
Communications
Sch em e 2
Sch em e 3
F igu r e 1. Structural view of 2a showing 20% thermal
ellipsoids (PF6- omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ru-C(1-5)av ) 2.221(3), Ru-C(6)
) 1.897(2), Ru-C(7) ) 2.232(2), Ru-C(11) ) 2.174(2), Ru-
C(12) ) 2.123(2), C(6)-C(7) ) 1.403(3), C(7)-C(11) )
1.426(3), C(11)-C(12) ) 1.432(3), C(7)-C(8) ) 1.513(3),
C(8)-C(9) ) 1.542(4), C(9)-C(10) ) 1.537(4), C(10)-C(11)
) 1.514(3), C(12)-P(1) ) 1.778(2); C(6)-C(7)-C(11) )
116.3(2), C(7)-C(11)-C(12) ) 122.0(2), Ru-C(6)-C(7) )
83.7(1), C(6)-C(7)-C(11)-C(12) ) 16.6(3).
3-positions (Scheme 2). A mechanism to account for the
formation of 2 may involve a metallacyclopentatriene
intermediate (Scheme 1). Subsequently, migration of the
tertiary phosphine to one of the two electrophilic car-
bene carbon atoms leads to the formation of an allyl
carbene complex. It has to be mentioned that analogous
ruthenacyclopentatriene complexes are stable species
if potential nucleophilic ligands are absent.3
at 236.5 ppm and a doublet resonance at 31.9 ppm (J CP
) 75.6 Hz) assignable to the carbene carbon atom C1
and the terminal allyl carbon atom C4 bearing the
phosphine substituent. The NMR spectra of 2b and 2c
are similar to those of 2a and are not discussed here.
The structure of 2a has been confirmed by X-ray
crystallography (Figure 1).6 Obviously C-C coupling
had occurred between the internal sp carbons of the 1,6-
heptadiyne ligand, forming an allyl carbene system with
all four carbon atoms of the C4 chain bonded to the
RuCp fragment. The C4 chain is nearly planar with a
torsion angle C(6)-C(7)-C(11)-C(12) of 16.6(3)°. The
Ru-C(6) bond is very short (1.897(2) Å), suggesting that
C(6) is an alkylidene carbon doubly bonded to the
ruthenium center. The remaining three carbons of the
C4 chain have Ru-C(7), Ru-C(11), and Ru-C(12)
distances of 2.232(2), 2.174(2), and 2.123(2) Å, respec-
tively, in accordance with an η3-allyl system. In view of
the near-planarity of C(1-4), the π-system of the allyl
unit is able to interact with the RudC π bond. In
agreement with these observations the C-C distances
within the allyl carbene moiety are 1.403(3), 1.426(3),
and 1.432(3) Å, respectively. On the other hand, the
unusual high-field shift of C4 indicates a substantial sp3
character of this atom, requiring a major contribution
from a ruthenacyclopenta-1,3-diene resonance struc-
ture.7
Preliminary reactivity studies revealed that com-
plexes 2 are capable of reacting with both nucleophiles
and electrophiles. Thus, treatment of 2d with 1 equiv
of PPh3 results in the formation of [CpRu(-CPMe3d
CPh-η2-CHdCHPh)(PPh3)]PF6 (3) (Scheme 2). This
reaction involves a 1,4-hydrogen shift. Furthermore, 2a
reacts with CF3COOH to afford the η4-diene complex
[CpRu(η4-CH2dC(CH2)3CdCHPMe3)(η1(O)-CF3COO)]-
PF6 (4) in 80% isolated yield (Scheme 3). When the
protonation was carried out with CF3COOD instead of
CF3COOH, the isotopomer 4-d 1 was formed. Compari-
1
son of the H NMR spectra of 4 and 4-d 1 showed that
deuterium had been incorporated exclusively into the
anti position of the 1,3-diene moiety,8 most likely
involving delivery of the proton (deuterium) on the CR
via the inside face of the molecule. In this case the
carbene carbon atom of 2 is nucleophilic.
(7) For related allyl carbene complexes see: (a) Crocker, M.; Green,
M.; Orpen, A. G.; Neumann, H. P.; Schaverin, C. J . J . Chem. Soc.,
Chem. Commun. 1984, 1351. (b) Carlton, L.; Davidson, J . L.; Ewing,
P.; Manjlovic-Muir, L.; Muir, K. W. J . Chem. Soc., Chem. Commun.
1985, 1474. (c) Morrow, J . R.; Tonker, T. L.; Templeton, J . J . Am. Chem.
Soc. 1985, 107, 5004. (d) Morrow, J . R.; Tonker, T. L.; Templeton, J .
J . Am. Chem. Soc. 1985, 107, 5004. (e) Crocker, M.; Froom, S. F. T.;
Green, M.; Nagle, K. R.; Orpen, A. G.; Thomas, D. M. J . Chem. Soc.,
Dalton Trans. 1987, 2803. (f) Crocker, M.; Green, M.; Nagle, K. R.;
Orpen, A. G.; Neumann, H. P.; Morton, C. E.; Schaverin, C. J .
Organometallics 1990, 9, 1422.
In a similar fashion, 1a reacts with HCtCR′ (R′ )
Ph, C6H9, n-Bu, H) to give the allyl carbene complexes
[CpRu(dC(R′)-η3-CHC(R′)CHPMe3)]PF6 (2d -g) in high
yields with the substituents exclusively in the 1- and
(6) Crystal data for 2a : monoclinic space group P21/n (No. 14), a )
8.456(2) Å, b ) 10.942(2) Å, c ) 19.917(4) Å, â ) 92.63(1)°, V ) 1840.9-
(7) Å3, Z ) 4, R1 ) 0.037 (all data), wR2 ) 0.081 (all data), 5343
reflections, 224 refined parameters.
(8) Crocker, M.; Dunne, B. J .; Green, M.; Orpen, A. G. J . Chem. Soc.,
Dalton Trans. 1991, 1589.

Communications
Organometallics, Vol. 18, No. 23, 1999 4683
Sch em e 4
In addition, these species are capable of activating
C-H bonds of alkyl groups in tertiary phosphine
ligands, provided they are sufficiently bulky. While 2a
and 2b are stable even at elevated temperatures, 2c
reacts readily with one cyclohexyl substituent of the
phosphine ligand to give 5, featuring an η2-coordinated
cyclohexenyl ligand (Scheme 4). The formation of 5
involves hydrogen transfer from a cyclohexyl ring of
PCy3 to the C4 chain of the allyl carbene moiety.
Notably, related reactions have been reported recently,
requiring in some cases the presence of extra added
olefin as an external hydrogen acceptor.9 In addition to
spectroscopic and analytical characterizations of 5 (see
the Supporting Information), the solid-state structure
of 5 in the form of 5‚1/2Et2O was determined by single-
crystal X-ray diffraction.10 An ORTEP diagram of
5‚1/2Et2O is shown in Figure 2 with selected bond
distances and angles reported in the caption. Clearly,
one cyclohexyl substituent of PCy3 has been dehydro-
genated and is bound in an η2-fashion to the metal
center. The allyl functionality is asymmetrically bonded
to the metal with the Ru-C bond distance to the central
allyl carbon atom C(7) (2.181(5) Å) distinctly shorter
than the Ru-C bonds to the outer carbon atoms C(6)
F igu r e 2. Structural view of 5‚1/2Et2O showing 20%
thermal ellipsoids (most H atoms, PF6-, and Et2O omitted
for clarity). Only one of the two crystallographically
independent complexes is shown. Selected bond lengths (Å)
and angles (deg): Ru(1)-C(1-5)av ) 2.234(5), Ru(1)-C(6)
) 2.214(5), Ru(1)-C(7) ) 2.181(5), Ru(1)-C(11) ) 2.242(4),
Ru(1)-C(13) ) 2.221(4), Ru(1)-C(14) ) 2.195(4), C(6)-C(7)
) 1.409(7), C(7)-C(11) ) 1.424(6), C(13)-C(14) ) 1.417(6),
C(12)-P(1) ) 1.799(5), C(13)-P(1) ) 1.802(5), C(19)-P(1)
) 1.829(5), C(25)-P(1) ) 1.840(5); C(6)-C(7)-C(11) )
123.5(4), C(11)-C(12)-P(1) ) 108.7(3), P(1)-C(13)-C(14)
) 116.2(3).
and C(11) (2.214(5) and 2.242(4) Å, respectively). The
olefin moiety of the cyclohexenyl ligand is also asym-
metrically bonded to the metal center, with the Ru-C
bonds to the carbon atoms C(13) and C(14) being 2.221-
(4) and 2.195(4) Å, respectively. The C(13)-C(14) bond
distance is 1.417(6) Å.
Ack n ow led gm en t. Financial support by the “J ubi-
la¨umsfond der O¨ sterreichischen Nationalbank” is grate-
fully acknowledged (Project No. 6474).
(9) (a) Arliguie, T.; Chaudret, B.; Chung, G.; Dahan, F. Organome-
tallics 1991, 10, 2973. (b) Christ, M. L.; Sabo-Etienne, S.; Chaudret,
B. Organometallics 1995, 14, 1082. (c) Borowski, A. F.; Sabo-Etienne,
S.; Christ, M. L.; Donnadieu, B.; Chaudret, B. Organometallics 1996,
15, 1427. (d) Hietkamp, S.; Hufkens, D. J .; Vrieze, K. J . Organomet.
Chem. 1978, 152, 347. (e) Six, C.; Gabor, B.; Go¨rls, H.; Mynott, R.;
Philipps, P.; Leitner, W. Organometallics 1999, 18, 3316.
Su p p or tin g In for m a tion Ava ila ble: Text giving full
experimental details and spectroscopic analytical data for
complexes 2a -c and 3-5 and tables of X-ray structural data,
including data collection parameters, positional and thermal
parameters, and bond distances and angles for complexes 2a
and 5‚1/2Et2O. This material is available free of charge via the
Internet at http://pubs.acs.org.
(10) Crystal data for 5‚1/2Et2O: triclinic, space group P1h (No. 2), a
) 14.775(6) Å, b ) 15.067(6) Å, c ) 17.187(6) Å, R ) 89.89(2)°, â )
75.75(2)°, γ ) 63.07(2)°, V ) 3280(2) Å3, Z ) 4, R1 ) 0.078 (all data),
wR2 ) 0.13 (all data), 8985 reflections, 768 refined parameters.
OM9905409