A tertiary phosphine that is too bulky: preparation of catalytically less active carbene and vinylidene ruthenium(II) complexes

Article abstract of DOI:10.1016/S0022-328X(01)01300-6

Tricyclooctylphosphine PCoc₃ (1), which has been prepared from PCl₃ and cyclooctyl Grignard reagent, reacts under an atmosphere of H₂ with the dimer [RuCl₂(η³:η³ -C₁₀H₁₆

Full text of DOI:10.1016/S0022-328X(01)01300-6

Journal of Organometallic Chemistry 641 (2002) 203–207
www.elsevier.com/locate/jorganchem
A tertiary phosphine that is too bulky: preparation of catalytically
less active carbene and vinylidene ruthenium(II) complexes
Wolfram Stu¨er, Justin Wolf, Helmut Werner *
Institut fu¨r Anorganische Chemie der Uni6ersita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg, Germany
Received 23 August 2001; accepted 23 August 2001
Dedicated to Professor Rolf Gleiter on the occasion of his 65th birthday
Abstract
Tricyclooctylphosphine PCoc3 (1), which has been prepared from PCl3 and cyclooctyl Grignard reagent, reacts under an
atmosphere of H2 with the dimer [RuCl2(h3:h3-C10H16)]2 (2) to give the hydrido(dihydrogen) complex [RuHCl(H2)(PCoc3)2] (4);
in contrast, treatment of 2 with PPh3 under the same conditions affords [RuHCl(PPh3)3] (3). The reaction of 4 with acetylene in
the presence of MgCl2 and water leads to the formation of the ruthenium carbene [RuCl2(ꢀCHCH3)(PCoc3)2] (5) in 70% isolated
yield. In the absence of MgCl2 and water, 4 reacts with acetylene at low temperature to give the hydrido(vinylidene) complex
[RuHCl(ꢀCꢀCH2)(PCoc3)2] (6) almost quantitatively. Compounds 5, 6 and [RuH(k2-O2CCF3)(ꢀCꢀCH2)(PCoc3)2] (7), the latter
being obtained from 6 and CF3CO2K by ligand exchange, are poor catalysts for ROMP and cross olefin metathesis. © 2002
Elsevier Science B.V. All rights reserved.
Keywords: Ruthenium; Carbene complexes; Vinylidene complexes; Hydride complexes; Dihydrogen complexes
to prepare tricyclooctylphosphine PCoc3 for which no
preparative procedure was known [5]. In the present
1. Introduction
paper we describe the synthesis of some hydrido, car-
bene and vinylidene compounds with Ru(PCoc3)2 as the
molecular core and show that they are catalytically less
active than the related Ru(PCy3)2 complexes.
After it was convincingly illustrated that the car-
beneruthenium(II) complexes [RuCl2(ꢀCHR)(PCy3)2]
first reported by Grubbs et al. [1] are excellent catalysts
for olefin metathesis [2], numerous attempts have been
made to modify the coordination sphere of the metal in
these five-coordinate molecules with the hope to find an
even better application profile [3]. With regard to the
type of the phosphine ligand, it was found that the
corresponding bis(triphenylphosphine)- and bis(triiso-
propylphosphine)ruthenium derivatives are catalytically
less active than the bis(tricyclohexylphosphine) counter-
part [1c,1d] which was explained by the reduced size of
PPh3 and PiPr3 compared with PCy3 [4]. Since there are
to the best of our knowledge no reports about using
even more bulky tertiary phosphines than PCy3 as
ligands for the carbeneruthenium catalysts, we set out
2. Results and discussion
The stepwise procedure for the preparation of PCoc3
(1) is outlined in Eq. (1). After we failed to obtain
cyclooctylchloride from cyclooctanol and ZnCl2–HCl
[6], we used the related bromide as precursor for the
Grignard reagent and treated PCl3 with c-C8H15MgBr
in ether–toluene. The phosphine 1 was isolated as a
colorless viscous oil and characterized by H-, 13C- and
1
31P-NMR spectroscopy. The relatively modest yield of
1 is probably due to the known tendency of Grignard
compounds containing larger cycloalkyl groups to gen-
erate the corresponding cycloalkanes by radical-type
reactions [7].
* Corresponding author. Fax: +49-931-8884623.
E-mail
address:
helmut.werner@mail.uni-wuerzburg.de
(H.
Werner).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01300-6

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W. Stu¨er et al. / Journal of Organometallic Chemistry 641 (2002) 203–207
the RuꢀC carbon atom, the position of which is nearly
identical to that of [RuCl2(ꢀCHCH3)(PiPr3)2] [10]. With
regard to the formation of 5 from 4 as the precursor,
we assume that in the first step 4 reacts with acetylene
to give the hydrido(vinylidene) compound 6 which in
the presence of a chloride source such as MgCl2 gener-
ates the anionic vinylruthenium(II) species [RuCl2-
(CHꢀCH2)(PCoc3)2]−. The reaction of this intermediate
with water could give 5. In this context we note that
recently the first dicationic ruthenium carbene
Scheme 1.
[Ru(ꢀCHCH3)(CH3CN)2(PCy3)2]2+
(with
BF−4 or
B(Arf)−4 as the counterion; Arf=3,5-bis(trifluoro-
methyl)phenyl) has been prepared in our laboratory by
protonation of the vinylruthenium(II) monocation
[Ru(CHꢀCH2)(CH3CN)2(PCy3)2]+ with HBF4 or
Brookhart’s acid in dichloromethane [11].
(2)
Scheme 2.
(1)
The vinylidene complex 6, which is formed from 4
and acetylene in the absence of a protic reagent, is a
brown, moderately air-sensitive solid which is readily
soluble in all common organic solvents. We assume, in
agreement with ab initio DFT calculations by Eisen-
stein et al. for the related compounds [RuHCl-
(ꢀCꢀCHR)(PtBu2Me)2] [12], that 6 possesses a distorted
trigonal–bipyramidal geometry with the two phosphi-
nes in the apical positions. The reaction of 6 with
CF3CO2K leads to an exchange of the anionic ligand
and results in the formation of the carboxylato complex
7 in 87% isolated yield (Scheme 2). The bidentate
coordination of the CF3CO−2 anion is indicated by the
IR spectrum of 7 in which the symmetric and asymmet-
ric w(OCO) stretching modes appear in the region char-
acteristic for M(k2-O2CR) compounds [13]. The
1H-NMR spectra of 6 and 7 show the hydride reso-
nance as a triplet at, respectively, l −15.95 (for 6) and
−12.61 (for 7) while the 13C-NMR spectra of 6 and 7
display in the low-field region the signals for the a- and
b-carbon atoms of the vinylidene ligand at, respectively,
l 326.4 and 86.9 (for 6) and l 334.4 and 86.5 (for 7).
All these resonances are split into triplets due to P,H
and P,C couplings.
The reaction of [RuCl2(h3:h3-C10H16)]2 (2), which we
had already used as starting material for the prepara-
tion of [RuHCl(H2)(PiPr3)2] and [RuHCl(H2)(PCy3)2]
[8], with 1 in a solvent mixture of isopropanol and
toluene leads, under an atmosphere of dihydrogen, to
the bis(tricyclooctylphosphine)ruthenium(II) complex 4
in 68% isolated yield (Scheme 1). Typical spectroscopic
features of the light yellow, air-sensitive solid are the
RuꢁH stretching modes in the IR spectrum at 2104,
2056 and 1905 cm−1 and the high-field resonance at l
1
−16.0 in the H-NMR spectrum, the latter being at
room temperature a broad singlet as is also found for
other ruthenium(II) compounds with RuH(H2) as a
molecular fragment [9]. In contrast to 1, triphenylphos-
phine reacts with 2 in the presence of dihydrogen to
give the hydride complex 3 in excellent yield. Attempts
to prepare [RuHCl(H2)(PR3)2] with PR3=PiPr2Ph,
PCy2Me by using the same methodology as applied to
4 failed.
Similarly to [RuHCl(H2)(PiPr3)2] and [RuHCl(H2)-
(PCy3)2], the Ru(PCoc3)2 counterpart 4 also reacts with
acetylene in dichloromethane at −80 °C to afford
quantitatively the hydrido(vinylidene) complex 6. If the
reaction of 4 with acetylene is carried out in the pres-
ence of MgCl2 and water, instead of 6 the car-
bene(dichloro) derivative 5 is obtained (Eq. (2)). Key to
The hope that the five-coordinate carbene- and
vinylideneruthenium complexes 5 and 6 with phosphine
ligands, which are more bulky than PCy3, would be
catalytically more active than the Ru(PCy3)2 counter-
parts was not fulfilled. Neither in ROMP of cis-cy-
clooctene nor that of dicyclopentadiene could the
ruthenium carbene 5 compete with [RuCl2(ꢀCHCH3)-
(PCy3)2] in catalytic activity under identical conditions.
Similarly, the hydrido(vinylidene) derivative 6, in the
1
the structural assignment of 5 from the H-NMR spec-
trum are the quartet at l 19.54 for the ꢀCH and the
doublet at l 2.72 for the carbene CH3 protons. The
13C-NMR spectrum of 5 displays a signal at l 314.3 for

W. Stu¨er et al. / Journal of Organometallic Chemistry 641 (2002) 203–207
205
presence of HBF4 in ether, does not catalyze with the
same rate as the cation [RuHCl(ꢂCCH3)(OEt2)-
(PCy3)2]+, formed from [RuHCl(ꢀCꢀCH2)(PCy3)2] and
ethereal HBF4 [14], the ring-opening metathesis of cy-
clopentene with methyl acrylate. The conclusion is that
among the tertiary phosphines PR3 the compound with
R=cyclohexyl obviously provides the most favorable
conditions for generating, from [RuCl2(ꢀCHR%)(PR3)2]
as the precursor, a 14-electron species [RuCl2(ꢀCHR%)-
(PR3)] that is supposed to be the active catalyst in
various types of olefin metathesis [2m].
compound. This phase was treated with 20 ml of ether,
20 ml of water and as long as with KOH until the aq.
phase reached pH 9. The ethereal phase was separated,
and the aq. phase was furthermore extracted twice with
10 ml of ether. The combined ethereal solutions were
evaporated in vacuo to give a colorless viscous oil
which did not crystallize even upon storing at −20 °C
1
for days; yield 54 g (22%). H-NMR (200 MHz, C6D6):
l 2.00–1.81, 1.76–1.73, 1.58–1.48 (all m, 45H, C8H15).
2
13C-NMR (50.3 MHz, C6D6): l 31.8 [d, J(P,C)=14.5
1
Hz, C2 and C8 of C8H15], 31.2 [d, J(P,C)=22.2 Hz,
3
C1 of C8H15], 27.5 [d, J(P,C)=6.2 Hz, C3 and C7 of
C8H15], 27.3, 26.8 (both s, C4ꢁC6 of C8H15). 31P-NMR
(81.0 MHz, C6D6): l 30.7 (s).
3. Experimental
All experiments were carried out under an atmo-
sphere of Ar by Schlenk techniques. NMR spectra were
recorded at room temperature (r.t.) on Bruker AC 200
and AMX 400 instruments and IR spectra on a
Perkin–Elmer 1420 IR spectrometer. Melting points
were determined by DTA. Abbreviations used: s, sin-
glet; d, doublet; t, triplet; vt, virtual triplet; q, quartet;
m, multiplet; br, broadened signal; N=3J(P,H)+
3.2. Preparation of [RuHCl(PPh3)3] (3) from 2
A suspension of 105 mg (0.17 mmol) of 2 in 10 ml of
C3H8O was treated with 357 mg (1.36 mmol) of PPh3 at
r.t. After the Ar atmosphere was partially replaced by
dihydrogen (0.8 bar), the solution was warmed to
60 °C and stirred for 30 min at this temperature. A
small quantity of a violet solid was precipitated. After
the solution was cooled to 20 °C and stored for 12 h,
the obtained violet solid was separated from the mother
liquor, washed twice with 10 ml of C3H8O and dried in
vacuo; yield 292 mg (93%). The compound was charac-
1
5J(P,H) or J(P,C)+3J(P,C). The starting material 2
[15] was prepared as described in the literature. Cy-
clooctylbromide was prepared following a modified
procedure to that given by Willsta¨tter and Waser [16].
The reaction of cis-cyclooctene with HBr was carried
out in water (4 h, 80 °C) instead of AcOH as solvent.
The fractional distillation gave first unreacted cis-cy-
clooctene, then cyclooctane, and finally cyclooctylbro-
mide (b.p. 86 °C at 7 mbar) with a yield of 73%.
1
terized by comparing the H- and 31P-NMR spectro-
scopic data with those given in the literature [17].
3.3. Preparation of [RuHCl(H2)(PCoc3)2] (4)
A suspension of 204 mg (0.33 mmol) of 2 in 10 ml of
C3H8O was treated with 9.5 ml of a 0.30 M solution of
1 (2.89 mmol) in C6H5CH3 at r.t. After the Ar atmo-
sphere was partially replaced by dihydrogen (0.8 bar),
the reaction mixture was warmed to ca. 50 °C and
stirred for 10 min at this temperature. The obtained red
solution was cooled to 20 °C, the solvent was removed
in vacuo, and the oily residue was treated with 10 ml of
C3H6O. After ca. 1 h a light yellow solid precipitated,
which was separated from the mother liquor, washed
three times with 10 ml of C3H6O and dried in vacuo;
yield 396 mg (68%), m.p. (dec.) 102 °C. Anal. Found:
C, 66.33; H, 10.73. Calc. for C48H93ClP2Ru: C, 66.36;
3.1. Preparation of tricyclooctylphosphine (PCoc3) (1)
In a three-necked flask equipped with a reflux con-
denser and a dropping funnel 6.1 g (0.25 mol) of Mg
filings were covered with 20 ml of ether and activated
by addition of 1.80 ml (0.21 mol) of 1,2-dibromoethane.
After addition of 30 ml of ether, the mixture was
treated dropwise with a solution of 40.0 g (0.21 mol) of
cyclooctylbromide in 60 ml of ether and then heated for
1 h under reflux. After the solution (containing the
Grignard reagent with a concentration of 0.78 M) was
cooled to r.t., it was filtered and the filtrate was added
dropwise to a solution of 2.25 ml (25.7 mmol) of PCl3
in 200 ml of C6H5CH3 at −50 °C. After 2/3 of the
solution with the Grignard reagent was added, the
C3H6O–dry ice bath was removed. While the formation
of an off-white precipitate was observed, ca. 100 ml of
the solvent was distilled off. The remaining solution
was kept at 0 °C and treated with 20 ml of aq. HCl.
After the reaction was finished, three phases separated
which were investigated by spectroscopic techniques.
The 31P-NMR spectra revealed that solely the rather
viscous middle phase contained an organophosphorus
H, 10.79%. IR (KBr): w(RuH) 2104, 2056, 1905 cm−1
.
1H-NMR (200 MHz, C6D6): l 2.52, 2.16, 1.72–1.45 (all
m, 90H, C8H15), −16.0 [br s, 3H, RuH(H2)]. 13C-NMR
(100.6 MHz, C6D6): l 34.1 (vt, N=14.6 Hz, C1 of
C8H15), 31.5, 27.7, 27.6, 26.4 (all s, C8H15). 31P-NMR
(162.0 MHz, C6D6): l 76.7 (s).
3.4. Preparation of [RuCl2(ꢀCHCH3)(PCoc3)2] (5)
A solution of 200 mg (0.23 mmol) of 4 in 10 ml of
THF was treated with an excess of MgCl2 (200 mg, 2.10

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W. Stu¨er et al. / Journal of Organometallic Chemistry 641 (2002) 203–207
mmol). The suspension was cooled to −40 °C, the
Schlenk tube was evacuated and then filled with C2H2.
Under continuous stirring, the reaction mixture was
slowly warmed to r.t., which led to a gradual change of
color from yellow to pale brown. The solution was
treated with 0.1 ml (5.55 mmol) of water, and after it
was stirred for 20 min at 25 °C, the solvent was re-
moved in vacuo. The residue was extracted with 15 ml
of C5H12, and the extract brought to dryness in vacuo
to give a red–violet solid; yield 151 mg (70%), m.p.
(dec.) 89 °C. Anal. Found: C, 65.03; H, 9.77. Calc. for
C50H94Cl2P2Ru: C, 64.63; H, 10.20%. 1H-NMR (400
MHz, C6D6): l 19.54 [q, 3J(H,H)=5.6 Hz, 1H,
RuꢀCHCH3], 3.06 (br s, 6H, C8H15), 2.72 [d,
3J(H,H)=5.6 Hz, 3H, RuꢀCHCH3], 2.10 (br m, 12H,
C8H15), 1.75–1.44 (m, 72H, C8H15). 13C-NMR (100.6
C, 64.37; H, 9.66%. IR (KBr): w(RuꢀCꢀCH2) 2072,
w(RuH) 1907, w(OCOas) 1629, 1602, w(OCOsym) 1466,
1444 cm−1 1H-NMR (200 MHz, C6D6): l 2.86 [t,
.
4J(P,H)=3.0 Hz, 2H, RuꢀCꢀCH2], 2.71 (m, 6H, PCH),
2.48–2.19 (m, 12H, C8H15), 1.90–1.39 (m, 72H, C8H15),
−12.61 [t, 2J(P,H)=16.0 Hz, 1H, RuH]. 13C-NMR
(100.6 MHz, C6D6): l 334.4 [t, 2J(P,C)=13.0 Hz,
RuꢀCꢀCH2], 163.1 [q, 2J(C,F)=36.9 Hz, CF3CO2],
115.4 [q, 1J(C,F)=286 Hz, CF3CO2], 86.5 [t,
3J(P,C)=3 Hz, RuꢀCꢀCH2], 33.2 (vt, N=14.8 Hz, C1
of C8H15), 31.5, 31.0, 27.8, 27.6, 27.5, 26.0, 25.9 (all s,
C8H15). 19F-NMR (188.0 MHz, C6D6): l −75.4 (s).
31P-NMR (81.0 MHz, C6D6): l 64.6 (s).
Acknowledgements
MHz, C6D6):
l
314.3 [t, 2J(P,C)=6.3 Hz,
RuꢀCHCH3], 48.5 (s, RuꢀCHCH3), 30.8 (vt, N=16.3
Hz, C1 of C8H15), 27.6 (vt, N=8.6 Hz, C8H15), 30.9,
27.9, 25.9 (all s, C8H15). 31P-NMR (162.0 MHz, C6D6):
l 62.9 (s).
We thank the Deutsche Forschungsgemeinschaft
(SFB 347) and the Fonds der Chemischen Industrie for
financial support, the latter in particular for a Ph.D.
grant to W.S. Moreover, we acknowledge support by
R.S. and C.P.K. (elemental analysis and DTA), M.-L.S.
and Dr W.B. (NMR spectra) and BASF AG for gifts of
chemicals.
3.5. Preparation of [RuHCl(ꢀCꢀCH2)(PCoc3)2] (6)
A Schlenk tube containing a solution of 84 mg (0.10
mmol) of 4 in 10 ml of CH2Cl2 was cooled to −80 °C,
shortly evacuated and then filled with acetylene. A
quick change of color from yellow to red brown took
place. After the solution was stirred for 30 s, the solvent
was evaporated in vacuo. A brown solid remained,
which was washed with small quantities of C5H12
(0 °C) and dried; yield 88 mg (99%), m.p. (dec.)
122 °C. Anal. Found: C, 67.18; H, 10.34. Calc. for
C50H93ClP2Ru: C, 67.27; H, 10.50%. IR (KBr):
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