Reactivity of Ru(H)(H2)Cl(PCy3)2 with propargyl and vinyl chlorides: New methodology to give metathesis-active ruthenium carbenes

Article abstract of DOI:10.1021/om9705259

A procedure for generating the ruthenium hydride complex Ru(H)(H₂)Cl(PCy₃)₂ in 95% yield is presented. Following a novel insertion - elimination pathway, this hydride can react with propargyl or vinyl halides to make metathesis-active vinyl and alkyl carbene species with the general formulas (PCy₃)₂Cl₂-Ru=CH-CH=CR₂ and (PCy₃)₂Cl₂Ru=CHR, respectively. Tertiary propargyl chlorides work best, giving Ru-vinyl carbenes in extremely high yield.

Full text of DOI:10.1021/om9705259

© Copyright 1997
Volume 16, Number 18, September 2, 1997
American Chemical Society
Communications
Rea ctivity of Ru (H)(H2)Cl(P Cy3)2 w ith P r op a r gyl a n d
Vin yl Ch lor id es: New Meth od ology To Give
Meta th esis-Active Ru th en iu m Ca r ben es
Thomas E. Wilhelm, Toma´s R. Belderrain, Seth N. Brown, and
Robert H. Grubbs*
The Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and
Chemical Engineering, California Institute of Technology, Pasadena, California 91101
Received J une 23, 1997X
Summary: A procedure for generating the ruthenium
hydride complex Ru(H)(H2)Cl(PCy3)2 in 95% yield is
presented. Following a novel insertion-elimination
pathway, this hydride can react with propargyl or vinyl
halides to make metathesis-active vinyl and alkyl car-
bene species with the general formulas (PCy3)2Cl2-
RudCH-CHdCR2 and (PCy3)2Cl2RudCHR, respec-
tively. Tertiary propargyl chlorides work best, giving
Ru-vinyl carbenes in extremely high yield.
oxygen, protic solvents, and many functional groups.8-10
While these compounds can be prepared in moderate
to high yields, existing syntheses rely on relatively in-
accessible or unstable organic compounds such as 3,3-
diphenylcyclopropene10 or phenyl diazomethane.9 Here,
we describe a simple, high-yield preparation of a ru-
thenium hydride system which can be condensed with
a variety of propargyl or vinyl halides to give meta-
thesis-active ruthenium carbenes via a novel insertion-
elimination sequence.
The use of olefin metathesis has expanded tremen-
dously in recent years, with applications including the
construction of macrocycles in peptides and other sys-
tems,1-4 tandem ring opening/ring closing and construc-
tion of fused ring systems,5-7 and ring-opening meta-
thesis polymerization in aqueous media.8 Especially
useful are metathesis catalysts based on ruthenium,
which have demonstrated remarkable stability toward
The demonstration that osmium11-14 and ruthen-
ium15-17 hydride systems could be used to generate
(9) (a) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc.
1996, 118, 100-110. (b) Schwab, P.; France, M. B.; Ziller, J . W.;
Grubbs, R. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2039-2041.
(10) Nguyen, S. T.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc.
1993, 115, 9858.
(11) Espuelas, J .; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A.; Ruiz,
N. J . Am. Chem. Soc. 1993, 115, 4683-4689.
X Abstract published in Advance ACS Abstracts, August 1, 1997.
(1) Miller, S. J .; Blackwell, H. E.; Grubbs, R. H. J . Am. Chem. Soc.
1996, 118, 9606-9614.
(12) Esteruelas, M. A.; Lahoz, F. J .; Onate, E.; Oro, L. A.; Zeier, B.
Organometallics 1994, 13, 1662-1668.
(13) Hiraki, K.; Matsunaga, T.; Kawano, H. Organometallics 1994,
13, 1878-1885.
(14) Esteruelas, M. A.; Lahoz, F. J .; Onate, E.; Oro, L. A.; Valero,
C.; Zeier, B. J . Am. Chem. Soc. 1995, 117, 7935-7942.
(15) Esteruelas, M. A.; Lahoz, F. J .; Onate, E.; Oro, L. A.; Zeier, B.
Organometallics 1994, 13, 4258-4265.
(16) (a) Grunwald, C.; Gevert, O.; Wolf, J .; Gonzales-Herrero, P.;
Werner, H. Organometallics 1996, 15, 1960-1962. (b) Burrow, T.;
Saboetienne, S.; Chaudret, B. Inorg. Chem. 1995, 34, 2470-2472.
(17) Xia, H. P.; J ia, G. Organometallics 1997, 16, 1-4.
(2) Furstner, A. J . Org. Chem. 1996, 61, 3942.
(3) Rutjes, F. P. J .; Schoemaker, H. E. Tetrahedron Lett. 1997, 38,
677.
(4) McKerrvey, M. A.; Pitarch, M. Chem. Commun. 1996, 1689.
(5) Zuercher, W. J .; Hashimoto, M.; Grubbs, R. H. J . Am. Chem.
Soc. 1996, 118, 6634-6640.
(6) Clark, J . S.; Kettle, J . G. Tetrahedron Lett. 1997, 38, 123.
(7) Barrett, A. G. M.; Gibson, V. C. Chem. Commun. 1997, 155.
(8) Mohr, B.; Lynn, D. M.; Grubbs, R. H. Organometallics 1996, 15,
4317-4325.
S0276-7333(97)00525-6 CCC: $14.00 © 1997 American Chemical Society

3868 Organometallics, Vol. 16, No. 18, 1997
Sch em e 1. In ser tion -Elim in a tion w ith P r op a r gyl Ch lor id es
Communications
carbenes suggested to us that metal hydrides might be
an efficient system for the generation of metathesis-
active carbene complexes of general form (PCy3)2-
Cl2RudCHR. A suitable ruthenium hydride starting
material is Ru(H)(H2)Cl(PCy3)2 (1),18,19 which contains
the appropriate number of phosphines and lacks tightly
bound carbonyl ligands. Previous multistep syntheses
of 1 focused on the transformation from Ru(1,3,5-
cyclooctatriene)(1,5-cyclooctadiene) either directly or
through isolation of Ru(H)2(H2)2(PCy3)2.18 Recently, in
the preparation of Ru(H)2(Cl)2(PiPr3)2, the similar spe-
cies Ru(H)(H2)Cl(PiPr3)2 was proposed as an intermedi-
ate in a reaction with [RuCl2(COD)]x (2), PiPr3, and H2
in sec-butyl alcohol.16 Further, it was demonstrated
that a solution of this intermediate could be reacted with
acetylenes to give ruthenium carbene species.16
indicates that it is complete in less than 10 min, even
at -30 °C, and integration against an internal standard
shows that the yield is ∼99.5%.
Other propargylic halides react similarly. Alkynes
with tertiary (1-ethynylchlorocyclohexane, to form
(PCy3)2Cl2RudCHsCHdC(CH2)5 (5)) or benzylic (HCt
CCH(Ph)Cl, to form (PCy3)2Cl2RudCHsCHdCHPh (6))
chlorides react essentially quantitatively, although a
trace of the ruthenium(IV) complex 3 is seen as a by-
product. The amount of 3 formed increases as the steric
bulk of the propargyl group decreases, with the mono-
methyl-substituted HCtCCH(CH3)Cl giving (PCy3)2Cl2-
RudCHsCHdCHMe (7) and 3 in an 8:1 ratio and the
parent propargyl chloride HCtCCH2Cl giving (PCy3)2-
Cl2RudCHsCHdCH2 (8) and 3 in a 0.8:1 ratio. Chang-
ing the halogen from chlorine to bromine also increases
the amount of 3 formed: the dimethyl-substituted pro-
pargyl bromide, HCtCC(Me)2Br, gives a 30:1 ratio of
the expected mixed halogen carbene (PCy3)2ClBrRud
CH-CHdCMe2 (9) to the mixed halogen Ru(IV) species
Ru(H)2ClBr(PCy3)2 (10), which is substantially different
from the >200:1 ratio seen with the corresponding
chloride. The ratios of carbene to 3 can be improved
dramatically if the solvent is changed from dichlo-
romethane to benzene or toluene: from 0.8:1 to 30:1 for
8, from 8:1 to 37:1 for 7, and to no detectable Ru(IV) in
the generation of 6 and 9.
Attempts to make 1 via 2 following the above method
were promising, giving 1 in 40% yield along with a
large amount of a Ru(IV) species presumed to be Ru-
1
(H)2(Cl)2(PCy3)2 (3) from H and 31P NMR data. Since
the reaction between isolated 1 and HCl gives the same
Ru(IV) species and since HCl is produced in the reac-
tion that forms 1, it was surmised that the addition of
base to the reaction mixture would improve the yield of
1. Reacting [RuCl2(COD)]x, PCy3, H2, and NEt3 in sec-
butyl alcohol for 8 h at 80 °C gives the desired orange,
air-sensitive hydride Ru(H)(H2)Cl(PCy3)2 (1) in 94%
yield.20
The hydrido chloride complex Ru(H)(H2)Cl(PCy3)2 (1)
reacts rapidly with a variety of propargylic halides to
yield ruthenium vinylcarbene complexes. For example,
1 reacts immediately with commercially available
3-choro-3-methyl-1-butyne in methylene chloride to give
the dimethylvinylcarbene complex (PCy3)2Cl2Rud
CH-CHdCMe2 (4) in 95% isolated yield (Scheme 1, R1
) R2 ) Me).21 Monitoring the reaction by 1H NMR
The proposed mechanism for the formation of vinyl-
carbene complexes (Scheme 1) involves insertion of the
alkyne into the Ru-H bond to form a γ-chloroalkenyl
group, which rapidly undergoes rearrangement to give
formal addition of chloride to ruthenium. It is less clear
how the ruthenium(IV) product is formed, but the
observed steric and solvent effects are consistent with
a competing pathway involving direct oxidative addi-
tion of the carbon-halogen bond. Alkyne insertion is
(18) Christ, M. L.; Sabo-Etienne, S.; Chaudret, B. Organometallics
1994, 13, 3800-3804.
(21) (P Cy3)2Cl2Ru (dCH-CHdCMe2) (2): Ru(H)(H2)2Cl(PCy3)2 (1)
(1.00 g, 1.43 mmol) under an inert atmosphere is dissolved in 30
mL of dichloromethane cooled to -30 °C, and 3-chloro-3-methyl-1-
butyne (170 µL, 1.5 mmol) is added. The solution instantly turns
dark red-purple and is allowed to stir for 15 min before removing
the flask from the cooling bath and concentrating to a viscous oil.
Degassed methanol (20 mL) is added to precipitate the purple solid,
which is then washed with methanol (3 × 10 mL) and dried to give
1.09 g, 95% of the carbene 2. Selected NMR data (CD2Cl2): 1H NMR
δ 19.26 (d, RuCH, J HH ) 11.7 Hz), 7.81 (d, RuCHCH, J HH ) 11.7 Hz);
31P NMR δ 36.4 (s, RuPCy3); 13C NMR δ 288.4 (t, RuCH, J CP ) 9.6
Hz), 146.9 (s), 133.5 (s). All other reactions with 1 were done in a
similar fashion but on a 20 mg scale in 0.5 mL of CD2Cl2. Noncom-
mercially available alkynes were made following the procedures in
Brandsma, L. Preparative Acetylenic Chemistry; Elsevier: Amsterdam,
1988.
(19) Beatty, R. P.; Paciello, R. A. U.S. Patent 5,554,778, 1996.
(20) Ru (H)(H2)Cl(P Cy3)2 (1): [RuCl2(COD)]x (3) (4.00 g, 14.28
mmol) and tricyclohexylphosphine (Strem, 97% pure, 8.46 g, 29.26
mmol) were placed in a 500 mL high-pressure system equipped with
a pressure gauge. To this system, 200 mL of degassed sec-butyl alcohol
and triethylamine (1.99 mL, 14.28 mmol) were added. After purging
with hydrogen, the system was pressurized with 1.5 atm of hydrogen
and heated to 80 °C for a total of 20 h, repressurizing as needed.
Generation of (1) can also be accomplished in a suitably-sized, thick-
walled Teflon-valved Straus flask. The air-sensitive orange solid was
isolated by cooling the system to room temperature, adding a volume
(200 mL) of degassed methanol to ensure complete precipitation before
filtering, washing with methanol (3 × 50 mL), and drying in vacuo to
give 9.26 g, 94% of 1.

Communications
Organometallics, Vol. 16, No. 18, 1997 3869
Sch em e 2. F or m a tion of Ca r ben es by In ser tion -Elim in a tion w ith Vin yl Ch lor id es
well-precedented for closely related complexes such
as MHCl(CO)(PiPr3)2 (M ) Os, Ru).12,15,22 Ionization
at the γ-carbon is also precedented, as in the formation
of [trans-Cl(CO)(PiPr3)2RudCHCHdCR2]BF4 on proto-
nation of the γ-hydroxyvinyl complex trans-Cl(CO)-
(PiPr3)2RusCHdCHsC(OH)R2.15 Evidently the se-
quence of insertion-elimination made possible in this
system by the presence of both an alkyne and a leaving
group allows extremely efficient access to vinylcarbene
species.
Another possible reaction type which could follow the
same general insertion-elimination pathway is between
metal hydrides and vinylic halides (Scheme 2). Again,
insertion of olefins into Ru-H bonds is well-known,13,23
and if the proper regiochemistry can be achieved, this
opens the possibility of R-halide elimination to give
carbenes (â-halogen elimination can yield only ruthe-
nium halide and dehalogenated alkene).
Consistent with the insertion-elimination mecha-
nism, the ruthenium hydride complex 1 does react with
alkenyl halides to give carbene products, but the reac-
tions are significantly less clean than those observed
with propargyl halides. For example, 1 reacts with an
excess of vinyl chloride to give the expected carbene
(PCy3)2Cl2RudCHsCH3 (11),9 the methylidene complex
(PCy3)2Cl2RudCH2 (12),9 (arising from cross-metathesis
of 11 with vinylchloride to give 12 and 1-chloropropene),
and the Ru(IV) species 3. The ratio of total carbenes:3
is a modest 2.1:1. Increasing the steric bulk at the â-
carbon (to suppress â-addition) does not improve the
yield of carbene, with 1 and a mixture of cis- and trans-
1-chloro-1-propene reacting to give the propylidene
complex (PCy3)2Cl2RudCHCH2CH3 (13)9 and 3 in a
ratio of 0.8:1. This suggests that â-addition is not the
dominant pathway in the generation of 3 from 1 and
vinyl chlorides. The â-disubstituted olefin 1-chloro-2-
methyl-1-propene produces no carbene and only gives
3 very slowly (several days vs <10 min for all other
reactions).
In conclusion, we have presented a high-yield prepa-
ration for the ruthenium hydride starting material 1
and have shown that it can be used in conjunction with
bulky propargyl chlorides to give ruthenium vinyl car-
benes in excellent overall yields. In addition to its quan-
titative improvements, this process offers other advan-
tages over previously available preparations: the need
to waste 3 equiv of triphenylphosphine in the prepara-
tion of catalyst intermediates is eliminated and the
organic fragment does not require a complex or danger-
ous synthetic methodology. The high yield and simple
procedures involved appear to make this a nearly ideal
preparation of 3,3-disubstituted vinylcarbene complexes
(PCy3)2Cl2RudCHsCHdCR2 which are known to have
significant activity in olefin metathesis.10 The reaction
of 1 with alkenyl chlorides generates the more reactive
alkyl carbenes,9 but with too many byproducts to be
synthetically useful. Current investigations focus on
expanding the scope of the insertionselimination method
for the generation of ruthenium carbenes, as well as on
the mechanisms of the transformations involved.
OM9705259
(22) Werner, H.; Meyer, U.; Peters, K.; von Schnering, H. G. Chem.
Ber. 1989, 122, 2097-2107.
(23) Hiraki, K.; Ochi, N.; Sasada, Y.; Hayashida, H.; Fuchita, Y.;
Yamanaka, S. J . Chem. Soc., Dalton Trans. 1985, 873-877.