[Ru(η3-2-C3H4Me)(CO)(dppf)][SbF 6]: A mononuclear 16e- ruthenium(II) catalyst for propargylic substitution and isomerization of HC≡CCPh2(OH)

Article abstract of DOI:10.1039/b410812d

The 16e^- derivative [Ru(η³-2-C₃H ₄Me)(CO)(dppf][SbF₆] catalyzes: (i) the propargylic substitution reaction of 1,1-diphenyl-2-propyn-1-ol with alcohols to produce propargylic ethers, and (ii) the formal isomerization of 1,1-diphenyl-2-propyn- 1-ol into 3,3-diphenyl-2-propenal.

Full text of DOI:10.1039/b410812d

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[Ru(g3-2-C3H4Me)(CO)(dppf)][SbF6]: a mononuclear 16e2
ruthenium(II) catalyst for propargylic substitution and isomerization of
HCMCCPh2(OH){
Victorio Cadierno,* Josefina D´ıez, Sergio E. Garc´ıa-Garrido and Jose´ Gimeno*
Departamento de Qu´ımica Orga´nica e Inorga´nica, I.U.Q.O.E.M. (Unidad Asociada al CSIC), Facultad de
Qu´ımica, Universidad de Oviedo, E-33071 Oviedo, Spain. E-mail: jgh@uniovi.es (J. Gimeno);
vcm@uniovi.es (V. Cadierno); Fax: 134985103446; Tel: 134985103461
Received (in Cambridge, UK) 15th July 2004, Accepted 7th September 2004
First published as an Advance Article on the web 14th October 2004
The 16e2 derivative [Ru(g3-2-C3H4Me)(CO)(dppf)][SbF6]
with its unsaturated nature, 2 readily reacts with two-electron
donor ligands such as acetonitrile, carbon monoxide and benzyl
isocyanide to afford the corresponding 18e2 derivatives [Ru(g3-2-
C3H4Me)(CO)(L)(dppf)][SbF6] (3–5) in excellent yields (91–95%
yield; see Scheme 2).§ The structure of complex 5 has been
unequivocally confirmed by X-ray crystallography (see ESI}).
However, the reaction of complex 2 with 1,1-diphenyl-2-propyn-1-
ol, using different solvents and conditions, does not lead to the
catalyzes: (i) the propargylic substitution reaction of 1,1-
diphenyl-2-propyn-1-ol with alcohols to produce propargylic
ethers, and (ii) the formal isomerization of 1,1-diphenyl-2-
propyn-1-ol into 3,3-diphenyl-2-propenal.
Although the Nicholas reaction constitutes a direct and widely used
methodology for stoichiometric propargylic substitutions,1 the
search for a catalytic route has been a main synthetic goal.
Nevertheless, only a few examples have been reported to date.2 In
this context, M. Hidai, S. Uemura and co-workers have recently
disclosed an efficient ruthenium-catalyzed substitution reaction of
terminal propargylic alcohols with various heteroatom- and
carbon-centered nucleophiles (see Scheme 1).3 We note that
while secondary propargylic alcohols HCMCCHR(OH) have
been extensively used in these transformations, only a few examples
involving tertiary alcohols HCMCCR2(OH) have been reported.3a
Scheme 2 Synthesis and reactivity of the 16e2 complex 2. Reagents and
conditions: i, AgSbF6 (1 equiv.), CH2Cl2, r.t.; ii, L (excess), CH2Cl2, r.t.
Table 1 Ru-catalyzed propargylic substitution reactions of 1,1-
diphenyl-2-propyn-1-ol with alcoholsa
Scheme 1 Ruthenium-catalyzed propargylic substitution reactions.
These catalytic processes proceed via an allenylidene-ruthenium
intermediate [Ru]LCLCLCR1R2, which is generated from chalco-
genolate-bridged diruthenium(III) complexes [Cp*RuCl(m2-XR)2-
RuCp*Cl] and [Cp*RuCl(m2-XR)2RuCp*(H2O)][OTf] (Cp* ~
g5-C5Me5; X = S, Se) by dehydration of the propargylic alcohol,
and subsequent attack of the nucleophile at the electrophilic Cc
atom.4 Surprisingly, mononuclear Ru(II) derivatives such as
[RuCl2(PPh3)3], [RuCl2(dppe)2], [RuCl(PPh3)2Cp] (Cp ~ g5-
C5H5) or [RuCl(g5-C9H7)(PPh3)2] are inactive despite their
known ability to generate allenylidene complexes from propargylic
alcohols.4–6 Intramolecular charge transfer across the Ru–Ru bond
in the dinuclear species has been proposed as a key factor to
promote such catalytic transformations (synergistic effect).3e In
contrast to these results, we have now found that the 16e2
mononuclear (g3-allyl)-ruthenium(II) derivative [Ru(g3-2-
C3H4Me)(CO)(dppf)][SbF6] (2; dppf ~ 1,1’-bis(diphenylphosphi-
no)ferrocene) is an efficient catalyst for the propargylic substitution
reaction of 1,1-diphenyl-2-propyn-1-ol with a large variety of
alcohols, demonstrating that the presence of a Ru–Ru framework
is not essential.
Entry
ROH
Time
Yield of 6b
Yield of 7b
1
2
3
MeOH
EtOH
4 h
6 h
5 h
6a, 80% (75%)
6b, 76% (72%)
6c, 94% (87%)
10%
19%
4%
4
8 h
6d, 86% (80%)
14%
5
24 h
6e, 73% (68%)
24%
6
7
24 h
24 h
6f, 62% (56%)
6g, 93% (89%)
31%
7%
The cationic 16e2 complex 2 was prepared in 97% yield by
treatment of a dichloromethane solution of [RuCl(g3-2-C3H4Me)(-
CO)(dppf)]7 with 1 equiv. of AgSbF6 (Scheme 2). Complex 2,
which has been isolated as an air-stable yellow solid, has been
characterized by conductance measurements, mass spectrum
(FAB), elemental analyses and IR and NMR spectroscopy, all
data being fully consistent with the structural proposal.{ In accord
8
9
11 h
10 h
6h, 90% (81%)
6i, 93% (90%)
10%
0%
a Reactions performed under N2 atmosphere at 75 uC using 1 mmol
of HCMCCPh2(OH) (1.0 M in the corresponding alcohol) and
0.05 mmol of 2. b Yields determined by GC (isolated yields in
parentheses).
{ Electronic supplementary information (ESI) available: experimental
section. See http://www.rsc.org/suppdata/cc/b4/b410812d/
2 7 1 6
C h e m . C o m m u n . , 2 0 0 4 , 2 7 1 6 – 2 7 1 7
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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expected 18e2 diphenylallenylidene derivative [Ru(LCLCLCPh2)-
(g3-2-C3H4Me)(CO)(dppf)][SbF6], giving instead a complex reac-
tion mixture. Remarkably, GC/MS analysis of the reaction with an
excess of HCMCCPh2(OH) in methanol at 75 uC shows the total
disappearance of the propargylic alcohol with concomitant
formation of HCMCCPh2(OMe) (6a). On the basis of these
observations a catalytic reaction was performed (5 mol% of 2) in
methanol and ethanol at 75 uC affording the corresponding
propargylic ethers 6a,b in 80 and 76% GC yield, respectively (75
and 72% isolated yield; entries 1–2 in Table 1). The generality of
this catalytic transformation has been confirmed by using
functionalized alcohols such as allylic (entries 3–6), homoallylic
(entry 7), propargylic (entry 8) and homopropargylic (entry 9)
alcohols, allowing the isolation of the corresponding enynes (6c–g)
and diynes (6h,i) in high yields (56–90%). Minor amounts of 3,3-
diphenyl-2-propenal 7 are in all the cases formed (with the
exception of entry 9), its proportion being dependent on the steric
properties of the alcohol used (compare entries 3–6). Remarkably,
this a,b-unsaturated aldehyde, which results from the formal
isomerization of the propargylic alcohol,8 can be selectively
obtained (95% yield) if the catalytic reaction is carried out in the
absence of alcohol using undistilled THF as solvent (5 mol% of Ru,
1 M solution, 1.5 h at 75 uC; see ESI). The formal isomerization of
propargylic alcohols into the corresponding a,b-unsaturated
aldehydes is a useful synthetic process which proceeds with a
total atom economy.
isomerization with disubstituted derivatives8a in one single step.8b
Further studies on the scope of these catalytic reactions,9 as well as
detailed mechanistic investigations, are now in progress.
This work was supported by the MCyT of Spain (Project
BQU2003-00255). S.E.G.-G. and V.C. thank the MCyT for the
award of a Ph.D. grant and a Ramo´n y Cajal contract.
Notes and references
{ Synthesis and characterization of 2: A solution of 1 (0.774 g, 1 mmol) in
dichloromethane (50 cm3) was treated with AgSbF6 (351 mg, 1 mmol) and
stirred for 15 min at room temperature in the absence of light. The AgCl
formed was then filtered off (Kieselguhr) and the resulting solution
evaporated to dryness to afford a yellow solid which was washed with
diethyl ether (3 6 50 cm3) and vacuum-dried. Yield: 0.945 g, 97% (Found:
C, 47.92; H, 3.71. RuFeC39H35F6P2OSb requires C, 48.08; H, 3.62%); LM
(acetone, 20 uC) 113.4 V21 cm2 mol21; n/cm21 (CO) 1944s (KBr); dP
(CD2Cl2) 39.79 (s); dH (CD2Cl2) 1.26 (s, 2 H, CHH(anti)), 2.21 (s, 3 H, CH3),
3.79 (s, 2 H, CHH(syn)), 4.31, 4.51, 4.69 and 4.93 (br, 2 H each, C5H4), 7.10–
7.70 (m, 20 H, Ph); dC (CD2Cl2) 26.07 (s, CH3), 60.87 (m, second-order
system, CH2), 72.96, 73.18, 75.16 and 75.47 (br, CH of C5H4), 81.24 (d,
1J(C,P) ~ 48.8 Hz, C of C5H4), 121.72 (s, C), 127.80–135.50 (m, Ph),
205.01 (t, 2J(C,P) ~ 16.8 Hz, CO); MS (FAB) m/z 739 [M1], 655 [M1 2
CO 2 C3H4Me].
§ Compounds 3–5 have been characterized by NMR spectroscopy and
elemental analyses. See ESI.
} CCDC 245208. See http://www.rsc.org/suppdata/cc/b4/b410812d/ for
crystallographic data in .cif or other electronic format.
The catalytic activity of complex 2 is higher than that shown by
the dimers [Cp*RuCl(m2-XR)2RuCp*Cl], i.e. using 5 mol% of
[Cp*RuCl(m2-SMe)2RuCp*Cl] (10 mol% of Ru) and 10 mol% of
NH4BF4 as co-catalyst HCMCCPh2(OH) was transformed into
HCMCCPh2(OEt) in 62% yield after 20 h at 60 uC in EtOH (to be
compared with entry 2).3a It is also worth mentioning that catalyst
2 is also active with functionalized alcohols (entries 3–9) showing a
remarkable chemoselectivity towards the coordination of the
terminal alkynol vs. the CLC and CMC bonds of the alcohols. No
similar activity has been reported previously.
Formation of both 6 and 7 most probably involves a highly
reactive Ru-allenylidene intermediate which undergoes the nucleo-
philic addition of the alcohols and water at the electrophilic Cc and
Ca atoms of the unsaturated chain, respectively (intermediates A
and B in Scheme 3).4 Thus, demetalation of vinylidenes A and
hydroxycarbene B could generate ethers 6 and 3,3-diphenyl-2-
propenal 7, respectively.
1 For reviews on the Nicholas reaction see: K. M. Nicholas, Acc. Chem.
Res., 1987, 20, 207; J. R. Green, Curr. Org. Chem., 2001, 5, 809;
B. J. Teobald, Tetrahedron, 2002, 58, 4133.
2 Cu(I)-, Ti(IV)- and Ir(I)-catalyzed nucleophilic substitution of propargylic
esters with alcohols, amines, amides and enoxysilanes are known:
Y. Imada, M. Yuasa, I. Nakamura and S.-I. Murahashi, J. Org. Chem.,
1994, 59, 2282; R. Mahrwald and S. Quint, Tetrahedron, 2000, 56, 7463;
R. Mahrwald and S. Quint, Tetrahedron Lett., 2001, 42, 1655;
R. Mahrwald, S. Quint and S. Scholtis, Tetrahedron, 2002, 58, 9847;
I. Matsuda, K.-I. Komori and K. Itoh, J. Am. Chem. Soc., 2002, 124,
9072.
3 See for example: (a) Y. Nishibayashi, I. Wakiji and M. Hidai, J. Am.
Chem. Soc., 2000, 122, 11019; (b) Y. Nishibayashi, I. Wakiji, Y. Ishii,
S. Uemura and M. Hidai, J. Am. Chem. Soc., 2001, 123, 3393;
(c) Y. Nishibayashi, M. Yoshikawa, Y. Inada, M. Hidai and S. Uemura,
J. Am. Chem. Soc., 2002, 124, 11846; (d) Y. Nishibayashi, G. Onodera,
Y. Inada, M. Hidai and S. Uemura, Organometallics, 2003, 22, 873;
(e) Y. Nishibayashi, H. Imajima, G. Onodera, M. Hidai and S. Uemura,
Organometallics, 2004, 23, 26; (f) Y. Nishibayashi, M. Yoshikawa,
Y. Inada, M. Hidai and S. Uemura, J. Org. Chem., 2004, 69, 3408.
4 For general reviews on the chemistry of allenylidene complexes see:
M. I. Bruce, Chem. Rev., 1998, 98, 2797; V. Cadierno, M. P. Gamasa
and J. Gimeno, Eur. J. Inorg. Chem., 2001, 571.
5 We have described a number of stoichiometric propargylic substitution
reactions mediated by the indenyl complex [RuCl(g5-C9H7)(PPh3)2]:
V. Cadierno, S. Conejero, M. P. Gamasa and J. Gimeno, Dalton Trans.,
2003, 3060 and references therein.
6 Complexes [RuClL2Cp] (L ~ PPh3; L2 ~ COD) have been found to
catalyze the S-propargylation of thiols with internal propargylic
carbonates via (s-propargyl)-ruthenium intermediates: T. Kondo,
Y. Kanda, A. Baba, K. Fukuda, A. Nakamura, K. Wada,
Y. Morisaki and T. Mitsudo, J. Am. Chem. Soc., 2002, 124, 12960.
7 V. Cadierno, P. Crochet, J. D´ıez, S. E. Garc´ıa-Garrido, J. Gimeno and
S. Garc´ıa-Granda, Organometallics, 2003, 22, 5226.
8 (a) One-step isomerization of monosubstituted propargylic alcohols
HCMCCHR(OH) into RCHLCHCHO using [RuCl(PMe3)2Cp] as
catalyst under neutral conditions (iPrOH/H2O) has been recently
reported (disubstituted propargylic alcohols do not react at all):
T. Suzuki, M. Tokunaga and Y. Wakatsuki, Tetrahedron Lett., 2002,
43, 7531; (b) A general two-step transformation of propargylic alcohols
into a,b-unsaturated aldehydes using a [Ru(g3-2-C3H4Me)2(dppe)]/
PhCO2H/PTSA catalytic system is known: M. Picquet, A. Ferna´ndez,
C. Bruneau and P. H. Dixneuf, Eur. J. Org. Chem., 2000, 2361.
9 Complex 2 catalyzes also the propargylic substitution reaction of
monosubstituted derivatives HCMCCHR(OH) with alcohols. As an
example, under the same reaction conditions, HCMCCHPh(OH) reacts
with CH2LCHCH2OH to afford HCMCCHPh(OCH2CHLCH2) in 67%
yield after 6 h (an uncharacterised by-product is also formed in ca. 30%
yield).
Scheme 3 Proposed [Ru]-intermediates in the formation of 6 and 7.
In summary, a new mononuclear ruthenium(II) catalyst active in
both propargylic substitution and isomerization of 1,1-diphenyl-2-
propyn-1-ol is reported. Two main features deserve to be
mentioned: (i) complex 2 is the first mononuclear ruthenium(II)
complex active in propargylic substitutions starting from pro-
pargylic alcohols, and (ii) although other ruthenium(II) catalysts
are active in the transformation of propargylic alcohols into
a,b-unsaturated aldehydes, this is the first to perform the
C h e m . C o m m u n . , 2 0 0 4 , 2 7 1 6 – 2 7 1 7
2 7 1 7