Hydration of nitrosylruthenium acetylide complexes having a tris(pyrazol-1-yl)borate in the presence of protic acid: Formation of ketonyl and acyl complexes

Article abstract of DOI:10.1021/om0303597

The hydration of nitrosylruthenium acetylide complexes having a tris(pyrazol-1-yl)borate in the presence of protic acid was studied. The protonation of the monoacetylide complexes caused a hydration reaction, producing ketonyl complexes and unsaturated acyl complexes. Spectroscopic data confirmed the ketonyl complex and the α,β-unsaturated acyl complexes.

Full text of DOI:10.1021/om0303597

3354
Organometallics 2003, 22, 3354-3356
Hyd r a tion of Nitr osylr u th en iu m Acetylid e Com p lexes
Ha vin g a Tr is(p yr a zol-1-yl)bor a te in th e P r esen ce of
P r otic Acid : F or m a tion of Keton yl a n d Acyl Com p lexes
Yasuhiro Arikawa, Yoshimasa Nishimura, Hiroyuki Kawano,† and
Masayoshi Onishi*
Department of Applied Chemistry, Faculty of Engineering, Nagasaki University,
Bunkyo-machi 1-14, Nagasaki 852-8521, J apan
Received May 12, 2003
Summary: Treatment of the monoacetylide complexes
TpRuCl(CtCR)(NO) (R ) Ph (1a ), p-CH3C6H4 (1b),
tBu (1c), CH2CH2OH (1d ), CH2OH (1e), C(Me)2OH (1f),
C(Ph)2OH (1g); Tp ) BH(pyrazol-1-yl)3) with HBF4‚Et2O
in methanol afforded the ketonyl complexes TpRuCl-
(CH2C(O)R)(NO) (R ) Ph (2a ), p-CH3C6H4 (2b), tBu (2c),
CH2CH2OMe (2d ), CH2OH (2e)) and the R,â-unsaturated
acyl complexes TpRuCl(C(O)CHdCR′2)(NO) (R′ ) Me
(3f), Ph (3g)), respectively. While the latter were produced
by hydration via allenylidene species, the former were
presumably generated from the reaction of η2-coordinat-
ed 1-alkyne species with adventitious water.
erated because of the reactions with adventitious water.
The former is the first structurally characterized ex-
ample of ketonyl ruthenium complexes that are formed
through hydration of acetylide complexes.
The σ-acetylide complexes TpRuCl(CtCR)(NO) (R )
t
Ph (1a ), p-CH3C6H4 (1b), Bu (1c), CH2CH2OH (1d ),
CH2OH (1e), C(Me)2OH (1f), C(Ph)2OH (1g)) were
prepared from TpRuCl2(NO) and an excess of the
corresponding terminal alkynes HCtCR in the presence
of Et3N, producing poly(acetylene) as byproducts in the
1
cases of 1a and 1b. The H NMR spectra of complexes
1a -g exhibit three distinct sets of pyrazol-1-yl reso-
nances in addition to those of acetylide units. In the
IR spectra of these complexes, characteristic NO+ and
CtC stretching bands were observed.
The chemistry of ruthenium vinylidene and allen-
ylidene complexes has attracted increasing attention
because of their occurrence as key intermediates in
stoichiometric and catalytic transformations of organic
molecules.1 Their complexes supported by cyclopenta-
dienyl or tris(pyrazolyl)borate have been widely stud-
ied.2 Many coligands in TpRu (Tp ) BH(pyrazol-1-yl)3)
complexes have not been used other than phosphines,
amines, and diene. We are interested in the electron-
withdrawing coligand NO+ and have begun to investi-
gate the use of TpRuCl2(NO)3 as a starting material.
We first attempted to prepare the vinylidene and
allenylidene species with a TpRuCl(NO) fragment by
the reactions with terminal acetylenes and propargyl
alcohols in the presence of the appropriate salts such
When TpRuCl(CtCPh)(NO) (1a ) was reacted with
HBF4‚Et2O in THF (distilled) under reflux for 6 h, the
ketonyl complex TpRuCl(CH2C(O)Ph)(NO) (2a ) was
obtained in 38% yield. No reaction was found between
1a and acetic acid in refluxing THF.
The IR spectrum of 2a shows two characteristic bands
at 1855 and 1633 cm-1, which are assigned to NO+ and
1
CO stretching, respectively. In the H NMR spectrum
of 2a , two doublets at δ 4.82 and 3.45, coupled to each
other (J ) 6.0 Hz), were attributed to nonequivalent,
i.e. diastereotopic, protons in the ruthenium-bonded
methylene group. The carbonylic and methylene carbons
give rise to 13C{1H} NMR signals at δ 204.8 and 31.7,
respectively. The former is very close to those for ketonyl
as NH4PF6, AgBF4, and NaBArF (ArF ) 3,5-C6H3-
4
(CF3)2). These reactions, however, did not take place.
Thus another strategy for their syntheses focused on
the protonation of σ-acetylide complexes. However, the
ketonyl and R,â-unsaturated acyl complexes were gen-
complexes described in the literatures.4
A
13C-DEPT
experiment confirms these assignments. Furthermore,
released acetophenone was detected by GC analysis
when the mixture of complex 2a and concentrated HCl
* To whom correspondence should be addressed. E-mail: onishi@
net.nagasaki-u.ac.jp.
1
in benzene was refluxed. Since H NMR shows that 2a
† Present address: Kogakuin University, 2665-1 Nakano, Hachioji,
Tokyo 192-0015, J apan.
was produced quantitatively before column chromato-
graphic purification, the formation of 2a would occur
by the reaction with traces of water present in the
reaction mixture. Addition of H2O to the mixture
increased the yield of 2a (75%). Analogous high reactiv-
ity toward water has been found in protonation reaction
of (arene)ruthenium alkynyl complex, where the vin-
ylidene intermediate is proposed, followed by hydration
(1) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197-257. (b) Bruce, M. I.
Chem. Rev. 1998, 98, 2797-2858. (c) Touchard, D.; Dixneuf, P. H.
Coord. Chem. Rev. 1998, 178-180, 409-429. (d) Bruneau, C.; Dixneuf,
P. H. Acc. Chem. Res. 1999, 32, 311-323. (e) Puerta, M. C.; Valerga,
P. Coord. Chem. Rev. 1999, 193-195, 977-1025. (f) Cadierno, V.;
Gamasa, M. P.; Gimeno, J . Eur. J . Inorg. Chem. 2001, 571-579. (g)
Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001, 101, 2067-
2096. (h) Grotjahn, D. B.; Incarvito, C. D.; Rheingold, A. L. Angew.
Chem., Int. Ed. 2001, 40, 3884-3887. (i) Ritleng, V.; Sirlin, C.; Pfeffer,
M. Chem. Rev. 2002, 102, 1731-1769. (j) Inada, Y.; Nishibayashi, Y.;
Hidai, M.; Uemura, S. J . Am. Chem. Soc. 2002, 124, 15172-15173.
(2) (a) Bennett, M. A.; Khan, K.; Wenger, E. In Comprehensive
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon Press: Oxford, UK, 1995; Vol. 7, p 513. (b) Slugovc,
C.; Schmid, R.; Kirchner, K. Coord. Chem. Rev. 1999, 185-186, 109-
126.
(4) (a) Hartwig, J . F.; Bergman, R. G.; Andersen, R. A. Organome-
tallics 1991, 10, 3326-3344. (b) Vicente, J .; Bermu¨dez, M.-D.; Carrillo,
M.-P.; J ones, P. G. J . Chem. Soc., Dalton Trans. 1992, 1975-1980. (c)
Veya, P.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1993,
12, 4899-4907. (d) Lin, Y.-S.; Misawa, H.; Yamada, J .; Matsumoto,
K. J . Am. Chem. Soc. 2001, 123, 569-575.
(3) Onishi, M. Bull. Chem. Soc. J pn. 1991, 64, 3039-3045.
10.1021/om0303597 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 07/24/2003

Communications
Organometallics, Vol. 22, No. 17, 2003 3355
Sch em e 1
to produce the acyl complex.5 When 1a was treated with
HBF4‚Et2O in methanol instead of THF, the reaction
was immediately completed at room temperature and
a slight increase of the yield was observed (80%).6a
Similarly, other ketonyl complexes TpRuCl(CH2C-
(O)R)(NO) (R ) p-CH3C6H4 (2b), tBu (2c), CH2CH2OMe
(2d)) also were synthesized by reactions between TpRuCl-
F igu r e 1. Molecular structure of 2b (thermal ellipsoids
at the 50% level). One of the two crystallographically
independent molecules of 2b is drawn. Crystal solvent and
hydrogen atoms were omitted for clarity. Selected bond
lengths (Å): Ru(1)-Cl(1), 2.3627(7); Ru(1)-N(1), 1.742(2);
Ru(1)-C(10), 2.151(2); O(1)-N(1), 1.128(3); O(2)-C(11),
1.237(3); C(10)-C(11), 1.474(4). Selected bond angles
(deg): Ru(1)-N(1)-O(1), 178.9(3); Ru(1)-C(10)-C(11),
113.2(2); O(2)-C(11)-C(10), 120.8(2); O(2)-C(11)-C(12),
118.0(2); C(10)-C(11)-C(12), 121.2(2).
t
(CtCR)(NO) (R ) p-CH3C6H4 (1b), Bu (1c), CH2CH2-
OH (1d )) and HBF4‚Et2O in methanol (Scheme 1). The
terminal hydroxide of 1d is converted into an OMe
group during the formation of 2d . These complexes were
characterized spectroscopically. The presence of NO+
and CO groups was identified by the IR spectra of 2b-
d , and characteristic diastereotopic protons in the
ruthenium-bonded methylene groups are also observed
Sch em e 2
1
1
in the H NMR spectra. In particular, in the H-1H 2D
COSY spectrum of 2d , the resonances of methylene
protons (RuCH2C(O)R) clearly do not show any cross-
peaks except for geminal ones. The chemical shifts in
13C{1H} NMR for the carbonylic carbons in 2b-d are
similar to that in 2a . Moreover, the EI mass spectrum
of 2c shows the signal of [TpRuCl(CH2C(O))(NO)]+
(m/z: 422) along with the parent ion, which assists its
formulation. The ketonyl form was confirmed by X-ray
analysis of 2b.6b
Although two molecules are present per one asym-
metric unit, both structures are not significantly dif-
ferent. One of the molecular structures is presented in
Figure 1. The ruthenium center possesses a distorted
octahedral geometry defined by a facial Tp ligand
together with ketonyl group, nitrosyl, and chloride
ligands. The CH2-C(O) (1.474(4), 1.479(3) Å) and CdO
(1.237(3), 1.227(3) Å) distances in the ketonyl group
correspond well to single and double bonds, respectively.
On the other hand, for the γ-hydroxyacetylide deriva-
tives of 1e-g, TpRuCl(CtCC(R′)2OH)(NO) with H, Me,
and Ph as R′, respectively, similar treatment with
HBF4‚Et2O afforded the ketonyl complex TpRuCl-
(CH2C(O)CH2OH)(NO) (2e) and the R,â-unsaturated
acyl complexes TpRuCl(C(O)CHdCR′2)(NO) (R′ ) Me
(3f), Ph (3g)) (Scheme 2).
(5) Mene´ndez, C.; Morales, D.; Pe´rez, J .; Riera, V.; Miguel, D.
Organometallics 2001, 20, 2775-2781.
(6) (a) Representative procedure: Tetrafluoroboric acid, HBF4 (14
µL, 0.10 mmol, 54% in diethyl ether), was added to a MeOH solution
(10 mL) of TpRuCl(CtCPh)(NO) (1a ) (50 mg, 0.10 mmol). The solution
was stirred for 1 h at room temperature and was concentrated to
dryness. The residue was chromatographed on a silica gel column using
CH2Cl2 as an eluent to give 2a as a red solid (40 mg, 80%). IR (KBr,
pellet): ν(BH) 2508 (w), ν(NtO) 1855 (s), ν(CdO) 1633 (s). 1H NMR-
(CDCl3): δ 8.35 (d, J ) 6.8 Hz, 2H of Ph), 8.25 (d, J ) 2.0 Hz, 1H of
pz), 7.94 (d, J ) 2.2 Hz, 1H of pz), 7.85 (d, J ) 1.9 Hz, 1H of pz), 7.80
(d, J ) 2.4 Hz, 1H of pz), 7.70 (d, J ) 2.2 Hz, 1H of pz), 7.62 (d, J )
2.4 Hz, 1H of pz), 7.6-7.4 (3H of Ph), 6.40 (t, J ) 1.8 Hz, 1H of pz),
6.33 (t, J ) 2.2 Hz, 1H of pz), 6.29 (t, J ) 2.2 Hz, 1H of pz), 4.82 (d, J
) 6.0 Hz, 1H of CH2), 3.45 (d, J ) 6.0 Hz, 1H of CH2). 13C{1H} NMR
(CDCl3): δ 204.8 (s, CO), 143.6 (s, pz), 142.5 (s, pz), 142.2 (s, pz), 137.9
(s, Ph), 137.0 (s, pz), 135.5 (s, pz), 132.5 (s, Ph), 129.0 (s, Ph), 128.3 (s,
Ph), 107.3 (s, pz), 106.9 (s, pz), 106.4 (s, pz), 31.7 (s, CH2). EI-MS (m/
z): 481 (M+), 451 ([TpRuCl(CH2C(O)Ph)]+), 345 ([TpRu(NO)]+), 315
([TpRu]+). Anal. Calcd for C17H17ClBN7O2Ru: C, 40.94; H, 3.44; N,
19.66. Found: C, 40.93; H, 3.57; N, 19.30. (b) Crystal data for 2b:
Spectroscopic data observed for 2e are sufficient for
the assignment to the ketonyl complex, while the
presence of R,â-unsaturated acyl groups in 3f and 3g is
also confirmed. The EI-MS spectra of 3f and 3g include
the fragment peak corresponding to [TpRu(CO)]+ (m/z:
343) without the signal at m/z 422 of [TpRuCl(CH2C-
1
(O))(NO)]+. The most relevant features of the H NMR
C
18H19N7O2BClRu‚1/2(CH3OH) (Mr ) 528.24); triclinic, space group P1h
(No. 2), a ) 10.0179(3) Å, b ) 12.2652(7) Å, c ) 19.6601(8) Å, R )
spectra of 3f and 3g are the resonances of the olefinic
protons, which are observed as singlets at δ 6.72 (3f)
and 7.63 (3g). An X-ray structural analysis carried out
94.213(2)°, â ) 95.7850(9)°, γ ) 109.8535(5)°, V ) 2245.5(2) Å3, Z ) 4,
F
calcd ) 1.562 g cm-3, R (Rw) ) 0.043 (0.069) for 559 variables and 9571
unique reflections (all data).

3356 Organometallics, Vol. 22, No. 17, 2003
Communications
formation of ketonyl species has been suggested as an
important catalytic process, which involves the nucleo-
philic attack of H2O on η2-coordinated alkynes. Ketonyl
platinum(III) dinuclear complexes were reported to be
generated by a similar mechanism.15 Therefore, in the
production of 2a -e, the protonation of the acetylide
complexes would afford the vinylidene species, which
rapidly isomerize to η2-alkyne intermediates.16 Vin-
ylidene species of ruthenium(II) have been regarded to
be thermodynamically more stable than tautomeric η2-
alkyne species.9,11 The back-bonding dπ(metal)-pπ-
(vinylidene) interaction would be essential to the sta-
bility of the vinylidene species. The presence of the NO+
ligand, which is a strong π-acceptor group, reduces the
interaction to convert vinylidene into η2-alkyne species.
Kirchner et al. have reported a similar view, based on
the experimental and theoretical results.17 To detect the
η2-alkyne intermediate or its tautomers, reaction of 1a
F igu r e 2. Molecular structure of 3g (thermal ellipsoids
at the 50% level). Hydrogen atoms were omitted for clarity.
Selected bond lengths (Å): Ru-Cl, 2.3654(8); Ru-N(1),
1.737(2); Ru-C(10), 2.064(3); O(1)-N(1), 1.138(3); O(2)-
C(10), 1.180(4); C(10)-C(11), 1.517(4); C(11)-C(12),
1.345(4). Selected bond angles (deg): Ru-N(1)-O(1),
177.0(3); Ru-C(10)-C(11), 114.7(2); Ru-C(10)-O(2),
123.8(2); O(2)-C(10)-C(11), 121.0(3); C(10)-C(11)-C(12),
126.5(3). Torsion angle (deg): O(2)-C(10)-C(11)-C(12),
-87.5(4).
with HBArF (ArF ) 3,5-C6H3(CF3)2) was monitored by
4
1H NMR experiments in dried CD3OD, on warming from
-40 °C to room temperature. Only a mixture of 1a and
2a was observed at -20 °C without any intermediates,
although no reaction occurred at lower temperatures.
on a single crystal of 3g, which was grown from benzene/
hexane, confirmed the TpRuCl(C(O)CHdCPh2)(NO)
formulation.7
1
Even if the H NMR experiment was carried out using
tBu analogue 1c, where the hydration reaction pro-
ceeded more slowly than that of 1a , the η2-alkyne
species were not detected either.
The molecular structure of 3g is depicted in Figure
2. The coordination geometry is approximately octahe-
dral, with the Tp ligand occupying three facial sites. The
Ru-C(10) distance of 2.064(3) Å is very close to that of
CpRu(C(O)CHdCPh2)(CO)(PiPr3) (2.060(2) Å).8 The
C(10)-O(2) and C(11)-C(12) distances are 1.180(4) and
1.345(4) Å, respectively, which are in the region of
double-bond distances, indicating no appreciable con-
jugation over them.
In the case of γ-hydroxyacetylide derivatives except
for 1e, the protonation easily leads to the allenylidene
species through the dehydration process at the γ-carbon
and then the addition of H2O at the R-carbon resulted
in the R,â-unsaturated acyl complexes. Since the dehy-
dration of the protonated 1e is likely difficult as
expected for a primary alcohol,18 the reaction does not
proceed via the allenylidene form but the η2-alkyne
form.
In conclusion, the protonation of the monoacetylide
complexes 1a -g caused a hydration reaction, producing
ketonyl complexes 2a -e via the η2-alkyne form and R,â-
unsaturated acyl complexes 3f and 3g via the allen-
ylidene species. Future work will be focused on the
preparation of bis-acetylide complexes with TpRu(NO)
fragments and their reactivities.
Tautomerism of η2-coordinated 1-alkyne to the vin-
ylidene form is well-known.9 Stoichiometric hydration
via vinylidene species “MdCdCHR” has been reported
in detail by Bianchini et al. to give a Ru(II)-CO complex
by C-C triple-bond cleavage reactions, where metal-
acyl intermediates “M-C(O)CH2R” are involved.10
A
recent mechanistic study of catalytic hydration also
proposes the vinylidene intermediate.11 On the other
hand, the 1-alkyne hydration reactions with some metal
catalysts such as Hg(II),12 Pt(II),13 and Ru(III)14 give rise
to methyl ketones as the Markovnikov products, where
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas
(No. 15036101, “Reaction Control of Dynamic Com-
plexes”) from the Ministry of Education, Culture, Sports,
Science and Technology, J apan.
(7) Crystal data for 3g: C24H21N7O2BClRu (Mr ) 586.81), triclinic,
space group P1h (No. 2), a ) 8.9275(6) Å, b ) 10.182(2) Å, c ) 14.495-
(3) Å, R ) 98.086(4)°, â ) 91.767(2)°, γ ) 107.388(1)°, V ) 1241.2(4)
Å3, Z ) 2, Fcalcd ) 1.570 g cm-3, R (Rw) ) 0.053 (0.075) for 325 variables
and 5386 unique reflections (all data).
(8) Esteruelas, M. A.; Go´mez, A. V.; Lahoz, F. J .; Lo´pez, A. M.;
On˜ate, E.; Oro, L. A. Organometallics 1996, 15, 3423-3435.
(9) For a recent experimental and theoretical study, see: Bustelo,
E.; Carbo´, J . J .; Lledo´s, A.; Mereiter, K.; Puerta, M. C.; Valerga, P. J .
Am. Chem. Soc. 2003, 125, 3311-3321.
(10) (a) Bianchini, C.; Casares, J . A.; Peruzzini, M.; Romerosa, A.;
Zanobini, F. J . Am. Chem. Soc. 1996, 118, 4585-4594. (b) Bianchini,
C.; Peruzzini, M.; Zanobini, F.; Lopez, C.; de los R´ıos, I.; Romerosa, A.
Chem. Commun. 1999, 443-444.
(11) Tokunaga, M,; Suzuki, T.; Koga, N.; Fukushima, T.; Horiuchi,
A.; Wakatsuki, Y. J . Am. Chem. Soc. 2001, 123, 11917-11924.
(12) (a) March, J . Advanced Organic Chemistry; Wiley: New York,
1992; p 762. (b) J anout, V.; Regen, S. L. J . Org. Chem. 1982, 47, 3331-
3333.
(13) (a) Hiscox, W.; J ennings, P. W. Organometallics 1990, 9, 1997-
1999. (b) Hartman, J . W.; Hiscox, W. C.; J ennings, P. W. J . Org. Chem.
1993, 58, 7613-7614. (c) J ennings, P. W.; Hartman, J . W.; Hiscox, W.
C. Inorg. Chim. Acta 1994, 222, 317-322.
(14) (a) Halpern, J .; J ames, B. R.; Kemp, A. L. W. J . Am. Chem.
Soc. 1961, 83, 4097-4098. (b) Halpern, J .; J ames, B. R.; Kemp, A. L.
W. J . Am. Chem. Soc. 1966, 88, 5142-5147. (c) Khan, M. M. T.;
Halligudi, S. B.; Shukla, S. J . Mol. Catal. 1990, 58, 299-305.
Su p p or tin g In for m a tion Ava ila ble: Spectroscopic data
for the compounds prepared in this study and X-ray crystal-
lographic data for 2b and 3g. These materials are available
free of charge via the Internet at http://pubs.acs.org.
OM0303597
(15) Matsumoto, K.; Ochiai, M. Coord. Chem. Rev. 2002, 231, 229-
328.
(16) The possibility of a direct formation of η2-alkyne without
vinylidene species should not be ruled out at the present stage. While
acetylide complexes 1a and 1b were treated with CF3SO3CH3 in CDCl3,
any significant reactions, such as methylation at â-carbon, did not
occur.
(17) Slugovc, C.; Sapunov, V. N.; Wiede, P.; Mereiter, K.; Schmid,
R.; Kirchner, K. J . Chem. Soc., Dalton Trans. 1997, 4209-4216.
(18) A similar observation is described in the hydroxyvinylidene
complex [Cp*Ru{dCdCH(CH2OH)}(PEt3)2](BPh4), which is not dehy-
drated by any methods: Bustelo, E.; J ime´nez-Tenorio, M.; Puerta, M.
C.; Valerga, P. Organometallics 1999, 18, 4563-4573.