Reactions of a dihydride-osmium(IV) complex with aldehydes: Influence of the substituent at the carbonyl group

Article abstract of DOI:10.1021/om701075d

The reactivity of the dihydride-acetone complex [OsH₂(η ⁵-C₅H₅)(κ¹-OCMe ₂)(PⁱPr₃)[BF₄ (1) toward cinnamal-dehyde, isovaleraldehyde, and benzaldehyde has been investigated. In addition to the reduction of the aldehydes, three different reaction patterns have been observed, which depend on the alkenyl, alkyl, and aryl nature of the substituent at the carbonyl group. As a result, the complexes [Os(η⁵-C₅H₅)(CO)(η²-PhCH= CH₂)(PⁱPr₃)]BF₄ (2), [Os(η⁵-C₅H₅)(CO)₂(P ⁱPr₃)]BF₄ (3), and [OsH(η⁵- C₅H₅)[C₆H₄C(O)H}(P ⁱPr₃)]BF₄ (6) have been isolated and characterized, including the X-ray structure of 2.

Full text of DOI:10.1021/om701075d

Organometallics 2008, 27, 799–802
799
Reactions of a Dihydride-Osmium(IV) Complex with Aldehydes:
Influence of the Substituent at the Carbonyl Group
Miguel A. Esteruelas,* Yohar A. Hernández, Ana M. López,* Montserrat Oliván, and
Lucía Rubio
Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, UniVersidad de
ZaragozasCSIC, 50009 Zaragoza, Spain
ReceiVed October 25, 2007
Complex 1 also reduces R,ꢀ-unsaturated and aromatic ke-
tones.5 The reactions afford [Os(η5-C5H5)(PiPr3)]BF4. Although
this metal fragment activates a Cꢀ(sp2)-H bond of both types
of molecules, the exclusive activation of the olefinic bond is
observed in substrates containing both olefinic and aromatic
substituents at the carbonyl group.
Summary: The reactiVity of the dihydride-acetone complex
[OsH2(η5-C5H5)(κ1-OCMe2)(PiPr3)]BF4 (1) toward cinnamal-
dehyde, isoValeraldehyde, and benzaldehyde has been inVesti-
gated. In addition to the reduction of the aldehydes, three
different reaction patterns haVe been obserVed, which depend
on the alkenyl, alkyl, and aryl nature of the substituent at the
carbonyl group. As a result, the complexes [Os(η5-C5H5)(CO)(η2-
PhCHdCH2)(PiPr3)]BF4 (2), [Os(η5-C5H5)(CO)2(PiPr3)]BF4
Aldehydes are ketone counterparts with the carbonyl group
bonded to a hydrogen atom. The activation of this OC-H bond
is a reaction of great interest, due to its connection with the
decarbonylation of these substrates6 and by its importance in
organometallic7 and organic synthesis.8 Our interest in under-
standing the influence of the substituents in the reactions of the
organic molecules with transition-metal complexes, in particular
hydride derivatives,9 prompted us to investigate the reactions
of 1 with cinnamaldehyde, isovaleraldehyde, and benzaldehyde
(Scheme 1).
(3), and [OsH(η5-C5H5){C6H4C(O)H}(PiPr3)]BF4 (6) haVe been
isolated and characterized, including the X-ray structure of 2.
The characteristic chemical reactions of an organic compound
are determined by an specific moiety within the molecule. Those
parts of the compound attached to this core have influence in
the reactivity of the compound but play a secondary role.
Transition-metal elements have the remarkable ability to enhance
the reactivity of some parts of the organic molecules and to
inhibit the reactions of others. A crucial consequence of this
ability is the dramatic increase of the influence of the substituents
in the reactions of the organic compounds with the transition-
metal complexes. An attractive illustration may be found in the
reactions of the dihydride-solvento complex [OsH2(η5-C5H5)(κ1-
OCMe2)(PiPr3)]BF4 (1) with alkynes.1
Treatment of 1 with 3.0 equiv of cinnamaldehyde in dichlo-
romethane at 50 °C for 24 h gives rise to the reduction of the
C-C double bond of 1 equiv of aldehyde and the formation of
(5) Esteruelas, M. A.; Hernández, Y. A.; López, A. M.; Oliván, M.;
Oñate, E. Organometallics 2005, 24, 5989.
The reactions of 1 with 1-phenyl-1-propyne and 2-butyne give
rise to γ-(η3-allyl)-R-alkenylphosphine [OsH(η5-C5H5){κ4P,C,C,C-
CH2C[CH2C(dCH2)PiPr2]CHR}]BF4 (R ) Ph, CH3) deriv-
atives.1a On the other hand, phenylacetylene leads to the
allenylcarbene [Os(η5-C5H5){dCPh(η2-CHdCdCHPh)}(Pi-
Pr3)]BF4.1b Although both processes take place through the same
type of key intermediate, π-alkyne species [Os(η5-C5H5)(η2-
R′CtCR′′)(PiPr3)]BF4,2 the trend of phenylacetylene to generate
vinylidene complexes3 determinates the difference in behavior
between the terminal and internal alkynes. While 1-phenyl-1-
propyne and 2-butyne promote the dehydrogenation of an
isopropyl group of the phosphine to afford an isopropenyl
substituent,4 which leads to the γ-(η3-allyl)-R-alkenylphosphine
via an ene-type reaction with a new alkyne molecule,1a the
vinylidene resulting from the tautomerization of phenylacetylene
undergoes a [2 + 2] cycloaddition with the new alkyne molecule
to give the allenylcarbene ligand.1b
(6) See for example: (a) Beck, C. M.; Rathmill, S. E.; Park, Y. J.; Chen,
J.; Crabtree, R. H.; Liable-Sands, L. M.; Rheingold, A. L. Organometallics
1999, 18, 5311. (b) Gutiérrez-Puebla, E.; Monge, A.; Paneque, M.; Poveda,
M. L.; Salazar, V.; Carmona, E. J. Am. Chem. Soc. 1999, 121, 248. (c)
Alaimo, P. J.; Arndtsen, B. A.; Bergman, R. G. Organometallics 2000, 19,
2130. (d) Coalter, J. N., III; Huffman, J. C.; Caulton, K. G. Organometallics
2000, 19, 3569. (e) Cordaro, J. G.; Bergman, R. G. J. Am. Chem. Soc.
2004, 126, 3432. (f) Graham, P. M.; Mocella, C. J.; Sabat, M.; Harman,
W. D. Organometallics 2005, 24, 911. (g) Kreis, M.; Palmelund, A.; Bunch,
L.; Madsen, R. AdV. Synth. Catal. 2006, 348, 2148. (h) Lee, J. P; Pittard,
K. A.; DeYonker, N. J.; Cundari, T. R.; Gunnoe, T. B.; Petersen, J. L.
Organometallics 2006, 25, 1500.
(7) See for example: (a) Garralda, M. A.; Hernández, R.; Ibarlucea, L.;
Pinilla, E.; Torres, M. R. Organometallics 2003, 22, 3600. (b) Corkey, B. K.;
Taw, F. L.; Bergman, R. G.; Brookhart, M. Polyhedron 2004, 23, 2943.
(c) Garralda, M. A.; Hernández, R.; Ibarlucea, L.; Pinilla, E.; Torres, M. R.;
Zarandona, M. Organometallics 2007, 26, 1031. (d) Song, X.; Chan, K. S.
Organometallics 2007, 26, 965. (e) Chan, K. S.; Lau, C. M.; Yeung, S. K.;
Lai, T. H. Organometallics 2007, 26, 1981.
(8) See for example: (a) Jun, C.-H.; Jo, E.-A.; Park, J.-W. Eur. J. Org.
Chem. 2007, 1869. (b) Lantos, D.; Contel, M.; Sanz, S.; Bodor, A.; Horváth,
I. T. J. Organomet. Chem. 2007, 692, 1799. (c) Wile, B. M.; McDonald,
R.; Ferguson, M. J.; Stradiotto, M. Organometallics 2007, 26, 1069. (d)
Roy, A. H.; Lenges, C. P.; Brookhart, M. J. Am. Chem. Soc. 2007, 129,
2082.
* To whom correspondence should be addressed. E-mail: maester@
unizar.es (M.A.E.); amlopez@unizar.es (A.M.L.).
(1) (a) Esteruelas, M. A.; Hernández, Y. A.; López, A. M.; Oliván, M.;
Oñate, E. Organometallics 2007, 26, 2193. (b) Esteruelas, M. A.; Hernández,
Y. A.; López, A. M.; Oñate, E. Organometallics 2007, 26, 6009.
(2) Carbó, J. J.; Crochet, P.; Esteruelas, M. A.; Jean, Y.; Lledós, A.;
López, A. M.; Oñate, E. Organometallics 2002, 21, 305.
(3) (a) Esteruelas, M. A.; López, A. M. Organometallics 2005, 24, 3584.
(b) Esteruelas, M. A.; López, A. M.; Oliván, M. Coord. Chem. ReV. 2007,
251, 795.
(9) See for example: (a) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.;
Lledós, A.; Maseras, F.; Oñate, E.; Tomàs, J. Organometallics 2001, 20,
442. (b) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; Oñate, E. Organo-
metallics 2001, 20, 2635. (c) Barrio, P.; Esteruelas, M. A.; Oñate, E.
Organometallics 2002, 21, 2491. (d) Barrio, P.; Esteruelas, M. A.; Oñate,
E. Organometallics 2003, 22, 2472. (e) Esteruelas, M. A.; Lledós, A.;
Oliván, M.; Oñate, E.; Tajada, M. A.; Ujaque, G. Organometallics 2003,
22, 3753. (f) Barrio, P.; Esteruelas, M. A.; Oñate, E. Organometallics 2004,
23, 3627. (g) Eguillor, B.; Esteruelas, M. A.; Oliván, M.; Oñate, E.
Organometallics 2005, 24, 1428.
(4) Baya, M.; Buil, M. L.; Esteruelas, M. A.; Oñate, E. Organometallics
2004, 23, 1416.
10.1021/om701075d CCC: $40.75
2008 American Chemical Society
Publication on Web 01/31/2008

800 Organometallics, Vol. 27, No. 4, 2008
Notes
Scheme 1
Scheme 2
NMR spectrum in dichloromethane-d2 at room temperature the
resonances corresponding to the vinylic protons are observed
at 4.90, 3.91, and 2.85 ppm, whereas in the 13C{1H} NMR
spectrum the resonances due to the coordinated carbon atoms
of the olefin appear at 56.4 (CHPh) and 19.9 (CH2) ppm.
The formation of 2 can be rationalized as an OC-H bond
activation-decarbonylation tandem process (Scheme 2). The
reduction of the C-C double bond of an aldehyde molecule
should afford the 14-valence-electron species [Os(η5-
C5H5)(PiPr3)]+, which could selectively activate the OC-H bond
of a second aldehyde in the presence of the olefinic group. In
this context, it should be noted that the OC-H bond of an
aldehyde is about 19 kcal mol-1 weaker than the C-H bond of
an alkenyl group. The resulting hydride-acyl species could
evolve into 2 by deinsertion of the styryl substituent of the acyl
ligand and subsequent reductive elimination of styrene.
The substituent at the OC-H unit has a marked influence on
the nature of the resulting products of the reactions of 1 with
aldehydes. In contrast to cinnamaldehyde, isovaleraldehyde gives
the dicarbonyl complex [Os(η5-C5H5)(CO)2(PiPr3)]BF4 (3) in
addition to 3-methyl-1-butanol and isobutane (Scheme 1). Its
formation can be rationalized as a double OC-H bond
activation-decarbonylation tandem process (Scheme 3), which
takes place via two acyl intermediates through elemental steps
similar to those shown in Scheme 2. The stronger coordination
power of styrene with regard to isobutane explains the observed
differences between the reactions of cinnamaldehyde and
isovaleraldehyde.
the carbonyl-π-styrene derivative [Os(η5-C5H5)(CO)(η2-Ph-
CHdCH2)(PiPr3)]BF4 (2), which is isolated as a beige solid in
84% yield.
As a consequence of the chirality of the osmium atom and
the prochirality of the olefin, four pairs of diastereoisomers could
be formed: CPh carbon atom cisoid to the phosphine with the
phenyl group toward or away from the osmium atom and CPh
carbon atom cisoid to the carbonyl ligand with the phenyl group
toward or away from the osmium atom. However, only the pair
with the lowest steric hindrance is obtained, suggesting a
thermodynamic control of the reaction. Figure 1 shows a view
of the structure of one of the enantiomers of the obtained pair.
The geometry around the metal center is close to octahedral,
with the cyclopentadienyl group occupying three sites of a face
and the CPh carbon atom C(2) cisoid to the carbonyl ligand
with the phenyl ring away from the metal center. The Os-styrene
coordination exhibits Os-C(1) and Os-C(2) bond lengths of
2.167(8) and 2.214(7) Å, respectively, which agree well with
those found in other osmium-olefin complexes (between 2.13
and 2.28 Å).10Similarly, the olefin bond distance C(1)-C(2) of
1.404(10) Å is within the range reported for transition-metal
olefin complexes (between 1.340 and 1.445 Å).11
Complex 3 is isolated as a beige solid in 73% yield. The
most noticeable spectroscopic feature of this compound is the
presence of two ν(CO) bands at 2033 and 1968 cm-1 in the IR
spectrum.
1,3-Hydrogen shifts from the metal center to the oxygen atom
in hydride-acyl complexes afford hydroxycarbene tautomers.12
The equilibrium between both species has been studied in some
cases.13 The substituent at the carbonyl group of the aldehyde also
appears to have a marked influence on the stability of
the hydroxycarbene form in this case. Thus, while only 1 and 2
are observed by NMR spectroscopy during the reaction with
cinnamaldehyde, the alkoxycarbene derivatives [OsH2(η5-
In agreement with the presence of a carbonyl ligand in 2, its
1
IR in Nujol contains a ν(CO) band at 1973 cm-1. In the H
(10) (a) Baya, M.; Esteruelas, M. A.; Oñate, E. Organometallics 2002,
21, 5681. (b) Esteruelas, M. A.; González, A. I.; López, A. M.; Oñate, E.
Organometallics 2003, 22, 414. (c) Esteruelas, M. A.; Lledós, A.; Maseras,
F.; Oliván, M.; Oñate, E.; Tajada, M. A.; Tomàs, J. Organometallics 2003,
22, 2087. (d) Baya, M.; Buil, M. L.; Esteruelas, M. A.; Oñate, E.
Organometallics 2005, 24, 2030. (e) Esteruelas, M. A.; Fernández-Alvarez,
F. J.; Oliván, M.; Oñate, E. J. Am. Chem. Soc. 2006, 128, 4596. (f)
Esteruelas, M. A.; García-Yebra, C.; Oliván, M.; Oñate, E. Inorg. Chem.
2006, 45, 10162.
Figure 1. Molecular diagram of the cation of 2. Selected bond
lengths (Å) and angles (deg): Os-P ) 2.374(2), Os-C(1) )
2.167(8), Os-C(2) ) 2.214(7), Os-C(9) ) 1.822(9), C(1)-C(2)
) 1.404(10), C(9)-O ) 1.199(9); C(1)-Os-P ) 87.2(2),
C(1)-Os-C(9) ) 104.0(3), C(2)-O-P ) 111.8(2), C(2)-Os-C(9)
) 76.5(3), C(1)-Os-C(2) ) 37.4(3), C(9)-Os-P ) 89.5(2).
(11) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard, O.;
Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson, D. G.
J. Chem. Inf. Comput. Sci. 1991, 31, 187.
(12) Kunz, D. Angew. Chem., Int. Ed. 2007, 46, 3405.
(13) Casey, C. P.; Czerwinski, C. J.; Fusie, K. A.; Hayashi, R. K. J. Am.
Chem. Soc. 1997, 119, 3971.

Notes
Organometallics, Vol. 27, No. 4, 2008 801
Scheme 3
C5H5){dC(OH)CH2CH(CH3)2}(PiPr3)]BF4 (4) and [Os(η5-
C5H5){dC(OH)CH2CH(CH3)2}(CO)(PiPr3)]BF4 (5) were detected
and spectroscopically characterized for the reaction with isoval-
eraldehyde. Complex 4 (Scheme 3) is the result of the oxidative
addition of the OC-H bond of the aldehyde to the unsaturated
species [OsH2(η5-C5H5)(PiPr3)]+, generated by dissociation of
acetone from 1, and the subsequent migration of a hydride ligand
from the metal center to the oxygen atom of the acyl group.
Complex 5 is produced by a similar pathway starting from the
16-valence-electron monocarbonyl intermediate [Os(η5-
C5H5)(CO)(PiPr3)]+, which is generated from the reduction of an
aldehyde molecule and the decarbonylation of another. Both 4 and
5 are products of kinetic control, which do not play any significant
role in the decarbonylation process. In this context, it should be
mentioned that hydroxycarbene species have been detected as
reactive intermediates in the reactions of CR-Cꢀ bonds of alle-
nylidene14 and alkynyl15 groups with water to give carbonyl ligands
and alkene and alkane, respectively. However, the key steps for
the CR-Cꢀ bond cleavage are the hydroxycarbene-hydride acyl
tautomerization and the deinsertion of the substituent at the carbonyl
group of the acyl ligand.14,15
In the 1H NMR spectrum of 4 the most noticeable resonance of
the hydroxycarbene ligand is that corresponding to the OH proton,
which is observed at 13.48 ppm as a broad singlet. In the high-
field region of the spectrum, the hydride ligands give rise to a
doublet (JHP ) 32.7 Hz) at -10.16 ppm. The presence of two
hydrogen atoms bonded to the metal is supported not only by the
1H NMR spectrum but also by the 31P{1H} NMR spectrum, which
shows a singlet at 40.6 ppm that under off-resonance conditions is
split into a triplet. In the 13C{1H} NMR spectrum, the resonance
due to the CR atom of the hydroxycarbene ligand appears at 280.5
ppm. Characteristic resonances of the hydroxycarbene ligand of 5
are a broad singlet at 12.80 ppm due to the OH proton in the 1H
NMR spectrum and a doublet (JCP ) 7 Hz) at 278.8 ppm,
corresponding to the CR atom in the 13C{1H} NMR spectrum. The
carbonyl ligand gives rise to a doublet (JCP ) 10 Hz) at 182.5
ppm in the latter spectrum.
orthometalated derivative [Os(η5-C5H5)(CO){C6H4C(O)H}-
(PiPr3)]BF4 (6), which is isolated as a yellow solid in 74% yield.
The 1H NMR spectrum of 6 is consistent with a four-legged
piano-stool structure with the hydride cisoid to the triisopro-
pylphosphine ligand. Thus, it shows at -13.74 ppm a doublet
with a H-P coupling constant of 32.1 Hz, which is a typical
value for this arrangement.16 The OC-H resonance is observed
at 9.40 ppm as a singlet. The 13C{1H} NMR spectrum supports
the formation of the heterometallacycle and the transoid
disposition of the metalated carbon atom and the phosphine
ligand.5,16 In agreement with the coordination of the oxygen
atom of the aldehyde to the metal, the resonance due to the OC
carbon appears as a doublet (JCP ) 2 Hz) at 211.6 ppm. The
signal corresponding to the metalated atom of the phenyl group
is observed at 184.2 ppm also as a doublet (JCP ) 3 Hz). The
31P{1H} NMR spectrum contains a singlet at 28.0 ppm, which
is split into a doublet under off-resonance conditions.
Complex 6 is a result of the reduction of 1 equiv of aldehyde
and the subsequent o-CH addition of the phenyl substituent of
a second aldehyde molecule to the resulting 14-valence-electron
fragment [Os(η5-C5H5)(PiPr3)]+. The behavior of 1 agrees well
with that observed for the trihydride OsH3(SnPh2Cl){κ3P,C,C-
[CH2dC(CH3)]PiPr2}(PiPr3), which also reacts with aromatic
aldehydes to form ortho-metalated species.17 However, it is in
contrast with that reported for the hexahydride OsH6(PiPr3)2,
which upon treatment with benzaldehyde affords the hydride-
phenyl-dicarbonyl complex OsHPh(CO)2(PiPr3)2.18
The OC-H bonds are about 23 kcal mol-1 weaker than the
C-H bonds of a phenyl group. This could be one of the reasons
why the o-CH bond activation of aromatic aldehydes has been
rarely observed.19 According to a recent density functional study
on the o-CH addition of benzaldehyde to the 14-valence-electron
(16) See for example: Esteruelas, M. A.; Gutiérrez-Puebla, E.; López,
A. M.; Oñate, E.; Tolosa, J. I. Organometallics 2000, 19, 275. (b) Baya,
M.; Crochet, P.; Esteruelas, M. A.; Gutiérrez-Puebla, E.; López, A. M.;
Modrego, J.; Oñate, E.; Vela, N. Organometallics 2000, 19, 2585. (c) Baya,
M.; Crochet, P.; Esteruelas, M. A.; Oñate, E. Organometallics 2001, 20,
240. (d) Baya, M.; Esteruelas, M. A.; Oñate, E. Organometallics 2001, 20,
4875. (e) Esteruelas, M. A.; González, A. I.; López, A. M.; Oñate, E.
Organometallics 2004, 23, 4858.
In contrast to the reactions with cinnamaldehyde and iso-
valeraldehyde, the treatment of dichloromethane solutions of 1
with 3.0 equiv of benzaldehyde leads to benzyl alcohol and the
(17) Eguillor, B.; Esteruelas, M. A.; Oliván, M.; Oñate, E. Organome-
tallics 2004, 23, 6015.
(14) See for example: Esteruelas, M. A.; Gómez, A. V.; Lahoz, F. J.;
López, A. M.; Oñate, E.; Oro, L. A. Organometallics 1996, 15, 3423. (b)
Bustelo, E.; Dixneuf, P. H. AdV. Synth. Catal. 2005, 347, 393. (c) Bustelo,
E.; Dixneuf, P. H. AdV. Synth. Catal. 2007, 349, 933.
(18) Barrio, P.; Esteruelas, M. A.; Oñate, E. Organometallics 2004, 23,
1340.
(19) (a) Robinson, N. P.; Main, L.; Nicholson, B. K. J. Organomet.
Chem. 1988, 349, 209. (b) Cambie, R. C.; Metzler, M. R.; Rutledge, P. S.;
Woodgate, P. D. J. Organomet. Chem. 1990, 398, C22. (c) Kakiuchi, F.;
Sato, T.; Igi, K.; Chatani, N.; Murai, S. Chem. Lett. 2001, 386.
(15) Buil, M. L.; Esteruelas, M. A.; López, A. M.; Oñate, E. Organo-
metallics 1997, 16, 3169.

802 Organometallics, Vol. 27, No. 4, 2008
Notes
Scheme 4
presence of isovaleraldehyde and 3-methyl-1-butanol. Anal. Calcd for
C16H26BF4O2OsP: C, 34.42; H, 4.69. Found: C, 34.57; H, 4.52. IR
(ATR, cm-1): ν(CO) 2033 (s), 1968 (s). 1H NMR (300 MHz): 5.92
(s, 5H, C5H5), 2.48 (m, 3H, PCH), 1.29 (dd, JHP ) 15.8, JHH ) 7.1,
18H, PCHCH3). 31P{1H} NMR (121.49 MHz): 32.1 (s). 13C{1H}
NMR (75.48 MHz): 176.0 (d, JCP ) 9, CO), 87.3 (s, C5H5), 29.5 (d,
JCP ) 31, PCH), 20.3 (d, JCP ) 2, PCHCH3). MS (MALDI-TOF):
m/z 473.1 (M+).
Reaction of [OsH2(η5-C5H5)(K1-OCMe2)(PiPr3)]BF4 with
Isovaleraldehyde: Formation of [OsH2(η5-C5H5){dC(OH)CH2-
CH(CH3)2}(PiPr3)]BF4 (4) and [Os(η5-C5H5){dC(OH)CH2-
CH(CH3)2}(CO)(PiPr3)]BF4 (5). An NMR tube containing 1 (51
mg, 0.09 mmol) in 0.5 mL of dichloromethane-d2 was treated with
isovaleraldehyde (35 µL, 0.32 mmol) at room temperature for 12 h.
After that, the NMR spectra showed the presence of 4 and 5 in the
molar ratio 1:1.5. Spectroscopic data for 4 are as follows. 1H NMR
(300 MHz): 13.48 (br s, 1H, OH), 5.44 (s, 5H, C5H5), 2.90 (d, JHH
) 6.9, 2H, CH2), 2.50-2.05 (m, 4H, PCH and CH(CH3)2),
1.34-1.18 (m, 18H, PCHCH3), 1.09 (d, JHH ) 6.9, 6H, CH(CH3)2),
-10.16 (d, JHP ) 32.7, 2H, Os-H). 31P{1H} NMR (121.49 MHz):
40.6 (s, t in off-resonance). 13C{1H} NMR (75.48 MHz): 280.5 (s,
OsdC), 82.9 (s, C5H5), 76.5 (s, CH2), 29.5 (d, JCP ) 32, PCH),
27.6 (s, CH(CH3)2), 22.3 (s, CH(CH3)2), 19.4 (s, PCHCH3), 19.2
(d, JCP ) 2, PCHCH3). Spectroscopic data for 5 are as follows. 1H
NMR (300 MHz): 12.80 (br s, 1H, OH), 5.69 (s, 5H, C5H5), 3.20
(dd, JHH ) 11.5 and 6.0, 1H, CH2), 2.78 (dd, JHH ) 11.5 and 8.3,
1H, CH2), 2.50-2.05 (m, 4H, PCH and CH(CH3)2), 1.34-1.18
(18H, PCHCH3), 0.98 (d, JHH ) 6.6, 3H, CH(CH3)2), 0.91 (d, JHH
) 6.6, 3H, CH(CH3)2). 31P{1H} NMR (121.49 MHz): 27.0 (s).
13C{1H} NMR (75.48 MHz): 278.8 (d, JCP ) 7, OsdC), 182.5 (d,
JCP ) 10, CO), 86.8 (s, C5H5), 71.5 (s, CH2), 30.1 (d, JCP ) 30,
PCH), 29.1 (s, CH(CH3)2), 22.5 and 22.0 (s, CH(CH3)2), 19.4 (s,
PCHCH3), 19.3 (d, JCP ) 2, PCHCH3).
fragment Ru(CO)(PH3)2,20 the C-H bond activation process should
involve the elemental steps shown in Scheme 4. Initially the formyl
oxygen coordinates to the metal center. Then the cleavage of the
closest o-CH bond takes place in two steps. First an o-OsC bond
is formed, being driven by the change in the π bonds of the
conjugated system. Subsequently, in this intermediate, containing
the o-OsC bond and a CH-agostic interaction, the hydrogen of the
agostic CH bond is transferred to the osmium atom.21
In conclusion, the nature of the products of the reactions of
the dihydride-solvento complex [OsH2(η5-C5H5)(κ1-OCMe2)-
(PiPr3)]BF4 with aldehydes is a function of the reactivity of the
substituent at the carbonyl group of the aldehyde toward the
unsaturated metal fragment [Os(η5-C5H5)(PiPr3)]+, which is
generated as a consequence of the hydride transfer from the
metal center of the starting complex to a first aldehyde molecule.
Thus, three different reaction patterns are observed: monode-
carbonylation, double decarbonylation, and aromatic o-CH bond
activation, depending on the alkenyl, alkyl, and aryl nature,
respectively, of the substituent.
Preparation of [OsH(η5-C5H5){C6H4C(O)H}(PiPr3)]BF4 (6).
This complex was prepared as described for 2 starting from 1 (139
mg, 0.25 mmol) and benzaldehyde (100 µL, 0.74 mmol). Yellow solid.
Yield: 111 mg (74%). GC-MS analysis of the mother liquor showed
the presence of benzaldehyde and benzyl alcohol. Anal. Calcd for
C21H32BF4OOsP: C, 41.45; H, 5.30. Found: C, 41.01; H, 5.02. IR
Experimental Section
Solvents were dried by the usual procedures and distilled under
argon prior to use. The starting material 1 was prepared as
previously described.1a Commercial aldehydes were distilled and
stored over 4 Å molecular sieves. NMR spectra were recorded in
CD2Cl2 at 293 K, chemical shifts (expressed in ppm) are referenced
to residual solvent peaks (1H, 13C{1H}) or external H3PO4
(31P{1H}), and coupling constants, J, are given in hertz.
1
(Nujol, cm-1): ν(OsH) 2120 (m), ν(CO) 1590 (s). H NMR (300
MHz): 9.40 (s, 1H, CHO), 8.27, 8.24 (both d, JHH ) 7.5, each 1H,
Ph), 7.30, 7.16 (both dd, JHH ) 7.5, each 1H, Ph), 5.68 (s, 5H, C5H5),
2.36 (m, 3H, PCH), 1.22 (dd, JHP ) 15.1, JHH ) 7.0, 9H, PCHCH3),
Preparation of [Os(η5-C5H5)(CO)(η2-PhCHdCH2)(PiPr3)]-
BF4 (2). A solution of 1 (151 mg, 0.27 mmol) in 2.5 mL of
dichloromethane was treated with cinnamaldehyde (100 µL, 0.80
mmol) at 50 °C for 24 h. The resulting solution was concentrated to
ca. 1 mL. The addition of diethyl ether caused the formation of a beige
solid. Yield: 124 mg (84%). GC-MS analysis of the mother liquor
showed the presence of cinnamaldehyde and 3-phenylpropanal. Anal.
Calcd for C23H34BF4OOsP: C, 43.54; H, 5.40. Found: C, 43.55; H,
5.15. IR (Nujol, cm-1): ν(CO) 1973 (s). 1H NMR (400 MHz): 7.35
(m, 5H, Ph), 5.32 (s, 5H, C5H5), 4.90 (dd, JHH ) 12.6 and 8.4, 1H,
dCHPh), 3.91 (d, JHH ) 12.6, 1H, dCHHtrans), 2.85 (dd, JHH ) 8.4,
JHP ) 8.4, 1H, dCHHcis), 2.54 (m, 3H, PCH), 1.28 (dd, JHP ) 15.6,
JHH ) 7.2, 9H, PCHCH3), 1.24 (dd, JHP ) 16.8, JHH ) 7.2, 9H,
PCHCH3). 31P{1H} NMR (121.49 MHz): 17.8 (s). 13C{1H} NMR
(75.48 MHz): 184.9 (d, JCP ) 13, CO), 141.6, 129.6, 129.2, and 127.3
(all s, Ph), 89.7 (s, C5H5), 56.4 (s, dCH), 29.2 (d, JCP ) 30, PCH),
20.3 (s, PCHCH3), 20.1 (d, JCP ) 2, PCHCH3), 19.9 (s, dCH2). MS
(MALDI-TOF): m/z 444.8 (M+ - styrene).
0.97 (dd, JHP ) 14.2, JHH ) 7.0, 9H, PCHCH3), -13.74 (d, JHP
)
32.1, 1H, Os-H). 31P{1H} NMR (121.49 MHz): 28.0 (s). 13C{1H}
NMR (75.48 MHz): 211.6 (d, JCP ) 2, CHO), 184.2 (d, JCP ) 3,
Os-C), 148.1, 145.0, 135.3, 134.7, and 124.8 (all s, Ph), 86.9 (s, C5H5),
27.9 (d, JCP ) 30, PCH), 20.3 (s, PCHCH3), 19.0 (d, JCP ) 2,
PCHCH3). MS (MALDI-TOF): m/z 522.9 (M+).
Acknowledgment. Financial support from the MEC of
Spain (Projects CTQ2005-00656 and Consolider Ingenio 2010
CSD2007-00006) and Diputación General de Aragón (E35) is
acknowledged. Y.A.H. thanks the Spanish MEC for his grant.
Supporting Information Available: Text giving additional
details on the preparation of the BF4 salt of 2 and crystal structure
determination and a CIF file giving crystal data for compound 2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Preparation of [Os(η5-C5H5)(CO)2(PiPr3)]BF4 (3). This com-
plex was prepared as described for 2 by starting from 1 (154 mg, 0.27
mmol) and isovaleraldehyde (105 µL, 0.96 mmol). Beige solid. Yield:
112 mg (73%). GC-MS analysis of the mother liquor showed the
OM701075D
(21) It should be noted that the o-CH addition of aromatic aldehydes,
according to this mechanism, requires two empty valence orbitals in the
metallic fragment promoting the activation. Thus, the 14-valence-electron
character of the metal fragment [Os(η5-C5H5)(PiPr3)]+ appears to be
determinant for the addition in this case.
(20) Matsubara, T.; Koga, N.; Musaev, D. G.; Morokuma, K. Organo-
metallics 2000, 19, 2318.