Reactions of a Hexahydride-Osmium Complex with Aldehydes: Double C-H α Activation-Decarbonylation and Single C-Hα Activation-Hydroxylation Tandem Processes and Catalytic Tishchenko Reactions

Article abstract of DOI:10.1021/om034389l

The activation of hexahydride-osmium complex by the C-h_α bond of aldehydes was studied. The intermediate complex promoted carbon hydrogen activation-decarbonylation and carbon hydrogen activation-hydroxylation. The coordination geometry around the osmium atom was described as a distorted pentagonal bipyramid with the phosphorus atoms of the phosphines occupying axial positions. The reactions of transition metal polyhydrides with aldehydes shows that the hexahydride and related compounds are active catalyst precursors for the Tishchenko reaction.

Full text of DOI:10.1021/om034389l

1340
Organometallics 2004, 23, 1340-1348
Rea ction s of a Hexa h yd r id e-Osm iu m Com p lex w ith
Ald eh yd es: Dou ble C-Hr Activa tion -Deca r bon yla tion
a n d Sin gle C-Hr Activa tion -Hyd r oxyla tion Ta n d em
P r ocesses a n d Ca ta lytic Tish ch en k o Rea ction s
Pilar Barrio, Miguel A. Esteruelas,* and Enrique On˜ate
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
Received December 19, 2003
The hexahydride complex OsH6(PiPr3)2 (1) activates the C-HR bond of aldehydes. In toluene
under reflux, the reactions with benzaldehyde, cyclohexanecarboxaldehyde, and isobutyral-
dehyde lead to products resulting from two C-HR activation-decarbonylation tandem
processes. The reaction with benzaldehyde gives the hydride-phenyl-cis-dicarbonyl derivative
OsHPh(CO)2(PiPr3)2 (2) and benzene, while cyclohexanecarboxaldehyde and isobutyraldehyde
yield the cis-dihydride-cis-dicarbonyl compound OsH2(CO)2(PiPr3)2 (3) and the corresponding
alkane. In the presence of water 1 reacts with benzaldehyde to give 2. However, cyclohex-
anecarboxaldehyde and isobutyraldehyde afford the carboxylate complexes OsH3(κ2-O2CR)-
(PiPr3)2 (R ) Cy (4), (CH3)2CH (5)), which can also be obtained by reaction of 1 and the
corresponding carboxylic acid. Similarly, the treatment of 1 with benzoic acid gives OsH3
(κ2-O2CPh)(PiPr3)2 (6). The structure of 5 in the solid state has been determined by X-ray
diffraction analysis. The coordination geometry around the osmium atom can be described
as a distorted pentagonal bipyramid with the phosphorus atoms of the phosphines occupying
axial positions. In solution, the central hydride ligand of 4-6 exchanges its position with
that of the hydrides disposed cisoid to the oxygen atoms. The activation parameters for the
exchange process are ∆Hq ) 10.2 ( 0.4 kcal‚mol-1 and ∆Sq ) -4.3 ( 1.0 cal‚mol-1‚K-1 for
4, ∆Hq ) 10.6 ( 0.3 kcal‚mol-1 and ∆Sq ) 1.1 ( 0.9 cal‚mol-1‚K-1 for 5, and ∆Hq ) 10.4 (
0.4 kcal‚mol-1 and ∆Sq ) -1.3 ( 1.2 cal‚mol-1‚K-1 for 6. Complexes 1, 3, and 4 are active
catalyst precursors for classical Tishchenko dimerization of cyclohexanecarboxaldehyde.
Complexes 1 and 3 are also active catalyst precursors for the classical Tishchenko
dimerization of benzaldehyde and for the homo aldo-Tishchenko trimerization of isobutyral-
dehyde to (3-hydroxy-2,2,4-trimethylpentyl)-2-methylpropionate.
In tr od u ction
In addition to the activation of aromatic ketones,
intermediate OsH2(η2-H2)(PiPr3)2 is capable of producing
the triple C-H activation of the cyclohexylmethyl
We have recently shown that the saturated d2 hexahy-
dride OsH6(PiPr3)2 can be thermally activated to gener-
ate the unsaturated short-lived dihydride-dihydrogen
OsH2(η2-H2)(PiPr3)2.1 This species activates ortho-CH
bonds of aromatic ketones and imines2 and ortho-CF
bonds of partially fluorinated aromatic ketones.1 The
reactions give complexes that are reminiscent of the
intermediates proposed by Murai for the insertion of
olefins into ortho-CH bonds of ketones and imines3 and
for the arylation of aromatic ketones with arylbor-
onates.4 For partially fluorinated aromatic ketones, the
ortho-CH activation is preferred over the ortho-CF
activation in ketones containing only one aromatic ring.
However, the ortho-CF activation is preferred over the
ortho-CH activation in 2,3,4,5,6-pentafluoroacetophe-
none.1
ketone to afford the cyclohexenyl-keto derivative OsH3-
{C6H8C(O)CH3}(PiPr3)2.5 The formation of this complex
suggests that cycloalkyl ketones should be able to afford
alkylcycloalkenyl ketones by the Murai method.
The activation of the C-HR bond of aldehydes is a
reaction of great interest due to its connection with the
catalytic decarbonylation of these substrates6 and by its
importance in organometallic7 and organic8 synthesis.
Our interest in the activation processes of carbonyl
compounds promoted by the species OsH2(η2-H2)(PiPr3)2
(5) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. Orga-
nometallics 2001, 20, 2635.
(6) See for example: (a) Tsuji, J .; Ohno, K. Tetrahedron Lett. 1965,
3969. (b) Ohno, K.; Tsuji, J . J . Am. Chem. Soc. 1968, 90, 99. (c)
Domazetis, G.; Tarpey, B.; Dolphin, D.; J ames, B. R. J . Chem. Soc.,
Chem. Commun. 1980, 939. (d) Belani, R. M.; J ames, B. R.; Dolphin,
D.; Rettig, S. J . Can. J . Chem. 1988, 66, 2072. (e) O’Connor, J . M.;
Ma, J . J . Org. Chem. 1992, 57, 5075. (f) Chapuis, C.; Winter, B.;
Schulte-Elte, K. H. Tetrahedron Lett. 1992, 33, 6135. (g) Abu-
Hasanayn, F.; Goldman, M. E.; Goldman, A. S. J . Am. Chem. Soc. 1992,
114, 2520. (h) O’Connor, J . M.; Ma, J . Inorg. Chem. 1993, 32, 1866. (i)
Beck, C. M.; Rathmill, S. E.; Park, Y. J .; Chen, J .; Crabtree, R. H.
Organometallics 1999, 18, 5311.
* Corresponding author. E-mail: maester@posta.unizar.es.
(1) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; Lledo´s, A.;
Maseras, F.; On˜ate, E.; Toma`s, J . Organometallics 2001, 20, 442.
(2) Barea, G.; Esteruelas, M. A.; Lledo´s, A.; Lo´pez, A. M.; On˜ate,
E.; Tolosa, J . I. Organometallics 1998, 17, 4065.
(3) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826.
(4) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani, N.; Murai, S. J . Am. Chem.
Soc. 2003, 125, 1698.
10.1021/om034389l CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/13/2004

Reactions of a Hexahydride-Osmium Complex
Organometallics, Vol. 23, No. 6, 2004 1341
Sch em e 1
prompted us to study the activation of the C-HR bond
of aldehydes, in particular those containing aryl and
cyclohexyl groups.
This paper reveals that the intermediate OsH2
(η2-H2)(PiPr3)2 promotes two different stoichiometric
tandem processes: carbon hydrogen activation-decar-
bonylation and carbon hydrogen activation-hydroxy-
lation. Furthermore, it shows that the hexahydride
OsH6(PiPr3)2 and related compounds are active catalyst
precursors for the Tishchenko reaction.
Resu lts a n d Discu ssion
1. C-Hr Activation -Decar bon ylation . The hexahy-
dride complex OsH6(PiPr3)2 (1) reacts with benzalde-
hyde, cyclohexanecarboxaldehyde, and isobutyraldehyde
in toluene under reflux to give organometallic and
organic (identified by gas chromatography-MS) prod-
ucts, which are the result of C-HR activation-decar-
bonylation tandem processes between 2 equiv of alde-
hyde and 1 equiv of hexahydride.
The reaction of 1 with benzaldehyde leads to benzene
and the hydride-phenyl-dicarbonyl derivative OsHPh-
(CO)2(PiPr3)2 (2), according to eq 1.
spectrum, the protons of the aryl group display reso-
nances at 8.26 and 8.11 (o-H), 7.1-6.9 (m-H), and 7.00
(p-H) ppm, whereas the hydride ligand gives rise to a
triplet at -6.59 ppm with a H-P coupling constant of
22.1 Hz. The 31P{1H} NMR spectrum shows a singlet
at 22.0 ppm.
The reactions of 1 with cyclohexanecarboxaldehyde
and isobutyraldehyde lead to the previously reported cis-
dihydride, cis-dicarbonyl derivative OsH2(CO)2(PiPr3)2
10
(3) and the corresponding alkane, according to eq 2.
Scheme 1 shows a sequence of steps that rationalizes
the products of these reactions.
Complex 2 was isolated as a white solid in 82% yield.
In the IR spectrum in KBr the most noticeable features
are the presence of a ν(Os-H) absorption at 2016 cm-1
and two ν(CO) bands at 1959 and 1887 cm-1. The
mutual cis disposition of the carbonyl groups is strongly
supported by the intensity ratio (1.02) of the ν(CO)
bands, which suggests an angle between these ligands
of 90.6°.9 In agreement with this, the 13C{1H} NMR
spectrum contains resonances corresponding to in-
equivalent carbonyl groups at 191.4 and 185.6 ppm.
These resonances are observed as triplets with C-P
coupling constants of 5.8 and 8.5 Hz, respectively. In
addition, the spectrum shows six resonances due to the
aryl carbon atoms, at 150.4, 147.0, 145.7, 127.1, 126,9,
and 121.9 ppm. The resonance at 147.0 appears as a
triplet with a C-P coupling constant of 10.6 Hz and was
assigned to the Os-C carbon atom. In the 1H NMR
The dissociation of a hydrogen molecule from the
hexahydride starting complex affords the short-lived
intermediate OsH2(η2-H2)(PiPr3)2 (H4[Os] in Scheme 1),
which is capable of selectively activating the C-HR bond
of aldehydes, in the presence of aromatic or aliphatic
C-H bonds, to give saturated H5-acyl intermediates. In
this context, it should be noted that the C-HR bond of
an aldehyde is about 23 kcal‚mol-1 weaker than the
C-H bonds of a phenyl group and about 14 kcal‚mol-1
weaker than the C-H bonds of an alkyl group.
The loss of a second hydrogen molecule from the
saturated H5-acyl intermediates should lead to unsatur-
ated species, which could evolve by deinsertion of R and
subsequent reductive elimination of R-H, into the
unsaturated dihydride-carbonyl-osmium(II) intermedi-
ate OsH2(CO)(PiPr3)2 (H2[Os]-CO in Scheme 1). This
short-lived derivative has been previously proposed as
the key species for the formation of the hydride-alkynyl
complexes OsH(C2R)(CO)(PiPr3)2 (R ) Ph, SiMe3),11 by
(7) See for example: (a) Go´mez, M.; Kisenyi, J . M.; Sunley, G. J .;
Maitlis, P. M. J . Organomet. Chem. 1985, 296, 197. (b) Alaimo, P. J .;
Arndtsen, B. A.; Bergman, R. G. J . Am. Chem. Soc. 1997, 119, 5269.
(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.
(8) See for example: (a) Naota, T.; Takaya, H.; Murahashi, S.-I.
Chem. Rev. 1998, 98, 2599. (b) Fujimura, O.; Honma, T. Tetrahedron
Lett. 1998, 39, 625. (c) Dyker, G. Angew. Chem., Int. Ed. 1999, 38,
1698. (d) Frantz, D. E.; Fa¨ssler, R.; Tomooka, C. S.; Carreira, E. M.
Acc. Chem. Res. 2000, 33, 373. (e) Lebel, H.; Paquet, V.; Prouxl, C.
Angew. Chem., Int. Ed. 2001, 40, 2887. (f) Chen, Z.; Xiong, W.; J iang,
B. Chem. Commun. 2002, 2098. (g) Li, C.-J .; Wei, C. Chem. Commun.
2002, 268. (h) Lu, G.; Li, X.; Chan, W. L.; Chan, A. S. C. Chem.
Commun. 2002, 172. (i) Mirafzal, G. A.; Cheng, G.; Woo, L. K. J . Am.
Chem. Soc. 2002, 124, 176. (j) Shibata, T.; Toshida, N.; Takagi, K. Org.
Lett. 2002, 4, 1619. (k) Ko, S.; Lee, C.; Choi, M.-G.; Na, Y.; Chang, S.
J . Org. Chem. 2003, 68, 1607. (l) Wang, M.; Yang, X.-F.; Li, C.-J . Eur.
J . Org. Chem. 2003, 998. (m) Keh, C. C. K.; Wei, C.; Li, C.-J . J . Am.
Chem. Soc. 2003, 125, 4062. (n) Wei, C.; Li, C.-J . J . Am. Chem. Soc.
2003, 125, 9584. (o) Zhang, X.; Chen, P. Chem. Eur. J . 2003, 9, 1852.
(9) I(higher ν)]/[I(lower ν)] ) tan2(θ/2).
(10) Werner, H.; Esteruelas, M. A.; Meyer, U.; Wrackmeyer, B.
Chem. Ber. 1987, 120, 11.
(11) (a) Espuelas, J .; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A.:
Valero, C. Organometallics 1993, 12, 663. (b) Esteruelas, M. A.; Oro,
L. A. Adv. Organomet. Chem. 2001, 47, 1.

1342 Organometallics, Vol. 23, No. 6, 2004
Barrio et al.
reaction of the dihydride-dihydrogen OsH2(η2-H2)(CO)
(PiPr3)2 with the corresponding alkyne.
12
The oxidative addition of a second molecule of alde-
hyde to OsH2(CO)(PiPr3)2 should lead to saturated H3-
carbonyl-acyl species. The dissociation of a new hydro-
gen molecule from these intermediates, followed by the
deinsertion of R, should give 2 (R ) Ph) or hydride-alkyl
intermediates. In contrast to 2, these hydride-alkyl
intermediates are unstable under the reaction condi-
tions and evolve by reductive elimination of alkane into
an unsaturated osmium(0) species. The oxidative addi-
tion of molecular hydrogen to the latter should yield 3.
We note that the dimeric ruthenium complex [RuHCl-
(PiPr3)2]2 also reacts with aldehydes to give C-HR
activation-decarbonylation products. However, in con-
trast to 1, this ruthenium derivative is capable of
producing only one tandem process.7d The reactions with
alkyl aldehydes lead to the well-known compound
RuHCl(CO)(PiPr3)2 13 and alkane, while in the presence
of benzalehyde, the phenyl derivative RuPhCl(CO)
(PiPr3)2 is formed. Although complex RuHCl(CO)(PiPr3)2
is formally an unsaturated compound, at first glance
as the short-lived intermediate OsH2(CO)(PiPr3)2, the
mutually trans disposition of the Cl and CO ligands
increases the π-donor capacity of chloro by means of the
“push-pull” effect, making this molecule not a truly 16-
valence-electron species14 and therefore less reactive
than OsH2(CO)(PiPr3)2.
The higher stability of 2 in comparison with the
related hydride-alkyl species should be attributed to an
osmium-carbon bond much stronger for aryl than for
alkyl. In this context, it should be mentioned that
although the arene C-H bond is between 14 and 8
kcal‚mol-1 stronger than the alkane C-H bond, in
general, the arene C-H activation is thermodynamically
favored with regard to the alkane C-H activation.15
2. C-Hr Activa tion -Hyd r oxyla tion . In the pres-
ence of 30 equiv of water the reaction of 1 with
benzaldehyde leads to 2 and benzene. However the
reactions of 1 with cyclohexanecarboxaldehyde and
isobutyraldehyde give the trihydride-carboxylate com-
pounds OsH3(κ2-O2CR)(PiPr3)2 (R ) Cy (4), (CH3)2CH
(5)), according to eq 3. In this case the formation of
alkane is not observed.
F igu r e 1. Molecular diagram of the complex OsH3(κ2-O2-
CCH(CH3)2)(PiPr3)2 (5).
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for th e Com p lex
OsH3[K2-O2CCH(CH3)2](P iP r 3)2 (5)
Os-P(1)
Os-P(2)
Os-O(1)
Os-O(2)
Os-H(01)
2.3227(9)
2.3198(9)
2.208(2)
2.2509(19)
1.42(3)
Os-H(02)
Os-H(03)
O(1)-C(1)
O(2)-C(1)
C(1)-C(2)
1.44(3)
1.45(3)
1.262(4)
1.266(3)
1.514(4)
P(1)-Os-P(2)
P(1)-Os-O(1)
P(1)-Os-O(2)
P(1)-Os-H(01)
P(1)-Os-H(02)
P(1)-Os-H(03)
P(2)-Os-O(1)
P(2)-Os-O(2)
P(2)-Os-H(01)
P(2)-Os-H(02)
P(2)-Os-H(03)
O(1)-Os-O(2)
O(1)-Os-H(01)
174.14(3)
93.37(6)
92.67(6)
90.2(10)
88.5(10)
87.7(11)
92.19(6)
91.82(6)
87.6(10)
85.6(10)
88.3(11)
58.35(8)
93.8(11)
O(1)-Os-H(02)
O(1)-Os-H(03)
O(2)-Os-H(01)
O(2)-Os-H(02)
O(2)-Os-H(03)
H(01)-Os-H(02)
H(01)-Os-H(03)
H(02)-Os-H(03)
Os-O(1)-C(1)
154.9(12)
151.8(11)
152.1(11)
146.6(12)
93.5(11)
61.2(13)
114.4(15)
53.2(13)
92.5(2)
90.47(19)
118.6(3)
119.5(3)
121.9(3)
Os-O(2)-C(1)
O(1)-C(1)-O(2)
O(1)-C(1)-C(2)
O(2)-C(1)-C(2)
scopies. Complex 5 was further characterized by an X-ray
crystallographic study. A view of the molecular geom-
etry of this compound is shown in Figure 1. Selected
bond distances and angles are listed in Table 1.
The coordination geometry around the osmium atom
can be rationalized as a distorted pentagonal bipyramid
with the two phosphorus atoms of the triisopropylphos-
phine ligands occupying axial positions (P(2)-Os-P(1)
) 174.14(3)°). The osmium sphere is completed by the
hydride ligands and the carboxylate group, which acts
with a bite angle of 58.35(8)°.
The IR spectra of these compounds in KBr exhibit two
ν(OsH) bands at 2156 and 2142 (4) and 2159 and 2144
(5) cm-1 as well as the νasym(OCO) (1524 (4) and 1534
Complexes 4 and 5 were isolated as yellow solids in
high yield and characterized by MS, elemental analysis,
and IR and 1H, 13C{1H}, and 31P{1H} NMR spectro-
(5) cm-1) and νsym(OCO) (1447 (4) and 1484 (5) cm-1
)
absorptions corresponding to the carboxylate groups,
which are separated by 77 (4) and 50 (5) cm-1, in
agreement with the chelate coordination mode of these
ligands.16 In the 13C{1H} NMR spectra, the resonances
due to the C(sp2) carbon atom of the carboxylate groups
appear at 185.7 (4) and 186.3 (5) ppm, as triplets with
C-P coupling constants of 1.4 and 1.2 Hz, respectively.
(12) Gusev, D. G.; Kuhlman, R. L.; Renkema, K. B.; Eisenstein, O.;
Caulton, K. G. Inorg. Chem. 1996, 35, 6775.
(13) Esteruelas, M. A.; Werner, H. J . Organomet. Chem. 1986, 303,
221.
(14) (a) Poulton, J . T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg.
Chem. 1992, 31, 3190. (b) Poulton, J . T.; Sigalas, M. P.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1993, 32, 5490. (c) Heyn, R. H.;
Huffman, J . C.; Caulton, K. G. New J . Chem. 1994, 17, 797. (d) Poulton,
J . T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein, O.; Caulton,
K. G. Inorg. Chem. 1994, 33, 1476.
(15) J ones, W. D.; Feher, F. J . Acc. Chem. Res. 1989, 22, 91.
(16) Deacon, G. B.; Phillips, R. J . Coord. Chem. Rev. 1980, 33, 227.

Reactions of a Hexahydride-Osmium Complex
Organometallics, Vol. 23, No. 6, 2004 1343
The 31P{1H} NMR spectra show singlets at 40.7 (4) and
40.5 (5) ppm, in accordance with the mutually trans
position of the phosphine ligands.
Sch em e 2
The 31P{1H} NMR spectra are temperature invariant
1
between 293 and 203 K. However, the H NMR spectra
are temperature dependent and consistent with the
operation of a thermally activated exchange process
between the central hydride and those disposed cisoid
to the oxygen atoms of the carboxylate. At 293 K, for
both compounds, the exchange process proceeds at a
rate sufficient to lead to single hydride resonances,
which appear at -14.51 (4) and -14.97 (5) ppm as
triplets with H-P coupling constants of 11.8 and 11.7
Hz, respectively. Lowering the sample temperature
leads to broadening of the resonances. At 213 K decoa-
lescence occurs and AB2X2 (X ) 31P) spin systems are
observed, which become well resolved at 203 K. The
1H{31P} NMR spectra are simplified to the expected AB2
spin systems. They are defined by δA ) -14.33, δB
)
-14.52, and J A-B ) 18.03 Hz (4) and δA ) -14.76, δB )
-15.27, and J A-B ) 20.7 Hz (5).
Line-shape analysis of the 1H{31P} NMR spectra
allows the calculation of the rate constants for the
thermal exchange processes at different temperatures.
The activation parameters obtained from the corre-
sponding Eyring analysis are ∆Hq ) 10.2 ( 0.4
kcal‚mol-1 and ∆Sq ) -4.3 ( 1.0 cal‚mol-1‚K-1 for 4
and ∆Hq ) 10.6 ( 0.3 kcal‚mol-1 and ∆Sq ) 1.1 ( 0.9
cal‚mol-1‚K-1 for 5. The values for the entropy of
activation, close to zero, are in agreement with an
intramolecular process, whereas the values for the
enthalpy of activation lie in the range reported for
thermal exchange processes in related osmium-trihy-
dride complexes.1-3,17
The spectroscopic data of 6 agree well with those of 4
and 5. The IR spectrum contains two ν(OsH) bands at
2160 and 2140 cm-1 along with the νasym(OCO) and
ν
sym(OCO) absorptions at 1525 and 1465 cm-1, respec-
tively. In the 13C{1H} NMR spectrum, the resonance due
to the CO2-carbon atom of the carboxylate appears as a
singlet at 176.2 ppm. The 31P{1H} shows a singlet at
40.2 ppm.
As for 4 and 5, the 1H NMR spectra of 6 are consistent
with the operation of a thermally activated exchange
process between the central hydride and those disposed
cisoid to the oxygen atoms of the carboxylate. Thus, at
room temperature, the spectrum shows only one hydride
resonance at -14.38 ppm, which appears as a triplet
with a H-P coupling constant of 11.6 Hz, while at 193
K the characteristic AB2X2 (X ) 31P) spin system for a
structure as that shown in Figure 1 is observed. In the
1H{31P} NMR spectrum, the simplified AB2 spin system
The T1 values of the hydrogen nuclei of the OsH3 unit
of 4 and 5 were determined over the temperature range
293-183 K. T1(min) values of 74 ( 2 (4) and 82 ( 1 (5)
ms were obtained at 220 K. They support the trihydride
character of both compounds.18
The reactions shown in eq 3 describe C-HR activa-
tion-hydroxylation tandem processes for cyclohexan-
ecarboxaldehyde and isobutyraldehyde, which can be
rationalized according Scheme 2. The nucleophilic ad-
dition of water to the H5-acyl intermediates of Scheme
1 leads to the corresponding carboxylic acid, regenerat-
ing 1. The subsequent reactions of 1 with the acids
afford 4 and 5. The fact that benzaldehyde does not react
in the same manner as cyclohexanecarboxaldehyde and
isobutyraldehyde suggests that the deinsertion of R is
faster for phenyl than alkyl, which could be related to
the higher stability of the M-Ph bonds in comparison
with the M-alkyl bonds.
is defined by δA ) -14.03, δB ) -14.37, and J A-B
)
22.04 Hz. The activation parameters for the exchange
are ∆Hq ) 10.4 ( 0.4 kcal‚mol-1 and ∆Sq ) -1.3 ( 1.2
cal‚mol-1‚K-1. These values are very similar as those
obtained for 4 and 5 and suggest that the substituent
R of the carboxylate has no significant contribution to
the properties of the OsH3 unit of these compounds.
The T1 values of the hydrogen nuclei of the OsH3 unit
of 6 were determined over the temperature range 293-
193 K. T1(min) values of 68 ( 3 (δA) and 78 ( 2 (δB) ms
were obtained at 218 K, after the decoalescence. They
are consistent with a separation HA-HB of between 1.5
and 1.6 Å.18
In agreement with Scheme 2, we have observed that
1 reacts with cyclohexanecarboxylic acid and isobutyric
acid to give 4 and 5, respectively. Similarly, the reaction
of 1 with benzoic acid affords OsH3(κ2-O2CPh)(PiPr3)2
(6), as a yellow solid in 78% yield (eq 4).
3. Ca ta lytic Tish ch en k o Rea ction s. The classical
Tishchenko reaction, by which an aldehyde can be
(17) (a) Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, A. M.; On˜ate, E.; Oro,
L. A.; Ruiz, N.; Sola, E.; Tolosa, J . I. Inorg. Chem. 1996, 35, 7811. (b)
Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N. J . Am. Chem. Soc.
1997, 119, 9691. (c) Castillo, A.; Barea, G.; Esteruelas, M. A.; Lahoz,
F. J .; Lledo´s, A.; Maseras, F.; Modrego, J .; On˜ate, E.; Oro, L. A.; Ruiz,
N.; Sola, E. Inorg. Chem. 1999, 38, 1814.
(18) J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155.

1344 Organometallics, Vol. 23, No. 6, 2004
Ta ble 2. Ca ta lytic Tish ch en k o Rea ction Resu lts
Barrio et al.
converted into a simple monofunctional ester, has
important industrial applications. Thus, for example,
the Tishchenko ester of 3-cyclohexenecarbaldehyde is
the precursor for the formation of epoxy resine, and
benzylbenzoate is used as a dye carrier. Traditionally
aluminum19 or transition metal20 alkoxides, lithium
tungsten dioxide,21 SmI2,22 or boric acid,23 have been
employed as catalysts. More recently transition metal
complexes, including phosphine-rhodium-24 and cyclo-
pentadienyl-nickel-enolates,25 lanthanide amides,26
Cp*2La[CH(SiMe3)2],27 Cp2ZrH2,28 RuH2(PPh3)4,29 or
K2[Fe(CO)4],30 are used. To our knowledge osmium
catalysts have not been reported.
reflux in the aldehyde (cyclohexanecarboxaldehyde and
benzaldehyde) or toluene (isobutyraldehyde) as solvent,
using a 1:100 catalyst:aldehyde molar ratio. The formed
products and the yields of the reactions are given in
Table 2.
Complex 1 is a very active catalyst precursor for the
Tishchenko dimerization of cyclohexanecarboxaldehyde
(eq 5). Thus, after 10 min, the ester is formed in 90%
yield. All the aldehyde is converted to ester (98%) and
cyclohexane (2%) after 30 min. In agreement with the
formation of the alkane, the 1H and 31P{1H} NMR
spectra of the residue resulting from the evaporation
of the ester under reduced pressure show the charac-
teristic resonances of the dihydride-dicarbonyl deriva-
tive 3. However, complex 3 is not the responsible species
for the fast formation of the ester. In fact, complex 3 is
also an active catalyst precursor for the reaction shown
in eq 5, but its activity (92% yield after 22 h) is much
lower than that of 1. Furthermore, in the presence of 3
the formation of methylcyclohexanol, in about 5% yield,
was also observed. The formation of 3 seems to be the
result of the stoichiometric reaction of 1 with cyclohex-
anecarboxaldehyde at the end of the catalysis. The
acetate complex 4 is also active for the Tishchenko
dimerization of cyclohexanecarboxaldehyde. Its activity
(76% yield after 22 h) is even lower than that of 3.
This absence prompted us to explore the catalytic
activity of complexes 1-6 for the Tishchenko dimeriza-
tions of cyclohexanecarboxaldehyde, benzaldehyde, and
isobutyraldehyde. The reactions were carried out under
(19) (a) Tishchenko, V. E. Zh. Russ. Fiz-Khim. Ova. 1906, 38, 482.
(b) Villani, T. J .; Nord, F. F. J . Am. Chem. Soc. 1947, 69, 2605. (c) Lin,
I.; Day, A. R. J . Am. Chem. Soc. 1952, 74, 5133. (d) Ogata, Y.;
Kawasaki, A.; Kishi, I. Tetrahedron 1967, 23, 825. (e) Saegusa, T.;
Kitagawa, S.; Uesima, T. Bull. Chem. Soc. J pn. 1967, 40, 1960. (f)
Ogata, Y.; Kawasaki, A. Tetrahedron 1969, 25, 929.
(20) (a) Bernard, K. A.; Atwood, J . D. Organometallics 1988, 7, 235.
(b) Bernard, K. A.; Atwood, J . D. Organometallics 1989, 8, 795. (c)
J acobsen, E. N.; Zhang, W.; Muci, A. R.; Ecker, J . R.; Deng, L. J . Am.
Chem. Soc. 1991, 113, 7063. (d) Mascarenhas, C. M.; Miller, S. P.;
White, P. S.; Morken, J . P. Angew. Chem., Int. Ed. 2001, 40, 601.
(21) Villacorta, G. M.; San Filippo, J ., J r. J . Org. Chem. 1983, 48,
1151.
(22) Lu, L.; Chang, H.-Y.; Fang, J .-M. J . Org. Chem. 1999, 64, 843.
(23) Stapp, P. R. J . Org. Chem. 1973, 38, 1433.
(24) Slough, G. A.; Ashbaugh, J . R.; Zannoni, L. A. Organometallics
1994, 13, 3587.
(25) Burkhardt, E. R.; Bergman, R. G.; Heathcock, C. H. Organo-
metallics 1990, 9, 30.
(26) (a) Berberich, H.; Roesky, P. W. Angew. Chem., Int. Ed. 1998,
37, 1569. (b) Bu¨rgstein, M. R.; Berberich, H.; Roesky, P. W. Chem. Eur.
J . 2001, 7, 3078.
(27) Onozawa, S.; Sakakura, T.; Tanaka, M.; Shiro, M. Tetrahedron
1996, 52, 4291.
(28) (a) Morita, K.-I.; Nishiyama, Y.; Ishii, Y. Organometallics 1993,
12, 3748. (b) Umekawa, Y.; Sakaguchi, S.; Nishiyama, Y.; Ishii, Y. J .
Org. Chem. 1997, 62, 3409.
The Tishchenko dimerization of cyclohexanecarbox-
aldehyde in the presence of 1 can be rationalized
according to Scheme 3. The insertion of an aldehyde
molecule into one of the Os-H bonds of the H3-acyl
intermediate shown in Scheme 1 should afford an acyl-
alkoxy species, which could evolve by reductive elimina-
(29) Ito, T.; Horino, H.; Koshiro, Y.; Yamamoto, A. Bull. Chem. Soc.
J pn. 1982, 55, 504.
(30) Yamashita, M.; Ohishi, T. Appl. Organomet. Chem. 1993, 7, 357.
(31) Atwood, J . D. Inorganic and Organometallic Reaction Mecha-
nisms: VCH Publisher: New York, 1997; Chapter 3.

Reactions of a Hexahydride-Osmium Complex
Organometallics, Vol. 23, No. 6, 2004 1345
Sch em e 3
the first molecule of aldehyde reacts to afford an alkoxy
intermediate. In a subsequent step, this species could
activate the C-HR bond of a second molecule of aldehyde
to give the acyl-alkoxy intermediate.
The reductive elimination of alcohol from the inter-
mediate (Ln-1)OsH(OCH2R) could afford an unsaturated
(Ln-1)Os species, which should also catalyze the dimer-
ization of the aldehyde by an alternative pathway
involving osmium(0) and osmium(II) intermediates
instead of osmium(II) and osmium(IV) species (cycle B
in Scheme 4).
Complex 1 is also an active catalyst precursor for the
dimerization of benzaldehyde (eq 6). However its stabil-
ity under the reaction conditions is very low, and it
rapidly undergoes deactivation. After 2, 24, and 75 h,
the yields of the reaction are 8%, 18%, and 20%,
respectively. The resulting species from the deactivation
process is the hydride-phenyl derivative 2. This is
1
supported by the H and 31P{1H} NMR spectra of the
residue obtained from removing the volatiles of the
catalytic mixture, after 24 h of reaction, which show the
characteristic resonances of 2, and by the fact that 2 is
inactive for the Tishchenko dimerization of benzalde-
hyde. The transformation of 1 into 2 during the catalysis
suggests that the deinsertion of the phenyl of the acyl
group occurs at a rate comparable with the rate of
insertion of benzaldehyde into an Os-H bond, and it
agrees well with the null tendency shown by this
aldehyde to be hydroxylated according to eq 3.
tion of ester to give a 14-electron OsH2(PiPr3)2 interme-
diate. The oxidative addition of the C-HR bond of
another molecule of aldehyde to this species should
regenerate the key H3-acyl intermediate.
Since complex 3 is a saturated species, and therefore
initially inactive, it seems reasonable to think that its
activation involves the dissociation of a carbonyl or/and
phosphine group. Thus an unsaturated dihydride could
catalyze the formation of the ester via osmium(II) and
osmium(IV) intermediates (cycle A in Scheme 4). The
lower activity of 3 in comparison with 1 can be related
to the low tendency shown by the saturated osmium-
(II) complexes toward the dissociation of any ligand.31
According to cycle A, the dimerization of the aldehyde
should also involve an acyl-alkoxy intermediate, similar
to that shown in Scheme 3. However, the formation of
traces of cyclohexanemethanol during the reaction car-
ried out in the presence of 3 suggests that, in this case,
For the Tishchenko dimerization of benzaldehyde, the
dihydride-dicarbonyl complex 3 is also a catalyst pre-
cursor less active than 1. Thus after 50 h of reaction in
the presence of 3, the yield of the dimerization is only
10%. However, it is much more stable than 1 and does
not undergo deactivation. The reaction shows a uniform
rate for the formation of the ester, which becomes 92%
after 141 h.
It should be noted that the dimerization of cyclohex-
anecarboxaldehyde is faster than the dimerization of
Sch em e 4

1346 Organometallics, Vol. 23, No. 6, 2004
Barrio et al.
benzaldehyde. This can be due to the fact that the
insertion of cyclohexanecarboxaldehyde into an Os-H
bond is favored with regard to the insertion of benzal-
dehyde. In this context, it should be mentioned that the
formation of alcohol is not observed during the dimer-
ization of benzaldehyde and that, in general, the cata-
lytic reduction of cycloalkyl ketones is faster than the
catalytic reduction of aromatic ketones.32
Complex 1 and 3 are also active catalyst precursors
for the homo aldo-Tishchenko trimerization of isobu-
tyraldehyde. The reactions lead selectively to (3-hy-
droxy-2,2,4-trimethylpentyl)-2-methylpropionate (eq 7).
dride are formed. The subsequent reaction between both
leads finally to the trithydride-acetate derivatives
OsH3(κ2-O2CR)(PiPr3)2 (R ) Cy, (CH3)2CH).
The capacity shown by OsH2(η2-H2)(PiPr3)2 to activate
the C-HR bond of aldehydes together with the presence
of hydride ligands in the resulting addition product,
which have the property of inserting a second aldehyde
molecule, makes the hexahydride an active catalyst
precursor for the classical Tishchenko dimerization of
aldehydes. The stability of the catalyst precursor during
the reaction is a function of the tendency of the R
substituent of the acyl group of the Os-C(O)R interme-
diate to undergo deinsertion. Thus, while cyclohexan-
ecarboxaldehyde can be rapidly converted into the ester
dimer (90% yield after 10 min), and the transformation
of the catalyst precursor into OsH2(CO)2(PiPr3)2 occurs
only at the end of the catalysis, benzaldehyde deacti-
vates the catalyst precursor to give OsHPh(CO)2(PiPr3)2
during the first cycles of the catalysis.
In the presence of 3, the reaction is slow, but the rate
is uniform until the end. After 126 h the product is
obtained in 100% yield, and the catalyst precursor can
be recovered in high yield from the resulting solution,
by removing the trimer under reduced pressure and
subsequent addition of methanol.
In the presence of 1, the reaction shows some signifi-
cant differences. Initially an induction period of about
1 day is observed. Subsequently, the rate is uniform but
lower than that with 3. Thus, after 140 h, only 86% of
product is formed. Attempts to identify the catalyst of
the reaction were unsuccessful. From the catalytic
solution, a complex mixture of metallic compounds was
isolated. However, it does not contain either 1 or 3.
The acetate complexes 5 and 6 are not active for the
catalytic reactions shown in eqs 7 and 6, respectively.
In conclusion, the reactions of transition metal poly-
hydrides with aldehydes should merit more attention
than that given until now. They afford short-lived
hydride-acyl species, which are the key to prepare
several types of complexes and to generate catalytic
processes.
Exp er im en ta l Section
All reactions were carried out with rigorous exclusion of air
using Schlenk-tube techniques. Solvents were dried by the
usual procedures and distilled under argon prior to use. The
starting materials OsH6(PiPr3)2
and OsH2(CO)2(PiPr3)2
32b
33
were prepared by published methods. Commercial aldehydes
were freshly distilled over 4 Å molecular sieves.
1H, 31P{1H}, and 13C{1H} NMR spectra were recorded on
either a Varian UNITY 300, a Varian Gemini 2000, or a
Bruker AXR 300 MHz instrument. Chemical shifts (expressed
in parts per million) are referenced to residual solvent peaks
(1H, 13C{1H}) or external H3PO4 (31P{1H}). Coupling constants,
J and N (N ) J P-H + J P′-H for 1H and N ) J P-C + J P′-C for
13C{1H}) are given in hertz. Infrared spectra were run on a
Perkin-Elmer 1730 spectrometer as solids (KBr pellet). C and
H analyses were carried out in a Perkin-Elmer 2400 CHNS/O
analyzer. For the organometallic compounds, mass spectral
analyses were performed with a VG Austospec instrument. In
FAB+ mode, ions were produced with the standard Cs+ gun
at ca. 30 kV, and 3-nitrobenzyl alcohol (NBA) was used in the
matrix. For the organic products of the catalytic reactions,
GC-MS analyses were run on an Agilent 5973 mass selective
detector interfaced to an Agilent 6890 series gas chromato-
graph system. Samples were injected into a 30 m × 250 µm
HP-5MS 5% phenyl methyl siloxane column with a film
thickness of 0.25 µm (Agilent). The GC oven temperature was
programmed as follows: 35 °C for 6 min, 35 to 280 °C at 25
°C/min, 280 °C for 4 min. The carrier gas was helium at a flow
rate of 1 mL/min.
Con clu d in g Rem a r k s
This study reveals that the short-lived dihydride-
dihydrogen species OsH2(η2-H2)(PiPr3)2, generated by
thermal activation of the hexahydride OsH6(PiPr3)2,
activates the C-HR bond of aromatic and alkyl alde-
hydes to afford short-lived acyl derivatives. These
species are highly unstable and rapidly evolve to give
different types of isolated compounds, depending upon
the reaction conditions.
In the absence of water, the acyl intermediates
undergo deinsertion of the R substituent (alkyl or
phenyl) and subsequent reductive elimination of R-H.
The resulting species are capable of promoting the
activation-deinsertion tandem process of a second
aldehyde molecule to give OsH2(CO)2(PiPr3)2 (cyclohex-
anecarboxaldehyde and isobutyraldehyde) or OsHPh-
(CO)2(PiPr3)2 (benzaldehyde).
The deinsertion of R is faster for phenyl than for alkyl.
Thus, while in the presence of water and the aldehyde,
the acyl group of the short-lived Os-C(O)Ph species
evolves into OsHPh(CO)2(PiPr3)2, and the acyl group of
the Os-C(O)alkyl intermediates undergoes nucleophilic
addition of water before the deinsertion. As a result, the
corresponding carboxylic acid and the starting hexahy-
1
Kin etic An a lysis. Complete line-shape analysis of the H-
{31P} NMR spectra of complexes 4, 5, and 6 was achieved using
the program gNMR (Cherwell Scientific Publishing Limited).
The rate constants for various temperatures were obtained by
fitting calculated to experimental spectra by full line-shape
iterations. The transverse relaxation time, T2, was estimated
at the lowest interval of temperatures using the resonances
corresponding to the hydride ligands. The activation param-
eters ∆Hq and ∆Sq were calculated by least-squares fit of ln-
(k1/T) versus 1/T (Eyring equation). Error analysis assumed a
(32) (a) Esteruelas, M. A.; Sola, E.; Oro, L. A.; Wener, H.; Meyer,
U. J . Mol. Catal. 1988, 45, 1. (b) Aracama, M.; Esteruelas, M. A.; Lahoz,
F. J .; Lo´pez, J . A.; Meyer, U.; Oro, L. A.; Werner, H. Inorg. Chem. 1991,
30, 288. (c) Chaloner, P.; Esteruelas, M. A.; J oo´, F.; Oro, L. A.
Homogeneous Hydrogenation: Kluwer Academic Publishers: Dor-
drecht, 1994.
(33) Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, J . A.; Oro, L. A.;
Schlu¨nken, C.; Valero, C.; Werner, H. Organometallics 1992, 11, 2034.

Reactions of a Hexahydride-Osmium Complex
Organometallics, Vol. 23, No. 6, 2004 1347
10% error in the rate constant and 1 K in the temperature.
Errors were computed by published methods.34
CHCy), 28.9 (s, CH2(Cy)), 26.7 (vt, N ) 23.9 Hz, PCH), 26.2 (s,
p-CH2(Cy)), 25.9 (s, CH2(Cy)), 20.3 (s, PCHCH3). MS (FAB+): m/z
640 (M+ - 2H). T1(min) (ms, OsH3, 300 MHz, C7D8, 220 K): 74
( 2 (-14.51 ppm, 3H).
Rea ction of OsH6(P iP r 3)2 w ith Ben za ld eh yd e. A color-
less solution of 1 (212.6 mg, 0.411 mmol) in 15 mL of toluene
was treated with 2.0 equiv of benzaldehyde (84 µL, 0.826
mmol) and heated under reflux for 5 h. An analysis of the
resulting solution by chromatography revealed the presence
of benzene. The pale yellow solution obtained was filtered
through Celite and dried in vacuo. Methanol was added to
afford the complex OsHPh(CO)2(PiPr3)2 as a white solid, which
was washed with further portions of methanol and dried in
vacuo. Data for OsHPh(CO)2(PiPr3)2 (2): Yield: 218.4 mg (82%).
Anal. Calcd for C26H48O2OsP2: C 48.43, H 7.50. Found: C
47.97, H 7.31. IR (KBr, cm-1): ν(OsH) 2016 (s), ν(CO) 1959
(s), 1887 (s). 1H NMR (300 MHz, C6D6, 293 K): δ 8.26 and
8.11 (both m, 1H, o-Ph), 7.1-6.9 (both m, 1H, m-Ph), 7.00 (m,
1H, p-Ph), 1.97 (m, 6H, PCH), 1.11 and 1.09 (both dvt, N )
14.1 Hz, J H-H ) 7.3 Hz, 18H, PCHCH3), -6.59 (t, J H-P ) 22.1
Hz. 1H, OsH). 31P{1H} NMR (121.42 MHz, C6D6, 293 K): δ
22.0 (s). 13C{1H} NMR (75.42 MHz, C6D6, 293 K, plus APT):
δ 191.4 (t, J P-C ) 5.8 Hz, CO), 185.6 (t, J P-C ) 8.5 Hz, CO),
150.4 (s, Ph), 147.0 (t, J P-C ) 10.6 Hz, Cipso(Ph)), 145.7, 127.1,
126.9, and 121.9 (all s, Ph), 26.3 (vt, N ) 13.9 Hz, PCH), 19.5
and 19.2 (both s, PCHCH3). MS (FAB+): m/z 645 (M+ - H).
Rea ction of OsH6(P iP r 3)2 w ith Cycloh exa n eca r boxa l-
d eh yd e. A colorless solution of 1 (150.0 mg, 0.290 mmol) in
15 mL of toluene was treated with 2.0 equiv of cyclohexan-
ecarboxaldehyde (70 µL, 0.578 mmol) and heated under reflux
for 5 h. An analysis of the resulting solution by chromatogra-
phy revealed the presence of cyclohexane. The yellow solution
obtained was filtered through Celite and dried in vacuo.
Methanol at 243 K was added to afford the complex OsH2(CO)2
(PiPr3)2 (3) as a white solid, which was washed with further
portions of cold methanol and dried in vacuo. Yield: 125.3 mg
(76%). Data for cis,cis,trans-OsH2(CO)2(PiPr3)2 (3) (in agree-
ment with the previously reported data):10 1H NMR (300 MHz,
C6D6, 293 K): δ 1.99 (m, 6H, PCH), 1.14 (dvt, N ) 13.7 Hz,
J H-H ) 7.1 Hz, 18H, PCHCH3), -9.59 (t, J H-P ) 22.1 Hz, 2H,
OsH). 31P{1H} NMR (121.42 MHz, C6D6, 293 K): δ 41.9 (s).
Rea ction of OsH6(P iP r 3)2 w ith Isobu tyr a ld eh yd e. A
colorless solution of 1 (150.0 mg, 0.290 mmol) in 15 mL of
toluene was treated with 2.0 equiv of isobutyraldehyde (53 µL,
0.583 mmol) and heated under reflux for 5 h. The yellow
solution obtained was filtered through Celite and dried in
vacuo. Methanol at 243 K was added to afford the complex
OsH2(CO)2(PiPr3)2 (3) as a white solid, which was washed with
further portions of cold methanol and dried in vacuo. Yield:
102.3 mg (62%).
Rea ction of OsH6(P iP r 3)2 w ith Isobu tyr a ld eh yd e in th e
P r esen ce of Wa ter . A colorless solution of 1 (157.0 mg, 0.304
mmol) in 15 mL of toluene was treated with isobutyraldehyde
(33 µL, 0.363 mmol) and water (0.25 mL, 0.014 mol) and heated
under reflux for 5 h. The yellow solution obtained was filtered
through Celite and dried in vacuo. Methanol at 243 K was
added to afford the complex OsH3(κ2-O2CCH(CH3)2)(PiPr3)2 (5)
as a yellow solid, which was washed with further portions of
cold methanol and dried in vacuo. Yield: 113.1 mg (62%). Data
for OsH3(κ2-O2CCH(CH3)2)(PiPr3)2 (5): Anal. Calcd for C22H52O2-
OsP2: C 43.98, H 8.72. Found: C 43.65, H 9.07. IR (KBr, cm-1):
ν(OsH) 2159 (s), 2144 (s); νasym(OCO) 1534 (s), νsym(OCO) 1484
1
(s). H NMR (300 MHz, CD2Cl2, 293 K): δ 2.24 (sept, J H-H
)
6.9 Hz, 1H, CH), 2.02 (m, 6H, PCH), 1.17 (dvt, N ) 12.9 Hz,
J H-H ) 6.9 Hz, 36H, PCHCH3), 1.08 (d, J H-H ) 6.9 Hz, 6H,
1
C(CH3)2), -14.97 (t, J H-P ) 11.7 Hz. 3H, OsH). H{31P} NMR
(300 MHz, CD2Cl2, 203 K, high-field region (OsH3 unit)): AB2
spin system, δA ) -14.76, δB ) -15.27, J A-B ) 20.7 Hz. 31P-
{1H} NMR (121.42 MHz, C6D6, 293 K): δ 40.5 (s). 13C{1H}
NMR (75.42 MHz, C6D6, 293 K, plus APT): δ 186.3 (t, J C-P
1.2 Hz, OCO), 37.7 (s, CH), 26.9 (vt, N ) 23.5 Hz, PCH), 20.4
(s, PCHCH3), 18.6 (s, C(CH3)2). MS (FAB+): m/z 598 (M+
)
-
4H). T1(min) (ms, OsH3, 300 MHz, C7D8, 220 K): 82 ( 1 (-14.76
ppm, 3H).
Rea ction of OsH6(P iP r 3)2 w ith Cycloh exa n eca r boxylic
Acid . A colorless solution of 1 (185.5 mg, 0.359 mmol) in 15
mL of toluene was treated with 1.0 equiv of cyclohexanecar-
boxylic acid (45 µL, 0.363 mmol) and heated under reflux for
5 h. The yellow solution obtained was filtered through Celite
and dried in vacuo. Methanol at 243 K was added to afford
the complex OsH3(κ2-O2CCy)(PiPr3)2 (4) as a yellow solid, which
was washed with further portions of cold methanol and dried
in vacuo. Yield: 176.0 mg (77%).
Rea ction of OsH6(P iP r 3)2 w ith Isobu tyr ic Acid . A color-
less solution of 1 (157.0 mg, 0.304 mmol) in 15 mL of toluene
was treated with isobutyric acid (34 µL, 0.367 mmol) and
heated under reflux for 5 h. The yellow solution obtained was
filtered through Celite and dried in vacuo. Methanol at 243 K
was added to afford the complex OsH3(κ2-O2CCH(CH3)2)(PiPr3)2
(5) as a yellow solid, which was washed with further portions
of cold methanol and dried in vacuo. Yield: 155.1 mg (85%).
Rea ction of OsH6(P iP r 3)2 w ith Ben zoic Acid . A colorless
solution of 1 (304.2 mg, 0.589 mmol) in 15 mL of toluene was
treated with benzoic acid (75.4 mg, 0.617 mmol) and heated
under reflux for 5 h. The yellow solution obtained was filtered
through Celite and dried in vacuo. Methanol was added to
afford the complex OsH3(κ2-O2CPh)(PiPr3)2 as a yellow solid,
which was washed with further portions of methanol and dried
in vacuo. Yield: 292.3 mg (78%). Data for OsH3(κ2-O2CPh)
(PiPr3)2 (6): Anal. Calcd for C25H50O2OsP2: C 47.30, H 7.94.
Found: C 47.24, H 8.02. IR (KBr, cm-1): ν(OsH) 2160 (s), 2140
(s); νasym(OCO) 1525 (s), νsym(OCO) 1465 (s). 1H NMR (300 MHz,
C7D8, 293 K): δ 8.24 (m, 2H, o-Ph), 7.11 (m, 1H, p-Ph), 7.09
(m, 2H, m-Ph), 1.95 (m, 6H, PCH), 1.21 (dvt, N ) 12.6 Hz,
J H-H ) 6.9 Hz, 36H, PCHCH3), -14.38 (t, J H-P ) 11.6 Hz. 3H,
OsH). 1H{31P} NMR (300 MHz, C7D8, 193 K, high-field region
(OsH3 unit)): AB2 spin system, δA ) -14.03, δB ) -14.37, J A-B
) 22.04 H. 31P{1H} NMR (121.42 MHz, C6D6, 293 K): δ 40.2
(s). 13C{1H} NMR (75.42 MHz, C6D6, 293 K, plus APT): δ 176.2
(s, OCO), 135.4 (s, Cipso(Ph)), 131.5, 128.3, and 128.2 (all s, Ph),
26.9 (vt, N ) 24.1 Hz, PCH), 20.4 (s, PCHCH3). MS (FAB+):
m/z 634 (M+ - 2H). T1(min) (ms, OsH3, 300 MHz, C7D8, 218 K):
68 ( 3 (-14.17 ppm, 1H), 78 ( 2 (-14.46 ppm, 2H).
Rea ction of OsH6(P iP r 3)2 w ith Cycloh exa n eca r boxa l-
d eh yd e in th e P r esen ce of Wa ter . A colorless solution of 1
(185.5 mg, 0.359 mmol) in 15 mL of toluene was treated with
cyclohexanecarboxaldehyde (56 µL, 0.462 mmol) and water
(0.25 mL, 0.014 mol) and heated under reflux for 5 h. The
yellow solution obtained was filtered through Celite and dried
in vacuo. Methanol at 243 K was added to afford the complex
OsH3(κ2-O2CCy)(PiPr3)2 (4) as a yellow solid, which was washed
with further portions of cold methanol and dried in vacuo.
Yield: 147.3 mg (64%). Data for OsH3(κ2-O2CCy)(PiPr3)2 (4):
Anal. Calcd for C25H56O2OsP2: C 46.85, H 8.81. Found: C
47.01, H 8.73. IR (KBr, cm-1): ν(OsH) 2156 (s), 2142 (s);
1
ν
asym(OCO) 1524 (s), νsym(OCO) 1447 (s). H NMR (300 MHz,
C7D8, 293 K): δ 2.3-1.0 (all s, 11H, Cy), 1.99 (m, 6H, PCH),
1.24 (dvt, N ) 12.7 Hz, J H-H ) 6.5 Hz, 36H, PCHCH3), -14.51
1
(t, J H-P ) 11.8 Hz 3H, OsH). H{31P} NMR (300 MHz, C7D8,
203 K, high-field region (OsH3 unit)): AB2 spin system, δΑ
-14.33, δΒ -14.52, J A-B ) 18.03 Hz. 31P{1H} NMR (121.42
MHz, C6D6, 293 K): δ 40.7 (s). 13C{1H} NMR (75.42 MHz, C6D6,
293 K, plus APT): δ 185.7 (t, J P-C ) 1.4 Hz, OCO), 47.1 (s,
Gen er a l P r oced u r e for th e Tish ch en k o Rea ction . The
freshly distilled aldehyde was added at room temperature into
the Schlenk tube containing catalyst (100:1 catalyst:aldehyde
molar ratio). The reactions were carried out under reflux either
(34) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.

1348 Organometallics, Vol. 23, No. 6, 2004
Barrio et al.
Ta ble 3. Cr ysta l Da ta a n d Da ta Collection a n d
in the aldehyde (cyclohexanecarboxaldehyde and benzalde-
hyde) or in toluene (isobutyraldehyde). The reactions were
monitored by GS-MS. The products were identified by com-
parison of their mass spectra with those of the G1045B
Spectral Library (Willey 7N, Agilent Technologies, 2000). In
addition (3-hydroxy-2,2,4-trimethylpentyl)-2-methylpropionate
was characterized by mass spectrum (m/z ) 217 (M+)) and by
1H and 13C{1H} NMR spectroscopy. 1H NMR (300 MHz, CDCl3,
293 K): AB spin system, δ 3.88 (∆ν ) 97.8 Hz, J A-B ) 11.1
Hz, 2H, CH2), 3.19 (dd, J H-H ) 6.3 Hz, J H-H ) 2.1 Hz, 1H,
CHOH), 2.52 (sept, J H-H ) 6.9 Hz, 1H, C(O)CH(CH3)2), 2.18
(d, J H-H ) 6.3 Hz, 1H, OH), 1.85 (double sept, J H-H ) 6.9 Hz,
J H-H ) 2.1 Hz, 1H, CH(OH)CH), 1.12 (d, J H-H ) 6.9 Hz, 6H,
C(O)CH(CH3)2), 0.96 (s, 3H, CH2C(CH3)2), 0.92 (d, J H-H ) 6.9
Hz, 3H, CH(OH)CH(CH3)2), 0.90 (s, 3H, CH2C(CH3)2), 0.87 (d,
J H-H ) 6.9 Hz, 3H, CH(OH)CH(CH3)2). 13C{1H} NMR (75.42
MHz, CDCl3, 293 K): δ 177.2 (CdO), 79.0 (CH(OH)), 71.1
(CH2), 39.0, 33.8, and 28.3 (all s, C(CH3)2), 23.2, 21.8, 19.3,
18.9, 18.7, 16.4 (CH3).
Refin em en t for OsH3[K2-O2CCH(CH3)2](P iP r 3)2 (5)
Crystal Data
formula
C22H52O2OsP2
molecular wt
600.78
color and habit
symmetry, space group
light yellow, plate
monoclinic, P21/n
16.107(3)
8.9282(15)
20.093(3)
112.585(2)
2667.8(8)
4
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
D
calc, g cm-3
1.496
Data Collection and Refinement
diffractometer
λ(Mo KR), Å
Bruker Smart APEX
0.71073
graphite oriented
ω scans
4.913
monochromator
scan type
µ, mm-1
When the reactions were stopped, the resulting solutions
were concentrated in vacuo and the residues were analyzed
2θ, range deg
3, 56
100
temp, K
1
by H and 31P{1H} NMR spectroscopy. The observed organo-
no. of data collect
no. of unique data
no. of params/restraints
26 977
6350 (Rint) 0.0486)
268/0
0.0246
0.0389
0.735
metallic complexes are indicated below.
Cycloh exa n eca r b oxa ld eh yd e. When OsH6(PiPr3)2 or
OsH2(CO)2(PiPr3)2 was used as catalyst, only OsH2(CO)2(PiPr3)2
was observed.
a
R1 [F2 > 2σ(F2)]
b
wR2 [all data]
Sc [all data]
Ben za ld eh yd e. When OsH6(PiPr3)2 was used as catalyst,
OsHPh(CO)2(PiPr3)2 was formed.
R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. wR2(F2)){∑[w(Fo - Fc2)2]/
a
b
2
∑[w(Fo2)2]}1/2
the number of reflections, and
parameters.
.
c Goof ) S ) {∑[Fo - Fc2)2]/(n - p)}1/2, where n is
2
Isobu tyr a ld eh yd e. When OsH6(PiPr3)2 was used as cata-
lyst, a complex mixture of unidentified metallic compounds
was obtained. When OsH2(CO)2(PiPr3)2 was used as catalyst,
this complex was observed as the unique organometallic
compound at the end of the reaction, and it could be recovered
by precipitation with methanol.
p is the number of refined
The hydrogen atoms were observed or calculated and refined
riding on the bonded carbon atoms. The hydride ligands were
observed in the difference Fourier maps and refined freely with
a common thermal parameter. Weighted R factors (Rw) and
goodness of fit (S) are based on F2; conventional R factors are
based on F. Crystal data and details of the data collection and
refinement are given in Table 3.
X-r a y An a lysis of 5. An irregular crystal of size 0.16 ×
0.14 × 0.02 mm (5) was mounted on a Bruker Smart APEX
CCD diffractometer at 100.0(2) K equipped with a normal
focus, 2.4 kW sealed tube source (molybdenum radiation, λ )
0.71073 Å) operating at 50 kV and 30 mA. Data were collected
over the complete sphere by a combination of four sets. Each
frame exposure time was 10 s covering 0.3° in ω. The cell
parameters were determined and refined by least-squares fit
of 941 collected reflections. The first 100 frames were collected
at the end of the data collection to monitor crystal decay.
Absorption correction was performed with the SADABS35
program. Lorentz and polarization corrections were also
performed. The structures were solved by Patterson and
Ack n ow led gm en t . Financial support from the
MCYT of Spain (Projects BQU2002-00606 and PPQ2000-
0488-P4-02) is acknowledged. P.B. thanks the “Minis-
terio de Educacio´n, Cultura y Deporte” for her grant.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and displacement parameters, crystallographic data, and bond
lengths and angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
Fourier methods and refined by full matrix least-squares using
the Bruker SHELXTL36 program package minimizing w(Fo
-
2
OM034389L
Fc2)2. The non-hydrogen atoms were anisotropically refined.
(36) SHELXTL Package, v. 6.10; Bruker-AXS: Madison, WI, 2000.
Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997.
(35) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33. SADABS,
Area-detector absorption correction; Bruker-AXS: Madison, WI, 1996.