Rhodium(III) acyl hydrido, acyl hydroxyalkyl, diacyl, acyl hydrido aldehyde, and acyl hydrido alcohol complexes. Reduction of aldehyde to alcohol through rhodium hydroxyalkyl complexes

Article abstract of DOI:10.1021/om060978q

[RhCl(COD)]₂ (COD = 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh₂-(o-C₆H ₄CHO)) (Rh/P = 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh₂-(o-C₆H₄CO))(py) ₂] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl₂(PPh₂(o-C₆H₄CO))(py) ₂] (2). The reactions of 1 with PPh₃ and of 2 with biacetyl dihydrazone (bdh) gives the pyridine substitution products [RhHCl(PPh₂(o-C₆H₄CO))(PPh₃)(py)] (4) and [RhCl₂(PPh₂(o-C₆H₄CO))-(bdh) ] (3), respectively. By using a 1:2 ratio of Rh to PPh₂(o-C ₆H₄CHO) [RhHCl(PPh₂(o-C₆H ₄CO))(κ¹-PPh₂(o-C₆H ₄CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo two different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh₂(o-C₆H₄CO))- (PPh₂(o-C₆H₄CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoes dehydrogenation, with H₂ evolution, to afford the diacyl derivative [RhCl(PPh ₂(o-C₆H₄CO))₂(py)] (8), which shows fluxional behavior in solution, with the values ΔH^? = 8.8 ± 0.4 kcal mol^-1 and ΔS^? = - 16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde [RhH(PPh ₂(o-C₆H₄CO))(κ²-PPh ₂(o-C₆H₄CHO))(py)]⁺ (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to a mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh₂(o-C₆H ₄CO))(κ²-PPh₂(o-C₆H ₄-CH₂OH))(py)]⁺ (11). The spectroscopic characterization of some intermediates in this reaction evidence a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the reaction of 5 with NaBH₄ in methanol solution.

Full text of DOI:10.1021/om060978q

Organometallics 2007, 26, 1031-1038
1031
Rhodium(III) Acyl Hydrido, Acyl Hydroxyalkyl, Diacyl, Acyl
Hydrido Aldehyde, and Acyl Hydrido Alcohol Complexes. Reduction
of Aldehyde to Alcohol through Rhodium Hydroxyalkyl Complexes
Mar´ıa A. Garralda,*,† Ricardo Herna´ndez,† Lourdes Ibarlucea,† Elena Pinilla,‡
M. Rosario Torres,‡ and Malkoa Zarandona†
Facultad de Qu´ımica de San Sebastia´n, UniVersidad del Pa´ıs Vasco, Apdo. 1072, 20080 San Sebastia´n,
Spain, and Departamento de Qu´ımica Inorga´nica, Laboratorio de Difraccio´n de Rayos X, Facultad de
Ciencias Qu´ımicas, UniVersidad Complutense, 28040 Madrid, Spain
ReceiVed October 24, 2006
[RhCl(COD)]2 (COD ) 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh2-
(o-C6H4CHO)) (Rh/P ) 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh2-
(o-C6H4CO))(py)2] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl2(PPh2(o-
C6H4CO))(py)2] (2). The reactions of 1 with PPh3 and of 2 with biacetyl dihydrazone (bdh) gives the
pyridine substitution products [RhHCl(PPh2(o-C6H4CO))(PPh3)(py)] (4) and [RhCl2(PPh2(o-C6H4CO))-
(bdh)] (3), respectively. By using a 1:2 ratio of Rh to PPh2(o-C6H4CHO) [RhHCl(PPh2(o-C6H4CO))(κ1-
PPh2(o-C6H4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo
two different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh2(o-C6H4CO))-
(PPh2(o-C6H4CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoes
dehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8),
which shows fluxional behavior in solution, with the values ∆Hq ) 8.8 ( 0.4 kcal mol-1 and ∆Sq )
-16.7 ( 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In
methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde
[RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))(py)]+ (10), which can be isolated if precipitated im-
mediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to a
mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4-
CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidence
a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the
hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the
reaction of 5 with NaBH4 in methanol solution.
to be involved in the H-transfer reduction of ketones or
aldehydes with secondary alcohols promoted by rhodium
derivatives,6 though when the catalyst contains chiral diamine
ligands recent theoretical studies7 suggest that the enantiose-
lectivity of the reaction is related to an outer-sphere hydrogen
transfer mechanism similar to that operating in ketone hydro-
genations catalyzed by ruthenium diamine compounds.8 Met-
allohydroxyalkyl complexes are generally prepared as kinetic
products from the reaction of metallocarbonyl or metalloacyl
species with reducing agents, and when they are unstable, a
frequent decomposition path involves their dissociation into
Introduction
Organometallic rhodium complexes play an important role
in the transformation of many organic compounds.1,2 The
catalytic hydrogenation of aldehydes or ketones is a key reaction
in chemical syntheses. In their reduction to alcohols, and also
in the conversion of syngas to methanol or ethylene glycol,
alkoxy or hydroxyalkyl intermediates are believed to be
involved.3 Both alkoxy and hydroxyalkyl compounds are well-
known for late transition metals.4 The hydrogenation of alde-
hydes with molecular hydrogen in protic solvents and with
rhodium complexes as catalysts has been reported to proceed
via hydroxyalkyl intermediates.5 The alkoxy species are believed
(4) (a) Creutz, C.; Chou, M. H.; Fujita, E.; Szalda, D. J. Coord. Chem.
ReV. 2005, 249, 375. (b) Hubert-Pfalzgraf, L. G. Coord. Chem. ReV. 1998,
178-180, 967. (c) Sisak, A.; Sa´mpa´r-Szerencse´s, E.; Galamb, V.; Ne´meth,
L.; Ungva´ry, F.; Pa´lyi, G. Organometallics 1989, 8, 1096. (d) Bryndza, H.
E.; Tam, W. Chem. ReV. 1988, 88, 1163.
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155, 163. (b) MacDougall, J. K.; Simpson, M. C.; Green, M. J.; Cole-
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Organometallics 2000, 19, 5715. (b) Guiral, V.; Delbecq, F.; Sautet, P.
Organometallics 2001, 20, 2207.
* To whom correspondence should be addressed. E-mail:
mariaangeles.garralda@ehu.es.
† Universidad del Pa´ıs Vasco.
‡ Universidad Complutense.
(1) (a) Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. ComprehensiVe
Organometallic Chemistry II; Pergamon: Oxford, U.K., 1995; Vol. 12. (b)
Cornils, B., Herrmann, W. A., Eds. Applied Homogeneous Catalysis with
Organometallic Compounds. A ComprehensiVe Handbook; Wiley-VCH:
Weinheim, Germany, 2000.
(2) (a) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. ReV. 2002, 102, 1731.
(b) Fagnou, K.; Lautens, M. Chem. ReV. 2003, 103, 169. (c) Eilbracht, P.;
Ba¨rfacker, L.; Buss, C.; Hollmann, C.; Kitsos-Rzychon, B. E.; Kranemann,
C. L.; Rische, T.; Roggenbuck, R.; Schmidt, A. Chem. ReV. 1999, 99, 3329.
(3) (a) Fahey, D. R. J. Am. Chem. Soc. 1981, 103, 136. (b) Milstein, D.
J. Am. Chem. Soc. 1986, 108, 3525.
(8) (a) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001,
66, 7931. (b) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem.
ReV. 2004, 248, 2201.
10.1021/om060978q CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/19/2007

1032 Organometallics, Vol. 26, No. 4, 2007
Garralda et al.
metal hydride and aldehyde units.9 Therefore, the insertion of
an aldehyde into an M-H bond to afford hydroxyalkyls is rarely
observed.4c,10 Rhodium hydride complexes containing porphy-
rins, RhH(N4), and showing some acidic character react with
RCHO to give the hydroxyalkyl derivatives Rh(CH(OH)R)-
(N4).9,11 Also, chelate assistance has been used to stabilize the
hydroxyalkyl derivative Mn(CO)4(PPh2(o-C6H4CHOH)), formed
by insertion of o-(diphenylphosphine)benzaldehyde (PPh2(o-
C6H4CHO)) into the M-H bond of HMn(CO)5.12 The course
of the reaction between PPh2(o-C6H4CHO) and metal hydride
derivatives depends markedly on the metal and also on the
coligands present in the complex undergoing the reaction. Thus,
PtH(PPh2O)(PPh2OH)2 gives the cyclic platinum alkoxide Pt-
(PPh2O)(PPh2OH)(PPh2(o-C6H4CH2O)).13 Neutral complexes
such as [IrHCl(PPh2(o-C6H4CO))(CO)(κ1-PPh2(o-C6H4CHO))],
containing a P-coordinated PPh2(o-C6H4CHO) ligand, or [RhHCl-
(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))], containing a chelat-
ing P-aldehyde PPh2(o-C6H4CHO) ligand, have not been
reported to undergo any insertion reaction,14 and cationic
rhodium derivatives containing a P-coordinated PPh2(o-C6H4-
CHO) ligand and chelating diimines (NN) such as [RhH(PPh2-
(o-C6H4CO))(κ1-PPh2(o-C6H4CHO))(NN)]+ undergo the inser-
tion reaction to afford the hydroxyalkyl derivatives [Rh(PPh2(o-
C6H4CO))(PPh2(o-C6H4CHOH))(NN)]+.15
In this work we report the reactions of the rhodium(I)
compound [RhCl(COD)]2 (COD ) 1,5-cyclooctadiene) with
PPh2(o-C6H4CHO) in the presence of pyridine to yield different
products that include acyl hydrido complexes formed by
oxidative addition of aldehyde, acyl hydroxyalkyl species
formed by insertion of aldehyde into the Rh-H bond, a diacyl
derivative formed by dehydrogenation of the acyl hydroxyalkyl
species, and an acyl hydrido aldehyde complex that can be
hydrogenated to the corresponding acyl hydrido alcohol com-
pound. Experimental evidence for an ionic hydrogenation
mechanism of aldehyde involving proton and hydride transfer
furnished by the acyl hydroxyalkyl species is also provided.
Scheme 1
ppm, consistent with a hydride cis to phosphorus (J(P,H) ) 18
Hz) and trans to chloride.18 Complex 1 shows low stability in
chlorinated solvents, and in chloroform exchange of hydride
by chloride occurs to afford the complex [RhCl2(PPh2(o-C6H4-
CO))(py)2] (2), as shown by the appearance of a resonance at
5.30 ppm due to formation of dichloromethane when the reaction
is performed in CDCl3. Such a reaction has several precedents.19
Complex 2 reacts with the chelating diimine biacetyl dihydra-
zone (H2NNdC(CH3)C(CH3)dNNH2, bdh), which displaces
pyridine to afford [RhCl2(PPh2(o-C6H4CO))(bdh)] (3). The 31P-
{1H} NMR spectra of 2 and 3 are very similar; therefore, we
believe that in 2 both pyridine ligands are mutually cis.
Complex 1 reacts also with triphenylphosphine, which
displaces one pyridine ligand to afford the complex [RhHCl-
(PPh2(o-C6H4CO))(py)(PPh3)] (4), as shown in Scheme 1. The
hydride chemical shift (-14.55 ppm) and the J(P,P) coupling
constant (375 Hz) are characteristic of hydride trans to chloride
and of two mutually trans phosphorus atoms. In accordance with
this observation, the reaction of [RhCl(COD)]2 with PPh2(o-
C6H4CHO) (Rh:P ) 1:2) in the presence of pyridine leads to
the chelate-assisted oxidative addition of one phosphine-
aldehyde ligand, with displacement of 1,5-cyclooctadiene, and
to the coordination of the second phosphine-aldehyde ligand
as a P-monodentate ligand to afford the neutral derivative
[RhHCl(PPh2(o-C6H4CO))(κ1-PPh2(o-C6H4CHO))(py)] (5), simi-
lar to 4 and with a dangling aldehyde group, as shown in eq 1.
Results and Discussion
The reaction of [RhCl(COD)]2 with PPh2(o-C6H4CHO) (Rh:P
) 1:1) in the presence of pyridine (py) leads to the acyl hydrido
derivative [RhHCl(PPh2(o-C6H4CO))(py)2] (1) with displace-
ment of 1,5-cyclooctadiene, as shown in Scheme 1. This reaction
is in line with the well-known ability of the aldehyde-phosphine
ligand to promote the chelate-assisted oxidative addition of the
aldehyde to late-transition-metal complexes.16 Complex 1 shows
the expected spectroscopic features. The 31P{1H} NMR spectrum
contains only one doublet at the characteristic low field due to
1
the five-membered-ring effect,17 and the H NMR spectrum
shows a doublet of doublets in the high-field region, at -15.93
(9) Van Voorhees, S. L.; Wayland, B. B. Organometallics 1985, 4, 1887.
(10) Vaughn, G. D.; Gladysz, J. A. J. Am. Chem. Soc. 1981, 103, 5608.
(11) (a) Fu, X.; Basickes, L.; Wayland, B. B. Chem. Commun. 2003,
520. (b) Fu, X.; Wayland, B. B. J. Am. Chem. Soc. 2005, 127, 16460.
(12) (a) Vaughn, G. D.; Strouse, C. E.; Gladysz, J. A. J. Am. Chem.
Soc. 1986, 108, 1462. (b) Vaughn, G. D.; Gladysz, J. A. J. Am. Chem. Soc.
1986, 108, 1473.
Complex 5 is extremely reactive and was identified only in
solution (see the Experimental Section). Its free aldehyde group
(13) Van Leeuwen, P. W. N. M.; Roobeek, C. F.; Orpen, A. G.
Organometallics 1990, 9, 2179.
(14) (a) Landvatter, E. F.; Rauchfuss, T. B. Organometallics 1982, 1,
506. (b) El Mail, R.; Garralda, M. A.; Herna´ndez, R.; Ibarlucea, L. J.
Organomet. Chem. 2002, 648, 149.
(15) (a) El Mail, R.; Garralda, M. A.; Herna´ndez, R.; Ibarlucea, L.; Pinilla,
E.; Torres, M. R. Organometallics 2000, 19, 5310. (b) Brockaart, G.;
Garralda, M. A.; Herna´ndez, R.; Ibarlucea, L.; Santos, J. I. Inorg. Chim.
Acta 2002, 338, 249.
(18) (a) Anderson, G. K.; Kumar, R. Inorg. Chim. Acta 1988, 146, 89.
(b) Garralda, M. A.; Herna´ndez, R.; Ibarlucea, L.; Pinilla, E.; Torres, M.
R.; Zarandona, M. Inorg. Chim. Acta 2004, 357, 2818.
(19) (a) Tejel, C.; Ciriano, M. A.; Millaruelo, M.; Lo´pez, J. A.; Lahoz,
F. J.; Oro, L. A. Inorg. Chem. 2003, 42, 4750. (b) Rourke, J. P.; Stringer,
G.; Chow, P.; Deeth, R. J.; Yufit, D. S.; Howard, J. A. K.; Marder, T. B.
Organometallics 2002, 21, 429. (c) Gutie´rrez-Puebla, E.; Monge, A.;
Nicasio, M. C.; Pe´rez, P. J.; Poveda, M. L.; Rey, L.; Ruiz, C.; Carmona, E.
Inorg. Chem. 1998, 37, 4538. (d) Green, M. L. H.; Jones, D. J. AdV. Inorg.
Radiochem. 1965, 7, 115.
(16) Garralda, M. A. C. R. Chim. 2005, 8, 1413.
(17) Garrou, P. E. Chem. ReV. 1981, 81, 229.

Rhodium(III) Acyl Complexes
Scheme 2
Organometallics, Vol. 26, No. 4, 2007 1033
Scheme 3
of the hydroxyalkyl groups bonded to rhodium,12,21 trans to the
phosphorus atom of the acyl-phosphine chelate. The 13C
resonances appear in the 93-97 ppm range as doublets of
doublets due to coupling with rhodium (J(Rh,C) ) 22 Hz) and
with a trans phosphorus atom (J(P,C) ) 98 Hz). In the HSQC
experiment, correlation of the resonance due to the major species
with a resonance at 6.75 (CHOH) ppm is observed and this
signal makes COSY with a resonance at 8.48 ppm (CHOH). In
undergoes different reactions, including hydrogenation and
dehydrogenation, depending on the reaction conditions.
Hydroxyalkyl Formation from Complex 5 and Its Sub-
sequent Dehydrogenation. In benzene solution complex 5
reacts readily to afford the hydroxyalkyl derivative [RhCl(PPh2-
(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6) (see Scheme 2),
which is a mixture of the two isomers 6a and 6b in a 3:1 ratio.
In line with previous observations,10,11 this behavior suggests a
certain acidic character of the hydride in complex 5. The
transformation of this acyl hydrido complex, also containing a
dangling aldehyde group and two mutually trans phosphorus
atoms, into acyl hydroxyalkyl derivatives with two mutually
cis phosphorus atoms requires two different steps to occur,
namely isomerization and insertion of the aldehyde into the
Rh-H bond. By following the reaction in C6D6 by NMR, we
observed that the presence of an excess of pyridine made the
overall reaction slower. Thus, after 15 min, the ratio of 6 to 5
was 2:1 when using a Rh to py ratio of 1:1 while, when using
a Rh to py ratio of 1:2, the ratio of 6 to 5 was only 1:2, as
concluded from the 31P{1H} NMR spectra. Longer reaction
periods led to the complete transformation of 5 into 6. Former
studies have shown that the formation of rhodium(III) acyl
hydroxyalkyl derivatives from rhodium(III) acyl hydrido species
is favored when the phosphorus atoms are mutually cis;15a
therefore, our proposal is that the isomerization reaction occurs
first, through a pyridine dissociation step, to afford a species
with two mutually cis phosphorus atoms. Protonation of the
aldehyde group by an acidic Rh-H can then afford the final
product 6. As shown in Scheme 2, compound 6 can be obtained,
also as a 3:1 mixture of 6a and 6b, by the reaction of pyridine
with an acyl hydrido complex containing a phosphine-aldehyde
chelating ligand, [RhHCl(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4-
CHO))] (7),14b in which the hydroxyalkyl formation reaction is
not observed. Inspection of the in situ reaction performed in
C6D6 by NMR indicates that the coordinated aldehyde group
in 7 is displaced by pyridine to afford complex 5, which then
gives 6. As has been previously observed,15,20 N-donor ligands
favor the hydroxyalkyl formation in rhodium hydrido complexes
by migration of the hydride to the more nucleophilic oxygen
atom of the aldehyde.
1
the H NMR spectra the alkyl resonance is obscured by the
phenyl rings and the hydroxy signal is clearly observed. The
latter disappears upon addition of a few drops of CD3OD, and
its low-field appearance suggests some extent of hydrogen bond
formation, most likely with the cis chloride ligand. The 31P-
{1H} NMR spectrum shows two doublets of doublets for each
isomer with mutually cis phosphines (J(P,P) ) 20 Hz). Isomers
6a and 6b differ in the groups, chlorine or pyridine, trans to
acyl and to phosphorus of the hydroxyalkyl-phosphine chelate.
When the electronic effects are taken into account, higher
stability for a species where the best σ-donor is trans to the
poorer σ-donor can be expected.22 According to this, the major
isomer 6a should contain the lowest trans effect ligand, chlorine,
trans to the acyl group, whose trans effect is almost as high as
that of hydride.23 The 31P resonances of the hydroxyalkyl-
phosphine chelate appear around 54 ppm, and the coupling
constant J(Rh,P), lower for the major isomer 6a (155 Hz) than
for the minor isomer 6b (160 Hz), is in line with the phosphorus
being trans to the pyridine nitrogen with higher trans effect in
6a.24
Compound 6 has low stability in benzene or in chloroform
solution, so that after 24 h it is completely transformed into the
diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8) (see Scheme
3) with hydrogen loss, as evidenced by the appearance of a small
1
resonance at 4.63 ppm in the H NMR spectra of a CDCl3
solution of 6.25 In methanol the reaction is faster and 6 is
completely transformed into 8 in ca. 45 min. Complex 6 shows
lower stability than the related compound [Rh(PPh2(o-C6H4-
CO))(PPh2(o-C6H4CHOH))(bdh)]BPh4,15a containing a better
donor ligand such as the bidentate diimine instead of pyridine
and chloride. This is not surprising,12a but the usual decomposi-
tion paths reported for hydroxyalkyl complexes include regen-
eration of the M-H bond and free aldehyde or, if an acid is
(21) Thorn, D. L.; Tulip, T. H. Organometallics 1982, 1, 1580.
(22) Blum, O.; Carmielli, R.; Martin, J. M. L.; Milstein, D. Organome-
tallics 2000, 19, 4608.
(23) Coe, B. J.; Glenwright, S. J. Coord. Chem. ReV. 2000, 203, 5.
(24) Appleton, T. G.; Clark, H. C.; Manzer, L. I. Coord. Chem. ReV.
1973, 10, 335.
Compound 6 has been fully characterized by NMR, including
2D experiments. The obtained spectra confirm the formation
(20) (a) Wei, M.; Wayland, B. B. Organometallics 1996, 15, 4681. (b)
Del Rossi, K. J.; Zhang, X.; Wayland, B. B. J. Organomet. Chem. 1995,
504, 47.
(25) Sellmann, D.; Prakash, R.; Heinemann, F. W. Dalton Trans. 2004,
3991.

1034 Organometallics, Vol. 26, No. 4, 2007
Garralda et al.
added, disproportionation with hydride transfer to yield an acyl
and an alkyl complex.12,21 No presence of 5 was observed in
the NMR spectra recorded during the transformation of 6 into
8, thus excluding the reversal of 6 into 5.
We were unable to detect any intermediate during the
dehydrogenation reaction, but as an unusual mechanism appears
to operate in this reaction, we considered the possibility of a
ligand dissociation step, which would decrease the electronic
density on the metal and the stability of the hydroxyalkyl10 and
would allow transfer of R-hydrogen from carbon to rhodium to
give an intermediate such as the hydrido hydroxycarbene 9
depicted in Scheme 3. Although not frequent for late-transition-
metal complexes, R-H elimination to give hydridocarbene
species is known.26 Iridium hydroxycarbene complexes obtained
from the reaction of iridium compounds with aldehydes27 or
hydrido hydroxycarbene derivatives formed by protonation of
iridium hydrido formyl derivatives28 have been reported. Also,
hydrido hydroxycarbene formation has been shown to operate
in the decarbonylation of aldehydes by [RuH(Cl)(PiPr3)2]229 and
in the hydrocarbonylation of olefins, leading to alcohols30 or,
in the reaction of CO with ethene, to give pentan-3-one31 using
rhodium trialkylphosphine complexes in protic solvents. The
interaction of the hydride, behaving as a proton acceptor,29,32
with the alcoholic proton in intermediate 9 would give complex
8 with hydrogen loss. This mechanism would also explain the
overall reaction being faster in methanol, where chloride
dissociation is easy. The described hydroxyalkyl formation and
its dehydrogenation would involve rhodium(III) hydrido deriva-
tives that behave as proton donors (complex 5) or as hydride
donors (species 9). Both modes of reactivity are now well
established for transition-metal hydrides, and recently the ability
of the palladium hydride [PdH(dppe)2]+ to transfer a hydride
or a proton to carbocations or carboanions, respectively, has
been reported.33 We believe that other evidence reported later
in this work point to the formation of hydrido hydroxycarbene
species from 6.
Figure 1. Variable-temperature 31P{1H} NMR spectra of 8 in
CDCl3: (left) experimental; (right) calculated.
Complex 8 is prepared in better yield by reaction of [RhCl-
(COD)]2 with PPh2(o-C6H4CHO) in the presence of pyridine
in methanol (see the Experimental Section) and has been fully
characterized by NMR. At 253 K its 31P{1H} NMR spectrum
shows an ABX spin pattern with J(P,P) ) 336 Hz, indicating
the trans disposition of both phosphorus atoms, while the 13C-
{1H} NMR spectrum shows in the low-field region, at ca. 230
ppm, two doublets due to two inequivalent acyl groups trans to
chloride and pyridine, respectively. Complex 8 is fluxional in
solution, as shown by inspection of the 31P{1H} NMR spectra.
Due to 8 being insoluble in toluene-d8, the spectra were obtained
from CDCl3 solutions in the 253-328 K range. When the
temperature is raised, the signals due to the ABX pattern broaden
and coalescence occurs near 330 K (see Figure 1). From line-
shape analysis34 of the variable-temperature 31P{1H} NMR
spectra of complex 8, the activation parameters ∆Hq ) 8.8 (
0.4 kcal mol-1 and ∆Sq ) -16.7 ( 1 cal K-1 mol-1 have been
determined. The entropy of activation is indicative of an
intramolecular rearrangement responsible for the exchange of
pyridine and chloride.35 We believe that opening of the acyl-
phosphine chelate can account for the observed fluxional
behavior.
An X-ray diffraction study of 8 confirms the structure
depicted in Scheme 3. Selected bond distances and angles are
listed in Table 1, and Figure 2 gives a molecular drawing. The
geometry about the metal atom is distorted octahedral; the
maximum deviation of 10.4° corresponds to the angle C20-
Rh1-P1. Four positions are occupied by the phosphorus and
carbon atoms of the two bidentate ligands, and the other two
positions are occupied by the nitrogen atom of the pyridine and
by chloride. Both phosphorus atoms are mutually trans, and the
acyl groups are mutually cis. The distances comprising the
chelate ligands are in the expected ranges,15a,36 and we find some
differences in the features of the acylphosphine ligands. The
best least-squares plane for the Rh1, C20, C21, C22, and P2
atoms and the C21, C22, C24, C25, C26 plane are almost
(26) (a) Salem, H.; Ben-David, Y.; Shimon, L. J. W.; Milstein, D.
Organometallics 2006, 25, 2292 and references therein. (b) Lara, P.;
Paneque, M.; Poveda, M. L.; Salazar, V.; Santos, L. L.; Carmona, E. J.
Am. Chem. Soc. 2006, 128, 3512.
(27) Gutie´rrez-Puebla, E.; Monge, A.; Paneque, M.; Poveda, M. L.;
Salazar, V.; Carmona, E. J. Am. Chem. Soc. 1999, 121, 248.
(28) Lilga, M. A.; Ibers, J. M. Organometallics 1985, 4, 590.
(29) Coalter, J. N., III; Huffman, J. C.; Caulton, K. G. Organometallics
2000, 19, 3569.
(30) Cheliatsidou, P.; White, D. F. S.; Cole-Hamilton, D. J. Dalton Trans.
2004, 3425.
(31) Robertson, R. A. M.; Poole, A. D.; Payne, M. J.; Cole-Hamilton,
D. J. Dalton Trans. 2000, 1817.
(32) (a) Yao, W.; Crabtree, R. H. Inorg. Chem. 1996, 35, 3007. (b)
Epstein, L. M.; Shubina, E. S. Coord. Chem. ReV. 2002, 231, 165. (c) Cugny,
J.; Schmalle, H. W.; Fox, T.; Blacque, O.; Alfonso, M.; Berke, H. Eur. J.
Inorg. Chem. 2006, 540.
(33) Aresta, M.; Dibenedetto, A.; Pa´pai, I.; Schubert, G.; Macchioni,
A.; Zuccaccia, D. Chem. Eur. J. 2004, 10, 3708.
(34) Budzelaar, P. H. M. gNMR Software version 5.0; Adept Scientific
plc: Letchworth, U.K., 2004.
(35) Buisman, G. J. H.; Van der Veen, L. A.; Kamer, P. C. J.; Van
Leeuwen, P. W. N. M. Organometallics 1997, 16, 5681.
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P.; Chakravorty, A. Organometallics 1999, 18, 1486.

Rhodium(III) Acyl Complexes
Organometallics, Vol. 26, No. 4, 2007 1035
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complex 8, Including the Hydrogen-Bond Geometry
Rh1-P2
Rh1-N1
Rh1-C20
O2-C20
O3-H3
2.300(1)
2.261(4)
1.994(5)
1.217(5)
0.840
Rh1-P1
Rh1-Cl1
Rh1-C(1)
O1-C1
2.367 (1)
2.521(1)
2.002(5)
1.206(5)
2.590
H3‚‚‚O1
O3‚‚‚O1
3.289(9)
C20-Rh1-C1
C1-Rh1-N1
C1-Rh1-P2
C20-Rh1-P1
N1-Rh1-P1
C20-Rh1-Cl1
N1-Rh1-Cl1
P1-Rh1-Cl1
88.6(2)
C20-Rh1-N1
C20-Rh1-P2
N1-Rh1-P2
C1-Rh1-P1
P2-Rh1-P1
C1-Rh1-Cl1
P2-Rh1-Cl1
O3-H3‚‚‚O1
90.6(2)
84.8(1)
95.1(1)
81.3(1)
170.0(4)
92.0(1)
89.5(4)
141.9
174.3(2)
90.4(1)
100.6(1)
93.4(1)
174.3(1)
89.3(1)
85.1(4)
coplanar, with a dihedral angle of 5.0(1)°, whereas the best least-
squares plane for the Rh1, C1, C2, C3, and P1 atoms forms a
dihedral angle of 20.8(1)° with the corresponding phenyl ring.
Also, the Rh-P2 and Rh-P1 distances, 2.300(1) and 2.367(1)
Å, respectively, are significantly different. These different
features are probably due to the expected distortion of having
two five-membered chelate rings. The presence of a solvent
molecule, methanol, bonded to the oxygen atom O1 of an acyl
group, can also have some influence in the observed features.
Hydroxyalkyl as Source of Proton and Hydride for the
Hydrogenation of Coordinated Aldehyde. In methanol solu-
tion complex 5 reacts readily to undergo displacement of
chloride by the aldehyde, affording the cationic acyl hydrido
complex [RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))(py)]+
(10), containing a phosphine-aldehyde chelate (see Scheme 4),
as confirmed by following the in situ reaction in CD3OD by
NMR (vide infra). The isolation of 10 requires the immediate
addition of a bulky anion salt such as NaBPh4. [10]BPh4 can
thus be obtained in up to 80% yield.
Figure 2. PLUTO view of complex 8 showing the atomic
numbering and the intermolecular hydrogen bond. All but one of
the hydrogen atoms and the labels of some C atoms have been
omitted for clarity.
Scheme 4
The spectroscopic data allow its unambiguous characteriza-
tion. As observed in other rhodium(III) aldehyde complexes,16,37
the aldehyde coordination of PPh2(o-C6H4CHO) in 10 is the
σ-aldehyde mode. The IR spectrum shows ν(CdO) absorptions
at lower wavenumber than for the free ligand, and in the 13C-
{1H} NMR spectrum a resonance at slightly lower field than
for the free aldehyde is observed. The 1H NMR spectrum shows
a sharp singlet at slightly higher field than for the free aldehyde,
and the appearance of a resonance at -13.88 ppm indicates the
presence of a hydride trans to nitrogen. A shift of the 31P{1H}
resonance of the phosphine-aldehyde ligand in 5 toward higher
field upon formation of 10 is in accordance with the presence
of a six-membered ring,17 and the J(P,P) coupling constant of
346 Hz agrees with a trans arrangement of the phosphorus atoms.
Complex 10, prepared in situ in methanol solution, reacts
with NaBH4 to undergo the aldehyde hydrogenation, leading
to the complex [RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CH2-
OH))(py)]+ (11), which contains a phosphine-alcohol chelate.
Complex 11 was isolated as the perchlorate salt, [11]ClO4, by
addition of NaClO4 and was characterized by spectroscopic
the J(P,P) coupling constant of 336 Hz agrees with a trans
arrangement of the phosphorus atoms. The chemical shift of
the hydride, -14.25 ppm, indicates it being trans to the nitrogen
atom of the pyridine ligand.
If longer reaction periods are allowed, up to 2 h, complex 5
reacts in methanol to give a mixture of the diacyl derivative 8,
the acyl hydrido alcohol species 11, and a small amount of the
acyl hydrido aldehyde complex 10. Complex 8 could be
separated by filtration with a maximum yield of ca. 40% with
respect to the starting rhodium material. The remaining solution
contained complex 11 that was always contaminated with at
least 10% of 10. Attempts to obtain 11 as the main product by
performing the reaction with bubbling of hydrogen gas proved
unsuccessful and led to the same product distribution as that
obtained in the absence of H2.
1
means, including 2D experiments. The H and 13C{1H} NMR
spectra confirm the formation of the alcoholic group bonded to
rhodium. Its 13C resonance appears at 67.6 ppm as a doublet,
most likely due to coupling with the P atom of the alcohol-
1
phosphine chelate (J(P,C) ) 7 Hz), and the H resonances
appear at 5.12 and 4.44 ppm as doublets of doublets for the
methylene group and at 6.19 {t} ppm for the hydroxy group,
which disappears upon addition of a few drops of CD3OD. The
31P{1H} NMR spectrum shows two doublets of doublets, and
By following the reaction of 5 in CD3OD by NMR, we have
observed at 253 K the initial formation of the cationic complex
10. When the temperature is raised up to 293 K, a mixture
(37) Joubert, J.; Delbecq, F. J. Organomet. Chem. 2006, 691, 1030.

1036 Organometallics, Vol. 26, No. 4, 2007
Garralda et al.
drides containing OH groups.38 The hydrogenation of polar
bonds involving outer-sphere mechanisms do not require
coordination of the substrate to the transition metal.8 In the
present case an outer-sphere mechanism appears to be involved
but O-coordination of the aldehyde to the rhodium atom of
another molecule is required to effectively undergo hydrogena-
tion.
Scheme 5
Conclusions
This report has demonstrated that rhodium acyl hydrido
complexes containing N-donor ligands show some acidic
character of the Rh-H bond and are able to form acyl
hydroxyalkyl derivatives by their reaction with aldehydes. In
protic solvents, where the formation of rhodium acyl hydrido
aldehyde complexes is also possible, hydrogenation to the
rhodium acyl hydrido alcohol complexes can occur. According
to the experimental observations, a bimolecular bifunctional
ionic mechanism, involving formation of a transient hydrido
hydroxycarbene as a source of proton and hydride and interact-
ing with a coordinated aldehyde, appears feasible. The same
transient species can explain the dehydrogenation of the acyl
hydroxyalkyl species to afford a diacyl derivative.
Experimental Section
General Procedures. The preparation of the metal complexes
was carried out at room temperature under nitrogen by standard
39
Schlenk techniques. [RhCl(COD)]2 and complex 714b were
containing almost equimolar amounts of complexes 10, 6, and
11 is observed along with the appearance of a precipitate that
corresponds to the diacyl derivative 8 (see Scheme 5). Most
likely, dissociation of the aldehyde group in the initially formed
10 allows partial formation of 6. After 2 h the resonances due
to complexes 6 and 10 decrease while the amount of 11 in the
solution and also the amount of precipitated 8 increases
markedly. No incorporation of deuterium in the hydrogenated
aldehyde is observed, thus excluding a mechanism involving
H-transfer from methanol to aldehyde. The resonances due to
the methylene group of the hydrogenated complex 11 appear
as two sharp doublets, at 4.83 and 4.30 ppm (Jgem ) 12.8 Hz),
respectively. The coupling with the hydroxy proton is lost, due
to its exchange with the deuterated solvent.
prepared as previously reported. Microanalysis were carried out
with a Leco CHNS-932 microanalyser. Conductivities were mea-
sured in acetone solution with a Metrohm 712 conductimeter. IR
spectra were recorded with a Nicolet FTIR 510 spectrophotometer
in the range 4000-400 cm-1 using KBr pellets. NMR spectra were
recorded with a Bruker Avance DPX 300 or Bruker Avance 500
1
spectrometer; H and 13C{1H} (TMS internal standard), 31P{1H}
(H3PO4 external standard), and 2D spectra were measured from
CDCl3, C6D6, toluene-d8, or CD3OD solution. Mass spectra were
recorded on a VG Autospec instrument, by liquid secondary ion
(LSI) MS using nitrobenzyl alcohol as matrix and a cesium gun
(Universidad de Zaragoza).
Warning! Perchlorate salts and transition-metal perchlorate
complexes may be explosive. Preparations on a scale larger than
that reported herein should be avoided.
These observations point to a bimolecular bifunctional ionic
mechanism as being responsible for the hydrogenation of the
cationic phosphine-aldehyde complex 10 to give the phos-
phine-alcohol derivative 11, with the hydroxyalkyl complex 6
being the source of both proton and hydride, as shown in
Scheme 5. The transient hydrido hydroxycarbene 9, formed from
6 by R-hydrogen transfer, contains a hydride and a hydroxy
group that can interact with the O-coordinated CdO bond in
complex 10. The experimental evidence for this mechanism can
be summarized as follows. (i) The coordinated aldehyde in 10
requires the presence of proton and hydride to undergo the
hydrogenation. It reacts with a hydride source, borohydride, in
a protic solvent, methanol, but fails to react with H2. (ii) In the
absence of NaBH4, the reaction products 8 and 11 are always
contaminated with the aldehyde derivative 10 because the
intermediate 9 can lose H2 (see Scheme 3), thus preventing the
complete reduction of the aldehyde. (iii) In a separate experiment
we have observed that complex 8 fails to react with NaBH4 in
methanol, and therefore 8 is not a source for 11 under these
reaction conditions. This mechanism is similar to the hydroge-
nation process reported by Casey et al. for the catalytic
hydrogenation of ketones and aldehydes with ruthenium hy-
[RhHCl(PPh2(o-C6H4CO))(py)2] (1). To a benzene solution of
[RhCl(COD)]2 (30 mg, 0.06 mmol) was added pyridine (19 mg,
0.24 mmol), whereupon a yellow solid was formed. Addition of
PPh2(o-C6H4CHO) (35 mg, 0.12 mmol) and stirring for 2 h gave a
yellow solid that was filtered off, washed with benzene, and
vacuum-dried. Yield: 76%. IR (KBr, cm-1): 2061 (m), ν(RhH);
1620 (s), ν(CdO). 1H NMR (CDCl3): δ -15.93 (dd, 1H, J(Rh,H)
) 23.8 Hz, J(P,H) ) 18.3 Hz, RhH). 31P{1H} NMR (CDCl3): δ
78.2 (d, J(Rh,P) ) 165 Hz). Anal. Calcd for C29H25ClN2OPRh:
C, 59.35; H, 4.29; N, 4.77. Found: C, 59.01; H, 4.62; N, 4.66.
[RhCl2(PPh2(o-C6H4CO))(py)2] (2). A chloroform solution of
[RhHCl(PPh2(o-C6H4CO))(py)2] (1; 46 mg, 0.078 mmol) was stirred
for 24 h. Addition of methanol to the solution gave a yellow solid
that was filtered off, washed with methanol, and vacuum-dried.
Yield: 13%. IR (KBr, cm-1): 1649 (s), ν(CdO). 31P{1H} NMR
(CDCl3): δ 59.4 (d, J(Rh,P) ) 134 Hz). 13C{1H} NMR (CDCl3):
δ 229.2 (dd, J(Rh,C) ) 28 Hz, J(P,C) ) 3 Hz, RhCO). FAB MS
(m/z): calcd for C29H24Cl2N2OPRh, 620; observed, 585 [M - Cl]+.
(38) (a) Casey, C. P.; Singer, S. W.; Powell, D. R.; Hayashi, R. K.;
Kavana, M. J. Am. Chem. Soc. 2001, 123, 1090. (b) Bullock, R. M. Chem.
Eur. J. 2004, 10, 2366. (c) Casey, C. P.; Strotman, N. A.; Beetner, S. E.;
Johnson, J. B.; Priebe, D. C.; Guzei, I. A. Organometallics 2006, 25, 1236.
(39) Chatt, J.; Venanzi, L. M. J. Chem. Soc. A 1957, 4735.

Rhodium(III) Acyl Complexes
Organometallics, Vol. 26, No. 4, 2007 1037
Anal. Calcd for C29H24Cl2N2OPRh‚0.75CHCl3: C, 50.27; H, 3.51;
0.24 mmol), whereupon a yellow solid was formed. Adding PPh2-
(o-C6H4CHO) (70 mg, 0.24 mmol) and stirring overnight gave a
yellow solid that was filtered off, washed with methanol, and
vacuum-dried. Yield: 36%. IR (KBr, cm-1): 1637 (s), ν(CdO).
31P{1H} NMR (253 K, CDCl3): δ 61.8 (dd, J(Rh,P) ) 152 Hz,
J(P,P) ) 336 Hz, PA); 51.6 (dd, J(Rh,P) ) 138 Hz, PB). 13C{1H}
NMR (253 K, CDCl3): δ 234.2 (d, J(Rh,C) ) 36 Hz, RhCO); 232.8
(d, J(Rh,C) ) 33 Hz, RhCO). Anal. Calcd for C43H33ClNO2P2Rh‚
CH3OH: C, 63.82; H, 4.50; N, 1.69. Found: C, 63.46; H, 4.16; N,
1.95.
[RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CHO))(py)]BPh4 ([10]-
BPh4). To a benzene solution of [RhCl(COD)]2 (30 mg, 0.06 mmol)
was added pyridine (19 mg, 0.24 mmol), whereupon a yellow solid
was formed. Addition of PPh2(o-C6H4CHO) (70 mg, 0.24 mmol)
led to a solution. Evaporation of the solvent, dissolution of the solid
residue in methanol, and addition of NaBPh4 (41 mg, 0.12 mmol)
led to a yellow solid that was filtered off, washed with methanol,
and vacuum-dried. Yield: 80%. IR (KBr, cm-1): 2032 (m), ν-
(RhH); 1655 (s), 1635 (s), ν(CdO). ΛM (Ω-1 cm2 mol-1): 63
(acetone). 1H NMR (CDCl3): δ -13.88 (ddd, 1H, J(RhH) ) 20.6
Hz, J(PPh2(o-C6H4CHO),H) ) 14.1 Hz, J(PPh2(o-C6H4CO),H) )
6.0 Hz, RhH); 8.61 (s, CHO). 31P{1H} NMR (CDCl3): δ 59.4 (dd,
J(Rh,P) ) 134 Hz, J(P,P) ) 346 Hz, PPh2(o-C6H4CO)); 32.1 (dd,
J(Rh,P) ) 128 Hz, PPh2(o-C6H4CHO)). 13C{1H} NMR (CDCl3):
δ 228.4 (d, J(Rh,C) ) 34 Hz, RhCO); 201.3 (s, CHO). FAB MS
(m/z): calcd for C43H35NO2P2Rh, 762; observed, 762 [M]+. Anal.
Calcd for BC67H55NO2P2Rh‚CH3OH: C, 73.32; H, 5.34; N, 1.26.
Found: C, 73.18; H, 5.16; N, 1.43.
N, 3.94. Found: C, 49.98; H, 3.70; N, 3.97.
[RhCl2(PPh2(o-C6H4CO))(bdh)] (3). To a dichloromethane
solution of [RhCl2(PPh2(o-C6H4CO))(py)2] (2; 31 mg, 0.05 mmol)
was added biacetyl dihydrazone (9 mg, 0.075 mmol). Stirring for
2 h followed by addition of diethyl ether gave a yellow solid that
was filtered off, washed with diethyl ether, and vacuum-dried.
Yield: 46%. IR (KBr, cm-1): 3386 (s), 3340 (s), 3295 (s), ν(NH2);
1655(s), ν(CdO). 1H NMR (CDCl3): δ 2.50 (s, 3H, CH3); 2.19 (s,
3H, CH3). 31P{1H} NMR (CDCl3): δ 60.1 (d, J(Rh,P) ) 134 Hz).
Anal. Calcd for C23H24Cl2N4OPRh: C, 47.86; H, 4.19; N, 9.71.
Found: C, 48.03; H, 4.36; N, 10.39.
[RhHCl(PPh2(o-C6H4CO))(PPh3)(py)] (4). To a dichloromethane
solution of 1 (46 mg, 0.078 mmol) was added triphenylphosphine
(21 mg, 0.078 mmol). Stirring for 1 h followed by addition of
diethyl ether gave a yellow solid that was filtered off, washed with
diethyl ether, and vacuum-dried. Yield: 42%. IR (KBr, cm-1): 2044
(m), ν(RhH); 1623 (s), ν(CdO). 1H NMR (CDCl3): δ -14.55 (ddd,
1H, J(Rh,H) ) 18.3 Hz, J(PPh3,H) ) 11.9 Hz, J(PPh2(o-C6H4-
CO),H) ) 4.6 Hz, RhH). 31P{1H} NMR (CDCl3): δ 63.72 (dd,
J(Rh,P) ) 140 Hz, J(P,P) ) 375 Hz, PPh2(o-C6H4CO)); 42.7 (dd,
J(Rh,P) ) 124 Hz, PPh3). Anal. Calcd for C42H35ClNOP2Rh: C,
65.51; H, 4.58; N, 1.82. Found: C, 64.98; H, 4.65; N, 1.87.
Formation and Characterization of [RhHCl(PPh2(o-C6H4CO))-
(κ1-PPh2(o-C6H4CHO))(py)] (5). To a toluene-d8 solution of [RhCl-
(COD)]2 (15 mg, 0.03 mmol) at 253 K was added pyridine (10
mg, 0.12 mmol), whereupon a yellow solid was formed. Addition
of PPh2(o-C6H4CHO) (35 mg, 0.12 mmol) led to a solution for
which the NMR spectra were obtained at 253 K. Data for 5 are as
follows. 1H NMR (toluene-d8): δ 10.72 (s, 1H, PPh2(o-C6H4CHO));
-13.85 (m, 1H, RhH). 31P{1H} NMR (toluene-d8): δ 67.9 (dd,
J(Rh,P) ) 139 Hz, J(P,P) ) 370 Hz, PPh2(o-C6H4CO)); 42.9 (dd,
J(Rh,P) ) 123 Hz, PPh2(o-C6H4CHO)).
[RhCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6). Meth-
od a. To a benzene suspension of [RhHCl(PPh2(o-C6H4CO))(κ2-
PPh2(o-C6H4CHO))] (7; 43 mg, 0.06 mmol) was added pyridine
(5 mg, 0.06 mmol), whereupon dissolution of the solid occurred.
After the mixture was stirred for 4 h, the solvent was evaporated
and the solid residue was dissolved in dichloromethane. Addition
of diethyl ether gave a yellow solid that was filtered off, washed
with diethyl ether, and vacuum-dried. Yield: 62%.
Method b. To a benzene solution of [RhCl(COD)]2 (30 mg, 0.06
mmol) was added pyridine (10 mg, 0.12 mmol), whereupon a
yellow solid was formed. Addition of PPh2(o-C6H4CHO) (70 mg,
0.24 mmol) and stirring for 90 min gave a cloudy solution that
was filtered. The solvent was evaporated, and the solid residue was
dissolved in dichloromethane. Addition of diethyl ether gave a
yellow solid that was filtered off, washed with diethyl ether, and
vacuum-dried. Yield: 22%. The solid obtained was suspended in
methanol, stirred for 5 min, filtered off, washed with methanol,
and vacuum-dried to obtain an analytically pure sample (yield 35%).
IR (KBr, cm-1): 3564 (m, br), ν(OH); 1614 (s), ν(CdO). Anal.
Calcd for C43H35ClNO2P2Rh.0.75CH3OH: C, 63.92; H, 4.66; N,
1.70. Found: C, 63.94; H, 4.56; N, 1.75. Data for 6a are as follows.
1H NMR (CDCl3): δ 8.48 (s, 1H, PPh2(o-C6H4CHOH)); 6.75 (from
HSQC correlation, PPh2(o-C6H4CHOH)). 31P{1H} NMR (CDCl3):
δ 54.1 (dd, J(Rh,P) ) 155 Hz, J(P,P) ) 19 Hz, PPh2(o-C6H4-
CHOH)); 30.9 (dd, J(Rh,P) ) 85 Hz, PPh2(o-C6H4CO)). 13C{1H}
NMR (CDCl3): δ 243.7 (dd, J(Rh,C) ) 34 Hz, J(P,C) ) 8 Hz,
RhCO); 93.1 (dd, J(Rh,C) ) 22 Hz, J(P,C) ) 100 Hz, RhCHOH).
Data for 6b are as follows. 31P{1H} NMR (CDCl3): δ 53.3 (dd,
J(Rh,P) ) 160 Hz, J(P,P) ) 20 Hz, PPh2(o-C6H4CHOH)); 33.6
(dd, J(Rh,P) ) 88 Hz, PPh2(o-C6H4CO)). 13C{1H} NMR (CDCl3):
δ 234.8 (m, RhCO); 96.4 (dd, J(Rh,C) ) 22 Hz, J(P,C) ) 96 Hz,
RhCHOH).
[RhH(PPh2(o-C6H4CO))(κ2-PPh2(o-C6H4CH2OH))(py)]ClO4
([11]ClO4). To a benzene solution of [RhCl(COD)]2 (30 mg, 0.06
mmol) was added pyridine (19 mg, 0.24 mmol), whereupon a
yellow solid was formed. Addition of PPh2(o-C6H4CHO) (70 mg,
0.24 mmol) led to a solution. The solvent was evaporated, and the
solid residue was dissolved in methanol. Addition of NaBH4 (5
mg, 0.12 mmol) and NaClO4 (15 mg, 0.12 mmol) with vigorous
stirring gave a yellow solid that was filtered off, washed with
methanol, and vacuum-dried. Yield: 65%. IR (KBr, cm-1): 3432
(m, br), ν(OH); 2035 (w), ν(RhH); 1634 (s), ν(CdO). ΛM (Ω-1
1
cm2 mol-1): 114 (acetone). H NMR (CDCl3): δ -14.25 (ddd,
1H, J(RhH) ) 20.1 Hz, J(PPh2(o-C6H4CH2OH),H) ) 13.2 Hz,
J(PPh2(o-C6H4CO),H) ) 5.5 Hz, RhH); 5.12 (dd, 1H, Jgem ) 12.8
Hz, J(H,H) ) 4.6 Hz, CH2); 4.44 (dd, 1H, J(H,H) ) 5.5 Hz, CH2);
6.19 (pseudotriplet, 1H, OH). 31P{1H} NMR (CDCl3): δ 62.3 (dd,
J(Rh,P) ) 136 Hz, J(P,P) ) 336 Hz, PPh2(o-C6H4CO); 29.3 (dd,
J(Rh,P) ) 126 Hz, PPh2(o-C6H4CH2OH). 13C{1H} NMR (CDCl3):
δ 230.1 (d, J(Rh,C) ) 32 Hz, RhCO); 67.6 (d, J(P,C) ) 7 Hz,
CH2OH). FAB MS (m/z): calcd for C43H37NO2P2Rh, 764; observed,
764 [M]+. Anal. Calcd for C43H37ClNO6P2Rh: C, 59.77; H, 4.32;
N, 1.62. Found: C, 59.25; H, 4.52; N, 1.66.
Reaction of [RhHCl(PPh2(o-C6H4CO))(κ1-PPh2(o-C6H4CHO))-
(py)] (5) in Methanol. To a benzene solution of [RhCl(COD)]2
(50 mg, 0.10 mmol) was added pyridine (32 mg, 0.40 mmol),
whereupon a yellow solid was formed. Addition of PPh2(o-C6H4-
CHO) (118 mg, 0.40 mmol) led to a solution of 5. The solvent
was evaporated, the solid residue was dissolved in methanol, and
stirring for 2 h gave a yellow precipitate that was filtered, washed
with methanol, and vacuum-dried. This solid was identified
spectroscopically as complex 8 (yield 40% with respect to the
rhodium starting material). The remaining solution was taken to
dryness. According to the NMR spectra, the solid residue contained
complex 11 with a 10% impurity of 10, on the basis of the
integration of the hydride resonances of both compounds.
X-ray Structure Determination of 8. Yellow prismatic single
crystals of complex 8, suitable for X-ray diffraction, were success-
fully grown from a solution of 9 mg of complex 6 in 1 mL of
methanol at room temperature. Data collection was carried out at
room temperature on a Bruker Smart CCD diffractometer using
[RhCl(PPh2(o-C6H4CO))2(py)] (8). To a methanol suspension
of [RhCl(COD)]2 (30 mg, 0.06 mmol) was added pyridine (19 mg,

1038 Organometallics, Vol. 26, No. 4, 2007
Garralda et al.
Table 2. Crystal and Refinement Data for
[RhCl(PPh2(o-C6H4CO))2(py)]‚MeOH (8)
hemisphere of the reciprocal space by combination of three exposure
sets. Each exposure of 10 s covered 0.3° in ω. The first 100 frames
were re-collected at the end of the data collection to monitor crystal
decay after X-ray exposition, and no appreciable drop in the
intensities was observed. A summary of the fundamental crystal
data is given in Table 2. The structure was solved by direct methods
and conventional Fourier techniques. The refinement was made by
full-matrix least squares on F2 (SHELX-97).40 Anisotropic param-
eters were used in the last cycles of refinement for all non-hydrogen
atoms, with some exceptions. After the last cycles of refinement
the Fourier difference map showed electronic density; this was
assigned to one solvent molecule of CH3OH. The carbon and
oxygen atoms were refined in three isotropical cycles, and in
subsequent cycles their thermal parameters were kept constant while
their coordinates were refined with geometric restraints and a
variable common C-O distance. All hydrogen atoms were calcu-
lated at geometrical positions and refined as riding on their
respective carbon atoms. These features led to R and Rw factors of
0.0414 (4671 reflections observed) and 0.1127 (all reflections),
respectively. The largest residual peak in the final difference map
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
[C43H33ClNO2P2Rh]‚CH3OH
828.05
293(2)
0.71073
triclinic
P1h
9.2621(6)
b (Å)
c (Å)
10.6197(7)
20.613(1)
89.520(1)
86.157(1)
69.962(1)
R (deg)
â (deg)
γ (deg)
V (Å3)
1900.3(2)
Z
2
calcd density (g cm-3
)
1.447
0.646
848
abs coeff (mm-1
F(000)
)
cryst size (mm3)
0.22 × 0.13 × 0.09
0.99-25.00
-10 e h e 11, -12 e k e 12,
-19 e l e 24
9983
θ range for data collecn (deg)
index ranges
is 0.503 e Å-3
.
no. of rflns collected
no. of indep rflns
6603 (R(int) ) 0.0341)
Acknowledgment. Partial financial support by the UPV and
the Diputacio´n Foral de Guipuzcoa are gratefully acknowledged.
completeness to θ ) 25.00° (%)
no. of data/restraints/params
goodness of fit on F2
98.8
6603/1/229
1.019
0.0417 (4671 obsd rflns)
0.1113
Supporting Information Available: A CIF file giving crystal-
lographic data for complex 8. This material is available free of
charge via the Internet at http://pubs.acs.org.
final Ra indices (I > 2σ(I))
Rwb indices (all data)
largest diff peak and hole (e Å-3
)
0.510 and -0.902
2
2
2
a ∑[|Fo| - |Fc|]/∑|Fo|. b {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
OM060978Q
graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å)
operating at 50 kV and 20 mA. The data were collected over a
(40) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Deter-
mination; University of Go¨ttingen, Go¨ttingen, Germany, 1997.