New acylhydrido- and diacylrhodium(III) organocomplexes derived from 8-quinolinecarbaldehyde and/or O-(diphenylphosphanyl)benzaldehyde

Article abstract of DOI:10.1002/ejic.201100904

The acylhydridorhodium(III) complex [RhHCl{PPh₂(o-C ₆H₄CO)}(py)₂] (1) reacts with 8-quinolinecarbaldehyde (C₉H₆NCHO) to afford mixed diacyl [RhCl(C₉H₆NCO){PPh₂(o-C₆H ₄CO)}(py)] (2) with acyl groups trans to chlorine and to pyridine. Complex 1 undergoes displacement of pyridine by 2-(aminomethyl)pyridine (ampy) or diphosphanes to give hydridoacyl neutral [RhHCl{PPh₂(o-C ₆H₄CO)}(LL)] [LL = ampy (3), bis(diphenylphosphanyl) methane (dppm, 5), 1,3-bis(diphenylphosphanyl)propane (dppp, 6), 1,2-bis(diphenylphosphanyl)ethane (dppe, 7)] with hydride trans to chloride. Complex 3 exchanges hydride with chloride to give [Rh(Cl)₂{PPh ₂(o-C₆H₄CO)}(ampy)] (4). The reaction of 2 with bidentate N-donor ligands yields cationic mixed diacyl [Rh(C₉H ₆NCO){PPh₂(o-C₆H₄CO)}(NN)] ⁺ species [NN = 2,2′-bipyridine (bipy, 8), ampy (9)]. Neutral or cationic diacyl complexes that contain two acylquinoline fragments can be obtained by the reaction of dimer [Rh(μ-Cl)(C₉H ₆NCO)₂]₂ (10) with pyridine to give [Rh(Cl)(C₉H₆NCO)₂(py)] (11) or with bidentate N- or P-donor ligands (LL) to afford [Rh(C₉H₆NCO) ₂(LL)]⁺ [LL = dppm (12), dppe (13), dppp (14), 1,4-bis(diphenylphosphanyl)butane (15), ampy (16), 8-aminoquinoline (17), biacetyldihydrazone (18), bipy (19)] with the acyl groups trans to LL. Complex 11 is highly fluxional in solution. At low temperatures, the acylquinoline chelate opens to allow an intramolecular exchange between 11a and 11b (δH^? = 10.1±a0.2 kcalamol^-1 and δS^? = 1.0±a0.1 calaK^-1amol ^-1), and pyridine dissociation occurs at room temperature. All the complexes were characterized spectroscopically. Single crystal X-ray diffraction analysis was performed on 2. Hydridoacylrhodium(III) (1) reacts with chelating ligands to afford new neutral acylhydrido complexes with hydride trans to chloride. The reaction with 8-quinolinecarbaldehyde affords a diacyl compound, which may give cationic diacyl derivatives with donor atoms trans to the acyl groups.

Full text of DOI:10.1002/ejic.201100904

FULL PAPER
DOI: 10.1002/ejic.201100904
New Acylhydrido- and Diacylrhodium(III) Organocomplexes Derived from
8-Quinolinecarbaldehyde and/or o-(Diphenylphosphanyl)benzaldehyde
Montserrat Barquín,[a] María A. Garralda,*[a] Ricardo Hernández,[a] Lourdes Ibarlucea,[a]
Claudio Mendicute-Fierro,[a] M. Carmen Torralba,[b] M. Rosario Torres,[b]
Virginia San Nacianceno,[a] and Itziar Zumeta[a]
Keywords: Rhodium / Chelates / Acyl ligands / Hydrogenation
The acylhydridorhodium(III) complex [RhHCl{PPh2(o-C6H4-
CO)}(py)2] (1) reacts with 8-quinolinecarbaldehyde
(C9H6NCHO) to afford mixed diacyl [RhCl(C9H6NCO)-
{PPh2(o-C6H4CO)}(py)] (2) with acyl groups trans to chlorine
plexes that contain two acylquinoline fragments can be ob-
tained by the reaction of dimer [Rh(μ-Cl)(C9H6NCO)2]2 (10)
with pyridine to give [Rh(Cl)(C9H6NCO)2(py)] (11) or with
bidentateN- or P-donor ligands(LL) toafford [Rh(C9H6NCO)2-
and to pyridine. Complex 1 undergoes displacement of pyr- (LL)]+ [LL = dppm (12), dppe (13), dppp (14), 1,4-bis(diphen-
idine by 2-(aminomethyl)pyridine (ampy) or diphosphanes to
give hydridoacyl neutral [RhHCl{PPh2(o-C6H4CO)}(LL)] [LL
= ampy (3), bis(diphenylphosphanyl)methane (dppm, 5), 1,3-
bis(diphenylphosphanyl)propane (dppp, 6), 1,2-bis(diphenyl-
phosphanyl)ethane (dppe, 7)] with hydride trans to chloride.
Complex 3 exchanges hydride with chloride to give [Rh(Cl)2-
{PPh2(o-C6H4CO)}(ampy)] (4). The reaction of 2 with biden-
tate N-donor ligands yields cationic mixed diacyl
[Rh(C9H6NCO){PPh2(o-C6H4CO)}(NN)]+ species [NN = 2,2Ј-
bipyridine (bipy, 8), ampy (9)]. Neutral or cationic diacyl com-
ylphosphanyl)butane (15), ampy (16), 8-aminoquinoline (17),
biacetyldihydrazone (18), bipy (19)] with the acyl groups
trans to LL. Complex 11 is highly fluxional in solution. At low
temperatures, the acylquinoline chelate opens to allow an in-
tramolecular exchange between 11a and 11b (ΔH‡
=
10.1Ϯ0.2 kcalmol–1 and ΔS‡ = 1.0Ϯ0.1 calK–1 mol–1), and
pyridine dissociation occurs at room temperature. All the
complexes were characterized spectroscopically. Single crys-
tal X-ray diffraction analysis was performed on 2.
analogous complexes that contain only acylphosphane
groups. In alcoholic media and in the presence of strong
bases, iridium acyls can afford iridium acylhydrides.[6]
Acylhydrido metal complexes can be easily prepared by the
oxidative addition of aldehydes to low-valent transition
metal complexes.[7] We have reported that o-(diphenylphos-
phanyl)benzaldehyde reacts with rhodium(I) complexes to
afford saturated acylhydridorhodium(III) derivatives such
as [RhHCl{PPh2(o-C6H4CO)}(py)2] or [RhHCl{PPh2(o-
C6H4CO)}{κ1-PPh2(o-C6H4CHO)}(py)]. The latter con-
tains an uncoordinated aldehyde and may afford acyl-
Introduction
Organometallic rhodium complexes that contain phos-
phorus ligands play an important role in the transformation
of many organic compounds.[1] More recently, nitrogen li-
gands have been more widely used in the design of regio-
and/or enantioselective catalytic systems.[2] The transfer hy-
drogenation of C=O bonds with 2-propanol as a source of
hydrogen is an attractive method for the preparation of sec-
ondary alcohols by avoiding the use of molecular hydrogen
and pressure apparatus.[3] Metal hydrides, often prepared in
situ, may catalyze the transfer hydrogenation of ketones.[4]
Complexes that contain N- and P-donor ligands, such as 2-
(aminomethyl)pyridine phosphane ruthenium(II) com-
plexes, are among the most active catalysts for this reac-
tion.[5] Iridium complexes that contain an acylphosphane
chelate and an acylquinoline chelate have been found to be
more useful for the transfer hydrogenation reaction than
hydroxyalkyl
[RhCl{PPh2(o-C6H4CO)}{PPh2(o-C6H4-
CHOH)}(py)] complexes by migration of hydride or diacyl
[RhCl{PPh2(o-C6H4CO)}2(py)] derivatives by hydrogen
loss.[8]
Cationic
diacyl
complexes
[Rh{PPh2(o-
C6H4CO)}2(NN)]+ have also been obtained by displace-
ment reactions of pyridine and chloride with N-donor bi-
dentate ligands (NN).[9] 8-Quinolinecarbaldehyde allows
the chelate-assisted oxidative addition of the aldehyde to
[a] Facultad de Química de San Sebastián, Universidad del País rhodium(I) derivatives to produce stable saturated and un-
Vasco,
saturated rhodium(III) acylhydrides and has also been re-
Apdo. 1072, 20080 San Sebastián, Spain
ported to promote the loss of H2.[10]
E-mail: mariaangeles.garralda@ehu.es
[b] Departamento de Química Inorgánica, Laboratorio de
We report the reactivity of the acylhydridorhodium(III)
Difracción de Rayos X, Facultad de Ciencias Químicas,
complex [RhHCl{PPh2(o-C6H4CO)}(py)2] (1) with 8-quin-
olinecarbaldehyde or with bidentate N- or P-donor ligands
Universidad Complutense,
28040 Madrid, Spain
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M. A. Garralda et al.
FULL PAPER
to afford neutral, mixed diacyl- or acylhydridorhodium(III) [RhCl{PPh2(o-C6H4CO)}2(L)] complexes that contain dif-
complexes, respectively. Neutral and cationic diacyl com- ferent pyridine ligands (L), the acyl groups are trans to
plexes derived from 8-quinolinecarbaldehyde are also re- chlorine and pyridine.[8,9a]
ported. The catalytic activity of acylhydrido- and of di-
The X-ray diffraction study of 2a confirmed the pro-
acylrhodium(III) complexes in the transfer hydrogenation posed structure. This compound crystallized in the P21/n
of cyclohexanone has been studied.
monoclinic space group, and the crystal consisted of a neu-
tral Rh compound and a dichloromethane solvent mole-
cule. The molecular structure of 2a is shown in Figure 1.
The geometry around the metal atom is distorted octahe-
dral with four positions occupied by the two bidentate li-
gands and the other two positions occupied by the pyridine
and the chloride ligands, trans to C20 and C1 of the
acylquinoline and acylphosphane fragments, respectively.
The distances that comprise the chelate rings are in the ex-
pected ranges.[9a,11,12] The Rh1–N2 distance with N2 trans
to acyl is 0.15(1) Å longer than the Rh1–N1 distance with
N1 trans to phosphorus. These distances agree with the
trans influence order of the ligands: acyl Ͼ phosphane.[13]
The rhodium atom is practically included in the acylquin-
oline ligand plane, whereas the acylphosphane chelate ring
forms a dihedral angle of 19.97(2)° between the C1–Rh1–
P1 plane and the corresponding phenyl ring.
Results and Discussion
The reaction of 1 with 8-quinolinecarbaldehyde led to
[RhCl(C9H6NCO){PPh2(o-C6H4CO)}(py)] (2) as a mixture
of two diacyl complexes 2a and 2b in a 2a/2b ratio of 6:1,
which was shown by the 31P{1H} NMR spectrum. The ap-
pearance of two close doublets at 69.6 and 64.5 ppm with
J(Rh,P) values of 188 and 177 Hz, respectively, suggests
that in both complexes the phosphorus atom is trans to an
electronegative group. This mixture remains unchanged in
the 298–233 K range. In the 13C{1H} NMR spectrum, only
a broad doublet due to the acyl groups bonded to rhodium
is observed at 225 ppm. The separation of 2a and 2b was
unsuccessful. The spectroscopic features and the X-ray dif-
fraction of 2a led us to propose the structures for 2a and
2b shown in Scheme 1 (see i). In related diacylrhodium
Figure 1. ORTEP view of 2a, which shows the atomic numbering
(20% probability ellipsoids). The hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [°]: Rh1–C1 2.01(1),
Rh1–C20 1.979(9), Rh1–P1 2.259(2), Rh1–N1 2.12(1), Rh1–N2
2.27(1), Rh1–Cl1 2.507(3), C1–O1 1.21(1), C20–O2 1.23(1), Cl1–
Rh1–C1 175.5(3), Cl1–Rh1–C20 89.0(3), C20–Rh1–N1 82.9(4),
C20–Rh1–C1 86.5(4), C20–Rh1–P1 91.9(3), C20–Rh1–N2
173.3(3), N1–Rh1–P1 172.6(2).
The reaction shown in Scheme 1 (i) formally involves al-
dehyde C–H bond activation and hydrogen evolution. Alde-
hyde activation by complexes of metals in higher oxidation
states has been proposed to occur mainly by oxidative ad-
dition or σ-bond metathesis.[7i] The former appears less
likely in our case because it would involve scarce RhV inter-
mediates.[14] The σ-bond metathesis, or a related σ complex-
assisted metathesis mechanism,[15] is more feasible. We have
Scheme 1. i) C9H6N–CHO. ii) 2-(aminomethyl)pyridine (ampy).
iii) PP = bis(diphenylphosphanyl)methane (dppm, 5), 1,3-bis(di-
phenylphosphanyl)propane (dppp, 6), 1,2-bis(diphenylphosphan-
yl)ethane (dppe, 7). iv) NN = 2,2Ј-bipyridine (bipy, 8), ampy (9).
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New Acylhydrido- and Diacylrhodium(III) Organocomplexes
observed that the acylnorbornenylrhodium(III) complex unobservable or 46 Hz] and –18.2 (dd) (5a) or 0.7 (ddd) (6a)
[RhCl(C9H6NCO)(norbornenyl)(κ2-C9H6NCHO)], which ppm due to PC trans to the acyl group [J(Rh,PC) = 54 or
contains
a
coordinated κ2-N,O-aldehydequinoline, un- 69 Hz]. The 13C{1H} NMR spectra contain the expected
dergoes H transfer from the coordinated aldehyde to the σ- resonances due to an acyl group coordinated to rhodium at
norbornenyl group to release norbornene.[12] Therefore, we 239.1 (dd) (5a) or 241.9 (dd) (6a) ppm [J(Rh,C) = 28 Hz]
believe that the reaction shown in Scheme 1 (i) occurs by and trans to phosphorus [J(P,C) = 122 or 141 Hz].
aldehyde–quinoline displacement of pyridine from 1, H
transfer from the coordinated C9H6NCHO to the hydride ane (dppe) gave a 1:1 mixture of two isomers 7a and 7b.
and H2 release. The NMR spectra allow the unambiguous characterization
The reaction of 1 with 1,2-bis(diphenylphosphanyl)eth-
The reaction of 1 with 2-(aminomethyl)pyridine (= of both complexes that differ in the group trans to the most
ampy; Scheme 1, ii) shows the easy displacement of electronegative chloride, which is hydride in 7a and acyl in
pyridine by chelating ligands, which led to the formation of 7b. Complex 7a contains a hydride (–15.32 ppm) bonded to
neutral
acylhydridorhodium(III)
[RhHCl{PPh2(o- rhodium [J(Rh,H) = 25.3 Hz], which is cis to three phos-
C6H4CO)}(ampy)] (3), which contains an acylphosphane phorus atoms [J(P,H) = 12.1, 12.0 and 6.5 Hz], whose reso-
fragment and a bidentate N-donor ligand. The NMR spec- nances in the 31P{1H} NMR spectrum are similar to those
tra show that 3 is a mixture of two isomers 3a and 3b in a of 6a and appear at 59.8 (ddd), 50.6 (ddd) and 33.5 (ddd)
3:1 ratio. The 31P{1H} NMR spectrum contains two dou- ppm. In the 13C{1H} NMR spectrum, the resonance of the
blets in the 73.1–73.5 ppm range with J(Rh,P) of 163 Hz, acyl group at 244.7 (dd) ppm trans to phosphorus [J(P,C)
1
and the H NMR spectrum shows two triplets in the high = 120 Hz] is observed. Complex 7b contains a hydride
field region at –16.45 and –15.07 ppm, which are consistent (–7.46 ppm) bonded to rhodium [J(Rh,H) = 18.2 Hz],
with hydrides cis to phosphorus [J(P,H) = J(Rh,H) = which is trans to phosphorus [J(P,H) = 161.8 Hz] and cis to
25 Hz] and trans to chloride. The resonances due to the the other two phosphorus atoms [J(P,H)cis = unobservable
amino groups at 4.95 and 4.23 ppm for the more abundant and 8.9 Hz]. The 31P{1H} NMR spectrum contains the ex-
3a and at 2.77 and 2.23 ppm for 3b indicate different envi- pected splitting pattern for the resonances at 65.8 (ddd),
ronments for the amino groups in both isomers. In the ab- 58.6 (ddd) and 28.5 (ddd) ppm due to 7b and the 13C{1H}
sence of other effects, the corresponding signals are ex- NMR spectrum shows the expected doublet of the acyl
pected to shift downfield upon coordination, but the ring group at 232.2 ppm due to rhodium coupling [J(Rh,C) =
current effects originated by the aromatic rings of the phos- 32 Hz]. Attempts to separate the isomers led to decomposi-
phane can shift the signals upfield.[16] Therefore, we assign tion. The reaction of 1 with 1,4-bis(diphenylphosphanyl)-
the two resonances at lower field, 4–5 ppm, to the isomer butane (dppb) led to a complex mixture of compounds,
that contains the amino group trans to phosphorus, 3a, and which included compounds of the type 7a and 7b along
the signals at higher field, 2–3 ppm, to the isomer that con- with other unidentified species.
tains the amino group cis to phosphorus, 3b. In solution, 3
Complex 2 reacted with bidentate N-donor ligands (NN)
showed low stability, which precluded the separation of the such as 2,2Ј-bipyridine (bipy) or 2-(aminomethyl)pyridine
isomers. In chlorinated solvents, the exchange of hydride by to undergo displacement of pyridine and chloride and
chloride afforded [RhCl2{PPh2(o-C6H4CO)}(ampy)] (4) as afford cationic, mixed diacyl [Rh(C9H6NCO){PPh2(o-
a mixture of two isomers 4a and 4b in a 4:1 ratio. When C6H4CO)}(NN)]+ derivatives [NN = bipy (8), ampy (9)],
performing the reaction in CDCl3, the appearance of a res- which were isolated as tetraphenylborate compounds
1
onance at 5.30 ppm in the H NMR spectrum due to for- (Scheme 1, iv) and behave as 1:1 electrolytes.[18] Their
mation of dichloromethane was observed. Such a reaction 31P{1H} NMR spectra contain one doublet in the 65.2–
has several precedents.[8,17]
63.6 ppm range with J(Rh,P) values from 179–166 Hz,
The reaction of 1 with diphosphanes afforded the acylhy- which is consistent with phosphorus lying trans to nitrogen.
drides [RhHCl{PPh2(o-C6H4CO)}{Ph2P(CH2)nPPh2}] (5– The 13C{1H} NMR spectra show two doublets in the low
7, Scheme 1, iii). With bis(diphenylphosphanyl)methane field region due to acyl groups bonded to rhodium and cis
(dppm) and 1,3-bis(diphenylphosphanyl)propane (dppp), to a phosphorus atom at 235.0 [J(Rh,C) = 31 Hz] and 229.0
single isomers 5a and 6a were obtained, respectively, which [J(Rh,C) = 37 Hz] ppm for 8 or at 237.0 [J(Rh,C) = 31 Hz]
contain the hydride trans to chloride, and were unambigu- and 233.2 [J(Rh,C) = 37 Hz] ppm for 9. For complex 8, the
1
ously characterized by NMR spectroscopy. The H NMR formation of only one species is observed. Its 1H NMR
spectra show multiplets in the high field region at –13.92 spectrum shows resonances due to the amino group at 3.79
(5a) or –18.91 ppm (6a) due to rhodium-coordinated hy- and 2.37 ppm. All these data suggest the structure depicted
drides cis to three phosphorus atoms [J(Rh,H) = 26.3 or in Scheme 1 (iv), in which the phosphorus atom lies trans
24.3 Hz; J(P,H) = 12.6 or 12.8, 9.0 or 10.7 and 5.3 Hz or to the quinolinic N-atom and the acyl groups lie trans to
unobserved]. The 31P{1H} NMR spectra contain reso- the bidentate N-donor ligand. On spectroscopic grounds
nances at 61.0 (ddd) (5a) or 51.6 (ddd) ppm (6a) due to PA alone it is not possible to determine whether the amino
coordinated to rhodium [J(Rh,PA) = 128 or 119 Hz] trans group of ampy is trans to the acyl group of the acylquino-
to PB [J(PB,PA) = 374 or 335 Hz] and cis to PC [J(PC,PA) = line or the acylphosphane. Unfortunately, repeated attempts
23 or 27 Hz]; –7.0 (dd) (5a) or 14.5 (ddd) (6a) ppm due to obtain single crystals suitable for X-ray diffraction were
to PB [J(Rh,PB) = 114 or 121 Hz] cis to PC [J(PC,PB) = unsuccessful.
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Neutral or cationic diacyl complexes that contain two
acylquinoline fragments were obtained by the reaction of
dimeric [Rh(μ-Cl)(C9H6NCO)2]2 (10)[12] with pyridine or
bidentate N- or P-donor ligands, respectively (Scheme 2).
Scheme 2. i) pyridine. ii) LL = dppm (12), dppe (13), dppp (14),
dppb (15), ampy (16), 8-aminoquinoline (aqui, 17), biacetyldi-
hydrazone (bdh, 18), bipy (19).
The reaction of 10 with pyridine (Scheme 2, i) led to the
cleavage of the chlorine bridge to afford neutral
[Rh(Cl)(C9H6NCO)2(py)] (11), which was highly fluxional
in solution and underwent two different fluxional processes:
i) exchange between 11a and 11b at low temperatures and
ii) pyridine dissociation at room temperature. As shown in
Figure 2, at 183 K three resonances are observed in the low
1
Figure 2. Variable-temperature H NMR spectra of 11 in CD2Cl2
from 183–303 K.
1
field region of the H NMR spectrum at δ = 10.10, 9.41
and 8.64 ppm. We attribute the low field resonance to H2
of the coordinated 8-acylquinoline group. Deshielding of
this signal with respect to free C9H6NCHO has been ob-
served in neutral (acylquinoline)palladium complexes.[19]
The resonances at 9.41 and 8.64 ppm are attributed to H2
of the coordinated pyridine ring, which is present in 11a
and 11b (Scheme 2, i). Although other geometries cannot
be excluded, our proposal is based on the structure of 2 and
the observed tendency of acylquinoline derivatives to locate
the acyl group trans to chloride and the nitrogen atom trans
to another nitrogen atom when available.[12,19] A tempera-
ture increase led to the broadening of the resonances at 9.41
and 8.64 ppm, followed by coalescence at 233 K with the
emergence of a new signal at δ = 9.11 ppm, which became
sharp at 253 K. In the 183–253 K range the resonance at
10.10 ppm is clearly observed. From line-shape analysis
1
(Figure 3) of the variable temperature H NMR spectra in
the 183–253 K range,[20] the activation parameters ΔH‡ =
10.1Ϯ0.2 kcalmol–1 and ΔS‡ = 1.0Ϯ0.1 calK–1 mol–1 were
determined. The relatively small value of the entropy of ac-
tivation falls in the range between 11 and –10 calK–1 mol–1,
which could be indicative of an intramolecular rearrange-
ment processes.[21] Fast exchange between 11a and 11b by
the opening of the acylquinoline chelate could explain the
fluxional behaviour. As shown in Figure 2, at temperatures
1
Figure 3. Variable-temperature H NMR spectra of 11 in CD2Cl2
higher than 263 K, the broadening and collapse of the reso- from 183–263 K: (left) experimental and (right) calculated.
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New Acylhydrido- and Diacylrhodium(III) Organocomplexes
nances at 9.11 and 10.10 ppm occurred, which indicates the it is apparent that 1 reaches 70% conversion to cyclohex-
dissociation of pyridine and the presence of a mixture of 10 anol after 180 min [turnover frequency (TOF) = 202]. As
and free pyridine at room temperature and above. Repeated shown in Table 1, 3, which contains 2-(aminomethyl)pyr-
attempts to obtain single crystals of 11 suitable for X-ray idine, and 6 and 7, which contain dppp and dppe, respec-
diffraction were unsuccessful.
tively, show a higher catalytic activity, and reach over 80%
The reaction of 10 with different bidentate ligands (LL), conversion in 60 min. The presence of two chelates in these
such as diphosphanes Ph2P(CH2)nPPh2 (n = 1, 2, 3 or 4), complexes markedly enhances their catalytic properties,
N-donor ligands of the aminoimino type (aqui or ampy) or which has been observed in bis(chelated) RhIII bis(carbene)
with aromatic (bipy) or aliphatic (bdh) diimines, afforded complexes.[26] The catalytic activity of 6 and 7 is comparable
cationic diacyl [Rh(C9H6NCO)2(LL)]+ derivatives (12–19, to that reported for chelated or pincer RhIII carbene com-
Scheme 2, ii), which were isolated as tetraphenylborate plexes[27] and higher than that shown by related acyliridium
compounds. The complexes show the expected features in complexes.[6b,25] The presence of dppm in 5 inhibits the
their IR spectra and behave as 1:1 electrolytes in acetone catalytic activity. The diacyl complexes show lower catalytic
solution. In the 31P{1H} NMR spectra of 12–15 only one activity than the hydridoacyl derivatives. Complex 20,
doublet is observed with J(Rh,P) in the 63–72 Hz range, which contains two acylphosphane chelates, required
which is consistent with equivalent phosphorus atoms being 180 min to reach 80% conversion (TOF = 360). The substi-
trans to acyl groups.[22] The chemical shifts and their dis- tution of acylphosphane chelates by acylquinoline chelates
placement upon coordination (ΔF) are as expected for com- resulted in a decrease in the catalytic activity. The mixed
plexes that contain four- [dppm, –16.2 (ΔF = +5) ppm], compound 2 reached only 66% conversion after 180 min
five- [dppe, +27.9 (ΔF = +35) ppm], six- [dppp, –6.9 (ΔF = (TOF = 360) due to fast catalyst deactivation, and 10,
+10) ppm] or seven-membered [dppb, –2.3 (ΔF = +12) which contains two acylquinoline chelates, gave only 18%
ppm] metallacycles.[23] Accordingly, the 13C{1H} NMR conversion, or 24% conversion in the presence of pyridine,
spectrum of 13 shows a doublet of doublets at low field after 180 min.
(232.3 ppm) due to equivalent acyl groups bonded to rho-
dium [J(Rh,C) = 27 Hz] and trans to phosphorus atoms
[J(P,C) = 95 Hz]. Complexes 16–19, which contain N-donor
Table 1. Transfer hydrogenation of cyclohexanone with hydridoacyl
complexes.[a]
Complex
Conversion [%][b]
TOF[c]
ligands adopt an analogous geometry. The 13C{1H} NMR
spectra of 16–17, which contain asymmetric ligands, show
two doublets in the 235–226 ppm range due to nonequiva-
lent rhodium-bonded acyl groups [J(Rh,C) = 33 Hz]. For
18–19, which contain symmetric ligands, only one doublet
in the 231–229 ppm range due to equivalent rhodium-
1
3
5
6
7
50/59
80/92
65/76
90/96
88/93
202
324
68
415
381
[a] Reaction conditions: 0.1 m substrate in iPrOH (40 cm3) with
0.5 mol-% precatalyst loading at 83 °C. [KOH]/[Rh] 10:1. [b] Reac-
tion time: 60/90 min. [c] Calculated after 10 min and expressed in
mol of product/(mol of complex ϫ h).
1
bonded acyl groups [J(Rh,C) = 33 Hz] is observed. The H
NMR spectrum of 18, which contains biacetyldihydrazone
[H2NN=C(CH3)C(CH3)=NH2], confirms the presence of
two equivalent imino fragments.
Complexes 2, 8 and 9 contain the best σ-donor acyl
groups trans to more electronegative atoms such as chlorine
or nitrogen and phosphorus atoms trans to nitrogen as ex-
pected when electronic effects are taken into consideration.
Conclusions
The reaction between [RhHCl{PPh2(o-C6H4CO)}(py)2]
In contrast, in 12–15 the nitrogen atoms are mutually trans and C9H6NCHO to afford mixed diacyl [RhCl(C9H6NCO)-
and the acyl groups are trans to the phosphorus atoms. We {PPh2(o-C6H4CO)}(py)] may occur by quinolinealdehyde
believe that 12–15 are the kinetically favoured products of coordination, followed by H transfer from coordinated al-
the reaction of the diphosphanes with 10, which contains dehyde to hydride to release H2. Neutral hydridoacyl com-
mutually trans N-atoms and bridging chlorides. This behav- pounds, with hydride trans to chloride, and cationic diacyl
iour has also been observed in the formation of triscyclome- complexes, with acyl groups trans to phosphorus or nitro-
tallated homoleptic (C,N)3 iridium(III) complexes, where gen, were easily formed by the reaction with bidentate P-
the isomerization of the kinetic mer isomer to the thermo- or N-donor ligands. Hydridoacyl complexes catalyze the
dynamically favoured fac isomer requires reaction tempera- hydrogen transfer from 2-propanol to cyclohexanone to af-
tures higher than 200 °C or a photochemical reaction.[24]
The use of acyl complexes in the transfer hydrogenation
of ketones with alcohols has been limited to a few iridium
complexes.[6b,25] We have studied the catalytic activity of hy-
dridoacyl complexes 1, 3, 5–7, diacyl complexes 2 and 10
and related [RhCl{PPh2(o-C6H4CO)}2(py)] (20),[8] which
contains two acylphosphane chelates, in the hydrogen trans-
fer from 2-propanol to cyclohexanone in iPrOH in the pres-
ford cyclohexanol.
Experimental Section
General Procedures: The preparation of the metal complexes was
carried out at room temperature under nitrogen with the use of
standard Schlenk techniques. [RhClH{PPh2(o-C6H4CO)}(py)2][8]
(1), [RhCl{PPh2(o-C6H4CO)}2(py)][8] (20), [Rh(μ-Cl)(C9H6-
ence of a strong base. From the transfer hydrogenation data NCO)2]2 (10) and 8-quinolinecarbaldehyde[19] were prepared as
[12]
Eur. J. Inorg. Chem. 2012, 1445–1452
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1449

M. A. Garralda et al.
FULL PAPER
previously reported. Microanalysis was carried out with a Leco
CHNS–932 microanalyzer. Conductivities were measured in ace-
tone 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 including 2D ex-
periments were recorded with Bruker Avance DPX 300 or Bruker
Avance 500 spectrometers, 1H and 13C{1H} (Me4Si internal stan-
128, J(PB,PA) = 374, J(PC,PA) = 23 Hz, PA], –6.95 [dd, J(Rh,PB) =
114 Hz, PB], –18.20 [dd, J(Rh,PC) = 54 Hz, PC] ppm. 13C{1H}
NMR (CD2Cl2): δ = 239.1 [dd, J(P,C) = 122, J(Rh,C) = 28 Hz,
CO] ppm. C44H36ClOP3Rh (813.06): calcd. C 65.00, H 4.59; found
C 65.40, H 5.23. Data for 6a: Yield 73 mg, 73%. IR (KBr): ν =
˜
1
2107 [m, ν(Rh–H)], 1616 [s, ν(C=O)] cm–1. H NMR (CD2Cl2): δ
= –18.91 [m, J(Rh,H) = 24.3, J(P,H) = 12.8 and 10.7 Hz, 1 H,
dard) and 31P{1H} NMR (H3PO4 external standard) spectra were RhH] ppm. 31P{1H} NMR (CD2Cl2): δ = 51.6 [ddd, J(Rh,PA) =
measured from CDCl3 or CD2Cl2 solutions.
119, J(PB,PA) = 335, J(PC,PA) = 27 Hz, PA], 14.5 [ddd, J(Rh,PB) =
121, J(PC,PB) = 46 Hz, PB], 0.7 [ddd, J(Rh,PC) = 69 Hz, PC] ppm.
13C{1H} NMR (CD2Cl2): δ = 241.9 [dd, J(P,C) = 141, J(Rh,C) =
29 Hz, CO] ppm. C46H40ClOP3Rh (841.12): calcd. C 65.69, H 4.91;
[RhCl(C9H6NCO){PPh2(o-C6H4CO)}(py)] (2): To a methanol sus-
pension of [RhClH{PPh2(o-C6H4CO)}(py)2] (1) (180 mg,
0.307 mmol) was added 8-quinolinecarbaldehyde (48 mg,
0.307 mmol). The suspension was stirred at room temperature for
3 h. The solid was collected by filtration, washed with methanol
found C 65.34, H 5.07. Data for 7: Yield 58 mg, 59%. IR (KBr): ν
˜
= 1939 [m, ν(Rh–H)], 1622 [s, ν(C=O)] cm–1. Data for 7a: 1H NMR
(CDCl3): δ = –15.32 [m, J(Rh,H) = 25.3, J(P,H) = 12.1, 12.0 and
6.5 Hz, 1 H, RhH] ppm. 31P{1H} NMR (CDCl3): δ = 59.8 [ddd,
J(Rh,PA) = 121, J(PB,PA) = 356, J(PC,PA) = 19 Hz, PA], 50.6 [ddd,
J(Rh,PB) = 120, J(PC,PB) = 13 Hz, PB], 33.5 [ddd, J(Rh,PC) =
68 Hz, PC] ppm. 13C{1H} NMR (CD2Cl2): δ = 244.7 [dd, J(P,C) =
and dried under vacuum; yield 100 mg, 49%. IR (KBr): ν = 1660
˜
(m), 1626 [s, ν(C=O)] cm–1. 31P{1H} NMR (CDCl3): δ = 69.6 [d,
J(Rh,P) = 188 Hz, P2a], 64.5 [d, J(Rh,P) = 177 Hz, P2b] ppm.
13C{1H} NMR (CDCl3): δ = 225.0 [d, J(Rh,C) = 35 Hz, CO] ppm.
C34H25ClN2O2PRh·CH3OH (694.96): calcd. C 60.49, H 4.21, N
4.03; found C 60.13, H 3.82, N 4.12.
1
120, J(Rh,C) = 28 Hz, CO] ppm. Data for 7b. H NMR (CDCl3):
δ = –7.46 [ddd, J(Rh,H) = 18.2, J(P,H)trans = 161.8, J(P,H)cis
=
8.9 Hz, 1 H, RhH] ppm. 31P{1H} NMR (CDCl3): δ = 65.8 [ddd,
J(Rh,PA) = 122, J(PB,PA) = 359, J(PC,PA) = 16 Hz, PA], 58.6 [ddd,
J(Rh,PB) = 130, J(PC,PB) = 18 Hz, PB], 28.5 [ddd, J(Rh,PC) =
88 Hz, PC] ppm. 13C{1H} NMR (CD2Cl2): δ = 232.2 [d, J(Rh,C)
= 32 Hz, CO] ppm. C45H38ClOP3Rh (827.09): calcd. C 65.35, H
4.75; found C 65.26, H 4.65.
[RhHCl{PPh2(o-C6H4CO)}(ampy)] (3): To a benzene suspension of
1
(75 mg, 0.128 mmol) was added 2-(aminomethyl)pyridine
(13.3 μL, 0.128 mmol). After stirring for 1 h, the colour of the sus-
pension changed to afford a white solid, which was collected by
filtration, washed with benzene and dried under vacuum; yield
51 mg, 75%. IR (KBr): ν = 3272 (m), 3230 [m, ν(NH )], 2065 [m,
˜
2
ν(Rh–H)], 1602 [s, ν(C=O)] cm–1. Data for 3a: 1H NMR (CD2Cl2):
δ = 4.95 (m, 1 H, NH2), 4.76 (m, 1 H, CH2), 4.46 (m, 1 H, CH2),
4.23 (br., 1 H, NH2), –16.45 [t, J(Rh,H) = J(P,H) = 25.0 Hz, 1 H,
RhH] ppm. 31P{1H} NMR (CD2Cl2): δ = 73.1 [d, J(Rh,P) =
[Rh(C9H6NCO){PPh2(o-C6H4CO)}(NN)]BPh4 [NN = 2,2Ј-bipyr-
idine (8), 2-(aminomethyl)pyridine (9)]: To a dichloromethane solu-
tion of 2 (30 mg, 0.045 mmol) was added a stoichiometric amount
of the corresponding ligand (0.045 mmol). After stirring at room
temperature for 60 min, the solution was concentrated, and a meth-
anol solution of NaBPh4 (15.5 mg, 0.045 mmol) was added to af-
ford a yellow precipitate, which was collected by filtration, washed
with methanol and dried under vacuum. Data for 8: Yield 14 mg,
1
163 Hz] ppm. Data for 3b: H NMR (CD2Cl2): δ = 4.71 (m, 1 H,
CH2), 4.41 (m, 1 H, CH2), 2.77 (br., 1 H, NH2), 2.23 (br., 1 H,
NH2), –15.07 [t, J(Rh,H) = J(P,H) = 25.7 Hz, 1 H, RhH] ppm.
31P{1H} NMR (CD2Cl2): δ = 73.5 [d, J(Rh,P) = 164 Hz] ppm.
C25H23ClN2OPRh (536.80): calcd. C 55.94, H 4.32, N 5.22; found
C 55.68, H 4.34, N 5.44.
30%. IR (KBr): ν = 1663 (m), 1631 [s, ν(C=O)] cm–1. Λ
˜
M
(ohm–1 cm2 mol–1): 93 (acetone). 31P{1H} NMR (CDCl3): δ = 65.2
[d, J(Rh,P) = 179 Hz] ppm. 13C{1H} NMR (CDCl3): δ = 235.0
[d, J(Rh,C) = 31 Hz, CO], 229 [d, J(Rh,C) = 37 Hz, CO] ppm.
C63H48BN3O2PRh·0.5CH2Cl2 (1066.26): calcd. C 71.53, H 4.63, N
3.94; found C 71.70, H 4.62, N 4.08. Data for 9: Yield 27 mg, 62%.
[Rh(Cl)2{PPh2(o-C6H4CO)}(ampy)] (4): Stirring a dichloromethane
solution of 3 (50 mg, 0.093 mmol) for 18 h afforded an orange solu-
tion. Addition of diethyl ether gave a yellow solid, which was col-
lected by filtration, washed with diethyl ether and dried under vac-
uum; yield 28 mg, 53%. IR (KBr): ν = 3314 (w), 3272 (w), 1652 [s,
˜
IR (KBr): ν = 3287 (m), 3237 [w, ν(NH)], 1660 (s), 1626 [s, ν(C=O)]
˜
ν(C=O)]. ΛM (ohm–1 cm2 mol–1): 13 (acetone). Data for 4a: 1H
NMR (CDCl3): δ = 5.40 (br., 1 H, CH2), 4.83 (br., 1 H, NH2), 4.73
(br., 1 H, NH2), 4.64 (br., 1 H, CH2) ppm. 31P{1H} NMR (CDCl3):
δ = 55.7 [d, J(Rh,P) = 139 Hz] ppm. 13C{1H} NMR (CDCl3): δ =
229.8 [d, J(Rh,C) = 27 Hz, CO], 51.3 (s, CH2) ppm. Data for 4b:
1H NMR (CDCl3): δ = 4.64 (br., 1 H, CH2), 4.43 (br., 1 H, CH2),
4.29 (br., 1 H, NH2), 4.12 (br., 1 H, NH2) ppm. 31P{1H} NMR
(CDCl3): δ = 56.4 [d, J(Rh,P) = 137 Hz] ppm. 13C{1H} NMR
(CDCl3): δ = 229.0 [d, J(Rh,C) = 24 Hz, CO], 48.2 (s, CH2) ppm.
C25H22Cl2N2OPRh·0.5CH2Cl2 (613.72): calcd. C 49.91, H 3.78, N
4.57; found C 49.63, H 3.76, N 5.09.
1
cm–1. ΛM (ohm–1 cm2 mol–1): 87 (acetone). H NMR (CDCl3): δ =
3.79 (br. s, 1 H, NH2), 3.53 (m, 1 H, CH2), 3.05 (m, 1 H, CH2),
2.37 (br. s, 1 H, NH2) ppm. 31P{1H} NMR (CDCl3): δ = 63.6 [d,
J(Rh,P) = 166 Hz] ppm. 13C{1H} NMR (CDCl3): δ = 237.0 [dd,
J(Rh,C) = 31, J(P,C) = 10 Hz, CO], 233.2 [dd, J(Rh,C) = 35, J(P,C)
= 3 Hz, CO] ppm. C59H48BN3O2PRh (975.74): calcd. C 72.63, H
4.96, N 4.31; found C 71.93, H 4.94, N 4.38.
[RhCl(C9H6NCO)2(py)] (11): To
a MeOH suspension of 10
(22.5 mg, 0.025 mmol) was added pyridine (8.4 μL, 0.11 mmol). Af-
ter stirring for 2 h, the yellow precipitate was collected by filtration
and dried under vacuum; yield 19 mg, 67%. IR (KBr): ν = 1665
˜
[RhHCl{PPh2(o-C6H4CO)}(PP)] [PP = dppm (5a), dppp (6a), dppe
(s), 1630 [s ν(C=O)] cm–1. C25ClH17N3O2Rh (529.79): calcd. C
(7)]: To
a benzene solution of the corresponding ligand
56.68, H 3.23, N 7.93; found C 56.69, H 3.25, N 7.72.
(0.119 mmol) (room temperature for 5a and 7 or 40 °C for 6a) was
added 1 (70 mg, 0.119 mmol) to afford a yellow solution. After
stirring for 15 min, hexane was added to afford a yellow precipitate,
which was collected by filtration, washed with hexane and dried
[Rh(C9H6NCO)2(LL)]BPh4 [LL = dppm (12), dppe (13), dppp (14),
dppb (15), ampy (16), aqui (17), bdh (18), bipy (19)]: To a CH2Cl2/
MeOH suspension of 10 (25 mg, 0.028 mmol) was added LL
(0.056 mmol). After stirring for 30 min, dissolution occurred to
under vacuum. Data for 5a: Yield 78 mg, 80%. IR (KBr): ν = 2051
˜
[m, ν(Rh–H)], 1623 [s, ν(C=O)] cm–1. 1H NMR (CDCl3): δ = give a light yellow solution. After stirring for a further 30 min,
–13.92 [m, J(Rh,H) = 26.3, J(P,H) = 12.6, 9.0 and 5.3 Hz, 1 H,
NaBPh4 (19.2 mg, 0.056 mmol) was added to result in the immedi-
ate precipitation of yellow-orange solids, which were collected by
RhH] ppm. 31P{1H} NMR (CDCl3): δ = 61.0 [ddd, J(Rh,PA) =
1450
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1445–1452

New Acylhydrido- and Diacylrhodium(III) Organocomplexes
filtration, washed with methanol and dried under vacuum. Data
combination of three exposure sets. Each frame exposure was of
for 12: Yield 42 mg, 65%. IR (KBr): ν = 1664 (s), 1640 [s, ν(C=O)] 20 s and covered 0.3° in ω. The cell parameters were determined
˜
1
cm–1. ΛM (ohm–1 cm2 mol–1): 93 (acetone). H NMR (CDCl3): δ =
and refined by least-squares fit of all reflections collected. The first
100 frames were recollected at the end of the data collection to
4.20 [t, J(P,H) = 8.6, 2 H, CH2] ppm. 31P{1H} NMR (CDCl3): δ =
–16.2 [d, J(Rh,P) = 63 Hz] ppm. C69H54BN2O2P2Rh·0.5(CH2Cl2) monitor crystal decay, and no appreciable drop in the intensities
(1161.34): calcd. C 71.88, H 4.77, N 2.41; found C 71.73, H 4.53,
was observed. An empirical absorption correction was performed.
The structure was solved by direct methods and conventional Fou-
rier techniques and refined by applying full-matrix least-squares on
N 2.47. Data for 13: Yield 36 mg, 55%. IR (KBr): ν = 1659 (s),
˜
1634 [s, ν(C=O)] cm–1. ΛM (ohm–1 cm2 mol–1): 79 (acetone). 1H
NMR (CDCl3): δ = 2.21 [d, J(P,H) = 10.0, 4 H, CH2] ppm. 31P{1H} F2 with anisotropic thermal parameters for the non-hydrogen
NMR (CDCl3): δ = 27.9 [d, J(Rh,P) = 72 Hz] ppm. 13C{1H} NMR atoms with exceptions: the solvent molecule was refined iso-
(CDCl3): δ = 232.3 [dd, J(P,C) = 95, J(Rh,C) = 27 Hz, CO] ppm.
C70H56BN2O2P2Rh·CH3OH (1164.94): calcd. C 73.20, H 5.19, N
2.40; found C 73.22, H 5.30, N 2.50. Data for 14: Yield 41 mg,
tropically with restrained C–Cl distances. The hydrogen atoms were
included at their calculated positions determined by molecular ge-
ometry and refined riding on the corresponding bonded atom. The
largest first peaks in the final difference map are near to a solvent
62%. IR (KBr): ν = 1658 (s), 1634 [s, ν(C=O)] cm–1. Λ
˜
M
(ohm–1 cm2 mol–1): 86 (acetone). 1H NMR (CDCl3): δ = 2.6–2.0 (m, molecule. All the calculations were carried out with SHELX-97.[28]
6 H, CH2) ppm. 31P{1H} NMR (CDCl3): δ = –6.9 [d, J(Rh,P)
Table 2. Crystal data and structure refinement for 2a.
= 70 Hz] ppm. C71H58N2O2P2BRh·0.5CH2Cl2 (1189.40): calcd. C
72.20, H 5.00, N 2.36; found C 71.99, H, 4.95, N 2.39. Data for
Empirical formula
Formula mass
Wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
[C34H25ClN2O2PRh]CH2Cl2
747.82
0.71073
monoclinic
P21/n
10.4539(6)
19.242(1)
16.536(1)
104.438(1)
3221.1(3)
4
15: Yield 43 mg, 64%. IR (KBr): ν = 1656 (s), 1631 [s, ν(C=O)]
˜
1
cm–1. ΛM (ohm–1 cm2 mol–1): 78 (acetone). H NMR (CDCl3): δ =
2.9–2.1 (m, 8 H, CH2) ppm. 31P{1H} NMR (CDCl3): δ = –2.3 [d,
J(Rh,P) = 66 Hz] ppm. C72H60BN2O2P2Rh·0.5CH2Cl2 (1203.42):
calcd. C 72.36, H 5.11, N 2.33; found C 72.41, H 5.07, N 2.44.
Data for 16: Yield 19 mg, 39%. IR (KBr): ν = 1669 (s), 1628 [s,
˜
c [Å]
ν(C=O)] cm–1. ΛM (ohm–1 cm2 mol–1): 78 (acetone). 1H NMR
(CDCl3): δ = 3.23–2.95 (m, 2 H, CH2), 1.30 (m, 1 H, NH2), 0.79
(m, 1 H, NH2) ppm. 13C{1H} NMR (CDCl3): δ = 232.5 [d, J(Rh,C)
= 33 Hz, CO], 226.9 [d, J(Rh,C) = 33 Hz, CO], 49.1 (s, CH2) ppm.
C50H40BN4O2Rh·CH3OH (874.66): calcd. C 70.03, H 5.07, N 6.41;
found C 70.18, H 4.25, N 6.49. Data for 17: Yield 22 mg, 43%. IR
β [°]
Volume [Å3]
Z
Density (calcd.) [gcm–3]
Absorption coefficient [mm–1]
Scan technique
F(000)
1.542
0.864
ω and φ
1512
(KBr): ν = 1667 (s), 1628 [s, ν(C=O)] cm–1. Λ (ohm–1 cm2 mol–1):
˜
M
78 (acetone). 1H NMR (CDCl3): δ = 3.39 (s, 2 H, NH2) ppm.
13C{1H} NMR (CDCl3): δ = 235.5 [d, J(Rh,C) = 34 Hz, CO], 233.4
[d, J(Rh,C) = 33 Hz, CO] ppm. C53H40BN4O2Rh·CH3OH (910.69):
calcd. C 71.22, H 4.87, N 6.15; found C 71.33, H 4.59, N 6.17.
θ range [°]
Index ranges
1.65 to 25.00
(–11, –16, –19 to 12, 22, 13)
16690
5580 [R(int) = 0.0685]
100.0%
5680/2/382
1.025
0.0720 (3442 observed)
0.2289
Reflections collected
Independent reflections
Completeness to θ
Data/restraints/parameters
Goodness-of-fit on F2
Data for 18: Yield 28 mg, 57%. IR (KBr): ν = 1671 (s), 1636 [s,
˜
ν(C=O)] cm–1. ΛM (ohm–1 cm2 mol–1): 88 (acetone). 1H NMR
(CDCl3): δ = 5.22 (s, 4 H, NH2), 1.63 (s, 6 H, CH3) ppm. 13C{1H}
Final R[a] indices [IϾ2σ(I)]
[b]
NMR (CDCl3): δ = 231.2 [d, J(Rh,C) = 33 Hz, CO], 14.0 (s, CH3) wR2 indices (all data)
Largest diff. peak and hole [eÅ3] 2.369 and –1.234
ppm. C48H42BN6O2Rh·0.5CH2Cl2 (891.09): calcd. C 65.37, H 4.86,
N 9.43; found C 65.20, H 5.05, N 9.50. Data for 19: Yield 29 mg,
[a] Σ[|Fo| – |Fc|]/Σ|Fo|. [b] {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
56%. IR (KBr): ν = 1670 (s), 1637 [s, ν(C=O)] cm–1. Λ
˜
M
(ohm–1 cm2 mol–1): 91 (acetone). 13C{1H} NMR (CDCl3): δ = 229.7
[d, J(Rh,C) = 33 Hz, CO] ppm. C54H40BN4O2Rh·CH3OH (922.70):
calcd. C 71.59, H 4.81, N 6.07; found C 71.74, H 4.87, N 6.12.
CCDC-836821 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Catalytic Reactions: The transfer hydrogenation reactions were car-
ried out under nitrogen in 2-propanol under reflux conditions with
magnetic stirring. The equipment consisted of a 100 mL round-
bottomed flask, fitted with a condenser and septum cap. The cata-
lysts were prepared by adding KOH (0.2 mmol) in 2-propanol
(10 mL) to solutions (30 mL) of the catalyst precursor (0.02 mmol).
The resulting solutions were heated to 83 °C and the substrate
(4 mmol) was injected. Analysis of the catalytic reactions was car-
ried out with a Shimadzu GC-14A chromatograph, connected to a
Shimadzu C-R6A calculation integrator.
Acknowledgments
Financial support from Ministerio de Ciencia
e Innovación
(MICINN) (CTQ2008-2967/BQU), Universidad del País Vasco and
Diputación Foral de Gipuzkoa is gratefully acknowledged. I. Z. is
grateful to Gobierno Vasco for a scholarship.
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Eur. J. Inorg. Chem. 2012, 1445–1452
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1451

M. A. Garralda et al.
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Received: August 26, 2011
Published Online: December 14, 2011
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