Synthesis and reactivity of new rhenium(I) complexes containing iminophosphorane-phosphine ligands: Application to the catalytic isomerization of propargylic alcohols in ionic liquids

Article abstract of DOI:10.1021/ic4003687

[ReBr(CO)₅] reacts with the iminophosphorane-phosphine ligands Ph₂PCH₂P(=NR)Ph₂ (R = P(=O)(OEt)₂ (1a), P(=O)(OPh)₂ (1b), P(=S)(OEt)₂ (1c), P(=S)(OPh) ₂ (1d), 4-C₆F₄CHO (1e), 4-C₆F ₄CN (1f), 4-C₅F₄N (1g)) affording the neutral complexes [ReBr(κ²-P,X-Ph₂PCH₂P{=NP(=X) (OR)₂}Ph₂)(CO)₃] (X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph (2d)) and [ReBr{κ²-P,N-Ph ₂PCH₂P(=NR)Ph₂}(CO)₃] (R = P(=O)(OEt)₂ (3a), P(=O)(OPh)₂ (3b), 4-C₆F ₄CHO (3e), 4-C₆F₄CN (3f), 4-C₅F ₄N (3g)). The reactivity of the cationic complex [Re(κ ³-P,N,S-Ph₂PCH₂P{=NP(=S)(OPh) ₂}Ph₂)(CO)₃][SbF₆] (4d) has been explored allowing the synthesis of the cationic [Re(L)(κ²-P,S- Ph₂PCH₂P{=NP(=S)(OPh)₂}Ph₂)(CO) ₃][SbF₆] (L = acetone (5a), CH₃C≡N (5b), pyridine (5c), PPh₃ (5d)) and the neutral [ReY(κ²-P, S-Ph₂PCH₂P{=NP(=S)(OPh)₂}Ph₂)(CO) ₃] (Y = Cl (6a), I (6b), N₃ (6c)) complexes. The catalytic activity of complex 4d in the regioselective isomerization of terminal propargylic alcohols HC≡CCR¹R²(OH) into α,β-unsaturated aldehydes R¹R²C=CHCHO or ketones R³R⁴C=CR¹COMe (if R² = CHR³R⁴) under neutral conditions in ionic liquids has being studied. Isolation and X-ray characterization of the key intermediate rhenium(I) oxocyclocarbene complex [Re{=C(CH₂)₃O} (κ²-P,S-Ph₂PCH₂P{=NP(=S)(OPh) ₂}Ph₂)(CO)₃][SbF₆] (5e) seems to indicate that the catalytic reaction proceeds through tautomerization of the terminal alkynols to yield vinilydene-type species.

Full text of DOI:10.1021/ic4003687

Article
pubs.acs.org/IC
Synthesis and Reactivity of New Rhenium(I) Complexes Containing
Iminophosphorane-Phosphine Ligands: Application to the Catalytic
Isomerization of Propargylic Alcohols in Ionic Liquids
́
Joaquín García-Alvarez,* Josefina Díez, Jose Gimeno, Christine M. Seifried, and Cristian Vidal
́
Laboratorio de Compuestos Organometal
́
icos y Catal
́
isis (Unidad Asociada al CSIC), Departamento de Química Organ
́
ica e
Inorganica, Instituto Universitario de Química Organometal
́
́
ica “Enrique Moles,” Facultad de Química, Universidad de Oviedo,
E-33071, Oviedo, Spain
S
* Supporting Information
ABSTRACT: [ReBr(CO)5] reacts with the iminophosphorane−phosphine ligands Ph2PCH2P(NR)Ph2 (R = P(O)(OEt)2
(1a), P(O)(OPh)2 (1b), P(S)(OEt)2 (1c), P(S)(OPh)2 (1d), 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-C5F4N (1g))
affording the neutral complexes [ReBr(κ2-P,X-Ph2PCH2P{NP(X)(OR)2}Ph2)(CO)3] (X = O, R = Et (2a), Ph (2b); X = S,
R = Et (2c), Ph (2d)) and [ReBr{κ2-P,N-Ph2PCH2P(NR)Ph2}(CO)3] (R = P(O)(OEt)2 (3a), P(O)(OPh)2 (3b), 4-
C6F4CHO (3e), 4-C6F4CN (3f), 4-C5F4N (3g)). The reactivity of the cationic complex [Re(κ3-P,N,S-Ph2PCH2P{NP(
S)(OPh)2}Ph2)(CO)3][SbF6] (4d) has been explored allowing the synthesis of the cationic [Re(L)(κ2-P,S-Ph2PCH2P{NP(
S)(OPh)2}Ph2)(CO)3][SbF6] (L = acetone (5a), CH3CN (5b), pyridine (5c), PPh3 (5d)) and the neutral [ReY(κ2-P,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)) complexes. The catalytic activity of complex 4d in
the regioselective isomerization of terminal propargylic alcohols HCCCR1R2(OH) into α,β-unsaturated aldehydes R1R2C
CHCHO or ketones R3R4CCR1COMe (if R2 = CHR3R4) under neutral conditions in ionic liquids has being studied. Isolation
and X-ray characterization of the key intermediate rhenium(I) oxocyclocarbene complex [Re{C(CH2)3O}(κ2-P,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (5e) seems to indicate that the catalytic reaction proceeds through
tautomerization of the terminal alkynols to yield vinilydene-type species.
Ph2PCH2P(NR)Ph2 (readily accessible by selective mono-
INTRODUCTION
■
imination of bis(diphenylphosphine)methane (dppm) with
azides via Staudinger reaction)3,4 are an important class of
hemilabile ligands belonging to the wide series of those
containing phosphorus−nitrogen donor atoms.5 During the
past decade, we have used extensively the iminophosphorane−
phosphines Ph2PCH2P(NR)Ph2 (R = P(O)(OEt)2 (1a),
P(O)(OPh)2 (1b), P(S)(OEt)2 (1c), P(S)(OPh)2
(1d), 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-C5F4N (1g); see
Figure 1) as ligands in a wide series of ruthenium(II)6a−e,g and
palladium(II)6f complexes and studied their catalytic activity in
organic reactions such as the transfer hydrogenation of
The coordination chemistry of bidentate phosphines with
hemilabile properties has spurred great interest because these
ligands combine the presence of a phosphorus atom (with
strong metal bond) together with a more labile donor group
(i.e., N atom in aminophosphines or O atom in ether-
phosphines). The main feature of these heteroditopic ligands
stems from the ability of the “hard” N and O atoms to
dissociate reversibly from a “soft” metal giving rise to a free
coordination site.1 Such behavior has been exploited in
homogeneous catalysis since the formation of unsaturated
intermediate species is often favored. Closely related hemilabile
ligands are diphosphine monoxides of general formula R2P−Y−
P(O)R2 (Y = divalent bridging group), which have also been
used as ligands in a large number of efficient catalytic
transformations.2 Iminophosphorane−phosphines of the type
Received: February 12, 2013
Published: April 17, 2013
© 2013 American Chemical Society
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the regio and selective isomerization of propargylic alcohols
into α,β-unsaturated aldehydes (Meyer−Schuster rearrange-
ment)10a or ketones (Rupe rearrangement),10b using ionic
liquids as reaction media.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Neutral
Complexes [ReBr(κ2-P,X-Ph2PCH2P{NP(X)(OR)2}Ph2)-
(CO)3] (X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph
(2d)] and [ReBr(κ2-P,N-Ph2PCH2P{NR}Ph2)(CO)3] (R =
P(O)(OEt)2 (3a), P(O)(OPh)2 (3b), 4-C6F4CHO (3e), 4-
C6F4CN (3f), 4-C6F5N (3g)). As expected from our previous
results,6c the treatment of the complex [ReBr(CO)5] with an
equimolecular amount of Ph2PCH2P{NP(O)(OR)2}Ph2
(1a,b) in refluxing THF results in the formation of an
inseparable mixture of the κ2-P,O and κ2-P,N neutral complexes
[ReBr(κ2-P,O-Ph2PCH2P{NP(O)(OR)2}Ph2)(CO)3] (R
= Et (2a), Ph (2b)) and [ReBr(κ2-P,N-Ph2PCH2P{NP(
O)(OR)2}Ph2)(CO)3] (R = Et (3a), Ph (3b); see Scheme
1).11 In contrast, under the same reaction conditions but using
the N-thiophosphorylated iminophosphorane ligands 1c,d,
selective coordination of the diphenylphosphino (PPh2) and
thiophosphoryl group ((RO)2PS) to the rhenium(I) center
is achieved to afford the neutral complexes [ReBr(κ2-P,S-
Ph2PCH2P{NP(S)(OR)2}Ph2)(CO)3] (R = Et (2c), Ph
(2d)).12 Similarly, selective formation of the κ2-P,N-
iminophosphorane complexes [ReBr(κ2-P,N-Ph2PCH2P{
NRF}Ph2)(CO)3] (3e−g) also occurs by using the fluorinated
ligands 1e−g.13
Figure 1. Iminophosphorane−phosphine ligands Ph2PCH2P(
NR)Ph2 (1a−g).
ketones6b−d and the cycloisomerization of (Z)-3-methylpent-2-
en-4-yn-1-ol into 2,3-dimethylfuran.6f
Following our interest in using this type of ligand and taking
into account that ruthenium(II) and rhenium(I) are isoelec-
tronic d6 species and show analogous coordination chemistry,7
we sought the synthesis of new iminophosphorane−phosphine
rhenium(I) derivatives and explored their catalytic activity. In
this regard, we have recently reported the first series of
tricarbonyl rhenium(I) complexes 4c,d (Figure 2), which are
Compounds 2a−d and 3a,b,e−g have been isolated as air-
stable white solids in 82−96% yields. The characterization of
these complexes (see Supporting Information) was achieved by
means of standard spectroscopic techniques (1H, 31P{1H},
19F{1H}, 13C{1H} NMR and IR) as well as elemental analyses.
In particular, IR spectra show the presence of three ν(CO)
absorptions at 1887−2026 cm−1 in accordance with the fac-
arrangement of the three carbonyl ligands. 31P{1H} NMR
spectra allow the coordination mode adopted by the
iminophosphorane−phosphine ligand in 2, 3a,b to be
distinguished (see Experimental Section). Thus, for 3a,b the
κ2-P,N coordination is reflected in an important downfield shift
of both the PPh2 (ΔδP ca. 27 ppm) and Ph2PN (ΔδP ca. 40
ppm) signals with respect to those found in the free ligands
1a−b,6c while the κ2-P,O coordination in complexes 2a,b is
revealed in (i) an appreciable downfield shift only in the PPh2
(ΔδP ca. 27 ppm) signals and (ii) a slightly downfield shift for
resonances of the (RO)2PO signal (ΔδP ca. 5 ppm), in
comparison with those found in the free ligands 1a,b,6c
confirming the direct involvement of these groups in the
bonding to the metallic center. Concerning complexes 2c,d,
downfield shifts are also observed for the Ph2P signals with
respect to the free iminophosphorane−phosphine ligands 1c,d
(ΔδP ca. 26 ppm).6d This fact along with the slight high-field
shifting of the (RO)2PS resonances (ΔδP ca. 4 ppm, similar
to those previously observed in the S-coordination of the unit
-PN−P(=S)(OR)2 to Au(I),14 Ag(I),15 Cu(I),16 Ru(II),17
and Pd(II)18 fragments), allows us to propose that, in this case,
rhenium complexation takes place selectively on the (RO)2P
S vs Ph2PN groups. Finally, for complexes 3e−g, selective κ2-
P,N coordination of the PPh2 (ΔδP ca. 37 ppm) and Ph2PN
Figure 2. Structure of the rhenium(I) complexes containing
iminophosphorane−phosphine ligands 1a−g.
highly active catalysts in the isomerization of propargylic
alcohols into α,β-unsaturated carbonyl compounds in THF.8,9
Thus, continuing with these studies, herein we report a new
family of rhenium(I) derivatives containing iminophosphorane-
phosphine ligands, namely, complexes 2a−d, 3a−b,e−g, 5a−e
and 6a−c (Figure 2). The following features can be remarkable:
(i) First is the synthesis of complexes 5a−d and 6a−c (Figure
2), obtained by the reaction of the hemilabile complex 4d with
monodentate neutral and anionic ligands, respectively, which
proceeds through a change of the coordination mode from k3-
P,N,S into k2-P,S. (ii) Next is the synthesis of the cationic
oxacyclic−carbene complex 5e, obtained from the reaction of
complex 4d with the alkynol HCC−CH2−CH2OH, via the
formation of an intermediate hydroxyvinylidene complex
[Re]+CC(H)CH2(OH) and followed by the intramolec-
ular nucleophilic addition of the OH group to the carbenic
carbon atom. This process sheds light on the proposed
mechanism of the catalytic isomerization of propargylic
alcohols. (iii) The high catalytic activity of complexes 4c,d in
1
(ΔδP ca. 40 ppm) groups is observed. H and 13C{1H} NMR
spectra exhibit signals in accordance with the proposed
formulations, the most significant features being those
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Scheme 1. Synthesis of the Neutral Re(I) Complexes 2−3
concerning the methylenic PCH2P group of the ligands 1a−g:
1
(i) in the H NMR, two unresolved multiplet signals at 3.40−
5.88 ppm for 2a−d and 3a,b,e−g and (ii) in the 13C{1H}
NMR, a characteristic doublet of doublets in the range of
22.90−28.35 ppm (JCP = 79.4−10.8 Hz) for 3b,e-g and 2c,d; a
doublet of doublets of doublets at 33.11 ppm (JCP = 78.7 and
3
12.9 Hz, JCP = 9.6 Hz) for 2b; and one unresolved multiplet
signal at 30.08 ppm for the mixture of compounds 2,3a.
Moreover, the structure of the complex [Re(κ2-P,N-
Ph2PCH2P{N(4-C6F4CHO)}Ph2)(CO)3] (3e) was unam-
biguously confirmed by means of a single-crystal X-ray
diffraction study. An ORTEP-type view of the molecule is
shown in Figure 3; selected bond distances and angles are listed
in the caption. The geometry around the metal is slightly
distorted octahedral (see values of the P(2)−Re−N(1), P(2)−
Re−Br(1), N(1)−Re−Br(1), and those containing the C atoms
of the carbonyl ligands), being bonded to three carbon
monoxide molecules, the nitrogen atom of the iminophosphor-
anyl group, the phosphorus atom of the diphenylphosphino
unit, and a bromine atom. The Re−P(2), Re−N(1), and Re−
Br(1) bond distances in complex 3e are in a good agreement
with those previously described for other tricarbonyl−Re(I)
complexes containing iminophosphorane−phosphine ligands
(Re−P = 2.453(3) Å; Re−N = 2.20(1) Å; Re−Br = 2.548(2)
Å).9
Figure 3. ORTEP-type view of the structure of the complex [ReBr(κ2-
P,N-Ph2PCH2P{N(4-C6F4CHO)}Ph2)(CO)3] (3e) showing the
crystallographic labeling scheme. Hydrogen atoms are omitted for
clarity. Thermal ellipsoids are drawn at the 20% probability level.
Selected bond lengths (Å) and angles (deg): Re−P(2) = 2.477(2);
Re−N(1) = 2.268(5); Re−Br(1) = 2.622(1); Re−C(1) = 1.87(1);
Re−C(2) = 1.96(1); Re−C(3) = 1.892(9); P(2)−C(4) = 1.857(7);
C(4)−P(1) = 1.788(7); P(1)−N(1) = 1.614(5); P(2)−Re−N(1) =
83.5(1); P(2)−Re−Br(1) = 83.12(5); N(1)−Re−Br(1) = 85.4(1);
C(1)−Re−C(2) = 89.2(4); C(2)−Re−C(3) = 88.9(3); C(1)−Re−
C(3) = 88.7(4); C(3)−Re−Br(1) = 176.3(2).
Reactivity of the Cationic Complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) toward
Neutral and Anionic Ligands. We have recently reported
that the high catalytic activity of complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) in
the isomerization of propargylic alcohols into carbonyl
derivatives stems from the lability of the Re−N bond, giving
rise to the κ2-P,S coordination mode of the ligand.8 This fact
provides the required free coordination site on the metal
allowing the coordination of the propargylic CC bond. In
order to assesses the generality of this behavior, we set out the
synthesis of κ2-P,S iminophosphorane complexes 5a−d by the
reaction of complex 4d with two electron ligands.19
(CO)3][SbF6] (L = Me2CO (5a), CH3CN (5b), pyridine (5c),
PPh3 (5d)). We found that just by dissolving the cationic
complex 4d in acetone, the solvato-complex [Re(κ1-O-Me2C
O)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6]
(5a) was readily obtained as inferred by its 31P{1H} NMR
spectrum (shielding in the Ph2PN group resonance of ca. 35
ppm was observed, see Experimental Section), which clearly
indicates the selective cleavage of the Re−N bond and
concomitant coordination of the acetone to the rhenium
center (see Scheme 2). All attempts to isolate this solvato
complex failed, leading instead to its precursor 4d quantitatively
after evaporation of the solvent. The reversibility of this process
evidences clearly the hemilability of the PN unit in complex
a. Synthesis and Characterization of the Cationic
Complexes [Re(L)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)-
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of the molecular structure is depicted in Figure 4. The rhenium
atom is in a slightly distorted octahedral environment, being
Scheme 2. Reactivity of Complex 4d Towards Neutral and
Anionic Ligands
Figure 4. ORTEP-type view of the structure of the cation [Re(κ1-N-
NCCH3)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]+ of 5b
showing the crystallographic labeling scheme. Hydrogen atoms are
omitted for clarity, and only the ipso-carbons of the phenyl rings are
shown. Thermal ellipsoids are drawn at the 20% probability level.
Selected bond lengths (Å) and angles (deg): Re−P(1) = 2.469(3);
Re−N(2) = 2.138(9); Re−S(1) = 2.553(3); Re−C(1) = 1.89(1); Re−
C(2) = 1.91(2); Re−C(3) = 1.91(1); P(1)−C(4) = 1.83(1); C(4)−
P(2) = 1.836(9); P(2)−N(1) = 1.587(9); N(1)−P(3) = 1.556(9);
P(3)−S(1) = 1.978(4); N(2)−C(41) = 1.14(1); C(41)−C(42) =
1.47(2); N(2)−Re−P(1) = 87.4(3); N(2)−Re−S(1) = 80.5(3);
P(1)−Re(1)−S(1) = 89.45(9); C(1)−Re−C(2) = 87.2(5); C(1)−
Re−C(3) = 88.4(5); C(2)−Re−C(3) = 90.2(6); Re−C(1)−O(1) =
174.0(9); Re−C(2)−O(2) = 173.1(9); Re−C(3)−O(3) = 178.1(9);
Re−N(2)−C(41) = 177.0(1).
bonded to three carbon monoxide molecules, the sulfur atom of
the N-thiophosphorylated group, the phosphorus atom of the
diphenylphosphino unit, and the nitrogen atom of the
acetonitrile ligand. As expected, all the carbon monoxide
ligands and the acetonitrile molecule are bounded to rhenium
in a nearly linear fashion [Re−C−O and Re−N−C angles
within the range 173.1(9)−178.0(9)°], with metal carbon
distances (Re−C) of 1.89(1)−1.92(2) Å and a Re−N bond
length of 2.138(9) Å. These bonding parameters fit well with
those reported in the literature for other tricarbonyl−
acetonitrile−rhenium(I) complexes.9a Both Re−P(1)
(2.469(3) Å) and Re−S(1) (2.553(3) Å) distances are in
good agreement with those found in complex 4c.8
4d.20 In contrast, for other neutral ligands such as acetonitrile
(5b), pyridine (5c), or triphenylphosphine (5d), a lack of
reversibility in the Re−N bond cleavage was observed. The
results obtained are summarized in Scheme 2. Complexes 5b−
d, isolated as air-stable white solids in 92−98% yields, formally
result from the opening of the κ2-P,N chelate ring and
concomitant coordination of the corresponding two-electron
ligand to rhenium, while the Re−S bond remains intact.
Characterization of complexes 5b−d was straightforward,
following their analytical and spectroscopic data (details are
given in the Experimental Section and the Supporting
Information). In particular, the κ2-P,S coordination of the N-
thiophosphorylated ligand is fully supported by the 31P{1H}
NMR (see Experimental Section), and as previously seen for
the unstable solvato complex 5a, a remarkable shielding in the
Ph2PN group resonance (δP 14.79−16.23 ppm) with respect
to that shown by the parent compound 4d (δP 50.13 ppm) was
observed. In contrast, the diphenylphosphino Ph2P and
thiophosphoryl (EtO)2PS units are considerably less affected
by the coordination of the incoming ligand (δP −1.13−4.02 vs
13.46 ppm; and 43.10−44.91 vs 50.13 ppm, respectively).
Moreover, the structure of the acetonitrile adduct [Re(κ1-N-
NCCH3)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]-
[SbF6] (5b) was unambiguously determined by means of a
single-crystal X-ray diffraction study. An ORTEP-type drawing
b. Synthesis and Characterization of the Neutral
Complexes [ReY(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)-
(CO)3] (Y = Cl (6a), I (6b), N3 (6c)). The ability shown by
the iminophosphorane Ph2PN unit in complex 4d to be
displaced by neutral ligands prompted us to study the lability of
the Re−N bond but using, in this case, anionic ligands. The
results obtained with typical anionic ligands such as Cl−, I−, and
−
N3 are summarized in Scheme 2. Thus, we found that the
treatment of dichloromethane solutions of 4d with an excess
(ca. 10 equiv., see Scheme 2) of the corresponding sodium salts
NaCl, NaI, and NaN3, at room temperature, results in the
selective formation of complexes [ReY(κ2-P,S-Ph2PCH2P{
NP(S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)),
via selective Re−N bond cleavage. Complexes 6a−c could be
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isolated in pure form in 94−97% yield and were analytically and
spectroscopically characterized (see Experimental Section and
Supporting Information). The bidentate κ2-P,S coordination of
the iminophosphorane−phosphine ligand 1d was clearly
evidenced by the 31P{1H} spectrum, showing characteristic
doublet signals at ca. 15 ppm assigned to the noncoordinated
Ph2PN unit (see Experimental Section).
pounds,23,24 efforts devoted to developing catalytic systems
able to operate in nonconventional solvents, like ionic liquids,
have been scare. In fact, only a very limited number of catalysts
active in the Meyer−Schuster rearrangement of propargylic
alcohols have been described up to now in the literature using
ionic liquids as a solvent.8,25 In this sense, and to prove the
catalytic potential of complexes 2a−d, 3a,b,e−g, and 4c,d, we
decided to evaluate their catalytic activity in the isomerization
of the commercially available 1,1-diphenyl-2-propyn-1-ol (7a)
into 3,3-diphenylpropenal (8a) in ionic liquids as a model
reaction (see Scheme 3). Thus, in a typical experiment, the
The structure of complex [ReCl(κ2-P,S-Ph2PCH2P{
NP(S)(OPh)2}Ph2)(CO)3] (6a) was unambiguously con-
firmed by means of a single-crystal X-ray diffraction study. An
ORTEP-type view of the molecule is shown in Figure 5;
Scheme 3. Re(I)-Catalyzed Isomerization of 1,1-Diphenyl-2-
propyn-1-ol (7a) into 3,3-Diphenylpropenal (8a) in
a
[BMIM][PF6]
a
Reactions were performed under a N2 atmosphere at 80 °C, using 1
mmol of the alkynol 7a. [Substrate]/[Re] ratio =100:5.
corresponding Re(I) precursor (5 mol % of Re) was added to a
solution of the propargylic alcohol 7a in [BMIM][PF6] (BMIM
= 1-butyl-3-methylimidazolium) at 80 °C, the course of the
reaction being monitored by gas chromatography.26 The
catalytic activity of all complexes (2a−d, 3a,b,e−g, and 4c,d)
was checked, but only the cationic complexes [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OR)2}Ph2)(CO)3][SbF6] (R = Et
(4c), Ph (4d)) were found to be active leading to the selective
isomerization to the enal 8a as the unique reaction product.
These results are in accord with the hemilabile behavior of
complexes 4c,d in contrast to the inertness of the rest of the
complexes toward the isomerization of the propargylic alcohol.
The best result was obtained for complex 4d, which led to the
enal 8a in quantitative yield (99%) after only 10 min of reaction
vs 15 min of reaction for complex 4c. For comparison, only
73% isomerization of the alkynol 7a into the corresponding
enal 8a was achieved with the catalyst 4d in a 5 mol % loading
at 80 °C using conventional organic solvent (THF) after 24 h.8
As observed for 1,1-diphenyl-2-propyn-1-ol (entry 1, Table
1), complex 4d was also found to be an efficient catalyst for the
selective isomerization of other tertiary (entries 2−5, Table 1)
and secondary (entry 6, Table 1) propargylic alcohols to the
corresponding enals. It is important to note that all reactions
proceeded to completion in the absence of any cocatalyst.
Influence of the electronic properties of the aryl rings on the
reaction rates was observed. Thus, alkynols with electron-
withdrawing groups showed less reactivity (entries 2,3) as
compared to the substrates with electron-donating groups
(entries 4,5). Interestingly, for the secondary alcohol 1-phenyl-
1-propyn-1-ol (7f), the resulting enal 8f was exclusively
obtained as the thermodynamically more stable E isomer.27
Nowadays it is well-known that one of the most important
advantages associated with the use of ionic liquids as a solvent
is the possibility of recycling the catalytic system by separation
of the product of the catalytic reaction with a simple process of
extraction with organic solvents.22a In addition, the lifetime and
the level of reusability are very important factors for any
catalytic system.28 In this sense, we have studied the
recyclability of catalyst 4d in the isomerization of the
Figure 5. ORTEP-type view of the structure of the complex [ReCl(κ2-
P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3] (6a) showing the
crystallographic labeling scheme. Hydrogen atoms are omitted for
clarity, and only the ipso-carbons of the phenyl rings are shown.
Thermal ellipsoids are drawn at the 20% probability level. Selected
bond lengths (Å) and angles (deg): Re−P(1) = 2.494(4); Re−Cl(1) =
2.484(4); Re−S(1) = 2.532(4); Re−C(1) = 1.91(2); Re−C(2) =
1.99(2); Re−C(3) = 1.94(2); P(1)−C(4) = 1.84(2); C(4)−P(2) =
1.79(2); P(2)−N(1) = 1.58(1); N(1)−P(3) = 1.56(1); P(3)−S(1) =
1.977(6); Cl(1)−Re−P(1) = 81.3(1); Cl(1)−Re−S(1) = 81.6(2);
P(1)−Re(1)−S(1) = 95.7(1); C(1)−Re−C(2) = 87.5(8); C(1)−Re−
C(3) = 89.4(8); C(2)−Re−C(3) = 85.6(7); Re−C(1)−O(1) =
178.6(2); Re−C(2)−O(2) = 175.1(2); Re−C(40)−O(5) = 178.0(2).
selected bond distances and angles are listed in the caption.
The geometry around the metal is slightly distorted octahedral,
the Re−C, Re−P, and Re−S bond distances and interligand
angles fitting well with those previously observed by us in
complex 5b, both containing the κ2-P,S coordinated imino-
phosphorane−phosphine ligand 1d. The Re−Cl bond distance
(2.483(4) Å) is in a good agreement with those previously
described for other tricarbonyl−Re(I) complexes.21
Catalytic Isomerization of Propargylic Alcohols into
α,β-Unsaturated Carbonyl Compounds in Ionic Liquids.
Over the past decade, there has been increasing interest in
searching for new catalytic approaches using nonconventional
solvents as reaction media. In this sense, a large number of
organometallic catalysts have been successfully applied to a
variety of organic transformations using water, supercritical
CO2, ionic liquids, glycerol, perfluorinated compounds, and
low-boiling point polymers as alternative solvents to volatile
organic solvents (VOCs).22 However, and despite the growing
interest in the study of the metal-catalyzed isomerization of
propargylic acids into α,β-unsaturated carbonyl com-
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Article
h and with yields of 82−99% (TON 115). These data clearly
reveal that the catalytic system suffered a gradual decrease of
the activity after each recycling for all the substrates used
(propargylic alcohols 7a−f). Thus, in all cases, for the first
cycles (see Supporting Information) less than 1 h was needed
to achieve quantitative conversion, while more than 9 h for the
last cycle was always required, probably due to both leaching
during the workup and decomposition of the catalyst.
Table 1. Isomerization of Propargylic Alcohols 7a−f into
Enals 8a−f Catalyzed by Complex 4d Using [BMIM][PF6]
a
As Solvent
The catalytic activity of complex 4d was then tested in the
isomerization of propargylic alcohols which contain a C−H
bond in the β-position with respect to the alcohol group (9a,b),
which proceeds in a different way, giving rise to the selective
formation of α,β-unsaturated methyl ketones (10a,b) as the
result of a formal Rupe-type rearrangement of the alkynol (see
Table 2).29 A quantitative transformation is also achieved
although (i) a higher temperature with respect to the
aforementioned Meyer−Schuster rearrangement (130 vs 80
°C) and (ii) a longer reaction time were needed (see Table 1).
The catalyst 4d could be also recycled but remains active
through a lower number of consecutive runs, i.e., for 9a [first
cycle, 3 h (96%); second cycle, 14.5 h (93%); third cycle, 48 h
(46%)]; for 9b [first cycle, 1.5 h (99%); second cycle, 3.5 h
(99%); third cycle, 5 h (98%); fourth cycle, 20 h (97%)]. This
catalytic transformation can also be applied successfully to a
more elaborated substrate such as the hormonal steroid
mestranol (9c, entry 3, Table 2). The corresponding enone
10c, which is an important building block in the chemistry of
steroids, has been obtained selectively in a pure form with
excellent yield (99%). Unfortunately, the catalytic activity of 4d
with mestranol remained active for only one further cycle
(quantitative transformation after 10 h) and without the
formation of byproducts (GC or NMR spectra).
GC yield
time [%], isolated
entry
R1
R2
product [min]
(%)
1
2
3
4
5
6
Ph
Ph
8a
8b
8c
8d
8e
8f
10
15
30
10
5
99(91)
97(94)
99(92)
99(94)
97(94)
99(93)
p-F(C6H4)
p-Cl(C6H4)
p-MeO(C6H4)
p-Me(C6H4)
H
p-F(C6H4)
p-Cl(C6H4)
p-MeO(C6H4)
p-Me(C6H4)
Ph
15
a
Reactions were performed under a N2 atmosphere at 80 °C, using 1
mmol of the corresponding alkynol in 1 g of [BMIM][PF6] and with a
catalyst loading of 5 mol % in Re.
propargylic alcohols 8a−f, using [BMIM][PF6] as a solvent
under the same catalytic conditions described in Table 1.
Catalyst 4d was recycled up to (see Supporting Information):
(i) 10 consecutive runs for 7a, with reaction times from 10 min
to 10 h and with yields of 96−99% (accumulative TON 200);
(ii) nine consecutive runs for 7b, with reaction times from 15
min to 18 h and with yields of 96−99% (accumulative TON
176); (iii) six consecutive runs for 7c, with reaction times from
30 min to 9 h and with yields of 95−99% (accumulative TON
118); (iv) nine consecutive runs for 7d, with reaction times
from 10 min to 9 h and with yields of 92−99% (TON 175); (v)
10 consecutive runs for 7e, with reaction times from 5 min to 9
h and with yields of 94−99% (TON 195); and (vi) six
consecutive runs for 7f, with reaction times from 15 min to 10
When internal propargylic alcohols such as PhCCC(OH)-
Ph2 or MeCCCH2(OH) were used as substrates, no
transformation was observed (polymerization is observed with
Table 2. Isomerization of Propargylic Alcohols 9a−c into α,β-Unsaturated Ketones 10a−c Catalyzed by Complex 4d in
a
[BMIM][PF6].
a
Reactions were performed under a N2 atmosphere at 130 °C, using 1 mmol of the corresponding alkynol in 1 g of [BMIM][PF6] and with a catalyst
loading of 5 mol % in Re.
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Scheme 4. Synthesis of the Cationic Tricarbonyl Re(I) Oxacyclic Carbene Complex 5e
the primary propargylic alcohol HCCCH2OH). The absence
of catalytic activity with internal alkynols is in accord with the
proposed catalytic mechanism which seems to be based on the
key intermediate hydroxyvinylidene complex [Re]+C
C(H)C(OH)R2.30 As is well-known, only terminal alkynols
are able to undergo tautomerization to yield vinilydene-type
species.31 In order to assess the formation of the required
intermediate rhenium(I) hydroxyvinylidene complex, the
stoichiometric reaction of catalyst 4d with various alkynols
was carried out in [BMIM][PF6]. Unfortunately, all attempts to
isolate or characterize the reaction product have been
unsuccessful. In contrast, when the reaction of complex 4d
with 3-butyn-1-ol (see Scheme 4) was performed in refluxing
THF instead of the ionic liquid, the new Re-oxocyclocarbene
complex [Re{C(CH2)3O}(κ2-P,S-Ph2PCH2P{NP=S)-
(OPh)2}Ph2)(CO)3][SbF6] (5e) was selectively obtained.
This carbene results from the well established intramolecular
attack of the hydroxyl group on the α-carbon of the vinylidene
intermediate complex (Scheme 4).32 The rhenium(I)−
oxacyclocarbene 5e was characterized by multinuclear NMR
Figure 6. ORTEP-type view of the structure of the cation [Re{
C(CH2)3O}(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]+ of
5e showing the crystallographic labeling scheme. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are drawn at the 20%
probability level. Selected bond lengths (Å) and angles (deg): Re−
P(1) = 2.461(1); Re−C(41) = 2.121(5); Re−S(1) = 2.574(1); Re−
C(1) = 1.964(5); Re−C(2) = 1.979(5); Re−C(3) = 1.909(5); P(1)−
C(4) = 1.847(4); C(4)−P(2) = 1.816(4); P(2)−N(1) = 1.592(3);
N(1)−P(1) = 1.570(4); P(3)−S(1) = 1.991(2); P(1)−Re−S(1) =
88.34(3); P(1)−Re−C(41) = 89.3(12); S(1)−Re(1)−C(41) =
85.69(13); C(2)−Re−C(41) = 176.75(18); C(1)−Re−C(41) =
89.46(19); C(3)−Re−C(41) = 89.56(19).
(1H, 31P{1H}, and 13C{1H}, see Experimental Section and
1
Supporting Information). In particular, H and 13C{1H} NMR
spectra display the expected signals for the metalacycle
fragment: (i) four proton resonances for the six protons of
the five-membered ring appearing as multiplets at 4.56 ppm
(2H), 3.09 and 2.70 (1H each), and 1.59 (2H) ppm and (ii)
three carbon resonances at 20.07, 60.88, and 88.91 ppm, for the
four carbon atoms of the five-membered ring along with a
doublet of doublet signal at 305 (JCP = 8.6 and 8.5 Hz) ppm,
indicating the presence of the carbene ReC bound.32 In
addition, the 31P{1H} spectrum displays the expected signals for
a κ2-P,S coordination of the iminophosphorane−phosphine
ligand 1d (see Experimental Section).
Moreover, the structure of cationic tricarbonyl−rhenium(I)
oxacyclic carbene complex 5e was unambiguously confirmed by
means of a single-crystal X-ray diffraction study. An ORTEP-
type view of the molecule is shown in Figure 6; selected bond
distances and angles are listed in the caption. Again, the
geometry around the metal is slightly distorted octahedral (see
values in caption of Figure 6), the Re−CO, Re−P, and Re−S
bond distances and interligand angles fitting well with those
previously observed by us in complexes 5b and 6a, both
containing the κ2-P,S coordinated iminophosphorane−phos-
phine ligand 1d. The ReC bond distance (2.121(5) Å) is
equal to that previously described for an analogous Re-
cycloxycarbene complex (2.121(9) Å).32 The isolation of 5e is
in accord with the formation of hydroxyvinylidene species as
key intermediates in the ruthenium catalyzed rearrangement of
propargylic alcohols into α,β-unsaturated carbonyl compound-
s.27a The absence of reaction with internal alkynols which are
not able to form vinylidene species, and the fact that the
catalytic reactions do not proceed without the presence of the
catalyst 4d in the ionic liquid at 80 °C, points to the classic
mechanism based on the π-coordination of the propargylic
alcohol and subsequent formation of vinylidene complex via a
[1,2]-shift.33,34
CONCLUSION
■
In summary, in the present work we have described the high-
yield synthesis of a series of new tricarbonyl rhenium(I)
complexes containing the iminophosphorane−phosphine li-
gands Ph2PCH2P(NR)Ph2 (1a−g), which show a versatile
coordination ability: (a) κ2-P,O- in complexes [ReBr(κ2-P,O-
Ph2PCH2P{NP(O)(OR)2}Ph2)(CO)3] (R = Et (2a), R =
Ph (2b)), (b) κ2-P,S- in complexes [ReBr(κ2-P,S-Ph2PCH2P{
NP(S)(OR)2}Ph2)(CO)3] (R = Et (2c), Ph (2d)); (c) κ2-
P,N- in complexes [ReBr(κ2-P,N-Ph2PCH2P{NR}Ph2)-
(CO)3] (R = P(O)(OEt)2 (3a), P(O)(OPh)2 (3b), 4-
C6F4CHO (3e), 4-C6F4CN (3f), 4-C6F5N (3g)), and (d) κ3-
P,N,S- in complexes [Re(κ3-P,N,S-Ph2PCH2P{NP(S)-
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Ph2PCH2P(NRF)Ph2 (RF = 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-
C6F5N (1g)) the neutral complexes 3e−g were selectively obtained in
91% (0.421 g), 87% (0.401 g), and 93% (0.418 g) yields, respectively.
For the N-thiophosphorylated ligands 1c,d, the neutral complexes 2c,d
were selectively obtained in 94% (0.423 g) and 96% (0.479 g) yields,
respectively. 31P{1H} NMR signals for 2a in (CD3)2SO: 0.59 (s,
(OR)2}Ph2)(CO)3][SbF6] (R = Et (4c), R = Ph (4d)).
Furthermore, the potential hemilabile properties of ligand 1d
have been proven in the reactivity of the cationic complex
[Re(κ3-P,N,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]-
[SbF6] (4d), which reacts under very mild reaction conditions
(via selective cleavage of the Re−N bond in the κ3-P,N,S
chelating ring) with the appropriate neutral (L) or anionic (Y−)
ligand to afford, respectively, the cationic derivatives [Re(L)(κ2-
P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (L =
Me2CO (5a), CH3CN (5b), pyridine (5c), PPh3 (5d))
and the neutral derivatives [ReY(κ2-P,S-Ph2PCH2P{NP(
S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)), in
excellent yields.
2
2
PPh2), 7.45 (d, JPP = 41.6 Hz, P(O)(OEt)2), 8.90 (d, JPP = 41.6
Hz, Ph2PN). For 2b 31P{1H} NMR (CD2Cl2): −4.18 (d, 2JPP = 45.8
2
Hz, P(O)(OPh)2), 0.93 (s, PPh2), 9.64 (d, JPP = 45.8 Hz, Ph2P
3
N). For 2c 31P{1H} NMR (CD2Cl2): −5.12 (d, JPP = 6.0 Hz, PPh2),
2
13.38 (d, 2JPP = 30.5 Hz, Ph2PN), 57.04 (dd, JPP = 30.5 Hz, 3JPP
=
6.0 Hz, P(S)(OEt)2). For 2d 31P{1H} NMR (CD2Cl2): −5.23 (d,
3JPP = 7.1 Hz, PPh2), 14.37 (d, JPP = 27.8 Hz, Ph2PN), 48.95 (dd,
2
2JPP = 27.8 Hz, JPP = 7.1 Hz, P(S)(OPh)2). For 3a 31P{1H} NMR
3
2
3
In addition, the cationic complex [Re(κ3-P,N,S-Ph2PCH2P-
{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) is a highly
efficient catalyst for the isomerization of terminal propargylic
alcohols into enals (Meyer−Schuster rearrangement) or enones
(Rupe rearrangement) using the ionic liquid [BMIM][PF6] as
nonconventional media. The isolation and X-ray character-
ization of the rhenium(I) oxacyclocarbene complex [Re{
C(CH2)3O}(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)-
(CO)3][SbF6] (5e) obtained from the intramolecular attack of
the hydroxyl group on the α-carbon of the vinylidne
intermediate complex is also reported. The isolation of complex
5e is in accord with the formation of hydroxyvinylidene species
as key intermediates in ruthenium catalyzed rearrangement of
propargylic alcohols into α,β-unsaturated carbonyl compounds.
(CD2Cl2): 9.00 (dd, JPP = 14.4 Hz, JPP = 7.9 Hz, P(O)(OEt)2),
11.89 (dd, 2JPP = 32.7 Hz, 3JPP = 7.9 Hz, PPh2), 54.82 (dd, 2JPP = 32.7
and 14.4 Hz, Ph2PN). For 3b 31P{1H} NMR (CD2Cl2): 0.36 (dd,
2JPP = 17.8 Hz, 3JPP = 8.3 Hz, P(O)(OPh)2), 10.81 (dd, 2JPP = 32.2
3
2
Hz, JPP = 8.3 Hz, PPh2), 55.49 (dd, JPP = 32.2 and 17.8 Hz, Ph2P
N). For 3e 31P{1H} NMR (CD2Cl2): 10.31 (d, 2JPP = 32.7 Hz, PPh2),
49.21 (d, 2JPP = 32.7 Hz, Ph2PN). For 3f 31P{1H} NMR (CD2Cl2):
2
2
10.83 (d, JPP = 35.7 Hz, PPh2), 52.07 (d, JPP = 35.7 Hz, Ph2PN).
For 3g 31P{1H} NMR ((CD3)2SO): 10.80 (d, JPP = 35.7 Hz,
2
2
PPh2), 51.67 (d, JPP = 35.7 Hz, Ph2PN).
[Re(κ1-O-Me2CO)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)-
(CO)3][SbF6] (5a). A solution of the cationic complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) (0.576 g, 0.5
mmol) in acetone (30 mL) was stirred at room temperature for 1 min,
and the solvate complex 5a was immediately obtained in quantitative
NMR yield (deuterated acetone was added to the sample to get the
lock signal for the NMR measurement). Evaporation to dryness results
in the regeneration of the precursor complex 4d. 31P{1H} NMR
((CD3)2CO): 10.80 (s, PPh2), 15.45 (d, 2JPP = 30.7 Hz, Ph2PN),
[Re(κ1-N-NCCH3)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]-
[SbF6] (5b). A solution of the cationic complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) (0.576 g,
0.5 mmol) in acetonitrile (30 mL) was stirred at room temperature
for 15 min and then evaporated to dryness. The resulting white oil was
washed with diethyl ether (3 × 20 mL), affording a white solid which
was vacuum-dried (97%, 0.580 g). 31P{1H} NMR (CD2Cl2): 4.02 (s,
EXPERIMENTAL SECTION
■
General Comments. The manipulations were performed under an
atmosphere of dry nitrogen using vacuum-line and standard Schlenck
techniques. All reagents were obtained from commercial suppliers and
used without further purification with the exception of compounds
2
43.83 (d, JPP = 30.7 Hz, P(S)(OPh2)).
Ph2PCH2P{NP(X)(OR)2}Ph2 (X = O, R = Et (1a), Ph (1b);6c
X
= S, R = Et (1c), Ph (1d)6d), Ph2PCH2P(NRF)Ph2 (RF = 4-
C6F4CHO (1e), 4-C6F4CN (1f), 4-C6F5N (1g)),6b,13 and [ReBr-
(CO)5],35 which were prepared by following methods reported in the
literature. Propargylic alcohols 7a−f and 9a−c were obtained from
commercially suppliers or synthesized by following the classical
Midland’s procedure.36 Infrared spectra were recorded on a Perkin-
Elmer 1720-XFT spectrometer. The C, H, and N analyses were carried
out with a Perkin-Elmer 2400 microanalyzer. NMR spectra were
recorded on a Bruker DPX300 instrument at 300 MHz (1H), 121.5
MHz (31P), or 75.4 MHz (13C) using SiMe4 or 85% H3PO4 as
standards. DEPT experiments have been carried out for all the
compounds reported in this paper. GC measurements were made on
Hewlett−Packard HP6890 chromatograph equipped with an HP-
INNOWAX cross-linked poly(ethyleneglycol) (30 m, 250 mm) or
Supelco Beta-Dex 120 (30 m, 250 mm) column. GC/MS measure-
ments were performed on Agilent 6890N equipment coupled to a
5973 mass detector (70 eV electron impact ionization) using a HP-
1MS column.
2
2
PPh2), 15.45 (d, JPP = 31.7 Hz, Ph2PN), 44.91 (d, JPP = 31.7 Hz,
P(S)(OPh2)).
[Re(L)(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (L =
pyridine (5c), PPh3 (5d)). A solution of the cationic complex
[Re(κ3-P,N,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6]
(4d) (0.576 g, 0.5 mmol) and the appropriate two electron ligand (5
mmol) in dichloromethane (30 mL) was stirred at room temperature
for the indicated time. The solution was then concentrated to ca. 2 mL,
and diethyl ether was added, yielding a yellow microcrystallyne solid
which was washed with diethyl ether (3 × 20 mL) and vacuum-dried.
(5c) Reaction time: 10 h. Yield 98% (0.604 g). 31P{1H} NMR
2
(CD2Cl2): 5.72 (s, PPh2), 14.79 (d, JPP = 31.7 Hz, Ph2PN), 43.10
2
(d, JPP = 31.7 Hz, P(S)(OPh2)). (5d) Reaction time: 2 h. Yield
92% (0.651 g). 31P{1H} NMR (CD2Cl2): −10.22 (m, PPh3), −1.13
(m, PPh2), 16.23 (m, Ph2PN), 44.52 (m, P(S)(OPh2)).
Preparations. [ReBr(κ2-P,X-Ph2PCH2P{NP(X)(OR)2}Ph2)(CO)3]
(X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph (2d)] and [ReBr(κ2-
P,N-Ph2PCH2P(NR)Ph2)(CO)3] (R = P(O)(OEt)2 (3a), P(O)-
(OPh)2 (3b), 4-C6F4CHO (3e), 4-C6F4CN (3f), 4-C6F5N (3g)). A solution
of the Re(I) precursor [ReBr(CO)5] (0.203 g, 0.5 mmol) and the
corresponding iminophosphorane−phosphine ligand 1a−g (0.5
mmol) in 30 mL of THF was stirred at refluxing temperature for 8
h. The solution was then concentrated to ca. 2 mL, and hexane (30
mL) was added, yielding a white microcrystalline solid which was
washed with diethyl ether (3 × 20 mL) and vacuum-dried. Starting
from the N-phosphorylated ligands 1a,b, in both cases, an inseparable
mixture containing complexes 2a and 3a in a 3:2 ratio in 82% yield
(0.363 g) for 1a and an inseparable mixture containing complexes 2b
and 3b in a 1:1 ratio in 92% yield (0.451 g) for 1b was obtained,
respectively. In contrast, starting from the aryl-fluorinated ligands
[Re{C(CH2)3O}(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3]-
[SbF6] (5e). A solution of the cationic complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) (0.576 g,
0.5 mmol) and but-3-yn-1-ol (0.038 mL, 0.5 mmol) in THF (30
mL) was stirred at refluxing temperature for 5 h. The solution was
then concentrated to ca. 2 mL, and hexane was added, yielding a white
microcrystallyne solid which was washed with diethyl ether (3 × 20
mL) and vacuum-dried. Yield 89% (0.545 g). 31P{1H} NMR
2
(CD2Cl2): −2.15 (s, PPh2), 16.11 (d, JPP = 32.6 Hz, Ph2PN),
[ReY(κ2-P,S-Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I
(6b), N3 (6c)). A solution of the cationic complex [Re(κ3-P,N,S-
Ph2PCH2P{NP(S)(OPh)2}Ph2)(CO)3][SbF6] (4d) (0.576 g, 0.5
mmol) and the appropriate sodium salt NaX (5 mmol) in
2
49.13 (d, JPP = 32.6 Hz, P(S)(OPh2)).
5435
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Inorganic Chemistry
Article
dichloromethane (30 mL) was stirred at room temperature for one
hour. The suspension was filtered through Kieselghur and the resulting
clear solution concentrated to ca. 2 mL. The addition of diethyl ether
(40 mL) afforded a white microcrystalline solid which was washed
with diethyl ether (3 × 20 mL) and vacuum-dried. (6a) Yield 95%
Inorg. Chem. 1999, 48, 233. (g) Braunstein, P.; Naud, F. Angew. Chem.,
Int. Ed. 2001, 40, 680. (h) Braunstein, P. J. Organomet. Chem. 2004,
689, 3953. (i) Bassetti, M. Eur. J. Inorg. Chem. 2006, 4473. (j) Kwong,
F. Y.; Chan, A. S. C Synlett 2008, 1440−1448.
(2) See for example: Grushin, V. V. Organometallics 2001, 20, 3950
and references therein.
3
(0.453 g). 31P{1H} NMR ((CD3)2CO): −0.59 (d, JPP = 6.8 Hz,
PPh2), 13.84 (d, 2JPP = 25.0 Hz, Ph2PN), 47.62 (dd, 2JPP = 25.0 Hz,
(3) (a) Staudinger, H.; Meyer, J. Helv. Chim. Acta 1919, 2, 635. For
reviews on the Staudinger reaction, see: (b) Gololobov, Y. G.;
Zhmurova, I. N.; Kasukhin, L. F. Tetrahedron 1981, 37, 437.
(c) Gololobov, Y. G.; Kasukhin, L. F. Tetrahedron 1992, 48, 1353.
(d) Johnson, A. W. In Ylides and Imines of Phosphorus; Wiley:
NewYork, 1993; p 403. (e) Palacios, F.; Aparicio, D.; Rubiales, G.;
Alonso, C.; de los Santos, J. M. Curr. Org. Chem. 2006, 10, 2371.
(f) Bebbington, M. W. P.; Bourissou, D. Coord. Chem. Rev. 2009, 253,
1248. (g) van Berkel, S. S.; van Eldijk, M. B.; van Hest, J. C. M. Angew.
Chem., Int. Ed. 2011, 50, 8806.
(4) Selective monoiminations of bis-phosphines are reported in:
(a) Gilyarov, V. A.; Kovtum, V. Y.; Kabachmich, M. I. Izv. Akad. Nauk
SSSR, Ser. Khim. 1967, 5, 1159. (b) Katti, K. V.; Cavell, R. G. Inorg.
Chem. 1989, 28, 413. (c) Katti, K. V.; Batchelor, R. J.; Einstein, F. W.
B.; Cavell, R. G. Inorg. Chem. 1990, 29, 808. (d) Cavell, R. G.; Reed, R.
W.; Katti, K. V.; Balakrishna, M. S.; Collins, P. W.; Mozol, V.; Bartz, I.
Phosphorus, Sulfur Silicon Relat. Elem. 1993, 76, 9. (e) Balakrishna, M.
S.; Santarsiero, B. D.; Cavell, R. G. Inorg. Chem. 1994, 33, 3079.
(f) Reed, R. W.; Santarsiero, B.; Cavell, R. G. Inorg. Chem. 1996, 35,
4292. (g) Avis, M. W.; Goosen, M.; Elsevier, C. J.; Veldman, N.;
Kooijman, H.; Spek, A. L. Inorg. Chim. Acta 1997, 264, 43. (h) Molina,
P.; Arques, A.; García, A.; Ramírez de Arellano, M. C. Tetrahedron Lett.
1997, 38, 7613. (i) Molina, P.; Arques, A.; García, A.; Ramírez de
Arellano, M. C. Eur. J. Inorg. Chem. 1998, 1359. (j) Pandurangi, R. S.;
Katti, K. V.; Stillwell, L.; Barnes, C. L. J. Am. Chem. Soc. 1998, 120,
3JPP = 6.8 Hz, P(S)(OPh2)). (6b) Yield 94% (0.491 g). 31P{1H}
2
NMR ((CD3)2CO): 11.08 (s, PPh2), 15.87 (d, JPP = 31.5 Hz,
Ph2PN), 44.17 (d, 2JPP = 31.5 Hz, P(S)(OPh2)). (6c) Yield 97%
(0.465 g). 31P{1H} NMR ((CD3)2CO): 3.39 (s, PPh2), 14.91 (d,
2
2JPP = 25.5 Hz, Ph2PN), 45.32 (d, JPP = 25.5 Hz, P(S)(OPh2)).
General Procedure for the Catalytic Propargylic Isomer-
ization in [BMIM][PF6]. The rhenium catalyst 4d, the ionic liquid
[BMIM][PF6] (1 g), and the corresponding alkynol (1 mmol) were
introduced into a Schlenck tube undera nitrogen atmosphere. The
mixture was then heated at 80 or 130 °C for the indicated time (the
course of the reaction was monitored by regular sampling and analysis
by GC). After completion of the reaction, the organic product was
extracted with diethyl ether (3 × 5 mL). The organic crude reaction
was purified by flash chromatography over silica gel using EtOAc/
hexane (1:10) as an eluent. The identity of the resulting α,β-
unsaturated carbonyl compounds was assessed by comparison of their
1H and 13C{1H} NMR spectroscopic data with those reported in the
literature and by their fragmentation in GC/MS.
ASSOCIATED CONTENT
* Supporting Information
■
S
Analytical and spectroscopic data for compounds 2a−d, 3a−
b,e−g, 5b−e, and 6a−c have been provided. The recycling
procedure for catalyst 4d in the isomerization of propagylic
alcohols 7a−f using [BMIM][PF6] as solvent is described.
Crystallographic data for 3e, 5b, 5e, and 6a are also reported.
This material is available free of charge via the Internet at
http://pubs.acs.org.
11364. (k) Alajarín, M.; Lop
Bautista, D. Synthesis 2000, 2085. (l) Arques, A.; Molina, P.; Aunon,
́
ez-Leonardo, C.; Llamas-Lorente, P.;
̃
D.; Vilaplana, M. J.; Desamparados Velasco, M.; Martínez, F.; Bautista,
D.; Lahoz, F. J. J. Organomet. Chem. 2000, 598, 329. (m) Balakrishna,
M. S.; Teipel, S.; Pinkerton, A. A.; Cavell, R. G. Inorg. Chem. 2001, 40,
1802.
AUTHOR INFORMATION
Corresponding Author
*E-mail: garciajoaquin@uniovi.es.
(5) For overviews on the coordination chemistry of Ph2PCH2P(
NR′)Ph2 ligands, see: (a) Katti, K. V.; Cavell, R. G. Comments Inorg.
Chem. 1990, 10, 53. (b) Cavell, R. G. Curr. Sci. 2000, 78, 440. For
■
more recent reports, see: (c) Arques, A.; Aunon, D.; Molina, P.
̃
Notes
Tetrahedron Lett. 2004, 45, 4337. (d) Co, T. T.; Shim, S. C.; Cho, C.
S.; Kim, T.-J.; Kang, S. O.; Han, W.-S.; Kim, J. K. Organometallics
The authors declare no competing financial interest.
́
2005, 24, 4824. (e) Boubekeur, L.; Ulmer, S.; Ricard, L.; Mezailles, N.;
́
ACKNOWLEDGMENTS
We are indebted to the Ministerio de Ciencia e Innovacion
(MICINN) of Spain (Projects CTQ2008-00506, CTQ2010-
14796 and RYC-2011-08451) and Consolider Ingenio 2010
(CSD2007-00006) for financial support. J.G.-A. thanks the
MICINN and the European Social Fund for the award of a
Le Floch, P. Organometallics 2006, 25, 315. (f) Díaz-Alvarez, A. E.;
Crochet, P.; Zablocka, M.; Cadierno, V.; Duhayon, C.; Gimeno, J.;
Majoral, J.-P. New. J. Chem. 2006, 30, 1295. (g) Venkateswaran, R.;
Balakrishna, M. S.; Mobin, S. M. Eur. J. Inorg. Chem. 2007, 1930.
(h) Buchard, A.; Heuclin, H.; Auffrant, A.; Le Goff, X. F.; Le Floch, P.
Dalton Trans. 2009, 1659. (i) Buchard, A.; Payet, E.; Auffrant, A.; Le
Goff, X. F.; Le Floch, P. New J. Chem. 2010, 34, 2943. (j) Picot, A.;
Dyer, H.; Buchard, A.; Auffrant, A.; Vendier, L.; Le Floch, P.; Sabo-
Etienne, S. Inorg. Chem. 2010, 49, 1310. (k) Dyer, H.; Picot, A.;
Vendier, L.; Auffrant, A.; Le Floch, P.; Sabo-Etienne, S. Organometallics
2011, 30, 1478. (l) Cao, T.-P.-A.; Labouille, S.; Auffrant, A.; Jean, Y.;
Le Goff, X. F.; Le Floch, P. Dalton Trans. 2011, 40, 10029.
■
́
́
“Juan de la Cierva” and a “Ramon y Cajal” contract. C.M.S.
(from the University of Hamburg, Germany) thanks the
Erasmus Program. We thank the support of the Scientific and
Technical Services (UniOvi) X-Ray Single Crystal Diffraction.
́
(m) Alajarín, M.; Lopez-Leonardo, C.; Llamas-Lorente, P.; Raja, R.;
DEDICATION
■
Bautista, D.; Orenes, R.-A. Dalton Trans. 2012, 41, 12259.
(n) Martínez-Arripe, E.; Jean-Baptiste-dit-Dominique, F.; Auffrant,
A.; Le Goff, X.-F.; Thuilliez, J.; Nief, F. Organometallics 2012, 31, 4854.
(6) (a) Cadierno, V.; Díez, J.; García-Garrido, S. E.; García-Granda,
S.; Gimeno, J. J. Chem. Soc., Dalton Trans. 2002, 1465. (b) Cadierno,
Dedicated to Professor Irina Petrovna Beletskaya for her
contribution to metal-catalyzed reactions and Professor
Antonio Laguna on the occasion of his 65th birthday.
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́
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hydration step were unsuccessful disabling the selective synthesis of
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́
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(34) 31P{1H} NMR spectrum of the crude mixture after the catalytic
reaction confirms the presence of the complex 4d in the catalytic
medium.
́
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5437
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